• 한국가시화정보학회:학술대회논문집
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• 2004.11a
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• pp.76-79
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• 2004

Dynamic oscillation motion of a pendant drop has been Investigated experimentally when acoustic wave is applied. This problem is of particular interest in the understanding of transport phenomena, accompanied by liquid drop. In this experiment, pendant drop was made to oscillate by inducing the acoustic wave and the subsequent drop motion was recorded by a high-speed camera. The results obtained indicate that liquid drop hanging on the flat surface has resonant frequencies on each shape oscillation modes. It is also found that exists the swing mode of oscillation on the pendant drop.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.193-196
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• 2002

The relativistic theory has not been properly taken up by the marine hydrodynamicists. To take on a relativistic view, we confine ourselves to a simple vector case of a wave train in spacetime, to be shown to represent a sound wave or a surface wave, and bring in an observer who is travelling on another platform. We are interested in relative position of each event on these two worldlines. It, then, will be shown that the velocity, the acceleration, the encounter frequency, the group velocity, and the time and the space distance between the wave and the observer on the worldlines should all be derivable in principle. This is interpreted to mean that we really have the relativistic events taking place with different values of time dilation in the sense of 'spacetime', and that the well-known ${\lceil}special Theory of Relativity{\rfloor}$ applies just as well in hydrodynamic waves.

• Laser Solutions
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• v.6 no.2
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• pp.27-33
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• 2003

A laser shock cleaning technology is a new dry cleaning methodology for the effective removal of small particles from the surface. This technique uses a plasma shock wave produced by a breakdown of air due to an intense laser pulse. In order to optimize the laser shock cleaning process, it needs to evaluate the cleaning performance quantitatively by using a monitoring technique. In this paper, an acoustic monitoring technique was attempted to investigate the laser shock cleaning process with an aim to optimize the cleaning process. A wide-band microphone with high sensitivity was utilized to detect acoustic signals during the cleaning process. It was found that the intensity of the shock wave was strongly dependent on the power density of laser beam and the gas species at the laser beam focus. As a power density was larger, the shock wave became stronger. It was also seen that the shock wave became stronger in the case of Ar gas compared with air and N$_2$ gas.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1993.10a
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• pp.193-198
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• 1993

This paper presents a systematic procedure to obtain shape functions of the infinite elements for soil-structure interaction analysis. The function spaces are derived from the analytical solutions and appropriate assumptions based on physical interpretation. The function spaces are complete for the surface wave components, but approximate for the body wave components. Three different infinite elements are developed by using the wave functions of the derived function spaces. Numerical example analysis is presented for demonstrating the effectiveness of the present infinite elements.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.6
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• pp.90-96
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• 2009

Ultrasonic method using SH(shear horizontal) wave has been developed to determine the surface damage in fatigued material. Fatigue damages based on propagation energy were analyzed by multi-regression analysis in interrupted fatigue test specimen including CrMoV and 12Cr alloy steel. From the test results, as the fatigue damage increased the propagation time of the launched waves increased and amplitude of wavelet decreased. Also, analysis for the waveform modulation showed a reliable estimation, with confidence limit of 97% for 12Cr steel and 95% for CrMoV steel, respectively. Therefore, It is thought that SH ultrasonic wave technique can be applied to determine fatigue damage of in-service component nondestructively.

• Journal of Ocean Engineering and Technology
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• v.31 no.1
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• pp.1-7
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• 2017

There are two wave modes induced by an oscillating body on the free surface of a two-layer fluid: the barotropic and baroclinic modes. To investigate the generated waves composed of two modes, a radiation problem involving a heaving rectangular body was solved in a numerical wave tank. A new artificial damping zone scheme was developed and applied in the frequency-domain analysis. The performance of this damping scheme was compared with given radiation boundary conditions for various conditions. The added mass and radiation damping coefficients for the heaving rectangular body were also calculated for various fluid-density ratios.

• Journal of Advanced Research in Ocean Engineering
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• v.4 no.3
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• pp.135-145
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• 2018

This paper deals with the added resistance of a ship in waves using computational fluid dynamics (CFD). The ship added resistance is one of the key considerations in the design of energy-efficient ship. In this study, the added resistance of a LNG carrier in head waves is computed using a CFD code to consider the nonlinearity and the viscous effects. The unsteady Reynolds Averaged Navier-Stokes equation (RANS) is numerically solved and the volume of fluid (VOF) approach is used to simulate the free surface flows. The length of incident wave varies from half the ship length to twice the ship length. To investigate the nonlinearity effect, both the linear wave condition and the nonlinear wave condition are considered. The heave and pitch motions are calculated along with the added resistance, and the wave contours are obtained. Grid convergence test is conducted thoroughly to achieve the converged motion and resistance values. The calculated results are compared and validated with experimental data.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.20 no.4
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• pp.370-378
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• 1987

Wave reflection control functions of mound for the foundation of composite and perforated break-waters were investigated through the theoretical considerations. The theory developed is based on a simple summation of components of reflected waves. The applicability of the theory is assured by the comparative studies of the theoretical calculation and experimental data on the sea surface elevation in front of a breakwater. It is found that the reflection is mainly controlled by depth and width of the mound. In the design of composite type perforated breakwaters, the width of perforated part of the upright section can be decreased to less than half of the conventional design width for the same reflection by using the reflection control function of mound part and the reflection can be reduced until less than $30\%$ of that in the composite breakwaters. Using the results, a design method of mounds is proposed, by which the reduction of wave reflection is assured under the given wave conditions.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.32 no.3
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• pp.286-293
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• 1996

This paper established the analytical model of sea surface oscilation of simple type fishing port with vertical wave absorbor. This model is composed by MAEM(Matched Asymptotic Expansion Method) for wave amplification in fishing port and EEM(Eigen - function Expansion Method) for wave absorbing characteristics against vertical perforated plates. Dimensionless porosity by adopting Darcy's law was introduced to evaluate wave absorbing characteristics of the perforated structure. Using the model, the efficiency of the vertical perforated plates was studied for fishing port tranqulity with number of plates, array method and plate intervals. Optimal design and arrangement of perforated plates can be applied to develop multipurpose fishing ports and villages.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1997.04a
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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.