The nonlinear evolution of inviscid Goertler vortices in three-dimensional boundary layers
Blackaby, Nicholas; Dando, Andrew; Hall, Philip
1995-09-01
The nonlinear development of inviscid Gortler vortices in a three-dimensional boundary layer is considered. We do not follow the classical approach of weakly nonlinear stability problems and consider a mode which has just become unstable. Instead we extend the method of Blackaby, Dando, and Hall (1992), which considered the closely related nonlinear development of disturbances in stratified shear flows. The Gortler modes we consider are initially fast growing and we assume, following others, that boundary-layer spreading results in them evolving in a linear fashion until they reach a stage where their amplitudes are large enough and their growth rates have diminished sufficiently so that amplitude equations can be derived using weakly nonlinear and non-equilibrium critical-layer theories. From the work of Blackaby, Dando and Hall (1993) is apparent, given the range of parameters for the Gortler problem, that there are three possible nonlinear integro-differential evolution equations for the disturbance amplitude. These are a cubic due to viscous effects, a cubic which corresponds to the novel mechanism investigated in this previous paper, and a quintic. In this paper we shall concentrate on the two cubic integro-differential equations and in particular, on the one due to the novel mechanism as this will be the first to affect a disturbance. It is found that the consideration of a spatial evolution problem as opposed to temporal (as was considered in Blackaby, Dando, and Hall, 1992) causes a number of significant changes to the evolution equations.
Filamentation with nonlinear Bessel vortices.
Jukna, V; Milián, C; Xie, C; Itina, T; Dudley, J; Courvoisier, F; Couairon, A
2014-10-20
We present a new type of ring-shaped filaments featured by stationary nonlinear high-order Bessel solutions to the laser beam propagation equation. Two different regimes are identified by direct numerical simulations of the nonlinear propagation of axicon focused Gaussian beams carrying helicity in a Kerr medium with multiphoton absorption: the stable nonlinear propagation regime corresponds to a slow beam reshaping into one of the stationary nonlinear high-order Bessel solutions, called nonlinear Bessel vortices. The region of existence of nonlinear Bessel vortices is found semi-analytically. The influence of the Kerr nonlinearity and nonlinear losses on the beam shape is presented. Direct numerical simulations highlight the role of attractors played by nonlinear Bessel vortices in the stable propagation regime. Large input powers or small cone angles lead to the unstable propagation regime where nonlinear Bessel vortices break up into an helical multiple filament pattern or a more irregular structure. Nonlinear Bessel vortices are shown to be sufficiently intense to generate a ring-shaped filamentary ionized channel in the medium which is foreseen as opening the way to novel applications in laser material processing of transparent dielectrics.
ANALYTICAL SOLUTION OF NONLINEAR BAROTROPIC VORTICITY EQUATION
Institute of Scientific and Technical Information of China (English)
WANG Yue-peng; SHI Wei-hui
2008-01-01
The stability of nonlinear barotropic vorticity equation was proved. The necessary and sufficient conditions for the initial value problem to be well-posed were presented. Under the conditions of well-posedness, the corresponding analytical solution was also gained.
The compressible Gortler problem in two-dimensional boundary layers
Dando, Andrew H.; Seddougui, Sharon O.
1993-01-01
In this paper the authors investigate the growth rates of Gortler vortices in a compressible flow in the inviscid limit of large Gortler number. Numerical solutions are obtained for O(1) wavenumbers. The further limits of (i) large Mach number and (ii) large wavenumber with O(1) Mach number are considered. It is shown that two different types of disturbance mode can appear in this problem. The first is a wall layer mode, so named as it has its eigenfunctions trapped in a thin layer near the wall. The other mode investigated is confined to a thin layer away from the wall and termed a trapped-layer mode for large wavenumbers and an adjustment-layer mode for large Mach numbers, since then this mode has its eigenfunctions concentrated in the temperature adjustment layer. It is possible to investigate the near crossing of the modes which occurs in each of the limits mentioned. The inviscid limit does not predict a fastest growing mode, but does enable a most dangerous mode to be identified for O(1) Mach number. For hypersonic flow the most dangerous mode depends on the size of the Gortler number.
Decay of high order optical vortices in anisotropic nonlinear optical media
DEFF Research Database (Denmark)
Mamaev, A.V.; Saffman, M.; Zozulya, A.A.
1997-01-01
We present an experimental and theoretical study of the decay of high order optical vortices in media with an anisotropic nonlocal nonlinearity. Vortices with charge n decay into an aligned array of n vortices of unit charge.......We present an experimental and theoretical study of the decay of high order optical vortices in media with an anisotropic nonlocal nonlinearity. Vortices with charge n decay into an aligned array of n vortices of unit charge....
Effect of pressure gradients on Gortler instability
Ragab, S. A.; Nayfeh, A. H.
1980-01-01
Gortler instability for boundary-layer flows over generally curved walls is considered. The full linearized disturbance equations are obtained in an orthogonal curvilinear coordinate system. A perturbation procedure to account for second-order effects is used to determine the effects of the displacement thickness and the variation of the streamline curvature on the neutral stability of the Blasius flow. The pressure gradient in the mean flow is accounted for by solving the nonsimilar boundary-layer equations. Growth rates are obtained for the actual mean flow and the Falkner-Skan flows. The results demonstrate the strong influence of the pressure gradient and the nonsimilarity of the basic flow on the stability characteristics.
Vortices and ring dark solitons in nonlinear amplifying waveguides
Zhang, Jie-Fang; Li, Lu; Mihalache, Dumitru; Malomed, Boris A
2010-01-01
We consider the generation and propagation of (2+1)-dimensional beams in a nonlinear waveguide with the linear gain. Simple self-similar evolution of the beams is achieved at the asymptotic stage, if the input beams represent the fundamental mode. On the contrary, if they carry vorticity or amplitude nodes (or phase slips), vortex tori and ring dark solitons (RDSs) are generated, featuring another type of the self-similar evolution, with an exponentially shrinking vortex core or notch of the RDS. Numerical and analytical considerations reveal that these self-similar structures are robust entities in amplifying waveguides, being \\emph{stable} against azimuthal perturbations.
Linear and Nonlinear Evolution of Disturbances in Supersonic Streamwise Vortices
Khorrami, Mehdi R.; Chang, Chau-Lyan; Wie, Yong-Sun
1997-11-01
Effective control of compressible streamwise vortices play a significant role in both external and internal aerodynamics. In this study, evolution of disturbances in a supersonic vortex is studied by using quasi-cylindrical linear stability analysis and parabolized stability equations (PSE)footnote M. R. Malik and C.-L. Chang, AIAA Paper 97-0758. formulation. Appropriate mean-flow profilesfootnote M. K. Smart, I. M. Kalkhoran, and J. Bentson, AIAA Paper 94-2576. suitable for stability analysis were identified and modeled successfully. Using linear stability analysis, the stability characteristics of axisymmetric vortices were mapped thoroughly. The results indicate that viscosity has very little effect while increasing Mach number significantly stabilizes the disturbance. Linear PSE analysis shows that the effect of streamwise mean flow variation is small for the case considered here. Nonlinear evolution of helical modes is also studied by using PSE. The growth of the disturbances results in the appearance of coherent large scale motion and significant mean flow distortion in the axial velocity and temperature fields. In the end, nonlinear effects tend to stabilize the vortex.
Non-linear vorticity upsurge in Burgers flow
Lam, F
2016-01-01
We demonstrate that numerical solutions of Burgers' equation can be obtained by a scale-totality algorithm for fluids of small viscosity (down to one billionth). Two sets of initial data, modelling simple shears and wall boundary layers, are chosen for our computations. Most of the solutions are carried out well into the fully turbulent regime over finely-resolved scales in space and in time. It is found that an abrupt spatio-temporal concentration in shear constitutes an essential part during the flow evolution. The vorticity surge has been instigated by the non-linearity complying with instantaneous enstrophy production while ad hoc disturbances play no role in the process. In particular, the present method predicts the precipitous vorticity re-distribution and accumulation, predominantly over localised regions of minute dimension. The growth rate depends on viscosity and is a strong function of initial data. Nevertheless, the long-time energy decay is history-independent and is inversely proportional to ti...
Weakly nonlinear stability of vicsous vortices in three-dimensional boundary layers
Bassom, Andrew P.; Otto, S. R.
1993-01-01
Attention is given to the weakly nonlinear stability of essentially viscous vortices in 3D boundary layers. These modes are unstable in the absence of crossflow, but the imposition of small crossflow has a stabilizing effect. Bassom and Hall (1991) demonstrated the existence of neutrally stable vortices for certain crossflow/wave number combinations, and the weakly nonlinear stability properties of these disturbances are described. It is shown that the effect of crossflow is to stabilize the nonlinear modes, and the present calculations allow stable finite-amplitude vortices to be found. Predictions are made concerning the likelihood of observing some of these viscous modes within a practical setting.
The velocity shear and vorticity across redshifts and non-linear scales
Libeskind, Noam I; Gottlöber, Stefan
2013-01-01
The evolution of the large scale distribution of matter in the universe is often characterized by the density field. Here we take a complimentary approach and characterize it using the cosmic velocity field, specifically the deformation of the velocity field. The deformation tensor is decomposed into its symmetric component (known as the "shear tensor") and its anti-symmetric part (the "vorticity"). Using a high resolution cosmological simulation we examine the relative orientations of the shear and the vorticity as a function of spatial scale and redshift. The shear is found to be remarkable stable to the choice of scale, while the vorticity is found to quickly decay with increasing spatial scale or redshift. The vorticity emerges out of the linear regime randomly oriented with respect to the shear eigenvectors. Non-linear evolution drives the vorticity to lie within the plane defined by the eigenvector of the fastest collapse. Within that plane the vorticity first gets aligned with the middle eigenvector an...
On the Stability of Nonlinear Viscous Vortices in Three-Dimensional Boundary Layers
1992-04-01
wave disturbances in stable and unsta- ble parallel flows , Part 2. The development of a solution for plane Poiseuille and plane Couette flow . J. Fluid...unstable parallel flows , Part 1. The basic behaviour in plane Poiseuille flow . J. Fluid Mech. 9, 353-370. Watson, J. 1960 On the nonlinear mechanics of...vortices which a particular boundary layer may support. According to a linearised theory vortices within a high G6rtler number flow can take one of
Integral Invariance and Non-linearity Reduction for Proliferating Vorticity Scales in Fluid Dynamics
Lam, F
2013-01-01
A vorticity theory for incompressible fluid flows in the absence of solid boundaries is proposed. Some apriori bounds are established. They are used in an interpolation theory to show the well-posedness of the vorticity Cauchy problem. A non-linear integral equation for vorticity is derived and its solution is expressed in an expansion. Interpretations of flow evolutions starting from given initial data are given and elaborated. The kinetic theory for Maxwellian molecules with cut-off is revisited in order to link microscopic properties to flow characters on the continuum.
Relativistic superfluidity and vorticity from the nonlinear Klein-Gordon equation
Xiong, Chi; Guo, Yulong; Liu, Xiaopei; Huang, Kerson
2014-01-01
We investigate superfluidity, and the mechanism for creation of quantized vortices, in the relativistic regime. The general framework is a nonlinear Klein-Gordon equation in curved spacetime for a complex scalar field, whose phase dynamics gives rise to superfluidity. The mechanisms discussed are local inertial forces (Coriolis and centrifugal), and current-current interaction with an external source. The primary application is to cosmology, but we also discuss the reduction to the non-relativistic nonlinear Schr\\"{o}dinger equation, which is widely used in describing superfluidity and vorticity in liquid helium and cold-trapped atomic gases.
Efficient nonlinear generation of high power, higher order, ultrafast "perfect" vortices in green
Chaitanya, N Apurv; Samanta, G K
2016-01-01
We report on efficient nonlinear generation of ultrafast, higher order "perfect" vortices at the green wavelength. Based on Fourier transformation of the higher order Bessel-Gauss beam generated through the combination of spiral phase plate and axicon we have transformed the Gaussian beam of the ultrafast Yb-fiber laser at 1060 nm into perfect vortices of power 4.4 W and order up to 6. Using single-pass second harmonic generation (SHG) of such vortices in 5-mm long chirped MgO-doped, periodically poled congruent LiNbO$_3$ crystal we have generated perfect vortices at green wavelength with output power of 1.2 W and vortex order up to 12 at single-pass conversion efficiency of 27% independent of its order. This is the highest single-pass SHG efficiency of any optical beams other than Gaussian beams. Unlike the disintegration of higher order vortices in birefringent crystals, here, the use of quasi-phase matching process enables generation of high quality vortices even at higher orders. The green perfect vortice...
Topological charge algebra of optical vortices in nonlinear interactions.
Zhdanova, Alexandra A; Shutova, Mariia; Bahari, Aysan; Zhi, Miaochan; Sokolov, Alexei V
2015-12-28
We investigate the transfer of orbital angular momentum among multiple beams involved in a coherent Raman interaction. We use a liquid crystal light modulator to shape pump and Stokes beams into optical vortices with various integer values of topological charge, and cross them in a Raman-active crystal to produce multiple Stokes and anti-Stokes sidebands. We measure the resultant vortex charges using a tilted-lens technique. We verify that in every case the generated beams' topological charges obey a simple relationship, resulting from angular momentum conservation for created and annihilated photons, or equivalently, from phase-matching considerations for multiple interacting beams.
Nonlinear modes in the hollow-cores of liquid vortices
Amaouche, Mustapha
2013-09-01
In this paper we show that the wave patterns observed on the interfacial contours of hollow-core vortices, produced within a shallow layer of fluid contained in stationary cylinder and driven by a rotating disk at the bottom [G.H. Vatistas, H.A. Abderrahmane, M.H. Kamran Siddiqui, Experimental confirmation of Kelvin\\'s equilibria, Phys. Rev. Lett. 100 (2008) 174503-174504], can be described as travelling cnoidal waves. These rotating stationary waves are obtained as solutions of a Korteweg-de Vries type equation, in accordance with the geometrical and kinematic characteristics of the observed polygonal patterns. © 2013 Elsevier Masson SAS. All rights reserved.
Solitons and vortices in nonlinear two-dimensional photonic crystals of the Kronig-Penney type.
Mayteevarunyoo, Thawatchai; Malomed, Boris A; Roeksabutr, Athikom
2011-08-29
Solitons in the model of nonlinear photonic crystals with the transverse structure based on two-dimensional (2D) quadratic- or rhombic-shaped Kronig-Penney (KP) lattices are studied by means of numerical methods. The model can also applies to a Bose-Einstein condensate (BEC) trapped in a superposition of linear and nonlinear 2D periodic potentials. The analysis is chiefly presented for the self-repulsive nonlinearity, which gives rise to several species of stable fundamental gap solitons, dipoles, four-peak complexes, and vortices in two finite bandgaps of the underlying spectrum. Stable solitons with complex shapes are found, in particular, in the second bandgap of the KP lattice with the rhombic structure. The stability of the localized modes is analyzed in terms of eigenvalues of small perturbations, and tested in direct simulations. Depending on the value of the KP's duty cycle (DC, i.e., the ratio of the void's width to the lattice period), an internal stability boundary for the solitons and vortices may exist inside of the first bandgap. Otherwise, the families of the localized modes are entirely stable or unstable in the bandgaps. With the self-attractive nonlinearity, only unstable solitons and vortices are found in the semi-infinite gap.
Nonlinear stability of non-stationary cross-flow vortices in compressible boundary layers
Gajjar, J. S. B.
1995-01-01
The nonlinear evolution of long wavelength non-stationary cross-flow vortices in a compressible boundary layer is investigated and the work extends that of Gajjar (1994) to flows involving multiple critical layers. The basic flow profile considered in this paper is that appropriate for a fully three-dimensional boundary layer with O(1) Mach number and with wall heating or cooling. The governing equations for the evolution of the cross-flow vortex are obtained and some special cases are discussed. One special case includes linear theory where exact analytic expressions for the growth rate of the vortices are obtained. Another special case is a generalization of the Bassom & Gajjar (1988) results for neutral waves to compressible flows. The viscous correction to the growth rate is derived and it is shown how the unsteady nonlinear critical layer structure merges with that for a Haberman type of viscous critical layer.
DEFF Research Database (Denmark)
Mamaev, A.V.; Saffman, M.; Zozulya, A.A.
1996-01-01
We analyze the evolution of (1+1) dimensional dark stripe beams in bulk media with a photorefractive nonlinear response. These beams, including solitary wave solutions, are shown to be unstable with respect to symmetry breaking and formation of structure along the initially homogeneous coordinate....... Experimental results show the complete sequence of events starting from self-focusing of the stripe, its bending due to the snake instability, and subsequent decay into a set of optical vortices....
Two species of vortices in massive gauged non-linear sigma models
Energy Technology Data Exchange (ETDEWEB)
Alonso-Izquierdo, A. [Departamento de Matemática Aplicada, Universidad de Salamanca,Facultad de Ciencias Agrarias y Ambientales, Av. Filiberto Villalobos 119, E-37008 Salamanca (Spain); Fuertes, W. García [Departamento de Física, Universidad de Oviedo, Facultad de Ciencias, Calle Calvo Sotelo s/n, E-33007 Oviedo (Spain); Guilarte, J. Mateos [Departamento de Física Fundamental, Universidad de Salamanca, Facultad de Ciencias, Plaza de la Merced, E-37008 Salamanca (Spain)
2015-02-23
Non-linear sigma models with scalar fields taking values on ℂℙ{sup n} complex manifolds are addressed. In the simplest n=1 case, where the target manifold is the S{sup 2} sphere, we describe the scalar fields by means of stereographic maps. In this case when the U(1) symmetry is gauged and Maxwell and mass terms are allowed, the model accommodates stable self-dual vortices of two kinds with different energies per unit length and where the Higgs field winds at the cores around the two opposite poles of the sphere. Allowing for dielectric functions in the magnetic field, similar and richer self-dual vortices of different species in the south and north charts can be found by slightly modifying the potential. Two different situations are envisaged: either the vacuum orbit lies on a parallel in the sphere, or one pole and the same parallel form the vacuum orbit. Besides the self-dual vortices of two species, there exist BPS domain walls in the second case. Replacing the Maxwell contribution of the gauge field to the action by the second Chern-Simons secondary class, only possible in (2+1)-dimensional Minkowski space-time, new BPS topological defects of two species appear. Namely, both BPS vortices and domain ribbons in the south and the north charts exist because the vacuum orbit consits of the two poles and one parallel. Formulation of the gauged ℂℙ{sup 2} model in a reference chart shows a self-dual structure such that BPS semi-local vortices exist. The transition functions to the second or third charts break the U(1)×SU(2) semi-local symmetry, but there is still room for standard self-dual vortices of the second species. The same structures encompassing N complex scalar fields are easily generalized to gauged ℂℙ{sup N} models.
Nonlinear Development and Secondary Instability of Traveling Crossflow Vortices
Li, Fei; Choudhari, Meelan M.; Duan, Lian; Chang, Chau-Lyan
2014-01-01
Transition research under NASA's Aeronautical Sciences Project seeks to develop a validated set of variable fidelity prediction tools with known strengths and limitations, so as to enable "sufficiently" accurate transition prediction and practical transition control for future vehicle concepts. This paper builds upon prior effort targeting the laminar breakdown mechanisms associated with stationary crossflow instability over a swept-wing configuration relevant to subsonic aircraft with laminar flow technology. Specifically, transition via secondary instability of traveling crossflow modes is investigated as an alternate scenario for transition. Results show that, for the parameter range investigated herein, secondary instability of traveling crossflow modes becomes insignificant in relation to the secondary instability of the stationary modes when the relative initial amplitudes of the traveling crossflow instability are lower than those of the stationary modes by approximately two orders of magnitudes or more. Linear growth predictions based on the secondary instability theory are found to agree well with those based on PSE and DNS, with the most significant discrepancies being limited to spatial regions of relatively weak secondary growth, i.e., regions where the primary disturbance amplitudes are smaller in comparison to its peak amplitude. Nonlinear effects on secondary instability evolution is also investigated and found to be initially stabilizing, prior to breakdown.
Directory of Open Access Journals (Sweden)
Daohong Song
2012-01-01
Full Text Available We provide a brief overview on our recent experimental work on linear and nonlinear localization of singly charged vortices (SCVs and doubly charged vortices (DCVs in two-dimensional optically induced photonic lattices. In the nonlinear case, vortex propagation at the lattice surface as well as inside the uniform square-shaped photonic lattices is considered. It is shown that, apart from the fundamental (semi-infinite gap discrete vortex solitons demonstrated earlier, the SCVs can self-trap into stable gap vortex solitons under the normal four-site excitation with a self-defocusing nonlinearity, while the DCVs can be stable only under an eight-site excitation inside the photonic lattices. Moreover, the SCVs can also turn into stable surface vortex solitons under the four-site excitation at the surface of a semi-infinite photonics lattice with a self-focusing nonlinearity. In the linear case, bandgap guidance of both SCVs and DCVs in photonic lattices with a tunable negative defect is investigated. It is found that the SCVs can be guided at the negative defect as linear vortex defect modes, while the DCVs tend to turn into quadrupole-like defect modes provided that the defect strength is not too strong.
Energy Technology Data Exchange (ETDEWEB)
Moro, Antonio, E-mail: a.moro@lboro.ac.u [School of Mathematics, Loughborough University, Loughborough, Leicestershire, LE11 3TU (United Kingdom)
2009-08-17
Vortices are screw phase dislocations associated with helicoidal wave-fronts. In nonlinear optics, vortices arise as singular solutions to the phase-intensity equations of geometric optics. They exist for a general class of nonlinear response functions. In this sense, vortices possess a universal character. Analysis of geometric optics equations on the hodograph plane leads to deformed vortex type solutions that are sensitive to the form of the nonlinearity. The case of a Kerr type nonlinear response is discussed as a specific example.
Charge flipping vortices in the discrete nonlinear Schrödinger trimer and hexamer
Jason, Peter; Johansson, Magnus
2015-02-01
We examine the existence and properties of charge flipping vortices (CFVs), vortices which periodically flip the topological charge, in three-site (trimer) and six-site (hexamer) discrete nonlinear Schrödinger lattices. We demonstrate numerically that CFVs exist as exact quasiperiodic solutions in continuous families which connect two different stationary solutions without topological charge, and that it is possible to interpret the dynamics of certain CFVs as the result of perturbations of these stationary solutions. The CFVs are calculated with high numerical accuracy and we may therefore accurately determine many of their properties, such as their energy and linear stability, and the CFVs are found to be stable over large parameter regimes. We also show that, like in earlier studies for lattices with a multiple of four sites, trimer and hexamer CFVs can be obtained by perturbing stationary constant amplitude vortices with certain linear eigenmodes. However, in contrast to the former case where the perturbation could be infinitesimal, the magnitude of the perturbations for trimers and hexamers must overcome a quite large threshold value. These CFVs may be interpreted as exact quasiperiodic CFVs, with a small perturbation applied. The concept of a charge flipping energy barrier is introduced and discussed.
Leblond, Hervé; Malomed, Boris A; Mihalache, Dumitru
2005-03-01
We consider basic types of two-dimensional (2D) vortex solitons in a three-wave model combining quadratic chi((2)) and self-defocusing cubic chi((3))(-) nonlinearities. The system involves two fundamental-frequency (FF) waves with orthogonal polarizations and a single second-harmonic (SH) one. The model makes it possible to introduce a 2D soliton, with hidden vorticity (HV). Its vorticities in the two FF components are S(1,2) = +/-1 , whereas the SH carries no vorticity, S(3) = 0 . We also consider an ordinary compound vortex, with 2S(1) = 2S(2) = S(3) = 2 . Without the chi((3))(-) terms, the HV soliton and the ordinary vortex are moderately unstable. Within the propagation distance z approximately 15 diffraction lengths, Z(diffr), the former one turns itself into a usual zero-vorticity (ZV) soliton, while the latter splits into three ZV solitons (the splinters form a necklace pattern, with its own intrinsic dynamics). To gain analytical insight into the azimuthal instability of the HV solitons, we also consider its one-dimensional counterpart, viz., the modulational instability (MI) of a one-dimensional CW (continuous-wave) state with "hidden momentum," i.e., opposite wave numbers in its two components, concluding that such wave numbers may partly suppress the MI. As concerns analytical results, we also find exact solutions for spreading localized vortices in the 2D linear model; in terms of quantum mechanics, these are coherent states with angular momentum (we need these solutions to accurately define the diffraction length of the true solitons). The addition of the chi((3))(-) interaction strongly stabilizes both the HV solitons and the ordinary vortices, helping them to persist over z up to 50 Z(diffr). In terms of the possible experiment, they are completely stable objects. After very long propagation, the HV soliton splits into two ZV solitons, while the vortex with S(3) = 2S(1,2) = 2 splits into a set of three or four ZV solitons.
Gamma ray vortices from nonlinear inverse Compton scattering of circularly polarized light
Taira, Yoshitaka; Katoh, Masahiro
2016-01-01
Inverse Compton scattering (ICS) is an elemental radiation process that produces high-energy photons both in nature and in the laboratory. Non-linear ICS is a process in which multiple photons are converted to a single high-energy photon. Here, we theoretically show that the photon produced by non-linear ICS of circularly polarized photons is a vortex, which means that it possesses a helical wave front and carries orbital angular momentum. Our work explains a recent experimental result regarding non-linear Compton scattering that clearly shows an annular intensity distribution as a remarkable feature of a vortex beam. Our work implies that gamma ray vortices should be produced in various situations in astrophysics in which high-energy electrons and intense circularly polarized light fields coexist. They should play a critical role in stellar nucleosynthesis. Non-linear ICS is the most promising radiation process for realizing a gamma ray vortex source based on currently available laser and accelerator technol...
Lagrange form of the nonlinear Schrödinger equation for low-vorticity waves in deep water
Abrashkin, Anatoly; Pelinovsky, Efim
2017-06-01
The nonlinear Schrödinger (NLS) equation describing the propagation of weakly rotational wave packets in an infinitely deep fluid in Lagrangian coordinates has been derived. The vorticity is assumed to be an arbitrary function of Lagrangian coordinates and quadratic in the small parameter proportional to the wave steepness. The vorticity effects manifest themselves in a shift of the wave number in the carrier wave and in variation in the coefficient multiplying the nonlinear term. In the case of vorticity dependence on the vertical Lagrangian coordinate only (Gouyon waves), the shift of the wave number and the respective coefficient are constant. When the vorticity is dependent on both Lagrangian coordinates, the shift of the wave number is horizontally inhomogeneous. There are special cases (e.g., Gerstner waves) in which the vorticity is proportional to the squared wave amplitude and nonlinearity disappears, thus making the equations for wave packet dynamics linear. It is shown that the NLS solution for weakly rotational waves in the Eulerian variables may be obtained from the Lagrangian solution by simply changing the horizontal coordinates.
Directory of Open Access Journals (Sweden)
M. Finizio
Full Text Available Starting from a number of observables in the form of time-series of meteorological elements in various areas of the northern hemisphere, a model capable of fitting past records and predicting monthly vorticity time changes in the western Mediterranean is implemented. A new powerful statistical methodology is introduced (MARS in order to capture the non-linear dynamics of time-series representing the available 40-year history of the hemispheric circulation. The developed model is tested on a suitable independent data set. An ensemble forecast exercise is also carried out to check model stability in reference to the uncertainty of input quantities.
Key words. Meteorology and atmospheric dynamics · General circulation ocean-atmosphere interactions · Synoptic-scale meteorology
Helfrich, Karl R.
2006-08-01
The nonlinear evolution of a localized layer of buoyant, uniform potential vorticity fluid with depth H, width w and length L released adjacent to a wall in a rotating system is studied using reduced-gravity shallow-water theory and numerical modeling. In the interior, far from the two ends of the layer, the initial adjustment gives, after ignoring inertia-gravity waves, a geostrophic flow of width w and layer velocities parallel to the wall directed in the downstream direction (defined by Kelvin wave propagation). This steady geostrophic flow serves as the initial condition for a semigeostrophic solution using the method of characteristics. At the downstream end, the theory shows that the fluid intrudes along the wall as rarefaction terminating at a nose of vanishing width and depth. However, in a real fluid the presence of the lower layer leads to a blunt gravity current head. The theory is amended by introducing a gravity current head condition that has a blunt bore joined to the rarefaction by a uniform gravity current. The upstream termination of the initial layer produces a Kelvin rarefaction that propagates downstream, decreasing the layer depth along the wall, and initiating upstream flow adjacent to the wall. The theoretical solution compares favorably to numerical solutions of the reduced-gravity shallow-water equations. The agreement between theory and numerical solutions occurs regardless of whether the numerical runs are initiated with an adjusted geostrophic solution or with the release of a stagnant layer. The latter case excites inertia-gravity waves that, despite their large amplitude and breaking, do not significantly affect the evolution of the geostrophic flow. At times beyond the validity of the semigeostrophic theory, the numerical solutions evolve into a stationary array of vortices. The vortex formation can be interpreted as the finite-amplitude manifestation of a linear instability of the new flow established by the passage of the Kelvin
Kevrekidis, P G; Saxena, A; Frantzeskakis, D J; Bishop, A R
2014-01-01
We consider a two-dimensional (2D) generalization of a recently proposed model [Phys. Rev. E 88, 032905 (2013)], which gives rise to bright discrete solitons supported by the defocusing nonlinearity whose local strength grows from the center to the periphery. We explore the 2D model starting from the anti-continuum (AC) limit of vanishing coupling. In this limit, we can construct a wide variety of solutions including not only single-site excitations, but also dipole and quadrupole ones. Additionally, two separate families of solutions are explored: the usual "extended" unstaggered bright solitons, in which all sites are excited in the AC limit, with the same sign across the lattice (they represent the most robust states supported by the lattice, their 1D counterparts being what was considered as 1D bright solitons in the above-mentioned work), and the vortex cross, which is specific to the 2D setting. For all the existing states, we explore their stability (analytically, whenever possible). Typical scenarios ...
The 3D solitons and vortices in 3D discrete monatomic lattices with cubic and quartic nonlinearity
Institute of Scientific and Technical Information of China (English)
Xu Quan; Tian Qiang
2006-01-01
By virtue of the method of multiple-scale and the quasi-discreteness approach, we have discussed the nonlinear vibration equation of a 3D discrete monatomic lattice with its nearest-neighbours interaction. The 3D simple cubic lattices have the same localized modes as a ID discrete monatomic chain with cubic and quartic nonlinearity. The nonlinear vibration in the 3D simple cubic lattice has 3D distorted solitons and 3D envelop solitons in the direction of kx = ky = kz = k and k =±π/6a0 in the Brillouin zone, as well as has 3D vortices in the direction of kx = ky = kz = k and k =±π/a0 in the Brillouin zone.
Formation of columnar baroclinic vortices in thermally stratified nonlinear spin-up
Pacheco, J.R.; Verzicco, R.
2012-01-01
We investigate the mechanisms that affect the formation of columnar vortices for spin-up in a cylinder where the temperatures at the horizontal walls are prescribed. Numerical results from the three-dimensional Navier–Stokes equations show that a short-lived instability, suppressed by the combined e
Deguchi, K.; Altmeyer, S.
2013-04-01
Interactions between nearly bicritical modes in Taylor-Couette flow, which have been concerned with the framework of weakly nonlinear theory, are extended to fully nonlinear Navier-Stokes computation. For this purpose, a standard Newton solver for axially periodic flows is generalized to compute any mixed solutions having up to two phases, which typically arise from interactions of two spiral or Taylor vortex modes. Also, a simple theory is developed in order to classify the mixed solutions. With these methods, we elucidate pattern formation phenomena, which have been observed in a Taylor-Couette flow experiment. Focusing on the counter-rotating parameter range, all possible classes of interaction of various solutions with different azimuthal and axial wave numbers are considered within our computational restriction, and we observe numerous connection branches, e.g., footbridge solutions. Some of the mixed solutions result in a three-dimensional wavy spiral solution with axial relative periodicity or an axially doubly periodic toroidally closed vortex solution. The possible connection of the former solution family to spiral turbulence, which has been observed in highly counter-rotating Taylor-Couette flow, is discussed.
Garcia-Melendo, E.; Legarreta, J.; Sanchez-Lavega, A.
2012-12-01
Direct measurements of the structure of the zonal winds of Jupiter and Saturn below the upper cloud layer are very difficult to retrieve. Except from the vertical profile at a Jupiter hot spot obtained from the Galileo probe in 1995 and measurements from cloud tracking by Cassini instruments just below the upper cloud, no other data are available. We present here our inferences of the vertical structure of Jupiter and Saturn zonal wind across the upper troposphere (deep down to about 10 bar level) obtained from nonlinear simulations using the EPIC code of the stability and interactions of large-scale vortices and planetary-scale disturbances in both planets. Acknowledgements: This work has been funded by Spanish MICIIN AYA2009-10701 with FEDER support, Grupos Gobierno Vasco IT-464-07 and UPV/EHU UFI11/55. [1] García-Melendo E., Sánchez-Lavega A., Dowling T.., Icarus, 176, 272-282 (2005). [2] García-Melendo E., Sánchez-Lavega A., Hueso R., Icarus, 191, 665-677 (2007). [3] Sánchez-Lavega A., et al., Nature, 451, 437- 440 (2008). [4] Sánchez-Lavega A., et al., Nature, 475, 71-74 (2011).
Olmez, O.; Ozbulut, M.; Yildiz, M.; Goren, O.
2016-06-01
The present study investigates the vortical and nonlinear effects in the roll motion of a 2-D body with square cross-sections by using Smoothed Particle Hydrodynamics (SPH). A 2-D rigid body with square cross-section is taken into account for the benchmark study and subjected to the oscillatory roll motion with a given angular frequency. The governing equations are continuity equation and Euler's equation with artificial viscosity term. Weakly Compressible SPH (WCSPH) scheme is employed for the discretization of the governing equations. Velocities of the fluid particles are updated by means of XSPH+Artificial Particle Displacement (VXSPH+APD) algorithm. In this method only the free surface fluid particles are subjected to VXSPH algorithm while the APD algorithm is employed for the fully populated flow regions. The hybrid usage of numerical treatment keeps free surface particles together by creating an artificial surface tension on the free surface. VXSPH+APD is a proven numerical treatment to provide the most accurate results for this type of free surface flows (Ozbulut et al. 2014). The results of the present study are compared with those of the experimental studies as well as with those of the numerical methods obtained from the current literature.
Wu, Jie-Zhi; Zhou, Ming-De
2015-01-01
This book is a comprehensive and intensive book for graduate students in fluid dynamics as well as scientists, engineers and applied mathematicians. Offering a systematic introduction to the physical theory of vortical flows at graduate level, it considers the theory of vortical flows as a branch of fluid dynamics focusing on shearing process in fluid motion, measured by vorticity. It studies vortical flows according to their natural evolution stages,from being generated to dissipated. As preparation, the first three chapters of the book provide background knowledge for entering vortical flows. The rest of the book deals with vortices and vortical flows, following their natural evolution stages. Of various vortices the primary form is layer-like vortices or shear layers, and secondary but stronger form is axial vortices mainly formed by the rolling up of shear layers. Problems are given at the end of each chapter and Appendix, some for helping understanding the basic theories, and some involving specific ap...
Vortices as degenerate metrics
Baptista, J M
2012-01-01
We note that the Bogomolny equation for abelian vortices is precisely the condition for invariance of the Hermitian-Einstein equation under a degenerate conformal transformation. This leads to a natural interpretation of vortices as degenerate hermitian metrics that satisfy a certain curvature equation. Using this viewpoint, we rephrase standard results about vortices and make some new observations. We note the existence of a conceptually simple, non-linear rule for superposing vortex solutions, and we describe the natural behaviour of the L^2-metric on the moduli space upon certain restrictions.
Alonso-Izquierdo, Alberto
2016-01-01
In this paper zero modes of fluctuation are dissected around the two species of BPS vortices existing in the critical Higgs phase, where the scalar and vector meson masses are equal, of a gauged $\\mathbb{U}(1)$ nonlinear $\\mathbb{CP}^1$-model. If $2\\pi n$, $n\\in \\mathbb{Z}$, is the quantized magnetic flux of the two species of BPS vortex solutions, $2n$ linearly independent vortex zero modes for each species are found and described. The existence of two species of moduli spaces of dimension $2n$ of these stringy topological defects is thus locally shown.
Cohen, J.; Shukhman, I. G.; Karp, M.; Philip, J.
2010-10-01
Recent experimental and numerical studies have shown that the interaction between a localized vortical disturbance and the shear of an external base flow can lead to the formation of counter-rotating vortex pairs and hairpin vortices that are frequently observed in wall bounded and free turbulent shear flows as well as in subcritical shear flows. In this paper an analytical-based solution method is developed. The method is capable of following (numerically) the evolution of finite-amplitude localized vortical disturbances embedded in shear flows. Due to their localization in space, the surrounding base flow is assumed to have homogeneous shear to leading order. The method can solve in a novel way the interaction between a general family of unbounded planar homogeneous shear flows and any localized disturbance. The solution is carried out using Lagrangian variables in Fourier space which is convenient and enables fast computations. The potential of the method is demonstrated by following the evolved structures of large amplitude disturbances in three canonical base flows, including simple shear, plane stagnation (extensional) and pure rotation flows, and a general case. The results obtained by the current method for plane stagnation and simple shear flows are compared with the published results. The proposed method could be extended to other flows (e.g. geophysical and rotating flows) and to include periodic disturbances as well.
Indian Academy of Sciences (India)
Leena K Sahoo; R C Budhani; D Kanjilal; G K Mehta
2002-05-01
Understanding the dynamics of vortex matter subjected to random and correlated pinning disorders in layered superconductors remains a topic of considerable interest. The dynamical behavior of vortices in these systems shows a rich variety of effects due to many competing interactions. Here, we study the ac response of as-grown as well as heavy-ion-irradiated Tl2Ba2CaCu2O8 (Tl-2212) thin ﬁlms by using a micro Hall-probe susceptometer. We ﬁnd that the dynamics of vortices in the high-temperature, low-ﬁeld regime of the - phase diagram investigated here depends on the nature of pinning defects. While the decay of screening currents () indicates a glassy behavior in both types of samples, the nature of the glassy phase is different in the two cases. Samples with columnar defects show distinct signature of a Bose glass in the measurement of () and the angular dependence of the irreversibility ﬁeld (irr).
Subwavelength vortical plasmonic lattice solitons.
Ye, Fangwei; Mihalache, Dumitru; Hu, Bambi; Panoiu, Nicolae C
2011-04-01
We present a theoretical study of vortical plasmonic lattice solitons, which form in two-dimensional arrays of metallic nanowires embedded into nonlinear media with both focusing and defocusing Kerr nonlinearities. Their existence, stability, and subwavelength spatial confinement are investigated in detail.
Energy Technology Data Exchange (ETDEWEB)
Ruge, J.; Li, Y.; McCormick, S.F. [and others
1994-12-31
The formulation and time discretization of problems in meteorology are often tailored to the type of efficient solvers available for use on the discrete problems obtained. A common procedure is to formulate the problem so that a constant (or latitude-dependent) coefficient Poisson-like equation results at each time step, which is then solved using spectral methods. This both limits the scope of problems that can be handled and requires linearization by forward extrapolation of nonlinear terms, which, in turn, requires filtering to control noise. Multigrid methods do not suffer these limitations, and can be applied directly to systems of nonlinear equations with variable coefficients. Here, a global barotropic semi-Lagrangian model, developed by the authors, is presented which results in a system of three coupled nonlinear equations to be solved at each time step. A multigrid method for the solution of these equations is described, and results are presented.
Bazeia, D; Marques, M A; Menezes, R; Zafalan, I
2016-01-01
We study a family of Maxwell-Higgs models, described by the inclusion of a function of the scalar field that represent generalized magnetic permeability. We search for vortex configurations which obey first-order differential equations that solve the equations of motion. We first deal with the asymptotic behavior of the field configurations, and then implement a numerical study of the solutions, the energy density and the magnetic field. We work with the generalized permeability having distinct profiles, giving rise to new models, and we investigate how the vortices behave, compared with the solutions of the corresponding standard models. In particular, we show how to build compact vortices, that is, vortex solutions with the energy density and magnetic field vanishing outside a compact region of the plane.
Energy Technology Data Exchange (ETDEWEB)
Bazeia, D.; Losano, L.; Marques, M.A.; Zafalan, I. [Universidade Federal da Paraiba, Departamento de Fisica, Joao Pessoa, PB (Brazil); Menezes, R. [Universidade Federal da Paraiba, Departamento de Ciencias Exatas, Rio Tinto, PB (Brazil); Universidade Federal de Campina Grande, Departamento de Fisica, Campina Grande, PB (Brazil)
2017-02-15
We study a family of Maxwell-Higgs models, described by the inclusion of a function of the scalar field that represent generalized magnetic permeability. We search for vortex configurations which obey first-order differential equations that solve the equations of motion. We first deal with the asymptotic behavior of the field configurations, and then implement a numerical study of the solutions, the energy density and the magnetic field. We work with the generalized permeability having distinct profiles, giving rise to new models, and we investigate how the vortices behave, compared with the solutions of the corresponding standard models. In particular, we show how to build compact vortices, that is, vortex solutions with the energy density and magnetic field vanishing outside a compact region of the plane. (orig.)
Defining Coherent Vortices Objectively from the Vorticity
Haller, George; Farazmand, Mohammad; Huhn, Florian
2015-01-01
Rotationally coherent Lagrangian vortices are formed by tubes of deforming fluid elements that complete equal bulk material rotation relative to the mean rotation of the deforming fluid volume. We show that initial positions of such tubes coincide with tubular level surfaces of the Lagrangian-Averaged Vorticity Deviation (LAVD), the trajectory integral of the normed difference of the vorticity from its spatial mean. LAVD-based vortices are objective, i.e., remain unchanged under time-dependent rotations and translations of the coordinate frame. In the limit of vanishing Rossby numbers in geostrophic flows, cyclonic LAVD vortex centers are precisely the observed attractors for light particles. A similar result holds for heavy particles in anticyclonic LAVD vortices. We also establish a relationship between rotationally coherent Lagrangian vortices and their instantaneous Eulerian counterparts. The latter are formed by tubular surfaces of equal material rotation rate, objectively measured by the Instantaneous V...
Sutyrin, G. G.; Radko, T.
2017-03-01
Nonlinear evolution of pancake-like vortices in a uniformly rotating and stratified fluid is studied using a 3D Boussinesq numerical model at large Rossby numbers. After the initial stage of viscous decay, the simulations reveal exponential growth of toroidal circulation cells (aka Taylor vortices) at the peripheral annulus with a negative Rayleigh discriminant. At the nonlinear stage, these thin cells redistribute the angular momentum and density differently at the levels of radial outflow and inflow. Resulting layering, with a vertical stacking of sharp variations in velocity and density, enhances small-scale mixing and energy decay. Characteristic detectable stretching patterns are produced in the density field. The circulation patterns, induced by centrifugal instability, tend to homogenize the angular momentum in the vicinity of the unstable region. We demonstrate that the peak intensity of the cells and the vortex energy decay are dramatically reduced by the earth's rotation due to conservation of total absolute angular momentum. The results have important implications for better understanding the fate of pancake vortices and physical mechanisms of energy transfer in stratified fluids.
Instability of isolated hollow vortices with zero circulation
Hiejima, Toshihiko
2016-04-01
Inviscid linear stability analysis and numerical simulations are used to investigate how temporal disturbances evolve in double-annular hollow vortices with an opposite-signed vorticity (the total circulation is zero). Two extrema exist in the vorticity profile and constitute a factor of instability. The dispersion relation is expressed as a simple cubic equation. The results show that the instabilities of vortices are strongly enhanced by the hollow effect of the annular vorticity. In addition, the growth rate of the dominant modes significantly increases with decreasing negative-vorticity thickness. During the initial stage, the dominant unstable modes obtained from simulations are consistent with those obtained from the linear analysis. In nonlinear developments, the flow field stretches out in one direction depending on the motion of the plural vortex pair formed by rolling up the positive and negative vorticities. Once such structures in the vortex are generated, the vortex immediately breaks down and does not become metastable.
Onset of Vortices in Thin Superconducting Strips and Wires
Aranson, I S; Shapiro, B Y
1994-01-01
Spontaneous nucleation and the consequent penetration of vortices into thin superconducting films and wires, subjected to a magnetic field, can be considered as a nonlinear stage of primary instability of the current-carrying superconducting state. The development of the instability leads to the formation of a chain of vortices in strips and helicoidal vortex lines in wires. The boundary of instability was obtained analytically. The nonlinear stage was investigated by simulations of the time-dependent generalized Ginzburg-Landau equation.
Generation and propagation of optical vortices
Rozas, David
Optical vortices are singularities in phase fronts of laser beams. They are characterized by a dark core whose size (relative to the size of the background beam) may dramatically affect their behavior upon propagation. Previously, only large-core vortices have been extensively studied. The object of the research presented in this dissertation was to explore ways of generating small-core optical vortices (also called optical vortex filaments ), and to examine their propagation using analytical, numerical and experimental methods. Computer-generated holography enabled us to create arbitrary distributions of optical vortex filaments for experimental exploration. Hydrodynamic analogies were used to develop an heuristic model which described the dependence of vortex motion on other vortices and the background beam, both qualitatively and quantitatively. We predicted that pair of optical vortex filaments will rotate with angular rates inversely proportional to their separation distance (just like vortices in a fluid). We also reported the first experimental observation of this novel fluid-like effect. It was found, however, that upon propagation in linear media, the fluid-like rotation was not sustained owing to the overlap of diffracting vortex cores. Further numerical studies and experiments showed that rotation angle may be enhanced in nonlinear self-defocusing media. The results presented in this thesis offer us a better understanding of dynamics of propagating vortices which may result in applications in optical switching, optical data storage, manipulation of micro-particles and optical limiting for eye protection.
Spatio-temporal optical vortices
Jhajj, N; Rosenthal, E W; Zahedpour, S; Wahlstrand, J K; Milchberg, H M
2016-01-01
We present the first experimental, theoretical, and numerical evidence of spatio-temporal optical vortices (STOVs). Quantized STOVs are a fundamental element of the nonlinear collapse and subsequent propagation of short optical pulses in material media. A STOV consists of a ring-shaped null in the electromagnetic field about which the phase is spiral, forming a dynamic torus which is concentric with and tracks the propagating pulse. Depending on the sign of the material dispersion, the local electromagnetic energy flow is saddle or spiral about the STOV. STOVs are born and evolve conserving topological charge; they can be simultaneously created in pairs with opposite windings, or generated from a point null. Our results, here obtained for optical pulse collapse and filamentation in air, are generalizable to a broad class of nonlinearly propagating waves.
Eto, Minoru; Gudnason, Sven Bjarke; Konishi, Kenichi; Nagashima, Takayuki; Nitta, Muneto; Ohashi, Keisuke; Vinci, Walter
2009-01-01
We study what might be called fractional vortices, vortex configurations with the minimum winding from the viewpoint of their topological stability, but which are characterized by various notable substructures in the transverse energy distribution. The fractional vortices occur in diverse Abelian or non-Abelian generalizations of the Higgs model. The global and local features characterizing these are studied, and we identify the two crucial ingredients for their occurrence - the vacuum degeneracy leading to non-trivial vacuum moduli M, and the BPS nature of the vortices. Fractional vortices are further classified into two kinds. The first type of such vortices appear when M has orbifold Z_n singularities; the second type occurs in systems in which the vacuum moduli space M possesses either a deformed geometry or some singularity. These general features are illustrated with several concrete models.
Hall, P.
1985-01-01
The Taylor-Gortler vortex instability equations are formulated for steady and unsteady interacting boundary layer flows of the type which arise in triple-deck theory. The effective Gortler number is shown to be a function of the all shape in the boundary layer and the possibility of both steady and unsteady Taylor-Gortler modes exists. As an example the steady flow in a symmetrically constricted channel is considered and it is shown that unstable Gortler vortices exist before the boundary layers at the wall develop the Goldstein singularity. As an example of an unsteady spatially varying basic state the instability of high frequency large amplitude Tollmien-Schlichting waves in a curved channel were considered. It is shown that they are unstable in the first Stokes layer stage of the hierarchy of nonlinear states. The Tollmien-Schlichting waves are shown to be unstable in the presence of both convex and concave curvature.
Stability of periodic arrays of vortices
Dauxois, T; Tuckerman, L S; Dauxois, Thierry; Fauve, Stephan; Tuckerman, Laurette
1995-01-01
The stability of periodic arrays of Mallier-Maslowe or Kelvin-Stuart vortices is discussed. We derive with the energy-Casimir stability method the nonlinear stability of this solution in the inviscid case as a function of the solution parameters and of the domain size. We exhibit the maximum size of the domain for which the vortex street is stable. By adapting a numerical time-stepping code, we calculate the linear stability of the Mallier-Maslowe solution in the presence of viscosity and compensating forcing. Finally, the results are discussed and compared to a recent experiment in fluids performed by Tabeling et al.~[Europhysics Letters {\\bf 3}, 459 (1987)]. Electromagnetically driven counter-rotating vortices are unstable above a critical electric current, and give way to co-rotating vortices. The importance of the friction at the bottom of the experimental apparatus is also discussed.
On relation between scalar interfaces and vorticity in inviscid flows
Ramesh, O. N.; Patwardhan, Saurabh
2013-11-01
A great variety of applications like pollutant mixing in the atmosphere, mixing of reactants in combustion highlight the importance of passive scalar dynamics in fluid flows. The other dynamically important variable in the study of fluid flow is the vorticity. Vorticity though, unlike a passive scalar, does affect the fluid motion. The dynamics of scalar (linear) and vorticity (non-linear) are governed by the equations which inherently have different characteristics. This paper addresses the question of the faithfulness of representation of vorticity by scalar marker and the motivation for this comes from the experiment of Head and Bandyopadhyay (1981) which showed the existence of coherent vortices by using smoke flow visualization in a turbulent boundary layer. We will show analytically in regions where the molecular diffusion effects are negligible, the vorticity and scalar gradients are orthogonal to each other. The iso- surface of scalar follows the vorticity in an inviscid situation. Also, we will demonstrate that in the case of unsteady burgers vortex and vortex shedding behind a finite circular cylinder, the scalar gradient is orthogonal to vorticity and inner product of vorticity and scalar gradients is zero in regions away from the wall.
Vortices and Vortical Structures in Internal Aerodynamics
Institute of Scientific and Technical Information of China (English)
RudolfDvorak
1997-01-01
The paper aims at summarizing the author's recent phenomenological study of the origin,development and identification of vortical structures in internal aerodynamics.A connection between evolution of these structures and flow separation in closed curved channels is also discussed.It has been shown that in real fluids the individual vortex cores very sonn lose their identity and merge into a new dissipative structure,the properties of which still have to be defined.
Breathers on Quantized Superfluid Vortices
Salman, Hayder
2013-01-01
We consider the propagation of breathers along a quantised superfluid vortex. Using the correspondence between the local induction approximation (LIA) and the nonlinear Schr\\"odinger equation, we identify a set of initial conditions corresponding to breather solutions of vortex motion governed by the LIA. These initial conditions, which give rise to a long-wavelength modulational instability, result in the emergence of large amplitude perturbations that are localised in both space and time. The emergent structures on the vortex filament are analogous to loop solitons. Although the breather solutions we study are exact solutions of the LIA equations, we demonstrate through full numerical simulations that their key emergent attributes carry over to vortex dynamics governed by the Biot-Savart law and to quantized vortices described by the Gross-Pitaevskii equation. The breather excitations can lead to self-reconnections, a mechanism that can play an important role within the cross-over range of scales in superfl...
Migration of anticyclonic vortices in the protoplanetary disk
Surville, Clément
2012-01-01
This contribution describes the evolution of the protoplanetary disk using 2D numerical simulations. The 2D Euler equations are solved with the finite volume method. The numerical simulations are used to study the persistence and migration of anticyclonic vortices. Two cases are presented : (1) vortices produced by a Rossby wave instability, (2) a non-linear vortex model initially implemented into the disk. The migration of the vortices is due to spiral density waves excited by the vortex in the gas of the disk
Interaction of plasma vortices with resonant particles
DEFF Research Database (Denmark)
Jovanovic, D.; Pécseli, Hans; Juul Rasmussen, J.
1990-01-01
Kinetic effects associated with the electron motion along magnetic field lines in low‐beta plasmas are studied. Using the gyrokinetic description of electrons, a kinetic analog of the reduced magnetohydrodynamic equations is derived, and it is shown that in the strongly nonlinear regime they poss......Kinetic effects associated with the electron motion along magnetic field lines in low‐beta plasmas are studied. Using the gyrokinetic description of electrons, a kinetic analog of the reduced magnetohydrodynamic equations is derived, and it is shown that in the strongly nonlinear regime...... particles. The evolution equations indicate the possibility of excitation of plasma vortices by electron beams....
Dynamics of circular arrangements of vorticity in two dimensions
Swaminathan, Rohith V.; Ravichandran, S.; Perlekar, Prasad; Govindarajan, Rama
2016-07-01
The merger of two like-signed vortices is a well-studied problem, but in a turbulent flow, we may often have more than two like-signed vortices interacting. We study the merger of three or more identical corotating vortices initially arranged on the vertices of a regular polygon. At low to moderate Reynolds numbers, we find an additional stage in the merger process, absent in the merger of two vortices, where an annular vortical structure is formed and is long lived. Vortex merger is slowed down significantly due to this. Such annular vortices are known at far higher Reynolds numbers in studies of tropical cyclones, which have been noticed to a break down into individual vortices. In the preannular stage, vortical structures in a viscous flow are found here to tilt and realign in a manner similar to the inviscid case, but the pronounced filaments visible in the latter are practically absent in the former. Five or fewer vortices initially elongate radially, and then reorient their long axis closer to the azimuthal direction so as to form an annulus. With six or more vortices, the initial alignment is already azimuthal. Interestingly at higher Reynolds numbers, the merger of an odd number of vortices is found to proceed very differently from that of an even number. The former process is rapid and chaotic whereas the latter proceeds more slowly via pairing events. The annular vortex takes the form of a generalized Lamb-Oseen vortex (GLO), and diffuses inward until it forms a standard Lamb-Oseen vortex. For lower Reynolds number, the numerical (fully nonlinear) evolution of the GLO vortex follows exactly the analytical evolution until merger. At higher Reynolds numbers, the annulus goes through instabilities whose nonlinear stages show a pronounced difference between even and odd mode disturbances. Here again, the odd mode causes an early collapse of the annulus via decaying turbulence into a single central vortex, whereas the even mode disturbance causes a more
Vortices and Jacobian varieties
DEFF Research Database (Denmark)
Manton, Nicholas S.; M. Romão, Nuno
2011-01-01
We investigate the geometry of the moduli space of N-vortices on line bundles over a closed Riemann surface of genus g > 1, in the little explored situation where 1 = 1, the vortex metric typically degenerates as the dissolving limit is approached, the degeneration occurring precisely...
Theory of Concentrated Vortices
DEFF Research Database (Denmark)
Alekseenko, Sergey; Kuibin, Pavel; Okulov, Valery
This book presents comprehensive and authoritative coverage of the wide field of concentrated vortices observed in nature and technique. The methods for research of their kinematics and dynamics are considered. Special attention is paid to the flows with helical symmetry. The authors have describ...
CSIR Research Space (South Africa)
Roux, FS
2014-02-01
Full Text Available Optical vortices are always created or annihilated in pairs with opposite topological charges. However, the presence of such a vortex dipole does not directly indicate whether they are associated with a creation or an annihilation event. Here we...
Moist Potential Vorticity and Up-Sliding Slantwise Vorticity Development
Institute of Scientific and Technical Information of China (English)
GUI Xiao-Peng; GAO Shou-Ting; WU Guo-Xiong
2003-01-01
By using the moist potential vorticity equation derived from complete atmospheric equations including the effect of mass forcing, the theory of up-sliding slantwise vorticity development (USVD) is proposed based on the theory of slantwise vorticity development. When an air parcel slides up along a slantwise isentropic surface, its vertical component of relative vorticity is developed. Based on the theory of USVD, a complete vertical vorticity equation is expected with mass forcing, which explicitly includes the effect of both internal forcings and external forcings.
The Finiteness of Moffatt vortices
Kalita, Jiten C; Panda, Swapnendu; Unal, Aynur
2016-01-01
Till date, the sequence of vortices present in the solid corners of internal viscous incompressible flows, widely known as Moffatt vortices was thought to be infinite. In this paper, we propose two topological equivalence classes of Moffatt vortices in terms of orientation-preserving homeomorphism as well as critical point theory. We further quantify the centers of vortices as fixed points through Brower fixed point theorem and define boundary of a vortex as circle cell. With the aid of these new developments and some existing theorems in topology, we provide six proofs establishing that the sequence of Moffatt vortices cannot be infinite; in fact it is at most finite.
Vortices and nanostructured superconductors
2017-01-01
This book provides expert coverage of modern and novel aspects of the study of vortex matter, dynamics, and pinning in nanostructured and multi-component superconductors. Vortex matter in superconducting materials is a field of enormous beauty and intellectual challenge, which began with the theoretical prediction of vortices by A. Abrikosov (Nobel Laureate). Vortices, vortex dynamics, and pinning are key features in many of today’s human endeavors: from the huge superconducting accelerating magnets and detectors at the Large Hadron Collider at CERN, which opened new windows of knowledge on the universe, to the tiny superconducting transceivers using Rapid Single Flux Quanta, which have opened a revolutionary means of communication. In recent years, two new features have added to the intrinsic beauty and complexity of the subject: nanostructured/nanoengineered superconductors, and the discovery of a range of new materials showing multi-component (multi-gap) superconductivity. In this book, leading researche...
Cropp, Bethan; Turcati, Rodrigo
2015-01-01
In the analogue gravity framework, the acoustic disturbances in a moving fluid can be described by an equation of motion identical to a relativistic scalar massless field propagating in a curved spacetime. This description is possible only when the fluid under consideration is barotropic, inviscid and irrotational. In this case, the propagation of the perturbations is governed by an acoustic metric which depends algebrically on the local speed of sound, density and the background flow velocity, the latter assumed to be vorticity free. In this work we provide an straightforward extension in order to go beyond the irrotational constraint. Using a charged --- relativistic and non-relativistic --- Bose--Einstein condensate as a physical system, we show that in the low momentum limit and performing the eikonal approximation we can derive a d'Alembertian equation of motion for the charged phonons where the emergent acoustic metric depends on a flow velocity in the presence of vorticity.
Cropp, Bethan; Liberati, Stefano; Turcati, Rodrigo
2016-06-01
In the analog gravity framework, the acoustic disturbances in a moving fluid can be described by an equation of motion identical to a relativistic scalar massless field propagating in curved space-time. This description is possible only when the fluid under consideration is barotropic, inviscid, and irrotational. In this case, the propagation of the perturbations is governed by an acoustic metric that depends algebrically on the local speed of sound, density, and the background flow velocity, the latter assumed to be vorticity-free. In this work we provide a straightforward extension in order to go beyond the irrotational constraint. Using a charged—relativistic and nonrelativistic—Bose-Einstein condensate as a physical system, we show that in the low-momentum limit and performing the eikonal approximation we can derive a d’Alembertian equation of motion for the charged phonons where the emergent acoustic metric depends on flow velocity in the presence of vorticity.
Vorticity in holographic fluids
Caldarelli, Marco M; Petkou, Anastasios C; Petropoulos, P Marios; Pozzoli, Valentina; Siampos, Konstadinos
2012-01-01
In view of the recent interest in reproducing holographically various properties of conformal fluids, we review the issue of vorticity in the context of AdS/CFT. Three-dimensional fluids with vorticity require four-dimensional bulk geometries with either angular momentum or nut charge, whose boundary geometries fall into the Papapetrou--Randers class. The boundary fluids emerge in stationary non-dissipative kinematic configurations, which can be cyclonic or vortex flows, evolving in compact or non-compact supports. A rich network of Einstein's solutions arises, naturally connected with three-dimensional Bianchi spaces. We use Fefferman--Graham expansion to handle holographic data from the bulk and discuss the alternative for reversing the process and reconstruct the exact bulk geometries.
Puffed Noncommutative Nonabelian Vortices
Bouatta, N; MacCaferri, C; Bouatta, Nazim; Evslin, Jarah; Maccaferri, Carlo
2007-01-01
We present new solutions of noncommutative gauge theories in which coincident unstable vortices expand into unstable circular shells. As the theories are noncommutative, the naive definition of the locations of the vortices and shells is gauge-dependent, and so we define and calculate the profiles of these solutions using the gauge-invariant noncommutative Wilson lines introduced by Gross and Nekrasov. We find that charge 2 vortex solutions are characterized by two positions and a single nonnegative real number, which we demonstrate is the radius of the shell. We find that the radius is identically zero in all 2-dimensional solutions. If one considers solutions that depend on an additional commutative direction, then there are time-dependent solutions in which the radius oscillates, resembling a braneworld description of a cyclic universe. There are also smooth BIon-like space-dependent solutions in which the shell expands to infinity, describing a vortex ending on a domain wall.
Vortices and Jacobian varieties
Manton, Nicholas S
2010-01-01
We investigate the geometry of the moduli space of N-vortices on line bundles over a closed Riemann surface of genus g > 1, in the little explored situation where 1 = 1, the vortex metric typically degenerates as the dissolving limit is approached, the degeneration occurring precisely on the critical locus of the Abel-Jacobi map at degree N. We describe consequences of this phenomenon from the point of view of multivortex dynamics.
Vortices around Dragonfly Wings
Kweon, Jihoon; Choi, Haecheon
2009-01-01
Dragonfly beats its wings independently, resulting in its superior maneuverability. Depending on the magnitude of phase difference between the fore- and hind-wings of dragonfly, the vortical structures and their interaction with wings become significantly changed, and so does the aerodynamic performance. In this study, we consider hovering flights of modelled dragonfly with three different phase differences (phi=-90, 90, 180 degrees). The three-dimensional wing shape is based on that of Aesch...
Drift and ion acoustic wave driven vortices with superthermal electrons
Energy Technology Data Exchange (ETDEWEB)
Ali Shan, S. [Theoretical Plasma Physics Division, PINSTECH, P.O. Nilore, Islamabad (Pakistan); National Centre For Physics (NCP), Shahdra Valley Road, QAU Campus, 44000 Islamabad (Pakistan); Pakistan Institute of Engineering and Applied Sciences (PIEAS), Islamabad (Pakistan); Haque, Q. [Theoretical Plasma Physics Division, PINSTECH, P.O. Nilore, Islamabad (Pakistan); National Centre For Physics (NCP), Shahdra Valley Road, QAU Campus, 44000 Islamabad (Pakistan)
2012-08-15
Linear and nonlinear analysis of coupled drift and acoustic mode is presented in an inhomogeneous electron-ion plasma with {kappa}-distributed electrons. A linear dispersion relation is found which shows that the phase speed of both the drift wave and the ion acoustic wave decreases in the presence of superthermal electrons. Several limiting cases are also discussed. In the nonlinear regime, stationary solutions in the form of dipolar and monopolar vortices are obtained. It is shown that the condition for the boundedness of the solution implies that the speed of drift wave driven vortices reduces with increase in superthermality effect. Ignoring density inhomogeniety, it is investigated that the lower and upper limits on the speed of the ion acoustic driven vortices spread with the inclusion of high energy electrons. The importance of results with reference to space plasmas is also pointed out.
Remarks on stability of the rotating shallow-water vortices in the frontal dynamics regime
Energy Technology Data Exchange (ETDEWEB)
Jelloul, M.B.; Zeitlin, V. [P. et M. Curie Univ., Paris (France). Lab. de Meteorologie Dynamique
1999-12-01
Stability properties of large-scale strongly nonlinear isolated vortices in the rotating shallow water on the f-plane are analysed. Working first in the framework of the balanced frontal dynamics equations, the authors demonstrate that vortices of arbitrary sign with monotonous profiles of the free-surface elevation are formally stable and establish criteria for nonlinear stability. Stability in the framework of the full rotating shallow-water equations is also discussed and a conditional stability criterion is obtained.
Vorticity from irrotationally forced flow
Del Sordo, Fabio
2010-01-01
In the interstellar medium the turbulence is believed to be forced mostly through supernova explosions. In a first approximation these flows can be written as a gradient of a potential being thus devoid of vorticity. There are several mechanisms that could lead to vorticity generation, like viscosity and baroclinic terms, rotation, shear and magnetic fields, but it is not clear how effective they are, neither is it clear whether the vorticity is essential in determining the turbulent diffusion acting in the ISM. Here we present a study of the role of rotation, shear and baroclinicity in the generation of vorticity in the ISM.
General vorticity conservation
Gümral, H
1998-01-01
The motion of an incompressible fluid in Lagrangian coordinates involves infinitely many symmetries generated by the left Lie algebra of group of volume preserving diffeomorphisms of the three dimensional domain occupied by the fluid. Utilizing a 1+3-dimensional Hamiltonian setting an explicit realization of this symmetry algebra and the related Lagrangian and Eulerian conservation laws are constructed recursively. Their Lie algebraic structures are inherited from the same construction. The laws of general vorticity and helicity conservations are formulated globally in terms of invariant differential forms of the velocity field.
Bullimore, Mathew; Gaiotto, Davide; Hilburn, Justin; Kim, Hee-Cheol
2016-01-01
In three-dimensional gauge theories, monopole operators create and destroy vortices. We explore this idea in the context of 3d N=4 gauge theories in the presence of an Omega-background. In this case, monopole operators generate a non-commutative algebra that quantizes the Coulomb-branch chiral ring. The monopole operators act naturally on a Hilbert space, which is realized concretely as the equivariant cohomology of a moduli space of vortices. The action furnishes the space with the structure of a Verma module for the Coulomb-branch algebra. This leads to a new mathematical definition of the Coulomb-branch algebra itself, related to that of Braverman-Finkelberg-Nakajima. By introducing additional boundary conditions, we find a construction of vortex partition functions of 2d N=(2,2) theories as overlaps of coherent states (Whittaker vectors) for Coulomb-branch algebras, generalizing work of Braverman-Feigin-Finkelberg-Rybnikov on a finite version of the AGT correspondence. In the case of 3d linear quiver gaug...
Vortices revealed: Swimming faster
van Houwelingen, Josje; van de Water, Willem; Kunnen, Rudie; van Heijst, Gertjan; Clercx, Herman
2016-11-01
Understanding and optimizing the propulsion in human swimming requires insight into the hydrodynamics of the flow around the swimmer. Experiments and simulations addressing the hydrodynamics of swimming have been conducted in studies before, including the visualization of the flow using particle image velocimetry (PIV). The main objective in this study is to develop a system to visualize the flow around a swimmer in practice inspired by this technique. The setup is placed in a regular swimming pool. The use of tracer particles and lasers to illuminate the particles is not allowed. Therefore, we choose to work with air bubbles with a diameter of 4 mm, illuminated by ambient light. Homogeneous bubble curtains are produced by tubes implemented in the bottom of the pool. The bubble motion is captured by six cameras placed in underwater casings. A first test with the setup has been conducted by pulling a cylinder through the bubbles and performing a PIV analysis. The vorticity plots of the resulting data show the expected vortex street behind the cylinder. The shedding frequency of the vortices resembles the expected frequency. Thus, it is possible to identify and follow the coherent structures. We will discuss these results and the first flow measurements around swimmers.
Bethuel, Fabrice; Helein, Frederic
2017-01-01
This book is concerned with the study in two dimensions of stationary solutions of uɛ of a complex valued Ginzburg-Landau equation involving a small parameter ɛ. Such problems are related to questions occurring in physics, e.g., phase transition phenomena in superconductors and superfluids. The parameter ɛ has a dimension of a length which is usually small. Thus, it is of great interest to study the asymptotics as ɛ tends to zero. One of the main results asserts that the limit u-star of minimizers uɛ exists. Moreover, u-star is smooth except at a finite number of points called defects or vortices in physics. The number of these defects is exactly the Brouwer degree – or winding number – of the boundary condition. Each singularity has degree one – or as physicists would say, vortices are quantized. The singularities have infinite energy, but after removing the core energy we are lead to a concept of finite renormalized energy. The location of the singularities is completely determined by minimiz...
Tidal and residual flows in the western Dutch Wadden Sea III: Vorticity balances
Ridderinkhof, H.
A vorticity-dynamics approach is used to examine the origin of the small-scale residual current field in the western Dutch Wadden Sea. For a representative part of the Wadden Sea, the magnitude of vorticity and of terms in the balance equation for vorticity is determined on the basis of results from a two-dimensional numerical model. The torque from bottom friction along the side walls of the tidal channels appears to be the dominating mechanism in generating tidal relative vorticity, the magnitude of which is much larger than planetary vorticity. Especially near a tidal inlet, stretching and squeezing of fluid columns is of importance in increasing/decreasing relative vorticity. Averaging over a tidal period shows, compared to the tidal equations, an increased influence of the non-linear advective and streching/squeezing terms in the tidally-averaged balance. However, although the relative influence of these strong non-linear terms increases, the influence of the weak non-linear terms originating in bottom friction cannot be ignored. The mechanism responsible for the headland eddies near a tidal inlet and the topographical eddies in the channels of the Wadden Sea is essentially the same, viz. the transfer of vorticity from a source region where this vorticity is produced by differential bottom friction, to adjacent regions. This transfer of tidal vorticity, or advection, is most effective near a transition from straight to curved isobaths where a gradient in the production of tidal vorticity occurs. This is illustrated by showing the vorticity possessed by a particular fluid column during a tidal excursion. The dominant influence of the bathymetry on the small scale residual current pattern is used for a qualitative discussion of the residual flow field in other parts of our numerical model.
How strong are the Rossby vortices?
Meheut, H; Lai, D
2013-01-01
The Rossby wave instability, associated with density bumps in differentially rotating discs, may arise in several different astrophysical contexts, such as galactic or protoplanetary discs. While the linear phase of the instability has been well studied, the nonlinear evolution and especially the saturation phase remain poorly understood. In this paper, we test the non-linear saturation mechanism analogous to that derived for wave-particle interaction in plasma physics. To this end we perform global numerical simulations of the evolution of the instability in a two-dimensional disc. We confirm the physical mechanism for the instability saturation and show that the maximum amplitude of vorticity can be estimated as twice the linear growth rate of the instability. We provide an empirical fitting formula for this growth rate for various parameters of the density bump. We also investigate the effects of the azimuthal mode number of the instability and the energy leakage in the spiral density waves. Finally, we sh...
Abelian Vortices with Singularities
Baptista, J M
2012-01-01
Let L --> X be a complex line bundle over a compact connected Riemann surface. We consider the abelian vortex equations on L when the metric on the surface has finitely many point degeneracies or conical singularities and the line bundle has parabolic structure. These conditions appear naturally in the study of vortex configurations with constraints, or configurations invariant under the action of a finite group. We first show that the moduli space of singular vortex solutions is the same as in the regular case. Then we compute the total volume and total scalar curvature of the moduli space singular vortex solutions. These numbers differ from the case of regular vortices by a very natural term. Finally we exhibit explicit non-trivial vortex solutions over the thrice punctured hyperbolic sphere.
Brief Analysis of Vorticity in Soil Hydrodynamics
Nader, José Jorge
2014-01-01
This note discusses basic properties of vorticity in groundwater flow theory. An evolution equation for the vorticity vector is derived to demonstrate that, when present, vorticity decreases very rapidly. In addition, it is shown how vorticity affects, though very little, the hydraulic head directional variation in the vicinity of a point.
Fresnel Lens with Embedded Vortices
Directory of Open Access Journals (Sweden)
Sunil Vyas
2012-01-01
Full Text Available Vortices of different charges are embedded in a wavefront that has quadratic phase variation, and the intensity distribution near the focal plane is studied. This method may be useful in realizing complicated beam profiles. We have experimentally demonstrated the generation of vortex arrays having integer as well as fractional topological charges that produce different intensity profiles at the focal plane. The phase variation realized on a spatial light modulator (SLM acts as a Fresnel lens with embedded vortices.
Primordial vorticity and gradient expansion
Giovannini, Massimo; Rezaei, Zahra
2012-02-01
The evolution equations of the vorticities of the electrons, ions and photons in a pre-decoupling plasma are derived, in a fully inhomogeneous geometry, by combining the general relativistic gradient expansion and the drift approximation within the Adler-Misner-Deser decomposition. The vorticity transfer between the different species is discussed in this novel framework and a set of general conservation laws, connecting the vorticities of the three-component plasma with the magnetic field intensity, is derived. After demonstrating that a source of large-scale vorticity resides in the spatial gradients of the geometry and of the electromagnetic sources, the total vorticity is estimated to lowest order in the spatial gradients and by enforcing the validity of the momentum constraint. By acknowledging the current bounds on the tensor to scalar ratio in the (minimal) tensor extension of the ΛCDM paradigm, the maximal comoving magnetic field induced by the total vorticity turns out to be, at most, of the order of 10-37 G over the typical comoving scales ranging between 1 and 10 Mpc. While the obtained results seem to be irrelevant for seeding a reasonable galactic dynamo action, they demonstrate how the proposed fully inhomogeneous treatment can be used for the systematic scrutiny of pre-decoupling plasmas beyond the conventional perturbative expansions.
Primordial vorticity and gradient expansion
Giovannini, Massimo
2012-01-01
The evolution equations of the vorticities of the electrons, ions and photons in a pre-decoupling plasma are derived, in a fully inhomogeneous geometry, by combining the general relativistic gradient expansion and the drift approximation within the Adler-Misner-Deser decomposition. The vorticity transfer between the different species is discussed in this novel framework and a set of general conservation laws, connecting the vorticities of the three-component plasma with the magnetic field intensity, is derived. After demonstrating that a source of large-scale vorticity resides in the spatial gradients of the geometry and of the electromagnetic sources, the total vorticity is estimated to lowest order in the spatial gradients and by enforcing the validity of the momentum constraint. By acknowledging the current bounds on the tensor to scalar ratio in the (minimal) tensor extension of the $\\Lambda$CDM paradigm the maximal comoving magnetic field induced by the total vorticity turns out to be, at most, of the or...
Nonautonomous Vortices in (2+1)-Dimensional Graded-Index Waveguide
Lai, Xian-Jing; Cai, Xiao-Ou; Zhang, Jie-Fang
2015-05-01
With the help of self-similarity transformation, we construct and study the nonautonomous vortices with different topological charges inside a planar graded-index nonlinear waveguide, analytically, and numerically. Although these vortices are approximate, they can reflect the real properties of self-similar optical beam during a short-term propagation. Existence of these autonomous vortices require delicate balances between the system parameters such as diffraction, nonlinearity, gain, and external potential. We are concerned with some special but interesting situations, and discussing the changes of the height, width, energy, and central position of the vortices as the increase of propagation distance. Moreover, we are also interested in the azimuthal modulational instability of the system, and comparing our prediction for the modulational instability growth rates to numerical results.
The role of coherent vorticity in turbulent transport in resistive drift-wave turbulence
Bos, Wouter J T; Benkadda, Sadruddin; Farge, Marie; Schneider, Kai; 10.1063/1.2956640
2011-01-01
The coherent vortex extraction method, a wavelet technique for extracting coherent vortices out of turbulent flows, is applied to simulations of resistive drift-wave turbulence in magnetized plasma (Hasegawa-Wakatani system). The aim is to retain only the essential degrees of freedom, responsible for the transport. It is shown that the radial density flux is carried by these coherent modes. In the quasi-hydrodynamic regime, coherent vortices exhibit depletion of the polarization-drift nonlinearity and vorticity strongly dominates strain, in contrast to the quasiadiabatic regime.
The variety of stable vortical solitons in Ginzburg-Landau media with radially inhomogeneous losses
Skarka, V; Leblond, H; Malomed, B A; Mihalache, D
2010-01-01
Using a combination of the variation approximation (VA) and direct simulations, we consider the light transmission in nonlinearly amplified bulk media, taking into account the localization of the gain, i.e., the linear loss shaped as a parabolic function of the transverse radius, with a minimum at the center. The balance of the transverse diffraction, self-focusing, gain, and the inhomogeneous loss provide for the hitherto elusive stabilization of vortex solitons in a large zone of the parameter space. Adjacent to it, stability domains are found for several novel kinds of localized vortices, including spinning elliptically shaped ones, eccentric elliptic vortices which feature double rotation, spinning crescents, and breathing vortices.
Potential Vorticity Evolution in the Co-orbital Region of Embedded Protoplanets
Energy Technology Data Exchange (ETDEWEB)
Koller, J. [Rice Univ., Houston, TX (United States)
2004-04-01
This thesis presents two-dimensional hydrodynamic disk simulations with embedded protoplanets, emphasizing the non-linear dynamics in the co-orbital region. In particular, it demonstrates how a protoplanetary disk responds to embedded low mass planets at the inviscid limit. Since the potential vorticity (PV) flow is not conserved, due to the spiral shocks and possibly boundary layer effects emanating from the planet, the PV profile develops inflection points which eventually render the flow unstable. Vortices are produced in association with the potential vorticity minima. Born in the separatrix region, these vortices experience close encounters with the planet, consequently exerting strong torques on the planet. The existence of these vortices, if confirmed, have important implications on planetary migration rates. The formation of vortices is discussed in more detail and a key parameter is found which depends solely on planet mass and sound speed. With this key parameter, one can predict the disk evolution, PV growth rates, and threshold conditions for forming vortices in the co-orbital region. An analytical estimate for the change of PV due to shocks is compared to the actual change in PV in the hydrodynamic simulations. They match well except in the inner region where vortices form. In addition, extensive resolution tests were carried out but uncertainties remain about the physics of this particular region.
Potential Vorticity Evolution in the Co-orbital Region of Embedded Protoplanets
Energy Technology Data Exchange (ETDEWEB)
J. Koller
2004-09-01
This thesis presents two-dimensional hydrodynamic disk simulations with embedded protoplanets, emphasizing the non-linear dynamics in the co-orbital region. In particular, it demonstrates how a protoplanetary disk responds to embedded low mass planets at the inviscid limit. Since the potential vorticity (PV) flow is not conserved, due to the spiral shocks and possibly boundary layer effects emanating from the planet, the PV profile develops inflection points which eventually render the flow unstable. Vortices are produced in association with the potential vorticity minima. Born in the separatrix region, these vortices experience close encounters with the planet, consequently exerting strong torques on the planet. The existence of these vortices, if confirmed, have important implications on planetary migration rates. The formation of vortices is discussed in more detail and a key parameter is found which depends solely on planet mass and sound speed. With this key parameter, one can predict the disk evolution, PV growth rates, and threshold conditions for forming vortices in the co-orbital region. An analytical estimate for the change of PV due to shocks is compared to the actual change in PV in the hydrodynamic simulations. They match well except in the inner region where vortices form. In addition, extensive resolution tests were carried out but uncertainties remain about the physics of this particular region.
Energy Technology Data Exchange (ETDEWEB)
Gaber, Tobias
2007-07-01
In this thesis static and dynamic properties of fractional vortices in long Josephson junctions are investigated. Fractional vortices are circulating supercurrents similar to the well-known Josephson fluxons. Yet, they show the distinguishing property of carrying only a fraction of the magnetic flux quantum. Fractional vortices are interesting non-linear objects. They spontaneously appear and are pinned at the phase discontinuity points of so called 0-{kappa} junctions but can be bend or flipped by external forces like bias currents or magnetic fields. 0-{kappa} junctions and fractional vortices are generalizations of the well-known 0-{pi} junctions and semifluxons, where not only phase jumps of pi but arbitrary values denoted by kappa are considered. By using so-called artificial 0-{kappa} junctions that are based on standard Nb-AlO{sub x}-Nb technology the classical dynamics of fractional vortices has been investigated experimentally for the very first time. Here, half-integer zero field steps could be observed. These voltage steps on the junction's current-voltage characteristics correspond to the periodic flipping/hopping of fractional vortices. In addition, the oscillatory eigenmodes of fractional vortices were investigated. In contrast to fluxons fractional vortices have an oscillatory eigenmode with a frequency within the plasma gap. Using resonance spectroscopy the dependence of the eigenmode frequency on the flux carried by the vortex and an applied bias current was determined. (orig.)
Superconducting vortices in semilocal models.
Forgács, Péter; Reuillon, Sébastien; Volkov, Mikhail S
2006-02-01
It is shown that the SU(2) semilocal model--the Abelian Higgs model with two complex scalars--admits a new class of stationary, straight string solutions carrying a persistent current and having finite energy per unit length. In the plane orthogonal to their direction they correspond to a nontrivial deformation of the embedded Abrikosov-Nielsen-Olesen (ANO) vortices by the current flowing through them. The new solutions bifurcate with the ANO vortices in the limit of vanishing current. They can be either static or stationary. In the stationary case, the relative phase of the two scalars rotates at constant velocity, giving rise to an electric field and angular momentum, while the energy remains finite. The new static vortex solutions have lower energy than the ANO vortices and could be of considerable importance in various physical systems (from condensed matter to cosmic strings).
General aspects of optical vortices
CSIR Research Space (South Africa)
Roux, FS
2009-01-01
Full Text Available . Stef Roux CSIR National Laser Centre PO Box 395, Pretoria 0001, South Africa CSIR National Laser Centre – p.1/32 Contents . Definition of an optical vortex . Topological charge and vortex morphology . How to detect a vortex — interferometry . How... to generate optical vortices CSIR National Laser Centre – p.2/32 Persistent dark spots Optical vortices CSIR National Laser Centre – p.3/32 Speckle field Amplitude Phase CSIR National Laser Centre – p.4/32 Singular phase function CSIR National Laser Centre – p...
On the Stability of Dust-Laden Protoplanetary Vortices
Chang, Philip
2010-01-01
The formation of planetesimals via gravitational instability of the dust layer in a protoplanetary disks demands that there be local patches where dust is concentrated by a factor of $\\sim$ a few $\\times 10^3$ over the background value. Vortices in protoplanetary disks may concentrate dust to these values allowing them to be the nurseries of planetesimals. The concentration of dust in the cores of vortices increases the dust-gas ratio of the core compared to the background disk, creating a "heavy vortex." In this work, we show that these vortices are subject to an instability which we have called the heavy-core instability. Using Floquet theory, we show that this instability occurs in elliptical protoplanetary vortices when the gas-dust density of the core of the vortex is heavier than the ambient gas-dust density by a few tens of percent. The heavy-core instability grows very rapidly, with a growth timescale of a few vortex rotation periods. While the nonlinear evolution of this instability remains unknown, ...
Streaming vorticity flux from oscillating walls with finite amplitude
Wu, J. Z.; Wu, X. H.; Wu, J. M.
1993-01-01
How to describe vorticity creation from a moving wall is a long standing problem. This paper discusses relevant issues at the fundamental level. First, it is shown that the concept of 'vorticity flux due to wall acceleration' can be best understood by following fluid particles on the wall rather than observing the flow at fixed spatial points. This is of crucial importance when the time-averaged flux is to be considered. The averaged flux has to be estimated in a wall-fixed frame of reference (in which there is no flux due to wall acceleration at all); or, if an inertial frame of reference is used, the generalized Lagrangian mean (GLM) also gives the same result. Then, for some simple but typical configurations, the time-averaged vorticity flux from a harmonically oscillating wall with finite amplitude is analyzed, without appealing to small perturbation. The main conclusion is that the wall oscillation will produce an additional mean vorticity flux (a fully nonlinear streaming effect), which is partially responsible for the mechanism of vortex flow control by waves. The results provide qualitative explanation for some experimentally and/or computationally observed phenomena.
Streaming vorticity flux from oscillating walls with finite amplitude
Wu, J. Z.; Wu, X. H.; Wu, J. M.
1993-01-01
How to describe vorticity creation from a moving wall is a long standing problem. This paper discusses relevant issues at the fundamental level. First, it is shown that the concept of 'vorticity flux due to wall acceleration' can be best understood by following fluid particles on the wall rather than observing the flow at fixed spatial points. This is of crucial importance when the time-averaged flux is to be considered. The averaged flux has to be estimated in a wall-fixed frame of reference (in which there is no flux due to wall acceleration at all); or, if an inertial frame of reference is used, the generalized Lagrangian mean (GLM) also gives the same result. Then, for some simple but typical configurations, the time-averaged vorticity flux from a harmonically oscillating wall with finite amplitude is analyzed, without appealing to small perturbation. The main conclusion is that the wall oscillation will produce an additional mean vorticity flux (a fully nonlinear streaming effect), which is partially responsible for the mechanism of vortex flow control by waves. The results provide qualitative explanation for some experimentally and/or computationally observed phenomena.
Topological Vortices in Superfluid Films
Institute of Scientific and Technical Information of China (English)
WANGJun-Ping; DUANYi-Shi
2005-01-01
We study the topological structure of the vortex system in a superfluid film. Explicit expressions for the vortex density and velocity field as functions of the superfluid order parameter are derived. The evolution of vortices is also studied from the topological properties of the superfluid order parameter field.
Extreme-Ultraviolet Vortices from a Free-Electron Laser
Directory of Open Access Journals (Sweden)
Primož Rebernik Ribič
2017-08-01
Full Text Available Extreme-ultraviolet vortices may be exploited to steer the magnetic properties of nanoparticles, increase the resolution in microscopy, and gain insight into local symmetry and chirality of a material; they might even be used to increase the bandwidth in long-distance space communications. However, in contrast to the generation of vortex beams in the infrared and visible spectral regions, production of intense, extreme-ultraviolet and x-ray optical vortices still remains a challenge. Here, we present an in-situ and an ex-situ technique for generating intense, femtosecond, coherent optical vortices at a free-electron laser in the extreme ultraviolet. The first method takes advantage of nonlinear harmonic generation in a helical undulator, producing vortex beams at the second harmonic without the need for additional optical elements, while the latter one relies on the use of a spiral zone plate to generate a focused, micron-size optical vortex with a peak intensity approaching 10^{14} W/cm^{2}, paving the way to nonlinear optical experiments with vortex beams at short wavelengths.
Computational simulations of vorticity enhanced diffusion
Vold, Erik L.
1999-11-01
Computer simulations are used to investigate a phenomenon of vorticity enhanced diffusion (VED), a net transport and mixing of a passive scalar across a prescribed vortex flow field driven by a background gradient in the scalar quantity. The central issue under study here is the increase in scalar flux down the gradient and across the vortex field. The numerical scheme uses cylindrical coordinates centered with the vortex flow which allows an exact advective solution and 1D or 2D diffusion using simple numerical methods. In the results, the ratio of transport across a localized vortex region in the presence of the vortex flow over that expected for diffusion alone is evaluated as a measure of VED. This ratio is seen to increase dramatically while the absolute flux across the vortex decreases slowly as the diffusion coefficient is decreased. Similar results are found and compared for varying diffusion coefficient, D, or vortex rotation time, τv, for a constant background gradient in the transported scalar vs an interface in the transported quantity, and for vortex flow fields constant in time vs flow which evolves in time from an initial state and with a Schmidt number of order unity. A simple analysis shows that for a small diffusion coefficient, the flux ratio measure of VED scales as the vortex radius over the thickness for mass diffusion in a viscous shear layer within the vortex characterized by (Dτv)1/2. The phenomenon is linear as investigated here and suggests that a significant enhancement of mixing in fluids may be a relatively simple linear process. Discussion touches on how this vorticity enhanced diffusion may be related to mixing in nonlinear turbulent flows.
Vorticity production through rotation, shear and baroclinicity
Del Sordo, Fabio
2010-01-01
In the absence of rotation and shear, and under the assumption of constant temperature or specific entropy, purely potential forcing by localized expansion waves is known to produce irrotational flows that have no vorticity. Here we study the production of vorticity under idealized conditions when there is rotation, shear, or baroclinicity, to address the problem of vorticity generation in the interstellar medium in a systematic fashion. We use three-dimensional periodic box numerical simulations to investigate the various effects in isolation. We find that for slow rotation, vorticity production in an isothermal gas is small in the sense that the ratio of the root-mean-square values of vorticity and velocity is small compared with the wavenumber of the energy carrying motions. For Coriolis numbers above a certain level, vorticity production saturates at a value where the aforementioned ratio becomes comparable with the wavenumber of the energy carrying motions. Shear also raises the vorticity production, but...
Formation and evolution of vortices in a collisional strongly coupled dusty plasma
Energy Technology Data Exchange (ETDEWEB)
Jana, Sayanee [Saha Institute of Nuclear Physics, a/AF Bidhannagar, Kolkata 700 064 (India); Banerjee, Debabrata, E-mail: debu@ustc.edu.cn [Institute for Plasma Research, Bhat, Gandhinagar 382428 (India); Chakrabarti, Nikhil [Saha Institute of Nuclear Physics, a/AF Bidhannagar, Kolkata 700 064 (India)
2016-07-29
Formation and evolution of vortices are studied in a collisional strongly coupled dusty plasma in the framework of a Generalized Hydrodynamic model (GH). Here we mainly present the nonlinear dynamical response of this strongly coupled system in presence of dust-neutral collisional drag. It is shown that the interplay between the nonlinear elastic stress and the dust-neutral collisional drag results in the generation of non-propagating monopole vortex for some duration before it starts to propagate like transverse shear wave. It is also found that the interaction between two unshielded monopole vortices having both same (co-rotating) and opposite (counter rotating) rotations result in the formation of two propagating dipole vortices of equal and unequal strength respectively. These results will provide some new understanding on the transport properties in such a strongly coupled system. The numerical simulation is carried out using a de-aliased doubly periodic pseudo-spectral code with Runge–Kutta–Gill time integrator. - Highlights: • A numerical study of vortex evolution in strongly coupled dusty plasma is presented. • Dust-neutral drag is first time considered with the Generalized Hydrodynamic model (GH). • Dust-neutral drag force balances the nonlinear effect of elastic stress. • Localized non-propagating monopole structure is generated for some duration. • Dipole vortices are produced after interaction between two monopole vortices.
Mattner, Trent; Chong, Min; Joubert, Peter
2000-11-01
Vortical flow past a sphere in a constant diameter pipe was studied experimentally in a guide vane apparatus similar to those used in fundamental experimental studies of vortex breakdown. The initial effect of swirl was to shorten the downstream separation bubble. For a small range of the swirl intensity, an almost stagnant upstream separation bubble formed. As the swirl intensity was increased, the bubble became unstable and an unsteady spiral formed. At high swirl intensity there was a mean recirculation region which penetrated far upstream while the flow on the downstream hemisphere was attached. Measurements of the velocity field were obtained using laser Doppler velocimetry. Analysis of these results suggests that the onset of upstream separation is associated with the formation of a negative azimuthal vorticity component which slows the axial flow near the axis of symmetry. This is consistent with inviscid distortion of the vortex filaments in the diverging flow approaching the sphere.
Numerical Simulation of Protoplanetary Vortices
2003-12-01
UNCLASSIFIED Center for Turbulence Research 81 Annual Research Briefs 2003 Numerical simulation of protoplanetary vortices By H. Lin, J.A. Barranco t AND P.S...planetesimals and planets. In earlier works ( Barranco & Marcus 2000; Barranco et al. 2000; Lin et al. 2000) we have briefly described the possible physical...transport. In particular, Barranco et al. (2000) provided a general mathe- matical framework that is suitable for the asymptotic regime of the disk
Vortical structures in a flume
Gurka, R.; Liberzon, A.; Hetsroni, G.
2006-03-01
We report the results of statistical spatial characterization of coherent structures in turbulent boundary layer in a flume. The characterization approach is based on the proper orthogonal decomposition (POD) of vorticity, elucidating large-scale coherent patterns in a turbulent boundary layer. The method was successfully applied to the two- and three-dimensional experimental data extracted from particle image velocimetry (PIV), and multi-plane stereoscopic PIV (XPIV) respectively, and the three-dimensional data from direct numerical simulation (DNS) in a channel flow. The large-scale structure was obtained by using linear combination of POD eigenmodes of vorticity. POD allows for methodological analysis of the properties of the educed structure in the different measurement planes (orthogonal in the case of 2D PIV and parallel in the case of XPIV) and in the different cross-sections of the DNS data. Based on the statistical approach we suggest a conceptual model of large-scale coherent structures in a turbulent boundary layer flow that incorporates the experimental and the numerical results. The proposed conceptual model is a spiral vortical structure attached to the wall and expanding in both the spanwise and the wall-normal directions. Its shape resembles a funnel structure and a `double-cone eddy' concept. The relationship of the model to the structures in the near wall region is presented.
Self-focusing instability of two-dimensional solitons and vortices
DEFF Research Database (Denmark)
Kuznetsov, E.A.; Juul Rasmussen, J.
1995-01-01
The instability of two-dimensional solitons and vortices is demonstrated in the framework of the three-dimensional nonlinear Schrodinger equation (NLSE). The instability can be regarded as the analog of the Kadomtsev-Petviashvili instability [B. B. Kadomtsev and V. I. Petviashvili, Sov. Phys. Dokl...
Vortical sources of aerodynamic force and moment
Wu, J. Z.; Wu, J. M.
1989-01-01
It is shown that the aerodynamic force and moment can be expressed in terms of vorticity distribution (and entropy variation for compressible flow) on near wake plane, or in terms of boundary vorticity flux on the body surface. Thus the vortical sources of lift and drag are clearly identified, which is the real physical basis of optimal aerodynamic design. Moreover, these sources are highly compact, hence allowing one to concentrate on key local regions of the configuration, which have dominating effect to the lift and drag. A detail knowledge of the vortical low requires measuring or calculating the vorticity and dilatation field, which is however still a challenging task. Nevertheless, this type of formulation has some unique advantages; and how to set up a well-posed problem, in particular how to establish vorticity-dilatation boundary conditions, is addressed.
Vorticity production through rotation, shear and baroclinicity
Del Sordo, Fabio; Brandenburg, Axel
2010-01-01
In the absence of rotation and shear, and under the assumption of constant temperature or specific entropy, purely potential forcing by localized expansion waves is known to produce irrotational flows that have no vorticity. Here we study the production of vorticity under idealized conditions when there is rotation, shear, or baroclinicity, to address the problem of vorticity generation in the interstellar medium in a systematic fashion. We use three-dimensional periodic box numerical simulat...
"Explosively growing" vortices of unstably stratified atmosphere
Onishchenko, O. G.; Horton, W.; Pokhotelov, O. A.; Fedun, V.
2016-10-01
A new type of "explosively growing" vortex structure is investigated theoretically in the framework of ideal fluid hydrodynamics. It is shown that vortex structures may arise in convectively unstable atmospheric layers containing background vorticity. From an exact analytical vortex solution the vertical vorticity structure and toroidal speed are derived and analyzed. The assumption that vorticity is constant with height leads to a solution that grows explosively when the flow is inviscid. The results shown are in agreement with observations and laboratory experiments
A Vorticity-Magnetic Field Dynamo Instability
1997-01-01
We generalize the mean field magnetic dynamo to include local evolution of the mean vorticity in addition to the mean magnetic field. The coupled equations exhibit a general mean field dynamo instability that enables the transfer of turbulent energy to the magnetic field and vorticity on larger scales. The growth of the vorticity and magnetic field both require helical turbulence which can be supplied by an underlying global rotation. The dynamo coefficients are derived including the backreac...
Reconstruction of Propagating Kelvin-Helmholtz Vortices at Mercury's Magnetopause
Sundberg, Torbjoern; Boardsen, Scott A.; Slavin, James A.; Blomberg, Lars G.; Cumnock, Judy A.; Solomon, Sean C.; Anderson, Brian J.; Korth, Haje
2011-01-01
A series of quasi-periodic magnetopause crossings were recorded by the MESSENGER spacecraft during its third flyby of Mercury on 29 September 2009, likely caused by a train of propagating Kelvin-Helmholtz (KH) vortices. We here revisit the observations to study the internal structure of the waves. Exploiting MESSENGER s rapid traversal of the magnetopause, we show that the observations permit a reconstruction of the structure of a rolled-up KH vortex directly from the spacecraft s magnetic field measurements. The derived geometry is consistent with all large-scale fluctuations in the magnetic field data, establishes the non-linear nature of the waves, and shows their vortex-like structure. In several of the wave passages, a reduction in magnetic field strength is observed in the middle of the wave, which is characteristic of rolled-up vortices and is related to the increase in magnetic pressure required to balance the centrifugal force on the plasma in the outer regions of a vortex, previously reported in computer simulations. As the KH wave starts to roll up, the reconstructed geometry suggests that the vortices develop two gradual transition regions in the magnetic field, possibly related to the mixing of magnetosheath and magnetospheric plasma, situated at the leading edges from the perspectives of both the magnetosphere and the magnetosheath.
Vitality of optical vortices (Presentation)
CSIR Research Space (South Africa)
Roux, FS
2014-02-01
Full Text Available stream_source_info Roux3_2014.pdf.txt stream_content_type text/plain stream_size 3018 Content-Encoding UTF-8 stream_name Roux3_2014.pdf.txt Content-Type text/plain; charset=UTF-8 Title Vitality of optical vortices F Stef... Roux Presented at Complex Light and Optical Force VIII SPIE Photonics West 2014 Moscone Center, San Francisco, California USA 5 February 2014 CSIR National Laser Centre, Pretoria, South Africa – p. 1/11 Speckle Amplitude Phase – p. 2/11 Vortex...
Separation vortices and pattern formation
DEFF Research Database (Denmark)
Andersen, Anders Peter; Bohr, Tomas; Schnipper, Teis
2010-01-01
In this paper examples are given of the importance of flow separation for fluid patterns at moderate Reynolds numbers—both in the stationary and in the time-dependent domain. In the case of circular hydraulic jumps, it has been shown recently that it is possible to generalise the Prandtl–Kármán–P...... results for the vortex patterns behind a flapping foil in a flowing soap film, which shows the interaction and competition between the vortices shed from the round leading edge (like the von Kármán vortex street) and those created at the sharp trailing edge....
Making sound vortices by metasurfaces
Energy Technology Data Exchange (ETDEWEB)
Ye, Liping; Qiu, Chunyin, E-mail: cyqiu@whu.edu.cn; Lu, Jiuyang; Tang, Kun; Ke, Manzhu; Peng, Shasha [Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072 (China); Jia, Han [State Key Laboratory of Acoustics and Key Laboratory of Noise and Vibration Research, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190 (China); Liu, Zhengyou [Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072 (China); Institute for Advanced Studies, Wuhan University, Wuhan 430072 (China)
2016-08-15
Based on the Huygens-Fresnel principle, a metasurface structure is designed to generate a sound vortex beam in airborne environment. The metasurface is constructed by a thin planar plate perforated with a circular array of deep subwavelength resonators with desired phase and amplitude responses. The metasurface approach in making sound vortices is validated well by full-wave simulations and experimental measurements. Potential applications of such artificial spiral beams can be anticipated, as exemplified experimentally by the torque effect exerting on an absorbing disk.
Making sound vortices by metasurfaces
Ye, Liping; Lu, Jiuyang; Tang, Kun; Jia, Han; Ke, Manzhu; Peng, Shasha; Liu, Zhengyou
2016-01-01
Based on the Huygens-Fresnel principle, a metasurface structure is designed to generate a sound vortex beam in airborne environment. The metasurface is constructed by a thin planar plate perforated with a circular array of deep subwavelength resonators with desired phase and amplitude responses. The metasurface approach in making sound vortices is validated well by full-wave simulations and experimental measurements. Potential applications of such artificial spiral beams can be anticipated, as exemplified experimentally by the torque effect exerting on an absorbing disk.
Self-dual vortices in Chern-Simons hydrodynamics
Li, D K
2001-01-01
One studies effect of nonlinear quantum potential on planar vortices occurring in (2+1)-dimensional problem for the Schroedinger equation with interaction with the Chern-Simons (CS) gauge field. Classical dynamics of a charged nonrelativistic particle moving in U(1)-gauge field is described in the form of the Schroedinger nonlinear (SN) wave equation with quantum potential. it is shown that deformation introduction into coupling constant of quantum potential depending on the Plank constant results either in the Schroedinger standard model or in diffusion-antidiffusion equations. The gauge theory in the form of the Abelian CS-theory interacting with SN field boils down to the theory of vortex hydrodynamics. Problem for a static flux moving with speed equal to quantum speed boils down to the Liouville equation. Paper contains description of the relevant vortex configurations
Superexchange-Driven Magnetoelectricity in Magnetic Vortices
Delaney, Kris T.; Mostovoy, Maxim; Spaldin, Nicola A.
2009-01-01
We demonstrate that magnetic vortices in which spins are coupled to polar lattice distortions via superexchange exhibit an unusually large linear magnetoelectric response. We show that the periodic arrays of vortices formed by frustrated spins on kagome lattices provide a realization of this concept
Nonquasineutral electron vortices in nonuniform plasmas
Energy Technology Data Exchange (ETDEWEB)
Angus, J. R.; Richardson, A. S.; Swanekamp, S. B.; Schumer, J. W. [Plasma Physics Division, Naval Research Laboratory, Washington, District of Columbia 20375 (United States); Ottinger, P. F. [Engility Corporation, Chantilly, Virginia 20151 (United States)
2014-11-15
Electron vortices are observed in the numerical simulation of current carrying plasmas on fast time scales where the ion motion can be ignored. In plasmas with nonuniform density n, vortices drift in the B × ∇n direction with a speed that is on the order of the Hall speed. This provides a mechanism for magnetic field penetration into a plasma. Here, we consider strong vortices with rotation speeds V{sub ϕ} close to the speed of light c where the vortex size δ is on the order of the magnetic Debye length λ{sub B}=|B|/4πen and the vortex is thus nonquasineutral. Drifting vortices are typically studied using the electron magnetohydrodynamic model (EMHD), which ignores the displacement current and assumes quasineutrality. However, these assumptions are not strictly valid for drifting vortices when δ ≈ λ{sub B}. In this paper, 2D electron vortices in nonuniform plasmas are studied for the first time using a fully electromagnetic, collisionless fluid code. Relatively large amplitude oscillations with periods that correspond to high frequency extraordinary modes are observed in the average drift speed. The drift speed W is calculated by averaging the electron velocity field over the vorticity. Interestingly, the time-averaged W from these simulations matches very well with W from the much simpler EMHD simulations even for strong vortices with order unity charge density separation.
On generating counter-rotating streamwise vortices
Winoto, S H
2015-09-23
Counter-rotating streamwise vortices are known to enhance the heat transfer rate from a surface and also to improve the aerodynamic performance of an aerofoil. In this paper, some methods to generate such counter-rotating vortices using different methods or physical conditions will be briefly considered and discussed.
Instability of two-dimensional solitons and vortices in defocusing media
Kuznetsov, E. A.; Rasmussen, J. Juul
1995-05-01
In the framework of the three-dimensional nonlinear Schrödinger equation the instability of two-dimensional solitons and vortices is demonstrated. The soliton instability can be considered as the analog of the Kadomtsev-Petviashvili instability (Dokl. Akad. Nauk SSSR 192, 753 (1970) [Sov. Phys. Dokl. 15, 539 (1970)]) of one-dimensional acoustic solitons in media with positive dispersion. For large distances between the vortices, this instability transforms into the Crow instability [AIAA J. 8, 2172 (1970)] of two vortex filaments with opposite circulations.
Ginzburg-Landau vortices driven by the Landau-Lifshitz-Gilbert equation
Energy Technology Data Exchange (ETDEWEB)
Kurzke, Matthias; Melcher, Christof; Moser, Roger; Spirn, Daniel
2009-06-15
A simplified model for the energy of the magnetization of a thin ferromagnetic film gives rise to a version of the theory of Ginzburg-Landau vortices for sphere-valued maps. In particular we have the development of vortices as a certain parameter tends to 0. The dynamics of the magnetization is ruled by the Landau-Lifshitz-Gilbert equation, which combines characteristic properties of a nonlinear Schroedinger equation and a gradient flow. This paper studies the motion of the vortex centers under this evolution equation. (orig.)
Theory of concentrated vortices an introduction
Alekseenko, S V; Okulov, V L
2007-01-01
Vortex motion is one of the basic states of a flowing continuum. Intere- ingly, in many cases vorticity is space-localized, generating concentrated vortices. Vortex filaments having extremely diverse dynamics are the most characteristic examples of such vortices. Notable examples, in particular, include such phenomena as self-inducted motion, various instabilities, wave generation, and vortex breakdown. These effects are typically ma- fested as a spiral (or helical) configuration of a vortex axis. Many publications in the field of hydrodynamics are focused on vortex motion and vortex effects. Only a few books are devoted entirely to v- tices, and even fewer to concentrated vortices. This work aims to highlight the key problems of vortex formation and behavior. The experimental - servations of the authors, the impressive visualizations of concentrated vortices (including helical and spiral) and pictures of vortex breakdown primarily motivated the authors to begin this work. Later, the approach based on the hel...
Separation vortices and pattern formation
DEFF Research Database (Denmark)
Andersen, Anders Peter; Bohr, Tomas; Schnipper, Teis
2010-01-01
In this paper examples are given of the importance of flow separation for fluid patterns at moderate Reynolds numbers—both in the stationary and in the time-dependent domain. In the case of circular hydraulic jumps, it has been shown recently that it is possible to generalise the Prandtl–Kármán–P...... results for the vortex patterns behind a flapping foil in a flowing soap film, which shows the interaction and competition between the vortices shed from the round leading edge (like the von Kármán vortex street) and those created at the sharp trailing edge.......-time evolution of the sand ripple pattern, which has the surprising features that it breaks the local sand conservation and has long-range interaction, features that can be underpinned by experiments. Very similar vortex dynamics takes place around oscillating structures such as wings and fins. Here, we present...
Electroweak Vortices and Gauge Equivalence
MacDowell, Samuel W.; Törnkvist, Ola
Vortex configurations in the electroweak gauge theory are investigated. Two gauge-inequivalent solutions of the field equations, the Z and W vortices, have previously been found. They correspond to embeddings of the Abelian Nielsen-Olesen vortex solution into a U(1) subgroup of SU(2)×U(1). It is shown here that any electroweak vortex solution can be mapped into a solution of the same energy with a vanishing upper component of the Higgs field. The correspondence is a gauge equivalence for all vortex solutions except those for which the winding numbers of the upper and lower Higgs components add to zero. This class of solutions, which includes the W vortex, corresponds to a singular solution in the one-component gauge. The results, combined with numerical investigations, provide an argument against the existence of other vortex solutions in the gauge-Higgs sector of the Standard Model.
Generation and Growth of Single Hairpin Vortices
Haji-Haidari, Ahmad
The behavior of selectively generated single hairpin vortices are examined within a laminar boundary layer environment over a range of Reynolds numbers, the hairpin vortices are experimentally generated by means of controlled fluid injection from a streamwise slot. Flow visualization using both dye and hydrogen bubble wire is employed in conjunction with hot film anemometry to investigate the growth characteristics and evolution of these single hairpin vortices. Qualitatively, it is established that hairpin vortices form by local destabilization at the interface between the low-speed fluid introduced through the slot and the higher speed boundary layer flow. Kinematical considerations of the hairpin vortex are established. It is observed that a hairpin vortex generally displays visualization and velocity signatures characteristic of those observed for a turbulent boundary layer. Hydrogen-bubble wire visualization results specifically indicate that hairpin vortices generate two purely turbulent-like flow patterns. The first is a low-speed streak pattern developing immediately adjacent to the surface due to surface interaction by the counter -rotating legs of the hairpin vortex; the second pattern is a turbulent pocket-like pattern farther removed from the surface. It is determined from the visualization data that hairpin vortices manifest the necessary flow characteristics which give rise to the regenerative and sustained process required for maintenance of turbulence. The regeneration and the growth process takes place through the formation of similar hairpin-like vortices by one of two means. The first is an inviscid lateral propagation of the initial disturbance which gives rise to outboard (subsidiary), vortices which cause the lateral spreading of the structure. A more complicated and eruptive process occurs by means of viscous-inviscid interactions which give rise to trailing vortices (secondary), which cause the streamwise elongation of the disturbance. A
Vortical light bullets in second-harmonic-generating media supported by a trapping potential
Sakaguchi, Hidetsugu
2013-01-01
We introduce a three-dimensional (3D) model of optical media with the quadratic ($\\chi ^{(2)}$) nonlinearity and an effective 2D isotropic harmonic-oscillator (HO) potential. While it is well known that 3D \\chi^2 solitons with embedded vorticity ("vortical light bullets") are unstable in the free space, we demonstrate that they have a broad stability region in the present model, being supported by the HO potential against the splitting instability. The shape of the vortical solitons may be accurately predicted by the variational approximation (VA). They exist above a threshold value of the total energy (norm) and below another critical value, which determines a stability boundary. The existence threshold vanishes is a part of the parameter space, depending on the mismatch parameter, which is explained by means of the comparison with the 2D counterpart of the system. Above the stability boundary, the vortex features shape oscillations, periodically breaking its axisymmetric form and restoring it. Collisions be...
Varieties of stable vortical solitons in Ginzburg-Landau media with radially inhomogeneous losses.
Skarka, V; Aleksić, N B; Leblond, H; Malomed, B A; Mihalache, D
2010-11-19
Using a combination of the variation approximation and direct simulations, we consider the model of the light transmission in nonlinearly amplified bulk media, taking into account the localization of the gain, i.e., the linear loss shaped as a parabolic function of the transverse radius, with a minimum at the center. The balance of the transverse diffraction, self-focusing, gain, and the inhomogeneous loss provides for the hitherto elusive stabilization of vortex solitons, in a large zone of the parameter space. Adjacent to it, stability domains are found for several novel kinds of localized vortices, including spinning elliptically shaped ones, eccentric elliptic vortices which feature double rotation, spinning crescents, and breathing vortices.
Vorticity in Heavy-Ion Collisions
Deng, Wei-Tian
2016-01-01
We study the event-by-event generation of flow vorticity in RHIC Au + Au collisions and LHC Pb + Pb collisions by using the HIJING model. Different definitions of the vorticity field and velocity field are considered. A variety of properties of the vorticity are explored, including the impact parameter dependence, the collision energy dependence, the spatial distribution, the event-by-event fluctuation of the magnitude and azimuthal direction, and the time evolution. In addition, the spatial distribution of the flow helicity is also studied.
Vorticity in heavy-ion collisions
Deng, Wei-Tian; Huang, Xu-Guang
2016-06-01
We study the event-by-event generation of flow vorticity in the BNL Relativistic Heavy Ion Collider Au +Au collisions and CERN Large Hadron Collider Pb +Pb collisions by using the hijing model. Different definitions of the vorticity field and velocity field are considered. A variety of properties of the vorticity are explored, including the impact parameter dependence, the collision energy dependence, the spatial distribution, the event-by-event fluctuation of the magnitude and azimuthal direction, and the time evolution. In addition, the spatial distribution of the flow helicity is also studied.
Correlations between Abelian monopoles and center vortices
Hosseini Nejad, Seyed Mohsen; Deldar, Sedigheh
2017-04-01
We study the correlations between center vortices and Abelian monopoles for SU(3) gauge group. Combining fractional fluxes of monopoles, center vortex fluxes are constructed in the thick center vortex model. Calculating the potentials induced by fractional fluxes constructing the center vortex flux in a thick center vortex-like model and comparing with the potential induced by center vortices, we observe an attraction between fractional fluxes of monopoles constructing the center vortex flux. We conclude that the center vortex flux is stable, as expected. In addition, we show that adding a contribution of the monopole-antimonopole pairs in the potentials induced by center vortices ruins the Casimir scaling at intermediate regime.
Harrison, D. E.; Holland, W. R.
1981-01-01
A mean vorticity budget analysis is presented of Holland's (1978) numerical ocean general circulation experiment. The stable budgets are compared with classical circulation theory to emphasize the ways in which the mesoscale motions of the model alter (or leave unaltered) classical vorticity balances. The basinwide meridional transports of vorticity by the mean flow and by the mesoscale flow in the mean are evaluated to establish the role(s) of the mesoscale in the larger scale equilibrium vorticity transports. The vorticity equation for this model fluid system is presented and the budget analysis method is described. Vorticity budgets over the selected regions and on a larger scale are given, and a summary of budget results is provided along with remarks about the utility of this type of analysis.
Harrison, D. E.; Holland, W. R.
1981-01-01
A mean vorticity budget analysis is presented of Holland's (1978) numerical ocean general circulation experiment. The stable budgets are compared with classical circulation theory to emphasize the ways in which the mesoscale motions of the model alter (or leave unaltered) classical vorticity balances. The basinwide meridional transports of vorticity by the mean flow and by the mesoscale flow in the mean are evaluated to establish the role(s) of the mesoscale in the larger scale equilibrium vorticity transports. The vorticity equation for this model fluid system is presented and the budget analysis method is described. Vorticity budgets over the selected regions and on a larger scale are given, and a summary of budget results is provided along with remarks about the utility of this type of analysis.
Wavenumber selection for small-wavelength Goertler vortices in curved channel flows
Dando, Andrew; Hall, Philip
1995-04-01
The problem of wavenumber selection for fully nonlinear, small-wavelength Goertler vortices in a curved channel flow is considered. These types of Goertler vortices were first considered by Hall & Lakin (1988) for an external boundary layer flow. They proved particularly amenable to asymptotic description, it was possible to consider vortices large enough so that the mean flow correction driven by them is as large as the basic state, and this prompted the authors to consider them in a curved channel flow as an initial application of the phase-equation approach to Goertler vortices. This involves the assumption that the phase variable of these Goertler vortices varies on slow spanwise and time scales, then an analysis of both inside and outside the core region, to which vortex activity is restricted, leads to a system of partial differential equations which can be solved numerically for the wavenumber. The authors consider in particular the effect on the wavenumber of the outer channel wall varying on the same slow spanwise scale as the phase variable.
Vortices in simulations of solar surface convection
Moll, R; Schüssler, M
2011-01-01
We report on the occurrence of small-scale vortices in simulations of the convective solar surface. Using an eigenanalysis of the velocity gradient tensor, we find the subset of high vorticity regions in which the plasma is swirling. The swirling regions form an unsteady, tangled network of filaments in the turbulent downflow lanes. Near-surface vertical vortices are underdense and cause a local depression of the optical surface. They are potentially observable as bright points in the dark intergranular lanes. Vortex features typically exist for a few minutes, during which they are moved and twisted by the motion of the ambient plasma. The bigger vortices found in the simulations are possibly, but not necessarily, related to observations of granular-scale spiraling pathlines in "cork animations" or feature tracking.
Refutation of stability proofs for dipole vortices
DEFF Research Database (Denmark)
Nycander, J.
1992-01-01
Five stability proofs for dipole vortices (modons) that have been presented by various authors are examined. It is shown that they are all incorrect, and that westward-propagating dipoles are in fact unstable, in contradiction to some of the proofs.......Five stability proofs for dipole vortices (modons) that have been presented by various authors are examined. It is shown that they are all incorrect, and that westward-propagating dipoles are in fact unstable, in contradiction to some of the proofs....
Chaotic vortical flows and their manifestations
Baznat, M.; Gudima, K.; Sorin, A.; Teryaev, O.
2016-11-01
We study vorticity and hydrodynamic helicity in semi-peripheral heavy-ion collisions using the kinetic model of Quark-Gluon Strings. The angular momentum, which is a source of P-odd observables, is preserved with a good accuracy. We observe formation of the specific toroidal structures of the vorticity field. Their existence, accompanied by the strange chemical potential, is mirrored in the polarization of hyperons of the percent order.
Acoustic-gravity nonlinear structures
Directory of Open Access Journals (Sweden)
D. Jovanović
2002-01-01
Full Text Available A catalogue of nonlinear vortex structures associated with acoustic-gravity perturbations in the Earth's atmosphere is presented. Besides the previously known Kelvin-Stewart cat's eyes, dipolar and tripolar structures, new solutions having the form of a row of counter-rotating vortices, and several weakly two-dimensional vortex chains are given. The existence conditions for these nonlinear structures are discussed with respect to the presence of inhomogeneities of the shear flows. The mode-coupling mechanism for the nonlinear generation of shear flows in the presence of linearly unstable acoustic-gravity waves, possibly also leading to intermittency and chaos, is presented.
Vortices and vortex lattices in quantum ferrofluids
Martin, A. M.; Marchant, N. G.; O’Dell, D. H. J.; Parker, N. G.
2017-03-01
The experimental realization of quantum-degenerate Bose gases made of atoms with sizeable magnetic dipole moments has created a new type of fluid, known as a quantum ferrofluid, which combines the extraordinary properties of superfluidity and ferrofluidity. A hallmark of superfluids is that they are constrained to rotate through vortices with quantized circulation. In quantum ferrofluids the long-range dipolar interactions add new ingredients by inducing magnetostriction and instabilities, and also affect the structural properties of vortices and vortex lattices. Here we give a review of the theory of vortices in dipolar Bose–Einstein condensates, exploring the interplay of magnetism with vorticity and contrasting this with the established behaviour in non-dipolar condensates. We cover single vortex solutions, including structure, energy and stability, vortex pairs, including interactions and dynamics, and also vortex lattices. Our discussion is founded on the mean-field theory provided by the dipolar Gross–Pitaevskii equation, ranging from analytic treatments based on the Thomas–Fermi (hydrodynamic) and variational approaches to full numerical simulations. Routes for generating vortices in dipolar condensates are discussed, with particular attention paid to rotating condensates, where surface instabilities drive the nucleation of vortices, and lead to the emergence of rich and varied vortex lattice structures. We also present an outlook, including potential extensions to degenerate Fermi gases, quantum Hall physics, toroidal systems and the Berezinskii–Kosterlitz–Thouless transition.
Nonlinear Excitation of Inviscid Stationary Vortex in a Boundary-Layer Flow
Choudhari, Meelan; Duck, Peter W.
1996-01-01
We examine the excitation of inviscid stationary crossflow instabilities near an isolated surface hump (or indentation) underneath a three-dimensional boundary layer. As the hump height (or indentation depth) is increased from zero, the receptivity process becomes nonlinear even before the stability characteristics of the boundary layer are modified to a significant extent. This behavior contrasts sharply with earlier findings on the excitation of the lower branch Tollmien-Schlichting modes and is attributed to the inviscid nature of the crossflow modes, which leads to a decoupling between the regions of receptivity and stability. As a result of this decoupling, similarity transformations exist that allow the nonlinear receptivity of a general three-dimensional boundary layer to be studied with a set of canonical solutions to the viscous sublayer equations. The parametric study suggests that the receptivity is likely to become nonlinear even before the hump height becomes large enough for flow reversal to occur in the canonical solution. We also find that the receptivity to surface humps increases more rapidly as the hump height increases than is predicted by linear theory. On the other hand, receptivity near surface indentations is generally smaller in comparison with the linear approximation. Extension of the work to crossflow receptivity in compressible boundary layers and to Gortler vortex excitation is also discussed.
Evolution of finite-amplitude localized vortices in planar homogeneous shear flows
Karp, Michael; Shukhman, Ilia G.; Cohen, Jacob
2017-02-01
An analytical-based method is utilized to follow the evolution of localized initially Gaussian disturbances in flows with homogeneous shear, in which the base velocity components are at most linear functions of the coordinates, including hyperbolic, elliptic, and simple shear. Coherent structures, including counterrotating vortex pairs (CVPs) and hairpin vortices, are formed for the cases where the streamlines of the base flow are open (hyperbolic and simple shear). For hyperbolic base flows, the dominance of shear over rotation leads to elongation of the localized disturbance along the outlet asymptote and formation of CVPs. For simple shear CVPs are formed from linear and nonlinear disturbances, whereas hairpins are observed only for highly nonlinear disturbances. For elliptic base flows CVPs, hairpins and vortex loops form initially, however they do not last and break into various vortical structures that spread in the spanwise direction. The effect of the disturbance's initial amplitude and orientation is examined and the optimal orientation achieving maximal growth is identified.
Analytical Derivation of Three Dimensional Vorticity Function for wave breaking in Surf Zone
Dutta, R
2015-01-01
In this report, Mathematical model for generalized nonlinear three dimensional wave breaking equations was de- veloped analytically using fully nonlinear extended Boussinesq equations to encompass rotational dynamics in wave breaking zone. The three dimensional equations for vorticity distributions are developed from Reynold based stress equations. Vorticity transport equations are also developed for wave breaking zone. This equations are basic model tools for numerical simulation of surf zone to explain wave breaking phenomena. The model reproduces most of the dynamics in the surf zone. Non linearity for wave height predictions is also shown close to the breaking both in shoaling as well as surf zone. Keyword Wave breaking, Boussinesq equation, shallow water, surf zone. PACS : 47.32-y
Hydrodynamic Model of Desalination by "Overlimiting" Electrodialysis with Electroconvective Vortices
Kwak, Rhokyun; Pham, Van Sang; Han, Jongyoon
2016-11-01
In 1968, Sonin and Probstein developed a hydrodynamic theory of desalination by electrodialysis. Under a laminar flow between ion exchange membranes, linear ion concentration gradients are developed near the membranes by ion concentration polarization (ICP) in Ohmic-limiting current regimes. This linear ICP determines the relations between current, voltage, and desalting performance. Here, we revisit the hydrodynamic model with nonlinear ICP phenomenon at overlimiting currents. In this regime, electroconvective vortices on the membrane induce flat and extremely low concentration zones. Based on the previous prediction of the vortex height under shear flow, we verify that the height directly represents the amount of the removed salt because there is almost no ion in the vortices. Next, from the mass continuity of ions, the amount of the removed salts is equal to the ion flux through the membrane (i.e. current); as a result, we can develop the relations between current, voltage, and salt removal. Lastly, from these relations, power consumption and desalination cost can be calculated to find the optimal operating condition of overlimiting electrodialysis.
On the Stability of Elliptical Vortices in Accretion Discs
Lesur, G
2009-01-01
(Abriged) The existence of large-scale and long-lived 2D vortices in accretion discs has been debated for more than a decade. They appear spontaneously in several 2D disc simulations and they are known to accelerate planetesimal formation through a dust trapping process. However, the issue of the stability of these structures to the imposition of 3D disturbances is still not fully understood, and it casts doubts on their long term survival. Aim: We present new results on the 3D stability of elliptical vortices embedded in accretion discs, based on a linear analysis and several non-linear simulations. Methods: We derive the linearised equations governing the 3D perturbations in the core of an elliptical vortex, and we show that they can be reduced to a Floquet problem. We solve this problem numerically in the astrophysical regime and we present several analytical limits for which the mechanism responsible for the instability can be explained. Finally, we compare the results of the linear analysis to some high ...
Spontaneous locking of optical vortices in coupled semiconductor lasers
Yadin, Yoav; Scheuer, Jacob; Gross, Yoav; Orenstein, Meir
2014-09-01
Non-conventional emission of light, comprising engaged rotating light cogs, is measured and analyzed. The source of this unique emission is an array of coupled surface emitting lasers, each emitting an optical vortex. The complex rotating light structures are formed spontaneously by specific combinations of the individual vortices, each carrying two types of "charge": orbital angular momentum (±1 topological charge) and a relative engagement phase (0 or π). These charges determine the specific form in which the individual rotating fields are engaged to generate the emanated light gear. The experimentally observed formations and dynamic evolution of the light gears stem from the complex nonlinear dynamics of the coupled rotating-field emitters, a mechanism which we have successfully modeled and utilized for interpreting the obtained results. The engaged light gears can be used in controlled generation and transmission of multiple degrees of freedom photons, for high-bit-rate classic and quantum telecommunications, particle manipulation, and super-resolution imaging.
Stability of helical tip vortices in a rotor far wake
DEFF Research Database (Denmark)
Okulov, Valery; Sørensen, Jens Nørkær
2007-01-01
, corresponding to Rankine, Gaussian and Scully vortices, at radial extents ranging from the core radius of a tip vortex to several rotor radii. The analysis shows that the stability of tip vortices largely depends on the radial extent of the hub vorticity as well as on the type of vorticity distribution. As part......As a means of analysing the stability of the wake behind a multi-bladed rotor the stability of a multiplicity of helical vortices embedded in an assigned flow field is addressed. In the model the tip vortices in the far wake are approximated by infinitely long helical vortices with constant pitch...... and radius. The work is a further development of a model developed in Okulov (J. Fluid Mech., vol. 521, p. 319) in which the linear stability of N equally azimuthally spaced helical vortices was considered. In the present work the analysis is extended to include an assigned vorticity field due to root...
Combined effect of horizontal magnetic field and vorticity on Rayleigh Taylor instability
Banerjee, Rahul
2016-01-01
In this research, the height, curvature and velocity of the bubble tip in Rayleigh-Taylor instability at arbitrary Atwood number with horizontal magnetic field are investigated. To support the earlier simulation and experimental results, the vorticity generation inside the bubble is introduced. It is found that, in early nonlinear stage, the temporal evolution of the bubble tip parameters depend essentially on the strength and initial perturbation of the magnetic field, although the asymptotic nature coincides with the non magnetic case. The model proposed here agrees with the previous linear, nonlinear and simulation observations.
Viscous tilting and production of vorticity in homogeneous turbulence
Holzner, M.; Guala, M.; Lüthi, B.; Liberzon, A.; Nikitin, N.; Kinzelbach, W.; Tsinober, A.
2010-06-01
Viscous depletion of vorticity is an essential and well known property of turbulent flows, balancing, in the mean, the net vorticity production associated with the vortex stretching mechanism. In this letter, we, however, demonstrate that viscous effects are not restricted to a mere destruction process, but play a more complex role in vorticity dynamics that is as important as vortex stretching. Based on the results from three dimensional particle tracking velocimetry experiments and direct numerical simulation of homogeneous and quasi-isotropic turbulence, we show that the viscous term in the vorticity equation can also locally induce production of vorticity and changes of the orientation of the vorticity vector (viscous tilting).
Use of acoustic vortices in acoustic levitation
DEFF Research Database (Denmark)
Cutanda Henriquez, Vicente; Santillan, Arturo Orozco; Juhl, Peter Møller
2009-01-01
Acoustic fields are known to exert forces on the surfaces of objects. These forces are noticeable if the sound pressure is sufficiently high. Two phenomena where acoustic forces are relevant are: i) acoustic levitation, where strong standing waves can hold small objects at certain positions......, counterbalancing their weight, and ii) acoustic vortices, spinning sound fields that can impinge angular momentum and cause rotation of objects. In this contribution, both force-creating sound fields are studied by means of numerical simulations. The Boundary Element Method is employed to this end. The simulation...... of acoustical vortices uses an efficient numerical implementation based on the superposition of two orthogonal sound fields with a delay of 90° between them. It is shown that acoustic levitation and the use of acoustic vortices can be combined to manipulate objects in an efficient and controlled manner without...
Vortices and vortex lattices in quantum ferrofluids
Martin, A M; O'Dell, D H J; Parker, N G
2016-01-01
The achievement of quantum-degenerate Bose gases composed of atoms with sizeable magnetic dipole moments has realized quantum ferrofluids, a form of fluid which combines the extraordinary properties of superfluidity and ferrofluidity. A hallmark of superfluids is that they are constrained to circulate through vortices with quantized circulation. These excitations underpin a variety of rich phenomena, including vortex lattices, quantum turbulence, the Berenzinksii-Kosterlitz-Thouless transition and Kibble-Zurek defect formation. Here we provide a comprehensive review of the theory of vortices and vortex lattices in quantum ferrofluids created from dipolar Bose-Einstein condensates, exploring the interplay of magnetism with vorticity and contrasting this with the established behaviour in non-dipolar condensates. Our discussion is based on the mean-field theory provided by the dipolar Gross-Pitaevskii equation, from analytic treatments based on the Thomas-Fermi and variational approaches to full numerical simula...
Cosmological Perturbations: Vorticity, Isocurvature and Magnetic Fields
Christopherson, Adam J
2014-01-01
In this paper I review some recent, interlinked, work undertaken using cosmological perturbation theory -- a powerful technique for modelling inhomogeneities in the Universe. The common theme which underpins these pieces of work is the presence of non-adiabatic pressure, or entropy, perturbations. After a brief introduction covering the standard techniques of describing inhomogeneities in both Newtonian and relativistic cosmology, I discuss the generation of vorticity. As in classical fluid mechanics, vorticity is not present in linearized perturbation theory (unless included as an initial condition). Allowing for entropy perturbations, and working to second order in perturbation theory, I show that vorticity is generated, even in the absence of vector perturbations, by purely scalar perturbations, the source term being quadratic in the gradients of first order energy density and isocurvature, or non-adiabatic pressure perturbations. This generalizes Crocco's theorem to a cosmological setting. I then introduc...
On n-quantum vortices in superconductors
Marchenko, V I
2002-01-01
The conditions of the n-quantum vortices observation in the superconductors are discussed. It is established in the course of calculating the coefficient by the |psi| sup 6 (psi - the order parameter) in the Ginzburg-Landau theory for the BCS standard model that the sign of this coefficient is negative. This favours the possibility of observing the n-quantum vortices in the superconductors, wherein the vortex lattice with gravitation is formed. The existence of gravitation is manifested in the magnetization finite jump in the H sub 0 = H sub c sub sup 1 field. When by the temperature change the superconductor behavior changes in such a way, that its magnetization in the H sub 0 = H sub c field reduces to the zero, than the observation of the n-quantum vortices near this transition is possible
Martian polar vortices: Comparison of reanalyses
Waugh, D. W.; Toigo, A. D.; Guzewich, S. D.; Greybush, S. J.; Wilson, R. J.; Montabone, L.
2016-09-01
The structure and evolution of the Martian polar vortices is examined using two recently available reanalysis systems: version 1.0 of the Mars Analysis Correction Data Assimilation (MACDA) and a preliminary version of the Ensemble Mars Atmosphere Reanalysis System (EMARS). There is quantitative agreement between the reanalyses in the lower atmosphere, where Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) data are assimilated, but there are differences at higher altitudes reflecting differences in the free-running general circulation model simulations used in the two reanalyses. The reanalyses show similar potential vorticity (PV) structure of the vortices: There is near-uniform small PV equatorward of the core of the westerly jet, steep meridional PV gradients on the polar side of the jet core, and a maximum of PV located off of the pole. In maps of 30 sol mean PV, there is a near-continuous elliptical ring of high PV with roughly constant shape and longitudinal orientation from fall to spring. However, the shape and orientation of the vortex varies on daily time scales, and there is not a continuous ring of PV but rather a series of smaller scale coherent regions of high PV. The PV structure of the Martian polar vortices is, as has been reported before, very different from that of Earth's stratospheric polar vortices, but there are similarities with Earth's tropospheric vortices which also occur at the edge of the Hadley Cell, and have near-uniform small PV equatorward of the jet, and a large increase of PV poleward of the jet due to increased stratification.
Up-Sliding Slantwise Vorticity Development and the Complete Vorticity Equation with Mass Forcing
Institute of Scientific and Technical Information of China (English)
崔晓鹏; 高守亭; 吴国雄
2003-01-01
The moist potential vorticity (MPV) equation is derived from complete atmospheric equations includingthe effect of mass forcing, with which the theory of Up-sliding Slantwise Vorticity Development (USVD)is proposed based on the theory of Slantwise Vorticity Development (SVD). When an air parcel slides upalong a slantwise isentropic surface, its vertical component of relative vorticity will develop, and the steeperthe isentropic surface is, the more violent the development will be. From the definition of MPV and theMPV equation produced here in, a complete vorticity equation is then put forward with mass forcing, whichexplicitly includes the effects of both internal forcings, such as variations of stability, baroclinicity, andvertical shear of horizontal wind, and external forcings, such as diabatic heating, friction, and mass forcing.When isentropic surfaces are flat, the complete vorticity equation matches its traditional counterpart. Thephysical interpretations of some of the items which are included in the complete vorticity equation butnot in the traditional one are studied with a simplified model of the Changjiang-Huaihe Meiyu front. A60-h simulation is then performed to reproduce a torrential rain event in the Changjiang-Huaihe regionand the output of the model is studied qualitatively based on the theory of USVD. The result shows thatthe conditions of the theory of USVD are easily satisfied immediately in front of mesoscale rainstorms inthe downwind direction, that is, the theory of USVD is important to the development and movement ofthese kinds of systems.
Vorticity Confinement Applied to Turbulent Wing Tip Vortices for Wake-Integral Drag Prediction
Pierson, Kristopher; Povitsky, Alex
2013-11-01
In the current study the vorticity confinement (VC) approach was applied to tip vortices shed by edges of stationary wings in order to predict induced drag by far-field integration in Trefftz plane. The VC parameter was evaluated first by application to convection of vortices in 2-D uniform flow and then to tip vortices shed in 3-D simulation of finite-aspect ratio rectangular wing in subsonic flight. Dependence of VC parameter on the flight Mach number and the angle of attack was evaluated. The aerodynamic drag results with application of VC to prevent numerical diffusion are much closer to analytic lifting line theory compared to integration over surface of wing while the viscous profile drag is more accurately evaluated by surface integration. To apply VC to viscous and turbulent flows, it is shown that VC does not affect the physical rate of dissipation of vortices in viscous/turbulent flows at time scales corresponding to convection of vortices from the wing to Trefftz plane of integration. To account for turbulent effects on tip vortices, VC was applied in combination with Spalart-Allmaras, k- ɛ, and six Reynolds stresses models of turbulence. The results are compared to experiments to validate the physical dissipation of tip vortex. This research was supported by The Dayton Area Graduate Studies Institute (DAGSI) and US Air Force Research Laboratory (AFRL) grants in 2009-2013, US Army Research Office (ARO) in 2012-2013 and ASEE/AFRL summer faculty grant.
Slow light vortices in periodic waveguides
DEFF Research Database (Denmark)
Sukhorukov, Andrey A.; Ha, Sangwoo; Desyatnikov, Anton S.
2009-01-01
We reveal that the reduction of the group velocity of light in periodic waveguides is generically associated with the presence of vortex energy flows. We show that the energy flows are gradually frozen for slow-light at the Brillouin zone edge, whereas vortices persist for slow-light states havin...... non-vanishing phase velocity inside the Brillouin zone. We also demonstrate that presence of vortices can be linked to the absence of slow-light at the zone edge, and present calculations illustrating these general results....
Slow-light vortices in periodic waveguides
DEFF Research Database (Denmark)
Sukhorukov, Andrey A.; Ha, Sangwoo; Desyatnikov, Anton S.
2009-01-01
We reveal that the reduction of the group velocity of light in periodic waveguides is generically associated with the presence of vortex energy flows. We show that the energy flows are gradually frozen for slow-light at the Brillouin zone edge, whereas vortices persist for slow-light states havin...... non-vanishing phase velocity inside the Brillouin zone. We also demonstrate that presence of vortices can be linked to the absence of slow-light at the zone edge, and present calculations illustrating these general results....
Use of acoustic vortices in acoustic levitation
DEFF Research Database (Denmark)
Cutanda Henriquez, Vicente; Santillan, Arturo Orozco; Juhl, Peter Møller
2009-01-01
Acoustic fields are known to exert forces on the surfaces of objects. These forces are noticeable if the sound pressure is sufficiently high. Two phenomena where acoustic forces are relevant are: i) acoustic levitation, where strong standing waves can hold small objects at certain positions...... of acoustical vortices uses an efficient numerical implementation based on the superposition of two orthogonal sound fields with a delay of 90° between them. It is shown that acoustic levitation and the use of acoustic vortices can be combined to manipulate objects in an efficient and controlled manner without...
Inward propagating chemical waves in Taylor vortices.
Thompson, Barnaby W; Novak, Jan; Wilson, Mark C T; Britton, Melanie M; Taylor, Annette F
2010-04-01
Advection-reaction-diffusion (ARD) waves in the Belousov-Zhabotinsky reaction in steady Taylor-Couette vortices have been visualized using magnetic-resonance imaging and simulated using an adapted Oregonator model. We show how propagating wave behavior depends on the ratio of advective, chemical and diffusive time scales. In simulations, inward propagating spiral flamelets are observed at high Damköhler number (Da). At low Da, the reaction distributes itself over several vortices and then propagates inwards as contracting ring pulses--also observed experimentally.
Dust Devils and Convective Vortices on Mars
Ordonez-Etxeberria, I.; Hueso, R.; Sánchez-Lavega, A.
2017-03-01
Dust devils are low pressure convective vortices able to lift dust from the surface of a planet. They are a common feature on Mars and they can also be found on desertic locations on Earth. On Mars they are considered an important part of the atmospheric dust cycle. Dust in Mars is an essential ingredient of the atmosphere where it affects the radiative balance of the planet. Here we review observations of these dusty vortices from orbit, from in situ measurements on the surface of Mars and some of the models developed to simulate them.
Horizontal Roll Vortices and Crown Fires.
Haines, Donald A.
1982-06-01
Observational evidence from nine crown fires suggests that horizontal roll vortices are a major mechanism in crown-fire spread. Post-burn aerial photography indicates that unburned tree-crown streets are common with crown fire. Investigation of the understory of these crown streets after two fires showed uncharred tree trunks along a center line. This evidence supports a hypothesis of vortex action causing strong downward motion of air along the streets. Additionally, photographs of two ongoing crown fires show apparent horizontal roll vortices. Discussion also includes laboratory and numerical studies in fluid dynamics that may apply to crown fires.
Tracking Surface Cyclones with Moist Potential Vorticity
Institute of Scientific and Technical Information of China (English)
Zuohao CAO; Da-Lin ZHANG
2004-01-01
Surface cyclone tracks are investigated in the context of moist potential vorticity (MPV). A prognostic equation of surface absolute vorticity is derived which provides a basis for using negative MPV (NMPV) in the troposphere as an alternative approach to track surface cyclones. An observed case study of explosive lee cyclogenesis is performed to test the effectiveness of the MPV approach. It is shown that when a surface cyclone signal is absent due to the blocking of the Rocky Mountains, the surface cyclone can be well identified by tracing the peak NMPV.
Lahaye, Noé; Paci, Alexandre; Smith, Stefan Llewellyn
2016-04-01
We examine the instability of lenticular vortices -- or lenses -- in a stratified rotating fluid. The simplest configuration is one in which the lenses overlay a deep layer and have a free surface, and this can be studied using a two-layer rotating shallow water model. We report results from laboratory experiments and high-resolution direct numerical simulations of the destabilization of vortices with constant potential vorticity, and compare these to a linear stability analysis. The stability properties of the system are governed by two parameters: the typical upper-layer potential vorticity and the size (depth) of the vortex. Good agreement is found between analytical, numerical and experimental results for the growth rate and wavenumber of the instability. The nonlinear saturation of the instability is associated with conversion from potential to kinetic energy and weak emission of gravity waves, giving rise to the formation of coherent vortex multipoles with trapped waves. The impact of flow in the lower layer is examined. In particular, it is shown that the growth rate can be strongly affected and the instability can be suppressed for certain types of weak co-rotating flow.
Experimental Observations of Ion Phase-Space Vortices
DEFF Research Database (Denmark)
Pécseli, Hans; Armstrong, R. J.; Trulsen, J.
1981-01-01
Experimental observations of ion phase-space vortices are reported. The ion phase-space vortices form in the region of heated ions behind electrostatic ion acoustic shocks. The results are in qualitative agreement with numerical and analytic studies....
Ring vortex solitons in nonlocal nonlinear media
DEFF Research Database (Denmark)
Briedis, D.; Petersen, D.E.; Edmundson, D.;
2005-01-01
or higher charge fundamental vortices as well as higher order (multiple ring) vortex solitons. Our results pave the way for experimental observation of stable vortex rings in other nonlocal nonlinear systems including Bose-Einstein condensates with pronounced long-range interparticle interaction....
Cyclones and attractive streaming generated by acoustical vortices.
Riaud, Antoine; Baudoin, Michael; Thomas, Jean-Louis; Bou Matar, Olivier
2014-07-01
Acoustical and optical vortices have attracted great interest due to their ability to capture and manipulate particles with the use of radiation pressure. Here we show that acoustical vortices can also induce axial vortical flow reminiscent of cyclones, whose topology can be controlled by adjusting the properties of the acoustical beam. In confined geometry, the phase singularity enables generating "attractive streaming" with the flow directed toward the transducer. This opens perspectives for contactless vortical flow control.
Vorticity, Gyroscopic precession, and Spin-Curvature Force
Liang, Wei Chieh; Lee, Si Chen
2012-01-01
In investigating the relation between vorticity and gyroscopic precession, we calculate the vorticity vector in Godel, Kerr, Lewis, Schwarzschild, Minkowski metric and find out the vorticity vector of the specific observers is the angular velocity of gyroscopic precession. Furthermore, considering space-time torsion will flip the vorticity and spin-curvature force to opposite sign. This result is very similar to the behavior of positive and negative helicity of quantum spin in Stern-Gerlach f...
Cyclones and attractive streaming generated by acoustical vortices
Riaud, Antoine; Thomas, Jean-Louis; Matar, Olivier Bou
2014-01-01
Acoustical and optical vortices have attracted large interest due to their ability in capturing and manipulating particles with the use of the radiation pressure. Here we show that acoustical vortices can also induce axial vortical flow reminiscent of cyclones whose topology can be controlled by adjusting the properties of the acoustical beam. In confined geometry, the phase singularity enables generating attractive streaming with a flow directed toward the transducer. This opens perspectives for contact-less vortical flow control.
Confinement and fat-center-vortices model
Deldar, S
2004-01-01
In this paper I review shortly potentials obtained for SU(2), SU(3) and SU(4) static sources from fat-center-vortices model. Results confirm the confinement of quarks in all three gauge groups. Proportionality of string tensions with flux tube counting is better than Casimir scaling especially for SU(4).
Equilibration of centrifugally unstable vortices: A review
Carnevale, G.F.; Kloosterziel, R.C.; Orlandi, P.
2016-01-01
In three-dimensional flow, a vortex can become turbulent and be destroyed through a variety of instabilities. In rotating flow, however, the result of the breakup of a vortex is usually a state comprising several vortices with their axes aligned along the ambient rotation direction. This article is
Long Term Changes in the Polar Vortices
Braathen, Geir O.
2016-04-01
As the amount of halogens in the stratosphere is slowly declining and the ozone layer slowly recovers it is of interest to see how the meteorological conditions in the vortex develop over the long term since such changes might alter the foreseen ozone recovery. In conjunction with the publication of the WMO Antarctic and Arctic Ozone Bulletins, WMO has acquired the ERA Interim global reanalysis data set for several meteorological parameters. This data set goes from 1979 - present. These long time series of data can be used for several useful studies of the long term development of the polar vortices. Several "environmental indicators" for vortex change have been calculated, and a climatology, as well as trends, for these parameters will be presented. These indicators can act as yardsticks and will be useful for understanding past and future changes in the polar vortices and how these changes affect polar ozone depletion. Examples of indicators are: vortex mean temperature, vortex minimum temperature, vortex mean PV, vortex "importance" (PV*area), vortex break-up time, mean and maximum wind speed. Data for both the north and south polar vortices have been analysed at several isentropic levels from 350 to 850 K. A possible link between changes in PV and sudden stratospheric warmings will be investigated, and the results presented. The unusual meteorological conditions of the 2015 south polar vortex and the 2010/11 and 2015/16 north polar vortices will be compared to other recent years.
Vorticity dynamics in an intracranial aneurysm
Le, Trung; Borazjani, Iman; Sotiropoulos, Fotis
2008-11-01
Direct Numerical Simulation is carried out to investigate the vortex dynamics of physiologic pulsatile flow in an intracranial aneurysm. The numerical solver is based on the CURVIB (curvilinear grid/immersed boundary method) approach developed by Ge and Sotiropoulos, J. Comp. Physics, 225 (2007) and is applied to simulate the blood flow in a grid with 8 million grid nodes. The aneurysm geometry is extracted from MRI images from common carotid artery (CCA) of a rabbit (courtesy Dr.Kallmes, Mayo Clinic). The simulation reveals the formation of a strong vortex ring at the proximal end during accelerated flow phase. The vortical structure advances toward the aneurysm dome forming a distinct inclined circular ring that connects with the proximal wall via two long streamwise vortical structures. During the reverse flow phase, the back flow results to the formation of another ring at the distal end that advances in the opposite direction toward the proximal end and interacts with the vortical structures that were created during the accelerated phase. The basic vortex formation mechanism is similar to that observed by Webster and Longmire (1998) for pulsed flow through inclined nozzles. The similarities between the two flows will be discussed and the vorticity dynamics of an aneurysm and inclined nozzle flows will be analyzed.This work was supported in part by the University of Minnesota Supercomputing Institute.
RENORMALIZED ENERGY WITH VORTICES PINNING EFFECT
Institute of Scientific and Technical Information of China (English)
Ding Shijin
2000-01-01
This paper is a continuation of the previous paper in the Journal of Partial Differential Equations [1]. We derive in this paper the renormalized energy to further determine the locations of vortices in some case for the variational problem related to the superconducting thin films having variable thickness.
Prometheus Induced Vorticity In Saturns F Ring
Sutton, Phil J
2016-01-01
Saturns rings are known to show remarkable real time variability in their structure. Many of which can be associated to interactions with nearby moons and moonlets. Possibly the most interesting and dynamic place in the rings, probably in the whole Solar System, is the F ring. A highly disrupted ring with large asymmetries both radially and azimuthally. Numerically non zero components to the curl of the velocity vector field (vorticity) in the perturbed area of the F ring post encounter are witnessed, significantly above the background vorticity. Within the perturbed area rich distributions of local rotations is seen located in and around the channel edges. The gravitational scattering of ring particles during the encounter causes a significant elevated curl of the vector field above the background F ring vorticity for the first 1-3 orbital periods post encounter. After 3 orbital periods vorticity reverts quite quickly to near background levels. This new found dynamical vortex life of the ring will be of grea...
Potential vorticity formulation of compressible magnetohydrodynamics.
Arter, Wayne
2013-01-04
Compressible ideal magnetohydrodynamics is formulated in terms of the time evolution of potential vorticity and magnetic flux per unit mass using a compact Lie bracket notation. It is demonstrated that this simplifies analytic solution in at least one very important situation relevant to magnetic fusion experiments. Potentially important implications for analytic and numerical modelling of both laboratory and astrophysical plasmas are also discussed.
Motion of three vortices near collapse
Leoncini, X.; Kuznetsov, L.; Zaslavsky, G. M.
2000-08-01
A system of three point vortices in an unbounded plane has a special family of self-similarly contracting or expanding solutions: during the motion, the vortex triangle remains similar to the original one, while its area decreases (grows) at a constant rate. A contracting configuration brings three vortices to a single point in a finite time; this phenomenon known as vortex collapse is of principal importance for many-vortex systems. Dynamics of close-to-collapse vortex configurations depends on the way the collapse conditions are violated. Using an effective potential representation, a detailed quantitative analysis of all the different types of near-collapse dynamics is performed when two of the vortices are identical. We discuss time and length scales, emerging in the problem, and their behavior as the initial vortex triangle is approaching an exact collapse configuration. Different types of critical behaviors, such as logarithmic or power-law divergences are exhibited, which emphasize the importance of the way the collapse is approached. Period asymptotics for all singular cases are presented as functions of the initial vortice's configurations. Special features of passive particle mixing by near-collapse flows are illustrated numerically.
Bilinear Relative Equilibria of Identical Point Vortices
DEFF Research Database (Denmark)
Aref, H.; Beelen, Peter; Brøns, Morten
2012-01-01
-axis and n on the x-axis. We define generating polynomials q(z) and p(z), respectively, for each set of vortices. A second-order, linear ODE for p(z) given q(z) is derived. Several results relating the general solution of the ODE to relative equilibrium configurations are established. Our strongest result......A new class of bilinear relative equilibria of identical point vortices in which the vortices are constrained to be on two perpendicular lines, conveniently taken to be the x- and y-axes of a Cartesian coordinate system, is introduced and studied. In the general problem we have m vortices on the y......, obtained using Sturm’s comparison theorem, is that if p(z) satisfies the ODE for a given q(z) with its imaginary zeros symmetric relative to the x-axis, then it must have at least n−m+2 simple, real zeros. For m=2 this provides a complete characterization of all zeros, and we study this case in some detail...
Controlled Manipulation of Individual Vortices in a Superconductor
Energy Technology Data Exchange (ETDEWEB)
Straver, E.W.J.
2010-04-05
We report controlled local manipulation of single vortices by low temperature magnetic force microscope (MFM) in a thin film of superconducting Nb. We are able to position the vortices in arbitrary configurations and to measure the distribution of local depinning forces. This technique opens up new possibilities for the characterization and use of vortices in superconductors.
Prometheus Induced Vorticity in Saturn's F Ring
Sutton, Phil J.; Kusmartsev, Feo V.
2016-11-01
Saturn's rings are known to show remarkable real time variability in their structure. Many of which can be associated to interactions with nearby moons and moonlets. Possibly the most interesting and dynamic place in the rings, probably in the whole Solar System, is the F ring. A highly disrupted ring with large asymmetries both radially and azimuthally. Numerically non-zero components to the curl of the velocity vector field (vorticity) in the perturbed area of the F ring post encounter are witnessed, significantly above the background vorticity. Within the perturbed area rich distributions of local rotations is seen located in and around the channel edges. The gravitational scattering of ring particles during the encounter causes a significant elevated curl of the vector field above the background F ring vorticity for the first 1-3 orbital periods post encounter. After 3 orbital periods vorticity reverts quite quickly to near background levels. This new found dynamical vortex life of the ring will be of great interest to planet and planetesimals in proto-planetary disks where vortices and turbulence are suspected of having a significant role in their formation and migrations. Additionally, it is found that the immediate channel edges created by the close passage of Prometheus actually show high radial dispersions in the order 20-50 cm/s, up to a maximum of 1 m/s. This is much greater than the value required by Toomre for a disk to be unstable to the growth of axisymmetric oscillations. However, an area a few hundred km away from the edge shows a more promising location for the growth of coherent objects.
Prometheus Induced Vorticity in Saturn's F Ring
Sutton, Phil J.; Kusmartsev, Feo V.
2016-09-01
Saturn's rings are known to show remarkable real time variability in their structure. Many of which can be associated to interactions with nearby moons and moonlets. Possibly the most interesting and dynamic place in the rings, probably in the whole Solar System, is the F ring. A highly disrupted ring with large asymmetries both radially and azimuthally. Numerically non-zero components to the curl of the velocity vector field (vorticity) in the perturbed area of the F ring post encounter are witnessed, significantly above the background vorticity. Within the perturbed area rich distributions of local rotations is seen located in and around the channel edges. The gravitational scattering of ring particles during the encounter causes a significant elevated curl of the vector field above the background F ring vorticity for the first 1-3 orbital periods post encounter. After 3 orbital periods vorticity reverts quite quickly to near background levels. This new found dynamical vortex life of the ring will be of great interest to planet and planetesimals in proto-planetary disks where vortices and turbulence are suspected of having a significant role in their formation and migrations. Additionally, it is found that the immediate channel edges created by the close passage of Prometheus actually show high radial dispersions in the order ~20-50 cm/s, up to a maximum of 1 m/s. This is much greater than the value required by Toomre for a disk to be unstable to the growth of axisymmetric oscillations. However, an area a few hundred km away from the edge shows a more promising location for the growth of coherent objects.
An eddy closure for potential vorticity
Energy Technology Data Exchange (ETDEWEB)
Ringler, Todd D [Los Alamos National Laboratory
2009-01-01
The Gent-McWilliams (GM) parameterization is extended to include a direct influence in the momentum equation. The extension is carried out in two stages; an analysis of the inviscid system is followed by an analysis of the viscous system. In the inviscid analysis the momentum equation is modified such that potential vorticity is conserved along particle trajectories following a transport velocity that includes the Bolus velocity in a manner exactly analogous to the continuity and tracer equations. In addition (and in contrast to traditional GM closures), the new formulation of the inviscid momentum equation results in a conservative exchange between potential and kinetic forms of energy. The inviscid form of the eddy closure conserves total energy to within an error proportional to the time derivative of the Bolus velocity. The hypothesis that the viscous term in the momentum equation should give rise to potential vorticity being diffused along isopycnals in a manner analogous to other tracers is examined in detail. While the form of the momentum closure that follows from a strict adherence to this hypothesis is not immediately interpretable within the constructs of traditional momentum closures, three approximations to this hypothesis results in a form of dissipation that is consistent with traditional Laplacian diffusion. The first two approximations are that relative vorticity, not potential vorticity, is diffused along isopyncals and that the flow is in approximate geostrophic balance. An additional approximation to the Jacobian term is required when the dissipation coefficient varies in space. More importantly, the critique of this hypothesis results in the conclusion that the viscosity parameter in the momentum equation should be identical to the tradition GM closure parameter {Kappa}. Overall, we deem the viscous form of the eddy closure for potential vorticity as a viable closure for use in ocean circulation models.
Rossby Wave Instability of Thin Accretion Disks - III. Nonlinear Simulations
Li, H; Wendroff, B; Liska, R
2000-01-01
(abridged) We study the nonlinear evolution of the Rossby wave instability in thin disks using global 2D hydrodynamic simulations. The key questions we are addressing in this paper are: (1) What happens when the instability becomes nonlinear? Specifically, does it lead to vortex formation? (2) What is the detailed behavior of a vortex? (3) Can the instability sustain itself and can the vortex last a long time? Among various initial equilibria that we have examined, we generally find that there are three stages of the disk evolution: (1) The exponential growth of the initial small amplitude perturbations. This is in excellent agreement with the linear theory; (2) The production of large scale vortices and their interactions with the background flow, including shocks. Significant accretion is observed due to these vortices. (3) The coupling of Rossby waves/vortices with global spiral waves, which facilitates further accretion throughout the whole disk. Even after more than 20 revolutions at the radius of vortic...
Sparsified-dynamics modeling of discrete point vortices with graph theory
Taira, Kunihiko; Nair, Aditya
2014-11-01
We utilize graph theory to derive a sparsified interaction-based model that captures unsteady point vortex dynamics. The present model builds upon the Biot-Savart law and keeps the number of vortices (graph nodes) intact and reduces the number of inter-vortex interactions (graph edges). We achieve this reduction in vortex interactions by spectral sparsification of graphs. This approach drastically reduces the computational cost to predict the dynamical behavior, sharing characteristics of reduced-order models. Sparse vortex dynamics are illustrated through an example of point vortex clusters interacting amongst themselves. We track the centroids of the individual vortex clusters to evaluate the error in bulk motion of the point vortices in the sparsified setup. To further improve the accuracy in predicting the nonlinear behavior of the vortices, resparsification strategies are employed for the sparsified interaction-based models. The model retains the nonlinearity of the interaction and also conserves the invariants of discrete vortex dynamics; namely the Hamiltonian, linear impulse, and angular impulse as well as circulation. Work supported by US Army Research Office (W911NF-14-1-0386) and US Air Force Office of Scientific Research (YIP: FA9550-13-1-0183).
Energy and vorticity decay in Haloclines and Thermoclines
Redondo, Jose M.; Matulka, Annia M.; Peco, Cristian
2010-05-01
Experiments at different Reynolds numbers on the vertical and horizontal mixing structure and efficiency of mixing across a thermocline or halocline are used to investigate the decay of the turbulence [1-3]. Vertical and horizontal grids are used to mix an initialy sharp density interface (mostly made up with brine). Visualization methods are used to derive the velocity and vorticity horizontal fields and density probes allow to evaluate mixing. The vortex behavior is analyzed in detail as well as the process of energy decay and the transfer from kinetic to potential energy.By using the multi-fractal "Box counting Algorithm" [1] on the kinetic energy and vorticity fields and a suitable non dimensional Damkholer type of decay time, based on the local dissipation in the experiments that model ocean haloclines and surface ROFI, it is possible to relate certain patterns to physical processes similar to those in the ocean as in[4]. Diffusion, Spectral variations, Intermittency and higher order estimations of local mixing are presented as functions of the Richardson number and these predictions are compared with practical ocean flows and pollution situations[5]. [1] Redondo J.M. and Garzon G."Multifractal structure and intermittency in Rayleigh-Taylor Driven Fronts". Ed. S. Dalziel www.damtp.cam.ac.uk/iwpctm9/proceedings/IWPCTM9/Papers/Programme.htm. 2004. [2] Redondo, J.M. and Cantalapiedra I.R. "Mixing in Horizontally Heterogeneous Flows". Jour. Flow Turbulence and Combustion. 51. 217-222. 1993. [3] Castilla R, Redondo J.M., Gamez P.J., Babiano A. "Coherent vortices and Lagrangian Dynamics in 2D Turbulence". Non-Linear Processes in Geophysics 14. 139-151. 2007. [4] Bezerra,M.O. M. Diez, C. Medeiros, A. Rodriguez, E. Bahia., A. Sanchez-Arcilla and J.M. Redondo. "Study on the influence of waves on coastal diffusion using image analysis". Jour. Flow Turbulence and Combustion 59,.191-204. 1998. [5] Peco, C. "Mixing in the Thermocline and Halocline Ms". Thesis, ETSECCPB
Viscous tilting and production of vorticity in homogeneous turbulence
Holzner, M; Lüthi, B; Liberzon, A; Nikitin, N; Kinzelbach, W; Tsinober, A
2010-01-01
Viscous depletion of vorticity is an essential and well known property of turbulent flows, balancing, in the mean, the net vorticity production associated with the vortex stretching mechanism. In this letter we however demonstrate that viscous effects are not restricted to a mere destruction process, but play a more complex role in vorticity dynamics that is as important as vortex stretching. Based on results from particle tracking experiments (3D-PTV) and direct numerical simulation (DNS) of homogeneous and quasi isotropic turbulence, we show that the viscous term in the vorticity equation can also locally induce production of vorticity and changes of its orientation (viscous tilting).
Vortical versus skyrmionic states in mesoscopic p -wave superconductors
Fernández Becerra, V.; Sardella, E.; Peeters, F. M.; Milošević, M. V.
2016-01-01
We investigate the superconducting states that arise as a consequence of mesoscopic confinement and a multicomponent order parameter in the Ginzburg-Landau model for p -wave superconductivity. Conventional vortices, but also half-quantum vortices and skyrmions, are found as the applied magnetic field and the anisotropy parameters of the Fermi surface are varied. The solutions are well differentiated by a topological charge that for skyrmions is given by the Hopf invariant and for vortices by the circulation of the superconducting velocity. We revealed several unique states combining vortices and skyrmions, their possible reconfiguration with varied magnetic field, as well as temporal and field-induced transitions between vortical and skyrmionic states.
Injection of Orbital Angular Momentum and Storage of Quantized Vortices in Polariton Superfluids.
Boulier, T; Cancellieri, E; Sangouard, N D; Glorieux, Q; Kavokin, A V; Whittaker, D M; Giacobino, E; Bramati, A
2016-03-18
We report the experimental investigation and theoretical modeling of a rotating polariton superfluid relying on an innovative method for the injection of angular momentum. This novel, multipump injection method uses four coherent lasers arranged in a square, resonantly creating four polariton populations propagating inwards. The control available over the direction of propagation of the superflows allows injecting a controllable nonquantized amount of optical angular momentum. When the density at the center is low enough to neglect polariton-polariton interactions, optical singularities, associated with an interference pattern, are visible in the phase. In the superfluid regime resulting from the strong nonlinear polariton-polariton interaction, the interference pattern disappears and only vortices with the same sign are persisting in the system. Remarkably, the number of vortices inside the superfluid region can be controlled by controlling the angular momentum injected by the pumps.
A possible theory for the interaction between convective activities and vortical flows
Directory of Open Access Journals (Sweden)
N. Zhao
2011-10-01
Full Text Available Theoretical studies usually attribute convections to the developments of instabilities such as the static or symmetric instabilities of the basic flows. However, the following three facts make the validities of these basic theories unconvincing. First, it seems that in most cases the basic flow with balance property cannot exist as the exact solution, so one cannot formulate appropriate problems of stability. Second, neither linear nor nonlinear theories of dynamical instability are able to describe a two-way interaction between convection and its background, because the basic state which must be an exact solution of the nonlinear equations of motion is prescribed in these issues. And third, the dynamical instability needs some extra initial disturbance to trigger it, which is usually another point of uncertainty. The present study suggests that convective activities can be recognized in the perspective of the interaction of convection with vortical flow. It is demonstrated that convective activities can be regarded as the superposition of free modes of convection and the response to the forcing induced by the imbalance of the unstably stratified vortical flow. An imbalanced vortical flow provides not only an initial condition from which unstable free modes of convection can develop but also a forcing on the convection. So, convection is more appropriately to be regarded as a spontaneous phenomenon rather than a disturbance-triggered phenomenon which is indicated by any theory of dynamical instability. Meanwhile, convection, particularly the forced part, has also a reaction on the basic flow by preventing the imbalance of the vortical flow from further increase and maintaining an approximately balanced flow.
Solitonic vortices in Bose-Einstein condensates
Tylutki, M.; Donadello, S.; Serafini, S.; Pitaevskii, L. P.; Dalfovo, F.; Lamporesi, G.; Ferrari, G.
2015-04-01
We analyse, theoretically and experimentally, the nature of solitonic vortices (SV) in an elongated Bose-Einstein condensate. In the experiment, such defects are created via the Kibble-Zurek mechanism, when the temperature of a gas of sodium atoms is quenched across the BEC transition, and are imaged after a free expansion of the condensate. By using the Gross-Pitaevskii equation, we calculate the in-trap density and phase distributions characterizing a SV in the crossover from an elongated quasi-1D to a bulk 3D regime. The simulations show that the free expansion strongly amplifies the key features of a SV and produces a remarkable twist of the solitonic plane due to the quantized vorticity associated with the defect. Good agreement is found between simulations and experiments.
Vortices in Low-Dimensional Magnetic Systems
Costa, B. V.
2011-05-01
Vortices are objects that are important to describe several physical phenomena. There are many examples of such objects in nature as in a large variety of physical situations like in fluid dynamics, superconductivity, magnetism, and biology. Historically, the interest in magnetic vortex-like excitations begun in the 1960s. That interest was mainly associated with an unusual phase-transition phenomenon in two-dimensional magnetic systems. More recently, direct experimental evidence for the existence of magnetic vortex states in nano-disks was found. The interest in such model was renewed due to the possibility of the use of magnetic nano-disks as bit elements in nano-scale memory devices. The goal of this study is to review some key points for the understanding of the vortex behavior and the progress that have been done in the study of vortices in low-dimensional magnetic systems.
Statistical mechanics of vortices from field theory
Kajantie, Keijo; Neuhaus, T; Rajantie, A; Rummukainen, K
1999-01-01
We study with lattice Monte Carlo simulations the interactions and macroscopic behaviour of a large number of vortices in the 3-dimensional U(1) gauge+Higgs field theory, in an external magnetic field. We determine non-perturbatively the (attractive or repelling) interaction energy between two or more vortices, as well as the critical field strength H_c, the thermodynamical discontinuities, and the surface tension related to the boundary between the Meissner phase and the Coulomb phase in the type I region. We also investigate the emergence of vortex lattice and vortex liquid phases in the type II region. For the type I region the results obtained are in qualitative agreement with mean field theory, except for small values of H_c, while in the type II region there are significant discrepancies. These findings are relevant for superconductors and some models of cosmic strings, as well as for the electroweak phase transition in a magnetic field.
Mimicking graphene with polaritonic spin vortices
Gulevich, Dmitry R.; Yudin, Dmitry
2017-09-01
Exploring the properties of strongly correlated systems through quantum simulation with photons, cold atoms, or polaritons represents an active area of research. In fact, the latter sheds light on the behavior of complex systems that are difficult to address in the laboratory or to tackle numerically. In this study, we discuss an analog of graphene formed by exciton-polariton spin vortices arranged into a hexagonal lattice. We show how graphene-type dispersion at different energy scales arises for several types of exciton-polariton spin vortices. In contrast to previous studies of exciton polaritons in artificial lattices, the use of exciton-polariton spin vortex modes offers a richer playground for quantum simulations. In particular, we demonstrate that the sign of the nearest-neighbor coupling strength can be inverted.
Holographic Fluids with Vorticity and Analogue Gravity
Leigh, Robert G; Petropoulos, P Marios
2012-01-01
We study holographic three-dimensional fluids with vorticity in local equilibrium and discuss their relevance to analogue gravity systems. The Fefferman-Graham expansion leads to the fluid's description in terms of a comoving and rotating Papapetrou-Randers frame. A suitable Lorentz transformation brings the fluid to the non-inertial Zermelo frame, which clarifies its interpretation as moving media for light/sound propagation. We apply our general results to the Lorentzian Kerr-AdS_4 and Taub-NUT-AdS_4 geometries that describe fluids in cyclonic and vortex flows respectively. In the latter case we associate the appearance of closed timelike curves to analogue optical horizons. In addition, we derive the classical rotational Hall viscosity of three-dimensional fluids with vorticity. Our formula remarkably resembles the corresponding result in magnetized plasmas.
Cryptology transmitted message protection from deterministic chaos up to optical vortices
Izmailov, Igor; Romanov, Ilia; Smolskiy, Sergey
2016-01-01
This book presents methods to improve information security for protected communication. It combines and applies interdisciplinary scientific engineering concepts, including cryptography, chaos theory, nonlinear and singular optics, radio-electronics and self-changing artificial systems. It also introduces additional ways to improve information security using optical vortices as information carriers and self-controlled nonlinearity, with nonlinearity playing a key "evolving" role. The proposed solutions allow the universal phenomenon of deterministic chaos to be discussed in the context of information security problems on the basis of examples of both electronic and optical systems. Further, the book presents the vortex detector and communication systems and describes mathematical models of the chaos oscillator as a coder in the synchronous chaotic communication and appropriate decoders, demonstrating their efficiency both analytically and experimentally. Lastly it discusses the cryptologic features of analyze...
Analytic Modeling of Severe Vortical Storms.
1980-07-08
AD---AO86 919 TR DEFENSE AND SPACE SYSTEMS GROUP REDONDO BEACH CA -ETC F/6 4/2 ANALYTIC MODELING OF SEVERE VORTICAL, STDRMS.CW),7JUL G0 F FENDELL ...and Space Systems Group One Space 1ark ___Redondo Beach, California 90278 Francis E. Fendell , Principal Investigator for Artic and Earth Sciences... Fendell , principal investigator, and Phillip Feldman, numerical analyst, of TRW Defense and Space Systems Group, and George Carrier of Harvard University
Vortices in a Bose-Einstein Condensate
Haljan, Paul C.
2004-05-01
Since the advent of Bose-Einstein condensation in the dilute alkalis, there has been considerable interest in observing effects in atomic condensates akin to the hallmark effects associated with superfluidity and superconductivity. In particular, the study of quantized vortices and vortex lattices represents an important connection between the traditional ``super" systems such as liquid Helium and this new atomic system. This thesis explores some of the first vortex experiments in a condensate of magnetically trapped Rubidium-87. Single vortex lines and rings are created using a wavefunction engineering technique, which is an ideal starting point to study the dynamical behavior of vortices within the condensate. An entirely different approach of ``intrinsic nucleation" has been developed to create rapidly rotating condensates with large amounts of vorticity. A novel variation of forced evaporation is used to simultaneously cool and spin up an ultracold gas. In this way, condensates can be formed that are rotating in excess of 95% of the centrifugal limit and contain large, extraordinarily regular lattices of well over 100 vortices. Direct detection of the vortex cores makes it possible to study the microscopic structure of the vortex arrangements both at equilibrium and under dynamical conditions where severe applied stresses distort the lattice far from its equilibrium configuration. In conclusion, the techniques developed in this work have helped to open up a new area of rotating condensate physics and, in the future, may lead to regimes of extreme rotation and quantum Hall physics. This work was performed at the University of Colorado, Boulder, under the supervision of Prof. Eric A. Cornell.
Vorticity, Stokes' Theorem and the Gauss's Theorem
Narayanan, M.
2004-12-01
Vorticity is a property of the flow of any fluid and moving fluids acquire properties that allow an engineer to describe that particular flow in greater detail. It is important to recognize that mere motion alone does not guarantee that the air or any fluid has vorticity. Vorticity is one of four important quantities that define the kinematic properties of any fluid flow. The Navier-Stokes equations are the foundation of fluid mechanics, and Stokes' theorem is used in nearly every branch of mechanics as well as electromagnetics. Stokes' Theorem also plays a vital role in many secondary theorems such as those pertaining to vorticity and circulation. However, the divergence theorem is a mathematical statement of the physical fact that, in the absence of the creation or destruction of matter, the density within a region of space can change only by having it flow into, or away from the region through its boundary. This is also known as Gauss's Theorem. It should also be noted that there are many useful extensions of Gauss's Theorem, including the extension to include surfaces of discontinuity in V. Mathematically expressed, Stokes' theorem can be expressed by considering a surface S having a bounding curve C. Here, V is any sufficiently smooth vector field defined on the surface and its bounding curve C. Integral (Surface) [(DEL X V)] . dS = Integral (Contour) [V . dx] In this paper, the author outlines and stresses the importance of studying and teaching these mathematical techniques while developing a course in Hydrology and Fluid Mechanics. References Arfken, G. "Gauss's Theorem." 1.11 in Mathematical Methods for Physicists, 3rd ed. Orlando, FL: Academic Press, pp. 57-61, 1985. Morse, P. M. and Feshbach, H. "Gauss's Theorem." In Methods of Theoretical Physics, Part I. New York: McGraw-Hill, pp. 37-38, 1953. Eric W. Weisstein. "Divergence Theorem." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/DivergenceTheorem.html
Motion of Three Vortices near Collapse
Leoncini, X; Zaslavsky, G M
2000-01-01
A system of three point vortices in an unbounded plane has a special family of self-similarly contracting or expanding solutions: during the motion, vortex triangle remains similar to the original one, while its area decreases (grows) at a constant rate. A contracting configuration brings three vortices to a single point in a finite time; this phenomenon is known as vortex collapse and is of principal importance for many-vortex systems. The self-similar motion (contracting or expanding) is not generic, it arises when vortex strengths and initial positions satisfy two special collapse conditions. Dynamics of close-to-collapse vortex configurations depends on the way the collapse conditions are violated. We show, that when two of the vortices are identical, it is possible to reduce a three-vortex system to a problem of motion of a particle in an effective potential, defined by initial conditions. Using the effective potential representation, a detailed quantitative analysis of different types of near-collapse d...
Semi-analytic variable charge solitary waves involving dust phase-space vortices (holes)
Energy Technology Data Exchange (ETDEWEB)
Tribeche, Mouloud; Younsi, Smain; Amour, Rabia; Aoutou, Kamel [Plasma Physics Group, Faculty of Sciences-Physics, Theoretical Physics Laboratory, University of Bab-Ezzouar, USTHB BP 32, El Alia, Algiers 16111 (Algeria)], E-mail: mtribeche@usthb.dz
2009-09-15
A semi-analytic model for highly nonlinear solitary waves involving dust phase-space vortices (holes) is outlined. The variable dust charge is expressed in terms of the Lambert function and we take advantage of this transcendental function to investigate the localized structures that may occur in a dusty plasma with variable charge trapped dust particles. Our results which complement the previously published work on this problem (Schamel et al 2001 Phys. Plasmas 8 671) should be of basic interest for experiments that involve the trapping of dust particles in ultra-low-frequency dust acoustic modes.
Study on direct measurement method of vorticity from particle images
Institute of Scientific and Technical Information of China (English)
RUAN Xiaodong; FU Xin; YANG Huayong
2007-01-01
To overcome the shortcomings of conventional methods for vorticity measurement,a new direct measurement of vorticity (DMV) method extracting vorticity from particle images was proposed.Based on the theory of fluid flow,two matched particle patterns were extracted from particle images in the DMV method.The pattern vorticity was determined from the average angular displacement of rotation between the two matched particle patterns.The method was applied on standard particle images,and was compared with the second and third order central finite difference methods.Results show that the accuracy of DMV method is independent of the spatial resolution of the sampling,and the uncertainty errors in the velocity measurement are not propagated into the vorticity.The method is applicable for measuring vorticity of a stronger rotational flow.The time interval of image sampling should be shortened to increase the measurement ranges for higher shearing distortion flows.
A Measure of Flow Vorticity with Helical Beams of Light
Rosales-Guzmán, Aniceto Belmonte Carmelo
2015-01-01
Vorticity describes the spinning motion of a fluid, i.e., the tendency to rotate, at every point in a flow. The interest in performing accurate and localized measurements of vorticity reflects the fact that many of the quantities that characterize the dynamics of fluids are intimately bound together in the vorticity field, being an efficient descriptor of the velocity statistics in many flow regimes. It describes the coherent structures and vortex interactions that are at the leading edge of laminar, transitional, and turbulent flows in nature. The measurement of vorticity is of paramount importance in many research fields as diverse as biology microfluidics, complex motions in the oceanic and atmospheric boundary layers, and wake turbulence on fluid aerodynamics. However, the precise measurement of flow vorticity is difficult. Here we put forward an optical sensing technique to obtain a direct measurement of vorticity in fluids using Laguerre-Gauss (LG) beams, optical beams which show an azimuthal phase vari...
Strong swirl approximation and intensive vortices in the atmosphere
Klimenko, A Y
2014-01-01
This work investigates intensive vortices, which are characterised by the existence of a converging radial flow that significantly intensifies the flow rotation. Evolution and amplification of the vorticity present in the flow play important roles in the formation of the vortex. When rotation in the flow becomes sufficiently strong - and this implies validity of the strong swirl approximation developed by Einstein and Li (1951), Lewellen (1962), Turner (1966) and Lundgren (1985) - the analysis of Klimenko (2001a-c) and of the present work determine that further amplification of vorticity is moderated by interactions of vorticity and velocity. This imposes physical constraints on the flow resulting in the so-called compensating regime, where the radial distribution of the axial vorticity is characterised by the 4/3 and 3/2 power laws. This asymptotic treatment of a strong swirl is based on vorticity equations and involves higher order terms. This treatment incorporates multiscale analysis indicating downstream...
Hassanzadeh, Pedram
Large coherent vortices are abundant in geophysical and astrophysical flows. They play significant roles in the Earth's oceans and atmosphere, the atmosphere of gas giants, such as Jupiter, and the protoplanetary disks around forming stars. These vortices are essentially three-dimensional (3D) and baroclinic, and their dynamics are strongly influenced by the rotation and density stratification of their environments. This work focuses on improving our understanding of the physics of 3D baroclinic vortices in rotating and continuously stratified flows using 3D spectral simulations of the Boussinesq equations, as well as simplified mathematical models. The first chapter discusses the big picture and summarizes the results of this work. In Chapter 2, we derive a relationship for the aspect ratio (i.e., vertical half-thickness over horizontal length scale) of steady and slowly-evolving baroclinic vortices in rotating stratified fluids. We show that the aspect ratio is a function of the Brunt-Vaisala frequencies within the vortex and outside the vortex, the Coriolis parameter, and the Rossby number of the vortex. This equation is basically the gradient-wind equation integrated over the vortex, and is significantly different from the previously proposed scaling laws that find the aspect ratio to be only a function of the properties of the background flow, and independent of the dynamics of the vortex. Our relation is valid for cyclones and anticyclones in either the cyclostrophic or geostrophic regimes; it works with vortices in Boussinesq fluids or ideal gases, and non-uniform background density gradient. The relation for the aspect ratio has many consequences for quasi-equilibrium vortices in rotating stratified flows. For example, cyclones must have interiors more stratified than the background flow (i.e., super-stratified), and weak anticyclones must have interiors less stratified than the background (i.e., sub-stratified). In addition, this equation is useful to
Thick vortices in SU(2) lattice gauge theory
Cheluvaraja, Srinath
2004-01-01
Three dimensional SU(2) lattice gauge theory is studied after eliminating thin monopoles and the smallest thick monopoles. Kinematically this constraint allows the formation of thick vortex loops which produce Z(2) fluctuations at longer length scales. The thick vortex loops are identified in a three dimensional simulation. A condensate of thick vortices persists even after the thin vortices have all disappeared. The thick vortices decouple at a slightly lower temperature (higher beta) than t...
Direct observation of rectified motion of vortices by Lorentz microscopy
Indian Academy of Sciences (India)
Yoshihiko Togawa; Ken Harada; Tetsuya Akashi; Hiroto Kasai; Tsuyoshi Matsuda; Atsutaka maeda; Akira Tonomura
2006-01-01
We have investigated the vortex dynamics for the `ratchet' operation in a niobium superconductor via a direct imaging of Lorentz microscopy. We directly observe one-directional selective motion of field-gradient-driven vortices along fabricated channels. This results from the rectification of vortices in a spatially asymmetric potential under the oscillating magnetic field in a temporally symmetric manner. Based on the observation of the individual motion of vortices, we clarify the elementary process involved in this rectification.
SIMULATION OF AIRCRAFT CONDENSATION TRAILS AND WAKE VORTICES INTERACTION
Directory of Open Access Journals (Sweden)
T. O. Aubakirov
2015-01-01
Full Text Available A technique of calculation of aircraft condensation trails (contrails and wake vortices interaction is described. The technique is based on a suitable for real-time applications mathematical model of far wake utilizes the method of discrete vortices. The technique is supplemented by account of the influence of axial velocities in the vortex nucleus on contrail and wake vortex location. Results of calculations of contrails and wake vortices interaction for Il-76 and B-747 aircraft are presented.
Analysis of the Caudal Vortices Evolvement around Flapping Foil
Institute of Scientific and Technical Information of China (English)
Wang Zhi-dong; Zhang Xiao-qing; Su Yu-min; Xu Yu-ru
2005-01-01
The viscous flow field around two-dimensional flapping (heaving and pitching) foils was numerically computed. The structural characteristics of caudal vortices were investigated and the contour curves at different phase angles were obtained.The relationships between the structural characteristics of the vortices and the force acting on the foil and between the widths of the caudal vortex street and of the caudal flow field were analyzed. A method to determine the shedding frequency of the vortices was proposed.
Quantum signatures of charge flipping vortices in the Bose-Hubbard trimer.
Jason, Peter; Johansson, Magnus
2016-11-01
In this work we study quantum signatures of charge flipping vortices, found in the classical discrete nonlinear Schrödinger trimer, by use of the Bose-Hubbard model. We are able to identify such signatures in the quantum energy eigenstates, for instance when comparing the site amplitudes of the classical charge flipping vortices with the probability distribution over different particle configurations. It is also discussed how to construct quantum states that correspond to the classical charge flipping vortices and which effects can lead to deviations between the classical and quantum dynamics. We also examine properties of certain coherent states: classical-like quantum states that can be used to derive the classical model. Several quantum signatures are identified when studying the dynamics of these coherent states, for example, when comparing the average number of particles on a site with the classical site amplitude, when comparing the quantum and classical currents and topological charge, and when studying the evolution of the quantum probability amplitudes. The flipping of the quantum currents are found to be an especially robust feature of these states.
Energy Technology Data Exchange (ETDEWEB)
Garaud, J.
2010-09-15
In this dissertation, we analyze in detail the properties of new string-like solutions of the bosonic sector of the electroweak theory. The new solutions are current carrying generalizations of embedded Abrikosov-Nielsen-Olesen vortices. We were also able to reproduce all previously known features of vortices in the electroweak theory. Generically vortices are current carrying. They are made of a compact conducting core of charged W bosons surrounded by a nonlinear superposition of Z and Higgs field. Far away from the core, the solution is described by purely electromagnetic Biot and Savart field. Solutions exist for generic parameter values including experimental values of the coupling constants. We show that the current whose typical scale is the billion of Amperes can be arbitrarily large. In the second part the linear stability with respect to generic perturbations is studied. The fluctuation spectrum is qualitatively investigated. When negative modes are detected, they are explicitly constructed and their dispersion relation is determined. Most of the unstable modes can be eliminated by imposing periodic boundary conditions along the vortex. However there remains a unique negative mode which is homogeneous. This mode can probably be eliminated by curvature effects if a small piece of vortex is bent into a loop, stabilized against contraction by the electric current. (author)
Mutabazi, Innocent; Yoshikawa, Harunori; Peixinho, Jorge; Kahouadji, Lyes
2013-11-01
Görtler vortices appear in a flow over a concave wall as a result of centrifugal instability [Saric, Annu. Rev. Fluid Mech. 26, 379 (1994)]. They may have a strong influence on heat transfer [Momayez et al., Int. J. heat Mass transfer 47, 3783 (2004)]. The purpose of this work is to model heat transfer by Görtler vortices using a weakly nonlinear analysis of Smith &-Haj- Hariri [Phys. Fluids A 5, 2815 (1993)]. We have investigated the coupling of the convective heat transfer by the stationary vortices with the heat conduction inside the solid wall. The finite thickness and thermal conductivity of the wall enter into the boundary conditions of the problem through the ratio δ of the wall thickness to the boundary layer thickness and through the ratio K of the thermal conductivities of the fluid and the wall. The parametric dependence Nu (δ , K) of the Nusselt number is performed and it is shown that found the heat transfer is quite well modified by these two parameters. The local thermal stress can be estimated in order to analyze the effects on ageing of the wall material. The authors acknowledge the financial support of the french Agence Nationale de la Recherche (ANR), through the program ``Investissements d'Avenir'' (ANR-10-LABX-09-01), LabEx EMC3.
Effect of streamwise vortices on Tollmien-Schlichting waves
Nayfeh, A. H.
1981-01-01
The method of multiple scales is used to determine a first-order uniform expansion for the effect of counter-rotating steady streamwise vortices in growing boundary layers on oblique Tollmien-Schlichting waves. The results show that such vortices have a strong tendency to amplify oblique Tollmien-Schlichting waves having a spanwise wavelength that is twice the wavelength of the vortices. An analytical expression is derived for the growth rates of these waves. These exponential growth rates increase linearly with increasing amplitudes of the vortices. Numerical results are presented. They suggest that this mechanism may dominate the instability.
Vorticity, gyroscopic precession, and spin-curvature force
Liang, Wei Chieh; Lee, Si Chen
2013-02-01
In investigating the relationship between vorticity and gyroscopic precession, we calculate the vorticity vector in Godel, Kerr, Lewis, Schwarzschild, and Minkowski metrics and find that the vorticity vector of the specific observers is the angular velocity of the gyroscopic precession. Furthermore, when space-time torsion is included, the vorticity and spin-curvature force change sign. This result is very similar to the behavior of the positive and negative helicities of quantum spin in the Stern-Gerlach force. It implies that the inclusion of torsion will lead to an analogous property of quantum spin even in classical treatment.
Vorticity, Gyroscopic precession, and Spin-Curvature Force
Liang, Wei Chieh
2012-01-01
In investigating the relation between vorticity and gyroscopic precession, we calculate the vorticity vector in Godel, Kerr, Lewis, Schwarzschild, Minkowski metric and find out the vorticity vector of the specific observers is the angular velocity of gyroscopic precession. Furthermore, considering space-time torsion will flip the vorticity and spin-curvature force to opposite sign. This result is very similar to the behavior of positive and negative helicity of quantum spin in Stern-Gerlach force. It implies that the inclusion of torsion will lead to analogous property of quantum spin even in classical treatment.
Dynamics of circular arrangements of vorticity in two dimensions
Swaminathan, Rohith V; Perlekar, Prasad; Govindarajan, Rama
2015-01-01
The merger of two like-signed vortices is a well-studied problem, but in a turbulent flow, we may often have more than two like-signed vortices interacting. We study the merger of three or more identical co-rotating vortices initially arranged on the vertices of a regular polygon. At low to moderate Reynolds numbers, we find an additional stage in the merger process, absent in the merger of two vortices, where an annular vortical structure is formed and is long-lived. Vortex merger is slowed down significantly due to this. Such annular vortices are known at far higher Reynolds numbers in studies of tropical cyclones, which have been noticed to break down into individual vortices. In the pre-annular stage, vortical structures in a viscous flow tilt and realign in a manner similar to the inviscid case, but the pronounced filaments visible in the latter are practically absent in the former. Five or fewer vortices initially elongate radially, and then reorient their long axis closer to the azimuthal direction so ...
Vortices in Ionization Collisions by Positron Impact
Navarrete, F; Fiol, J; Barrachina, R O
2013-01-01
The presence of vortices in the ionisation of hydrogen atoms by positrons at intermediate impact energies is investigated. The present findings show that a previously reported minima in the fully-differential cross section is the signature of a vortex in the continuum positron-electron-proton system. The behaviour of the real and imaginary parts of the complex-valued transition matrix is studied in order to determine and characterize the vortex in momentum space. The obtained information is translated to fully-differential ionisation cross sections, feasible of being measured with currently available techniques.
Internal waves and vortices in satellite images
Sparavigna, Amelia Carolina
2012-01-01
Some recent papers proposed the use of the satellite images of Google Earth in teaching physics, in particular to see some behaviours of waves. Reflection, refraction, diffraction and interference are easy to be found in these satellite maps. Besides Google Earth, other sites exist, such as Earth Observatory or Earth Snapshot, suitable for illustrating the large-scale phenomena in atmosphere and oceans In this paper, we will see some examples for teaching surface and internal sea waves, and internal waves and the K\\'arm\\'an vortices in the atmosphere. Aim of this proposal is attracting the interest of students of engineering schools to the physics of waves.
A splitting-free vorticity redistribution method
Kirchhart, M.; Obi, S.
2017-02-01
We present a splitting-free variant of the vorticity redistribution method. Spatial consistency and stability when combined with a time-stepping scheme are proven. We propose a new strategy preventing excessive growth in the number of particles while retaining the order of consistency. The novel concept of small neighbourhoods significantly reduces the method's computational cost. In numerical experiments the method showed second order convergence, one order higher than predicted by the analysis. Compared to the fast multipole code used in the velocity computation, the method is about three times faster.
Effects of the parametric interaction on the toplogical charge of acoustical vortices.
Marchiano, Régis; Thomas, Jean-Louis
2008-06-01
Acoustical vortices are one of the three kinds of phase singularity corresponding to screw dislocations of the wavefront. They are characterized by an helical phase winding up around their axis of propagation along which the phase is singular (undefined). This kind of waves possesses several interesting properties like robustness to wavefront distortion in heterogeneous media or non diffracting propagation due to their relation to Bessel beams. Here we are interested by their potential to transmit information and perform basic arithmetics. We experimentally show that parametric interaction has a double effect on such a beam. First of all, the classical effect of creation of frequencies corresponding to all linear combinations of the primary frequencies is recovered. This classical manifestation of the quadratic nonlinearity in fluids is not new but leads to interesting properties for the spatial information of acoustical vortices as it is possible to do some arithmetics with acoustical vortices. Indeed, it is observed that for a frequency generated by a linear combination of the primary frequencies, the topological charge (number of twists made by the wavefront for one wavelength) is obtained by the same linear combination applied to the topological charges of the primary frequencies. For instance, vortices with negative topological charge appear for a secondary beam at the frequency corresponding to the difference of two primary beams with a positive topological charge when the highest frequency corresponds to the lowest topological charge. This phenomenon is studied for frequencies without and with a common divisor. In the latter case, generated frequencies can be degenerated, i.e two different linear combinations give the same frequency. However there is no reason to have the same common divisor for the topological charge so that two waves at the same frequency but with two different charges are propagating colinearly. In this case, the topological charge can be
How Do Hydrodynamic Instabilities Affect 3D Transport in Geophysical Vortices?
Wang, P.; Ozgokmen, T. M.
2014-12-01
Understanding three-dimensional (3D) transport in ocean eddies is important for processes at a variety of scales, ranging from plankton production to climate variability. It is well known that geophysical vortices are subject to various hydrodynamic instabilities. Yet the influence of these instabilities on 3D material transport in vortex systems is not well investigated. Focusing on barotropic, inertial and 3D instabilities, we analyze these instabilities with normal-mode method, and reproduce their characteristics via highly-resolved numerical simulations using a spectral element Navier-Stokes solver. By comparing the simulation results of stable and unstable vortices, we investigate the joint impacts of instabilities on 3D transport through three major aspects: (i) energy transfer, (ii) overturning transport of the secondary circulation, and (iii) rates of vertical exchange and mixing. It is found that instabilities can enhance local nonlinear interactions and cause the kinetic energy wavenumber spectrum to have slopes between the conventional -5/3 and -3 at inertial ranges. The cascade of a new quantity is proposed to explain these non-conventional slopes. One of our main results is the discovery of material exchange between the central vortex and satellite vortices through 3D pathways, called funnels. These funnels modify the concept of elliptic regions that can trap material when confined to 2D dynamics. Thus, we show that a family of vortices, created by the hydrodynamic instabilities of the initially unstable vortex, can still continue to operate in unity in order to complete the 3D transport in these systems. We also show that flow instabilities can double the magnitude of vertical velocity, increase the rate of vertical exchange by an order of magnitude and enhance mixing rate more than 100%.
Dynamics of Quantized Vortices Before Reconnection
Andryushchenko, V. A.; Kondaurova, L. P.; Nemirovskii, S. K.
2016-12-01
The main goal of this paper is to investigate numerically the dynamics of quantized vortex loops, just before the reconnection at finite temperature, when mutual friction essentially changes the evolution of lines. Modeling is performed on the base of vortex filament method using the full Biot-Savart equation. It was discovered that the initial position of vortices and the temperature strongly affect the dependence on time of the minimum distance δ (t) between tips of two vortex loops. In particular, in some cases, the shrinking and collapse of vortex loops due to mutual friction occur earlier than the reconnection, thereby canceling the latter. However, this relationship takes a universal square-root form δ ( t) =√{( κ /2π ) ( t_{*}-t) } at distances smaller than the distances, satisfying the Schwarz reconnection criterion, when the nonlocal contribution to the Biot-Savart equation becomes about equal to the local contribution. In the "universal" stage, the nearest parts of vortices form a pyramid-like structure with angles which neither depend on the initial configuration nor on temperature.
Motion Equation of Vorticity for Newton Fluid
Jianhua, X
2005-01-01
The vorticity plays an important role in aerodynamics and rotational flow. Usually, they are studied with modified Navier-Stokes equation. This research will deduce the motion equation of vorticity from Navier-Stokes equation. To this propose, the velocity gradient field is decomposed as the stack of non-rotation field and pure-rotation field. By introducing the Chen S+R decomposition, the rotational flow is redefined. For elastic fluid, the research shows that for Newton fluid, the local average rotation always produces an additional pressure on the rotation plane. This item is deterministic rather than stochastic (as Reynolds stress) or adjustable. For non-elastic fluid, such as air, the research shows that the rotation will produce an additional stress along the rotation axis direction, that is on the normal direction of rotation plane. This result can be used to explain the lift force connected with vortex. The main purpose of this research is to supply a solvable mathematical model for the calculation of...
Quantum vortices and trajectories in particle diffraction
Delis, N; Contopoulos, G
2011-01-01
We investigate the phenomenon of the diffraction of charged particles by thin material targets using the method of the de Broglie-Bohm quantum trajectories. The particle wave function can be modeled as a sum of two terms $\\psi=\\psi_{ingoing}+\\psi_{outgoing}$. A thin separator exists between the domains of prevalence of the ingoing and outgoing wavefunction terms. The structure of the quantum-mechanical currents in the neighborhood of the separator implies the formation of an array of \\emph{quantum vortices}. The flow structure around each vortex displays a characteristic pattern called `nodal point - X point complex'. The X point gives rise to stable and unstable manifolds. We find the scaling laws characterizing a nodal point-X point complex by a local perturbation theory around the nodal point. We then analyze the dynamical role of vortices in the emergence of the diffraction pattern. In particular, we demonstrate the abrupt deflections, along the direction of the unstable manifold, of the quantum trajector...
Development and Breakdown of Goertler Vortices in High Speed Boundary Layers
Li, Fei; Choudhari, Meelan; Chang, Chau-Lyan; Wu, Minwei; Greene, Ptrick T.
2010-01-01
The nonlinear development of G rtler instability over a concave surface gives rise to a highly distorted stationary flow in the boundary layer that has strong velocity gradients in both spanwise and wall-normal directions. This distorted flow is susceptible to strong, high frequency secondary instability that leads to the onset of transition. For high Mach number flows, the boundary layer is also subject to the second mode instability. The nonlinear development of G rtler vortices and the ensuing growth and breakdown of secondary instability, the G rtler vortex interactions with second mode instabilities as well as oblique second mode interactions are examined in the context of both internal and external hypersonic configurations using nonlinear parabolized stability equations, 2-D eigenvalue analysis and direct numerical simulation. For G rtler vortex development inside the Purdue Mach 6 Ludwieg tube wind tunnel, multiple families of unstable secondary eigenmodes are identified and their linear and nonlinear evolution is examined. The computation of secondary instability is continued past the onset of transition to elucidate the physical mechanisms underlying the laminar breakdown process. Nonlinear breakdown scenarios associated with transition over a Mach 6 compression cone configuration are also explored.
Downstream Evolution of Longitudinal Embedded Vortices with Helical Structure
DEFF Research Database (Denmark)
Velte, Clara Marika; Okulov, Valery; Hansen, Martin Otto Laver
2009-01-01
In the present work the downstream development of device induced vortices with helical symmetry embedded in wall bounded flow on a bump is studied with the aid of Stereoscopic Particle Image Velocimetry (SPIV). The downstream evolution of characteristic parameters of helical vortices is studied...
Gyrofluid potential vorticity equation and turbulent equipartion states
DEFF Research Database (Denmark)
Madsen, Jens; Juul Rasmussen, Jens; Naulin, Volker;
2015-01-01
An equation governing potential vorticity in a magnetized plasmas is derived. The equation is analogous to Ertel's theorem. In the long wave-length limit the potential vorticity equals the ratio of the gyro-frequency plus the E × B- and diamagnetic polarization densities to the particle density...
Decay or collapse: Aircraft wake vortices in grid turbulence
Ren, M.; Elsenaar, A.; Heijst, van G.J.F.; Kuczaj, A.K.; Geurts, B.J.
2006-01-01
Trailing vortices are naturally shed by airplanes and they typically evolve into a counter-rotating vortex pair. Downstream of the aircraft, these vortices can persist for a very long time and extend for several kilometers. This poses a potential hazard to following aircraft, particularly during tak
A phase analysis of vorticity vectors associated with tropical convection
Institute of Scientific and Technical Information of China (English)
Cui Xiao-Peng
2008-01-01
Three new vorticity vectors have been proposed by Gao et al to study the two-dimensional tropical convection. In the present paper, phase relations between surface rain rate and the vorticity vectors are analysed with the calculations of lag correlation coefficients based on hourly zonally-averaged mass-integrated cloud-resolving simulation data. The cloud-resolving model is integrated with the vertical velocity, zonal wind, horizontal thermal and moisture advections, and sea surface temperature observed and derived from tropical ocean global atmosphere - coupled ocean atmosphere response experiment (TOGA-COARE) for 10 days. Maximum local increase of the vertical component of the convective vorticity vector leads maximum surface rain rate by 2 hours mainly due to the interaction between vorticity and zonal gradient of ice heating. While maximum local increase of the vertical component of the moist vorticity vector leads maximum surface rain rate by 2 hours mainly because of the interaction between zonal specific humidity gradient and zonal buoyancy gradient. And the maximum local decrease of the zonal component of the dynamic vorticity vector leads maximum surface rain rate by 2 hours mainly due to the interactions between vorticity and vertical pressure gradient as well as vorticity and buoyancy.
Vorticity amplification near the stagnation point of landing gear wheels
Feltham, G.; Ekmekci, A.
2014-04-01
The vicinity near the forward stagnation point of landing-gear wheels has been found to support a mechanism for oncoming streams of weak vorticity to collect, grow, and amplify into discrete large-scale vortical structures that then shed with a distinct periodicity. To the authors' knowledge, such a flow phenomenon has never been reported before for landing gear wheels, which are in essence finite (three-dimensional) cylinders. To gain further insight into this phenomenon, a detailed experimental study has been undertaken employing the hydrogen bubble visualization and Particle Image Velocimetry techniques. A very thin platinum wire, similar to those used in hydrogen bubble visualization applications, was placed upstream of the wheel model to produce two streams of weak vorticity (with opposite sign) that convected toward the model. As the vorticity streams enter the stagnation region of the wheels, significant flow deceleration and vorticity stretching act to collect, grow, and amplify the incoming vorticity streams into large-scale vortical structures. Experiments were performed at a fixed Reynolds number, with a value of 32 500 when defined based on the diameter of the wheel and a value of 21 based on the diameter of the vorticity-generating upstream wire. First, to establish a baseline, the natural flow field (without the presence of an upstream wire) was characterized, where experimentally determined values for the stagnation boundary-layer thickness and the velocity profile along the stagnation streamline were both found to agree with the values provided in the literature for two-dimensional cylinders. Subsequently, the dynamics of vorticity collection, growth, amplification, and shedding were studied. The size, stand-off distance and the shedding frequency of the vortical structures forming near the stagnation region were all found to strongly depend on the impingement location of the inbound vorticity on the wheel. A simple relationship between the non
Generation of speckle vortices by Archimedes' spiral micro-holes
Sun, Haibin; Liu, Tingting; Chen, Jun; Sun, Ping
2016-10-01
Speckle plays an important role in the optical field. Optical vortices which exist in random speckle fields usually contain useful phase information. The distribution of speckle field is determined by these optical vortices. In order to study speckle vortices quantitatively, we established a micro-holes array model based on the law of Archimedes' spiral arrangement. Speckle vortices can be generated by the random diffuse reflection points (spiral micro-holes). In the experiments, the gray image of Archimedes' spiral micro-holes are displayed on the screen of liquid crystal spatial light modulator (LC-SLM), and the output optical field is captured by a CCD camera. The numerical simulations and experimental results show that the model can be used to generate speckle vortices.
Generation of Optical Vortices by Linear Phase Ramps
Directory of Open Access Journals (Sweden)
Sunil Vyas
2012-01-01
Full Text Available Generation of optical vortices using linear phase ramps is experimentally demonstrated. When two regions of a wavefront have opposite phase gradients then along the line of phase discontinuity vortices can be generated. It is shown that vortices can evolve during propagation even with the unequal magnitude of tilt in the two regions of the wavefront. The number of vortices and their location depend upon the magnitude of tilt. vortex generation is experimentally realized by encoding phase mask on spatial light modulator and their presence is detected interferometrically. Numerical simulation has been performed to calculate the diffracted intensity distribution from the phase mask, and presence of vortices in the diffracted field is detected by computational techniques.
Gyrofluid potential vorticity equation and turbulent equipartion states
DEFF Research Database (Denmark)
Madsen, Jens; Juul Rasmussen, Jens; Naulin, Volker
2015-01-01
An equation governing potential vorticity in a magnetized plasmas is derived. The equation is analogous to Ertel's theorem. In the long wave-length limit the potential vorticity equals the ratio of the gyro-frequency plus the E × B- and diamagnetic polarization densities to the particle density....... The equation is relevant for transport barriers in magnetically confined plasmas because particle density, ion temperature and the radial electric field are mutually coupled through the potential vorticity. The potential vorticity equation is derived from an energy conserving, four-field, electrostatic, full......-F gyrofluid model. It is shown that the gyrofluid model possesses two exact Lagrangian invariants. In systems where mixing uniformly distribute the Lagrangian invariants we derive the corresponding turbulent equipartion states. It is shown that the system is driven towards constant potential vorticity. Given...
Nanoscale assembly of superconducting vortices with scanning tunnelling microscope tip
Ge, Jun-Yi; Gladilin, Vladimir N.; Tempere, Jacques; Xue, Cun; Devreese, Jozef T.; van de Vondel, Joris; Zhou, Youhe; Moshchalkov, Victor V.
2016-12-01
Vortices play a crucial role in determining the properties of superconductors as well as their applications. Therefore, characterization and manipulation of vortices, especially at the single-vortex level, is of great importance. Among many techniques to study single vortices, scanning tunnelling microscopy (STM) stands out as a powerful tool, due to its ability to detect the local electronic states and high spatial resolution. However, local control of superconductivity as well as the manipulation of individual vortices with the STM tip is still lacking. Here we report a new function of the STM, namely to control the local pinning in a superconductor through the heating effect. Such effect allows us to quench the superconducting state at nanoscale, and leads to the growth of vortex clusters whose size can be controlled by the bias voltage. We also demonstrate the use of an STM tip to assemble single-quantum vortices into desired nanoscale configurations.
Large-deviation statistics of vorticity stretching in isotropic turbulence.
Johnson, Perry L; Meneveau, Charles
2016-03-01
A key feature of three-dimensional fluid turbulence is the stretching and realignment of vorticity by the action of the strain rate. It is shown in this paper, using the cumulant-generating function, that the cumulative vorticity stretching along a Lagrangian path in isotropic turbulence obeys a large deviation principle. As a result, the relevant statistics can be described by the vorticity stretching Cramér function. This function is computed from a direct numerical simulation data set at a Taylor-scale Reynolds number of Re(λ)=433 and compared to those of the finite-time Lyapunov exponents (FTLE) for material deformation. As expected, the mean cumulative vorticity stretching is slightly less than that of the most-stretched material line (largest FTLE), due to the vorticity's preferential alignment with the second-largest eigenvalue of strain rate and the material line's preferential alignment with the largest eigenvalue. However, the vorticity stretching tends to be significantly larger than the second-largest FTLE, and the Cramér functions reveal that the statistics of vorticity stretching fluctuations are more similar to those of the largest FTLE. In an attempt to relate the vorticity stretching statistics to the vorticity magnitude probability density function in statistically stationary conditions, a model Kramers-Moyal equation is constructed using the statistics encoded in the Cramér function. The model predicts a stretched-exponential tail for the vorticity magnitude probability density function, with good agreement for the exponent but significant difference (35%) in the prefactor.
Vorticity is a marker of right ventricular diastolic dysfunction.
Fenster, Brett E; Browning, James; Schroeder, Joyce D; Schafer, Michal; Podgorski, Chris A; Smyser, Jamie; Silveira, Lori J; Buckner, J Kern; Hertzberg, Jean R
2015-09-15
Right ventricular diastolic dysfunction (RVDD) is an important prognostic indicator in pulmonary arterial hypertension (PAH). RV vortex rings have been observed in healthy subjects, but their significance in RVDD is unknown. Vorticity, the local spinning motion of an element of fluid, may be a sensitive measure of RV vortex dynamics. Using four-dimensional (4D) flow cardiac magnetic resonance imaging (CMR), we investigated the relationship between right heart vorticity with echocardiographic indexes of RVDD. Thirteen (13) PAH subjects and 10 controls underwent same-day 4D flow CMR and echocardiography. RV diastolic function was assessed using trans-tricuspid valve (TV) early (E) and late (A) velocities, E/A ratio, and e' and a' tissue Doppler velocities. RV and right atrial (RA) integrated mean vorticity was calculated for E and A-wave filling periods using 4D datasets. Compared with controls, A-wave vorticity was significantly increased in RVDD subjects in both the RV [2343 (1,559-3,295) vs. 492 (267-2,649) 1/s, P = 0.028] and RA [30 (27-44) vs. 9 (5-27) 1/s, P = 0.005]. RA E vorticity was significantly decreased [13 (7-22) vs. 28 (15-31) 1/s, P = 0.038] in RVDD. E-wave vorticity correlated TV e', E-,and TV E/A (P < 0.05), and A-wave vorticity associated with both TV A and E/A (P < 0.02). RVDD is associated with alterations in E- and A-wave vorticity, and vorticity correlates with multiple echocardiographic markers of RVDD. Vorticity may be a robust noninvasive research tool for the investigation of RV fluid and tissue mechanical interactions in PAH. Copyright © 2015 the American Physiological Society.
Dipole vortices in the Great Australian Bight
DEFF Research Database (Denmark)
Cresswell, George R.; Lund-Hansen, Lars C.; Nielsen, Morten Holtegaard
2015-01-01
Shipboard measurements from late 2006 made by the Danish Galathea 3 Expedition and satellite sea surface temperature images revealed a chain of cool and warm mushroom' dipole vortices that mixed warm, salty, oxygen-poor waters on and near the continental shelf of the Great Australian Bight (GAB......) with cooler, fresher, oxygen-rich waters offshore. The alternating jets' flowing into the mushrooms were directed mainly northwards and southwards and differed in temperature by only 1.5 degrees C; however, the salinity difference was as much as 0.5, and therefore quite large. The GAB waters were slightly...... denser than the cooler offshore waters. The field of dipoles evolved and distorted, but appeared to drift westwards at 5km day-1 over two weeks, and one new mushroom carried GAB water southwards at 7km day(-1). Other features encountered between Cape Leeuwin and Tasmania included the Leeuwin Current...
Gradient evolution for potential vorticity flows
Directory of Open Access Journals (Sweden)
S. Balasuriya
2001-01-01
Full Text Available Two-dimensional unsteady incompressible flows in which the potential vorticity (PV plays a key role are examined in this study, through the development of the evolution equation for the PV gradient. For the case where the PV is conserved, precise statements concerning topology-conservation are presented. While establishing some intuitively well-known results (the numbers of eddies and saddles is conserved, other less obvious consequences (PV patches cannot be generated, some types of Lagrangian and Eulerian entities are equivalent are obtained. This approach enables an improvement on an integrability result for PV conserving flows (if there were no PV patches at time zero, the flow would be integrable. The evolution of the PV gradient is also determined for the nonconservative case, and a plausible experiment for estimating eddy diffusivity is suggested. The theory is applied to an analytical diffusive Rossby wave example.
Abrikosov Gluon Vortices in Color Superconductors
Ferrer, Efrain J
2010-01-01
In this talk I will discuss how the in-medium magnetic field can influence the gluon dynamics in a three-flavor color superconductor. It will be shown how at field strengths comparable to the charged gluon Meissner mass a new phase can be realized, giving rise to Abrikosov's vortices of charged gluons. In that phase, the inhomogeneous gluon condensate anti-screens the magnetic field due to the anomalous magnetic moment of these spin-1 particles. This paramagnetic effect can be of interest for astrophysics, since due to the gluon vortex antiscreening mechanism, compact stars with color superconducting cores could have larger magnetic fields than neutron stars made up entirely of nuclear matter. I will also discuss a second gluon condensation phenomenon connected to the Meissner instability attained at moderate densities by two-flavor color superconductors. In this situation, an inhomogeneous condensate of charged gluons emerges to remove the chromomagnetic instability created by the pairing mismatch, and as a ...
Analytical BPS Maxwell-Higgs vortices
Casana, R; da Hora, E; Santos, C dos
2014-01-01
We have established a prescription for the calculation of analytical vortex solutions in the context of generalized Maxwell-Higgs models whose overall dynamics is controlled by two positive functions of the scalar field. We have also determined a natural constraint between these functions and the Higgs potential allowing the existence of axially symmetric Bogomol'nyi-Prasad-Sommerfield (BPS) solutions possessing finite energy. Furthermore, when the generalizing functions are chosen suitably, the nonstandard BPS equations can be solved exactly. We have studied some examples, comparing them with the usual Abrikosov-Nielsen-Olesen (ANO) solution. The overall conclusion is that the analytical self-dual vortices are well-behaved in all relevant sectors, strongly supporting the generalized models they belong themselves. In particular, our results mimic well-known properties of the usual (numerical) configurations, as localized energy density, while contributing to the understanding of topological solitons and their...
Instantons and vortices on noncommutative toric varieties
Cirio, Lucio S.; Landi, Giovanni; Szabo, Richard J.
2014-09-01
We elaborate on the quantization of toric varieties by combining techniques from toric geometry, isospectral deformations and noncommutative geometry in braided monoidal categories, and the construction of instantons thereon by combining methods from noncommutative algebraic geometry and a quantized twistor theory. We classify the real structures on a toric noncommutative deformation of the Klein quadric and use this to derive a new noncommutative four-sphere which is the unique deformation compatible with the noncommutative twistor correspondence. We extend the computation of equivariant instanton partition functions to noncommutative gauge theories with both adjoint and fundamental matter fields, finding agreement with the classical results in all instances. We construct moduli spaces of noncommutative vortices from the moduli of invariant instantons, and derive corresponding equivariant partition functions which also agree with those of the classical limit.
Vorticity Fluctuations in Plane Couette Flow
Ortiz de Zarate, Jose; Sengers, Jan V.
2010-11-01
In this presentation we evaluate the flow-induced amplification of the thermal noise in plane Couette configuration. The physical origin of the noise is the random nature of molecular collisions, that contribute with a stochastic component to the stress tensor (Landau's fluctuating hydrodynamics). This intrinsic stochastic forcing is then amplified by the mode- coupling mechanisms associated to shear flow. In a linear approximation, noise amplification can be studied by solving stochastic Orr-Sommerfeld and Squire equations. We compare the efficiency of the different mechanisms, being the most important the direct coupling between Squire and Orr-Sommerfed equations. The main effect is to amplify wall-normal vorticity fluctuations with an spanwise modulation at wave number around 1.5, a configuration that resembles the streaks that have been proposed as precursors of the flow instability.
Dynamic Assembly of Magnetic Colloidal Vortices
Energy Technology Data Exchange (ETDEWEB)
Mohorič, Tomaž; Kokot, Gašper; Osterman, Natan; Snezhko, Alexey; Vilfan, Andrej; Babič, Dušan; Dobnikar, Jure
2016-04-29
Magnetic colloids in external time-dependent fields are subject to complex induced many-body interactions governing their self-assembly into a variety of equilibrium and out-of-equilibrium structures such as chains, networks, suspended membranes, and colloidal foams. Here, we report experiments, simulations, and theory probing the dynamic assembly of superparamagnetic colloids in precessing external magnetic fields. Within a range of field frequencies, we observe dynamic large-scale structures such as ordered phases composed of precessing chains, ribbons, and rotating fluidic vortices. We show that the structure formation is inherently coupled to the buildup of torque, which originates from internal relaxation of induced dipoles and from transient correlations among the particles as a result of short-lived chain formation. We discuss in detail the physical properties of the vortex phase and demonstrate its potential in particle-coating applications.
Non-Abelian Chern-Simons Vortices
Lozano, G S; Moreno, E F; Schaposnik, F A
2007-01-01
We consider the bosonic sector of a ${\\cal N} = 2$ supersymmetric Chern-Simons-Higgs theory in 2 + 1 dimensions. The gauge group is $U(1)\\times SU(N)$ and has $N_f$ flavors of fundamental matter fields. The model supports non-Abelian (axially symmetric) vortices when $N_f \\geq N$, which have internal (orientational) moduli. When $N_f > N$, the solutions acquire additional collective coordinates parameterizing their transverse size. We solve the BPS equations numerically and obtain local ($N_f = N$) and semi-local ($N_f > N$) string solutions. A $CP^{N-1}$ low-energy effective action for the orientational moduli is obtained in both cases. In the semilocal case there is an additional term in the effective action induced by the transverse size moduli. We find such term in the limit of large transverse size, where exact solutions can be obtained analytically.
Vortices in superconducting bulk, films and SQUIDs
Indian Academy of Sciences (India)
Ernst Helmut Brandt
2006-01-01
The properties of the ideal periodic vortex lattice in bulk superconductors and in films of any thickness can be calculated from Ginzburg-Landau theory by an iteration method using Fourier series. The London theory yields general analytic expressions for the magnetic field and energy of arbitrary arrangements of straight or curved vortex lines. The elasticity of the vortex lattice is highly nonlocal. The magnetic response of superconductors of realistic shapes like thin and thick strips and disks or thin rectangular plates or films, containing pinned vortices, can be computed within continuum theory by solving an integral equation. A useful example is a thin square with a central hole and a radial slit, used as superconducting quantum interference device (SQUID).
Vortices and hysteresis in a rotating Bose-Einstein condensate with anharmonic confinement
DEFF Research Database (Denmark)
Jackson, A.D.; Kavoulakis, G.M.
2004-01-01
Vortices; Bose-Einstein condensation; phase diagrams; phase transformation Udgivelsesdato: 4 August......Vortices; Bose-Einstein condensation; phase diagrams; phase transformation Udgivelsesdato: 4 August...
Dynamics of Giant Planet Polar Vortices
Brueshaber, Shawn R.; Sayanagi, Kunio M.
2016-10-01
The polar atmospheres of the giant planets have come under increasing interest since a compact, warm-core, stable, cyclonic polar vortex was discovered at each of Saturn's poles. In addition, the south pole of Neptune appears to have a similar feature, and Uranus' north pole is exhibiting activity that could indicate the formation of a polar vortex. We investigate the formation and maintenance of these giant planet polar vortices by varying several key atmospheric dynamics parameters in a forced-dissipative, 1.5-layer shallow water model. Our simulations are run using the EPIC (Explicit Planetary Isentropic Coordinate) global circulation model, to which we have added a gamma-plane rectangular grid option appropriate for simulating polar atmospheric dynamics.In our numerical simulations, we vary the atmospheric deformation radius, planetary rotation rate, storm forcing intensity, and storm vorticity (cyclone-to-anticyclone) ratio to determine what combination of values favors the formation of a polar vortex. We find that forcing the atmosphere by injecting small-scale mass perturbations ("storms") to form either all cyclones, all anticyclones, or equal numbers of both, may all result in a cyclonic polar vortex. Additionally, we examine the role of eddy momentum convergence in the intensification and maintenance of a polar cyclone.Our simulation results are applicable to understanding all four of the solar system giant planets. In the future, we plan to expand our modeling effort with a more realistic 3D primitive equations model, also with a gamma-plane rectangular grid using EPIC. With our 3D primitive equations model, we will study how various vertical atmospheric stratification structures influence the formation and maintenance of a polar cyclone. While our shallow-water model only involves storms of a single layer, a 3D primitive equations model allows us to study how storms of finite vertical extent and at differing levels in the atmosphere may further favor
Coherence vortices of partially coherent beams in the far field
Institute of Scientific and Technical Information of China (English)
Liu Pu-Sheng; Lü Bai-da
2007-01-01
Based on the propagation law of cross-spectral density function, studied in this paper are the coherence vortices of partially coherent, quasi-monochromatic singular beams with Gaussian envelope and Schell-model correlator in the far field, where our main attention is paid to the evolution of far-field coherence vortices into intensity vortices of fully coherent beams. The results show that, although there are usually no zeros of intensity in partially coherent beams with Gaussian envelope and Schell-model correlator, zeros of spectral degree of coherence exist. The coherence vortices of spectral degree of coherence depend on the relative coherence length, mode index and positions of pairs of points.If a point and mode index are kept fixed, the position of coherence vortices changes with the increase of the relative coherence length. For the low coherent case there is a circular phase dislocation. In the coherent limit coherence vortices become intensity vortices of fully coherent Laguerre-Gaussian beams.
Nonlinear spacial instability of a fluid sheet
Rangel, R. H.; Hess, C. F.
1990-01-01
The mechanism of nonlinear distortion of a fluid sheet leading to atomization is investigated numerically with the use of vortex dynamics and experimentally by means of holography. The configuration investigated consists of a planar fluid sheet emerging from a rectangular slit with and without coflowing air. The numerical model is two-dimensional, inviscid, and includes surface tension effects. The experimental results indicate the existence of well-defined three-dimensional structures. These are formed mainly by the nonlinear interaction of transverse and streamwise disturbances. The transverse disturbances are associated with the Kelvin-Helmholtz instability while the streamwise disturbances appear related to streamwise vortices possibly originating inside the nozzle.
On the link between martian total ozone and potential vorticity
Holmes, James A.; Lewis, Stephen R.; Patel, Manish R.
2017-01-01
We demonstrate for the first time that total ozone in the martian atmosphere is highly correlated with the dynamical tracer, potential vorticity, under certain conditions. The degree of correlation is investigated using a Mars global circulation model including a photochemical model. Potential vorticity is the quantity of choice to explore the dynamical nature of polar vortices because it contains information on winds and temperature in a single scalar variable. The correlation is found to display a distinct seasonal variation, with a strong positive correlation in both northern and southern winter at poleward latitudes in the northern and southern hemisphere respectively. The identified strong correlation implies variations in polar total ozone during winter are predominantly controlled by dynamical processes in these spatio-temporal regions. The weak correlation in northern and southern summer is due to the dominance of photochemical reactions resulting from extended exposure to sunlight. The total ozone/potential vorticity correlation is slightly weaker in southern winter due to topographical variations and the preference for ozone to accumulate in Hellas basin. In northern winter, total ozone can be used to track the polar vortex edge. The ozone/potential vorticity ratio is calculated for both northern and southern winter on Mars for the first time. Using the strong correlation in total ozone and potential vorticity in northern winter inside the polar vortex, it is shown that potential vorticity can be used as a proxy to deduce the distribution of total ozone where satellites cannot observe for the majority of northern winter. Where total ozone observations are available on the fringes of northern winter at poleward latitudes, the strong relationship of total ozone and potential vorticity implies that total ozone anomalies in the surf zone of the northern polar vortex can potentially be used to determine the origin of potential vorticity filaments.
Heat transfer enhancement using tip and junction vortices
Gentry, Mark Cecil
1998-10-01
Single-phase convective heat transfer can be enhanced by modifying the heat transfer surface to passively generate streamwise vortices. The swirling flow of the vortices modifies the temperature field, thinning the thermal boundary layer and increasing surface convection. Tip vortices generated by delta wings and junction vortices generated by hemispherical protuberances were studied in laminar flat-plate and developing channel flows. Local and average convective measurements were obtained, and the structure of the vortices was studied using quantitative flow visualization and vortex strength measurements. The pressure drop penalty associated with the heat transfer enhancement was also investigated. Tip vortices generated by delta wings enhanced local convection by as much as 300% over a flat-plate boundary layer flow. Vortex strength increased with Reynolds number based on chord length, wing aspect ratio, and wing angle of attack. As the vortices were advected downstream, they decayed because of viscous interactions. In the developing channel flow, tip vortices produced a significant local heat transfer enhancement on both sides of the channel. The largest spatially averaged heat transfer enhancement was 55%; it was accompanied by a 100% increase in the pressure drop relative to the same channel flow with no delta-wing vortex generator. Junction vortices created by hemispherical surface protuberances provided local heat transfer enhancements as large as 250%. Vortex strength increased with an increasing ratio of hemisphere radius to local boundary layer thickness on a flat plate. In the developing channel flows, heat transfer enhancements were observed on both sides of the channel. The largest spatially averaged heat transfer enhancement was 50%; it was accompanied by a 90% pressure drop penalty relative to the same channel flow with no hemispherical vortex generator. This research is important in compact heat exchanger design. Enhancing heat transfer can lead to
Study of Initial Vorticity Forcing for Block Onset by a 4-Dimensional Variational Approach
Institute of Scientific and Technical Information of China (English)
QIAO Fangli; ZHANG Shaoqing; YIN Xunqiang
2005-01-01
With the aid of a global barotropic model, the role of the interaction of the synoptic-scale disturbance and the planetary flow in block onset is examined by a 4-dimensional variational approach. A cost function is defined to measure the squared errors of the forecasted stream functions during block onset period (day 4 and day 5 in this study) over a selected blocking domain. The sensitivity of block onset with respect to the initial synoptic-scale disturbance is studied by examining the gradient of the defined cost function with respect to the initial (during the first 24 hours) vorticity forcing, which is evaluated by the adjoint integration. Furthermore, the calculated cost function and gradient are connected with the limited-memory quasi-Newton optimization algorithm for solving the optimal initial vorticity forcing for block onset. For two studied cases of block onset (northern Atlantic and northern Pacific) introducing the optimal initial vorticity forcing, the nonlinear barotropic advection process mostly reconstructs these blocking onset processes. The results show that the formation of blocking can be correctly described by a barotropic nonlinear advection process, in which the wave- (synoptic-scale) flow (planetary-scale)interaction plays a very important role. On an appropriate planetary-scale flow, a certain synoptic-scale disturbance can cause the blocking onset by the interaction between the synoptic scale perturbations and the planetary scale basic flows. The extended forecasts show that the introduction of the optimal initial vorticity forcing can predict the blocking process up to the 7th or 8th day in this simple model case. The experimental results in this study show that the 4-dimensional variational approach has a good potential to be applied to study the dynamics of the medium-range weather processes. This simple model case study is only an initial trial. Applying the framework in this study to a complex model will further our understanding of
A continuous-vorticity panel method for lifting surfaces
Yen, A.; Mook, D. T.; Nayfeh, A. H.
1981-01-01
A continuous-vorticity panel method is developed and utilized to predict the steady aerodynamic loads on lifting surfaces having sharp-edge separation. Triangular panels with linearly varying vorticity are used. The velocity field generated by an individual element is obtained in closed form. An optimization scheme is constructed for finding the vorticity at the nodes of the elements. The method is not restricted by aspect ratios, angles of attack, planforms, or camber. Rectangular and delta wings are presented as numerical examples. The numerical results are in good agreement with the experimental data for incompressible flows.
Interaction of Vortices with a progressive Surface Wave
Institute of Scientific and Technical Information of China (English)
LinlinWANG; HuiyangMA
1996-01-01
Interaction of submerged vortices with a progressive surface wave is investigated by the finite-difference numerical solution of Navier-Stokes equations.The progressive wave is the surface gravity water wave in a finite depth.The initial vortex model is Oseen vortex.The numerical computations show that a special pattern of the wave surface may be observed by the interaction from the submerged vortices.The influences of Froude number,the initial geometric configuration of vortices,and the amplitude,inital phase of surface wave on the wave pattern are discussed.
Kinetic study of ion-acoustic plasma vortices
Energy Technology Data Exchange (ETDEWEB)
Khan, S. A. [National Centre for Physics (NCP), Quaid-i-Azam University Campus, Islamabad 45320 (Pakistan); Aman-ur-Rehman, E-mail: amansadiq@gmail.com [Pakistan Institute of Engineering and Applied Sciences (PIEAS), P.O. Nilore, Islamabad 45650 (Pakistan); Mendonca, J. T. [IPFN, Instituto Superior Téchnico, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal)
2014-09-15
The kinetic theory of electron plasma waves with finite orbital angular momentum has recently been introduced by Mendonca. This model shows possibility of new kind of plasma waves and instabilities. We have extended the theory to ion-acoustic plasma vortices carrying orbital angular momentum. The dispersion equation is derived under paraxial approximation which exhibits a kind of linear vortices and their Landau damping. The numerical solutions are obtained and compared with analytical results which are in good agreement. The physical interpretation of the ion-acoustic plasma vortices and their Landau resonance conditions are given for typical case of Maxwellian plasmas.
Image simulations of kinked vortices for transmission electron microscopy
DEFF Research Database (Denmark)
Beleggia, Marco; Pozzi, G.; Tonomura, A.
2010-01-01
We present an improved model of kinked vortices in high-Tc superconductors suitable for the interpretation of Fresnel or holographic observations carried out with a transmission electron microscope. A kinked vortex is composed of two displaced half-vortices, perpendicular to the film plane...... observations of high-Tc superconducting films, where the Fresnel contrast associated with some vortices showed a dumbbell like appearance. Here, we show that under suitable conditions the JV segment may reveal itself in Fresnel imaging or holographic phase mapping in a transmission electron microscope....
Computer simulation studies of pulsed Doppler signals from vortices
Institute of Scientific and Technical Information of China (English)
CHEN Sizhong; WANG Yuanyuan; WANG Weiqi
2001-01-01
A computer simulation method for pulsed Doppler signals from vortices was proposed to generate simulated vortex Doppler signals under various given circumstances. The relative waveforms, such as the maximum frequency waveform, the mean frequency waveform and the bandwidth waveform, were obtained using the short time Fourier analysis of those simulated signals. The relations were studied between several spectrum parameters obtained from these waveforms and given simulation conditions, such as the position and the size of the sample volume, the distance between two vortices, the free stream velocity and the maximum tangent velocity of the vortex. The sensitive parameters were found to detect vortices using the pulsed Doppler techniques.
Quantised vortices and mutual friction in relativistic superfluids
Andersson, N; Vickers, J A
2016-01-01
We consider the detailed dynamics of an array of quantised superfluid vortices in the framework of general relativity, as required for quantitative modelling of realistic neutron star cores. Our model builds on the variational approach to relativistic (multi-) fluid dynamics, where the vorticity plays a central role. The description provides a natural extension of, and as it happens a better insight into, existing Newtonian models. In particular, we account for the mutual friction associated with scattering of a second "normal" component in the mixture off of the superfluid vortices.
Energy Technology Data Exchange (ETDEWEB)
Haque, Q. [Theoretical Physics Division, PINSTECH, P.O. Nilore, Islamabad (Pakistan); Zakir, U. [Department of Physics, University of Peshawar, Khyber Pakhtun Khwa 25000 (Pakistan); Department of Physics, University of Malakand, Khyber Pakhtun Khwa 18800 (Pakistan); Qamar, A. [Department of Physics, University of Peshawar, Khyber Pakhtun Khwa 25000 (Pakistan)
2015-12-15
Linear and nonlinear dynamics of electron temperature gradient mode along with parallel electron dynamics is investigated by considering hydrodynamic electrons and non-Maxwellian ions. It is noticed that the growth rate of η{sub e}-mode driven linear instability decreases by increasing the value of spectral index and increases by reducing the ion/electron temperature ratio along the magnetic field lines. The eigen mode dispersion relation is also found in the ballooning mode limit. Stationary solutions in the form of dipolar vortices are obtained for both circular and elliptic boundary conditions. It is shown that the dynamics of both circular and elliptic vortices changes with the inclusion of inhomogeneity and non-Maxwellian effects.
Hasheminejad, S.M.
2017-04-03
Development of streamwise counter-rotating vortices induced by leading edge patterns with different pattern shape is investigated using hot-wire anemometry in the boundary layer of a flat plate. A triangular, sinusoidal and notched patterns with the same pattern wavelength λ of 15mm and the same pattern amplitude A of 7.5mm were examined for free-stream velocity of 3m/s. The results show a good agreement with earlier studies. The inflection point on the velocity profile downstream of the trough of the patterns at the beginning of the vortex formation indicates that the vortices non-linearly propagate downstream. An additional vortex structure was also observed between the troughs of the notched pattern.
Rampf, Cornelius; Villa, Eleonora; Bertacca, Daniele; Bruni, Marco
2016-10-01
We study the nonlinear gravitational dynamics of a universe filled with a pressureless fluid and a cosmological constant Λ in the context of Newtonian gravity, and in the relativistic post-Friedmann approach proposed in paper I [I. Milillo et al., Phys. Rev. D 92, 023519 (2015)]. The post-Friedmann approximation scheme is based on the 1 /c expansion of the space-time metric and the energy-momentum tensor, and includes nonlinear Newtonian cosmology. Here we establish the nonlinear post-Friedmann framework in the Lagrangian-coordinates approach for structure formation. For this we first identify a Lagrangian gauge which is suitable for incorporating nonzero vorticity. We analyze our results in two limits: at the leading order we recover the fully nonlinear Newtonian cosmological equations in the Lagrangian formulation, and we provide a space-time metric consistent from the perspective of general relativity. We then linearize our expressions and recover the relativistic results at first order in cosmological perturbation theory. Therefore, the introduced approximation scheme provides a unified treatment for the two leading-order regimes, from the small scales described by Newtonian gravity to the large linear scale, where first-order relativistic cosmological perturbation theory gives a very good description of structure formation.
Formation and stability of tri-polar vortices in stratified geostrophic flows
Energy Technology Data Exchange (ETDEWEB)
Corread, S.M.; Carton, X.J. [French Navy Oceanography Center, Brest (France)
1999-12-01
The formation, stationary and stability of tri-polar vortices are investigated in a two-layer quasi-geostrophic model. On the f-plane, these tripoles form from the barotropic and baroclinic instabilities of circular isolated vortices. Various horizontal and vertical potential vorticity distributions, both piecewise constant and continuous, are considered here for these circular vortices.
Point Vortices: Finding Periodic Orbits and their Topological Classification
Smith, Spencer A
2015-01-01
The motion of point vortices constitutes an especially simple class of solutions to Euler's equation for two dimensional, inviscid, incompressible, and irrotational fluids. In addition to their intrinsic mathematical importance, these solutions are also physically relevant. Rotating superfluid helium can support rectilinear quantized line vortices, which in certain regimes are accurately modeled by point vortices. Depending on the number of vortices, it is possible to have either regular integrable motion or chaotic motion. Thus, the point vortex model is one of the simplest and most tractable fluid models which exhibits some of the attributes of weak turbulence. The primary aim of this work is to find and classify periodic orbits, a special class of solutions to the point vortex problem. To achieve this goal, we introduce a number of algorithms: Lie transforms which ensure that the equations of motion are accurately solved; constrained optimization which reduces close return orbits to true periodic orbits; o...
On the definition of a moist-air potential vorticity
Marquet, Pascal
2014-01-01
A new potential vorticity is derived by using a specific entropy formulation expressed in terms of a moist-air entropy potential temperature. The new formulation is compared with Ertel's version and with others based on virtual and equivalent potential temperatures. The new potential vorticity is subject to conservative properties ensured by the Second Law applied to the moist-air material derivatives. It is shown that the upper tropospheric and stratospheric (dry) structures are nearly the same as those obtained with Ertel's component. Moreover, new structures are observed in the low troposphere, with negative values associated with moist frontal regions. The negative values are observed in the frontal regions where slantwise convection instabilities may take place, but they are smaller than those observed with the equivalent potential vorticity. The main purpose of the article is to diagnose the behaviour of the new potential vorticity from numerical output generated by the ARPEGE NWP model, with the help o...
Magnus and other forces on vortices in superfluids and superconductors
Energy Technology Data Exchange (ETDEWEB)
Stone, Michael [University of Illinois, IL (United States)
1998-07-01
I discuss some of the forces acting on vortices in charged superfluids, paying particular attention to the way that the Berry and Aharonov-Casher phases combine to reflect the classical magnetohydrodynamics. (Author). 28 refs.
Are Superfluid Vortices in Pulsars Violating the Weak Equivalence Principle?
de Matos, Clovis Jacinto
2010-01-01
In the present paper we argue that timing irregularities in pulsars, like glitches and timing noise, could be associated with the violation of the weak equivalence principle for vortices in the superfluid core of rotating neutron stars.
Stability of superfluid vortices in dense quark matter
Alford, Mark G; Vachaspati, Tanmay; Windisch, Andreas
2016-01-01
Superfluid vortices in the color-flavor-locked (CFL) phase of dense quark matter are known to be energetically disfavored relative to well-separated triplets of "semi-superfluid" color flux tubes. However, the short-range interaction (metastable versus unstable) has not been established. In this paper we perform numerical calculations using the effective theory of the condensate field, mapping the regions in the parameter space of coupling constants where the vortices are metastable versus unstable. For the case of zero gauge coupling we analytically identify a candidate for the unstable mode, and show that it agrees well with the results of the numerical calculations. We find that in the region of the parameter space that seems likely to correspond to real-world CFL quark matter the vortices are unstable, indicating that if such matter exists in neutron star cores it is very likely to contain semi-superfluid color flux tubes rather than superfluid vortices.
Propagation dynamics of vortices in Helico-Conical optical beams
Bareza, Nestor
2015-01-01
We present the dynamics of optical vortices (OVs) that came from the propagation of helico-conical optical beam. This dynamics is investigated numerically by tracking the OVs at several distances using rigorous scalar diffraction theory. To ensure that our numerical calculations are correct, we compare the intensity profiles and their corresponding interferograms taken at different propagation distances between simulations and experiments. We observe that the peripheral isopolar vortices transport radially inward, toward the optical axis along the transverse spatial space as the beam propagates. When the beam has a central vortex, these vortices have significant induced angular rates of motion about the optical axis. These propagation dynamics of vortices influence the internal energy flow and the wave profile reconstruction of the beam, which can be important when deciding their applications.
Vortical Structures in CT-based Breathing Lung Models
Choi, Jiwoong; Lee, Changhyun; Hoffman, Eric; Lin, Ching-Long
2016-11-01
The 1D-3D coupled computational fluid dynamics (CFD) lung model is applied to study vortical structures in the human airways during normal breathing cycles. During inhalation, small vortical structures form around the turbulent laryngeal jet and Taylor-Gőrtler-like vortices form near the curved walls in the supraglottal region and at airway bifurcations. On exhalation elongated vortical tubes are formed in the left main bronchus, whereas a relatively slower stream is observed in the right main bronchus. These structures result in helical motions in the trachea, producing long lasting high wall shear stress on the wall. The current study elucidates that the correct employment of image-based airway deformation and lung deflation information is crucial for capturing the physiologically consistent regional airflow structures. The pathophysiological implications of these structures in destruction of tracheal wall will be discussed.
Artificial ice using superconducting vortices (Conference Presentation)
Trastoy Quintela, Juan; Malnou, Maxime; Ulysse, Christian; Bernard, Rozenn; Bergeal, Nicolas; Faini, Giancarlo; Lesueur, Jerome; Briatico, Javier; Villegas, Javier E.
2016-10-01
We use magnetic flux quanta (superconducting vortices) on artificial energy landscapes (pinning arrays) to create a new type of artificial ice. This vortex ice shows unusual temperature effects that offer new possibilities in the study of ice systems. We have investigated the matching of the flux lattice to pinning arrays that present geometrical frustration. The pinning arrays are fabricated on YBCO films using masked O+ ion irradiation. The details of the magneto-resistance imply that the flux lattice organizes into a vortex ice. The absence of history-dependent effects suggests that the vortex ice is highly ordered. Due to the technique used for the artificial energy landscape fabrication, we have the ability to change the pinning array geometry using temperature as a control knob. In particular we can switch the geometrical frustration on and off, which opens the door to performing a new type of annealing absent in other artificial ice systems. * Work supported by the French ANR "MASTHER", and the Fundación Barrié (Galicia, Spain)
Analytical BPS Maxwell-Higgs Vortices
Directory of Open Access Journals (Sweden)
R. Casana
2014-01-01
Full Text Available We have established a prescription for the calculation of analytical vortex solutions in the context of generalized Maxwell-Higgs models whose overall dynamics is controlled by two positive functions of the scalar field, namely, fϕ and wϕ. We have also determined a natural constraint between these functions and the Higgs potential Uϕ, allowing the existence of axially symmetric Bogomol'nyi-Prasad-Sommerfield (BPS solutions possessing finite energy. Furthermore, when the generalizing functions are chosen suitably, the nonstandard BPS equations can be solved exactly. We have studied some examples, comparing them with the usual Abrikosov-Nielsen-Olesen (ANO solution. The overall conclusion is that the analytical self-dual vortices are well-behaved in all relevant sectors, strongly supporting the consistency of the respective generalized models. In particular, our results mimic well-known properties of the usual (numerical configurations, as localized energy density, while contributing to the understanding of topological solitons and their description by means of analytical methods.
Chirp-driven giant phase space vortices
Trivedi, Pallavi; Ganesh, Rajaraman
2016-06-01
In a collisionless, unbounded, one-dimensional plasma, modelled using periodic boundary conditions, formation of steady state phase space coherent structures or phase space vortices (PSV) is investigated. Using a high resolution one-dimensional Vlasov-Poisson solver based on piecewise-parabolic advection scheme, the formation of giant PSV is addressed numerically. For an infinitesimal external drive amplitude and wavenumber k, we demonstrate the existence of a window of chirped external drive frequency that leads to the formation of giant PSV. The linear, small amplitude, external drive, when chirped, is shown to couple effectively to the plasma and increase both streaming of "untrapped" and "trapped" particle fraction. The steady state attained after the external drive is turned off and is shown to lead to a giant PSV with multiple extrema and phase velocities, with excess density fraction, defined as the deviation from the Maxwellian background, Δ n / n 0 ≃ 20 % - 25 % . It is shown that the process depends on the chirp time duration Δt. The excess density fraction Δn/n0, which contains both trapped and untrapped particle contribution, is also seen to scale with Δt, only inhibited by the gradient of the distribution in velocity space. Both single step drive and multistep chirp processes are shown to lead to steady state giant PSV, with multiple extrema due to embedded holes and clumps, long after the external drive is turned off.
Large-Eddy Simulations of Dust Devils and Convective Vortices
Spiga, Aymeric; Barth, Erika; Gu, Zhaolin; Hoffmann, Fabian; Ito, Junshi; Jemmett-Smith, Bradley; Klose, Martina; Nishizawa, Seiya; Raasch, Siegfried; Rafkin, Scot; Takemi, Tetsuya; Tyler, Daniel; Wei, Wei
2016-11-01
In this review, we address the use of numerical computations called Large-Eddy Simulations (LES) to study dust devils, and the more general class of atmospheric phenomena they belong to (convective vortices). We describe the main elements of the LES methodology. We review the properties, statistics, and variability of dust devils and convective vortices resolved by LES in both terrestrial and Martian environments. The current challenges faced by modelers using LES for dust devils are also discussed in detail.
Energy Technology Data Exchange (ETDEWEB)
Onishchenko, O. G., E-mail: onish@ifz.ru [Institute of Physics of the Earth, 10 B. Gruzinskaya, 123242 Moscow, Russian Federation and Space Research Institute, 84/32 Profsouznaya str., 117997 Moscow (Russian Federation); Pokhotelov, O. A., E-mail: pokh@ifz.ru [Institute of Physics of the Earth, 10 B. Gruzinskaya, 123242 Moscow (Russian Federation); Horton, W., E-mail: wendell.horton@gmail.com [Institute for Fusion Studies and Applied Research Laboratory, University of Texas at Austin, Austin, Texas 78713 (United States); Scullion, E., E-mail: scullie@tcd.ie [School of Physics, Trinity College Dublin, Dublin 2 (Ireland); Fedun, V., E-mail: v.fedun@sheffield.ac.uk [Department of Automatic Control and Systems Engineering, University of Sheffield, Sheffield S13JD (United Kingdom)
2015-12-15
The new type of large-scale vortex structures of dispersionless Alfvén waves in collisionless plasma is investigated. It is shown that Alfvén waves can propagate in the form of Alfvén vortices of finite characteristic radius and characterised by magnetic flux ropes carrying orbital angular momentum. The structure of the toroidal and radial velocity, fluid and magnetic field vorticity, the longitudinal electric current in the plane orthogonal to the external magnetic field are discussed.
On the temperature dependence of the chiral vortical effects
Kalaydzhyan, Tigran
2014-01-01
We discuss the origins of temperature dependence of the axial vortical effect (AVE), i.e. generation of an axial current in a rotating chiral medium along the rotation axis. We show that the corresponding transport coefficient depends on the number of light weakly interacting degrees of freedom, rather than on the gravitational anomaly. We also comment on the role of low-dimensional defects in the rotating medium, and appearance of the chiral vortical effect due to them.
Visualization and Quantification of Rotor Tip Vortices in Helicopter Flows
Kao, David L.; Ahmad, Jasim U.; Holst, Terry L.
2015-01-01
This paper presents an automated approach for effective extraction, visualization, and quantification of vortex core radii from the Navier-Stokes simulations of a UH-60A rotor in forward flight. We adopt a scaled Q-criterion to determine vortex regions and then perform vortex core profiling in these regions to calculate vortex core radii. This method provides an efficient way of visualizing and quantifying the blade tip vortices. Moreover, the vortices radii are displayed graphically in a plane.
The role of vortices in animal locomotion in fluids
Directory of Open Access Journals (Sweden)
Dvořák R.
2014-12-01
Full Text Available The aim of this paper is to show the significance of vortices in animal locomotion in fluids on two deliberately chosen examples. The first example concerns lift generation by bird and insect wings, the second example briefly mentiones swimming and walking on water. In all the examples, the vortices generated by the moving animal impart the necessary momentum to the surrounding fluid, the reaction to which is the force moving or lifting the animal.
Simulating living organisms with populations of point vortices
Energy Technology Data Exchange (ETDEWEB)
Schmieder, R.W.
1995-07-01
The author has found that time-averaged images of small populations of point vortices can exhibit motions suggestive of the behavior of individual organisms. As an example, the author shows that collections of point vortices confined in a box and subjected to heating can generate patterns that are broadly similar to interspecies defense in certain sea anemones. It is speculated that other simple dynamical systems can be found to produce similar complex organism-like behavior.
Conditions for Two-Cell Structure in Severe Vortical Storms.
1984-02-01
SEVERE VORTICAL STORMS by G. F. Carrier, F. E. Fendell , P. S. Feldman, and S. F. Fink TRW Space and Technology Group, Redondo Beach, CA 90278 Thi...Claification Conditions for Two-Call Structure in Severe Vortical Storms (U) 12. PERSONAL AUTHOR(S) Carrier. G. F. (Harvard U.): Fendell , F. E., Feldman...cell structure will occur. Very roughly, about half of all tropical storms ( Fendell 1974), and about one-quarter to one-half of meso- cyclones (Brooks
On Ginzburg-Landau Vortices of Superconducting Thin Films
Institute of Scientific and Technical Information of China (English)
Shi Jin DING; Qiang DU
2006-01-01
In this paper, we discuss the vortex structure of the superconducting thin films placed in a magnetic field. We show that the global minimizer of the functional modelling the superconducting thin films has a bounded number of vortices when the applied magnetic field hex ＜ Hc1 + K log |log ε|where Hc1 is the lower critical field of the film obtained by Ding and Du in SIAM J. Math. Anal.,2002. The locations of the vortices are also given.
Vorticity analysis in the Zagros orogen, Shiraz area, Iran
Sarkarinejad, Khalil; Heibati, Zahra
2016-10-01
Quantitative vorticity analyses in orogenic belts are essential for studying the kinematics of deformation and can be performed using a range of methods. The combination of microstructural analysis for vorticity with other methods creates a more rigorous analysis. In order to determine the degree of non-coaxiality and spatial pattern of vorticity during deformation in the Zagros Orogenic Belt, a study area containing the boundary of the Zagros Folded Belt and the Zagros Fold-and-Thrust Belt is selected. The study area is situated in the Shiraz region of E-Zagros in Iran. The kinematic vorticity analysis is carried out using 4 methods based on: (1) the degree of asymmetry of the calcite c-axis fabric, (2) the assumption that the orientation of the long axes of calcite within an oblique stylolite foliation delineates the direction of the instantaneous stretching axis, (3) the assumption that the tension gash tips determine the direction of the instantaneous stretching axis and (4) stylolite teeth determine the direction of the instantaneous stretching axis. C-axis data from calcite give a kinematic vorticity number between 0.68 and 0.83, and the orientation of the long axes of calcite grains yields a range between 0.5 and 0.84. Stylolites provide a kinematic vorticity number between 0.5 and 0.79, and tension gashes provide a kinematic vorticity number between 0.56 and 0.81. This range of vorticity numbers confirms the contributions of both simple (33-59%) and pure shear (41-67%). Twining of calcite also reveals that the last stage of deformation occurred at a temperature of 170-200 °C. Spatial analysis reveals an increase in the simple shear component from the SW of the Zagros Folded Belt to the NE of the Zagros Fold-and-Thrust Belt.
Comparison between ionospheric convection vortices and the associated equivalent currents
Liang, J.; Benkevitch, L.; Sofko, G. J.; Koustov, A. V.
2004-12-01
The equivalent current pattern derived from CANOPUS, NRCAN/GSC and MACCS magnetometers has been compared with the ionospheric convection pattern observed by SuperDARN HF radars. The discrepancies between the equivalent convection (EQC) and the SuperDARN-observed convection (SDC) patterns are explained in terms of the effect of day-night photoionization conductance gradient and the coupling between field-aligned currents (FACs) and ionospheric conductances. In particular, the agreement between the EQC and SDC patterns is usually worse for a counterclockwise convection vortex than for a clockwise cell, but a consistent pattern of discrepancy for counterclockwise convection vortices has been found. We suggest that the discrepancies are due to a downward FAC-conductance coupling process. Since the counterclockwise vortices and clockwise vortices occur predominantly in the dawn and dusk sectors, respectively, in accordance with the usual 2-cell global convection pattern, the asymmetry between the EQC and SDC patterns for counterclockwise vortices and clockwise vortices would naturally lead to a dawn-dusk asymmetry as well. This is revealed by a global statistical study of the deviation of direction between the magnetic equivalent convection and the SuperDARN convection in different time sectors and latitudes. In the dawn sector, the statistical results reveal that, at lower latitudes, the EQC direction deviation is slightly counterclockwise with respect to the SDC direction, whereas the deviation is significantly clockwise at high latitudes. These deviations are consistent with the discrepancy pattern for counterclockwise convection vortices, as found in the individual vortex event studies.
Bloembergen, Nicolaas
1996-01-01
Nicolaas Bloembergen, recipient of the Nobel Prize for Physics (1981), wrote Nonlinear Optics in 1964, when the field of nonlinear optics was only three years old. The available literature has since grown by at least three orders of magnitude.The vitality of Nonlinear Optics is evident from the still-growing number of scientists and engineers engaged in the study of new nonlinear phenomena and in the development of new nonlinear devices in the field of opto-electronics. This monograph should be helpful in providing a historical introduction and a general background of basic ideas both for expe
Energy Technology Data Exchange (ETDEWEB)
Geniet, F; Leon, J [Physique Mathematique et Theorique, CNRS-UMR 5825, 34095 Montpellier (France)
2003-05-07
A nonlinear system possessing a natural forbidden band gap can transmit energy of a signal with a frequency in the gap, as recently shown for a nonlinear chain of coupled pendulums (Geniet and Leon 2002 Phys. Rev. Lett. 89 134102). This process of nonlinear supratransmission, occurring at a threshold that is exactly predictable in many cases, is shown to have a simple experimental realization with a mechanical chain of pendulums coupled by a coil spring. It is then analysed in more detail. First we go to different (nonintegrable) systems which do sustain nonlinear supratransmission. Then a Josephson transmission line (a one-dimensional array of short Josephson junctions coupled through superconducting wires) is shown to also sustain nonlinear supratransmission, though being related to a different class of boundary conditions, and despite the presence of damping, finiteness, and discreteness. Finally, the mechanism at the origin of nonlinear supratransmission is found to be a nonlinear instability, and this is briefly discussed here.
Stabilization of vortex beams in Kerr media by nonlinear absorption
Porras, Miguel A.; Carvalho, Márcio; Leblond, Hervé; Malomed, Boris A.
2016-11-01
We elaborate a solution for the problem of stable propagation of transversely localized vortex beams in homogeneous optical media with self-focusing Kerr nonlinearity. Stationary nonlinear Bessel-vortex states are stabilized against azimuthal breakup and collapse by multiphoton absorption, while the respective power loss is offset by the radial influx of the power from an intrinsic reservoir. A linear stability analysis and direct numerical simulations reveal a region of stability of these vortices. Beams with multiple vorticities have their stability regions too. These beams can then form robust tubular filaments in transparent dielectrics as common as air, water, and optical glasses at sufficiently high intensities. We also show that the tubular, rotating, and specklelike filamentation regimes, previously observed in experiments with axicon-generated Bessel beams, can be explained as manifestations of the stability or instability of a specific nonlinear Bessel-vortex state, which is fully identified.
Stabilization of vortex beams in Kerr media by nonlinear absorption
Porras, Miguel A; Leblond, Hervé; Malomed, Boris A
2016-01-01
We elaborate a new solution for the problem of stable propagation of transversely localized vortex beams in homogeneous optical media with self-focusing Kerr nonlinearity. Stationary nonlinear Bessel-vortex states are stabilized against azimuthal breakup and collapse by multiphoton absorption, while the respective power loss is offset by the radial influx of the power from an intrinsic reservoir. A linear stability analysis and direct numerical simulations reveal a region of stability of these vortices. Beams with multiple vorticities have their stability regions too. These beams can then form robust tubular filaments in transparent dielectrics as common as air, water and optical glasses at sufficiently high intensities. We also show that the tubular, rotating and speckle-like filamentation regimes, previously observed in experiments with axicon-generated Bessel beams, can be explained as manifestations of the stability or instability of a specific nonlinear Bessel-vortex state, which is fully identified.
Pattern formation due to non-linear vortex diffusion
Wijngaarden, Rinke J.; Surdeanu, R.; Huijbregtse, J. M.; Rector, J. H.; Dam, B.; Einfeld, J.; Wördenweber, R.; Griessen, R.
Penetration of magnetic flux in YBa 2Cu 3O 7 superconducting thin films in an external magnetic field is visualized using a magneto-optic technique. A variety of flux patterns due to non-linear vortex diffusion is observed: (1) Roughening of the flux front with scaling exponents identical to those observed in burning paper including two distinct regimes where respectively spatial disorder and temporal disorder dominate. In the latter regime Kardar-Parisi-Zhang behavior is found. (2) Fractal penetration of flux with Hausdorff dimension depending on the critical current anisotropy. (3) Penetration as ‘flux-rivers’. (4) The occurrence of commensurate and incommensurate channels in films with anti-dots as predicted in numerical simulations by Reichhardt, Olson and Nori. It is shown that most of the observed behavior is related to the non-linear diffusion of vortices by comparison with simulations of the non-linear diffusion equation appropriate for vortices.
Mokhov, Igor I; Chefranov, A G
2016-01-01
We get point vortices dynamics equations on a rotating sphere surface directly from the hydrodynamic equations as representing their weak exact solution contrary to the conventional case of the use of a kinematic relationship between a given singular vortex field and velocity field. It is first time that the effect of a sphere rotation on the vortices interaction is accounted for in exact form. We show that only the stream function of a vortex pair of antipodal vortices (APV), and only it satisfies the original three-dimensional hydrodynamics equations on a sphere. We prove that only APV pair with two point vortices in the diameter-conjugated points of a sphere with equal by quantity but different sign circulations may be correctly considered as an elementary (stationary, not self-affecting) singular point object on a sphere. We suggest using the axis connecting the two point vortices in an APV for describing of an axis of rotation of the global vortices introduced in (Barrett, 1958) to reflect the observed g...
A potential vorticity perspective on atmospheric blocking?
Croci Maspoli, M.; Schwierz, C.
2003-04-01
A persistent large-scale anomaly of the west to east flow in the midlatitudes with a weakening and meridional splitting of the jet can be specified as atmospheric blocking. Lifetimes last from several days up to weeks so that blocking can therefore significantly determine monthly circulation index values. The vertical range affected by this phenomenon covers the entire troposphere as mirrored in increased surface pressure as well as an elevated tropopause and is also felt in the lower-stratosphere. Here we seek to shed more light on the physical mechanisms related to blocking by adopting the PV (potential vorticity) perspective with a focus on tropopause-level dynamics. Processes such as Rossby-wave breaking and diabatic heating can modify the conservative behaviour of the PV and are therefore important features for the formation and maintenance of atmospheric blocking. This motivates the definition of a novel blocking index based upon the three-dimensional structure of the phenomenon. A vertically integrated measure (PV within the 500 - 150 hPa layer, VIPV) is calculated, underlining the quasi-barotropic nature of blocked atmospheric state. Benefits of the new index include: representation of the two-dimensional structure of the phenomenon, its lifecycle and geographical distribution. The investigation is conducted over the period 1979 to 2001 using ECMWF reanalysis data. Characteristics of the VIPV field are presented. The new VIPV index is compared to a standard blocking index (e.g. Tibaldi and Molteni (1989)) on a case study basis and also with respect to seasonal variability. Relations to climate modes/indices (NAO, AO) are also discussed.
Quantum information processing with optical vortices
Energy Technology Data Exchange (ETDEWEB)
Khoury, Antonio Z. [Universidade Federal Fluminense (UFF), Niteroi, RJ (Brazil)
2012-07-01
Full text: In this work we discuss several proposals for quantum information processing using the transverse structure of paraxial beams. Different techniques for production and manipulation of optical vortices have been employed and combined with polarization transformations in order to investigate fundamental properties of quantum entanglement as well as to propose new tools for quantum information processing. As an example, we have recently proposed and demonstrated a controlled NOT (CNOT) gate based on a Michelson interferometer in which the photon polarization is the control bit and the first order transverse mode is the target. The device is based on a single lens design for an astigmatic mode converter that transforms the transverse mode of paraxial optical beams. In analogy with Bell's inequality for two-qubit quantum states, we propose an inequality criterion for the non-separability of the spin-orbit degrees of freedom of a laser beam. A definition of separable and non-separable spin-orbit modes is used in consonance with the one presented in Phys. Rev. Lett. 99, 2007. As the usual Bell's inequality can be violated for entangled two-qubit quantum states, we show both theoretically and experimentally that the proposed spin-orbit inequality criterion can be violated for non-separable modes. The inequality is discussed both in the classical and quantum domains. We propose a polarization to orbital angular momentum teleportation scheme using entangled photon pairs generated by spontaneous parametric down conversion. By making a joint detection of the polarization and angular momentum parity of a single photon, we are able to detect all the Bell-states and perform, in principle, perfect teleportation from a discrete to a continuous system using minimal resources. The proposed protocol implementation demands experimental resources that are currently available in quantum optics laboratories. (author)
Complex Convective Thermal Fluxes and Vorticity Structure
Redondo, Jose M.; Tellez, Jackson; Sotillos, Laura; Lopez Gonzalez-Nieto, Pilar; Sanchez, Jesus M.; Furmanek, Petr; Diez, Margarita
2015-04-01
Local Diffusion and the topological structure of vorticity and velocity fields is measured in the transition from a homogeneous linearly stratified fluid to a cellular or layered structure by means of convective cooling and/or heating[1,2]. Patterns arise by setting up a convective flow generated by an array of Thermoelectric devices (Peltier/Seebeck cells) these are controlled by thermal PID generating a buoyant heat flux [2]. The experiments described here investigate high Prandtl number mixing using brine and fresh water in order to form density interfaces and low Prandtl number mixing with temperature gradients. The set of dimensionless parameters define conditions of numeric and small scale laboratory modeling of environmental flows. Fields of velocity, density and their gradients were computed and visualized [3,4]. When convective heating and cooling takes place the combination of internal waves and buoyant turbulence is much more complicated if the Rayleigh and Reynolds numbers are high in order to study entrainment and mixing. Using ESS and selfsimilarity structures in the velocity and vorticity fieds and intermittency [3,5] that forms in the non-homogeneous flow is related to mixing and stiring. The evolution of the mixing fronts are compared and the topological characteristics of the merging of plumes and jets in different configurations presenting detailed comparison of the evolution of RM and RT, Jets and Plumes in overall mixing. The relation between structure functions, fractal analysis and spectral analysis can be very useful to determine the evolution of scales. Experimental and numerical results on the advance of a mixing or nonmixing front occurring at a density interface due to body forces [6]and gravitational acceleration are analyzed considering the fractal and spectral structure of the fronts like in removable plate experiments for Rayleigh-Taylor flows. The evolution of the turbulent mixing layer and its complex configuration is studied
Storage and retrieval of (3+1)-dimensional weak-light bullets and vortices in a coherent atomic gas
Chen, Zhiming; Li, Hui-jun; Hang, Chao; Huang, Guoxiang
2016-01-01
A robust light storage and retrieval (LSR) in high dimensions is highly desirable for light and quantum information processing. However, most schemes on LSR realized up to now encounter problems due to not only dissipation, but also dispersion and diffraction, which make LSR with a very low fidelity. Here we propose a scheme to achieve a robust storage and retrieval of weak nonlinear high-dimensional light pulses in a coherent atomic gas via electromagnetically induced transparency. We show that it is available to produce stable (3+1)-dimensional light bullets and vortices, which have very attractive physical property and are suitable to obtain a robust LSR in high dimensions.
Characteristics and controllability of vortices in ferromagnetics, ferroelectrics, and multiferroics
Zheng, Yue; Chen, W. J.
2017-08-01
Topological defects in condensed matter are attracting e significant attention due to their important role in phase transition and their fascinating characteristics. Among the various types of matter, ferroics which possess a switchable physical characteristic and form domain structure are ideal systems to form topological defects. In particular, a special class of topological defects—vortices—have been found to commonly exist in ferroics. They often manifest themselves as singular regions where domains merge in large systems, or stabilize as novel order states instead of forming domain structures in small enough systems. Understanding the characteristics and controllability of vortices in ferroics can provide us with deeper insight into the phase transition of condensed matter and also exciting opportunities in designing novel functional devices such as nano-memories, sensors, and transducers based on topological defects. In this review, we summarize the recent experimental and theoretical progress in ferroic vortices, with emphasis on those spin/dipole vortices formed in nanoscale ferromagnetics and ferroelectrics, and those structural domain vortices formed in multiferroic hexagonal manganites. We begin with an overview of this field. The fundamental concepts of ferroic vortices, followed by the theoretical simulation and experimental methods to explore ferroic vortices, are then introduced. The various characteristics of vortices (e.g. formation mechanisms, static/dynamic features, and electronic properties) and their controllability (e.g. by size, geometry, external thermal, electrical, magnetic, or mechanical fields) in ferromagnetics, ferroelectrics, and multiferroics are discussed in detail in individual sections. Finally, we conclude this review with an outlook on this rapidly developing field.
Slowly-growing gap-opening planets trigger weaker vortices
Hammer, Michael; Kratter, Kaitlin M.; Lin, Min-Kai
2017-04-01
The presence of a giant planet in a low-viscosity disc can create a gap edge in the disc's radial density profile sharp enough to excite the Rossby wave instability. This instability may evolve into dust-trapping vortices that might explain the 'banana-shaped' features in recently observed asymmetric transition discs with inner cavities. Previous hydrodynamical simulations of planet-induced vortices have neglected the time-scale of hundreds to thousands of orbits to grow a massive planet to Jupiter size. In this work, we study the effect of a giant planet's runaway growth time-scale on the lifetime and characteristics of the resulting vortex. For two different planet masses (1 and 5 Jupiter masses) and two different disc viscosities (α = 3 × 10-4 and 3 × 10-5), we compare the vortices induced by planets with several different growth time-scales between 10 and 4000 planet orbits. In general, we find that slowly-growing planets create significantly weaker vortices with lifetimes and surface densities reduced by more than 50 per cent. For the higher disc viscosity, the longest growth time-scales in our study inhibit vortex formation altogether. Additionally, slowly-growing planets produce vortices that are up to twice as elongated, with azimuthal extents well above 180° in some cases. These unique, elongated vortices likely create a distinct signature in the dust observations that differentiates them from the more concentrated vortices that correspond to planets with faster growth time-scales. Lastly, we find that the low viscosities necessary for vortex formation likely prevent planets from growing quickly enough to trigger the instability in self-consistent models.
MHD Flow Visualization of Magnetopause and Polar Cusps Vortices
Collado-Vega, Y. M.; Kessel, R. L.; Shao, X.; Boller, R. A.
2007-01-01
Detailed analysis of Wind, Geotail, and Cluster data shows how magnetopause boundary and polar cusps vortices associated with high speed streams can be a carrier of energy flux to the Earth's magnetosphere. For our analysis time interval, March 29 . - April 5 2002, the Interplanetary Magnetic Field (IMF) is primarily northward and MHD simulations of vortices along the flanks within nine hours of the time interval suggest that a Kelvin Helmholtz (KH) instability is likely present. Vortices were classified by solar wind input provided by the Wind satellite located 70-80 RE upstream from Earth. We present statistics for a total of 304 vortices found near the ecliptic plane on the magnetopause flanks, 273 with northward IMF and 31 with southward IMF. The vortices generated under northward IMF were more driven into the dawnside than into the duskside, being substantially more ordered on the duskside. Most of the vortices were large in scale, up to 10 RE, and with a rotation axis closely aligned with the Z(sub GSE) direction. They rotated preferentially clockwise on the dawnside, and. counter-clockwise on the duskside. Those generated under southward IMF were less ordered, fewer in number, and also smaller in diameter. Significant vortex activity occurred on the nightside region of the magnetosphere for these southward cases in contrast to the northward IMF cases on which most of the activity was driven onto the magnetopause flanks. Magnetopause crossings seen by the Geotail spacecraft for the time interval were analyzed and compared with the MHD simulation to validate our results. Vortices over the polar cusps are also being analyzed and the simulation results will be compared to the multi-point measurements of the four Cluster satellites.
The vorticity and angular momentum budgets of Asian summer monsoon
Indian Academy of Sciences (India)
P L S Rao; U C Mohanty; P V S Raju; M A Arain
2004-09-01
The study delineates the vorticity and angular momentum balances of Asian summer monsoon during the evolution and established phases. It also elucidates the differences between these balances in the National Centre for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalysis and the National Centre for Medium Range Weather Forecasts (NCM- RWF) analysis fields. The NCEP/NCAR reanalysis for a 40 year period (1958-97) and the NCM- RWF analysis for a three year (1994-96) period are made use of for the purpose. The time mean summer monsoon circulation is bifurcated into stable mean and transient eddy components and the mean component is elucidated. The generation of vorticity due to stretching of isobars balances most of the vorticity transported out of the monsoon domain during the evolution period. However, during the established period, the transportation by the relative and planetary vorticity components exceeds the generation due to stretching. The effective balancing mechanism is provided by vorticity generation due to sub-grid scale processes. The flux convergence of omega and relative momenta over the monsoon domain is effectively balanced by pressure torque during the evolution and established phases. Nevertheless, the balance is stronger during the established period due to the increase in the strength of circulation. Both the NCMRWF and NCEP fields indicate the mean features related to vorticity and angular momentum budgets realistically. Apart from the oceanic bias (strong circulation over oceans rather than continents), the summer monsoon circulation indicated by the NCEP is feeble compared to NCMRWF. The significant terms in the large-scale budgets of vorticity and angular momentum enunciate this aspect.
Rampf, Cornelius; Bertacca, Daniele; Bruni, Marco
2016-01-01
We study the gravitational dynamics of a Universe filled with a pressure-less fluid and a cosmological constant $\\Lambda$ in the context of Newtonian gravity, and in the relativistic post-Friedmann approach proposed by Milillo et al.\\ in \\cite{Milillo:2015cva}. The post-Friedmann approximation scheme is based on the $1/c$ expansion of the space-time metric and the energy-momentum tensor, and includes non-linear Newtonian cosmology. %, assuming a flat $\\Lambda$CDM cosmological model. Here we establish the non-linear post-Friedmann framework in the Lagrangian-coordinates approach for structure formation. For this we first identify a Lagrangian gauge which is suitable for incorporating non-zero vorticity. We analyze our results in two limits: at the leading order we recover the fully non-linear Newtonian cosmological equations in the Lagrangian formulation, and we provide a space-time metric consistent from the perspective of general relativity. We then linearize our expressions and recover the relativistic resu...
2016-07-01
Advanced Research Projects Agency (DARPA) Dynamics-Enabled Frequency Sources (DEFYS) program is focused on the convergence of nonlinear dynamics and...Early work in this program has shown that nonlinear dynamics can provide performance advantages. However, the pathway from initial results to...dependent nonlinear stiffness observed in these devices. This work is ongoing, and will continue through the final period of this program . Reference 9
Nayfeh, Ali Hasan
1995-01-01
Nonlinear Oscillations is a self-contained and thorough treatment of the vigorous research that has occurred in nonlinear mechanics since 1970. The book begins with fundamental concepts and techniques of analysis and progresses through recent developments and provides an overview that abstracts and introduces main nonlinear phenomena. It treats systems having a single degree of freedom, introducing basic concepts and analytical methods, and extends concepts and methods to systems having degrees of freedom. Most of this material cannot be found in any other text. Nonlinear Oscillations uses sim
Yoshida, Zensho
2010-01-01
This book gives a general, basic understanding of the mathematical structure "nonlinearity" that lies in the depths of complex systems. Analyzing the heterogeneity that the prefix "non" represents with respect to notions such as the linear space, integrability and scale hierarchy, "nonlinear science" is explained as a challenge of deconstruction of the modern sciences. This book is not a technical guide to teach mathematical tools of nonlinear analysis, nor a zoology of so-called nonlinear phenomena. By critically analyzing the structure of linear theories, and cl
Nanda, Sudarsan
2013-01-01
"Nonlinear analysis" presents recent developments in calculus in Banach space, convex sets, convex functions, best approximation, fixed point theorems, nonlinear operators, variational inequality, complementary problem and semi-inner-product spaces. Nonlinear Analysis has become important and useful in the present days because many real world problems are nonlinear, nonconvex and nonsmooth in nature. Although basic concepts have been presented here but many results presented have not appeared in any book till now. The book could be used as a text for graduate students and also it will be useful for researchers working in this field.
Philip, Jimmy; Karp, Michael; Cohen, Jacob
2016-01-01
Streaks and hairpin-vortices are experimentally generated in a laminar plane Poiseuille crossflow by injecting a continuous jet through a streamwise slot normal to the crossflow, with air as the working media. Small disturbances form stable streaks, however, higher disturbances cause the formation of streaks which undergo instability leading to the generation of hairpin vortices. Particular emphasis is placed on the flow conditions close to the generation of hairpin-vortices. Measurements are carried out in the cases of natural and phase-locked disturbance employing smoke visualisation, particle image velocimetry, and hot-wire anemometry, which include, the dominant frequency, wavelength, and the disturbance shape (or eigenfunctions) associated with the coherent part of the velocity field. A linear stability analysis for both one- and two-dimensional base-flows is carried out to understand the mechanism of instability and good agreement of wavelength and eigenfunctions are obtained when compared to the experimental data, and a slight under-prediction of the growth-rates by the linear stability analysis consistent with the final nonlinear stages in transitional flows. Furthermore, an energy analysis for both the temporal and spatial stability analysis revels the dominance of the symmetric varicose mode, again, in agreement with the experiments, which is found to be governed by the balance of the wallnormal shear and dissipative effects rather than the spanwise shear. In all cases the anti-symmetric sinuous modes governed by the spanwise shear are found to be damped both in analysis and in our experiments.
Control of Trapped Vorticity in an Offset Diffuser
Burrows, Travis J.; Vukasinovic, Bojan; Glezer, Ari
2015-11-01
Vorticity concentrations trapped within in a recessed section in the moldline of an offset diffuser are manipulated using fluidic actuation to alter the flow evolution within the diffuser. Trapped vorticity is engendered by deliberate local flow separation owing to the aggressive moldline curvature. The strength and scale of the trapped vortex and its interaction with the cross flow are controlled by a spanwise array of streamwise, surface-integrated fluidic actuators that are placed just upstream of the recessed moldline. The local and global characteristics of the diffuser flow in the absence and presence of the actuation are investigated at Mach numbers up to M = 0 . 7 , using static pressure distributions, hot-wire anemometry, and particle image velocimetry. It is shown that flow distortion as measured by cross sectional variations of the total pressure distribution within the diffuser can be significantly modified by manipulation of the trapped vorticity, and is reduced (by over 50%) with increasing momentum of the actuation jets. The mitigation of flow distortion by trapped vorticity actuation is associated with manipulation of the evolution of streamwise secondary vortices within the diffuser. Supported by ONR.
Vortical structures in pool fires: Observation, speculation, and simulation
Energy Technology Data Exchange (ETDEWEB)
Tieszen, S.R.; Nicolette, V.F.; Gritzo, L.A.; Moya, J.L. [Sandia National Labs., Albuquerque, NM (United States); Holen, J.K. [SINTEF/NTH, Trondheim (Norway). Div. Thermodynamics; Murray, D. [Naval Air Warfare Center, China Lake, CA (United States)
1996-11-01
While all fires are complex and involve many phenomena, this report is limited to large, turbulent liquid-hydrocarbon pool fires. Large, liquid-hydrocarbon pool fires present a risk in petrochemical storage and processing facilities and transportation systems that contain large amounts of liquid hydrocarbons. This report describes observations, speculations, and numerical simulations of vortical structures in pool fires. Vortical structures are observed in fires with length scales ranging from those that bend millimeter-thick flame zones to those that entrain air many meters from the edge of the fire to its centerline. The authors propose that baroclinic vorticity generation is primarily responsible for production of rotational motion at small scale and that amalgamation is responsible for the production of large-scale rotational structures from the myriad of small-scale structures. Numerical simulations show that vortical structures having time-mean definitions can be resolved with a Reynolds-Average Navier-Stokes (RANS) approach. However, for vortical structures without time-mean definition, RANS is inappropriate, and another technique, such as Large Eddy Simulation (LES), should be employed. 39 refs., 52 figs., 3 tabs.
Stationary bathtub vortices and a critical regime of liquid discharge
Stepanyants, Yury A.; Yeoh, Guan H.
A modified Lundgren model is applied for the description of stationary bathtub vortices in a viscous liquid with a free surface. Laminar liquid flow through the circular bottom orifice is considered in the horizontally unbounded domain. The liquid is assumed to be undisturbed at infinity and its depth is taken to be constant. Three different drainage regimes are studied: (i) subcritical, where whirlpool dents are less than the fluid depth; (ii) critical, where the whirlpool tips touch the outlet orifice; and (iii) supercritical, where surface vortices entrain air into the intake pipe. Particular attention is paid to critical vortices; the condition for their existence is determined and analysed. The influence of surface tension on subcritical whirlpools is investigated. Comparison of results with known experimental data is discussed.
On the local stability of vortices in differentially rotating discs
Railton, A D
2014-01-01
In order to circumvent the loss of solid material through radial drift towards the central star, the trapping of dust inside persistent vortices in protoplanetary discs has often been suggested as a process that can eventually lead to planetesimal formation. Although a few special cases have been discussed, exhaustive studies of possible quasi-steady configurations available for dust-laden vortices and their stability have yet to be undertaken, thus their viability or otherwise as locations for the gravitational instability to take hold and seed planet formation is unclear. In this paper we generalise and extend the well known Kida solution to obtain a series of steady state solutions with varying vorticity and dust density distributions in their cores, in the limit of perfectly coupled dust and gas. We then present a local stability analysis of these configurations, considering perturbations localised on streamlines. Typical parametric instabilities found have growthrates of $~0.05\\Omega_P$, where $\\Omega_P$...
Transverse commensurability effect for vortices on periodic pinning arrays
Energy Technology Data Exchange (ETDEWEB)
Reichhardt, Charles [Los Alamos National Laboratory; Reichhardt, Cynthia J [Los Alamos National Laboratory
2008-01-01
Using computer simulations, we demonstrate a type of commensurability that occurs for vortices moving longitudinally through periodic pinning arrays in the presence of an additional transverse driving force. As a function of vortex density, there is a series of broad maxima in the transverse critical depinning force that do not fall at the matching fields where the number of vortices equals an integer multiple of the number of pinning sites. The commensurability effects are associated with dynamical states in which evenly spaced structures consisting of one or more moving rows of vortices form between rows of pinning sites. Remarkably, the critical transverse depinning force can be more than an order of magnitude larger than the longitudinal depinning force.
Stability of model flocks in a vortical flow
Baggaley, A. W.
2016-06-01
We investigate the stability of self-propelled particle flocks in the Taylor-Green vortex, a steady vortical flow. We consider a model in which particles align themselves to a combination of the orientation and the acceleration of particles within a critical radius. We identify two distinct regimes: If alignment with orientation is dominant, the particles tend to be expelled from regions of high vorticity. In contrast, if anticipation is dominant, the particles accumulate in areas of large vorticity. In both regimes, the relative order of the flock is reduced. However, we show that there can be a critical balance of the two effects that stabilizes the flock in the presence of external fluid forcing. This strategy could provide a mechanism for animal flocks to remain globally ordered in the presence of fluid forcing, and it may also have applications in the design of flocking autonomous drones and artificial microswimmers.
Rapid expulsion of microswimmers by a vortical flow.
Sokolov, Andrey; Aranson, Igor S
2016-03-23
Interactions of microswimmers with their fluid environment are exceptionally complex. Macroscopic shear flow alters swimming trajectories in a highly nontrivial way and results in dramatic reduction of viscosity and heterogeneous bacterial distributions. Here we report on experimental and theoretical studies of rapid expulsion of microswimmers, such as motile bacteria, by a vortical flow created by a rotating microparticle. We observe a formation of a macroscopic depletion area in a high-shear region, in the vicinity of a microparticle. The rapid migration of bacteria from the shear-rich area is caused by a vortical structure of the flow rather than intrinsic random fluctuations of bacteria orientations, in stark contrast to planar shear flow. Our mathematical model reveals that expulsion is a combined effect of motility and alignment by a vortical flow. Our findings offer a novel approach for manipulation of motile microorganisms and shed light on bacteria-flow interactions.
Rapid expulsion of microswimmers by a vortical flow
Sokolov, Andrey; Aranson, Igor S.
2016-01-01
Interactions of microswimmers with their fluid environment are exceptionally complex. Macroscopic shear flow alters swimming trajectories in a highly nontrivial way and results in dramatic reduction of viscosity and heterogeneous bacterial distributions. Here we report on experimental and theoretical studies of rapid expulsion of microswimmers, such as motile bacteria, by a vortical flow created by a rotating microparticle. We observe a formation of a macroscopic depletion area in a high-shear region, in the vicinity of a microparticle. The rapid migration of bacteria from the shear-rich area is caused by a vortical structure of the flow rather than intrinsic random fluctuations of bacteria orientations, in stark contrast to planar shear flow. Our mathematical model reveals that expulsion is a combined effect of motility and alignment by a vortical flow. Our findings offer a novel approach for manipulation of motile microorganisms and shed light on bacteria–flow interactions. PMID:27005581
Vorticity production and survival in viscous and magnetized cosmologies
Dosopoulou, F; Tsagas, C G; Brandenburg, A
2011-01-01
We study the role of viscosity and the effects of a magnetic field on a rotating, self-gravitating fluid, using Newtonian theory and adopting the ideal magnetohydrodynamic approximation. Our results confirm that viscosity can generate vorticity in inhomogeneous environments, while the magnetic tension can produce vorticity even in the absence of fluid pressure and density gradients. Linearizing our equations around an Einstein-de Sitter cosmology, we find that viscosity adds to the diluting effect of the universal expansion. Typically, however, the dissipative viscous effects are confined to relatively small scales. We also identify the characteristic length bellow which the viscous dissipation is strong and beyond which viscosity is essentially negligible. In contrast, magnetism seems to favor cosmic rotation. The magnetic presence is found to slow down the standard decay-rate of linear vortices, thus leading to universes with more residual rotation than generally anticipated.
Inelastic scattering of xenon atoms by quantized vortices in superfluids
Pshenichnyuk, I A
2016-01-01
We study inelastic interactions of particles with quantized vortices in superfluids by using a semi-classical matter wave theory that is analogous to the Landau two-fluid equations, but allows for the vortex dynamics. The research is motivated by recent experiments on xenon doped helium nanodroplets that show clustering of the impurities along the vortex cores. We numerically simulate the dynamics of trapping and interactions of xenon atoms by quantized vortices in superfluid helium and the obtained results can be extended to scattering of other impurities by quantized vortices. Different energies and impact parameters of incident particles are considered. We show that inelastic scattering is closely linked to the generation of Kelvin waves along a quantized vortex during the interaction even if there is no capture. The capture criterion of an impurity is formulated in terms of the binding energy.
Instabilities of coherent vortices in a free shear layer
Couet, B.
The LARGE-SCALE structures observed in a shear layer can be described by a family of well-defined vortices. A Lagrangian vortex method is most appropriate to study the behavior of these vortices, provided an accurate initial representation can be obtained for the simulation. Using the vortex-in-cell method, a full three-dimensional numerical simulation of the steady-state vortices discovered by Stuart is presented here. The subharmonic pairing instability is examined both in its two-dimensional (vortex pairing) and its three-dimensional form (helical pairing) and the growth rates are compared with the stability results of Pierrehumbert and Widnall. Three-dimensionality is also generated in this flow by means of the broadband translative instability identified experimentally as the streamwise streak structure. Growth rates for the translative modes are also compared with the stability analysis.
Gurka, R.; Diamessis, P.; Liberzon, A.
2009-04-01
The characterization of three-dimensional space and time-dependent coherent structures and internal waves in stratified environment is one of the most challenging tasks in geophysical fluid dynamics. Proper orthogonal decomposition (POD) is applied to 2-D slices of vorticity and horizontal divergence obtained from 3-D DNS of a stratified turbulent wake of a towed sphere at Re=5x103 and Fr=4. The numerical method employed solves the incompressible Navier-Stokes equations under the Boussinesq approximation. The temporal discretization consists of three fractional steps: an explicit advancement of the nonlinear terms, an implicit solution of the Poisson equation for the pseudo-pressure (which enforces incompressibility), and an implicit solution of the Helmholtz equation for the viscous terms (where boundary conditions are imposed). The computational domain is assumed to be periodic in the horizontal direction and non-periodic in the vertical direction. The 2-D slices are sampled along the stream-depth (Oxz), span-depth (Oyz) and stream-span planes (Oxy) for 231 times during the interval, Nt ∈ [12,35] (N is the stratification frequency). During this interval, internal wave radiation from the wake is most pronounced and the vorticity field in the wake undergoes distinct structural transitions. POD was chosen amongst the available statistical tools due to its advantage in characterization of simulated and experimentally measured velocity gradient fields. The computational procedure, applied to any random vector field, finds the most coherent feature from the given ensemble of field realizations. The decomposed empirical eigenfunctions could be referred to as "coherent structures", since they are highly correlated in an average sense with the flow field. In our analysis, we follow the computationally efficient method of 'snapshots' to find the POD eigenfunctions of the ensemble of vorticity field realizations. The results contains of the separate POD modes, along with
Vorticity and Capillaries at the Surface of a Jet
Andre, Matthieu A
2012-01-01
Shear layer instability at the free surface of a water jet is studied. The accompanying video shows experimental data recorded using measurement methods such as Planar Laser Induced Fluorescence (PLIF) and Particle Image Velocity (PIV). These results reveal the mechanisms leading to the formation of capillary waves on the surface due to the roll-up of the shear layer. These capillary waves eventually collide to each other, injecting vorticity in the bulk of the flow. Shear layer and injected vorticity interact to form a counter rotating vortex pair that moves down to the flow.
Observation of Solitonic Vortices in Bose-Einstein Condensates
Donadello, Simone; Serafini, Simone; Tylutki, Marek; Pitaevskii, Lev P.; Dalfovo, Franco; Lamporesi, Giacomo; Ferrari, Gabriele
2014-08-01
We observe solitonic vortices in an atomic Bose-Einstein condensate (BEC) after free expansion. Clear signatures of the nature of such defects are the twisted planar density depletion around the vortex line, observed in absorption images, and the double dislocation in the interference pattern obtained through homodyne techniques. Both methods allow us to determine the sign of the quantized circulation. Experimental observations agree with numerical simulations. These solitonic vortices are the decay product of phase defects of the BEC order parameter spontaneously created after a rapid quench across the BEC transition in a cigar-shaped harmonic trap and are shown to have a very long lifetime.
Nontopological self-dual Maxwell-Higgs vortices
Bazeia, D; Ferreira, M M; da Hora, E
2015-01-01
We study the existence of self-dual nontopological vortices in generalized Maxwell-Higgs models recently introduced in Ref. \\cite{gv}. Our investigation is explicitly illustrated by choosing a sixth-order self-interaction potential, which is the simplest one allowing the existence of nontopological structures. We specify some Maxwell-Higgs models yielding BPS nontopological vortices having energy proportional to the magnetic flux, $\\Phi_{B}$, and whose profiles are numerically achieved. Particularly, we investigate the way the new solutions approach the boundary values, from which we verify their nontopological behavior. Finally, we depict the profiles numerically found, highlighting the main features they present.
Toroidal vortices as a solution to the dust migration problem
Loren-Aguilar, Pablo
2015-01-01
In an earlier letter, we reported that dust settling in protoplanetary discs may lead to a dynamical dust-gas instability that produces global toroidal vortices. In this letter, we investigate the evolution of a dusty protoplanetary disc with two different dust species (1 mm and 50 cm dust grains), under the presence of the instability. We show how toroidal vortices, triggered by the interaction of mm grains with the gas, stop the radial migration of metre-sized dust, potentially offering a natural and efficient solution to the dust migration problem.
Hamiltonian dynamics of several rigid bodies interacting with point vortices
Weissmann, Steffen
2013-01-01
We introduce a Hamiltonian description for the dynamics of several rigid bodies interacting with point vortices in an inviscid, incompressible fluid. We adopt the idea of Vankerschaver et al. (2009) to derive the Hamiltonian formulation via symplectic reduction of a canonical Hamiltonian system on a principle fibre bundle. On the reduced phase space we determine the magnetic symplectic form directly, without resorting to the machinery of mechanical connections on principle fibre bundles. We derive the equations of motion for the general case, and also for the special Lie-Poisson case of a single rigid body and zero total vorticity. Finally we give a partly degenerate Lagrangian formulation for the system.
Vortices in the Two-Dimensional Simple Exclusion Process
Bodineau, T.; Derrida, B.; Lebowitz, Joel L.
2008-06-01
We show that the fluctuations of the partial current in two dimensional diffusive systems are dominated by vortices leading to a different scaling from the one predicted by the hydrodynamic large deviation theory. This is supported by exact computations of the variance of partial current fluctuations for the symmetric simple exclusion process on general graphs. On a two-dimensional torus, our exact expressions are compared to the results of numerical simulations. They confirm the logarithmic dependence on the system size of the fluctuations of the partial flux. The impact of the vortices on the validity of the fluctuation relation for partial currents is also discussed in an Appendix.
Random organization of vortices under an anisotropic condition
Ienaga, K.; Dobroka, M.; Shirahata, Y.; Kawamura, Y.; Kaneko, S.; Okuma, S.
2017-07-01
Many colliding particles that are periodically sheared by ac drive self-organize to avoid future collisions, which is known as random organization. Recently, we have observed the random organization in the vortex system of a strip-shaped amorphous Mo x Ge1-x film, where the vortices experience periodic local shear from ac drive and the random pinning potential. In this work, we study how random organization changes in the vortex system under the tilted field, where an anisotropic vortex-vortex interaction is introduced. We find that characteristic times of random organization for the vortices driven in the tilted direction are significantly smaller than those in the untilted field.
Unfolding of Vortices into Topological Stripes in a Multiferroic Material
Wang, X.; Mostovoy, M.; Han, M. G.; Horibe, Y.; Aoki, T.; Zhu, Y.; Cheong, S.-W.
2014-06-01
Multiferroic hexagonal RMnO3 (R =rare earths) crystals exhibit dense networks of vortex lines at which six domain walls merge. While the domain walls can be readily moved with an applied electric field, the vortex cores so far have been impossible to control. Our experiments demonstrate that shear strain induces a Magnus-type force pulling vortices and antivortices in opposite directions and unfolding them into a topological stripe domain state. We discuss the analogy between this effect and the current-driven dynamics of vortices in superconductors and superfluids.
Experimental results on chiral magnetic and vortical effects
Wang, Gang
2016-01-01
Various novel transport phenomena in chiral systems result from the interplay of quantum anomalies with magnetic field and vorticity in high-energy heavy-ion collisions, and could survive the expansion of the fireball and be detected in experiments. Among them are the chiral magnetic effect, the chiral vortical effect and the chiral magnetic wave, the experimental searches for which have aroused extensive interest. The goal of this review is to describe the current status of experimental studies at Relativistic Heavy Ion Collider at BNL and the Large Hadron Collider at CERN, and to outline the future work in experiment needed to eliminate the existing uncertainties in the interpretation of the data.
Giant vortices in the Ginzburg-Landau model
DEFF Research Database (Denmark)
Sørensen, Mads Peter
The time-dependent Ginzburg-Landau equation is solved in a region of two spatial dimensions and with complex geometry using the finite element method. The geometry has a marked influence on the vortex distribution and we have observed generation of giant vortices at boundary defects.......The time-dependent Ginzburg-Landau equation is solved in a region of two spatial dimensions and with complex geometry using the finite element method. The geometry has a marked influence on the vortex distribution and we have observed generation of giant vortices at boundary defects....
Intrinsic nonadiabatic topological torque in magnetic skyrmions and vortices
Akosa, Collins Ashu
2017-03-01
We propose that topological spin currents flowing in topologically nontrivial magnetic textures, such as magnetic skyrmions and vortices, produce an intrinsic nonadiabatic torque of the form Tt∼[(∂xm×∂ym)·m]∂ym. We show that this torque, which is absent in one-dimensional domain walls and/or nontopological textures, is responsible for the enhanced nonadiabaticity parameter observed in magnetic vortices compared to one-dimensional textures. The impact of this torque on the motion of magnetic skyrmions is expected to be crucial, especially to determine their robustness against defects and pinning centers.
Is the Chiral Vortical Effect Vanishing in Heavy Ion Collisions?
Landsteiner, Karl; Pena-Benitez, Francisco
2013-01-01
We study the frequency dependence of all the chiral vortical and magnetic conductivities for a relativistic chiral gas of free fermions and for a strongly coupled CFT with holographic dual in four dimensions. Both systems present gauge and gravitational anomalies and we compute their contribution to the conductivities. The chiral vortical conductivities and the chiral magnetic conductivity in the energy current show an unexpected frequency dependence in the form of a delta centered at zero frequency. We argue that this makes the CVE practically unobservable in heavy ion collisions. In the appendix we discuss why the CME seems to vanish in the consistent current for a particular implementation of the axial chemical potential.
Explosion of relativistic electron vortices in laser plasmas
Lezhnin, K V; Esirkepov, T Zh; Bulanov, S V; Gu, Y; Weber, S; Korn, G
2016-01-01
The interaction of high intensity laser radiation with underdense plasma may lead to the formation of electron vortices. Though being quasistationary on an electron timescales, these structures tend to expand on a proton timescale due to Coloumb repulsion of ions. Using a simple analytical model of a stationary vortex as initial condition, 2D PIC simulations are performed. A number of effects are observed such as vortex boundary field intensification, multistream instabilities at the vortex boundary, and bending of the vortex boundary with the subsequent transformation into smaller electron vortices.
Nonlinear Wave-Currents interactions in shallow water
Lannes, David
2015-01-01
We study here the propagation of long waves in the presence of vorticity. In the irrotational framework, the Green-Naghdi equations (also called Serre or fully nonlinear Boussinesq equations) are the standard model for the propagation of such waves. These equations couple the surface elevation to the vertically averaged horizontal velocity and are therefore independent of the vertical variable. In the presence of vorticity, the dependence on the vertical variable cannot be removed from the vorticity equation but it was however shown in [?] that the motion of the waves could be described using an extended Green-Naghdi system. In this paper we propose an analysis of these equations, and show that they can be used to get some new insight into wave-current interactions. We show in particular that solitary waves may have a drastically different behavior in the presence of vorticity and show the existence of solitary waves of maximal amplitude with a peak at their crest, whose angle depends on the vorticity. We als...
Zhu, Hong-Ming; Pen, Ue-Li; Chen, Xuelei; Yu, Hao-Ran
2016-01-01
We present a direct approach to non-parametrically reconstruct the linear density field from an observed non-linear map. We solve for the unique displacement potential consistent with the non-linear density and positive definite coordinate transformation using a multigrid algorithm. We show that we recover the linear initial conditions up to $k\\sim 1\\ h/\\mathrm{Mpc}$ with minimal computational cost. This reconstruction approach generalizes the linear displacement theory to fully non-linear fields, potentially substantially expanding the BAO and RSD information content of dense large scale structure surveys, including for example SDSS main sample and 21cm intensity mapping.
Boyd, Robert W
2013-01-01
Nonlinear Optics is an advanced textbook for courses dealing with nonlinear optics, quantum electronics, laser physics, contemporary and quantum optics, and electrooptics. Its pedagogical emphasis is on fundamentals rather than particular, transitory applications. As a result, this textbook will have lasting appeal to a wide audience of electrical engineering, physics, and optics students, as well as those in related fields such as materials science and chemistry.Key Features* The origin of optical nonlinearities, including dependence on the polarization of light* A detailed treatment of the q
Mokhov, Igor I; Chefranov, Alexander G
2012-01-01
It is shown for the first time that only an antipodal vortex pair (APV) is the elementary singular vortex object on the sphere compatible with the hydrodynamic equations. The exact weak solution of the absolute vorticity equation on the rotating sphere is obtained in the form of Hamiltonian dynamic system for interacting APVs. This is the first model describing interaction of Barrett vortices corresponding to atmospheric centers of action (ACA). In particular, new steady-state conditions for N=2 are obtained. These analytical conditions are used for the analysis of coupled cyclone-anticyclone ACAs over oceans in the Northern Hemisphere.
3D optical vortices generated by micro-optical elements and its novel applications
Institute of Scientific and Technical Information of China (English)
BU J.; LIN J.; K. J. Moh; B. P. S. Ahluwalia; CHEN H. L.; PENG X.; NIU H. B.; YUAN X.C.
2007-01-01
In this paper we report on recent development in the areas of optical vortices generated by micro-optical elements and applications of optical vortices, including optical manipulation, radial polarization and secure free space optical communication
Slowly-growing gap-opening planets trigger weaker vortices
Hammer, Michael; Lin, Min-Kai
2016-01-01
The presence of a giant planet in a low-viscosity disc can create a gap edge in the disc's radial density profile sharp enough to excite the Rossby Wave Instability. This instability may evolve into dust-trapping vortices that might explain the "banana-shaped" features in recently observed asymmetric transition discs with inner cavities. Previous hydrodynamical simulations of planet-induced vortices have neglected the timescale of hundreds to thousands of orbits to grow a massive planet to Jupiter-size. In this work, we study the effect of a giant planet's runaway growth timescale on the lifetime and characteristics of the resulting vortex. For two different planet masses (1 and 5 Jupiter masses) and two different disc viscosities ($\\alpha$=3$\\times 10^{-4}$ and 3$\\times10^{-5}$), we compare the vortices induced by planets with several different growth timescales between 10 and 4000 planet orbits. In general, we find that slowly-growing planets create significantly weaker vortices with lifetimes and surface d...
Hamiltonian vortices and reconnection in a magnetized plasma
Kuvshinov, B. N.; Lakhin, V. P.; Pegoraro, F.; Schep, T. J.
1998-01-01
Hamiltonian vortices and reconnection in magnetized plasmas are investigated analytically and numerically using a two-fluid model. The equations are written in the Lagrangian form of three fields that are advected with different velocities. This system can be considered as a generalization and exten
Propagation of magnetic vortices using nanocontacts as tunable attractors
Manfrini, M.; Kim, Joo-Von; Petit-Watelot, S.; van Roy, W.; Lagae, L.; Chappert, C.; Devolder, T.
2014-02-01
Magnetic vortices in thin films are in-plane spiral spin configurations with a core in which the magnetization twists out of the film plane. Vortices result from the competition between atomic-scale exchange forces and long-range dipolar interactions. They are often the ground state of magnetic dots, and have applications in medicine, microwave generation and information storage. The compact nature of the vortex core, which is 10-20 nm wide, makes it a suitable probe of magnetism at the nanoscale. However, thus far the positioning of a vortex has been possible only in confined structures, which prevents its transport over large distances. Here we show that vortices can be propagated in an unconstrained system that comprises electrical nanocontacts (NCs). The NCs are used as tunable vortex attractors in a manner that resembles the propelling of space craft with gravitational slingshots. By passing current from the NCs to a ferromagnetic film, circulating magnetic fields are generated, which nucleate the vortex and create a potential well for it. The current becomes spin polarized in the film, and thereby drives the vortex into gyration through spin-transfer torques. The vortex can be guided from one NC to another by tuning attractive strengths of the NCs. We anticipate that NC networks may be used as multiterminal sources of vortices and spin waves (as well as heat, spin and charge flows) to sense the fundamental interactions between physical objects and fluxes of the next-generation spintronic devices.
Numerical and Experimental Study of Electromagnetically Driven Vortical Flows
Kenjeres, S.; Verdoold, J.; Tummers, M.J.; Hanjalic, K.; Kleijn, C.R.
2009-01-01
The paper reports on numerical and experimental investigations of electromagnetically driven vortical flows of an electrically conductive fluid in a generic setup. Two different configurations of permanent magnets are considered: a 3-magnet configuration in which the resulting Lorentz force is focus
The vorticity budget of developing Typhoon Nuri (2008
Directory of Open Access Journals (Sweden)
D. J. Raymond
2010-07-01
Full Text Available The formation of west Pacific tropical cyclone Nuri (2008 was observed over four days from easterly wave to typhoon stage by aircraft using scanning Doppler radar and dropsonde data. This typhoon intensified rapidly in a significantly sheared environment. In spite of the shear, overlapping closed circulations existed in the storm frame of reference in the boundary layer and at 5 km elevation, providing a deep region protected from environmental influences. The vorticity budget was analyzed and it was found that vorticity convergence dominated vortex tilting on the storm scale in the lower troposphere. At times vorticity convergence also greatly exceeded frictional spindown in the boundary layer. Thus, the Ekman pumping hypothesis was found to be a poor approximation in the early stages of the development of this typhoon. As Nuri developed, convective sources of boundary layer vorticity became fewer but more intense, culminating in a single nascent eyewall at the tropical storm stage. A non-developing tropical wave case was also analyzed. This system started with much weaker circulations in the boundary layer and aloft, leaving it unprotected against environmental intrusion. This may explain its failure to develop.
Ionospheric travelling convection vortices observed by the Greenland magnetometer chain
DEFF Research Database (Denmark)
Kotsiaros, Stavros; Stolle, Claudia; Friis-Christensen, Eigil
2013-01-01
The Greenland magnetometer array continuously provides geomagnetic variometer data since the early eighties. With the polar cusp passing over it almost every day, the array is suitable to detect ionospheric traveling convection vortices (TCVs), which were rst detected by Friis-Christensen et al...
Quantitative flow analysis of swimming dynamics with coherent Lagrangian vortices
Huhn, F.; van Rees, W. M.; Gazzola, M.; Rossinelli, D.; Haller, G.; Koumoutsakos, P.
2015-08-01
Undulatory swimmers flex their bodies to displace water, and in turn, the flow feeds back into the dynamics of the swimmer. At moderate Reynolds number, the resulting flow structures are characterized by unsteady separation and alternating vortices in the wake. We use the flow field from simulations of a two-dimensional, incompressible viscous flow of an undulatory, self-propelled swimmer and detect the coherent Lagrangian vortices in the wake to dissect the driving momentum transfer mechanisms. The detected material vortex boundary encloses a Lagrangian control volume that serves to track back the vortex fluid and record its circulation and momentum history. We consider two swimming modes: the C-start escape and steady anguilliform swimming. The backward advection of the coherent Lagrangian vortices elucidates the geometry of the vorticity field and allows for monitoring the gain and decay of circulation and momentum transfer in the flow field. For steady swimming, momentum oscillations of the fish can largely be attributed to the momentum exchange with the vortex fluid. For the C-start, an additionally defined jet fluid region turns out to balance the high momentum change of the fish during the rapid start.
Self-similar motion of three point vortices
DEFF Research Database (Denmark)
Aref, Hassan
2010-01-01
One of the counter-intuitive results in the three-vortex problem is that the vortices can converge on and meet at a point in a finite time for certain sets of vortex circulations and for certain initial conditions. This result was already included in Groumlbli's thesis of 1877 and has since been...
Restrictions on the geometry of the periodic vorticity equation
Escher, Joachim
2010-01-01
We prove that several evolution equations arising as mathematical models for fluid motion cannot be realized as metric Euler equations on the Lie group of all smooth and orientation-preserving diffeomorphisms on the circle. These include the quasi-geostrophic model equation, the axisymmetric Euler flow in higher space dimensions, and De Gregorio's vorticity model equation.
The decay of wake vortices in the convective boundary layer
Energy Technology Data Exchange (ETDEWEB)
Holzaepfel, F.; Gerz, T.; Frech, M.; Doernbrack, A.
2000-03-01
The decay of three wake vortex pairs of B-747 aircraft in a convectively driven atmospheric boundary layer is investigated by means of large-eddy simulations (LES). This situation is considered as being hazardous as the updraft velocities of a thermal may compensate the induced descent speed of the vortex pair resulting in vortices stalled in the flight path. The LES results, however, illustrate that (i) the primary rectilinear vortices are rapidly deformed on the scale of the alternating updraft and downdraft regions; (ii) parts of the vortices stay on flight level but are quickly eroded by the enhanced turbulence of an updraft; (iii) longest living sections of the vortices are found in regions of relatively calm downdraft flow which augments their descent. Strip theory calculations are used to illustrate the temporal and spatial development of lift and rolling moments experienced by a following medium weight class B-737 aircraft. Characteristics of the respective distributions are analysed. Initially, the maximum rolling moments slightly exceed the available roll control of the B-737. After 60 seconds the probability of rolling moments exceeding 50% of the roll control, a value which is considered as a threshold for acceptable rolling moments, has decreased to 1% of its initial probability. (orig.)
Generalized self-dual Chern-Simons vortices
Bazeia, D.(Departamento de Física, Universidade Federal da Paraíba, João Pessoa, PB, 58051-970, Brazil); da Hora, E.; Santos, C. dos(Centro de Física e Departamento de Física e Astronomia, Faculdade de Ciências da Universidade do Porto, 4169-007, Porto, Portugal); Menezes, R.(Departamento de Física, Universidade Federal de Campina Grande, 58109-970 Campina Grande, PB, Brazil)
2010-01-01
We search for vortices in a generalized Abelian Chern-Simons model with a nonstandard kinetic term. We illustrate our results, plotting and comparing several features of the vortex solution of the generalized model with those of the vortex solution found in the standard Chern-Simons model.
Vorticity and non-coaxiality in progressive deformations
Means, W.D.; Hobbs, B.E.; Lister, G.S.; Williams, P.F.
1980-01-01
A measure of the non-coaxiality involved in progressive deformation histories is proposed in the form of the kinematical vorticity number, Wk. This number is a measure of the relative effects of rotation of material lines (relative to the instantaneous stretching axes) and of stretching of these mat
Instability of helical tip vortices in rotor wakes
DEFF Research Database (Denmark)
Sørensen, Jens Nørkær
2011-01-01
The conditions for the appearance of instabilities in systems of helical vortices constitute an intriguing problem that still remains partly unsolved. The experimental study of Felli, Camussi & Di Felice (J. Fluid Mech., this issue, vol. 682, 2011, pp. 5-53) has shed new light on some of the basi...
Ionospheric travelling convection vortices observed by the Greenland magnetometer chain
DEFF Research Database (Denmark)
Kotsiaros, Stavros; Stolle, Claudia; Friis-Christensen, Eigil
2013-01-01
The Greenland magnetometer array continuously provides geomagnetic variometer data since the early eighties. With the polar cusp passing over it almost every day, the array is suitable to detect ionospheric traveling convection vortices (TCVs), which were rst detected by Friis-Christensen et al...
Quantitative flow analysis of swimming dynamics with coherent Lagrangian vortices.
Huhn, F; van Rees, W M; Gazzola, M; Rossinelli, D; Haller, G; Koumoutsakos, P
2015-08-01
Undulatory swimmers flex their bodies to displace water, and in turn, the flow feeds back into the dynamics of the swimmer. At moderate Reynolds number, the resulting flow structures are characterized by unsteady separation and alternating vortices in the wake. We use the flow field from simulations of a two-dimensional, incompressible viscous flow of an undulatory, self-propelled swimmer and detect the coherent Lagrangian vortices in the wake to dissect the driving momentum transfer mechanisms. The detected material vortex boundary encloses a Lagrangian control volume that serves to track back the vortex fluid and record its circulation and momentum history. We consider two swimming modes: the C-start escape and steady anguilliform swimming. The backward advection of the coherent Lagrangian vortices elucidates the geometry of the vorticity field and allows for monitoring the gain and decay of circulation and momentum transfer in the flow field. For steady swimming, momentum oscillations of the fish can largely be attributed to the momentum exchange with the vortex fluid. For the C-start, an additionally defined jet fluid region turns out to balance the high momentum change of the fish during the rapid start.
Vortices as Nurseries for Planetesimal Formation in Protoplanetary Discs
Heng, Kevin
2010-01-01
Turbulent, two-dimensional, hydrodynamic flows are characterized by the emergence of coherent, long-lived vortices without a need to invoke special initial conditions. Vortices have the ability to sequester particles, with typical radii from about 1 mm to 10 cm, that are slightly decoupled from the gas. A generic feature of discs with surface density and effective temperature profiles that are decreasing, power-law functions of radial distance is that four vortex zones exist for a fixed particle size. In particular, two of the zones form an annulus at intermediate radial distances within which small particles reside. Particle capture by vortices occurs on a dynamical time scale near and at the boundaries of this annulus. As the disc ages and the particles grow via coagulation, the size of the annulus shrinks. Older discs prefer to capture smaller particles, a phenomenon we term "vortex aging". More viscous, more dust-opaque and/or less massive discs can have vortices that age faster and trap a broader range o...
Data Mining for Vortices on the Earth's Magnetosphere
Collado-Vega, Y. M.; Kalb, V.; Sibeck, D. G.
2016-12-01
This research validates a method to detect and characterize vortices based on velocity from simulation data. The current algorithm involves systematically searching the 3-dimensional velocity fields to identify critical points, points where the magnitude of the velocity vector field vanishes, making these points candidates for vortex centers. We utilize the Community Coordinated Modeling Center (CCMC) run on request capability to create a series of model runs initialized from the conditions observed by the Cluster mission in the Hwang et al., 2011 analysis of Kelvin Helmholtz vortices observed during southward IMF. The fast data characterization and vortex detection will permit the scientist to focus in on different magnetosphere locations for further investigation in large data sets. This not only saves time to scientist, but also diminishes the potential for missing features of interest. We also analyze further the properties of the vortices found including the velocity changes within their motion across the magnetosheath, and the potential of our tool to characterize transient features (e.g. Flux Transfer Event (FTEs)) with vortical internal structures.
Tip vorticity reduction and optimization of lifting surfaces
Sparenberg, JA
2001-01-01
In linearized optimization theory, lifting surfaces, moving in an inviscid and incompressible fluid, shed tip vorticity of which the strength has infinite square-root singularities. Here we discuss that an optimization procedure can be coupled to constraints so that the strength of the shed vorticit
Ruszczynski, Andrzej
2011-01-01
Optimization is one of the most important areas of modern applied mathematics, with applications in fields from engineering and economics to finance, statistics, management science, and medicine. While many books have addressed its various aspects, Nonlinear Optimization is the first comprehensive treatment that will allow graduate students and researchers to understand its modern ideas, principles, and methods within a reasonable time, but without sacrificing mathematical precision. Andrzej Ruszczynski, a leading expert in the optimization of nonlinear stochastic systems, integrates t
On the evaluation of vorticity using cardiovascular magnetic resonance velocity measurements.
Garcia, J; Larose, E; Pibarot, P; Kadem, L
2013-12-01
Vorticity and vortical structures play a fundamental role affecting the evaluation of energetic aspects (mainly left ventricle work) of cardiovascular function. Vorticity can be derived from cardiovascular magnetic resonance (CMR) imaging velocity measurements. However, several numerical schemes can be used to evaluate the vorticity field. The main objective of this work is to assess different numerical schemes used to evaluate the vorticity field derived from CMR velocity measurements. We compared the vorticity field obtained using direct differentiation schemes (eight-point circulation and Chapra) and derivate differentiation schemes (Richardson 4* and compact Richardson 4*) from a theoretical velocity field and in vivo CMR velocity measurements. In all cases, the effect of artificial spatial resolution up-sampling and signal-to-noise ratio (SNR) on vorticity computation was evaluated. Theoretical and in vivo results showed that the eight-point circulation method underestimated vorticity. Up-sampling evaluation showed that the artificial improvement of spatial resolution had no effect on mean absolute vorticity estimation but it affected SNR for all methods. The Richardson 4* method and its compact version were the most accurate and stable methods for vorticity magnitude evaluation. Vorticity field determination using the eight-point circulation method, the most common method used in CMR, has reduced accuracy compared to other vorticity schemes. Richardson 4* and its compact version showed stable SNR using both theoretical and in vivo data.
Fundamental interactions of vortical structures with boundary layers in two-dimensional flows
DEFF Research Database (Denmark)
Coutsias, E.A.; Lynov, Jens-Peter
1991-01-01
in the vorticity-stream function representation for bounded geometries. Fundamental processes connected to vorticity detachment from the boundary layers caused by the proximity of vortical structures are described. These processes include enstrophy enhancement of the main flow during bursting events, and pinning...
Internal and vorticity waves in decaying stratified flows
Matulka, A.; Cano, D.
2009-04-01
Most predictive models fail when forcing at the Rossby deformation Radius is important and a large range of scales have to be taken into account. When mixing of reactants or pollutants has to be accounted, the range of scales spans from hundreds of Kilometers to the Bachelor or Kolmogorov sub milimiter scales. We present some theoretical arguments to describe the flow in terms of the three dimensional vorticity equations, using a lengthscale related to the vorticity (or enstrophy ) transport. Effect of intermittent eddies and non-homogeneity of diffusion are also key issues in the environment because both stratification and rotation body forces are important and cause anisotropy/non-homogeneity. These problems need further theoretical, numerical and observational work and one approach is to try to maximize the relevant geometrical information in order to understand and therefore predict these complex environmental dispersive flows. The importance of the study of turbulence structure and its relevance in diffusion of contaminants in environmental flows is clear when we see the effect of environmental disasters such as the Prestige oil spill or the Chernobil radioactive cloud spread in the atmosphere. A series of Experiments have been performed on a strongly stratified two layer fluid consisting of Brine in the bottom and freshwater above in a 1 square meter tank. The evolution of the vortices after the passage of a grid is video recorded and Particle tracking is applied on small pliolite particles floating at the interface. The combination of internal waves and vertical vorticity produces two separate time scales that may produce resonances. The vorticity is seen to oscilate in a complex way, where the frecuency decreases with time.
Nonlinear ion acoustic waves scattered by vortexes
Ohno, Yuji; Yoshida, Zensho
2016-09-01
The Kadomtsev-Petviashvili (KP) hierarchy is the archetype of infinite-dimensional integrable systems, which describes nonlinear ion acoustic waves in two-dimensional space. This remarkably ordered system resides on a singular submanifold (leaf) embedded in a larger phase space of more general ion acoustic waves (low-frequency electrostatic perturbations). The KP hierarchy is characterized not only by small amplitudes but also by irrotational (zero-vorticity) velocity fields. In fact, the KP equation is derived by eliminating vorticity at every order of the reductive perturbation. Here, we modify the scaling of the velocity field so as to introduce a vortex term. The newly derived system of equations consists of a generalized three-dimensional KP equation and a two-dimensional vortex equation. The former describes 'scattering' of vortex-free waves by ambient vortexes that are determined by the latter. We say that the vortexes are 'ambient' because they do not receive reciprocal reactions from the waves (i.e., the vortex equation is independent of the wave fields). This model describes a minimal departure from the integrable KP system. By the Painlevé test, we delineate how the vorticity term violates integrability, bringing about an essential three-dimensionality to the solutions. By numerical simulation, we show how the solitons are scattered by vortexes and become chaotic.
Management of the orbital angular momentum of vortex beams in a quadratic nonlinear interaction
Bovino, Fabio A; Bertolotti, Mario; Sibilia, Concita
2011-01-01
Light intensity control of the orbital angular momentum of the fundamental beam in a quadratic nonlinear process is theoretically and numerically presented. In particular we analyzed a seeded second harmonic generation process in presence of orbital angular momentum of the interacting beams due both to on axis and off axis optical vortices. Examples are proposed and discussed.
Vortex Nucleation in a Dissipative Variant of the Nonlinear Schroedinger Equation Under Rotation
2014-12-01
Vortices in Nonlinear Fields (Clarendon, UK, 1999). [2] Yu.S. Kivshar and B. Luther -Davies, Physics Reports 298, 81–197 (1998). [3] Y.S. Kivshar, J...Christou, V. Tikhonenko, B. Luther -Davies and L. Pismen, Optics Comm. 152, 198–206 (1998). [4] H.J. Lugt, Vortex Flow in Nature and Technology (John
In, Visarath; Longhini, Patrick; Kho, Andy; Neff, Joseph D.; Leung, Daniel; Liu, Norman; Meadows, Brian K.; Gordon, Frank; Bulsara, Adi R.; Palacios, Antonio
2012-12-01
The nonlinear channelizer is an integrated circuit made up of large parallel arrays of analog nonlinear oscillators, which, collectively, serve as a broad-spectrum analyzer with the ability to receive complex signals containing multiple frequencies and instantaneously lock-on or respond to a received signal in a few oscillation cycles. The concept is based on the generation of internal oscillations in coupled nonlinear systems that do not normally oscillate in the absence of coupling. In particular, the system consists of unidirectionally coupled bistable nonlinear elements, where the frequency and other dynamical characteristics of the emergent oscillations depend on the system's internal parameters and the received signal. These properties and characteristics are being employed to develop a system capable of locking onto any arbitrary input radio frequency signal. The system is efficient by eliminating the need for high-speed, high-accuracy analog-to-digital converters, and compact by making use of nonlinear coupled systems to act as a channelizer (frequency binning and channeling), a low noise amplifier, and a frequency down-converter in a single step which, in turn, will reduce the size, weight, power, and cost of the entire communication system. This paper covers the theory, numerical simulations, and some engineering details that validate the concept at the frequency band of 1-4 GHz.
A numerical method of tracing a vortical axis along local topological axis line
Nakayama, Katsuyuki; Hasegawa, Hideki
2016-06-01
A new numerical method is presented to trace or identify a vortical axis in flow, which is based on Galilean invariant flow topology. We focus on the local flow topology specified by the eigenvalues and eigenvectors of the velocity gradient tensor, and extract the axis component from its flow trajectory. Eigen-vortical-axis line is defined from the eigenvector of the real eigenvalue of the velocity gradient tensor where the tensor has the conjugate complex eigenvalues. This numerical method integrates the eigen-vortical-axis line and traces a vortical axis in terms of the invariant flow topology, which enables to investigate the feature of the topology-based vortical axis.
Free-space propagation of guided optical vortices excited in an annular core fiber.
Yan, Hongwei; Zhang, Entao; Zhao, Baoyin; Duan, Kailiang
2012-07-30
The analytical expression for the propagation of guided optical vortices through free space is derived and used to study the dynamic evolution of guided optical vortices after passing through the free space, and the dependence of guided optical vortices on the control parameters where the effect of propagation distance is stressed. It is shown that the motion, pair creation and annihilation of guided optical vortices may take place. In particular, the creation and annihilation of a pair of guided optical vortices do not take place by varying fiber length.
A Climatological Investigation of the Activity of Summer Subtropical Vortices
Institute of Scientific and Technical Information of China (English)
LUO Zhexian; DAI Kan
2008-01-01
By applying a new vortex detection method to the ECMWF 40-yr reanalysis (ERA40) data from 1985 to 2002, the climatology of summer vortices has been investigated in five subtropical regions, i.e., the northwestern Pacific, northeastern Pacific, northwestern Atlantic, northeastern Atlantic, and Australia-South Pacific, followed by validation with NCEP/NCAR reanalysis data. Results are as follows: (1) The spatial distributions of ERA40 vortex activities (VAC) were well consistent with those of NCEP/NCAR reanalysis (NRA) results in all regions, especially in northwestern Pacific. (2) Because of different model resolutions, both the number and intensity of vortices obtained from NRA were significantly weaker thanERA40's. (3) Vortices mainly cruised in coasts and the adjacent seas, from where to the land or the open sea vortex activities were gradually decreased. (4) There were two active centers in the northwestern Pacific:one was located in South China Sea and the other, as the largest center of the five regions, spread from the east side of the Philippines to Japan. (5) Over the northwestern Atlantic, most vortices occurred in Panama and its west-side offshore. (6) The spatial distributions of vortices were alike between the northeastern Pacific and northeastern Atlantic, both spreading from coasts to the west-side sea at 5°-20°N. (7) In the Anstralia-South Pacific, vortices were not as active as those in the other four regions, and mostly took place in the equator-side of near ocean areas. (8) Except the northwestern Pacific and northwestern Atlantic, the VAC interannual variations in the other three regions were different between ERA40 and NRA data. (9)In the northwestern Pacific and northwestern Atlantic, the VAC interannual variation could be separated to several distinct stages. (10) Since the mid 1980s, mean vortex intensity was getting increased in the northwestern Pacific, which was most significant in the subtropical areas on a global basis. In the western
Energy Technology Data Exchange (ETDEWEB)
Turchetti, G. (Bologna Univ. (Italy). Dipt. di Fisica)
1989-01-01
Research in nonlinear dynamics is rapidly expanding and its range of applications is extending beyond the traditional areas of science where it was first developed. Indeed while linear analysis and modelling, which has been very successful in mathematical physics and engineering, has become a mature science, many elementary phenomena of intrinsic nonlinear nature were recently experimentally detected and investigated, suggesting new theoretical work. Complex systems, as turbulent fluids, were known to be governed by intrinsically nonlinear laws since a long time ago, but received purely phenomenological descriptions. The pioneering works of Boltzmann and Poincare, probably because of their intrinsic difficulty, did not have a revolutionary impact at their time; it is only very recently that their message is reaching a significant number of mathematicians and physicists. Certainly the development of computers and computer graphics played an important role in developing geometric intuition of complex phenomena through simple numerical experiments, while a new mathematical framework to understand them was being developed.
ASYMMETRIC VORTICES FLOW OVER SLENDER BODY AND ITS ACTIVE CONTROL AT HIGH ANGLE OF ATTACK
Institute of Scientific and Technical Information of China (English)
DENG Xueying; WANG Yankui
2004-01-01
The studies of asymmetric vortices flow over slender body and its active control at high angles of attack have significant importance for both academic field and engineering area. This paper attempts to provide an update state of art to the investigations on the fields of forebody asymmetric vortices. This review emphasizes the correlation between micro-perturbation on the model nose and its response and evolution behaviors of the asymmetric vortices. The critical issues are discussed,which include the formation and evolution mechanism of asymmetric multi-vortices; main behaviors of asymmetric vortices flow including its deterministic feature and vortices flow structure; the evolution and development of asymmetric vortices under the perturbation on the model nose; forebody vortex active control especially discussed micro-perturbation active control concept and technique in more detail. However present understanding in this area is still very limited and this paper tries to identify the key unknown problems in the concluding remarks.
Numerical study of the evolution of vortices in a linearly stratified fluid
Energy Technology Data Exchange (ETDEWEB)
Beckers, M.; Clercx, H.J.H.; Van Heijst, G.J.F. [Eindhoven University of Technology, Eindhoven (Netherlands). J.M. Burgers Centre fro Fluid Dynamics; Verzicco, R. [Rome Univ. La Sapienza, Rome (Italy). Dipt. di Meccanica e Aeronautica
1999-12-01
This paper presents a numerical study in which the evolution of vortices in a Stafford fluid is compared to the evolution of two-dimensional vortices. The influence of the Reynolds number and the Froude number are investigated, for the evolution of axisymmetric vortices, for their azimuthal instability and for the subsequent formation of tripoles. It is found that due to radial diffusion axisymmetric vortices with various initial vorticity profiles all evolve towards the same profile. This evolution reduces the growth of azimuthal instabilities which may lead to the formation of a tripole. For vortices in a stratified fluid the effect of the ambient stratification on the evolution of the vortices is investigated. It is found that a process of vortex stretching, which becomes more pronounced for increasing Froude numbers, leads to a weaker tripole formation.
Adiabatic Limit and the Slow Motion of Vortices in a Chern-Simons-Schrödinger System
Demoulini, Sophia; Stuart, David
2009-09-01
We study a nonlinear system of partial differential equations in which a complex field (the Higgs field) evolves according to a nonlinear Schrödinger equation, coupled to an electromagnetic field whose time evolution is determined by a Chern-Simons term in the action. In two space dimensions, the Chern-Simons dynamics is a Galileo invariant evolution for A, which is an interesting alternative to the Lorentz invariant Maxwell evolution, and is finding increasing numbers of applications in two dimensional condensed matter field theory. The system we study, introduced by Manton, is a special case (for constant external magnetic field, and a point interaction) of the effective field theory of Zhang, Hansson and Kivelson arising in studies of the fractional quantum Hall effect. From the mathematical perspective the system is a natural gauge invariant generalization of the nonlinear Schrödinger equation, which is also Galileo invariant and admits a self-dual structure with a resulting large space of topological solitons (the moduli space of self-dual Ginzburg-Landau vortices). We prove a theorem describing the adiabatic approximation of this system by a Hamiltonian system on the moduli space. The approximation holds for values of the Higgs self-coupling constant λ close to the self-dual (Bogomolny) value of 1. The viability of the approximation scheme depends upon the fact that self-dual vortices form a symplectic submanifold of the phase space (modulo gauge invariance). The theorem provides a rigorous description of slow vortex dynamics in the near self-dual limit.
Generation and propagation of high-order Bessel vortices in linear and non-linear crystals
CSIR Research Space (South Africa)
Belyi, VN
2009-08-01
Full Text Available E⊥ of the electric field for these beams are given by the following expressions: ( ))2exp()()( )( )exp( 20 1 10 ϕρρ iqJqJ qw zikA i zoo −+⊥ += eeE , (1) с Uniaxial crystal θs Bs2ω(ρ) Bsω(ρ) Figure 1: Geometry of SHG when wave vectors cone of Bessel...
Vortex Identification from Local Properties of the Vorticity Field
Elsas, J H
2016-01-01
A number of systematic procedures for the identification of coherent structures have been developed as a way to address their possible kinematical and dynamical roles in structural formulations of turbulence. It has been broadly acknowledged, however, that vortex detection algorithms, usually based on linear-algebraic properties of the velocity gradient tensor, are plagued with severe shortcomings and are also dependent on the choice of subjective threshold parameters in their implementations. In two-dimensions, a large class of standard vortex identification prescriptions turn out to be equivalent to the "swirling strength criterion", which is critically revisited in this work. We classify the instances where the $\\lambda_{ci}$-criterion blatantly fails and propose an alternative vortex detection scheme based on the local curvature properties of the vorticity graph -- the "vorticity curvature criterion" -- which improves over the results obtained with the $\\lambda_{ci}$-criterion in controlled Monte-Carlo te...
On the refracted patterns produced by liquid vortices
Institute of Scientific and Technical Information of China (English)
Yasser Aboelkassem; Georgios H.Vatistas
2007-01-01
A theoretical analysis of the refracted shad-ows produced by steady and time-decaying liquid vor-tices under uniform illumination from above is givenin this article.An expression for the induced shadowintensity is derived and found to be a function of thevortex's free surface profile,i.e.,function of the staticpressure distribution.The patterns for different focus-ing depth are given and compared with previous visu-alization results from the literature.The phenomenonis examined and illustrated as a bench mark case byusing both steady and time-decaying algebraic vortexmodels.However,this study can be extended to checkthe feasibility of recovering the main flow properties byanalyzing the luminous image intensity of the refractedpatterns.The present analysis is valid only when the swirlvelocity is order of magnitude higher than the meridi-onal flow components and the vorticity is concentratedwithin the core region and of intense conditions.
A study of optical vortices inside the Talbot interferometer
Panthong, Pituk; Pattanaporkratana, Apichart; Chiangga, Surasak; Deachapunya, Sarayut
2015-01-01
The optical Talbot interferometer has been used to explore the topological charges of optical vortices. We recorded the self-imaging of a diffraction grating in the near-field regime with the optical vortex of several topological charges. Our twisted light was generated by a spatial light modulator (SLM). Previous studies showed that interferometric methods can determine the particular orbital angular momentum (OAM) states, but a large number of OAM eigenvalues are difficult to distinguish from the interference patterns. Here, we show that the Talbot patterns can distinguish the charges as well as the OAM of the vortices with high orders. Owing to high sensitivity and self-imaging of Talbot effect, several OAM eigenvalues can be distinguished by direct measurement. We assure the experimental results with our theory. The present results are useful for classical and quantum metrology as well as future implementations of quantum communications.
Mechanism for Influence of Nose Bluntness on Asymmetric Vortices
Institute of Scientific and Technical Information of China (English)
WANG Gang; LIANG Xin-Gang
2004-01-01
@@ Pressure distributions on slender bodies are measured at various roll angles; it is found that the side loads on the blunted-nose slender body are as small as one-third of that on a pointed-nose one, or even zero at some roll angles. Numerical simulation shows that different flow structures are generated on the leeside of the bodies with different noses. The results confirm that a structure of U-shaped horseshoe vortex develops on the top of the blunted nose due to the closed type of surface flow separation. The shear layer separated from the nose is entrapped into the horseshoe vortex core and forms two main vortices on the two sides of the body. The function of this structure is to hold in the two main nose vortices and to restrict the emergence of asymmetry.
Supersymmetry Breaking on Gauged Non-Abelian Vortices
Konishi, Kenichi; Vinci, Walter
2012-01-01
There are a large number of systems characterized by a completely broken gauge symmetry, but with an unbroken global color-flavor diagonal symmetry, i.e., systems in the so-called color-flavor locked phase. If the gauge symmetry breaking supports vortices, the latter develop non-Abelian orientational zero-modes and become non-Abelian vortices, a subject of intense study in the last several years. In this paper we consider the effects of weakly gauging the full exact global flavor symmetry in such systems, deriving an effective description of the light excitations in the presence of a vortex. Surprising consequences are shown to follow. The fluctuations of the vortex orientational modes get diffused to bulk modes through tunneling processes. When our model is embedded in a supersymmetric theory, the vortex is still 1/2 BPS saturated, but the vortex effective action breaks supersymmetry.
Nontopological self-dual Maxwell-Higgs vortices
Bazeia, D.; Casana, R.; Ferreira, M. M., Jr.; da Hora, E.
2015-01-01
We study the existence of self-dual nontopological vortices in generalized Maxwell-Higgs models recently introduced in Bazeia D. et al., Eur. Phys. J. C, 71 (2001) 1833. Our investigation is explicitly illustrated by choosing a sixth-order self-interaction potential, which is the simplest one allowing the existence of nontopological structures. We specify some Maxwell-Higgs models yielding BPS nontopological vortices having energy proportional to the magnetic flux, Φ B , and whose profiles are numerically achieved. Particularly, we investigate the way the new solutions approach the boundary values, from which we verify their nontopological behavior. Finally, we depict the numerically found profiles, highlighting the main features they present.
Interactions and excitations of non-Abelian vortices
Energy Technology Data Exchange (ETDEWEB)
Alford, M.G.; Benson, K.; Coleman, S.; March-Russell, J. (Lyman Laboratory of Physics, Harvard University, Cambridge, Massachusetts 02138 (USA)); Wilczek, F. (Institute for Advanced Study, Princeton, New Jersey 08540 (USA))
1990-04-02
We examine bosonic zero modes of vortices formed in the gauge breaking {ital G}{r arrow}{ital H}. For non-Abelian {ital G}, zero modes are generic. Their solutions depend on global symmetry structure. Vortices render the embedding {ital H}{contained in}{ital G} space dependent, with a dynamically determined subgroup {ital {tilde H}} single valued. They Aharonov-Bohm scatter gauge bosons associated with multivalued generators. Alice strings ({ital H}=O(2), {ital {tilde H}}={ital openZ}{sub 2}) attract charges and scatter SO(2) photons,'' and a two-string system has zero modes with unlocalizable Cheshire'' charge. The resulting superconductivity has novel electrodynamics.
Temporally optimized spanwise vorticity sensor measurements in turbulent boundary layers
Morrill-Winter, C.; Klewicki, J.; Baidya, R.; Marusic, I.
2015-12-01
Multi-element hot-wire anemometry was used to measure spanwise vorticity fluctuations in turbulent boundary layers. Smooth wall boundary layer profiles, with very good spatial and temporal resolution, were acquired over a Kármán number range of 2000-12,700 at the Melbourne Wind Tunnel at the University of Melbourne and the University of New Hampshire's Flow Physics Facility. A custom hot-wire probe was necessary to simultaneously obtain velocity and spanwise vorticity measurements centered at a fixed point in space. A custom calibration/processing scheme was developed to utilize single-wall-parallel wires to optimize the accuracy of the measured wall-normal velocity fluctuations derived from the sensor's ×-array.
Mass deformed world-sheet action of semi local vortices
Energy Technology Data Exchange (ETDEWEB)
Jiang, Yunguo [School of Space Science and Physics, Shandong University at Weihai,264209 Weihai (China); Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment,264209 Weihai (China)
2014-02-10
The mass deformed effective world-sheet theory of semi local vortices was constructed via the field theoretical method. By Euler-Lagrangian equations, the Ansatze for both the gauge field and the adjoint scalar were solved, this ensures that zero modes of vortices are minimal excitations of the system. Up to the 1/g{sup 2} order, all profiles are solved. The mass deformed effective action was obtained by integrating out the transverse plane of the vortex string. The effective theory interpolates between the local vortex and the lump. Respecting certain normalization conditions, the effective theory shows a Seiberg-like duality, which agrees with the result of the Kähler quotient construction.
Are vortices in rotating superfluids breaking the Weak Equivalence Principle?
de Matos, Clovis Jacinto
2009-01-01
Due to the breaking of gauge symmetry in rotating superfluid Helium, the inertial mass of a vortex diverges with the vortex size. The vortex inertial mass is thus much higher than the classical inertial mass of the vortex core. An equal increase of the vortex gravitational mass is questioned. The possibility that the vortices in a rotating superfluid could break the weak equivalence principle in relation with a variable speed of light in the superfluid vacuum is debated. Experiments to test this possibility are investigated on the bases that superfluid Helium vortices would not fall, under the single influence of a uniform gravitational field, at the same rate as the rest of the superfluid Helium mass.
Experimental Results on Chiral Magnetic and Vortical Effects
Directory of Open Access Journals (Sweden)
Gang Wang
2017-01-01
Full Text Available Various novel transport phenomena in chiral systems result from the interplay of quantum anomalies with magnetic field and vorticity in high-energy heavy-ion collisions and could survive the expansion of the fireball and be detected in experiments. Among them are the chiral magnetic effect, the chiral vortical effect, and the chiral magnetic wave, the experimental searches for which have aroused extensive interest. The goal of this review is to describe the current status of experimental studies at Relativistic Heavy-Ion Collider at BNL and the Large Hadron Collider at CERN and to outline the future work in experiment needed to eliminate the existing uncertainties in the interpretation of the data.
Clustering of heavy particles in vortical flows: a selective review
Indian Academy of Sciences (India)
S RAVICHANDRAN; P DEEPU; RAMA GOVINDARAJAN
2017-04-01
Heavy particles in a turbulent flow tend to leave regions of high vorticity and cluster into regions of high strain. The consequences of such clustering have been studied in a variety of situations over the past few decades, and this problem has seen several review papers already. Our objectives in this paper are three-fold. (i) We introduce the reader to the basic ideas, and explain why the problem is interesting. (ii) Using an N-vortex system we present an interesting case where particles are attracted to the vicinity of vortices. A new scaling forthe critical Stokes number of attraction is obtained. (iii) We review a number of papers, which are related to cloud physics in this context.
Characterization of vortical gusts produced by a heaving plate
Hufstedler, Esteban; McKeon, Beverley J.
2016-11-01
To experimentally investigate the interaction between a wing and a spanwise vortical gust, a simple gust generator has been built and tested. This consists of a transversely heaving flat plate that changes direction to release a vortex, which then convects downstream to interact with a wing. Previous experiments have shown that, immediately downstream of the plate, the circulation of the generated vortex is proportional to the heaving speed of the plate. The forces that the gusts exert on a downstream wing were shown to be strongly repeatable and consistent with a passing vortex. This presentation will discuss the properties of the vortical gusts as they move downstream, and relate those properties to the important dimensionless parameters of the flow. These properties include the convection speed and circulation of the vortex, as well as the enstrophy due to the wake of the plate. This research is funded by the Gordon and Betty Moore Foundation through Grant GBMF#2645 to the California Institute of Technology.
Stretching vortices as a basis for the theory of turbulence
Sirota, V A
2014-01-01
Turbulent flows play an important role in many aspects of nature and technics from sea storms to transport of particles or chemicals. Transport of energy from large scales to small fluctuations is the essential feature of three-dimensional turbulence. What mechanism is responsible for this transport and how do the small fluctuations appear? The conventional conception implies a cascade of breaking vortices. But it faces crucial problems in explaining the mechanism of the breaking, and fails to explain the observed long-living structures in turbulent flows. We suggest a new concept based on recent analysis of stochastic Navier-Stokes equation: stretching of vortices instead of their breaking may be the main mechanism of turbulence. This conception is free of the disadvantages of the cascade paradigm; it also does not need finite-time singularities to explain the observed statistical properties of turbulent flows. Moreover, the introduction of the new conception allows immediately to get velocity scaling parame...
Charge redistribution from anomalous magneto-vorticity coupling
Hattori, Koichi
2016-01-01
We investigate novel transport phenomena in a chiral fluid originated from an interplay between a vorticity and strong magnetic field, which induces a redistribution of vector charges in the system and an axial current along the magnetic field. The corresponding transport coefficients are obtained from an energy-shift argument for the chiral fermions in the lowest Landau level (LLL) due to a spin-vorticity coupling and also from diagrammatic computations on the basis of the linear response theory. Based on consistent results from the both methods, we observe that the transport coefficients are proportional to the anomaly coefficient and are independence of temperature and chemical potential. We therefore speculate that these transport phenomena are connected to quantum anomaly.
Sunspots are in many ways similar to terrestrial vortices
Vatistas, Georgios H
2011-01-01
In this letter we identify similarities amongst sunspots and terrestrial vortices. The dark appearance of the central part of any sunspot is currently justified by an anticipated cooling effect experienced by the ionized gas. However, it cannot single-handedly reconcile the halo that surrounds the penumbra, the subsequent second dim ring that could be possibly followed by a second halo. In antithesis, light refraction due to density variations in a compressible whirl can give reason for all of these manifestations. Certain data of Wilson's depression fit better the geometric depth profile of a two-celled vortex. The last provides a hurricane equivalent manifestation for the normal and reverse Evershed effect. There is compelling evidence that alike to atmospheric vortices sunspots do also spawn meso-cyclones.
Spiral density wave generation by vortices in Keplerian flows
Bodo, G; Murante, G; Tevzadze, A; Rossi, P; Ferrari, A
2005-01-01
We perform a detailed analytical and numerical study of the dynamics of perturbations (vortex/aperiodic mode, Rossby and spiral-density waves) in 2D compressible disks with a Keplerian law of rotation. We draw attention to the process of spiral-density wave generation from vortices, discussing, in particular, the initial, most peculiar stages of wave emission. We show that the linear phenomenon of wave generation by vortices in smooth (without inflection points) shear flows found by using the so-called non-modal approach, is directly applicable to the present case. After an analytical non-modal description of the physics and characteristics of the spiral-density wave generation/propagation in the local shearing-sheet model, we follow the process of wave generation by small amplitude coherent circular vortex structures, by direct global numerical simulation, describing the main features of the generated waves.
Pattern selection as a nonlinear eigenvalue problem
Büchel, P
1996-01-01
A unique pattern selection in the absolutely unstable regime of driven, nonlinear, open-flow systems is reviewed. It has recently been found in numerical simulations of propagating vortex structures occuring in Taylor-Couette and Rayleigh-Benard systems subject to an externally imposed through-flow. Unlike the stationary patterns in systems without through-flow the spatiotemporal structures of propagating vortices are independent of parameter history, initial conditions, and system length. They do, however, depend on the boundary conditions in addition to the driving rate and the through-flow rate. Our analysis of the Ginzburg-Landau amplitude equation elucidates how the pattern selection can be described by a nonlinear eigenvalue problem with the frequency being the eigenvalue. Approaching the border between absolute and convective instability the eigenvalue problem becomes effectively linear and the selection mechanism approaches that of linear front propagation. PACS: 47.54.+r,47.20.Ky,47.32.-y,47.20.Ft
The Finiteness of vortices in steady incompressible viscous fluid flow
Kalita, Jiten C; Panda, Swapnendu
2016-01-01
In this work, we provide two novel approaches to show that incompressible fluid flow in a finite domain contains at most a finite number vortices. We use a recently developed geometric theory of incompressible viscous flows along with an existing mathematical analysis concept to establish the finiteness. We also offer a second proof of finiteness by roping in the Kolmogorov's length scale criterion in conjunction with the notion of diametric disks.
Helicity and topology of a small region of quantum vorticity
Mesgarnezhad, M; Baggaley, A W; Barenghi, C F
2016-01-01
We numerically study the evolution of a small turbulent region of quantised vorticity in superfluid helium, a regime which can be realised in the laboratory. We show that the turbulence achieves a fluctuating steady-state in terms of dynamics (energy), geometry (length, writhing) and topology (linking). After defining the knot spectrum, we show that, at any instant, the turbulence consists of many unknots and few large loops of great geometrical and topological complexity.
Seider, Warren D.; Ungar, Lyle H.
1987-01-01
Describes a course in nonlinear mathematics courses offered at the University of Pennsylvania which provides an opportunity for students to examine the complex solution spaces that chemical engineers encounter. Topics include modeling many chemical processes, especially those involving reaction and diffusion, auto catalytic reactions, phase…
Numerical evaluation of gas core length in free surface vortices
Cristofano, L.; Nobili, M.; Caruso, G.
2014-11-01
The formation and evolution of free surface vortices represent an important topic in many hydraulic intakes, since strong whirlpools introduce swirl flow at the intake, and could cause entrainment of floating matters and gas. In particular, gas entrainment phenomena are an important safety issue for Sodium cooled Fast Reactors, because the introduction of gas bubbles within the core causes dangerous reactivity fluctuation. In this paper, a numerical evaluation of the gas core length in free surface vortices is presented, according to two different approaches. In the first one, a prediction method, developed by the Japanese researcher Sakai and his team, has been applied. This method is based on the Burgers vortex model, and it is able to estimate the gas core length of a free surface vortex starting from two parameters calculated with single-phase CFD simulations. The two parameters are the circulation and the downward velocity gradient. The other approach consists in performing a two-phase CFD simulation of a free surface vortex, in order to numerically reproduce the gas- liquid interface deformation. Mapped convergent mesh is used to reduce numerical error and a VOF (Volume Of Fluid) method was selected to track the gas-liquid interface. Two different turbulence models have been tested and analyzed. Experimental measurements of free surface vortices gas core length have been executed, using optical methods, and numerical results have been compared with experimental measurements. The computational domain and the boundary conditions of the CFD simulations were set consistently with the experimental test conditions.
Hilbert Statistics of Vorticity Scaling in Two-Dimensional Turbulence
Tan, H S; Meng, Jianping
2014-01-01
In this paper, the scaling property of the inverse energy cascade and forward enstrophy cascade of the vorticity filed $\\omega(x,y)$ in two-dimensional (2D) turbulence is analyzed. This is accomplished by applying a Hilbert-based technique, namely Hilbert-Huang Transform, to a vorticity field obtained from a $8192^2$ grid-points direct numerical simulation of the 2D turbulence with a forcing scale $k_f=100$ and an Ekman friction. The measured joint probability density function $p(C,k)$ of mode $C_i(x)$ of the vorticity $\\omega$ and instantaneous wavenumber $k(x)$ is separated by the forcing scale $k_f$ into two parts, which corresponding to the inverse energy cascade and the forward enstrophy cascade. It is found that all conditional pdf $p(C\\vert k)$ at given wavenumber $k$ has an exponential tail. In the inverse energy cascade, the shape of $p(C\\vert k)$ does collapse with each other, indicating a nonintermittent cascade. The measured scaling exponent $\\zeta_{\\omega}^I(q)$ is linear with the statistical ord...
Ricci magnetic geodesic motion of vortices and lumps
Alqahtani, L S
2014-01-01
Ricci magnetic geodesic (RMG) motion in a k\\"ahler manifold is the analogue of geodesic motion in the presence of a magnetic field proportional to the ricci form. It has been conjectured to model low-energy dynamics of vortex solitons in the presence of a Chern-Simons term, the k\\"ahler manifold in question being the $n$-vortex moduli space. This paper presents a detailed study of RMG motion in soliton moduli spaces, focusing on the cases of hyperbolic vortices and spherical $\\mathbb{C}P^1$ lumps. It is shown that RMG flow localizes on fixed point sets of groups of holomorphic isometries, but that the flow on such submanifolds does not, in general, coincide with their intrinsic RMG flow. For planar vortices, it is shown that RMG flow differs from an earlier reduced dynamics proposed by Kim and Lee, and that the latter flow is ill-defined on the vortex coincidence set. An explicit formula for the metric on the whole moduli space of hyperbolic two-vortices is computed (extending an old result of Strachan's), an...
Magnetorheological effect in the magnetic field oriented along the vorticity
Energy Technology Data Exchange (ETDEWEB)
Kuzhir, P., E-mail: pavel.kuzhir@unice.fr; Magnet, C.; Fezai, H.; Meunier, A.; Bossis, G. [Laboratory of Condensed Matter Physics, CNRS UMR7336, University of Nice-Sophia Antipolis, 28 Avenue Joseph Vallot, 06100 Nice (France); Rodríguez-Arco, L.; López-López, M. T. [Department of Applied Physics, University of Granada, Campus de Fuentenueva, 18071 Granada (Spain); Zubarev, A. [Department of Mathematical Physics, Ural Federal University, 51 Prospekt Lenina, 620083 Ekaterinburg (Russian Federation)
2014-11-01
In this work, we have studied the magnetorheological (MR) fluid rheology in the magnetic field parallel to the fluid vorticity. Experimentally, the MR fluid flow was realized in the Couette coaxial cylinder geometry with the magnetic field parallel to the symmetry axis. The rheological measurements were compared to those obtained in the cone-plate geometry with the magnetic field perpendicular to the lower rheometer plate. Experiments revealed a quasi-Bingham behavior in both geometries with the stress level being just a few dozens of percent smaller in the Couette cylindrical geometry at the same internal magnetic field. The unexpectedly high MR response in the magnetic field parallel to the fluid vorticity is explained by stochastic fluctuations of positions and orientations of the particle aggregates. These fluctuations are induced by magnetic interactions between them. Once misaligned from the vorticity direction, the aggregates generate a high stress independent of the shear rate, and thus assimilated to the suspension apparent (dynamic) yield stress. Quantitatively, the fluctuations of the aggregate orientation are modeled as a rotary diffusion process with a diffusion constant proportional to the mean square interaction torque. The model gives a satisfactory agreement with the experimental field dependency of the apparent yield stress and confirms the nearly quadratic concentration dependency σ{sub Y}∝Φ{sup 2.2}, revealed in experiments. The practical interest of this study lies in the development of MR smart devices with the magnetic field nonperpendicular to the channel walls.
Seismometer Detection of Dust Devil Vortices by Ground Tilt
Lorenz, Ralph D; Murdoch, Naomi; Lognonné, Philippe; Kawamura, Taichi; Mimoun, David; Banerdt, W Bruce
2015-01-01
We report seismic signals on a desert playa caused by convective vortices and dust devils. The long-period (10-100s) signatures, with tilts of ~10$^{-7}$ radians, are correlated with the presence of vortices, detected with nearby sensors as sharp temporary pressure drops (0.2-1 mbar) and solar obscuration by dust. We show that the shape and amplitude of the signals, manifesting primarily as horizontal accelerations, can be modeled approximately with a simple quasi-static point-load model of the negative pressure field associated with the vortices acting on the ground as an elastic half space. We suggest the load imposed by a dust devil of diameter D and core pressure {\\Delta}Po is ~({\\pi}/2){\\Delta}PoD$^2$, or for a typical terrestrial devil of 5 m diameter and 2 mbar, about the weight of a small car. The tilt depends on the inverse square of distance, and on the elastic properties of the ground, and the large signals we observe are in part due to the relatively soft playa sediment and the shallow installatio...
Jovian Vortices and Barges: HST observations 1994-1998
Morales, R.; Sanchez-Lavega, A.; Lecacheux, J.; Colas, F.; Miyazaki, I.
2000-10-01
We have used the HST-WFPC2 archived images of Jupiter in the period 1994-1998 to study the zonal and meridional distributions, long-term motions, lifetimes, interactions and other properties of the vortices larger than 2 degrees. The latitude range covered spans from +75 to -75 degrees. High-resolution images obtained with the 890nm, 410nm and 953nm wavelength filters allowed us to make a morphological classification based on their appearance in each filter. The vortices are anticyclones, and their long-term motions have been completed with ground-based images and are compared to the mean Jovian zonal wind profile. Significant differences are found between the vortex velocities and the mean zonal winds. Some vortices exhibited important drift changes in short period times. We analyze a possible correlation between their size and zonal wind velocity. On the other hand, the "barges" lie in the cyclone domains of the wind-profile and have been identified in several latitudes. Their latitudinal size is similar in all of them (typically 1.6 degrees) but their longitudinal size ranges from 1 to 32 degrees. We discuss the temporal evolution of some of these cyclonic regions. The Spanish team was supported by Gobierno Vasco PI 034/97. The French team was supported by the "Programme National de Planetologie." RM acknowledges a fellowship from Universidad Pais Vasco.
Some exact BPS solutions for exotic vortices and monopoles
Ramadhan, Handhika S
2015-01-01
We present several analytical solutions of BPS vortices and monopoles in the generalized Abelian Maxwell-Higgs and Yang-Mills-Higgs theories, respectively. These models have recently been extensively studied and several exact solutions have already been obtained in~\\cite{Casana:2014qfa, Casana:2013lna}. In each theory, the dynamics is controlled by the additional two positive scalar-field-dependent functions, $f(|\\phi|)$ and $w(|\\phi|)$. For the case of vortices, we work in the ordinary symmetry-breaking Higgs potential, while for the case of monopoles we have the ordinary condition of the Prasad-Sommerfield limit. Our results generalize that of exact solutions found previously. We also present solutions for BPS vortices with higher winding number. These solutions suffer from the condition that $w(|\\phi|)$ has negative value at some finite range of $r$, but we argue that since it satisfies the weaker positive-value conditions then the corresponding energy density is still positive-definite and, thus, they are...
Lagrangian structures in time-periodic vortical flows
Directory of Open Access Journals (Sweden)
S. V. Kostrykin
2006-01-01
Full Text Available The Lagrangian trajectories of fluid particles are experimentally studied in an oscillating four-vortex velocity field. The oscillations occur due to a loss of stability of a steady flow and result in a regular reclosure of streamlines between the vortices of the same sign. The Eulerian velocity field is visualized by tracer displacements over a short time period. The obtained data on tracer motions during a number of oscillation periods show that the Lagrangian trajectories form quasi-regular structures. The destruction of these structures is determined by two characteristic time scales: the tracers are redistributed sufficiently fast between the vortices of the same sign and much more slowly transported into the vortices of opposite sign. The observed behavior of the Lagrangian trajectories is quantitatively reproduced in a new numerical experiment with two-dimensional model of the velocity field with a small number of spatial harmonics. A qualitative interpretation of phenomena observed on the basis of the theory of adiabatic chaos in the Hamiltonian systems is given. The Lagrangian trajectories are numerically simulated under varying flow parameters. It is shown that the spatial-temporal characteristics of the Lagrangian structures depend on the properties of temporal change in the streamlines topology and on the adiabatic parameter corresponding to the flow. The condition for the occurrence of traps (the regions where the Lagrangian particles reside for a long time is obtained.
A study of vorticity formation in high energy nuclear collisions
Energy Technology Data Exchange (ETDEWEB)
Becattini, F. [Universita di Firenze, Dipartimento di Fisica e Astronomia, Sesto F.no (Firenze) (Italy); INFN, Sezione di Firenze, Sesto F.no (Firenze) (Italy); Inghirami, G. [Universita di Firenze, Dipartimento di Fisica e Astronomia, Sesto F.no (Firenze) (Italy); Johann Wolfgang Goethe University, Frankfurt Institute for Advanced Studies (FIAS), Frankfurt am Main (Germany); Rolando, V.; Pagliara, G. [Universita di Ferrara, Dipartimento di Fisica e Scienze della Terra, Ferrara (Italy); INFN, Sezione di Ferrara, Ferrara (Italy); Beraudo, A.; De Pace, A.; Nardi, M. [INFN, Sezione di Torino, Turin (Italy); Del Zanna, L. [Universita di Firenze, Dipartimento di Fisica e Astronomia, Sesto F.no (Firenze) (Italy); INFN, Sezione di Firenze, Sesto F.no (Firenze) (Italy); INAF, Osservatorio Astrofisico di Arcetri, Florence (Italy); Chandra, V. [Indian Institute of Technology Gandhinagar, Ahmedabad, Gujrat (India)
2015-09-15
We present a quantitative study of vorticity formation in peripheral ultrarelativistic heavy-ion collisions at √(s{sub NN}) = 200 GeV by using the ECHO-QGP numerical code, implementing relativistic dissipative hydrodynamics in the causal Israel-Stewart framework in 3 + 1 dimensions with an initial Bjorken flow profile. We consider different definitions of vorticity which are relevant in relativistic hydrodynamics. After demonstrating the excellent capabilities of our code, which proves to be able to reproduce Gubser flow up to 8 fm/c, we show that, with the initial conditions needed to reproduce the measured directed flow in peripheral collisions corresponding to an average impact parameter b = 11.6 fm and with the Bjorken flow profile for a viscous Quark Gluon Plasma with η/s = 0.1 fixed, a vorticity of the order of some 10{sup -2} c/fm can develop at freeze-out. The ensuing polarization of Λ baryons does not exceed 1.4 % at midrapidity. We show that the amount of developed directed flow is sensitive to both the initial angular momentum of the plasma and its viscosity. (orig.)
Nonabelian Superconductors: Vortices and Confinement in ${\\cal N}=2$ SQCD
Auzzi, R; Evslin, J; Konishi, K; Yung, A; Auzzi, Roberto; Bolognesi, Stefano; Evslin, Jarah; Konishi, Kenichi; Yung, Alexei
2003-01-01
We study nonabelian vortices (flux tubes) in SU(N) gauge theories, which are responsible for the confinement of (nonabelian) magnetic monopoles. In particular a detailed analysis is given of ${\\cal N}=2$ SQCD with gauge group SU(3) deformed by a small adjoint chiral multiplet mass. Tuning the bare quark masses (which we take to be large) to a common value $m$, we consider a particular vacuum of this theory in which an SU(2) subgroup of the gauge group remains unbroken. We consider $5 \\ge N_f \\ge 4$ flavors so that the SU(2) sub-sector remains non asymptotically free: the vortices carrying nonabelian fluxes may be reliably studied in a semi-classical regime. We show that the vortices indeed acquire exact zero modes which generate global rotations of the flux in an $SU(2)_{C+F}$ group. We study an effective world-sheet theory of these orientational zero modes which reduces to an ${\\cal N}=2$ O(3) sigma model in (1+1) dimensions. Mirror symmetry then teaches us that the dual SU(2) group is not dynamically broken...
The impact of intraglottal vortices on vocal fold dynamics
Erath, Byron; Pirnia, Alireza; Peterson, Sean
2016-11-01
During voiced speech a critical pressure is produced in the lungs that separates the vocal folds and creates a passage (the glottis) for airflow. As air passes through the vocal folds the resulting aerodynamic loading, coupled with the tissue properties of the vocal folds, produces self-sustained oscillations. Throughout each cycle a complex flow field develops, characterized by a plethora of viscous flow phenomena. Air passing through the glottis creates a jet, with periodically-shed vortices developing due to flow separation and the Kelvin-Helmholtz instability in the shear layer. These vortices have been hypothesized to be a crucial mechanism for producing vocal fold vibrations. In this study the effect of vortices on the vocal fold dynamics is investigated experimentally by passing a vortex ring over a flexible beam with the same non-dimensional mechanical properties as the vocal folds. Synchronized particle image velocimetry data are acquired in tandem with the beam dynamics. The resulting impact of the vortex ring loading on vocal fold dynamics is discussed in detail. This work was supported by the National Science Foundation Grant CBET #1511761.
Sensing and exploitation of vortices for a schooling fish
Gao, Amy; Maertens, Audrey; Triantafyllou, Michael
2016-11-01
The question of whether fish are capable of actively sensing and using individual vortices while schooling has long been debated. Prior research has shown that fish can gain a hydrodynamic benefit when swimming in the wake of another fish. However, it remains unclear if lateral line feedback is necessary, and if so, how a fish may adjust its motion to maximize its energy savings. To begin to address this, we study though numerical simulations the hydrodynamic interactions between two fish swimming in tandem, focusing on the interaction of individual vortices with the following fish. Using a potential flow model, we show that the pressure sensed by the following fish can be captured with a low number of states, which provide information that allows the fish to locate near-field vortices and phase its undulating motion accordingly. We will discuss how vortex interactions along the fish can be beneficial, the signals they induce, and which strategies a fish may use to save the most energy.
Some exact BPS solutions for exotic vortices and monopoles
Ramadhan, Handhika S.
2016-07-01
We present several analytical solutions of BPS vortices and monopoles in the generalized Abelian Maxwell-Higgs and Yang-Mills-Higgs theories, respectively. These models have recently been extensively studied and several exact solutions have already been obtained in [1,2]. In each theory, the dynamics is controlled by the additional two positive scalar-field-dependent functions, f (| ϕ |) and w (| ϕ |). For the case of vortices, we work in the ordinary symmetry-breaking Higgs potential, while for the case of monopoles we have the ordinary condition of the Prasad-Sommerfield limit. Our results generalize the exact solutions found previously. We also present solutions for BPS vortices with higher winding number. These solutions suffer from the condition that w (| ϕ |) has negative value at some finite range of r, but we argue that since it satisfies the weaker positive-value conditions then the corresponding energy density is still positive-definite and, thus, they are acceptable BPS solutions.
Dust-trapping Rossby vortices in protoplanetary disks
Meheut, H; Varniere, P; Benz, W
2012-01-01
One of the most challenging steps in planet formation theory is the one leading to the formation of planetesimals of kilometre size. A promising scenario involves the existence of vortices able to concentrate a large amount of dust and grains in their centres. Up to now this scenario has been studied mostly in 2D razor thin disks. A 3D study including, simultaneously, the formation and resulting dust concentration of the vortices with vertical settling, was still missing. The Rossby wave instability self-consistently forms 3D vortices, which have the unique quality of presenting a large scale vertical velocity in their centre. Here we aim to study how this newly discovered effect can alter the dynamic evolution of the dust. We perform global 3D simulations of the RWI in a radially and vertically stratified disk using the code MPI-AMRVAC. After the growth phase of the instability, the gas and solid phases are modelled by a bi-fluid approach, where the dust is considered as a fluid without pressure. Both the dr...
Models of Vortices and Spirals in White Dwarf's Accretion Binaries
Boneva, Daniela
2010-11-01
The main aim in the current survey is to suggest models of the development of structures, such as vortices and spirals, in accretion white dwarf's binaries. On the base of hydrodynamical analytical considerations it is applied numerical methods and simulations. It is suggested in the theoretical model the perturbation's parameters of the accretion flow, caused by the influences of the tidal wave over the flux of accretion matter around the secondary star. To examine such disturbed flow, the numerical code has involved in the calculations. The results reveal us an appearing of structure with spiral shape due to the tidal interaction in the close binaries. Our further simulations give the solution, which expresses the formation of vortical configurations in the accretion disc's zone. The evolution of vortices in areas of the flow's interaction is explored using single vortex and composite vortex models. Gas in the disc matter is considered to be compressible and non-ideal. The longevity of all these structures is different and each depends of time period of the rotation, density and velocity of the accretion matter.
Measurements of leading edge vortices in a supersonic stream
Milanovic, Ivana Milija
An experimental investigation of the leading edge vortices from a 75° sweptback, sharp edge delta wing has been carried out in a Mach 2.49 stream. Five-hole conical probe traverses were conducted vertically and horizontally through the primary vortices at the trailing edge and at one half chord downstream station for 7° and 12° angles of attack. The main objective was to determine the Mach number and pressure distributions in the primary vortex and to present comparisons of flow properties at different survey stations. In response to the continued interest in efficient supersonic flight vehicles, particularly in the missile arena, the motivation for this research has been to provide the quantitative details of supersonic leading edge vortices, the understanding of which up to now has been largely based on flow visualizations and presumed similarity to low speed flows. As a prerequisite to the measurement campaign, the employed five-hole conical probe was numerically calibrated using a three-dimensional Thin Layer Navier-Stokes solver in order to circumvent the traditional experimental approach vastly demanding on resources. The pressure readings at the probe orifices were computed for a range of Mach numbers and pitch angles, and subsequently verified in wind tunnel tests. The calibration phase also demonstrated the profound influence of the probe bluntness on the nearby static pressure ports, its relevance to the ultimate modeling strategy and the resulting calibration charts. Flow diagnostics of the leading edge vortices included both qualitative flow visualizations, as well as quantitative measurements. Shadowgraphs provided information regarding the trajectory and relative size of the generated vortices while assuring that no probe-induced vortex breakdown occurred. Surface oil patterns revealed the general spanwise locations of leeward vortices, and confirmed topological similarity to their low speed counterparts. The probe measurements revealed substantial
Bandyopadhyay, Promode R.; Hellum, Aren M.
2014-10-01
Many slow-moving biological systems like seashells and zebrafish that do not contend with wall turbulence have somewhat organized pigmentation patterns flush with their outer surfaces that are formed by underlying autonomous reaction-diffusion (RD) mechanisms. In contrast, sharks and dolphins contend with wall turbulence, are fast swimmers, and have more organized skin patterns that are proud and sometimes vibrate. A nonlinear spatiotemporal analytical model is not available that explains the mechanism underlying control of flow with such proud patterns, despite the fact that shark and dolphin skins are major targets of reverse engineering mechanisms of drag and noise reduction. Comparable to RD, a minimal self-regulation model is given for wall turbulence regeneration in the transitional regime--laterally coupled, diffusively--which, although restricted to pre-breakdown durations and to a plane close and parallel to the wall, correctly reproduces many experimentally observed spatiotemporal organizations of vorticity in both laminar-to-turbulence transitioning and very low Reynolds number but turbulent regions. We further show that the onset of vorticity disorganization is delayed if the skin organization is treated as a spatiotemporal template of olivo-cerebellar phase reset mechanism. The model shows that the adaptation mechanisms of sharks and dolphins to their fluid environment have much in common.
2015-01-01
From the Back Cover: The emphasis throughout the present volume is on the practical application of theoretical mathematical models helping to unravel the underlying mechanisms involved in processes from mathematical physics and biosciences. It has been conceived as a unique collection of abstract methods dealing especially with nonlinear partial differential equations (either stationary or evolutionary) that are applied to understand concrete processes involving some important applications re...
Haque, Q.; Mirza, Arshad M.; Iqbal, Javed
2016-04-01
Linear and nonlinear characteristics of electrostatic waves in a multicomponent magnetoplasma comprising of Boltzmann distributed electrons, Cairn's distributed hot electrons, and cold dynamic ions are studied. It is found that the effect of superthermal electrons, ion-neutral collisions, and ion shear flow modifies the propagation of ion-acoustic and drift waves. The growth rate of the ion shear flow instability varies with the addition of Cairn's distributed hot electrons. It is also investigated that the behavior of different type of vortices changes with the inclusion of superthermal hot electrons. The relevance of this investigation in space plasmas such as in auroral region and geomagnetic tail is also pointed out.
Towards laboratory detection of topological vortices in superfluid phases of QCD
Das, Arpan; De, Somnath; Srivastava, Ajit M
2016-01-01
Topological defects arise in a variety of systems, e.g. vortices in superfluid helium to cosmic strings in the early universe. There is an indirect evidence of neutron superfluid vortices from glitches in pulsars. One also expects that topological defects may arise in various high baryon density phases of quantum chromodynamics (QCD), e.g. superfluid topological vortices in the color flavor locked (CFL) phase. We investigate the possibility of detecting these topological superfluid vortices in laboratory experiments, namely heavy-ion collisions. Using hydrodynamic simulations, we show that vortices can qualitatively affect the power spectrum of flow fluctuations. This can give unambiguous signal for superfluid transition resulting in vortices, allowing for check of defect formation theories in a relativistic quantum field theory system.
Half-plane diffraction of Gaussian beams carrying two vortices of equal charges
Institute of Scientific and Technical Information of China (English)
He De; Gao Zeng-Hui; Lü Bai-Da
2011-01-01
This paper derives explicit expressions for the propagation of Ganssian beams carrying two vortices of equal charges m =±1 diffracted at a half-plane screen,which enables the study of the dynamic evolution of vortices in the diffraction field.It shows that there may be no vortices,a pair or several pairs of vortices of opposite charges m =+l,-1 in the diffraction field.Pair creation,annihilation and motion of vortices may appear upon propagation.The off-axis distance additionally affects the evolutionary behaviour.In the process the total topological charge is equal to zero,which is unequal to that of the vortex beam at the source plane.A comparison with the free-space propagation of two vortices of equal charges and a further extension are made.
Sharp asymptotic estimates for vorticity solutions of the 2D Navier-Stokes equation
Directory of Open Access Journals (Sweden)
Yuncheng You
2008-12-01
Full Text Available The asymptotic dynamics of high-order temporal-spatial derivatives of the two-dimensional vorticity and velocity of an incompressible, viscous fluid flow in $mathbb{R}^2$ are studied, which is equivalent to the 2D Navier-Stokes equation. It is known that for any integrable initial vorticity, the 2D vorticity solution converges to the Oseen vortex. In this paper, sharp exterior decay estimates of the temporal-spatial derivatives of the vorticity solution are established. These estimates are then used and combined with similarity and $L^p$ compactness to show the asymptotical attraction rates of temporal-spatial derivatives of generic 2D vorticity and velocity solutions by the Oseen vortices and velocity solutions respectively. The asymptotic estimates and the asymptotic attraction rates of all the derivatives obtained in this paper are independent of low or high Reynolds numbers.
Nezlin, Mikhail V
1993-01-01
This book can be looked upon in more ways than one. On the one hand, it describes strikingly interesting and lucid hydrodynamic experiments done in the style of the "good old days" when the physicist needed little more than a piece of string and some sealing wax. On the other hand, it demonstrates how a profound physical analogy can help to get a synoptic view on a broad range of nonlinear phenomena involving self-organization of vortical structures in planetary atmo spheres and oceans, in galaxies and in plasmas. In particular, this approach has elucidated the nature and the mechanism of such grand phenomena as the Great of galaxies. A number of our Red Spot vortex on Jupiter and the spiral arms predictions concerning the dynamics of spiral galaxies are now being confirmed by astronomical observations stimulated by our experiments. This book is based on the material most of which was accumulated during 1981-88 in close cooperation with our colleagues, experimenters from the Plasma Physics Department of the...
Detecting and tracking eddies in oceanic flows: A vorticity based Euler-Lagrangian method
Vortmeyer-Kley, Rahel; Gräwe, Ulf; Feudel, Ulrike
2016-04-01
Algae blooms as recurrent events in the Baltic Sea are an increasing natural hazard. Sandulescu et al. show in numerical simulation in [1] that eddies can play the role of an incubator for an algae bloom. Inside the eddy nutrients and plankton are trapped and can then be transported across rather long distances. To gain insight in mechanisms of algae bloom evolution detection and tracking of eddies is of interest. Based on the idea to interpret an eddy as a region that is bounded by manifolds and has an elliptic fixed point inside them, we develop an Euler-Lagrangian eddytracking tool using the idea of Lagrangian descriptors [2] and the vorticity. To test how well the tool detects eddy tracks and shapes, and estimates eddy lifetimes, the method is applied to a synthetic van Karman-Vortex Street. The results are compared to an eddytracking tool by Nencioli et al. [3]. Even velocity fields incorporated with different types of noise are taken into account to test the robustness of the tool. Finally, both methods are applied to velocity fields of the Baltic Sea. [1] M. Sandulescu, C. Lopez, E. Hernandez-Garcia and U. Feudel, Nonlinear Proc. Geophys., 14, 443-454, (2007). [2] J. Jimenez-Madrid and A. Mancho, Chaos, 19, 013111-1-18, (2009). [3] F. Nencioli, C. Dong, T. Dickey, L. Washburn, and J.C. McWilliams, J. Atmos. Ocean Tech., 27, 564-579, (2010).
Topological duality between vortices and planar skyrmions in BPS theories with APD symmetries
Adam, C; Wereszczynski, A; Zakrzewski, W J
2012-01-01
The BPS baby Skyrme models are submodels of baby Skyrme models, where the nonlinear sigma model term is suppressed. They have skyrmion solutions saturating a BPS bound, and the corresponding static energy functional is invariant under area-preserving diffeomorphisms (APDs). Here we show that the solitons in the BPS baby Skyrme model, which carry a nontrivial topological charge $Q_{b} \\in \\pi_2(S^2)$ (a winding number), are dual to vortices in a BPS vortex model with a topological charge $Q_{v}\\in \\pi_1(S^1)$ (a vortex number), in the sense that there is a map between the BPS solutions of the two models. The corresponding energy densities of the BPS solutions of the two models are identical. A further consequence of the duality is that the dual BPS vortex models inherit the BPS property and the infinitely many symmetries (APDs) of the BPS baby Skyrme models. Finally, we demonstrate that the same topological duality continues to hold for the U(1) gauged versions of the models.
Adam, C.; Sanchez-Guillen, J.; Wereszczynski, A.; Zakrzewski, W. J.
2013-01-01
The Bogomol’nyi-Prasad-Sommerfield (BPS) baby Skyrme models are submodels of baby Skyrme models, where the nonlinear sigma model term is suppressed. They have Skyrmion solutions saturating a BPS bound, and the corresponding static energy functional is invariant under area-preserving diffeomorphisms (APDs). Here we show that the solitons in the BPS baby Skyrme model, which carry a nontrivial topological charge Qb∈π2(S2) (a winding number), are dual to vortices in a BPS vortex model with a topological charge Qv∈π1(S1) (a vortex number), in the sense that there is a map between the BPS solutions of the two models. The corresponding energy densities of the BPS solutions of the two models are identical. A further consequence of the duality is that the dual BPS vortex models inherit the BPS property and the infinitely many symmetries (APDs) of the BPS baby Skyrme models. Finally, we demonstrate that the same topological duality continues to hold for the U(1) gauged versions of the models.
Instability of coupled geostrophic density fronts and its nonlinear evolution
Scherer, Emilie; Zeitlin, Vladimir
Instability of coupled density fronts, and its fully nonlinear evolution are studied within the idealized reduced-gravity rotating shallow-water model. By using the collocation method, we benchmark the classical stability results on zero potential vorticity (PV) fronts and generalize them to non-zero PV fronts. In both cases, we find a series of instability zones intertwined with the stability regions along the along-front wavenumber axis, the most unstable modes being long wave. We then study the nonlinear evolution of the unstable modes with the help of a high-resolution well-balanced finite-volume numerical scheme by initializing it with the unstable modes found from the linear stability analysis. The most unstable long-wave mode evolves as follows: after a couple of inertial periods, the coupled fronts are pinched at some location and a series of weakly connected co-rotating elliptic anticyclonic vortices is formed, thus totally changing the character of the flow. The characteristics of these vortices are close to known rodon lens solutions. The shorter-wave unstable modes from the next instability zones are strongly concentrated in the frontal regions, have sharp gradients, and are saturated owing to dissipation without qualitatively changing the flow pattern.
Magnetic moment of single vortices in YBCO nano-superconducting particle: Eilenberger approach
Zakharchuk, I.; Sharafeev, A.; Belova, P.; Safonchik, M.; Traito, K. B.; Lähderanta, E.
2013-12-01
Temperature dependence of single vortex magnetic moment in nanosize superconducting particles is investigated in the framework of quasiclassical Eilenberger approach. Such nanoparticles can be used for preparation of high-quality superconducting thin films with high critical current density. In contrast to bulk materials where the vortex magnetic moment is totally determined by flux quantum, in nano-sized specimens (with characteristic size, D, much less than effective penetration depth, λeff) the quantization rule is violated and magnetic moment is proportional to D2/λ2eff(T). Due to strong repulsion between vortices in nanoparticles only a single vortex can be trapped in them. Because of small size of particles the screening current of the vortex is located near the vortex core where the current is quite high and comparable to depairing currents. Therefore, the superconducting electron density, ns, depends on the current value and the distance from the vortex core. This effect is especially important for superconductors having gap nodes, such as YBCO. The current dependence of ns in nanoparticles is analogous to the Volovik effect in flux-line lattice in bulk samples. The magnitude of the effect can be obtained by comparing the temperature dependence of magnetic moment in the vortex and in the Meissner states. In the last case the value of screening current is small and superconducting response to the external field is determined by London penetration depth. Because of importance of nonlinear and nonlocal effects, the quantum mechanical Eilenberger approach is applied for description of the vortex in nanoparticles. The flattening of 1/λ2eff(T) dependence has been found. A comparison of the theoretical results with experimental magnetization data in Meissner and mixed states of YBCO nanopowders has been done. The presence of nonlinear and nonlocal effects in vortex current distribution is clearly visible. The obtained results are important for the description
Conservation of Total Vorticity for a 2D Stochastic Navier Stokes Equation
Directory of Open Access Journals (Sweden)
Peter M. Kotelenez
2011-01-01
Full Text Available We consider point vortices whose positions satisfy a stochastic ordinary differential equation on ℝ2 perturbed by spatially correlated Brownian noise. The associated signed point measure-valued empirical process turns out to be a weak solution to a stochastic Navier-Stokes equation (SNSE with a state-dependent stochastic term. As the number of vortices tends to infinity, we obtain a smooth solution to the SNSE, and we prove the conservation of total vorticity in this continuum limit.
A numerical study of the stabilitiy of helical vortices using vortex methods
Energy Technology Data Exchange (ETDEWEB)
Walther, J H [Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Lyngby (Denmark); Guenot, M [Enginering College in Industrial Systems, FR-17041, La Rochelle (France); Machefaux, E [Enginering College in Industrial Systems, FR-17041, La Rochelle (France); Rasmussen, J T [Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Lyngby (Denmark); Chatelain, P [Computational Laboratory, ETH Zurich, CH-8092 Zurich (Switzerland); Okulov, V L [Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Lyngby (Denmark); Soerensen, J N [Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Lyngby (Denmark); Bergdorf, M [Computational Laboratory, ETH Zurich, CH-8092 Zurich (Switzerland); Koumoutsakos, P [Computational Laboratory, ETH Zurich, CH-8092 Zurich (Switzerland)
2007-07-15
We present large-scale parallel direct numerical simulations using particle vortex methods of the instability of the helical vortices. We study the instability of a single helical vortex and find good agreement with inviscid theory. We outline equilibrium configurations for three double helical vortices-similar to those produced by three blade wind turbines. The simulations confirm the stability of the inviscid model, but predict a breakdown of the vortical system due to viscosity.
Velocity-vorticity formulation of three-dimensional, steady, viscous, incompressible flows
Energy Technology Data Exchange (ETDEWEB)
Meir, A.J. [Auburn Univ., AL (United States)
1994-12-31
In this work we discuss some aspects of the velocity-vorticity formulation of three-dimensional, steady, viscous, incompressible flows. We describe reasonable boundary conditions that should be imposed on the vorticity and a compatibility condition that the vorticity must satisfy. This formulation may give rise to efficient numerical algorithms for approximating solutions of the Stokes problem, which in turn yields an iterative method for approximating solutions of the Navier-Stokes equations.
Parallel numerical simulations for quantized vortices in Bose-Einstein condensates
Institute of Scientific and Technical Information of China (English)
Huang Zhao-Hui; Wang De-Sheng
2007-01-01
We employ the parallel computing technology to study numerically the three-dimensional structure of quantized vortices of Bose-Einstein condensates. For anisotropic cases, the bending process of vortices is described in detail by the decrease of Gross-Pitaevskii energy. A completely straight vortex and the steady and symmetrical multiple-vortex configurations are obtained. We analyse the effect of initial conditions and angular velocity on the number and shape of vortices.
Buoyancy in tropical cyclones and other rapidly rotating atmospheric vortices
Smith, Roger K.; Montgomery, Michael T.; Zhu, Hongyan
2005-07-01
Motivated primarily by its application to understanding tropical-cyclone intensification and maintenance, we re-examine the concept of buoyancy in rapidly rotating vortices, distinguishing between the buoyancy of the symmetric balanced vortex or system buoyancy, and the local buoyancy associated with cloud dynamics. The conventional definition of buoyancy is contrasted with a generalized form applicable to a vortex, which has a radial as well as a vertical component. If, for the special case of axisymmetric motions, the balanced density and pressure distribution of a rapidly rotating vortex are used as the reference state, the buoyancy field then characterizes the unbalanced density perturbations, i.e. the local buoyancy. We show how to determine such a reference state without approximation. The generation of the toroidal circulation of a vortex, which is necessary for vortex amplification, is characterized in the vorticity equation by the baroclinicity vector. This vector depends, inter-alia, on the horizontal (or radial) gradient of buoyancy evaluated along isobaric surfaces. We show that for a tropical-cyclone-scale vortex, the buoyancy so calculated is significantly different from that calculated at constant height or on surfaces of constant σ ( σ = ( p - p*)/( ps - p*), where p is the actual pressure, p* some reference pressure and ps is the surface pressure). Since many tropical-cyclone models are formulated using σ-coordinates, we examine the calculation of buoyancy on σ-surfaces and derive an expression for the baroclinicity vector in σ-coordinates. The baroclinic forcing term in the azimuthal vorticity equation for an axisymmetric vortex is shown to be approximately equal to the azimuthal component of the curl of the generalized buoyancy. A scale analysis indicates that the vertical gradient of the radial component of generalized buoyancy makes a comparatively small contribution to the generation of toroidal vorticity in a tropical cyclone, but may be
Polar Vortex Oscillation Viewed in an Isentropic Potential Vorticity Coordinate
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The stratospheric polar vortex oscillation (PVO) in the Northern Hemisphere is examined in a semiLagrangian θ-PVLAT coordinate constructed by using daily isentropic potential vorticity maps derived from NCEP/NCAR reanalysis Ⅱ dataset covering the period from 1979 to 2003. In the semi-Lagrangian θ-PVLAT coordinate, the variability of the polar vortex is solely attributed to its intensity change because the changes in its location and shape would be naturally absent by following potential vorticity contours on isentropic surfaces. The EOF and regression analyses indicate that the PVO can be described by a pair of poleward and downward propagating modes. These two modes together account for about 82% variance of the daily potential vorticity anomalies over the entire Northern Hemisphere. The power spectral analysis reveals a dominant time scale of about 107 days in the time series of these two modes,representing a complete PVO cycle accompanied with poleward propagating heating anomalies of both positive and negative signs from the equator to the pole. The strong polar vortex corresponds to the arrival of cold anomalies over the polar circle and vice versa. Accompanied with the poleward propagation is a simultaneous downward propagation. The downward propagation time scale is about 20 days in high and low latitudes and about 30 days in mid-latitudes. The zonal wind anomalies lag the poleward and downward propagating temperature anomalies of the opposite sign by 10 days in low and high latitudes and by 20 days in mid-latitudes. The time series of the leading EOF modes also exhibit dominant time scales of 8.7, 16.9, and 33.8 months. They approximately follow a double-periodicity sequence and correspond to the 3-peak extratropical Quasi-Biennial Oscillation (QBO) signal.
Distributional Enstrophy Dissipation Via the Collapse of Three Point Vortices
Gotoda, Takeshi; Sakajo, Takashi
2016-10-01
Dissipation of enstrophy in 2D incompressible flows in the zero viscous limit is considered to play a significant role in the emergence of the inertial range corresponding to the forward enstrophy cascade in the energy spectrum of 2D turbulent flows. However, since smooth solutions of the 2D incompressible Euler equations conserve the enstrophy, we need to consider non-smooth inviscid and incompressible flows so that the enstrophy dissipates. Moreover, it is physically uncertain what kind of a flow evolution gives rise to such an anomalous enstrophy dissipation. In this paper, in order to acquire an insight about the singular phenomenon mathematically as well as physically, we consider a dispersive regularization of the 2D Euler equations, known as the Euler-α equations, for the initial vorticity distributions whose support consists of three points, i.e., three α -point vortices, and take the α → 0 limit of its global solutions. We prove with mathematical rigor that, under a certain condition on their vortex strengths, the limit solution becomes a self-similar evolution collapsing to a point followed by the expansion from the collapse point to infinity for a wide range of initial configurations of point vortices. We also find that the enstrophy always dissipates in the sense of distributions at the collapse time. This indicates that the triple collapse is a mechanism for the anomalous enstrophy dissipation in non-smooth inviscid and incompressible flows. Furthermore, it is an interesting example elucidating the emergence of the irreversibility of time in a Hamiltonian dynamical system.
Prescribed Velocity Gradients for Highly Viscous SPH Fluids with Vorticity Diffusion.
Peer, Andreas; Teschner, Matthias
2016-12-06
Working with prescribed velocity gradients is a promising approach to efficiently and robustly simulate highly viscous SPH fluids. Such approaches allow to explicitly and independently process shear rate, spin, and expansion rate. This can be used to, e.g., avoid interferences between pressure and viscosity solvers. Another interesting aspect is the possibility to explicitly process the vorticity, e.g. to preserve the vorticity. In this context, this paper proposes a novel variant of the prescribed-gradient idea that handles vorticity in a physically motivated way. In contrast to a less appropriate vorticity preservation that has been used in a previous approach, vorticity is diffused. The paper illustrates the utility of the vorticity diffusion. Therefore, comparisons of the proposed vorticity diffusion with vorticity preservation and additionally with vorticity damping are presented. The paper further discusses the relation between prescribed velocity gradients and prescribed velocity Laplacians which improves the intuition behind the prescribed-gradient method for highly viscous SPH fluids. Finally, the paper discusses the relation of the proposed method to a physically correct implicit viscosity formulation.
Effect of thin film on the generation of vorticity by surface waves
Parfenyev, V M; Lebedev, V V
2016-01-01
Recently a theoretical scheme explaining the vorticity generation by surface waves in liquids was developed [S. Filatov et al., Phys. Rev. Lett. 116, 054501 (2016)]. Here we study how a thin (monomolecular) film presented at the surface of liquid affects the generated vorticity. We demonstrate that the vorticity becomes parametrically larger than for the case with a clean surface and now it depends on viscosity of the liquid. We also discuss the motion of particles passively advected by the generated surface flow. The results can be used in different applications: from the analysis of pollutants' diffusion on the ocean surface till the reconstruction of vorticity based on the particle image velocimetry (PIV) measurements.
Imaging of trapped vortices in YBCO coated conductor by scanning SQUID microscope
Energy Technology Data Exchange (ETDEWEB)
Inoue, M. [Department of EESE, Kyushu University, Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581 (Japan)]. E-mail: inoue@ees.kyushu-u.ac.jp; Kiss, T. [Department of EESE, Kyushu University, Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581 (Japan); Koyanagi, S. [Department of EESE, Kyushu University, Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581 (Japan); Imamura, K. [Department of EESE, Kyushu University, Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581 (Japan); Takeo, M. [Department of EESE, Kyushu University, Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581 (Japan); Iijima, Y. [Fujikura Ltd., Tokyo 135-8512 (Japan); Kakimoto, K. [Fujikura Ltd., Tokyo 135-8512 (Japan); Saitoh, T. [Fujikura Ltd., Tokyo 135-8512 (Japan); Matsuda, J. [Superconductivity Research Laboratory, Tokyo 130-0062 (Japan); Tokunaga, Y. [Superconductivity Research Laboratory, Tokyo 130-0062 (Japan); Izumi, T. [Superconductivity Research Laboratory, Tokyo 130-0062 (Japan); Shiohara, Y. [Superconductivity Research Laboratory, Tokyo 130-0062 (Japan)
2005-10-01
We investigated trapped vortices in Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) coated conductor by using a scanning SQUID microscope (SSM). Several peculiar properties of the vortices were observed such as a large bundle of vortices at a certain position and a coexistence of positive- and negative-sign vortices. Comparing the SSM images with that of low temperature scanning laser microscopy (LTSLM) and SEM, we identified the relationship between local dissipation and position of current blocking defect. Furthermore, regular vortex images were also observed by the SSM in the region where higher J {sub c} has been identified by the LTSLM.
Spin vortices in the Abelian-Higgs model with cholesteric vacuum structure
Peterson, Adam J.; Shifman, Mikhail; Tallarita, Gianni
2015-12-01
We continue the study of U(1) vortices with cholesteric vacuum structure. A new class of solutions is found which represent global vortices of the internal spin field. These spin vortices are characterized by a non-vanishing angular dependence at spatial infinity, or winding. We show that despite the topological Z2 behavior of SO(3) windings, the topological charge of the spin vortices is of the Z type in the cholesteric. We find these solutions numerically and discuss the properties derived from their low energy effective field theory in 1 + 1 dimensions.
Spin vortices in the Abelian-Higgs model with cholesteric vacuum structure
Peterson, Adam; Tallarita, Gianni
2015-01-01
We continue the study of $U(1)$ vortices with cholesteric vacuum structure. A new class of solutions is found which represent global vortices of the internal spin field. These spin vortices are characterized by a non-vanishing angular dependence at spatial infinity, or winding. We show that despite the topological $\\mathbb{Z}_2$ behavior of $SO(3)$ windings, the topological charge of the spin vortices is of the $\\mathbb{Z}$ type in the cholesteric. We find these solutions numerically and discuss the properties derived from their low energy effective field theory in $1+1$ dimensions.
Yoon, Min; Ahn, Junsun; Hwang, Jinyul; Sung, Hyung Jin
2016-08-01
The relationship between the frictional drag and the velocity-vorticity correlations in wall-bounded turbulent flows is derived from the mean vorticity equation. A formula for the skin friction coefficient is proposed and evaluated with regards to three canonical wall-bounded flows: turbulent boundary layer, turbulent channel flow, and turbulent pipe flow. The frictional drag encompasses four terms: advective vorticity transport, vortex stretching, viscous, and inhomogeneous terms. Drag-reduced channel flow with the slip condition is used to test the reliability of the formula. The advective vorticity transport and vortex stretching terms are found to dominate the contributions to the frictional drag.
Fine tuned vortices in lattice SU(2) gluodynamics
Gubarev, F V; Polikarpov, M I; Syritsyn, S N; Zakharov, V I
2003-01-01
We report measurements of the action associated with center vortices in the lattice SU(2) pure gauge theory. In the lattice units the excess of the action on the plaquettes belonging to the vortex is approximately a constant, independent on the lattice spacing 'a'. Therefore the action of the center vortex is of order A/a^2, where 'A' is its area. Since the area A is known to scale in the physical units, the observation suggests that the suppression due to the surface action is balanced, or fine tuned to the entropy factor which is to be an exponential of A/a^2.
A Probe of Primordial Gravity Waves and Vorticity
Energy Technology Data Exchange (ETDEWEB)
Kamionkowski, M. [Department of Physics, Columbia University, 538 West 120th Street, New York, New York 10027 (United States); Kosowsky, A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 (United States)]|[and Department of Physics, Lyman Laboratory, Harvard University, Cambridge, Massachusetts 02138 (United States); Stebbins, A. [NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laboratory, Batavia, Illinois 60510-0500 (United States)
1997-03-01
A formalism for describing an all-sky map of the polarization of the cosmic microwave background is presented. The polarization pattern on the sky can be decomposed into two geometrically distinct components. One of these components is not coupled to density inhomogeneities. A nonzero amplitude for this component of polarization can only be caused by tensor or vector metric perturbations. This allows unambiguous identification of long-wavelength gravity waves or large-scale vortical flows at the time of last scattering. {copyright} {ital 1997} {ital The American Physical Society}
Close pairs of relative equilibria for identical point vortices
DEFF Research Database (Denmark)
Dirksen, Tobias; Aref, Hassan
2011-01-01
Numerical solution of the classical problem of relative equilibria for identical point vortices on the unbounded plane reveals configurations that are very close to the analytically known, centered, symmetrically arranged, nested equilateral triangles. New numerical solutions of this kind are found...... also has this property, and new relative equilibria close to the nested, symmetrically arranged, regular heptagons have been found. The centered regular nonagon is also marginally stable. Again, a new family of close relative equilibria has been found. The closest relative equilibrium pairs occur...
Quantized Vortices and Four-Component Superfluidity of Semiconductor Excitons.
Anankine, Romain; Beian, Mussie; Dang, Suzanne; Alloing, Mathieu; Cambril, Edmond; Merghem, Kamel; Carbonell, Carmen Gomez; Lemaître, Aristide; Dubin, François
2017-03-24
We study spatially indirect excitons of GaAs quantum wells, confined in a 10 μm electrostatic trap. Below a critical temperature of about 1 K, we detect macroscopic spatial coherence and quantized vortices in the weak photoluminescence emitted from the trap. These quantum signatures are restricted to a narrow range of density, in a dilute regime. They manifest the formation of a four-component superfluid, made by a low population of optically bright excitons coherently coupled to a dominant fraction of optically dark excitons.
Sound Generation in the Interaction of Two Isentropic Vortices
2012-02-02
difference in their spacial scales. Mu = −0.8, Md = 0.25, d = 2.2, rcu = 1 and rcd = 0.2. 11 X S o u n d P re ss u re -200 -100 0 100 200 -0.0004 -0.0002 0...counter-rotating vortices in the case of Mu = −0.5, Md = 0.5, d = 2.2, rcu = 1 and rcd = 0.2. References [1] Lighthill M. J. (1952). On sound generated
The numerical solution of the vorticity transport equation
Dennis, S C R
1973-01-01
A method of approximating the two-dimensional vorticity transport equation in which the matrix associated with the difference equations is diagonally dominant and the truncation error is the same as that of the fully central-difference approximation, is discussed. An example from boundary layer theory is given by calculating the viscous stagnation point flow at the nose of a cylinder. Some new solutions of the Navier-Stokes equations are obtained for symmetrical flow past a flat plate of finite length. (16 refs).
Spins in the vortices of a high-temperature superconductor
DEFF Research Database (Denmark)
Lake, B.; Aeppli, G.; Clausen, K.N.
2001-01-01
Neutron scattering is used to characterize the magnetism of the vortices for the optimally doped high-temperature superconductor La2-xSrxCuO4 (x = 0.163) in an applied magnetic field. As temperature is reduced, Low-frequency spin fluctuations first disappear with the loss of vortex mobility......, but then reappear. We find that the vortex state can be regarded as an inhomogeneous mixture of a superconducting spin fluid and a material containing a nearly ordered antiferromagnet. These experiments show that as for many other properties of cuprate superconductors, the important underlying microscopic forces...
Dynamical properties of vortical structures on the beta-plane
DEFF Research Database (Denmark)
Sutyrin, G.G.; Hesthaven, J.S.; Lynov, Jens-Peter;
1994-01-01
into a rotating tripole. A critical value of the vortex intensity is found, below which the tripolar structure does not appear even in the case of an initially shielded vortex. Weak monopolar vortices are able to trap particles and provide some west-meridional fluid transport, even in the case when they decay...... with a decaying amplitude (meridional case), thereby carrying trapped particles predominantly eastward. A steady state is not reached if the dipole intensity is below a critical value which depends on the initial direction of propagation. Weak dipoles either decay and shrink owing to Rossby wave radiation...
How can vorticity be produced in irrotationally forced flows?
Del Sordo, Fabio
2010-01-01
A spherical hydrodynamical expansion flow can be described as the gradient of a potential. In that case no vorticity should be produced, but several additional mechanisms can drive its production. Here we analyze the effects of baroclinicity, rotation and shear in the case of a viscous fluid. Those flows resemble what happens in the interstellar medium. In fact in this astrophysical environment supernovae explosion are the dominant flows and, in a first approximation, they can be seen as spherical. One of the main difference is that in our numerical study we examine only weakly supersonic flows, while supernovae explosions are strongly supersonic.
Shock Wave Induced Separation Control by Streamwise Vortices
Institute of Scientific and Technical Information of China (English)
Ryszard SZWABA
2005-01-01
Control of shock wave and boundary layer interaction finds still a lot of attention. Methods of this interaction control have been especially investigated in recent decade. This research was mostly concerned with flows without separation. However, in many applications shock waves induce separation often leads to strong unsteady effects. In this context it is proposed to use streamwise vortices for the interaction control. The results of experimental investigations are presented here. The very promising results were obtained, meaning that the incipient separation was postponed and the separation size was reduced for the higher Mach numbers. The decrease of the RMS of average shock wave oscillation was also achieved.
First characterization of coherent optical vortices from harmonic undulator radiation.
Hemsing, E; Dunning, M; Hast, C; Raubenheimer, T; Xiang, Dao
2014-09-26
We describe the experimental generation and measurement of coherent light that carries orbital angular momentum from a relativistic electron beam radiating at the second harmonic of a helical undulator. The measured helical phase of the light is shown to be in agreement with predictions of the sign and magnitude of the phase singularity and is more than 2 orders of magnitude greater than the incoherent signal. Our setup demonstrates that such optical vortices can be produced in modern free-electron lasers in a simple afterburner arrangement for novel two-mode pump-probe experiments.
Energy Density of Vortices in the Schroedinger Picture
Laenge, J D; Reinhardt, H
2003-01-01
The one-loop energy density of an infinitely thin static magnetic vortex in SU(2) Yang-Mills theory is evaluated using the Schroedinger picture. Both the gluonic fluctuations as well as the quarks in the vortex background are included. The energy density of the magnetic vortex is discussed as a function of the magnetic flux. The center vortices correspond to local minima in the effective potential. These minima are degenerated with the perturbative vacuum if the fermions are ignored. Inclusion of fermions lifts this degeneracy, raising the vortex energy above the energy of the perturbative vacuum.
Targeted mixing in an array of alternating vortices.
Bachelard, R; Benzekri, T; Chandre, C; Leoncini, X; Vittot, M
2007-10-01
Transport and mixing properties of passive particles advected by an array of vortices are investigated. Starting from the integrable case, it is shown that a special class of perturbations allows one to preserve separatrices which act as effective transport barriers, while triggering chaotic advection. In this setting, mixing within the two dynamical barriers is enhanced while long range transport is prevented. A numerical analysis of mixing properties depending on parameter values is performed; regions for which optimal mixing is achieved are proposed. Robustness of the targeted mixing properties regarding errors in the applied perturbation are considered, as well as slip/no-slip and/or boundary conditions for the flow.
Institute of Scientific and Technical Information of China (English)
CAI Shuqun; ZHENG Shu; HE Yinghui
2012-01-01
Based on the EOF analyses of Absolute Dynamic Topography satellite data,it is found that,in summer,the northern South China Sea (SCS) is dominated by an anticyclonic gyre whilst by a cyclonic one in winter.A connected single-layer and two-layer model is employed here to investigate the dynamic mechanism of the circulation in the northern SCS.Numerical experiments show that the nonlinear term,the pressure torque and the planetary vorticity advection play important roles in the circulation of the northern SCS,whilst the contribution by seasonal wind stress curl is local and limited.Only a small part of the Kuroshio water intrudes into the SCS,it then induces a positive vorticity band extending southwestward from the west of the Luzon Strait (LS) and a negative vorticity band along the 200 m isobath of the northern basin.The positive vorticity field induced by the local summer wind stress curl is weaker than that induced in winter in the northern SCS.Besides the Kuroshio intrusion and monsoon,the water transports via the Sunda Shelf and the Sibutu Passage are also important to the circulation in the northern SCS,and the induced vorticity field in summer is almost contrary to that in winter.The strength variations of these three key factors (Kuroshio,monsoon and the water transports via the Sunda Shelf and the Sibutu Passage) determine the seasonal variations of the vorticity and eddy fields in the northern SCS.As for the water exchange via the LS,the Kuroshio intrusion brings about a net inflow into the SCS,and the monsoon has a less effect,whilst the water transports via the Snnda Shelf and the Sibutu Passage are the most important influencing factors,thus,the water exchange of the SCS with the Pacific via the LS changes dramatically from an outflow of the SCS in summer to an inflow into the SCS in winter.
Nonlinear Sigma Models with Compact Hyperbolic Target Spaces
Gubser, Steven; Schoenholz, Samuel S; Stoica, Bogdan; Stokes, James
2015-01-01
We explore the phase structure of nonlinear sigma models with target spaces corresponding to compact quotients of hyperbolic space, focusing on the case of a hyperbolic genus-2 Riemann surface. The continuum theory of these models can be approximated by a lattice spin system which we simulate using Monte Carlo methods. The target space possesses interesting geometric and topological properties which are reflected in novel features of the sigma model. In particular, we observe a topological phase transition at a critical temperature, above which vortices proliferate, reminiscent of the Kosterlitz-Thouless phase transition in the $O(2)$ model. Unlike in the $O(2)$ case, there are many different types of vortices, suggesting a possible analogy to the Hagedorn treatment of statistical mechanics of a proliferating number of hadron species. Below the critical temperature the spins cluster around six special points in the target space known as Weierstrass points. The diversity of compact hyperbolic manifolds suggest...
Aerodynamic forces and vortical structures in flapping butterfly's forward flight
Yokoyama, Naoto; Senda, Kei; Iima, Makoto; Hirai, Norio
2013-02-01
Forward flights of a bilaterally symmetrically flapping butterfly modeled as a four-link rigid-body system consisting of a thorax, an abdomen, and left and right wings are numerically simulated. The joint motions of the butterflies are adopted from experimental observations. Three kinds of the simulations, distinguished by ways to determine the position and attitude of the thorax, are carried out: a tethered simulation, a prescribed simulation, and free-flight simulations. The upward and streamwise forces as well as the wake structures in the tethered simulation, where the thorax of the butterfly is fixed, reasonably agree with those in the corresponding tethered experiment. In the prescribed simulation, where the thoracic trajectories as well as the joint angles are given by those observed in a free-flight experiment, it is confirmed that the butterfly can produce enough forces to achieve the flapping flights. Moreover, coherent vortical structures in the wake and those on the wings are identified. The generation of the aerodynamic forces due to the vortical structures are also clarified. In the free-flight simulation, where only the joint angles are given as periodic functions of time, it is found that the free flight is longitudinally unstable because the butterfly cannot maintain the attitude in a proper range. Focusing on the abdominal mass, which largely varies owing to feeding and metabolizing, we have shown that the abdominal motion plays an important role in periodic flights. The necessity of control of the thoracic attitude for periodic flights and maneuverability is also discussed.
Survival and Structure of Dusty Vortices in Protoplanetary Discs
Crnkovic-Rubsamen, Ivo; Stone, James M
2015-01-01
We have studied the impact of dust feedback on the survival and structure of vortices in protoplanetary discs using 2-D shearing box simulations with Lagrangian dust particles. We consider dust with a variety of sizes (stopping time $t_s = 10^{-2}\\Omega^{-1} - 10^{2}\\Omega^{-1}$, from fully coupled with the gas to the decoupling limit. We find that a vortex is destroyed by dust feedback when the total dust-to-gas mass ratio within the vortex is larger than 30-50%, independent of the dust size. The dust distribution can still be asymmetric in some cases after the vortex has been destroyed. With smaller amounts of dust, a vortex can survive for at least 100 orbits, and the maximum dust surface density within the vortex can be more than 100 times larger than the gas surface density, potentially facilitating planetesimal formation. On the other hand, in these stable vortices, small ($t_s \\Omega^{-1}$) dust grains concentrate differently and affect the gas dynamics in different ways. The distribution of large dus...
Hamiltonian Dynamics of Several Rigid Bodies Interacting with Point Vortices
Weißmann, Steffen
2014-04-01
We derive the dynamics of several rigid bodies of arbitrary shape in a two-dimensional inviscid and incompressible fluid, whose vorticity is given by point vortices. We adopt the idea of Vankerschaver et al. (J. Geom. Mech. 1(2): 223-226, 2009) to derive the Hamiltonian formulation via symplectic reduction from a canonical Hamiltonian system. The reduced system is described by a noncanonical symplectic form, which has previously been derived for a single circular disk using heavy differential-geometric machinery in an infinite-dimensional setting. In contrast, our derivation makes use of the fact that the dynamics of the fluid, and thus the point vortex dynamics, is determined from first principles. Using this knowledge we can directly determine the dynamics on the reduced, finite-dimensional phase space, using only classical mechanics. Furthermore, our approach easily handles several bodies of arbitrary shape. From the Hamiltonian description we derive a Lagrangian formulation, which enables the system for variational time integrators. We briefly describe how to implement such a numerical scheme and simulate different configurations for validation.
Helical vortices generated by flapping wings of bumblebees
Farge, Marie; Engels, Thomas; Kolomenskiy, Dmitry; Schneider, Kai; Lehmann, Fritz; Sesterhenn, Jörn
2016-11-01
We analyze high resolution numerical simulation data of a bumblebee with fixed body and prescribed wing motion, flying in a numerical wind tunnel, presented in. The inflow condition of the tunnel varies from unperturbed laminar to strongly turbulent. The flow generated by the flapping wings indicates the important role of the leading edge vortex (LEV), responsible for elevated lift production and which is not significantly altered by the inflow turbulence. The LEV has a conical structure due to the three-dimensional motion of the wings. This flow configuration produces strong vorticity on the sharp leading edge and the outwards velocity (from the root to the tip of the wing) in the spanwise direction. Flow visualizations show that the generated vortical structures are characterized by a strong helicity. We study the evolution of the mean helicity for each wing and analyze the impact of turbulent inflow. We thankfully acknowledge financial support from the French-German AIFIT project funded by DFG and ANR (Grant 15-CE40-0019). DK gratefully acknowledges financial support from the JSPS postdoctoral fellowship.
Optical vortices as potential indicators of biophysical dynamics
Majumdar, Anindya; Kirkpatrick, Sean J.
2017-03-01
Laser speckle patterns are granular patterns produced as a result of random interference of light waves. Optical vortices (OVs) are phase singularities in such speckle fields, characterized by zero intensity and an undefined phase. Decorrelation of the speckle fields causes these OVs to move in both time and space. In this work, a variety of parameters of these OVs have been studied. The speckle fields were simulated to undergo three distinct decorrelation behaviors- Gaussian, Lorentzian and constant decorrelations. Different decorrelation behaviors represent different dynamics. For example, Lorentzian and Gaussian decorrelations represent Brownian and ordered motions, respectively. Typical dynamical systems in biophysics are generally argued to be a combination of these. For each of the decorrelation behaviors under study, the vortex trails were tracked while varying the rate of decorrelation. Parameters such as the decorrelation length, average trail length and the deviation of the vortices as they traversed in the speckle field, were studied. Empirical studies were also performed to define the distinction between trails arising from different speckle decorrelation behaviors. The initial studies under stationary speckle fields were followed up by similar studies on shifting fields. A new idea to employ Poincaŕe plots in speckle analysis has also been introduced. Our studies indicate that tracking OVs can be a potential method to study cell and tissue dynamics.
Borneo Vortices: A case study and its relation to climatology
Braesicke, P.; Ooi, S. H.; Samah, A. A.
2012-04-01
Borneo vortices (BVs) develop over the South China Sea and are main drivers for the formation of deep convection and heavy rainfall in East Malaysia. We present a case study of a cold-surge-induced BV during January 2010 in which the export of potential energy lead to a strengthening of the subtropical jet. Potential vorticity (PV) and water vapour analyses confirm a significant impact of the BV on upper tropospheric composition. Dry, high PV air is found far below 100 hPa in the vicinty of the vortex. Using a PV threshold analysis of ERA-Interim data we construct a climatological composite of similar events and characterise the thermal, dynamical and composition structure of a 'typical' BV. We note the preferential formation of BVs during ENSO cold conditions and show that two effects contribute to the formation of the dry upper layer above a BV: Air is vertically transported upwards in the BV whilst precipitating and the large scale flow in which the BV is embedded advect dry, ozone rich air from the equatorial TTL over the BV. Thus the occurence frequency of BVs is important for the regional variability of upper tropospheric/lower stratospheric composition.
Metastable States of Josepshon Vortices: Thermal Processes and Quantum Effects
Wallraff, A.; Kemp, A.; Koval, Yu.; Ustinov, A. V.; Fistul, M. V.
2001-03-01
We experimentally study the dynamics of a single Josephson vortex in a tilted periodic potential. In the presence of a bias current applied uniformly to a long Josephson junction, metastable vortex-states are induced by the interaction of the vortex with an artificially formed inhomogeneity in the junction, or by shaping the junction subject to a small external magnetic field [1]. At high temperatures, we observe the thermal escape of the vortex out of the metastable state. As temperature and damping is reduced, the macroscopic quantum properties of Josephson vortices, such as energy level quantization and quantum tunneling, are expected to manifest themselves [2,3]. We report on our current experimental work to observe these effects. Our interest in this macroscopic quantum system is related to the possibility of using quantum states of Josephson vortices for performing quantum computation. We have suggested that a vortex trapped in a double-well potential in a narrow long junction can be used as a scalable and well-controllable qubit [1]. [1] A. Wallraff et al. , J. Low Temp. Phys. J. Low Temp. Phys. 188, 543 (2000). [2] T. Kato and M. Imada, J. Phys. Soc. Japan 65, 2963 (1996). [3] A. Shnirman, E. Ben-Jacob, and B. Malomed, Phys. Rev. B 56, 14677 (1997).
Management of Vortices Trailing Flapped Wings via Separation Control
Greenblatt, David
2005-01-01
A pilot study was conducted on a flapped semi-span model to investigate the concept and viability of near-wake vortex management via separation control. Passive control was achieved by means of a simple fairing and active control was achieved via zero mass-flux blowing slots. Vortex sheet strength, estimated by integrating surface pressure ports, was used to predict vortex characteristics by means of inviscid rollup relations. Furthermore, vortices trailing the flaps were mapped using a seven-hole probe. Separation control was found to have a marked effect on vortex location, strength, tangential velocity, axial velocity and size over a wide range of angles of attack and control conditions. In general, the vortex trends were well predicted by the inviscid rollup relations. Manipulation of the separated flow near the flap edges exerted significant control over both outboard and inboard edge vortices while producing negligible lift excursions. Dynamic separation and attachment control was found to be an effective means for dynamically perturbing the vortex from arbitrarily long wavelengths down to wavelengths less than a typical wingspan. In summary, separation control has the potential for application to time-independent or time-dependent wake alleviation schemes, where the latter can be deployed to minimize adverse effects on ride-quality and dynamic structural loading.
Formation And Ingestion Of Vortices Into Jet Engines During Operation
Hua, Ho Wei; Jermy, Mark
2009-01-01
Vortices can be produced and ingested into the intake of a turbofan and turbojet aero engine during high power operation near solid surfaces. This can happen either on the runway during take-off or during engine test runs in a test cell. The vortex can throw debris into the intake or cause the compressor to stall causing significant damage to the engine and may require major overhaul. The ability to predict the onset of a vortex is therefore extremely valuable to the industry and could potentially save millions of dollars in overhaul costs. The factors that determines whether or not a vortex forms include engine thrust level, geometric factors such as the distance between the engine core and the ground and the size of the engine core, and flow conditions such as ambient vorticity and height of boundary layer. Computational fluid dynamic studies have been carried out by the authors to attempt to predict the effects that these factors have on the threshold of vortex formation. These works include the first reported studies of numerical predictions of the vortex formation threshold on both the runway or test cell scenarios and include factors that have not been previously studied either numerically or experimentally.
Geometric phase mediated topological transport of sound vortices
Wang, Shubo; Chan, C T
2016-01-01
When a physical system undergoes a cyclic evolution, a non-integrable phase can arise in addition to the normal dynamical phase. This phase, depending only on the geometry of the path traversed in the parameter space and hence named geometric phase, has profound impact in both classical and quantum physics, leading to exotic phenomena such as electron weak anti-localization and light spin-Hall effect. Experimental observations of the geometric phase effect in classical system are typically realized using vector waves such as light characterized by a polarization. We show here that such an effect can also be realized in scalar wave systems such as sound wave. Using a helical hollow waveguide, we show that the geometric phase effect associated with the transportation of sound vortices, i.e. sound wave carrying intrinsic orbital angular momentum, can serve as a potential mechanism to control the flow of sound vortices with different topological charges, resulting in geometric phase-based sound vortex filters.
Thermoconvective vortices in a cylindrical annulus with varying inner radius.
Castaño, D; Navarro, M C; Herrero, H
2014-12-01
This paper shows the influence of the inner radius on the stability and intensity of vertical vortices, qualitatively similar to dust devils and cyclones, generated in a cylindrical annulus non-homogeneously heated from below. Little relation is found between the intensity of the vortex and the magnitude of the inner radius. Strong stable vortices can be found for both small and large values of the inner radius. The Rankine combined vortex structure, that characterizes the tangential velocity in dust devils, is clearly observed when small values of the inner radius and large values of the ratio between the horizontal and vertical temperature differences are considered. A contraction on the radius of maximum azimuthal velocity is observed when the vortex is intensified by thermal mechanisms. This radius becomes then nearly stationary when frictional force balances the radial inflow generated by the pressure drop in the center, despite the vortex keeps intensifying. These results connect with the behavior of the radius of the maximum tangential wind associated with a hurricane.
Melt pool vorticity in deep penetration laser material welding
Indian Academy of Sciences (India)
N Kumar; S Dash; A K Tyagi; Baldev Raj
2011-04-01
In the present study, the vorticity of melt motion in the keyhole and weld pool has been evaluated in case of high power CO2 laser beam welding. The circulation of vorticity is obtained as a function of Reynolds number for a given keyhole volume which is linked to Mach number variation. The shear stress and thermal ﬂuxes present in the turbulent pool are linked to diffusivity and Prandtl number variation. It was shown that below a critical value of Rayleigh number, the conduction mode of melt transfer signifying beam absorption becomes dominant. Above this value, convective heat transfer indicates melting and evaporation occurring in the weld pool during laser welding. The evaporative recoil pressure expels the liquid while surface tension and hydrostatic pressure help to retain the melt in the keyhole cavity in this high power laser beam welding. The understanding of several hydrodynamic phenomena occuring in the weld pool is valuable not only for understanding basic mechanistic aspects but also for process optimization involved in laser beam welding.
Scanning Tunnelling Spectroscopy of Vortices with Normal and Superconducting tips
Rodrigo, J. G.; Suderow, H.; Vieira, S.
Scanning tunnelling microscopy and spectroscopy (STM/S) has proved to be a powerful tool to study superconductivity down to atomic level. Vortex lattice studies require characterizing areas of enough size to contain a large number of vortices. On the other hand, it is necessary to combine this capability with high spectroscopic and microscopic resolution. This is a fundamental aspect to measure and detect the subtle changes appearing inside and around a single vortex. We report in this chapter our approach to the use of STM/S, using normal and superconducting tips, to observe the lattice of vortices in several compounds, and the information acquired inside these fascinating entities. The combination of superconducting tips and scanning tunneling spectroscopy, (ST)2S, presents advantages for the study of superconducting samples. It allows to distinguish relevant features of the sample density of states, which manifest itself as small changes in the Josephson coupling between sample and tip condensates, and it has also shown to be very efficient in the study of the ferromagnetic-superconductor transition in the re-entrant superconductor ErRh4B4.
EFT for Vortices with Dilaton-dependent Localized Flux
Burgess, C P; Williams, M
2015-01-01
We study how codimension-two objects like vortices back-react gravitationally with their environment in theories (such as 4D or higher-dimensional supergravity) where the bulk is described by a dilaton-Maxwell-Einstein system. We do so both in the full theory, for which the vortex is an explicit classical `fat brane' solution, and in the effective theory of `point branes' appropriate when the vortices are much smaller than the scales of interest for their back-reaction (such as the transverse Kaluza-Klein scale). We extend the standard Nambu-Goto description to include the physics of flux-localization wherein the ambient flux of the external Maxwell field becomes partially localized to the vortex, generalizing the results of a companion paper to include dilaton-dependence for the tension and localized flux. In the effective theory, such flux-localization is described by the next-to-leading effective interaction, and the boundary conditions to which it gives rise are known to play an important role in how (and...
Axisymmetrically Tropical Cyclone-like Vortices with Secondary Circulations
Sun, Liang
2013-01-01
The secondary circulation of the tropical cyclone (TC) is related to its formation and intensification, thus becomes very important in the studies. The analytical solutions have both the primary and secondary circulation in a three-dimensionally nonhydrostatic and adiabatic model. We prove that there are three intrinsic radiuses for the axisymmetrically ideal incompressible flow. The first one is the radius of maximum primary circular velocity $r_m$. The second one is radius of the primary kernel $r_k>r_m$, across which the vorticity of the primary circulation changes sign and the vertical velocity changes direction. The last one is the radius of the maximum primary vorticity $r_d$, at which the vertical flow of the secondary circulation approaches its maximum, and across which the radius velocity changes sign. The first TC-like vortex solution has universal inflow or outflow. The relations between the intrinsic length scales are $r_k=\\sqrt{2}r_m$ and $r_d=2r_m$. The second one is a multi-planar solution, per...
Classification of hemispheric monthly mean stratospheric potential vorticity fields
Directory of Open Access Journals (Sweden)
R. Huth
Full Text Available Monthly mean NCEP reanalysis potential vorticity fields at the 650 K isentropic level over the Northern and Southern Hemispheres between 1979 and 1997 were studied using multivariate analysis tools. Principal component analysis in the T-mode was applied to demonstrate the validity of such statistical techniques for the study of stratospheric dynamics and climatology. The method, complementarily applied to both the raw and anomaly fields, was useful in determining and classifying the characteristics of winter and summer PV fields on both hemispheres, in particular, the well-known differences in the behaviour and persistence of the polar vortices. It was possible to identify such features as sudden warming events in the Northern Hemisphere and final warming dates in both hemispheres. The stratospheric impact of other atmospheric processes, such as volcanic eruptions, also identified though the results, must be viewed at this stage as tentative. An interesting change in behaviour around 1990 was detected over both hemispheres.
Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; general circulation; climatology
Rajasekar, Shanmuganathan
2016-01-01
This introductory text presents the basic aspects and most important features of various types of resonances and anti-resonances in dynamical systems. In particular, for each resonance, it covers the theoretical concepts, illustrates them with case studies, and reviews the available information on mechanisms, characterization, numerical simulations, experimental realizations, possible quantum analogues, applications and significant advances made over the years. Resonances are one of the most fundamental phenomena exhibited by nonlinear systems and refer to specific realizations of maximum response of a system due to the ability of that system to store and transfer energy received from an external forcing source. Resonances are of particular importance in physical, engineering and biological systems - they can prove to be advantageous in many applications, while leading to instability and even disasters in others. The book is self-contained, providing the details of mathematical derivations and techniques invo...
Institute of Scientific and Technical Information of China (English)
1996-01-01
3.1 A Unified Nonlinear Feedback Functional Method for Study Both Control and Synchronization of Spatiotemporal Chaos Fang Jinqing Ali M. K. (Department of Physics, The University of Lethbridge,Lethbridge, Alberta T1K 3M4,Canada) Two fundamental questions dominate future chaos control theories.The first is the problem of controlling hyperchaos in higher dimensional systems.The second question has yet to be addressed:the problem of controlling spatiotemporal chaos in a spatiotemporal system.In recent years, control and synchronization of spatiotemporal chaos and hyperchaos have became a much more important and challenging subject. The reason for this is the control and synchronism of such behaviours have extensive and great potential of interdisciplinary applications, such as security communication, information processing, medicine and so on. However, this subject is not much known and remains an outstanding open.
Energy Technology Data Exchange (ETDEWEB)
Wilczek, M; Friedrich, R [Institute for Theoretical Physics, University of Muenster, Wilhelm-Klemm-Str. 9, 48149 Muenster (Germany); Kadoch, B [Aix-Marseille Universite and M2P2-CNRS Ecole Centrale de Marseille, 38 Rue Joliot-Curie, 13451 Marseille Cedex 20 (France); Schneider, K [M2P2-CNRS and CMI, Universite de Provence, 39 Rue Joliot-Curie, 13453 Marseille Cedex 13 (France); Farge, M, E-mail: mwilczek@uni-muenster.de [LMD-CNRS, Ecole Normale Superieure, 24 Rue Lhomond, 75231 Paris Cedex 5 (France)
2011-12-22
We study the conditional balance of vortex stretching and vorticity diffusion of fully developed three-dimensional homogeneous isotropic turbulence with respect to coherent and incoherent flow contributions. This decomposition is achieved by the Coherent Vorticity Extraction based on orthogonal wavelets applied to DNS data, which yields insights into the influence of the different contributions as well as their interaction.
Imparting small vorticity to a Bianchi type-VIh empty spacetime
Batakis, Nikos A.
1981-04-01
We present and briefly discuss a Bianchi type-VIh empty spacetime. The field equations have been solved after being linearized with respect to a parameter which imparts vorticity to the model. The limit of zero vorticity is an already known solution.
Controlled Flow Distortion in an Offset Diffuser using Hybrid Trapped Vorticity
Burrows, T. J.; Vukasinovic, B.; Glezer, A.
2016-11-01
Trapped vorticity concentration engendered by deliberate modification of the internal surface of an offset diffuser is coupled with a spanwise array of surface-integrated fluidic-oscillating jets for hybrid flow control of streamwise vorticity concentrations that dominate the base flow and give rise to flow distortions at the engine inlet. The local and global characteristics of the diffuser flow in the absence and presence of the actuation are investigated at Mach numbers up to M = 0.7, using surface oil-flow visualization and pressure distributions, and particle image velocimetry. It is shown that two sources of streamwise vorticity dominate the base flow distortion, namely, corner and a central pair of counter-rotating vortices. The present investigations demonstrate that the actuation affects the topology, strength and scale of the trapped vorticity and thereby its coupling to and interaction with the counter rotating streamwise vortices, where the central vortex pair becomes fully suppressed. As a result, the actuation significantly alters the evolution of the flow within the diffuser, and leads to significant suppression of pressure distortion at the engine inlet (by about 80%) at actuation level that is less than 0.7% of the diffuser's mass flow rate. These findings indicate the utility of hybrid trapped vorticity actuation for mitigating adverse effects of secondary vorticity concentrations formed by local separation and corner flows. Supported by ONR.
Evidence for the movement of macro-vortices on high critical temperature superconductors
Galán, Guillermo Briones; Quelle, Iria; Gonzalez-Jorge, Higinio; Romani, Luis; Domarco, Gerardo
2016-10-01
In this work, a procedure for inserting currents in rings and their respective vortices was developed. The current circulating around the ring was determined by measuring the magnetic field in its axis. Current and vortices were separated by eliminating the current using a resistor placed in the section through which the whole current circulates. The vortices undergo a Lorentz force traveling over the superconducting net and it dissipate energy. This movement is interrupted by the obstacles found on their way (pinning) and can be seen on the decaying curves especially toward the end of the experiment when the forces get weaker due to the decreasing vortices. This movement of vortices was evidenced by resorting to a long time, during which the vortices have come to a stop. The vortices amount was manipulated by means of the injection of anti-vortices that allowed us to eliminate part of them. This allowed us to observe the decrease in travel speed and the dissipation of energy.
Formation mechanism of hairpin vortices in the wake of a truncated square cylinder in a duct
Dousset, Vincent
2010-01-01
We investigate the laminar shedding of hairpin vortices in the wake of a truncated square cylinder placed in a duct, for Reynolds numbers around the critical threshold of the onset of vortex shedding. We single out the formation mechanism of the hairpin vortices by means of a detailed analysis of the flow patterns in the steady regime. We show that unlike in previous studies of similar structures, the dynamics of the hairpin vortices is entwined with that of the counter-rotating pair of streamwise vortices, which we found to be generated in the bottom part of the near wake (these are usually referred to as base vortices). In particular, once the hairpin structure is released, the base vortices attach to it, forming its legs, so these are streamwise, and not spanwise as previously observed in unconfined wakes or behind cylinders of lower aspect ratios. We also single out a trail of Omega-shaped vortices, generated between successive hairpin vortices through a mechanism that is analogous to that active in near-...
Diagnostic study on the relation between ozone and vorticity potential
Energy Technology Data Exchange (ETDEWEB)
Abdel Basset, H. [Department of Astronomy and Meteorology, Faculty of Science, Al Azhar University, Nasr City, Cairo (Egypt); Gahein, A. [Egyptian Meteorological Authority, Cairo (Egypt)
2003-04-01
A diagnostic analysis of a Mediterranean system and the associated tropopause folding for the period 27 February to 10 March, 1987 is presented. Geopotential height, potential vorticity (PV) and relative humidity distributions were diagnosed. The analysis indicates clear correlation between the development of the cut-off low and the tropopause folding. A series of vertical cross-sections at the ends of the jet streaks demonstrated that a fold could be captured using potential vorticity and relative humidity. Q-vectors were employed to investigate vertical motion in the vicinity of the fold and showed the exact positions of descent corresponding to the fold along the entire length of the jet streak. The analysis also shows that the strong correlation between total ozone and column integrated vorticity potential holds well for all levels. As both quantities are integrals through the atmosphere, this result is consistent with, but does not prove, a high independent linear dependence between ozone and PV. More case studies are needed to assure the high linear dependence between ozone and PV. The maximum transport of ozone from the stratosphere to the troposphere is coinciding with the maximum developing system, and also with the maximum values of PV. [Spanish] Se presenta un analisis diagnostico de un Sistema mediterraneo y del pliegue de la tropopausa asociado durante el periodo del 27 de febrero al 10 de marzo de 1987. Se diagnosticaron la altitud neopotencial, el potencial de vorticidad y la distribucion de la humedad relativa. El analisis indica una correlacion clara entre el desarrollo de la baja segregada y el pliegue de la tropopausa. Una serie de cortes verticales en los extremos de las trazas del chorro demostraron que el pliegue puede ser capturado utilizando el potencial de vorticidad y la humedad relativa. Para investigar la movilidad vertical en la vecindad del pliegue se utilizaron vectores Q, y se demostraron las posiciones exactas de descenso
Analysis of scalar dissipation in terms of vorticity geometry in isotropic turbulence
Gonzalez, Michel
2016-01-01
The mechanisms promoting scalar dissipation through scalar gradient production are scrutinized in terms of vorticity alignment with respect to strain principal axes. For that purpose, a stochastic Lagrangian model for the velocity gradient tensor and the scalar gradient vector is used. The model results show that the major part of scalar dissipation occurs for stretched vorticity, namely when the vorticity vector aligns with the extensional and intermediate strain eigenvectors. More specifically, it appears that the mean scalar dissipation is well represented by the sample defined by alignment with the extensional strain, while the most intense scalar dissipation is promoted by the set of events for which vorticity aligns with the intermediate strain. This difference is explained by rather subtle mechanisms involving the statistics of both the strain intensities and the scalar gradient alignment resulting from these special alignments of vorticity. The analysis allowing for the local flow structure confirms t...
Baroclinic Vorticity Production in Protoplanetary Disks; Part II: Vortex Growth and Longevity
Petersen, M R; Julien, K; Petersen, Mark R.; Stewart, Glen R.; Julien, Keith
2006-01-01
The factors affecting vortex growth in convectively stable protoplanetary disks are explored using numerical simulations of a two-dimensional anelastic-gas model which includes baroclinic vorticity production and radiative cooling. The baroclinic feedback, where anomalous temperature gradients produce vorticity through the baroclinic term and vortices then reinforce these temperature gradients, is found to be an important process in the rate of growth of vortices in the disk. Factors which strengthen the baroclinic feedback include fast radiative cooling, high thermal diffusion, and large radial temperature gradients in the background temperature. When the baroclinic feedback is sufficiently strong, anticyclonic vortices form from initial random perturbations and maintain their strength for the duration of the simulation, for over 600 orbital periods. Based on both simulations and a simple vortex model, we find that the local angular momentum transport due to a single vortex may be inward or outward, dependin...
Numerical and Experimental Study on Negative Buoyance Induced Vortices in N-Butane Jet Flames
Xiong, Yuan
2015-07-26
Near nozzle flow field in flickering n-butane diffusion jet flames was investigated with a special focus on transient flow patterns of negative buoyance induced vortices. The flow structures were obtained through Mie scattering imaging with seed particles in a fuel stream using continuous-wave (CW) Argon-ion laser. Velocity fields were also quantified with particle mage velocimetry (PIV) system having kHz repetition rate. The results showed that the dynamic motion of negative buoyance induced vortices near the nozzle exit was coupled strongly with a flame flickering instability. Typically during the flame flickering, the negative buoyant vortices oscillated at the flickering frequency. The vortices were distorted by the flickering motion and exhibited complicated transient vortical patterns, such as tilting and stretching. Numerical simulations were also implemented based on an open source C++ package, LaminarSMOKE, for further validations.
Proposed Aharonov-Casher interferometry of non-Abelian vortices in chiral p-wave superconductors
Grosfeld, Eytan; Seradjeh, Babak; Vishveshwara, Smitha
2011-03-01
We propose a two-path vortex interferometry experiment based on the Aharonov- Casher effect for detecting the non-Abelian nature of vortices in a chiral p-wave superconductor. The effect is based on observing vortex interference patterns upon enclosing a finite charge of externally controllable magnitude within the interference path. We predict that when the interfering vortices enclose an odd number of identical vortices in their path, the interference pattern disappears only for non-Abelian vortices. When pairing involves two distinct spin species, we derive the mutual statistics between half quantum and full quantum vortices and show that, remarkably, our predictions still hold for the situation of a full quantum vortex enclosing a half quantum vortex in its path. We discuss the experimentally relevant conditions under which these effects can be observed. Work supported by ICMT at UIUC, NSERC of Canada, CAS fellowship at UIUC, and the U.S. Department of Energy.
Swirling around filaments: are large-scale structure vortices spinning up dark halos?
Laigle, Clotilde; Codis, Sandrine; Dubois, Yohan; Borgne, Damien le; Pogosyan, Dmitri; Devriendt, Julien; Peirani, Sebastien; Prunet, Simon; Rouberol, Stephane; Slyz, Adrianne; Sousbie, Thierry
2013-01-01
The kinematic analysis of dark matter and hydrodynamical simulations suggests that the vorticity in large-scale structure is mostly confined to, and predominantly aligned with their filaments, with an excess of probability of 20 per cent to have the angle between vorticity and filaments direction lower than 60 degrees relative to random orientations. The cross sections of these filaments are typically partitioned into four quadrants with opposite vorticity sign, arising from multiple flows, originating from neighbouring walls. The spins of halos embedded within these filaments are consistently aligned with this vorticity for any halo mass, with a stronger alignment for the most massive structures up to an excess of probability of 165 per cent. On large scales, adiabatic/cooling hydrodynamical simulations display the same vorticity in the gas as in the dark matter. The global geometry of the flow within the cosmic web is therefore qualitatively consistent with a spin acquisition for smaller halos induced by th...
Features of wavy vortices in a curved channel from experimental and numerical studies
Ligrani, P. M.; Finlay, W. H.; Fields, W. A.; Fuqua, S. J.; Subramanian, C. S.
1992-01-01
Results are reported from an experimental study obtaining evidence of time-dependent, wavy vortex motions associated with undulating and twisting Dean vortices in a curved channel with 40-to-1 aspect ratio, and mild curvature (radius ratio = 0.979). The results are compared with direct numerical simulations of time-dependent 3D Navier-Stokes equations using boundary conditions in the spanwise and streamwise directions. When viewed in cross section, experimental visualizations of undulating and twisting vortex flows show rocking motion and changes in the direction of the flow between vortices that are like those observed in the simulations. Experimental spectra show that undulating vortices are replaced by the higher-frequency, shorter streamwise wavelength twisting vortices at higher Reynolds numbers. When undulating vortices are present, experimental power spectra and visualizations give frequencies that are somewhat lower than the most unstable frequencies predicted by linear stability analysis.
Sharp vorticity gradients in two-dimensional turbulence and the energy spectrum
DEFF Research Database (Denmark)
Kuznetsov, E.A.; Naulin, Volker; Nielsen, Anders Henry;
2010-01-01
Formation of sharp vorticity gradients in two-dimensional (2D) hydrodynamic turbulence and their influence on the turbulent spectra are considered. The analog of the vortex line representation as a transformation to the curvilinear system of coordinates moving together with the di-vorticity lines...... is developed and compressibility of this mapping appears as the main reason for the formation of the sharp vorticity gradients at high Reynolds numbers. In the case of strong anisotropy the sharp vorticity gradients can generate spectra which fall off as k −3 at large k, which appear to take the same form...... as the Kraichnan spectrum for the enstrophy cascade. For turbulence with weak anisotropy the k dependence of the spectrum due to the sharp gradients coincides with the Saffman spectrum: E(k) ~ k −4. Numerical investigations of decaying turbulence reveal exponential growth of di-vorticity with a spatial distributed...
Langfellner, J; Birch, A C
2015-01-01
Flow vorticity is a fundamental property of turbulent convection in rotating systems. Solar supergranules exhibit a preferred sense of rotation, which depends on the hemisphere. This is due to the Coriolis force acting on the diverging horizontal flows. We aim to spatially resolve the vertical flow vorticity of the average supergranule at different latitudes, both for outflow and inflow regions. To measure the vertical vorticity, we use two independent techniques: time-distance helioseismology (TD) and local correlation tracking of granules in intensity images (LCT) using data from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). Both maps are corrected for center-to-limb systematic errors. We find that 8-h TD and LCT maps of vertical vorticity are highly correlated at large spatial scales. Associated with the average supergranule outflow, we find tangential (vortical) flows that reach about 10 m/s in the clockwise direction at 40{\\deg} latitude. In average inflow regio...
Time-distance helioseismology: A new averaging scheme for measuring flow vorticity
Langfellner, Jan; Birch, Aaron C
2014-01-01
Time-distance helioseismology provides information about vector flows in the near-surface layers of the Sun by measuring wave travel times between points on the solar surface. Specific spatial averages of travel times have been proposed for distinguishing between flows in the east-west and north-south directions and measuring the horizontal divergence of the flows. No specific measurement technique has, however, been developed to measure flow vorticity. Here we propose a new measurement technique tailored to measuring the vertical component of vorticity. Fluid vorticity is a fundamental property of solar convection zone dynamics and of rotating turbulent convection in particular. The method consists of measuring the travel time of waves along a closed contour on the solar surface in order to approximate the circulation of the flow along this contour. Vertical vorticity is related to the difference between clockwise and counter-clockwise travel times. We applied the method to characterize the vortical motions ...
Performance of a transverse vorticity probe in a turbulent channel flow
Energy Technology Data Exchange (ETDEWEB)
Zhou, T.; Antonia, R.A.; Zhu, Y. [Newcastle upon Tyne Univ. (United Kingdom). Dept. of Mechanical Engineering; Orlandi, P. [Dipartimento di Meccanica e Aeronautica, Universita Degli Studi di Roma ``La Sapienza``, I-00184 Rome (Italy); Esposito, P. [INSEAN - Istituto Nazionale per Studi ed Esperienze di Architettura Navale, Via di Vallerano 139, I-00128 Rome (Italy)
1998-05-01
The performance of a four hot-wire transverse vorticity probe is tested by comparing measurements in a fully developed turbulent channel flow with corresponding data obtained from direct numerical simulations (DNS) of the same flow. In the inner region, the probe performs poorly, the rms vorticities being consistently smaller than the DNS values. In the outer region of the flow, there is reasonable agreement between measured and DNS vorticity statistics, especially after correcting the measurements for the effect of spatial resolution. In this region, the imbalance indicated by the vorticity form of the streamwise momentum equation is approximately constant. The magnitude of the imbalance can be reduced to an acceptable level of accuracy by considering sources of error which affect the velocity-vorticity correlations. (orig.) With 11 figs., 30 refs.
DEFF Research Database (Denmark)
Hourigan, K.; Rao, A.; Brøns, Morten
2013-01-01
The wake transitions of generic bluff bodies, such as a circular cylinder, near a wall are important because they provide understanding of different transition paths towards turbulence, and give some insight into the effect of surface modifications on the flow past larger downstream structures....... In this article, the fundamentals of vorticity generation and transport for the two-dimensional flow of incompressible Newtonian fluids are initially reviewed. Vorticity is generated only at boundaries by tangential pressure gradients or relative acceleration. After generation, it can cross......-annihilate with opposite-signed vorticity, and can be stored at a free surface, thus conserving the total vorticity, or circulation. Vorticity generation, diffusion and storage are demonstrated for a cylinder translating and rotating near a wall. The wake characteristics and the wake transitions are shown to change...
Nonlinear ion acoustic waves scattered by vortexes
Ohno, Yuji
2015-01-01
The Kadomtsev--Petviashvili (KP) hierarchy is the archetype of infinite-dimensional integrable systems, which describes nonlinear ion acoustic waves in two-dimensional space. This remarkably ordered system resides on a singular submanifold (leaf) embedded in a larger phase space of more general ion acoustic waves (low-frequency electrostatic perturbations). The KP hierarchy is characterized not only by small amplitudes but also by irrotational (zero-vorticity) velocity fields. In fact, the KP equation is derived by eliminating vorticity at every order of the reductive perturbation. Here we modify the scaling of the velocity field so as to introduce a vortex term. The newly derived system of equations consists of a generalized three-dimensional KP equation and a two-dimensional vortex equation. The former describes `scattering' of vortex-free waves by ambient vortexes that are determined by the latter. We say that the vortexes are `ambient' because they do not receive reciprocal reactions from the waves (i.e.,...
Nonlinear Materials Characterization Facility
Federal Laboratory Consortium — The Nonlinear Materials Characterization Facility conducts photophysical research and development of nonlinear materials operating in the visible spectrum to protect...
Coherent vorticity extraction in turbulent boundary layers using orthogonal wavelets
Energy Technology Data Exchange (ETDEWEB)
Khujadze, George; Oberlack, Martin [Chair of Fluid Dynamics, Technische Universitaet Darmstadt (Germany); Yen, Romain Nguyen van [Institut fuer Mathematik, Freie Universitaet Berlin (Germany); Schneider, Kai [M2P2-CNRS and CMI, Universite de Provence, Marseille (France); Farge, Marie, E-mail: khujadze@fdy.tu-darmstadt.de [LMD-IPSL-CNRS, Ecole Normale Superieure, Paris (France)
2011-12-22
Turbulent boundary layer data computed by direct numerical simulation are analyzed using orthogonal anisotropic wavelets. The flow fields, originally given on a Chebychev grid, are first interpolated on a locally refined dyadic grid. Then, they are decomposed using a wavelet basis, which accounts for the anisotropy of the flow by using different scales in the wall-normal direction and in the planes parallel to the wall. Thus the vorticity field is decomposed into coherent and incoherent contributions using thresholding of the wavelet coefficients. It is shown that less than 1% of the coefficients retain the coherent structures of the flow, while the majority of the coefficients corresponds to a structureless, i.e., noise-like background flow. Scale-and direction-dependent statistics in wavelet space quantify the flow properties at different wall distances.
Improvement of a near wake model for trailing vorticity
DEFF Research Database (Denmark)
Pirrung, Georg; Hansen, Morten Hartvig; Aagaard Madsen, Helge
2014-01-01
to temporal discretization, both regarding numerical stability and quality of the results. The modified near wake model is coupled to an aerodynamics model, which consists of a blade element momentum model with dynamic inflow for the far wake and a 2D shed vorticity model that simulates the unsteady buildup......A near wake model, originally proposed by Beddoes, is further developed. The purpose of the model is to account for the radially dependent time constants of the fast aerodynamic response and to provide a tip loss correction. It is based on lifting line theory and models the downwash due to roughly...... the first 90 degrees of rotation. This restriction of the model to the near wake allows for using a computationally efficient indicial function algorithm. The aim of this study is to improve the accuracy of the downwash close to the root and tip of the blade and to decrease the sensitivity of the model...
The effect of dust on the martian polar vortices
Guzewich, Scott D.; Toigo, A. D.; Waugh, D. W.
2016-11-01
The influence of atmospheric dust on the dynamics and stability of the martian polar vortices is examined, through analysis of Mars Climate Sounder observations and MarsWRF general circulation model simulations. We show that regional and global dust storms produce "transient vortex warming" events that partially or fully disrupt the northern winter polar vortex for brief periods. Increased atmospheric dust heating alters the Hadley circulation and shifts the downwelling branch of the circulation poleward, leading to a disruption of the polar vortex for a period of days to weeks. Through our simulations, we find this effect is dependent on the atmospheric heating rate, which can be changed by increasing the amount of dust in the atmosphere or by altering the dust optical properties (e.g., single scattering albedo). Despite this, our simulations show that some level of atmospheric dust is necessary to produce a distinct northern hemisphere winter polar vortex.
Manipulating Josephson junctions in thin-films by nearby vortices
Energy Technology Data Exchange (ETDEWEB)
Kogan, V G; Mints, R G
2014-07-01
It is shown that a vortex trapped in one of the banks of a planar edge-type Josephson junction in a narrow thin-film superconducting strip can change drastically the dependence of the junction critical current on the applied field, I-c(H). When the vortex is placed at certain discrete positions in the strip middle, the pattern I-c(H) has zero at H = 0 instead of the traditional maximum of '0-type' junctions. The number of these positions is equal to the number of vortices trapped at the same location. When the junction-vortex separation exceeds similar to W, the strip width, I-c(H) is no longer sensitive to the vortex presence. The same is true for any separation if the vortex approaches the strip edges. (C) 2014 Elsevier B.V. All rights reserved.
Footprints of funnel vortices in a turbulent boundary layer
Gurka, Roi; Liberzon, Alex; Hetsroni, Gad
2003-11-01
The topology of large scale funnel structures in a turbulent boundary layer in a flume is investigated experimentally. The large scale structure is reconstructed from the proper orthogonal decomposition (POD) eigenmodes, calculated from the two-dimensional projections of the fluctuated vorticity field realizations. The instantaneous two-dimensional velocity field realizations are obtained using Particle Image Velocimetry (PIV) technique. The dominant funnel structure appears to have a longitudinal streamwise orientation, an inclination angle of 8 degrees, streamwise length of 1000 wall units, and a distance between the neighboring structures of about 100 wall units in the spanwise direction. The spatial characteristics of the funnel structure, measured in the streamwise - wall normal plane of the flume, has been found to be independent of the Reynolds number. The identification technique is based on all the data set and provide a statistical descrition of the structure footprint.
Vortices in gauge models at finite density with vector condensates
Gorbar, E V; Miransky, V A; Jia, Junji
2006-01-01
There exists a class of gauge models incorporating a finite density of matter in which the Higgs mechanism is provided by condensates of gauge (or gauge and scalar) fields, i.e., there are vector condensates in this case. We describe vortex solutions in the simplest model in this class, the gauged $SU(2)\\times U(1)_Y$ $\\sigma$-model with the chemical potential for hypercharge $Y$, in which the gauge symmetry is completely broken. It is shown that there are three types of topologically stable vortices in the model, connected either with photon field or hypercharge gauge field, or with both of them. Explicit vortex solutions are numerically found and their energy per unit length are calculated. The relevance of these solutions for the gluonic phase in the dense two-flavor QCD is discussed.
Non-Abelian Vortices with an Aharonov-Bohm Effect
Evslin, Jarah; Nitta, Muneto; Ohashi, Keisuke; Vinci, Walter
2014-01-01
The interplay of gauge dynamics and flavor symmetries often leads to remarkably subtle phenomena in the presence of soliton configurations. Non-Abelian vortices -- vortex solutions with continuous internal orientational moduli -- provide an example. Here we study the effect of weakly gauging a U(1)_R subgroup of the flavor symmetry on such BPS vortex solutions. Our prototypical setting consists of an SU(2) x U(1) gauge theory with N_f=2 sets of fundamental scalars that break the gauge symmetry to an "electromagnetic" U(1). The weak U(1)_R gauging converts the well-known CP1 orientation modulus |B| of the non-Abelian vortex into a parameter characterizing the strength of the magnetic field that is responsible for the Aharonov-Bohm effect. As the phase of B remains a genuine zero mode while the electromagnetic gauge symmetry is Higgsed in the interior of the vortex, these solutions are superconducting strings.
Static vortices in long Josephson junctions of exponentially varying width
Semerdjieva, E. G.; Boyadjiev, T. L.; Shukrinov, Yu. M.
2004-06-01
A numerical simulation is carried out for static vortices in a long Josephson junction with an exponentially varying width. At specified values of the parameters the corresponding boundary-value problem admits more than one solution. Each solution (distribution of the magnetic flux in the junction) is associated to a Sturm-Liouville problem, the smallest eigenvalue of which can be used, in a first approximation, to assess the stability of the vortex against relatively small spatiotemporal perturbations. The change in width of the junction leads to a renormalization of the magnetic flux in comparison with the case of a linear one-dimensional model. The influence of the model parameters on the stability of the states of the magnetic flux is investigated in detail, particularly that of the shape parameter. The critical curve of the junction is constructed from pieces of the critical curves for the different magnetic flux distributions having the highest critical currents for the given magnetic field.
Topological vortices in generalized Born-Infeld-Higgs electrodynamics
Casana, R; Rubiera-Garcia, D; Santos, C dos
2015-01-01
A consistent BPS formalism to study the existence of topological axially symmetric vortices in generalized versions of the Born-Infeld-Higgs electrodynamics is implemented. Such a generalization modifies the field dynamics via introduction of three non-negative functions depending only in the Higgs field, namely, $G(|\\phi|)$, $w(|\\phi|) $ and $V(|\\phi|)$. A set of first-order differential equations is attained when these functions satisfy a constraint related to the Ampere law. Such a constraint allows to minimize the system energy in such way that it becomes proportional to the magnetic flux. Our results provides an enhancement of topological vortex solutions in Born-Infeld-Higgs electrodynamics. Finally, we analyze a set of models such that a generalized version of Maxwell-Higgs electrodynamics is recovered in a certain limit of the theory.
Topological vortices in generalized Born-Infeld-Higgs electrodynamics
Casana, R.; Hora, E. da; Rubiera-Garcia, D.; Santos, C. dos
2015-08-01
A consistent BPS formalism to study the existence of topological axially symmetric vortices in generalized versions of the Born-Infeld-Higgs electrodynamics is implemented. Such a generalization modifies the field dynamics via the introduction of three nonnegative functions depending only in the Higgs field, namely, , , and . A set of first-order differential equations is attained when these functions satisfy a constraint related to the Ampère law. Such a constraint allows one to minimize the system's energy in such way that it becomes proportional to the magnetic flux. Our results provides an enhancement of the role of topological vortex solutions in Born-Infeld-Higgs electrodynamics. Finally, we analyze a set of models entailing the recovery of a generalized version of Maxwell-Higgs electrodynamics in a certain limit of the theory.
Stationary Vortices and Pair Currents in a Trapped Fermion Superfluid
Capuzzi, P.; Hernández, E. S.; Szybisz, L.
2015-05-01
We examine the effects of stationary vortices in superfluid Li atoms at zero temperature in the frame of the recently developed fluiddynamical scheme, that includes the pair density and its associated pair current and pair kinetic energy in addition to the fields appearing in the hydrodynamical description of normal fluids. In this frame, the presence of any particle velocity field gives rise to the appearance of a pair current. As an illustration, we consider a stationary vortex with cylindrical geometry in an unpolarized fluid, and examine the effects of the rotational velocity field on the spatial structure of the equilibrium gap and the profiles of the pair current. We show that the latter is intrinsically complex and its imaginary part is the source of a radial drift for the velocity field. We discuss the consequences on the stationary regime.
Topological vortices in generalized Born-Infeld-Higgs electrodynamics
Energy Technology Data Exchange (ETDEWEB)
Casana, R. [Universidade Federal do Maranhao, Departamento de Fisica, Sao Luis, Maranhao (Brazil); Hora, E. da [Universidade Federal do Maranhao, Departamento de Fisica, Sao Luis, Maranhao (Brazil); Universidade Federal do Maranhao, Coordenadoria Interdisciplinar de Ciencia e Tecnologia, Sao Luis, Maranhao (Brazil); Rubiera-Garcia, D. [Fudan University, Department of Physics, Center for Field Theory and Particle Physics, Shanghai (China); Santos, C. dos [Faculdade de Ciencias da Universidade do Porto, Centro de Fisica e Departamento de Fisica e Astronomia, Porto (Portugal)
2015-08-15
A consistent BPS formalism to study the existence of topological axially symmetric vortices in generalized versions of the Born-Infeld-Higgs electrodynamics is implemented. Such a generalization modifies the field dynamics via the introduction of three nonnegative functions depending only in the Higgs field, namely,G(vertical stroke φ vertical stroke), w(vertical stroke φ vertical stroke), and V (vertical stroke φ vertical stroke). A set of first-order differential equations is attained when these functions satisfy a constraint related to the Ampere law. Such a constraint allows one to minimize the system's energy in such way that it becomes proportional to the magnetic flux. Our results provides an enhancement of the role of topological vortex solutions in Born-Infeld-Higgs electrodynamics. Finally, we analyze a set of models entailing the recovery of a generalized version of Maxwell-Higgs electrodynamics in a certain limit of the theory. (orig.)
The influence of trailed vorticity on flutter speed estimations
DEFF Research Database (Denmark)
Pirrung, Georg; Aagaard Madsen, Helge; Kim, Taeseong
2014-01-01
. The influence of the near wake model on the aeroelastic stability of the blades of the NREL 5 MW turbine in overspeed conditions is investigated in the second part of the paper. The analysis is based on a runaway case in which the turbine is free to speed up without generator torque and vibrations start...... building up at a critical rotor speed. Blades with modified torsional and flapwise stiffness are also investigated. A flutter analysis is often part of the stability investigations for new blades but is normally carried out with engineering models that do not include the influence of unsteady trailed...... vorticity. Including this influence results in a slightly increased safety margin against classical flutter in all simulated cases....
Topology of streamlines and vorticity contours for two - dimensional flows
DEFF Research Database (Denmark)
Andersen, Morten
Considering a coordinate-free formulation of helical symmetry rather than more traditional definitions based on coordinates, we discuss basic properties of helical vector fields and compare results from the literature. For inviscid flow where a velocity field is generated by a sum of helical vortex...... generated by a helical vortex filament in an ideal fluid. The classical expression for the stream function obtained by Hardin (Phys. Fluids 25, 1982) contains an infinite sum of modified Bessel functions. Using the approach by Okulov (Russ. J. Eng. Thermophys. 5, 1995) we obtain a closed-form approximation...... by a point vortex above a wall in inviscid fluid. There is no reason to a priori expect equivalent results of the three vortex definitions. However, the study is mainly motivated by the findings of Kudela & Malecha (Fluid Dyn. Res. 41, 2009) who find good agreement between the vorticity and streamlines...
Destroying a topological quantum bit by condensing Ising vortices.
Hao, Zhihao; Inglis, Stephen; Melko, Roger
2014-12-09
The imminent realization of topologically protected qubits in fabricated systems will provide not only an elementary implementation of fault-tolerant quantum computing architecture, but also an experimental vehicle for the general study of topological order. The simplest topological qubit harbours what is known as a Z2 liquid phase, which encodes information via a degeneracy depending on the system's topology. Elementary excitations of the phase are fractionally charged objects called spinons, or Ising flux vortices called visons. At zero temperature, a Z2 liquid is stable under deformations of the Hamiltonian until spinon or vison condensation induces a quantum-phase transition destroying the topological order. Here we use quantum Monte Carlo to study a vison-induced transition from a Z2 liquid to a valence-bond solid in a quantum dimer model on the kagome lattice. Our results indicate that this critical point is beyond the description of the standard Landau paradigm.
Driven phase space vortices in plasmas with nonextensive velocity distribution
Trivedi, Pallavi; Ganesh, Rajaraman
2017-03-01
The evolution of chirp-driven electrostatic waves in unmagnetized plasmas is numerically investigated by using a one-dimensional (1D) Vlasov-poisson solver with periodic boundary conditions. The initial velocity distribution of the 1D plasma is assumed to be governed by nonextensive q distribution [C. Tsallis, J. Stat. Phys. 52, 479 (1988)]. For an infinitesimal amplitude of an external drive, we investigate the effects of chirp driven dynamics that leads to the formation of giant phase space vortices (PSV) for both Maxwellian (q = 1) and non-Maxwellian ( q ≠ 1 ) plasmas. For non-Maxwellian plasmas, the formation of giant PSV with multiple extrema and phase velocities is shown to be dependent on the strength of "q". Novel features such as "shark"-like and transient "honeycomb"-like structures in phase space are discussed. Wherever relevant, we compare our results with previous work.
Arrays of optical vortices formed by "fork" holograms
Bekshaev, A Ya; Mohammed, K A
2014-01-01
Singular light beams with optical vortices (OV) are often generated by means of thin binary gratings with groove bifurcation ("fork holograms") that produce a set of diffracted beams with different OV charges. Usually, only single separate beams are used and investigated; here we consider the whole set of diffracted OV beams that, at certain conditions, are involved in efficient mutual interference to form a characteristic pattern where the ring-like structure of separate OV beams is replaced by series of bright and dark lines between adjacent diffraction orders. This pattern, well developed for high diffraction orders, reflects the main spatial properties of the diffracted beams as well as of the fork grating used for their generation. In particular, it confirms the theoretical model for the diffracted beams (Kummer beam model) and enables to determine the sign and the absolute value of the phase singularity embedded in the hologram.
Tropical upper tropospheric humidity variations due to potential vorticity intrusions
Sandhya, M.; Sridharan, S.; Indira Devi, M.
2015-09-01
Four cases (March 2009, May 2009, April 2010 and February 2012) are presented in which the ERA-interim relative humidity (RH) shows consistent increase by more than 50 % in the upper troposphere (200-250 hPa) over tropics at the eastward side of the potential vorticity (PV) intrusion region. The increase in RH is confirmed with the spaceborne microwave limb sounder observations and radiosonde observations over Gadanki (13.5° N, 79.2° E) and is observed irrespective of whether the PV intrusions are accompanied by deep convection or not. It is demonstrated that the increase in RH is due to poleward advection induced by the PV intrusions in their eastward side at the upper tropospheric heights. It is suggested that the low-latitude convection, which is not necessarily triggered by the PV intrusion, might have transported water vapour to the upper tropospheric heights.
Scattering of instantons, monopoles and vortices in higher dimensions
Ivanova, Tatiana A
2016-01-01
We consider Yang-Mills theory on manifolds ${\\mathbb R}\\times X$ with a $d$-dimensional Riemannian manifold $X$ of special holonomy admitting gauge instanton equations. Instantons are considered as particle-like solutions in $d+1$ dimensions whose static configurations are concentrated on $X$. We study how they evolve in time when considered as solutions of the Yang-Millsequations on ${\\mathbb R}\\times X$ with moduli depending on time $t\\in{\\mathbb R}$. It is shown that in the adiabatic limit, when the metric in the $X$ direction is scaled down, the classical dynamics of slowly moving instantons corresponds to a geodesic motion in the moduli space $\\cal M$ of gauge instantons on $X$. Similar results about geodesic motion in the moduli space of monopoles and vortices in higher dimensions are briefly discussed.
Microalga propels along vorticity direction in a shear flow
Chengala, Anwar; Hondzo, Miki; Sheng, Jian
2013-05-01
Using high-speed digital holographic microscopy and microfluidics, we discover that, when encountering fluid flow shear above a threshold, unicellular green alga Dunaliella primolecta migrates unambiguously in the cross-stream direction that is normal to the plane of shear and coincides with the local fluid flow vorticity. The flow shear drives motile microalgae to collectively migrate in a thin two-dimensional horizontal plane and consequently alters the spatial distribution of microalgal cells within a given suspension. This shear-induced algal migration differs substantially from periodic rotational motion of passive ellipsoids, known as Jeffery orbits, as well as gyrotaxis by bottom-heavy swimming microalgae in a shear flow due to the subtle interplay between torques generated by gravity and viscous shear. Our findings could facilitate mechanistic solutions for modeling planktonic thin layers and sustainable cultivation of microalgae for human nutrition and bioenergy feedstock.
Hyperbolic spin vortices and textures in exciton-polariton condensates
Manni, F.; Léger, Y.; Rubo, Y. G.; André, R.; Deveaud, B.
2013-10-01
From cosmology to the microscopic scales of the quantum world, the study of topological excitations is essential for the understanding of phase conformation and phase transitions. Quantum fluids are convenient systems to investigate topological entities because well-established techniques are available for their preparation, control and measurement. Across a phase transition, a system dramatically changes its properties because of the spontaneous breaking of certain continuous symmetries, leading to generation of topological defects. In particular, attention is given to entities that involve both spin and phase topologies. Exciton-polariton condensates are quantum fluids combining coherence and spin properties that, thanks to their light-matter nature, bring the advantage of direct optical access to the condensate order parameter. Here we report on the spontaneous occurrence of hyperbolic spin vortices in polariton condensates, by directly imaging both their phase and spin structure, and observe the associated spatial polarization patterns, spin textures that arise in the condensate.
Kinematical vortices in double photoionization of helium by attosecond pulses
DEFF Research Database (Denmark)
Djiokap, J. M. Ngoko; Meremianin, A. V.; Manakov, N. L.
2017-01-01
-order perturbation theory analysis and numerical solutions of the two-electron, time-dependent Schrodinger equation in six spatial dimensions. The helical vortex structures originate from Ramsey interference of a pair of ionized two-electron wave packets, each having a total angular momentum of unity, and appear...... detection geometries. However, the vortex structures only occur when the angular separation beta = cos(-1)((p) over cap (1) . (p) over cap (2)) between the electron momenta p(1) and p(2) is held fixed. The vortex structures can also be observed in the fourfold differential DPI probability distribution...... obtained by averaging the sixfold differential probability over the emission angles of one electron. Such kinematical vortices are a general phenomenon that may occur in any ionization process, initiated by two time-delayed short pulses with opposite ellipticities, for particular detection geometries....
Holographic Three-Dimensional Fluids with Nontrivial Vorticity
Leigh, Robert G; Petropoulos, P Marios
2011-01-01
Three-dimensional fluids with nontrivial vorticity can be described holographically. It is well-known that the Kerr-AdS geometry gives rise to a cyclonic flow. Here we note that Taub--NUT--AdS4 geometries give rise to a rotating fluid with vortex flow. The Randers and Zermelo forms of the boundary metrics provide alternative descriptions of the fluid by inertial co-moving or by accelerated observers. Such fluids possess acoustic horizons. Moreover, light propagation on the boundary Taub--NUT fluid will encounter an optical horizon associated with closed timelike curves. In the latter case the Misner string introduces a multi-valuedness of the scalar fluctuations which can be attributed to the anyonic nature of the boundary vortex.