We discuss a novel instability in inertia-less electron **magneto**-**hydrodynamics** (EMHD), which arises from a combination of electron velocity shear and electron density gradients. The unstable modes have a lengthscale longer than the transverse density scale, and a growth-rate of the order of the inverse Hall timescale. We suggest that this density-shear instability may be of importance in magnetic reconnection re- gions on scales smaller than the ion skin depth, and in neutron star crusts. We demonstrate that the so-called Hall drift instability, previously argued to be relevant in neutron star crusts, is a resistive tearing instability rather than an instability of the Hall term itself. We argue that the density-shear instability is of greater significance in neutron stars than the tearing instability, because it generally has a faster growth- rate and is less sensitive to geometry and boundary conditions. We prove that, for uniform electron density, EMHD is “at least as stable” as regular, incompressible MHD, in the sense that any field configuration that is stable in MHD is also stable in EMHD. We present a connection between the density-shear instability in EMHD and the **magneto**-buoyancy instability in anelastic MHD.

25 Read more

The objective of the project is to develop electricity from moving speed boat in sea water. This can be achieved by using **magneto** **hydrodynamics** generator attached to the outlet nozzle of the jet ump inside speed boat. When salt water flows through the MHD setup, EMF is induced in the electrodes which can be further stored in batteries. By this electric energy is regenerated from speed boats. The kinetic energy of flowing sea water to again generate electricity using MHD generator called as regeneration. The force of seawater from the speed boats is too high. It has high thrust force to drive the whole boat at full knots.

With the rapid development of modern equipment machines, the increasing use of fluids containing microstructures such as additives, suspensions and long- chained polymers has received great attention. The porous squeeze film technology plays an important role in many areas of engineering practice and applied science. Due to the change of temperature, an unexpected variation of lubricant viscosity occurs. To prevent this, an increasing use of an electrically conducting fluid as the lubricant with an external magnetic field has become of common interest. In the presence of an external magnetic fluid, the load- carrying capacity of **Magneto**-**hydrodynamics** (MHD) porous squeeze films is increased.

13 Read more

The study of flows in convergent-divergent channel is very important due to its industrial, aerospace, chemical, civil, environmental, mechanical and biomechanical engineering applications. Various applications of this type of mathematical model are to understand the flow of rivers and canals and the blood flow in the human body. Jeffery [1] and Hamel [2] first studied the two- dimensional steady motion of a viscous fluid through convergent-divergent channels which is called classical Jeffery-Hamel flow in fluid dynamics. Later, this problem has been extensively studied by various researchers. A survey of information on this problem can be found in [3]. The theory of **Magneto**- **hydrodynamics** (MHD) is inducing current in a moving conductive fluid in the presence of magnetic field; such induced current results force on ions of the conductive fluid. The theoretical study of MHD channel has been a subject of great interest due to its extensive applications in designing cooling systems with liquid metals, MHD generators, accelerators, pumps, and flow meters [4, 5].

Jaw-Ren Lin and Rong-Fang Lu. 2010. Dynamic characteristics for **magneto**-hydrodynamic wide slider bearings with an exponential film profile. Journal of Marine Science and Technology. 18: 268-276. Sundarammal K. Ali. J. Chamkha and Santhana Krishnan N. 2014. MHD squeeze film characteristics between porous parallel rectangular plates with surface roughness. International Journal of Numerical methods for heart and fluid flow. 24(7): 1595-1609.

where h c is the central minimum film thickness and k is the curved shape parameter. Assume that the thin film lubrication theory as Hamrock[3] is applicable and the induced magnetic field is small when comparing with the magnetic field. Following the MHD flow equation of Lin [6] and thestokesmicrocontinuum theory [10], the **Magneto**-hydrodynamic Non-Newtonian (MHNN) couple stress momentum equations and the continuity equation can be expressed in axially cylindrical coordinates as follows:

11 Read more

Natural Over the last several decades, mixed convection heat transfer has received considerable attention by researchers and scholars. Natural and Mixed convection has many engineering application such as cooling of electronic components, energy conservation, electronic packaging, printing and printing process, material processing etc. Moallemi and Jang [1] studied numerically mixed convection flow in a bottom heated square lid driven enclosure andanalyzed the effect of Prandtl number on the flow and heat transfer process. They obtained that the effects of buoyancy are more effective for higher values of Prandtl number. Shahidul et al. [2] conducted a numerical study on mixed **magneto** convection in a lid driven square enclosure with a sinusoidal vertical wall and joule heating. He

Attia et al. [5] studied the heat transfer effect in Couette flow under pressure gradient along with Hall current. Hossain, et al. [6] have analyzed flow of viscous incompressible fluid over a permeable wedge with uniform heat flux. Chemical reaction on unsteady **magneto**- **hydrodynamics** was studied by Mythreye et al. [7]. They used perturbation technique to solve the governing equations. Cowling [8] studied Magnetohydrodynamics. Rajput and Kanaujia

12 Read more

chemically reactive species in a laminar boundary layer flow. Das et al[8] investigated the Effects of mass transfer on flow past an impulsively started infinite vertical plate with chemical reaction. Ibrahim[9] analyzed the Radiation effects on chemically reacting **magneto** **hydrodynamics** (MHD) boundary layer flow of heat and mass transfer through a porous vertical flat plate.

Theoretical **hydrodynamics** may lead one into serious delusions. This article is focused on three of them. First, using flowing around a sphere as an exam- ple it is shown that the known potential solutions of the flow-around prob- lems are not unique and there exist nonpotential solutions. A nonpotential solution has been obtained for flowing around a sphere. A general solution of the problem of flowing around an arbitrary surface has been obtained in the quadrature form. To single out a physically realisable solution among a great number of others, it is necessary to add supplementary conditions to the known boundary ones, in particular, to find a solution with the minimum to- tal energy. The hypothesis explaining the reason for stalled flows by viscosity is erroneous. When considering a flow-around problem one should use stalled and broken solutions of the continuity equation along with the conti- nuous ones. If the minimum total energy is achieved by the continuous solu- tion, it is a continuous flow that will be implemented. If it is achieved by the broken solution, a stalled flow will be realised. Second, the **hydrodynamics** of a flow is considered exclusively at each point of it. Differential equations are used to describe the flows that are written for a randomly small volume of a flow, i.e. , for a point. The integral characteristics of a flow and its inertial properties are neglected in the consideration, which results in the misunders- tanding of the mechanism of the formation of a vortex. The reason for the formation of vortices is related to viscosity, which is a mistake. The formation of vortices is the result of the inhomogeneity of the acceleration field and the inertial properties of a flow. Third, the fictitious values of viscous stresses are used in **hydrodynamics**. As a matter of fact, viscosity is the momentum diffu- sion and it should be described by the diffusion equation included into the Euler system of equations for a viscous fluid. The momentum diffusion leads to the necessity of including the volume momentum sources produced by diffusion into the continuity equation and excluding the viscosity forces from the equation of motion. The problem of a viscous fluid flowing around a thin plate has been solved analytically, the velocity profiles satisfying the experi- ment have been obtained. The superfluidity of helium is not its property. It is How to cite this paper: Ivanchin, A. (2018)

29 Read more

This paper concerns the **hydrodynamics** in a lagoonal ecosys- tem (called Berre lagoon) which was occupied, at the turn of the 20th century, by extensive Zostera noltii meadows (over 6000 ha), which shrinked to about 1.5 ha in 2004 due to envi- ronmental impacts of hydroelectric power and other anthro- pogenic developments as it is reported by Warner (2012). Over the last decades, there have been global declines in sea- grass abundance in many places in the world, and manage- ment decisions aimed at protecting and restoring submerged aquatic vegetation have been taken in many places (Fonseca et al., 1996; Koch et al., 2006; Pickerell et al., 2005; Van der Heide et al., 2007; Cardoso et al., 2008; Koch et al., 2009, Shafer and Bergstrom, 2010; Vacchi et al., 2012). Of course, it is known that there are a lot of abiotic and biotic factors, which can affect the losses of seagrasses and their lack of re- covery. In particular, as kindly pointed out by one reviewer,

10 Read more

preservation of an endothelial germ layer packed with goblet cells. However, modern teleost ctenoid scales are normally only found in turbulent flow regions of the body, where their comb-like spines (‘ctenii’) probably increase the surface area for mucous deposition near the wall [15]. Ctenii can be preserved in quite exceptional detail (e.g. [99]), but even if such evidence were found in Palaeozoic taxa, there is enor- mous variation in the drag-reducing influence of mucus from different species, and there does not appear to be a con- sistent correlation with swimming speed [97 –101]. Mucus is clearly an important factor in fish **hydrodynamics** largely ignored in previous studies, however even well-informed approximations of epidermal thickness are of limited use for experimental analysis because they do not control for the volume or fluid properties of any mucus.

10 Read more

Activated sludge bioreactors are multiphase systems that consist of interactions between gas, liquid and solid phases. The formation of suspended sludge flocs creates a complex non- Newtonian gas-liquid-solid system that affects both the particle circulation and the **hydrodynamics** associated with the flow regime. Designing the aeration tank in an activated sludge process determines the overall efficiency and economics because aeration is one of the most cost- and energy-intensive steps in biological wastewater treatment. To design efficient aeration, factors such as the hydrodynamic, physical and biochemical characteristics of the liquid come to play. Hydrodynamic properties depend on the configuration and size of the reactor, physical properties of the fluid, and aeration dynamic characteristics. Bubble columns and airlift reactors have also been used in addition to conventional aeration tanks [16].

130 Read more

A vortex ring is a torus-shaped vortex consisting of a region of fluid spinning around an imaginary axis line that forms a closed loop. It is an important phenomenon in animal kingdom and engineering applications. Birds and flying insects use buoyant vortex ring to glide higher altitudes; squid and jellyfish produce vortex rings during propulsion; vortex rings also participate in the blood flow through the human hearts. With the help of the vortex ring, animals can move fast and produce large thrust. In engineering, the Underwater Compressed Air Energy Storage (UWCAES) system uses surplus electricity to compress air into flexible accumulators (balloons) to store energy underwater. Balloons of stored compressed air may rupture when over-pressurized or pierced by a sharp object. This may generate a large-scale buoyant vortex ring, leading to water surface disruptions and undesirable waves. As a result, it is a necessity to study the **hydrodynamics** of a buoyant vortex ring.

122 Read more

We would like to thank Thelma Williams and John Carling for stimulating our interest in anguilliform **hydrodynamics**, Ulrike Müller for productive discussions of the interaction between kinematics and wake structure, and Paul Webb for many ideas and thoughts on the balance of thrust and drag. Promode Bandyopadhyay, L. Mahadevan and Peter Madden provided comments on a draft of the manuscript, and Tonia Hsieh, Jimmy Liao, Matt McHenry and Christoffer Johanssen were helpful for advice throughout this project. Alexander Smits and James Buchholz provided some thought-provoking information on the wake structure behind flapping membranes. We also owe thanks to Laura Farrell, who maintained the animals used in this study. This research was supported by the NSF under grants IBN9807021 and IBN0316675 to G.V.L.

17 Read more

Smoothed Particle **Hydrodynamics** (SPH) was invented to simulate nonaxisymmetric phenomena in astrophysics (Lucy, 1977) and (Gingold and Monaghan, 1977). It is a pure Lagrangian based method i.e. a particle based method, in contrast to Eulerian methods which are grid based methods. The main difference between the two methods is related to the derivatives. In the Eulerian picture derivatives are calculated at a fixed point in the space, on the other hand in the Lagrangian description they are calculated in a coordinate system attached to a moving fluid element.

52 Read more

cope up with such nonlinearities. Several approximation techniques have been developed to fulfill this purpose [21-30]. Flow of electrically conducting non-Newtonian fluid is a very important phenomenon as in most of the practical situations we have to deal with the flow of conducting fluid which exhibits different behaviors under the influence of magnetic forces. In these cases **magneto** hydro dynamic (MHD) aspect of the flow is also needed to be considered. Homotopy perturbation solution for Two-dimensional MHD squeezing flow between parallel plates has been determined by Siddiqui et al [31]. Domairry and Aziz (2009) [32] investigated the same problem for the flow between parallel disksHe investigate the combined effect of inertia, electromagnetic forces, and suction or injection. With the introduction of a similarity transformation, the continuity and momentum equations governing the squeeze flow are reduced to a single, nonlinear, ordinary differential equation. Recently, Mustafa et al [33] in 2012 examined heat and mass transfer for squeezing flow between parallel plates using the homotopy analysis method (HAM). It is clear from his literature survey that the squeezing flow of a Newtonian fluid between the plates moving normal to their own surface is yet to be inspected. Due to the inherent nonlinearity of the equations governing the fluid flow exact solutions are very rare. Even where they are available immense simplification assumptions have been imposed. Those overly imposed suppositions may not be used for more realistic flows. However to deal with this hurdle many analytical approximation techniques have been developed which are commonly used nowadays. Rashidi in 2008 studied the problem of laminar, isothermal, incompressible, and viscous ?ow in a rectangular domain bounded by two moving porous walls using the homotopy analysis method [34]. We will extend the work of Rashidi. We will include temperature distribution and variable magnetic field. Constant magnetic field is simple and not so complicated because it only contributed a constant value with velocity equation but the variable magnetic field separately gives two more equations.

17 Read more

directly identiﬁed using the dE / dx , as well as elliptic ﬂow of protons reconstructed from impure pos- itive pion sample. The obtained results are compared with those from the NA49 experiment at CERN and from the STAR experiment at RHIC. Also, the results are compared with ideal **hydrodynamics** predictions. That comparisons show faster decrease of experimental v 2 values towards low p T , getting

Flow around a circular cylinder is a fundamental fluid mechanics problem of practical importance. It has potential relevance to a large number of practical applications such as submarines, off shore structures, bridge piers, pipelines etc. The laminar and turbulent unsteady viscous flow behind a circular cylinder has been the subject of numerous experimental and numerical studies, especially from the **hydrodynamics** point of view. External flows past objects have been studied extensively because of their many practical applications. For example, airfoils are made into streamline shapes in order to increase the lifts, and at the same time, reducing the aerodynamic drags exerted on the wings. On the other hand, flow past a blunt body,

1. Model validation during modelling it became clear that there is a shortage of measurements of specific locations to really validate the model. The sensitivity analysis showed that the sedimentation/erosion pattern is only sensitive for the type of sediments. This implies that with relatively little measurements (bathymetry, water level variation, tree characteristics and sediment type) the **hydrodynamics**, sediment dynamics and sedimentation/erosion pattern can be modelled. Model validation should lead to more confidence in the modelling results. To validate the model it is recommended to go to a specified mangrove forest location and measure flow velocities inside and outside the forest (especially on locations where high velocities are expected), sediment concentrations, bed load transport and sediment accretion inside and outside the forest. At this moment (September 2006) a PhD research is carried out at the Vrije Universiteit van Brussel (the Mangrove Management Group) to propagule (seed of mangroves) transport inside and outside mangrove forest. One of the objectives is to model the propagule transport, so a hydrodynamical model is needed as a boundary condition for this transport. Together with the VUB a hydrodynamical model can be developed using Delft3D. This can be used for both propagule transport and sediment transport. This is a great opportunity to validate the Delft3D model for mangrove shorelines using the vegetation module.

195 Read more