23 - understanding autogem limits and settings

7/27/2019 23 - Understanding AutoGEM Limits and Settings

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TheoryandMechanicaModelTopics

UnderstandingAutoGEMLimitsandSettings Lecture

Understanding_AutoGEM_Limits_and_Settings.mp3

Understanding AutoGEM Limits and Settings

Limits and settings can be used to affect the default behavior of

AutoGEM.

Edge and Face Angle Examples Aspect Ratio

Max Edge Turn = 90 Max Edge Turn = 30

LectureNotes

AutoGEM Limits

AutoGEM limits enable you to customize which limit settings are permitted during thecreation of mesh elements. The limit settings are:

Allowable Angles (Refer to the figure on the upper left for an example of Edgeand Face angles).

o Max/Min Edge Angles: Edge angles are the angles formed at the verticesof the edges of single facets.

o Max/Min Face Angles: Face angles are the angles formed betweenadjacent facets.


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Max Aspect Ratio: The aspect ratio is the ratio between the longest and shortestleg lengths of a facet. The example shown on the upper right side of this slideshows a ratio of 4:2 or 2.0.

Max Edge Turn: The edge turn angle is the maximum angle subtended by anedge that is permitted. The two figures on the bottom of the slide (shown ingreen) show examples of a model that was meshed with the Max Edge Turn

limit set to 90 degrees (on the left) and 30 degrees (on the right). In simpleterms, it is the maximum number of degrees that the normal to a given edge ofa facet can turn from its start to its end.

AutoGEM Settings

AutoGEM settings enable you to customize the parameters that determine how mesh

elements are created. Settings include:

Insert Points: Enables the addition of points to create a valid mesh. Move or Delete Existing Points: Enables the relocation/removal of existing

points for optimal element configuration. Modify or Delete Existing Elements: Permits modification/deletion of existing

elements to optimize/complete element creation.

Automatic Interrupt: Stops AutoGEM automatically after it creates a specifiedpercentage of elements.

Ignore Unpaired Surfaces: Unpaired surfaces are excluded from the mesh. Remove Unopposed Surfaces: Unopposed surfaces are excluded from the mesh. Create Links Where Needed: Enables the creation of links when needed to

connect shell/solid elements or solid quadrilateral/solid triangular faces.

Create Bonding Elements: Permits creation of bonding elements that link partsin assemblies.

Detailed Fillet Modeling: Creates more elements near fillets for smoother fringeplots.

Display AutoGEM Prompts: Display the prompts or message boxes which requireaction/confirmation to continue meshing.

Element Types: Direct AutoGEM to allow the creation of certain element typesfor shells and solids. For shell elements, the default setting is to have AutoGEMcreate quadrilateral and triangular elements but you can also restrict AutoGEMto the creation of triangular elements only. For solid elements, the defaultsetting is to have AutoGEM create only tetrahedral elements, but you could also

allow AutoGEM to create tetrahedral and wedge type elements, or tetrahedral,wedge, and brick type elements.

Best Practices

For solids and shells, the software default limits work well for most scenarios.However, better shell model results are often obtained when the following limits areused: Edge Max and Face Max= 165; Edge Min and Face Min= 15; Max Aspect Ratio=5; Max Edge Turn= 85.


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Additionally, AutoGEM can be directed to create nodes where datum points are

encountered. This method can be used to force nodes into specific areas of an analysis

model.

UnderstandingAutoGEMLimitsandSettings Demonstration

Understanding_AutoGEM_Limits_and_Settings_demo.mp4

UnderstandingAutoGEMLimitsandSettings Procedure

Procedure: Understanding AutoGEM Limits and Settings

ScenarioApply different AutoGEM limits to a model.

AutoGEM_limits limits_example.prt

Task 1. Create a P-mesh using AutoGEM default limits.

1. Click Applications > Mechanica.

2. Click Create and click Create from the AutoGEM dialog box to create a mesh

using the default settings.

Note that the current mesh contains a total of 41 elements.

3. After examining the resulting mesh, click Close > Close > No to leave theAutoGEM mode. You can click Close to close the Diagnostics dialog box if desired.


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Task 2. Modify the default AutoGEM limits.

1. Click AutoGem > Settings... and select the Limits tab.

2. Verify that the Limits for field are set to Creating and type the following values in

the fields specified:

Field Value

Edge Max 165

Edge Min 15

Face Max 165

Face Min 15

Max Aspect Ratio 5

Max Edge Turn 85

3. Click OK in the AutoGEM Settings dialog box.


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4. After reviewing the warning, click OK to close the Information dialog box.

Task 3. Create a P-mesh using the modified AutoGEM limits.

1. Click Create and select Create from the AutoGEM dialog box to create a meshusing the modified settings.

Note the change in the general shape of each element and the increase in

the total number of elements from 41 to 137.

2. After examining the resulting mesh, click Close > Close > No to leave the

AutoGEM mode. You can click Close to close the Diagnostics dialog box if desired.


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3. Return to the Standard Pro/ENGINEER mode by clicking Applications > Standard.

4. Click Save from the main toolbar and click OK to save the model.5. Click File > Erase > Current > Yes to erase the model from memory.

This completes the procedure.

23 - understanding autogem limits and settings

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