Creating new groups from existing groups using Boolean operations

You can use Boolean operations to create new groups from existing groups. The available Boolean operations are union, intersection, exclusive or, and subtraction.

When you create a group using a Boolean operation, the software automatically names the new group and assigns a numerical label to it.

To select groups as operands for the Boolean commands, in the Group Manager dialog box, in the Groups list, select one of the groups of interest. To select the other groups of interest, press and hold Ctrl as you select each group.

Union, Intersection, and Exclusive OR commands

You can use the Union , Intersection , and Exclusive OR commands to create a new group from two or more existing groups.

For example, suppose you have three existing groups whose entities are elements.

Group name	Label	Element numbers
Group(1)	1	1, 2, 3, 4, 5, 6
Group(2)	2	5, 6, 7, 8, 9, 10, 11, 12
Group(3)	3	20, 21, 22

The following table shows the contents of the groups that the software creates from the existing groups when you use the Union, Intersection, and Exclusive OR commands.

Groups selected	Boolean command	Element numbers in the new group
Group(1) Group(2)	Union	1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12
Group(1) Group(2) Group(3)	Union	1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 20, 21, 22
Group(1) Group(2)	Intersection	5, 6
Group(1) Group(2) Group(3)	Intersection	Because no elements are common to all three groups, a new group is not created.
Group(1) Group(2)	Exclusive OR	1, 2, 3, 4, 7, 8, 9, 10, 11, 12
Group(1) Group(2) Group(3)	Exclusive OR	1, 2, 3, 4, 7, 8, 9, 10, 11, 12, 20, 21, 22

Subtraction command

You can use the Subtraction command to create a new group from two existing groups only.

When you use the Subtraction command, the software subtracts entities from the target group that are also contained in the tool group. The target group is the group whose numerical label is algebraically smaller. Thus, the order in which you select the two groups is unimportant.

The following table shows the contents of the groups that the software creates from the existing groups when you use the Subtraction command.

Groups selected	Boolean command	Element numbers in the new group
Group(1) Group(2)	Subtraction	1, 2, 3, 4
Group(1) Group(3)	Subtraction	1, 2, 3, 4, 5, 6

Boolean commands and heterogeneous groups

The previous examples show how the Boolean commands operate on groups that contain one type of entity only. However, groups can contain combinations of different types of FE and geometric entities. Groups that contain combinations of different types of FE and geometric entities are referred to as heterogeneous groups. When the software evaluates Boolean operations on heterogeneous groups, it performs the Boolean operation on each type of FE or geometric entity in the groups separately.

For example, suppose you have the following two heterogeneous groups:

Group name	Label	Contents
Group(4)	1	Nodes: N1, N2, N3, N4, N5, N6 Polygon faces: PF15
Group(5)	2	Nodes: N5, N6, N7, N8, N9, N10 Polygon faces: PF15, PF20

The following table shows the contents of the groups that the software creates from the heterogeneous groups when you use the various Boolean commands.

Groups selected	Boolean command	Contents of the new group
Group(4) Group(5)	Union	Nodes: N1, N2, N3, N4, N5, N6, N7, N8, N9, N10 Polygon faces: PF15, PF20
Group(4) Group(5)	Intersection	Nodes: N5, N6 Polygon faces: PF15, PF20
Group(4) Group(5)	Exclusive OR	Nodes: N1, N2, N3, N4, N7, N8, N9, N10 Polygon faces: PF20
Group(4) Group(5)	Subtraction	Nodes: N1, N2, N3, N4

Automatic naming of groups created from Boolean commands

When you use the Boolean commands to create a group, the software automatically names the new group.

For example, when you use the Union command, the software names the new group UnionGroup(1) if no group with that name exists. If a group named UnionGroup(1) exists, the software names the new group UnionGroup(2), and so on.

The other Boolean commands name the new groups similarly, except that the prefix of Union is replaced by Intersection, Xor, or Subtract, whichever is applicable.

Where do I find it?

Application	Pre/Post, Design Simulation
Command Finder	Manage Groups
Simulation Navigator	Right-click the Groups node→Manage
Location in dialog box	Boolean group

How do I

Create a group by manually selecting the contents

Create a group automatically from an element quality check

Create groups with the Automatic Group command

Copy a group

Edit a group

Apply a force to the entities in an existing group

Use groups to control model visibility

Learn more

Groups

Automatic group command

Group Elements by Boundary

Group selection options

Smart selection methods with groups

Controlling the display of nodes in groups

Quick links

Command reference

Pre/Post video examples

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Creating new groups from existing groups using Boolean operations, Simcenter 3D 2021.1 Series

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