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 topics:

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 (Modal and Substructure Generation only)

Load Vector Assignment: Options include Program Controlled (default) and Manual. When set to Manual for a:

Modal Analysis

Specify any integer value greater than 0 when the Load Vector Assignment property is set to Manual. One of the load vector number properties listed below displays based on the setting of the Direction property. A setting of 1 is reserved if analysis contains base excitations or is a pre-stress Modal and the Load Control property on the Pre-Stress object is set to Keep All, Keep Displacement Constraints, or Keep Inertia And Displacement Constraints.

  • X Load Vector Number

  • Y Load Vector Number

  • Z Load Vector Number

Substructure Generation Analysis

Specify any value greater than 1 in the Load Vector Number property. A setting of 1 is reserved for pre-stress Substructure Generation analyses.

Important:

  • When using the Program Controlled setting for a Modal analysis, the load vector number property displays as a read-only field. The application populates the field with a load vector number following the solution. You can then use this value to transfer and scale the generated load vector to a linked MSUP system that includes the Load Application object.

  • If multiple loads/load components have the same load vector numbers, the application groups these loads/load components 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.