Systematic identification of drag coefficients for a heaving wave follower

Abstract

This paper describes the implementation of an extended Kalman filter for point absorbing wave energy converter models. The extended Kalman filter was used to observe the dynamic states and estimate the viscous drag coefficient of a heaving float in irregular waves. Numerical data was generated to recreate the conditions of a wave tank test performed on a 1:10 scale wave energy conversion system. Three lumped parameter models were evaluated for use in the extended Kalman filter. A modification to the extended Kalman filter to ensure stability of the state space realization of the radiation is discussed. A systematic estimate of the process noise covariance based on the steady state response of the heaving object and the incident wave was implemented. The drag identification and state observation capabilities are shown to be effective with limited sampled data and imperfect estimations of the process noise covariance. Some simplified models are shown to be effective if only state identification is needed, but a detailed model is needed for parameter identification. With the use of a sufficiently detailed model the extended Kalman filter is shown to be able to identify a time varying drag coefficient of a semi-submerged floating object.