Extract higher order frequencies from blade acceleration data

Wind & Water Structural Analysis
1

Hi everyone,

I’m currently working on a project where I analyze acceleration data measured in edge- and flapwise direction of a rotor blade. As validation of measurement data, I wanted to see how the acceleration data generated in a FAST simulation looks like. Therefore I did several runs on the NREL 5MW onshore turbine and extracted some SpnALxb and SpnALyb values and did a FFT on the signals.

This is when I realized that FAST only uses one edgewise and two flapwise blade modes to generate the acceleration signals. Also when looking into the FASTKinetics formulas, only these three eigenmodes are taken into account. Since I am more interested in higher order eigenmodes of the blades, which I can see in real measurement data, is it possible to add more blade eigenmodes to the simulation? I’m especially interested in changes in higher order frequencies due to damages or atmospheric icing.

Best regards

2

Dear Florian,

A similar question was asked and answered in the following forum topic: FAST Blade Input Properties - #2 by Jason.Jonkman (see my post dated Tue Feb 09, 2016).

Note that a blades dominated by bending (as ElastoDyn assumes), the lowest modes are most critical for calculating structural loading.

Best regards,

3

Dear Jason,

thank you for linking the forum topic where a similar question was discussed already. By setting the CompElast value to 2 (that means using BeamDyn for blade simulation) the frequency response of the simulated acceleration signals looks much more similar to measured signals and also higher order eigenfrequencies can be recognized.

Best regards,
Florian