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.
Highlights
Wave energy converters (WECs) must be designed to perform well and provide energy, often through operating at resonance, over the wide range of frequencies at which energy is carried by ocean waves
We have found that the fit is generally good when using multiple input single output (MISO) models with pressure as an input
Using empirical data collected during testing, three separate models to predict the heave velocity of a WEC were constructed
Summary
Wave energy converters (WECs) must be designed to perform well and provide energy, often through operating at resonance, over the wide range of frequencies at which energy is carried by ocean waves. Standard practices for wave tank testing and model development of WECs have grown out of practices in the naval architecture field for ships and offshore oil and gas structures. In this approach, experiments are built around the linear decomposition model formulation commonly used for wave-body interaction, separating the problem in radiation and excitation components. Excitation and radiation frequency response functions can be constructed from the discrete frequency components This approach, while systematic and time-tested, fails to utilize a number of system identification (SID) approaches which have proven greatly beneficial in other fields (see, e.g., Ljung [5], Pintelon and Schoukens [6]). The uncertainty of these models is considered and a systematic validation study is performed to compare the accuracy of the different models
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