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 (one of the predefined Physical Constants).
The Gravity node is only available with some COMSOL products (see www.comsol.com/products/specifications/).
Gravity is not available in 1D axisymmetry.
Coordinate System Selection
The Global coordinate system is selected by default. The Coordinate system list contains all applicable coordinate systems in the component. The coordinate system must have orthonormal coordinate axes, and be defined in the spatial frame. 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.
Gravity
Enter the components for the acceleration due to 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
Solid Mechanics, Explicit Dynamics > Gravity
Shell > Gravity
Layered Shell > Gravity
Plate > Gravity
Membrane > Gravity
Beam > Gravity
Truss > Gravity
Truss, Explicit Dynamics > Gravity
Wire > Gravity
Multibody Dynamics > Gravity
Ribbon
Physics tab with a structural mechanics interface selected:
Global > Gravity