• 산업경영시스템학회지
• /
• 제23권56호
• /
• pp.1-8
• /
• 2000

We present in this paper an optimal stocking policy for a repairable inventory system under reliability improvement. For this purpose we illustrate commercial flight lines with a large number of planes. This model is supported by a central repair facility. For modeling the nonstationary M/M/s system we implemented SIMAN for computing the time dependent number of units in the repair facility with any number of units. In this model we provide the required inventory level at each location. 1y month. for various levels of associated stock-out risk.

• 한국경영과학회지
• /
• 제30권2호
• /
• pp.117-129
• /
• 2005

This paper considers a make-to-order inventory-production system in which customer orders are admitted only when the number of outstanding customer orders is below a value committed by the system. We deal with general distributions for the customer order Inter-arrival, production, and replenishment lead time processes. Monotonicities of the optimal average cost with respect to these distribution parameters are established using sample path coupling arguments. When distributions are given as an exponential one, we implement a sensitivity analysis on the optimal inventory policy and show that it has monotonicities with respect to system costs using dynamic programming.

• 대한산업공학회지
• /
• 제12권1호
• /
• pp.43-48
• /
• 1986

In this paper, the one period multi-item inventory model is considered in which it is required to determine the production quantity and selling price of each item which maximize the probability of realizing predetermined level of profit. The objective function of this model is the sum of weighted probabilities which represent the possibility of obtaining the predetermined level of profit for each item. Budget constraint, inventory site constraint and constraints of price are considered. Finally this paper shows a numerical example in which random demand of each item has exponential distribution.

• 한국컴퓨터정보학회논문지
• /
• 제20권1호
• /
• pp.163-173
• /
• 2015

본 논문에서는 자전거 쉐어링 사업을 중심으로 창원시 누비자 자전거 쉐어링 서비스의 최적 재고 수준을 유지하며 시스템 운영비용을 최소화하는 방법을 제안한다. 쉐어링 서비스란 일반적으로 시간단위로 차량을 렌트하는 개념으로 렌터카보다 편리한 서비스로 이용자의 수가 많아지고 있는 추세이다. Vehicle sharing service는 다음 세대 차량과 함께 sustainable transportation 의 수단으로써 급부상하고 있다. 지구 온난화의 심화와 함께 이산화탄소 배출량의 감소에 관심이 집중되면서 기존의 차량의 내연 기관을 하이브리드 혹은 전기차로 변화하고 있으며, 기존의 대중교통 시스템을 다각화로 발전하고 있다. 그 중 실현 가능성이 높은 분야인 자전거 쉐어링 분야이며, 이미 지방 자치 단체 중심으로 자전거 쉐어링 사업이 이루어지고 있다. 본 연구에서는 자전거 쉐어링 서비스의 각 터미널간 최적 자전거 보유수준(S-s)을 제안하는 시뮬레이션을 설계하여 운영비용을 최소화시키는 자전거 터미널의 재고수준을 제안하였다.

• 한국경영과학회:학술대회논문집
• /
• 대한산업공학회/한국경영과학회 1996년도 춘계공동학술대회논문집; 공군사관학교, 청주; 26-27 Apr. 1996
• /
• pp.285-288
• /
• 1996

This paper deals with an (s, S) spare-part inventory model with general leadtime. In the model, if the inventory level falls to a reorder point s, a replenishment order quantity Q is ordered. Assumming that the number of operating units is one and the lifetime of a unit follows an exponential distribution, we derive the expected cost rate and suggest a procedure to obtain the optimal pair of (s, S) minimizing the cost rate.

• 품질경영학회지
• /
• 제14권1호
• /
• pp.33-38
• /
• 1986

This paper deals with probabilistic order level inventory system which the quantity ordered at the end of the scheduling period is dependent on lead times. To find an optimal solution, pearson system of distributions is used to approximate the probability density function of the on-order quantity. An example is solved and sensitivity analysis is performed to examine the relation between lead times and the ordering quantity.

• 산업경영시스템학회지
• /
• 제30권3호
• /
• pp.89-93
• /
• 2007

In this study, we consider an assembly line operated under a base-stock policy. A product consists of two parts, and a finished product transfers to a warehouse in which demands are satisfied. Assume that demands arrive according to a Poisson process and processing times at each production line are exponentially distributed. Whenever a demand arrives, it is satisfied immediately from an inventory in the warehouse if available; otherwise, it is backlogged and satisfied later by the next product exiting from production lines. In either case, an arriving demand automatically triggers the production of a part at both production lines. These two parts will be assembled into a product that eventually transfers to the warehouse. We obtain a closed form formula of approximation for delay time or lead time distribution of a demand when a base- stock level is s. Moreover, it can be applied to the optimal base-stock level which minimizes the total inventory cost. Numerical examples are presented to show our optimal base-stock level's quality.

• 대한안전경영과학회지
• /
• 제15권1호
• /
• pp.217-229
• /
• 2013

As customers' demands for diversified small-quantity products have been increased, there have been great efforts for a firm to respond to customers' demands flexibly and minimize the cost of inventory at the same time. To achieve that goal, in SCM perspective, many firms have tried to control the inventory efficiently. We present an mathematical model to determine the near optimal (s, S) policy of the supply chain, composed of multi suppliers, a warehouse and multi retailers. (s, S) policy is to order the quantity up to target inventory level when inventory level falls below the reorder point. But it is difficult to analyze inventory level because it is varied with stochastic demand of customers. To reflect stochastic demand of customers in our model, we do the analyses in the following order. First, the analysis of inventory in retailers is done at the mathematical model that we present. Then, the analysis of demand pattern in a warehouse is performed as the inventory of a warehouse is much effected by retailers' order. After that, the analysis of inventory in a warehouse is followed. Finally, the integrated mathematical model is presented. It is not easy to get the solution of the mathematical model, because it includes many stochastic factors. Thus, we get the solutions after the stochastic demand is approximated, then they are verified by the simulations.

• 시스템엔지니어링학술지
• /
• 제13권1호
• /
• pp.79-88
• /
• 2017

For the PBL contract, it is necessary for the contracting parties to share information regarding the reasonable inventory-level and the cost of its repair parts for the estimated demand. There are various models which can be used for this purpose. Among them, V-METRIC model is considered to be the most efficient and is most frequently applied. However, this model is usually used for optimizing the inventory level of the repair parts of the system under operation. The model uses a time series forecast model to determine the demand rate, which is a mandatory input factor for the model, based on past field data. However, since the system at the deployment stage has no operational performance record, it is necessary to find another alternative to be used as the demand rate of the model application. This research applies the V-METRIC model to find the optimal inventory level and cost estimation for repairable items to meet the target operational availability, which is a key performance indicator, at the time of the PBL contract for the deployment system. This study uses the calculated value based on the allocated MTBF to the system as the demand rate, which is used as input data for the model. Also, we would like to examine changes in inventory level and cost according to the changes in target operational availability and MTBF allocation.

• 대한안전경영과학회지
• /
• 제16권4호
• /
• pp.323-330
• /
• 2014

Various inventory control theories have tried to modelling and analyzing supply chains by using quantitative methods and characterization of optimal control policies. However, despite of various efforts in this research filed, the existing models cannot afford to be applied to the realistic problems. The most unrealistic assumption for these models is customer demand. Most of previous researches assume that the customer demand is stationary with a known distribution, whereas, in reality, the customer demand is not known a priori and changes over time. In this paper, we propose a reinforcement learning based adaptive echelon base-stock inventory control policy for a multi-stage, serial supply chain with non-stationary customer demand under the service level constraint. Using various simulation experiments, we prove that the proposed inventory control policy can meet the target service level quite well under various experimental environments.