Third-order hydrodynamic loads on an oscillating vertical cylinder in water

The third-harmonic component of the third-order hydrodynamic loads on a ver tical circular cylinder oscillating in water is calculated by a conventiona l perturbation method within the framework of a potential theory. Although the third-order forces are expressed in terms of the first, second, and thi rd-order components of the velocity potential, the latter is not directly r equired for the calculation. It is replaced by a properly defined linearize d radiation potential via Haskind-like theorem. The results of the study ar e applicable to the analysis of high-frequency resonances of deepwater offs hore structures under earthquake excitation or under steep waves (ringing p roblem).