About wave kinematics in mooring calculations

Dear everyone,
I have a problem with wave kinematics. I read an article called “Verification and Validation of the New Dynamic Mooring Modules Available in FAST v8” and there was this sentence: FEAMooring and MoorDyn, wave kinematics are not considered for the calculation of the hydrodynamic line loads, meaning that the hydrodynamic load calculations assume still water. The results show that the FEAMooring and MoorDyn methods do not take into account wave kinematics.
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In the article “Validation of a lumped-mass mooring line model with DeepCwind semisubmersible model test data”, expert Matthew Hall mentions: Fig. 6 also shows, between 300 s and 320 s, how the inclusion of wave kinematics in the drag calculations affects the fairlead tension. It seems to me that the Can, Cat, Cdn and Cdt coefficients are related to wave kinematics.

So my question now is whether MoorDyn takes into account wave kinematics, If not considered ‘how the inclusion of wave kinematics in the drag calculations affects the fairlead tension’ the phrase refers to the wave What does kinematics represent?

Hi Yushun,

I had wave kinematics in MoorDyn at the very beginning (which is how the comparison in the paper was done) but then disabled that feature because there was no easy way to transmit wave kinematics into MoorDyn from other codes like FAST. So MoorDyn v1 did not officially include wave kinematics.

We have added wave kinematics in MoorDyn v2, which is in recent releases of OpenFAST. You’ll find some information about how to use wave kinematics here: About wave kinematics in mooring calculations The basic idea is to tell MoorDyn to look for a water kinematics input file, then that file specifies a wave grid and points to a wave-elevation time-series file. That time series could be the wave elevation output by OpenFAST/HydroDyn.

Matt

I would just add that we have plans in the future to add a direct coupling between the upcoming SeaState module of OpenFAST (which separates out the incident wave kinematics from HydroDyn) to MoorDyn so that the seperate water kinematics input file will not be needed once that functionality is released.

Best regards,

Thank you for your reply, which helped me a lot!
Best regards,

Thank you for your response and look forward to the release of openfast.
Best regards,