Estimation of ship roll damping and natural frequency using an extended Kalman filter applied to URANS output

This article discusses an alternative way of evaluating the roll damping coefficient and natural frequency of a floating body. Experimental values are required for the data assimilation process. In this study rather than performing an actual experiment, pseudo-experimental values were derived through computational fluid dynamics (CFD). An extended Kalman filtering (EKF) technique with CFD for estimation of the equivalent linear damping coefficient and natural frequency of free roll decay motion was determined. For the free roll decay motion, the roll angle values obtained from the CFD simulations were given as input to the EKF, and the parameter estimation was performed. CFD analyses were performed to simulate free roll decay by using the Unsteady Reynolds-Averaged Navier-Stokes (URANS) approach with success. Using calculated data of roll response inverse analyses were carried out to identify roll damping and natural frequency for the 3-D floating body. The effects of uncertainty in the process and measurement noise statistics on performance were examined. The measured residual was compared to the theoretical estimate for filtering correctness. It is found that the variation of the damping coefficient and natural frequency with time was determined by EKF within very small error limits.