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ilyachaban16-Pearl
16-Pearl
November 28, 2023
Question

CREO Time dependence table function completely destroys simulation

  • November 28, 2023
  • 1 reply
  • 1787 views

Hello, today I've been trying to start contact simulation of some sort of an assembly. (sorry can't do any screenshots or give a model)

I've started slowly and made my way as smooth as possible to make sure results are valid. 

1. geometry was prepeared acording to drawing documentation

2. adding simulation features

3. doing small sub assemblies to check if everything is connected

4. finally adding time dependent force to act on assymbly 

 

and boom nothing is working. Spending 8more hours to find the error. Nothing has been found everythin has been checked. 

 

and than after 12 hours of search and tests i'm turning  back Time dependence from my table defined function back to ramp(predefined function) and somehow it starts to work without any problem. 

 

Has anyone of you met this problem??? What should i do next. It is 5 full workdays to completely rebuild model from scratch. I don't want to(

1 reply

S
SweetPeasHub17-Peridot
17-Peridot
November 28, 2023
  1.  Is the max amplitude the same with ramp default (0 to 1) and your table? (Does your table go above amplitude 1?)
  2. What non-linearities are you using?(large displacement, contacts, material?)
  3. How have you defined output steps? Automatic?
  4. What do the simulation diagnostics say?
  5. Why do you need a time dependent load other than ramp? Is it for stagger of loads or for more steps to help unloading?
  6. Compare the first load step magnitude from the ramped to the custom table.
  7. Have you tried a custom table that matches the ramp with just two rows, 1,0 and 1,1?

When I use staggered loads it is often because I am applying a spring load before the primary load. For example a friction clutch. In this case the spring load cannot be applied too abruptly, or it needs many more output steps during application of the initial spring load.

For example: 

Spring (ramp from time 0 to 0.1 and hold)

0,0  0,0

0.1,  1.0

1.0, 1.0

 

testload (ramp from time 0.2 to 1)

0.0 0.0

0.2 0.0

1.0 1.0

 

User Defined Output steps (finer steps for the spring load)

0.0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.20

0.30

0.4

0.5

0.6

0.7

0.8

0.9

1.0

 

Also, are you getting residual norms in the checkpoints output?

Iteration     Residual norm
------------- -------------
           1             1 Tue Nov 28, 2023 13:40:43
           2   1.84514e-08 Tue Nov 28, 2023 13:40:44
           3   1.58651e-15 Tue Nov 28, 2023 13:40:44

 

 

I
ilyachaban16-PearlAuthor
16-Pearl
November 29, 2023

Hello, 
1. amplitude is the same 
     ramp that I'm using is 0, 0; 1, 0.1; 2, 1; 3, 0.1

2. contact and elastoplastic material

3. steps are automatic and are defined by creo from my ramp 0 1 2 3 

4. 

** Warning: 
 Excessive motion detected at contact regions.
 Cutting load step size. 
*** A fatal error has occurred. ***
The nonlinear iteration did not converge for the
time value: 0.00000e+00

 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.

 o The deformations may be large enough that you must
 further refine the mesh. To locate potential problem
 areas, it may help to run an analysis with reduced
 loads and examine the deformed shape of the model.

 o The model may have a static instability.

 o It is possible that the load is too large for the model's 
 material or the model is insufficiently constrained. Check 
 the constraints and material properties, or reduce the maximum load.

5. this function is defined in standards in my case i only need to apply it correctly

6.  1st one converged(ramp), with custom table it didn't converged and finished with fatal error

7. yes, it didn't work.

 

What you are saying at the end is true and my table is spring case. 

 

I was even trying to delete 0 from my table so it is defined by creo itseld. Didn't work(

 

 

S
SweetPeasHub17-Peridot
17-Peridot
November 29, 2023

Ok thanks,

“Cutting Load step size” = user defined steps instead of automatic (I suggest 41 steps.)

Also, try turning on contact friction if it is currently frictionlesss, it can help when there is not full and proper constraints.

If you have parts that are free and only held by contact boundary conditions, it might help to add some low stiffness springs to keep it in position during the zero load case.

You also might want to mess around with the press fit / interpenetration in the analysis definition.

There are also way to relax the contacts with allowing more interpenetration (15% instead of default 5%) as well as configuration options that loosen the contact convergence tolerance.

This is no guarantee, contact with elastoplastic on assemblies can be difficult.

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