Investigating Bagnold's Booming Sand Dune Theory Through Computational Aided Approaches - Neil K. Coutinho '09
Booming sand is a rare natural phenomenon which manifests itself when an avalanche on a sand dune results in a continuous, loud droning sound. This acoustic emission is notable because it is composed of one dominant audible frequency ranging from 70 to 105 Hz. This study takes the approach of building computer simulations to model sand grains at the microscopic level to determine whether the synchronized movement of flowing sand grains in the avalanche, as proposed by Bagnold, is primarily responsible for booming. A Mathematica model was developed to numerically integrate the coupled differential equations for a 1-dimensional model of avalanching grains. In addition, a Java based 2-dimensional rendering of idealized sand grains collisions was also used to investigate oscillatory motion for replicated optimal booming dune conditions. Findings from the 1-D model, though showing well-defined peaks at certain frequencies, are not in agreement with those predicted by Bagnold’s. However a proportional relationship between frequency and linear concentration was observed, inline with Bagnold’s model. Simulated unfavorable booming conditions, such as rigidity in the packing structure and variably sized particles, seemed to indicate loss in the booming effect. The 2-D Java rendering currently accurately simulates grain collision, however recent data is inconclusive to suggest any synchronized motion in the avalanching layer. Further development of this simulation is required before any viable data can be analyzed.
For more information, contact Dr. Brian Watson
Optical Transmission and Resistivity Measurements of Pd/Mg Film Hydrides - Corey Griffin '09
Abstract: In this work, we observe the drastic changes that occur simultaneously in optical transmission, sheet resistance, and Hall resistance due to the absorption of gaseous hydrogen in custom made palladium/magnesium bilayer film samples. Initial data showed a factor of 70 increase in both Hall and sheet resistance data, as well as a significant increase in optical transparency. Hydrogen absorption causes charge carrier density to decrease, particularly in magnesium. This results in a transition from electrical conductor to insulator, and is measured quantitatively by the Hall resistance. At the same time, the material visibly changes from opaque to transparent. Our in situ measurement of the three separate quantities during hydrogen cycling is unique among previous testing. The custom film samples were tailored to facilitate the van der Pauw method of resistivity measurement, and the sample holder included permanent magnets to create the required magnetic field, as well as a monochromatic LED and photo detector to measure optical transmittance. This type of system has received attention due to potential applications it has for hydrogen storage and switchable mirror devices.
For more information, contact Dr. Daniel Koon