A simheuristic for bi-objective stochastic permutation flow shop scheduling problem

This paper addresses the stochastic permutation flow shop problem (SPFSP) in which the stochastic parameters are the processing times. This allows the modeling of setups and machine breakdowns. Likewise, it is proposed a multi-objective greedy randomized adaptive search procedure (GRASP) coupled with Monte-Carlo Simulation to obtain expected makespan and expected tardiness. To manage the bi-objective function, a sequential combined method is considered in the construction phase of the meta-heuristic. Moreover, the local Search combines 2-optimal interchanges with a Pareto Archived Evolution Strategy (PAES) to obtain the Pareto front. Also, some Taillard benchmark instances of deterministic permutation flow shop problem were adapted in order to include the variation in processing times. Accordingly, two coefficients of variation (CVs) were tested: one depending on expected processing times values defined as twice the expected processing time of a job, and a fixed value of 0.25. Thus, the computational results on benchmark instances show that the variable CV provided lower values of the expected makespan and tardiness, while the con-stant CV presented higher expected measures. The computational results present insights for further analysis on the behavior of stochastic scheduling problems for a better approach in real-life scenarios at industrial and service systems

Metaheurística para la solución del Transit Network Design Problem multiobjetivo con demanda multiperiodo

In this paper we study the Tranport Network Design Problem (TNDP). It consists in finding the ideal combination of routes and frequencies that allow the decision maker to balance the interests of the users and the tran- sit operators, which are opposite. The TNDP uses as input a graph, with their transportation costs (in this case time), and the demands associated to each pair of nodes. Our proposed approach to solve the TNDP is based on a Variable Neighborhood Search (VNS) metaheuristic. VNS has been used to solve different kinds of combinatorial optimization problems and it consists in searching competitive solutions by iterative changes of the neighborhood. The VNS is tested first for the case study designed by Mandl, which consists in 15 nodes and 21 arcs, and a symmetric demand matrix. Posteriorly the VNS was tested for other 11 instances of (15, 30 and 45 nodes). In the first place, the model was run for that original case to compare it with other authors who worked this problem in the past. Then, we tested the VNS approach for a changing demand model in 3 moments of the day (Morning, afternoon and night) to prove the positive results obtained in the first exercise and give a greater scope to the problem solution.En este artículo se estudia el problema de Red de Transporte, usualmente conocido como TNDP (Transit Network Design Problem) multiobjetivo. Este consiste en encontrar la combinación ideal de rutas y frecuencias, que permita realizar un balance entre los intereses de los usuarios y los opera- dores, que se contraponen. Utiliza como datos de entrada un grafo con sus respectivos costos de transporte (en este caso tiempos) y demandas aso- ciadas a cada par de nodos. Como método de solución a este problema de optimización combinatoria multiobjetivo, se propone el uso de la metaheu- rística Búsqueda en Vecindades Variables (VNS), que resuelve problemas de optimización buscando soluciones competitivas mediante el cambio de vecindario iterativamente. El método propuesto fue probado inicialmente en el caso de estudio diseñado por Mandl, que consiste en 15 nodos y 21 arcos, y una matriz de demandas simétrica; y posteriormente para otras 11 instancias con tres tamaños de grafo diferentes (15, 30, 45 nodos). El mode- lo primero se corrió con el caso original para compararlo con autores que en oportunidades pasadas han trabajado el mismo problema. Posteriormente el VNS propuesto se probó con un modelo de demanda cambiante en 3 momentos del día (Mañana, tarde y noche) para corroborar los resultados positivos obtenidos en el primer ejercicio y darle un alcance mayor a la solución del problema

Propuesta para el mejoramiento de los procesos productivos de la Empresa Servioptica Ltda.

Ingeniero (a) IndustrialPregrad

GRASP to minimize total weighted tardiness in a permutation flow shop environment

This paper addresses the scheduling problem in a Permutation Flow Shop (PFS) environment, which is associated with many types of industries such as chemical, petrochemical, automobile manufacturing, metallurgical, textile, etc. Thus, this work intends to solve a PFS scheduling problem in order to minimize the total weighted tardiness, since it is an important sequencing criterion not only for on time delivery jobs but also for customer satisfaction. To solve the problem, GRASP (Greedy Randomized Adaptive Search Procedure) metaheuristic is proposed as a solution, which has shown competitive results compared with other combinatorial problems. In addition, two utility functions called Weighted Modified Due Date (WMDD) and Apparent Tardiness Cost (ATC) are proposed to develop GRASP. These are based on dynamic dispatching rules and also known for solving the problem of total weighted tardiness for single machine scheduling problem. Next, an experimental design was carried out for comparing the GRASP performance with both utility functions and against the WEDD dispatching rule results. The results indicate that GRASP-WMDD could improve the total weighted tardiness in 47.8% compared with WEDD results. Finally, the GRASP-WMDD performance for the PFS total tardiness problem was evaluated, obtaining a relative deviation index of 13.89% and ranking the method over 26 heuristics and metaheuristics

Metaheurística para la solución del Transit Network Design Problem multiobjetivo con demanda multiperiodo

En este artículo se estudia el problema de Red de Transporte, usualmente conocido como TNDP (Transit Network Design Problem) multiobjetivo. Este consiste en encontrar la combinación ideal de rutas y frecuencias, que permita realizar un balance entre los intereses de los usuarios y los operadores, que se contraponen. Utiliza como datos de entrada un grafo con sus respectivos costos de transporte (en este caso tiempos) y demandas asociadas a cada par de nodos. Como método de solución a este problema de optimización combinatoria multiobjetivo, se propone el uso de la metaheurística Búsqueda en Vecindades Variables (VNS), que resuelve problemas de optimización buscando soluciones competitivas mediante el cambio de vecindario iterativamente. El método propuesto fue probado inicialmente en el caso de estudio diseñado por Mandl, que consiste en 15 nodos y 21 arcos, y una matriz de demandas simétrica; y posteriormente para otras 11 instancias con tres tamaños de grafo diferentes (15, 30, 45 nodos). El modelo primero se corrió con el caso original para compararlo con autores que en oportunidades pasadas han trabajado el mismo problema. Posteriormente, el VNS propuesto se probó con un modelo de demanda cambiante en 3 momentos del día (Mañana, tarde y noche) para corroborar los resultados positivos obtenidos en el primer ejercicio y darle un alcance mayor a la solución del problema

Flow-shop scheduling problem under uncertainties: Review and trends

Among the different tasks in production logistics, job scheduling is one of the most important at the operational decision-making level to enable organizations to achieve competiveness. Scheduling consists in the allocation of limited resources to activities over time in order to achieve one or more optimization objectives. Flow-shop (FS) scheduling problems encompass the sequencing processes in environments in which the activities or operations are performed in a serial flow. This type of configuration includes assembly lines and the chemical, electronic, food, and metallurgical industries, among others. Scheduling has been mostly investigated for the deterministic cases, in which all parameters are known in advance and do not vary over time. Nevertheless, in real-world situations, events are frequently subject to uncertainties that can affect the decision-making process. Thus, it is important to study scheduling and sequencing activities under uncertainties since they can cause infeasibilities and disturbances. The purpose of this paper is to provide a general overview of the FS scheduling problem under uncertainties and its role in production logistics and to draw up opportunities for further research. To this end, 100 papers about FS and flexible flow-shop scheduling problems published from 2001 to October 2016 were analyzed and classified. Trends in the reviewed literature are presented and finally some research opportunities in the field are proposed

A GRASP-based approach to the multi activity combined timetabling and crew scheduling problem considering a heterogeneous workforce

This paper tackles an extension to the Multi-activity Combined Timetabling and Crew Scheduling Problem (MCTCSP). The goal of the original problem is to schedule the minimum number of homogenous workers required, in order to visit a set of customers characterized by services needed against schedule availability. However, since in home services it is common to have specialized workers, a mathematical model considering a heterogeneous workforce is proposed. As a solution, a GRASP-based algorithm is designed. In order to test the metaheuristic performance, 110 instances from the literature are adapted to include categorical skills. In addition, another 10 instances are randomly generated to consider large problems. The results show that the proposed GRASP finds optimal solutions in 46% of the cases and saves 40–96% computational time

A comparison of dispatching rules hybridised with Monte Carlo Simulation in stochastic permutation flow shop problem

11 páginasThis paper presents a comparison of several well-known dispatching rules hybridised with Monte Carlo simulation to solve the Permutation Flow Shop Scheduling Problem with stochastic processing times. The aim of the paper is to show the importance of making an accurate probability distribution fitting of the uncertain parameter for adequate decision-making, especially if a robust schedule is desired. An experimental design was carried out to test the performance of 13 dispatching rules with three probability distributions and different coefficients of variation for the processing times. Experimental results were obtained for the expected mean and the standard deviation of five objective functions: makespan, flowtime, tardiness, maximum tardiness and tardy jobs. Results show that dispatching rules behave differently for mean and standard deviation regardless of the objective function. Hence, selected dispatching rules must be different if the goal is obtaining a robust schedule or to minimise the expected mean of a specific objective. Additionally, performance of dispatching rules depends on the coefficients of variation of processing times. These results demonstrate the importance of collecting enough and precise information of uncertain parameters to determine the probability distribution that fits the best

Uso de una heurística híbrida para resolver el problema de enrutamiento equilibrado de vehículos con restricciones de carga

26 páginasThe Vehicle Routing Problem with Loading Constraints (VRPLC) is strongly related to real life applications in distribution logistics. It addresses the simultaneous loading and routing of vehicles, which are two crucial activities in transportation. Since treating these operations separately may result in impractical solutions, the development of applications for VRPLCs has gained the attention of researchers in recent years. Several heuristic methods have been proposed, but they consider only a limited group of practical characteristics that arise in real world situations. This study proposes a hybrid heuristic method based on the Greedy Randomized Adaptive Search Procedure (GRASP) metaheuristic and the Clarke and Wright Savings algorithm, to solve a VRPLC with several loading and routing constraints that have not been considered simultaneously before. Experimental results show that the proposed procedure produces competitive solutions in short processing times. Lastly, the impact of the added operational constraints is also analyzedEl problema de enrutamiento de vehículos con restricciones de carga (VRPLC) está fuertemente relacionado con la vida real Aplicaciones en logística de distribución. Aborda la carga y el enrutamiento simultáneos de vehículos, que son dos actividades cruciales en el transporte. Dado que el tratamiento de estas operaciones por separado puede dar lugar a soluciones poco prácticas, el desarrollo de aplicaciones para VRPLC ha llamó la atención de los investigadores en los últimos años. Se han propuesto varios métodos heurísticos, pero consideran solo un grupo limitado de características prácticas que surgen en el mundo real. situaciones Este estudio propone un método heurístico híbrido basado en el Greedy Randomized Metaheurística del Procedimiento de búsqueda adaptable (GRASP) y los ahorros de Clarke y Wright algoritmo, para resolver un VRPLC con varias restricciones de carga y enrutamiento que no han sido considerado simultáneamente antes. Los resultados experimentales muestran que el procedimiento propuesto produce soluciones competitivas en cortos tiempos de procesamiento. Por último, el impacto del agregado también se analizan las limitaciones operativa

Efecto del entrenamiento mental en la capacitación de aprendices en cirugía laparoscópica

Introduction: this study assesses the effect of mental training on the tasks execution times of laparoscopic skills training.Methods: A Repeated Measures Experimental Design was executed. Two study groups were formed (an intervention group with mental training and a control group). Each group consisted in eight participants. Execution times in four tasks to practice four basic skills were registered three times in a period of one moth. Evaluated basic skills were cut, dissection, displacement and suture.Results: Intervention group times had a significant reduction on three of the four tasks (displacement, dissection, and suture).Conclusions: This protocol could be used as a complement on basic training for novices. It can reduce times and costs in a Laparoscopic course.Introducción: Este estudio evalúa el efecto de la implementación de la técnica entrenamiento mental en la formación, y especialmente en el tiempo de ejecución de tareas, de aprendices de cirugía laparoscópica.Métodos: Se realizó un diseño experimental de medidas repetidas con dos grupos de estudio (un grupo control y un grupo con “entrenamiento mental”) con ocho participantes cada uno. A los participantes de ambos grupos se les realizaron tres mediciones, en un periodo de un mes, en cuatro habilidades básicas (corte, disección, desplazamiento y sutura) mediante cuatro pruebas evaluativas dispuestas en cajas de entrenamiento.Resultados: Se observó que el grupo con “entrenamiento mental” tuvo una disminución significativa en el tiempo de ejecución de las actividades en tres de las pruebas (desplazamiento, disección y sutura).Conclusiones: Este protocolo podría ser usado como complemento delentrenamiento básico que reciben los estudiantes disminuyendo tiempos y costos en un curso de laparoscopia