• 한국항행학회논문지
• /
• 제9권1호
• /
• pp.41-47
• /
• 2005

본 논문에서는 유럽의 DVB-H (Digital Video Broadcasting-Handheld) 시스템을 위한 여러 채널 추정 기법의 성능을 분석하였다. 채널 보상 기법으로는 주파수 영역에서 사용되는 선형 보간법, 이차 보간법, cubic-spline 보간법, time-domain 보간법을 사용하였고, 레일리와 라이시안 페이딩 채널 환경에서 시뮬레이션을 통해 MSE (Mean Square Error)와 BER (Bit Error Rate) 성능과 연산의 복잡도를 비교, 분석하였다. 시뮬레이션 결과 높은 $E_b/N_0$ 환경에서 가장 우수한 채널 추정 방식은 cubic spline 보간법임을 확인할 수 있었다.

• Journal of Electrical Engineering and Technology
• /
• 제12권2호
• /
• pp.586-593
• /
• 2017

Modeling busbar distribution system as a transmission line is an important subject of power line communication in the smart grid concept. This requires extraction of busbar RLGC parameters, accurately. In this study, a comparison is made between conventional and modified method for the aspect of optimum RLGC parameters extraction in the 1 MHz to 50 MHz frequency band. The usefulness of these methods is shown both in time and frequency-domain analysis. The frequency-domain analyzes show that the inherent power of modified method can eliminate the errors especially due to the discontinuities arise in conventional method. This makes the modeling approach of modified method more advantageous for the busbars due to its robustness against disturbances in the S-parameters measurements which cannot be eliminated with the calibration procedure. On the other hand, time-domain simulations show that the transmission line representation of the modified method is closer to physical reality by handling causality issues.

• 전기학회논문지P
• /
• 제58권2호
• /
• pp.136-141
• /
• 2009

An AC generator is an important components in producing a electric power and so it requires highly reliable protection relays to minimize the possibility of demage occurring under fault conditions. Conventionally, a DFT based RDR has been used for protecting the generator stator winding. However, when DFTs based on Fourier analysis are used, it has been pointed out that defects can occur during the process of transforming a time domain signal into a frequency domain one which can lead to loss of time domain information. This paper proposes the internal fault detection and fault type discrimination for the stator winding by applying the detailed coefficients by Daubechies Wavelet Transform to overcome the defects in the DFT process. For the case studies reported in the paper, a model system was established for the simulations utilizing the ATP, and this verified the effectiveness of the proposed technique through various off-line tests carried out on the collected data. The propose method is shown to be able to rapidly identify internal fault and did not operate a miss-operation for all the external fault tested.

• 한국해양공학회지
• /
• 제30권5호
• /
• pp.341-348
• /
• 2016

The fatigue damage caused by wide band loadings has generally been predicted using fatigue damage models in the frequency domain rather than a rain-flow counting method in the time domain because of its computation cost. This study showed that these fatigue damage models can be simplified in the form of normalized fatigue damage as a function of the S-N curve slope and bandwidth parameters. Based on numerical simulations of various wide band spectra, it was found that fatigue damage models in the form of normalized fatigue damage with one S-N curve slope and two bandwidth parameters( α₁ , α₂ ) provided less reasonable fatigue damage. Therefore, an additional bandwidth parameter needs to be considered based on a sensitivity study using various neural networks, which proved that α_1-5 would be the dominant factor of a fatigue damage model as an additional bandwidth parameter.

• 한국항해항만학회:학술대회논문집
• /
• 한국항해항만학회 2013년도 춘계학술대회
• /
• pp.299-300
• /
• 2013

본 연구에서는 선박의 정박과정 중 거동을 분석하기 위하여 저속과 고속의 전진속도에 쓰이는 서로 다른 수학 모델을 비교하며 시간변위 시뮬레이션이 수행되었고 그 결과가 제시되었다. 시뮬레이션 프로그램 개발의 첫 번째 단계로 선박의 속도와 타각 제어를 위하여 일반적인 PD (Proportional Derivative) 제어기가 사용되었으며 시뮬레이션 모델로서 탱커가 사용되었다. 본 연구는 선박의 정박과정을 위한 효과적인 시간변위 시뮬레이션 프로그램을 개발하기 위하여 정박 시뮬레이션에서의 비교 분석 결과를 제시한다.

• Wind and Structures
• /
• 제9권4호
• /
• pp.255-270
• /
• 2006

Several analytical procedures available in literature, for the evaluation of wind induced fatigue damage of structures, either assume the wide band random stress variations as narrow band random process or use correction factors along with narrow band assumption. This paper compares the correction factors obtained using the Rainflow Cycle (RFC) counting of the measured stress time histories on a lamp mast and a lattice tower, with those evaluated using different frequency domain methods available in literature. A Bi-modal spectral method has been formulated by idealising the single spectral moment method into two modes of background and resonant components, as considered in the gust response factor, for the evaluation of fatigue of slender structures subjected to "along-wind vibrations". A closed form approximation for the effective frequency of the background component has been developed. The simplicity and the accuracy of the new method have been illustrated through a case study by simulating stress time histories at the base of an urban light pole for different mean wind speeds. The correction factors obtained by the Bi-modal spectral method have been compared with those obtained from the simulated stress time histories using RFC counting method. The developed Bi-modal method is observed to be a simple and easy to use alternative to detailed time and frequency domain fatigue analyses without considerable computational and experimental efforts.

• 한국공작기계학회논문집
• /
• 제13권6호
• /
• pp.94-101
• /
• 2004

The purpose of this raper is to assess the benefits of frequency domain fatigue analysis and compare it with more conventional time domain techniques. The multi-body dynamic analysis, FE analysis and fatigue life prediction technique are applied for the frequency domain fatigue analysis. To obtain the dynamic load history used in the frequency domain fatigue analysis, the computer simulations running over typical road Profiles are carried out by utilizing vehicle dynamic model. The fatigue life estimation for the rear suspension system of small-sized passenger car is performed by using resonance durability analysis technique, and the estimation results are compared with the conventional quasi-static durability analysis results. For the pothole simulation, the percent changes, of the fatigue life between the two durability analysis techniques don't exceed 10%. But for the Belgian road simulation because of the resonance effect, the fatigue life using the resonance durability analysis technique are much smaller estimated than the quasi-static durability analysis results.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2000년도 춘계학술대회논문집
• /
• pp.1292-1297
• /
• 2000

외부로부터 불규칙 교란을 받는 동력학계에 대해 '허-확률 제어기법'을 이용하여 설계된 제어기의 성능을 수치모사를 통하여 검증하였다. 압전소자를 알루미늄 보에 부착하여 다중입출력의 복합재료보로 만들고, 기반에 불규칙한 외부교란을 받는계에 대한 모델링을 수행하였으며, Ito의 확률미분방정식과 F-P-K방정식을 이용하여 동적 모멘트 방정식을 유도하여 시스템의 확률영역에서의 특성을 알아보았다. 본 연구에서 제어기의 목표는 외부교란의 입력에 의해 발생하는 시스템의 모멘트 응답크기를 줄이는 방향으로 전개하였고, 확률영역에서의 MIMO PI제어기('허-확률 MIMO PI 제어기')를 설계하여 시간영역에서의 응답형태를 관찰하였다.

• 한국음향학회지
• /
• 제25권6호
• /
• pp.298-304
• /
• 2006

본 논문에서는 천해 음파전달 모의에 적합한 음선기반 광대역 주파수 신호 모의기법을 제안하였다. 본 기법은 깊이에 따라 음속이 선형적으로 변하는 환경 및 층매질에서의 음선추적을 기반으로 평면파 및 구형파의 반사 및 투과, 굴절 그리고 감쇠 등을 고려해 각 고유음선의 위상 및 크기로부터 신호를 모의한다. 본 기법의 가장 큰 특징은 주파수영역을 거치지 않고 시간영역에서 이산화된 신호를 직접 모의함으로써 주파수 대역에 관계없이 계산시간을 단축할 수 있다는 것이다. 끝으로 제안된 기법을 네 가지의 테스트환경에 적용하여 기존의 검증된 모텔 (ORCA, Ram) 의 결과와 비교하여 그 효용성을 검증하였다

• 전자공학회논문지B
• /
• 제31B권3호
• /
• pp.141-149
• /
• 1994

In this paper, we could find optimum quantum sequence(OQS) to minimize the output ripple voltage of the quantum series resonant converter(QSRC). This sequence control is so general that it is irrelevant to the voltage gain so far as it is operating in the continuous conduction mode(CCM). Further more the dynamic range of QSRC is much extended by the optimum quantum sequence control(OQSC). Througuout the time-domain analysis, the solution of steady state and the boundary condition between continuous and discontinuous mode is QSRC is obtained. This feature is verified by simulations and experiments with good agreements.