Calculation of Fn, Phi and Xi in SSI-Cov

[Ayubirad]

Dear @dagghe

I have reviewed the current method used in calculating the final values of the modal parameters, which relies on selecting a single stable pole based on the user's input and the defined relative tolerance (rtol). To enhance this approach and potentially improve accuracy, I would like to propose incorporating a method inspired by the CESSIPy project.

The CESSIPy library, as described in its repository (https://github.com/MatheusCarini/CESSIPy), employs a strategy that clusters close stable poles to represent a single mode. This method involves calculating the mean values of natural frequencies (Fn), damping ratios (ξ), and mode shapes (Φ), and it also provides the standard deviation for these parameters.

Could you please consider integrating this methodology into your codebase? Specifically, the stable_modes(FN, ZT, V, stb, tol=0.01, spo=6) function from CESSIPy.py.

Thank you for considering this suggestion. I believe that adopting this method could significantly improve the reliability and effectiveness of the modal parameter calculations.

Best regards,
Ayubirad

[dagghe]

We used a similar approach in pyOMA (averaging the results from multiple stable poles) however, we have opted to omit this step in the new version in favor of the more common method of extracting results from poles at specific model orders, as you correctly noted. In a future release, we plan to incorporate methods for calculating the uncertainty bounds of the modal parameters, as demonstrated by Dholer.