GMS:Conductance: Difference between revisions
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Darcy's law states: | Darcy's law states: | ||
[[Image:eq_cond1. | [[Image:eq_cond1.png]] | ||
<!--{{hide in print| <math>\ Q=kiA</math>}}--> | <!--{{hide in print| <math>\ Q=kiA</math>}}--> | ||
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Darcy's law can also be expressed as: | Darcy's law can also be expressed as: | ||
[[Image:eq_cond2. | [[Image:eq_cond2.png]] | ||
<!--<math>\ Q=k \frac{\Delta H}{L} A</math>--> | <!--<math>\ Q=k \frac{\Delta H}{L} A</math>--> | ||
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Since the unknown on the right side is the head, it is convenient to group all of the other terms together and call them conductance: | Since the unknown on the right side is the head, it is convenient to group all of the other terms together and call them conductance: | ||
[[Image:eq_cond3. | [[Image:eq_cond3.png]] | ||
<!--<math>\ Q=C \Delta H</math>--> | <!--<math>\ Q=C \Delta H</math>--> | ||
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This results in the following general definition for conductance: | This results in the following general definition for conductance: | ||
[[Image:eq_cond4. | [[Image:eq_cond4.png]] | ||
<!--<math>\ C= \frac{k}{L} A</math>--> | <!--<math>\ C= \frac{k}{L} A</math>--> | ||
This may be represented more specifically in the following form. | This may be represented more specifically in the following form. | ||
[[Image:eq_cond5. | [[Image:eq_cond5.png]] | ||
<!--<math>\ C= \frac{k}{b} lw</math>--> | <!--<math>\ C= \frac{k}{b} lw</math>--> | ||
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=== Arcs === | === Arcs === | ||
[[File:Arc-conductance.png|thumb|400 px|Arc conductance]] | |||
Fortunately, GMS can automatically calculate the lengths of arcs and areas of polygons. Therefore, when a conductance is entered for an [[GMS:Feature Objects#Arcs|arc]], it should be entered in terms of '''conductance per unit length'''. For example, in the case of rivers, conductance should be entered as: | Fortunately, GMS can automatically calculate the lengths of arcs and areas of polygons. Therefore, when a conductance is entered for an [[GMS:Feature Objects#Arcs|arc]], it should be entered in terms of '''conductance per unit length'''. For example, in the case of rivers, conductance should be entered as: | ||
[[Image:eq_cond6. | [[Image:eq_cond6.png]] | ||
<!--<math>\ C_{arc}= \dfrac{\tfrac{k}{t} lw}{L} = \frac{k}{t} w</math>--> | <!--<math>\ C_{arc}= \dfrac{\tfrac{k}{t} lw}{L} = \frac{k}{t} w</math>--> | ||
where: | where: | ||
:'' | :''C<sub>arc</sub>'' = conductance per unit length [(L^2/T)/L] or [L/T] | ||
:''t'' = the thickness of the material [L] | :''t'' = the thickness of the material [L] | ||
:''w'' = the width of the material along the length of the arc [L] | :''w'' = the width of the material along the length of the arc [L] | ||
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=== Polygons === | === Polygons === | ||
For [[GMS:Feature Objects#Polygons|polygons]], conductance should be entered in a | For [[GMS:Feature Objects#Polygons|polygons]], conductance should be entered in a ''conductance per unit area'' form: | ||
[[Image:eq_cond7. | [[Image:eq_cond7.png]] | ||
<!--<math>\ C_{poly}= \dfrac{\tfrac{k}{t} lw}{A} = \frac{k}{t} </math>--> | <!--<math>\ C_{poly}= \dfrac{\tfrac{k}{t} lw}{A} = \frac{k}{t} </math>--> | ||
where: | where: | ||
:'' | :''C<sub>poly</sub>'' = conductance per unit area [(L^2/T)/L^2] or [1/T] | ||
:''t'' = the thickness of the material [L] | :''t'' = the thickness of the material [L] | ||
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===Parameter Factors=== | ===Parameter Factors=== | ||
Beginning with GMS version 7.0, the Well, Drain, River, General head, and Stream boundary conditions have a parameter factor field that is associated with each boundary condition. The parameter factor is used with the parameter value to compute the final value of conductance for a given boundary condition (or in the case of the well package the final Q value). The parameter factor is automatically set by GMS when doing the | Beginning with GMS version 7.0, the Well, Drain, River, General head, and Stream boundary conditions have a parameter factor field that is associated with each boundary condition. The parameter factor is used with the parameter value to compute the final value of conductance for a given boundary condition (or in the case of the well package the final Q value). The parameter factor is automatically set by GMS when doing the '''Map→MODFLOW''' command. This value will be set to the length of the arc in the cell or the area of the polygon in the cell associated with the boundary condition; for a point feature the factor is set to 1.0. | ||
==See also== | ==See also== | ||
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[[Category:MODFLOW]] | [[Category:MODFLOW]] | ||
[[Category:Equations| | [[Category:Equations|Conductance]] | ||
