• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 2000년도 춘계공동학술대회 논문집
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• pp.502-508
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• 2000

정보 시스템과 전자 상거래의 보편화로 실시간 판매 정보 공유가 용이하여짐에 따라, 공유 정보를 적절히 활용하는 재고 정책의 필요성이 증가하고 있다. 본 연구에서는 정보 공유 환경하의 one-warehouse multi-retailer 모델에서 개별 공유 정보를 보다 정확히 활용하여 재주문점 결정을 할 수 있는 방안을 제시하였다. 기존의 하위 계층의 재고량의 합에 기반하는 echelon stock policy 의 경우 상세 정보의 손실을 발생하는 문제가 있는 반면 본 연구에서는 개별 retailer 들의 재고량에 기반한 marginal savings의 개념을 정의하고, 이를 바탕으로 상세 정보에 기반한 재주문 정책을 제시하였다. 제시된 정책은 기존의 echelon stock policy 에 비해 우수한 결과를 나타냄을 실험을 통해 입증하였다.

• 한국경영과학회지
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• 제37권3호
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• pp.95-116
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• 2012

The purpose of this paper is to show the effect of information sharing strategy on the supply chain performances. While traditional information sharing models assumed centralized stock information, recent supply chain practices often implement fully shared stock information, where real-time stock information is accessible on retailers. When retailers are competing with each other, this fully shared stock information may incur retailers' strategic order behaviors. Thus, this paper analyzes a simple two-level supply chain consisting of one warehouse and two identical competing retailers where the real time stock information is fully shared. The warehouse uses the traditional echelon stock policy. Under this environment the retailers' reorder decisions are derived using the order risk concept and the retailer competition mechanism is analyzed. Computational results show that the supply chain performace degradation in the fully shared stock information is quite significant, implying the importance of designing information sharing strategies in the supply chain design phase.

• 한국경영과학회:학술대회논문집
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• 한국경영과학회 2004년도 추계학술대회 및 정기총회
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• pp.566-569
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• 2004

본 연구에서는 생산능력의 제한이 있는 다계층(multi-echelon) 공급사슬에서의 효과적인 분배계획수립을 목적으로 한다. 수요 정보는 계획 기간(planning horizon) 동안 확정적인 형태로 주어지고 이러한 상황 하에서 전체 공급사슬에서 발생하는 재고유지 비용(holding cost)과 재고이월 비용(backorder cost)의 합을 최소화하는 분배 문제의 해법을 제시하고자 한다. 본 연구에서는 총비용을 최소화하는 각 노드별 분배량을 결정하기 위해서 look-ahead 기법을 사용한다. Look-ahead 기법을 통해 분배 계획 수립 시 해당 기간의 수요 정보뿐만 아니라 미래 수요를 함께 반영함으로써 생산능력 제한에 효과적으로 대처할 수 있도록 하였다. Look-ahead 기법을 적용하기 위해 본 문제를 단일 기계 일정계획(single machine scheduling) 문제로 전환하고 이에 대한 효율적인 발견적 기법을 제시한다. 또한 제안된 발견적 기법의 성능을 평가하기 위해 다양한 실험 조건하에서 제안된 알고리듬과 기존의 미래 수요를 고려하지 않는 계층 재고 정책(echelon stock policy)의 결과를 비교하여 본 연구의 우수성을 입증하였다.

• 경영과학
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• 제31권3호
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• pp.61-76
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• 2014

There are three methods for calculating the optimal level for spare part inventories in a MIME (Multi Indenture and Multi Echelon) system : marginal analysis, Lagrangian relaxation method, and genetic algorithm. However, their solutions are sub-optimal solutions because the MIME system is neither convex nor separable by items. To be more specific, SRUs (Shop Replaceable Units) are required to fix a defected LRU (Line Replaceable Unit) because one LRU consists of several SRUs. Therefore, the level of both SRU and LRU cannot be calculated independently. Based on the limitations of three existing methods, we proposes a improved algorithm applying marginal analysis on determining LRU stock level and genetic algorithm on determining SRU stock level. It can draw optimal combinations on LRUs through separating SRUs. More, genetic algorithm enables to extend the solution search space of a SRU which is restricted in marginal analysis applying greedy algorithm. In the numerical analysis, we compare the performance of three existing methods and the proposed algorithm. The research model guarantees better results than the existing analytical methods. More, the performance variation of the proposed method is relatively low, which means one execution is enough to get the better result.

• 한국경영과학회지
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• 제31권4호
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• pp.125-138
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• 2006

This paper considers a periodic review, two-echelon inventory system with one central warehouse and several re-tailers facing normally distributed demand. The goal is to attain target fill rates, while the systemwide total holding costs are minimized. An important aspect of this problem is material rationing in the case of shortages. If a central warehouse has insufficient inventory to deliver all replenishment orders to retailers, all order quantities are should be adjusted according to some rationing rule. A simple but efficient rationing rule is proposed and compared with the Balanced Stock (BS) rationing as introduced by Heijden which is known to be the best rationing policy in the literature. Numerical results show that the proposed rationing rule is more cost effective than BS rationing, especially for the differences in holding costs between retailers are large.

• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 2004년도 춘계공동학술대회 논문집
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• pp.441-445
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• 2004

In this paper, we deal with an inventory model of a multi-stage, serial supply chain system where a single product type and nonstationary customer demand pattern are considered. The retailer and suppliers place their orders according to an echelon-stock based replenishment control policy. We assume that the suppliers can access online information on the demand history and use this information when making their replenishment decisions. Using a reinforcement learning technique, the inventory control parameters are designed to adaptively change as the customer demand pattern is altered, in order to maintain a given target service level. Through a simulation based experiment, we verified that our approach is good for maintaining the target service level.

• 한국경영과학회:학술대회논문집
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• 한국경영과학회 2004년도 추계학술대회 및 정기총회
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• pp.578-581
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• 2004

본 연구에서는 수요가 정규분포의 형태를 따르는 N차 시리얼(serial) 시스템을 대상으로 한다. 최상위 노드는 상위의 공급자로부터 받고자 하는 물량을 제한 없이 받을 수 있으며 하위 노드로 이러한 물량을 공급하게 된다. 최하위 노드에서는 고객의 직접적인 수요가 발생하고 만족시키지 못한 수요는 다음 기간으로 이월된다. 이러한 환경 하에서 전체시스템에서 발생하는 재고유지 비용(holding cost)과 재고이월 비용(backorder cost)의 합을 최소화하는 각 노드별 최적의 기초 재고 수준(base stock level)을 결정하는 문제를 다룬다. 본 논문에서는 모의실험과 계층 재고(echelon stock)의 개념을 통해 수요 분포 내의 적절한 분위수(quantile)를 결정하는 접근방법으로 각 노드의 기초 재고 수준을 구하는 방안을 제시하고자 한다.

• 한국경영과학회지
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• 제39권4호
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• pp.153-165
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• 2014

We present a new framework for rental capacity management in which rental capacity is dynamically managed by means of temporary inventory addition/return. While serving customers with its own (native) capacity, the rental firm rents additional rental capacity from an upper echelon rental company so that it can avoid lost sales which may occur when stock is not sufficient, and returns it when stock becomes sufficiently large enough to cope with demands. Formulating the model as a Markov decision process, we investigate a flexible capacity addition/return policy that maximizes the firm's profit with respect to system costs. Numerical study indicates that rental operation with capacity addition/return can be economically favorable over rental operation without capacity expansion/return and can contribute the reduction in the size of native rental capacity.

• 산업경영시스템학회지
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• 제38권3호
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• pp.8-13
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• 2015

One of the most usual indicators to measure the performance of any inventory policy is the mean physical stock. In general, when estimating the mean physical stock in periodic review inventory systems, approximate approaches are often utilized by practitioners and researchers. The mean physical stock is generally calculated by a simple approximation. Still these simple methods are frequently used to analyze various single stockpoint and multi-echelon inventory systems. However, such a simple approximation can be very inaccurate. This is particularly true for low service levels. Even though exact methods to calculate the mean physical stock have been derived, they are available for specific cases only and computationally not very efficient, and therefore less useful in practice. In literature, approximate approaches, such as the simple, the linear, and Simpson approximations, were derived for the periodic review inventory systems that allow backorders. This paper modifies the approximate approaches for the lost sales case and evaluates the modified approximate approaches. Through computational experiments, average (and maximum) percentage deviations of mean physical stock between the exact method and the modified approximations are compared in the periodic review inventory system with lost sales. The same comparison between the modified and the original approximations are also conducted, in order to examine the performance of modified approximations. The results show that all modified approximations perform well for high service levels, but also that the performance may deteriorate fast with decreasing service level. The modified Simpson approximation is clearly better. In addition, the comparison between the modified and the original approximations in the periodic review inventory system with lost sales shows that the modified approximation outperforms the original approximation.

• 대한산업공학회지
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• 제35권3호
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• pp.203-212
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• 2009

The bullwhip effect refers to the phenomenon where demand variability is amplified when one moves upward a supply chain. In this paper, we exactly quantify the bullwhip effect for cases of seasonal demand processes in a two-echelon supply chain with a single retailer and a single supplier. In most of the previous research, some measures of performance for the bullwhip effect are developed for cases of non-seasonal demand processes. The retailer performs demand forecast with a multiplicative seasonal mixed model by using the minimum mean square error forecasting technique and employs a base stock policy. With the developed bullwhip effect measure, we investigate the impact of seasonal factor on the bullwhip effect. Then, we prove that seasonal factor plays an important role on the occurrence of the bullwhip effect.