Nonlinear Acoustic Effects Research Articles

Non-linear acoustic analysis of the pressure rise of the compression wave generated by a train entering a tunnel

Hara's formula is used to predict the pressure rise of a compression wave generated by a high-speed train entering a tunnel. The acoustic theory is used to predict its waveform. Hara's formula was derived from the shock theory. Meanwhile, the acoustic theory produces the same non-dimensional formula as Hara's formula up to order OM4, where M is the train Mach number, when the non-linear acoustic effect in the vortex sound theory is considered. However, the relationship between the shock and acoustic theories remains unclear because the closed formula produced by the vortex sound theory apparently differs from that of Hara's formula. This study shows that Hara's formula can be deductively obtained from the non-linear acoustic theory. A general equation used to predict the compression waveform with a relative error of Op/ρ0c02, where p/ρ0c02 is the non-dimensional acoustic pressure to the atmospheric density ρ0 and the sound speed c0, is shown herein using the non-linear acoustic theory.

Nonlinear acoustics in studies of structural features of materials

Abstract

Self-propulsive swimmers: Two linked acoustic radiating spheres

We propose a simple, practical, and versatile acoustic-driven swimmer, composed of two spherical bodies that may radiate the sound field, monochromatically, at monopole state (breathing mode of vibration) and are linked by a rigid rod. Considering the nonlinear acoustic effects, the net acoustic radiation force exerted on the device is analytically derived and it is shown that the resultant radiation force exerted on the swimmer may be nonzero. Two different configurations are considered: In the first, both spheres radiate, and in the second, one of the spheres is off. In both cases, the full manipulability conditions of swimmers are obtained and the effects of size factors, frequency of radiation, etc., are discussed. Assuming low Reynolds number swimming condition, the frequency-dependent swimming velocity is obtained via the so-called reflection method and the optimal radiating states are discussed. Finally, the challenge of random walk due to host medium fluctuations is discussed and it is shown that the Brownian noise is negligible. Our methodology will open a path toward self-propulsive controllable devices, which may play the role of carriers, machines, or mechanisms at small scales.

Nonlinear Acoustic Effects in Rod Resonators with Rigid Boundaries

We theoretically study nonlinear acoustic effects (amplitude-dependent loss, resonant-frequency shift, and the second-harmonic generation) and determine the thresholds of parametric generation of subharmonic oscillations at fractional frequencies in the rod resonators with rigid boundaries and various nonlinearity types (elastic, hysteretic, different-modulus, etc.).

Dolphin and bat sonar: Nonlinear acoustic effects

Both dolphin and bat sonars operate in an amplitude and frequency regime where nonlinear effects can be observed, particularly distortion and the generation of harmonics. Computations illustrating these nonlinear effects are presented, quantifying effects that could be observed in experiments on echolocating signals conducted with wideband sensors. The mathematical model used is the Khokhlov-Zabolotskaya-Kuznetsov (KZK) nonlinear parabolic wave equation, which includes diffraction and absorption for directional beams, with computations performed in the time domain using a finite-difference scheme. Inputs to the computations are sample dolphin echolocation transients (clicks) and bat echolocation tone bursts (FM Chirps—fundamental component), taken from the literature for a few species of high-amplitude emitters. Calculations begin in the water or air media. Propagating high-amplitude dolphin clicks are shown to distort, create harmonics, and suffer nonlinear attenuation at ranges of tens of meters. Propagating high-amplitude bat chirps are shown capable of undergoing some nonlinear distortion at ranges within 10 m. The results may be useful in understanding the significance of nonlinear effects for work with these animals. (Work supported by ARL:UT Austin.)

Harmonic generation and frequency mixing at nonlinear imperfect interfaces

Imperfect interfaces can be found in a variety of natural and artificial systems. Some examples of such interfaces that are objects of ultrasonic evaluation and diagnostics include contacting mechanical components as well as closed defects in structural components. A remarkable feature of these interfaces is that they exhibit highly nonlinear responses to ultrasonic waves. Harmonic generation (generation of, e.g., double frequency signals at the incidence of a wave with a certain frequency) and frequency mixing (generation of sum/difference frequency signals at the incidence of waves of two different frequencies) are typical phenomena at these interfaces. In this presentation, a theoretical analysis of these phenomena is presented based on modeling the interface as a nonlinear spring-type interface between two similar linearly elastic media. Unlike the corresponding nonlinear acoustic effects due to material nonlinearity, the interfacial nonlinear effects considered here do not require the spatial accumulation of nonlinearly generated harmonic or sum/difference frequency components. The propagation directions and amplitudes of these nonlinearly generated components are derived for plane mono- or dichromatic incident waves. Some relevant experimental results for a contacting interface of metallic blocks subjected to different applied pressures are also presented.

Assessment of a Two-Way Coupling Methodology Between a Flow and a High-Order Nonlinear Acoustic Unstructured Solvers

A two-way coupling on unstructured meshes between a flow and a high-order acoustic solvers for jet noise prediction is considered. The flow simulation aims at generating acoustic sources in the near field while the acoustic simulation solves the full Euler equations, thanks to a discontinuous Galerkin method, in order to take into account nonlinear acoustic propagation effects. This methodology is firstly validated on academic cases involving nonlinear sound propagation, shock waves and convection of aerodynamic perturbations. The results are compared to analytical solutions and direct computations. A good behaviour of the coupling is found regarding the targeted space applications. An application on a launch pad model is then simulated to demonstrate the robustness and reliability of the present approach.

Scattering cross-sectional modulation in photoacoustic remote sensing microscopy.

Modeling and observations of large scattering cross-sectional modulations in absorbing optical scatterers due to a pulsed laser excitation are reported. Rapid laser-induced thermo-elastic expansion produces nontrivial perturbations to the local refractive indices. This mechanism forms the basis of a recent non-contact photoacoustic technique known as photoacoustic remote sensing microscopy. A time-evolution model is constructed and discussed, comparing it with existing planar models, time-independent models, and experiments. Fractional scattering cross-sectional modulations greater than 20 times that of the unperturbed particles are predicted and observed for the first time, to the best of our knowledge. A nonlinear acoustic enlargement effect is likewise predicted and observed. Implications of system and material properties are explored.

Pressure and tension waves from bubble collapse near a solid boundary: A numerical approach.

The acoustic waves being generated during the motion of a bubble in water near a solid boundary are calculated numerically. The open source package OpenFOAM is used for solving the Navier-Stokes equation and extended to include nonlinear acoustic wave effects via the Tait equation for water. A bubble model with a small amount of gas is chosen, the gas obeying an adiabatic law. A bubble starting from a small size with high internal pressure near a flat, solid boundary is studied. The sequence of events from bubble growth via axial microjet formation, jet impact, annular nanojet formation, torus-bubble collapse, and bubble rebound to second collapse is described. The different pressure and tension waves with their propagation properties are demonstrated.

Experimental study of nonlinear acoustic effects of orifices in duct systems

Researchers focused on reduced emissions hydrocarbon fuel combustion systems have developed new high-efficiency furnace and gas turbine engine technologies that, unfortunately, regularly suffer from detrimental combustion instabilities. Engineering design tools developed to predict these instabilities in combustion systems frequently neglect nonlinear acoustic effects. However, boundaries and duct junctions, e.g., area changes, valves, and orifices, often exhibit nonlinear effects even at low acoustic pressure amplitudes. Experimental data of these nonlinear effects are required to accurately model engine and duct acoustics and to predict combustion instabilities. This experimental investigation focuses on understanding the nonlinear acoustic response of an orifice with and without steady flow. Various orifices were mounted in a multiple-microphone impedance tube and the acoustic impedance of the combination was used to measure the nonlinear acoustic response and impedance of the orifices at amplitudes from 114 to 190 dB and over frequencies from 100 to 1500 Hz. The preliminary results of the experimental study suggest that the impedance is dependent on the acoustic velocity amplitude. This indicates significant nonlinear effects. These experimental data will assist the development of nonlinear acoustic models of orifices in combustion systems.

Nonlinear acoustic phenomena in a quartzite rod resonator

Here we have presented the results of experimental and theoretical studies of nonlinear acoustic effects (such as low-frequency amplitude-dependent losses, resonant frequency shifts, and high harmonic generation as well as a damping and carrier phase delay of weak ultrasonic pulses under powerful low-frequency pumping wave) in a rod resonator made of a crystalline rock – quartzite. Also, we have given an analytical description of the observed phenomena within the frameworks of the phenomenological equations of state that contain low-frequency hysteretic nonlinearity and both dissipative and reactive high-frequency nonlinearities. Comparison of experimental and analytical amplitude–frequency dependencies of the nonlinear phenomena allowed us to determine quartzite acoustic nonlinearities parameter values.

Improved object detection sonar using nonlinear acoustical effects in bubbly media

Clutter from air bubbles can significantly impact the performance of object detection sonar in shallow water environments where bubbles are present due to breaking waves, wakes, or organic matter. Nonlinear acoustical effects can be excited in bubbly liquids at sound pressures below that required in bubble-free media and hence can be used to discriminate between bubbles and solid objects or to suppress bubble-related clutter altogether. Whereas such effects are widely exploited for ultrasonic biomedical imaging enhancement and it is hypothesized that dolphins exploit them in their biosonar, relatively less attention has been given to their use in naval, commercial, or oceanographic manmade sonar. Here, we describe laboratory tank experiments and modeling efforts aimed at exploiting these effects to improve object detection sonar. A bubble dynamics model was employed to investigate parameter space for nonlinear effects such as subharmonic and higher-order harmonic generation from regions of bubbly liquid and sonar-induced bubble translation. Laboratory experiments were conducted to verify the presence of these effects. Finally, a laboratory demonstration of a nonlinear bubble/object discriminating sonar, in which nonlinear effects are used to place markers on returns from regions of bubbly liquid, will be presented. [Work supported by ONR.]

Effect of the ultrasonic emitter on the distortion performance of the parametric array loudspeaker

Abstract The parametric array loudspeaker (PAL) is a type of directional loudspeaker that utilizes the nonlinear acoustic effect to create the audible sound in an ultrasonic beam. Due to this unusual sound principle, it is inevitable that nonlinear distortion is incurred in the sound transmission of the PAL. Numerous modulation methods aiming to reduce the nonlinear distortion have been developed on the basis of the Berktay’s far-field solution, but they often perform in an unexpected manner. The degraded practical performance has been credited to the inaccuracy of the Berktay’s far-field solution. In this paper, we demonstrate the effect of the ultrasonic emitter on the distortion performance of the PAL and suggest that the Berktay’s far-field solution remains to be a good model equation.

Seadrome: Increasing the safety of takeoff and landing operations in the seaplane basin

This paper presents the method of preparing the water area of a seaplane basin. It is proposed to use the network structure of the bottom transmitter-receiver antenna assemblies, generating ultrasound in an aqueous medium due to the nonlinear acoustic effects, for echolocation with the adjustable angular resolution of submerged objects.

Finite-difference lattice Boltzmann simulation on acoustics-induced particle deposition

Particle manipulation by acoustics has been investigated for many years. By a proper design, particle deposition can be induced by the same principle. The use of acoustics can potentially be developed into an energy-efficient technique for particle removal or filtration system as the pressure drop due to acoustic effects is low and the flow velocity is not necessary to be high. Two nonlinear acoustic effects, acoustic streaming and acoustic radiation pressure, are important. Acoustic streaming introduces vortices and stagnation points on the surface of an air duct and removes the particles by deposition. Acoustic radiation pressure causes particles to form agglomerates and enhances inertial impaction and/or gravitational sedimentation. The objective of this paper is to develop a numerical model to investigate the particle deposition induced by acoustic effects. A three-step approach is adopted and lattice Boltzamnn technique is employed as the numerical method. This is because the lattice Boltzmann equation is hyperbolic and can be solved locally, explicitly, and efficiently on parallel computers. In the first step, the acoustic field and its mean square fluctuation values are calculated. Due to the advantage of the lattice Boltzmann technique, a simple, stable and fast lattice Boltzmann method is proposed and verified. The result of the first step is input into the second step to solve for acoustic streaming. Another finite difference lattice Boltzmann method, which has been validated by a number of flows and benchmark cases in the literature, is used. The third step consists in tracking the particle's motion by a Lagrangian approach where the acoustic radiation pressure is considered. The influence of the acoustics effects on particle deposition is explained. The numerical result matches with an experiment. The model is a useful tool for optimizing the design and helps to further develop the technique.

Saw-Tooth Acoustic Waves in Media with Hysteresis Nonlinearity

We study propagation of periodic saw-tooth waves in nondispersive media with quadratic elastic and hysteresis nonlinearity. By comparing exact solutions for saw-tooth waves and their spectral characteristics, we identified regularities in the behavior of nonlinear acoustic effects in such media. It is shown that as distinct from the case of a medium with quadratic elastic nonlinearity, the effects of nonlinear dispersion can manifest themselves in hysteresis media.

Exploitation of nonlinear acoustical effects of air bubbles in water for a bubble/target discriminating sonar

Target detection by traditional sonar can be undermined by air bubbles in various environments, including the surf zone, within gas-bearing sediments, or within seagrass beds. Bubbles introduce a variety of strong acoustical effects, including the onset of many nonlinear effects at sound pressure levels far below that required in bubble-free water. This paper describes laboratory tank experiments demonstrating a bubble/target discriminating sonar that exploits some of these nonlinear effects. Bubble plumes were generated in the tank by releasing compressed air through a porous ceramic plate. Rigid targets were also positioned at various locations in the tank. A high amplitude driving pulse excited translation of bubbles in the water column yielding Doppler signatures from conventional imaging sonar, while Doppler signatures were absent from the heavy rigid targets ensonified by the same driving signal. For sufficient bubble density, subharmonic generation was also observed in regions of bubbly water, but not from the rigid targets. The goal of this work is to use one or both of these nonlinear effects to identify and reduce clutter caused by bubbles and improve target detection for sonar operation in areas where bubbles are present. [Work supported by ARL:UT and ONR.]

Nonlinear effects in a model of a thermoacoustic refrigerator driven by a loudspeaker

It is known that acoustic nonlinear effects in thermoacoustic refrigerators are unfavorable to the performance because they transfer the acoustic energy of the fundamental wave to harmonic waves, while only the former is useful for refrigeration. To study the nonlinear effects in loudspeaker-drive thermoacoustic refrigerators, we measure the acoustic performance in a coupling system composed of a resonant pipe driven by an electrodynamic loudspeaker via an inverse horn. It is found that the nonlinear effects increase both the acoustic pressure of fundamental wave in the resonant pipe and the electroacoustic transfer efficiency of the system. Then, a theoretical model is established to study the nonlinear effects in the coupling system, in which the nonlinearities arising from the loudspeaker, inverse horn, and resonant pipe are taken into account, and the simulated results are used to explain the experimental phenomena.

Simulation and Phantom Study of the Acoustic Nonlinear B/A Parameter for Biological Tissues by Using Comparative Method

The nonlinearity parameter B/A is an important indicator of the nonlinear acoustical effects for biological tissues. This paper investigates nonlinear B/A parameter for biological tissues by using comparative method. The investigations are carried out in both computer simulation and phantom study. In simulation study, Pseudo-spectral time domain (PSTD) method for second-order acoustic equation with a novel un-split Perfectly Matched Layer is proposed to improve the simulation efficiency and meanwhile maintain high accuracy. In phantom study, an experimental platform based on the Ritec SNAP-5000 system is designed. Experiments in simulation and phantom study achieve high estimation accuracy for B/A with percentage error less than 3%. Experimental results show that the comparative method can provide accurate B/A measurement for biological tissues.

Nonlinear acoustic effects in a resonator with saturation of hysteretic loss

Nonlinear wave processes in an acoustic rod resonator with hysteretic nonlinearity under harmonic excitation are studied. The characteristics of longitudinal nonlinear modes of the resonator with hard and soft boundaries (amplitude-dependent loss, shifts of resonance frequencies, and amplitudes of the second and third harmonics) are determined. The comparison of the theoretical and experimental dependences of nonlinear acoustic effects in a resonator that is made of annealed polycrystalline copper is used to determine the parameters of the hysteretic nonlinearity.