I have a question about the content shown on page 28 - 29 in NREL report - NREL/TP-500-38060:
Not including platform motion, the higher fidelity ADAMS model of the land-based version of the wind turbine incorporates 438 DOFs as follows:
• One hundred and two DOFs in each of the three blades, including flapwise and edgewise shear and bending, torsion, and extension DOFs
• One blade-pitch actuator DOF in each of the three blades
• One variable-generator speed DOF and one driveshaft torsional DOF
• One nacelle-yaw actuator DOF
• One hundred and twenty-six DOFs in the tower, including fore-aft and side-to-side shear and bending, torsion, and extension DOFs.
The questions are:
- How can we count the number of degree of freedoms in ADAMS model?
- What are the flapwise and edgewise shear and bending? Do they still use the modal analysis based on the mode shapes?
The number of DOFs in an ADAMS model is identified in the command window when you run the simulation with ADAMS/Solver.
By “flapwise shear and bending” I’m refering to translational and rotational DOFs in the flapwise and edgewise directions of the blade.
ADAMS does not use modal-based DOFs; instead, ADAMS is a general multibody dynamics program where each “body” has six DOFs. (A blade is modeled as a series of 6-DOF rigid bodies.)
Thanks for your response.
So, I still want to make sure I am understanding the model right:
“One hundred and two DOFs in each of the three blades” may yeild 17 rigid bodies of each blade and is equal to BldNodes. The aerodynamic force can only be determined for the 17 nodes. FAST will interpolate the NBlInpSt = 49 to the 17 blade node location to do aeroelasticity calculation.
“One hundred and twenty-six DOFs in the tower” may yeild 21 ridid bodies of tower. Since the TwrNodes = 20, did you include 6 DoFs of the platform in your model?
I agree with your 1st comment. If the blade had a tip mass separate from the distributed mass, the tip mass would introduce another 6-DOF rigid body.
For the 2nd comment, the extra rigid 6-DOF rigid body comes from the yaw bearing, not the platform. If the platform DOFs are enabled, they would introduce another 6-DOF rigid body.
You should be able to examine subroutine FAST2ADAMS.f90/MakeACF() to see how the FAST model DOFs are related to the DOFs enabled in the ADAMS model.
I hope that helps.