• 대한기계학회논문집
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• 제17권8호
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• pp.1931-1939
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• 1993

The wave propagation characteristics of laminated composites subjected to a transverse high-velocity impact of a steel ball is investigated. For this purpose, high-velocity impact experiments were conducted to obtain the strain response histories, and a finite element analysis based on the higher-order shear deformation theory in conjunction with the static contact law is used. Test materials for investigation are glass/epoxy laminated composite materials with $[0^{\circ}/45^{\circ}/0^{\circ}/-45^{\circ}]_{2s}$ and $[90^{\circ}/-45^{\circ}/90^{\circ}-45^{\circ}/90^{\circ}]_{2s}$ stacking sequences. As a result, the strain responses obtained from the experiments represented the wave propagation characteristics in the transversely impact, also the wave propagation velocities obtained from high-velocity impact experiments and wave propagation theory agree well.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.97-103
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• 2006

A modified one-sided measurement technique is proposed for Rayleigh wave (R-wave) velocity measurement in concrete. The scattering from heterogeneity may affect the waveforms of R-waves in concrete, which may make the R-waves dispersive. Conventional one-sided techniques do not consider the scattering dispersion of R-waves in concrete. In this study, the maximum energy arrival concept is adopted to determine the wave velocity by employing its continuous wavelet transform. Experimental study was performed to show the effectiveness of the proposed method. The present method is applied to monitor the strength development of early-age concrete. A series of experiments were performed on early-age concrete specimens with various curing conditions. Results reveal that the proposed method can be effectively used to measure the R-wave velocity in concrete structures and to monitor the strength development of early-age concrete.

• 한국음향학회지
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• 제20권4호
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• pp.54-61
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• 2001

자왜 재료는 비선형 자기-탄성 특성을 갖는다고 알려져 있다. 그러나 비선형 특성을 표현하는 자왜 재료의 비선형 구조 방정식을 4차 텐서를 이용하여 유도하였고, 준선형 (quasi-linear)화시킨 압자구조방정식을 이용하여 자왜 재료 내의 파동 방정식을 유도하였다. 유도된 식을 바탕으로 자왜 재료에서 평면파가 자계 방향을 따라 전파될 때의 탄성파 속도를 구하였다. 나아가 자왜 재료 중에서 가장 널리 사용되고 있는 Terfenol-D의 탄성파 속도를 측정하여 본 연구에서 유도한 자왜 재료 비선형 구조 방정식의 타당성을 검증하였다.

• 대한기계학회논문집B
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• 제24권7호
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• pp.924-929
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• 2000

This paper addresses a new technique of measuring the mean flow velocity over the cross sectional area of the pipe using sound field reconstruction. When fluid flows in the pipe and two plane waves propagate oppositely through the medium, the flow velocity causes the change of wave number of the plane waves. The wave number of the positive going plane wave decreases and that of negative going one increases in comparison to static medium in the pipe. Theoretical backgrounds of this method are introduced in detail and the measurement of mean flow velocity using the sound field reconstruction is not affected by velocity profile upstream of microphones.

• 한국지반공학회논문집
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• 제33권4호
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• pp.17-24
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• 2017

지진과 같은 외부 하중하에서 CFRD 거동은 사력존의 전단파 속도(또는 전단 탄성계수)분포에 큰 영향을 받는다. 일반적으로 사력존의 전단파 속도 분포는 주상도의 형태로 표면파 시험과 같은 비파괴 시험에 의해 결정될 수 있다. 이때 한정된 수의 실험에서 결정된 전단파 속도 주상도에는 불확실성이 존재하며, 이러한 불확실성은 사력존에 존재하는 물성치 공간 변동성에 의해 발생하게 된다. 내진 해석과 같은 다양한 해석에서 물성치 변동성에 의해 발생할 수 있는 해석 결과의 불확실성은 신뢰성 기반 해석을 통해 고려될 수 있다. 신뢰성 기반해석에서는 재료 물성치의 변동계수 결정을 통해 이러한 불확실성을 해석에 반영한다. 본 연구에서는 국내 CFRD 사력존을 위한 전단파 속도변동계수를 결정하였다. 이를 위해 국내 CFRD 사력존에서 결정된 전단파 속도 주상도들과 하모닉 웨이브릿 해석에 기반한 기법을 사용하여 국내 CFRD 사력존에 존재 가능한 600개의 전단파 속도 주상도를 생성하고 이를 이용하여 사력존 전단파 속도 분포의 깊이별 변동계수를 결정하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 춘계 학술발표회 논문집
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• pp.137-146
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• 2006

Shear wave velocity of uncemented soil can be expressed as the function of effective stresses when capillary phenomenons are negligible. However, the terms of effective stresses are divided to the direction of wave propagation and polarization because stress states are generally anisotropy. The shear wave velocities are affected by parameters and exponents that are experimentally determined. The exponents are controlled contact effects of particulate materials(sizes, shapes, and structures of particles) and the parameters are changed contact behaviors between particles, material properties of particles, and type of packing(i.e., void ratio and coordination number). In this study, consolidation tests are performed by using clay, mica and sand specimens. Shear wave velocities are measured during consolidation tests to investigate the stress-induced and inherent anisotropies through bender elements. Results show the shear wave velocities depends on the stress-induced anisotropy for round particles. Furthermore the shear wave velocity is dependent on particle alignment under the constant effective stress. This study suggests that the shear wave velocity and the shear modulus should be carefully calculated and used for the design and construction of geotechnical structures.

• Geomechanics and Engineering
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• 제11권5호
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• pp.713-723
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• 2016

Shear wave velocities of three selected sandy soils subject to drained triaxial compression test were continuously measured using the bender elements. The shear wave velocity during isotropic compression, as widely recognized, increased as confining pressure increased and they were correlated well. However, during drained shearing, the mean effective stress could no further provide a suitable correlation. The shear wave velocity during this stage was almost constant with respect to the mean effective stress. The vertical stress was found to be more favorable at this stage (since confining stress was kept constant). When sample was attained its peak stress, the shear wave velocity reduced and deviated from the previously existed trend line. This was probably caused by the non-uniformity induced by the formation of shear band. Subsequently, void ratios computed based on external measurements could not provide reasonable fitting to the initial stage of post-peak shear wave velocity. At very large strain levels after shear band formation, the digital images revealed that sample may internally re-arrange itself to be in a more uniform loose stage. This final stage void ratio estimated based on the proposed correlation derived during pre-peak state was close to the value of the maximum void ratio.

• International Journal of Reliability and Applications
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• 제5권1호
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• pp.1-13
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• 2004

It is recently well recognized that the technique for the one-sided stress wave velocity measurement in structural materials provides measurement in structural materials provides valuable information on the state of the material such as quality, uniformity, location of cracked or damaged area. This technique is especially effective to measure velocities of longitudinal and Rayleigh waves when access to only one surface of structure is possible. However, one of problems for one-sided stress wave velocity measurement is to get consistent and reliable source for the generation of elastic wave. In this study, the laser based surface elastic wave was used to provide consistent and reliable source for the generation of elastic wave into the materials. The velocities of creeping wave and Rayleigh wave in materials were measured by the one-sided technique using laser based surface elastic wave. These wave velocities were compared with bulk wave velocities such as longitudinal wave and shear wave velocities to certify accuracy of measurement. In addition, the mechanical properties such as poisson's ratio and specific modulus(E/p) were calculated with the velocities of surface elastic waves.

• 대한조선학회논문집
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• 제42권6호
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• pp.559-565
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• 2005

As the wave impinges on and overtops the structure, a large highly aerated region is created in front of the structure and water splashs on top of the structure. The broken wave in front of the structure and associated green water on top of the structure are highly aerated containing not only a large number of bubbles but also very large sizes of bubbles. In this paper, the velocity field of the highly aerated region and the splashing water on the top is measured using a modified PIV method incorporating the traditional PIV method with the shadowgraphy technigue by correlating the ' texture ' of the bubble images. The velocity fields of a plunging wave impacting on a structure in a two-dimensional wave flume is measured. It is found that the maximum fluid particle velocity in flout of the structure during the impinging process is about 1.5 times the phase speed of the wave, while the maximum horizontal velocity above the top is less than the phase speed, It is also found that the dam breaking solution does not work well in predicting the green water velocity.

• 한국지진공학회논문집
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• 제13권5호
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• pp.1-9
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• 2009

본 연구에서는, 필댐 사력죤의 전단파속도 특성을 분석하고자 하였으며, 필댐 사력죤의 특성상 주로 표면에서 비파괴적으로 수행되는 표면파 탐사 기법을 적용하여 전단파속도를 도출 하였다. 대표적 표면파 기법인 SASW기법과 새롭게 개발된 HWAW 기법을 이용하여 6개댐 사력죤에서 시험을 통해 심도별 전단파속도와 구속압에 따른 전단파속도를 산정하고 그 결과를 기존에 많이 사용되었던 Sawada와 Takahashi의 결과와 비교 분석하였다.