Measurement of stress fluctuations in externally driven granular systems
The transport of force through a bed of grains (sand, salt, powders, ball
bearings, ...) follows complex, fractal-like networks. When grain positions
are rearranged even slightly (such as by changing the temperature or vibrating
the bed) these networks can change dramatically leading to what are termed
"giant stress fluctuations." These fluctuations do not follow the usual
law of large numbers and are certainly NOT normally distributed. In this
project, we will build an apparatus to shake a bed of glass beads and to
measure the resulting force fluctuations. The intent is to build up large
data sets to analyze using some techniques recently developed by Benoit
Mandelbrot for non-Guassian variation in time series.