• Journal of Ocean Engineering and Technology
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• v.24 no.1
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• pp.133-139
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• 2010

From the ancient times, there are waves in the ocean. And all the moving body have energy. We have a kind of hope to convert the wave energy into electric one. Finally we can find out a power generator mechanism that mainly use the principle of pulleys. We have made drawings for this and completed the wave energy converter. This wave energy converter consists of several pulleys, rope, generator, buoys and anchors. The distance between an anchor and buoy is changed according to the hight of waves. Several sets of anchors, pulleys and buoys can make the movement of rope, and the ropes wind up a converter axis. In case of 1 meter movement of the buoy, the winding distance will be amplified 2 or 3 times if we use several moving and fixed pulleys. Based on this concept, we developed 2 kind of prototypes. One is for the test in the laboratory and the other is for the field test. Through the two test, we could confirm the usability of this mechanism.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.4
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• pp.437-446
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• 2012

An ocean buoy energy farm is considered for Green energy generation and delivery to small towns along the Korean coast. The present study presents that the floating buoy-type energy farm appears to be sufficiently feasible for trapping more energy compared to affixed cylinder duck array. It is also seen from the numerical results that the resonated waves between spaced buoys are further trapped by floating buoy motion.Our numerical study is analyzed by a plane-wave approximation, in which evanescent mode effects are included in a modified mild-slope equation based on the scattering characteristics for a single buoy.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.5
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• pp.651-659
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• 2018

A multi-level overtopping wave energy converter was designed according to the large tidal range and small wave heights in China. It consists of two reservoirs with sloping walls at different levels. The reservoirs share a common outflow duct and a low-head axial turbine. The experimental study was carried out in a laboratory wave-flume to investigate the overtopping performance of the device. The depth-gauges were used to measure the variation of the water level in the reservoirs. The data was processed to derive the time-averaged overtopping discharges. It was found that the lower reservoir can store wave waters at the low water level and break the waves which try to climb up to the upper reservoir. The upper sloping angle and the opening width of the lower reservoir both have significant effects on the overtopping discharges, which can provide more information to the design and optimization of this type of device.

• International Journal of Naval Architecture and Ocean Engineering
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• v.2 no.3
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• pp.155-170
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• 2010

Availability of economic and efficient energy resources is crucial to a nation's development. Because of their low cost and advancement in drilling and exploration technologies, oil and gas based energy systems are the most widely used energy source throughout the world. The inexpensive oil and gas based energy systems are used for everything, i.e., from transportation of goods and people to the harvesting of crops for food. As the energy demand continues to rise, there is strong need for inexpensive energy solutions. An offshore platform is a large structure that is used to house workers and machinery needed to drill wells in the ocean bed, extract oil and/or natural gas, process the produced fluids, and ship or pipe them to shore. Depending on the circumstances, the offshore platform can be fixed (to the ocean floor) or can consist of an artificial island or can float. Semi-submersibles are used for various purposes in offshore and marine engineering, e.g. crane vessels, drilling vessels, tourist vessels, production platforms and accommodation facilities, etc. The challenges of deepwater drilling have further motivated the researchers to design optimum choices for semi-submersibles for a chosen operating depth. In our series of eight papers, we discuss the design and production aspects of all the types of offshore platforms. In the present part I, we present an introduction and critical analysis of semi-submersibles.

• Journal of Ocean Engineering and Technology
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• v.31 no.3
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• pp.208-218
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• 2017

The performance of a wave energy converter (WEC) that uses the rolling motion of a partially submerged pendulum plate in front of a quay wall was analyzed. The wave exciting moment and hydrodynamic moment were obtained using a matched eigenfunction expansion method (MEEM) based on the linear potential theory, and then the roll motion response of a pendulum plate, time averaged extracted power, and efficiency were investigated. The optimal PTO damping coefficient was suggested to give the optimal extracted power. The peak value of the optimal extracted power occurs at the resonant frequency. The resonant peak and its width increase as the submergence depth of the pendulum plate decreases and thickness of the pendulum plate increases. An increase in the wave incidence angle reduces the efficiency of the wave energy converter. In addition, the WEC using a rolling pendulum plate contributes not only to the extraction of the wave energy, but also to a reduction in the waves reflected from the quay wall, which helps to stabilize ships going near the quay wall.

• Ocean Systems Engineering
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• v.4 no.1
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• pp.63-82
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• 2014

Declutching control is applied to a hemispherical wave energy converter with direct linear electric Power-Take-Off systems oscillating in heave direction in both regular and irregular waves. The direct linear Power-Take-Off system can be simplified as a mechanical spring and damper system. Time domain model is applied to dynamics of the hemispherical wave energy converter in both regular and irregular waves. And state space model is used to replace the convolution term in time domain equation of the heave oscillation of the converter due to its inconvenience in analyzing the controlled motion of the converters. The declutching control strategy is conducted by optimal command theory based on Pontryagin's maximum principle to gain the controlled optimum sequence of Power-Take-Off forces. The results show that the wave energy converter with declutching control captures more energy than that without control and the former's amplitude and velocity is relatively larger. However, the amplification ratio of the absorbed power by declutching control is only slightly larger than 1. This may indicate that declutching control method may be inapplicable for oscillating wave energy converters with direct linear Power-Take-Off systems in real random sea state, considering the error of prediction of the wave excitation force.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.1
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• pp.1-6
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• 2017

Tungsten carbide (WC) has been suggested as a new buffer layer for the GaN-on-Si technology. We have investigated and optimized the sputtering condition of WC layer on the Si-substrate. We confirmed the suppression of the Si melt-back phenomenon. In addition, surface energy of WC/Si layer was measured to confirm the possibility as a buffer layer for GaN growth. We found that the surface energy(${\gamma}=82.46mJ/cm^2$) of WC layer is very similar to that of sapphire substrate(${\gamma}=82.71mJ/cm^2$). We grow GaN layer on the WC buffer by using gas-source MBE, and confirm that it is available to grow a single crystalline GaN layer.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.180-183
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• 2008

This paper is about the ocean current power generation using sea water incoming into the lake surrounded by barrages and sea water discharged from a dam made of artificial structures. In operation of a tidal power plant, the sea water discharged from a turbine structure and a gate structure of a tidal power plant is faster than the tidal current caused by tides in nature and has better characteristics than that to run ocean current turbines. It is shown that the sea water discharged after generating electricity through a turbine generator of a tidal power plant and the sea water discharged from a gate structure of a tidal dam still have kinetic energy high enough to run an ocean current turbine and produce valuable electricity.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2006.06a
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• pp.257-258
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• 2006

해양에너지는 지구의 70%를 점유하는 해양이 태양에너지를 받아서 그것을 내부 에너지로 저장하는 것으로 지속적 보급을 받고 있는 재생 가능한 에너지이다. 본 논문은 해양에너지를 실용화 하는 연구개발 분야 중 최근 주목받고 있는 조력 및 조류에너지에 대해 국내의 동향을 소개하고자 한다.

• Coastal and Ocean
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• v.5 no.2
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• pp.62-70
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• 2012