mechanical-nonlin 13.0 ws-08a pipe
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Customer Training Material
or s op
Nonlinear Stabilization
Structural Nonlinearities
WS8A-1ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
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ANSYS Mechanical Structural Nonlinearities
Customer Training MaterialWorkshop 8A: Nonlinear Stabilization
Goal
Use Nonlinear Stabilization tools together with restart technology
to predict maximum plastic strain.
Model Description
3D Pipe
BISO plasticity
Meshed with 3D Shell elements
Fixed support at one end
7000 lbf-in bending moment
applied to opposite end
WS8A-2ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material Workshop 8A: Nonlinear Stabilization
Steps to Follow:
Restore Archive browse for file W8a_pipe.wbpz
Save as
File name: W8a_pipe
*
WS8A-3ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material Workshop 8A: Nonlinear Stabilization
The project Schematic should look like the
picture to the right.
From this Schematic, you can see that the
already been defined (green check marks). It remains to set up and run the FE model in
Mechanical
Open the Engineering Data Cell (highlight and
double click OR Right Mouse Button (RMB)>Edit).
To see relevant dialog boxes, it might be
necessary to go to Utility Menu > View..
Click on Properties and Outline
Verify that the units are in US Eng units (lb, in,)system. If not, fix this by clicking on
Utility Menu > Units > US Engineering(lb, in,)
WS8A-4ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material Workshop 8A: Nonlinear Stabilization
Return to Project Schematic
Utility Menu > Return to Project
Double click on the Model Cell to open the FE Model (Mechanical
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December 2010
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material Workshop 8A: Nonlinear Stabilization
Once inside the Mechanical application, verify the working unit system
Unit > US English (lb,in,,,)
The pipe model is already set up with a fixed boundary condition and a
.
Highlight the Fixed Support and Force Load to confirm that the model isproperly supported and loaded.
WS8A-6ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material Workshop 8A: Nonlinear Stabilization
Note the Analysis Settings Specifications:
Auto Time Stepping = ON
Initial Substeps = 10 (min=2,max=100)
,
Weak Springs = OFF Stabilization = OFF
Run the Solution
WS8A-7ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material Workshop 8A: Nonlinear Stabilization
After a few bisections, the model fails to converge at about 93% of the
total load
WS8A-8ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material Workshop 8A: Nonlinear Stabilization
Highlight Analysis Settings and set up for
a manual restart and utilizing Stabilization
Restart specifications:
Restart Point = Load Step 1, Substep 6 Stabilization specifications:
Constant
Energy method
Energy Dissipation Ratio = 0.05
Activation = On Nonconvergence
Execute the restart
WS8A-9ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material Workshop 8A: Nonlinear Stabilization
With Stabilization activated upon nonconvergence after substep 6, the
solution now converges successfully in a total of ten substeps
Compare this convergence pattern with that illustrated on slide WS8A-8 before
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material Workshop 8A: Nonlinear Stabilization
Postprocess results
- Consider first the Strain Energy as compared to the Stabilization Energy to
understand the amount of error that Stabilization is introducing in the model
. - . -
- Given that the stabilization energy is less then 1% of the structural strain energy,
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December 2010
we can conclude that its influence on overall result error is neglegibile.
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material Workshop 8A: Nonlinear Stabilization
Postprocess results (contd)
- Notice the summation of the forces at the fixed
boundary all balance to near zero as expected
- Notice the summation of moments at the fixedboundary (6457.5 lbf-in) falls short of the total
applied at the other end (7000 lbf-in)
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December 2010
- w u u
becomes unstable
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material Workshop 8A: Nonlinear Stabilization
Postprocess results (contd)
- Plot plastic strain, eqv stress, total deformation, etc
- Notice the structure is beginning to uniformly yield across the top and
WS8A-13ANSYS, Inc. Proprietary
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bottom surfaces and it appears unable to resist any further loading without
becoming unstable. Hence, the reason for the original nonconvergence.
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material Workshop 8A: Nonlinear Stabilization
It is always important to be mindful of the error that can be introduced
when using the Stabilization tools by checking the stabilization energy
against the strain energy and also verifying the balance of forces.
WS8A-15ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010