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Berntsson, F., Karlsson, M., Kozlov, V. & Nazarov, S. A. (2018). A Modification to the Kirchhoff Conditions at a Bifurcation and Loss Coefficients.
Open this publication in new window or tab >>A Modification to the Kirchhoff Conditions at a Bifurcation and Loss Coefficients
2018 (English)Report (Other academic)
Abstract [en]

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

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

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

Publisher
p. 11
Series
LiTH-MAT-R, ISSN 0348-2960 ; 2018:5
National Category
Mathematics
Identifiers
urn:nbn:se:liu:diva-147718 (URN)LiTH-MAT-R--2018/05--SE (ISRN)
Available from: 2018-05-07 Created: 2018-05-07 Last updated: 2018-05-07Bibliographically approved
Gupta, V., Lantz, J., Henriksson, L., Engvall, J., Karlsson, M., Persson, A. & Ebbers, T. (2018). Automated three-dimensional tracking of the left ventricular myocardium in time-resolved and dose-modulated cardiac CT images using deformable image registration. Journal of Cardiovascular Computed Tomography, 12(2), 139-148
Open this publication in new window or tab >>Automated three-dimensional tracking of the left ventricular myocardium in time-resolved and dose-modulated cardiac CT images using deformable image registration
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2018 (English)In: Journal of Cardiovascular Computed Tomography, ISSN 1934-5925, Vol. 12, no 2, p. 139-148Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Cardiac computed tomography; 4D CT; Image registration; Strain analysis; Myocardial deformation; Torsion
National Category
Medical Image Processing
Identifiers
urn:nbn:se:liu:diva-147433 (URN)10.1016/j.jcct.2018.01.005 (DOI)000428247900008 ()29402736 (PubMedID)
Funder
Knut and Alice Wallenberg Foundation, KAW 2013.0076
Available from: 2018-05-17 Created: 2018-05-17 Last updated: 2018-06-18Bibliographically approved
Lantz, J., Gupta, V. & Henriksson, L. (2018). Intracardiac Flow at 4D CT: Comparison with 4D Flow MRI. Radiology
Open this publication in new window or tab >>Intracardiac Flow at 4D CT: Comparison with 4D Flow MRI
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2018 (English)In: Radiology, ISSN 0033-8419, E-ISSN 1527-1315Article in journal (Refereed) Epub ahead of print
Abstract [en]

Purpose

To investigate four-dimensional (4D) flow CT for the assessment of intracardiac blood flow patterns as compared with 4D flow MRI.

Materials and Methods

This prospective study acquired coronary CT angiography and 4D flow MRI data between February and December 2016 in a cohort of 12 participants (age range, 36–74 years; mean age, 57 years; seven men [age range, 36–74 years; mean age, 57 years] and five women [age range, 52–73 years; mean age, 64 years]). Flow simulations based solely on CT-derived cardiac anatomy were assessed together with 4D flow MRI measurements. Flow patterns, flow rates, stroke volume, kinetic energy, and flow components were quantified for both techniques and were compared by using linear regression.

Results

Cardiac flow patterns obtained by using 4D flow CT were qualitatively similar to 4D flow MRI measurements, as graded by three independent observers. The Cohen κ score was used to assess intraobserver variability (0.83, 0.79, and 0.70) and a paired Wilcoxon rank-sum test showed no significant change (P > .05) between gradings. Peak flow rate and stroke volumes between 4D flow MRI measurements and 4D flow CT measurements had high correlation (r = 0.98 and r = 0.81, respectively; P < .05 for both). Integrated kinetic energy quantified at peak systole correlated well (r = 0.95, P < .05), while kinetic energy levels at early and late filling showed no correlation. Flow component analysis showed high correlation for the direct and residual components, respectively (r = 0.93, P < .05 and r = 0.87, P < .05), while the retained and delayed components showed no correlation.

Conclusion

Four-dimensional flow CT produced qualitatively and quantitatively similar intracardiac blood flow patterns compared with the current reference standard, four-dimensional flow MRI.

Place, publisher, year, edition, pages
Oak Brook, IL United States: Radiological Society of North America, Inc., 2018
National Category
Fluid Mechanics and Acoustics Cardiac and Cardiovascular Systems Medical Image Processing
Identifiers
urn:nbn:se:liu:diva-149320 (URN)10.1148/radiol.2018173017 (DOI)29944089 (PubMedID)
Funder
Knut and Alice Wallenberg Foundation, Seeing Organ FunctionSwedish Heart Lung Foundation
Available from: 2018-06-28 Created: 2018-06-28 Last updated: 2018-08-08Bibliographically approved
Johannes, E., Ekman, P., Huge-Brodin, M. & Karlsson, M. (2018). Sustainable Timber Transport: Economic Aspects of Aerodynamic Reconfiguration. Sustainability, 10(6), 1-18
Open this publication in new window or tab >>Sustainable Timber Transport: Economic Aspects of Aerodynamic Reconfiguration
2018 (English)In: Sustainability, ISSN 2071-1050, E-ISSN 2071-1050, Vol. 10, no 6, p. 1-18Article in journal (Refereed) Published
Abstract [en]

There is a need to reduce fuel consumption, and thereby reduce CO2-emissions in all parts of the transport sector. It is also well known that aerodynamic resistance affects the fuel consumption in a major way. By improving the aerodynamics of the vehicles, the fuel consumption will also decrease. A special type of transportation is that of timber, which is performed by specialized trucks with few alternative uses. This paper follows up on earlier papers concerning Swedish timber trucks where aerodynamic improvements for timber trucks were tested. By mapping the entire fleet of timber trucks in Sweden and investigating reduced fuel consumption of 2–10%, financial calculations were performed on how these improvements would affect the transport costs. Certain parameters are investigated, such as investment cost, extra changeover time and weight of installments. By combining these results with the mapping of the fleet, it can be seen under which circumstances these improvements would be sustainable. The results show that it is possible through aerodynamics to lower the transportation costs and make an investment plausible, with changeover time being the most important parameter. They also show that certain criteria for a reduced transportation cost already exist within the vehicle fleet today.

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
timber trucks; fuel consumption; aerodynamic design; financial consequences
National Category
Business Administration Fluid Mechanics and Acoustics Transport Systems and Logistics
Identifiers
urn:nbn:se:liu:diva-150163 (URN)10.3390/su10061965 (DOI)
Available from: 2018-08-14 Created: 2018-08-14 Last updated: 2018-08-14
Jansson, M., Andersson, M., Pettersson, M. & Karlsson, M. (2017). Water Hammer Induced Cavitation - A Numerical and Experimental Study. In: Fluid Power in the Digital Age: . Paper presented at The 15th Scandinavian International Conference on Fluid Power, SICFP’17, Linköping, Sweden, June 7-9, 2017.
Open this publication in new window or tab >>Water Hammer Induced Cavitation - A Numerical and Experimental Study
2017 (English)In: Fluid Power in the Digital Age, 2017Conference paper, Oral presentation only (Other academic)
Abstract [en]

Cavitation erosion is one of the main concerns in hydraulic rock drills and can reduce both performance as well as life span. Current simulation tools can detect a potential risk of cavitation, however, the equations do not include cavitation physics and therefore cannot estimate the severity nor erosion locations. In order to evaluate the cavitation damage, long term tests are performed which are both costly and time consuming. With better computational capacity and more accurate numerical flow models, the possibilities to simulate the course of cavitation have increased. So far, most numerical studies on cavitation focus on steady-state problems while studies on hydraulic transients and water hammer effects have received less attention. This paper is a step towards simulation of water hammer induced cavitation and cavitation erosion in pipe flow using Computational Fluid Dynamics (CFD). In order to validate the results, experimental measurements are performed with a test equipment that creates hydraulic transients in a pipe and records these using piezoelectric pressure sensors. The results from CFD are compared to both the experimental data and to numerical results from a software called Hopsan, a one-dimensional multi-domain system simulation tool that uses wave characteristics to calculate pressures and flows. For smaller transients where no cavitation occur, all results show good agreement. For larger transients with cavitation, the results from Hopsan do not longer agree with the measurements, while the CFD model still performs well and is able to predict both formation and collapse of cavitation.

Keywords
Cavitation, Water hammer, Hydraulic transients, Rock drills, CFD
National Category
Fluid Mechanics and Acoustics Applied Mechanics
Identifiers
urn:nbn:se:liu:diva-142541 (URN)
Conference
The 15th Scandinavian International Conference on Fluid Power, SICFP’17, Linköping, Sweden, June 7-9, 2017
Available from: 2017-10-31 Created: 2017-10-31 Last updated: 2018-04-26Bibliographically approved
Berntsson, F., Karlsson, M., Kozlov, V. & Nazarov, S. A. (2016). A one-dimensional model of viscous blood flow in an elastic vessel. Applied Mathematics and Computation, 274, 125-132
Open this publication in new window or tab >>A one-dimensional model of viscous blood flow in an elastic vessel
2016 (English)In: Applied Mathematics and Computation, ISSN 0096-3003, E-ISSN 1873-5649, Vol. 274, p. 125-132Article in journal (Refereed) Published
Abstract [en]

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

Place, publisher, year, edition, pages
ELSEVIER SCIENCE INC, 2016
Keywords
Blood flow; Linear model; Asymptotic analysis; Dimension reduction; Numerical simulation
National Category
Mathematics Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-124453 (URN)10.1016/j.amc.2015.10.077 (DOI)000367521900013 ()
Available from: 2016-02-02 Created: 2016-02-01 Last updated: 2017-11-30
Ingels, Jr, N. B. & Karlsson, M. (2016). Appendix A   Marker Sites and Datafile Columns. In: Neil B Ingels, Jr and Matts Karlsson (Ed.), Mitral Valve Mechanics: (pp. A.1-A.3). Linköping University Electronic Press
Open this publication in new window or tab >>Appendix A   Marker Sites and Datafile Columns
2016 (English)In: Mitral Valve Mechanics / [ed] Neil B Ingels, Jr and Matts Karlsson, Linköping University Electronic Press, 2016, p. A.1-A.3Chapter in book (Other academic)
Abstract [en]

Datafiles (provided in this Appendix) associated with the six heart (H1-H6) study

Place, publisher, year, edition, pages
Linköping University Electronic Press, 2016
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-124259 (URN)10.3384/book.diva-117057 (DOI)978-91-7685-952-0 (ISBN)
Available from: 2016-01-25 Created: 2016-01-25 Last updated: 2016-03-14
Ingels, Jr, N. B. & Karlsson, M. (2016). Appendix B NAC-MAD Composite Dataset. In: Neil B Ingels, Jr and Matts Karlsson (Ed.), Mitral Valve Mechanics: (pp. B.1-B.2). Linköping University Electronic Press
Open this publication in new window or tab >>Appendix B NAC-MAD Composite Dataset
2016 (English)In: Mitral Valve Mechanics / [ed] Neil B Ingels, Jr and Matts Karlsson, Linköping University Electronic Press, 2016, p. B.1-B.2Chapter in book (Other academic)
Abstract [en]

Here, we describe an attempt to model, as accurately as possible in 3-D space, the geometric relationship between the various components of the left ventricle, the mitral valve, and the aortic valve during systole and diastole.

Place, publisher, year, edition, pages
Linköping University Electronic Press, 2016
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-124260 (URN)10.3384/book.diva-117057 (DOI)978-91-7685-952-0 (ISBN)
Available from: 2016-01-25 Created: 2016-01-25 Last updated: 2016-03-14
Ingels, Jr, N. B. & Karlsson, M. (2016). Appendix C Computational Details. In: Neil B Ingels, Jr and Matts Karlsson (Ed.), Mitral Valve Mechanics: (pp. C.1-C.6). Linköping University Electronic Press
Open this publication in new window or tab >>Appendix C Computational Details
2016 (English)In: Mitral Valve Mechanics / [ed] Neil B Ingels, Jr and Matts Karlsson, Linköping University Electronic Press, 2016, p. C.1-C.6Chapter in book (Other academic)
Place, publisher, year, edition, pages
Linköping University Electronic Press, 2016
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-124262 (URN)10.3384/book.diva-117057 (DOI)978-91-7685-952-0 (ISBN)
Available from: 2016-01-25 Created: 2016-01-25 Last updated: 2016-03-14
Ingels, Jr, N. B. & Karlsson, M. (2016). Appendix D Mitral Valve Animations. In: Neil B Ingels, Jr and Matts Karlsson (Ed.), Mitral Valve Mechanics: (pp. D.1-D.1). Linköping University Electronic Press
Open this publication in new window or tab >>Appendix D Mitral Valve Animations
2016 (English)In: Mitral Valve Mechanics / [ed] Neil B Ingels, Jr and Matts Karlsson, Linköping University Electronic Press, 2016, p. D.1-D.1Chapter in book (Other academic)
Abstract [en]

The PowerPoint mitral valve animations in this Appendix can be accessed by double-clicking the filenames. Both side view (LEFT PANEL, looking from posterior to anterior) and top view (RIGHT PANEL, looking from base to apex) are provided. All graphs have Marker #22 at the origin, Marker #1 on the Z-axis, and Marker #18 in the X-Z plane. The animations can be stepped forward with the right arrow and backwards with the left arrow with time-steps of 16.67 ms. The left ventricular pressure associated with each time step is indicated by the black dot on the LVP curve imbedded in the graph. Hit Escape to exit each animation. The H1-H6 datasets are located in Appendix A.

Place, publisher, year, edition, pages
Linköping University Electronic Press, 2016
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-124264 (URN)10.3384/book.diva-117057 (DOI)978-91-7685-952-0 (ISBN)
Available from: 2016-01-25 Created: 2016-01-25 Last updated: 2016-03-14
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-5526-2399

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