Cross Section

In a node’s sequence you can add a node (

). By default, this computes the cross section of all 3D objects generated by preceding nodes in the geometry sequence. You can also select specific 3D objects to intersect with the work plane. You can also add a new 2D or 2D axisymmetric and add the node there. In that case, you can select which to use. For example, if you have a 3D geometry that is symmetric about an axis, you can add a work plane that contains the axis. In the axisymmetric 2D Component, you then get the cross section and can use a 2D axisymmetric component, which is computationally efficient compared to a full 3D component. A node can also be useful to extract a planar surface for modeling a thin flat 3D structure using shell elements, for example. Another use for a cross section is to form a surface that you can extrude into a 3D solid from a closed curve that lie in a plane. Then also add a node below the node to make the closed curve into a 2D surface.

To add a cross section, right-click a node under a node or a 2D node and select (

). Then enter the properties of the cross section using the following sections:

If you add the node to a 2D or 2D axisymmetric geometry, first select the work plane to use for the cross section from the list.

From the list, choose (the default) to intersect all 3D geometry objects with the work plane, or choose to intersect only the geometry objects that you add to the list that appears. Click the button to toggle between turning ON and OFF the selections.

You can change the settings for the list if you experience problems with the cross section operation. Geometric entities that have a distance less than the repair tolerance are merged.

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The default value in the list is , which for 3D objects represented using the CAD kernel determines the repair tolerance internally. For 3D objects represented using the COMSOL kernel, and for 2D and 1D objects, means a relative repair tolerance of 10−6.

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Choose to enter a value for the field (the default is determined by the main node’s setting). This value is relative to the largest absolute value of the coordinates of all input objects.

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Choose to enter a value for the field (the default is determined by the main node’s setting; SI unit: m). This value uses the same unit as the geometry sequence’s length unit.

When you build this feature, the relative and absolute repair tolerances are set to the values that are used for the last object that the cross section is generated for (with a precision of two digits). This is useful to find out the tolerance used by the operation. After the feature is built, you can set the to either or , then check the values displayed in the or fields.

Select the check box to create predefined selections (for all levels — objects, domains, boundaries, edges, and points — that are applicable) in subsequent nodes in the geometry sequence. Use the list (for nodes in a node’s ) or the list (or nodes in 2D or 2D axisymmetric geometries) to choose for which geometric entity level the selection should be created. All applicable levels, as well as and , are available. From the list, choose a color for highlighting the resulting objects selection. See Selection Colors.

Select the check box to create selections in 2D based on the selections from the 3D geometry. Each selection that is produced by a 3D geometry feature preceding the work plane in the 3D geometry sequence and each 3D cumulative selection are intersected with the work plane to give a selection in 2D. These selections are available if the node under a Plane Geometry node in a work plane or under a 2D component’s node. In the latter case, you can also select the check box to make the selections from 3D available in physics and materials settings, for example.

If you want to make the resulting entities contribute to a cumulative selection, select a cumulative selection from the list (the default, , gives no contribution), or click the button to create a new cumulative selection (see Cumulative Selections).

From the list choose to make the resulting objects available only in the feature’s geometry sequence. The default option means that the resulting objects become construction geometry if all input objects are construction geometry. Choose to never output construction geometry objects. For more information see Construction Geometry.