Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 20 for “"Nonlinear acoustic"”.
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Nonlinear acoustic pulse propagation in range-dependent underwater environments
The nonlinear progressive wave equation (NPE) is a time-domain formulation of Euler's fluid equations designed to model low angle wave propagation using a wave-following computational domain. The standard formulation consists of four separate mathematical quantities that physically represent …
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Coalescence of nonlinear acoustic waves, with application to supersonic jet noise
… of coalescence that occurs when neighboring acoustic waveforms propagate in nearly the same direction and intersect to form a larger-amplitude waveform with increased nonlinear distortion. Coalescence is proposed as an explanation for the observation of steepened Mach waveforms and crackle …
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Nonlinear Acoustic Waves Generated by Surface Disturbances and Their Effect on Lower Thermospheric Composition
<p>Recent nonlinear atmospheric models have provided important insight into acoustic waves generated by seismic events, which may steepen into shocks or saw-tooth trains while also dissipating strongly in the thermosphere. Although they have yielded results that agree with observations of …
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Application of the nonlinear progressive wave equation to simulate nonlinear acoustic propagation near an interface
Includes bibliographical references (leaves 37-38).
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A finite difference numerical model for the propagation of finite amplitude acoustical blast waves outdoors over hard and porous surfaces
… of finite amplitude, i.e. weakly non-linear, acoustical blast waves from explosions over hard and porous media models of outdoor ground surfaces. The nonlinear acoustic propagation effects require a numerical solution in the time domain. To model a porous ground surface, which in the frequency …
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Trans-skull Ultrasound for Imaging and Therapy
… passive reconstruction of the acoustic field through human skull with applications including improved targeting for exploitation of nonlinear acoustic effects in the brain, controlling the microbubble dynamics, and super-resolution imaging.
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Computer simulation of finite amplitude standing waves in rigid-walled ducts.
… Coppens-Sanders theory for the one-dimensional, nonlinear, acoustic wave equation with dissipative term describing the viscous and thermal energy losses encountered in a rigid-walled, closed tube of large length-to-diameter ratio was applied to finite-amplitude standing waves by the use of the …
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Multi-functional Holographic Acoustic Lenses for Modulating Low- to High-Intensity Focused Ultrasound
… an essential role in clinical and contactless acoustic energy transfer applications. These applications have critical criteria for the acoustic pressure level, the creation of complex pressure patterns, spatial management of the complicated acoustic field, and the degree of nonlinear waveform …
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Sound from ultrasound : the parametric array as an audible sound source
A parametric array exploits the nonlinearity of the propagation medium to emit or detect acoustic waves in a spatially versatile manner, permitting concise, narrow directivity patterns otherwise possible only with physically very large transducer geometries. This thesis explores the use of the …
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The (travel) times they are a changing : a computational framework for the diagnosis of non-alcoholic fatty liver disease (NAFLD)
… through subcutaneous fat. Validation using nonlinear acoustic simulations indicated the proposed method's ability to predict the speed of sound within a medium under examination with little sensitivity to the transducer's frequency (errors less than 2%). Additionally, ex vivo testing on …
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Enhancing Nonlinear Ultrasonic Methods for Laboratory and Clinical Applications
… addresses the underlying physics associated with nonlinear ultrasonic field propagation, measurements of the nonlinear properties of materials, and mechanisms contributing to the observed systematic variation of backscattered ultrasonic energy from the heart over the heart cycle. Studies were …
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Spectroscopic perspectives on ultrafast coupling phenomena in perovskite oxides
… the technique to investigate the linear and nonlinear acoustic response in bulk SrTiO_3, which displays a ferroelastic phase transition from a cubic to a tetragonal structural phase at T_a=105 K. In the linear regime, I observe a coupling of the observed acoustic phonon mode to the softening …
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Acoustic propagation in nonuniform circular ducts carrying near sonic mean flows
… the propagation of axisymmetric and spinning acoustic modes in hard-walled and lined nonuniform circular ducts carrying near sonic mean flows. This method is valid for large as well as small axial variations, as long as the mean flow does not separate. The wave-envelope technique is based on …
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Non-destructive quantitative assessment of oxidation in aged and rejuvenated asphalt concrete pavements using a non-collinear wave mixing approach
… need by employing non-collinear wave mixing, a nonlinear acoustic technique, to evaluate the level of oxidation of the pavement. To implement the nonlinear technique, the linear acoustic parameters, i.e., dilatational and shear velocities and attenuations, of asphalt concrete specimens with …
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Nonlinear Effects in Contactless Ultrasound Energy Transfer Systems
Ultrasound acoustic energy transfer (UAET) is an emerging contactless technology that offers the capability to safely and efficiently power sensors and devices while eliminating the need to replace batteries, which is of interest in many applications. It has been proposed to recharge and …
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Elastic wave tailoring at the macro/micro/nano- scales using intentional strongly nonlinear coupling
In acoustics, wave tailoring refers to the manipulation of the propagation of waves or energy that are generated due to some form of dynamic loading. It includes real world examples ranging from impact mitigation to sensors and communication applications and is typically accomplished through the …
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Anharmonic Acoustic Technique for Detection of Surface-bound Particles
… biomolecular linkers and analyses the resulting nonlinear acoustic modulation of the resonator from the transduced electrical signal. Physisorbed and specific interactions both in air and liquid medium are studied using thickness shear mode quartz crystal resonators and streptavidin-coated …
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Design and Experimental Demonstration of a Scalable Acoustic Analogue of Quantum Computers
… disturbances. The analogy between topological acoustic waves and quantum mechanics offers a path toward the design and operation of an acoustic quantum-analogue computer which does not suffer from the fragility of qubits. In this work, we present the demonstration and characterization of such a …
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Strongly nonlinear dynamics and acoustics of coupled granular sonic vacua: theoretical and experimental studies
… (or granules) interact elastically in a highly nonlinear fashion. These highly discontinuous media have strongly nonlinear behavior owing to Hertzian interactions between granules in compression, and separations – collisions of the same granules in the absence of compression. Depending on the …
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Theoretical and experimental studies of the dynamics and acoustics of forced ordered granular networks
… is highly tunable ranging from being strongly nonlinear and non-smooth in the absence of static pre-compression, to reducing to weakly nonlinear and smooth for large static pre-compression. The nonlinearity in uncompressed granular media arises from two sources: First, nonlinear Hertzian …