• 한국지진공학회논문집
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• 제13권6호
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• pp.11-25
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• 2009

본 연구에서는 지진파의 푸리에 가속도스펙트럼(Fourier Acceleration Spectrum)에 기반한 계측진도 평가방법(Sokolov and Wald, 2002)을 국내에 적용하기 위해 국내 지진 MMI ${\leq}$ IV 범위에 대한 진도별 FAS 통계특성(평균과 표준편차) 모델을 기상청 발표 진도자료로 부터 도출된 65개 지진에 대한 등진도구역도(Isoseismal Maps)와 등진도구역도 상의 일관된 부지특성을 갖는 580개 수평성분 FAS 자료를 기반으로 경험적으로 도출하였다. 일관된 부지특성을 갖는 FAS는 특정 지진관측소에서 관측된 FAS를 국내 지반물성을 대표할 수 있는 D 등급관측소(연관희와 서정희, 2007)의 부지증폭특성을 갖도록 변환하여 도출하였다. 국내 지진의 MMI ${\leq}$ IV의 FAS 평균값은 로그영역에서 진도에 비례하는 선형성을 나타내었으며, 진도 IV에 대한 FAS 평균은 전 세계 모델과 유사한 특징을 보였다. 또한 진도 MMI ${\leq}$ IV의 FAS 표준편차는 진도 V 이상의 전 세계적인 모델의 표준편차 보다는 크게 평가되었으나, 진도 IV에 대한 전 세계적인 모델의 표준편차보다는 현저히 낮은 값을 나타내었다.

• 한국기계가공학회지
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• 제21권1호
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• pp.41-48
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• 2022

Vehicle vibration was introduced in the time and frequency domains using fast Fourier transform (FFT) analysis. In particular, a vibration mode analysis and characteristics of the frequency response function (FRF) in a sport utility vehicle (SUV) passing over a bump barrier at different speeds was performed systematically. The response behavior of the theoretical acceleration was obtained using a numerical method applied to the forced vibration model. The amplitude and frequency of the external force on the vehicle cause various power spectra with individual intrinsic system frequencies. In this regard, several modes of power spectra were acquired from the spectra and are discussed in this paper. The proposed technique can be used for monitoring the acceleration in a vehicle passing over a bump barrier. To acquire acceleration signals, various experimental runs were performed using the SUV. These acceleration signals were then used to acquire the FRF and to conduct mode analysis. The vehicle characteristics according to the vehicle condition were analyzed using FRF. In addition, the vehicle structural system and bump passing frequencies were discriminated based on their power spectra and other FRF spectra.

• 센서학회지
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• 제24권3호
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• pp.169-174
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• 2015

In this study, we developed a system to detect the various defects in the metallic objects using the phenomenon that the defects cause the changes of the natural resonant frequencies. Our system consists of a FFT Amp, an Auto Impact Hammer, a Hammer controller and a PC. Auto Impact Hammer creates vibrations in the metallic objects when tapped on the surface. These vibrational signals are converted to the voltage signals by an acceleration sensor attached to the metallic part surface. These analog voltage signals were fed into an ADC (analog-digital converter) and an FFT (fast fourier transform) conversion in the FFT Amp to obtain the digital data in the frequency domain. Labview graphical program was used to process the digital data from th FFT amp to display the spectrum. We compared those spectra with the standard spectrum to find the shifts in the resonant frequencies of the metal parts, and thus detecting the defects. We used PCB's acceleration sensor and TI's TMS320F28335 DSP (digital signal processor) to obtain the resolution of 2.93 Hz and to analyze the frequencies up to 44 kHz.

• 한국지진공학회논문집
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• 제2권2호
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• pp.35-44
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• 1998

최근의 중.소규모의 연이은 지진활동은 한반도도 지진에 대하여 안전지대는 아닌 것으로 생각되고 있으며, 1995년 일본의 Kobe 지진 대 참사는 국내에도 지진에 관한 많은 관심을 고조시키고 있다. 그러나, 국내의 구조물의 내진설계를 위한 사용되는 지진파에 대한 연구는 매우 미흡하며, 최근까지도 국내에서는 외국의 설계용 지진파를 그대로 사용하거나 설계응답스펙트럼을 이용하고 있는 실정이다. 본 논문에서는 국내지진파의 물리적 특성, 즉, 주기-빈도 분포, 확률밀도분포, Fourier Spectrum 및 응답스펙트럼을 구하여 비교.분석하였다. 또한 이상화된 인공지진파를 산출하여 이를 현재 교통량의 폭발적인 증가와 도로의 선형성을 이유로 사각을 가진 교량구조물이 많이 건설되고 있는바, 70$^{\circ}$사각슬래브교에 대한 지진해석을 수행하여 인공지진의 합리적 해석 횟수를 규명하였다.

• 한국지진공학회논문집
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• 제13권6호
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• pp.27-37
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• 2009

지진파의 푸리에 가속도스펙트럼(Fourier Acceleration Spectrum)에 기반한 계측진도 평가방법(Sokolov and Wald, 2002)의 국내 적용성을 평가하기 위해 관련 논문(연관희 등, 2009)에서 평가된 국내 지진의 진도 MMI ${leq}$ IV 범위에 대한 진도별 FAS 평균(m)과 표준편차(${\sigma}$) 모델을 이용하여, FAS 진도평가방법의 타당성을 평가하여 보았다. FAS 통계특성 모델 평가시 사용된 지진관측자 료의 FAS를 이용하고 본 연구에서 프로그램으로 구현된 FAS 진도평가기법을 적용할 경우 관측된 진도를 ${\sigma}$ = 0.74 MMI의 오차로 추정할 수 있었으며, 오차의 지진규모-거리 의존성을 추가로 보정할 경우 오차를 ${\sigma}$ = 0.61 MMI 까지도 저감할 수 있었다. 또한 본 방법을 MMI ${\leq}$ IV에 대한 국내 FAS 통계특성 모델과 MMI ${\geq}$ V에 대한 전 세계 FAS 통계특성 모델을 함께 이용하여, 진도 VI 이상인 국내 피해지진의 진도를 미소지진관측자료의 지진원특성을 이론적으로 증가시켜 도출된 스펙트럼을 이용하여 추정한 결과 최대 진도추정 오차 0.63 이내로 예측할 수 있었다.

• Geomechanics and Engineering
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• 제21권1호
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• pp.35-51
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• 2020

In this study, the seismic response analysis of embankment dams was investigated through numerical modeling. The seismic behavior of dams under main earthquake records and wavelet-based records were studied. Earthquake records were decomposed using de-noising method (DNM) and down-sampling method (DSM) up to five levels. In decomposition process, low and high frequencies of the main earthquake record were separated into two signals. Acceleration response, spectral acceleration, and Fourier amplitude spectrum at the crest of embankment dams under different decomposition levels were evaluated. The seismic behavior under main and decomposed earthquake records was compared. The results indicate an acceptable agreement between the seismic responses of embankment dams under wavelet-based decomposed records and main earthquake motions. Dynamic analyses show that the DNM-based decomposed earthquake records have a better performance compared to DSM-based records. DNM-based records up to level 4 and DSM-based records up to level 2 have a high accuracy in assessment of seismic behavior of embankment dams. The periods corresponding to the maximum values of acceleration spectra and the frequencies corresponding to the maximum values of Fourier amplitude spectra of embankment dam crest under main and decomposed records are in good agreement. The results demonstrate that the main earthquake records can be replaced by wavelet-based decomposed records in seismic analysis of embankment dams.

• 한국지진공학회논문집
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• 제20권7_spc호
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• pp.527-536
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• 2016

This paper investigates seismic damage potential of recent September 12 M5.8 Gyeongju earthquake from diverse earthquake engineering perspectives using the accelerograms recorded at three stations near the epicenter. In time domain, strong motion durations are evaluated based on the accelerograms and compared with statistical averages of the ground motions with similar magnitude, epicentral distance and soil conditions, while Fourier analysis using FFT is performed to identify damaging frequency contents contained in the earthquake. Effective peak ground accelerations are evaluated from the calculated response spectra and compared with apparent peak ground accelerations and the design spectrum in KBC 2016. All these results are used to consistently explain the reason why most of seismic damage in the earthquake was concentrated on low-rise stiff buildings but not quite significant. In order to comparatively appraise the damage potential, the constant ductility spectrum constructed from the Gyeongju earthquake is compared with that of the well-known 1940 El Centro earthquake. Deconvolution analysis by using one accelerogram speculated to be recorded at a stiff soil site is also performed to estimate the soil profile conforming to the response spectrum characteristics. Finally, response history analysis for 39- and 61-story tall buildings is performed as a case study to explain significant building vibration felt on the upper floors of some tall buildings in Busan area during the Gyeongju earthquake. Seismic design and retrofit implications of M5.8 Gyeongju earthquake are summarized for further research efforts and improvements of relevant practice.

• Structural Engineering and Mechanics
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• 제20권3호
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• pp.347-362
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• 2005

The input energy to a base-isolated (BI) building during an earthquake is considered and formulated in the frequency domain. The frequency-domain approach for input energy computation has some notable advantages over the conventional time-domain approach. Sensitivities of the input energy to the BI building are derived with respect to uncertain parameters in the base-isolation system. It is demonstrated that the input energy can be of a compact form via the frequency integration of the product between the input component (Fourier amplitude spectrum of acceleration) and the structural model component (so-called energy transfer function). With the help of this compact form, it is shown that the formulation of earthquake input energy in the frequency domain is essential for deriving the sensitivities of the input energy to the BI building with respect to uncertain parameters. The sensitivity expressions provide us with information on the most unfavorable combination of the uncertain parameters which leads to the maximum energy input.

• 한국지진공학회논문집
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• 제27권2호
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• pp.111-118
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• 2023

The 2017 Pohang earthquake afflicted more significant economic losses than the 2016 Gyeongju earthquake, even if these earthquakes had a similar moment magnitude. This phenomenon could be due to local site conditions that amplify ground motions. Local site effects could be estimated from methods using the horizontal-to-vertical spectral ratio, standard spectral ratio, and the generalized inversion technique. Since the generalized inversion method could estimate the site effect effectively, this study modeled the site effects in the Korean peninsula using the generalized inversion technique and the Fourier amplitude spectrum of ground motions. To validate the method, the site effects estimated for seismic stations were tested using recorded ground motions, and a ground motion prediction equation was developed without considering site effects.

• 융합신호처리학회논문지
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• 제13권4호
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• pp.166-172
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• 2012

일반적인 파고 측정 시스템은 스펙트럼 분석을 통하여 파고를 측정한다. 하지만 스펙트럼 분석은 fast fourier transform(FFT)을 이용하기 때문에 구조가 복잡하며, 또한 FFT를 사용하기 위해서는 먼저 데이터를 저장해야 하기 때문에 실시간 처리가 어렵다. 본 논문에서는 칼만필터와 관성센서를 사용하여 실시간으로 데이터를 처리하는 알고리즘을 개발하고 성능을 평가하였다. 칼만필터 이론은 비교적 복잡한 알고리즘이지만 FFT를 사용하는 것에 비하여 간단하며, 가속도 데이터를 적분하여 위치를 효율적으로 추정할 수 있다. 하지만 가속도 데이터를 적분할 때 오차의 누적이 발생되는데, 파고의 특징을 이용한 알고리즘을 개발하여 누적오차 문제를 해결하였다. 본 논문에서는 다양한 조건의 해파를 모델링하여 성능평가를 수행하였으며, 실험을 통하여 풍랑측정에 한해서 평균 오차율 3.5%로 우수한 측정 성능을 확인할 수 있었다.