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Graduation Thesis from 2011
Kang, Kyoung Wan
M.S. |
Disassembly leveling and lot-sizing for multiple product types: basic model and an extention This paper considers two interrelated problems occured in disassembly systems: disassembly leveling and disassembly lot-sizing for multiple product types. Disassembly leveling, one of disassembly process planning decisions, is to determine disassembly structure that specifies parts and/or subassemblies to be obtained from products, and disassembly lot-sizing, one of disassembly operations to satisfy the demands of parts and/or subassemblies. For disassembly leveling, in partidular, we consider a general case that disassembly levels may be different even for the same product type. Unlike most existing studies, this thesis considers the two problems at the same time for the intergrated problem are considered. The first one is the basic problem without parts commonality. For this case, an integer programming model is suggested and then a simple polynomial-time optimal algorithm is suggested. The second one is an extended problem with parts commonality. For the extended case, we show that the problem is NP-hard, and due to its complexity, a simple heuristic is suggested. Test result on a number of randomly generated instances are reported. |
Lee, Jae Ho
M.S. |
A tabu search algorithm for unrelated parallel machine scheduling with sequence-and machine-dependent setups:minimizing total tardiness The problem addressed in this thesis is the scheduling of n independent jobs on m unrelated parallel machines with sequence-dependent setup times for the objective of minimizing total tardiness. Due to the characteristics of unrelated machines, processing time of a job depends on the machine to which the job is assigned. i.e., setup times depend on both sequence and machine. Since one can easily see that the problem is NP-hard, optimal solutions can be found only for small sized instances. Based on this observation, we suggest a tabu search algorithm that incorporates eight neighborhood generation nethods. Computational experiments were done on a number of randomly generated test instances and the results show that the tabu search algorithm suggested in this thesis outperforms the existing search heuristic significantly. |
Go, Hun
M.S. |
A mathematical model and solution algorithms for preventive maintenance scheduling of containerships This thesis considers the problem of determining operation and maintenance schedules for a containership equipped with various components during its sailing according to a pre-determined schedule. The operation schedule, which specifies working times of each component, determines the due0date of each maintenance activity. The main constraints are component requirements, workforce availability, working time limitation, and inter-maintenance time. To represent the problem mathematically, a mixed integer programming model is suggested. Then, due to the complexity of the problem, we suggest a heuristic algorithm for the objective of minimizing the sum of earliness and tardiness between the due-date and the starting time of each maintenance activity. Computational experiments were done on a number of randomly generated test instances and the results are reported. Also, a case study was done on real data and a significant amount of improvement is reported. |
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