Saeed Alinezhad; Seyyed-Mahdi Hosseini-Motalgh
Abstract
Most studies on decision making issue have supposed the problem in deterministic environment, and because uncertainty makes the decisions taken suboptimal, so in this paper we propose a credibility based fuzzy model for the Vehicle Routing Problem with Simultaneous Delivery and Pickup and Time Windows ...
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Most studies on decision making issue have supposed the problem in deterministic environment, and because uncertainty makes the decisions taken suboptimal, so in this paper we propose a credibility based fuzzy model for the Vehicle Routing Problem with Simultaneous Delivery and Pickup and Time Windows (VRPSDPTW). The dispatching cost of vehicles and customers’ time windows are supposed to be trapezoidal fuzzy numbers. We also proposed a hybrid meta-heuristic algorithm called Improved Particle Swarm Optimization (IPSO) for solving the problem. The proposed algorithm is the combination of Particle Swarm Optimization (PSO) and some removal and insertion techniques which helps to improve the searching ability and maintain diversity of solutions. Finally, to demonstrate the applicability of the proposed model in the real world we studied the distribution of dairy products among customers by a distribution company in Fars province. The computational results show that distributors can use this method to reduce operating costs of the company.
Mina Nouri Harzvili; Seyyed-Mahdi Hosseini-Motalgh; Mohammadreza Nematollahi
Abstract
Supply chain (SC) coordination is one of the major issues which has been considered in the investigations of supply chains. In this study, a two-echelon supply chain with one retailer and one supplier is considered. Demand is stochastic and has a normal distribution and lead time is assumed deterministic. ...
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Supply chain (SC) coordination is one of the major issues which has been considered in the investigations of supply chains. In this study, a two-echelon supply chain with one retailer and one supplier is considered. Demand is stochastic and has a normal distribution and lead time is assumed deterministic. The retailer uses a periodic review inventory system for his replenishment decisions and faces partial shortages. Review period and order-up-to-level are decision variables of the retailer. First, the optimized values of the variables in both decentralized and centralized decision-making structures are obtained. Although Centralized decision making increases the whole SC’s profitability, it reduces the profitability of the retailer in comparison with the decentralized model; In order to make centralized decisions and to encourage the retailer to change his decisions, a coordination model is proposed. Quantity discount contract is used as an incentive scheme in the coordinated model. For calculating the exact value of the discount factor in this contract, the both member’s profit is considered. Furthermore, to fairly share the extra profit achieved by the coordinated model, a profit-sharing strategy, based on the bargaining power of the members, is proposed. A set of numerical experiments and sensitivity analysis, which is performed with respect to several key parameters of the study, reveal that, from economic viewpoint, the proposed coordination model for the supplier-distributor channel, can increase the channel profit up to its optimal profit level and guarantee the improvement of channel members’ profit in comparison with their profit under the decentralized model. From inventory management viewpoint, the proposed discount contract reduces the distributor’s inventory shortage risk. Moreover, results of evaluating the proposed model under high levels of demand uncertainty shows that the proposed model is capable of coordinating the SC under various conditions such as demand frequencies and high quantities of standard deviation of the demand
