Hi Dr. Jonkman,
I hope you’re doing well. I had a couple of quick questions about OpenFAST that I was hoping you could help me with.
First, I was wondering whether OpenFAST performs linear or nonlinear analysis when no active control systems are involved—just to better understand the assumptions behind the simulation.
Second, is there a way to extract the instantaneous natural frequency of the structure during a simulation? I’m trying to figure out if there’s a specific output channel or method that can provide that information.
Thank you so much for your time and support—I truly appreciate it.
Best regards,
Anise Ziamehr
Dear @Anis.Ziamehr,
Here are my responses:
- Time-domain simulations in OpenFAST include nonlinearities in most physics-based modules (aerodynamics, hydrodynamics, structural dynamics, controls). OpenFAST also supports the ability to extract a linear-equivalent model, linearized around an operating, when some features are disabled.
- The full-system natural frequencies are not directly calculated and output by OpenFAST, but you can compute the natural frequencies in a post-processing step, e.g., via Eigenalaysis of the linearized state matrix after generating a linear-equiavlent model through a linearization analysis or via a system-identification technique applied directly to the time-series output.
Best regards,