Wave Energy Conversion Efficiency Research Articles

An experimental study on a trapezoidal pendulum wave energy converter in regular waves

Experimental studies were conducted on a trapezoidal pendulum wave energy converter in regular waves. To obtain the incident wave height, the analytical method (AM) was used to separate the incident and reflected waves propagating in a wave flume by analysing wave records measured at two locations. The response amplitude operator (RAO), primary conversion efficiency and the total conversion efficiency of the wave energy converter were studied; furthermore, the power take-off damping coefficients corresponding to the load resistances in the experiment were also obtained. The findings demonstrate that the natural period for a pendulum wave energy converter is relatively large. A lower load resistance gives rise to a larger damping coefficient. The model shows relatively higher wave energy conversion efficiency in the range of 1.0–1.2 s for the incident wave period. The maximum primary conversion efficiency achieved was 55.5%, and the maximum overall conversion efficiency was 39.4%.

Research on the Hydrodynamic Performance of a Wave Energy Converter

Under the pressure of fossil energy shortage, rational exploitation of ocean wave energy is propitious to establish an environmentally friendly society. This paper presents the results of a practical research done in a test tank, on the hydrodynamic performance of a wave energy converter with swing arms and floaters designed purposely. Fixed on a trailer, the converter was composed of two floaters, two swing arms, mechanical transmission devices and generators. The method of this research was to measure the floater’s acceleration and the output voltages of the generator under the movement of waves, analysis the influence of wave height and period on floaters’ movement, then compute the wave energy conversion efficiency. At last, the research findings show that the converter performed well with heaving motion performance and high energy conversion efficiency.

Evaluation of the Wave Energy Conversion Efficiency in Various Coastal Environments

The main objective of the present work was to assess and compare the wave power resources in various offshore and nearshore areas. From this perspective, three different groups of coastal environments were considered: the western Iberian nearshore, islands and an enclosed environment with sea waves, respectively. Some of the most representative existent wave converters were evaluated in the analysis and a second objective was to compare their performances at the considered locations, and in this way to determine which is better suited for potential commercial exploitation. In order to estimate the electric power production expected in a certain location, the bivariate distributions of the occurrences corresponding to the sea states, defined by the significant wave height and the energy period, were constructed in each coastal area. The wave data were provided by hindcast studies performed with numerical wave models or based on measurements. The transformation efficiency of the wave energy into electricity is evaluated via the load factor and also through the capture width, defined as the ratio between the electric power estimated to be produced by each specific wave energy converters (WEC) and the expected wave power corresponding to the location considered. Finally, by evaluating these two different indicators, comparisons of the performances of three WEC types (Aqua Buoy, Pelamis and Wave Dragon) in the three different groups of coastal environments considered have been also carried out. The work provides valuable information related to the effectiveness of various technologies for the wave energy extraction that would operate in different coastal environments.

Numerical Simulation of the Pendulum System in a Buoy-pendulum Wave Energy Converter

Sea conditions have a significant impact on the efficiency of wave energy converters (WECs). Based on the buoy-pendulum WEC presented in the paper, the energy-collection principle of the pendulum system is described, and the motion response of the pendulums under three wave conditions is simulated. It is shown that the optimal wave direction for pendulum system's operation is 45°; the pendulum is apt to reach balance when wave height is less than 0.6 m. In addition, a method to estimate the average conversion efficiency of the pendulum system is proposed based on the fitting function software, and the efficiencies under five ideal wave conditions are calculated. The results show that the greater the wave period and the wave height, the lower the collection efficiency of the pendulum.

Mooring system influence on the efficiency of wave energy converters

The paper presents an analysis of the mooring system effects on the dynamics of an arbitrary floating wave energy converter (WEC) and on the efficiency of the device. The mooring system dynamics are calculated by a finite differences method, which accounts for the lines’ physical characteristics such as mass and stiffness, as well as for the hydrodynamic inertial and damping characteristics. A method is proposed and applied to consider the inertial, damping and stiffness effects of the mooring system on the WEC’s linear dynamics. An identification method is used to determine the linear mooring system coefficients from pre-calculated nonlinear time domain forces of the mooring system on the floater (the importance of nonlinear effects is assessed as well). Finally the mooring system dynamics is represented by additional inertial, damping and stiffness matrices which are added to the ones of the WEC. The influence of the mooring system on the WEC dynamics and efficiency is assessed in terms of wave induced motions and absorbed power. Results are presented for the transfer functions, statistics in selected stationary sea states and the expected annual absorbed energy. A wave scatter diagram representative of the Portuguese Pilot Zone is used for the annual predictions.

Experimental study on a pendulum wave energy converter

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 carried 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.

The Design of a Data Acquisition System for Wave Energy Conversion Efficiency Measurement System Based on the Serial Communication

This paper mainly introduces the design and programming ideas of data acquisition system for wave energy conversion efficiency test system. The design ideas of this software is that using VC6.0 as a design platform, multi-channel data acquisition through the serial port, and real-time curve display and save the data collected. The serial programming is to use the MSComm control to achieve serial communication between the sensor and PC serial. The software can be used in engineering practice after several tests stable and reliable performance.

A New Time Domain Analysis of the Wave Power

The present frequency domain method of calculating wave power may not be accurate enough for calculating the incident wave power of a specific site, which is primary measurement for evaluating the efficiency of wave energy converters (WECs) and an alternative measure, the time domain method, is proposed. Three sites including two nearshore sites and one deepwater site at Chengshantou sea area were selected, and a sample wave parameters data set was obtained from wave model SWASH to demonstrate the application of these two methods. A comparison of the results of each method was also performed and two influential parameters used in calculation were analyzed. The results show that frequency domain method is very likely to overestimate the wave power at both deepwater and nearshore site. The time domain method proposed in this paper is believed to be more superior in calculating the incident wave power during a short term.

The Design of a Data Acquisition System for Wave Energy Conversion Efficiency Measurement System

This paper mainly introduces the design ideas of data acquisition system for wave energy conversion efficiency test system and the usage of data acquisition card.Visual C++6.0 is used as the design platform for the design of the software. The acquisition process is controlled by the multimedia timer and the real-time multi-channel data is collected through the data acquisition card Then the real-time data curve is displayed on the software interface. The collected data can be used as an effective basis for optimizing energy conversion devices.

고정식 진동 수주형 파력 발전기(OWC) 형상 파라미터의 실험 연구

The aim of this experimental study was to analyze the effect of the shape parameters and chamber pressure of a land-based oscillating water column (OWC) in regular incident waves. The magnitude of the free surface elevations inside the chamber was measured in a two-dimensional wave tank for various chamber skirt drafts and bottom slope angles. The surface elevations were also measured under both open chamber and partially open chamber conditions. From these measurements, the optimum shape of the OWC device could be predicted for the maximum wave energy conversion efficiency. It was found that the resonance frequency of the OWC system associated with incident waves moved toward the long wave region with increments of the draft of the chamber skirt and bottom slope. The behavior of the free surface elevation inside the chamber was also found to be dependent on the chamber pressure.

고정식 진동수주형 파력 발전장치의 챔버 유동 및 파에너지 변환효율 해석

A two-dimensional time-domain, potential-theory-based fully nonlinear numerical wave tank (NWT) was developed by using boundary element method and the mixed Eulerian-Lagrangian (MEL) approach for free-surface node treatment. The NWT was applied to prediction of primary wave energy conversion efficiency of a bottom-mounted oscillating water column (OWC) wave power device. The nonlinear free-surface condition inside the chamber was specially devised to represent the pneumatic pressure due to airflow velocity and viscous energy loss at the chamber entrance due to wave column motion. The newly developed NWT technique was verified through comparison with given experimental results. The maximum energy extraction was estimated with various chamber-air duct volume ratios.

Optimal latching control of a wave energy device in regular and irregular waves

This paper describes two methods which can be used to assess the benefit that latching control can bring to the efficiency of wave energy converters. The first method is based on the analytical solution of the equation of motion of the Wave Energy Converter (WEC) in the time domain, using matrix exponentials; it can be used to compute the optimal latching delay. The second one derives from optimal command theory; it is based on a hamiltonian formulation and Pontryagin’s maximum principle. A weak modelling is used to describe latching control prior to applying the optimal command theory. These methods are applied to two different WECs. The first one is a generic one degree of freedom wave energy converter, an heaving buoy, and the second one is the four degrees of freedom wave energy converter called SEAREV. It is shown that latching control based on optimal command theory applied to this weak formulation is not fully optimal in regular waves. However, it can be used to generate optimally controlled time domain sequences of the WEC motions in a random sea, and so it provides an answer to the question: what is the maximum benefit latching control could bring to my wave energy device in a random sea?

Investigation of blast waves generated by laser induced damage processes

Spherical blast waves generated by laser induced damage processes were studied in the weak shock region using wideband microphone detection. Shock wavefront propagation was examined and a comparison with the predictions of the point explosion model was made. Based on the agreement between the theory and experiment, blast wave energy and energy conversion efficiency were determined.

An experimental study of wave power conversion by a heaving, vertical, circular cylinder in restricted waters

Results of an experimental study of a heaving, vertical, circular cylinder show that there is a relationship between water depth, draft and tank width for which minimum motion damping occurs. In addition, there is a minimum value of added-mass for a depth-diameter relationship. When the cylinder is in a resonant heaving condition at these ‘minimum’ parametric values, the wave energy conversion efficiency of the cylinder is shown to exceed the theoretically predicted maximum deep water value. Finally, for a cylinder spacing (tank width) of one radiant wavelength, the optimum depth value is shown to be four times the draft of the cylinder.