Creating Load Densities

Load densities apply pure force (no moments) to lines, faces, groups of lines, or groups of faces. Load densities are defined as net loads shared by the supports, and they can be applied only in mechanical steps.

The magnitude of a load density 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 load density (for more information, see Applying Knowledgeware).

By default, the components of a load density are associated with the global, rectangular Cartesian axis system. You can specify a local coordinate system for the definition of load densities, and you can define the local system as a Cartesian, cylindrical, or spherical axis system. Local coordinate systems are defined in the CATIA Part Design workbench.

Load densities can be applied to lines, faces, or groups; however, if load densities are applied to groups, the groups can contain supports of only one type.

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

  1. Click the Load Density icon .

    The Load Density dialog box appears, and a Load Density 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 geometry supports (lines or faces). 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 groups containing lines or faces.

    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 force components Force 1, Force 2, and Force 3.

    Tip:  You can drag the compass onto the model to align the directions used for specifying the force with the local model directions. For more information, see Axis System Type in the “Creating Distributed Forces” procedure in the CATIA V5 Generative Structural Analysis User's Guide.

    The Force Norm field is updated to show the total resultant force that will be applied to the model.

    Moments are not used with load densities.

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

  6. Click More to access additional load density options.

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

      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.

    3. If desired, change the local orientation from Cartesian to Cylindrical or Spherical. See Using Local Coordinate Systems for more information.

  7. Click OK in the Load Density dialog box.

    Symbols representing the applied force are displayed on the geometry.

Load densities cannot be modified when they are propagated into other analysis steps. They can be edited only in the step in which they were created. For more information on propagation, see Propagation.