M. Tech. (Engineering, Industrial, Dept. Industrial Engineering and Operations management, Faculty of Engineering and Technology) Vaal University of Technology| / This research work focused on welded titanium alloy (grade 5) pipes, to ascertain if the weld joints can withstand the immediate and accumulated effects of fluid flow in (industrial) applications. Modeling of welded pipes was done using Pro/ENGINEER Wildfire 5.0. The cylindrical pipe models were of 206,375mm inner and 219,075mm outer diameter respectively; made of Ti6Al4V material. Three models were made: one of unwelded pipes, another with a seam weldment and the third with a circumferential weld. The welds were modeled as autogenous gas tungsten arc welding and the models included calculated heat affected zones. The pipes were modeled with a flowing fluid under pressure exerted evenly on all sides of the pipe walls (circumference). The boundary conditions were such that the pipe ends were supported as if the pipe were continuous. Stress and strain analysis on the pipe models were performed by the Finite Element Method using Pro/ENGINEER Wildfire 5.0. The results of the Finite Element Analysis (FEA) indicated that stress vary very negligibly along the pipe. A comparison of the FEA modeling results to the analytically determined value of the stress showed very low or zero percentage deviation.

One of the benefits of electric vehicles (EVs) and hybrid vehicles (HVs) is their potential to recuperate braking energy. Regenerative braking (RB) will minimize duty levels on the brakes, giving advantages including extended brake rotor and friction material life and, more significantly, reduced brake mass and minimised brake pad wear. In this thesis, a mathematical analysis (MATLAB) has been used to analyse the accessibility of regenerative braking energy during a single-stop braking event. The results have indicated that a friction brake could be downsized while maintaining the same functional requirements of the vehicle braking in the standard brakes, including thermomechanical performance (heat transfer coefficient estimation, temperature distribution, cooling and stress deformation). This would allow lighter brakes to be designed and fitted with confidence in a normal passenger car alongside a hybrid electric drive. An approach has been established and a lightweight brake disc design analysed FEA and experimentally verified is presented in this research. Thermal performance was a key factor which was studied using the 3D model in FEA simulations. Ultimately, a design approach for lightweight brake discs suitable for use in any car-sized hybrid vehicle has been developed and tested. The results from experiments on a prototype lightweight brake disc were shown to illustrate the effects of RBS/friction combination in terms of weight reduction. The design requirement, including reducing the thickness, would affect the temperature distribution and increase stress at the critical area. Based on the relationship obtained between rotor weight, thickness and each performance requirement, criteria have been established for designing lightweight brake discs in a vehicle with regenerative braking.

<div>Thin walled structures find wide applications in automotive industry as energy absorption devices. A great deal of research has been conducted to design thin walled structures, where the main objective is to reduce peak crushing forces and increase energy absorption capacity. With the advancement of computers and mathematics, it has been possible to develop 2D patterns which when folded turn into complex 3D structures. This technology can be used to develop patterns for getting structures with desired properties. </div><div>In this study, square origami tubes with folding pattern (Yoshimura pattern) is designed and studied extensively using numerical analysis. An accurate Finite Element Model (FEM) is developed to conduct the numerical analysis. A parametric study was conducted to study the influence of geometric parameters on the mechanical properties like peak crushing force, mean crushing force, load uniformity and maximum intrusion, when subjected to dynamic loading. </div><div>The results from this analysis are studied and various conclusions are drawn. It is found that, when the tube is folded with the pattern having specific dimension, the performance is enhanced significantly, with predictable and stable collapse. It is also found that the stiffness of the module varies with geometrical parameters. With a proper study it is possible to develop origami structures with functionally graded stiffness, the performance of which can be tuned as per requirement, hence, showing promising capabilities as an energy absorption device where progressive collapse from near to end impact end is desired.</div><div><br></div>

AN ABSTRACT OF THE THESIS OF

In 1994 there was an earthquake occurred in Northridge, California which caused damage in structures built with Steel Moment Frames (SMF) due to the brittle fractures in the beam and column connections. It has led to the major modifications and improvements in the connection detailing prior to the earthquake occurred in the Northbridge. These changes came up with better materials for welding and introduced the use of cover plate and Reduced Beam Section (RBS). RBS connections are the most widely used connection today and it allows the SMF systems to yield extensively and deform plastically by avoiding brittle fracturing at connections. The most important factors that affect the response along with the design of Steel Moment Frames (SMF) and Reduced Beam Section (RBS) connections are connection strength, stiffness, connection type, use of deep columns and phenomena associated with its instability, the strength of ductility of the column panel zone-beam instability.

The present paper studied the buckling phenomena of membranes under tensile load with and without central crack.  The studies of fracture mechanics are tested within certain conditions of membranes. The tensile test has been performed with Al-foil in different crack lengths, i.e. 0 mm, 12.5 mm, 25 mm and 50 mm. The numerical analysis has been carried out by Finite Element Analysis (FEA) and comparing with the theoretical and experimental results.  In this paper, the critical buckling behavior is tested, validated and compared. Same observation of patterns in experiments and the simulation are found. The influence of scale factor for imperfection setting are tested.

ABSTRACT An evaluation of glass reinforced plastic pipe stub-flange behaviour during hydrostatic pressure testing is presented. Similar flanges made according to different manufacturing methods were analysed. Linear static analysis using MSC Patran / Nastran was performed to predict the critically loaded regions subjected to high stress concentrations. These regions were used for experimental strain gauge locations. Hydrostatic testing designed according to BS 5480 and ASTM F 37 was performed on assembled flange joints to initiate both leakage and ultimate material failure. Experimental strain results were compared to finite element numerical results at the selected locations. Fibre dominated failure characterised by cracks extending through the stub and matrix dominated failure characterised by interlaminar debonding were noticed. The need for further work analyzing GRP flanges subject to mechanical load and taking into account induced residual thermal stress effects is suggested.

ABSTRACT The multi-disciplinary accelerator based facilities at iThemba LABS are used intensively for nuclear physics experiments, radiotherapy and the production of radioisotopes. To increase the beam intensity for radioisotope production and to improve the beam quality of the 66 MeV proton beam, a double-gap horizontal half-wave flat-topping resonator has been developed for the separated-sector cyclotron to operate at the associated fixed frequency. This type of flattopping resonator has never before been implemented in a cyclotron and this study is the first to show that it can be done, featuring a special characteristic not offered by other types. The resonator is reviewed against the other types of resonators that are already in use at other institutes around the world. The flat-topping voltage of the selected type has a sinusoidal half-wave distribution along a radial line in each of its acceleration gaps with the nodal points located on the injection and extraction orbits. The flat-topping voltage therefore progressively increases from zero at both of the two most critical orbits in a cyclotron to a maximum at about halfway between them. As a result will this resonator, apart from its basic function to reduce the energy spread in the beam, not decrease the orbit separation at the injection and extraction orbits in the cyclotron, as is the case with other types of flat-topping resonators. This advantageous feature implies that the beam pattern in the cyclotron is not affected in the regions of the delicate injection and extraction components and therefore will these components or the operational control of the beam not require any modification to accommodate the resonator. In order to design a resonator that will meet our requirements, the theory of the beam dynamics and resonator characteristics were studied to ascertain the expected improvement in beam quality and beam intensity when a flat-topping resonator is implemented with the cyclotron. All resonator types were considered and studied in terms of their power dissipation, voltage distribution, harmonic number, space requirements and influence on the beam. The horizontal half-wave resonator type, with two acceleration gaps, was selected as the most suitable for our application, because of its preferred electromagnetic characteristics and its geometric shape that permits the installation inside an existing vacuum chamber through an existing flange. Initially a half-scale resonator model was build to test the feasibility of such a resonator and also to verify the calculation methods. Transmission line methods and numerical field analysis in 3D were applied to determine the resonator characteristics. In the former method a computer program, POISSON, was used to calculate curvilinear squares on sections through a triangular-shaped transmission line and in the latter method a commercial computer program, SOPRANO, was used. SOPRANO is part of an internationally acclaimed suite of programs and the acquired knowledge and skill to use this state-of-the-art software for the studying and designing of such and other electromagnetic devices also put the institute amongst the front-runners in the world. The calculated characteristics of the half- and full-scale resonator models, the study of the different electromagnetic modes that resonate in close proximity to the required frequency, the heat transport modelling and the theory and implementation of the coupling and tuning devices are all in good agreement with their respective measured results and are reported in this document. This study lead the way to have the first-ever double-gap horizontal half-wave flat-topping resonator in a cyclotron successfully commissioned at iThemba LABS and the first tests with beam report very stable operation. Accelerator physicists now have another option to utilize for the establishing of flat-topped acceleration voltages.

<p>Due to the slender geometries of aboveground storage tanks, maintaining the stability under wind gusts of these tanks has always been a challenge. Therefore, this thesis aims to provide a through insight on the behavior of tanks under wind gusts using finite element analysis and computational fluid dynamic (CFD) analysis. The present thesis is composed of three independent studies, and different types of analysis were conducted. In Chapter 2, the main purpose is to model the wind loading dynamically and to investigate whether a resonance can be triggered. Research on tanks subjected to static wind load have thrived for decades, while only few studies consider the wind loading dynamically. Five tanks with different height (<i>H</i>) to diameter (<i>D</i>) ratios, ranging from 0.2 to 4, were investigated in this chapter. To ensure the quality of the obtained solution, a study on the time step increment of an explicit dynamic analysis, and a on the mesh convergence were conducted before the analyses were performed. The natural vibration frequencies and the effective masses of the selected tanks were first solved. Then, the tanks were loaded with wind gusts with the magnitude of the pressure fluctuating at the frequency associating with the most effective mass and other frequencies. Moreover, tanks with eigen-affine imperfections were also considered. It was concluded that resonance was not observed in any of these analyses. However, since the static buckling capacity and the dynamic buckling capacity has a relatively large difference for tall tanks (<i>H</i>/<i>D </i>≥ 2.0), a proper safety factor shall be included during the design if a static analysis is adopted. </p> <p> </p> <p>Chapter 3 focus on the effect of an internal pressure generated by wind gusts on open-top tanks. Based on boundary layer wind tunnel tests (BLWT), a significant pressure would be generated on the internal side of the tank shell when a gust of wind blow through an open-top tank. This factor so far has not been sufficiently accounted for by either ASCE-7 or API 650, despite the fact that this internal pressure may almost double the design pressure. Therefore, to investigate the effect of the wind profile along with the internal pressure, multiple wind profiles specified in different design documents were considered. The buckling capacities of six tanks with aspect ratios (<i>H</i>/<i>D</i>) ranging from 0.1 to 4 were analyzed adopting geometrically nonlinear analysis with imperfection using an arc-length algorithm (Riks analysis). Material nonlinearity was also included in some analyses. It was observed that the buckling capacity of a tank obtained using ASCE-7/API 650 wind profile is higher than buckling capacities obtained through any other profiles. It was then concluded that the wind profile dictated by the current North American design documents may not be conservative enough and may need a revision. </p> <p> </p> <p>Chapter 4 investigates how CFD can be applied to obtain the wind pressure distribution on tanks. Though CFD has been widely employed in different research areas, to the author’s best knowledge, only one research has been dedicated to investigate the interaction between wind gusts and tanks using CFD. Thus, a literature review on the guideline of selecting input parameter for CFD and a parametric study as how to choose proper input parameters was presented in Chapter 4. A tank with an aspect ratio of 0.5 and a flat roof was employed for the parametric study. To ensure the validity of the input parameters, the obtained results were compared with published BLWT results. After confirming that the selected input parameters produces acceptable results, tanks with aspect ratio ranging from 0.4 to 2 were adopted and wind pressure distribution on such tanks were reported. It was concluded that the established criteria for deciding the input parameters were able to guarantee converged results, and the obtained pressure coefficients agree well with the BLWT results available in the literature. </p>

Visando melhorar a qualidade de vida dos pacientes com perdas de estrutura maxilar faz-se necessária sua reabilitação, seja ela cirúrgica ou protética por meio de próteses obturadoras, esta última, um recurso terapêutico que minimiza os distúrbios funcionais, estéticos e psicológicos. Este estudo avaliou o comportamento biomecânico de prótese obturadora maxilar Classe II de Okay retida por implantes e sistema de retenção ERA®, observando as tensões geradas no tecido gengivo-mucoso e ósseo maxilar. A Análise de Elementos Finitos foi realizada empregando-se um modelo digital desenvolvido a partir da tomografia computadorizada de um indivíduo adulto. Quatro implantes foram posicionados na maxila, em região de incisivo lateral, canino, segundo pré-molar e primeiro molar esquerdos, onde as estruturas do sistema de retenção ERA® foram posicionadas nas extremidades de uma barra metálica e convertidas para serem representadas por superfícies. Utilizou-se o programa Rhinoceros® versão 5.0 para gerar o modelo maxilar BioCAD 3D, incorporando-se os modelos CAD dos implantes, UCLAS e o CAD do sistema de retenção ERA®. O CAD do sistema ERA®, fundido em metal, foi desenvolvido a partir de imagens geradas pelo microCT SkyScan 1176 Bruke no formato BMP e TIFF. Essas imagens no formato TIFF foram exportadas para o software img2dcm, convertidas para o formato DICOM e então exportadas para o software Invesalius que reconstruiu tridimensionalmente gerando uma malha no formato STL. As estruturas finalizadas foram exportadas para software Hyperworks 13.0 e pós-processadas com a visualização de resultados pelo Hyperview, tendo sido aplicada uma força de 80N na plataforma oclusal e de 35N na plataforma incisal. Foi realizada uma análise qualitativa, correspondente à escala de máxima tensão principal e os valores quantitativos expressos em MPa. Ocorreu um deslocamento máximo da prótese obturadora na região sem suporte ósseo, tendo como fulcro a linha de ressecção óssea. Observou-se menos forças de tração do que de compressão. As forças analisadas se mostraram bastante favoráveis à estabilidade da prótese obturadora implanto-retida por se apresentarem bem distribuídas pelo tecido gengivo-mucoso e ósseo da maxila remanescente, indicando que o sistema ERA® de retenção é adequado para reabilitação maxilar das perdas ósseas Classe II de Okay. / Searching to improve quality of life of the patients that had sustained structural maxillary loss with the necessity of rehabilitation, either through surgery or obturator prosthesis, which is a therapeutic resource to minimize functional, esthetic and psychological impairments. This study evaluated the biomechanical behavior of an Okay Class II obturator prosthesis implant retained and ERA® system, analyzing the resultant stress on the soft and bone tissue. The finite element analysis was made with a digital model constructed from a computed tomography. Four implants were positioned on the left maxillae, on the following regions: lateral incisor, canine, second premolar and first molar, with the ERA® system positioned on the extremities of a metallic bar. The software used to create the BioCAD 3D model was Rhinoceros v. 5.0, including the CAD models from the implants, UCLAS and ERA® system. The ERA® CAD model was obtained from a microCT SkyScan 1176 Bruke images, on the BMP and TIFF format. The TIFF images were exported to the img2dcm software, converted in DICOM format and finally exported to the software Invesalius, were the STL mesh was created. All mesh were imported into the software Hyperworks v. 13.0 and the post-processing was visualized on Hyperview. The force applied was of 80N over the occlusal platform and of 35N over the incisal platform. A quantitative analysis was performed, corresponding to the maximum main stress, expressed in MPa. The obturator prosthesis suffered its maximum dislocation on the region with no bone support, with the bone resection line as fulcrum. Less tension forces were observed, when comparing to compression. The forces observed were favorable to maintain the implant retained prosthesis stabilization, with good distribution over the soft and bone tissues, suggesting that the ERA® retention system is suitable to Okay Class II maxillary bone loss.