Abdolazim Houshyar

A heuristic for assigning facilities to locations to minimize WIP travel distance in a linear facility

SUMMARY Many manufacturing systems require an assignment of machines to locations along a straight track, so as to optimize material flow. This paper uses a cut approach to the corresponding quadratic assignment problem, and derives a heuristic which generates a good solution. In addition, a modified lower bound to the assignment problem is also developed, which is always better than the classical lower bound. Results showing the performance of the heuristic are demonstrated, along with a comparison of the modified and classical lower bound. In almost all the test problems, the solution generated by the heuristic was either optimal or better than any solution obtained by other methods. Extension of the heuristic to more general cases also is considered.

Financial analysis of a theoretical lean manufacturing implementation using hybrid simulation modeling

Abstract Many researchers have identified the negative impact that accounting methods have on reported profits as inventories are being rapidly reduced. This research explores the magnitude and duration of the negative impact on reported profits experienced during a lean manufacturing implementation. The effect on reported profit is evaluated under five accounting methods (full absorption costing, activity-based costing, direct costing, throughput costing, and order activity costing) and three levels of inventory reduction rate. The findings reported here indicate that the period-by-period gains in operational efficiency, resulting from process improvements brought by a lean program, will not counteract the negative impact from the accounting system on the income statement while inventories continue to be reduced. This could lead to the early termination of a lean program that is, in fact, bringing operational improvement in the present time, but the improvement is being erased by poor inventory control practices from past periods. This research uses a multi-period simulation model of a production operation that incorporates a manufacturing planning and inventory tracking system. A hybrid simulation approach is employed using Microsoft® Excel to model the Manufacturing Resource Planning (MRPII) function, while ProModel simulation software is used for the development and operation of the model production environment. Microsoft® Visual Basic® is used to create a bridge between systems for schedule dissemination and inventory updates. The integrated computer simulation modeling approach developed to conduct this research is novel in the sense that multi-period simulation, incorporating MRP, has not been widely used based on available literature.

Computer aided facility layout: an interactive multi-goal approach

Abstract This paper describes an interactive multi-goal approach for combining the quantitative and qualitative aspects of facility layout. The two objectives which may be conflicting are minimizing the materials handling cost and maximizing a closeness rating measure. Assuming that the decision maker is capable of responding to a paired comparison of alternatives, an interactive algorithm is developed that iteratively reduces the feasible space of the decision makers weighing factor that combines the two goals. The algorithm stops when the predetermined bounds on the weighing factor are reached, and/or the optimality criteria is reached. A graphical method is presented that helps analyze the sensitivity of the optimum layout to small variations in the estimated value of the decision makers preferred weight. Few examples are presented, and conclusions are made.

A simulation study of an automotive foundry plant manufacturing engine blocks

This paper discusses the initial efforts to implement simulation modeling as a visual management and analysis tool at an automotive foundry plant manufacturing engine blocks. The foundry process was modeled using Pro Model to identify bottlenecks and evaluate machine performance, cycle times and production data (total parts, rejects, throughput, products/hr) essential for efficient production control. Results from the current system identified assembly machine work area as the bottleneck (although utilization was greater than 95% for two assembly machines) resulting in high work-in-process (WIP) inventory level, low resource and machine utilization. Based on these results, optimum numbers were identified through use of scenarios by varying the number of assembly machines and processing time of each machine. In addition to these scenarios, strategies for production control involving buffer sizes were also made.

Biomechanical tolerance limits for manual lifting tasks: a tool to control back injuries

Develops biomechanical tolerance limit (BTL) guidelines for manual lifting tasks based on the published literature. The information is invaluable to researchers and practitioners of occupational safety and health for the prevention of back injuries due to manual lifting tasks. A summary of the compressive loads on the lumbar spine from various sources is provided. Conclusions are drawn from this data about the mean compressive strength of the lumbar spine.<<ETX>>

Using simulation to compare different automated storage/retrieval system designs

Abstract The Automated Storage and Retrieval Systems (AS/RS) are highly specialized material handling systems that are becoming increasingly popular for high capacity, effective use of warehouse space, and smoothing the flow of operations. In order to avoid expensive over-building, and even more expensive bottlenecks due to poorly designed systems, a simulation model is developed that evaluates the behavior of the system under some realistic assumptions. The model employs random inter-arrival time for storage and retrieval, and for assignment of unit loads to storage locations, and uses such parameters as S/R cycle time, conveyor speed and number of I/O buffers to study the system performance. The result of this study is a better understanding of the affect of different parameters on the effectiveness of the system and its overall cost performance.

What can be done to screen progressive diseases optimally

Abstract A stochastic model for a screening program is presented in which the natural history of the disease is assumed to progress through a set of stages before detection. A model of the whole process is developed to address the interaction of the disease process and screening process. The purpose of the model is to develop insight into the disease process and derive policies which are optimal relative to the particular objectives chosen.

A mathematical model for scheduling screening tests for progressive diseases

In this paper, a mathematical model describing the stochastic process underlying the etiology of noncontagious, curable, progressive diseases is developed. In our previous study of progressive diseases, the reliabilities of screening tests were assumed to be constants, independent of how long the individual has had the disease. The purpose of this study is to develop more insight into modeling the disease process, and the interaction of screening tests with the natural behavior of the disease. To accomplish this task, more realistic screening parameters are selected, and optimum policies for mass screening programs under different reliabilities of screening tests are developed. These modifications make the model general enough to be applicable to a larger class of progressive diseases that includes breast cancer. Solutions to two simplified versions of the model for childhood neuroblastoma illustrate the use of our proposed procedure.

Consideration of instage and central buffers in two-stage production system

Abstract In this paper, the effect of instage buffer storage and central buffer for bulk storage on the system cost of a two-stage production line is considered for the case where the two production units have different production rates. A mathematical model is developed to determine optimal ready buffer size and number of material handler trips while minimizing total system cost. The model also performs a cost comparison of two potential alternate manufacturing strategies.

Optimization Techniques in Occupational Biomechanics

In most detailed representations of joint mechanics incorporating the effects of muscle forces in biomechanical models the number of available force-carrying structures crossing the joints are in excess of the number of available equilibrium of the joint. Unless one makes gross anatomical and functional simplifications, the mathematical description of joint mechanics involves an undetermined set of equations. Different approaches have been taken by researchers to solve this statically indeterminate problem, but the intuitive reasonableness of optimization in body function has led investigators to use numeral optimization procedures in the prediction of muscle force activity. This paper reviews and evaluates various optimization techniques applied to occupational biomechanics.