• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.6
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• pp.557-563
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• 2016

The energy absorption efficiency of a wave power generation system is calculated as the ratio of the wave power to the power of the system. Because absorption efficiency depends on the dynamic behavior of the wave power generation system, a dynamic analysis of the wave power generation system is required to estimate the energy absorption efficiency of the system. In this study, a dynamic analysis of the wave power generation system under wave loads is performed to estimate the energy absorption efficiency. RecurDyn is employed to carry out the dynamic analysis of the system, and the Morison equation is used for the wave load model. According to the results, the lower the wave height and the shorter the period, the higher is the absorption efficiency of the system.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.3
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• pp.223-232
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• 2015

The present paper considers the conceptual design of floating wave-offshore wind hybrid power generation system. The worldwide demand for ocean renewable energy is increasing rapidly. Wave and offshore wind energy have been attractive among the various ocean renewable energy sources, and the site to generate electricity from wave and offshore wind accords well together. This means that a hybrid power generation system, which uses wave and offshore wind energy simultaneously has many advantages and several systems have been already developed in Western Europe. A R&D project for a 10 MW class floating wave-offshore wind hybrid power generation system has been also launched in Korea. A semi-submersible platform, which has four vertical columns at each corner of the platform to be connected with horizontal pontoons, was designed for this system considering arrangements of multiple wind turbines and wave energy converters. A mooring system and power cable were also designed based on the metocean data of installation site. In the present paper, those results are presented, and the difficulties and design method in the design of hybrid power generation system are presented.

• The KSFM Journal of Fluid Machinery
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• v.18 no.3
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• pp.26-32
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• 2015

The authors are developing a motion of floater body type wave energy converter of the float-counterweight system. This consists of the driving pulley, wire, float and counterweight suspended from idler pulleys and rachet mechanism. Though it has succeeded in solving the major structural strength problem in which the floats would slam against adjacent structure(s) by wave load acting horizontally. In order to overcome this problem. We propose a new system in which the wire transmitting the power is wound around the pulleys and the float receiving the wave power is pulled by the wire from both its upper and lower ends to avoid the occurrence of slackening during the wave cycle. In the paper, we developed the dynamics model for the proposed system. Energy gain has been calculated for realistic wave conditions and compared with the original float-counterweight device. The important differences from the float-counterweight system are that (1) both upward and downward motions of water surface can be utilized without problem. (2) slackening of energy gain and wire tension are effectively suppressed, and (4) for the same time averaged energy gain, the maximum wire tension is fairly lowered.

• Ocean Systems Engineering
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• v.3 no.3
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• pp.203-217
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• 2013

A PTO (power-take-off) mechanism by using relative heave motions between a floating buoy and its inner mass (magnet or amateur) is suggested. The inner power take-off system is characterized by a mass with linear stiffness and damping. A vertical truncated cylinder is selected as a buoy and a special station-keeping system is proposed to minimize pitch motions while not affecting heave motions. By numerical examples, it is seen that the maximum power can actually be obtained at the optimal spring and damper condition, as predicted by the developed WEC(wave energy converter) theory. Then, based on the developed theory, several design strategies are proposed to further enhance the maximum PTO, which includes the intentional mismatching among heave natural frequency of the buoy, natural frequency of the inner dynamic system, and peak frequency of input wave spectrum. By using the intentional mismatching strategy, the generated power is actually increased and the required damping value is significantly reduced, which is a big advantage in designing the proposed WEC with practical inner LEG (linear electric generator) system.

• Journal of Ocean Engineering and Technology
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• v.31 no.3
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• pp.202-207
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• 2017

This paper presents the results of an experimental study on the motions and mooring characteristics of a floating vertical axis wind turbine system. Based on a comparison of regular wave experiment results, the motions of structures with different types of mooring are almost the same. Based on the tension response results of a regular wave experiment with a catenary mooring system, the mooring lines in front of the structure have a larger tension effect than the back of the structure by the drifted offset of the structure. The dynamic response spectrum of the structure in the irregular wave experiments showed no significant differences in response to differences in the mooring system. As a result of the comparison of the tension response spectra, the mooring lines have a larger value with a drifted offset for the structure, as shown in the previous regular wave experiment. The results of the dynamic response of the structure under irregular wave and wind conditions showed that the heave motion response is influenced by the coupled effect with the mooring lines of the surge and pitch motion due to the drifted offset and steady heeling. In addition, the mooring lines in front of the structure have a very large tension force compared to the mooring lines in back of the structure as a result of the drifted offset of the structure.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.470-475
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• 2019

This paper deals with a 30kW grid-connected PCS (Power Conversion System) for an Oscillating Water Column (OWC) wave-power generation system. Wave power generation in marine energy is suitable for Korea with the characteristics of a peninsula with three sides facing the sea. In the case of coastal disasters, wave generators can act as a breakwater to reduce damage, and can be integrated with other marine power generation systems to increase efficiency. Wave power generation systems are classified into various types, such as oscillating bodies, OWC, and overtopping according to the operation principle, and they can also be classified into two types according to the installation method: a fixed structure and floating structure. This paper proposes a 30kW grid-connected PCS topology and model for OWC wave power generation that is structurally stable with a turbine and generator that are relatively easy to maintain, and then provide a control method required for grid connection, including DC link voltage control. Simulation verification was performed to verify the proposed PCS.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.167.2-167.2
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• 2011

Motions in nature, for example ocean wave, has been playing a significant role for generating electricity production in our modern life. This paper presents an innovative approach for electric power conversion of the vast ocean wave energy. Here, a floating-buoy wave energy converter (WEC) using hydrostatic transmission (HST), which is shortened as HSTWEC, is proposed and designed to enhance the wave energy harvesting task during all wave fluctuations. In this HSTWEC structure, the power take-off system (PTO) is a combination of the designed HST circuit and an electric generator to convert mechanical energy generated by ocean wave into electrical energy. Several design concepts of the HSTWEC have been considered in this study for an adequate investigation. Modeling and simulations using MATLAB/Simulink and AMESim are then carried out to evaluate these design concepts to find out the best solution. In addition, an adaptive controller is designed for improving the HSTWEC performance. The effectiveness of the proposed HSTWEC control system is finally proved by numerical simulations.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.4
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• pp.739-749
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• 2015

A new conceptual dual-buoy Wave Energy Converter (WEC) for the enhancement of energy extraction efficiency is suggested. Based on actual wave data, the design process for the suggested WEC is conducted in such a way as to ensure that it is suitable in real sea. Actual wave data measured in Korea's East Sea (position: $36.404N^{\circ}$ and $129.274E^{\circ}$) from May 1, 2002 to March 29, 2005 were used as the input wave spectrum for the performance estimation of the dual-buoy WEC. The suggested WEC, a point absorber type, consists of two concentric floating circular cylinders (an inner and a hollow outer buoy). Multiple resonant frequencies in proposed WEC affect the Power Ttake-off (PTO) performance of the WEC. Based on the numerical results, several design strategies are proposed to further enhance the extraction efficiency, including intentional mismatching among the heave natural frequencies of dual buoys, the natural frequency of the internal fluid, and the peak frequency of the input wave spectrum.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2014.10a
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• pp.17-18
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• 2014

Wave energy generation system is sorted as oscillating water chamber type, over topping device type and wave activating body type. The wave activating body type converts from wave energy to kinetic of the machine one and the power generation amount increases while the motion of a activating body increases. In this paper the wave energy convertor consists of a main body which has a generation system and the activating body. They are connected by a bar type bridge. The twisting moment and angular velocity at a shaft of convertor are calculated when various condition of the incident wave, a diversity of connection methods between the main body and the activating body. It can be used as basic idea for determining the design of wave activating body type convertor.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.8
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• pp.905-911
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• 2012

To establish a floating offshore wind turbine simulation model, a tension leg platform is added to an onshore wind turbine. The wind load is calculated by using meteorological administration data and a power law that defines the wind velocity according to the height from the sea surface. The wind load is applied to the blade and wind tower at a regular distance. The relative Morison equation is employed to generate the wave load. The rated rotor speed (18 rpm) is applied to the hub as a motion. The dynamic behavior of a 2-MW floating offshore wind turbine subjected to the wave excitation and wind load is analyzed. The flexible effects of the wind tower and the blade are analyzed. The flexible model of the wind tower and blade is established to examine the natural frequency of the TLP-type offshore wind turbine. To study the effect of the flexible tower and blade on the floating offshore wind turbine, we modeled the flexible tower model and flexible tower-blade model and compared it with a rigid model.