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) [1], as well as the Natural Excitation Technique (NExT) [2], are used. First, the response of a SDOF to white noise is simulated in the time domain using [3]. 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.

The present submission contains:

• a function RDT.,m that implements to Random Decrement Technique (RDT)
• a function NExT that implements the Natural Excitation Technique (NExT)
• a function expoFit that determine the modal damping ratio by fitting an exponential decay to the envelope of the IRF.
• a function CentDiff used to simulate the response to a white noise load of a SDOF in the time domain.
• An example file Example.m

Any question, comment or suggestion is welcomed.

[1] Ibrahim, S. R. (1977). Random decrement technique for modal identification of structures. Journal of Spacecraft and Rockets, 14(11), 696-700.

[2] James III, O. H., & Came, T. G. (1995). The natural excitation technique (next) for modal parameter extraction from operating structures.

[3] http://www.mathworks.com/matlabcentral/fileexchange/53854-harmonic-excitation-of-a-sdof