optistuct - static analyis - large deformations problem

Sid_22073
Sid_22073 Altair Community Member
edited April 2023 in Community Q&A

Hello,

I am running a static analysis with the below subcases : 

 

$$------------------------------------------------------------------------------$
$$                      Case Control Cards                                      $
$$------------------------------------------------------------------------------$


$
SUBCASE       10
  LABEL loadstep10
ANALYSIS STATICS
  SPC =       10
  PRETENSION =       11
$
$HMNAME LOADSTEP              11"loadstep11"       1
$
SUBCASE       11
  LABEL loadstep11
ANALYSIS STATICS
  SPC =       10
  LOAD =      127
  PRETENSION =       11

$
BEGIN BULK
$$
$$  


$$  PTADD cards
$$
$HMNAME LOADCOL               11"All_pretensions"
$HWCOLOR LOADCOL              11      35
PTADD   11      1.0     1.0     9       1.0     8       1.0     7       
+       1.0     6       1.0     5       1.0     1       1.0     3       
+       1.0     4       1.0     2       
$$
$$
$$  LOADADD cards
$$
$HMNAME LOADCOL              127"All_pressures"
$HWCOLOR LOADCOL             127      17
$$ This is pressure loads
LOADADD      127     1.0     1.0      89     1.0     100     1.0      93
+            1.0     108     1.0     104     1.0     126     1.0     116
+            1.0     112

 

The solution solved without errors, but I get strange animation for subcase 11...

I got the below warning message in the outfile....

*** WARNING # 312
 In static load case 11 
 the compliance is negative or large 1.05465e+16.
 Optimization/buckling analysis cannot be performed.
 due to possible rigid body mode.

Is there any problem in my model.

Please let me know how to slove this,

 

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Best Answer

  • Adriano A. Koga
    Adriano A. Koga
    Altair Employee
    edited April 2023 Answer ✓

    this is a generic message, but it essentially is telling you that there is a huge displacement in your analysis, and thus a huge compliance.

    There is probably some issue with your boundary conditions or some model connection not properly realized.

    I see that you're running pretension loadcase. Is there contacs in your model? If yes, are you sure they're properly connecting the model?

     

    You can open your .h3d file in HyperView, and plot the results with a 'deformed' scale factor very small, so that you are able to see how your part is moving, and if there is some specific part flying away.

Answers

  • Adriano A. Koga
    Adriano A. Koga
    Altair Employee
    edited April 2023 Answer ✓

    this is a generic message, but it essentially is telling you that there is a huge displacement in your analysis, and thus a huge compliance.

    There is probably some issue with your boundary conditions or some model connection not properly realized.

    I see that you're running pretension loadcase. Is there contacs in your model? If yes, are you sure they're properly connecting the model?

     

    You can open your .h3d file in HyperView, and plot the results with a 'deformed' scale factor very small, so that you are able to see how your part is moving, and if there is some specific part flying away.

  • Sid_22073
    Sid_22073 Altair Community Member
    edited April 2023

    Hi,

    Thanks for the answer, you are right I applied the pressure in wrong units, because I created the bearing pressure in simlab and exported without changing the units to  (mm t s ).

    I copied these pressure directly from the simlab output files and copied in my optistruct run.

    So this cause the huge pressure.

    Now I corrected the model and let me see if this works correctly.

     

    Anyway thanks that you told me to check the deformation in very small scale... I did not think about this.

     

    Kind regards,

    SId

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