Biomedical Engineering Reference
In-Depth Information
Fig. 8.15
Boundary condi-
tions setup (
a
) fixed supports
were placed at all branches
ends for the structure domain,
(
b
) pressure inlet and velocity
outlets were prescribed at
the inlet and two outlets of
the fluid domain. ICA is the
internal carotid artery; ECA
is the external carotid artery
where.
I
1
and.
I
2
are the first and second deviatoric strain invariants and
J
is the
determinant of the elastic deformation gradient tensor. The 0.5 mm thickness is as-
signed to the arterial vessel, and all model parameters being used are listed below:
C
10
= 0.070 MPa,
C
20
= 3.2 MPa,
C
21
= 0.0716 MPa,
D
1
= 0.1 MPa, and
C
ij
= 0 MPa
for the remaining tensors, following the method by Koshiba et al. (2007). The time
step size was set as 0.002 s, and 500 time steps were implemented for a cardiac
cycle. 24 hours of CPU time was used for a simulation of one cardiac cycle by using
two Xeon CPUs with a speed of 2.83 GHz.
8.3.2
Haemodynamics Inside the Healthy Carotid Artery
Qualitative comparison of flow velocity between a CFD simulation (rigid wall as-
sumption) and a fully coupled FSI simulation (elastic wall assumption) is illustrated
in Fig.
8.16
. The time-averaged blood flow velocity, averaged over one cardiac
cycle, is used for comparison. The CFD simulation predicts the maximum aver-
aged velocity occurring at the moderate stenosed site on the ICA (internal carotid
artery) branch, and the maximum velocity value is 0.63 m/s (Fig.
8.16a
). Compared
with the FSI approach (Fig.
8.16b
), the CFD model results show an over prediction
of 14.5 %. By allowing deformation of the arterial vessel, the carotid artery ves-
sel deforms in response to the mechanical loading induced by the pulsatile blood
pressure - especially at the moderate stenosis site located at the downstream ICA
branch. Therefore, more blood flow can be transported via ICA branch. Due to
the fixed arterial geometry for the CFD simulation, the flow resistance of the ICA
branch is greater than the FSI simulation, and more blood flow is distributed to the
ECA branch.
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