• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 한국해양공학회 2001년도 춘계학술대회 논문집
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• pp.20-25
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• 2001

부유식 파랑에너지 변환시스템(Oscillating Water Column)에서 에너지 변환은 입력파와 챔버, 챔버내 공기의 상호작용으로 이루어진다. 이 논문은 파랑에너지를 기계적 운동으로 변환하는 기계적 특성을 해석한다. 단일 진동수 규칙파가 입력되었을 때에 파에 의하여 챔버의 상하운동이 선형적으로 발생하며, 이 상하운동은 챔버내의 압력 변화에 영향을 받는다. 상하운동과 챔버내로 투과한 파, 그리고 챔버내 압력에 의해 발생되는 파에 의해 챔버내의 상대운동을 정하고, 그 상대운동에 의한 공기의 압축 팽창과 온도상승을 근사적 열역학적 방정식으로 해석하여 오리피스를 통한 유량과 압력을 기준으로 에너지 변환요율을 결정하였다. 얻어진 식은 간단하면서도 관련요소의 영향을 전반적으로 표현한다. 개구율 변화에 따른 운동응답을 비교하였다.

• Journal of Ocean Engineering and Technology
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• 제18권6호
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• pp.1-7
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• 2004

This paper deals with the performance analysis of the impulse turbine for a owe type wave energy conversion device. Numerical analysis was performed using the commercially-available software FLUENT. This parametric study includes variation of the setting angle of the guide vane. Since parametric study at various flow coefficients requires a tremendous amount of computing time, two-dimensional cascade flow approximation was employed to determine the optimum principal particulars in a rather simple manner. A Full three-dimensional calculation was also performed for several cases to confirm the validity of the two-dimensional approach. Results were compared to other experimental data, such as Setoguchi et al. (2001)'s extensive set of data, and found that the usefulness of 2-D analysis was well demonstrated. The advantages of each method were also evaluated.

• Nuclear Engineering and Technology
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• 제45권3호
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• pp.361-366
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• 2013

An imaging technique to visualize the internal defects in a plate-type nuclear fuel specimen was developed by using an active optical interferometer for a nondestructive quality inspection. A periodic thermal wave having a sinusoidal intensity pattern induced a periodical strain variation for the specimen. The varying strain image was acquired using an optical laser interferometer. The strain distribution over the internal defects will be distorted in an acquired strain image because a part of the thermal wave will be reflected from these defects during propagation. In this paper, internal defects were efficiently visualized by sequentially accumulating the extracted defect components. The experimental results confirmed that the developed visualization system can be a valuable tool to detect the internal defects in plate-type nuclear fuel.

• Journal of Radiation Industry
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• 제7권2_3호
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• pp.201-207
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• 2013

Soil liquefaction by tsunami or wave induced currents can cause serious damages to coastlines and coastal infrastructures. Although liquefaction caused by regular waves over sea beds has been extensively investigated, studies of tsunami-induced liquefaction near coastal area have been relatively rare. In this work, the hydraulic scale model has been designed and constructed to investigate the variations of wave height and sediment transport by tsunami. The distorted hydraulic scale model based on the Froude similarity was adopted to represent hydrodynamics and sediment transport in a coastal area. The scale model was composed of control box, screw axis, wave paddle and rotating coastal structure.

• Journal of the Korea Institute of Military Science and Technology
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• 제14권1호
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• pp.147-153
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• 2011

A series of nonequilibrium molecular dynamics(NEMD) simulations are performed to investigate the kinetic energy and velocity distributions of molecules in shock waves. In the simulations, argon molecules are used as a medium gas through which shock waves are propagating. The kinetic energy distribution profiles reveals that as a strong shock wave whose Mach number is 27.1 is applied, 39.6% of argon molecules inside the shock wave have larger kinetic energy than molecular ionization energy. This indicates that an application of a strong shock wave to argon gas can give rise to an intense light. The velocity distribution profiles in z direction along which shock waves propagate clearly represent two Maxwell-Boltzmann distributions of molecular velocities in two equilibrium regions and one bimodal velocity distribution profile that is attributed to a nonequilibrium region. The peak appearing in the directional temperature in z direction is discussed on a basis of the bimodal velocity distribution in the nonequilibrium region.

• Journal of the Korean Society for Marine Environment & Energy
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• 제13권2호
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• pp.112-120
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• 2010

In this paper time series wave data measured continuously for 24 hours during a storm in Yura Sea Area are used to investigate statistical characteristics of nonlinear waves. The exceedance probability of wave height is compared using the Rayleigh distribution and the Edgeworth-Rayleigh (ER) distribution. Wave data which show stationary state for 10 hours contain 4600 waves approximately. The Gram-Chalier distribution fits the probability of wave elevation better than the Gaussian distribution. The Rayleigh ($H_{rms}$) distribution follows the exceedance probability of wave height in general and predicts the probability of freak waves well. The ER distribution overpredicts the exceedance probability of wave heights and the occurrence of freak waves. If wave data measured for 30 minute period which contains 250 waves are used, the ER distribution can predict the occurrence probability of freak waves well. But it overpredicts the probability of overall wave height If no freak wave occurs, the Rayleigh ($H_{rms}$) distribution agrees well with wave height distribution for the most of wave height ranges. The wave height distribution of freak waves of which height are less than 10 m shows similar tendency compared with freak waves greater than 10 m. The value of $H_{max}/H_{1/3}$ is related to the kurtosis of wave elevation. It seems that there exists threshold value of the kurtosis for the occurrence of freak waves.

• Journal of information and communication convergence engineering
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• 제7권2호
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• pp.223-230
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• 2009

For pulse trigger way and the energy injection rate according to PET ($Pause^{10-90}$ $Energy^{20-40}$ $Trigger^{1-7}$) function, indeed, human body condition, period of dormancy in this research about this back correctly adjustment possible and designed harmless micro carrying along style hair exclusion so that can design and manufacture and run special quality examination and Xenon flash lamp to crawl in human body. Because creating individual's skin model to do stable treatment by light transmission way by skin impedance and measure, must embody treatment special quality of most suitable that draw skin color, energy, wave length, approximately, transmission time, pulse delay etc. and want. Specially, saved standard of war treatment pulse modeling by skin impedance, and manufacture pulse modeling system of most suitable by skin subordinate, and embody suitable treatment pulse. Specially, embody as could do root of a hair exclusion being emitted in pulse form using multi wave length of 560nm, 590nm, 640nm, 755nm and embodied clinical data. If become research repletion furthermore little more, is seen that can approximate in commercialization.

• Journal of the Korean Society for Nondestructive Testing
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• 제32권4호
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• pp.347-354
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• 2012

Using a single-line pulsed laser beam is well known as a useful noncontact method to generate a directional surface acoustic wave. In this method, different laser beam energy profiles produce different waveforms and frequency characteristics. In this paper, we considered two typical kinds of laser beam energy profiles, Gaussian and square-like, to find out a difference in the frequency characteristics. To achieve this, mathematical models were proposed first for Gaussian laser beam profile and square-like respectively, both of which depended on the laser beam width. To verify the theoretical models, experimental setups with a cylindrical lens and a line-slit mask were respectively designed to produce a line laser beam with Gaussian spatial energy profile and square-like. The frequency responses of the theoretical models showed good agreement with experimental results in terms of the existence of harmonic frequency components and the shift of the first peak frequencies to low.

• The Transactions of the Korean Institute of Power Electronics
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• 제5권6호
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• pp.610-619
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• 2000

This paper presents an off-line UPS using the high temperature superconductive magnetic bearing. FES(Flywheel Energy Storage) system has good advantages in compare with lead acid battery. So, high efficiency FES using high temperature SMB(superconductive magnetic bearing) was composed in this paper. The outer rotor type of PMSM(Permanent Magnet Synchronous Motor) as motor/generator was used for the experiment, and square wave current and sinusoidal wave control methods was compared for high efficiency operation of motor/generator. The circuit for in phase sinusoidal wave current control with EMF in the full speed range was designed and the proposed flywheel energy storage system was applied in single phase off-line UPS system. As the stable operation characteristics of prototype system was confirmed, the its excellence as energy storage device in Off-line UPS was proved.

• Nuclear Engineering and Technology
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• 제41권6호
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• pp.841-848
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• 2009

A simple model to analyze non-linear density-wave instability in a sodium-cooled helically coiled steam generator is developed. The model is formulated with three regions with moving boundaries. The homogeneous equilibrium flow model is used for the two-phase region and the shell-side energy conservation is also considered for the heat flux variation in each region. The proposed model is applied to the analysis of two-phase instability in a JAEA (Japan Atomic Energy Agency) 50MWt No.2 steam generator. The steady state results show that the proposed model accurately predicts the six cases of operating temperatures on the primary and secondary sides. The sizes of three regions, the secondary side pressure drop according to the flow rate, and the temperature variation in the vertical direction are also predicted well. The temporal variations of the inlet flow rate according to the throttling coefficient, the boiling and superheating boundaries and the pressure drop in the two-phase and superheating regions are obtained from the unsteady analysis.