Dear Lingling,
It is not possible in the current version of FAST to directly enable a coupled springs or distributed springs model solely through settings in the input file. Instead, a slight customization (requiring recompile) of FAST is currently required. The coupled springs model can be implemented in FAST through the UserPtfmLd routine, which allows one to apply a discrete load at the platform reference point. The distributed springs model can be implemented in FAST through the UserTwrLd routine, which allows one to apply distributed loads (loads per unit length) along the flexible tower. Please find the UserPtfmLd and UserTwrLd routines that I created for modeling the coupled springs and distributed springs models in the IEA Wind Task 23 Subtask 2 Offshore Code Comparison Collaboration (OC3) project attached. You should be able to use/adapt these attachments to introduce soil flexibility into your FAST model.
The current version of HydroDyn for monopiles accounts for regular or irregular linear waves (with or without stretching) and sea currents and uses the relative form of Morison’s equation for the load calculation. Because the module does not currently have a higher-order wave kinematics model built into it (e.g., Stream Function theory), if you want to model severe regular waves, you would have to use GH Bladed or some other wave kinematics code to generate the higher-order wave kinematics data before running a simulation with HydroDyn. The WaveMod = 4 feature was added so that HydroDyn could read data generated externally by GH Bladed or an equivalent code.
Best regards,
UserTwrLd_DS.f90.txt (10.6 KB)
UserPtfmLd_CS.f90.txt (6.35 KB)