Introduction to Random Vibration

Your dictionary is not likely to help you even to understand the word “vibration.” The definition found in most dictionaries would better fit “sinusoidal vibration”; some dictionaries employ the phrase “simple harmonic motion”. A better definition of “vibration” — a mechanical oscillation or motion about a reference point of equilibrium. Or, per Ann Landers: “a motion that can’t make up its mind which way it’s going”. These definitions are sufficiently broad to include random vibration.

Random vibration is difficult to define. Let’s together develop an understanding of the term. The concept of a continuous spectrum, a spectrum with no “holes,” of vibration occurring simultaneously at all frequencies, is somewhat difficult for newcomers to random vibration. Perhaps this will help. Recall in high school physics how you beamed white light through a prism? Remember the continuous spectrum of colors thrown onto the wall? Random vibration is something like that. The same kinds of analyzer we studied back in ebook 11, that gave us line spectra (indicating vibration at discrete frequencies) will now display continuous spectra. Let’s also understand ASD/PSD in g2/Hz units.


20.1 Introduction to random vibration

20.2 Sources of random vibration

20.3 Aerospace (vibration source)

20.4 Rocket liftoff

20.5 Land and sea vehicles

20.6 Musical instruments - complex spectra

20.7 Hash and trash

20.8 Continuous spectrum - a difficult concept

20.9 Road inputs to automobiles

20.10 Random vibration video demonstration

20.11 Simulating random vibrations in the lab

20.12 What is PSD? ASD? g2/Hz?

20.13 Conversion: g2/Hz to ‘tustins’

20.14 PSD/ASD in m2/s3