• Journal of the Korean Geotechnical Society
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• v.17 no.5
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• pp.97-105
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• 2001

현장타설말뚝의 건전도 평가에서 충격반향, 충격응답기법과 같은 비검측공 시험법을 적용하는 사례가 점차로 증가되는 추세에 있다. 비검측공시험법의 적용성을 체계적으로 평가하기 위해 수행된 일련의 연구결과 중에서 본 논문에서는 시험법의 결함탐지 능력을 평가하기 위해 수행된 해석적 연구결과에 관해 논한다. 이 연구에서는 시험법의 결함탐지능력에 대한 제반 영향인자 중에서 결함의 유형, 위치 및 크기의 영향을 평가하고자 하였다. 이를 위해서 여러 가지 조건에서 말뚝머리에 작용하는 충격하중에 대한 흙-말뚝 구조의 동적응답을 ABAQUS를 이용한 유한요소법으로 해석하였다. 이로부터 얻은 신호를 충격반향 혹은 충격응답기법으로 처리.분석하여 각 시험법의 결함탐지 능력을 평가해 보았다. 연구결과 이들 두 기법 모두 결함의 위치와 유형은 비교적 정확하게 탐지하는 것으로 나타났다. 그러나 충격응답기법을 이용하여 추정한 결함 크기는 신뢰도가 매우 낮았다. 이 문제를 해소하여 시험법의 적용성을 향상시키기 위해서는 측정된 동적응답신호를 이용하여 적절한 역계산 기법을 개발하여 적용할 필요가 있다는 결론을 얻었다.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.3
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• pp.117-122
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• 2001

The shock test of shipboard equipments is performed for the evaluation of the shock-resistant. capability by analyzing the maximum acceleration, the effective time duration and the shock response spectrum, etc. But some measured signals have impulsive noise and gaussian white noise because of the ambient noise, the acquisition equipment error and the transient movement of cables during the shock test. The improved transient signal analysis method which removes the noise of measured signal using the threshold policy of the median filter and the orthogonal wavelet coefficients is proposed. It was verified that the signal-to-noise ratio was improved about 30dB by the numerical simulation. And the shock response spectrum was extracted using the denoised shock response signal which was applied by this proposed method.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.5
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• pp.105-112
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• 2013

In this study, the applicability of impact-echo method for assessment of residual strength of fire-damaged concrete is investigated. A series of standard fire test is performed to obtain fire-damaged concrete specimens. Impact-echo tests are executed on the specimens and the responses are analyzed. Compressive strengths of the fire-damaged concrete are evaluated and correlated with the ultrasonic wave velocities determined from the impact-echo responses. The effectiveness of impact-echo based ultrasonic wave velocity measurement for assessment of residual strength of fire-damaged concrete is discussed.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.2
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• pp.75-84
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• 1996

The structural response of naval surface ships subjected to underwater shock loadings is a very important problem in viewpoint ship survivability. In practice, among others the case of noncontact underwater explosions is the only one shock loading considered in designing naval surface ships to resist underwater explosions. In orator to efficiently design naval surface ships and their equipment to resist such shock loadings it seems necessary to prepare theoretical analysis tools and/or empirical design criteria which can predict the three dimensional transmission of shock waves. This paper describes a simplified method to analyse shock responses for ship hull girder, which uses a loading function to approximate the shock loadings on ship structures due to noncontact underwater explosions. A couple of examples to apply this method are provided.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.4 s.70
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• pp.373-383
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• 2005

The cask is used to transfer the radioactive material in various fields required to withstand hypothetical accident condition such as 9m drop impact in accordance with the requirement of the domestic requlations and IAEA. So far the impact force has been obtained by the finite element method with complex computational procedure. In this study, the dynamic impact response of the cask body is analyzed using the mode superposition method, and the analysis method is proposed. The results we also validated by comparing with previous experimental results and finite element analysis results. The present method Is simpler than finite element method and can be used to predict the global impact response of cask

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.557-560
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• 2004

본 논문에서는 실내음향을 측정하기 위해 사용되는 음향 측정 신호인 blank pistol, maximum length sequence, sine sweep 을 이용한 충격응답 특성을 분석한다. 각 충격응답의 실내음향 인자들을 먼저 비교 분석하고 sine sweep 속도에 따른 충격응답 특성을 분석하여 최적의 실내음향 인자를 찾기 위한 sine sweep 속도를 결정한다.

• 한국지구물리탐사학회:학술대회논문집
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• 2009.10a
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• pp.185-189
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• 2009

Integrated analysis of GPR, impact echo and impulse response for detection of the rear cavity of concrete was performed on the test-bed which was made in the same scale and component ratio to the real concrete structure. GPR survey may roughly delineate the location of the cavity, but applying the IE and IR technique to the test-bed, the location was clearly identified.

• Journal of the Korean Society for Marine Environment & Energy
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• v.10 no.4
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• pp.218-226
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• 2007

In modern naval ships, the design of submarines has continually evolved to improve survivability and it is also important to design ship against shock response. Exiting underwater ship design has been peformed due to results of static analysis considering shock acceleration by simple method. However, it can not be anticipated good assesment. The present study applied the Arbitrary Lagrangian-Eulerian (ALE) technique, a fluid-structure interaction approach, to simulate an underwater explosion and investigate the survival capability of a damaged submarine liquefied oxygen tank. The Lagrangian-Eulerian coupling algorithm and the equations of state for explosives and seawater were also reviewed. It is shown that underwater explosion analysis using the ALE technique can accurately evaluate structural damage after attack. This procedure could be applied quantitatively to real structural design.

• Geophysics and Geophysical Exploration
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• v.12 no.4
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• pp.338-346
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• 2009

Integrated analysis of GPR, impact echo (IE) and impulse response (IR) was performed to detect the rear cavity of concrete for a test-bed which was made with the same scale and component ratio to the real concrete structure. The test-bed was designed to be capable of observing various response reflecting the existence of iron reinforcing bar and cavity. GPR survey did not clearly resolve the existence of the cavity, although distinguishable responses were observed in the presence of the cavity. In contrast, IE and IR method showed distinct responses, indicating the existence of the cavity. Finally, integrated application of the three methods makes it possible to exactly identify the location of the cavity, although the iron reinforcing bar made a little variation of response.

• The Journal of the Acoustical Society of Korea
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• v.27 no.7
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• pp.333-341
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• 2008

In this paper, a new interpolation model for the head related transfer function (HRTF) was proposed. In the method herein, we assume that the impulse response of the HRTF for each azimuth angle is given by linear interpolation of the time-delayed neighboring impulse responses of HRTFs. The time delay of the HRTF for each azimuth angle is given by sum of the sound wave propagation time from the ears to the sound source, which can be estimated by using azimuth angle, the physical shape of the underlying head and the distance between the head and sound source, and the refinement time yielding the minimum mean square error. Moreover, in the proposed model, the interpolation intervals were not fixed but varied, which were determined by minimizing the total number of HRTFs while the synthesized signals have no perceptual difference from the original signals in terms of sound location. To validate the usefulness of the proposed interpolation model, the proposed model was applied to the several HRTFs that were obtained from one dummy-head and three human heads. We used the HRTFs that have 5 degree azimuth angle resolution at 0 degree elevation (horizontal plane). The experimental results showed that using only $30\sim40%$ of the original HRTFs were sufficient for producing the signals that have no audible differences from the original ones in terms of sound location.