Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2005. / This study involved the modeling and verification of the finger follower valve train arrangement with the focus on the non-linear behaviour of high speed valve springs. The project was divided into three phases namely; the measuring of valve train dynamics, modeling of the valve train and the verification of the dynamic models by comparing the results from the two aforementioned two phases. Acceleration and force were measured on a running engine. A force transducer was specially developed for this purpose. Digital signal processing was used in the analysis and implementation of all measured data. The spring model was developed systematically from a solid model, into a finite element model, and finally into a dynamic model. All development steps were continually checked with experiments and calculations. The primary concept used in the spring modeling lends itself to modal analysis theory in conjunction with the superimposing of non-linearities onto a linear model. The dynamic model was verified and good correlations were found, especially at high engine speeds where valve train dynamics play an important role. Parameter adjustments could be made in the dynamic model and the effect that some engine mechanisms, such as engine oil aeration, had on the valve train dynamics were identified. The project was concluded with a case study of a cam profile optimisation project. Dynamic problems were found that would normally not have been identified without the dynamic model.

MScEng / Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / Research conducted on Marion Island aims at predicting the consequence of climate change in the Subantarctic region, as well as for other terrestrial ecosystems. The island has the ideal ecosystem, due to its size, isolation and relative simplicity, to be studied as a prediction model for the consequence of climate change and the interaction between various climate related parameters. The cushion plant, Azorella selago, is the focal point of this project due to the important functional roles it fulfils as well as its wide spread distribution over the island. A. selago grows in three different shapes; hemispherical, elliptical and crescent. The changes in airflow due to varying plant size are investigated as well as the exertion of force on the plant. The grass species Agrostis magellanica has the tendency to grow on top of A. selago. In addition it has been observed that the grass species grows more vibrantly on the leeward side of the cushion plant. In the light of this observation the particle deposition of grass seeds on A. selago is also investigated. Computational fluid dynamic analyses are conducted for various sizes of each shape of the plant. These studies are augmented by wind tunnel and in situ measurements and observation and experimental determining of particle drag coefficients. Time independent, incompressible, turbulent flow is modelled by means of a high Reynolds number turbulence model with a modified Law-of-the- Wall to accommodate for the significant surface roughness. Nine different dimensions over the various shapes were identified. Each shape is analysed and the patterns that emerged discussed. The windward pattern for all shapes display similar qualities. On the leeward side the shapes display distinctly different airflow patterns. The hemisphere shows two trailing lines typically associated with the horseshoe vortex phenomenon. The ellipse displays one distinctive trailing line. The most interesting flow patterns are found when analysing the crescent shape. Three trailing lines are observed, the side lines quickly dissipates with increasing height while the middle line remains distinctive. The complex recirculation patterns that emerge are further visualized by means of air particle tracks. The furthermost number of light particle deposition of A. magellanica seeds on A. selago are found at the windward location while physical evidence clearly indicates growth primarily on the leeward position. The leeward location on A. selago is protected from the harsh environmental conditions; wind speeds are minimal in this area. It will therefore be a more suitable site for the fostering of a vulnerable seedling that on the exposed windward side. A force analysis done on the plants reveals that the total force is two orders of magnitude higher that the shear force. Furthermore, the magnitude of the total force is directly proportional to the size of the plant. Three critical areas on the plant are common irrespective of shape or size: the stagnation point at the windward side, the apex region at the top and the leeward side of the plant.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2005. / In this document the reduced order simulation and optimisation of the passive suspension systems of a locally produced forty ton articulated dump truck is discussed. The linearization of the suspension parameters were validated using two and three dimensional MATLAB models. A 24 degree-of-freedom, three dimensional ADAMS/VIEW model with linear parameters was developed and compared to measured data as well as with simulation results from a more complex 50 degree-of-freedom non-linear ADAMS/CAR model. The ADAMS/VIEW model correlated in some aspects better with the experimental data than an existing higher order ADAMS/CAR model and was used in the suspension system optimisation study. The road profile over which the vehicle was to prove its comfort was generated, from a spatial PSD (Power Spectral Density), to be representative of a typical haul road. The weighted RMS (Root Mean Squared) and VDV (Vibration Dose Value) values are used in the objective function for the optimisation study. The optimisation was performed by four different algorithms and an improvement of 30% in ride comfort for the worst axis was achieved on the haul road. The improvement was realised by softening the struts and tires and hardening the cab mounts. The results were verified by simulating the optimised truck on different road surfaces and comparing the relative improvements with the original truck’s performance.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / Vehicles are expected to deliver adequate power for the engine size and vehicle class. They must also deliver good response to the driver’s desired action as well as deliver the lowest possible fuel consumption in all possible conditions and comply with emissions regulations. The combination of these factors is termed good driveability. Evaluating driveability is time and cost intensive and is most commonly evaluated from a subjective driver prospective. Advanced control systems allow for more accurate control of the vehicles response to the drivers demands. The objective of this document was to develop a quantitative driveability evaluation model for engine management calibration. The important aspects of engine management control for driveability, as well as how they are manipulated to deliver acceptable driveability were identified. Test procedures were developed to measure and quantify all these important factors. The test procedures can be evaluated for their different sections or for a complete driveability evaluation method. An optimised driveability evaluation method was developed to reduce the driveability evaluation time. Verification of the driveability evaluation model did provide different results for a different engine management calibration.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / A refrigerated semi-trailer was designed to solve manufacturing and operational problems. This was achieved by using advanced pultruded composites. The static and dynamic material response was determined. The dynamic loading on the vehicles was also measured and is presented along with static load cases. These boundary conditions were used in a finite element model to determine the structural performance of the trailer. The results show good static performance with some problem areas which still need attention. Initial poor fatigue performance is improved by increasing the ultimate shear stress of the material. A fatigue optimisation technique is suggested for future use.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / Inspired by Sigmund’s 99-line MATLAB code for minimum compliance (maximum stiffness) topology optimisation, this thesis presents an open source software (OSS) version developed in Python, denoted ToPy. ToPy extends the 99-line code of Sigmund in a number of ways. Firstly, ToPy can solve three different problem types, namely minimum compliance, heat conduction and mechanism synthesis, in two-dimensional (2D) or three-dimensional (3D) space. This is accomplished by simply changing an input file. Secondly, by using established open source software (Pysparse and its iterative solver) for solving the sparse finite element (FE) systems of equations, the ToPy code provides improved speed and scalability. ToPy also provides for grey-scale filtering (GSF) to yield predominantly, or even purely, solid-void or black-and-white designs in 2D and 3D space. In addition, an exponential approximation to the objective function is implemented. This approximation is a generalisation of the reciprocal approximation so popular in structural optimisation; the values of the exponents may be based on gradient information in previously visited iterates, or fixed exponents may be prescribed, in the spirit of optimality criterion (OC) methods. As a further generalisation, the diagonal quadratic approximation to the exponential approximation in an SAO setting is also implemented. What is more: the diagonal quadratic approximation to the exponential approximation was successfully used in combination with GSF. This is a novelty of some importance as it was previously suggested that GSF can only be used in combination with strictly monotonic objective functions, like the reciprocal approximation.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2005. / This study involved the modelling and verification of the Shielded Metal Arc Welding of mild steel with the focus on displacement and temperature distribution prediction of welded plates. The project was divided into three phases namely; the literature survey into finite element modelling of welding processes, the modelling of a welding process and verification of the modelling with experimental results. A working welding model was created using a commercial finite element software package with the capabilities to model welding processes. The welding model was systematically developed from a two-dimensional model into a threedimensional full physics process model. Experimental measured welding heat input parameters were applied in the model, temperature dependent material properties were applied and actual structural restraints from the experiments were modelled. Displacement and temperature distributions were measured on mild steel plates welded with the Shielded Metal Arc Welding process. The plate temperature was measured at various locations with K-type thermocouples spot welded onto the plates. Plate deformation was measured at various stages of the manufacturing process. Tendencies in plate displacement were investigated with a change in certain welding parameters. The finite element model was verified and good correlations were found, especially for the temperature distribution in the welded plates.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / NUMERICAL design optimization provides a powerful tool that assists designers in improving their products. Design optimization automatically modifies important design parameters to obtain the best product that satisfies all the design requirements. This thesis explores the use of Support Vector Regression (SVR) and demonstrates its usefulness in the numerical optimization of a low-speed wind turbine for the power coe cient, Cp. The optimization design problem is the three-dimensional optimization of a wind turbine blade by making use of four two-dimensional radial stations. The candidate airfoils at these stations are selected from the 4-digit NACA range. A metamodel of the lift and drag coe cients of the NACA 4-digit series is created with SVR by using training points evaluated with XFOIL software. These SVR approximations are used in conjunction with the Blade Element Momentum theory to calculate and optimize the Cp value for the entire blade. The high accuracy attained with the SVR metamodels makes it a viable alternative to using XFOIL directly, as it has the advantages of being faster and easier to couple with the optimizer. The technique developed allows the optimization procedure the freedom to select profiles, angles of attack and chord length from the 4-digit NACA series to find an optimal Cp value. As a result of every radial blade station consisting of a NACA 4-digit series, the same lift and drag metamodels are used for each station. This technique also makes it simple to evaluate the entire blade as one set of design variables. The thesis contains a detailed description of the design and optimization problem, the implementation of the SVR algorithm, the creation of the lift and drag metamodels with SVR and an alternative methodology, the BEM theory and a summary of the results.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / Dragline bucket designers are required to evaluate new bucket designs by building and testing scale buckets. Concerns about the reliability and accuracy of scale testing have been raised in recent years, but there was no alternative. However, recent advances in computing power and granular flow modeling are changing this and, we are entering an era where it is possible to numerically simulate dragline bucket filling. However, verification of the numerical simulation is necessary before useable data can be obtained. This thesis explains the algorithm used by modern discrete element codes to simulate granular materials. The process used to create the numerical model and calibrate the material will be discussed. An experimental test bench was also built to record experimental data for the verification the numerical model. As the project progressed it became clear that the time needed to run a single simulation dramatically limits the number of simulations that could be run. Consequently, different approaches that could reduce simulation time were also investigated. Unlike the other material parameters, there is no test that can be used to directly calibrate the damping. An array of numerical simulations were therefore conducted testing different damping schemes. The comparison performed between the numerical and experimental data showed that the numerical models could not accurately simulate the experimental measurements of the scale model dragline bucket. The numerical model did, however, predict many of the trends identified in the experimental simulation. With more realistic contact models and better computer facilities, nonetheless, it is highly probable that numerical models will be capable of simulating dragline bucket filling accurately. Further study is, therefore, justified.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / Thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering Science (Mechanical) at the University of Stellenbosch. / ENGLISH ABSTRACT: This thesis examines the development of a specialized, high-speed bearing in order to reduce vibration levels, reduce cutting times and increase blade stability during diamond sawing. The sawing process is required to be smooth, straight and unhindered – a task which is made difficult by the extreme hardness of the diamond as well as unseen grains which could potentially ruin the cut by deflecting the blade. This has an adverse effect on the quality of the cut and the yield obtained from the stone. The current equipment used for diamond sawing is very basic and a significant improvement can be made in terms of quality and sawing speed with the addition of an improved bearing. An aerostatic bearing was designed in order to achieve lower vibration levels and increased spindle speeds. A speed of 18 500 rpm was achieved with this bearing. A numerical model of the bearing was built with the aim of predicting the bearing’s dynamic behaviour. A finite element method (FEM) analysis was done to confirm the rigid body assumption made. Experimental modal analysis (EMA) was done to determine the frequencies and damping ratios of the natural modes of the rotor. The model was seen to predict the frequencies of the modes to within 6%. This model would be used for future design work to ensure that the frequencies of these modes are designed outside of the operating speed range of the aerostatic bearing. Tests were done to compare the vibration levels between the conventional machine and the aerostatic machine during sawing. The overall RMS acceleration was reduced by 70% on the housing of the aerostatic machine and by 50% on the diamond clamp. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die ontwikkeling van ‘n gespesialeerde, hoë-spoed laer om vibrasie en sny tye te verminder, asook om lem stabilitiet te verhoog in die diamant sny proses. Die sny proses moet glad, reguit en akkuraat wees, maar dit is nie altyd moontlik nie as gevolg van die variasie in hardheid van die diamant asook die naat in die daimant wat die lem maklik kan laat afwyk. Hierdie het ‘n negative effek op die kwalitiet van die snit. Die konvensionele diamant saag masjien is baie eenvoudig en ‘n groot verbetering in die snit kwalitiet en lemspoed is moontlik as ‘n nuwe laer ontwerp en implementeer kan word. ‘n Aerostatiese laer en rotor is ontwikkel om die vibrasie te verminder en die lemspoed to verhoog. ‘n Lemspoed van 18 500 rpm was verkry met die nuwe laer. ‘n Numeriese model is ontiwkkel om die beweging van die rotor dinamies te bereken. Die Eindige Element Metode (EEM) is gebruik om te bepaal of die aanname dat die rotor rigied is, wel aanvaarbaar is. Eksperimentele Modale Analise (EMA) is gebuik om die natuurlike frekwensies en die dempingsverhoudings vir die rotor te bepaal. Die model het die frekwensies tot binne 6% van die werklike waardes bereken. Hierdie model sal in die toekoms gebruik kan word vir die ontwerp van aerostatiese laers om te verseker dat die natuurlike frekwensies buite die spoedbereik van die aerostatiese masjien val. Toetse is gedoen om die vibrasievlakke van die huidige en die aerostatise masjien te meet tydens die snyproses. Die totale WGK versnelling het met 70% op die huls van die aerostatiese masjien, en met 50% op die diamant dop, verminder.