Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / Electronic engine control systems utilise tables, or maps, of data to determine the set-points of the various actuators on the engine and to calculate the values of variables that cannot be directly measured. To ensure accurate control of the engine processes the values in these maps have to be accurately calibrated for the particular engine being controlled. Due to the complex interaction of the various systems in the engine it is becoming more and more difficult for human calibration engineers to be able to take all the effects of changes to a particular parameter into account. This problem is made worse by increasingly strict emissions regulations and performance demands from the customer. The process of calibrating the maps in an Electronic Control Unit (ECU) is also very resource intensive since it involves taking a test engine installed in an engine test cell to every operating point on the various maps and adjusting the map values until the desired response is achieved. The aim of this project was to develop a solution to this problem in the form of a simulation based calibration system. The proposed system would use an accurate model of the engine to simulate the effect of various map values on the engine response. This data would then be used to find the map values that would enable the engine to deliver a desired torque curve. In the case where it is not practical to use engine simulation the system would be able to process a database created by testing an actual engine. This testing could also be automated. To achieve this aim the AutoCal program was created. This program can manage a commercial engine simulation code to create a database of the effect of various calibration values on the engine response. It can then evaluate the created database subject to user defined operating constraints and find calibration values that will deliver a desired torque curve. It can also be used to evaluate and process databases created by engine testing. To provide the data required for the development and testing of the AutoCal program, a naturally-aspirated engine was turbo-charged and tested at various operating points. The resulting data was used to calibrate and validate a model of the engine created and simulated with the WAVE software package from Ricardo. The project was focused on finding calibration values for the maps used to control the turbo-charger wastegate and ignition timing of the test engine. Work was limited to the full load operating region and fixed Air/Fuel Ratio (AFR) values were used. The project showed that simulation based calibration can be used to calibrate control system maps once an accurate model of the engine being controlled has been created. Very useful insight was gained into the process of building, testing and modelling a turbo-charged internal-combustion engine and calibrating modern electronic engine control systems. The end result is a useful engineering tool with the following functions: ² Automatically simulating the effect of various control inputs on engine performance. ² Determining the correct calibration settings to deliver the desired performance subject to user-definable constraints. This can be done using results from simulation or physical engine testing in the case of simulation tools not being available. ² Providing the data required when calibrating the engine model used during simulation by processing and displaying the outputs of the simulation program compared to test data. ² Plotting any test or simulation results in a format configured by the user. Using this tool facilitates a more structured and less resource intensive approach to engine control system calibration. / Imported from http://etd.sun.ac.za April 2010. / np2010

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.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2008. / Low Cost Automation (LCA) is of immense importance to industry, and even more so for small scale industries. In implementing LCA determining cost effective and efficient actuator alternatives present challenges for design engineers. Most often decisions are experiential or entirely based on manufacturer recommendations. Experience based decisions are most often biased with respect to the engineers’ knowledge. Similarly, manufacturer recommendations are restricted to their own products and are as such also biased. Either way, sub-optimum drive alternatives may sometimes be chosen. This demonstrates the need for making better informed decisions based on more than experience and what is available for use. This thesis reports the development of an electric actuator selection procedure and aid for use in the early layout design phase. It provides readily accessible information on technically viable actuator options. Experiential knowledge of experts in the field, commercial information, as well as data obtained from experimentation was used in its development. Being orientated towards LCA, the procedure has been targeted at the application of electric motors and their associated control technologies but can be extended to hydraulic, pneumatic and other actuators. In achieving a wider applicability of the selection aid, a generic set of actuator properties descriptive of most actuators was formulated. An AC drives control evaluation was conducted for developing the selection procedure and aid. It provided a means to validate some selection aid rules associated with actuator controllability. Quantitative data on speed and positioning accuracies of common AC three phase motors and their associated inverter technologies were the targeted results of the experimentation.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--Stellenbosch University, 2008. / Aortic valve replacements are frequently performed during heart surgery. However, since this is quite a stressful procedure, many patients are turned down for medical reasons. Stented valves, designed and manufactured for percutaneous insertion, eliminate many of the risks involved in open-heart surgery, thus providing a solution to patients not deemed strong enough for open-chest aortic valve replacements. The aortic valve is a complex structure, and therefore numerical simulation is necessary to obtain flow and stress data to support the design of a prosthetic heart valve in the absence of viable physical measuring methods. To aid in the design of a prosthetic heart valve, various finite element valve models were created, and the fluid structure interaction (FSI) between the valves and the blood was simulated using commercial finite element software. The effect of the geometry of the leaflets on the haemodynamic behaviour over the cardiac cycle was investigated. It was found that leaflet dimensions should be chosen judiciously, because of their considerable effect on the stress distribution and performance of the valve. A simple leaflet geometry optimisation was done for a 20 mm and 26 mm valve, respectively, by means of existing geometry relationships found in the literature. Simulations were done to obtain the maximum leaflet attachment forces that can be used by a stent designer for fatigue loading, or to investigate the structural strength of the stent. These simulations were numerically validated. The effect of leaflet thickness and stiffness on resistance to opening, stress distribution and strain were investigated. Results showed that leaflet thickness has a greater effect on the performance of the valve than leaflet stiffness, and thereby validated the results of similar tests contained in the literature. After simulating over-, as well as under-dilation of a stented valve, it was found that problems associated with over-dilation can be minimised to a certain extent by increasing the coaptation1 region of the leaflets. A simple pulse duplicator was designed based on a four-element Windkessel model. The pulse duplicator was used to study the performance of the prototype valves by means of high-speed photography, the results of which were fed into one of the numerical finite element models and compared to real valve performance. Some of the prototype valves showed efficiencies of 88%.