Browsing by Author "Venter, Lieschen"
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- ItemMetaheuristics for petrochemical blending problems(Stellenbosch : University of Stellenbosch, 2010-03) Venter, Lieschen; Visagie, S. E.; University of Stellenbosch. Faculty of Economic and Management Sciences. Dept. of Logistics.ENGLISH ABSTRACT: The main aim in blending problems is to determine the best blend of available ingredients to form a certain quantity of product(s). This product should adhere to strict speci cations. In this study the best blend means the least-cost blend of ingredients (input) required to meet a minimum level of product (output) speci cations. The most prevalent tools to solve blending problems in the industry are by means of spreadsheets, simulators and mathematical programming. While there may be considerable bene t in using these types of tools to identify potential opportunities and infeasibilities, there is a potentially even greater bene t in searching automitically for alternative solutions that are more economical and e cient. Heuristics and metaheuristics are presented as useful alternative solution approaches. In this thesis di erent metaheuristic techniques are developed and applied to three typical blending problems of varied size taken from the petrochemical industry. a fourth instance of real life size is also introduced. Heuristics are developed intuitively, while metaheuristics are adopted from the literature. Random search techniques, such as blind random search and local random search, deliver fair results. Within the class of genetic algorithms the best results for all three problems were obtained using ranked tness assignment with tournament selection of individuals. Good results are also obtained by means of tabu search approaches - even considering the continuous nature of these problems. A simulated annealing approach also yielded fair results. A comparison of the results of the di erent approaches shows that the tabu search technique delivers the best result with respect to solution quality and execution time for all three the problems under consideration. Simulated annealing, however, delivers the best result with respect to solution quality and execution time for the introduced real life size problem.
- ItemOn the solution of petrochemical blending problems with classical metaheuristics(Operations Research Society of South Africa, 2016) Venter, Lieschen; Visagie, S. E.ENGLISH SUMMARY : In this paper a comparison of classical metaheuristic techniques over different sizes of petrochemical blending problems is presented. Three problems are taken from the literature and used for initial comparisons and parameter setting. A fourth instance of real world size is then introduced and the best performing algorithm of each type is then applied to it. Random search techniques, such as blind random search and local random search, deliver fair results for the smaller instances. Within the class of genetic algorithms the best results for all three problems were obtained using ranked fitness assignment with tournament selection. Good results are also obtained by means of continuous tabu search approaches. A simulated annealing approach also yielded fair results. Comparisons of the results for the different approaches shows that the tabu search technique delivers the best results with respect to solution quality and execution time for all of the three smaller problems under consideration. However, simulated annealing delivers the best result with respect to solution quality and execution time for the introduced real world size problem.
- ItemPetrochemical blending problem instances(2013-06-27) Venter, Lieschen; Visagie, Stephan E.This file supplies the input data for four petrochemical blending problems.
- ItemA systems perspective of basic education in South Africa(Stellenbosch : Stellenbosch University, 2020-03) Venter, Lieschen; Visagie, Stephan E.; Stellenbosch University. Faculty of Economic and Management Sciences. Dept. of Logistics. Logistics.ENGLISH SUMMARY : South Africa has one of the highest measures of economic inequality and one of the worst performing basic education systems in the world. The majority of learners from poorer communities are attending dysfunctional schools, while a minority of learners from richer communities are achieving adequately in a functional system. The economic disparity creates an intuition that allocating more funds can solve low academic performance, but this approach has yielded little return for a number of years. In this dissertation the impact of school leadership on learners' academic performance is considered in the South African context. School management is a systemic concept and elements thereof cannot be analysed in isolation. A series of system dynamics simulation models is developed to understand the effect of various school management interventions on communities, teachers, resources, and learners within the basic education system. The School Effectiveness Model simulates the South African basic education system and reveals that improvement interventions must be made early, continously and in multiple areas for them to be effective. The Teacher Effectiveness Model simulates the career progression of Western Cape public teachers and reveals that the number of the teachers appointed in a primary school has a greater impact on their effectiveness than the quality of the teachers appointed. The Early Childhood Development Model simulates the preschool career of Western Cape children and reveals that improving the quality of Early Childhood Development programmes has a greater impact on their primary school readiness than increasing the number of children enrolled into programmes. The Primary School Model simulates the progression of learners from Grade 1 to Grade 7 in the Western Cape and reveals that improving learners' social circumstance at home has a greater impact on their academic performance than improving their classroom experience. Finally, the expanded School Effectiveness Model brings all the models together to reveal that a combination of interventions is needed to decrease the academic performance gap between poorer and richer communities within the Western Cape.