Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2005. / Vehicle Noise, Vibration and Harshness (NVH) is now a more important component of the vehicle design process than ever. Road noise is one of the key criteria used by potential buyers (albeit subconsciously) to choose what they perceive as the best vehicle. Road rumble is a key concern for vehicle manufacturers. Light Utility Vehicles (LUVs) are especially sensitive to a low frequency booming noise due to the fundamental acoustic mode that exists in the vehicle cabin. An investigation into this booming noise in an LUV is documented. The noise is identified and quantified after which the source of the noise in the vehicle cabin is identified using NVH techniques such as Acoustic Modal Analysis (AMA), Experimental Modal Analysis (EMA) and Transfer Path Analysis (TPA). The cabin’s fundamental acoustic mode lay at 100 Hz. Finally the source of the vibrations in the vehicle leading to the booming noise in the cabin is identified, along with its transfer path to the cabin. Solutions for the specific vehicle’s booming noise are proposed, two of which are tested with some success. Solutions to the problems associated with the fundamental acoustic mode of LUVs are also proposed and discussed.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / Elderly patients suffering from aortic valvular dysfunction are often denied aortic valve replacement due to the fact that they are classified as too old and fragile to handle the physical stress of open-heart surgery and cardio-pulmonary bypass. There exists a need for an alternative solution which places less physical stress on the body. The development of a percutaneous aortic heart valve (PAHV), which may be implanted through a minimally invasive procedure, will provide a solution to old and fragile patients who otherwise have a very limited life expectancy. The development of such a device entails a costly and time-consuming process which involves a number of phases, including a prototype development phase, an in-vitro testing phase, an animal trial phase and a human trial phase. This thesis focuses on the design and analysis of the stent component for a PAHV, suitable for implantation in sheep (animal trial phase). The process of developing a first prototype, involved an analysis of the stent design requirements. This analysis was followed by a concept generation phase as well as comprehensive finite element (FE) analyses of the most promising concepts. The objective of the FE analyses was to determine the effects of a variation in strut width on the performance characteristics of the concepts. Based on the results of the FE analyses, final geometries were selected for each of the two most promising concepts. Subsequent to the selection of the final geometries, a number of prototypes were manufactured. The prototypes were subjected to an electro-polishing process. An experimental analysis was also conducted on the prototypes to evaluate the accuracy of the (FE) simulations as well as the actual performance of the stent prototypes. The results of the FE analyses and experimental analyses indicated that strut width had a substantial influence on the parameters that were defined to characterise stent performance. The results of the analyses also highlighted the advantages and disadvantages of each concept and aided in identifying the concept that would be most suitable for the required application. Limitations of the study were identified and recommendations were made to assist the continued research and development of the device.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2008. / Suspension seats are commonly used for earth moving machinery to isolate vehicle operators from vibrations transmitted to the vehicle body. To provide the required stiffness and damping for these seats, air-springs are typically used in conjunction with dampers. However, to eliminate the need for additional dampers, air-springs can be used in conjunction with auxiliary air volumes to provide both spring stiffness and damping. The damping is introduced through the flow restriction connecting the two air volumes. In this study, simplified models of an air-spring were derived followed by a model including the addition of an auxiliary volume. Subsequent to simulations, tests were performed on an experimental apparatus to validate the models. The air-spring models were shown to predict the behaviour of the experimental apparatus. The air-spring and auxiliary volume model followed the trend predicted by literature but showed approximately 27 % lower transmissibility amplitude and 21 % lower system natural frequency than obtained by tests when using large flow restriction diameters. This inaccuracy was assumed to be introduced by the simplified mass transfer equations defining the flow restriction between air-spring and auxiliary volume. The models however showed correlation when the auxiliary volume size was decreased by two thirds of the volume actually used for the experiment. This design of a prototype air-spring and auxiliary volume is presented for a suspension seat used in articulated or rigid frame dump trucks. The goal of this study was to design a suspension seat for this application and to obtain a SEAT value below 1,1. The design was optimised by varying auxiliary volume size, flow diameter and load. A SEAT value of less than 0,9 was achieved.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / Vibrating a tillage tool is an effective way of reducing the draft force required to pull it through the soil. The degree of draft force reduction is dependent on the combination of operating parameters and soil conditions. It is thus necessary to optimize the vibratory implement for different conditions. Numerical modelling is more flexible than experimental testing and analytical models, and less costly than experimental testing. The Discrete Element Method (DEM) was specifically developed for granular materials such as soils and can be used to model a vibrating tillage tool for its design and optimization. The goal was thus to evaluate the ability of DEM to model a vibratory subsoiler and to investigate the cause of the draft force reduction. The DEM model was evaluated against data obtained from field testing done with a full scale single tine vibratory subsoiler. Soil testing was also done for material characterization and for the calibration of DEM material properties. The subsoiler was simulated using a commercial code, PFC3D. The effect on the simulation results of particle diameter, different bonding models and damping models was investigated. The final simulations were evaluated against the experimental results in terms of the draft force and material behaviour. The cause of the draft force reduction due to vibration was also investigated with the aid of the DEM model. From the results it was concluded that DEM is able to model the vibratory subsoiler for its design and optimization. The DEM model also provided valuable insight into the cause of the draft force reduction such as the increased peak stresses due to vibration and the increase in particle kinetic energy.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2005. / The two-dimensional flow-field through the stationary blade row of a radial inflow turbine in a torque converter was analysed by means of a potential flow model and a viscous flow model. The purpose was to compare the accuracy with which the two flow models predict the flow field through the static turbine blade row. The freestream turbulence level necessary to optimise the accuracy of the viscous flow model was also investigated. A first order source-vortex panel method with flat panels was used to apply the potential flow model. A radial inflow freestream was used. It was found that the stator blade row directly upstream of the turbine had to be included in the analysis to direct the flow at the turbine inlet. Even then the panel method did not satisfactorily predict the pressure distribution on a typical blade of the static 2nd turbine blade row. A two-dimensional viscous flow model gave excellent results. Furthermore, the two-dimensional viscous flow model was simple to set up due to the fact that symmetry boundary conditions could be used. This facilitated useful predictions of the salient features of the two-dimensional flow through the middle of the radial turbine blade row.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / Noise, Vibrations and Harshness (NVH) characteristics are becoming ever more significant in today’s vehicle manufacturing industry. Similar to good vibration and harshness characteristics, the perception of a vehicle’s quality is enhanced by a well sounding vehicle interior. This study’s main aim was to develop objective equations to directly optimise interior sound quality of light commercial vehicles ( ½ ton LCVs) on the South African market. The effects the noise of the engine, the wind and road/tyre interaction during steady-state conditions have on the interior sound quality of eleven comparable vehicles was investigated with the aid of a binaural head. Steady-state condition in this content refers to the fact that vehicles were tested at constant speeds, no acceleration involved. A strong emphasis was laid on the influence road noise has on the interior sound quality of LCVs. Other objectives for the thesis were, to provide a method to benchmark the interior SQ of LCVs and to develop target values for objective metrics for these vehicles. Establishing a comprehensive literature survey formed another objective of this study. It seeks to provide a summary of the modern SQ analysis procedure and the findings of a number of studies. The survey also presents an opportunity to compare this thesis’s results with previous studies. A last objective was to develop a list of possible hardware modifications that would improve the vehicle interior sound quality, influenced by different noise sources. A strong correlation between vehicle and engine speed and Zwicker loudness as well as Aure sharpness was found, for all test conditions. The road surface roughness was observed to also have a strong influence on the objective metrics of vehicle interior SQ. Loudness was found to be around 25% higher and sharpness around 5.6% lower in vehicles driving on rough tar roads than on smooth roads. Good correlations between a newly developed metric (the SPF), an equation in Zwicker loudness and Aure sharpness, and subjective ratings was obtained for a number of test conditions. Four objective equations, as well as target values for loudness and sharpness have been developed to objectively optimise the sound quality of LCVs. Benchmarking interior sound quality utilising the developed equations, will ensure continuous improvements in the SQ sector for future LCVs.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2008. / This thesis aims to contribute to the modelling and analysis of MEMS gyroscope technologies. Various gyroscope types are studied, and the phase-based vibratory gyroscope is then selected for further investigation. In the literature, vibratory MEMS gyroscopes are mostly used in a single excitation and amplitude detection mode. However, a dual excitation and phase detection mode has recently been proposed, since phase-based detection, as opposed to amplitude-based detection modes, may be expected to increase measurement accuracy (in turn since improved signal-to-noise ratios may be expected). However, the presented analytical model was relatively crude, and the assumptions made appear unrealistic. Accordingly, in this thesis, an improved analyticalmodel is developed. To describe the dual excitation and phase detection problem more comprehensively, principles of classical dynamics are used herein to investigate the dual excitation of a two degree of freedom spring-mass-damper system subjected to an applied rotation rate. In doing so, an analytical formulation including mechanical coupling effects is extended into a generalized form, after which the amplitude and phase responses of the mechanically uncoupled system are interpreted. The differences between the amplitude and phase measurement techniques are illustrated. Finally, the system is modelled numerically, and the scale factor of a hypothetical device based on the phase-based detection method is optimized, subject to constraints on the nonlinearity of the device, using constrained mathematical optimization techniques.

o trabalho tem como objetivo o estudo e a aplicação da técnica de hardware-in-the-loop como uma ferramenta de suporte no processo de desenvolvimento de uma mão artificial robótica. Os esforços se concentram no desenvolvimento de um ambiente computacional e um ambiente experimental para trabalharem em conjunto e simultaneamente. No ambiente computacional foi desenvolvido o modelo do sistema simulado em tempo real. No ambiente experimental, partes do protótipo da mão robótica foram implementadas. Em ambos os casos, foram desenvolvidos e empregados um controlador seguidor multivariável. Adotando este tipo de abordagem, partes do sistema simulado em tempo real poderão ser substituídas - à medida de suas necessidades - por partes físicas, como por exemplo: sensores, atuadores e novos hardwares de controle, possibilitando uma considerável redução de investimento em hardware e de tempo de projeto. / The purpose of this work is the study and the application of the hardware-in-the-loop technique as a support tool in the development process of an artificial robotic hand. The efforts concentrate on the development of a computational and experimental environment to work together and simultaneously. In the computational environment, the simulated system model was developed in real-time. In the experimental environment, prototype parts of the robotic hand were implemented. In both cases, a multivariable controIler was developed and utilized. By adopting this approach, parts of the system simulated in real time can be substituted - according to the needs - by physical parts, such as: sensors, actuators, and new control hardware, allowing a considerable investment reduction in hardware and in time of project.

Les travaux présentés dans ce mémoire proposent une méthode originale de génération automatique de tests à partir de modèles SysML pour la validation de systèmes embarqués. Un sous-ensemble du langage SysML (appelé SysML4MBT) regroupant les éléments de modélisation pris en compte dans notre approche a été défini et une stratégie de génération de tests dédiée (intitulée ComCover) a été créée. Cette stratégie, basée sur les principes du critère de couverture de modèles bien connu Def-Use, s'intéresse à la couverture des communications (envois / réceptions) au sein du système et entre le système et son environnement.La mise en œuvre opérationnelle d'un prototype, basé sur un générateur de tests à partir de modèle UML, a nécessité la définition de règles de réécriture permettant la transformation du modèle SysML4MBT vers le format d'entrée natif du générateur de tests tout en conservant l'expressivité de SysML4MBT. Finalement, les étapes de concrétisation des tests en scripts exécutables et l'établissement automatique du verdict lors de l'exécution sur banc de test définis durant le projet VETESS permettent l'établissement d'une chaîne outillée opérationnelle de génération et d'exécution automatique de tests à partir de spécifications SysML. Cette chaîne outillée a été étrennée sur plusieurs cas d'étude automobile tels que l'éclairage avant, les essuie-glaces ou la colonne de direction de véhicule. Sur ce dernier exemple, nous avons eu l'opportunité d'exécuter les tests sur un banc de test physique. Ces cas d'étude ont permis de valider chacune des étapes de l'approche proposée. / The work introduced in this thesis is in line with an original SysML Model-Based Testing approach to validate automotive mechatronic systems. A subset of SysML notation (called SysML4MBT) supported to express the test model is defined and a dedicated test generation strategy (called ComCover) is created. This strategy, based on the well-known Def-Use criteria, deals with the coverage of communications (sends / receives) inside the system and between the system and its environment.The development of an operational prototype, based on a UML-based test generator, has required the definition of rewriting rules to derive the input model of the UML test generator from the SysML4MBT model, by preserving the SysML4MBT expressivity.Finally, the concretization of tests in executable scripts and the assignment of a verdict by executing tests on test bench defined during the VETESS project, complete the operational toolchain that allows tests generation and execution from SysML models.This toolchain has been tried out on several automotive case studies as front lightings, wiper or steering column. Concerning this last experimentation, we have had the opportunity to execute test on a physical test bench. These case studies allow validating each step of the proposed approach.

o trabalho tem como objetivo o estudo e a aplicação da técnica de hardware-in-the-loop como uma ferramenta de suporte no processo de desenvolvimento de uma mão artificial robótica. Os esforços se concentram no desenvolvimento de um ambiente computacional e um ambiente experimental para trabalharem em conjunto e simultaneamente. No ambiente computacional foi desenvolvido o modelo do sistema simulado em tempo real. No ambiente experimental, partes do protótipo da mão robótica foram implementadas. Em ambos os casos, foram desenvolvidos e empregados um controlador seguidor multivariável. Adotando este tipo de abordagem, partes do sistema simulado em tempo real poderão ser substituídas - à medida de suas necessidades - por partes físicas, como por exemplo: sensores, atuadores e novos hardwares de controle, possibilitando uma considerável redução de investimento em hardware e de tempo de projeto. / The purpose of this work is the study and the application of the hardware-in-the-loop technique as a support tool in the development process of an artificial robotic hand. The efforts concentrate on the development of a computational and experimental environment to work together and simultaneously. In the computational environment, the simulated system model was developed in real-time. In the experimental environment, prototype parts of the robotic hand were implemented. In both cases, a multivariable controIler was developed and utilized. By adopting this approach, parts of the system simulated in real time can be substituted - according to the needs - by physical parts, such as: sensors, actuators, and new control hardware, allowing a considerable investment reduction in hardware and in time of project.