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Although oscillating water column type wave energy devices are nearing the stage of commercial exploitation, there is still much to be learnt about many facets of their hydrodynamic performance. This research uses the commercially available FLUENT computational fluid dynamics flow solver to model a complete OWC system in a two dimensional numerical wave tank. A key feature of the numerical modelling is the focus on the influence of the front wall geometry and in particular the effect of the front wall aperture shape on the hydrodynamic conversion efficiency. In order to validate the numerical modelling, a 1:12.5 scale experimental model has been tested in a wave tank under regular wave conditions. The effects of the front lip shape on the hydrodynamic efficiency are investigated both numerically and experimentally and the results compared. The results obtained show that with careful consideration of key modelling parameters as well as ensuring sufficient data resolution, there is good agreement between the two methods. The results of the testing have also illustrated that simple changes to the front wall aperture shape can provide marked improvements in the efficiency of energy capture for OWC type devices.

Hemodynamic factors play a role in atherogenesis and the localization of atherosclerotic plaques. The human aorta and coronary arteries are susceptible to arterial disease, and there have been many studies of flows in models of these vessels. However, previous work has been limited in that investigations have not modeled both the geometry and flow conditions in specific individuals. The first aim of the research was to develop a methodology that combined computational fluid dynamics (CFD) and magnetic resonance imaging (MRI) to simulate the blood flow patterns found in the human aorta. The methodology included MR image processing, 3D model reconstruction and flow simulation using in vivo velocity boundary conditions obtained from phase contrast (PC)-MRI scanning. The CFD simulations successfully reproduce the unusual right-hand helical flow pattern that has been reported in the ascending aorta, giving confidence in the accuracy of the methodology. The second aim was to investigate the causes of the right-hand helical flow. It was found that the correct flow dynamics could only be produced by including the specific aortic motion caused by the beating heart; and it is concluded that this is a significant factor in producing the observed in vivo helical flow patterns. The entrance flows of coronary arteries are expected to be affected by flow in the aortic root, and the third aim was to explore these effects using models that include aorta and coronary arteries. The simulation results demonstrate that a pair of axial vortexes with different rotating directions exists in the entrance segments of the right and left coronary arteries during systole and early diastole, producing asymmetrical wall shear stress (WSS) distributions. The last aim of the research was to examine possible relationships between WSS distributions induced by the entry flow patterns and the frequency distributions of atherosclerosis in the proximal segments of coronary arteries reported in the clinical literature. A close correspondence between low WSS and higher frequency of plaque occurrence was observed. The tools developed in this study provide a promising avenue for future study of cardiovascular disease because of the ability to investigate phenomena in individual human subjects.

A finite-volume procedure, comprising a gradient-reconstruction technique and a multidimensional limiter, has been proposed for upwind algorithms on unstructured grids. The high-resolution strategy, with its inherent dependence on a wide computational stencil, does not suffer from a catastrophic loss of accuracy on a grid with poor connectivity as reported recently is the case with many unstructured-grid limiting procedures. The continuously-differentiable limiter is shown to be effective for strong discontinuities, even on a grid which is composed of highly-distorted triangles, without adversely affecting convergence to steady state. Numerical experiments involving transient computations of two-dimensional scalar convection to steady-state solutions of Euler and Navier-Stokes equations demonstrate the capabilities of the new procedure.

This thesis presents the author's contribution <p>to the design and implementation of COOLFluiD,<p>an object oriented software platform for <p>the high performance simulation of multi-physics phenomena on unstructured grids. In this context, the final goal has been to provide a reliable tool for handling high speed aerothermodynamic <p>applications. To this end, we introduce a number of design techniques that have been developed in order to provide the framework with flexibility<p>and reusability, allowing developers to easily integrate new functionalities such as arbitrary mesh-based data structures, numerical algorithms (space discretizations, time stepping schemes, linear system solvers, ),and physical models. <p>Furthermore, we describe the parallel algorithms <p>that we have implemented in order to efficiently <p>read/write generic computational meshes involving <p>millions of degrees of freedom and partition them <p>in a scalable way: benchmarks on HPC clusters with <p>up to 512 processors show their effective suitability for large scale computing. <p>Several systems of partial differential equations, <p>characterizing flows in conditions of thermal and <p>chemical equilibrium (with fixed and variable elemental fractions)and, particularly, nonequilibrium (multi-temperature models) <p>have been integrated in the framework. <p>In order to simulate such flows, we have developed <p>two state-of-the-art flow solvers: <p>1- a parallel implicit 2D/3D steady and unsteady cell-centered Finite Volume (FV) solver for arbitrary systems of PDE's on hybrid unstructured meshes; <p>2- a parallel implicit 2D/3D steady vertex-centered Residual Distribution (RD) solver for arbitrary systems of PDE's on meshes with simplex elements (triangles and tetrahedra). <p>The FV~code has been extended to handle all <p>the available physical models, in regimes ranging from incompressible to hypersonic. <p>As far as the RD code is concerned, the strictly conservative variant of the RD method, denominated CRD, has been applied for the first time in literature to solve high speed viscous flows in thermochemical nonequilibrium, yielding some preliminary outstanding results on a challenging double cone flow simulation. <p>All the developments have been validated on real-life testcases of current interest in the aerospace community. A quantitative comparison with experimental measurements and/or literature has been performed whenever possible. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

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