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  • 51.
    Dyverfeldt, Petter
    et al.
    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. Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Sigfridsson, Andreas
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Clinical Physiology. Linköping University, Department of Biomedical Engineering, Medical Informatics. Linköping University, The Institute of Technology.
    Escobar Kvitting, John-Peder
    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 Centre, Department of Thoracic and Vascular Surgery.
    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. Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Quantification of intravoxel velocity standard deviation and turbulence intensity by generalizing phase-contrast MRI2006In: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 56, no 4, p. 850-858Article in journal (Refereed)
    Abstract [en]

    Turbulent flow, characterized by velocity fluctuations, is a contributing factor to the pathogenesis of several cardiovascular diseases. A clinical noninvasive tool for assessing turbulence is lacking, however. It is well known that the occurrence of multiple spin velocities within a voxel during the influence of a magnetic gradient moment causes signal loss in phase-contrast magnetic resonance imaging (PC-MRI). In this paper a mathematical derivation of an expression for computing the standard deviation (SD) of the blood flow velocity distribution within a voxel is presented. The SD is obtained from the magnitude of PC-MRI signals acquired with different first gradient moments. By exploiting the relation between the SD and turbulence intensity (TI), this method allows for quantitative studies of turbulence. For validation, the TI in an in vitro flow phantom was quantified, and the results compared favorably with previously published laser Doppler anemometry (LDA) results. This method has the potential to become an important tool for the noninvasive assessment of turbulence in the arterial tree.

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  • 52.
    Dyverfeldt, Petter
    et al.
    Linköping University, Department of Medical and Health Sciences, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart Centre, Department of Clinical Physiology.
    Sigfridsson, Andreas
    Linköping University, Department of Medical and Health Sciences, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart Centre, Department of Clinical Physiology.
    Knutsson, Hans
    Linköping University, Department of Biomedical Engineering, Medical Informatics. Linköping University, The Institute of Technology.
    Ebbers, Tino
    Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart Centre, Department of Clinical Physiology. Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    A novel MRI framework for the quantification of any moment of arbitrary velocity distributions2011In: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 65, no 3, p. 725-731Article in journal (Refereed)
    Abstract [en]

    MRI can measure several important hemodynamic parameters but might not yet have reached its full potential. The most common MRI method for the assessment of flow is phase-contrast MRI velocity mapping that estimates the mean velocity of a voxel. This estimation is precise only when the intravoxel velocity distribution is symmetric. The mean velocity corresponds to the first raw moment of the intravoxel velocity distribution. Here, a generalized MRI framework for the quantification of any moment of arbitrary velocity distributions is described. This framework is based on the fact that moments in the function domain (velocity space) correspond to differentials in the Fourier transform domain (kv-space). For proof-of-concept, moments of realistic velocity distributions were estimated using finite difference approximations of the derivatives of the MRI signal. In addition, the framework was applied to investigate the symmetry assumption underlying phase-contrast MRI velocity mapping; we found that this assumption can substantially affect phase-contrast MRI velocity estimates and that its significance can be reduced by increasing the velocity encoding range.

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  • 53.
    Ebbers, Tino
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology. Östergötlands Läns Landsting, Heart and Medicine Centre, Department of Clinical Physiology UHL.
    Flow Imaging: Cardiac Applications of 3D Cine Phase-Contrast MRI2011In: Current Cardiovascular Imaging Reports, ISSN 1941-9074, Vol. 4, no 2, p. 127-133Article, review/survey (Refereed)
    Abstract [en]

    Global and regional blood flow dynamics are of pivotal importance to cardiac function. Fluid mechanical forces can affect hemolysis and platelet aggregation, as well as myocardial remodeling. In recent years, assessment of blood flow patterns based on time-resolved, three-dimensional, three-directional phase-contrast MRI (3D cine PC MRI) has become possible and rapidly gained popularity. Initially, this technique was mainly known for its intuitive and appealing visualizations of the cardiovascular blood flow. Most recently, the technique has begun to go beyond compelling images toward comprehensive and quantitative assessment of blood flow. In this article, cardiac applications of 3D cine PC MRI data are discussed, starting with a review of the acquisition and analysis techniques, and including descriptions of promising applications of cardiac 3D cine PC MRI for the clinical evaluation of myocardial, valvular, and vascular disorders.

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    FULLTEXT01
  • 54. EIDENVALL, L
    et al.
    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.
    DETERMINATION OF REGURGITANT FLOW IN A PULSATILE MODEL BY INTEGRATING VELOCITIES FROM THE ENTIRE 3D PROXIMAL VELOCITY-FIELD1993In: Circulation, ISSN 0009-7322, E-ISSN 1524-4539, Vol. 88, no 4, 2Article in journal (Refereed)
  • 55. Eidenvall, Lars
    et al.
    Sjöberg, Birgitta Janero
    Linköping University, Department of Medical and Health Sciences, Clinical Physiology. 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.
    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.
    Two-dimensional color Doppler flow velocity profiles can be time corrected with an external ECG-delay device.1992In: Journal of the American Society of Echocardiography, ISSN 0894-7317, E-ISSN 1097-6795, Vol. 5, no 4, p. 405-413Article in journal (Refereed)
    Abstract [en]

    Although two-dimensional ultrasound color flow imaging is often considered to be a real-time technique, the acquisition time for two-dimensional color images may be up to 200 msec. Time correction is therefore necessary to obtain correct flow velocity profiles. We have developed a time-correction method in which a specially designed unit detects the QRS complex from the patient and creates a trig pulse that is delayed incrementally in relation to the QRS complex. This trig pulse controls the acquisition of the ultrasound images. A number of consecutively delayed images, with known incremental delay between the sweeps, can thus be stored in the memory of the echocardiograph and transferred digitally to a computer. The time-corrected flow velocity profile is obtained by interpolation of data from the time-delayed profiles. The system was evaluated in a Doppler string phantom test. With this technique it is possible to study time-corrected flow velocity profiles without the need to alter existing ultrasound Doppler equipment.

  • 56. Eidenvall, Lars
    et al.
    Sjöberg, Birgitta Janero
    Linköping University, Department of Medical and Health Sciences, Clinical Physiology. 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.
    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.
    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.
    INFORMATION IN THE AORTIC BLOOD VELOCITY SIGNAL - A SIMULATION STUDY1991In: PROCEEDINGS OF THE ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY, VOL 13, PTS 1-5, 1991, p. 2248-2249Conference paper (Refereed)
  • 57.
    Ekman, Petter
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    A Sensitivity Study of Some Numerical and Geometrical Parameters Affecting Lift2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Volvo Car Corporation (VCC) uses Computational Fluid Dynamics (CFD) and wind tunnel during the aerodynamic development of new vehicles. In the past VCC main focus has been on the drag force correlation to the wind tunnel measurements but in recent years improved methods for lift force correlations has been highly wanted. Three objectives were considered in this study to improve the lift force correlation between the CFD simulations and wind tunnel measurements for geometrical configurations of the V60 and S60 models.Poor mesh resolution for the wall bounded flow existed for the VCC mesh method and therefore prisms layers were considered in this thesis to increase the mesh resolution inside the boundary layer.As slick tyres generally were used in the CFD simulations better geometrical correlation was wanted to be studied as it could improve the lift force correlation between CFD simulations and wind tunnel measurements. Therefore detailed tyres were considered in this study.As the coarsest surface mesh size was used for the underbody and the components inside the engine bay, where some of the highest flow velocities occurred, mesh refinements were investigated for engine bay and underbody in this study.The prisms layers improved the predicted behavior for the boundary layer as it captured the large velocity gradients more accurately. Due to this, the skin friction prediction was also improved. Different flow behavior around the front wheels and rear wake occurred due to earlier separation. The different flow field caused an improved correlation for the lift force but worsened correlation for the drag force due to increased pressure at the rear of the cars. However, the front lift force trend correlation for the considered configurations was improved with the prisms layer mesh method.The detailed tyres caused slight more disturbances for the underbody flow which caused more attached flow around the rear of the car hence lowered pressure. Earlier separation around the front wheels also occurred for the detailed tyre geometry as the disturbed flow around the wheels was increased. Slight improved correlation for the front and rear lift forces to the wind tunnel measurements could be seen with the detailed tyre compared to the slick tyre.The mesh refinements for the engine bay and underbody showed significant differences for the flow at the underbody which had significant impact on the flow at the rear wake for the V60 model. Minor differences could be seen for the aerodynamic forces for the baseline configuration for the V60 model while great differences occurred for the configurations affecting the underbody. Due to this significant improved correlation for the front and rear lift force trends were achieved for the underbody configurations with the refined engine bay and underbody mesh method.Conclusions could be drawn that the prisms layer caused earlier separation due to its increased mesh resolution for the wall bounded flow. However, finer mesh resolution was needed inside the boundary layer to ensure consistent separation behavior for both the considered models. Improved correlation for the front lift force could however be seen. The detailed tyre only had minor effects on the flow field and aerodynamic forces and therefore not so important to include for further studies. The refined engine bay and underbody caused significant improved lift force trend correlation to the wind tunnel measurements and should be considered for future studies. To improve the correlation between CFD simulations and wind tunnel measurements increased mesh resolution for the wall bounded flow should be considered to better capture the large velocity gradients close to the wall.

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    A Sensitivity Study of Some Numerical and Geometrical Parameters Affecting Lift
  • 58. Order onlineBuy this publication >>
    Ekman, Petter
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Important Factors for Accurate Scale-Resolving Simulations of Automotive Aerodynamics2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Road transports are responsible for almost 18 % of the greenhouse gas emission in Europe and are today the leading cause of air pollution in cities. Aerodynamic resistance has a significant effect on fuel consumption and hence the emission of vehicles. For electric vehicles, emissions are not affected by the aerodynamics as such but instead have a significant effect on the effective range of the vehicle.

    In 2017, a new measurement procedure was introduced, Worldwide Harmonized Light Vehicles Test Procedure (WLTP), for measuring emissions, fuel consumption, and range. This procedure includes a new test cycle with increased average driving speed compared to the former procedure, which thereby increases the importance of the aerodynamic resistance, as it drastically increases with speed. A second effect is that the exact car configuration sold to the customer needs to be certified in terms of fuel consumption and emissions. The result is that every possible combination of optional extras, which might affect the aerodynamic resistance, needs to be aerodynamically analyzed and possibly improved. From 2021, the European Commission will introduce stricter emission regulations for new passenger cars, with the fleet-wide average lowered to 95 grams CO2=km, which puts an even higher demand on achieving efficient aerodynamics.

    Virtual development of the aerodynamics of road vehicles is today used to a great extent, using Computational Fluid Dynamics, as it enables faster and cheaper development. However, achieving high accuracy for the prediction of the flow field and aerodynamic forces is challenging, especially given the complexity of both the vehicle geometry in itself and the surrounding flow field. Even for a simplified generic bluff body, accurately predicting the flow field and aerodynamic forces is a challenge. The main reason for this challenge of achieving results with high accuracy is the prediction of the complex behavior of turbulence. Scale-resolving simulation (SRS) methods, such as Large Eddy Simulation (LES), where most of the turbulent structures are resolved has in many studies shown high accuracy but unfortunately to a very high computational cost. It is primarily the small turbulent structures within the near-wall region that requires a _ne resolution in both space (the mesh) and in time. This fine resolution is the reason for the very high computational cost and makes LES unfeasible for practical use in industrial aerodynamic development at present and in the near future. By modeling the turbulent structures within the near-wall region using a Reynolds-Averaged Navier-Stokes (RANS) model, and resolving the turbulence outside the region with a LES model, a coarser resolution is possible to use, resulting in significantly lower computational cost. Which used RANS model is of high importance, and especially how much turbulent viscosity the model generates, as too high values can result in suppression of the resolved turbulence.

    The transitioning between the RANS and LES regions have a significant effect on the results. Faster transition enables more resolved turbulence, favorable for higher accuracy, but needs to be balanced with sufficient shielding of the RANS region. If resolving the turbulence occurs within the near-wall region, and the mesh is not sufficiently fine, it can result in poor accuracy.

    By increasing the time-step size and disregarding best-practice guides, the computational cost can be significantly reduced. The accuracy is reasonably insensitive to the larger time step sizes until a certain degree, thereby enabling computationally cheaper SRS to achieve high accuracy of aerodynamic predictions needed to meet present and future emission regulations.

    List of papers
    1. Aerodynamic Drag Reduction - from Conceptual Design on a Simplified Generic Model to Full-Scale Road Tests
    Open this publication in new window or tab >>Aerodynamic Drag Reduction - from Conceptual Design on a Simplified Generic Model to Full-Scale Road Tests
    2015 (English)In: SAE 2015 World Congress & Exhibition, SAE International , 2015Conference paper, Published paper (Refereed)
    Abstract [en]

    Road transportation by trucks is the major part of the goods transportations system in the European Union (EU), and there is a need for increased fuel efficiency. While truck manufacturers already spend significant resources in order to reduce the emissions from their vehicles, most truck manufacturers do not control the shape of the trailer and/or swap bodies. These devices are usually manufactured by different companies that cannot consider the overall aerodynamics around the complete vehicle.By use of Computational Fluid Dynamics (CFD) and previous wind tunnel experiments, the flow around a simplified generic tractor-trailer model has been investigated. With better understanding of the flow features around the tractor with attached trailer or swap bodies, an improved design of the trailer and swap body can be achieved, which is the aim for the project. Special emphasis is put on achieving simple, easy to install or implement drag-reducing geometrical modifications to the trailer or swap bodies that can be mounted on existing trucks.Reynolds-Averaged Navier-Stokes (RANS) simulations were used for the conceptual development phase where trends in drag reduction due to the modified geometries were studied using a parameter study, while more advanced scale resolving simulations (SRS) were used in order to investigate the details of the flow fields.The investigation indicates that aerodynamic drag reduction is possible with quite simple geometrical modifications. Some of the results have also been verified through road tests of vehicles in commercial use, which has shown reduced fuel consumption of up to 5%.

    Place, publisher, year, edition, pages
    SAE International, 2015
    National Category
    Vehicle Engineering
    Identifiers
    urn:nbn:se:liu:diva-164920 (URN)10.4271/2015-01-1543 (DOI)
    Conference
    SAE 2015 World Congress & Exhibition
    Available from: 2020-04-02 Created: 2020-04-02 Last updated: 2020-04-02Bibliographically approved
    2. Aerodynamic Drag Reduction of a Light Truck - from Conceptual Design to Full Scale Road Tests
    Open this publication in new window or tab >>Aerodynamic Drag Reduction of a Light Truck - from Conceptual Design to Full Scale Road Tests
    2016 (English)In: SAE 2016 World Congress and Exhibition, SAE International , 2016Conference paper, Published paper (Refereed)
    Abstract [en]

    Considerable amounts of the everyday goods transports are done using light trucks. In the last ten years (2005-2015), the number of light trucks has increased by 33 % in Sweden. The majority of these light trucks are fitted with a swap body and encounter the same problem as many other truck configurations, namely that several different manufacturers contribute to the final shape of the vehicle. Due to this, the aerodynamics of the final vehicle is often not fully considered. Hence there appears to be room for improving the aerodynamic performance. In this study the flow around a swap body fitted to a light truck has been investigated using Computational Fluid Dynamics. The focus has been on improving the shape of the swap body in order to reduce both the aerodynamic drag and fuel consumption, while still keeping it usable for daily operations. Reynolds-Averaged Navier-Stokes simulations were used for concept evaluation while more advanced Detached Eddy Simulations were performed on the best concept in order to investigate details of the flow. Various concepts were evaluated from which it could be seen that a more streamlined top of the swap body together with a lowered top trailing edge had a significant positive effect on the aerodynamic drag. A full scale light truck was equipped with a swap body with with these modifications for road tests. During a test period, a mean fuel consumption reduction of 12 % was measured, thus indicating a significantly reduced aerodynamic drag.

    Place, publisher, year, edition, pages
    SAE International, 2016
    National Category
    Vehicle Engineering
    Identifiers
    urn:nbn:se:liu:diva-164923 (URN)10.4271/2016-01-1594 (DOI)
    Conference
    SAE 2016 World Congress and Exhibition
    Available from: 2020-04-02 Created: 2020-04-02 Last updated: 2020-04-02Bibliographically approved
    3. Aerodynamics of an Unloaded Timber Truck - A CFD Investigation
    Open this publication in new window or tab >>Aerodynamics of an Unloaded Timber Truck - A CFD Investigation
    2016 (English)In: SAE International Journal of Commercial Vehicles, ISSN 1946-391X, E-ISSN 1946-3928, Vol. 9, no 2, p. 217-223Article in journal (Refereed) Published
    Abstract [en]

    Reducing energy consumption and emissions are ongoing challenges for the transport sector. The increased number of goods transports emphasize these challenges even more, as greenhouse gas emissions from these vehicles increased by 20 % between 1990 and 2013, in Sweden. One special case of goods transports is the transport of timber. Today in Sweden, around 2000 timber trucks transport around six billion ton kilometers every year. For every ton kilometer these vehicles use around 0.025 liter diesel, and there should exist large possibilities to reduce the fuel consumption and the emissions for these vehicles. Timber trucks spend most of their operation time travelling in speeds of around 80 km/h. At this speed aerodynamic drag contributes to around 30 % of the total vehicle resistance, which makes the aerodynamic drag a significant part of the energy consumption. One of the big challenges with timber trucks is that they travel unloaded half of the time. This put higher demands on possible drag reduction modifications, as they need to function and be practical for both when the timber truck is loaded and unloaded. In this study an unloaded timber truck has been investigated by use of computational fluid dynamics. The recently released Stress Blended Eddy Simulation model has been used for simulating the flow over a timber truck at a Reynolds number of 1.1 million, based on the square root of its frontal area. From the results it could be seen that 52.8 % of the drag is generated by the cab. By investigating a drag reduction device that covered the gap between the bulkhead and the first stake pair, a drag reduction up to 6.7 % was possible, which shows potential for simple modifications that not influence the daily usage.

    Place, publisher, year, edition, pages
    SAE INT, 2016
    National Category
    Transport Systems and Logistics
    Identifiers
    urn:nbn:se:liu:diva-163998 (URN)10.4271/2016-01-8022 (DOI)000389233800010 ()
    Available from: 2020-03-05 Created: 2020-03-05 Last updated: 2020-04-02
    4. Accuracy and Speed for Scale-Resolving Simulations of the DrivAer Reference Model
    Open this publication in new window or tab >>Accuracy and Speed for Scale-Resolving Simulations of the DrivAer Reference Model
    2019 (English)In: WCX SAE World Congress Experience, SAE International , 2019Conference paper, Published paper (Refereed)
    Abstract [en]

    In aerodynamic development of ground vehicles, the use of Computational Fluid Dynamics (CFD) is crucial for improving the aerodynamic performance, stability and comfort of the vehicle. Simulation time and accuracy are two key factors of a well working CFD procedure. Using scale-resolving simulations, accurate predictions of the flow field and aerodynamic forces are possible, but often leads to long simulation time. For a given solver, one of the most significant aspects of the simulation time/cost is the temporal resolution. In this study, this aspect is investigated using the realistic vehicle model DrivAer with the notchback geometry as the test case. To ensure a direct and accurate comparison with wind tunnel measurements, performed at TU Berlin, a large section of the wind tunnel is included in the simulation domain. All simulations are performed at a Reynolds number of 3.12 million, based on the vehicle length. Three spatial resolutions were compared, where it could be seen that a hybrid element mesh consisting of 102 million cells only revealed small differences to the finest mesh investigated, well as showing excellent agreement with wind tunnel measurements. An investigation of the temporal resolution is performed, in order to see its effect on the simulation time/cost and accuracy of the results. The finest temporal resolution resulted in a Courant-Friedrichs-Lewy number less than unity, while the coarsest reached a CFL number of around 100. From these results, it is seen that it is possible to reduce the simulation time with more than 90 % (CFL 20) and still keep sufficient accuracy of the forces and important features of the flow field.

    Place, publisher, year, edition, pages
    SAE International, 2019
    National Category
    Vehicle Engineering
    Identifiers
    urn:nbn:se:liu:diva-164924 (URN)10.4271/2019-01-0639 (DOI)
    Conference
    WCX SAE World Congress Experience
    Available from: 2020-04-02 Created: 2020-04-02 Last updated: 2020-04-02Bibliographically approved
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    fulltext
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  • 59.
    Ekman, Petter
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Gårdhagen, Roland
    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).
    Virdung, Torbjorn
    ANSYS, 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).
    Aerodynamic Drag Reduction of a Light Truck - from Conceptual Design to Full Scale Road Tests2016In: SAE 2016 World Congress and Exhibition, SAE International , 2016Conference paper (Refereed)
    Abstract [en]

    Considerable amounts of the everyday goods transports are done using light trucks. In the last ten years (2005-2015), the number of light trucks has increased by 33 % in Sweden. The majority of these light trucks are fitted with a swap body and encounter the same problem as many other truck configurations, namely that several different manufacturers contribute to the final shape of the vehicle. Due to this, the aerodynamics of the final vehicle is often not fully considered. Hence there appears to be room for improving the aerodynamic performance. In this study the flow around a swap body fitted to a light truck has been investigated using Computational Fluid Dynamics. The focus has been on improving the shape of the swap body in order to reduce both the aerodynamic drag and fuel consumption, while still keeping it usable for daily operations. Reynolds-Averaged Navier-Stokes simulations were used for concept evaluation while more advanced Detached Eddy Simulations were performed on the best concept in order to investigate details of the flow. Various concepts were evaluated from which it could be seen that a more streamlined top of the swap body together with a lowered top trailing edge had a significant positive effect on the aerodynamic drag. A full scale light truck was equipped with a swap body with with these modifications for road tests. During a test period, a mean fuel consumption reduction of 12 % was measured, thus indicating a significantly reduced aerodynamic drag.

  • 60.
    Ekman, Petter
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Gårdhagen, Roland
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Virdung, Torbjorn
    ANSYS Sweden, Sweden.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Aerodynamics of an Unloaded Timber Truck - A CFD Investigation2016In: SAE International Journal of Commercial Vehicles, ISSN 1946-391X, E-ISSN 1946-3928, Vol. 9, no 2, p. 217-223Article in journal (Refereed)
    Abstract [en]

    Reducing energy consumption and emissions are ongoing challenges for the transport sector. The increased number of goods transports emphasize these challenges even more, as greenhouse gas emissions from these vehicles increased by 20 % between 1990 and 2013, in Sweden. One special case of goods transports is the transport of timber. Today in Sweden, around 2000 timber trucks transport around six billion ton kilometers every year. For every ton kilometer these vehicles use around 0.025 liter diesel, and there should exist large possibilities to reduce the fuel consumption and the emissions for these vehicles. Timber trucks spend most of their operation time travelling in speeds of around 80 km/h. At this speed aerodynamic drag contributes to around 30 % of the total vehicle resistance, which makes the aerodynamic drag a significant part of the energy consumption. One of the big challenges with timber trucks is that they travel unloaded half of the time. This put higher demands on possible drag reduction modifications, as they need to function and be practical for both when the timber truck is loaded and unloaded. In this study an unloaded timber truck has been investigated by use of computational fluid dynamics. The recently released Stress Blended Eddy Simulation model has been used for simulating the flow over a timber truck at a Reynolds number of 1.1 million, based on the square root of its frontal area. From the results it could be seen that 52.8 % of the drag is generated by the cab. By investigating a drag reduction device that covered the gap between the bulkhead and the first stake pair, a drag reduction up to 6.7 % was possible, which shows potential for simple modifications that not influence the daily usage.

  • 61.
    Ekman, Petter
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Gårdhagen, Roland
    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).
    Virdung, Torbjörn
    ANSYS, 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).
    Aerodynamic Drag Reduction - from Conceptual Design on a Simplified Generic Model to Full-Scale Road Tests2015In: SAE 2015 World Congress & Exhibition, SAE International , 2015Conference paper (Refereed)
    Abstract [en]

    Road transportation by trucks is the major part of the goods transportations system in the European Union (EU), and there is a need for increased fuel efficiency. While truck manufacturers already spend significant resources in order to reduce the emissions from their vehicles, most truck manufacturers do not control the shape of the trailer and/or swap bodies. These devices are usually manufactured by different companies that cannot consider the overall aerodynamics around the complete vehicle.By use of Computational Fluid Dynamics (CFD) and previous wind tunnel experiments, the flow around a simplified generic tractor-trailer model has been investigated. With better understanding of the flow features around the tractor with attached trailer or swap bodies, an improved design of the trailer and swap body can be achieved, which is the aim for the project. Special emphasis is put on achieving simple, easy to install or implement drag-reducing geometrical modifications to the trailer or swap bodies that can be mounted on existing trucks.Reynolds-Averaged Navier-Stokes (RANS) simulations were used for the conceptual development phase where trends in drag reduction due to the modified geometries were studied using a parameter study, while more advanced scale resolving simulations (SRS) were used in order to investigate the details of the flow fields.The investigation indicates that aerodynamic drag reduction is possible with quite simple geometrical modifications. Some of the results have also been verified through road tests of vehicles in commercial use, which has shown reduced fuel consumption of up to 5%.

  • 62.
    Ekman, Petter
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Larsson, Torbjörn
    Linköping University, Department of Mathematics, Optimization . Linköping University, Faculty of Science & Engineering.
    Virdung, Torbjörn
    Volvo Car Corporation, Göteborg, Sverige.
    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).
    Accuracy and Speed for Scale-Resolving Simulations of the DrivAer Reference Model2019In: WCX SAE World Congress Experience, SAE International , 2019Conference paper (Refereed)
    Abstract [en]

    In aerodynamic development of ground vehicles, the use of Computational Fluid Dynamics (CFD) is crucial for improving the aerodynamic performance, stability and comfort of the vehicle. Simulation time and accuracy are two key factors of a well working CFD procedure. Using scale-resolving simulations, accurate predictions of the flow field and aerodynamic forces are possible, but often leads to long simulation time. For a given solver, one of the most significant aspects of the simulation time/cost is the temporal resolution. In this study, this aspect is investigated using the realistic vehicle model DrivAer with the notchback geometry as the test case. To ensure a direct and accurate comparison with wind tunnel measurements, performed at TU Berlin, a large section of the wind tunnel is included in the simulation domain. All simulations are performed at a Reynolds number of 3.12 million, based on the vehicle length. Three spatial resolutions were compared, where it could be seen that a hybrid element mesh consisting of 102 million cells only revealed small differences to the finest mesh investigated, well as showing excellent agreement with wind tunnel measurements. An investigation of the temporal resolution is performed, in order to see its effect on the simulation time/cost and accuracy of the results. The finest temporal resolution resulted in a Courant-Friedrichs-Lewy number less than unity, while the coarsest reached a CFL number of around 100. From these results, it is seen that it is possible to reduce the simulation time with more than 90 % (CFL 20) and still keep sufficient accuracy of the forces and important features of the flow field.

  • 63.
    Engvall, Jan
    et al.
    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.
    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.
    Coarctation of the aorta--a theoretical and experimental analysis of the effects of a centrally located arterial stenosis.1991In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 29, no 3, p. 291-296Article in journal (Refereed)
    Abstract [en]

    Aortic coarctation is a local constriction of the aorta that may severely affect haemodynamics. It is therefore important to quantify these effects. Using Bernoulli's equation and the momentum theorem, the pressure drop is described including the pressure recovery distal to the coarctation and the effects of collateral flow; both laminar and turbulent. Assuming the coarctation and collaterals to be stiff, a quadratic relationship between flow and pressure drop is expected for flow through the coarctation and for turbulent collateral flow. For laminar collateral flow, a linear relationship is expected. The coarctation flow was studied in a model consisting of a rigid tube with local constriction, connected to a flooded-level tank, containing a 36 per cent by weight solution of sucrose, with a viscosity equivalent to that of blood at body temperature. The pressure drop across the constriction showed a quadratic relationship to flow in agreement with theoretical expectations. Pressure recovery in this model was very slight (0-4 mm Hg). Nine patients with aortic coarctation were catheterised. Cardiac output and pressure drop across the coarctation were measured at rest and during supine cycle exercise at two different workloads. The relationship between mean pressure drop and cardiac output tended to be either 'parabolic' or, in some cases, approximately linear, suggesting that the flow situation in aortic coarctation can be quantified by expressions that either linearly or quadratically relate pressure and flow.

  • 64.
    Eriksson, Jonatan
    et al.
    Linköping University, Faculty of Health Sciences. Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Physiology.
    Dyverfeldt, Petter
    Linköping University, Department of Medical and Health Sciences, Cardiology. Linköping University, Faculty of Health Sciences. 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. Östergötlands Läns Landsting, Heart and Medicine Centre, Department of Clinical Physiology UHL.
    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.
    Bolger, Ann F
    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, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Centre, Department of Clinical Physiology UHL. Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Carlhäll, Carljohan
    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. Linköping University, Center for Medical Image Science and Visualization, CMIV.
    Quantification of presystolic blood flow organization and energetics in the human left ventricle2011In: AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY, ISSN 0363-6135, Vol. 300, no 6, p. H2135-H2141Article in journal (Refereed)
    Abstract [en]

    Intracardiac blood flow patterns are potentially important to cardiac pumping efficiency. However, these complex flow patterns remain incompletely characterized both in health and disease. We hypothesized that normal left ventricular (LV) blood flow patterns would preferentially optimize a portion of the end-diastolic volume (LVEDV) for effective and rapid systolic ejection by virtue of location near and motion towards the LV outflow tract (LVOT). Three-dimensional cine velocity and morphological data were acquired in 12 healthy persons and 1 patient with dilated cardiomyopathy using MRI. A previously validated method was used for analysis in which the LVEDV was separated into four functional flow components based on the bloods locations at the beginning and end of the cardiac cycle. Each components volume, kinetic energy (KE), site, direction, and linear momentum relative to the LVOT were calculated. Of the four components, the LV inflow that passes directly to outflow in a single cardiac cycle (Direct Flow) had the largest volume. At the time of isovolumic contraction, Direct Flow had the greatest amount of KE and the most favorable combination of distance, angle, and linear momentum relative to the LVOT. Atrial contraction boosted the late diastolic KE of the ejected components. We conclude that normal diastolic LV flow creates favorable conditions for ensuing ejection, defined by proximity and energetics, for the Direct Flow, and that atrial contraction augments the end-diastolic KE of the ejection volume. The correlation of Direct Flow characteristics with ejection efficiency might be a relevant investigative target in cardiac failure.

  • 65.
    Escobar Kvitting, John-Peder
    et al.
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medicine and Health Sciences, Physiology . Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart Centre, Department of Thoracic and Vascular Surgery.
    Dyverfeldt, Petter
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medicine and Health Sciences, Clinical Physiology . Linköping University, Faculty of Health Sciences. Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics . Linköping University, The Institute of Technology.
    Sigfridsson, Andreas
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medicine and Health Sciences, Clinical Physiology . Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart Centre, Department of Clinical Physiology.
    Franzén, Stefan
    Östergötlands Läns Landsting, Heart Centre, Department of Cardiology.
    Wigström, Lars
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medicine and Health Sciences, Clinical Physiology . Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart Centre, Department of Clinical Physiology.
    Bolger, Ann F.
    Linköping University, Department of Medicine and Health Sciences, Clinical Physiology . Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart Centre, Department of Clinical Physiology.
    Ebbers, Tino
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medicine and Health Sciences, Clinical Physiology . Linköping University, Faculty of Health Sciences. Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics . Linköping University, The Institute of Technology.
    In Vitro Assessment of Flow Patterns and Turbulence Intensity in Prosthetic Heart Valves Using Generalized Phase-Contrast Magnetic Resonance ImagingManuscript (preprint) (Other academic)
    Abstract [en]

    Purpose: To assess in vitro the three-dimensional mean velocity field and the extent and degree of turbulenceintensity in different prosthetic heart valves using a generalization of phase-contrast magnetic resonance imaging(PC-MRI).

    Material and Methods: Four 27 mm aortic valves (Björk-Shiley Monostrut tilting-disc, St. Jude MedicalStandard bileaflet, Medtronic Mosaic stented and Freestyle stentless porcine valve) were tested under steadyinflow conditions in a Plexiglas phantom. Three-dimensional PC-MRI data were acquired to measure the meanvelocity field and the turbulent kinetic energy (TKE), a direction-independent measure of turbulence intensity.

    Results: Velocity and turbulence intensity estimates could be obtained up and downstream of the valves, exceptwhere metallic structure in the valves caused signal void. Distinct differences in the location, extent and peakvalues of velocity and turbulence intensity were observed between the valves tested. The maximum values ofTKE varied between the different valves: tilting disc, 100 J/m3; bileaflet, 115 J/m3; stented, 200 J/m3; stentless,145 J/m3.

    Conclusion: The turbulence intensity downstream from a prosthetic heart valve is dependent on the specificvalve design. Generalized PC-MRI can be used to quantify velocity and turbulence intensity downstream fromprosthetic heart valves, which may allow assessment of these aspects of prosthetic valvular function inpostoperative patients.

  • 66.
    Ewerbring, Carl-Arvid
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Konsumentvänlig Energibesparingsmodell: Ett verktyg som hjälper småhusägare att sänka sina energikostnader2012Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    Energy awareness is growing among the Swedish population and a one­‐to­‐two-family dwelling can save energy. The purpose of this paper is to design a tool that helps these home owners reduce their energy costs.

    The paper develops a model that gives them an indication of how much energy they can save. For the majority of homeowners, the next step in the quest to reduce theirs is most likely an energy audit. Therefore, information to help home owners to get a good energy audit performed is included in the model.

    A prototype running the operating system iOS is created and validated against existing models, as well as an energy audit. 

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    Konsumentvänlig Energibesparingsmodell
  • 67.
    Farhanieh, Arman
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Investigation on methods to improve heat loadprediction of the SGT-600 gas turbine2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In modern gas turbines, with the increase of inlet gas temperature to raise thework output, the importance of accurate aero-thermal analysis has become of vitalimportance. These analysis are required for temperature prediction throughoutthe turbine and to predict the thermal stresses and to estimate the cooling requiredfor each component.In the past 20 years, computational fluid dynamics (CFD) methods have becomea powerfool tool aero-thermal analysis. Due to reasons including numericallimitation, flow complications caused by blade row interactions and the effect offilm cooling, using simple steady state CFD methods may result in inaccuratepredictions. Even though employing transient simulations can improve the accuracyof the simulations, it will also greatly increase the simulation time and cost.Therefore, new methods are constantly being developed to increase the accuracywhile keeping the computational costs relatively low. Investigating some of thesedeveloped methods is one of the main purposes of this study.A simplification that has long been applied in gas turbine simulations hasbeen the absence of cooling cavities. Another part of this thesis will focus onthe effect of cooling cavities and the importance of including them in the domain.Therefore, all transient and steady state simulations have been examined for twocases; a simplified case and a detailed case. The results are then compared tothe experimental measurements to evaluate the importance of their presence inthe model. The software used to perform all simulations is the commercial codeANSYS CFX 15.The findings suggest that even though including cooling cavities would improvethe results, the simulations should be run in transient. One important finding wasthat when performing transient simulations, especially the Time Transformationmethod, not only is the pitch ratio between every subsequent blade row important,but also the pitch ratio between the stators is highly influential on the accuracyof the results.

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    fulltext
  • 68.
    Farhanieh, Arman
    et al.
    Siemens Ind Turbomachinery AB, Sweden.
    Mau, Christoph
    Siemens Ind Turbomachinery AB, Sweden.
    Annerfeldt, Mats
    Siemens Ind Turbomachinery AB, Sweden.
    Nadali Najafabadi, Hossein
    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.
    Unsteady Effects in the Heat Load Predictions for a Two-Stage Compressor Turbine2016In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2016, VOL 5A, AMER SOC MECHANICAL ENGINEERS , 2016, no UNSP V05AT13A025Conference paper (Refereed)
    Abstract [en]

    Heat load analysis play an important role in the estimation of hot gas components lifetime. To achieve a high level of accuracy in heat load analysis, predicting the temperature distribution on the vane and blades is one area where further development is needed. Due to strong flow unsteadiness and mixing effects from blade row interactions and cooling injections, accurate heat load predictions have become an engineering challenge. This study uses both steady and time-accurate computational fluid dynamics (CFD) simulations to investigate the unsteady and mixing effects in a two-stage compressor turbine. The commercial code ANSYS CFX-15 is utilized to evaluate the performance of the steady state, mixing plane (MP) method, versus time-accurate, profile transformation (PT) and time transformation (TT) methods. The presence or absence of the rotor-stator cavities from which purge or cooling air is entering the main flowpath can also play an important role in the unsteadiness and mixing properties. Therefore the unsteady effects have been examined for two cases; a simplified model without any cavity and a detailed geometry with all the cavities included. In the simplified case, the cooling has been implemented as local patches. The results are then compared with gas temperature measurements from the real engine tests using thermo-crystals. The measurements include temperature profiles in front of the leading edge of each stator and rotor for both stages. The findings suggest that including cooling cavities may not improve the results in steady state simulations, however their presence in transient simulations can lead to mixing prediction improvements. Moreover, the results indicate that the transient simulations will improve the mixing predictions mainly in the second stage of the turbine. The results also indicate that in transient simulations, number of passages and pitch ratio between the stators of consecutive stages directly affect the results regardless of which transient method is used.

  • 69.
    Fattahi, Sadegh
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Månsson, Philip
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Computational and experimental study of fuel leakage through a ventilation valve during various driving conditions2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Fuel leakage through a fill limit vent valve (FLVV) inside a fuel tank is an important factor to consider during the design of a new tank. The performance of the carbon canister which absorbs the hydrocarbon can be compromised if fuel manages to escape through the valve, so called Liquid Carry Over (LCO) and thus not fulfilling the fuel emission requirements. As of today this is not thoroughly investigated using experiments nor Computational Fluid Dynamics.

    The main focus of this study was to develop a method to simulate the behaviour of the FLVV during various driving conditions at an early design stage and if this gives rise to fuel escaping through the FLVV. This method was later to be validated with an experimental set-up and later used to perform some simulations to investigate LCO by varying different parameters such as fuel level and different types of driving. What happens when the canister is purging was also investigated to see if it has a pronounced effect on LCO. Purging is when hydrocarbons, absorbed by the canister, are sent to the engine and giving rise to an under pressure in the tank.The method was developed to run on a cluster utilizing 200 Central Processing Unit Cores where each simulated physical second required an average of 3 hours of simulation time.The flow inside the tank was simulated using a Volume Of Fluid (VOF) multiphase model and the dynamic behaviour of the floater inside the FLVV was simulated using an overset mesh with a Dynamic Fluid Body Interaction.The movement of the simulated dynamic floater was validated with an experimental set-up specifically developed for the overset mesh validation and the motion of the floater was captured at a fairly accurate level.A prototype for an experimental tank was also developed and produced to validate the VOF set-up used for sloshing inside the tank which was utilized on the real tank but due to time limitation the experiments were not performed.

    The results from the parameter investigation showed that LCO was present in cases with high fuel level inside the tank 95 % and that an aggressive driving gives rise to a higher level of LCO compared to normal driving. Simulations with a fuel level of 85 % and lower showed no evidence of LCO for this particular tank model. The purging of the tank induced a pumping effect giving rise to a higher level of LCO pumped through by the floater.

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  • 70.
    Folkesson, Maggie
    et al.
    Linköping University, Department of Medical and Health Sciences, Division of Drug Research. Linköping University, Faculty of Medicine and Health Sciences.
    Sadowska, Natalia
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Vikingsson, Svante
    Linköping University, Department of Medical and Health Sciences, Division of Drug Research. Linköping University, Faculty of Medicine and Health Sciences.
    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, Carl-Johan
    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).
    Länne, Toste
    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 Thoracic and Vascular Surgery.
    Wågsäter, Dick
    Linköping University, Department of Medical and Health Sciences, Division of Drug Research. Linköping University, Faculty of Medicine and Health Sciences.
    Jensen, Lasse
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Clinical Pharmacology.
    Differences in cardiovascular toxicities associated with cigarette smoking and snuff use revealed using novel zebrafish models2016In: Biology Open, ISSN 2046-6390, Vol. 5, no 7, p. 970-978Article in journal (Refereed)
    Abstract [en]

    Tobacco use is strongly associated with cardiovascular disease and the only avoidable risk factor associated with development of aortic aneurysm. While smoking is the most common form of tobacco use, snuff and other oral tobacco products are gaining popularity, but research on potentially toxic effects of oral tobacco use has not kept pace with the increase in its use. Here, we demonstrate that cigarette smoke and snuff extracts are highly toxic to developing zebrafish embryos. Exposure to such extracts led to a palette of toxic effects including early embryonic mortality, developmental delay, cerebral hemorrhages, defects in lymphatics development and ventricular function, and aneurysm development. Both cigarette smoke and snuff were more toxic than pure nicotine, indicating that other compounds in these products are also associated with toxicity. While some toxicities were found following exposure to both types of tobacco product, other toxicities, including developmental delay and aneurysm development, were specifically observed in the snuff extract group, whereas cerebral hemorrhages were only found in the group exposed to cigarette smoke extract. These findings deepen our understanding of the pathogenic effects of cigarette smoking and snuff use on the cardiovascular system and illustrate the benefits of using zebrafish to study mechanisms involved in aneurysm development.

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    fulltext
  • 71.
    Fredriksson, Alexandru G
    et al.
    Linköping University, Department of Medical and Health Sciences, Cardiology. Linköping University, Faculty of Health Sciences. Linköping University, Center for Medical Image Science and Visualization, CMIV.
    Zajac, Jakub
    Linköping University, Department of Medical and Health Sciences, Cardiology. Linköping University, Faculty of Health Sciences. Linköping University, Center for Medical Image Science and Visualization, CMIV.
    Eriksson, Jonatan
    Linköping University, Faculty of Health Sciences. Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Physiology.
    Dyverfeldt, Petter
    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. Linköping University, Center for Medical Image Science and Visualization, CMIV.
    Bolger, Ann F
    University of California San Francisco.
    Ebbers, Tino
    Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Centre, Department of Clinical Physiology UHL. Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Carlhäll, Carljohan
    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. Linköping University, Center for Medical Image Science and Visualization, CMIV.
    4-D blood flow in the human right ventricle2011In: American Journal of Physiology. Heart and Circulatory Physiology, ISSN 0363-6135, E-ISSN 1522-1539, Vol. 301, no 6, p. H2344-H2350Article in journal (Refereed)
    Abstract [en]

    Right ventricular (RV) function is a powerful prognostic indicator in many forms of heart disease, but its assessment remains challenging and inexact. RV dysfunction may alter the normal patterns of RV blood flow, but those patterns have been incompletely characterized. We hypothesized that, based on anatomic differences, the proportions and energetics of RV flow components would differ from those identified in the left ventricle (LV) and that the portion of the RV inflow passing directly to outflow (Direct Flow) would be prepared for effective systolic ejection as a result of preserved kinetic energy (KE) compared with other RV flow components. Three-dimensional, time-resolved phase-contrast velocity, and balanced steady-state free-precession morphological data were acquired in 10 healthy subjects using MRI. A previously validated method was used to separate the RV and LV end-diastolic volumes into four flow components and measure their volume and KE over the cardiac cycle. The RV Direct Flow: 1) followed a smoothly curving route that did not extend into the apical region of the ventricle; 2) had a larger volume and possessed a larger presystolic KE (0.4 +/- 0.3 mJ) than the other flow components (P andlt; 0.001 and P andlt; 0.01, respectively); and 3) represented a larger part of the end-diastolic blood volume compared with the LV Direct Flow (P andlt; 0.01). These findings suggest that diastolic flow patterns distinct to the normal RV create favorable conditions for ensuing systolic ejection of the Direct Flow component. These flow-specific aspects of RV diastolic-systolic coupling provide novel perspectives on RV physiology and may add to the understanding of RV pathophysiology.

  • 72.
    Gardell, Jens
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Benchmark of RELAP5 Check Valve Models against Experimental Data2013Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    The use of check valves in the nuclear industry is of great importance from a safety precaution point ofview (McElhaney, 1995). Choosing check valves for these high-pressurized systems comes with agreat challenge. The valves causes what is called check valve slams when closing, leading to a hugepressure wave traveling through the system. To prevent this from happening calculations have to bedone to see what kind of forces are generated during a check valve slam. When the forces are known itis easier designing systems that will endure these slams. A commonly used software in the nuclearindustry is RELAP5 (Reactor Excursion and Leak Analysis Program), its main purpose is to calculatetransients in piping systems. This program can also be used when calculating a check valve slam. Buthow precise is the code compared to the real event?

    By doing an experiment measuring pressures created by swing check valves during slams, the codewas compared to real data and analyzed to decide what was of importance when modeling for thesetypes of simulations.

    The RELAP5 code was not initially designed to calculate transients during a check valve slam. This isclearly shown when the code overestimates the pressure waves in the system when using themanufacturer data for the check valve model. Matching the data from the simulations in RELAP5 withthe data recorded from the experiment is not easy. The parameters used for this have no connection tothe specifications for the check valve, which means that transients are hard to estimate withoutexperimental data.

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    Check valve slam report
  • 73.
    Genberg, Anna
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Vidareutveckling av Siemens spridarrigg för studier av bränslespray2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [sv]

    Examensarbetet har utförts på Siemens Industrial Turbomachinery AB (Siemens) i Finspång. De utvecklar och tillverkar bland annat gasturbiner som kan drivas på både gasformigt- och flytande bränsle. Syftet för arbetet är att skapa förutsättningar för att öka förståelsen för spraybildning av flytande bränsle, till detta används och vidareutvecklas en spridarrigg på Siemens.

    Siemens äldsta gasturbin SGT-500 utvecklades och sattes i drift under 1950 talet. Vid denna tid var det en spridare med spillflöde och ett munstycke med roterande atomisering som visade bäst egenskaper. Höga tryck i munstycket genererar en spraykon med finfördelade droppar. Förhållandet mellan huvud- och spillbränsletryck i munstycket är en viktig faktor för spraykonens vinkel. Det är viktigt att sprayen är enhetlig och ihålig med dropparna koncentrerade till sprayens ytterkanter. Även bränslets kinematiska viskositet (viskositet) påverkar spraykonens struktur och egenskaper.

    Siemens kunder som har SGT-500 ställer idag förfrågningar gällande att använda bränslen med högre viskositet. Idag har Siemens en begränsning på 16 cSt för gasturbinen, dock konstruerades den för en viskositet upp till 22 cSt. Siemens vill idag skaffa mer erfarenhet för dessa högre värden på viskositeten innan de kan ge några nya rekommendationer till kund.

    I detta examensarbete har modifieringar och en testserie genomförts i sprayriggen där spraykonen studerats för varierande viskositet och tryck. Resultaten visade att spraykonen var enhetlig med ett myller av droppar för viskositeten 18-22 cSt och ett huvudbränsletryck på 20 bar. Spraykonens vinkel minskade för ökande viskositet. God fördelning uppvisades och sprayen var ihålig för en viskositet upp till 39 cSt med några undantag. För att dra paralleller mellan resultaten i spridarriggen och SGT-500 verkliga förhållanden är det nödvändigt att utreda väsentliga skillnader mellan de två fallen och hur dessa påverkar resultaten för spraykonen. Ett lämpligt steg vidare från dessa resultat är att testa en övre gräns för viskositeten under ett förbränningstest i en fullskalig SGT-500. Det vore även intressant att undersöka möjligheterna att testa fler modeller av spridare tillhörande andra turbiner i spridarriggen.

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  • 74.
    Gorur, Murat
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    ECC-D4 Electostatic Oil Cleaner Design for Heavy-Duty Gas Turbine Applications2010Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    The turbine technology improvements from 1980 onwards have considerably increased mechanical and thermal stresses on turbine oils which, cause oil oxidation and thereby turbine oil degradation (Livingstone et al., 2007; Sasaki & Uchiyama, 2002). If the oil degradation problem is ignored, this might result in serious turbine system erratic trips and start-up operational problems (Overgaag et al., 2009). Oil oxidation by-products, in other words, sludge and varnish contaminants, lead stated turbine operation-tribological problems. Hence, sludge and varnish presence in turbine oil become a major reason for declining turbine reliability and availability.

    In the power generation industry, heavy-duty gas turbines as well as steam turbines have been lubricated with mineral based turbine oils for many decades (Okazaki & Badal, 2005). First, generally Group I oils (mineral base oils produced by solvent extraction, dewaxing) were used. Nevertheless, this group of oils has lower oxidation resistance. Therefore, modern gas turbines demand oils which have better oil oxidation resistance, and lower sludge and varnish contaminants tendency (Hannon, 2009).

    Today, there are many turbine lubricants available on the market. Besides Group I oils, more and more Group II oils (mineral base oils produced by hydro cracking and hydro treating) are selected in service, and having increased oil oxidation resistance. However field inspections demonstrate that Group II oils also experience sludge and varnish problems as well as Group I oils. Primary reason for these phenomena is the antioxidant additive packages that are used in Group II oils (Overgaag et al., 2009). In any case with recent oil formulations, oil degradation products still exist in current turbine oils, and will continue to do so in natural process. These sludge and varnish contaminants are less than 1 micron in size. Thus, they can pass turbine oil system standard mechanical filters without obstruction. With regard to keep the turbine systems in best operational conditions, external turbine oil cleaning practices became crucial to remove these less than 1 micron size oil degradation products from turbine oils. Current effective method for removing the sludge and varnish is to use electrostatic oil cleaners (Moehle & Gatto et al., 2007).

    Since the majority of turbine user and operator population have been shifted to use Group II based oils to counter the increased sludge and varnish problems, traditional oil cleaners became insufficient to remove sludge and varnish from Group II. (Due to Group II oils have different oil characteristics such as oil oxidation stability and solvency capability). With this awareness, thesis project is looking for ways to introduce and develop an Advanced Electrostatic Oil Cleaner to increase the availability and reliability figures of heavy-duty gas turbines against the rising amount of oil degradation products in modern formulated turbine oils.

    ECC (Electrostatic Cooled Cleaner) is an electrostatic oil cleaner device to clean and cool mineral based turbine oils for heavy-duty gas turbine applications by removing the sludge and varnish - oil contaminants from turbine oils. The basic principle of the ECC is based on the electrostatic force produced by parallel positioned electrodes which are charged with a high D.C. voltage. Oil contaminants- sludge and varnish have polar nature. Therefore, they are attracted by electrostatic forces whose intensity is proportional to the voltage applied. With the oil flowing in parallel to these electrodes, the polar particles in the oil (which is only neutral /no polar) are caught by filter media positioned between these electrodes.

    Small investments on advanced oil cleaner result in big savings on turbine system performance. Increased turbine availability and reliability predominantly reduce maintenance costs and risks besides, and thus maximizing revenue by extending heavy-duty gas turbine operational life.

    An introduced prototype of the ECC-D4 model was tested using two Group II and one Group I oils. The amounts of 200 liter (each) test oils were circulated approximately 300 times through the ECC-D4. In each 3 oil cleaning test sessions, it is proved that the oil insolubles content decreased approximately 40% in tested turbine oils within about 240 ECC-D4 operating hours.

    With taken base of heavy-duty gas turbine characteristics such as 400 MW power production capacity, annually 8000 operating hours, and 15000 liter oil reservoir volume; it is estimated that the ECC-D4 can extend the oil service-life from 24000 to 48000 operating hours (which is approximately the oil service end-life). In addition to that, assuming the ECC-D4 investment cost as 30k€, about 15k€ savings per year through the new turbine oil and component replacement costs, besides turbine operation profit losses. Moreover, the ECC-D4 returns on investment with a rate of 39 % for defined heavy-duty gas turbine.

    In general perspective of ECC-D4, it makes heavy-duty gas turbine infrastructure innovative, fully integrated and committed to fulfilling the need for clean, efficient, reliable power production practices in an environmental manner.

     

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  • 75.
    Gunnesby, Michael
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    On Flow Predictions in Fuel Filler Pipe Design - Physical Testing vs Computational Fluid Dynamics2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The development of a fuel filler pipe is based solely on experience and physical experiment. The challenge lies in designing the pipe to fulfill the customer needs. In other words designing the pipe such as the fuel flow does not splash back on the fuel dispenser causing a premature shut off. To improve this “trial-and-error” based development a computational fluid dynamics (CFD) model of the refueling process is investigated. In this thesis a CFD model has been developed that can predict the fuel flow in the filler pipe.

    Worst case scenario of the refueling process is during the first second when the tank is partially filled. The most critical fluid is diesel due to the commercially high volume flow of 55 l/min. Due to limitations of computational resources the simulations are focused on the first second of the refueling process. The challenge in this project is creating a CFD model that is time efficient, thus require the least amount of computational resources necessary to provide useful information.

    A multiphase model is required to simulate the refueling process. In this project the implicit volume of fluid (VOF) has been used which has previously proven to be a suitable choice for refueling simulations.

    The project is divided into two parts. Part one starts with experiments and simulations of a simplified fuel system with water as acting liquid with a Reynolds number of 90 000. A short comparison between three different turbulence models has been investigated (LES, DES and URANS) where the most promising turbulence model is URANS, specifically the SST k-ω model. A sensitivity analysis was performed on the chosen turbulence model. Between the chosen mesh and the densest mesh the difference of streamwise velocity in the boundary layer was 2.6 %. The chosen mesh with 1.9 M cells and a time step of 1e-4 s was found to be the best correlating model with respect to the experiments.

    In part two a real fuel filling system was investigated both with experiments and simulations with the same computational model as the chosen one from part one. The change of fluid and geometry resulted in a lower Reynolds number of 12 000. Two different versions of the fuel system was investigated; with a bypass pipe and without a bypass pipe. Because of a larger volumetric region the resulting mesh had 3.7 M cells.

    The finished model takes about 230 h on a local workstation with 11 cores. On a cluster with 200 cores the same simulation takes 30 h. The resulting model suffered from interpolation errors at the inlet which resulted in a volume flow of 50 l/min as opposed to 55 l/min in the experiments. Despite the difference the model could capture the key flow characteristics. With the developed model a new filler pipe can be easily implemented and provide results in shorter time than a prototype filler pipe can be ordered. This will increase the chances of ordering one single prototype that fulfills all requirements. While the simulation model cannot completely replace verification by experiments it provides information that transforms the development of the filler pipe to knowledge based development.

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  • 76.
    Gupta, Vikas
    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).
    Henriksson, Lilian
    Linköping University, Department of Medical and Health Sciences, Division of Radiological Sciences. Linköping University, Faculty of Medicine and Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV). Region Östergötland, Center for Diagnostics, Department of Radiology in Linköping.
    Engvall, Jan
    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).
    Persson, Anders
    Linköping University, Department of Medical and Health Sciences, Division of Radiological Sciences. 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).
    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).
    Automated three-dimensional tracking of the left ventricular myocardium in time-resolved and dose-modulated cardiac CT images using deformable image registration2018In: Journal of Cardiovascular Computed Tomography, ISSN 1934-5925, Vol. 12, no 2, p. 139-148Article in journal (Refereed)
    Abstract [en]

    Background Assessment of myocardial deformation from time-resolved cardiac computed tomography (4D CT) would augment the already available functional information from such an examination without incurring any additional costs. A deformable image registration (DIR) based approach is proposed to allow fast and automatic myocardial tracking in clinical 4D CT images.

    Methods Left ventricular myocardial tissue displacement through a cardiac cycle was tracked using a B-spline transformation based DIR. Gradient of such displacements allowed Lagrangian strain estimation with respect to end-diastole in clinical 4D CT data from ten subjects with suspected coronary artery disease. Dice similarity coefficient (DSC), point-to-curve error (PTC), and tracking error were used to assess the tracking accuracy. Wilcoxon signed rank test provided significance of tracking errors. Topology preservation was verified using Jacobian of the deformation. Reliability of estimated strains and torsion (normalized twist angle) was tested in subjects with normal function by comparing them with normal strain in the literature.

    Results Comparison with manual tracking showed high accuracy (DSC: 0.99± 0.05; PTC: 0.56mm± 0.47 mm) and resulted in determinant(Jacobian) > 0 for all subjects, indicating preservation of topology. Average radial (0.13 mm), angular (0.64) and longitudinal (0.10 mm) tracking errors for the entire cohort were not significant (p > 0.9). For patients with normal function, average strain [circumferential, radial, longitudinal] and peak torsion estimates were: [-23.5%, 31.1%, −17.2%] and 7.22°, respectively. These estimates were in conformity with the reported normal ranges in the existing literature.

    Conclusions Accurate wall deformation tracking and subsequent strain estimation are feasible with the proposed method using only routine time-resolved 3D cardiac CT.

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  • 77.
    Gustafsson, Daniel
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Larsson, Isak
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Solvärme i Singapore2015Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    The world faces big issues regarding its energy supply and its impact on the environment. Something has to be done in order to stop this. One way to do that is to make energy generation more sustainable by shifting from fossil fuels to renewable energy sources. Solar energy is one of them, and this report covers hot water produced from it.

    A country that should have good conditions to harvest solar power is Singapore. The country has a very limited land area and almost no natural resources. Because of this, most of its energy is supplied by imported natural gas. In this report, a case has been created to evaluate the performance and profitability of a hot water solar system in a villa in Singapore. In order to do this, literature about the sun, solar heating systems and Singapore has been looked into. Further, thermodynamical correlations have been studied and used in calculations to draw conclusions.

    The result of this report is that an installation of a solar water heating system in a villa in Singapore is feasible and profitable. Other applications of solar thermal power have been evaluated qualitatively and the conclusion is that these also have big potential in Singapore. Ultimately, this could lead Singapore to be less relying on imported energy and also reduce its impact on the environment.

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    Solvärme i Singapore
  • 78. Order onlineBuy this publication >>
    Gårdhagen, Roland
    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).
    Turbulent Flow in Constricted Blood Vessels: Quantification of Wall Shear Stress Using Large Eddy Simulation2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The genesis of atherosclerosis has previously been shown to be affected by the frictional load from the blood on the vessel wall, called the wall shear stress (WSS). Assessment of WSS can therefore provide important information for diagnoses, intervention planning, and follow‐up. Calculation of WSS requires high‐resolved velocity data from the vessel, which in turn can be obtained using computational fluid dynamics (CFD). In this work large eddy simulation LES was successfully used to simulate transitional flow in idealized as well as subject specific vessel models. It was shown that a scale resolving technique is to prefer for this application, since much valuable information otherwise is lost. Besides, Reynolds‐Averaged Navier‐Stokes (RANS) models have generally failed to predict this type of flow.

    Non‐pulsating flows of Reynolds numbers up to 2 000 in a circular constricted pipe showed that turbulence is likely to occur in the post‐stenotic region, which resulted in a complex WSS pattern characterized by large spatial as well temporal fluctuations in all directions along the wall. Time averaged streamwise WSS was relatively high, while time averaged circumferential WSS was low, meaning that endothelial cells in that region would be exposed to oscillations in a stretched state in the streamwise direction and in a relaxed state in the circumferential direction.

    Since every vessel is unique, so is also its WSS pattern. Hence the CFD simulations must be done in subject specific vessel models. Such can be created from anatomical information acquired with magnetic resonance imaging (MRI). MRI can also be used to obtain velocity boundary conditions for the simulation. This technique was used to investigate pulsating flow in a subject specific normal human aorta. It was shown that even the flow in healthy vessels can be very disturbed and turbulence like, and even for this case large WSS variations were seen. It was also shown that regions around branches from the aorta, known to be susceptible for atherosclerosis, were characterized by high time averaged WSS and high oscillatory shear index.

    Finally, the predictive capability of CFD was investigated. An idealized model of a human aorta with a coarctation and post‐stenotic dilatation was studied before and after a possible repair of the constriction. The results suggested that small remaining abnormalities in the geometry may deteriorate the chances for a successful treatment. Also, high values of shear rate and Reynolds stresses were found in the dilatation after the constriction, which previous works have shown means increased risk for thrombus formation and hemolysis.

    List of papers
    1. Feasibility of Patient Specific Aortic Blood Flow CFD Simulation
    Open this publication in new window or tab >>Feasibility of Patient Specific Aortic Blood Flow CFD Simulation
    Show others...
    2006 (English)In: Medical Image Computing and Computer-Assisted Intervention – MICCAI 2006: 9th International Conference, Copenhagen, Denmark, October 1-6, 2006. Proceedings, Part I / [ed] Rasmus Larsen, Mads Nielsen and Jon Sporring, Springer Berlin/Heidelberg, 2006, 1, Vol. 4190, p. 257-263Conference paper, Published paper (Refereed)
    Abstract [en]

    Patient specific modelling of the blood flow through the human aorta is performed using computational fluid dynamics (CFD) and magnetic resonance imaging (MRI). Velocity patterns are compared between computer simulations and measurements. The workflow includes several steps: MRI measurement to obtain both geometry and velocity, an automatic levelset segmentation followed by meshing of the geometrical model and CFD setup to perform the simulations follwed by the actual simulations. The computational results agree well with the measured data.

    Place, publisher, year, edition, pages
    Springer Berlin/Heidelberg, 2006 Edition: 1
    Series
    Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349 ; 4190
    National Category
    Medical Image Processing
    Identifiers
    urn:nbn:se:liu:diva-36902 (URN)10.1007/11866565_32 (DOI)000241556300032 ()32988 (Local ID)3-5404-4707-5 (ISBN)978-3-540-44727-6 (ISBN)978-3-540-44707-8 (ISBN)32988 (Archive number)32988 (OAI)
    Conference
    The 9th MICCAI Conference, Copenhagen, Denmark, 1-6 October 2006
    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2018-02-20Bibliographically approved
    2. Large Eddy Simulation of Stenotic Flow for Wall Shear Stress Estimation - Validation and Application
    Open this publication in new window or tab >>Large Eddy Simulation of Stenotic Flow for Wall Shear Stress Estimation - Validation and Application
    2011 (English)In: WSEAS Transactions on Biology and Biomedicine, ISSN 1109-9518, Vol. 8, no 3, p. 86-101Article in journal (Refereed) Published
    Abstract [en]

    Turbulent flow in the cardiovascular system may increase the risk for severe arterial disease. This workaddresses the feasibility of Large Eddy Simulation (LES) using a general purpose code as a tool for assessmentof cardiovascular flow and investigates Wall Shear Stress (WSS) in steady as well as pulsating turbulent pipeflow. Poiseuille flow was specified at the inlet, and with a suitable ammount of perturbations at the inlet it waspossible to predict experimental data. The extent of the recirculation zone was affected by the inlet disturbances,and magnitude as well as direction of the WSS vector varied significantly at the reattachment point. For thepulsating flow, WSS shows a complex pattern with different spatial and temporal variation along the pipe. Thewall shear stress gradient was calculated on the entire post-stenotic surface and each component in the gradientwas investigated. The off-diagonal components in the gradient are usually assumed to be small, but here they werefound to be on the same order of magnitude as the diagonal terms. This work demonstrates the need for a scaleresolving simulation technique to accurately model cardiovascular flows.

    Keywords
    Turbulence, Large Eddy Simulation, Cardiovascular Flow, Wall Shear Stress
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:liu:diva-73211 (URN)
    Available from: 2011-12-22 Created: 2011-12-22 Last updated: 2016-03-14
    3. Quantifying Turbulent Wall Shear Stress in a Stenosed Pipe Using Large Eddy Simulation
    Open this publication in new window or tab >>Quantifying Turbulent Wall Shear Stress in a Stenosed Pipe Using Large Eddy Simulation
    2010 (English)In: Journal of Biomechanical Engineering, ISSN 0148-0731, E-ISSN 1528-8951, Vol. 132, no 6Article in journal (Refereed) Published
    Abstract [en]

    Large eddy simulation was applied for flow of Re = 2000 in a stenosed pipe in order to undertake a thorough investigation of the wall shear stress (WSS) in turbulent flow. A decomposition of the WSS into time averaged and fluctuating components is proposed. It was concluded that a scale resolving technique is required to completely describe the WSS pattern in a subject specific vessel model, since the poststenotic region was dominated by large axial and circumferential fluctuations. Three poststenotic regions of different WSS characteristics were identified. The recirculation zone was subject to a time averaged WSS in the retrograde direction and large fluctuations. After reattachment there was an ante grade shear and smaller fluctuations than in the recirculation zone. At the reattachment the fluctuations were the largest, but no direction dominated over time. Due to symmetry the circumferential time average was always zero. Thus, in a blood vessel, the axial fluctuations would affect endothelial cells in a stretched state, whereas the circumferential fluctuations would act in a relaxed direction.

    Place, publisher, year, edition, pages
    American Society Mechanical Engineers, 2010
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-58347 (URN)10.1115/1.4001075 (DOI)000278965500002 ()
    Available from: 2010-08-13 Created: 2010-08-11 Last updated: 2017-12-12
    4. Quantifying turbulent wall shear stress in a subject specific human aorta using large eddy simulation
    Open this publication in new window or tab >>Quantifying turbulent wall shear stress in a subject specific human aorta using large eddy simulation
    2012 (English)In: Medical Engineering and Physics, ISSN 1350-4533, E-ISSN 1873-4030, Vol. 34, no 8, p. 1139-1148Article in journal (Refereed) Published
    Abstract [en]

    In this study, large-eddy simulation (LES) is employed to calculate the disturbed flow field and the wall shear stress (WSS) in a subject specific human aorta. Velocity and geometry measurements using magnetic resonance imaging (MRI) are taken as input to the model to provide accurate boundary conditions and to assure the physiological relevance. In total, 50 consecutive cardiac cycles were simulated from which a phase average was computed to get a statistically reliable result. A decomposition similar to Reynolds decomposition is introduced, where the WSS signal is divided into a pulsating part (due to the mass flow rate) and a fluctuating part (originating from the disturbed flow). Oscillatory shear index (OSI) is plotted against time-averaged WSS in a novel way, and locations on the aortic wall where elevated values existed could easily be found. In general, high and oscillating WSS values were found in the vicinity of the branches in the aortic arch, while low and oscillating WSS were present in the inner curvature of the descending aorta. The decomposition of WSS into a pulsating and a fluctuating part increases the understanding of how WSS affects the aortic wall, which enables both qualitative and quantitative comparisons.

    Place, publisher, year, edition, pages
    Elsevier, 2012
    Keywords
    Human aorta, Atherosclerosis, Wall shear stress, Computational fluid dynamics, Scale resolving turbulence model, Reynolds decomposition
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-84887 (URN)10.1016/j.medengphy.2011.12.002 (DOI)000309028800016 ()
    Note

    Funding Agencies|Swedish research council|VR 2007-4085VR 2010-4282|National Supercomputer Centre (NSC)|SNIC022/09-11|

    Available from: 2012-11-01 Created: 2012-10-26 Last updated: 2017-12-07
    5. Large Eddy Simulation of Pulsating Flow Before and After CoA Repair - CFD for Intervention Planning
    Open this publication in new window or tab >>Large Eddy Simulation of Pulsating Flow Before and After CoA Repair - CFD for Intervention Planning
    2015 (English)In: Advances in Mechanical Engineering, ISSN 1687-8132, E-ISSN 1687-8140, Vol. 7, no 2Article in journal (Refereed) Published
    Abstract [en]

    Large eddy simulation was applied to investigate hemodynamics in a model with coarctation of the aorta (CoA) and post-stenotic dilatation. Special focus was put on the role of hemodynamics for success of CoA repair. Several parameters previously identified as related to cardiovascular disease were studied. Known risk factors were observed both with CoA and after repair, and the restoration of the anatomy seems to be crucial for a successful result.

    Place, publisher, year, edition, pages
    Hindawi Publishing Corporation / SAGE Publications, 2015
    Keywords
    Coarctation of the Aorta, CFD, Intervention Planning, Turbulence, Wall Shear Stress, Shear Rate
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-100917 (URN)10.1155/2014/971418 (DOI)000354083600087 ()
    Available from: 2013-11-14 Created: 2013-11-14 Last updated: 2017-12-06Bibliographically approved
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    Turbulent Flow in Constricted Blood Vessels: Quantification ofWall Shear Stress Using Large Eddy Simulation
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  • 79.
    Gårdhagen, Roland
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Carlsson, Fredrik
    FS Dynamics Sweden AB, Göteborg, Sweden.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Large Eddy Simulation of Pulsating Flow Before and After CoA Repair - CFD for Intervention Planning2015In: Advances in Mechanical Engineering, ISSN 1687-8132, E-ISSN 1687-8140, Vol. 7, no 2Article in journal (Refereed)
    Abstract [en]

    Large eddy simulation was applied to investigate hemodynamics in a model with coarctation of the aorta (CoA) and post-stenotic dilatation. Special focus was put on the role of hemodynamics for success of CoA repair. Several parameters previously identified as related to cardiovascular disease were studied. Known risk factors were observed both with CoA and after repair, and the restoration of the anatomy seems to be crucial for a successful result.

    Download full text (pdf)
    fulltext
  • 80.
    Gårdhagen, Roland
    et al.
    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.
    Carlsson, Fredrik
    ANSYS Sweden, Gothenburg, 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.
    Large Eddy Simulation of Steady and Pulsating Flow in Asymmetric Stenosed Pipe2010In: ASME 2010 Summer Bioengineering Conference: Parts A and B, The American Society of Mechanical Engineers (ASME) , 2010, p. 573-574Conference paper (Refereed)
    Abstract [en]

    Local hemodynamics and its impact on the development of cardiovascular disease and the blood itself have gained increasing attention during the last decades. Regions with low and/or oscillatory Wall Shear Stress (WSS) have been correlated with increased risk for development of atherosclerosis [1]; and turbulence in the cardio vascular system is suggested to increase the risk for hemolysis as well as platelet activation and thrombus formation [2, 3]. Furthermore, turbulent flows are inherently oscillatory with large spatial as well as temporal fluctuation, and hence possibly a risk for atherosclerosis development per se.

  • 81.
    Gårdhagen, Roland
    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.
    Carlsson, Fredric
    FS Dynamics Sweden AB, Gothenburg.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Large Eddy Simulation of Stenotic Flow for Wall Shear Stress Estimation - Validation and Application2011In: WSEAS Transactions on Biology and Biomedicine, ISSN 1109-9518, Vol. 8, no 3, p. 86-101Article in journal (Refereed)
    Abstract [en]

    Turbulent flow in the cardiovascular system may increase the risk for severe arterial disease. This workaddresses the feasibility of Large Eddy Simulation (LES) using a general purpose code as a tool for assessmentof cardiovascular flow and investigates Wall Shear Stress (WSS) in steady as well as pulsating turbulent pipeflow. Poiseuille flow was specified at the inlet, and with a suitable ammount of perturbations at the inlet it waspossible to predict experimental data. The extent of the recirculation zone was affected by the inlet disturbances,and magnitude as well as direction of the WSS vector varied significantly at the reattachment point. For thepulsating flow, WSS shows a complex pattern with different spatial and temporal variation along the pipe. Thewall shear stress gradient was calculated on the entire post-stenotic surface and each component in the gradientwas investigated. The off-diagonal components in the gradient are usually assumed to be small, but here they werefound to be on the same order of magnitude as the diagonal terms. This work demonstrates the need for a scaleresolving simulation technique to accurately model cardiovascular flows.

  • 82.
    Gårdhagen, Roland
    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.
    Carlsson, Fredrik
    ANSYS Sweden, Gothenburg, Sweden.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Large Eddy Simulation of Flow through a Stenosed Pipe2009In: ASME 2008 Summer Bioengineering Conference, Parts A and B, American Society of Mechanical Engineers , 2009, p. 445-446Conference paper (Refereed)
    Abstract [en]

    A majority of all deaths in the developed world are related to atherosclerosis, i.e. obstruction of blood vessels caused by growth of the vessel wall. Hemodynamic phenomena, especially wall shear stress, are since several decades thought to influence the risk to develop atherosclerosis; hence simulation of blood flow, either in order to elucidate the relation between the hemodynamic and disease initiation or to study the flow pattern, is an area of intense research [1,2].

  • 83.
    Gårdhagen, Roland
    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.
    Carlsson, Fredrik
    ANSYS Sweden.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics . Linköping University, The Institute of Technology.
    Quantifying Turbulent Wall Shear Stress in a Stenosed Pipe Using Large Eddy Simulation2010In: Journal of Biomechanical Engineering, ISSN 0148-0731, E-ISSN 1528-8951, Vol. 132, no 6Article in journal (Refereed)
    Abstract [en]

    Large eddy simulation was applied for flow of Re = 2000 in a stenosed pipe in order to undertake a thorough investigation of the wall shear stress (WSS) in turbulent flow. A decomposition of the WSS into time averaged and fluctuating components is proposed. It was concluded that a scale resolving technique is required to completely describe the WSS pattern in a subject specific vessel model, since the poststenotic region was dominated by large axial and circumferential fluctuations. Three poststenotic regions of different WSS characteristics were identified. The recirculation zone was subject to a time averaged WSS in the retrograde direction and large fluctuations. After reattachment there was an ante grade shear and smaller fluctuations than in the recirculation zone. At the reattachment the fluctuations were the largest, but no direction dominated over time. Due to symmetry the circumferential time average was always zero. Thus, in a blood vessel, the axial fluctuations would affect endothelial cells in a stretched state, whereas the circumferential fluctuations would act in a relaxed direction.

  • 84.
    Gårdhagen, Roland
    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.
    Carlsson, Fredrik
    ANSYS Sweden.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Wall Shear Stress in Turbulent Pipe Flow2009In: Proceedings of the ASME Summer Bioengineering Conference 2009, 2009, p. 963-964Conference paper (Refereed)
    Abstract [en]

    Low and/or oscillatory Wall Shear Stress (WSS) has been correlated with elevated risk for increased intima media thickness and atherosclerosis in several studies during the last decades [1, 2]. Most of the studies have addressed laminar flows, in which the oscillations mainly are due to the pulsating nature of blood flow. Turbulent flows however show significant spatial and temporal fluctuations although the mean flow is steady.

  • 85.
    Gårdhagen, Roland
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Renner, Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Länne, Toste
    Linköping University, Department of Medicine and Health Sciences, Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart Centre, Department of Thoracic and Vascular Surgery.
    Karlsson, Matts
    Linköping University, Department of Biomedical Engineering, Biomedical Modelling and Simulation. Linköping University, The Institute of Technology.
    Subject Specific Wall Shear Stress in the Human Thoracic Aorta2006In: WSEAS Transaction on biology and biomedicine, ISSN 1109-9518, Vol. 10, no 3, p. 609-614Article in journal (Refereed)
    Abstract [en]

    Numerous studies have shown a correlation between Wall Shear Stress (WSS) and atherosclerosis, but few have evaluated the reliability of estimation methods and measures used to assessWSS, which is the subject of this work. A subject specific vessel model of the aortic arch and thoracic aorta is created fromMRI images and used for CFD simulations with MRI velocity measurements as inlet boundary condition. WSS is computed from the simulation results. Aortic WSS shows significant spatial as well as temporal variation during a cardiac cycle, which makes circumferential values very uninformative, and approximate estimates using Hagen-Poiseuille fails predict the averageWSS. Highly asymmetric flow, especially in the arch, causes the spatial WSS variations.

  • 86.
    Ha, Hojin
    et al.
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Lantz, Jonas
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Haraldsson, Henrik
    University of Calif San Francisco, CA 94143 USA.
    Casas Garcia, Belén
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Ziegler, Magnus
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    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).
    Saloner, David
    University of Calif San Francisco, CA 94143 USA.
    Dyverfeldt, Petter
    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). Region Östergötland, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    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).
    Assessment of turbulent viscous stress using ICOSA 4D Flow MRI for prediction of hemodynamic blood damage2016In: SCIENTIFIC REPORTS, ISSN 2045-2322, Vol. 6, article id 39773Article in journal (Refereed)
    Abstract [en]

    Flow-induced blood damage plays an important role in determining the hemodynamic impact of abnormal blood flow, but quantifying of these effects, which are dominated by shear stresses in highly fluctuating turbulent flow, has not been feasible. This study evaluated the novel application of turbulence tensor measurements using simulated 4D Flow MRI data with six-directional velocity encoding for assessing hemodynamic stresses and corresponding blood damage index (BDI) in stenotic turbulent blood flow. The results showed that 4D Flow MRI underestimates the maximum principal shear stress of laminar viscous stress (PLVS), and overestimates the maximum principal shear stress of Reynolds stress (PRSS) with increasing voxel size. PLVS and PRSS were also overestimated by about 1.2 and 4.6 times at medium signal to noise ratio (SNR) = 20. In contrast, the square sum of the turbulent viscous shear stress (TVSS), which is used for blood damage index (BDI) estimation, was not severely affected by SNR and voxel size. The square sum of TVSS and the BDI at SNR amp;gt;20 were underestimated by less than 1% and 10%, respectively. In conclusion, this study demonstrated the feasibility of 4D Flow MRI based quantification of TVSS and BDI which are closely linked to blood damage.

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  • 87.
    Ha, Hojin
    et al.
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Lantz, Jonas
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Ziegler, Magnus
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Casas Garcia, Belén
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    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).
    Dyverfeldt, Petter
    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).
    Estimating the irreversible pressure drop across a stenosis by quantifying turbulence production using 4D Flow MRI2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 46618Article in journal (Refereed)
    Abstract [en]

    The pressure drop across a stenotic vessel is an important parameter in medicine, providing a commonly used and intuitive metric for evaluating the severity of the stenosis. However, non-invasive estimation of the pressure drop under pathological conditions has remained difficult. This study demonstrates a novel method to quantify the irreversible pressure drop across a stenosis using 4D Flow MRI by calculating the total turbulence production of the flow. Simulation MRI acquisitions showed that the energy lost to turbulence production can be accurately quantified with 4D Flow MRI within a range of practical spatial resolutions (1-3 mm; regression slope = 0.91, R-2 = 0.96). The quantification of the turbulence production was not substantially influenced by the signal-to-noise ratio (SNR), resulting in less than 2% mean bias at SNR amp;gt; 10. Pressure drop estimation based on turbulence production robustly predicted the irreversible pressure drop, regardless of the stenosis severity and post-stenosis dilatation (regression slope = 0.956, R-2 = 0.96). In vitro validation of the technique in a 75% stenosis channel confirmed that pressure drop prediction based on the turbulence production agreed with the measured pressure drop (regression slope = 1.15, R-2 = 0.999, Bland-Altman agreement = 0.75 +/- 3.93 mmHg).

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  • 88.
    Hamedi, Naser
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Numerical Study of NOx and Flame Shape of a DLE Burner2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    For natural gas combustion, there is a large amount of experience in the gas turbine industry. However, much of the design work is based on costly combustion tests due to insufficient accuracy of existing prediction tools for data such as emissions and effects due to fuel composition. In the present work, Computational Fluid Dynamics (CFD) approach is used to study partially premixed combustion in the 3rd generation DLE (Dry Low Emission) burner that is used in SGT-700 and SGT-800 gas turbines. The fuels that are studied here are natural gas and enriched hydrogen fuel. The CFD models which are used in this work are an axisymmetric and a 3D model and the softwares are ANSYS CFX and ANSYS FLUENT.

    One of the main objectives of this thesis is the study of flame shape and NOx emission in hydrogen enriched combustion. In the first study of the present work, effect of adding hydrogen to non-preheated gas combustion was investigated and the results were compared with the available measurement data. Calculated laminar burning velocity with CANTERA showed a good agreement with the experimental and numerical references. Also, the accuracy of generated flamelet libraries in CFD tools to calculate adiabatic flame temperature was compared with different available tools. Results showed good agreement between available tools for the ranges of interest.

    In addition, flame shape and NOx prediction was studied in the gas turbine burner. Adding hydrogen to the fuel increased significantly turbulent burning velocity and OH distribution in the domain. The effect of hydrogen on the central stagnation point was studied and the simulation results did not show a significant effect on the stagnation point location.

    Beside the flame shape, this study showed that although the CFD NOx prediction tools in ANSYS CFX and ANSYS FLUENT predict the trend of NOx and the flame propagation in the right manner, in order to use as a reliable prediction tool in the gas turbine industry they need to be improved. 

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  • 89.
    Haraldsson, Henrik
    et al.
    Univ Calif San Francisco, CA 94143 USA.
    Kefayati, Sarah
    Univ Calif San Francisco, CA 94143 USA.
    Ahn, Sinyeob
    Siemens Healthcare, Germany.
    Dyverfeldt, Petter
    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).
    Lantz, Jonas
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    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).
    Laub, Gerhard
    Siemens Healthcare, Germany.
    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).
    Saloner, David
    Univ Calif San Francisco, CA 94143 USA; Vet Affairs Med Ctr, CA 94121 USA.
    Assessment of Reynolds stress components and turbulent pressure loss using 4D flow MRI with extended motion encoding2018In: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 79, no 4, p. 1962-1971Article in journal (Refereed)
    Abstract [en]

    PurposeTo measure the Reynolds stress tensor using 4D flow MRI, and to evaluate its contribution to computed pressure maps. MethodsA method to assess both velocity and Reynolds stress using 4D flow MRI is presented and evaluated. The Reynolds stress is compared by cross-sectional integrals of the Reynolds stress invariants. Pressure maps are computed using the pressure Poisson equationboth including and neglecting the Reynolds stress. ResultGood agreement is seen for Reynolds stress between computational fluid dynamics, simulated MRI, and MRI experiment. The Reynolds stress can significantly influence the computed pressure loss for simulated (eg, -0.52% vs -15.34% error; Pamp;lt;0.001) and experimental (eg, 30611 vs 203 +/- 6 Pa; Pamp;lt;0.001) data. A 54% greater pressure loss is seen at the highest experimental flow rate when accounting for Reynolds stress (Pamp;lt;0.001). Conclusion4D flow MRI with extended motion-encoding enables quantification of both the velocity and the Reynolds stress tensor. The additional information provided by this method improves the assessment of pressure gradients across a stenosis in the presence of turbulence. Unlike conventional methods, which are only valid if the flow is laminar, the proposed method is valid for both laminar and disturbed flow, a common presentation in diseased vessels. Magn Reson Med 79:1962-1971, 2018. (c) 2017 International Society for Magnetic Resonance in Medicine.

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  • 90.
    Haraldsson, Henrik
    et al.
    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.
    Sigfridsson, Andreas
    Linköping University, Department of Medical and Health Sciences, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart Centre, Department of Clinical Physiology.
    Sakuma, Hajime
    Engvall, Jan
    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.
    Ebbers, Tino
    Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart Centre, Department of Clinical Physiology. Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Center for Medical Image Science and Visualization, CMIV.
    Influence of the FID and off-resonance effects in dense MRI2011In: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 65, no 4, p. 1104-1112Article in journal (Refereed)
    Abstract [en]

    Accurate functional measurement in cardiovascular diseases is important as inaccuracy may compromise diagnostic decisions. Cardiac function can be assessed using displacement encoding with stimulated echoes, resulting in three signal components. The free induction decay (FID), arising from spins undergoing T1-relaxation, is not displacement encoded and impairs the displacement acquired. Techniques for suppressing the FID exist; however, a residual will remain. The effect of the residual is difficult to distinguish and investigate in vitro and in vivo. In this work, the influence of the FID as well as of off-resonance effects is evaluated by altering the phase of the FID in relation to the stimulated echo. The results show that the FID and off-resonance effects can impair the accuracy of the displacement measurement acquired. The influence of the FID can be avoided by using an encoded reference. We therefore recommend the assessment of this influence of the FID for each displacement encoding with stimulated echoes protocol.

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  • 91.
    Hedbrant, Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    [Common sense against rolls of fat--should we reduce our intake of carbohydrates?].: Folkvett mot fettvalk – bör vi minska vårt kolhydratintag?2003In: Läkartidningen, ISSN 0023-7205, E-ISSN 1652-7518, Vol. 100, no 47, p. 3889-3890Article in journal (Refereed)
    Abstract [sv]

    Västvärldens kostexperter har utifrån ett primitivt energibalanstänkande lanserat budskapet att äta kolhydrater, som är mindre energitäta än fett och borde ge lägre energiintag. Istället har man råkat öka aptiten eftersom kosten innehållit mindre andel protein, samt ökat kroppsfettmassan då ökat kolhydratintag medfört ökade insulinhalter och fettinlagring samt blockerad fettförbränning.

  • 92.
    Hedbrant, Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Kostråd till diabetiker baseras inte på studier av diabetiker!: en kritik av ovetenskapen inom vetenskapen2006In: 2000-Talets Vetenskap, ISSN 1654-7810, no 2, p. 14-15Article in journal (Other academic)
    Abstract [sv]

    Övervikten i Sverige började öka sedan nyckelhålsmärkningen infördes 1989. I USA som ligger före Sverige vad gäller övervikt ökar nu typ-2-diabetes. Som intresserad lekman undrar man förstås varför, och det är glädjande att även näringsexperter börjar intressera sig för tänkbara orsaker. Johan Hedbrant har studerat det vetenskapliga underlaget för kostråden och funnit häpnadsväckande brister.

    I två artiklar i Läkartidningen hänvisar Larsson, Rothenberg och Vessby till nyligen uppdaterade kostråd av Diabetes Nutrition Study Group (DNSG), och noterar en skillnad jämfört med en typ av dieter som visat sig ge stora fördelar vid övervikt och typ-2-diabetes. De senare bygger på en reduktion av kolhydratinnehållet, medan DNSG ekommenderar upp till 60 energiprocent kolhydrat. I skenet av råden att äta mer kolhydrat och tredubblingen av typ-2-diabetes, undrar man lite över vetenskapen bakom att rekommendera mer av det näringsämne typ-2-diabetiker inte tål.

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  • 93.
    Hedbrant, Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    [Meagre knowledge about obesity].: Mager kunskap om fetma.2003In: Läkartidningen, ISSN 0023-7205, E-ISSN 1652-7518, Vol. 100, no 21, p. 1922-Article in journal (Refereed)
  • 94.
    Hedbrant, Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Somatisk tinnitus och Ménières sjukdom: nya metoder för behandling2005In: Medikament, ISSN 1402-3881, no 3, p. 54-57Article in journal (Other academic)
    Abstract [sv]

    Forskningsresultat kring somatisk, eller somatosensorisk, tinnitus är relativt färska. Flera studier har visat ett samband mellan tinnitus och dysfunktion i käkregionen, samt mellan Ménières sjukdom och dysfunktion i nackregionen.

    I denna artikel diskuterar Johan Hedbrant möjligheter till behandling av tinnitus och Ménières sjukdom från ett somatiskt eller somatosensoriskt perspektiv. Artikeln är en fortsättning på Johan Hedbrants artikel i Medikament nr 1/05.

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  • 95.
    Hedbrant, Johan
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Bjorne, Assar
    Specialisttandvården, Lasarettet Ystad.
    Ny mätmetod för käkmuskulaturen kan finna orsaken till tinnitus: Slutrapport Nutek 92-119041997Report (Other academic)
    Abstract [sv]

    Tinnitus är en åkomma som i lindrigare eller allvarligare former drabbar 17% av västvärldens befolkning. Ca 85 000 svenskar har tinnitus på invalidiserande nivå. Förutom mänskligt lidande orsakar tinnitus samhällskostnader på ca 1.5 miljard kr årligen. Orsaken är till största delen okänd.

    Vissa tecken tyder på ett samband mellan tinnitus och funktionsstörning i en käkmuskel. Några olika icke–invasiva metoder för mätning av muskelstörning i M Pterygoideus Lateralis har utvärderas. Två av dessa är intressanta för fortsatta studier.

    Termografi användes för att diagnosticera muskelstörningar på ytligt liggande muskler. Vi såg åtskilliga varma områden på ytliga käk– och nackmuskler på de patienter som hade käkledsstörningar, samt möjligen tecken på onormal värme från M Pterygoideus Lateralis. Mätförhållandena var dock ej ideala.

    En metod att mäta EMG med adaptiv noise cancelling provades. EMG från en ryggmuskel, stört av en “EKG–signal” från hjärtat användes. Metoden fungerade bra. Fortsatt metodutveckling på t.ex. ryggmuskler borde göras.

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  • 96.
    Hedbrant, Johan
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Nordfeldt, Sam
    Linköping University, Department of Medical and Health Sciences, Division of Health Care Analysis. Linköping University, Faculty of Health Sciences.
    Nordfeldt, Sam
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Molecular and Clinical Medicine, Pediatrics.
    Ludvigsson, Johnny
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Molecular and Clinical Medicine, Pediatrics. Östergötlands Läns Landsting, Center of Paediatrics and Gynaecology and Obstetrics, Department of Paediatrics in Linköping.
    Ludvigsson, Johnny
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Molecular and Clinical Medicine, Pediatrics. Östergötlands Läns Landsting, Center of Paediatrics and Gynaecology and Obstetrics, Department of Paediatrics in Linköping.
    The Särimner Diabetes Simulator - A Look in the Rear View Mirror2007In: Diabetes Technology & Therapeutics, ISSN 1520-9156, E-ISSN 1557-8593, Vol. 9, no 1, p. 10-16Article in journal (Refereed)
    Abstract [en]

      

  • 97.
    Hellberg, Viktor
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Fredriksson, Rikard
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Calculation of Fluid Dynamic Loads on a Projectile During Firing: Development of a CFD-modelling Approach2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The transition from inner to outer ballistics is a crucial part of the launch of a projectile from a recoilless rifle. Since a launch of the rifle is a rapid process and due to the extreme conditions in terms of accelerations and temperature, physical measurements are hard to achieve.

    To gain knowledge about the fluid dynamic loads that act on the projectile during a launch CFD can be a useful technique. In this work a CFD model of the launch process has been developed. Different methods to implement the most important parts of the launch process have been evaluated and compared. An unsteady RANS-model have been utilised in combination with a dynamic mesh to handle the motion of the projectile.

    In this work, a spin-stable type of projectile has been analysed. To force the projectile to spin, helical grooves are used inside the launch tube. If the projectile does not fill out and seal the grooves completely, propellant gas can leak through these grooves. In the model it has been evaluated if the leak flow has an impact on the flow field around the projectile and its stability. To simplify the model the grooves were approximated as a gap with constant thickness between the tube and the projectile.

    Two different methods to implement the propellant burning have been tested. In the first case a pressure curve known from measurements are implemented. In the second, the mass flow from the combustion is modelled.

    This work shows that it is possible to predict the behaviour of the flow during a launch with a CFD model. The leak flow was found to have a significant impact on the flow field in front of the projectile. However, it has also been found that the leakage only have a limited effect on the fluid dynamic forces that works on the projectile during the transition phase.

    From this work it has been concluded that CFD can be a useful complement to physical tests and it gives a deeper understanding about the flow when the projectile leaves the launch tube. It has also been concluded that the launch process is an extensive topic and contains many different disciplines; therefore more work is needed to refine the model. 

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  • 98.
    Huge-Brodin, Maria
    et al.
    Linköping University, Department of Management and Engineering, Logistics & Quality Management. Linköping University, Faculty of Science & Engineering.
    Martinsen Sallnäs, Uni
    Linköping University, Department of Management and Engineering, Logistics & Quality Management. 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).
    Sustainable Logistics Service Providers: A strategic perspective on green logistics service provision2015In: Proceedings from the 20th Annual Logistics Research Network Conference: Resource Efficiency and Sustainability in Logistics and Supply Chain Management / [ed] Lim, M., Jones, C., Day, J. and Smith, S., Derby: The Chartered Institute of Logistics and Transport & Derby University , 2015, p. 1-8Conference paper (Refereed)
    Abstract [en]

    Purpose: Environmental sustainability is of increasing importance. The Logistics Service Industry is of specific interest: its impact from mainly transports is still increasing. However, the sustainability of any company also includes a long-term prosperous business. The purpose of this paper is to demonstrate how a hauler, as an example of a logistics service provider (LSP), through approaching environmental sustainability from an overall strategic business perspective, can succeed long-term.

    Research Approach: The paper builds on an in-depth case study of a medium sized privately held LSP. The case was selected as it stands out compared to its competitors with respect to environmental engagement and long-term commitment to sustainability related issues. Starting from a framework based on RBT (Resource Based Theory), the case is analysed regarding how various types of resources and dynamic capabilities can contribute to sustainable competitive advantage.

    Findings and Originality: The case study illustrates how an LSP can put various resources to work and how resources can be combined. It is demonstrated that these combinations of resources are valuable, rare and perfectly inimitable, and that they to a high extent are well established in the company, and hence not rely in certain individuals. The cases study further demonstrates how an LSP can sense possibilities, seize opportunities and, when needed, reshape its business accordingly, and hence possess critical dynamic capabilities. This research contributes by analysing an LSP that, in contrast to most of its competitors, has succeeded in making its sustainable development a strategic asset. This asset reaches beyond the commonly acknowledged efficiency gains, and is an interesting example of how an LSP through its dynamic capabilities can gain a unique position.

    Research Impact: The strategic perspective through an RBT lens has previously been applied to LSPs mainly in survey based research. The results of this paper are rare, as they build on a real-case situation of a successful and sustainable LSP, while the extant research of success among LSPs going greener mostly suggest future development to become successful. This paper suggests how sustainable development can become a strategic asset for an LSP, and how dynamic capabilities can support that. Theories on dynamic capabilities have previously only been applied to a very limited extent on the analysis of LSPs aiming for going greener

    Practical Impact: Based on this case, other LSPs may get inspiration to how they can develop their business to become more sustainable. The analysis points to that greening efforts cannot be seen in isolation, rather it is the combination of efforts, uniquely orchestrated for each case, that can make a difference. Therefore, the results point to relationships between various efforts, as well as how the different greening efforts fit the context of the LSP.

  • 99.
    Huge-Brodin, Maria
    et al.
    Linköping University, Department of Management and Engineering, Logistics Management. Linköping University, The Institute of Technology.
    Martinsen, Uni
    Linköping University, Department of Management and Engineering, Logistics Management. Linköping University, The Institute of Technology.
    Karlsosn, 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).
    The Slowness of Greening Transports in Supply Chains: Barriers and Enablers when Introducing Green Activities2014In: Competitiveness through Supply Chain Management and Global Logistics: Proceedings form the 26th Conference of the Nordic Logistics Research Network / [ed] Gammelgard, B. et al., 2014, p. 962-964Conference paper (Refereed)
  • 100.
    Hyvärinen, Jari
    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.
    Zhou, Lin
    Creo Dynam AB, Linkoping, Sweden.
    Study of concept for hydraulic hose dynamics investigations to enable understanding of the hose fluid-structure interaction behavior2020In: Advances in Mechanical Engineering, ISSN 1687-8132, E-ISSN 1687-8140, Vol. 12, no 4, article id 1687814020916110Article in journal (Refereed)
    Abstract [en]

    Fatigue failure of a hydraulic hose systems, caused by violent vibrations, has become a critical factor creating operational and maintenance cost for the end user of rock drill equipment. Similar behavior is also appearing in, for example, forestry machines. Hoses are used as parts of the energy feeding system in machines such as the ones use for mining and civil construction operations. This work aims to create an understanding of the dynamic behavior of a selected hydraulic hose. The numerical modeling approach selected includes a boundary element method approach in the fluid-elastic analysis of the dynamics of a pressurized hose with conveying fluid. Experimental modal analysis was used to validate the numerical model. Pre-tension and pressure-induced tension were monitored with an in-house-developed strain gauge-based load cell. The analysis and experiments show that a complex coupling, of pure structural bending modes, appears when the hose is subjected to internal flow. Some of the modeshapes show a circular motion of the hose cross sections. As shown in this article, these coupled modes become increasingly sensitive to external or internal excitation with increasing flow rate. To illustrate the strength of the proposed approach, the second part of the work in this article presents a parametric study of hose dynamics for hoses with typical dimensions used in industrial applications. This investigation of how different parameters influence the dynamic characteristics of hydraulic hoses shows, for example, that hose end-support stiffness has a large impact on the stability and dynamic behavior of the hose. A soft support tends to create a static instability-type behavior where the lowest frequency mode frequency decreases to levels close to zero with increasing flow speed. Pre-tension of the hose has a stabilizing effect on the hose dynamics. In the case when the internal pressure of the hydraulic hose does not generate tension of the hose, then the increase or decrease in the internal pressure has limited influence on the hose dynamics: this is at least a conclusion valid in the investigated 100-210 bar pressure range. In addition, a smaller diameter hose is more sensitive than a larger diameter hose, and this is valid as long as the pre-tension is high enough to maintain static stability in the entire flow rate range.

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