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  • 1.
    Alfredson, Jens
    et al.
    SAAB, Linköping, Sweden.
    Johansson, Björn
    Linköping University, Department of Computer and Information Science, Human-Centered systems. Linköping University, Faculty of Arts and Sciences.
    Gonzaga Trabasso, Luis
    Aeronautics Institute of Technology, Brazil.
    Schminder, Jörg
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Granlund, Rego
    Research Institutes of Sweden SICS East, Linköping, Sweden.
    Gårdhagen, Roland
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    DESIGN OF A DISTRIBUTED HUMAN FACTORS LABORATORY FOR FUTURE AIRSYSTEMS2018In: ICAS congress proceeding, International Council of the Aeronautical Sciences , 2018, article id ICAS2018_0305Conference paper (Other academic)
    Abstract [en]

    This paper presents a rationale for structuring a distributed human factors laboratory for future air systems. The distributed herein refers to two aspects: content and geographic. As for content, the laboratory is structured in two levels, namely, individual, and team. As for geographic, the laboratory infrastructure is distributed in three physically separate facilities, namely, Department of Computer and Information Science (IDA) and Department of Management and Engineering (IEI) from Linköping University – Sweden and the Competence Center in Manufacturing from the Aeronautics Institute of Technology (ITA) – Brazil.

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    fulltext
  • 2. Order onlineBuy this publication >>
    Andersson, Magnus
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Turbulence Descriptors in Arterial Flows: Patient-Specific Computational Hemodynamics2021Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    At this very moment, there are literally millions of people who suffer from various types of cardiovascular diseases (CVDs), many of whom will experience reduced quality of life or premature lift expectancy. The detailed underlying pathogenic processes behind many of these disorders are not well understood, but were abnormal dynamics of the blood flow (hemodynamics) are believed to play an important role, especially atypical flow-mediated frictional forces on the intraluminal wall (i.e. the wall shear stress, WSS). Under normal physiological conditions, the flow is relatively stable and regular (smooth and laminar), which helps to maintain critical vascular functions. When these flows encounter various unfavorable anatomical obstructions, the flow can become highly unstable and irregular (turbulent), giving rise to abnormal fluctuating hemodynamic forces, which increase the bloodstream pressure losses, can damage the cells within the blood, as well as impair essential structural and functional regulatory mechanisms. Over a prolonged time, these disturbed flow conditions may promote severe pathological responses and are therefore essential to foresee as early as possible.

    Clinical measurements of blood flow characteristics are often performed non-invasively by modalities such as ultrasound and magnetic resonance imaging (MRI). High-fidelity MRI techniques may be used to attain a general view of the overall large-scale flow features in the heart and larger vessels but cannot be used for estimating small-scale flow variations nor capture the WSS characteristics. Since the era of modern computers, fluid motion can now also be predicted by computational fluid dynamics (CFD)simulations, which can provide discrete mathematical approximations of the flow field with much higher details (resolution) and accuracy compared to other modalities. CFD simulations rely on the same fundamental principles as weather forecasts, the physical laws of fluid motion, and thus can not only be used to assess the current flow state but also to predict (foresee) important outcome scenarios in e.g. intervention planning. To enable blood flow simulations within certain cardiovascular segments, these CFD models are usually reconstructed from MRI-based anatomical and flow image-data. Today, patient-specific computational hemodynamics are essentially only performed within the research field, where much emphasis is dedicated towards understanding normal/abnormal blood flow physiology, developing better individual-based diagnostics/treatments, and evaluating the results reliability/generality in order to approach clinical applicability.

    In this thesis, advanced CFD methods were adopted to simulate realistic patient-specific turbulent hemodynamics in constricted arteries reconstructed from MRI data. The main focus was to investigate novel, comprehensive ways to characterize these abnormal flow conditions, in the pursuit of better clinical decision-making tools; from more in-depth analyzes of various turbulence-related tensor characteristics to descriptors that evaluate the hemodynamics more globally in the domain. Results from the studies in this thesis suggest that these turbulence descriptors can be useful to: i) target cardiovascular sites prone to specific turbulence characteristics, both in the bulk flow and on the intraluminal wall, ii) provide a more extensive view of the general flow severity within malformed vascular regions, and iii) evaluated and potentially improve cardiovascular modeling strategies and MRI-measured turbulence data.

    The benefit of these descriptors is that they all, in principle, can be measured by different MRI procedures, making them more accessible from a clinical perspective. Although the significance of these suggested flow-mediated phenotypes has not yet been evaluated clinically, this work opens many doors of opportunities for making more thorough and longitudinal patient-specific studies, including large cohorts of patients with various CVDs susceptible to turbulent-like conditions, as well as performing more in-depth CFD-MRI validation analyzes.

    List of papers
    1. Quantitative Assessment of Turbulence and Flow Eccentricity in an Aortic Coarctation - Impact of Virtual Interventions
    Open this publication in new window or tab >>Quantitative Assessment of Turbulence and Flow Eccentricity in an Aortic Coarctation - Impact of Virtual Interventions
    2015 (English)In: Cardiovascular Engineering and Technology, ISSN 1869-408X, E-ISSN 1869-4098, Vol. 6, no 6, p. 281-293Article in journal (Refereed) Published
    Abstract [en]

    Turbulence and flow eccentricity can be measured by magnetic resonance imaging (MRI) and may play an important role in the pathogenesis of numerous cardiovascular diseases. In the present study, we propose quantitative techniques to assess turbulent kinetic energy (TKE) and flow eccentricity that could assist in the evaluation and treatment of stenotic severities. These hemodynamic parameters were studied in a pre-treated aortic coarctation (CoA) and after several virtual interventions using computational fluid dynamics (CFD), to demonstrate the effect of different dilatation options on the flow field. Patient-specific geometry and flow conditions were derived from MRI data. The unsteady pulsatile flow was resolved by large eddy simulation (LES) including non-Newtonian blood rheology. Results showed an inverse asymptotic relationship between the total amount of TKE and degree of dilatation of the stenosis, where turbulent flow proximal the constriction limits the possible improvement by treating the CoA alone. Spatiotemporal maps of TKE and flow eccentricity could be linked to the characteristics of the jet, where improved flow conditions were favored by an eccentric dilatation of the CoA. By including these flow markers into a combined MRI-CFD intervention framework, CoA therapy has not only the possibility to produce predictions via simulation, but can also be validated pre- and immediate post treatment, as well as during follow-up studies.

    Place, publisher, year, edition, pages
    Springer, 2015
    Keywords
    Computational fluid dynamics, Large eddy simulation, Turbulent kinetic energy, Flow displacement, Non-Newtonian, Virtual treatment, Magnetic resonance imaging
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-114496 (URN)10.1007/s13239-015-0218-x (DOI)000380356800007 ()
    Note

    Funding agencies: Swedish Research Council; Center for Industrial Information Technology (CENIIT); Swedish National Infrastructure for Computing (SNIC)

    Available from: 2015-02-24 Created: 2015-02-24 Last updated: 2021-04-26Bibliographically approved
    2. Multidirectional WSS disturbances in stenotic turbulent flows: A pre- and post-intervention study in an aortic coarctation
    Open this publication in new window or tab >>Multidirectional WSS disturbances in stenotic turbulent flows: A pre- and post-intervention study in an aortic coarctation
    2017 (English)In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 51Article in journal (Refereed) Published
    Abstract [en]

    Wall shear stress (WSS) disturbances are commonly expressed at sites of abnormal flow obstructions and may play an essential role in the pathogenesis of various vascular diseases. In laminar flows these disturbances have recently been assessed by the transverse wall shear stress (transWSS), which accounts for the WSS multidirectionality. Site-specific estimations of WSS disturbances in pulsatile transitional and turbulent type of flows are more challenging due to continuous and unpredictable changes in WSS behavior. In these complex flow settings, the transWSS may serve as a more comprehensive descriptor for assessing WSS disturbances of general nature compared to commonly used parameters. In this study large eddy simulations (LES) were used to investigate the transWSS properties in flows subjected to different pathological turbulent flow conditions, governed by a patient-specific model of an aortic coarctation pre and post balloon angioplasty. Results showed that regions of strong near-wall turbulence were collocated with regions of elevated transWSS and turbulent WSS, while in more transitional-like near-wall flow regions a closer resemblance was found between transWSS and low, and oscillatory WSS. Within the frame of this study, the transWSS parameter demonstrated a more multi-featured picture of WSS disturbances when exposed to different types of flow regimes, characteristics which were not depicted by the other parameters alone. (C) 2016 Published by Elsevier Ltd.

    Place, publisher, year, edition, pages
    ELSEVIER SCI LTD, 2017
    Keywords
    Transverse wall shear stress; Turbulent kinetic energy; Large eddy simulation; Hemodynamics; Disturbed blood flow; Oscillatory shear index
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:liu:diva-136073 (URN)10.1016/j.jbiomech.2016.11.064 (DOI)000393927500002 ()27919417 (PubMedID)
    Note

    Funding Agencies|Center for Industrial Information Technology (CENIIT) [09.03]; Swedish National Infrastructure for Computing (SNIC) [SNIC 2014/11-22, SNIC2015/16-32]

    Available from: 2017-03-27 Created: 2017-03-27 Last updated: 2021-04-26
    3. Characterization and estimation of turbulence-related wall shear stress in patient-specific pulsatile blood flow
    Open this publication in new window or tab >>Characterization and estimation of turbulence-related wall shear stress in patient-specific pulsatile blood flow
    2019 (English)In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 85, p. 108-117Article in journal (Refereed) Published
    Abstract [en]

    Disturbed, turbulent-like blood flow promotes chaotic wall shear stress (WSS) environments, impairing essential endothelial functions and increasing the susceptibility and progression of vascular diseases. These flow characteristics are today frequently detected at various anatomical, lesion and intervention-related sites, while their role as a pathological determinant is less understood. To present-day, numerous WSS-based descriptors have been proposed to characterize the spatiotemporal nature of the WSS disturbances, however, without differentiation between physiological laminar oscillations and turbulence-related WSS (tWSS) fluctuations. Also, much attention has been focused on magnetic resonance (MR) WSS estimations, so far with limited success; promoting the need of a near-wall surrogate marker. In this study, a new approach is explored to characterize the tWSS, by taking advantage of the tensor characteristics of the fluctuating WSS correlations, providing both a magnitude and an anisotropy measure of the disturbances. These parameters were studied in two patient-specific coarctation models (sever and mild), using large eddy simulations, and correlated against near-wall reciprocal Reynolds stress parameters. Collectively, results showed distinct regions of differing tWSS characteristics, features which were sensitive to changes in flow conditions. Generally, the post-stenotic tWSS was governed by near axisymmetric fluctuations, findings that where not consistent with conventional WSS disturbance predictors. At the 2-3 mm wall-offset range, a strong linear correlation was found between tWSS magnitude and near-wall turbulence kinetic energy (TKE), in contrast to the anisotropy indices, suggesting that MR-measured TKE can be used to assess elevated tWSS regions while tWSS anisotropy estimates request well-resolved simulation methods. (C) 2019 Elsevier Ltd. All rights reserved.

    Place, publisher, year, edition, pages
    ELSEVIER SCI LTD, 2019
    Keywords
    Computational fluid dynamics; Disturbed hemodynamics; Anisotropy invariant map; Aortic coarctation; Near-wall surrogate markers
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:liu:diva-156101 (URN)10.1016/j.jbiomech.2019.01.016 (DOI)000461725000014 ()30704762 (PubMedID)
    Available from: 2019-04-03 Created: 2019-04-03 Last updated: 2021-04-26
    4. Characterization of anisotropic turbulence behavior in pulsatile blood flow
    Open this publication in new window or tab >>Characterization of anisotropic turbulence behavior in pulsatile blood flow
    2021 (English)In: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 20, p. 491-506Article in journal (Refereed) Published
    Abstract [en]

    Turbulent-like hemodynamics with prominent cycle-to-cycle flow variations have received increased attention as a potential stimulus for cardiovascular diseases. These turbulent conditions are typically evaluated in a statistical sense from single scalars extracted from ensemble-averaged tensors (such as the Reynolds stress tensor), limiting the amount of information that can be used for physical interpretations and quality assessments of numerical models. In this study, barycentric anisotropy invariant mapping was used to demonstrate an efficient and comprehensive approach to characterize turbulence-related tensor fields in patient-specific cardiovascular flows, obtained from scale-resolving large eddy simulations. These techniques were also used to analyze some common modeling compromises as well as MRI turbulence measurements through an idealized constriction. The proposed method found explicit sites of elevated turbulence anisotropy, including a broad but time-varying spectrum of characteristics over the flow deceleration phase, which was different for both the steady inflow and Reynolds-averaged Navier-Stokes modeling assumptions. Qualitatively, the MRI results showed overall expected post-stenotic turbulence characteristics, however, also with apparent regions of unrealizable or conceivably physically unrealistic conditions, including the highest turbulence intensity ranges. These findings suggest that more detailed studies of MRI-measured turbulence fields are needed, which hopefully can be assisted by more comprehensive evaluation tools such as the once described herein.

    Place, publisher, year, edition, pages
    SPRINGER HEIDELBERG, 2021
    Keywords
    Barycentric anisotropy invariant map; Patient-specific scale-resolved computational hemodynamics; Reynolds stress and dissipation tensor; MRI turbulence measurements; Verification and validation
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:liu:diva-171404 (URN)10.1007/s10237-020-01396-3 (DOI)000582375000001 ()33090334 (PubMedID)
    Note

    Funding Agencies|Linkoping University

    Available from: 2020-11-30 Created: 2020-11-30 Last updated: 2021-06-01
    5. Model Verification and Error Sensitivity of Turbulence-Related Tensor Characteristics in Pulsatile Blood Flow Simulations
    Open this publication in new window or tab >>Model Verification and Error Sensitivity of Turbulence-Related Tensor Characteristics in Pulsatile Blood Flow Simulations
    2021 (English)In: Fluids, E-ISSN 2311-5521, Vol. 6, no 1, article id 11Article in journal (Refereed) Published
    Abstract [en]

    Model verification, validation, and uncertainty quantification are essential procedures to estimate errors within cardiovascular flow modeling, where acceptable confidence levels are needed for clinical reliability. While more turbulent-like studies are frequently observed within the biofluid community, practical modeling guidelines are scarce. Verification procedures determine the agreement between the conceptual model and its numerical solution by comparing for example, discretization and phase-averaging-related errors of specific output parameters. This computational fluid dynamics (CFD) study presents a comprehensive and practical verification approach for pulsatile turbulent-like blood flow predictions by considering the amplitude and shape of the turbulence-related tensor field using anisotropic invariant mapping. These procedures were demonstrated by investigating the Reynolds stress tensor characteristics in a patient-specific aortic coarctation model, focusing on modeling-related errors associated with the spatiotemporal resolution and phase-averaging sampling size. Findings in this work suggest that attention should also be put on reducing phase-averaging related errors, as these could easily outweigh the errors associated with the spatiotemporal resolution when including too few cardiac cycles. Also, substantially more cycles are likely needed than typically reported for these flow regimes to sufficiently converge the phase-instant tensor characteristics. Here, higher degrees of active fluctuating directions, especially of lower amplitudes, appeared to be the most sensitive turbulence characteristics.

    Place, publisher, year, edition, pages
    MDPI, 2021
    Keywords
    barycentric anisotropy invariant map; turbulence componentality; epistemic modeling errors; patient-specific computational hemodynamics; large eddy simulations; image-based cardiovascular flow modeling; phase-averaging; reynolds stresses
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:liu:diva-173432 (URN)10.3390/fluids6010011 (DOI)000610232000001 ()
    Available from: 2021-02-20 Created: 2021-02-20 Last updated: 2021-06-11
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    presentationsbild
  • 3.
    Andersson, Magnus
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Ebbers, Tino
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Clinical Physiology in Linköping. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Characterization and estimation of turbulence-related wall shear stress in patient-specific pulsatile blood flow2019In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 85, p. 108-117Article in journal (Refereed)
    Abstract [en]

    Disturbed, turbulent-like blood flow promotes chaotic wall shear stress (WSS) environments, impairing essential endothelial functions and increasing the susceptibility and progression of vascular diseases. These flow characteristics are today frequently detected at various anatomical, lesion and intervention-related sites, while their role as a pathological determinant is less understood. To present-day, numerous WSS-based descriptors have been proposed to characterize the spatiotemporal nature of the WSS disturbances, however, without differentiation between physiological laminar oscillations and turbulence-related WSS (tWSS) fluctuations. Also, much attention has been focused on magnetic resonance (MR) WSS estimations, so far with limited success; promoting the need of a near-wall surrogate marker. In this study, a new approach is explored to characterize the tWSS, by taking advantage of the tensor characteristics of the fluctuating WSS correlations, providing both a magnitude and an anisotropy measure of the disturbances. These parameters were studied in two patient-specific coarctation models (sever and mild), using large eddy simulations, and correlated against near-wall reciprocal Reynolds stress parameters. Collectively, results showed distinct regions of differing tWSS characteristics, features which were sensitive to changes in flow conditions. Generally, the post-stenotic tWSS was governed by near axisymmetric fluctuations, findings that where not consistent with conventional WSS disturbance predictors. At the 2-3 mm wall-offset range, a strong linear correlation was found between tWSS magnitude and near-wall turbulence kinetic energy (TKE), in contrast to the anisotropy indices, suggesting that MR-measured TKE can be used to assess elevated tWSS regions while tWSS anisotropy estimates request well-resolved simulation methods. (C) 2019 Elsevier Ltd. All rights reserved.

  • 4.
    Andersson, Magnus
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Characterization of anisotropic turbulence behavior in pulsatile blood flow2021In: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 20, p. 491-506Article in journal (Refereed)
    Abstract [en]

    Turbulent-like hemodynamics with prominent cycle-to-cycle flow variations have received increased attention as a potential stimulus for cardiovascular diseases. These turbulent conditions are typically evaluated in a statistical sense from single scalars extracted from ensemble-averaged tensors (such as the Reynolds stress tensor), limiting the amount of information that can be used for physical interpretations and quality assessments of numerical models. In this study, barycentric anisotropy invariant mapping was used to demonstrate an efficient and comprehensive approach to characterize turbulence-related tensor fields in patient-specific cardiovascular flows, obtained from scale-resolving large eddy simulations. These techniques were also used to analyze some common modeling compromises as well as MRI turbulence measurements through an idealized constriction. The proposed method found explicit sites of elevated turbulence anisotropy, including a broad but time-varying spectrum of characteristics over the flow deceleration phase, which was different for both the steady inflow and Reynolds-averaged Navier-Stokes modeling assumptions. Qualitatively, the MRI results showed overall expected post-stenotic turbulence characteristics, however, also with apparent regions of unrealizable or conceivably physically unrealistic conditions, including the highest turbulence intensity ranges. These findings suggest that more detailed studies of MRI-measured turbulence fields are needed, which hopefully can be assisted by more comprehensive evaluation tools such as the once described herein.

    Download full text (pdf)
    fulltext
  • 5.
    Andersson, Magnus
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Model Verification and Error Sensitivity of Turbulence-Related Tensor Characteristics in Pulsatile Blood Flow Simulations2021In: Fluids, E-ISSN 2311-5521, Vol. 6, no 1, article id 11Article in journal (Refereed)
    Abstract [en]

    Model verification, validation, and uncertainty quantification are essential procedures to estimate errors within cardiovascular flow modeling, where acceptable confidence levels are needed for clinical reliability. While more turbulent-like studies are frequently observed within the biofluid community, practical modeling guidelines are scarce. Verification procedures determine the agreement between the conceptual model and its numerical solution by comparing for example, discretization and phase-averaging-related errors of specific output parameters. This computational fluid dynamics (CFD) study presents a comprehensive and practical verification approach for pulsatile turbulent-like blood flow predictions by considering the amplitude and shape of the turbulence-related tensor field using anisotropic invariant mapping. These procedures were demonstrated by investigating the Reynolds stress tensor characteristics in a patient-specific aortic coarctation model, focusing on modeling-related errors associated with the spatiotemporal resolution and phase-averaging sampling size. Findings in this work suggest that attention should also be put on reducing phase-averaging related errors, as these could easily outweigh the errors associated with the spatiotemporal resolution when including too few cardiac cycles. Also, substantially more cycles are likely needed than typically reported for these flow regimes to sufficiently converge the phase-instant tensor characteristics. Here, higher degrees of active fluctuating directions, especially of lower amplitudes, appeared to be the most sensitive turbulence characteristics.

    Download full text (pdf)
    fulltext
  • 6.
    Andersson, Magnus
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering. Swedish E Science Research Centre SeRC, Sweden.
    Lantz, Jonas
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Swedish E Science Research Centre SeRC, Sweden.
    Ebbers, Tino
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Clinical Physiology in Linköping. Linköping University, Center for Medical Image Science and Visualization (CMIV). Swedish E Science Research Centre SeRC, Sweden.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering. Linköping University, Center for Medical Image Science and Visualization (CMIV). Swedish E Science Research Centre SeRC, Sweden.
    Correction: Quantitative Assessment of Turbulence and Flow Eccentricity in an Aortic Coarctation: Impact of Virtual Interventions (vol 6, pg 281, 2015)2015In: Cardiovascular Engineering and Technology, ISSN 1869-408X, E-ISSN 1869-4098, Vol. 6, no 4, p. 577-589Article in journal (Refereed)
    Abstract [en]

    Turbulence and flow eccentricity can be measured by magnetic resonance imaging (MRI) and may play an important role in the pathogenesis of numerous cardiovascular diseases. In the present study, we propose quantitative techniques to assess turbulent kinetic energy (TKE) and flow eccentricity that could assist in the evaluation and treatment of stenotic severities. These hemodynamic parameters were studied in a pre-treated aortic coarctation (CoA) and after several virtual interventions using computational fluid dynamics (CFD), to demonstrate the effect of different dilatation options on the flow field. Patient-specific geometry and flow conditions were derived from MRI data. The unsteady pulsatile flow was resolved by large eddy simulation (LES) including non-Newtonian blood rheology. Results showed an inverse asymptotic relationship between the total amount of TKE and degree of dilatation of the stenosis, where the pre-stenotic hypoplastic segment may limit the possible improvement by treating the CoA alone. Spatiotem-poral maps of TKE and flow eccentricity could be linked to the characteristics of the post-stenotic jet, showing a versatile response between the CoA dilatations. By including these flow markers into a combined MRI-CFD intervention framework, CoA therapy has not only the possibility to produce predictions via simulation, but can also be validated pre-and immediate post treatment, as well as during follow-up studies.

  • 7.
    Andersson, Magnus
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Lantz, Jonas
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Ebbers, Tino
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Clinical Physiology in Linköping. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Multidirectional WSS disturbances in stenotic turbulent flows: A pre- and post-intervention study in an aortic coarctation2017In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 51Article in journal (Refereed)
    Abstract [en]

    Wall shear stress (WSS) disturbances are commonly expressed at sites of abnormal flow obstructions and may play an essential role in the pathogenesis of various vascular diseases. In laminar flows these disturbances have recently been assessed by the transverse wall shear stress (transWSS), which accounts for the WSS multidirectionality. Site-specific estimations of WSS disturbances in pulsatile transitional and turbulent type of flows are more challenging due to continuous and unpredictable changes in WSS behavior. In these complex flow settings, the transWSS may serve as a more comprehensive descriptor for assessing WSS disturbances of general nature compared to commonly used parameters. In this study large eddy simulations (LES) were used to investigate the transWSS properties in flows subjected to different pathological turbulent flow conditions, governed by a patient-specific model of an aortic coarctation pre and post balloon angioplasty. Results showed that regions of strong near-wall turbulence were collocated with regions of elevated transWSS and turbulent WSS, while in more transitional-like near-wall flow regions a closer resemblance was found between transWSS and low, and oscillatory WSS. Within the frame of this study, the transWSS parameter demonstrated a more multi-featured picture of WSS disturbances when exposed to different types of flow regimes, characteristics which were not depicted by the other parameters alone. (C) 2016 Published by Elsevier Ltd.

  • 8.
    Andersson, Magnus
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Lantz, Jonas
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Ebbers, Tino
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV). Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Quantitative Assessment of Turbulence and Flow Eccentricity in an Aortic Coarctation - Impact of Virtual Interventions2015In: Cardiovascular Engineering and Technology, ISSN 1869-408X, E-ISSN 1869-4098, Vol. 6, no 6, p. 281-293Article in journal (Refereed)
    Abstract [en]

    Turbulence and flow eccentricity can be measured by magnetic resonance imaging (MRI) and may play an important role in the pathogenesis of numerous cardiovascular diseases. In the present study, we propose quantitative techniques to assess turbulent kinetic energy (TKE) and flow eccentricity that could assist in the evaluation and treatment of stenotic severities. These hemodynamic parameters were studied in a pre-treated aortic coarctation (CoA) and after several virtual interventions using computational fluid dynamics (CFD), to demonstrate the effect of different dilatation options on the flow field. Patient-specific geometry and flow conditions were derived from MRI data. The unsteady pulsatile flow was resolved by large eddy simulation (LES) including non-Newtonian blood rheology. Results showed an inverse asymptotic relationship between the total amount of TKE and degree of dilatation of the stenosis, where turbulent flow proximal the constriction limits the possible improvement by treating the CoA alone. Spatiotemporal maps of TKE and flow eccentricity could be linked to the characteristics of the jet, where improved flow conditions were favored by an eccentric dilatation of the CoA. By including these flow markers into a combined MRI-CFD intervention framework, CoA therapy has not only the possibility to produce predictions via simulation, but can also be validated pre- and immediate post treatment, as well as during follow-up studies.

  • 9.
    Andersson, Magnus
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Lantz, Jonas
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Modeling of Subject Arterial Segments Using 3D Fluid Structure Interaction and 1D-0D Arterial Tree Network Boundary Condition2011Conference paper (Refereed)
    Abstract [en]

    Modeling of Subject Specific Arterial Segments Using 3D Fluid Structure Interaction and a 1D-0D Arterial Tree Network Boundary Condition

     

    Magnus Andersson, Jonas Lantz , Matts Karlsson

     

    Department of Management and Engineering, Linköping University, SE-581 83 Linköping, Sweden

     

    Introduction

    In recent years it has been possible to simulate 3D blood flow through CFD including the dilatation effect in elastic arteries using Fluid-Structure Interaction (FSI) to better match in vivo data. Patient specific imposed boundary condition (BC) is often used as the velocity profiles at the inlets. However, for the outlet BC a time-resolved pressure is required and often lacking as it is obtained by an invasive procedure. Numerous models have been developed for capturing the main effects of the vascular bed at these sites, which have been shown crucial and difficult to implement accurately. This work focus on a full scaled FSI simulation at an arterial section including the abdominal aorta, renal arteries and iliac bifurcations, obtained from MRI of an healthy individual. The outlet BC at the iliac arteries is connected with a 1D systemic arterial tree which is truncated with a 0D lumped model. This 3D-(0D-1D) connection can provide the essential features of the peripheral flow and, in contrast to the imposed BC, the 1D-0D coupling allow for investigation of cardiovascular diseases including stenoses and/or hypertension.

     

    Methods

    The MRI images were segmented using an in-house software to obtain a 3D surface of the vessel lumen, Figure 1. The surfaces were meshed with high quality hexahedral element using ANSYS ICEM CFD 12.0 (ANSYS Inc, Canonsburg, PA, USA). A PC-MRI time-resolved massflow at the descending aorta were used as inlet BC, where 22% of the flow was forced into the renal bifurcations assuming negligible pressure wave reflection. The wall was modelled with an isotropic elastic model with addition of an elastic support mimicking the damping effect of the surrounding tissue. The 1D model is based on transmission-line theory which involves an impedance model for the pressure-flow relationship. The arterial topology was extracted from literature and only the central arteries after the iliacs was considered. At the truncation sites a 3-element Windkessel model (known as RRC) was implemented and is the most common model of choice for describing the main effects of all the distal vessels.  The 1D system solves the Fourier frequency impedance coefficients over one heart cycle accounting for wave reflection by using the 15 first harmonics to obtain the corresponding pressure. The 3D-1D connection is done offline, which allows for an independent and more stable 3D simulation. This step is iteratively repeated until convergence is reach between the present 3D outlet flow and previous implemented 1D outlet flow. The simulation was utilized in ANSYS CFX, ANSYS Mechanical, and coupled by ANSYS Multi-Field.

     

    Results

    The (0D-1D)-3D model showed convergence of pressure/flow at the iliac outlets, Figure 2. The method provides realistic pressure and flow responses based on the input parameters and even capture the relative difference in flow/pressure distribution between the right and left illiac artery due to subject specific geometric variability. Parameters such as velocity profiles and WSS can be extracted in the 3D domain.

     

    Conclusions

    This method allows for a better insight of large scale vascular networks effect of the local 3D flow features and also gives a better representation of the peripheral flow compared to a pure 0D (lumped parameter/Windkessel) model. PC-MRI will provide data for validation of velocity profiles in the 3D model. Future work includes a subject specific 1D vascular topology to be combined with the 3D model.   

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  • 10.
    Andersson, Magnus
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Lantz, Jonas
    Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    NON-INVASIVE INTERVENTION PLANNING OF STENOTIC FLOWS USING SCALE-RESOLVED IMAGE-BASED COMPUTATIONAL FLUID DYNAMICS2013Conference paper (Refereed)
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    Poster
  • 11.
    Andersson, Magnus
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Lantz, Jonas
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Turbulence Quantification of Stenotic Blood Flow Using Image-Based CFD: Effect of Different Interventions2014In: WCB 2014, 2014Conference paper (Other academic)
    Abstract [en]

    Turbulent blood flow is often associated with some sort of cardiovascular disease, e.g. sharp bends and/or sudden constrictions/expansions of the vessel wall. The energy losses associated with the turbulent flow may increase the heart workload in order to maintain cardiac output (CO). In the present study, the amount of turbulent kinetic energy (TKE) developed in the vicinity of an aortic coarctation was estimated pre-intervention and in a variety of post-intervention configurations, using scale-resolved image-based computational fluid dynamics (CFD). TKE can be measured using magnet resonance imaging (MRI) and have also been validated with CFD simulations [1], i.e. a parameter that not only can be quantified using simulations but can also be measured by MRI.

    Patient-specific geometry and inlet flow conditions were obtained using contrast-enhanced MR angiography and 2D cine phase-contrast MRI, respectively. The intervention procedure was mimicked using an inflation simulation, where six different geometries were obtained. A scale-resolving turbulence model, large eddy simulation (LES), was utilized to resolve the largest turbulent scales and also to capture the laminar-to-turbulent transition. All cases were simulated using baseline CO and with a 20% CO increase to simulate a possible flow adaption after intervention.

    For this patient, results shows a non-linear decay of the total amount of TKE integrated over the cardiac phase as the stenotic cross-sectional area is increased by the intervention.  Figure 1 shows the original segmented geometry and two dilated coarctation with corresponding volume rendering of the TKE at peak systole. Due to turbulent transition at a kink upstream the stenosis further dilation of the coarctation tends to restrict the TKE to a plateau, and continued vessel expansion may therefore only induce unnecessary stresses onto the arterial wall. 

    This patient-specific non-invasive framework has shown the geometrical impact on the TKE estimates. New insight in turbulence development indicates that the studied coarctation can only be improved to a certain extent, where focus should be on the upstream region, if further TKE reduction is motivated. The possibility of including MRI in a combined framework could have great potential for future intervention planning and follow-up studies.  

    [1] J. Lantz, T. Ebbers, J. Engvall and M. Karlsson, Numerical and Experimental Assessment of Turbulent Kinetic Energy in an Aortic Coarctation, Journal of Biomechnics, 2013. 46(11): p. 1851-1858.

  • 12.
    Andersson, Magnus
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Nadali Najafabadi, Hossein
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Wren, Joakim
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Improving Written Communcation Skills in Engineering Programs2016In: Proceedings of the International CDIO Conference, 2016, article id 225Conference paper (Refereed)
    Abstract [en]

    This study focuses on the improvement of students’ written communication skill in highereducation, aiming at higher quality of reports at different course levels. Towards this aim, twosupportive guideline documents, “report structure” and “report format”, have been writtenaligned with the courses’ syllabi and introduced as complementary material.

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    Poster
  • 13. Andersson, R
    et al.
    Loyd, Dan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Pressure sensed non-invasively directly on the extra corporeal bloodline tube2001In: PROCEEDINGS OF THE 23RD ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY, VOLS 1-4: BUILDING NEW BRIDGES AT THE FRONTIERS OF ENGINEERING AND MEDICINE, 2001, Vol. 23, p. 3179-3181Conference paper (Refereed)
    Abstract [en]

    To clinically measure blood pressure at extra corporeal bloodlines involves a hazard due to the infection risk and a risk for thrombosis formation. The aim was to design a non-invasive pressure sensor, measuring directly on a tube section. A modified tube cross-section was used to improve sensitivity. Using the developed sensing principle, a consistent relation (r=0.999) was obtained between pressure and output signal. The output was stable and an acceptable drift within the temperature-range. The method shows great promise for applications in monitoring of the dialysis process.

  • 14.
    Aneq Åström, Meriam
    et al.
    Linköping University, Department of Medical and Health Sciences, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Centre, Department of Clinical Physiology UHL.
    Nylander, Eva
    Linköping University, Department of Medical and Health Sciences, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Centre, Department of Clinical Physiology UHL.
    Ebbers, Tino
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Faculty of Health Sciences. Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Engvall, Jan
    Linköping University, Department of Medical and Health Sciences, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Centre, Department of Clinical Physiology UHL.
    Determination of right ventricular volume and function using multiple axially rotated MRI slices2011In: Clinical Physiology and Functional Imaging, ISSN 1475-0961, E-ISSN 1475-097X, Vol. 31, no 3, p. 233-239Article in journal (Refereed)
    Abstract [en]

    Pandgt;Background: The conventional magnetic resonance imaging (MRI) method for right ventricular (RV) volume and motion, using short-axis (SA) orientation, is limited by RV anatomy and shape. We suggest an orientation based on six slices rotated around the long axis of the RV, rotated long axis (RLA). Materials and methods: Three phantoms were investigated in SA and RLA using cine balanced steady-state free precession MRI. Volumes were calculated based on segmentation and checked against true volumes. In 23 healthy male volunteers, we used six long-axis planes from the middle of the tricuspid valve to the RV apex, rotated in 30 degrees increments. For comparison, short-axis slices were acquired. Imaging parameters were identical in both acquisitions. Results: Right ventricular end-diastolic (EDV), end-systolic (ESV) and stroke volumes (SV) determined in the RLA 179 center dot 1 +/- 29 center dot 3; 80 center dot 1 +/- 17 center dot 1; 99 center dot 3 +/- 16 center dot 9 ml and in the SA were 174 center dot 0 +/- 21 center dot 1; 78 center dot 8 +/- 13 center dot 6; 95 center dot 3 +/- 14 center dot 5 ml with P-values for the difference from 0 center dot 17 to 0 center dot 64 (ns). Interobserver variability ranged between 3 center dot 2% and 6 center dot 6% and intraobserver variability between 2 center dot 8% and 6 center dot 8%. In SA views, consensus for the definition of the basal slice was necessary in 39% of the volunteers for whom the average volume change was 20% in ESV and 10% in EDV. Conclusions: The RLA method results in better visualization and definition of the RV inflow, outflow and apex. Accurate measurement of RV volumes for diagnosis and follow-up of cardiac diseases are enhanced by the RLA orientation, even though additional acquisition time is required.

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  • 15.
    Anjaneya Reddy, Yuvarajendra
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Master Thesis - Towards a Virtual Climate Chamber: A numerical study using CFD software2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    For each generation of electronic equipment there is a trend towards higher power den-sities. Increased heat generation is an undesired consequence that the thermal design unit in a company must handle. The goal of thermal design engineer/unit is to utilizethe same volume to more efficiently transfer more heat from the equipment. This can bedone by exploring more complex and advanced heat sink geometries, optimizing the finshapes and so on. The new prototypes developed will be tested for their reliability and endurance in special chambers called climate chambers, that simulate desired environ-ments. The measurements by thermal design teams in these kind of climate chambers are mainly of outdoor products, whose cooling is based on natural convection. Forcedcooling using fans is optional for these outdoor products.

    The climate chambers in general provides temperature measurement as the outputto the analysis, though there are other important parameters that define the operationalfunctionality of an equipment. The ability to visualize the flow characteristics duringthe process of testing is a valuable aid in the design process. A virtual/CFD form of thephysical climate chamber (CC) would empower the design process, while alleviating theusage of the climate chambers for such analyses. CFD offers a wide range of capabilitiesthat lets the user change the boundary conditions with great ease compared to that ofthe experimental setup.

    The numerical model developed in this thesis project provides results, that help inunderstanding the physics involved in fluid flow inside the physical climate chamber.Turbulence quantification of the flow is the main aim of this thesis project, which wouldbe resourceful in future works. Experiments are conducted inside the climate chamber, in order to aid the construction of numerical model as well as serve as source of vali-dation for the numerical results. Laminar transient case simulations are preferred over use of any turbulence models, to limit any kind of predictions made by these turbulencemodels. Integral length scales and turbulence intensities are compared and reason fordiscrepancies are addressed.

    The results from the comparisons show that, the numerical model emulates physicsof actual flow inside the climate chamber. However, there are many factors that directlyaffect the results, making it difficult to precisely quantify the error, within the time periodof this thesis project.

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    Towards_A_Virtual_Climate_Chamber-Numerical_Study-Yuvraj_Reddy
  • 16.
    Ask, Per
    et al.
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    ENGVALL, J
    Loyd, Dan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Wranne, Bengt
    Linköping University, Department of Medicine and Care, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    THEORETICAL AND EXPERIMENTAL-ANALYSIS OF AORTIC COARCTATION1989In: IMAGES OF THE TWENTY-FIRST CENTURY, PTS 1-6, 1989, Vol. 11, p. 103-103Conference paper (Refereed)
    Abstract [en]

    Aortic coarctation, which could severely influence the haemodynamic conditions of the body, is discussed. A theory has been developed which relates the pressure drop over the coarctation to the flow. This theory indicates that the pressure drop across the actual coarctation is related to the flow squared. For the collateral flow the expected pressure drop is either linearly or quadratically related to the flow. Model experiments and patient data support the present theoretical model

  • 17.
    Ask, Per
    et al.
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Hök, B
    Loyd, Dan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Teriö, H
    Bio-acoustic signals from stenotic tube flow: state of the art and perspectives for future methodological development.1995In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 33, no 5, p. 669-675Article in journal (Refereed)
    Abstract [en]

    To study the degree of stenosis from the acoustic signal generated by the turbulent flow in a stenotic vessel, so-called phonoangiography was first suggested over 20 years ago. A reason for the limited use of the technique today may be that, in the early work, the theory of how to relate the spectrum of the acoustic signal to the degree of the stenosis was not clear. However, during the last decade, the theoretical basis for this and other biological tube flow applications has been clarified. Now there is also easy access to computers for frequency analysis. A further explanation for the limited diagnostic use of bio-acoustic techniques for tube flow is the strong competition from ultrasound Doppler techniques. In the future, however, applications may be expected in biological tube flow where the non-invasive, simple and inexpensive bio-acoustic techniques will have a definite role as a diagnostic method.

  • 18.
    Ask, Per
    et al.
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Loyd, Dan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Wranne, Bengt
    Linköping University, Department of Medicine and Care, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    Regurgitant flow through heart valves: a hydraulic model applicable to ultrasound Doppler measurements.1986In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 24, no 6, p. 643-646Article in journal (Refereed)
  • 19.
    Bapat, Pranav
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Design and Fluid Simulation of a Fluidic Growth Chamber2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Filamentous fungi are of interest for biotechnologists particularly because of thefungi’s ability of producing commercial products after undergoing certain industrialprocess. Although because of the complicated and intricate internal mechanism ofthe fungi there are certain aspects which need to be studied to maximize the produc-tion output. A team at Chair of Measurement and Control Bioprocess Group at TUBerlin studies the internal behavior of the fungi when they are exposed to certainamount of wall shear stress (WSS) by performing small-scale experimentation. Forthis purpose a backward facing step (BFS) chamber is used.  This thesis work aims to perform Computational Fluid Dynamics (CFD) analysesto study the flow in the BFS chamber and to find appropriate locations to adherethe fungi spores on the chamber’s bottom wall.

    Commercially available CFD software Star CCM+ has been used for the CFD calcu-lations. The BFS chamber has been divided into two parts namely ’inflow channel’and ’step channel’ and simulations are performed separately. RANS model SST k-ωhas been used to simulate the flow in the inflow channel and Large Eddy Simulation(LES) model has been used in the step channel.

    The simulation result predicted that the streamwise WSS (WSS x ) is highest (≈ 8Pa) at the primary reattachment location downstream of the step. Due to reverseflow it is observed that WSS x is high (≈ 5 Pa) in the primary separation region.Standard deviation WSS x is highest (≈ 0.35 Pa) in the region around 28 x/h distancedownstream of the step on the bottom wall of the step channel and it is observedthat this is the region where the turbulence kinetic energy (TKE) is also maximumin the mean flow of the step channel. It is observed that there is small WSS x devi-ation in the primary reattachment region as well.                From the study it is concluded that the overall flow in the chamber is laminar withsome level of unsteadiness at few locations. To adhere the fungi spores on the bot-tom wall suitable location will be in the region where maximum variation in WSS xis observed.

    Keywords: Filamentous fungus, computational fluid dynamics, large eddy simula-tion, wall shear stress, backward facing step, turbulence kinetic energy

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  • 20. Barclay, Susan A
    et al.
    Eidenvall, Lars
    Karlsson, Matts
    Andersson, Gunnar
    Xiong, Changsheng
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Loyd, Dan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Wranne, Bengt
    Linköping University, Department of Medicine and Care, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    The shape of the proximal isovelocity surface area varies with regurgitant orifice size and distance from orifice: computer simulation and model experiments with color M-mode technique.1993In: Journal of the American Society of Echocardiography, ISSN 0894-7317, E-ISSN 1097-6795, Vol. 6, no 4, p. 433-445Article in journal (Refereed)
    Abstract [en]

    The hemispheric proximal isovelocity surface area method for quantification of mitral regurgitant flow (i.e., Qc = 2 pi r2v), where 2 pi r2 is the surface area and v is the velocity at radius r, was investigated as distance from the orifice was increased. Computer simulations and steady flow model experiments were performed for orifices of 4, 6, and 8 mm. Flow rates derived from the centerline velocity and hemispheric assumption were compared with true flow rates. Proximal isovelocity surface area shape varied as distance from each orifice was increased and could only be approximated from the hemispheric equation when a certain distance was exceeded: > 7, > 10, and > 12 mm for the 4, 6, and 8 mm orifices, respectively. Prediction of relative error showed that the best radial zone at which to make measurements was 5 to 9, 6 to 14 and 7 to 17 mm for the 4, 6, and 8 mm orifices, respectively. Although effects of a nonhemispheric shape could be compensated for by use of a correction factor, a radius of 8 to 9 mm can be recommended without the use of a correction factor over all orifices studied if a deviation in calculated as compared with true flow of 15% is considered acceptable. These measurements therefore have implications for the technique in clinical practice.

  • 21.
    Bech-Hanssen, O.
    et al.
    Department of Clinical Physiology, Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden.
    Gjertsson, P.
    Gjertsson, P..
    Houltz, E.
    Department of Clinical Physiology, Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden.
    Wranne, Bengt
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medical and Health Sciences, Clinical Physiology. Östergötlands Läns Landsting, Heart Centre, Department of Clinical Physiology.
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Loyd, Dan
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Caidahl, K.
    Caidahl, K..
    Net Pressure Gradients in Aortic Prosthetic Valves can be Estimated by Doppler2003In: Journal of the American Society of Echocardiography, ISSN 0894-7317, E-ISSN 1097-6795, Vol. 16, no 8, p. 858-866Article in journal (Refereed)
    Abstract [en]

    Background: In aortic prosthetic valves, both the Doppler-estimated gradients and orifice areas are misleading in the assessment of hemodynamic performance. The parameter of major interest is the net pressure gradient after pressure recovery (PR). We, therefore, investigated, in vitro, our ability to predict the net pressure gradient and applied the formulas in a representative patient population with 2 different valve designs. Methods: We studied the St Jude Medical (SJM) standard valve (size 19-27) and SJM Biocor (size 21-27) in an in vitro steady-flow model with simultaneous Doppler-estimated pressure and catheter pressure measurements. Using echocardiography, we also studied patients who received the SJM (n = 66) and SJM Biocor (n = 45). Results: In the SJM, we observed PR both within the prosthesis and aorta, whereas in the SJM Biocor, PR was only present in the aorta. We estimated the PR within the valve and within the aorta separately from echocardiographic in vitro data, combining a regression equation (valve) with an equation on the basis of fluid mechanics theory (aorta). The difference between estimated and catheter-obtained net gradients (mean ± SD) was 0.6 ± 1.6 mm Hg in the SJM and - 0.2 ± 1.9 mm Hg in the SJM Biocor. When these equations were applied in vivo, we found that PR had an overall value of 57 ± 7% of the peak Doppler gradient in the SJM and 33 ± 9% in the SJM Biocor. Conclusions: The in vitro results indicate that it is possible to predict the net pressure gradient by Doppler in bileaflet and stented biologic valves. Our data indicate that important PR is also present in stented biologic valves.

  • 22.
    Berglund, Martina
    et al.
    Linköping University, Department of Management and Engineering, Logistics & Quality Management. Linköping University, Faculty of Science & Engineering.
    Andersson, Torbjörn
    Linköping University, Department of Management and Engineering, Machine Design. Linköping University, Faculty of Science & Engineering.
    Hedbrant, Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Pavlasevic, Vanja
    Linköping University, Department of Management and Engineering, Machine Design. Linköping University, Faculty of Science & Engineering.
    Stålhand, Jonas
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Understanding the user beyond ‘common sense’ – teaching Product Ergonomics to design engineering students2015In: Proceedings 19th Triennial Congress of the IEA, International Ergonomics Association , 2015Conference paper (Refereed)
    Abstract [en]

    Multidisciplinary frameworks are needed to develop products that fit the human. Ergonomics is a multifaceted field that encompasses physical, cognitive and organizational aspects, and it is therefore a suitable subject to be taught to design engineering students.

    The objective of this paper was to describe and reflect upon how a systems perspective on Ergonomics is developed and conveyed in a course in Product Ergonomics to engineering students at the Design and Product Development (DPD) programme at Linköping University, Sweden. The paper is based on the authors’ experiences from teaching the course in Product Ergonomicsas well ason 52 students’ written reflections about their view on Ergonomics before and after taking the course.

    Means and ideas for teaching Ergonomics with a systems perspective included organizing a theoretical introduction into weekly themes and thereafter integrating and applying these themes in a product concept project under supervision of a multidisciplinary teacher team.

    The paper also reflects on how the systems perspective of Ergonomics is planned for and realized in the intended, implemented and attained curriculum.

  • 23.
    Berglund, Martina
    et al.
    Linköping University, Department of Management and Engineering, Logistics & Quality Management. Linköping University, Faculty of Science & Engineering.
    Pavlasevic, Vanja
    Linköping University, Department of Management and Engineering, Machine Design. Linköping University, Faculty of Science & Engineering.
    Andersson, Torbjörn
    Linköping University, Department of Management and Engineering, Machine Design. Linköping University, Faculty of Science & Engineering.
    Hedbrant, Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Stålhand, Jonas
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Theme-based assessment of education in design and product development2014In: Proceedings of the 10th International CDIO Conference, Universitat Politècnica de Catalunya, 2014Conference paper (Other academic)
    Abstract [en]

    One fundamental challenge in choosing an examination form to assess student achievements is to find an examination which, both encourages students to continuously elaborate the course content and constitutes a learning process itself. The objective of this paper is to share and reflect on the development and implementation of a new theme-based examination in a six credit course in Product Ergonomics given in the engineering programme Design and Product Development at Linköping University, Sweden. The course runs during four months and has two parts: one theoretical and one applied. The former focuses on theoretical ergonomic topics, models and methods while the latter is a project aiming at consolidating the students’ understanding of the theory by implementing the knowledge in a product development case. To encourage the students to adapt a deep learning approach, the traditional written mid-term exam for the theoretical part was abandoned and another concept developed. In the new concept, the theoretical part was split onto six weekly themes. Each theme was introduced at the beginning of the week by high-lighting main theories and models followed by a group-work assignment to be elaborated on by the students during the week. The theme was examined at the end of the week through a short written exam and a seminar to discuss and reflect upon the theme. From a student perspective, the positive outcome of the theme-based examination was peer learning and a more active learning style. The students appreciated the theme-based structure of the course. Occasionally, some students commented that weekly examinations could be perceived as stressful. The teachers perceived the students to be more acquainted with ergonomics theory and methods which increased the quality of the course project. The reported theme-based assessment is one example of implementing among others the CDIO syllabus parts 2.2 and 3.1and CDIO standards 8 and 11.

  • 24.
    Berntsson, Fredrik
    et al.
    Linköping University, Department of Mathematics, Computational Mathematics. Linköping University, Faculty of Science & Engineering.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Kozlov, Vladimir
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Nazarov, Sergei A.
    St Petersburg State University, Russia; St Petersburg State Polytech University, Russia.
    A Modification to the Kirchhoff Conditions at a Bifurcation and Loss Coefficients2018Report (Other academic)
    Abstract [en]

    One dimensional models for fluid flow in tubes are frequently used tomodel complex systems, such as the arterial tree where a large numberof vessels are linked together at bifurcations. At the junctions transmission conditions are needed. One popular option is the classic Kirchhoffconditions which means conservation of mass at the bifurcation andprescribes a continuous pressure at the joint.

    In reality the boundary layer phenomena predicts fast local changesto both velocity and pressure inside the bifurcation. Thus it is not appropriate for a one dimensional model to assume a continuous pressure. In this work we present a modification to the classic Kirchhoff condi-tions, with a symmetric pressure drop matrix, that is more suitable forone dimensional flow models. An asymptotic analysis, that has beencarried out previously shows that the new transmission conditions hasen exponentially small error.

    The modified transmission conditions take the geometry of the bifurcation into account and can treat two outlets differently. The conditions can also be written in a form that is suitable for implementationin a finite difference solver. Also, by appropriate choice of the pressuredrop matrix we show that the new transmission conditions can producehead loss coefficients similar to experimentally obtained ones.

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  • 25.
    Berntsson, Fredrik
    et al.
    Linköping University, Department of Mathematics, Computational Mathematics. Linköping University, Faculty of Science & Engineering.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Kozlov, Vladimir
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Nazarov, Sergey A.
    St Petersburg State University, St Petersburg State Polytechnical University, and Institute of Problems of Mechanical Engineering RAS, Russia..
    A one-dimensional model of a false aneurysm2017In: International Journal of Research in Engineering and Science (IJRES), ISSN 2320-9356, Vol. 5, no 6, p. 61-73Article in journal (Refereed)
    Abstract [en]

     A false aneurysm is a hematoma, i.e. collection ofblood outside of a blood vessel, that forms due to a hole  in the wall of an artery . This represents a serious medical condition that needs to be monitored and, under certain conditions, treatedurgently. In this work a one-dimensional model of a false aneurysm isproposed. The new model is based on a one-dimensional model of anartery previously presented by the authors and it takes into accountthe interaction between the hematoma  and the surrounding musclematerial. The model equations are derived  using rigorous asymptoticanalysis for the case of a simplified geometry.   Even though the model is simple it still supports a realisticbehavior for the system consisting of the vessel and the  hematoma. Using numerical simulations we illustrate the behavior ofthe model. We also investigate the effect  of changing the size of the hematoma. The simulations show that ourmodel can reproduce realistic solutions. For instance we show thetypical strong pulsation of an aneurysm by blood entering the hematoma during the work phase of the cardiac cycle, and the blood returning tothe vessel during the resting phase. Also we show that the aneurysmgrows  if the pulse rate is increased due to, e.g., a higher work load. 

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    A one-dimensional model of a false aneurysm
  • 26.
    Berntsson, Fredrik
    et al.
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Kozlov, Vladimir
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Nazarov, Sergey A.
    St Petersburg State University, Russia; St Petersburg State Polytech University, Russia; RAS, Russia.
    A one-dimensional model of viscous blood flow in an elastic vessel2016In: Applied Mathematics and Computation, ISSN 0096-3003, E-ISSN 1873-5649, Vol. 274, p. 125-132Article in journal (Refereed)
    Abstract [en]

    In this paper we present a one-dimensional model of blood flow in a vessel segment with an elastic wall consisting of several anisotropic layers. The model involves two variables: the radial displacement of the vessels wall and the pressure, and consists of two coupled equations of parabolic and hyperbolic type. Numerical simulations on a straight segment of a blood vessel demonstrate that the model can produce realistic flow fields that may appear under normal conditions in healthy blood vessels; as well as flow that could appear during abnormal conditions. In particular we show that weakening of the elastic properties of the wall may provoke a reverse blood flow in the vessel. (C) 2015 Elsevier Inc. All rights reserved.

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  • 27.
    Biju, Dona
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    A parametric study of oil-jet lubrication in gear wheels2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A parametric study of oil-jet lubrication in gear wheels is conducted using Computational Fluid Dynamics (CFD) to study the effect of the different design parameters on the cooling performance in a gearbox. Flow in oil jet lubrication is found to be complex with the formation of oil ligaments and droplets. Various hole radii of 1.5, 2 and 2.5 mm along with five oil velocities is analyzed and it is found that at lower volumetric rates, velocity has more effect on the cooling and at higher volumetric rates, hole size has more effect on the cooling. At higher velocities, the heat transfer is much greater than the actual heat production in the gear wheel, hence these velocity ratios are considered less suitable for jet lubrication. At low velocity ratios of below 2, the oil doesn’t fully impinge the gear bottom land and the sides leading to low cooling. Based on the cooling, impingement length and amount of oil lost to the casing surface, 2 mm hole with a velocity ratio of 2.225 is selected for a successful oil jet lubrication. Varying the inlet position in X, Y and Z directions (horizontal, vertical and lateral respectively) is found to have no improvement on the cooling. Making the oil jet hit the gear wheel surface at an angle is found to increase the cooling. Analysis with the use of a pipe to supply oil was conducted with circular and square inlet and it was found that the heat transfer decreases in both cases due to the splitting of oil jet caused by the combination of the effects of high pressure from the pipe and vorticity in the air field. A method has been developed for two gear analysis using overset meshes which can be used for further studies of jet lubrication in multi-gear systems. Single inlet is found to be better for cooling two gear wheels as it would require a reduced volumetric flow rate compared to double inlets. Oil system requirements for jet lubrication was studied and it was concluded that larger pumps have to be used to provide the high volumetric rates and highly pressurized oil required. On comparing the experimental losses from dip lubrication and the analytical losses for jet lubrication, dip lubrication is found to have lesser loses and more suitable for this case. Good quality lubrication would reduce the fuel consumption and also increase the longevity of gearboxes and hence more research into analyzing alternate lubrication systems can be carried out using the results from this thesis.

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  • 28.
    Björck, Hanna M.
    et al.
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Faculty of Health Sciences.
    Renner, Johan
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Maleki, Shohreh
    Atherosclerosis Research Unit, Center for Molecular Medicine, Department of Medicine, Karolinska Institute, Sweden.
    Nilsson, Siv F.E.
    Linköping University, Department of Medical and Health Sciences, Pharmacology. Linköping University, Faculty of Health Sciences.
    Kihlberg, Johan
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Radiology. Linköping University, Faculty of Health Sciences.
    Folkersen, Lasse
    Atherosclerosis Research Unit, Center for Molecular Medicine, Department of Medicine, Karolinska Institute, Sweden.
    Karlsson, Matts
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Ebbers, Tino
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Centre, Department of Clinical Physiology UHL.
    Eriksson, Per
    Atherosclerosis Research Unit, Center for Molecular Medicine, Department of Medicine, Karolinska Institute, Sweden.
    Länne, Toste
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Centre, Department of Thoracic and Vascular Surgery in Östergötland.
    Characterization of Shear-Sensitive Genes in the NormalRat Aorta Identifies Hand2 as a Major Flow-ResponsiveTranscription Factor2012In: PLOS ONE, E-ISSN 1932-6203, Vol. 7, no 12Article in journal (Refereed)
    Abstract [en]

    Objective: Shear forces play a key role in the maintenance of vessel wall integrity. Current understanding regarding shear-dependent gene expression is mainly based on in vitro or in vivo observations with experimentally deranged shear, hence reflecting acute molecular events in relation to flow. Our objective was to determine wall shear stress (WSS) in the rat aorta and study flow-dependent vessel wall biology under physiological conditions.

    Methods and Results: Animal-specific aortic WSS magnitude and vector direction were estimated using computational fluid dynamic simulation based on aortic geometry and flow information acquired by MRI. Two distinct flow pattern regions were identified in the normal rat aorta; the distal part of the inner curvature being exposed to low WSS and a non-uniform vector direction, and a region along the outer curvature being subjected to markedly higher levels of WSS and a uniform vector direction. Microarray analysis revealed a strong differential expression between the flow regions, particularly associated with transcriptional regulation. In particular, several genes related to Ca2+-signalling, inflammation, proliferation and oxidative stress were among the most highly differentially expressed.

    Conclusions: Microarray analysis validated the CFD-defined WSS regions in the rat aorta, and several novel flow-dependent genes were identified. The importance of these genes in relation to atherosusceptibility needs further investigation.

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  • 29.
    Björe Dahl, Emilia
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Sjöqvist, Mikaela
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Ökad resurseffektivitet i kraftvärmesystem genom säsongslagring av värme2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Increased resource efficiency in an energy system could result in large economic and environmental benefits. Tekniska verken i Linköping AB (Tekniska verken) is responsible for the district heating network in Linköping. Their vision is to create the world’s most resource efficient region. An important step towards this vision is more efficient usage of produced heat, something which could be achieved through integration of a seasonal heat storage in the energy system. The purpose of the Master’s thesis is therefore to explore the economic and technical potential for a seasonal heat storage in Tekniska verken’s energy system. The investigated technology is borehole thermal energy storage using two different kinds of borehole heat exchangers; u-pipe and annular coaxial heat exchanger.

    To evaluate how Tekniska verken’s energy system changes through integration of a seasonal heat storage a calculation model has been developed in MATLAB. The heat from the seasonal storage needs to be upgraded in order to be used in the ordinary district heating network. Therefore two kinds of heat pumps have been evaluated in the model; absorption heat pumps and compression heat pumps. The main method used for calculations on the heat transfer processes in the storage is the finite difference method. During economic calculations, the economic potential of the investment is expressed solely in relation to the scenario that the storage is not built.

    Four different combinations of borehole heat exchangers and heat pumps have been simulated over a twenty year period. The simulated storages have a depth of 200-250 meters and a radius of approximately 100 meters which relates to1500 boreholes. The result shows small differences between the two types of heat exchangers. The choice of heat pump has though a crucial importance of the economic result. The systems with absorption heat pumps uses drive heat from existing steam production and can cover a major part of the peak load during winter. Meanwhile the compression heat pumps have a large cost for electricity. This causes a negative net present value according to the result, while the systems with absorption heat pumps have a discounted pay-back time of 12 years. Another positive effect of the systems with absorption heat pumps is the decrease in carbon dioxide emissions from the heat production.

    The result of the Master thesis shows that both economic advantages and increased resource efficiency can be achieved through integration of a borehole thermal energy storage with absorptions heat pumps.  To further investigate this potential seems therefore beneficial.  

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    Ökad resurseffektivitet i kraftvärmesystem genom säsongslagring av värme_Björe Dahl_Sjöqvist
  • 30.
    Björk, Andreas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Enander, Tobias
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Validering och utveckling av matematisk modell av rökgaskondensering: En undersökning av matematiska modeller avrökgaskondensering samt en studie av hur yttre faktorerpåverkar rökgaskondenseringen i kraftvärmeverk2019Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    When burning fuels with high water or hydrogen content, much of the combustion energy follows themoist air that leaves the chimney at the plant. A common example is the combustion of wood fuel orhousehold waste in CHP-plants. In order to increase the plant's efficiency and at the same time clean theair from sulfur dioxide and metals, a flue gas condensation of scrubber-type can be used. Cool water isinjected into a filling bed and meets the hot flue gas. When the flue gases are cooled, energy is released bythe water in the flue gases when vapor turns into liquid form, energy that can be used e.g. to heat thedistrict heating network's return line.

    This work has been carried out on behalf of Hifab DU-teknik, which in the past year has carried outstudies and calculations of the flue gas condensation at the Torsvik CHP plant, which has led to improvedefficiency. Through simulations and calculations in Matlab, this report tries to verify the optimalcondensate flow calculated by DU technology and study how the plant is affected by changed flows andtemperatures in the district heating network’s return line.

    The authors of this work have put a lot of effort into understanding the theory of heat exchangers andenergy in moist air in depth. The theoretical framework we set up can be seen as a thorough introductionto the subjects and an in-depth study compared to the usual course content during the Bachelor's degreeprogram in mechanical engineering at Linköping University.

    The goal of the preparatory method work has been to find expressions of the different temperatures inthe plant that make it possible to simulate changes in the plant. Models have been developed to be able tosimulate and calculate the outgoing temperatures given different mass flows using the ingoingtemperatures in a heat exchanger. The model has proven to work well for the heat exchanger, which isconnected to the district heating network. In the calculations of temperatures out of the filling bed, twomethods have been tested. The authors’ has studied what happens if the condensate temperature out ofthe filling bed is set to the dew temperature of the flue gases. Attempts have also been made to considerthe filling bed as a kind of heat exchanger.

    The result of the authors' calculations of condensate flow differs to a certain extent from the DU-teknik’scalculated condensate flows during a changed boiler load in the plant. To end up at the same result, thehot condensate temperature needed to take a slightly higher temperature than the dew temperature. Theassumption is reasonable to make, but it is difficult to draw any conclusions about the magnitude.

    Regarding the method of considering the filling bed as a heat exchanger, there are both successes andshortcomings. The success lies in that the trend for the different temperatures seems to be in line with thetheory that the authors have presented for heat exchangers and what happens when the massflowsincrease or decrease in a heat exchanger. However, the shortcomings lie in the fact that the method doesnot take into account that heat is released during the condensation, but is based entirely on the fact thatthe fluid in the filling bed do not undergo phase transformations.

    Two important proposals for continued work are highlighted at the end of the report. It would beinteresting to study the possibility of considering the filling bed as two separate heat exchangers, where thedry flue gases encounter a partial current of the condensate and the moisture in the flue gases meetsanother partial current of the condensate. Furthermore, a desire is made to test the flue gas condensationin the future at different condensate flows for a longer period of time in order to achieve stationaryconditions in the temperatures. The data can later be used to produce mathematical expressions of whathappens to the outgoing temperatures of the filling bed when the condensate flow changes or when theingoing temperature of the filling bed increases or decreases.

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  • 31. Bolger, A F
    et al.
    Eidenvall, L
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Loyd, Dan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Wranne, Bengt
    Linköping University, Department of Medicine and Care, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    Understanding continuous-wave Doppler signal intensity as a measure of regurgitant severity.1997In: Journal of the American Society of Echocardiography, ISSN 0894-7317, E-ISSN 1097-6795, Vol. 10, no 6, p. 613-622Article in journal (Refereed)
    Abstract [en]

    Continuous-wave Doppler signal intensity is commonly expected to reflect the severity of mitral regurgitation. Physical principles predict that alignment of the imaging beam, flow velocity, and turbulence can also be important or even dominant determinants of continuous-wave Doppler signal intensity. The reliability of tracking regurgitant severity with continuous-wave Doppler signal intensity was assessed in vitro with varying volume, velocity, turbulence, and beam alignment. The conditions wherein continuous-wave Doppler signal intensity increased with regurgitant volume were specific but poorly predictable combinations of orifice size, flow volume, and perfect beam alignment. Under other conditions flow velocity and turbulence effects dominated, and continuous-wave Doppler signal intensity did not reflect changing regurgitant volume. Continuous-wave Doppler signal intensity-based impressions of regurgitant severity may be unreliable and even misleading under some circumstances.

  • 32.
    Bolger, Ann F
    et al.
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    Eidenvall, Lars
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Loyd, Dan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Wranne, Bengt
    Linköping University, Department of Medicine and Care, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    THE MULTIPLE DETERMINANTS OF CONTINUOUS WAVE SIGNAL INTENSITY1992In: Circulation, ISSN 0009-7322, E-ISSN 1524-4539, Vol. 86, no 4, SArticle in journal (Refereed)
  • 33.
    Boqvist, Emil
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Investigation of a swing check valve using CFD2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master’s thesis is made to increase the understanding of the dynamic characteristics of a typical large swing check valve used in a system that transports pressurized water to a reactor tank.3D FSI-simulations are performed for a number of transients in order to study the dynamic characteristics their dependence of the deceleration rate. The purpose is to find information about the dynamics that could be used in a future improvement of a 1D-model.Steady state simulations are performed for angles in the whole spectrum. Seven transient FSI-simulations with different constantly decelerating flows from 630 kg/s2 (6.7 m/s2) to 40 320 kg/s2 (430 m/s2) have been performed. The pressure on the disc caused by the hydraulic torque is integrated and the corresponding torque contribution, together with the weight torque, is used in the second law of motion to calculate the movement of the disc throughout the transients.Steady state simulations yield the pressure drop over the valve, which could be compared with field measurements in order to validate the CFD-simulations. Comparison of the pressure distribution on the disc for the steady state and transient simulations shows the importance of taking the disc angular velocity into account when modelling in 1D. Correlations between the angle, angular velocity, torque and mass flow are obtained from the transient FSI-simulations. Torque coefficients according to (Li & Liou, Vol. 125) are also brought out from the simulated transients, but in order to create a model in line with this approach further simulations have to be performed. A prediction of the pressure rise that occurs when a swing check valve closes in backward flow according to the Joukowsky equation is brought out and gives an idea of the loadings that the system has to be able to handle.

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    Master Thesis Emi Boqvist
  • 34.
    Borger, Hendrik
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Model development for large scale intake manifold optimization using CFD2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Continued improvement of combustion engines to operate with lower fuel usage and lower harmful emissions leads to more and more complex engine designs. Computational fluid dynamics (CFD) is a method which helps predicting engine performance, reducing the reliance on engine tests. CFD can be used to optimise a geometry using a design of experiments (DOE). This study focuses on developing a simulation method to use for such large scale optimisation of air intake manifolds.

    The main focus in this study was the difference in flow quantities such as swirl number and pressure drop between the different cylinders for a given manifold. Four different simulation approaches were tested: one steady-state, two transient and one transient with a moving mesh. These simulation methods were tested on five different geometries based on a six cylinder, 13L spark ignited (Otto) combustion engine and a six cylinder, 13L compression ignited (Diesel) combustion engine. The five geometries were compared using the different simulation methods, with the main goal of determining if the different simulation methods provide the same optimal geometry. The most complex simulation model, the transient simulation with moving mesh, was chosen as main reference case in absence of experimental results.

    Results of this mock design of experiments show that the different simulation approaches do not perform consistently enough to recommend using any of the tested methods in further optimisation studies. While the various methods showed significantly different results when comparing the differences in flow parameters between cylinders, using the steady-state or transient methods to predict the flow parameters in a single cylinder is a viable approach.

    Multiple possible causes for the inconsistent results are discussed, chief among which is the chosen grid generation approach and selected convergence criteria. A recommendation is made to improve the reference, moving mesh, case using scale resolving models.

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  • 35.
    Borgström, Fredrik
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Coyet, Jonas
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Waste heat recovery system with new thermoelectric materials2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Increasing fuel prices, higher demands on "greener" transports and tougher international emission regulations puts requirements on companies in the automotive industry in improving their vehicle fuel efficiency. On a typical heavy duty Scania truck around 30% of the total fuel energy is wasted through the exhaust system in terms of heat dissipated to the environment. Hence, several investigations and experiments are conducted trying to find ways to utilize this wasted heat in what is called a waste heat recovery (WHR) system. At Scania several techniques within the field of WHR are explored to find the profits that could be made.

    This report will cover a WHR-system based on thermoelectricity, where several new thermoelectric (TE) materials will be investigated to explore their performance. A reference material which is built into modules will be mounted in the exhaust gas stream on a truck to allow for measurements in a dyno cell. To analyze new materials a Simulink model of the WHR-system is established and validated using the dyno cell measurements. By adjusting the model to other thermoelectric material properties and data, the performance of new TE materials can be investigated and compared with today’s reference material.

    From the results of the simulations it was found that most of the investigated TE materials do not show any increased performance compared to the reference material in operating points of daily truck driving. This is due to dominance of relatively low exhaust gas temperatures in average, while most advantages in new high performing TE-materials are seen in higher temperature regions. Still, there are candidates that will be of high interest in the future if nanotechnology manufacturing process is enhanced. By using nanostructures, a quantum well based BiTe material would be capable of recovering 5-6 times more net heat power compared to the reference BiTe material. Another material group that could be of interest are TAGS which in terms of daily driving will increase the power output with pending values between 40-80 %. It is clear that for a diesel truck application, materials with high ZT-values in the lower temperature region (100-350°C) must be developed, and with focus put on exhibiting low thermal conductivity for a wide temperature span.

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  • 36. Order onlineBuy this publication >>
    Bradley, Andreas
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    CFD Simulations for Film Cooling: Reduced Models at Engine Like Conditions2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In gas turbines some parts are exposed to combustion gases with temperatures well above the melting temperature of the material. Therefore, various cooling techniques are utilized in order to protect the parts exposed to these hot gases. One such technique, film cooling, is a common and well established way to protect the exposed parts. Film cooling involves the ejection of cold air on the surface of the parts that are to be protected, thus creating a film of colder air between the surface and the hot gases.

    Computational Fluid Dynamics (CFD) is a way of calculating fluid flow, and can be used to calculate the effectiveness of a cooling film in film cooling applications. CFD is demanding in terms of computer power, especially when advanced methods are to be used. Even the simpler methods, such as Reynolds Average Navier-Stokes (RANS), can be quite demanding, time and computer power-wise, and require resources not always available. Finding ways of limiting the needed computer power is therefore of large interest.

    The aim of this thesis is to reduce the computational time of film cooling CFD-simulations, by using reduced models. To achieve this, simulations has been conducted and compared to experiments. The investigated setup is of an enginelike equipment, where a guide vane is investigated for heat transfer coefficient and film effectiveness. The geometry in the experimental setup is constructed in such a way as to give the same pressure distribution around the guide vane as can be seen in a real gas turbine, although at lower temperatures than those in the real turbine. The CFD-simulations conducted on the test rig includes RANS-simulations using the realizable k- and the SST k-! turbulence models.

    The reduced model contains only the central part of the vane. The walls of the test rig is replaced with periodic boundary conditions. This narrow model gives good agreement with the full model for heat transfer coefficient. Due to the large computational cost required to conduct simulations with cooling on the full model no comparison were made between the cooled narrow and cooled full model.

    To further reduce the size of the computational domain, two additional models were investigated. The first one involves a reduction of the full domain to only include the section being studied, in this case the suction side of the guide vane.

    This infers a reduction of the mesh size to less than ten percent of the size of what a mesh of the cooled full domain would be. The next step to reduce the size of the model and mesh is to make a narrow version of the already shortened model. The results for these two models show that they perform adequately to each other and (in the cases where a comparison is possible), to the full domain.

    List of papers
    1. Fan Shaped And Cylindrical Holes Studied in a Vane Film Cooling Test Rig
    Open this publication in new window or tab >>Fan Shaped And Cylindrical Holes Studied in a Vane Film Cooling Test Rig
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    2010 (English)In: Proceedings of the Asme Turbo Expo 2010, Vol 4, Pts a and B, 2010, p. 1777-1784Conference paper, Published paper (Refereed)
    Abstract [en]

    In order to optimize the vane film cooling and thereby increase the efficiency of a gas turbine, different film cooling configurations were experimentally investigated. Dynamic similarity was obtained regarding main flow Reynolds number, airfoil pressure coefficient, adiabatic wall temperature and film cooling ejection ratio. The maximum reached Mach number was 0.52. The geometry of the test section, consisting of one vane and two flow paths, was modified in order to meet the dimensionless pressure coefficient distribution around the airfoil experienced by a full stage airfoil. This would ascertain that scaled but engine realistic pressure gradients would be achieved in the rig test.

    During the test, the cold airfoil was suddenly imposed to a hot main stream and the evaluation of both the film cooling effectiveness and the heat transfer coefficient distribution on the visiable surface could be done at one single test using timeresolved temperature measurements obtained through IR thermography. A high resolution MWIR camera was used together with a silicon viewing window. The post-processing allowed for corrections regarding emissions and determination of the desired parameters on the vane surface.

    Results, heat transfer coefficients and film cooling effectiveness, for fan shaped and cylindrical film cooling holes configurations are compared. The results show clear benefit of using shaped holes over cylindrical ditto, especially on the suction side where near hole film effectiveness is enhanced by approximately 25%, but the results also show that this benefit diminishes to nothing in the suction side trailing edge region.

    The local heat transfer coefficients are generally lower for the shaped hole configurations. Contrary to the film effectiveness the shaped holes configurations show lower heat transfer coefficients also at the suction side trailing edge region, making use of the shaped hole configurations superior to cylindrical ones as the heat flux to the surface is reduced.

    Numerical predictions using a boundary layer code, TEXSTAN, and CFD, for a smooth wall configuration corresponds well with the measured results.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-91707 (URN)10.1115/GT2010-23308 (DOI)000290693500155 ()978-0-7918-4399-4 (ISBN)978-0-7918-3872-3 (ISBN)
    Conference
    ASME Turbo Expo 2010: Power for Land, Sea, and Air, GT 2010; Glasgow; United Kingdom
    Available from: 2013-04-30 Created: 2013-04-30 Last updated: 2016-03-14Bibliographically approved
    2. Towards Efficient CFD-Simulations of Engine LikeTurbine Guide Vane Film Cooling
    Open this publication in new window or tab >>Towards Efficient CFD-Simulations of Engine LikeTurbine Guide Vane Film Cooling
    Show others...
    2011 (English)Conference paper, Published paper (Other academic)
    Abstract [en]

    It is well known that the efficiency of a gas turbine can be increased by using higher combustion temperatures and that this demands improved cooling. This study focuses on strategies to decrease the turnaround time for numerical predictions of film cooling while keeping the ability to resolve details of the flow. Simulations have been carried out for a real vane geometry at close to engine-like conditions and results are compared with corresponding experiments. The investigation includes an un-cooled situation for aerodynamic validation and to determine baseline heat transfer coefficent. Simulations and experiments of film effectiveness and heat transfer coefficient and their dependence of blowing ratio are investigated.

    Place, publisher, year, edition, pages
    ARC Aerospace Research Central, 2011
    Keywords
    Film cooling, gas turbines, CFD
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:liu:diva-75567 (URN)10.2514/6.2011-708 (DOI)978-1-60086-950-1 (ISBN)
    Conference
    49th AIAA Aerospace Science Meeting including the New Horizons Forum and Aerospace Exposition, January 4-7, Orlando, Florida, USA
    Available from: 2012-03-08 Created: 2012-03-08 Last updated: 2016-03-14Bibliographically approved
    3. CFD Simulations Using Reduced Models for Film Cooling Design
    Open this publication in new window or tab >>CFD Simulations Using Reduced Models for Film Cooling Design
    Show others...
    2011 (English)In: 49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 2011, American Institute of Aeronautics and Astronautics, 2011, p. AiAA 2011-710-Conference paper, Published paper (Other academic)
    Abstract [en]

    Film cooling technologies are widely used for attaining high efficiency in gas turbine engines. In this study we have investigated the potential for reduced models to capture different aspects of film cooling by means of CFD at low turn-around time while maintaining the accuracy at a reasonable level. CFD simulations and experiments were carried out for an engine-like setting. Subsequently, the computational domain was reduced in two steps in order to decrease the simulation time. Results for all models are compared with experimental data, including aerodynamic validation, heat transfer coefficient and film effectiveness. The aerodynamic results are very similar for experiments and simulations, and the heat transfer coefficient and film cooling effectiveness showed similarities within the expected range. Thus, this strategy could be very useful for e.g. early vane and film cooling design.

    Place, publisher, year, edition, pages
    American Institute of Aeronautics and Astronautics, 2011
    Keywords
    Film Cooling, Gas Turbines, CFD
    National Category
    Mechanical Engineering
    Identifiers
    urn:nbn:se:liu:diva-76905 (URN)10.2514/6.2011-710 (DOI)978-1-60086-950-1 (ISBN)
    Conference
    49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 4–7 January 2011, Orlando, Florida
    Available from: 2012-04-24 Created: 2012-04-24 Last updated: 2016-05-11Bibliographically approved
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    CFD Simulations for Film Cooling: Reduced Models at Engine Like Conditions
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  • 37.
    Bradley, Andreas
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Prediction of vane lm cooling in gas turbines Correlations and Parameters2009Report (Other academic)
    Abstract [en]

    When designing gas turbines, a high combustion temperature is desirable to obtain a good thermal eciency. At the same time, the thermal limitations of the gas turbines components must not be exceeded. High temperatures can lead to large thermal stresses that can reduce the life span of the components and increase the risk of fatigue and failure.

    The trade-o between eciency on the one hand, and reliability, life span, service interval etc. on the other hand, must be handled early in the design process. At the same time, many other aspects such as aerodynamics, structural strength, manufacturing and assembly must be considered simultaneously.

    In the combustor and high pressure turbine, lm cooling is extensively used as one of the major ways to protect parts from the gases of combustion. Film cooling was introduced about 50 years ago, and is today normally actualized by taking air from the compressor and ejecting it out through rows of holes placed on the surfaces that are to be protected.

    Film cooling is a complex process, in uenced by many parameters related to the hole geometry, the flow through the hole, and the free stream above the surface of interest, see e.g. A number of governing parameters have been identied, and their effect has been analyzed, see e.g.

    In order to handle the design of lm cooling along with the rest of the design process, fast and relatively accurate tools for prediction and comparison of film cooling congurations are essential. One early attempt to describe film cooling by a correlation was carried out in the sixties. Since then a number of correlations have been developed and scrutinized, but most of them have considered  at plates without pressure gradients, a case that is not always representative for gas turbine lm cooling. Furthermore, most correlations are developed utilizing experiments, where at least some of the parameters in the correlation have been adopted to t particular experimental data. This give rise to questions regarding, among others, the possibility to generalize the result of the correlations to other presumptions. This investigation summarize some of the correlations presented in the open literature, and discuss their strengths and weaknesses.

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    Prediction of vane lm cooling in gas turbines Correlations and Parameters
  • 38.
    Bradley, Andreas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Gårdhagen, Roland
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Bird-Like Wing Conguration for Pitch Control of a Tailless Aircraft2012Conference paper (Other academic)
    Abstract [en]

    A numerical study of a small bird-like aircraft has been performed. The aim of the study was to investigate how a swing wing (actualized through a constant span morphing wing) can be used for pitch control of a tailless aircraft. The results show that a swing wing can be successfully used, and that the aircraft can be maintained in a trimmed state by only small adjustments of part of the wing. A comparison was also made with a Vortex lattice method, but these results significantly deviated from those obtained with CFD. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc.

  • 39.
    Bradley, Andreas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Nadali Najafabadi, Hossein
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Wren, Joakim
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Utriainen, Esa
    Kinell, Mats
    Towards Efficient CFD-Simulations of Engine LikeTurbine Guide Vane Film Cooling2011Conference paper (Other academic)
    Abstract [en]

    It is well known that the efficiency of a gas turbine can be increased by using higher combustion temperatures and that this demands improved cooling. This study focuses on strategies to decrease the turnaround time for numerical predictions of film cooling while keeping the ability to resolve details of the flow. Simulations have been carried out for a real vane geometry at close to engine-like conditions and results are compared with corresponding experiments. The investigation includes an un-cooled situation for aerodynamic validation and to determine baseline heat transfer coefficent. Simulations and experiments of film effectiveness and heat transfer coefficient and their dependence of blowing ratio are investigated.

  • 40.
    Bradley, Andreas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Wren, Joakim
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Comparison of Correlations and Experiments for Prediction of Vane Film Cooling in Gas Turbines2010Report (Other academic)
    Abstract [en]

    In an earlier report by Bradley, a number of correlations from the open literature were presented and evaluated. All these correlations manage to accurately describe the film cooling eectiveness for the experiments they are based on, but there is doubts regarding the general predictive value of these correlations, especially for engine-like conditions. The correlations have now been analysed to investigate their predictive capabilities - especially the general applicability of correlations is in focus, for example for geometries or flow conditions slightly dierent than those for which the correlations were originally designed.

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    Comparison of Correlations and Experiments for Prediction of Vane Film Cooling in Gas Turbines
  • 41.
    Bäck, Sophia
    et al.
    Linköping University, Department of Health, Medicine and Caring Sciences, Division of Diagnostics and Specialist Medicine. Linköping University, Faculty of Medicine and Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Henriksson, Lilian
    Linköping University, Department of Health, Medicine and Caring Sciences, Division of Diagnostics and Specialist Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Radiology in Linköping.
    Bolger, Ann F
    Linköping University, Department of Health, Medicine and Caring Sciences, Division of Diagnostics and Specialist Medicine. Linköping University, Faculty of Medicine and Health Sciences. Univ Calif San Francisco, CA USA.
    Carlhäll, Carljohan
    Linköping University, Department of Health, Medicine and Caring Sciences, Division of Diagnostics and Specialist Medicine. Linköping University, Faculty of Medicine and Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV). Region Östergötland, Heart Center, Department of Clinical Physiology in Linköping.
    Persson, Anders
    Linköping University, Department of Health, Medicine and Caring Sciences, Division of Diagnostics and Specialist Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Radiology in Linköping. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Ebbers, Tino
    Linköping University, Department of Health, Medicine and Caring Sciences, Division of Diagnostics and Specialist Medicine. Linköping University, Faculty of Medicine and Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Assessment of transmitral and left atrial appendage flow rate from cardiac 4D-CT2023In: Communications Medicine, E-ISSN 2730-664X, Vol. 3, no 1, article id 22Article in journal (Refereed)
    Abstract [en]

    Plain language summaryAssessing the blood flow inside the heart is important in diagnosis and treatment of various cardiovascular diseases, such as atrial fibrillation or heart failure. We developed a method to accurately track the motion of the heart walls over the course of a heartbeat in three-dimensional Computed Tomography (CT) images. Based on the motion, we calculated the amount of blood passing through the mitral valve and the left atrial appendage orifice, which are markers used in the diagnostic of heart failure and assessment of stroke risk in atrial fibrillation. The results agreed well with measurements from 4D flow MRI, an imaging technique that measures blood velocities. Our method could broaden the use of CT and make additional exams redundant. It can even be used to calculate the blood flow inside the heart. BackgroundCardiac time-resolved CT (4D-CT) acquisitions provide high quality anatomical images of the heart. However, some cardiac diseases require assessment of blood flow in the heart. Diastolic dysfunction, for instance, is diagnosed by measuring the flow through the mitral valve (MV), while in atrial fibrillation, the flow through the left atrial appendage (LAA) indicates the risk for thrombus formation. Accurate validated techniques to extract this information from 4D-CT have been lacking, however.MethodsTo measure the flow rate though the MV and the LAA from 4D-CT, we developed a motion tracking algorithm that performs a nonrigid deformation of the surface separating the blood pool from the myocardium. To improve the tracking of the LAA, this region was deformed separately from the left atrium and left ventricle. We compared the CT based flow with 4D flow and short axis MRI data from the same individual in 9 patients.ResultsFor the mitral valve flow, good agreement was found for the time span between the early and late diastolic peak flow (bias: <0.1 s). The ventricular stroke volume is similar compared to short-axis MRI (bias 3 ml). There are larger differences in the diastolic peak flow rates, with a larger bias for the early flow rate than the late flow rate. The peak LAA outflow rate measured with both modalities matches well (bias: -6 ml/s).ConclusionsOverall, the developed algorithm provides accurate tracking of dynamic cardiac geometries resulting in similar flow rates at the MV and LAA compared to 4D flow MRI. Back et al. describe a motion tracking algorithm to measure the flow rate through the mitral valve (MV) and the left atrial appendage (LAA) from 4D-CT data. The developed algorithm provided accurate tracking of dynamic cardiac geometries resulting in similar flow rates at the MV and LAA to those measured by 4D flow MRI.

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  • 42.
    Casas Garcia, Belén
    et al.
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Lantz, Jonas
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Viola, Federica
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Cedersund, Gunnar
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Bolger, Ann F.
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Clinical Physiology in Linköping. University of Calif San Francisco, CA USA.
    Carlhäll, Carljohan
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Clinical Physiology in Linköping. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Ebbers, Tino
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Clinical Physiology in Linköping. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Bridging the gap between measurements and modelling: a cardiovascular functional avatar2017In: Scientific Reports, E-ISSN 2045-2322, Vol. 7, article id 6214Article in journal (Refereed)
    Abstract [en]

    Lumped parameter models of the cardiovascular system have the potential to assist researchers and clinicians to better understand cardiovascular function. The value of such models increases when they are subject specific. However, most approaches to personalize lumped parameter models have thus far required invasive measurements or fall short of being subject specific due to a lack of the necessary clinical data. Here, we propose an approach to personalize parameters in a model of the heart and the systemic circulation using exclusively non-invasive measurements. The personalized model is created using flow data from four-dimensional magnetic resonance imaging and cuff pressure measurements in the brachial artery. We term this personalized model the cardiovascular avatar. In our proof-of-concept study, we evaluated the capability of the avatar to reproduce pressures and flows in a group of eight healthy subjects. Both quantitatively and qualitatively, the model-based results agreed well with the pressure and flow measurements obtained in vivo for each subject. This non-invasive and personalized approach can synthesize medical data into clinically relevant indicators of cardiovascular function, and estimate hemodynamic variables that cannot be assessed directly from clinical measurements.

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  • 43.
    Casas Garcia, Belén
    et al.
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Lantz, Jonas
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Viola, Federica
    Linköping University, Department of Health, Medicine and Caring Sciences, Division of Diagnostics and Specialist Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Cedersund, Gunnar
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Bolger, Ann F.
    Linköping University, Department of Health, Medicine and Caring Sciences, Division of Diagnostics and Specialist Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart Center, Department of Clinical Physiology in Linköping. Department of Medicine, University of California San Francisco, San Francisco, California, USA.
    Carlhäll, Carl-Johan
    Linköping University, Department of Health, Medicine and Caring Sciences, Division of Diagnostics and Specialist Medicine. Linköping University, Faculty of Medicine and Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV). Region Östergötland, Heart Center, Department of Clinical Physiology in Linköping.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Ebbers, Tino
    Linköping University, Department of Health, Medicine and Caring Sciences, Division of Diagnostics and Specialist Medicine. Linköping University, Faculty of Medicine and Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Publisher Correction: Bridging the gap between measurements and modelling: a cardiovascular functional avatar2020In: Scientific Reports, E-ISSN 2045-2322, Vol. 10, no 1Article in journal (Other academic)
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  • 44.
    Casas Garcia, Belén
    et al.
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Viola, Federica
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Cedersund, Gunnar
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Bolger, Ann F
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Clinical Physiology in Linköping. Univ Calif San Francisco, CA USA.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Carlhäll, Carljohan
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Clinical Physiology in Linköping. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Ebbers, Tino
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Clinical Physiology in Linköping. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Non-invasive Assessment of Systolic and Diastolic Cardiac Function During Rest and Stress Conditions Using an Integrated Image-Modeling Approach2018In: Frontiers in Physiology, E-ISSN 1664-042X, Vol. 9, article id 1515Article in journal (Refereed)
    Abstract [en]

    Background: The possibility of non-invasively assessing load-independent parameters characterizing cardiac function is of high clinical value. Typically, these parameters are assessed during resting conditions. However, for diagnostic purposes, the parameter behavior across a physiologically relevant range of heart rate and loads is more relevant than the isolated measurements performed at rest. This study sought to evaluate changes in non-invasive estimations of load-independent parameters of left-ventricular contraction and relaxation patterns at rest and during dobutamine stress. Methods: We applied a previously developed approach that combines non-invasive measurements with a physiologically-based, reduced-order model of the cardiovascular system to provide subject-specific estimates of parameters characterizing left ventricular function. In this model, the contractile state of the heart at each time point along the cardiac cycle is modeled using a time-varying elastance curve. Non-invasive data, including four-dimensional magnetic resonance imaging (4D Flow MRI) measurements, were acquired in nine subjects without a known heart disease at rest and during dobutamine stress. For each of the study subjects, we constructed two personalized models corresponding to the resting and the stress state. Results: Applying the modeling framework, we identified significant increases in the left ventricular contraction rate constant [from 1.5 +/- 0.3 to 2 +/- 0.5 (p = 0.038)] and relaxation constant [from 37.2 +/- 6.9 to 46.1 +/- 12 (p = 0.028)]. In addition, we found a significant decrease in the elastance diastolic time constant from 0.4 +/- 0.04 s to 0.3 +/- 0.03 s = 0.008). Conclusions: The integrated image-modeling approach allows the assessment of cardiovascular function given as model-based parameters. The agreement between the estimated parameter values and previously reported effects of dobutamine demonstrates the potential of the approach to assess advanced metrics of pathophysiology that are otherwise difficult to obtain non-invasively in clinical practice.

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  • 45.
    CHHETRI, SASHWAT
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Improvement of the 1D CFD method for Thermal management of a Battery Electric Vehicle2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Electrification of vehicles is necessary to combat greenhouse gas emissions, whichcauses global warming and climate change. There has been a demand in the use ofBattery Electric Vehicles due to this increased awareness of sustainability. However,they have been beset with issues such as range and conservation of energy. A partof the solution could be an energy-efficient thermal management system. A 1-Dimensional (1-D) complete vehicle thermal model in GT-SUITE is used topredict the energy efficiency of the vehicle at the conceptual stage. The model helpspredict results quickly and is used for complete system-level simulations. This thesisfocuses on optimizing the method for predicting the realistic and accurate energyconsumption of the thermal management system in the vehicle at the 1-D level. TheCompact Modular Architecture (CMA) platform, which is the vehicle platform usedin current production cars by Volvo Cars will be used for the study and all studiesare performed using a standardized drive cycle. Initial sensitivity studies with afully open grille are performed to understand the operating points of the variouscomponents of interest to investigate. The mass flow rate, ambient temperature,battery temperature, and cooling fan speed are varied.The Active Grille Shutters (AGS) which provides aerodynamic benefit at high speedis implemented in the existing thermal model which could previously accommodateonly the fully open grille. This allows the grille shutters to vary at different anglesbased on cooling demand. The previous existing thermal model method also neededto be optimized to accommodate the AGS. The cooling fan control logic needed tobe improved for better accuracy and energy consumption prediction. Furthermore,the grille shutters and cooling fan speed is needed to regulate the amount of air flowthrough the heat exchangers for the model to behave as close to a real productionvehicle. A code was developed which generated fan speed and grille shutter anglesbased on mass flow rate values to input in the model.Further investigations were made with the optimized thermal model with AGS tostudy the influence of additional mass flow rate on the mass power consumptionof the thermal management system components of interest. It was observed in the initial sensitivity studies that the additional mass flow rate saw significant power savings. However, with the implementation of AGS and additional mass airflowinto the system, the power due to the variation of shutters is taken into account.The results indicate that the total power consumption gradually decreases with theincreasing mass flow rate. But, this is up to a certain extent where the energyconsumption due to the shutter opening takes over the overall power consumptionof the vehicle and overcomes the savings seen by other components in the system causing the total power to increase.

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    Improvement of the 1-D CFD Method for Thermal Management of a Battery Electric Vehicle
  • 46.
    Colombi, Raffaele
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    CFD Investigation of Aerodynamic Drag Reduction for an Unloaded Timber Truck2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The road transport industry is facing a strong need for fuel consumption reduction, driven by the necessity of decreasing polluting emissions, such as CO2 and NOX, as well as coping with strict regulations and increasing fuel costs. For road vehicles the aerodynamic drag constitutes a major source of energy consumption, and for this reason improving the aerodynamic performance of the vehicle is an established approach for reducing fuel consumption and greenhouse gases emissions.

    In this Thesis work, Computational Fluid Dynamics (CFD) investigations have been carried out in order to investigate and improve the aerodynamic performance of an unloaded timber truck. The work has been divided in two parts. In a first phase, a preliminary study was carried out on a simplified tractor-trailer model in order to establish a suitable computational grid and turbulence model. The hexcore-mesh showed a better performance over the tet- and poly-mesh types. Among the selected RANS turbulence models, the Realizable kε with Enhanced Wall Treatment (EWT) and y+ > 30 showed the highest reliability of results in

    comparison with experimental data and existing CFD investigations.

    In a second phase, the flow field around the baseline unloaded timber truck was analysed in order to highlight potential regions for drag reduction. The truck cabin-bulkhead gap, bunks, the exposed wheels and the stakes were found make key contribution to the drag build-up. The analysis confirmed the 5-yaw case to be the most representative for the wind-averaged drag coefficient.

    Geometry modifications were implemented in order to improve the aerodynamic performance in the selected areas, and subsequently combined into aero-kits in order to enhance the performance, analysed for the 5-yaw case. The combination of extended side skirts, bulkhead shield and collapsed stakes yielded a remarkable result of more than 30% decrease in the wind-averaged drag coefficient, achieved by reducing the flow separation on the cabin leeward A-pillar, and by shielding areas of high stagnation pressure from the side wind.

    Furthermore, a parallel study was conducted on the development of a procedure for the automatic post-processing of results. The outcome was a set of Python scripts to be used with Kitaware Paraview in order to automatically obtain figures of surface variables distributions, iso-surfaces, velocity profiles, drag build-up and total pressure contours. The procedure was finally extended to include the case comparison.

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  • 47.
    Cruz, Igor
    et al.
    Linköping University, Department of Management and Engineering, Energy Systems. Linköping University, Faculty of Science & Engineering.
    Johansson, Maria
    Linköping University, Department of Management and Engineering, Energy Systems. Linköping University, Faculty of Science & Engineering.
    Wren, Joakim
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Assessment of the potential for small-scale CHP production using Organic Rankine Cycle (ORC) systems in different geographical contexts: GHG emissions impact and economic feasibility2022In: Energy Reports, E-ISSN 2352-4847, Vol. 8, p. 7680-7690Article in journal (Refereed)
    Abstract [en]

    According to the European Commission’s 2050 Climate Strategy, renewable electricity is the most important driver for decarbonising the energy system. The intermittent nature of wind and solar creates a demand for dispatchable electricity production that can contribute to a stable and steady supply all year. This supply can be provided, for example, by biomass boilers with combined heat and power production. This paper analyses the potential for small-scale electricity production in Organic Rankine Cycle systems (ORC) in different geographical contexts. The focus is on installing ORC systems with existing biomass-fired boilers in district heating (DH) systems or industry, and with industrial excess heat streams. Economic and climate effects are studied in three countries with different climates and energy-market conditions, namely Sweden, the United Kingdom and Brazil. The results show that there is the potential to install ORC systems around the world that are both economically viable and reduce global greenhouse gas emissions. Equipment size has a large effect on the profitability of the investments. Moreover, the benefits of tax exemptions and certificates for renewable electricity production significantly impact profitability, particularly for smaller equipment sizes.

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  • 48.
    Danielsson, Örjan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Sukkaew, Pitsiri
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    A Systematic Method for Predictive In Silico Chemical Vapor Deposition2020In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 124, no 14, p. 7725-7736Article in journal (Refereed)
    Abstract [en]

    A comprehensive systematic method for chemical vapor deposition modeling consisting of seven well-defined steps is presented. The method is general in the sense that it is not adapted to a certain type of chemistry or reactor configuration. The method is demonstrated using silicon carbide (SiC) as a model system, with accurate matching to measured data without tuning of the model. We investigate the cause of several experimental observations for which previous research reports only have had speculative explanations. In contrast to previous assumptions, we can show that SiCl2 does not contribute to SiC deposition. We can confirm the presence of larger molecules at both low and high C/Si ratios, which have been thought to cause so-called step-bunching. We can also show that high concentrations of Si lead to other Si molecules other than the ones contributing to growth, which also explains why the C/Si ratio needs to be lower at these conditions to maintain high material quality as well as the observed saturation in deposition rates. Due to its independence of a chemical system and reactor configuration, the method paves the way for a general predictive CVD modeling tool.

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  • 49.
    de Vries, Frank
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics .
    Inverkan av värme på lagerlägets cylindricitet i ett lagerhus2010Independent thesis Basic level (university diploma), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [sv]

    Det här examensarbetet har utförts hos och med stöd av SKF Mekan i Katrineholm. Grundfrågeställningen som innebar upphovet till examensarbetet är om värme påverkar lagerlägets cylindricitet hos ett lagerhus. Detta avgränsas senare till att gälla enbart värmepåverkan under produktion för en typ av lagerhus i en storlek men tre olika materialval. Därmed koncentreras arbetet på gjuterilinan för de mindre lagerhusen samt den bearbetningslina som kallas ”Robot line”.

    Inledningsvis ges en presentation vad lager och lagerhus är samt vilken funktion de fyller. Därefter ges en överblick av gjuteriet samt bearbetningen. Berörda linor betraktas mer ingående men även övriga linor ges en övergripande bild av. Övriga resurser såsom mätrum samt testlabb presenteras också.

    De tre olika materialen granskas för att se vilka avgörande skillnader som finns dem emellan. Detta med hjälp av litteratur samt intervjuer med medarbetare hos SKF Mekan, personal vid Linköpings universitet samt SWEREA.

    Två test som genomförts under arbetets gång beskrivs, varav det ena lyckat men det andra misslyckat. Dock fick det andra testet ett överraskande resultat.

    Befintliga kontroller längs med produktionskedjan omtalas.

    Slutligen sammanfattas vilka moment inom gjuteri- samt bearbetningsprocessen där toleransen för cylindriciteten hos lagerläget riskerar att under-/överskridas samt vad som då är orsaken.

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    FULLTEXT01
  • 50.
    Delir, Aryan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Geometrical Improvement of Fuel Nozzle Locations in the SGT-750 Gas Turbine: An investigation into fuel-air mixing in main channels 1 & 22022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This study was conducted on SGT-750, which utilizes can type fourth generation DLE burner, developed at Siemens Energy AB, in Finspång, Sweden. The aim of this study is to obtain a flat fuel profile at the outlet of main channel 1 and main channel 2, demonstrating a proper mixing of fuel and air in the main channels leading to reducing local high-temperature points, and thus, reducing thermal NOx emissions. Furthermore, it is of prime importance to minimize fuel concentrations near the walls of the main channels to decrease laminar flame speed, such that if highly reactive fuels are used, the risk of flashbacks into the burner is eliminated. STAR-CCM+ is the software used for CFD simulations, and Design Manager is used for sweeping the location of fuel nozzles tangentially. Firstly, three grids are generated for the grid independence study with four, nine, and sixteen million cells. The parameters of interest for this evaluation are the mass flow rate and standard deviation of equivalence ratio, as well as velocity and fuel profiles at the outlet of main channels 1 and 2. It is found that the grid with nine million cells has an acceptable balance between the computational costs and the accuracy required. Moreover, the grid independence study revealed that as the grid becomes finer, tangential average of equivalence ratio is lower at the low radius and higher at the high radius. Thereafter, with the proper choice of the grid, three turbulence models namely, k-ε Realizable, k-ε Lag EB, and k-ω SST have been used to find the most stable RANS turbulence model to minimize the risk of non-convergence issues during design iterations in the improvement phase. It is depicted that the k-ε Realizable is the most stable RANS model among the models tested for this case, and this model is used for further improvements on the location of fuel nozzles. Ultimately three design improvements have been presented for both main channels based on dividing the outlet plane into four parts and minimizing the difference between the tangential average of equivalence ratio for the two middle portions and minimizing the tangential average of equivalence ratio for the near wall portions. It is demonstrated that design 3 is the best choice for main channel 1 due to lower fuel concentrations near the wall and flat fuel profile in the middle of the channel. However, for main channel 2, it was noticed that the Baseline Design is the best choice when non-highly reactive fuels are used, while Design 3 is most suitable for highly reactive fuels.

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    Aryan Delir_Master Thesis
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