مدل‌‌سازي يك‌پارچه توليد‌كننده ـ خرده‌فروشان بر پايه مديريت موجودي توسط فروشنده

An Integrated Model of Manufacture-Retailers Based on Vendor Managed Inventory

در اين نوشتار يك زنجيره‌ي تامين دو‌سطحي شامل يك توليدكننده و چندين خرده‌فروش در حالت چندمحصولي ارايه مي‌‌شود. در اين مدل، توليدكننده براساس سيستم «مديريت موجوي توسط فروشنده» به تصميم‌گيري در رابطه با سطوح موجودي زنجيره مي‌پردازد. بدين‌منظور در اين پژوهش تقاضا براي خرده‌فروشان تابعي غيرخطي از قيمت فروش در نظر گرفته شده است. هدف از اين پژوهش، بيشينه‌سازي سود توليد‌كننده و نيز سود خرده‌فروشان، به‌صورت يك‌پارچه و بدون در نظر گرفتن ساختار سلسله‌مراتبي، در زنجيره‌ي تامين است. سپس يك مدل دو‌هدفه‌ي غيرخطي، ارايه و با استفاده از دو الگوريتم فراابتكاري چند‌هدفه ــ با در نظر گرفتن شش مسيله با تعداد خرده‌فروشان مختلف ــ حل و نتايج مورد ارزيابي قرار مي‌‌گيرد. در پايان، هر دو الگوريتم براساس ميزان كارايي در حل مسايل رتبه‌بندي مي‌‌شوند.

Vendor Managed Inventory (VMI) is a continuous replenishment program designed to provide major cost saving benefits for both vendor and retailers. Under VMI, instead of the customer monitoring its sales and inventory for triggering replenishment orders, the vendor assumes responsibility for these activities. This paper, considers a two-level supply chain system with a single-manufacture and multi-retailers at each level. The manufacture is vendor and responses the needs of retailers. The manufacturer produces multi-product at the multi-wholesale price to several retailers. Inventory level’s decisions are based on vendor managed inventory system and are taken by the manufacture. In this supply chain, demand of each product is influenced by price. It is assumed that demand is a decreasing and convex function of the retail price. Previous mentioned works use a game theory and Stackelberg game framework. In the Stackelberg game model, the manufacturer is the leader, and retailers are followers. However, in this paper an integrated approach is applied. The purpose of this study is to develop an integrated model for maximizing manufacture’s profit and retailer’s profits at the same time. In other words, the manufacturer and its retailers determine wholesale prices, retail prices, replenishment cycles and backorder quantity to maximize their profits. In this paper, two-objective non-linear model is presented and two solution procedures, including Non-dominated sorting Genetic Algorithm-II (NSGA-II) and Non-dominated Ranking Genetic Algorithm (NRGA) are proposed. To assess the efficiency of the proposed model, several numerical experiments are implemented. To this aim, six test problems with different sizes in terms of retailers are considered and for each size, the experiments are performed under NSGA-II and NRGA. The obtained results show that the proposed NRGA, in most of the problems, can perform much better than NSGA-II in terms of spread and convergence factors spread of solutions and faster convergence near the true Pareto-optimal front compared to NSGA-II. Finally, the both algorithms are ranked by simple additive weighting method.