• Journal of Ship and Ocean Technology
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• v.10 no.1
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• pp.38-46
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• 2006

The objective of this paper is to summarize current ultra-deepwater (i.e., up to 3,500 meters water depth) pipeline mechanical design methodologies as part of the limit state design. The standard mechanical design for ultra-deepwater pipelines in the Gulf of Mexico (GOM) is based on API RP 1111. API code also has been used for deepwater projects in west Africa. DNV code OS-F101 was mostly used for deepwater projects in offshore Brazil and Europe. Some pipeline designs in the GOM have started to incorporate parts of the DNV design methodology. A discussion of failure under collapse only and combined loading (i.e. pressure + bending) is presented. The best design criteria are obtained from physical full-scale collapse testing. The comparison of the physical test data and collapse calculations using the DNV and API codes will be presented. It was found that the conservatism still exists in the collapse prediction for ultra-deepwater pipeline using modem design codes such as DNV OS-F101 and API RP 1111.

• Geomechanics and Engineering
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• v.18 no.2
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• pp.153-159
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• 2019

This paper examines the results from three-dimensional dynamic finite element analysis undertaken to develop a new dynamically installed anchor (DIA). Several candidate shapes of new DIAs were selected after an investigation into previous researches of existing DIA designs. The performances of selected DIAs during the installation and loading in non-homogeneous clay were investigated through large deformation finite element (LDFE) analyses. Findings were compared to the current anchors in operation (i.e., Torpedo and Omni-Max DIA) to assess the viability of the new designs in the field. Overall, the anchor embedment depths of the novel DIAs lied under the results of OMNI-Max DIA. And also, the tracked anchor trajectory confirmed that, the novel DIAs dove deeper with stiffer travelling angle, compared to the OMNI-Max DIA. These elements are more critical and beneficial especially in a field where the achieved embedment depths are generally low.

• Journal of Ocean Engineering and Technology
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• v.9 no.2
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• pp.53-60
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• 1995

A multi-leg spread mooring system for floating offshore structures is important, but the multi-leg static analysis is complicated due to the nonlinear behavior of each line and the effect of current which affects each line differently. The pretensioned position of the multi-leg mooring system obtained from the static equilibrium condition changes into a different position due to external loads and current. In this paper, the new position and the static tension at each line are caculated. The relation between the initial static equilibrium position and the new position due to the external loads is expressed in terms of the Taylor's series expansion. The Runge-Kutta $4^{th}$ method is employed in analyzing the 3-dimensional static cable nonlinear equations.

• Ocean Systems Engineering
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• v.3 no.4
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• pp.309-325
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• 2013

Ocean Thermal Energy Conversion (OTEC) systems utilize the temperature difference between the surface water and deep ocean water to generate electrical energy. In addition to ocean surface waves, wind and current, in certain locations like the Andaman Sea, Sulu Sea and the South China Sea the presence of strong internal waves may become a concern in floating OTEC system design. The current paper focuses on studying the dependence of the CWP hydrodynamic drag on relative velocity of the flow around the pipe, the effect of drag amplification due to vortex induced vibrations and the influence of internal waves on the floating semi and the cold water pipe integrated OTEC system. Two CWP sizes are modeled; the 4m diameter pipe represents a small scale prototype and the 10m diameter pipe represents a full commercial size CWP. are considered in the study.

• Fisheries and Aquatic Sciences
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• v.12 no.3
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• pp.240-248
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• 2009

Distribution and abundance of planktonic shrimps were studied in the southern sea of Korea from 1987 to 1991. Nine species of five genera belonging to three families were identified. Of these, Leptochela sydniensis and Lucifer intermedius were predominant species and Lucifer penicilifer and Lucifer typus were common species. Remaining five species, Acetes chinensis, Leptochela gracilis, Lucifer chacei, Process wheeleri and Sergestes similis occurred sporadically and rarely. The distribution pattern of planktonic shrimps varied with species and sampling periods. L. intermedius occurred abundantly along inshore waters. L. penicilifer and L. typus appeared in both inshore and offshore waters, but more abundantly in offshore waters under influence of the Tsushima Current. In conclusion, the distribution patterns of planktonic shrimps may be related with hydrographic characteristics and seasonality in the southern sea of Korea.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.1
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• pp.8-14
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• 2004

As the number of offshore structure is glowing in deep waters, there have been increased damages of it. These floating structures in offshore locations exposed to harsh environmental conditions. In recent years, there has been a slowing attention around damages on bow and deck on FPSO caused by waves in steep storm condition. This paper describes a study of the water on deck due to the dynamic behavior of a FPSO with turret mooring system. The nonlinear motions of the FPSO are simulated under external forces due to wave, current, wind, and mooring forces in the time domain. The direct integration method is employed to estimate low frequency drift wave forces. The current forces are calculated by using slow motion maneuvering equations in the horizontal plane. The coefficients of a model for wind forces are calculated from Isherwood's experimental data and the variation of wind speed is estimated by wind spectrum according to the guidelines of API-RP2A.

• Proceedings of the KSRS Conference
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• 2004.10a
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• pp.553-556
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• 2004

Spatial and temporal aspects of toxic dinoflagellate Cochlodinium.p blooms and consequences of physical features in complex coastal ecosystems, off the southern Korean coast, have been investigated using data obtained from SeaWiFS and AVHRR as well as in-situ observations. Hydrographic parameters measured using CTD sensors were used to elucidate physical factors affecting the spatial distribution and abundance of Cochlodinium.p blooms. The results show spatial and temporal variations of chlorophyll-a (Chl-a) and sea surface temperature (SST) and reveal significant information about Cochlodinium.p blooms and process underlying their evolution. Satellitederived Chl-a estimates appear to be potential in explicating the evolution, movement and distribution of Cochlodinium.p blooms in the enclosed bays of the South Sea. The existence of thromohaline waters offshore provide favorable conditions for the rapid growth and subsequent southward initiation of Cochlodinium.p blooms that are influenced to flow on the offshore branch (OB) during September. It was observed that there was a significant variation in the sun-induced chlorophyll-a fluorescence signal in the remote sensing fluorescence spectra and its high-intensity was recognized during the period of exponential growth and physical transport. Satellite-derived Chl-a concentration during September 1999 ranged between $3­60mg/m^3$ inside the Jin-hae and adjacent Bays and $1-6mg/m^3$ in offshore waters, with varying Cochlodinium.p abundances 1500 to 26000 cells $ml^{-1}.$ The closely spaced CTD surveys and satellite-derived SST give a complete overview on the initiation of Cochlodinium.p blooms in hydrodynamically active regions of the offshore southern East Sea by the influence of Tsushima Warm Current (TWC).

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2012.06a
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• pp.388-389
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• 2012

Current offshore wind power towers are made of steel. As the capacity of wind power increases, the tower structures become higher. Steel structures have buckling problem and their increased slenderness ratios make them weak against buckling and vibration. In this study, double skinned composite tubular (DSCT) offshore wind power tower was proposed and its optimum design method was suggested. Fiber reinforced polymer (FRP) and steel were considered as material of the tubes. And both materials satisfied the required capacity.

• Wind and Structures
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• v.20 no.6
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• pp.751-761
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• 2015

A multi-platform offshore wind farm is receiving the worldwide attention for the sake of maximizing the wind power capacity and the dynamic stability at sea. But, its wind power efficiency is inherently affected by the interference of wake disturbed by the rotating blades, so its layout should be appropriately designed to minimize such wake interference. In this context, the purpose of this paper is to introduce a layout optimization for multi-platform offshore wind farm consisted of 2.5MW spar-type floating wind turbines. The layout is characterized by the arrangement type of wind turbines, the spacing between wind turbines and the orientation of wind farm to the wind direction, but the current study is concerned with the spacing for a square-type wind farm oriented with the specific angle. The design variable and the objective function are defined by the platform length and the total material volume of the wind farm. The maximum torque loss and overlapping section area are taken as the constraints, and their meta-models expressed in terms of the design variable are approximated using the existing experimental data and the geometry interpretation of wake flow.

• Journal of Ocean Engineering and Technology
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• v.27 no.1
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• pp.9-15
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• 2013

This paper calculates the mating dynamic forces of a semi-submersible offshore structure's topside module, where a hull moored in the sea is combined with a topside module carried by a heavy lift vessel, as a mating installation method. The environmental conditions include various wave directions and wave heights, with constant wind and current speeds. Appropriate ballast and de-ballast plans for the heavy lift vessel and hull of the semi-rig should be performed in order to safely obtain these forces, whereas a fixed platform or the GBS (Gravity based structure) type of offshore structure only needs a ballast plan for the heavy lift vessel. From this paper, the allowable wave height or wave direction for the mating procedure can be investigated based on the standard DAF (Dynamic amplitude factor) of the rules and regulations.