Modal Analysis Errors
A modal analysis was rejected or did not converge. Why, and how to fix it.
If you only have 2 minutes
Modal analysis solves for natural frequencies and mode shapes. It needs solid elements and real supports, and it does not accept stabilization springs. Most failures are the element type, a stabilization-spring boundary condition, or the eigensolver not converging.
Common errors
- Error 317: the mesh contains a beam or shell element. Modal analysis supports only solid (3D) elements (rotary inertia for beam and shell elements is not supported). Re-mesh the part with solid elements.
- Error 331: stabilization springs cannot be used in a modal analysis. They add artificial stiffness that shifts every eigenfrequency and turns the rigid-body modes into spurious ones. Constrain the model with a displacement boundary condition instead, or run it free-free and accept the six zero-frequency rigid-body modes (those are normal).
- Error 354: the modal solver returned fewer modes than requested, even after enlarging its workspace and restarting. Request fewer modes, or accept that the problem is numerically hard (the message reports the best residual reached).
How modal analysis works, and why the six rigid-body modes are expected, is explained in Modal Analysis.