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Title: Ultrasonic visco-inertial dissipation in dilute particulate suspensions
Author: Richards, Simon David
ISNI:       0000 0001 3517 1289
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2002
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Coastal seas are often characterized by relatively high concentrations of suspended mineral particles, compared to the open ocean. These suspensions can degrade the performance of high frequency (tens of kHz and above) sonars and other acoustic sensors operating in turbid environments. Existing sonar performance prediction models do not include the effects of suspended particles. There is therefore a requirement to investigate the effects of suspended particles on acoustic propagation and develop techniques for accounting for these effects in sonar performance models. The purpose of the research described in this thesis was to address that requirement. The effects of suspended solid particles on ultrasonic propagation have therefore been investigated through theory, modelling and laboratory experimentation. The effects considered were: visco-inertial absorption; thermal absorption; scattering; and changes to the phase speed. A numerical model which accounts for each of these effects in suspensions of spherical particles is described. The complexity of this model is such that it obscures physical insight, and more intuitive, approximate models for visco-inertial absorption and scattering have been employed throughout much of this thesis. It is demonstrated that visco-inertial absorption is the dominant effect for most sonar performance applications, with scattering only becoming important at the highest frequencies considered. Furthermore, it is shown that thermal absorption and changes to the speed of sound may usually be neglected in sonar performance studies. In order to validate the model for visco-inertial absorption by dilute suspensions of spherical particles, and study absorption by more natural particle shapes, a laboratory measurement technique has been developed. Measurement of the absorption due to dilute suspensions in a laboratory-scale experiment was found to be challenging, and a novel experimental configuration was adopted to address these challenges.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Coastal waters