For a standard pontoon after a 3DDIFF hydrodynamic run, if I export the damping matrix from the freq_res menu using matrices or equ_sum I do not see a change in the roll damping value irrespective of the wave steepness I use in the RAO command prior. The value is also the same as that generated from v_matrices in the Hydrodynamic menu. Therefore I conclude that it does not include the viscous component of damping contrary to my expectation. Please advise how do I include the linearised viscous component in the damping matrix reporting??
Hello John,
Attached is an altered difbox sample. Please compare output pages 2 and 4. The command file shows how to get the two reports.
Please have a review and let me know of any questions.
Georgina Maldonado
difbox.zip
Thanks a lot Georgina for the quick response and example. This is the same approach I was using. Indeed, in your Faltinsen box there is a difference in the wave damping coefficient derived from Hydrodynamics and Freq_res, but this appears to be due to the damping from the #area components and not from Tanaka viscous damping. If I comment out the #area then the linearised drag is the same from both menus as per attached. Therefore I conclude that if I want to use the damping matrix properly outside of MOSES or establish the propotion of linearised damping due to viscous effects I have to switch off tanaka damping and add damping from tube or area elements. Please could you confirm. edited Faltinsen example attached. Kind Regards JDmodified faltinsen.zip
Hi John,
You are correct the v_matrices do not include tanaka damping. This has to do with the values in the matrices being linearized. Have you reviewed the b_keels sample file? There the changing in damping is done via a logarithmic decrement test.
I hope this helps.
Thanks Georgina for the confirmation, I will look at that example.
Kind Regards
JD