• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.352-366
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• 2021

To decrease Europe's harmful emissions, the European Union aims to substantially increase its offshore wind energy capacity. To further develop offshore wind energy, investment in ever-larger construction vessels is necessary. However, this market is characterised by seemingly unpredictable growth of market demand, turbine capacity and distance from shore. Currently it is difficult to deal with such market uncertainty within the ship design process. This research aims to develop a method that is able to deal with market uncertainty in early ship design by increasing knowledge when design freedom is still high. The method uses uncertainty modelling prior to the requirement definition stage by performing global research into the market, and during the concept design stage by iteratively co-evolving the vessel design and business case in parallel. The method consists of three parts; simulating an expected market from data, modelling multiple vessel designs, and an uncertainty model that evaluates the performance of the vessels in the market. The case study into offshore wind foundation installation vessels showed that the method can provide valuable insight into the effect of ship parameters like main dimensions, crane size and ship speed on the performance in an uncertain market. These results were used to create a value robust design, which is capable of handling uncertainty without changes to the vessel. The developed method thus provides a way to deal with market uncertainty in the early ship design process.

• New & Renewable Energy
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• v.20 no.2
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• pp.17-25
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• 2024

In this study, the effect of the time step specified in a computational fluid dynamics (CFD) simulation on load response is analyzed and the drag coefficients of the floating body of floating offshore wind turbines (FOWTs) are estimated. By evaluating the error in the FOWT load response and the change in the drag-coefficient values based on the density of the time intervals, this study aims to establish a time-interval setting that minimizes the time and cost of CFD simulations for selecting drag-coefficient values. Practical CFD utilization strategies necessary for the calibration of medium-to high-fidelity analysis tools are presented. Based on a comparative analysis of CFD simulations conducted at various time intervals, the results confirmed that under a certain time interval that sufficiently considers various factors, the accuracy of the FOWT response with respect to density shows minimal differences, thereby providing an efficient utilization method for CFD simulations in FOWT design and analysis.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.4
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• pp.191-199
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• 2018

In this paper, wind data at 20 locations are collected and analyzed in order to review optimal candidate site for offshore wind farm around Korean marginal seas. Observed wind data is fitted to Rayleigh and Weibull distribution and annual energy production is estimated according to wind frequency. As the model of wind turbine generator, seven kinds of output of 1.5~5 MW were selected and their performance curves were used. As a result, Repower-5 MW turbines showed high energy production at wind speeds of 7.15 m/s or higher, but G128-4.5 MW turbines were found to be favorable at lower wind speeds. In the case of Marado, Geojedo and Pohang, where the rate of occurrence of wind speeds over 10 m/s was high, the capacity factor of REpower's 5 MW offshore wind turbine was 56.49%, 50.92% and 50.08%, respectively.

• Journal of Wind Energy
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• v.14 no.4
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• pp.5-12
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• 2023

In this study, a structural and fatigue strength evaluation of the Fairlead Chain Stopper (FCS) was performed as a part of the development of a disconnectable mooring system to be applied to 10MW floating offshore wind power generation systems. To estimate the load acting on the FCS, a 10 MW semi-submersible floater was designed using the 10 MW wind turbine developed by Technical University of Denmark(DTU). The minimum breaking load (MBL) of the grade R5 and 147mm mooring chain was applied for the FCS strength analysis. The fatigue load was obtained from the coupled analysis results conducted by a collaborating research institute. The structural and fatigue safety of FCS were evaluated in accordance with DNV codes. From the evaluation results, it was confirmed that the FCS satisfies the structural and fatigue safety requirements.

• Journal of the Korean Society for Marine Environment & Energy
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• v.16 no.4
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• pp.276-289
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• 2013

In developing offshore wind farms, many environmental issues arise because of the concentration on supply demand and economic logic. Accordingly, community conflict is induced. Especially, recent studies regarding the capacity and location of offshore wind development have been conducted considering wind states and ocean conditions, etc. of coastal seas in Republic of Korea. Nevertheless, studies on the impact of marine environments and ecosystems are very limited so far. Environmental monitoring that follows development projects has been actively done in the offshore wind farms in many developed European countries. In contrast, there is no domestic monitoring data regarding environmental impacts caused by installing and operating offshore wind power. Therefore, the environmental impacts under construction and operation phases as well as the guidelines in the stage of environmental impact assessment suited for domestic coastal seas are well presented in this study by analyzing monitoring cases and references of overseas offshore wind farm. For this reason, this research is ultimately aimed at minimizing the environmental impact in offshore wind farm development and thus simplify administrative procedures in Korea.

• Earthquakes and Structures
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• v.13 no.1
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• pp.39-50
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• 2017

Displacement response and corresponding maximum response energy of structures are key parameters to assess the dynamic effect or even more destructive structural damage of the structures. By employing them, this research has compared the structural responses of jacket supported offshore wind turbine (OWT) subjected to seismic excitations apprehending earthquake incidence, when (a) soil-structure interaction (SSI) has been ignored and (b) SSI has been considered. The effect of earthquakes under arbitrary angle of excitation on the OWT has been investigated by means of the energy based wavelet transformation method. Displacement based fragility analysis is then utilized to convey the probability of exceedance of the OWT at different soil site conditions. The results show that the uncertainty arises due to multi-component seismic excitations along with the diminution trend of shear wave velocity of soil and it tends to reduce the efficiency of the OWT to stand against the ground motions.

• Wind and Structures
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• v.31 no.4
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• pp.373-380
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• 2020

For large-scale 5MW offshore wind turbines, the discrete equation of fluid domain and the motion equation of structural domain with geometric nonlinearity were built, the three-dimensional modeling of the blade considering fluid-structure interaction (FSI) was achieved by using Unigraphics (UG) and Geometry modules, and the numerical simulation and the analysis of the vibration characteristics for wind turbine structure under rotating effect were carried out based on ANSYS software. The results indicate that the rotating effect has an apparent effect on displacement and Von Mises stress, and the response and the distribution of displacement and Von Mises stress for the blade in direction of wingspan increase nonlinearly with the equal increase of rotational speeds. Compared with the single blade model, the blade vibration period of the whole machine model is much longer. The structural coupling effect reduces the response peak value of the blade displacement and Von Mises stress, and the increase of rotational speed enhances this coupling effect. The maximum displacement difference between two models decreases first and then increases along wingspan direction, the trend is more visible with the equal increase of rotational speed, and the boundary point with zero displacement difference moves towards the blade root. Furthermore, the Von Mises stress difference increases gradually with the increase of rotational speed and decreases nonlinearly from the blade middle to both sides. The results can provide technical reference for the safe operation and optimal design of offshore wind turbines.

• KIPS Transactions on Computer and Communication Systems
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• v.1 no.3
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• pp.161-170
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• 2012

In recent years, many researchers and developers have been interested in renewable energy all over the world. Particularly, the development of wind power is being processed actively due to its high economic efficiency. A few years ago, Korean government has started the research for building a large-scale offshore wind farm in domestic west-southern area. Current domestic SCADA technology level for operating wind farm is very low compared with foreign SCADA technology level. In this paper, we found IT issues and solutions for developing SCADA system. Based on these solutions, we designed SCADA system for a large-scale offshore wind farm.

• Journal of the Korean Society for Marine Environment & Energy
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• v.16 no.4
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• pp.239-247
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• 2013

Recently renewable energy such as offshore wind energy takes a higher interest due to the depletion of fossil fuel and the environmental pollution. This paper deals with multi-body dynamics (MBD) analysis technique for offshore wind turbine system considering aerodynamic loads and Thevenin equation used for determination of electric generator torque. Dynamic responses of 5MW offshore wind turbine system are evaluated via the MBD analysis, and the system is the horizontal axis wind turbine (HAWT) which generates electricity from the three blades horizontally installed at upwind direction. The aerodynamic loads acting on the blades are computed by AeroDyn code, which is capable of accommodating a generalized dynamic wake using blade element momentum (BEM) theory. In order that the characteristics of dynamic loads and torques on the main joint parts of offshore wind turbine system are simulated similarly such an actual system, flexible body modeling including the actual structural properties are applied for both blade and tower in the multi-body dynamics model.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.2
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• pp.127-138
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• 2023

A variety of decarbonized energy sources are being developed globally to realize carbon neutrality (Net Zero) by 2050 as a measure to address the global climate crisis. As the Korean government has also established a Renewable Energy 3020 policy and promoted energy development plans using solar or wind power, large-scale offshore development projects not present before in coastal waters, such as offshore wind farms, are being promoted. From ships' point of view, offshore facilities present obstacles to safe navigation, and with the installation of marine facilities, ship collisions or contact accidents between ships and marine facilities may occur in the narrowed water areas. In addition, there are concerns about environmental pollution and human casualties caused by marine accidents. Accordingly, we review overseas and domestic offshore wind farm development plans, analyze whether institutional devices are in place to ensure the safe passage of ships in wind farm areas, and study the safe operation of large-scale offshore wind farms and safe passage of ships along the Korean coast by comparing overseas legislative cases with domestic laws and presenting a proposal to illuminate the legal blind sectors.