Bubble Oscillations Research Articles

Roles of underwater explosion bubble accelerating expansion cut-off state in bubble dynamics and energy output

The process of the bubble accelerating expansion plays an important role in underwater explosion, which determines the energy output and affects the bubble oscillation subsequently. In this paper, we treated the accelerating expansion cut-off state as the critical state and applied it to the division of the expansion work, energy output, and the initial condition for bubble oscillation. It found that the Rayleigh–Plesset equation was considered appropriate to investigate the roles of underwater explosion bubble accelerating expansion cut-off state compared to the Keller equation, volume acceleration model (VAM), and pu-diagram method, and that was verified by the experimental data. Furthermore, the influence of the critical state on the expansion work and energy distribution in the accelerating expansion process was clarified, the larger critical relative volume leads to higher expansion work efficiency and total expansion work, and the shorter critical time increases the portion of the shock wave energy in the expansion work. Our finding provides a method to study the initial condition for the bubble oscillation, and that has significance in the energy output research.

A tractable mathematical model for rectified diffusion

A core unresolved challenge in rectified diffusion is the lack of predictive models, which allow accurate modelling of the growth of bubbles over millions of cycles of oscillation. The spherically symmetric problem involves two asymptotic regions in space for the convection and diffusion of the dissolved gas in the liquid, an inner region adjacent to the bubble and an outer region. It also involves three time scales: the shortest time scale associated with the bubble oscillation, the intermediate and the longest time scales for the mass transport across the bubble interface and the outer region, respectively. The problem is analysed systematically using matched asymptotic expansions in space and multi-scales in time, the large parameter being the Péclet number for mass transfer. A tractable mathematical model is formulated for rectified diffusion. It comprises the Rayleigh–Plesset equation for the spherical oscillations of the bubble on the shortest time scale, an ordinary differential equation for the mass of gas in the bubble on the intermediate time scale and a diffusion equation on the longest time scale and the long length scale. Predictions of this simplified model have excellent agreement with experimental results for a single spherical bubble in the bulk over millions of cycles of oscillation. A parametric study is undertaken with several new phenomena/features observed for acoustic frequencies in the range 12 to 62 kHz, acoustic field $0.12$ to $0.22$ bar and the initial gas concentration in the liquid being $0.95$ to $1.0$ of the saturation concentration.

Improved mechanical performances of dynamically solidified Mg97.7Y1.4Al0.9 alloy by three dimensional ultrasounds

Three dimensional (3D) ultrasounds with 20 kHz frequency and 14–22 μm amplitudes were applied to the solidification process of Mg97.7Y1.4Al0.9 alloy. With the increase of ultrasonic dimension and amplitude, both the primary Al2Y particles and the principal α-Mg phase were significantly refined in combination with an increased proportion of Al2Y/α-Mg parallel growth interfaces, while the eutectic Al2Y phase changed from long strip to fine granular shape. The dynamic solidification mechanism was further explained on the basis of in-situ acoustic spectrum measurements. It was found that once tiny primary Al2Y and α-Mg nuclei formed, they immediately strengthened acoustic field by facilitating bubble formation at their solid/liquid interfaces, and the subsequent bubble oscillation and collapsing in turn promoted their further nucleation by improving wettability and increasing local undercooling. The ultrasonically solidified alloy showed superior mechanical performances as compared with static solidification structures. The maximum tensile strength and plasticity achieved 271 MPa and 12.8% which were 1.41 and 1.36 times higher than static values, and the high temperature creep properties were enhanced as well.

Acoustic modeling of ducted propagation in the New England Mud Patch

Experiments were conducted on the New England Mud Patch in 2017, 2021, and 2022. The 2017 Seabed Characterization Experiment (SBCEX17) utilized Signal Underwater Sound (SUS) charges, model Mk64, to produce an impulsive acoustic waveform. However, recent work in 2022 has additionally utilized the Rupture Induced Underwater Sound Source (RIUSS) to produce a high-amplitude, broadband waveform with minimal bubble oscillations. Results from these experiments suggested the presence of a surficial layer of mud with a sound speed lower than that of the underlying mud and overlying water. The SBCEX22 experiment included the deployment of nine RIUSS devices and the use of Ocean Bottom Recorders (OBX) to measure the acoustic pressure and three components of particle velocity at range of about 1 km. Conductivity, temperature, and depth measurements from CTD surveys were taken from several locations around the mud patch and used to generate sound speed profiles. These were input into the RAM parabolic equation model to analyze the effect of the sound speed in mud on propagation. Results from the RAM modeling indicates that at mid-frequencies (1-3 kHz) the lower sound speed at the top of the mud layer creates a duct where the transmission loss is reduced.

De-noising of radiation pressure signal generated by bubble oscillation based on ensemble empirical mode decomposition

De-noising of radiation pressure signal generated by bubble oscillation based on ensemble empirical mode decomposition

Optimal intermittent ultrasound-assisted ultrafiltration for membrane fouling remediation

One of the most critical issues encountered in membrane-based separation processes is the permeate flux decline over a long period of operation. This study considered the potential advantages of applying intermittent ultrasound (US) to the ultrafiltration (UF) processes to control long term membrane fouling. The particles in the feed solution tend to attach to the membrane's internal pores and accumulate on the membrane surface, which impedes the filtration process and limits separation efficiency and significantly increases the power consumption. US-generated microbubbles create local turbulence and shear effect near the membrane surface, which disrupt the concentration polarization and fouling layer, resulting in flux improvement. In this regard, remediation of ceramic membrane fouling by an in-line intermittent US system was investigated. Bubble generation under different frequencies (20 kHz, 28 kHz, and 40 kHz), power intensities (50 W, 60 W, and 100 W) and time intervals were evaluated to determine the optimal US condition for enhanced filtration. A real time in-situ imaging of US-generated bubbles was employed, using a synchrotron propagation-based imaging (PBI) at the Canadian Light Source (CLS). A novel non-invasive method was employed to improve the contrast between the liquid and gas inside the bubble (interface of liquid and gas) facilitating the qualitative and quantitative analysis of US-generated bubbles. In addition, a piezoelectric ultrasonic transducer was integrated into a UF unit that was used to filter a 0.5 wt% latex paint solution. The microbubble dynamics at different US conditions were analyzed in order to correlate it with latex particles’ detachment, cake formation control and flux enhancement from data obtained with filtration experiments. It was found that the flux enhancement at 20 kHz and 28 kHz were significant, while the flux enhancement at 100 kHz was not noticeable. It was also observed that the amount of deposited particles on the membrane decreased when the frequency was increased. Oscillation of large bubbles leads to liquid movement around the bubbles and reduces the probability of the particle-membrane attachment. Our results showed that the bubble velocity increased as the frequency was increased from 20 kHz to 40 kHz. In addition, more bubbles were created when the US irradiation was turned on; however, the bubbles did not disappear when the US was off, which represent the long lifetime of the bubbles. The optimal flux was achieved when the ultrasound was set at a frequency of 28 kHz and power intensity of 50 W, while the interval of intermittent ultrasound was set at 60 s.

Gas Bubble Photonics: Manipulating Sonoluminescence Light with Fluorescent and Plasmonic Nanoparticles

Oscillations of gas bubbles in liquids irradiated with acoustic pressure waves may result in an intriguing physical phenomenon called sonoluminescence, where a collapsing bubble emits the in a broad optical spectral range. However, the intensity of the so-generated light is typically weak for practical purposes. Recently, it has been demonstrated that nanoparticles can be used to increase the efficiency of sonoluminescence, thereby enabling one to generate light that is intense enough for a number of applications in photonics, biomedicine, and materials science. In this article, we review the latest achievements in the field of nanoparticle-enhanced sonoluminescence and showcase the perspectives of their practical applications.

Multiscale interactions of liquid, bubbles and solid phases in ultrasonic fields revealed by multiphysics modelling and ultrafast X-ray imaging

The volume of fluid (VOF) and continuous surface force (CSF) methods were used to develop a bubble dynamics model for the simulation of bubble oscillation and implosion dynamics under ultrasound. The model was calibrated and validated by the X-ray image data acquired by ultrafast synchrotron X-ray. Coupled bubble interactions with bulk graphite and freely moving particles were also simulated based on the validated model. Simulation and experiments quantified the surface instability developed along the bubble surface under the influence of ultrasound pressure fields. Once the surface instability exceeds a certain amplitude, bubble implosion occurs, creating shock waves and highly deformed, irregular gas-liquid boundaries and smaller bubble fragments. Bubble implosion can produce cyclic impulsive stresses sufficient enough to cause µs fatigue exfoliation of graphite layers. Bubble-particle interaction simulations reveal the underlying mechanisms for efficient particle dispersion or particle wrapping which are all strongly related to the oscillation dynamics of the bubbles and the particle surface properties.

Dilatational and shear rheology of soluble and insoluble monolayers with a Langmuir trough

HypothesisThe surface dilatational and shear moduli of surfactant and protein interfacial layers can be derived from surface pressures measured with a Wilhelmy plate parallel, ΔΠpar and perpendicular ΔΠperp to the barriers in a Langmuir trough. ExperimentalApplying area oscillations, A0+ ΔAeiωt, in a rectangular Langmuir trough induces changes in surface pressure, ΔΠpar and ΔΠperp for monolayers of soluble palmitoyl-lysophosphatidylcholine (LysoPC), insoluble dipalmitoylphosphatidylcholine (DPPC), and the protein β-lactoglobulin to evaluate Es∗+Gs∗=A0ΔΠparΔA and Es∗-Gs∗=A0ΔΠperpΔA. Gs∗ was independently measured with a double-wall ring apparatus (DWR) and Es∗ by area oscillations of hemispherical bubbles in a capillary pressure microtensiometer (CPM) and the results were compared to the trough measurements. FindingsFor LysoPC and DPPC, A0ΔΠparΔA≅A0ΔΠperpΔA meaning Es∗≫Gs∗ and Es∗≅A0ΔΠparΔA≅A0ΔΠperpΔA. Trough values for Es∗ were quantitatively similar to CPM when corrected for interfacial curvature. DWR showed G∗ was 4 orders of magnitude smaller than Es∗ for both LysoPC and DPPC. For β-lactoglobulin films, A0ΔΠparΔA>A0ΔΠperpΔA and Es∗ and Gs∗ were in qualitative agreement with independent CPM and DWR measurements. For β-lactoglobulin, both Es∗ and Gs∗ varied with film age and history on the trough, suggesting the evolution of the protein structure.

Biomechanical Sensing Using Gas Bubbles Oscillations in Liquids and Adjacent Technologies: Theory and Practical Applications.

Gas bubbles present in liquids underpin many natural phenomena and human-developed technologies that improve the quality of life. Since all living organisms are predominantly made of water, they may also contain bubbles—introduced both naturally and artificially—that can serve as biomechanical sensors operating in hard-to-reach places inside a living body and emitting signals that can be detected by common equipment used in ultrasound and photoacoustic imaging procedures. This kind of biosensor is the focus of the present article, where we critically review the emergent sensing technologies based on acoustically driven oscillations of bubbles in liquids and bodily fluids. This review is intended for a broad biosensing community and transdisciplinary researchers translating novel ideas from theory to experiment and then to practice. To this end, all discussions in this review are written in a language that is accessible to non-experts in specific fields of acoustics, fluid dynamics and acousto-optics.

Light-Induced Raman Spectra Oscillations and Macroscopic Propulsion of Graphene Bubbles

Atomically thin graphene bubbles can form on a flat substrate due to trapped substances between graphene and the substrate, providing an impressive case to study the intriguing properties of graphene with a nanoscale curvature. The energy balance between the van der Waals interaction of graphene to the substrate and the elastic energy required to deform graphene determines the shape, size, and internal pressure of the graphene bubble. In this work, light interference-induced Newton rings were clearly resolved not only in optical microscopy images but also in Raman spectroscopy maps of the graphene bubble, which originated from the optical standing waves formed in the graphene/SiO2/Si microcavity. Importantly, for the first time, such optical standing waves were directly visualized by imaging the spatial temperature distribution of laser-irradiated graphene bubbles through Raman scan mapping. Raman spectra oscillations can be explained by the laser-induced local heating effect and nonuniform temperature on the surface of the graphene bubble. Furthermore, with a higher laser power of illumination, a direct light propulsion of the bubble was observed on a macroscopic scale. The trajectory of the graphene bubble movement can be effectively manipulated by controlling the position and travel direction of the laser beam. These results offer an exciting opportunity to tune the optoelectronic properties of graphene and other two-dimensional materials at nanoscale confinement and to achieve the direct light manipulation of matter.

Natural frequencies of a bubble near a solid sphere

This paper presents an analytical and computational method to describe natural frequencies of a spherical bubble residing near a solid sphere of an arbitrary size in an otherwise unbounded fluid. Under low capillary and Reynolds number limits, the relevant hydrodynamic fields are converted into time-invariant but frequency-dependent quantities by temporal Fourier transform. Then, the spatial variations in the velocity and the pressure can be expressed in terms of two sets of harmonic basis functions involving spherical coordinates centered around the particle and the bubble. A subsequent derivation of transformation coefficients between the aforementioned two sets allows a matrix equation relating the unknown amplitudes to the boundary conditions at all interfaces. Finally, natural frequencies corresponding to different modes of pulsation are obtained from the eigenvalues of the constructed matrix. The results show fast convergence of the computed frequencies with the increasing number of basis functions. These values change significantly with the distance of the bubble from the particle and even decay to zero for some modes when their surface-to-surface separation vanishes. Furthermore, bubble oscillation near a solid plate is also discussed when the radius of the solid sphere is increased to an infinitely large dimension. Thus, this article renders a comprehensive study of naturally pulsating submerged bubbles in the presence of a nearby solid surface of various kinds.

The influence of dissolved gas on dynamics of a cavitation bubble in an elastic micro-confinement

The mass transport problem for a single cavitation bubble in a spherical liquid cell surrounded by an infinite elastic solid is considered. To study the rectified diffusion phenomenon, the time-periodic pressure in the solid far away from the bubble is used as an external driving. The work is based on engineering approximation following the assumption by (Fyrillas and Szeri, 1994) that the bubble oscillations are fast and the growth/reduction of the mean bubble size is slow. According to this engineering approximation the problem is splitted into two problems. In the first problem, the effect of the mass transport in the system on the fast bubble oscillations is neglected, whereas in the second problem the bubble growth/reduction is considered at average, assuming that during the period of the external driving the mass of gas in the bubble does not noticeably change. The equations for the dynamics of the soluble bubble in confined liquid are derived, and the discussion of the dependence of the solution on the initial gas concentration in the liquid is reported. Three possible regimes of the bubble dynamics are revealed: 1) total bubble dissolution, when the gas concentration in the liquid is not enough to compensate the mass fluxes in and out of the bubble; 2) partial bubble dissolution, when the small gas concentration in the liquid is enough to compensate the mass fluxes in and out of the bubble, which shrinks to a resulting stable bubble size; 3) bubble growth, when the concentration of dissolved gas is enough to provide a resulting stable bubble with a larger size than the initial one. The influence of the gas diffusion in the bubble-in-cell system on the cavitation threshold is considered. The parametric study of the impact of the gas concentration in the liquid on the resulting stable bubble size is conducted for different initial bubble radii, liquid cell sizes, pressure amplitudes, and frequencies of the external driving.

Effects of translational motion on the Bjerknes forces of bubbles activated by strong acoustic waves

The motion of a small cavitation bubble is influenced by a neighboring large bubble, and these two bubbles can be mutually attractive or repulsive. The state of the bubble pair is strongly related to the secondary Bjerknes force in a strong acoustic field. Non-spherical oscillations are easily observed when a small cavitation bubble approaches a large bubble. The effects of translational motion and non-spherical oscillations of the small cavitation bubble on the secondary Bjerknes force are considered numerically in this paper, at large (greater than20 μm) and small (3 μm) bubble pair sizes. We show that the radial oscillation of the cavitation bubble is suppressed by the large bubble when the two are close to each other, and the magnitude and direction of the secondary Bjerknes force on the cavitation bubble are significantly different to those predicted results without considering translational motion. With the increase in size of the large bubble, the value of the secondary Bjerknes force varies from negative to positive, implying a transition between attraction and repulsion. The secondary Bjerknes force is sensitive to changes in the size of the large bubble, as there are many spikes in the curve in the range 20 μm < R10 < 100 μm. Moreover, the cavitation bubble is slightly repulsed when the large bubble is larger than 100 μm. There is a critical distance that can lead to a transition between mutual attraction and repulsion of bubbles. Cavitation bubbles can be driven toward the larger bubble by increasing acoustic pressure. The findings presented here will be helpful in understanding the complex behavior of cavitation bubbles in practical applications in which large bubbles exist and may interact with cavitation.

Parametrical investigation of acoustic cavitation and extraction enhancement in ultrasonic microreactors

Experimental studies on acoustic cavitation and ultrasound-assisted extraction process were systematically investigated in the laboratory-built ultrasonic microreactors. The cavitation evolution process of microbubble after ultrasound exposure was first analyzed, finding that surface tension plays a vital role on bubble oscillation. The effects of fluid property as well as ultrasound frequency on cavitation activity were then investigated, and a discriminating criterion was established on the basis of experimental data, which can well predict the bubble cavitation mode. In addition to acoustic cavitation, the effects of varying parameters, e.g., ultrasound frequency, input mode, on ultrasound-assisted extraction process were also investigated, the result of which, correlates well with the cavitation research from a meso-scale perspective. It was found that the overall mass transfer coefficients are solely related to the specific energy dissipation rate under all circumstances. At specific energy dissipation rate 3–675 W/kg, the overall mass transfer coefficients were measured to be 0.01–0.24 s−1, being comparable to that of reciprocating plate column and far high than the passive microreactor.

Dynamics of a gas bubble near the aperture of a perforated concave rigid plate

The dynamics of a gas bubble close to intact and perforated concave rigid plates located in unlimited liquid domain is studied using boundary element method combined with finite difference method. First, we examine the effect of bubble-plate distance on the behavior of the bubble near an intact plate. Next, for a perforated plate, we investigate the influence of bubble-hole distance and hole size on the bubble dynamics and provide the pressure field and velocity vectors of the surrounding liquid to better understand and interpret the results. It was found that in the case of intact plate there is only an inward high-speed liquid jet pointing to the plate. However, in the case of the perforated plate, depending on the values of bubble-hole distance and hole size there might be also a low-speed outward liquid jet pointing away from the plate. Three different bubble oscillation scenarios were found based on the relative values of the two parameters: bubble-hole distance and hole size. These scenarios are: (I) two liquid jets, (II) an inward liquid jet pointing to the hole and (III) a fairly spherical bubble oscillation without induced jets.

Amplification of high-intensity pressure waves and cavitation in water using a multi-pulsed laser excitation and black-TiOx optoacoustic lens.

A method for amplification of high-intensity pressure waves generated with a multi-pulsed Nd:YAG laser coupled with a black-TiOx optoacoustic lens in the water is presented and characterized. The investigation was focused on determining how the multi-pulsed laser excitation with delays between 50 µs and 400 µs influences the dynamics of the bubbles formed by a laser-induced breakdown on the upper surface of the lens, the acoustic cavitation in the focal region of the lens, and the high-intensity pressure waves generation. A needle hydrophone and a high-speed camera were used to analyze the spatial distribution and time-dependent development of the above-mentioned phenomena. Our results show how different delays (td ) of the laser pulses influence optoacoustic dynamics. When td is equal to or greater than the bubble oscillation time, acoustic cavitation cloud size increases 10-fold after the fourth laser pulse, while the pressure amplitude increases by more than 75%. A quasi-deterministic creation of cavitation due to consecutive transient pressure waves is also discussed. This is relevant for localized ablative laser therapy.

3D Printed Acoustically Programmable Soft Microactuators.

The concept of creating all-mechanical soft microrobotic systems has great potential to address outstanding challenges in biomedical applications, and introduce more sustainable and multifunctional products. To this end, magnetic fields and light have been extensively studied as potential energy sources. On the other hand, coupling the response of materials to pressure waves has been overlooked despite the abundant use of acoustics in nature and engineering solutions. In this study, we show that programmed commands can be contained on 3D nanoprinted polymer systems with the introduction of selectively excited air bubbles and rationally designed compliant mechanisms. A repertoire of micromechanical systems is engineered using experimentally validated computational models that consider the effects of primary and secondary pressure fields on entrapped air bubbles and the surrounding fluid. Coupling the dynamics of bubble oscillators reveals rich acoustofluidic interactions that can be programmed in space and time. We prescribe kinematics by harnessing the forces generated through these interactions to deform structural elements, which can be remotely reconfigured on demand with the incorporation of mechanical switches. These basic actuation and analog control modules will serve as the building blocks for the development of a novel class of micromechanical systems powered and programmed by acoustic signals.

Ultrasound-Assisted Synthesis of Potentially Food-Grade Nano-Zinc Oxide in Ionic Liquids: A Safe, Green, Efficient Approach and Its Acoustics Mechanism.

In food application, nano-zinc oxide (nano-ZnO) is a very important nano metal material; thus, it is necessary to prepare potentially food-grade nano-ZnO. Nano-ZnO synthesized by the ultrasound-assisted method can reach a safe level because of its import physical processing characteristics. Firstly, the micromorphology and microstructure of nano-ZnO synthesized by the ultrasonic method were compared with that by the mechanical stirring method through atomic force microscopy, X-ray diffraction, and Fourier-transform infrared. Secondly, the on-line monitoring of different ultrasonic fields in real-time was studied during the whole synthesis process of nano-ZnO by polyvinylidene fluoride sensor, and two control groups (water medium) were set. The results showed that nano-ZnO obtained by the ultrasonic method were smaller in size and had less surface roughness compared with the mechanical stirring method. The nucleation and crystallization process of nano-ZnO was controlled by the ultrasonic method with sharp diffraction peaks of higher intensities. Moreover, for the ultrasonic mechanism, it was found that the oscillation behavior of bubbles varied from liquid to liquid, and variation was also found in the same liquid under different restraint of interfaces. Based on voltage waveforms monitored in the three liquid media, differences in the life cycle of cavitation bubble oscillation, cycle of collapse stage, maximum voltage amplitude, and acoustic intensity were observed. The physical mechanism of ultrasound-assisted synthesis of nano-ZnO was revealed through voltage fluctuations of the acoustics signal, which can lay a theoretical foundation for the controllability of food ultrasonic physical processing.

Numerical prediction of cavitation erosion risk in an axisymmetric nozzle using a multi-scale approach

In the present study, a two-way coupling Eulerian–Lagrangian approach is developed to assess the cavitation erosion risk in an axisymmetric nozzle. Macroscopic cavitation structures are simulated using the large eddy simulation along with the volume of fluid method. The compressible Rayleigh–Plesset equation and the bubble motion equation are introduced to resolve the microscopic bubble dynamics. The calculated results agree favorably with the experimental data and can capture more flow details, which is associated with the potential erosion risk. Based on the bubble information in multi-scale cavitating flow, a new asymmetric bubble collapse model is proposed to calculate the impact pressure, which is then used to quantitatively assess the cavitation erosion risk in the nozzle. The results show that, compared with the traditional Euler method, the location and value of the potential maximum cavitation erosion risk predicted by this new method are closer to the experimental measurement. The advantages of the newly proposed method are further elaborated systematically. The study found that the high environmental pressure triggered by the collapse of shedding clouds can cause the near-wall bubbles to shrink and even collapse, releasing impulsive pressure, which directly damages the material surface. This phenomenon is considered to be closer to the actual cavitation erosion process. Finally, analyzing the relationship between multi-scale cavitation structures and erosion risk reveals that the high risk of cavitation erosion is mainly due to the oscillation and collapse of near-wall bubbles which are generated near the attached cavity closure line or surrounding the shedding clouds.