An Investigation of the Multiple Scattering of Waves in Two-Dimensional Random Media

Numerical studies of the ensemble average, or coherent, wave in a two-dimensional random medium have been undertaken for the steady-state and transient cases. The medium consisted of a tensioned mesh with a uniform distribution of point masses attached at the intersection points of the mesh. For the steady-state case, a random distribution of springs was also added to the mesh points. Scatterer density and scatterer strength were varied by changing the number of added springs and their stiffness, respectively. The average center deflection for several hundred mesh configurations of a given scatterer density and strength were compared with the predictions of the quasicrystalline approximation (QCA) and coherent potential approximation (CPA) theories. For the transient case, a random distribution of additional point masses was added to act as the scatterers. The mesh was subjected to an impulse force at one end, and the measured phase speed and attenuation were again compared with the predictions of the QCA and CPA theories. In addition, spatial-averaged results were compared with ensemble-averaged results for the transient mesh. In both the steady-state and transient cases, the comparisons indicate that neither theory holds a distinct advantage over the other in terms of accuracy, and both may appear valid to the experimentalist in the lab or field. Finally, the use of multiple scattering theory to predict the modal density of a random medium was demonstrated for a thin plate with circular holes.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Theoretical and Applied Mechanics

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Romack, George Michael

Contributors dc:contributor

• Weaver, Richard L.

• Applied Mechanics
• Physics, Acoustics

Identifier

(UMI)AAI9314932

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/72620