Dynamic modeling of the motions of variable-shape wave energy converters

TL;DR

This paper develops a dynamic model for variable-shape wave energy converters using a Lagrangian approach, incorporating elastic shell theory and fluid-structure interaction, demonstrating improved energy harvesting in simulations.

Contribution

It introduces a novel dynamic modeling framework for flexible spherical buoys, including new equations and hydrodynamic coefficients, enhancing wave energy conversion analysis.

Findings

Flexible buoys harvest more energy across tested conditions.

The new model accurately predicts buoy motion and power output.

Coupled simulations show improved energy capture with shape adaptability.

Abstract

In the recently introduced Variable-Shape heaving wave energy converters, the buoy changes its shape actively in response to changing incident waves. In this study, a Lagrangian approach for the dynamic modeling of a spherical Variable-Shape Wave Energy Converter is described. The classical bending theory is used to write the stress-strain equations for the flexible body using Love's approximation. The elastic spherical shell is assumed to have an axisymmetric vibrational behavior. The Rayleigh-Ritz discretization method is adopted to find an approximate solution for the vibration model of the spherical shell. A novel equation of motion is presented that serves as a substitute for Cummins equation for flexible buoys. Also, novel hydrodynamic coefficients that account for the buoy mode shapes are proposed. The developed dynamic model is coupled with the open-source boundary element method software NEMOH. Two-way and one-way Fluid-Structure Interaction simulations are performed using MATLAB to study the effect of using a flexible shape buoy in the wave energy converter on its trajectory and power production. Finally, the variable shape buoy was able to harvest more energy for all the tested wave conditions.