Modelo de programación matemática para la cadena productiva del biocombustible biodiésel, en el departamento del Meta, Colombia

Trabajo de investigaciónLos beneficios asociados a los biocombustibles se ven reflejados en un creciente número de países, introduciendo o planeando introducir, políticas para incrementar la proporción de su producción dentro de su matriz energética. Actualmente, sólo pequeñas cantidades de biocombustibles se transan en los mercados internacionales ya que la mayoría se consume domésticamente. Sin embargo, se espera que el comercio de biocombustibles se expanda rápidamente dado que numerosos países no tendrán la capacidad doméstica para abastecer sus mercados internos. Con base en el tendiente crecimiento del negocio de los biocombustibles, tanto a nivel mundial como local, resulta pertinente contar con herramientas técnicas que apoyen la toma de decisiones en la gestión agroindustrial para aprovechar de mejor manera un mercado por ahora naciente, pero que a mediano y largo plazo se escenifica como un gran sector productivo que podrá generar desarrollo a las regiones productivas. Esta investigación presenta un estado del arte sobre la cadena de abastecimiento del biocombustible biodiesel y un Modelo de Programación Lineal Entera Mixta, en el Departamento del Meta, Colombia, desarrollado para apoyar la toma de decisiones en la gestión de la cadena de suministro mencionada.MaestríaMagister en Ingeniería Industria

Selection and Penalty Strategies for Genetic Algorithms Designed to Solve Spatial Forest Planning Problems

Genetic algorithms (GAs) have demonstrated success in solving spatial forest planning problems. We present an adaptive GA that incorporates population-level statistics to dynamically update penalty functions, a process analogous to strategic oscillation from the tabu search literature. We also explore performance of various selection strategies. The GA identified feasible solutions within 96%, 98%, and 93% of a nonspatial relaxed upper bound calculated for landscapes of 100, 500, and 1000 units, respectively. The problem solved includes forest structure constraints limiting harvest opening sizes and requiring minimally sized patches of mature forest. Results suggest that the dynamic penalty strategy is superior to the more standard static penalty implementation. Results also suggest that tournament selection can be superior to the more standard implementation of proportional selection for smaller problems, but becomes susceptible to premature convergence as problem size increases. It is therefore important to balance selection pressure with appropriate disruption. We conclude that integrating intelligent search strategies into the context of genetic algorithms can yield improvements and should be investigated for future use in spatial planning with ecological goals

Search reversion within s-metaheuristics: impacts illustrated with a forest planning problem

The use of a reversion technique during the search process of s-metaheuristics has received little attention with respect to forest management and planning problems. Reversion involves the interruption of the sequence of events that are used to explore the solution space and the re-initiation of the search process from a high-quality, known starting point. We explored four reversion rates when applied to three different types of s-metaheuristics that have previously shown promise for the forest planning problem explored, threshold accepting, tabu search, and the raindrop method. For two of the s-metaheuristics, we also explored three types of decision choices, a change to the harvest timing of a single management unit (1-opt move), the swapping of two management unit's harvest timing (2-opt moves), and the swapping of three management unit's harvest timing (3-opt moves). One hundred independent forest plans were developed for each of the metaheuristic / reversion rate combinations, all beginning with randomly-generated feasible starting solutions. We found that (a) reversion does improve the quality of the solutions generated, and (b) the rate of reversion is an important factor that can affect solution quality.Keywords: forest planning, threshold accepting, heuristics, tabu search, patial harvest scheduling, mixed integer goal programming, adjacency constraint

Integration of fire management in forest planning management in Portugal

Doutoramento em Engenharia Florestal e dos Recursos Naturais - Instituto Superior de AgronomiaThe importance of ecological and socio - economic forest fires shows the relevance of research techniques and approaches for integrating the planning processes of forest management and fire management . This PhD aimed to investigate these approaches and contributing to the effectiveness of strategies for preventing fires both at the stand level or landscape level. In this context, probabilistic models of fire occurrence and estimated mortality to the main Portuguese forest species (maritime pine and eucalyptus) in pure composition of regular and irregular structures were developed. These were later integrated into a management model that optimizes harvests scheduling for each stand in order to create more fire resistant landscapes. It’s being developed a technologic platform to test these models and their combination with an innovative approach to incorporate fire risk and protective objectives in forest management planning

Gestión de la cadena de abastecimiento del biodiésel: una revisión de la literatura

The benefi ts of biofuels have been refl ected in an increasing number of countries that are introducing (or planning to introduce) policies to increase the proportion of biofuels in their energy mix. Currently, only small quantities of biofuels are traded on international markets because most of these fuels are consumed domestically. However, a rapid expansion of bio-fuel trade is expected since many countries have no domestic capacity to supply their own demand.Based on the expected-growth trend of the bio-fuels business, both globally and locally, it seems appropriate to have the technical tools to support decision making in agribusiness management so as to make better use of a so-far nascent market; yet knowing that in the medium and long term, such a market may become a large manufacturing sector that brings development to its productive regions. This paper attempts to present a comprehensive survey of the bio-diesel supply chain together with mathematical models intended to support decision-making in supply chain management.Los beneficios asociados a los biocombustibles se ven reflejados en un creciente número de países, introduciendo o planeando introducir, políticas para incrementar la proporción de su producción dentro de su matriz energética. Actualmente, sólo peque-ñas cantidades de biocombustibles se transan en los mercados internacionales ya que la mayoría se consume domésticamente. Sin embargo, se espera que el comercio de bio-combustibles se expanda rápidamente dado que numerosos países no tendrán la capa-cidad doméstica para abastecer sus mercados internos.Con base en el tendiente crecimiento del negocio de los biocombustibles, tanto a ni-vel mundial como local, resulta pertinente contar con herramientas técnicas que apoyen la toma de decisiones en la gestión agroindustrial para aprovechar de mejor manera un mercado por ahora naciente, pero que a mediano y largo plazo se escenifica como un gran sector productivo que podrá generar desarrollo a las regiones productivas. Este trabajo tiene el fin de presentar un estado del arte sobre la cadena de abastecimiento-del biodiésel y los modelos matemáticos desarrollados para apoyar la toma de decisio-nes en la gestión de la cadena de suministro

New decision support tools for forest tactical and operational planning

Doutoramento em Engenharia Florestal e dos Recursos Florestais - Instituto Superior de AgronomiaThe economic importance of the forest resources and the Portuguese forest-based industries motivated several studies over the last 15 years, particularly on strategic forest planning. This thesis focuses on the forest planning processes at tactical and operational level (FTOP). These problems relate to harvesting, transportation, storing, and delivering the forest products to the mills. Innovative Operation Research methods and Decision Support Systems (DSS) were developed to address some of these problems that are prevalent in Portugal. Specifically, Study I integrates harvest scheduling, pulpwood assortment, and assignment decisions at tactical level. The solution method was based in problem decomposition, combining heuristics and mathematical programming algorithms. Study II presents a solution approach based on Revenue Management principles for the reception of Raw Materials. This operational problem avoids truck congestion during the operation of pulpwood delivery. Study III uses Enterprise Architecture to design a DSS for integrating the operations performed over the pulpwood supply chain. Study IV tests this approach on a toolbox that handled the complexity of the interactions among the agents engaged on forest planning at regional level. Study V proposes an innovative technological framework that combines forest planning with forest operations' control

Optimization and Simulation for Designing the Supply Chain of the Cellulosic Biofuel Industry

The purpose of this dissertation is to provide an effective approach to design the supply chain (SC) of the cellulosic biofuel industry in order that it will support and accelerate the successful commercialization of the cellulosic biofuel industry. The methods of approach to this problem are (1) to assess the state-of-the-art biofuel SC studies, (2) to provide a decision support tool based on a mixed integer programming (MIP) model for the cellulosic biofuel supply chain design problem (BSCP), (3) to devise an exact solution method to solve large-scale instances of BSCP, (4) to evaluate a biomass logistics system based on biomass modules, by using new simulation elements for new machines, and (5) to compare several biomass logistics systems based on biomass module, bale, and silage, using simulation models. The first part of this dissertation broadly reviews the literature on biofuel SCs, analyzing the state-of-the-art biofuel and petroleum-based fuel SC studies as well as relating generic SC models that have been published over the last decade to the biofuel SC (An et al., 2010a). The resulting analysis proposes fertile opportunity for future research to contribute to improving biofuel SC. The second part of this dissertation formulates BSCP as a MIP model, which is a time-staged, multi-commodity flow, network design problem with an objective of maximizing profit (An et al., 2010b). The model prescribes strategic level decisions (i.e., facility locations, capacities, and technology types) as well as plans for transportation routes and material flows (i.e., quantities produced, stored, and transported) in each time period. A case study demonstrates managerial use in application to a region in Central Texas. The third part of this dissertation provides an exact solution method to solve BSCP. An embedded structure can be transformed to a generalized minimum cost flow problem, which is used as a sub-problem in a CG approach. This study proposes a dynamic programming algorithm to solve the sub-problem in O(m), generating improving path-flows. To accelerate branch-and-bound (B&B) search, it develops an inequality, called the partial objective constraint (POC), which is based on the portion of the objective function associated with binary variables. The fourth part of this dissertation evaluates a biomass module system, which is a conceptual logistics system based on large packages of chopped biomass with sufficient size and density to provide maximized legal highway loads and quick load/unload times. The last part of this dissertation evaluates economic benefits of the biomass module system, comparing it to bale and silage systems

Branch-and-price and multicommodity flows

Tese de doutoramento em Engenharia de Produção e Sistemas, área de Investigação OperacionalIn this Thesis, we address column generation based methods for linear and integer programming and apply them to three multicommodity flow problems. For (mixed) integer programming problems, the approach taken consists in reformulating an original model, using the Dantzig-Wolfe decomposition principle, and then combining column generation with branch-and-bound (branch-and-price) in order to obtain optimal solutions. The main issue when developing a branch-and-price algorithm is the branching scheme. The approach explored in this work is to branch on the variables of the original model, keeping the structure of the subproblems of the column generation method unchanged. The incorporation of cuts (branch-and-price-and-cut), again without changing the structure of the subproblem, is also explored. Based on that general methodology, we developed a set of C++ classes (ADDing - Automatic Dantzig-Wolfe Decomposition for INteger column Generation), which implements abranch-and-price algorithm. Its main distinctive feature is that it can be used as a “black-box”: all the user is required to do is to provide the original model. ADDing can also be customised to meet a specific problem, if the user is willing to provide a subproblem solver and/or specific branching schemes. We developed column generation based algorithms for three multicommodity flow problems. In this type of problems, it is desired to route a set of commodities through a capacitated network at a minimum cost. In the linear problem, each unit of each commodity is divisible. By using a model with variables associated with paths and circuits, we obtained significant improvements on the solution times over the standard column generation approach, for instances defined in planar networks (in several instances the relative improvement was greater than 60%). In the integer problem, each unit of each commodity is indivisible; the flow of a commodity can be split between different paths, but the flow on each of those paths must be integer. In general, the proposed branch-and-price algorithm was more efficient than Cplex 6.6 in the sets of instances where each commodity is defined by an origin-destination pair; for some of the other sets of instances, Cplex 6.6 gave better time results. In the binary problem, all the flow of each commodity must be routed along a single path. We developed a branch-and-price algorithm based on a knapsack decomposition and modified (by using a different branching scheme) a previously described branch-and-price-and-cut algorithm based on a path decomposition. The outcome of the computational tests was surprising, given that it is usually assumed that specific methods are more efficient than general ones. For the instances tested, a state-of-the-art general-purpose (Cplex 8.1) gave, in general, much better results than both decomposition approaches.Nesta Tese, abordam-se métodos de geração de colunas para programação linear e inteira. A sua aplicação é feita em três problemas de fluxo multicomodidade. Para problemas de programação inteira (mista), a abordagem seguida é a de reformular um modelo original, utilizando o princípio de decomposição de Dantzig-Wolfe, e combinar geração de colunas com o método de partição e avaliação (partição e geração de colunas) para a obtenção de soluções óptimas. A questão essencial no desenvolvimento de um algoritmo deste tipo é a estratégia de partição. A abordagem seguida neste trabalho é a de realizar a partição nas variáveis do modelo original, mantendo a estrutura do subproblema do método de geração de colunas. A incorporação de cortes, ainda sem alteração da estrutura do subproblema, é também explorada. Com base nesta metodologia geral, foi desenvolvido um conjunto de classes em C++ (ADDing - Automatic Dantzig-Wolfe Decomposition for INteger column Generation), que implementa um algorithmo de partição e geração de colunas. A sua característica fundamental é apenas ser requerido ao utilizador a definição de um modelo original. Num modo mais avançado, o utilizador pode implementar algoritmos para resolver o subproblema e/ou esquemas de partição. Foram desenvolvidos algoritmos baseados em geração de colunas para três problemas de fluxo multicomodidade. Neste tipo de problemas, pretende-se encaminhar um conjunto de comodidades através de uma rede capacitada, minimizando o custo. No problema linear, cada unidade de cada comodidade é divisível. Utilizando um modelo com variáveis associadas a caminhos e a circuitos, obtiveram-se melhorias significativas nos tempos de resolução em relação ao método de geração de colunas usual, para instâncias definidas em redes planares (em várias instâncias a melhoria relativa foi superior a 60%). No problema inteiro, cada unidade de cada comodidade é indivisível; o fluxo de uma comodidade pode ser dividido por diferentes caminhos, mas o fluxo em cada um deles tem de ser inteiro. Em geral, o algoritmo de partição e geração de colunas foi mais eficiente do que o software Cplex 6.6 nos conjuntos de instâncias em que cada comodidade é definida por um par origem-destino; para alguns dos outros conjuntos de instâncias, o software Cplex 6.6 obteve melhores resultados. No problema binário, todo o fluxo de cada comodidade apenas pode utilizar um caminho. Foi desenvolvido um algoritmo de partição e geração de colunas baseado numa decomposição de mochila e modificado (através de um esquema de partição diferente) um algoritmo de partição e geração de colunas com cortes, previamente descrito, baseado numa decomposição por caminhos. Os resultados dos testes computacionais foram surpreendentes, dado que é usualmente assumido que métodos específicos são mais eficientes do que métodos gerais. Para as instâncias testadas, o software Cplex 8.1 obteve, em geral, resultados muito melhores do que as duas decomposições