Learning Forum

[S.S.S.ShankaVasuki]

Hi,

Thanks for the reply. 

(1) 

• When you say compare the actual responses with the diffraction RAOs do you mean I calculate the RAO of the time domain analysis as follows - RAO_TD = (Maximum motion amplitude using the "actual" response from aqwa) / (wave amplitude)?
• When you say including mooring lines, do you mean including the connection stiffness matrix in the diffraction analysis? Or do you mean something else?
• Regarding the wave amplitudes, these are the values mentioned in the reference paper.

(2) I checked the input files and both the additional damping matrix and the mooring line definitions seems to be considered in the time domain analysis as shown in the images below.

I think I have checked all the factors and everything seems to be alright. But yet, the time domain results from my simulation and that of the reference article do not match. Only the frequency domain seems to match as shown in the figure (in this fig, wave frequency is 0.33 rad/sec and amplitude is 1.12m). 

y axis - ("RAO based" response from aqwa) / (wave amplitude)

x- axis - Time (taken from 100 to 200 seconds from aqwa to ignore the wave development region)

I am not sure on what I am missing because I think I have tried many things but the time domain responses of the pitch and the surge response dont seem to match with the reference at all even after adding the addtional damping.

It is suprising that the effect of damping is shown in the diffraction analysis clearly but that does seem to work for the time domain analysis even after considering it.

Do you have any other suggestion that I could try?