Meshing for FEM acoustic analysis

In Simcenter Nastran FEM acoustic and vibro-acoustic analyses, you model the acoustic mesh as a 3D volume mesh. This mesh can represent the acoustic fluid in both the interior and the exterior of the model.

The process for creating the mesh depends on the type of acoustics problem you want to analyze. For example, you can analyze:

• Acoustics of an interior cavity.

• Sound radiation or sound transmission exterior to a part.

• Sound transmission from the interior to the exterior of the part or from the exterior to the interior of the part.

Vibro-acoustic analysis of a stereo speaker with a 3D fluid mesh on both the (1) exterior and (2) interior of the speaker

Meshing for interior acoustic analysis

In an interior acoustic analysis, you must generate an acoustic fluid mesh within the interior or cavity. For example, you can analyze the interior acoustics of an automobile or aircraft cabin. To create a mesh for an acoustic analysis within a cavity, you must determine the boundary of the cavity (a closed surface) and mesh the interior volume with 3D elements.

Step	Summary	Detailed help topic
1. Create a surface wrap around the interior of the part.	You can use the Surface Wrap Recipe command with the Face and Normal Vector Toward the Interior or Interior Point method to surface wrap the interior. You can output either a 2D mesh or a polygon body.Use the 2D Mesh Only option to create a 2D mesh that wraps around the interior of the structural mesh.Use the Surface Wrap Body option to create a polygon surface wrap body.	Surface Wrap RecipeCreate an interior surface wrap body
2. Generate the acoustic fluid mesh	If you use the Surface Wrap Recipe command to create a 2D mesh, use the Solid from Shell command to create the acoustic fluid mesh.If you use the Surface Wrap Recipe command to create a polygon body, use the 3D Tetrahedral Mesh command to create the acoustic fluid mesh inside that body.	Solid from Shell meshing3D tetrahedral meshing
3. Create a microphone mesh to output acoustic results, such as pressure, at locations within or exterior to the fluid domain.	Use the appropriate mesh or mesh primitive command to create a microphone mesh in the appropriate shape and location.	Using microphone mesh to capture analysis results

Meshing for exterior acoustic analyses

In an exterior acoustic analysis, you must generate a 3D mesh that represents the acoustic fluid domain, such as water or air, around the exterior of the part. For example, you use an exterior acoustic analysis to analyze radiated noise from an engine.

In an exterior acoustic analysis, the 3D fluid mesh has an inner boundary that is typically derived from the structural mesh. For exterior acoustics, the outer boundary for the fluid mesh is defined by a convex mesh on which you define an Automatically Matched Layer simulation object. The Automatically Matched Layer command defines a non-reflecting boundary condition that simulates an infinite propagation area.

For more information on the Automatically Matched Layer command, see Modeling exterior acoustic problems using automatically matched layers.

Step	Substep	Details	Related help topic
1. Simplify outer skin of the structural mesh.	a. If the structural mesh is a 3D mesh, create a 2D mesh from the 3D mesh.	Use the Surface Coat command to create a 2D skin mesh from the existing 3D structural mesh.	Surface coat of 2D elements
b. Defeature the 2D mesh.	Use commands, such as Remove Rib, to remove features from your model that are not significant to the frequency range of the analysis.	Rib detection and removal within a mesh
c. Remove holes from the 2D mesh that are not significant to the acoustic analysis.	Use the Mesh from Boundary command to fill holes in the 2D mesh with elements.	Creating a mesh inside an existing boundary
d. Make the 2D mesh a closed and manifold mesh.	Use the Thicken Mesh command to convert an open and non-manifold shell mesh into a closed and manifold mesh. This command ensures that the acoustic fluid is present on both sides of thin regions within the part.	Convex meshes for FEM acoustics analyses
2. Create a 2D mesh that wraps around the exterior surfaces of the part. This mesh defines the inner boundary of the fluid mesh.		If the structural mesh is a 3D mesh, you can use the Surface Wrap Recipe command with the Wrap Around the Exterior and the 2D Mesh Only options to create a 2D mesh that wraps around the entire exterior of the structural mesh.You can also use the Surface Coat command to create a 2D skin mesh from the existing mesh.	Surface Wrap RecipeSurface coat of 2D elements
3. Verify that the 2D mesh is closed and manifold.		Use the Element Edges command to verify that the mesh does not contain any free or non-manifold edges.	Checking for free and non-manifold element edges
4. Create the 2D mesh that defines the outer fluid boundary.		Use the Convex Mesh command to create a 2D shell mesh that surrounds the inner fluid boundary. This mesh corresponds to the outer boundary of the fluid domain.	Convex meshes for FEM acoustics analyses
5. Create the 3D acoustic fluid mesh between the inner and outer fluid boundaries.		Use the Solid from Shell command to fill the space between the inner and outer boundaries of the fluid domain with the 3D fluid mesh.Note: You can later define an Automatically Matched Layer simulation object on the outer free faces of the fluid mesh.	Solid from Shell meshingModeling exterior acoustic problems using automatically matched layers
6. Create a microphone mesh to output acoustic results, such as pressure.		Use the appropriate mesh or mesh primitive command to create a microphone mesh in the appropriate shape and location.	Using microphone mesh to capture analysis results

How do I

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Meshing for acoustic analyses

Supported element types for FEM acoustic analysis

Element size for acoustic analysis

Solution stabilization options

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Fluid materials for acoustic analyses

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Meshing for FEM acoustic analysis, Simcenter 3D 2021.1 Series

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