Update README.md

Author: ECheynet

README.md

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-# OMA_1SDOF
+# OMA_1SDOF
+
+
+## Summary
+If the free-decay response (FDR) of a SDOF 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.
+
+## Content
+
+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.
+
+## References
+
+[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