3.17. Thermo-Viscous BLI Boundary

Acoustic waves propagating in viscous-thermal media include a complex propagating constant in the frequency domain. The attenuation of the acoustic wave is proportional to the shear and bulk viscosity and the thermal conduction coefficient of the media. The interaction between the viscous fluid and rigid walls is taken into account using the Thermo-Viscous BLI Boundary condition.

Analysis Types

The Thermo-Viscous BLI Boundary loading condition is available for Coupled Field Harmonicand 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 Thermo-Viscous BLI Boundary boundary condition include:

  • Solid: Supported.

  • Surface/Shell: Not Supported.

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

Topology: The following topology selection options are supported for Thermo-Viscous BLI Boundary.

  • Body: Not Supported.

  • Face: Supported.

  • Edge: Not Supported.

  • Vertex: Not Supported.

  • Nodes: Not Supported.

  • Element Face: Not Supported.

  • Element: Not Supported.

Loading Data Definition: Not applicable.

Boundary Condition Application

To apply an Thermo-Viscous BLI Boundary:

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

  2. Define the Scoping Method.

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 - Thermo-Viscous BLI Boundary.

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

Mechanical APDL References and Notes

This boundary condition is applied using the BLI label of SF command. For additional information, see the Boundary Layer Impedance (BLI) Model topic in the Mechanical APDL Acoustic Analysis Guide.

API Reference

See the Thermo-Viscous BLI Boundary section of the ACT API Reference Guide for specific scripting information.