• Title/Summary/Keyword: dispersion of surface waves

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Analytical Study for dispersed Phase Velocity Information of Love Waves (러브파의 위상속도 분산정보에 관한 해석적 연구)

  • 이일화
    • Journal of the Korean Society for Railway
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    • v.7 no.4
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    • pp.391-399
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    • 2004
  • This paper investigated the dispersion characteristics of horizontal surface waves as means to apply conversional SASW techniques. To verify this proposal, 3D finite element analysis and Transfer matrix solution were performed. SH wave(Love waves) has the some advantages in comparison with Rayleigh wave. Representatively, Love wave has a characteristics not affected by compression wave. These characteristics have the robust applicability for the surface wave investigation techniques. In this study, for the purpose of employing Love wave in the SASW method, the dispersion characteristics of the Love wave was extensively investigated by the theoretical and numerical approaches. The 3-D finite element and transfer matrix analyses for the half space and two-layer systems were performed to determine the phase velocities from Love wave as well as from both the vertical and the horizontal components of Rayleigh wave. Preliminary, numerical simulations and theoretical solutions indicated that the dispersion characteristics of horizontal surface wave(Love waves) can be sufficiently sensitive and appliable to SASW techniques.

Comparison of Shear-wave Velocity Sections from Inverting SH-wave Traveltimes of First Arrivals and Surface Wave Dispersion Curves (SH파 초동주시 역산과 표면파 분산곡선 역산으로부터 구한 횡파속도 단면 비교)

  • Lee, Chang-Min;Kim, Ki-Young
    • Journal of the Korean Geophysical Society
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    • v.8 no.2
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    • pp.67-74
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    • 2005
  • Two-dimensional S-wave velocity sections from SH-wave refraction tomography and surface wave dispersions were obtained by inverting traveltimes of first arrivals and surface wave dispersions, respectively. For the purpose of comparison, a P-wave velocity tomogram was also obtained from a P-wave refraction profiling. P and Rayleigh waves generated by vertical blows on a plate with a sledgehammer were received by 100- and 4.5-Hz geophones, respectively. SH-waves generated by horizontal blows on both sides of a 50 kg timber were received by 8 Hz horizontal geophones. The shear-wave signals were enhanced subtracting data of left-side blows from ones of the right-side blows. Shear-wave velocities from tomography inversion of first-arrival times were compared with ones from inverting dispersion curves of Rayleigh waves. Although the two velocity sections look similar to each other in general, the one from the surface waves tends to have lower velocities. First arrival picking of SH waves is troublesome since P and PS-converted waves arrive earlier than SH waves. Application of the surface wave method, on the other hand, is limited where lateral variation of subsurface tructures is not mild.

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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.

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.

Dispersion Characteristics of Cylindrical Shells Submerged in the Fluid (유체에 잠긴 원통형 실린더의 파동 분산 특성)

  • Jung, Byung-Kyoo;Hong, Chinsuk;Ryue, Jungsoo;Jeong, Weui-Bong;Shin, Ku-Kyun
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.25 no.8
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    • pp.575-582
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    • 2015
  • This paper deals with the dispersion relation of the waves sustained in a cylindrical shell submerged in the fluid. The waveguide finite method and the boundary element method are used to predict the dispersion characteristic of the cylindrical shell. The dispersion diagram of the cylinder is estimated from the eigenvalue problem and the forced vibration response. It follows that the water-loading leads to the decrease of the cut-on frequencies and the phase speeds of the bending waves. On the contrary, the longitudinal waves and the torsional waves are hardly affected by the fluid, and therefore the order of the cut-on frequencies of the waves is changed. The acoustic dispersion diagram is also estimated from the forced acoustic response to identify the characteristics of the wave radiated to the fluid. It follows that the acoustic waves on and near the surface of the cylinder are the same as those in the structure. But at the far field the acoustic waves caused by subsonic waves e.g., the bending waves disappear as the increase of the distance. Conclusively, the characteristics of waves in cylindrical shells are significantly affected by water-loading in terms of the cut-on frequency, the wave speed, the order of the cut-on and radiation.

Torsional surface waves in a non-homogeneous isotropic layer over viscoelastic half-space

  • Kakar, Rajneesh;Gupta, Kishan Chand
    • Interaction and multiscale mechanics
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    • v.6 no.1
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    • pp.1-14
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    • 2013
  • The aim of this paper is to study the propagation of torsional surface waves in non-homogeneous isotropic layer of finite thickness placed over a homogeneous viscoelastic half-space, when both density and rigidity of the non-homogeneous medium are assumed to vary exponentially with depth. The frequency equations are obtained by using simple method of separation of variables. Further, it is seen that when viscoelastic parameter and non-homogeneity parameter is neglected, the dispersion equation gives the dispersion equations of Love waves in homogeneous, elastic and isotropic layer placed over homogeneous viscoelastic medium. The problem has been solved numerically and the effects of various inhomogeneities of the medium on torsional waves have been illustrated graphically.

OBSERVATIONS BY SATELLITE ALTIMETRY OF SHORT SURFACE WAVE ENERGY IN THE DECEMBER 2004 SUMATRA TSUNAMI

  • Gower, Jim
    • Proceedings of the KSRS Conference
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    • v.1
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    • pp.43-46
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    • 2006
  • The main tsunami wave triggered by the December 2004 Sumatra tsunami was detected in the ocean south of India by satellite altimeters on Jason, Topex/Poseidon and Envisat. All three altimeters also detected shorter-wavelength (10 to 100 km), slower-propagating surface waves, spreading from the site of the earthquake. The shorter waves give additional information about the tsunami event, and can be used to better define the generating region in this, and future tsunamis. The properties of the area of shorter tsunami-generated waves may also be important in designing a future satellite-based detection system.

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Shear waves propagation in an initially stressed piezoelectric layer imperfectly bonded over a micropolar elastic half space

  • Kumar, Rajneesh;Singh, Kulwinder;Pathania, D.S.
    • Structural Engineering and Mechanics
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    • v.69 no.2
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    • pp.121-129
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    • 2019
  • The present study investigates the propagation of shear waves in a composite structure comprised of imperfectly bonded piezoelectric layer with a micropolar half space. Piezoelectric layer is considered to be initially stressed. Micropolar theory of elasticity has been employed which is most suitable to explain the size effects on small length scale. The general dispersion equations for the existence of waves in the coupled structure are obtained analytically in the closed form. Some particular cases have been discussed and in one particular case the dispersion relation is in well agreement to the classical-Love wave equation. The effects of various parameters viz. initial stress, interfacial imperfection and micropolarity on the phase velocity are obtained for electrically open and mechanically free system. Numerical computations are carried out and results are depicted graphically to illustrate the utility of the problem. The phase velocity of the shear waves is found to be influenced by initial stress, interface imperfection and the presence of micropolarity in the elastic half space. The theoretical results obtained are useful for the design of high performance surface acoustic devices.

ARTICLES : MULTICHANNEL ANALYSIS OF SURFACE WAVES (MASW) - AN OVERVIEW

  • ChoonB.Park
    • Journal of the Korean Geophysical Society
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    • v.6 no.2
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    • pp.99-105
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    • 2003
  • Rayleigh waves which has more than 70% of the total seismic energy is the principal component of ground roll. Frequency component of a surface wave has a different propagation velocity, that is, phase velocity, which results in a different wavelength called dispersion. Rayleigh wave is one of the most common ways to use the dispersive properties of surface waves. MASW is a seismic method to evaluate shear-wave velocity information of the ground.

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Electro-magneto-thermoelastic surface waves in non-homogeneous orthotropic granular half space

  • Kakar, Rajneesh;Kakar, Shikha
    • Geomechanics and Engineering
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    • v.7 no.1
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    • pp.1-36
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    • 2014
  • The effect of various parameters on the propagation of surface waves in electro-magneto thermoelastic orthotropic granular non-homogeneous medium subjected to gravity and initial compression has been studied. All material coefficients are obeyed the same exponent-law dependence on the depth of the granular elastic half space. Some special cases investigated by earlier researchers have also been deduced. Dispersion curves are computed numerically and presented graphically.