# PorousFlowDarcyVelocityComponentLowerDimensional

Darcy velocity on a lower-dimensional element embedded in a higher-dimensional mesh. Units m3.s-1.m-2, or m.s-1. Darcy velocity = -(k_ij * krel /(mu * a) (nabla_j P - w_j)), where k_ij is the permeability tensor, krel is the relative permeability, mu is the fluid viscosity, P is the fluid pressure, a is the fracture aperture and w_j is the fluid weight. The difference between this AuxKernel and PorousFlowDarcyVelocity is that this one projects gravity along the element's tangent direction. NOTE! For a meaningful answer, your permeability tensor must NOT contain terms that rotate tangential vectors to non-tangential vectors.

This AuxKernel records the Darcy velocity within a lower-dimensional element living in a higher-dimensional mesh. For instance, to study flow within a fractured material, you might have created a 3D mesh with its own 3D subdomains (blocks of elements representing different aquifers and aquitards, for example) and within that 3D mesh you might have included 2D elements to represent the fractures. Those 2D elements must share nodes with the 3D elements for the MOOSE model to make sense. The 2D elements belong to a different set of subdomains, and those subdomains typically have different Material properties assigned to them (for example, high permeability and porosity). If you want to measure Darcy velocity within those lower-dimensional subdomains, then use this AuxKernel.

This AuxKernel calculates the x, y, or z component of the Darcy velocity for fluid phase , where and are projected onto the tangent direction of the lower-dimensional element. All parameters are defined in the nomenclature.

Notice that the denominator of this expression includes , which is the fracture aperture. If the user doesn't want to divide by , the default value of should be used. However, it is likely that when using this AuxKernel the dimensions of permeability will be m, because of a pre-multiplication by the fracture aperture. The denominator includes so that the unconventional units of permeability may be accounted for if desired.

note

As this AuxKernel uses material properties, only elemental (Monomial) AuxVariables can be used. The AuxVariables must be defined on the lower-dimensional subdomain only.

warning

For the result to make sense, the permeability tensor, , must not rotate tangential vectors to non-tangential vectors. For instance, an isotropic permeability tensor is sensible.

## Input Parameters

• variableThe name of the variable that this object applies to

C++ Type:AuxVariableName

Options:

Description:The name of the variable that this object applies to

• componentThe spatial component of the Darcy flux to return

C++ Type:MooseEnum

Options:x y z

Description:The spatial component of the Darcy flux to return

• PorousFlowDictatorThe UserObject that holds the list of PorousFlow variable names

C++ Type:UserObjectName

Options:

Description:The UserObject that holds the list of PorousFlow variable names

• gravityGravitational acceleration vector downwards (m/s^2)

C++ Type:libMesh::VectorValue

Options:

Description:Gravitational acceleration vector downwards (m/s^2)

### Required Parameters

• aperture1.0Aperture of the fracture

Default:1.0

C++ Type:std::vector

Options:

Description:Aperture of the fracture

• execute_onLINEAR TIMESTEP_ENDThe list of flag(s) indicating when this object should be executed, the available options include NONE, INITIAL, LINEAR, NONLINEAR, TIMESTEP_END, TIMESTEP_BEGIN, FINAL, CUSTOM.

Default:LINEAR TIMESTEP_END

C++ Type:ExecFlagEnum

Options:NONE INITIAL LINEAR NONLINEAR TIMESTEP_END TIMESTEP_BEGIN FINAL CUSTOM

Description:The list of flag(s) indicating when this object should be executed, the available options include NONE, INITIAL, LINEAR, NONLINEAR, TIMESTEP_END, TIMESTEP_BEGIN, FINAL, CUSTOM.

• boundaryThe list of boundary IDs from the mesh where this boundary condition applies

C++ Type:std::vector

Options:

Description:The list of boundary IDs from the mesh where this boundary condition applies

• fluid_phase0The index corresponding to the fluid phase

Default:0

C++ Type:unsigned int

Options:

Description:The index corresponding to the fluid phase

• blockThe list of block ids (SubdomainID) that this object will be applied

C++ Type:std::vector

Options:

Description:The list of block ids (SubdomainID) that this object will be applied

### Optional Parameters

• control_tagsAdds user-defined labels for accessing object parameters via control logic.

C++ Type:std::vector

Options:

Description:Adds user-defined labels for accessing object parameters via control logic.

• enableTrueSet the enabled status of the MooseObject.

Default:True

C++ Type:bool

Options:

Description:Set the enabled status of the MooseObject.

• seed0The seed for the master random number generator

Default:0

C++ Type:unsigned int

Options:

Description:The seed for the master random number generator

• use_displaced_meshFalseWhether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.

Default:False

C++ Type:bool

Options:

Description:Whether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.