Mechanical-Nonlin 13.0 WS-08A Pipe

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Customer Training Material

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Nonlinear Stabilization

Structural Nonlinearities

WS8A-1ANSYS, Inc. Proprietary

2010 ANSYS, Inc. All rights reserved.Release 13.0

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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



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Customer Training Material Workshop 8A: Nonlinear Stabilization

Steps to Follow:

Restore Archive browse for file W8a_pipe.wbpz

Save as

File name: W8a_pipe

*



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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,)



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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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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.



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Note the Analysis Settings Specifications:

Auto Time Stepping = ON

Initial Substeps = 10 (min=2,max=100)

,

Weak Springs = OFF Stabilization = OFF

Run the Solution



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After a few bisections, the model fails to converge at about 93% of the

total load



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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



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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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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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we can conclude that its influence on overall result error is neglegibile.


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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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- w u u

becomes unstable


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Postprocess results (contd)

- Plot plastic strain, eqv stress, total deformation, etc

- Notice the structure is beginning to uniformly yield across the top and



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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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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.



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Mechanical-Nonlin 13.0 WS-08A Pipe

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