Alberto Garcia-Diaz

A network flow approach to solve clustering problems in group technology

A fundamental group technology (GT) problem is the identification of part families and the decomposition of the manufacturing system into machine cells. The objective of the network flow methodology developed in this article is to measure the functional similarity between machines and then to group the machines into cells in such a way that all the parts in each family can be processed in a machine cell. The solution to the GT problem is obtained in terms of one complete-loop and several sub-loops identified by using a state-of-the-art relaxation method for solving the network flow problem. The concept of using a network flow model for cluster analysis is a new approach. It appears to have an excellent potential to provide computationally efficient optimal solutions when compared to the p-median model.

Network flow procedures for the analysis of cellular manufacturing systems

A three-phase network-flow-based procedure is developed for minimizing intercellular part moves in machine-part grouping problems. The unique feature of this methodology is its consideration of several variations related to the number of cells, the number of machines in each cell, and the part family size. The first phase computes a functional relationship between machines on the basis of either a machine-part matrix or actual operation sequences for the parts being considered. The final purpose of this phase is a network modeling of the problem. The second phase partitions the network according to mutually exclusive sets of nodes that represent manufacturing cells. A 0-1 integer programming model and a 0-1 quadratic programming model are discussed and network-flow-based solution procedures are developed. Finally, the third phase identifies the part families. A 0-1 integer programming model is formulated and the solution of this model is again performed through a network approach that allows the identific...

Dynamic Programming Analysis of Special Multi-Stage Inspection Systems

Abstract A branch-compression dynamic programming approach is developed to investigate the degree of repeated inspection resulting in minimal expected quality control cost in a special class of nonserial production processes. The total cost includes inspection and reworking costs at each stage of the process, plus a penalty cost due to defective product which is not detected by the inspection scheme.

A computer simulation approach to evaluating assembly line balancing with variable operation times

Purpose – The purpose of this paper is to develop a computer simulation model to evaluate the bowl phenomenon and the allocation at the end of the line of stations with either greater mean operation times or higher variability of operation times.Design/methodology/approach – The model was developed on the basis of a realistic case problem and applied to a six‐station assembly line. The evaluation criteria were the: minimization of the total elapsed time; maximization of the average percentage of working time; and minimization of the average time in the system.Findings – The performance of an assembly line with independently normally distributed operation times could be improved by applying the bowl phenomenon. The allocation of large operation mean times to stations located near the end of the line did not produce improved results. Instead a more balanced allocation proved to be more significantly effective. On the other hand, the assignment of larger variability of operation times to the stations near th...

Markovian Models for Investigating Failure and Repair Characteristics of Production Systems

Abstract This paper presents a Markov chain approach for investigating the steady-state production capability of manufacturing systems in terms of specified reliability and maintainability characteristics. Three general classes of models are developed. The first model considers a system with only elements which cause the system to immediately shut down when the first failure happens; the second model considers a system with only elements which cannot be repaired while other elements are functioning; the third model considers a system with only elements which can be repaired while other elements are in operation.

A polyhedral graph theory approach to revenue management in the airline industry

Revenue management is a business principle that balances supply and demand to control price and/or inventory availability in order to maximize revenue and profit growth. Airlines offer a variety of fare products to the marketplace to preserve their regular customers, reduce unsold seats by attracting lower fare customers, and maintain a competitive image. This article develops a new analytical procedure for joint pricing and seat allocation problem considering demand forecasts, number of fare classes, and aircraft capacities. The proposed polyhedral graph theoretical approach utilizes split graphs and cutting planes and achieves significant computer timesavings when compared to a general-purpose integer programming commercial software. Although this article focuses on the airline industry, the proposed approach has a potential utilization in such service and transportation related industries as lodging, car rental, trucking, rail, cargo, broadcasting, housing, cruise lines, manufacturing, entertainment, energy, and health care.

Highway cost allocation: An application of the theory of nonatomic games

The purpose of all highway cost allocation procedures is to divide in a fair and rational manner the cost building or rehabilitating highway facilities among the highways users. This article proposes a solution approach to the highway cost allocation problem based on game theory. In this approach, every passage made on the road is viewed as a player in a game that has a large number of insignificant players. For this reason, it can be assumed to be a nonatomic game. Of all highway costs, pavement costs are the most difficult to allocate on the basis of relative damage caused by the user of a highway. A distinctive feature of the analysis conducted in this article is the consideration of a nonlinear programming model that optimizes the total cost of pavement as the characteristic function of the game. The distribution of pavement construction costs proposed by the Federal Highway Administration is essentially a numerical procedure for obtaining value. A solution to the nonatomic game is presented based on a set of axioms that result in allocations that are desirable for its properties. The solution obtained by the proposed approach is compared to existing highway cost allocation methodologies.

Factor selection guidelines for job evaluation: A computerized statistical procedure

A computer-aided statistical procedure based on standard measures of central tendency, dispersion and correlations was developed to identify meaningful compensable factors and scales in a point job evaluation plan. The procedure specifically examines the degree of field overlapping between factors, their ability to be reliable wage indicators, as well as their ability to discriminate among jobs. To facilitate the execution of the statistical procedure a computer program was written in Visual Basic. The use of the proposed methodology was demonstrated by means of a case or sample problem.

Minimal-cost network flow problems with variable lower bounds on arc flows

The minimal-cost network flow problem with fixed lower and upper bounds on arc flows has been well studied. This paper investigates an important extension, in which some or all arcs have variable lower bounds. In particular, an arc with a variable lower bound is allowed to be either closed (i.e., then having zero flow) or open (i.e., then having flow between the given positive lower bound and an upper bound). This distinctive feature makes the new problem NP-hard, although its formulation becomes more broadly applicable, since there are many cases where a flow distribution channel may be closed if the flow on the arc is not enough to justify its operation. This paper formulates the new model, referred to as MCNF-VLB, as a mixed integer linear programming, and shows its NP-hard complexity. Furthermore, a numerical example is used to illustrate the formulation and its applicability. This paper also shows a comprehensive computational testing on using CPLEX to solve the MCNF-VLB instances of up to medium-to-large size.

Cost-effective selection and multi-period scheduling of pavement maintenance and rehabilitation strategies

An optimization methodology is developed for determining the most cost-effective maintenance and rehabilitation (M&R) activities for each pavement section in a highway pavement network, along an extended planning horizon. A multi-dimensional 0–1 knapsack problem with M&R strategy-selection and precedence-feasibility constraints is formulated to maximize the total dollar value of benefits associated with the selected pavement improvement activities. The solution approach is a hybrid dynamic programming and branch-and-bound procedure. The imbedded-state approach is used to reduce multi-dimensional dynamic programming to a one-dimensional problem. Bounds at each stage are determined by using Lagrangian optimization to solve a relaxed problem by means of a sub-gradient optimization method. Tests for the proposed solution methodology are conducted using typical data obtained from the Texas Department of Transportation.