Date of Award

Spring 2018

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering - (M.S.)

Department

Civil and Environmental Engineering

First Advisor

Jay N. Meegoda

Second Advisor

Bruce G. Bukiet

Third Advisor

Lucia Rodriguez-Freire

Abstract

High-intensity ultrasonic wave has several engineering, biological, medical and chemical applications. High intensity acoustic waves can lead to a desired change in a medium by initiating one or more diverse mechanisms such as acoustic cavitation, heating, radiation pressure, or chemical reactions. Nonlinear nature of intense acoustic waves opens an entire new spectrum of applications. Hence there is need to understand and model the mechanism of nonlinear wave motion for practical applications of intense acoustic waves.

In this research, one-dimensional motion of shock waves in an ideal fluid is studied to include nonlinearity. In nonlinear acoustics, the propagation velocity of different sections of the waveform are different, which causes distortion in the waveform and results in formation of a shock (discontinuity). Intense acoustic pressure causes particles in fluid to move forward as if pushed by a piston to generate a shock. As the piston retracts, a rarefaction, a smooth fan zone of continuously changing pressure, density, and velocity, are generated. When the piston stops, another shock is sent into the medium. The wave speed can be calculated by solving a Riemann problem. This study examined the interaction of shocks with rarefactions. The flow field resulting from these interactions shows that the shock waves are attenuated to a Mach wave and the pressure distribution within the flow field shows the initial wave becoming severely distorted at a distance from the source. The developed theory was applied to waves generated by 20kHz, 500kHz and 2MHz transducer with 50W, 150W, 500W and 1500W power levels to examine the variation in flow fields.

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