• Journal of Korean Port Research
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• v.8 no.1
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• pp.41-47
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• 1994

The present paper discusses the nonlinear wave deformation due to a submerged coastal structure. Theory is based on the frequency-domain method using the third order perturbation and boundary integral method. Theoretical development to the second order perturbation and boundary integral method. Theoretical development to the second order Stokes wave for a bottom-seated submerged breakwater to the sea floor is newly expanded to the third order for a submerged coastal structure shown in Figure 1. Validity is demonstrated by comparing numerical results with the experimental ones of a rectangular air chamber structure, which has the same dimensions as that of this study. Nonlinear waves become larger and larger with wave propagation above the crown of the structure, and are transmitted to the onshore side of the structure. These characteristics are shown greatly as the increment of Ursell number on the structure. The total water profile depends largely on the phase lag among the first, second and third order component waves.

• Journal of the Korean earth science society
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• v.22 no.3
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• pp.179-185
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• 2001

Borehole tests are commonly used as a tool to obtain the physical properties of soils and rocks. The results of borehole tests are, however, discontinuous. Interpolation methods are applied to interpret the data gap between the borehole test points. The interpolation is valid only if the horizontal variations of the ground between the test points are small enough to ignore. A surface wave inversion method was used to study the S wave velocity of the very soft soil to provide the continuous 2 dimensional S wave velocity structure. The resolution of the S wave velocity structure was used to interpret the inversion results.

• Geophysics and Geophysical Exploration
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• v.9 no.1
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• pp.108-113
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• 2006

Urban conditions, such as existing underground facilities and ambient noise due to cultural activity, restrict the general application of conventional geophysical techniques. At a tunnelling site in an urban area along an existing railroad, we used the refraction microtremor (REMI) technique (Louie, 2001) as an alternative way to get geotechnical information. The REMI method uses ambient noise recorded by standard refraction equipment and a linear geophone array to derive a shear-wave velocity profile. In the inversion procedure, the Rayleigh wave dispersion curve is picked from a wavefield transformation, and iteratively modelled to get the S-wave velocity structure. The REMI survey was carried out along the line of the planned railway tunnel. At this site vibrations from trains and cars provided strong seismic sources that allowed REMI to be very effective. The objective of the survey was to evaluate the rock mass rating (RMR), using shear-wave velocity information from REMI. First, the relation between uniaxial compressive strength, which is a component of the RMR, and shear-wave velocity from laboratory tests was studied to learn whether shear-wave velocity and RMR are closely related. Then Suspension PS (SPS) logging was performed in selected boreholes along the profile, in order to draw out the quantitative relation between the shear-wave velocity from SPS logging and the RMR determined from inspection of core from the same boreholes. In these tests, shear-wave velocity showed fairly good correlation with RMR. A good relation between shear-wave velocity from REMI and RMR could be obtained, so it is possible to estimate the RMR of the entire profile for use in design of the underground tunnel.

• Ocean Systems Engineering
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• v.6 no.1
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• pp.23-60
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• 2016

The major objective of this study was to develop further understanding of 3D nearshore hydrodynamics under a variety of wave and tidal forcing conditions. The main tool used was a comprehensive 3D numerical model - combining the flow module of Delft3D with the WAVE solver of XBeach - of nearshore hydro- and morphodynamics that can simulate flow, sediment transport, and morphological evolution. Surf-swash zone hydrodynamics were modeled using the 3D Navier-Stokes equations, combined with various turbulence models (${\kappa}-{\varepsilon}$, ${\kappa}-L$, ATM and H-LES). Sediment transport and resulting foreshore profile changes were approximated using different sediment transport relations that consider both bed- and suspended-load transport of non-cohesive sediments. The numerical set-up was tested against field data, with good agreement found. Different numerical experiments under a range of bed characteristics and incident wave and tidal conditions were run to test the model's capability to reproduce 3D flow, wave propagation, sediment transport and morphodynamics in the nearshore at the field scale. The results were interpreted according to existing understanding of surf and swash zone processes. Our numerical experiments confirm that the angle between the crest line of the approaching wave and the shoreline defines the direction and strength of the longshore current, while the longshore current velocity varies across the nearshore zone. The model simulates the undertow, hydraulic cell and rip-current patterns generated by radiation stresses and longshore variability in wave heights. Numerical results show that a non-uniform seabed is crucial for generation of rip currents in the nearshore (when bed slope is uniform, rips are not generated). Increasing the wave height increases the peaks of eddy viscosity and TKE (turbulent kinetic energy), while increasing the tidal amplitude reduces these peaks. Wave and tide interaction has most striking effects on the foreshore profile with the formation of the intertidal bar. High values of eddy viscosity, TKE and wave set-up are spread offshore for coarser grain sizes. Beach profile steepness modifies the nearshore circulation pattern, significantly enhancing the vertical component of the flow. The local recirculation within the longshore current in the inshore region causes a transient offshore shift and strengthening of the longshore current. Overall, the analysis shows that, with reasonable hypotheses, it is possible to simulate the nearshore hydrodynamics subjected to oceanic forcing, consistent with existing understanding of this area. Part II of this work presents 3D nearshore morphodynamics induced by the tides and waves.

• Publications of The Korean Astronomical Society
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• v.10 no.1
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• pp.15-30
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• 1995

It has been recognized that the morphologies of the SNRs from the radio observation are "barrel shaped". To interpret the mechanism of the radiation and the physical state of the environments, we have analytically calculated the dynamical structure of the interacting region in the case where the ejectum has a steep power-law density profile($\rho{\sim}r^{-n}$) and the ambient medium has a shallow power-law density profile($\rho{\sim}r^{-s}$), assuming that the cosmic rays are isotropically accelerated in the shock wave and the magnetic fields are very weak. The calculated synchrotron radio maps show that the emission from the equator is intense and the emissions from the central and polar regions are less intense. Also the thicknesses of the shell are strongly dependent on s and weakly on n. The azimuthal intensity ratio $\alpha$ increases as the efficiency of the cosmic ray acceleration increases and s decreases. We compared the results with the morphology of the SNR A. D. 1006(type I SNR). It does agree with the case of s = 0, w = 0.3 - 0.5. This value for w is consistent with the results by Eichler(1979). It provides us the evidence of the cosmic ray acceleration in the shock wave.

• Journal of Ocean Engineering and Technology
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• v.19 no.2 s.63
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• pp.29-33
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• 2005

The accuracy of predicting wave transformation in the nearshore is very important to wave hydrodynamics, sediment transport, and design of coastal structures. Numerical experiments are conducted to identify the shoaling and breaking characteristics of a fully nonlinear Boussinesq equation-based model. Simulated shoaling showed good agreement with the Shouto's formula, and the results of the breaking experiment agreed well with experimented data, over several beach profile.

• Journal of applied mathematics & informatics
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• v.42 no.1
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• pp.105-121
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• 2024

We consider incompressible, inviscid, stratified shear flows in β plane. First, we obtained an unbounded instability region intersect with semi-ellipse region. Second, we obtained a bounded instability regions depending on Coriolis, stratification parameters and basic velocity profile. Third, we obtained a criterion for wave stability. This has been illustrated with standard examples. Also, we obtained upper bound for growth rate.

• Journal of Industrial Technology
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• v.16
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• pp.83-95
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• 1996

The equilibrium beach profiles with the effects of random waves and nonuniform grain size in the surf zone are derived from the Thornton and Guza(1983)'s energy dissipation model. The derived beach profiles are the functions of the breaking wave strength, the frequency of the incident wave, and the wave induced-energy dissipation at breaking point. It is not confirmed that the equilibrium beach profiles are better agreement with the measured profiles than the classical profiles. However, the characteristic of the changes of the beach profiles with respect to the breaking wave stgrngth and the frequency of the incident wave can be analyzed which has not been studied by the classical model.

• Geomechanics and Engineering
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• v.13 no.5
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• pp.775-791
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• 2017

Surface wave techniques are widely used as non-invasive method for geotechnical site characterization. Field surface wave data are collected and analyzed using different processing techniques to generate the dispersion curves, which are further used to extract the shear wave velocity profile by inverse problem solution. Characteristics of a dispersion curve depend on the subsurface layering information of a vertically heterogeneous medium. Sometimes soft layer can be found between two stiff layers in the vertically heterogeneous media, and it can affect the wave propagation dramatically. Now most of the surface wave techniques use the fundamental mode Rayleigh wave propagation during the inversion, but this may not be the actual scenario when a soft layer is present in a vertically layered medium. This paper presents a detailed and comprehensive study using finite element method to examine the effect of soft layers which sometimes get trapped between two high velocity layers. Determination of the presence of a soft layer is quite important for proper mechanical characterization of a soil deposit. Present analysis shows that the thickness and position of the trapped soft layer highly influence the dispersion of Rayleigh waves while the higher modes also contribute in the resulting wave propagation.

• Nuclear Engineering and Technology
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• v.40 no.6
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• pp.477-488
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• 2008

The objective of the paper is to analyze the thermally induced density wave oscillations in water cooled boiling water reactors. A transient thermal hydraulic model is developed with a characteristics-based implicit finite-difference scheme to solve the nonlinear mass, momentum and energy conservation equations in a time-domain. A two-phase flow was simulated with a one-dimensional homogeneous equilibrium model. The model treats the boundary conditions naturally and takes into account the compressibility effect of the two-phase flow. The axial variation of the heat flux profile can also be handled with the model. Unlike the method of characteristics analysis, the present numerical model is computationally inexpensive in terms of time and works in a Eulerian coordinate system without the loss of accuracy. The model was validated against available benchmarks. The model was extended for the purpose of studying the flow-induced density wave oscillations in forced circulation and natural circulation boiling water reactors. Various parametric studies were undertaken to evaluate the model's performance under different operating conditions. Marginal stability boundaries were drawn for type-I and type-II instabilities in a dimensionless parameter space. The significance of adiabatic riser sections in different boiling reactors was analyzed in detail. The effect of the axial heat flux profile was also investigated for different boiling reactors.