Wave-current interaction effects on waves and their loads on a vertical cylinder

This paper uses a novel approach to investigate the effect of wave-current interactions on the wave loads on a vertical surface piercing cylinder in representative current and wave conditions in the North Sea wind farms. We used an iterative method in the experiments to ensure the same nominal sea states at the location of the installed cylinder in different current conditions for each sea state. While earlier studies have focused on the current effect on crest statistics, we here look at the force statistics. With using a first-principle engineering model, the representative force coefficients for all of the cases were computed. The force coefficients for the cases with current are consistently smaller than the cases without current. In the investigation of the measured force distribution in depth, at the time of the peak force, we observed that the force distribution of opposing currents cases were concentrated closer to the free surface compared to the cases with no and following currents. Using the harmonic separation method, the surface elevation time series of waves on following current and the inline force time series of waves on the no-current cases were the most linear while the the surface elevation time series of waves on the opposing current were the most nonlinear. The consequence of neglecting different wave-current interaction effects in calculation of wave loads was investigated and it was observed that the most significant effect is the change of the force coefficients in presence of currents.