Defining acoustic impedance

You can model acoustic impedance by providing boundary impedances or nonreflecting boundaries for acoustic and coupled acoustic-structural analyses. Select InteractionCreate from the main menu bar, and select the surface to form an acoustic boundary. Acoustic impedance interactions are active only in dynamic steps that utilize the acoustic degree of freedom. You can create an acoustic impedance interaction in a static step; Abaqus ignores the acoustic effects in the static step but propagates the interaction through any applicable linear perturbation steps that follow. If you create an acoustic impedance interaction in a linear perturbation step, the interaction is not propagated to any of the subsequent steps.

See Also
Interaction editors
In Other Guides
Acoustic and Shock Loads

Context:

For a brief overview of acoustic impedance, see Understanding interactions. For a more detailed discussion, see Acoustic and Shock Loads.

  1. From the main menu bar, select InteractionCreate.

    Tip: You can also create an acoustic impedance interaction using the tool in the Interaction module toolbox.

  2. In the Create Interaction dialog box that appears, do the following:

    • Name the interaction. For more information about naming objects, see Using basic dialog box components.

    • Select the step. Acoustic impedance is active only in dynamic steps that utilize the acoustic degree of freedom.

    • Select the Acoustic impedance type of interaction.

  3. Click Continue to close the Create Interaction dialog box.
  4. Use one of the following methods to select the surface:

    • Use an existing surface to define the region. On the right side of the prompt area, click Surfaces. Select an existing surface from the Region Selection dialog box that appears, and click Continue.

      Note:

      The default selection method is based on the selection method you most recently employed. To revert to the other method, click Select in Viewport or Surfaces on the right side of the prompt area.

    • Use the mouse to select a region in the viewport. (For more information, see Selecting objects within the current viewport.)

      If the model contains a combination of mesh and geometry, click one of the following from the prompt area:

      • Click Geometry if you want to select the surface from a geometry region.

      • Click Mesh if you want to select the surface from a native or orphan mesh selection.

      You can use the angle method to select a group of faces or edges from geometry or a group of element faces from a mesh. For more information, see Using the angle and feature edge method to select multiple objects.

  5. In Definition field in the Edit Interaction dialog box that appears, choose one of the following:

    • Choose Tabular to define impedance using a table of admittance or impedance values in an acoustic impedance property.

    • Choose Nonreflecting to define nonreflecting boundaries for impedance.

  6. If you selected the Tabular definition option, select an acoustic impedance property. If desired, click to create the interaction property; see Defining an acoustic impedance interaction property.
  7. If you selected the Nonreflecting definition option, click the arrow to the right of the Nonreflecting type field; and select one of the options from the list that appears to define the nonreflecting geometry.

    • Select Planar to specify a radiation condition appropriate for plane waves normally incident to a planar boundary.

    • Select Improved planar to specify a radiation condition appropriate for plane waves with arbitrary angles of incidence. In linear perturbation steps, improved planar acoustic impedance interactions default to planar acoustic impedance interactions.

    • Select Circular to specify a radiation condition appropriate for a circular boundary in two dimensions or a right circular cylinder in three dimensions.

    • Select Spherical to specify a radiation condition appropriate for a spherical boundary.

    • Select Elliptical to specify a radiation condition appropriate for an elliptical boundary in two dimensions or a right elliptical cylinder in three dimensions.

    • Select Prolate spheroidal to specify a radiation condition appropriate for a prolate spheroidal boundary.

  8. If you selected the Circular or Spherical nonreflecting definition option, enter the radius of the circle or sphere defining the boundary surface in the Radius field.
  9. If you selected the Elliptical or Prolate spheroidal nonreflecting definition option, perform the following steps:
    1. In the Axis length field, enter the semimajor axis length, a, of the ellipse or prolate spheroid defining the surface. a is 1/2 of the maximum distance between two points on the ellipse or spheroid, analogous to the radius of a circle or sphere.
    2. In the Eccentricity field, enter the eccentricity, ϵ, of the ellipse or prolate spheroid. The eccentricity is the square root of one minus the square of the ratio of the semiminor axis, b, to the semimajor axis, a: ϵ=1-(b/a)2.
    3. In the Center coordinates field, enter the X-coordinate, Y-coordinate, and Z-coordinate of the center of the ellipse or prolate spheroid defining the radiating surface.
    4. In the Direction cosine field, enter the X-component, Y-component, and Z-component of the direction cosine of the major axis of the ellipse or prolate spheroid defining the radiating surface.