Modelling of a hydrokinetic energy converter for flow-induced vibration based on experimental data

The VIVACE Converter is a novel and highly efficient renewable energy device in Marine Hydrokinetic (MHK) energy. The operational principle of the converter is to immerse a slender body with bluff cross-section in a flow and extract energy from the transverse oscillations induced by the unsteady von Kármán vortex street. In general, the Converter consists of one or more mass-spring-damper oscillators subjected to non-linear hydrodynamic forces. These forces are strongly influenced by variations of the inflow velocity, damping, stiffness and mass ratio, which in turn influence the harnessed power and efficiency of the Converter. For a reliable model of the hydrodynamic forces, experimental and numerical research plays a key role in the study of the hydrodynamic characteristics of the Converter. This study focuses on modelling the harnessed power and efficiency of the Converter based on a surrogate model methodology, in vortex-induced vibration (VIV) and galloping region. To avoid excessive experimentation or computational inaccuracy, the surrogate model is constructed from a Radial Basis Function (RBF) network by using experimental data of equal-interval harnessing damping-ratio and stiffness in a specified design domain. The harnessed power at different flow velocities is computed by the present model and is found to be consistent with experimental results. Optimization is performed to obtain the maximum harnessed power and efficiency and the corresponding harnessed damping-ratio and stiffness distributions in both the VIV and galloping regions. The method introduced in this study provides a novel tool for numerical modelling of oscillators in flow-induced vibrations, which can be used in engineering applications such as optimization of MHK energy converters.