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(2011)ThesisA comprehensive literature review on the AWJ cutting technology and associated sciences has been carried out and reported. It has been found that little research effort has been made to the AWJ cutting process for AMM laminations. As a result, the first comprehensive study on AWJ cutting of AMM laminations using various cutting techniques is presented in this thesis, with a view to understanding and improving the cutting performance, i.e. the depth of cut, the top kerf width and the kerf taper angle. An experimental study in the traditional way of AWJ operation (i.e. placing the nozzle perpendicularly to the work surface without nozzle oscillation) was carried out first to gain the basic understanding of the cutting process and cutting performance. Studies with cutting performance enhancement techniques, i.e. the nozzle oscillation and kerf taper compensation techniques, were then undertaken. The experimental studies included about 200 test runs to provide sufficient data for statistical analysis. Plausible trends of the cutting performance measures with respect to the process parameters have been found from the statistical analyses of the experimental data. In general, an increase in the water pressure and a decrease in the nozzle traverse speed and abrasive mass flow rate within the tested ranges increase the depth of cut. An increase in the kerf taper compensation angle decreases the kerf taper angle almost linearly. Nozzle oscillation cutting can reduce the kerf taper angle to less than 1o, and the kerf taper compensation cutting technique can eliminate the kerf taper if the process parameters are properly selected. Recommendations have been made on the selection of the most appropriate process parameters to be used in practice for each cutting technique. Predictive models for the various cutting performance measures have finally been developed. The depth of cut models were developed using the energy conservation approach, while those for the top kerf width and kerf taper angle were developed empirically. The models were then assessed both qualitatively and quantitatively. It has been found that the model predictions are in good agreement with the experimental data and can give adequate predictions of the cutting performance measures.
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(2017)ThesisSwitched reluctance motors offer many benefits such as simplicity of construction, low costs, fault-tolerance and a high torque to inertia ratio. They also have no reliance on rare earth metals and therefore have no demagnetisation temperature limitation. These benefits have made switched reluctance motors an attractive contender for use in a plethora of applications. These benefits however have been hindered by problems such as noise, torque ripple and lower torque density. It is only in recent times that reluctance machines can begin to compete with existing motor technologies through the use of new machine topologies. With advanced machine design and the holistic development of power electronics and microprocessor control methods, the advantages of these motors are brought to the fore. In recent years, field oriented control has been implemented on stepper motor drives in order to achieve servo-like performance. This performance can be achieved at a fraction of the cost of a traditional permanent magnet synchronous servo system. While this is suitable for small size motors, larger size stepper motors with a high output power, large speed range and low cogging torque do not exist. A class of motors with these characteristics is needed to provide a low cost alternative to costly torque motors and to allow machine designers to reap the benefits of direct drive systems. Direct drive motors offer many advantages and allow a gearbox or other speed reduction measures to be eliminated. Such advantages include the lowering of the system cost, design simplification, higher reliability and lower maintenance. In the development of the novel reluctance machine, techniques to alleviate these problems have been developed with minimal compromise of the machine performance while minimising the cost of the motor. An ideal application for the motor design, and one of the case studies in this thesis, is its use as the principle actuator for a delta robot lever arm. This has been published in the Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture titled Design for scalability of industrial processes using modular components.
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(2017)ThesisWith increasing awareness of environmental concerns, ejector refrigeration system which utilizes the low-grade thermal energy, such as industrial waste heat and solar energy, becomes increasingly popular. Nevertheless, due to the relatively low coefficient of performance of the ejector refrigeration system, it is necessary to improve its efficiency. As the core component of this system, the effectiveness of the steam ejector is the key factor to improve the overall performance. The complicated flow structure and mixing process within the steam ejector lead to a relatively low entrainment ratio. Many numerical studies based on the ideal gas assumption have been carried out to investigate the flow structure and impact factors of the performance for the steam ejector. Considering the actual experiment cases, spontaneously condensing phenomenon happened in the whole working process, while most simulations focus on only the nozzle part of the steam ejector leading to a significant deviation between numerical and experimental results. In this thesis study, a wet steam model was proposed to investigate the working process and the condensation effect occurred within the steam ejector of the entire system. Compared with simulation results generated by the ideal gas model, the present results utilizing wet steam model show good agreement with the referenced experimental data and improve the accuracy of the numerical prediction on the axial pressure distribution. Furthermore, the geometry of the mixing chamber has been studied and the optimized size of the steam ejector was discovered, which improves the performance of the steam ejector with the same operating conditions. Moreover, the influence of the primary flow pressure on the condensation effect was studied. Increasing primary flow pressure did not significantly affect the condensation of droplets and the occurrence of the shock wave is shifted further within the system. Finally, the influence of the wetness of inlet flows on the performance of steam ejector is also investigated. Under numerical conditions, it is found that reducing the wetness of secondary flows has a positive impact on improving the entrainment ratio of the steam ejector.
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(2013)ThesisA large portion of the high temperature critical components, used in the power, petroleum, and chemical plants etc. of the world have been in operation for long time like 30 to 40 years, are welded. In comparison to the parent metal, the mechanical and structure characteristics and properties of as-welded and weld metal are different, i.e. Hardness values of weld metal are significantly larger. Moreover, the heat affected zone causes structural differences in the comparison to the unaffected parent metal. Therefore, it is very important to determine possible degradation processes occurring in the weld joint inducing the properties changes during long term service and study the behaviour of each zone of the weld joints in the service conditions, as if critical welded components can be replaced before their failure during in the long term operation of those plants. In this thesis, a new model has been introduced and implemented to predict the remaining life of weld joints subjected to creep failure at high temperature and compared with other existing models. This proposed model contains two independent methods, stress analysis approach and strain analysis approach, to predict the remaining life of welded joints. To calculate the creep life, at first finite element analysis of the experimental cases has been done on the basis of Norton s creep law and then numerical results have been used for further calculation according to the proposed model theory. Finite element analysis showed that strain energy density has its maximum value in the heat affected zone, so creep failure occurs there, which is similar to the experimental observations. A new creep parameter has been found during the implementation of the proposed model which is the function of temperature and material properties for both the approaches, independently. This parameter plays a significant role to control the margin of error of the proposed model. Furthermore, stress analysis approach of the proposed creep life model has more good accuracy than the strain analysis approach. The whole study showed that proposed model goes with excellent accuracy with the experimental cases than the other existing creep life prediction models.