Risk pooling via unidirectional inventory transshipments in a decentralized supply chain

We study risk pooling via unidirectional lateral transshipments between two locations under local decision-making. Unidirectional transshipments can be applicable when cost structures and/or capabilities differ between locations, and it is also a common practice in dual channel supply chains with online and offline sales channels. We show that such a system cannot be coordinated only with varying transshipment prices. The transshipment receiver orders more and the transshipment giver orders less than the respective optimal centralised order quantities. In order to remove this discrepancy, we suggest horizontal coordinationmechanisms by introducing a leftover subsidy for the location providing the transshipments or a shortage subsidy for the location receiving transshipments as well as a combination of shortage and leftover subsidy. Further, we evaluate the impact of network structure by comparing the equilibrium order quantities and profits under the uni- and bidirectional systems as well as a system without transshipments. Since demand correlation is a critical aspect in risk pooling we provide a detailed numerical study to discuss its impact on our findings

A review of non-cooperative newsvendor games with horizontal inventory interactions

There are numerous applications of game theory in the analysis of supply chains where multiple actors interact with each other in order to reach their own objectives. In this paper we review the use of non-cooperative game theory in inventory management within the newsvendor framework describing a single period inventory control model with the focus on horizontal interactions among multiple independent newsvendors. We develop a framework for identifying these types of horizontal interactions including, for example, the models with the possibility of inventory sharing via transshipments, and situations with substitutable products sold by multiple newsvendors. Based on this framework, we discuss and relate the results of prior research and identify future research opportunities

Inventory planning for spare parts networks with delivery time requirements

Motivated by real life, we introduce a new inventory model for spare parts where we explicitly take delivery time requirements into account. In this single-echelon, multilocation network, demand of a customer can be satisfied from multiple warehouses, but only if the customer can be reached from a warehouse within a time limit that is specified in the service contract of the customer. A delivery to a customer from a warehouse other than the closest one is referred to as a lateral transshipment. We develop a fast and accurate approximate algorithm to evaluate the performance of the network under given base stock levels and propose a fast and effective heuristic to set base stock levels. Numerical experiments show that planning with lateral transshipments can lead to cost savings up to 47% when compared to planning without lateral transshipments. Furthermore, we show the importance of taking lateral transshipments into account when designing a spare parts network

Inventory models with lateral transshipments : a review

Lateral transshipments within an inventory system are stock movements between locations of the same echelon. These transshipments can be conducted periodically at predetermined points in time to proactively redistribute stock, or they can be used reactively as a method of meeting demand which cannot be satised from stock on hand. The elements of an inventory system considered, e.g. size, cost structures and service level denition, all in uence the best method of transshipping. Models of many dierent systems have been considered. This paper provides a literature review which categorizes the research to date on lateral transshipments, so that these dierences can be understood and gaps within the literature can be identied

Evaluating Lateral Transshipment Policy in a Two-Echelon Inventory System

Emergency shipments from higher and/or same echelon levels are one of the popular tools to handle the stock-out position at some warehouse. Our paper deals with a lateral stock transshipment model involving one plant and two warehouses, lateral transshipment is considered as an option at each re-order decision under the standard (r,Q) inventory replenishment policy. We focus on incorporating the above stock transfer feature in the order fulfillment decision and designed an simulation to find the effect of lateral stock transfer policy on various parameters viz. average inventory at each warehouse, average number of stock-out days at each warehouse, total cost (comprising of inventory cost, stock-out cost and transportation cost). The experimental results show that the stock transfer policy has the potential to reduce the total cost, average inventory and average stock-out days. We have also compared the cases where information is shared online or with some delay. The delay is because of serial communication between the supply chain players. The results show that there are benefits of no information delay i.e. online information sharing over the case with information delay

Framework for Evaluation of Strategies for Pooling of Repairable Spare Parts

Background: The ability to quickly provide parts for the supply of advanced technical systems in equipment-intensive industries (such as airlines and nuclear power plants) is critical to the systems overall performance. In order to maintain a targeted system availability large quantities of spare parts are often required which in turn results in excessive inventory costs. Seeing as inventory systems often account for a large proportion of a business‟ costs a tough issue faced by companies in these industries is how to reduce the total inventory cost without having a negative impact on the system availability. An approach that may successfully deal with such a problem is pooling. Pooling refers to an arrangement in which multiple owners of the same type of technical systems cooperate by sharing their inventories. Purpose: The theoretical purpose of the thesis is to emphasize different pooling strategies and to identify and assess the characteristics of the strategies. The practical purpose of the thesis is to develop a robust method that facilitates a fair comparison of considered strategies. The objective is thus to develop a generic model that evaluates soft values (here, referred to as soft aspects) for each strategy, and also, to put the soft aspects in relation to the annual cost of a strategy in a final model. iv Methodology: The initial phase of the thesis was dedicated to a desk study review of current literature within the field of study. Recently published scientific articles, papers authored by consultants at Systecon, and literature used in courses at the Faculty of Engineering at Lund University lay the basis for the theoretical framework. The framework developed is derived from discussions with the supervisors in connection with interviews carried out with; relevant Systecon customers and company representatives at two trade fairs, Offshore Wind 2009 and Nordic Rail 2009. Conclusion: This thesis presents a framework for evaluation of strategies (stand alone, ad hoc cooperation, cooperative pooling, and commercial pooling) for pooling of repairable spare parts. Characteristics of all strategies are emphasized and assessed. From the characteristics, which are provided in Table 5.3, a model to evaluate soft values of each strategy is derived. The model, named evaluation of soft values, is provided in Table 5.4 and Table 5.5. Also, a methodical approach to derive a final strategy is provided in section 5.7. To make sure that a decision-maker is well aware of how the model should be applied, a fictitious case study is build up in where every step of the decision making process is thoroughly described. Furthermore, in the case study a final model that facilitates the derivation of a best strategy is presented. By means of a specified weighting coefficient and properly chosen set of scales, the final model provides with a final strategy. The outcome of the final model is based on the outcomes of the cost models and the outcomes of the evaluation of soft values model

A Disaster Relief Inventory Model Based on Transshipment

This research study is an effort to shed light on how transshipment may help improve the management of inventory in a disaster relief system. System dynamics simulation was used to compare inventory control and costs in a humanitarian supply chain without transshipment vs. one with transshipment. A framework for this approach is given along with the results of simulations on a system consisting of two warehouses where transshipment is allowed compared to the alternative where transshipment is not allowed. The preliminary results of this study indicate that transshipment can reduce costs and improve service to disaster victims based on inventory levels maintained in the warehouses. In some cases, transshipment may be more expensive, but this assumes the cost of replenishing inventory as a result of emergency purchase costs

Improving Logistics Processes in a Global Spares Supply Organization

This thesis studies logistics processes related to balancing of the inventories between supply channels. Balancing operations are based on lateral transshipments, which are a recent field of studies and have been on the focus of the optimization studies during the past few years. The findings of the study model current processes and material flows, reveals issues related to processes, studies cost figures and provides alternative solutions for improvement. The main objective of the study is to provide a construction that makes it possible to improve decision-making related to inventory balancing between the distribution centers of the organization. This study answers three main questions: How does the existing inventory network look like? What kind of issues and development areas are there? How is it possible to improve current inventory pooling operations? This study is a single case study carried out in a global spares supply organization willing to improve their logistics processes. To achieve the objects of the study, several methods were needed: literature survey on logistics models, sourcing methods and logistics cost models, qualitative information through interviews in the case company, study of the existing process descriptions and contract terms in addition to several quantitative analyses on the performance of the operations. Due to multiple methods, reliability and validity is increased as is the extent of the study. Findings of this study demonstrate that the expansion of the company on Asian markets is in its infancy and that the processes lack standardization and appropriate tools. Asian Distribution Center is highly dependent on European suppliers. Despite the strategic aspect of Asian supplier markets, supplier base does not yet provide a comprehensive alternative for balancing transshipments from Europe. This underlines the importance of processes on inventory balancing as they provide significant cost reductions against local sourcing in Asia at the moment. It is recommended to continue balancing using European supply chains, but to set up ocean deliveries for major flows and to focus sourcing efforts on establishing local suppliers for materials that have the highest importance by their total value. Future studies should provide more detailed information on quality and sourcing related costs to improve cost analysis and comparisons in addition to benchmarking values and ratios. /Kir1