Sai Ho Chung

Survey of Green Vehicle Routing Problem: Past and future trends

Green Logistics has emerged as the new agenda item in supply chain management. The traditional objective of distribution management has been upgraded to minimizing system-wide costs related to economic and environmental issues. Reflecting the environmental sensitivity of vehicle routing problems (VRP), an extensive literature review of Green Vehicle Routing Problems (GVRP) is presented. We provide a classification of GVRP that categorizes GVRP into Green-VRP, Pollution Routing Problem, VRP in Reverse Logistics, and suggest research gaps between its state and richer models describing the complexity in real-world cases. The purpose is to review the most up-to-date state-of-the-art of GVRP, discuss how the traditional VRP variants can interact with GVRP and offer an insight into the next wave of research into GVRP. It is hoped that OR/MS researchers together with logistics practitioners can be inspired and cooperate to contribute to a sustainable industry.

An adaptive genetic algorithm with dominated genes for distributed scheduling problems

This paper proposes an adaptive genetic algorithm for distributed scheduling problems in multi-factory and multi-product environment. Distributed production strategy enables factories to be more focused on their core product types, to achieve better quality, to reduce production cost, and to reduce management risk. However, when comparing with single-factory production, scheduling problems involved in multi-factory one are more complicated, since different jobs distributed to different factories will have different production scheduling, consequently affect the performance of the supply chain. Distributed scheduling problems deal with the assignment of jobs to suitable factories and determine their production scheduling accordingly. In this paper, a new crossover mechanism named dominated gene crossover will be introduced to enhance the performance of genetic search, and eliminate the problem of determining optimal crossover rate. A number of experiments have been carried out. For the comparison purpose, five multi-factory models have been solved by different well known optimization approaches. The results indicate that significant improvement could be obtained by the proposed algorithm.

A heuristic methodology for order distribution in a demand driven collaborative supply chain

This paper studies vertical and horizontal supply chain collaboration, and proposes a demand sharing methodology based on a set of predefined collaboration rules. Supply chain collaboration is prevalent, and has been recognized to be one of the important issues in improving competition strength. However, implementation of supply chain collaboration encounters many barriers, such as type, scope and security of information sharing, equity in benefits sharing, joint decision making, coordination tasks etc. For these reasons this paper proposes a framework of a central coordination system, which is equipped with a multi-criteria genetic optimization feature. The optimization methodology combines an analytic hierarchy process with genetic algorithms. It deploys an analytic hierarchy process to model the collaboration rules, govern the demand allocations, and evaluate the fitness values of chromosomes. The implementation of the proposed central coordination system is demonstrated by a hypothetical three-echelons supply chain network.

Multicriterion genetic optimization for due date assigned distribution network problems

This paper focuses on the demand due date factor in multiechelon distribution network problems and its impact on the production scheduling in manufacturing plants. A reliable demand due date is critical in winning of customer orders. However, this may usually require high collaboration among entities in the network. Mismatching of one single schedule may seriously influence the reliability. In this connection, holistically optimizing the schedule of each entity among the network is essential. In addition, on time delivery may induce high operating cost. A trade-off between earliness, on time, and tardiness should also be considered. Hence, a multicriterion genetic optimization methodology is developed to holistically optimize them. It determines the optimized schedule to collaborate each entity to fulfill the demands. For enabling multicriterion decision-making, the proposed algorithm combines analytic hierarchy process with genetic algorithms (GAs). The problem is divided into two parts-(i) demand allocation and transportation problem, and (ii) production scheduling problem. The optimization approach is applied to iteratively optimize part (i), and then part (ii). Three experiments have been carried out, and the computation results show that the effect of due date is critical, and the ability of the proposed algorithms in taking trade-off between earliness and tardiness.

A modified genetic algorithm approach for scheduling of perfect maintenance in distributed production scheduling

Distributed Scheduling (DS) problems have attracted attention by researchers in recent years. DS problems in multi-factory production are much more complicated than classical scheduling problems because they involve not only the scheduling problems in a single factory, but also the problems in the higher level, which is: how to allocate the jobs to suitable factories. It mainly focuses on solving two issues simultaneously: (i) allocation of jobs to suitable factories and (ii) determination of the corresponding production schedules in each factory. Its objective is to maximize system efficiency by finding an optimal plan for a better collaboration among various processes. However, in many papers, machine maintenance has usually been ignored during the production scheduling. In reality, every machine requires maintenance, which will directly influence the machines availability, and consequently the planned production schedule. The objective of this paper is to propose a modified genetic algorithm approach to deal with those DS models with maintenance consideration, aiming to minimize the makespan of the jobs. Its optimization performance has been compared with other existing approaches to demonstrate its reliability. This paper also tests the influence of the relationship between the maintenance repairing time and the machine age to the performance of scheduling of maintenance during DS in the studied models.

A multi-criterion genetic algorithm for order distribution in a demand driven supply chain

This paper develops a multi-criterion genetic optimization procedure, specifically designed for solving optimization problems in supply chain management. The proposed algorithm is discussed with an order distribution problem in a demand driven supply chain network. It combines the analytic hierarchy process (AHP) with genetic algorithms. AHP is utilized to evaluate the fitness values of chromosomes. The proposed algorithm allows decision-makers to give weighting for criteria using a pair-wise comparison approach. The numerical results obtained from the proposed algorithm are compared with the one obtained from the multi-objective mixed integer programming approach. The comparison shows that the proposed algorithm is reliable and robust. In addition, it provides more control and information for the decision-makers to gain a better insight of the supply chain network.

A modified genetic algorithm for quay crane scheduling operations

The demand for the maritime transportation has significantly increased over the past 20years due to the rapid pace of globalization. Terminal managers confront the challenge in establishing the appropriate quay crane schedule to achieve the earliest departure time of ship and provide efficient service. In general, quay crane schedule problems include two main issues (1) the allocation of quay cranes to handle the discharging and loading operations, and (2) the service sequence of ship bays in a vessel of each quay crane. Traditionally, the terminal planners determine the quay crane schedule based on their experience and own judgment. In addition, the interference among cranes and the increased in ship size further magnify its difficulty dramatically. Accordingly, this paper proposed a modified genetic algorithm to deal with the problem. To test the optimization reliability of the proposed algorithm, a set of well known benchmarking problem is solved, and the results obtained are being compared with other well known existing algorithms. The comparison demonstrates that the proposed algorithm performs as good as many existing algorithms and obtains better solutions than the best known ones in certain instances. In addition, the computational time(s) required are significantly much lesser, allowing it to be more applicable in practical situation.

Application of genetic algorithms with dominant genes in a distributed scheduling problem in flexible manufacturing systems

Multi-factory production networks have increased in recent years. With the factories located in different geographic areas, companies can benefit from various advantages, such as closeness to their customers, and can respond faster to market changes. Products (jobs) in the network can usually be produced in more than one factory. However, each factory has its operations efficiency, capacity, and utilization level. Allocation of jobs inappropriately in a factory will produce high cost, long lead time, overloading or idling resources, etc. This makes distributed scheduling more complicated than classical production scheduling problems because it has to determine how to allocate the jobs into suitable factories, and simultaneously determine the production scheduling in each factory as well. The problem is even more complicated when alternative production routing is allowed in the factories. This paper proposed a genetic algorithm with dominant genes to deal with distributed scheduling problems, especially in a flexible manufacturing system (FMS) environment. The idea of dominant genes is to identify and record the critical genes in the chromosome and to enhance the performance of genetic search. To testify and benchmark the optimization reliability, the proposed algorithm has been compared with other approaches on several distributed scheduling problems. These comparisons demonstrate the importance of distributed scheduling and indicate the optimization reliability of the proposed algorithm.

Optimization of order fulfillment in distribution network problems

This paper focuses on optimization of order due date fulfillment reliability in multi-echelon distribution network problems with uncertainties present in the production lead time, transportation lead time, and due date of orders. Reliability regarding order due date fulfillment is critical in customer service, and customer retention. However, this reliability can be seriously influenced by supply chain uncertainties, which may induce tardiness in various stages throughout the supply chain. Supply chain uncertainty is inevitable, since most input values are predicted from historical data, and unexpected events may happen. Hence, a multi-criterion genetic integrative optimization methodology is developed for solving this problem. The proposed algorithm integrates genetic algorithms with analytic hierarchy process to enable multi-criterion optimization, and probabilistic analysis to capture uncertainties. The optimization involves determination of demand allocations in the network, transportation modes between facilities, and production scheduling in manufacturing plants. A hypothetical three-echelon distribution network is studied, and the computation results demonstrated the reliability of the proposed algorithms.

A joint production scheduling approach considering multiple resources and preventive maintenance tasks

In reality, preventive maintenance (PM) tasks usually include lubrication, cleaning, inspection, adjustment, alignment and/or replacement. They should be planned before failure occurs, aiming to improve the overall reliability and availability of the production system. In the literature on PM scheduling, researchers usually consider maintenance as a single task and schedule it together with the production schedule. This may result in poor predictions on maintenance scheduling since different kinds of PM tasks have different maintenance intervals and require different durations. Production also involves various kinds of resources, such as plastics production requiring injection machines and moulds. These resources require different sets of maintenance treatment. If maintenance schedules for different resources are not harmonised, the planned production will be disturbed dramatically by the non-availability of resources. In this aspect, this paper proposes a joint scheduling (JS) method to handle production–maintenance scheduling that considers multiple resources and maintenance tasks. A genetic algorithm approach is applied to hypothetical numerical examples with the objective of minimising the makespan. The numerical solutions obtained show that the proposed JS method significantly reduces the makespan in this new scheduling problem.