Forum
Important Notice for New User Registrations
To combat an increasing number of spam and bot registrations, we now manually approve all new user registrations. While this may cause a delay until your account is approved, this step is essential to ensure the quality and security of this forum.
To help us verify your registration as legitimate, please use a clear name as user name or an official email address (such as a work, university, or similar address). If you’re concerned that we may not recognize your registration as non-spam, feel free to email us at with a request to approve your username.
QFEM Torsional Stiffness
Hi David,
i am trying to understand the calculation of the torsional stiffness. When i change the pitch axis location, QFEM ist calculating a different value for GJ, but isnt the torsional moment of intertia independent of the chosen coordiante system? So QFEM calculating the polare moment of intertia as an approximation for the torsional moment of intertia?
Best regards
Linus Adam
Hi Linus,
Yes, you are correct. QFEM uses the polar second moment of area (J=Ix+Iy) as an approximation for the torsional constant.
This was calculated about the pitch axis, which caused GJ to change when the pitch-axis position was modified. To be more consistent I have corrected this issue for the next release, so that this value is reprojected to shear modulus weightes centroid, independent of the pitch axis location.
Keep in mind that QFEM is a highly simplified tool for the estimation of blade structural properties, meinly intended for educational purpose. It uses basic cross-sectional integration and does not account for effects such as shear flow, warping, or composite layups. So, the calculated GJ is only an approximation, and for more accurate sectional properties I would recommend using a dedicated cross-sectional solver.
Best regards,
David
Hi David,
I highly appreciate your detailed answers to my questions!
Best regards
Linus
