Decay of large underwater bubble oscillations

Pressure-time series from breathing-mode oscillation of large (centimeter scale or larger) underwater bubbles reveal much higher decay rates than can be explained using viscous, thermal, or radiative mechanisms which apply to microbubbles. It is shown that if one assumes energy transfer to shape oscillations (surface capillary waves) of large amplitude in subharmonic resonance with the breathing mode [M. S. Longuet-Higgins, J. Acoust. Soc. Am. 91, 1414 (1992)], then the shape oscillations can drive fluid motions outside the bubble capable of exciting turbulent instabilities. Application of an appropriate eddy viscosity from mixing-length theory to the viscous decay mechanism appears to offer a credible explanation for the observed large decay rates. An analysis is given to show that energy is transferred from the breathing mode to surface capillaries fast enough to make the proposed decay mechanism viable.     

Regimes of bubble volume oscillations in a pipe

The effect of an acoustically driven bubble on the acoustics of a liquid-filled pipe is theoretically analyzed and the dimensionless groups of the problem are identified. The different regimes of bubble volume oscillations are predicted theoretically with these dimensionless groups. Three main regimes can be identified: (1) For small bubbles and weak driving, the effect of the bubble oscillations on the acoustic field can be neglected. (2) For larger bubbles and still small driving, the bubble affects the acoustic field, but due to the small driving, a linear theory is sufficient. (3) For large bubbles and large driving, the two-way coupling between the bubble and the flow dynamics requires the solution of the full nonlinear problem. The developed theory is then applied to an air bubble in a channel of an inkjet printhead. A numerical model is developed to test the predictions of the theoretical analysis. The Rayleigh-Plesset equation is extended to include the influence of the bubble volume oscillations on the acoustic field and vice versa. This modified Rayleigh-Plesset equation is coupled to a channel acoustics calculation and a Navier-Stokes solver for the flow in the nozzle. The numerical simulations indeed confirm the predictions of the theoretical analysis.     

Magnetic bubble domains with twisted walls

The total energy, radius and wall width of a magnetic bubble with a cylindrically symmetric twisted wall are calculated here and compared with those for the corresponding domain with untwisted wall. Instability conditions are also considered.     

Gradientless propulsion of magnetic bubble domains

We find that some types of magnetic bubbles can be propelled by homogeneous fields: a modulated bias field superimposed on a steady in-plane field. Characteristic velocity vectors are observed which can discriminate among wall configurations having a common winding number s. Two particular complementary bubbles having s = 1 move in opposite directions nearly orthogonal to the in-plane field because the translational coercive force couples to motions of the wall radius and two Bloch lines.     

Surface bubble nucleation stability

Recent research has revealed several different techniques for nanoscopic gas nucleation on submerged surfaces, with findings seemingly in contradiction with each other. In response to this, we have systematically investigated the occurrence of surface nanobubbles on a hydrophobized silicon substrate for various different liquid temperatures and gas concentrations, which we controlled independently. We found that nanobubbles occupy a distinct region of this parameter space, occurring for gas concentrations of approximately 100%-110%. Below the nanobubble region we did not detect any gaseous formations on the substrate, whereas micropancakes (micron wide, nanometer high gaseous domains) were found at higher temperatures and gas concentrations. We moreover find that supersaturation of dissolved gases is not a requirement for nucleation of bubbles.     

Energy analysis during acoustic bubble oscillations: Relationship between bubble energy and sonochemical parameters

In this work, energy analysis of an oscillating isolated spherical bubble in water irradiated by an ultrasonic wave has been theoretically studied for various conditions of acoustic amplitude, ultrasound frequency, static pressure and liquid temperature in order to explain the effects of these key parameters on both sonochemistry and sonoluminescence. The Keller–Miksis equation for the temporal variation of the bubble radius in compressible and viscous medium has been employed as a dynamics model. The numerical calculations showed that the rate of energy accumulation, dE/dt, increased linearly with increasing acoustic amplitude in the range of 1.5–3.0 atm and decreased sharply with increasing frequency in the range 200–1000 kHz. There exists an optimal static pressure at which the power w is highest. This optimum shifts toward a higher value as the acoustic amplitude increases. The energy of the bubble slightly increases with the increase in liquid temperature from 10 to 60 °C. The results of this study should be a helpful means to explain a variety of experimental observations conducted in the field of sonochemistry and sonoluminescence concerning the effects of operational parameters.     

Collective bubble oscillations as a component of surf infrasound

Plunging surf is a known generator of infrasound, though the mechanisms have not been clearly identified. A model based on collective bubble oscillations created by demise of the initially entrained air pocket is examined. Computed spectra are compared to infrasound data from the island of Kauai during periods of medium, large, and extreme surf. Model results suggest that bubble oscillations generated by plunging waves are plausible generators of infrasound, and that dynamic bubble plume evolution on a temporal scale comparable to the breaking wave period may contribute to the broad spectral lobe of dominant infrasonic energy observed in measured data. Application of an inverse model has potential to characterize breaking wave size distributions, energy, and temporal changes in seafloor morphology based on remotely sensed infrasound.     

Collective oscillations of fresh and salt water bubble plumes

Bubble plumes of various void fractions and sizes were produced by varying the flow velocity of a water jet impinging normally on a water surface. The bubbles entrained at the surface were carried downwards by the fluid flow to depths ranging from 33 to 65 cm, and formed roughly cylindrical plumes with diameters ranging from 12 to 27 cm. The acoustic emissions from the plumes were recorded onto digital audio tape using a hydrophone placed outside the cloud at distances ranging from 50 cm to 16.0 m. Closeup video images of the individual bubbles within the plume were also taken in order to gain knowledge of the bubble size distributions. The experiments were performed in both fresh-water and salt-water environments. The fresh-water clouds emitted sounds with a modal structure that was significantly different from that produced by the salt-water clouds. Furthermore, the smaller bubbles present in the salt-water clouds have a fundamental effect on the amplification of turbulence noise, generating sound at significant levels for frequencies up to several hundred Hertz.     

Stable bubble oscillations beyond Blake’s critical threshold

The equilibrium radius of a single spherical bubble containing both non-condensable gas and vapor is determined by the mechanical balance at the bubble interface. This expression highlights the fact that decreasing the ambient pressure below the so called Blake’s critical threshold, the bubble has no equilibrium state at all. In the last decade many authors have tried to find evidence for the existence of stable bubble oscillation under harmonic forcing in this regime, that is, they have tried to stabilize the bubble motion applying ultrasonic radiation on the bubble. The available numerical results provide only partial proof for the existence as they are usually based on linearized or weakly nonlinear (higher order approximation) bubble models. Here, based on numerical techniques of the modern nonlinear and bifurcation theory, the existence of stable bubble motion has been proven without any restrictions in nonlinearities. Although the model, applied in this paper, is the rather simple Rayleigh–Plesset equation, the presented technique can be extended to more complex bubble models easily.     

Influence of gas motion inside a charged bubble in a liquid on the parameters of bubble oscillations

The influence of a finite rate of leveling of the gas pressure inside a charged bubble in an ideal incompressible liquid on the bubble volume and surface oscillations is studied in a linear approximation with respect to the surface oscillation amplitude. It is shown that the bubble shape is governed by superposition of spherical harmonics with amplitudes strongly depending on their frequencies, as well as on the physical properties of the gas inside the bubble and the ambient liquid.     

Dynamics of laser-induced bubble and free-surface oscillations in an absorbing liquid

A series of laser-driven dynamic photocapillary effects in absorbing liquid are described. We have observed self-oscillations of the free surface of a liquid (iodine solution in ethanol) and laser-induced bubble trapping and oscillations excited by a low power cw argon laser.     

Behavior of vertical-Bloch-line chains of hard domains in garnet bubble films

As a main micromagnetic structure of domain walls in garnet bubble films, vertical-Bloch-line (VBL) chains play an important role in the characteristics of hard domains. In the 1970s, their study progressed rapidly during the period in which bubble devices were developed. When ultra-high-density Bloch line memory (BLM) was proposed in 1983, VBL chain behavior again attracted attention. This review will introduce the early achivements focusing primarily on the results of the last decade. A convenient method of forming VBL chains, a new classification scheme of hard domains and the unsolved “number effect” of VBLs will be discussed. Various behaviors of VBL chains under static compression, and in-plane magnetic fields will also be presented. Finally, the temperature stability of VBL chains will be reported.     

Surface plasma oscillations in layer metal particles

Light scattering cross section and positions of two surface plasma resonances in a layer metal particle containing dielectric foreign nucleus are calculated within the random phase approximation. The results obtained provide a possible explanation of contradictions in size dependence of surface plasma resonance position [1, 2] and are able to explain two peak structure of photoabsorption cross section of small silver particle observed in [1].     

Surface quantum oscillations in tellurium inversion layers

We report results and the analysis of properties of the two-dimensional inversion layer in the [0001] plane at the surface of tellurium, showing special features associated with the dispersion relation of the conduction band of tellurium.     

Synchrotron radiation of electrons moving in an elliptical orbit when axial oscillations are present

It is shown that if axial oscillations and the departure of the shape of the equilibrium orbit from circular are taken into account, there is a considerable change in the spectral-angular and polarization characteristics of synchrotron radiation compared with the case when the electron moves in a circular orbit of constant radius.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 96–100, November, 1973.The authors thank Professor A. A. Sokolov for useful discussions and for suggesting the problem, and also O. P. Shatalov for carrying out the numerical calculations.     

Induced bubble shape oscillations and their impact on the rise velocity

When a 2-4 mm diameter bubble rising with constant velocity hits a thin wire, bubble shape oscillations can be induced. As a consequence also the bubble rise velocity strongly oscillates. With the help of a force balance we show that these velocity oscillations are an added-mass effect. Received 9 April 2002 / Received in final form 11 July 2002 Published online 14 October 2002 RID="a" ID="a"e-mail: lohse@tn.utwente.nl     

Experimental study of detonating gas bubble oscillations using a shock tube

Oscillations of bubbles containing a mixture of a detonating gas with argon in their interior are studied. The bubbles are excited for oscillations by a pressure step generated in a shock tube. A bubble wall motion is observed by a rotating mirror camera and a radiated pressure wave by a needle hydrophone. For weak pressure steps the bubble behaves as an ordinary gas bubble. However, above a certain pressure step threshold ignition of the detonating gas occurs. Due to released heat the bubble oscillation intensity is amplified. The data obtained are used to estimate pressures and temperatures in the compressed bubble.The experimental part of this research was carried out during the author's stay at the Shock Wave Laboratory of the Technical University in Aachen. The author wishes to thank Professor A. E. Beylich for enabling him to do this work, and H. Kleine for taking all the photographs. The author is also grateful to Dr. K. Hel for helpful discussion on the ignition of gas mixtures. During this research the author was the recipient of a grant awarded by the Heinrich Hertz Foundation, which is gratefully acknowledged.     

Radial and translational oscillations of an acoustically levitated bubble in aqueous ethanol solutions

The radial and translational oscillations of a single cavitation bubble in a standing ultrasound wave were investigated experimentally at various driving acoustic pressures for aqueous ethanol solutions with different bulk molar fractions of ethanol range of 0-1.3 × 10(-3). The results show that both the lower and upper stability thresholds of the acoustic driving pressure decreased as the concentration of ethanol was increased. At a given driving pressure the ambient and maximum bubble sizes increased with increasing ethanol concentration. In addition, as the ethanol was increased, the sonoluminescence intensity decreased while the bubble dynamics remained largely unchanged. The translational oscillation of the levitated bubble, however, became increasingly violent with increasing ethanol concentration. The displacement of the bubble reached 0.7 mm at the highest concentration studied (1.3 × 10(-3)) and the maximum bubble size was found to change as the bubble jumped up and down. This bubble translation may be responsible for the decrease of the acoustic driving pressure threshold and suggests that repetitive injection of ethanol molecules into the bubble takes place. These results may account for the different sensitivities of single bubble and multi-bubble sonoluminescence to the presence of volatile additives.