Gravity

When you add a 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 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 is selected by default.

Gravity

Enter the components for 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.

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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.


	Only features that have a geometrical selection contribute to the mass forces. The Mass and Moment of Inertia nodes are global features and will not get any contribution from Gravity. You may need to add extra force contributions if such nodes are present.


	Frame Acceleration Forces

In versions earlier than 6.1, the node was a feature with domain selection. In a model created in an earlier version, the old 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 is appropriate.

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If the current 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 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

Ribbon

Physics tab with a structural mechanics interface selected: