Analytical Formulation of Nonlinear Froude-Krylov Forces for Surging-Heaving-Pitching Point Absorbers

Accurate and computationally efficient mathematical models are fundamental for designing, optimizing, and controlling wave energy converters. Wave energy devices are likely to exhibit significant nonlinear behaviour, over their full operational envelope, so that nonlinear models may become indispens...

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Bibliographic Details
Published in:Volume 10: Ocean Renewable Energy
Main Authors: Giuseppe Giorgi, John V. Ringwood
Other Authors: Giorgi, Giuseppe, Ringwood, John V.
Format: Conference Object
Language:English
Published: American Society of Mechanical Engineers (ASME) 2018
Subjects:
Online Access:http://hdl.handle.net/11583/2730204
https://doi.org/10.1115/OMAE2018-77072
http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2704861
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Summary:Accurate and computationally efficient mathematical models are fundamental for designing, optimizing, and controlling wave energy converters. Wave energy devices are likely to exhibit significant nonlinear behaviour, over their full operational envelope, so that nonlinear models may become indispensable. Froude-Krylov nonlinearities are of great importance in point absorbers but, in general, their calculation requires an often unacceptable increase in model complexity and computational time. However, if the body is assumed to be axisymmetric, it is possible to describe the whole geometry analytically, thereby allowing faster calculation of nonlinear Froude-Krylov forces. In this paper, a convenient parametrization of axisymmetric body geometries is proposed, applicable to devices moving in surge, heave, and pitch. In general, the Froude-Krylov integrals must be solved numerically. Assuming small pitch angles, it is possible to further simplify the problem, and achieve an algebraic solution, which is considerably faster than numerical integration.