ABSTRACT In a wave energy generation system, MPPT (maximum power point tracking) control can maximize the output power of a WEG (wave energy generator) according to the change of the waves. Due to the irregular movement of the waves and the characteristics of the LMMHD (liquid metal magneto-hydrodynamic) generator, the output of the LMMHD WEG is characterized by low voltage, high current, and irregular variation. Therefore, to withstand the large current the PCS (power conversion system) needs to be designed in parallel with multiple modules, which needs to solve the problem of current sharing. On the other hand, a control system with fast response speed is needed for the MPPT to track wave changes quickly. In this paper, a system model of the LMMHD WEG is analyzed firstly, and an MPPT control strategy that can automatically identify the sea state and can automatically realize current sharing is proposed based on the output characteristics of LMMHD WEG. Then, a MPPT control system is designed for a given LMMHD WEG, and a simulation experiment with changing sea state is carried out in MATLAB/Simulink. The comparison between the experimental results and theoretical values verifies the validity of the proposed MPPT control method. INTRODUCTION With the increase of human activities at sea, the human demand for marine energy is also increasing. Wave energy has the characteristics of wide distribution, high energy density and large reserves, and it is one of the most promising marine energy. Wave energy generation is the main method of wave energy utilization. The WEGS (wave energy generation system) can provide continuous power supply for ocean power users such as UUV (Unmanned Underwater Vehicle) underwater charging platform, subsea scientific observation network, and ocean ranch, etc., which can solve the power problem of marine users. However, because of the characteristics of random variation of the waves, the wave energy captured by the WEG is also randomly changing. MPPT control can maximize the output power of a WEG according to the change of the waves. (Hugo and Martinez 2016; Chen, Yang and Yang 2017; Zheng, Yang, Lin, Huang and Duan 2107).

ABSTRACT In the present paper, two types of wave energy converters (WECs) in uni-/multi-directional waves are investigated using a potential-flow model. The first example is a flap-type oscillating wave surge converter (OWSC) which is similar to the configurations of Oyster wave power device. The second case is an attenuator-type WEC which is based on the Pelamis P2 machine; the modelled WEC is simplified as 5 interconnected rigid modules. Both hydrodynamic interactions and mechanical connections have been considered in the present analyses. The emphases have been put on the effects of directional spreading on the performance of the WECs. Significant reductions of power output have been found in multi-directional seas. INTRODUCTION There have been many designs or concepts to harness wave power from the ocean. Wave energy converters (WECs) can be divided into different groups according to the method used to capture the wave power ( http://www.emec.org.uk/marine-energy/wave-devices/ ), i.e. attenuator, point absorber, oscillating wave surge converters (OWSC), oscillating water column (OWC), overtopping/terminator device, submerged pressure differential, bulge wave, rotating mass, etc. Most wave energy devices convert kinetic energy into mechanical motions to generate electricity. They usually include moving components and complicated mechanical conversion systems (e.g. power take-off systems). So both hydrodynamic and dynamic interactions have to be considered in numerical investigations. Numerical methods for hydrodynamic modelling fall into potential- or viscous-flow frames (Li and Yu, 2012). Linear or nonlinear wave theories can be used for potential-flow analyses. Linear wave theory is usually used for operational sea states and nonlinear wave theory is adopted for the analyses of strongly non-linear waves and extreme events (Coe and Neary, 2014). When viscous effects cannot be neglected, empirical viscous coefficients have been introduced to provide reasonable predictions. However, these coefficients are geometry dependent and limited to model scale. The difficulty of this approach has been highlighted by Pauw et al. (2007) and Sun et al. (2015). A good alternative is to use a computational fluid dynamic (CFD) model such as that presented by Wei et al. (2013).

ABSTRACT This study presents results of numerical simulations on the effects of the presence of breakwaters on the OWC (Oscillating Water Column) performance. CFD (Computational Fluid Dynamics) simulations using a commercial code, Star-CCM+, are done for evaluating performances of the OWC without and with considering the breakwaters in regular waves. Flow fields of the OWC in regular waves are shown as continuous contours, and the effects of the breakwater on the performance of OWC are evaluated. Finally, the cause of the performance improvement and reduction of OWC due to breakwater is discussed. INTRODUCTION Economic feasibility of the OWC (Oscillating Water Column) WEC (Wave Energy Converter) can be improved by combining it with existing or newly constructed breakwaters. The OWC WEC, which has a sloped chamber with same inclination as the breakwaters, has been developed for installation in a breakwater on isolated islands since 2016 by the R&D Project funded by the Korean government (Park et al., 2018). Demonstration tests of the developed breakwater OWC will be done in the future after completion of construction for the OWC with modifying the existing breakwater in Chuja Island, Korea, based on the design for the integrated system composed of OWC chamber, turbine, generator, controller, energy storage system, and micro-grid system. Fig. 1 shows a conceptual diagram of the present OWC system integrated with the breakwater. The OWC chamber producing a reciprocating airflow that operates a turbine from ocean waves functions as the device for primary energy conversion. Earlier studies had performed experimental and numerical analysis for OWC chamber without considering the presence of the breakwater (Elhanafi et al., 2017; Vyzikas et al., 2017; López et al., 2015; 2014; Iturrioz et al., 2015; Kamath et al., 2015; 2015). They evaluated the performance of the independent OWC by measuring or calculating wave elevations in the chamber, the differential pressure between the inside of the chamber and atmosphere, and airflow speed through the duct. In addition, interactions between water surfaces in the chamber and the turbine were considered by modeling it as the orifice representing a damping effect for an impulse turbine of the present OWC system.

ABSTRACT Wave Energy Converters (WECs) have excellent potential as a source of renewable energy that is yet to be commercially realised. Recent attention has been focused on the installation of Oscillating Water Column (OWC) devices as part of breakwaters or harbour walls to provide advantages of cost-sharing structures and proximity of power generation facilities to existing infrastructure. In this paper, a time- domain numerical model of a fixed Multi-Chamber Oscillating Water Column (MC-OWC) is developed in MATLAB. This model is validated against a scale model experiments performed in a wave flume and good agreement is found. The validated model is used to investigate the effect of the power take-off damping on device performance parameters for a given environmental condition. INTRODUCTION There is a growing interest around the world in utilising wave energy for the generation of electrical power (Falnes 2007). For coastal regions or some remote islands, wave energy is a promising renewable power source due to its predictability. Recently, prototypes of various Wave Energy Converters (WECs) have been developed around the world to try to meet renewable energy targets (Esteban et al . 20'2; Hayward et al . 2011). Most WECs are at the early stage of development (Clément et al . 2002; Delmonte et al. 2016; Magagna et al. 2015). The Oscillating Water Column device (OWC) is considered as one of the more successful devices for extracting energy from sea waves (Falnes 2007). The device can be deployed as a shore-based structure, such as the Pico plant in Portugal (Falcão 2000), integrated in a breakwater, such as in the harbour of Sakata, Japan (Takahashi et al. 1993), near-shore bottom-standing strctures, such as the PK1 prototype that was tested off the coast of Port- Kembla in 2005 by Oceanlinx Ltd (Alcorn et al . 2005), or a floating platform, such as the Mighty Whale developed by the Japan Marine Science and Technology Center (Washio et al. 2000). Several articles have presented reviews on general wave power research and the status of several ongoing wave energy projects (Falcão et al. 2015). The aim of future phases in the development of wave energy devices is the installation of multiple devices in various configurations (Khan et al. 2017; Uihlein et al. 2016). This will allow extraction of significant power using more economically viable wave farms based on the economy of large-scale deployment. In this paper, the physical measurements from Shalby et al. (2016b) are employed to validate a simplified time-domain model developed in the Simulink/MATLAB environment to assess device performance.

ABSTRACT Wind power generation is gradually expanding from land to sea. In floating offshore wind turbine, the position of floater is maintained by the mooring line, and it is difficult to predict the behavior by the combined action of wind and wave forces. To create optimal design conditions of floater and mooring line, a combined analysis of aerodynamics and hydrodynamics should be performed. Therefore, in this study, we have analyzed the behavior of the floater under wind and wave loads considering the aerodynamic damping effects of rotating blade. We used FAST provided by NREL for numerical simulations. Experiments were carried out in the Ocean Engineering Wide Tank, University of Ulsan, using the reduced OC3 Spar type platform model. INTRODUCTION Since the Paris Conference of the Parties in 2015, interest in renewable energy around the world is higher than ever. Among them, wind power generation has achieved remarkable growth so that power generation cost can compete with the coal-fired power plant. Wind turbines on the land has a disadvantage of making noise caused by the blades, and it is difficult to secure a tract of land. On the other hand, offshore wind turbine is relatively easy to secure a large area, and it is free from noise even in the enlargement of the turbine. Also, it can obtain more persistent and stronger wind than on land. Therefore, wind power generation is gradually expanding from land to sea. In floating offshore wind turbine, to create optimal design conditions of floater and mooring line, a combined analysis of aerodynamics and hydrodynamics should be performed. Therefore, in this study, we have analyzed the behavior of the floater under wind and wave loads considering the aerodynamic damping effects of rotating blade. There are several papers (Salzmann and Temple, 2005; Myers and Valamanesh, 2014) that have already been studied. In this paper, presents the estimated results from the numerical simulations and the model scale experiments of the OC3-Hywind 5-MW Floating Offshore Wind Turbine. With a 1/128 scale ratio, model tests were carried out in the Ocean Engineering Wide Tank of University of Ulsan. Numerical simulations done by NREL-FAST v8. FAST v8 was performed according to following FAST User's Guide (Buhl and Jonkman, 2005). The objective is to analyze motion of floater considering aerodynamic damping effect at the combined wind/wave conditions.

ABSTRACT The paper considers the technologies of the perspective marine industrial complex of aquaculture with energy supply from renewable sources. Technological schemes of structures and devices of the onshore plant for the cultivation of hydrobionts, a marine underwater farm and a supply vessel for working with marine plantations are presented. A universal autonomous mobile wave device is presented as a variant of using the energy of waves of the open ocean. INTRODUCTION Currently, self-contained, civilian, volatile devices for navigational equipment of the seas, research submarine and surface autonomous devices, mainly receive power from batteries. The number of these facilities is more than one million and the priority task is to prevent adverse ecological consequences of energy supply for the world ocean, regardless of costs. For these purposes, separate developments are used for solar energy, wind energy, waves, currents, temperature differences and salinity of sea water. The optimal result will be the transfer of production and processing ships to hydrogen technologies. A more complex factor threatening the Earth's ecology is due to the rapid growth of industrial coastal marine aquaculture enterprises. PERSPECTIVE COMPLEX OF MARICULTURE A comprehensive program for the development of marine aquaculture technologies is required, taking into account the need for clean energy and the future creation of marine underwater plantations, while preserving the coastal environment and local aquatic organisms. Modular plant for breeding hydrobionts The future network complex developed by Loshchenkov, Knyazhev (2014) for the coasts of the Far East of Russia can serve as a contribution to the development of the Program. The complex contains a coastal enterprise for the cultivation of hydrobionts, bottom plantations in the natural environment and underwater plantations in the water column in the shelf zone. Coastal breeding plant, due to placement in remote, inaccessible ecologically clean areas of the coast, with valuable local species, is semi-automatic, in a modular design. The plant is located, after studying local geological, meteorological, hydrological and hydrobiological parameters in the places of maximum energy flows, Pool modules and energy modules are manufactured depending on the type of hydrobiont and local natural renewable energy sources. The scheme of the plant for the cultivation of hydrobionts on island of Popov of the Peter the Great Gulf developed for the mariculture enterprise is shown in Fig. 1.

Abstract The tripod foundation has been used as a popular support structure for offshore wind turbine (OWT). Typically, only deterministic computational model is considered by applying relevant standards and codes during the preliminary design of the foundations of OWT. However, uncertain parameters should also be considered in preliminary design due to complex configuration of tripod structure. In order to balance conflicting design parameters against design requirements, uncertainties from both design loads and geometric dimensions of structural components were considered to identify the dominant loads and key structural design parameters for tripod foundation. Nonlinear finite element methods were utilized to investigate the mechanical behaviors of tripod foundation and Monte Carlo simulations (MCS) were conducted to obtain sensitive design parameters of tripod foundation of OWTs. Based on the results, it is highlighted that which design parameters should be considered carefully and which design parameters can be selected relying on engineering judgment during the preliminary structural design stage of tripod foundation. Introduction The exploration of offshore wind energy has been expanding rapidly worldwide in the past five years, as shown in Fig. 1. According to statistical report studies from the Global Wind Energy Council (GWEC, 2015), the global cumulative offshore wind energy capacity has stood at 12,105 MW, after 3,392 MW were added in 2015. Besides, the development of increasingly larger OWT in deeper water highlights the trend of the future wind turbine technology, and design and construction of foundation structures have represented important safety and cost factors of offshore wind turbine (OWT) technology. Currently, most of OWTs are located in shallow water and 75% OWTs in Europe are supported by mono-pile foundations (LORC). But as turbine size and water depth increase, traditional mono-pile support structures encounter economic and technical limitations for larger wind turbines in water depth exceeding 30 m. Tripod foundations are potential alternative in offshore wind farms because of their good stability and overall stiffness in water depth ranging from 20 to 40 m (Herion, 2007). They have been successfully installed in Borkum West 2, Global Tech 1 (Fig.2) and Alpha Ventus wind farms, and total capacity is 830 MW with 166 installed turbines, 5 MW in average for each turbine (Madjid, 2014).

Abstract The energy from a tidal stream is abundant and renewable resource whose power is predictable and sustainable. To generate power effectively from the stream a unique counter rotating type tidal stream power unit, whose tandem rotors drive inner and outer armatures in a generator, has been provided by the authors. At the tidal power station located in narrow straits, the unit needs to be reoriented so that useful output power can be obtained from both flood and ebbing tides. In this paper, the counter rotating tandem rotor turbine was designed for operation in a bidirectional tidal stream and the performance was analyzed. The maximum output power is somewhat lower than that of the rotors designed exclusively for a unidirectional stream. The relative flow has a positive angle of attack at the leading edge and discharges from the trailing edge along the blade camber. The angular momentum change, namely the rotor work, is seen to always be accompanied with a shock loss at the leading edge. Introduction Currently, interest in renewable energy sources is growing worldwide. Among these sources, ocean energy is seen as one of the promising resources that can solve the energy supply depletion problem and cope with the warming global environment due to carbon dioxide emissions from the combustion of fossil fuels. To capture the energy available from the ocean, many methods of energy conversion have been proposed (Antonio, 201 0). One of these methods converts the kinetic energy in a tidal stream via a horizontal or vertical axis turbine. The unit does not adversely affect the surrounding marine environment significantly and is environmentally friendly. For most tidal turbines, the horizontal axis tidal turbine is the most advanced and commercially feasible (Laws and Epps, 2016). The operating principles of such a turbine are similar to wind turbines and it is possible to utilize the design methodology and benefit from advanced technologies in the wind industry (Ng, 2013; Ben Elghali, 2007).

Abstract In this paper, three typical floating offshore wind turbines (FOWTs) were studied, with the generic 5MW wind turbine. The dynamic responses of three FOWTs are calculated in both frequency and time domain in operational and survival case under the same environmental conditions. During the calculation, the coupled load effects of aerodynamic and hydrodynamic loads are considered as well as the structure and mooring lines. By comparing the motions and mooring line tensions of three FOWTs to conclude that Semi-submersible shows better dynamic response and safer factor of strength of the mooring systems. And the sensitivities of three FOWTs to the environmental conditions as wave height and wind speed are also studied.

ABSTRACT: Wave energy conversion technique is now actively being developed all over the world. In order to construct the system which is safe, durable in severe sea conditions and of high cost performance, it is necessary to guide the motion of water body near the converter to a preferable one. For this purpose this study is planned to experimentally investigate the motion of water introduced in the water chambers, which are made by partly submerged vertical walls, in array parallel to the direction of wave propagation. In the laboratory experiment, the amplitude of vertical motion of the water surface in the water chambers was measured and the amplification ratio has been investigated. It is shown that the ratio of horizontal length of each chamber to wave length should be smaller than one-tenth. In some conditions, amplification ratio increases with the increase of the draft/wave height ratio and wave period/natural period ratio of the U-shaped water oscillation. INTRODUCTION Controlling the direction of motion of the water due to water wave whose frequency and wave height are relatively high is a key point in the practical use of wave energy conversion. Indeed, all the systems of oscillating water column type control the motion of the water due to water wave in order to utilize the air flow as energy intake (Takahashi et al., 1989). On the other hand, several movable body types also use water chamber for the benefit of the operation of those systems. Figure 1 shows the schematic diagram of the float counterweight type wave energy converter in which the float is located in such water chamber (Hadano et al., 2002; Hadano et al., 2006). In this case, since the structure will receive severe wave force, it should be strong and this raises the cost (Koirala et al., 2009).

ABSTRACT: The models of some wave energy converters are considered. To study physical processes of hydrodynamics in wave power converters the numerical calculations for several variants of structures like OWEC and OWSC are performed. The results of model experiments on irregular wind waves for OWSC model are presented. The new variants of converters are proposed. To improve efficiency of wave converters the additional devices for receiving and converting wave's energy are offered. INTRODUCTION Power industry of Kamchatka and Kuril Islands uses mainly imported fuel. Price of energy here is higher to five times than in the world due to transport costs. On the other hand, here there are favorable climatic conditions for the development of sea wave power stations. The average potential of wave energy on the east coast is estimated at 40 kW/m. If we assume, that the efficiency of wave power converters is 50%, the technical potential of wave power on the coast of 10 km long can be 150 MW - this is existing energy consumption of entire Kamchatka. Korobkov (1986), Sichkarev et. al (1989), Falnes et. al (1991) describe many patents of wave converters. Nevertheless, to achieve their practical efficiency, careful analysis and coordination of functional elements is required with taking into account real local conditions. It is known that sea waves have a wide frequency range. Power plant, designed only to large waves, will not work at weak waves, and the installation is designed only for weak waves, can be easily destroyed by storm waves. Therefore, at a designing of power plants need to lay a large reserve of strength. OWEC MODEL Fig. 1 shows a diagram of OWEC cross-section. Working pressure Δ h is created because of overtopping waves and filling the tank between the front and back walls.

ABSTRACT: The paper presents the proposed structural solutions and the applicable conditions of the wind turbine foundation available to offshore wind farm, and the approaches to perform the analysis of typical technical issues like the foundation structure, erosion to surrounding seabed, bearing capacity of pile foundation etc and corresponding handling measures for the offshore wind farm in China. The above outcomes are concluded through study on the construction environment conditions concerning the marine hydrology, meteorology, topography and geology; and the situation of force on structure of the wind turbine foundation for offshore wind farm in China. They are worth to recommend as a reference for the construction of the wind turbine foundation of offshore wind farm in the future. PREFACE Wind energy has caught the attention of various countries in the world. Wind power is a recycle and everlasting applicable energy from nature, characterized by its advantages such as huge storage, wide distribution, pollution free etc. With the elevated technologies for development and the cost drop of wind power generation, it has turned out to be one of power generation forms in the new energy field and compared with other forms it enjoys most favorable condition to develop on large scale and promote for commercial orientation. China has long coastal lines and is very rich in offshore wind energy resources. The space for power grid market and the power grid will then support the scale development of offshore wind power and make its prospects to grow abroad. The development of offshore wind power has been brought very much to the attention in China. Since 2007, pilot WTG units in the capacity of 1.5 MW, 2.0 MW, 2.5 MW, 3.0 MW, 3.6 MW and 5 MW have been built in Shanghai municipality, Jiangsu, and Fujian provinces etc.

ABSTRACT: New results of numerical hydrodynamic analysis of the novel offshore cross-flow vertical axis wind turbine with large floating rotor (WEMU design) are presented. The research goals are to investigate a spatial movement of rotary pontoon in incoming regular and irregular waves as well as their influence upon the water ring. Waves are launched by two components of flow velocity and free surface elevation at inlet boundary. Irregular wave is presented according to Pierson - Moskowitz spectrum by sum of first order waves with random phases. Wave loads acting on the pontoon are predicted and hydrodynamic power loss due to waves is calculated. INTRODUCTION Offshore wind power engineering is among leaders in the renewable energy sector already for years. And potentially, after solving essential technological and economical problems, its leadership can become absolute. Offshore wind power plants have obvious advantages against located onshore. First, their ecological restrictions are softer; blade speed can be higher, and therefore, an increased efficiency is reachable offshore. Moreover, visual impact of distant offshore wind farms is diminished and territory cost is practically excluded. At the same time, modern offshore turbines inherited their design (propeller installed on tall tower) from onshore and differ only by support structures. So, wellknown drawbacks of propellers could not be excluded. We must indicate here the limited unit power capacity, infrasound emission, and harmful effects on birds and animals. Wind energy cost is still higher than that from conventional power plants. Technological problems quickly grow in large-scale turbines so some research (e.g., Klinger F. et al, 2002) has revealed that an efficient 10MW turbine could not be developed in the one-propeller concept. In this case, wind energy cost will remain relatively high. A technological breakthrough in offshore wind power engineering is still absolutely necessary.

ABSTRACT: Overtopping Wave Energy Convertor (OWEC) is an offshore wave energy convertor, which comprises the circular ramp and reservoir. It collects the overtopped waves and converting water pressure head into electric power through the hydro-turbines installed in the vertical duct, which is fixed in the sea bed. The performance of OWEC can be represented by the operating water heads of the device, which depends on the amount of the wave water overtopping into the reservoir. In the present paper, the reservoir with the duct connecting to the sea water are studied in the 3D numerical wave tank, which has been developed based on the computational fluid dynamics software Fluent 6.3. Both the overtopping motion and the discharges of the reservoir are investigated together, and several shape parameters and incident wave conditions are varied to demonstrate their effects on the performance of OWEC. INTRODUCTION The generation of electric power utilizing clean and renewable ocean resources is one of the most important alternative energy technologies for overcoming shortages in energy resources caused by excessive use of fossil fuels. Among various ocean resources, wave energy is the most abundantly available and applicable in most coastal and offshore areas. Due to the advantages of simple converting technique and producing cost over other types of ocean energy, the wave energy conversion system is feasible to be established for the commercial power production. Plenty of wave energy absorption devices have been invented, and several of them have been utilized in the electricity generation. Recently, the Oscillating Water Column (OWC) type has been widely employed in the application for the wave energy conversion. The disadvantage of this device is the low wave energy converting efficiency. Overtopping Wave Energy Convertor (OWEC) has the sloping walls and reservoirs to lift waves to the levels above the average surrounding ocean.

ABSTRACT: Recently renewable energy has been recognized as the countermeasure against global warming and establishment of sustainable society. Therefore in the field of ocean engineering, development of energy converters including wave energy converter devices (Brooke, 2003) to extract energy from the ocean are active in the world. The authors have proposed a new type of floating wave power converter system with multiple columns (Yasuzawa and Nagashima, 2009). The wave power generation floating system is composed of deck structures and multiple columns underneath. Some columns are used as power generation units which are based on OWC (Oscillating Water Columns) principle and convert wave energy into electric energy, and the other columns have the function of buoyancy. In the present study, dynamic response characteristics of the fixed cylindrical OWC column in regular waves are investigated as basic information before estimation of the floating system. Acrylic cylinder models of the OWC have been designed and manufactured, and the experiment has been performed in the wave tank in Ocean Energy Institute of Saga University. In the experiment, amplitude of water level and pressure in the OWC have been measured to obtain energy absorption of the OWC. Horizontal shear force, vertical force, and pitching moment at the column root have been measured to clarify wave force acting on the columns simultaneously as well. Finally efficiency of primary energy conversion of the OWC columns has been calculated for various conditions based on experimental results on amplitude of water level and pressure in the OWC by using some theories and discussed. INTRODUCTION Recently it has become important to start an action against global warming and to control the consumption of the fossil fuel for reducing emissions of greenhouse gases such as carbon dioxide. Renewable energy has been paid attention these days.

ABSTRACT: This paper presents the unique wave power station, where a pair of the floats supporting the platform is lined up at the interval of one wave length in the ocean swell/wave and the counter-rotating type hydroelectric unit with the vertical shaft is submerged at the center position of the platform. The station can get sufficiently higher energy than the traditional OWC types. That is, the flow velocity through the runners is two times faster than the oscillating ocean swell, and the platform works fruitfully in acceptable response to the swell oscillation regardless of the weight and the wave length. Besides, the motion of the platform can be predicted numerically and simply by the equation of oscillation. INTRODUCTION For the next leap in the exploitations of the renewable/sustainable energies, we are under obligations not only to cope with the warming global environment but also to conserve natural ecosystem and to coexist with nature. As for the fluid energy resources in the world, we can newly exploit the hydro-resources of about 2 TW on the land, the wind-resources of about 72 TW and the ocean-resources more than 2x103 TW. That is, the ocean-resources should occupy the attention of the sustainable power generation, and it is more required to prepare several kinds of the power unit suitable for the individual ocean circumstance. At the traditional wave power stations, the ocean swell, which is called in place of the wave to distinguish precisely between the ocean wave and the technical term "wave" as for the physically vibrating/oscillating phenomena, is changed to the oscillating air flow in the caisson or the buoy (OWC), and the air flow rotates the turbines such as Wells types, impulse types (Dorrell and Hsieh, 2008; Korean Fluid Machinery Association, 2007).

ABSTRACT: This study proposes a potential use of an oscillating water column (OWC) located inside a perforated caisson breakwater. Based on the linear potential theory, the interaction of water wave with the OWC is decomposed as a diffraction problem and a radiation problem as usual. This study only gives the analytical solution of the diffraction problem by means of the matched eigenfunction expansion method. Three parameters of engineering interest, the reflection coefficient, the vertical flux inside the OWC and the wave force acting on the whole structure, are examined. Some useful results are presented. The present study may provide an alternative low reflection OWC for engineers. INTRODUCTION Recently, various technologies of sea wave energy utilization have been extensively studied all over the world. A latest review on this topic has been given by Falcão (2010). The oscillating water column (OWC) is one of widely used wave power extraction devices. It generally includes a partially-immersed chamber with bottom open and with one or several Wells turbines. The incident wave induced oscillating motion of water surface inside the OWC can push the air through the Wells turbines, and then an electrical generator is driven by the turbines. In practice, the OWC devices are often installed on the coast or coastal structures rather than offshore, for reducing the costs of construction, maintenance, storage and so on. Especially, installing OWC devices on breakwaters seems to be a fine idea (e.g., Boccotti, 2007; Martins-Rivas and Mei, 2009). Perforated caisson breakwater is often used as a new type structure. It is initially proposed by Jarlan (1961) and consists of a perforated front wall, a solid rear wall and a wave absorbing chamber between the two walls. The advantages of perforated caissons are the lower reflection coefficient and smaller wave force (Li, 2007).

ABSTRACT: This paper investigates numerically the effect of tension pulley on various physical quantities such as the flattening power output and the cable tension for the float counterweight wave energy converter (Hadano 2006). The tension pulley, a combination of a spring and a pulley, is located on the float side to maintain tension in the suspension cable when the tension generated by the weight of the counterweight is not sufficient to prevent the slackening of the cable. The current dynamics model has been modified to incorporate the dynamics of the tension pulley. Calculation results indicate that this application is successful in suppressing large fluctuations of the cable tension and also in preventing the occurrence of negative tension. INTRODUCTION The authors have developed a novel device that can extract the energy from ocean waves utilizing the heaving motion of a floating mass. The major components of the energy converter are: a float, a counterweight, a cable, a driving pulley, two idler pulleys, a ratchet, and a generator shown in Fig. 1. The device generates power through the tension force in the cable and the weight difference between the float and the counterweight. When the system is at static free condition, the tension in the cable is equal to the weight of the counterweight which is minimum. Therefore it is desirable to keep the counterweight lighter than the float. As a result, the float descends rapidly during the subsequent lowering of the water level. This causes sharp and instantaneous fluctuations of the cable tension force which accelerates the wearing of the device components and the cable itself. In addition, a large fluctuation in the resulting mechanical work rate and the electrical power output is also observed since these quantities depend on the tension force.

ABSTRACT: The purpose of this study is to investigate numerically the blade aerodynamic noise and to predict the noise map in offshore wind-farm. For the analysis of the flow field around wind turbine blade, the unsteady vortex lattice method is applied, the panel code X-FOIL is used for boundary layer properties of airfoil. The acoustic analogy and semi-empirical method is used for modeling of various aerodynamic noise sources and the ENPRO as a propagation model is applied for the simulation of noise map. The used methodology for noise prediction could be applied efficiently to blade design stage for development of low noise blade and to noise assessment of wind-farm. INTRODUCTION Wind power is one of most cost effective, reliable renewable energy source. A lot of country have installed the wind turbine in onshore/offshore and investigated the wind power for more efficiency and reliability. However, there have been many adverse effects such as site pollution, TV interference and noise (unwanted sound) pollution when turbine is installed and operated. In order to resolve these environment problems and to increase the efficiency of wind power, the wind-farm has been built up in offshore area or far region from residence area. Especially, it is predicted that offshore wind-farm would be promoted further due to the better wind properties suitable to high megawatt wind turbine. Among the environmental problems, the noise problem is still the major obstacle in the tremendous development of wind turbine over the last years. Noise gives an adverse effect to marine animal as well as human being. Fig. 1 shows the typical pile-fixed type offshore wind turbine and noise propagation mechanism from wind turbine to observer in air and underwater. When noise propagates through phase discontinuity surface, there is a transmission loss and refraction due to density difference.

ABSTRACT: Among several ocean renewable energy sources, the TCP (Tidal Current Power) has number of advantages over others. The power from TCP is continuous and predictable and reliable regardless of weather conditions or seasonal changes since the current speed and orientation can be predictable. The western coast of Korea has many potential sites for TCP with strong current speed caused from more 10 meter tidal range. Also in the south, there are numbers of promising TCP areas with high flow speed between narrow channels between islands. To extract sizable energy from tidal current, the TCP farm having numbers of device units is required. However, the size of TCP farm is limited and is to be minimized not to disturb the ship channel or the fishing areas. As being known, the distance or gap between devices should be maintained to ensure the maximum performance. The interference between devices for various gaps is not the same. This interference has direct impact to the performance or the efficiency of the device. This paper introduces the performance study of TCP devices considering the interference between rotating rotors with axial, transverse and diagonal arrangements. Series of experiments have been carried out in CWC (Circulating Water Channel) and the various cases are analyzed by CFD model. INTRODUCTION The ocean renewable energy resources have the greater potential over the other resources due to the high density where the power generation is proportional to the flow density. Not like the other renewable sources, the TCP is very predictable and reliable energy source. Many studies have been introduced on the application of tidal current power system such as those by Garbuglia et al. (1993) and Young (1995). Bernshtein (1995) has introduced a new concept for a current stream power system and has also carried out experiments in the sea.