There is a need to derive a PSD envelope for nonstationary acceleration time histories, including launch vehicle data, which may be similar to that shown in the above figure. A PSD can be derived using rainflow fatigue cycle counting along with a Miners-type relative fatigue… Read more
There is a need in certain structural dynamics finite element analysis problems to perform a response analysis in the time domain. This would be the case, for example, if the stiffness was non-linear. Loss-of-clearance or contact between two adjacent vibrating parts is another analysis example.… Read more
I will be teaching two tutorial sessions at: 84th Shock & Vibration Symposium November 3-7, 2013 Atlanta, GA The sessions are: Shock Response Spectra and Time History Synthesis Rainflow Cycle Counting for Random Vibration Fatigue Analysis You are invited to participate. Further information is given… Read more
A colleague recently wrote to me regarding the merits of using statistical energy analysis to predict the vibration levels in a NASA launch vehicle. Here is my reply: I use “old-school” empirical scaling techniques. These work reasonably well for deriving component-level maximum predicted environments. I… Read more
Consider a single-degree-of-freedom system subject to base excitation. Assume a case where the base input is a sine tone which must be converted to an “equivalent” narrowband PSD. The narrowband PSD must be greater than or equal to the sine tone in terms of peak… Read more
Please send me an Email if you are going to use this package. Also, you are welcome to participate in the Shock & Vibration courses. Thank you,Tom IrvineEmail: tom@irvinemail.org * * * License information: The software packages on the following links are freely placed in… Read more
Ideal random vibration has a normal distribution histogram. (In contrast, measured random vibration in the field may be nonstationary and thus vary from this ideal. ) Here are some resources: An Introduction to Random Vibration Integration of the Normal Distribution Paper Here is a software… Read more
Here is a paper for… Extending Steinberg’s Fatigue Analysis of Electronics Equipment Methodology to a Full Relative Displacement vs. Cycles Curve electronic_rd_n.pdf extending_Steinberg.pptx This paper also shows in a very roundabout way that “fatigue damage equivalence” between sine and random vibration occurs when the sine… Read more
This blog entry is a work-in-progress. Fatigue analysis can be performed in the time domain using rainflow cycle counting. This is an elegant, brute-force approach. One advantage of the time domain approach is that it tends to highlight the occurrences of peaks above 3-sigma for… Read more
Consider a lightly damped, single-degree-of-freedom system subjected to broadband random base excitation. The system will tend to behave as a bandpass filter. The bandpass filter center frequency will occur at or near the system’s natural frequency. The system response will thus tend to be narrowband… Read more