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This thesis is concerned with long-range sound propagation in deep water.  The main area of interest is the stability of acoustic ray paths in wave guides in which there is a transition from single to double duct sound speed profiles, or vice-versa.  Sound propagation is modelled within a ray theoretical framework, which facilitates a dynamical systems approach of understanding long-range propagation phenomena, and the use of its tools of analysis. Alternative reduction techniques to the Poincaré sections are presented, by which the stability of acoustic rays can be graphically determined.  Beyond periodic driving, these techniques prove to be useful in case of the simplest quasiperiodic driving of the ray equations.  One of the techniques facilitates a special representation of ray trajectories for periodic driving. Namely, the space of sectioned trajectories is partitioned into nonintersecting regular and chaotic regions as with the Poincaré sections, when quasiperiodic and chaotic trajectories are represented by curve segments and area filling points, respectively.  In case of the simplest quasiperiodic driving – speaking about the same technique – regular trajectories are represented by curves similar to Lissajous curves, which are opened or closed depending on whether the two driving frequencies involved make relative primes or not. It is confirmed for a perturbed canonical profile that the background sound speed structure controls ray stability. It is also demonstrated for a particular double duct profile, when the singularity of the nonlinearity parameter for the homoclinic trajectory associated with this profile refers to the strong instability of corresponding perturbed trajectories.

<p>Turbomachinery flow fields are inherently unsteady and complex which makes the related CFD analyses computationally intensive. Physically based preliminary design tools are desirable for parametric studies early in the design stage, and to provide deep physical insight and a good starting point for the later CFD analyses. Four analytical/semi-analytical models are developed in this study: 1) a generalized flat plate cascade model for investigating the unsteady aerodynamics of a blade row with non-uniformly spaced blades; 2) a multistage interaction model for investigating rotor-stator interactions; 3) an analytical solution for quantifying the impeller wake convection and pressure wave propagating between a centrifugal compressor impeller and diffuser vane; and 4) a semi-analytical model based Lifting line theory for unified propeller and horizontal-axis turbine optimization. Each model has been thoroughly validated with existing models. </p><p> With these models, non-uniformly spaced blade rows and vane clocking are investigated in detail for their potential use as a passive control technique to reduce forced response, flutter and aeroacoustic problems in axial compressors. Parametric studies with different impeller blade numbers and back sweep angles are conducted to investigate their effect on impeller wake and pressure wave propagation. Results show that the scattered pressure waves with high circumferential wave numbers may be an important excitation source to the impeller as their amplitude grows much faster as they travel inwardly than the lower order primary pressure waves. Detailed analysis of Lifting line theory reveals the mathematical and physical equivalence of Lifting line models for propellers and horizontal-axis turbines. With a new implementation, the propeller optimization code can be used for horizontal-axis turbine optimization without any modification. The newly developed unified propeller and horizontal-axis turbine optimization code based on lifting line theory and interior point method has been shown to be a very versatile tool with the capability of hub modelling, working with non-uniform inflow and including extra user specified constraints. </p>

The objective of this study was to determine how a new experimental methodology for measuring Total-Harmonic-Distortion (THD) of operational amplifiers functioned when compared with two standard methodologies, and whether the new methodology offers any improvement in noise floor and dynamic range along with distortion canceling of the sine-wave source used in the testing. The new methodology (THD) is being tested against two standard methodologies: Spectral Analysis using a tuned receiver type Spectrum Analyzer with Notch Filter pre-processing, and a digitized Fast Fourier Transform (FFT) using Notch Filter pre-processing. The THD results appear to agree across all methodologies, and across all items of the sample within all methodologies, to within a percent or less. The distortion and noise canceling feature of the new methodology appeared to function as expected and in accordance with theory. The sample tested in the study consisted of thirty-five NE5534 operational amplifiers produced by Texas Instruments, Inc. and purchased from a local store. The NE5534 is a low-noise, low-distortion, operational amplifier that is widely used in industry and is representative of today's best audio amplifiers.

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This thesis presents a preliminary investigation into the determination of enginerring important surface texture (of around a few microns) using ultrasonic pulse-echo signals. Current texture measurements and parameterisation techniques are reviewed, identifying their deficiencies, the requirements of a texture measurement device and the potential benefits of an ultrasonic technique. Plane compressional wave, high resolution, commercial NDT probes are considered, with the received signal being modelled as a first type Fredholm equation. The characteristics of these probes are considered in detail and realistic numerical simulations are presented, showing the variation in sound field and receiver voltage with the geometry and electrical condition of the test configuration. Inversion of the signal model is considered as a direct and useful route to characterising the surface. Techniques for this inversion are reviewed indicating their salient features and showing their inter-relationships. Several linear inversion techniques are considered in detail, using numerical simulations. These demonstrate their characteristics and the predictability of their performance. A simple 'interpolation' technique is shown to yield excellent results when applied under appropriate conditions. The Maximum Entropy algorithm is shown to yield significant improvements over linear techniques, in terms of reduced noise and filter artefacts and also possibly in improved resolution. Various characteristics of the algorithm performance are considered. Finally, preliminary results using real pulse echo signals are considered, with Maximum Entropy again yielding considerably superior results. While the achievable resolution is still somewhat below that desired, these results clearly demonstrate that the use of ultrasonics for surface texture evaluation is highly feasible and that the continued investigation of these, and other, ultrasonic techniques is fully justified.

Acoustics is a vast subject that has been utilised in many forms for millennia. Recent work has, amongst other things, explored the control of sound using geometric structure to complement inherent material properties. In this thesis, structured plates and surfaces are exploited to engineer specific acoustic responses. The acoustic transmittance and reflectance of these systems is explored in air and underwater to further understanding and develop structures that possess tailored acoustic properties. Original investigations are presented across six chapters. The first three investigations explore the transmittance of periodically perforated plates in air. The fourth investigation considers a non-resonant mechanism of obtaining complete transmission by varying the fluid environment and the fluid in the apertures of a periodically perforated plate is explored. The fifth investigation considers the transmittance through a slit in an acoustically soft plate underwater. Finally, the surface waves supported on periodically structured surfaces are explored by observing the reflectance of the surface. An acoustic field incident upon a perforated plate is partly transmitted. However, at frequencies dictated by the thickness of the plate, the acoustic field is completely transmitted. Stacking two plates with a small separation creates a resonant cavity between the plates that is the origin of a narrow acoustic stop-band at the frequency of the resonance. By varying the offset of the stacked plates and by varying the gap between the plates the frequency of this acoustic stop band is controlled. Altering the geometry of the plate surface within the gaps allows the gap to behave like an array of Helmholtz resonators, in doing so the frequency of the acoustic stop-band is significantly lowered. Varying the acoustic properties of the fluid contained within the apertures of a periodically perforated plates changes how sound is transmitted through the structure. By careful choice of the fluid environment and aperture media, it is demonstrated numerically that broadband total transmittance can be obtained. Acoustic tunnelling is demonstrated through an acoustically soft-walled slit underwater. The slit exhibits a cut-off frequency below which no propagating waves can exist, in contrast to a rigid-walled slit where propagating waves exist down to zero frequency. Resonant acoustic tunnelling is observed through two closely spaced slits in a series connection, at a frequency below the cut-off frequency of the lowest supported propagating mode. A preliminary study of pseudo surface acoustic waves on periodically structured surfaces observes the excitation of surface waves in reflection. A long pitch grating, added to the surface allows diffractive coupling of incident acoustic radiation to the surface wave. However, the height of the grating above the sample is shown to strongly affect the frequency at which the surface wave is detected. All the structures investigated may be designed to provide a desired response by careful choice of the geometry and materials.

The purpose of this thesis was to design, build, and test a device capable of simulating the acoustic pulse expected from the interaction between an Ultra-High Energy (UHE) neutrino and seawater. When a neutrino interacts with seawater, the reaction creates a long, narrow shower of sub-atomic particles. The energy from this reaction causes nearly instantaneous heating of the seawater on an acoustic timescale. The acoustic pulse created by the resulting thermal expansion of the water is predicted to be bipolar in shape. This work was undertaken to support a Stanford experiment, the Study of Acoustic Ultra-high energy Neutrino Detection (SAUND), that uses existing hydrophone arrays to detect UHE neutrinos from the acoustic pulse generated by their rare interactions with seawater. The device fabricated for this thesis uses the discharge current from a 4 microFarads capacitor charged to 2.5kV to heat the seawater between two copper plates. The anode and cathode plates of this "zapper" design were 6 cm in diameter and 20 cm apart. The acoustic pulse generated by the zapper was measured both in a small test tank at NPS and at the Acoustic Test Facility located at NUWC Keyport. Bipolar pulses observed at NPS on two separate test dates had average pulse lengths of 110 microseconds +/- 10 microseconds and 160 +/- 20 microseconds and average amplitudes at 1m of 1.9 +/- 0.3Pa and 4.7 +/- 0.6Pa. The average pulse length recorded at Keyport was 49 +/- 6 microseconds and the average amplitude at 1m was 6.4 +/- 0.9Pa. The pulse lengths recorded at NPS were reasonably consistent with theory, however all pressure amplitudes were about 100 times lower than predicted. The cause of the amplitude discrepancy is not completely understood at this time.