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Mesh requirements in patient-specific computational fluid dynamics for accurate assessment of wall shear stress

Gianluca De Santis UGent, Peter Mortier UGent, Matthieu De Beule UGent, Patrick Segers UGent, Pascal Verdonck UGent and Benedict Verhegghe (2010) Biomechanics in Vascular Biology and Cardiovascular Disease, 5th International symposium, Abstract book.
abstract
Introduction: Measuring in vivo blood flow and Wall Shear Stress (WSS) in particular is still limited by current imaging technology and is generally overcome using Computational Fluid Dynamics (CFD). Pre-processing and mesh generation required to discretize the fluid domain are time-consuming, operator-dependent, and the quality of the resulting mesh is often suboptimal, especially for WSS calculations. Methods: A biplane angiogram of a left coronary artery was acquired using the Allura 3D-CA (Philips Medical System) and exported into the open-source pyFormex (http://www.pyformex.org) to generate a structured and conformal hexahedral computational mesh [1]. Starting from the same coronary tree, seven hexahedral meshes (HEX series) were generated with the new procedure as well as nine tetrahedral meshes with prismatic boundary layer (TET series) for comparison using Gambit and TGrid. All the meshes of the HEX and the TET series (50,000 to 3,200,000 cells) have been used for steady state CFD calculations under identical conditions (Fluent). WSS has been reported to be a critical parameter in grid-independence analysis and therefore has been chosen as quantity to use for comparison [2]. Results: Area-weighted-WSS values on two bifurcations (indicated in Fig. 1) show that the HEX series converges faster than the TET series (Fig. 2 top panel). Stronger difference has been found on the local hemodynamics, evaluated by measuring the WSS along a line as indicated in Fig. 1. The WSS predicted with TET meshes up to 1,000,000 cells is quantitatively but also qualitatively wrong (Fig. 2, bottom left panel). The minimum number of cells needed to reach grid–independent WSS values (percentage difference relative to the finest mesh < 5 %) were 300,000 and 2,000,000 for the HEX and the TET series respectively, requiring 14-fold longer CPU time for the TET series on the same computing infrastructure [1]. Conclusions: HEX and TET meshes perform differently in reaching mesh-independent values of WSS (mesh-independent value is a necessary, not sufficient, condition for the correctness of CFD results): HEX meshes predict the final WSS pattern and approximate the final values of WSS even with low number of cells, while TET meshes may provide misleading results in complex flow areas not only quantitatively (e.g. peak value of the WSS) but also qualitatively (e.g. spatial location of the peak value) when not converged, and require much longer computational time. Such effects are related to high numerical diffusion associated to unstructured meshes and are likely to be amplified in case of pulsatile flow simulations. The novel meshing framework is also applicable to triangulated surface models (e.g. STL) [3]. References [1] De Santis G et al., 2010, Med Biol Eng Comput, in press. [2] Prakash S, Ethier CR, 2001, J Biomech Eng 123:134. [3] De Santis G et al., CMBBE, submitted.
Please use this url to cite or link to this publication:
author
organization
year
type
conference
publication status
published
subject
in
Biomechanics in Vascular Biology and Cardiovascular Disease, 5th International symposium, Abstract book
conference name
5th International symposium on Biomechanics in Vascular Biology and Cardiovascular Disease
conference location
Rotterdam, The Netherlands
conference start
2010-04-15
conference end
2010-04-16
language
English
UGent publication?
yes
classification
C3
copyright statement
I have transferred the copyright for this publication to the publisher
id
1148411
handle
http://hdl.handle.net/1854/LU-1148411
date created
2011-02-14 08:55:52
date last changed
2016-12-19 15:35:20
@inproceedings{1148411,
  abstract     = {Introduction: Measuring in vivo blood flow and Wall Shear Stress (WSS) in particular is still limited by current imaging technology and is generally overcome using Computational Fluid Dynamics (CFD). Pre-processing and mesh generation required to discretize the fluid domain are time-consuming, operator-dependent, and the quality of the resulting mesh is often suboptimal, especially for WSS calculations.
Methods: A biplane angiogram of a left coronary artery was acquired using the Allura 3D-CA (Philips Medical System) and exported into the open-source pyFormex (http://www.pyformex.org) to generate a structured and conformal hexahedral computational mesh [1]. Starting from the same coronary tree, seven hexahedral meshes (HEX series) were generated with the new procedure as well as nine tetrahedral meshes with prismatic boundary layer (TET series) for comparison using Gambit and TGrid. All the meshes of the HEX and the TET series (50,000 to 3,200,000 cells) have been used for steady state CFD calculations under identical conditions (Fluent). WSS has been reported to be a critical parameter in grid-independence analysis and therefore has been chosen as quantity to use for comparison [2].
Results: Area-weighted-WSS values on two bifurcations (indicated in Fig. 1) show that the HEX series converges faster than the TET series (Fig. 2 top panel). Stronger difference has been found on the local hemodynamics, evaluated by measuring the WSS along a line as indicated in Fig. 1. The WSS predicted with TET meshes up to 1,000,000 cells is quantitatively but also qualitatively wrong (Fig. 2, bottom left panel). The minimum number of cells needed to reach grid--independent WSS values (percentage difference relative to the finest mesh {\textlangle} 5 \%) were 300,000 and 2,000,000 for the HEX and the TET series respectively, requiring 14-fold longer CPU time for the TET series on the same computing infrastructure [1].
Conclusions: HEX and TET meshes perform differently in reaching mesh-independent values of WSS (mesh-independent value is a necessary, not sufficient, condition for the correctness of CFD results): HEX meshes predict the final WSS pattern and approximate the final values of WSS even with low number of cells, while TET meshes may provide misleading results in complex flow areas not only quantitatively (e.g. peak value of the WSS) but also qualitatively (e.g. spatial location of the peak value) when not converged, and require much longer computational time. Such effects are related to high numerical diffusion associated to unstructured meshes and are likely to be amplified in case of pulsatile flow simulations. The novel meshing framework is also applicable to triangulated surface models (e.g. STL) [3].
References
[1] De Santis G et al., 2010, Med Biol Eng Comput, in press.
[2] Prakash S, Ethier CR, 2001, J Biomech Eng 123:134.
[3] De Santis G et al., CMBBE, submitted.},
  author       = {De Santis, Gianluca and Mortier, Peter and De Beule, Matthieu and Segers, Patrick and Verdonck, Pascal and Verhegghe, Benedict},
  booktitle    = {Biomechanics in Vascular Biology and Cardiovascular Disease, 5th International symposium, Abstract book},
  language     = {eng},
  location     = {Rotterdam, The Netherlands},
  title        = {Mesh requirements in patient-specific computational fluid dynamics for accurate assessment of wall shear stress},
  year         = {2010},
}

Chicago
De Santis, Gianluca, Peter Mortier, Matthieu De Beule, Patrick Segers, Pascal Verdonck, and Benedict Verhegghe. 2010. “Mesh Requirements in Patient-specific Computational Fluid Dynamics for Accurate Assessment of Wall Shear Stress.” In Biomechanics in Vascular Biology and Cardiovascular Disease, 5th International Symposium, Abstract Book.
APA
De Santis, G., Mortier, P., De Beule, M., Segers, P., Verdonck, P., & Verhegghe, B. (2010). Mesh requirements in patient-specific computational fluid dynamics for accurate assessment of wall shear stress. Biomechanics in Vascular Biology and Cardiovascular Disease, 5th International symposium, Abstract book. Presented at the 5th International symposium on Biomechanics in Vascular Biology and Cardiovascular Disease.
Vancouver
1.
De Santis G, Mortier P, De Beule M, Segers P, Verdonck P, Verhegghe B. Mesh requirements in patient-specific computational fluid dynamics for accurate assessment of wall shear stress. Biomechanics in Vascular Biology and Cardiovascular Disease, 5th International symposium, Abstract book. 2010.
MLA
De Santis, Gianluca, Peter Mortier, Matthieu De Beule, et al. “Mesh Requirements in Patient-specific Computational Fluid Dynamics for Accurate Assessment of Wall Shear Stress.” Biomechanics in Vascular Biology and Cardiovascular Disease, 5th International Symposium, Abstract Book. 2010. Print.