Torsional spring: preload

Alice7

Hi,

I'm doing an FSI simulation of a pitching and plunging NACA 0012 and I'm trying to model the structure.

In the image below, you can see the airfoil , with an initial pitch of 5deg, which has 2 DoF: rotation and vertical movement. These two DoF have been represented with 2 springs (PBUSH), a vertical and a torsional one.

The problem is that the equilibrium position of the torsional spring is 0deg. So the starting point (5deg) should be preloaded.

How can I do this in Optistruct?

Thank you for your help,

Alice

FaroukMaabs

Hello Alice,

Thank you for reaching out to Altair Support. Below are some recommendations for your consideration:

1. Pre-rotation subcase

This idea involves adding an imposed rotation in order to bring the wing into the desired position.

2. PBUSH with PBUSHT

PBUSHT allows for the definition of non-linear stiffness such as M = K(\theta) x \theta. This, enables the definition of a behaviour law where, for the starting position (5 deg), \theta=0 and M != 0. The idea is to shift the behaviour law M = K. \theta

3. Hinge joint element with PJOINTG (using PROPERTY=NELA with or without CREF)

This approach is similar to PBUSHT, where non-linear properties can be defined using NELA. A shifted behaviour law can be established, accounting for the starting position where the moment is not equal to 0.

I hope these suggestions meet your requirements. Should you need any further assistance, please feel free to contact us.

Best regards,