Figure 8.6: Nonconservative (Path-Dependent) Behavior
Plastichingeformshere FFu1 231238.2.2. Substeps
When using multiple substeps, you need to achieve a balance between accuracy and economy: more
substeps (that is, small time step sizes) usually result in better accuracy, but at a cost of increased run
times. The program provides automatic time stepping designed for this purpose.
Automatic time stepping adjusts the time step size as needed, gaining a better balance between accuracy
and economy. Automatic time stepping activates the bisection feature.
Bisection provides a means of automatically recovering from a convergence failure. This feature cuts a
time step size in half whenever equilibrium iterations fail to converge and automatically restart from
the last converged substep. If the halved time step again fails to converge, bisection again cuts the
time step size and restart, continuing the process until convergence is achieved or until the minimum
time step size (specified by you) is reached.
8.2.3. Load Direction in a Large-Deflection Analysis
Consider what happens to loads when your structure experiences large deflections. In many instances,
the loads applied to your system maintain constant direction no matter how the structure deflects. In
other cases, forces change direction, "following" the elements as they undergo large rotations.
The program can model both situations, depending on the type of load applied.Accelerations and
concentrated forces maintain their original orientation, regardless of the element orientation.Pressure
loads always act normal to the deflected element surface, and can be used to model "following" forces.
Figure 8.7: Load Directions Before and Aft er Deflection (p. 199) illustrat es constant-direction and following
forces.
Nodal coordinate system orientations are not updated in a large deflection analysis. Calculated displace-
ments are therefore output in the original directions.
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