• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.447-449
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• 2004

The purpose of this study is measured surface acoustic wave(SAW) characteristics to confirm utilization possibility as SAW sensor using new Pb(Mg$_{1}$3/Nb$_{2}$3/) $O_3$-PbTiO$_3$ (PMN-PT) piezoelectric substrate. We have tried to see if the material can be practically available as a new surface acoustic wave (SAW) biosensor to detect protein. The experimental results clarified that the frequency filtering of the central frequency of the PMN-PT substrate is a superior result to that of the LiTaO$_3$ (LT) substrate, but the result was not completely satisfactory. We know there is a problem in the design of inter-digital transducer (IDT) pattern. The waves transferred through the input terminal forms SAW which is sure to be transferred to the direction of the output terminal and the backward direction of the input terminal. This reflected wave is reiterated with SAW, which is transferred to the output direction, and so the frequency filtering gives a not good result. The electromechanical coupling coefficient of the PMN-PT substrate is excellent, and we can use it as a SAW sensor, in the near future, provided that there will be a new IDT design to increase the frequency filtering.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.5
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• pp.340-346
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• 1999

Minimum reflection and backward radiation methods on liquid/solid interrace were used to determine the velocity dispersion relation of acoustical surface wave for brass and aluminum substrates and copper/stainless steel nickel/brass, and nickel/aluminum layered substrates. Dispersion data agreed to dispersion characteristics of a generalized Lamb wave. The difference between velocities determined by two phenomena was closely related to the dispersion characteristics. This correspondence was explained by considering the generation mechanism of surface waves and the concept of group velocity.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.3
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• pp.219-231
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• 2009

Numerical simulations have been carried out for a 138K LNG Carrier (KLNG) model ship with free surface, using WAVIS 2.0 and Fluent 6.3.26 with various $y^+$ values and different grid densities. Level-set method for free surface capturing was adopted in WAVIS, while VOF has been used in Fluent. The calculated results were compared with the experiment data. Resistance coefficient, wave pattern, wave profile along the hull surface, axial velocity contours and transverse vectors had been analyzed. When the first $y^+$ value was fixed at 60, the simulation results from both WAVIS and Fluent were improved as the number of grids increased. The convergence time of WAVIS was much shorter than that of Fluent. Furthermore, WAVIS predicted the velocity field and the wave profile along the hull surface better than Fluent. However, Fluent gave better wave patterns.

• Journal of Ocean Engineering and Technology
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• v.24 no.1
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• pp.1-9
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• 2010

A series of experiments employing particle image velocimetry (PIV) technique was conducted to produce benchmark wave kinematics data for regular waves having four different wave slopes in 2-D wave tank. Water velocities and accelerations near the free surface of regular waves were computed from image pair obtained by PIV systems. With the measured wave velocity field, the wave accelerations were computed using a centered finite difference scheme. Both local and convective components of the total accelerations are obtained from experimental data. With increasing the wave slope, the horizontal velocity and the vertical accelerations near the wave crest obtained by PIV technique became larger than theoretical results, which are well-known phenomena of the wave nonlinearity. It is noted that the relative magnitude of convective acceleration to the local acceleration became larger with increasing wave slope.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.3
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• pp.205-211
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• 2005

In this study, a new numerical procedure for the generation of a nonlinear tailored group of waves is presented. The procedure is based on the transient wave group technique. In order to integrate the nonlinearity during the wave propagation in the computational method, the Navier-Stokes equations are applied as governing equations. The governing equations are discretized by finite volume approximation. The deformation of the free water surface in each time step is pursued with a moving grid. A two-dimensional, numerical wave tank for the simulation of the wave propagation is developed and tested in detail. The numeric results are compared first with analytical wave theories and with measurements, in order to examine the correctness of the numerical wave tank. Wave surface elevation and associated fields of velocity and pressure are numerically computed and compared with measurements. Very good agreements show up.

• Journal of the Korean Society for Marine Environment & Energy
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• v.5 no.1
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• pp.11-18
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• 2002

Directional breaking waves are generated by the component wave focusing both in direction and frequency based on constant wave steepness and constant wave amplitude spectrum models. The generated breaking waves are classified in the incipient, single and multi breaking waves. The characteristics of directional breaking waves are investigated in terms of surface profile parameters of wave crest steepness and asymmetry. The evolution of breaking wave characteristics is analyzed in a view of focusing efficiency. It shows that the front steepness and vertical asymmetry play an important role in breaking process, while the crest rear steepness and horizontal asymmetry are nearly constant during the process. The superposition of directional components greatly enhances the focusing efficiency and it suggests that characteristics of directional breaking waves may significantly different from uni-directional ones.

• Journal of Korea Multimedia Society
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• v.19 no.8
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• pp.1377-1385
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• 2016

Conventional X-band marine radar has been used as one of the effective tools for collecting and retrieving ocean surface information parameters for three decades. Several wave information extracting algorithms have been designed in such a way that they can be utilized for efficiently estimating sea surface wave parameters such as current velocities, wave direction, significant wave heights in VTS (Vessel Traffic Service). However, their performances are still restricted. For the purpose of overcoming the performance limits, in this paper, first the conventional algorithms are analyzed and their performances are compared, and then a new control algorithm is proposed. Furthermore, we try to improve the estimation performances of typical wave parameters including wave directions and significant wave heights by introducing linear regression model in the process of computing wave information extraction. Through several simulations with the X-band radar images, it is shown that the proposed method is very effective in estimating the wave information compared to the real measured buoy data.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2003.05a
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• pp.147-156
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• 2003

In order to improve navigational safety of ships, on ocean wave prediction model of high precision within a short time, dealing with multi-directional random waves from the information of the sea surface winds encountered at the planned ship's course, was introduced for construction of ocean wave forecasting system on the ship. In this paper, we investigated a sea disaster occurred by a stormy weather in the past. We analyzed the sea surface winds first and then carried out ocean wave hindercasting simulations according to the routes of the sunken vessel. From the result of this study, we concluded that the sea disaster was caused by rapidly developed low pressure system in Okhotsk Sea and the predicted values by the third generation wave prediction model(WAM) was agreed well with the observed significant wave height, was period, and directional wave spectrum. It gives a good applicability for construction of a practical on-board calculation system.

• Journal of the Korean Ceramic Society
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• v.40 no.9
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• pp.886-890
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• 2003

The etching characteristics of a LiNbO$_3$ single crystal have been investigated using helicon wave plasma source with bias power and the mixture of CF$_4$, HBr, SF$_{6}$ gas parameters. The etching rate of LiNbO$_3$ with etching parameters was evaluated by surface profiler. The etching surface was evaluated by Atomic Force Microscopy (AFM). The surface morphology of the etched LiNbO$_3$ changed with bias power and the mixture of CF$_4$/Ar/Cl$_2$, HBr/Ar/Cl$_2$, and SF$_{6}$/Ar/Cl$_2$ parameters. Optimum etching conditions, considering both the surface flatness and etch rate were determined.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4C
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• pp.239-245
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• 2008

In this study, a fundamental-level study was performed to establish knowledge-base for the development of optimal surface-wave method for urban areas with adjacent structures. First, theoretical modelling was performed to investigate the influence of adjacent structures on dispersion characteristics of surface waves. Later, the geotechnical sites with a concrete model of adjacent structure and a real subway box structure were tested by surface-wave method to investigate the influence of adjacent structures. The major influencing factors of adjacent structures on surface-wave propagation were direct distance between measurement array and adjacent structure, stiffness contrast between layers and type of seismic source.