• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.727-732
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• 2014

The goal is to find the position of the sound source with the TRM at reflections and refractions environment. The Fermat's principle applied to the ray tracing method are expected to follow the acoustic path in order to obtain acoustic distance and transmittance to. Utilizing them in the TRM was confirmed rear reflectance affect on estimated position, resolution and side lobe. And the TRM performance were superior to one of the beam forming techniques.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.736-738
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• 2014

The paper deals with the accuracy comparison between two kinds of ultrasonic paths for flow rate measurement. In the Z-path, two transducers are installed on the opposite side of each other on a pipe, and the ultrasonic waves generated of one transducer propagate and arrive at the other one only through refraction. In the V-path, two transducers are installed on one side of a pipe, and the ultrasonic waves reflected at the inner wall of the pipe are received. The backgrounds were established to select one path to fit the usage by considering the advantages and disadvantages.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.2
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• pp.124-132
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• 2015

The paper deals with the energy transmission of the elastic waves obliquely transmitting and refracting through a plate and a pipe. By calculating the transmitting ratio depending on the incidence angle, the angle corresponding to the maximum transmission was determined theoretically and considered in the design of ultrasonic transducers for flow velocimetry. Experiments were carried out by using prototypes of the transducers. Experimentally-obtained transmission ratios were compared with and confirmed the theoretically-calculated results.

• Water Engineering Research
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• v.1 no.3
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• pp.187-197
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• 2000

This paper describes an adaptive quadtree-based 2DH wave-current interaction model which is able to predict wave breaking, shoaling, refraction, diffraction, wave-current interaction, set-up and set-down, mixing processes (turbulent diffusion), bottom frictional effects, and movement of the land-water interface at the shoreline. The wave period-and depth-averaged governing equations are discretised explictly by means of an Adams-Bashforth second-order finite difference technaique on adaptive hierarchical staggered quadtree grids. Grid adaptation is achieved through seeding points distributed according to flow criteria(e.g. local current gradients). Results are presented for nearshore circulation at a sinusoidal beach. Enrichment permits refined modelling of important localised flow features.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.1 no.1
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• pp.1-7
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• 1989

Theoretical studies have been made to analyze combined refraction diffraction of the wind waves propagating on a large scale current in water of varying depth. The governing equation for monochromatic waves was derived through splitting a mild slope equation into two equations. A numerical model is developed using finite difference scheme which is computationally very efficient for modelling large area. Numerical examples concerning the interactions between waves and rip currents over a gentle slope are presented, in which the current effects on the wave diffraction in the caustic region are closely examined.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.1 no.1
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• pp.50-62
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• 1989

Shoreline change of Haeundae beach was predicted by one-line model considering interaction of seawalls and longshore variation of wave height . Wave deformation was calculated by combined wave refraction-diffraction model . In this shoreline change model, empirical constants and offshore sediment transport rate are treated as calibration parameters, and the calculated results are in good agreement with the observed data.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.792-795
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• 1988

Titanium dioxide antireflection (AR) Coating, which is deposited on Si substrates using an organotitanium solution by the spinning technique, has been studied. The coated films on Si substrates were subsequently heated to $450^{\circ}C$. The thickness and index of refraction of films were varied continuousely from $740{\AA}$ to $1380{\AA}$ and from 1.7 to 2.1 respectively as a function of heat treatment temperature and time. Silicon solar cells AR-coated by the spinning technique showed as much as 31% improvement in conversion efficiency over the uncoated cell.

• Proceedings of the KIEE Conference
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• 2001.11b
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• pp.101-105
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• 2001

Due to their elastic anisotropy, ultrasonic testing of austenitic welds, frequently used in nuclear power plants, is much more difficult than that of isotropic elements. For accurate testing of austenitic welds, ultrasonic wave phenomena therein must be full understood. This study uses an accurate and effective numerical model, the mass-spring lattice model, for such phenomena. By comparing the numerical results with the corresponding analytical results, it is shown that the model is capable of accurately predicting the generation, reflection, refraction, and scattering phenomena of ultrasonic waves in anisotropic austenite welds. Therefore, the mass-spring lattice model will provide a very useful tool for simulating ultrasonic testing of austenitic welds, and thus will contribute to the enhancement of reliability of such ultrasonic testing.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2057-2059
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• 1999

This paper describes the phenomena of the refraction and reflection when the ultrasonic signals generated by PD(Partial Discharge) in a transformer propagate through the boundary between insulating oil and the tank of the transformer. In this paper, considering the characteristic of the ultrasonic signal and the velocity of the propagation in medium, propagation time from PD source to sensor for incidence angle was calculated. As a result, it was found that the shortest time at specific angle exists. Taking into account the velocity of the propagation in medium, the shortest time with a computer was simulated. It was shown that the simulation was same as experimental result at a real PD source in the transformer.

• Korean Journal of Optics and Photonics
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• v.25 no.1
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• pp.14-20
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• 2014

The equivalent of a thick lens is a lens which has the same power of refraction and paraxial imaging characteristics for a reference ray, but with a different axial thickness. In this study, thick lenses of an optical system were converted to their equivalent lenses referenced to pupil imaging. Aberration changes due to the lens conversion were compared to the general equivalent lens conversion referenced to object imaging.