HydroGeoSphere/Specified Flux

This is also known as a second-type, Neumann, specified or constant flux boundary condition. It is an areal property and so you should first choose the subset of faces for which you want to apply the condition. These faces should normally be part of the outer boundary of the grid.

The following instructions can be used as input to the Type instruction inside the Boundary condition...End instruction group to assign various specified flux boundary conditions:

Flux

Sets the input type to be a general specified flux boundary condition and converts fluxes to nodal volumetric fluxes [L³ T⁻¹] by multiplying by the contributing area of the chosen face.

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For example:

boundary condition
    type
    flux

    face set
    top

    time raster table
    0.0    recharge.asc
    end

end ! new specified head

would define a specified flux that is mapped from the raster file recharge.asc and is applied from time zero for the duration of the simulation for all of the nodes contained in the face set top.

Rain

Sets the input type to be a general specified flux boundary condition and converts fluxes to nodal volumetric fluxes [L³ T⁻¹] by multiplying by the contributing area of the chosen face when projected onto the xy-plane.

• • •

Flux nodal

Sets the input type to be a general specified flux boundary condition and treats the fluxes as nodal volumetric fluxes [L³ T⁻¹] which are applied directly to nodes in the given node set.

• • •

For example:

boundary condition
    type
    flux nodal

    node set
    top

    time file table
    0.0 nflux.txt
    end

end ! new specified head

would assign a specified nodal flux that is read from the input file nflux.txt and is applied from time zero for the duration of the simulation for all of the nodes contained in the node set top. Note that the number of entries in the file must be the same as the number of nodes in the set.

These fluxes can be interpolated or turned on and off as discussed in Section 5.7. In cases where flux boundary inputs overlap, fluid fluxes will be accumulated. Note that the definition of wells or tile drains (see Section 5.8.2.4) in the problem may create a non-zero specified flux boundary condition.