• 한국통신학회논문지
• /
• 제33권2A호
• /
• pp.191-197
• /
• 2008

시변 무선채널에서 버스트한 패킷을 효율적으로 전송하기 위해서는 다중사용자 다이버시티 이득을 극대화할 수 있는 opportunistic 스케줄링 기법이 중요한 기술적 요소가 되고 있다. 본 논문에서는 무선 LAN 네트워크에 적용 가능한 분산화된 opportunistic 스케줄링기법을 제안하였다. Opportunistic 스케줄링방식의 하나인 비례공정 알고리즘은 중앙집중형 네트워크에 적용되었으나 본 논문에서는 확률적 방식을 이용하여 분산화된 방식의 비례공정 스케줄링 (DPFS: Distributed Proportional Fair Scheduling) 방식과 매체 접근제어 방식을 설계하였다. 제안한 DPFS방식에서는 각각의 수신기들은 채널상태를 파악한 후 독립적으로 자신의 우선순위를 확률적 방법으로 계산하기 때문에 모든 수신기의 채널 정보를 수집하는데 필요한 오버헤드를 크게 줄일 수 있다. 성능분석을 위하여 시뮬레이션을 수행하였으며 제안된 스케줄링 방식이 기존의 분산 스케줄링방식에 비하여 전송률 성능에서 우수함을 보이고 있으며 관련 파라미터를 조절함으로써 공평성과 전송률성능에 대한 제어가 가능함을 보이고 있다.

• Structural Engineering and Mechanics
• /
• 제31권6호
• /
• pp.737-749
• /
• 2009

The problem of estimating the dynamic response of a distributed parameter system excited by a moving vehicle with random initial velocity and random vehicle body mass is investigated. By adopting the Galerkin's method and modal analysis, a set of approximate governing equations of motion possessing time-dependent uncertain coefficients and forcing function is obtained, and then the dynamic response of the coupled system can be calculated in deterministic sense. The statistical characteristics of the responses of the system are computed by using improved perturbation approach with respect to mean value. This method is simple and useful to gather the stochastic structural response due to the vehicle-passenger-bridge interaction. Furthermore, some of the statistical numerical results calculated from the perturbation technique are checked by Monte Carlo simulation.

• 한국항해항만학회지
• /
• 제27권5호
• /
• pp.487-492
• /
• 2003

이 논문에서는 해양사고 예보 시스템(K-MACFOS) 개발의 주요부분 중 하나인 해양사고 예측 모델 구현에 관해서 기술했다. 셀분할 선형 파라미터 모델(CD-LIP)을 제안하여 그 유효성을 Baltic 모델과 수정 LIP 모델과 비교하면서 검토하였다. 회귀 분산분석기법에 의한 평가결과, CD-LIP 모델이 연구대상 해역의 해양사고 수량화 D/B에 최적 성능을 나타냈다.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1989년도 한국자동제어학술회의논문집; Seoul, Korea; 27-28 Oct. 1989
• /
• pp.255-259
• /
• 1989

A suboptimal output feedback controller is designed and applied to a flexible rotor bearing system in order to control the unstable or lilghtly damped vibrations. The reduced order model is the truncated modal equation of the distributed parameter system obtained through the singular perturbation. The instability problem arising from the spillover effects caused by the uncontrolled high frequency modes is prevented through the constrained optimization by incorporating the spillover term into the performance index. The efficiency of the proposed method is demonstrated experimentally with a flexible rotor by using a magnetic bearing.

• 한국항해항만학회:학술대회논문집
• /
• 한국항해항만학회 2003년도 춘계공동학술대회논문집
• /
• pp.60-65
• /
• 2003

이 논문에서는 해양사고 예보 시스템 (MCFS)의 주요 부분 중 하나인 해양사고 예측 모델 개발에 관해서 기술했다. 셀분할 선형 파라미터 모델(CD-LIP)을 개발하여 Baltic 모델과 희귀 분산분석기법으로 비교하였다. 그 결과, CD-LIP 모델이 Baltic 모델과 비교하여 잔차가 작았으며, 연구대상지역의 해양사고 수량화 D/B에 최적 성능을 나타냈다.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2001년도 추계학술대회논문집 II
• /
• pp.838-843
• /
• 2001

Internal damping plays an important role in some rotor dynamic systems with the use of various materials for shafts, for example, composite material. However, although the effects of internal damping have been investigated for a couple of decades, there are several different internal damping models in use, none of which are accepted as the most reliable model. The purpose of this paper is to compare the results of dynamic analysis of rotor systems with several different internal damping models. The exact dynamic element method is used to formulate and analyze the problem. The simulation results provided in this paper may be useful for the dynamic analysis of high rotor systems subject to significant internal damping.

• KIEE International Transaction on Systems and Control
• /
• 제2D권2호
• /
• pp.78-91
• /
• 2002

In the thermal power plant, there are six manipulated variables: main steam flow, feedwater flow, fuel flow, air flow, spray flow, and gas recirculation flow. There are five controlled variables: generator output, main steam pressure, main steam temperature, exhaust gas density, and reheater steam temperature. Therefore, the thermal power plant control system is a multinput and output system. In the control system, the main steam temperature is typically regulated by the fuel flow rate and the spray flow rate, and the reheater steam temperature is regulated by the gas recirculation flow rate. However, strict control of the steam temperature must be maintained to avoid thermal stress. Maintaining the steam temperature can be difficult due to heating value variation to the fuel source, time delay changes in the main steam temperature versus changes in fuel flow rate, difficulty of control of the main steam temperature control and the reheater steam temperature control system owing to the dynamic response characteristics of changes in steam temperature and the reheater steam temperature, and the fluctuation of inner fluid water and steam flow rates during the load-following operation. Up to the present time, the Proportional-Integral-Derivative Controller has been used to operate this system. However, it is very difficult to achieve an optimal PID gain with no experience, since the gain of the PID controller has to be manually tuned by trial and error. This paper focuses on the characteristic comparison of the PID controller and the modified 2-DOF PID Controller (Two-Degrees-Freedom Proportional-Integral-Derivative) on the DCS (Distributed Control System). The method is to design an optimal controller that can be operated on the thermal generating plant in Seoul, Korea. The modified 2-DOF PID controller is designed to enable parameters to fit into the thermal plant during disturbances. To attain an optimal control method, transfer function and operating data from start-up, running, and stop procedures of the thermal plant have been acquired. Through this research, the stable range of a 2-DOF parameter for only this system could be found for the start-up procedure and this parameter could be used for the tuning problem. Also, this paper addressed whether an intelligent tuning method based on immune network algorithms can be used effectively in tuning these controllers.

• 조명전기설비학회논문지
• /
• 제24권4호
• /
• pp.73-80
• /
• 2010

접지임피던스는 접지전극의 크기를 증가시켜도 낮아지지 않고, 토양의 특성과 주파수 조건에 따라 접지 임피던스가 최소값을 보이는 접지전극의 길이가 존재하며, 이 접지전극의 길이를 각 토양 특성과 주파수에 따른 임계길이라 한다. 본 논문에서는 대지구조의 조건을 고려하는 새로운 분포정수회로모델을 제안하였으며, 새로이 제안된 해석모델을 적용하여 MATLAB프로그램으로 수직접지전극의 임계길이와 접지임피던스를 해석하였다. 그 결과, 수직접지전극의 임계길이와 접지임피던스의 주파수의존성에 대한 대지구조의 영향이 크며, 접지시스템의 최적 설계를 위해서는 대지구조를 고려하는 것이 바람직한 것으로 밝혀졌다.

• 대한산업공학회지
• /
• 제33권1호
• /
• pp.70-75
• /
• 2007

This paper discusses condition based preventive replacement for deteriorating systems. The system continuouslydeteriorates in time and fails at any deterioration level which is always monitored, It is replaced at failure or atsome deteriorated level preventively before failure. The deterioration process is represented by a Weibulldistribution with a time-linear scale parameter. The cost rate function is formed considering replacement costand opportunity loss cost and deterioration dependent failure distribution, If the system has an increasingdeterioration dependent failure rate, the optimal deterioration level for preventive replacement can be determinedfrom minimizing the cost rate. An illustrative example is given for a Weibull deterioration dependent failuredistribution.

• 한국생산제조학회지
• /
• 제8권2호
• /
• pp.27-34
• /
• 1999

The growth-strain method was used for shape optimization, which carries out the optimization by distributing uniformly the distributed parameter such as von Mises stress and shear strain energy density. Shape optimization is carried out by iteration of stress analysis and growth strain analysis. In this study, the effect of growth ratio in the method was investigated and then the range of the adequate value of the growth ratio was determined. Also the growth-strain method was improved by applying the linear PID control theory in order to control volume required by a designer. Finally, an automatic shape optimization system was built up by the improved growth-strain method with a commercial software using finite element method. The effectiveness and practicability of the developed shape optimization system was verified by some examples.