Creating CBEND elements

In the Nastran environment, you can use the 1D Mesh and Element Create commands to create CBEND elements. The CBEND element is a one-dimensional bending element that connects two nodes and has a constant radius of curvature (circular arc). You can use CBEND elements to model curved pipes. curved beams, pipe elbows or miter bends. For example, you can use CBEND elements to model pressurized pipe systems.

To create a CBEND element:

• Use the 1D Mesh command to create CBEND elements that are associated with the underlying geometry.

• Use the Element Create command to create CBEND elements that are not associated with any geometry.

CBEND element

Creating a CBEND element

When you create CBEND elements in Nastran, you must specify an orientation vector or orientation node to define the centerline of the element (X1, X2, X3 or G0 fields). You must also specify the geometry characteristics of the element (GEOM field). In Pre/Post, you:

• Use the Element Orientation options in the Mesh Associated Data dialog box to orient the centerline of the element.Note: If you select a polygon edge or curve to define the mesh, the software uses that curve or edge to calculate the appropriate orientation vector.

• Use the Bend Dimension options in the PBEND (Pipe) to define the geometric characteristics of the element. For example, you can specify a bend radius or a bend angle for the element.

If you do not specify an orientation vector and the Bend Dimension options, then the software displays the CBEND element as a straight line that connects two nodes.

For more information, see CBEND in the Simcenter Nastran Quick Reference Guide. and CBEND Element in the Simcenter Nastran Element Library Reference Guide.

Defining properties for CBEND elements

You can use the options in the PBEND (Pipe) dialog box to define the physical characteristics of CBEND elements, such as their diameter values and bend radii, as well as assign other properties, such as an internal pressure value.

The process for defining the physical characteristics of a CBEND element is slightly different in Pre/Post than the process in Nastran.

• In Nastran, you use the RM field on the PBEND entry to specify the mean cross-sectional radius of the curved pipe. You use the T field on the PBEND entry to specify the wall thickness of the CBEND element.

• In Pre/Post, you use the Inner Diameter and Outer Diameter options in the PBEND (Pipe) dialog box to specify inner and outer diameter values for the element. To create a CBEND element with a solid, circular cross-section, specify an Inner Diameter value of 0.0.Pre/Post uses the diameter values to calculate the mean radius value and the wall thickness of the element as follows:If the Inner Diameter value is 0.0, then the mean radius (RM) value = the Outer Diameter value/2. The wall thickness value (T) = 0.0If the Inner Diameter value is set to any value other than 0.0, then the mean radius (RM) value = (the Outer Diameter value + the Inner Diameter value)/4. The wall thickness value (T) = (the Outer Diameter value - the Inner Diameter value)/2.

CBEND element cross section

	(1) Outer diameter of the element
(2) Inner diameter of the element
(3) Mean radius value (T) Thickness value

The options in the PBEND dialog box correspond to the fields for the Nastran PBEND bulk data entry. Pre/Post currently supports the alternate format of the PBEND entry for curved pipes only.

For more information, see PBEND in the Simcenter Nastran Quick Reference Guide. and PBEND Format in the Simcenter Nastran Element Library Reference Guide.

Limitations of CBEND elements

You cannot select CBEND elements with the following commands:

• Element Extrude

• Element Revolve

• Mesh from Boundary

Importing CBEND elements

There are special considerations when you import CBEND elements and PBEND physical properties into Pre/Post.

• For the GEOM field on the CBEND bulk data entry, Pre/Post supports options 3 and 4 only. Pre/Post does not import CBEND entries where the GEOM field has a value of 1 or 2.

• If an input file contains multiple CBEND entries with different values for the GEOM field that reference the same PBEND entry, Pre/Post imports the first CBEND entry only.

• For the CBEND entry, Pre/Post always imports the orientation vector information (either the X1, X2, X3 fields or the G0 field) as element associated data.

• Pre/Post does not support the import of CBEND references on the PLOAD1 entry.

• Pre/Post supports the import of CBEND and PBEND references on the NSM, NSM1, NSML, and NSML1 bulk data entries.

• Pre/Post imports PBEND entries that are defined with the alternate format (FSI methodology) only. If the input file contains a PBEND entry that is not defined with the alternate format, the software issues a message and imports the PBEND entry with an FSI field equal to 1.

• If a PBEND entry has a wall thickness value of 0.0 defined on the T field (solid cylinder), the software creates a CBEND element with an Inside Diameter value of 0.0.

• You can use the Data Compaction options in the Import Simulation dialog box to import PBEND entries as element associated data. For more information, see Importing physical property data as element-associated data.

• The Solid Properties Check command does not compute the solid properties of CBEND elements.

Where do I find it?

Application	Pre/Post
Prerequisite	A FEM file as the work part and displayed partSimcenter Nastran or MSC Nastran as the specified solver
Command Finder	1D Mesh Element Create

Learn more

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Creating Interpolated Constraint (RSPLINE) elements

Defining constraint equations as elements

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Creating CBEND elements, Simcenter 3D 2021.1 Series

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