• 한국시스템다이내믹스연구
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• 제9권2호
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• pp.5-25
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• 2008

This paper analysed the impact of return policy as a coordination mechanism for decentralized supply chain with one capacitated supplier and two competing retailers under random demand distribution. In this study, Shortage gaming also considered to reflect a competing environment of two retailers. System dynamics approach was used to model the baseline two echelon supply chain and return policy on it. Given each of 4 experiment settings being used for 100 simulations with different random seeds, 400 random samples were used in a t-test. The result show that return policy significantly enhance the supply chain profits and fillrates. The analysis suggest that the supply chain performance can be build up by implementing a return policy even though under consideration of a capacitated supplier and competing retailers.

• 대한교통학회지
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• 제24권1호
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• pp.97-108
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• 2006

현재 우리나라에서는 버스 노선의 정류장 수 및 간격 산정을 위해 전문가의 주관적인 판단에 의존하는 경우가 많다. 좀 더 객관적인 절차를 통해 신뢰성 있는 결과를 얻기 위해 최적 정류장 수 및 간격을 구하는 기존 모형들을 살펴보았지만 하차수요와 임의적인 수요분포를 고려하지 못한다는 한계점을 안고 있었다. 본 연구는 기존 모형들의 이러한 한계를 인식하고 수요를 승차와 하차로 구분하고 그 분포에 라라 일정한 구간별로 서로 다른 최적 정류장 수와 간격을 탄력적으로 산출해 낼 수 있는 모형을 정립하였다. 정립된 모형을 다양한 수요분포를 가지는 간단한 예제노선에 적용해본 결과 승차 혹은 하차수요에 비례하여 구간별 정류장 수가 탄력적으로 산출됨을 알 수 있었다.

• 대한산업공학회지
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• 제2권1호
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• pp.79-83
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• 1976

This paper deals with a computer simulation for the stochastic inventory system in which the decision rules are associated with the problem of forecasting uncertain demand, lead time, and amount of shortages. The model consists of mainly three parts; part I$\cdots$the model calculates the expected demand during lead time through the built-in subrou tine program for random number generator and the probability distribution of the demand, part II$\cdots$the model calculates all the possible expected shortages per lead time period, part III$\cdots$finally the model calculates all the possible total inventory cost over the simulation period. These total inventory costs are compared for searching the optimal inventory cost with the best ordering quantity and reorder point. An application example of the simulation program is given.

• 한국시스템다이내믹스연구
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• 제12권4호
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• pp.157-175
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• 2011

The purpose of this paper is to find out the effects of the gambler's fallacy bias on the supply chain. For this study, the simulation was based on a casual structure of the Beer Distribution Game from Sterman(2000)'s Business Dynamics and designed into 2 different models : the first model carries the exact same structure as the reference mentioned above and for the second model, the comparison model is used reflecting gambler's fallacy bias. Each model has 2 different demand patterns. The 4 cases of models was tested with 1,000 different random number seeds. The results for the simulation are following : In the aspect of the inventory and out of stock, the basic model resulted better than the comparison. However, in the bullwhip effect, the comparison model has less than the basic in terms of the level demand pattern. But there was no significant difference in the cycle demand.

• 한국통신학회논문지
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• 제36권7A호
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• pp.662-668
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• 2011

본 논문에서는 MANET (Mobile Ad hoc Network)를 위한 가장 대표적인 라우팅 프로토콜인 AODV (Ad hoc On-demand Distance Vector)와 OLSR (Optimized Link State Routing)의 성능을 노드 이동성 모델에 따라 분석한다. 노드의 이동성은 망 토폴로지의 변화를 일으키므로 라우팅 프로토콜의 성능에 많은 영향을 미친다. 따라서, MANET 라우팅 프로토콜의 성능을 정확하게 평가하기 위해서는 노드의 이동 패턴에 가장 적합한 이동성 모델을 사용하는 것이 무엇보다 중요하다. 본 논문에서는 기존 MANET 라우팅 프로토콜 성능분석에 가장 많이 사용되고 있는 random way point 모델과 최근에 실제 인간의 이동 패턴과 가창 유사하다고 발표된 Levy walk 모델을 기반으로 AODV와 OLSR의 성능을 ns-2 시뮬레이션을 통해 비교 분석한다.

• 한국수소및신에너지학회논문집
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• 제30권2호
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• pp.178-187
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• 2019

Due to the increasing demand of high rank coal, the use of low rank coal, which has economically advantage, is rising in various industries using carbonaceous solid fuels. In addition, the severe disaster of global warming caused by greenhouse gas emissions is becoming more serious. The Republic of Korea set a goal to reduce greenhouse gas emissions by supporting the use of biomass from the Paris International Climate Change Conference and the 8th Basic Plan for Electricity Supply and Demand. In line with these worldwide trends, this paper focuses on investigating the combustibility of high rank coal Carboone, low rank coal Adaro from Indonesia, Baganuur from Mongolia and, In biomass, wood pellet and herbaceous type Kenaf were simulated as kinetic reactivity model. The accuracy of the pore development model were compared with experimental result and analyzed using carbon conversion and tau with grain model, random pore model, and flexibility-enhanced random pore model. In row lank coal and biomass, FERPM is well-matched kinetic model than GM and RPM to using numerical simulations.

• 대한산업공학회지
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• 제29권2호
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• pp.135-144
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• 2003

Traffic performance in a microcellular system is much more affected by cell dwell time and channel holding time in each cell. Cell dwell time of a call is characterized by its mobility pattern, i.e., stochastic changes of moving speed and direction. Cell dwell time provides important information for other analyses on traffic performance such as channel holding time, handover rate, and the average number of handovers per call. In the next generation mobile communication system, the cell size is expected to be much smaller than that of current one to accommodate the increase of user demand and to achieve high bandwidth utilization. As the cell size gets small, traffic performance is much more affected by variable mobility of users, especially by that of pedestrians. In previous work, analytical models are based on simple probability models. They provide sufficient accuracy in a simple second-generation cellular system. However, the role of them is becoming invalid in a picocellular environment where there are rapid change of network traffic conditions and highly random mobility of pedestrians. Unlike in previous work, we propose an improved probability model evolved from so-called Random walk model in order to mathematically formulate variable mobility of pedestrians and analyze the traffic performance. With our model, we can figure out variable characteristics of pedestrian mobility with stochastic correlation. The above-mentioned traffic performance measures are analyzed using our model.

• 유통과학연구
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• 제13권6호
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• pp.11-15
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• 2015

Purpose - Robot path planning, a constrained optimization problem, has been an active research area with many methods developed to tackle it. This study proposes the use of a Rapidly-exploring Random Tree and Particle Swarm Optimizer algorithm for path planning. Research design, data, and methodology - The grid method is built to describe the working space of the mobile robot, then the Rapidly-exploring Random Tree algorithm is applied to obtain the global navigation path and the Particle Swarm Optimizer algorithm is adopted to obtain the best path. Results - Computer experiment results demonstrate that this novel algorithm can rapidly plan an optimal path in a cluttered environment. Successful obstacle avoidance is achieved, the model is robust, and performs reliably. The effectiveness and efficiency of the proposed algorithm is demonstrated through simulation studies. Conclusions - The findings could provide insights to the validity and practicability of the method. This method makes it is easy to build a model and meet real-time demand for mobile robot navigation with a simple algorithm, which results in a certain practical value for distribution environments.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권12호
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• pp.3152-3165
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• 2012

Wireless sensor networks (WSN) often employ asynchronous MAC scheduling, which allows each sensor node to wake up independently without synchronizing with its neighbor nodes. However, this asynchronous scheduling may not deal with collisions due to hidden terminals effectively. Although most of the existing asynchronous protocols exploit a random back-off technique to resolve collisions, the random back-off cannot secure a receiver from potentially repetitive collisions and may lead to a substantial increase in the packet latency. In this paper, we propose a new collision resolution algorithm called Transient Coordinator (TC) for asynchronous WSN MAC protocols. TC resolves a collision on demand by ordering senders' transmissions when a receiver detects a collision. To coordinate the transmission sequence both the receiver and the collided senders perform handshaking to collect the information and to derive a collision-free transmission sequence, which enables each sender to exclusively access the channel. According to the simulation results, our scheme can improve the average per-node throughput by up to 19.4% while it also reduces unnecessary energy consumption due to repetitive collisions by as much as 91.1% compared to the conventional asynchronous MAC protocols. This demonstrates that TC is more efficient in terms of performance, resource utilization, and energy compared to the random back-off scheme in dealing with collisions for asynchronous WSN MAC scheduling.

• 전기전자학회논문지
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• 제24권2호
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• pp.543-549
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• 2020

산업의 발전과 인터넷의 발전으로 보안의 중요성이 증가하면서 암호화에 필수적인 요소인 암호화 키의 생성에 사용되는 난수 발생기의 연구가 활발하게 이루어지고 있다. 외부 공격으로부터 안전한 고성능의 암호화 키를 생성하기 위해서는 예측하기 어려운 품질 좋은 난수 발생기가 필수적이다. 일반적으로 사용되는 의사 난수 발생기는 충분한 성능의 난수를 발생하기 위해서 많은 양의 하드웨어 리소스가 요구됨에도 외부에서 암호화 키를 외부에서 알아낼 가능성이 존재한다. 그러므로, 다양한 잡음을 통해 난수를 발생시켜 외부에서 예측 불가능하며 품질 좋은 진 난수 발생기에 대한 요구가 증가하고 있다. 본 논문은 진 난수 생성기술로 대표적인 준안정성 및 발진기를 통한 진 난수 발생기의 최신구조가 랜덤소스를 생성하는 방식을 조사 및 비교한다. 또한, NIST에서 제공하는 난수 검증용 도구인 SP 800-22 테스트를 통해 발진기 기반 진 난수 발생기 성능을 검증한 자료를 분석한다.