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. |
