# Coupled blade modes in FAST

**URL:** <https://forums.nlr.gov/t/coupled-blade-modes-in-fast/314>\
**Category:** Computer-Aided Engineering Software Tools\
**Created:** [December 13, 2010, 10:51am UTC](https://forums.nlr.gov/t/coupled-blade-modes-in-fast/314 "2010-12-13T10:51:13Z")\
**Posts on this page:** 1\
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**Author:** ![Matthias.Taubert](https://avatars.discourse-cdn.com/v4/letter/m/76d3ee/32.png) [@Matthias.Taubert](https://forums.nlr.gov/u/Matthias.Taubert)\
**Post date:** [December 13, 2010, 10:51am UTC](https://forums.nlr.gov/t/coupled-blade-modes-in-fast/314/1 "2010-12-13T10:51:13Z")

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Hello to everyone,

I created blade modes with the help of BModes and applied the polynomial coefficients to my FAST model  
in order to parameterize the flexible blade model. After running a few different simulations I applied  
an FFT to the output results like flapwise and edgewise tip deflection. I expected to see for the  
flapwise deflection the two flap mode frequencies and for the edgewise deflection the edge mode frequency.  
In addition to the edgewise frequency (1.35 Hz) I also found the first flapwise frequency (0.75 Hz) in  
the edge deflection results.

 ![FFT_TipDyb1.png](https://europe1.discourse-cdn.com/nrel/original/1X/320efcaca988e112d2a0e3698f798208b0381fb8.png)

This phenomen I would have expected if flap and edge-modes are coupled.  
Does the blade model in FAST supports coupled modes or is there another reason for the described affect possible?

Is the blade model in FAST linear or nonlinear?

Any help is much appreciated!

Best regards,

Matthias

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