Thesis (Ph.D. (Physics)) -- University of Limpopo, 2016 / Refer to the document / National Research Foundation

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The objective of this study was to develop a new Steer Tilt Control (STC) algorithm inspired by real driver behaviour and to test it in simulation with an experimentally validated non-linear vehicle model. In order to develop an exhaustive simulation model of the vehicle and to process experimental data correctly, a large number of modelling aspects were taken into consideration. The objective of the study was to identify the unique kinematics of a three-wheeled tilting vehicle and determine the importance of the kinematic effects on the vehicle system. In order to fully understand this unique class of vehicle, the effect of the driver’s mass on the vehicle inertia’s and the effect of the tilting on the vehicle’s yaw inertia were considered. A wide-ranging expression for the driver’s perceived acceleration was derived and the roll dynamics of the non-tilting part of the three-wheeled tilting vehicle assembly were modelled. The steering torque of the vehicle as fully analysed and, using the simulation model, methods to model the effect of a crosswind on the vehicle, to test the effect of driving up or downhill, and to determine the effect of road camber on the vehicle dynamics were considered. To create a better understanding of the control task, road experiments were carried out using an instrumented tilting three-wheeler to investigate the driver steer inputs necessary to both balance the vehicle and follow a fixed trajectory. The experimental results demonstrated that the drivers’ steering inputs varied even though they had to complete identical tasks. This result confirmed that there are multiple ways to control the roll of the vehicle. The results also showed that the tilt angle always led the steering angle and for a transient manoeuvre, the tilt angle was larger than the balanced tilt angle at the start of the manoeuvre and smaller than the balanced angle at the end of the manoeuvre. The next step in the investigation was the development of a comprehensive non-linear dynamics model of a tilting three-wheeler including a tyre model and a driver model. A new method was developed to estimate the parameters of a Magic Formula Tyre model using the road testing data. The vehicle and tyre model were validated using data from a range of test runs. The importance of a driver in the loop was recognised and the elements of a driver trajectory-tracking model were studied. The aim was to develop a driver model that demonstrated good i tracking and some similarity to real driver behaviour. The final model used the yaw rate demand to determine an anticipatory control steer angle and the current heading error and the vehicle’s lateral position error measured in the vehicle’s local axis system to make small steering adjustments. The STC method based on Proportional Integral Derivative (PID) control was tested with the vehicle model to determine its performance with the non-linear dynamics and the driver in the loop. It was shown that the driver model had the tendency to act against the STC and that the two could only act simultaneously for a very limited range of demand trajectory and velocity combinations. The crosswind, hill driving, and road camber models were combined with the vehicle simulation without a driver but with the PID based STC. The simulations showed that these environmental factors made the control task significantly more difficult. More importantly, it showed that these factors demanded an increased number of vehicle states to be fed back to the controller. A new algorithm for STC was developed using the full vehicle and driver model. One of the criteria was that the control algorithm had to be realizable in practice. The resulting controller was a logic algorithm that would choose an action based on the steering angle and velocity and the vehicle speed with online gain adjustment based on direction and order of magnitude of the perceived acceleration. The basis of the control was adjustment of the driver's steering input and it was shown that the vehicle's deviation from the driver's intended path was minimal.

The field of lighting design is a highly specialised one. The control and manipulation of both natural and artificial light is a difficult aspect of building design. Proficient architects, interior designers and engineers must currently draw on their own experience and resources to evaluate their lighting designs. However, most often lighting design is overlooked and not fully understood by building designers. Those lighting designers that do have a good understanding of lighting are hampered by current conventional design methods when dealing with alternative and creative lighting designs. This is especially the case when dealing with natural daylight which tends to be under utilised, particularly in climatic areas that differ greatly from the European standard daylight design skies.There is clearly a need for a tool that enables building designers to quickly and accurately evaluate their use of localised natural light and specific artificial light in their building designs.The recent development of accurate, physically based computer models and the resulting photo realistic computer rendered images, can provide the basis of a platform for lighting designers to visualise their lighting designs. Such lighting platform enables designers to make more informed design decisions when looking at new approaches and unusual situations.The aim of this thesis is to explore and formulate a working example of such a lighting design platform, where by designers can easily evaluate lighting and daylighting designs based upon real world lighting and localised atmospheric conditions. / The designer is presented with an easy to use graphical user interface, that is able to produce a photometrically accurate photo realistic computer image.This platform was achieved through the development of three key areas. The first was the creation of a process of integrating a specific physical based rendering program, RADIANCE (Ward 1996)into an existing three dimensional computer aided design modelling package. The second area consisted of creating a localised daylight model suitable to improve the accuracy of the physical based renderer when dealing with specific local atmospheric conditions. This daylight model was based on Kittlers' sky irradiance model (Kittler 1982a). The final area was the development of a graphical user interface that provides an easy to use, front end to the lighting design platform.The results of this thesis exist in a working suite of programs and graphical user interfaces where local daylight and atmospheric condition can be specified and a photo realistic image of a design produced. The success of this platform can be demonstrated by the quality of the images that are produced. A designer can begin to use the interface with ease after very little instruction and thus start to quickly evaluate their design in terms of lighting manipulation and control. This ability to visualise and assess lighting and its effects, both natural daylight and artificial, will inevitably lead to a higher quality of successful building designs.

The main purpose of this research project was to implement a combination of computer graphics and processing to generate displays that will aid in the visualization of the colour rendering properties of a range of light sources, including the new generation of high-output LEDs (light emitting diodes) that are becoming widely adopted in general lighting service. The CIE (International Commission on Illumination) has developed a colour appearance model CIECAM02 for use in colour imaging and colour management, and this model is utilized in this work. This thesis describes the design and construction of a computer-based model that can be used as a research tool for the simulation and demonstration of the colour rendering properties of various artificial light sources. It is a comprehensive study of the colour models and measurement procedures currently in use in the lighting industry, as recommended by the CIE. This research project focused on the display of a set of surface colour patches as if they were illuminated by a specific light source, and the simultaneous display of two such sets to demonstrate the surface colour differences arising from the use of the two different light sources. A VIS (virtual imaging system) has been developed to display the colour properties of a series of test colour samples under different light sources. This thesis describes the computer models developed for the representation and display of surface colours in general, and colour rendering in particular. The designed system computes and displays the colour of each sample from a knowledge of the light-source spectrum and the spectral reflectance of each surface. It can simultaneously display the colours resulting from illumination by two different sources. In addition, the system computes the colour appearance differences for two sets of colours using the CIECAM02 colour appearance model. Subjective and objective tests were taken to validate the computed results. The VIS has been designed and implemented. It also has been tested by 21 observers and we believe that it will be a powerful research tool for the lighting industry, especially in relation to colour rendering.

The main purpose of this research project was to implement a combination of computer graphics and processing to generate displays that will aid in the visualization of the colour rendering properties of a range of light sources, including the new generation of high-output LEDs (light emitting diodes) that are becoming widely adopted in general lighting service. The CIE (International Commission on Illumination) has developed a colour appearance model CIECAM02 for use in colour imaging and colour management, and this model is utilized in this work. This thesis describes the design and construction of a computer-based model that can be used as a research tool for the simulation and demonstration of the colour rendering properties of various artificial light sources. It is a comprehensive study of the colour models and measurement procedures currently in use in the lighting industry, as recommended by the CIE. This research project focused on the display of a set of surface colour patches as if they were illuminated by a specific light source, and the simultaneous display of two such sets to demonstrate the surface colour differences arising from the use of the two different light sources. A VIS (virtual imaging system) has been developed to display the colour properties of a series of test colour samples under different light sources. This thesis describes the computer models developed for the representation and display of surface colours in general, and colour rendering in particular. The designed system computes and displays the colour of each sample from a knowledge of the light-source spectrum and the spectral reflectance of each surface. It can simultaneously display the colours resulting from illumination by two different sources. In addition, the system computes the colour appearance differences for two sets of colours using the CIECAM02 colour appearance model. Subjective and objective tests were taken to validate the computed results. The VIS has been designed and implemented. It also has been tested by 21 observers and we believe that it will be a powerful research tool for the lighting industry, especially in relation to colour rendering.

Submitted in fulfilment to the Department of Planning and Administration of the requirements for the degree of Doctor in Education in the Faculty of Education at the University of Zululand’ 2018. / Studies pertaining to the relationship and effect of prior spatial experience, gender and how they influence three-dimensional (3D) solid modelling as well as different cognitive styles on the spatial visualisation skills has little to no evidence, especially in graphics design students at rural–universities. Additionally, graphics design students often struggle to understand, process and convert multi-faceted objects from orthographic two-dimensional (2D) views into isometric projections (3D). However, ongoing study established a strong link between spatial visualisation skills and the effective completion of graphics design content. Moreover, conventional teaching and learning practice using textbooks, physical models, and pencil drawings were found to be insufficient for improving spatial visualisation skills among pre-service teacher students at a rural-university. These challenges formed the basis of the present study which focused on the relation and effect of prior spatial experience, gender, three-dimensional (3D) solid modelling software and different cognitive styles on the spatial visualisation skills of graphics design students at a rural–university. Students at this university are from disadvantaged and under-resourced schools and they arrive at university with little or no computer-based experience. Underpinned by Piaget’s perception and imagery theory, the study determined the effect of 3D solid computer modelling on students’ spatial visualisation skills. The study was carried out at the University of Zululand (UNIZULU) a rural-based university, comprising 200 pre-service teachers undertaking a graphics design module. Research method included mixed methods sequential research design. The study employed a spatial experience questionnaire, the Purdue Spatial Visualisation Test and semi-structured interviews to evaluate students’ prior spatial experiences, gender differences, spatial visualisation skills and cognitive styles before and after a 3D solid computer modelling intervention. Based on the research focus, the findings showed no relation between prior spatial experience, gender and spatial visualisation skills, however, mathematics and sketching activity emerged as strong predictors for spatial visualisation. The findings also showed that there was a significant difference with a moderate positive effect in the spatial visualisation skills between the students in the experimental group and those in the control group. As a consequence, a model was developed, aimed at improving rural-based instruction and learning for 2D to 3D drawing.

Please read the abstract in the section 00front of this document / Dissertation (MSc)--University of Pretoria, 2006. / Geography, Geoinformatics and Meteorology / MSc / Unrestricted