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OpenFAST / openfast

Main repository for the NREL-supported OpenFAST whole-turbine and FAST.Farm wind farm simulation codes.
http://openfast.readthedocs.io
Apache License 2.0
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MoorDyn #2274

Open WS991106 opened 4 months ago

WS991106 commented 4 months ago

Dear @jjonkman，

I'd like to know what that means.Would you mind explaining this to me? image

Best Regards，

andrew-platt commented 4 months ago

@RyanDavies19, could you answer this?

RyanDavies19 commented 4 months ago

@WS991106 that warning just means that the initial catenary profile solve for the line failed so the line is initializing as linear. If you allow for dynamic relaxation (TmaxIC > 0 in the MoorDyn options), then this won't impact your simulation. Dynamic relaxation will allow the lines to "fall" into place by solving for the steady state solution of the system before the simulation begins.

WS991106 commented 4 months ago

@RyanDavies19 Thank you for your answer.

WS991106 commented 3 months ago

@andrew-platt I only give line 1 a DeltaL=5 signal and then output the tension of cable guide 1 found that there is a big step at first and then it quickly returns to normal. May I ask why this is? image image image

andrew-platt commented 3 months ago

Dear @WS991106,

After you shorten the cable really quickly, the entire cable line will experience a spike in tension. This tension will of course relax as the platform moves and the cable move in response.

5 m is a very large cable change for a single timestep. You may want to consider what a realistic cable shortening would be.

Regards,

WS991106 commented 3 months ago

Dear @andrew-platt,

Thank you for your answer, what is the time step for this? Is it the same as DT=0.125 in the .fst file, or is it modified somewhere else? And I would like to know if DeltaL can be set to a negative value? And is there any upper or lower limit for DeltaL?

Best Regards,