Learning Forum

[asceduardo]

I'm currently analysing the dynamics of a beam coupled with a spring-mass system. The spring can be linear or not. However, as shown in the attached pictures, for some reason the mass will not move when the non-linear spring is set. I did not set any constraint for the mass. The Transient Analysis was set with Weak Springs and Large Deflection on. Does anyone know how can I solve that? I need the move to move freely. When I perform a linear analysis for the linear spring, the spring-mass behaves as I need. Thanks in advance.

 

[dlooman]

This is a Full (not Mode-Sup) transient, correct?  I tried it and it works for me.  I verified it by scoping a deformation result to the named selection I had to create to scope the spring to the mass.  An indirect way to check if it is moving is to create a probe for the nonlinear spring.  

[asceduardo]

Right, it is a full transient analysis. In fact, I have created a probe point to verify the motion of the spring's mass. It gives me zero for all instants of time:

In case it helps, these were the paramers set for the non-linear spring and the analysis:

Could you share your simulation file, so that I can understand why in your case the non-linear spring works properly?

[dlooman]

I wish I could!  Your set up is the same as mine.  If you probe the spring force is it zero also?  If you were now to change the spring back to linear the probe would show non-zero displacements?  It's hard to imagine how that could be.  Are there any warnings in the gui or the Solution Information?

[asceduardo]

If I change the spring back to linear, the probe point moves freely, as it should:

For the analysis with a non-linear spring, I got the following warnings:

• One or more MPC or Lagrange Multiplier formulation based contact regions or remote boundary conditions may have conflicts with other applied boundary conditions or other contact or symmetry regions. This may reduce solution accuracy. For MPC based remote points, setting the relaxation method may help eliminate overconstraint. Tip: You may graphically display FE Connections from the Solution Information Object for non-cyclic analysis. Refer to Troubleshooting in the Help System for more details.
• Point Mass does not have Rigid behavior and it will be ignored by the Explicit solver during the analysis.
• Primary Assembly BaseMesh File is not available. You will need to re-mesh to recover the file before re-connecting the mesh.
• One or more objects may have lost some scoping attachments during the geometry update. You can identify these tree objects by activating the Scoping Wizard in the Selection Toolbar, or by filtering the tree using the Scoping option set to Partial.

I suspect the problem has something to do with the second warning (in bold). Do you have any idea how can I deal with that?

[dlooman]

Yes, the message seems to explain the issue.  Hard to imagine how making a spring non-linear turns a Transient Structural System into an Explicit (Rigid Dynamics) system!  When you change the spring to linear you make no other changes?  You don't use another project?