Porous Medium
The Porous Medium node adds the equations for modeling flow through porous domains. By default these are Equation 4-6 and Equation 4-7 (excluding any mass sources).
(4-6)
(4-7)
For a steady-state problem the first term in Equation 4-6 disappears. When Gravity is active Equation 4-7 is of the following form:
(4-8)
The Porous Medium feature has two default subfeatures — the Fluid subfeature where the fluid density ρ (SI unit: kg/m3) and dynamic viscosity μ (SI unit: Pa·s) are defined and the Porous Matrix subfeature where the permeability κ (SI unit: m2) and porosity εp (dimensionless) are specified.
Coordinate System Selection
Select a coordinate system from the Coordinate system list for the interpretation of directions in anisotropic material properties. The default is the Global coordinate system, and the list contains any additional orthonormal coordinate system (except boundary coordinate systems) added under the Definitions node.
The subnodes inherit these coordinate system settings. In particular, the Permeability or Hydraulic conductivity (in the Porous Matrix subnode) should be set according to the coordinate system selected in this section.
Flow Model
Define if the flow follows a linear or nonlinear pressure-velocity relationship.
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Darcian flow (default) defines a linear relationship using Equation 4-6 and Equation 4-7.
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Non-Darcian flow defines a nonlinear relationship using Equation 4-6 and
where the nonlinear parameter β (SI unit: 1/m) is further specified in the Porous Matrix subfeature.
Storage Model
Equation 4-6 can also be formulated with respect to a storage term.
(4-9)
The storage coefficient S can be interpreted as the weighted compressibility of the porous material and the fluid. Define the time dependent storage term by selecting one of the following options from the drop-down menu:
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From density and porosity (default), uses the formulation of Equation 4-6
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Linearized storage, where the following linear equation is used to define the storage:
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Poroelastic storage, where S = εpχf
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Quasistatic, where the storage term is set to zero
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User defined to directly specify the storage coefficient S
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Porous Material in the COMSOL Multiphysics Reference Manual
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About Darcian and Non-Darcian Flow in the Porous Media Flow Module User’s Guide
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Storage Model in the Subsurface Flow Module User’s Guide
Note that some options are only available in some modules. For a detailed overview of the functionality available in each product, visit https://www.comsol.com/products/specifications/