ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

Three pieces of software are utilized in this study. The software SOLIDWORKS 2010
(Concorde, Massachusetts, USA) is used to create an idealized 3D aortic dissection
model, which is based on a contrast-enhanced Computerized Tomography (CT) scan
image of a patient. Clinically, the size (diameter) of the dissected aorta can serve as an
indicator in the decision for medical treatment [12]. It is the greatest dimension of the
swollen part of the dissected aorta (see Fig.1). To assess the effect of this factor
quantitatively, five dissection models with different diameters (L as defined in Fig. 1a =
40, 50, 60, 70, and 80 mm) are investigated. The two channels, namely the true and
false lumens, are separated by the intimal flap, which is treated as a rigid wall with
negligible thickness. For the next stage of the analysis, the software GAMBIT 2.4.6
(developed by FLUENT) is adopted for mesh generation and mesh quality control.
Finally, the FLUENT 6.3.26 (ANSYS, Canonsburg, Pennsylvania, USA) will carry out
the task for blood flow simulations.
Fig. 1 False lumen with partial thrombosis: (a) planar view; (b) three dimensional view
3.2 Fluid properties
In the present simulations, blood behaves as an incompressible and Newtonian fluid,
this assumption is reasonable when blood flows in large arteries [13]. The density and
dynamic viscosity of blood are taken as 1060 kg m -3 and 0.0035 kg m -1 s -1 respectively.
The effects of red blood cells and platelets can be ignored, because the diameters of red
blood cells (7.6 m) and platelets (2.5 m) [14] are sufficiently small as compared to
the size of the aorta (40-80 mm).
3.3 Governing equations
The governing principles of the motion of a 3D fluid are the conservation laws of mass
and momentum, i.e. the continuity and Navier-Stokes equations
ui
ui
ui
1 p
1
ij
0 and u j
(1)
x
t
x
x
x
i
j
i
j
where = fluid density; ui (i = 1, 2, 3) = components of the velocity vector; ij = normal
and shear stresses; and p = pressure. These equations can be iteratively solved using the
unsteady solver of the FLUENT. The time step size is taken as 0.005s. To ensure better
convergence of each time step, the residual error is set as 10 -6 . Tetrahedral / hybrid
elements and T-grids mesh are used for computation, and the spatial grid size of the
mesh is 1.5 mm.
3.4 Boundary conditions
The pulsatile velocity waveform (Fig. 2a) mimics a realistic patient condition and it
contains a maximum value of 0.186 m s -1 ; a minimum value of -0.0336 m s -1 ; and a