Defining the Adaptive Time-Step

When you model nonlinear phenomena, such as buckling or snap-through, the simulation time-step must be sufficiently small to capture the relevant physics. However, using a small time-step for the entire simulation can increase the computation time considerably.

To reduce the computation time while retaining accuracy, you can activate the Adaptive Time-Step model, which automatically adjusts the time-step size during the simulation based on specified criteria.
To activate the model:
  1. Right-click the Continua > [Physics Continuum] > Models node and select Select Models....
  2. In the Model Selection window, select the Adaptive Time-Step model and click Close.
Simcenter STAR-CCM+ allows you to set the solid stress time-step provider to modify the time-step according to a computed displacement change or according to a monitored value that you select. To do this:
  1. Right-click the Models > Adaptive Time-Step > Time-Step Providers node and select New > Solid Stress Time-Step Provider.
  2. Select the [Solid Stress Time-Step Provider] > Conditions > Monitored Field node and select one of the following options:
    • To set the time-step in response to a calculated displacement change:
      1. Set Monitored Field to Displacement Change.
      2. Select the Monitored Field > Displacement Change, and select a Norm Type.

        For more information on norm types, see Residual and Variable Increment Norms.

    • To set the time-step in response to a calculated variable monitor value:
      1. Set Monitored Field to Monitor.
      2. Select the Monitored Field > Monitor node, and specify the relevant properties.

        For more information, see Solid Stress Time-Step Provider Reference.

    By default, the solid stress time-step provider proposes a time-step based on a single control method that applies to the entire range [-infinity, infinity] of the monitored field change. You can subdivide the range of expected changes into intervals and provide a different control method for each interval.
To subdivide the range of changes:
  1. Select the Solid Stress Time-Step Provider > Conditions > Range Input node and set the List of Interval Points.
  2. Select the Solid Stress Time-Step Provider > Intervals > [Interval [-inf, inf]] node and set the relevant properties.
    For example, if you are monitoring displacement change with the list of interval points set to [0.002,0.005,0.0075,0.01]m you could do the following:
    Interval Control Method Adaptive Time-Step
    [-inf, 0.002] Constant Scaling of 2.0 If the displacement change falls into this interval, the new proposed time-step is twice the current time-step.
    [0.002,0.005] Maximum Time Step If the displacement change falls into this interval, the new proposed time-step is the time-step size defined in the implicit unsteady solver.
    [0.005,0.0075] Target Control - Linear with a target value of 0.007 m If the displacement change falls into this interval, the new proposed time-step is calculated by multiplying the previous time-step by the linear scale factor calculated as the ratio of the target value to the monitored displacement change.
    [0.0075, 0.01] Specified Time Step If the displacement change falls into this interval, you specify the proposed time-step directly using the Specified property.
    [0.01,inf] Minimum Time Step If the displacement change falls into this interval, the new proposed time-step is the minimum time-step size defined by the adaptive time-step solver.
    For more information, see Solid Stress Time-Step Provider Reference.
To define the initial and minimum time-steps as well as the limits on the scale factor applied to the time-step:
  1. Select the Solvers > Adaptive Time-Step node and set the relevant properties.
    For more information see Adaptive Time-Step Model Reference.