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Insufficient Contraints

Level 1

Insufficient Contraints

So I'm trying to Run an analysis on an assembly and I am getting the error of (see picture). I have been able to run a few successful analysis but lately they are coming up with this Analysis. Any suggestions?

6 REPLIES 6

Re: Insufficient Contraints

Something is moving without generating any opposing force.

Assuming that you have constrained your assembly fully (every component prevented from translating or rotating?) then other things to check are that a) you've assigned a material to each component, and b) each material has a (sensible) value for Young's Modulus.

Re: Insufficient Contraints

The assembly is fully constrained, I do have material assigned for everything (includes density and Young's Modules). The only thing I changed between the first time I ran the analysis (when things were working) and now was changed the units on my forces because I had the wrong units.

Re: Insufficient Contraints

Sometimes the suggestion of "running a constrained Modal analysis with rigid mode search" does actually help. If you do that and animate the results, it often shows which component is underconstrained, and in which direction.

Re: Insufficient Contraints

It appears your model is a 3D analysis, did you follow the rule of constraints for a 3D analysis - rotational DOFs are not present for solid elements? Only translational DOFs can be assigned if this model is a "solid" element analysis. You will get this error if you assign rotational DOFs to try to constrain the part/assembly.

Just a thought.

Re: Insufficient Contraints

I've a vague memory of that kind of error being caused by a bad mesh -- those red elements might indicate an element connectivity problem. Possibly, higher displacements (due to changing the force units) brought out the mesh weaknesses. You could try lowering the forces until it does solve, then check max displacements to see if they are 'small'. Also try some mesh controls (e.g., larger min angles) for a different and more robust mesh.

Re: Insufficient Contraints

Jonathan's second reply is correct. Run the mofdal analysis, with rigid mode search.

Inn the results you will find modes with 0 Hertz. Animated displacements will show you the parts that are not attached.

This can happen when two parts interfere, they will both be meshed, but will not be attached to each other, soone of them will be able to move freely.

Run the modal!