Academic literature on the topic 'Bubble domain dynamics'
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Journal articles on the topic "Bubble domain dynamics"
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Ban, Zhen Hong, Kok Keong Lau, and Mohd Sharif Azmi. "Bubble Nucleation and Growth of Dissolved Gas in Solution Flowing across a Cavitating Nozzle." Applied Mechanics and Materials 773-774 (July 2015): 304–8. http://dx.doi.org/10.4028/www.scientific.net/amm.773-774.304.
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Computational modelling of dissolved gas bubble formation and growth in supersaturated solution is essential for various engineering applications, including flash vaporisation of petroleum crude oil. The common mathematical modelling of bubbly flow only caters for single liquid and its vapour, which is known as cavitation. This work aims to simulate the bubble nucleation and growth of dissolved CO2 in water across a cavitating nozzle. The dynamics of bubble nucleation and growth phenomenon will be predicted based on the hydrodynamics in the computational domain. The complex interrelated bubble dynamics, mass transfer and hydrodynamics was coupled by using Computational Fluid Dynamics (CFD) and bubble nucleation and growth model. Generally, the bubbles nucleate at the throat of the nozzle and grow along with the flow. Therefore, only the region after the throat of the nozzle has bubbles. This approach is expected to be useful for various types of bubbly flow modelling in supersaturated condition.
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Nguyen, Van Luc, Tomohiro Degawa, and Tomomi Uchiyama. "Numerical simulation of annular bubble plume by vortex in cell method." International Journal of Numerical Methods for Heat & Fluid Flow 29, no. 3 (March 4, 2019): 1103–31. http://dx.doi.org/10.1108/hff-03-2018-0094.
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PurposeThis study aims to provide discussions of the numerical method and the bubbly flow characteristics of an annular bubble plume.Design/methodology/approachThe bubbles, released from the annulus located at the bottom of the domain, rise owing to buoyant force. These released bubbles have diameters of 0.15–0.25 mm and satisfy the bubble flow rate of 4.1 mm3/s. The evolution of the three-dimensional annular bubble plume is numerically simulated using the semi-Lagrangian–Lagrangian (semi-L–L) approach. The approach is composed of a vortex-in-cell method for the liquid phase and a Lagrangian description of the gas phase.FindingsFirst, a new phenomenon of fluid dynamics was discovered. The bubbly flow enters a transition state with the meandering motion of the bubble plume after the early stable stage. A vortex structure in the form of vortex rings is formed because of the inhomogeneous bubble distribution and the fluid-surface effects. The vortex structure of the flow deforms as three-dimensionality appears in the flow before the flow fully develops. Second, the superior abilities of the semi-L–L approach to analyze the vortex structure of the flow and supply physical details of bubble dynamics were demonstrated in this investigation.Originality/valueThe semi-L–L approach is applied to the simulation of the gas–liquid two-phase flows.
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WANG, Q. X., and J. R. BLAKE. "Non-spherical bubble dynamics in a compressible liquid. Part 1. Travelling acoustic wave." Journal of Fluid Mechanics 659 (July 27, 2010): 191–224. http://dx.doi.org/10.1017/s0022112010002430.
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Micro-cavitation bubbles generated by ultrasound have wide and important applications in medical ultrasonics and sonochemistry. An approximate theory is developed for nonlinear and non-spherical bubbles in a compressible liquid by using the method of matched asymptotic expansions. The perturbation is performed to the second order in terms of a small parameter, the bubble-wall Mach number. The inner flow near the bubble can be approximated as incompressible at the first and second orders, leading to the use of Laplace's equation, whereas the outer flow far away from the bubble can be described by the linear wave equation, also for the first and second orders. Matching between the two expansions provides the model for the non-spherical bubble behaviour in a compressible fluid. A numerical model using the mixed Eulerian–Lagrangian method and a modified boundary integral method is used to obtain the evolving bubble shapes. The primary advantage of this method is its computational efficiency over using the wave equation throughout the fluid domain. The numerical model is validated against the Keller–Herring equation for spherical bubbles in weakly compressible liquids with excellent agreement being obtained for the bubble radius evolution up to the fourth oscillation. Numerical analyses are further performed for non-spherical oscillating acoustic bubbles. Bubble evolution and jet formation are simulated. Outputs also include the bubble volume, bubble displacement, Kelvin impulse and liquid jet tip velocity. Bubble behaviour is studied in terms of the wave frequency and amplitude. Particular attention is paid to the conditions if/when the bubble jet is formed and when the bubble becomes multiply connected, often forming a toroidal bubble. When subjected to a weak acoustic wave, bubble jets may develop at the two poles of the bubble surface after several cycles of oscillations. A resonant phenomenon occurs when the wave frequency is equal to the natural oscillation frequency of the bubble. When subjected to a strong acoustic wave, a vigorous liquid jet develops along the direction of wave propagation in only a few cycles of the acoustic wave.
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Wang, Ping-Ping, A.-Man Zhang, Xiang-Li Fang, Abbas Khayyer, and Zi-Fei Meng. "Axisymmetric Riemann–smoothed particle hydrodynamics modeling of high-pressure bubble dynamics with a simple shifting scheme." Physics of Fluids 34, no. 11 (November 2022): 112122. http://dx.doi.org/10.1063/5.0123106.
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High-pressure bubble dynamics often involves many complex issues, including large deformations and inhomogeneities, strong compression, moving interfaces, and large discontinuities, that bring challenges to numerical simulations. In this work, an axisymmetric Riemann–smoothed particle hydrodynamics (SPH) method is used to simulate high-pressure bubbles near different boundaries. This Riemann–SPH can adopt the real sound speed instead of the artificial one for the air phase in the bubble. Therefore, the real compressibility of the air phase can be considered, and the corresponding time step is significantly increased. To avoid unphysical interface penetration and maintain relatively homogeneous particle distribution, a new and simple particle shifting scheme for multiphase flows is proposed. Additionally, to minimize the influence of the unphysical boundary on the bubble, a large fluid domain with an optimized initial particle distribution is adopted to reduce the particle number. Several high-pressure bubbles under different boundary conditions are considered, including in a free field, near a free surface, near a solid boundary, and near a rigid sphere. Numerical results show that these bubble dynamic behaviors can be reproduced with satisfactory accuracy.
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Chahine, Georges L., and Ramani Duraiswami. "Dynamical Interactions in a Multi-Bubble Cloud." Journal of Fluids Engineering 114, no. 4 (December 1, 1992): 680–86. http://dx.doi.org/10.1115/1.2910085.
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Results of studies on the dynamics of “clouds” of bubbles via both an analytical technique using asymptotic expansions, and via numerical simulation using a three-dimensional boundary element technique (BEM) are reported. The asymptotic method relies on the assumption that the characteristic bubble size is much smaller than the characteristic inter-bubble distance. Results obtained from the two methods are compared, and are found to agree in the domain of validity of the asymptotic technique, which is for very low void fractions. Next, results of several numerical experiments conducted using the BEM algorithm are reported. The results indicate the influence of the mutual interaction on the dynamics of multiple bubble clouds.
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Tao, Sijia, Guangtai Shi, Yexiang Xiao, Zongliu Huang, and Haigang Wen. "Effect of Operating Parameters on the Coalescence and Breakup of Bubbles in a Multiphase Pump Based on a CFD-PBM Coupled Model." Journal of Marine Science and Engineering 10, no. 11 (November 8, 2022): 1693. http://dx.doi.org/10.3390/jmse10111693.
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When the multiphase pump is running, the internal medium often exists as bubble flow. In order to investigate the bubble occurrence characteristics in the pressurization unit of the multiphase pump more accurately, this paper couples computational fluid dynamics (CFD) with a population balance model (PBM) to investigate the bubble size distribution law of the multiphase pump under different operating conditions, taking into account the bubble coalescence and breakup. The research shows that the mean bubble size in the impeller domain gradually decreases from 1.7013 mm at the inlet to 0.6179 mm at the outlet along the axis direction; the average bubble diameter in the diffuser domain fluctuates around 0.60 mm. The bubbles in the impeller region gradually change from the trend of coalescence to the trend of breakup along the axial and radial directions, and the bubbles in the diffuser tend to be broken by the vortex entrainment. The bubble size development law is influenced by the inlet gas volume fraction (IGVF) and the rotational speed, showing a more obvious rule, where the gas phase aggregation phenomenon enhanced by the increase in IGVF promotes the trend of bubble coalescence and makes the bubble size gradually increase. The increased blade shearing effect with the increase in rotational speed promotes the trend of bubble breakup, which gradually reduces the size of the bubbles. In addition, increasing the bubble coalescence probability is a key factor leading to changes in bubble size; the bubble size development law is not very sensitive to changes in flow, and the bubble size is at its maximum under design conditions. The research results can accurately predict the performance change of the multiphase pump and provide technical guidance for its safe operation and optimal design.
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Speidel, S., S. Iwata, and S. Uchiyama. "Dynamics of stripe domain walls in bubble films." Journal of the Magnetics Society of Japan 10, no. 2 (1986): 125–28. http://dx.doi.org/10.3379/jmsjmag.10.125.
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Speidel, S., S. Iwata, and S. Uchiyama. "Dynamics of Stripe Domain Walls in Bubble Films." IEEE Translation Journal on Magnetics in Japan 2, no. 6 (June 1987): 505–11. http://dx.doi.org/10.1109/tjmj.1987.4549508.
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Sedlář, Milan, Patrik Zima, and Martin Komárek. "Numerical Prediction of Erosive Potential of Unsteady Cavitating Flow around Hydrofoil." Applied Mechanics and Materials 565 (June 2014): 156–63. http://dx.doi.org/10.4028/www.scientific.net/amm.565.156.
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The paper attempts to assess the erosive potential of cavitation bubbles in unsteady flow of liquid over a prismatic hydrofoil using two-way coupling of the URANS and the Rayleigh-Plesset equations. The erosive potential of the cavitating flow is evaluated from the energy dissipated during the collapses of imploding cavitation bubbles near the solid surface of the hydrofoil. The bubbles are assumed spherical and the phase slip is neglected. Bubble fission is modelled using a simple break-up model. The interaction between bubbles is considered by superposing the pressure change due to pressure waves generated by collapsing bubbles and propagated in the computational domain over the local pressure in the liquid (external to the bubble). The rate of erosion of the solid material is not studied in this work. The flow is analysed using the in-house three-dimensional solver for unsteady turbulent flow with bubble dynamics. The results are demonstrated on the NACA 2412 hydrofoil with the incidence angle of 8 degrees and the cavitation number 1.37, which corresponds to the regime of oscillating partial cavity with periodic shedding of bubble cloud downstream of the cavity.
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Hou, Jiacheng, Zhongquan Charlie Zheng, and John S. Allen. "Time-domain simulation of acoustic wave scattering and internal propagation from a gas bubble of various shapes." Journal of the Acoustical Society of America 153, no. 3 (March 2023): 1468–79. http://dx.doi.org/10.1121/10.0017386.
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Acoustic scattering and resonances of gas bubbles are computed using a time-domain simulation based on numerical solutions of the conservation laws. The time histories of scattered pressure and fluid velocity, outside and inside the bubble, are obtained simultaneously from an immersed-boundary method allowing for the investigation of exterior and interior fields for non-spherical geometries. The acoustic resonances of the bubble are investigated for various bubble sizes, shapes, and inner gas parameters and compared in limiting cases to the partial wave scattering solutions for spherical bubbles. The dynamics of the gas motion and its associated contribution to resonance response has received little attention in previous analytical and numerical formulations. In this study, the acoustic propagation and motion inside the interior gas is investigated with respect to the monopole resonance with the combined time-domain simulation and immersed-boundary method. For the non-spherical prolate and oblate shapes, the scattering and resonance behaviors are compared with the approximate analytical results based on the shape factor method. The simulation method can be extended to less-understood shapes relevant to underwater and physical acoustics, such as “pancake-shaped” or “cigar-shaped” bubbles, as well as to spatial and time-dependent forcing.
Dissertations / Theses on the topic "Bubble domain dynamics"
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SARMA, BHASKARJYOTI. "Effect of Disorder on Domain Wall Dynamics." Doctoral thesis, Politecnico di Torino, 2018. http://hdl.handle.net/11583/2713359.
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The purpose of this work is to study the effects of disorders on domain wall dynamics in perpendicular magnetic anisotropy ultra-thin ferromagnetic materials. It is done, firstly, by experimental study of domain wall dynamics in Ta/CoFeB/MgO material where distributions and strengths of pinning points are controlled by light ion irradiation and secondly, by micromagnetic study of the dynamics and morphology of a bubble domain in a disorder induced PMA material with Dzyaloshinskii-Moriya interaction. By studying the effects of He^{+} ion irradiation on domain wall dynamics, it is found that irradiation influences the distribution of pinning points as well as their strengths, thereby influencing the velocities of domain walls. The velocities
are found to be lowest for non-irradiated samples, then it is observed to increase with irradiation and then decrease at higher irradiations suggesting that there is an optimum irradiation where velocity should be maximum. On the other hand, by studying the dynamics of bubble domain using micromagnetic simulations in ultra-thin films with disorder and Dzyaloshinskii-Moriya interaction, it is found, as expected that magnetic bubbles expand asymmetrically
along the axis of the in-plane field under the simultaneous application of out-of-plane and in-plane fields. Remarkably, the shape of the bubble was found to have a ripple-like part which caused a kink-like (steep decrease) feature in the velocity versus in-plane field curve. It is shown that these ripples originate due to the nucleation and interaction of vertical Bloch lines. Furthermore, it is also shown that the Dzyaloshinskii-Moriya interaction field is not constant, in contradiction with the results of experiments, but rather depends on the in-plane field.
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Zebiri, Boubakr. "Étude numérique des interactions onde de choc / couche limite dans les tuyères propulsives Shock-induced flow separation in an overexpanded supersonic planar nozzle A parallel high-order compressible flows solver with domain decomposition method in the generalized curvilinear coordinates system Analysis of shock-wave unsteadiness in conical supersonic nozzles." Thesis, Normandie, 2020. http://www.theses.fr/2020NORMIR06.
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La nécessité d’une meilleure compréhension du mécanisme d’entrainement pour l’instabilité à basse fréquence observée dans un écoulement dans une tuyère sur-détendue a été discutée. Le caractère instable de l’onde de choc/couche limite reste un défi pratique important pour les problèmes des écoulements dans les tuyères. De plus, pour une couche limite turbulente incidente donnée, ce type d’écoulement présente généralement des mouvements de choc à basse fréquence plus élevées qui sont moins couplés aux échelles de temps de la turbulence en amont. Cela peut être bon du point de vue d’un expérimentateur, en raison de difficultés à mesurer des fréquences plus élevées, mais c’est plus difficile d’un point de vue calcul numérique en raison de la nécessité d’obtenir des séries temporelles plus longues pour résoudre les mouvements à basse fréquence. En excellent accord avec les résultats expérimentaux, une série de calcul LES de très longue durée a été réalisée, il a été clairement démontré l’existence de mouvements énergétiques à basse fréquence et à large bande près du point de séparation. Des efforts particuliers ont été faits pour éviter tout forçage à basse fréquence en amont, et il a été explicitement démontré que les oscillations de choc à basse fréquence observées n’étaient pas liées à la génération de turbulence d’entrée, excluant la possibilité d’un artefact numérique. Différentes méthodes d’analyse spectrales, et en décomposition en mode dynamique ont été utilisées pour montrer que les échelles de temps impliquées dans un tel mécanisme sont environ deux ordres de grandeur plus grandes que les échelles de temps impliquées dans la turbulence de la couche limite, ce qui est cohérent avec les mouvements de basse fréquence observés. En outre, ces échelles de temps se sont avérées être fortement modulées par la quantité de flux inversé à l’intérieur de la bulle de séparation. Ce scénario peut, en principe, expliquer à la fois l’instabilité des basses fréquences et sa nature à large bandeThe need for a better understanding of the driving mechanism for the observed low-frequency unsteadiness in an over-expanded nozzle flows was discussed. The unsteady character of the shock wave/boundary layer remains an important practical challenge for the nozzle flow problems. Additionally, for a given incoming turbulent boundary layer, this kind of flow usually exhibits higher low-frequency shock motions which are less coupled from the timescales of the incoming turbulence. This may be good from an experimenter’s point of view, because of the difficulties in measuring higher frequencies, but it is more challenging from a computational point of view due to the need to obtain long time series to resolve low-frequency movements. In excellent agreement with the experimental findings, a very-long LES simulation run was carried out to demonstrate the existence of energetic broadband low-frequency motions near the separation point. Particular efforts were done in order to avoid any upstream low-frequency forcing, and it was explicitly demonstrated that the observed low-frequency shock oscillations were not connected with the inflow turbulence generation, ruling out the possibility of a numerical artefact. Different methods of spectral analysis and dynamic mode decomposition have been used to show that the timescales involved in such a mechanism are about two orders of magnitude larger than the time scales involved in the turbulence of the boundary layer, which is consistent with the observed low-frequency motions. Furthermore, those timescales were shown to be strongly modulated by the amount of reversed flow inside the separation bubble. This scenario can, in principle, explain both the low-frequency unsteadiness and its broadband nature
Conference papers on the topic "Bubble domain dynamics"
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Jayaprakash, Arvind, Sowmitra Singh, and Georges Chahine. "Bubble Dynamics in a Two-Phase Bubbly Mixture." In ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-40509.
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The dynamics of a primary relatively large bubble in a water mixture including very fine bubbles is investigated experimentally and the results are provided to several parallel on-going analytical and numerical approaches. The main/primary bubble is produced by an underwater spark discharge from two concentric electrodes placed in the bubbly medium, which is generated using electrolysis. A grid of thin perpendicular wires is used to generate bubble distributions of varying intensities. The size of the main bubble is controlled by the discharge voltage, the capacitors size, and the pressure imposed in the container. The size and concentration of the fine bubbles can be controlled by the electrolysis voltage, the length, diameter, and type of the wires, and also by the pressure imposed in the container. This enables parametric study of the factors controlling the dynamics of the primary bubble and development of relationships between the bubble characteristic quantities such as maximum bubble radius and bubble period and the characteristics of the surrounding two-phase medium: micro bubble sizes and void fraction. The dynamics of the main bubble and the mixture is observed using high speed video photography. The void fraction/density of the bubbly mixture in the fluid domain is measured as a function of time and space using image analysis of the high speed movies. The interaction between the primary bubble and the bubbly medium is analyzed using both field pressure measurements and high-speed videography. Parameters such as the primary bubble energy and the bubble mixture density (void fraction) are varied, and their effects studied. The experimental data is then compared to simple compressible equations employed for spherical bubbles including a modified Gilmore Equation. Suggestions for improvement of the modeling are then presented.
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Gupta, Amit, and Ranganathan Kumar. "Lattice Boltzmann Simulation to Study Multiple Bubble Dynamics." In ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-43218.
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Lattice Boltzmann method (LBM) has been used in this study to understand the behavior of bubble motion and bubble coalescence in liquids. For a fully periodic domain, bubble dynamics and shape for a single bubble and multiple bubbles are dependent on Eotvos number, Reynolds number and Morton number. Drag coefficient for single bubble motion under buoyancy has been computed and compared with existing correlations provided in terms of the flow parameters. For multiple bubbles, the bubble dynamics is dictated by vortex pattern of the leading bubble, which allows the bubbles to coalesce. Such simulations have also been run for different configurations of the initial bubble distribution for both in-line and staggered bubble configuration to show the effect of vortex shedding on the oscillatory motion of the bubbles.
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Alnaimat, Fadi, Bobby Mathew, and Omar Alhammadi. "Numerical Investigation of Single Bubble Dynamics Passing a Mesh-Based Structure." In ASME 2020 Heat Transfer Summer Conference collocated with the ASME 2020 Fluids Engineering Division Summer Meeting and the ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/ht2020-9063.
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Abstract In this article, investigations of the dynamic behaviors of a single bubble flowing across a mesh-based structure domain was conducted using the volume of fluid (VOF) model. The study was investigated in various mesh structure sizes, including hole size and gap distance. The fundamental behavior of bubble deformation and the effects of gap sizes were analyzed. Subsequently, the predicted dynamics of the deforming bubble area and the effect of the surface tension were examined inside the mesh holes. The discharging bubbles from the mesh structure resulted in a slight difference in the physical features from the original bubble dynamics before entering the mesh (flow restriction). This drafted the bubbles in different trajectories and led to behave differently based on the mesh characteristics. The complex interactions and the subsequent deformations were observed between different mesh sizes. For the validation of the bubble dynamics, the results of computational fluid dynamics (CFD) simulation were tested under different mesh sizes detailing the velocity field, exiting trajectory, bubbles deformation, and residence time, which helps to reveal the affected parameters on the separation mechanism of the original bubble.
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Ma, Jingsen, Chao-Tsung Hsiao, and Georges L. Chahine. "Shared-Memory Parallelization for Two-Way Coupled Euler-Lagrange Modeling of Bubbly Flows." In ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting collocated with the ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/fedsm2014-22057.
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Cavitating bubbly flows are encountered in many engineering problems involving propellers, pumps, valves, ultrasonic biomedical applications, … etc. In this contribution an OpenMP parallelized Euler-Lagrange model of two-phase flow problems and cavitation is presented. The two-phase medium is treated as a continuum and solved on an Eulerian grid, while the discrete bubbles are tracked in a Lagrangian fashion with their dynamics computed. The intimate coupling between the two description levels is realized through the local void fraction, which is computed from the instantaneous bubble volumes and locations, and provides the continuum properties. Since, in practice, any such flows will involve large numbers of bubbles, schemes for significant speedup are needed to reduce computation times. We present here a shared-memory parallelization scheme combining domain decomposition for the continuum domain and number decomposition for the bubbles; both selected to realize maximum speed up and good load balance. The Eulerian computational domain is subdivided based on geometry into several subdomains, while for the Lagrangian computations, the bubbles are subdivided based on their indices into several subsets. The number of fluid subdomains and bubble subsets are matched with the number of CPU cores available in a share-memory system. Computation of the continuum solution and the bubble dynamics proceeds sequentially. During each computation time step, all selected OpenMP threads are first used to evolve the fluid solution, with each handling one subdomain. Upon completion, the OpenMP threads selected for the Lagrangian solution are then used to execute the bubble computations. All data exchanges are executed through the shared memory. Extra steps are taken to localize the memory access pattern to minimize non-local data fetch latency, since severe performance penalty may occur on a Non-Uniform Memory Architecture multiprocessing system where thread access to non-local memory is much slower than to local memory. This parallelization scheme is illustrated on a typical non-uniform bubbly flow problem, cloud bubble dynamics near a rigid wall driven by an imposed pressure function.
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Guse, Fabian, Enrico Pasquini, and Katharina Schmitz. "Consideration of Air Bubble Dynamics in 1D Hydraulic Pipeline Simulation – Source Term Development and Verification Utilizing Transmission Line Theory." In ASME/BATH 2021 Symposium on Fluid Power and Motion Control. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/fpmc2021-66944.
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Abstract In fluid power systems, the presence of undissolved air greatly influences the properties of the liquid-gas mixture. Even marginal amounts of undissolved air may drastically reduce the apparent bulk modulus of the mixture. In current state-of-the-art 1D simulation tools, the estimation of the apparent bulk modulus of the mixture is based on the assumption that both liquid and gas fractions act as springs. However, the so-called Rayleigh-Plesset equation frequently used for cavitation analysis shows that the gas bubbles should rather be regarded as non-linear mass-spring-damper systems, implicating a frequency-dependent stiffness of the gas phase. In the present paper, these dynamic effects are investigated by considering monodisperse as well as polydisperse mixtures. For the polydisperse case, a log-normal bubble size distribution is used. First, a frequency domain solution for the bubble dynamics is developed by linearizing the Rayleigh-Plesset equation. An expression of the mixture bulk modulus is derived, which is complex-valued and frequency-dependent. Based on the bulk modulus, a theoretical solution for the dynamics of a whole pipeline is developed by utilizing transmission line theory. It is shown that the dynamics of the bubbles leads to a significant shift of the system’s natural frequencies towards lower values — a phenomenon that needs to be accounted for during the design phase of a fluid power system. After the development of this analytical solution, by introducing a bubble dynamics source term, an established numerical scheme for 1D pipe simulation based on the method of characteristics is expanded. Finally, the newly developed numerical approach is compared with the analytical solution in order to determine its accuracy. The findings and simulation approaches in this work will enable fluid power system engineers to predict dynamic system behavior more precisely during early stages of system layout.
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Yoshida, Hiroyuki, Taku Nagatake, Kazuyuki Takase, Akiko Kaneko, Hideaki Monji, and Yutaka Abe. "Development of Prediction Technology of Two-Phase Flow Dynamics Under Earthquake Acceleration: (14) Numerical Simulation of Two-Phase Flow in Subchannels Under Accelerating Condition." In 2014 22nd International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/icone22-30153.
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An earthquake is one of the most serious phenomena to consider for the safety of a nuclear reactor in Japan. Therefore, structural safety of nuclear reactors has been studied and nuclear reactors were contracting with structural safety for a big earthquake. However, it is not enough for safety operation of nuclear reactors because thermal-fluid safety is not confirmed under the earthquake. For instance, behavior of gas-liquid two-phase flow is unknown in seismic conditions. Especially, fluctuation of void fraction is an important factor for the safety operation of the nuclear reactor. In previous work, fluctuation of void faction in bubbly flow was studied experimentally and theoretically to investigate the stability of the bubbly flow. In such studies, flow rate or void fraction fluctuations were given to the steady bubbly flow. In case of the earthquake, the fluctuation is not only the flow rate, but also a body force on the two-phase flow and shear force through the pipe wall. Interactions of gas and liquid through their interface also act on the behavior of the two-phase flow. The fluctuation of the void fraction is not clear for such complicated situation during the earthquake. Therefore, the behavior of gas-liquid two-phase flow is investigated experimentally and numerically in a series of studies. In this study, to develop the predictive technology of two-phase flow dynamics under earthquake acceleration, a detailed two-phase flow simulation code with an advanced interface tracking method TPFIT (Two-Phase Flow simulation code with Interface Tracking) was expanded to two-phase flow simulation in seismic conditions. In a previous study, we performed a numerical simulation of a two-phase bubbly flow in a horizontal pipe and a vertical bubble motion in a water tank in seismic conditions. And it was confirmed that the modified TPFIT can be applicable to the bubbly flow in seismic conditions. In this paper, the two-phase bubbly flow in a simulated single-subchannel excited by oscillation acceleration was simulated by using the expanded TPFIT. A calculation domain used in this simulation was a simplified subchannel in a BWR core. And time-series of void fraction distributions were evaluated based on predicted bubble distributions. When no oscillation acceleration was added, void fraction concentrated in a region near the wall. When oscillation acceleration was added, void fraction distribution was changed by time. And coalesces of bubbles occurred in the numerical simulation, and bubbles with relatively large diameter were observed. In the results, complicated void fraction distribution was observed, because the response of void fraction distribution on the oscillation acceleration was dependent on not only imposed acceleration, but also the bubble diameter.
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Samiei, Ehsan, Mehrzad Shams, and Reza Ebrahimi. "Numerical Study on Mass Transfer Effects on Spherical Cavitation Bubble Collapse in an Acoustic Field." In ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis. ASMEDC, 2010. http://dx.doi.org/10.1115/esda2010-24606.
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A numerical code to simulate mass transfer effects on spherical cavitation bubble collapse in an acoustic pressure domain in quiescent water has been developed. Gilmore equation is used to simulate bubble dynamics, with considering mass diffusion and heat transfer. Bubbles with different initial radii were considered in quiescent infinite water in interaction with sinusoidal shock waves with different magnitudes of amplitude and frequency. Simulations were done in two cases; with and without considering mass transfer. Good agreement with reference data was achieved. For bubbles with small radii in high frequency pressure field with low amplitude, mass transfer causes larger maximum radii and growth time, and more violent resultant collapse. Decreasing pressure frequency or increasing its amplitude causes larger maximum radii, longer collapse time, and more violent collapse. But, in cases with mass transfer because at the last moments of collapse stage a large amount of water vapor is trapped inside the bubble, the collapse will become less violent. For larger bubbles collapse becomes more violent for the cases without mass transfer in all pressure amplitudes and higher frequencies. But decreasing pressure frequency makes the collapse of the bubbles with mass transfer more violent. However, mass transfer effects decreases with increasing initial bubble radius.
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Ma, Jingsen, Aswin Gnanaskandan, Chao-Tsung Hsiao, and Georges L. Chahine. "MPI Parallelization for Two-Way Coupled Euler-Lagrange Simulation of Microbubble Enhanced HIFU." In ASME 2020 Fluids Engineering Division Summer Meeting collocated with the ASME 2020 Heat Transfer Summer Conference and the ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/fedsm2020-20404.
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Abstract Microbubble enhanced High Intensity Focused Ultrasound (HIFU) is of great interest to tissue ablation for tumor treatment such as in liver and brain cancers, in which ultrasonic contrast agent microbubbles are injected to the targeted region to promote local heating while reducing pre-focal damage. To accurately characterize the acoustic and thermal fields during this process, a compressible Euler-Lagrange model is used. The non-linear ultrasound field is modeled using compressible N-S equations on an Eulerian grid, while the microbubbles are tracked as discrete singularities in a Lagrangian fashion with their dynamics computed. Their intimate coupling is realized through the local void fraction, which is computed from the instantaneous bubble volumes and locations, and then fed to the fluid continuum model. Owing to demanding computational cost in real applications, schemes for significant speedup are highly desirable. We present here a MPI parallelization scheme based on domain decomposition for both the continuum fluid and the discrete bubbles. The Eulerian computational domain is subdivided into several subdomains having each the same number of grids, while the bubbles are subdivided based on their locations corresponding to each subdomain. During each computation time step, MPI processors, each handling one subdomain, are 1) first used to execute the fluid computation, and 2) then to execute the bubble computations, 3) followed by the coupling procedure, which maps the void fraction from the Lagrangian bubble solutions into the Eulerian grids. Steps 1) and 2) are relatively straightforward by routinely following regular MPI procedures. However, step 3) becomes challenging as the effect of the bubbles through the void fraction at an Eulerian point near a subdomain border will require information from bubbles located in different subdomains. Similarly, a bubble near a border between subdomains will spread its contribution to the void fraction of different subdomains. This is addressed by a special utilization of ghost cells surrounding each fluid subdomain, which allows bubbles to spread their void fraction effects across subdomain edges without the need of exchanging directly bubble information between subdomains and significantly increasing overhead. This void fraction implementation is verified by gas volume conservation before and after spreading the bubble effects. Other bubble effects such as thermal effects are handled in a similar way. This parallelization scheme is validated and illustrated on a typical microbubble enhanced HIFU problem, followed by parallelization scaling tests and efficiency analysis.
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Ma, Jingsen, Xiaolong Deng, Chao-Tsung Hsiao, and Georges L. Chahine. "Hybrid MPI-OpenMP Accelerated Euler-Lagrange Simulations of Microbubble Enhanced HIFU." In ASME 2021 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/fedsm2021-65815.
Full textAbstract:
Abstract Microbubble enhanced High Intensity Focused Ultrasound (HIFU) is of great interest to tissue ablation for solid tumor treatments such as in liver and brain cancers, in which contrast agents/microbubbles are injected into the targeted region to promote heating and reduce pre-focal tissue damage. A compressible Euler-Lagrange coupled model has been developed to accurately characterize the acoustic and thermal fields during this process. This employs a compressible Navier-Stokes solver for the ultrasound acoustic field and a discrete singularities model for bubble dynamics. To address the demanding computational cost in practical biological applications, a multi-level hybrid MPI-OpenMP parallelization scheme is developed to take advantage of both scalability of MPI and load balancing of OpenMP. At the first level, the Eulerian computational domain is divided into multiple subdomains and the bubbles are subdivided in groups based on which subdomain they fall into. At the next level, in each subdomain containing bubbles, multiple OpenMP threads are activated to speed up the bubble computations. More OpenMP threads are used inside each subdomain where the bubbles are clustered. By doing this, MPI load imbalance issue due to non-uniformity of bubble presence is compensated. The hybrid MPI-OpenMP Euler-Lagrange solver is used to conduct simulations and physical studies of bubble-enhanced HIFU problems containing a large number of microbubbles. The phenomenon of acoustic shadowing caused by the bubble cloud is then analyzed and discussed. Hybrid parallelization efficiency tests and demonstration of its advantages against using MPI alone are presented.
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Bin Shahadat, Muhammad Rubayat, AKM M. Morshed, Amitav Tikadar, Titan C. Paul, and Jamil A. Khan. "Nano Sized Bubble Formation, Growth and Collapse in Liquid Water by Central Heating: A Molecular Dynamics Simulation." In ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-11794.
Full textAbstract:
Abstract Non-equilibrium Molecular Dynamics (NEMD) Simulation has been employed to investigate the nanobubble generation, growth and collapse in liquid water. The center molecules (240 water molecule) of the simulation domain were heated at five different temperatures (400K, 800K, 1500K, 2100K and 2800K) by velocity scaling for a very short period of time and the radius of the nano sized bubble was calculated. At 400K temperature, no nano bubble is formed but as temperature increases, nano bubble forms and the radius of the nano bubble increases. TIP-3P potential model has been used to predict the structural parameters of water molecules. The SHAKE algorithm has been employed to hold the bonds of O-H and H-O-H as rigid. The results obtained from the simulation were then compared with the results got from Rayleigh-Plesset Equation in order to show the discrepancy of MD simulation and the Hydrodynamic model. The simulation results indicate that Rayleigh-Plesset equation is not valid for prediction the formation, growth and collapse of nano bubble in liquid water because of its uncertainty in predicting the surface tension and ignoring the viscosity.