Ultrasonic guided waves are used to inspect an interface for disbonds between a composite layer and an aluminum half space. The hybrid analytical finite element method is used to model the problem which involves gener...
Ultrasonic guided waves are used to inspect an interface for disbonds between a composite layer and an aluminum half space. The hybrid analytical finite element method is used to model the problem which involves generating dispersion curves and wave structures and searching for optimum excitation points for inspection. A physical experiment inspects from on top of the metal in a Rayleigh to leaky Rayleigh wave problem. Detection of the defect is achieved using peak frequency shift and signal difference coefficient as features.
We address model-based processing approaches for source depth and range estimation using passive sonar. Two model-based methods have been investigated to date: temporal variations in received amplitude (Jemmott and Cu...
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ISBN:
(纸本)9781622761920
We address model-based processing approaches for source depth and range estimation using passive sonar. Two model-based methods have been investigated to date: temporal variations in received amplitude (Jemmott and Culver, 2011) and spectral striation (waveguide invariant) matching (Sell and Culver, 2011). We have shown that both methods provide satisfactory results when the environment is sufficiently well known to produce accurate acoustic model predictions. The methods are incoherent or energy-based and are thus less demanding than matched field processing (MFP). Another model-based source depth estimation method that shows promise is mode-filtering (Premus, 1997). It too is model-based and successful application depends upon sufficient environmental knowledge, and again is distinct and less demanding than MFP. Current research is directed toward comparing these methods in terms of correct classification, as well as robustness to errors in environmental knowledge. Work sponsored by ONR Undersea Signal Processing.
We recently reported on a simple standing-wave thermoacoustic engine that was intended for use as a self-powered monitor of temperature within a resonator that was similar to a nuclear fuel rod [JASA 132 (3) Pt. 2, 19...
We recently reported on a simple standing-wave thermoacoustic engine that was intended for use as a self-powered monitor of temperature within a resonator that was similar to a nuclear fuel rod [JASA 132 (3) Pt. 2, 1993-1994 (2012)]. An additional potential benefit of such a device is the enhanced heat transfer between the heat source and the surrounding coolant produced by the acoustic streaming generated by the high-amplitude acoustic standing wave within the resonator. By adding a remotely-operated linear actuator that can depresses a valve at the ambient-temperature end of the resonator, we are able to squelch the acoustic resonance by modification of that boundary condition without changing any other operating parameters (e.g., heater power). We will report heat transfer measurements made in a calorimeter at several input thermal power levels with and without the presence of the thermoacoustic oscillations. [Work supported by the U.S. Department of Energy.]
We are interested in acoustic scattering by bubble clouds in water at frequencies and densities such that the acoustic wavelength is large relative to the average distance between bubbles and large relative to that co...
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The correlation length of a rough interface is often used as a criterion for the validity of many approximate scattering models such as small roughness perturbation theory or the Kirchhoff approximation. A common inpu...
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ISBN:
(纸本)9781622761920
The correlation length of a rough interface is often used as a criterion for the validity of many approximate scattering models such as small roughness perturbation theory or the Kirchhoff approximation. A common input to these models is the power spectrum of the surface, which usually follows a band-limited power-law form (i.e., a von Karman spectrum). The fractal-like behavior of a von Karman surface breaks down at some outer scale which is closely related to the correlation length. First-order terms in approximate scattering models will not be sufficient when interface roughness correlation lengths are much larger than an acoustic wavelength. Given that first-order perturbation theory has generally been accepted as sufficient to predict scattered levels, the use of the true geophysical correlation length as a criterion for determining the validity of scattering models is suspect. In contrast to the infinite surface assumption used in most scattering models, scattering measurements are always made on patches of finite size;results of finite transmit pulses and beamwidths. In terms of correlation length, these finite-sized patches will act to window the roughness seen by the incident acoustic pulse, possibly negating the usefulness of using the true geophysical correlation length as a validity criterion. In this work we present results of a study on the link between the behavior of seafloor roughness power spectra and the finite windows resulting from measurement systems.
An experiment was conducted to measure the transmission loss of an acoustic signal in shallow water with a stable ice cover. Transmission loss was measured at acoustic receivers in the water and in air over 30 meters....
An experiment was conducted to measure the transmission loss of an acoustic signal in shallow water with a stable ice cover. Transmission loss was measured at acoustic receivers in the water and in air over 30 meters. Received levels at the microphones were greatly attenuated relative to the hydrophones with over 100 dB reduction across the spectrum. The experiment was modeled with the OASES model for estimating propagation in the time domain. Results indicated that despite the high transmission losses, enough acoustic energy can propagate through ice to air to make this a propagation pathway for ice dependent pinniped communication.
The coherent control of optical images has garnered attention because the range of information embedded in optical images is expected to be controlled in high efficiency. Recently, the storage of optical images using ...
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ISBN:
(纸本)9781557529398
The coherent control of optical images has garnered attention because the range of information embedded in optical images is expected to be controlled in high efficiency. Recently, the storage of optical images using coherent control techniques opened a method for multiple information storage. Image control in coherent medium might move up new era of quantum information technology since the generation of entangled image pairs was realized with parametric process in coherent medium. One of the most important optical controls is switch for information distribution. Here, phase-controlled optical image switching with low light intensity was demonstrated in a double-Λ system. Switching by interference in a double-Λ system was observed as having a 90 % switching depth between incoherent image pixels. Two independent laser sources were adopted for a double-Λ system such that images inscribed in two weak probe lights were incoherent with each other.
Bond integrity is of interest to researchers in non-destructive evaluation because it is used as an indicator when assessing the health of structures. In this study, a plate waveguide on a half space is examined to fi...
Bond integrity is of interest to researchers in non-destructive evaluation because it is used as an indicator when assessing the health of structures. In this study, a plate waveguide on a half space is examined to find features associated with bond integrity. Analytical and finite element models are developed to describe wave propagation. Mode and frequency selection optimization is discussed. Preliminary results suggest that changes in arrival time and amplitude can be used to detect the length of a very weak bond when using a special mode of strong in-plane displacement at the interface.
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