J. Soeiro Ferreira

TOPOS – A new constructive algorithm for nesting problems

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 to 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.Zusammenfassung. In dem vorliegenden Beitrag entwickeln die Autoren ein neues Konstruktionsverfahren für das „Nesting-Problem”, d.h. für ein zweidimensionales Zuschneideproblem mit unregelmäßigen Objekten. Das Schnittmuster wird dadurch gebildet, dass sukzessive zuzuschneidende Objekte (Teile) einer Teillösung angegliedert und damit neue Teillösungen gebildet werden. Verschiedene Kriterien zur Auswahl des jeweils anzuordnenden Teils und seiner Orientierung werden vorgestellt. Außerdem werden verschiedene Zielfunktionen zur Bewertung der Teillösungen herangezogen. Insgesamt ergeben sich so 126 Varianten des Konstruktionsverfahrens, die systematisch anhand von Datensätzen aus der Literatur getestet werden. Für einige Testprobleme stellt das neue Verfahren Lösungen bereit, die besser sind als die besten bisher in der Literatur beschriebenen Lösungen.

A two-phase roll cutting problem

Abstract A two-phase roll cutting problem appearing in the iron and steel industry is considered in this paper. It consists of optimizing the planning of roll cutting that, for technological reasons, is effected in two phases, i.e., each raw material roll is cut into intermediate primary rolls, which in turn are cut to obtain the constituent rolls of the final product. Apart from an inherent complexity to the cutting problem resulting from the large variety of final product dimensions, other supplementary difficulties also exist. These are related to the existence of numerous restrictions involved in the whole process and the link between the two cutting phases. A heuristic was developed and tested, that is based on an automatic sequential search with defined objectives, so as to obtain a good compromise between pattern usage and trim loss, respecting the various technological impositions. Finally, a real example taken from the steel industry together with the solution obtained from a computerized version developed for microcomputers, is presented.

Reel and sheet cutting at a paper mill

This work describes a real-world industrial problem of production planning and cutting optimization of reels and sheets, occurring at a Portuguese paper mill. It will focus on a particular module of the global problem, which is concerned with the determination of the width combinations of the items involved in the planning process: the main goal consists in satisfying an order set of reels and sheets that must be cut from master reels. The width combination process will determine the quantity/weight of the master reels to be produced and their cutting patterns, in order to minimize waste, while satisfying production orders.A two-phase approach has been devised, naturally dependent on the technological process involved. Details of the models and solution methods are presented. Moreover some illustrative computational results are included.

CYLINDER PACKING BY SIMULATED ANNEALING

Este artigo aborda o problema de posicionamento de objetos de base circular (tubos, rolos, ...) sobre uma base retangular de maiores dimensoes. Por razoes praticas, considera-se que todos os objetos a carregar apresentam a mesma altura. A resolucao do problema consiste na determinacao do padrao de posicionamento das bases circulares dos referidos objetos sobre a base de forma retangular, tendo como objetivo a maximizacao do numero de objetos estritamente posicionados no interior dessa base. Este padrao de posicionamento sera repetido em cada uma das camadas a carregar sobre a base retangular. Apresentam-se dois algoritmos para a resolucao do problema. Estes algoritmos baseiam-se numa meta-heuristica, Simulated Annealling, cuja afinacao de parâmetros requereu a execucao de testes intensivos com o objetivo de atingir um elevado grau de eficiencia no seu desempenho. As caracteristicas dos algoritmos implementados permitiram que a sua extensao a consideracao de circulos com raios diferentes fosse facilmente conseguida.

Multimethodology in Metaheuristics

As a combination of different methodologies or parts of methodologies, Multimethodology is becoming more frequent in OR practice. This paper contributes with a new proposal and a new field of application: the employment of Multimethodology in problem solving with Metaheuristics (Mh). A convenient selection of soft and hard methods will be considered, from Soft OR, Creativity and Metaheuristics, such as Strategic Choice Approach, SWOT Analysis and Divergent and Convergent thinking. Formulating the ‘right’ optimisation problem, choosing a method based on Mh and accomplishing an effective implementation is an imprecise decision-making process, which may require skills and ideas that are beyond the ordinary boundaries of Mh practice. The relevance and success of Mh have been well-known for decades, but some open questions concerning choice and implementation strategies, for instance, still remain. If these questions are not adequately answered, they may lose credibility in the long term. The quality of solutions and computational times are not the only criteria used to analyse Mh, nor are they the most important. Very often, the effectiveness of an approach has to be evaluated from the perspective of modelling and practical problem solving. This paper investigates the advantages of Multimethodology and, furthermore, it sketches a framework for a coherent and comprehensive comparison of Mh and recommends a dynamic guiding tool for their implementation.

Integrated resolution of assignment, sequencing and cutting problems in paper production planning

The integrated planning of several activities implicated in paper production can lead to remarkable gains in terms of raw materials and resource usage. However, activities such as order assignment, production sequencing and cutting planning are usually addressed separately while ignoring the interactions among these processes. But the quality of the solution resulting from the juxtaposition of the partial solutions is not guaranteed, and may have a significant impact in terms of inefficiency of global performance. This article considers production planning in a pulp and paper industry in order to meet a set of orders of diverse types of products, admitting the possibility of producing simultaneously in two or more paper machines with their own features. The developed approach, ASC-3Steps, considers not only cutting optimisation but also extends itself to the processes of assigning orders to paper machines and production sequencing at each machine. Minimisation of wasted paper is assumed to be the overall goal. A set of computational results based on real data is presented.

Sectors and Routes in Solid Waste Collection

Collecting and transporting solid waste is a constant problem for municipalities and populations in general. Waste management should take into account the preservation of the environment and the reduction of costs. The goal with this paper is to address a real-life solid waste problem. The case reveals some general and specific characteristics which are not rare, but are not widely addressed in the literature. Furthermore, new methods and models to deal with sectorization and routing are introduced, which can be extended to other applications. Sectorization and routing are tackled following a two-phase approach. In the first phase, a new method is described for sectorization based on electromagnetism and Coulomb’s Law. The second phase addresses the routing problems in each sector. The paper addresses not only territorial division, but also the frequency with which waste is collected, which is a critical issue in these types of applications. Special characteristics related to the number and type of deposition points were also a motivation for this work. A new model for a Mixed Capacitated Arc Routing Problem with Limited Multi-Landfills is proposed and tested in real instances. The computational results achieved confirm the effectiveness of the entire approach.