• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.05a
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• pp.191-197
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• 2002

The motion of a floating OWC chamber in waves is studied taking account of fluctuating.air pressure in the air chamber. An atmospheric pressure drop occurs across the upper opening of the chamber which causes not only hydrodynamic but also pneumatic added mass and damping forces to the floating chamber. A velocity potential in the water due to the free surface oscillating pressure patch is added to the conventional radiation-diffraction potential problem. The potential problem inside the chamber is formulated by making use of the Green integral equation associated with the Rankine Green function while the outer problem with the Kelvin Green function. The two integral equations are solved simultaneously by making use of a matching boundary condition at the lower opening of the chamber to the outer water region. The chamber motion in the frequency domain is calculated for various values of parameters related to the atmospheric pressure drop. The present methods can also be used for the analysis of air-cushion vehicle motion as well as for the design oj a floating owe wave energy absorber.

• Journal of Wind Energy
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• v.14 no.4
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• pp.29-42
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• 2023

In this study, research and empirical cases of floating offshore wind turbine systems with a tension-leg platform are investigated, and hydrodynamic and structural characteristics according to platform shapes and characteristics during transportation and installation are confirmed. Most platforms are composed of pontoons or corner columns, and these are mainly located below the waterline to minimize the impact of breaking waves and supplement the lack of buoyancy of the center column. These pontoons and corner columns are designed with a simple shape to reduce manufacturing and assembly costs, and some platforms additionally have reinforcements such as braces to improve structural strength. Most of the systems are assembled in the yard and then moved by tugboat and installed, and some platforms have been developed with a dedicated barge for simultaneous assembly, transportation and installation. In this study, we intend to secure the basic data necessary for the design, transportation, and installation procedures of floating offshore wind turbine systems with a tension-leg platform.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.305-314
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• 2017

Ocean wave energy harvesting is still too expensive despite developing a variety of wave energy converter (WEC) devices. For the cost-effective wave energy harvesting, it can be an effective measure to use existing breakwaters or newly installed breakwaters for both wave control and energy harvesting purposes. In this study, we investigated the functionality of both breakwater and wave-power generator for the oscillating water column (OWC)-type wave energy converter (WEC) installed in a pneumatic floating breakwater, which was originally developed as a floating breakwater. In order to verify the performance of the breakwater as a WEC, the air flow velocity from air-chamber to WEC has to be evaluated properly. Therefore, air flow velocity, wave transformation and motion of floating structure was numerically implemented based on BEM from linear velocity potential theory without considering the compressibility of air within the chamber. Air pressure, meanwhile, was assumed to be fluctuated by the motions of structure and the water level change within air-chamber. The validity of the obtained values can be determined by comparing the previous results from the numerical analysis for different shapes. Based on numerical model results, wave transformation characteristics around OWC system mounted on the fixed and floating breakwaters, and motions of the structure with air flow velocities are investigated. In summary, all numerical results are almost identical to the previous research considering air compressibility. Therefore, it can be concluded that this analysis not considering air compressibility in the air chamber is more efficient and practical method.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.5 no.4
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• pp.295-304
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• 2000

Vertical measurement of CTDT at about 30 min intervals and spatial surface temperature, salinity, and concentration of suspended particulate matters were conducted to elucidate the character of water column and the dispersal pattern in a floating ice-dominated fjord, Marian Cove, West Antarctica. Marian Cove showed two distinct water layers in terms of turbidity; 1) cold, fresh, and turbid surface plume in the upper 2 m,2) warm, saline, and relatively clean Maxwell Bay inflow between 15-45 m in water depth. Thermal melting of Maxwell Bay inflow and tidewater glacier/floating ices developed the surface mixed layer and the activity of floating ices cause Maxwell Bay inflow to be unstable. Due to the unstable water column, the development of Maxwell Bay inflow and subsequent surface plume are not influenced by tidal frequency. Coastal current generated by strong northwesterly wind may extend warm, saline, and turbid surface plume into the central part of the cove along the northern coast via the western coast of Weaver Peninsula. Terrigenous sediments of meltwaters from the glaciated ice cliffs near the corner of tidewater glacier and some coasts enter into the cove and their dispersion depends upon the hydrographic regimes (tide, wind, wave etc.). At the period of spring tide, the strong wind stress with the northwesterly wind direction reserve suspended sediment-fed surface plume and so allow the possibility of deposition of terrigenous sediments within the basin of cove.

• Journal of Ocean Engineering and Technology
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• v.13 no.4 s.35
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• pp.159-168
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• 1999

부유식 파랑에너지 변환시스템(Oscillating Water Column)에 대한 해석은 입력파와 챔버, 챔버내 공기의 상호작용으로 인하여 어려움이 많다. 이 논문은 이와 같은 요소를 고려하면서도 쉽고 간편한 해석법을 제시한다. 파랑에너지에 의한 자가발전은 파랑에너지를 기계적 운동으로 변환하고 이를 전기에너지로 변환함으로써 가능하다. 본 논문은 파랑에너지에서 기계적 에너지로 변환하는 과정에 집중하여 그 부분의 성능을 해석한다. 단일 진동수 규칙파가 입력되었을 때에 파에 의하여 챔버의 상하운동이 선형적으로 발생하는 것으로 보며, 이 상하운동에 챔버내의 압력 영향을 고려하였다. 상하운동과 챔버내로 투과한 파, 그리고 챔버내 압력에 의해 발생되는 파에 의해 챔버내의 상대운동을 정하고, 그 상대 운동에 의한 공기의 압축 팽창과 온도상승을 근사적 열역학적 방정식으로 해석하였고 오리피스를 통한 유량을 결정하였다. 얻어진 식은 간단하면서도 관련요소의 영향을 전반적으로 표현한다. 결과에 따르면 고정식의 에너지 변환식은 부유식의 특별한 경우로서 파악되었다. 또한 고정식의 시스템을 그대로 부유식으로 바꿨을 때 그 변환효율은 적어지는 것으로 나타났다. 본 해석법은 계산이 간편하므로 설계단계에서 유용하게 활용될 수 있을 것으로 기대된다.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.46 no.3
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• pp.273-281
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• 2013

The movement patterns of fish aggregations swimming freely near artificial reefs on August 24, 2006, at Suyeong Man, Busan, Korea, were acoustically investigated and analyzed. Acoustic surveys were conducted using a 70kHz split-beam echo sounder, 330 kHz side-scan sonar and a 310 kHz imaging sonar. Algorithms for tracking the movement of fish aggregations swimming in response to artificial reefs were developed. The travel direction and the swimming speed for two aggregations of fish were estimated from the trajectory orientations of echo responses recorded by the imaging sonar.The first group was floating just above the reef structure, while remaining in the midwater column, and the second group was swimming through and around artificial reefs near the seabed. The mean swimming speed was estimated to be 0.40 m/s for the midwater fish aggregation and 0.17 m/s for the bottom aggregation close to artificial reefs. These results suggest that the swimming behavior of fish aggregations passing close to artificial reefs near the seabed displayed a slower moving pattern than fish floating just above the reef structure in the midwater column.

• Journal of Ocean Engineering and Technology
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• v.26 no.6
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• pp.53-58
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• 2012

An experimental study on the hydrodynamic performance of a backward bent duct buoy (BBDB) was performed in a 2D wave tank. The BBDB is one of the promising oscillating water column (OWC) types of floating wave energy converters. Two different corner-shaped BBDBs (sharp-corner and round-corner) were used to measure the maximum chamber surface elevations and body motions for various incident wave conditions, and their hydrodynamic characteristics were compared. In order to investigate the effect of the pneumatic pressure inside the chamber, the heave and pitch angle interacted with elevations were compared for both open chamber and partially open chamber BBDBs. From the comparison study, the deviation in the chamber surface elevations between the two shapes of BBDBs was found to be significant near the resonance period, which may be explained by viscous energy loss. It was also found that the pneumatic pressure noticeably affected the chamber surface elevation and body motions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.4
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• pp.629-636
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• 1987

An experiment is carried out to study the surface-tension driven flow characteristics in a cylindrical liquid column heated from above (which is the low gravity floating zone simulated on earth) with varing the aspect ratio and diameter of the liquid column. Hexadecane, octadecane, silicon oil(10cs), FC-40 and water are used as the test liquids. The free surface shape varies sinusoidally for Ma>M $a_{cr}$ and its frequency is found to be the same as that of temperature oscillation. It is verified that the surface temperature profile changes from linear to S-shaped profile for Ma>M $a_{cr}$ . The frequency of temperature oscillation decreases with increasing liquid volume, while its level increases. M $a_{cr}$ decreases with increasing aspect ratio, and also decreases with increasing Prandtl number in the range of 25

• Journal of Power System Engineering
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• v.18 no.3
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• pp.36-41
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• 2014

The structure of a variable liquid column oscillator(a VLCO) is analogous to that of the tuned liquid column damper used to suppress oscillatory motion in large structures like tall buildings and cargo ships. The VLCO is a system absorbing high kinetic energy of accelerated motions of the multiple floating bodies in the effect of air springs occurred by installation of inner air chambers. Thus, VLCO can improve the efficiency of energy than wave energy converters of the activating object type made in Pelamis Company. In this research, the experiment was performed in two models of same draft. The one is that weights were filled, and the other is that water was filled. The numerical results were estimated by assuming that do not exist internal flow, and the results were compared with the results of experiments.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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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.