Um método de redução para programação semi-infinita não linear baseado numa técnica de penalidade exacta

Tese de doutoramento em Engenharia Industrial e de SistemasOs problemas de programação semi-infinita (PSI) aparecem nas mais diversas áreas da Engenharia, tais como, no planeamento da trajectória de robôs, no controlo da poluição atmosférica, no planeamento da produção, no desenho óptimo de conjuntos de sinais e desenhos de filtros digitais. Esta tese é dedicada a problemas de PSI não linear na sua forma mais geral. Os problemas considerados são caracterizados por possuírem um número finito de variáveis e um conjunto infinito de restrições. Os métodos numéricos existentes para a resolução de problemas de PSI podem ser divididos em três classes principais: métodos de discretização, métodos das trocas e métodos de redução. Os métodos de redução são os que possuem melhores propriedades teóricas de convergência. São, também, os mais exigentes em termos numéricos uma vez que exigem a resolução de problemas auxiliares, em que se pretende a determinação de todos os óptimos globais e locais (optimização multi-local). Nas últimas décadas foram apresentados vários algoritmos para problemas de PSI. Contudo há pouco software disponível e nenhum fornece uma implementação de um método pertencente à classe de redução. Neste trabalho é proposto um algoritmo de redução local baseado na técnica de penalidade. A função usada considera uma extensão de uma função de penalidade de norma-1 aumentada. A escolha desta função de penalidade para propor a extensão às restrições finitas deve-se à obtenção de melhores resultados numéricos para um conjunto de problemas teste de PSI sem restrições finitas, em comparação com as funções de penalidade baseadas na norma 1, 2 e ∞ da violação das restrições. Fez-se o estudo das propriedades teóricas da função de penalidade estendida. É feita uma implementação do algoritmo de redução local proposto. O solver desenvolvido é designado por SIRedAl (Semi-Infinite Reduction Algorithm). Este solver foi implementado em MATLAB e é capaz de resolver problemas de PSI na forma mais geral com dimensão infinita máxima de 2. O código do solver usa dois algoritmos diferentes na minimização da função de penalidade e dois na resolução dos problemas multi-locais. O solver foi testado com 117 problemas teste da base de dados SIPAMPL e os resultados numéricos confirmaram a potencialidade do algoritmo proposto.Semi-infinite programming (SIP) problems arise in several engineering areas such as, for example, robotic trajectory planning, production planning, digital filter design and air pollution control. This thesis is devoted to SIP problems in the most general form. These problems are characterized to have a finite number of variables and an infinite set of constraints. The existing numerical methods for solving SIP problems can be divided into three major classes: discretization, exchange and reduction type methods. The reduction type methods are the ones with better theoretical properties, but they are also the most de- manding in computation terms, since they require to solve sub-problems to the local and global optimality (multi-local optimization). In last decades several algorithms were proposed for SIP, but there are not many pu- blicly available software and none provides an implementation of a method belonging to the reduction type class. In this work we propose a reduction type algorithm based on a penalty technique. The penalty function used is an extension of a penalty function of 1-norm, allowing the inclu- sion of finite constraints. In order to define the best penalty function, a numerical study of penalty functions based on the standard 1, 2 and ∞ norms are performed, considering test problems without finite constraints. A theoretical study of the extended penalty function is also performed. The proposed reduction algorithm is implemented in a solver coined as SIRedAl (Semi- Infinite Reduction Algorithm). The solver has been implemented in MATLAB and is capable of solving SIP problems in the most general form with a maximum of two infinite variables. The solver code uses two different algorithms in the minimization of the penalty function and also two different algorithms for solving the multi-local problems. The solver has been tested with 117 test problems from the database SIPAMPL and numerical results confirmed the algorithm potential.Instituto Superior de Engenharia do Port

Analysis of methods for supplier selection

This work seeks to determine the criteria and methods used in the problem of selecting suppliers, thus contributing to the support of entities wishing to start a selection of suppliers more effectively. To achieve these objectives, an analysis was performed of articles that make the literature review of the methods and criteria from the year 1985 to the year 2012. With the data obtained from these reviews, it was possible to verify which are the three main methods used over the years, namely data envelopment analysis (DEA), Analytical hierarchy process (AHP) and Fuzzy set theory and the main criteria used in the selection of suppliers. In this work, we present an overview of the decision making and the methods used in multi-criteria decision making. It’s tackled the problem of supplier selection, the process of selection and the reviews of literary methods and criteria used in recent years. Finally is presented the contribution to the selection of suppliers of the study conducted during the development of this dissertation, being presented and explained the main methods of selection of suppliers as well as the criteria used.info:eu-repo/semantics/publishedVersio

An algorithm of a costing system for electroplating

Businesses are increasingly competitive and rigorous and it is essential the existence of a strong, effective and realistic costing system. Decisions taken on the basis of the costing are very important, they can make the difference between success and failure of the organization. This paper explains the construction of an initial algorithm that aims to calculate the costs associated with electroplating of metal articles, in a specific company. This work can act as a possible guide for the construction of the costing system algorithms in this type of industry.info:eu-repo/semantics/publishedVersio

Adaptations of a resources system selection problem of Distributed/Agile/Virtual Enterprises for using genetic algorithms

The selection of resource systems is still a difficult matter to solve in distributed / Agile / Virtual enterprises ( D/A/V Es ) integration. Attempts to solve the resources selection problem, has originated several models and consequently different algorithms have been applied to obtain solutions. The exact algorithms have good performance (in terms of computational time) for low dimension problems. However, become ineffective as the complexity increases. Genetic algorithms are considered robust and versatile. These have been applied to complex problems in several application areas and gained popularity in innumerable research works. To improve the computational time in solving the resources selection problem, we pretend to apply a genetic algorithm. Due to the characteristics of the model, the application of this algorithm forced adjustments in the initial model. In this work, we present the adaptations performed in the study model in order to use genetic algorithms.info:eu-repo/semantics/publishedVersio

Optimal trajectory approximation by cubic splines on fed-batch control problems

Optimal control problems appear in several engineering fields and in particular on the control of fedbatch fermentation processes. These problems are often described by sets of nonlinear differential and algebraic equations, usually subject to constraints in the state and control variables. Tradicional approaches to the optimal feed trajectory computation consists in getting a linear spline that approximates the trajectory, which optimizes a given performance of the fed-batch fermentation process. This approach leads to non-differentiable trajectories that can pose some problems to implement in practice, resulting in a possible discrepancy of the simulated and real performances. In this paper we develop a technique to obtain a cubic spline for the approximate trajectory, leading to a smooth approximation function. We provide numerical results for a set of case studies where the AMPL modeling language, CVODE ordinary differential equations solver and a particle swarm algorithm were used.Algoritmi Research Center.Fundação para a Ciência e a Tecnologia (FCT)

Determinação de trajectória óptima em processos de fermentação semi-contínua

Uma grande parte de produtos valiosos são produzidos usando processos de fermentação e consequentemente a optimização destes processos reveste-se de uma grande importância económica. Em geral a modelação dos processos de fermentação envolvem equações diferenciais não lineares e complexas para as quais frequentemente não é possível obter uma solução analítica. Neste trabalho propõe-se uma resolução do problema de determinação da trajectória de alimentação óptima num processo de fermentação semi-contínuo, através do uso de splines cúbicas para a sua aproximação. É apresentada uma reformulação do problema de controlo óptimo através do uso de conceitos de programação semiinfinita no tratamento das restrições. É apresentada uma formulação do problema na linguagem de modelação AMPL, permitindo o uso de software específico para a sua resolução

Fed-batch trajectory optimal control problems with cubic splines

Optimal control problems in fed-batch fermentation processes are often described by sets of nonlinear differential and algebraic equations. The presence of constraints in the state and control variables presents an additional challenge for the optimization of these processes. In the feed trajectory planning optimization problem the tradicional approach consists in computing a linear spline that best fits the optimal feed trajectory. The resulting trajectory is thereof non-differentiable and problems can arise in its practical implementation, resulting in a possible discrepancy between the simulated and real performance. In this paper we develop a technique to obtain a cubic spline for the approximate trajectory, leading to a smooth approximation function. We provide numerical results for a set of case studies where the best trajectory approximation and initial dynamic system conditions are computed. The AMPL modeling language, CVODE ordinary differential equations solver and a particle swarm algorithm were used to obtain the numerical results.Algoritmi Research CenterFundação para a Ciência e a Tecnologia (FC

Supplier's selection model based on an empirical study

The problem of selecting suppliers/partners is a crucial and important part in the process of decision making for companies that intend to perform competitively in their area of activity. The selection of supplier/partner is a time and resource-consuming task that involves data collection and a careful analysis of the factors that can positively or negatively influence the choice. Nevertheless it is a critical process that affects significantly the operational performance of each company. In this work, there were identified five broad selection criteria: Quality, Financial, Synergies, Cost, and Production System. Within these criteria, it was also included five sub-criteria. After the identification criteria, a survey was elaborated and companies were contacted in order to understand which factors have more weight in their decisions to choose the partners. Interpreted the results and processed the data, it was adopted a model of linear weighting to reflect the importance of each factor. The model has a hierarchical structure and can be applied with the Analytic Hierarchy Process (AHP) method or Value Analysis. The goal of the paper it's to supply a selection reference model that can represent an orientation/pattern for a decision making on the suppliers/partners selection proces

Collaborative planning in non-hierarchical networks - an intelligent negotiation-based framework

In today’s competing business market, companies are constantly challenged to dynamically adapt to customer expectations by diminishing the time response that goes from the beginning of the business opportunity to the satisfaction of the customer need. Simultaneously, there is increased recognition of the advantages that companies obtain in focusing on their core business and seeking other competencies through partnerships with other partners by forming collaborative networks. These new collaborative organizational structures require a new set of methods and tools to support the management of manufacturing processes across the entire supply chain. The present paper addresses the collaborative production planning problem in networks of non-hierarchical, decentralized, and independent companies. By proposing a collaborative planning intelligent framework composed of a web-based set of methods, tools, and technologies, the present study intends to provide network stakeholders with the necessary means to responsively and efficiently address each one of the market business opportunities. Through this new holistic framework, the managers of the networked companies can address the challenges posed during collaborative network formation and supply chain production planning.The research leading to these results received funding from the European Union’s Seventh Framework Program (FP7/2007-2013) under grant agreement No. 260169. This work was also financed by national funds through the Portuguese funding agency, FCT—Fundação para a Ciência e a Tecnologia, within project LA/P/0063/2020

Framework for a risk assessment model to apply in virtual/collaborative enterprises

Risk assessment is a theme of large spectrum applied in different fields. In the context of Virtual / Collaborative Enterprises there are several risks whose assessment should be aware to avoid undesirable consequences either for entire networked or for a partner in particular. The objective of this work is centered on the creation of a framework / guidelines to serve as a basis for the creation of a better risk assessment model for Virtual / Collaborative Enterprises. This work analyzed the few models available in the literature and identified some gaps that were used to purpose complementary guidelines for the design and / or improve the future risk assessment models. The pointed guidelines covered three important topics: risk factors; assessment methods; and the impact in different life cycle phases of a Virtual / Collaborative Enterprise. Considering the results of the work it is our conviction that there is space to improve the research in this field and a more robust and flexible risk assessment model should be developed. (C) 2021 The Authors. Published by Elsevier B.V.- (undefined