Gravity

A gravity load is a general translational acceleration load.

You must apply a gravity load to the entire model.

There are two different ways that you can define a gravity load. In the Type list in the Gravity dialog box:

• If you select Magnitude and direction, you can define the load by specifying the magnitude of the acceleration and specifying a vector to define the direction in which to apply that force.

• If you select Components, you specify a coordinate system in which to define the load and then specify a separate magnitude for each component. For example, if you apply the load in a cylindrical coordinate system, you would define the magnitude of the acceleration in the Ar, At, and Ap directions.

Defining a gravity load in the Nastran environment

In the Nastran environment, the options in the Gravity dialog box correspond to the fields on the GRAV bulk data entry. For Nastran models, you can use the Gravity dialog box to define the direction and magnitude of a gravity vector in any coordinate system you specify.

When you solve your model, Nastran multiplies components of the gravity vector by the mass matrix to obtain the components of the gravity force at each node. Since Nastran uses the mass matrix to compute the forces, you must have mass defined in the model, usually in the material assigned to the mesh.

For more information, see:

• Using GRAV in the Simcenter Nastran User’s Guide.

• GRAV in the Simcenter Nastran Quick Reference Guide.

Defining a gravity load in the Abaqus environment

In the Abaqus environment, the options in the Gravity dialog box correspond to the *DLOAD keyword. For Abaqus models, you can use the Gravity dialog box to define the magnitude of the uniform acceleration in a fixed direction that you specify with a vector.

When you solve your model, Abaqus uses the specified material density together with the magnitude of the gravity load and the direction to calculate the gravity loading. With Abaqus, you can use the Field option in the Acceleration list to vary the magnitude with time in a given step. However, Abaqus always applies the direction of the gravity field at the beginning of the step, and that direction remains fixed during the step.

For more information, see Distributed Loads in the Abaqus Analysis User’s Manual.

Defining a gravity load in the ANSYS enivronment

In the ANSYS environment, the options in the Gravity dialog box correspond to the ACEL command. For ANSYS models, you can use the Gravity dialog box to define the linear acceleration of the structure in a specifiesd direction.

For more information, see ACEL in the ANSYS Commands Reference.

Where do I find it?

Application	Pre/Post
Prerequisite	A Simulation file as the work part and displayed part and an active solutionSimcenter Nastran, Abaqus, or ANSYS as the specified solverStructural as the specified Analysis Type
Command Finder	Gravity
Simulation Navigator	Right-click Load Container→New Load Gravity

How do I

Define a gravity load using magnitude and direction

Define a gravity load using components

Quick links

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

Browse Simcenter 3D help by product area

Gravity, Simcenter 3D 2021.1 Series

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