Solver automatic load factor reduction

346gnu · ‎Oct 26, 2015

Hi All,

When carrying out a large deformation study with contacts, load factor steps are crucial to success.

The warning that one can get in the .pas file :

** Warning:

Large displacements detected at one or more contac regions.

This can be caused by a very flexible model or disconnected

volumes or components. Temporarary overriding load factor with: 0.1

Which seems fair enough except my original load factor was 0.001.

The question is :

Has the solver replaced my 0.001 load factor by a much larger load factor 0.1; in which case it won't work

OR

Is it multiplying mine by 0.1 making the load factor being applied 0.0001 (which seems a bit too fine) ??

I have raised a support call but it seems my model is required to answer the question. I can't send my model but I have promised to build another to demo this but pushed for time.

Very frustrating.

Any thoughts?

Thanks

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unickque · ‎Oct 27, 2015

In Creo2 the solver shows what the new load factor is:

Load Factor:

0.00125

Iteration

Residual norm

contact Area

------------- ------------- ---------------

	1 2.52932e-009 243.333	Tue Oct 27, 2015 11:06:40
	2 1.98708e-009 243.333	Tue Oct 27, 2015 11:06:52
	3 2.23639e-009 243.353	Tue Oct 27, 2015 11:07:06
	4 4.66306e-008 242.942	Tue Oct 27, 2015 11:07:10

Excessive motion detected at contact regions. Cutting load step size

Load Factor:

0.001125

Iteration

Residual norm

contact Area

------------- ------------- ---------------

	1 2.04585e-009 243.335	Tue Oct 27, 2015 11:07:21
	2 1.61116e-009 243.335	Tue Oct 27, 2015 11:07:33
	3 1.80889e-009 243.355	Tue Oct 27, 2015 11:07:47
	4 4.10039e-008 242.944	Tue Oct 27, 2015 11:07:51

Excessive motion detected at contact regions. Cutting load step size

Load Factor:

0.0010625

But maybe you are using a different Creo version?

346gnu · ‎Oct 28, 2015

Hi Patrick,

Yes I agree, the load factor is reported in the pas file but I was hoping the reporting methodology had changed (or some other explanation) that I had failed to read in release notes or the help. Hence my post. I'm using Creo3.0 M030.

Below is extract from a model I let run just to see what would happen. I am convinced it's not working as it should!

There is still opportunity for it to be user error of course.

I will update my support call accordingly and let you know the result.

Begin Time Step 0 of 42: 0.00000e+00
Sun Oct 25, 2015 10:01:54

Begin Contact Pressure Calculations
Sun Oct 25, 2015 10:03:39

Begin Displacement and Stress Calculation
Sun Oct 25, 2015 10:03:39

Begin Reaction Calculation
Sun Oct 25, 2015 10:04:53

Begin Convergence Check Pass 1
Sun Oct 25, 2015 10:05:31

Begin Time Step 1 of 42: 1.00000e+00
Sun Oct 25, 2015 10:06:39

** Warning:
            Large displacements detected at one or more contac regions.
            This can be caused by a very flexible model or disconnected
            volumes or components. Temporarary overriding load factor with: 0.1

Iteration     Residual norm    contact Area
------------- ------------- ---------------
            1       103.536 37222.7     Sun Oct 25, 2015 10:29:11
            2      0.100549 37621.7     Sun Oct 25, 2015 10:45:06
            3             1 31000.2     Sun Oct 25, 2015 10:53:12
            4   0.000736543 25505.7     Sun Oct 25, 2015 11:01:14
            5   7.7893e-007 14855.3     Sun Oct 25, 2015 11:09:26
reset load factor to: 1
            6    0.00337315 27654.7     Sun Oct 25, 2015 11:22:19
            7      0.297397 18784.5     Sun Oct 25, 2015 11:32:20
            8      0.147715 18801.1     Sun Oct 25, 2015 12:07:59
            9             1 29247.3     Sun Oct 25, 2015 12:19:12
           10     0.0107504 31755.9     Sun Oct 25, 2015 12:28:57
           11      0.333253 18310.7     Sun Oct 25, 2015 12:46:38

** Warning:
Excessive motion detected at contact regions.
Cutting load step size.

Load Factor: 0.5

Iteration     Residual norm    contact Area
------------- ------------- ---------------
            1     0.0614236 31622.2     Sun Oct 25, 2015 12:59:20
            2             1 26811.3     Sun Oct 25, 2015 13:04:53
            3       87406.7 25715.7     Sun Oct 25, 2015 13:15:24
            4       444.189 25715.7     Sun Oct 25, 2015 13:15:40

Load Factor: 0.25

Iteration     Residual norm    contact Area
------------- ------------- ---------------
            1     0.0138464 21575.8     Sun Oct 25, 2015 14:50:05
            2             1 16727.6     Sun Oct 25, 2015 14:55:27
            3       48.2272 20434.3     Sun Oct 25, 2015 15:06:00
            4             1 20434.3     Sun Oct 25, 2015 15:06:15

Load Factor: 0.125

Iteration     Residual norm    contact Area
------------- ------------- ---------------
            1    0.00105901 33570.6     Sun Oct 25, 2015 16:58:26
            2             1 10514.1     Sun Oct 25, 2015 17:03:16
            3       1.87402 16070.9     Sun Oct 25, 2015 17:14:09

** Warning:
Excessive motion detected at contact regions.
Cutting load step size.

Load Factor: 0.0625

Iteration     Residual norm    contact Area
------------- ------------- ---------------
            1     0.0048524 10264.1     Sun Oct 25, 2015 17:28:02
            2             1 10148.1     Sun Oct 25, 2015 17:37:56
            3     0.0289352 8962.77     Sun Oct 25, 2015 17:47:13
            4             1 7921.68     Sun Oct 25, 2015 17:53:55
            5             1 7921.68     Sun Oct 25, 2015 17:54:25
***Looser residual tolerance accepted because area and force
   converged for all contacts

Load Factor: 0.125

Load Factor: 0.09375

Load Factor: 0.078125

Load Factor: 0.0703125

Load Factor: 0.0664063

Load Factor: 0.0644531

Load Factor: 0.0634766
*** A fatal error has occurred. ***
The nonlinear iteration did not converge for the
time value: 6.34766e-02

   o The model may have a buckling mode with a load factor
     smaller than this value. You may determine the smallest
     (linear) buckling load factor by running a buckling
     analysis.

unickque · ‎Oct 28, 2015

Okay I didn't realise you were using a load function.

Have you tried to play in the Static Analysis Definition in the Output tab, using output steps?

You can create user-defined step sizes. That works okay for me, and it probably does away with the need for the load function definition.

(Of course it would still be interesting to see if you have run into a bug, but at least you have a workaround).

346gnu · ‎Oct 29, 2015

Thanks Patrick and well reminded.

I have used the output tab in the past but usually use the load function. I have never really understood why we still have this in the output tab since load steps came along; their capability overlaps. I know full results can be selectively switched off using the output tab method and that when using functions each load can have a different function. Using load functions always calculates full results at each time step.

I'll experiment with the output tab.