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1
DAVOUST, L., M. D. COWLEY, R. MOREAU i R. BOLCATO. "Buoyancy-driven convection with a uniform magnetic field. Part 2. Experimental investigation". Journal of Fluid Mechanics 400 (10.12.1999): 59–90. http://dx.doi.org/10.1017/s002211209900645x.
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In this paper, an experimental study of laminar magnetohydrodynamic (MHD) buoyancy-driven flow in a cylindrical cell with axis horizontal is described. A steady uniform magnetic field is applied vertically to the mercury-filled cell, which is also subjected to a horizontal temperature gradient. The main features of this internal MHD thermogravitational flow are made experimentally evident from temperature and electric potential measurements. Whatever the level of convection, raising the Hartmann number Ha to a value of the order of 10 is sufficient to stabilize an initially turbulent flow. At much higher values of the Hartmann number (Ha∼100) the MHD effects cause a change of regime from boundary-layer driven to core driven. In this latter regime an inviscid inertialess MHD core flow is bounded by a Hartmann layer on the horizontal cylindrical wall and viscous layers on the endwalls. Since the Hartmann layer is found to stay electrically inactive along the cell, the relevant asymptotic (Ha[Gt ]1) laws for velocity and heat transfer are found from the balance between the curl of buoyancy and Lorentz forces in the core, together with the condition that the flow of electric current between core and Hartmann layer is negligible. A modified Rayleigh number RaG/Ha2, which is a measure of the ratio of thermal convection to diffusion when there is a balance between buoyancy and Lorentz forces, is the determining parameter for the flow.
2
Hanasz, Michał, K. Otmianowska-Mazur, H. Lesch, G. Kowal, M. Soida, D. Wóltański, K. Kowalik, R. K. Pawłaszek i B. Kulesza-Żydzik. "Cosmic-ray driven dynamo in galactic disks". Proceedings of the International Astronomical Union 4, S259 (listopad 2008): 479–84. http://dx.doi.org/10.1017/s1743921309031147.
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AbstractWe present new developments on the Cosmic–Ray driven, galactic dynamo, modeled by means of direct, resistive CR–MHD simulations, performed with ZEUS and PIERNIK codes. The dynamo action, leading to the amplification of large–scale galactic magnetic fields on galactic rotation timescales, appears as a result of galactic differential rotation, buoyancy of the cosmic ray component and resistive dissipation of small–scale turbulent magnetic fields. Our new results include demonstration of the global–galactic dynamo action driven by Cosmic Rays supplied in supernova remnants. An essential outcome of the new series of global galactic dynamo models is the equipartition of the gas turbulent energy with magnetic field energy and cosmic ray energy, in saturated states of the dynamo on large galactic scales.
3
Davoust, L., R. Moreau, M. D. Cowley, P. A. Tanguy i F. Bertrand. "Numerical and analytical modelling of the MHD buoyancy-driven flow in a Bridgman crystal growth configuration". Journal of Crystal Growth 180, nr 3-4 (październik 1997): 422–32. http://dx.doi.org/10.1016/s0022-0248(97)00238-8.
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Prakash, J., S. Gouse Mohiddin i S. Vijaya Kumar Varma. "Free Convective MHD Flow Past a Vertical Cone with Variable Heat and Mass Flux". Journal of Fluids 2013 (18.11.2013): 1–8. http://dx.doi.org/10.1155/2013/405985.
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A numerical study of buoyancy-driven unsteady natural convection boundary layer flow past a vertical cone embedded in a non-Darcian isotropic porous regime with transverse magnetic field applied normal to the surface is considered. The heat and mass flux at the surface of the cone is modeled as a power law according to qwx=xm and qw*(x)=xm, respectively, where x denotes the coordinate along the slant face of the cone. Both Darcian drag and Forchheimer quadratic porous impedance are incorporated into the two-dimensional viscous flow model. The transient boundary layer equations are then nondimensionalized and solved by the Crank-Nicolson implicit difference method. The velocity, temperature, and concentration fields have been studied for the effect of Grashof number, Darcy number, Forchheimer number, Prandtl number, surface heat flux power-law exponent (m), surface mass flux power-law exponent (n), Schmidt number, buoyancy ratio parameter, and semivertical angle of the cone. Present results for selected variables for the purely fluid regime are compared with the published results and are found to be in excellent agreement. The local skin friction, Nusselt number, and Sherwood number are also analyzed graphically. The study finds important applications in geophysical heat transfer, industrial manufacturing processes, and hybrid solar energy systems.
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Wood, Charles E., i Chris J. Lawn. "Two-phase MHD energy conversion from buoyancy-driven flows of liquid metal coolant in a fusion reactor". Fusion Engineering and Design 151 (luty 2020): 111288. http://dx.doi.org/10.1016/j.fusengdes.2019.111288.
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Liu, Zhipeng, Chaowei Jiang, Xueshang Feng, Pingbing Zuo i Yi Wang. "Numerical Simulation of Solar Magnetic Flux Emergence Using the AMR–CESE–MHD Code". Astrophysical Journal Supplement Series 264, nr 1 (22.12.2022): 13. http://dx.doi.org/10.3847/1538-4365/ac9d2b.
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Abstract Magnetic flux emergence from the solar interior to the atmosphere is believed to be a key process in the formation of solar active regions and driving solar eruptions. Due to the limited capabilities of observations, the flux emergence process is commonly studied using numerical simulations. In this paper, we develop a numerical model to simulate the emergence of a twisted magnetic flux tube from the convection zone to the corona, using the AMR–CESE–MHD code, which is based on the conservation-element solution-element method, with adaptive mesh refinement. The results of our simulation agree with those of many previous studies with similar initial conditions, but by using different numerical codes. In the early stage, the flux tube rises from the convection zone, being driven by magnetic buoyancy, until it reaches close to the photosphere. The emergence is decelerated there, and with the piling up of the magnetic flux, the magnetic buoyancy instability is triggered, which allows the magnetic field to partially enter into the atmosphere. Meanwhile, two gradually separated polarity concentration zones appear in the photospheric layer, transporting the magnetic field and energy into the atmosphere through their vortical and shearing motions. Correspondingly, the coronal magnetic field is also reshaped into a sigmoid configuration, containing a thin current layer, which resembles the typical pre-eruptive magnetic configuration of an active region. Such a numerical framework of magnetic flux emergence as established will be applied to future investigations of how solar eruptions are initiated in flux emergence active regions.
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Subhrajit Kanungo i Tumbanath Samantara. "Flow And Heat Transfer of Unsteady Two-Phase Boundary Layer Flow Past an Inclined Permeable Stretching Sheet with Electrification of Particles". CFD Letters 15, nr 5 (16.03.2023): 134–44. http://dx.doi.org/10.37934/cfdl.15.5.134144.
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In the present study, an analysis has been carried out for a particle laden boundary layer flow with existence of electrification of particles has been studied over an inclined permeable stretching sheet. In most of the MHD fluid flow problems, either the plate is externally supplied by the magnetic/electric field or the fluid is electrically conducting. In the present problem, neither the plate is electrified nor the fluid is electrically conducted, but due to the random motion of the particles, collision of particle-particle and particle–wall, the particles are electrified. This electric field affects the fluid flow and heat transfer of the flow problem. Again, in the previous literatures, Buoyancy force is considered in momentum equations of fluid phase only. But in reality, both the phases are affected by the buoyancy force. For this reason, a reasonable mathematical model for two-phase buoyancy driven flow has been formulated with the consideration of electrification of particles in both fluid and particle phase. The governing system of PDEs are transferred to system of ODEs by applying similarity transformations and then computed by implementing Runga-Kutta method. The impact of electrification and other fluid parameters on flow and heat transfer has been studied. The results are represented through graphs and tables
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Gouse, Mohiddin, Anwar Bég i Vijaya Varma. "Numerical study of free convective MHD flow past a vertical cone in non-Darcian porous media". Theoretical and Applied Mechanics 41, nr 2 (2014): 119–40. http://dx.doi.org/10.2298/tam1402119g.
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A numerical study of buoyancy-driven unsteady natural convection boundary layer flow past a vertical cone embedded in a non-Darcian isotropic porous regime with transverse magnetic field applied normal to the surface is considered. The heat and mass flux at the surface of the cone is modeled as a power-law according to qw(x) = xm and q*w (x) = xn respectively, where x denotes the coordinate along the slant face of the cone. Both Darcian drag and Forchheimer quadratic porous impedance are incorporated into the two-dimensional viscous flow model. The transient boundary layer equations are then non-dimensionalized and solved by the Crank-Nicolson implicit difference method. The velocity, temperature and concentration fields have been studied for the effect of Grashof number, Darcy number, Forchheimer number, Prandtl number, surface heat flux power-law exponent (m), surface mass flux power-law exponent (n), Schmidt number, buoyancy ratio parameter and semi-vertical angle of the cone. Present results for selected variables for the purely fluid regime are compared with the non-porous study by Hossain and Paul [9] and are found to be in excellent agreement. The local skin friction, Nusselt number and Sherwood number are also analyzed graphically. The study finds important applications in geophysical heat transfer, industrial manufacturing processes and hybrid solar energy systems.
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Suzuki, Takeru K., Yasuo Fukui, Kazufumi Torii, Mami Machida, Ryoji Matsumoto i Kensuke Kakiuchi. "Investigating Magnetic Activity in the Galactic Centre by Global MHD Simulation". Proceedings of the International Astronomical Union 11, S322 (lipiec 2016): 137–40. http://dx.doi.org/10.1017/s1743921316012461.
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AbstractBy performing a global magnetohydrodynamical (MHD) simulation for the Milky Way with an axisymmetric gravitational potential, we propose that spatially dependent amplification of magnetic fields possibly explains the observed noncircular motion of the gas in the Galactic centre (GC) region. The radial distribution of the rotation frequency in the bulge region is not monotonic in general. The amplification of the magnetic field is enhanced in regions with stronger differential rotation, because magnetorotational instability and field-line stretching are more effective. The strength of the amplified magnetic field reaches ≳ 0.5 mG, and radial flows of the gas are excited by the inhomogeneous transport of angular momentum through turbulent magnetic field that is amplified in a spatially dependent manner. As a result, the simulated position-velocity diagram exhibits a time-dependent asymmetric parallelogram-shape owing to the intermittency of the magnetic turbulence; the present model provides a viable alternative to the bar-potential-driven model for the parallelogram shape of the central molecular zone. In addition, Parker instability (magnetic buoyancy) creates vertical magnetic structure, which would correspond to observed molecular loops, and frequently excited vertical flows. Furthermore, the time-averaged net gas flow is directed outward, whereas the flows are highly time dependent, which would contribute to the outflow from the bulge.
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Hanasz, M., D. Woltanski i K. Kowalik. "Interstellar and intergalactic dynamos". Proceedings of the International Astronomical Union 8, S294 (sierpień 2012): 225–36. http://dx.doi.org/10.1017/s1743921313002573.
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AbstractWe review recent developments of amplification models of galactic and intergalactic magnetic field. The most popular scenarios involve variety of physical mechanisms, including turbulence generation on a wide range of physical scales, effects of supernovae, buoyancy as well as the magnetorotational instability. Other models rely on galaxy interaction, which generate galactic and intergalactic magnetic fields during galaxy mergers. We present also global galactic-scale numerical models of the Cosmic Ray (CR) driven dynamo, which was originally proposed by Parker (1992). We conduct a series of direct CR+MHD numerical simulations of the dynamics of the interstellar medium (ISM), composed of gas, magnetic fields and CR components. We take into account CRs accelerated in randomly distributed supernova (SN) remnants, and assume that SNe deposit small-scale, randomly oriented, dipolar magnetic fields into the ISM. The amplification timescale of the large-scale magnetic field resulting from the CR-driven dynamo is comparable to the galactic rotation period. The process efficiently converts small-scale magnetic fields of SN-remnants into galactic-scale magnetic fields. The resulting magnetic field structure resembles the X-shaped magnetic fields observed in edge-on galaxies.
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Mliki, Bouchmel, Rached Miri, Ridha Djebali i Mohamed A. Abbassi. "CuO–Water MHD Mixed Convection Analysis and Entropy Generation Minimization in Double-Lid–Driven U-Shaped Enclosure with Discrete Heating". Acta Mechanica et Automatica 17, nr 1 (15.02.2023): 112–23. http://dx.doi.org/10.2478/ama-2023-0013.
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Abstract The present study explores magnetic nanoliquid mixed convection in a double lid–driven U-shaped enclosure with discrete heating using the lattice Boltzmann method (LBM) numerical method. The nanoliquid thermal conductivity and viscosity are calculated using the Maxwell and Brinkman models respectively. Nanoliquid magnetohydrodynamics (MHD) and mixed convection are analyzed and entropy generation minimisation has been studied. The presented results for isotherms, stream isolines and entropy generation describe the interaction between the various physical phenomena inherent to the problem including the buoyancy, magnetic and shear forces. The operating parameters’ ranges are: Reynolds number (Re: 1–100), Hartman number (Ha: 0–80), magnetic field inclination (γ: 0°– 90°), nanoparticles volume fraction (ϕ: 0–0.04) and inclination angle (α: 0°– 90°). It was found that the N um and the total entropy generation augment by increasing Re, ϕ: and γ. conversely, an opposite effect was obtained by increasing Ha and α. The optimum magnetic field and cavity inclination angles to maximum heat transfer are γ = 90° and α = 0.
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Otieno, Opiyo Richard, Alfred W. Manyonge i Jacob K. Bitok. "Numerical computation of steady buoyancy driven MHD heat and mass transfer past an inclined infinite flat plate with sinusoidal surface boundary conditions". Applied Mathematical Sciences 11 (2017): 711–29. http://dx.doi.org/10.12988/ams.2017.7127.
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Ahmed, Sameh E., M. A. Mansour i A. Mahdy. "MHD mixed convection in an inclined lid-driven cavity with opposing thermal buoyancy force: Effect of non-uniform heating on both side walls". Nuclear Engineering and Design 265 (grudzień 2013): 938–48. http://dx.doi.org/10.1016/j.nucengdes.2013.06.023.
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Pal, Dulal, i Babulal Talukdar. "Influence of fluctuating thermal and mass diffusion on unsteady MHD buoyancy-driven convection past a vertical surface with chemical reaction and Soret effects". Communications in Nonlinear Science and Numerical Simulation 17, nr 4 (kwiecień 2012): 1597–614. http://dx.doi.org/10.1016/j.cnsns.2011.08.038.
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Mahdy, A., S. E. Ahmed i M. A. Mansour. "Entropy generation for MHD natural convection in enclosure with a micropolar fluid saturated porous medium with Al2O3Cu water hybrid nanofluid". Nonlinear Analysis: Modelling and Control 26, nr 6 (1.11.2021): 1123–43. http://dx.doi.org/10.15388/namc.2021.26.24940.
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This contribution gives a numerical investigation of buoyancy-driven flow of natural convection heat transfer and entropy generation of non-Newtonian hybrid nanofluid (Al2O3-Cu) within an enclosure square porous cavity. Hybrid nanofluids represent a novel type of enhanced active fluids. During the current theoretical investigation, an actual available empirical data for both thermal conductivity and dynamic viscosity of hybrid nanofluids are applied directly. Numerical simulation have been implemented for solid nanoparticles, the volumetric concentration of which varies from 0.0% (i.e., pure fluid) to 0.1% of hybrid nanofluids. Heat and sink sources are situated on a part of the left and right sides of the cavity with length B, while the upper and bottom horizontal sides are kept adiabatic. The stated partial differential equations describing the flow are mutated to a dimensionless formulas, then solved numerically via the help of an implicit finite difference approach. The acquired computations are given in terms of streamlines, isotherms, isomicrorotations, isoconcentraions, local Began number, total entropy, local and mean Nusselt numbers. The data illustrates that variations of ratio of the average Nusselt number to the averageNusselt of pure fluid Num+ is a decreasing function of Ha and φ, while e+ is an increasing function of Ha and φ parameters of hybrid nanofluid.
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Makinde, O. D., N. Sandeep, T. M. Ajayi i I. L. Animasaun. "Numerical Exploration of Heat Transfer and Lorentz Force Effects on the Flow of MHD Casson Fluid over an Upper Horizontal Surface of a Thermally Stratified Melting Surface of a Paraboloid of Revolution". International Journal of Nonlinear Sciences and Numerical Simulation 19, nr 2 (25.04.2018): 93–106. http://dx.doi.org/10.1515/ijnsns-2016-0087.
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AbstractConsidering the recent aspiration of experts dealing with the painting of aircraft and bonnet of cars to further understand the relevance of skin friction and heat transfer while painting all these objects that are neither horizontal nor vertical, neither a cone/wedge or cylinder but upper horizontal surface of a paraboloid of revolution; a two-dimensional electrically conducting Casson fluid flow on an upper horizontal thermally stratified surface of a paraboloid of revolution is analyzed. The influence of melting heat transfer and thermal stratification are properly accounted for by modifying classical boundary condition of temperature. Plastic dynamic viscosity and thermal conductivity of the fluid are assumed to vary linearly with temperature. In view of this, all necessary models were modified to suit the case$T_m<T_\infty$. It is assumed that natural convection is driven by buoyancy; hence the suitable model of Boussinesq approximation is adopted. A suitable similarity transformation is applied to reduce the governing equations to coupled ordinary differential equations. These equations along with the boundary conditions are solved numerically by using Runge–Kutta technique along with shooting method. Effects of the magnetic field, temperature-dependent plastic dynamic viscosity and buoyancy parameters on the velocity and temperature are showed graphically and discussed. Normal influence of Lorentz force exists on Casson fluid flow when the thickness of the surface is small. Scientists and experts are urge to note an adverse effect of this force occurs on the fluid flow when the thickness of the surface is large.
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Pal, Dulal, i Hiranmoy Mondal. "Influence of Soret and Dufour on MHD buoyancy-driven heat and mass transfer over a stretching sheet in porous media with temperature-dependent viscosity". Nuclear Engineering and Design 256 (marzec 2013): 350–57. http://dx.doi.org/10.1016/j.nucengdes.2012.08.015.
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Nayak, M. K., F. Mabood i O. D. Makinde. "Heat transfer and buoyancy‐driven convective MHD flow of nanofluids impinging over a thin needle moving in a parallel stream influenced by Prandtl number". Heat Transfer 49, nr 2 (26.11.2019): 655–72. http://dx.doi.org/10.1002/htj.21631.
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Parveen, Rujda, Tapas Ray Mahapatra i B. C. Saha. "Study of Entropy Generation and Magnetohydrodynamic (MHD) Natural Convection in a Curved Enclosure Having Various Amplitude and Filled with Cu–TiO2/Water Hybrid Nanofluid". Journal of Nanofluids 10, nr 3 (1.09.2021): 339–54. http://dx.doi.org/10.1166/jon.2021.1794.
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We have studied the buoyancy-driven convection enhancement and entropy production in a Cu–TiO2/water (water with copper and titanium dioxide nanoparticles) hybrid nanofluid filled curved enclosure subjected to a uniform magnetic field. The enclosure has a sinusoidally heated right wall, cold left wall, uniformly heated bottom wall, and thermally insulated upper curved wall. The effect of different amplitudes (concave, square, and convex) of the upper curved wall is considered. The non-linear governing equations are non-dimensionalized and written in stream function-velocity formulation. Bi Conjugate Gradient Stabilized (BiCGStab) method is employed followed by a Tri-diagonal matrix algorithm (TDMA) for the numerical simulation. The considered parameters are as follows: Rayleigh number (Ra), Hartmann number (Ha), phase angle (ε), the amplitude of the curved wall (a), and nanoparticle volume fraction (Φ). The influence of the model parameters on entropy production, fluid flow, and heat transfer phenomenon has been investigated, and the simulated results are displayed in terms of flow fields and temperature fields. According to the studies, increasing the Rayleigh number and volume percentage of nanoparticles has a significant impact on heat transmission and hence dominates the convection effect, whereas increasing the Hartmann number has the opposite effect.
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Nazeer, Mubbashar, N. Ali i Tariq Javed. "Numerical simulation of MHD flow of micropolar fluid inside a porous inclined cavity with uniform and non-uniform heated bottom wall". Canadian Journal of Physics 96, nr 6 (czerwiec 2018): 576–93. http://dx.doi.org/10.1139/cjp-2017-0639.
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Buoyancy-driven, incompressible, two-dimensional flow of a micropolar fluid inside an inclined porous cavity in the presence of magnetic field is investigated. The nonlinear partial differential equations are solved by employing a robust Galerkin finite element scheme. The pressure term in this scheme is eliminated by using the penalty method. The results are exhibited in the form of streamlines, isotherms, and local and average Nusselt numbers for two cases, namely, the constant and the sinusoidal heated lower wall of the conduit. In both cases, the side walls of the cavity are cold and the upper side is insulated. The main difference between the two cases is observed from temperature contours. For constant heated bottom wall a finite discontinuity appears in the temperature distribution at the corners of the bottom wall. In contrast, no such discontinuity appears in the temperature distribution for non-uniform heated bottom wall. The quantitative changes in temperature contours in different portions of the cavity are identified by comparing the results for both cases. The code is also validated and benchmarked with the previous numerical data available in the literature. It is found that the magnetic field inclined at a certain angle either suppresses or enhances the intensity of primary circulations depending on the inclination of the cavity. Further, the average Nusselt number at the bottom wall is higher when magnetic field is applied vertically irrespective of the inclination of cavity. The analysis presented here has potential application in solar collectors and porous heat exchangers.
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Pipin, V. V., A. G. Kosovichev i V. E. Tomin. "Effects of Emerging Bipolar Magnetic Regions in Mean-field Dynamo Model of Solar Cycles 23 and 24". Astrophysical Journal 949, nr 1 (1.05.2023): 7. http://dx.doi.org/10.3847/1538-4357/acaf69.
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Abstract We model the physical parameters of Solar Cycles 23 and 24 using a nonlinear dynamical mean-field dynamo model that includes the formation and evolution of bipolar magnetic regions (BMRs). The Parker-type dynamo model consists of a complete MHD system in the mean-field formulation: the 3D magnetic induction equation, and 2D momentum and energy equations in the anelastic approximation. The initialization of BMRs is modeled in the framework of Parker’s magnetic buoyancy instability. It defines the depths of BMR injections, which are typically located at the edge of the global dynamo waves. The distribution with longitude and latitude and the size of the initial BMR perturbations are taken from the NOAA database of active regions. The modeling results are compared with various observed characteristics of the solar cycles. Only the BMR perturbations located in the upper half of the convection zone lead to magnetic active regions on the solar surface. While the BMRs initialized in the lower part of the convection zone do not emerge on the surface, they still affect the global dynamo process. Our results show that BMRs can play a substantial role in the dynamo processes and affect the strength of the solar cycles. However, the data driven model shows that the BMR’s effect alone cannot explain the weak Cycle 24. This weak cycle and the prolonged preceding minimum of magnetic activity were probably caused by a decrease of the turbulent helicity in the bulk of the convection zone during the decaying phase of Cycle 23.
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Sarson, Graeme R., i David Gubbins. "Three-dimensional kinematic dynamos dominated by strong differential rotation". Journal of Fluid Mechanics 306 (10.01.1996): 223–65. http://dx.doi.org/10.1017/s0022112096001292.
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In the kinematic dynamo problem a fluid motion is specified arbitrarily and the induction equation is solved for non-decaying magnetic fields; it forms part of the larger magnetohydrodynamic (MHD) dynamo problem in which the fluid flow is buoyancy-driven. Although somewhat restrictive, the kinematic problem is important for two reasons: first, it suffers from numerical difficulties that are holding up progress on the MHD problem; secondly, for the geodynamo, it is capable of reproducing details of the observable magnetic field. It is more efficient to study these two aspects for the kinematic dynamo than for the full MHD dynamo. We explore solutions for a family of fluid flows in a sphere, first studied by Kumar & Roberts (1975), that is heuristically representative of convection in a rotating sphere such as the Earth's core. We guard against numerical difficulties by comparing our results with well-understood solutions from the axisymmetric (αω) limit of Braginskii (1964a) and with solutions of the adjoint problem, which must yield identical eigenvalues in an adequate numerical treatment. Previous work has found a range of steady dipolar solutions; here we extend these results and find solutions of other symmetries, notably oscillatory and quadrupolar fields. The surface magnetic fields, important for comparison with observations, have magnetic flux concentrated by downwelling flow. Roberts (1972) found that meridional circulation promoted stationary solutions of the αω-equations, preferred solutions being oscillatory when no such circulation was present. We find analogous results for the full three-dimensional problem, but note that in the latter case the ‘effective’ meridional circulation arising from the non-axisymmetric convection (a concept made precise in the asymptotic limit of Braginskii 1964a) must be considered. Thus stationary solutions are obtained even in the absence of ‘true’ meridional circulation, and the time-dependence can be controlled by the strength of the convection as well as by the meridional circulation. The preference for fields of dipole or quadrupole parity is largely controlled by the sign of the velocity: a reversal of velocity from a case favouring a dipole will favour quadrupole parity, and vice versa. For the comparison problem of Proctor (1977b) this symmetry is exact; for the physical problem the boundary conditions make a difference. The boundary effect is first removed by surrounding the dynamo region with a thick layer of quiescent conducting fluid, and then studied numerically by progressively reducing the thickness of this layer to zero. The insulating boundary contributes to the difficulty of obtaining dynamo action, and to the numerical difficulties encountered. The effect of an inner boundary on dynamo action is also considered, but found to be slight.
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Selimefendigil, Fatih, i Ali J. Chamkha. "MHD mixed convection of nanofluid in a three-dimensional vented cavity with surface corrugation and inner rotating cylinder". International Journal of Numerical Methods for Heat & Fluid Flow 30, nr 4 (18.02.2019): 1637–60. http://dx.doi.org/10.1108/hff-10-2018-0566.
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Purpose This study aims to numerically examine mixed convection of CuO-water nanofluid in a three-dimensional (3D) vented cavity with inlet and outlet ports under the influence of an inner rotating circular cylinder, homogeneous magnetic field and surface corrugation effects. In practical applications, it is possible to encounter some of the considered configurations in a vented cavity such as magnetic field, rotating cylinder and it is also possible to specially add some of the active and passive control means to control the convection inside the cavity such as adding nanoparticles, corrugating the surfaces. The complicated physics with nanofluid under the effects of magnetic field and inclusion of complex 3D geometry make it possible to use the results of this numerical investigation for the design, control and optimization of many thermal engineering systems as mentioned above. Design/methodology/approach The bottom surface is corrugated with a rectangular wave shape, and the rotating cylinder surface and cavity bottom surface were kept at constant hot temperatures while the cold fluid enters the inlet port with uniform velocity. The complicated interaction between the forced convection and buoyancy-driven convection coupled with corrugated and rotating surfaces in 3D configuration with magnetic field, which covers a wide range of thermal engineering applications, are numerically simulated with finite element method. Effects of various pertinent parameters such as Richardson number (between 0.01 and 100), Hartmann number (between 0 and 1,000), angular rotational speed of the cylinder (between −30 and 30), solid nanoparticle volume fraction (between 0 and 0.04), corrugation height (between 0 and 0.18H) and number (between 1 and 20) on the convective heat transfer performance are numerically analyzed. Findings It was observed that the magnetic field suppresses the recirculation zone obtained in the lower part of the inlet port and enhances the average heat transfer rate, which is 10.77 per cent for water and 6.86 per cent for nanofluid at the highest strength. Due to the thermal and electrical conductivity enhancement of nanofluid, there is 5 per cent discrepancy in the Nusselt number augmentation with the nanoadditive inclusion in the absence and presence of magnetic field. The average heat transfer rate of the corrugated surface enhances by about 9.5 per cent for counter-clockwise rotation at angular rotational speed of 30 rad/s as compared to motionless cylinder case. Convective heat transfer characteristics are influenced by introducing the corrugation waves. As compared to number of waves, the height of the corrugation has a slight effect on the heat transfer variation. When the number of rectangular waves increases from N = 1 to N = 20, approximately 59 per cent of the average heat transfer reduction is achieved. Originality/value In this study, mixed convection of CuO-water nanofluid in a 3D vented cavity with inlet and outlet ports is numerically examined under the influence of an inner rotating circular cylinder, homogeneous magnetic field and surface corrugation effects. To the best of authors knowledge such a study has never been performed. In practical applications, it is possible to encounter some of the considered configurations in a vented cavity such as magnetic field, rotating cylinder and it is also possible to specially add some of the active and passive control means to control the convection inside the cavity such as adding nanoparticles, corrugating the surfaces. The complicated physics with nanofluid under the effects of magnetic field and inclusion of complex 3D geometry make it possible to use the results of this numerical investigation for the design, control and optimization of many thermal engineering systems as mentioned above.
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Laidoudi, Houssem, Aissa Abderrahmane, Abdulkafi Mohammed Saeed, Kamel Guedri, Wajaree Weera, Obai Younis, Abed Mourad i Riadh Marzouki. "Irreversibility Interpretation and MHD Mixed Convection of Hybrid Nanofluids in a 3D Heated Lid-Driven Chamber". Nanomaterials 12, nr 10 (20.05.2022): 1747. http://dx.doi.org/10.3390/nano12101747.
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This paper presents a numerical simulation of a magneto-convection flow in a 3D chamber. The room has a very specific permeability and a zigzag bottom wall. The fluid used in this study is Al2O3-Cu/water with 4% nanoparticles. The Galerkin finite element technique (GFEM) was developed to solve the main partial equations. The hybrid nanofluid inside the container is subjected to the horizontal motion of the upper wall, an external magnetic field, and a thermal buoyancy force. The present numerical methodology is validated by previous data. The goal of this investigation was to understand and determine the percentage of heat energy transferred between the nanofluid and the bottom wall of the container under the influence of a set of criteria, namely: the movement speed of the upper wall of the cavity (Re = 1 to 500), the amount of permeability (Da = 10−5 to 10−2), the intensity of the external magnetic field (Ha = 0 to 100), the number of zigzags of the lower wall (N = 1 to 4), and the value of thermal buoyancy when the force is constant (Gr = 1000). The contours of the total entropy generation, isotherm, and streamline are represented in order to explain the fluid motion and thermal pattern. It was found that the heat transfer is significant when (N = 4), where the natural convection is dominant and (N = 2), and the forced convection is predominant.
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Vishniac, E. T. "The Internal Wave Driven Dynamo in Accretion Disks". Symposium - International Astronomical Union 157 (1993): 211–15. http://dx.doi.org/10.1017/s0074180900174145.
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We present the results of recent work on a model of angular momentum transport in thin, ionized, accretion disks. In particular, we consider three physical effects, each of which can be represented in terms of a local MHD mode in such a disk. First, we discuss the generation and propagation of internal modes within accretion disks, pointing out certain features which make them particularly promising as the driving force behind a strong, fast dynamo in accretion disks. Second, we point ou that the magnetic shearing instability (MSI) first discussed by Velikhov, and more recently by Balbus and Hawley in the specific context of these disks, provides a natural saturation mechanism for any disk dynamo, leading to an approximate equality between the dimensionless viscosity and the ratio of the dynamo growth rate to the local shear. Third, we argue that magnetic buoyancy is largely suppressed by the turbulence generated by the shearing instability. This prevents it from removing magnetic flux from the disk any faster than random turbulent diffusion. We find that the dimensionless viscosity α scales as (H/r)4/3, where H is the disk height and r is its radius.
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Sekar, R., i K. Raju. "Effect of magnetic field dependent viscosity on Soret-driven ferrothermohaline convection saturating an anisotropic porous medium of sparse particle suspension". World Journal of Engineering 11, nr 3 (1.06.2014): 213–28. http://dx.doi.org/10.1260/1708-5284.11.3.213.
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Thermoconvective instability with Soret effect in multi-component fluids has wide range of applications in heat and mass transfer. This work deals with the theoretical investigation of the effect of magnetic field dependent (MFD) viscosity on Soret-driven ferrothermohaline convection heated and salted from below in an anisotropic porous medium subjected to a transverse uniform magnetic field. The resulting eigen value problem is solved using Brinkman model. An exact solution is obtained for the case of two free boundaries and the stationary and oscillatory instabilities are investigated by using linear stability analysis and normal mode technique for the vertical of anisotropic porous medium. The analysis has been made for different parameters like porosity, anisotropy, ratio of heat transport to mass transport, buoyancy magnetization, non-buoyancy magnetization, Soret parameter and Salinity Rayleigh number. The effect of MFD viscosity is assumed to be isotropy. It is found that the presence of MFD viscosity has a stabilizing effect, whereas magnetization has a destabilizing effect.
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Shree, Venkatesh Vidya, Chandrappa Rudresha, Chandrashekar Balaji i Sokalingam Maruthamanikandan. "Effect of Magnetic Field Dependent Viscosity on Darcy-Brinkman Ferroconvection with Second Sound". East European Journal of Physics, nr 4 (6.12.2022): 112–17. http://dx.doi.org/10.26565/2312-4334-2022-4-10.
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The problem of buoyancy-driven convection in a ferromagnetic fluid saturated porous medium with the Maxwell-Cattaneo law and MFD viscosity is investigated by the method of small perturbation. The fluid motion is described using the Brinkman model. It is assumed that the fluid and solid matrices are in local thermal equilibrium. For simplified boundary conditions, the eigenvalue problem is solved exactly, and closed form solutions for stationary instability are obtained. Magnetic forces and second sound were found to enhance the beginning of Brinkman ferroconvection. However, ferroconvection is hampered when the porous parameters are increased. The results show that MFD viscosity inhibits the beginning of Darcy-Brinkman ferroconvection and that MFD viscosity stabilizing effect is decreased when the magnetic Rayleigh number is significant. Furthermore, it is demonstrated that oscillatory instability arises before stationary instability, assuming that the Prandtl and Cattaneo numbers are sufficiently large.
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Jin, Yan, Xiaosen Dong, Fu Yang, Changgui Cheng, Yang Li i Wei Wang. "Removal Mechanism of Microscale Non-Metallic Inclusions in a Tundish with Multi-Hole-Double-Baffles". Metals 8, nr 8 (6.08.2018): 611. http://dx.doi.org/10.3390/met8080611.
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To effectively remove microscale inclusions in the tundish, the Multi-Hole-Double-Baffles (MHDB), a novel flow control device in the tundish for continuous casting, was developed. The hole array mode of the MHDB will directly affect the trajectories of the inclusions. The effect and removal mechanism of the inclusions with sizes of 1 µm to 50 μm in the tundish with MHDB were studied by numerical simulation. The hole array mode of MHDB could affect the inclusions’ trajectories and distribution, and the mechanism underlying the effect of the MHDB was investigated using the discrete phase model (DPM). A 1:2.5 physical model was built to verify the accuracy of numerical simulation. The results showed that micro-inclusions were primarily driven by the drag force exerted by the molten steel flow, micro-inclusion trajectories followed the molten steel streamlines almost exactly, but buoyancy still played a role in the removal of the micro-inclusions near the molten steel surface; the hole array mode affected the trajectories of the micro-inclusions and controlled and decelerated the flow of molten steel, increasing the residence time of the molten steel flow a the value that is 15 times larger than the theoretical value; and “upper-in-lower-out” type MHDB showed the most efficient removal of micro-inclusions, with the removal rate being increased by 13–49% compared to the removal rates for the other type MHDB. The results of numerical simulation were well verified by physical simulation.
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Keller Jr., Douglas, Yonatan Givon, Romain Pennel, Shira Raveh-Rubin i Philippe Drobinski. "Untangling the mistral and seasonal atmospheric forcing driving deep convection in the Gulf of Lion: 2012–2013". Ocean Science 18, nr 2 (8.04.2022): 483–510. http://dx.doi.org/10.5194/os-18-483-2022.
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Abstract. Deep convection in the Gulf of Lion is believed to be primarily driven by the mistral winds. However, our findings show that the seasonal atmospheric change provides roughly two-thirds of the buoyancy loss required for deep convection to occur for the year 2012 to 2013, with the mistral supplying the final third. Two NEMOMED12 ocean simulations of the Mediterranean Sea were run from 1 August 2012 to 31 July 2013, forced with two sets of atmospheric-forcing data from a RegIPSL coupled run within the Med-CORDEX framework. One set of atmospheric-forcing data was left unmodified, while the other was filtered to remove the signal of the mistral. The control simulation featured deep convection, while the seasonal simulation did not. A simple model was derived by relating the anomaly scale forcing (the difference between the control and seasonal runs) and the seasonal scale forcing to the ocean response through the stratification index. This simple model revealed that the mistral's effect on buoyancy loss depends more on its strength rather than its frequency or duration. The simple model also revealed that the seasonal cycle of the stratification index is equal to the net surface heat flux over the course of the year, with the stratification maximum and minimum occurring roughly at the fall and spring equinoxes.
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"Buoyancy-driven MHD flow in electrically insulated rectangular ducts". Magnetohydrodynamics 43, nr 3 (wrzesień 2007): 315–22. http://dx.doi.org/10.22364/mhd.43.3.3.
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Gürbüz, Merve, i Münevver Tezer-Sezgin. "Numerical Solution of MHD Incompressible Convection Flow in Channels". European Journal of Computational Mechanics, 18.12.2019. http://dx.doi.org/10.13052/ejcm2642-2085.2852.
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The purpose of this paper is to study numerically the influence of the magnetic field, buoyancy force and viscous dissipation on the convective flow and temperature of the fluid in a square cavity, lid-driven cavity, and lid-driven cavity with an obstacle at the center. The continuity, momentum and energy equations are coupled including buoyancy and magnetic forces, and energy equation contains Joule heating and viscous dissipation. The equations are solved in terms of stream function, vorticity and temperature by using polynomial radial basis function (RBF) approximation for the inhomogeneity and particular solution. The numerical solutions are obtained for several values of Grashof number (Gr), Hartmann number (M) for fixed Prandtl number Pr = 0:71 and fixed Reynolds number Re = 100 with or without viscous dissipation. It is observed that in the absence of obstacle, viscous dissipation changes the symmetry of the isotherms, and the dominance of buoyancy force increases with an increase in Gr, whereas decreases when the intensity of magnetic field increases. The obstacle in the lid-driven cavity causes a secondary flow on its left part. The effect of moving lid is weakened on the flow and isotherms especially for large Gr when the cavity contains obstacle.
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Tayebi, Tahar, i Ali J. Chamkha. "MHD buoyancy‐driven flow in a nanoliquid filled‐square enclosure divided by a solid conductive wall". Mathematical Methods in the Applied Sciences, 14.06.2020. http://dx.doi.org/10.1002/mma.6598.
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"MHD Free Convective Heat Transfer in a Triangular Enclosure Filled with Copper-Water Nanofluid". International Journal of Material and Mathematical Sciences, 29.04.2020, 29–38. http://dx.doi.org/10.34104/ijmms.020.029038.
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Two-dimensional time-independent free convective flow and temperature flow into a right-angled triangle shape cavity charged by Cu-H2O nanofluid has been performed. The horizontal side of the enclosure is warmed uniformly T=Th whilst the standing wall is cooled at low-temperature T=Tc and hypotenuse of the triangular is insulated. The dimensionless non-linear governing PDEs have been solved numerically employing the robust PDE solver the Galerkin weighted residual finite element technique. An excellent agreement is founded between the previous, and present studies. The outcomes are displayed through streamline contours, isotherm contours, and local and average Nusselt number for buoyancy-driven parameter Rayleigh number, Hartmann number, and nanoparticles volume fraction. The outcomes show that the temperature flow value significantly changes for the increases of Rayleigh number, Hartmann number, and nanoparticles volume fraction. Average Nusselt number is increased for the composition of nanoparticles whereas diminishes with the increase of Hartmann number.
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F. Baiyeri, J., M. A. Mohammed, O. A. Esan, T. O. Ogunbayo i O. E. Enobabor. "Ohmic Dissipative MHD Pressure-driven Coupled-flow and Heat Transfer Across a Porous Medium with Thermal Radiation". Journal of Energy Research and Reviews, 17.07.2018, 1–10. http://dx.doi.org/10.9734/jenrr/2018/v1i29800.
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In this study, a pressure driven flow of a magnetohydrodynamic steady coupled-flow across a porous layer horizontal bottom plate with buoyancy force is investigated. The heat transfer problem is also examined by taking viscous and Ohmic dissipation and radiation effects in the energy equation into consideration. The velocity and temperature slip boundary conditions are taken at the plate and at the interface of the porous medium and clear fluid, it is assumed that velocity components to be continuous and the jump in shearing stresses. The solutions to the problem are obtained by employing fourth order Runge-Kutta scheme along with shooting technique and the effects of the pertinent parameters entrenches in the flow system are shown graphically and quantitatively discussed. The results shows that an increase in the thermal convection and pressure gradient enhances the flow rate in both region but the effect was great at the clear region than the porous medium region.
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Singh, Jitendra Kumar, i S. Vishwanath. "Hall and induced magnetic field effects on MHD buoyancy-driven flow of Walters’B fluid over a magnetised convectively heated inclined surface". International Journal of Ambient Energy, 8.04.2021, 1–10. http://dx.doi.org/10.1080/01430750.2021.1909652.
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Ahmed, Sameh E., i Anas A. M. Arafa. "3D MHD dusty nanofluid flow within cubic heterogeneous porous enclosures with hot and cold cylinders using non-homogeneous nanofluid model". Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering, 25.07.2022, 095440892211152. http://dx.doi.org/10.1177/09544089221115271.
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The heterogeneity of the porous medium properties is an important topic due to the important wide practical applications in the reservoir rocks and the petroleum reservoirs. This study aims to examine both the heterogeneity of the permeability, thermal conductivity and the nanofluid model on the dusty nanofluid within a three-dimensional cubic container. The convective transport is due to the buoyancy–driven flow resulting from two inner hot/cold cylinders separated by variable distance [Formula: see text]. The nanofluids are simulated by a non-homogeneous two phase model and the impact of a constant magnetic field in Z -direction is considered. Two systems of the governing equations are introduced for the dusty and nanofluid phase and the boundary conditions for the nanoparticle function are passively controlled. The major findings revealed that the flow structures can be well-controlled using the distance between the inner cylinders. Also, the heterogeneity in [Formula: see text] plane gives a higher rate of the heat transfer. Furthermore, the maximizing of the dusty parameter is better for enhancing the dusty temperature and velocities.
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"Chaos in geophysical fluids I. General introduction". Philosophical Transactions of the Royal Society of London. Series A: Physical and Engineering Sciences 348, nr 1688 (15.09.1994): 431–43. http://dx.doi.org/10.1098/rsta.1994.0102.
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Irregular buoyancy-driven flows occur in the atmospheres and fluid interiors of the Earth and other planets, and of the Sun and other stars, where they influence and often control the transfer of heat. Their presence is manifest in or implied by a wide variety of observed phenomena, including external magnetic fields generated by self-exciting magnetohydrodynamic (MHD ) dynamo action. Based on the laws of classical mechanics, thermodynamics and, in the case of electrically conducting fluids, electrodynamics, the governing mathematical equations are well known, but they are generally intractable owing to their essential nonlinearity. Computers play a key role in modern theoretical research in geophysical and astrophysical fluid dynamics, where ideas based on chaos theory are being applied in the analysis of models and the assessment of predictability. The aim of this paper is to provide a largely qualitative survey for non-specialists. The survey comprises two parts, namely a general introduction (Part I) followed by a discussion of two representative areas of research, both concerned with phenomena attributable to symmetry-breaking bifurcations caused by gyroscopic (Coriolis) forces (Part II), namely ( a ) large-scale waves and eddies in the atmospheres of the Earth, Jupiter and other planets (where, exceptionally, laboratory experiments have been influential), and ( b ) MHD dynamos. Various combinations of Faraday disc dynamos have been studied numerically as low-dimensional nonlinear electromechanical analogues of MHD dynamos, particularly in efforts to elucidate the complex time series of geomagnetic polarity reversals over geological time. The ability of the intensively studied Rikitake coupled disc dynamo system to behave chaotically appears to be a consequence of the neglect of mechanical friction, the inclusion of which renders the system structurally unstable.
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Tharakkal, Devika, Anvar Shukurov, Frederick A. Gent, Graeme R. Sarson, Andrew P. Snodin i Luiz Felippe S. Rodrigues. "Steady states of the Parker instability". Monthly Notices of the Royal Astronomical Society, 31.08.2023. http://dx.doi.org/10.1093/mnras/stad2610.
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Abstract We study the linear properties, nonlinear saturation and a steady, strongly nonlinear state of the Parker instability in galaxies. We consider magnetic buoyancy and its consequences with and without cosmic rays. Cosmic rays are described using the fluid approximation with anisotropic, non-Fickian diffusion. To avoid unphysical constraints on the instability (such as boundary conditions often used to specify an unstable background state), nonideal MHD equations are solved for deviations from a background state representing an unstable magnetohydrostatic equilibrium. We consider isothermal gas and neglect rotation. The linear evolution of the instability is in broad agreement with earlier analytical and numerical models; but we show that most of the simplifying assumptions of the earlier work do not hold, such that they provide only a qualitative rather than quantitative picture. In its nonlinear stage the instability has significantly altered the background state from its initial state. Vertical distributions of both magnetic field and cosmic rays are much wider, the gas layer is thinner, and the energy densities of both magnetic field and cosmic rays are much reduced. The spatial structure of the nonlinear state differs from that of any linear modes. A transient gas outflow is driven by the weakly nonlinear instability as it approaches saturation.
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Selimefendigil, Fatih, i Ali J. Chamkha. "Magnetohydrodynamics Mixed Convection in a Lid-Driven Cavity Having a Corrugated Bottom Wall and Filled With a Non-Newtonian Power-Law Fluid Under the Influence of an Inclined Magnetic Field". Journal of Thermal Science and Engineering Applications 8, nr 2 (8.03.2016). http://dx.doi.org/10.1115/1.4032760.
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In this study, the problem of magnetohydrodynamics (MHD) mixed convection of lid-driven cavity with a triangular-wave shaped corrugated bottom wall filled with a non-Newtonian power-law fluid is numerically studied. The bottom corrugated wall of the cavity is heated and the top moving wall is kept at a constant lower temperature while the vertical walls of the enclosure are considered to be adiabatic. The governing equations are solved by the Galerkin weighted residual finite element formulation. The influence of the Richardson number (between 0.01 and 100), Hartmann number (between 0 and 50), inclination angle of the magnetic field (between 0 deg and 90 deg), and the power-law index (between 0.6 and 1.4) on the fluid flow and heat transfer characteristics are numerically investigated. It is observed that the effects of free convection are more pronounced for a shear-thinning fluid and the buoyancy force is weaker for the dilatant fluid flow compared to that of the Newtonian fluid. The averaged heat transfer decreases with increasing values of the Richardson number and enhancement is more effective for a shear-thickening fluid. At the highest value of the Hartmann number, the averaged heat transfer is the lowest for a pseudoplastic fluid. As the inclination angle of the magnetic field increases, the averaged Nusselt number generally enhances.
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Foglizzo, Thierry, Rémi Kazeroni, Jérôme Guilet, Frédéric Masset, Matthias González, Brendan K. Krueger, Jérôme Novak i in. "The Explosion Mechanism of Core-Collapse Supernovae: Progress in Supernova Theory and Experiments". Publications of the Astronomical Society of Australia 32 (2015). http://dx.doi.org/10.1017/pasa.2015.9.
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AbstractThe explosion of core-collapse supernova depends on a sequence of events taking place in less than a second in a region of a few hundred kilometers at the centre of a supergiant star, after the stellar core approaches the Chandrasekhar mass and collapses into a proto-neutron star, and before a shock wave is launched across the stellar envelope. Theoretical efforts to understand stellar death focus on the mechanism which transforms the collapse into an explosion. Progress in understanding this mechanism is reviewed with particular attention to its asymmetric character. We highlight a series of successful studies connecting observations of supernova remnants and pulsars properties to the theory of core-collapse using numerical simulations. The encouraging results from first principles models in axisymmetric simulations is tempered by new puzzles in 3D. The diversity of explosion paths and the dependence on the pre-collapse stellar structure is stressed, as well as the need to gain a better understanding of hydrodynamical and MHD instabilities such as standing accretion shock instability and neutrino-driven convection. The shallow water analogy of shock dynamics is presented as a comparative system where buoyancy effects are absent. This dynamical system can be studied numerically and also experimentally with a water fountain. The potential of this complementary research tool for supernova theory is analysed. We also review its potential for public outreach in science museums.
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Prince, Hasib Ahmed, Md Mehrab Hossen Siam, Amit Ghosh i Mohammad Arif Hasan Mamun. "Application of Artificial Intelligence on Predicting the Effects of Buoyancy Ratio on MHD Double-Diffusive Mixed Convection and Entropy Generation in Different Nanofluids and Hybrid-Nanofluids". Journal of Thermal Science and Engineering Applications, 23.05.2023, 1–28. http://dx.doi.org/10.1115/1.4062613.
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Abstract The present computational investigation aims to investigate the effect of varied buoyancy ratio on mixed convection and entropy formation in a lid-driven trapezoidal enclosure under magnetic field with two rotating cylinders. The effects of SWCNT-water, Cu-water, and Al2O3-water nanofluids individually, as well as effects of three different types of SWCNT-Cu-Al2O3-water hybrid nanofluids are examined. The governing Navier-Stokes, thermal energy, and mass conservation equations are solved using the Galerkin weighted residual finite element method to obtain results as average Nusselt number, Sherwood number, temperature, and Bejan number as output parameters inside the enclosure for different parameter values. Then, an innovative artificial neural network model for effective prediction is created using the simulation data. The optimum values of each of these input parameters are obtained by FEM and ANN, and a comparative study between FEM and ANN is done to get best results for the output parameters. The performance of the created ANN model for novel scenarios is evaluated using Cu-Al2O3-water hybrid nanofluid. The proposed innovative ANN model predicts the findings with less time and sufficient accuracy for each type of studied governing fluids. The model's accuracy for predicting convective heat and mass transfer, along with average dimensionless temperature and Bejan number, was 96.81% and 98.74%, respectively, when tested on training and validation data. On test data, the accuracy was 97.03% for convective heat and mass transfer and 99.17% for average dimensionless temperature and Bejan number.
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Anee, Meratun Junnut, Sadia Siddiqa, Md Farhad Hasan i Md Mamun Molla. "Lattice Boltzmann simulation of natural convection of ethylene glycol-alumina nanofluid in a C-shaped enclosure with MFD viscosity through a parallel computing platform and quantitative parametric assessment". Physica Scripta, 12.07.2023. http://dx.doi.org/10.1088/1402-4896/ace704.
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Abstract The multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) was considered in this study to numerically analyse the effects of magnetic field dependent (MFD) viscosity on the natural convection of ethylene glycol (C$_2$H$_6$O$_2$)-alumina (Al$_2$O$_3$) nanofluid in a side heated two-dimensional C-shaped enclosure using graphics processing unit (GPU) by a computing unified device architecture (CUDA) C parallel computing platform. Numerical simulations were performed at multifarious Rayleigh numbers, Hartmann numbers, and the different magnetic field inclination angles to study the heat transfer and various flow patterns under magnetic field-dependent (MFD) viscosity. The numerical solutions were presented by varying volume fraction of nanoparticles, Rayleigh numbers, viscous parameters, magnetic inclination angles, and Hartman numbers on streamlines, isotherm, local and average Nusselt number and temperature. Further correlation developments were conducted through Levenberg-Marquardt data-driven algorithm to investigate the influence of all the parameters on average Nusselt numbers, entropy generation, and fluid irreversibility parameter. The findings demonstrated that as the Rayleigh numbers augmented, the average Nusselt number increased significantly due to the influence of buoyancy, whereas under the influence of Hartmann numbers, average Nusselt numbers decreased due to the dominance of magnetic field strength and Lorentz force. However, the heat transfer continued to improve if the concentration of the nanoparticles increased, thus showcasing the importance of hybrid nanofluid. In addition, the entropy generation impact across the cavity for the ethylene glycol-alumina nanofluid was greatly enhanced by a stronger buoyancy influence. The findings from this study provide major evidence that the inclusion of nanofluid can be a great alternative fluid to improve the heat transfer efficiency under the influence of magnetic field strength, which can be implemented and further investigated in electronic cooling system and chip designing industry which extensively work with C-shaped equipment.