• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.2
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• pp.232-240
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• 2013

This paper presents recent advances in damage visualization algorithms of laser generated ultrasonic propagation imaging(UPI) system. An effective damage evaluation method is required to extract correct information from raw data to properly characterize anomalies present in structure. A temporal-reference free imaging system provides easy and rapid defect inspection capability with less computational complexity. In this paper a number of methods such as ultrasonic wave propagation imaging(UWPI), anomalous wave propagation imaging(AWPI), ultrasonic spectral imaging(USI), wavelet ultrasonic propagation imaging(WUPI), variable time window amplitude mapping(VTWAM), time point adjustment(TPA), time of flight and amplitude mapping(ToF&Amp) and ultrasonic wavenumber imaging(UWI) are discussed with instances of successful implementation on various structures.

• Journal of Ocean Engineering and Technology
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• v.19 no.3
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• pp.11-17
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• 2005

The effect of frequency and amplitude of the OWC (Oscillating Water Column) motion on the nonlinear reaction forces in an air duct are studied experimentally. Experimental owe model is idealized as a simple circular cylinder with an orifice type air duct located at the middle oj the top rid. Reaction forces due to forced heave oscillation are measured and analyzed. By subtracting the effect of inertia forces and restoring forces, pneumatic damping force and added spring force are deduced. The effects of the frequency and amplitude of the heave motion are discussed. Also, the effects of solidity of the duct on the reaction forces are discussed.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.943-947
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• 2008

Dynamic response characteristics of a beam undergoing impulsive force are investigated using the wavelet transform method in this study. When an impulse is applied to an arbitrary position of a beam, it will generate a structural deformation wave. The characteristics of the wave are changing in the domain of time and space. The maximum amplitude of each natural frequency mode and the time to reach the maximum amplitude are obtained in this study. The effects of the location of impulse on the variations of the dynamic characteristics is also investigated.

• Water for future
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• v.13 no.4
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• pp.33-40
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• 1980

It has been very difficult to analyse, clearly, the mechanism of the suspended sediment that changes, largely, the coastline, on-shore and off-shore. It is due to not only the complexity of the factors in nature but the measurement technique of suspended sediment characteristics both in nature and loboratory. The purpose of this paper are to obtain the time-rate of change in the concentration of suspended sediment, the vertical distribution of it and the effect of the fall velocity of its particle, and to make clear the mechanism of sand transportation in suspension, analysing the diffusion equation, by the computer, due to the small amplitude wave theory.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.11a
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• pp.233-239
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• 1999

The feasibility of an ultrasonic technique using a pulse-echo method of normal-incident compressional waves was evaluated for its sensitivity to the worn surface and near surface damage due to wear. Worn surfaces were generated at various oscillation frequency under a given load and amplitude and these surface were in situ monitored using a ultrasonic wave detection system. Analysis of the ultrasonic waves received from the worn surface revealed a close relationship between the surface and near-surface damage and the maximum echo-amplitude of the compressional waves. The ultrasonic technique was successful in assessing the level of severity of the worn surface in real time during the wear process. It is also shown that the wear depth can be easily measured by the calculation of change of the specimen thickness based on the wave speed measured for the specimen medium.

• Korean Journal of Human Ecology
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• v.2 no.1
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• pp.110-113
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• 1999

Clothing shape is principally described in seven factors that are composed of clothing design, clothing material, clothing size, pattern design, sewing method and body motion etc. The aims of this study was to measurement out-line space-shape variation of clothing fitness with body by using the image processing. The subjects for direct anthropometric measurements were 248 female college students aged from 19 to 22. The data were statistically analyzed by principal analysis and cluster analysis. The results selected one somatotype. for the out-line space-shape variation of clothing fitness with body, there dimensional clothing shapes measured. and cross-sectional clothing shape obtained by the measurement was considered to be space wave form. The out-line space-shape variation of clothing fitness with body was observed between the node number and amplitudes of clothing wave form, and node number was determined at the maxim of space-shape amplitude, and the space-shape amplitudes have related with aspect ratio of cross-sectional shape. (Korean J of Human Ecology 2(1) :110-113, 1999)

• 한국해양학회지
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• v.17 no.2
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• pp.69-73
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• 1982

Wind wave generation is generally accompanied by a strong wind drift currint near the surface. The current can not be considered irrotational. The classical eqration gorerning free surface wave is formulated on the basis of irrptationality. To deal with the situation proterly, an equation governing free surface fluctuation of small amplitude is derived when the mean flow can not be assumed irrotational. The equation encompass the [lassical one as a limiting case as expected.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.10a
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• pp.413-420
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• 1998

In this study, an expert system is developed to evaluate a safety of tunnel structures. Using a dynamic finite element analysis module, this expert system predicts dynamic responses of a concrete lining surface which a transient force is applied on and estimates the condition between the concrete lining and surrounding ground. The evaluation parameter values of the module are multi-reflected wave frequency and amplitude of the dynamic responses. The multi-reflected wave frequency represents the depth of concrete lining, and the other parameter, the amplitude of the frequency, is utilized for detecting the internal flaws. A comparison of the dynamic responses between numerical and experimental model test verifies an effectiveness of this system. By this expert system, the safety of tunnel structures and the detection of internal flaws of concrete linings are estimated quantitatively.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.4
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• pp.38-44
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• 2004

The motion response analysis of a submerged elliptic cylinder in waves is presented and the elliptic cylinder is a simplification of the section of submarine in this paper. The method is based on boundary integral method and two-dimensional 3 degree motions are calculated in regular harmonic waves. The fully nonlinear free surface boundary condition is assumed in an numerical domain and this solution is matched along an assumed boundary as a linear solution composed of transient Green function, The large amplitude motions of an elliptic cylinder are directly simulated and effects of wave frequency, wave amplitude and the distance from buoyancy center to gravity center are discussed.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.11a
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• pp.212-219
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• 2004

The effect of frequency and amplitude of the OWC (Oscillating Water Column) motion on the nonlinear reaction forces in an air duct arc studied experimentally. Experimental OWC model is idealized as a simple circular cylinder with an orifice type air duct located at the middle of the top rid. Reaction forces due to forced heave oscillation are measured and analyzed. By subtracting the effect of inertia forces and restoring forces, pneumatic damping force and added spring force are deduced. The effects of the frequency and amplitude of the heave motion are discussed. Also, the effects of solidity of the duct on the reaction forces are discussed.