• Journal of Korea Water Resources Association
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• v.34 no.6
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• pp.651-657
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• 2001

The second-order long waves generated by short wave groups propagating over a step are theoretically investigated. The diffraction of short waves is firstly formulated and the governing equations of second-order long waves are then derived by using a multiple-scale perturbation method. It is observed that free and locked long waves are generated and propagated with different velocities.

• The Journal of the Acoustical Society of Korea
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• v.15 no.1E
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• pp.70-76
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• 1996

We proposed to use shear waves instead of longitudinal waves in a STAM (scanning tomographic acoustic microscope system) in which the specimens are solid. For any specimen with a shear modulus, mode conversion will take place at the water-solid interface. Some of the energy of the insonifying longitudinal waves in the water will convert to shear wave energy within the specimen. The shear wave energy is detectable and can be used for tomographic reconstruction. The resolution limitation of STAM depends on the available angular view and the acoustic wavelength. While wave transmission in most solid specimens is limited to about 20°for longitudinal waves, we show that it is about twice that high for shear waves. Since the wavelength of the shear wave is shorter than that of the longitudinal wave, we are able to achieve the high resolution. In order to compare the operation of a shear-wave STAM with that of the conventional longitudinal-wave STAM we have simulated tomographic reconstruction for each. Our simulation results with aluminum specimen and back-and-forth propagation algorithm showed resolution of a shear-wave STAM is better than that of a longitudinal-wave STAM.

• Journal of Mechanical Science and Technology
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• v.20 no.11
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• pp.1950-1960
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• 2006

Based on Banach fixed point theorem, a method to calculate nonlinear superposition for three interacting Stokes' waves is proposed in this paper. A mathematical formulation for the nonlinear superposition in deep water and some numerical solutions were investigated. The authors carried out the numerical study with three progressive linear potentials of different wave numbers and succeeded in solving the nonlinear wave profiles of their three wave-interaction, that is, using only linear wave potentials, it was possible to realize the corresponding nonlinear interacting wave profiles through iteration of the method. The stability of the method for the three interacting Stokes' waves was analyzed. The calculation results, together with Fourier transform, revealed that the iteration made it possible to predict higher-order nonlinear frequencies for three Stokes' waves' interaction. The proposed method has a very fast convergence rate.

• The Journal of the Acoustical Society of Korea
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• v.22 no.4
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• pp.250-260
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• 2003

Since a bubble in water is a highly nonlinear acoustic scatterer, the acoustic scattered waves from underwater bubbles show highly nonlinear acoustic properties. These acoustic scattered waves can be observed at the second or higher harmonics as well as at the fundamental primary frequency of incident acoustic wave. When two primary acoustic waves of different frequencies are incident on a bubble, the acoustic scattered waves can be also observed at the sum and the difference frequencies of the primary waves. In this study, when the two primary acoustic waves were incident on a bubble screen in water, we observed that the amplitude of difference frequency wave was amplified by the bubble nonlinearity and its directivity was oriented in the propagation directions of primary waves. The directivity of scattered difference frequency wave was analyzed as a coherent scattering for virtual source by using the directivity of the primary acoustic wave.

• Journal of Korea Water Resources Association
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• v.37 no.9
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• pp.729-736
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• 2004

Analysis of reflection of random waves propagating over rectangular submerged non-porous breakwaters was performed by using the eigenfunction expansion method. In this study, random waves were generated by superposition of several monochromatioc waves. Reflection coefficients were calculated by summing each numerical results of regular waves. Predicted results from the eigenfunction expansion method were in a good agreement with the results of laboratory measurements. Reflection coefficients of random waves were also resonated at the Bragg reflection condition.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.5
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• pp.292-302
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• 2016

In this study, shallow-water design waves are estimated for various return periods based on statistical analysis of extreme waves observed 13 years at four stations on the Korean east coast (Sokcho, Mukho, Hupo, Jinha). These values are compared with the results from SWAN simulation by using the deep water design waves conventionally used in Korea (KORDI, 2005). It was found that the simulated values of the shallow-water design waves are comparatively smaller than the values from the extreme value analysis, expecially below 30 years frequency, which implies possible under-estimation of the deep-water design waves on the Korean east coast.

• Ocean Systems Engineering
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• v.3 no.4
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• pp.309-325
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• 2013

Ocean Thermal Energy Conversion (OTEC) systems utilize the temperature difference between the surface water and deep ocean water to generate electrical energy. In addition to ocean surface waves, wind and current, in certain locations like the Andaman Sea, Sulu Sea and the South China Sea the presence of strong internal waves may become a concern in floating OTEC system design. The current paper focuses on studying the dependence of the CWP hydrodynamic drag on relative velocity of the flow around the pipe, the effect of drag amplification due to vortex induced vibrations and the influence of internal waves on the floating semi and the cold water pipe integrated OTEC system. Two CWP sizes are modeled; the 4m diameter pipe represents a small scale prototype and the 10m diameter pipe represents a full commercial size CWP. are considered in the study.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.470-475
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• 2012

The downstream piping system of the water supply system in a supercritical power plant is affected by the fluctuation pressure waves induced by accessing to the acoustic modes of the piping systems with the rotation and impeller passing pulsations of the feed water pump. There are the phenomena amplified at the same time in the range of 415 ~ 455Hz, 830 ~ 910Hz, 1245 ~ 1365Hz and 1660 ~ 1820Hz on the spectrums of the vibration, the sound pressure, and the pressure fluctuation waves.

• Water for future
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• v.7 no.1
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• pp.55-64
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• 1974

The knowledge of the waves passing through the breakwater makes an important role in the efficient breakwater design. Wave diffraction is an important factor in this role, but some usable development about it have not been made in our country as yet. The diffraction of sea-water waves round the end of a semi-infinite impermeable breakwater has been investigated, applying a solution of the water wave diffraction problems given by Penney & Price. The wave pattern and heights on both the leewardside and the windward-side of the breakwater have been calculated and summarized in the form of diagrams with diffraction factors between $r/{\lambda}=0~50$. This involves some extension of the diffraction diagrams made previously. The theory and computation methods with computer program in fortran IV developed in this study make an efficient use for estimating the diffraction effects at a semi-infinite breakwater.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.12 no.1
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• pp.39-52
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• 2000

The triad interactions have been known to be important only for shoaling waves or finite depth wind waves. In deep water, they are insignificant compared with the quadruplet interactions in respect to the evolution of wind waves due to energy transfer among the wave components. However, the triad interactions may be important even for deep water waves because they may closely be related to the wave steepness, which definitely affects wave breaking, drag of air flow over t.'Ie sea, or navigation of ships, especially during the early stage of the development of wind waves. This study reports a series of laboratory experiments, whose data are subjected to bispectral analyses to investigate the triad interactions of deep-water wind waves. It is found that the bicoherence at the spectral peak frequency and the wave steepness are almost directly proportional, indicating that the steep waves with peaked crests and flat troughs are resulted from the triad interactions. Both bicoherence and wave steepness increase with the wave age during the early stage of wave generation and then drop off as the waves grow old. It seems that the energy of the secondary spectral peak developed by the triad interactions during the early stage of wave generation is redistributed to the neighboring frequencies by the quadruplet interactions during the later stage.