Rigid body motion in abq

[Ephore]

Hello,

I am trying to write an Abq input file from a python script to perform a displacement-driven simulation. But I have some troubles when applying the boundary conditions.

The data I have are the coordinates of moving objects for each frame of the motion. Objects are modeled as rigid bodies in Abq. For each frame, I compute the rotation matrix and the translation needed to move each object from their first position to their current position. The transformation is computed for a rotation around the reference point. I then compute the axis-angle representation of the rotation matrix, which is used as angles for the boundary conditions. Rotation angles and translation values are stored in an amplitude, and I apply that in a single step. The problem is that the resulting motion is not correct. How exactly Abaqus is combining rotation and translation in the boundary conditions? Does anybody has a clue to solve my problem?

 

[akabarten]

Hello,

I am not sure is this will be helpful for you but please take a look here:
Abaqus Analysis User's Manual, 1.2.2 Conventions, Finite rotations

Regards,
Bartosz

 

[Ephore]

Thank you for your answer. Actually, I would like to know how translations are combined with rotations when applying boundary conditions. Is this a translation followed by a rotation or a rotation followed by a translation, or a translation and a rotation applied "simultaneously" ?

Anyway, it seems that calculating the motion between each frame (instead of calculating it between the first frame and the current frame) and cumulating these motions in the amplitude defined for the boundary conditions solved my problem.