Slow drift damping force acting on cylinder in waves

The hydrodynamic forces acting on a vertical or a horizontal cylinder undergoing the slow drift oscillation in waves were investigated experimentally and numerically. In the experimental study, the forced oscillation tests with the low frequency and large amplitude in regular waves and the forced two-harmonic oscillation with combined low and high frequencies were carried out. In the numerical study, a finite difference method was used to simulate the viscous flows around a two dimensional oscillating cylinder. The results show that the slow drift damping force coefficient depends mainly on the reduced velocity defined by the maximum velocity of slow oscillation, the period of incident wave and diameter of column. However, a rectangular cylinder oscillating slowly in waves has much higher damping coefficients than that oscillating in two-harmonic mode. The numerical study revealed some relations between damping force coefficients and vortex shedding patterns.