17.6.1.2. Standard Earth Gravity

This boundary condition simulates gravitational effects on a body in the form of an external force.

Gravity is a specific example of acceleration with an opposite sign convention and a fixed magnitude. Gravity loads cause a body to move in the direction of gravity. Acceleration loads cause a body to move in the direction opposite of the acceleration. Refer to the example shown under Acceleration for details.

This page includes the following sections:

Analysis Types

Standard Earth Gravity is available for the following analysis types:
Dimensional Types

The supported dimensional types for the Standard Earth Gravity boundary condition include:

  • 3D Simulation

  • 2D Simulation

Geometry Types and Topology Selection Options

By virtue of Standard Earth Gravity’s physical characteristics, this boundary condition is always applied to all bodies of a model.

Magnitude Options

Standard Earth Gravity is defined using a Coordinate System as the loading quantity. This boundary condition is also constant. Only the direction may be modified.

Applying a Standard Earth Gravity Boundary Condition

To apply a Standard Earth Gravity:

  1. On the Environment Context tab, click Inertial>Standard Earth Gravity.

    Or, right–click the Environment object in the tree or in the Geometry window and select Insert>Standard Earth Gravity.

  2. Define the Coordinate System and/or Direction of the Standard Earth Gravity.

Details Pane Properties

The selections available in the Details pane are described below.

CategoryProperty/Options/Description
ScopeGeometry: Read-only field indicating All Bodies.
Definition

Coordinate System: Drop-down list of available coordinate systems. Global Coordinate System is the default. When using cyclic symmetry, the referenced coordinate system must be the same coordinate system specified on the Cyclic Region. For a 2D axisymmetric model the referenced coordinate system must be the Global Coordinate System. The referenced coordinate system must be Cartesian.

X Component: Read-only field with values for components based upon the Direction specification.

Y Component: Read-only field with values for components based upon the Direction specification.

Z Component: Read-only field with values for components based upon the Direction specification.

Suppressed: Include (No - default) or exclude (Yes) the boundary condition.

Direction: Define the vector in terms of any of the following directions: +x, -x, +y, -y, +z, -z.

Load Vector Controls (Substructure Generation analysis only)

Load Vector Assignment: Options include Program Controlled (default) and Manual. When set to Manual, the Load Vector Number property displays.

Load Vector Number: Specify a Load Vector Number using any value greater than 1. A setting of 1 is reserved for a pre-stress Substructure Generation analysis. If multiple loads have the same Load Vector Number, the application groups these loads during the solution process to generate a single load vector that is the combined effect of all grouped loads.

Mechanical APDL References and Notes

Standard Earth Gravity is applied using the ACEL command.

Note:  Should both an Acceleration and a Standard Earth Gravity boundary condition be specified, a composite vector addition of the two is delivered to the solver.

API Reference

For specific scripting information, see the Standard Earth Gravity section of the ACT API Reference Guide.