• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.1000-1005
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• 2010

국내에 대표적인 표면파 탐사법인 MASW, SASW, HWAW를 비교한 결과에 따르면, 세기법들의 결과가 매우 유사하게 도출되는 것을 확인할 수 있었으나, 각 현장별로 획득한 탐사심도의 차이가 존재하였다. 넓은 시험 측선을 필요로 하는 SASW 및 MASW 기법의 경우 현장 상황 및 조건에 따라 15m 정도의 얕은 심도의 물성만을 획득하였다. 표면파 기법은 토사층에서는 매우 신뢰성있는 결과를 도출하였으며 2차원 영상화를 통한 넓은 영역의 물성치를 빠르고 경제적으로 획득할 수 있는 장점이 있다. 현재 지반조사 시 소수의 시추자료를 이용하여 부지의 특성을 파악하기 때문에 시추공간 물성치 및 지반구조에 대해서 확실한 파악이 이뤄지지 않고 있기 때문에 표면파 기법은 토사층의 물성산출 뿐만 아니라 시추공탐사법을 보완하여 시추공간 물성변화를 파악하는 유용한 시험법이라고 판단된다.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.162-162
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• 2011

표면파 속도 측정은 근래 토목분야에서는 비파괴 지반조사기법으로 활용되고 있다. 최근에는 디지털 신호처리기술의 발달과 함께, 더욱 정확해진 자료분석 알고리즘을 통하여 표면파 탐사관련 기술이 향상되어 3차원의 공간연속적인 시험이 가능해졌다. 본 연구는 표면파의 분산 특성을 이용하여 콘크리트 구조물의 깊이별 강성평가를 하는 SASW(Spectral Analysis of Surface Waves)기법과 STFT(Short time Fourier Transform)과 HWT(Harmonic Wavelet Transform)를 이용한 주파수영역에서의 공진주파수를 통한 부재평가 기법인 IE(Impact Echo)기법을 이용하여 대상부재의 강도평가를 수행하기 위한 시제품 개발을 수행하였다. 시제품은 메인프레임과 2개의 센서로 이루어져 측정을 수행하며 측정장치와 DAQ장치 및 S/W로 구성되어 있다. 메인프레임의 진동특성영향을 제거하기 위하여 2개의 센서는 프레임과 띄움구조로 설계하였고 센싱하는 위치는 대상 재료의 밀착되어 계측할 수 있도록 설계하였다. 탄성파를 계측하여 대상 재료의 깊이별 측정된 표면파의 속도를 계측하며 개발된 시제품의 구조물별 적용성 평가를 위한 실험을 수행하였고 평균 표면파 속도를 통해 추정한 콘크리트 두께와 결함 및 강도 추정의 적용성을 평가하였다. 시제품을 이용해 시험콘크리트 표면파를 측정한 결과 SASW기법을 이용하여 깊이에 대한 위상속도 분포와 IE기법의 결과로 개발된 시제품의 합리적 적용성이 평가되었다. 그러나 재료의 강도추정에 있어서는 각각 알고리즘의 주파수분석 요소들에 의해 변동되는 경향을 보여 추후 많은 테스트를 통해 속도-강도 추정의 회귀곡선식을 S/W에 탑재시키고 다양한 방법으로 조합하는 알고리즘으로 신뢰성있는 강도추정을 위한 알고리즘을 개발하여야 한다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1509-1521
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• 2013

Social demand for the stability of structures lead to the development of the technology to accomplish it. The non-destructive seismic technique, which is able to assess structural integrity of infrastructures, belongs to this category. Seismic technique is focused on the measurement of seismic velocity propagating through the material, and has to utilize sensors coupled to material surface, which does not allow the testing to be performed on the fly. In this paper, a general vocal microphone, which works as a non-contact sensor, was adopted to facilitate seismic testing with mobility and efficiency improved. The target of using microphones was oriented toward quality assessment of compacted subgrade, stiffness evaluation and health monitoring of concrete structures. Experimental parametric study and field applications were performed to investigate reliability and efficiency of microphones. Finally, the optimal test configuration of microphones was suggested for resonance tests and surface-wave tests.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.207-218
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• 2013

One of the input parameters in the evaluation of seismic performance of rockfill dams is shear-wave velocity of rock debris and clay core. Reliable evaluation of shear-wave velocity by surface-wave methods requires overcoming the problems of rock-debris discontinuity, material inhomogeneity and sloping boundary. In this paper, for the shear-wave velocity investigation of rockfill dams, SBF (Short-Array Beamforming) technique was proposed using the principles of conventional beamforming technique and adopted to solve limitations of the conventional surface-wave techniques. SBF technique utilizes a 3- to 9-m long measurement array and a far-field source, which allowed the technique to eliminate problems of near-field effects and investigate local anomalies. This paper describes the procedure to investigate shear-wave velocity profile of rockfill dams by SBF technique and IRF (Impulse-response filtration) technique with accuracy and reliability. Validity of the proposed SBF technique was verified by comparisons with downhole tests and CapSASW (Common-Array-Profiling Spectral-Analysis-of-Surface-Waves) tests at a railroad embankment compacted with rock debris.

• Journal of the Korean Geotechnical Society
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• v.15 no.1
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• pp.41-52
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• 1999

In order to assess the quality and depth of ground densification by compaction, SPT and/or CPT are performed before and after compaction. Both methods are intrusive and one point tests, require a substantial time to evaluate a large area, and their results are quite dependent on the operation technique and soil type. In this paper, the quality and extent of ground densification by compaction was evaluated by using in situ SASW test and laboratory resonant column (RC) test results. SASW test was used to determine the shear wave velocity profiles before and after compaction, and RC test was adopted to determine the correlation between the normalized shear wave velocity and the density of the site, which is almost uniquely independent of confinement. Testing and data reduction procedures of both tests were discussed, and a simplified evaluation procedure of ground densification was proposed. Finally, the feasibility of the proposed method was verified by performing field study at Inchon International Airport Project. Field densities determined by the proposed method matched well with those determined by sand cone tests.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.2
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• pp.171-175
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• 2014

In this study, we suggest a method to measure the thickness of thin films nondestructively using the dispersion characteristics of a surface acoustic wave propagating along the thin film surface. To measure the thickness of thin films, we deposited thin films with different thicknesses on a Si (100) wafer substrate by controlling the deposit time using the E-beam evaporation method. The thickness of the thin films was measured using a scanning electron microscope. Subsequently, the surface wave velocity of the thin films with different thicknesses was measured using the V(z) curve method of scanning acoustic microscopy. The correlation between the measured thickness and surface acoustic wave velocity was verified. The wave velocity of the film decreased as the film thickness increased. Therefore, thin film thickness can be determined by measuring the dispersion characteristics of the surface acoustic wave velocity.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.415-420
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• 2009

This paper reports the results of a case study for the evaluation of surface damage by using acoustic nonlinearity of surface wave. In this study, the experimental system was constructed to measure the acoustic nonlinear parameter of surface wave in an Aluminum 6061 T6 specimen of which surface was damaged by the three point bending fatigue test, and magnitudes of nonlinear parameter measured before and after the fatigue test were compared. Especially, since the surface fatigue damage by the three point bending is concentrated at the central position of loading, the change in the nonlinear parameter around this position was monitored. Experimental results showed that the measured nonlinear parameter at the outside of this position after the fatigue test was almost same as the initial value before the fatigue test, since the fatigue damage at this position was little. However, clear increase in the nonlinear parameter was noticed after the fatigue test at the central position of specimen where the surface fatigue damage is expected to be concentrated.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.5
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• pp.1-9
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• 2009

In this study, the properties of shear wave velocity of coarse gravel in filldams are analyzed. Shear wave velocity is derived using the surface wave analysis method, which can be used nondestructively on the surface of filldams. These values are acquired through the tests for the rock zone of six filldams by SASW and HWAW methods. These analytical results are compared with results obtained through the frequently-used empirical method of Sawada and Takahashi.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2022.06a
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• pp.408-409
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• 2022

슬릿을 통한 표면파 통신 가능성을 시험 검증하고 이를 통한 선박 밀폐구역에서의 선박 IoT 무선통신 시스템 구현 방안을 고찰하기 위해 선박 밀폐구역에서의 표면파 통신 환경을 구현하였고, 슬릿의 크기, 모양, 재질 변화 조건에 따라 표면파 통신 가능 여부와 전송속도 변화를 확인하였다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2022.11a
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• pp.115-116
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• 2022

선박 밀폐구역에서의 적정 표면파 통신성능 구현방안을 도출하기 위해 가상의 선박 밀폐구역 환경을 구성하고 슬릿의 크기, 두께, 모양에 따른 조건 변화를 통한 표면파 기반 데이터 통신성능 변화를 확인하였다.