Updated 14 May 2020
If the free-decay response (FDR) of a Single Degree-of-Freedom (SDOF) system is not directly available, it is possible to use ambient vibrations data yo estimate the modal damping ratio. Here, the Random Decrement Technique (RDT) , as well as the Natural Excitation Technique (NExT) , are used. First, the response of a SDOF to white noise is simulated in the time domain using . Then the IRF is computed using the RDT or NExT. Finally, and an exponential decay is fitted to the envelop of the IRF to obtain the modal damping ratio.
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Any question, comment or suggestion is welcomed.
 Ibrahim, S. R. (1977). Random decrement technique for modal identification of structures. Journal of Spacecraft and Rockets, 14(11), 696-700.
 James III, O. H., & Came, T. G. (1995). The natural excitation technique (next) for modal parameter extraction from operating structures.
Cheynet, E. Damping Ratio Estimation from Ambient Vibrations (SDOF). Zenodo, 2020, doi:10.5281/ZENODO.3827107.
Inspired by: Harmonic excitation of a SDOF
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