This section describes how to create a geometric restriction in a topology or sizing optimization. The following topics are covered:
You can select regions of your model that will not be modified during a topology or sizing optimization. The regions continue to contribute to variables such as the weight and the inertia of the model. You can freeze regions that are contacting other parts, such as regions that are used to support the model and regions that form bearing surfaces. It is recommended that you freeze regions to which prescribed conditions are applied. You can freeze these regions using a geometric restriction; or you can request that the Optimization module freeze them automatically when you create a topology optimization task, as described in “Creating an optimization task,” Section 18.6.1. Freezing these regions stabilizes the optimization and often leads to a significantly lower number of iterations.
To create a frozen area geometric restriction:
From the main menu bar, select Geometric Restriction
Create. The Create Geometric Restriction dialog box appears.
Tip: You can initiate the Create procedure in two other ways:
Click Create in the Geometric Restriction Manager. (You can display the Geometric Restriction Manager by selecting Geometric RestrictionManager from the main menu bar.)
Click the 
tool in the Optimization module toolbox.
From the Create Geometric Restriction dialog box that appears, enter the name of the geometric restriction.
Select Frozen area or Frozen area (Sizing) from the list of geometric restrictions, and click Continue.
From the viewport, select the regions that will be frozen.
By default, Abaqus/CAE allows you to select all of the model. To select faces or cells, use the Selection toolbar to change the type of object that you can select to Face or Cells. For more information, see “Filtering your selection based on the type of object,” Section 6.3.2.
If you would rather select from a list of existing sets, do the following:
Click Sets on the right side of the prompt area.
Abaqus/CAE displays the Region Selection dialog box containing a list of available sets.
Select the set of interest, and click Continue.
Note: The default selection method is based on the selection method you most recently employed. To revert to the other method, click Select in Viewport or Sets on the right side of the prompt area.
When you have finished selecting the region to freeze, click Done in the prompt area. For more information on selecting objects, see Chapter 6, “Selecting objects within the viewport.”
The Edit Geometric Restriction dialog box appears.
Click OK to freeze the selected regions and to exit the editor.
For a topology optimization you can specify the minimum or maximum size of selected regions of your model; for example, the minimum size of a region in which the optimization creates trusses. You can also specify the minimum distance between trusses. Specifying a maximum member size forces the optimization to split thick regions into several smaller regions and prevents it from creating large contiguous regions that may be difficult to cast. Specifying a minimum member size avoids thin trusses that may be difficult to manufacture. The minimum member size must be greater than twice the average element size to prevent the results from being dependent on the mesh size.
In most cases you can specify the same value for both the minimum and maximum member size, and the Optimization module creates trusses that are approximately equal to the specified value. To prevent the structure from collapsing, the Optimization module tries to avoid creating thin trusses in regions where prescribed conditions are applied.
Specifying the minimum or maximum member size is very computationally expensive and should be used only where necessary. You should perform an optimization without member size restrictions to identify any regions where the restrictions should be applied.
Note: You can combine a member size constraint and a demold constraint only for a general topology optimization.
To create a member size geometric restriction:
From the main menu bar, select Geometric RestrictionCreate.
The Create Geometric Restriction dialog box appears.
Tip: You can initiate the Create procedure in two other ways:
Click Create in the Geometric Restriction Manager. (You can display the Geometric Restriction Manager by selecting Geometric RestrictionManager from the main menu bar.)
Click the tool in the Optimization module toolbox.
From the Create Geometric Restriction dialog box that appears, enter the name of the geometric restriction.
Select Member size (Topology) from the list of geometric restrictions, and click Continue.
From the viewport, select the region to which the member size restriction will be applied or click Done to apply the member size restriction to the entire model.
By default, Abaqus/CAE allows you to select all of the model. To select faces or cells, use the Selection toolbar to change the type of object that you can select to Face or Cells. For more information, see “Filtering your selection based on the type of object,” Section 6.3.2.
If you would rather select from a list of existing sets, do the following:
Click Sets on the right side of the prompt area.
Abaqus/CAE displays the Region Selection dialog box containing a list of available sets.
Select the set of interest, and click Continue.
Note: The default selection method is based on the selection method you most recently employed. To revert to the other method, click Select in Viewport or Sets on the right side of the prompt area.
When you have finished selecting the geometric restriction region, click Done in the prompt area. For more information on selecting objects, see Chapter 6, “Selecting objects within the viewport.”
The Edit Geometric Restriction dialog box appears.
Do one of the following:
Select Minimum thickness, and enter the minimum member thickness.
Select Maximum thickness, and enter the maximum member thickness.
Select Envelope, and enter the following:
The Minimum member thickness.
The Maximum member thickness.
The Minimum gap between members.
Click OK to create the frozen area geometric restriction and to exit the editor.
You can specify a cyclic symmetry geometric restriction for a topology or sizing optimization. A cyclic symmetry geometric restriction replicates a selected region over a specified distance, as shown in Figure 18–3.
The selected region is replicated along an axis of a coordinate system. You can use the global coordinate system, or you can create a datum coordinate system (see “An overview of the methods for creating a datum coordinate system,” Section 62.5.4, for more information). You can choose to remove frozen regions from the symmetry restriction.To create a cyclic symmetry restriction:
From the main menu bar, select Geometric RestrictionCreate.
The Create Geometric Restriction dialog box appears.
Tip: You can initiate the Create procedure in two other ways:
Click Create in the Geometric Restriction Manager. (You can display the Geometric Restriction Manager by selecting Geometric RestrictionManager from the main menu bar.)
Click the tool in the Optimization module toolbox.
From the Create Geometric Restriction dialog box that appears, enter the name of the geometric restriction.
Select Cyclic symmetry or Cyclic symmetry (Sizing) from the list of geometric restrictions, and click Continue.
From the viewport, select the region that will be replicated by the cyclic symmetry or click Done to apply the cyclic symmetry restriction to the entire model.
By default, Abaqus/CAE allows you to select all of the model. To select faces or cells, use the Selection toolbar to change the type of object that you can select to Face or Cells. For more information, see “Filtering your selection based on the type of object,” Section 6.3.2.
If you would rather select from a list of existing sets, do the following:
Click Sets on the right side of the prompt area.
Abaqus/CAE displays the Region Selection dialog box containing a list of available sets.
Select the set of interest, and click Continue.
Note: The default selection method is based on the selection method you most recently employed. To revert to the other method, click Select in Viewport or Sets on the right side of the prompt area.
When you have finished selecting the geometric restriction region, click Done in the prompt area. For more information on selecting objects, see Chapter 6, “Selecting objects within the viewport.”
The Edit Geometric Restriction dialog box appears.
Select the coordinate system, and select the axis along which the region will be replicated.
Enter the distance that the selected region will be translated along the axis.
If desired, toggle on Ignore frozen area to remove any frozen regions from the region that will be translated.
Click OK to create the cyclic symmetry geometric restriction and to exit the editor.
You can specify a planar symmetry geometric restriction for a topology or sizing optimization. A planar symmetry geometric restriction forces the optimized model to be symmetric about a specified plane, as shown in Figure 18–4:
You specify the plane of symmetry by selecting the axis of a coordinate system that is the normal to the plane of symmetry. You can use the global coordinate system, or you can create a datum coordinate system (see “An overview of the methods for creating a datum coordinate system,” Section 62.5.4, for more information). You can choose to remove frozen regions from the symmetry restriction.To create a planar symmetry restriction:
From the main menu bar, select Geometric RestrictionCreate.
The Create Geometric Restriction dialog box appears.
Tip: You can initiate the Create procedure in two other ways:
Click Create in the Geometric Restriction Manager. (You can display the Geometric Restriction Manager by selecting Geometric RestrictionManager from the main menu bar.)
Click the tool in the Optimization module toolbox.
From the Create Geometric Restriction dialog box that appears, enter the name of the geometric restriction.
Select Planar symmetry or Planar symmetry (Sizing) from the list of geometric restrictions, and click Continue.
From the viewport, select the region in which the planar symmetry will be enforced or click Done to apply the planar symmetry restriction to the entire model.
By default, Abaqus/CAE allows you to select all of the model. To select faces or cells, use the Selection toolbar to change the type of object that you can select to Face or Cells. For more information, see “Filtering your selection based on the type of object,” Section 6.3.2.
If you would rather select from a list of existing sets, do the following:
Click Sets on the right side of the prompt area.
Abaqus/CAE displays the Region Selection dialog box containing a list of available sets.
Select the set of interest, and click Continue.
Note: The default selection method is based on the selection method you most recently employed. To revert to the other method, click Select in Viewport or Sets on the right side of the prompt area.
When you have finished selecting the geometric restriction region, click Done in the prompt area. For more information on selecting objects, see Chapter 6, “Selecting objects within the viewport.”
The Edit Geometric Restriction dialog box appears.
Select the coordinate system, and select the axis of the coordinate system that represents the normal to the plane of symmetry.
If desired, toggle on Ignore frozen area to remove any frozen regions from the symmetry restriction.
Click OK to create the planar symmetry geometric restriction and to exit the editor.
You can specify a rotational symmetry geometric restriction for a topology or sizing optimization. A rotational symmetry geometric restriction forces the optimized model to be symmetric about a specified axis, as shown in Figure 18–5:
You specify the axis of symmetry by selecting the axis of a coordinate system. You can use the global coordinate system, or you can create a datum coordinate system (see “An overview of the methods for creating a datum coordinate system,” Section 62.5.4, for more information). In addition, you must enter an angle that specifies the size of the repeating segment. You can choose to remove frozen regions from the symmetry restriction.To create a rotational symmetry restriction:
From the main menu bar, select Geometric RestrictionCreate.
The Create Geometric Restriction dialog box appears.
Tip: You can initiate the Create procedure in two other ways:
Click Create in the Geometric Restriction Manager. (You can display the Geometric Restriction Manager by selecting Geometric RestrictionManager from the main menu bar.)
Click the tool in the Optimization module toolbox.
From the Create Geometric Restriction dialog box that appears, enter the name of the geometric restriction.
Select Rotational symmetry or Rotational symmetry (Sizing) from the list of geometric restrictions, and click Continue.
From the viewport, select the region in which the rotational symmetry will be enforced or click Done to apply the rotational symmetry restriction to the entire model.
By default, Abaqus/CAE allows you to select all of the model. To select faces or cells, use the Selection toolbar to change the type of object that you can select to Face or Cells. For more information, see “Filtering your selection based on the type of object,” Section 6.3.2.
If you would rather select from a list of existing sets, do the following:
Click Sets on the right side of the prompt area.
Abaqus/CAE displays the Region Selection dialog box containing a list of available sets.
Select the set of interest, and click Continue.
Note: The default selection method is based on the selection method you most recently employed. To revert to the other method, click Select in Viewport or Sets on the right side of the prompt area.
When you have finished selecting the geometric restriction region, click Done in the prompt area. For more information on selecting objects, see Chapter 6, “Selecting objects within the viewport.”
The Edit Geometric Restriction dialog box appears.
Select the coordinate system, and select the axis of the coordinate system that represents the axis of symmetry.
Enter the Repeating segment size, which is the angle (in degrees) specifying the size of the repeating segment. The value must be greater than or equal to 2°.
If desired, toggle on Ignore frozen area to remove any frozen regions from the symmetry restriction.
Click OK to create the rotational symmetry geometric restriction and to exit the editor.
You can specify a point symmetry geometric restriction for a topology or sizing optimization. A point symmetry geometric restriction forces the optimized model to be symmetric about a specified point, as shown in Figure 18–6.
You specify the point of symmetry by selecting a coordinate system (the point of symmetry is assumed to be the origin of the coordinate system). You can use the global coordinate system, or you can create a datum coordinate system (see “An overview of the methods for creating a datum coordinate system,” Section 62.5.4, for more information). You can choose to remove frozen regions from the symmetry restriction.To create a point symmetry restriction:
From the main menu bar, select Geometric RestrictionCreate.
The Create Geometric Restriction dialog box appears.
Tip: You can initiate the Create procedure in two other ways:
Click Create in the Geometric Restriction Manager. (You can display the Geometric Restriction Manager by selecting Geometric RestrictionManager from the main menu bar.)
Click the tool in the Optimization module toolbox.
From the Create Geometric Restriction dialog box that appears, enter the name of the geometric restriction.
Select Point symmetry or Point symmetry (Sizing) from the list of geometric restrictions, and click Continue.
From the viewport, select the region in which the point symmetry will be enforced or click Done to apply the point symmetry restriction to the entire model.
By default, Abaqus/CAE allows you to select all of the model. To select faces or cells, use the Selection toolbar to change the type of object that you can select to Face or Cells. For more information, see “Filtering your selection based on the type of object,” Section 6.3.2.
If you would rather select from a list of existing sets, do the following:
Click Sets on the right side of the prompt area.
Abaqus/CAE displays the Region Selection dialog box containing a list of available sets.
Select the set of interest, and click Continue.
Note: The default selection method is based on the selection method you most recently employed. To revert to the other method, click Select in Viewport or Sets on the right side of the prompt area.
When you have finished selecting the geometric restriction region, click Done in the prompt area. For more information on selecting objects, see Chapter 6, “Selecting objects within the viewport.”
The Edit Geometric Restriction dialog box appears.
Select the coordinate system. The point of symmetry is assumed to be the origin of the selected coordinate system.
If desired, toggle on Ignore frozen area to remove any frozen regions from the symmetry restriction.
Click OK to create the point symmetry geometric restriction and to exit the editor.
A sizing optimization determines the optimal element thickness when modeling a sheet metal structure with shell elements. Specifying the minimum width of a region containing elements of the same thickness prevents narrow slivers of elements with equal thickness from appearing in the solution after a sizing optimization. Specifying a minimum width will also prevent oscillations in the shell thickness or a “checkerboard” pattern of element thicknesses. The minimum width must be larger than the average length of the element edges.
To create a minimum width geometric restriction:
From the main menu bar, select Geometric RestrictionCreate.
The Create Geometric Restriction dialog box appears.
Tip: You can initiate the Create procedure in two other ways:
Click Create in the Geometric Restriction Manager. (You can display the Geometric Restriction Manager by selecting Geometric RestrictionManager from the main menu bar.)
Click the tool in the Optimization module toolbox.
From the Create Geometric Restriction dialog box that appears, enter the name of the geometric restriction.
Select Member size (Sizing) from the list of geometric restrictions and click Continue.
From the viewport, select the region to which the minimum width restriction will be applied or click Done to apply the minimum width restriction to the entire model.
By default, Abaqus/CAE allows you to select all of the model. To select faces or cells, use the Selection toolbar to change the type of object that you can select to Face or Cells. For more information, see “Filtering your selection based on the type of object,” Section 6.3.2.
If you would rather select from a list of existing sets, do the following:
Click Sets on the right side of the prompt area.
Abaqus/CAE displays the Region Selection dialog box containing a list of available sets.
Select the set of interest, and click Continue.
Note: The default selection method is based on the selection method you most recently employed. To revert to the other method, click Select in Viewport or Sets on the right side of the prompt area.
When you have finished selecting the geometric restriction region, click Done in the prompt area. For more information on selecting objects, see Chapter 6, “Selecting objects within the viewport.”
The Edit Geometric Restriction dialog box appears.
Select Minimum width and enter the minimum width.
Click OK to create the minimum width geometric restriction and to exit the editor.
You can specify upper and lower bounds on the thickness of shell elements when you are configuring a sizing optimization. The value can be an absolute thickness or a fraction of the initial thickness.
To create a thickness control geometric restriction:
From the main menu bar, select Geometric RestrictionCreate.
The Create Geometric Restriction dialog box appears.
Tip: You can initiate the Create procedure in two other ways:
Click Create in the Geometric Restriction Manager. (You can display the Geometric Restriction Manager by selecting Geometric RestrictionManager from the main menu bar.)
Click the tool in the Optimization module toolbox.
From the Create Geometric Restriction dialog box that appears, enter the name of the geometric restriction.
Select Thickness control (Sizing) from the list of geometric restrictions, and click Continue.
From the viewport, select the region to which the thickness control restriction will be applied or click Done to apply the thickness control restriction to the entire model.
By default, Abaqus/CAE allows you to select all of the model. To select faces or cells, use the Selection toolbar to change the type of object that you can select to Face or Cells. For more information, see “Filtering your selection based on the type of object,” Section 6.3.2.
If you would rather select from a list of existing sets, do the following:
Click Sets on the right side of the prompt area.
Abaqus/CAE displays the Region Selection dialog box containing a list of available sets.
Select the set of interest, and click Continue.
Note: The default selection method is based on the selection method you most recently employed. To revert to the other method, click Select in Viewport or Sets on the right side of the prompt area.
When you have finished selecting the geometric restriction region, click Done in the prompt area. For more information on selecting objects, see Chapter 6, “Selecting objects within the viewport.”
The Edit Geometric Restriction dialog box appears.
Do one of the following:
Select Thickness by value to enter the absolute value of the shell element thickness.
Select Thickness by fraction to enter a fraction of the shell element thickness relative to the initial value.
Select Minimum and enter the minimum thickness.
Select Maximum and enter the maximum thickness.
Click OK to create the thickness control geometric restriction and to exit the editor.
You can specify that selected regions contain clusters of shell elements of equal thickness after a sizing optimization. You can use clustering to generate strengthening ribs or rings in the sheet metal structure you are optimizing or to define borders between regions of equal thickness. Clustered regions can be reproduced in manufacturing using sheets of constant thickness; for example, a vehicle “body in white” formed by welding and stamping individual sheet metal structures. To allow for maximum design flexibility, you should first optimize your structure without specifying clustering and use the initial design to decide which regions to cluster in your final optimization.
To create a thickness clustering geometric restriction:
From the main menu bar, select Geometric RestrictionCreate.
The Create Geometric Restriction dialog box appears.
Tip: You can initiate the Create procedure in two other ways:
Click Create in the Geometric Restriction Manager. (You can display the Geometric Restriction Manager by selecting Geometric RestrictionManager from the main menu bar.)
Click the tool in the Optimization module toolbox.
From the Create Geometric Restriction dialog box that appears, enter the name of the geometric restriction.
Select Cluster areas (Sizing) from the list of geometric restrictions, and click Continue.
The Edit Geometric Restriction dialog box appears.
From the list of Eligible Sets, select the sets specifying regions that will contain clusters of shell elements of equal thickness after the optimization.
Note:
If the desired set does not exist, click 
to create it.
Click the arrow to move the selected sets to the list of Selected Sets.
Click OK to create the thickness clustering geometric restriction and to exit the editor.
You can specify a demold geometric restriction for a topology optimization. A demold geometric restriction forces the optimized model to satisfy specified manufacturing requirements; for example, it can prevent undercuts and hollow regions in a part that must be extracted from a mold.
To create a demold restriction:
From the main menu bar, select Geometric RestrictionCreate.
The Create Geometric Restriction dialog box appears.
Tip: You can initiate the Create procedure in two other ways:
Click Create in the Geometric Restriction Manager. (You can display the Geometric Restriction Manager by selecting Geometric RestrictionManager from the main menu bar.)
Click the tool in the Optimization module toolbox.
From the Create Geometric Restriction dialog box that appears, enter the name of the geometric restriction.
Select Demold from the list of geometric restrictions, and click Continue.
From the viewport, select the region in which the demold restriction will be enforced or click Done to apply the demold symmetry restriction to the entire model.
By default, Abaqus/CAE allows you to select all of the model. To select faces or cells, use the Selection toolbar to change the type of object that you can select to Face or Cells. For more information, see “Filtering your selection based on the type of object,” Section 6.3.2.
If you would rather select from a list of existing sets, do the following:
Click Sets on the right side of the prompt area.
Abaqus/CAE displays the Region Selection dialog box containing a list of available sets.
Select the set of interest, and click Continue.
Note: The default selection method is based on the selection method you most recently employed. To revert to the other method, click Select in Viewport or Sets on the right side of the prompt area.
When you have finished selecting the geometric restriction region, click Done in the prompt area. For more information on selecting objects, see Chapter 6, “Selecting objects within the viewport.”
The Edit Geometric Restriction dialog box appears.
By default, the region in which the Optimization module checks for collisions is the same as the region in which it enforces the demold restriction. If desired, select 
from the top of the Edit Geometric Restriction dialog box, and select the collision check region. To avoid cavities, the collision check region should include the demold region and any cells that are adjacent to the demold region.
Choose one of the following demold techniques:
Choose Demolding with a central plane and select how the Optimization module will determine the central plane:
Choose Determine automatically. The Optimization module determines the optimal location of the central plane such that the optimization adds or removes material only in the pull direction or in the opposite direction. Toggle on Prevent hole formation to prevent the optimization from removing material from the central plane.
Choose Specify, and click to select a point on the central plane. The Optimization module creates a structure that can be released from a mold in both pull directions away from the central plane.
Choose Forging (deform only in the pull direction). The central plane, the plane at which two halves of a mold meet, is assumed to lie at the back of the model and perpendicular to the pull direction. The optimization adds or removes material only in the pull direction.
Choose Stamping. If the Optimization module decides to remove an element from the structure, it also removes all the elements behind or in front of the element (relative to the vector indicating the pull direction).
Choose Demolding at the region surface to force the optimization to add or remove material only from the surface of the constrained region.
Click , and select two points specifying the vector along the pull direction.
Enter the Draft angle. The draft angle is a small angle relative to the pull direction that will be introduced to the optimized model to ensure the part can be removed from its mold. Normally the value is between 0° and 10°.
Click OK to create the demold geometric restriction and to exit the editor.
