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1.
The main objective of this article is to study the effect of spherical geometry on dynamic transitions and pattern formation for the Rayleigh-Bénard convection. The study is mainly motivated by the importance of spherical geometry and convection in geophysical flows. It is shown in particular that the system always undergoes a continuous (Type-I) transition to a 2l c -dimensional sphere ${S^{2l_c}}$ , where l c is the critical wave number corresponding to the critical Rayleigh number. Furthermore, it has shown in Ma and Wang (Physica D 239:3–4, 167–189, 2010) that it is critical to add nonisotropic turbulent friction terms in the momentum equation to capture the large-scale atmospheric and oceanic circulation patterns. We show in particular that the system with turbulent friction terms added undergoes the same type of dynamic transition, and obtain an explicit formula linking the critical wave number (pattern selection), the aspect ratio, and the ratio between the horizontal and vertical turbulent friction coefficients. 相似文献
2.
This paper points out the former work does not fulfill the boundaryconditions that the concentrated force at the four corner points should notexist.Therefore,Ritz method adopted by the author concerned in the illus-trative example will not be convergent in the best way.Moreover,Garlerkinmethod which is illustrated in this paper may carry out incorrect results ifwe apply its formulae.We have proved that the boundary conditions whichgovern the concentrated force equal to zero at the four corner points areindispensable if the problem is properly set. 相似文献
3.
This paper points out the former work does not fulfill the boundary conditions that the concentrated force at the four corner points should not exist. Therefore, Ritz method adopted by the author concerned in the illustrative example will not be convergent in the best way. Moreover, Garlerkin method which is illustrated in this paper may carry out incorrect results if we apply its formulae. We have proved that the boundary conditions which govern the concentrated force equal to zero at the four corner points are indispensable if the problem is properly set. 相似文献
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5.
Sathish Gurupatham Bhavin Dalal Md.Shahadat Hossain Ian S.Fischer Pushpendra Singh Daniel D.Joseph 《中国颗粒学报》2011,9(1)
This paper is concerned with the dispersion of particles on the fluid-liquid interface. In a previous study we have shown that when small particles, e.g., flour, pollen, glass beads, etc., contact an air-liquid interface, they disperse rapidly as if they were in an explosion. The rapid dispersion is due to the fact that the capillary force pulls particles into the interface causing them to accelerate to a large velocity. In this paper we show that motion of particles normal to the interface is inertia domin... 相似文献
6.
The condensation heat transfer of the ethanol–water mixtures on the vertical tube over a wide range of ethanol concentrations
was investigated. The condensation curves of the heat flux and the heat transfer coefficients revealed nonlinear characteristics
and had peak values, with respect to the change of the vapor-to-surface temperature difference. This characteristic applies
to all ethanol concentrations under all experimental conditions. With the decrease of the ethanol concentrations, the condensation
heat transfer coefficient increased notably, especially when the ethanol concentration was very low. The maximum heat transfer
coefficient of the vapor mixtures increased to 9 times as compared with that of pure steam at ethanol vapor mass concentration
of 1%. With the increase of the ethanol concentrations, the condensation heat transfer coefficient decreased accordingly.
When the ethanol concentration reached 50%, the heat transfer coefficient was smaller than that of the pure steam. 相似文献
7.
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8.
Wolfgang A. Wall Peter Gamnitzer Axel Gerstenberger 《International Journal of Computational Fluid Dynamics》2013,27(6):411-427
This paper presents two domain decomposition techniques for fixed grid fluid–structure interaction simulations that can be applied to the interaction of general structures with incompressible flows. One approach is based on an overlapping domain decomposition idea while the other uses non-overlapping domains. The first technique combines a fixed grid Chimera approach with arbitrary Lagrangean Eulerian based methods, the second one is based on an eXtended Finite Element Method (XFEM) strategy. Both techniques are used in a partitioned and strong coupling fluid–structure framework. The usage of such fixed-grid methods considerably increases the range of possible applications. Several test examples demonstrate key features of both methods. 相似文献
9.
《中国颗粒学报》2005,3(3):196-196
Professor Fengsheng Li of the Nanjing University of Science and Technology has been working in the field of superfine powders for many years, and at the turn of the century he started to write a series of monographs, now five, on the technology ofsuperfine powders including their preparation, measurement and application, andranging from catalysts through medicines and cosmetics to pyrotechnics. 相似文献
10.
《Particuology》2022
Effects of some important structural parameters, i.e. slat pitch, and layout position, on dynamic forces acting on the baffles were examined in the fluidized bed of FCC particles operating under different superficial gas velocities. The experimental baffles were made of multiple inclined slats. We found that the forces acting on the baffles decreased significantly with reducing pitch between the slats. For the baffles with a small slat pitch, the forces acting on the baffles increased slightly and then decreased with increasing superficial gas velocity, which is very different from the measured results of a single slat or tube immersed in fluidized beds. The different results are greatly related to the appearance of the “gas cushion” beneath the baffles, whose height increases with increasing superficial gas velocity. On the other hand, a region with stronger particle circulation induced by the inclined slat array was observed in the experiments. The slat near the wall and located below the region of downward-flowing particles was found to be subjected to the severest forces. Therefore, the slats located in similar locations of industrial baffles are suggested to be reinforced to increase their structural strength. 相似文献
11.
This paper is motivated by the works of Dickinson et al. (Science 284:1954–1960, 1999) and Sun and Tang (J Exp Biol 205:55–70, 2002) which provided two different perspectives on the influence of wing–wake interaction (or wake capture) on lift generation
during flapping motion. Dickinson et al. (Science 284:1954–1960, 1999) hypothesize that wake capture is responsible for the additional lift generated at the early phase of each stroke, while Sun
and Tang (J Exp Biol 205:55–70, 2002) believe otherwise. Here, we take a more fundamental approach to study the effect of wing–wake interaction on the aerodynamic
force generation by carrying out simultaneous force and flow field measurements on a two-dimensional wing subjected to two
different types of motion. In one of the motions, the wing at a fixed angle of attack was made to follow a motion profile
described by “acceleration-constant velocity-deceleration”. Here, the wing was first linearly accelerated from rest to a predetermined
maximum velocity and remains at that speed for set duration before linearly decelerating to a stop. The acceleration and deceleration
phase each accounted for only 10% of the stroke, and the stroke covered a total distance of three chord lengths. In another
motion, the wing was subjected to the same above-mentioned movement, but in a back and forth manner over twenty strokes. Results
show that there are two possible outcomes of wing–wake interaction. The first outcome occurs when the wing encounters a pair
of counter-rotating wake vortices on the reverse stroke, and the induced velocity of these vortices impinges directly on the
windward side of the wing, resulting in a higher oncoming flow to the wing, which translates into a higher lift. Another outcome
is when the wing encounters one vortex on the reverse stroke, and the close proximity of this vortex to the windward surface
of the wing, coupled with the vortex suction effect (caused by low pressure region at the center of the vortex), causes the
net force on the wing to decrease momentarily. These results suggest that wing–wake interaction does not always lead to lift
enhancement, and it can also cause lift reduction. As to which outcome prevails depend very much on the flapping motion and
the timing of the reverse stroke. 相似文献
12.
The pseudoplastic flow of suspensions, alumina or styrene-acrylamide copolymer particles in water or an aqueous solution of glycerin has been studied by the step-shear-rate method. The relation between the shear rate,D, and the shear stress,, in the step-shear-rate measurements, where the state of dispersion was considered to be constant, was expressed as = AD
1/2 +CD. The effective solid volume fraction,ø
F, andA were dependent on the shear rate and expressed byø
F =aD
b andA = D
. Combining the above relations, the steady flow curve was expressed by = D
1/2 + +
0 (1 – a D
b/0.74)–1.85
D, where
0 is the viscosity of the medium.With an increase in solid volume fraction and a decreases in the absolute value of the-potential, the flow behavior of the suspensions changed from Newtonian ( = = b = 0), slightly pseudoplastic ( = b = 0), pseudoplastic ( = 0) to a Bingham-like behavior.The change in viscosity of the medium had an effect on the change in the effective volume fraction. 相似文献
13.
《中国颗粒学报》2003,1(6):273-274
Need for Energy Utilization of Biomass in China China is on the way to be the most important energy market of the world. Economic growth and improvement in peo-ple抯 livelihood are leading to enormous increases in energy consumption. In view of the mainly coal dominated structure of the energy supply in China, however, this growth not only leads to increasing pressure on the available resources, but also possesses long-range effects on matters of the environment. At present, the national en… 相似文献
14.
Theoretical aspects of variational data assimilation (VDA) for a simple model with both global and local observational data are discussed. For the VDA problems with global observational data, the initial conditions and parameters for the model are revisited and the model itself is modified. The estimates of both error and convergence rate are theoretically made and the validity of the method is proved. For VDA problem with local observation data, the conventional VDA method are out of use due to the ill-posedness of the problem. In order to overcome the difficulties caused by the ill-posedness, the initial conditions and parameters of the model are modified by using the improved VDA method, and the estimates of both error and convergence rate are also made. Finally, the validity of the improved VDA method is proved through theoretical analysis and illustrated with an example, and a theoretical criterion of the regularization parameters is proposed. 相似文献
15.
Latifa Debbi 《Journal of Mathematical Fluid Mechanics》2016,18(1):25-69
In this work, we introduce and study the well-posedness of the multidimensional fractional stochastic Navier–Stokes equations on bounded domains and on the torus (briefly dD-FSNSE). For the subcritical regime, we establish thresholds for which a maximal local mild solution exists and satisfies required space and time regularities. We prove that under conditions of Beale–Kato–Majda type, these solutions are global and unique. These conditions are automatically satisfied for the 2D-FSNSE on the torus if the initial data has H 1-regularity and the diffusion term satisfies growth and Lipschitz conditions corresponding to H 1-spaces. The case of 2D-FSNSE on the torus is studied separately. In particular, we established thresholds for the global existence, uniqueness, space and time regularities of the weak (strong in probability) solutions in the subcritical regime. For the general regime, we prove the existence of a martingale solution and we establish the uniqueness under a condition of Serrin’s type on the fractional Sobolev spaces. 相似文献
16.
Zheng Xu Xiaozheng Yu Zhigang Shen 《中国颗粒学报》2007,5(5):345-350
Magnetron sputtering was used to coat various metals on micropowder surfaces. By using this method, the fine particles are better dispersed and can therefore be coated more homogeneously. The micro-powders used include cenospheres from fly ash of coal-burning electric power plants (diameter 40-200 μm and particle density 0.7 ± 0.1 g/cm^3), as well as carborundum particles of different sizes. Aluminum, silver, copper, cobalt and nickel were used as the coating metals. Tests showed that the coated metal film was compact adhering tightly on the base powders, and the coated powders possess adequate flow properties. 相似文献
17.
Xuecheng Wu Kefa Cen Zhongyang Luo Qinhui Wang Mengxiang Fang 《Experiments in fluids》2008,45(6):1117-1128
When a two-dimensional (2D) imaging system is used to visualize particle motion in a 3D gas–solid flow, the particle rotation
speed was found extremely difficult to be accurately measured due to the fact that the direction of rotation axis was usually
random and hard to be distinguished. The paper presents a method to calculate the particle rotation speed from particle images
based on the identification of its rotation axis using two or more characteristic points on its surface. The idea was analyzed
and realized in a mathematical way and based on which a calculation program was given. The measurement method was verified
with an experiment using a small sphere with known rotation axis and rotation speed. The effects of several factors, including
the direction of the particle rotation axis, the particle image resolution, the types and positions of characteristic points,
etc., on the measurement error are discussed. The error is found to be acceptable for most cases. The measurement method was
finally applied to those small glass beads in a real 3D gas–solid flow inside a cold circulating fluidized bed (CFB) riser,
which indicates that the problems of 2D imaging system applying to 3D particulate system could be solved by using this mathematical
method. 相似文献
18.
Zhang Rongye 《应用数学和力学(英文版)》1996,17(8):751-764
In this paper we discuss Newtonian Mechanics on Kahler Manifold, and also givefoe complex mathematical aspects of Newton’s law, the law of kinetic energy, the lawof kinetic quantity,the equation of motion and the "general equation of dynamics",and so on. 相似文献
19.
Nonlinear Dynamics - Piezoelectric ceramic actuators show nonlinear hysteresis characteristics due to material properties. In order to modify the inverse piezoelectric effect as an ideal linear... 相似文献
20.
Cables of cable-stayed bridges may vibrate with large amplitude under wind and rain, which is known as rain–wind induced vibration (RWIV). According to the pervious researches, the formations and oscillations of rivulets on stay cable surface play important roles in RWIV. In this paper, four different 2D models are presented based on lubrication theory, and the best way of simulating RWIV through lubrication theory is confirmed by the comparisons of rivulet motions and cable vibration responses between these four models and pervious researches. On this basis, the relations among rivulet motions, cable aerodynamic forces and vibration responses are investigated to reveal the mechanism of RWIV. Numerical simulation results show that when RWIV occurs, the periodic oscillations of rivulets around cable lead to the periodic fluctuations of cable lift and drag, whose frequencies are almost equal and close to cable natural frequency. Under the periodically fluctuant lift and drag, cable vibrates with large amplitude in across-wind and along-wind directions, which may further enhance the circumferential oscillations of rivulets conversely. These confirm the conclusion that the resonance between rivulets and cable oscillation may be one of the main reasons for RWIV. 相似文献