• 한국경영과학회:학술대회논문집
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• 한국경영과학회 2003년도 추계학술대회 및 정기총회
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• pp.81-84
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• 2003

The ability to determine the optimal frequencies and offsets for independent and unrestricted ordering cycles for multiple items can be very valuable for managing storage capacity constrained facilities in a supply chain. The complexity of this problem has resulted in researchers focusing on more tractable surrogate problems that are special cases of the base problem. Murthy et al. (European Journal of Operation Research 2003) developed insights leading to solution of the original problem and present a heuristic for offsetting independent and unrestricted ordering cycles for items to minimize their joint storage requirements. However, their study cannot find optimal solution due to the Greedy Heuristic solution procedure. In this paper, we present a complete procedure to find the optimal solution for the model with a integer programming optimization approach and genetic algorithm. Numerical examples are included to compare each model with that of Murthy et at. Research of this type may prove useful in solving the more general problem of selecting order policies to minimize combined holding, ordering, and storage costs.

• Management Science and Financial Engineering
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• 제17권2호
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• pp.1-21
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• 2011

This paper considers an integrated inventory-distribution system with a fleet of heterogeneous vehicles employed where a single warehouse distributes a single type of products to many spatially distributed retailers to satisfy their dynamic demands. The problem is to determine order planning at the warehouse, and also vehicle schedules and delivery quantities for the retailers with the objective of minimizing the sum of ordering cost at the warehouse, inventory holding cost at both the warehouse and retailers, and transportation cost. For the problem, we give a Mixed Integer Programming formulation and develop a Lagrangean heuristic procedure for computing lower and upper bounds on the optimal solution value. The Lagrangean dual problem of finding the best Lagrangrean lower bound is solved by subgradient optimization. Computational experiments on randomly generated test problems showed that the suggested algorithm gives relatively good solutions in a reasonable amount of computation time.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권8호
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• pp.2626-2646
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• 2014

This study presents a power and Physical Resource Blocks (PRBs) joint allocation algorithm to coordinate uplink (UL) interference in the device-to-device (D2D) underlaying Long Term Evolution-Advanced (LTE-A) networks. The objective is to find a mechanism to mitigate the UL interference between the two subsystems and maximize the weighted sum throughput as well. This optimization problem is formulated as a mixed integer nonlinear programming (MINLP) which is further decomposed into PRBs assignment and transmission power allocation. Specifically, the scenario of applying imperfect channel state information (CSI) is also taken into account in our study. Analysis reveals that the proposed PRBs allocation strategy is energy efficient and it suppresses the interference not only suffered by the LTE-A system but also to the D2D users. In another side, a low-complexity technique is proposed to obtain the optimal power allocation which resides in one of at most three feasible power vectors. Simulations show that the optimal power allocation combined with the proposed PRBs assignment achieves a higher weighted sum throughput as compared to traditional algorithms even when imperfect CSI is utilized.

• 산업경영시스템학회지
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• 제32권3호
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• pp.40-48
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• 2009

In this article, scheduling of a casting sequence is studied in a casting foundry which must deliver products according to the Just-in-time(JIT) production policy of a customer. When a foundry manufactures a variety of casts with an identical alloy simultaneously, it frequently faces the task of production scheduling. An optimal casting schedule should be emphasized in order to maximize the production rate and raw material efficiency under the constraints of limited resources; melting furnaces and operation time for a casting machine. To solve this practical problem-fulfilling the objectives of casting the assigned mixed orders for the highest raw material efficiency in a way specified by the customer's JIT schedule, we implement simple integer programming. A simulation to solve a real production problem in a typical casting plant proves that the proposed method provides a feasible solution with a high accuracy for a complex, multi-variable and multi-constraint optimization problem. Employing this simple methodology, a casting foundry having an automated casting machine can produce a mixed order of casts with a maximum furnace utilization within the due date, and provide them according to their customer's JIT inventory policy.

• 센서학회지
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• 제26권4호
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• pp.274-279
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• 2017

LCD(Liquid Crystal Display) panel cutting problem is a sort of two dimensional cutting stock problem. A cutting stock problem is problem that it minimizes the loss of the stock when a stock is cut into various parts. In the most research of the two dimensional cutting stock problem, it is supposed that the relative angle of a stock and parts is not important. Usually the angle is regarded as horizontal or perpendicular. In the manufacturing of polarizing film of LCD, the relative angle should be maintained at some specific angle because of the physical and/or chemical characteristics of raw material. We propose a mathematical model for solving this problem, a two-dimensional non-Guillotine cutting stock problem that is restricted by an arranged angle. Some example problems are solved by the C++ program using ILOG CPLEX classes. We could get the verification and validation of the suggested model based on the solutions.

• 한국산업정보학회논문지
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• 제15권5호
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• pp.187-196
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• 2010

네트워크 최적화 문제는 의사결정 문제 중에서 노드와 아크로 표현되는 수 많은 문제를 포함하고 있어서, 그 응용범위가 매우 다양할 뿐만 아니라 매우 실질적인 문제를 해결하는 좋은 방법론이다. 직접적으로 관련이 없는 많은 최적화 문제들도 네트워크로 적절히 표현할 수 있는 경우가 많으며 이를 통해 보다 섬도 있는 문제에 대한 이해와 해의 도출이 가능하게 된다. 이처럼 광범위한 응용분야를 가지는 네트워크 최적화 문제는 경영과학 및 산업공학에서 기본이 중요 학문이며, 이를 체계적으로 이해하고 실제 문제를 해결하려면 최적화 이론, 계산이론, 프로그래밍 등의 종합적인 지식을 필요로 한다. 본 연구에서는 네트워크 최적화 문제를 실질적으로 해결하는 필요한 지식 전달에 중점을 두고, 선형계획법 및 정수계획법을 위한 소프트웨어인 LPSolve를 소개하고 이 LPSolve와 엑셀을 연동하는 방법을 알아본다. 또한 네트워크 자체를 엑셀에서 그리는 방법을 알아보고, 이를 통해 네트워크 최적화 문제를 보다 실질적인 다룰 수 있도록 한다.

• Korean Chemical Engineering Research
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• 제52권4호
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• pp.475-480
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• 2014

플랜트 배치 최적화 문제의 목적은 장치를 연결하는 파이프의 길이를 최소화 하는데 있다. 하지만, 기존 연구들은 대체적으로 단일 층의 배치 문제를 다루고 있으며, 또한 장치 간 유지 보수에 필요한 최소 공간 확보, 사고 예방을 위한 장치 간 이격 거리등 안전 요소를 간과해 왔다. 본 연구에서는 장치 간 유지 보수에 필요한 최소 거리 확보 및 안전 이격 거리를 고려하여 플랜트 배치 문제를 MILP(Mixed Integer Linear Programming) 형태의 문제로 정의하였다. 본 문제의 목적함수는 장치 간 연결하는 파이프 비용이며 제약조건은 안전을 위한 장치 간 최소 이격 거리, 유지 보수에 필요한 공간으로 설정하였다. 하지만, 공정 특성에 따라 필요한 공간 및 작업자의 통행 등 다양한 제약조건을 수반하게 된다. 이에 따라 플랜트 배치 문제를 일반적인 수학식으로 표현하는 데 많은 제약이 있으며, 따라서 함수의 미분식을 이용하는 기존 최적화 방법론을 이용하여 문제를 해결하는 데 많은 어려움이 있다. 본 연구에서는 함수의 미분식을 적용하지 않고 이용이 가능한 경험적 최적화 기법 중 하나인 PSO(Particle Swarm Optimization)를 이용하여 최적화를 수행하였다. 본 연구에서 개발한 모델의 검증을 위해 Ethylene Oxide 공정을 2층으로 배치하는 최적화를 수행하였다.

• Journal of Electrical Engineering and Technology
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• 제6권6호
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• pp.786-792
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• 2011

The present paper presents an optimal capacitor placement (OCP) algorithm for voltagestability enhancement. The OCP issue is represented using a mixed-integer problem and a highly nonlinear problem. The hybrid particle swarm optimization (HPSO) algorithm is proposed to solve the OCP problem. The HPSO algorithm combines the optimal power flow (OPF) with the primal-dual interior-point method (PDIPM) and ordinary PSO. It takes advantage of the global search ability of PSO and the very fast simulation running time of the OPF algorithm with PDIPM. In addition, OPF gives intelligence to PSO through the information provided by the dual variable of the OPF. Numerical results illustrate that the HPSO algorithm can improve the accuracy and reduce the simulation running time. Test results evaluated with the three-bus, New England 39-bus, and Korea Electric Power Corporation systems show the applicability of the proposed algorithm.

• 대한산업공학회지
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• 제40권2호
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• pp.184-194
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• 2014

Numerous studies have been studied to provide an efficient solution for the Nurse Rostering Problem (NRP), most of which have suffered from its complexity arising from incorporating nurse's work shift and ability. The test-bed data for the NRP is released for the public Competition in 2010. This study suggests a new mixed integer programming for Nurse Rostering Problem and develops a hybrid approach, where a hierarchical decomposition and the corresponding optimization are combined. The computation experiment is performed to show that the suggested algorithms may give a better solution in various instances, compared to the one appeared in the literature.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2004년도 춘계종합학술대회
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• pp.381-385
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• 2004

본 논문에서는 앞으로 광대역통합망에서 사용자의 요구사항에 따른 QoS를 제공하기 위한 연구의 일환으로 여러 가지 서비스 모델과 메커니즘을 살펴보고, 라우팅 최적화를 위한 유전 알고리즘과 hybrid 유전알고리즘에 대하여 논한다. OSPF에 바탕을 둔 라우팅 최적화만으로 QoS가 충분하지 않은 경우 약간의 MPLS 경로가 QoS를 개선하기 위해 설정될 수 있다. 이러한 상보형 MPLS 라우팅을 위한 두 개의 MIP 모델을 제안하고, 적절한 네트워크 QoS 대책으로 네트워크 내의 최대 링크 이용을 고찰한다.