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Abstract

A major medical problem in the circulatory system is the frequent occurrence of atherosclerosis and thrombosis in arterial bends and bifurcations. Although the exact mechanism remains unclear, it has been suggested that the local fluid dynamics plays an important role. Therefore, detailed analysis of flow phenomena and hemodynamic stresses in arterial bifurcations is of immediate interest.

In addition to in vivo and in vitro experiments, numerical simulations of blood flow in arterial bifurcation models also contribute to a better understanding of the flow patterns and shear stress distributions in these bifurcations, and thereby help to clarify the link between fluid dynamics and atherogenesis.

The problem of blood flow in an arterial bifurcation involves many complicating factors, four of them are considered to be important, namely (i) the three-dimensional geometry of the bifurcation, (ii) the pulsatile nature of the flow, (iii) the non-Newtonian character of the blood, and (iv) the distensibility of the arterial wall. In this dissertation, a full analytical treatment of blood flow in 3-D arterial bifurcations is presented. The incompressible 3-D time-dependent Navier-Stokes equations are employed to describe the flow, and a finite volume code ASTEC, which has an unstructured finite element mesh, is adopted to solve the equations. In the predictions, the non-Newtonian characteristics of the blood are taken into account and their effects on bifurcation flow fields investigated. Possibilities of accommodating the vessel wall compliance are also explored, and a simplified approach is proposed, in which the flow equations and wall displacements are solved separately within a time step, but are coupled in the sense that the boundary conditions of the former are updated through the solution of the later. This approach is valid provided that the wall movement is much slower than the motion of fluid and the flow is generally parallel to the wall. It has been applied to a straight circular tube. For bifurcation predictions, however, the vessel wall is assumed to be rigid.

A comprehensive range of code validation exercises are carried out, especially for T-bifurcations. The predictions are proved reliable by comparison with published laboratory measurements.

Finally, numerical predictions for physiological flow in canine femoral bifurcations are performed, in which the true bifurcation geometries are used. Results are validated against the best available in vivo measurements so far obtained. It is demonstrated that the presented numerical modelling scheme in conjunction with the new generation of super-computers can be used as an efficient and reliable tool for detailed analysis of blood flow in arterial bifurcations. Incorporation of the distensibility of the arterial wall in the bifurcation prediction will complete such an analysis.

Some of the material published during the course of the project is included in Appendix F.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QA Mathematics T Technology > TJ Mechanical engineering and machinery
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses School of Science & Technology > Engineering

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