Underwater intrusion detection is an ongoing security concern in port and harbor areas. Of particular interest is to detect SCUBA divers, unmanned underwater vehicles and small boats from their acoustic signature. A thorough understanding of the effects of the shallow water propagating medium on acoustic signals can help develop new technologies and improve the performance of existing acoustic based surveillance systems. The Hudson River Estuary provides us with such a shallow water medium to conduct research and improve our knowledge of shallow water acoustics. Acoustic propagation in the Hudson River Estuary is highly affected by the temporal and spatial variability of salinity and temperature due to tides, freshwater inflows, winds etc. The primary goal of this research is to help develop methodologies to predict the formation of an acoustic field in the realistic environment of the lower Hudson River Estuary. Shallow water high-frequency acoustic propagation experiments were conducted in the Hudson River near Hoboken, New Jersey. Channel Impulse Response (CIR) measurements were carried out in the frequency band from 10 to 100 kHz for distances up to 200 meters in a water depth of 8-10 meters which formed the basis for experimental Transmission Loss (TL). CIR data was also utilized to demonstrate multi-path propagation in shallow water. Acoustic propagation models based on Ray Theory and Parabolic Equation methods were implemented in the frequency band from 10 to 100 kHz and TL was estimated. The sound velocity profiles required as input by acoustic propagation models were calculated from in-situ measurements of temperature, salinity and depth. Surface reflection loss was obtained from CIR data and incorporated into the acoustic propagation models. Experimentally obtained TL was used to validate the acoustic model predictions. An outcome of this research is an operational acoustic transmission loss (TL) forecast system based on the existing, Stevens New York Harbor observation and prediction system (NYHOPS) which provides 48-hour forecasts of salinity and temperature profiles. Initial results indicate that the NYHOPS forecast of sound speed profiles used in conjunction with the acoustic propagation model is able to make realistic forecasts of TL in the Hudson River Estuary.

Acoustically driven stable cavitation may improve treatments of diseases in which passive penetration of drug into the target tissue is poor. Examples include atherosclerosis, in which the endothelium can prevent penetration of therapeutics into the plaque, and ischemic stroke, in which pathologically low flow of blood impedes the delivery of intravenous drugs to the clot. Understanding the way in which ultrasound cavitation agents nucleate cavitation in flowing blood-mimicking solutions is an important step in optimizing ultrasound-enhanced drug delivery. The use of a perfused, living ex vivo artery model permitted study of this phenomenon while still providing information on arterial bioeffects. Cavitation-enhanced delivery of anti-ICAM-1-targeted echogenic liposomes into and beyond the ex vivo murine aortic endothelium was demonstrated using 1-MHz continuous wave ultrasound. Acoustic cavitation had no apparent effect on the health of the murine arterial tissue. A method of maximizing the energy of stable cavitation through the use of intermittent 120-kHz ultrasound with quiescent periods to allow contrast agent inflow was developed. Using this insonificaiton method, sonothrombolysis was studied in ex vivo porcine carotid arteries using a 120-kHz center frequency and 0.44 MPa peak-to-peak pressure amplitude. Clot mass loss was used as a metric of thrombolytic efficacy. Clots exposed to recombinant tissue plasminogen activator and the ultrasound contrast agent, DefinityRTM in flowing porcine plasma without ultrasound experienced 34% mass loss. When robust stable cavitation was induced via 120-kHz insonation, the mean clot mass loss rose to 83%, which constituted a significant improvement (n ＝ 6, p&lt；0.0001). Without DefinityRTM there was no thrombolytic enhancement by ultrasound exposure alone at the same insonation pressure (n ＝ 6, p&lt；0.0001). Significant loss of endothelium occurred in 64% of the porcine carotid arteries, possibly due to poor oxygen delivery by the low flow of plasma. However, no correlation was observed between arterial tissue damage and treatment type. In this perfused ex vivo artery model, acoustic stable cavitation was shown to enhance both the delivery of endothelium-targeted therapeutics into the arterial wall and the lysis of whole blood clots in the presence of rt-PA.

Fibrous materials have been used successfully as the stack element in thermoacoustic devices but analysis and measurement of all the thermoacoustic properties has not been performed successfully. The acoustic thermoviscous functions that characterize the material can be measured experimentally, but the gain component of the thermoacoustic wave equation has proven difficult to measure [Simmons, 2003]. A theory has been proposed [Roh, 2007] that predicts the gain coefficient from the thermoviscous functions but it has not been tested experimentally. For the present work, a computational method has been developed for thermoacoustics in a three-dimensional stack element that has been validated successfully against analytical solutions for parallel pored stack geometries. The simulated results for a fibrous geometry are compared against the predicted thermoacoustic gain coefficient and it is found that the theory matches well for the imaginary component, but that the real component is larger than the theory predicts. This suggests that the theory underestimates the gain for a fibrous stack in a traveling wave device while being a good approximation for standing waves. Simmons, T. 2003). Experimental Determination of Thermoacoustic Stack Properties. PhD Dissertation: University of Mississippi Roh, H.S., Raspet, R., Bass, H.E. 2007). J. Acoust. Soc. Am ., 1213), 1413-1422

A mixing layer is a common model used to study the noise generation and mixing characteristics of the near-nozzle region of jets. This work presents three separate but related studies that investigate sound generation and active control for noise mitigation and mixing enhancement of such mixing layers. High-fidelity direct numerical simulations of temporal and spatial mixing layers are used for this in two and three dimensions. The first study investigates the role of turbulence scales in generating the radiated far-field sound from temporally-developing, Mach 0.9 mixing layers. To do this, four mixing layers were simulated, starting from the same initial conditions but with Reynolds numbers that varied by a factor of twelve. Above a momentum thickness Reynolds number of 300, all the mixing layers radiate over 85 percent of the acoustic energy of the apparently asymptotically high-Reynolds-number value we are able to compute. Wavenumber spectra of turbulence energy and pressure show the expected Reynolds number dependence: the two highest Reynolds number simulations show evidence of an inertial range and Kolmogorov scaling at the highest wavenumbers. Farfield pressure spectra all decay much more rapidly with wavenumber than the corresponding near-field spectra and show significantly less sensitivity to Reynolds number. Low wavenumbers account for nearly all of the radiated acoustic energy. Implications of these results for jet noise large-eddy simulations are discussed. The second study uses direct numerical simulations of Mach 1.3 mixing layers to characterize the physical mechanisms of flow actuation by localized arc-filament plasma actuators. A validated numerical model of the actuator is devised and placed, as in corresponding experiments, in a cavity in the nozzle near its exit. A rapid Joule heating caused by the plasma is thought to be the root mechanism of flow actuation based upon experimental observation. Simulations show that in the confined space of the cavity, the actuator creates a rapid flow expansion, which transfers fluid mass upward and outward creating a synthetic-jet-like perturbation to the boundary layer. The actuation promotes vortex creation much closer to the nozzle than the baseline flow without actuation, increases the layer growth rate, and organizes the large flow structures. Placing the actuator in a cavity of half the original width increases the velocities responsible for the jet-like boundary layer perturbation and downstream mixing layer growth rate. An actuator model designed to produce the same pressure response without the rapid heating provides similar control authority. The final study implements an automatic optimization procedure based on the adjoint of the perturbed and linearized flow equations. An algorithm is formulated to provide optimized control actuation for noise reduction and mixing enhancement objectives. The method is demonstrated to be successful on several model problems in two and three dimensions, in cases both with an explicitly represented “splitter” plate and cases where an appropriate inflow condition is imposed in its place. Cost functionals for noise reduction and mixing enhancement based on cross-stream velocity and pressure are formulated. Two-dimensional mixing layers with near-wall control are presented with velocity- and pressure-based spreading enhancement cost functionals. Both controls are able to maximize their respective cost functionals by over 50% and increase mixing layer thickness by 10-15% over the optimization time horizon. A three-dimensional, turbulent spatially-developing) mixing layer is simulated and optimized with a noise reduction cost functional. The control successfully reduces the noise on a target plane below the mixing layer by 28% after 4 line search iterations of the optimization scheme.

The novel application of acoustic emission as a real time, non-destructive and non-invasive technique for the monitoring of two pharmaceutical unit operations is described in this thesis. Acoustic emission was shown to be a very reproducible technique that is capable of determining granule particle size, particle size distribution, moisture content and density in a high-shear granulation process regardless of equipment or granulating conditions. Prior studies for monitoring a high-shear granulation had used narrow frequency transducers. This study utilized two sensors that had a combined sensitive over the frequency range of 20-1000 kHz. Additionally, factors impacting the acoustic signal in a granulator were explored. These included sensor location, type of sensor, mass, and the formulation. The acoustic process signature appears to be formulation dependant, and can be attributed to the combination of the individual acoustic response of the excipients in the formulation. In a second pharmaceutical application, acoustic emission from the compaction of powders was examined by the attachment of a small acoustic sensor to the outer wall of tablet die. The method was capable of providing the tensile strength of tablets from the sounds the powder admitted during compaction in a hydraulic press. The technique likewise served useful in elucidating the functionality of two different grades of HPMC that exhibited similar compaction properties, but differed in their physical properties.

The sounds generated by a writing instrument (‘pen-chant’) provide a rich and underutilized source of information for pattern recognition. We examine the feasibility of recognition of handwritten cursive text, exclusively through an analysis of acoustic emissions. We design and implement a family of recognizers using a template matching approach, with templates and similarity measures derived variously from: smoothed amplitude signal with fixed resolution, discrete sequence of magnitudes obtained from peaks in the smoothed amplitude signal, and ordered tree obtained from a scale space signal representation. Test results are presented for recognition of isolated lowercase cursive characters and for whole words. We also present qualitative results for recognizing gestures such as circling, scratch-out, check-marks, and hatching. Our first set of results, using samples provided by the author, yield recognition rates of over 70% (alphabet) and 90% (26 words), with a confidence of ＋/-8%, based solely on acoustic emissions. Our second set of results uses data gathered from nine writers. These results demonstrate that acoustic emissions are a rich source of information, usable—on their own or in conjunction with image-based features—to solve pattern recognition problems. In future work, this approach can be applied to writer identification, handwriting and gesture-based computer input technology, emotion recognition, and temporal analysis of sketches.

A prototype micro-transponder has been designed and built to track, in real-time, the positions of objects or animals within the water column. Commercially available data storage tags, which help monitor the behavior of underwater animals, do not provide real-time interrogation and data dissemination capabilities in a form factor and acoustic frequency band acceptable for active tracking applications. This prototype is 18.5 cm3 and weighs 43.7 g in air. It operates at an acoustic frequency of 160 kHz and uses a mixed-signal topology with low-power components and a microcontroller, which allows for firmware updates and addition of external sensors. It is powered by a lithium battery that provides enough energy for an 8-day deployment at a 1-second interrogation interval. Tests carried out in a tank confirmed the functionality of the design with coded replies being transmitted at source levels of 167 dB re 1 microPa at 1 m.

Acoustic networks of autonomous underwater vehicles (AUVs) show great promise, but a lack of simulation tools and reliance on protocols originally developed for terrestrial radio networks has hindered progress. This work addresses both issues. A new simulator of underwater communication among AUVs provides accurate communication modeling and flexible vehicle behavior, while a new routing protocol, location-aware source routing (LASR) provides superior network performance. The new simulator was used to evaluate communication without networking, and then with networking using the flooding or dynamic source routing (DSR) protocols. The results confirmed that a network was essential to ensure effective fleet-wide communication. The flooding protocol provided extremely reliable communication but with low message volumes. The DSR protocol, a popular routing protocol due to its effectiveness in terrestrial radio networks, proved to be a bad choice in an acoustic environment: in most cases, it suffered from both poor reliability and low message volumes. Due to the high acoustic latency, even moderate vehicle speeds caused the network topology to change faster than DSR could adapt. DSR’s reliance on shortest-path routing also proved to be a significant disadvantage. Several DSR optimizations were also tested； most proved to be unhelpful or actually harmful in an underwater acoustic network. LASR was developed to address the problems noted in flooding and DSR. LASR was loosely derived from DSR, most significantly retaining source routes and the reply/request route discovery technique. However, LASR added features which proved, in simulation, to be significant advantages two of the most effective were a link/route metric and a node tracking system. To replace shortest-path routing, LASR used the expected transmission count (ETX) metric. This allowed LASR to make more informed routing decisions which greatly increased performance compared to DSR. The node tracking system was the most novel addition: using only implicit communication coupled with the use of time-division multiple access (TDMA), the tracking system provided predicted node locations. These predictions made it possible for LASR to proactively respond to topology changes. In most cases, LASR outperformed flooding and DSR in message delivery reliability and message delivery volume.

Digital measurement of the analog acoustical parameters of a concert hall is difficult. The aim of such work is to create a digital acoustical derivation that is an accurate numerical representation of the complex analog characteristics of the hall. The present study illustrates the exponential sine sweep (ESS) measurement process in the derivation of the acoustical impulse response function (AIRF) of a music performance hall. Particularly, it examines specific difficulties of the process, such as preventing the external effects of the measurement transducers from corrupting the derivation, and provides solutions, such as filtering techniques in order to remove such unwanted effects. In addition, the thesis presents a novel method of numerical verification through mean-squared error (MSE) analysis in order to determine how accurately the derived AIRF represents the acoustical behaviour of the actual hall.

In recent years, there has been an increased awareness of the effects maritime operations civilians and military) can have on marine mammal populations. In the past, one had to rely on the use of an experienced human operator EHO) to acoustically detect such animals. The Canadian Forces are actively trying to develop automated ways to detect mammals in order to mitigate the danger associated with the use of powerful sonar and explosives in local population of marine mammals. Different methods have been developed for the detection of mammal vocalizations: spectrogram correlation, hidden Markov model, matched filter, band limited energy detector and the fast orthogonal search FOS). There are a wide variety of vocalizations: songs, moans, grunts, whistles, and echolocation clicks. This work is aimed at detecting echolocation clicks using a transient signal energy detector called the Teager-Kaiser Energy Operator. Two ways of classifying an echolocation click in different species of marine mammals have been developed.