Mechanical Nonlin 13.0 WS 09A Diagnostics
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Transcript of Mechanical Nonlin 13.0 WS 09A Diagnostics
8/12/2019 Mechanical Nonlin 13.0 WS 09A Diagnostics
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material Workshop 9A: Diagnostics
• Goal
Diagnose convergence trouble with surface body contact model
• Model Description
– 3D Spring plate –Surface Body
– 3D Rigid Target Body
– Linear steel material
– Meshed with 3D SHELL elements
– Spring Fixed support at one end, A
– Rigid Body displaced into Spring 19mm
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© 2010 ANSYS, Inc. All rights reserved.Release 13.0
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material …Workshop 9A: Diagnostics
Steps to Follow:
• Restore Archive… browse for file “W9a-diagnostics.wbpz”
• Save as
– File name: “W9a-diagnostics”
– *
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
The project Schematic should look like the
picture to the right.
– From this Schematic, you can see that the
Engineering (material) Data and Geometry have
already been defined (green check marks).
– It remains to set up and run the FE model in
ec an ca
– Highlight the Engineering Data Cell and open by
(RMB)=>Edit to verify the linear material
properties.
– Verif that the units are in Metric Tonne mm ..
system. If not, fix this by clicking on…
• Utility Menu=>Units=>Metric(Tonne, mm,..)
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
• Return to Project Schematic
– Utility Menu > Return to Project
• ou e c c on e o e e o open e o e ec an ca
Session) (or RMB=>Edit…)
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© 2010 ANSYS, Inc. All rights reserved.Release 13.0
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
• Once inside the Mechanical application, verify the working unit system
– “Unit > Metric (mm,kg,N,s,mV,mA)”
• The spring assembly is already set up with frictionless contact pairs, a fixed
.
• Highlight the entities beneath each folder to become familiar with the modeland to confirm that it is properly supported and loaded and ready to solve.
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
• After solution run is complete, highlight the Solution Information folder
and scroll to near the bottom of the output.
– The model solves without error.
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
• Review the Total Deformation results.
– Something is wrong. The contact relationship between the two parts has
obviously failed.
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
With 25 initial substeps and Auto Time Stepping turned On, the contact should
have engaged. In an effort to determine the problem, we will evaluate what the
initial condition of the contact pairs are.
• Highlight the Connections Folder: RMB> Insert> Contact Tool
• Highlight the Contact Tool: RMB>Initial Information>Generate Initial Contact
Results. This will run a partial solve to establish initial contact parameters
(i,e. Initial status, gap, penetration, etc…).
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
• Review the Initial Contact Information.
• Note the following:
– The two active pairs both have an initial status of “Far Open”
– ot pa rs ave a p n a ra us o mm. s mm enoug
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
• By studying a profile of the undeformed geometry we can see that the
initial gap is less then 1.50mm. Hence, the Pinball Radius of 4mm should
be sufficient for this contact pair to be in an initial status of ‘near-open’.
Rigid Target
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
• g g e con ac reg on represen ng e con ac e ween e spr ng
and target.
– In order for contact to work properly, the contact element normals must be facing
the tar et element normals.
– Recall that surface bodies are meshed with shell elements that have a ‘top’ and a
‘bottom’ face. The reason this contact pair is not working is because the contact
normals are on the wrong side of the surface body with normals that face away
. .
Contact element
normal direction
Target element
normal direction
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
• From the details window of the contact region, switch the ‘contact shell face’
from Bottom to Top . The red color highlighting the contact side should
switch.
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
• Highlight the Solution Information Branch
– Set Newton-Raphson Residuals = 3
– This will save force imbalance data for the last
‘ ’ - .
especially helpful information for
troubleshooting troubling contact convergence
problems.
• Rerun the solution
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
• From the Solution Information Branch, the contact is now engaging, but
the solution fails to converge after several iterations.
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
These first two converged substeps likely represent the trivial solutions
that occur as the small gap between the two parts is being closed and no
contact has been made yet.
s rs sp e n e ew on- ap son res ua measure
of imbalance) likely occurs at the point when contact firstengages. From there on out, the solution struggles and
fails after two bisections and man iterations to find a
balance.
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
A plot of Newton-Raphson Residual (measure of force imbalance in the model)
confirms that the point where contact is engaged is the source of the highest
imbalance .
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
• Highlight both Contact Regions and change the
contact specifications in the details window.
Augmented Lagrange is
recommended for general
contact
Reducing the contact
stiffness factor will reduce
the calculated force
generated at the contact
the imbalance
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• Re-run the solution
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
The solution now converges very nicely with no bisections
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
• ev ew e o a e orma on resu s. – Although this solution is now converged, notice the excessive penetration.
This is because, by default the shell contact detection points are at themidplane of the shells.
– This can be remedied by adding a command object to the contact elementswith the following command: KEYOPT,cid,11,1 (refer to Element manualdocumentation on CONTA174 and the KEYOPT command)
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– This command will include an adjustment for the shell thickness.
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
EXTRA CREDIT !!
• Highlight each Contact Region
an nser omman s
– Inside the command object andtype the command as shown
*
* Refer to Element Reference documentation onCONTA174 along with Command Manual
documentation on ‘KEYOPT ’
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• Re-run the solution
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ANSYS Mechanical Structural Nonlinearities
Customer Training Material … Workshop 9A: Diagnostics
• Review the Total Deformation results as before.
– Shell thickness is now properly accounted for.
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