Simultaneous implementation of an actively-controlled wavemaker and controlled motion of a cylinder allows examination of the effect of the relative motion of the
cylinder on the process of vortex formation and the associated loading. The cylinder is programmed to undergo a desired orbital motion relative to the orbital motion
of the wave. Simultaneous high-image-density PIV and high-sensitivity force measurements provide insight into the mechanisms of enhancement and mitigation of the
unsteady loading. Use of high resolution film allows the entire domain of the cylinder wake and the free-surface to be captured in a single image with adequate spatial
definition, such that the instantaneous vorticity field is characterized relative to distortions of the free-surface. Crucial for effective control are the ratio of the cylinder frequency to the wave frequency and, for matched frequencies, the phase shift between the arrival of the crest of the incident wave and the crest of the cylinder
trajectory.