Two tools exist to calculate relevant harmonic indices to include for an accurate response in a specified nodal diameter range in a multiharmonic multistage cyclic symmetry analysis:
A Python script described here.
An Add-on for the Mechanical Application: see Multistage Harmonic Choice Wizard in the Mechanical Add-ons Guide and a tutorial on its use, Calculating the Harmonic Indices for a Multistage Analysis in the Mechanical Tutorials.
For more information on the underlying procedure and equations that these equivalent tools are based on, see Multiharmonic Analysis in the Mechanical Tutorials.
Download the Python script and instructions for using it here.
The Python script requires the following inputs:
Number of sectors in each stage
The main harmonic index for the response, which depends on the engine order of interest
The following optional inputs can also be provided to improve the selection process:
Stage connection information
Nodal diameter range, or maximum number of nodal diameters for which you want an accurate response. This is required only if you select the "First extension of fundamental nodal diameters" or the "All couplings" method to select additional HIs to include in the analysis for improved accuracy. For a detailed description of these methods, see Multistage Harmonic Choice Wizard in the Mechanical Add-ons Guide.
Note the trade-off between accuracy and computational costs that depends on the specified nodal diameter range:
A low number will select a minimal number of harmonic Indices, which is computationally efficient but gives accurate results for a smaller frequency range.
A higher number will select more harmonic Indices and provide more accurate results over a wider frequency range at the price of higher computational costs.
The script calculates and lists the following outputs:
The main harmonic indices (HIs) required for each stage to establish a baseline of accuracy. These HIs are chosen based on the fundamental nodal diameters.
Additional harmonic indices to be included based on added nodal diameters to improve accuracy across that nodal diameter range. These additional HIs are determined by one of the following methods (for details, see Multistage Harmonic Choice Wizard in the Mechanical Add-ons Guide):
First extension of fundamental nodal diameters
All couplings
Note: If the nodal diameters are not the same for every stage, there may be slight inaccuracies in the response.