3.3. Diffuse Sound Field

You use the Diffuse Sound Field excitation condition to create random excitation waves. The diffuse sound field is approached by the asymptotic model summing a high number of uncorrelated plane waves with random phases from all directions in free space. For additional information, see the DFSWAVE section in the Mechanical APDL Command Reference.

Analysis Types

The Diffuse Sound Field excitation condition is available for Coupled Field Harmonic and Harmonic Acoustics analyses.

Common Characteristics

This section describes the characteristics of the boundary condition, including the application requirements, support limitations, and loading definitions and values.

Dimensional Types

3D Simulation: Supported.
2D Simulation: Not Supported.

Geometry Types: Geometry types supported for the Diffuse Sound Field excitation condition include:

Solid: Supported.
Surface/Shell: Supported.
Wire Body/Line Body/Beam: Not Supported.

Topology: The following topology selection options are supported for Diffuse Sound Field.

Body: Not Supported.
Face: Supported.
Edge: Not Supported.
Vertex: Not Supported.
Nodes: Not Supported.
Element: Not Supported.
Element Face: Not Supported.

Loading Data Definition: The Diffuse Sound Field excitation condition is defined as a constant.

Boundary Condition Application

To apply a Diffuse Sound Field:

On the Environment Context tab: select Acoustic Excitations > Diffuse Sound Field. Or, right-click the Environment tree object or click in the Geometry window and select Insert > Acoustics > Diffuse Sound Field.
Define the Scoping Method: options include Geometry Selection (default) and Named Selection. For either scoping type, you must use the Face selection filter (on the Graphics Toolbar) for geometry selection or Named Selection definition. Only faces specified in the structural Physics Region(s) can be selected or defined.
Define Coordinate System such that the +Z axis of the Cartesian coordinate system is consistent with the panel’s outward normal unit vector on the panel’s incident diffuse sound field side.

Details View Properties

The selections available in the Details view are described below.

Category	Fields/Options/Description
Scope	Scoping Method - Options include: Geometry Selection: This is the default setting and indicates that the boundary condition is applied to a geometry or geometries, you select using a graphical selection tools. Geometry: Visible when the Scoping Method is set to Geometry Selection. Displays the type of geometry (Face selection only) and the number of geometric entities (for example: 1 Face, 2 Faces) to which the boundary has been applied using the selection tools. Named Selection: This option Indicates that the geometry selection is defined by a Named Selection. Named Selection: Visible when the Scoping Method is set to Named Selection. This field provides a drop-down list of available user-defined Named Selections.
Definition	Type: Read-only field that displays boundary condition type - Diffuse Sound Field. Coordinate System: Drop-down list of available coordinate systems. Global Coordinate System is the default. For this Coordinate System selection, the positive Z axis (Cartesian) must align with the normal of the selected face or faces (the outward normal unit vector). Radius of Reference Sphere Define By, the options for this property include: Program Controlled: The application selects the Radius automatically. User Defined: This option enables you to specify the Radius. Reference Power Spectral Density: Entry field. The default value is `1 W/Hz`. Maximum Incident Angle: Entry field. The default value is `0°`. Suppressed - Include (No - default) or exclude (Yes) the boundary condition.
Base Medium	Material Assignment: Select a material to define material properties (Mass Density and Speed of Sound) of the Base Medium. Mass Density: Read-only field whose value is updated based on the selected Material Assignment. Speed of Sound: Read-only field whose value is updates based on the selected Material Assignment.
Advanced	Number of Divisions on the Reference Sphere: Entry field. The default value is `20`. Random Sampling Type: the options for this property include All (default), Multiple, and Single. Number of Samplings: Entry field. The default value is `1`. Norm Convergence Tolerance: Entry field. The default value is `0.05`. Frequency of Norm Convergence Check: Entry field. The default value is `5`.

Mechanical APDL References and Notes

The Mechanical APDL command DFSWAVE is used to apply the acoustic Diffuse Sound Field excitation condition. For more information, refer to the Random Excitation with Diffuse Sound Field section in the Mechanical APDL Acoustic Analysis Guide.

Important: Acoustic analyses use the MSOLVE command for the solution. This command creates multiple solutions for the analysis. As a result, the result file contains multiple solution sets for the loading condition. For the result types that have the By property under the Definition category, such as Total Deformation, the By property has only one option, Set. You can evaluate these results for a specific Set Number as desired.

API Reference

See the Diffuse Sound Field section of the ACT API Reference Guide for specific scripting information.