• 비파괴검사학회지
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• 제33권3호
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• pp.257-263
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• 2013

Acoustic nonlinearity of surface waves is an effective method to evaluate the micro damage on the surface of materials. In this method, the $A_1$ (magnitude of the fundamental wave) and $A_2$ (magnitude of the second-order harmonic wave) are measured for evaluation of acoustic nonlinearity. However, if there is another source of second-order harmonic wave other than the material itself, the linear relationship between $A_1{^2}$ and $A_2$ will not be guaranteed. Therefore, the second-order harmonic generation by another source should be fully suppressed. In this paper, we investigated the initial second-order harmonic generation in narrowband surface waves by multi-line laser beams. The spatial profile of laser beam was considered in the cases of Gaussian and square-like. The temporal profile was assumed to be Gaussian. In case of Gaussian spatial profile, the generation of the initial second-order harmonic wave was inevitable. However, when the spatial profile was square-like, the generation of the initial second-order harmonic wave was able to be fully suppressed at specific duty ratio. These results mean that the multi-line laser beams of square-like profile with a proper duty ratio are useful to evaluate the acoustic nonlinearity of the generated surface waves.

• Journal of Electrical Engineering and Technology
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• 제10권4호
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• pp.1738-1745
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• 2015

Radiation characteristics of a probe-fed rectangular microstrip patch antenna printed on a finite grounded high permittivity substrate are investigated systematically for various square grounded dielectric substrate sizes with several thicknesses and dielectric constants by experiment and full wave simulation. The effect of the substrate size on the radiation characteristics of a rectangular patch antenna is mainly determined by the effective dielectric constant of surface waves on a grounded dielectric substrate. As the effective dielectric constant of surface waves increases, the substrate sizes for the maximum broadside gain and the required onset for a large magnitude of squint angle decrease, while the variations of the broadside gain, the front-to-back ratio, and the magnitude of squint angle versus the substrate size increase due to the increase of the power of the surface wave.

• 지구물리
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• 제4권1호
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• pp.47-55
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• 2001

한반도를 중심으로 32～44°N, 123～133°E 사이에서 발생한 지진 중 M_0와 함께 m_b 또는 M_s가 결정된 50개의 계기지진을 이용하여 실체파(m_b), 표면파(M_b), 또는 둘 다로부터 지진 모멘트(M_0)를 계산하는 환산식을 개발하였다. 진원깊이 70km 이상은 심발지진으로, 이하는 천발지진으로 분류하였으며, M_0의 단위는 dyne-cm이다. 표면파규모의 경우 심발지진이 천발지진보다 큰 지진모멘트를 갖는 것으로 나타났다. 심발지진과 천발지진 환산식에 수반된 표준편차는 모멘트 규모로 각각 0.25과 0.16이며 그 관계식은 각각 다음과 같다. (심발지진) (천발지진) 실체파규모의 경우 환산식은 진원깊이에 크게 영향을 받지 않는 것으로 나타났다. 환산식에 수반된 표준편차는 모멘트 규모로 0.28이며 그 관계식은 다음과 같다. 실체파와 표면파가 동시에 결정된 경우 새로운 규모 을 정의하여 별도의 환산식을 구했다. 천발지진만이 분석에 이용되었으며, 환산식에 수반된 표준편차는 모멘트 규모로 0.14이고 그 관계식은 다음과 같다. 이상의 분석결과는 한반도 및 인근 지역의 지진 크기를 하나의 지진규모, 즉 모멘트 규모로 통일하는데 이용될 수 있다.

• 대한조선학회지
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• 제17권1호
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• pp.31-37
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• 1980

Herein the flow past a submerged circular cylinder with a free surface is mapped onto a reference plane, in which the free surface is transformed to a straight line and the cylinder to a certain shape. A global mapping function between two planes is sought in a manner that linear free-surface elevation is generated in the physical plane. Hereby the Froude mumber $F_h$, based on the submergence depth h', is assumed to be of order 0(1) and the ratio a'/h'(a'=cylinder radius) of order o(1). Wave thus obtained are slightly different in magnitude and phase from usual linear solution. The resulting free wave starts advanced ahead compared to the classical result and its amount depends on Froude number. Based on the present concept wave forces are calculated. In this type of approach the body boundary condition gives more influence on wave resistance than that by the free surface in the speed range $F_h>1$.

• 비파괴검사학회지
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• 제26권4호
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• pp.239-245
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• 2006

이방성을 지닌 복합재료에서 측정한 군속도와 램파 방정식을 이용하여 계산한 군속도는 서로 일치하지 않는다. 이러한 차이는 이방성 재료에서 군속도 방향과 위상속도 방향이 서로 일치하지 않는 현상에서 기인된 것이다. 본 연구에서는 램파 분산방정식을 이용하여 이방성을 지닌 단일방향, 양방향, 준등방성 복합재료 판에서 $S_0$모드 위상속도곡선을 전파 방향 변화에 따라 구하고, 위상속도의 역수 값으로 구성되는 slowness surface를 이용하여 군속도의 방향과 크기를 결정하였다. 이와 같이 계산된 군속도는 측정한 군속도와 잘 일치함을 확인하였다.

• 한국해양공학회지
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• 제37권3호
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• pp.89-98
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• 2023

Analyzing the interactions of free surface waves caused by a submerged-body movement is important as a fundamental study of submerged-body motion. In this study, a two-dimensional mini-towing tank was used to tow an underwater body for analyzing the generation and propagation characteristics of free surface waves. The magnitude of the maximum wave height generated by the underwater body motion increased with the body velocity at shallow submerged depths but did not increase further when the generated wave steepness corresponded to a breaking wave condition. Long-period waves were generated in the forward direction as the body moved initially, and then short-period waves were measured when the body moved at a constant velocity. In numerical simulations based on potential flow, the fluid pressure changes caused by the submerged-body motion were implemented, and the maximum wave height was accurately predicted; however, the complex physical phenomena caused by fluid viscosity and wave breaking in the downstream direction were difficult to implement. This research provides a fundamental understanding of the changes in the free surface caused by a moving underwater body.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2002년도 추계 학술발표회 논문집
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• pp.3-10
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• 2002

The strong ground motion data recorded in the Sino-Korea Craton are analysed toobtain attenuation relations valid for 5 < M < 8, r < 400 km applicable to the Korean Peninsula. The result is logA : -1.83+0.386M- log${\gamma}$-0.0015${\gamma}$ where A is peak horizontal acceleration in g, M is surface-wave magnitude, and r is hypocentral distance in km. Our result is compared with the existing attenuation relations of Western North America and Eastern North America and the prior predictive equations for the Southern part of Korean Peninsula. Our result compares better with those of North America than those of the Southern part of the Korean Peninsula. More theoretical and empirical studies are required for better attenuation relations appropriate for the Korean Peninsula.

• 한국해양공학회지
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• 제24권1호
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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.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 C
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• pp.1862-1864
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• 2000

Recently diagnostic techniques have been investigated to detect a partial discharge(PD) associated with a dielectric material defect in a high-voltage electrical apparatus. Among the PD measuring method, detecting electromagnetic wave generated by PD is one of the most effective method because PD radiates wide frequency of electromagnetic wave up to UHF. From the above points of view, we have investigated the polarization and distance characteristics of electromagnetic wave radiated by an insertion of solid insulators between needle-plane electrodes in the air. According to the magnitude of applied voltage, the frequency spectrum of radiated electromagnetic waves were increased about under 100(MHz), compared with background noise. The electromagnetic wave magnitude is attenuated about 4$\sim$7.6[dB] at the point 3[m] away from PD.

• 한국광학회지
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• 제12권6호
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• pp.437-445
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• 2001

We examine theoretically the properties of the force on Mie particles induced by evanescent fields at a system of multilayer films (including a metal film), at which the surface plasmon resonance is excited by a p-polarized plane electromagnetic wave. An expression of the surface plasmon-coupled evanescent fields produced in Kretschmann (or Sarid) geometry is expanded in terms of vector spherical wave functions, while multiple reflections between the Mie particle and the metal boundary are taken into account. The Cartesian components of the force on Mie particles by the evanescent fields are analytically formulated and numerically evaluated. The force components are increased by one or two orders of magnitude at metal boundaries over those at dielectric boundaries. As a result, we can confirm the possibility of stable manipulation or rotation of a finite-sized object by forces of surface plasmon-coupled evanescent fields.