Two asymmetric types of floating breakwaters integrated with a wave energy converter(WEC-FBs),a floating square box with a triangle(trapezoidal type)or a wave baffle(L type)attached to its rear side,have been proposed...Two asymmetric types of floating breakwaters integrated with a wave energy converter(WEC-FBs),a floating square box with a triangle(trapezoidal type)or a wave baffle(L type)attached to its rear side,have been proposed.In this research,the hydrodynamic performance,including capture width ratio(CWR),wave transmission coefficient,heave motion,and force coefficient,were studied and compared between the two types.A numerical simulation model based on the Navier-Stokes equation was employed.The effects of power take-off(PTO)damping coefficient,wave periods,and draft/displacement on the hydrodynamic performance of the two structure shapes were simulated and investigated.The results reveal that the L type performs better in shorter wave periods,and the trapezoidal type exhibits a higher CWR in intermediate wave periods.This study offers knowledge of the design and protection of the two WEC-FB types.展开更多
In this work,an oscillating-body wave energy converter(OBWEC)with a hydraulic power take-off(PTO)system named“Dolphin 1”is designed,in which the hydraulic PTO system is equivalent to a transfer station and plays a c...In this work,an oscillating-body wave energy converter(OBWEC)with a hydraulic power take-off(PTO)system named“Dolphin 1”is designed,in which the hydraulic PTO system is equivalent to a transfer station and plays a crucial role in ensuring the stability of the electrical energy output and the efficiency of the overall system.A corresponding mathematical model for the hydraulic PTO system has been established,the factors that influence its performance have been studied,and an algorithm for solving the optimal working pressure has been derived in this paper.Moreover,a PID control method to enable the hydraulic PTO system to automatically achieve optimal performance under different wave conditions has been designed.The results indicate that,compared with single-chamber hydraulic cylinders,double-chamber hydraulic cylinders have a wider application range and greater performance;the accumulator can stabilize the output power of the hydraulic PTO system and slightly increase it;excessively large or small hydraulic motor displacement hinders system performance;and each wave condition corresponds to a unique optimal working pressure for the hydraulic PTO system.In addition,the relationship between the optimal working pressure P_(m)and the pressure P_(h)of the wave force acting on the piston satisfies P_(m)^(2)=∫_(t_(1))^(t_(2))P_(h)^(2)dt/(t_(2)-t_(1)).Furthermore,adjusting the hydraulic motor displacement automatically via a PID controller ensures that the actual working pressure of the hydraulic PTO system consistently reaches or approaches its theoretically optimal value under various wave conditions,which is a very effective control method for enhancing the performance of the hydraulic PTO system.展开更多
This paper provides an overview of the global wave resource for energy exploration.The most popular metrics and estimators for wave energy resource characterization have been compiled and classified by levels of energ...This paper provides an overview of the global wave resource for energy exploration.The most popular metrics and estimators for wave energy resource characterization have been compiled and classified by levels of energy exploration.A review of existing prospective wave energy resource assessments worldwide is also given,and those studies have been collated and classified by continent.Finally,information about forty existing open sea wave energy test sites worldwide and their characteristics is depicted and displayed on a newly created global map.It has been found that wave power density is still the most consensual metric used for wave energy resource assessment purposes among researchers.Nonetheless,to accomplish a comprehensive wave resource assessment for exploitation,the computation of other metrics at the practicable,technical,and socio-economic levels has also been performed at both spatial and temporal domains.Overall,regions in latitudes between 40°and 60°of both hemispheres are those where the highest wave power density is concentrated.Some areas where the most significant wave power density occurs are in offshore regions of southern Australia,New Zealand,South Africa,Chile,the British Isles,Iceland,and Greenland.However,Europe has been the continent where most research efforts have been done targeting wave energy characterisation for exploitation.展开更多
This review paper examines the various types of electrical generators used to convert wave energy into electrical energy.The focus is on both linear and rotary generators,including their design principles,operational ...This review paper examines the various types of electrical generators used to convert wave energy into electrical energy.The focus is on both linear and rotary generators,including their design principles,operational efficiencies,and technological advancements.Linear generators,such as Induction,permanent magnet synchronous,and switched reluctance types,are highlighted for their direct conversion capability,eliminating the need for mechanical gearboxes.Rotary Induction generators,permanent magnet synchronous generators,and doubly-fed Induction generators are evaluated for their established engineering principles and integration with existing grid infrastructure.The paper discusses the historical development,environmental benefits,and ongoing advancements in wave energy technologies,emphasizing the increasing feasibility and scalability of wave energy as a renewable source.Through a comprehensive analysis,this review provides insights into the current state and future prospects of electrical generators in wave energy conversion,underscoring their potential to significantly reduce reliance on fossil fuels and mitigate environmental impacts.展开更多
Offshore wind power is a kind of important clean renewable energy and has attracted increasing attention due to the rapid consumption of non-renewable energy.To reduce the high cost of energy,a possible try is to util...Offshore wind power is a kind of important clean renewable energy and has attracted increasing attention due to the rapid consumption of non-renewable energy.To reduce the high cost of energy,a possible try is to utilize the combination of wind and wave energy considering their natural correlation.A combined concept consisting of a semi-submersible wind turbine and four torus-shaped wave energy converters was proposed and numerically studied under normal operating conditions.However,the dynamic behavior of the integrated system under extreme sea conditions has not been studied yet.In the present work,extreme responses of the integrated system under two different survival modes are evaluated.Fully coupled time-domain simulations with consideration of interactions between the semi-submersible wind turbine and the torus-shaped wave energy converters are performed to investigate dynamic responses of the integrated system,including mooring tensions,tower bending moments,end stop forces,and contact forces at the Column-Torus interface.It is found that the addition of four tori will reduce the mean motions of the yaw,pitch and surge.When the tori are locked at the still water line,the whole integrated system is more suitable for the survival modes.展开更多
Salter's duck,an asymmetrical wave energy converter(WEC)device,showed high efficiency in extracting energy from 2D regular waves in the past;yet,challenges remain for fluctuating wave conditions.These can potentia...Salter's duck,an asymmetrical wave energy converter(WEC)device,showed high efficiency in extracting energy from 2D regular waves in the past;yet,challenges remain for fluctuating wave conditions.These can potentially be addressed by adopting a negative stiffness mechanism(NSM)in WEC devices to enhance system efficiency,even in highly nonlinear and steep 3D waves.A weakly nonlinear model was developed which incorporated a nonlinear restoring moment and NSM into the linear formulations and was applied to an asymmetric WEC using a time domain potential flow model.The model was initially validated by comparing it with published experimental and numerical computational fluid dynamics results.The current results were in good agreement with the published results.It was found that the energy extraction increased in the range of 6%to 17%during the evaluation of the effectiveness of the NSM in regular waves.Under irregular wave conditions,specifically at the design wave conditions for the selected test site,the energy extraction increased by 2.4%,with annual energy production increments of approximately 0.8MWh.The findings highlight the potential of NSM in enhancing the performance of asymmetric WEC devices,indicating more efficient energy extraction under various wave conditions.展开更多
A multi-chamber oscillating water column wave energy converter(OWC-WEC)integrated to a breakwater is investigated.The hydrodynamic characteristics of the device are analyzed using an analytical model based on the line...A multi-chamber oscillating water column wave energy converter(OWC-WEC)integrated to a breakwater is investigated.The hydrodynamic characteristics of the device are analyzed using an analytical model based on the linear potential flow theory.A pneumatic model is employed to investigate the relationship between the air mass flux in the chamber and the turbine characteristics.The effects of chamber width,wall draft and wall thickness on the hydrodynamic performance of a dual-chamber OWC-WEC are investigated.The results demonstrate that the device,with a smaller front wall draft and a wider rear chamber exhibits a broader effective frequency bandwidth.The device with a chamber-width-ratio of 1:3 performs better in terms of power absorption.Additionally,results from the analysis of a triplechamber OWC-WEC demonstrate that reducing the front chamber width and increasing the rearward chamber width can improve the total performance of the device.Increasing the number of chambers from 1 to 2 or 3 can widen the effective frequency bandwidth.展开更多
A two-dimensional numerical Computational Fluid Dynamics(CFD)model is established on the basis of viscous CFD theory to investigate the motion response and power absorption performance of a bottom-hinged flap-type wav...A two-dimensional numerical Computational Fluid Dynamics(CFD)model is established on the basis of viscous CFD theory to investigate the motion response and power absorption performance of a bottom-hinged flap-type wave energy converter(WEC)under regular wave conditions.The convergence study of mesh size and time step is performed to ensure that wave height and motion response are sufficiently accurate.Wave height results reveal that the attenuation of wave height along the wave tank is less than 5%only if the suitable mesh size and time step are selected.The model proposed in this work is verified against published experimental and numerical models.The effects of mechanical damping,wave height,wave frequency,and water depth on the motion response,power generation,and energy conversion efficiency of the flap-type WEC are investigated.The selection of the appropriate mechanical damping of the WEC is crucial for the optimal extraction of wave power.The optimal mechanical damping can be readily predicted by using potential flow theory.It can then be verified by applying CFD numerical results.In addition,the motion response and the energy conversion efficiency of the WEC decrease as the incident wave height increases because the strengthened nonlinear effect of waves intensifies energy loss.Moreover,the energy conversion efficiency of theWEC decreases with increasing water depth and remains constant as the water depth reaches a critical value.Therefore,the selection of the optimal parameters during the design process is necessary to ensure that the WEC exhibits the maximum energy conversion efficiency.展开更多
Among the wave energy converters (WECs), oscillating buoy is a promising type for wave energy development in offshore area. Conventional single-freedom oscillating buoy WECs with linear power take-off (PTO) system are...Among the wave energy converters (WECs), oscillating buoy is a promising type for wave energy development in offshore area. Conventional single-freedom oscillating buoy WECs with linear power take-off (PTO) system are less efficient under off-resonance conditions and have a narrow power capture bandwidth. Thus, a multi-freedom WEC with a nonlinear PTO system is proposed. This study examines a multi-freedom WEC with 3 degrees of freedom: surge, heave and pitch. Three different PTO systems (velocity-square, snap through, and constant PTO systems) and a traditional linear PTO system are applied to the WEC. A time-domain model is established using linear potential theory and Cummins equation. The kinematic equation is numerically calculated with the fourth-order Runge–Kutta method. The optimal average output power of the PTO systems in all degrees of freedom are obtained and compared. Other parameters of snap through PTO are also discussed in detail. Results show that according to the power capture performance, the order of the PTO systems from the best to worst is snap through PTO, constant PTO, linear PTO and velocity-square PTO. The resonant frequency of the WEC can be adjusted to the incident wave frequency by choosing specific parameters of the snap through PTO. Adding more DOFs can make the WEC get a better power performance in more wave frequencies. Both the above two methods can raise the WEC’s power capture performance significantly.展开更多
The present study proposed a floating multi-body wave energy converter composed of a floating central platform,multiple oscillating bodies and multiple actuating arms. The relative motions between the oscillating bodi...The present study proposed a floating multi-body wave energy converter composed of a floating central platform,multiple oscillating bodies and multiple actuating arms. The relative motions between the oscillating bodies and the floating central platform capture multi-point wave energy simultaneously. The converter was simplified as a forced vibration system with three degrees of freedom, namely two heave motions and one rotational motion. The expressions of the amplitude-frequency response and the wave energy capture width were deduced from the motion equations of the converter. Based on the built mathematical model, the effects of the PTO damping coefficient, the PTO elastic coefficient, the connection length between the oscillating body and central platform, and the total number of oscillating bodies on the performance of the wave energy converter were investigated. Numerical results indicate that the dynamical properties and the energy conversion efficiency are related not only to the incident wave circle frequency but also to the converter’s physical parameters and interior PTO coefficients. By adjusting the connection length, higher wave energy absorption efficiencies can be obtained. More oscillating bodies installed result in more stable floating central platform and higher wave energy conversion efficiency.展开更多
This work investigated the influence of two types of mooring systems on the hydrodynamic performance of a two-body floating wave energy converter(WEC). It also investigated the effects of the physical parameters of th...This work investigated the influence of two types of mooring systems on the hydrodynamic performance of a two-body floating wave energy converter(WEC). It also investigated the effects of the physical parameters of the mooring system on the amount of extractable power from incident waves in the frequency domain. The modeled converter comprised a floating body(a buoy), a submerged body with two mooring systems, and a coupling system for two bodies. The coupling system was a simplified power take-off system that was modeled by a linear spring-damper model. The tension leg mooring system could drastically affect the heave motion of the submerged body of the model and increase relative displacement between the two bodies. The effects of the stiffness parameter of the mooring system on power absorption exceeded those of the pretension tendon force.展开更多
This paper considers controlling and maximizing the absorbed power of wave energy converters for irregular waves. With respect to physical constraints of the system, a model predictive control is applied. Irregular wa...This paper considers controlling and maximizing the absorbed power of wave energy converters for irregular waves. With respect to physical constraints of the system, a model predictive control is applied. Irregular waves’ behavior is predicted by Kalman filter method. Owing to the great influence of controller parameters on the absorbed power, these parameters are optimized by imperialist competitive algorithm. The results illustrate the method’s efficiency in maximizing the extracted power in the presence of unknown excitation force which should be predicted by Kalman filter.展开更多
According to Newton＇s Second Law and the microwave theory, mechanical analysis of multiple buoys which form Sharp Eagle wave energy converter （WEC） is carried out. The movements of every buoy in three modes couple ...According to Newton＇s Second Law and the microwave theory, mechanical analysis of multiple buoys which form Sharp Eagle wave energy converter （WEC） is carried out. The movements of every buoy in three modes couple each other when they are affected with incident waves. Based on the above, mechanical models of the WEC are established, which are concerned with fluid forces, damping forces, hinge forces, and so on. Hydrodynamic parameters of one buoy are obtained by taking the other moving buoy as boundary conditions. Then, by taking those hydrodynamic parameters into the mechanical models, the optimum external damping and optimal capture width ratio are calculated out. Under the condition of the optimum external damping, a plenty of data are obtained, such as the displacements amplitude of each buoy in three modes （sway, heave, pitch）, damping forces, hinge forces, and speed of the hydraulic cylinder. Research results provide theoretical references and basis for Sharp Eagle WECs in the design and manufacture.展开更多
Small moving vehicles represent an important category of marine engineering tools and devices(equipment)typically used for ocean resource detection and maintenance of marine rights and interests.The lack of efficient ...Small moving vehicles represent an important category of marine engineering tools and devices(equipment)typically used for ocean resource detection and maintenance of marine rights and interests.The lack of efficient power supply modes is one of the technical bottlenecks restricting the effective utilisation of this type of equipment.In this work,the performance characteristics of a new type of elastic-blade/wave-energy converter(EBWEC)and its core energy conversion component(named wave energy absorber)are comprehensively studied.In particular,computational fluid dynamics(CFD)simulations and experiments have been used to analyze the hydrodynamics and performance characteristics of the EBWEC.The pressure cloud diagrams relating to the surface of the elastic blade were obtained through two-way fluid-solid coupling simulations.The influence of blade thickness and relative speed on the performance characteristics of EBWEC was analyzed accordingly.A prototype of the EBWEC and its bucket test platform were also developed.The power characteristics of the EBWEC were analyzed and studied by using the blade thickness and motion cycle as control variables.The present research shows that the EBWEC can effectively overcome the performance disadvantages related to the transmission shaft torque load and power curve fluctuations of rigid blade wave energy converters(RBWEC).展开更多
In this paper, we conducted a numerical analysis on the bottom-hinged flap-type Wave Energy Convertor (WEC). The basic model, implemented through the study using ANSYS-AQWA, has been validated by a three-dimensional p...In this paper, we conducted a numerical analysis on the bottom-hinged flap-type Wave Energy Convertor (WEC). The basic model, implemented through the study using ANSYS-AQWA, has been validated by a three-dimensional physical model of a pitching vertical cylinder. Then, a systematic parametric assessment has been performed on stiffness, damping, and WEC direction against an incoming wave rose, resulting in an optimized flap-type WEC for a specific spot in the Persian Gulf. Here, stiffness is tuned to have a near-resonance condition considering the wave rose, while damping is modified to capture the highest energy for each device direction. Moreover, such sets of specifications have been checked at different directions to present the best combination of stiffness, damping, and device heading. It has been shown that for a real condition, including different wave heights, periods, and directions, it is very important to implement the methodology introduced here to guarantee device performance.展开更多
Many of the existing wave energy converters （WEC） are of oscillating water column （OWC） and point absorber （PA） types. Fewer references have been published in public on the pendulum type WEC. A series of experim...Many of the existing wave energy converters （WEC） are of oscillating water column （OWC） and point absorber （PA） types. Fewer references have been published in public on the pendulum type WEC. A series of experimental tests on a bottom-hinged pendulum WEC model are carded out and some results are revealed in the present study. The purpose of this paper is to present a detailed description of the tests. It is found that wave energy conversion efficiency varies with the applied damping and wave conditions. In addition, special attention is given to the effect of the water ballast on the efficiency of the wave energy converter. It is demonstrated that the ballast plays an important role in energy extraction. Better understanding on how the performance of the device is influenced by damping, wave height, wave period and ballast is shown.展开更多
Wave energy from the ocean is currently a very popular renewable energy, and its development has primarily focused on the shape of the wave energy converter(WEC) used to efficiently convert wave energy into electrical...Wave energy from the ocean is currently a very popular renewable energy, and its development has primarily focused on the shape of the wave energy converter(WEC) used to efficiently convert wave energy into electrical energy. However, the free surface ocean wave problem is very complex and the parameters affecting WEC behavior are difficult to understand. In this paper, based on the Lattice-Boltzmann method, we present particle-based CFD simulation results for the pivoted-type WEC that exhibits both vertical and horizontal motions. In this method, the computation domain need not be a mesh and complex geometry is not a limiting factor. Using a free-surface turbulence model, we simulated the fluid-structure interaction. We detail our simulation results, which show good agreement with those in the literature.展开更多
The " Sharp Eagle” device is a wave energy converter of a hinged double floating body. The wave-absorbing floating body hinges on the semi-submerged floating body structure. Under the action of wave, the wave-ab...The " Sharp Eagle” device is a wave energy converter of a hinged double floating body. The wave-absorbing floating body hinges on the semi-submerged floating body structure. Under the action of wave, the wave-absorbing floating body rotates around the hinge point, and the wave energy can be converted into kinetic energy. In this paper, the power take-off system of " Sharp Eagle Ⅱ” wave energy converter (the second generation of " Sharp Eagle”) was studied, which adopts the hydraulic type power take-off system. The 0-1 power generation mode was applied in this system to make the " Sharp Eagle Ⅱ” operate under various wave conditions. The principle of power generation was introduced in detail, and the power take-off system was simulated. Three groups of different movement period inputs were used to simulate three kinds of wave conditions, and the simulation results were obtained under three different working conditions. In addition, the prototype of " Sharp Eagle Ⅱ” wave energy converter was tested on land and in real sea conditions. The experimental data have been collected, and the experimental data and simulation results were compared and validated. This work has laid a foundation for the design and application of the following " Sharp Eagle” series of devices.展开更多
The double-body heave wave energy converter(WEC)is one of the most conducive devices to absorb the wave energy from relative motion while the law of which is not well understood.This paper makes an in-depth study on t...The double-body heave wave energy converter(WEC)is one of the most conducive devices to absorb the wave energy from relative motion while the law of which is not well understood.This paper makes an in-depth study on this wave energy converter,by means of the combination of theoretical analysis and physical model experiment.The hydrodynamic characteristics and energy capture of the double-buoy under constant and linear Power Take-Off(PTO)damping are investigated.Influences of absolute mass and mass ratio are discussed in the theoretical model.Relative displacement amplitude and average power output are tested in the experiment to analyze the effect of the wave period and outer buoy’s mass,while the capture width ratio(CWR)is also calculated.Results show that the wave period and mass of the buoys have a significant effect on the converter.Different forms of PTO damping have no influence on the optimal wave period and mass ratio of this device.It is recommended to select the double-buoy converter with a mass ratio of 0.80 and to place it in an area with the frequent wave period close to the natural period of the outer buoy to achieve the optimal energy capture.展开更多
Based on two- and three-dimensional potential flow theories, the width effects on the hydrodynamics of a bottom-hinged trapezoidal pendulum wave energy converter are discussed. The two-dimensional eigenfunction expans...Based on two- and three-dimensional potential flow theories, the width effects on the hydrodynamics of a bottom-hinged trapezoidal pendulum wave energy converter are discussed. The two-dimensional eigenfunction expansion method is used to obtain the diffraction and radiation solutions when the converter width tends to be infinity. The trapezoidal section of the converter is approximated by a rectangular section for simplification. The nonlinear viscous damping effects are accounted for by including a drag term in the two- and three-dimensional methods. It is found that the three- dimensional results are in good agreement with the two-dimensional results when the converter width becomes larger, especially when the converter width is infinity, which shows that both of the methods are reasonable. Meantime, it is also found that the peak value of the conversion efficiency decreases as the converter width increases in short wave periods while increases when the converter width increases in long wave periods.展开更多
基金Supported by Shandong Provincial Natural Science Foundation,China(ZR2020ME259)Open Fund of Shandong Key Laboratory of Civil Engineering Disaster Prevention and Mitigation(CDPM2021KF21).
文摘Two asymmetric types of floating breakwaters integrated with a wave energy converter(WEC-FBs),a floating square box with a triangle(trapezoidal type)or a wave baffle(L type)attached to its rear side,have been proposed.In this research,the hydrodynamic performance,including capture width ratio(CWR),wave transmission coefficient,heave motion,and force coefficient,were studied and compared between the two types.A numerical simulation model based on the Navier-Stokes equation was employed.The effects of power take-off(PTO)damping coefficient,wave periods,and draft/displacement on the hydrodynamic performance of the two structure shapes were simulated and investigated.The results reveal that the L type performs better in shorter wave periods,and the trapezoidal type exhibits a higher CWR in intermediate wave periods.This study offers knowledge of the design and protection of the two WEC-FB types.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52071094 and 51979065).
文摘In this work,an oscillating-body wave energy converter(OBWEC)with a hydraulic power take-off(PTO)system named“Dolphin 1”is designed,in which the hydraulic PTO system is equivalent to a transfer station and plays a crucial role in ensuring the stability of the electrical energy output and the efficiency of the overall system.A corresponding mathematical model for the hydraulic PTO system has been established,the factors that influence its performance have been studied,and an algorithm for solving the optimal working pressure has been derived in this paper.Moreover,a PID control method to enable the hydraulic PTO system to automatically achieve optimal performance under different wave conditions has been designed.The results indicate that,compared with single-chamber hydraulic cylinders,double-chamber hydraulic cylinders have a wider application range and greater performance;the accumulator can stabilize the output power of the hydraulic PTO system and slightly increase it;excessively large or small hydraulic motor displacement hinders system performance;and each wave condition corresponds to a unique optimal working pressure for the hydraulic PTO system.In addition,the relationship between the optimal working pressure P_(m)and the pressure P_(h)of the wave force acting on the piston satisfies P_(m)^(2)=∫_(t_(1))^(t_(2))P_(h)^(2)dt/(t_(2)-t_(1)).Furthermore,adjusting the hydraulic motor displacement automatically via a PID controller ensures that the actual working pressure of the hydraulic PTO system consistently reaches or approaches its theoretically optimal value under various wave conditions,which is a very effective control method for enhancing the performance of the hydraulic PTO system.
文摘This paper provides an overview of the global wave resource for energy exploration.The most popular metrics and estimators for wave energy resource characterization have been compiled and classified by levels of energy exploration.A review of existing prospective wave energy resource assessments worldwide is also given,and those studies have been collated and classified by continent.Finally,information about forty existing open sea wave energy test sites worldwide and their characteristics is depicted and displayed on a newly created global map.It has been found that wave power density is still the most consensual metric used for wave energy resource assessment purposes among researchers.Nonetheless,to accomplish a comprehensive wave resource assessment for exploitation,the computation of other metrics at the practicable,technical,and socio-economic levels has also been performed at both spatial and temporal domains.Overall,regions in latitudes between 40°and 60°of both hemispheres are those where the highest wave power density is concentrated.Some areas where the most significant wave power density occurs are in offshore regions of southern Australia,New Zealand,South Africa,Chile,the British Isles,Iceland,and Greenland.However,Europe has been the continent where most research efforts have been done targeting wave energy characterisation for exploitation.
文摘This review paper examines the various types of electrical generators used to convert wave energy into electrical energy.The focus is on both linear and rotary generators,including their design principles,operational efficiencies,and technological advancements.Linear generators,such as Induction,permanent magnet synchronous,and switched reluctance types,are highlighted for their direct conversion capability,eliminating the need for mechanical gearboxes.Rotary Induction generators,permanent magnet synchronous generators,and doubly-fed Induction generators are evaluated for their established engineering principles and integration with existing grid infrastructure.The paper discusses the historical development,environmental benefits,and ongoing advancements in wave energy technologies,emphasizing the increasing feasibility and scalability of wave energy as a renewable source.Through a comprehensive analysis,this review provides insights into the current state and future prospects of electrical generators in wave energy conversion,underscoring their potential to significantly reduce reliance on fossil fuels and mitigate environmental impacts.
基金supported by the National Natural Science Foundation of China(Grant Nos.52171289,42176210,and 52201330)the Guangdong Basic and Applied Basic Research Foundation,China(Grant No.2022B1515250005)Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(Grant No.311023014).
文摘Offshore wind power is a kind of important clean renewable energy and has attracted increasing attention due to the rapid consumption of non-renewable energy.To reduce the high cost of energy,a possible try is to utilize the combination of wind and wave energy considering their natural correlation.A combined concept consisting of a semi-submersible wind turbine and four torus-shaped wave energy converters was proposed and numerically studied under normal operating conditions.However,the dynamic behavior of the integrated system under extreme sea conditions has not been studied yet.In the present work,extreme responses of the integrated system under two different survival modes are evaluated.Fully coupled time-domain simulations with consideration of interactions between the semi-submersible wind turbine and the torus-shaped wave energy converters are performed to investigate dynamic responses of the integrated system,including mooring tensions,tower bending moments,end stop forces,and contact forces at the Column-Torus interface.It is found that the addition of four tori will reduce the mean motions of the yaw,pitch and surge.When the tori are locked at the still water line,the whole integrated system is more suitable for the survival modes.
基金financially supported by Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(Grant No.2022R1I1A1A01069442)the 2024 Hongik University Research Fund。
文摘Salter's duck,an asymmetrical wave energy converter(WEC)device,showed high efficiency in extracting energy from 2D regular waves in the past;yet,challenges remain for fluctuating wave conditions.These can potentially be addressed by adopting a negative stiffness mechanism(NSM)in WEC devices to enhance system efficiency,even in highly nonlinear and steep 3D waves.A weakly nonlinear model was developed which incorporated a nonlinear restoring moment and NSM into the linear formulations and was applied to an asymmetric WEC using a time domain potential flow model.The model was initially validated by comparing it with published experimental and numerical computational fluid dynamics results.The current results were in good agreement with the published results.It was found that the energy extraction increased in the range of 6%to 17%during the evaluation of the effectiveness of the NSM in regular waves.Under irregular wave conditions,specifically at the design wave conditions for the selected test site,the energy extraction increased by 2.4%,with annual energy production increments of approximately 0.8MWh.The findings highlight the potential of NSM in enhancing the performance of asymmetric WEC devices,indicating more efficient energy extraction under various wave conditions.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.U22A20242,52271260,52001054)Natural Science Foundation of Liaoning Province(Grant No.2021-BS-060)Fundamental Research Funds for the Central Universities(Grant No.DUT23RC(3)017)。
文摘A multi-chamber oscillating water column wave energy converter(OWC-WEC)integrated to a breakwater is investigated.The hydrodynamic characteristics of the device are analyzed using an analytical model based on the linear potential flow theory.A pneumatic model is employed to investigate the relationship between the air mass flux in the chamber and the turbine characteristics.The effects of chamber width,wall draft and wall thickness on the hydrodynamic performance of a dual-chamber OWC-WEC are investigated.The results demonstrate that the device,with a smaller front wall draft and a wider rear chamber exhibits a broader effective frequency bandwidth.The device with a chamber-width-ratio of 1:3 performs better in terms of power absorption.Additionally,results from the analysis of a triplechamber OWC-WEC demonstrate that reducing the front chamber width and increasing the rearward chamber width can improve the total performance of the device.Increasing the number of chambers from 1 to 2 or 3 can widen the effective frequency bandwidth.
基金supported by the National Natural Science Foundation of China(51409066,51761135013)the High Technology Ship Scientific Research Project from the Ministry of Industry and Information Technology of the People’s Republic of China–Floating Security Platform Project(the second stage,201622)the Fundamental Research Fund for the Central University (HEUCFJ180104,HEUCFP1809)
文摘A two-dimensional numerical Computational Fluid Dynamics(CFD)model is established on the basis of viscous CFD theory to investigate the motion response and power absorption performance of a bottom-hinged flap-type wave energy converter(WEC)under regular wave conditions.The convergence study of mesh size and time step is performed to ensure that wave height and motion response are sufficiently accurate.Wave height results reveal that the attenuation of wave height along the wave tank is less than 5%only if the suitable mesh size and time step are selected.The model proposed in this work is verified against published experimental and numerical models.The effects of mechanical damping,wave height,wave frequency,and water depth on the motion response,power generation,and energy conversion efficiency of the flap-type WEC are investigated.The selection of the appropriate mechanical damping of the WEC is crucial for the optimal extraction of wave power.The optimal mechanical damping can be readily predicted by using potential flow theory.It can then be verified by applying CFD numerical results.In addition,the motion response and the energy conversion efficiency of the WEC decrease as the incident wave height increases because the strengthened nonlinear effect of waves intensifies energy loss.Moreover,the energy conversion efficiency of theWEC decreases with increasing water depth and remains constant as the water depth reaches a critical value.Therefore,the selection of the optimal parameters during the design process is necessary to ensure that the WEC exhibits the maximum energy conversion efficiency.
基金financially supported by the Shandong Provincial Natural Science Key Basic Program(Grant No.ZR2017ZA0202)the Qingdao Municipal Science&Technology Program(Grant No.15-8-3-7-jch)Special Project for Marine Renewable Energy(Grant No.GHME2016YY02)
文摘Among the wave energy converters (WECs), oscillating buoy is a promising type for wave energy development in offshore area. Conventional single-freedom oscillating buoy WECs with linear power take-off (PTO) system are less efficient under off-resonance conditions and have a narrow power capture bandwidth. Thus, a multi-freedom WEC with a nonlinear PTO system is proposed. This study examines a multi-freedom WEC with 3 degrees of freedom: surge, heave and pitch. Three different PTO systems (velocity-square, snap through, and constant PTO systems) and a traditional linear PTO system are applied to the WEC. A time-domain model is established using linear potential theory and Cummins equation. The kinematic equation is numerically calculated with the fourth-order Runge–Kutta method. The optimal average output power of the PTO systems in all degrees of freedom are obtained and compared. Other parameters of snap through PTO are also discussed in detail. Results show that according to the power capture performance, the order of the PTO systems from the best to worst is snap through PTO, constant PTO, linear PTO and velocity-square PTO. The resonant frequency of the WEC can be adjusted to the incident wave frequency by choosing specific parameters of the snap through PTO. Adding more DOFs can make the WEC get a better power performance in more wave frequencies. Both the above two methods can raise the WEC’s power capture performance significantly.
基金financially supported by the National Natural Science Foundation of China(Grant No.51779104)the Natural Science Foundation of Fujian Province,China(Grant Nos.2016J01247 and 2016J01245)+1 种基金the New Century Talent Support Program of Fujian Province,China(Grant No.JA13170)the Foreign Cooperation Program of Fujian Province,China(Grant No.2016I010003)
文摘The present study proposed a floating multi-body wave energy converter composed of a floating central platform,multiple oscillating bodies and multiple actuating arms. The relative motions between the oscillating bodies and the floating central platform capture multi-point wave energy simultaneously. The converter was simplified as a forced vibration system with three degrees of freedom, namely two heave motions and one rotational motion. The expressions of the amplitude-frequency response and the wave energy capture width were deduced from the motion equations of the converter. Based on the built mathematical model, the effects of the PTO damping coefficient, the PTO elastic coefficient, the connection length between the oscillating body and central platform, and the total number of oscillating bodies on the performance of the wave energy converter were investigated. Numerical results indicate that the dynamical properties and the energy conversion efficiency are related not only to the incident wave circle frequency but also to the converter’s physical parameters and interior PTO coefficients. By adjusting the connection length, higher wave energy absorption efficiencies can be obtained. More oscillating bodies installed result in more stable floating central platform and higher wave energy conversion efficiency.
文摘This work investigated the influence of two types of mooring systems on the hydrodynamic performance of a two-body floating wave energy converter(WEC). It also investigated the effects of the physical parameters of the mooring system on the amount of extractable power from incident waves in the frequency domain. The modeled converter comprised a floating body(a buoy), a submerged body with two mooring systems, and a coupling system for two bodies. The coupling system was a simplified power take-off system that was modeled by a linear spring-damper model. The tension leg mooring system could drastically affect the heave motion of the submerged body of the model and increase relative displacement between the two bodies. The effects of the stiffness parameter of the mooring system on power absorption exceeded those of the pretension tendon force.
文摘This paper considers controlling and maximizing the absorbed power of wave energy converters for irregular waves. With respect to physical constraints of the system, a model predictive control is applied. Irregular waves’ behavior is predicted by Kalman filter method. Owing to the great influence of controller parameters on the absorbed power, these parameters are optimized by imperialist competitive algorithm. The results illustrate the method’s efficiency in maximizing the extracted power in the presence of unknown excitation force which should be predicted by Kalman filter.
基金supported by the National Natural Science Foundation of China(Grant No.41406102)the Special Foundation for Ocean Renewable Energy(Grant No.GHME2016YY01)
文摘According to Newton＇s Second Law and the microwave theory, mechanical analysis of multiple buoys which form Sharp Eagle wave energy converter （WEC） is carried out. The movements of every buoy in three modes couple each other when they are affected with incident waves. Based on the above, mechanical models of the WEC are established, which are concerned with fluid forces, damping forces, hinge forces, and so on. Hydrodynamic parameters of one buoy are obtained by taking the other moving buoy as boundary conditions. Then, by taking those hydrodynamic parameters into the mechanical models, the optimum external damping and optimal capture width ratio are calculated out. Under the condition of the optimum external damping, a plenty of data are obtained, such as the displacements amplitude of each buoy in three modes （sway, heave, pitch）, damping forces, hinge forces, and speed of the hydraulic cylinder. Research results provide theoretical references and basis for Sharp Eagle WECs in the design and manufacture.
基金financially supported by the National Natural Science Foundation of China(Grant Number 51475465)the Hunan Provincial Innovation Foundation for Postgraduate(Grant Number CX2015B014).
文摘Small moving vehicles represent an important category of marine engineering tools and devices(equipment)typically used for ocean resource detection and maintenance of marine rights and interests.The lack of efficient power supply modes is one of the technical bottlenecks restricting the effective utilisation of this type of equipment.In this work,the performance characteristics of a new type of elastic-blade/wave-energy converter(EBWEC)and its core energy conversion component(named wave energy absorber)are comprehensively studied.In particular,computational fluid dynamics(CFD)simulations and experiments have been used to analyze the hydrodynamics and performance characteristics of the EBWEC.The pressure cloud diagrams relating to the surface of the elastic blade were obtained through two-way fluid-solid coupling simulations.The influence of blade thickness and relative speed on the performance characteristics of EBWEC was analyzed accordingly.A prototype of the EBWEC and its bucket test platform were also developed.The power characteristics of the EBWEC were analyzed and studied by using the blade thickness and motion cycle as control variables.The present research shows that the EBWEC can effectively overcome the performance disadvantages related to the transmission shaft torque load and power curve fluctuations of rigid blade wave energy converters(RBWEC).
文摘In this paper, we conducted a numerical analysis on the bottom-hinged flap-type Wave Energy Convertor (WEC). The basic model, implemented through the study using ANSYS-AQWA, has been validated by a three-dimensional physical model of a pitching vertical cylinder. Then, a systematic parametric assessment has been performed on stiffness, damping, and WEC direction against an incoming wave rose, resulting in an optimized flap-type WEC for a specific spot in the Persian Gulf. Here, stiffness is tuned to have a near-resonance condition considering the wave rose, while damping is modified to capture the highest energy for each device direction. Moreover, such sets of specifications have been checked at different directions to present the best combination of stiffness, damping, and device heading. It has been shown that for a real condition, including different wave heights, periods, and directions, it is very important to implement the methodology introduced here to guarantee device performance.
基金financially supported by the Special Fund for Marine Renewable Energy of the Ministry of Finance of China (Grant No. GD2010ZC02)
文摘Many of the existing wave energy converters （WEC） are of oscillating water column （OWC） and point absorber （PA） types. Fewer references have been published in public on the pendulum type WEC. A series of experimental tests on a bottom-hinged pendulum WEC model are carded out and some results are revealed in the present study. The purpose of this paper is to present a detailed description of the tests. It is found that wave energy conversion efficiency varies with the applied damping and wave conditions. In addition, special attention is given to the effect of the water ballast on the efficiency of the wave energy converter. It is demonstrated that the ballast plays an important role in energy extraction. Better understanding on how the performance of the device is influenced by damping, wave height, wave period and ballast is shown.
基金sponsored by the Energy Policy and Planning Office,Ministry of Energy,Thailand(Contract No.07-02-57-014)
文摘Wave energy from the ocean is currently a very popular renewable energy, and its development has primarily focused on the shape of the wave energy converter(WEC) used to efficiently convert wave energy into electrical energy. However, the free surface ocean wave problem is very complex and the parameters affecting WEC behavior are difficult to understand. In this paper, based on the Lattice-Boltzmann method, we present particle-based CFD simulation results for the pivoted-type WEC that exhibits both vertical and horizontal motions. In this method, the computation domain need not be a mesh and complex geometry is not a limiting factor. Using a free-surface turbulence model, we simulated the fluid-structure interaction. We detail our simulation results, which show good agreement with those in the literature.
基金financially supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA13040202)the Special Funding Program for Marine Renewable Energy of the State Oceanic Administration(Grant No.GHME2017SF01)
文摘The " Sharp Eagle” device is a wave energy converter of a hinged double floating body. The wave-absorbing floating body hinges on the semi-submerged floating body structure. Under the action of wave, the wave-absorbing floating body rotates around the hinge point, and the wave energy can be converted into kinetic energy. In this paper, the power take-off system of " Sharp Eagle Ⅱ” wave energy converter (the second generation of " Sharp Eagle”) was studied, which adopts the hydraulic type power take-off system. The 0-1 power generation mode was applied in this system to make the " Sharp Eagle Ⅱ” operate under various wave conditions. The principle of power generation was introduced in detail, and the power take-off system was simulated. Three groups of different movement period inputs were used to simulate three kinds of wave conditions, and the simulation results were obtained under three different working conditions. In addition, the prototype of " Sharp Eagle Ⅱ” wave energy converter was tested on land and in real sea conditions. The experimental data have been collected, and the experimental data and simulation results were compared and validated. This work has laid a foundation for the design and application of the following " Sharp Eagle” series of devices.
基金financially supported by the National Key R&D Program of China(Grant No.2018YFB1501900)the National Natural Science Foundation of China(Grant No.52071303)Shandong Provincial Key Research and Development Program(SPKR&DP-MSTIP)(Grant No.2019JZZY010902)。
文摘The double-body heave wave energy converter(WEC)is one of the most conducive devices to absorb the wave energy from relative motion while the law of which is not well understood.This paper makes an in-depth study on this wave energy converter,by means of the combination of theoretical analysis and physical model experiment.The hydrodynamic characteristics and energy capture of the double-buoy under constant and linear Power Take-Off(PTO)damping are investigated.Influences of absolute mass and mass ratio are discussed in the theoretical model.Relative displacement amplitude and average power output are tested in the experiment to analyze the effect of the wave period and outer buoy’s mass,while the capture width ratio(CWR)is also calculated.Results show that the wave period and mass of the buoys have a significant effect on the converter.Different forms of PTO damping have no influence on the optimal wave period and mass ratio of this device.It is recommended to select the double-buoy converter with a mass ratio of 0.80 and to place it in an area with the frequent wave period close to the natural period of the outer buoy to achieve the optimal energy capture.
基金supported by the Special Fund for Marine Renewable Energy of the Ministry of Finance of China(No.GD2010ZC02)
文摘Based on two- and three-dimensional potential flow theories, the width effects on the hydrodynamics of a bottom-hinged trapezoidal pendulum wave energy converter are discussed. The two-dimensional eigenfunction expansion method is used to obtain the diffraction and radiation solutions when the converter width tends to be infinity. The trapezoidal section of the converter is approximated by a rectangular section for simplification. The nonlinear viscous damping effects are accounted for by including a drag term in the two- and three-dimensional methods. It is found that the three- dimensional results are in good agreement with the two-dimensional results when the converter width becomes larger, especially when the converter width is infinity, which shows that both of the methods are reasonable. Meantime, it is also found that the peak value of the conversion efficiency decreases as the converter width increases in short wave periods while increases when the converter width increases in long wave periods.
