admin Consider a single-degree-of-freedom (SDOF) system subjected to base excitation. There are certain cases where the response of a system is known, but the base input acceleration is unknown. An example would be a seismic sensor which behaved as an SDOF system. The seismometer data would… Read more
Clintonville, Wisconsin is an inland community, adjacent to Lake Pigeon. USA Today reported on March 21, 2012 that a series of mysterious booms have been fraying residents’ nerves. City administrator Lisa Kuss said the booms have roused people from their beds and into the streets… Read more
I posted a newsletter at: http://www.vibrationdata.com/Newsletters/March2012_NL.pdf The topics are: James Webb Space Telescope Isolation The Prandtl-Glauert Singularity Seneca Guns Loudest Stadium Crowd Please also see my profile at: http://www.nasa.gov/offices/nesc/academy/Tom_Irvine_bio.html Tom Irvine
The Iwate-Miyagi Nairiku earthquake struck northeast Honshu, Japan, on 14 June 2008. This earthquake had a moment magnitude Mw 6.9 according to the USGS. The peak ground acceleration (PGA) had a maximum vector sum (3 component) value of 4278 cm/sec^2 (4.36 G). This is the highest ever recorded… Read more
Shock and vibration test specifications for avionics and military equipment have almost always been specified in terms of acceleration. The main reason is that acceleration can easily be measured by accelerometers. Velocity sensors are also available but are less common. Gaberson, Chamblers et al, claim… Read more
Introduction Neither shock nor vibration response should be used to cover rigid-body acceleration because material limits depend on the strain rate and on the duration of the load. Furthermore, static deflection shapes differ from dynamic mode shapes. Material Stress Limits The following is an excerpt… Read more
The flight accelerometer data was measured on a launch vehicle which shall remain anonymous. This was due to an oscillating thrust vector control (TVC) system during the burn-out of a solid rocket motor. This created a “tail wags dog” effect. The resulting vibration occurred throughout… Read more
Response Spectrum Response spectrum is a plot of the maximum responses (acceleration, velocity, or displacement) of idealized single-degree-of-freedom oscillators as a function of the natural frequencies of the oscillators for a given damping value. The response spectrum is calculated for a specified vibratory motion input… Read more
Launch vehicle avionics components must be designed and tested to withstand random vibration environments. These environments are often derived from flight accelerometer data of previous vehicles. This data tends to be nonstationary as shown in the figure above. The typical method for post-processing is to… Read more
The most widely used algorithm for the Shock Response Spectrum (SRS) calculation for base excitation is the ramp invariant digital recursive filtering relationship given in: David O. Smallwood, An Improved Recursive Formula for Calculating Shock Response Spectra, Shock and Vibration Bulletin, No. 51, May 1981.… Read more