• 비파괴검사학회지
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• 제27권6호
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• pp.582-590
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• 2007

Imperfectly jointed interface serves as mechanical waveguide for elastic waves and gives rise to two distinct kinds of guided wave propagating along the interface. Contact acoustic nonlinearity (CAN) is known to plays major role in the generation of these interface waves called generalized Rayleigh waves in non-welded interface. Closed crack is modeled as non-welded interface that has nonlinear discontinuity condition in displacement across its boundary. Mathematical analysis of boundary conditions and wave equation is conducted to investigate the dispersive characteristics of the interface waves. Existence of the generalized Rayleigh wave(interface wave) in nonlinear contact interface is verified in theory where the dispersion equation for the interface wave is formulated and analyzed. It reveals that the interface waves have two distinct modes and that the phase velocity of anti-symmetric wave mode is highly dependent on contact conditions represented by linear and nonlinear dimensionless specific stiffness.

• Structural Engineering and Mechanics
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• 제56권3호
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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.

• Structural Engineering and Mechanics
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• 제25권5호
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• pp.597-611
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• 2007

Many works have been done in classical theory of thermoelasticity in materials with memory by researchers like Nunziato, Chen and Gurtine and many others. No work is located in generalized thermoelasticity regarding materials with memory till date. The present paper deals with the wave propagation in materials with memory in generalized thermoelasticity. Plane progressive waves and Rayleigh waves have been discussed in details. In the classical theory of heat conduction it was observed that heat propagates with infinite speed. This paradox has been removed in the present discussion. The set of governing equations has been developed in the present analysis. The results of wave velocity and attenuation coefficient corresponding to low and high frequency have been obtained. For thermal wave the results show appreciable differences with those in the usual thermoelasticity theory.

• Steel and Composite Structures
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• 제42권6호
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• pp.723-732
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• 2022

The present research is concerned to study the effect of fractional parameter and rotation on the propagation of Rayleigh waves in an orthotropic magneto-thermoelastic media with three-phase-lags in the context of fractional order theory of generalized thermoelasticity with combined effect of rotation and hall current. The secular equations of Rayleigh waves are derived by using the appropriate boundary conditions. The wave properties such as phase velocity, attenuation coefficient are computed numerically and the numerical simulated results are presented through graphs to show the effect on all the components. Some special cases are also discussed in the present investigation.

• 비파괴검사학회지
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• 제27권3호
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• pp.224-230
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• 2007

This work is aimed to explore a possibility of using the generalized Lamb waves for nondestructive evaluation of the bonding quality of layered substrates. For this purpose, we prepared two sets of specimens with imperfect bonding at their interfaces; 1) TiN-coated specimens with various wear conditions, and 2) CVD diamond specimens with various cleaning conditions. A dispersion simulation performed for layered substrates with imperfect interfaces are carried out to get the characteristics of dispersion curves that can be used for bonding quality evaluation. Then the characteristics of dispersion curves of the fabricated specimens are experimentally determined by use of an ultrasonic backward radiation measurement technique. The results obtained in the present study show that the lowest velocity mode (Rayleigh-like) of the generalized Lamb waves are sensitively affected by the bonding quality. Therefore, the generalized Lamb waves can be applied for nondestructive evaluation of imperfect bonding quality in various layered substrates.

• Geomechanics and Engineering
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• 제16권1호
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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.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1997년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Fall 1997
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• pp.128-135
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• 1997

The indirect boundary integral equation is formulated to analyze the behavior of a cavity in a multilayered half-plane subjected to earthquake waves. This formulation uses the fundamental solutions that are numerically calculated by the generalized transmission and reflection coefficient method. The free surface of the cavity without external excitation influences the behavior of the half-plane. Consequently this analysis adds the consideration of scattering-field into the analysis and the total motion field of the cavity is decomposed into the free-field and scattering-field motions. The free-field motion is obtained from the modification of the transmission and reflection coefficient method. The scattering-field motion is calculated is calculated by the indirect boundary value problem which has the ficticious boundaries and sources. In this study, P wave, SV wave, SH wave, and Rayleigh wave are analyzed respectively.

• Structural Engineering and Mechanics
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• 제53권2호
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• pp.277-296
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• 2015

The objective of this paper is to investigate the surface waves in fibre-reinforced anisotropic thermoelastic medium subjected to gravity field. The theory of generalized surface waves has firstly developed and then it has been employed to investigate particular cases of waves, viz., Stoneley waves, Rayleigh waves and Love waves. The analytical expressions for displacement components, force stress and temperature distribution are obtained in the physical domain by using the harmonic vibrations. The wave velocity equations have been obtained in different cases. The numerical results are given and presented graphically in Green-Lindsay and Lord-Shulman theory of thermoelasticity. Comparison was made with the results obtained in the presence and absence of gravity, anisotropy, relaxation times and parameters for fibrereinforced of the material medium. The results indicate that the effect of gravity, anisotropy, relaxation times and parameters for fibre-reinforced of the material medium are very pronounced.

• E2M - 전기 전자와 첨단 소재
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• 제6권2호
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• pp.109-114
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• 1993

본 논문에서는 0.05Pb(Sn$_{1}$2/Sb$_{1}$2/)-0.35PbTiO$_{3}$-0.60PbZrO $_{3}$+0.4[wt%] MnO$_{2}$ 조성을 갖는 3성분계 압전세라믹스에 Cr$_{2}$O$_{3}$ 의 첨가량을 변화시켜서 지연선을 제작하고 탄성표면파를 여기시켜 전파속도를 측정하였으며 EMMAS 기준에 따라 각 시편의 재료정수를 측정하고 이를 압전방정식에 적용하여 매질에 따라 여기되는 탄성표면파의 계산속도를 이론적으로 산출한 후 이를 지연선에서 측정된 실험속도와 비교하여 재료의 특성이 탄성표면파의 전파특성에 미치는 영향을 조사하였다. 그 결과 SAW 지연선에서 측정된 탄성표면파는 Generalized Rayleigh Wave였으며 재료의 특성이 우수한 시편일 수록 계산속도와 측정속도와의 차가 적었던 것으로 나타났고 오차한도는 평균 99.39[%]였으므로 실험속도 측정방법이 feed through 현상없이 우수한 측정방법이었음을 알 수 있었다.

• 한국전자파학회논문지
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• 제11권2호
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• pp.242-251
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• 2000

Ka 및 mm파 대역에서의 강우감쇠는 무선회선설계에 큰 영향을 미친다. 본 논문에서는 전반적인 기초가 되는 Mie 산란이론을 이용하여 국내환경에 적합한 강우감쇠를 추정하기 위해 중요한 요소인 빗방울 크기분포를 여러 자료를 비교하여 분석하였고. 일반화된 식을 통해 수치해석적 접근을 시도함으로써 각 파라미터별 강우감 쇠에 미치는 정도를 분석하여 이론적으로 국내 강우환경에서의 강우감쇠를 추정하기 위한 근거를 제공하고자 하였다.