# Traction and pressure as a function of position

Hi, I’m receiving this warning when performing my analysis,

“Traction and pressure as a function of position are not follower loads with this solver.
The force is determined by the initial modeled positions of the nodes, not their deformed positions.”

¿Should I understand that pressure is not perpendicular anymore if the surface where it is applied rotates during the system evolution?

If that’s the case, ¿Is there any option to turn pressure and traction followers?.

Thanks

In Abaqus there’s a parameter for *Dload nad *Dsload keywords to make these loads rotate with geometry in geometrically nonlinear analyses: FOLLOWER = YES. CalculiX doesn’t have such a parameter but here’s what the documentation says about pressure loading:

In a large deformation analysis the pressure is applied to the deformed face of the element. Thus, if you pull a rod with a constant pressure, the total force will decrease due to the decrease of the cross-sectional area of the rod. This effect may or may not be intended. If not, the pressure can be replaced by nodal forces.

However, it may not apply to some non-standard (spatially-varying and/or traction) types of loads available in Mecway (I assume that this is were you got this warning message).

Hi Calc_em and thanks for the super fast answer,

I can recognize that effect pointed in the documentation.
I have experienced it when looking at the difference between Engineering and True Stress and it is due to Poisson’s ratio volumetric change in the Rod.

You are right, in my case the functions are more elaborated and there are significant rotations involved in the body.

What a pitty
Well , many thanks anyway,…

HI again,

¿May I ask how this was done?. It came to my mind just now. Result should be completely wrong as there are faces which finishes almost vertical.

Uniform pressure was used for this example: CalculiX-Examples/static.inp at master · calculix/CalculiX-Examples · GitHub
and for this type of load geometric nonlinearity is taken into account, like I said above.

Oooh, I see.

Thanks,

I have applied a pressure and traction loads with a value proportional to the Y coordinate and perpendicular to the surface. Once the loads are applied, I have rotated the body arround Z and I have confirmed that none of the load’s properties are updated (magnitude or direction).