Richards’ Equation Model

The node adds Richards’ equation (Equation 4-14) for flow in variably saturated porous media and provides an interface for defining the fluid properties as well as the retention model. The source term can be included as separate feature.

The default uses the (the material defined for the domain). Select another material as needed.

The default ρ (SI unit: kg/m3) uses values based on selected. For enter another value or expression. The default is 0 kg/m3.

The default μ (SI unit: Pa·s) uses values based on the selected. For enter another value or expression. The default is 0 Pa·s.

	If Hydraulic conductivity is selected as the Permeability model (see the Matrix Properties section), dynamic viscosity is not available. The hydraulic conductivity is defined using a combination of fluid and matrix properties and replaces the need of defining the dynamic viscosity.

The default uses the (the material defined for the domain) for the porous matrix. Select another material as needed.

Select a to specify the capacity of the porous material to transmit flow. Select to define the permeability of the porous matrix, to define a combination of fluid permeability and dynamic viscosity, or to define the permeability from the porosity and mean particle diameter.

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For κs (SI unit: m2) the default uses values as defined by the selected. For select to define a scalar value or , , or to enter a tensor value.

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For Ks (SI unit: m/s) enter a value or expression. Select to define a scalar value or , , or to enter a tensor value.

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For , enter a value or expression for the mean particle diameter dp (SI unit: m), the default value is 0.5 mm.

The property that defines the pore volume in Richards’ Equation is the θs. Enter a value, which is a fraction (a dimensionless number between 0 and 1). The default is 0.25.

If there is a residual volume of liquid that cannot move through the pore network, also enter a θr. Enter a value, which is a fraction (a dimensionless number between 0 and 1). The default is 0.

Select a S (SI unit: 1/Pa) — or . For enter a S (SI unit: 1/Pa) value or expression. Select to use the following linear equation to define the storage:

This expression is equivalent to the Reuss average of the fluid and solid compressibilities. Enter the value or expression for these properties to define the linear storage — χf (SI unit: 1/Pa) and χp (SI unit: 1/Pa).

Select a — , , or .

Select to use the retention model according to van Genuchten (see Equation 4-15). Then enter the values for these . The constitutive parameter m is equal to 1 − 1 / n.

Select to use the retention model according to Brooks and Corey (see Equation 4-16). The same parameters as for the van Genuchten model also define the Brook and Corey model: α, n, and l.

Select to specify a retention model in Equation 4-14, instead of van Genuchten (Equation 4-15) or Brooks and Corey (Equation 4-16) models:

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θ. The default is θs (the thetas variable).

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Cm (SI unit: 1/m). The default is 0 (1/m).