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• Analysis and Modelling of the Internal Stress Field close to a Weld (June 2009)
• Multiscale Modelling of the Stability of a Pelvis Implant under Dynamic Loading (June 2009)
• Efficient fluid-structure interaction models for cardiovascular and respiratory simulations (June 2009)

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ANALYSIS AND MODELLING OF THE INTERNAL STRESS FIELD CLOSE TO A WELD This thesis is part of the SINUS research program involving several Belgian research centres including CENAERO. The general objective of the SINUS program is to develop a numerical tool allowing the simulation of various thermomechanical processes such as welding and reparation (filling) of turbine blades by laser cladding. A thorough experimental and theoretical study will be carried out aside of the development and the programming of the computer code itself. This study will be aimed at defining an original, pertinent method of verification of the numerical predictions. One thinks, in particular, about the internal stress field resulting from the localized heating of the metallic part (for instance close to a weld) which may induce geometrical distortions or be a preferential site for damage nucleation. Nowadays, the accurate measurement and the prediction of such stresses is a real challenge for industry. The candidate will have three main tasks: (i) elaborate an experimental set up (geometry of the weld or cladding, loading of the sample, cooling...) allowing accurate measurement of the induced stresses; (ii) perform the measurements (for example by X-ray or neutron diffraction); (iii) interpret these results by focusing on the metal rheology at high temperature, and interact with the developers of the numerical code. The candidate will have to demonstrate a strong basis formation in at least two of the following disciplines: (i) materials science, (ii) solid mechanics, (iii) thermomechanical processes (welding, forming, machining...). Partial knowledge of French is an advantage Ask further information | Send resume : Prof. Laurent Delannay , Prof. Bruno de Meester | 15/06/2009 |

MULTISCALE MODELLING OF THE STABILITY OF A PELVIS IMPLANT UNDER DYNAMIC LOADING Surgery of a tumour in the hip is complicated by the geometry of the pelvis ring. In order to avoid amputation of the leg, the tumour is resected and the bone deficit is filled by an allograft. This reconstruction is done by traditional means of osteosynthesis (Fig. 1). Since consolidation between bone implant and pelvis is not immediate, the weeks following the surgery are critical. Fracture of the assembly may be the consequence of a too rapid, or simply inadequate, loading. The aim of the thesis is to help the surgeon to optimize such immediate stability of the reconstruction, so as to quickly restore the patient mobility. In this project, the student task will be to develop a computational tool that estimates the load partitioning throughout the assembly (and the potential damage). Simulations will rely on advanced modelling of the bone micromechanics (mean-field homogenization). They will also entail a realistic representation of the pelvis and the implant within a finite element code. Based on medical imaging data, a segmentation technique (such as the level set method) will be used to reconstruct the 3D geometry (Fig. 2). External loading of the pelvis will be determined using an existing walk simulator based on multibody dynamics theory. Model predictions will be assessed based on experimental data. Profile: the candidate should have basic training in at least two of the three following disciplines: (i) Materials science, (ii) Computational mechanics (eg the finite element method), (iii) Tensor calculus in continuum mechanics. He/she must also demonstrate the potential to acquire sufficient autonomy in his/her research, in particular w.r.t. programming the computer code. Ask further information | Send resume : Prof. Laurent Delannay , Prof. Paul Fisette , Prof. Emilie Marchandise | 15/06/2009 |

EFFICIENT FLUID-STRUCTURE INTERACTION MODELS FOR CARDIOVASCULAR AND RESPIRATORY SIMULATIONS The department of Mechanics at the Université catholique de Louvain is accepting applications for a PhD or post-doc position in the context of the NHEMO project (numerical hemodynamics). The NHEMO project is a joint project of the biomechanical group at UCL and the Department of Vascular Surgery at the University Hospital St-Luc. Its research activities are aimed at: * modeling the flow of biological fluids, more especially blood in large vessels and also air in the respiratory tracts, both in normal and pathological states * developing and analyzing efficient, robust and reliable numerical methods for the simulation of such flows. * developing simulation software to guide medical decisions and to design more efficient medical devices. The research will focus on efficient fluid-structure interaction models for cardiovascular and respiratory simulations. Indeed, fluid-structure coupling occurs both in the circulatory and the respiratory systems. Most of the time, the fluid-structure interaction problem involves a coupling between the 3D Navier-Stokes equations and a 3D non-linear structure in large displacement. In the context of physiological systems, this coupling procedure is complex for several reasons: (1) the displacement of the wall cannot be supposed to be infinitesimal, geometric non-linearities are therefor present in the structure and the fluid problem has to be solved in a moving domain (2) in case of the cardiovascular system, the densities of the artery walls and the blood being close, the coupling is strong and has to be tackled very carefully (implicitly) to avoid numerical instabilities, (3) naïve boundary conditions on the artificial boundaries induce spurious reflection phenomena. Because of the above mentioned difficulties, the interaction between the flow and the structure are often neglected or is considered only for a small portion of the cardiovascular or respiratory system since the computational cost of such a fully coupled procedure is still very expensive. The aim of this work is to focus on more efficient fluid-structure interaction algorithms such as a coupling between the 3D Navier-Stokes equations and a 1D structure model or a MRI dynamic geometric model. The applicant work within the developed codes and with a dynamic interdisciplinary team. The position will be mentored by Emilie Marchandise, professor of Biomechanics and Jean-François Remacle, Professor of Civil Engineering. The work will take place at the Applied Mechanics Division at UCL: http://www.uclouvain.be/mema. The candidate should have a solid background in numerical methods and simulation. He should have a genuine interest in nonlinear fluid/solid mechanics, constitutive modeling. In order to better understand the physiological problems, interest in the human physiology is welcome to consider the specific modeling challenges of cardiovascular and respiratory systems. It is anticipated that the successful candidate will start by January of 2009, with an immediate start being preferred. Ask further information | Send resume : Prof. Emilie Marchandise , Prof. Jean-Francois Remacle | 23/06/2009 |