Random variation of modal frequencies: experiments and analysis
The purpose of this investigation is to establish an analytic technique for the estimation of the second order statistical moments (mean, variance, covariance) of modal frequencies when one or more underlying structural parameters are random variables. (The moments of the underlying random variables are assumed to be known from experiments.) The results of a simple laboratory experiment are summarized to show that the analytic technique yields accurate results in a particular case. The analytical investigation summarized here shows that the moments of modal frequencies can be defined in terms of some simpler measure of structural characteristics. The second order moments of a structural system can be evaluated approximately. Some examples are presented. The first example shows the results of a sequence of experiments in which the fundamental frequency of a cantilever beam is evaluated repeatedly. The fundamental frequency varies randomly, and its mean and variance are estimated from measured data. In the same example, the mean and variance of an underlying random variable (base stiffness of the cantilever beam) are estimated from data, and it is shown that these moments can be used in the analytic framework developed here to estimate the mean and variance of the fundamental frequency. Good agreement exists between the experimental and analytical results. Two other numerical examples are presented to show how random variation occurs in higher modal frequencies and how random variation occurs when more than one underlying variable is random.
- Research Organization:
- Sandia National Labs., Albuquerque, NM (USA)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 5026396
- Report Number(s):
- SAND-85-1379C; ON: DE86000434
- Country of Publication:
- United States
- Language:
- English
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