Plotting Results

You create plots to monitor the CFL Number, the time-step, and the total mass of water of the simulation. To verify the quality of the simulation, you create a plot to monitor the Mass Conservation Error report and monitor the iteration error for the conservation of mass in the water phase.

The CFL Number plot lets you check that the CFL number is maintained at an appropriate level. The target value of 2 is not a global limit, as the estimate of the Free Surface Implicit Multi-Step time-step provider is based on the flow field and mesh from the previous time-step, while the CFL number report evaluates the CFL number on the current mesh and solution. However, the CFL number should remain within reasonable limits. The Time-Step plot should show some correlation with the CFL Number plot, in that the time-step decreases as the CFL number increases.

The Mass Conservation Error lets you check that the water phase is conserved as the simulation proceeds, and that numerical errors are minimal.

To create the CFL Number report:
  1. Right-click the Reports node and select New > User > Maximum.
  2. Rename the Maximum 1 node to CFL Number.
  3. Select the Reports > CFL Number node and set Field Function to Convective Courant Number.
  4. Set Parts to Regions > Tank.


To create the Time-Step report:
  1. Create another Maximum report and rename it to Time-Step.
  2. Select the Reports > Time-Step node and set Field Function to Time Step.
  3. Set Parts to Regions > Tank.
Create monitors and plots from these reports.
  1. Multi-select the CFL Number and Time-Step nodes. Right-click the selected nodes and select Create Monitor and Plot from Report.
  2. In the Create Plot From Reports dialog, click Multiple Plots (one per report).
    The new monitors and plots are created.
The Water Mass report requires a user field function to calculate the mass of the Water phase. To create the necessary field function and report:
  1. Right-click the Automation > Field Functions node and select New > Scalar.
  2. Rename the User Field Function 1 node to Water Mass.
  3. Select the Water Mass node and set the following properties:
    Property Setting
    Function Name WaterMass
    Dimensions Mass
    Definition ${VolumeFractionWater}*${DensityWater}*${Volume}
  4. Create a Sum report and rename it to Water Mass.
  5. Select the Reports > Water Mass node and set Field Function to Water Mass.
  6. Set Parts to Regions > Tank.
To create the Mass Conservation Error report:
  1. Right-click the Reports node and select New > Flow/Energy > Mass Conservation Error.
  2. Select the Reports > Mass Conservation Error node and set Phase to Water.
For unsteady simulations, you are advised to monitor the cumulative mass conservation error, which provides an integral measure of the mass gain/loss throughout the simulation.

To create a cumulative monitor and plot of the phase mass conservation error:

  1. Right-click the Mass Conservation Error 1 report and select Create Cumulative Monitor and Plot from Report.


  2. Save the simulation.