• Earthquakes and Structures
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• 제16권1호
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• pp.109-118
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• 2019

This study, analyses the seismic response for a rigid massless square foundation resting on a viscoelastic soil layer limited by rigid bedrock. The foundation is subjected either to externally applied forces or to obliquely incident seismic body or surface harmonic seismic waves P, SV and SH. A 3-D frequency domain BEM formulation in conjunction with the thin layer method (TLM) is adapted here for the solution of elastodynamic problems and used for obtained the seismic response. The mathematical approach is based on the method of integral equations in the frequency domain using the formalism of Green's functions (Kausel and Peck 1982) for layered soil, the impedance functions are calculated by the compatibility condition. In this study, The key step is the characterization of the soil-foundation interaction with the input motion matrix. For each frequency the impedance matrix connects the applied forces to the resulting displacement, and the input motion matrix connects the displacement vector of the foundation to amplitudes of the free field motion. This approach has been applied to analyze the effect of soil-structure interaction on the seismic response of the foundation resting on a viscoelastic soil layer limited by rigid bedrock.

• Structural Engineering and Mechanics
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• 제58권5호
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• pp.887-903
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• 2016

This study analyses the seismic response of a three-dimensional (3-D) rigid massless square foundation resting or embedded in a viscoelastic soil limited by rigid bedrock. The foundation is subjected to harmonic oblique seismic waves P, SV, SH and R. The key step is the characterization of the soil-foundation interaction by computing the impedance matrix and the input motion matrix. A 3-D frequency boundary element method (BEM) in conjunction with the thin layer method (TLM) is adapted for the seismic analysis of the foundation. The dynamic response of the rigid foundation is solved from the wave equations by taking into account the soil-foundation interaction. The solution is formulated using the frequency BEM with the Green's function obtained from the TLM. This approach has been applied to analyze the effect of soilstructure interaction on the seismic response of the foundation as a function of the kind of incident waves, the angles of incident waves, the wave's frequencies and the embedding of foundation. The parametric results show that the non-vertical incident waves, the embedment of foundation, and the wave's frequencies have important impact on the dynamic response of rigid foundations.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2007년도 공동학술대회 논문집
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• pp.237-240
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• 2007

The evaluation of shear modulus (or shear wave velocity) profile of site is very important in the various fields of geotechnical engineering. To obtain shear wave velocity profile, various in-situ seismic methods using surface waves have been developed. These surface wave based in-situ seismic methods have their own strength and weakness. In this study, new seismic site characterization method using the harmonic wavelet analysis of wave (HWAW) was proposed to overcome some of weaknesses in the existing surface wave based seismic site characterization methods. HWAW method which is based on time-frequency analysis using harmonic wavelet transform have been developed to determine phase and group velocities of waves. In order to estimate the applicability of HWAW method, field tests were performed. Through field applications and comparison with other test results, the applicability of the proposed method were verified.

• 대한토목학회논문집
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• 제41권6호
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• pp.687-695
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• 2021

최근 국내에서 큰 규모의 지진이 발생하게 되면서 내진설계의 중요성이 크게 증가하였다. 내진설계기준에서는 중요구조물 또는 특수구조물에 대해서는 동적시간이력해석을 수행하도록 규정하고 있다. 이러한 중요 또는 특수 구조물의 내진해석 및 설계에 있어 합리적 설계 입력 지진파를 결정하는 것은 해석 및 설계의 신뢰도를 확보하는데 매우 중요한 요소이다. 내진설계기준에서 합리적 설계 지진파는 해당 지역(단층)의 특성을 반영하면서 동시에 내진 성능 수준별 설계응답스펙트럼을 만족해야 한다. 이러한 요구조건은 해당 지역(단층)에서 계측됐던 실 지진파를 설계응답스펙트럼에 상응하게 수정하여 부분적으로 만족시킬 수 있다. 본 연구에서는 하모닉웨이브릿변환(Harmonic Wavelet Transform)을 이용하여 실 계측 지진파를 기반으로 설계응답스펙트럼에 상응하게 지진파시간이력 수정·생성 하는 방법을 제안하였다. 제안한 기법의 적용성 검토를 위해 경주(2016년)와 포항(2017년)에서 발생했던 각 규모 5.8과 5.4의 지진에 제안된 기법을 적용하여 설계응답스펙트럼에 상응한 지진파시간이력을 수정·생성 하였다

• Geomechanics and Engineering
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• 제18권6호
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• pp.605-614
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• 2019

The present paper seeks to investigate propagation and reflection of waves at free surfaces of homogeneous, anisotropic and rotating micropolar fibre-reinforced medium with voids. It has been observed that, in particular when P-wave is incident on the free surface, there exist four coupled reflected plane waves traveling in the medium; quasi-longitudinal displacement (qLD) wave, quasi-transverse displacement (qTD) wave, quasi-transverse microrotational wave and a wave due to voids. Normal mode Analysis usually called harmonic solution method is adopted in concomitant with Snell's laws and appropriate boundary conditions in determination of solution to the micropolar fibre reinforced modelled problem. Amplitude ratios which correspond to reflected waves in vertical and horizontal components are presented analytically. Also, the Reflection Coefficients are presented using numerical simulated results in graphical form for a particular chosen material by the help of Mathematica software. We observed that the micropolar fibre-reinforced, voids and rotational parameters have various degrees of effects to the modulation, propagation and reflection of waves in the medium. The study would have impact to micropolar fibre-reinforecd rotational-acoustic machination fields and future works about behavior of seismic waves.

• Earthquakes and Structures
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• 제5권2호
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• pp.161-205
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• 2013

We study seismically induced, anti-plane strain wave motion in a non-homogeneous geological region containing tunnels. Two different scenarios are considered: (a) The first models two tunnels in a finite geological region embedded within a laterally inhomogeneous, layered geological profile containing a seismic source. For this case, labelled as the first boundary-value problem (BVP 1), an efficient hybrid technique comprising the finite difference method (FDM) and the boundary element method (BEM) is developed and applied. Since the later method is based on the frequency-dependent fundamental solution of elastodynamics, the hybrid technique is defined in the frequency domain. Then, an inverse fast Fourier transformation (FFT) is used to recover time histories; (b) The second models a finite region with two tunnels, is embedded in a homogeneous half-plane, and is subjected to incident, time-harmonic SH-waves. This case, labelled as the second boundary-value problem (BVP 2), considers complex soil properties such as anisotropy, continuous inhomogeneity and poroelasticity. The computational approach is now the BEM alone, since solution of the surrounding half plane by the FDM is unnecessary. In sum, the hybrid FDM-BEM technique is able to quantify dependence of the signals that develop at the free surface to the following key parameters: seismic source properties and heterogeneous structure of the wave path (the FDM component) and near-surface geological deposits containing discontinuities in the form of tunnels (the BEM component). Finally, the hybrid technique is used for evaluating the seismic wave field that develops within a key geological cross-section of the Metro construction project in Thessaloniki, Greece, which includes the important Roman-era historical monument of Rotunda dating from the 3rd century A.D.

• Earthquakes and Structures
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• 제22권4호
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• pp.373-386
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• 2022

The development of performance-based design methodologies requires a reasonable definition of a displacement-response spectrum. Although ground motions are known to be significantly affected by the resonant-like amplification behavior caused by multiple wave reflections within the surface soil, such a soil-resonance effect is seldom explicitly considered in current-displacement spectral models. In this study, an analytical approach is developed for the construction of displacement-response spectra by considering the soil-resonance effect. For this purpose, a simple and rational equation is proposed for the response spectral ratio at the site fundamental period (SRTg) to represent the soil-resonance effect based on wave multiple reflection theory. In addition, a bilinear model is adopted to construct the soil displacement-response spectra. The proposed model is verified by comparing its results with those obtained from actual observations and SHAKE analyses. The results show that the proposed model can lead to very good estimations of SRTg for harmonic incident seismic waves and lead to reasonable estimations of SRTg and soil displacement-response spectra for earthquakes with a relatively large magnitude, which are generally considered for seismic design, particularly in high-seismicity regions.

• 지구물리와물리탐사
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• 제2권4호
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• pp.180-183
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• 1999

도시화된 인구밀접지역과 인공잡음(예, 소음, 진동, 전력선 등)이 매우 심한 환경에서 양질의 탄성파 자료를 획득하기 위하여 기준점을 이용한 실험적 수준의 탄성파 측정시스템을 개발하였다. 소음과 전자파 잡음에 대한 상관측정(소음에 대한 상관측정의 센서는 마이크와 수진기 사용, 전자파에 대한 상관측정의 센서는 EM루프와 수진기 사용)을 각각 김포공항과 전라북도 김제시에서 수행하였으며, 또한 각 잡음의 측정 시계열에 대해 스펙트림 분석도 실시하였다. 소음에 의한 두 센서(마이크와 수진기)반응은 높은 상관성을 갖고 있으나, 두 센서 반응의 가장 큰 차이는 200Hz를 기준으로 저주파수 그리고 고주파수대역에서 일어나고 있다. 200Hz 이하의 주파수대역에서는 수진기를 통하여 측정한 잡음의 스펙트럴 에너지가 상대적으로 크고(예, 10Hz와 100Hz에서 각각 20dB 이상 큼) 200Hz 이상의 상대적인 고주파수에서는 마이크를 통하여 측정된 잡음의 수준이 높다(예, 500Hz에서 30dB 이상). 전체적으로 수진기를 통하여 측정된 잡음의 스팩트럴 파워는 주로 600Hz 이하에 집중되어 있는 반면에 마이크에 측정된 잡음의 파워는 주로 200Hz이상에서 분포하고 있다. 전력선 잡음을 가정하여 교류직류 인버터에서 발생한 전자파잡음에 대한 EM루프와 수진기를 통하여 측정한 전자파잡음은 각 센서에서 그 파형이 매우 일정하며, 또한 서로 간에 높은 상관성을 보였다. EM루프에 측정된 전자파잡음의 경우 60Hz에 대한 기수 조화주파수가 우수 조화주파수에 비하여 그 스펙트럴 에너지가 매우 크지만, 수진기의 경우는 그 차이가 거의 없었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.7-13
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• 2008

To obtain a shear-wave velocity profile in geotechnical practice, various seismic investigation methods which have their own strength and weakness are being frequently used. Generally, geotechnical site have lateral variation of the properties, so it is needed to determine 2-dimensional shear wave velocity imaging of the site. In this study, harmonic wavelet analysis of wave (HWAW) method is applied to determination of 2-D $V_s$ imaging. HWAW method which is based on time-frequency analysis using harmonic wavelet transform have been developed to determine phase and group velocities of waves. HWAW method uses the signal portion of the maximum local signal/noise ratio to evaluate the phase velocity to minimize the effects of noise. HWAW method determine detailed local $V_s$ profile because one experimental setup which consists of one pair of receivers with spacing of 1~3m is used to determine the dispersion curve of the whole depth. So, 2-D Vs imaging with relatively high resolution can be determined through a series of HWAW test. In order to estimate the applicability of HWAW method, field tests were performed in 4 sites. Through field applications and comparison with other test results, the good accuracy and applicability of the proposed method were verified.

• 비파괴검사학회지
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• 제27권2호
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• pp.105-114
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• 2007

수평적 변화가 심한 국내 지반에서는 지반의 2차원 전단파 속도를 비관입적인 방법에 의해 도출하는 것이 중요하며 많은 연구가 수행되어 왔다. 본 연구에서는 속도 도출에 있어 기존의 표면파 탐사법의 단점을 극복한 HWAW(harmonic wavelet analysis of wave) 기법을 적용성을 평가하였다. 이 기법은 하모닉 웨이블릿 변환을 이용하여 파의 그룹(위상)속도를 결정하는 기법으로, 2개의 감지기로 구성된 단일한 실험구성을 사용한다. 주변 잡음의 영향을 효과적으로 제거하기 위해 신호 대 잡음비의 최대 부분을 이용하며 단일 어레이 역산을 사용한다. 또한 짧은 감지기 간격을 이용하여 지반의 국부적인 특성을 파악할 수 있다. 따라서 기존 방법에 비해 간단하고 빠른 현장 시험을 수행하며 신뢰성 있는 지반의 2차원 영상화를 도출 할 수 있다. 제안된 기법으로 구한 2차원 영상화의 적용성을 확인하기 위하여 2곳의 부지에서 시험을 수행하였고, 시추결과 및 다른 기법들의 비교 분석을 통해 제안된 기법의 적용성을 검증하였다.