• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.2
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• pp.111-117
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• 2012

Oscillating water column is the most widely used ocean energy converting systems all over the world. The operating performance is influenced by the efficiencies of the two converting stages in the OWC chamber-turbine integrated system. In order to consider the effects of the turbine, the orifice model are carried out. The VOF based Numerical Wave Tank (NWT) is utilized to simulate the water column oscillation inside the chamber and the results are compared with corresponding experimental data. This paper reviews the state of the art in interaction among wave elevation inside the chamber and air flow rate in the duct, which are considered the turbine effects. Effects of incident wave conditions and several shape parameters on the operating performance of OWC chamber are investigated numerically. The effects of the impulse turbine on the integrated system and interaction among the wave elevation, pressure and air flow velocities variations are investigated.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.961-966
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• 2001

The Wells turbine is one of the simplest and most promising self-rectifying air turbines which are useful for the systems of alternative energy development in near future, and it is economically desirable from the point of view of the practical use, as well. To investigate the effect of blade sweep on the performance of the Wells turbine, computations of a fully 3-D Navier-Stokes are carried out under steady flow conditions of NACA0020 blade. It is known that the performance of the Wells turbine is considerably influenced by the blade sweep. An optimum blade sweep ratio(f=0.35) for the NACA0020 is found to be the most promising for the practical use, and this value is in good agreement with the previous experiments. It is also found that the overall turbine performance for the NACA0020 is better than that for the CA9.

• 유체기계공업학회:학술대회논문집
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• 2000.12a
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• pp.325-333
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• 2000

The aerodynamics of the Wells turbine has been studied using a 3-dimensional, unstructured mesh flow solver for the Reynolds-averaged Navier-Stokes equations. The basic feature of the Wells turbine is that even though the cyclic airflow produces oscillating axial forces on the airfoil blades, the tangential force on the rotor is always in the same direction. Geometry used to define the 3-dimensional numerical grid is based upon that of an experimental test rig. The 3-dimensional Wells turbine model, consisting of approximate 220,000 cells is tested at four axial flow rates. In the calculations the angle of attack has been varied between $10^{\circ}$ and $30^{\circ}$ of blades. Representative results from each case are presented graphically and analyzed. It is concluded that this method holds much promise for future development of Wells turbines.

• Journal of the Korean Society for Marine Environment & Energy
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• v.14 no.1
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• pp.32-39
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• 2011

When the laws about the security of ships are revised, or voyage conditions are changed, ship owners have converted rather than built new passenger ships including cruise ships recently. As conversion causes a lot of changes in principal dimension, structural strength, hydrodynamic performance, the number of passengers, and cargo capacity, detailed pre-review is needed. But any studies on conversion have not been carried out yet, this study investigated and analyzed the trend of consulting companies' reports (Delta Marine Report, 2005, 2008). As a result, it was found that lengthening conversion brought about the main changes in principal dimension, and performance. Also it was suggested that there be factors for consideration like hull scantling, hull form, and cutting point to minimize side effects when ship owners build ships having lengthening conversion in mind.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.336-339
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• 2003

A digital data logging system has been developed for the purpose of a compact offline Ocean Bottom Seismometer(OBS). The Digital Data Logger(DDL) consists of A/D system, Micom with storage memory and firmware managing data files. The A/D system acquires data of 16bit/4ch with sampling rate of 250Hz per channel. The Micom, a micro controller board with T33521 processor of 8051 class, was equipped with 8 flash memories of 128MB for data storage capacity of 1GB. The firmware stores the acquiring data in form of binary files. The DDL was designated to be compact and light and to consume low energy as possible. The DDL is to interface with PC through USB(Universal Serial Bus). The performance of the DDL has been validated through tests with respect to a 3-axis seismometer.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.9
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• pp.557-567
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• 2016

In this study, the optimal design of heat exchangers, including the evaporator and condenser of a solar-heating ocean thermal energy conversion (SH-OTEC), is investigated. The power output of the SH-OTEC is assumed to be 100 kW, and the SH-OTEC uses the working fluid of R134a and high-performance commercial tubes. The surface heat transfer area and the pressure drop were strongly dependent on the number of tubes, as well as the number of tube passes. To solve the reciprocal tendency between the heat transfer area and pressure drop with respect to the number of tubes, as well as the number of tube passes, a genetic algorithm (GA) with two objective functions of the heat transfer area (the capital cost) and operating cost (pressure drop) was used. Optimal results delineated the feasible regions of heat transfer area and operating cost with respect to the pertinent number of tubes and tube passes. Pareto fronts of the evaporator and condenser obtained from multi-objective GA provides designers or investors with a wide range of optimal solutions so that they can select projects suitable for their financial resources. In addition, the surface heat transfer area of the condenser took up a much higher percentage of the total heat transfer area of the SH-OTEC than that of the evaporator.

• Journal of the Korean Solar Energy Society
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• v.34 no.4
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• pp.51-56
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• 2014

In this paper, OTEC(Ocean Thermal Energy Conversion) system with vapor-vapor ejector is newly proposed. And 6 wet refrigerants are applied into the proposed OTEC system for performance comparison. The results of comparison performance are as follows. In the view of system efficiency, R32/R744(90:10) has the highest efficiency among the 6 refrigerants. In case of evaporation capacity, pump work and mass flow rate of working fluid, R744, R717 and R717 is lowest value, respectively. As this results, the vapor-vapor ejector is able to increase the efficiency of system. And It is necessary to select the optimized working fluid considering environmental and economic factors.

• Journal of the Korean Solar Energy Society
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• v.34 no.4
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• pp.45-50
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• 2014

In this paper, the Ocean Thermal Energy Conversion(OTEC) with vapor-vapor ejector is proposed newly. At this OTEC system, a vapor-vapor ejector is installed at inlet of condenser. The vapor-vapor ejector plays a very important role in increasing of the production work of low-stage turbine throughout the decrement of outlet pressure of ejector. The performance analysis is conducted for optimizing the system with HYSYS program. The procedure of performance analysis consists of outlet pressure of high turbine, the mass ratio of working fluid at separator, total working fluid rate, and nozzle diameters of vapor-vapor ejector. The main results is summarized as follows. The nozzle diameter is most important thing in this study. When each nozzle diameter of vapor-vapor ejector is 10 mm, the efficiency of OTEC system with vapor-vapor ejector shows the highest value. So it is necessary to set the optimized nozzle diameters of vapor-vapor ejector for achieving the high efficiency OTEC power system.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.235-240
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• 2004

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

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.4
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• pp.291-297
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• 2015

The wave spectrum was generated from wave data measured at the Chagwi-do site in Jeju, where a 10MW class floating wave-offshore wind hybrid power generation system will be installed. The latching control technology (Sheng et al.[2015]) was applied in order to improve the extracted power from WEC (Wave Energy Converter), which is heaving in corresponding irregular waves. The peak period as a representative value of irregular waves was used when we determined the latching duration. From the numerical results in the time-domain analysis, the latching control technology can significantly improve the extracted power about 50%.