Extract higher order frequencies from blade acceleration data

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Florian.Rieger
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Joined: Mon Jul 15, 2019 7:27 am
Organization: TU Munich
Location: Germany

Extract higher order frequencies from blade acceleration data

Postby Florian.Rieger » Tue Jul 16, 2019 2:30 am

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 Spn*ALxb* and Spn*ALyb* 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

Jason.Jonkman
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Re: Extract higher order frequencies from blade acceleration data

Postby Jason.Jonkman » Tue Jul 16, 2019 7:03 am

Dear Florian,

A similar question was asked and answered in the following forum topic: viewtopic.php?f=4&t=1489&p=6638 (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,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Florian.Rieger
Posts: 2
Joined: Mon Jul 15, 2019 7:27 am
Organization: TU Munich
Location: Germany

Re: Extract higher order frequencies from blade acceleration data

Postby Florian.Rieger » Thu Jul 18, 2019 6:22 am

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


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