We'll model and simulate a simple artery using pressure-based and velocity-based inlet profiles by Adina systems, Comsol Multiphysics, Ansys CFX & structural coupling and Ansys Fluent & structural coupling.

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?