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Float Response within an Array: Numerical and Experimental Comparison

Date: November 01, 2013 at 11:27 GMT

Numerical studies have shown that the power capture and displacement amplitude of a body located within an array can be significantly greater than that of the same body in
isolation. Linear models of array interactions, such as those compared by Mavrakos and McIver (1997) [1] have received only limited comparison to experimental measurements and may be inadequate for predicting the response of even an isolated device, particularly if the float is of shallow draft (Vantorre et al., 2005 [2]). This paper compares numerical predictions of the response of an array of shallow draft heaving floats to experimental measurements. Numerical simulations are based on hydrodynamic forcing obtained from analysis of the full array using WAMIT. Comparisons are drawn between the displacement amplitude of an isolated device and devices within linear arrays of varying orientation. The main focus is on a linear array of 5 hemispherical floats similar to the arrangement studied in [1] and [3]. Response predictions are made for tuned systems and two fixed masses. In the experimental work, floats are supported from a lowfriction pulley at separations of four radii. Measurements indicate that interactions within arrays can be significant for closely spaced bodies with float displacements of up to four times the wave amplitude occurring under some conditions. In general, the mean response amplitude is found to be greater than that of the same device in isolation when the wave period is greater than the natural period of the device. Comparison with linear array interaction models indicate reasonable agreement for the case of tuned response whilst float response amplitude is less than the wave amplitude. 

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