Masters Degrees (Mechanical Engineering)

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Analysis of residual stresses and distortions resulting from multi-pass welding of nozzles to cylindrical pressure vessels.
(2012) Zondi, Mthobisi Clyde.; Adali, Sarp.
The purpose of the present study is to obtain insight into the formation, behaviour and magnitude of welding-induced residual stresses and distortions resulting from welding nozzles onto cylindrical pressure vessels. A hybrid methodology that comprises numerical analysis, experimental measurements and empirical calculations is used in the present study. The welding process induces a high thermal gradient on the material due to non-uniform temperature distribution; thereby causing the portion of the material that is exposed to high temperatures to expand. However, the relatively cooler material portion that is away from the weld pool resists such expansion, thereby subjecting the structure to stresses and distortions around the fusion zone (FZ) and the heat-affected zone (HAZ). Over the last two decades a number of studies have been done in an effort to predict the effect of welding-induced residual stresses on the integrity of welded structures. However, to this end, such studies have focussed on analysing residual stresses on bead-on-plate, plate-to-plate and [to a less extent] on pipe-to-pipe weld joints. Fewer studies have looked at nozzle-cylinder joints of pressure vessels as is the case in this study. The second chapter gives a detailed review of applicable literature. The constitutive model described in the third chapter includes a two-phase sequentially-coupled thermo-mechanical analysis, which incorporates metallurgical effects. The non-linear transient problem is solved using an axisymmetric 2D model with ‘element birth’ technique, developed on ABAQUS. The first phase comprises the thermal analysis based on Goldak’s moving heat source model that is used to determine temperature histories. The second phase is a sequel stress/strain analysis wherein the temperature fields are used as input loads. The results discussed in chapters three and four show that there is a high concentration of residual stresses close to the weld centre-line, and these die down as distance away from centre-line increases. It is also shown that the inside surface is under tensile stresses, while the outer surface is under compressive stress, whose magnitude approaches yield strength of the material. Axial deflections of up to 0.384mm and radial shrinkage of 0.0237mm are observed. Distortion decreases as distance away from weld centre-line increases. Minimum axial shrinkage, which is close to zero, is observed at the restrained end. The analytical results show adequate corroboration and agreement with the experimental measurements. A number of mitigation techniques are suggested in order to alleviate the impact of residual stress and distortions on fatigue performance of welded structures.
Buckling of short, thin-walled cylinders, as applied to storage tanks.
(2001) Du Poujol, Geraldine Touche.; Bodger, Robert.; Adali, Sarp.
This is an investigation of the buckling characteristics of short, thin-walled cylinders. This study was required as large storage tanks, which were converted from Boating roof to fixed roofed tanks, were found to buckle when severe atmospheric temperature drops and thus pressure differentials occurred. These severe ambient temperature changes are characteristic of the Highveld in South Africa where the tanks in question are situated. Since this modification is an uncommon procedure, codes of practice for storage vessels do not cover this type of cylinder. For the same reason, research performed in this field is limited. Buckling due to axial loading, lateral external pressure, hydrostatic pressure and a combination of axial loading and hydrostatic pressure are explored in this study. To compare with and verify theory, existing research for each case is examined, and the Finite Element Analysis package MSC Nastran used to determine trends. In some cases, to the best of the author's knowledge, no research exists and numerical analysis is performed to establish the relationships present in those cases. The study is extended to include the design of imperfect cylinders, as defined in the tank code AD Merkblatter where it is stated as being dependant on the major and minor diameters of the imperfect section . The study is also extended to the case of variable wall thickness cylinders, where the thickness variation is symmetrical about the axis of the cylinder.
Buckling of woven fibre and graphene platelet reinforced nanocomposite laminates.
(2021) Sewnath, Kiren.; Adali, Sarp.; Drosopoulos, Georgios A.
Composite materials are known for exhibiting high specific stiffness, strength and light weight. Their properties can be optimized by designers for a specific application. They currently have many applications in various industries such as aerospace, automotive and building industries. Fibre reinforced polymer composites are a large portion of the composite material market. The use of such materials has many advantages. Recently, nanosized reinforcements such as carbon nanotubes and graphene nanoplatelets have also been used as filler materials in composites. Graphene is one of the strongest materials available today and exhibits excellent mechanical properties. The study presented here is an investigation into the buckling of a woven glass fibre and graphene nanoplatelet reinforced epoxy composite. A laminate analogy is utilised. The analytical equations governing these types of laminates are presented and incorporated into Matlab, a computer simulation software that makes use of matrix implementations. The programme is then used to investigate the effects of various design parameters on the buckling load, by generating 2D and 3D graphs. In this study, a laminate analogy is used for the woven glass fibres whereby undulation of the fibres is neglected, and the composite is regarded as an assembly of cross-ply laminates with woven fibres orientated at 90° to each other. The Halpin-Tsai equations are used to incorporate the graphene nanoplatelets into the epoxy matrix. The laminate that is investigated consists of 4 plies, each reinforced by woven glass fibres and graphene nanoplatelets. The laminate is symmetric about its midpoint, such that the two outer layers are identical, and the two middle layers are identical. Layer thicknesses are non-uniform and the reinforcements are distributed non-uniformly in the layers. The thickness ratio of the laminate is defined as the ratio of the total width of the outer layers to the entire laminate thickness. The governing equations of classical laminate theory for buckling of a simply-supported rectangular plate under biaxial loading are used to predict the critical buckling load of the laminate. The bending-twisting coupling terms are neglected. The results generated display the influence of various design parameters on the buckling load. The design parameters investigated are the woven glass fibre volume fraction, woven glass fibre orientation, woven glass fibre balancing coefficient, graphene platelet weight fraction, laminate thickness ratio and laminate aspect ratio. The results show that the graphene nanoplatelets have a greater effect on the buckling load than the woven glass fibres. High graphene content can obscure the effect of the woven fibre orientation and laminate aspect ratio on the buckling load. At low graphene contents, a more concentrated fibre distribution in a single direction (warp or weft) is preferred for the buckling load. At higher graphene content, a more evenly balanced distribution is preferred. Furthermore, for high thickness ratios, more focus must be placed in the reinforcements in the outer layer of the laminate for a cost-effective design.
A comparative study on the effects of internal vs external pressure for a pressure vessel subjected to piping loads at the shell-to-nozzle junction.
(2003) Maharaj, Ashveer.; Adali, Sarp.; Von Klemperer, Christopher Julian.
This investigation seeks to perform a comparative study between the combined effects of internal pressure and piping loads versus external pressure and piping loads on a pressure vessel. There are currently several well-known and widely-used procedures for predicting the stress situation and the structural stability of pressure vessels under internal pressure when external piping loads (due to thermal expansion, weight, pressure, etc.) are applied at the nozzles. This project familiarises one with several international pressure vessel design Codes and standards, including AS ME (American Society of Mechanical Engineers) pressure vessel code sections and WRC (Welding Research Council) bulletins. It has been found that many vessels are designed to operate under normal or steam-out conditions (in vacuum). The combined effect of the external atmospheric pressure and the piping loads at the nozzle could be catastrophic if not addressed properly - especially when the stability of the structure is a crucial consideration, i.e. when buckling is a concern. The above-mentioned codes and standards do not directly address procedures or provide acceptance criteria for external loads during vacuum conditions. The approach to the study was, firstly, to investigate the effects of internal pressure and piping loads at the shell-to-nozzle junction. Theoretical stresses were compared with Finite Element results generated using the software package MSC PATRAN. Finite Element Methods provide a more realistic approach to the design of pressure vessels as compared to theoretical methods. It was necessary to determine if the theoretical procedures currently used were adequate in predicting the structural situation of a pressure vessel. Secondly, the buckling effects of vessels subjected to external atmospheric pressure and piping loads were also investigated. Buckling of the shell-to-nozzle region was explored with the aid of Finite Element software. The results gained were used to develop appropriate procedures for the design of vessels under external atmospheric pressure and piping loads. The design is such that it indicates if buckling will occur at the shell-to-nozzle junction. These design procedures form the basis for future exploration in this regard.
Design and optimisation of a composite space frame chassis including experimental and computational analysis.
(2017) Narsai, Mikhail.; Adali, Sarp.; Padayachee, Jared.; Veale, Kirsty Lynn.
Composites are used in lightweight structural designs. In this dissertation, a robust carbon fibre reinforced polymer (CFRP) space frame chassis for a lightweight electric tricycle is produced. In large, most composite research is directed toward flat laminates rather than closed sections. This dissertation addresses the complexities of stresses at joints and buckling (local and global). The space frame design consists of two segments of iterations. The second and more important segment is based on optimisation using NX Nastran finite element analysis (FEA). The final design incorporates the use of steel sleeves to address stress concentrations at joins and local buckling. The design and execution of a new test method was developed to validate FEA results. The test method involves applying compressive stress on tubes fabricated using unidirectional (UD) fibre set at 35°, to induce compressive and shear stresses along the primary fibres. In this way, four major failure criteria were compared: Tsai-Wu, Hoffman, Hill and Maximum Strain. The Hoffman and Tsai-Wu criteria were shown to be accurate and conservative. The Hill criteria showed inaccuracy by having incorrectly high strength ratios, while the Maximum Strain criteria had the highest strength ratio, proving to be the least conservative and most inaccurate. This dissertation shows that certain failure criteria may be used confidently in applications such as filament winding and continuous pulComposites are used in lightweight structural designs. In this dissertation, a robust carbon fibre reinforced polymer (CFRP) space frame chassis for a lightweight electric tricycle is produced. In large, most composite research is directed toward flat laminates rather than closed sections. This dissertation addresses the complexities of stresses at joints and buckling (local and global). The space frame design consists of two segments of iterations. The second and more important segment is based on optimisation using NX Nastran finite element analysis (FEA). The final design incorporates the use of steel sleeves to address stress concentrations at joins and local buckling. The design and execution of a new test method was developed to validate FEA results. The test method involves applying compressive stress on tubes fabricated using unidirectional (UD) fibre set at 35°, to induce compressive and shear stresses along the primary fibres. In this way, four major failure criteria were compared: Tsai-Wu, Hoffman, Hill and Maximum Strain. The Hoffman and Tsai-Wu criteria were shown to be accurate and conservative. The Hill criteria showed inaccuracy by having incorrectly high strength ratios, while the Maximum Strain criteria had the highest strength ratio, proving to be the least conservative and most inaccurate. This dissertation shows that certain failure criteria may be used confidently in applications such as filament winding and continuous pultrusion methods, which are widely used in producing closed sections.trusion methods, which are widely used in producing closed sections.
A design methodology investigation and the design of a material handling system.
(2000) Govender, Daryl Sebastian.; Adali, Sarp.; Verijenko, Viktor.
This dissertation is undertaken under the auspices of both the CSIR, Division of Mining Technology and the University of Natal, School of Mechanical Engineering. The CSIR have outlined two fundamental objectives of the dissertation. Firstly, the need for competent design engineers has become increasingly evident. To this end, an evaluation and research into the science of design methodology has been conducted and regarded as a significant component of the thesis. The rationale behind this aim is that the subject of design has been practiced for thousands of years, but an understanding of the process is comparably in its infancy. The importance of the steps involved in the mechanical design process can in no uncertain terms be overemphasized as the adherence there to results in designs that are least likely prone to failure as well as the attainment of highly efficient product design time scales. This is vitally important more especially when the drive towards multifunctional multidisciplinary teams is rapidly developing in the global market place. Secondly, the CSIR, having done the appropriate market research, have defined the need for the design of a timber handling system to be implemented in a deep level mining environment. It is the authors expressed intent not to separate the theory from the design at hand but rather to allow this thesis to become, for the reader, forum where a holistic and integrated approach to design can be presented.
Development of a design methodology of a composite monocoque chassis.
(2018) Denny, Jason Andrew.; Adali, Sarp.; Veale, Kirsty Lynn.; Leverone, Fiona Kay.
The concept of the composite monocoque chassis has been implemented in many vehicle designs; however, there is little open-access literature defining the primary considerations when simulating one. The purpose of this research is to develop a methodology for determining the structural integrity of a composite monocoque chassis, through finite element analysis, with the intention of developing a lightweight solar powered vehicle. Factors that influence this methodology include; the definition of the vehicle loading conditions, failure criteria, and important design parameters, chief among which is the torsional stiffness. Chassis design specifications were developed from the 2017 Bridgestone World Solar Challenge rules and regulations as these are the most common and complete specifications for this particular type of vehicle. The primary design criteria considered is the torsional stiffness, which was determined from the application requirements and literature, and resulted in a suitable value of 4000 Nm/deg. Siemens NX Nastran was used to develop a torsional stiffness model, which uses the torsional loading condition, to determine the torsional stiffness value. The design methodology then follows an iterative process where various geometry and layup modifications were considered, under the same loading conditions, with the aim of increasing the torsional stiffness to achieve the required value. Aerodynamic properties were adapted from existing UKZN solar vehicle knowledge; however, this research does not consider the optimisation of the aerodynamic properties of a monocoque chassis. Only a structural simulation was conducted. The ultimate strength of the material was also considered throughout the simulation process, however in all cases the model failed to meet the required torsional stiffness parameter before material failure modes. The door recesses had the most significant effect on the torsional stiffness. By compacting the door recesses the torsional stiffness was increased by 29.04 %. A final torsional stiffness was of 4097 Nm/deg was attained with the implementation of an aluminium honeycomb core. Additionally; an analysis of the mounting points was conducted to ensure that the layup can withstand the concentrated loads at the suspension mounts. This analysis is concerned with the principal stresses, where the principal stresses give insight into the most suitable orientation of the layup. The torsional stiffness model resulted in a maximum principal stress of 81.68 MPa, below the 464.4 MPa tensile strength of the reinforcement material orientated in the direction of the fibres. To verify the significance of the torsional stiffness failure criterion, vertical and lateral bending analyses were conducted. A vertical bending model was developed where the chassis is modelled as a simply supported beam, simulating the squatting and diving of a chassis under acceleration and deceleration respectively. The maximum deflection was 5.28 mm, which is below the vi maximum allowable deflection of 12.29 mm, determined from a maximum deflection ratio of 1/360th of chassis length. A lateral bending model modelled the chassis as a simply supported beam with the maximum stress being analysed. The maximum stress experienced by the chassis under this loading condition was 18.73 MPa, which was 75.8 % less when compared to the maximum stress exhibited by the chassis under the torsional loading condition. Flexural bending tests were conducted on various laminate sandwich structures used in the finite element analysis to validate the simulation material properties. The peak load and mid-span deflection of each specimen was recorded to determine the maximum flexural stress and flexural modulus of elasticity. The flexural stress at specific midspan deflections was compared, under the same loading conditions, to that of the bending stress exhibited by a flexural bend test model finite element analysis conducted in Siemen’s NX Nastran. Graphs of the stress versus midspan deflection were plotted for each specimen layup type and the curves of the simulated and experimental results were compared. In each laminate sandwich structure case, the simulation curve exhibited a linear relationship between the midspan deflection and flexural bend stress and the experimental curve exhibited a linear relationship until the elastic limit of the specimens was reached. Thereafter the curve exhibited an exponential relationship as plastic deformation occurs until the specimen failure. An iterative finite element analysis design methodology was used to develop a composite monocoque chassis. The design process of a composite monocoque chassis is simplified by using finite element analysis to iterate through many different configurations, such as core thicknesses, layup orientations, and geometry features, to customise the properties of the structure. With these properties, it is possible to determine chassis performance. The finite element analysis results illustrated that geometry modifications, such as compacting door recesses, and applying strategic layup orientations, such as implementing a honeycomb core, significantly affected the torsional stiffness of a chassis. In addition, a chassis with sufficient torsional stiffness exhibits sufficient bending stiffness. The methodology presented in this research stands to be supportive in designing a fully composite monocoque chassis for lightweight race vehicle applications.
Effect of displacement feedback control on the frequencies of cantilevered beams with tip mass and axial load using piezo actuators.
(2014) Moutlana, Malesela K.; Adali, Sarp.
This work provides a study of the natural frequencies of a cantilevered beam with tip mass and axial load. Displacement feedback control is applied using piezo actuators attached to the top and bottom of the beam. The center of gravity of the mass and its rotary inertia are accounted for in the solution. The analysis of flexible components is essential to provide for the successful design of various engineering structures. This study provides an analytical solution to the dynamic behavior of a cantilevered beam carrying a mass at the free end, while being subjected to constant axial load. The structure is modeled using the Euler-Bernoulli theory and the contributions of the mass, thickness and stiffness of the piezoelectric actuators to the structure are taken into account. The effects of the piezo input voltage polarity is also taken into account. The natural frequencies of the beam can be altered by applying a voltage in the desired polarity and thereby causing an extension or contraction in the piezo actuator. This mechanical response alters the frequencies of the piezoelectric beam. The piezoelectric effect causes a compression or extension strain when a voltage is applied along the direction of polarization. The strain in the piezoelectric beam causes a moment at the free end, which directly affects the natural frequencies. By applying a voltage in the same or opposite direction of the poling of the piezo, the result is a compression or extension perpendicular to the poling. An applied voltage in the same direction can be considered positive and reduces the frequencies, whilst in the opposite direction negative and increases the natural frequencies. In this investigation the piezo layer thickness is varied, which in turn allows for a variable voltage input. For a thicker layer, the voltage can be increased and the actuation strain increased. The frequency content of the dynamically varying forces applied to a structure has the potential to excite the structure at one or more of its natural frequencies. Using piezo actuators, the natural frequencies and the natural frequency gaps can be maximized. Maximizing the natural frequencies is useful to avoid resonance when the external excitation frequency is less than the natural frequency.
Low-cost sensory glove for human-robot collaboration.
(2020) Bright, Tyrone William John.; Adali, Sarp.; Athol-Webb, Avern Malcom.
Human Robot Collaboration (HRC) is a technique that enables humans and robots to co-exist in the same environment by preforming operations together. HRC has become a vital goal for industry to achieve progress towards the fourth industrial revolution (Lotz, Himmel, & Ziefle, 2019) as it focuses on creating advanced production/manufacturing plants that have high levels of productivity, efficiency, quality and automation. Sensory gloves can be used to enhance the Human Robot Collaboration environment in order to achieve progress towards Industry 4.0. It can provide a safe environment where humans and robots can interact and work in conjunction. However, challenges exist in terms of cost, accuracy, repeatability and dynamic range of such devices. The project researched and developed a low-cost sensory glove to enable a user to collaborate with an industrial robot in a production environment. The sensory glove was used to provide a process whereby humans could collaborate with the robot through physical interaction under safe conditions. The sensory glove used IMU sensors in order to track the orientation of the user’s hand accurately. An algorithm was developed and designed to extract the data from the glove and create a simulated three-dimensional render of the hand as it moved through free space. This involved the design and development of an electronic system architecture that powers the glove. A control system was developed to enable the extraction of data and create the simulated three-dimensional hand model. It produced the image that the robot would sense when interacting with the worker. Testing was conducted on the cost, accuracy, dynamic range, repeatability and potential application of the system. The results showed that it was an innovative and low-cost method for humans and robots to collaborate in a safe environment. The apparatus established a process whereby humans and robots could perform operations together.
Multiscale nanocomposites and laminates reinforced by carbon nanotubes and fibres.
(2020) Zeeman, Morné.; Adali, Sarp.
The addition of nanomaterials to conventional composites as reinforcement results in a new generation of composites, namely, multiscale composites. Multiscale composites comprise of reinforcements from two or more different length scales such as macro, micro and nano hence the name multiscale. Developing a computational modelling approach which analyses the flexural response of nanocomposites at the nanoscale, which is not restricted by time scales, would benefit future studies in the field of nanotechnology. The dissertation details the analysis of carbon nanotube reinforced composites. The key focus areas include micromechanical modelling of both two and three phase nanocomposites along with their applications to structural elements. Furthermore, the flexural behaviour of a simply supported hybrid plate element subjected to a uniform transverse pressure is analysed under various conditions. Firstly, both carbon and glass fibre reinforced composites are investigated along with a nanomaterial such as carbon nanotubes (CNT) to form a multiscale epoxy composite. Modelling techniques such as Mori-Tanaka and Halpin-Tsai approaches are furthered in order to investigate the mechanical properties of both two-phase and three-phase composites. The results obtained from these models are compared to theoretical and experimental results available in the literature. Secondly, the material properties obtained are then used to investigate the bending behaviour of a CNT/fibre/polymer cross-ply laminate by incorporating micromechanical modelling techniques with structural mechanics. Numerical results are then obtained and used to study the effect of various problem parameters such as agglomeration, different fibre reinforcements, material layup and nanotube diameter. The numerical results given in this study provides a quantitative analysis of the effects of different types of CNT parameters, fibre reinforcements and the volume fractions on the static behaviour of laminated composites.
The optimisation of train make-up and train handling-simulating longitudinal train dynamics.
(2000) Majola, Lumko.; Verijenko, Viktor.; Adali, Sarp.
The South African rail industry is undergoing a phase of restructuring and much focus is concentrated on re-engineering i.e. optimising the utilisation of available assets and using existing technology in order to improve efficiency; attention shifts to improved heavy haul asset management through train performance models. The computer programs presented in this thesis have been developed to calculate longitudinal in-train forces accruing in long heavy haul trains and their effect on train operations. The model of the train is implemented by dedicated differential equations for the movements of each vehicle. The simulation is menu driven for all input and output decisions using Microsoft Excel while the engine for the dynamic analysis is ACSL (Advanced Continuous Simulation Language). The main program is capable of simulating the operation of any train configuration over any route, including remote operation. The thesis comprises: - • a discussion on the need for alternative train configurations based on the current fleet and the potential of such operating changes; • the comparison of the dynamic response of trains operating with only head-end locomotives, trains operating with both head-end locomotives and remote locomotives and trains operating with different class locomotives in one locomotive consist; • the investigation of the lateral effects in the different train consists as a function of the longitudinal in-train force in the simulation environment; • the advantages of operating with remote locomotives in terms of increased train length, reduced force spectrum on vehicle components and improved energy consumption; • the implications of the optimum position of the in-train locomotive consist on loading and unloading operations; • the implications of different train configurations on driver technique or train handling and the need for an optimum driving strategy to gain maximum benefit from the locomotives.
Parametric studies on the temperature dependent behaviour of steel structures within a fire context.
(2012) Govender, Stanton Wesley.; Adali, Sarp.
The mechanical and material properties of structural steel at elevated temperatures play an important role in structural fire design. The South African 350W and S355 structural steels are common in building structures with S355 slowly replacing the older 350W. The cost and feasibility of full scale fire tests are some of the causes for the lack of experimental data on the behaviour of steel structures when exposed to fire. Therefore excessively conservative design codes based on isolated laboratory experiments are used in practice which leads to increased material costs. Another area of concern with respect to building safety is the reusability of structural steels post fire exposure, which is not effectively addressed within these codes. This study aims to establish greater insight into structural fire design and simulation on which further research can be built. Experimental programs on the temperature dependent behaviour of these steel members loaded axially are conducted and compared with theory and the Eurocode 3 standard [1]. The reusability of steel exposed to fire and after being cooled down is investigated and compared to the findings by Outinen [2]. Further testing on material to determine the relationship between remaining life and hardness degradation after cooling down was conducted. Experimental data from various external studies are used to develop novel computer models using the finite element analysis software, SimXpert [3]. These are verified against the original data and compared to existing design codes. A parametric approach is used with these models to demonstrate the advantages of computer simulations in structural fire design. Different cross sections and slenderness ratios are evaluated for their susceptibility to buckling at elevated temperatures. The results of this study show that as temperature and exposure time increase the integrity of steel members decrease. The current design codes accurately predict the behaviour of isolated specimens but lack data on real situations where the specimen is part of a complex structure. It was found that steel members can be reused if their exposure temperature does not exceed 700°C, after which their strength can reduce to 90%. This temperature dependant behaviour was successfully modelled using basic computer simulations and then demonstrated the ease in which they can be used in place of experimental regimes. The parametric advantages of these simulations were demonstrated by predicting the effects of slenderness ratios and geometry cross sections on the buckling behaviour.
Power efficiency of industrial equipment.
(2011) Veale, Kirsty Lynn.; Roberts, Lancian Willett.; Adali, Sarp.
Power conservation has become a high priority to South African industries due to recent environmental assessments and electricity price hikes. This research aims to demonstrate to Industry the many simple and cost effective ways to increase their industrial efficiency with simple modifications, as well as making them more aware of common assembly errors that significantly increase power consumption. This has been accomplished with the design, construction and testing of a test rig capable of producing the desired test results which simulate Industry usage. A test rig was required to test certain energy efficient equipment. This dissertation contains an explanation of the tests required, as well as how they were conducted. These test requirements directed the design outcomes of the test rig. Due to the variety of equipment to be tested, and the accuracy required, the test rig had to be fully adjustable. The design process is explained in this dissertation, along with relevant theory with regard to the testing procedures. The testing procedures were designed to be as accurate as possible. The setup equipment and procedure is briefly explained to ensure an understanding of the capabilities of the test rig. This dissertation contains the results obtained from testing a variety of couplings, belts and motors under different conditions. The results obtained show the difference between the efficiency of a standard motor and that of a high efficiency motor. The efficiency comparison of the Poly V TM, Poly Chain® and SPB V-belts showed very distinct advantages and disadvantages of each belt. The coupling testing was conducted under conditions of misalignment, and resulted in distinct differences in the efficiencies of each coupling at different degrees of misalignments. The couplings tested were the Fenaflex®, the Quick-Flex®, and the Fenagrid® coupling. All results obtained were analyzed and discussed in the relevant sections. The results obtained showed that the high efficiency motor is significantly more efficient than the standard motor at full load, although at low loading, the motor efficiencies were very similar. The coupling tests showed the negative effects misalignment has on the efficiency of the Quick-Flex® and Fenagrid® coupling as well as the capability of the Fenaflex® coupling to withstand the effects of large misalignments without significant efficiency loss. v The belt testing revealed the advantages and disadvantages of each type of belt used. This showed that although the synchronous belt did not lose efficiency with decreased tension, it became unstable, and was difficult to keep on the pulley if not aligned correctly. The V-belts can handle low tension well. Prolonged use of the belts can cause them to stretch, lowering the tension into a “danger zone” that will cause the belts to slip. This slip can damage the belt and pulley. At the lower tension of the V-belt, although the efficiency increases slightly, the vibration of the slack side of the belt is significant, and can be dangerous as the belt could jump off the pulley. The Poly V TM belt has some of the advantages of the V-belt, except that it is unable to maintain its friction at low tension, as the belt width prevents it from being wedged into the grooves like the V-belt. The fluid coupling tests showed that the shock loading on a high inertia system can be significantly reduced with the aid of a fluid coupling. The reduced shock loading can reduce energy consumption, and increase the life of electric motors and the equipment that they drive by preventing excessive overloading.
Response characterisation of nanostructures subjected to uncertain loading and material conditions by convex modelling.
(2014) Radebe, Isaac Sfiso.; Adali, Sarp.
Nanostructures are fast becoming the material of choice consequentially opening a new research frontier. Classical continuum computational techniques have proven insu cient in modelling the mechanical behaviour of these structures. The surface and nonlocal e ects contributes to the size dependence of nanomaterial mechanical properties. Convex modelling techniques are employed in dealing with uncertainties associated with the lack of accurate measurements of nanostructures, molecular defects, and manufacturing anomalies. Numerical results are produced relating the level of uncertainty to maximum de ection for the nonlocal nanobeam, as well as determining the lowest buckling load subject to the e ects of material uncertainty for nanoplates.

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Browsing Masters Degrees (Mechanical Engineering) by Author "Adali, Sarp."