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AFRIKAANS: 'n Basiese toets spesifikasie, vir die toets van bak-kappies van ligte kommersieële voertuie word voorgestel. Die toets spesifikasie is 'n eerste stap na die kwalifikasie van die sterkte van bakkie-kappies tydens ongelukke. Die toets is ontwerp spesifiek met die omrol scenario in gedagte. Verskillende toets metodes is geëvalueer vir toepaslikheid, gemak van implementasie en finansiele beperkings gedurende die navorsingsfase. Die massa-, en geometriese-eienskappe van drie verskillende I ton bakkies is eksperimenteel gevind om as basis vir energie berekeninge te dien. Die energie wat elkeen van hierdie voertuie besit net voor dit omrol is bereken en as voorlopige toets kriterium gebruik. 'n Pendulum impak toets-prosedure sowel as 'n Eindige Element Analise (EEA) prosedure is in die voorlopige toets kriterium ingesluit. Die voorlopige toets kriterium is gedurende 'n volskaal impak toets op 'n bakkie-kappie toegepas. 'n Detail eindige element analise van die kappie struktuur is ook volgens die kriterium gedoen. Daar is bewys dat beide hierdie metodes lewensvatbaar is vir implementasie en dat dit gebruik kan word vir die verifieëring van die sterkte van bakkie-kappies. Die resultate gevind gedurende hierdie toetse is gebruik om die voorlopige toets kriterium aan te pas om 'n basiese toets-spesifikasie te verkry waarmee bakkie-kappies deur toets owerhede geevalueer kan word. ENGLISH: In this thesis a basic test specification for a canopy that covers the load¬bed-area of a light commercial vehicle (LCY) is proposed. The test specification is a first step towards the qualification of the strength of a canopy during an accident. The test is designed specifically with the rollover scenario in mind. Different testing methods were evaluated for applicability, ease of use and financial constraints during the research phase. The mass and geometric characteristics of three different 1 ton LCY's were found experimentally in order to set a basis for the energy calculations. The energy each of these vehicles possesses just prior to roll over was calculated and used to create preliminary testing criteria. A pendulum impact testing procedure as well as a Finite Element Analysis (FEA) procedure were incorporated into the preliminary testing criteria. The preliminary testing criteria were applied during a full scale pendulum impact test on a canopy and were also applied during a detailed finite element analysis of the canopy structure. It was shown that both of these test methods are viable and that they can be used as a canopy strength qualifying means. Finally the results found during the tests were used to adjust the preliminary testing criteria to form a basic test specification that can be used by testing and qualification facilities. / Dissertation (M Eng (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted

Phase change in solidification and melting can be described with the aid of discontinuous functions. The aim of this project is to establish effective methodologies for the solution of discontinuous phase-change problems. The classic capacitance method, which distributes the effect of any discontinuity present over a finite region (typically an element), can suffer from inaccurate energy transport. Improvement is possible with the application of the classic non-physical enthalpy method. However, this approach is known to suffer with the imposition of material velocity, which gives rise to negative thermal capacitance providing a source of error and instability. In order to improve on the performance of the capacitance method and the classic non-physical enthalpy method, this research introduces a series of new non-physical variables. Firstly, a new non-physical enthalpy is defined via the weak form of the energy transport equation. The classical non-physical enthalpy was defined using a temporal integral term. In the new definition, the non-physical enthalpy involves both a temporal and an advection term, which is shown to avoid the generation of negative capacitance and improve the stability of advection heat transfer in numerical methods. Secondly, control volume analysis is performed on weighted and unweighted forms of the governing energy equation involving non-physical enthalpy. The analysis is shown to reveal non-physical source terms that facilitate the removal of phase-change discontinuities. Thirdly, it is demonstrated in the thesis how a non-physical heat source must be introduced into the governing non-physical transport equation to remove discontinuities arising from non-physical terms related to advection. To demonstrate the accuracy and stability of the new method, it is implemented in the finite element method for both one-dimensional linear rod elements and two dimensional triangular elements. Update techniques and root finding methods, such as the predictor-corrector method, the secant method and the homotopy method, are applied to solve the non-linear system of equations, which are constructed with the new theory. Results returned from the one-dimensional numerical experiments are compared with exact solutions, which show reasonable accuracy. Numerical experiments for isothermal solidification with advection-diffusion in both one and two dimensions demonstrate the feasibility of the new methodology.

Laser cleaning is a non contact, highly controllable process for the removal of contaminants from a surface with minimum or no damage to the substrate material. Laser cleaning has been applied mainly on flat and curved surfaces. Little is known on the phenomena and feasibility of laser cleaning of slotted structures. Slots are common structures in engineering, and can be found in many components. In this PhD work, the feasibility of laser cleaning of alpha case on flat titanium alloy surfaces was initially explored, and then an investigation was made on the use of a pulsed laser for the cleaning of micro to macro slots in silicon and metallic materials. The effects of laser processing parameters on the contaminant removal from these slots were experimentally studied. Laser cleaning thresholds and cleanliness was examined. Meanwhile, finite element modelling (FEM) and time domain finite difference modelling techniques were used to simulate the processes involved to aid the understanding of the technique for process optimisation. The experiments were undertaken to verify if such models are able to accurately predict the cleaning thresholds. The surface and sub-surface characteristics before and after laser cleaning were examined using optical microscopy and scanning electron microscopy (SEM). It has been shown that the slot structure and its material properties were not damaged or changed by laser cleaning process. A novel contribution is that surface morphology after the laser ablation could be used as a diagnostic method to indentify the presence of alpha case and measure its thickness due to the specific characteristics of the surface roughness and generated cracks on the ablated surface after laser irradiation. Besides, it has been found that an axial beam which propagates into the narrow slots can successfully clean the tiny particles on the slot sidewalls whose width ranges from 3.5 mm to 13mm. These phenomena had never been reported before.

D.Ing. / This study is a numerical investigation into the behaviour of cracks in uPVC pipes under pressure. This study is a continuation of a Masters dissertation which showed that leakage exponents vary significantly from the theoretical orifice exponent of 0.5 for cracks in pipes for different materials. This study looks at the behaviour of cracks in more detail and specifically with regard to the parameters of the pipe and crack. Using Finite Element Analysis the relationship between the pressure head and the leak area in pipes with longitudinal, spiral and circumferential cracks was investigated. It was found that the longitudinal, spiral and circumferential crack areas increase linearly with pressure. The slope of this linear relationship depends on various parameters, including loading state, pipe dimensions and pipe material properties. The effect that the individual pipe parameters had on the pressure-area slope was investigated. These parameters included the material properties of the pipe (Young’s modulus, Poisson’s ratio and longitudinal stress), the geometry of the pipe (internal diameter and wall thickness) as well as the geometry of the crack (length of the crack and the width of the crack). Once the effect of the pressure-area slope m is known, the link between the conventional leakage exponent N1 and the pressure-area slope m was further investigated and the effect of each parameter on the leakage exponent N1 was found. Using various data techniques the above data was combined and processed to find mathematical relationships that give reasonable descriptions of the pressure-area slopes of longitudinal, spiral and circumferential cracks. Once these equations for the pressure-area slopes were determined it was possible to obtain three new relationships for leakage from longitudinal, spiral and circumferential cracks.

This thesis reviews the development and current methods of numerical convection heat transfer from available literature, encompassing an analysis of the various finite element formulations available for investigating convection. It further describes the finite element formulation for the primitive variable convection heat transfer equations via a Galerkin weighted residual scheme and using mixed interpolation, and it demonstrates the capability of this method by means of five practical examples, namely natural convection in a thermally driven square cavity, a thermally driven vertical slot, a thermally driven triangular cavity, and a liquid convective diode, and forced convection in a cooling pond. This study also provides the background and framework for the problem of transient convection heat transfer, and for further steady-state studies using parameters outside those considered herein.

Thesis: M.S., Massachusetts Institute of Technology, Department of Civil Engineering, 1976 / Bibliography: leaves 126-131. / by Joseph A. Martore. / M.S. / M.S. Massachusetts Institute of Technology, Department of Civil Engineering

This diploma thesis is focused on Formula Student upright analysis using final element method. The main goal is to review an effect of different boundary conditions on stress and deformation. Nowadays, the topologic optimization is a commonly used tool for design process of the upright, to create the lightest and the most rigid design possible. Boundary conditions, which should approximate reality really well, are one of inputs to topological optimization.

Master's thesis deals with a fast cross roll bar straightening algorithm and its modifications to allow for an automatic calculation of a large number of simulations and an arbitrary straightening machine configuration. Modified program is then verified using the original algorithm. It also deals with the algorithm's application to straightening process optimization using neural networks.

This master‘s thesis deals with computational modelling of human vocal folds in phonation position using finite element method. There are described larynx anatomy, voice generation theories and overview of so far published computational models of vocal folds. Next part of the paper deals with a redesign of vocal folds and soft tissues‘ geometry, creation of finite element mesh and implementation of active stress in thyroarytenoid muscle. The problem was solved using Ansys 19.2 software. Computation of stress and deformation of soft tissues in phonation position has been made for 7 variations with different combination of active cartilages and muscles. Lastly, there was evaluated an effect of different cartilages and active muscle stress to final stress and deformation of soft tissues of vocal folds.