change the sampling period(DT)

[clun1]

May I ask if I want to change the sampling time in fast.farm and change the interval of each sampling from 0.01s to 0.1s? Besides modifying the DT parameter in the fst file, what else needs to be modified so that the following error will not be reported

[jjonkman]

Dear @clun1.

You can't set the time step (DT) in OpenFAST arbitrarily because the required DT is tied to the intrinsic dynamics of the wind turbine model. If you want to change the sampling time of the OpenFAST output, you can set DT_Out in the OpenFAST primary (*.fst) input file to be an integer multiple of DT. In your case, it sounds like you should revert DT back to 0.01 s and set DT_Out equal to 0.1 s.

Best regards,

[clun1]

Dear jjonkman

Thank you very much for your guidance. My purpose is to change the sampling period in fast.farm, or the interaction time between DLL and fast.farm data from the original 0.01s to 0.1s, and put the wind turbine parameters read in the sampling period 0.1s into MPC (Model Predictive Control) for calculation. But I don't know how to modify the sampling period in fast.farm. Therefore, the DT parameter in the fst file was modified, and the parameter was changed from the original 0.01s to 0.1s, but the error in the above picture would appear. I would like to know how I can modify the DLL to read the data of the fast.farm stroke unit every 0.1s?

Best regards,

[jjonkman]

Dear @clun1

OpenFAST communicates with controller DLL's at time step defined by DLL_DT in the ServoDyn input file. It sounds like you want to set DLL_DT = 0.1 s, while reverting DT back to 0.01 s.

It also sounds like you are using the super controller functionality of FAST.Farm; is that correct? The super controller will be called by FAST.Farm at a time step of DT_Low, which is the same time step used by FAST.Farm to call OpenFAST (but OpenFAST will take smaller time steps of DT via subcycling). Regardless of the value of DT or DLL_DT, the data passed from the supercontroller to OpenFAST and to the DLL will be updated at a time step of DT_Low.

Best regards,

[clun1]

Dear jjonkman

Thank you very much. Your answer has helped me a lot. Now I can change the time interval of communication

Best regards,