• Title/Summary/Keyword: Rayleigh wave

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An Analysis of Stress Waves in an Elastic Half Space to a Normal Point Force of Ramp Type in Time (램프형 포인트하중에 의한 반무한 탄성체의 응력파해석)

  • Kim, Hyun-Sil;Kim, Jae-Seung;Kang, Hyun-Joo;Kim, Sang-Ryul
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.4
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    • pp.673-678
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    • 1997
  • Stress wave propagations in an elastic half space to a normal point force of ramp type in time are analyzed. The governing equations are transformed by applying the Laplace and Hankel transforms with respect to time and radial distance. The inversion of Laplace transforms are performed by employing the Cagniard-de Hoop method, where the Rayleigh waves at surface are obtained by including the residue terms. The stress waves computed at the location very cose to the surface are shown to be almost identical to the surface waves obtained by the residue method except the Rayleigh wavefront. It is found that at the surface, the stresses are dominated by the Rayleigh waves, whose amplitudes increase linearly with time when time is very large. It is also found that in the interior part, the radial stress has a logarithmic singularity at the shear wavefront, while tangential stress shows no singularity.

Determination of Shear Wave Velocity Profiles of Natural Soils and Pavement Systems Using Surface Wave Technique (표면파 기법을 이용한 자연지반 및 포장지반의 전단파 속도 분포 추정에 관한 연구)

  • Woo, Je Yoon;Kim, Soo Il
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.8 no.4
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    • pp.49-57
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    • 1988
  • A new analytical inversion technique is developed to determine the shear wave velocity profiles of natural soils and pavement systems from the dispersion curves of Rayleigh waves. Haskell's theory on the dispersion of the surface waves in multi-layered elastic solids is utilized. A frequency-unlimited dispersion equation is developed by use of the delta matrix technique. Rigid halfspace is assumed at the depth of the one wavelength of Rayleigh waves. Computer program is coded and validity of the technique is verified through the numerical model tests.

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NATURAL CONVECTION BETWEEN TWO HORIZONTAL PLATES WITH SMALL MAGNITUDE NON-UNIFORM TEMPERATURE IN THE LOWER PLATE : Pr=0.7 (아래 평판이 미소한 불균일 온도를 갖는 두 수평 평판 사이에서의 자연 대류 : Pr=0.7)

  • Yoo, Joo-Sik
    • Journal of computational fluids engineering
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    • v.18 no.2
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    • pp.35-40
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    • 2013
  • Natural convection of air with Pr=0.7 between two horizontal plates with small magnitude non-uniform temperature distribution[${\in}{\Delta}Tsin({\kappa}X/H)$, H : gap width, X : horizontal coordinate] in the lower plate is numerically(${\in}=0.01$) investigated. In the conduction-dominated regime with $Ra{\leq}1700$, two upright cells are formed over one wave length($2{\pi}/{\kappa}$). For small wave number, the flow becomes unstable with increase of Rayleigh number, and multicellular convection occurs above a critical Rayleigh number. The flow patterns are classified by the number of eddies over one wave length. When ${\kappa}=1$, a transition of $2{\rightarrow}4{\rightarrow}6$ eddy flow occurs with increase of Rayleigh number, and no hysteresis phenomenon is observed. Dual and triple solutions are found for ${\kappa}=1$, and transitions of $10{\rightarrow}8$, $8{\rightarrow}6$, $6{\rightarrow}4{\rightarrow}2$ eddy flow occur with decrease of Rayleigh number.

Modeling of Radiation Beams from Ultrasonic Transducers in a Single Medium (단일 매체에서의 평면 초음파 탐촉자의 방사 음장 모델링 기법)

  • Song, Sung-Jin;Kim, Hak-Joon
    • Journal of the Korean Society for Nondestructive Testing
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    • v.20 no.2
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    • pp.91-101
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    • 2000
  • Modeling of radiation beam from ultrasonic transducers has been investigated extensively, since it is one of the most important, fundamental issues that have great influence on the accuracy of an ultrasonic measurement model. Here, three popular radiation models, namely the Rayleigh-Sommerfeld integral model, the boundary diffraction wave model and the edge element model, are discussed briefly, and the radiation beam fields from ultrasonic transducers with planar, circular and rectangular cross-sections are calculated using these three models. Then, the accuracy and the time-efficiency of these methods are compared based on the calculation results.

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Generalized Rayleigh wave propagation in a covered half-space with liquid upper layer

  • Negin, Masoud
    • Structural Engineering and Mechanics
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    • v.56 no.3
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    • pp.491-506
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    • 2015
  • Propagation of the generalized Rayleigh waves in an initially stressed elastic half-space covered by an elastic layer is investigated. It is assumed that the initial stresses are caused by the uniformly distributed normal compressional forces acting on the face surface of the covering layer. Two different cases where the compressional forces are "dead" and "follower" forces are considered. Three-dimensional linearized theory of elastic waves in initially stressed bodies in plane-strain state is employed and the elasticity relations of the materials of the constituents are described through the Murnaghan potential where the influence of the third order elastic constants is taken into consideration. The dispersion equation is derived and an algorithm is developed for numerical solution to this equation. Numerical results for the dispersion of the generalized Rayleigh waves on the influence of the initial stresses and on the influence of the character of the external compressional forces are presented and discussed. These investigations provide some theoretical foundations for study of the near-surface waves propagating in layered mechanical systems with a liquid upper layer, study of the structure of the soil of the bottom of the oceans or of the seas and study of the behavior of seismic surface waves propagating under the bottom of the oceans.

Statisticall Characteristics of Sea Waves at Mookho (묵호항의 파랑특성)

  • 심명필;안수한
    • Water for future
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    • v.10 no.1
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    • pp.101-117
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    • 1977
  • The statatistical characteristics and spectra of sea waves at Mookho were analysed by several statistical methods. As the results, the following conclusions are obtained: 1. Values of surface elevation of sea wave are better fitted to Gram Charlier distribution than Gaussian distribution. This proves that sea waves have not only characters of irregularity but also non-linearity. 2. Distribution of maxima of surface elevation practically follows the distribution of Cartwright and Longuet-Higgins, also spectral width parameter is found to be increased with the increase of root mean square of surface elevation. 3. Sea wave may have spectrum of broad frequency band, however distributions of wave heights and periods follow the Rayleigh distribution which is derived from the assumption of narrow frequency band. 4. Ratios among mean wave heights from observed data show good agreements with theoretical values from Rayleigh distribution. 5. Spectral density and spectral width parameter increase with increase of wind velocity. And wave period at optimum band gas higher value than significant wave period by about 10 percent.

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The Measurements of Rayleigh Velocity and the Non-Destructive Evaluation by Using Backscattering Signal (후방산란신호에 의한 Rayleigh 파의 속도측정 및 비파괴검사)

  • Ban, Cheon-Sik;Kim, Jang-Kwon;Jun, Kye-Suk
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.26 no.2
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    • pp.163-168
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    • 1989
  • In this paper, Rayleigh wave velocity has been measured by detecting the backscattered signal generating near the Rayleigh critical angle in the elastic medium. The rotating system has been made for the measurment of Rayleigh angle. It has been shown that the measured velocity for the stainless steel, brass aluminum, copper has been good agreement with the theoretical value. The method of non-destructive evaluation using backscattering signal has been presented and the c-scan acoustic image for internal of IC sample has been displayed.

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Inversion of Rayleigh-wave Dispersion Curves for Near-surface Shear-wave Velocities in Chuncheon Area (춘천지역의 천부 횡파속도를 구하기 위한 레일리파 분산곡선 역산)

  • Kim, Ki-Young;Kim, Woo-Jung;Park, Yeong-Hwan
    • Geophysics and Geophysical Exploration
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    • v.15 no.1
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    • pp.1-7
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    • 2012
  • To evaluate methods of determining near-surface shear-wave velocities (${\nu}_s$), we derived dispersion curves of Rayleigh waves generated by both passive and active sources in Chuncheon, Korea. Microtremors were recorded for 5 minutes in each of four triangular arrays with radii of 5 ~ 40 m. Those data were analyzed using the Spatial Autocorrelation method. Rayleigh waves were also generated by a hammer source and recorded in the same area for 2 s using 24 4.5-Hz geophones. Multichannel Analysis of Surface Waves was applied to those data. Velocity spectra were derived with relatively high signal-to-noise ratios in the frequency ranges of 7 ~ 19 and 11 ~ 50 Hz for the microtremors and synthetically generated Rayleigh waves, respectively. The resultant dispersion curves were combined as one and then input to inversion to derive shear wave velocities that were compared with a lithology log from a nearby well. Shearwave velocities in the top soil and soft-rock layers are almost constant with values of 221 and 846 m/s, respectively; while the inverse-modeled ${\nu}_s$ increases linearly in the gravelly sand, cobbles, and weathered-rock layers. If rock type is classified based on shear-wave velocity, the inversion-derived boundary between weathered-rock and soft rock may be about 5 m deeper than in the well log.

A Study on Surface Acoustic-Wave Amplfication in Piezo-electric Crystals (Piezo 압전 결정체에서의 표면탄성파 증폭에 관한 연구)

  • 이윤현
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.6 no.1
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    • pp.51-57
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    • 1981
  • Carriers moving in a semiconductor can impart gain or loss to an acousic wave traveling through Piezo-electric materials. In this paper, surface a coustic wave amplifiers, which employ the interaction between carriers drifting in a semiconduct or film and electic fields accompanying a Rayleigh wave propagating on a Piezoelectric substrate, are described. The effect of various electromagnetic boundary condition on th propagation of surface waves in Piezoelectrics is considered. An expression for the dependence of surface wave velocity on electic boundary conditions is derived. Calculations show that, for properly prepared material, significant amplification is expected up to the microwave frequencies. At high frequencies, gain is reduced because electro diffusion smooths out the electron bucning necessary for amplification.

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An Experimental Study of Ground Motion under the Dynamic Load (동하중재하시 지반진동에 관한 실험적 연구)

  • 김문겸
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • 1997.10a
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    • pp.126-131
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    • 1997
  • Recently, the ground motion occurred by vehicles or trains has been recognized one of the major factors of damage of structures nearly the motion source. To isolate the environments from ground motions, it is necessary to understand the wave propagation in half spaces. Especially, Rayleigh wave is the primary concern because it transmits a major portion of the total source energy and decays the energy more slowly with response to distance than the other waves. In this study, the preliminary data(wave length and damping effect) to design the isolating system are obtained. For this, a field dynamic test is performed, using the exciter which can generate the 100kN vertical cyclic load in the range of 1-60 Hz is used. The fifteen accelerometers to measure the ground response are set up in 3 radial direction at intervals of 10 meters in each row. The wave lengths are calculated using the distance and the phase between the measuring points. The damping effects of the Rayleigh-wave are also observed from the experiments.

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