I ran into a solver hang that unfortunately burned significant core time and I’m hoping someone can help me understand what happened and confirm my proposed fix before I burn more hours.
The Project: A custom phono turntable plinth constructed from laminated plywood sheets and including pockets of dense material (tungsten putty) intended to damp structural acoustics.
Simulations: Harmonic Analysis, Modal-Based numerics, 2nd-order elements, 192 cores. A typical run of this simulation (see “SIM 4”) completed successfully in ~49 minutes / ~155 core hours.
What Changed: I duplicated SIM 4 and removed nine cylindrical solid bodies (~25mm diameter cylinders filled with the tungsten putty) from the geometry. These bodies had bonded contacts to the surrounding plywood volume. The contacts were deleted along with the bodies — confirmed gone. Re-meshed. Everything else identical: same boundary conditions, same material assignments, same numerics, same simulation control settings.
What happened: Job launched, and with the expectation of similar wall clock/compute time, I walked away from the desk for 3 hours. When I returned, the sim was hanging at 0% and had burned more than 600 core hours. Simulation killed manually.
Mesh quality is probably the issue:
Non-orthogonality max: 88.4 (acceptable ceiling: 88.0)
Edge ratio max: 242.8 (acceptable ceiling: 100.0) ← likely culprit
Volume ratio max: 110.3 (acceptable ceiling: 100.0)
Skewness max: 4.0 (acceptable: fine)
Aspect ratio max: 51.1 (acceptable: fine)
The edge ratio overage is the obvious red flag. My hypothesis: Deleting the cylindrical bodies leaves open voids in the mesh, and I suspect I’m getting bad elements at the boundary between the finer mesh of the empty pocket walls and the coarser surrounding material.
My proposed fix: Add local Volume custom sizing refinement regions around each pocket location using geometry primitives (spheres or cylinders placed at pocket coordinates, sized ~1.5× pocket diameter, fineness 5.7 vs global 5.0). This should force smooth mesh grading through the transition zone rather than the abrupt jump that’s generating the degenerate elements. I’ve set this up and am ready to re-mesh, but would love insights from the community before pressing the button:
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Does my diagnosis sound right — is the edge ratio 242.8 the solver killer, and is the mechanism what I think it is?
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Is local primitive-based volume refinement the right fix, or is there a cleaner approach to meshing around open cylindrical voids in a solid body?
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Is there any way to pre-validate that a mesh will not produce a singular stiffness matrix before launching the full harmonic run?
Any input appreciated!