V-shaped semi-submersible wind turbine model

[Haoxuan.Shen]

Dear Dr. Jason.

I am in the process of designing a V-shaped tripod semi-submersible wind turbine with the tower located on the first side column. I currently have some confusion regarding the reference points and the center of gravity in both HydroDyn and ElastoDyn.

Following your previous responses, I have set the WAMIT hydrodynamic reference point and the platform center of gravity to the origin (0,0,0) in my HydroDyn modeling. The intersection of the tower centerline with the horizontal plane is also at point 0. I adjusted the COG in ElastoDyn to (51.9, 0, 2.21) and adjusted the COB in HydroDyn, and the mooring line position in MoorDyn is set to match the HydroDyn model. However, after making these adjustments, I encountered the following errors. Could you please advise on how to correct them? Attached are the relevant configuration screenshots for your reference.

Best regards,

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption1:ED_HD_InputOutputSolve:HydroDyn_CalcOutp
ut: Angles in GetSmllRotAngs() are larger than 0.4 radians.
HydroDyn_CalcOutput:HDOut_MapOutputs: Angles in GetSmllRotAngs() are larger than 0.4 radians.
ED_HD_InputOutputSolve:HydroDyn_CalcOutput: Angles in GetSmllRotAngs() are larger than 0.4
radians.
HydroDyn_CalcOutput:HDOut_MapOutputs: Angles in GetSmllRotAngs() are larger than 0.4 radians.

 NaN detected at time    77.0775000000000       in Line            3  in MoorDyn
 .
 NaN detected at time    77.0775000000000       in Line            4  in MoorDyn
 .
NaN detected at time 77.078 in MoorDyn.
NaN detected at time 77.078 in MoorDyn.

FAST_Solution:FAST_AdvanceStates: NaN state detected.

 OpenFAST encountered an error at simulation time 77.075 of 600 seconds.
 Simulation error level: FATAL ERROR

[Jason.Jonkman]

Dear @Haoxuan.Shen,

Well, your model is numerically or hydrostatically unstable, but you haven’t provided enough information for me to understand why. If you are not already, I would suggest simplifying the model to debug, e.g., disable all structural degrees of freedom (DOFs) in ElastoDyn except for the 6 platform DOFs, disable aerodynamics, and use still water in HydroDyn. What happens then?

Perhaps the following forum topics are of use to you?:

Platform Movements Signal

Hi, Could you explain why analyzing the platform movements in an still water case, with no wind and no current, the structure is moving upwards and downwards constantly? It shouldn’t be like that, should it? I can’t understand why this is happening (and you have much more experience). Last week I was abel to reproduce your Hywind platform very well in both versions v7.02 and v 8.0. Now, I’m simulating a semisubergible platform in v 8.0 but it is being strange. Thank you very much. Kind regar…

OC$-Phase II Centre of Gravity and Mass

Dear Dr. Jason Jonkman I am doing the analysis of OC4 model using FAST8 and using strip theory solution (Morison Equation only) for hydrodynamic forces. I found the difference among the inertia and mass values given in the “Elastodyn” and in the report “Definition of the semi-submersible floating system for phase ii of OC4”. I also found the explanation for the difference in one of the post (AddCLin for OC4 Semisubmersible - #3 by Jason.Jonkman). I have few questions and would highly appreciate…

Best regards,