A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2016 / The blind headings created in room and pillar mining are known to be the high risk areas of the coal mine, since this is where the coal production is actually taking place and hence the liberation of maximum quantity of methane. The ventilation of this region called the localized ventilation is carried out using auxiliary ventilation devices. This ventilation may be planned and be the subject of mine standards, but it is not very well understood and implementation on a day to day basis is usually left to the first level of supervisory staff. Majority of the methane explosions have been found to occur in these working areas and blind headings. The correct use of auxiliary ventilation devices can only be carried out once the effect of the system variables associated with each device is very well understood and can be calculated mathematically. Presently, no mathematical models or empirical formulas exist to estimate the effect of the associated system variables on the flow rates close to the face of the heading. The extent of ventilation of a heading ventilated without the use of any auxiliary device is not clear. Furthermore, to design additional engineering solutions, the flow patterns inside these heading ventilated with the auxiliary ventilation devices needs to be understood. The study of the face ventilation systems and the effect of the system variables associated system with each auxiliary ventilation device can be carried out experimentally, but doing a large number of experiments underground is very difficult as it disturbs the mine production cycles. Furthermore, studying the flow patterns experimentally is even more cumbersome, and can only be done to some extent using smoke or tracer gas. Therefore, Computational Fluid Dynamic‟s (CFD) advanced numerical code ANSYS Fluent was used to study the effect of a number of system variables associated with the face ventilation systems used in blind headings. As part of the procedure, the CFD model used was validated using four validation studies, in which the numerical results were compared with the actual experimental results. The numerical results differed to a maximum of 10% for all the experimental results. The system variables associated with ventilation of a heading, without the use of any auxiliary device, with the use of Line Brattice (LB) and fan with duct were selected. A range of values was chosen for each variable, and scenarios were created using every possible combination of these variables. All the scenarios were simulated in Ansys Fluent, the air flow rates, air velocities, velocity vectors, and velocity contours were calculated and drawn at different locations inside the heading. The effect of each system variable was found using a comparative analysis. The results were represented in simple user-friendly form and can be used to estimate the air flows at the exit of the LB and face of the heading for various settings of the LB and fan and duct face ventilation systems. The analysis of the ventilation of a heading without the use of LB shows that a maximum penetration depth is found with the Last Through Road (LTR) velocity of 1.35m/s. The flow rates and the maximum axial velocities increase with the increase in the LTR velocity up to a depth of 10m (maximum air flowing into a heading of 1.26m3/s and 1.58m3/s is found for the 3m and 4m high heading using 2m/s LTR velocity). For the LB ventilation system the LTR velocities, heading height, length of the LB in the LTR and heading, angle of the LB in LTR, and distance of the LB to the wall of the heading (side wall) were varied to identify clearly the effect of these control variables, on the flow rate at the exit of the LB, and close to the face of the heading. The flow rate at the exit of the LB is found to be proportional to the product of the distance of the LB to the wall in the LTR and heading. The flow rate at the exit of the LB, face of the heading, and inside the heading is found proportional to the LTR velocity and height of the heading. It is found that a minimum length of LB is associated with each distance of the LB to the wall in the heading, to maximize the delivery of air close to the face of the heading. This length is found to be equal to 15m for 1m LB to wall distance, and 10m for 0.5m LB to wall distance. Mathematical models were developed to estimate the effect of each studied system variables on the flow rates at the exit of the LB and close to face of the heading. For the fan and duct systems the length, diameter, and the fan design flow rates were varied. It is found that for a force fan duct system only a maximum of 50% of the total air that reaches the face is fresh and the remaining 50% is recirculated air. The flow rate with the exhaust fan system is found to be much lower than the force fan duct system. It increases with the reduction in duct mouth to heading face distance, and increase in duct diameter. Mathematical models are developed to calculate the flow rates at the face of the heading using the effect of each studied system variable. The research reveals that the ANSYS numerical code is an appropriate tool to evaluate the face ventilation of a heading in a three dimensional environment using full scale models. The South African coal mining industry can benefit from the outcomes of this study, specially the mathematical models, in a number of ways. Ventilation engineers can now estimate the flow rates close to the face of the heading for different practical mining scenarios and ensure sufficient ventilation by using the appropriate auxiliary ventilation settings. The results can easily be developed into training aids using easy to use excel spread sheets to ensure that mineworkers at the coal face have a better understanding of the working of the auxiliary ventilation devices. It can also serve Academia as part of the curriculum to teach the future mining engineers how the different variables associated with the auxiliary ventilation system affect the ventilation in a heading. The research therefore, has the potential to provide a significant step toward, understanding airflow rates delivered by the auxiliary devices close to the face of the heading and the air flow patterns inside the heading as a basis for improving the working environment for underground mineworkers. / MT2017

As demandas do mercado da construção civil têm exigido vãos cada vez maiores e ao mesmo tempo alturas cada vez menores das vigas. Isto tem levado muitos projetistas à adoção da solução do pavimento em laje lisa em concreto armado ou protendido. No entanto, a ausência das vigas torna possível a ruptura das lajes por puncionamento junto aos pilares. A norma NBR-6118:2014 prescreve as disposições para o projeto de lajes sob punção. O trabalho proposto teve como objetivo principal a análise da confiabilidade da ligação laje-pilar interno sob o efeito da punção em lajes que se apoiam diretamente sobre pilares de acordo com a NBR-6118:2014. Primeiramente, com o intuito de se entender melhor o fenômeno da punção, realizou-se uma breve revisão bibliográfica, identificando os principais parâmetros que influenciam na resistência da ligação, assim como os principais métodos de análise e trabalhos realizados na área. Em seguida, estudou-se o software de análise em elementos finitos ANSYS (Analysis Systems Incorporated), especificamente a ferramenta UPF (User Programmable Features), que foi utilizada para adoção de um modelo constitutivo para o concreto. Utilizando o software, foram modeladas lajes estudadas por outros autores, visando a validação do modelo numérico. Para o estudo da confiabilidade foi dimensionado um conjunto de lajes lisas seguindo as prescrições da NBR 6118:2014. A análise da confiabilidade foi realizada utilizando a ferramenta PDS (Probabilistic Design System), empregando o método de simulação numérica de Monte Carlo com amostragem por Latin Hypercube. Por fim, determinou-se o índice de confiabilidade em cada projeto e realizaram-se análises paramétricas com as variáveis adotadas no trabalho. Os resultados obtidos mostraram que as lajes lisas sem armadura de cisalhamento projetadas segundo a NBR 6118:2014 obtiveram, em sua maioria, índices de confiabilidade adequados. Porém, para as lajes lisas com armadura de cisalhamento, o índice de confiabilidade foi, em grande parte, menor que o índice de confiabilidade alvo adotado. / The demands of the construction market have required increasingly large spans while diminishing of the beam heights. This has led many designers to adopt the pavement solucion of reinforced or prestressed concrete flat slab. However, the absence of the beams makes it possible to slabs failure by punching shear. The Standard NBR-6118: 2014 prescribes the requirements for the design of slabs under punching. The aim of this work was to analyze the reliability of the internal slab-column intersection under punching in slabs supported directly on columns according to NBR-6118: 2014. Firstly, in order to better understand the punching phenomenon, a brief bibliographic review was carried out, identifying the main parameters that influence the connection strength, as well as the main methods of analysis and published in the area. Then, the finite element analysis software ANSYS (Analysis Systems Incorporated), specifically the UPF (User Programmable Features) tool, was used to adopt a concrete constitutive model. Using the software, slabs studied by other authors were modeled, aiming at the validation of the numerical model. For the reliability study, a set of flat slabs was designed following the requirements of NBR 6118: 2014. The reliability analysis was performed using the PDS (Probabilistic Design System) tool, using the Monte Carlo numerical simulation method with Latin Hypercube sampling. Finally, the reliability index was determined in each project and parametric analyzes were performed with the variables adopted in the study. The results from this study show that the flat slabs without shear reinforcement designed according to NBR Standarts obtained appropriate reliability index. However, for the flat slabs with shear reinforcement, the reliability index, in most cases, did not achieve the target reliability index.

abstract: The advancements in additive manufacturing have made it possible to bring life to designs that would otherwise exist only on paper. An excellent example of such designs are the Triply Periodic Minimal Surface (TPMS) structures like Schwarz D, Schwarz P, Gyroid, etc. These structures are self-sustaining, i.e. they require minimal supports or no supports at all when 3D printed. These structures exist in stable form in nature, like butterfly wings are made of Gyroids. Automotive and aerospace industry have a growing demand for strong and light structures, which can be solved using TPMS models. In this research we will try and understand some of the properties of these Triply Periodic Minimal Surface (TPMS) structures and see how they perform in comparison to the conventional models. The research was concentrated on the mechanical, thermal and fluid flow properties of the Schwarz D, Gyroid and Spherical Gyroid Triply Periodic Minimal Surface (TPMS) models in particular, other Triply Periodic Minimal Surface (TPMS) models were not considered. A detailed finite element analysis was performed on the mechanical and thermal properties using ANSYS 19.2 and the flow properties were analyzed using ANSYS Fluent under different conditions. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2019

Tese de mestrado integrado. Engenharia Civl (especialização em Geotecnia). Faculdade de Engenharia. Universidade do Porto. 2008

Estágio realizado na CaetanoBus e orientado pelo Eng.º Mário Filipe Dias Fernandes / Tese de mestrado integrado. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 2010

Hundreds of thousands of dollars could be lost due to failures during the fabrication of Trunnion-Hub-Girder (THG) assemblies of bascule bridges. Two different procedures are currently utilized for the THG assembly. Crack formations in the hubs of various bridges during assembly led the Florida Department of Transportation (FDOT) to commission a project to investigate why the assemblies failed. Consequently, a research contract was granted to the Mechanical Engineering department at USF in 1998 to conduct theoretical, numerical and experimental studies. It was found that the steady state stresses were well below the yield strength of the material and could not have caused failure. A parametric finite element model was designed in ANSYS to analyze the transient stresses, temperatures and critical crack lengths in the THG assembly during the two assembly procedures. The critical points and the critical stages in the assembly were identified based on the critical crack length. Furthermore, experiments with cryogenic strain gauges and thermocouples were developed to determine the stresses and temperatures at critical points of the THG assembly during the two assembly procedures. One result revealed by the studies was that large tensile hoop stresses develop in the hub at the trunnion-hub interface in AP1 when the trunnion-hub assembly is cooled for insertion into the girder. These stresses occurred at low temperatures, and resulted in low values of critical crack length. A suggestion to solve this was to study the effect of thickness of the hub and to understand its influence on critical stresses and crack lengths. In addition, American Association of State Highway and Transportation Officials (AASHTO) standards call for a hub radial thickness of 0.4 times the inner diameter while currently a thickness of 0.1 to 0.2 times the inner diameter is used. In this thesis, the geometrical dimensions are changed according to the design of experiments standards to find the sensitivity of these parameters on critical stresses and critical crack lengths during the assembly. Parameters changed are hub radial thickness to trunnion outer diameter ratio, trunnion outer diameter to trunnion bore diameter ratio and variations of the interference. The radial thickness of the hub was found to be the most influential parameter on critical stresses and critical crack lengths.

The application of advanced composite materials, such as graphite/epoxy, has been on the rise for the last four decades. The mechanical advantages, such as their higher specific stiffness and strength as compared to monolithic materials, make them attractive for aerospace and automotive applications. Despite these advantages, composites with brittle fibers have lower ductility and fracture toughness than monolithic materials. One way to increase the fracture toughness of composites is to have a weak fiber-matrix interface that would blunt crack tips by crack deflection into the interface and hence enhance fracture toughness. However, this also reduces the transverse properties of the composite. Therefore, an optimum fiber-matrix interface would be the one that is just weak enough to cause crack deflection into interface. This study investigates the effect of fiber-to-matrix moduli ratio, fiber-volume fraction, fiber orthotropy, and thermal stresses on the possibility of crack deflection. A finite element model is used to analyze a 2-D axisymmetric representative volume element- a three-phase composite cylinder made of fiber, matrix, and composite. A penny shaped crack is assumed in the fiber. To determine whether the crack would deflect into the interface or propagate into the matrix, maximum stresses at the fiber-matrix interface and in the matrix are compared to the interface and matrix strengths. As opposed to most studies in the literature, this study found that fiber-volume fractions do have an impact on crack deflection and this impact increases with large fiber-to-matrix moduli ratios. The presence of orthotropic fiber in the composite increases the possibility of crack deflection with increasing fibervolume fraction in the early and middle stages of the fiber crack growth. The thermal stresses decrease the likelihood of crack deflection when the thermal expansion coefficient of the matrix is larger than that of the fiber.

Many different hub assembly procedures have been utilized over the years in bascule bridge construction. The first assembly procedure (AP1) involves shrink fitting a trunnion component into a hub, followed by the shrink fitting of the entire trunnion-hub (TH) assembly into the girder of the bridge. The second assembly procedure (AP2) involves shrink fitting the hub component first into the girder, then shrink fitting the trunnion component into the hub-girder (HG) assembly. The final assembly procedure uses a warm shrink fitting process whereby induction coils are placed on the girder of the bridge and heat is applied until sufficient thermal expansion of the girder hole allows for insertion of the hub component. All three assembly procedures use a cooling method at some stage of the assembly procedure to contract components to allow the insertion of one part into the next. Occasionally, during these cooling and heating procedures, cracks can develop in the material due to the large thermal shock and subsequent thermal stresses. Previous works conducted a formal design of experiments analysis on AP1 to determine the overall effect of various factors on the critical design parameters, overall minimum stress ratio (OMSR) and overall minimum critical crack length (OMCCL). This work focuses on conducting a formal design of experiments analysis on AP1, AP2 and AP3 using the same cooling methods and parameters as in previous studies with the addition of the bridge size as a factor in the experiment. The use of the medium bridge size in AP1 yields the largest OMCCL values of any bridge and the second largest OMSR values. The large bridge size has the largest OMSR values versus all factors for AP1. The OMCCL and OMSR increases for every bridge size with an increase in the alpha ratio for AP1. The smallest bridge showed the largest OMCCL and OMSR values for every cooling method and every alpha ratio for AP2 and AP3. The OMCCL and OMSR decrease for every bridge size with an increase in the alpha ratio for AP2 and AP3.

The aim of this study is to investigate the fluid-structural response to pulsatile Newtonian and non-Newtonian blood flow through an axisymmetric stenosed vessel using FLOTRAN and ANSYS. This is to provide a basic understanding of atherosclerosis. The flow was set to be laminar and follows a sinusoidal waveform. The solid model was set to have isotropic elastic properties. The Fluid-Structural Interaction (FSI) coupling was two-way and iterative. Rigid and Newtonian cases were investigated to provide an understanding on the effects of incorporating FSI into the model. The wall expansion was found to decrease the axial velocity and increase the recirculation effects of the flow. To validate the models and methods used, the results were compared with the study by Lee and Xu [2002] and Ohja et al [1989]. Close comparisons were achieved, suggesting the models used were valid. Two non-Newtonian models were investigated with FSI: Carreau and Power Law models. The Carreau model fluid behaviour was very close to the Newtonian model. The Power Law model produced significant difference in viscosity, velocity and wall shear stress distributions. Pressure distribution for all models was similar. In order to quantify the changes, Importance Factor (IG) was introduced to determine the overall non-Newtonian effects at two regions: the entire flow model and about the vessel wall. The Carreau model showed reasonable values of IG whereas the Power Law model showed excessive values. Transient and geometrical effects were found to affect the Importance Factor. The stress distributions for all models were found to be similar. Highest stress occurred at the shoulders of the stenosis where a stress concentration occurred due to sharp corners of the geometry and large bending moments. The highest stresses were in the axial direction. Notable circumferential stress was found at the ends of the vessel. Carreau model produced slightly higher stresses than the other models. Wall stresses were found to be primarily influenced by internal pressure, rather than wall shear stresses.

<p>The purpose of this thesis for Sapa Heat Transfer is to examine a furnace in which aluminium is pre-heated before hot rolling. The project is modeled in a computer environment in which the air flow in the furnace and the heat transfer to the aluminium solids are included. The computer environment and its governing equations, as well as boundary conditions and generalizations, are presented and explained.</p><p>The simulations are based on two models. The first model has an asymmetric solid placement, which is how it looks in today's ovens. It is validated against collected data. The second model has a symmetric solid placement, in which improvements are introduced and evaluated.</p><p>The results indicate that a symmetric positioning of metal solids in the oven is preferable in order to achieve a good airflow distribution. The use of plates has been proven useful for steering the air to critial areas and to get an even distribution of the airflow. Lastly the simulations indicate that an increased airflow can compensate the less optimal flow distribution that arises with asymmetric solid placements.</p>