The cepstrum function was originally developed for characterizing the seismic echoes resulting from earthquake and bomb explosions. It has also been used to determine the fundamental frequency of human speech, to analyze radar signal returns, and to evaluate machinery vibration. A cepstrum of time history… Read more
Cross-correlation is a measure of similarity of two waveforms as a function of a time-lag applied to one of them. Autocorrelation is the cross-correlation of a signal with itself. It is a time domain analysis useful for determining the periodicity or repeating patterns of a… Read more
I had the opportunity to give the keynote speech at the workshop. Here is my presentation, which is rather non-technical. Enjoy… Dynamics Engineering: A Call to Serve – Tom
The scripts in: cross_psd.zip calculate the cross power spectral density of two signals. These scripts have an option to sub-divide the data into segments and then take an ensemble average. This tends to smooth the resulting magnitude and phase curves, but the spectral frequency resolution… Read more
FAA Federal Aviation Regulations FAR-25 Appendix G, Continuous Gust Design Criteria, requires a continuous turbulent gust analysis for transport aircraft. The gust PSD function is given in: The von Karman Vertical Gust Spectrum A Matlab script for generating a continuous gust velocity PSD is given… Read more
There are many variables which affect the touchdown shock level of an aircraft. These include: Descent or sink rate Forward and side velocities Roll, pitch, and yaw angles and corresponding rates Weight and center of gravity Cross wind, wind shear, gusts, etc. Runway contact loads… Read more
There is a occasional need in shock & vibration analysis for a user to generate his or her own time history. The resulting time history could be used to test a modal transient script, for example. The scripts in generate.zip can be used to output the… Read more
These Matlab scripts apply a two-pole Bessel lowpass filter to a time history signal: Bessel_lowpass_filter.zip The main script is: Bessel_lowpass_filter.m The remaining scripts are supporting functions. The filter coefficients were derived using a bilinear transformation, as shown in Bessel_filter_two_pole.pdf * * * The U.S. Navy… Read more
Consider a component which is to be subjected to a shock test using a shaker table. The test specification for this example is a Shock Response Spectrum (SRS). The control computer must synthesize a time history for the test. The typical method is via a… Read more
Time Waveform Replication (TWR) for shock testing on shaker systems has been receiving some attention in MIL-STD-810G and elsewhere. The goal is to test components to measured field time histories for realism. I did some related work with NASA’s Robin Ferebee a few years ago,… Read more