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Modal parameters identification from ambient vibrations (SDOF)

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The modal damping ratio of a SDOF is measured by using ambient vibrations data



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When no impulse response function (IRF) is available to determine the modal properties of a SDOF, it is possible to use ambient vibrations data.
The goal is to obtain a decaying sinusoid that has the same properties as the IRF. Here, the Random Decrement Tecnique (RDT) [1] as well as the Natural Excitation Technique (NExT) [2] are used. First, the response of a SDOF to a 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 envelop of the IRF.
- a function CentDiff used to simulate the response to a white noise of a SDOF in the time domain.
- An example file Example.m
All credits go to the original authors. There is nothing new in this submission. This is the first version of the submission, some bugs are expected. 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 paranieter extraction from operating structures.

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javad karimi

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