• Journal of Korea Water Resources Association
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• v.36 no.3 s.134
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• pp.413-422
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• 2003

Numerical analysis for the Bragg reflection due to sinusoidally varying seabeds tying on a sloping beach was performed by using a couple of ordinary differential equations derived from the Boussinesq equations. Incident waves were wane groups generated by two short waves with slightly different phases. Effects of the slope of a seabed to the reflection were investigated in detail. It is shown that the reflection of long waves enhanced by increasing the slope of a seabed. This phenomenon caused by increase of wave amplitude due to increase of nonlinearity and shoaling.

• Journal of Ocean Engineering and Technology
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• v.24 no.6
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• pp.34-40
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• 2010

Bragg reflection of nonlinear waves is simulated by a 2D fully nonlinear numerical wave tank (NWT). The developed NWT was based on the Boundary Element Method (BEM) with potential theory and the mixed Eulerian-Lagrangian (MEL) time marching scheme with Runge-Kutta 4th-order time integration. A spatial variation of wave elevations and their Fourier amplitudes of each component are compared to investigate the effect of sea bottom ripples and their relative heights. The incident waves over an undulated sea bottom are partially reflected and changed to partial standing waves due to Bragg reflection. The present results are verified with linear calculations and experimental data. It is found that the 1st-order wave component is mainly affected by Bragg reflection and its spatial modulation is significant in front of the bottom ripples.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.807-814
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• 2004

Land seismic reflection survey has been increasingly demanded in various civil engineering works because of its own ability to delineate layers, water table, to detect cavities or fracture zones, to estimate seismic velocities of each layer. However, our shallow subsurface structures are very complex. The relatively thin layer(mostly soil) to the wavelength directly followed by a basic rock with high impedance used to generate complicated surface waves, kind of channel waves with high amplitude that is dominate in entire seismograms and hence the useful reflection events will be almost hopelessly immersed in the undesired surface waves. Thus, it would seem that the use of traditional seismic survey could not be likely to provide in itself a satisfactory information about our exploration targets. This paper hence introduces an efficient measuring strategy illustrating a properly controlled arrangement of the vertical single force sources commonly used, yielding a very sharply elongated form of P-energy with a minimum of S radiation energy, what we call, P-beam source. Abundant experiments of physical modeling showed that in that way the surface waves could be enormously reduced and the reflection events would be additive and thus reinforced. Examples of field data are also illustrated. The contribution of P-beam source will be great in civil engineering area as well as in general geological exploration area.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.1
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• pp.29-37
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• 2007

In this study, transmission and reflection of multi-directional random waves propagating over impermeable submerged breakwaters are calculated by using eigenfunction expansion method. A series of mutiderectional random waves is generated by using the Bretschneider-Mitsuyasu frequency and Mitsuyasu type directional spectrum. Strong reflection is occurred at the Bragg reflection condition of the peak frequency. If the row of breakwaters is fixed at 3 and the relative height of breakwater is fixed at 0.6, more than 25% of incident wave energy is reflected to offshore. It is also found that the reflection of directionally spreading random waves increases as the maximum spreading parameter $s_{max}$ increases.

• Structural Engineering and Mechanics
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• v.78 no.1
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• pp.23-30
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• 2021

In this paper, we established the generalized thermoelasticity phenomenon in an isotropic elastic medium considering the electromagnetic field, rotation and two-temperature. Three theories of generalized thermoelasticity have been applied: Lord-Shulman (one relaxation time), Green-Lindsay (two relaxation times), as well as the coupled theory. We discussed some particular cases in the context of the wave propagation phenomenon in thermoelasticity. From solving the fundamental equations, we arrived that there are three waves: P-, T- and SV-waves that we calculated their velocities. The boundary conditions for mechanical stress and Maxwell's stress and thermal insulated or isothermal have been applied to determine the amplitudes ratios (reflection coefficients) for P-, T - and SV waves. Some utilitarian aspects are obtained from the reflection coefficients, presented graphically, and the new conclusions have been presented. Comparisons are made for the results predicted by different theories (CT, LS, GL) in the absence and presence of the electro-magnetic field, rotation, as well as two-temperature on the reflection of generalized thermoelastic waves. The results obtained concluded that the external parameters as the angle of incidence, electromagnetic field, rotation as well as the theories parameters have strong effect on the phenomenon.

• Structural Engineering and Mechanics
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• v.31 no.2
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• pp.117-135
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• 2009

The reflection and transmission of micropolar thermoelastic plane waves at the interface between an elastic solid and micropolar generalized thermoelastic solid is discussed. The interface boundary conditions obtained contain interface stiffness (normal stiffness and transverse stiffness). The expressions for the reflection and transmission coefficients which are the ratios of the amplitudes of reflected and transmitted waves to the amplitude of incident waves are obtained for normal force stiffness, transverse force stiffness and welded contact. Numerical calculations have been performed for amplitude ratios of various reflected and transmitted waves. The variations of amplitude ratios with angle of incident wave have been depicted graphically. It is found that the amplitude ratios of reflected and transmitted waves are affected by the stiffness, micropolarity and thermal distribution of the media.

• Journal of Ocean Engineering and Technology
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• v.15 no.1
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• pp.31-35
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• 2001

By applying the Boundary Integral Equation Method (BIEM) to obliquely incident for Rubble Mound Breakwater (RMB), wave reflection and transmission the coefficients are studied numerically. The validity of and the present BIEM is confirmed by comparing it with 1)numerical results of the eigenfunction expansion method of Dalrymple et al.(1991), and 2)numerical results of the BIEM of Kojima et al.(1988). Therefore, the characteristics of RMB for obliquely incident waves are investigated according to the variations of the wave period, equivalent linear nondimensional friction coefficient and direction of incident waves. It is revealed that the wave transformations of obliquely incident waves are different from those of normally incident waves.

• Earthquakes and Structures
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• v.8 no.6
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• pp.1299-1323
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• 2015

A model for reflection and refraction of magneto-thermoelastic SV-waves at the interface of two transversely isotropic and homogeneous solid half spaces under initial stress by applying classical dynamical theory of thermoelasticity is purposed. The reflection and refraction coefficients of SV-waves are obtained with ideal boundary conditions for SV-wave incident on the solid-solid interface. The effects of magnetic field, temperature and initial stress on the amplitude ratios after numerical computations are shown graphically with MATLAB software for the particular model.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.3
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• pp.189-194
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• 2001

The present study describes the Bragg reflection of monochromatic water waves propagating over a train of doubly-sinusoidally varying topographies. A numerical model based on the boundary element method is firstly verified by calculating reflection and transmission coefficients of waves over a trench. Calculated solutions are compared with those of the eigenfunction expansion method. The model is then used to simulated reflection of monochromatic water waves propagating over doubly-sinusoidally varying bottom topographies. Obtained reflection coefficients are compared with those of available laboratory measurements, those of the eigenfunction expansion method and the extended mild-slope equation. A reasonable agreement is shown.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.3
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• pp.292-301
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• 2008

A linearized model for hysteretic acoustic nonlinearity of imperfectly joined interface is proposed and analyzed by using Coulomb damping to investigate the characteristics of the reflection and transmission coefficients for harmonic waves at the contact interface. Closed crack is modeled as non welded interface that has nonlinear discontinuity condition in displacement across its boundary. Based on the hysteretic contact stiffness of the contact interface, the reflected and transmitted waves are determined by deriving the tractions on both sides of the interface in terms of the discontinuous displacements across the interface. It is found that the amplitudes of the reflected and transmitted waves are dependent on the frequency and the hysteretic stiffness. As the frequency of the incident wave increases, the higher reflection and lower transmission are obtained. It also shows that the hysteresis of the interface increases the reflection coefficient, but reduces the transmission coefficient. A fatigue crack is also made in aluminum specimen to demonstrate these characteristics of the reflection and transmission of contact interfaces.