• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.5
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• pp.407-413
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• 2013

This paper deals with the analysis of dynamic characteristics of mooring system of floating-type offshore wind turbine. A spar-type floating structure which consists of a nacelle, a tower and the platform excepting blades, is used to model the floating wind turbine and connect three catenary cables to substructure. The motion of floating structure is simulated when the mooring system is attached using irregular wave Pierson-Moskowitz model. The mooring system is analyzed by changing cable position of floating structure. The dynamic behavior characteristics of mooring system are investigated comparing with cable tension and 6-dof motion of floating structure. These characteristics are much useful to initial design of floating-type structure. From the simulation results, the optimized design parameter that is cable position of connect point of mooring cable can be obtained.

• The KSFM Journal of Fluid Machinery
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• v.14 no.5
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• pp.48-54
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• 2011

Structural modifications of a ship may cause a fatal accident such as sinking and wrecking of ship. Especially, barge ship can be easily reconstructed to load more bulk cargo. In this study, for a real accident case, change of mooring force due to structural modification was analyzed to evaluate accident risk. A two dimensional dynamic model for the barge ship was constructed to compute mooring forces with related to floating motion. The equation of motion was established in Matlab code and buoyancy was calculated by using direct integration of submerged volume. The results showed that wind force, current force, and mooring force after rebuilding was approximately 4.3 kN, 14 kN, 1,561 kN respectively. The maximum force of mooring force according to the length of mooring cable were 1,614 kN at 30 m of mooring cable. Thus, an arbitrary modification of ship lead instability and unreliable result so that illegal rebuilding of ship should be avoided.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.3
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• pp.232-239
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• 2002

This paper studies the behavior of mooring line of silt protector according to the change of sea level. It is found from the analysis of the behavior that if the taut cable length has been determined appropriately within the range of safety factor, the tensioned cable has almost constant tension regardless of the water depth. The whole structure, however, becomes unstable due to the loss (zero tension) of the released cable tension. It is also recognized from the investigation for the effect of intial straight line angle on the behavior of mooring line that the design through the conceptually combined consideration of the cable tension, total scope and buoy deflection has to be required in the mooring analysis. Finally, the material of cable is not damaged because the cable tension is reduced by attached shellfish, but the whole structure may be also unstable by the effect on the anchor angle, total scope and buoy deflection.

• Journal of Ocean Engineering and Technology
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• v.10 no.1
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• pp.92-99
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• 1996

Longline type aquaculture facilities are being used for scallpop culture in 30 m of water 2.5 km off the coast of Joomoonjin, Kangwon-do. In this paper, the facilities are modeled by the cabele-buoy-weight system, subject to the nonlinear behaviors of the mooring lines and the effects of current. Its static configuration is shown as a solution of 3-D nonlinear static equation and Runge-Kutta $4^{th}$ method is employed.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.4
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• pp.375-385
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• 2016

Given the rapid progress made in understanding the dynamics of an offshore floating body in an ocean environment, the present study aimed to simulate ocean waves in a small-sized wave flume and to observe the motion of a cylindrical floating body placed in an offshore environment. To generate regular ocean waves in a wave flume, we combined a wave generator and a wave absorber. In addition, to precisely visualise the oscillation of the body, a set of light-emitting diode illuminators and a high-speed charge-coupled device camera were installed in the flume. This study also focuses on the spectral analysis of the movement of the floating body. The wave generator and absorbers worked well to simulate stable regular waves. In addition, the simulated waves agreed well with the plane waves predicted by shallow-water theory. As the period of the oncoming waves changed, the movement of the floating body was substantially different when tethered to a tension-leg mooring cable. In particular, when connected to the tension-leg mooring cable, the natural frequency of the floating body appeared suddenly at 0.391 Hz as the wave period increased.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.4
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• pp.162-174
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• 1996

Longline type aquaculture facilities in the open sea are based on the cable-buoy-weight mooring system. For their optimal design it is necessary to estimate tensions along the mooring lines including the attachment points of buoys and weights. However, the dynamic analysis is very complicated due to the nonlinear behaviors of the mooring lines and the effects of wave and current. In this paper, parametric studies for various buoy-weight cases are shown. Finite difference scheme is employed in obtaining eigenfrequencies in the frequency domain. Nonlinear hydrodynamic drag forces are equivalently linearized.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.3
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• pp.559-579
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• 2015

An experimental study of the effect of mooring systems on the dynamics of a SPAR buoy-type floating offshore wind turbine is presented. The effects of the Center of Gravity (COG), mooring line spring constant, and fairlead location on the turbine's motion in response to regular waves are investigated. Experimental results show that for a typical mooring system of a SPAR buoy-type Floating Offshore Wind Turbine (FOWT), the effect of mooring systems on the dynamics of the turbine can be considered negligible. However, the pitch decreases notably as the COG increases. The COG and spring constant of the mooring line have a negligible effect on the fairlead displacement. Numerical simulation and sensitivity analysis show that the wind turbine motion and its sensitivity to changes in the mooring system and COG are very large near resonant frequencies. The test results can be used to validate numerical simulation tools for FOWTs.

• Journal of Wind Energy
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• v.13 no.3
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• pp.72-78
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• 2022

This study performed a numerical analysis on the effect of platform shape and damaged mooring lines on the movement of the semi-submersible floating offshore wind turbines (FOWT). The NREL 5 MW-OC4-DeepCwind semi-submersible wind turbine was selected as the reference model. In order to find the effect of the semi-submersible floating platform shape, the dynamic movement and feasibility of three different models were observed with and without the presence of turbine blades. In addition, extreme conditions were considered by having one of the mooring lines detached to determine the effects on the FOWT. As a result, the remaining mooring lines deviated to change the surge and sway motion, which could cause a collision with nearby marine structures, and the variation of yaw angle might lead to critical accidents such as rollover. Since the response of the floating platform after receiving mooring line damage may vary depending on the mooring pattern, the location of the mooring damage, and the direction of the wind and waves, detailed simulations showed substantial variation of damage patterns.

• Journal of Ocean Engineering and Technology
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• v.3 no.2
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• pp.526-526
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• 1989

• Ocean Systems Engineering
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• v.3 no.4
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• pp.257-273
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• 2013

Top tensioned riser (TTR) is often used in a floating oil/gas production system deployed in deep water for oil/gas transport. This study focuses on the extension of the existing numerical code, known as CABLE3D, to allow for static and dynamic simulation of a TTR connected to a floating structure through a tensioner system or buoyancy can, and restrained by riser guides at different elevations. A tensioner system usually consists of three to six cylindrical tensioners. Although the stiffness of individual tensioner is assumed to be linear, the resultant stiffness of a tensioner system may be nonlinear. The vertical friction between a TTR and the hull at its riser guide is neglected assuming rollers are installed there. Near the water surface, a TTR is forced to move horizontally due to the motion of the upper deck of a floating structure as well as related riser guides. The extended CABLE3D is then integrated into a numerical code, known as COUPLE, for the simulation of the dynamic interaction among the hull of a floating structure, such as spar or TLP, its mooring system and riser system under the impact of wind, current and waves. To demonstrate the application of the extended CABLE3D and its integration with COUPLE, the numerical simulation is made for a truss spar under the impact of Hurricane "Ike". The mooring system of the spar consists of nine mooring lines and the riser system consists of six TTRs and two steel catenary risers (SCRs).