Wave-induced motion of floating cylinders fitted with bilge keels

The effects of small bilge keels fitted at the corners of a rectangular cyl inder are investigated experimentally and computationally. The freely float ing cylinder is subjected to incident beam waves. As fluid viscosity affect s the motion of the cylinder, a prediction of the motion response requires the solution of the Navier-Stokes equations with additional complexities co ming from free-surface effects and free-body motion. The fully nonlinear pr oblem is solved by using the Free-Surface Random-Vortex Method (Yeung and V aidhyanathan, 1994), with recent extensions to include the effects of free- body motion (Yeung and Liao, 1999). Frequency-domain response in waves is o btained by simulating this 3DOF system in the time domain over a range of f requency, Comparison with experiments is seen to be rather satisfactory. Bo th experiments and time-domain solutions indicate a strong drift velocity, which is relatively insensitive to the presence or size of the keels, but d ependent on the wave frequency. As expected, the keels are found to be effe ctive in reducing the resonant modes of motion, heave and roll, near their respective resonant response peaks.