APPLICATION OF THEFINITE-VOLUME METHOD TOFLUID-STRUCTURE INTERACTIONANALYSIS

Abstract

This Thesis describes the numerical simulation of fluid-structure interaction (FSI)problems. A finite-volume based stress analysis code was developed and coupled toan existing in-house CFD code to form a general purpose FSI solver capable of beingused with the advanced turbulence and near-wall models developed within the researchgroup. The code has been used to study a number of physiological flows in the presentwork, although the general nature of the solver allows it to be used for other applicationsalso.By using the same numerical method, implemented in a consistent manner, forboth fluid and solid domains, the inefficiencies associated with using separate packagesfor the fluid and solid were avoided. Separate packages typically store informationin different data structures; some form of software interface is required to transferinformation between the two packages. This additional software layer, which is calledduring each FSI iteration, causes a considerable overhead. By using a single numericalmesh across both domains, the inaccuracies associated with boundary interpolationwere also avoided. Typically, separate packages use meshes which do not conform attheir common boundary. In order to find nodal values of the fluid pressure, say, atthe solid nodes, some form of interpolation is necessary. The interpolation leads to theintroduction of truncation errors. These improvements allow for more accurate andefficient FSI simulations, particularly transient cases, to be performed.The solid solver was verified against analytical solutions for a number of test cases,including: planar stress distribution in a square plate with a circular hole in the centre;axisymmetric stress in a thick walled cylinder under internal pressure, and unsteadydisplacement of a cantilevered beam under free vibration.Before coupled analyses were performed, the flow solver was also validated througha number of rigid walled test cases, including steady flow through a stenosed tube andunsteady flow through an aneurysm. Many physiological flows are difficult to capturedue to flow separation and early transition to turbulence. The use of a low-Reynoldsnumber k-ǫ turbulence model was successful at capturing the flow field over a range ofphysiologically relevant flow rates.Once the solid body and flow solvers had been validated in isolation, they werecoupled together and applied to a number of physiological flows, namely: steady flowthrough an initially straight tube with a compliant wall; steady flow through a complaintstenosis, and unsteady flow through a compliant aneurysm. The results from allthree test cases showed good agreement with the available experimental and numericaldata in terms of wall deformation.The solid body solver also proved itself to be capable of producing high qualitynumerical meshes for use in other simulations. The fluid mesh was considered to be asolid body with arbitrary material properties; the required deformation was specifiedas prescribed displacement boundary conditions. The main benefit of this method,compared to simple elliptical grid generation methods, is that near-wall grid spacingwas preserved throughout the coupled simulation.

Date of Award	1 Aug 2012
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Hector Iacovides (Supervisor) & Timothy Craft (Supervisor)