A rational model for maneuvering in irregular waves with the effect of waves on the propeller and rudder inflow taken into account

Abstract

A modular model for maneuvering in regular and irregular waves is presented. A new model is presented for the y-component of the rudder inflow. Moreover, an efficient time-domain method for estimation of slowly varying drift loads in irregular waves is presented. Simulations of turning circles in irregular waves with the time-domain method, are compared to simulations where the difference-frequency loads, with the Newman approximation, is used to estimate the slowly varying drift loads. These two methods show similar accuracy, but the time-domain method is significantly faster. The numerical simulations are compared with new free running experiments of the Duisburg Test Case (DTC). Based on extensive wave documentation in the Ocean basin at SINTEF Ocean, the uncertainty in maneuvering experiments, due to variation of wave height throughout the basin, is investigated. The uncertainty is not insignificant, but it is less than expected. The sensitivity to number of realizations in the same irregular wave spectrum is investigated, both experimental and numerical. For some responses, up to 20 repetitions are needed before the width of the 95% confidence intervals approach convergence.