Journal articles on the topic 'Fundamental and theoretical fluid dynamics'
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1
Chen, Hudong, Chris Teixeira, and Kim Molvig. "Digital Physics Approach to Computational Fluid Dynamics: Some Basic Theoretical Features." International Journal of Modern Physics C 08, no. 04 (August 1997): 675–84. http://dx.doi.org/10.1142/s0129183197000576.
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Andreotti, Bruno, and Jacco H. Snoeijer. "Statics and Dynamics of Soft Wetting." Annual Review of Fluid Mechanics 52, no. 1 (January 5, 2020): 285–308. http://dx.doi.org/10.1146/annurev-fluid-010719-060147.
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The laws of wetting are well known for drops on rigid surfaces but change dramatically when the substrate is soft and deformable. The combination of wetting and the intricacies of soft polymeric interfaces have provided many rich examples of fluid–structure interactions, both in terms of phenomenology and from a fundamental perspective. In this review we discuss experimental and theoretical progress on the statics and dynamics of soft wetting. In this context we critically revisit the foundations of capillarity, such as the nature of solid surface tension, the microscopic mechanics near the contact line, and the dissipative mechanisms that lead to unexpected spreading dynamics.
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ROBISON, ROSALYN A. V., HERBERT E. HUPPERT, and M. GRAE WORSTER. "Dynamics of viscous grounding lines." Journal of Fluid Mechanics 648 (April 7, 2010): 363–80. http://dx.doi.org/10.1017/s0022112009993119.
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We have used viscous fluids in simple laboratory experiments to explore the dynamics of grounding lines between marine ice sheets and the freely floating ice shelves into which they develop. We model the ice sheets as shear-dominated gravity currents, and the ice shelves as extensional gravity currents having zero shear to leading order. We consider the flow of viscous fluid down an inclined plane into a dense inviscid ‘ocean’. A fixed flux of fluid is supplied at the top of the plane, which is at ‘sea level’. The fluid forms a gravity current flowing down and attached to the plane for some distance before detaching to form a freely floating extensional current. We have derived a mathematical model of the flow that incorporates a new dynamic boundary condition for the position of the grounding line, where the gravity current loses contact with the solid base. The grounding line initially advances and eventually reaches a steady position. Good agreement between our theoretical predictions and experimental measurements and observations gives confidence in the fundamental assumptions of our model.
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Zhang, Zewei, Hongyong Yuan, Ming Fu, Tao Chen, Yan Gao, and Guoliang Feng. "Theoretical Investigation on the Characteristics of Leak Noise for Natural Gas Pipelines." Journal of Theoretical and Computational Acoustics 28, no. 03 (September 2020): 2050005. http://dx.doi.org/10.1142/s259172852050005x.
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This paper is concerned with the spectral characteristics of leak noise at the source relevant to fluid dynamics for natural gas pipelines. Comparison is made between the flow field characteristics for the buried and above-ground pipelines to demonstrate the differences in aero-acoustics generation mechanism. The fundamental spectral parameters including the sound pressure level (SPL) and power spectral density (PSD), are extracted to characterize the leak noise under different pipeline conditions of operation pressure and leak orifice diameter. Numerical results show that the leak noise of buried pipelines has less energy and are more concentrated at lower frequencies, compared with that of above-ground pipelines. It is demonstrated that leak noise is predominantly governed by the dipole and the quadrupole sources, generated from the gas–solid interaction and turbulent disturbance, respectively. It is shown that the dipole source is attenuated and the quadrupole source is amplified with the leak orifice diameter for buried pipelines whereas both are amplified for above-ground pipelines. Moreover, it is suggested that the feature parameters of fluid dynamics, such as the average dynamic pressure and turbulent kinetic energy, can be used to characterize the leak noise mechanism for natural gas pipelines.
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Kadau, Kai, John L. Barber, Timothy C. Germann, Brad L. Holian, and Berni J. Alder. "Atomistic methods in fluid simulation." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 368, no. 1916 (April 13, 2010): 1547–60. http://dx.doi.org/10.1098/rsta.2009.0218.
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Atomistic methods, such as molecular dynamics and direct simulation Monte Carlo, constitute a powerful and growing set of techniques for fluid-dynamics simulation. The more fundamental nature of such methods, which exhibit nonlinear transport effects and small-scale fluctuations, extends their modelling accuracy to a significantly wider range of scales and regimes than the more traditional Navier–Stokes-based continuum fluid-simulation techniques. In this paper, we describe the current state of the art in atomistic fluid simulation, from both a theoretical and a computational standpoint, and outline the advantages and limitations of such methods. In addition, we present an overview of some recent atomistic-simulation results on fluid instabilities and on the physical scaling of atomistic techniques. Finally, we suggest possible avenues of future research in the field.
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Aarão, Jorge. "Fundamental Solutions for Some Partial Differential Operators from Fluid Dynamics and Statistical Physics." SIAM Review 49, no. 2 (January 2007): 303–14. http://dx.doi.org/10.1137/050624030.
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SETA, TAKESHI, KOJI KONO, and SHIYI CHEN. "LATTICE BOLTZMANN METHOD FOR TWO-PHASE FLOWS." International Journal of Modern Physics B 17, no. 01n02 (January 20, 2003): 169–72. http://dx.doi.org/10.1142/s021797920301728x.
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A lattice Boltzmann method (LBM) for two-phase nonideal fluid flows is proposed based on a particle velocity-dependent forcing scheme. The resulting macroscopic dynamics via the Chapman-Enskog expansion recover the full set of thermohydrodynamic equations for nonideal fluids. Numerical verification of fundamental properties of thermal fluids, including thermal conductivity and surface tension, agrees well with theoretical predictions. Direct numerical simulations of two-phase phenomena, including phase-transition, bubble deformation and droplet falling and bubble rising under gravity are carried out, demonstrating the applicability of the model.
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Velescu, Cornel, and Nicolae Calin Popa. "Laminar Motion of the Incompressible Fluids in Self-Acting Thrust Bearings with Spiral Grooves." Scientific World Journal 2014 (2014): 1–10. http://dx.doi.org/10.1155/2014/478401.
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We analyze the laminar motion of incompressible fluids in self-acting thrust bearings with spiral grooves with inner or external pumping. The purpose of the study is to find some mathematical relations useful to approach the theoretical functionality of these bearings having magnetic controllable fluids as incompressible fluids, in the presence of a controllable magnetic field. This theoretical study approaches the permanent motion regime. To validate the theoretical results, we compare them to some experimental results presented in previous papers. The laminar motion of incompressible fluids in bearings is described by the fundamental equations of fluid dynamics. We developed and particularized these equations by taking into consideration the geometrical and functional characteristics of these hydrodynamic bearings. Through the integration of the differential equation, we determined the pressure and speed distributions in bearings with length in the “pumping” direction. These pressure and speed distributions offer important information, both quantitative (concerning the bearing performances) and qualitative (evidence of the viscous-inertial effects, the fluid compressibility, etc.), for the laminar and permanent motion regime.
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Hashemi, M., and X. B. Chen. "THEORETICAL INVESTIGATION INTO THE PERFORMANCE OF THE ROTARY-SCREW FLUID DISPENSING PROCESS." Transactions of the Canadian Society for Mechanical Engineering 32, no. 3-4 (September 2008): 325–32. http://dx.doi.org/10.1139/tcsme-2008-0021.
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This paper represents the development of a dynamic model for the rotary-screw dispensing process, by taking into accounts for both fluid compressibility and non-Newtonian flow behavior. In particular, the flow behavior of the fluid being dispensed is characterized by using the power law equation; and then based on the fundamentals of flow in the screw channel and needle, a model is developed to represent the dynamics of the flow rate in the rotary-screw dispensing process. Simulations are carried out to investigate the process performance, with an emphasis on identifying the influence of the key process parameters.
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Cremaschini, Claudio, Jiří Kovář, Zdeněk Stuchlík, and Massimo Tessarotto. "Polytropic representation of the kinetic pressure tensor of non-ideal magnetized fluids in equilibrium toroidal structures." Physics of Fluids 35, no. 1 (January 2023): 017123. http://dx.doi.org/10.1063/5.0134320.
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Non-ideal fluids are generally subject to the occurrence of non-isotropic pressure tensors, whose determination is fundamental in order to characterize their dynamical and thermodynamical properties. This requires the implementation of theoretical frameworks provided by appropriate microscopic and statistical kinetic approaches in terms of which continuum fluid fields are obtained. In this paper, the case of non-relativistic magnetized fluids forming equilibrium toroidal structures in external gravitational fields is considered. Analytical solutions for the kinetic distribution function are explicitly constructed, to be represented by a Chapman–Enskog expansion around a Maxwellian equilibrium. In this way, different physical mechanisms responsible for the generation of non-isotropic pressures are identified and proved to be associated with the kinetic constraints imposed on single and collective particle dynamics by phase-space symmetries and magnetic field. As a major outcome, the validity of a polytropic representation for the kinetic pressure tensors corresponding to each source of anisotropy is established, whereby directional pressures exhibit a specific power-law functional dependence on fluid density. The astrophysical relevance of the solution for the understanding of fluid plasma properties in accretion-disk environments is discussed.
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Rehman, Umer, Muhammad Bilal, and Mubbashir Sheraz. "Theoretical Analysis of Magnetohydrodynamical Waves for Plasma based Coating Process of Isothermal Viscous-Plastic Fluid." WSEAS TRANSACTIONS ON HEAT AND MASS TRANSFER 17 (February 21, 2022): 54–65. http://dx.doi.org/10.37394/232012.2022.17.7.
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A mathematical formulation on coating of a thin film for a compressible isothermal magnetohydrodynamic (MHD) viscous-plastic fluid flowing across a narrow gap between two rotating rolls is described in this article. The lubrication approximation theory is used to create and simplify the equations of motion required for the fluid injected for coating. The relation explaining MHD wave dynamics and instability is obtained by analytical calculations. According to the current investigation, the growth rate in the unstable MHD waves are numerically evaluated as the function of the concerned parameters, It's worth noting that the Lundquist and Prandtl's numbers are growth rate control parameters in unstable MHD modes. The results show that the viscous-plastic parameter and ratio of diffusion rate have a significant impact on the fundamental MHD dynamics. It is also concluded that the MHD effects have had a significant impact on the coating of Casson material.
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Orlov, Sergei S., Snezhana I. Abarzhi, Se Baek Oh, George Barbastathis, and Katepalli R. Sreenivasan. "High-performance holographic technologies for fluid-dynamics experiments." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 368, no. 1916 (April 13, 2010): 1705–37. http://dx.doi.org/10.1098/rsta.2009.0285.
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Modern technologies offer new opportunities for experimentalists in a variety of research areas of fluid dynamics. Improvements are now possible in the state-of-the-art in precision, dynamic range, reproducibility, motion-control accuracy, data-acquisition rate and information capacity. These improvements are required for understanding complex turbulent flows under realistic conditions, and for allowing unambiguous comparisons to be made with new theoretical approaches and large-scale numerical simulations. One of the new technologies is high-performance digital holography. State-of-the-art motion control, electronics and optical imaging allow for the realization of turbulent flows with very high Reynolds number (more than 10 7 ) on a relatively small laboratory scale, and quantification of their properties with high space–time resolutions and bandwidth. In-line digital holographic technology can provide complete three-dimensional mapping of the flow velocity and density fields at high data rates (over 1000 frames per second) over a relatively large spatial area with high spatial (1–10 μm) and temporal (better than a few nanoseconds) resolution, and can give accurate quantitative description of the fluid flows, including those of multi-phase and unsteady conditions. This technology can be applied in a variety of problems to study fundamental properties of flow–particle interactions, rotating flows, non-canonical boundary layers and Rayleigh–Taylor mixing. Some of these examples are discussed briefly.
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Panchariya, Dev Arastu. "The Fluid Discontinuity Theory." European Journal of Applied Physics 4, no. 3 (June 23, 2022): 66–70. http://dx.doi.org/10.24018/ejphysics.2022.4.3.171.
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Theoretical Physics is perhaps the only class of philosophies that has really enhanced and evolved itself to a lot of extent seeking clues towards the ultimate nature of reality. Stretching from the Theory of General Relativity and Quantum Physics, it’s been diversified with quite peculiar answers to multiple deep facets. However, still there is a significant fragment of Physics which is yet to be developed in that theoretical frame of system where the mathematical analysis turns in a more definitive role and thus, holds the intersection of certain other branches of the field and this area is Fluid Dynamics or Hydrodynamics. Although there is no question over some forsooth brilliant contributions in the regime but still, this discovery will deal with a nonpareil strand in order to fill some gaps which will determine new findings to lead the coming times much exclusively through the realm. The proposed discovery in this paper, being chronicle on the most primordial basis; is about quilting the distinction of waves as a whole in the fluid being in layered form and its impact via penetration of mass into those in form of respective disturbance in its fabrication of fundamental geometry. In other words, the idea proposed is about investigating and evolving the understanding of fluid discontinuity in distinctive extents forming geometrical patterns which is the idea that has also been undertaken to insights by some of the greatest Philosophers, Physicists, and Mathematicians of the last two centuries from Helmholtz to Lord Kelvin to Einstein but unfortunately it could not be attained in a full turn of deeper understanding in terms of Theoretical and Mathematical evolution as attempted by all these greatest forefathers of Sciences. In order to extract the idea with the overlap of modern mathematical integration, the entire formation of the defined system is taken into the account by establishing geometrical interpretations which will also develop more protean insights into the field and fill many further gaps in the classical regime of the Dynamics and gives a modern turn to it. The fabrication of the idea is systematically unfolded in terms of both Theoretical & Mathematical engagements concerning to the respective structures taking place in form of different theories partaking in an evolutionary methodology.
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Hernández, Raúl Josué Hernández, Thomas M. Fischer, and Pietro Tierno. "Dynamics and interactions of magnetically driven colloidal microrotors." Applied Physics Letters 120, no. 8 (February 21, 2022): 081601. http://dx.doi.org/10.1063/5.0076574.
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We study the pair interactions between magnetically driven colloidal microrotors with an anisotropic shape. An external precessing magnetic field induces a torque to these particles spinning them at a fixed angular frequency. When pair of rotors approach each other, the anisotropic particles interact via dipolar forces and hydrodynamic interactions (HIs) excited by their rotational motion. For applied field spinning close to the magic angle, [Formula: see text], dipolar interactions vanish and the dynamic assembly of the pair is driven only by HIs. Further, we provide a theoretical description based on the balance between dipolar forces and HIs that allow understanding the role of anisotropy on the collective dynamics. Investigating microscopic colloidal rotors and understanding their collective dynamics are important tasks for both fundamental reasons, but also to engineer similar fluid stirrers that can be readily used for precise microscale operations or as microrheological probes.
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Agop, Maricel, Tudor-Cristian Petrescu, Dumitru Filipeanu, Claudia Elena Grigoraș-Ichim, Ana Iolanda Voda, Andrei Zala, Lucian Dobreci, Constantin Baciu, and Decebal Vasincu. "Toward Complex Systems Dynamics through Flow Regimes of Multifractal Fluids." Symmetry 13, no. 5 (April 27, 2021): 754. http://dx.doi.org/10.3390/sym13050754.
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In the framework of the Multifractal Theory of Motion, which is expressed by means of the multifractal hydrodynamic model, complex system dynamics are explained through uniform and non-uniform flow regimes of multifractal fluids. Thus, in the case of the uniform flow regime of the multifractal fluid, the dynamics’ description is “supported” only by the differentiable component of the velocity field, the non-differentiable component being null. In the case of the non-uniform flow regime of the multifractal fluid, the dynamics’ description is “supported” by both components of the velocity field, their ratio specifying correlations through homographic transformations. Since these transformations imply metric geometries explained, for example, by means of Killing–Cartan metrics of the SL(2R)-type algebra, of the set of 2 × 2 matrices with real elements, and because these metrics can be “produced” as Cayleyan metrics of absolute geometries, the dynamics’ description is reducible, based on a minimal principle, to harmonic mappings from the usual space to the hyperbolic space. Such a conjecture highlights not only various scenarios of dynamics’ evolution but also the types of interactions “responsible” for these scenarios. Since these types of interactions become fundamental in the self-structuring processes of polymeric-type materials, finally, the theoretical model is calibrated based on the author’s empirical data, which refer to controlled drug release applications.
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Tu, Qingsong, Wice Ibrahimi, Steven Ren, James Wu, and Shaofan Li. "A Molecular Dynamics Study on Rotational Nanofluid and Its Application to Desalination." Membranes 10, no. 6 (June 6, 2020): 117. http://dx.doi.org/10.3390/membranes10060117.
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In this work, we systematically study a rotational nanofluidic device for reverse osmosis (RO) desalination by using large scale molecular dynamics modeling and simulation. Moreover, we have compared Molecular Dynamics simulation with fluid mechanics modeling. We have found that the pressure generated by the centrifugal motion of nanofluids can counterbalance the osmosis pressure developed from the concentration gradient, and hence provide a driving force to filtrate fresh water from salt water. Molecular Dynamics modeling of two different types of designs are performed and compared. Results indicate that this novel nanofluidic device is not only able to alleviate the fouling problem significantly, but it is also capable of maintaining high membrane permeability and energy efficiency. The angular velocity of the nanofluids within the device is investigated, and the critical angular velocity needed for the fluids to overcome the osmotic pressure is derived. Meanwhile, a maximal angular velocity value is also identified to avoid Taylor-Couette instability. The MD simulation results agree well with continuum modeling results obtained from fluid hydrodynamics theory, which provides a theoretical foundation for scaling up the proposed rotational osmosis device. Successful fabrication of such rotational RO membrane centrifuge may potentially revolutionize the membrane desalination technology by providing a fundamental solution to the water resource problem.
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Tuck, Adrian F. "Theoretical Chemistry and the Calculation of the Atmospheric State." Atmosphere 12, no. 6 (June 6, 2021): 727. http://dx.doi.org/10.3390/atmos12060727.
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Theoretical chemists have been actively engaged for some time in processes such as ozone photodissociation, overtone photodissociation in nitric acid, pernitric acid, sulphuric acid, clusters and in small organic acids. The last of these have shown very different behaviours in the gas phase, liquid phase and importantly at the air–water interface in aqueous aerosols. The founder of molecular dynamics, B J Alder, pointed out long ago that hydrodynamic behaviour emerged when the symmetry of a random, thermalised population of hard spheres—billiard balls—was broken by a flux of energetic molecules. Despite this, efforts over two centuries to solve turbulence by finding top-down solutions to the Navier–Stokes equation have failed. It is time for theoretical chemistry to try a bottom-up solution. Gibbs free energy that drives the circulation arises from the entropy difference between the incoming low-entropy beam of visible and ultraviolet photons and the outgoing higher-entropy flux of infrared photons over the whole 4π solid angle. The role of the most energetic molecules with the highest velocities will affect the rovibrational line shapes of water, carbon dioxide and ozone in the far wings, where there is the largest effect on radiative transfer and hence on calculations of atmospheric temperature. The atmospheric state is determined by the interaction of radiation, chemistry and fluid dynamics on the microscopic scale, with propagation through the mesoscale to the macroscale. It will take theoretical chemistry to simulate that accurately. A challenging programme of research for theoretical chemistry is proposed, involving ab initio simulation by molecular dynamics of an air volume, starting in the upper stratosphere. The aim is to obtain scaling exponents for turbulence, providing a physical method for upscaling in numerical models. Turbulence affects chemistry, radiation and fluid dynamics at a fundamental, molecular level and is thus of basic concern to theoretical chemistry as it applies to the atmosphere, which consists of molecules in motion.
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Abarzhi, Snezhana I., Daniil V. Ilyin, William A. Goddard, and Sergei I. Anisimov. "Interface dynamics: Mechanisms of stabilization and destabilization and structure of flow fields." Proceedings of the National Academy of Sciences 116, no. 37 (August 6, 2018): 18218–26. http://dx.doi.org/10.1073/pnas.1714500115.
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Interfacial mixing and transport are nonequilibrium processes coupling kinetic to macroscopic scales. They occur in fluids, plasmas, and materials over celestial events to atoms. Grasping their fundamentals can advance a broad range of disciplines in science, mathematics, and engineering. This paper focuses on the long-standing classic problem of stability of a phase boundary—a fluid interface that has a mass flow across it. We briefly review the recent advances in theoretical and experimental studies, develop the general theoretical framework directly linking the microscopic interfacial transport to the macroscopic flow fields, discover mechanisms of interface stabilization and destabilization that have not been discussed before for both inertial and accelerated dynamics, and chart perspectives for future research.
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Kim, Jiyeon, Hongsuck Kim, Byunggoon Kim, and Jaecheul Yu. "Computational fluid dynamics analysis in microbial fuel cells with different anode configurations." Water Science and Technology 69, no. 7 (January 24, 2014): 1447–52. http://dx.doi.org/10.2166/wst.2014.041.
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A key criterion in microbial fuel cell (MFC) design is that the bio-electrochemical reaction between bacteria and the bulk solution should occur evenly on the electrode surface in order to improve electricity generation. However, experimental optimization of MFC design over a wide range of conditions is limited. Computational fluid dynamics (CFD) technology makes it possible to evaluate physicochemical phenomena such as fluid flows, mass transfer and chemical reaction, which can assist in system optimization. Twelve MFCs (M1–M12) with different internal structures were subjected to CFD analysis. The dead (DS) and working spaces (WS) of the anode compartment were calculated. The flow patterns of the anodic fluid varied according to the internal structures. The WS where the bio-electrochemical reaction can actually occur varied over the range of 0.14–0.57 m2. Based on the above results, the power densities were estimated under the assumption that a monolayer biofilm was formed on the electrode. M11, with 18 rectangular-type internal structures, showed the largest WS of 0.57 m2 and a theoretical maximum power density of 0.54 W/m2. Although the optimization of the MFC configuration with only CFD analysis remains limited, the present study results are expected to provide fundamental data for MFC optimization.
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Yeoh, Guan Heng, and Xiaobin Zhang. "Computational fluid dynamics and population balance modelling of nucleate boiling of cryogenic liquids: Theoretical developments." Journal of Computational Multiphase Flows 8, no. 4 (November 22, 2016): 178–200. http://dx.doi.org/10.1177/1757482x16674217.
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The main focus in the analysis of pool or flow boiling in saturated or subcooled conditions is the basic understanding of the phase change process through the heat transfer and wall heat flux partitioning at the heated wall and the two-phase bubble behaviours in the bulk liquid as they migrate away from the heated wall. This paper reviews the work in this rapid developing area with special reference to modelling nucleate boiling of cryogenic liquids in the context of computational fluid dynamics and associated theoretical developments. The partitioning of the wall heat flux at the heated wall into three components – single-phase convection, transient conduction and evaporation – remains the most popular mechanistic approach in predicting the heat transfer process during boiling. Nevertheless, the respective wall heat flux components generally require the determination of the active nucleation site density, bubble departure diameter and nucleation frequency, which are crucial to the proper prediction of the heat transfer process. Numerous empirical correlations presented in this paper have been developed to ascertain these three important parameters with some degree of success. Albeit the simplicity of empirical correlations, they remain applicable to only a narrow range of flow conditions. In order to extend the wall heat flux partitioning approach to a wider range of flow conditions, the fractal model proposed for the active nucleation site density, force balance model for bubble departing from the cavity and bubble lifting off from the heated wall and evaluation of nucleation frequency based on fundamental theory depict the many enhancements that can improve the mechanistic model predictions. The macroscopic consideration of the two-phase boiling in the bulk liquid via the two-fluid model represents the most effective continuum approach in predicting the volume fraction and velocity distributions of each phase. Nevertheless, the interfacial mass, momentum and energy exchange terms that appear in the transport equations generally require the determination of the Sauter mean diameter or interfacial area concentration, which strongly governs the fluid flow and heat transfer in the bulk liquid. In order to accommodate the dynamically changing bubble sizes that are prevalent in the bulk liquid, the mechanistic approach based on the population balance model allows the appropriate prediction of local distributions of Sauter mean diameter or interfacial area concentration, which in turn can improve the predictions of the interfacial mass, momentum and energy exchanges that occur across the interface between the phases. Need for further developments are discussed.
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Glover, Paul W. J., Emilie Walker, and Matthew D. Jackson. "Streaming-potential coefficient of reservoir rock: A theoretical model." GEOPHYSICS 77, no. 2 (March 2012): D17—D43. http://dx.doi.org/10.1190/geo2011-0364.1.
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The streaming potential is that electrical potential which develops when an ionic fluid flows through the pores of a rock. It is an old concept that is recently being applied in many fields from monitoring water fronts in oil reservoirs to understanding the mechanisms behind synthetic earthquakes. We have carried out fundamental theoretical modeling of the streaming-potential coefficient as a function of pore fluid salinity, pH, and temperature by modifying the HS equation for use with porous rocks and using input parameters from established fundamental theory (the Debye screening length, the Stern-plane potential, the zeta potential, and the surface conductance). The model also requires the density, electrical conductivity, relative electric permittivity and dynamic viscosity of the bulk fluid, for which empirical models are used so that the temperature of the model may be varied. These parameters are then combined with parameters that describe the rock microstructure. The resulting theoretical values have been compared with a compilation of data for siliceous materials comprising 290 streaming-potential coefficient measurements and 269 zeta-potential measurements obtained experimentally for 17 matrix-fluid combinations (e.g., sandstone saturated with KCl), using data from 29 publications. The theoretical model was found to ably describe the main features of the data, whether taken together or on a sample by sample basis. The low-salinity regime was found to be controlled by surface conduction and rock microstructure, and was sensitive to changes in porosity, cementation exponent, formation factor, grain size, pore size and pore throat size as well as specific surface conductivity. The high-salinity regime was found to be subject to a zeta-potential offset that allows the streaming-potential coefficient to remain significant even as the saturation limit is approached.
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Huang, Yuanlong, Matthew M. Coggon, Ran Zhao, Hanna Lignell, Michael U. Bauer, Richard C. Flagan, and John H. Seinfeld. "The Caltech Photooxidation Flow Tube reactor: design, fluid dynamics and characterization." Atmospheric Measurement Techniques 10, no. 3 (March 9, 2017): 839–67. http://dx.doi.org/10.5194/amt-10-839-2017.
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Abstract. Flow tube reactors are widely employed to study gas-phase atmospheric chemistry and secondary organic aerosol (SOA) formation. The development of a new laminar-flow tube reactor, the Caltech Photooxidation Flow Tube (CPOT), intended for the study of gas-phase atmospheric chemistry and SOA formation, is reported here. The present work addresses the reactor design based on fluid dynamical characterization and the fundamental behavior of vapor molecules and particles in the reactor. The design of the inlet to the reactor, based on computational fluid dynamics (CFD) simulations, comprises a static mixer and a conical diffuser to facilitate development of a characteristic laminar flow profile. To assess the extent to which the actual performance adheres to the theoretical CFD model, residence time distribution (RTD) experiments are reported with vapor molecules (O3) and submicrometer ammonium sulfate particles. As confirmed by the CFD prediction, the presence of a slight deviation from strictly isothermal conditions leads to secondary flows in the reactor that produce deviations from the ideal parabolic laminar flow. The characterization experiments, in conjunction with theory, provide a basis for interpretation of atmospheric chemistry and SOA studies to follow. A 1-D photochemical model within an axially dispersed plug flow reactor (AD-PFR) framework is formulated to evaluate the oxidation level in the reactor. The simulation indicates that the OH concentration is uniform along the reactor, and an OH exposure (OHexp) ranging from ∼ 109 to ∼ 1012 molecules cm−3 s can be achieved from photolysis of H2O2. A method to calculate OHexp with a consideration for the axial dispersion in the present photochemical system is developed.
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Dussan V., E. B., and François M. Auzerais. "Buoyancy-induced flow in porous media generated near a drilled oil well. Part 1. The accumulation of filtrate at a horizontal impermeable boundary." Journal of Fluid Mechanics 254 (September 1993): 283–311. http://dx.doi.org/10.1017/s0022112093002137.
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A substantial amount of drilling fluid can invade a permeable bed during the drilling of an oil well. The presence of this fluid, often referred to as filtrate, can greatly influence the performance of instruments lowered into the wellbore for the purpose of locating these permeable beds. The invaded filtrate can also substantially alter the physical properties of the porous rock. For these reasons, it is of great interest to known where the filtrate goes upon entering the bed. The objective of this study is to quantify the influence of the difference in density between the filtrate and the naturally occurring formation fluid on the shape of the filtrate front as the filtrate invades the formation. This type of phenomenon is often referred to as buoyancy or gravity segregation. In this study, Part 1, we determine the behaviour of the filtrate as it accumulates (and spreads out) at a horizontal impermeable barrier within the formation. This is a combined theoretical and experimental study in which an X-ray CT scanner is extensively used to determine the appropriateness and limitations of the simplifying assumptions used in the theory. In Part 2, the flow of the invading filtrate within the entire bed will be presented. The problem addressed in Part 1 may be viewed from the broader, more fundamental, perspective, as a well-defined model fluid mechanics problem for flow in porous media. One fundamental issue infrequently addressed concerns the consequence on the dynamics of the fluids of heterogeneities, always present to some degree, in consolidated porous solids. The X-ray CT scanner enables the assessment of the appropriateness of modelling such porous solids as spatially homogeneous, a very popular assumption. This study also addresses the limitation of the small-slope approximation when a fluid–fluid interface occurs in a porous solid, an approximation which has enjoyed great success in free-surface fluid mechanics problems when no porous media is present.
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Yano, Jun-Ichi, Michał Z. Ziemiański, Mike Cullen, Piet Termonia, Jeanette Onvlee, Lisa Bengtsson, Alberto Carrassi, et al. "Scientific Challenges of Convective-Scale Numerical Weather Prediction." Bulletin of the American Meteorological Society 99, no. 4 (April 2018): 699–710. http://dx.doi.org/10.1175/bams-d-17-0125.1.
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AbstractAfter extensive efforts over the course of a decade, convective-scale weather forecasts with horizontal grid spacings of 1–5 km are now operational at national weather services around the world, accompanied by ensemble prediction systems (EPSs). However, though already operational, the capacity of forecasts for this scale is still to be fully exploited by overcoming the fundamental difficulty in prediction: the fully three-dimensional and turbulent nature of the atmosphere. The prediction of this scale is totally different from that of the synoptic scale (103 km), with slowly evolving semigeostrophic dynamics and relatively long predictability on the order of a few days.Even theoretically, very little is understood about the convective scale compared to our extensive knowledge of the synoptic-scale weather regime as a partial differential equation system, as well as in terms of the fluid mechanics, predictability, uncertainties, and stochasticity. Furthermore, there is a requirement for a drastic modification of data assimilation methodologies, physics (e.g., microphysics), and parameterizations, as well as the numerics for use at the convective scale. We need to focus on more fundamental theoretical issues—the Liouville principle and Bayesian probability for probabilistic forecasts—and more fundamental turbulence research to provide robust numerics for the full variety of turbulent flows.The present essay reviews those basic theoretical challenges as comprehensibly as possible. The breadth of the problems that we face is a challenge in itself: an attempt to reduce these into a single critical agenda should be avoided.
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Parhi, Dayal R., and Adik R. Yadao. "Analysis of dynamic behavior of multi-cracked cantilever rotor in viscous medium." Proceedings of the Institution of Mechanical Engineers, Part K: Journal of Multi-body Dynamics 230, no. 4 (August 3, 2016): 416–25. http://dx.doi.org/10.1177/1464419315618033.
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The present investigation is an attempt to evaluate the dynamic behaviours of multi-cracked cantilever rotor shaft with an additional mass attached at the tip of the shaft, which is partially submerged in the viscous fluid. In this work, theoretical expressions are developed to find the fundamental natural frequency and amplitude of the multi-cracked rotor shaft with attached mass, using influence coefficient method. Navier–Stoke’s equations are used for the analysis of external fluid forces acting on the rotor. Viscosities of the fluid and relative crack locations are taken as main variable parameters. For the analysis, suitable theoretical expressions are considered, and the Matlab programming is made to obtain the results. Experimental verifications are also performed to prove the validity of the theory developed.
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Julien, Jean-Daniel, and Karen Alim. "Oscillatory fluid flow drives scaling of contraction wave with system size." Proceedings of the National Academy of Sciences 115, no. 42 (October 3, 2018): 10612–17. http://dx.doi.org/10.1073/pnas.1805981115.
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Flows over remarkably long distances are crucial to the functioning of many organisms, across all kingdoms of life. Coordinated flows are fundamental to power deformations, required for migration or development, or to spread resources and signals. A ubiquitous mechanism to generate flows, particularly prominent in animals and amoebas, is actomyosin cortex-driven mechanical deformations that pump the fluid enclosed by the cortex. However, it is unclear how cortex dynamics can self-organize to give rise to coordinated flows across the largely varying scales of biological systems. Here, we develop a mechanochemical model of actomyosin cortex mechanics coupled to a contraction-triggering, soluble chemical. The chemical itself is advected with the flows generated by the cortex-driven deformations of the tubular-shaped cell. The theoretical model predicts a dynamic instability giving rise to stable patterns of cortex contraction waves and oscillatory flows. Surprisingly, simulated patterns extend beyond the intrinsic length scale of the dynamic instability—scaling with system size instead. Patterns appear randomly but can be robustly generated in a growing system or by flow-generating boundary conditions. We identify oscillatory flows as the key for the scaling of contraction waves with system size. Our work shows the importance of active flows in biophysical models of patterning, not only as a regulating input or an emergent output, but also as a full part of a self-organized machinery. Contractions and fluid flows are observed in all kinds of organisms, so this concept is likely to be relevant for a broad class of systems.
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Guzmán, Eduardo, Armando Maestro, Carlo Carbone, Francisco Ortega, and Ramón G. Rubio. "Dilational Rheology of Fluid/Fluid Interfaces: Foundations and Tools." Fluids 7, no. 10 (October 20, 2022): 335. http://dx.doi.org/10.3390/fluids7100335.
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Fluid/fluid interfaces are ubiquitous in science and technology, and hence, the understanding of their properties presents a paramount importance for developing a broad range of soft interface dominated materials, but also for the elucidation of different problems with biological and medical relevance. However, the highly dynamic character of fluid/fluid interfaces makes shedding light on fundamental features guiding the performance of the interfaces very complicated. Therefore, the study of fluid/fluid interfaces cannot be limited to an equilibrium perspective, as there exists an undeniable necessity to face the study of the deformation and flow of these systems under the application of mechanical stresses, i.e., their interfacial rheology. This is a multidisciplinary challenge that has been evolving fast in recent years, and there is currently available a broad range of experimental and theoretical methodologies providing accurate information of the response of fluid/fluid interfaces under the application of mechanical stresses, mainly dilational and shear. This review focused on providing an updated perspective on the study of the response of fluid/fluid interfaces to dilational stresses; to open up new avenues that enable the exploitation of interfacial dilational rheology and to shed light on different problems in the interest of science and technology.
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Kao, A., T. Gan, C. Tonry, I. Krastins, and K. Pericleous. "Thermoelectric magnetohydrodynamic control of melt pool dynamics and microstructure evolution in additive manufacturing." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 378, no. 2171 (April 13, 2020): 20190249. http://dx.doi.org/10.1098/rsta.2019.0249.
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Large thermal gradients in the melt pool from rapid heating followed by rapid cooling in metal additive manufacturing generate large thermoelectric currents. Applying an external magnetic field to the process introduces fluid flow through thermoelectric magnetohydrodynamics. Convective transport of heat and mass can then modify the melt pool dynamics and alter microstructural evolution. As a novel technique, this shows great promise in controlling the process to improve quality and mitigate defect formation. However, there is very little knowledge within the scientific community on the fundamental principles of this physical phenomenon to support practical implementation. To address this multi-physics problem that couples the key phenomena of melting/solidification, electromagnetism, hydrodynamics, heat and mass transport, the lattice Boltzmann method for fluid dynamics was combined with a purpose-built code addressing solidification modelling and electromagnetics. The theoretical study presented here investigates the hydrodynamic mechanisms introduced by the magnetic field. The resulting steady-state solutions of modified melt pool shapes and thermal fields are then used to predict the microstructure evolution using a cellular automata-based grain growth model. The results clearly demonstrate that the hydrodynamic mechanisms and, therefore, microstructure characteristics are strongly dependent on magnetic field orientation. This article is part of the theme issue ‘Patterns in soft and biological matters'.
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BASTRUKOV, S. I., H. K. CHANG, E. H. WU, and I. V. MOLODTSOVA. "SELF-GRAVITATING ASTROPHYSICAL MASS WITH SINGULAR CENTRAL DENSITY VIBRATING IN FUNDAMENTAL MODE." Modern Physics Letters A 24, no. 40 (December 28, 2009): 3257–74. http://dx.doi.org/10.1142/s0217732309032137.
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The fluid-dynamical model of a self-gravitating mass of viscous liquid with singular density at the center vibrating in fundamental mode is considered in juxtaposition with that for Kelvin fundamental mode in a homogeneous heavy mass of incompressible inviscid liquid. Particular attention is given to the difference between spectral formulas for the frequency and lifetime of f-mode in the singular and homogeneous models. The newly obtained results are discussed in the context of theoretical asteroseismology of pre-white dwarf stage of red giants and stellar cocoons — spherical gas-dust clouds with dense star-forming core at the center.
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Ly, Nguyen, Zvi Rusak, and Shixiao Wang. "Swirling flow states of compressible single-phase supercritical fluids in a rotating finite-length straight circular pipe." Journal of Fluid Mechanics 849 (June 21, 2018): 576–614. http://dx.doi.org/10.1017/jfm.2018.394.
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Steady states of inviscid, compressible and axisymmetric swirling flows of a single-phase, inert, thermodynamically supercritical fluid in a rotating, finite-length, straight, long circular pipe are studied. The fluid thermodynamic behaviour is modelled by the van der Waals equation of state. A nonlinear partial differential equation for the solution of the flow streamfunction is derived from the fluid equations of motion in terms of the inlet flow specific total enthalpy, specific entropy and circulation functions. This equation reflects the complicated, nonlinear thermo-physical interactions in the flows, specifically when the inlet state temperature and density profiles vary around the critical thermodynamic point, flow compressibility is significant and the inlet swirl ratio is high. Several types of solutions of the resulting nonlinear ordinary differential equation for the axially independent case describe the flow outlet state when the pipe is sufficiently long. The approach is applied to an inlet flow described by a solid-body rotation with uniform profiles of the axial velocity and temperature. The solutions are used to form the bifurcation diagrams of steady compressible flows of real fluids as the inlet swirl level and the centreline inlet density are increased at a fixed inlet Mach number and temperature. Focus is on heavy-molecule fluids with low values of $R/C_{v}$. Computed results provide theoretical predictions of the critical swirl levels for the exchange of stability of the columnar state and for the appearance of non-columnar states and of vortex breakdown states as a function of inlet centreline density. The difference in the dynamical behaviour between that of a calorically perfect gas and of a real gas is explored. The analysis sheds new fundamental light on the complex dynamics of high-Reynolds-number, compressible, subsonic swirling flows of real gases.
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Chashechkin, Yuli D. "Foundations of Engineering Mathematics Applied for Fluid Flows." Axioms 10, no. 4 (October 29, 2021): 286. http://dx.doi.org/10.3390/axioms10040286.
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Based on a brief historical excursion, a list of principles is formulated which substantiates the choice of axioms and methods for studying nature. The axiomatics of fluid flows are based on conservation laws in the frames of engineering mathematics and technical physics. In the theory of fluid flows within the continuous medium model, a key role for the total energy is distinguished. To describe a fluid flow, a system of fundamental equations is chosen, supplemented by the equations of the state for the Gibbs potential and the medium density. The system is supplemented by the physically based initial and boundary conditions and analyzed, taking into account the compatibility condition. The complete solutions constructed describe both the structure and dynamics of non-stationary flows. The classification of structural components, including waves, ligaments, and vortices, is given on the basis of the complete solutions of the linearized system. The results of compatible theoretical and experimental studies are compared for the cases of potential and actual homogeneous and stratified fluid flow past an arbitrarily oriented plate. The importance of studying the transfer and transformation processes of energy components is illustrated by the description of the fine structures of flows formed by a free-falling drop coalescing with a target fluid at rest.
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Vidal, Valérie, and Aurélien Gay. "Future challenges on focused fluid migration in sedimentary basins: insight from field data, laboratory experiments and numerical simulations." Papers in Physics 14 (July 22, 2022): 140011. http://dx.doi.org/10.4279/pip.140011.
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In a present context of sustainable energy and hazard mitigation, understanding fluid migration in sedimentary basins – large subsea provinces of fine saturated sands and clays – is a crucial challenge. Such migration leads to gas or liquid expulsion at the seafloor, whichmay be the signature of deep hydrocarbon reservoirs, or precursors to violent subsea fluid releases. If the former may orient future exploitation, the latter represent strong hazards for anthropic activities such as offshore production, CO$_2$ storage, transoceanic telecom fibers or deep-sea mining. However, at present, the dynamics of fluid migration in sedimentary layers, in particular the upper 500 m, still remains unknown in spite of its strong influence on fluid distribution at the seafloor. Understanding the mechanisms controlling fluid migration and release requires the combination of accurate field data, laboratory experiments and numerical simulations. Each technique shall lead to the understanding of the fluid structures, the mechanisms at stake, and deep insights into fundamental processes ranging from the grain scale to the kilometers-long natural pipes in the sedimentary layers.Here we review the present available techniques, advances and challenges still open for the geosciences, physics, and computer science communities.
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Chen, X. L., C. A. Wheeler, T. J. Donohue, and A. W. Roberts. "Investigation of Belt Conveyor Transfer Chute Configurations to Reduce Dust Generation Using CFD Modeling." Applied Mechanics and Materials 26-28 (June 2010): 1126–31. http://dx.doi.org/10.4028/www.scientific.net/amm.26-28.1126.
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“Passive” dust control systems for belt conveyor transfer stations have become increasingly popular in recent years. Effective design relies on a fundamental understanding of the flow of granular material and air throughout the transfer chute. This paper presents an investigation into the flow properties of the air and particles in the enclosure for different transfer chutes based on computational fluid dynamics (CFD) modelling. A multiphase Euler-Euler model was applied to develop a 3D model of the transfer chute. Experiments were undertaken to verify the theoretical models, with overall results indicating good correlation. Furthermore, a number of alternative transfer chute configurations were modelled to investigate the effect of geometry on dust generation.
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Chen, Tao, and Tianshu Liu. "Boundary vorticity dynamics of two-phase viscous flow." Physics of Fluids 34, no. 12 (December 2022): 122107. http://dx.doi.org/10.1063/5.0123110.
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From the Navier–Stokes–Korteweg equations, the exact relations between the fundamental surface physical quantities for the two-phase viscous flow with the diffuse interface are derived, including density gradient, shear stress, vorticity, pressure, enstrophy flux, and surface curvature. These theoretical results provide a solid foundation of the boundary/interfacial vorticity dynamics and a new tool for the analysis of complex interfacial phenomena in two-phase viscous flows. To demonstrate the application of the developed results, simulation of a droplet impacting and spreading on a solid wall is conducted by using a recently developed well-balanced discrete unified gas kinetic scheme, focusing on the spreading process when the separation bubbles form inside the droplet. The distributions of shear stress, pressure, and enstrophy flux at the interface and the wall are analyzed, particularly near the moving contact points and other characteristic points. This example gives an unique perspective to the physics of droplet impingement on a wall.
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Cremaschini, Claudio, John C. Miller, and Massimo Tessarotto. "Theory of quasi-stationary kinetic dynamos in magnetized accretion discs." Proceedings of the International Astronomical Union 6, S274 (September 2010): 228–31. http://dx.doi.org/10.1017/s1743921311006995.
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AbstractMagnetic fields are a distinctive feature of accretion disc plasmas around compact objects (i.e., black holes and neutron stars) and they play a decisive role in their dynamical evolution. A fundamental theoretical question related with this concerns investigation of the so-called gravitational MHD dynamo effect, responsible for the self-generation of magnetic fields in these systems. Experimental observations and theoretical models, based on fluid MHD descriptions of various types support the conjecture that accretion discs should be characterized by coherent and slowly time-varying magnetic fields with both poloidal and toroidal components. However, the precise origin of these magnetic structures and their interaction with the disc plasmas is currently unclear. The aim of this paper is to address this problem in the context of kinetic theory. The starting point is the investigation of a general class of Vlasov-Maxwell kinetic equilibria for axi-symmetric collisionless magnetized plasmas characterized by temperature anisotropy and mainly toroidal flow velocity. Retaining finite Larmor-radius effects in the calculation of the fluid fields, we show how these configurations are capable of sustaining both toroidal and poloidal current densities. As a result, we suggest the possible existence of a kinetic dynamo effect, which can generate a stationary toroidal magnetic field in the disc even without any net radial accretion flow. The results presented may have important implications for equilibrium solutions and stability analysis of accretion disc dynamics.
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Satyadharma, Adhika, and Harinaldi. "The Performance of a Gradient-Based Method to Estimate the Discretization Error in Computational Fluid Dynamics." Computation 9, no. 2 (January 24, 2021): 10. http://dx.doi.org/10.3390/computation9020010.
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Although the grid convergence index is a widely used for the estimation of discretization error in computational fluid dynamics, it still has some problems. These problems are mainly rooted in the usage of the order of a convergence variable within the model which is a fundamental variable that the model is built upon. To improve the model, a new perspective must be taken. By analyzing the behavior of the gradient within simulation data, a gradient-based model was created. The performance of this model is tested on its accuracy, precision, and how it will affect a computational time of a simulation. The testing is conducted on a dataset of 36 simulated variables, simulated using the method of manufactured solutions, with an average of 26.5 meshes/case. The result shows the new gradient based method is more accurate and more precise then the grid convergence index(GCI). This allows for the usage of a coarser mesh for its analysis, thus it has the potential to reduce the overall computational by at least by 25% and also makes the discretization error analysis more available for general usage.
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Gritsenko, Dmitry, Roberto Paoli, and Jie Xu. "The Effect of Acceleration on the Separation Force in Constrained-Surface Stereolithography." Applied Sciences 12, no. 1 (January 3, 2022): 442. http://dx.doi.org/10.3390/app12010442.
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Constrained-surface-based stereolithography has recently attracted much attention from both academic and industrial communities. Despite numerous experimental, numerical and theoretical efforts, the fundamental need to reduce the separation force between the newly cured part and constrained surface has not yet been completely solved. In this paper, we develop a fluid dynamics approach, proposed in our previous work, to theoretically model the separation force in 3D printing of a cylindrical part for flat and patterned windows. We demonstrate the possibility of separation force reduction with an accelerated movement of the printing platform. In particular, we investigate behaviors of transient parameter, its reduction rate, and separation force reduction with respect to elevation speed and time. The proposed approach involves deceleration and acceleration stages and allows to achieve the force reduction for the entire printing process. Finally, we provide implicit analytical solutions for time moments when switching between the stages can be done without noticeable increase of separation force and explicit expression for separation force in case of patterned window.
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Zhao, Long, Wenchao Lu, Musahid Ahmed, Marsel V. Zagidullin, Valeriy N. Azyazov, Alexander N. Morozov, Alexander M. Mebel, and Ralf I. Kaiser. "Gas-phase synthesis of benzene via the propargyl radical self-reaction." Science Advances 7, no. 21 (May 2021): eabf0360. http://dx.doi.org/10.1126/sciadv.abf0360.
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Polycyclic aromatic hydrocarbons (PAHs) have been invoked in fundamental molecular mass growth processes in our galaxy. We provide compelling evidence of the formation of the very first ringed aromatic and building block of PAHs—benzene—via the self-recombination of two resonantly stabilized propargyl (C3H3) radicals in dilute environments using isomer-selective synchrotron-based mass spectrometry coupled to theoretical calculations. Along with benzene, three other structural isomers (1,5-hexadiyne, fulvene, and 2-ethynyl-1,3-butadiene) and o-benzyne are detected, and their branching ratios are quantified experimentally and verified with the aid of computational fluid dynamics and kinetic simulations. These results uncover molecular growth pathways not only in interstellar, circumstellar, and solar systems environments but also in combustion systems, which help us gain a better understanding of the hydrocarbon chemistry of our universe.
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SUN, HAO, ZHANDONG LI, and JIANGUO TAO. "INTEGRATED 3D MULTI-PHYSICAL SIMULATION OF A MICROFLUIDIC SYSTEM USING FINITE ELEMENT ANALYSIS." Journal of Mechanics in Medicine and Biology 15, no. 06 (December 2015): 1540043. http://dx.doi.org/10.1142/s0219519415400436.
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Microfluidics technology has emerged as an attractive approach in physics, chemistry and biomedical science by providing increased analytical accuracy, sensitivity and efficiency in minimized systems. Numerical simulation can improve theoretical understanding, reduce prototyping consumption, and speed up development. In this paper, we setup a 3D model of an integrated microfluidic system and study the multi-physical dynamics of the system via the finite element method (FEM). The fluid–structure interaction (FSI) of fluid and an immobilized single cell within the cell trapping component, and the on-chip thermodynamics have been analyzed. The velocity magnitude and streamline of flow field, the distribution of von Mises stress and Tresca stress on the FSI interface have been studied. In addition, the on-chip heat transfer performance and temperature distribution in the heating zone have been evaluated and analyzed respectively. The presented approach is capable of optimizing microfluidic design, and revealing the complicated mechanism of multi-physical fields. Therefore, it holds the potential for improving microfluidics application in fundamental research and clinical settings.
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Sluysmans, Thierry, and Steven D. Colan. "Theoretical and empirical derivation of cardiovascular allometric relationships in children." Journal of Applied Physiology 99, no. 2 (August 2005): 445–57. http://dx.doi.org/10.1152/japplphysiol.01144.2004.
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Basic fluid dynamic principles were used to derive a theoretical model of optimum cardiovascular allometry, the relationship between somatic and cardiovascular growth. The validity of the predicted models was then tested against the size of 22 cardiovascular structures measured echocardiographically in 496 normal children aged 1 day to 20 yr, including valves, pulmonary arteries, aorta and aortic branches, pulmonary veins, and left ventricular volume. Body surface area (BSA) was found to be a more important determinant of the size of each of the cardiovascular structures than age, height, or weight alone. The observed vascular and valvar dimensions were in agreement with values predicted from the theoretical models. Vascular and valve diameters related linearly to the square root of BSA, whereas valve and vascular areas related to BSA. The relationship between left ventricular volume and body size fit a complex model predicted by the nonlinear decrease of heart rate with growth. Overall, the relationship between cardiac output and body size is the fundamental driving factor in cardiovascular allometry.
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Giustini, Giovanni. "Modelling of Boiling Flows for Nuclear Thermal Hydraulics Applications—A Brief Review." Inventions 5, no. 3 (September 14, 2020): 47. http://dx.doi.org/10.3390/inventions5030047.
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The boiling process is utterly fundamental to the design and safety of water-cooled fission reactors. Both boiling water reactors and pressurised water reactors use boiling under high-pressure subcooled liquid flow conditions to achieve high surface heat fluxes required for their operation. Liquid water is an excellent coolant, which is why water-cooled reactors can have such small sizes and high-power densities, yet also have relatively low component temperatures. Steam is in contrast a very poor coolant. A good understanding of how liquid water coolant turns into steam is correspondingly vital. This need is particularly pressing because heat transfer by water when it is only partially steam (‘nucleate boiling’ regime) is particularly effective, providing a great incentive to operate a plant in this regime. Computational modelling of boiling, using computational fluid dynamics (CFD) simulation at the ‘component scale’ typical of nuclear subchannel analysis and at the scale of the single bubbles, is a core activity of current nuclear thermal hydraulics research. This paper gives an overview of recent literature on computational modelling of boiling. The knowledge and capabilities embodied in the surveyed literature entail theoretical, experimental and modelling work, and enabled the scientific community to improve its current understanding of the fundamental heat transfer phenomena in boiling fluids and to develop more accurate tools for the prediction of two-phase cooling in nuclear systems. Data and insights gathered on the fundamental heat transfer processes associated with the behaviour of single bubbles enabled us to develop and apply more capable modelling tools for engineering simulation and to obtain reliable estimates of the heat transfer rates associated with the growth and departure of steam bubbles from heated surfaces. While results so far are promising, much work is still needed in terms of development of fundamental understanding of the physical processes and application of improved modelling capabilities to industrially relevant flows.
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Yan, Guanxi, Zi Li, Thierry Bore, Sergio Andres Galindo Torres, Alexander Scheuermann, and Ling Li. "Discovery of Dynamic Two-Phase Flow in Porous Media Using Two-Dimensional Multiphase Lattice Boltzmann Simulation." Energies 14, no. 13 (July 5, 2021): 4044. http://dx.doi.org/10.3390/en14134044.
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The dynamic two-phase flow in porous media was theoretically developed based on mass, momentum conservation, and fundamental constitutive relationships for simulating immiscible fluid-fluid retention behavior and seepage in the natural geomaterial. The simulation of transient two-phase flow seepage is, therefore, dependent on both the hydraulic boundaries applied and the immiscible fluid-fluid retention behavior experimentally measured. Many previous studies manifested the velocity-dependent capillary pressure–saturation relationship (Pc-S) and relative permeability (Kr-S). However, those works were experimentally conducted on a continuum scale. To discover the dynamic effects from the microscale, the Computational Fluid Dynamic (CFD) is usually adopted as a novel method. Compared to the conventional CFD methods solving Naiver–Stokes (NS) equations incorporated with the fluid phase separation schemes, the two-phase Lattice Boltzmann Method (LBM) can generate the immiscible fluid-fluid interface using the fluid-fluid/solid interactions at a microscale. Therefore, the Shan–Chen multiphase multicomponent LBM was conducted in this study to simulate the transient two-phase flow in porous media. The simulation outputs demonstrate a preferential flow path in porous media after the non-wetting phase fluid is injected until, finally, the void space is fully occupied by the non-wetting phase fluid. In addition, the inter-relationships for each pair of continuum state variables for a Representative Elementary Volume (REV) of porous media were analyzed for further exploring the dynamic nonequilibrium effects. On one hand, the simulating outcomes reconfirmed previous findings that the dynamic effects are dependent on both the transient seepage velocity and interfacial area dynamics. Nevertheless, in comparison to many previous experimental studies showing the various distances between the parallelly dynamic and static Pc-S relationships by applying various constant flux boundary conditions, this study is the first contribution showing the Pc-S striking into the nonequilibrium condition to yield dynamic nonequilibrium effects and finally returning to the equilibrium static Pc-S by applying various pressure boundary conditions. On the other hand, the flow regimes and relative permeability were discussed with this simulating results in regards to the appropriateness of neglecting inertial effects (both accelerating and convective) in multiphase hydrodynamics for a highly pervious porous media. Based on those research findings, the two-phase LBM can be demonstrated to be a powerful tool for investigating dynamic nonequilibrium effects for transient multiphase flow in porous media from the microscale to the REV scale. Finally, future investigations were proposed with discussions on the limitations of this numerical modeling method.
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Jadhav, Pravin, and Neeraj Agrawal. "Numerical Study on Choked Flow of CO2 Refrigerant in Helical Capillary Tube." International Journal of Air-Conditioning and Refrigeration 26, no. 03 (September 2018): 1850027. http://dx.doi.org/10.1142/s201013251850027x.
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This paper presents a numerical study on an adiabatic helical capillary tube employing homogenous and choked flow conditions of a CO2 transcritical system. The theoretical model is based on the fundamental principle of fluid dynamics and thermodynamics. The result of the present model validates with the previously published data. The influence of operating and geometric parameters on the performance of the capillary tube has been evaluated. Flow characterizations of choked and unchoked flow conditions are determined. As the evaporator pressure drops, from unchoked condition to choked state, the percentage change in mass flow rate is minimal. A simulation graph is developed which has been helpful for the design of the helical capillary tube. The choked flow condition in a capillary tube is avoided by either increasing tube diameter of the fixed length tube or decreasing the length of the fixed tube diameter.
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BILLANT, PAUL, and JEAN-MARC CHOMAZ. "Theoretical analysis of the zigzag instability of a vertical columnar vortex pair in a strongly stratified fluid." Journal of Fluid Mechanics 419 (September 25, 2000): 29–63. http://dx.doi.org/10.1017/s0022112000001166.
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A general theoretical account is proposed for the zigzag instability of a vertical columnar vortex pair recently discovered in a strongly stratified experiment.The linear inviscid stability of the Lamb–Chaplygin vortex pair is analysed by a multiple-scale expansion analysis for small horizontal Froude number (Fh = U/LhN, where U is the magnitude of the horizontal velocity, Lh the horizontal lengthscale and N the Brunt–Väisälä frequency) and small vertical Froude number (Fv = U/LvN, where Lv is the vertical lengthscale) using the scaling of the equations of motion introduced by Riley, Metcalfe & Weissman (1981). In the limit Fv = 0, these equations reduce to two-dimensional Euler equations for the horizontal velocity with undetermined vertical dependence. Thus, at leading order, neutral modes of the flow are associated, among others, to translational and rotational invariances in each horizontal plane. To each broken invariance is related a phase variable that may vary freely along the vertical. Conservation of mass and potential vorticity impose at higher order the evolution equations governing the phase variables that we derive for Fh [Lt ] 1 and Fv [Lt ] 1 in the spirit of phase dynamics techniques established for periodic patterns. In agreement with the experimental observations, this asymptotic analysis shows the existence of an instability consisting of a vertically modulated rotation and a translation of the columnar vortex pair perpendicular to the travelling direction. The dispersion relation as well as the spatial eigenmode of the zigzag instability are determined. The analysis predicts that the most amplified vertical wavelength should scale as U/N and the maximum growth rate as U/Lh.Our main finding is thus that the typical thickness of the ensuing layers will be such that Fv = O(1) and not Fv [Lt ] 1 as assumed by Riley et al. (1981) and Lilly (1983). This implies that such strongly stratified flows are not described by two- dimensional horizontal equations. These results may help to understand the layering commonly observed in stratified turbulence and the fundamental differences with strictly two-dimensional turbulence.
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Gavassino, Lorenzo, Marco Antonelli, and Brynmor Haskell. "Multifluid Modelling of Relativistic Radiation Hydrodynamics." Symmetry 12, no. 9 (September 18, 2020): 1543. http://dx.doi.org/10.3390/sym12091543.
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The formulation of a universal theory for bulk viscosity and heat conduction represents a theoretical challenge for our understanding of relativistic fluid dynamics. Recently, it was shown that the multifluid variational approach championed by Carter and collaborators has the potential to be a general and natural framework to derive (hyperbolic) hydrodynamic equations for relativistic dissipative systems. Furthermore, it also allows keeping direct contact with non-equilibrium thermodynamics, providing a clear microscopic interpretation of the elements of the theory. To provide an example of its universal applicability, in this paper we derive the fundamental equations of the radiation hydrodynamics directly in the context of Carter’s multifluid theory. This operation unveils a novel set of thermodynamic constraints that must be respected by any microscopic model. Then, we prove that the radiation hydrodynamics becomes a multifluid model for bulk viscosity or heat conduction in some appropriate physical limits.
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Krafcik, Andrej, Peter Babinec, Oliver Strbak, and Ivan Frollo. "A Theoretical Analysis of Magnetic Particle Alignment in External Magnetic Fields Affected by Viscosity and Brownian Motion." Applied Sciences 11, no. 20 (October 15, 2021): 9651. http://dx.doi.org/10.3390/app11209651.
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The interaction of an external magnetic field with magnetic objects affects their response and is a fundamental property for many biomedical applications, including magnetic resonance and particle imaging, electromagnetic hyperthermia, and magnetic targeting and separation. Magnetic alignment and relaxation are widely studied in the context of these applications. In this study, we theoretically investigate the alignment dynamics of a rotational magnetic particle as an inverse process to Brownian relaxation. The selected external magnetic flux density ranges from 5μT to 5T. We found that the viscous torque for arbitrary rotating particles with a history term due to the inertia and friction of the surrounding ambient water has a significant effect in strong magnetic fields (range 1–5T). In this range, oscillatory behavior due to the inertial torque of the particle also occurs, and the stochastic Brownian torque diminishes. In contrast, for weak fields (range 5–50μT), the history term of the viscous torque and the inertial torque can be neglected, and the stochastic Brownian torque induced by random collisions of the surrounding fluid molecules becomes dominant. These results contribute to a better understanding of the molecular mechanisms of magnetic particle alignment in external magnetic fields and have important implications in a variety of biomedical applications.
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Colonna, P., N. R. Nannan, A. Guardone, and T. P. van der Stelt. "Erratum to “On the computation of the fundamental derivative of gas dynamics using equations of state” [Fluid Phase Equilibr. 286 (1) (2009) 43–54]." Fluid Phase Equilibria 288, no. 1-2 (January 2010): 162–74. http://dx.doi.org/10.1016/j.fluid.2009.11.003.
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Braudeau, Erik, and Rabi H. Mohtar. "Hydrostructural Pedology, Culmination of the Systemic Approach of the Natural Environment." Systems 9, no. 1 (January 22, 2021): 8. http://dx.doi.org/10.3390/systems9010008.
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The subject of this article is the dynamics of water in a soil pedostructure sample whose internal environment is subjected to a potential gradient created by the departure of water through surface evaporation. This work refers entirely to the results and conclusions of a fundamental theoretical study focused on the molecular thermodynamic equilibrium of the two aqueous phases of the soil pedostructure. The new concepts and descriptive variables of the hydro-thermodynamic equilibrium state of the soil medium, which have been established at the molecular level of the fluid phases of the pedostructure (water and air) in a previous article, are recalled here in the systemic paradigm of hydrostructural pedology. They allow access to the molecular description of water migration in the soil and go beyond the classical mono-scale description of soil water dynamics. We obtain a hydro-thermodynamic description of the soil′s pedostructure at different hydro-functional scale levels including those relating to the water molecule and its atoms. The experimental results show a perfect agreement with the theory, at the same time validating the systemic approach that was the framework.
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Fraser, Adrian E., Meridith Joyce, Evan H. Anders, Jamie Tayar, and Matteo Cantiello. "Characterizing Observed Extra Mixing Trends in Red Giants using the Reduced Density Ratio from Thermohaline Models." Astrophysical Journal 941, no. 2 (December 1, 2022): 164. http://dx.doi.org/10.3847/1538-4357/aca024.
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Abstract Observations show an almost ubiquitous presence of extra mixing in low-mass upper giant branch stars. The most commonly invoked explanation for this is thermohaline mixing. One-dimensional stellar evolution models include various prescriptions for thermohaline mixing, but the use of observational data directly to discriminate between thermohaline prescriptions has thus far been limited. Here, we propose a new framework to facilitate direct comparison: using carbon-to-nitrogen measurements from the Sloan Digital Sky Survey-IV APOGEE survey as a probe of mixing and a fluid parameter known as the reduced density ratio from one-dimensional stellar evolution programs, we compare the observed amount of extra mixing on the upper giant branch to predicted trends from three-dimensional fluid dynamics simulations. Using this method, we are able to empirically constrain how mixing efficiency should vary with the reduced density ratio. We find the observed amount of extra mixing is strongly correlated with the reduced density ratio and that trends between reduced density ratio and fundamental stellar parameters are robust across choices for modeling prescription. We show that stars with available mixing data tend to have relatively low density ratios, which should inform the regimes selected for future simulation efforts. Finally, we show that there is increased mixing at low reduced density ratios, which is consistent with current hydrodynamical models of thermohaline mixing. The introduction of this framework sets a new standard for theoretical modeling efforts, as validation for not only the amount of extra mixing, but trends between the degree of extra mixing and fundamental stellar parameters is now possible.
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Vuong, S. T., and S. S. Sadhal. "Growth and translation of a liquid-vapour compound drop in a second liquid. Part 2. Heat transfer." Journal of Fluid Mechanics 209 (December 1989): 639–60. http://dx.doi.org/10.1017/s0022112089003253.
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The present work is a comprehensive theoretical study of the heat transfer associated with a 3-singlet compound drop that is growing because of change of phase. The geometry is the same as in Part 1, i.e. a vapour bubble partially surrounded by its own liquid in another immiscible liquid. The attempt here is to gain fundamental understanding of the transport processes that take place in connection with direct-contact heat exchange. The fluid dynamics associated with its growth and translation is treated in Part 1. Here, that flow field solution is used to obtain the temperature field and hence the evaporation rate. The energy equation for the system consisting of a single compound drop is solved numerically by finite-difference methods. The results give the complete time history of evaporation of the drop. In addition, useful quantities such as the Nusselt number are given and compared with existing experimental data. Most of the results have good agreement with experimental data.