System Identification of a Heaving Point Absorber: Design of Experiment and Device Modeling

Abstract

Empirically based modeling is an essential aspect of design for a wave energy converter. Empirically based models are used in structural, mechanical and control design processes, as well as for performance prediction. Both the design of experiments and methods used in system identification have a strong impact on the quality of the resulting model. This study considers the system identification and model validation process based on data collected from a wave tank test of a model-scale wave energy converter. Experimental design and data processing techniques based on general system identification procedures are discussed and compared with the practices often followed for wave tank testing. The general system identification processes are shown to have a number of advantages, including an increased signal-to-noise ratio, reduced experimental time and higher frequency resolution. The experimental wave tank data is used to produce multiple models using different formulations to represent the dynamics of the wave energy converter. These models are validated and their performance is compared against one another. While most models of wave energy converters use a formulation with surface elevation as an input, this study shows that a model using a hull pressure measurement to incorporate the wave excitation phenomenon has better accuracy.

A Survey of WEC Reliability, Survival and Design Practices

“…By assuming small motions, the radiation and diffraction phenomena can be decoupled. In practice, a frequency-domain model for a WEC can be obtained either numerically, using boundary element model tools such as WAMIT [67] and Nemoh [68], or through experimental system identification (see, e.g., [69]). Note that some nonlinear frequency-domain approaches, such as Volterra models (see, e.g., [70]), can also be applied.…”

“…One example was shown by Gkikas and Athanassoulis [71], in which the pressure of an oscillating water column WEC was modeled using a Volterra formulation. Another option is to employ local linear models, which may be tuned to provide a suitable representation of WEC dynamics within a regime [69].…”

On the Development of an Offshore Version of the CECO Wave Energy Converter

“…The dynamic-based approach allows estimating the behaviour of WECs in a wide range of operational sea states with a reasonable computational effort [37]. This numerical approach requires validation with experimental data as was the case, for instance, while developing the CECO [20] and for the heaving point absorber treated by Bacelli et al [38].…”

Model Predictive Control Tuning by Inverse Matching for a Wave Energy Converter

“…To investigate the potential of this approach, we consider a single body one degree-of-freedom (1DOF) WEC. The WEC plant model was estimated from real experimental data including power take-off system dynamics and was described in a linear transfer function form with the control force as the input and the velocity of the buoy as the output [20]. Based on this model, an MPC matching problem is solved to yield proper weight matrices.…”