Dear Jason,
I’m currently researching the dynamics of flexible semi-submersible floating offshore wind turbines. I’ve been attempting to integrate SubDyn into an OpenFAST simulation of the OC4 semi-sub structure with the NREL 5MW turbine, but I’ve run into persistent issues.
Following the detailed guidance you’ve provided—as well as insights from other experienced users—I’ve ensured that all members and joints are properly connected in both the OC4 configuration and the SubDyn input file as recommended in your comments (The simulation of floating offshore wind turbines considering substructure hydroelasticity · Issue #1250 · OpenFAST/openfast · GitHub) , and this solved SubDyn rigid mode zero eigen issues.
However, I keep encountering a “NaN state detected error “ in MoorDyn. From what I understand, this may be due to structural instabilities.
I also tried your recommended approach (from MD_UpdateStates: NaN state detected - #2 by Jason.Jonkman) of removing MoorDyn from the simulation and compensating by introducing additional stiffness, AddF0, AddCLin, in specific degrees of freedom via the HydroDyn module, but unfortunately, the issue persists.
Would you be able to offer any advice or point me toward a possible solution?
Many thanks,
Paul
