Abstract
A comprehensive characterization of a Wave Energy Converter (WEC) requires an overall analysis of the hull, which is identified by inertial terms like mass, added mass and inertia. Being the considered WEC a f loating body, since pre-design phases until final stages such as optimization and executive design, equation of motion, both in time and frequency domain, must be solved accurately. All the terms of the equation must be identified a priori via experimental campaigns or numerical simulation like Boundary Element Methods (BEMs) or Computational Fluid Dynamics (CFD) techniques. One the one hand, parameters like added mass, inertial terms, or even roll and pitch damping coefficients can be identified via well-known methodologies, for instance, free decay; on the other hand, the damping related to yaw degree of freedom (DOF) can be difficult to handle, since the absence of an equilibrium condition. This work deals with a novel identification method of yaw viscous damping starting from handling equation of motion throughout 3D fully viscous and non-linear CFD simulation. The outcomes consist of all those terms that can be used to tune and refine lower-fidelity models like BEMs, which require damping parameters of every DOF, included the non-linear ones, for instance, proportional to the square of velocity about the corresponding axis. Furthermore, numerical models with the pursue of studying WECs or their validation via experimental tests, must be enhanced including the abovementioned parameters and damping coefficients both in terms of numerical stability and feasibility of the results. The work proposes two different methodologies to identify the viscous damping along the rotational degree of freedom (DOF) of yaw: the first involves the imposition of different rotation rates about yaw-axis to compute moments and fluid forces via CFD, then the identification of damping terms; the second methodology consists on imposing an impulse function instead of a constant rotation rate. The methodology shown in this work try to give a tool of computation of damping coefficient when classical free decay tests can not be performed.