• Structural Engineering and Mechanics
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• v.52 no.3
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• pp.633-646
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• 2014

A semi-analytical numerical approach for the effective structural dynamic response analysis of spar floating substructure for offshore wind turbine subject to wave-induced excitation is introduced in this paper. The wave-induced rigid body motions at the center of mass are analytically solved using the dynamic equations of rigid ship motion. After that, the flexible structural dynamic responses of spar floating substructure for offshore wind turbine are numerically analyzed by letting the analytically derived rigid body motions be the external dynamic loading. Restricted to one-dimensional sinusoidal wave excitation at sea state 3, pitch and heave motions are considered. Through the numerical experiments, the time responses of heave and pitch motions are solved and the wave-induced dynamic displacement and effective stress of flexible floating substructure are investigated. The hydrodynamic interaction between wave and structure is modeled by means of added mass and wave damping, and its modeling accuracy is verified from the comparison of natural frequencies obtained by experiment with a 1/100 scale model.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.367-375
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• 2020

This paper presents an integrated analysis about dynamic performance of a Floating Offshore Wind Turbine (FOWT) OC4 DeepCwind with semi-submersible platform under real sea environment. The emphasis of this paper is to investigate how the wave mean drift force and slow-drift wave excitation load (Quadratic transfer function, namely QTF) influence the platform motions, mooring line tension and tower base bending moments. Second order potential theory is being used for computing linear and nonlinear wave effects, including first order wave force, mean drift force and slow-drift excitation loads. Morison model is utilized to account the viscous effect from fluid. This approach considers floating wind turbine as an integrated coupled system. Two time-domain solvers, SIMA (SIMO/RIFLEX/AERODYN) and FAST are being chosen to analyze the global response of the integrated coupled system under small, moderate and severe sea condition. Results show that second order mean drift force and slow-drift force will drift the floater away along wave propagation direction. At the same time, slow-drift force has larger effect than mean drift force. Also tension of the mooring line at fairlead and tower base loads are increased accordingly in all sea conditions under investigation.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.3
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• pp.183-191
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• 2002

In general, the salient features of the floating breakwater have excellent regulation of sea-water keeping the marine always clean, up and down free movement with the incoming and outgoing tides, capable of being installed without considering the geological condition of sea-bed at any water depth. This study discusses the three dimensional wave transformation of the floating breakwater moored by piers, and its dynamic response numerically. Numerical method is based on the boundary integral method and eigenfunction expansion method. It is known that pier mooring system has higher absorption of wave energy than the chain mooring system. Pier mooring system permit only vertical motion (heaving motion) of floating breakwater, other motions restricted. It is assumed in the present study that a resistant force as friction between piers and floating pontoon is not applied far the vertical motion of the floating breakwater. According to the numerical results, draft and width of the floating breakwater affect on the wave transformations greatly, and incident wave of long period is well transmitted to the rear of the floating breakwater, And the vertical motion come to be large for the short wave period.

• Geomechanics and Engineering
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• v.10 no.4
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• pp.387-403
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• 2016

In this paper, an integrated model for the wave (current)-induced seabed response is presented. The present model consists of two parts: hydrodynamic model for wave-current interactions and poro-elastic seabed model for pore accumulations. In the wave-current model, based on the fifth-order wave theory, ocean waves were generated by adding a source function into the mass conservation equation. Then, currents were simulated through imposing a steady inlet velocity on one domain and pressure outlet on the other side. In addition, both of the Reynolds-Averaged Navier-Stokers (RANS) Equations and $k-{\varepsilon}$ turbulence model would be applied in the fluid field. Once the wave pressures on the seabed calculated through the wave-current interaction model, it would be applied to be boundary conditions on the seabed model. In the seabed model, the poro-elastic theory would be imposed to simulate the seabed soil response. After comparing with the experimental data, the effect of currents on the seabed response would be examined by emphasize on the residual mechanisms of the pore pressure inside the soil. The build-up of the pore water pressure and the resulted liquefaction phenomenon will be fully investigated. A parametric study will also be conducted to examine the effects of waves and currents as well as soil properties on the pore pressure accumulation.

• The Journal of the Korea Contents Association
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• v.22 no.10
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• pp.861-869
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• 2022

In patients with Tourette's syndrome, a tic occurs when Mu wave synchronization is broken. Conversely, when Mu wave synchronization is achieved, a tick does not occur. When the tic is suppressed, the cognitive control response process is changed, and if the neurofeedback training that adjusts the EEG frequency power is performed with the changed, the patient will be treated autonomously without artificially suppressing the tic. The results of the research test suggest that if the tic patient does not artificially synchronize mu waves in the premotor cortex (Frontal Cortical 3 site), and if EEG control is performed autonomously like neurofeedback training, as a result, tics do not occur. Cognitive control response processes are altered when a subject is inhibited from tics. By training the altered cognitive control with neurofeedback that modulates EEG frequency power, the patient can be treated autonomously without artificially suppressing the tic.Mu-wave synchronizationcan now be added to existing neurofeedback treatment protocols such as SMR reinforcement, theta-beta-wave imbalance correction, and alpha-wave reinforcement. This study will be used in follow-up studies and clinical trials to more scientifically verify the neurofeedback treatment protocol, a treatment for patients with Tourette's syndrome.

• Journal of Ship and Ocean Technology
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• v.6 no.4
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• pp.13-18
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• 2002

Active control has been partly applied to suppress the re-reflecting waves in wave basin with plunger-type wave maker to obtain desirable waves. This limitation comes from the non-confirmable theoretical background to the control algorithm. This paper proposes control logic to overcome this drawback, based on the impulse response function for propagating waves between control input and the wave height. The performances have been verified as reasonable in practical application by comparing with the propagating wave components in numerical wave basin, using wave decomposition method. Moreover, the control logic can also give useful wave-absorbing performance after cessation of wave generation.

• Journal of Power System Engineering
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• v.14 no.5
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• pp.48-55
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• 2010

When a large ship is advancing in waves, ship undergoes the hydroelastic response, which has influences on structural stability and the fatigue destruction etc. of the ship. Therefore, to predict accurate hydroelastic response, it is necessary to analyze hydroelastic response including fluid-structure interaction. In this research, a ship is divided into many hull elements to calculate the fluid forces and wave exciting forces on each elements using three-dimensional source distribution method. The calculated fluid forces and wave exciting forces are assigned to nodes of hull elements. The neighbor nodes are connected with elastic beam elements. We analyzed hydroelastic responses, and those are formulated by using finite element method. Particularly, to estimate the influence of forward speed on the hydroelastic responses, we use two different methods : Full Hull Rotation Method(FHRM) and Sectional Hull Rotation Method(SHRM).

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.6
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• pp.577-583
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• 2012

Structures floating in the ocean experience various kinds of external loads, among which wave load is considered as determining factor in structural design. Its relative size compared with wavelength may be used to classify whether the structure is relatively small or large. Traditionally, the small structures are assumed to have little diffraction and the wave loads on large structure are usually calculated by only considering inertia force according to diffraction. In this paper, rectangular floating structures usually used in the ocean, river, and lake are used to find the relationship between hydrodynamic forces and its structural response.

• Journal of Ocean Engineering and Technology
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• v.12 no.2 s.28
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• pp.33-42
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• 1998

In the presence of incident waves with different frequencies, the second order sum and difference frequency waves due to the nonlinearity of the incident waves come into existence. Although the magnitudes of the forces produced on a Tension Leg Platform(TLP) by these nonlinear waves are small, they act on the TLP at sum and difference frequencies away from those of the incident waves. So, the second order sum and difference frequency wave loads produced close to the natural frequencies of TLPs often give greater contributions to high and low frequency resonant responses. The second order wave exciting forces and moments have been obtained by the method based on direct integration of pressure acting on the submerged surface of a TLP. The components of the second order forces which depend on first order quantities have been evaluated using the three dimensional source distribution method. The numerical results of time domain analysis for the nonlinear wave exciting forces in regular waves are compared with the numerical ones of frequency domain analysis. The results of comparison confirmed the validity of the proposed approach.

• Ocean Systems Engineering
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• v.10 no.2
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• pp.131-161
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• 2020

The objective of this study was to evaluate the downtime cost of side-by-side offloading operations in Malaysian waters. With the help of a numerical time domain tool, the structure and cable response of moored FPSO vessel was simulated for heading and beam sea-states under irregular waves. The weather downtime was assessed by comparing the response under operational wave condition with the pre defined industrial safe offloading criteria. Additionally, two cases of cable failure were simulated for each sea-state. The novel study on downtime cost was presented for three different location of Malaysia subcontinent for which the location specific wave scatter diagram facilitated to estimate the probability of occurrence of operational wave condition. It was concluded that an unpredictable increment in wave height by 0.5 m can significantly impact the production cost.