How to add an external force on a certain point of the platform?

[YuYuJou]

I want to get the force_displacement curve, but I don't know how to add the external force, or there is an output of restoring force?
Thanks

[jjonkman]

Dear @YuYuJou,

Presumably you are referring to the force-displacement curve of the mooring system of a floating offshore wind turbine. To generate this, you can output the reaction forces/tension at the fairlead from the mooring module you are using, related to the platform displacement.

To add user-prescribed external point loads (forces, moments) to an OpenFAST model, you can use the StC_DOF_MODE = 4 option of the Structural Control (StC) submodel of ServoDyn, with one point load implemented per instance of StC in the blades, nacelle, tower, or substructure. See the ServoDyn (https://openfast.readthedocs.io/en/main/source/user/servodyn/input.html#servodyn-primary-input-file) and StC (https://openfast.readthedocs.io/en/main/source/user/servodyn-stc/StC_input.html) input file documentation on readthe docs for more information.

Best regards,

[YuYuJou]

Sorry, I tried and read the example file.
But it didn't work.

[jjonkman]

ServoDyn input SStCfiles should point to the name of an StC input file, not a prescribed load time series file. The name of the prescribed load time series file should be specified within the StC input file. And presumably, you meant to set StC_DOF_MODE to 4 in the StC file rather than NumSStC to 4. (Setting NumSStC to 4 would generate 4 StCs in the substructure, which I presume is not what you want to do.)

Best regards,

[YuYuJou]

Is it correct that I create a new file to write StC file?




I don't understand what [The variable "Echo"] means

[jjonkman]

Dear @YuYuJou,

Like other OpenFAST input files, the StC file requires a specific format. The StC input file is documented within OpenFAST readthedocs here: https://openfast.readthedocs.io/en/main/source/user/servodyn-stc/StC_input.html. And you can find an example StC input file in the r-test: https://github.com/OpenFAST/r-test/blob/main/glue-codes/openfast/5MW_Baseline/NRELOffshrBsline5MW_ServoDyn_StC.dat. Echo is the first input on line 4 of the StC input file.

Best rears,