5.5. Activation/Deactivation of Loads in Explicit Dynamics

You can activate or deactivate a load (which includes it in, or excludes it from, the analysis) within the time span of a step. For most loads (for example, pressure or force) deleting the load is the same as setting the load value to zero. But for certain loads, such as a specified displacement, this is not the case.

Note:  Changing the method of how a multiple-step load value is specified (such as Tabular to Constant), the Activation/Deactivation state of all steps resets to the default, Active.

To activate or deactivate a load in a stepped analysis:

  1. Highlight the load within a step in the Graph or a specific step in the Tabular Data window.

  2. Click the right mouse button and choose Activate/Deactivate at this step!.

Note:  For displacements and remote displacements, it is possible to deactivate a selection of degrees of freedom within a step.

Supported Constraints

Step deactivation is (by design) not applicable for:

  • Hydrostatic Pressure

  • Detonation Point

  • Fixed support

  • Impedance Boundary

  • Limit Boundary

Application of Load Steps

Here are some example scenarios where load deactivation is useful:

  • Springback of a cantilever beam after a plasticity analysis.

  • Locking a joint or remote point in a certain location by setting the velocities to zero.

  • Specifying different initial velocities for different parts in an Explicit Dynamics analysis during the analysis by activating an acceleration during a load step.

  • Multistep type of analysis to keep track of loads in a logical way.

Caution:  Reactivation of translational and rotational displacement boundary conditions is not allowed. The explicit solver is not able to fulfill such a constraint in one cycle when the boundary condition becomes active. This will result in an error message:

Boundary condition <bcname> contains a load step which has been reactivated after being deactivated. The constraint cannot be fulfilled because it would cause very large displacements in one solver cycle. Instead use a velocity based boundary condition.

In the following example the nodes would be free to move during load step 2. Adhering to the constraint at the start of load step 3 would cause the deformations to become too large. This restriction does not apply for non-displacement type of boundary conditions.