Iterative Flattening Search for the Flexible Job Shop Scheduling Problem

This paper presents a meta-heuristic algorithm for solving the Flexible Job Shop Scheduling Problem (FJSSP). This strategy, known as Iterative Flattening Search (IFS), iteratively applies a relaxation-step, in which a subset of scheduling decisions are randomly retracted from the current solution; and a solving-step, in which a new solution is incrementally recomputed from this partial schedule. This work contributes two separate results: (1) it proposes a constraint-based procedure extending an existing approach previously used for classical Job Shop Scheduling Problem; (2) it proposes an original relaxation strategy on feasible FJSSP solutions based on the idea of randomly breaking the execution orders of the activities on the machines and opening the resource options for some activities selected at random. The efficacy of the overall heuristic optimization algorithm is demonstrated on a set of well-known benchmarks

Exploiting Iterative Flattening Search to Solve Job Shop Scheduling Problems with Setup Times

No abstract availableThis paper presents a heuristic algorithm for solving a jobshop scheduling problem with sequence dependent setup times (SDST-JSSP). This strategy, known as Iterative Flattening Search (IFS), iteratively applies two steps: (1) a relaxation-step, in which a subset of scheduling decisions are randomly retracted from the current solution; and (2) a solving-step, in which a new solution is incrementally recomputed from this partial schedule. The algorithm relies on a core constraint-based search procedure, which generates consistent orderings of activities that require the same resource by incrementally imposing precedence constraints on a temporally feasible solution. Key to the effectiveness of the search procedure is a conflict sampling method biased toward selection of the most critical conflicts. The efficacy of the overall heuristic optimization algorithm is demonstrated empirically on a set of well known SDST-JSSP benchmarks

Job Shop Scheduling with Routing Flexibility and Sequence-Dependent Setup Times

This paper presents a meta-heuristic algorithm for solving a job shop scheduling problem involving both sequence dependent setup-times and the possibility of selecting alternative routes among the available machines. The proposed strategy is a variant of the Iterative Flattening Search (IFS ) schema. This work provides three separate results: (1) a constraint-based solving procedure that extends an existing approach for classical Job Shop Scheduling; (2) a new variable and value ordering heuristic based on temporal flexibility that take into account both sequence dependent setup-times and flexibility in machine selection; (3) an original relaxation strategy based on the idea of randomly breaking the execution orders of the activities on the machines with a activity selection criteria based on their proximity to the solution\u27s critical path. The efficacy of the overall heuristic optimization algorithm is demonstrated on a new benchmark set which is an extension of a well-known and difficult benchmark for the Flexible Job Shop Scheduling Problem

Iterative Flattening Search for Resource Constrained Scheduling

Iterative flattening search (ifs) is a meta-heuristic strategy for solving multi-capacity scheduling problems. Given an initial solution, ifs iteratively applies: (1) a relaxation-step, in which a subset of scheduling decisions are randomly retracted from the current solution; and (2) a flattening-step, in which a new solution is incrementally recomputed from this partial schedule. Whenever a better solution is found, it is retained, and, upon termination, the best solution found during the search is returned. Prior research has shown ifs to be an effective and scalable heuristic procedure for minimizing schedule makespan in multi-capacity resource settings. In this paper we experimentally investigate the impact on ifs performance of algorithmic variants of the flattening step. The variants considered are distinguished by different computational requirements and correspondingly vary in the type and depth of search performed. The analysis is centered around the idea that given a time bound to the overall optimization procedure, the ifs optimization process is driven by two different and contrasting mechanisms: the random sampling performed by iteratively applying the “relaxation/flattening” cycle and the search conducted within the constituent flattening procedure. On one hand, one might expect that efficiency of the flattening process is key: the faster the flattening procedure, the greater the number of iterations (and number of sampled solutions) for a given time bound; and hence the greater the probability of finding better quality solutions. On the other hand, the use of more accurate (and more costly) flattening procedures can increase the probability of obtaining better quality solutions even if their greater computational cost reduces the number of ifs iterations. Comparative results on well-studied benchmark problems are presented that clarify this tradeoff with respect to previously proposed flattening strategies, identify qualitative guidelines for the design of effective ifs procedures, and suggest some new directions for future work in this area.</p

Proposal of method for determination time buffer in a multi project environment with use of critical chain

Orientador: Olívio NovaskiTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: O presente trabalho tem por objetivo apresentar uma proposta para a integração de ferramentas de gerenciamento de projeto e a determinação do pulmão de tempo em um ambiente de múltiplos projetos pelo uso de corrente crítica. Para o gerenciamento de projetos, utilizou-se um conjunto de ferramentas integradas e heurísticas de nivelamento de recursos. Para a determinação do pulmão de tempo foram escolhidas cinco variáveis de influência, tais como: flexibilidade na atividade; variação de consumo de recursos no tempo estimado; duração dos tempos estimados nas atividades, complexidade na rede e variável do atributo da incerteza e complexidade do projeto. Para tal, foi realizada uma comparação da proposta desenvolvida pelo o "Método Cortar e Colar" (C&PM) e o "Método da Raiz Quadrada do Erro" (RSEM), por intermédio dos indicadores: maior tempo de consumo do pulmão, tempo médio de consumo, número de vezes que o pulmão foi consumido. A presente proposta atende pela utilização de maior número de caraterísticas específicas da natureza de projeto no dimensionamento dos pulmões de tempo em relação aos dois métodos. Para essa comparação, foi realizada a aplicação da proposta de estudos de casos em três projetos. Após a análise dos Fatores Críticos de Sucesso (FCS), verificou que dos três projetos, dois alcançaram a faixa de projeto sucesso total, e o terceiro a faixa de projeto sucesso parcial. Acredita-se que a proposta desenvolvida pode ser utilizada para qualquer projeto e organização, e permite tomar decisões mais efetivas em ambientes de incerteza e complexidades em múltiplos projetos. E que seja uma opção de monitoramento para as empresas gerenciar seus projetos pelo uso da Corrente CríticaAbstract: The present work aims to present a proposal for the integration of project management tools and the determination of the time buffer in a multiple project environment by the use of critical chain. For project management, a set of integrated resource leveling tools and heuristics was used. For the determination of the time buffer, five variables of influence were chosen, such as: flexibility in the activity; variation of resource consumption over the estimated time; duration of estimated activities times, complexity in the network and attribute variable of uncertainty and complexity of the project. To do this, a comparison was made of the proposal developed by the "Cut and Paste Method" (C & PM) and the "Square Root Error Method" (RSEM), through the indicators: longer buffer consumption time, consumption, the number of times the buffer was consumed. The present proposal addresses the use of a greater number of specific characteristics of the nature of design in the design of the buffers of time in relation to the two methods. For this comparison, the proposal of case studies was applied in three projects. After analyzing the Critical Success Factors (FCS), it was verified that of the three projects, two reached the total success project track, and the third the partial success project track. It is believed that the proposal developed can be used for any project and organization, and allows to make more effective decisions in environments of uncertainty and complexities in mult projects. And it is a monitoring option for companies to manage their projects through the use of Critical ChainDoutoradoMateriais e Processos de FabricaçãoDoutor em Engenharia Mecânica33003017CAPE