Institute for Systems Research
Permanent URI for this communityhttp://hdl.handle.net/1903/4375
Browse
2 results
Search Results
Item Modeling Separations of Plant Layout Problems(2014-08) Herrmann, JeffreyThis paper describes the results of a simulation study that evaluated the performance of different separations of the plant layout problem solved by bounded rational decision-makers. Seven problem instances from the literature were studied. We simulated the solution of a problem by a bounded rational decision-maker as a random search over the solution space. The problem was separated by identifying “subsets” of adjacent locations. The subset assignment problem partitioned the departments into subsets corresponding to these subsets of locations. Then, the subset layout problem assigned the locations in the subset to the departments. We considered separations with 2, 3, and 4 subsets. We also considered separations that first aggregated the departments before assigning them to subsets of locations. The results showed that separating the problem can lead to better solutions than solving the problem all-at-once, but some separations lead to worse solutions. Maximizing the flow inside the subsets generated better solutions than maximizing the adjacency of the departments inside the subsets. When fewer subsets are used, minimizing the cost inside each subset generated better solutions than minimizing the total cost. These results show that the quality of the solutions created by a design process is influenced by the choice of subproblems that make up the design process.Item Scheduling Perfectly Periodic Services Quickly with Aggregation(2013-03) Herrmann, JeffreyThe problem of scheduling periodic services that have different period lengths seeks to find a schedule in which the workload is nearly the same in every time unit. A time unit’s workload is the sum of the workloads of the services scheduled for that time unit. A level workload minimizes the variability in the resources required and simplifies capacity and production planning. This paper considers the problem in which the schedule for each service must be perfectly periodic, and the schedule length is a multiple of the services’ period lengths. The objective is to minimize the maximum workload. The problem is strongly NP-hard, but there exist heuristics that perform well when the number of services is large. Because many services will have the same period length, we developed a new aggregation approach that separates the problem into subproblems for each period length, uses the subproblem solutions to form aggregate services, schedules these, and then creates a solution to the original instance. We also developed an approach that separates the problem into subproblems based on a partition of the period lengths. Computational experiments show that using aggregation generates high-quality solutions and reduces computational effort. The quality of the partition approach depended upon the partition used.