Load Stepping: Applying Loads Progressively

Nonlinearities in simulations with nonlinear geometry or nonlinear materials (plastic or hyperelastic) can cause slow convergence or divergence of the solution. To improve the convergence of nonlinear cases, you can ramp the mechanical loads using the Solid Stress Load Step solver.

This solver applies the external loads progressively over several steps and is compatible with both the Steady and Implicit Unsteady models. For more information on load stepping, see 载荷步进.

To activate the Solid Stress Load Step solver:

Select the Solvers > Solid Stress Solver node and activate Load stepping.
Simcenter STAR-CCM+ adds the Solid Stress Load Step node under Solvers.

Simcenter STAR-CCM+ provides two methods for incrementing the external load—a static method, where the load increment at each load step is constant, and an adaptive method, where the load increment at each load step is calculated based on convergence of multiple previous load steps. To specify the method:

Select the Solvers > Solid Stress Load Step node and set Load Step Control to one of the following:
- Static Load Step Control—with this method, you specify the number of steps over which the the load is applied. The solver divides the full load value equally over the specified number of steps.
- Linear Load Step Control—with this method, you specify the initial increment and the optimal number of Newton iterations that are required for convergence. At each load step, the solver increments the load by linearly ramping the load value of previous load steps. The ramping factor is calculated as the ratio between the specified optimal number and the number of iterations that where required to reach convergence over the previous time steps, see (Load Stepping).

Edit the Solvers > Solid Stress Load Step node and set the following properties:


Property	Setting
Max Load Step	Specify the maximum number of intervals in which the load is incrementally applied (that is, the number of load steps). If the load is not completely applied after reaching the maximum number of load steps, the load stepping continues in the next iterations until the complete load is applied.
Max Newton Steps	Specify the maximum number of Newton iterations per load step.

When using the Linear Load Step Control, edit the Solvers > Solid Stress Load Step > Linear Load Step Control node and specify the initial load increment and the optimal number of Newton iterations.

If required, you can modify the stopping criteria for the Solid Stress Load Step solver:

Expand the Solvers > Solid Stress Load Step > Stopping Criteria node.
The stopping criteria available for this solver are based on the convergence of the displacement, force, contact constraint, contact pressure, and strain energy residuals. For the stopping criterion, you can change the convergence threshold by setting the Minimum Value property.

For more information on the solver properties and settings, see Solid Stress Load Step Solver Reference.