• Journal of Ship and Ocean Technology
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• 제7권2호
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• pp.20-28
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• 2003

A table of annual sea state occurrences is prepared based on the significant wave heights and modal periods, two parameters representing a Bretschneider wave spectrum. Measurements of them were done by the Korean Ocean Research and Development Institute (KORDI) at 67points around the Korean peninsula for 22 years. Also the average values of parameters over 4 regions and 4 seasons were derived. Comparative seakeeping calculations using wave parameters prevalent around Korea and those of the North Pacific at sea state numbers 3, 4, and 5 respectively, show some differences in the assessed seakeeping performance.

• 한국지진공학회논문집
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• 제18권3호
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• pp.151-160
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• 2014

Probabilistic tsunami hazard analysis (PTHA) is based on the approach of probabilistic seismic hazard analysis (PSHA) which is performed using various seismotectonic models and ground-motion prediction equations. The major difference between PTHA and PSHA is that PTHA requires the wave parameters of tsunami. The wave parameters can be estimated from tsunami propagation analysis. Therefore, a tsunami simulation analysis was conducted for the purpose of evaluating the wave parameters required for the PTHA of Uljin nuclear power plant (NPP) site. The tsunamigenic fault sources in the western part of Japan were chosen for the analysis. The wave heights for 80 rupture scenarios were numerically simulated. The synthetic tsunami waveforms were obtained around the Uljin NPP site. The results show that the wave heights are closely related with the location of the fault sources and the associated potential earthquake magnitudes. These wave parameters can be used as input data for the future PTHA study of the Uljin NPP site.

• The Journal of the Acoustical Society of Korea
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• 제18권2E호
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• pp.18-23
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• 1999

This paper proposes a method of separately determining three intrinsic mechanical parameters of an unknown object in the framework of ultrasound inverse scattering tomography. Those parameters are the speed of sound, density, and absorption whose values are given as the solution of an inhomogeneous Helmholtz wave equation. The separate reconstruction method is mathematically formulated, the integral equations are discretized using the sinc basis functions, and the Newton-Raphson method is adopted as a numerical solver in a measurement configuration where the object is insonified by an incident plane wave over 360˚ and the scattered field is measured by detectors arranged in a rectangular fashion around it. Two distinct frequencies are used to separate each parameter of three Gaussian objects that are either located at the same position or separately from each other. Computer simulation results show that the separate reconstruction method is able to separately reconstruct the three mechanical parameters. The absorption parameter turns out to be a little difficult to reconstruct as compared with the other two parameters.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권1호
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• pp.77-99
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• 2017

Offshore oscillating water columns (OWC) represent one of the most promising forms of wave energy converters. The hydrodynamic performance of such converters heavily depends on their interactions with ocean waves; therefore, understanding these interactions is essential. In this paper, a fully nonlinear 2D computational fluid dynamics (CFD) model based on RANS equations and VOF surface capturing scheme is implemented to carry out wave energy balance analyses for an offshore OWC. The numerical model is well validated against published physical measurements including; chamber differential air pressure, chamber water level oscillation and vertical velocity, overall wave energy extraction efficiency, reflected and transmitted waves, velocity and vorticity fields (PIV measurements). Following the successful validation work, an extensive campaign of numerical tests is performed to quantify the relevance of three design parameters, namely incoming wavelength, wave height and turbine damping to the device hydrodynamic performance and wave energy conversion process. All of the three investigated parameters show important effects on the wave-pneumatic energy conversion chain. In addition, the flow field around the chamber's front wall indicates areas of energy losses by stronger vortices generation than the rear wall.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.799-809
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• 2020

In this study, the supercavitating flow of a high-velocity moving body near air-water surface is calculated and analyzed based on a commercial CFD software ANSYS Fluent. The effect of regular wave parameters including both wave height and wavelength on the cavitating flow and force characteristics of a body at different velocities is investigated. It is found that the cavity shape, lift coefficient and drag coefficient of the body vary periodically with wave fluctuation, and the variation period is basically consistent with wave period. When the wavelength is much greater than the cavity length, the effect of wave on supercavitation is the alternating effect of axial compression and radial compression. However, when the wavelength varies around the cavity length, the cavity often crosses two adjacent troughs and is compressed periodically by the two wave troughs. With the variation of wavelength, the average area of cavity shows a different trend with the change of wave height.

• 한국해안·해양공학회논문집
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• 제26권3호
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• pp.131-139
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• 2014

주기가 약 1~3분인 외중력파는 항만 내의 계류선박의 거동해석 및 연안 표사이동 해석에 직접적인 영향을 미치는 인자이다. 먼 바다의 유의미한 외중력파가 항만으로 전파되어 증폭될 경우 대형선박의 하역작업을 중단시켜 경제적인 손실을 유발할 수 있다. 본 연구에서는 포항신항의 항외 및 항내에서 약 5년 동안 동시 관측한 파랑 자료에 대한 통계분석 및 전달함수를 사용하여 항만 외부로부터 내부로의 외중력파 전파특성을 분석하였다. 전파 특성분석은 외중력파의 파고가 0.1 m 이상이 되는 사상만을 이용하였다. 통계적인 특성분석 결과, 항만 내부의 파고분포는 외부와 유사한 반면 주기분포는 항만 외부보다 분산이 컸다. 전달함수의 매개변수는 각각의 사상에 대하여 최적 추정하였다. 항만 내부의 파고 추정 평균 RMS 오차는 0.013 m 수준이었다. 추정 매개변수는 외중력파의 파고, 주기 및 파향의 선형조합 정보와 강한 상관관계가 있었다(R = 0.95). 본 연구에서 제안한 전달함수는 사전 예측된 외중력파 정보를 이용하여 항만 내부의 외중력파 정보를 빠르고 간단하게 추정할 수 있으므로 예상하지 못한 항만이용 제한에 따른 피해를 저감할 수 있을 것으로 기대된다.

• 한국해안해양공학회지
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• 제19권4호
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• pp.313-319
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• 2007

장기간의 극치 및 평상시 파고는 연안 및 항만구조물의 계획 및 설계에서 매우 중요한 환경인자이다. 그러나, 한국 연안 심해파의 관측 자료가 한정되어 있기 때문에, 심해설계파의 정보는 기상정보로부터 사후추정 한 장기간의 파랑자료를 이용하고 있다. 본 연구에서는 한국해양연구원(2003)에서 제시한 1979년부터 1998년까지의 한국연안 67개 지점의 16방향별 최대 유의파 산출자료를 이용하여 극치분포 분석을 수행하였다. 특성분석에 사용된 극치분포함수는 FT-I과 Weibull 분포이며, 각 분포함수의 매개변수는 Goda(2004)의 방법을 이용하여 추정하였다. 또한 Goda and Gobune(1990)가 제안한 MIR 값을 산정하여 가장 적합한 확률분포형을 결정하였다. 분석결과 FT-I 분포가 886개 지점, Weibull(k=0.75) 분포가 81개 지점 및 Weibull(k=1.00) 분포가 105개 지점의 확률분포형으로 적합한 것으로 판단된다.

• The Journal of the Acoustical Society of Korea
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• 제16권1E호
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• pp.49-56
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• 1997

Ultrasonic cleaning at high frequency around 1 MHz, called megasonic cleaning, is commonly used to remove particles less than 1 ㎛ by generating high frequency accelerations on the cleaning objects. Cleaning is performed in an ultrasonically-excited liquid contained in a double-structured container. Ultrasonic waves generated by piezoelectric transducers propagate in the outer container and are transmitted through the inner container. The bottom of the inner container is inclined to make oblique incidence of the ultrasonic wave in order to raise the efficiency of the transmission through the bottom plate. This work deals with the efficiency of the transmission, which directly affects the cleaning performance. The transmission characteristics of the ultrasonic wave in the megasonic cleaner have been obtained analytically and numerically for the variations of some parameters, such as the thickness and inclined angle of the bottom plate of the inner container and the chemical ratio and temperature of the cleaning liquid. The calculated results have yielded the optimum cleaning condition in terms of the sound power transmitted into the cleaning liquid.

• 한국분무공학회지
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• 제13권2호
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• pp.73-78
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• 2008

An experimental study was performed to explore the drop formation and atomization characteristics in electrohydrodynarnic atomization with flow rate, power supply, voltage frequency, and nozzle size. A basic electrohydrodynarnic atomizer equipment was developed for the analysis of spray visualization and tested for the exploration of relationship between several experimental parameters. In results, the varicose wave had been taken place and the small droplets had been generated less than outer diameter of nozzle on the conditions of 25G of nozzle, flow rate of 2 mL/min, and applied frequency of 50kV at AC power over 5kV voltage. The whipping motion had been grown at applied frequency of 400kV and AC power around 2kV voltage

• 한국철도학회논문집
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• 제15권5호
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• pp.436-441
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• 2012

열차가 터널에 고속으로 진입하면, 압력파가 발생한다. 열차 선두부의 진입에 의하여 발생한 압축파는 터널을 따라 진행되어 터널 출구에서 반사되어 팽창파로 되돌아오며, 후미부의 진입에 의하여 발생한 팽창파도 터널을 따라 전파되어 터널 출구에서 압축파로 반사되어 터널 입구로 되돌아 온다. 열차 선두부 및 후미부에 의하여 발생한 이러한 압력파는 터널 입구 및 출구에서 각각 반사되어 터널 내부를 왕복하며, 차량 객실에 탑승한 승객들에게는 이명감을 일으키고, 터널 출구에서는 환경소음의 일종인 미기압파를 발생시킨다. 터널에서의 큰 압력 변동은 터널의 최적 단면적 설계에도 주요 인자로 고려되고 있으며, 차체의 반복 피로 하중으로 작용하므로, 이에 대한 정량적 및 정성적 분석이 필요하다. 본 연구에서는 고정 격자계를 이용한 특성 해법을 개발하였으며, KTX를 이용한 실차 시험 결과와 비교하였으며, 해석 결과는 시험 결과와 잘 일치하였다.