Abstract

Abstract

Abstract
This paper presents a very special cutting path determination problem appearing in a high precision tools factory, and provides two new heuristics for its resolution. Particular features of both the cutting process, and of the material to be cut, bring in a set of unusual constraints, when compared with other cutting processes, which confer additional complexity and originality to the problem. In particular, this is a matter of practical and economic relevance, since the solution methods are intended to be implemented in a real-life industrial environment. The concept of dynamic graph is exploited to deal with the arc routing problem under study, which is modelled as a dynamic rural postman problem. The constructive heuristics developed, the "higher up vertex heuristic" (HUV) and the "minimum empty path heuristic" (MEP) are tested with real data sets.

Abstract
In this paper we present a new constructive algorithm for nesting problems. The layout is built by successively adding a new piece to a partial solution, i.e. to the set of pieces previously nested. Several criteria to choose the next piece Co place and its orientation are proposed and tested. Different objective functions are also proposed to evaluate and compare partial solutions. A total of 126 variants of the algorithm, generated by the complete set of combinations of criteria and objective functions, are computationally tested. The computational experiments are based on data sets published in the literature or provided by other authors. In some cases this new algorithm generates better solutions than the best known (published) solutions.

Abstract
The paper concerns a flexible flowline scheduling problem, which arises in the footwear industry. Flexibility of the line allows for manufacturing simultaneously more products in lower quantities, but it also increases the complexity of the task of balancing the line, specially because the mix of products changes everyday. A simulation model to deal with the flexible line is developed and several job sequencing rules and different part input criteria are implemented. The impact of each rule on the quality of the schedules is measured, namely, according to makespan, productivity and average machine utilisation. Computational results concerning a real application are also presented. SIMPLE++ is the simulation language used.

Abstract
In this paper the problem of minimizing the total cost of a pump-pipe system in series is considered. The route of the pipeline and the number of pumping stations are known. The optimization will then consist in determining the control variables, diameter and thickness of the pipe and the size of the pumps. A general mathematical model is formulated and Dynamic Programming is used to find an optimal solution. Practical reasons, derived from the techniques engineers generally use to cope with such problems, and special characteristics of the mathematical structure of the model justified the consideration of particular cases of the system. This analysis, based on Dynamic Programming, enabled us to elaborate a simple heuristic method, condensing those techniques, and supplied sufficient conditions for the heuristic to operate as an optimal procedure. The solution of a realistic example confirms the viability of the conditions developed and tests the formulation (also presented) of the optimization problem by the Discrete-Time Optimum Principle for the general control problem.