ISO Power (ISO3744) Mesh Primitives

You can use the ISO Power (ISO3744) command to create mesh primitives to model a microphone array based on the standards for determining sound power levels specified in the ISO 3744 publication. Each node in the mesh primitive represents a microphone location and comprises the measurement surface. You can use ISO Power (ISO374) primitives, for example, to simulate semi-anechoic test conditions.

You can use the Definition Type options to create an ISO Power (ISO374) primitive to position microphones in the following shapes to measure sound pressure:

• A spherical or hemispherical surface

• A rectangular parallelepiped (box)

Selecting the model around which to create the primitive

Use the Select Model at the Center option to select all or a part of the model that defines the sound source. The software creates the ISO power primitive to envelop the model or a portion of the model.

Creating a spherical or hemispherical primitive

If you select the Fine or Coarse options from the Definition Type list, the software creates a microphone array in the shape of a sphere or a hemisphere. Each node represents a microphone location. This type of array is generally useful when the sound source is located in a larger or open area under satisfactory acoustical conditions, and a larger measurement distance is appropriate.

• Select the Fine definition type to create a mesh with microphone locations in 10 key positions and in 9 additional positions, as specified in ISO 3744. By default, the software creates a spherical mesh. To create a hemispherical mesh, you can use the Cutting Plane option to model the half of the mesh that you need for the analysis.(1) Model that defines the sound source (2) Spherical, fine ISO 3744 mesh primitive(1) Model that defines the sound source (2) Hemispherical, fine ISO 3744 mesh primitive created by applying a cutting plane in the XY direction

• Select the Coarse definition type to create a spherical mesh with microphone locations in 10 key positions only as specified in ISO 3744. By default, the software creates a spherical mesh. To create a hemispherical mesh, you can use the Cutting Plane option to model the half of the mesh that you need for the analysis.(1) Model that defines the sound source (2) Spherical, coarse ISO 3744 mesh primitive(1) Model that defines the sound source (2) Hemispherical, coarse ISO 3744 mesh primitive created by applying a cutting plane in the XY direction

Note:

The key microphone locations are selected to minimize the errors that can be caused by interference between the sound wave reaching the microphone directly and the wave reflected by cutting plane. These locations are described in the ISO 3744 publication.

For more information on trimming mesh primitives with cutting planes, see Trimming mesh primitives with cutting planes.

Creating a parallelepiped primitive

If you select the Parallelepiped option from the Model Definition list, the software creates a box-shaped mesh around the sound source. The perpendicular distance between the mesh primitive and the measurement surface in the source model is always 1m. This type of array is generally useful when the sound source is located in a room or in a space with unfavorable acoustic conditions, such as many reflecting objects or lots of background noise. In those cases, a smaller measurement distance is necessary.

(1) Model that defines the sound source (2) ISO 3744 parallelepiped primitive

By default, the software creates a 2D mesh comprised of triangular elements You can also use the Refinement Level option to specify a positive integer factor greater than 1 that the software uses to further refine the mesh, which increases the number of microphone locations according to specifications in ISO 3744.

By default, software tries to create microphone locations that are approximately 3m apart in all directions. Between those locations, the software creates the smallest possible number of equal-sized elements. These elements have a maximum edge length equal to 3m. As you increase the Refinement Level value, the software reduces the distance between microphone points and increases the number of element layers in all directions. For example:

Refinement Level of 1 (4 elements per face)	Refinement Level of 2 (16 elements per face)	Refinement Level of 3 (36 elements per face)

Using a cutting plane to trim an ISO 3744 mesh primitive

You can use the Cutting Plane option to divide an ISO Power (ISO3744) primitive in half along the XY, YZ, or ZX planes. Use this option when you need to model only a portion of the primitive for your analysis.

(1) Model that defines the sound source (2) ISO 3744 parallelepiped primitive trimmed with an XY cutting plane

Note:

With an ISO Power (ISO3744) mesh primitive, the software always creates the cutting plane through the center of the primitive.

For more information on trimming mesh primitives with cutting planes, see Trimming mesh primitives with cutting planes.

Where do I find it?

Application	Pre/Post
Prerequisites	A FEM file as the work part and displayed partSimcenter Nastran or Simcenter 3D Acoustics BEM as the specified solver
Command Finder	ISO Power (ISO3744) Mesh Primitive

Learn more

Mesh primitives for acoustics and vibro-acoustics analysis

Mesh primitive types for acoustics and vibro-acoustics analysis

Trimming mesh primitives with cutting planes

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ISO Power (ISO3744) Mesh Primitives, Simcenter 3D 2021.1 Series

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