Gravity
The Gravity node is automatically added when Include gravity is selected at interface level in the Darcy’s Law settings and it is active in all domains in which the Darcy’s Law interface is applied.
This feature requires a specific license. For a detailed overview of the functionality available in each product visit http://www.comsol.com/products/specifications/.
Coordinate System Selection
The Global coordinate system is selected by default. The Coordinate system list contains any additional coordinate systems that the model includes. It can be used when prescribing the direction of the gravitational forces.
Gravity
Specify either the acceleration vector or — in case you have a Subsurface Flow Module license — the elevation.
When Acceleration is selected from the list, enter the components of the Gravity vector g. The default value is g_const which is the physical constant having the value 9.8066 m/s2.
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For 3D and 2D axisymmetric models, the default value is -g_const in the z direction.
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For 2D models, the default value is -g_const in the y direction.
When Elevation is selected from the list, specify the Elevation D (SI unit: m). Select the check box Specify reference position to define a reference elevation.
Select the acceleration of gravity from either the Darcy’s Law interface Settings (default), or specify a user defined value. When the check box Include gravity is not selected in the Darcy’s Law interface Settings, the elevation D is set equal to zero.