Doctoral Degrees (Industrial Engineering)

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Browsing Doctoral Degrees (Industrial Engineering) by browse.metadata.advisor "Bekker, James F."

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    Design and development of a real-time scheduling system in a sensorised job shop using cloud-based simulation with mobile device access
    (Stellenbosch : Stellenbosch University, 2019-12) Snyman, Stephan; Bekker, James F.; Stellenbosch University. Faculty of Engineering. Dept. of Industrial Engineering.
    ENGLISH ABSTRACT: Traditional scheduling approaches used in manufacturing systems address scheduling problems before production commences, which poses possible problems when the system is interrupted by unexpected events. Managers must then react in a timely fashion, by developing a new or revised schedule to mitigate the effects of the interruptions on the productivity of the system. This can be done by a real-time scheduling system, which is used in conjunction with the actual manufacturing system. Technological advances, including cloud-based computing, the omnipresence of mobile devices, and the improved capabilities of sensor networks, have opened up the opportunity to design a real-time scheduling system, as well as create software architectures to support such a system. The purpose of this research project is therefore to develop a prototype of a real-time simulation scheduling system, which will serve as a decision support tool for real-time rescheduling of machine steps in a job shop. The prototype incorporates a cloud-based information system for the storage of data and a cloud-based simulation scheduler that generates schedules. It also includes web pages for logging data changes and selecting a new schedule and sensors that keep track of the movement of jobs through the job shop. The preliminary test results of the developed simulation scheduler suggest that metaheuristics should be considered to generate schedules, due to the metaheuristics outperforming the common dispatching rules. The model was then expanded from the single-objective to the multi-objective domain, which is a better representation of the real-world job shop environment. Several metaheuristics were adapted to solve the bi-objective job shop scheduling problem, after which comparison tests were conducted. The tests revealed that the NSGAII performed best of all the metaheuristics and it was selected for further implementation. The final phase of this research project was to implement a newly developed ranking and selection procedure for discrete stochastic simulation problems, called MMY. The MMY procedure finds the minimum number of simulation replications for each solution, while guaranteeing that the probability of correct selection of the best solutions exceeds a desired value. In this study, MMY finds the best simulated schedules while the probability of correct selection is guaranteed.
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    Integrated feedstock optimisation for multi-product polymer production
    (Stellenbosch : Stellenbosch University, 2022-04) Marnus, van Wyk; Bekker, James F.; Stellenbosch University. Faculty of Engineering. Dept. of Industrial Engineering.
    ENGLISH ABSTRACT: A chemical complex can have multiple value chains, some of which may span across geographical locations. Decisions regarding the distribution of feedstock and intermediate feedstock to different production units can occur at different time intervals. This is highlighted as two problems, a feedstock distribution problem and an intermediate feedstock distribution problem. Unexpected events can cause an imbalanced value chain which requires timely decision-making to mitigate further adverse consequences. Scheduling methods can provide decision support during such events. The purpose of this research study is to develop an integrated decision support system which handles the two problems as a single problem and maximises profit in the value chain for hourly and daily decision-making. A high-level DSS architecture is presented that incorporates metaheuristic algorithms to generate production schedules for distribution of feedstock through the value chain. The solution evaluation process contains a balancing period to enable the application of metaheuristics to this type of problem and a novel encoding scheme is proposed for the hourly interval problem. It was found that metaheuristics algorithms can be used for this problem and integrated into the proposed decision support system.