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    SimScale DocumentationAnalysis TypesMulti-purpose AnalysisVariable Time Step in Multi-purpose Analysis

    Variable Time Step in Multi-purpose Analysis

    With the variable time step feature, users can manually enter a series of time steps to optimize their transient simulations. For example, start with a fine time step to accurately capture the initial transient behavior, and then increase the time step as the simulation progresses towards convergence. By setting a coarser time step later in the simulation, one can achieve faster results and save computational resources.

    As is obvious, this feature is only available for transient multi-purpose simulations.

    Variable Time Step Settings

    Under the Simulation control item in the simulation tree, the settings panel is as depicted in Figure 1:

    simulation control settings for variable time step
    Figure 1: Table icon highlighted to define different time steps for corresponding end times

    On clicking the table icon, the following panel appears:

    time and time step settings in simscale multi-purpose variable time step
    Figure 2: Settings panel to define the end time and respective time steps in a transient multi-purpose simulation

    Example

    The explanation for the above example is as follows:

    TimeTime stepCalculated time steps
    0.10.01[0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1]
    0.60.2[0.3, 0.5, 0.6]
    1.1250.1[0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.125]
    Table 1: For end times 0-0.1, 0.1-0.6, and 0.6-1.125 seconds, the respective time step sizes and the time steps for which the simulation is computed are mentioned.

    For the time 0 to 0.1 seconds, the time step defined is 0.01 seconds. The calculated time steps are derived using the formula:

    $$Calculated\ time\ steps = \frac{Time} {Time\ step}$$

    In a similar fashion, a time step of 0.2 seconds is used as the simulation continues from 0.1 seconds to 0.6 seconds. This process continues until the end time of 1.125 seconds.

    Important

    For each simulation duration, the end time is respected irrespective of the defined time step. Every consequent run will start from the end of the previous run’s duration. For e.g., row 2 in Table 1 calculates the time step 0.6 despite being just 0.1 seconds time step away from 0.5. Similar behavior is observed in row 3 with the time step 1.125, and the simulation stops.

    Continuing from the above example, a typical simulation result control plot with varying time steps would look as follows:

    Figure 3: Transient multi-purpose simulation with varying time steps of 0.01, 0.2, and 0.1 seconds

    The Pressure difference plot against time in Figure 3 visually depicts the same concept as explained in Table 1.

    Last updated: September 9th, 2025

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