• Journal of Ocean Engineering and Technology
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• v.33 no.2
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• pp.116-122
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• 2019

Among the various wave power systems, Salter's duck (rotor) is one of the most effective wave absorbers for extracting wave energy. The rotor shape is designed such that the front part faces the direction of the incident wave, which forces it to bob up and down due to wave-induced water particle motion, whereas the rear part, which is mostly circular in shape, reflects no waves. The asymmetric geometric shape of the duck makes it absorb energy efficiently. In the present study, the rotor was investigated using WAMIT (a program based on the linear potential flow theory in three-dimensional diffraction/radiation analyses) in the frequency domain and verified using OrcaFlex (design and analysis program of marine system) in the time domain. Then, an experimental investigation was conducted to assess the performance of the rotor motion based on the model scale in a two-dimensional (2D) wave tank. Initially, a free decay test (FDT) was carried out to obtain the viscous damping coefficient. The pitch response was extracted from the experimental time series in a periodic regular wave for two different wave heights (1 cm and 3 cm). In addition, the viscous damping coefficient was calculated from the FDT result and fluid forces, obtained from WAMIT, are incorporated into the final response of the rotor. Finally, a comparative study based on experimental and numerical results (WAMIT & OrcaFlex) was performed to confirm the performance reliability of the designed rotor.

• Journal of the Korean Society of Marine Environment & Safety
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• v.19 no.2
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• pp.200-206
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• 2013

The paper was investigated on the mooring forces(or tension) and motion response characteristics for a 8-point mooring floating dock in regular waves using a commercial code(AQWA). To achieve the aim of the research, a numerical simulation was adapted on an inner port environment condition, which the water depth is 10 meters, significant wave amplitude(1.05 m). wave period(3.85 sec), wind speed(20.21 m/s), wind and current direction ($90^{\circ}$), incident waves(${\chi}=180^{\circ}$, $135^{\circ}$ and $90^{\circ}$). The dimension of the numerical model is length(140 m), breadth(32 m), depth(14.6 m). The maximum length of a mooring line is 120m. We can expected that roll and pitch motions appeared in beam seas better than head sea. the mooring forces also indicated higher in bean seas than in head seas including wind forces.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.1
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• pp.72-80
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• 1994

A discrete spectral model of wind waves for arbitrary depth and current is presented This model incorporates wave growth. decay by opposite int bottom friction and wave-current interaction. Depth dependent factor was also added to the fully developed spectrum in order to consider finite depth effects. The physical behavior for the effect of depth and bottom friction was analyzed for an artificially-imposed wind field.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.38.1-38.1
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• 2011

This study investigates the effects of Pierson-Moskowitz, Jonswap spectrum that are typical irregular wave spectrums for wind turbine system with jacket support structure. Also various offshore environmental parameters based on korean local condition were used in our study. The loads acting on the system was considered by referring to the Design Load Case from IEC guide line. And improved von Karman model was used as a turbulence model. As a result, various significant wave height and peak spectral period cause noticeable difference of extreme and fatigue loads prediction.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.889-901
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• 2021

The tension of cables and motion response significantly affect safety of an immersed tunnel element in the immersion process. To investigate those, a hydrodynamic scale-model test was carried out and the model experiments was conducted under wind, current and wave loads simultaneously. The immersion standby (the process that the position of the immersed tunnel element should be located before the immersion process) and immersion process conditions have been conducted and illustrated. At the immersion standby conditions, the maximum force of the cables and motion is much larger at the side of incoming wind, wave and current, the maximum force of Element-6 (6 cables directly tie on the element) is larger than for Pontoon-8 (8 cables tie on pontoon of the element), and the flexible connection can reduce the maximum force of the mooring cables and motion of element (i.e. sway is expecting to decrease approximate 40%). The maximum force of the mooring cables increases with the increase of current speed, wave height, and water depth. The motion of immersed tunnel element increases with increase of wave height and water depth, and the current speed had little effect on it. At the immersion process condition, the maximum force of the cables decrease with the increase of immersion depth, and dramatically increase with the increase of wave height (i.e. the tension of cable F4 of pontoons at wave height of 1.5 m (83.3t) is approximately four times that at wave height of 0.8 m). The current speed has no much effect on the maximum force of the cables. The weight has little effect on the maximum force of the mooring cables, and the maximum force of hoisting cables increase with the increase of weight. The maximum value of six-freedom motion amplitude of the immersed tunnel element decreases with the increase of immersion depth, increase with the increase of current speed and wave height (i.e. the roll motion at wave height of 1.5 m is two times that at wave height of 0.8 m). The weight has little effect on the maximum motion amplitude of the immersed tunnel element. The results are significant for the immersion safety of element in engineering practical construction process.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1993.07a
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• pp.20-25
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• 1993

In coastal waters, more often than not, waves propagate on currents driven by tidal forces, earth’s gravity, or wind. There have been a number of studies for dealing with the change of wave spectrum due to tile presence of current. Based on the conservation of wave action, Hedges et al. (1985) have proposed an equation which describes the influence of current on the change of wave spectrum in water of finite depth. (omitted)

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.271-272
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• 2008

Renewable energy resources such as wind, wave, solar, micro hydro, tidal and biomass etc are becoming important stage by stage, considering the effect of environment. Wind energy is one of the most successful sources of renewable energy for the production of electrical energy. What's more, due to wind speed random variation the wind turbine generators can not make two-state model as conventional generators. The method of obtaining reliability evaluation indices of wind turbine generators is different from the conventional generators. This paper presents a study on the reliability evaluation of power system considering wind turbine generators with a simplified multi-state model.

• Wind and Structures
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• v.22 no.5
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• pp.525-541
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• 2016

An offshore wind turbine supported by a spar buoy floating platform is the subject of this study on tower and rotor extreme loads. The platform, with a 120-meter draft and assumed to be sited in 320 meters of water, supports a 5 MW wind turbine. A baseline model for this turbine developed at the National Renewable Energy Laboratory (NREL) is employed in stochastic response simulations. The support platform, along with the mooring system consisting of three catenary lines, chosen for loads modeling, is based on the "Hywind" floating wind turbine concept. Our interest lies in gaining an understanding of the dynamic coupling between the support platform motion and the turbine loads. We first investigate short-term response statistics using stochastic simulation for a range of different environmental wind and wave conditions. From this study, we identify a few "controlling" environmental conditions for which long-term turbine load statistics and probability distributions are established.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.6
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• pp.383-396
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• 2016

In this study, wave model was conducted on the presence or absence of water level changes and currents effects in coastal waters coexisting with waves and currents, then the results were compared. The flow field applied the results of the RIAMOM model and the wave model applied the SWAN model. Among ECMWF, NCEP and JMA, wind data applied JMA data sets which agreed well with the observed data comparatively. Numerical simulation was conducted for 8 months from January to August 2016. For each case, the deviation of wave height was calculated for the high wave of more than 2.5 m for comparison with observed data. As a result, the deviation of wave height was not significant both considering water level changes and currents effects or not at wave observation stations installed in deep waters. However, a significant deviation of wave height of 5~10% was obtained depending on water level changes and currents effects at the comparison point in shallow waters.

• Wind and Structures
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• v.24 no.4
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• pp.333-350
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• 2017

Differing from the fixed-type, the dynamic motion of floating-type offshore wind turbines is very sensitive to wind and wave excitations. Thus, the sensing and monitoring of its motion is important to evaluate the dynamic responses to the external excitation. In this context, a monitoring system for sensing and processing the wind-induced dynamic motion of spar-type floating offshore wind turbine is developed in this study. It is developed by integrating a 1/00 scale model of 2.5MW spar-type floating offshore wind turbine, water basin equipped with the wind generator, sensing and data acquisition systems, real-time CompactRIO controller and monitoring program. The scale model with the upper rotatable blades is installed within the basin by means of three mooring lines, and its translational and rotational motions are detected by 3-axis inclinometer and accelerometers and gyroscope. The detected motion signals are processed using a real-time controller CompactRIO to calculate the acceleration and tilting angle of nacelle and the attitude of floating platform. The developed monitoring system is demonstrated and validated by measuring and evaluating the time histories and trajectories of nacelle and platform motions for three different wind velocities and for eight different fairlead positions.