• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.1
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• pp.7-17
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• 2016

The present study experimentally considers dynamic performance of large floating wave-offshore hybrid power generation platform in extreme conditions. In order to evaluate the motion performance of the large floating hybrid power generation platform, 1/50 scaled model was manufactured. A mooring line was also manufactured, and free-decay and static pull-out tests were carried out to check the mooring model. A mooring line table was introduced to satisfy the water depth, and environmental conditions were checked. Motion responses in regular waves were measured and complicated environmental conditions including wave, wind, and current were applied to see the dynamic performance in extreme/survival conditions. Maximum motion and acceleration were judged following the design criteria, and maximum offset and mooring tension were also checked based on the rule. The characteristics of hybrid power generation platform are discussed based on these data.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.14 no.2
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• pp.113-116
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• 1978

To ascertain the feasibility of the energy utilization in the sea adjacent to Korea, the distribution of the vertical temperature difference and the seasonal variation in the southeastern Yellow Sea are studied in relation to the sea water circulation. In summer, a region of high vertical temperature difference of approximately 16$^{\circ}C$ was found at a distance of approximately 40 miles from the western coast of Korea. It is located at the west of 125${\circ}$ 30`E and at the north of 34${\circ}$N. The vertical temperature structure is sustained by the inflow of Yellow Sea Warm Current water, the warming of the surface water of the Yellow Sea and the periodical renewal of the Yellow Sea Cold Water. It may be stated that power can be obtained from the sea water by making the use of the temperature difference. The vertical temperature difference was around 14$^{\circ}C$ in the western and southern waters of Jejudo Island. The vertical temperature difference decreases in autumn, and disappears due chiefly to the vigorous convective vertical mixing in winter when the northwest monsoon prevails. The power can be obtained from sea throughout the year, if power generation by the temperature difference is combined with that by wind and wave, and systemized in such a way that the former is employed in the hot season of summer, while the latter in winter and spring.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.3
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• pp.123-127
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• 2013

In this study, the buckling behaviors during the installation of a bucket foundation for an offshore wind turbine tower were investigated. The objective structure was modeled by using a commercial structural analysis program, and the buckling behavior of the model was estimated as Batdorf's parameter Z in the design code. The surrounding soil conditions and loading condition were applied to the verified analysis model. The effects of parameters such as the longitudinal stiffeners and driven depth were estimated for the buckling capacity. As a result, it was found that the longitudinal stiffeners could drastically increase the buckling capacity in a specific region. In addition, the buckling capacities increased linearly when considering the effect of the surrounding soil.

• Journal of Ocean Engineering and Technology
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• v.32 no.3
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• pp.202-207
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• 2018

This paper presents the efficiency of a floating vertical axis wind turbine with variable-pitch. A model was designed to use the lift force and drag force for blades with various pitch angles. The blade's pitch angle is controlled by the stopper. To validate the efficiency of the wind turbine discussed in this paper, a model test was carried out through a single model efficiency experiment and wave tank experiment. The parameters of the single model efficiency experiment were the wind speed, electronic load, and pitch angle. The wave tank experiment was performed using the most efficient pitch angle from the results of the single model efficiency experiment. According to the results of the wave tank experiment, the surge and pitch motion of a structure slightly affect the efficiency of a wind turbine, but the heave motion has a large effect because the heights of the wind turbine and wind generator are almost the same.

• Journal of Ocean Engineering and Technology
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• v.25 no.5
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• pp.69-75
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• 2011

The purpose of this study was to develop a buckling analysis technique for a windpower system structure under environmental loadings (hydrostatic pressure) using FEM. We analyzed an isotropic material and composite material and made a comparison using buckling pressure formulas. First, finite element analyses for an isotropic material (SC410) were performed to obtain the variation of buckling pressure for the number of elements and boundary conditions in a pressure-shell model, and the numerical results were compared with those of existing empirical formulas. Then, additional finite element analyses based on the results of the isotropic material (SC410) were performed to determine the optimum lamination angle and pattern for a composite material (URN300). The results of the FE analyses for the composite material were also compared with those of existing empirical formulas. The ply orientations (lamination angles) used in the FE analyses were $0^{\circ}$, $15^{\circ}$, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, $75^{\circ}$, and. The lamination patterns in the FE analyses were and. The lamination pattern was assumed to be the equivalent model of. The results of the FE analyses for the isotropic material (SC410) indicated that the optimal values for the number of elements and the boundary conditions were 6000 and both simply supported, respectively. The results of the FE analyses for the composite material (URN300) showed that the optimal ply orientation was $60^{\circ}{\sim}75^{\circ}$.

• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.5
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• pp.815-824
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• 2022

The growing integration of intermittent renewable sources like offshore wind energy increases the need for transferring electric energy over long distances, which may include sea crossings. One of the solutions available for bulk electric power transmission across large distances encompassing wide and deep sea is using HVDC submarine power cables. However, there are no standards or research related to the calculation of the continuous allowable current with various ocean conditions of a DC power cable that does not have an alternating magnetic field. In this study, assuming the typical two types of subsea cable models and two areas of the south coast and the west coast marine conditions, a continuous allowable current simulation of DC cables was performed. As a simulation result, the DC cable continuous allowable current find out the gradient reduction characteristics based on subsea base depth.

• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.3
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• pp.185-193
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• 2016

In this study, the present deployment of the multiple wave energy converters (WECs) in a floating wind-wave hybrid power generation platform was estimated considering the interaction effect among WEC buoys. The interaction processes of multiple buoys were very complex, since scattered and radiated waves from each buoy affected the others in the array. The interaction analysis of the diffraction and radiation problem by the array of WECs was applied by matched eigenfunction expansion method (MEEM). The analytical solutions were compared with the results of numerical calculation based on WAMIT. The overall performance of 24 WECs installed in the hybrid power generation platform was evaluated by the q-factor representing the interaction effect among buoys.

• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.4
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• pp.399-405
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• 2011

Recently, the navigation risk is increasing significantly with growth of marine traffic volume and construction of marine facilities, water bridges, port development and marine wind farm etc. To reduce this kinds of risk, Ministry of Land, Transport and Maritime Affairs enacted a new law called MSA(Maritime Safety Audit) as a comprehensive maritime traffic safety management scheme in order to ensure safety improvements from the early planning stage to post managing of the development which affect the maritime traffic environment. MSA as a tool for improving maritime traffic safety is a formal safety assessment in the existing or future ship's fairway by an independent audit team. It examines the potential hazards of maritime traffic safety, if necessary, and is to ensure the implementation of appropriate safety measures. The object of this paper is to comprehensively evaluate the achievements and implementation problems of MSA about the 2 years, to define the fundamental problems of MSA by conceptualizing and analyzing MSA limits. MSA requires further examination about the introduction of screening and scoping in order to increase the efficiency and objectivity. It will be required the measures concerning policies directions as a tool for planning process for project owner. It will lead to right understanding concerning audit scheme and used in various ways such as amendments to related law.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.5
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• pp.479-487
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• 2023

Recently, the destructive power of typhoons is continuously increasing owing to global warming. In a situation where the installation of floating wind turbines is increasing worldwide, concerns about the huge loss and collapse of floating offshore wind turbines owing to strong typhoons are deepening. A new type of disconnectable mooring system must be developed for the safe operation of floating offshore wind turbines. A new submersible mooring pulley considered in this study is devised to more easily attach or detach the floating of shore wind turbine with mooring lines compared with other disconnectable mooring apparatuses. To investigate the structural safety of the initial design of submersible mooring pulley that can be applied to an 8MW-class floating type offshore wind turbine, scale-down structural models were developed using a 3-D printer and structural tests were performed on the models. For the structural tests of the scale-down models, tensile specimens of acrylonitrile butadiene styrene material that was used in the 3-D printing were prepared, and the material properties were evaluated by conducting the tensile tests. The finite element analysis (FEA) of submersible mooring pulley was performed by applying the material properties obtained from the tensile tests and the same load and boundary conditions as in the scale-down model structural tests. Through the FEA, the structural weak parts on the submersible mooring pulley were reviewed. The structural model tests were conducted considering the main load conditions of submersible mooring pulley, and the FEA and test results were compared for the locations that exceeded the maximum tensile stress of the material. The results of the FEA and structural model tests indicated that the connection structure of the body and the wheel was weak in operating conditions and that of the body and the chain stopper was weak in mooring conditions. The results of this study enabled to experimentally verify the structural safety of the initial design of submersible mooring pulley. The study results can be usefully used to improve the structural strength of submersible mooring pulley in a detailed design stage.

• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.73-78
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• 2011

The purpose of this study was to investigate the natural frequency of filament-wound composite towers for large scale wind-turbines using the finite element method (FEM). To define the material properties, we used both the effective property method and the stacking properties method. The effective properties method assumes that a composite consists of one ply. The stacking properties method assumes that a composite consists of several stacked plies. First, a modal analysis of the tower, filament-wound with angles of $[{\pm}30]$, was carried out using the two methods for composite material properties, the stacking method and effective method. Then, an FE analysis was performed for composite towers using filament winding angles of $[{\pm}30]$, $[{\pm}45]$, and $[{\pm}60]$. The FE analysis results using the stacking properties of the composite were in good agreement with the results from the effective properties method. The difference between the FEM and material properties methods was approximately 0~0.6%