• Journal of the Korean Operations Research and Management Science Society
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• v.22 no.1
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• pp.59-73
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• 1997

This papaer analyzes a system with consists of two workstations that are separated by finite buffer storage. In this system, we assume that the processing time in each station in a random variable and each station is not vulnerable to failure. To control the in-process inventory in the serial production system we use the (R, r) policy which is similar to the (s, S) policy in the inventory theory. Under the (R, r) policy the preceding station is forced down when the inventory level in the buffer reaches R and starts operation again when the inventory level falls to r. For the model developed, we analyze the system characteristics and the system performances.

• Journal of the Korea Society for Simulation
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• v.20 no.2
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• pp.19-27
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• 2011

This study investigates impact of smoothed replenishment ordering policy on the performance measures such as lead time, order fulfillment ratio, and inventory cost. We consider a two-echelon supply chain: a single retailer orders using smoothed order up to replenishment policy and a manufacturer produces the retailer's orders on a make to order basis. Simulation result confirms that lead time from the manufacturer can be reduced by smoothed ordering policy as expected. However, smoothing orders may deteriorate the customer order fulfillment ratio and inventory cost in a retailer. We also observe that variance of manufacturing time contributes more than mean of manufacturing time to both order fulfillment ratio and inventory cost. Therefore, variability of upstream manufacturing time should be minimized.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.33 no.2
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• pp.170-175
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• 2010

Maintaining a complex repairable system can be achieved by repairing, replacing, or any other activities. This paper proposes a joint optimization policy that is composed with ordering and replacing under minimal repair for the complex system. For this purpose, we derive the expected cost due to the minimal repair, ordering, downtime, inventory costs, and salvage value of units that follow generally distribution. Some properties about the optimum ordering policy that are suggested for our purpose shows that the optimum ordering policy minimizing the expected cost is either one of the two typical policies : (1) the original unit is replaced as soon as the ordered spare is delivered, or (2) the delivered spare is used as inventory part until the original unit fails.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.722-725
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• 2004

In most manufacturing systems, all customers are expected to take deliveries from inventory. However, in some situations, management may keep inventory only for some customers and not keep inventory for the others. The reason is that they would like to make as much benefit as possible from the first group of customers and this may help sell these customers on further products. This paper attempts to determine the cutoff between the group of customers who are given products immediately when their orders come and other customers who will be served but have to wait for the production of their products. The optimum set of customers to be served immediately and the optimum set of customers who have to wait for the production are found using linear programming to optimize perceived manufacturer benefits measured as the product of the benefit factor and the corresponding profit per customer. The results indicate that it is not necessarily wise to keep inventory for all customers.

• Proceedings of the Society of Korea Industrial and System Engineering Conference
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• 2002.05a
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• pp.349-357
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• 2002

This research is basically deals with an inventory distribution system with several regional sales branches. Under the continuous review policy, each sales branch places an order to its supplier whenever on hand plus on order inventory falls on the order point, and the order quantity is received after elapsing a certain lead time. This research first shows the method how to apply the product with low lever of demand into the continuous review policy. For the application, we use an order level as the maximum level of inventory during an order cycle. Also we analyze the lost sales case as a customer behavior. Further we use variable demands and variable lead times for more realistic situation. Based on the above circumstances, the research mainly discusses those methods to decide the optimal order level, order point, and order quantity for each sales branch which guarantees the system wide goal level of service, while keeping the minimum level of the system wide total inventory.

• Journal of the Korean Operations Research and Management Science Society
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• v.25 no.4
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• pp.27-44
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• 2000

In this study we consider a spares provisioning problem for repairable items in which a parts inventory system is incorporated. If a machine fails, a replacement part must be obtained at the parts inventory system before the failed machine enters the repair center. The inventory policy adopted at the parts inventory system is the (S, Q) policy. Operating times of the machine before failure, ordering lead times and repair times are assumed to follow a two-stage Coxian distribution. For this system, we develop an approximation method to obtain the performance measures such as steady state probabilities of the number of machines at each station and the probability that a part will wait at the parts inventory system. For the analysis of the proposed system, we model the system as a closed queueing network and analyze it using a product-form approximation method. A recursive technique as well as an iterative procedure is used to analyze the sub-network. Numerical tests show that the approximation method provides fairly good estimation of the performance measures of interest.

• Journal of Korean Institute of Industrial Engineers
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• v.30 no.3
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• pp.197-204
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• 2004

This paper deals with a supply chain with a company and its contractor that produces products by the OEM contract with the company. The supply chain of interest has two distinct features. First, the company is the supplier of raw material required in the production at the contractor. Second, the company and its contractor make a delivery shipment arrangement that the replenishment lead time is determined depending on demand process. We show that the optimal inventory policy is monotonically changed as either the replenishment setup cost or inventory holding cost becomes increased or decreased. We also present asymptotic properties of the optimal inventory policy when either the number of outstanding customer orders or the inventory level becomes very large.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2006.11a
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• pp.142-146
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• 2006

This paper considers a SCM issue concerned with an integrated problem of inventory control and dynamic pricing strategies when demands are price and time dependent. The associated price markdowns are conducted for inventory control in a two-layer market consisting of retailer and outlet as in fashion apparel market. The objective function consists of revenue terms (sales revenue and salvage value) and purchasing cost term. Specifically, decisions on price markdowns and order quantity are made to maximize total profit in the supply chain so as to have zero inventory level at the end of the sales horizon. To solve the proposed problem, a gradient method is applied, which shows an optimal decision on both the initial inventory level and the discount pricing policy. Sensitivity analysis is conducted on the demand parameters and the final comments on the practical use of the proposed model are presented.

• Journal of the Korean Operations Research and Management Science Society
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• v.37 no.2
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• pp.45-56
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• 2012

This paper considers a supply chain consisting of a component manufacturer and a product manufacturer. The component manufacturer provides components for the product manufacturer based on a vendor-managed inventory type of supply contract, and also faces demands from the market with the option of to accept or reject each incoming demand. Using the Markov decision process model, we examine the structure of the optimal production control and inventory rationing policy. Two types of heuristics are presented. One is the fixed-buffer policy and the other uses two linear functions. We implement a computational study and present managerial insights based on the observations.

• Journal of the Korean Operations Research and Management Science Society
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• v.16 no.1
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• pp.13-34
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• 1991

A production/inventory system is considered in which a production facility produces one type of product. The demand for the product is given by a compound Poison process and is supplied directly from inventory when inventory is available and is lost when inventory is out of stock. The processing time to produce one item is assumes to follow a general distribution. An (s, S) policy is considered in which production stops at the instant the stock on hand reachs S and the setup of the production facility begins at an inspection point when the stock on hand drops to or below s for the first time. The time interval between two successive inspection points during a non-production period is a random variable which follows a general distribution.