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As competition has intensified, many American manufacturers have sought alternatives to rejuvenate their production systems. Cellular manufacturing systems have received considerable interest from both academics and practitioners. This research examines three major issues in cellular manufacturing that have not been adequately addressed: applicability, structural design, and operational design. Applicability, in this study, is concerned with discerning the circumstances in which cellular manufacturing is the system of choice. The methodology employed is simulation and two experimental studies are conducted. The objective of Experiment I, a 2 x 3 x 3 factorial design, is to investigate the role of setup time and move time on system performance and to gain insight into why and how one layout could outperform another. The results of Experiment I suggest that move time is a significant factor for job shops and that workload variation needs to be reduced if the performance of cellular manufacturing is to be improved. Experiment II evaluates the impact of setup time reduction and operational standardization on the performance of cellular manufacturing. The results of Experiment II suggest that cellular manufacturing is preferred if the following conditions exist: (1) well balanced workload, (2) standardized products, (3) standardized operations, and (4) setup times independent from processing times. / Ph. D.

The problem of unit commitment in an electric utility system is analyzed. The types of generating units considered include nuclear-steam, fossil-steam, thermalpeaking, conventional and pumped-storage hydro. The large problem of generating unit commitment, due to the inclusion of the nuclear unit, is decomposed into two stages. In the first stage, the relatively stable nuclear generation is optimized with respect to the generation from the large fossil-steam unit. Hourly generation levels for all the units in the system are determined in the second stage. AS a result of considering the startup-shutdown cost, the objective function has a fixed charge component in addition to first and second degree polynomials. Representation of the minimum turndown level and minimum Shutdown duration of the generator necessitates the use of O-1 variables along with continuous variables. The solution methodology presented here, applying an extension of the Lambda-Separable Programming, can handle these requirements efficiently. Application of the algorithm results in a minimum-cost generation schedule for all units in the system. Optimum generation levels of energy limited units are determined without using a preselected unit commitment order. The effect of startup-shutdown costs on the number of hours a Plant should operate is established. The cost and benefit of spent nuclear fuel reprocessing is analyzed and the effect of uranium prices on it (reprocessing) is shown. The model is tested using a sample system of six generating units. Hourly generation schedules, includig purchase and sale, are determined for two one-week periods while the nuclear generation is optimized for an entire year. / Ph. D.

This thesis presents a methodology for determining faculty/course assignments based on preferences for the goals faculty members feel are important and seek to attain in selecting the courses they would like to teach. The heuristic procedure seeks to maximize faculty goal and preference attainments for the courses. Several operations research techniques have been used to solve this problem, but the limitations of the techniques minimize their usefulness. A discussion of these techniques and their sources of information are given. The assignment model uses faculty preferences for courses based on course-specific goals, faculty availability, and maximum teaching load as constraining factors. The model was implemented using three Advanced BASIC programs with interactive capability. The model was tested in the Department of Industrial Engineering and Operations Research at Virginia Tech. System analysis was performed utilizing pre-test measures of satisfaction with the teaching assignments determined by the current scheduling system and post-test measures of satisfaction with the teaching assignments determined by the proposed scheduling system. An analysis of the results is included. / Master of Science

Scheduling workers in a restaurant is a difficult and time consuming task that involves matching the needs of the restaurant with respect to filling various shifts for different positions, the varying availabilities of the workers, along with their seniority levels and qualifications, among other factors. The restaurant manager/scheduler must adhere to these individual workers' restrictions, while at the same time satisfy the restaurant's needs. Another issue that a manager tries to accommodate is to equitably assign shifts to workers, attempting to balance their expressed wishes with their relative merits and qualifications; although in practice, this goal is rarely achieved. In this thesis, a mathematical model is developed to solve the scheduling problem, with attention focused on maximizing worker satisfaction levels, considering their seniority levels and their qualifications, while meeting with the restaurant's needs of filling various required shifts for various positions with capable workers. We show that this model possesses a hidden network structure that can be revealed via some simple variable substitutions. Consequently, an efficient network-flow approach can be used to solve the model and derive an optimal (integer) solution. We illustrate the model and the proposed algorithmic approach by generating a schedule using real data obtained via specially designed surveys from the Cheddar's restaurant in Newport News, Virginia. Further results on a variety of test problems are used to evaluate the performance of the algorithm, and suitable pre- and post-processor considerations are addressed to permit the use of this technology in a productive environment. / Master of Science

This research presents two switching techniques using SOT and SLACK, as complementary sequencing rules, to show that they are practical procedures to control a job shop. These two approaches are: Static switching of the complementary rules. Dynamic switching of the complementary rules. This study also presents questions which arise in creating different switching rules or procedures for an interactive scheduling system. It is also developed a normalized objective function to measure the balance of the best properties produced by SOT (low flow time) and SLACK (low tardiness). It should be noted that even though such a system could be viewed as complex and expensive,it is not. Computational requirement will be slightly increased, but no more data is required than is expected for a typical scheduling procedure. Finally, a procedure to calculate the upper and lower limits is presented for dynamic switching procedures. / Master of Science

The topic of unit commitment has been and continues to be of interest to many researchers and is a primary operation for most utilities. Past research has utilized integer programming, dynamic programming, linear programming, gradient, and heuristic techniques. This research combines both linear programming and dynamic programming for unit commitment decisions within a weekly time frame. The result provides most of the advantages of linear programming and dynamic programming with less stringent requirements on the pre solution information needed for unit transition sequences. Further, the research yields a new tool for the solution of the Transaction Evaluation problem. / Ph. D. / incomplete_metadata

Scheduling is one of the most important functions in a factory and it is determining when and with what resources jobs should be accomplished. An important factor that affects the scheduling of jobs is the dynamic variation of factory status. Existing computer based scheduling systems do not address the need of making effective decisions dynamically with the variations in factory status. Traditionally, Operations Research techniques have provided an effective tool in solving manufacturing planning problems. But these methods have not been able to effectively address real time control problems in the manufacturing environment. To address some of these problems, this research investigates applying an expert system approach to develop an interactive real time dynamic scheduling system. Specifically, a knowledge base structure is developed and applied to a case study representing a two stage production system. A Blackboard concept has been utilized to organize and maintain the dynamic data base. The major knowledge representation schemes used in the system include, frame structures, relational tables, and production rules. The system was tested on a case study, by conducting a sample interactive session on a set of simulated dynamic situations. The test demonstrated the viability of implementing knowledge based systems for dynamic scheduling at the operational level of a plant. / Master of Science