Low-frequency Acoustic Field Research Articles

RHEOLOGICAL AND COLLOID-STRUCTURAL BEHAVIOUR OF HIGH-VISCOSITY CRUDE OIL AND EMULSION AFTER WAVE ACTION

One of the main problems in oil production is the formation of stable oil-water emulsions that cause corrosion of pipelines, malfunction of pumping equipment, and poisoning of catalysts at refineries. The features of the viscosity-temperature behaviour of high-viscosity resinous crude oil from the Russkoye field (Yamal-Nenets autonomous district) and its 30 wt% emulsion after exposure to electromagnetic and low-frequency acoustic fields are investigated. Electromagnetic treatment of crude oil leads to a decrease in the phase transition temperature and the yield strength coefficient. Low-frequency acoustic processing of the emulsion is accompanied by a decrease in the effective viscosity and the yield strength coefficient. After a complex wave action, the viscosity-temperature characteristics of crude oil continue to fall, and the stability of the formed emulsions decreases due to the intense coalescence of water-phase droplets. It is shown that the amount of released asphaltenes in oil-containing systems decreases after wave treatment. On the contrary, after a complex impact, their content in crude oil increases, while in the emulsion it continues to decrease. This is likely to occur due to the release of hydrocarbons occluded in the asphaltene structure into the liquid oil phase.

High-order Bragg forward scattering and frequency shift of low-frequency underwater acoustic field by moving rough sea surface

Acoustic scattering modulation caused by an undulating sea surface on the space–time dimension seriously affects underwater detection and target recognition. Herein, underwater acoustic scattering modulation from a moving rough sea surface is studied based on integral equation and parabolic equation. And with the principles of grating and constructive interference, the mechanism of this acoustic scattering modulation is explained. The periodicity of the interference of moving rough sea surface will lead to the interference of the scattering field at a series of discrete angles, which will form comb-like and frequency-shift characteristics on the intensity and the frequency spectrum of the acoustic scattering field, respectively, which is a high-order Bragg scattering phenomenon. Unlike the conventional Doppler effect, the frequency shifts of the Bragg scattering phenomenon are multiples of the undulating sea surface frequency and are independent of the incident sound wave frequency. Therefore, even if a low-frequency underwater acoustic field is incident, it will produce obvious frequency shifts. Moreover, under the action of ideal sinusoidal waves, swells, fully grown wind waves, unsteady wind waves, or mixed waves, different moving rough sea surfaces create different acoustic scattering processes and possess different frequency shift characteristics. For the swell wave, which tends to be a single harmonic wave, the moving rough sea surface produces more obvious high-order scattering and frequency shifts. The same phenomena are observed on the sea surface under fully grown wind waves, however, the frequency shift slightly offsets the multiple peak frequencies of the wind wave spectrum. Comparing with the swell and fully-grown wind waves, the acoustic scattering and frequency shift are not obvious for the sea surface under unsteady wind waves.

Pressure Sensitivity Kernel and Travel-Time Gradient for Geoacoustic Parameters Perturbations of Sediment in Shallow Water

In shallow sea, the effect of geoacoustic characteristics of seabed sediments on acoustic propagation cannot be neglected, which is closely related to acoustic detection and seabed inversion. Aiming at the problem of low-frequency acoustic propagation, the sound pressure sensitivity kernel (PSK) and travel-time gradient (TTG) of the shallow low-frequency acoustic field for the geoacoustic parameters of sediment were presented by using normal mode model and perturbation approximation. Combined with the benchmark shallow sea model, the numerical simulation was carried out. The simulation results show that the PSK for the sound velocity of sediment are showing some interference pattern in velocity-range plane and velocity-frequency plane, and its strength is attenuated with the increase of range. TTGs have different sensitivity to the sound velocity of sediment at different range, which is more sensitive at mid-range. The PSK and TTG show some frequency selectivity.

Interference Pattern Anomaly of an Acoustic Field Induced by Bottom Elasticity in Shallow Water

This paper reports the interference pattern of an acoustic field in the 100–300 Hz frequency band observed in a shallow water experiment. Assuming there is a conventional fluid sea bottom, the observed interference pattern is first demonstrated to potentially be abnormal, as a measured waveguide invariant of 1.03 corresponding to the 200–300 Hz frequency band could indicate that the bottom sound speed is relatively high, which is inconsistent with another observation from the interference pattern that the sound field is dominated by only one mode if the frequency is lower than 150 Hz. The numerical analysis shows that, owing to the high bottom sound speed, the third mode can still strongly interfere with the first mode at a frequency of 150 Hz, at least. Accordingly, a dual-layer sea bottom model consisting of a fluid sediment layer and an underlying half-space elastic substrate was proposed to interpret the observed anomaly. The results reveal that the acoustic leakage attenuation due to the elastic substrate plays a major role in the observed dominance of one mode in the sound field occurring below a frequency of 150 Hz. Therefore, the deep bottom’s elasticity may have a significant impact on the interference characteristics of low-frequency acoustic fields in shallow water under certain conditions.

A low-frequency acoustic sensing scheme based on cladding mode of large-angle tilted fiber Bragg grating

A novel low frequency acoustic sensor based on the cladding mode of large-angle tilted fiber Bragg grating (TFBG) is proposed and verified in this work. It mainly uses the characteristic that the coupling mode of the core and cladding mode in TFBG is easy to change when the TFBG experiences micro-bend, which will finally causes a dramatic drift in the spectrum. By combining a large-angle TFBG with the designed polyethylene terephthalate (PET) transducer diaphragm and cavity structure, an effective low-frequency acoustic sensing system is obtained in this work. Under the action of applied acoustic wave, the transducer membrane will have periodic vibrations, which will makes the fixed TFBG dynamically bend, directly leading to a wavelength shift of the cladding mode spectrum. The experimental results show that the sensing system can achieve high-sensitivity acoustic detection in a frequency range of 45–220 Hz, and a maximum acoustic pressure sensitivity of 115.88 mV/Pa at 54 Hz. Moreover, the minimum detection sound pressure can achieve 539.2 μPa/Hz<sup>1/2</sup>@54 Hz. Therefore, the sensor has the advantages of high sensitivity, good repeatability, simple structure, easy processing, etc. It has a great development prospect in the low-frequency acoustic detection related application fields.

Statistic evaluation of low-frequency acoustic wave impact on rainfall stimulation

For securing more water resources, traditional solutions including seawater desalination are limited due to high cost and restricted operating conditions. Thus, acoustic stimulation of rainfall is a potential alternative method due to its low cost and convenient operation. Low-frequency acoustic fields can be used to stimulate rainfall through evoking wavy motion of air particles in clouds which will significantly enhance the process of collision coalescence of cloud droplets and lead to their volume increase. Nevertheless, there is still a lack of rational methods to evaluate the effect of acoustic enhancement of rainfall in field experiments. To this end, in this study, nearly two-month field experiments of acoustic rainfall enhancement with 39 trials were carried out by our research team in the Tibetan Plateau. Statistical analysis was applied to evaluate the effect of acoustic wave on precipitation stimulation. The results of average rainfall intensity distribution using ordinary least square analysis disclose that acoustic interference has a considerable effect on rainfall enhancement. Such a rainfall enhancement effect increases significantly along with the increase of rainfall duration which is the index of cloud precipitation potential. For rainfall events with the duration more than two hours, the average rainfall intensity was improved by 72% with the acoustic wave effect at the experiment site. The phenomena are consistent with the fact that clouds with larger precipitation potential contain more cloud droplets which are beneficial to the acoustic coagulation process.

Destruction of a Water-in-Oil Emulsion under Combined Action of a Low-Frequency Acoustic Field and a Demulsifier

Destruction of a Water-in-Oil Emulsion under Combined Action of a Low-Frequency Acoustic Field and a Demulsifier

Quantifying low-frequency acoustic fields in urban environments

SUMMARY Infrasound data contain contributions from incoherent noise, coherent noise and signals of interest. The design of an infrasound array to target sources of interest requires a quantification of array response, individual sensor response, propagation effects (topography and meteorological conditions), signal spectrum and the noise environment. The Comprehensive Nuclear-Test-Ban Treaty community has spent significant effort in quantifying the acoustic field in rural environments for frequencies up to 7 Hz. Given that the nuclear monitoring and tactical infrasound community have growing interests in monitoring sources in or near populated regions, there is an emergent need to measure and understand acoustic fields in these environments as well. This paper focuses on quantification of the acoustic field in three different urban environments: (1) arrays installed within Dallas, TX, a metropolitan area, (2) an array installed at the rural–suburban interface near San Diego, CA and (3) an array installed in Vicksburg, MS, a small city with multiple major transportation corridors. A minimum of five months of data was recorded and used for each site characterization. The analysis focuses on frequencies from 0.1 to 45 Hz. The quantification of the data from these three sites is accomplished with statistical noise models that capture the total ambient acoustic field, separation of the coherent portion of the field and trend analysis to link temporal and seasonal variations to wind speed and anthropogenic activities. The resulting physical interpretation of the data demonstrates that the total acoustic field in urban regions is overall higher and inversely related to the number of coherent detections observed by an array. Furthermore, this study presents an analysis framework for characterizing additional urban arrays and provides a basis for future array site selection and installation.

Rayleigh scattering of a cylindrical sound wave by parallel, infinite cylinders

Scattering of sound by a target can be described as a wave radiated by virtual point sources inside the target. In the Rayleigh scattering regime, the strength of the virtual sources can be calculated analytically, and the number of linear sources is finite. When a target is located close to the ocean surface or another reflecting boundary, reflections of the incident and single-scattered waves from the boundary lead to multiple scattering from the target, with the target being insonified by nearby virtual sources. The virtual source method has recently been applied to study low-frequency acoustic fields in the vicinity of cylindrical targets near a pressure release surface or a hard bottom. This method is extended here to study the acoustic field in the near- and far-field of parallel cylindrical targets for arbitrary positions of the sound source. Multiple scattering solutions for scattering from soft, hard, and fluid targets are considered.

Characteristics of Low-Frequency Acoustic Wave Propagation in Ice-Covered Shallow Water Environment

Mastering the sound propagation law of low-frequency signals in the Arctic is a major frontier basic research demand to improve the level of detection, communication, and navigation technology. It is of practical significance for long-distance sound propagation and underwater target detection in the Arctic Ocean. Therefore, how to establish an effective model to study the characteristics of the acoustic field in the Arctic area has always been a hot topic in polar acoustic research. Aimed at solving this problem, a mathematical polar acoustic field model with an elastic seafloor is developed based on a range-dependent elastic parabolic equation theory. Moreover, this method is applied to study the characteristics of polar sound propagation for the first attempt. The validity and effectiveness of the method and model are verified by the elastic normal mode method. Simultaneously, the propagation characteristics of low-frequency signals are studied in a polar sound field from three aspects, which are seafloor parameters, sea depth, and ice thickness. The results show that the elastic parabolic equation method can be well utilized to the Arctic low-frequency acoustic field. The analysis of the influence factors of the polar sound field reveals the laws of sound transmission loss of low-frequency signals, which is of great significance to provide information prediction for underwater submarine target detection and target recognition.

Interaction of Two Nearly Contacting Gas Bubbles Pulsating in a Liquid in an Alternating Pressure Field

The conditions for the coalescence of two pulsating spherical bubbles in a liquid in a weak low-frequency acoustic pressure field, as well as the conditions for absence of such a fusion, have been studied. Since the frequency of the pressure field is much lower than natural frequencies, the bubbles pulsate with identical relative amplitudes and phases. At large distances, bubbles approach according to the Bjerknes law. However, viscous forces near a contact can compensate the attraction force and bubbles do not coalesce. It has been shown that bubbles coalesce when the ratio of radii is smaller than 3; otherwise, periodic oscillations are established at a small gap between the surfaces of bubbles and coalescence does not occur. These theoretical results have been confirmed by existing experiments.

Особенности окислительно-восстановительного процесса в поле низкочастотного воздействия

The investigation concerned the effects of low-frequency vibrations on a system consisting of two biochemically active components: methylene blue dye and ascorbic acid. Each component can be reversibly oxidized and reduced. This system allows us to trace the effect that a low-frequency vibration field has on the reciprocal reduction-oxidation process and detect specific features of this type of exposure. We discovered that reduction-oxidation processes in such systems do not accelerate but slow down when exposed to low frequencies, unlike those in the previously studied clathrate and chelate structures. We observe an inhibition effect concerning the sonochemical process in a low-frequency acoustic field. We performed a qualitative estimation of the effect.

Enhancement of water droplet evaporation rate by application of low frequency acoustic field

Evaporation rates of low-density water aerosols in a cylindrical acoustic resonator were investigated experimentally, motivated by the potential use of water droplet aerosols in two-phase thermoacoustic devices. Measurements of water aerosol evaporation rates were conducted using a novel direct visualization method combining mass balance quantification based on the light scattering from water droplets and two-dimensional PIV measurements with the droplets acting as the flow visualization particles. Water droplet aerosol evaporation was monitored at a location between the resonator pressure and velocity anti-nodes, while being subjected to a low frequency (110 Hz) acoustic standing wave with various acoustic pressure amplitude (APA) values. Application of the acoustic field was found to significantly increase water droplet evaporation rates, exhibiting a linear dependency on the applied APA in the range 600 Pa < APA < 1720 Pa Normalization of the obtained results using a simple dimensional model enabled the identification of the main governing parameters controlling droplet evaporation rates. These were found to be the known Reynolds number based on relative droplet motion, the newly introduced acoustic drive ratio, and droplet-to-air temperature difference over air water vapor concentration ratio. In addition, significant variations in the acoustic intensity, detected during the experiments, were shown to be a useful marker for measurements of droplet evaporation rate.

Distortion of the ambient low-frequency acoustic field by moorings

Moored receivers are often employed to collect long time series of underwater acoustic data to monitor the ocean. Moorings typically contain a float and other elements, acoustic parameters of which are rather distinct from those of seawater. In the frequency range of primary interest in seismo-acoustics and noise interferometry, the size of a mooring and dimensions of its float may be of the order of the acoustic wavelength or smaller. Then, acoustic measurements are performed in the near field of a strong scatterer. Assuming a spherical shape of the float, this paper aims to quantify the difference between the ambient and measured characteristics of low-frequency acoustic fields. Diffraction is shown to significantly affect low-frequency acoustic fields in a vicinity of a compact object even when the object is small compared to the wavelength. Scattering-induced low-frequency perturbations in oscillatory velocity are generally much larger than pressure perturbations in the vicinity of sub-wavelength objects. These perturbations prevent mounted vector sensors from measuring correctly the direction of the free-field oscillatory velocity. The feasibility of a posteriori compensation of the distortions in scalar and vector sensor measurements will be discussed. [Work supported by ONR.]Moored receivers are often employed to collect long time series of underwater acoustic data to monitor the ocean. Moorings typically contain a float and other elements, acoustic parameters of which are rather distinct from those of seawater. In the frequency range of primary interest in seismo-acoustics and noise interferometry, the size of a mooring and dimensions of its float may be of the order of the acoustic wavelength or smaller. Then, acoustic measurements are performed in the near field of a strong scatterer. Assuming a spherical shape of the float, this paper aims to quantify the difference between the ambient and measured characteristics of low-frequency acoustic fields. Diffraction is shown to significantly affect low-frequency acoustic fields in a vicinity of a compact object even when the object is small compared to the wavelength. Scattering-induced low-frequency perturbations in oscillatory velocity are generally much larger than pressure perturbations in the vicinity of sub-wavelength obje...

Inhibition of oxidated reducing reactions in the field of low frequency impacts

The effect of low-frequency oscillations on a system consisting of two biochemically active components: the dye of methylene blue and ascorbic acid is investigated. Each of these components can be reversibly oxidized and reduced. The system is interesting in that it makes it possible to trace the influence of the low-frequency acoustic field on the mutual redox process and to reveal the features of the effect of such oscillations. It was found that, in this system, with the introduction of low-frequency effects, redox processes are not accelerated, but slowed down. There is an effect inhibition of the sound-chemical process in the field of low-frequency acoustic effects. The effect is quantified.

Local Enhanced Microstreaming for Controllable High-Speed Acoustic Rotary Microsystems

Acoustically driven micro- and nanomachines seem promising, by virtue of their simplicity and universality, but effective methods to realize controllable high-speed rotation at these length scales are still lacking. This study investigates an actuation mechanism based on local enhanced microstreaming in a low-frequency acoustic field, and proposes a high-speed acoustic rotary microsystem. Using this simple, controllable methodology, a polystyrene rotor 10 $\ensuremath{\mu}$m in diameter can be spun at 5000 rpm, which should be useful in lab-on-a-chip applications.

INFLUENCE OF LOW-FREQUENCY ACOUSTIC FIELD AND POLYMER ADDITIVE ON STRUCTURAL AND MECHANICAL PROPERTIES OF OIL

The goal of this work is to study the influence of low-frequency acoustic field and polymer additive on structural and mechanical properties of problematic quick-freezing oil. The results were acquired by methods of rotational viscosimetry and finding phase transition temperatures by using optical density of infrared light as well as optical microscopy method. Highly paraffinic low-resin oil (Tomsk region) was exposed to low-frequency acoustic field (f = 50 Hz, 1 and 3 min of processing at 0 °С), a chemical reagent, the complex-action polymer additive D-210 (0.05% mass concentration in oil) and complex physical-chemical processing This work studies external influence on viscosity, temperature and energy characteristics, phase transition temperature as well as structure of oil residue. It was shown that in the case of problematic oil at a temperature close to freezing point, the acoustic influence leads to increase of viscosity and temperature properties. After adding the additive to processed oil during the complex processing, the thixotropic structure is destroyed, which is followed by a sharp decrease in viscosity, cloud point and freezing point. There is also a decrease in energy parameters, such as activation energy of viscous flow and internal energy of a disperse system. To determine the temperature of spontaneous crystallization we plotted the differential curves of viscosity coefficient dependence on the temperature of the medium. Study of the microstructure of the oil residue had shown that it contains small linear single-crystal and spherical formations prior to acoustic processing. After processing, however, such formations display a significant growth. The structure of the residue after complex processing is represented by many large plate paraffin crystallites.&#x0D;

Relationship between acoustic cavitation bubble behavior and output signal from tough hydrophone using high-speed camera in high-frequency and low-frequency acoustic fields

In previous works, our developed tough hydrophone was resistant to high-pressure fields (15 MPa). During the experiment, acoustic cavitation bubbles were generated around the tough hydrophone tip, because the tip was slightly larger than the wavelength and was flat. In this study, the influence of the tough hydrophone on high-intensity 1 MHz and 22 kHz acoustic fields was investigated by visualizing bubbles around the hydrophone and recording the waveform from the hydrophone at the same time. As a result, the hydrophone with a flat tip can be used for measurements in 1 MHz and 22 kHz high-intensity acoustic fields under certain conditions where acoustic bubble cloud generation on the hydrophone tip is avoided. The change in output waveforms from the hydrophone was negligibly small, even when collision and sticking of the acoustic bubble to the hydrophone tip occurred.

Dependence of the Mean Intensity of a Low-Frequency Acoustic Field on the Bottom Parameters of a Shallow Sea with Random Volumetric Water-Layer Inhomogeneities

The study is devoted to statistical modeling of low-frequency acoustic signal propagation in a twodimensionally inhomogeneous random shallow sea with a thermocline and differing penetrability of the bottom. Calculations are performed using the local-mode representation of the solution in the one-way propagation approximation. Plots are presented for the behavior of the mean acoustic field intensity for different sound velocity and density values in the bottom. It is shown that the earlier described effect of a decrease in propagation losses in a model randomly inhomogeneous shallow sea with an absorbing bottom significantly depends on the parameters of bottom sediments and is more strongly manifested for bottom boundaries with greater penetrability.

Numerical investigation of characteristic frequency excited highly underexpanded jets

A highly underexpanded jet with a nozzle pressure ratio of 5.60 is excited simultaneously by the inherent characteristic frequencies in the steady jet of 14.569 kHz, 37.086 kHz, and 45.695 kHz as well as other two reference frequencies of 1.0 kHz and 40.0 kHz. The flow characteristic of the excited jets is revealed by comparing to the steady jet using large eddy simulation technique. For low-frequency excitation (fe=1.0 kHz), the flow and acoustic fields of the forcing jet are similar with the steady jet. However, when the jet is excited by high frequencies, the acoustic source moves to the nozzle exit, and the jet potential core together with the near-field shocks oscillate periodically at the excitation frequency. The excitation at fe=1.0 kHz increases the mixing area since y/D=24 from the nozzle exit, which is contrary to the effect of other high frequencies that enhances the mixing in the near-field region but decreases the mixing area since y/D=18. The peak frequency of the excited jets generally becomes identical to the excitation frequency once being excited, except the fe=1.0 kHz and fe=40.0 kHz jets. High-order harmonics of the dominant frequency are observed in the pressure spectrum of jets excited by high frequencies, and the dominant mode turns into the axisymmetric mode from the original helical one accordingly. In particular, forcing the jet with the axisymmetric mode of fe=14.569 kHz provides the fewest shock cells but the largest amplitude in shock oscillation, the most harmonics in the spectrum, and the largest mixing area within 8≤y/D≤12.