*ACOUSTIC MEDIUM

Specify an acoustic medium.

This option is used to define the properties of an acoustic medium used with acoustic or coupled poroelastic acoustic elements. The ACOUSTIC MEDIUM option must be used in conjunction with the MATERIAL option. The ACOUSTIC MEDIUM option can be used multiple times to specify all the properties of an acoustic medium.

This page discusses:

Optional, mutually exclusive parameters

BULK MODULUS

Include this parameter to define the bulk modulus for the acoustic medium (default).

CAVITATION LIMIT

This parameter applies only to Abaqus/Explicit analyses.

Include this parameter to define the cavitation pressure limit for the acoustic medium. When the fluid absolute pressure drops to this limit, the acoustic medium undergoes free volume expansion or cavitation without a further decrease in the pressure. A negative cavitation limit value represents an acoustic medium that is capable of sustaining a negative absolute pressure up to the specified limit value. Any nonzero initial acoustic static pressure values such as those due to the atmospheric pressure and/or the hydrostatic loading can be specified using the INITIAL CONDITIONS, TYPE=ACOUSTIC STATIC PRESSURE option.

If this parameter is omitted, the fluid is assumed not to cavitate even under arbitrarily large negative pressure conditions.

COMPLEX BULK MODULUS

Include this parameter to define the complex bulk modulus for the acoustic medium.

COMPLEX DENSITY

Include this parameter to define the complex density for the acoustic medium.

POROUS MODEL

This parameter applies only to Abaqus/Standard analyses.

Set POROUS MODEL=DELANY BAZLEY or DELANY-BAZLEY (default) to use the Delany-Bazley model to compute the frequency-dependent complex density and the complex bulk modulus.

Set POROUS MODEL=MIKI to use the Delany-Bazley-Miki model to compute the frequency-dependent complex density and the complex bulk modulus.

Set POROUS MODEL=BIOT-JOHNSON to use the model of Biot and Johnson et al. to compute the frequency-dependent properties of the coupled poroelastic acoustic material.

Set POROUS MODEL=BIOT-ATALLA to use the coupled poroelastic-acoustic material model of Biot and Atalla et al. together with the COMPLEX BULK MODULUS and COMPLEX DENSITY parameters specified as separate options.

VOLUMETRIC DRAG

Include this parameter to define the volumetric drag coefficient for the acoustic medium.

Optional parameters

DEPENDENCIES

Set this parameter equal to the number of field variable dependencies included in the definition of the acoustic medium, in addition to temperature. If this parameter is omitted, it is assumed that the acoustic medium property is constant or depends only on temperature. See Material Data Definition for more information.

Data lines to define the bulk modulus of an acoustic material

First line

  1. Bulk modulus. (Units of FL−2.)

  2. Temperature.

  3. First field variable.

  4. Second field variable.

  5. Etc., up to six field variables.

Subsequent lines (only needed if the DEPENDENCIES parameter has a value greater than six)

  1. Seventh field variable.

  2. Etc., up to eight field variables per line.

Repeat this set of data lines as often as necessary to define the bulk modulus as a function of temperature and other predefined field variables.

Data lines to define the cavitation pressure limit of an acoustic material

First line

  1. Cavitation pressure limit. (Units of FL−2.)

  2. Temperature.

  3. First field variable.

  4. Second field variable.

  5. Etc., up to six field variables.

Subsequent lines (only needed if the DEPENDENCIES parameter has a value greater than six)

  1. Seventh field variable.

  2. Etc., up to eight field variables per line.

Repeat this set of data lines as often as necessary to define the cavitation pressure limit as a function of temperature and other predefined field variables.

Data line to define the complex bulk modulus of an acoustic material

First line

  1. Real part of the bulk modulus. (Units of FL−2.)

  2. Imaginary part of the bulk modulus. (Units of FL−2.)

  3. Frequency. (Units of T−1.)

Repeat this data line as often as necessary to define the complex bulk modulus as a function of frequency.

Data line to define the complex density of an acoustic material

First line

  1. Real part of the density. (Units of ML−3.)

  2. Imaginary part of the density. (Units of ML−3.)

  3. Frequency. (Units of T−1.)

Repeat this data line as often as necessary to define the complex density as a function of frequency.

Data lines to define the volumetric drag of an acoustic material

First line

  1. Volumetric drag coefficient. (Units of FTL−4.)

  2. Frequency. (Cycles/time.) Frequency dependence is active only during frequency domain procedures in Abaqus/Standard.

  3. Temperature.

  4. First field variable.

  5. Second field variable.

  6. Etc., up to five field variables.

Subsequent lines (only needed if the DEPENDENCIES parameter has a value greater than five)

  1. Sixth field variable.

  2. Etc., up to eight field variables per line.

Repeat this set of data lines as often as necessary to define the volumetric drag as a function of frequency, temperature, and other predefined field variables.

Data line when POROUS MODEL=DELANY BAZLEY, DELANY-BAZLEY, or MIKI

First (and only) line

  1. Flow resistivity. (Units of FTL−4.)

Data line when POROUS MODEL=BIOT-ATALLA

First (and only) line

  1. Fluid density. (Units of ML−3.)

  2. Tortuosity. (Dimensionless.)

  3. Structural material bulk modulus. (Units of FL−2.)

  4. Fluid-structure coupling factor. (Dimensionless, default=1.)

Data lines when POROUS MODEL=BIOT-JOHNSON

First line

  1. Fluid density. (Units of ML−3.)

  2. Tortuosity. (Dimensionless.)

  3. Structural material bulk modulus. (Units of FL−2.)

  4. Fluid-structure coupling factor. (Dimensionless, default=1.)

Second line

  1. Static flow resistivity. (Units of FTL−4.)

  2. Viscous characteristic length. (Units of L.)

  3. Thermal characteristic length. (Units of L.)

  4. Fluid dynamic shear viscosity. (Units of MT−1L−1.)

  5. Ambient fluid standard pressure. (Units of FL−2.)

  6. Ambient fluid heat capacity ratio of the specific heat per unit mass at constant pressure over the specific heat per unit mass at constant volume. (Dimensionless.)

  7. Prandtl number, the ratio of viscous diffusion rate over the thermal diffusion rate. (Dimensionless.)

 

See Also
Acoustic Medium
Poroelastic Acoustic Medium