No description available.

Transcatheter aortic valve implantation (TAVI) is an effective alternative treatment option for patients with severe aortic stenosis, who are at a high risk for conventional surgical aortic valve replacement or considered inoperable. Despite the short- and mid-term survival benefits of TAVI, adverse clinical events, such as paravalvular leak, aortic rupture, and coronary occlusion, have been reported extensively. Many of these adverse events can be explained from the biomechanics perspective. Therefore, an in-depth understanding of biomechanical interaction between the device and native tissue is critical to the success of TAVI. The objective of this thesis was to investigate the biomechanics involved in the TAVI procedure using patient-specific finite element (FE) simulations. Patient-specific FE models of the aortic roots were reconstructed using pre-procedural multi-slice computed tomography images. The models incorporated aged human aortic material properties with material failure criteria obtained from mechanical tests, and realistic stent expansion methods. TAV deployment and tissue-device interaction were simulated; and the simulation results were compared to the clinical observations. Additionally, parametric studies were conducted to examine the influence of the model input on TAVI simulation results and subsequently the potential clinical complications such as paravalvular leak, annular rupture, and coronary artery occlusion. The methodology presented in this thesis could be potentially utilized to develop valuable pre-procedural planning tools to evaluate device performance for TAVI and eventually improve clinical outcomes.

No description available.

No description available.

Disc brake calipers are subjected to complex mechanical loading and interaction of individual components in a typical brake assembly makes design improvement very challenging. To analyse caliper behaviour, complex Finite Element models were created and successfully validated using a variety of experimental techniques, including exceptionally suitable Digital Image Correlation. A novel methodology to optimise caliper design was developed, using non-linear contact Finite Element Analysis and topology optimisation, to generate lightweight, high performance brake calipers. The method was used on a Formula 1 brake assembly and significant improvement in structural design was achieved, with the new caliper being lighter and stiffer than the original. The same approach was used on more conventional 4 pistons calipers using various boundary conditions with particular focus on mass reduction and considerably lighter designs were achieved. The influence of specific features of the optimised calipers on the structural performance was also successfully investigated.

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Dunnage bags are an inflatable dunnage variant, positioned and inflated between goods in multi-modal containers to restrain and protect the goods while in transit. This project endeavours to develop a simple method of generating new numerical prototypes for dunnage bags suitable for simulating operational loading of the bags. Previous research has produced a model that simulates the inflation of a paper dunnage bag using a simple pressure load. A dunnage bag reinforced with plain-woven polypropylene was chosen as the test case. Woven polypropylene is a highly non-linear, non-continuous, non-homogeneous material that requires specialised material models to simulate. A key aspect of this project was to develop a simple method for characterising woven-polypropylene and replicating it's response with material models native to LS-DYNA. The mechanical response of the plain-woven polypropylene was tested using a bi-axial tensile test device. The material response from physical testing was then mapped to two material models using the numerical optimiser LS-OPT. The response of the calibrated material models was found to correlate well with the measured response of the woven material. Dunnage bags are subjected to cyclic loading in operation. In order to capture the effects of compressing the contained gas, a gas inflation model was added to the model that calculates the pressure in the bag based on the Ideal Gas Law. A full bag model making use of the calibrated material models and the inflation model was subjected to a cycled boundary condition simulating loading and unloading of an inflated dunnage bag. The two prototype models captured the pressure drop in the bag due to material plastic deformation and the restraining force produced by the bag to within 10 %. The prototype models were also found suitable for predicting burst pressure in voids of arbitrary size and shape. / AFRIKAANSE OPSOMMING: Stusakke is 'n opblaasbare soort stumateriaal wat tussen goedere in multimodale vraghouers geposisioneer en opgeblaas word om sodoende die goedere vas te druk en te beskerm tydens vervoer. Hierdie projek poog om 'n eenvoudige manier te ontwikkel om nuwe numeriese prototipes vir stusakke, geskik om operasionele lading van die sakke te simuleer, te ontwikkel. Vorige navorsing het 'n model ontwikkel wat die opblaas van 'n papier stusak met eenvoudige drukkrag simlueer. 'n Hoë-vlak stusak versterk met plein-geweefde polipropileen, is gekies om getoets te word. Geweefde polipropoleen is 'n hoogs nie-lineêre, onderbroke, nie-homogene materiaal wat gespesialiseerde materiaalmodelle nodig het vir simulasie. Een van die fokuspunte van hierdie projek is om 'n eenvoudige metode te ontwikkel om die karaktereienskappe van polipropoleen te identifiseer en die gedrag daarvan na te maak met die materiaalmodelle van LSDYNA. Die meganiese reaksie van die plein-geweefde polipropoleen is getoets met 'n biaksiale/tweeassige trektoets-toestel. Die materiaal se reaksie op die fisiese toets is ingevoer op 'n numeriese optimiseerder, LS-OPT, om op die materiaalmodelle te toets. Die reaksie van die gekalibreerde materiaalmodelle het goed gekorelleer met die gemete reaksie van die geweefde materiaal. Stusakke word tydens diens onderwerp aan sikliese lading. Om die effek van die saamgepersde gas vas te stel is 'n gas-opblaasbare model bygevoeg by die model wat die druk in die sak bereken, soos gebaseer op die Ideale Gas Wet. 'n Volskaalse sakmodel wat gebruik maak van die gekalibreerde materiaalmodelle en die opblaas-model is onderwerp aan sikliese grensvoorwaardes wat die lading en ontlading van 'n opblaasbare stusak simuleer. Die twee prototipe modelle het die drukverlies in die sak a.g.v. die materiaal-plastiek vervorming en die bedwingingskrag van die sak beperk tot 10 %. Die protoyipe modelle is ook geskik bevind om barsdruk in arbitrêre leemtes te voorspel.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Orthopaedics and Traumatology / Master / Master of Philosophy

Finite element analysis is versatile and used widely in a range of engineering andscientific disciplines. As time passes, the problems that engineers and designers areexpected to solve are becoming more computationally demanding. Often theproblems involve the interplay of two or more processes which are physically andtherefore mathematically coupled. Although parallel computers have been availablefor about twenty years to satisfy this demand, finite element analysis is still largelyexecuted on serial machines. Parallelisation appears to be difficult, even for thespecialist. Parallel machines, programming languages, libraries and tools are used toparallelise old serial programs with mixed success. In some cases the serialalgorithm is not naturally suitable for parallel computing. Some argue that rewritingthe programs from scratch, using an entirely different solution strategy is a betterapproach. Taking this point of view, using MPI for portability, a mesh free elementby element method for simple data distribution and the appropriate iterative solvers,a general parallel strategy for finite element analysis is developed and assessed.