• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.5
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• pp.1-6
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• 2008

Most of seismic design code provisions provide the design response spectra for defining design earthquake ground motions. The design spectra in the code provisions generally come under the 5% of critical damping value, which corresponds to the responses of common structure under the design earthquake. Energy dissipation devices and seismic isolation systems became more popular and the design response spectra at higher damping levels are required. Damping coefficients can be effectively used in conversion of 5%-damped design spectra into other damping levels. These coefficients in the current seismic design code provisions are based on the strong ground motion records. Since the weak and moderate earthquake data have different characteristics from those of strong earthquake data, the application of these coefficients should be investigated in the weak and moderate earthquakes zones. In this study, damping coefficients based on the weak and moderate ground motions were developed and compared to those of current seismic design code provisions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.3
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• pp.115-122
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• 2002

구조감쇠가 복합적층판의 초음속 패널 플러터에 미치는 영향을 연구하기 위해 에너지법을 활용하여 지배방정식을 유도하였다. 구조 모델링은 일반적인 고전 적층판 이론을 적용하고 이의 해석은 진동 모우드를 가정하는 Rayleigh-Ritz법을 이용하였다. 비정상 공기력은 피스톤 이론(piston theory)을 적용하였다. 구조감쇠가 패널의 플러터에 미치는 일반적인 영향을 고찰하기 위해 등방성 평판의 구조감쇠의 크기에 따른 임계동압을 계산하였으며 이로부터 구조감쇠가 플러터 안정성을 감소시킬 수 있음을 확인하였다. 또한 복합적층판의 적층각에 따른 임계동압을 계산하여 패널 플러터와 구조감쇠와의 관계를 파악하였다. 구조감쇠는 낮은 공력감쇠에서는 플러터 안정성에 중요한 역할을 하지만 높은 공력감쇠에서는 거의 영향을 미치지 않았다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.926-931
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• 2003

본 연구는 비압축성 유동에 노출되어 있는 2-D wing-flap 시스템의 공탄성 응답의 능동제어를 다루고 있다. 본 연구 논문의 목표는 LQG 제어법칙을 수행함으로써 임계 비행속도하에서 플러터의 비안정성을 억제하고 돌풍이나 blast load에 의한 임계 공탄성 응답의 성능을 향상시키는 것과 동적응답을 감쇠하는 수행능력들을 증명하는데 있다.

• Journal of the Korean Society for Railway
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• v.16 no.1
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• pp.1-6
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• 2013

In this study, the natural frequency and damping ratio of a four-harness satin woven glass/epoxy composite material are evaluated by means of modal tests and a finite element analysis. To achieve this goal, glass/epoxy beam specimens with different lengths and thicknesses were manufactured via autoclave curing. In the test, the maximum damping ratio was found to occur at the lowest test frequency. As the test frequency increased, the damping ratio decreased exponentially to a critical value. After that value, the damping ratio increased gradually to the maximum test frequency.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.11A
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• pp.1642-1651
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• 2000

위성통신시스템에서의 10GHz이상의 Ku 또는 Ka 대역은 수십 dB의 크기를 갖는 강우에 의한 감쇠 현상이 심각하여 이러한 감쇠는 위성 링크의 심각한 성능 정하를 가져온다. 본 논문은 위성통신 링크 상에서의 강우 감쇠 보상을 위한 알고리즘을 제시하고, Ku 대역의 강우 감쇠 데이터를 사용한 시뮬레이션을 통하여 그 성능을 비교 분석하였다. 예측 기법 측면에서, 적응형 알고리즘을 적용한 기법과 신호 레벨 변화량에 근거한 예측 기법은 거의 동일한 예측 오차를 보였고, 따라서, 급속한 신호레벨 변화에 적응성을 요하지 않은 강우 감쇠 예측의 경우, 알고리즘 측면에서 비교적 간단한 예측 기법으로도 충분한 성능을 얻을 수 있음을 확인하였다. 또한, 제시된 전송 방식 결정 알고리즘은 기존의 임계값 기반 알고리즘에 비해 품질 저하율이 0.6%에서 0.01% 이하로 감소하였고, 거의 동일한 전송 효율을 가지면서 약 5배의 적은 전송 방식 전환을 요구한다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.3
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• pp.329-337
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• 2001

In this study a compound planetary gear combined with three planet gears, which is used for continuously variable transmission, is modeled that consider variable nonlinear gear mesh stiffness and damping when gear rotates, and thus equation of motion of compound planetary gear is derived. Locus of sun gear center causing noise and vibration is being determined from performing derived state equation with numerical analysis in fourth order Runge-Kutta method.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.7
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• pp.688-694
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• 2008

A rotordynamic analysis is performed for a high thrust class liquid rocket engine turbopump considering the dynamic characteristics of ball bearings and pump noncontact seals. Complex eigenvalue problems are solved to predict the rotating natural frequencies and damping ratios as a function of rotating speeds. Synchronous rotor mass unbalance response and time transient response analyses are also performed to figure out the rotor critical speed and the onset speed of instability. From the numerical analysis, it is found that the rear bearing stiffness is most important parameter for the critical speed and instability because the 1st mode is turbine side shaft bending mode. The pump seal effect on the critical speed is enlarged as the rear bearing stiffness decreases and the front bearing stiffness increases.

• Journal of the Korean Society for Railway
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• v.16 no.4
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• pp.305-310
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• 2013

In general, it is difficult to measure dynamic responses of a bridge with stepwise increasing speed of a train during commercial service on a high speed railroad. However, before opening the 2nd stage of the Gyeongbu high speed railroad, there was an opportunity for field tests and measurements of the bridge with stepwise increasing speed(from 170km/ h to 315km/h). The measured responses were compared with the results of a developed bridge/train interaction analysis. Although good agreement was found throughout almost the entire range of speeds, relatively large differences were found in the vicinity of the critical speed at which resonance behavior of the bridge occurs. To investigate the cause of this, reanalyses are performed with re-estimated damping ratios from field tests.

• The Journal of the Acoustical Society of Korea
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• v.13 no.2
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• pp.76-85
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• 1994

A speech enhancement algorithm which attenuates nonstationary colored noise is presented In this paper. The algorithm consists of a stationary Kalman filter and the simple speech/nonspeech detector. While the conventional enhancement systems are focused on a stationary and/or white background noise, this study Is focused on the mort realistic nonstationary and nonwhite noise. An AR model-based vector Kalman filter is used as a noise suppression system and a short-time energy threshold logic is used as a speech/nonspeech classifier. For Kalman filtering. noise coefficients are estimated in the nonspeech frame, and speech coefficients are estimated by applying the EM iteration algorithm. Simulation results using the car noise are presented based on the signal-to-noise ratio and informal listening tests. According to the experimental results, background noises in the nonspeech frames are eliminated almost completely, while some distortions are noticed in the speech frames. The distortion becomes severer as the SNR is reduced to 0dB and -5dB. Intelligibility, however, is not degraded significantly.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.4
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• pp.27-34
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• 2005

The paper discussed on the stability of cantilevered pipe conveying fluid subjected to distributed follower force. Governing equations of motion are derived by extended Hamilton's principle, and the numerical scheme using finite element method is applied to obtain the discretized equations. The critical flow velocity as a function of the distributed follower force for the various mass ratio is determined. The flutter configurations of the pipes at the critical flow velocities are drawn graphically at every twelfth period to define the order of quasi-mode of flutter configuration The critical mass ratios, at which the transference of the eigenvalue branches related to flutter take place, are definitely determined. Also, the effect of damping on the stability of the system is considered.