Special Effect Vulnerability and Hardening Program. Volume 2. Random Imperfections for Dynamic Pulse Buckling.
Final technical rept. 1 Jan-1 Sep 85,
APTEK INC SAN JOSE CA
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Pure white noise and wavelength dependent random imperfections are explored as representations of imperfections to be used in numerical investigation of dynamic pulse buckling. Both forms provide imperfections with a broad spectrum of wavelengths, which is needed to allow the numerical analysis to select the most amplified wavelengths as part of the solution. Example results from a closed form solution are used to show how these imperfections are related to equivalent single mode imperfections and to demonstrate the statistics of typical buckled forms. Both random imperfection forms are represented by Fourier series with random coefficients having a Gaussian distribution with zero mean value. In white noise, the standard deviation is constant for all wavelengths. The proposed alternate form has standard deviations that decrease as 1sq. rt. n with increasing mode number n. This gray noise is a convenient form that is shown to represent imperfections that are proportional to an appropriate combination of wall thickness and wavelengths of the buckle modes. Example random imperfection shapes and growing buckle shapes are given to demonstrate the advantage of using gray noise rather than pure white noise imperfections. In addition, distributions of peak-to-peak buckle amplitudes and buckle wavelengths are calculated by the Monte Carlo method for a large population of random buckle shapes. It is shown that estimates for the statistics of these distributions can be made to resonable accuracy by a single calculation in which about 15 or more buckle waves appear.
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