关键词: 供应商管理库存, 产品替代, 紧急供货, 风险厌恶

Abstract: In a traditional supply chain, each member makes inventory decisions based on maximizing its individual profit, resulting in ordering quantities amplified from retailers, distributors, and suppliers, generating the bullwhip effect and causing supply chain costs to surge. In order to improve customer service and reduce the bullwhip effect, the vendor management inventory (VMI) model has emerged. The core idea of the VMI model is that the supplier sets the retailer's inventory level by sharing the retailer's current inventory information. This model greatly reduces the waste of resources caused by the uncertainty of independent forecasts of both supply and demand and improves the operational efficiency of the supply chain. It is important to note that even under the VMI model, decision-making based on a stochastic inventory system still faces many risks. Although some companies would adopt the sales season emergency supply (replenishment) behavior to avoid the risk of stock-outs, they still cannot completely avoid the decision-making risk of stochastic demand. In view of this, this paper introduces the VMI model into the stochastic demand supply chain system with product substitution andemergency supply. The impact of product substitution and emergency supply on supply strategy and supply chain performance under the VMI model is investigated. And based on the fact that two suppliers can supply urgently, we consider the expansion scenario of the risk-averse situation of two suppliers. Based on our theoretical analysis, we provide managerial insights into inventory management practices in enterprises.
Specifically, this paper considers a two-echelon supply chain system consisting of a retailer and two suppliers. For this system, under stochastic demand and the VMI mode, the retailer sells two substitute products with similar functions, and the two products are provided by two suppliers, respectively. Prior to the start of the selling season, the two suppliers determine their respective supply quantities to the retailer. At the beginning of the season, market demand is clear, and if a customer's preferred product is out of stock, some customers choose not to replace it, while others choose a substitute. At the end of the selling season, the suppliers dispose of the unsold products and receive clearance proceeds. For this system, the scenario of no product substitution is considered first, and then the scenarios of product substitution and emergency supply are considered separately. Through the cost-benefit analysis, we provide the optimal supply strategy to each supplier under the above scenarios. Moreover, to make our research more practical, we consider an extension scenario in which both risk-averse suppliers can provide emergency supply. Then, we analyze the optimal supply strategy and profit of each risk-averse supplier.
Our research shows that both supply quantity and total product sales increase under product substitution compared to the no-product-substitution scenario. In addition, product substitution results in a win-win situation for both suppliers and retailer, with the effect increasing as the substitution rate increases. When only one supplier is available for emergency supply, the supplier with emergency supply capability benefits the most and achieves a win-win situation with the retailer. At the same time, the supplier with emergency supply capability does not blindly increase supply quantity before the start of the selling season, which greatly avoids the loss of oversupply due to excessive initial inventory. When both suppliers are available for emergency supply, product stock-outs will be effectively avoided, and retailer profit will be maximized. When both risk-averse suppliers can provide emergency supply, the risk faced by the supplier mainly will come from the oversupply of the product. In order to effectively avoid the risk of oversupply caused by the fluctuation of market demand, the supplier's optimal supply decreases with the increase in risk-aversion degree. However, for risk-averse suppliers, risk minimization and expected profit maximization are conflicting objectives, and they should balance the risk and profit when formulating supply strategies to avoid losing sight of the other.
Nevertheless, this paper still has some limitations. Only two product substitutions in the current market under the VMI model are examined in this paper. Supplier supply strategies with multiple products and the presence of adjacent market influences will be an interesting research direction in the future. In addition, this paper is only based on the conventional VMI model, and the introduction of supply chain disruption, revenue sharing contract or cost sharing contract into the VMI model deserves further research.

Key words: vendor managed inventory, product substitution, emergency supply, risk averse