Browsing by Author "Visagie, S. E."
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- ItemLogistieke beplanning met behulp van simulasie modellering : 'n gevallestudie(Operations Research Society of South Africa (ORSSA), 2002) Loubser, J. S.; Visagie, S. E.; Pienaar, W. J.Hierdie artikel bied ’n uiteensetting van die gekombineerde gebruik van objek-georiënteerde programmering en simulasie, met die doel om ’n onderneming se logistieke funksies te ontleed en te beplan. Die huidige bedryfstelsel van ’n koerieronderneming se ontvangs- en verspreidingsaanleg word geëvalueer deur gebruik te maak van ’n objek-georiënteerde simulasie. Uit die simulasieresultate blyk dit dat daar ’n wanbalans in die kapasiteitsbelading van sommige werkstasies bestaan. Die onderneming se benutting van die meeste van sy hulpbronne is redelik goed, maar deur ’n herstrukturering van aktiwiteite is dit moontlik om ’n meer doeltreffende stelsel te verkry. Die model is die eerste rekenaarmatige voorstelling van die onderneming se aktiwiteite, en vul ’ n leemte in die beplanningsfunksie. Aangesien die model die verwagte resultate van aanpassings in die werkswyse en/of fisiese veranderinge aan die aanleg kan bereken, kan dit ook gebruik word vir strategiese besluite.
- ItemMetaheuristic approaches to order sequencing on a unidirectional picking line(Operations Research Society of South Africa (ORSSA), 2013) De Villiers, A. P.; Matthews, J.; Visagie, S. E.In this paper the sequencing of orders on a unidirectional picking line is considered. The aim of the order sequencing is to minimise the number of cycles travelled by a picker within the picking line to complete all orders. A tabu search, simulated annealing, genetic algorithm, generalised extremal optimisation and a random local search are presented as possible solution approaches. Computational results based on real life data instances are presented for these metaheuristics and compared to the performance of a lower bound and the solutions used in practise. The random local search exhibits the best overall solution quality, however, the generalised extremal optimisation approach delivers comparable results in considerably shorter computational times.
- ItemA multi-objective approach to the assignment of stock keeping units to unidirectional picking lines(Southern African Institute for Industrial Engineering, 2017) Le Roux, G. J.; Visagie, S. E.An order picking system in a distribution centre consisting of parallel unidirectional picking lines is considered. The objectives are to minimise the walking distance of the pickers, the largest volume of stock on a picking line over all picking lines, the number of small packages, and the total penalty incurred for late distributions. The problem is formulated as a multi-objective multiple knapsack problem that is not solvable in a realistic time. Population-based algorithms, including the artificial bee colony algorithm and the genetic algorithm, are also implemented. The results obtained from all algorithms indicate a substantial improvement on all objectives relative to historical assignments. The genetic algorithm delivers the best performance.
- 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.
- ItemSingle fixed crane optimisation within a distribution centre(Southern African Institute for Industrial Engineering, 2011-11) Matthews, J.; Visagie, S. E.This paper considersthe optimisation of the movement of a fixed crane operating in a single aisle of a distribution centre. The crane must move pallets in inventory between docking bays, storage locations, and picking lines. Both a static and a dynamic approach to the problem are presented. The optimisation is performed by means of tabu search, ant colony metaheuristics,and hybrids of these two methods. All these solution approaches were tested on real life data obtained from an operational distribution centre. Results indicate that the hybrid methods outperform the other approaches.
- ItemSKU assignment to unidirectional picking lines using correlations(Operations Research Society of South Africa, 2015-07) Matthews, J.; Visagie, S. E.A real life order picking system consisting of a set of unidirectional picking lines is inves- tigated. Batches of stock keeping units (SKUs) are processed in waves defined as a set of SKUs and their corresponding store requirements. Each wave is processed independently on one of the parallel picking lines as pickers walk in a clockwise direction picking stock. Once all the orders for a wave are completed a new mutually exclusive set of SKUs are brought to the picking line for a new wave. SKUs which differ only in size classification, for example small, medium and large shirts, are grouped together into distributions (DBNs) and must be picked in the same wave. The assignment of DBNs to available picking lines for a single day of picking is considered in this paper. Different assignments of DBNs to picking lines are evaluated using three measures, namely total walking distance, the number of resulting small cartons and work balance. Several approaches to assign DBNs to picking lines have been investigated in literature. All of these approaches seek to minimise walking distance only and include mathematical formulations and greedy heuristics. Four different correlation measures are introduced in this paper to reduce the number of small cartons produced and reduce walking distance simultaneously. These correlation measures are used in a greedy insertion algorithm. The correlation measures were compared to historical assignments as well as a greedy approach which is known to address walking distances effectively. Using correlation measures to assign DBNs to picking lines reduces the total walking distance of pickers by 20% compared to the historical assignments. This is similar to the greedy approach which only considers walking distance as an objective, however, using correlations reduced the number of small cartons produced by the greedy approach.
- ItemToewysingsheuristieke om die volgorde van bestellings vir 'n uitsoeklyn te bepaal(LitNet, 2012) De Villiers, A. P.; Visagie, S. E.’n Sisteem vir die opmaak van bestellings word ondersoek. Die sisteem vereis dat die werkers in ’n kloksgewyse rigting om ’n uitsoeklyn beweeg. Die uitsoeklyn bestaan uit vaste vakkies wat elk ’n unieke produk bevat. Die bestellings en die produkte in die vakkies is bekend voordat bestellings opgemaak word. Die volgorde moet bepaal word waarin die bestellings in ’n uitsoeklyn opgemaak moet word sodat die totale afstand afgelê deur die werkers geminimeer word. Die probleem word opgelos met twee klasse van heuristieke. Die eerste klas is gebaseer op ’n veralgemeende toewysingsprobleem. Die tweede klas gebruik voorkeurverhoudings. Al die heuristieke word vergelyk op grond van hulle oplossingskwaliteit vir werklike datastelle. Een van die metodes wat die voorkeurverhoudings in ag neem lewer die beste resultate.
- ItemTour construction heuristics for an order sequencing problem(Southern African Institute for Industrial Engineering, 2012-11) De Villiers, A. P.; Matthews, J.; Visagie, S. E.An order picking system that requires pickers to move in a clockwise direction around a picking line with fixed locations is considered. The problem is divided into three tiers. The tier in which orders must be sequenced is addressed. Eight tour construction heuristics are developed and implemented for an order picking system operating in unidirectional picking lines. Two classes of tour construction heuristics the tour construction starting position ( ) and the tour construction ending position ( ) are developed to sequence orders in a picking line. All algorithms are tested and compared using real life data sets. The best solution quality was obtained by a heuristic with adaptations.