Error reading displacements

[Anonymous]

What does the error message "Error reading displacements" mean? It occurs every now and then, with no hint as to what might be wrong. Usually it shows after the very first iteration, and the analysis aborts.

Björn

[S.LI]

Hi, Björn,

Are you using AMG solvers when this error comes up?

I think this error implies that no displacement results has been obtained after one iteration, so it failed for some code trying to read these displacement results.

[Anonymous]

Yes, I am.

How can I solve it?

[S.LI]

I'm not very sure here since I have no idea about your model.

But I guess the first thing is you should make sure your model is all right. For examples,  for static analysis the model should be tied down.

Another thing is to switch the solver to BCS, and to see if more information comes out.

[Anonymous]

The model is fine, as far as I can see. It's tied down, and I have run it before with isotropic material models. The only thing I switched is the material model to a Mooney-Rivlin model. If I try the BCS, I get an error message saying that zero pivot elements were encountered. That's the reason I switched to AMG in the first place.

[S.LI]

According to your description, material properties could be one of the reasons.

Do you get material properties from Algor material lib or your source?

[Anonymous]

I haven't got any material properties for the particular application available, so I used what I found online. I guess the problem might be that I only could find simple tension test data, though. I had to make the data up for the equibiaxial test (this is just a trial simulation, after all).

I've noticed that it's possible to run a simulation with only simple tension test data, also. What would be the consequences of this, apart from getting erroneous results?

[S.LI]

Curve fit, I bet that's what you are using here, is a way to obtain material properties, but it could not always guarantee material properties are reliable, especially for cases with few testing data.

What are your material data from these fitting, such as first const., second const., and Bulk modulus? 

[Anonymous]

In the case where I guessed my equibiaxial data

Low-Density PolyEthylene

C10: 0.783

C01: 0.3373

C20: 0.024

C11: -0.025

C02: 0.001928

K1: 1121

Polyamide:

C10: 7.89

C01: 3.21

C20: 0.23

C11: -0.20

C02: 0.012

K1: 11094

As compared to using only simple uniaxial tensile stress/strain-data:

LDPE

C10: -51.5

C01: 69.4

C20: 0.1772

C11: -1.63

C02: 17.5

K1: 7834

PA:

C10: -700

C01: 860

C20: 19.8

C11: -114

C02: 372

K1: 159926

So I can see there's a lot of difference there, but I don't know enough about polymers to judge which is reasonable and which is not. Can you help me here? Also, I noticed that the model has a lot harder to converge if I use both uniaxial and equibaxial data for some reason.

Thanks,

Björn

[S.LI]

I'm not an expert on material property testing.

My personal suggestion is to start it with the simplest cast.

For examples, "order of model" starts with "2-constants", instead of high-order standard.

This will make both testing and simulation easily.

[Anonymous]

Alright, I will keep it in mind. Do you think using a simpler material model might also help the model to converge more easily?

[S.LI]

Yes, I do think so.

There is a very good example, isotropic hardening vs. curved isotropic hardening.

Generally, the former is much easier.

[Anonymous]

I just exprienced the problem again. The very strange thing is that the iteration started before, but now for some reason, with the very same model where I haven't changed anything, now I get this error. Do you have any other recommendations except switching solver? It's a very large model, II'm not sure how well it will run with the BCS solver.

Thanks

Björn

[Anonymous]

To bump this topic a little bit, this error is occuring very frequently, and it is really a show-stopper. It seems to especially occur when I have created an archive file, and then tries to run the analysis that worked previously, but now I get this error again instead.

Is there no help on this? It happens all the time.

Here's the log file, if it's any help

 
 Autodesk Algor Accupak/VE Mechanical Event Simulation
 Version 2011.00.00.0111-W64/X64 12-MAR-2010
 Copyright (c) 2010, Autodesk, Inc. All rights reserved.
 
 ** Warning: when <MES with Nonlinear Material Models> is used
             for the models having (general) contact element,
             general suface contact, or impact planes,
            <Large deformation> is recommended for all parts.
 
 ** Total available memory = 5653300 (KB).
 ** Options executed are:
    NOMIN   - NO optimization for matrix storage
    RUN     - Execute processor
    STRAIN  - Output strain data for Superview
    DUPLEX  - Duplex communication with tWAIT=5 seconds
    PRRO    - Output reaction force data, n=2
    PRCD    - Output contact diagnostics data


    NUMNP    DOF NEGL NEGNL MODEX      NSTE        DT    TSTART IPRI IPSF
   141218 000000   48   103     1        22 0.500E-01 0.000E+00    1    3

 ** Perform analysis
 ** Open output files ...
 ** Open temporary files ...
 ** Reading input file ...

                   PROGRAM VERSION: 201100000111
           alg-win-x64.dll VERSION: 201100000111
     algconfig-win-x64.dll VERSION: 201100000111
      agsdb_ar-win-x64.dll VERSION: 201100000111
              amgsolve.exe VERSION:   0360000000
 
    Model=C:\Users\Public\Documents\Projekt\Teroc AB\1089\CAD\Square and straight bolt holes, split concrete with plates, split surfaces, square top pipe - Fungerar\Pipe plane split\kopia\Tower_assy.ds_data\11\ds

 **** Model Unit System Settings:
      --------------------------------------------
       Unit System              : Custom
       Force                    : N
       Length                   : mm
       Time                     : s
       Temperature (Absolute)   : deg C (K)
       Thermal Energy           : J
       Voltage                  : V
       Current                  : A
       Electrical Resistance    : ohm
       Mass                     : N*s^2/mm
      --------------------------------------------

    No. of nodes             = 141218     No. of equations = 423782
    Maximum no. of iteration =     30     No. of steps     =     22
    Convergence tolerance    =  1.0000E-02
 ** Input elements...
 ** 3-D continuum element calculation, number of element =      2678
 ** 3-D continuum element calculation, number of element =      5568
 ** 3-D continuum element calculation, number of element =      9408
 ** 3-D continuum element calculation, number of element =     10258
 ** 3-D continuum element calculation, number of element =     10031
 ** 3-D continuum element calculation, number of element =      2706
 ** 3-D continuum element calculation, number of element =      2489
 ** 3-D continuum element calculation, number of element =      6855
 ** 3-D continuum element calculation, number of element =      2644
 ** 3-D continuum element calculation, number of element =      2874
 ** 3-D continuum element calculation, number of element =      4191
 ** 3-D continuum element calculation, number of element =     10687
 ** 3-D continuum element calculation, number of element =     10753
 ** 3-D continuum element calculation, number of element =     10649
 ** 3-D continuum element calculation, number of element =      3532
 ** 3-D continuum element calculation, number of element =      2977
 ** 3-D continuum element calculation, number of element =      2544
 ** 3-D continuum element calculation, number of element =      2610
 ** 3-D continuum element calculation, number of element =      5271
 ** 3-D continuum element calculation, number of element =     12447
 ** 3-D continuum element calculation, number of element =     11854
 ** 3-D continuum element calculation, number of element =     10699
 ** 3-D continuum element calculation, number of element =      3811
 ** 3-D continuum element calculation, number of element =      3598
 ** 3-D continuum element calculation, number of element =      2961
 ** 3-D continuum element calculation, number of element =      2123
 ** 3-D continuum element calculation, number of element =      5496
 ** 3-D continuum element calculation, number of element =     13884
 ** 3-D continuum element calculation, number of element =     12127
 ** 3-D continuum element calculation, number of element =     11640
 ** 3-D continuum element calculation, number of element =      3876
 ** 3-D continuum element calculation, number of element =      3675
 ** 3-D continuum element calculation, number of element =      2643
 ** 3-D continuum element calculation, number of element =      3119
 ** 3-D continuum element calculation, number of element =      4783
 ** 3-D continuum element calculation, number of element =     11950
 ** 3-D continuum element calculation, number of element =     10580
 ** 3-D continuum element calculation, number of element =     12401
 ** 3-D continuum element calculation, number of element =      3980
 ** 3-D continuum element calculation, number of element =      3610
 ** 3-D continuum element calculation, number of element =      2777
 ** 3-D continuum element calculation, number of element =      2995
 ** 3-D continuum element calculation, number of element =      4492
 ** 3-D continuum element calculation, number of element =     10224
 ** 3-D continuum element calculation, number of element =      9568
 ** 3-D continuum element calculation, number of element =     13211
 ** 3-D continuum element calculation, number of element =      3735
 ** 3-D continuum element calculation, number of element =      3607
 ** 3-D continuum element calculation, number of element =      2596
 ** 3-D continuum element calculation, number of element =      3304
 ** 3-D continuum element calculation, number of element =      3737
 ** 3-D continuum element calculation, number of element =      4036
 ** 3-D continuum element calculation, number of element =      3957
 ** 3-D continuum element calculation, number of element =      3532
 ** 3-D beam element calculation, number of element =       180
 ** 3-D beam element calculation, number of element =         9
 ** 3-D beam element calculation, number of element =       180
 ** 3-D beam element calculation, number of element =         9
 ** 3-D beam element calculation, number of element =       180
 ** 3-D beam element calculation, number of element =         9
 ** 3-D beam element calculation, number of element =       180
 ** 3-D beam element calculation, number of element =         9
 ** 3-D beam element calculation, number of element =       180
 ** 3-D beam element calculation, number of element =         9
 ** 3-D beam element calculation, number of element =        25
 ** 3-D beam element calculation, number of element =        40
 ** 3-D beam element calculation, number of element =        40
 ** 3-D beam element calculation, number of element =        25
 ** 3-D beam element calculation, number of element =        60
 ** 3-D beam element calculation, number of element =         2
 ** 3-D beam element calculation, number of element =         2
 ** 3-D beam element calculation, number of element =       510
 ** 3-D membrane element calculation, number of element =      3691
 ** 3-D membrane element calculation, number of element =      3532
 ** 3-D membrane element calculation, number of element =      3259
 ** 3-D membrane element calculation, number of element =      3475
 ** 3-D membrane element calculation, number of element =      3651
 ** 3-D membrane element calculation, number of element =      3842
 ** 3-D beam element calculation, number of element =         1
 ** 3-D surface contact element calculation, number of element =       228
 ** 3-D surface contact element calculation, number of element =       710
 ** Warning: S-S contact is NOT necessary for contact pair, 3 !
             P-S contact is recommended.
    1st and 2nd parts in contact pair, 3, should be switched.
 ** 3-D surface contact element calculation, number of element =       115
 ** Warning: S-S contact is NOT necessary for contact pair, 4 !
             P-S contact is recommended.
    1st and 2nd parts in contact pair, 4, should be switched.
 ** 3-D surface contact element calculation, number of element =        91
 ** 3-D surface contact element calculation, number of element =       614
 ** 3-D surface contact element calculation, number of element =       204
 ** Warning: S-S contact is NOT necessary for contact pair, 7 !
             P-S contact is recommended.
    1st and 2nd parts in contact pair, 7, should be switched.
 ** 3-D surface contact element calculation, number of element =       100
 ** Warning: S-S contact is NOT necessary for contact pair, 8 !
             P-S contact is recommended.
    1st and 2nd parts in contact pair, 8, should be switched.
 ** 3-D surface contact element calculation, number of element =        82
 ** 3-D surface contact element calculation, number of element =       228
 ** Warning: S-S contact is NOT necessary for contact pair, 10 !
             P-S contact is recommended.
    1st and 2nd parts in contact pair, 10, should be switched.
 ** 3-D surface contact element calculation, number of element =       116
 ** 3-D surface contact element calculation, number of element =       691
 ** Warning: S-S contact is NOT necessary for contact pair, 12 !
             P-S contact is recommended.
    1st and 2nd parts in contact pair, 12, should be switched.
 ** 3-D surface contact element calculation, number of element =        91
 ** Warning: S-S contact is NOT necessary for contact pair, 13 !
             P-S contact is recommended.
 ** 3-D surface contact element calculation, number of element =      1140
 ** 3-D surface contact element calculation, number of element =       240
 ** Warning: S-S contact is NOT necessary for contact pair, 15 !
             P-S contact is recommended.
 ** 3-D surface contact element calculation, number of element =      1033
 ** 3-D surface contact element calculation, number of element =       228
 ** 3-D surface contact element calculation, number of element =       240
 ** Warning: S-S contact is NOT necessary for contact pair, 18 !
             P-S contact is recommended.
 ** 3-D surface contact element calculation, number of element =       917
 ** 3-D surface contact element calculation, number of element =       234
 ** Warning: S-S contact is NOT necessary for contact pair, 20 !
             P-S contact is recommended.
 ** 3-D surface contact element calculation, number of element =      1054
 ** Warning: S-S contact is NOT necessary for contact pair, 21 !
             P-S contact is recommended.
 ** 3-D surface contact element calculation, number of element =       915
 ** 3-D surface contact element calculation, number of element =       228
 ** Warning: S-S contact is NOT necessary for contact pair, 23 !
             P-S contact is recommended.
 ** 3-D surface contact element calculation, number of element =      1198
 ** 3-D surface contact element calculation, number of element =       234
 ** Warning: S-S contact is NOT necessary for contact pair, 25 !
             P-S contact is recommended.
 ** 3-D surface contact element calculation, number of element =       919
 ** 3-D surface contact element calculation, number of element =       228
 ** 3-D surface contact element calculation, number of element =       766
 ** 3-D surface contact element calculation, number of element =       216
 ** 3-D surface contact element calculation, number of element =       228
 ** Warning: S-S contact is NOT necessary for contact pair, 30 !
             P-S contact is recommended.
 ** 3-D surface contact element calculation, number of element =      1098
 ** Warning: S-S contact is NOT necessary for contact pair, 31 !
             P-S contact is recommended.
 ** 3-D surface contact element calculation, number of element =      1019
 ** 3-D surface contact element calculation, number of element =       222
 ** Warning: S-S contact is NOT necessary for contact pair, 33 !
             P-S contact is recommended.
 ** 3-D surface contact element calculation, number of element =      1507
 ** 3-D surface contact element calculation, number of element =       216
 ** 3-D surface contact element calculation, number of element =       899
 ** 3-D surface contact element calculation, number of element =       222
 ** Warning: S-S contact is NOT necessary for contact pair, 37 !
             P-S contact is recommended.
 ** 3-D surface contact element calculation, number of element =      1016
 ** 3-D surface contact element calculation, number of element =       216
 ** 3-D surface contact element calculation, number of element =       813
 ** 3-D surface contact element calculation, number of element =       204
 ** Warning: S-S contact is NOT necessary for contact pair, 41 !
             P-S contact is recommended.
 ** 3-D surface contact element calculation, number of element =      1069
 ** 3-D surface contact element calculation, number of element =       216
 ** Warning: S-S contact is NOT necessary for contact pair, 43 !
             P-S contact is recommended.
 ** 3-D surface contact element calculation, number of element =      1001
 ** 3-D surface contact element calculation, number of element =       210
 ** 3-D surface contact element calculation, number of element =       885
 ** 3-D surface contact element calculation, number of element =       204
 ** Warning: S-S contact is NOT necessary for contact pair, 47 !
             P-S contact is recommended.
 ** 3-D surface contact element calculation, number of element =      1106
 ** 3-D surface contact element calculation, number of element =       210
 ** 3-D surface contact element calculation, number of element =       204
 ** 3-D surface contact element calculation, number of element =      1015
 ** 3-D surface contact element calculation, number of element =       904
 ** 3-D surface contact element calculation, number of element =       204
 ** 3-D surface contact element calculation, number of element =      1004
 ** 3-D surface contact element calculation, number of element =       204
 ** Warning: S-S contact is NOT necessary for contact pair, 55 !
             P-S contact is recommended.
 ** 3-D surface contact element calculation, number of element =      1033
 ** 3-D surface contact element calculation, number of element =       204
 ** 3-D surface contact element calculation, number of element =       861
 ** 3-D surface contact element calculation, number of element =       198
 ** Warning: S-S contact is NOT necessary for contact pair, 59 !
             P-S contact is recommended.
 ** 3-D surface contact element calculation, number of element =      1017
 ** 3-D surface contact element calculation, number of element =       204
 ** 3-D surface contact element calculation, number of element =       198
 ** 3-D surface contact element calculation, number of element =      1122
 ** 3-D surface contact element calculation, number of element =      1190
 ** 3-D surface contact element calculation, number of element =       192
 ** 3-D surface contact element calculation, number of element =      1204
 ** 3-D surface contact element calculation, number of element =       198
 ** 3-D surface contact element calculation, number of element =      1399
 ** 3-D surface contact element calculation, number of element =       204
 ** 3-D surface contact element calculation, number of element =      1306
 ** 3-D surface contact element calculation, number of element =       192
 ** 3-D surface contact element calculation, number of element =      1348
 ** 3-D surface contact element calculation, number of element =       204
 ** Maximum hits per equation (EQN:279456) = 2559
    Nonzero entries estimated in upper triangle matrix = 89680649
 ** Parallel AMG Iterative Solver Solution
 ** Warning: K-node lies within 1 degree angle of the beam axis
             Element =    33      Group =     73
             **Further warnings are suppressed

Time        Percent     DT       L Iter. Residual
   0.000000   0.00     0.050000  1   0   0.0000E+00

 ** ERROR READING DISPLACEMENTS
 ** Error (1)
 ** Job started           : 2011-03-11  13:43:39
 ** Job finished          : 2011-03-11  13:49:13
 ** Total elapsed time    : 5:33 (minutes:seconds)
  !! Program aborted !

[S.LI]

Basically, this is NOT a bug itself. This message means that program can NOT find displacement when using it.

The reason is from AMG solver. AMG solver is a kind of iteration equations solver, which always try to solve the system even there might be some error in the equation system, such as zero pivoting value.

This message implies that something is so wrong that AMG could not solve it and generate the displacement solution.

Several thing you can try, I can suggestion, :

1.) change it to BCS (direct solver)

2.)   If BCS fails with serious errors, we can know there must be something wrong, either code or model settings.

BTW:

did you figure out what the material properties are?

Thanks. 

[Anonymous]

Yes, I know it must be the first iteration that crashes the solver. If I try the BCS solver, I get an error message saying to check for abrupt stiffness changes and make sure the model is tied enough.

However, it seems this is a problem that occurs when I have one model which I wish to make duplicates of. If I create an archive file, unpack it at a different location, the design scenario that ran fine before, suddenly gives me this error message, so there's nothing wrong with the model itself. Could it be something that interferes with creating the new ds-folder or something?

This is unrelated to the previous problem with the material properties, I just thought it was unnecessary to create a new topic about it. However, I didn't find any good data, but we found out that we could just use elastic properties and still get a good enough approximation. Thanks. 🙂

[zhuangs]

There is a warning in the log file:

 "** Warning: when <MES with Nonlinear Material Models> is used
             for the models having (general) contact element,
             general suface contact, or impact planes,
            <Large deformation> is recommended for all parts"

I would recommend that large deformation is used for all the parts for contact models.

As for the error message saying to check for abrupt stiffness changes, I would recommend

(1) Check the boundary condition you set,

(2) Check the areae of beam part: whether it is too large if compared with the mesh size of solid part the beam connect,

(3) Use a small value (such as 10000) of "user-defined" contact stiffness for all contact pairs.

(4) Check If "Bonded" is default in FEA Editor.  If not necessary to use "Bonded", try to use "Free/no contact".

-Shoubing

[Anonymous]

I've done all that.

Is there a way to identify which part number is not using a large displacement formulation? I have over 100 parts.

But still, this occurs often when I create an archive or save the model as a new model, mostly. So there's nothing wrong with the model itself.

[S.LI]

I notice that your model path is 202-character long.

I can not say this is the reason, but it might be.

Is this really necessary?

Could you try a simple shorter one, such as c:\temp?

Thanks.

[Anonymous]

Hm, I will try to see after the weekend and see what happens.