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creo simulate, multi-pass adaptive, number of passes

ptc-5277933
1-Newbie

creo simulate, multi-pass adaptive, number of passes

I am conducting a study using the stress analysis features in creo simulate but I can't explain the steps the process is taking. I am using the multi-pass adaptive convergence method using maximum von mises stress as my measurement with a targeted convergence of 1%. I set the minimum P-order to 1 and the maximum P-order to 9.

 

What I can not explain is why this method is using only 7 passes to calculate a solution. The solution is not converging until the 9th order bias functions so it is not stopping because it has converged.

 

I would expect the method to run a pass for each polynomial order and increase those elements that have not yet converged until the maximum p-order is reached or all elements have converged. The method appears to be skipping a couple of these passes for the 3rd and 5th polynomial order.

 

I have attached the run status summary file from my analysis. It can be seen that the second pass uses 2nd order functions and the third pass jumps to 4th order functions. the same jump can be seen between the fourth and fifth passes.

 

I tried setting the maximum p-order to 3 and the results returned a maximum p-order of 2. If I set the maximum p-order to 4 and the results returned a maximum p-order of 4 and included elements with a p-order of 3.

 

Can anyone can shed some light on why the multi-pass adaptive method is not running a pass for each p-order or why the solution returned (which had not converged) when I set the maximum p-order to 3 did not include 3rd order elements.

 

Thank you,


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3 REPLIES 3

It is normal for a MPA to skip orders if it detects that the difference between runs is nowhere close enough for converging with the next order. I suspect the idea being to save you time in running the analysis by skipping orders that won't help much. I wouldn't be surprised if that is the case for the runs that didn't converge and never used the maximum order setting. If nearly every element and edge hasn't converged, there's almost no way on earth that the next run will converge within 1%. I don't know what the criteria is for Simulate to make these kinds of decisions but that is the reason behind only selecting the maximum and minimum orders. Let their algorythm do it's job to optimize the time spent on the analysis.

You might want to do a plot of the element orders in the model so you can see if there is something in the geometry that the automesher needs help with by manually increasing the number of elements in a particular area using AutoGEM controls, adjusting the geometry, tolerance, etc.

Depending on the geometry and discretization of your part, 1st order and perhaps 2nd order runs can be useless and even misleading...particularly for the p-method which uses less elements....unless, of course, that is your aim. The default minimum is 3rd order and I'm usually inclined to leave it there so that the shape functions can accurately depect the geometry.

Finally, are you only converging on the max vm stress measure? That could be misleading and dangerous, espcially if you run into a nasty singularity in another analysis...doesn't appear to be the case this time. Is there a particular reason you didn't want the default options of local displacement, strain energy, and RMS stress? Ultimately, you might want to include more measures for convergence. In the report, is looks like max plane stress values for convergence are high even if the values are low. Displacement in Y also didn't converge to your target of 1% (which might be too strict). Just my $0.02, hope that helps.

ehaenen
4-Participant
(To:ptc-5277933)

Benjamin, and also Eric

Convergence scheme for MPA is quite intricate. Iif there's no convergence for an element edge, order of the displacement field is increased by one. If there's no convergence for an element face, order is increased by two.

Problems theta go "over 7" probably have a severe discontinuity or singularity. Refine the model, remove singularity and try again.

Erik

Interesting, that would explain it. Thanks Erik!

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