Abstract
This paper describes the optimisation of arrays of wave energy converters (WECs) of point absorber type. The WECs are spherical in shape and operate in heave only. Previous work is extended to an optimisation of array layouts without a prescribed geometry. The objective function is chosen as the mean of the array interaction factor over a prescribed range of incident wave angles. This formulation forces the array to perform optimally over a specified range of wave angle, without direct concern for wavelength variations. Both constrained and unconstrained WEC motions are considered, with constrained optimisations limiting device displacements to two or three times the incident wave amplitude. The increased freedom in this more general optimisation results in a 70% to 140% increase in objective function values compared to the analogous linear array optimisations. As in previous studies of this nature, unconstrained arrays tend to contain closely spaced WECs and larger displacement amplitudes, whereas constrained optimal arrays are more widely spaced. It is shown that the prescribed range of incident wave angle has a great effect on the optimal array layout, with better performance achieved for smaller ranges of wave angle due to better tuning of the array members. A previously identified trade-off in linear arrays, between performance stability to different incident wave parameters, is shown not to apply to general array layouts.
Highlights
The fundamental modelling on arrays of wave-power devices was presented independently by Evans [1] and Falnes [2]
General two-dimensional arrays of five devices were optimised by Fitzgerald [9] and reported in [6], where the array layouts were optimised by maximising the interaction factor in a point absorber regime
This high sensitivity was identified and addressed in [8]. This was done by setting the objective function of the optimisation to be the mean of the interaction factor over a certain range of array variables, which resulted in arrays that performed well over a broader range of variables and were more stable to small changes in these variables
Summary
The fundamental modelling on arrays of wave-power devices was presented independently by Evans [1] and Falnes [2]. Within [3], [4], [6], [7], [9], arrays were optimised by directly maximising the performance of the array, either power absorbed or interaction factor, with respect to the array layout This resulted in arrays which are high performing and highly sensitive to small variations in array variables. This high sensitivity was identified and addressed in [8] This was done by setting the objective function of the optimisation to be the mean of the interaction factor over a certain range of array variables, which resulted in arrays that performed well over a broader range of variables and were more stable to small changes in these variables. The interaction factor, or q-factor, is defined as
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