COMPARISON OF NSGA-II AND SPEA2 ALGORITHMS IN A BI-OBJECTIVE ROBUST SCENARIO-BASED SUPPLY CHAIN CONSIDERING MATERIAL WASTE

Nowadays, increasing the quality level in production systems and reducing costs are two of the signicant goals of manufacturers. More manufacturers pay for more qualitative raw materials, more skilled labor, and more advanced and accurate machines the more waste is reduced. Increasing quality levels and decreasing costs become more complex when some parameters are under uncertainty. One of the methods to encounter uncertainties is robust optimization, where uncertainty probability distribution is unknown. As a consequence, the robust scenario-based approach, which is presented by Mulvey, is applied. In this paper, we present a biobjective scenario-based supply chain model. In this model, three echelons including suppliers, manufacturers, and customers are considered. Also, we consider uncertainty in backorder, demand, and cost values. The rst objective function aims to minimize supply chain costs including production, raw material purchasing, production inventory holding, raw material inventory holding, transportation, and backorder. The second objective function aims to minimize the total amount of raw material wastes in the production line and supplier batch. The proposed model has been dened as a multi-product, multi-period, multiple suppliers, multiple customers, and multiple transportation modes mixed-integer linear programming model. Also, in this model, workforce e- ciency, storage and transportation capacities, and inventory planning are considered. The model parameters are considered randomly distributed. The Epsilon constraint method, NSGA-II, and SPEA2 algorithms are applied to solving the proposed model. Also, the Taguchi method is applied to tune the parameters of the algorithms. Then, a comparison between the quality of results and the CPU time of these methods is provided. This comparison indicates that the use of evolutionary algorithms provides close results with the exact method in a shorter CPU time. Afterward, the Mean Ideal Distance (MID) and Analytic Hierarchy Process (AHP) methods are respectively employed to evaluate Pareto fronts performance and make a decision about selecting the best cost and quality level policy.