*DIFFUSIVITY

Specify mass diffusivity or slurry concentration diffusivity.

This option is used to define the mass diffusivity of a material diffusing through a base material in a mass-diffusion analysis (Mass Diffusion Analysis) or to define the diffusivity of particles in a slurry flow during a coupled pore fluid flow and stress analysis (Coupled Pore Fluid Diffusion and Stress Analysis).

If the DIFFUSIVITY option is used to define mass diffusivity in a mass diffusion analysis, it must be used in conjunction with the SOLUBILITY option.

This page discusses:

Defining mass diffusivity of a material diffusing through a base material in a mass-diffusion analysis
Defining the diffusivity of particles in a slurry flow during a coupled pore fluid flow and stress analysis

Defining mass diffusivity of a material diffusing through a base material in a mass-diffusion analysis

Optional parameters

DEPENDENCIES

Set this parameter equal to the number of field variables included in the definition of diffusivity. If this parameter is omitted, the diffusivity is assumed not to depend on any field variables but might still depend on concentration and temperature. See Material Data Definition for more information.

LAW

Set LAW=GENERAL (default) to choose general mass diffusion behavior.

Set LAW=FICK to choose Fick's diffusion law.

LAW=FICK and the KAPPA, TYPE=TEMP option are mutually exclusive.

TYPE

Set TYPE=ISO (default) to define isotropic diffusivity. Set TYPE=ORTHO to define orthotropic diffusivity. Set TYPE=ANISO to define fully anisotropic diffusivity.

Data lines to define isotropic mass diffusivity (TYPE=ISO)

First line

Diffusivity, D. (Units of L²T⁻¹.)
Concentration, c.
Temperature, $θ$ .
First field variable.
Second field variable.
Etc., up to five field variables.

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

Sixth field variable.
Etc., up to eight field variables per line.

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

Data lines to define mass orthotropic diffusivity (TYPE=ORTHO)

First line

$D_{11}$ . (Units of L²T⁻¹.)
$D_{22}$ .
$D_{33}$ .
Concentration, c.
Temperature, $θ$ .
First field variable.
Second field variable.
Third field variable

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

Fourth field variable.
Etc., up to eight field variables per line.

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

Data lines to define anisotropic mass diffusivity (TYPE=ANISO)

First line

$D_{11}$ . (Units of L²T⁻¹.)
$D_{12}$ .
$D_{22}$ .
$D_{13}$ .
$D_{23}$ .
$D_{33}$ .
Concentration, c.
Temperature, $θ$ .

Subsequent lines (only needed if the DEPENDENCIES parameter is used)

First field variable.
Etc., up to eight field variables per line.

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

Defining the diffusivity of particles in a slurry flow during a coupled pore fluid flow and stress analysis

Optional parameters

DEPENDENCIES

SLURRY

This parameter applies only to Abaqus/Standard analyses.

Include this parameter to define the diffusivity of the particles in a slurry in a geotechnical analysis that models slurry transport and placement. The diffusivity of the particles must be isotropic.

This parameter cannot be used in conjunction with the LAW and TYPE parameters.

TYPE

Set TYPE=ISO to define isotropic diffusivity.

Data lines to define the diffusivity of the particles in a slurry

First line

Diffusivity, D. (Units of L²T⁻¹.)
Temperature, $θ$ .
First field variable.
Second field variable.
Etc., up to six field variables.

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

Seventh field variable.
Eighth field variable.

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