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- 1. Numerical simulation of blood flow in flexible arteries using Fluid Structure Interaction Mostafa Ghadamyari, B.Sc Project Ferdowsi university of Mashhad, Iran Summer 2013
- 2. Simulating blood - Issues Unsteady flow: To be more accurate, the flow is steady-periodic. Blood viscosity differs: Blood is a Non-Newtonian fluid, Viscosity depends on shear rate Arteries material are complex: Different layers, different properties Arteries wall deform: Inside flow Pressure -> Artery expands or collapses -> Change inside flow Complex geometry: Arteries bifurcate and join again.
- 3. Model definition Modeling blood: Non-Newtonian blood Carreau model : Artery material: Elastic isotropic Unsteady flow model: 1. Pressure cycle 2. Velocity cycle Both cases will be discussed Modeling Flexible walls : Fluid structure interaction : Fluid and Solid equations are solved coupled Geometry model : Modeling part of the blood system, with realistic boundary conditions
- 4. 1.Pulsatile Pressure flow model simulation Outlet flow : 0 Pa (Static gauge pressure) Inlet flow (Static gauge pressure) Fixed inlet & outlet wall FSI Boundary P inlet = 100 + 100*sin(pi*t) [Pa] 1mm or 2mm Wall thickness Mr. Shaik model (Part of PHD. Thesis):
- 5. Pulsatile pressure model – answer We started with ADINA simulation PHD Thesis model answer : Centerline velocity Ave. 0.9m/s, Range : 0.05m/s Ave. 0.3m/s, Range : 0.2m/s
- 6. Pulsatile pressure model – answer Ansys CFX : Ave. 0.9m/s, Range : 0.5m/s Comsol answer : Centerline velocity Ansys Fluent doesn’t accept static pressure at INLET ! Only Total pressure can be defined -> Velocity is included. Ave. 1.9m/s, Range : 0.5m/s
- 7. Inconsistent pulsatile pressure model – Why ? We found this while searching for ‘Why fluent doesn’t accept static pressure at inlet?’
- 8. 2.Pulsatile velocity flow model simulation Outlet flow : 100mmHg ~ 13332 Pa (Static gauge pressure) Inlet flow (Velocity inlet) Fixed inlet & outlet wall FSI Boundary Mr. Wangn, journal paper :
- 9. 2.Pulsatile velocity flow model simulation Adina: - Very light ~ 300mb - Simple GUI - Fastest in our simulation (default settings) - The least problems in convergency in our model Comsol: - Medium size ~ 4GB - Smart GUI – Fastest in modeling - Slowest in our simulation (default settings) - Special solver settings needed (Good for professionals)
- 10. Software comparison (continued.) Fluent: - The most famous software - Can be coupled to Ansys structural (Using system coupling) CFX: - Famous software - Can be coupled to Ansys structural (direct coupling) Ansys : Large ~ 6.5G, Complicated, Stable
- 11. Pulsatile velocity result – Velocity Differences are due to : - Different mesh sizes - Different solvers Outlet surface midpoint velocity , ADINA : Ave. 0.3m/s Max. 1.1m/s COMSOL : Ave. 0.35m/s Max. 1.32m/s CFX : Ave. 0.33 m/s Max. 1.05 m/s
- 12. Pulsatile velocity result – Pressure ADINA : Ave. 13.48 KPa Max. 14.50 KPa COMSOL : Ave. 13.4 KPa Max. 14.80 KPa CFX : Ave. 13.48 KPa Max. 14.55 KPa Results differ less than 0.5% Inlet surface midpoint pressure :
- 13. Pulsatile velocity result – Pressure ADINA - 0.45mm initial disp. (4.5%) - 0.03mm cyclic disp. (0.3%) Middle surface Top Point displacement CFX - 0.65mm initial disp. (6.5%) - 0.03mm cyclic disp. (0.3%)
- 14. Study 1: FSI vs CFD Outlet surface midpoint velocity, CFD (Green) vs FSI (Blue) : Max. Velocity: Rigid -> 1.2m/s Deformable -> 1.1 m/s ~ 10% error if walls were considered rigid -> Pressure : 1.6% error We performed a rigid wall analysis with ADINA and compare the results to deformable wall case.
- 15. Study 2, wall thickness and displacement: We halved thickness of the artery, displacement of middle artery plane Top point : 2mm thickness case - 0.45mm initial disp. (4.5%) - 0.03mm cyclic disp. (0.3%) 1mm thickness case - 1.1mm initial disp. (4.5%) - 0.03m cyclic disp. (0.3%)
- 16. FSI could be even more important … Max. Displacement : 4mm ( 40%) Max. Displacement: -1.5 mm (-15%) This is a sample analysis of blood flow in a bifurcate , in this case : V in = 0.3 m/s , P in = 0Pa (case1) & -2.13Pa (case2), wall thickness=0.5mm
- 17. Conclusion Wall shear stress -> Low WSS -> More susceptible to Atherosclerosis Study more complex geometries (bifurcates, …) Newtonian vs. Non-Newtonian blood Solver settings (specially Comsoll) Continue this project … Pressure pulse vs. Velocity pulse -> Pressure model should be used with considerations Rigid walls vs. Deformable walls -> 10% error in velocity profile Halved thickness -> doubled displacement
- 18. Acknowledgement Thanks to Dr. M. Pasandideh Fard. my supporter and advisor throughout my career at Ferdowsi university of Mashhad, who gave me the opportunity to work on this project and introduced me to the fascinating field of computational fluid dynamics… Case show Animation
- 19. Thank you ! Any questions?

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