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1-Newbie

## Convergence of Mechanica FEA

I have a rather complex structure. I am having trouble with it not converging. I have tried the following things: 1 â€“ AutoGen Settings / Limits turned down to. 150 / 150 / 5 / 5 with a max AR of 3. This should have increased the number of elements and I am fairly certain it did. 2 â€“ Analysis and Design Studies Settings: Turned on Iterations after run 1 3 â€“ Max Polynomial order to 9 4 â€“ Percent Convergence Limits set to 10% The runs are now taking hours to days but still not converging (close though). It still shows: &gt;&gt; Pass 7 &lt;&lt; Calculating Element Equations (02:52:10) Total Number of Equations: 1396924 Maximum Edge Order: 9 Solving Equations (03:00:54) Load Set: LoadSet1 Iterative Solver Iterations: 115 (04:25:27) Post-Processing Solution (04:29:07) Calculating Disp and Stress Results (04:31:34) Checking Convergence (04:34:11) Elements Not Converged: 49 Edges Not Converged: 0 Local Disp/Energy Index: 34.4% Global RMS Stress Index: 11.7% RMS Stress Error Estimates: Load Set Stress Error % of Max Prin Str ---------------- ------------ ----------------- LoadSet1 1.09e+02 0.2% of 6.04e+04 ** Warning: Convergence was not obtained because the maximum polynomial order of 9 was reached. Name Value Convergence -------------- ------------- ----------- max_beam_bending: 0.000000e+00 0.0% max_beam_tensile: 0.000000e+00 0.0% max_beam_torsion: 0.000000e+00 0.0% max_beam_total: 0.000000e+00 0.0% max_disp_mag: 2.457011e-06 0.4% max_disp_x: 3.398798e-07 0.4% max_disp_y: -2.252106e-06 0.5% max_disp_z: 1.196406e-06 0.2% max_prin_mag: -6.042908e+04 16.6% max_rot_mag: 0.000000e+00 0.0% max_rot_x: 0.000000e+00 0.0% max_rot_y: 0.000000e+00 0.0% max_rot_z: 0.000000e+00 0.0% max_stress_prin: 6.797264e+03 14.1% max_stress_vm: 4.761940e+04 14.6% max_stress_xx: -2.803036e+04 16.6% max_stress_xy: -2.076851e+04 16.7% max_stress_xz: 6.008733e+03 13.4% max_stress_yy: -4.675738e+04 18.1% max_stress_yz: 9.303615e+03 10.8% max_stress_zz: -1.922502e+04 12.1% min_stress_prin: -6.042908e+04 16.6% strain_energy: 5.680392e-03 0.8% Any other suggestions to converge.
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5 REPLIES 5
1-Newbie
(To:ptc-1894396)
I contacted the help desk, and they suggested I look at the p-level of the elements. That helps identify which are the offending elements. Then use the AutoGen controls to increase the number of points on that element. However, I keep bumping into memory issues. Currently the model has 18,000+ elements and at a p-level of 9 it generates 1.2+ million equations to solve. Very time and memory consuming. I am currently trying to balance the number of elements with the convergence. Tricky.
1-Newbie
(To:ptc-1894396)
Check to make sure that you do not have a singularity anywhere in the model. For instance, a constraint or load at a point is a typical one. This would make the stress graidients very large, there by forcing mechanica to move to most likely the max p order of 9. Also, see if you can simplify large regions of relatively think material with shell elements insead solid elements. Also, if you are interested in the stress in a particular region of the model you can always create measures in that region that track the value of the measured quantity. That way you can check to see if those critical regions are converging on stress or displacmenet. Mechanica also makes is such that instead of trying to converge the model globally (which is the default) you can for the p-element convergence to take place with respect to a given set of user created measures. I have analyzed some pretty huge models in the past (e.g. 30,000+ elements). But that was only possible due to the analysis converging with a max p order of 6 or 7.
1-Newbie
(To:ptc-385258)
Thanks for the help. There are no singularities such as point loads. I wish you could see the model. Its a bunch of plates making a structure with a bunch of boxes hanging off it. Is there was a way to not analises the boxes (dont need to) but still have their weights and moments applied to the structure without inputting 8+ simple beams and a point mass? Right now I am running the FEA looking at the P level results and refining the points in the area of high P levels, and reducing the points in the area of low P levels. This is helping, but I still have ~100 out of 20,000 faces still not converged. I am also running into memory issues, with too many elements. I have 3 gigs of RAM but at high P levels the FEA is solving 2 million equations and asks for an aditional XXXX amount of RAM or Page. I have the default RAM setting of 128. Anyway, the nonconverged elements/faces appear to be in noncritical areas so I think I am just going to go with it.
1-Newbie
(To:ptc-1894396)
If you wanted me to take a look at it you could try emailing me the Pro/Engineer files. I could try running it to see if there is anything that I see. My email is -. Send me a test email first though. We have a ridiculous email filtering system that filters out more business email than spam. Steve
1-Newbie
(To:ptc-385258)
After conciterable fiddeling. I have gotten it to converge (9% yea). Thanks for the help.
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