8.1.4. Derived Variables Tab

Derived variables are calculated from monitor variables to visualize plot trends. For example, derived variables can offset an existing plot or calculate statistics for the specified monitor variables on moving intervals. Derived variables are not written to results files, but their values can be saved by exporting plot data.

Derived variables may be applied to monitor variables through the Monitor Properties dialog box. For details, see CFX-Solver Manager Monitor Properties Dialog Box.

Note:  CFX-Solver can also create equivalent statistics for certain monitor points. For details on setting up monitor statistics in CFX-Pre, see [Monitor Name]: Monitor Statistics in the CFX-Pre User's Guide.

 

8.1.4.1. Creating Derived Variables

Derived variables can be created in Workspace Properties. However, they can also be created directly from the Workspace menu by selecting New Derived Variable. For details, see New Derived Variable Command.

Note:  To create derived variables using the Monitor Properties dialog box, follow the procedure below from Step 2.

  1. Select Workspace > Workspace Properties.

  2. Select Derived Variables.

  3. Click New  .

    The New Derived Variable dialog box is displayed.

  4. Under Name, type the name of the new derived variable.

  5. Click OK.

    The Derived Variable Properties dialog box is displayed.

  6. Configure the derived variable as required.

 

8.1.4.2. Modifying Derived Variables

Derived variables can be modified in Workspace Properties

Note:  To modify derived variables using the Monitor Properties dialog box, follow the procedure below from Step 2.

  1. Select Workspace > Workspace Properties.

  2. Select Derived Variables.

  3. Select the derived variable to modify.

  4. Click Edit  .

    The Derived Variable Properties dialog box is displayed.

  5. Configure the derived variable as required.

 
8.1.4.2.1. Derived Variable Properties

All adjustable Derived Variable Properties settings appear in the General Settings tab. The two types of adjustable settings are Statistics and Offsets

Statistics

  • From the Statistics Type drop-down, select a single statistical quantity for the derived variable. If you select None, no other Statistics settings will be available. For a list of available statistics and calculation details, see [Monitor Name]: Monitor Statistics in the CFX-Pre User's Guide.

  • Interval Option controls how frequently the values of the selected statistics are updated. Each update, the values are calculated using the most recent iterations that fit into the interval. Select one of the following:

    • Moving Interval

      Updates statistical values every iteration.

    • Previous Complete Interval

      Updates statistical values at the completion of the previous interval. The values remain fixed until each subsequent interval is complete.

  • Interval Definition controls the size of the evaluation interval. Different options are available for steady-state and transient cases.

    The following options are available for steady-state cases and harmonic balance cases:

    • Timesteps

      Specifies the interval as a number of solver iterations.

    The following settings are available for transient cases:

    • Time Periods

      Specifies the interval as a number of operational periods. This setting is only available for transient blade row cases in which both the time step and the number of time steps per period are constant (including across any restarts).

    • Time

      Specifies the interval as an amount of simulation time.

    • Timesteps

      Specifies the interval as a number of time steps. All time steps within an interval are given equal statistical weight, regardless of time step length.

Note:  The value of the statistic is always displayed at the end of the interval.

Offsets

  • Change the X Axis Offset Type to Timesteps to shift the plot line by a specified number of timesteps. By convention, a positive integer shifts the data to the right.

  • Change the Y Axis Offset Type to Specified Offset to add a constant value to all data points. The constant value is assumed to be in the displayed units for the given data.

 

8.1.4.3. Deleting Derived Variables

Note:  To delete derived variables using the Monitor Properties dialog box, follow the procedure below from Step 2.

  1. Select Workspace > Workspace Properties.

  2. Select Derived Variables.

  3. Select the derived variable to delete.

  4. Click Delete  .