GPU accelerated study of a dual-frequency driven single bubble in a 6-dimensional parameter space: The active cavitation threshold.

The active cavitation threshold of a dual-frequency driven single spherical gas bubble is studied numerically. This threshold is defined as the minimum intensity required to generate a given relative expansion (R-R)/R, where R is the equilibrium size of the bubble and R is the maximum bubble radius during its oscillation. The model employed is the Keller-Miksis equation that is a second order ordinary differential equation.

Membrane cleaning with ultrasonically driven bubbles.

A laboratory filtration plant for drinking water treatment is constructed to study the conditions for purely mechanical in situ cleaning of fouled polymeric membranes by the application of ultrasound. The filtration is done by suction of water with defined constant contamination through a membrane module, a stack of five pairs of flat-sheet ultrafiltration membranes. The short cleaning cycle to remove the cake layer from the membranes includes backwashing, the application of ultrasound and air flushing.

Comparison of winding-number sequences for symmetric and asymmetric oscillatory systems.

The bifurcation sets of symmetric and asymmetric periodically driven oscillators are investigated and classified by means of winding numbers. It is shown that periodic windows within chaotic regions are forming winding-number sequences on different levels. These sequences can be described by a simple formula that makes it possible to predict winding numbers at bifurcation points.

Nonequilibrium kinetic boundary condition at the vapor-liquid interface of argon.

A boundary condition for the Boltzmann equation (kinetic boundary condition, KBC) at the vapor-liquid interface of argon is constructed with the help of molecular dynamics (MD) simulations. The KBC is examined at a constant liquid temperature of 85 K in a wide range of nonequilibrium states of vapor. The present investigation is an extension of a previous one by Ishiyama, Yano, and Fujikawa [Phys.

Bubble dynamics in a standing sound field: the bubble habitat.

Bubble dynamics is investigated numerically with special emphasis on the static pressure and the positional stability of the bubble in a standing sound field. The bubble habitat, made up of not dissolving, positionally and spherically stable bubbles, is calculated in the parameter space of the bubble radius at rest and sound pressure amplitude for different sound field frequencies, static pressures, and gas concentrations of the liquid. The bubble habitat grows with static pressure and shrinks with sound field frequency.

Ice crystallization induced by optical breakdown.

Ice crystallization in supercooled water has been initiated by focused Nd:YAG laser pulses at 1064 nm wavelength. The pulses of 8 ns duration and up to 2 mJ energy produce a bubble in the supercooled liquid after optical breakdown and plasma formation. The subsequent collapse and disintegration of the bubble into fragments was observed to be followed by ice crystal nucleation in many, but not all cases.

Optic cavitation in an ultrasonic field.

Cavitation bubbles are generated in water by low-energy femtosecond laser pulses in the presence of an ultrasonic field. Bubble dynamics and cavitation luminescence are investigated by CCD photography and photomultiplier measurements in dependence on the phase of the acoustic cycle at which the bubbles are generated. The experimental results demonstrate that the initially small laser-generated bubbles can be expanded significantly by the sound field and that weak cavitation luminescence can be observed in two small intervals of the seeding phase.

Acoustic cavitation, bubble dynamics and sonoluminescence.

Basic facts on the dynamics of bubbles in water are presented. Measurements on the free and forced radial oscillations of single spherical bubbles and their acoustic (shock waves) and optic (luminescence) emissions are given in photographic series and diagrams. Bubble cloud patterns and their dynamics and light emission in standing acoustic fields are discussed.

High-speed observation of acoustic cavitation erosion in multibubble systems.

Cleaning and erosion of objects by ultrasound in liquids are caused by the action of acoustic cavitation bubbles. Experiments have been performed with respect to the erosive effect of multibubble structures on painted glass surfaces and on aluminium foils in an ultrasonic standing wave field at 40 kHz. High-speed imaging techniques have been employed to investigate the mechanisms at work, in particular bubble interaction and cluster formation near and at the object surfaces.

Stereoscopic high-speed recording of bubble filaments.

Filamentary formations of acoustic cavitation bubbles in an ultrasonic resonator are recorded by high-speed stereoscopic means. The bubble locations and motions are reconstructed in three dimensions, and a velocity distribution of bubbles is obtained. Experimental bubble trajectories are compared to a one-to-one simulation by a particle modeling approach which shows reasonable agreement.

Single-bubble sonoluminescence in air-saturated water.

Single bubble sonoluminescence (SBSL) is realized in air-saturated water at ambient pressure and room temperature. The behavior is similar to SBSL in degassed water, but with a higher spatial variability of the bubble position. A detailed view on the dynamics of the bubbles shows agreement between calculated shape stability borders but differs slightly in the equilibrium radii predicted by a mass diffusion model.

Two-frequency driven single-bubble sonoluminescence.

Sonoluminescing single bubbles driven simultaneously by two harmonic frequencies were recently reported to increase the maximum light output up to a factor of 3 with respect to single mode excitation. In this paper, experimental and numerical results on single-bubble sonoluminescence (SBSL) in an air/water system using the fundamental mode of 25 kHz and the second harmonic at 50 kHz are presented. The region of light emission is mapped in the three-dimensional parameter space spanned by the two driving pressure amplitudes and their relative phase.

Luminescence of transient bubbles at elevated ambient pressures.

The light emission of transient laser-produced cavitation bubbles in water is investigated in a range of ambient pressures up to 5 bar and laser energies up to 30 mJ. At elevated pressures bubble luminescence can be increased more than two fold for bubbles created with the same laser energy, and up to almost an order of magnitude comparing bubbles of the same maximum radius. Both the conversion of large laser energies into mechanical energy of the bubble, and the conversion of mechanical energy into light are improved at higher pressure.

Observation of acoustic cavitation bubbles at 2250 frames per second.

Acoustically induced cavitation at 20 kHz is observed by means of high speed CCD recording at a frame-rate of 2250 per second. Using digital image processing the bubbles' trajectories are reconstructed. The experimental data reveal that collision and coalescence of bubbles is a predominant phenomenon that limits their individual lifetime.

Acoustic cavitation structures and simulations by a particle model.

Cavitation bubbles in acoustic resonators are observed to arrange in branch-like patterns. We give a brief review of the anatomy of such structures and outline an approach for simulation by individual, moving bubbles. This particle model can reproduce an experimentally observed transition between different structure types in a rectangular resonator cell.

Fast nearest-neighbor searching for nonlinear signal processing.

A fast algorithm for exact and approximate nearest-neighbor searching is presented that is suitable for tasks encountered in nonlinear signal processing. Empirical benchmarks show that the algorithm's performance depends mainly on the (fractal) dimension D(d) of the data set, which is usually smaller than the dimension D(s) of the vector space in which the data points are embedded. We also compare the running time of our algorithm with those of two previously proposed algorithms for nearest-neighbor searching.

Cavitation bubble dynamics.

The dynamics of cavitation bubbles on water is investigated for bubbles produced optically and acoustically. Single bubble dynamics is studied with laser produced bubbles and high speed photography with framing rates up to 20.8 million frames per second.

High-speed off-axis holographic cinematography with a copper-vapor-pumped dye laser.

A series of coherent light pulses is generated by pumping a dye laser with the pulsed output of a copper-vapor laser at rates of as much as 20 kHz. Holograms are recorded at this pulse rate on a rotating holographic plate. This technique of high-speed holographic cinematography is demonstrated by viewing the bubble filaments that appear in water under the action of a sound field of high intensity.