ABSTRACT Crop rotation plays an important role in agricultural production models with sustainabil... more ABSTRACT Crop rotation plays an important role in agricultural production models with sustainability considerations. Commonly associated strategies include the alternation of botanical families in the plots, the use of fallow periods and the inclusion of green manure crops. In this article, we address the problem of scheduling vegetable production in this context. Vegetables crop farmers usually manage a large number of crop species with different planting periods and growing times. These crops present multiple and varied harvesting periods and productivities. The combination of such characteristics makes the generation of good vegetable crop rotation schedules a hard combinatorial task. We approach this problem while considering two additional important practical aspects: standard plot sizes (multiples of a base area) and total area minimisation. We propose an integer programming formulation for this problem and develop a branch-price-and-cut algorithm that includes several performance-enhancing characteristics, such as the inclusion of a family of subadditive valid inequalities, two primal heuristics and a strong branching rule. Extensive computational experiments over a set of instances based on real-life data validate the efficiency and robustness of the proposed method.
In this article, we introduce two new variants of the assembly line worker assignment and balanci... more In this article, we introduce two new variants of the assembly line worker assignment and balancing problem that allow parallelization of and collaboration between heterogeneous workers. These new line balancing approaches introduce an additional level of flexibility in the assignment and planning process, which may be particularly useful in practical situations where the aim is to progressively integrate slow or limited workers in conventional assembly lines. We present linear models and heuristic procedures for these two new problems. Computational results show the efficiency of the proposed approaches and the efficacy of the studied layouts in different situations.
ABSTRACT We propose the Assembly Line Worker Integration and Balancing Problem (ALWIBP), a new as... more ABSTRACT We propose the Assembly Line Worker Integration and Balancing Problem (ALWIBP), a new assembly line balancing problem arising in lines with conventional and disabled workers. The goal of this problem is to maintain high productivity levels by minimizing the number of workstations needed to reach a given output, while integrating in the assembly line a number of disabled workers. Being able to efficiently manage a heterogeneous workforce is especially important in the current social context where companies are urged to integrate workers with different profiles. In this paper we present mathematical models and heuristic methodologies that can help assembly line managers to cope with this additional complexity. We demonstrate by means of a robust benchmark how this integration can be done with losses of productivity that are much lower than expected.
AbSTRAcT This chapter is concerned with a set of optimization problems associated to crop rotatio... more AbSTRAcT This chapter is concerned with a set of optimization problems associated to crop rotation scheduling in the context of vegetable crop production according to some ecological criteria: no crop of the same botanic family is planted in sequence, green manure and fallow periods must be present in any schedule. A core mathematical model called the crop rotation scheduling model is proposed to represent these ecological criteria together with specific technical constraints associated to the growing of vegetable crops. Three ...
Abstract The Steiner tree problem with revenues, budget and hop constraints is a variant of the S... more Abstract The Steiner tree problem with revenues, budget and hop constraints is a variant of the Steiner tree problem with two main modifications:(a) besides the costs associated with arcs, there are also revenues associated with the vertices, and (b) there are additional budget and hop constraints, which impose limits on the total cost of the network and on the number of edges between any vertex and the root, respectively. This article introduces and compares several mathematical models for this problem and describes two branch-and- ...
International Journal of Production Economics, 2013
We investigate the problem of balancing assembly lines with heterogeneous workers while consideri... more We investigate the problem of balancing assembly lines with heterogeneous workers while considering job rotation schedules. This problem typically occurs in assembly lines in sheltered work centers for disabled. We propose a hybrid algorithm that uses a Mixed Integer Programming (MIP) to select appropriate schedules from a pool of heuristically constructed solutions. A local search based on MIP neighborhoods is used as a post-optimization method. Our results show that this approach is fast, flexible and accurate ...
The final contents of total and individual trans-fatty acids of sunflower oil, produced during th... more The final contents of total and individual trans-fatty acids of sunflower oil, produced during the deacidification step of physical refining were obtained using a computational simulation program that considered cis-trans isomerization reaction features for oleic, linoleic, and linolenic acids attached to the glycerol part of triacylglycerols. The impact of process variables, such as temperature and liquid flow rate, and of equipment configuration parameters, such as liquid height, diameter, and number of stages, that influence the ...
This article describes and compares three heuristics for a variant of the Steiner tree problem wi... more This article describes and compares three heuristics for a variant of the Steiner tree problem with revenues, which includes budget and hop constraints. First, a greedy method which obtains good approximations in short computational times is proposed. This initial solution ...
ABSTRACT Crop rotation plays an important role in agricultural production models with sustainabil... more ABSTRACT Crop rotation plays an important role in agricultural production models with sustainability considerations. Commonly associated strategies include the alternation of botanical families in the plots, the use of fallow periods and the inclusion of green manure crops. In this article, we address the problem of scheduling vegetable production in this context. Vegetables crop farmers usually manage a large number of crop species with different planting periods and growing times. These crops present multiple and varied harvesting periods and productivities. The combination of such characteristics makes the generation of good vegetable crop rotation schedules a hard combinatorial task. We approach this problem while considering two additional important practical aspects: standard plot sizes (multiples of a base area) and total area minimisation. We propose an integer programming formulation for this problem and develop a branch-price-and-cut algorithm that includes several performance-enhancing characteristics, such as the inclusion of a family of subadditive valid inequalities, two primal heuristics and a strong branching rule. Extensive computational experiments over a set of instances based on real-life data validate the efficiency and robustness of the proposed method.
In this article, we introduce two new variants of the assembly line worker assignment and balanci... more In this article, we introduce two new variants of the assembly line worker assignment and balancing problem that allow parallelization of and collaboration between heterogeneous workers. These new line balancing approaches introduce an additional level of flexibility in the assignment and planning process, which may be particularly useful in practical situations where the aim is to progressively integrate slow or limited workers in conventional assembly lines. We present linear models and heuristic procedures for these two new problems. Computational results show the efficiency of the proposed approaches and the efficacy of the studied layouts in different situations.
ABSTRACT We propose the Assembly Line Worker Integration and Balancing Problem (ALWIBP), a new as... more ABSTRACT We propose the Assembly Line Worker Integration and Balancing Problem (ALWIBP), a new assembly line balancing problem arising in lines with conventional and disabled workers. The goal of this problem is to maintain high productivity levels by minimizing the number of workstations needed to reach a given output, while integrating in the assembly line a number of disabled workers. Being able to efficiently manage a heterogeneous workforce is especially important in the current social context where companies are urged to integrate workers with different profiles. In this paper we present mathematical models and heuristic methodologies that can help assembly line managers to cope with this additional complexity. We demonstrate by means of a robust benchmark how this integration can be done with losses of productivity that are much lower than expected.
AbSTRAcT This chapter is concerned with a set of optimization problems associated to crop rotatio... more AbSTRAcT This chapter is concerned with a set of optimization problems associated to crop rotation scheduling in the context of vegetable crop production according to some ecological criteria: no crop of the same botanic family is planted in sequence, green manure and fallow periods must be present in any schedule. A core mathematical model called the crop rotation scheduling model is proposed to represent these ecological criteria together with specific technical constraints associated to the growing of vegetable crops. Three ...
Abstract The Steiner tree problem with revenues, budget and hop constraints is a variant of the S... more Abstract The Steiner tree problem with revenues, budget and hop constraints is a variant of the Steiner tree problem with two main modifications:(a) besides the costs associated with arcs, there are also revenues associated with the vertices, and (b) there are additional budget and hop constraints, which impose limits on the total cost of the network and on the number of edges between any vertex and the root, respectively. This article introduces and compares several mathematical models for this problem and describes two branch-and- ...
International Journal of Production Economics, 2013
We investigate the problem of balancing assembly lines with heterogeneous workers while consideri... more We investigate the problem of balancing assembly lines with heterogeneous workers while considering job rotation schedules. This problem typically occurs in assembly lines in sheltered work centers for disabled. We propose a hybrid algorithm that uses a Mixed Integer Programming (MIP) to select appropriate schedules from a pool of heuristically constructed solutions. A local search based on MIP neighborhoods is used as a post-optimization method. Our results show that this approach is fast, flexible and accurate ...
The final contents of total and individual trans-fatty acids of sunflower oil, produced during th... more The final contents of total and individual trans-fatty acids of sunflower oil, produced during the deacidification step of physical refining were obtained using a computational simulation program that considered cis-trans isomerization reaction features for oleic, linoleic, and linolenic acids attached to the glycerol part of triacylglycerols. The impact of process variables, such as temperature and liquid flow rate, and of equipment configuration parameters, such as liquid height, diameter, and number of stages, that influence the ...
This article describes and compares three heuristics for a variant of the Steiner tree problem wi... more This article describes and compares three heuristics for a variant of the Steiner tree problem with revenues, which includes budget and hop constraints. First, a greedy method which obtains good approximations in short computational times is proposed. This initial solution ...
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