• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1996.10a
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• pp.19-22
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• 1996

Extreme sea statistics and combinations of environmental events or response for structures are very important problem in performance evaluation and design of coastal and Offshore structures. A probabilistic method is developed that leads to the combination of Typhoon (Hurricane) or winter storm induces winds, waves, currents and surge for a generic site. The traditional recommendation for the fixed structures is a combination of the 100 years maximum wave height with the 100 years wind and current. (omitted)

• Ocean Systems Engineering
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• v.14 no.2
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• pp.171-210
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• 2024

This paper focuses on the rigorous and holistic fatigue analysis of mooring chains for a deep draft semi-submersible platform in the challenging environment of the central Gulf of Mexico (GoM). Known for severe hurricanes and strong loop/eddy currents, this region significantly impacts offshore structures and their mooring systems, necessitating robust designs capable of withstanding extreme wind, wave and current conditions. Wave scatter and current bin diagrams are utilized to assess the probabilistic distribution of waves and currents, crucial for calculating mooring chain fatigue. The study evaluates the effects of Vortex Induced Motion (VIM), Out-of-Plane-Bending (OPB), and In-Plane-Bending (IPB) on mooring fatigue, alongside extreme single events such as 100-year hurricanes and loop/eddy currents including ramp-up and ramp-down phases, to ensure resilient mooring design. A detailed case study of a deep draft semi-submersible platform with 16 semi-taut moorings in 2,500 meters of water depth in the central GoM provides insights into the relative contributions of wave scatter diagram, VIMs from current bin diagram, the combined stresses of OPB/IPB/TT and extreme single events. By comparing these factors, the study aims to enhance understanding and optimize mooring system design for safety, reliability, and cost-effectiveness in offshore operations within the central GoM. The paper addresses a research gap by proposing a holistic approach that integrates findings from various contributions to advance current practices in mooring design. It presents a comprehensive framework for fatigue analysis and design optimization of mooring systems in the central GoM, emphasizing the critical importance of considering environmental conditions, OPB/IPB moments, and extreme single events to ensure the safety and reliability of mooring systems for offshore platforms.

• Ocean Systems Engineering
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• v.7 no.2
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• pp.121-141
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• 2017

The purpose of this paper is to understand and model the slow current (~2 m/s) effects on the global response of a floating offshore platform in waves. A time-domain numerical simulation of full wave-current-body interaction by a quadratic boundary element method (QBEM) is applied to compute the hydrodynamic loads and motions of a floating body under the combined influence of waves and current. The study is performed in the context of linearized potential flow theory that is sufficient in understanding the leading-order current effect on the body motion. The numerical simulations are validated by quantitative comparisons of the hydrodynamic coefficients with the WAMIT prediction for a truncated vertical circular cylinder in the absence of current. It is found from the simulation results that the presence of current leads to a loss of symmetry in flow dynamics for a tension-leg platform (TLP) with symmetric geometry, resulting in the coupling of the heave motion with the surge and pitch motions. Moreover, the presence of current largely affects the wave excitation force and moment as well as the motion of the platform while it has a negligible influence on the added mass and damping coefficients. It is also found that the current effect is strongly correlated with the wavelength but not frequency of the wave field. The global motion of a floating body in the presence of a slow current at relatively small encounter wave frequencies can be satisfactorily approximated by the response of the body in the absence of current at the intrinsic frequency corresponding to the same wavelength as in the presence of current. This finding has a significant implication in the model test of global motions of offshore structures in ocean waves and currents.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.2
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• pp.242-251
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• 2013

Recently, while global concern over offshore resources exploration and development is being increased rapidly, offshore plant industry is highlighted as an industry of high added value. Along with this global trend, domestic concern over offshore plant development is being increased as well. In the overseas case, a marine geotechnical survey guideline for confirming characteristics of seabed sediments is available at the time of installation of offshore plant but such guideline is not available in our country. In this study, survey techniques fit for domestic marine environment was applied according to overseas guideline at southern coastal area, Korea. Among the marine geophysical survey techniques being proposed abroad, magnetic survey and seabed photograph were excluded. However, highly reliable data analysis was enabled for marine geophysical survey, which includes in-situ coring investigation and laboratory soil test. In addition, continuous ocean current survey was included to find scour potential due to the current around the offshore plant. Although coring depth is not so deep, we predicted geological structure through the analysis of amplitude features of seismic data. Characteristics of seabed sediments cold be obtained regionally and directly through combined analysis of marine geophysical survey data and coring data.

• Corrosion Science and Technology
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• v.6 no.3
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• pp.90-95
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• 2007

Cathodic protection technology has been widely used on ship's outer hull and inner side of ballast water tanks as a supplementary corrosion protection measure in combination with protective organic coatings. Impressed current cathodic protection system is typically opted for the ship's hull and, sacrificial anode system, for ballast water tanks. The anticipation and interest in cathodic protection system for ships has been surprisingly low-eyed to date in comparison with protective coatings. Computational analysis for the verification of cathodic protection design has been tried sometimes for offshore marine structures, however, in commercial shipbuilding section, decades old design practice is still applied, and no systematic or analytical verification work has been done for that. In this respect, over-rotection from un-erified initial design protocol has been also concerned by several experts. Especially, it was frequently reported in sacrificial anode system that even after full design life time, anode was remaining nearly intact. Another issue for impressed current system, for example, is that the anode shield area design for ship's outer hull should be compromised with actual application situation, because the state-of-the-art design equation is quite impractical from the applicator's stand. Besides that, in this study, some other critical design issues for sacrificial anode and impressed current cathodic protection system were discussed.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.702-703
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• 2011

Large offshore wind farms using high voltage direct current transmission system (HVDC) have been considered and exploited in many countries in the world. The maintenance of the stable operation of wind farm and interconnected system is an important issue, especially in the case of fault. To ensure the stable operation after fault clearance, the PCC voltage must be restored as soon as possible and meet the grid code requirement. This paper will evaluate the PCC voltage recovery ability of a large offshore wind farm as it is connected to a weak grid via a VSC-HVDC.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.1008-1016
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• 2007

The purpose of this paper is to investigate the Natural Frequency behavior characteristic of Wind Turbine Tower model, and calculated the stress values of thrust load, wave load, wind load, current load, and gravity load. The offshore Jacket Type Tower which was installed in Vitenam South China Sea is used for the study. Natural frequency and mode shape are calculated with commercial program using the measured vibration. The finite element analysis is performed with commercial F.E.M program(ANSYS) on the basis of the natural frequency and mode shape.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.8
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• pp.1108-1114
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• 2013

This paper presents a new winding topology for MW class offshore wind generator having modular and dual 3-phase. Based on proposed simplified relationship between magnetic flux and phase current in the air gap, several new windings for modular and dual 3-phase are made. In case of one inverter operation or faulty operation, the proposed model can have balanced 3-phase induced voltage whereas the conventional generator with modular winding has unbalanced induced voltage, which can be important issue in offshore generator. The model was applied into 6MW prototype machine with dual 3-phase. Using finite element analysis, induced voltage, inductance were investigated. The results show that the proposed modular winding can be applicable to dual inverter system with electrically balanced voltage.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.5
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• pp.750-756
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• 2017

This paper presents a method for DC voltage control of HVDC system connection of offshore wind farms. In the event of fault in AC grid, HVDC system need to meet LVRT regulations. When HVDC system meet LVRT regulation, unbalance is caused between power input and power output for DC link. Therefore, LVRT regulation lead to DC voltage increase of HVDC system. To control the DC voltage increase, the chopper resistor can be suggested. In this paper, DC voltage suppression is proposed using chopper resistor and de-loading. The effectiveness of the chopper resistor was verified using PSCAD/EMTDC.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.21 no.1
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• pp.1-10
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• 1988

The vertical temperature profiles of the Yellow Sea in summer are investigated by means of the nine air temperature (AT) patterns which are classified with the AT of winter and summer. The sea surface temperature (SST) is high when the AT of summer is high, and vice versa. The gradient of thermocline in the offshore region is higher than that in the coastal region and is not always favorable with the AT patterns. The relation between sea bottom temperature (SBT) and the AT of winter is favorable when the SBT is averaged in the coastal and offshore stations. In addition, the SST of coastal stations is higher than that of offshore stations because of the strong mixing by the tidal current in the coastal region. The correlation between the AT and the SST of August is favorable (r=0.44-0.69), while the correlation between the AT of February and the SBT of August is not favorable except the stations, A2 (r=0.57) and B2 (r=0.61).