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Biblioteca Digital do IPB (53.442 recursos)

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Mostrando recursos 1 - 20 de 33

  1. Simulation a decision support tool in maintenance float systems – system availability versus total maintenance cost

    Peito, Francisco; Pereira, Guilherme; Leitão, Armando; Dias, Luís M.S.
    This paper is concerned with the use of simulation as a decision support tool in maintenance systems, specifically in MFS (Maintenance Float Systems). For this purpose and due to its high complexity, in this paper the authors explore and present a possible way to construct a MFS model using Arena® simulation language, where some of the most common performance measures are identified, calculated and analysed. Nevertheless this paper would concentrate on the two most important performance measures in maintenance systems: system availability and maintenance total cost. As far as these two indicators are concerned, it was then quite clear that they...

  2. Simulation as a decision support tool in maintenance float systems

    Peito, Francisco; Pereira, Guilherme; Leitão, Armando; Dias, Luís M.S.
    This paper is concerned with the use of simulation as a decision support tool in maintenance systems, specifically in MFS (Maintenance Float Systems). For this purpose and due to its high complexity, in this paper the authors explore and present a possible way to construct a MFS model using Arena® simulation language, where some of the most common performance measures are identified, calculated and analysed.

  3. Heuristic approaches for lot splitting and scheduling in identical parallel machines

    Pimentel, Carina; Alvelos, Filipe; Carvalho, J.M. Valério de; Duarte, António J.S.T.
    In this paper we address a practical lot splitting and scheduling problem of a textile company that produces fine knitted garments. The problem consists of finding a weekly production plan for the knitting section, in which the garment components are produced in a set of parallel machines. We solve the problem in two steps using heuristic approaches. In the first step one of two heuristics (a network flow heuristic and a constructive heuristic) is applied to find an initial solution and in the second step local search based algorithms are applied to improve the quality of the solutions.

  4. A scheduling model for a knitting planning problem

    Pimentel, Carina; Alvelos, Filipe; Duarte, António J.S.T.; Carvalho, J.M. Valério de
    In this paper we present two planning and scheduling models for a real problem of a textile industry that produces fine knitted goods. In both of them we develop plans to assist the knitting planning of one of three knitting subsections. In this problem we intend to assign and sequence, within a set of available and identical parallel machines, the demand associated with each component or garment part. This demand can be split in lots of smaller quantities and these lots can be independently produced at any time in one or more of the available machines. In the first model we...

  5. A fast heuristic for a lot splitting and scheduling problem of a textile industry

    Pimentel, Carina; Alvelos, Filipe; Carvalho, J.M. Valério de; Duarte, António J.S.T.
    In this paper we address a lot splitting and scheduling problem of a Textile factory that produces garment pieces. Each garment piece is made of a set of components that are produced on the knitting section of the company. The problem consists of finding a weekly production plan for the knitting section, establishing the quantities to produce of each component (organized in one or several lots), and where and when starting/completion times) to produce them. The main contribution of this work is the development of a constructive heuristic that generates automated knitting scheduling plans. The heuristic produces solutions very fast...

  6. Metodologia de apoio à gestão logística em unidades de saúde

    Vaz, Clara B.
    No sector da saúde, verifica-se a necessidade de planear, implementar e controlar, de forma eficiente e eficaz, os fluxos directos e inversos de serviços (e materiais) e toda a informação associada, desde o ponto de origem ao ponto de atendimento, de forma a satisfazer os requisitos da prestação de cuidados de saúde aos utentes. Geralmente, reconhece-se que existem vários exemplos reais de desperdícios nas unidades de saúde, associados aos fluxos de materiais e serviços, que poderiam ser reduzidos ou eliminados, sem por em causa a qualidade dos serviços de saúde prestados aos utentes. Nesta óptica, propõe-se uma metodologia de apoio...

  7. An integrated approach for warehouse design and planning

    Geraldes, Carla A.S.; Carvalho, Sameiro; Pereira, Guilherme
    Warehouse design and planning is a great challenge in the field of Supply Chain Management. Inventory level management, warehouse design and operations, and customers’ requirements are examples of important challenges in this context. Throughout this work we discuss a mathematical model aiming to support some warehouse management decisions and inventory decisions. Our aim is to show model’s potentialities and weaknesses when applied to real world problems and to identify challenging research opportunities for developing more global warehouse decision support models to fill the gap between researchers and warehouse practitioners.

  8. Avaliação de desempenho de lojas de retalho utilizando um modelo de Data Envelopment Analysis multi-nível

    Vaz, Clara B.; Camanho, Ana; Guimarães, Rui
    Este artigo descreve um método de avaliação de desempenho de lojas de retalho baseado na técnica de Data Envelopment Analysis(DEA). O método desenvolvido tem em conta que as lojas são organizações complexas que agregam várias secções, com alguma autonomia de gestão. Assim, desenvolveu-se um modelo de DEA multi-nível, que considera dois níveis de análise: a loja e as secções que a constituem. A análise do desempenho de cada secção comercial resulta da comparação com secções similares localizadas noutras lojas da cadeia e permite averiguar se existe disparidade no seu desempenho. A avaliação ao nível da loja permite definir objectivos de melhoria de desempenho, tendo em conta que as secções partilham...

  9. Avaliação de desempenho no sector do retalho

    Vaz, Clara B.; Camanho, Ana
    O objectivo deste estudo é avaliar a eficiência das lojas de uma empresa de retalho de base alimentar, recorrendo à técnica de Data Envelopment Analysis. A eficiência é avaliada ao nível operacional e ao nível comercial, numa perspectiva de maximização de outputs. Os modelos foram definidos tendo em conta as características gerais do negócio de retalho, assim como a forma de funcionamento específica da empresa utilizada como caso de estudo. O modelo de eficiência operacional analisa a capacidade de cada loja em gerar vendas com o mínimo de recursos (i.e., área, stock, custos das vendas, encargos gerais e encargos com pessoal)...

  10. Avaliação de desempenho de lojas de retalho utilizando um modelo de Data Envelopment Analysis multinível

    Vaz, Clara B.; Camanho, Ana; Guimarães, Rui
    Este artigo descreve um método de avaliação de desempenho de lojas de retalho baseado na técnica de Data Envelopment Analysis (DEA). O método desenvolvido tem em conta que as lojas são organizações complexas que agregam várias secções, com alguma autonomia de gestão. Assim, desenvolveu-se um modelo de DEA multi-nível, que considera dois níveis de análise: a loja e as secções que a constituem. A análise do desempenho de cada secção comercial resulta da comparação com secções similares localizadas noutras lojas da cadeia e permite averiguar se existe disparidade no seu desempenho. A avaliação ao nível da loja permite definir objectivos...

  11. Tratamento de variáveis não controláveis em Data Envelopment Analysis (DEA): revisão de metodologias

    Camanho, Ana; Vaz, Clara B.; Portela, Maria
    Os modelos de DEA mais comuns assumem geralmente que ou os inputs ou os outputs do modelo são controláveis, dependendo deste pressuposto a escolha da orientação do modelo (orientado aos inputs se estes são controláveis ou orientado aos outputs se estes são controláveis). Na maior parte das situações, contudo, existem factores não controláveis que são na sua maior parte características do contexto ambiental das unidades de produção e que afectam o seu desempenho. Existem vários métodos para tratar variáveis não controláveis. O objectivo deste artigo é rever as abordagens que têm sido mais utilizadas na literatura no tratamento deste tipo...

  12. Performance measurement in retailing organisations using DEA

    Vaz, Clara B.; Camanho, Ana
    This study describes an application of to the assessment of efficiency of grocery stores from a major retailer. The objective of this study is to assess both operational and commercial efficiency. These two perspectives are important for the managerial control of the store network performance. The operational perspective assesses the activities that take place at the store. The model analysis the ability to maximize the number of transactions and value of sales given the resources used (i.e., area, stock, operational costs and working hours). The effect of environmental variables on store performance, such as population and the number of competitors...

  13. Performance measurement in retailing organisations using DEA

    Vaz, Clara B.; Camanho, Ana
    This study describes an application of DEA to the assessment of operational and commercial efficiency of grocery stores from a major retailer. The operational perspective assesses the sales and income generated at the store. The commercial perspective assesses the sales of individual sections within the store. The effect of environmental variables on store performance, such as the population and the number of competitors in the surrounding area, is also analysed. These models are refined with the inclusion of weight restrictions to reflect accurately the relative importance of the input and output variables on the store performance.

  14. The assessment of retailing eficiency using network DEA

    Vaz, Clara B.; Camanho, Ana
    The objective of this paper is to develop a methodology, based on Data Envelopment Analysis, to assess and improve the performance of retailing organisations with multiple units (shops). The methodology developed is applied to a case-study consisting of 78 supermarkets to ensure its relevance and applicability to real-world assessments. The Decision Making Units (DMUs) of retailing organisations are complex and often include multiple sub-units. For example, in the case of supermarkets, the shops are usually organised in sections that sell different products (e.g., grocery, perishables, textiles, light bazaar and heavy bazaar). This paper proposes assessing the retailing shops considering the...

  15. Assessing group performance with Malmquist indices: the evaluation of the brand effect in retailing

    Camanho, Ana; Vaz, Clara B.
    This study explores the differences in performance between two groups of grocery stores with different brands. The paper develops a Malmquist-type index to distinguish internal inefficiencies from those associated with the group (or brand) characteristics. A fundamental characteristic of the new index is to compare in a static setting.

  16. Analysis of the effect of environmental conditions on the performance of retailing stores

    Vaz, Clara B.; Camanho, Ana
    The assessment of performance in retailing services has gained considerable attention in recent years. The increased competition motivated the organisations to strive for efficiency in order to cut costs and deliver better customer services. This paper develops a method based on Data Envelopment Analysis (DEA) for the efficiency assessment of retailing stores. The method enables the quantification of inefficiencies taking into account the effect of exogenously factors (i.e., non-discretionary inputs and outputs). The method developed starts with the identification of the factors that affect the DMUs’ performance, including those outside the decision makers’ control. The statistical significance of the effect of...

  17. Assessing the brand effect on the efficiency of retailing stores

    Vaz, Clara B.; Camanho, Ana
    This paper explores the differences in performance between two groups of grocery stores that operate with different brands. The study develops a Malmquist-type index to distinguish internal inefficiencies from those associated with the group (or brand) characteristics. A fundamental characteristic of the new index is to compare groups in a static setting. The study described in this paper combines the use of a Malmquist-type index with statistical testes. The Malmquist-type index is decomposed into sub-indexes for comparing the efficiency spread between groups and the productivity differences between the best-practice frontiers of the groups. The hypothesis tests are used to verify...

  18. Comparison of two alternative store formats using a Malmquist-type index

    Vaz, Clara B.; Camanho, Ana
    This paper explores the differences in performance between two groups of retailing stores that operate with different formats. The study described in this paper combines the use of a Malmquist-type index (in a static setting) with statistical tests. This index is decomposed into sub-indexes for comparing the efficiency spread between groups and the productivity differences between the best-practice frontiers of the groups. The hypothesis tests are used to verify if the differences between groups captured by the Malmquist-type index and its components are statistically significant.

  19. Comparison of two alternative store formats using a Malmquist-type index

    Camanho, Ana; Vaz, Clara B.
    This paper explores the differences in performance between two groups of retailing stores that operate with different formats. The study uses a Malmquist-type index to distinguish internal inefficiencies from those associated with the group (or format) characteristics. A fundamental characteristic of the new index is to compare groups in a static setting. The study described in this paper combines the use of the Malmquist index with statistical tests. The Malmquist-type index is decomposed into sub-indexes for comparing the efficiency spread between groups and the productivity differences between the best-practice frontiers of the groups. The hypothesis tests are used to verify...

  20. Performance comparison between retailing stores using a Malmquist-type index

    Vaz, Clara B.; Camanho, Ana
    This study develops a methodology that combines different management science methods (Data Envelopment Analysis, Malmquist indices and statistical tests) to provide insights concerning the performance of stores. Firstly, the methodology enables to specificate appropriate targets for stores in a retail network, by using Data Envelopment Analysis. This is performed by comparing similar stores which belong to the same group, i.e., supermarkets and hypermarkets. Secondly, the methodology compares globally the performance between those groups by characterizing their productivity levels. For this, the methodology combines the use of a Malmquist-type index with statistical tests. This index is decomposed into sub-indices for comparing...

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