This directory contains: Input files for all precedence graphs included in the data sets of: Scho... more This directory contains: Input files for all precedence graphs included in the data sets of: Scholl, Armin (1993): Data of Assembly Line Balancing Problems. Schriften zur Quantitativen Betriebswirtschaftslehre 16/93, Th Darmstadt. Format of in2-files: line 1: number n of tasks lines 2-n+1: integer task times lines n+2,...: direct precedence relations in form "i,j" last line: end mark "-1,-1" (optional)
In the oil supply chain, products transportation by pipelines is the most used distribution modal... more In the oil supply chain, products transportation by pipelines is the most used distribution modal, justified by its high volume capacity, reliability, and safety compared to the other transportation modes. The scheduling of pumping and delivery operations in pipelines is a complex problem. Thus, a better usage of the involved resources calls for the existence of tools that can help the associated decision-making process. This work explores this need and proposes a decomposition approach that integrates Mixed Integer Linear Programming models and heuristics to solve the scheduling of a single-source and multiple distribution centers (DCs) pipeline network, where a repumping DC operation, not yet considered in the literature in the area, is often used in practice. This operation corresponds to a situation where the repumping DC acts as the final DC of the network, receiving all batches arriving and, at the same time, operates as a source node. The DC repumps products previously receiv...
This paper addresses the problem of scheduling commodities in a multi-product pipeline. It is dev... more This paper addresses the problem of scheduling commodities in a multi-product pipeline. It is developed an auxiliary model for the operational decision-making process. It is considered a study upon a tank farm and a pipeline connecting a refinery to a harbour. The objective is the operating cost minimisation. This cost is determined by storage tank changeovers, by sequencing of activities, by plug product usage, and by electric pumping cost. It is employed the classical scheduling approach based on mixed integer linear programming with uniform time discretization. The proposed model is able to predict operating procedures based on a computer-optimised structure. The current pipeline operation is based on experience. Finally, simulation examples demonstrate a significant cost saving achieved by this scheduling methodology.
Abstract This paper addresses the long-term scheduling of pumping and delivery operations on stra... more Abstract This paper addresses the long-term scheduling of pumping and delivery operations on straight multiproduct pipeline systems connecting multiple-sources to multiple-destinations. A generic solution framework is proposed, combining heuristic procedures and mixed integer linear programming (MILP) models. The pipeline scheduling problem is decomposed into two sub-problems: the allocation and sequencing of pumping operations of the initial source, and the scheduling of delivery operations and also pumping operations of the intermediate sources. An innovative execution procedure using a rolling horizon strategy is developed to solve both problems. We focus on a new discrete-time MILP model formulation, covering several operational aspects of real-world pipeline systems, such as rigorous treatment of forbidden sequences and preventive tank maintenance and pipeline maintenance periods, while considering rigorous inventory management during the scheduling horizon. The approach is validated by solving an illustrative example and two real-world based pipeline problems. Results show that the proposed framework is able to obtain solutions in reasonable run time with detailed inventory management and respecting several operational constraints of the system.
Assembly line balancing usually presupposes binary task-station assignments. Some authors have pr... more Assembly line balancing usually presupposes binary task-station assignments. Some authors have previously described efficiency increases due to fractional task allocations or work-sharing. However,...
Abstract Multi-manned assembly lines are widely applied to manufacturing industries that produce ... more Abstract Multi-manned assembly lines are widely applied to manufacturing industries that produce large-size products and are concerned with high levels of productivity. Such lines are commonly found in automotive industries, where different tasks are simultaneously performed by more than one worker on the same product in multi-operated stations, giving rise to a class of balancing problem that aims to minimize the line’s cycle time. This clear practical application had made the type-2 multi-manned assembly line balancing problem to be explored in the past. However, only few small-size instances could be solved by preceding exact solution approaches, whereas large and real-life cases still lack optimality proofs since they were tackled by heuristics. In this work, a new Mixed-Integer Linear Programming model is presented and its modeling decisions discussed. Moreover, an innovative exact solution procedure employing a combination of decomposition techniques and combinatorial Benders’ cuts is presented to solve large and real-life instances optimally. Tests on an extended literature dataset and a real-life assembly plant case study have demonstrated that the proposed algorithm outperforms previously developed methods in terms of solution quality by an ample margin in efficiency gains. Synergies between the algorithm’s components are also revealed. Finally, the proposed exact method has been able to yield 60 optimal results out of a 108-instance dataset, with the remaining 48 solutions presenting a small integer gap (less than 2%).
This paper proposes a mathematical model based on mixed integer linear programming (MILP). This m... more This paper proposes a mathematical model based on mixed integer linear programming (MILP). This model aids the decision-making process in local generation use and demand response application to power demand contract adequacy by Brazilian consumers/prosumers. Electric energy billing in Brazil has some specificities which make it difficult to consider the choice of the tariff modality, the determination of the optimal contracted demand value, and demand response actions. In order to bridge this gap, the model considers local generation connected to the grid (distributed generation) and establishes an optimized solution indicating power energy contract aspects and the potential reduction in expenses for the next billing period (12 months). Different alternative sources already available or of interest to the consumer can be considered. The proposed mathematical model configures an optimization tool for the feasibility analysis of local generation use and, concomitantly, (i) checking th...
Abstract Mixed-model assembly lines are large scale production layouts that often operate under u... more Abstract Mixed-model assembly lines are large scale production layouts that often operate under uncertainties such as stochastic product sequences. Balancing such lines can be particularly challenging as throughput estimation can be difficult to determine, especially when asynchronous pace and buffers are considered. Recent works have addressed problem variants with a given target throughput, but few authors consider a variant of the throughput maximization of mixed-model assembly line balancing problem. This paper addresses the balancing optimization problem for an assembly line with a given number of workstations and buffers between them. A make-to-order environment is considered, modeled as stochastic sequence of products with known demand rates. A novel specialized cycle time simulator (CTS) is introduced, as well as a simheuristic approach (PSH) that exploits CTS to assess the cycle time of an assembly line and provide good balancing solutions. The proposed simheuristic PSH is applied to a dataset with several buffer layouts, and its solutions are then compared to those of literature benchmarks. Performance comparisons show that PSH’s solutions outperform the benchmarks’ ones, with statistically significant differences. Furthermore, the solution quality difference was greater for instances with more buffers, highlighting PSH capacity to conveniently exploit buffers in assembly lines. Lastly, analyses on the average processing times of stations, obtained for each buffer layout, partially verifies and question established results of the “bowl phenomenon” on unpaced assembly lines.
This paper proposes a decomposition approach combining heuristic algorithms and Mixed Integer Lin... more This paper proposes a decomposition approach combining heuristic algorithms and Mixed Integer Linear Programming (MILP) models to solve the long-term scheduling of a multiproduct pipeline connecting a single-source to multiple distribution centers. The solution considers many operational aspects, such as simultaneous deliveries, pipeline maintenance periods, deliveries of multiple products during the same pumping run, and rigorous inventory control. A long-term scheduling problem from the literature was solved to validate the proposed approach. This problem is composed of a straight pipeline connecting a refinery to 3 distribution centers and transporting 4 different oil derivatives. The approach was able to obtain an operational solution in less than half a minute of CPU time. Moreover, additional tests using the same scenario were executed in order to analyze the performance of the developed decomposition approach.
This directory contains: Input files for all precedence graphs included in the data sets of: Scho... more This directory contains: Input files for all precedence graphs included in the data sets of: Scholl, Armin (1993): Data of Assembly Line Balancing Problems. Schriften zur Quantitativen Betriebswirtschaftslehre 16/93, Th Darmstadt. Format of in2-files: line 1: number n of tasks lines 2-n+1: integer task times lines n+2,...: direct precedence relations in form "i,j" last line: end mark "-1,-1" (optional)
In the oil supply chain, products transportation by pipelines is the most used distribution modal... more In the oil supply chain, products transportation by pipelines is the most used distribution modal, justified by its high volume capacity, reliability, and safety compared to the other transportation modes. The scheduling of pumping and delivery operations in pipelines is a complex problem. Thus, a better usage of the involved resources calls for the existence of tools that can help the associated decision-making process. This work explores this need and proposes a decomposition approach that integrates Mixed Integer Linear Programming models and heuristics to solve the scheduling of a single-source and multiple distribution centers (DCs) pipeline network, where a repumping DC operation, not yet considered in the literature in the area, is often used in practice. This operation corresponds to a situation where the repumping DC acts as the final DC of the network, receiving all batches arriving and, at the same time, operates as a source node. The DC repumps products previously receiv...
This paper addresses the problem of scheduling commodities in a multi-product pipeline. It is dev... more This paper addresses the problem of scheduling commodities in a multi-product pipeline. It is developed an auxiliary model for the operational decision-making process. It is considered a study upon a tank farm and a pipeline connecting a refinery to a harbour. The objective is the operating cost minimisation. This cost is determined by storage tank changeovers, by sequencing of activities, by plug product usage, and by electric pumping cost. It is employed the classical scheduling approach based on mixed integer linear programming with uniform time discretization. The proposed model is able to predict operating procedures based on a computer-optimised structure. The current pipeline operation is based on experience. Finally, simulation examples demonstrate a significant cost saving achieved by this scheduling methodology.
Abstract This paper addresses the long-term scheduling of pumping and delivery operations on stra... more Abstract This paper addresses the long-term scheduling of pumping and delivery operations on straight multiproduct pipeline systems connecting multiple-sources to multiple-destinations. A generic solution framework is proposed, combining heuristic procedures and mixed integer linear programming (MILP) models. The pipeline scheduling problem is decomposed into two sub-problems: the allocation and sequencing of pumping operations of the initial source, and the scheduling of delivery operations and also pumping operations of the intermediate sources. An innovative execution procedure using a rolling horizon strategy is developed to solve both problems. We focus on a new discrete-time MILP model formulation, covering several operational aspects of real-world pipeline systems, such as rigorous treatment of forbidden sequences and preventive tank maintenance and pipeline maintenance periods, while considering rigorous inventory management during the scheduling horizon. The approach is validated by solving an illustrative example and two real-world based pipeline problems. Results show that the proposed framework is able to obtain solutions in reasonable run time with detailed inventory management and respecting several operational constraints of the system.
Assembly line balancing usually presupposes binary task-station assignments. Some authors have pr... more Assembly line balancing usually presupposes binary task-station assignments. Some authors have previously described efficiency increases due to fractional task allocations or work-sharing. However,...
Abstract Multi-manned assembly lines are widely applied to manufacturing industries that produce ... more Abstract Multi-manned assembly lines are widely applied to manufacturing industries that produce large-size products and are concerned with high levels of productivity. Such lines are commonly found in automotive industries, where different tasks are simultaneously performed by more than one worker on the same product in multi-operated stations, giving rise to a class of balancing problem that aims to minimize the line’s cycle time. This clear practical application had made the type-2 multi-manned assembly line balancing problem to be explored in the past. However, only few small-size instances could be solved by preceding exact solution approaches, whereas large and real-life cases still lack optimality proofs since they were tackled by heuristics. In this work, a new Mixed-Integer Linear Programming model is presented and its modeling decisions discussed. Moreover, an innovative exact solution procedure employing a combination of decomposition techniques and combinatorial Benders’ cuts is presented to solve large and real-life instances optimally. Tests on an extended literature dataset and a real-life assembly plant case study have demonstrated that the proposed algorithm outperforms previously developed methods in terms of solution quality by an ample margin in efficiency gains. Synergies between the algorithm’s components are also revealed. Finally, the proposed exact method has been able to yield 60 optimal results out of a 108-instance dataset, with the remaining 48 solutions presenting a small integer gap (less than 2%).
This paper proposes a mathematical model based on mixed integer linear programming (MILP). This m... more This paper proposes a mathematical model based on mixed integer linear programming (MILP). This model aids the decision-making process in local generation use and demand response application to power demand contract adequacy by Brazilian consumers/prosumers. Electric energy billing in Brazil has some specificities which make it difficult to consider the choice of the tariff modality, the determination of the optimal contracted demand value, and demand response actions. In order to bridge this gap, the model considers local generation connected to the grid (distributed generation) and establishes an optimized solution indicating power energy contract aspects and the potential reduction in expenses for the next billing period (12 months). Different alternative sources already available or of interest to the consumer can be considered. The proposed mathematical model configures an optimization tool for the feasibility analysis of local generation use and, concomitantly, (i) checking th...
Abstract Mixed-model assembly lines are large scale production layouts that often operate under u... more Abstract Mixed-model assembly lines are large scale production layouts that often operate under uncertainties such as stochastic product sequences. Balancing such lines can be particularly challenging as throughput estimation can be difficult to determine, especially when asynchronous pace and buffers are considered. Recent works have addressed problem variants with a given target throughput, but few authors consider a variant of the throughput maximization of mixed-model assembly line balancing problem. This paper addresses the balancing optimization problem for an assembly line with a given number of workstations and buffers between them. A make-to-order environment is considered, modeled as stochastic sequence of products with known demand rates. A novel specialized cycle time simulator (CTS) is introduced, as well as a simheuristic approach (PSH) that exploits CTS to assess the cycle time of an assembly line and provide good balancing solutions. The proposed simheuristic PSH is applied to a dataset with several buffer layouts, and its solutions are then compared to those of literature benchmarks. Performance comparisons show that PSH’s solutions outperform the benchmarks’ ones, with statistically significant differences. Furthermore, the solution quality difference was greater for instances with more buffers, highlighting PSH capacity to conveniently exploit buffers in assembly lines. Lastly, analyses on the average processing times of stations, obtained for each buffer layout, partially verifies and question established results of the “bowl phenomenon” on unpaced assembly lines.
This paper proposes a decomposition approach combining heuristic algorithms and Mixed Integer Lin... more This paper proposes a decomposition approach combining heuristic algorithms and Mixed Integer Linear Programming (MILP) models to solve the long-term scheduling of a multiproduct pipeline connecting a single-source to multiple distribution centers. The solution considers many operational aspects, such as simultaneous deliveries, pipeline maintenance periods, deliveries of multiple products during the same pumping run, and rigorous inventory control. A long-term scheduling problem from the literature was solved to validate the proposed approach. This problem is composed of a straight pipeline connecting a refinery to 3 distribution centers and transporting 4 different oil derivatives. The approach was able to obtain an operational solution in less than half a minute of CPU time. Moreover, additional tests using the same scenario were executed in order to analyze the performance of the developed decomposition approach.
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