• 산업경영시스템학회지
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• 제18권34호
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• pp.193-204
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• 1995

Many studies show that the value of the warehouse is good. However, studies explicitly mention the tradeoff between costs of operating the warehouse and benefits from the warehouse. Also, it is important to know when the benefits overcome the costs. We study a one-warehouse/N-retailer(s,Q) distribution system with stochastic lead times in order to answer two questions: "What are the optimal policies of the system that minimizes total system costs\ulcorner" and given the optimal policies, "Is the value of the warehouse always good\ulcorner" We use an analytical model for answering the questions. We find that the optimal policies are different from those with deterministic lead times. In fact it is reverse. We alse find the existence of the breakeven point beyond which the benefits starts overcomming the costs. And, we show that one of the breakeven points is the mean ratio of a supplier's lead time to transportation lead time between the warehouse and the retailer. Finally, we show that the breakeven point is sensitive to the ratio of holding costs of the warehouse and the retailer and it is also sensitive to the unit backorder costs at the retailer.sts at the retailer.

• 한국시뮬레이션학회논문지
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• 제12권3호
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• pp.31-40
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• 2003

This paper studies an optimal policy for a certain class of (s, S) inventory control systems, where the demands are characterized by the renewal arrival process. To minimize the average cost over a simulation period, we apply a stochastic optimization algorithm which uses the gradients of parameters, s and S. We obtain the gradients of objective function with respect to ordering amount S and reorder point s via a combined perturbation method. This method uses the infinitesimal perturbation analysis and the smoothed perturbation analysis alternatively according to occurrences of ordering event changes. The optimal estimates of s and S from our simulation results are quite accurate. We consider that this may be due to the estimated gradients of little noise from the regenerative system simulation, and their effect on search procedure when we apply the stochastic optimization algorithm. The directions for future study stemming from this research pertain to extension to the more general inventory system with regard to demand distribution, backlogging policy, lead time, and inter-arrival times of demands. Another direction involves the efficiency of stochastic optimization algorithm related to searching procedure for an improving point of (s, S).

• 한국시뮬레이션학회논문지
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• 제12권2호
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• pp.1-11
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• 2003

In this paper, we focus an optimal policy focus optimal class of (s, S) inventory control systems. To this end, we use the perturbation analysis and apply a stochastic optimization algorithm to minimize the average cost over a period. We obtain the gradients of objective function with respect to ordering amount S and reorder point s via a combined perturbation method. This method uses the infinitesimal perturbation analysis and the smoothed perturbation analysis alternatively according to occurrences of ordering event changes. Our simulation results indicate that the optimal estimates of s and S obtained from a stochastic optimization algorithm are quite accurate. We consider that this may be due to the estimated gradients of little noise from the regenerative system simulation, and their effect on search procedure when we apply the stochastic optimization algorithm. The directions for future study stemming from this research pertain to extension to the more general inventory system with regard to demand distribution, backlogging policy, lead time, and review period. Another directions involves the efficiency of stochastic optimization algorithm related to searching procedure for an improving point of (s, S).

• 한국철도학회:학술대회논문집
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• 한국철도학회 2002년도 추계학술대회 논문집(I)
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• pp.727-732
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• 2002

This study is to develop the model of alignment optimization based on design criteria by approaching through alignment of railway design and problems in economy, environment and technology for satisfying traffic volume of the main roads caused by economical and social developments. Now, Geographic Information System isn't applied when designing a present railway in home. And the design of railway alignment is still set on importance of transition curves and cant according to passenger comfort in abroad so tile study of railway alignment is at initiation phase so far. This paper is about decision of optimal alignment between two stations such as starting point and ending point automatically using GIS in optimization of railway alignment. A route between Sungsan city and Shinpung city is the training area and the study compared and evaluated optimal railway route by GIS automatically with present railway route designed. Present optimal fomulas was used in this study for optimization of railway alignment. The model of optimization of railway alignment was developed through topographical elements and it was mentioned by the model of road alignment because of the similarity in design of alignment. But the design of lateral track irregularities, cant fur passenger comfort and motion sickness fellowed by train rolling have to be considered more. Anyway, this study farmed the basis of using GIS and the study should be keep going on in the future.

• 대한전기학회논문지:전력기술부문A
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• 제48권1호
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• pp.36-43
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• 1999

This paper proposes a new hybrid genetic algorithm for auto-tuning fuzzy controllers improving the performance. In general, fuzzy controllers use pre-determined moderate membership functions, fuzzy rules, and scaling factors, by trial and error. The presented algorithm estimates automatically the optimal values of membership functions, fuzzy rules, and scaling factors for fuzzy controllers, using a hybrid genetic algorithm. The object of the proposed algorithm is to promote search efficiency by the hybrid optimization technique. The proposed hybrid genetic algorithm is based on both the standard genetic algorithm and a modified gradient method. If a maximum point is not be changed around an optimal value at the end of performance during given generation, the hybrid genetic algorithm searches for an optimal value using the the initial value which has maximum point by converting the genetic algorithms into the MGM(Modified Gradient Method) algorithms that reduced the number of variables. Using this algorithm is not only that the computing time is faster than genetic algorithm as reducing the number of variables, but also that can overcome the disadvantage of genetic algoritms. Simulation results verify the validity of the presented method.

• 한국주조공학회지
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• 제19권5호
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• pp.393-402
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• 1999

The reheating of the billet in the semi-solid state as quickly and homogeneously as possible is one of the most important aspects. From this point of view, an optimal design of the induction coil is necessary. The objective of inductive coil designsi a uniform induction heating over the length of the billet. The effect of coil length, diameter, the gap between coil surface and billet and axial position of the billet on temperature distribution of billet has been investigated. These design parameters have an important effectiveness on the electro-magnetic field. Therefore, in this study an optimal coil design to minimize electromagnetic ed effect will be proposed by defining the relationship between billet length and coil length. In particular, key point in induction heating process is focussed on optimizing the coil design with regard to the size of the heating billet and the frequency of induction heating system. After demonstrating the suitability of an optimal coil design through the FEM simulation of the induction heating process, the results of the coil design are also applied to the reheating process to obtain a fine globular microstructure. Its considered that the reheating conditions of aluminum alloys for thixoforging and a new CAE model of the induction heating process are very useful for thixoforging practitioners including induction heating ones.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2014년도 전력전자학술대회 논문집
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• pp.335-336
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• 2014

This paper investigates the design of coupled inductor for minimum inductor current ripple in rapid traction battery charger systems. Based on the general circuit model of coupled inductor together with the operating principles of dc-dc converter, the relationship between the ripple size of inductor current and the coupling factor is derived under the different duty ratio. The optimal coupling factor which corresponds to a minimum inductor ripple current becomes -1, i.e. a complete inverse coupling without leakage inductance, as the steady-state duty ratio operating point approaches 0.5. In an opposite manner, the optimal coupling factor value of zero, i.e. zero mutual inductance, is required when the steady-state duty ratio operating point approaches either zero or one. Coupled inductors having optimal coupling factor can minimize the ripple current of inductor and battery current resulting in a reliable and efficient operation of battery chargers.

• 한국멀티미디어학회논문지
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• 제12권8호
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• pp.1182-1189
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• 2009

컴퓨터 기반 교육의 잠재적인 이점은 개별화 교습이다. 결국 수준별 교육과정의 운영과 열린 교육의 실천을 위하여 어떻게 학습자 개개인에 대해서 신속하고 정확하게 평가할 수 있는가에 대한 문제가 제기된다. 본 연구에서는 평가를 위한 문항 수가 두드러지게 감소하면서 반면에 합격과 불합격 판정이 비교적 정확한 기존의 SPRT(Sequential Probability Ratio Testing) 판정 방법에 대한 문제점을 보완하여 보다 최적의 판정을 내릴 수 있는 방안을 시뮬레이션 연구를 통하여 제안한다. 이를 위하여 실제 측정에 의해서 얻어진 피험자 자료를 활용하여 SPRT판정의 정확도 검증을 위한 시뮬레이션과 최적의 SPRT판정을 위한 초기 설정치와 다단계 (Multilevel) SPRT 모형 및 판정 기준을 제시하고 시뮬레이션을 통하여 타당성을 알아본다.

• Smart Structures and Systems
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• 제2권2호
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• pp.189-208
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• 2006

Monitoring large-scale civil engineering structures such as offshore platforms and high-large buildings requires a large number of sensors of different types. Innovative sensor data information technologies are very extremely important for data transmission, storage and retrieval of large volume sensor data generated from large sensor networks. How to obtain the optimal sensor set and placement is more and more concerned by researchers in vibration-based SHM. In this paper, a method of determining the sensor location which aims to extract the dynamic parameter effectively is presented. The method selects the number and place of sensor being installed on or in structure by through the tolerance domain statistical inference algorithm combined with second order sensitivity technology. The method proposal first finds and determines the sub-set sensors from the theoretic measure point derived from analytical model by the statistical tolerance domain procedure under the principle of modal effective independence. The second step is to judge whether the sorted out measured point set has sensitive to the dynamic change of structure by utilizing second order characteristic value sensitivity analysis. A 76-high-building benchmark mode and an offshore platform structure sensor optimal selection are demonstrated and result shows that the method is available and feasible.

• Journal of Information Processing Systems
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• 제17권2호
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• pp.306-317
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• 2021

The unbalance between system ergodic sum rate and high fairness is one of the key issues affecting the performance of non-orthogonal multiple access (NOMA) system. To solve the problem, this paper proposes a power allocation algorithm to realize the ergodic sum rate maximization of NOMA system. The scheme is mainly achieved by the construction algorithm of fair model based on α fair utility function and the optimal solution algorithm based on the interior point method of penalty function. Aiming at the construction of fair model, the fair target is added to the traditional power allocation model to set the reasonable target function. Simultaneously, the problem of ergodic sum rate and fairness in power allocation is weighed by adjusting the value of α. Aiming at the optimal solution algorithm, the interior point method of penalty function is used to transform the fair objective function with unequal constraints into the unconstrained problem in the feasible domain. Then the optimal solution of the original constrained optimization problem is gradually approximated within the feasible domain. The simulation results show that, compared with NOMA and time division multiple address (TDMA) schemes, the proposed method has larger ergodic sum rate and lower Fairness Index (FI) values.