Work 2 presented in the the Thirteenth International Conference on Civil, Structural and Environmental Engineering Computing (Chania, Crete)


J. Marcé-Nogué, A. Castillo, M. Quero, Ll. Gil, V.M. Paredero, E. Hernández, “Inclusion of the Permeability in a Stent-Graft Fluid-Structure Model as a Hole-Proportion in the Surface“, in B.H.V. Topping, Y. Tsompanakis, (Editors), “Proceedings of the Thirteenth International Conference on Civil, Structural and Environmental Engineering Computing”, Civil-Comp Press, Stirlingshire, UK, Paper 240, 2011. doi:10.4203/ccp.96.240 [url].
Summary

In this work, a reconstruction of the abdominal area of the aorta, a generation of abdominal aortic aneurysm and the generation of the different stent grafts studied and their inclusion in diseased aortic aneurysm are done in order to study the behaviour of different commercial stent grafts in order to compare them with quality indicators. The new approach presented here includes the permeability of the stents, where permeability is a measure of the ability of a porous material to transmit fluids. A new concept is included in the design of the model. The value of the total permeability of the stent-graft is considered generating holes in the surface of the stent.

A medical image reconstruction is done using a computed tomography (CT) from a real aorta to create a three-dimensional solid model to be capable analysis using finite element software. The model is analysed using the finite element software ANSYSR 12.0 for Windows XP (32-bit system). The fluid-structure interaction is done automatically using the mechanical module and the CFX module of the package which allows us to solve this kind of problem. In this work, the blood is assumed as a non-Newtonian fluid using the Carreau-Yasuda model of viscosity and the shear-stress transport model for the turbulence and the stent graft are modelled using structural shell elements for the surface model and structural beam elements for the skeleton.

Although the permeabilities of the materials are known, in this case there are other factors that influence in this property such as the sutures and there is difficulty in defining these properties. In this paper we consider the value of the total permeability of the material (the total blood that can be transmitted across the stent) generating holes in the surface of the stent to obtain the same value as a porous material was supposed. This method facilitates the solution of the problem of the fluid-structure using finite element software.

The inclusion of the permeability in the model as a hole proportion in the surface of the stent graft allows the finite element analysis to solve the fluid-structure interaction easily and to obtain qualitative indicators to compare the behaviour of the different commercial stents studied such as: structural stiffness, stress values, endoleaks, pressure losses, etc. These quality indicators can be added to other clinical considerations as the material of the different parts of the stent, the modular system, the fixation system or the installation system to help optimal clinical decisions to be made prior to surgery.

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