Research Publications (Engineering and Built Environment)
Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/215
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Item A particle swarm optimization approach for model independent tuning of PID control loops(IEEE, 2007-09) Nelendran Pillay; Poobalan GovenderThe paper proposes a model independent tuning technique that yields optimal proportional-integral-derivative parameters for a range of typical process control loops. The proposed tuning technique utilizes the particle swarm optimization algorithm to generate optimal tuning parameters. The PSO tuning method is applied to typical process models. Comparisons are made between the proposed PSO technique and other conventional methods. ©2007 IEEE.Item PWM-VSI inverter-assisted stand-alone dual stator winding induction generator(Institute of Electrical and Electronics Engineers (IEEE), 2000-11) Ojo, Olorunfemi; Davidson, Innocent EweanThis paper presents a novel usage of a dual stator winding three-phase induction machine as a stand-alone generator with both controlled output load voltage magnitude and frequency. This generator, with both three-phase power and control windings housed in the stator structure, has the load connected to the power winding and a three-phase pulsewidth modulation (PWM) voltage-source inverter sourcing the control winding. The input to the PWM inverter is either a battery source or a charged dc capacitor. The operational characteristics of these generator schemes with either of the two inverter sources are investigated and shown to have desirable performance. How the load voltage magnitude depends on the various control and design parameters such as rotor speed, compensating capacitance, and load impedance is determined using a detailed mathematical model of the system.Item Evaluation and effective management of non-technical losses in power networks(2002-10) Davidson, Innocent EweanMarket-driven economies and deregulated electricity industry environment have stimulated the minimization of technical and non-technical losses (NTL) even though they do not constitute major operational or quality of supply problems. Their impact is economic and utilities often passed down the costs to consumers. NTL need to be addressed to determine the overall performance of power networks, as these losses are expected to be more dominant at the sub-transmission (132kV-33kV) and reticulation (22kV and 11kV) levels of the electricity supply industry value chain. In some national grid operations, NTL are estimated to account for up to 30% in revenue losses to electric utilities, and overhead expenditure in added maintenance costs. This paper discusses a method for NTL evaluation and an effective management approach to loss minimization and revenue collection. Copyright © 2002 IEEE.Item Performance analysis of a shaded-pole linear induction motor using symmetrical components, field analysis, and finite element method(Institute of Electrical and Electronics Engineers (IEEE), 2000-03) Davidson, Innocent Ewaen; Gieras, Jacek F.The application of symmetrical components of two-phase asymmetric systems, field theory, and finite element method (FEM) to the performance calculation of the shaded-pole linear induction motor (LIM) is presented. The results compared with measurements are satisfactory though the performance of the shaded-pole single-phase LIM is poor when compared to three-phase LIMs. LIMs generally have low efficiencies due to their open airgap. The maximum efficiency of rotary shaded-pole induction motors with cage-rotors rated at 100 W usually does not exceed 20%.Item Logistics CIM modeling and simulation(2003) Li, Qingxue; Bright, G.This study presents a development of a method for Logistic Computer Integrated Manufacturing (LCIM) modelling. Based on this new model, a small LCIM cell simulation system was developedItem A method for optimally designing laminated plates subject to fatigue loads for minimum weight using a cumulative damage constraint(Elsevier, 2000) Walker, MarkA procedure to optimally design laminated plates for a specific cyclic life using a cumulative damage constraint is described. The objective is minimum weight, and the design variables are the fiber orientation, and the plate thickness. The plates are subjected to cyclic bending loads, and the finite element method, in conjunction with the Golden Section method, is used to determine the design variables optimally. The FE formulation is based on Mindlin theory for moderately thick laminated plates and shells, and the formulation includes bending–twisting coupling. In order to demonstrate the procedure, several plates with differing events, load magnitudes and type, aspect ratios, boundary conditions and cyclic lives are optimised, and compared.Item Multiobjective optimisation of laminated I-beams for maximum crippling, buckling and postbuckling strength(Elsevier, 1998) Walker, MarkThe present study deals with the optimal design of uniaxially loaded laminated I-beams for a maximum combination of crippling and buckling load, in the first instance, and a maximum combination of buckling load and postbuckling stiffness, in the second instance. The method of solution involves defining a design index comprising a weighted average of the objective functions and identifying candidate configurations which have to be optimised and compared to determine the best stacking sequence. This multiobjective approach leads to improved crippling, buckling and postbuckling strength. The multiobjective results are compared to single objective results, and the effect of various problem parameters on the optimal designs are numerically studied.Item A methodology to design fibre reinforced laminated composite structures for maximum strength(Elsevier, 2003) Walker, Mark; Smith, Ryan E.A procedure to select the optimal fibre orientations and determine the maximum load carrying capacity of symmetrically laminated fibre reinforced composite structures is described. Cylindrical shells subject to combinations of torque and in-plane forces are used to illustrate the methodology and are optimally designed for maximum strength. Torque tubes are generally used as control mechanisms, for example, in the tail fins of aircraft. The finite element method, based on Mindlin plate and shell theory, is used in this application in conjunction with an optimisation routine in order to obtain the optimal designs. The methodology consists of two stages; the objective of the first is to maximise the strength of the cylindrical shells by determining the fibre orientations optimally while the objective of the second stage is to maximise the in-plane compression loading subject to a failure criterion. The effect of different shell aspect ratios, wall thickness, layer numbers and boundary conditions on the results is investigated.Item A computational methodology to select the best material combinations and optimally design composite sandwich panels for minimum cost(Elsevier, 2002) Walker, Mark; Smith, Ryan E.A procedure to select the best material combination and optimally design sandwich laminates with fibre reinforced skins and low density cores for minimum cost is described. Sandwich constructions generally provide improved stiffness/mass ratios and provide more tailoring opportunities than monolithics, and thus greater chance of satisfying design constraints. The objective of the optimisation is to minimise the laminate cost by selecting the skin and core material combination, layer thicknesses and skin fibre angles optimally, subject to load and mass constraints. As the optimisation problem contains a number of continuous (ply angles and thicknesses) and discrete (material combinations) design variables, a sequential solution procedure is devised in which the optimal variables are computed in different stages. The methodology and its benefits are demonstrated using graphite, glass or kevlar/epoxy facings, and balsa or PVC cores.Item A shape control model for piezo-elastic structures based on divergence free electric displacement(Elsevier, 2003) Kekana, Marino; Tabakov, Pavel Y.; Walker, MarkA model simulating the effects of the control potential on the static configuration of a piezo-elastic structure is presented. This model is centred on the electric displacement field, which is shown to be divergence free. Thus, the surface charge effect no control over the configuration of a piezo-elastic structure, save for the control potential derived through passive or active control. Results show that at zero gain the proposed model resembles a structure free from piezoelectric control. Thus, no fictituous stiffness is introduced as is the case with models presented in the literature.