용량 확장과 반납을 갖는 렌탈 자원 관리모델

김은갑,변진호 한국경영과학회 2006 한국경영과학회지 Vol.31 No.3

We consider a rental company that dynamically manages its capacity level through capacity addition and return. While serving customer with its own capacity, the company expands its capacity by renting items from an outside source so that it can avoid lost opportunities of rental which occur when stock is not sufficient. If stock becomes sufficiently large enough to cope with demands, the company returns expanded capacity to the outside source. Formulating the model into a Markov decision problem, we identify an optimal capacity management policy which states when the company should expand its capacity and when it should return expanded capacity after capacity addition. Since it is intractable to analytically find the optimal capacity management policy and the optimal size of capacity expansion, we present a numerical procedure that finds these optimal values based on the value iteration method. Numerical analysis is implemented and we observe monotonic properties of the optimal performance measures by system parameters, which are meaningful in developing effective heuristic policies.

Optimal Control for Cash Management with Investment and Retrieval

김은갑,변진호,배재현 대한산업공학회 2011 산업공학 Vol.24 No.4

We develop a cash management model in which firms face randomly occurred investment projects and retrieve investments upon the maturity of these projects. Using the Markov Decision Problem approach, we examine a control policy which dynamically adjusts the cash balance under the discounted cost criterion. The existence of an optimal policy is shown under some conditions. The optimal solution procedure is developed to find the optimal points and the optimal sizes for adjusting the cash balance. In numerical experiment, we investigate important structural properties of the optimal cash management policy.

The Effects of Lead Time Variability on Managing Component Replenishment for Customized Manufacturing

김은갑 한국생산관리학회 2010 韓國生産管理學會誌 Vol.21 No.3

We study the impact of lead time variability on inventory management in a make-to-order system that processes customized manufacturing using a common component. Components are purchased from a supplier with Erlang lead times. In this paper, we investigate the structure of the optimal replenishment policy and examine how the lead time variability affects replenishment decision and supply chain cost. Explicit incorporation of setup cost and lead time variability into the model is the essential contribution to the current literature. To provide better managerial insights on the problem, we perform numerical experiment under different operating conditions of the system parameters.

두 단계 푸쉬-풀 공급망에서 공급자 주도 재고 관리의 구현 - 가변 생산량이 갖는 영향을 중심으로

김은갑 한국SCM학회 2010 한국SCM학회지 Vol.10 No.2

We consider a supply chain with a component manufacturer and a customized end item manufacturer in stage under a vendor-managed inventory (VMI) agreement. The component manufacturer continuously reviews both component inventory and backorder status at the end item manufacturer. Based on this information, the component manufacturer dynamically determines production scheduling and lot size which is the multiple of the basic lot size. The goal of this paper is to find the component manufacturer's production policy which minimizes the total supply chain cost. From numerical experiment, we investigate the impact of the variable production lot size on the supply chain cost.

Component Outsourcing Contracts in a Two-Component Assembly System

김은갑 대한산업공학회 2009 산업공학 Vol.22 No.2

This paper considers a two-component assembly system that makes different types of purchasing contracts by component type and studies the issue of coordinating those contracts. Acquisition of type 1 component is based on the long-term contract. In contrast, type 2 component is intermittently purchased under the sort-term contract. We identify the structural properties of the optimal short-term contract and investigate how the changes in system parameters affect the optimal performance. To provide managerial insights, we compare the short-term and long-term contracts for type 2 component and discuss the conditions that make the short-term contract preferable to the long-term contract. We also present a result which shows that coordinating the contracts of type 1 and type 2 components can be significantly profitable over uncoordinating them.

제한된 주문허용 수준을 갖는 주문생산 재고시스템을 위한 민감도 분석

김은갑,김지승 한국경영과학회 2005 한국경영과학회지 Vol.30 No.2

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.

Customer Order Admission Control and Inventory Management in a Make-to-order System - The Effects of Replenishment Setup Cost

김은갑 한국산업경영학회 2010 경영연구 Vol.25 No.1

We study the customer order admission control and inventory management decision in a make-to-order system that processes customer orders using common component. Each incoming customer order can be accepted or rejected based on the system status. The component is purchased from a supplier under stochastic lead times and setup costs. In this paper, we investigate the structure of joint admission and inventory control and examine the impact of setup cost on it. To provide a better understanding of the structure of the optimal policy, we compared its performance with two heuristic policies; the one with static admission control and dynamic replenishment control and the other with static admission and replenishment controls. The paper contributes to the current literature of make-to-order production-inventory systems in the following two essential aspects. First, we study the problem of simultaneously considering admission control and inventory management decisions. Second, we explicitly incorporate the replenishment setup cost into the model and examine its impact on the optimal cost function and the optimal policy.

복수고객 군을 갖는 주문생산 제조시스템에서 에너지소비효율 최적화와 생산순서, 생산속도 및 주문수용 통제의 통합 구현에 관한 연구

김은갑 한국생산관리학회 2019 한국생산관리학회지 Vol.30 No.4

We study a joint production sequencing, production rate, and order admission controls for maximizing energy consumption efficiency in a multi-class make-to-order manufacturing firm. Recently, production rate control has received attention in research because of its effectiveness in reducing demand variability and incorporating the energy consumption problem into production planning for sustainable manufacturing. We presented a Markov decision process model to investigate the effect of production sequencing, production rate, and order admission controls on the firm’s profit and implemented numerical investigation using the value iteration algorithm. The numerical results indicate that production sequencing is only affected by backorder cost and is unaffected by unit sales revenue or order rejection cost. They also show that systems with variable production rates achieve a higher profit than those with a fixed rate. In particular, it is observed that the variable production rate option is more effective as the energy consumption cost becomes larger. We also observe that the higher the revenue parameter and ratio of backorder costs between two customer classes are, the more valuable the variable production rate option is. 본 논문은 복수고객 군을 갖는 주문생산 제조기업을 대상으로 에너지소비효율 최적화와 생산순서, 생산속도 및 주문수용 통제를 통합적으로 수립하는 문제를 제안하고 있다. 수요 변동성을 완화시키는데 효과적이고, 지속가능한 제조 관점에서 에너지 소비 이슈를 생산계획수립에 반영할 필요성이 커졌기 때문에, 최근에 제조시스템의 생산속도 통제를 다루는 연구들이 주목을 받고 있다. 본 논문은 주문수용통제, 생산속도통제, 생산순서통제가 기업수익에 미치는 영향을 분석하기 위하여 마코프 의사결정모형을 제시하였고, 가치반복알고리즘을 사용하여 수치 분석을 수행하였다. 수치실험 결과, 주문처리순서는 계층별 판매단가와 주문거절비용의 크기에는 영향을 받지 않고, 계층별 지연재고비용의 크기에 의해서만 결정된다는 사실을 알 수 있었다. 이는 고객수용 통제와 서비스속도 통제가 이루어지지 않는 복수고객 군 시스템의 최적 서비스 순서 통제 전략인 규칙(지연주문비용과 서비스 속도의 곱의 크기 순서대로 고객 군들에 대한 서비스를 진행)이 본 연구 모형의 생산순서 통제에서도 최적 전략이 될 수 있음을 시사하는 결과이다. 본 논문은 다양한 수치 예제들에 대한 실험을 통해 생산속도가 평균값으로 고정된 시스템보다는 탄력적으로 통제되는 시스템에서 더 높은 기대수익을 올릴 수 있음을 알 수 있었다. 수치실험 결과에 따르면 생산속도 통제옵션은 에너지소비비용이 낮을 때보다 높을 때, 판매단가가 높을 때보다 낮을 때, 그리고 두 고객계층 간 지연재고비용 비율이 낮을 때보다 높을 때 더 효과적이었다. 주문거절비용이 판매단가 이하일 경우에는 주문수용 통제옵션에 의한 수익성 개선 효과가 뚜렷하지만, 반대일 경우에는 제한적이었다. 기대수익에 대한 주문수용 통제옵션의 영향은 두 고객 군의 제품판매단가 비율에 의해 크게 달라질 수 있음도 알 수 있었다. 한편, 수치실험 결과는 생산속도 통제를 구현하기 위해 많은 생산속도 선택 옵션을 가져갈 필요가 없으며, 세 가지의 생산속도 선택 옵션만으로도 고정생산속도를 사용할 때보다 높은 수익성 개선 효과를 도모할 수 있음을 보여 주었다.

조세범 처벌에 관한 문제점 및 개선방안

김은갑 서울市立大學校 經商大學 稅務學科 2004 稅務學論集 Vol.17 No.1

조세범 처벌에 관한 문제점 및 개선안

경쟁 기반의 부품 생산과 협업 기반의 완성품 생산 시스템에서 생산과 수요 통제의 통합적 고찰

김은갑 대한산업공학회 2009 산업공학 Vol.22 No.4

This paper considers a two-stage supply system consisting of two make-to-stock facilities. The facility in the first stage produces a single type of component in anticipation of future demands from the market and the end item production while the facility in the second stage produces the end item in anticipation of future demands from the OEM customers. The facility in the first stage has the option of to accept or reject each incoming demand from the market. In this paper, we address the problem of how to control the exogenous component demand and how to manage the production of the end item and the component so as to maximize the system’s profit subject to the system costs. In this paper, we present a heuristic policy that is the base-stock production policy combined with a linear switching curve for component demand control. Numerical study is implemented under different operating conditions of the system and it shows that the performance of the heuristic is very promising compared to that of the optimal policy for the Markov model.