Susumu Morito

Efficient simulation/optimization of dispatching priority with “fake” processing time

An efficient simulation/optimization approach is presented for finding a dynamic dispatching priority in a static job shop environment under the presence of multiple identical jobs. The key ingredients of the proposed approach are (1) an efficient processingtime-based dispatching rule, (2) simulation of a job shop, and (3) a mechanism to “fake” (or modify) job processing times based on the information of job slack obtained from simulation. The paper presents an overall approach to fake processing times, and also identifies alternative strategies for algorithm design. Experimental results of the proposed approach yield a dispatching priority with more than 10% better due date performance than the priority generated by a good processing-time-based dispatching rule in roughly 20 simulation runs.

Design and analysis of a flexible manufacturing system with simulation-effects of flexibility on FMS performance

An extensive simulation model is developed to analyze Mazatrol flexible manufacturing systems (FMSs). The Mazatrol FMS is a module-type FMS consisting of several machining centers, load/unload stations, a stacker crane, a pallet stocker, etc. An analysis of the effects of various types of flexibility on FMS performance is presented. In particular, attention is given to the effects of such factors as the number of alternative machines that can perform a particular operation (called RFLEX) and the number of pallets for each type of operation. It is found that the flexibility of the overall system depends very much on RFLEX. When RFLEX=1 (i.e. one-to-one correspondence between an operation and a machine as in a standard job shop model), the system has limited flexibility; flexibility increases substantially when RFLEX is increased from 1 to 2, whereas further increase in RFLEX contributes only marginally to flexibility.<<ETX>>

Cooperative Dispatching – Exploiting the Flexibility of an FMS by Means of Incremental Optimization

Abstract We present a new control scheme for releasing parts into a flexible manufacturing system (FMS) that is based on incremental optimization. Our objective is to exploit the available routing flexibility of parts in an enhanced manner by viewing part release as an assignment problem using system status information. In particular, we propose an “intelligent” part release mechanism with some look-ahead and optimization features in order to allow for optimization-based “cooperation” of workcenters. The cooperative dispatching concept is implemented in an object-oriented computer simulation model, and experiments with a varying degree of average routing flexibility are performed. The experimental results are used for a statistical analysis of the benefits of cooperative dispatching versus the common approach of standard dispatching. Finally, we investigate the robustness of the presented FMS control scheme in the case of random machine breakdowns.

Minimum directed 1-subtree relaxation for score orienteering problem

Score orienteering is a variant of the orienteering game where competitors start at a specified control point, visit as many control points as possible and thereby collect prizes, and return to the starting point within a prescribed amount of time. The competitor with the highest amount of prizes wins the game. In this paper, we propose the minimum directed 1-subtree problem as a new relaxation to this problem and develop two methods to improve its lower bound. We describe a cut and dual simplex method and a Lagrangian relaxation method, and construct an algorithm that combines these two methods in an appropriate way. Computational experiments are carried out to analyse the behavior of the proposed relaxation with respect to the characteristics of the test problems. Especially for large-scale instances, we find that the proposed relaxation is superior to the ordinary assignment relaxation.

Planning a dental practice with a management game

This paper describes how a dentist can use a new management tool, a computerized dental practice management game, to plan his or her own practice. After reviewing factors to be considered in planning a dental practice, we briefly describe the game with special emphasis on what it can and cannot do. After identifying the information required to make such an exercise useful in planning a specific practice, the paper gives an example that shows how the game can be so used.

The Design of an Interactive Computer Software System for the Frequency-Assignment Problem

This paper discusses the problem of finding an interferencefree frequency assignment in a large communication system (e. g., in a large Naval fleet). In particular, the problem scenario, and the two algorithms, one an optimization procedure, and the second a heuristic technique, are discussed. The optimization algorithm is of the enumerative type and, in scenarios with a large communication system, may not terminate within a reasonable amount of computer time. To overcome this difficulty, an interactive heuristic-based software system is described which can be used by an astute decision maker to obtain a usable assignment relatively quickly.

An efficient alorithm for the general multiple-choice knapsack problem (GMKP)

A common problem frequently faced by business firms and individual investors is to select a few investment opportunities from many available possibilities. This problem, in its simplest form, can be modeled as a 0–1 knapsack problem. In a more general investment scenario, however, we obtain a model which is a general knapsack problem with a multiple-choice constraint. To solve this problem, an efficient enumerative algorithm is developed. The algorithm includes an efficient procedure to solve the LP-relaxed problem, a reduction algorithm which may allow the initial fixing of some of the variables, and various other implicit enumeration criteria derived from the group problem. Extensive computational experience illustrates the efficiency of the algorithm and related results.

Combination of multiplicative congruential random-number generators with safe prime modulus

Two or more multiplicative congruential random-number generators with prime modulus combined by means of a method proposed by Wichmann and Hill (1982) yield a random-number generator equivalent to a multiplicative congruential random-number generator with modulus equal to the product of the moduli of the component multiplicative congruential generators. The period of a random-number sequence obtained by the Wichmann-Hill method is equal to the least common multiple of the periods of the combined sequences. One of the two purposes of this paper is to present a necessary and sufficient set of efficiently verifiable conditions for the period to be equal to its maximum, which is the maximum of the least common multiple. Each of the conditions is always satisfied or is more easily verifiable when the modulus of each of the component generators is a safe prime. The other purpose of this paper is to derive an efficiently evaluatable formula for serial correlations of the maximum-period sequences by the Wichmann-Hill method. The authors recommend (i) to make the modulus of each of the component generators a safe prime, and (ii) to chose the multipliers of the components so as to (a) maximize the period and (b) make the serial correlations small in absolute value.

Development of a simulation-based planning system for a flexible manufacturing system

This paper discusses authors’ continued study on development of a discrete-event simulation model and associated software for a real-life commercial moduletype flexible manufacturing systems (FMS). After describing the organization of the developed system, simulation analysis of the FMS would be given. In contrast to our previous study where makespan was taken as the performance measure, this analysis focuses on machine utilization and sojourn time, and the effects of routing flexibility and of the numbers of operations and pallets are examined. Our analysis shows that increased routing flexibilityy achieved by having several alternative machines, which was found to help reduce makespan, also lesds to improved machine utilization and reduced sojourn time. As in the case of makespan, most of improvement would be achieved by having two alternative machines, and contributions expected from further increase are only marginal It is also shown that an incresse in the number of operations reduces machine utilization. The relationshipp between the number of operations and machine utilization is roughly linear, and the slope depends on the degree of routing flexibility. The paper also describes possible uses of the simulation system which could lead us to a simulation-based planning system.

Unit Commitment by Column Generation

The unit commitment problem is to determine the schedule of power generating units and the generating level of each unit. The decisions involve which units to commit at each time period and at what level to generate power to meet the electricity demand. We consider the heuristic column generation algorithm to solve this problem. Previous methods used the approach in which each column corresponds to the start–stop schedule and output level. Since power output is a continuous quantity, it takes time to generate the required columns efficiently. In our proposed approach, the problem to be solved is not a simple set partitioning problem, because the columns generated contain only a schedule specified by 0–1 value. It is shown that the proposed heuristic approach is effective to solve the problem.