Significant Discrepancy in Natural Period Calculation Between OpenFAST and AQWA for Floating Platform

[cx330-xxr]

Hello everyone,

I have some questions I’d like to ask. When calculating the natural period of a novel floating platform through free decay analysis in OpenFAST, I noticed a significant difference compared to the results from AQWA for the same platform. I have already followed Professor Jonkman’s suggestions and adjusted the relevant parameters to ensure consistency, but there are still some discrepancies. As shown in the figure below, could you please advise if I might have missed any parameters or made any incorrect settings?

Thank you in advance for your help!

[jjonkman]

Dear @cx330-xxr,

You haven't shared any information on your model set up in OpenFAST or AQWA to really comment. Overall, it looks like the surge free-decay response is similar between OpenFAST and AQWA, with quite similar damping levels, but with a small difference in natural period. This suggests a small difference in the body mass, added mass, or mooring stiffness in the surge direction

Best regards,

[cx330-xxr]

Thanks for responding,Professor Jonkman
This is my .fst file setting

this is elastodyn.dat


this is hydrodyn.dat

[cx330-xxr]

Here are the details of how I was involved in the calculation.

[jjonkman]

Dear @cx330-xxr,

Does the full-system mass as reported in the ElastoDyn summary (*.ED.sum) file match total mass from your table, which presumably is the mass you entered in AQWA?

Does the added-mass in surge from WAMIT that you are using in HydroDyn (marin_semi.1) match that of AQWA?

Is your mooring model set up similar in AQWA as it is in MoorDyn?

Best regards

[cx330-xxr]

Thank you very much. I will check them one by one.