Wave forces on horizontal cylinders at low keulegan-carpenter and reynolds numbers

Hydrodynamic forces on a horizontal cylinder with circular and elongated rectangular cross-section in regular waves are studied experimentally and numerically. In the laboratory experiment, the cylinder is fixed beneath waves with its axis parallel to the wave crests. The kinematics of the wave flow are determined from linear wave using measured wave height and period, and the experiment is conducted at low K_c and relatively low R_e values (K_c < 6 and 10,000 < R_e < 30,000). In addition, we present a numerical simulation method for a two dimensional flow around a cylinder undergoing orbital motion in still water. Results on the horizontal cylinder show that the trend of both drag and inertia coefficients is quite different from those obtained from planar oscillatory flow test (or a vertical cylinder). From the numerical simulation it is found that vortex shedding begins at about K_c = 1.5 for a circular cylinder in orbital motion, much smaller than that in planar oscillation. For the elongated rectangular cylinder, the force coefficients are much more complicated than the circular cylinder because the flow always separates. It is found that the forces on a elongated rectangular cylinder fixed in waves are generally much larger than that harmonically oscillating in still water at the same K_c and R_e numbers.