Experimental passive and reactive control of a Laboratory Scale WEC Point Absorber

Abstract

Scaled testing is an important and valuable step in the process of determining best practices of WEC development, validating numerical models of WEC systems, and/or preparing for larger scale testing. Validation and verification of numerical models are very important as there are physical phenomena that are hard to numerically model such as non-linear frictional effects. This paper builds on the 2021 EWTEC paper [1] in performing and evaluating experimental testing of the Laboratory Upgrade Point Absorber (LUPA). Since this last paper, LUPA has been fabricated and deployed and an initial characterization has been performed. Particularly passive (damping), and reactive (damping and stiffness) control methodologies are employed in regular waves to characterize and evaluate the mechanical power extracted from the waves. Reactive control allows us to invest energy
in the system to get a greater average energy out as compared to damping control.

The LUPA project has just finished its first deployment in the Large Wave Flume at the O.H. Hinsdale Wave Research Laboratory at Oregon State University as shown in Figure 1. Three modes of operation were tested, namely one body heave only, two body heave only, and six degrees of freedom. The one body heave only mode restricts the motion to linear and vertical and fixes the spar body so that the float is the only body free to move. The two body heave only maintains the vertical linear motion, but unlocks the float such that the float and spar are free to heave. The six degrees of freedom case is a floating moored mode with no restrictions on motion.

This paper will focus on comparing passive and reactive control for the one body heave only case and the six degrees
of freedom case with preliminary results shown in Figure 2. Regular waves were tested, focusing on a single wave height
and sweeping the wave period. Results will be presented in power (W) units and in capture width (m). Fig. 2. Top shows max power output vs input wave period for one body and two body configurations and just damping and damping and stiffness cases.
Take note of differing input wave height. Bottom shows capture width.

The LUPA project will provide a valuable testing platform for students and researchers. It will also provide a publicly available open source design and dataset for the research community here: https://github.com/PMECOSU/LUPA. This paper will serve as documentation of the initial testing of the system, providing baseline control results to be compared in future testing.