• 한국소음진동공학회논문집
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• 제27권1호
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• pp.20-27
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• 2017

This study investigated the problems in current practice of drive-train resonance analysis procedure and suggested solutions. The first problem is the resonance occurrence at the un-identified resonance point by the current practice, as for a solution the force spectrum analysis for each critical force transmitting component was suggested. The second one is the inaccurate estimation of potential resonance point in eigenfrequency analysis because of the non-consideration about the eigenfrequency dependency on rotor-speed, the fine linearization at each rotor speed point all over operational range was proposed to account for the affection. Lastly the insufficient time for resonance activation under run-up simulation condition was recognized as a problem in resonance load increasing analysis, as an alternative, steady state condition was suggested to estimate the maximum load increasing level.

• 한국위성정보통신학회논문지
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• 제3권1호
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• pp.15-21
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• 2008

OFDM (직교 주파수 분할 다중화) 신호의 높은 PAPR은 시스템의 송신단에서 전력증폭기의 비선형적 특성으로 인해 비선형 왜곡이 불가피하게 발생한다. 이 현상은 대역 내 왜곡과 대역 외 방사를 초래한다. 본 논문에서는 다항식 (polynomial) 모델에 기반한 사전왜곡(pre-distortion) 기법으로 이러한 문제를 보상하는 기법을 제안한다. 비선형 및 역비선형 다항식 모델 추정은 LSE(Least Square Error) 알고리즘으로 수행한다. 또한 시스템의 성능 향상을 위해 피크제거와 클리핑 결합기법을 이용해 OFDM 신호가 전력증폭기의 포화 영역 근처에서 동작함으로써 발생하는 왜곡된 신호의 진폭을 제거한다.

• Structural Engineering and Mechanics
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• 제53권3호
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• pp.607-623
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• 2015

The wind-induced dynamic response of large-span flexible structures includes two important components-background response and resonant response. However, it is difficult to separate the two components in time-domain. To solve the problem, a relational expression of wavelet packet coefficients and power spectrum is derived based on the principles of digital signal processing and the theories of wavelet packet analysis. Further, a new approach is proposed for separation of the background response from the resonant response. Then a numerical example of frequency detection is provided to test the accuracy and the spectral resolution of the proposed approach. In the engineering example, the approach is applied to compute the power spectra of the wind-induced response of a large-span roof structure, and the accuracy of spectral estimation for stochastic signals is verified. The numerical results indicate that the proposed approach is efficient and accurate with high spectral resolution, so it is applicable for power spectral computation of various response signals of structures induced by the wind. Moreover, the background and the resonant response time histories are separated successfully using the proposed approach, which is sufficiently proved by detailed verifications. Therefore, the proposed approach is a powerful tool for the verification of the existing frequency-domain formulations.

• Wind and Structures
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• 제18권5호
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• pp.567-598
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• 2014

In this paper, wind induced aerodynamic loads on a standard tall building have been evaluated through large-eddy simulation (LES) technique. The flow parameters of an open terrain were recorded from the downstream of an empty boundary layer wind tunnel (BLWT) and used to prescribe the transient inlet boundary of the LES simulations. Three different numerically generated inflow boundary conditions have been investigated to assess their suitability for LES. A high frequency pressure integration (HFPI) approach has been employed to obtain the wind load. A total of 280 pressure monitoring points have been systematically distributed on the surfaces of the LES model building. Similar BLWT experiments were also done to validate the numerical results. In addition, the effects of adjacent buildings were studied. Among the three wind field generation methods (synthetic, Simirnov's, and Lund's recycling method), LES with perturbation from the synthetic random flow approach showed better agreement with the BLWT data. In general, LES predicted peak wind loads comparable with the BLWT data, with a maximum difference of 15% and an average difference of 5%, for an isolated building case and however higher estimation errors were observed for cases where adjacent buildings were placed in the vicinity of the study building.

• Wind and Structures
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• 제30권1호
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• pp.85-97
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• 2020

The accurate estimation of the buffeting response of a bridge pylon is related to the quality of the bridge construction. To evaluate the influence of wind field characteristics on the buffeting response of a pylon in a trumpet-shaped mountain pass, this paper deduced a multimodal coupled buffeting frequency domain calculation method for a variable-section bridge tower under the twisted wind profile condition based on quasi-steady theory. Through the long-term measurement of the wind field of the trumpet-shaped mountain pass, the wind characteristics were studied systematically. The effects of the wind characteristics, wind yaw angles, mean wind speeds, and wind profiles on the buffeting response were discussed. The results show that the mean wind characteristics are affected by the terrain and that the wind profile is severely twisted. The optimal fit distribution of the monthly and annual maximum wind speeds is the log-logistic distribution, and the generalized extreme value I distribution may underestimate the return wind speed. The design wind characteristics will overestimate the buffeting response of the pylon. The buffeting response of the pylon is obviously affected by the wind yaw angle and mean wind speed. To accurately estimate the buffeting response of the pylon in an actual construction, it is necessary to consider the twisted effect of the wind profile.

• 한국음향학회지
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• 제20권7호
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• pp.3-12
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• 2001

본 연구에서는 소리에 대한 주관적 평가 인자 중 하나인 러프니스 계산 모델을 구현하였다. 구현된 러프니스 모델은 기존 모델의 고찰을 통해 계산 모델을 구체화하였으며, 주파수 영역으로부터 상호 상관 인자를 구하는 방법 등을 이용하여 계산 효율 및 정확도를 향상시켰다. 또한 기존의 주관적인 러프니스 평가치와의 비교를 통해 구현된 모델의 유용성을 확인하였다. 한편 기존 모델 및 구현된 러프니스 계산 모델을 통해 얻을 수 있는 러프니스 스펙트럼이 주파수 영역에서의 슬롭 가진(slope excitation)의 영향으로 인해 실제 변조되는 주파수 대역을 탐색하기 어려운 점을 발견하고, 구현된 모델의 상관 인자 계산 부분을 실제 변조가 발생하는 임계 대역에서만 러프니스 스펙트럼 값이 존재하도록 수정하여, 러프니스 기여성분의 탐색이 보다 용이해진 방법을 제안하였다.

• 한국음향학회지
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• 제16권3호
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• pp.18-25
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• 1997

본 연구에서는 성문파에 의한 음원 특성과 입술에서 음성이 방사될 때 발생하는 방사 특성을 효과적으로 제거하기 위하여 성문파의 음원 특성과 입술에서의 방사 특성은 근사적으로 음파의 에너지와 비례한다고 가정하고, 정규화된 단구간 에너지를 이용하는 에너지 의존 프리엠퍼시스 기법을 제안하며, 이를 이용하여 비안정 구간인 발음의 시작 부분과 천이구간에 대하여 음성 신호 분석 성능을 개선하고자 한다. 제안된 프리엠퍼시스 기법을 이용하여 5개 한국어 단모음의 스펙트럼 및 형성음 주파수 추출 등의 음성 신호 분석을 수행하고, 기존에 널리 이용되던 두 가지 프리엠퍼시스 기법과 성능을 비교하여 본 결과, 제안된 방법에 의한 스펙트럼의 형태가 기존의 방법에 비하여 상당히 개선되었고, 보다 더 정확한 형성음 주파수를 나타내며, 인접한 두 형성음 주파수가 증첩되는 현상이 제거되었음을 알 수 있었다.

• 한국정보과학회논문지:소프트웨어및응용
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• 제37권1호
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• pp.74-79
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• 2010

단백질의 아미노산 조성은 생물정보학의 여러 문제를 해결하기 위한 기초적인 정보로 자주 활용된다. 본 논문에서는 아미노산간의 진화적인 연관성을 정의한 BLOSUM 행렬에서 유도한 유사도 함수를 사용하여 아미노산 조성을 결정한다. 이러한 방법은 생물학적인 연관성이 있는 단백질 서열일수록 비슷한 아미노산 조성을 갖도록 한다. 또한 단백질의 구조와 기능에 중요한 역할을 하는 위치-특이적인 아미노산의 분포를 추정하기 위해서 레이더나 음성 신호의 스펙트럼 분석에 사용되는 개념인 시간-종속 분석, 시간 해상도와 주파수 해상도의 개념을 적용하였다. 제안한 방법을 단백질의 세포내 위치예측에 적용하여 기존의 아미노산 조성 추정 방법을 사용하는 것보다 크게 향상된 성능을 보임을 확인하였다.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1990년도 추계학술대회
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• pp.114-117
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• 1990

EEG signal is analyzed by two methods, analysis by visual inspection of EEG recording sheets and analysis by quantative method. Generally visual inspection method is used in the clinical field. But this method has its limitation because EEG signal is random signal. Therefore it is necessary to analyze EEG signals quantatively to obtain more precise and objective information of neural and brain. In this paper, power spectrum of EEG signal was estimated by AR(AutoRegressive) model in the frequency domain. This process is useful as a preprocessing stage for tomographic brain mapping (TBM) at each frequency, band. As a method for estimating power spectral density of EEG signals, periodogram method, autocorrelation method. covariance method, modified covariance method, and Burg method are tested in this paper.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1997년도 춘계학술대회
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• pp.275-278
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• 1997

Standard methods estimating the power spectral density(PSD) from an irregularly sampled cardiac event series require deriving a new evenly-spaced signal applicable to those methods. To avoid that requirement, in this study, the power spectrum of heart rate variability was estimated by Lomb-Scargle's algorithm, which is a means of obtaining PSD estimates directly from irregularly sampled timeseries observed in astronomy. To assess the performance of Lomb-Scargle algorithm in the power spectral analysis of heart rate variability, it was applied to various cardiac event series derived through integral pulse frequency modulation model(IPFM) simulation and from real ECG signals, and the resultant power spectra was compared with those obtained by a conventional method based on the FFT. In result, it is concluded that Lomb-Scargle's periodogram is very effective in the power spectral analysis of heart rate variability, especially in the presence of arrhythmia and/or dropouts of cardiac events.