Platform Motion Initiation

Dear Jason,

Is there any way in which the initiation time of platform motion can be defined in FAST? I’m using v7.02 and would like my platform DOFs to be activated at a particular time, before which I would like it to be stationary (no motion DOFs). I’ve scoured the manual and the input files but cannot figure out how to do this (if it’s even possible!).

The reason why I’d like to do this is because I want to compare the data I obtain from FAST with another program I’m using, WInDS. So basically I’d like to allow some run time to cater for transitional errors and have both programmes begin platform motion at the same time, to allow proper comparison in the time domain.

Any help would be greatly appreciated!

thanks in advance and best regards

Kurt

Dear Kurt,

As far as I know, there is no way to enable/disable FAST DoFs at times greater than 0. One possible option would be to model the turbine with the platform DoFs disabled up to the point you want to turn them on, record the state of the non-platform DoFs, and then use them as ICs for another simulation with the platform DoFs enabled. It’s far from perfect, but it may help you get some of what you need. You’ll probably still get some ringing at the start of the second simulation.

Jason may have other ideas…

Marshall

Dear Kurt,

Actually, in FAST v7 it is possible to enable a DOF at run time. For example, adding “DOF_Flag(PtfmSg) = .TRUE.” to the source code will enable the platform-surge DOF even if PtfmSgDOF is set to False within the platform input file. Variable DOF_Flag() and PARAMETER PtfmSg are stored in MODULE FAST_Mods.f90/DOFs(). You can also control the other platform DOFs (via PARAMETERS PtfmSw, PtfmHv, PtfmR, PtfmP, PtfmY) in this way.

More information (with the specific example of enabling/disable the rotor-teeter DOF at runtime) is available in the following forum topic: http://forums.nrel.gov/t/blocked-teeter/615/1.

Please note that it is not possible in FAST v8 to enable/disable DOFs at runtime in this manner.

Best regards,

Dear Marshall and Jason,

Thanks for your replies! I’ll look into this.

Best regards

Kurt