scholarly journals A Novel Method for Estimating Wave Energy Converter Performance in Variable Bathymetry Regions and Applications

Energies ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 2092 ◽  
Author(s):  
Kostas Belibassakis ◽  
Markos Bonovas ◽  
Eugen Rusu
Keyword(s):  
Wave Field ◽  
Wave Energy ◽  
Water Waves ◽  
Bottom Topography ◽  
Wave Energy Converter ◽  
Diffraction Radiation ◽  
Floating Bodies ◽  
Energy Converter ◽  
Coupled Mode ◽  
Energy Absorbers

A numerical model is presented for the estimation of Wave Energy Converter (WEC) performance in variable bathymetry regions, taking into account the interaction of the floating units with the bottom topography. The proposed method is based on a coupled-mode model for the propagation of the water waves over the general bottom topography, in combination with a Boundary Element Method for the treatment of the diffraction/radiation problems and the evaluation of the flow details on the local scale of the energy absorbers. An important feature of the present method is that it is free of mild bottom slope assumptions and restrictions and it is able to resolve the 3D wave field all over the water column, in variable bathymetry regions including the interactions of floating bodies of general shape. Numerical results are presented concerning the wave field and the power output of a single device in inhomogeneous environment, focusing on the effect of the shape of the floater. Extensions of the method to treat the WEC arrays in variable bathymetry regions are also presented and discussed.

Stochastic Analysis of a Nonlinear Energy Harvester Model

2014 ◽  
Author(s):  
P. D. Spanos ◽  
A. Richichi ◽  
F. Arena
Keyword(s):  
Dynamic Analysis ◽  
Wave Energy ◽  
Water Waves ◽  
Nonlinear Dynamic Analysis ◽  
Nonlinear Effects ◽  
Wave Energy Converter ◽  
Statistical Linearization ◽  
Energy Converter ◽  
Domain Integration ◽  
Stiffness And Damping

Floating oscillating-bodies are a kind of wave energy converter developed for harvesting the great amount of energy related to water waves (see Falcão [1] for a review). Although the assumptions of small-wave and linear behavior of oscillating system are reasonable for most of the time during which a floating point harvester is in operation, nonlinear effects may be significant in extreme sea states situations. In this paper a nonlinear dynamic analysis of a point harvester wave energy converter is conducted. The model involves a tightly moored single-body floating device; it captures motion in the horizontal and vertical directions. The stiffness and damping forces, being functions of the displacement and velocity components, make the system nonlinear and coupled. For the input forces, the erratic nature of the waves is modeled by a stochastic process. Specifically, wind-generated waves are modeled by means of the JONSWAP spectrum. The method of statistical linearization [2] is used to determine iteratively the effective linear stiffness and damping matrices and response statistics of the system and to proceed to conducting a dynamic analysis of the harvester model. The reliability of the linearization based approach is demonstrated by comparison with time domain integration, Monte Carlo simulation, data. This approach offers the appealing feature of conducting efficiently a variety of parameter studies which can expedite preliminary evaluations, inter alia, of competing design scenarios for the energy converter in a stochastic environmental setting.

scholarly journals Hydroelectromechanical modelling of a piezoelectric wave energy converter

2016 ◽  
Vol 472 (2195) ◽  
pp. 20160715 ◽  
Author(s):  
E. Renzi
Keyword(s):  
Wave Energy ◽  
Water Waves ◽  
Numerical Approach ◽  
Wave Energy Converter ◽  
Flexural Wave ◽  
Energy Converter ◽  
Flow Equations ◽  
Ocean Surface Waves ◽  
In Series ◽  
Surface Water Waves

We investigate the hydroelectromechanical-coupled dynamics of a piezoelectric wave energy converter. The converter is made of a flexible bimorph plate, clamped at its ends and forced to motion by incident ocean surface waves. The piezoceramic layers are connected in series and transform the elastic motion of the plate into useful electricity by means of the piezoelectric effect. By using a distributed-parameter analytical approach, we couple the linear piezoelectric constitutive equations for the plate with the potential-flow equations for the surface water waves. The resulting system of governing partial differential equations yields a new hydroelectromechanical dispersion relation, whose complex roots are determined with a numerical approach. The effect of the piezoelectric coupling in the hydroelastic domain generates a system of short- and long-crested weakly damped progressive waves travelling along the plate. We show that the short-crested flexural wave component gives a dominant contribution to the generated power. We determine the hydroelectromechanical resonant periods of the device, at which the power output is significant.

Performance Characteristics of a Tightly Moored Piston-Like Wave Energy Converter Under First- and Second-Order Wave Loads

2008 ◽  
Author(s):  
Spyros A. Mavrakos ◽  
George M. Katsaounis ◽  
Ioannis K. Chatjigeorgiou
Keyword(s):  
Wave Energy ◽  
Second Order ◽  
Wave Energy Converter ◽  
Performance Characteristics ◽  
Hydrodynamic Characteristics ◽  
Diffraction Radiation ◽  
Wave Loads ◽  
Energy Converter ◽  
Eigenfunction Expansions ◽  
First Order

The paper deals with the presentation of a model to predict performance characteristics of a tightly moored piston-like wave energy converter which is allowed to move in heave, pitch and sway modes of motion. The WEC’s piston-like arrangement consists of two floating concentric cylinders, the geometry of which allow the existence of a cylindrical moonpool between the external cylinder, the ‘torus’ and the inner cylinder, the ‘piston’. The first-order hydrodynamic characteristics of the floating device, i.e. exciting wave forces and hydrodynamic parameters, are evaluated using a linearized diffraction-radiation semi-analytical method of analysis that is suited for the type of bodies under consideration. According to the analysis method used, matched axisymmetric eigenfunction expansions of the velocity potentials in properly defined fluid regions around the body are introduced to solve the respective diffraction and radiation problems and to calculate the floats’ hydrodynamic characteristics in the frequency domain (Mavrakos et al. 2004, 2005). Based on these characteristics, the retardation forcing terms are calculated, which account for the memory effects of the motion. In this procedure, the coupling terms between the different modes of motion are properly formulated and taken into account (Cummins, 1962; Faltinsen, 1990). The floating WEC is connected to an underwater hydraulic cylinder that feeds a hydraulic system with pressurized oil. The performance of the system under the combined excitation of both first- and second order wave loads is here analyzed. To this end, the diffraction forces originated from the second order wave potentials are computed using a semi-analytical formulation which, by extension of the associated first-order solution, is based on matched axisymmetric eigenfunction expansions.

Measurement of the Effect of Power Absorption in the Lee of a Wave Energy Converter

2009 ◽  
Author(s):  
Ian G. C. Ashton ◽  
Lars Johanning ◽  
Brian Linfoot
Keyword(s):  
Wave Field ◽  
Wave Energy ◽  
Ocean Waves ◽  
Wave Climate ◽  
Wave Energy Converter ◽  
Energy Converter ◽  
Wave Measurements ◽  
Temporal And Spatial Variability ◽  
Power Capture ◽  
Local Wave

Monitoring the effect of floating wave energy converter (WEC) devices on the surrounding wave field will be an important tool for monitoring impacts on the local wave climate and coastlines. Measurement will be hampered by the natural variability of ocean waves and the complex response of WEC devices, causing temporal and spatial variability in the effects. Measurements taken during wave tank tests at MARINTEK are used to analyse the effectiveness of point wave measurements at resolving the influence of an array of WEC on the local wave conditions. The variability of waves is measured in front and in the lee of a device, using spectral analysis to identify changes to the incident wave field due to the operating WEC. The power capture and radiation damping are analysed in order to predict the measured changes. Differences in the wave field across the device are clearly observable in the frequency domain. However, they do not unanimously show a reduction in wave energy in the lee of a device and are not well predicted by measured power capture.

scholarly journals Study of Snap Loads for Idealized Mooring Configurations with a Buoy, Inextensible and Elastic Cable Combinations for the Multi-Float M4 Wave Energy Converter

Water ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 2818
Author(s):  
Peter Stansby ◽  
Efrain Carpintero Moreno
Keyword(s):  
Wave Energy ◽  
Dry Weight ◽  
Wave Energy Converter ◽  
Slight Reduction ◽  
Diffraction Radiation ◽  
Energy Converter ◽  
Operational Conditions ◽  
Highly Nonlinear ◽  
Wave Basin ◽  
Mooring Forces

There has been considerable modelling and wave basin validation of the multi-mode, multi-float, moored wave energy converter M4. The 6 float (2 power take off) (PTO) configuration is considered here with mooring from a buoy with light inextensible cables. Large mean mooring forces and very large peak or snap forces were measured in large waves while the rotational response about the hinges (for power take off in operational conditions) was predominantly linear. Modelling has been extended with elastic mooring cables connected directly to the base of the bow float and to the buoy. The experimental mean force is input to the linear diffraction/radiation model. The device response is effectively unchanged. The peak mooring force and tensions remain large with direct connection to the base of the bow float but are only slightly greater than the mean forces with elastic cables to the buoy, and an elastic hawser provides a further slight reduction. For the largest waves measured, the force was about 10% of the dry weight of the platform. The idealized efficient modelling may inform more detailed design while efficient methods for determining highly nonlinear mean forces remain to be established.

scholarly journals Experimental Measurement of Wave Field Variations around Wave Energy Converter Arrays

2017 ◽  
Vol 9 (1) ◽  
pp. 70 ◽  
Author(s):  
Louise O’Boyle ◽  
Björn Elsäßer ◽  
Trevor Whittaker
Keyword(s):  
Wave Field ◽  
Wave Energy ◽  
Experimental Measurement ◽  
Wave Energy Converter ◽  
Energy Converter

scholarly journals Multi-DOF WEC Performance in Variable Bathymetry Regions Using a Hybrid 3D BEM and Optimization

Energies ◽  
2019 ◽  
Vol 12 (11) ◽  
pp. 2108 ◽  
Author(s):  
Markos Bonovas ◽  
Kostas Belibassakis ◽  
Eugen Rusu
Keyword(s):  
Degrees Of Freedom ◽  
Bottom Topography ◽  
Diffraction Radiation ◽  
Layer Model ◽  
Floating Bodies ◽  
Power Extraction ◽  
Multiple Degrees Of Freedom ◽  
Coupled Mode ◽  
Wave Energy Converters ◽  
Oscillation Modes

In the present work a hybrid boundary element method is used, in conjunction with a coupled mode model and perfectly matched layer model, for obtaining the solution of the propagation/diffraction/radiation problems of floating bodies in variable bathymetry regions. The implemented methodology is free of mild-slope assumptions and restrictions. The present work extends previous results concerning heaving floaters over a region of general bottom topography in the case of generally shaped wave energy converters (WECs) operating in multiple degrees of freedom. Numerical results concerning the details of the wave field and the power output are presented, and the effects of WEC shape on the optimization of power extraction are discussed. It is demonstrated that consideration of heave in combination with pitch oscillation modes leads to a possible increase of the WEC performance.

A novel fully floating three-body system for direct-drive wave energy converter

2020 ◽  
pp. 1-16
Author(s):  
Chuan Liu ◽  
Renwen Chen ◽  
Yuxiang Zhang ◽  
Liping Wang ◽  
Jinchang Qin
Keyword(s):  
Wave Energy ◽  
Parametric Design ◽  
Wave Energy Converter ◽  
Direct Drive ◽  
Floating Bodies ◽  
Energy Converter ◽  
Halbach Array ◽  
Electromagnetic Power ◽  
Three Body ◽  
Multi Body

Converting persistent and renewable wave energy into electricity has been studied in recent years. This research develops a novel fully floating three-body direct-drive wave energy converter (DD-WEC) prepared for the research of the multi-body DD-WEC. Its prototype consists of three floating bodies, but both three bodies act as buoys to extract the wave energy, not just a body. And the relative motion of the buoys induces the voltage in Halbach array permanent magnet linear generators coils. Its feasibility is investigated theoretically by analyzing the dynamics of motion of the floating buoys. As a result, parametric design of the WEC is achieved. The load performance of the DD-WEC is investigated by using the Simulink, and it can be found that the relative displacements between buoys are different. Then, the electromagnetic power of the proposed WEC is much higher compared to a two-body DD-WEC by using numerical simulation Finally, the DD-WEC prototype is manufactured and tested in the wave tank. The results show that the WEC can produce the most electricity for the case with the wave period of 1.6 s, and the maximum voltage reaches 14.2 V, which is consistent with the simulation results. The results show that the proposed DD-WEC is well suited for wave energy conversion.

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