Hamdy A. Taha

The Economic Lot Sizes in Multistage Production Systems

Abstract This article develops a model for a single-product multistage production-inventory system with static deterministic demand, where the product moves between the stages in a serial fashion. In this model, it is assumed that the unfilled demand of the finished product is backlogged. Overproduction (with limitation) is allowed at the different stages so that each stage t may produce ki batches once every ki cycles. The decision variables for each stage i are the number of batches per run ki the batch size Qi , and the shortage quantity of the finished product Qs . These are determined by minimizing the total cost per unit time which includes the inventory holding cost, the shortage cost, and the setup cost. The problem is also considered for the case with storage constraints at the different stages.

A reliability simulation approach for use in the design process

A simulation model for use in the engineering design process is reported. The simulation model facilities reliability modeling by design engineers and reliability analysts early in the design process. The model applies to preliminary feasibility and design tradeoff studies. The authors describe the model, focus on applications to mission reliability analysis, and give a case study for the voice-communication system of the F-16 fighter aircraft. >

Simulation with SIMNET II

An outline of the SIMNET II simulation language is presented. SIMNET II is a network-based discrete simulation language that utilizes only four nodes: a source, a queue, a facility, and an auxiliary. Routing of transactions among the four nodes is effected by executing special assignments along the branches linking the nodes. SIMNET II offers powerful computational capabilities at a level equal to FORTRAN, thus eliminating the need for using external FORTRAN or C inserts as in other languages. The special assignments of SIMNET II also allow the modeler to exercise complete control over the internal characteristics of the nodes during execution. The system is totally interactive and is available in totally compatible version for mainframe, mini-, and microcomputers.<<ETX>>

A simulation-based software system for evaluating Hub-and-Spoke transportation networks

Abstract We present a simulation-based software system for evaluating Hub-and-Spoke transportation networks. A complete description of the software system, known as HUBNET, is presented. Major topics of discussion include the motivating problem environment of truckload trucking, the overall simulation solution architecture, and the primary components of the HUBNET system. The simulation driver, written in the SIMNET II language, is described in detail. Also discussed are the information management systems designed to create appropriate supporting information to drive the simulator and to integrate the software system with befitting data, and the user support facilities designed to enhance usability and to isolate the user of the system from detailed simulation coding tasks. Concluding remarks include a discussion of technology transfer and field use, and a discussion of ongoing and future research with the HUBNET simulator.

Sequencing by Implicit Ranking and Zero-One Polynomial Programming

Abstract A new model is formulated for sequencing n jobs on a single processor. This paper uses implicit ranking to combine three conflicting criteria in the same objective function; namely, the sequence-dependent setup cost; the inventory carrying cost; and the shortage cost. The effect of the setup time is also included. The formulation is based on the use of zero-one polynomial programming.

A heuristic model for the sequence-dependent lot scheduling problem

This paper presents a heuristic algorithm for finding a good solution for the sequence-dependent lot scheduling problem. Unlike available methods, the algorithm eliminates the need for creating new artificial problems and implementing feasibility tests. It also eliminates the tedious task of translating setup relationships into a mathematical programming formulation. The result is a conceptually simple solution technique that is practically motivated and easily implemented for use on the shop floor. Comparison of algorithm performance with published results demonstrates the efficacy of the approach.

Automatic generation of a class of simulation models from databases

The authors show the potential of using a higher-level language, such as BASIC, to automatically generate syntactically correct simulation models from functional databases. The resulting models may then be executed directly by the general-purpose simulation language of choice. The procedure is primarily developed for assembly line operations. The proposed approach is based on the observation that although the simulation logic of network-based models is generally simple, the structure of such models is highly input-data dependent. As an example a QuickBASIC program to generate SIMNET cost estimation is listed, and a SIMNET II simulation model for the example application is listed.<<ETX>>

An investigation of the use of goal programming to fit response surfaces

Abstract This paper deals with the development and implementation of goal programming models for fitting response surfaces where the observed data are characterized by certain peculiarities, such as the existence of ‘outliers’. A factorial statistical experiment is designed to compare (through Multivariate ANOVA) various forms of the goal programming algorithm with the traditional ordinary least squares method. The comparison is based on both the speed of convergence of the proposed algorithms and the accuracy of the estimated optimum solution relative to the true optimum of a pre-specified theoretical response surface. Results indicate that two different goal programming methods — each involving two secondary criteria — achieved a more accurate estimated solution than did the ordinary least squares method. This advantage is realized at the expense of slower convergence speed, however.

Unbiased statistics and simulation of continuous mail processing

Simulation is used to determine the number of sorting devices needed in an automated postal system facility. The model deals with mail types with great variability in processing characteristics. Interactions between continuously and sequentially processed batches at the sorting stations introduces a bias in conventionally collected statistics. This type of interaction in effect necessitates computation of statistics based on moving averages. Unfortu nately, none of the simulation languages provide this capability as a standard output. Although the logic of the basic simulation is straightforward, the model must be significantly modified to produce unbiased or undistorted statistics. SIMNET and SLAM II are used for independently developed final models.

A SIMNET simulation model for estimating system reliability

Abstract A general SIMNET simulation model is developed for estimating system reliability. The input data to the model is comprised of the minimal cut sets of the block diagram representing the system. The time-to-failure of the (parallel-series) components may be descriebd by different distributions. The model can be readily extended to include repair and maintenance of the components.