The frequency independent damping could come from water or any other sources, such as PTO.

Please read the Aqwa Theory manual, 4.1.1. General Formula in Zero Forward Speed Case, for the hydrodynamic damping calculation. If the structure in travelling with a constant speed, the encounter frequency, which is the function of the incident wave frequency, incident wave direction and the forward speed, will be calculated (see Aqwa theory manual,Â 4.9. Radiation Wave Properties at Negative Encounter Frequency).Â If the forward speed is zero, the encounter frequency will be the same as the incident wave frequency.Â In the time domain analysis, the hydrodynamic damping is used in the radiation force calculation (see 13.1. Radiation Force by Convolution Integration).