First- and higher-harmonic wave loads on a vertical circular cylinder are investigated
experimentally in a wave tank of small scale. The incoming waves are (periodic) Stokes
waves with wave slope up to 0.24. A large set of waves which are long compared to the
cylinder radius is calibrated. The first seven harmonic components of the measured
horizontal force on the cylinder are analysed. The higher-harmonic forces are significantly
smaller than the first-harmonic force for all wave parameters. The measurements
are continued until the wave amplitude is comparable to the cylinder radius,
where the second-, third- and fourth-harmonic forces become of comparable size.
Comparison with existing perturbation and fully nonlinear models shows, with a few
exceptions, an overall good agreement for small and moderate wave amplitude. A fully
nonlinear model agrees with the experiments even up to the seventh-harmonic force for
part of the amplitude range. For the large amplitudes the models mostly give conservative
predictions. It is important that the distance from the wave maker to the cylinder
is large in order to avoid parasitic effects in the incoming wave field. The limited
width of the wave tank is not important to the results except when close to resonance.