Hi,
I don’t mean to bother, but I am a control engineer and I need to run some FAST simulations to get signature signals of specific moments for my work. Now, I don’t have much of knowledge in mechanics, so, I think someone may have done this already, but I swear that I read all 23 pages of the forum and I couldn’t find something to answer about it. I am running simulations with a “lighter” blade, changing its density to cause some kind of unbalance and I liked the results, even tho I don’t know how it would work in a real situation.
So, to simulate a “crack”, I went to the blade file, took a span and changed its chord length to a smaller value ( 
) (not much smaller tho), so I would have in that span a “crack”. The thing is, I don’t really know how near-to-real-world it represents. Should stiffness changes be taken into account for my situation? I am running Wp_baseline from FAST V8 CertTests just in case.
Thank you everyone!
Best Regards.
Dear Leonardo,
If you’ve changed the chord, presumably you are changing the AeroDyn input file of FAST, but this input file is only used to define the aerodynamic properties of the simulation. I would expect cracks to impact the blade stiffness rather than the aerodynamics. Thus, you should change the structural blade input file from the ElastoDyn module (both stiffness and mode shapes).
That said; regarding blade failure, FAST can be used to calculate the reaction loads that would lead to blade failure, but the actual failure event is not generally modeled directly e.g. see: Making fault - #2 by Jason.Jonkman.
Best regards,
Dear Jason,
Thank you for your quick reply. So would you suggest that I create a blade in BMode to work with its “cracked” condition, in case I wanted to simulate a situation where the turbine has already some kind of failure instead of the simulation of the loads that lead to the failure?
Thank you again,
Best regards.
Dear Leanardo,
Yes, you’ll have to change the blade stiffness and the associated blade mode shape(s) in ElastoDyn. To derive the mode shapes, you can use BModes or the old Modes preprocessor.
Best regards,