Dissertations / Theses on the topic 'Acoustic Bubbles'
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Hardwick, Andrew John. "The acoustic sizing of bubbles in liquids." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260420.
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Harris, Ashley M. "Acoustic properties of toroidal bubbles and construction of a large apparatus." Thesis, Monterey, California. Naval Postgraduate School, 2004. http://hdl.handle.net/10945/1675.
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Approved for public release, distribution is unlimitedWhen a burst of air is produced in water, the result can be a toroidal bubble. This thesis is concerned with experimental investigations of three acoustical properties of toroidal bubbles: (i) propagation through high-intensity noise, (ii) emission, and (iii) scattering. In (i), an attempt to observe a recent prediction of the acoustic drag on a bubble is described, which is analogous to the Einstein-Hopf effect for an oscillating electric dipole in a fluctuating electromagnetic field. No effect was observed, which may be due to insufficient amplitude of the noise. In (ii), observations of acoustic emissions of volume oscillations of toroidal bubbles are reported. Surprisingly, the emission occurs primarily during the formation of a bubble, and is weak in the case of very smooth toroidal bubbles. In (iii), we describe an experiment to observe the effect of a toroidal bubble on an incident sound field. In addition to the acoustical investigations, we describe the construction of a large hallway apparatus for further investigations and for hands-on use by the public. The tank has cross section 2 feet by 2 feet and height 6 feet, and the parameters of reservoir pressure and time between air bursts are adjustable by the observer.
Lieutenant, United States Navy
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Ramble, David Gary. "Characterisation of bubbles in liquids using acoustic techniques." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390369.
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Simmons, Stephen Michael. "Non-linear modelling of the acoustic response of bubbles." Thesis, University of Newcastle Upon Tyne, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364761.
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McIntyre, Trevor A. "Ultrasonic acoustic characteristics of air bubbles in the surf zone." Thesis, Monterey, California. Naval Postgraduate School, 1995. http://hdl.handle.net/10945/26821.
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Understanding the movement of sediment in the nearshore region due to wave motion and longshore currents is important in beach erosion studies, and has tactical significance in beach front mine warfare. In the surf zone, an bubbles and sediment are both suspended within the water column. At the Naval Postgraduate School in Monterey, California, a sediment flux probe has been developed to study small scale processes. Using ultrasonic acoustic backscatter, the Coherent Acoustic Sediment Flux Probe (CASP) is capable of tracking the movement of scatterers within the surf zone. As it is important that the CASP system is capable of distinguishing between sediment and entrained air bubbles, laboratory experiments were run to determine the ultrasonic acoustic backscatter characteristics of surf zone bubbles. Bulk void fraction and optical sizing methods were explored to develop a means of measuring bubble populations produced in the laboratory for calibration of the backscattered energy received by the CASP system in the presence of bubbles
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Harris, Ashley M. "Accoustic properties of toroidal bubbles and contruction of a large apparatus /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Mar%5FHarris.pdf.
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Su, Yu-Hsuan 1965. "Numerical study of the nonlinear dynamics of the acoustic drops and bubbles." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9434.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.Includes bibliographical references.
The dynamics of liquid drops and bubbles held together by surface tension and perturbed by small disturbances is of great interest to many researchers. Its essential physical nature is characterized by a nonlinear moving-boundary problem complicated by the interfacial stress interaction between two domains, each governed by their own dynamical systems respectively. In this thesis, the dynamics of an acoustically levitated drop is investigated. A low dimensional phase plane approach is used to interpret the nonlinear dynamics of the drop motions. It is found that the stability of shape oscillations imposes an upper limit on the acoustic bond number that can be used, while the lower limit is set by the stability of translational motion. The static equilibrium shapes can be obtained by incorporating the artificial damping into the system. The static equilibrium shapes thus found agree very well with the experimental data. In addition, that two-to-one internal resonance of a single bubble between the volume mode and one of the shape modes is carefully examined. instability wedges for unstable volume oscillations on the plane of volume oscillation amplitude versus frequency are identified numerically. Furthermore, the dynamical behaviors of the bubbles with parameters within the instability wedges can be divided into stable bubble oscillations and transient bubble oscillations. Attention is focused on the transient bubble oscillations. Numerical simulation shows that liquid jets form at t.he two poles of the transient bubble and lead to the breakup of the bubble. A possible mechanism resulting in the formation of the liquid jets is proposed and demonstrated with numerical simulation examples. Bjerknes forces between two bubbles are also investigated. It is found that the Bjerknes forces between two attracting bubbles can be predicted with a formula derived by Crum with amazing accuracy. However, numerical simulations indicate that a multiplication factor is needed for the cases of two repelling bubbles within short distance. The effect of shape oscillations on the translational motions of two bubbles is also examined. Interestingly, the shape oscillation has little effect on attracting bubbles, while significant effect on the translational motion of two repelling bubbles within short distance is observed.
by Yu-Hsuan Su.
Ph.D.
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Parini, Michael R. "Biofilm Removal Using Bubbles and Sound." Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd958.pdf.
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Zhang, Yuning. "Analysis of radial oscillations of gas bubbles in Newtonian or viscoelastic mediums under acoustic excitation." Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/55427/.
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Acoustic cavitation plays an important role in a broad range of biomedical, chemical and oceanic engineering problems. For example, kidney stone can be crushed into the powder (being discharged naturally) by the acoustic cavitation generated by carefully controlled focused ultrasonic beams. Therefore, the prediction of generation of acoustic cavitation is essential to the aforementioned emerging non-invasive technique for kidney stone crushing. The objective of this PhD program is to study the generation of acoustic cavitation (e.g. through rectified mass diffusion across bubble interface) theoretically in the Newtonian fluids (e.g. water) or viscoelastic mediums (e.g. human soft tissue) under acoustic excitation of single or dual frequency. The compressibility and the viscosity of the liquid, heat and mass transfer across bubble-medium interface are all considered in this study. During this PhD program, the established works in the literature on the above topic have been re-examined. More physically general formulas of natural frequency and damping of gas bubble oscillations in Newtonian or viscoelastic mediums has been derived and further employed for solving the problem of bubble growth under acoustic field (i.e. rectified mass diffusion). For rectified mass diffusion of gas bubbles in Newtonian liquids, the predictions have been improved for high-frequency region of megahertz and above. Effects of medium viscoelasticity and dual-frequency acoustic excitation on rectified mass diffusion have also been studied. To facilitate the fast growth of bubble under acoustic field, dynamic-frequency and dual-frequency techniques have been proposed and demonstrated.
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Xi, Xiaoyu. "Controlled translation and oscillation of micro-bubbles near a surface in an acoustic standing wave field." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/10981.
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The removal of contamination particles from silicon wafers is critical in the semiconductor industry. Traditional cleaning techniques encounter difficulties in cleaning micro and nanometer-sized particles. A promising method that uses acoustically-driven micro-bubbles to clean contaminated surfaces has been reported. However, little is understood about the microscopic interaction between the micro-bubble and particle. This thesis explores the mechanism underlying the ultrasonic cleaning using micro-bubbles at the micrometer scale. The investigation was carried out from the perspective of bubble dynamics near a surface and bubble-particle interaction. Prior to contributing to the particle removal, micro-bubbles normally need to be transported to a target surface. The motion of a bubble was analyzed based on a force balance model for single and multi-bubble translations respectively. A good agreement is found between the observed bubble movement trajectories and the theoretical predictions. After arriving on a surface, a micro-bubble starts to disturb the flow field near the boundary through its oscillation. The characteristics of the flow field are closely related to the bubble oscillation modes. The influence of a wall on the change of bubble oscillation mode during its translation toward the boundary was studied. The relationship between bubble oscillation modes and the corresponding microstreaming around the bubble was established. The experimental results of bubble oscillation modes and the flow motion are quantitatively in good agreement with the simulation results. From a mechanic point of view, a possible ultrasonic cleaning mechanism is explained by exploring the relationship between different torques that are exerted on micro and sub-micrometer-sized particles. This estimation provides a qualitative insight into the ultrasonic cleaning process at a moderate pressure amplitude. The experimental investigation of the complicated particle detachment process requires improved test equipment to be developed in the future.
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Diaz, de la Rosa Mario Alfonso. "High-frequency ultrasound drug delivery and cavitation /." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1679.pdf.
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Combriat, Thomas. "Etude d'une assemblée de bulles microfluidiques excitées par une onde ultrasonore : transmission acoustique et phénomène de streaming." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY052/document.
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De par leur importante compressibilité et leur fréquence de résonance extrêmement basse, les bulles sont des objets physiques singuliers du point de vue de l'acoustique et de la mécanique des fluides. En utilisant la technique de la microfluidique afin de créer des assemblées de bulles bi-dimensionnelles, que nous excitons acoustiquement, nous étudions à la fois leur influence sur une onde sonore et sur le fluide présent à leur voisinage.Les bulles étant des résonateurs sub-longueur d'onde, nous montrons qu'une assemblée de micro-bulles va interagir avec une onde sonore de longueur d'onde bien plus importante que la taille des bulles individuelles. En proposant une méthode pour extraire la contribution des bulles au signal acoustique, nous montrons que leur résonance suit une loi légèrement modifiée par rapport à celle proposée par Minnaert pour des bulles sphériques.Nous avons également exploré le potentiel de ce système expérimental comme méta-matériau pour l'acoustique. Nous observons en effet une baisse de la transmission d'une onde sonore à travers ce matériau et ce, dans une gamme de fréquence située au-delà de la fréquence de résonance.Cette baisse de la transmission peut être ajustée à la fois en fréquence et en amplitude ce qui fait de ce système un méta-matériau adaptable dont les caractéristiques peuvent être facilement ajustéesBecause of the important compressibility of gas bubbles in water, inducing a very low resonance frequency, one can find interest in studying bubbles from an acoustic and a fluid mechanics point of view. Using microfluidics techniques in order to produce assemblies of acoustically driven bi-dimensional bubbles, we are studying their influence on both acoustic waves and the surrounding fluid.Bubbles being sub-wavelength resonators, we show that a micro-bubbles assembly interacts with acoustical waves which wavelengths that are substantially bigger than the bubbles size. Developing a way to extract bubbles contribution to the acoustic signal, we show that their resonance frequency follows a law slightly different from the one Minnaert had found for spherical bubbles. The impact of this medium on the acoustical wave has been studied and we show that a decrease in the acoustical transmission happens in a range of frequencies above the resonance. This decrease can be adjusted in amplitude and in frequency making our system an easily tunable metameterial.Because of the strong response of bubbles induced by acoustical waves, the bubbles surface oscillates with a great amplitude in the surrounding fluid. This oscillation, working together with a coupling present between the bubbles, can drive a strong steady streaming in the fluid. Systems of several bubbles are studied, and a theory is proposed in order to predict the flow they induce. The interaction between the streaming phenomenon and an external flow is also presented, showing that exclusion zones can be present under certain circumstances in these systems. These exclusion zones can be useful in micro-fluidics in order to trap particles or chemicals
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Onur, Cagla. "Acoustic Tracking Of Ship Wakes." Phd thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615656/index.pdf.
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Theories about ship wake structure, bubble dynamics, acoustic propagation through bubble clouds, backscattering and target strength of bubble clouds have been investigated and related Matlab simulations have been carried on. Research has been carried on algorithms for ship wake acoustic detection and tracking. Particle filter method has been simulated with Matlab for target tracking using wake echo measurements. Simulation results are promising.
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Kapodistrias, Georgios. "A theoretical and experimental study on multiple scattering from bubbles, with emphasis on scattering from a bubble located close to the air-sea interface /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/7150.
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Chan, Eugene Joseph Pilpa. "Acoustic-induced drag on a bubble." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA360380.
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Thesis (M.S. in Applied Physics) Naval Postgraduate School, March 1999."March 1999". Thesis advisor(s): Andres Larraza, Bruce C. Denardo. Includes bibliographical references (p. 27-28). Also available online.
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楊兆麟 and Siu-lun Patrick Yeung. "Effect of bubbly liquid on underwater sound transmission." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31237964.
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Yeung, Siu-lun Patrick. "Effect of bubbly liquid on underwater sound transmission /." Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19471221.
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Zhang, Yuning. "Bubble dynamics under dual-frequency acoustic excitation." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/71098/.
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Acoustic cavitation plays an important role in a broad range of biomedical, chemical and engineering applications, because of its magnificent mechanical and chemical effects. Particularly, the irradiation of the multi-frequency acoustic wave could be favouritely employed to promote these effects, such as enhancing the intensity of sonoluminescence, increasing the efficiency of sonochemical reaction, and improving the accuracy of ultrasound imaging and tissue ablation. Therefore, a thorough understanding of the bubble dynamics under the multi-frequency acoustic irradiation is essential for promoting these effects in the practical applications. The objective of this PhD programme is to investigate the bubble dynamics under dual-frequency excitation systematically with respect to bubble oscillations, the acoustical scattering cross section and the secondary Bjerknes force (a mutual interaction force between two oscillating bubbles). Spherical gas bubbles in water are considered. Both analytical analysis based on perturbation method and numerical simulations have been performed in this thesis. The analytical solutions of the acoustical scattering cross section and the secondary Bjerknes force under dual-frequency excitation have been obtained and validated. The value of the secondary Bjerknes force can be considered as the linear combination of the forces derived under the single-frequency approaches. The predictions of those analytical solutions will be impaired for the cases with large acoustic pressure amplitudes. The numerical simulations reveal some unique features of the bubble dynamics under dual-frequency excitation, e.g., the combination resonances (i.e., their corresponding frequencies corresponding to the linear combinations of the two component frequencies) and the simultaneous resonances (i.e., the simultaneous occurrence of two resonances in certain conditions). The influence of a number of paramount parameters (e.g., the pressure amplitude, the equilibrium bubble radii, the power allocation between the component waves, the phase difference and the driving frequency) on the bubble dynamics under dual-frequency excitation is also investigated with demonstrating examples. Based on that, the parameters for optimizing the dual-frequency approach are proposed. In addition, the effects of thermal effects and mass transfer on the bubble dynamics have also been discussed.
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Deymier, P. A., M. Keswani, N. Jenkins, C. Tang, and K. Runge. "Giant frequency down-conversion of the dancing acoustic bubble." NATURE PUBLISHING GROUP, 2016. http://hdl.handle.net/10150/622416.
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We have demonstrated experimentally the existence of a giant frequency down-conversion of the translational oscillatory motion of individual submillimeter acoustic bubbles in water in the presence of a high frequency (500 kHz) ultrasonic standing wave. The frequency of the translational oscillations (similar to 170 Hz) is more than three orders of magnitude smaller than that of the driving acoustic wave. We elucidate the mechanism of this very slow oscillation with an analytical model leading to an equation of translational motion of a bubble taking the form of Mathieu's equation. This equation illuminates the origin of the giant down conversion in frequency as arising from an unstable equilibrium. We also show that bubbles that form chains along the direction of the acoustic standing wave due to radiation interaction forces exhibit also translation oscillations that form a spectral band. This band extends approximately from 130 Hz up to nearly 370 Hz, a frequency range that is still at least three orders of magnitude lower than the frequency of the driving acoustic wave.
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Kuhn, de Chizelle Yan P. Acosta Allan J. Brennen Christopher E. "Hydrodynamics, acoustics and scaling of traveling bubble cavitation /." Diss., Pasadena, Calif. : California Institute of Technology, 1994. http://resolver.caltech.edu/CaltechETD:etd-10202005-152545.
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Husin, Shuib. "An experimental investigation into the correlation between Acoustic Emission (AE) and bubble dynamics." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/7318.
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Bubble and cavitation effects phenomena can be encountered in two-phase gas-liquid systems in industry. In certain industries, particularly high-risk systems such as a nuclear reactor/plant, the detection of bubble dynamics, and the monitoring and measurement of their characteristics are necessary in controlling temperature. While in the petro-chemical engineering industry, such as oil transportation pipelines, the detection and monitoring of bubbles/cavitation phenomena are necessary to minimise surface erosion in fluid carrying components or downstream facilities. The high sensitivity of Acoustic Emission (AE) technology is feasible for the detection and monitoring of bubble phenomena in a two phase gas-liquid system and is practical for application within the industry.
Underwater measurement of bubble oscillations has been widely studied using hydrophones and employing acoustic techniques in the audible range. However, the application of Acoustic Emission (AE) technology to monitor bubble size has hitherto not been attempted. This thesis presents an experimental investigation aimed at exploring AEs from gas bubble formation, motion and destruction. AE in this particular investigation covers the frequency range of between 100 kHz to 1000 kHz.
The AE waveform analysis showed that the AE parameter from single bubble inception and burst events, i.e. AE amplitude, AE duration and AE energy, increased with the increase of bubble size and liquid viscosity. This finding significantly extends the potential use of AE technology for detecting the presence of bubbles in two-phase flow.
It is concluded that bubble activity can be detected and monitored by AE technology both intrusively and non-intrusively. Furthermore, the bubble size can be determined by measurement of the AE and this forms the significant contribution of this thesis.
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Meers, Steven Douglas. "The estimation of bubble populations in the surf-zone by inversion of acoustic propagation." Thesis, University of Southampton, 2005. https://eprints.soton.ac.uk/426770/.
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For several decades the propagation characteristics of acoustic pulses (attenuation and sound speed) have heen inverted in attempts to measure the size distributions of gas bubbles in liquids, Primarily this has heen attempted in the ocean for defence and environmental purposes, however there are a growing number of biomedical and industrial applications. In order to simplify the inversion, previous investigators have assumed that the bubbles are undergoing linear, steady-state monochromatic pulsations in a free field, without interacting. These assumptions are always contravened to some extent. This study examines the validity of the assumptions and iclentifies the need for a new time-dependent nonlinear method of determining a bubble's extinction cross section. Such a model is developed and employed in an experiment to estimate the bubble population in the surf-zone, an important but seldom measured region of the ocean, where large populations of bubbles are generated by breaking waves. The necessary theoretical framework to exploit this new model (based on the current state-of-the-art technique) is developed and employs a new method of determining the optimal regularisation parameter for use in the inversion process. A series of laboratory tests and surf-zone sea trials are described that result in a set of bubble populations calculated using linear and, for the first time, nonlinear techniques.
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Wilson, Preston Scot. "Sound propagation and scattering in bubbly liquids." Thesis, Boston University, 2002. https://hdl.handle.net/2144/1369.
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In the ocean, natural and artificial processes generate clouds of bubbles which scatter and attenuate sound. Measurements have shown that at the individual bubble resonance frequency, sound propagation in this medium is highly attenuated and dispersive. Theory to explain this behavior exists in the literature, and is adequate away from resonance. However, due to excessive attenuation near resonance, little experimental data exists for comparison.
An impedance tube was developed specifically for exploring this regime. Using the instrument, unique phase speed and attenuation measurements were made for void fractions ranging from 6.2 × 10^−5 to 2.7 × 10^−3 and bubble sizes centered around 0.62 mm in radius. Improved measurement speed, accuracy and precision is possible with the new instrument, and both instantaneous and time-averaged measurements were obtained. Behavior at resonance was observed to be sensitive to the bubble population statistics and agreed with existing theory, within the uncertainty of the bubble population parameters.
Scattering from acoustically compact bubble clouds can be predicted from classical scattering theory by using an effective medium description of the bubbly fluid interior. Experimental verification was previously obtained up to the lowest resonance frequency. A novel bubble production technique has been employed to obtain unique scattering measurements with a bubbly-liquid-filled latex tube in a large indoor tank. The effective scattering model described these measurements up to three times the lowest resonance frequency of the structure.United States Navy Office of Naval Research Ocean Acoustics Program
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Dogan, Hakan. "Modelling of acoustic pressure waves in bubbly liquids with application to sonochemical reactors." Thesis, Wessex Institute of Technology, 2013. https://eprints.soton.ac.uk/376891/.
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This thesis investigates the acoustic wave propagation in bubbly liquids as part of the SONO project supported by the FP7 European Commission programme, which is aimed at developing a pilot sonochemical plant in order to produce antibacterial medical textile fabrics by coating of the textile with ZnO or CuO nanoparticles. The findings of this research are anticipated to aid the design procedures and also to provide better understanding of the micro scale physical and chemical events. Propagation of acoustic pressure waves in a bubbly liquid is modelled by using Helmholtz equation in this thesis. Computational models are developed based on meshless approaches, i.e. radial basis integral equation (RBIE) and local boundary integral equation (LBIE) methods. A major part of the research focuses on improving the efficiency and the accuracy of the developed methods. For this purpose, numerical tests are carried out with several example problems in order to cross-verify the applicability of the methods. As a result of these tests, the optimal parameters which should be used to minimize the numerical error are suggested. Further, strategies are proposed in order to handle the thin inclusions, such as textile fabric, in the domain. The wave propagation in bubbly liquids involves coupled effects of the sound field and bubble population field, such as dissipation of the acoustic energy by bubble oscillations. The problem is therefore non-homogeneous due to presence of bubbles and nonlinear due to coupled effects. The governing equations, derived from linearized or nonlinear theories, can be found in the literature. Examples of both linear and nonlinear wave propagation are solved in this study. Results related to a 3D sonoreactor including textile fabric are also presented. Effects of bubble size distribution and bubble volume fraction on the acoustic wave propagation are discussed in the example problems.
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Hedayetullah, Amin Mohammad. "Optimization of identification of particle impacts using acoustic emission." Thesis, Robert Gordon University, 2018. http://hdl.handle.net/10059/3116.
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Air borne or liquid-laden solid particle transport is a common phenomenon in various industrial applications. Solid particles, transported at severe operating conditions such as high flow velocity, can cause concerns for structural integrity through wear originated from particle impacts with structure. To apply Acoustic Emission (AE) in particle impact monitoring, previous researchers focused primarily on dry particle impacts on dry target plate and/or wet particle impacts on wet or dry target plate. For dry particle impacts on dry target plate, AE events energy, calculated from the recorded free falling or air borne particle impact AE signals, were correlated with particle size, concentration, height, target material and thickness. For a given system, once calibrated for a specific particle type and operating condition, this technique might be sufficient to serve the purpose. However, if more than one particle type present in the system, particularly with similar size, density and impact velocity, calculated AE event energy is not unique for a specific particle type. For wet particle impacts on dry or wet target plate (either submerged or in a flow loop), AE event energy was related to the particle size, concentration, target material, impact velocity and angle between the nozzle and the target plate. In these studies, the experimental arrangements and the operating conditions considered either did not allow any bubble formation in the system or even if there is any at least an order of magnitude lower in amplitude than the sand particle impact and so easily identifiable. In reality, bubble formation can be comparable with particle impacts in terms of AE amplitude in process industries, for example, sand production during oil and gas transportation from reservoir. Current practice is to calibrate an installed AE monitoring system against a range of sand free flow conditions. In real time monitoring, for a specific calibrated flow, the flow generated AE amplitude/energy is deducted from the recorded AE amplitude/energy and the difference is attributed to the sand particle impacts. However, if the flow condition changes, which often does in the process industry, the calibration is not valid anymore and AE events from bubble can be misinterpreted as sand particle impacts and vice versa. In this research, sand particles and glass beads with similar size, density and impact velocity have been studied dropping from 200 mm on a small cylindrical stepped mild steel coupon as a target plate. For signal recording purposes, two identical broadband AE sensors are installed, one at the centre and one 30 mm off centred, on the opposite of the impacting surface. Signal analysis have been carried out by evaluating 7 standard AE parameters (amplitude, energy, rise time, duration, power spectral density(PSD), peak frequency at PSD and spectral centroid) in the time and frequency domain and time-frequency domain analysis have been performed applying Gabor Wavelet Transform. The signal interpretation becomes difficult due to reflections, dispersions and mode conversions caused by close proximity of the boundaries. So, a new signal analysis parameter - frequency band energy ratio - has been proposed. This technique is able to distinguish between population of two very similar groups (in terms of size and mass and energy) of sand particles and glass beads, impacting on mild steel based on the coefficient of variation (Cv) of the frequency band AE energy ratios. To facilitate individual particle impact identification, further analysis has been performed using Support Vector Machine (SVM) based classification algorithm using 7 standard AE parameters, evaluated in both the time and frequency domain. Available data set has been segmented into two parts of training set (80%) and test set (20%). The developed model has been applied on the test data for model performance evaluation purpose. The overall success rate of individually identifying each category (PLB, Glass bead and Sand particle impacts) at S1 has been found as 86% and at S2 as 92%. To study wet particle impacts on wet target surface, in presence of bubbles, the target plate has been sealed to a cylindrical perspex tube. Single and multiple sand particles have been introduced in the system using a constant speed blower to impact the target surface under water loading. Two sensor locations, used in the previous sets of experiments, have been monitored. From frequency domain analysis it has been observed that characteristic frequency for particle impacts are centred at 300-350 kHz and for bubble formations are centred at 135 – 150 kHz. Based upon this, two frequency bands 100 – 200 kHz (E1) and 300 – 400 kHz (E3) and the frequency band energy ratio (E3E1,) have been identified as optimal for identification particle impacts for the given system. E3E1, > 1 has been associated with particle impacts and E3E1, < 1 has been associated with bubble formations. Applying these frequency band energy ratios and setting an amplitude threshold, an automatic event identification technique has been developed for identification of sand particle impacts in presence of bubbles. The method developed can be used to optimize the identification of sand particle impacts. The optimal setting of an amplitude threshold is sensitive to number of particles and noise levels. A high threshold of say 10% will clearly identify sand particle impacts but for multiparticle tests is likely to not detect about 20% of lower (impact) energy particles. A threshold lower than 3% is likely to result in detection of AE events with poor frequency content and wrong classification of the weakest events. Optimal setting of the parameters used in the framework such as thresholds, frequency bands and ratios of AE energy is likely to make identification of sand particle impacts in the laboratory environment within 10% possible. For this technique, once the optimal frequency bands and ratios have been identified, then an added advantage is that calibration of the signal levels is not required.
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Mekki-Berrada, Flore. "Oscillations couplées de microbulles sous champ ultrasonore et conséquences hydrodynamiques." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY069/document.
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Les propriétés acoustiques des bulles sont reconnues pour leur potentiel dans des applications tant biologiques que médicales. Capables de provoquer la lyse des cellules en générant des écoulements intenses, elles peuvent aussi servir d'agent de contraste en échographie.Ce manuscrit traite de la dynamique de vibration de bulles confinées entre les deux murs d'un canal microfluidique. Ces bulles exhibent une pulsation en volume aux faibles amplitudes d'excitation, à laquelle se superpose un mode de surface paramétrique aux plus fortes amplitudes. Le matériau constituant le canal étant élastique, la pulsation de la bulle confinée a pour effet de générer des ondes de Rayleigh sur les parois du canal. Grâce à ces ondes de surface, les bulles vont pouvoir se coupler les unes aux autres. Ce couplage a un effet sur les écoulements hydrodynamiques autour de ces bulles. En effet, la présence d'une bulle voisine engendre l'apparition d'un mode de translation de la bulle qui, couplé à sa pulsation en volume, conduira à la génération d'écoulements à longue portée. Ce même couplage permet aux bulles de s'auto-organiser en réseau. Afin d'étudier de manière contrôlée les effets collectifs des bulles, leur position a été fixée à l'aide de puits capillaires. Les conditions d'amplification et de synchronisation de la vibration des bulles sont recherchées en vue de créer de nouveaux méta-matériauxThe pulsation properties of air bubbles under ultrasound have received much attention since the development of sonoporation and contrast agents. Spherical bubbles are well known to induce streaming when excited by ultrasound.We report in this manuscript the acoustic vibration of microbubbles confined between the two walls of a microfluidic channel. These bubbles exhibit a volumetric pulsation at low intensities of ultrasound, superimposed with a parametric surface mode for higher intensities of the pressure field. Because the channel walls are elastic, the bubble pulsation leads to the generation of Rayleigh waves at the channel wall interface. The bubble coupling induced by these surface waves has hydrodynamic consequences. In fact, a neighbouring bubble will create a translation mode of the bubble, in addition to its volumetric pulsation. It gives rise to a long-range mixed-mode streaming. The Rayleigh waves lead also to a self-organization of the bubbles in a network. In order to study the collective effects of these bubble networks in a controlled manner, bubble positions were fixed by capillarity on micropits. Conditions for an amplification or a synchronization of the bubble pulsations are sought in order to develop new bubble metamaterials
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Ylonen, Markku. "Cavitation erosion monitoring by acoustic emission Cavitation Bubble Collapse Monitoring by Acoustic Emission in Laboratory Testing Cavitation Erosion Resistance Assessment and Comparison of Three Francis Turbine Runner Materials Estimation of Cavitation Pit Distributions by Acoustic Emission . Shedding Frequency in Erosion Evolution Tracking." Thesis, Université Grenoble Alpes, 2020. https://tel.archives-ouvertes.fr/tel-02613873.
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La cavitation est la formation de bulles de vapeur dans un liquide statique ou en écoulement. L’érosion de cavitation se produit quand ces bulles collapsent à cause de la récupération de pression. Ce phénomène peut endommager les parois à proximité desquelles les bulles collapsent. Il s’agit d’un problème majeur dans les machines hydrauliques. Par exemple, les turbines hydrauliques fonctionnent aujourd’hui souvent dans des régions défavorables du point de vue de la cavitation, pour réguler le réseau électrique. Mesurer la cavitation et le taux d’érosion est souvent très difficile voire impossible. L’émission acoustique (EA) est une méthode qui permet la mesure de cavitation sans accès direct à l’écoulement ; toutefois, les données sont difficiles à interpréter. Cette thèse présente quelques possibilités de traitement des données de l’EA pour quantifier les diamètres des indentations créées par impacts individuels de la cavitation et aussi pour évaluer l’érosion de cavitation. De plus, les taux d’érosion de trois matériaux d’aubes de turbine Francis ont été caractérisés. Les raisons pour les différences dans le taux d’érosion de deux aciers inoxydables et martensitiques sont analysées. Tous les essais de cavitation ont été réalisés dans le même tunnel de cavitation haute vitesse. Un premier résultat majeur de cette thèse est le développement d’une méthode pour compter les pics d’EA par une technique d’enveloppe du signal. Les distributions cumulées des pics d’EA sont comparées à celles des diamètres d’indentations. Une relation est proposée entre l’amplitude des pics d’EA et le diamètre des indentations. Le deuxième résultat majeur est le lien entre l’évolution de l’érosion de cavitation et la fréquence de lâcher des nuages de cavitation. Bien que les signaux d’EA soient mesurés en haute fréquence, un processus de démodulation a été mis en œuvre qui permet de mettre en évidence la basse fréquence de lâcher. Cette fréquence augmente avec la rugosité et la déformation de surface au fur et à mesure de la progression de l’endommagement. Par ailleurs, les raisons entre les différences de taux d’érosion des aciers inoxydables et martensitiques ont été identifiées : la taille des grains d’austénite initiale, les tailles des plaques et plaquettes et la quantité d’austénite résiduelle sont les principaux facteurs influants. Cette thèse propose plusieurs résultats directement utilisables, comme la classification entre les aciers inoxydables martensitiques, ainsi que des méthodes pour surveiller la cavitation mises au point en laboratoire dans un tunnel de cavitation et potentiellement applicables aux machines hydrauliques. Le résultat majeur est que l’EA a un fort potentiel pour surveiller la cavitation et l’érosion de cavitation avec l’avantage important qu’elle ne nécessite pas d’accès direct à l’écoulementCavitation is the formation of vapor bubbles either in a static liquid or in a liquid flow due to a drop in static pressure. When these bubbles collapse, as a result of pressure recovery, they may damage adjacent surfaces. These events are major causes of damage and nuisance in hydro machines. Modern hydro turbines are often used to regulate power grids; therefore, they may be operated out of their designed range. The flow-related optimal operation is different from the economic optimal usage. Detecting and characterizing cavitation and assessing damage during operation can be difficult or even impossible. Acoustic emission (AE) measurements provide a way to measure cavitation without access to the flow, but interpreting the data is challenging. This thesis presents insights in the ways of treating the AE data both in characterizing individual pits created by cavitation impacts and in tracking the evolution of cavitation erosion. Additionally, the erosion rates of three turbine materials were compared, and the main reasons behind the differing erosion rates of two martensitic turbine steels were discovered. The same high-speed cavitation tunnel was used in all cavitation experiments. This thesis firstly presents a method for enveloping an AE waveform signal and for counting the peak voltage values. The resulting cumulative distributions were compared to those of cavitation pit diameters, and from this comparison, a connection was proposed between AE peak voltage value and pit diameter. The second result was the connection between cavitation cloud shedding frequency and erosion evolution. The process of demodulating high frequency AE signals effectively promotes the low frequency shedding. The shedding frequency increased with accumulating material loss, and it was concluded that this increase is due to geometry effects, namely surface roughness. In addition to the two proposed methods, it was found that the decisive factors in the differing erosion rates of the martensitic stainless steels are the prior austenite grain size, packet and block sizes and the retained austenite fraction. This thesis provides guidelines directly applicable, such as the martensitic steel classifying, and methods that require further development, if one wishes to utilize them in hydro machine cavitation monitoring instead of laboratory measurements in a cavitation tunnel. The main outcome is that AE is a potential way to monitor cavitation, with the important benefit of not requiring any access to the flow
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Scognamiglio, Chiara. "Dynamique de bulles de cavitation dans des systèmes micro-confinés." Thesis, Université Côte d'Azur (ComUE), 2017. http://www.theses.fr/2017AZUR4126.
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Cette thèse porte sur l’étude de la cavitation, c’est-à-dire l’apparition d’une bulle dans un liquide soumis à une dépression. Le contrôle du processus est d’un grand intérêt dans plusieurs domaines, de l’hydrodynamique à la biologie. En fait ce phénomène, apparemment inoffensif, peut provoquer des graves dommages comme la fracture d’hélices ou la mort d’arbres. La première partie de la thèse se focalise sur la cavitation dans un système biomimétique. Il s’agit de micro-volumes d’eau encapsulés dans un milieu poro-élastique. L’évaporation de l’eau à travers l’hydrogel génère des pressions négatives et finalement l’apparition d’une bulle. Lorsque la première bulle de cavitation apparait dans une cellule, elle peut déclencher en quelques microsecondes l’apparition d’autres bulles dans les cellules voisines, en amorçant un effet d’avalanche ultra-rapide. Nous résolvons la dynamique et l’acoustique des bulles, dans le cas des événements uniques ou multiples. La réalisation d’un dispositif innovant ou les volumes du liquide sont encapsulés entre l’hydrogel et une lame de verre ouvre la voie à l’investigation de l’eau métastable. Une deuxième partie du travail a été consacrée à une étude interdisciplinaire où la microfluifique et la biologie sont combinées et appliqués à la livraison de médicament. Le dispositif est composé d’un vaisseau sanguin artificiel en communication avec un tissu cible placé dans un compartiment créé exprès. Les parois du canal microfluidique sont tapissées de cellules endothéliales pour reproduire la paroi réelle d’un vaisseau sanguin in vivo. Ce dispositif permet l’étude des effets des bulles activées par des ultrasons sur la barrière endothélialeThe present thesis focuses on cavitation process, meaning nucleation and dynamics of a bubble within a liquid as a result of pressure decrease. In particular, we investigate the growth of the vapor phase in micrometric volumes of water confined by a poro-elastic material. In systems where water is encapsulated in a porous medium, molecules can evaporate from the pores resulting in a remarkable pressure reduction and bubbles nucleation. Once a vapor bubble nucleates, it can trigger within few microseconds the appearance of other bubbles in the neighbor cavities, activating an ultra-fast avalanche-like phenomenon. We resolved the dynamics and acoustics of cavitation bubbles, in case of singles or multiple nucleation events. The realization of an innovative device where water is encapsulated between a porous material and a glass window opens the way for metastable water investigation. A second part of the manuscript is devoted to a new project where microfluidics and biology are combined and applied to drug delivery. The device consists of an artificial blood vessel in communication with the target tissue accommodated in a purposely designed compartment (tissue-on-a-chip). The walls of the microfluidic channel mimicking the vessel are lined with endothelial cells to reproduce the actual walls of in vivo blood vessels. This device allows to investigate the effects of ultrasound-activated bubbles on the blood vessels wall
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Elsey, Justin Rae. "Dynamic Modelling, Measurement and Control of Co-rotating Twin-Screw Extruders." University of Sydney. Department of Chemical Engineering, 2003. http://hdl.handle.net/2123/687.
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Co-rotating twin-screw extruders are unique and versatile machines that are used widely in the plastics and food processing industries. Due to the large number of operating variables and design parameters available for manipulation and the complex interactions between them, it cannot be claimed that these extruders are currently being optimally utilised. The most significant improvement to the field of twin-screw extrusion would be through the provision of a generally applicable dynamic process model that is both computationally inexpensive and accurate. This would enable product design, process optimisation and process controller design to be performed cheaply and more thoroughly on a computer than can currently be achieved through experimental trials. This thesis is divided into three parts: dynamic modelling, measurement and control. The first part outlines the development of a dynamic model of the extrusion process which satisfies the above mentioned criteria. The dynamic model predicts quasi-3D spatial profiles of the degree of fill, pressure, temperature, specific mechanical energy input and concentrations of inert and reacting species in the extruder. The individual material transport models which constitute the dynamic model are examined closely for their accuracy and computational efficiency by comparing candidate models amongst themselves and against full 3D finite volume flow models. Several new modelling approaches are proposed in the course of this investigation. The dynamic model achieves a high degree of simplicity and flexibility by assuming a slight compressibility in the process material, allowing the pressure to be calculated directly from the degree of over-fill in each model element using an equation of state. Comparison of the model predictions with dynamic temperature, pressure and residence time distribution data from an extrusion cooking process indicates a good predictive capability. The model can perform dynamic step-change calculations for typical screw configurations in approximately 30 seconds on a 600 MHz Pentium 3 personal computer. The second part of this thesis relates to the measurement of product quality attributes of extruded materials. A digital image processing technique for measuring the bubble size distribution in extruded foams from cross sectional images is presented. It is recognised that this is an important product quality attribute, though difficult to measure accurately with existing techniques. The present technique is demonstrated on several different products. A simulation study of the formation mechanism of polymer foams is also performed. The measurement of product quality attributes such as bulk density and hardness in a manner suitable for automatic control is also addressed. This is achieved through the development of an acoustic sensor for inferring product attributes using the sounds emanating from the product as it leaves the extruder. This method is found to have good prediction ability on unseen data. The third and final part of this thesis relates to the automatic control of product quality attributes using multivariable model predictive controllers based on both direct and indirect control strategies. In the given case study, indirect control strategies, which seek to regulate the product quality attributes through the control of secondary process indicators such as temperature and pressure, are found to cause greater deviations in product quality than taking no corrective control action at all. Conversely, direct control strategies are shown to give tight control over the product quality attributes, provided that appropriate product quality sensors or inferential estimation techniques are available.
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Cavaro, Matthieu. "Apport de l'accoustique non linéraire à la caractérisation de l'engagement du sodium liquide : application aux réacteurs nucléaires de quatrième génération." Thesis, Aix-Marseille 2, 2010. http://www.theses.fr/2010AIX22106/document.
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Le choix de la filière SFR (Sodium Fast Reactor : Réacteurs à neutrons rapides refroidis par du sodium liquide), par la France conduit à la réalisation d’un prototype de quatrième génération nommé ASTRID. Le développement de ce type de réacteurs présente plusieurs défis, en particulier du point de vue de l’amélioration de la démonstration de la sûreté et de la surveillance du fonctionnement. Cette dernière passe, entre autres, par la caractérisation de l’engazement du sodium liquide (présence de microbulles de gaz). La caractérisation de l’engazement est l’objet de cette étude, elle implique la détermination du taux de vide (fraction volumique de gaz) et de l’histogramme des rayons des microbulles. Le travail bibliographique réalisé a montré que les techniques acoustiques linéaires de caractérisation des nuages de bulles ne permettaient pas de répondre pleinement à cette problématique, en revanche des pistes prometteuses ont été identifiées en étudiant les techniques acoustiques non linéaires. Cette dernière voie a par conséquent été explorée. Un banc expérimental en eau permettant la génération et le contrôle optique de nuages de microbulles nous a permis de valider finement la reconstruction d’histogrammes des rayons grâce à une technique de mixage nonlinéaire d’une haute fréquence avec une basse fréquence. La potentialité du mixage de deux hautes fréquences, plus intéressante d’un point de vue industriel, a par ailleurs été démontrée. Enfin, les bases de la transposition originale d’une technique de spectroscopie de résonance non linéaire appliquée à un nuage de bulles ont été posées, grâce à la mise en place de résonateurs acoustiques. Les résultats obtenus offrent de nombreuses perspectives, tant du point de vue des applications industrielles que du point de vue plus fondamental de la compréhension du comportement acoustique non linéaire d’une bulle excitée par plusieurs fréquences et d’un nuage de bulles excité à basse fréquenceThe SFR system chosen (Sodium Fast Reactor: fast neutron reactors cooled by liquid sodium) by France led to afourth-generation prototype named ASTRID. The development of this kind of reactors presents several challenges, particularly in terms of improving the safety and monitoring operation. This involves, among other things, characterization of the bubbles presence in liquid sodium. The characterization of the bubbles presence is the subject of this thesis. It involves the determination of void fraction (gas volume fraction) and histogram of the radiiof bubbles. The bibliographic work done has shown that linear acoustic techniques for the characterization of bubble clouds are inadequate to achieve this. However promising leads have been identified by studying nonlinear acoustic techniques. This last idea has therefore been explored. An experimental water bench for the generation and optical control of microbubbles cloudallowed us to validate finely the reconstruction of histograms of radii through a technique of nonlinear mixing of a high frequency with a low frequency. The potential of the mixing of two high frequencies, more interesting for the industrial point of view has also been demonstrated. Finally, the bases of the transposition of an original technique of nonlinear resonance spectroscopy applied to a bubbles cloud were explored through the introduction of acoustic resonators. The results offer many interesting opportunities, both in terms of industrial applications and formore fundamental understanding of non-linear behavior of a bubble excited by multiple frequencies and of bubbles clouds excited at low frequency
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Diaz, Mario Alfonso. "High-Frequency Ultrasound Drug Delivery and Cavitation." BYU ScholarsArchive, 2007. https://scholarsarchive.byu.edu/etd/1050.
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The viability of a drug delivery system which encapsulates chemotherapeutic drugs (Doxorubicin) in the hydrophobic core of polymeric micelles and triggers release by ultrasound application was investigated at an applied frequency of 500 kHz. The investigation also included elucidating the mechanism of drug release at 70 kHz, a frequency which had previously been shown to induce drug release. A fluorescence detection chamber was used to measure in vitro drug release from both Pluronic and stabilized micelles and a hydrophone was used to monitor bubble activity during the experiments. A threshold for release between 0.35 and 0.40 in mechanical index was found at 70 kHz and shown to correspond with the appearance of the subharmonic signal in the acoustic spectrum. Additionally, drug release was found to correlate with increase in subharmonic emission. No evidence of drug release or of the subharmonic signal was detected at 500 kHz. These findings confirmed the role of cavitation in ultrasonic drug release from micelles. A mathematical model of a bubble oscillator was solved to explore the differences in the behavior of a single 10 um bubble under 70 and 500 kHz ultrasound. The dynamics were found to be fundamentally different; the bubble follows a period-doubling route to chaos at 500 kHz and an intermittent route to chaos at 70 kHz. It was concluded that this type of "intermittent subharmonic" oscillation is associated with the apparent drug release. This research confirmed the central role of cavitation in ultrasonically-triggered drug delivery from micelles, established the importance of subharmonic bubble oscillations as an indicator, and expounded the key dynamic differences between 70 and 500 kHz ultrasonic cavitation.
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Montes, Quiroz William. "Étude expérimentale de la stabilité d'une bulle unique de cavitation acoustique : application à la nucléation de la glace déclenchée par cavitation." Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2014. http://www.theses.fr/2014EMAC0002/document.
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Cette étude sur la stabilité d’une bulle unique de cavitation acoustique s’inscrit dans le cadre d’un projet ANR démarré en septembre 2009 (SONONUCLICE ANR-09-BLAN-0040-02). Elle se situe dans la continuité des travaux sur l’optimisation du procédé de lyophilisation de produits pharmaceutiques menés par l’équipe « Transferts couplés de matière et de chaleur » du laboratoire LAGEP (ESCPE/UCB, Lyon), équipe porteuse du projet, et des travaux sur la cristallisation assistée par ultrasons du laboratoire RAPSODEE. L’application des ultrasons de puissance dans un liquide produit des milliards de bulles. Ce phénomène est appelé cavitation acoustique. Les bulles formées ne font pas toutes la même taille, leurs oscillations ne sont pas en phase, et leur densité dans le fluide est très inhomogène : ce phénomène très complexe implique donc de nombreuses variables difficiles à isoler. Même si le phénomène est chaotique, la cavitation permet d’observer des effets macroscopiques notables sur la nucléation et la croissance des cristaux de glace dans une solution sous-refroidie. Ces effets sont d’une importance capitale pour des applications de congélation ou de lyophilisation. Bien que les effets des ultrasons présentent des intérêts certains sur la cristallisation, leur origine reste mal connue. L’observation directe des milliards de bulles ne fournit aucune piste sur les mécanismes microscopiques mis en jeu. Afin d’isoler l’acteur essentiel de ces effets, l’étude menée vise à isoler une bulle de cavitation acoustique. Pour cela, une cellule de lévitation carrée en verre a été conçue. Le verre a été retenu comme matériau pour sa rigidité et sa transparence. Dans cette cellule, une onde de pression acoustique est imposée par un piézoélectrique collé à la base de la cellule. Il a été possible de reconstruire la dynamique de la bulle. Les étapes d’expansion, d’implosion et de rebonds sont clairement visibles. En vue de l’étude de la cristallisation, un principe de détection des cristaux a été spécifiquement élaboré. Il repose sur le suivi de la modification de la périodicité de la bulle (mesurée par un microphone) provoquée par l’apparition d’un corps étranger à son voisinage. Une méthode utilisant la corrélation de signaux acoustiques du microphone filtré à la fréquence d’excitation du PZT et les harmoniques du signal du microphone directe a été développée. Elle permet de connaître le régime d’oscillation de la bulle et de détecter toutes les modifications de sa dynamique. Des expériences de perturbation de la bulle ont été menées à l’aide d’une micro fibre de 7 μm. Le principe de détection est alors mis en oeuvre pour déclencher l’enregistrement d’images par une caméra rapide lors des derniers instants d’existence de la bulle. Cette méthode devrait permettre de détecter l’apparition des premiers cristaux au voisinage de la bulle. Autour de la cellule de lévitation, différents systèmes ont été développés. Un système de dégazage et de remplissage de la cellule de cavitation ont permis de travailler avec de l’eau ayant des teneurs en gaz dissous de l’ordre de 20 % de la saturation. Un système d’éclairage avec une LED de puissance et un jeu de lentilles optiques a été conçu pour visualiser correctement la bulleThis study of the stability of an acoustic cavitation bubble is part of an ANR project started in September 2009 (SONONUCLICE ANR-09-BLAN-0040-02). It takes place in the continuity of the works on the optimization process of lyophilisation of pharmaceutical products conducted by the “Transferts couplés de matière et de chaleur” team of LAGEP (ESCPE/UCB, Lyon) laboratory, which is the project’s team leader, and the studies of ultrasound-assisted crystallization in the RAPSODEE Centre. The application of power ultrasound into liquids produces thousands of bubbles. This phenomenon is called acoustic cavitation. The bubbles formed don’t have the same size, their oscillations are not in phase, and their spatial density in the fluid is not homogeneous: this phenomenon is very complex and involves multiple variables very difficult to isolate. Even if this phenomenon is chaotic, it allows to observe macroscopic effects on the nucleation and crystal growth of ice in undercooled solutions. These effects have a capital importance for industrial applications such as freezing and lyophilisation (also called freeze drying). Although ultrasound has a noticeable influence on crystallization, the origin of these effects remains unclear. The multi-bubble approach doesn’t give any hint on the microscopic mechanisms involved. In order to isolate the main actor of these effects, this study aims at isolating a single cavitation bubble. To do that, a cubic levitation cell made of optical glass was build. In this cell, an acoustic pressure is applied by a piezoelectric glued to the bottom’s external face of the cell. With this cell is possible to rebuild all the oscillations states of the bubble, and in combination with our optical system we can see the bubble’s dynamics and its stages like: expansion, collapse and rebounds. For the crystallization part of this study, a crystal’s detection system was developed. It is based on the variations of the bubble’s periodicity (measured by a microphone pill) introduced by the sudden appearance of a foreign body in its vicinity. This method requires the correlation of the signals from a filtered microphone and the harmonics signals from a microphone, in order to known the oscillation state of the bubble and detect variations on the bubble’s dynamics. Experiments of bubble perturbations by a thin wire were made. The detection system was used to trigger the image recording of a fast camera, in order to capture the final moments of the bubble. This method should be allowing the early detection of new crystals in the proximity of the bubble. Around the levitation cell, various systems have been developed. A degassing and filling system for the cavitation cell allow us to work with degased water around the 20 % of its saturated concentration of air. An illumination system based in a power LED and a set of optical lenses was used to view the bubble correctly
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Looten-Baquet, Isabelle. "Etude et caractérisation de l'activité des champs de bulles générées par cavitation ultrasonore." Valenciennes, 1996. https://ged.uphf.fr/nuxeo/site/esupversions/1c0a52f3-bfd0-437a-8d3c-877eb1bb54f7.
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La cavitation ultrasonore intervient dans un liquide lorsque les variations locales de pression, causées par la propagation d'une onde ultrasonore de forte puissance, sont suffisamment importantes pour qu'il y ait création de microbulles, ou pour que les microbulles préexistantes dans le liquide se déforment notablement. Le comportement oscillatoire de chaque bulle formée dépend alors de l'amplitude de l'onde ultrasonore et de la taille des bulles par rapport à la longueur d'onde ultrasonore. Les bulles peuvent présenter deux régimes d'oscillations radiales différents: elles peuvent soit osciller de façon durable dans le liquide, soit disparaitre par implosion après quelques cycles de l'onde acoustique. Nous proposons, dans ce travail, des techniques de caractérisation des champs de bulles générées par cavitation ultrasonore. Dans un premier temps, nous considérons le liquide en état de cavitation comme un milieu diphasique particulier. Nous montrons alors que la forte non linéarité de ce milieu, constitue une difficulté majeure qui restreint les possibilités d'utilisation des techniques classiques de comptage et d'estimation de la taille des bulles (optiques et acoustiques). Nous proposons alors une technique acoustique originale de caractérisation des champs de bulles de cavitation, dans laquelle les instants de production et d'étude de la cavitation se succèdent. Toutefois, nous montrons que la sensibilité de cette technique est rapidement limitée par la large dispersion en taille des bulles de cavitation. C’est pourquoi nous développons un outil de caractérisation de l'état de cavitation base sur l'analyse du signal acoustique émis par le champ de bulles. à l'aide d'un dispositif ultrasonore préalablement calibre, nous montrons qu'il est possible d'étalonner l'état de cavitation en mesurant la puissance du bruit de cavitation. Nous montrons ensuite qu'il est possible de corréler les déformations du spectre et les variations de la puissance du bruit de cavitation, à la réactivité sono chimique d'une réaction d'oxydation
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Schneider, Julia. "Characterisation of Single and Multibubble Cavitation Through Analysis of Molecular, Atomic and Ionic Line Emissions." Thesis, Montpellier 2, 2012. http://www.theses.fr/2012MON20011.
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La cavitation acoustique (formation, croissance et effondrement de bulles de gaz dans un liquide soumis aux ultrasons) est à l'origine de réactions chimiques (sonochimie) via la génération de conditions extrêmes lors de l'effondrement des bulles. Des températures de 103-104K et des pressions de l'ordre de 1000 atm sont atteintes au cœur des bulles [1]. Dans ces conditions, les liaisons chimiques des molécules volatiles présentes dans les bulles peuvent être rompues, formant, dans le cas de solutions aqueuses, des radicaux OH et H. Par ailleurs, l'effondrement violent des bulles de cavitation peut être accompagné par l'émission de lumière, sonoluminescence (SL), qui est le sujet d'étude de ce travail. Cette émission lumineuse est formée d'un continuum, de l'UV au proche IR, similaire à l'émission d'un corps noir, sur lequel peuvent se superposer des lignes d'émission atomiques ou moléculaires.On distingue deux types de SL: la SL mono-bulle (SBSL) et la SL multibulle (MBSL). En général, les spectres de MBSL se différencient de ceux de SBSL par la présence de lignes d'émission (d'atomes alcalins, de radicaux hydroxy… [2]), si bien que les mécanismes d'émission ainsi que la nature des conditions à l'intérieur des bulles lors de leur effondrement ont longtemps été considérés comme différents pour les systèmes mono- et multi-bulles. Un pont a été érigé entre les deux systèmes par le travail de Liang et al. [3] qui mit en évidence les conditions expérimentales permettant l'apparition de lignes dans le spectre de SBSL. Dans ce contexte, l'objectif de ce travail était de comparer les émissions de SBSL (27 kHz) et MBSL à haute et basse fréquences (20, 203, 607 kHz) pour différentes solutions aqueuses. Un sonoréacteur monobulle a été développé, dans lequel la température, la nature et la pression de gaz dissous ainsi que la pression acoustique sont contrôlés. Les électrolytes étudiés étaient : NaCl et les chlorures de lanthanides luminescents Ce3+, Tb3+, Eu3+ et Gd3+. Ces derniers peuvent être excités soit par absorption de photons dans l'UV soit par collisions avec des particules énergétiques [4].Dans la première partie de ce travail, les conditions à l'intérieur d'une monobulle lors de son effondrement ont été estimées via un fit du continuum par l'équation de Planck du corps noir. Les températures du corps noir obtenues sont de l'ordre de 104K, en accord avec des études précédentes. Elles sont indépendantes de la présence de NaCl et de la pression acoustique alors que l'intensité de SL y est très sensible. Les résultats obtenus remettent en question l'utilisation du modèle du corps noir en SL. Des lignes d'émission atomique et moléculaire se superposent parfois au continuum de SL : en MBSL, et en SBSL dans certaines conditions particulières (pression d'argon suffisante, faible pression acoustique) [3, 5]. Ce travail met en évidence la similarité entre la forme de l'émission de OH en SBSL et en MBSL à 20kHz, ce qui indique des conditions intrabulles très proches dans les conditions expérimentales étudiées [6]. En SBSL sous 70mbar d'Ar, l'intensité des lignes diminue lorsque la pression acoustique augmente, jusqu'à leur disparition dans le continuum. Cette évolution peut apparaître comme un lien entre SBSL et MBSL.Par ailleurs, cette étude confirme que la concentration en sodium à l'interface bulle-liquide, qui peut être enrichie par l'utilisation d'un contre-ion tensioactif, est le paramètre clé de l'observation de l'émission du sodium en SBSL, suggérant que l'excitation du sodium a lieu soit à l'interface de la bulle, soit en son cœur, après injection de gouttelettes. La seconde partie de cette étude concerne l'effet de la fréquence ultrasonore et de la puissance acoustique sur l'intensité de luminescence des ions lanthanides en MBSL. La luminescence des ions Tb3+, Ce3+ et Eu3+ est ainsi observée. La comparaison des rendements de SL et de photoluminescence indique qu'à l'exception de Ce3+, l'excitation par photons est minThe importance of acoustic cavitation, i.e., the formation, growth and collapse of gaseous cavities in liquid exposed to ultrasound, in sonochemistry is based on the generation of extreme conditions upon bubble collapse. Temperatures and pressures inside the collapsing bubble are approximated to reach 104 K and 1000 atm, respectively [suslick-1999]. Under such conditions chemical bonds of the solvent vapour or volatile solutes present in the bubble core are easily cleaved, which in the case of aqueous systems, leads to the formation of chemically reactive OH and H radicals. These primary radicals either recombine leading to chemiluminescence, or diffuse into solution, where they are liable to react with other species. Of particular importance in this work is the light emission that accompanies cavitation, termed sonoluminescence (SL). This emission is a broad continuum ranging from 200nm to 900 nm, resembling the emission of a blackbody, which can be superimposed with atomic or molecular emission lines comparable to bremsstrahlung. It is necessary to distinguish two forms of SL, single-bubble (SBSL) and multibubble (MBSL). In general, MBSL spectra differ from SBSL spectra in that they contain emission lines, e.g., from alkali atoms or hydroxyl radicals [matula-1995]. Consequently, it was, until recently considered that the mechanisms of light emission, and the nature of the bubble interior upon collapse were fundamentally different for the single and multibubble systems. Considering that MBSL is a cloud of single bubbles a bridging theory is desired.With this background the objective of the present work was to conduct a comparative spectroscopic analysis of SBSL, driven at 27 kHz, and MBSL generated from low and high ultrasonic frequencies (20, 203 and 607 kHz) of aqueous electrolyte solutions. Therefore a single bubble sonoreactor was developed, where the temperature, gas content and type, as well as the acoustic pressure could be controlled. The electrolytes of choice were: sodium chloride and chlorides of the luminescent lanthanide ions, Ce3+, Tb3+, Eu3+ and Gd3+, which can be excited by UV light absorption and collisions with energetic particles [kulmala-1995]. In the first part of this work the conditions upon bubble collapse were approximated by fitting the broad-band continuum of SBSL spectra of water with 70 mbar of argon and a 0.5 M NaCl solution with 70 mbar of argon using Planck's law of blackbody radiation. The obtained blackbody temperatures are in the range of 104 K, which is in good agreement with previous studies, but with the discrepancy of being independent of the presence of NaCl and the acoustic pressure, whereas the SL intensity increased by a factor of more than 10 upon increased acoustic pressure. The different trends followed by SL intensity and blackbody temperatures question the blackbody model. Another observation questioning the blackbody model is the appearance of atomic and molecular emission lines in MBSL and as recently observed also in SBSL [liang-2007, young-2001]. The present work proofed that the key factors for line emission in SBSL are small amounts of argon and low acoustic pressure. Moreover, the work revealed that the shape of the OH• radical emission is very similar to that in MBSL spectra, indicating the strong similarity of intrabubble conditions in MBSL and SBSL under certain experimental conditions [schneider-2011]. An increase of the acoustic pressure caused the continuum to overlap the lines until they become indistinguishable giving the usually in SBSL observed featureless continuum. This advance is a big step toward bridging the gap between SBSL and MBSL. Furthermore this study reveals that the concentration of the sodium ion at the interface of a single bubble can be enriched with a surface active counterion and the concentration is crucial for the observation of the sodium line in SBSL, suggesting that excitation of sodium either takes place at the interface of the
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Monloubou, Martin. "Interaction d'une onde de souffle avec une mousse liquide : atténuation et rupture." Thesis, Rennes 1, 2015. http://www.theses.fr/2015REN1S067/document.
Full textAbstract:
Les mousses liquides sont utilisées dans de nombreux domaines de la vie quotidienne. Leur excellente capacité à dissiper de l'énergie en fait également des matériaux très utilisés dans le domaine militaire pour atténuer les ondes de souffle émises lors d'une explosion. Dans cette thèse, nous avons conçu un dispositif expérimental original nous permettant de visualiser la déformation d'une mousse liquide lors de l'impact d'une onde de souffle en sortie d'un tube à choc. Nous mesurons la surpression en plusieurs points de la mousse, sur une gamme de 5 à 50 kPa. Nous mettons en évidence une atténuation de pression qui augmente avec la taille des bulles puis sature, tous les autres paramètres, notamment la fraction liquide, étant maintenus constants. Ces résultats sont interprétés avec un modèle de dissipation thermique à l'échelle de la bulle suggérant l'existence d'un maximum d'atténuation pour une taille de bulles donnée. Nous caractérisons ensuite la vitesse de propagation de l'onde au sein de la mousse. Aux petites amplitudes, la vitesse suit le modèle de Wood, basé sur une propagation linéaire dans un milieu continu effectif. Aux plus hautes amplitudes, nous mettons en évidence l'apparition d'un régime non linéaire, avec une vitesse de propagation plus importante et une atténuation plus faible, ces deux phénomènes étant retrouvés à la fois théoriquement et numériquement. Près de la source, la mousse est détruite par le choc. Nous terminons notre étude avec des résultats plus qualitatifs sur la quantité de mousse détruite et la vitesse de propagation du front de rupture, visualisées pour la première fois dans une mousse tridimensionnelleLiquid foams are used in various domains in our everyday life. Their excellent ability to dissipate energy makes foams widely used in the military domain to mitigate blast waves produced after an explosion. In this Thesis, we have designed an original experimental setup allowing us to image the deformation of a liquid foam after the impact of a blast wave exiting a shock tube. We also measure the overpressure in the foam, within a range of 5 to 50\,kPa. We evidence a pressure attenuation, increasing and then saturating at increasing bubble size, while all the other parameters of the foam, especially liquid fraction, are kept constant. Those results are interpreted with a thermal dissipation model at the bubble scale, suggesting the existence of a maximum dissipation for a given bubble size. We then characterise the wave velocity in the foam. At small amplitudes, the velocity follows Wood's model, based on linear propagation in an effective continuous medium. At greater amplitudes, we show the apparition of a non-linear regime, with a higher propagation velocity and a lower attenuation, those two features being captured theoretically and numerically. Close to the source, the foam is destroyed by the shock. We close our study with more qualitative results on the quantity of destroyed foam and the propagation velocity of the rupture front, which have been evidenced for the first time in a three-dimensional foam
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Thieury, Margaux. "Développement de métamatériaux super-absorbants pour l’acoustique sous-marine." Thesis, Université Paris sciences et lettres, 2020. http://www.theses.fr/2020UPSLS004.
Full textAbstract:
L’évolution constante des performances des sonars nécessite de nouveaux designs de revêtements absorbants pour l’acoustique sous-marine. De tels revêtements sont utilisés pour améliorer la furtivité des sous-marins, mais ils permettent également d’accroître l’efficacité des systèmes de détection embarqués. Les méta-écrans bulleux (lointains descendants des revêtements de type Alberich) représentent une solution possible pour répondre à cet enjeu. Ils sont constitués d’une distribution périodique bi-dimensionnelle de cavités d’air de taille sub-longueur d’onde emprisonnées dans une matrice viscoélastique. Lorsqu’elles sont excitées par une onde acoustique, les cavités se comportent comme des bulles d’air, et présentent une résonance basse fréquence, dite de "Minnaert". Sous certaines conditions, le méta-écran bulleux permet d’atteindre une absorption totale lorsqu’il est placé devant un réflecteur parfait. Ce travail de thèse a permis la mise au point d’un modèle phénoménologique, validé par des simulations numériques et des mesures en cuve, pour prédire les coefficients de réflexion et de transmission d’un méta-écran bulleux en fonction de ses caractéristiques géométriques et rhéologiques. Ce modèle prend en compte l’influence de la température et de la pression statique sur les performances du méta-écran, ainsi que celle de la forme des cavitésThe constant evolution of sonar performance requires new designs of absorbent coatings for underwater acoustics. Such coatings are used to improve stealth of submarines but can also improve the efficiency of on-board detection systems. Bubble meta-screens (reminiscent of the so-called Alberich coatings) are a possible solution to tackle this issue. A bubble meta-screen consists of a periodic distribution of sub-wavelength air cavities trapped in a visco-elastic matrix. The cavities acoustically behave as bubbles and exhibit a low frequency resonance, known as the Minnaert resonance. Under certain conditions, the meta-screen can achieve a total absorption when placed in front of a perfect reflector. This doctoral work allowed us to build a phenomenological model, validated by numerical simulations and experiments, which can predict the reflection and transmission coefficients of the meta screen as a function of its geometric and rheological characteristics. Our model takes into account the influence of the temperature and static pressure on the performance of a meta-screen, as well as the role played by the shape of the cavities
37
Pham, Tuyet Mai. "La mesure des populations de germes de cavitation : qualification et optimisation d'un compteur dynamique à ogive centrale." Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10235.
Full textAbstract:
Le present travail est consacre a la realisation d'un appareil de mesure dynamique de populations de germes de cavitation. L'objectif de l'etude est de definir une conception de reference du compteur a ogive centrale la mieux caracterisee possible, tant sur le plan de la geometrie de l'appareil que sur le plan des limites de fonctionnement et des precisions de mesure. Notre etude s'articule autour de deux themes: la conception et la qualification de l'appareil. Une premiere etape consiste a optimiser le capteur hydrodynamique compte-tenu des contraintes imposees par les interactions entre la cavitation et la couche limite. Les innovations essentiellement apportees concernent la compensation des effets visqueux dans la section du col, ainsi que l'utilisation de dispositifs d'excitation de la turbulence pour eviter le decollement laminaire dans le divergent. Une qualification de l'appareil optimise est ensuite menee: des visualisations de l'ecoulement sous eclairage stroboscopique, des mesures de pressions statique et fluctuante permettent de valider la conception retenue. On etablit egalement les limites de fonctionnement du compteur conditions extremes de prelevement des echantillons, concentrations maximales de germes mesurables, taille des plus gros germes mesurables, et ses performances precision de mesure de la pression critique des germes et de leur nombre. La possibilite theorique de detecter acoustiquement les germes est discutee et aucune limitation en taille de germes n'a ete trouvee. En revanche, l'analyse par cinematographie rapide du fonctionnement du venturi a mis en evidence l'existence d'une valeur limite du parametre de cavitation en deca de laquelle le nombre de germes est surestime
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Krefting, Dagmar. "Untersuchung von Einzel- und Mehrblasensystemen in akustischen Resonatoren." Doctoral thesis, [S.l.] : [s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=97074675X.
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Greene, Chad Allen. "Low-frequency acoustic classification of methane hydrates." Thesis, 2010. http://hdl.handle.net/2152/ETD-UT-2010-12-2632.
Full textAbstract:
Methane hydrates are naturally-occurring ice-like substances found in permafrost and in ocean sediments along continental shelves. These compounds are often the source of cold seeps—plumes which vent methane into aquatic environments, and may subsequently release the potent greenhouse gas into the atmosphere. Methane hydrates and methane gas seeps are of particular interest both for their potential as an energy source and for their possible contribution to climate change. In an effort to improve location of hydrates through the use of seismic surveys and echo-sounding technology, this work aims to describe the low-frequency (10 Hz to 10 kHz) acoustic behavior of methane gas bubbles and methane hydrates in water under simulated ocean-floor conditions of low temperatures and high pressures. Products of the experiments and analysis presented in this thesis include (a) passive acoustic techniques for measurement of gas flux from underwater seeps, (b) a modified form of Wood's model of low-frequency sound propagation through a bubbly liquid containing real gas, and (c) low-frequency measurements of bulk moduli and dissociation pressures of four natural samples of methane hydrates. Experimental procedures and results are presented, along with analytical and numerical models which support the findings.text
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Zhang, Songhua. "Nonlinear acoustic method for gas bubbles identification in marine sediments." Thesis, 2006. http://hdl.handle.net/1828/2084.
Full textAbstract:
It is well known that gases are present in marine sediments. The gas found in the surficial layer of marine sediments is mostly due to biological origin or migration from deposits in deeper layers. A nonlinear acoustic remote sensing technique based on the nonlinear acoustic scattering theory of gas bubbles is introduced in this thesis to identify the gas bubbles in surficial layers of marine sediments and measure their concentrations. Two close transmitting frequencies were used to generate a nonlinear scattering effect from the gas bubbles in the sediments, and the nonlinear responses were generated only by gas bubbles instead of by other scatters in the sediments. An acoustic inversion was implemented on the nonlinear response, together with calibration results and scattering volume, to determine gas bubble concentrations. Results from the data collected at Gulf of Gdansk demonstrate that the nonlinear acoustic method is advantageous over other acoustic remote sensing methods in gas bubble identification and measurement, and provides more valuable information for seabed classification.
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Silva, João Pedro Santos Parente da. "Acoustic methods for assessment of bubbles produced by marine plants." Master's thesis, 2018. http://hdl.handle.net/10400.1/12166.
Full textAbstract:
The aim of this dissertation is to evaluate different acoustic methods to characterise air
bubbles and their application in the estimation of oxygen bubbles produced by marine
plants during the photosynthesis process. Several methods are described in the literature
to estimate the amount and distribution of air bubbles in marine waters however,
the existing methods focus essentially on bubbles at the ocean’s surface. Under certain
conditions, the oxygen released by marine plants during photosynthesis occurs in the
form of bubbles. The estimation of this bubbles is difficult and is often considered underestimated
by conventional methods. Acoustic methods can be used to estimate the
production of bubbles with greater precision and, moreover, to learn the dynamics of
their production.
It is necessary to evaluate the oxygen transfer process of the plants to the water,
the model of acoustic propagation in seagrass fields, the configuration of the system,
methods to filter the influence of unwanted parameters on the received signal (e.g.,
temperature changes, noise, tide, sound speed, salinity), and, to characterise environmental
and biological noise.
In this work, I propose to evaluate a suitability and generic bubble estimation
method described in the literature, or the development of new methods for the monitoring
of bubbles released by marine plants, in particular, seagrass Cymodocea Nodosa.
The reliability of a generic bubble estimation method described in the literature, as well as, new methods for monitoring the bubbles released by marine plants will
be tested. All the tests were conducted with the Cymodocea Nodosa seagrass species,
in tanks on IPMA-EPPO. Combining acoustic with other techniques (CTD data, tide
height) will allow the development of a robust and accurate acoustic measurement
system. The acquired signals can be processed to estimate the amount of oxygen bubbles
produced in that environment. With the use of this measurement system, I believe
that this innovative acoustic method can be used to accurately quantify the ecosystem
metabolism and that it will represent an important tool to manage and monitor the
production of coastal areas by integrating spatial and temporal scales.
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Liao, Chen-Ting, and 廖振廷. "Microscopic Particle Dynamics in Dust Acoustic Waves and Dusty Plasma Bubbles." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/64206471954393897580.
Full textAbstract:
碩士國立中央大學
物理研究所
95
Dust acoustic wave (DAW) can be self excited at low pressure in the dusty plasma liquid due to some instabilities. Particle motions are directly observed and analyzed in DAW by a high speed micro image system with suitable illumination. We investigate their interactions and dynamics as a connection between macroscopic and microscopic pictures of the longitudinal wave. Various instabilities and collective behaviors can be self generated, such as DAW, or driven externally such as plasma bubble. In experiments, we can measure the global behaviors of the wave including spatiotemporal evolution of the particle number density, the spatial distribution of the power spectrum, phase space portrait, etc. In microscopic viewpoint, individual particle trajectories are traced in DAW to get its displacement and velocity. It is found that when the particle colliding the wave crest, it may be carried by the wave front and travels together for a short time or it may be repelled by the wave front and turns back. Most particles behave as long time aperiodic or quasi periodic chaotic motion instead of the simple harmonic motion. Particles oscillate in their potential wells may have opportunity to jump to nearby potential wells as the hopping motion. Furthermore, all particle trajectories are traced at the same time to study the velocity distribution of the particles in the wave. In another part of the experiment, the same methods are used to observe the spatiotemporal evolution and particle dynamics for pulsed laser ablation induced plasma bubble, i.e., spherical dust cavity. The collapsing plasma bubble can be considered as a downward propagating supersonic dust shock wave. Consequently, we further investigate some interesting phenomena such as the wave-bubble interactions and the induced dust wake field behind the bubble when plasma bubble traveling through DAW.
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Schoen, Scott Joseph Jr. "Acoustic characterization of encapsulated microbubbles at seismic frequencies." Thesis, 2013. http://hdl.handle.net/2152/23911.
Full textAbstract:
Encapsulated microbubbles, whose diameters are on the order of microns, are widely used to provide acoustic contrast in biomedical applications. But well below the resonance frequencies of these microbubbles, any acoustic contrast is due solely to their relatively high compressibility compared to the surrounding medium. To estimate how well microbubbles may function as acoustic contrast agents in applications such as borehole logging or underground flow mapping, it must be determined how they behave both at atmospheric and down-well conditions, and how their presence affects the bulk acoustic properties of the surrounding medium, most crucially its specific acoustic impedance. Resonance tube experiments were performed on several varieties of acoustic contrast agents to determine their compressibility as a function of pressure and temperature, and the results are used to estimate the effect on sound propagation when they are introduced into rock formations.text
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Chan, Hsiang-Chih, and 湛翔智. "Acoustic Analysis of Nearshore Breaking Wave Bubbles Simulated by Piston-Type Wavemaker." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/96263626936033802781.
Full textAbstract:
碩士國立中山大學
海下技術研究所
90
This article studies ambient noise in the surf zone that was simulated by piston-type wavemaker in the tank. The experiment analyzed the bubbles of breaking wave by using a hydrophone to receive the acoustic signal, and the images of bubbles were recorded by a digital video camera to observe distribution of bubbles. The tank is in College of Marine Sciences, National Sun Yat-sen University, the dimensions of water tank are 35 m ×1 m ×1.2 m, and the slope of the simulated seabed is 1:5. The studied parameters of ambient noise generates by breaking wave bubbles were wave height, period, and water depth. Short-time Fourier Transform was applied to obtain the acoustic spectrum of bubbles, MATLAB programs were used to calculate mean sound pressure level, and determine number of bubbles. Bubbles with resonant frequency from 0.5 to 10 kHz were studied, counted from peaks in the spectrum. The number of bubbles generated by breaking waves could be estimated by bubbles energy distributions. The sound pressure level of ambient noise was highly related to the wave height and period, with correlation coefficient 0.7. The results were compared with other studies of ambient noise in the surf.
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Hay, Todd Allen 1979. "A model of the interaction of bubbles and solid particles under acoustic excitation." 2008. http://hdl.handle.net/2152/18109.
Full textAbstract:
The Lagrangian formalism utilized by Ilinskii, Hamilton and Zabolotskaya [J. Acoust. Soc. Am. 121, 786-795 (2007)] to derive equations for the radial and translational motion of interacting bubbles is extended here to obtain a model for the dynamics of interacting bubbles and elastic particles. The bubbles and particles are assumed to be spherical but are otherwise free to pulsate and translate. The model is accurate to fifth order in terms of a nondimensional expansion parameter R/d, where R is a characteristic radius and d is a characteristic distance between neighboring bubbles or particles. The bubbles and particles may be of nonuniform size, the particles elastic or rigid, and external acoustic sources are included to an order consistent with the accuracy of the model. Although the liquid is assumed initially to be incompressible, corrections accounting for finite liquid compressibility are developed to first order in the acoustic Mach number for a cluster of bubbles and particles, and to second order in the acoustic Mach number for a single bubble. For a bubble-particle pair consideration is also given to truncation of the model at fifth order in R/d via automated derivation of the model equations to arbitrary order. Numerical simulation results are presented to demonstrate the effects of key parameters such as particle density and size, liquid compressibility, particle elasticity and model order on the dynamics of single bubbles, pairs of bubbles, bubble-particle pairs and clusters of bubbles and particles under both free response conditions and sinusoidal or shock wave excitation.text
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Wu, Cheng-kang, and 吳政剛. "The Study of Effects of Gas Bubbles on Acoustic Wave Attenuation Using AST-Sonar System." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/69204416925635398037.
Full textAbstract:
碩士國立中山大學
海下技術研究所
95
Bubbles are often present in the natural ocean. Bubbly liquid will have the significant influence the sound propagation, and creates a significant disturbance to under water target''s detection. Therefore, it is an important research subject of bubble influence to the sound wave propagation. This study used the sonar training system which developed by British''s iTP corporation, through suitable additional design discuss the attenuation of sound propagating through a bubble screen. At first this study collects and infers the formula by the literature review. Secondly, the experimental design of measuring the attenuation of sound wave. The experiment process by using two parallel iron boards to carry on the measurement of gas-volume fraction. Then correlate with the sound pressure from the measurement of hydrophone. After curve fitting, we can clearly know the each other correlation. Finally taking the result compare with the attenuation coefficient formula. The experimental consists of two parts. The first part is to measure the gas-volume fraction of the bubbly liquid contained in the screen; while the second part is to measure the sound attenuation of the bubble screen. The result display that the bubble screen can attenuate about 8 dB per centimeter as the gas-volume fraction stay at 1 percent. At high gas-volume fraction the coefficient of attenuation has increased, and is different from theoretical value. This is because the bubble''s correlation has not been considered. In addition, the low frequency sound wave is close to theoretical value, but the high frequency sound wave has big different to theoretical value. Because the high frequency sound wave''s wavelength is too small to satisfy the condition. At experiment I suggest to use more appropriate transducers and precise bubble''s tube. Thus the experimental result will be better.
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Weber, Thomas C. "Acoustic propagation through bubble clouds." 2006. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-1168/index.html.
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Lin, Ying-Shen, and 林盈伸. "Acoustic Effects of Bubbly Liquids." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/47228755982208247800.
Full text
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Enenstein, Gregory Robert. "Two studies on the acoustics of multiphase materials : seagrass tissue and encapsulated bubbles." Thesis, 2014. http://hdl.handle.net/2152/26321.
Full textAbstract:
There are two focal points of this thesis: the acoustics of seagrass and the acoustical properties of encapsulated bubbles for underwater noise abatement. The acoustical properties of seagrass have applications in mine hunting, shallow water sonar, and environmental acoustic remote sensing. In order to optimize these applications, a predictive model of acoustic propagation in seagrass beds is sought. Previous laboratory research has indicated that the tissue acoustic properties of seagrass as well as the tissue physical structure and entrained air masses inside the leaves contribute to the overall acoustic behavior. The present research utilized a glass laboratory resonance tube to find the low frequency (1 kHz-4 kHz) acoustic compressibility of two species of seagrass, Thalassia testidinum and Halodule wrightii. By using a mixture of finely divided seagrass tissue suspended in seawater, the bulk moduli of the seagrass species were extracted. In the second section, encapsulated bubbles were analyzed as a method of abating underwater anthropogenic noise sources, since these sources, including marine piledriving and oil and gas exploration and production, pose potential harmful effects to marine life. Previous research, which used an array of rubber-shelled encapsulated bubbles, found the attenuation from these bubbles in be in close accordance with an existing encapsulated bubble model. Experiments were performed in a small laboratory resonance tank, a large outdoor acoustic tank, and at Lake Travis Test Station (LTTS) in order to determine the effects of varying an encapsulated bubble's wall thickness and fill material on bubble resonance frequency and damping. Results found that increasing the wall thickness tended to increase the balloon resonance frequencies measured in the small tank, which was strongly correlated to the frequency of maximum noise reduction in the large outdoor test tank and LTTS tests. The addition of polyester fibers and aluminum wool as fill materials decreased both the resonance frequency and quality factor, whereas helium-filled filled encapsulated bubbles had an increased resonance frequency but decreased quality factor as compared with air-filled bubbles. The resonance quality factor and void fraction further proved to affect the noise reduction near bubble resonance in the outdoor acoustic tank and LTTS tests. The measurements made with a single bubble in a small laboratory tank were correlated to measurements with a full-size system composed of many bubbles operating in open water.text
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Gilbert, Jeffrey. "Study of the self noise generated by supercavitating vehicles." Thesis, 2015. https://hdl.handle.net/2144/16307.
Full textAbstract:
This study investigates the self noise from a ventilated supercavitating vehicle.
A ventilated supercavity is a gaseous envelope surrounding an underwater vehicle
that significantly reduces the drag felt by the vehicle. But the hydrodynamic noise
generated by the creation of the supercavity could impact the successful deployment
of the vehicle. A principal source of self noise for these types of vehicles is sound
created by the ventilating gas jets impinging on the air-water interface. Analytical
models of the radiated sound through the interface have been developed. Sometimes
jets impinging on the interface entrain bubbles beneath the surface. This thesis
outlines a theory to predict the influence of bubbles near the interface.
Experimental measurements were made at the Naval Undersea Warfare Center
(NUWC) in Newport, RI to test the accuracy of the model. These measurements
include the unsteady force spectrum of a gas jet impinging on a rigid wall. The
acoustic pressure spectrum of a gas jet striking the air-water interface was also
recorded. The experimental results were compared to theoretical models for
validation.