Session: 09-05-03 Wave Energy: Mooring and Control

Submission Number: 156997

Streamlined Experimental Approach to System Identification of WEC Dynamics and Excitation Characteristics 

Understanding the dynamics of wave energy converters (WECs) is crucial for optimizing their design and performance. Empirically-based modeling can capture complex dynamics that are otherwise more difficult to model with first principles.
This study presents the system identification and validation of a multi-input, single-output model of the Lab Upgrade Point Absorber (LUPA), using a single experimental dataset to derive both the excitation transfer function and intrinsic admittance transfer function, expressed in a non-parametric form relative to the power take off (PTO) degree of freedom (DOF).

LUPA is a state of the art open-sourced laboratory-scaled WEC heaving point absorber housed at the O.H. Hinsdale Wave Research Laboratory available for experimental campaigns in the Large Wave Flume in various configurations with regards to DOFs.
For this testing campaign we deployed LUPA in the seven DOF configuration, 6-DOFs for the spar and 1-DOF for the float.

The dataset contains a series of six trials, employing two distinct amplitudes of white noise (WN) PTO force signals for actuation while running irregular waves with pink noise (PN) spectra, both implemented with multisine signals. For each amplitude we realized the input signals with three different phase vectors. The total testing duration of approximately 2 hours demonstrates significant efficiency compared to traditional week-long testing campaigns.

The results reveal that the PTO force signals exhibit nearly flat spectra, confirming the intended performance of the motor and drive systems. Despite the noise present in the wave input spectra, the repeatability of the multisine signals allowed for a robust analysis, yielding high-confidence system models. Validation experiments, including a chirp input force signal and a distinct PN wave with WN force, showed good agreement (approx. 70\%  goodness-of-fit) with the identified models, indicating the effectiveness of the approach.

Our findings suggest that the linear non-parametric models derived from multi-input, single-output open-loop experimental tests can accurately capture the complex multi-DOF dynamics of the LUPA 6-DOF heaving point absorber as well it's excitation properties using the same experiments, which historically was conducted in independent testing campaigns.
This work represents an advancement in the field of system identification for wave energy converters, paving the way for more efficient modeling techniques and enhanced WEC design when combining the linear models with frameworks for WEC control co-design.

This research was supported by the U.S. Department of Energy’s Water Power Technologies Office. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective
views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

Presenting Author: Daniel Gaebele Sandia National Laboratories

Presenting Author Biography: Daniel T. Gaebele received his Bachelor’s and Master’s degrees in Engineering Cybernetics from the University of Stuttgart, Germany, and a Ph.D. in Electrical and Computer Engineering from Oregon State University before joining Sandia as a Postdoctoral Appointee in 2021.
He currently is a Research and Development Electrical Engineer at Sandia National Laboratories’ Water Power Technologies Program.
His research focuses on wave energy converter (WEC) control co-design and control co-optimization, sociotechnical assessments of WECs for blue economy applications, and WEC seasonal deployments.