Edgewise mode

Hello,

I would just like to know if the EdgeDOF flag refers to the first edgewise mode, which is asymmetrical; or if it refers to the first symmetrical mode, which is actually the third one.

Regards,

Iñaki

Dear Iñaki,

Both. The EdgeDOF in FAST enables/disables the edgewise bending mode of all blades. Thus, the “asymmetrical” and “symmetrical” modes of the rotor will both be enabled when the EdgeDOF is enabled.

Best regards,

Dear Jason,

first of all, thank you for your answer, but now another doubt appears. If, as you say, both modes are implemented in the flag EdgeDOF, is there any way to enable/disable only one of them?

Regards,

Iñaki

Dear Iñaki,

To be precise, in the structural model of FAST v7 and the ElastoDyn module of FAST v8, the blade-bending DOFs are implemented distinctly for each blade. That is, the DOFs are implemented as blade modes, not rotor modes. Enabling or disabling the EdgeDOF will enable or disable the edgewise bending mode of each blade. By changing the source code, it would not be difficult to enable or disable the edgewise bending mode separately for each blade (although I’m not sure there would ever be a reason to do so). But because the DOFs are not rotor modes, it would not be easy to enable the asymmetric rotor modes without also enabling the symmetric rotor mode.

I hope that helps.

Best regards,

Dear Jason,

it helped, thank you for your time.

Regards,

Iñaki

Hello,

now I am trying to build a Simulink model of a wind turbine taking into account the edgewise mode of the blades (I am using what is called the “three mass model”). However, when I linearize it and compare it with the FAST linerization, the transfer functions are quite different (they have different number of zeros). If you could tell me what equations does FAST use, I would really appreciate it.

Regards,

Iñaki

Dear Iñaki,

Information on the theory basis of the structural model of FAST v7 and the ElastoDyn module of FAST v8 is provided in the following forum topic: http://forums.nrel.gov/t/coupled-blade-modes-in-fast/314/1.

Best regards,

Dear Jason,

thank you for your fast reply, I will take a look at it.

Regards,

Iñaki