Extracting F-X Spectra to a .trn File

Use the following steps:

  1. Create a plane section in derived parts, then set the Auto-Export to export the file in Surface fft files (.trn) format and use the previously created plane section as the input part. See below for an example of Auto Export settings.


  2. Run the simulation, then save the .sim file. This action also saves the .trn file.
  3. Import the .trn file as a CAE model while the original .sim file or a new one is open.
  4. Create a line probe on the plane section from the CAE model. Keep the line points equally spaced and close to cell centers to reduce interpolation error, as shown below.


  5. Map the .trn file into the Line Time History object:
    1. Right-click the Tools > Data Set Functions node and select New > Line Time History (h[l]).
      The h(l) node appears under Data Set Functions. This node stores the history on the line. Rename if desired.
    2. Right-click the h(l) > Imported node and select New derived data from imported surface and derived part. The node Multi-Point Imported opens below.
    3. Select Multi-Point Imported and set the following properties:
      Property Setting
      Field Function 1 Time History:Pressure
      Data Surfaces 1 The plane section
      Representation Volume Mesh
      Part The line probe
      Update Active Activated
  6. Right-click the Tools > Data Set Functions node and select New > Line Time Fourier Transform (G[h[l]]).
    Time-steps must be equally spaced for this step to work properly.
    The G[h[l]] node appears under Data Set Functions. This node stores the spectrum from history h(l) on the line. Rename if desired.
  7. Right-click the G[h[l]] > Imported node and select New derived data from derived data.
  8. Select Multi-Point Imported and set the following properties:
    Property Setting
    Input Time History G[h[l]] under its current name
    Update Active Activated
  9. Select Output control under G[h[l]] and set 3D profile type to the G[h[l]] node under its current name. This stores an F-X spectra surface, plotting frequency vs. distance.
  10. In post-processing, create a scalar scene.
  11. Select the derived data using the Parts property of the scalar displayer.
    1. Select the Scalar 1 > Parts node.
    2. In the Properties window, click the property customizer button for the Parts property.
      The Parts dialog appears.
    3. Select the derived data set.
    4. Click OK.
  12. Select the Scalar Field node and set its Function to the derived data.
The spectra contour is displayed in the scalar scene window. In the following example, the dominant frequency mode is around 900 Hz.

Repeat these steps with line probes in different positions, or after changing the position of the existing probe, to get a more comprehensive picture of the frequency distribution.

See also the Signal Post-Processing tutorial.