OMAE2015-41993 SENSITIVITY OF A WAVE ENERGY CONVERTER DYNAMICS MODEL TO NONLINEAR HYDROSTATIC MODELS

A three dimensional time-domain model, based on Cum-mins equation, has been developed for an axisymmetric point absorbing wave energy converter (WEC) with an irregular cross section. This model incorporates a number of nonlinearities to accurately account for the dynamics of the device: hydro-static restoring, motion constraints, saturation of the power-take-off force, and kinematic nonlinearities. Here, an interpo-lation model of the hydrostatic restoring reaction is developed and compared with a surface integral based method. The effects of these nonlinear hydrostatic models on device dynamics are ex-plored by comparing predictions against those of a linear model. For the studied WEC, the interpolation model offers a large im-provement over a linear model and is roughly two orders-of-magnitude less computationally expensive than the surface in-tegral based method. NOMENCLATURE WEC Wave energy converter. T3R2 “Three-translation, two-rotation ” WEC studied here. PCC Power-conversion-chain. PMT Planar-motion-table. 0n×n Empty matrix of size n. A ∞ Infinite added mass matrix for float. Ar, Br, Cr Radiation damping state-space system matrices. C(ξ ̇ ) Centripetal-Coriolis matrix. ∗Address all correspondence to this author. Cm Linear mooring matrix. G Linear hydrostatic matrix. IRB Rigid-body moments of inertia. In×n Identity matrix of size n. J(ϑ) Euler angle transformation matrix. J̇(ϑ) Time derivative of Euler angle transformation matrix. Kr Radiation damping kernel matrix. MRB Rigid-body inertia matrix for float. MPCC Rigid-body inertia matrix for power-conversion-chain. MPMT Rigid-body inertia matrix for planar-motion-table. S(λ) Skew symmetric matrix of the vector λ. Awp Area of the waterplane. g Gravitational acceleration. Hs Significant wave height. rG Center of gravity location (rG = xG yG z