A reader has a measured time history, he wants a low-frequency sine test level from it, and the FFT does not seem to give him the real amplitude at each frequency. His governing handbook sends him to something called ESI, which produces a swept sine… Read more
A reader sent in a question that every test engineer runs into sooner or later: For mission synthesis we get three-axis data from the real machine. What is the best way to simulate the same thing on a single-axis shaker table to create the same… Read more
A question that comes up whenever a laboratory is planning its first large electrodynamic shaker installation: the specification and the quotations keep referring to a seismic mass, or a reaction mass, or an inertia block. Is that a real, physically heavy object that has to… Read more
The Problem Here is a problem that comes up more often than the standards would suggest. An engineer is deriving a random vibration maximum predicted environment (MPE) for launch vehicle components mounted very close to the engines. Accelerometer data from engine test stand and stack… Read more
A recurring question in random vibration analysis is: How do we determine the relative displacement between two points when the structure is subjected to a Power Spectral Density (PSD) excitation? This quantity is often far more critical than the absolute response. Connector pin engagement, cable… Read more
Figure 1. Boeing 787 Aircraft Carbon fiber/epoxy laminates are widely used in aeronautic and aerospace structural components mainly because of their excellent specific mechanical properties. These laminates show mechanical properties similar or higher than the conventional metallic materials in terms of strength-to-weight and stiffness-to-weight ratios. The… Read more
Certain equipment must be designed and tested to withstand vibration. This is common in the automotive, aerospace, military and other industries. The equipment is typically mounted to a shaker table and then subjected to a base input random or sine sweep vibration test. The random… Read more
Equipment must be designed and tested to withstand shock and vibration. Ideally, all equipment would be tested on a shaker table with six-degree-of-freedom control (three translations and three rotations). Such tables and control systems exist but are very expensive. Furthermore, any multi-axis testing requires careful… Read more
This is a work-in-progress… I am creating a series of webinars with Matlab exercises for seismic testing. Here are the slides. Telcordia Technologies Generic Requirements GR-63-CORE: Bellcore_GR_63_Core.ppt This unit contains an alternative waveform for VERTEQII. CEI.IEC 980, Recommended practices for seismic qualification of electrical equipment… Read more
Stentor Satellite Equipment mounted in satellites must withstand acoustic-driven random vibration at liftoff and during the transonic and maximum dynamic pressure phases of flight. The equipment must be designed and test accordingly. The equipment is mounted on shaker tables for the random vibration testing,… Read more