Hydrodynamic State Research Articles

Theoretical Model and Experimental Research on Friction and Torque Characteristics of Hydro-viscous Drive in Mixed Friction Stage

The hydro-viscous drive (HVD) has been widely used in fan transmission in vehicles, fans, and scraper conveyors for step-less speed regulation or soft starting. In the mixed friction stage, the contact, friction, and torque characteristics of friction pairs are very complex and change at any time. The characteristics of the frictional and hydrodynamic lubrication states were studied in order to calculate and predict the friction and torque characteristics of the friction pairs in the mixed friction stage. The fluid torque was calculated by applying the average shear stress model and the load-carrying capacity of asperity was determined on the basis of the fractal contact theory. In addition, the contact friction coefficient of the friction pairs was taken into consideration and measured by using the MM1000-III friction and wear testing machine. The asperity friction torque and total torque in the mixed friction stage were obtained and finally, the test rig for the torque characteristics was set up. The results show that the contribution to the total torque is shared by the oil film and the asperity friction. The friction coefficient decreases sharply at first and then increases with a change in the relative rotational speed, following the Stribeck curve closely, and the contact frictional coefficient slowly decreases with increase in the pressure between the friction pairs. The torque between the friction pairs is provided by the asperity friction, and the torque due to the oil film reduces to zero. When the thickness of the oil film is small, a major contribution to the total torque is due to the asperity friction. The total torque also increases with the decrease in the film thickness ratio. Therefore, by theoretical analysis and experimental verification, the torque of the friction pairs in the mixed friction stage can be accurately calculated using the average shear stress model and asperity friction torque model.

Interaction of linear modulated waves and unsteady dispersive hydrodynamic states with application to shallow water waves

A new type of wave–mean flow interaction is identified and studied in which a small-amplitude, linear, dispersive modulated wave propagates through an evolving, nonlinear, large-scale fluid state such as an expansion (rarefaction) wave or a dispersive shock wave (undular bore). The Korteweg–de Vries (KdV) equation is considered as a prototypical example of dynamic wavepacket–mean flow interaction. Modulation equations are derived for the coupling between linear wave modulations and a nonlinear mean flow. These equations admit a particular class of solutions that describe the transmission or trapping of a linear wavepacket by an unsteady hydrodynamic state. Two adiabatic invariants of motion are identified that determine the transmission, trapping conditions and show that wavepackets incident upon smooth expansion waves or compressive, rapidly oscillating dispersive shock waves exhibit so-called hydrodynamic reciprocity recently described in Maiden et al. (Phys. Rev. Lett., vol. 120, 2018, 144101) in the context of hydrodynamic soliton tunnelling. The modulation theory results are in excellent agreement with direct numerical simulations of full KdV dynamics. The integrability of the KdV equation is not invoked so these results can be extended to other nonlinear dispersive fluid mechanic models.

Automatic control scheme development for process of sulfatizing roasting of iron-manganese concretions in fluidized bed

The article describes the problem of regulating the process of sulfatizing roasting in a fluidized bed (FB) furnace of an enlarged laboratory facility for processing iron-manganese concretions (IMC) together with pyrite concentrate in a continuous mode. The features of roasting in the fluidized bed and technological factors affecting the control process and, as a consequence, the quality indicators of the technology are considered. The results of large-scale laboratory studies on a continuous installation of a FB controlled in manual mode are given. There is a scheme of adaptive automatic control of the roasting process in the FB with regulation of feed charge components. It allows maintaining a stable hydrodynamic state of the fluidized bed and control of key parameters, such as granulometric composition of the cinder, dust removal from the FB, blast pressure, temperature, etc., affecting the sulfatization of IMC metals.

Diel Vertical Migrations of Hydrobionts in the Coastal Area of Lake Baikal

The nocturnal migratory complex (NMC) is formed in the coastal pelagic zone of seas and large lakes (including Lake Baikal) due to the diurnal vertical migrations of benthic animals and their mixing with pelagic hydrobionts. Studies of the structure and abundance of the NMC are performed using plankton nets and video surveillance in several areas of Lake Baikal different in abiotic conditions (water temperature, hydrodynamic state, and underwater landscapes) and thus characterized by the local specificity. When NMCs were observed with artificial lighting, the number of amphipods in the frame increased during the first several minutes and then usually slightly decreased. The expediency of applying underwater video observations of NMCs in environmental monitoring is recognized and appropriate guidelines are given.

Quantum Group Symmetry for Kaleidoscope of Hydrodynamic Images and Quantum States

The hydrodynamic flow in several bounded domains can be formulated by the image theorems, like the two circle, the wedge and the strip theorems, describing flow by q-periodic functions. Depending on geometry of the domain, parameter q has different geometrical meanings and values. In the special case of the wedge domain, with q as a primitive root of unity, the set of images appears as a regular polygon kaleidoscope. By interpreting the wave function in the Fock-Barman representation as complex potential of a flow, we find mod n projection operators in the space of quantum coherent states, related with operator q-numbers. They determine the units of quantum information as kaleidoscope of quantum states with quantum group symmetry of the q-oscillator. Expansion of Glauber coherent states to these units and corresponding entropy are discussed.

Experimental measurements of bubble size distributions in a water model and its influence on the aluminum kinetics degassing

ABSTRACTAn experimental study of the gas‐liquid dynamics in a water model of an aluminum ladle was conducted. The rotor degassing performance was evaluated for two commercial rotor‐injector devices compared to a new rotor design. In this work, the influence of the turbulent properties of the flow fields on the bubble size distribution is analyzed for a better understanding of its impact on the degassing efficiency in aluminum refinement operations. The degassing process was analyzed by two different methods: (a) a high‐speed camera was used to obtain the bubble size distribution into the container; and (b) the particle image velocimetry technique (PIV) was employed to obtain the liquid flow properties. It was found that the rotor geometry plays an important role on the average size and distribution of the bubbles. The energy dissipation rate contours show significant differences for the distinct rotors tested. These hydrodynamic states and bubbles distribution dominate the kinetic and efficiency of the degassing processes. It was shown that the new rotor configuration enhances the degassing kinetics, due to a more suitable bubble dispersion compared to the commercial rotors tested.

Quantifying hydrodynamic collective states of magnetic colloidal spinners and rollers

This work expands the scope of modern computational tools for predictive modeling of microscopic active systems, and provides insight into the intricate role of hydrodynamic interaction on the onset of collective behavior of living and synthetic active matter.

Magnonic Band Structure Established by Chiral Spin-Density Waves in Thin-Film Ferromagnets

Recent theoretical studies have demonstrated the possibility to excite and sustain noncollinear magnetization states in ferromagnetic nanowires. The resulting state is referred to as a spin-density wave (SDW). SDWs can be interpreted as hydrodynamic states with a constant fluid density and fluid velocity in systems with easy-plane anisotropy. Here, we consider the effect of the nonlocal dipole field arising from the finite thickness of magnetic thin films on the spatial profile of the SDW and on the associated magnon dispersion. Utilizing a hydrodynamic formulation of the Larmor torque equation, it is found that the nonlocal dipole field modulates the fluid velocity. Such a modulation induces a magnonic band structure unlike the typical dispersion relation for magnons on uniform magnetization. The analytical results are validated by micromagnetic simulations. Band gaps on the order of gigahertz are numerically observed to depend on the SDW fluid velocity and film thickness for realistic material parameters. The presented results suggest that SDWs can find applications as reconfigurable magnonic crystals.

Elastic hydrodynamic lubrication analysis for a sine movable tooth drive

The sine movable tooth drive has small radial dimension such that the heat, caused by friction, becomes an important factor in deciding its load-carrying ability. It is important to determine the amount of tooth lubrication in order to reduce the heat caused by the friction. This study provides equations for the meshing performance and provides the forces for the sine movable tooth drive. Using these equations, the minimum oil film thickness for the drive system is investigated. Results show that the minimum film thickness between the movable tooth and input shaft or shell changes periodically along the input shaft rotation angle. A large movable tooth radius and a movable tooth rotation radius could increase the film thickness between the movable tooth and the input shaft or the shell. In addition, a large speed ratio could increase the film thickness between the movable tooth and the input shaft, but this would also decrease the film thickness between the movable tooth and the shell. A large sine amplitude could increase the film thickness between the movable tooth and the input shaft, but this does not change the film thickness between the movable tooth and the shell. Under normal operation speeds, the hydrodynamic lubrication condition occurs between the movable tooth and the input shaft, and the partial membrane hydrodynamic state occurs between the movable tooth and the shell.

HerEOS: A framework for consistent treatment of the Equation of State in ALE hydrodynamics

We propose a general methodology and practical implementation of arbitrary Equations of State (EOS) evaluation for Lagrangian and ALE hydrodynamic simulations. This approach is based on higher-order interpolations of the Helmholtz free energy (HFE) and derived quantities. We also discuss several pitfalls related to thermodynamic consistency, physical relevance and robustness of the EOS calculations and demonstrate them for realistic values of temperature and density. The developed library HerEOS has been tested and used in various hydrodynamic codes for practical laser plasma simulations, some of which are presented here.

Axial mixing and vortex stability to in situ radial injection in Taylor–Couette laminar and turbulent flows

Taylor–Couette flows have been widely studied in part due to the enhanced mixing performance from the variety of hydrodynamic flow states accessible. These process improvements have been demonstrated despite the traditionally limited injection mechanisms from the complexity of the Taylor–Couette geometry. In this study, using a newly designed, modified Taylor–Couette cell, axial mass transport behaviour is experimentally determined over two orders of magnitude of Reynolds number. Four different flow states, including laminar and turbulent Taylor vortex flows and laminar and turbulent wavy vortex flows, were studied. Using flow visualization techniques, the measured dispersion coefficient was found to increase with increasing $Re$, and a single, unified regression is found for all vortices studied. In addition to mass transport, the vortex structures’ stability to radial injection is also quantified. A dimensionless stability criterion, the ratio of injection to diffusion time scales, was found to capture the conditions under which vortex structures are stable to injection. Using the stability criterion, global and transitional stability regions are identified as a function of Reynolds number, $Re$.

Hydrodynamic spin states.

We present the results of a theoretical investigation of hydrodynamic spin states, wherein a droplet walking on a vertically vibrating fluid bath executes orbital motion despite the absence of an applied external field. In this regime, the walker's self-generated wave force is sufficiently strong to confine the walker to a circular orbit. We use an integro-differential trajectory equation for the droplet's horizontal motion to specify the parameter regimes for which the innermost spin state can be stabilized. Stable spin states are shown to exhibit an analog of the Zeeman effect from quantum mechanics when they are placed in a rotating frame.

Dynamic characteristics of composite tilting pad journal bearing for turbine/generator applications

Tilting pad journal bearings have been employed for turbine, compressor, pump, and generator applications owing to their high loading capacity, excellent stability, and service durability at high operation speed compared to conventional journal bearings. For high-speed and high-performance applications, tilting pad journal bearings should reduce the rotor vibration. Therefore, the bearings are designed to have excellent damping characteristics. In this study, composite tilting pad journal bearings consisting of carbon fiber/epoxy composites and a backup metal are fabricated to increase the dynamic performance and durability. A modal analysis is performed to investigate dynamic stability of the composite tilting pad. Moreover, the damping coefficient of fluid film, oil film pressure, and orbit of rotor are calculated with respect to the liner materials under a hydrodynamic lubrication state. To verify the analysis results, hydrodynamic lubrication tests of composite and white metal tilting pad journal bearings are conducted using an industrial test bench. As a result, the composite tilting pad journal bearing has effectively reduced the rotor vibration and increased the stability and durability of the bearing system compared to the white metal tilting pad journal bearing.

Solitonic Dispersive Hydrodynamics: Theory and Observation.

Ubiquitous nonlinear waves in dispersive media include localized solitons and extended hydrodynamic states such as dispersive shock waves. Despite their physical prominence and the development of thorough theoretical and experimental investigations of each separately, experiments and a unified theory of solitons and dispersive hydrodynamics are lacking. Here, a general soliton-mean field theory is introduced and used to describe the propagation of solitons in macroscopic hydrodynamic flows. Two universal adiabatic invariants of motion are identified that predict trapping or transmission of solitons by hydrodynamic states. The result of solitons incident upon smooth expansion waves or compressive, rapidly oscillating dispersive shock waves is the same, an effect termed hydrodynamic reciprocity. Experiments on viscous fluid conduits quantitatively confirm the soliton-mean field theory with broader implications for nonlinear optics, superfluids, geophysical fluids, and other dispersive hydrodynamic media.

The Numerical Simulation of the Shock Wave of Coal Gas Explosions in Gas Pipe*

For the problem of large deformation and vortex, the method of Euler and Lagrange has both advantage and disadvantage. In this paper we adopt special fuzzy interface method(volume of fluid). Gas satisfies the conditions of conservation equations of mass, momentum, and energy. Based on explosion and three-dimension fluid dynamics theory, using unsteady, compressible, inviscid hydrodynamic equations and state equations, this paper considers pressure gradient’s effects to velocity, mass and energy in Lagrange steps by the finite difference method. To minimize transport errors of material, energy and volume in Finite Difference mesh, it also considers material transport in Euler steps. Programmed with Fortran PowerStation 4.0 and visualized with the software designed independently, we design the numerical simulation of gas explosion with specific pipeline structure, check the key points of the pressure change in the flow field, reproduce the gas explosion in pipeline of shock wave propagation, from the initial development, flame and accelerate the process of shock wave. This offers beneficial reference and experience to coal gas explosion accidents or safety precautions.

QGP Hydrodynamics to Tap Energy from Vacuum as Blackhole Analogues with Energy from Extra Dimension Vector Potential

It is possible to use QGP hydrodynamic state equivalents of blackhole centers as energy sources based on vacuum vector potential with charged quantum mechanical sources through inputs from extra dimension compact space fields. The space like regions are entangled with time like regions, as possibly a gravity interpretation of quantum state of superposition in extra dimension of compact space energy field, viewed in a gauge theory/gravity duality context. The QGP Hydrodynamic effects can cause temporal entanglement entropy which can be lost to 4-D vacuum space, quantum mechanically. The AdS/CFT correspondence as a familiar case of holographic principle can cause threshold thermal phase transitions as nuclear matter and radiation dense domains based on quantum state decoherence and information loss. The AdS space time could be decoupled at blackhole centers as entropy is transferred from interiors due to QGP hydrodynamic state. The Hawking radiation represents decay process and loss which indicates possibilities for tapping energy from vacuum, based on QGP fluids.

In situ polymer flocculation and growth in Taylor-Couette flows.

Flocculation of small particulates suspended in solution is a key process in many industries, including drinking water treatment. The particles are aggregated during mixing to form larger aggregates, known as flocs, through use of a polyelectrolyte flocculant. The flocculation of these particulates in water treatment, however, are subject to a wide spatial variation of hydrodynamic flow states, which has consequences for floc size, growth rate, and microstructure. Floc assembly dynamics are explored here using a commercially available cationic polyacrylamide, commonly used in water treatment, and anisotropic Na-bentonite clay particles under a variety of hydrodynamic mixing conditions. A Taylor-Couette cell with the unique ability to radially inject fluid into the rotating annulus was used to study how specific hydrodynamic flow fields affect assembly and structure of these materials during the flocculation process. Faster floc growth rates and decreased floc fractal dimensions were observed for higher order flow states, indicating improved mass transfer of the polymer flocculant and breakage at the edges of the flocs (shear rounding), respectively. This work sheds more light on the complexities of polymer-induced flocculation, towards improving dosing and efficiency of large-scale operations.

Fluidization of Nanoparticle Agglomerates at Elevated Temperatures

The behavior of hydrophobic and hydrophilic nanoparticles was investigated. In a novel approach, the interparticle force (IPF) was altered by changing the temperature of the gas–solid fluidized bed in the range 25–110 °C. The hydrodynamic state of the bed was monitored by examining pressure fluctuations using coherent and incoherent analysis. Formation, coalescence, eruption, and mobility of bubbles in the fluidized bed were determined in addition to investigating the behavior of agglomerates. The diameter of the agglomerate was calculated from the incoherent output of the power spectral density of pressure fluctuations in the agglomerate particulate fluidization (APF) regime at various temperatures. No bubbles were detected in the bed of the silica nanopowder at low temperatures whereas small bubbles form at higher temperature. In contrast, hydrophilic titania nanopowder becomes fluidized in the ABF regime at lower temperatures and tends to fluidize at the APF regime with increasing bed temperature.

Recent Coastal Geomorphological Evolution in the Negro River's Mouth (41°S), Argentinean Patagonia

ABSTRACT Vergara Dal Pont, I.P.; Caselli, A.T.; Moreiras, S.M., and Lauro, C., 2017. Recent coastal geomorphological evolution in the Negro River's mouth (41°S), Argentinean Patagonia. This paper analyzes the geomorphological evolution of the Negro River's mouth to understand how aerodynamic and hydrodynamic states of the Atlantic coast have developed to this date. Accordingly, the morphometry of the beach and the historical river flow record were studied. The results indicate a dichotomous state for this coast. The SW area is characterized by cliffs with an average recession rate of 0.69 m/y during the 1959–2011 period, whereas the NE area is characterized by beaches in stable and accretion states. In the latter zone, a relatively fast coastal accretion was corroborated with the advance of a berm of up to 170 m between 1986 and 2014; furthermore, the beach extension grew to 760 m during 1986–2004. Since 1936, a completely new phenomenon was observed at the Negro River's mouth: the displacement and accret...

On the hydrodynamic and magnetohydrodynamic stability of an inclined layer heated from below

In this paper we investigate the stability of either the rest state (Bénard problem) or parallel laminar flows in hydrodynamics and magnetohydrodynamics for inclined layers heated from below. In particular, we numerically investigate the linear instability under general three-dimensional perturbations of the basic state, and we also give conditions for the nonlinear stability. For particular basic states, a linear instability analysis shows that the critical Rayleigh numbers can be obtained for longitudinal perturbations (which can be studied analytically both, in the linear and nonlinear case) or for transversal perturbations depending on the inclination of the layer (and of course also on the velocity of the boundaries and the applied magnetic field). Remarkable is the presence of points of codimension-two: particular values of the critical Rayleigh numbers obtained for specific angles of inclination for which there exist two equally destabilising perturbations, one longitudinal and the other transversal.