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In this paper, the non-linear effects of viscosity on the performance of a Wave Energy Converter (WEC) system are analysed. A standard linear Model Predictive Control (MPC) is used to show the negative effects that the unaccounted non-linear viscosity force in the hydrodynamic system has on the power absorption. A non-linear MPC (NLMPC) is then implemented, where the non-linear viscosity effects are included in the optimisation. A linear drag coefficient estimate of the non-linear viscosity is then included in the linear MPC; creating a Linear Viscous Model Predictive Control. When constraints are incorporated, it is shown that a single choice of the linear viscous drag coefficient for use within the linear MPC can provide comparable results to the non-linear MPC approach, over a wide range of sea states.
O’Sullivan, A. C. M., & Lightbody, G. (2017). The Effect of Viscosity on the Maximisation of Electrical Power from a Wave Energy Converter under Predictive Control (Vol. 50, pp. 14698–14704). Elsevier B.V. https://doi.org/10.1016/j.ifacol.2017.08.2500