Comparison of different roll motion controls for a 49-m mono-hull passenger ship in beam waves

Abstract

Abstract– Influence of two roll control systems, one passive and another active, are compared in a 49-m length overall mono- hull ship in beam waves. For this objective, time integrations of the uncoupled ship roll response differential equation considering nonlinear behavior of righting arm and damping moments, are developed; fourth-order Runge-Kutta algorithm with constant time interval is employed. These numerical simulations are performed with the original naked hull, then including the effect of bilge keels, and, finally with bilge keel and an active foil control system. The righting arm is interpolated from the original values with a 7 th order polynomial. Damping moment is calculated for different amplitudes and cubically interpolated as a function of roll velocity. Excitation moment from irregular waves is applied at sea states 2, 3 and 4, considering a combination of 1000 harmonic components. To estimate the moment due to the active foil control, typical values for the constants of the transfer function are employed, based on its natural frequencies. Wind moment is estimated with sea state mean velocity and lateral projected area of the ship. With the time registers, spectral densities of roll angle and roll acceleration are calculated using Fourier transforms, and finally, RMS values are estimated from area under those curves. A comparison shows the reduction in roll angle and roll acceleration when the 17-m 2 bilge keels are installed, and when the 6-m 2 active fins are acting.