Abaqus Keywords Reference Guide  
How to find keyword examples

*IMPEDANCE
Define impedances for acoustic analysis.

This option is used to provide boundary impedances or nonreflecting boundaries for acoustic and coupled acoustic-structural analyses.

Products: Abaqus/Standard  Abaqus/Explicit  

Type: History data

Level: Step

References:

Required, mutually exclusive parameters: 

PROPERTY

Set this parameter equal to the name of the *IMPEDANCE PROPERTY option defining the table of impedance values to be used.

NONREFLECTING

Set NONREFLECTING=PLANAR (default) to specify the impedance corresponding to that of a normal incidence plane wave.

Set NONREFLECTING=IMPROVED to specify the impedance corresponding to that of a plane wave at an arbitrary angle of incidence. This parameter can be used only for transient dynamics.

Set NONREFLECTING=CIRCULAR to specify a radiation condition appropriate for a circular boundary in two dimensions or a right circular cylinder in three dimensions.

Set NONREFLECTING=SPHERICAL to specify a radiation condition appropriate for a spherical boundary.

Set NONREFLECTING=ELLIPTICAL to specify a radiation condition appropriate for an elliptical boundary in two dimensions or a right elliptical cylinder in three dimensions.

Set NONREFLECTING=PROLATE SPHEROIDAL to specify a radiation condition appropriate for a prolate spheroidal boundary.

Optional parameter:

OP

Set OP=MOD (default) to modify existing impedances or to define additional impedances.

Set OP=NEW if all existing impedances applied to the model should be removed. To remove only selected impedances, use OP=NEW and respecify all impedances that are to be retained.

Data line to define an impedance for PROPERTY, NONREFLECTING=PLANAR, or NONREFLECTING=IMPROVED: 

First (and only) line:

  1. Element number or element set label.

  2. Surface impedance type label, In, for impedance on face n.

Data line to define an absorbing boundary impedance for NONREFLECTING=CIRCULAR or NONREFLECTING=SPHERICAL: 

First (and only) line:

  1. Element number or element set label.

  2. Surface impedance type label, In, for impedance on face n.

  3. , the radius of the circle or sphere defining the absorbing boundary surface.

Data line to define an absorbing boundary impedance for NONREFLECTING=ELLIPTICAL or NONREFLECTING=PROLATE SPHEROIDAL: 

First (and only) line:

  1. Element number or element set label.

  2. Surface impedance type label, In, for impedance on face n.

  3. The semimajor axis, 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.

  4. The eccentricity, , 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: .

  5. Global X-coordinate of the center of the ellipse or prolate spheroid defining the radiating surface.

  6. Global Y-coordinate of the center of the ellipse or prolate spheroid defining the radiating surface.

  7. Global Z-coordinate of the center of the ellipse or prolate spheroid defining the radiating surface.

  8. X-component of the direction cosine of the major axis of the ellipse or prolate spheroid defining the radiating surface. The components of this vector need not be normalized to unit magnitude.

  9. Y-component of the direction cosine of the major axis of the ellipse or prolate spheroid defining the radiating surface.

  10. Z-component of the direction cosine of the major axis of the ellipse or prolate spheroid defining the radiating surface.