The Craig-Bampton method is method for reducing the size of a finite element model, particularly where two or more subsystems are connected. It combines the motion of boundary points with modes of the subsystem assuming the boundary points are held fixed. Here is a tutorial… Read more
Here is a Matlab script for Doppler shift calculations: doppler.mHere is a related Newsletter article and sound files: June2003_NL.pdfK5LA.wavcno_wav* * *See also: Vibrationdata Acoustics Page* * *- Tom Irvine
Here is a Matlab script and its supporting function for identifying the frequencies and amplitudes for one or more sine functions. sinefind.zip Trial-and-error curve-fitting is used with some convergence techniques. Here is measured accelerometer data from a channel beam excited by an impulse force. channel.txt… Read more
David O. Smallwood, An Improved Recursive Formula for Calculating Shock Response Spectra, Shock and Vibration Bulletin, No. 51, May 1981. DS_SRS1.pdf Time History Synthesis for Shock Testing on Shakers: th_syn.pdf The Shock Response Spectrum at Low Frequencies: low_srs.pdf A Family of Transients Suitable for Reproduction… Read more
The following animation file is useful for demonstrating the Shock Response Spectrum (SRS) concept : HS_SRS.avi & Alternate Link Each system is subjected to a common base input which is a 1 G, 1 second half-sine pulse. Each system has an amplification factor of Q=10.… Read more
Occasionally I receive questions regarding the equivalent SRS for a MIL-S-901 shock test. Alas, I have no experience with MIL-S-901 testing. But a “MIL-S-901 Medium Weight Shock Test” SRS plot is given on page 45 of the following document: Gaberson, Pseudo Velocity Shock Analysis, Shock Severity… Read more
Here is a unit conversion calculator, written in Microsoft Visual C/C++. units.exe Do a right mouse click to download and save. It may appear in your system tray after you download and run it. The contents in the Results box can be copied and pasted… Read more
Howard A. Gaberson (1931-2013) was a shock and vibration specialist with more than 45 years of dynamics experience. He was with the U.S. Navy Civil Engineering Laboratory and later the Facilities Engineering Service Center from 1968 to 2000, mostly conducting dynamics research. Gaberson specialized in… Read more
Some power spectral density test specifications are too high in amplitude for a given shaker system. Bandsplitting can be cautiously used in these cases. Here is a brief guideline paper: bandsplit.pdf Here is a Matlab script that implements bandsplitting per the guidelines: bandsplit.zip The main script… Read more
Making sound recordings is easy these days given that iPods, iPads and Android cell phones have this capability. Here is a freeware program that can be used to process the sound data: Audacity This program can also convert the sound file from one format to… Read more