AN IMPEDANCE TUBE FOR THE IN-SITU CLASSIFICATION OF BUBBLY LIQUIDS

It is well documented that the presence of even a few air bubbles in water can signifi- cantly alter the propagation and scattering of sound. Air bubbles are both naturally and artificially generated in all marine environments, especially near the sea surface. The abil- ity to measure the acoustic propagation parameters of bubbly liquids in situ has long been a goal of the underwater acoustics community. One promising solution is a submersible, thick-walled, liquid-filled impedance tube. Recent water-filled impedance tube work was successful at characterizing low void fraction bubbly liquids in the laboratory [1]. This work details the modifications made to the existing impedance tube design to allow for submersed deployment in a controlled environment, such as a large tank or a test pond. As well as being submersible, the useable frequency range of the device is increased from 5 - 9 kHz to 1 - 16 kHz and it does not require any form of calibration. The opening of the new impedance tube is fitted with a large stainless steel flange to better define the boundary condition on the plane of the tube opening. The new device was validated against the classic theoretical result for the complex reflection coefficient of a tube opening fitted with an infinite flange. The complex reflection coefficient was then measured with a bubbly liquid (order 250 micron radius and 0.1 - 0.5 % void fraction) outside the tube opening. Results from the bubbly liquid experiments were inconsistent with flanged tube theory using current bubbly liquid models. The results were more closely matched to unflanged tube theory, suggesting that the high attenuation and phase speeds in the bubbly liquid made the tube opening appear as if it were radiating into free space.US Navy Office of Naval Research

Problems at the Nexus of Geometry and Soft Matter: Rings, Ribbons and Shells

There has been an increasing appreciation of the role in which elasticity plays in soft matter. The understanding of many shapes and conformations of complex systems during equilibrium or non-equilibrium processes, ranging from the macroscopic to the microscopic, can be explained to a large extend by the theory of elasticity. We are motivated by older studies on how topology and shape couple in different novel systems and in this thesis, we present novel systems and tools for gaining fundamental insights into the wonderful world of geometry and soft matter. We first look at how defects, topology and geometry come together in the physics of thin membranes. Topological constraint plays a fundamental role on the morphology of crumpling membranes of genus zero and suggest how different fundamental shapes, such as platonic solids, can arise through a crumpling process. We present a way of classifying disclinations using a generalized “Casper-Klug” coordination number. We show that there exist symmetry breaking during the crumpling process, which can be described using Landau theory and that thin membranes preserve the memory of their defects. Next we consider the problem of the shapes of Bacillus spores and show how one can understand the folding patterns seen in bacterial coats by looking at the simplified problem of two concentric rings connected via springs. We show that when the two rings loses contact, rucks spontaneous formed leading to the complex folding patterns. We also develop a simple system of an extensible elastic on a spring support to study bifurcation in system that has adhesion. We explain the bifurcation diagram and show how it differs from the classical results. Lastly, we investigate the statistical mechanics of the Sadowsky ribbon in a similar spirit to the famous Kratky-Porod model. We present a detail theoretical and numerical calculations of the Sadowsky ribbon under the effect of external force and torsion. This model may be able to explain new and novel biopolymers ranging from actin, microtubules to rod-like viruses that lies outside the scope of WLC model. This concludes the thesis.Physic

A study of the mechanical properties of liquid crystal polymer fibres and their adhesion to epoxy resin using Laser Raman Spectroscopy

PhDA number of high performance fibres (aramid, PBZT and PBO) spun from liquid crystal polymer solutions were examined in this work. In particular, a thorough investigation of the mechanical response of these fibres under tensile and compressive deformations was carried out. The major experimental tool employed was the technique of Laser Raman Spectroscopy. It was found that stress-induced changes of these fibres at molecular level are proportional to the macroscopic deformation applied. This correlation is unique for the fibres. A method for converting spectroscopic data to predicted stress-strain curves in tension and compression was proposed. An estimation of their compressive strength was derived and an understanding of the nature of their compressive failure was discussed. The adhesion of these fibres to epoxy resin was also investigated by monitoring in situ the interfacial stresses developed along the interface/interphaseo f model single fibre composite coupons. The strength of the interfacial bond was measured. The effect of various parameters such as fibre modulus, fibre diameter and fibre nature upon the interfacial strength of the various systems was evaluated. The mechanisms of stress transfer along with the nature of interfacial damage was examined accurately. It was found that the major parameter controlling the above mechanisms was interfacial yielding in shear. A numerical appoximation (using Finite Element Analysis) was employed in order to evaluate the experimental results. Finally, general conclusions concerning the performance of these fibres were drawn.Pateras Foundation of Scholarshi