mixed integer programming

This paper proposes a bi-objective model for a green closed-loop supply chain network design. Four levels for forward and five levels for reverse flow were considered, including plants, distribution centers, online retailers, traditional retailers and customers for forward flow and customers, collecting centers, disposal centers, repair centers and plants for the reverse flow. The objectives are minimizing the GHG emission and maximizing profit by considering defective products and a second market for these products. Also, online retailers were considered alongside with traditional ones, since the Covid-19 pandemic has led to increase in the amount of online shopping. GAMS software and the Lpmetric technique were used to solve the model in the small and medium sizes. However, for the large size, we used Grasshopper Optimization Algorithm (GOA) as a meta-heuristic approach since solving the large size problem with GAMS is a complicated and time-consuming process. We provided Numerical and computational results to prove the efficiency and feasibility of the presented model. Finally, the managerial insights and future works were provided.

The ceramic and tile industry is one of the traditional Iranian jobs used in every historical period of different forms. Iran is one of the five largest producers of tiles and ceramics, which have been able to become the biggest exporter of these products in Western Asia by having a huge capacity in the industry. In recent years, ceramics and tiles exports have become one of the country's most important foreign trade. Therefore, to achieve a larger part of the export share, the competitive environment has dominated the industry. On the other hand, supply chain management is considered more and more attention due to the increasing globalization of industries and international competition. Many companies prefer to supply and manage their procurement, production and distribution sectors separately in several countries. Therefore, in dealing with global competitiveness, how to design a supply chain network with minimum cost and with emphasis on financial considerations, insurance and customs, has become an important issue for multinational companies. In this paper, using mixed integer programming method, a four level global positioning model is proposed considering the limitation of water consumption in the production line using GAMS software. The proposed model was used in one of the ceramic tile manufacturing industries in Yazd province to validate the model and investigate the effect of important parameters on strategic location decisions, which led to the location of two domestic warehouses and three foreign distribution centers in neighboring countries.

Recently, following the raise in expense pressures led to lower economic growth, an increasing number of manufacturers have begun to investigate eventuality of handling returned product in a more cost-effective and proper procedure. Significance of Reverse Logistics (RL) is becoming greater due to various governmental, societal, and environmental reasons. Number of papers present in the literature on RLs is a well index of its importance. In some industries, appropriately collected returned products could be used as raw material for another product, increasing Supply Chain (SC) profits and reducing the waste. Since, perishable goods have a limited shelf -life, they can be reusable if they are collected before they reach a critical time. Accordingly, in the present study, a Mixed Integer Linear Programming (MILP) model was introduced for a network of closed-loop SC with recycling of returned perishable goods, involving suppliers, producers, retailers, together with collection and disposal centers, in a multi-product, multi-period, and multi-level basis. To do this, a case study was performed on milk and yogurt products of a company in dairy industry. The model was solved and analyzed using GAMS software. Results obtained from assessment of the model indicated that, timely collection of perishable goods and their use in production of new products reduces total costs of perishable SC network.