Open duct end meshing for acoustics

You can use Simcenter Nastran FEM Acoustics to analyze the acoustics of open ducts. Use the Open Duct Mesh command to model the air volume around the end of the duct. This type of mesh is sometimes called a mushroom mesh because of its shape.

The Open Duct Mesh command creates a closed, surface mesh that folds back over the edge of the duct. You can define the radius of the portion of the mesh that folds back as a percentage of the duct radius. This cross section view shows how the open duct mesh folds back over the edge of the surface mesh on the duct.

The surface mesh that the software generates with this command is an automatically matched layer mesh that shares nodes with the mesh along the outer surface of the duct. You can use the Open Duct Mesh command when you need to:

• Model non-reflective duct terminations up to high frequencies.

• Simulate exterior radiated noise.

Selecting element edges to define the duct end

In the Open Duct Mesh dialog box, when you select the element edges that define the open end of the duct, the edges you select must form a closed loop that lies in a single plane. For example, you can create open duct meshes around circular, elliptical, and rectangular shaped duct ends.

Open duct end mesh around a rectangular shaped duct

Specifying the parameters for an open duct mesh

You can use the options in the Open Duct Mesh dialog box to control the size and length of the open duct mesh. You can specify:

• The overall size of the 2D elements in the open duct mesh (Element Size).

• How far the open duct mesh folds back onto the duct itself (Fold Back Distance).

• The radius of the portion of the open duct mesh that folds back over the duct (Fold Back Radius).

• The overall radius of the open duct mesh (Open Duct Surface Radius).Surface radius of 50mmSurface radius of 60mm

Tip:

In the Open Duct Mesh dialog box, the Automatic Element Size button computes an appropriate element size for the geometry and appropriate default values for the different open duct mesh parameters.

Working with an open duct mesh

• An open duct mesh is FE-based and is not associated with any underlying geometry. The software does not update FE-based meshes if any associated CAD geometry updates.

• You can edit existing open duct meshes to modify, for example, the element size or properties such as the Fold Back Distance.

• The software stores open duct meshes in an Open Duct Mesh node in the Simulation Navigator

• The software does not export open duct meshes to the solver input file.

Where do I find it?

Application	Pre/Post
Prerequisite	A FEM file as the displayed part and work part
Command Finder	Open Duct Mesh

How do I

Reset node and element IDs

Learn more

Manually creating elements

Extruding elements

Projecting elements

Reflecting elements

Revolving elements

Rotating elements

Translating elements

Splitting shell elements

Swapping the diagonals between triangular elements

Splitting 1D elements

Detaching elements from a mesh

Attaching elements into a mesh

Creating a mesh from a cloud of points

Rib detection and removal within a mesh

Thickening a 2D mesh

Convex meshes for FEM acoustics analyses

Acoustic chamber meshes for panel transmission loss analyses

Combining triangular elements

Modifying element order

Modifying the type of elements

Moving nodes in 2D elements

Modifying element labels

Modifying element connectivity

Deleting elements

Extracting elements from a mesh

Locking and unlocking a mesh

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Open duct end meshing for acoustics, Simcenter 3D 2021.1 Series

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