Simulation Mechanical

[runar.viggosson]

i get this error when I run a buckling analysis on a wire sheave

Code: 737
Improperly posed generalized symmetric eigenproblem.
Possible reason: The model may not be tied down enough
or you may have a change in stiffness somewhere in the
model which is too abrupt.
Suggestion: check model and boundary condition

Does anyone here know what this is and how to fix it?

[John_Holtz]

Hi Runar. Welcome to the Simulation Mechanical forum.

One part of the message is indicating that the model is not statically stable. In other words, no part is free to move in X, Y, Z translation or rotate about X, Y, Z. Do you have constraints on the model to prevent rigid body motion in all 6 directions? Are all of the parts connected together?

The other part of the message is about the range of stiffness in the model. For example, if you made one part artificially stiff (entered a modulus of elasticity that was thousands of times stiffer than steel, used rigid elements with a stiffness that was too high) and another part was aluminum foil (something with very little stiffness in bending), the software is not able to handle such a large range of stiffness. (Mathematically, it is difficult to distinguish between a very weak part and a part that is not statically stable.) Do you have this situation?

One thing that you can do is run the analysis as a linear natural frequency (modal) analysis. That analysis type can deal with rigid body modes, meaning parts that are not statically stable. If the first calculated frequency is 0 and some part has unexpected displacements, that would be the part that is unstable.