• 품질경영학회지
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• 제38권3호
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• pp.333-339
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• 2010

It is difficult to determine an optimal inventory level of aircraft engine and modules to achieve the target operational availability since F100-PW-200 & 229 engines of the F-16 & KF-16 aircraft are consisted of 5 modules with different failure rates and costs. This study presents a decision model, combining an integer programming problem and a regression metamodel. Data for the metamodel was attained from results of a simulation model, that represents operational and repair process of F-16 and KF-16. The objective function of an integer programming problem is maximizing the operational availability, representing pessimistic circumstances. Finally, an integer programming problem with a metamodel can make an optimal decision of the inventory level.

• 산업경영시스템학회지
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• 제40권4호
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• pp.105-111
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• 2017

Vendor Managed Inventory is a well-known vendor-retailer coordination approach in supply chain management where the vendor manages inventory of the retailer and determines the order interval and order quantity for the retailer. To consider practical situation, the upper limit of inventory for the retailer is set. If the inventory level for the retailer exceeds the upper limit, then the penalty cost is charged to the retailer. Furthermore, maximum allowable inventory level is set for the vendor to prevent the vendor from keeping much inventory. Single-vendor multi-retailer supply chain model with upper limit of inventory for vendor and retailers is studied. All the retailers' are assumed to have the common cycle time, and a vendor manages retailers' inventory and replenishes products. The mathematical formulation is introduced to minimize the total cost including the penalty cost violating the upper limit of inventory for retailers with the constraint of maximum allowable inventory level. The solution procedure based on Karush-Kuhn-Tucker (KKT) conditions is derived. KKT conditions are often applied to find an optimal solution of nonlinear programming problem with constraints. An illustrative example is used to show the application of the proposed solution procedure. Furthermore, sensitivity analysis is done to find out the relationship between maximum allowable inventory level and other values such as order quantity, the number of shipment, vendor's cost, retailer's cost, and total cost. As maximum allowable inventory level decreases, the number of shipment decreases but total cost increases. Order quantity has the trend of decline and is affected by the number of shipment.

• 벤처창업연구
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• 제9권2호
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• pp.81-86
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• 2014

본 논문에서는 그룹교체 정책과 예비품 재고정책을 동시에 고려하여 최적화하는 방안을 제시한다. 일반적으로 보전정책들은 예비품의 재고가 늘 가용하다고 가정하고 있으나 예비품의 재고 확보 여부에 의해 보전활동은 영향을 받을 수밖에 없다. 동일한 여러 유닛들이 동시에 운용될 때 이용되는 그룹교체정책을 바탕으로 이를 지원하기 위한 최적 재고수준을 결정한다. 일정한 개수의 유닛이 고장 나는 시점에서 그룹교체를 수행한다. 예비품의 재고는 일정 횟수의 그룹교체를 할 만큼 주문하여 유지한다. 보전비용과 재고비용 등 운용비용을 최소화할 수 있는 최적의 그룹교체 주기와 재고수준을 구한다.

• 한국군사과학기술학회지
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• 제22권3호
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• pp.416-424
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• 2019

This paper studies the optimal inventory levels of P-3 assemblies in order to assure the required operational availability. A simulation model is developed for identifying the impact of the inventory levels on operational availability. Based on the result of the simulation model, multiple regression analysis is performed. Finally, the optimal inventory levels of critical P-3 assemblies are determined with integer programming. Additionally, sensitivity analysis of depot maintenance period is also conducted for its impact on the operational availability.

• 수산경영론집
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• 제30권2호
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• pp.25-37
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• 1999

Some multi echelon inventory systems carry perishable products. The value of these product reduces as the period of time they spend in the system. In this paper We derive the necessary condition to determine optimal quantity, service level for a perishable product. The systems considered consist of two echelons and carry single item. To determine the optimal order quantity, the demand is assumed to be constant, the holding costs may be different in the echelons, and it allows no shortages. I assumed the price of product decreases by negative exponential function. To determine service level, following assumptions used in the model ㆍlead time is constant. ㆍdemand is normal distribution. ㆍthe product starts to perish at the second echelon. Service level is computed for different levels of lead times and for different variance of demands and for different price functions. The experimental results indicate that the service level in cost is a function of service level in demand and perishability of product. Results of the models exhibit that perishability and the age of the product are critical to determine the lot sizing and service level.

• Industrial Engineering and Management Systems
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• 제14권1호
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• pp.1-10
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• 2015

In this paper, we consider multi-item inventory management. When managing a multi-item inventory, we coordinate replenishment orders of items supplied by the same supplier. The associated problem is called the joint replenishment problem (JRP). One often-used approach to the JRP is to apply a can-order policy. Under a can-order policy, some items are re-ordered when their inventory level drops to or below their re-order level, and any other item with an inventory level at or below its can-order level can be included in this order. In the present paper, we propose a method for finding the optimal parameter of a can-order policy, the can-order level, for each item in a lost-sales model. The main objectives in our model are minimizing the number of ordering, inventory, and shortage (i.e., lost-sales) respectively, compared with the conventional JRP, in which the objective is to minimize total cost. In order to solve this multi-objective optimization problem, we apply a genetic algorithm. In a numerical experiment using actual shipment data, we simulate the proposed model and compare the results with those of other methods.

• 산업경영시스템학회지
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• 제20권43호
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• pp.25-36
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• 1997

The purpose of this paper is to structure a new integrated model that can minimize the total cost for the transportation and inventory systems between m origin points, where origin i has a supply of a commodity, such as distribution centers or warehouses, and n destination points, where destination j requires the commodity. In this case, demands of the destination points are assumed random variables which have a known probability distribution. We will find optimal distribution centers which transport the commodity to the destination points and suggest optimal inventory policy to the selected distribution center which find the optimal pair $$ and safety stock level that minimize total cost with back-ordered case. This new model is formulated as a 0-1 nonlinear integer programming problem. To solve the problem, this paper proposes heuristic computational procedures and program and provides numerical examples.

• 한국건설관리학회논문집
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• 제9권1호
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• pp.187-198
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• 2008

건설현장에서는 일반적으로 많은 양의 자재재고를 보유해 왔다. 이러한 자재재고는 현장의 불확실한 수요에 대응하여 공정지연을 방지하고, 원자재 가격 상승으로 인한 비용증가에 대비하는 등 순기능적 측면이 있다. 하지만 과도한 자재재고는 재고보유에 소요되는 재고유지비를 증가시키고 현장물류 공간배치의 효율성을 저하시키는 등 낭비요인으로 작용하기도 한다. 따라서 현장의 다양한 변동성을 고려하여 적정 자재재고 수준을 결정하고 관리하는 것은 건설공사의 효율성 측면에서 매우 중요한 요소이다. 본 연구는 시스템 접근방법의 절차에 의하여 철근가공 조립공정과 같이 현장에 투입되기 이전에 원자재 조립 가공과정을 갖는 건설 프로세스론 분석하고 이러한 흐름과정에서 재고수준을 적정화하는 알고리즘을 제시하였다. 이러한 재고관리 방안의 적용성을 확인하기 인하여 수도권지역 경전철 건설사업의 철근 가공장에서의 재고관리 사례를 분석하였다. 본 연구에서 제안한 알고리즘을 적용한 결과, 현장의 실제 철근 소요량과 가공장에 입고되는 철근 원자재의 입고량이 균형을 이루었고, 이에 따라 평균 재고량과 재고유시비용이 크게 감소되는 것으로 나타났다.

• 한국경영과학회:학술대회논문집
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• 한국경영과학회 2008년도 추계학술대회 및 정기총회
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• pp.267-284
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• 2008

Consider a supply chain where products are produced at a manufacturing system, shipped to a distribution center, and then supplied to customers. The distribution center controls inventory based on a base-stock policy, and whenever a unit of product is demanded by a customer, an order is released to the production system. Unsatisfied demand is backordered, and the inventory and backordered units are a function of the base-stock level. The manufacturing system is modeled as an M/M/s/c queueing system, and orders exceeding the limited buffer capacity are blocked and lost. The throughput of the manufacturing system and the steady state distribution of the outstanding orders are functions of number of servers and buffers of the manufacturing system. There is a profit obtained from throughput and costs due to servers and buffers of the manufacturing system, and also costs due to inventory positions of the distribution center, and we want to maximize the total production profit minus the total cost of the supply chain by simultaneously determining the optimal number of servers and buffers of the manufacturing system and the optimal base-stock level of the distribution center. We develope two algorithms, one analytical but without guarantee of the optimal solution and one optimal but without complete analytical proofs. The problem integrates strategic problem of the manufacturing system with tactical problem of the distribution center in a supply chain.

• 산업경영시스템학회지
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• 제20권42호
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• pp.31-38
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• 1997

The main objective of this research is to develop a model to select the optimal input service level for a distribution center - multi branch inventory distribution system. With the continuous review policy, the distribution center places an order for specific order quantity to an outside supplier, and the order quantity is replenished after a certain lead time. Also, each branch places an order for particular order quantity to the distribution center to satisfy the customer demands, and receives the replenishment after a lead time. When an out of stock condition occurs during an order cycle, a backorder is placed to the upper level to fill the unfilled demands. With these situation, variable demand and variable lead time are used for better industrial practice. Further, actual lead times with a generic lead time distribution are used in developing the control model. Under the actual lead time model, the customer service measures actually attained for the distribution center and each branch are explained as the effective customer service measures. Thus, throughout the optimal control (using computer search procedures), we can select the optimal input service levels for the distribution center and each branch to attain the effective service level for each branch which is consistent with the goal level of service for each branch. At the same time, the entire distribution system keeps minimum inventories.