3.12. Impedance Boundary

This boundary condition enables you to specify a complex form of impedance on an acoustic surface. It requires Resistance, Reactance, and Frequency entries. Refer to the Surface Impedance Boundary section in the Mechanical APDL Acoustic Analysis Guide for more information.

The application defines complex impedance on a selected surface based on the inputs to the Acoustic Impedance Boundary using the command: SF,Nlist,IMPD,VALUE,VALUE2.

The application calculates VALUE and VALUE2 using the following impedance and admittance definitions:

Impedance

The equation for Impedance:

where:

Admittance

The equation for Admittance (Y) = Inverse of Impedance:

where:

In Mechanical, you can use Impedance Boundary to define impedance or admittance (Modal Acoustics). The VALUE and VALUE2 fields for the SF command are based upon the Resistance and Reactance entries.

Harmonic Acoustics

VALUE = Resistance

VALUE2 = Reactance

Modal Acoustics

If Reactance = 0 (Impedance):

VALUE = Resistance
VALUE2 = 0

If Reactance != 0 (Admittance):

Analysis Types

The Impedance Boundary loading condition is available for Coupled Field Harmonic, Coupled Field Modal, Coupled Field Transient, Harmonic Acoustics, and Modal Acoustics analyses.

Common Characteristics

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

Types Supported

  • 3D Simulation: Supported.

  • 2D Simulation: Not Supported.

Geometry Types: Geometry types supported for the Impedance Boundary include:

  • Solid: Supported.

  • Surface/Shell: Not Supported.

  • Wire Body/Line Body/Beam: Not Supported.

Topology: The following topology selection options are supported for Impedance Boundary.

  • Body: Not Supported.

  • Face: Supported.

  • Edge: Not Supported.

  • Vertex: Not Supported.

  • Nodes: Not Supported.

  • Element: Not Supported.

  • Element Face: Not Supported.

Loading Data Definition: Enter loading data using one of the following options.

  • Constant

  • Tabular (Frequency Varying): Supported for Harmonic Acoustics only.

Boundary Condition Application

To apply a Impedance Boundary:

  1. On the Environment Context tab: click Acoustic Boundary Conditions> Impedance Boundary . Or, right-click the Environment tree object or in the Geometry window and select Insert>Acoustics>Impedance Boundary.

  2. Define the Scoping Method.

  3. Define the Resistance, Reactance, and Frequency of the Acoustic Impedance Boundary based on the above selections.

Details View Properties

The selections available in the Details view are described below.

CategoryFields/Options/Description
Scope

Scoping Method, options include:

  • Geometry Selection: Default setting, indicating that the boundary condition is applied to a geometry or geometries, which are chosen using a graphical selection tools.

    • Geometry (Face selection only): Visible when the Scoping Method property is set to Geometry Selection. Geometry selections must be made on bodies specified in the acoustic Physics Region.

      Use the Face selection filter to pick your geometry, click in the Geometry field, and then click the Apply button that displays. After you select the geometry, this property displays the geometric entities (1 Face, 3 Faces, etc.).

  • Named Selection: 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 (face-based only).

Definition

Type: Read-only field that describes the object - Impedance Boundary.

Resistance: Specify the resistance. This property can be designated as a parameter.

Reactance: Specify the reactance. This property can be designated as a parameter.

Frequency (Modal Acoustics): Specify a frequency value. This property is displayed for Modal Acoustics analyses when the Reactance property is specified as greater than zero or if it is parameterized. This property can be designated as a parameter.

Suppressed: Include (No - default) or exclude (Yes) the boundary condition.

Mechanical APDL References and Notes

Impedance Boundary is applied using the IMPD label of SF command.

API Reference

See the Impedance Boundary section of the ACT API Reference Guide for specific scripting information.