Defining normal flow across gap surfaces

You can model normal flow across gap surfaces by defining a fluid leak-off coefficient for the pore fluid material. This coefficient defines a pressure-flow relationship between the cohesive element's middle nodes and their adjacent surface nodes. The fluid leak-off coefficients can be interpreted as the permeability of a finite layer of material on the cohesive element surfaces. See the following sections for more information:

  1. From the menu bar in the Edit Material dialog box, select OtherPore FluidFluid Leakoff.

    (For information on displaying the Edit Material dialog box, see Creating or editing a material.)

  2. Click the arrow to the right of the Type field, and specify how you want to define the fluid leak-off coefficients:

    • Select Coefficients to enter the coefficients directly in the Edit Material dialog box.

    • Select User to define the coefficients in user subroutine UFLUIDLEAKOFF. If you select this option, skip to Step 6.

  3. Toggle on Use temperature-dependent data to define the fluid leak-off coefficients as a function of temperature.

    A column labeled Temp appears in the Data table.

  4. Click the arrows to the right of the Number of field variables field to increase or decrease the number of field variables on which the fluid leak-off coefficients depend.
  5. Enter the following data in the Data table:

    Top Coefficient

    Fluid leak-off coefficient at the top element surface.

    Bottom Coefficient

    Fluid leak-off coefficient at the bottom element surface.

    Temp

    Temperature.

    Field n

    Predefined field variables.

    For detailed information on how to enter data, see Entering tabular data.

  6. Click OK to close the Edit Material dialog box. Alternatively, you can select another material behavior to define from the menus in the Edit Material dialog box (see Browsing and modifying material behaviors, for more information).