Gravity
When you add a Gravity node, gravity forces are applied to all features in the physics interface with a density, mass, or mass distribution.
The gravity acts in a fixed spatial direction. The load intensity is g = ρgeg where g as a default is the acceleration of gravity (a predefined physical constant).
The Gravity node is only available with some COMSOL products (see https://www.comsol.com/products/specifications/).
Gravity is not available in 1D axisymmetry.
Coordinate System Selection
Select a coordinate system in which the gravity field vector is represented. Only systems with space-independent axis directions are consistent with the assumptions of this feature. The Global coordinate system is selected by default.
Gravity
Enter the components for Gravity g. The default value is g_const, which is the gravitational acceleration constant at mean sea level having the value 9.80665 m/s2.
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For 3D, the default is that the gravity acts in the negative z direction.
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For 2D, the default is that the gravity acts in the negative y direction, except in the Plate interface where the default is in the negative z direction.
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For 1D, the default is that the gravity acts in the negative x direction.
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For 2D axisymmetry, the default is that the gravity acts in the negative z direction.
Frame Acceleration Forces
In versions earlier than 6.1, the Gravity node was a feature with domain selection. In a model created in an earlier version, the old Gravity node remains unchanged. For such a model, it is recommended to use the newer functionality. There are different options:
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In most cases, switching to the new version of Gravity is appropriate.
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If the current Gravity node has a selection, which is not the entire model, or if it contains expressions that depends on the spatial coordinates, you can replace it by a Linearly Accelerated Frame node.
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If the current Gravity node is used to represent an acceleration imposed by the foundation, consider replacing it by a Base Excitation node.
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You can add a Harmonic Perturbation subnode for specifying a harmonic variation of the values of the prescribed displacements and rotations in a frequency domain analysis of perturbation type.
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You can assign this load to a load group. See Load Cases in the Structural Mechanics Modeling chapter.
Location in User Interface
Context Menus
Solid Mechanics > Gravity
Shell > Gravity
Layered Shell > Gravity
Plate > Gravity
Membrane > Gravity
Beam > Gravity
Truss > Gravity
Wire > Gravity
Multibody Dynamics > Gravity
Ribbon
Physics tab with a structural mechanics interface selected:
Global > Gravity