Estimation of Roll Motion Parameters using R-MISO System Identification Technique
Abhilash Somayajula and Jeffrey Falzarano
While the heave and pitch motions of a ship follow a fairly linear behavior, the roll motion exhibits a strong nonlinear behavior due to the presence of viscous damping and nonlinear stiffness. It exhibits complicated dynamics and hence is studied in much more detail as compared to other seakeeping modes. One of the important tasks before analyzing the roll motion of a ship is to get accurate estimates of these nonlinear parameters governing the dynamics. One of the easiest approach is to identify the parameters (such as damping and nonlinear stiffness) using experimental data and is known as system identification. Although there are a lot of system identification techniques available, in this paper we restrict ourselves to one of the popular technique known as the Reverse-Multiple Input Single Output (R-MISO) method. While this method has extensively been applied to obtain accurate predictions of heave and pitch hydrodynamic parameters, its applicability to the more sensitive roll motion has not received enough attention. This paper investigates the applicability of the R-MISO technique to accurately predict the parameters of the nonlinear roll motion of a ship. We specifically apply this technique to simulated data to later verify that the predicted parameters indeed match the values used in the simulations. While the results demonstrate the robustness of the method and its applicability to the extremely sensitive roll motion, the paper also discusses a few limitations of the approach.
Keywords: Reverse-Multiple Input Single Output; R-MISO; System identification; Roll parameter estimation; Nonlinear viscous damping; Nonlinear roll stiffness.