Development and Validation of an Inverted Pendulum Wave Energy Converter Model

This paper describes the theory and validation of a numerical model for an inverted pendulum based wave energy
converter to power oceanographic buoys. Governing equations of motion are derived to obtain linear and nonlinear
models of this configuration. The parameters of the numerical models are fine tuned through system identification
using experimental data from a bench test. To compare the linear and nonlinear model, varying frequencies and amplitudes
were input in the two models to evaluate root mean square error differences. Additional metrics, such as total
harmonic distortion, were used to quantify the nonlinearities captured in the nonlinear model. Results showed significant
nonlinearities at near-zero frequency and amplitude excitations, suggesting that static and Coulomb friction play
a pronounced role for these inputs. The linear model generally approximated the nonlinear model well, but exhibited
a lower degree of accuracy at high amplitudes and frequencies near resonance (i.e., when response amplitudes were
largest). This work provides valuable insight into modeling the dynamics of wave energy converters to allow for rapid
design optimization. In quantifying conditions where the linear model sufficiently approximates the nonlinear model,
future design iterations can apply the linear model to reduce computation complexity in assessing device behavior.
Future work will involve improving the inverted pendulum model and investigating additional nonlinearities that may
arise in a full-scale model.