(1) The regular wave time domain analysis includes the nonlinear Froude-Krylov force and the hydrostiatic force. As shown below, the RAO based reposne is defined, which also depends on the COG position in the time domain.Â I wonder if the RAO based respones could be closer to the frequency domain results when you use smaller wave amplitudes.

(2) The big differences of surge at low frequency for a freely floating structure may be possible, as there is no hydrostatic stiffness for any horizontal motion degrees of freedom (i.e. surge, sway, and yaw).Â

(3) Is the additional damping matrix included in your time domain analysis?

(4) Yes, the outputs of the rotational motion responses are in degree. Their RAOs are in [deg/m].

(5) The RAO-Based Response has been explained above.Â Based on the actual motion responses, the low pass filter is used to have the low-frequency responses. The wave frequency response is the difference between the actual response and the low-frequency response. Please see Aqwa theory manual, Section 13.5.3.

(6) When the wave amplitude is small, the time domain responses should be close to the frequency domain results of which the small amplitude of motion assumation is applied. The time domain analysis may include some nonlinear effects, such as nonlinear Froude-Krylov force and hydrostatic force, nonlinear wave theory (such as 2nd order Stokes waves) or the second order difference frequency and/or sum frequency wave forces, and drag forces if defined. They make differences when the wave amplitudes are not small.Â