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© 2000 PTC

A new approach!

Geometry and Mesh

Troubleshooting

© 2000 PTC 2

AutoGEM 2000i2AutoGEM 2000i2

What is AutoGEM?Geometry & Mesh TroubleshootingModel inspectionDiagnosticsExamples

AssembliesExample

Fixing the ProblemSummary

What is AutoGEM?Geometry & Mesh TroubleshootingModel inspectionDiagnosticsExamples

AssembliesExample

Fixing the ProblemSummary

© 2000 PTC 3

What is AutoGEM?What is AutoGEM?

Automatic Geometric Element Modeling (AutoGEM)The algorithm that automatically creates a p-type finite element mesh mapped to your model’s geometry. They are an idealization of the the real model

Automatic Geometric Element Modeling (AutoGEM)The algorithm that automatically creates a p-type finite element mesh mapped to your model’s geometry. They are an idealization of the the real model

solidssolidssolids shellsshells beamsbeamsElement types generated in Pro/MECHANICA:Element types generated in Pro/MECHANICA:

© 2000 PTC 4

Geometry & Mesh TroubleshootingGeometry & Mesh Troubleshooting

Model Inspection...Two types of AutoGEM problems

Geometry that causes a large number of elementsRemove geometry that is irrelevant to the simulationSuppress or delete unimportant features to optimize solution efficiencyModify dimensions or use tweak > replace to remove small surfaces

Geometry that is difficult to AutoGEM successfullyRedefine featuresRemodel sectionsModify dimensions“cover up” bad geometrySeed the Mesh

Model Inspection...Two types of AutoGEM problems

Geometry that causes a large number of elementsRemove geometry that is irrelevant to the simulationSuppress or delete unimportant features to optimize solution efficiencyModify dimensions or use tweak > replace to remove small surfaces

Geometry that is difficult to AutoGEM successfullyRedefine featuresRemodel sectionsModify dimensions“cover up” bad geometrySeed the Mesh

© 2000 PTC 5


Model Inspection...Examples of small surfaces created by rounds:

Model Inspection...Examples of small surfaces created by rounds:

© 2000 PTC 6


Model Inspection...Examples of small surfaces created by unaligned surfaces:

Model Inspection...Examples of small surfaces created by unaligned surfaces:

© 2000 PTC 7


Model Inspection...

Edges with zero angle:

Small surfaces and curves or zero angles typically do not cause a meshing failure, but do result in a less efficient analysisTIP: Suppress rounds and chamfers that remove material and leave those that add material.

A narrow surface created by exterior ribs on a round: Note that the rib on the left with the exterior rounds removed will AutoGEM with many fewer elements.

© 2000 PTC 8


Model Inspection...Model Inspection...

#Info#Geometry Check...Highlights any questionable geometry

#Analysis#Model Analysis#Short Edge...Identifies small edges

View in No-Hidden-line Mode or Shaded Mode

Inspect the model for sliver sections or bad surfaces

Pro/ENGINEER tools:

Possible troubled areas

No-Hidden-line Mode

Shaded Mode

© 2000 PTC 9

Eliminating small edgesEliminating small edgesPro/E can highlight all edges less than a specified lengthSuppress features, modify dimensions or use #Tweak #Replace to eliminate small edges/surfaces.

Geometry & Mesh Troubleshooting - Example 1Geometry & Mesh Troubleshooting - Example 1

Tweak > Replace allows you to replace a surface with another. This can be useful if you aren’t able to change the problem feature because of Parent-Child relationships.

Replace this surface with DTM2

Example #1Example #1

© 2000 PTC 10


AutoGEM DiagnosticsUnderstanding AutoGEM status messages is important for diagnosis

To view status in Integrated mode #Run#Summary... (*.rpt file)#Run#Log... (*.stt file)

Monitor the status of automeshing#Run#Diagnose

NEW in 2000i, expanded in 2000i²

AutoGEM DiagnosticsUnderstanding AutoGEM status messages is important for diagnosis

To view status in Integrated mode #Run#Summary... (*.rpt file)#Run#Log... (*.stt file)

Monitor the status of automeshing#Run#Diagnose

NEW in 2000i, expanded in 2000i²

© 2000 PTC 11

AutoGEM DiagnosticsAutoGEM Diagnostics

Identifies several problems with the model.In this example the message complains about "intersecting or overlapping" volumePro/Mechanica highlights the surfaces where AutoGEM could not finish

#Run#DiagnoseView status in Integrated mode

Note: Surfaces remain highlighted while you manipulate the model


© 2000 PTC 12

Fix the model in Pro/EFix the model in Pro/EThe bad geometry is caused by a “sweep” that was not aligned properly.


This results in a small gap between the flange and the rest of the part.

© 2000 PTC 13

Fix the model in Pro/E (Option #1 - quick fix)Fix the model in Pro/E (Option #1 - quick fix)

Add a surface-to-surface round to to "cover up" the bad geometry.The model now meshes successfully.


© 2000 PTC 14

Fix the model in Pro/E (Option #2 - better fix)Fix the model in Pro/E (Option #2 - better fix)Redefine the sweep

Align the swept section with the inside edge of the model.

The sweep section is aligned with the outside edge of the model. This produces a small gap between the flange and the rest of the model



© 2000 PTC 15

Solution: Eliminate the knife edge by suppressing/deleting the feature

AutoGEM DiagnosticsMessage #1 - Knife Edge

Cause: A cut resulted in a knife edge

Solution: modify dimensions of the sweep or round

Message #2 - Overlapping geometryCause: The shell feature created invalid geometry for MECHANICASolution: modify dimensions of the shell or round

Message #3 - Slope DiscontinuityCause: The edge of this sweep overlaps an edge of a round



© 2000 PTC 16

Run a modal analysis to determine which parts are disconnected

Geometry & Mesh Troubleshooting - AssembliesGeometry & Mesh Troubleshooting - Assemblies

Modify dimensions or assembly constraints to account for gaps, overlaps or unaligned surfaces

GapsWill not typically cause auto-meshing failures.Mechanica will inform you if parts are not connected.Analysis may result in failure due to insufficient constraints.

Increases number of elements.

InterferenceCan cause meshing problems if surfaces/edges overlapIdentify by performing a global interference check.

Unaligned geometry Will not typically cause auto-meshing failures.

What about contact analysis?

Note: Suppress unnecessary parts, use simplified reps or modify dimensions

© 2000 PTC 17

Trouble-shooting assemblies

Geometry will merge if any surfaces or curves overlap within a tolerance:

less than (1/12) × (Largest Absolute Accuracy Value of All Assembly Components) [see TAN #22423]Largest absolute accuracy = relative accuracy × largest part model size.

Determine the relative accuracy (Setup / Accuracy)

Geometry & Mesh Troubleshooting - MergeGeometry & Mesh Troubleshooting - Merge


Modify dimensions or assembly constraints to permit or prevent geometry from merging.

Measure the model size of each part (Info / Model Size)

It is often desirable to let Pro/MECHANICA merge the geometry between assembled components

Use rigid connections, end/perimeter/spot welds or beams to connect geometry

© 2000 PTC 18

Trouble-shooting assembliesFor contact analysis, you may want parts to interfere.Interference is OK if no surfaces or edges overlap (i.e. occupy the same space). Otherwise Mechanica will merge the overlapping geometry, and AutoGEM will likely fail.Change the assembly constraints to align offset. Note: there isstill interference, but the surfaces no longer overlapAdd enforced displacements to “move” the part back to the correct position.We now have “...2 disjoint bodies...”, so we know we’re OK.


Introduce align offset

Overlapping geometry at symmetry surfaces Example #5Example #5

© 2000 PTC 19

When models fail to mesh, you can also...

Change the part or assembly accuracy or use absolute accuracy. (This may be nearly impossible for complicated models as they may fail to regenerate.)Perform a Pro/E neutral file “roundtrip” - (#File #Export #Model #Neutral). This may clean up the model, but you will lose the history data.

Fixing AutoGEM ProblemsFixing AutoGEM Problems

Add seed points, curves or volume regions.

© 2000 PTC 20

SummarySummary

AutoGEM failures typically result because of small surfaces within geometry often due to modeling errors.

Spot problems early! Consider how Mechanica will handle features before you get too deep into the part creation. Pass this information on to the designers, if applicable.Make sure unnecessary features can be suppressed, limit geometry checks, and limit poor surface intersections.

Try to avoid breaking associativity to the CAD model.Contact customer support If the model still won’t auto-mesh. Search the Customer Support knowledge base for more information about AutoGEM, Geometry troubleshooting and other useful topics.Sign up to receive email notification when relevant Customer Support documents added or updated.

Use the new diagnostics features to trap problems within Pro/E

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