Creating Gravity Loads

Gravity loads represent uniform accelerations applied to selected degrees of freedom in a fixed direction.

Gravity loads can be applied only in mechanical steps.

The magnitude of a gravity load can vary with time during a step according to an amplitude definition (see Amplitudes for more information on defining amplitudes). You can also apply knowledgeware techniques to control the value of a gravity load (for more information, see Applying Knowledgeware).

By default, gravity load components are associated with the global, rectangular Cartesian axis system. You can specify a local coordinate system for the definition of gravity loads. Local coordinate systems are defined in the CATIA Part Design workbench.

Gravity loads can be applied to volume or part supports, point masses (distributed masses applied to one or more points), a body group, or a mesh part. If a gravity load is applied to geometry that is the support for a distributed mass object other than a point mass, the gravity load is also applied to the distributed mass. (See Creating Distributed Masses for more information.)

This task shows you how to create a gravity load on geometry.

  1. Click the Gravity Load icon .

    The Gravity dialog box appears, and a Gravity object appears in the specification tree under the Loads objects set for the current step.

  2. You can change the identifier of the load by editing the Name field.

  3. Select the geometry support (a volume, part, distributed mass object, or mesh part). Any selectable geometry is highlighted when you pass the cursor over it. You can select several supports to apply the load to all supports simultaneously. You can also select a body group.

    The Supports field is updated to reflect your selection. A temporary symbol will appear at the supports to indicate zero values until you apply a nonzero load.

  4. Enter values for the load components Component 1, Component 2, and Component 3.

  5. Right-click on a component field to add knowledgeware controls to the selected field (for more information, see Applying Knowledgeware).

  6. Click More to access additional gravity load options.

    1. Toggle on Selected amplitude, and select an amplitude from the specification tree to define a nondefault time variation for the gravity load.

      If you do not specify an amplitude in a Nonlinear Structural case, Abaqus applies the reference magnitude based on the Default load variation with time option that you selected when you created the step. Abaqus either applies the reference magnitude linearly over the step (Ramp) or applies it immediately at the beginning of the step and subsequently holds it constant (Instantaneous).

      If you do not specify an amplitude in an Explicit Dynamics case, Abaqus applies the reference magnitude immediately at the beginning of the step and subsequently holds it constant (Instantaneous).

      See About Prescribed Conditions in the Abaqus Prescribed Conditions Guide for more information.

    2. Toggle on Selected local system, and select a coordinate system to define local directions.

  7. Click OK in the Gravity dialog box.

    Symbols representing the applied force are displayed on the geometry.