3.16. Free Surface

This boundary condition enables you to specify a plane as a free surface in order to consider sloshing effects on your model. You should define an Acceleration load as well with Gravitational Acceleration values to properly define the sloshing problem.

Note:  The free surface must be aligned with the coordinate plane in the Global Cartesian Coordinate System. The gravitational acceleration input should always be positive regardless of how the model is set up.

Analysis Types

The Free Surface 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 Free Surface 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 Free Surface.

  • Body: Not Supported.

  • Face: Supported.

  • Edge: Not Supported.

  • Vertex: Not Supported.

  • Nodes: Not Supported.

  • Element: Not Supported.

  • Element Face: Not Supported.

Loading Data Definition: Not applicable.

Boundary Condition Application

To apply a Acoustic Free Surface:

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

  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 - Free Surface.

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

Mechanical APDL References and Notes

This boundary condition is applied using the FREE label of the SF command. Refer to the Free Surface (Sloshing Effect) Sources section in the Mechanical APDL Acoustic Analysis Guide for more information.