Theses and Dissertations (Industrial Engineering & Operations Management)

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Browsing Theses and Dissertations (Industrial Engineering & Operations Management) by Title

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    Optimisation of dynamic and stochastic production scheduling systems after random disruptions
    (Vaal University of Technology, 2013-05-20) Mapokgole, Johannes Bekane; Tengen, T. B., Dr
    The current business environments in many companies are characterized by markets facing tough competitions, from which customer requirements and expectations are becoming increasingly high in terms of quality, cost and delivery dates, etc. These emerging expectations are even getting stronger due to rapid development of new information and communication technologies that provide direct connections between companies and their clients. As a result, companies should have powerful control mechanisms at their disposal. To achieve this, companies rely on a number of functions including production scheduling. This function has always been present within companies, but today, it is facing increasing complexities because of the large number of jobs that must be executed simultaneously. Amongst many factors, it is time driven. This study demonstrates that several disciplines can be married into one model (i.e. a unified model) to solve scheduling problems after disruptions, and clears the way for future multi-disciplinary research efforts. Scheduling problem is modeled as follows: Ito’s stochastic differential rule is used to analyse the time evolution of random or stochastic processes. Multifactor productivity is used to unify various disruption factors. Theory of line balancing is also employed to determine the required number of resources to minimize bottleneck. Reliability: disruptions are considered to be equivalent to system failure. The failure rate of the system is translated to the reliability of the system mathematically. The probabilities of failure are used as indicators of disruptions, and the theory of reliability is then applied. Bernoulli’s principle is also employed to relate pressure to production flow and aid in managing bottleneck situations. Results indicate that the amount of resources needed after disruption depends on the nature of disruption, and that the scheduler should plan to increase number of facilities following a trend that is only predicted by the nature of disruptions. It is also shown that disruption of one type may not greatly affect productivity of a certain company layout, whilst similar disruptions can have devastating effect on another type. It is further concluded that impacts of disruption are dependent on the type of company layouts.
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    Optimizing inventory-ordering policies in supply chain management : a case study on a selected company from the Vaal Region
    (2014-12) Ebouele, Blaise Bolan Benga; Tengen, Thomas; Campbell, Harod
    Implementing either periodic or continuous inventory review model within most manufacturing-companies-supply chains, as a management tool, incurs higher costs. These high costs affect the system flexibility which in turn affects the level of service required to satisfy customers. However, these effects are not clearly understood. This may be due to the fact that lead time and demand which are important input parameters of the manufacturing supply chain are not designed to be fully utilized under different and uncertain conditions such as seasonality, poor manufacturing, poor supplies and delivery performance, etc. Coming up with a hybrid inventory model which may combine, in some sense a continuous (r, Q) and a periodic (R, S) inventory review models can be useful in dealing with such problem. Therefore, more attention should be first devoted to formulating accurate models for lead time and demand that incorporate uncertainty. This study presents a simulation based approach that assesses the effect of uncertainty on the cost of implementing a continuous (r, Q), periodic (R, S) and hybrid inventory review models while considering appropriate constraint such as customer service and system flexibility. The stochastic representations of demand and lead time are proposed and used in the simulation models. Results reveal that under a unique situation, implementing a continuous (r, Q) inventory review model may cause manager to under-budget while the use of a periodic (R, S) inventory review models may lead to over budget and vice versa. Further investigation shows that the cost of implementing the hybrid inventory model, although higher at the beginning of operation, seems to be the most cost effective one over time. The result also reveal optimal re-order point path and optimal review interval path which when followed, should lead to optimal inventory cost path as demand and lead time fluctuate. Thus, a management guide is proposed that can be used by managers in making inventory decision.
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    Redesigning a commuter rail system to accommodate passengers with special needs
    (Vaal University of Technology, 2019-01-25) Gabara, Tshegofatso; Benga Ebouele, B. B.; Tengen, T. B., Prof.
    In South Africa, the provision of equitable and accessible public transport is still in the early stage of development and growth. PRASA has adopted programmes that drive and promote the implementation and integration of a universal design that should meet the varying requirements of its customers. PRASA acknowledges that its facilities should be focused on the delivery of public service that acts as a catalyst and enabler within South Africa in overcoming differentiation in gender, race, income, opportunity and mobility. Facilities’ managers and especially rail managers, through facilities planning, should provide proactive service delivery to its stakeholders. In South Africa, the majority of train stations are not designed to cater for persons with special needs. Therefore, these facilities must comply with national imperatives; resulting in a need to design new facilities or redesign current train stations’ facilities so as to accommodate the diversity of human characteristics within the population, as a whole, in order to promote equal access to services and opportunities for persons with disabilities as expected in all spheres of government. This means that there are dynamic and heterogeneous elements that should be controlled in the commuter rail system design. The redesigning of some train stations had been undertaken and improvements achieved at some train stations e.g. Gautrain. The issue that arises is that there cannot be a one-to-one transfer of model to design another facilities. This is due to the constraints of space, monetary costs and information on customers or level of activeness in the facility. Companies don’t always have a lot of money at their disposal making money to become an issue. If there’s an abundance of space then one can design the train layout the way he/she wants. However this is not always the case and therefore, the available space has to be planned accordingly. Furthermore, one needs to know information on (the number of) their customers in order to plan and be able to meet their requirements. This project proposes the use of an improved flow-pattern measurement technique (i.e. integration of techniques), specifically improved From-To-Chart techniques, to assess the efficiency of the current layout while considering the constraints of variables expectations from customers and variable rewards for rendering services to different types of customers. An improved and effective layout was then proposed. The efficiency of the proposed new layout was compared with that of previous layout so as to ascertain on stakeholders’ confidence. Simulated Annealing was also used to compare different peak periods and their efficiencies so as to decide on the layout that is suitable for the commuter rail system under the different peak scenario. The Direct Clustering Algorithm was furthermore employed to try to group facilities that render similar services into cells so as to minimise movement or material handling. Results revealed that a flexible train station layout whose flow pattern can be regularly adjusted to minimize costs and to accommodate the ever-increasing expectations should be adopted. It is hoped that station managers who adopt such guides will improve on customer’s expectations.
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    Stress modelling of welded titanium alloy (grade 5) pipes
    (2010-12) Inyang, Etienying Edem; Mendonidis, P.; Oba, P.; Masu, L. M.
    This research work focused on welded titanium alloy (grade 5) pipes, to ascertain if the weld joints can withstand the immediate and accumulated effects of fluid flow in (industrial) applications. Modeling of welded pipes was done using Pro/ENGINEER Wildfire 5.0. The cylindrical pipe models were of 206,375mm inner and 219,075mm outer diameter respectively; made of Ti6Al4V material. Three models were made: one of unwelded pipes, another with a seam weldment and the third with a circumferential weld. The welds were modeled as autogenous gas tungsten arc welding and the models included calculated heat affected zones. The pipes were modeled with a flowing fluid under pressure exerted evenly on all sides of the pipe walls (circumference). The boundary conditions were such that the pipe ends were supported as if the pipe were continuous. Stress and strain analysis on the pipe models were performed by the Finite Element Method using Pro/ENGINEER Wildfire 5.0. The results of the Finite Element Analysis (FEA) indicated that stress vary very negligibly along the pipe. A comparison of the FEA modeling results to the analytically determined value of the stress showed very low or zero percentage deviation.