Numerical hydrodynamic modelling of a pitching wave energy converter

Two computational methodologies – computational fluid dynamics (CFD) and the numerical modelling using linear potential theory based boundary element method (BEM) are compared against experimental measurements of the motion response of a pitching wave energy converter. CFD is considered as relatively rigorous approach offering non-linear incorporation of viscous and vortex phenomenon and capturing of the flow turbulence to some extent, whereas numerical approach of the BEM relies upon the linear frequency domain hydrodynamic calculations that can be further used for the time-domain analysis offering robust preliminary design analysis. This paper reports results from both approaches and concludes upon the comparison of numerical and experimental findings

Numerical hydrodynamic modelling of a pitching wave energy converter

Two computational methodologies – computational fluid dynamics (CFD) and the numerical modelling using linear potential theory based boundary element method (BEM) are compared against experimental measurements of the motion response of a pitching wave energy converter. CFD is considered as relatively rigorous approach offering non-linear incorporation of viscous and vortex phenomenon and capturing of the flow turbulence to some extent, whereas numerical approach of the BEM relies upon the linear frequency domain hydrodynamic calculations that can be further used for the time-domain analysis offering robust preliminary design analysis. This paper reports results from both approaches and concludes upon the comparison of numerical and experimental findings

Numerical hydrodynamic modelling of a pitching wave energy converter

Two computational methodologies – computational fluid dynamics (CFD) and the numerical modelling using linear potential theory based boundary element method (BEM) are compared against experimental measurements of the motion response of a pitching wave energy converter. CFD is considered as relatively rigorous approach offering nonlinear incorporation of viscous and vortex phenomenon and capturing of the flow turbulence to some extent, whereas numerical approach of the BEM relies upon the linear frequency domain hydrodynamic calculations that can be further used for the time-domain analysis offering robust preliminary design analysis. This paper reports results from both approaches and concludes upon the comparison of numerical and experimental findings

A Frequency-Response Design Method for the Control of Wave Energy Converters in Irregular Seas.

In this paper we present a method of controlling wave energy converters (WECs) in irregular seas. The method controls the WEC so that its displacement frequency response achieves a predetermined characteristics, which is chosen to enhance performance. The design of the controller described is based upon a feedback structure, through deriving the control force from the required displacement of the WEC, rather than the actual displacement. The control setpoint (the required displacement) is synthesized from the incident wave, so prediction of the incoming waves is required, in common with other methods of control in irregular seas. The method is demonstrated using a linear time-domain model of a heaving cylinder. The control signal is generated using both impulse-response functions and transfer functions in order to compare the performance of each, in terms of control signal accuracy and power output, under conditions of reduced wave prediction time. The characteristics of the control force demand and power flow in the controlled system, and the effect on performance of errors both in synthesizing and predicting the incoming wave are investigated. The application of the controller design to a model incorporating non-linearity is also considere

Optimizing the shape of a surge-and-pitch wave energy collector using a genetic algorithm

This study forms part of research into the optimization of the shape of awave energy collector to improve energy extraction using genetic algorithms. The wave energy collector geometry uses a parametric description based upon bi-cubic B-spline surfaces, generated from a relatively small number of control points to reduce the dimensionality of the search space. The collector shapes that are optimized have either one or two planes of symmetry. An elementary cost function is used to determine the performance of each candidate solution. The collectors move in two degrees of freedom (surge-and-pitch), and are optimally tuned to absorb the greatest power from a number of incident regular waves, the results being weighted according to a generalized occurrence distribution. High velocities and large collector volumes are penalized. A benchmark collector shape, against which the optimized shapes are compared, is identified. The overall optimization strategy entails performing repeated runs of the algorithm for a fixed number of generations, then restarting the optimization with the run that produces the best result. An appraisal of the results is made, looking at the performance of all the shapes assessed as well as those deemed the best

Time series analysis-based adaptive tuning techniques for a heaving wave energy converter in irregular seas

The paper presents a time domain model of a heaving buoy wave-energy converter and investigates the tuning problem in irregular seas. The tuning issue is addressed by employing both fixed (passive) and adaptive (active) power-take-off settings. The fixed power-take-off tuning approach includes models based on tuning the device natural frequency to either the energy frequency or peak frequency of the sea-state or a weighted average of several peak frequencies. The adaptive tuning approaches employ a sliding discrete Fourier transform frequency analysis, or a time-series analysis of the measured wave elevation and device velocity to estimate a localized dominant wave frequency and hence calculate power-take-off settings. The paper presents details of these tuning techniques by discussing issues related to the modelling, simulation, and predicted power captures for each method. A comparative study of each method along with practical implications of the results and recommendations are also presented

POWER2008-60119 INVESTIGATING A POWER-OBSORBER WAVE ENERGY CONVERTER

ABSTRACT This paper presents the assessment of the optimum performance of a wave energy converter. In this device which is hinged at the seabed, wave forces act on the face of a collector body, carried on an arm that rotates about a fixed horizontal axis. The collector body oscillates at about the frequency of the ocean swell generating high power from this relatively small and economical device. The performance of the device is investigated using numerical hydrodynamic analysis and the wave tank experiment for a model at a nominal scale of 1/100. Also the optimum mean power output of the device in irregular wave climates is assessed. A first-order method is used to calculate the mean power spectrum of the device in waves of dissimilar spectra. It is shown that the choice of tuning period has a major effect on the power absorbed, hence on the power output