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Abstract
A general frequency domain dynamic model based on the DIFFRACT code has been developed to predict the motion and power generation of the threefloat multimode wave energy converter M4, modelled as a twobody problem. The machine has previously been shown experimentally and numerically to have broad band high capture widths for the range of wave periods typical of offshore sites. The float sizes increase from bow to stern; the bow and mid float are rigidly connected by a beam and the stern float is connected by a beam to a hinge above the mid float where the rotational relative motion is damped to absorb power. The floats are approximately half a wavelength apart so the float forces and motion in antiphase generate relative rotation. Here regular waves representative of swell are investigated and the model is shown to give accurate predictions of experimental results for motion and power for small wave heights and motion which are representative of operational conditions. A linear damper is used to model the power take off. Without changing the float geometry or the hinge position, adjusting the linear damping factor for each frequency is shown to increase the power by up to three times the experimental value, with a maximum close to the theoretical value for a single float. Increasing the height of the hinge point above the mid float increases the power for the higher periods but can reduce power at lower periods. Since float motion can be quite large this result can only be indicative of qualitative trends. The effect of small rows has been investigated, up to five machines, and it is shown in particular how the performance of wave energy devices in a row was affected by the multibody interactions and wave directions. These results are important since the optimum damping factor is shown to be frequency dependent, and increase power generation by up to three times. Furthermore, hydrodynamic interference between M4 machines in a row may significantly increase the power generation when appropriate spacings are chosen.
Original language  English 

Pages (fromto)  429438 
Journal  Journal of Ocean Engineering and Marine Energy 
Volume  2 
Issue number  4 
Early online date  17 Jun 2016 
DOIs  
Publication status  Published  Nov 2016 
Keywords
 wave energy converter
 hydrodynamic interaction
 power takeoff
 power absorption
 optimisation
 array
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Projects
 1 Finished

StepWEC: Step Change for Wave Energy Conversion through floating MultiBody MultiMode Systems in Swell
Engineering and Physical Sciences Research Council
1/07/13 → 30/09/16
Project: Research council
Equipment

High Performance Computing (HPC) Facility
Steven Chapman (Manager)
University of BathFacility/equipment: Facility