Interactions enhance the acoustic streaming around flattened microfluidic bubbles

2016 ◽  
Vol 797 ◽  
pp. 851-873 ◽  
Author(s):  
F. Mekki-Berrada ◽  
T. Combriat ◽  
P. Thibault ◽  
P. Marmottant
Keyword(s):  
Rayleigh Waves ◽  
Mixed Mode ◽  
Short Range ◽  
Acoustic Streaming ◽  
High Amplitude ◽  
Faraday Waves ◽  
Vortex Pairs ◽  
Near Resonance ◽  
Oscillating Bubbles ◽  
Translational Mode

The vibration of bubbles can produce intense microstreaming when excited by ultrasound near resonance. In order to study freely oscillating bubbles in steady conditions, we have confined bubbles between the two walls of a silicone microchannel and anchored them on micropits. We were thus able to analyse the microstreaming flow generated around an isolated bubble or a pair of interacting bubbles. In the case of an isolated bubble, a short-range microstreaming occurs in the channel gap, with additional in-plane vortices at high amplitude when Faraday waves are excited on the bubble periphery. For a pair of bubbles, we have observed long-range microstreaming and large recirculations describing a ‘butterfly’ pattern. We propose a model based on secondary acoustic Bjerknes forces mediated by Rayleigh waves on the silicone walls. These forces lead to attraction or repulsion of bubbles and thus to the excitation of a translational mode in addition to the breathing mode of the bubble. The mixed-mode streaming induced by the interaction of these two modes is shown to generate fountain or anti-fountain vortex pairs, depending on the relative distance between the bubbles.

Intermittency, Secondary Bifurcation and Mixed-Mode Oscillations in a Swirl-Stabilized Annular Combustor: Experiments and Modeling

2020 ◽  
Author(s):  
Samarjeet Singh ◽  
Amitesh Roy ◽  
Reeja K. V. ◽  
Asalatha Nair ◽  
Swetaprovo Chaudhuri ◽  
...  
Keyword(s):  
Mixed Mode ◽  
Equivalence Ratio ◽  
High Amplitude ◽  
The State ◽  
Turbulent Flames ◽  
Bulk Velocity ◽  
Thermoacoustic Instability ◽  
Mixed Mode Oscillations ◽  
Annular Combustor ◽  
Low Amplitude

Abstract We experimentally study thermoacoustic transitions in an annular combustor consisting of sixteen premixed, swirl-stabilized turbulent flames. We show the changes in the characteristics of bifurcations leading to the state of longitudinal thermoacoustic instability (TAI) when equivalence ratio and bulk velocity are systematically varied. Depending upon the bulk velocity, we observe different states of combustor operation when the equivalence ratio is varied. These states include combustion noise, intermittency, low-amplitude TAI, mixed-mode oscillations (MMO), and high-amplitude TAI. We closely examine the special case of MMO that is encountered during the transition from low-amplitude TAI to high-amplitude TAI. We also discuss the global and local flame dynamics observed during the state of MMO. We find that during epochs of low-amplitude oscillations of MMO, all the flames are partially synchronized, while during epochs of high-amplitude oscillations, all the flames are perfectly synchronized. Finally, we replicate the criticalities of bifurcation of the annular combustor in a phenomenological model containing sixth-order nonlinearities.

The seismic response of sediment-filled valleys. Part 2. The case of incident P and SV waves

1980 ◽  
Vol 70 (5) ◽  
pp. 1921-1941
Author(s):  
Pierre-Yves Bard ◽  
Michel Bouchon
Keyword(s):  
Seismic Response ◽  
Rayleigh Waves ◽  
High Amplitude ◽  
Ground Shaking ◽  
Resonance Modes ◽  
Long Duration ◽  
Time Domains ◽  
P And Sv Waves ◽  
Lateral Resonance ◽  
Main Component

abstract We present the extension to incident P and SV waves of our previous study (Bard and Bouchon, 1980) concerning the seismic response of sediment-filled bidimensional valleys to incident SH transient signals. The reliability of the Aki-Larner method is briefly discussed and the domain is estimated within which it provides accurate results. Then we investigate the response of three different valleys, having various geometrical and elastic parameters, to vertically incident P and SV waves, in both the frequency and time domains. The behavior of the valleys is shown to be qualitatively similar to their behavior for SH waves: the nonplanar interface causes surface waves (here Rayleigh waves) to be generated on valley edges, and to propagate laterally inside the basin. The amplitude of these Rayleigh waves depends greatly on the velocity contrast, the valley shape, and the incident wave type (P or SV), but it may be significantly higher than the disturbance associated with the direct incident signal. The frequency and direction of incident motion determine partly whether the fundamental or first higher mode will be predominantly excited, depending on the main component (vertical or horizontal) of the Rayleigh mode motion. Although the reflections of these Rayleigh waves on valley edges do not appear as clearly as in the SH case, a very long duration of the ground shaking inside the valley is still observed. In deep valleys, these laterally propagating Rayleigh waves may degenerate into a lateral resonance pattern, involving high-amplitude surface motion. These latter resonance modes, however, begin to appear in shallower valleys for incident SV waves than for incident P ones.

scholarly journals Rayleigh-to-shear wave conversion at the tunnel face — From 3D-FD modeling to ahead-of-drill exploration

Geophysics ◽  
2007 ◽  
Vol 72 (6) ◽  
pp. T67-T79 ◽  
Author(s):  
Thomas Bohlen ◽  
Ulrich Lorang ◽  
Wolfgang Rabbel ◽  
Christof Müller ◽  
Rüdiger Giese ◽  
...  
Keyword(s):  
Rayleigh Waves ◽  
Damage Zone ◽  
Tunnel Boring Machine ◽  
High Amplitude ◽  
Body Waves ◽  
Front Face ◽  
S Wave ◽  
Tunnel Face ◽  
S Waves ◽  
Cutter Head

For safe tunnel excavation, it is important to predict lithologic and structural heterogeneities ahead of construction. Conventional tunnel seismic prediction systems utilize body waves (P- and S-waves) that are directly generated at the tunnel walls or near the cutter head of the tunnel boring machine (TBM). We propose a new prediction strategy that has been discovered by 3D elastic finite-difference (FD) modeling: Rayleigh waves arriving at the front face of the tunnel are converted into high-amplitude S-waves propagating further ahead. Reflected or backscattered S-waves are converted back into Rayleigh waves which can be recorded along the sidewalls. We name these waves RSSR waves. In our approach, the front face acts as an S-wave transceiver. One technical advantage is that both the sources and the receivers may be placed behind the cutter head of the TBM. The modeling reveals that the RSSR waves exhibit significantly higher amplitudes than the directly reflected body waves. The excavation damage zone causes dispersion of the RSSR wave leading to multimodal reflection response. For the detection of geologic interfaces ahead, RSSR waves recorded along the sidewalls are corrected for dispersion and stacked. From the arrival times, the distance to the S-S reflection point can be estimated. A recurrent application, while the tunnel approaches the interface, allows one to quantify the orientation of the reflecting interfaces as well. Our approach has been verified successfully in a field experiment at the Piora adit of the Gotthard base tunnel. The distance to the Piora fault zone estimated from stacked RSSR events agrees well with the information obtained by geologic surveying and exploratory drilling.

scholarly journals Generation of Low-Frequency Ground Vibrations by Sound Waves Propagating in Underground Gas Pipes

1995 ◽  
Vol 14 (3) ◽  
pp. 143-149 ◽  
Author(s):  
V.V. Krylov
Keyword(s):  
Turbulent Flows ◽  
Rayleigh Waves ◽  
Low Frequency ◽  
Ground Vibration ◽  
High Amplitude ◽  
Vibration Velocity ◽  
Wave Spectra ◽  
Direct Impact ◽  
Sound Waves ◽  
Rayleigh Surface Waves

The hypothesis is examined about sources of disturbing low-frequency hums arising from buried gas or petrol pipes in which turbulent flows of gas or liquid generate sound waves of high amplitude propagating in pipe-lines as in waveguides. Theoretical investigation of this problem shows that if the velocities of sound inside the pipes (450 m/s for methane) are higher than the velocities of Rayleigh surface waves in the ground (typically 300–600 m/s) then ground Rayleigh waves are effectively generated by sound waves propagating inside the pipes, the mechanism of generation being similar to that of sonic boom from supersonic jets. The Rayleigh waves then propagate to buildings and cause building vibration and structure-borne noise. Central frequencies of generated Rayleigh wave spectra are in the range of 5–20 Hz and depend on pipe-depth. The amplitudes of ground vibration velocity may achieve 70 dB (relative to 10−9 m/s). This is quite enough to annoy some people both due to the direct impact of vibrations and to structure-borne noise. The results obtained may contribute to a fuller understanding of the nature of low-frequency hums.

The wedge model revisited: A physical modeling experiment

Geophysics ◽  
2010 ◽  
Vol 75 (2) ◽  
pp. T15-T21 ◽  
Author(s):  
Joanna K. Cooper ◽  
Don C. Lawton ◽  
Gary F. Margrave
Keyword(s):  
Physical Model ◽  
High Velocity ◽  
Mixed Mode ◽  
High Amplitude ◽  
P Wave ◽  
Seismic Survey ◽  
Pure Mode ◽  
Model Data ◽  
Zero Offset ◽  
Wave Migration

To assess seismic amplitude effects commonly associated with the classic wedge model in geophysics, we built a scaled physical model of a simple high-velocity wedge immersed in water. In addition to demonstrating the well-known tuning effect related to thin beds, a 2D marine zero-offset seismic survey over the physical model shows a surprising number of high-amplitude dipping events corresponding to elastic multimodes, multiples, and mixed-mode reflections having nonreciprocal raypaths. These events cause additional complexities in the amplitudes of the top-wedge and base-wedge reflections that are not observed in simple acoustic seismic responses of the wedge model. Finite-difference, acoustic, exploding-reflector numerical model data, calculated using the same wedge geometry and velocity model, assisted in the identification of these events. It was found that the amplitudes of mixed-mode multiples in data recorded over high-velocity rocks with a wedge-like geometry might be significant. We also discovered that there is a maximum number of zero-offset pure-mode multiples within the wedge for a given wedge taper angle. Conventional P-wave migration of the physical model data confirmed that the multimode reflections degrade the quality of the migrated image.

scholarly journals Streaming flow by oscillating bubbles: quantitative diagnostics via particle tracking velocimetry

2017 ◽  
Vol 820 ◽  
pp. 529-548 ◽  
Author(s):  
Rocío Bolaños-Jiménez ◽  
Massimiliano Rossi ◽  
David Fernandez Rivas ◽  
Christian J. Kähler ◽  
Alvaro Marin
Keyword(s):  
Particle Tracking ◽  
Acoustic Streaming ◽  
Three Dimensional ◽  
Theoretical Models ◽  
Flow Strength ◽  
Oscillating Bubbles ◽  
Linear Oscillation ◽  
The Stability ◽  
Streaming Flows ◽  
Streaming Flow

Oscillating microbubbles can be used as microscopic agents. Using external acoustic fields they are able to set the surrounding fluid into motion, erode surfaces and even to carry particles attached to their interfaces. Although the acoustic streaming flow that the bubble generates in its vicinity has been often observed, it has never been measured and quantitatively compared with the available theoretical models. The scarcity of quantitative data is partially due to the strong three-dimensional character of bubble-induced streaming flows, which demands advanced velocimetry techniques. In this work, we present quantitative measurements of the flow generated by single and pairs of acoustically excited sessile microbubbles using a three-dimensional particle tracking technique. Using this novel experimental approach we are able to obtain the bubble’s resonant oscillating frequency, study the boundaries of the linear oscillation regime, give predictions on the flow strength and the shear in the surrounding surface and study the flow and the stability of a two-bubble system. Our results show that velocimetry techniques are a suitable tool to make diagnostics on the dynamics of acoustically excited microbubbles.

Intermittency, Secondary Bifurcation and Mixed-Mode Oscillations in a Swirl-Stabilized Annular Combustor: Experiments and Modeling

2020 ◽  
Author(s):  
Samarjeet Singh ◽  
Amitesh Roy ◽  
K. V. Reeja ◽  
Asalatha Nair ◽  
Swetaprovo Chaudhuri ◽  
...  
Keyword(s):  
Mixed Mode ◽  
Equivalence Ratio ◽  
High Amplitude ◽  
The State ◽  
Turbulent Flames ◽  
Bulk Velocity ◽  
Thermoacoustic Instability ◽  
Mixed Mode Oscillations ◽  
Annular Combustor ◽  
Low Amplitude

Abstract We experimentally study thermoacoustic transitions in an annular combustor consisting of sixteen premixed, swirl-stabilized turbulent flames. We show the changes in the characteristics of bifurcations leading to the state of longitudinal thermoacoustic instability (TAI) when equivalence ratio and bulk velocity are systematically varied. Depending upon the bulk velocity, we observe different states of combustor operation when the equivalence ratio is varied. These states include combustion noise, intermittency, low-amplitude TAI, mixed-mode oscillations (MMO), and high-amplitude TAI. We closely examine the special case of MMO that is encountered during the transition from low-amplitude TAI to high-amplitude TAI. We also discuss the global and local flame dynamics observed during the state of MMO. We find that during epochs of low-amplitude oscillations of MMO, all the flames are partially synchronized, while during epochs of high-amplitude oscillations, all the flames are perfectly synchronized. Finally, we replicate the criticalities of bifurcation of the annular combustor in a phenomenological model containing sixth-order nonlinearities.

On Non-Ideal Simple Portal Frame Structural Model: Experimental Results under a Non-Ideal Excitation

2004 ◽  
Vol 1-2 ◽  
pp. 51-58 ◽  
Author(s):  
José Manoel Balthazar ◽  
Reyolando Manoel Lopes Rabelo da Fonseca Brasil ◽  
F.J. Garzeri
Keyword(s):  
Structural Model ◽  
Excitation Frequency ◽  
High Amplitude ◽  
Sudden Increase ◽  
Motor Speed ◽  
Symmetrical Mode ◽  
Near Resonance ◽  
Portal Frame ◽  
Non Linear ◽  
Limited Power

We present measurements of the non-linear oscillations of a portal frame foundation for a non-ideal motor. We consider a three-time redundant structure with two columns, clamped in their bases and a horizontal beam. An electrical unbalanced motor is mounted at mid span of the beam. Two non-linear phenomena are studied: a) mode saturation and energy transfer between modes; b)interaction between high amplitude motions of the structure and the rotation regime of a real limited power motor. The dynamic characteristics of the structure were chosen to have one-to-two internal resonance between the anti-symmetrical mode (sway motions) and the first symmetrical mode natural frequencies. As the excitation frequency reaches near resonance conditions with the 2nd natural frequency, the amplitude of this mode grows up to a certain level and then it saturates. The surplus energy pumped into the system is transferred to the sway mode, which experiences a sudden increase in its amplitude. Energy is transformed from low amplitude high frequency motion into high amplitude low frequency motion. Such a transformation is potentially dangerous. We consider the fact that real motors, such as the one used in this study, have limited power output. In this case, this energy source is said to be non-ideal, in contrast to the ideal source whose amplitude and frequency are independent of the motion of the structure. Our experimental research detected the Sommerfeld Effect: as the motor accelerates to reach near resonant conditions, a considerable part of its output energy is consumed to generate large amplitude motions of the structure and not to increase its own angular speed. For certain parameters of the system, the motor can get stuck at resonance not having enough power to reach higher rotation regimes. If some more power is available, jump phenomena may occur from near resonance to considerably higher motor speed regimes, no stable motions being possible between these two.

scholarly journals Spectral analysis of Rayleigh waves in south-eastern parts of Niger delta, Nigeria

2017 ◽  
Vol 6 (1) ◽  
pp. 51
Author(s):  
Aniwetalu Emmanuel ◽  
Ilechukwu Juliet ◽  
Oguadinma Vivian ◽  
Chiadikobi Kingsley ◽  
Nnaji Ezechimelu
Keyword(s):  
Power Spectrum ◽  
Rayleigh Waves ◽  
Energy Levels ◽  
Amplitude Spectrum ◽  
Power Spectra ◽  
High Amplitude ◽  
Oscillatory Behavior ◽  
Dispersion Pattern ◽  
Frequency Range ◽  
Ground Roll

Interference of ground roll energy on true seismic reflection records has continued to pose a serious challenge to exploration geophysicists. In view of this, amplitude and power spectra of the Rayleigh waves which are the precursor of the ground roll energy were derived from over 70 raw monitor records and plotted as a function of frequency. The objective is to determine the locus of ground energy in the seismic records, analyse their dispersion pattern and suggests viable ways of suppressing them. The results of the amplitude spectrum plots revealed that Rayleigh waved exhibit oscillatory behavior with very high-amplitude values, which correspond to the locus of ground roll energy. This energy is confined to very low frequency range of about 4-9Hz. The Power spectrum which was given as the square of the amplitude as a function of frequency showed appreciable lobes of breaths of the ground roll energy of about 0.5-0.7cm and their trend of dispersions. The power spectrum plots revealed several peaks excluding the early peaks that are direct indication of ground roll energy. The plots showed pronounced and constant decline in energy levels with increasing frequency and reaching very low decibel values of -60Db to -80Db at frequency range of 50Hz. This indicates that the environment is dispersive in nature which probably results from velocity layering. This is a precursor to seismic noise which among others can be suppressed in the field by designing filters with sharper cut off characteristics.

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