Dear Dr. Jonkman,
I’ve spent some more time experimenting with this problem. From what I can tell (mostly looking at out-of-plane tip deflection), the structural simulation seems to be behaving reasonably for the majority of the simulation, regardless of time step size. That said, comparing the disturbed wind speed, BαNβVDisx, and the structural speed, BαNβSTVx, as suggested in [url]AeroDyn v15 convergence issues - #7 by Jason.Jonkman] (since Vx = BαNβVDisx - BαNβSTVx) reveals some interesting behavior around the time of simulation failure. Here, I plot those two values at the 7th node (the problematic node) on blade 1 for both the problematic wind case (ECD-R-2.0, in green) and a non-problematic–but somewhat similar–case (ECD-R+2.0, in orange).
Clearly, the structural speed undergoes a sudden and significant change just before the failure. If that slope were to to stay the same (or increase), I can definitely imagine that Vx would equal zero for the next time step. This still seems a bit like numerical instability to me, but decreasing time step size doesn’t solve the problem.
Let me know if you have any additional thoughts or suggestions of what to try. I’m tempted to use AeroDyn v14 at this point since it apparently experiences this problem less for whatever reason, but I’d really like really prefer to use the most recent version if at all possible!
Thank you,
Austin