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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

The optimal design of laminated plates for maximum buckling load using finite element and analytical methods.

Walker, Mark. January 1994 (has links)
In the first part of the study, finite element solutions are presented for the optimal design of symmetrically laminated rectangular plates subject to a combination of simply supported, clamped and free boundary conditions. The design objective is the maximisation of the biaxial buckling load by determining the fibre orientations optimally with the effects of bending-twisting coupling taken into account. The finite element method coupled with an optimisation routine is employed in analysing and optimising the laminated plate designs. The effect of boundary conditions, the number of layers and bending-twisting coupling on the optimal ply angles and the buckling load are numerically studied. Optimal buckling designs of symmetrically laminated rectangular plates under in-plane uniaxial loads which have a nonuniform distribution along the edges are presented in the second part of the study. In particular, point loads, partial uniform loads and nonuniform loads are considered in addition to uniformly distributed in-plane loads which provide the benchmark solutions. Poisson's effect is taken into account when in-plane restraints are present along the unloaded edges. Restraints give rise to in-plane loads at unloaded edges which lead to biaxial loading, and may cause premature instability. The laminate behavior with respect to fiber orientation changes significantly in the presence of Poisson's effect as compared to that of a laminate where this effect is neglected. This change in behavior has significant implications for design optimisation as the optimal values of design variables with or without restraints differ substantially. In the present study, the design objective is the maximisation of the uniaxial buckling load by optimally determining the fiber orientations. Numerical results, determined using the finite element method, are given for a number of boundary conditions and for uniformly and non-uniformly distributed buckling loads. In the third part of the study, finite element solutions are presented for the optimal design of symmetrically laminated rectangular plates with central circular cut-outs subject to a combination of simply supported, clamped and free boundary conditions. The design objective is the maximisation of the biaxial buckling load by determining the fiber orientations optimally. The effect of boundary conditions and bending-twisting coupling on the optimal ply angles and the buckling load are numerically studied. The results are compared to those for laminates without holes. The fourth part of the present study gives optimal designs of symmetrically laminated angle-ply plates, which are obtained with the objective of maximising the initial post buckling stiffness. The design involves optimisation over the ply angles and the stacking sequence to obtain the best laminate configuration. The stacking sequence is chosen from amongst five candidate designs. It is shown that the best configuration depends on the ratio of the in-plane loads in the x and y directions. Results are also given for two additional configurations which do not exhibit bending-twisting coupling. The final section of the present study deals with the optimal design of uniaxially loaded laminated plates subject to elastic in-plane restraints along the unloaded edges for a maximum combination of prebuckling stiffness, postbuckling stiffness and buckling load. This multiobjective study illustrates that improved buckling and post buckling performance can be obtained from plates which are designed in this fashion. The multiobjective results are also compared to single objective design results. / Thesis (Ph.D.)-University of Natal, Durban, 1994.

Communication, mapping and navigational aspects for a free-ranging, automated guided vehicle.

Asbury, James. January 1992 (has links)
A free-ranging automated guided vehicle incorporating navigation and radio communication for use in a fully automated flexible manufacturing system has been developed. A vehicle, operating as a complete subsystem, was built and tested in an integrated control environment and proved to have promising results. various radio communication techniques are examined and the design and testing of a low cost, wireless, two way communication link is detailed. A novel, flexible infrared navigation technique was developed and incorporated into the AGV subsystem. Path planning and a flexible real time path modification system was formulated using an innovative program with an interpolative visual display unit and digitiser. Data transfer to and from the vehicles in a real time integrated system is covered. System integration for an free-ranging automatic guided vehicle is discussed covering aspects of communication, mapping and navigation. Specific needs for a free-ranging automatic guided vehicle, are presented. The unique design features of navigation and mapping outlined in this thesis has resulted in a low cost, free-ranging, autonomous automatic guided vehicle. / Thesis (Ph.D.)-University of Natal, Durban, 1992.

Development of thermal energy storage and cooker module for the integrated solar energy project.

Sulaiman, Abdulsalam S. A. January 2008 (has links)
Large percentages of the South African population have no access to grid power and are located at distances that make provision for such facility uneconomical. Also traditional fuels are under pressure. Most areas in South Africa receive 300 days of sunshine per year. The proposed solar system addresses the needs of such communities. A solar thermal energy storage system utilizing phase change material has been proposed that can overcome the time mismatch between solar availability and demand. The system consists of two types of thermal heat storage. The latent heat storage used Phase Change Materials (PCM) which melts at a sufficiently high temperature for cooking a variety of food types. By choosing a suitable PCM to take advantage of the latent heat absorbed during phase changes. Heat losses from both the latent heat storage and condenser are captured in the surrounding sensible heat store. The objective of this project to develop a prototype modules which together as a system could provide the essential domestic power requirements of the target groups. This includes power for cooking, hot water and in addition a limited electrical power supply for the system itself as well as for other minor loads. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2008.

An experimental and numerical convective heat transfer analysis over a transonic gas turbine rotor blade.

Cassie, Keith Baharath. January 2006 (has links)
An experimental and numerical investigation of the flow and convective heat transfer distribution around a high turning angle gas turbine rotor blade has been carried out at the University of Kwa-Zulu, Durban campus. This study in gas turbine blade aerothermodynamics was done to meet the research and development requirements of the CSIR and ARMSCOR. The experimental results were generated using an existing continuously running supersonic cascade facility which offers realistic engine conditions at low operating costs. These results were then used to develop and validate a 2-D model created using the commercially available Computational Fluid Dynamics (CFD) software package, FLUENT. An initial phase of the study entailed a restoration of what was an unoperational experimental facility to a state capable of producing test simulation conditions. In the analysis, a 4-blade cascade system with provisions for an interchangeable, test blade was subjected to the steady state conditions set up by the facility. Firstly, the flow was characterised by evaluating the static pressures around the midspan of a pressure measurement test blade. This was done using two pressure transducers, a scanivalve, an upgraded data acquisition system and LABview software. The method for measuring the heat transfer distributions made use of a transient measuring technique, whereby a pre-chilled Macor test blade, instrumented with thin film heat flux gauges was rapidly introduced into the hot cascade flow conditions by displacing an aluminum dummy blade while still maintaining the flow conditions. Measurement of the heat flux and generation of the isothermal heat transfer co-efficient distributions entailed re-instrumentation of the test blade section with gauges of increased temperature sensitivity along with modifications of the associated electrical circuitry to improve on the quality of experimental data. Both the experimental flow and heat transfer data were used to validate the CFD model developed in FLUENT. An investigation into different meshing strategies and turbulence models placed emphasis on the choice of model upon correlation. The outcome of which showed the k -co model's superiority in predicting the flow at transonic conditions. A feasibility study regarding a new means of implementing a film cooled turbine test blade at the supersonic cascade facility was also successfully investigated. The study comprised of experimental facility modifications as well as cascade and blade redesigns, all of which were to account for the requirements of film cooling. The implementation of this project, however, demanded the resources of both time and money of which neither commodity was available. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2006.

An automated apparatus for non-contact inspecting of mass produced custom products.

Davrajh, Shaniel. January 2009 (has links)
The evolution of the manufacturing industry may be viewed as proceeding from Dedicated Manufacturing Systems (DMS) to Reconfigurable Manufacturing Systems (RMS). Customer requirements change unpredictably, and so DMS are no longer able to meet modern manufacturing requirements. RMS are designed with the focus of providing rapid response to a change in product design, within specified part families. The movement from DMS to RMS facilitates mass-production of custom products. Custom parts require inspection routines that can facilitate variations in product parameters such as dimensions, shape, and throughputs. Quality control and part inspection are key processes in the lifecycle of a product. These processes are able to verify product quality; and can provide essential feedback for enhancing other processes. Mass-producing custom parts requires more complex and frequent quality control and inspection routines, than were implemented previously. Complex, and higher frequencies of inspection negatively impact inspection times, and inherently, production rates. For manufacturers to successfully mass-produce custom parts, processes which can perform complex and varying quality control operations need to be employed. Furthermore, such processes should perform inspections without significantly impacting production rates. A method of reducing the impact of high frequency inspection of customized parts on production rates is needed. This dissertation focuses on the research, design, construction, assembly, and testing of a Non- Contact Automated Inspection System (NCAIS). The NCAIS was focused on performing quality control operations whilst maintaining the maximum production rate of a particular Computer Integrated Manufacturing (CIM) cell. The CIM cell formed part of a research project in the School of Mechanical Engineering, University of KwaZulu-Natal; and was used to simulate mass-production of custom parts. Two methods of maintaining the maximum production rate were explored. The first method was the automated visual inspection of moving custom parts. The second method was to inspect only specified Regions of Interest (ROIs). Mechatronic engineering principles were used to integrate sensor articulation, image acquisition, and image processing systems. A specified maximum production rate was maintained during inspection, without stoppage of parts along the production line occurring. The results obtained may be expanded to specific manufacturing industries. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009.

The development of a catchment scale irrigation systems model for sugarcane.

Moult, Nicholas Greig. January 2005 (has links)
The implementation of the National Water Act (1998) requires significant changes in the institutional arrangements for water management and, to cater for human and environmental needs, as well as addressing historical inequities, water allocations to irrigated agriculture are likely to be affected. As a result, farmers are facing increasing pressure to use water more effectively, to justify existing water requirements and to budget and plan with growing uncertainty regarding water availability. Therefore, a tool to manage and assess catchment water supply and demand interactions and the associated impacts on the profitability of irrigated sugarcane would be of great value. Although there have been several independent model developments in the fields of water management and sugarcane growth, none provide the required management information in an integrated manner. However, these models provide the foundation for the development of the required modelling tool. An irrigation model for sugarcane, ACRUCane, was developed and incorporated into the ACRU2000 modelling system. The water budget simulated by ACRUCane is linked to a surrounding catchment, the hydrology of which is simulated by the ACRU model. In doing so, a tool has been developed that has the capacity to: • model the soil water balance at a field scale for irrigated areas and at a catchment scale for non-irrigated areas, • link an accurate estimation of crop water requirement for an irrigated area with the availability ofwater at a catchment scale, • explicitly account for the impact of the performance of different irrigation systems on the hydrology and, ultimately, on the sugarcane yield of an irrigated area, • assess the impact of different supply constraints on sugarcane yield, and • estimate both sugarcane and sucrose yield. Extensive verification of the model has been undertaken using data from an irrigation trial at La Mercy, South Africa and two separate trials conducted in the Lowveld of Zimbabwe, with the primary objective of the verification studies being to assess the model's ability to account for different scheduling strategies on sugarcane and sucrose yield. The results obtained show that the model accurately captured the relative differences in yield associated with different irrigation treatments and can thus be used evaluate the impact of different scheduling strategies. A case study was conducted where the feasibility of several hypothetical irrigation scenarios were compared. Different scenarios were created by varying application uniformity, scheduling strategies and system type. This case study illustrated how ACRUCane can be used to provide reliable decision support information to irrigators. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.

Design of an autonomous underwater vehicle : vehicle tracking and position control.

Holtzhausen, Servaas. January 2010 (has links)
This project proposes the development of an autonomous underwater vehicle that can be used to perform underwater research missions..The vehicle can be pre-programmed to complete a specified mission. Missions may include underwater pipe inspection, a survey of the sea floor or just the transport of given sensors to a certain depth or position and take measurements of underwater conditions. The Mechatronics and Micro Manufacturing group at the CSIR is engaged in developing a portfolio of autonomous vehicles as well as fur- ther research into the development and implementation of such vehicles. Underwater vehicles will form part of the portfolio of autonomous vehicle research. Autonomous underwater vehicles (AUVs) are mostly used for research purposes in oceanographic studies as well as climate studies. These scientists use AUVs to carry a payload of sensors to specified depths and take measurements of underwater conditions, such as water temperature, water salinity or carbon levels as carbon is being released by plankton or other ocean organisms. Very little information is available about what is happening below the surface of the oceans and AUVs are being used to investigate this relatively unknown environment. The area covered by the world's ocean is 361 million km2 with an average depth of 3790 m. The deepest surveyed depth point in the ocean is at a depth of about 11 000 m at the southern end of the Mariana Trench in the Pacific Ocean. This just shows the need for research into this mostly unexplored world. Research and exploration in the oceans can be achieved through the use of autonomous underwater vehicles. A big problem to overcome is the fact that GPS is not available for navigation in an underwater environment. Other sensors need to be found to be used for navigational purposes. The particular vehicle developed for this study will be used to facili- tate further research into underwater vehicle navigation and underwater robotics. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.

Accelerated environmental degradation of GRP composite materials.

Dlamini, Power Madoda. January 2004 (has links)
The use of fibre reinforced polymer composites and development of structural composites has expanded rapidly in the Southern African region over the past ten years. The long-term effect of placing these materials outdoors in the Southern African climate is unknown with exposure data for these materials being primarily European and North American based. This study intends to take a broad-based study to the problem of environmental degradation of advanced composite structures. This work is intended to study different degradation mechanisms. Work performed includes: a study of literature on degradation and protective measures; identification of dominant degradation mechanisms; manufacture of specimens; accelerated environmental testing; and an assessment of the effect of the exposure on the chemical properties The goal of this work is to produce information, which can be subsequently used to determine the rate of damage, methods of suitable protection and necessary maintenance intervals for polymer composite components. The approach was: to simulate outdoor exposure within a reduced period of time; to establish correlation of results with actual outdoor exposure; and to determine how the gel coats compare with other protective methods. As part of the objectives of the study (i.e. to assess the durability of polymer matrix composites materials subjected to environmental exposure), an experimental study was carried out to establish the durability of specific gel coats against ultraviolet (DV) and moisture degradation. An investigation of the effectiveness of the various protective measures has begun with a review of selected gel coats available as a protective coating. Laminates with these gel coats have been set up for both accelerated and natural exposure tests. 3000, 2500, 2000, 1600, and 800 hours of accelerated DV exposure tests were performed on polyester GRP laminates with gel coats. No measurable strength loss occurred on protected laminates; there was significant increase in yellowness on un-protected laminates; all protected specimens showed a fair retention of gloss; fibre prominence occurred on unprotected laminates; and the glass transition of samples had dropped from the normal polyester glass transition temperature range. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2004.

Design of an autonomous mobile robot for service applications.

De Villiers, Mark. January 2011 (has links)
This research project proposes the development of an autonomous, omnidirectional vehicle that will be used for general indoor service applications. A suggested trial application for this service robot will be to deliver printouts to various network users in their offices. The robot will serve as a technology demonstrator and could later also be used for other tasks in an office, medical or industrial environment. The robot will use Mecanum wheels (also known as Swedish 45° or Ilon wheels) to achieve omnidirectionality. This will be especially useful in the often cramped target environments, because the vehicle effectively has a zero radius turning circle and is able to change direction of motion without changing its pose. Part of the research will also be to investigate a novel propulsion system based on the Mecanum wheel. The robot will form part of a portfolio of service robots that the Mechatronics and Micro Manufacturing (MMM) group at the CSIR is busy developing. Service robots are typically used to perform Dull, Dangerous or Dirty work, where human presence is not essential if the robot can perform the task reliably and successfully. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

Design and construction of Meercat : an autonomous indoor and outdoor courier service robot.

Bosscha, Peter Antoon. January 2011 (has links)
This project details the construction and development of, and experimentation with a mobile service courier robot named Meercat. This robot has been built from the ground up using parts sourced from various places. The application for this service robot is the delivery of internal mail parcels between the buildings situated on the campus of the Council for Scientific and Industrial Research (CSIR) in Pretoria. To achieve this, the robot has to be able to localise and navigate through indoor office and laboratory environments and over outdoor tarred roads which interconnect the various buildings. Not many robots are intended for operation in both indoor and outdoor environments, and to achieve this, multiple sensing systems are implemented on the platform, where the correct selection of sensing inputs is a key aspect. Further testing and experiments will take place with algorithms for localisation and navigation. As a limited budget was available for the development of this robot, cost-effective solutions had to be found for the mechanical, sensing and computation needs. The Mechatronics group from the Mechatronics and Micro Manufacturing (MMM) competency area at the CSIR is involved with the development of various autonomous mobile robots. The particular robot developed in this project will be an addition to the CSIR’s current fleet of robots and will be used as a stepping stone for experimentation with new sensors and electronics, and the development of further positioning and navigation algorithms. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

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