Assembly M d li Modeling eLearning

Peter BarrettNovember 2012

© 2012 CAE Associates Inc. and ANSYS Inc. All rights reserved.

Assembly Modeling Webinar

Do you effectively manage how your assembly is tied together? Do you effectively manage how your assembly is tied together?

— Do you take advantage of bonded, no separation and/or frictional contact?

This webinar will provide examples on:

— Creating and managing your contact groups

— Understanding your unconverged solution

— Prevent rigid body motion

Ch ki th f l— Checking the accuracy of your analyses

— Interpreting your contact elements results

2

Manage Your Contact Groups

Rename Based on Definition

Adjust Auto Detection

Merge Selected Contact Regions Merge Selected Contact Regions

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Manage Your Contact Groups

Insert Contact Tool

Generate Initial Contact Results Before Solving

Review Initial Information

4

Utilize the Multiple Body Views for Selection / Checking

Manage Your Contact Groups

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Understanding Your Unconverged Solution

Force balance not obtained Rigid body motion Material Instabilities Element formulation error Element formulation error Combination of items 1-4 above

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Correct the Force Unbalance

Reduce Normal Stiffness Factor Reduce Normal Stiffness Factor

Increase the number of Substeps Increase the number of Substeps— General Rule – more nonlinearities – use more substeps

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Rigid Body Motion Error Messages DOF limit exceeded. Negative main diagonal. Small/Negative Pivot error. MAX DOF INC = “A very large number”

*** WARNING *** CP = 11.703 TIME= 16:15:15Smallest negative equation solver pivot term encountered at UX DOF of

node 98. Check for an insufficiently constrained model.

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Find the Rigid Body Motion

Plot the unconverged or last converged displacement solution and verify Plot the unconverged or last converged displacement solution and verify displacement scaling

— The example below is a converged solution where the rigid body motion is only restrained by weak springsrestrained by weak springs

— Note the unrealistic 10e-6 displacement scaling

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Correct the Rigid Body Motion

Isolate the error by creating a smaller simpler model – KISS!y g p— Make a 2d Sector model— Delete componets or fix DOF until you get an answer

Add supports and/or use displacement controlled solution Add supports and/or use displacement controlled solution— Adding a rigid region and pushing it with displacements will usually converge

better than a force loading. Use bonded contact for debuggingUse bonded contact for debugging

— If interfaces are all in compression, one might be able to leave as bonded— Modify to standard contact one pair at a time

Adjust the parts to all start in contact Adjust the parts to all start in contact— Can use adjust to touch ANSYS option, but be careful since the geometry will

be changed Increase pinball region Increase pinball region

— This is not recommended for parts with large gaps, but is very effective for interference fits

Add friction

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Add friction

Correct the Rigid Body Motion

Or Just Use Contact Stabilization!

Stab. Fact. 0 Fact = 2 Fact = .1 Fact=.01

Fact = 2Fact = .1

Fact 01

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Fact=.01

Correct the Rigid Body Motion

Or Just Use Contact Stabilization!

12

Quantify the Accuracy of Your Analyses

Check Penetration

Check Reactions

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Quantify the Accuracy of Your Analyses Contact Stiffness =1 Contact Stiffness = 10

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Interpret Results on Contact Elements

Display as Un-averaged Resultsp y g

Use Asymmetric contact

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Improve Performance in Subsequent Runs

The Force Convergence graph clearly indicates that starting with more The Force Convergence graph clearly indicates that starting with more substeps would eliminate the 27 iterations performed before the first bisection. Reducing the starting number of substeps might eliminate this bisectionbisection

Force Residual vs. Iterations

Time vs. Cumulative Iteration

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