Creating geometry dependent force

Hi,

I try to create a force that dependent on an angle, to simplify earodynamic forces. Therefore I created a variable "Angle" under definitions: Angle = asin(-t1z).

To check if my formula was right I plot the variable Angle and the result were as expected. However when I try to introduce a boundary load: Angle*1[N] I get this error:

Undefined variable.
- Variable: comp1.Angle
- Geometry: geom1
- Boundary: 6
Failed to evaluate Jacobian of expression.
- Expression: ((1/comp1.mbd.bndl1.selA)*comp1.mbd.bndl1.FTy)*dvol
Failed to evaluate Jacobian of expression.
- Expression: (comp1.mbd.bndl1.FTy*test(comp1.mbd.bndl1.uy)/comp1.mbd.bndl1.selA)*(dvol)

Has someone an idea how to solve this problem? A test simulation is added.

Thanks in advance!
Rijk