• Title/Summary/Keyword: Rayleigh Surface Wave

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Experimental Verification on the Detectability of Surface Flaws at Fillet Weld Hills by Ultrasonic Method (초음파에 의한 필렛 용접힐부의 표면결함 검출능에 관한 실험적 검증)

  • 박익근;이철구
    • Journal of Welding and Joining
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    • v.18 no.1
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    • pp.46-51
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    • 2000
  • Ultrasonic nondestructive evaluation (UNDE) technique is commonly used for detecting inner defects in the materials. Recently, new methods are trying to apply for detecting surface and subsurface flaws using Rayleigh wave or creeping wave. These techniques, however, have following problems. Echo amplitude is remarkably affected by the surface conditions and discrimination of echo pattern is usually difficult because shear wave propagate in the material at the same time. We can apply surface SH-wave(which is horizontally polarized shear wave traveling along near surface layer) technique to detect surface flaws. In this paper, directivity, distance amplitude characteristics and detectability of surface flaws at fillet weld hills of the 5 MHz and 2 MHz surface flaws at fillet weld hills of the 5 MHz and 2 MHz surface Sh-wave are experimentally investigated. As a result of the study, it was found out that these techniques are valuable for the detection of fatigue cracks at fillet weld heels which can not be detected by other ultrasonic techniques such as angle beam technique and which are inaccessible for non-destructive testings e.g. MT(magnetic particle testing) or PT(liquid penetrant testing).

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1-D Shear Wave Velocity Structure of Northwestern Part of Korean Peninsula (한반도 북서부의 1차원 전단파 속도구조)

  • Kim, Tae Sung
    • Economic and Environmental Geology
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    • v.52 no.6
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    • pp.555-560
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    • 2019
  • One-dimensional shear wave velocity structure of North Korea is constrained using short (2-sec) to long period (30-sec) Rayleigh waves generated from four seismic events in China. Rayleigh waves are well recorded at the five broadband seismic stations (BRD, SNU, CHNB, YKB, KSA) which are located near to the border between North and South Korea. Group velocities of fundamental-mode Rayleigh waves are estimated with the Multiple Filter Analysis and refined by using the Phase Matched Filter. Average group velocity dispersion curve ranging from 2.9 to 3.2 km/s, is inverted to constrain the shear wave velocity structures. Relatively low group velocity dispersion curves along the path between the events to BRD at period from 4 to 6 seconds may correspond to the sedimentary sequence of the West Korea Bay Basin (WKBB) in the Yellow Sea. The low velocity zone in deep layers (14-20 km) may be related to the deep sedimentary structure in Pyongnam basin. The fast shear wave velocity structure from the surface to the depth of 14 km is consistent with the existence of metamorphic rocks and igneous bodies in Nangrim massif and Pyongnam basin.

Experimental Verification on the Stability and Sound Pressure Transmission Coefficient of Surface SH-Wave (표면 SH파의 음압 통과율과 에코 안정성에 관한 실험적 검증)

  • 이명호
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.12 no.2
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    • pp.23-30
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    • 2003
  • It is very important to detect and evaluate the surface or subsurface flaws because of their influences on mechanical properties of materials. Rayleigh wave and creeping wave are commonly used for the detection of surface and subsurface flaws. These techniques, however, have following problems. Each amplitudes are remarkably affected by the surface condition and evaluation of echo pattern is usually difficult because shear wave mode propagate in the material at the same time. On the other hand, surface SH-wave which is horizontally polarized shear wave traveling along near surface layer is an attractive technique for the surface or subsurface material characterization and this technique is useful to solve the problems mentioned above. In this paper, The stability and transmission coefficient of SH waves through a viscous fluid layer is theoretically studied and simulated. Its results agreed well with the theoretical expectation for the experimental verification. These experimental results show that viscosity of couplants, thickness of couplant and surface roughness are closely related to transfer efficiency in surface SH angle beam method.

DISPERSION OF RAYLEIGH WAVES IN THE KOREAN PENINSULA (한반도의 레일리파 분산에 대한 연구)

  • Cho Kwang-hyun;Lee Kiehwa
    • 한국지구물리탐사학회:학술대회논문집
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    • 2005.05a
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    • pp.29-36
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    • 2005
  • The crustal structure of Korean Peninsula is investigated by analyzing phase velocity dispersion data of Rayleigh wave. Earthquakes recorded by three component seismographs during 1999 - 2004 in South Korea are used in this study. The fundamental mode signals of Rayleigh waves are obtained from vertical components of seismograms by multiple filter technique method and phase match filter method. Velocity dispersion curves of surface waves for 14 propagation paths on the great circle are computed from the fundamental mode signals on the great circle path by two-station method. Treating the shear velocity of each layer as an independent parameter, phase velocities of Rayleigh wave are inverted. The result models are regarded as average structure for surface wave propagation paths respectively. All the results can be explained by an earth model of the Korean Peninsula comprising crust of shear-wave velocity increasing from 2.8 to 3.25 km/sec from top to 33 km depth and uppermost mantle of shear-wave velocity between 4.55 and 4.67 km/sec.

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The Crustal and Upper Mantle Velocity Structure of the Southern Korean Peninsula from Receiver Functions and Surface-Wave Dispersion (수신함수와 표면파 분산의 동시역산을 이용한 한반도 남부지역의 지각과 상부맨틀 연구)

  • Yoo, H.J.;Lee, K.;Herrmann, R.B.
    • 한국지구물리탐사학회:학술대회논문집
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    • 2006.06a
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    • pp.61-70
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    • 2006
  • 3-D S-wave velocity model in the southern Korean Peninsula is investigated by using the joint inversion of receiver functions and surface-wave dispersion. A peninsula average Rayleigh-wave phase velocity in the 10-150 seconds range and tomographic estimates of the Rayleigh and Love wave group velocities in the 0.5-20 seconds period range determined using a $12.5{\times}12.5\;km$ grid for the southern part of the peninsula are used for the inversion. Receiver functions were determined from broadband (STS-2), short-period (SS-1) and acceleration (Episensor) channels of 95 stations. The dense distribution of the stations in the Peninsula permits us to examine the 3-D crustal structure in detail. The inversion result shows the variation and characteristics of S-wave velocity in the crust and upper mantle of the southern Korean Peninsula very well.

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Evaluation of Dynamic Properties of Natural Soils and Pavement Systems Using Surface Wave Technique - Theoretical Dispersion Curves - (표면파기법을 이용한 자연지반 및 포장구조의 동적물성 추정에 관한 연구 - 이론적 분산곡선 -)

  • Kim, Soo Il;Woo, Je Yoon
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.7 no.2
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    • pp.121-130
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    • 1987
  • A new analytical method to determine the theoretical dispersion curves of Rayleigh wave in multilayered elastic media is developed. The method developed in this study gives the solutions for unlimited frequency, and is essential part of surface wave techniques to evaluate the layer profiles and dynamic properties of soils and pavement systems. Delta-Matrix technique is utilized to overcome the overflow and loss of precision problem inherent in the original Thomson-Haskell formulation at high frequencies. Conventional inversion methods based on the original Thomson-Haskell formulation lead to erroneous results due to the limitations on the layer profiles and the magnitude of frequency. The method developed in this study establishes the base of the research on more accurate and efficient inversion method, especially for the pavement systems as well as the natural soils.

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The Evaluation of Roadbed Stiffness using Continuous Surface-Wave (CSW) Method (연속 표면파(CSW)기법을 활용한 노반 강성평가에 관한 연구)

  • Ko Hak-Song;Joh Sung-Ho;Hwang Sun-Kun;Lee Il-Hwa
    • Proceedings of the KSR Conference
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    • 2004.10a
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    • pp.868-873
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    • 2004
  • Recently, The surface-wave method has widely been used for the site investigation due to the economic advantage and the improved reliability. The typical surface-wave methods currently available are SASW method, MASW method and CSW method. The CSW method has a potential of high-quality measurement, but its inherent problems limited its use to the special cases such as the compaction-quality control. The CSW method uses the steady-state harmonic vibration for the seismic source as in the steady-state Rayleigh-wave method, which is superior to the impact source used for other methods. This study proposed a new procedure to solve the inherent problems of the CSW method and to improve the reliability of the CSW measurements. To verify the validity of the proposed in this study, the SASW results were compared with the CSW results for the numerical simulation of the CSW testing. Also, the feasibility of the proposed method was verified using the field measurements at a geotechnical site.

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A Study on Scattered Field of Ultrasonic Wave Using the Boundary Element Method (경계요소법을 이용한 초음파 산란장 해석에 관한 연구)

  • Lee, Joon-Hyun;Lee, Seo-Il
    • Journal of the Korean Society for Nondestructive Testing
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    • v.20 no.2
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    • pp.130-137
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    • 2000
  • Ultrasonic technique which is one of the most common and reliable nondestructive evaluation techniques has been applied to evaluate the integrity of structures by analyzing the characteristics of signal scattered from internal defects. Therefore, the numerical analysis of the ultrasonic scattered field is absolutely necessary for the accurate and quantitative estimation of internal defects. Various modeling techniques now play an important role in nondestructive evaluation and have been employed to solve elastic wave scattering problems. Because the elastodynamic boundary element method is useful to analyze the scattered field in infinite media. it has been used to calculate the ultrasonic wavefields scattered from internal defects. In this study, a review of the boundary element method used for elastic wave scattering problems is presented and, as examples of the boundary element method, the scattered fields due to a circular cavity subjected to incident SH-wave and due to a surface-breaking crack subjected to incident Rayleigh wave are illustrated.

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Temperature Characteristics of Elastic Surface Wave (탄성표면파의 온도특성)

  • 김종상
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.10 no.3
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    • pp.53-60
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    • 1973
  • Calculations of the temperature coefficients of the elastic surface wave velocity and delay time were performed for the propagation along the X axis of rotated Y cut plane of the LiNbO3 and LiTaO3. Measurements of the temperature dependence of delay time of the elastic surface wave were also performed for the propagation along the X axis of a 130" rotated Y cut plane of the LiNb03 at the temperature range from liquid He to room temperature. Experimental value 70$\times$10-6/$^{\circ}C$ of the temperature coefficient of the delay time of the elastic surface wave agrees well with the calculated value 72.7$\times$10-a/$^{\circ}C$. The temperature coefficient of delay time of elastic surface wave propagating along the X axis of a 130$^{\circ}$ rotated Y cut plane o( the LiNbO3 is approximately 16$\times$10-6/$^{\circ}C$ at the near temperature of liquid He.d He.

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Seismic surface waves in a pre-stressed imperfectly bonded covered half-space

  • Negin, Masoud
    • Geomechanics and Engineering
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    • v.16 no.1
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    • pp.11-19
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    • 2018
  • Propagation of the generalized Rayleigh waves in an elastic half-space covered by an elastic layer for different initial stress combinations and imperfect contact conditions is investigated. Three-dimensional linearized theory of elastic waves in initially stressed bodies in plane-strain state is employed, the corresponding dispersion equation is derived and an algorithm is developed for numerical solution to this equation. Numerical results on the influence of the initial stress patterns and on the influence of the contact conditions are presented and discussed. The case where the external forces are "follower forces" is considered as well. These investigations provide some theoretical foundations for the study of the near-surface waves propagating in layered mechanical systems and can be successfully used for estimation of the degree of the bonded defects between layers, fault characteristics and study of the behavior of seismic surface waves propagating under the bottom of the oceans.