Creating Velocity Boundary Conditions

Velocity boundary conditions constrain the selected degrees of freedom to a fixed velocity or to a prescribed velocity history.

You can apply velocity boundary conditions only in mechanical steps. Velocity boundary conditions can be applied to point/vertex, curve/edge, surface/face, or body supports or to a point, line, surface, or body group.

The magnitude of a velocity boundary condition can vary with time during a step according to an amplitude definition (see Amplitudes for more information on defining amplitudes). You can prescribe the time variation of the magnitude of a velocity boundary condition in a user subroutine, which is sometimes preferable when the time history of the magnitude is complex. You can also apply knowledgeware techniques to control the value of a velocity boundary condition (for more information, see Applying Knowledgeware).

By default, velocity components are associated with the global, rectangular Cartesian axis system. You can specify a local coordinate system for the definition of velocity boundary conditions, 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.

This task shows you how to create a velocity boundary condition on geometry.

  1. Click the Velocity Boundary Condition icon .

    The Velocity BC dialog box appears, and a Velocity object appears in the specification tree under the Boundary Conditions objects set for the current step.

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

  3. Select the geometry support (a point, an edge, a surface, or a body). Any selectable geometry is highlighted when you pass the cursor over it. You can select several supports to apply the boundary condition to all supports simultaneously. You can also select an appropriate group.

    The Supports field is updated to reflect your selection.

  4. Toggle on a degree of freedom to constrain it, and enter a value for the degree of freedom in the appropriate text field. Toggle off a degree of freedom to leave it unconstrained.

  5. Right-click on the text field for a translational or rotational velocity to add knowledgeware controls (for more information, see Applying Knowledgeware).

  6. Click More to access additional velocity boundary condition options.

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

      If you do not specify an amplitude, 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.

    4. Toggle on Apply user subroutine to define a nonuniform variation of the velocity boundary condition magnitude throughout the step in user subroutine DISP. For more information, see Using User Subroutines and DISP in the Abaqus User Subroutines Guide.

  7. Click OK in the Velocity BC dialog box.

    Symbols representing the constrained degrees of freedom are displayed on the geometry.