Browsing by Author "Kandiller, Levent"

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Open Access
Part family machine group formation problem in cellular manufacturing systems
(1989) Kandiller, Levent
The first and the most important stage in the design of Cellular Manufacturing (CM) systems is the Part Family Machine Group Formation (PF/MGF) problem. In this thesis, different approaches to the PF/MG-F problem are discussed. Initially, the design process of CM systems is overviewed. Heuristic techniques developed for the PF/MG-F problem are classified in a general framework. The PF/MG-F problem is defined and some efficiency indices designed to evaluate the PF/MG-F techniques are presented. One of the efficiency indices evaluates the inter-cell flows and inner-cell densities while another one measures the within-cell work-load balances. Another index measures the under-utilization levels of machines. A number of the most promising PF/MG-F techniques are selected for detailed analysis. These selected techniques are evaluated and compared in terms of the efficiency measures by employing randomly generated test problems. Finally, further research areas are addressed.
Open Access
Polyhedral Approaches to Hypergraph Partitioning and Cell Formation
(1994) Kandiller, Levent
Hypergraphs are generalizations of graphs in the sense that each hyperedge can connect more than two vertices. Hypergraphs are used to describe manufacturing environments and electrical circuits. Hypergraph partitioning in manufacturing models cell formation in Cellular Manufacturing systems. Moreover, hypergraph partitioning in VTSI design case is necessary to simplify the layout problem. There are various heuristic techniques for obtaining non-optimal hypergraph partitionings reported in the literature. In this dissertation research, optimal seeking hypergraph partitioning approaches are attacked from polyhedral combinatorics viewpoint. There are two polytopes defined on r-uniform hypergraphs in which every hyperedge has exactly r end points, in order to analyze partitioning related problems. Their dimensions, valid inequality families, facet defining inequalities are investigated, and experimented via random test problems. Cell formation is the first stage in designing Cellular Manufacturing systems. There are two new cell formation techniques based on combinatorial optimization principles. One uses graph approximation, creation of a flow equivalent tree by successively solving maximum flow problems and a search routine. The other uses the polynomially solvable special case of the one of the previously discussed polytopes. These new techniques are compared to six well-known cell formation algorithms in terms of different efficiency measures according to randomly generated problems. The results are analyzed statistically.