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

• 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: Arctic
• Online Access: http://hdl.handle.net/11583/2730204; https://doi.org/10.1115/OMAE2018-77072; http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2704861

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.