beam4 axial rotation

[dersman]

Hello,

I'm doing a large deflection analysis with BEAM4 elements but I'm having difficulties plotting the axial rotation due to torsion. The normal rotx DOF plot gives erroneous results because it is based on the nodal coordinate system instead of the element coordinate system. I tried modifying the results coordinate system with rsys but nothing helps. I would like to know the rotation of a pipeline modelled with beam4 elements at every point of the large deflection analysis.

Does any one know how to get the right values for the axial rotation?

Thanks!
dersman

 

[Stringmaker]

Dersman,
It's tough to understand what "erroneous results" are in this situation. Are you saying that your results are not continuous? I'd say the best way to get your question answered is to post a copy of your input file so that others can have a look at it. Your original post is a bit tough to piece together.

-Brian

 

[dersman]

Im not sure if my input file would be of much aid, since you have to run a >1 hour simulation to see what happens.

I will try to clarify my problem:
initially the beam elements are situated on the global x-axis. In the final deformed state the elements are still parallel with the x-axis, but on another location. I added a small protrusion to visualize rotation. Furthermore I numerically integrated the torsion stress output over the total pipe length to calculate the rotation. This calculated axial rotation complies with the visual rotation of the protrusion.

The normal, easiest way to plot axial rotation is the 'rotx' plot or list function and this is where I have a problem. Even though in the initial- and final situation the elements are parallel to the x-axis, the rotx function gives total different values compared to the visual rotation and the rotation calculated by integrating the torsion stress. My question is why the rotx function gives different results and if there is a way to solve this.

I know this problem is hard to explain but maybe one of the forum readers recognizes my problem. It s worth a shot at least!

Thanks in advance
dersman

 

[Stringmaker]

Dersman,
This is indeed a tough problem to diagnose. Are you positive that connectivity in your model is not a problem? In other words all elements are properly connected to one another and are compatible (have same DOF's). If not then check this carefully as this could cause such a problem. Have you tried to query the nodal solution to verify the results at individual nodes instead of doing so purely graphically? This can be done in /POST1 by selecting "Query Results" or something of the like. Don't have Ansys up in front of me right now.

-Brian

 

[ansysfreak]

Hi

Do you use stress stiffening for large defection?

Gtrz
Garry