Nonlinear traveling waves in confined ferrofluids.
Lira, Sérgio A; Miranda, José A
2012-11-01
We study the development of nonlinear traveling waves on the interface separating two viscous fluids flowing in parallel in a vertical Hele-Shaw cell. One of the fluids is a ferrofluid and a uniform magnetic field is applied in the plane of the cell, making an angle with the initially undisturbed interface. We employ a mode-coupling theory that predicts the possibility of controlling the speed of the waves by purely magnetic means. The influence of the tilted magnetic field on the waves shape profile and the establishment of stationary traveling wave structures are investigated. PMID:23214870
Parametrically driven surface waves on viscous ferrofluids
NASA Astrophysics Data System (ADS)
Müller, Hanns Walter
1998-11-01
Standing waves on the surface of a ferrofluid in a normal magnetic field can be excited by a vertical vibration of the container. A stability theory for the onset of these parametrically driven waves is developed, taking viscous dissipation and finite depth effects into account. It will be shown that a careful choice of the filling level permits the normal and anomalous dispersion branches to be measured. Furthermore it will be demonstrated that the parametric driving mechanism may lead to a delay of the Rosensweig instability. A bicritical situation can be achieved when Rosensweig and Faraday waves interact.
Hydrodynamic theory of polydisperse chain-forming ferrofluids.
Mahle, Stefan; Ilg, Patrick; Liu, Mario
2008-01-01
The larger magnetic particles in ferrofluids are known to form chains, causing the fluid to display non-Newtonian behavior. In this paper, a generalization of the familiar ferrofluid dynamics by Shliomis is shown capable of realistically accounting for these fluids. The modification consists of identifying the relaxing magnetization as that of the chain-forming particles, while accounting for the free magnetic particles by dissipative terms in the Maxwell equations. PMID:18351932
Nowak, J; Wiekhorst, F; Trahms, L; Odenbach, S
2014-04-30
Suspensions of magnetic nanoparticles have received increasing interest in the biomedical field. While these ferrofluids are already used for magnetic resonance imaging, emerging research on cancer treatment focuses, for example, on employing the particles as drug carriers, or using them in magnetic hyperthermia to destroy diseased cells by heating of the particles. To enable safe and effective applications, an understanding of the flow behaviour of the ferrofluids is essential. Regarding the applications mentioned above, in which flow phenomena play an important role, viscosity under the influence of an external magnetic field is of special interest. In this respect, the magnetoviscous effect (MVE) leading to an increasing viscosity if an external magnetic field of a certain strength is applied, is well-known for singlecore ferrofluids used in the engineering context. In the biomedical context, multicore ferrofluids are preferred in order to avoid remanence magnetization and to enable a deposition of the particles by the organism without complications. This study focuses on a comparison of the MVE for three ferrofluids whose composition is identical except in relation to their hydrodynamic diameter and core composition-one of the fluids contains singlecore particles, while the other two feature multicore particles. This enables confident conclusions about the influence of those parameters on flow behaviour under the influence of a magnetic field. The strong effects found for two of the fluids should be taken into account, both in future investigations and in the potential use of such ferrofluids, as well as in manufacturing, in relation to the optimization of flow behaviour. PMID:24721897
The dispersion of parametrically excited surface waves in viscous ferrofluids
NASA Astrophysics Data System (ADS)
Müller, Hanns Walter
1999-07-01
Surface waves on a ferrofluid, which is exposed to a normal magnetic field, may exhibit a non-monotonous behavior. Stationary standing waves can be excited mechanically by a vertical vibration of the vessel, or magnetically by a modulation of the applied field. A linear stability analysis for the onset of these parametrically excited waves is presented. It will be shown that a careful choice of the filling depth allows for a detection of the anomalous dispersion branch. Furthermore, a theoretical confirmation is provided for the synchronous wave response, recently observed in a magnetic Faraday experiment.
NASA Astrophysics Data System (ADS)
Molho, Pierre
A ferrofluid is a suspenson of small magnetic particles in a carrier liquid. We begin by discussing the characteristics of a ferrofluid, in particular the criteria for the stability of such a suspension, as well as methods of preparation. We then go on to describe the properties and the effects of a magnetic field: superparamagnetism, dipolar interactions leading to the formation of chains, birefringence, viscosity.... We also present a certain number of applications which, essentially, bring into play the effects of a magnetic field: confinement in field gradients, variations in permeability of the material through deformation of the fluid, variation of birefringence or of viscosity. We conclude by presenting a spectacular effect specific to ferrofluids which arises from the liquid state of this material: surface instabilities in the presence of a magnetic field.
Detonation waves in relativistic hydrodynamics
Cissoko, M. )
1992-02-15
This paper is concerned with an algebraic study of the equations of detonation waves in relativistic hydrodynamics taking into account the pressure and the energy of thermal radiation. A new approach to shock and detonation wavefronts is outlined. The fluid under consideration is assumed to be perfect (nonviscous and nonconducting) and to obey the following equation of state: {ital p}=({gamma}{minus}1){rho} where {ital p}, {rho}, and {gamma} are the pressure, the total energy density, and the adiabatic index, respectively. The solutions of the equations of detonation waves are reduced to the problem of finding physically acceptable roots of a quadratic polynomial {Pi}({ital X}) where {ital X} is the ratio {tau}/{tau}{sub 0} of dynamical volumes behind and ahead of the detonation wave. The existence and the locations of zeros of this polynomial allow it to be shown that if the equation of state of the burnt fluid is known then the variables characterizing the unburnt fluid obey well-defined physical relations.
Nonlinear waves in second order conformal hydrodynamics
NASA Astrophysics Data System (ADS)
Fogaça, D. A.; Marrochio, H.; Navarra, F. S.; Noronha, J.
2015-02-01
In this work we study wave propagation in dissipative relativistic fluids described by a simplified set of the 2nd order viscous conformal hydrodynamic equations corresponding to Israel-Stewart theory. Small amplitude waves are studied within the linearization approximation while waves with large amplitude are investigated using the reductive perturbation method, which is generalized to the case of 2nd order relativistic hydrodynamics. Our results indicate the presence of a "soliton-like" wave solution in Israel-Stewart hydrodynamics despite the presence of dissipation and relaxation effects.
Hydrodynamics of chains in ferrofluid-based magnetorheological fluids under rotating magnetic field.
Patel, Rajesh; Chudasama, Bhupendra
2009-07-01
Ferrofluid-based magnetorheological (MR) fluid is prepared by dispersing micron-size magnetic spheres in a ferrofluid. We report here the mechanism of chain formation in ferrofluid based MR fluid, which is quite different from conventional MR fluid. Some of the nanomagnetic particles of ferrofluid filled inside the microcavities are formed due to association of large particles, and some of them are attached at the end of large particles. Under rotating magnetic field, fragmentation of a single chain into three parts is observed. Two of them are chains of micron-size magnetic particles which are suspended in a ferrofluid, and the third one is the chain of nanomagnetic particles of ferrofluid, which may be the connecting bridge between the two chains of larger magnetic particles. The rupture of a single chain provides evidence for the presence of nanomagnetic particles within the magnetic field-induced chainlike structure in this bidispersed MR fluid. PMID:19658750
Raitt, D.; Riecke, H.
1997-05-01
Surface waves on ferrofluids exposed to a dc magnetic field exhibit a nonmonotonic dispersion relation. The effect of a parametric driving on such waves is studied within suitable coupled Ginzburg-Landau equations. Due to the nonmonotonicity the neutral curve for the excitation of standing waves can have up to three minima. The stability of the waves with respect to long-wave perturbations is determined via a phase-diffusion equation. It shows that the band of stable wave numbers can split up into two or three subbands. The resulting competition between the wave numbers corresponding to the respective subbands leads quite naturally to patterns consisting of multiple domains of standing waves which differ in their wave number. The coarsening dynamics of such domain structures is addressed. {copyright} {ital 1997} {ital The American Physical Society}
Simple Waves in Ideal Radiation Hydrodynamics
Johnson, B M
2008-09-03
In the dynamic diffusion limit of radiation hydrodynamics, advection dominates diffusion; the latter primarily affects small scales and has negligible impact on the large scale flow. The radiation can thus be accurately regarded as an ideal fluid, i.e., radiative diffusion can be neglected along with other forms of dissipation. This viewpoint is applied here to an analysis of simple waves in an ideal radiating fluid. It is shown that much of the hydrodynamic analysis carries over by simply replacing the material sound speed, pressure and index with the values appropriate for a radiating fluid. A complete analysis is performed for a centered rarefaction wave, and expressions are provided for the Riemann invariants and characteristic curves of the one-dimensional system of equations. The analytical solution is checked for consistency against a finite difference numerical integration, and the validity of neglecting the diffusion operator is demonstrated. An interesting physical result is that for a material component with a large number of internal degrees of freedom and an internal energy greater than that of the radiation, the sound speed increases as the fluid is rarefied. These solutions are an excellent test for radiation hydrodynamic codes operating in the dynamic diffusion regime. The general approach may be useful in the development of Godunov numerical schemes for radiation hydrodynamics.
Efficiency of magnetic plane wave pumping of a ferrofluid through a planar duct
NASA Astrophysics Data System (ADS)
Felderhof, B. U.
2011-09-01
The efficiency of ferrohydrodynamic pumping of a ferrofluid through a planar duct by means of a running magnetic plane wave is studied to second order in the amplitude of the exciting current density. The rate of dissipation in the fluid is calculated from the first order magnetic field and magnetization. It turns out that the efficiency, defined as the ratio of net flow velocity to power input, is comparable in magnitude to that for Stokes peristaltic pumping. The theory for electrohydrodynamic pumping of a polar liquid by means of a running electric plane wave is shown to be nearly identical.
Wave number of maximal growth in viscous ferrofluids.
NASA Astrophysics Data System (ADS)
Lange, A.; Reimann, B.; Richter, R.
2001-09-01
Within the frame of linear stability theory an analytical method is presented for the normal field instability in magnetic fluids. It allows to calculate the maximal growth rate and the corresponding wave number for arbitrary values of the layer thickness and viscosity. Applying this method to magnetic fluids of finite depth, the results are quantitatively compared to the wave number of the transient pattern observed experimentally after a jumplike increase of the field. The wave number grows linearly with increasing induction where the theoretical and the experimental data agree well. Figs 2, Refs 13.
An operator expansion method for computing nonlinear surface waves on a ferrofluid jet
NASA Astrophysics Data System (ADS)
Guyenne, Philippe; Părău, Emilian I.
2016-09-01
We present a new numerical method to simulate the time evolution of axisymmetric nonlinear waves on the surface of a ferrofluid jet. It is based on the reduction of this problem to a lower-dimensional computation involving surface variables alone. To do so, we describe the associated Dirichlet-Neumann operator in terms of a Taylor series expansion where each term can be efficiently computed by a pseudo-spectral scheme using the fast Fourier transform. We show detailed numerical tests on the convergence of this operator and, to illustrate the performance of our method, we simulate the long-time propagation and pairwise collisions of axisymmetric solitary waves. Both depression and elevation waves are examined by varying the magnetic field. Comparisons with weakly nonlinear predictions are also provided.
NASA Technical Reports Server (NTRS)
1993-01-01
A new Ferrofluidics exclusion seal promises improvement in controlling "fugitive emissions" -vapors that escape into the atmosphere from petroleum refining and chemical processing facilities. These are primarily volatile organic compounds, and their emissions are highly regulated by the EPA. The ferrofluid system consists of a primary mechanical seal working in tandem with a secondary seal. Ferrofluids are magnetic liquids - fluids in which microscopic metal particles have been suspended, allowing the liquid to be controlled by a magnetic force. The concept was developed in the early years of the Space program, but never used. Two Avco scientists, however, saw commercial potential in ferrofluids and formed a company. Among exclusion seal commercial applications are rotary feedthrough seals, hydrodynamic bearings and fluids for home and automotive loudspeakers. Ferrofluidics has subsidiaries throughout the world.
Hydrodynamic Performance of a Wave Energy Converter
NASA Astrophysics Data System (ADS)
Yang, Yingchen
2010-11-01
To harvest energy from ocean waves, a new wave energy converter (WEC) was proposed and tested in a wave tank. The WEC freely floats on the water surface and rides waves. It utilizes its wave-driven angular oscillation to convert the mechanical energy of waves into electricity. To gain the maximum possible angular oscillation of the WEC under specified wave conditions, both floatation of the WEC and wave interaction with the WEC play critical roles in a joint fashion. During the experiments, the submersion condition of the WEC and wave condition were varied. The results were analyzed in terms of the oscillation amplitude, stability, auto-orientation capability, and wave frequency dependency.
NASA Astrophysics Data System (ADS)
Odenbach, Professor Stefan
2006-09-01
Journal of Physics: Condensed Matter. The issue contains results emerging from the research programme as well as invited papers from researchers not participating in the programme but working in closely related areas. The issue is subdivided into five main sections dealing with synthesis, basic physical description, rheology, and both the medical and technical applications of ferrofluids. As can be expected from work done within an interdisciplinary context many of the papers would fit into more than one of these sections and catagorization is thus sometimes difficult. We have therefore tried to place them into the section reflecting the main field of research to which the respective results belong. The first section is on synthesis and characterization of magnetic suspensions. The first paper in this section is dedicated partly to magnetite ferrofluids but with special aspects concerning the particle size tailoring them for applications especially in the field of magnetic hyperthermia. After this, three different types of `new' ferrofluids are presented. Fluids based on pure metal particles exhibiting much stronger magnetic properties than the common magnetite fluids, fluids with a temperature sensitive surfactant shell allowing a change of the particle’s hydrodynamic diameter by variation of the fluid’s temperature and fluids containing spheres of nonmagnetic material with embedded magnetic particles which are already used in new medical applications. The second section is dedicated to the basic physics of ferrofluids and highlights three different topics. First the question of magnetization dynamics is discussed and different aspects of this fundamental problem, which determines the basic description of ferrofluids, are highlighted. The second topic is the well known surface instability appearing in ferrofluids in a homogeneous magnetic field perpendicular to the fluid surface. This part shows clearly how many undiscovered phenomena can be found, even in an area
Chiral Alfvén Wave in Anomalous Hydrodynamics.
Yamamoto, Naoki
2015-10-01
We study the hydrodynamic regime of chiral plasmas at high temperature. We find a new type of gapless collective excitation induced by chiral effects in an external magnetic field. This is a transverse wave, and it is present even in incompressible fluids, unlike the chiral magnetic and chiral vortical waves. The velocity is proportional to the coefficient of the gravitational anomaly. We briefly discuss the possible relevance of this "chiral Alfvén wave" in physical systems. PMID:26551804
Experiments on the interaction between hydrodynamic turbulence and surface waves
NASA Astrophysics Data System (ADS)
Jamin, Timothee; Berhanu, Michael; Falcon, Eric
2014-11-01
Different regimes of interaction between hydrodynamic turbulence and a free surface are investigated in a meter scale basin. A homogeneous and isotropic turbulence is generated by an 8×8 array of jets pointing upwards at the bottom of the tank. The 64 jets are driven individually to reach a random spatiotemporal forcing pattern and produce an intense turbulence. Using fluid velocity measurements, we characterize the turbulence obtained with this setup, then we investigate free-surface deformations induced by hydrodynamic turbulence. In a second stage an electromechanical shaker will generate gravity-capillary waves at the free surface. We aim to study reduction or amplification of surface waves and then measure energy exchange between hydrodynamic turbulence and wave turbulence. This work was supported by the DGA-CNRS Ph.D program and ANR Turbulon 12-BS04-0005.
Electron magneto-hydrodynamic waves bounded by magnetic bubble
NASA Astrophysics Data System (ADS)
Anitha, V. P.; Sharma, D.; Banerjee, S. P.; Mattoo, S. K.
2012-08-01
The propagation of electron magneto-hydrodynamic (EMHD) waves is studied experimentally in a 3-dimensional region of low magnetic field surrounded by stronger magnetic field at its boundaries. We report observations where bounded left hand polarized Helicon like EMHD waves are excited, localized in the region of low magnetic field due to the boundary effects generated by growing strengths of the ambient magnetic field rather than a conducting or dielectric material boundary. An analytical model is developed to include the effects of radially nonuniform magnetic field in the wave propagation. The bounded solutions are compared with the experimentally obtained radial wave magnetic field profiles explaining the observed localized propagation of waves.
Nonlinear Generalized Hydrodynamic Wave Equations in Strongly Coupled Dusty Plasmas
Veeresha, B. M.; Sen, A.; Kaw, P. K.
2008-09-07
A set of nonlinear equations for the study of low frequency waves in a strongly coupled dusty plasma medium is derived using the phenomenological generalized hydrodynamic (GH) model and is used to study the modulational stability of dust acoustic waves to parallel perturbations. Dust compressibility contributions arising from strong Coulomb coupling effects are found to introduce significant modifications in the threshold and range of the instability domain.
Hydrodynamic waves and correlation functions in dusty plasmas
Wang, X.; Bhattacharjee, A.
1997-11-01
A hydrodynamic description of strongly coupled dusty plasmas is given when physical quantities vary slowly in space and time and the system can be assumed to be in local thermodynamic equilibrium. The linear waves in such a system are analyzed. In particular, a dispersion equation is derived for low-frequency dust acoustic waves, including collisional damping effects, and compared with experimental results. The linear response of the system is calculated from the fluctuation-dissipation theorem and the hydrodynamic equations. The requirement that these two calculations coincide constrains the particle correlation function for slowly varying perturbations. It is shown that in the presence of weakly damped, long-wavelength dust-acoustic waves, the dust autocorrelation function is of the Debye{endash}H{umlt u}ckel form and the characteristic shielding distance is the dust Debye length. {copyright} {ital 1997 American Institute of Physics.}
On wave stability in relativistic cosmic-ray hydrodynamics
NASA Technical Reports Server (NTRS)
Webb, G. M.
1989-01-01
Wave stability of a two-fluid hydrodynamical model describing the acceleration of cosmic rays by the first-order Fermi mechanism in relativistic, cosmic-ray-modified shocks is investigated. For a uniform background state, the short- and long-wavelength wave speeds are shown to interlace, thus assuring wave stability in this case. A JWKB analysis is performed to investigate the stability of short-wavelength thermal gas sound waves in the smooth, decelerating supersonic flow upstream of a relativistic, cosmic-ray-modified shock. The stability of the waves is assessed both in terms of the fluid velocity and density perturbations, as well as in terms of the wave action. The stability and interaction of the short-wavelength cosmic-ray coherent mode with the background flow is also studied.
Visualization of hydrodynamic pilot-wave dynamics
NASA Astrophysics Data System (ADS)
Prost, Victor; Quintela, Julio; Harris, Daniel; Brun, Pierre-Thomas; Bush, John
2015-11-01
We present a low-cost device for examining the dynamics of droplets bouncing on a vibrating fluid bath, suitable for educational purposes. Dual control of vibrational and strobing frequency from a cell phone application allowed us to reduce the total cost to 60 dollars. Illumination with inhomogeneous colored light allows for striking visualization of the droplet dynamics and accompanying wave field via still photography or high-speed videography. Thanks to the NSF.
Hydrodynamic shock wave studies within a kinetic Monte Carlo approach
NASA Astrophysics Data System (ADS)
Sagert, Irina; Bauer, Wolfgang; Colbry, Dirk; Howell, Jim; Pickett, Rodney; Staber, Alec; Strother, Terrance
2014-06-01
We introduce a massively parallelized test-particle based kinetic Monte Carlo code that is capable of modeling the phase space evolution of an arbitrarily sized system that is free to move in and out of the continuum limit. Our code combines advantages of the DSMC and the Point of Closest Approach techniques for solving the collision integral. With that, it achieves high spatial accuracy in simulations of large particle systems while maintaining computational feasibility. Using particle mean free paths which are small with respect to the characteristic length scale of the simulated system, we reproduce hydrodynamic behavior. To demonstrate that our code can retrieve continuum solutions, we perform a test-suite of classic hydrodynamic shock problems consisting of the Sod, the Noh, and the Sedov tests. We find that the results of our simulations which apply millions of test-particles match the analytic solutions well. In addition, we take advantage of the ability of kinetic codes to describe matter out of the continuum regime when applying large particle mean free paths. With that, we study and compare the evolution of shock waves in the hydrodynamic limit and in a regime which is not reachable by hydrodynamic codes.
Hydrodynamic Waves and Correlation Functions in Dusty Plasmas
NASA Astrophysics Data System (ADS)
Bhattacharjee, A.; Wang, Xiaogang
1997-11-01
A hydrodynamic description of strongly coupled dusty plasmas is given when physical quantities vary slowly in space and time and the system can be assumed to be in local thermodynamic equilibrium. The linear waves in such a system are analyzed. In particular, a dispersion equation is derived for low-frequency dust acoustic waves, including collisional damping effects, and compared with experimental results. The linear response of the system is calculated from the fluctuation-dissipation theorem and the hydrodynamic equations. The requirement that these two calculations coincide constrains the particle correlation function for slowly varying perturbations [L. P. Kadanoff and P. C. Martin, Ann. Phys. 24, 419 (1963)]. It is shown that in the presence of the slow dust-acoustic waves, the dust auto-correlation function is of the Debye-Hekel form and the shielding distance is the dust Debye length. In the short-wavelength regime, an integral equation is derived from kinetic theory and solved numerically to yield particle correlation functions that display ``liquid-like'' behavior and have been observed experimentally [R. A.. Quinn, C. Cui, J. Goree, J. B. Pieper, H. Thomas and G. E. Morfill, Phys. Rev. E 53, R2049 (1996)].
Smoothed Particle Hydrodynamics for water wave propagation in a channel
NASA Astrophysics Data System (ADS)
Omidvar, Pourya; Norouzi, Hossein; Zarghami, Ahad
2015-01-01
In this paper, Smoothed Particle Hydrodynamics (SPH) is used to simulate the propagation of waves in an intermediate depth water channel. The major advantage of using SPH is that no special treatment of the free surface is required, which is advantageous for simulating highly nonlinear flows with possible wave breaking. The SPH method has an option of different formulations with their own advantages and drawbacks to be implemented. Here, we apply the classical and Arbitrary Lagrange-Euler (ALE) formulation for wave propagation in a water channel. The classical SPH should come with an artificial viscosity which stabilizes the numerical algorithm and increases the accuracy. Here, we will show that the use of classical SPH with an artificial viscosity may cause the waves in the channel to decay. On the other hand, we will show that using the ALE-SPH algorithm with a Riemann solver is more stable, and in addition to producing the pressure fields with much less numerical noise, the waves propagate in the channel without dissipation.
RADIATIVE HYDRODYNAMIC SIMULATIONS OF ACOUSTIC WAVES IN SUNSPOTS
Bard, S.; Carlsson, M.
2010-10-10
We investigate the formation and evolution of the Ca II H line in a sunspot. The aim of our study is to establish the mechanisms underlying the formation of the frequently observed brightenings of small regions of sunspot umbrae known as 'umbral flashes'. We perform fully consistent NLTE radiation hydrodynamic simulations of the propagation of acoustic waves in sunspot umbrae and conclude that umbral flashes result from increased emission of the local solar material during the passage of acoustic waves originating in the photosphere and steepening to shock in the chromosphere. To quantify the significance of possible physical mechanisms that contribute to the formation of umbral flashes, we perform a set of simulations on a grid formed by different wave power spectra, different inbound coronal radiation, and different parameterized chromospheric heating. Our simulations show that the waves with frequencies in the range 4.5-7.0 mHz are critical to the formation of the observed blueshifts of umbral flashes while waves with frequencies below 4.5 mHz do not play a role despite their dominance in the photosphere. The observed emission in the Ca II H core between flashes only occurs in the simulations that include significant inbound coronal radiation and/or extra non-radiative chromospheric heating in addition to shock dissipation.
Hydrodynamic view of wave-packet interference: quantum caves.
Chou, Chia-Chun; Sanz, Angel S; Miret-Artés, Salvador; Wyatt, Robert E
2009-06-26
Wave-packet interference is investigated within the complex quantum Hamilton-Jacobi formalism using a hydrodynamic description. Quantum interference leads to the formation of the topological structure of quantum caves in space-time Argand plots. These caves consist of the vortical and stagnation tubes originating from the isosurfaces of the amplitude of the wave function and its first derivative. Complex quantum trajectories display counterclockwise helical wrapping around the stagnation tubes and hyperbolic deflection near the vortical tubes. The string of alternating stagnation and vortical tubes is sufficient to generate divergent trajectories. Moreover, the average wrapping time for trajectories and the rotational rate of the nodal line in the complex plane can be used to define the lifetime for interference features. PMID:19659057
Hydrodynamic growth and decay of planar shock waves
NASA Astrophysics Data System (ADS)
Piriz, A. R.; Sun, Y. B.; Tahir, N. A.
2016-03-01
A model for the hydrodynamic attenuation (growth and decay) of planar shocks is presented. The model is based on the approximate integration of the fluid conservation equations, and it does not require the heuristic assumptions used in some previous works. A key issue of the model is that the boundary condition on the piston surface is given by the retarded pressure, which takes into account the transit time of the sound waves between the piston and any position at the bulk of the shocked fluid. The model yields the shock pressure evolution for any given pressure pulse on the piston, as well as the evolution of the trajectories, velocities, and accelerations on the shock and piston surfaces. An asymptotic analytical solution is also found for the decay of the shock wave.
Blast-Wave-Driven Instability Experiments Relevant To Supernova Hydrodynamics
NASA Astrophysics Data System (ADS)
Kuranz, Carolyn; Drake, R.; Grosskopf, M.; Budde, A.; Remington, B.; Robey, H.; Arnett, D.; Meakin, C.; Plewa, T.
2011-05-01
This presentation discusses experiments scaled to the blast wave driven instabilities at the He/H interface during the explosion phase of SN1987A. This core-collapse supernova was detected about 50 kpc from Earth making it the first supernova observed so closely to earth in modern times. The progenitor star was a blue supergiant with a mass of 18-20 solar masses. A blast wave occurred following the supernova explosion because there was a sudden, finite release of energy. Blast waves consist of a shock front followed by a rarefaction wave. When a blast wave crosses an interface with a decrease in density, hydrodynamic instabilities will develop. These experiments include target materials scaled in density to the He/H layer in SN1987A. About 5 kJ of laser energy from the Omega Laser facility irradiates a 150 µm plastic layer that is followed by a low-density foam layer. A blast wave structure similar to those in supernovae is created in the plastic layer. The blast wave crosses an interface with a drop in density and a precision-machined interface with multiple modes. The specific modal structure is based on simulation results of the evolution of the progenitor star. This produces unstable growth dominated by the Rayleigh-Taylor (RT) instability. We have detected the interface structure under these conditions, using dual orthogonal radiography, and will show some of the resulting data. This work is funded by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-FG52-09NA29548, and by the National Laser User Facility Program, grant number DE-FG52-09NA29034.
NASA Astrophysics Data System (ADS)
Odenbach, Professor Stefan
2006-09-01
This issue of Journal of Physics: Condensed Matter is dedicated to results in the field of ferrofluid research. Ferrofluids—suspensions of magnetic nanoparticles—exhibit as a specific feature the magnetic control of their physical parameters and of flows appearing in such fluids. This magnetic control can be achieved by means of moderate magnetic fields with a strength of the order of 10 mT. This sort of magnetic control also enables the design of a wide variety of technical applications such as the use of the magnetic forces for basic research in fluid dynamics. The overall field of ferrofluid research is already about 40 years old. Starting with the first patent on the synthesis of magnetic nanoparticle suspensions by S Papell in 1964, a vivid field of research activities has been established. Looking at the long time in which ferrofluids have been the focus of scientific interest, one can ask the question, what kind of recent developments justify a special issue of a scientific journal? New developments in a field, which depends strongly on a certain material class and which opens research possibilities in different scientific fields will nowadays usually require an interdisciplinary approach. This kind of approach starting from the synthesis of magnetic suspensions, including research concerning their basic properties and flow behaviour and focusing on new applications has been the core of a special research programme funded by the Deutsche Forschungsgemeinschaft (DFG) over the past 6 years. Within this programme—entitled `Colloidal Magnetic Fluids: Basics, Synthesis and Applications of New Ferrofluids'—more than 30 different research groups have been coordinated to achieve new results in various fields related to ferrofluid research. The basic approach of the program has been the assumption that new applications well beyond the typical ferrofluid techniques, for example loud speaker cooling or sealing of rotary shafts, will require tailored magnetic
Dispersion Relation and Numerical Simulation of Hydrodynamic Waves In Mar's Topside Ionosphere
NASA Astrophysics Data System (ADS)
Wang, J.-S.; Nielsen, E.
The dispersion relation for hydrodynamic waves in an ionosphere with at most a weak magnetic field shows, hydrodynamic hybrid waves may be excited in the topside iono- sphere of Mars and Venus owing to fluctuations in the solar wind pressure. The hy- brid waves result from coupling between two different hydrodynamic wave modes: the classic acoustic-gravity wave(AGW) and the newly developed background gradi- ent wave(BGW). Numerical simulations show that these waves will cause wave-like structures in the altitude profiles of the ionospheric plasma density. The wavelength and frequency are various but their prevailing values in Martian ionosphere are about 60km and 0.001-0.0001Hz, respectively. The amplitudes of the plasma density vari- ations decrease nearly exponentially with increasing altitude, and are of the same or- der of the magnitude as the uncertainty on all the previous measurements of Mar- tian ionospheric electron densities. Radio occultation observations at Mars and Venus show electron density fluctuations in the high altitude ionosphere. The fluctuations are mainly noise, but they may in part be caused by hydrodynamic wave activity. To verify wave activity more detailed measurements are required, and may be obtained with the low frequency radar planned for the Mars Express mission.
Colliding Shock Waves and Hydrodynamics in Small Systems
NASA Astrophysics Data System (ADS)
Chesler, Paul M.
2015-12-01
Using numerical holography, we study the collision of a planar sheet of energy with a bounded localized distribution of energy. The collision, which mimics proton-nucleus collisions, produces a localized lump of debris with transverse size R ˜1 /Teff with Teff the effective temperature, and has large gradients and large transverse flow. Nevertheless, the postcollision evolution is well described by viscous hydrodynamics. Our results bolster the notion that debris produced in proton-nucleus collisions may be modeled using hydrodynamics.
Barium hexaferrite ferrofluids - preparation and physical properties
NASA Astrophysics Data System (ADS)
Müller, R.; Hiergeist, R.; Steinmetz, H.; Ayoub, N.; Fujisaki, M.; Schüppel, W.
1999-07-01
Barium hexaferrite BaFe 12-2 xTi xCo xO 19 ferrofluids have been prepared for the first time using oleic acid as surfactant and Isopar M ® as carrier liquid. The initial susceptibility versus temperature for zero-field cooling of the ferrofluid was obtained by a vibrating sample magnetometer. TEM pictures of the fluid show isolated particles and only small agglomerates and a mean particle diameter of approx. 8 nm. Numerical calculations of the magneto-viscous effect, based on the local-equilibrium magnetic state model, clearly show the benefit for Ba-ferrite ferrofluids resulting from the high uniaxial anisotropy compared to magnetite ferrofluids. Rheological measurements were performed with a rotational-type viscometer with magnetic field perpendicular to the hydrodynamic vortex axis.
Colliding Shock Waves and Hydrodynamics in Small Systems.
Chesler, Paul M
2015-12-11
Using numerical holography, we study the collision of a planar sheet of energy with a bounded localized distribution of energy. The collision, which mimics proton-nucleus collisions, produces a localized lump of debris with transverse size R∼1/T_{eff} with T_{eff} the effective temperature, and has large gradients and large transverse flow. Nevertheless, the postcollision evolution is well described by viscous hydrodynamics. Our results bolster the notion that debris produced in proton-nucleus collisions may be modeled using hydrodynamics. PMID:26705624
Full wave solution for hydrodynamic behaviors of pile breakwater
NASA Astrophysics Data System (ADS)
Zhu, Da-tong
2013-06-01
Rayleigh expansion is used to study the water-wave interaction with a row of pile breakwater in finite water depth. Evanescent waves, the wave energy dissipated on the fluid resistance and the thickness of the breakwater are totally included in the model. The formulae of wave reflection and transmission coefficients are obtained. The accuracy of the present model is verified by a comparison with existing results. It is found that the predicted wave reflection and transmission coefficients for the zero order are all highly consistent with the experimental data (Hagiwara, 1984; Isaacson et al., 1998) and plane wave solutions (Zhu, 2011). The losses of the wave energy for the fluid passing through slits play an important role, which removes the phenomena of enhanced wave transmission.
Hydrodynamic roughness for wave and current flow over irregular beds (Invited)
NASA Astrophysics Data System (ADS)
Pawlak, G. R.; Bandet, M. D.; Jaramillo, S.
2010-12-01
The turbulent processes associated with wave and current flow over highly irregular boundaries, characteristic of coral reefs, have important effects on wave dissipation and sediment transport, critical aspects in modeling coastal currents and waves and, subsequently, beach and coastal changes. A fundamental aspect of characterizing these turbulent processes includes parametrization of hydrodynamically relevant roughness scales. AUV-based measurements of the physical roughness scales in the vicinity of the Kilo Nalu Observatory on the south shore of Oahu indicate that the reef roughness is described by a broad-banded spectral distribution. For these multi-scaled, inhomogeneous boundaries, the relationship between hydrodynamic roughness and the measurable roughness scales is not well established. We present field observations of wave and current boundary layer dynamics over a reef at Kilo Nalu that examine this link between physical and hydrodynamic roughness. Observations from a horizontal profiler are used to reconstruct a spatial average of the near-bed flow, augmented by high-resolution vertical profiling. Data resolve the vortical and dissipation structure in the wave boundary layer and show that the flow responds to a range of roughness scales that varies as a function of wave orbital diameter. Effects of roughness on reef scales are assessed using observations of the steady currents, which integrate the spatial roughness distribution and implicitly reflect the wave interactions with the boundary. Mean flow bed stress and hydrodynamic roughness obtained from fixed ADCP current profile data are related to AUV-based measurements of physical roughness. Current structure is also assessed using AUV DVL observations. Bed stress and hydrodynamic roughness are spatially variable, directionally dependent and are modulated in time by variations in the wave-current velocity ratio.
Hydrodynamic analysis of elastic floating collars in random waves
NASA Astrophysics Data System (ADS)
Bai, Xiao-dong; Zhao, Yun-peng; Dong, Guo-hai; Li, Yu-cheng
2015-06-01
As the main load-bearing component of fish cages, the floating collar supports the whole cage and undergoes large deformations. In this paper, a mathematical method is developed to study the motions and elastic deformations of elastic floating collars in random waves. The irregular wave is simulated by the random phase method and the statistical approach and Fourier transfer are applied to analyze the elastic response in both time and frequency domains. The governing equations of motions are established by Newton's second law, and the governing equations of deformations are obtained based on curved beam theory and modal superposition method. In order to validate the numerical model of the floating collar attacked by random waves, a series of physical model tests are conducted. Good relationship between numerical simulation and experimental observations is obtained. The numerical results indicate that the transfer function of out-of-plane and in-plane deformations increase with the increasing of wave frequency. In the frequency range between 0.6 Hz and 1.1 Hz, a linear relationship exists between the wave elevations and the deformations. The average phase difference between the wave elevation and out-of-plane deformation is 60° with waves leading and the phase between the wave elevation and in-plane deformation is 10° with waves lagging. In addition, the effect of fish net on the elastic response is analyzed. The results suggest that the deformation of the floating collar with fish net is a little larger than that without net.
Surface topography measurements for pilot-wave hydrodynamics
NASA Astrophysics Data System (ADS)
Damiano, Adam; Harris, Daniel; Brun, Pierre-Thomas; Bush, John
2015-11-01
We present the results of our attempt to refine the surface Schlieren technique originally developed by Moisy et al. (2009, 2012) to resolve the surface topography associated with capillary wave fields. Our technique is applied to infer the wave field that accompanies millimetric droplets self-propeling on the surface of a vibrating fluid bath. Apart from a shadow region on the order of the drop's cross-sectional area, the waves are resolved to a micron scale, allowing for quantitative comparison with existing theoretical models of the wave field. The technique is used to yield insight into the interaction between walking droplets and submerged barriers. Thanks to the NSF.
A Dynamic Analysis of Hydrodynamic Wave Journal Bearings
NASA Technical Reports Server (NTRS)
Ene, Nicoleta M.; Dimofte, Florin; Keith, Theo G.
2008-01-01
The purpose of this paper is to study the dynamic behavior of a three-wave journal bearing using a transient approach. The transient analysis permits the determination of the rotor behavior after the fractional frequency whirl appears. The journal trajectory is determined by solving a set of nonlinear equations of motion using the Runge-Katta method. The fluid film forces are computed by integrating the transient Reynolds equation at each time step location of the shaft with respect to the bearing. Because of the large values of the rotational speeds, turbulent effects were included in the computations. The influence of the temperature on the viscosity was also considered. Numerical results were compared to experimenta1 results obtained at the NASA Glenn Research Center. Comparisons of the theoretical results with experimental data were found to be in good agreement. The numerical and experimental results showed that the fluid film of a three-wave journal bearing having a diameter of 30 mm, a length of 27 mm, and a wave amplitude ratio greater than 0.15 is stable even at rotational speeds of 60,000 RPM. For lower wave amplitude ratios, the threshold speed at which the fluid film becomes unstable depends on the wave amplitude and on the supply pocket pressure. Even if the fluid film is unstable, the wave bearing maintains the whirl orbit inside the bearing clearance.
Technology Transfer Automated Retrieval System (TEKTRAN)
Longissimus lumborum samples were removed 24 h postmortem from six U.S. Utility carcasses to be utilized in determining the effects of tenderness enhancement methods and aging time on quality attributes of beef. Within each sample, sections were randomly assigned to hydrodynamic shock waves (HSW), b...
Hydrodynamic instabilities in supernova remnants - Self-similar driven waves
NASA Technical Reports Server (NTRS)
Chevalier, Roger A.; Blondin, John M.; Emmering, Robert T.
1992-01-01
An initial study aimed at elucidating the multidimensional aspects of the hydrodynamic instabilities in supernova remnants is presented. Self-similar solutions are found to exist for the interaction of a steep power-law density profile expanding into a relatively flat stationary power-law density profile. Consideration of the pressure and entropy profiles in the shocked 1D flows shows that the flows are subject to convective instability, by a local criterion. The growth rate for the instability becomes very large near the contact discontinuity between the two shocked regions. A linear analysis of the complete self-similar solutions shows that the solutions are unstable above a critical wavenumber and that the growth rate is greatest at the position of the contact discontinuity. The X-ray image of the remnant of SN 1572 (Tycho) shows emission from clumps of supernova ejecta, which is good evidence for instabilities in this remnant.
Application of CHAD hydrodynamics to shock-wave problems
Trease, H.E.; O`Rourke, P.J.; Sahota, M.S.
1997-12-31
CHAD is the latest in a sequence of continually evolving computer codes written to effectively utilize massively parallel computer architectures and the latest grid generators for unstructured meshes. Its applications range from automotive design issues such as in-cylinder and manifold flows of internal combustion engines, vehicle aerodynamics, underhood cooling and passenger compartment heating, ventilation, and air conditioning to shock hydrodynamics and materials modeling. CHAD solves the full unsteady Navier-Stoke equations with the k-epsilon turbulence model in three space dimensions. The code has four major features that distinguish it from the earlier KIVA code, also developed at Los Alamos. First, it is based on a node-centered, finite-volume method in which, like finite element methods, all fluid variables are located at computational nodes. The computational mesh efficiently and accurately handles all element shapes ranging from tetrahedra to hexahedra. Second, it is written in standard Fortran 90 and relies on automatic domain decomposition and a universal communication library written in standard C and MPI for unstructured grids to effectively exploit distributed-memory parallel architectures. Thus the code is fully portable to a variety of computing platforms such as uniprocessor workstations, symmetric multiprocessors, clusters of workstations, and massively parallel platforms. Third, CHAD utilizes a variable explicit/implicit upwind method for convection that improves computational efficiency in flows that have large velocity Courant number variations due to velocity of mesh size variations. Fourth, CHAD is designed to also simulate shock hydrodynamics involving multimaterial anisotropic behavior under high shear. The authors will discuss CHAD capabilities and show several sample calculations showing the strengths and weaknesses of CHAD.
Hydrodynamic responses of a thin floating disk to regular waves
NASA Astrophysics Data System (ADS)
Yiew, L. J.; Bennetts, L. G.; Meylan, M. H.; French, B. J.; Thomas, G. A.
2016-01-01
The surge, heave and pitch motions of two solitary, thin, floating disks, extracted from laboratory wave basin experiments are presented. The motions are forced by regular incident waves, for a range of wave amplitudes and frequencies. One disk has a barrier attached to its edge to stop the incident waves from washing across its upper surface. It is shown that the motions of the disk without the barrier are smaller than those of the disk with the barrier. Moreover, it is shown that the amplitudes of the motions, relative to the incident amplitude, decrease with increasing incident wave amplitude for the disk without a barrier and for short incident wavelengths. Two theoretical models of the disk motions are considered. One is based on slope-sliding theory and the other on combined linear potential-flow and thin-plate theories. The models are shown to have almost the same form in the long-wavelength regime. The potential-flow/thin-plate model is shown to capture the experimentally measured disk motions with reasonable accuracy.
The equations of nearly incompressible fluids. I. Hydrodynamics, turbulence, and waves
NASA Astrophysics Data System (ADS)
Zank, G. P.; Matthaeus, W. H.
1991-01-01
A unified analysis delineating the conditions under which the equations of classical incompressible and compressible hydrodynamics are related in the absence of large-scale thermal, gravitational, and field gradients is presented. By means of singular expansion techniques, a method is developed to derive modified systems of fluid equations in which the effects of compressibility are admitted only weakly in terms of the incompressible hydrodynamic solutions (hence ``nearly incompressible hydrodynamics''). Besides including molecular viscosity self-consistently, the role of thermal conduction in an ideal fluid is also considered. With the inclusion of heat conduction, it is found that two distinct routes to incompressibility are possible, distinguished according to the relative magnitudes of the temperature, density, and pressure fluctuations. This leads to two distinct models for thermally conducting, nearly incompressible hydrodynamics—heat-fluctuation-dominated hydrodynamics (HFDH's) and heat-fluctuation-modified hydrodynamics (HFMD's). For the HFD case, the well-known classical passive scalar equation for temperature is derived as one of the nearly incompressible fluid equations and temperature and density fluctuations are predicted to be anticorrelated. For HFM fluids, a new thermal transport equation, in which compressible acoustic effects are present, is obtained together with a more-complicated ``correlation'' between temperature, density, and pressure fluctuations. Although the equations of nearly incompressible hydrodynamics are envisaged principally as being applicable to homogeneous turbulence and wave propagation in low Mach number flow, it is anticipated that their applicability is likely to be far greater.
Simulation of wave mitigation by coastal vegetation using smoothed particle hydrodynamics method
NASA Astrophysics Data System (ADS)
Iryanto; Gunawan, P. H.
2016-02-01
Vegetation in coastal area lead to wave mitigation has been studied by some researchers recently. The effect of vegetation forest in coastal area is minimizing the negative impact of wave propagation. In order to describe the effect of vegetation resistance into the water flow, the modified model of framework smoothed hydrodynamics particle has been constructed. In the Lagrangian framework, the Darcy, Manning, and laminar viscosity resistances are added. The effect of each resistances is given in some results of numerical simulations. Simulation of wave mitigation on sloping beach is also given.
Calculation of Chemical Detonation Waves With Hydrodynamics and Thermochemical Equation of State
Howard, W M; Fried, L E; Souers, P C; Vitello, P A
2001-08-01
We model detonation waves for solid explosives, using 2-D Arbitrary Lagrange Eulerian (ALE) hydrodynamics, with an equation of state (EOS) based on thermochemical equilibrium, coupled with simple kinetic rate laws for a few reactants. The EOS for the product species is based on either a BKWC EOS or on an exponential-6 potential model, whose parameters are fitted to a wide range of shock Hugoniot and static compression data. We show some results for the non ideal explosive, urea nitrate. Such a model is a powerful tool for studying such processes as initiation, detonation wave propagation and detonation wave propagation as a function of cylindrical radius.
Ferrofluids: Thermophysical properties and formation of microstructures
NASA Astrophysics Data System (ADS)
Mousavi Khoeini, NargesSadat Susan
This work is a combined effort of experimental and theoretical studies toward better understanding the structural and physical properties of aqueous ferrofluids containing nano-sized magnetite (iron oxide magnetic particles) of about 10nm. Ferrofluids have attracted remarkable attention mainly because their properties can be controlled by means of an externally applied magnetic field. The dispersion of nano-sized magnets in a carrier liquid exhibits superparamagnetic behaviour while retaining its fluid properties. The interplay between hydrodynamic and magnetic phenomena has made ferrofluids an extremely promising and useful tool in wide spectra of applications, from technical applications to biomedical ones. In the presence of a magnetic field, magnetic moments of the nanomagnets suspended in the host liquid are aligned toward the field direction and begin to form microstructures such as short chains, strands and long stripes. As this process advances the microstructures may collapse into bundles and thick chains and form macrostructures. Upon the removal of the magnetic field, nanoparticles will be homogeneously redistributed throughout the sample due to thermal agitation. Zero-field structures, and especially the field-induced assembly of magnetic nanoparticles, are primarily responsible for the change in physical properties of ferrofluids, including thermophysical, optical, rheological, and magnetization properties. Because of the field-induced assembly of magnetic nanoparticles in the field direction, ferrofluids become strongly anisotropic and as a result, ferrofluids can significantly enhance directional heat transfer in a thermal system. Thermophysical properties of a ferrofluid are important in studying heat transfer processes in any thermal application, making the study of their behavior a necessity. Taking into account the influence of the formation and growth of microstructures on change in properties of ferrofluids, one can find the significance of
On the consistency of the drag between air and water in meteorological, hydrodynamic and wave models
NASA Astrophysics Data System (ADS)
van Nieuwkoop, Joana; Baas, Peter; Caires, Sofia; Groeneweg, Jacco
2015-07-01
For the design, assessment and flood control of water defences, hydraulic loads in terms of water levels and wave conditions are required and often obtained from numerical models. For these hydraulic loads to be reliable, accurate atmospheric forcing is required. Waves and surges are typically forced by surface stress. However, in most cases, the input for these models consists of 10-m wind velocities that are internally converted to surface stress by applying a particular drag relation. This procedure generally leads to inconsistencies, since the hydrodynamic, wave and atmospheric models often apply different drag relations. By means of a case study, we explored the consequences of this inconsistency in the drag formulation for a North Sea storm wave and surge hindcast. This was done by forcing the hydrodynamic and wave models using both the 10-m wind velocity and the surface stress fields computed by the atmospheric model. Our study results show significant differences between the wave parameter values and water levels computed with surface stress input and 10-m wind velocity input. Our goal is not to assess different drag parameterizations but to raise awareness for this issue and to plea for the use of a consistent drag relation in meteorological and hydrodynamic/wave models. The consistent use of one drag formulation facilitates the identification of problems and the eventual improvement of the drag formulation. Furthermore, we suggest using the so-called pseudo-wind, which is a translation of the surface stress to the 10-m wind speed using a reference drag relation.
Hydrodynamic sensing and behavior by oyster larvae in turbulence and waves.
Fuchs, Heidi L; Gerbi, Gregory P; Hunter, Elias J; Christman, Adam J; Diez, F Javier
2015-05-01
Hydrodynamic signals from turbulence and waves may provide marine invertebrate larvae with behavioral cues that affect the pathways and energetic costs of larval delivery to adult habitats. Oysters (Crassostrea virginica) live in sheltered estuaries with strong turbulence and small waves, but their larvae can be transported into coastal waters with large waves. These contrasting environments have different ranges of hydrodynamic signals, because turbulence generally produces higher spatial velocity gradients, whereas waves can produce higher temporal velocity gradients. To understand how physical processes affect oyster larval behavior, transport and energetics, we exposed larvae to different combinations of turbulence and waves in flow tanks with (1) wavy turbulence, (2) a seiche and (3) rectilinear accelerations. We quantified behavioral responses of individual larvae to local instantaneous flows using two-phase, infrared particle-image velocimetry. Both high dissipation rates and high wave-generated accelerations induced most larvae to swim faster upward. High dissipation rates also induced some rapid, active dives, whereas high accelerations induced only weak active dives. In both turbulence and waves, faster swimming and active diving were achieved through an increase in propulsive force and power output that would carry a high energetic cost. Swimming costs could be offset if larvae reaching surface waters had a higher probability of being transported shoreward by Stokes drift, whereas diving costs could be offset by enhanced settlement or predator avoidance. These complex behaviors suggest that larvae integrate multiple hydrodynamic signals to manage dispersal tradeoffs, spending more energy to raise the probability of successful transport to suitable locations. PMID:25788721
Pu, Jaan Hui; Shao, Songdong
2012-01-01
This research paper presents an incompressible smoothed particle hydrodynamics (ISPH) technique to investigate a regular wave overtopping on the coastal structure of different types. The SPH method is a mesh-free particle modeling approach that can efficiently treat the large deformation of free surface. The incompressible SPH approach employs a true hydrodynamic formulation to solve the fluid pressure that has less pressure fluctuations. The generation of flow turbulence during the wave breaking and overtopping is modeled by a subparticle scale (SPS) turbulence model. Here the ISPH model is used to investigate the wave overtopping over a coastal structure with and without the porous material. The computations disclosed the features of flow velocity, turbulence, and pressure distributions for different structure types and indicated that the existence of a layer of porous material can effectively reduce the wave impact pressure and overtopping rate. The proposed numerical model is expected to provide a promising practical tool to investigate the complicated wave-structure interactions. PMID:22919291
NASA Astrophysics Data System (ADS)
Fuchs, Heidi L.; Gerbi, Gregory P.
2016-02-01
Plankton exhibit diverse and dramatic responses to fluid motions, and these behaviors are likely critical for survival and fitness. Fluid motions can be generated by organisms or by physical processes, including turbulence and surface gravity waves. Physical processes vary geographically in their intensity and generate hydrodynamic signals experienced by plankton as fluid forces on their sensory receptors. In this synthesis, we review how turbulence and waves vary in space, the scales and statistics of their motions, and the forces exerted on plankton. We then quantify the hydrodynamic signals produced by turbulence and waves in four seascape types - surf zones, inlets and estuaries, the continental shelf, and the open ocean - using published dissipation rates, wind and wave data from buoys, and observations from two coastal sites in Massachusetts, USA. We relate these geographic patterns in signals to the observed behaviors of example species and to the forces sensed by typical plankters with different receptor types. Turbulence-generated shears are largest in the surf zone, inlets and estuaries, while wave-generated accelerations are larger offshore; as a result, each seascape exhibits some range of combined shears and accelerations that is distinct. These signals generate forces on plankton that vary among habitats and with plankton size and swimming speed. Spatial patterns in fluid forces create a potential mechanism for dispersing larvae to distinguish habitats by their hydrodynamic signatures. However, turbulence can be strong in all seascapes and may cause widespread interference in signaling among predators and prey. Plankton with a single receptor type could identify nearshore habitats, while those with multiple receptor types potentially could distinguish inshore vs. offshore seascapes or decode signals produced by physical processes and by other organisms.
Coupling hydrodynamic and wave propagation modeling for waveform modeling of SPE.
NASA Astrophysics Data System (ADS)
Larmat, C. S.; Steedman, D. W.; Rougier, E.; Delorey, A.; Bradley, C. R.
2015-12-01
The goal of the Source Physics Experiment (SPE) is to bring empirical and theoretical advances to the problem of detection and identification of underground nuclear explosions. This paper presents effort to improve knowledge of the processes that affect seismic wave propagation from the hydrodynamic/plastic source region to the elastic/anelastic far field thanks to numerical modeling. The challenge is to couple the prompt processes that take place in the near source region to the ones taking place later in time due to wave propagation in complex 3D geologic environments. In this paper, we report on results of first-principles simulations coupling hydrodynamic simulation codes (Abaqus and CASH), with a 3D full waveform propagation code, SPECFEM3D. Abaqus and CASH model the shocked, hydrodynamic region via equations of state for the explosive, borehole stemming and jointed/weathered granite. LANL has been recently employing a Coupled Euler-Lagrange (CEL) modeling capability. This has allowed the testing of a new phenomenological model for modeling stored shear energy in jointed material. This unique modeling capability has enabled highfidelity modeling of the explosive, the weak grout-filled borehole, as well as the surrounding jointed rock. SPECFEM3D is based on the Spectral Element Method, a direct numerical method for full waveform modeling with mathematical accuracy (e.g. Komatitsch, 1998, 2002) thanks to its use of the weak formulation of the wave equation and of high-order polynomial functions. The coupling interface is a series of grid points of the SEM mesh situated at the edge of the hydrodynamic code domain. Displacement time series at these points are computed from output of CASH or Abaqus (by interpolation if needed) and fed into the time marching scheme of SPECFEM3D. We will present validation tests and waveforms modeled for several SPE tests conducted so far, with a special focus on effect of the local topography.
Hydrodynamic instabilities and transverse waves in propagation mechanism of gaseous detonations
NASA Astrophysics Data System (ADS)
Mahmoudi, Y.; Mazaheri, K.; Parvar, S.
2013-10-01
The present study examines the role of transverse waves and hydrodynamic instabilities mainly, Richtmyer-Meshkov instability (RMI) and Kelvin-Helmholtz instability (KHI) in detonation structure using two-dimensional high-resolution numerical simulations of Euler equations. To compare the numerical results with those of experiments, Navier-Stokes simulations are also performed by utilizing the effect of diffusion in highly irregular detonations. Results for both moderate and low activation energy mixtures reveal that upon collision of two triple points a pair of forward and backward facing jets is formed. As the jets spread, they undergo Richtmyer-Meshkov instability. The drastic growth of the forward jet found to have profound role in re-acceleration of the detonation wave at the end of a detonation cell cycle. For irregular detonations, the transverse waves found to have substantial role in propagation mechanism of such detonations. In regular detonations, the lead shock ignites all the gases passing through it, hence, the transverse waves and hydrodynamic instabilities do not play crucial role in propagation mechanism of such regular detonations. In comparison with previous numerical simulations present simulation using single-step kinetics shows a distinct keystone-shaped region at the end of the detonation cell.
Acoustic waves in a stratified atmosphere. IV. Three-dimensional nonlinear hydrodynamics
NASA Astrophysics Data System (ADS)
Kalkofen, W.; Rossi, P.; Bodo, G.; Massaglia, S.
2010-09-01
Context. The quiet solar chromosphere in the interior of supergranulation cells is believed to be heated by the dissipation of acoustic waves that originate with a typical period of 3 min in the photosphere. Aims: We investigate how the horizontal expansion with height of acoustic waves traveling upward into an isothermal, gravitationally stratified atmosphere depends on the size of the source region. Methods: We have solved the three-dimensional, nonlinear, time-dependent hydrodynamic equations for impulsively-generated, upward-propagating acoustic waves, assuming cylindrical symmetry. Results: When the diameter of the source of acoustic waves is small, the pattern of the upward-propagating waves is that of a point source, for which the energy travels upward in a vertical cone, qualitatively matching the observed pattern of bright-point expansion with height. For the largest plausible size of a source region, i.e., with granular size of 1 Mm, wave propagation in the low chromosphere is approximately that of plane waves, but in the middle and upper chromosphere it is also that of a point source. The assumption of plane-wave propagation is not a good approximation in the solar chromosphere. The upward-directed energy flux is larger than that of the solar chromosphere, at least in the middle and upper chromosphere, and probably throughout. Conclusions: Simulations of impulsively generated acoustic waves emitted from source regions with diameters that are small compared to the pressure scale height of the atmosphere qualitatively reproduce the upward expansion observed in chromospheric bright points. The emission features in the cores of the H and K lines are predicted to be blueshifted for a pulse and redshifted for the waves in its wake. The contribution of internal gravity waves to the upward energy flux is small and decreases with increasing size of the source region.
A Stability Analysis for a Hydrodynamic Three-Wave Journal Bearing
NASA Technical Reports Server (NTRS)
Ene, Nicoleta M.; Dimofte, Florin; Keith, Theo G., Jr.
2007-01-01
The influence of the wave amplitude and oil supply pressure on the dynamic behavior of a hydrodynamic three-wave journal bearing is presented. Both, a transient and a small perturbation technique, were used to predict the threshold to fractional frequency whirl (FFW). In addition, the behavior of the rotor after FFW appeared was determined from the transient analysis. The turbulent effects were also included in the computations. Bearings having a diameter of 30 mm, a length of 27.5 mm, and a clearance of 35 microns were analyzed. Numerical results were compared to experimental results obtained at the NASA GRC. Numerical and experimental results showed that the above-mentioned wave bearing with a wave amplitude ratio of 0.305 operates stably at rotational speeds up to 60,000 rpm, regardless of the oil supply pressure. For smaller wave amplitude ratios, a threshold of stability was found. It was observed that the threshold of stability for lower wave amplitude strongly depends on the oil supply pressure and on the wave amplitude. When the FFW occurs, the journal center maintains its trajectory inside the bearing clearance and therefore the rotor can be run safely without damaging the bearing surfaces.
Brumley, Douglas R; Polin, Marco; Pedley, Timothy J; Goldstein, Raymond E
2012-12-28
From unicellular ciliates to the respiratory epithelium, carpets of cilia display metachronal waves, long-wavelength phase modulations of the beating cycles, which theory suggests may arise from hydrodynamic coupling. Experiments have been limited by a lack of organisms suitable for systematic study of flagella and the flows they create. Using time-resolved particle image velocimetry, we report the discovery of metachronal waves on the surface of the colonial alga Volvox carteri, whose large size and ease of visualization make it an ideal model organism for these studies. An elastohydrodynamic model of weakly coupled compliant oscillators, recast as interacting phase oscillators, reveals that orbit compliance can produce fast, robust synchronization in a manner essentially independent of boundary conditions, and offers an intuitive understanding of a possible mechanism leading to the emergence of metachronal waves. PMID:23368623
NASA Astrophysics Data System (ADS)
Brumley, Douglas R.; Polin, Marco; Pedley, Timothy J.; Goldstein, Raymond E.
2012-12-01
From unicellular ciliates to the respiratory epithelium, carpets of cilia display metachronal waves, long-wavelength phase modulations of the beating cycles, which theory suggests may arise from hydrodynamic coupling. Experiments have been limited by a lack of organisms suitable for systematic study of flagella and the flows they create. Using time-resolved particle image velocimetry, we report the discovery of metachronal waves on the surface of the colonial alga Volvox carteri, whose large size and ease of visualization make it an ideal model organism for these studies. An elastohydrodynamic model of weakly coupled compliant oscillators, recast as interacting phase oscillators, reveals that orbit compliance can produce fast, robust synchronization in a manner essentially independent of boundary conditions, and offers an intuitive understanding of a possible mechanism leading to the emergence of metachronal waves.
East Frisian Wadden Sea hydrodynamics and wave effects in an unstructured-grid model
NASA Astrophysics Data System (ADS)
Grashorn, Sebastian; Lettmann, Karsten A.; Wolff, Jörg-Olaf; Badewien, Thomas H.; Stanev, Emil V.
2015-03-01
An unstructured-grid model (FVCOM) coupled to a surface wave model (FVCOM-SWAVE) with two different setups is used to investigate the hydrodynamic and wave energy conditions during a moderate wind and a storm situation in the southern North Sea. One setup covers the whole North Sea with moderately increased grid resolution at the coast, whereas the other is a very high-resolution Wadden Sea setup that is one-way coupled to the coarser North Sea model. The results of both model setups are validated, compared to each other and analysed with a focus on longshore currents and wave energy. The numerical results show that during storm conditions, strong wave-induced longshore currents occur in front of the East Frisian Wadden Sea islands with current speeds up to 1 m/s. The model setup with the higher resolution around the islands shows even stronger currents than the coarser setup. The wave-current interaction also influences the surface elevation by raising the water level in the tidal basins. The calculated wave energies show large differences between moderate wind and storm conditions with time-averaged values up to 200 kW/m.
NASA Astrophysics Data System (ADS)
Bever, A. J.; MacWilliams, M.
2012-12-01
Under the conceptual model of sediment transport in San Pablo Bay, a sub-embayment of San Francisco Bay, proposed by Krone (1979), sediment typically enters San Pablo Bay during large winter and spring flows and is redistributed during summer conditions through wind wave resuspension and transport by tidal currents. A detailed understanding of how the waves and tides redistribute sediment within San Francisco Bay is critical for predicting how future sea level rise and a reduction in the sediment supply to the Bay will impact existing marsh and mudflat habitat, tidal marsh restoration projects, and ongoing maintenance dredging of the navigation channels. The three-dimensional UnTRIM San Francisco Bay-Delta Model was coupled with the Simulating WAves Nearshore (SWAN) wave model and the SediMorph morphological model, to develop a three-dimensional hydrodynamic, wind wave, and sediment transport model of the San Francisco Bay and the Sacramento-San Joaquin Delta. Numerical simulations of sediment resuspension due to tidal currents and wind waves and the subsequent transport of this sediment by tidal currents are used to quantify the spatial and temporal variability of sediment fluxes on the extensive shoals in San Pablo Bay under a range of tidal and wind conditions. The results demonstrate that suspended sediment concentration and sediment fluxes within San Pablo Bay are a complex product of tides and waves interacting spatially throughout the Bay, with concentrations responding to local resuspension and sediment advection. Sediment fluxes between the San Pablo Bay shoals and the deeper channel are highest during spring tides, and are elevated for up to a week following wave events, even though the greatest influence of the wave event occurs abruptly.
Hydrodynamics of a cold one-dimensional fluid: the problem of strong shock waves
NASA Astrophysics Data System (ADS)
Hurtado, Pablo I.
2005-03-01
We study a shock wave induced by an infinitely massive piston propagating into a one-dimensional cold gas. The cold gas is modelled as a collection of hard rods which are initially at rest, so the temperature is zero. Most of our results are based on simulations of a gas of rods with binary mass distribution, and we partcularly focus on the case of spatially alternating masses. We find that the properties of the resulting shock wave are in striking contrast with those predicted by hydrodynamic and kinetic approaches, e.g., the flow-field profiles relax algebraically toward their equilibrium values. In addition, most relevant observables characterizing local thermodynamic equilibrium and equipartition decay as a power law of the distance to the shock layer. The exponents of these power laws depend non-monotonously on the mass ratio. Similar interesting dependences on the mass ratio also characterize the shock width, density and temperature overshoots, etc.
Metachronal waves in the flagellar beating of Volvox and their hydrodynamic origin.
Brumley, Douglas R; Polin, Marco; Pedley, Timothy J; Goldstein, Raymond E
2015-07-01
Groups of eukaryotic cilia and flagella are capable of coordinating their beating over large scales, routinely exhibiting collective dynamics in the form of metachronal waves. The origin of this behavior--possibly influenced by both mechanical interactions and direct biological regulation--is poorly understood, in large part due to a lack of quantitative experimental studies. Here we characterize in detail flagellar coordination on the surface of the multicellular alga Volvox carteri, an emerging model organism for flagellar dynamics. Our studies reveal for the first time that the average metachronal coordination observed is punctuated by periodic phase defects during which synchrony is partial and limited to specific groups of cells. A minimal model of hydrodynamically coupled oscillators can reproduce semi-quantitatively the characteristics of the average metachronal dynamics, and the emergence of defects. We systematically study the model's behaviour by assessing the effect of changing intrinsic rotor characteristics, including oscillator stiffness and the nature of their internal driving force, as well as their geometric properties and spatial arrangement. Our results suggest that metachronal coordination follows from deformations in the oscillators' limit cycles induced by hydrodynamic stresses, and that defects result from sufficiently steep local biases in the oscillators' intrinsic frequencies. Additionally, we find that random variations in the intrinsic rotor frequencies increase the robustness of the average properties of the emergent metachronal waves. PMID:26040592
Metachronal waves in the flagellar beating of Volvox and their hydrodynamic origin
Brumley, Douglas R.; Polin, Marco; Pedley, Timothy J.; Goldstein, Raymond E.
2015-01-01
Groups of eukaryotic cilia and flagella are capable of coordinating their beating over large scales, routinely exhibiting collective dynamics in the form of metachronal waves. The origin of this behaviour—possibly influenced by both mechanical interactions and direct biological regulation—is poorly understood, in large part due to a lack of quantitative experimental studies. Here we characterize in detail flagellar coordination on the surface of the multicellular alga Volvox carteri, an emerging model organism for flagellar dynamics. Our studies reveal for the first time that the average metachronal coordination observed is punctuated by periodic phase defects during which synchrony is partial and limited to specific groups of cells. A minimal model of hydrodynamically coupled oscillators can reproduce semi-quantitatively the characteristics of the average metachronal dynamics, and the emergence of defects. We systematically study the model's behaviour by assessing the effect of changing intrinsic rotor characteristics, including oscillator stiffness and the nature of their internal driving force, as well as their geometric properties and spatial arrangement. Our results suggest that metachronal coordination follows from deformations in the oscillators' limit cycles induced by hydrodynamic stresses, and that defects result from sufficiently steep local biases in the oscillators' intrinsic frequencies. Additionally, we find that random variations in the intrinsic rotor frequencies increase the robustness of the average properties of the emergent metachronal waves. PMID:26040592
Two-temperature hydrodynamics of laser-generated ultrashort shock waves in elasto-plastic solids
NASA Astrophysics Data System (ADS)
Ilnitsky, Denis K.; Khokhlov, Viktor A.; Inogamov, Nail A.; Zhakhovsky, Vasily V.; Petrov, Yurii V.; Khishchenko, Konstantin V.; Migdal, Kirill P.; Anisimov, Sergey I.
2014-05-01
Shock-wave generation by ultrashort laser pulses opens new doors for study of hidden processes in materials happened at an atomic-scale spatiotemporal scales. The poorly explored mechanism of shock generation is started from a short-living two-temperature (2T) state of solid in a thin surface layer where laser energy is deposited. Such 2T state represents a highly non-equilibrium warm dense matter having cold ions and hot electrons with temperatures of 1-2 orders of magnitude higher than the melting point. Here for the first time we present results obtained by our new hybrid hydrodynamics code combining detailed description of 2T states with a model of elasticity together with a wide-range equation of state of solid. New hydro-code has higher accuracy in the 2T stage than molecular dynamics method, because it includes electron related phenomena including thermal conduction, electron-ion collisions and energy transfer, and electron pressure. From the other hand the new code significantly improves our previous version of 2T hydrodynamics model, because now it is capable of reproducing the elastic compression waves, which may have an imprint of supersonic melting like as in MD simulations. With help of the new code we have solved a difficult problem of thermal and dynamic coupling of a molten layer with an uniaxially compressed elastic solid. This approach allows us to describe the recent femtosecond laser experiments.
Negative magnetophoresis in diluted ferrofluid flow.
Hejazian, Majid; Nguyen, Nam-Trung
2015-07-21
We report magnetic manipulation of non-magnetic particles suspended in diluted ferrofluid. Diamagnetic particles were introduced into a circular chamber to study the extent of their deflection under the effect of a non-uniform magnetic field of a permanent magnet. Since ferrofluid is a paramagnetic medium, it also experiences a bulk magnetic force that in turn induces a secondary flow opposing the main hydrodynamic flow. Sheath flow rate, particle size, and magnetic field strength were varied to examine this complex behaviour. The combined effect of negative magnetophoresis and magnetically induced secondary flow leads to various operation regimes, which can potentially find applications in separation, trapping and mixing of diamagnetic particles such as cells in a microfluidic system. PMID:26054840
Ferrofluids: Thermophysical properties and formation of microstructures
NASA Astrophysics Data System (ADS)
Mousavi Khoeini, NargesSadat Susan
This work is a combined effort of experimental and theoretical studies toward better understanding the structural and physical properties of aqueous ferrofluids containing nano-sized magnetite (iron oxide magnetic particles) of about 10nm. Ferrofluids have attracted remarkable attention mainly because their properties can be controlled by means of an externally applied magnetic field. The dispersion of nano-sized magnets in a carrier liquid exhibits superparamagnetic behaviour while retaining its fluid properties. The interplay between hydrodynamic and magnetic phenomena has made ferrofluids an extremely promising and useful tool in wide spectra of applications, from technical applications to biomedical ones. In the presence of a magnetic field, magnetic moments of the nanomagnets suspended in the host liquid are aligned toward the field direction and begin to form microstructures such as short chains, strands and long stripes. As this process advances the microstructures may collapse into bundles and thick chains and form macrostructures. Upon the removal of the magnetic field, nanoparticles will be homogeneously redistributed throughout the sample due to thermal agitation. Zero-field structures, and especially the field-induced assembly of magnetic nanoparticles, are primarily responsible for the change in physical properties of ferrofluids, including thermophysical, optical, rheological, and magnetization properties. Because of the field-induced assembly of magnetic nanoparticles in the field direction, ferrofluids become strongly anisotropic and as a result, ferrofluids can significantly enhance directional heat transfer in a thermal system. Thermophysical properties of a ferrofluid are important in studying heat transfer processes in any thermal application, making the study of their behavior a necessity. Taking into account the influence of the formation and growth of microstructures on change in properties of ferrofluids, one can find the significance of
A Lagrangian description of nearshore hydrodynamics and rip currents forced by a random wave field
NASA Astrophysics Data System (ADS)
Leandro, S.; Cienfuegos, R.; Escauriaza, C. R.
2011-12-01
Nonlinear processes become important for waves propagating in the shoaling and surf zones. Wave shape changes when approaching the coast under the influence of bathymetry, becoming increasingly asymmetric until reaching the breaking limit. In the shoaling zone, non-linearities induce a net velocity in the direction of wave propagation, a phenomenon called Stokes drift, while in the surf zone, currents are mainly driven by spatio-temporal variations in energy dissipation gradients. In this work we aim at investigating and characterizing the nearshore circulation forced by a random wave field propagating over a variable bathymetry. We carry out numerical simulations over a laboratory experiment conducted in a wave basin over a realistic bathymetry [Michallet et al. 2010]. For the hydrodynamics, we use a 2D shock-capturing finite-volume model that solves the non-linear shallow water equations, taking into account energy dissipation by breaking, friction, bed-slope variations, and an accurate description for the moving shoreline in the swash zone [Marche et al. 2007;Guerra et al. 2010]. Model predictions are compared and validated against experimental data giving confidence for its use in the description of wave propagation in the surf/swash zone, together with mean eulerian velocities. The resulting wave propagation and circulation provided by the 2D model will then be used to describe drifter's patterns in the surf zone and construct Lagrangian particle tracking. The chosen experimental configuration is of great interest due to the random wave forcing (slowly modulated), the beach non-uniformities, and the existence of several bar-rip channels that enhance quasi-periodic rip instabilities. During the experiment, balloons filled with water, with a diameter between 5 and 10 cm, were placed in the surf zone in order to characterize circulation in a Lagrangian framework [Castelle et al. 2010]. The time-location of the balloons was continuously tracked by a shore
The dynamics analysis of a ferrofluid shock absorber
NASA Astrophysics Data System (ADS)
Yao, Jie; Chang, Jianjun; Li, Decai; Yang, Xiaolong
2016-03-01
The paper presents a shock absorber using three magnets as the inertial mass. Movement of the inertial mass inside a cylindrical body filled with ferrofluid will lead to a viscous dissipation of the oscillating system energy. The influence of a dumbbell-like ferrofluid structure on the energy dissipation is considered and the magnetic restoring force is investigated by experiment and theoretical calculation. A theoretical model of the hydrodynamics and energy dissipation processes is developed, which includes the geometrical characteristics of the body, the fluid viscosity, and the external magnetic field. The theory predicts the experimental results well under some condition. The shock absorber can be used in spacecraft technology.
NASA Astrophysics Data System (ADS)
Lasky, Paul D.; Bennett, Mark F.; Melatos, Andrew
2013-03-01
Hydrodynamic turbulence driven by crust-core differential rotation imposes a fundamental noise floor on gravitational wave observations of neutron stars. The gravitational wave emission peaks at the Kolmogorov decoherence frequency which, for reasonable values of the crust-core shear, ΔΩ, occurs near the most sensitive part of the frequency band for ground-based, long-baseline interferometers. We calculate the energy density spectrum of the stochastic gravitational wave background from a cosmological population of turbulent neutron stars generalizing previous calculations for individual sources. The spectrum resembles a piecewise power law, Ωgw(ν)=Ωανα, with α=-1 and 7 above and below the decoherence frequency respectively, and its normalization scales as Ωα∝(ΔΩ)7. Nondetection of a stochastic signal by Initial LIGO implies an upper limit on ΔΩ and hence by implication on the internal relaxation time scale for the crust and core to come into corotation, τd=ΔΩ/Ω˙, where Ω˙ is the observed electromagnetic spin-down rate, with τd≲107yr for accreting millisecond pulsars and τd≲105yr for radio-loud pulsars. Target limits on τd are also estimated for future detectors, namely Advanced LIGO and the Einstein Telescope, and are found to be astrophysically interesting.
NASA Astrophysics Data System (ADS)
Marques, Wilson, Jr.; Jacinta Soares, Ana; Pandolfi Bianchi, Miriam; Kremer, Gilberto M.
2015-06-01
A shock wave structure problem, like the one which can be formulated for the planar detonation wave, is analyzed here for a binary mixture of ideal gases undergoing the symmetric reaction {{A}1}+{{A}1}\\rightleftharpoons {{A}2}+{{A}2}. The problem is studied at the hydrodynamic Euler limit of a kinetic model of the reactive Boltzmann equation. The chemical rate law is deduced in this frame with a second-order reaction rate, in a chemical regime such that the gas flow is not far away from the chemical equilibrium. The caloric and the thermal equations of state for the specific internal energy and temperature are employed to close the system of balance laws. With respect to other approaches known in the kinetic literature for detonation problems with a reversible reaction, this paper aims to improve some aspects of the wave solution. Within the mathematical analysis of the detonation model, the equation of the equilibrium Hugoniot curve of the final states is explicitly derived for the first time and used to define the correct location of the equilibrium Chapman-Jouguet point in the Hugoniot diagram. The parametric space is widened to investigate the response of the detonation solution to the activation energy of the chemical reaction. Finally, the mathematical formulation of the linear stability problem is given for the wave detonation structure via a normal-mode approach, when bidimensional disturbances perturb the steady solution. The stability equations with their boundary conditions and the radiation condition of the considered model are explicitly derived for small transversal deviations of the shock wave location. The paper shows how a second-order chemical kinetics description, derived at the microscopic level, and an analytic deduction of the equilibrium Hugoniot curve, lead to an accurate picture of the steady detonation with reversible reaction, as well as to a proper bidimensional linear stability analysis.
Wave-driven Hydrodynamics for Different Reef Geometries and Roughness Scenarios
NASA Astrophysics Data System (ADS)
Franklin, G. L.; Marino-Tapia, I.; Torres-Freyermuth, A.
2013-05-01
In fringing reef systems where a shallow lagoon is present behind the reef crest, wave breaking appears to dominate circulation, controlling numerous key processes such as the transport and dispersion of larvae, nutrients and sediments. Despite their importance, there is a need for more detailed knowledge on the hydrodynamic processes that take place within the surf zone of these systems and the effects different combinations of geometries and roughness have on them. The present study focuses on the use of two-dimensional (2DV) numerical model simulations and data obtained during a field campaign in Puerto Morelos, Quintana Roo, Mexico to better understand the detailed surf zone processes that occur over a fringing reef. The model used is Cornell Breaking Wave and Structures (COBRAS), which solves Reynolds-Averaged Navier-Stokes (RANS) equations. Reef geometries implemented in the model include a reef flat and two different reef crests. The effect of roughness on wave setup, radiation stress, mean flows, and cross-shore spectral evolution for the model results was studied using different roughness coefficients (Nikuradse) and a bathymetric profile obtained in the field using the bottom track option of an Acoustic Doppler Current Profiler. Field data were also analysed for the configuration and roughness of Puerto Morelos. Model results reveal that for all profiles wave setup increased significantly (~22%) with increasing bed roughness, in agreement with previous findings for sandy beaches.For all wave heights and periods studied, increasing roughness also affected spectral wave evolution across the reef, with a significant reduction in energy, particularly at infragravity frequencies. The presence of a reef crest in the profile resulted in differences in behaviour at infragravity frequencies. For example, preliminary results suggest that there is a shift towards higher frequencies as waves progress into the lagoon when a crest is present, something that does not
Viscoelastic properties of ferrofluids.
Chirikov, D N; Fedotov, S P; Iskakova, L Yu; Zubarev, A Yu
2010-11-01
The paper deals with theoretical study of non linear viscoelastic phenomena in ferrofluids placed in magnetic field. Our attention is focused on the study of nonstationary flow and Maxwell-like relaxation of the macroscopical viscous stress after alternation of the shear rate. We propose that these phenomena can be explained by finite rate of evolution of chainlike aggregates, consisting of the ferrofluid particles. Statistical model of the chains growth-disintegration is suggested. In this model the chain-single particle mechanism of the chains evolution is considered, the effects of the chain-chain interaction are ignored. The proposed model allows us to estimate the time-dependent function of distribution over number of particles in the chain. Having determined this function and using methods of hydromechanics of ferrofluids with chainlike aggregates, we have studied evolution of the ferrofluid viscosity after stepwise alternation of the fluid shear rate. The estimated time of relaxation is in a reasonable agreement with experimental results. Thus, our analysis shows that the observed macroscopical viscoelastic phenomena in ferrofluids can be provided by evolution of the chain ensemble. PMID:21230477
NASA Astrophysics Data System (ADS)
Macayeal, D. R.
2009-12-01
The interaction between icebergs, their parent ice shelves and the fluid in which they float (seawater) is one of the most demanding problems in glaciology because the interactions involve multiple widely divergent time scales, a variety of constitutive behaviors along with free surfaces and disconnected domains. As calving begins, compressibility and surface tension of seawater comes into play as free-falling ice encounters the ocean surface, producing jets of spray and filling the water with plumes of bubbles. As calving proceeds, incompressible hydrodynamics describes the interaction between the iceberg and the surface waves (tsunamis) the calving event creates in the ocean. In regions where the Froude number (which inversely measures the ability of the water to relieve pressure on the iceberg, ice shelf and seabed by radiating free-surface gravity waves) is greater than 1, hydraulic pressure coupling can produce extraordinary tensile and compressive stresses in the iceberg and ice shelf, triggering further calving. Eventually, a hydrostatic pressure regime develops in which icebergs may further evolve through capsize, which often produces such strong elastic stress within the iceberg sufficient to cause its disintegration. This presentation will focus on the use of SPH as a means of modeling ice/ocean interaction during iceberg calving. Goals of the investigation will be methodological and will evaluate the efficiency and accuracy of the computation of boundary forces which act on icebergs, ice shelves and seabed/fjord walls during iceberg calving and capsize.
Ferrofluid mediated nanocytometry.
Kose, Ayse Rezzan; Koser, Hur
2012-01-01
We present a low-cost, flow-through nanocytometer that utilizes a colloidal suspension of non-functionalized magnetic nanoparticles for label-free manipulation and separation of microparticles. Our size-based separation is mediated by angular momentum transfer from magnetically excited ferrofluid particles to microparticles. The nanocytometer is capable of rapidly sorting and focusing two or more species, with up to 99% separation efficiency and a throughput of 3 × 10(4) particles/s per mm(2) of channel cross-section. The device is readily scalable and applicable to live cell sorting with biocompatible ferrofluids, offering competitive cytometer performance in a simple and inexpensive package. PMID:22076536
Flow control using ferrofluids
NASA Astrophysics Data System (ADS)
Cornat, Francois; Beck, David; Jacobi, Ian; Stone, Howard
2013-11-01
A novel flow control technique is proposed which employs a ferrofluidic lubricant infused in a micro-patterned substrate as a ``morphing surface'' for control of wall-bounded flows. Traditionally, morphing surfaces produce dynamic changes in the curvature and roughness of solid substrates for active control of high Reynolds number flow features such as boundary layer separation and turbulent streaks. We show how these surface modifications can be achieved with a thin liquid layer in the presence of a normal magnetic field. By impregnating a chemically-treated, micro-patterned surface with a fluorinated ferrofluid, the fluid is maintained as a thin super-hydrophobic film and can be redistributed on the substrate by magnetic forces to dynamically reveal or conceal the underlying surface roughness. Moreover, the surface topography of the ferrofluid film itself can be modified to produce an enhanced roughness, beyond the scale of the underlying substrate pattern. Both types of ferrofluidic surface modifications are studied in micro- and macro- scale channels in order to assess the feasibility of flow modification at low to moderate Reynolds numbers.
NASA Astrophysics Data System (ADS)
Wei, Xing
2016-09-01
To understand magnetic effects on dynamical tides, we study the rotating magnetohydrodynamic (MHD) flow driven by harmonic forcing. The linear responses are analytically derived in a periodic box under the local WKB approximation. Both the kinetic and Ohmic dissipations at the resonant frequencies are calculated, and the various parameters are investigated. Although magnetic pressure may be negligible compared to thermal pressure, the magnetic field can be important for the first-order perturbation, e.g., dynamical tides. It is found that the magnetic field splits the resonant frequency, namely the rotating hydrodynamic flow has only one resonant frequency, but the rotating MHD flow has two, one positive and the other negative. In the weak field regime the dissipations are asymmetric around the two resonant frequencies and this asymmetry is more striking with a weaker magnetic field. It is also found that both the kinetic and Ohmic dissipations at the resonant frequencies are inversely proportional to the Ekman number and the square of the wavenumber. The dissipation at the resonant frequency on small scales is almost equal to the dissipation at the non-resonant frequencies, namely the resonance takes its effect on the dissipation at intermediate length scales. Moreover, the waves with phase propagation that is perpendicular to the magnetic field are much more damped. It is also interesting to find that the frequency-averaged dissipation is constant. This result suggests that in compact objects, magnetic effects on tidal dissipation should be considered.
NASA Astrophysics Data System (ADS)
Chen, Jia-Lin; Hsu, Tian-Jian; Shi, Fengyan; Raubenheimer, Britt; Elgar, Steve
2015-06-01
The interactions between waves, tidal currents, and bathymetry near New River Inlet, NC, USA are investigated to understand the effects on the resulting hydrodynamics and sediment transport. A quasi-3-D nearshore community model, NearCoM-TVD, is used in this integrated observational and modeling study. The model is validated with observations of waves and currents at 30 locations, including in a recently dredged navigation channel and a shallower channel, and on the ebb tidal delta, for a range of flow and offshore wave conditions during May 2012. In the channels, model skills for flow velocity and wave height are high. Near the ebb tidal delta, the model reproduces the observed rapid onshore (offshore) decay of wave heights (current velocities). Model results reveal that this sharp transition coincides with the location of the breaker zone over the ebb tidal delta, which is modulated by semidiurnal tides and by wave intensity. The modulation of wave heights is primarily owing to depth changes rather than direct wave-current interaction. The modeled tidally averaged residual flow patterns show that waves play an important role in generating vortices and landward-directed currents near the inlet entrance. Numerical experiments suggest that these flow patterns are associated with the channel-shoal bathymetry near the inlet, similar to the generation of rip currents. Consistent with other inlet studies, model results suggest that tidal currents drive sediment fluxes in the channels, but that sediment fluxes on the ebb tidal delta are driven primarily by waves.
Towards ferrofluidics for μ-TAS and lab on-a-chip applications
NASA Astrophysics Data System (ADS)
Mao, Leidong; Koser, Hur
2006-02-01
In this paper, we show that ferrofluids can be pumped very effectively in closed-channel geometries both in the macro- and micro-scales using spatially travelling, sinusoidally time-varying magnetic fields. The results from numerical modelling demonstrate that the optimum pumping frequency is the reciprocal of the Brownian relaxation time constant of the magnetic nanoparticles inside the ferrofluid. Since the Brownian time constant depends in part on the overall hydrodynamic volume of the magnetic nanoparticles, this work has been carried with a view to developing functionalized ferrofluids that can be used as sensitive pathogen detectors in the context of ferrohydrodynamic pumping via travelling magnetic fields. A micro-ferrofluidic device has been designed and fabricated in order to demonstrate the potential development of this technology for pathogen detection. A cost-effective fabrication process combining insulated metal substrate etching and soft lithography is used to realize the prototype micro-ferrofluidic device. Results show good agreement between simulation and experiment. We finally propose a ferrofluid-based pathogen detection scheme that is expected to be insensitive to temperature and viscosity differences between the ferrofluid and the sample to be tested.
NASA Astrophysics Data System (ADS)
Busca, Claudia; Coluccelli, Alessandro; Valentini, Andrea; Benetazzo, Alvise; Bonaldo, Davide; Bortoluzzi, Giovanni; Carniel, Sandro; Falcieri, Francesco; Paccagnella, Tiziana; Ravaioli, Mariangela; Riminucci, Francesco; Sclavo, Mauro; Russo, Aniello
2014-05-01
The complex dynamics of the Adriatic Sea are the result of geographical position, orography and bathymetry, as well as rivers discharge and meteorological conditions that influence, more strongly, the shallow northern part. Such complexity requires a constant monitoring of marine conditions in order to support several activities (marine resources management, naval operations, emergency management, shipping, tourism, as well as scientific ones). Platforms, buoys and mooring located in Adriatic Sea supply almost continuously real time punctual information, which can be spatially extended, with some limitations, by drifters and remote sensing. Operational forecasting systems represent valid tools to provide a complete tridimensional coverage of the area, with a high spatial and temporal resolution. The Hydro-Meteo-Clima Service of the Emilia-Romagna Environmental Agency (ARPA-SIMC, Bologna, Italy) and the Dept. of Life and Environmental Sciences of Università Politecnica delle Marche (DISVA-UNIVPM, Ancona, Italy), in collaboration with the Institute of Marine Science of the National Research Council (ISMAR-CNR, Italy) operationally run several wave and hydrodynamic models on the Adriatic Sea. The main implementations are based on the Regional Ocean Modeling System (ROMS), the wave model Simulating WAves Nearshore (SWAN), and the coupling of the former two models in the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) system. Horizontal resolutions of the different systems range from the 2 km of AdriaROMS to the 0.5 km of the recently implemented northern Adriatic COAWST. Forecasts are produced every day for the subsequent 72 hour with hourly resolution. All the systems compute the fluxes exchanged through the interface with the atmosphere from the numerical weather prediction system named COSMO-I7, an implementation for Italy of the Consortium for Small-scale Modeling (COSMO) model, at 7 km horizontal resolution. Considering the several operational
Magnetorheological properties of some ferrofluids
NASA Astrophysics Data System (ADS)
Timko, M.; Zentko, A.; Zentkova, M.; Koneracka, M.; Kellnerova, V.; Zentkova, A.; Stepan, M.; Barbora, J.
1994-03-01
The effect of an external magnetic field, velocity of flow and concentration of the magnetite on the rheological properties of some mineral oil based ferrofluids have been investigated. It has been shown that the increase of viscosity in magnetic field depends upon the velocity flow of ferrofluid and concentration of magnetite.
Lacy, J.R.; Sherwood, C.R.; Wilson, D.J.; Chisholm, T.A.; Gelfenbaum, G.R.
2005-01-01
Hydrodynamic roughness is a critical parameter for characterizing bottom drag in boundary layers, and it varies both spatially and temporally due to variation in grain size, bedforms, and saltating sediment. In this paper we investigate temporal variability in hydrodynamic roughness using velocity profiles in the bottom boundary layer measured with a high-resolution acoustic Doppler profiler (PCADP). The data were collected on the ebb-tidal delta off Grays Harbor, Washington, in a mean water depth of 9 m. Significant wave height ranged from 0.5 to 3 m. Bottom roughness has rarely been determined from hydrodynamic measurements under conditions such as these, where energetic waves and medium-to-fine sand produce small bedforms. Friction velocity due to current u*c and apparent bottom roughness z0a were determined from the PCADP burst mean velocity profiles using the law of the wall. Bottom roughness kB was estimated by applying the Grant-Madsen model for wave-current interaction iteratively until the model u*c converged with values determined from the data. The resulting kB values ranged over 3 orders of magnitude (10-1 to 10-4 m) and varied inversely with wave orbital diameter. This range of kB influences predicted bottom shear stress considerably, suggesting that the use of time-varying bottom roughness could significantly improve the accuracy of sediment transport models. Bedform height was estimated from kB and is consistent with both ripple heights predicted by empirical models and bedforms in sonar images collected during the experiment. Copyright 2005 by the American Geophysical Union.
NASA Astrophysics Data System (ADS)
Bonelli, Giulio; Sciarappa, Antonio; Tanzini, Alessandro; Vasko, Petr
2014-07-01
We show that the exact partition function of U( N) six-dimensional gauge theory with eight supercharges on ℂ2 × S 2 provides the quantization of the integrable system of hydrodynamic type known as gl( N) periodic Intermediate Long Wave (ILW). We characterize this system as the hydrodynamic limit of elliptic Calogero-Moser integrable system. We compute the Bethe equations from the effective gauged linear sigma model on S 2 with target space the ADHM instanton moduli space, whose mirror computes the Yang-Yang function of gl( N) ILW. The quantum Hamiltonians are given by the local chiral ring observables of the six-dimensional gauge theory. As particular cases, these provide the gl( N) Benjamin-Ono and Korteweg-de Vries quantum Hamiltonians. In the four dimensional limit, we identify the local chiral ring observables with the conserved charges of Heisenberg plus W N algebrae, thus providing a gauge theoretical proof of AGT correspondence.
NASA Astrophysics Data System (ADS)
Shi, Chuanqi; An, Yi; Wu, Qiang; Liu, Qingquan; Cao, Zhixian
2016-06-01
We simulate the generation of a landslide-induced impulse wave with a newly-developed soil-water coupling model in the smoothed particle hydrodynamics (SPH) framework. The model includes an elasto-plastic constitutive model for soil, a Navier-Stokes equation based model for water, and a bilateral coupling model at the interface. The model is tested with simulated waves induced by a slow and a fast landslide. Good agreement is obtained between simulation results and experimental data. The generated wave and the deformation of the landslide body can both be resolved satisfactorily. All parameters in our model have their physical meaning in soil mechanics and can be obtained from conventional soil mechanics experiments directly. The influence of the dilatancy angle of soil shows that the non-associated flow rule must be selected, and the value of the dilatancy angle should not be chosen arbitrarily, if it is not determined with relative experiments.
Chain-induced effects in the Faraday instability on ferrofluids in a horizontal magnetic field
NASA Astrophysics Data System (ADS)
Mekhonoshin, V. V.; Lange, Adrian
2004-04-01
The linear stability analysis of the Faraday instability on a viscous ferrofluid in a horizontal magnetic field is performed. Strong dipole-dipole interactions lead to the formation of chains elongated in the field direction. The formation of chains results in a qualitative new behavior of the ferrofluid. This new behavior is characterized by a neutral stability curve similar to that observed earlier for Maxwell viscoelastic liquids and causes a significant weakening of the energy dissipation at high frequencies. In the case of a ferrofluid with chains in a horizontal magnetic field, the effective viscosity is anisotropic and depends on the field strength as well as on the wave frequency.
BCS-BEC crossover and quantum hydrodynamics in p-wave superfluids with a symmetry of the A1 phase
Kagan, M. Yu. Efremov, D. V.
2010-03-15
We solve the Leggett equations for the BCS-BEC crossover in a three dimensional resonance p-wave superfluid with the symmetry of the A1 phase. We calculate the sound velocity, the normal density, and the specific heat for the BCS domain ({mu} > 0), for the BEC domain ({mu} < 0), and close to the important point {mu} = 0 in the 100% polarized case. We find the indications of a quantum phase transition close to the point {mu}(T = 0) = 0. Deep in the BCS and BEC domains, the crossover ideas of Leggett, Nozieres, and Schmitt-Rink work quite well. We discuss the spectrum of orbital waves, the paradox of intrinsic angular momentum and the complicated problem of chiral anomaly in the BCS A1 phase at T = 0. We present two different approaches to the chiral anomaly, based on supersymmetric hydrodynamics and on the formal analogy with the Dirac equation in quantum electrodynamics. We evaluate the damping of nodal fermions due to different decay processes in the superclean case at T = 0 and find that a ballistic regime {omega}{tau} >> 1 occurs. We propose to use aerogel or nonmagnetic impurities to reach the hydrodynamic regime {omega}{tau} << 1 at T = 0. We discuss the concept of the spectral flow and exact cancelations between time derivatives of anomalous and quasiparticle currents in the equation for the total linear momentum conservation. We propose to derive and solve the kinetic equation for the nodal quasiparticles in both the hydrodynamic and ballistic regimes to demonstrate this cancelation explicitly. We briefly discuss the role of the other residual interactions different from damping and invite experimentalists to measure the spectrum and damping of orbital waves in the A phase of {sup 3}He at low temperatures.
NASA Astrophysics Data System (ADS)
Miura, Hitoshi; Nakamoto, Taishi
2007-05-01
Millimeter-sized, spherical silicate grains abundant in chondritic meteorites, which are called as chondrules, are considered to be a strong evidence of the melting event of the dust particles in the protoplanetary disk. One of the most plausible scenarios is that the chondrule precursor dust particles are heated and melt in the high-velocity gas flow (shock-wave heating model). We developed the non-linear, time-dependent, and three-dimensional hydrodynamic simulation code for analyzing the dynamics of molten droplets exposed to the gas flow. We confirmed that our simulation results showed a good agreement in a linear regime with the linear solution analytically derived by Sekyia et al. [Sekyia, M., Uesugi, M., Nakamoto, T., 2003. Prog. Theor. Phys. 109, 717-728]. We found that the non-linear terms in the hydrodynamical equations neglected by Sekiya et al. [Sekiya, M., Uesugi, M., Nakamoto, T., 2003. Prog. Theor. Phys. 109, 717-728] can cause the cavitation by producing negative pressure in the droplets. We discussed that the fragmentation through the cavitation is a new mechanism to determine the upper limit of chondrule sizes. We also succeeded to reproduce the fragmentation of droplets when the gas ram pressure is stronger than the effect of the surface tension. Finally, we compared the deformation of droplets in the shock-wave heating with the measured data of chondrules and suggested the importance of other effects to deform droplets, for example, the rotation of droplets. We believe that our new code is a very powerful tool to investigate the hydrodynamics of molten droplets in the framework of the shock-wave heating model and has many potentials to be applied to various problems.
Some results of the hydrodynamic theory of finite-amplitude waves
NASA Technical Reports Server (NTRS)
Sekerzh-Zenkovich, Y. I.
1975-01-01
Standing waves can be interpreted as free waves between two vertical walls; for a standing wave in an unlimited container there is no transport of liquid mass in the horizontal direction. Standing waves of finite amplitude also possess the following properties not possessed by the waves of the linear theory: (1) there are no motionless points, (2) the points of maximum amplitude (crests and troughs) are fixed, and coincide with the antinodes of the original linear wave, (3) the ordinates of the wave crests are greater in absolute magnitude than the ordinates of the troughs; the wave is similar to a trochoid curve; (4) the wave profile never becomes straight; and (5) the frequency of the oscillations depends not only on the wave length but also on the amplitude.
Oldenburg, Curtis; Moridis, George
1998-03-24
We have developed EOS7M, a ferrofluid flow and transport module for TOUGH2. EOS7M calculates the magnetic forces on ferrofluid caused by an external magnetic field and allows simulation of flow and advective transport of ferrofluid-water mixtures through porous media. Such flow problems are strongly coupled and well suited to the TOUGH2 framework. Preliminary applications of EOS7M to some simple pressure and flow problems for which experiments were carried out in the lab show good qualitative agreement with the laboratory results.
Magnetization of multicomponent ferrofluids.
Szalai, I; Dietrich, S
2011-08-17
The solution of the mean spherical approximation (MSA) integral equation for isotropic multicomponent dipolar hard sphere fluids without external fields is used to construct a density functional theory (DFT), which includes external fields, in order to obtain an analytical expression for the external field dependence of the magnetization of ferrofluidic mixtures. This DFT is based on a second-order Taylor series expansion of the free energy density functional of the anisotropic system around the corresponding isotropic MSA reference system. The ensuing results for the magnetic properties are in quantitative agreement with our canonical ensemble Monte Carlo simulation data presented here. PMID:21795777
Andreev, P. A.; Kuzmenkov, L. S.; Trukhanova, M. I.
2011-12-15
In this paper, we explicate a method of quantum hydrodynamics (QHD) for the study of the quantum evolution of a system of polarized particles. Although we focused primarily on the two-dimensional (2D) physical systems, the method is valid for three-dimensional (3D) and one-dimensional (1D) systems too. The presented method is based upon the Schroedinger equation. Fundamental QHD equations for charged and neutral particles were derived from the many-particle microscopic Schroedinger equation. The fact that particles possess the electric dipole moment (EDM) was taken into account. The explicated QHD approach was used to study dispersion characteristics of various physical systems. We analyzed dispersion of waves in a two-dimensional ion and hole gas placed into an external electric field, which is orthogonal to the gas plane. Elementary excitations in a system of neutral polarized particles were studied for 1D, 2D, and 3D cases. The polarization dynamics in systems of both neutral and charged particles is shown to cause formation of a new type of waves as well as changes in the dispersion characteristics of already known waves. We also analyzed wave dispersion in 2D exciton systems, in 2D electron-ion plasma, and in 2D electron-hole plasma. Generation of waves in 3D-system neutral particles with EDM by means of the beam of electrons and neutral polarized particles is investigated.
Exploring multifunctional potential of commercial ferrofluids by magnetic particle hyperthermia
NASA Astrophysics Data System (ADS)
Sakellari, Despoina; Mathioudaki, Stella; Kalpaxidou, Zoi; Simeonidis, Konstantinos; Angelakeris, Makis
2015-04-01
In this work we examine a selection of commercially available magnetic iron oxide nanoparticles as candidates for magnetic particle hyperthermia applications combining their primary modality with additional heat triggered actions. Contrary to lab-made magnetic nanoparticles, commercial ferrofluids may be rapidly pushed through the medical approval processes since their applicability has already been addressed successfully (i.e., formulation, reproducibility, toxicity and quality assurance) in conjunction with the strong companies‧ drive in the fast delivery of the new therapy to the patient. Four samples are under study with variable hydrodynamic diameters from two companies (Micromod and Chemicell) consisting of iron-oxide magnetic nanoparticles. The tunable magnetic heating characteristics of the ferrofluids were correlated with particle, field and colloidal solution features. Our work revealed a size-dependent magnetic heating efficiency together with fast thermal response, features that are crucial for adequate thermal efficiency combined with minimum treatment duration and show the potential of such materials as multifunctional theranostic agents.
NASA Astrophysics Data System (ADS)
Hennings, Ingo; Herbers, Dagmar
2006-10-01
The investigations carried out between 2002 and 2004 during six field experiments within the Operational Radar and Optical Mapping in monitoring hydrodynamic, morphodynamic and environmental parameters for coastal management (OROMA) project aimed to improve the effectiveness of new remote sensing monitoring technologies such as shipborne imaging radars in coastal waters. The coastal monitoring radar of the GKSS Research Center, Geesthacht, Germany, is based on a Kelvin Hughes RSR 1000 X band (9.42 GHz) vertical (VV) polarized river radar and was mounted on board the research vessel Ludwig Prandtl during the experiments in the Lister Tief, a tidal inlet of the German Bight in the North Sea. The important progress realized in this investigation is the availability of calibrated X band radar data. Another central point of the study is to demonstrate the applicability of the quasi-specular scattering theory in combination with the weak hydrodynamic interaction theory for the radar imaging mechanism of the seabed. Radar data have been taken at very low grazing angles ≤2.6° of flood and ebb tide-oriented sand wave signatures at the sea surface during ebb tidal current phases. Current speeds perpendicular to the sand wave crest ≤0.6 m s-1 have been measured at wind speeds ≤4.5 m s-1 and water depths ≤25 m. The difference between the maximum measured and simulated normalized radar cross section (NRCS) modulation of the ebb tide-oriented sand wave is 27%. For the flood tide-oriented sand wave, a difference of 21% has been calculated. The difference between the minimum measured and simulated NRCS modulation of the ebb tide-oriented sand wave is 10%, and for the flood tide-oriented sand wave, a value of 43% has been derived. Phases of measured and simulated NRCS modulations correspond to asymmetric sand wave slopes. The results of the simulated NRCS modulation show the qualitative trend but do not always quantitatively match the measured NRCS modulation profiles
Energy harvesting via ferrofluidic induction
NASA Astrophysics Data System (ADS)
Monroe, J. G.; Vasquez, Erick S.; Aspin, Zachary S.; Fairley, John D.; Walters, Keisha B.; Berg, Matthew J.; Thompson, Scott M.
2015-05-01
A series of experiments were conducted to investigate and characterize the concept of ferrofluidic induction - a process for generating electrical power via cyclic oscillation of ferrofluid (iron-based nanofluid) through a solenoid. Experimental parameters include: number of bias magnets, magnet spacing, solenoid core, fluid pulse frequency and ferrofluid-particle diameter. A peristaltic pump was used to cyclically drive two aqueous ferrofluids, consisting of 7-10 nm iron-oxide particles and commercially-available hydroxyl-coated magnetic beads (~800 nm), respectively. The solutions were pulsated at 3, 6, and 10 Hz through 3.2 mm internal diameter Tygon tubing. A 1000 turn copper-wire solenoid was placed around the tube 45 cm away from the pump. The experimental results indicate that the ferrofluid is capable of inducing a maximum electric potential of approximately +/- 20 μV across the solenoid during its cyclic passage. As the frequency of the pulsating flow increased, the ferro-nanoparticle diameter increased, or the bias magnet separation decreased, the induced voltage increased. The type of solenoid core material (copper or plastic) did not have a discernible effect on induction. These results demonstrate the feasibility of ferrofluidic induction and provide insight into its dependence on fluid/flow parameters. Such fluidic/magneto-coupling can be exploited for energy harvesting and/or conversion system design for a variety of applications.
Tunable optical and magneto-optical properties of ferrofluid in the terahertz regime.
Chen, Sai; Fan, Fei; Chang, Shengjiang; Miao, Yinping; Chen, Meng; Li, Jining; Wang, Xianghui; Lin, Lie
2014-03-24
The dielectric property and magneto-optical effects of ferrofluids have been investigated in the terahertz (THz) regime by using THz time-domain spectroscopy. The experiment results show that the refractive index and absorption coefficient of ferrofluid for THz waves rise up with the increase of nanoparticle concentration in the ferrofluid. Moreover, two different THz magneto-optical effects have been found with different external magnetic fields, of which mechanisms have been theoretically explained well by microscopic structure induced refractive index change in the magnetization process and the transverse magneto-optical effect after the saturation magnetization, respectively. This work suggests that ferrofluid is a promising magneto-optical material in the THz regime which has widely potential applications in THz functional devices for THz sensing, modulation, phase retardation, and polarization control. PMID:24663979
Hoeke, R.; Storlazzi, C.; Ridd, P.
2011-01-01
This paper examines the relationship between offshore wave climate and nearshore waves and currents at Hanalei Bay, Hawaii, an exposed bay fringed with coral reefs. Analysis of both offshore in situ data and numerical hindcasts identify the predominance of two wave conditions: a mode associated with local trade winds and an episodic pattern associated with distant source long-period swells. Analysis of 10 months of in situ data within the bay show that current velocities are up to an order of magnitude greater during long-period swell episodes than during trade wind conditions; overall circulation patterns are also fundamentally different. The current velocities are highly correlated with incident wave heights during the swell episodes, while they are not during the modal trade wind conditions. A phase-averaged wave model was implemented with the dual purpose of evaluating application to bathymetrically complex fringing reefs and to examine the propagation of waves into the nearshore in an effort to better explain the large difference in observed circulation during the two offshore wave conditions. The prediction quality of this model was poorer for the episodic condition than for the lower-energy mode, however, it illustrated how longer-period swells are preferentially refracted into the bay and make available far more nearshore wave energy to drive currents compared to waves during modal conditions. The highly episodic circulation, the nature of which is dependent on complex refraction patterns of episodic, long-period swell has implications for flushing and sediment dynamics for incised fringing reef-lined bays that characterize many high islands at low latitudes around the world.
Ferrofluid Photonic Dipole Contours
NASA Astrophysics Data System (ADS)
Snyder, Michael; Frederick, Jonathan
2008-03-01
Understanding magnetic fields is important to facilitate magnetic applications in diverse fields in industry, commerce, and space exploration to name a few. Large electromagnets can move heavy loads of metal. Magnetic materials attached to credit cards allow for fast, accurate business transactions. And the Earth's magnetic field gives us the colorful auroras observed near the north and south poles. Magnetic fields are not visible, and therefore often hard to understand or characterize. This investigation describes and demonstrates a novel technique for the visualization of magnetic fields. Two ferrofluid Hele-Shaw cells have been constructed to facilitate the imaging of magnetic field lines [1,2,3,4]. We deduce that magnetically induced photonic band gap arrays similar to electrostatic liquid crystal operation are responsible for the photographed images and seek to mathematically prove the images are of exact dipole nature. We also note by comparison that our photographs are very similar to solar magnetic Heliosphere photographs.
Ferrofluid-associated Cutaneous Dyschromia
Arfa, Kenneth S.
2016-01-01
Background: Ferrofluid is a colloidal suspension that usually consists of surfactant-coated nanoparticles of magnetite (Fe3O4) in a carrier liquid. Ferromagnetic fluid forms spikes when the liquid is exposed to a magnetic field. Purpose: The authors describe a man who developed temporary discoloration of his right palm and fingers after accidental cutaneous contact with ferrofluid and discuss some of the current and potential applications of this unique liquid. Methods: A 28-year-old man was evaluating the effects of magnetic fields using ferrofluid. He performed a modification of the “leaping ferrofluid” demonstration in which he held a superstrong (14,800 gauss magnetic field strength) N52 rare earth neodymium magnet in his palm and slowly lowered that hand over an open bowl that was filled with ferrofluid. Results: As the magnet approached the liquid, the ferrofluid became magnetized. The liquid leaped from the bowl and contacted not only the magnet, but also the palmar surface of his hand and fingers, resulting in a black-brown dyschromia of the affected skin. The discoloration completely resolved after two weeks without any adverse sequellae. Conclusion: Ferrofluid has numerous current and potential applications; in addition to being of value educationally and aesthetically (after being subjected to magnetic fields), it is also utilized for audio loudspeakers, medical innovations (such as a component of either a research tool, a diagnostic aid, or a treatment modality), and seals. Although the authors’ patient did not experience any acute or chronic toxicity from his cutaneous exposure to ferrofluid, conservative follow-up for individuals who experience skin contact with ferromagnetic fluid may be appropriate. PMID:27354890
NASA Astrophysics Data System (ADS)
Samaras, Achilleas G.; Gaeta, Maria Gabriella; Moreno Miquel, Adrià; Archetti, Renata
2016-07-01
Numerical modelling has become an essential component of today's coastal planning, decision support and risk assessment. High-resolution modelling offers an extensive range of capabilities regarding simulated conditions, works and practices and provides with a wide array of data regarding nearshore wave dynamics and hydrodynamics. In the present work, the open-source TELEMAC suite and the commercial software MIKE21 are applied to selected coastal areas of South Italy. Applications follow a scenario-based approach in order to study representative wave conditions in the coastal field; the models' results are intercompared in order to test both their performance and capabilities and are further evaluated on the basis of their operational use for coastal planning and design. A multiparametric approach for the rapid assessment of wave conditions in coastal areas is also presented and implemented in areas of the same region. The overall approach is deemed to provide useful insights on the tested models and the use of numerical models - in general - in the above context, especially considering that the design of harbours, coastal protection works and management practices in the coastal zone is based on scenario-based approaches as well.
Niederhaus, John; Ranjan, Devesh; Anderson, Mark; Oakley, Jason; Bonazza, Riccardo; Greenough, Jeff
2005-05-15
Experiments studying the compression and unstable growth of a dense spherical bubble in a gaseous medium subjected to a strong planar shock wave (2.8 < M < 3.4) are performed in a vertical shock tube. The test gas is initially contained in a free-falling spherical soap-film bubble, and the shocked bubble is imaged using planar laser diagnostics. Concurrently, simulations are carried out using a compressible hydrodynamics code in r-z axisymmetric geometry.Experiments and computations indicate the formation of characteristic vortical structures in the post-shock flow, due to Richtmyer-Meshkov and Kelvin-Helmholtz instabilities, and smaller-scale vortices due to secondary effects. Inconsistencies between experimental and computational results are examined, and the usefulness of the current axisymmetric approach is evaluated.
NASA Astrophysics Data System (ADS)
Dyer, Ashton; Blondin, J. M.; Reynolds, S. P.
2014-01-01
High resolution imaging of two young Type Ia supernova remnants (SNRs), Tycho and SN 1006, has revealed several morphological features which have resisted explanation with numerical simulations. One such feature is the presence of shocked ejecta blobs protruding beyond the mean forward shock radius. Two current theories explain the presence of such ejecta: highly dense ejecta shrapnel produced in the explosion penetrating the forward shock, or plumes generated by hydrodynamic instabilities long after the initial explosion. We investigate the shrapnel theory through hydrodynamic simulations in 2D and 3D of the evolution of dense ejecta clumps embedded in an exponential density profile, appropriate for Type Ia supernovae. We use high-resolution 2D simulations to identify relevant clump parameters which we investigate further in 3D. In contradiction to some former work, we find that sufficiently resolved clumps in 2D models shatter upon collision with the forward shock, yielding new protrusion features. In both 2D and 3D, shrapnel is capable of penetrating the forward shock, but the resultant protrusions in 3D simulations vary significantly from those in similar 2D runs, implying 2D simulations may not be an accurate method of investigating the shrapnel theory. We compare the our simulations with Chandra observations of projections seen in Tycho and SN 1006. This work was performed as part of NC State University's Undergraduate Research in Computational Astrophysics (URCA) program, an REU program supported by the National Science Foundation through award AST-1032736.
Magnetoviscosity in dilute ferrofluids from rotational brownian dynamics simulations.
Soto-Aquino, D; Rinaldi, C
2010-10-01
Ferrofluids are suspensions of magnetic nanoparticles which respond to imposed magnetic fields by changing their viscosity without losing their fluidity. Prior work on modeling the behavior of ferrofluids has focused on using phenomenological suspension-scale continuum equations. A disadvantage of this approach is the controversy surrounding the equation describing the rate of change of the ferrofluid magnetization, the so-called magnetization relaxation equation. In this contribution the viscosity of dilute suspensions of spherical magnetic nanoparticles suspended in a Newtonian fluid and under applied shear and constant magnetic fields is studied through rotational brownian dynamics simulations. Simulation results are compared with the predictions of suspension-scale models based on three magnetization relaxation equations. Excellent agreement is observed between simulation results and the predictions of an equation due to Martsenyuk, Raikher, and Shliomis. Good qualitative agreement is observed with predictions of other equations, although these models fail to accurately predict the magnitude and shear rate dependence of the magnetic-field-dependent effective viscosity. Finally, simulation results over a wide range of conditions are collapsed into master curves using a Mason number defined based on the balance of hydrodynamic and magnetic torques. PMID:21230393
Dynamic analysis of hydrodynamic behavior of a flatfish cage system under wave conditions
NASA Astrophysics Data System (ADS)
Cui, Yong; Guan, Chang-tao; Wan, Rong; Huang, Bin; Li, Jiao
2014-04-01
This paper presents a simulation model based on the finite element method. The method is used to analyze the motion response and mooring line tension of the flatfish cage system in waves. The cage system consists of top frames, netting, mooring lines, bottom frames, and floats. A series of scaled physical model tests in regular waves are conducted to verify the numerical model. The comparison results show that the simulated and the experimental results agree well under the wave conditions, and the maximum pitch of the bottom frame with two orientations is about 12°. The motion process of the whole cage system in the wave can be described with the computer visualized technology. Then, the mooring line tensions and the motion of the bottom frame with three kinds of weight are calculated under different wave conditions. According to the numerical results, the differences in mooring line tensions of flatfish cages with three weight modes are indistinct. The maximum pitch of the bottom frame decreases with the increase of the bottom weight.
Coloma, M; Schaffer, J D; Carare, R O; Chiarot, P R; Huang, P
2016-08-01
Beta-amyloid accumulation within arterial walls in cerebral amyloid angiopathy is associated with the onset of Alzheimer's disease. However, the mechanism of beta-amyloid clearance along peri-arterial pathways in the brain is not well understood. In this study, we investigate a transport mechanism in the arterial basement membrane consisting of forward-propagating waves and their reflections. The arterial basement membrane is modeled as a periodically deforming annulus filled with an incompressible single-phase Newtonian fluid. A reverse flow, which has been suggested in literature as a beta-amyloid clearance pathway, can be induced by the motion of reflected boundary waves along the annular walls. The wave amplitude and the volume of the annular region govern the flow magnitude and may have important implications for an aging brain. Magnitudes of transport obtained from control volume analysis and numerical solutions of the Navier-Stokes equations are presented. PMID:26729476
NASA Astrophysics Data System (ADS)
Suwa, T.; Imamura, F.; Sugawara, D.; Ogasawara, K.; Watanabe, M.; Hirahara, T.
2014-12-01
A tsunami simulator integrating a 3-D fluid simulation technology that runs on large-scale parallel computers using smoothed-particle hydrodynamics (SPH) method has been developed together with a 2-D tsunami propagation simulation technique using a nonlinear shallow water wave model. We use the 2-D simulation to calculate tsunami propagation of scale of about 1000km from epicenter to near shore. The 3-D SPH method can be used to calculate the water surface and hydraulic force that a tsunami can exert on a building, and to simulate flooding patterns at urban area of at most km scale. With our simulator we can also see three dimensional fluid feature such as complex changes a tsunami undergoes as it interacts with coastal topography or structures. As a result it is hoped that, e.g. , effect of the structures to dissipate waves energy passing over it can be elucidated. The authors utilize the simulator in the third of five fields of the Strategic Programs for Innovative Research, "Advanced Prediction Researches for Natural Disaster Prevention and Reduction," or the theme "Improvement of the tsunami forecasting system on the HPCI computer." The results of tsunami simulation using the K computer will be reported. We are going to apply it to a real problem of the disaster prevention in future.
Chabchoub, A; Hoffmann, N; Onorato, M; Genty, G; Dudley, J M; Akhmediev, N
2013-08-01
We report the experimental observation of multi-bound-soliton solutions of the nonlinear Schrödinger equation (NLS) in the context of hydrodynamic surface gravity waves. Higher-order N-soliton solutions with N=2, 3 are studied in detail and shown to be associated with self-focusing in the wave group dynamics and the generation of a steep localized carrier wave underneath the group envelope. We also show that for larger input soliton numbers, the wave group experiences irreversible spectral broadening, which we refer to as a hydrodynamic supercontinuum by analogy with optics. This process is shown to be associated with the fission of the initial multisoliton into individual fundamental solitons due to higher-order nonlinear perturbations to the NLS. Numerical simulations using an extended NLS model described by the modified nonlinear Schrödinger equation, show excellent agreement with experiment and highlight the universal role that higher-order nonlinear perturbations to the NLS play in supercontinuum generation. PMID:23952405
Dasgupta, B.; Burrows, R.; Zank, G. P.; Webb, G. M.
2006-08-15
In this work we investigate how reflected particles modify the Rankine-Hugoniot (RH) relations in a simple hydrodynamical framework. It is assumed that the ions are specularly reflected by the cross-shock potential. For simplicity, an exactly perpendicular shock is assumed, thus other reflection mechanisms, such as magnetic mirroring, can be neglected. Momentum and energy terms are introduced to model reflected particles at the shock and the RH conditions are examined using a geometrical entropy condition to distinguish the physically relevant states. Although such shocks have some common features with combustion shocks within a narrow range of reflection parameters, for a wide range of reflection parameters, particularly for highly oblique shocks, Chapman-Jouguet solutions do not exist. It is conjectured that these shocks comprise a distinct class. Decelerated solutions of the RH conditions are shown to exist only under specific conditions for shocks with reflected particles. Velocity flows both parallel and oblique to the perpendicular shock (with respect to an upstream magnetic field) are considered and found to be strongly sheared.
NASA Astrophysics Data System (ADS)
Mihalas, Dimitri
Basic Radiation Theory Specific Intensity Photon Number Density Photon Distribution Function Mean Intensity Radiation Energy Density Radiation Energy Flux Radiation Momentum Density Radiation Stress Tensor (Radiation Pressure Tensor) Thermal Radiation Thermodynamics of Thermal Radiation and a Perfect Gas The Transfer Equation Absorption, Emission, and Scattering The Equation of Transfer Moments of the Transfer Equation Lorentz Transformation of the Transfer Equation Lorentz Transformation of the Photon 4-Momentum Lorentz Transformation of the Specific Intensity, Opacity, and - Emissivity Lorentz Transformation of the Radiation Stress Energy Tensor The Radiation 4-Force Density Vector Covariant Form of the Transfer Equation Inertial-Frame Equations of Radiation Hydrodynamics Inertial-Frame Radiation Equations Inertial-Frame Equations of Radiation Hydrodynamics Comoving-Frame Equation of Transfer Special Relativistic Derivation (D. Mihalas) Consistency Between Comoving-Frame and Inertial-Frame Equations Noninertial Frame Derivation (J. I. Castor) Analysis of O (v/c) Terms Lagrangian Equations of Radiation Hydrodynamics Momentum Equation Gas Energy Equation First Law of Thermodynamics for the Radiation Field First Law of Thermodynamics for the Radiating Fluid Mechanical Energy Equation Total Energy Equation Consistency of Different Forms of the Radiating-Fluid Energy - and Momentum Equations Consistency of Inertial-Frame and Comoving-Frame Radiation Energy - and Momentum Equations Radiation Diffusion Radiation Diffusion Nonequilibrium Diffusion The Problem of Flux Limiting Shock Propagation: Numerical Methods Acoustic Waves Numerical Stability Systems of Equations Implications of Shock Development Implications of Diffusive Energy Transport Illustrative Example Numerical Radiation Hydrodynamics Radiating Fluid Energy and Momentum Equations Computational Strategy Energy Conservation Formal Solution Multigroup Equations An Astrophysical Example Adaptive-Grid Radiation
Preparation and Properties of an Aqueous Ferrofluid
NASA Astrophysics Data System (ADS)
Enzel, Patricia; Adelman, Nicholas B.; Beckman, Katie J.; Campbell, Dean J.; Ellis, Arthur B.; Lisensky, George C.
1999-07-01
Ferrofluids are colloidal suspensions of surfactant-coated magnetic particles in a liquid medium. This paper describes a simple synthesis of an aqueous-based ferrofluid that may be used in an introductory science or engineering laboratory. Magnetite (Fe3O4) particles are precipitated by combining FeCl3 and FeCl2 in a 2:1 stoichiometric ratio in aqueous ammonia solution. The resulting particles, ~10-20 nm in diameter based on powder X-ray diffraction, are then treated with aqueous tetramethylammonium hydroxide, which acts as a surfactant. When the resulting ferrofluid is placed near a magnet, it forms conical spikes. This paper also describes a method for repelling both oil- and water-based ferrofluid from solid surfaces that would otherwise be stained by the fluid. Finally, a demonstration of the interaction between ferrofluid and magnetic fields, in which ferrofluid is induced to leap upward by a stack of magnets, is described.
NASA Astrophysics Data System (ADS)
Inogamov, N. A.; Sunyaev, R. A.
2015-12-01
In the early Universe up to hydrogen recombination in the Universe, the radiation pressure was much greater than the pressure of baryons and electrons. Moreover, the energy density of cosmic microwave background (CMB) photons was greater than or close to the energy density contained in the rest mass of baryonic matter, i.e., the primordial plasma was a radiated-dominated one and the adiabatic index was close to 4/3. The small density perturbations from which the observed galaxies have grown grew as long as the characteristic perturbation scales exceeded the horizon of the Universe сt at that time. On smaller scales, the density perturbations were standing sound waves. Radiative viscosity and heat conduction must have led to the damping of sound waves on very small scales. After the discovery of the cosmic microwave background, J. Silk calculated the scales of this damping, which is now called Silk damping, knowing the CMBtemperature and assuming the density of baryons and electrons. Observations with the South Pole Telescope, the Atacama Cosmology Telescope, and the Planck satellite have revealed the predicted damping of acoustic peaks in the CMB power spectrum and confirmed one important prediction of the theory. In 1970, R.A. Sunyaev and Ya.B. Zeldovich showed that such energy release in the early Universe should lead to characteristic deviations of the CMB spectrum from the Planck one. The development of the technology of cryogenic detectors of submillimeter and millimeter wavelength radiation has made it possible to measure the CMB spectral distortions at 10-8 of its total intensity (PIXIE). This has sharply increased the interest of theoretical cosmologists in the problem of energy release when smallscale sound waves are damped. We have derived a relativistic formula for the energy of a standing sound wave in a photon-baryon-electron plasma from simple hydrodynamic and thermodynamic relations. This formula is applicable for an arbitrary relation between the
Fine-scale density wave structure of Saturn's rings: A hydrodynamic theory
NASA Astrophysics Data System (ADS)
Griv, E.; Gedalin, M.
2010-10-01
Aims: We examine the linear stability of the Saturnian ring disk of mutually gravitating and physically colliding particles with special emphasis on its fine-scale ~100 m density wave structure, that is, almost regularly spaced, aligned cylindric density enhancements and optically-thin zones with the width and the spacing between them of roughly several tens particle diameters. Methods: We analyze the Jeans' instabilities of gravity perturbations (e.g., those produced by a spontaneous disturbance) analytically by using the Navier-Stokes dynamical equations of a compressible fluid. The theory is not restricted by any assumptions about the thickness of the system. We consider a simple model of the system consisting of a three-dimensional ring disk that is weakly inhomogeneous and whose structure is analyzed by making a horizontally local short-wave approximation. Results: We demonstrate that the disk is probably unstable and that gravity perturbations grow effectively within a few orbital periods. We find that self-gravitation plays a key role in the formation of the fine structure. The predictions of the theory are compared with observations of Saturn's rings by the Cassini spacecraft and are found to be in good agreement. In particular, it appears very likely that some of the quasi-periodic microstructures observed in Saturn's A and B rings - both axisymmetric and nonaxisymmetric ones - are manifestations of these effects. We argue that the quasi-periodic density enhancements revealed in Cassini data are flattened structures, with a height to width ratio of about 0.3. One should analyze high-resolution of the order of 10 m data acquired for the A and B rings (and probably C ring as well) to confirm this prediction. We also show that the gravitational instability is a potential cluster-forming mechanism leading to the formation of porous 100-m-diameter moonlets of preferred mass ~107 g each embedded in the outer A ring, although this has yet to be directly measured.
Fine-Scale Density Wave Structure of Saturn's Main Rings: A Hydrodynamic Theory
NASA Astrophysics Data System (ADS)
Griv, Evgeny; Gedalin, Michael
The theoretical studies of Maxwell (1859) have showed that the rings around Saturn could not be solid or liquid, but rather a swarm of millions of individual particles rotating in separate concentric orbits at different speeds. A modern very popular model of the particles in Saturn's rings is a smooth ice sphere, whose restitution coefficient is quite high (exceeding 0.63) and decreases as the collision velocity increases. In this work, the linear stability of the Saturnian ring disk of mutually gravitating and physically colliding particles is examined with special emphasis on its fine-scale of the order of 100 m density wave structure, that is, almost regularly spaced, aligned cylindric density enhancements and optically-thin zones with the width and the spacing between them of roughly several tens particle diameters. Jeans' instabilities of small-amplitude gravity perturbations (e.g., those produced by a spontaneous disturbance) are analyzed analytically through the use of Navier-Stokes dynamical equations of a compressible fluid. An essential feature of this study is that the theory is not restricted by any assumptions regarding the thickness of the system. The simple model of the system is considered: the ring disk is considered to be thin, a weakly spatially inhomogeneous, and its structure is considered in a horizontally local short-wave approximation. We show that the disk is probably unstable and gravity perturbations grow effectively within a few orbital periods; self-gravitation plays a key role in the formation of the fine-scale structure while particle collisions play a secondary role. The predictions of the theory are compared with recent observations of Saturn's rings by the Cassini spacecraft and are found to be in good agreement. Particulary, it appears very likely that some of the microstructures observed in Saturn's A and B rings -both axisymmetric and nonaxisymmetric ones -are manifestations of these effects produced by Jeans' gravitational
NASA Astrophysics Data System (ADS)
Larmat, C. S.; Rougier, E.; Knight, E.; Yang, X.; Patton, H. J.
2013-12-01
A goal of the Source Physics Experiments (SPE) is to develop explosion source models expanding monitoring capabilities beyond empirical methods. The SPE project combines field experimentation with numerical modelling. The models take into account non-linear processes occurring from the first moment of the explosion as well as complex linear propagation effects of signals reaching far-field recording stations. The hydrodynamic code CASH is used for modelling high-strain rate, non-linear response occurring in the material near the source. Our development efforts focused on incorporating in-situ stress and fracture processes. CASH simulates the material response from the near-source, strong shock zone out to the small-strain and ultimately the elastic regime where a linear code can take over. We developed an interface with the Spectral Element Method code, SPECFEM3D, that is an efficient implementation on parallel computers of a high-order finite element method. SPECFEM3D allows accurate modelling of wave propagation to remote monitoring distance at low cost. We will present CASH-SPECFEM3D results for SPE1, which was a chemical detonation of about 85 kg of TNT at 55 m depth in a granitic geologic unit. Spallation was observed for SPE1. Keeping yield fixed we vary the depth of the source systematically and compute synthetic seismograms to distances where the P and Rg waves are separated, so that analysis can be performed without concern about interference effects due to overlapping energy. We study the time and frequency characteristics of P and Rg waves and analyse them in regard to the impact of free-surface interactions and rock damage resulting from those interactions. We also perform traditional CMT inversions as well as advanced CMT inversions, developed at LANL to take into account the damage. This will allow us to assess the effect of spallation on CMT solutions as well as to validate our inversion procedure. Further work will aim to validate the developed
NASA Astrophysics Data System (ADS)
Andreev, Pavel A.
2015-03-01
The quantum hydrodynamic (QHD) model of charged spin-1/2 particles contains physical quantities defined for all particles of a species including particles with spin-up and with spin-down. Different populations of states with different spin directions are included in the spin density (the magnetization). In this paper I derive a QHD model, which separately describes spin-up electrons and spin-down electrons. Hence electrons with different projections of spins on the preferable direction are considered as two different species of particles. It is shown that the numbers of particles with different spin directions do not conserve. Hence the continuity equations contain sources of particles. These sources are caused by the interactions of the spins with the magnetic field. Terms of similar nature arise in the Euler equation. The z projection of the spin density is no longer an independent variable. It is proportional to the difference between the concentrations of the electrons with spin-up and the electrons with spin-down. The propagation of waves in the magnetized plasmas of degenerate electrons is considered. Two regimes for the ion dynamics, the motionless ions and the motion of the degenerate ions as the single species with no account of the spin dynamics, are considered. It is shown that this form of the QHD equations gives all solutions obtained from the traditional form of QHD equations with no distinction of spin-up and spin-down states. But it also reveals a soundlike solution called the spin-electron acoustic wave. Coincidence of most solutions is expected since this derivation was started with the same basic equation: the Pauli equation. Solutions arise due to the different Fermi pressures for the spin-up electrons and the spin-down electrons in the magnetic field. The results are applied to degenerate electron gas of paramagnetic and ferromagnetic metals in the external magnetic field. The dispersion of the spin-electron acoustic waves in the partially spin
Andreev, Pavel A
2015-03-01
The quantum hydrodynamic (QHD) model of charged spin-1/2 particles contains physical quantities defined for all particles of a species including particles with spin-up and with spin-down. Different populations of states with different spin directions are included in the spin density (the magnetization). In this paper I derive a QHD model, which separately describes spin-up electrons and spin-down electrons. Hence electrons with different projections of spins on the preferable direction are considered as two different species of particles. It is shown that the numbers of particles with different spin directions do not conserve. Hence the continuity equations contain sources of particles. These sources are caused by the interactions of the spins with the magnetic field. Terms of similar nature arise in the Euler equation. The z projection of the spin density is no longer an independent variable. It is proportional to the difference between the concentrations of the electrons with spin-up and the electrons with spin-down. The propagation of waves in the magnetized plasmas of degenerate electrons is considered. Two regimes for the ion dynamics, the motionless ions and the motion of the degenerate ions as the single species with no account of the spin dynamics, are considered. It is shown that this form of the QHD equations gives all solutions obtained from the traditional form of QHD equations with no distinction of spin-up and spin-down states. But it also reveals a soundlike solution called the spin-electron acoustic wave. Coincidence of most solutions is expected since this derivation was started with the same basic equation: the Pauli equation. Solutions arise due to the different Fermi pressures for the spin-up electrons and the spin-down electrons in the magnetic field. The results are applied to degenerate electron gas of paramagnetic and ferromagnetic metals in the external magnetic field. The dispersion of the spin-electron acoustic waves in the partially spin
Transition to turbulence in Taylor-Couette ferrofluidic flow
Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng
2015-01-01
It is known that in classical fluids turbulence typically occurs at high Reynolds numbers. But can turbulence occur at low Reynolds numbers? Here we investigate the transition to turbulence in the classic Taylor-Couette system in which the rotating fluids are manufactured ferrofluids with magnetized nanoparticles embedded in liquid carriers. We find that, in the presence of a magnetic field transverse to the symmetry axis of the system, turbulence can occur at Reynolds numbers that are at least one order of magnitude smaller than those in conventional fluids. This is established by extensive computational ferrohydrodynamics through a detailed investigation of transitions in the flow structure, and characterization of behaviors of physical quantities such as the energy, the wave number, and the angular momentum through the bifurcations. A finding is that, as the magnetic field is increased, onset of turbulence can be determined accurately and reliably. Our results imply that experimental investigation of turbulence may be feasible by using ferrofluids. Our study of transition to and evolution of turbulence in the Taylor-Couette ferrofluidic flow system provides insights into the challenging problem of turbulence control. PMID:26065572
Transition to turbulence in Taylor-Couette ferrofluidic flow.
Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng
2015-01-01
It is known that in classical fluids turbulence typically occurs at high Reynolds numbers. But can turbulence occur at low Reynolds numbers? Here we investigate the transition to turbulence in the classic Taylor-Couette system in which the rotating fluids are manufactured ferrofluids with magnetized nanoparticles embedded in liquid carriers. We find that, in the presence of a magnetic field transverse to the symmetry axis of the system, turbulence can occur at Reynolds numbers that are at least one order of magnitude smaller than those in conventional fluids. This is established by extensive computational ferrohydrodynamics through a detailed investigation of transitions in the flow structure, and characterization of behaviors of physical quantities such as the energy, the wave number, and the angular momentum through the bifurcations. A finding is that, as the magnetic field is increased, onset of turbulence can be determined accurately and reliably. Our results imply that experimental investigation of turbulence may be feasible by using ferrofluids. Our study of transition to and evolution of turbulence in the Taylor-Couette ferrofluidic flow system provides insights into the challenging problem of turbulence control. PMID:26065572
NASA Astrophysics Data System (ADS)
Felderhof, B. U.
2011-09-01
Ferrohydrodynamic pumping of a ferrofluid through a circular tube by means of a running magnetic wave is studied in the framework of magnetostatics. The theory for electrohydrodynamic pumping of a polar liquid by means of a running electric wave is shown to be nearly identical. For given fluid parameters, the net flow rate can be optimized by suitable choice of wavenumber and frequency of the running wave.
Ferrofluid separator for nonferrous scrap separation
NASA Technical Reports Server (NTRS)
Kaiser, R.; Mir, L.
1974-01-01
Behavior of nonmagnetic objects within separator is essentially function of density, and independent of size or shape of objects. Results show close agreement between density of object and apparent density of ferrofluid required to float it. Results also demonstrate that very high separation rates are achievable by ferrofluid sink-float separation.
Static Magnetowetting of Ferrofluid Drops.
Rigoni, Carlo; Pierno, Matteo; Mistura, Giampaolo; Talbot, Delphine; Massart, René; Bacri, Jean-Claude; Abou-Hassan, Ali
2016-08-01
We report results of a comprehensive study of the wetting properties of sessile drops of ferrofluid water solutions at various concentrations deposited on flat substrates and subjected to the action of permanent magnets of different sizes and strengths. The amplitude and the gradient of the magnetic field experienced by the ferrofluid are changed by varying the magnets and their distance to the surface. Magnetic forces up to 100 times the gravitational one and magnetic gradients up to 1 T/cm are achieved. A rich phenomenology is observed, ranging from flattened drops caused by the magnetic attraction to drops extended normally to the substrate because of the normal traction of the magnetic field. We find that the former effect can be conveniently described in terms of an effective Bond number that compares the effective drop attraction with the capillary force, whereas the drop's vertical elongation is effectively expressed by a dimensionless number S, which compares the pressure jump at the ferrofluid interface because of the magnetization with the capillary pressure. PMID:27385506
Dispensing nano-pico droplets of ferrofluids
NASA Astrophysics Data System (ADS)
Irajizad, Peyman; Farokhnia, Nazanin; Ghasemi, Hadi
2015-11-01
Dispensing miniature volumes of a ferrofluid is of fundamental and practical importance for diverse applications ranging from biomedical devices, optics, and self-assembly of materials. Current dispensing systems are based on microfluidics flow-focusing approaches or acoustic actuation requiring complicated structures. A simple method is presented to continuously dispense the miniature droplets from a ferrofluid reservoir. Once a jet of the ferrofluid is subjected to a constrained flux through a membrane and an inhomogeneous magnetic field, the jet experiences a curvature-driven instability and transforms to a droplet. Ferrofluid droplets in the range of 0.1-1000 nl are dispensed with tunable dispensing frequencies. A model is developed that predicts the dispensed volume of the ferrofluid droplets with an excellent agreement with the measurements.
Behdadfar, Behshid; Kermanpur, Ahmad; Sadeghi-Aliabadi, Hojjat; Morales, Maria del Puerto; Mozaffari, Morteza
2012-03-15
Monodispersed aqueous ferrofluids of iron oxide nanoparticle were synthesized by hydrothermal-reduction route. They were characterized by X-ray diffraction analysis, Fourier transform infrared spectroscopy, scanning and transmission electron microscopy and dynamic light scattering. The results showed that certain concentrations of citric acid (CA) are required to obtain only magnetic iron oxides with mean particle sizes around 8 nm. CA acts as a modulator and reducing agent in iron oxide formation which controls nanoparticle size. The XRD, magnetic and heating measurements showed that the temperature and time of hydrothermal reaction can affect the magnetic properties of obtained ferrofluids. The synthesized ferrofluids were stable at pH 7. Their mean hydrodynamic size was around 80 nm with polydispersity index (PDI) of 0.158. The calculated intrinsic loss power (ILP) was 9.4 nHm{sup 2}/kg. So this clean and cheap route is an efficient way to synthesize high ILP aqueous ferrofluids applicable in magnetic hyperthermia. - Graphical abstract: Monodispersed aqueous ferrofluids of iron oxide nanoparticles were synthesized by hydrothermal-reduction method with citric acid as reductant which is an efficient way to synthesize aqueous ferrofluids applicable in magnetic hyperthermia. Highlights: Black-Right-Pointing-Pointer Aqueous iron oxide ferrofluids were synthesized by hydrothermal-reduction route. Black-Right-Pointing-Pointer Citric acid acted as reducing agent and surfactant in the route. Black-Right-Pointing-Pointer This is a facile, low energy and environmental friendly route. Black-Right-Pointing-Pointer The aqueous iron oxide ferrofluids were monodispersed and stable at pH of 7. Black-Right-Pointing-Pointer The calculated intrinsic loss power of the synthesized ferrofluids was very high.
Observing the Rosensweig instability of a quantum ferrofluid.
Kadau, Holger; Schmitt, Matthias; Wenzel, Matthias; Wink, Clarissa; Maier, Thomas; Ferrier-Barbut, Igor; Pfau, Tilman
2016-02-11
Ferrofluids exhibit unusual hydrodynamic effects owing to the magnetic nature of their constituents. As magnetization increases, a classical ferrofluid undergoes a Rosensweig instability and creates self-organized, ordered surface structures or droplet crystals. Quantum ferrofluids such as Bose-Einstein condensates with strong dipolar interactions also display superfluidity. The field of dipolar quantum gases is motivated by the search for new phases of matter that break continuous symmetries. The simultaneous breaking of continuous symmetries such as the phase invariance in a superfluid state and the translational symmetry in a crystal provides the basis for these new states of matter. However, interaction-induced crystallization in a superfluid has not yet been observed. Here we use in situ imaging to directly observe the spontaneous transition from an unstructured superfluid to an ordered arrangement of droplets in an atomic dysprosium Bose-Einstein condensate. By using a Feshbach resonance to control the interparticle interactions, we induce a finite-wavelength instability and observe discrete droplets in a triangular structure, the number of which grows as the number of atoms increases. We find that these structured states are surprisingly long-lived and observe hysteretic behaviour, which is typical for a crystallization process and in close analogy to the Rosensweig instability. Our system exhibits both superfluidity and, as we show here, spontaneous translational symmetry breaking. Although our observations do not probe superfluidity in the structured states, if the droplets establish a common phase via weak links, then our system is a very good candidate for a supersolid ground state. PMID:26829224
Observing the Rosensweig instability of a quantum ferrofluid
NASA Astrophysics Data System (ADS)
Kadau, Holger; Schmitt, Matthias; Wenzel, Matthias; Wink, Clarissa; Maier, Thomas; Ferrier-Barbut, Igor; Pfau, Tilman
2016-02-01
Ferrofluids exhibit unusual hydrodynamic effects owing to the magnetic nature of their constituents. As magnetization increases, a classical ferrofluid undergoes a Rosensweig instability and creates self-organized, ordered surface structures or droplet crystals. Quantum ferrofluids such as Bose-Einstein condensates with strong dipolar interactions also display superfluidity. The field of dipolar quantum gases is motivated by the search for new phases of matter that break continuous symmetries. The simultaneous breaking of continuous symmetries such as the phase invariance in a superfluid state and the translational symmetry in a crystal provides the basis for these new states of matter. However, interaction-induced crystallization in a superfluid has not yet been observed. Here we use in situ imaging to directly observe the spontaneous transition from an unstructured superfluid to an ordered arrangement of droplets in an atomic dysprosium Bose-Einstein condensate. By using a Feshbach resonance to control the interparticle interactions, we induce a finite-wavelength instability and observe discrete droplets in a triangular structure, the number of which grows as the number of atoms increases. We find that these structured states are surprisingly long-lived and observe hysteretic behaviour, which is typical for a crystallization process and in close analogy to the Rosensweig instability. Our system exhibits both superfluidity and, as we show here, spontaneous translational symmetry breaking. Although our observations do not probe superfluidity in the structured states, if the droplets establish a common phase via weak links, then our system is a very good candidate for a supersolid ground state.
Simard, J Marc; Pampori, Adam; Keledjian, Kaspar; Tosun, Cigdem; Schwartzbauer, Gary; Ivanova, Svetlana; Gerzanich, Volodymyr
2014-07-15
Traumatic brain injury (TBI) caused by an explosive blast (blast-TBI) is postulated to result, in part, from transvascular transmission to the brain of a hydrodynamic pulse (a.k.a., volumetric blood surge, ballistic pressure wave, hydrostatic shock, or hydraulic shock) induced in major intrathoracic blood vessels. This mechanism of blast-TBI has not been demonstrated directly. We tested the hypothesis that a blast wave impacting the thorax would induce a hydrodynamic pulse that would cause pathological changes in the brain. We constructed a Thorax-Only Blast Injury Apparatus (TOBIA) and a Jugular-Only Blast Injury Apparatus (JOBIA). TOBIA delivered a collimated blast wave to the right lateral thorax of a rat, precluding direct impact on the cranium. JOBIA delivered a blast wave to the fluid-filled port of an extracorporeal intravenous infusion device whose catheter was inserted retrograde into the jugular vein, precluding lung injury. Long Evans rats were subjected to sublethal injury by TOBIA or JOBIA. Blast injury induced by TOBIA was characterized by apnea and diffuse bilateral hemorrhagic injury to the lungs associated with a transient reduction in pulse oximetry signals. Immunolabeling 24 h after injury by TOBIA showed up-regulation of tumor necrosis factor alpha, ED-1, sulfonylurea receptor 1 (Sur1), and glial fibrillary acidic protein in veins or perivenular tissues and microvessels throughout the brain. The perivenular inflammatory effects induced by TOBIA were prevented by ligating the jugular vein and were reproduced using JOBIA. We conclude that blast injury to the thorax leads to perivenular inflammation, Sur1 up-regulation, and reactive astrocytosis resulting from the induction of a hydrodynamic pulse in the vasculature. PMID:24673157
Pampori, Adam; Keledjian, Kaspar; Tosun, Cigdem; Schwartzbauer, Gary; Ivanova, Svetlana; Gerzanich, Volodymyr
2014-01-01
Abstract Traumatic brain injury (TBI) caused by an explosive blast (blast-TBI) is postulated to result, in part, from transvascular transmission to the brain of a hydrodynamic pulse (a.k.a., volumetric blood surge, ballistic pressure wave, hydrostatic shock, or hydraulic shock) induced in major intrathoracic blood vessels. This mechanism of blast-TBI has not been demonstrated directly. We tested the hypothesis that a blast wave impacting the thorax would induce a hydrodynamic pulse that would cause pathological changes in the brain. We constructed a Thorax-Only Blast Injury Apparatus (TOBIA) and a Jugular-Only Blast Injury Apparatus (JOBIA). TOBIA delivered a collimated blast wave to the right lateral thorax of a rat, precluding direct impact on the cranium. JOBIA delivered a blast wave to the fluid-filled port of an extracorporeal intravenous infusion device whose catheter was inserted retrograde into the jugular vein, precluding lung injury. Long Evans rats were subjected to sublethal injury by TOBIA or JOBIA. Blast injury induced by TOBIA was characterized by apnea and diffuse bilateral hemorrhagic injury to the lungs associated with a transient reduction in pulse oximetry signals. Immunolabeling 24 h after injury by TOBIA showed up-regulation of tumor necrosis factor alpha, ED-1, sulfonylurea receptor 1 (Sur1), and glial fibrillary acidic protein in veins or perivenular tissues and microvessels throughout the brain. The perivenular inflammatory effects induced by TOBIA were prevented by ligating the jugular vein and were reproduced using JOBIA. We conclude that blast injury to the thorax leads to perivenular inflammation, Sur1 up-regulation, and reactive astrocytosis resulting from the induction of a hydrodynamic pulse in the vasculature. PMID:24673157
Stone, G.W.; Pepper, D.A.; Xu, Jie; Zhang, X.
2004-01-01
variable depths across the shoal crest and variable wave amplitudes during storms and fair-weather. Arctic surge fronts were associated with southerly storm waves, and southwesterly to westerly currents and sediment transport. Migrating cyclonic fronts generated northerly swell that transformed into southerly sea, and currents and sediment transport that were southeasterly overall. Waves were 36% higher and 9% longer on the seaward side of the shoal, whereas mean currents were 10% stronger landward, where they were directed onshore, in contrast to the offshore site, where seaward currents predominated. Sediment transport initiated by cold fronts was generally directed southeasterly to southwesterly at the offshore site, and southerly to westerly at the nearshore site. The data suggest that both cold fronts and the shoal, exert significant influences on regional hydrodynamics and sediment transport.
Controlling ferrofluid permeability across the blood–brain barrier model.
Shi, Di; Sun, Linlin; Mi, Gujie; Sheikh, Lubna; Bhattacharya, Soumya; Nayar, Suprabha; Webster, Thomas J
2014-02-21
In the present study, an in vitro blood–brain barrier model was developed using murine brain endothelioma cells (b.End3 cells). Confirmation of the blood–brain barrier model was completed by examining the permeability of FITCDextran at increasing exposure times up to 96 h in serum-free medium and comparing such values with values from the literature. After such confirmation, the permeability of five novel ferrofluid (FF) nanoparticle samples, GGB (ferrofluids synthesized using glycine, glutamic acid and BSA), GGC (glycine, glutamic acid and collagen), GGP (glycine, glutamic acid and PVA), BPC (BSA, PEG and collagen) and CPB (collagen, PVA and BSA), was determined using this blood–brain barrier model. All of the five FF samples were characterized by zeta potential to determine their charge as well as TEM and dynamic light scattering for determining their hydrodynamic diameter. Results showed that FF coated with collagen passed more easily through the blood–brain barrier than FF coated with glycine and glutamic acid based on an increase of 4.5% in permeability. Through such experiments, diverse magnetic nanomaterials (such as FF) were identified for: (1) MRI use since they were less permeable to penetrate the blood–brain barrier to avoid neural tissue toxicity (e.g. GGB) or (2) brain drug delivery since they were more permeable to the blood–brain barrier (e.g. CPB). PMID:24457539
Controlling ferrofluid permeability across the blood-brain barrier model
NASA Astrophysics Data System (ADS)
Shi, Di; Sun, Linlin; Mi, Gujie; Sheikh, Lubna; Bhattacharya, Soumya; Nayar, Suprabha; Webster, Thomas J.
2014-02-01
In the present study, an in vitro blood-brain barrier model was developed using murine brain endothelioma cells (b.End3 cells). Confirmation of the blood-brain barrier model was completed by examining the permeability of FITC-Dextran at increasing exposure times up to 96 h in serum-free medium and comparing such values with values from the literature. After such confirmation, the permeability of five novel ferrofluid (FF) nanoparticle samples, GGB (ferrofluids synthesized using glycine, glutamic acid and BSA), GGC (glycine, glutamic acid and collagen), GGP (glycine, glutamic acid and PVA), BPC (BSA, PEG and collagen) and CPB (collagen, PVA and BSA), was determined using this blood-brain barrier model. All of the five FF samples were characterized by zeta potential to determine their charge as well as TEM and dynamic light scattering for determining their hydrodynamic diameter. Results showed that FF coated with collagen passed more easily through the blood-brain barrier than FF coated with glycine and glutamic acid based on an increase of 4.5% in permeability. Through such experiments, diverse magnetic nanomaterials (such as FF) were identified for: (1) MRI use since they were less permeable to penetrate the blood-brain barrier to avoid neural tissue toxicity (e.g. GGB) or (2) brain drug delivery since they were more permeable to the blood-brain barrier (e.g. CPB).
Ferrofluid-based reconfigurable optofluidic switch
NASA Astrophysics Data System (ADS)
Valentino, Gianna; Mongeau, Eric; Gu, Yu
2014-03-01
We present a low-cost, reconfigurable optofluidic switch exploiting both the optical and magnetic properties of a water-based ferrofluid. This switch is composed of an integrated waveguide orthogonally crossing a microfluidic channel containing high-index oil and a ferrofluid plug. The switch is turned ``ON'' or ``OFF'' by the movement of the ferrofluid plug in response to an external magnetic field. Each switch exhibits a high contrast ratio and millisecond response time. Parallel geometries for both mode and multi-mode waveguides are shown. Saint Joseph's University summer research fund, McNulty Fellows Program.
NASA Astrophysics Data System (ADS)
Andreev, Pavel A.
2015-06-01
We discuss the complete theory of spin-1/2 electron-positron quantum plasmas, when electrons and positrons move with velocities mach smaller than the speed of light. We derive a set of two fluid quantum hydrodynamic equations consisting of the continuity, Euler, spin (magnetic moment) evolution equations for each species. We explicitly include the Coulomb, spin-spin, Darwin and annihilation interactions. The annihilation interaction is the main topic of the paper. We consider the contribution of the annihilation interaction in the quantum hydrodynamic equations and in the spectrum of waves in magnetized electron-positron plasmas. We consider the propagation of waves parallel and perpendicular to an external magnetic field. We also consider the oblique propagation of longitudinal waves. We derive the set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory to the linear wave behavior in absence of external fields. We calculate the contribution of the Darwin and annihilation interactions in the Landau damping of the Langmuir waves. We should mention that the annihilation interaction does not change number of particles in the system. It does not related to annihilation itself, but it exists as a result of interaction of an electron-positron pair via conversion of the pair into virtual photon. A pair of the non-linear Schrodinger equations for the electron-positron plasmas including the Darwin and annihilation interactions is derived. Existence of the conserving helicity in electron-positron quantum plasmas of spinning particles with the Darwin and annihilation interactions is demonstrated. We show that the annihilation interaction plays an important role in the quantum electron-positron plasmas giving the contribution of the same magnitude as the spin-spin interaction.
Andreev, Pavel A.
2015-06-15
We discuss the complete theory of spin-1/2 electron-positron quantum plasmas, when electrons and positrons move with velocities mach smaller than the speed of light. We derive a set of two fluid quantum hydrodynamic equations consisting of the continuity, Euler, spin (magnetic moment) evolution equations for each species. We explicitly include the Coulomb, spin-spin, Darwin and annihilation interactions. The annihilation interaction is the main topic of the paper. We consider the contribution of the annihilation interaction in the quantum hydrodynamic equations and in the spectrum of waves in magnetized electron-positron plasmas. We consider the propagation of waves parallel and perpendicular to an external magnetic field. We also consider the oblique propagation of longitudinal waves. We derive the set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory to the linear wave behavior in absence of external fields. We calculate the contribution of the Darwin and annihilation interactions in the Landau damping of the Langmuir waves. We should mention that the annihilation interaction does not change number of particles in the system. It does not related to annihilation itself, but it exists as a result of interaction of an electron-positron pair via conversion of the pair into virtual photon. A pair of the non-linear Schrodinger equations for the electron-positron plasmas including the Darwin and annihilation interactions is derived. Existence of the conserving helicity in electron-positron quantum plasmas of spinning particles with the Darwin and annihilation interactions is demonstrated. We show that the annihilation interaction plays an important role in the quantum electron-positron plasmas giving the contribution of the same magnitude as the spin-spin interaction.
NASA Astrophysics Data System (ADS)
Abou, B.; Néron de Surgy, G.; Wesfreid, J. E.
1997-08-01
We have calculated the general dispersion relationship for surface waves on a ferrofluid layer of any thickness and viscosity, under the influence of a uniform vertical magnetic field. The amplification of these waves can induce an instability called peaks instability (Rosensweig instability). The expression of the dispersion relationship requires that the critical magnetic field and the critical wavenumber of the instability depend on the thickness of the ferrofluid layer. The dispersion relationship has been simplified into four asymptotic regimes: thick or thin layer and viscous or inertial behaviour. The corresponding critical values are presented. We show that a typical parameter of the ferrofluid enables one to know in which regime, viscous or inertial, the ferrofluid will be near the onset of instability. Nous avons calculé la relation de dispersion des ondes de surface dans une couche de ferrofluide d'épaisseur et de viscosité quelconques, soumise à un champ magnétique normal à sa surface (instabilité de pics de Rosensweig). Cette relation montre que le champ magnétique critique et le vecteur d'onde critique de l'instabilité dépendent de l'épaisseur de la couche de fluide. La relation de dispersion a été simplifiée pour quatre régimes asymptotiques: couche épaisse ou mince et comportement visqueux ou inertiel. Nous avons calculé les valeurs critiques de l'instabilité dans ces quatre cas. Nous montrons qu'un paramètre typique du ferrofluide permet de savoir dans quel régime, visqueux ou inertiel, se situe le ferrofluide près du seuil de l'instabilité.
NASA Astrophysics Data System (ADS)
Rablau, Corneliu; Vaishnava, Prem; Regmi, Rajesh; Sudakar, Chandran; Black, Correy; Lawes, Gavin; Naik, Ratna; Lavoie, Melissa; Kahn, David
2009-03-01
We report studies of the structural, magnetic, magneto-thermal and magneto-optic properties of dextran, oleic acid, lauric acid and myristic acid surfacted Fe3O4 nanoparticles of hydrodynamic sizes ranging from 32 nm to 92 nm. All the samples showed saturation magnetization of ˜50 emu/g, significantly smaller than the bulk value for Fe3O4, together with superparamagnetic behavior. The ac magnetization measurements on the dextran coated nanoparticles showed frequency dependent blocking temperature, consistent with superparamgnetic blocking. The ferrofluid heating rates in a 250 Gauss, 100 kHz ac magnetic field varied with the chain lengths of the surfactants, with higher heating rates for longer chains. DC-magnetic-field-induced light scattering patterns produced by two orthogonal He-Ne laser beams passing through the ferrofluid sample revealed different optical signatures for different surfactants.
Temperature dependent light transmission in ferrofluids
NASA Astrophysics Data System (ADS)
Brojabasi, Surajit; Mahendran, V.; Lahiri, B. B.; Philip, John
2015-05-01
We investigate the influence of temperature on the magnetic field induced light transmission in a kerosene based ferrofluid containing oleic acid coated Fe3O4 nanoparticles, where the direction of propagation of light is parallel to the direction of the external magnetic field. At a fixed temperature the transmitted light intensity is found to monotonically increase with incident wavelength due to reduced extinction efficiency at higher wavelength. The transmitted intensity decreases with external magnetic field due to enhanced scattering from the field induced linear chain like structures along the direction of the external magnetic field and due to the build-up of standing waves inside the scattering medium. The extinction of the field induced transmitted light intensity is found to occur at a lower external field as the sample temperature is lowered. The rate of extinction of normalized transmitted light intensity decreased linearly with increasing sample temperature due to slower field induced aggregation kinetics because of an increased Brownian motion of the suspended nanoparticles and a reduced coupling constant. The observed temperature dependent magneto-optical properties of magnetic nanofluids can be exploited for applications in optical devices.
Ferrofluid-based Stretchable Magnetic Core Inductors
NASA Astrophysics Data System (ADS)
Lazarus, N.; Meyer, C. D.
2015-12-01
Magnetic materials are commonly used in inductor and transformer cores to increase inductance density. The emerging field of stretchable electronics poses a new challenge since typical magnetic cores are bulky, rigid and often brittle. This paper presents, for the first time, stretchable inductors incorporating ferrofluid as a liquid magnetic core. Ferrofluids, suspensions of nanoscale magnetic particles in a carrier liquid, provide enhanced magnetic permeability without changing the mechanical properties of the surrounding elastomer. The inductor tested in this work consisted of a liquid metal solenoid wrapped around a ferrofluid core in separate channels. The low frequency inductance was found to increase from 255 nH before fill to 390 nH after fill with ferrofluid, an increase of 52%. The inductor was also shown to survive uniaxial strains of up to 100%.
Rheological Properties of Iron Oxide Based Ferrofluids
NASA Astrophysics Data System (ADS)
Devi, M.; Mohanta, D.
2009-06-01
In the present work, we report synthesis and magneto-viscous properties of cationic and anionic surfactant coated, iron oxide nanoparticles based ferrofluids. Structural and morphological aspects are revealed by x-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. We compare the rheological/magneto-viscous properties of different ferrofluids for various shear rates (2-450 sec-1) and applied magnetic fields (0-100 gauss). In the absence of a magnetic field, and under no shear case, the ferrofluid prepared with TMAH coated particle is found to be 12% more viscous compared to its counterpart. The rheological properties are governed by non-Newtonian features, and for a definite shear rate, viscosity of a given ferrofluid is found to be strongly dependent on the applied magnetic field as well as nature of the surfactant.
Visualizing Magnetism with Optical Ferrofluid Cells
NASA Astrophysics Data System (ADS)
Snyder, Michael
2015-05-01
a novel technique for the visualization of magnetic fields. The ferrofluid cells are made up of two optically flat windows with a layer of Fe3O4/Fe2O3 ferrofluid between the glass. Using different magnet configurations and lighting, highly structured pictures are obtained of one of the universes forces. Characterized as the magneto-optic Kerr/displacement current effect on self assembled micrometer sized helical rods of Fe304/Fe203.
Ordered macromolecular structures in ferrofluid mixtures
Hayter, J.B.; Pynn, R.; Charles, S.; Skjeltorp, A.T.; Trewhella, J.; Stubbs, G.; Timmins, P.
1989-04-03
We have observed ordering of dilute dispersions of spherical and cylindrical macromolecules in magnetized ferrofluids. The order results from structural correlations between macromolecular and ferrofluid particles rather than from macroscopic magnetostatic effects. We have aligned elongated macromolecules by this technique and have obtained anisotropic neutron-diffraction patterns, which reflect the internal structure of the macromolecules. The method provides a tool for orienting suspended macromolecular assemblies which are not amenable to conventional alignment techniques.
Magnetic detection of ferrofluid injection zones
Borglin, S.; Moridis, G.; Becker, A.
1998-03-01
Ferrofluids are stable colloidal suspensions of magnetic particles that can be stabilized in various carrier liquids. In this study the authors investigate the potential of ferrofluids to trace the movement and position of liquids injected in the subsurface using geophysical methods. An ability to track and monitor the movement and position of injected liquids is essential in assessing the effectiveness of the delivery system and the success of the process. Ferrofluids can also provide a significant detection and verification tool in containment technologies, where they can be injected with the barrier liquids to provide a strong signature allowing determination of the barrier geometry, extent, continuity and integrity. Finally, ferrofluids may have unique properties as tracers for detecting preferential flow features (such as fractures) in the subsurface, and thus allow the design of more effective remediation systems. In this report the authors review the results of the investigation of the potential of ferrofluids to trace the movement and position of liquids injected in the subsurface using geophysical methods. They demonstrate the feasibility of using conventional magnetometry for detecting subsurface zones of injected ferrofluids used to trace liquids injected for remediation or barrier formation. The geometrical shapes considered were a sphere, a thin disk, a rectangular horizontal slab, and a cylinder. Simple calculations based on the principles of magnetometry are made to determine the detection depths of FTs. Experiments involving spherical, cylindrical and horizontal slabs show a very good agreement between predictions and measurements.
Investigation into loss in ferrofluid magnetization
NASA Astrophysics Data System (ADS)
Li, J.; Gong, X. M.; Lin, Y. Q.; Liu, X. D.; Chen, L. L.; Li, J. M.; Mao, H.; Li, D. C.
2014-07-01
Ferrofluids containing γ-Fe2O3/Ni2O3 nanoparticles (not chemically treated) were synthesized using water and mixed water-glycerol as carrier liquid and the ferrofluid viscosity was modified by varying the glycerol content in the carrier liquid. The apparent magnetization of the ferrofluids decreased with increasing glycerol content. The loss in magnetization is described by the ratio of effective magnetic volume fraction to physical volume fraction of nanoparticles in the ferrofluids as a characteristic parameter. We ascribe the loss to the formation of "dead aggregates" having a ring-like structure of closed magnetic flux rather than to any chemical reaction. Such dead aggregates exist in zero magnetic field and do not contribute to the magnetization in the low or high field regime, so that the effective magnetic volume fraction in the ferrofluids decrease. An increase in carrier liquid viscosity is similar to a weakening of the thermal effect, so the number of dead aggregates increases and the magnetization decreases in inverse proportion to the viscosity. This relationship between the apparent magnetization and ferrofluid carrier liquid viscosity can be termed the "viscomagnetic effect".
Parallel flow in hele-shaw cells with ferrofluids
Miranda; Widom
2000-02-01
Parallel flow in a Hele-Shaw cell occurs when two immiscible liquids flow with relative velocity parallel to the interface between them. The interface is unstable due to a Kelvin-Helmholtz type of instability in which fluid flow couples with inertial effects to cause an initial small perturbation to grow. Large amplitude disturbances form stable solitons. We consider the effects of applied magnetic fields when one of the two fluids is a ferrofluid. The dispersion relation governing mode growth is modified so that the magnetic field can destabilize the interface even in the absence of inertial effects. However, the magnetic field does not affect the speed of wave propogation for a given wave number. We note that the magnetic field creates an effective interaction between the solitons. PMID:11046508
Ejection of ferrofluid grains from a ferrofluid using nonlinear acoustic impulses
NASA Astrophysics Data System (ADS)
Manciu, Felicia S.; Manciu, Marian; Sen, Surajit
2000-03-01
We consider a model study of a dilute ferrofluid in a container with a flat base and an open top surface with monodisperse ferrofluid grains that form a stable colloid in water or oil. The grains are assumed to be under the influence of a strong, uniform, external magnetic field. It is well known that due to the influence of the field, such a system forms chains of ferrofluid grains between the base and the surface of the liquid. The phase-separated system is then subjected to non-linear acoustic impulses at its base. We show that for impulses of any magnitude, it is possible to generate non-dispersive bundles of energy through the chains. By carrying out detailed dynamical simulations of impulse propagation in the chains, we show that for appropriate impulse magnitudes, the ferrofluid grains in each of the chains, which are in the vicinity of the surface, will overcome the force due to surface tension and eject into air. Ferrofluid grains carry a coating of the host liquid, which can be colored for water-based ferrofluids and hence the system may potentially be used to design a nozzle-free inkjet printer. For ferrofluid grains of typical diameter of about 100 Angstroms, the proposed system could lead one to develop inkjet printers with dot sizes that are less than 200 Angstroms and hence to a printing system of unparalleled resolution. [1] S. Sen, M. Manciu and F.S. Manciu, Appl. Phys. Lett. 75, 1479 (1999).
A contribution about ferrofluid based flow manipulation and locomotion systems
NASA Astrophysics Data System (ADS)
Zimmermann, K.; Zeidis, I.; Bohm, V.; Popp, J.
2009-02-01
With the background of developing apedal bionic inspired locomotion systems for future application fields like autonomous (swarm) robots, medical engineering and inspection systems, this article presents a selection of locomotion systems with bifluidic flow control using ferrofluid. By controlling the change of shape, position and pressure of the ferrofluid in a secondary low viscous fluid by magnetic fields locomotion of objects or the ferrofluid itself can be realised. The locomotion of an object is caused in the first example by a ferrofluid generated flow of the secondary fluid and in the second and third case by the direct alteration of the ferrofluid position.
Ferrofluid Droplet Formation by Vibratory Stimulation
NASA Astrophysics Data System (ADS)
Bock, Paul; Hsu, Chang-Fang; Ashgriz, Nasser
1996-11-01
A new technique for the formation of ferrofluid droplets is developed. A vertically applied magnetic field is used to cause instabilities and then eventual droplet formation from a pool of ferrofluid. The magnetic field is created by a flat solenoid wrapped around a soft iron core. Instabilities are excited on the ferrofluid surface by applying a field strength below a critical strength for droplet formation. The ferrofluid is then subjected to vertical vibration. The surface vibration is achieved by mounting the ferrofluid container to a speaker. The frequency of this vibration is on the order of 10 Hz. This technique allows the variation of the droplet spacing, by changing the frequency of the pool oscillation, and the variation of the droplet size by changing the strength of the magnetic field. The main advantage of this technique over presently available droplet generators is that it does not require any orfices. The droplets can be formed directly from the surface of a pool of liquid. This eliminates the need for manufacturing minute orfices which may also be plugged easily.
Zablotsky, Dmitry; Blums, Elmars
2011-08-01
In this paper, we consider a concentration grating of magnetic nanoparticles optically induced by thermodiffusion in a layer of ferrofluid in the presence of the external homogeneous magnetic field. The applied field is directed along the concentration gradient and leads to the appearance of the internal nonhomogeneous demagnetizing fields. When the system reaches equilibrium, the optical pumping is switched off, and the grating is allowed to relax. We carry out a stability analysis using the Galerkin approach and numerical simulations of the full system of equations to determine the growth rates and the mode amplitudes of the hydrodynamic and concentration perturbations during the relaxation stage. PMID:21929102
Flow and heat transfer of ferrofluids over a flat plate with uniform heat flux
NASA Astrophysics Data System (ADS)
Khan, W. A.; Khan, Z. H.; Haq, R. U.
2015-04-01
The present work is dedicated to analyze the flow and heat transport of ferrofluids along a flat plate subjected to uniform heat flux and slip velocity. A magnetic field is applied in the transverse direction to the plate. Moreover, three different kinds of magnetic nanoparticles (Fe3O4, CoFe2O4, Mn-ZnFe2O4 are incorporated within the base fluid. We have considered two different kinds of base fluids (kerosene and water) having poor thermal conductivity as compared to solid magnetic nanoparticles. Self-similar solutions are obtained and are compared with the available data for special cases. A simulation is performed for each ferrofluid mixture by considering the dominant effects of slip and uniform heat flux. It is found that the present results are in an excellent agreement with the existing literature. The variation of skin friction and heat transfer is also performed at the surface of the plate and then the better heat transfer and of each mixture is analyzed. Kerosene-based magnetite Fe3O4 provides the higher heat transfer rate at the wall as compared to the kerosene-based cobalt ferrite and Mn-Zn ferrite. It is also concluded that the primary effect of the magnetic field is to accelerate the dimensionless velocity and to reduce the dimensionless surface temperature as compared to the hydrodynamic case, thereby increasing the skin friction and the heat transfer rate of ferrofluids.
Lorca, T A; Claus, J R; Eifert, J D; Marcy, J E; Sumner, S S
2003-07-01
The top surface of boneless skinless chicken breasts was inoculated with either green fluorescent protein (GFP)-labeled Escherichia coli (E. coli-GFP) or rifampicin-resistant E. coli (E. coli-Rif) and subjected to electrically generated hydrodynamic shock wave treatment (HVADH). Cryostat sampling in concert with laser scanning confocal microscopy or plating onto antibiotic selective agar was used to determine if HVADH treatment resulted in the movement of the inoculated bacteria from the outer inoculated surface to the interior of intact boneless skinless chicken breasts. In HVADH-treated boneless skinless chicken breasts, marker bacteria were detected within the first 200 microm below the inoculated surface, 50 to 100 microm beyond the depth of untreated surface inoculated boneless skinless chicken breasts. The exact depth at which the marker bacteria were found was dependent on the cryostat sampling distance used. These results suggest that HVADH treatments affect the movement of surface bacteria. PMID:12872981
Waves in Radial Gravity Using Magnetic Fluid
NASA Technical Reports Server (NTRS)
Ohlsen, Daniel R.; Hart, John E.; Weidman, Patrick D.
1996-01-01
We are beginning laboratory experiments using magnetically active ferrofluids to study surface waves in novel geometries. Terrestrial gravity is eliminated from the dynamics, and the magnetic body force felt by ferrofluid in the presence of a magnetic field gradient is used to create a geopotential field which is a section of or an entire sphere or cylinder. New optical, electromagnetic and ultrasonic diagnostic techniques are under development to initially study capillary-gravity wave propagation and interaction in such geometries.
Laouar, A; Guerziz, A; Boussaha, A
2016-01-01
This paper focuses on the mathematical study of the existence of solitary gravity waves (solitons) and their characteristics (amplitude, velocity, [Formula: see text]) generated by a piston wave maker lying upstream of a horizontal channel. The mathematical model requires both incompressibility condition, irrotational flow of no viscous fluid and Lagrange coordinates. By using both the inverse scattering method and a given initial potential [Formula: see text] we can transform the KdV equation into Sturm-Liouville spectral problem. The latter problem amounts to find negative discrete eigenvalues [Formula: see text] and associated eigenfunctions [Formula: see text], where each calculated eigenvalue [Formula: see text] gives a soliton and the profile of the free surface. For solving this problem, we can use the Runge-Kutta method. For illustration, two examples of the wave maker movement are proposed. The numerical simulations show that the perturbation of wave maker with hyperbolic tangent displacement under physical conditions affect the number of solitons emitted. PMID:27606157
Use of ferrofluids in machining of metals
NASA Astrophysics Data System (ADS)
Podgorkov, V. V.
1985-03-01
Ferrofluids controlled by an external magnetic field are suitable as lubricants for moving metal machining parts. Empirical relations of the form M sub c = kDt sub bs sup av sup c were established for the unit cutting torque M sub c as function of the drill diameter, the depth of hole t, the feed rate s, and the cutting rate v when holes in Al3V aluminum alloy, TsAM10-5 zinc alloy, VT1 titanium alloy, or 12Cr18Ni10Ti stainless are cut with a drill of R6M5 high-speed steel using a fixture made of nonmagnetic stainless and a ferrofluid based on MVP mineral tool oil as lubricant. Values of the coefficient and the exponents were determined by the Student significance test and Fisher adequacy test. It is found that ferrofluid as lubricant is more effective in machining of nonmagnetic materials.
Ferrofluid Microwave Devices With Magnetically Controlled Impedances
NASA Astrophysics Data System (ADS)
Fannin, P. C.; Stefu, N.; Marin, C. N.; Malaescu, I.; Totoreanu, R.
2010-08-01
Ferrofluid filled transmission lines are microwave electronic devices. The complex dielectric permittivity and the complex magnetic permeability of a kerosene based ferrofluid with magnetite nanoparticles, in the frequency range (0.5-6) GHz were measured, for several values of polarising field, H. Afterwards, the input impedance of a short-circuited transmission line filled with this ferrofluid was computed using the equation Z = Zc tanh(γl). Here Zc and l are the characteristic impedance and the length of the coaxial line and γ is the propagation constant, depending on the dielectric and magnetic parameters of the material within the line. It is demonstrated how the impedance displays a frequency and polarizing field dependence, which has application in the design of magnetically controlled microwave devices.
Therapeutic efficacy of ferrofluid bound anticancer agent
NASA Astrophysics Data System (ADS)
Alexiou, Ch.; Arnold, W.; Hulin, P.; Klein, R.; Schmidt, A.; Bergemannand, Ch.; Parak, F. G.
2001-09-01
Ferrofluids coated with starch polymers can be used as biocompatible carriers in a new field of locoregional tumor therapy called "magnetic drug targeting". Bound to medical drugs, such magnetic nanoparticles can be enriched in a desired body compartment using an external magnetic field. In the present study, we confirm the concentration of ferrofluids in VX2 squamous cell carcinoma tissue of the rabbit using histological investigations and MR imaging. The therapeutic efficacy of "magnetic drug targeting" was studied using the rabbit VX2 squamous cell carcinoma model. Mitoxantrone coupled ferrofluids were injected intraarterially into the artery supplying the tumor (femoral artery). The magnetic field (1.7 Tesla) was focused to the tumor placed at the medial portion of the hind limb of New Zealand White rabbits. Complete tumor remissions could be seen without any negative side effects by using only 20% of the normal systemic dosage of the chemotherapeutic agent mitoxantrone. Figs 3, Refs 14.
Magnetic Hyperthermia in ferrofluid-gel composites
NASA Astrophysics Data System (ADS)
Nemala, Humeshkar; Wadehra, Anshu; Dixit, Ambesh; Regmi, Rajesh; Vaishnava, Prem; Lawes, Gavin; Naik, Ratna
2012-02-01
Magnetic hyperthermia is the generation of heat by an external magnetic field using superparamagnetic nanoparticles. However, there are still questions concerning magnetic hyperthermia in tissue; in particular the confinement of the nanoparticles at mesoscopic scales. We used Agarose and Alginate gels as models for human tissue and embedded magnetic nanoparticles in them. We report the synthesis and characterization of dextran coated iron oxide (Fe3O4) nanoparticles. Characterization of these nanoparticles was done using X-ray diffraction, transmission electron microscopy, magnetometry, and hyperthermia measurements. Temperature dependent susceptibility measurements reveal a sharp anomaly in the ferrofluid sample at the freezing temperature. This is conspicuously absent in the ferrofluid-gel composites. Heat generation studies on these superparamagnetic gel-composites revealed a larger heat production in the ferrofluids(˜4W/g) as compared to the gels(˜1W/g), which we attribute to a reduction in Brownian relaxation for the nanoparticles embedded in Agarose and Alginate.
NASA Astrophysics Data System (ADS)
Suslov, Sergey A.; Bozhko, Alexandra A.; Putin, Gennady F.; Sidorov, Alexander S.
2012-11-01
Study of Boussinesq convection in a vertical differentially heated fluid layer is one of classical problems in hydrodynamics. It is well known that as the value of fluid's Grashof number increases the basic flow velocity profile becomes unstable with respect to stationary shear-driven disturbances (at Prandtl numbers Pr < 12.5) or thermogravitational waves propagating vertically (at larger values of Prandtl number). However linear stability studies of a similar flow of magnetopolarizable nanosuspensions (ferrofluids) placed in a uniform magnetic field perpendicular to a fluid layer predicted the existence of a new type of instability, oblique waves, that arise due to the differential local magnetisation of a non-uniformly heated fluid. The existence of such (thermomagnetic) waves has now been confirmed experimentally using a kerosene-based ferrofluid with magnetite particles of the average size of 10 nm stabilized with oleic acid. The heat transfer rate measurements using thermocouples and flow visualization using a thermosensitive film and an infrared camera have been performed. Perturbation energy analysis has been used to determine the physical nature of various observed instability patterns and quantitatively distinguish between thermogravitational and thermomagnetic waves.
Synchronization via Hydrodynamic Interactions
NASA Astrophysics Data System (ADS)
Kendelbacher, Franziska; Stark, Holger
2013-12-01
An object moving in a viscous fluid creates a flow field that influences the motion of neighboring objects. We review examples from nature in the microscopic world where such hydrodynamic interactions synchronize beating or rotating filaments. Bacteria propel themselves using a bundle of rotating helical filaments called flagella which have to be synchronized in phase. Other micro-organisms are covered with a carpet of smaller filaments called cilia on their surfaces. They beat highly synchronized so that metachronal waves propagate along the cell surfaces. We explore both examples with the help of simple model systems and identify generic properties for observing synchronization by hydrodynamic interactions.
Structure and hydrodynamics of colloidal systems
NASA Astrophysics Data System (ADS)
Hayter, John B.
1986-02-01
Invited paperColloidal phases (for example, micellar solutions, latex suspensions, ferrofluids and microemulsions) provide excellent model systems with which to test structural and hydrodynamic theories of the liquid state. Interparticle potentials may be attractive or repulsive, and the experimentalist is often free to control the strength, range and symmetry of the interactions. Small-angle neutron scattering (SANS) and small-angle neutron spin-echo (SANSE) provide excellent complementary tools for studying the structure and time-dependence of these systems, where correlation lengths typically vary from about one to several tens of nm. Correlation times are usually in the nsec to μsec range, but may be of order minutes in certain systems. This paper will review some of the current theories and their recent experimental tests, using colloidal systems in which the direct interaction potentials may have spherical, dipolar or cylindrical symmetry and the hydrodynamic interactions may be weak or strong.
Structure and hydrodynamics of colloidal systems
NASA Astrophysics Data System (ADS)
Hayter, J. B.
1985-07-01
Colloidal phases (for example, micellar solutions, latex suspensions, ferrofluids and microemulsions) provide excellent model systems with which to test structural and hydrodynamic theories of the liquid state. Interparticle potentials may be attractive or repulsive, and the experimentalist is often free to control the strength, range and symmetry of the interactions. Small-angle neutron scattering (SANS) and small-angle neutron spin-echo (SANSE) provide excellent complementary tools for studying the structure and time-dependence of these systems, where correlation lengths typically vary from about one to several tens of nm. Correlation times are usually in the nsec to (MU) sec range, but may be of order minutes in certain systems. This paper will review some of the current theories and their recent experimental tests, using colloidal systems in which the direct interaction potentials may have spherical, dipolar or cylindrical symmetry and the hydrodynamic interactions may be weak or strong.
Structure and hydrodynamics of colloidal systems
Hayter, J.B.
1985-07-01
Colloidal phases (for example, micellar solutions, latex suspensions, ferrofluids and microemulsions) provide excellent model systems with which to test structural and hydrodynamic theories of the liquid state. Interparticle potentials may be attractive or repulsive, and the experimentalist is often free to control the strength, range and symmetry of the interactions. Small-angle neutron scattering (SANS) and small-angle neutron spin-echo (SANSE) provide excellent complementary tools for studying the structure and time-dependence of these systems, where correlation lengths typically vary from about one to several tens of nm. Correlation times are usually in the nsec to ..mu..sec range, but may be of order minutes in certain systems. This paper will review some of the current theories and their recent experimental tests, using colloidal systems in which the direct interaction potentials may have spherical, dipolar or cylindrical symmetry and the hydrodynamic interactions may be weak or strong.
Hydrodynamics of insect spermatozoa
NASA Astrophysics Data System (ADS)
Pak, On Shun; Lauga, Eric
2010-11-01
Microorganism motility plays important roles in many biological processes including reproduction. Many microorganisms propel themselves by propagating traveling waves along their flagella. Depending on the species, propagation of planar waves (e.g. Ceratium) and helical waves (e.g. Trichomonas) were observed in eukaryotic flagellar motion, and hydrodynamic models for both were proposed in the past. However, the motility of insect spermatozoa remains largely unexplored. An interesting morphological feature of such cells, first observed in Tenebrio molitor and Bacillus rossius, is the double helical deformation pattern along the flagella, which is characterized by the presence of two superimposed helical flagellar waves (one with a large amplitude and low frequency, and the other with a small amplitude and high frequency). Here we present the first hydrodynamic investigation of the locomotion of insect spermatozoa. The swimming kinematics, trajectories and hydrodynamic efficiency of the swimmer are computed based on the prescribed double helical deformation pattern. We then compare our theoretical predictions with experimental measurements, and explore the dependence of the swimming performance on the geometric and dynamical parameters.
Passive Magnetic Bearing With Ferrofluid Stabilization
NASA Technical Reports Server (NTRS)
Jansen, Ralph; DiRusso, Eliseo
1996-01-01
A new class of magnetic bearings is shown to exist analytically and is demonstrated experimentally. The class of magnetic bearings utilize a ferrofluid/solid magnet interaction to stabilize the axial degree of freedom of a permanent magnet radial bearing. Twenty six permanent magnet bearing designs and twenty two ferrofluid stabilizer designs are evaluated. Two types of radial bearing designs are tested to determine their force and stiffness utilizing two methods. The first method is based on the use of frequency measurements to determine stiffness by utilizing an analytical model. The second method consisted of loading the system and measuring displacement in order to measure stiffness. Two ferrofluid stabilizers are tested and force displacement curves are measured. Two experimental test fixtures are designed and constructed in order to conduct the stiffness testing. Polynomial models of the data are generated and used to design the bearing prototype. The prototype was constructed and tested and shown to be stable. Further testing shows the possibility of using this technology for vibration isolation. The project successfully demonstrated the viability of the passive magnetic bearing with ferrofluid stabilization both experimentally and analytically.
Ferrofluid Would Seal Linear-Motion Valve
NASA Technical Reports Server (NTRS)
Chandler, J. A.
1983-01-01
Proposed valve employs ferrofluid to make tight seal. Seal requires no precisely machined parts, and hand lapping of valve seats are unnecessary. Magnetic fluid fills gap between shaft and annular pole piece in chamber wall. Precise shaft fit is not necessary.
Anomalous attenuation of ultrasound in ferrofluids under the influence of a magnetic field
NASA Technical Reports Server (NTRS)
Isler, W. E.; Chung, D. Y.
1978-01-01
Ultrasonic wave propagation has been studied in a water-base ferrofluid by pulse-echo methods. A commercial box-car integrator was used to measure the change in attenuation due to an external magnetic field applied at various angles relative to the ultrasonic propagation vector. Anomalous results were obtained when the attenuation was plotted as a function of the magnetic field strength. As the field increased, the attenuation reached a maximum and then decreased to a flat minimum before it approached saturation at a field of 2 KG. This variation of attenuation with magnetic field cannot be explained from the simple picture derivable from the work of McTague on the viscosity of ferrofluids. In no case was the viscosity seen to decrease with field, nor was the oscillatory behavior observed. The results of this study were compared with the theory developed by Parsons.
Floating and flying ferrofluid bridges induced by external magnetic fields
NASA Astrophysics Data System (ADS)
Ma, Rongchao; Zhou, Yixin; Liu, Jing
2015-04-01
A ferrofluid is a mixture that exhibits both magnetism and fluidity. This merit enables the ferrofluid to be used in a wide variety of areas. Here we show that a floating ferrofluid bridge can be induced between two separated boards under a balanced external magnetic field generated by two magnets, while a flying ferrofluid bridge can be induced under an unbalanced external magnetic field generated by only one magnet. The mechanisms of the ferrofluid bridges were discussed and the corresponding mathematical equations were also established to describe the interacting magnetic force between the ferro particles inside the ferrofluid. This work answered a basic question that, except for the well-known floating water bridges that are related to electricity, one can also build up a liquid bridge that is related to magnetism.
A Novel Implantable Glaucoma Valve Using Ferrofluid
Paschalis, Eleftherios I.; Chodosh, James; Sperling, Ralph A.; Salvador-Culla, Borja; Dohlman, Claes
2013-01-01
Purpose To present a novel design of an implantable glaucoma valve based on ferrofluidic nanoparticles and to compare it with a well-established FDA approved valve. Setting Massachusetts Eye & Ear Infirmary, Boston, USA. Methods A glaucoma valve was designed using soft lithography techniques utilizing a water-immiscible magnetic fluid (ferrofluid) as a pressure-sensitive barrier to aqueous flow. Two rare earth micro magnets were used to calibrate the opening and closing pressure. In-vitro flow measurements were performed to characterize the valve and to compare it to Ahmed™ glaucoma valve. The reliability and predictability of the new valve was verified by pressure/flow measurements over a period of three months and X-ray diffraction (XRD) analysis over a period of eight weeks. In vivo assessment was performed in three rabbits. Results In the in vitro experiments, the opening and closing pressures of the valve were 10 and 7 mmHg, respectively. The measured flow/pressure response was linearly proportional and reproducible over a period of three months (1.8 µl/min at 12 mmHg; 4.3 µl/min at 16 mmHg; 7.6 µl/min at 21 mmHg). X-ray diffraction analysis did not show oxidization of the ferrofluid when exposed to water or air. Preliminary in vivo results suggest that the valve is biocompatible and can control the intraocular pressure in rabbits. Conclusions The proposed valve utilizes ferrofluid as passive, tunable constriction element to provide highly predictable opening and closing pressures while maintaining ocular tone. The ferrofluid maintained its magnetic properties in the aqueous environment and provided linear flow to pressure response. Our in-vitro tests showed reliable and reproducible results over a study period of three months. Preliminary in-vivo results were very promising and currently more thorough investigation of this device is underway. PMID:23840691
Experimental method for the purification and reconditioning of ferrofluids
NASA Astrophysics Data System (ADS)
Cotae, Constantin
1987-03-01
The paper presents the theoretical aspects regarding the magnetogravimetric purification of ferrofluids both in the process of preparation and for their reconditioning from impurities. An experimental device used for magnetogravimetric purification is described together with experiments on some samples of oil-based ferrofluid that became impure with non-mixible solid, liquid, magnetic and nonmagnetic ingredients. The experiments resulted in a complete purification of the ferrofluid samples.
Resistive magneto-hydrodynamical cut-off of Alfvén wave in fully ionized plasmas
Vranjes, J.; Kono, M.
2014-01-15
The term cut-off in the theory of the Alfvén wave is used to describe several different phenomena. In this work, the cut-off due to magnetohydrodynamic resistive damping in fully ionized plasmas is revisited. This cut-off requires short enough wavelengths, it is routinely discussed in numerous works, and graphs depicting it are available even in textbooks. We show that this cut-off is hardly ever possible in real plasmas. This is due to the fact that some essential criteria and conditions become strongly violated in order to achieve the cut-off.
Hydrodynamics of Turning Flocks
NASA Astrophysics Data System (ADS)
Yang, Xingbo; Marchetti, M. Cristina
2015-12-01
We present a hydrodynamic model of flocking that generalizes the familiar Toner-Tu equations to incorporate turning inertia of well-polarized flocks. The continuum equations controlled by only two dimensionless parameters, orientational inertia and alignment strength, are derived by coarse-graining the inertial spin model recently proposed by Cavagna et al. The interplay between orientational inertia and bend elasticity of the flock yields anisotropic spin waves that mediate the propagation of turning information throughout the flock. The coupling between spin-current density to the local vorticity field through a nonlinear friction gives rise to a hydrodynamic mode with angular-dependent propagation speed at long wavelengths. This mode becomes unstable as a result of the growth of bend and splay deformations augmented by the spin wave, signaling the transition to complex spatiotemporal patterns of continuously turning and swirling flocks.
Hydrodynamics of Turning Flocks.
Yang, Xingbo; Marchetti, M Cristina
2015-12-18
We present a hydrodynamic model of flocking that generalizes the familiar Toner-Tu equations to incorporate turning inertia of well-polarized flocks. The continuum equations controlled by only two dimensionless parameters, orientational inertia and alignment strength, are derived by coarse-graining the inertial spin model recently proposed by Cavagna et al. The interplay between orientational inertia and bend elasticity of the flock yields anisotropic spin waves that mediate the propagation of turning information throughout the flock. The coupling between spin-current density to the local vorticity field through a nonlinear friction gives rise to a hydrodynamic mode with angular-dependent propagation speed at long wavelengths. This mode becomes unstable as a result of the growth of bend and splay deformations augmented by the spin wave, signaling the transition to complex spatiotemporal patterns of continuously turning and swirling flocks. PMID:26722945
Colloids on the frontier of ferrofluids. Rheological properties.
López-López, Modesto T; Gómez-Ramírez, Ana; Rodríguez-Arco, Laura; Durán, Juan D G; Iskakova, Larisa; Zubarev, Andrey
2012-04-17
This paper is devoted to the steady-state rheological properties of two new kinds of ferrofluids. One of these was constituted by CoNi nanospheres of 24 nm in diameter, whereas the other by CoNi nanofibers of 56 nm in length and 6.6 nm in width. These ferrofluids were subjected to shear rate ramps under the presence of magnetic fields of different intensity, and the corresponding shear stress values were measured. From the obtained rheograms (shear stress vs shear rate curves) the values of both the static and the dynamic yield stresses were obtained as a function of the magnetic field. The magnetoviscous effect was also obtained as a function of both the shear rate and the magnetic field. The experimental results demonstrate that upon magnetic field application these new ferrofluids develop yield stresses and magnetoviscous effects much greater than those of conventional ferrofluids, based on nanospheres of approximately 10 nm in diameter. Besides some expected differences, such as the stronger magnetorheological effect in the case of ferrofluids based on nanofibers, some intriguing differences are found between the rheological behaviors of nanofiber ferrofluids and nanosphere ferrofluid. First, upon field application the rheograms of nanofiber ferrofluids present N-shaped dependence of the shear stress on the shear rate. The decreasing part of the rheograms takes place at low shear rate. These regions of negative differential viscosity, and therefore, unstable flow is not observed in the case of nanosphere ferrofluids. The second intriguing difference concerns the curvature of the yield stress vs magnetic field curves. This curvature is negative in the case of nanosphere ferrofluid, giving rise to saturation of the yield stress at medium field, as expected. However, in the case of nanofiber ferrofluid this curvature is positive, which means a faster increase of the yield stress with the magnetic field the higher the magnitude of the latter. These interesting
Numerical Simulation of Ferrofluid Flow for Subsurface Environmental Engineering Applications
Oldenburg, Curtis M.; Borglin, Sharon E.; Moridis, George J.
1997-05-05
Ferrofluids are suspensions of magnetic particles of diameter approximately 10 nm stabilized by surfactants in carrier liquids. The large magnetic susceptibility of ferrofluids allows the mobilization of ferrofluid through permeable rock and soil by the application of strong external magnetic fields. We have developed simulation capabilities for both miscible and immiscible conceptualizations of ferrofluid flow through porous media in response to magnetic forces arising from the magnetic field of a rectangular permanent magnet. The flow of ferrofluid is caused by the magnetization of the particles and their attraction toward a magnet, regardless of the orientation of the magnet. The steps involved in calculating the flow of ferrofluid are (1) calculation of the external magnetic field, (2) calculation of the gradient of the external magnetic field, (3) calculation of the magnetization of the ferrofluid, and (4) assembly of the magnetic body force term and addition of this term to the standard pressure gradient and gravity force terms. We compare numerical simulations to laboratory measurements of the magnetic field, fluid pressures, and the two-dimensional flow of ferrofluid to demonstrate the applicability of the methods coded in the numerical simulators. We present an example of the use of the simulator for a field-scale application of ferrofluids for barrier verification.
Microstructure of bidisperse ferrofluids in a thin layer
Minina, E. S. Muratova, A. B.; Cerda, J. J.; Kantorovich, S. S.
2013-03-15
In this work we present a characterization of the bidisperse ferrofluid microstructures that appear in thin layers of ferrofluid. These layers have been studied by a combination of Langevin dynamics simulations and density functional theory. Our results allow us to compare the microstructures that exist in quasi-two-dimensional ferrofluid nanolayers with the microstructures found in three-dimensional bidisperse ferrofluids. Furthermore, our results allow us to explain the influence of the geometry of the sample on the topology and size-distribution of the observed aggregates of magnetic nanoparticles.
Optimized steric stabilization of aqueous ferrofluids and magnetic nanoparticles.
Jain, Nirmesh; Wang, Yanjun; Jones, Stephen K; Hawkett, Brian S; Warr, Gregory G
2010-03-16
The preparation and properties of an aqueous ferrofluid consisting of a concentrated (>65 wt %) dispersion of sterically stabilized superparamagnetic, iron oxide (maghemite) nanoparticles stable for several months at high ionic strength and over a broad pH range is described. The 6-8 nm diameter nanoparticles are individually coated with a short poly(acrylic acid)-b-poly(acrylamide) copolymer, designed to form the thinnest possible steric stabilizing layer while remaining strongly attached to the iron oxide surface over a wide range of nanoparticle concentrations. Thermogravimetric analysis yields an iron oxide content of 76 wt % in the dried particles, consistent with a dry polymer coating of approximately 1 nm in thickness, while the poly(acrylamide) chain length indicated by electrospray mass spectrometry is consistent with the 4-5 nm increase in the hydrodynamic radius observed by light scattering when the poly(acrylamide) stabilizing chains are solvated. Saturation magnetization experiments indicate nonmagnetic surface layers resulting from the strong chemical attachment of the poly(acrylic acid) block to the particle surface, also observed by Fourier transform infrared spectroscopy. PMID:19950943
Microstructural investigation of some biocompatible ferrofluids
NASA Astrophysics Data System (ADS)
Răcuciu, M.; Creangă, D. E.; Bădescu, V.; Sulitanu, N.
2007-09-01
Two batches of aqueous ferrofluids based on iron oxide particles as solid nanomagnetic phase have been prepared by applying the chemical precipitation method. Tetramethylammonium hydroxide (N(CH 3) 4OH) and citric acid (C 6H 8O 7) were used to functionalize magnetic cores. Physical tests have been performed in order to reveal the microstructural and magnetic features, both needed for biomedical utilization. The particle size was investigated using transmission electron microscopy (TEM), magnetization measurements and X-ray diffraction (for composition and phase information). The dimensional distribution of the ferrophase physical diameter was comparatively discussed using the box-plot statistical method revealing the fulfilling of the main requirements for ferrofluid stability.
Ferrofluid-based liquid-phase microextraction.
Shi, Zhi-Guo; Zhang, Yufeng; Lee, Hian Kee
2010-11-19
A new mode of liquid-phase microextraction based on a ferrofluid has been developed. The ferrofluid was composed of silica-coated magnetic particles and 1-octanol as the extractant solvent. The 1-octanol was firmly confined within the silica-coated particles, preventing it from being lost during extraction. Sixteen polycyclic aromatic hydrocarbons (PAHs) were used as model compounds in the development and evaluation of the extraction procedure in combination with gas chromatography-mass spectrometry. Parameters affecting the extraction efficiency were investigated in detail. The optimal conditions were as follows: 20mL sample volume, 10mg of the silica-coated magnetic particles (28mg of ferrofluid), agitation at 20Hz, 20min extraction time, and 2min by sonication with 100μL acetonitrile as the final extraction solvent. Under optimal extraction conditions, enrichment factors ranging from 102- to 173-fold were obtained for the analytes. The limits of detection and the limits of quantification were in the range of 16.8 and 56.7pgmL(-1) and 0.06 and 0.19ngmL(-1), respectively. The linearities were between 0.5-100 and 1-100ngmL(-1) for different PAHs. As the ferrofluid can respond to and be attracted by a magnet, the extraction can be easily achieved by reciprocating movement of an external magnet that served to agitate the sample. No other devices were needed in this new approach of extraction. This new technique is affordable, efficient and convenient for microextraction, and offers portability for potential onsite extraction. PMID:20961552
ERIC Educational Resources Information Center
Lafrance, Pierre
1978-01-01
Explores in a non-mathematical treatment some of the hydrodynamical phenomena and forces that affect the operation of ships, especially at high speeds. Discusses the major components of ship resistance such as the different types of drags and ways to reduce them and how to apply those principles for the hovercraft. (GA)
Ferrofluid based micro-electrical energy harvesting
NASA Astrophysics Data System (ADS)
Purohit, Viswas; Mazumder, Baishakhi; Jena, Grishma; Mishra, Madhusha; Materials Department, University of California, Santa Barbara, CA93106 Collaboration
2013-03-01
Innovations in energy harvesting have seen a quantum leap in the last decade. With the introduction of low energy devices in the market, micro energy harvesting units are being explored with much vigor. One of the recent areas of micro energy scavenging is the exploitation of existing vibrational energy and the use of various mechanical motions for the same, useful for low power consumption devices. Ferrofluids are liquids containing magnetic materials having nano-scale permanent magnetic dipoles. The present work explores the possibility of the use of this property for generation of electricity. Since the power generation is through a liquid material, it can take any shape as well as response to small acceleration levels. In this work, an electromagnet-based micropower generator is proposed to utilize the sloshing of the ferrofluid within a controlled chamber which moves to different low frequencies. As compared to permanent magnet units researched previously, ferrofluids can be placed in the smallest of containers of different shapes, thereby giving an output in response to the slightest change in motion. Mechanical motion from 1- 20 Hz was able to give an output voltage in mV's. In this paper, the efficiency and feasibility of such a system is demonstrated.
Recent development of hydrodynamic modeling
NASA Astrophysics Data System (ADS)
Hirano, Tetsufumi
2014-09-01
In this talk, I give an overview of recent development in hydrodynamic modeling of high-energy nuclear collisions. First, I briefly discuss about current situation of hydrodynamic modeling by showing results from the integrated dynamical approach in which Monte-Carlo calculation of initial conditions, quark-gluon fluid dynamics and hadronic cascading are combined. In particular, I focus on rescattering effects of strange hadrons on final observables. Next I highlight three topics in recent development in hydrodynamic modeling. These include (1) medium response to jet propagation in di-jet asymmetric events, (2) causal hydrodynamic fluctuation and its application to Bjorken expansion and (3) chiral magnetic wave from anomalous hydrodynamic simulations. (1) Recent CMS data suggest the existence of QGP response to propagation of jets. To investigate this phenomenon, we solve hydrodynamic equations with source term which exhibits deposition of energy and momentum from jets. We find a large number of low momentum particles are emitted at large angle from jet axis. This gives a novel interpretation of the CMS data. (2) It has been claimed that a matter created even in p-p/p-A collisions may behave like a fluid. However, fluctuation effects would be important in such a small system. We formulate relativistic fluctuating hydrodynamics and apply it to Bjorken expansion. We found the final multiplicity fluctuates around the mean value even if initial condition is fixed. This effect is relatively important in peripheral A-A collisions and p-p/p-A collisions. (3) Anomalous transport of the quark-gluon fluid is predicted when extremely high magnetic field is applied. We investigate this possibility by solving anomalous hydrodynamic equations. We found the difference of the elliptic flow parameter between positive and negative particles appears due to the chiral magnetic wave. Finally, I provide some personal perspective of hydrodynamic modeling of high energy nuclear collisions
Relaxation behavior measuring of transmitted light through ferrofluids film
NASA Astrophysics Data System (ADS)
Li, J.; Liu, X.-D.; Lin, Y.-Q.; Huang, Y.; Bai, L.
2006-01-01
In this paper, relaxation behavior of transmitted light through thin ferrofluid film under an applied magnetic field is measured. The results show that the intensity of transmitted light through a ferrofluid film increases quickly as soon as an external magnetic field is applied then weakens with time. If uniformity of the field is poor, the transmission of light continuously decreases in a measured duration. Otherwise, the transmission of light will tend increasingly towards a stable value after it decreases to a minimum value while the gradient of the field is low. The relaxation time would increase to an order of some hundreds seconds magnitude and is dependent on the strength of magnetic field and viscosity of the ferrofluids. The field-induced relaxation behaviors of transmitted light through ferrofluids correspond to anisotropic microstructure of the ferrofluids under applied magnetic field.
Long term stability of immiscible ferrofluid/water interfaces
NASA Astrophysics Data System (ADS)
Malouin, Bernard; Posada, David; Hirsa, Amir
2010-11-01
Recently we have demonstrated pinned-contact, coupled droplet pairs of aqueous ferrofluids in air that can form electromagnetically-activated capillary switches and oscillators. The great variety of available ferrofluids, however, enables the use of immiscible oil-based ferrofluid droplets in a water environment to obtain the same behavior. Such immersed ferrofluid oscillators exhibit natural frequencies (for 5 mm devices) of about 10 Hz. Here we report on the observation of a gradual increase in the resonant frequency of the system in time. Experimental observations suggest that the drift in the natural frequency is a consequence of changes occurring at the ferrofluid/water interface. The interfacial structure of such a complex system (water, oil, surfactant, iron particles) is examined along with its evolution in time, using various microscopy techniques.
Castor, J I
2003-10-16
The discipline of radiation hydrodynamics is the branch of hydrodynamics in which the moving fluid absorbs and emits electromagnetic radiation, and in so doing modifies its dynamical behavior. That is, the net gain or loss of energy by parcels of the fluid material through absorption or emission of radiation are sufficient to change the pressure of the material, and therefore change its motion; alternatively, the net momentum exchange between radiation and matter may alter the motion of the matter directly. Ignoring the radiation contributions to energy and momentum will give a wrong prediction of the hydrodynamic motion when the correct description is radiation hydrodynamics. Of course, there are circumstances when a large quantity of radiation is present, yet can be ignored without causing the model to be in error. This happens when radiation from an exterior source streams through the problem, but the latter is so transparent that the energy and momentum coupling is negligible. Everything we say about radiation hydrodynamics applies equally well to neutrinos and photons (apart from the Einstein relations, specific to bosons), but in almost every area of astrophysics neutrino hydrodynamics is ignored, simply because the systems are exceedingly transparent to neutrinos, even though the energy flux in neutrinos may be substantial. Another place where we can do ''radiation hydrodynamics'' without using any sophisticated theory is deep within stars or other bodies, where the material is so opaque to the radiation that the mean free path of photons is entirely negligible compared with the size of the system, the distance over which any fluid quantity varies, and so on. In this case we can suppose that the radiation is in equilibrium with the matter locally, and its energy, pressure and momentum can be lumped in with those of the rest of the fluid. That is, it is no more necessary to distinguish photons from atoms, nuclei and electrons, than it is to distinguish
Ferrofluids: Modeling, numerical analysis, and scientific computation
NASA Astrophysics Data System (ADS)
Tomas, Ignacio
This dissertation presents some developments in the Numerical Analysis of Partial Differential Equations (PDEs) describing the behavior of ferrofluids. The most widely accepted PDE model for ferrofluids is the Micropolar model proposed by R.E. Rosensweig. The Micropolar Navier-Stokes Equations (MNSE) is a subsystem of PDEs within the Rosensweig model. Being a simplified version of the much bigger system of PDEs proposed by Rosensweig, the MNSE are a natural starting point of this thesis. The MNSE couple linear velocity u, angular velocity w, and pressure p. We propose and analyze a first-order semi-implicit fully-discrete scheme for the MNSE, which decouples the computation of the linear and angular velocities, is unconditionally stable and delivers optimal convergence rates under assumptions analogous to those used for the Navier-Stokes equations. Moving onto the much more complex Rosensweig's model, we provide a definition (approximation) for the effective magnetizing field h, and explain the assumptions behind this definition. Unlike previous definitions available in the literature, this new definition is able to accommodate the effect of external magnetic fields. Using this definition we setup the system of PDEs coupling linear velocity u, pressure p, angular velocity w, magnetization m, and magnetic potential ϕ We show that this system is energy-stable and devise a numerical scheme that mimics the same stability property. We prove that solutions of the numerical scheme always exist and, under certain simplifying assumptions, that the discrete solutions converge. A notable outcome of the analysis of the numerical scheme for the Rosensweig's model is the choice of finite element spaces that allow the construction of an energy-stable scheme. Finally, with the lessons learned from Rosensweig's model, we develop a diffuse-interface model describing the behavior of two-phase ferrofluid flows and present an energy-stable numerical scheme for this model. For a
NASA Astrophysics Data System (ADS)
Alazmi, S.; Xu, Y.; Daqaq, M. F.
2016-07-01
When a container carrying a magnetized ferrofluid is subjected to external mechanical stimuli, the sloshing motion of the magnetized ferrofluid generates a time-varying magnetic flux, which can be used to induce an electromotive force in a coil placed adjacent to the container. This process generates an electric current in the coil, and therewith, can be used to transduce external vibrations into electric energy. In this article, we develop a nonlinear analytical model, which governs the electro-magneto-hydrodynamics of an electromagnetic ferrofluid-based vibratory energy harvester. Using perturbation methods, we obtain an approximate analytical solution of the model for a case involving primary resonance excitation of the first mode and a two-to-one internal resonance between the first two modes. This occurs when the external excitation is harmonic with a frequency close to the fundamental sloshing frequency and when the second modal frequency is nearly twice the first modal frequency. Theoretical results are compared to experimental findings illustrating very good qualitative agreement.
Mueller, Bernhard; Janka, Hans-Thomas; Marek, Andreas E-mail: thj@mpa-garching.mpg.de
2013-03-20
We present a detailed theoretical analysis of the gravitational wave (GW) signal of the post-bounce evolution of core-collapse supernovae (SNe), employing for the first time relativistic, two-dimensional explosion models with multi-group, three-flavor neutrino transport based on the ray-by-ray-plus approximation. The waveforms reflect the accelerated mass motions associated with the characteristic evolutionary stages that were also identified in previous works: a quasi-periodic modulation by prompt post-shock convection is followed by a phase of relative quiescence before growing amplitudes signal violent hydrodynamical activity due to convection and the standing accretion shock instability during the accretion period of the stalled shock. Finally, a high-frequency, low-amplitude variation from proto-neutron star (PNS) convection below the neutrinosphere appears superimposed on the low-frequency trend associated with the aspherical expansion of the SN shock after the onset of the explosion. Relativistic effects in combination with detailed neutrino transport are shown to be essential for quantitative predictions of the GW frequency evolution and energy spectrum, because they determine the structure of the PNS surface layer and its characteristic g-mode frequency. Burst-like high-frequency activity phases, correlated with sudden luminosity increase and spectral hardening of electron (anti-)neutrino emission for some 10 ms, are discovered as new features after the onset of the explosion. They correspond to intermittent episodes of anisotropic accretion by the PNS in the case of fallback SNe. We find stronger signals for more massive progenitors with large accretion rates. The typical frequencies are higher for massive PNSs, though the time-integrated spectrum also strongly depends on the model dynamics.
NASA Astrophysics Data System (ADS)
Lauga, Eric
2016-01-01
Bacteria predate plants and animals by billions of years. Today, they are the world's smallest cells, yet they represent the bulk of the world's biomass and the main reservoir of nutrients for higher organisms. Most bacteria can move on their own, and the majority of motile bacteria are able to swim in viscous fluids using slender helical appendages called flagella. Low-Reynolds number hydrodynamics is at the heart of the ability of flagella to generate propulsion at the micrometer scale. In fact, fluid dynamic forces impact many aspects of bacteriology, ranging from the ability of cells to reorient and search their surroundings to their interactions within mechanically and chemically complex environments. Using hydrodynamics as an organizing framework, I review the biomechanics of bacterial motility and look ahead to future challenges.
Elongational flow effects on the vortex growth out of Couette flow in ferrofluids.
Altmeyer, S; Leschhorn, A; Hoffmann, Ch; Lücke, M
2013-05-01
The growth behavior of stationary axisymmetric vortices and of oscillatory, nonaxisymmetric spiral vortices in Taylor-Couette flow of a ferrofluid in between differentially rotating cylinders is analyzed using a numerical linear stability analysis. The investigation is done as a function of the inner and outer cylinder's rotation rates, the axial wave number of the vortex flows, and the magnitude of an applied homogeneous axial magnetic field. In particular, the consequences of incorporating elongational flow effects in the magnetization balance equation on the marginal control parameters that separate growth from decay behavior are determined. That is done for several values of the transport coefficient that measures the strength of these effects. PMID:23767623
Magnetic field effects on viscous fingering of a ferrofluid in an anisotropic Hele-Shaw cell
NASA Astrophysics Data System (ADS)
Ballou, R.; Molho, P.
2005-12-01
When a viscous fluid is pushed into a more viscous one in a Hele-Shaw cell, the interface between the two fluids may become unstable, leading to fingering and ramified patterns. Anisotropy can be introduced by engraving a grid in one plate of the cell, allowing one to obtain dendritic patterns. The use of a ferrofluid as one of the viscous fluid is a way to introduce magnetism in the problem, especially the magnetic field as a control parameter. Magnetic field effects on viscous fingering of ferrofluids have already been studied: in a rectangular Hele-Shaw cell, a magnetic field applied in the cell plane is stabilizing when parallel to the interface between the two fluids and destabilizing when normal to the interface. A magnetic field perpendicular to the plane of a radial Hele-Shaw cell has the same destabilizing effect as the pressure. We have studied the effect of a magnetic field, normal to and in the plane of anisotropic radial Hele-Shaw cells te{5}, to characterize the competing effects of hydrodynamics, magnetic field and dipolar energy, and anisotropy. Here we study more precisely the effect of a magnetic field normal to a radial anisotropic Hele-Shaw cell. Figs 8, Refs 9.
Gravity waves in a realistic atmosphere.
NASA Technical Reports Server (NTRS)
Liemohn, H. B.; Midgley, J. E.
1966-01-01
Internal atmospheric gravity waves in isothermal medium, solving hydrodynamic equations, determining wave propagation in realistic atmosphere for range of wave parameters, wind amplitude, reflected energy, etc
Damping induced by ferrofluid seals in ironless loudspeaker
NASA Astrophysics Data System (ADS)
Pinho, M.; Génevaux, J. M.; Dauchez, N.; Brouard, B.; Collas, P.; Mézière, H.
2014-04-01
Damping induced by ferrofluid seals in ironless loudspeakers is investigated in this paper. The magnetic field is steady but not spatially constant. A model to determine the viscous damping coefficient induced by the ferrofluid seal is derived. It is a function of geometrical parameters and local viscosity of the ferrofluid in which dependence from magnetic field, shear rate and frequency is accounted for. Comparison with experimental results shows a good agreement for the thinner seals. An overestimation of the damping is observed for higher volumes. This discrepancy comes from geometric irregularities of the magnet assembly made out of several tiles.
Cytogenetic changes induced by aqueous ferrofluids in agricultural plants
NASA Astrophysics Data System (ADS)
Răcuciu, Mihaela; Creangă, Dorina
2007-04-01
In this paper, the authors present their results regarding the cellular division rate and the percentage of chromosomal aberrations in the root meristematic cells of agricultural plants when cultivated in the presence of different concentrations of aqueous ferrofluid, ranging between 10 and 250 μL/L. The agricultural species ( Zea mays) with a major role in the life of people was chosen for the experimental project. The water-based ferrofluid was prepared following the chemical co-precipitation method, using tetramethylammonium hydroxide as magnetite core stabilizer. Microscopic investigations (cytogenetic tests) resulted in the evaluation of the mitotic and chromosomal aberration index. They appeared to increase following ferrofluid addition.
Slow relaxation in structure-forming ferrofluids.
Sreekumari, Aparna; Ilg, Patrick
2013-10-01
We study the behavior of colloidal magnetic fluids at low density for various dipolar interaction strengths by performing extensive Langevin dynamics simulations with model parameters that mimic cobalt-based ferrofluids used in experiments. Our study mainly focuses on the structural and dynamical properties of dipolar fluids and the influence of structural changes on their dynamics. Drastic changes from chainlike to networklike structures in the absence of an external magnetic field are observed. This crossover plays an important role in the slowing down of dynamics that is reflected in various dynamical properties including the tracer diffusion and the viscosity and also in the structural relaxation. PMID:24229180
Slow relaxation in structure-forming ferrofluids
NASA Astrophysics Data System (ADS)
Sreekumari, Aparna; Ilg, Patrick
2013-10-01
We study the behavior of colloidal magnetic fluids at low density for various dipolar interaction strengths by performing extensive Langevin dynamics simulations with model parameters that mimic cobalt-based ferrofluids used in experiments. Our study mainly focuses on the structural and dynamical properties of dipolar fluids and the influence of structural changes on their dynamics. Drastic changes from chainlike to networklike structures in the absence of an external magnetic field are observed. This crossover plays an important role in the slowing down of dynamics that is reflected in various dynamical properties including the tracer diffusion and the viscosity and also in the structural relaxation.
Stable and water-tolerant ionic liquid ferrofluids.
Jain, Nirmesh; Zhang, Xiaoli; Hawkett, Brian S; Warr, Gregory G
2011-03-01
Ionic liquid ferrofluids have been prepared containing both bare and sterically stabilized 8-12 nm diameter superparamagnetic iron oxide nanoparticles, which remain stable for several months in both protic ethylammonium and aprotic imidazolium room-temperature ionic liquids. These ferrofluids exhibit spiking in static magnetic fields similar to conventional aqueous and nonaqueous ferrofluids. Ferrofluid stability was verified by following the flocculation and settling behavior of dilute nanoparticle dispersions. Although bare nanoparticles showed excellent stability in some ILs, they were unstable in others, and exhibited limited water tolerance. Stability was achieved by incorporating a thin polymeric steric stabilization layer designed to be compatible with the IL. This confers the added benefit of imbuing the ILF with a high tolerance to water. PMID:21338083
Multiphase ferrofluid flows for micro-particle sorting
NASA Astrophysics Data System (ADS)
Zhou, Ran; Wang, Cheng
2015-11-01
Utilizing negative magnetophoresis, ferrofluids have demonstrated great potential for sorting nonmagnetic micro-particles by size. Most of the existing techniques use single phase ferrofluids by pushing micro-particles to channel walls; the sorting speed is thus hindered. We demonstrate a novel sorting strategy by co-flowing a ferrofluid and a non-magnetic fluid in microchannels. Due to the magnetic force, the particles migrate across the ferrofluid stream at size-dependent velocities as they travel downstream. The laminar interface between the two fluids functions as a virtual boundary to accumulate particles, resulting in effective separation of particles. A stable and sharp interface is important to the success of this sorting technique. We investigate several factors that affect sorting efficiency, including magnetic field, susceptibility difference of the fluids, flow velocity, and channel geometry.
Ferrohydrodynamic evaluation of rotational viscosity and relaxation in certain ferrofluids.
Patel, Rajesh
2012-07-01
A significant effect of aggregation dynamics for aqueous ferrofluid (AF) and kerosene based ferrofluid (KF) using magnetic field dependent capillary viscosity and magneto-optical relaxation measurements is studied. For better comparison parameters of AF and KF are kept similar. Ferrohydrodynamic equations of chain forming ferrofluids, dilute ferrofluids, and Brownian dynamic simulations are compared. It is observed that the rotational viscosity of AF is larger than that of KF due to field induced aggregates in it and strong dipolar interactions. It is also observed that at Ωτ ~ 0.04 both AF and KF viscosity becomes almost similar, suggesting similar behavior at that shear rate. The magneto-optical relaxation in AF exhibits nonexponential behavior when relaxed from higher magnetic field and follows irreversible thermodynamics, whereas for KF the relaxation is exponential and follows the effective field method. This discrepancy is explained based on aggregation dynamics of magnetic particles. Results are well described by the corresponding theoretical models. PMID:23005542
Magnetic-Field Induced Diffraction Patterns from Ferrofluids
NASA Astrophysics Data System (ADS)
Rablau, Corneliu; Vaishnava, Prem; Lawes, Gavin; Naik, Ratna
2011-04-01
Ferrofluids are stable colloidal suspensions of superparamagnetic nanoparticles in a carrier liquid. We report studies of magneto-optic properties of two ferrofluid systems consisting of tetramethyl-ammonium-hydroxide (TMAH)-coated and of dextran-coated Fe3O4 nanoparticles of nominal sizes of 6 nm and 12 nm respectively suspended in water. Both samples showed superparamagnetic behavior. The static and time-dependent DC-magnetic-field-induced light scattering patterns produced by two orthogonal He-Ne laser beams passing through the ferrofluid samples revealed significant different optical signatures for the two surfactants. Notably, in contrast to the linear diffraction pattern produced by TMAH-coated nanoparticles, a circular diffraction pattern is reported -- for the first time -- in the dextran-coated ferrofluid.
Magnetophoretic control of water droplets in bulk ferrofluid
NASA Astrophysics Data System (ADS)
Katsikis, Georgios; Bréant, Alexandre; Prakash, Manu
2015-11-01
We present a microfluidic platform for 2-D manipulation of water droplets immersed in bulk oil-based ferrofluid. Although non-magnetic, the droplets are exclusively controlled by magnetic fields, without any pressure-driven flow. The diphasic fluid layer is trapped in a submillimeter Hele-Shaw chamber that includes permalloy tracks on its substrate. An in-plane rotating magnetic field magnetizes the permalloy tracks, thus producing local magnetic gradients, while an orthogonal magnetic field magnetizes the bulk ferrofluid. To minimize the magnetostatic energy of the system, droplets are attracted towards the locations of the tracks where ferrofluid is repelled. Using this technique, we demonstrate synchronous propagation of water droplets, analyze PIV data of the bulk ferrofluid flow and study the kinematics of propagation. In addition, we show droplet break-up, merging and derive relevant scaling laws. Finally, we discuss future applications owing to the biocompatibility of the droplets.
Preparation of magnetic ferrofluids in alternative carrier liquids
NASA Technical Reports Server (NTRS)
Rosensweig, R. E.
1970-01-01
Ferrofluids are made by grinding magnetic particles together with a polar surfactant and a nonpolar solvent. The surfactant is adsorbed on the particle surfaces and acts as a coupling agent between the particles and the solvent.
Pomraning, G.C.
1982-12-31
This course was intended to provide the participant with an introduction to the theory of radiative transfer, and an understanding of the coupling of radiative processes to the equations describing compressible flow. At moderate temperatures (thousands of degrees), the role of the radiation is primarily one of transporting energy by radiative processes. At higher temperatures (millions of degrees), the energy and momentum densities of the radiation field may become comparable to or even dominate the corresponding fluid quantities. In this case, the radiation field significantly affects the dynamics of the fluid, and it is the description of this regime which is generally the charter of radiation hydrodynamics. The course provided a discussion of the relevant physics and a derivation of the corresponding equations, as well as an examination of several simplified models. Practical applications include astrophysics and nuclear weapons effects phenomena.
Multiphase ferrofluid flows for micro-particle focusing and separation.
Zhou, Ran; Wang, Cheng
2016-05-01
Ferrofluids have demonstrated great potential for a variety of manipulations of diamagnetic (or non-magnetic) micro-particles/cells in microfluidics, including sorting, focusing, and enriching. By utilizing size dependent magnetophoresis velocity, most of the existing techniques employ single phase ferrofluids to push the particles towards the channel walls. In this work, we demonstrate a novel strategy for focusing and separating diamagnetic micro-particles by using the laminar fluid interface of two co-flowing fluids-a ferrofluid and a non-magnetic fluid. Next to the microfluidic channel, microscale magnets are fabricated to generate strong localized magnetic field gradients and forces. Due to the magnetic force, diamagnetic particles suspended in the ferrofluid phase migrate across the ferrofluid stream at the size-dependent velocities. Because of the low Reynolds number and high Péclet number associated with the flow, the fluid interface is sharp and stable. When the micro-particles migrate to the interface, they are accumulated near the interface, resulting in effective focusing and separation of particles. We investigated several factors that affect the focusing and separation efficiency, including susceptibility of the ferrofluid, distance between the microfluidic channel and microscale magnet, and width of the microfluidic channel. This concept can be extended to multiple fluid interfaces. For example, a complete separation of micro-particles was demonstrated by using a three-stream multiphase flow configuration. PMID:27190567
Static and Dynamic Contact Angles of Immersed Ferrofluid Droplets
NASA Astrophysics Data System (ADS)
Chatterjee, Souvick; Bhowmik, Dipanwita; Mukhopadhyay, Achintya; Ganguly, Ranjan
2013-11-01
Ferrofluid plug driven micro-pumps are useful for manipulating micro-volume of liquids by providing remote actuation using a localized magnetic field gradient. Inside a microchannel, the ferrofluid experiences combined actions of different relevant body forces. While the pressure, viscous and magnetic forces can be estimated using established techniques, the surface tension force requires information about the contact angle between the ferrofluid and glass capillary wall. We address this phenomenon through experimental characterization of static and dynamic contact angles of oil based ferrofluid (EFH3) droplets on glass surface immersed in pure or surfacted distilled water. The equilibrium static contact angle is found to significantly reduce in presence of a magnetic field. Dynamic contact angles are measured through high-speed imaging as the ferrofluid droplets slide along an inclined glass surface. Variation of contact angle hysteresis, which falls outside the Hoffmann Tanner equation for this case, is also investigated as a function of contact line velocity. A strong dependence is found between the contact angle hysteresis and the wetting time. Findings of the work is useful for designing ferrofluid plug-driven microfluidic plugs for different lab-on-a-chip applications.
Method and device for manipulating ferrofluids for use in cementing wells
Larson, D.B.; Nelson, E.B.
1989-02-07
A device is described for manipulating ferrofluids in a wellbore annulus between a pipe or casing and walls of a well, comprising: (a) means for generating a plurality of alternating magnetic fields distributed in a radial manner, the fields extending into a ferrofluid in the wellbore annulus separating the casing and walls of a subterranean formation; and (b) means for moving and plurality of magnetic fields relative to the ferrofluid, to facilitate movement of the ferrofluid. A method is also discussed for manipulating ferrofluids in a wellbore annulus between a pipe or casing and walls of a well, comprising the steps of: (a) generating at least one magnetic field by a permanently magnetized casing, and magnetic field extending into a ferrofluid in the wellbore annulus separating the casing and walls of a subterranean formation; and (b) moving the casing relative to the ferrofluid, to facilitate movement of the ferrofluid.
Experimental investigation of magnetically driven flow of ferrofluids in porous media
Borglin, S.E.; Moridis, G.J.; Oldenburg, C.M.
1998-08-01
This report presents experimental results of the flow of ferrofluids in porous media to investigate the potential for precisely controlling fluid emplacement in porous media using magnetic fields. Ferrofluids are colloidal suspensions of magnetic particles stabilized in various carrier liquids. In the presence of an external magnetic field, the ferrofluid becomes magnetized as the particles align with the magnetic field. Potential applications of ferrofluids to subsurface contamination problems include magnetic guidance of reactants to contaminated target zones in the subsurface for in situ treatment or emplacement of containment barriers. Laboratory experiments of magnetically induced ferrofluid flow in porous media in this report demonstrate the potential for mobilizing ferrofluid and controlling fluid emplacement through control of the external magnetic field. The pressures measured in ferrofluid due to the attraction of ferrofluid to a permanent magnet agree well with calculated values. The results show that a predictable pressure gradient is produced in the fluid which is strong near the magnet and drops off quickly with distance. This pressure gradient drives the fluid through sand without significant loss of ferrofluid strength due to filtration or dilution. Flow visualization experiments of ferrofluid in water-filled horizontal Hele-Shaw cells demonstrate that ferrofluid obtains a consistent final arc-shaped configuration around the magnet regardless of initial configuration or flow path toward the magnet. Analogous experiments in actual porous media showed similar features and confirm the ability of ferrofluid to move through porous media by magnetic forces.
Generalized hydrodynamics in the transient regime and irreversible thermodynamics.
Eu, Byung Chan
2004-08-15
In this article the thermodynamically consistent formulation of generalized hydrodynamics is reviewed and applications to shock-wave structures, ultrasonic wave absorption and dispersion and microchannel flows of the generalized hydrodynamics so formulated are discussed. The kinematic terms of the constitutive equations in the generalized hydrodynamic equations for liquids, which have been calculated by means of non-equilibrium grand canonical ensemble, are also presented. PMID:15306429
A ferrofluidic deformable mirror for ophthalmology
NASA Astrophysics Data System (ADS)
Macpherson, J. B.; Thibault, S.; Borra, E. F.; Ritcey, A. M.; Carufel, N.; Asselin, D.; Jerominek, H.; Campbell, M. C. W.
2005-09-01
Optical aberrations reduce the imaging quality of the human eye. In addition to degrading vision, this limits our ability to illuminate small points of the retina for therapeutic, surgical or diagnostic purposes. When viewing the rear of the eye, aberrations cause structures in the fundus to appear blurred, limiting the resolution of ophthalmoscopes (diagnostic instruments used to image the eye). Adaptive optics, such as deformable mirrors may be used to compensate for aberrations, allowing the eye to work as a diffraction-limited optical element. Unfortunately, this type of correction has not been widely available for ophthalmic applications because of the expense and technical limitations of current deformable mirrors. We present preliminary design and characterisation of a deformable mirror suitable for ophthalmology. In this ferrofluidic mirror, wavefronts are reflected from a fluid whose surface shape is controlled by a magnetic field. Challenges in design are outlined, as are advantages over traditional deformable mirrors.
Rotating Hele-Shaw cells with ferrofluids
NASA Astrophysics Data System (ADS)
Miranda, José A.
2000-08-01
We investigate the flow of two immiscible, viscous fluids in a rotating Hele-Shaw cell, when one of the fluids is a ferrofluid and an external magnetic field is applied. The interplay between centrifugal and magnetic forces in determining the instability of the fluid-fluid interface is analyzed. The linear stability analysis of the problem shows that a nonuniform, azimuthal magnetic field, applied tangential to the cell, tends to stabilize the interface. We verify that maximum growth rate selection of initial patterns is influenced by the applied field, which tends to decrease the number of interface ripples. We contrast these results with the situation in which a uniform magnetic field is applied normally to the plane defined by the rotating Hele-Shaw cell.
Low temperature viscosity in elongated ferrofluids
NASA Astrophysics Data System (ADS)
Alarcón, T.; Pérez-Madrid, A.; Rubí, J. M.
1997-12-01
We have studied the relaxation and transport properties of a ferrofluid in an elongational flow. These properties are influenced by the bistable nature of the potential energy. Bistability comes from the irrotational character of the flow together with the symmetry of the dipoles. Additionally, the presence of a constant magnetic field destroys the symmetry of the potential energy magnetizing the system. We have shown that at a moderate temperature, compared to the height of the energy barrier, the viscosity decreases with respect to the value it would have if the potential were stable. This phenomenon is known as the "negative viscosity" effect. Thermal motion induces jumps of the magnetic moment between the two stable states of the system leading to the aforementioned lowered dissipation effect.
Lithium ferrite nanoparticles for ferrofluid applications
NASA Astrophysics Data System (ADS)
Sankaranarayanan, V. K.; Prakash, Om; Pant, R. P.; Islam, Mohammad
2002-11-01
Nanoparticles of Lithium ferrite in the particle size range of 10 nm have been prepared by a citrate precursor method at a relatively low temperature of 200°C. The particles show characteristic infra red (IR) spectrum of lithium ferrite and broadened X-ray diffraction (XRD) patterns typical of the nanoparticle nature. The sample decomposed at 200°C has the β-LiFe 5O 8 type (a disordered type of spinel) structure which on annealing at 350°C transforms to the α-LiFe 5O 8 type (an ordered type spinel) structure as shown by both IR spectra and XRD studies. Magnetization curves indicate a particle size distribution consisting of both ferromagnetic particles and a superparamagnetic fraction. With 4 ΠMs values of 2000 G these particles could be useful for applications in certain low magnetization ferrofluids.
Linear viscoelasticity of an inverse ferrofluid.
de Gans, B J; Blom, C; Philipse, A P; Mellema, J
1999-10-01
A magnetorheological fluid consisting of colloidal silica spheres suspended in an organic ferrofluid is described. Its linear viscoelastic behavior as a function of frequency, magnetic field strength, and silica volume fraction was investigated with a specially designed magnetorheometer. The storage modulus G' is at least an order of magnitude larger than the loss modulus G" at all magnetic field strengths investigated. G' does depend only weakly on frequency, and linearly on volume fraction. A model is presented for the high frequency limit of the storage modulus G'(infinity). In the model our system is treated as a collection of single noninteracting chains of particles. Assuming a dipolar magnetic interaction, theory and experiment show reasonable agreement at high frequencies. PMID:11970308
Magnetic Properties of Dipolar Chains in Ferrofluids
NASA Astrophysics Data System (ADS)
Avgin, I.; Huber, D. L.
2014-06-01
We have investigated the dipole interaction energies per particle and the local dipole field distributions in a frozen-magnetization model of a ferrofluid chain in a saturating magnetic field. A lognormal distribution of particle diameters was assumed. The interaction energies were calculated for one-dimensional arrays of dipoles with moments parallel to the chain. We have computed the energies by various approximations related to the hard sphere particle diameter distribution. A similar approach was followed for the local field distributions. It was found that the energy per particle and mean local field were largely determined by the mean particle diameter, but the distribution of local fields was sensitive to both the mean diameter and the assumptions about spatial correlations between particles of different size. Detailed results are presented for water-soluble Fe3O4/PAA (polyacrylic acid).
A ferrofluid-based wireless pressure sensor
NASA Astrophysics Data System (ADS)
Chitnis, Girish; Ziaie, Babak
2013-12-01
This paper presents a wireless pressure sensor design based on magnetic fluid displacement over a planar coil and its corresponding inductance change. The design of the pressure sensor is presented followed by its fabrication and characterization. Experimental results show a good correlation with a nonlinear model relating the applied pressure to the change in coil self-resonant frequency. A prototype sensor (radius = 6 mm, thickness = 2 mm) based on the above principal using an oil-based ferrofluid (50 µl, ferrite concentration 2%), a polyimide-embedded planar coil (L = 1 µH), and a 25 µm thick polyimide membrane shows a sensitivity of 3 KHz mmHg-1 with a base-line resonant frequency of f0 = 109 MHz.
Viscoelasticity of mono- and polydisperse inverse ferrofluids.
Saldivar-Guerrero, Ruben; Richter, Reinhard; Rehberg, Ingo; Aksel, Nuri; Heymann, Lutz; Rodriguez-Fernández, Oliverio S
2006-08-28
We report on measurements of a magnetorheological model fluid created by dispersing nonmagnetic microparticles of polystyrene in a commercial ferrofluid. The linear viscoelastic properties as a function of magnetic field strength, particle size, and particle size distribution are studied by oscillatory measurements. We compare the results with a magnetostatic theory proposed by De Gans et al. [Phys. Rev. E 60, 4518 (1999)] for the case of gap spanning chains of particles. We observe these chain structures via a long distance microscope. For monodisperse particles we find good agreement of the measured storage modulus with theory, even for an extended range, where the linear magnetization law is no longer strictly valid. Moreover we compare for the first time results for mono- and polydisperse particles. For the latter, we observe an enhanced storage modulus in the linear regime of the magnetization. PMID:16965057
The extrinsic hysteresis behavior of dilute binary ferrofluids.
Lin, Lihua; Li, Jian; Lin, Yueqiang; Liu, Xiaodong; Chen, Longlong; Li, Junming; Li, Decai
2014-10-01
We report on the magnetization behavior of dilute binary ferrofluids based on γ-Fe(2)O(3)/Ni(2)O(3) composite nanoparticles (A particles), with diameter about 11 nm, and ferrihydrite (Fe(5)O(7)(OH) ・4H2O) nanoparticles (B particles), with diameter about 6 nm. The results show that for the binary ferrofluids with A-particle volume fraction φ(A) = 0.2% and B-particle volume fractions φ(B) = 0.1% and φ(B) = 0.6%, the magnetization curves exhibit quasi-magnetic hysteresis behavior. The demagnetizing curves coincide with the magnetizing curves at high fields. However, for single γ-Fe(2)O(3)/Ni(2)O(3) ferrofluids with φ(A) = 0.2% and binary ferrofluids with φ(A) = 0.2% and φ(B) = 1.0%, the magnetization curves do not behave in this way. Additionally, at high field (750 kA/m), the binary ferrofluid with φ(B) = 1.0% has the smallest magnetization. From the model-of-chain theory, the extrinsic hysteresis behavior of these samples is attributed to the field-induced effects of pre-existing A particle chains, which involve both Brownian rotation of the chains'moments and a Néel rotation of the particles' moments in the chains. The loss of magnetization for the ferrofluids with φ(B) = 1.0% is attributed to pre-existing ring-like A-particle aggregates. These magnetization behaviors of the dilute binary ferrofluids not only depend on features of the strongly magnetic A-particle system, but also modifications of the weaker magnetic B-particle system. PMID:25365919
NASA Astrophysics Data System (ADS)
Viallet, M.; Goffrey, T.; Baraffe, I.; Folini, D.; Geroux, C.; Popov, M. V.; Pratt, J.; Walder, R.
2016-02-01
This work is a continuation of our efforts to develop an efficient implicit solver for multidimensional hydrodynamics for the purpose of studying important physical processes in stellar interiors, such as turbulent convection and overshooting. We present an implicit solver that results from the combination of a Jacobian-free Newton-Krylov method and a preconditioning technique tailored to the inviscid, compressible equations of stellar hydrodynamics. We assess the accuracy and performance of the solver for both 2D and 3D problems for Mach numbers down to 10-6. Although our applications concern flows in stellar interiors, the method can be applied to general advection and/or diffusion-dominated flows. The method presented in this paper opens up new avenues in 3D modeling of realistic stellar interiors allowing the study of important problems in stellar structure and evolution.
Magneto-optical and rheological behaviors of oil-based ferrofluids and magnetorheological fluids
NASA Astrophysics Data System (ADS)
Getzie, Travis
The magneto-optical and rheological behaviors of magnetic fluids and magnetorheological (MR) fluids have been investigated. A magneto-optical apparatus was constructed which enabled us to investigate the birefringence and dichroism of ferrofluids at various levels of applied magnetic field. Specifically, the effects of the film thickness of oil-based ferrofluids and the concentration of surfactant in the oil-based ferrofluids on their magneto-optical behavior were investigated. A commercial magneto-rheological instrument (Physica MCR 301, Anton Paar) equipped with a cone-and-plate fixture was employed to investigate the transient and steady-state shear flow of both ferrofluids and MR fluids as a function of shear rate at various levels of applied magnetic fields. The rheological investigation has enabled us to determine the effect of applied magnetic field on the shear viscosity and yield stress of ferrofluids and MR fluids. A special ferrofluid was prepared by filtering out nearly all of the surfactant and small particles in an oil-based ferrofluid. We then compared its magneto-optical and rheological behaviors with those of an unfiltered ferrofluid. Further, we have found that the ferrofluid with a lower concentration of surfactant gave rise to larger birefringence and yield stress, and stronger shear thinning behavior than the ferrofluid containing a higher concentration of surfactant. This observation has lead us to conclude that an increase in unbound surfactant in a ferrofluid hindered chain formation of magnetic particles, leading to a decrease in the optical and rheological behaviors of the ferrofluid. Optical microscopy confirmed no visible chain formation of magnetic particles in the ferrofluid having a high concentration of surfactant owing to weak yield stress, birefringence, and shear thinning. On the other hand, we observed from optical microscopy that the filtered ferrofluid gave rise to larger yield stress, birefringence, and stronger shear thinning
Sink-float ferrofluid separator applicable to full scale nonferrous scrap separation
NASA Technical Reports Server (NTRS)
1973-01-01
Design and performance of a ferrofluid levitation separator for recovering nonferrous metals from shredded automobiles are reported. The scrap separator uses an electromagnet to generate a region of constant density within a pool of ferrofluid held between the magnetic poles; a saturated kerosene base ferrofluid as able to float all common industrial metals of interest. Conveyors move the scrap into the ferrofluid for separation according to density. Results of scrap mixture separation studies establish the technical feasibility of relatively pure aluminum alloy and zinc alloy fractions from shredded automobile scrap by this ferrofluid levitation process. Economic projections indicate profitable operation for shredders handling more than 300 cars per day.
Magnetic field induced flow pattern reversal in a ferrofluidic Taylor-Couette system
NASA Astrophysics Data System (ADS)
Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng
2015-12-01
We investigate the dynamics of ferrofluidic wavy vortex flows in the counter-rotating Taylor-Couette system, with a focus on wavy flows with a mixture of the dominant azimuthal modes. Without external magnetic field flows are stable and pro-grade with respect to the rotation of the inner cylinder. More complex behaviors can arise when an axial or a transverse magnetic field is applied. Depending on the direction and strength of the field, multi-stable wavy states and bifurcations can occur. We uncover the phenomenon of flow pattern reversal as the strength of the magnetic field is increased through a critical value. In between the regimes of pro-grade and retrograde flow rotations, standing waves with zero angular velocities can emerge. A striking finding is that, under a transverse magnetic field, a second reversal in the flow pattern direction can occur, where the flow pattern evolves into pro-grade rotation again from a retrograde state. Flow reversal is relevant to intriguing phenomena in nature such as geomagnetic reversal. Our results suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which can be realized in laboratory experiments with potential applications in the development of modern fluid devices.
Magnetic field induced flow pattern reversal in a ferrofluidic Taylor-Couette system
Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng
2015-01-01
We investigate the dynamics of ferrofluidic wavy vortex flows in the counter-rotating Taylor-Couette system, with a focus on wavy flows with a mixture of the dominant azimuthal modes. Without external magnetic field flows are stable and pro-grade with respect to the rotation of the inner cylinder. More complex behaviors can arise when an axial or a transverse magnetic field is applied. Depending on the direction and strength of the field, multi-stable wavy states and bifurcations can occur. We uncover the phenomenon of flow pattern reversal as the strength of the magnetic field is increased through a critical value. In between the regimes of pro-grade and retrograde flow rotations, standing waves with zero angular velocities can emerge. A striking finding is that, under a transverse magnetic field, a second reversal in the flow pattern direction can occur, where the flow pattern evolves into pro-grade rotation again from a retrograde state. Flow reversal is relevant to intriguing phenomena in nature such as geomagnetic reversal. Our results suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which can be realized in laboratory experiments with potential applications in the development of modern fluid devices. PMID:26687638
Magnetic field induced flow pattern reversal in a ferrofluidic Taylor-Couette system.
Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng
2015-01-01
We investigate the dynamics of ferrofluidic wavy vortex flows in the counter-rotating Taylor-Couette system, with a focus on wavy flows with a mixture of the dominant azimuthal modes. Without external magnetic field flows are stable and pro-grade with respect to the rotation of the inner cylinder. More complex behaviors can arise when an axial or a transverse magnetic field is applied. Depending on the direction and strength of the field, multi-stable wavy states and bifurcations can occur. We uncover the phenomenon of flow pattern reversal as the strength of the magnetic field is increased through a critical value. In between the regimes of pro-grade and retrograde flow rotations, standing waves with zero angular velocities can emerge. A striking finding is that, under a transverse magnetic field, a second reversal in the flow pattern direction can occur, where the flow pattern evolves into pro-grade rotation again from a retrograde state. Flow reversal is relevant to intriguing phenomena in nature such as geomagnetic reversal. Our results suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which can be realized in laboratory experiments with potential applications in the development of modern fluid devices. PMID:26687638
Hydrodynamics of Turning Flocks
NASA Astrophysics Data System (ADS)
Yang, Xingbo; Marchetti, M. Cristina
2015-03-01
We present a hydrodynamic model of flocking that generalizes the familiar Toner-Tu equations to incorporate turning inertia of well polarized flocks. The continuum equations are derived by coarse graining the inertial spin model recently proposed by Cavagna et al. The interplay between orientational inertia and bend elasticity of the flock yields spin waves that mediate the propagation of turning information throughout the flock. When the inertia is large, we find a novel instability that signals the transition to complex spatio-temporal patterns of continuously turning and swirling flocks. This work was supported by the NSF Awards DMR-1305184 and DGE-1068780 at Syracuse University and NSF Award PHY11-25915 and the Gordon and Betty Moore Foundation Grant No. 2919 at the KITP at the University of California, Santa Barbara.
Study on the magnetorheological properties of maghemite-kerosene ferrofluid.
Ghasemi, E; Mirhabibi, A; Edrissi, M; Aghababazadeh, R; Brydson, R M
2009-07-01
As the ferrofluids are synthesized in a controlled atmosphere to Prevent oxidation of the magnetite phase; most reports of rheological properties have been derived from magnetite based ferrofluids. In this paper a ferrofluid based on iron oxide was synthesized by co-precipitation with air. Lauric acid was used to coat magnetic nanoparticles in the kerosene. The microstructural features of the ferrofluid and the variation with time and temperature of its rheologic and magnetic properties were investigated. The results indicated that the magnetic particles had an average size of 10.6 nm consisting of maghemite as the major phase. Viscosity of ferrofluid showed considerable variation with time and temperature. It was specified that the time dependency of the magnetoviscousity is related to particle size and rearrangement of nanoparticles of product is independent from the magnetic field. Moreover at low shear rates (< 0.1 s(-1)) the interaction of nanoparticles is related to the van der waals forces which cause the increase of the viscosity with time. The temperature effect showed that the magnetoviscosity decreases considerably above 45 degrees C. PMID:19916442
Stress relaxation in a ferrofluid with clustered nanoparticles.
Borin, Dmitry Yu; Zubarev, Andrey Yu; Chirikov, Dmitry N; Odenbach, Stefan
2014-10-01
The formation of structures in a ferrofluid by an applied magnetic field causes various changes in the rheological behaviour of the ferrofluid. A ferrofluid based on clustered iron nanoparticles was investigated. We experimentally and theoretically consider stress relaxation in the ferrofluid under the influence of a magnetic field, when the flow is suddenly interrupted. It is shown that the residual stress observed in the fluid after the relaxation is correlated with the measured and theoretically predicted magnetic field-induced yield stress. Furthermore, we have shown that the total macroscopic stress in the ferrofluid after the flow is interrupted is defined by the presence of both linear chains and dense, drop-like bulk aggregates. The proposed theoretical approach is consistent with the experimentally observed behaviour, despite a number of simplifications which have been made in the formulation of the model. Thus, the obtained results contribute a lot to the understanding of the complex, magnetic field-induced rheological properties of magnetic colloids near the yield stress point. PMID:25229878
Motion of Ferrofluid Droplets Under Oscillating Magnetic Field
NASA Astrophysics Data System (ADS)
Gu, Yu; Chow, Huiyanangel; Morris, Karl
Ferrofluids are stable, colloidal suspensions of single-domain ferromagnetic particles of nanometer size. Because of their good sealing properties and ease of actuation, ferrofluids are ideal for applications in Lab-On-Chip, or micro-total analysis systems (μTAS). In particular, because of their changing viscosity and surface properties under magnetic fields, as well as previously reported nonlinear behavior in bulk volumes, understanding the periodic movement of ferrofluid droplets for applications in pumping, valving and switching is important. We characterize the movement of ferrofluid droplets with volumes from 80 nL to 200 nL under oscillating magnetic fields in the frequency range 1Hz to 100Hz. Oil-based ferrofluid droplets are placed in circular cross-sectional capillaries and motion is recorded using a high-speed camera, then distilled using computer-assisted image analysis. Kinematics variables such as the position and velocity of the droplets' centers of mass are observed. Nonlinear behaviors in droplet shape and travel distance per cycle of actuation are also presented. This work was supported by the Research Corporation for Science Advancement.
The Dynamics of Agglomerated Ferrofluid in Steady and Pulsatile Flows
NASA Astrophysics Data System (ADS)
Williams, Alicia; Stewart, Kelley; Vlachos, Pavlos
2007-11-01
Magnetic Drug Targeting (MDT) is a promising technique to deliver medication via functionalized magnetic particles to target sites in the treatment of diseases. In this work, the physics of steady and pulsatile flows laden with superparamagnetic nanoparticles in a square channel under the influence of a magnetic field induced by a 0.6 Tesla permanent magnet is studied. Herein, the dynamics of ferrofluid shedding from an initially accumulated mass in water are examined through shadowgraph imaging using two orthogonal cameras. Fundamental differences in the ferrofluid behavior occur between the steady and pulsatile flow cases, as expected. For steady flows, vortex ring shedding is visualized from the mass, and periodic shedding occurs only for moderate mass sizes where the shear forces in the flow interact with the magnetic forces. At Reynolds numbers below 500 with pulsatile flow, suction and roll up of the ferrofluid is seen during the low and moderate periods of flow, followed by the ejection of ferrofluid during high flow. These shadowgraphs illustrate the beauty and richness of ferrofluid dynamics, an understanding of which is instrumental to furthering MDT as an effective drug delivery device.
Hydrodynamic loading of tensegrity structures
NASA Astrophysics Data System (ADS)
Wroldsen, Anders S.; Johansen, Vegar; Skelton, Robert E.; Sørensen, Asgeir J.
2006-03-01
This paper introduces hydrodynamic loads for tensegrity structures, to examine their behavior in marine environments. Wave compliant structures are of general interest when considering large marine structures, and we are motivated by the aquaculture industry where new concepts are investigated in order to make offshore installations for seafood production. This paper adds to the existing models and software simulations of tensegrity structures exposed to environmental loading from waves and current. A number of simulations are run to show behavior of the structure as a function of pretension level and string stiffness for a given loading condition.
Three-dimensional diamagnetic particle deflection in ferrofluid microchannel flows
Liang, Litao; Zhu, Junjie; Xuan, Xiangchun
2011-01-01
Magnetic field-induced particle manipulation is a promising technique for biomicrofluidics applications. It is simple, cheap, and also free of fluid heating issues that accompany other common electric, acoustic, and optical methods. This work presents a fundamental study of diamagnetic particle motion in ferrofluid flows through a rectangular microchannel with a nearby permanent magnet. Due to their negligible magnetization relative to the ferrofluid, diamagnetic particles experience negative magnetophoresis and are repelled away from the magnet. The result is a three-dimensionally focused particle stream flowing near the bottom outer corner of the microchannel that is the farthest to the center of the magnet and hence has the smallest magnetic field. The effects of the particle’s relative position to the magnet, particle size, ferrofluid flow rate, and concentration on this three-dimensional diamagnetic particle deflection are systematically studied. The obtained experimental results agree quantitatively with the predictions of a three-dimensional analytical model. PMID:22662037
Structure, synthetic methods, magnetic properties and biomedical applications of ferrofluids.
Shokrollahi, H
2013-07-01
This paper is aimed at conducting a survey of the synthetic methods and magnetic properties of nanoparticles as ferrofluids used in biomedicine. As compared with other works in the field, the distinctive feature of the current work is the systematic study of recent advances in ferrofluids utilized in hyperthermia and magnetic resonance imaging (MRI). The most important feature for application of ferrofluids is super-paramagnetic behavior of magnetic cores with relatively high saturation magnetization. Although Fe3O4 nanoparticles have traditionally been used in medicine; the modified Mn-ferrite has recently received special attention due to its higher saturation magnetization and r2-relaxivity as a contrast agent in MRI. Co-ferrite nanoparticles are also good candidates for hyperthermia treatment because of their high coercivity and magnetocrystalline anisotropy. The thermal decomposition and hydrothermal methods are good candidates for obtaining appropriate super-paramagnetic particles. PMID:23623058
Continuous-flow sheathless diamagnetic particle separation in ferrofluids
NASA Astrophysics Data System (ADS)
Zhou, Yilong; Song, Le; Yu, Liandong; Xuan, Xiangchun
2016-08-01
Separating particles from a complex mixture is often necessary in many chemical and biomedical applications. This work presents a continuous-flow sheathless diamagnetic particle separation in ferrofluids through U-shaped microchannels. Due to the action of a size-dependent magnetic force, diamagnetic particles are focused into a single stream in the inlet branch of the U-turn and then continuously separated into two streams in its outlet branch. A 3D numerical model is developed to predict and understand the diamagnetic particle transport during this separation process. The numerical predictions are found to agree well with the experimental observations in a systematic study of the effects of multiple parameters including ferrofluid flow rate, concentration and magnet-channel distance. Additional numerical studies of the geometric effects of the U-turn reveal that increasing the outlet-branch width of the U-turn can significantly enhance the diamagnetic particle separation in ferrofluids.
Experimental demonstration of metamaterial ``multiverse'' in a ferrofluid
NASA Astrophysics Data System (ADS)
Smolyaninov, Igor I.; Yost, Bradley; Bates, Evan; Smolyaninova, Vera N.
2013-06-01
Extraordinary light rays propagating inside a hyperbolic metamaterial look similar to particle world lines in a 2+1 dimensional Minkowski spacetime [1]. Magnetic nanoparticles in a ferrofluid are known to form nanocolumns aligned along the magnetic field, so that a hyperbolic metamaterial may be formed at large enough nanoparticle concentration nH. Here we investigate optical properties of such a metamaterial just below nH. While on average such a metamaterial is elliptical, thermal fluctuations of nanoparticle concentration lead to transient formation of hyperbolic regions (3D Minkowski spacetimes) inside this metamaterial. Thus, thermal fluctuations in a ferrofluid look similar to creation and disappearance of individual Minkowski spacetimes (universes) in the cosmological multiverse. This theoretical picture is supported by experimental measurements of polarization-dependent optical transmission of a cobalt based ferrofluid at 1500 nm.
Experimental demonstration of metamaterial "multiverse" in a ferrofluid.
Smolyaninov, Igor I; Yost, Bradley; Bates, Evan; Smolyaninova, Vera N
2013-06-17
Extraordinary light rays propagating inside a hyperbolic metamaterial look similar to particle world lines in a 2 + 1 dimensional Minkowski spacetime. Magnetic nanoparticles in a ferrofluid are known to form nanocolumns aligned along the magnetic field, so that a hyperbolic metamaterial may be formed at large enough nanoparticle concentration nH. Here we investigate optical properties of such a metamaterial just below nH. While on average such a metamaterial is elliptical, thermal fluctuations of nanoparticle concentration lead to transient formation of hyperbolic regions (3D Minkowski spacetimes) inside this metamaterial. Thus, thermal fluctuations in a ferrofluid look similar to creation and disappearance of individual Minkowski spacetimes (universes) in the cosmological multiverse. This theoretical picture is supported by experimental measurements of polarization-dependent optical transmission of a cobalt based ferrofluid at 1500 nm. PMID:23787680
A capillary viscometer designed for the characterization of biocompatible ferrofluids
NASA Astrophysics Data System (ADS)
Nowak, J.; Odenbach, S.
2016-08-01
Suspensions of magnetic nanoparticles are receiving a growing interest in biomedical research. These ferrofluids can, e.g., be used for the treatment of cancer, making use of the drug targeting principle or using an artificially induced heating. To enable a safe application the basic properties of the ferrofluids have to be well understood, including the viscosity of the fluids if an external magnetic field is applied. It is well known that the viscosity of ferrofluids rises if a magnetic field is applied, where the rise depends on shear rate and magnetic field strength. In case of biocompatible ferrofluids such investigations proved to be rather complicated as the experimental setup should be close to the actual application to allow justified predictions of the effects which have to be expected. Thus a capillary viscometer, providing a flow situation comparable to the flow in a blood vessel, has been designed. The glass capillary is exchangeable and different inner diameters can be used. The range of the shear rates has been adapted to the range found in the human organism. The application of an external magnetic field is enabled with two different coil setups covering the ranges of magnetic field strengths required on the one hand for a theoretical understanding of particle interaction and resulting changes in viscosity and on the other hand for values necessary for a potential biomedical application. The results show that the newly designed capillary viscometer is suitable to measure the magnetoviscous effect in biocompatible ferrofluids and that the results appear to be consistent with data measured with rotational rheometry. In addition, a strong change of the flow behaviour of a biocompatible ferrofluid was proven for ranges of the shear rate and the magnetic field strength expected for a potential biomedical application.
Printing microstructures in a polymer matrix using a ferrofluid droplet
NASA Astrophysics Data System (ADS)
Abdel Fattah, Abdel Rahman; Ghosh, Suvojit; Puri, Ishwar K.
2016-03-01
We print complex curvilinear microstructures in an elastomer matrix using a ferrofluid droplet as the print head. A magnetic field moves the droplet along a prescribed path in liquid polydimethylsiloxane (PDMS). The droplet sheds magnetic nanoparticle (MNP) clusters in its wake, forming printed features. The PDMS is subsequently heated so that it crosslinks, which preserves the printed features in the elastomer matrix. The competition between magnetic and drag forces experienced by the ferrofluid droplet and its trailing MNPs highlight design criteria for successful printing, which are experimentally confirmed. The method promises new applications, such as flexible 3D circuitry.
Magnetic and structural investigations on barium hexaferrite ferrofluids
NASA Astrophysics Data System (ADS)
Müller, R.; Hiergeist, R.; Gawalek, W.; Hoell, A.; Wiedenmann, A.
2002-11-01
Barium hexaferrite BaFe 12-2 xTi xCo xO 19 ferrofluids have been prepared using oleic acid as surfactant and Isopar M ® or dodecane as carrier liquid. The ferrite particles were prepared by glass crystallization. Hysteresis parameters, the initial susceptibility versus temperature and the magnetic particle size were obtained by VSM. Ferrofluids with a partly deuterated carrier liquid were investigated by small angle neutron scattering (SANS). SANS curves lead to a bimodal size distribution consisting of single magnetic particles with an organic shell and aggregated particles with an incomplete organic layer.
Azimuthal field instability in a confined ferrofluid
NASA Astrophysics Data System (ADS)
Dias, Eduardo O.; Miranda, José A.
2015-02-01
We report the development of interfacial ferrohydrodynamic instabilities when an initially circular bubble of a nonmagnetic inviscid fluid is surrounded by a viscous ferrofluid in the confined geometry of a Hele-Shaw cell. The fluid-fluid interface becomes unstable due to the action of magnetic forces induced by an azimuthal field produced by a straight current-carrying wire that is normal to the cell plates. In this framework, a pattern formation process takes place through the interplay between magnetic and surface tension forces. By employing a perturbative mode-coupling approach we investigate analytically both linear and intermediate nonlinear regimes of the interface evolution. As a result, useful analytical information can be extracted regarding the destabilizing role of the azimuthal field at the linear level, as well as its influence on the interfacial pattern morphology at the onset of nonlinear effects. Finally, a vortex sheet formalism is used to access fully nonlinear stationary solutions for the two-fluid interface shapes.
Linear and nonlinear magnetic properties of ferrofluids.
Szalai, I; Nagy, S; Dietrich, S
2015-10-01
Within a high-magnetic-field approximation, employing Ruelle's algebraic perturbation theory, a field-dependent free-energy expression is proposed which allows one to determine the magnetic properties of ferrofluids modeled as dipolar hard-sphere systems. We compare the ensuing magnetization curves, following from this free energy, with those obtained by Ivanov and Kuznetsova [Phys. Rev. E 64, 041405 (2001)] as well as with new corresponding Monte Carlo simulation data. Based on the power-series expansion of the magnetization, a closed expression for the magnetization is also proposed, which is a high-density extension of the corresponding equation of Ivanov and Kuznetsova. From both magnetization equations the zero-field susceptibility expression due to Tani et al. [Mol. Phys. 48, 863 (1983)] can be obtained, which is in good agreement with our MC simulation results. From the closed expression for the magnetization the second-order nonlinear magnetic susceptibility is also derived, which shows fair agreement with the corresponding MC simulation data. PMID:26565247
Linear and nonlinear magnetic properties of ferrofluids
NASA Astrophysics Data System (ADS)
Szalai, I.; Nagy, S.; Dietrich, S.
2015-10-01
Within a high-magnetic-field approximation, employing Ruelle's algebraic perturbation theory, a field-dependent free-energy expression is proposed which allows one to determine the magnetic properties of ferrofluids modeled as dipolar hard-sphere systems. We compare the ensuing magnetization curves, following from this free energy, with those obtained by Ivanov and Kuznetsova [Phys. Rev. E 64, 041405 (2001), 10.1103/PhysRevE.64.041405] as well as with new corresponding Monte Carlo simulation data. Based on the power-series expansion of the magnetization, a closed expression for the magnetization is also proposed, which is a high-density extension of the corresponding equation of Ivanov and Kuznetsova. From both magnetization equations the zero-field susceptibility expression due to Tani et al. [Mol. Phys. 48, 863 (1983), 10.1080/00268978300100621] can be obtained, which is in good agreement with our MC simulation results. From the closed expression for the magnetization the second-order nonlinear magnetic susceptibility is also derived, which shows fair agreement with the corresponding MC simulation data.
Azimuthal field instability in a confined ferrofluid.
Dias, Eduardo O; Miranda, José A
2015-02-01
We report the development of interfacial ferrohydrodynamic instabilities when an initially circular bubble of a nonmagnetic inviscid fluid is surrounded by a viscous ferrofluid in the confined geometry of a Hele-Shaw cell. The fluid-fluid interface becomes unstable due to the action of magnetic forces induced by an azimuthal field produced by a straight current-carrying wire that is normal to the cell plates. In this framework, a pattern formation process takes place through the interplay between magnetic and surface tension forces. By employing a perturbative mode-coupling approach we investigate analytically both linear and intermediate nonlinear regimes of the interface evolution. As a result, useful analytical information can be extracted regarding the destabilizing role of the azimuthal field at the linear level, as well as its influence on the interfacial pattern morphology at the onset of nonlinear effects. Finally, a vortex sheet formalism is used to access fully nonlinear stationary solutions for the two-fluid interface shapes. PMID:25768610
NASA Astrophysics Data System (ADS)
Mekhonoshin, V. V.; Lange, Adrian
2002-06-01
A linear stability analysis of the free surface of a horizontally unbounded ferrofluid layer of arbitrary depth subjected to vertical vibrations and a horizontal magnetic field is performed. A nonmonotonic dependence of the stability threshold on the magnetic field is found at high frequencies of the vibrations. The reasons for the decrease of the critical acceleration amplitude caused by a horizontal magnetic field are discussed. It is revealed that the magnetic field can be used to select the first unstable pattern of Faraday waves. In particular, a rhombic pattern as a superposition of two different oblique rolls can occur. A scaling law is presented which maps all data into one graph for the tested range of viscosities, frequencies, magnetic fields, and layer thicknesses.
Algorithm refinement for fluctuating hydrodynamics
Williams, Sarah A.; Bell, John B.; Garcia, Alejandro L.
2007-07-03
This paper introduces an adaptive mesh and algorithmrefinement method for fluctuating hydrodynamics. This particle-continuumhybrid simulates the dynamics of a compressible fluid with thermalfluctuations. The particle algorithm is direct simulation Monte Carlo(DSMC), a molecular-level scheme based on the Boltzmann equation. Thecontinuum algorithm is based on the Landau-Lifshitz Navier-Stokes (LLNS)equations, which incorporate thermal fluctuations into macroscopichydrodynamics by using stochastic fluxes. It uses a recently-developedsolver for LLNS, based on third-order Runge-Kutta. We present numericaltests of systems in and out of equilibrium, including time-dependentsystems, and demonstrate dynamic adaptive refinement by the computationof a moving shock wave. Mean system behavior and second moment statisticsof our simulations match theoretical values and benchmarks well. We findthat particular attention should be paid to the spectrum of the flux atthe interface between the particle and continuum methods, specificallyfor the non-hydrodynamic (kinetic) time scales.
Oblique magnetic field effects over stability in superposed viscous ferrofluids
NASA Astrophysics Data System (ADS)
Jothimani, S.; Anjali Devi, S. P.
2000-12-01
The interface of two superposed viscous ferrofluids of infinite depth in the presence of an uniform magnetic field oblique to the interface is considered. The fluids are assumed to be incompressible and a surface tension T acts on the interface. Solutions of the linear problem and the linear dispersion relation are found. Exchange of stabilities are discussed for various cases.
The effects of polydispersity on the initial susceptibilities of ferrofluids
NASA Astrophysics Data System (ADS)
Camp, Philip J.; Elfimova, Ekaterina A.; Ivanov, Alexey O.
2014-11-01
The effects of particle-size polydispersity on the initial susceptibilities of concentrated ferrofluids are analyzed using a combination of theory and computer simulation. The study is focused on a model ferrofluid with a prescribed magnetic-core diameter distribution, a fixed non-magnetic surface layer (corresponding to a demagnetized layer and adsorbed surfactant) and a combination of dipolar and hard-core interactions. The non-trivial effects of polydispersity are identified by comparing the initial susceptibilities of monodisperse and polydisperse ferrofluids with the same Langevin susceptibility. The theory is based on a correction to the second-order modified mean-field theory arising from a formal Mayer-type cluster expansion; this correction is dependent on a parameter similar to the normal dipolar coupling constant, except that it contains a complicated double average over the particle-size distribution, which means that the initial susceptibility should depend significantly on polydispersity. Specifically, the theory predicts that the initial susceptibility is enhanced significantly by polydispersity. This prediction is tested rigorously against results from Monte Carlo simulations and is found to be robust. The qualitative agreement between theory and simulation is already satisfactory, but the quantitative agreement could be improved by a systematic extension of the cluster expansion. The overall conclusion is that polydispersity should be accounted for carefully in magnetogranulometric analyses of real ferrofluids.
The effects of polydispersity on the initial susceptibilities of ferrofluids.
Camp, Philip J; Elfimova, Ekaterina A; Ivanov, Alexey O
2014-11-12
The effects of particle-size polydispersity on the initial susceptibilities of concentrated ferrofluids are analyzed using a combination of theory and computer simulation. The study is focused on a model ferrofluid with a prescribed magnetic-core diameter distribution, a fixed non-magnetic surface layer (corresponding to a demagnetized layer and adsorbed surfactant) and a combination of dipolar and hard-core interactions. The non-trivial effects of polydispersity are identified by comparing the initial susceptibilities of monodisperse and polydisperse ferrofluids with the same Langevin susceptibility. The theory is based on a correction to the second-order modified mean-field theory arising from a formal Mayer-type cluster expansion; this correction is dependent on a parameter similar to the normal dipolar coupling constant, except that it contains a complicated double average over the particle-size distribution, which means that the initial susceptibility should depend significantly on polydispersity. Specifically, the theory predicts that the initial susceptibility is enhanced significantly by polydispersity. This prediction is tested rigorously against results from Monte Carlo simulations and is found to be robust. The qualitative agreement between theory and simulation is already satisfactory, but the quantitative agreement could be improved by a systematic extension of the cluster expansion. The overall conclusion is that polydispersity should be accounted for carefully in magnetogranulometric analyses of real ferrofluids. PMID:25327692
Magnetic sensing with ferrofluid and fiber optic connectors.
Homa, Daniel; Pickrell, Gary
2014-01-01
A simple, cost effective and sensitive fiber optic magnetic sensor fabricated with ferrofluid and commercially available fiber optic components is described in this paper. The system uses a ferrofluid infiltrated extrinsic Fabry-Perot interferometer (EFPI) interrogated with an infrared wavelength spectrometer to measure magnetic flux density. The entire sensing system was developed with commercially available components so it can be easily and economically reproduced in large quantities. The device was tested with two different ferrofluid types over a range of magnetic flux densities to verify performance. The sensors readily detected magnetic flux densities in the range of 0.5 mT to 12.0 mT with measurement sensitivities in the range of 0.3 to 2.3 nm/mT depending on ferrofluid type. Assuming a conservative wavelength resolution of 0.1 nm for state of the art EFPI detection abilities, the estimated achievable measurement resolution is on the order 0.04 mT. The inherent small size and basic structure complimented with the fabrication ease make it well-suited for a wide array of research, industrial, educational and military applications. PMID:24573312
Preparation and characterization of silicon oil based ferrofluid
NASA Astrophysics Data System (ADS)
Chen, H. J.; Wang, Y. M.; Qu, J. M.; Hong, R. Y.; Li, H. Z.
2011-10-01
Stable silicon oil based ferrofluid was prepared in the present investigation. Silicon oil surfactant ethoxy terminated polydimethylsiloxane was used to modify the Fe 3O 4 nanoparticles. The Fe 3O 4 nanoparticles were firstly coated with a SiO 2 layer by the hydrolysis of tetraethoxysilane. Then using the active hydroxyl groups on the surface of the SiO 2, silicon oil surfactant was covalently grafted onto the Fe 3O 4 nanoparticles surface. The ethoxy terminated polydimethylsiloxane has similar molecular chain structure and good compatibility with that of the carrier liquid, thus ensuring stable dispersion of modified Fe 3O 4 in the carrier silicon oil. The interaction between Fe 3O 4 and the modifier was characterized by IR and XPS. The crystal structure and the magnetic properties of the Fe 3O 4 nanoparticles were determined by XRD and VSM, respectively. The size and morphology of the particles were observed using TEM. The properties of the silicon oil based ferrofluid were characterized by Gouy magnetic balance. The results indicated that the ferrofluid had high magnetism and good stability. The rheological properties and thermostability of the ferrofluid were also investigated.
Smolyaninov, Igor I; Smolyaninova, Vera N; Smolyaninov, Alexei I
2015-08-28
In the presence of an external magnetic field, cobalt nanoparticle-based ferrofluid forms a self-assembled hyperbolic metamaterial. The wave equation, which describes propagation of extraordinary light inside the ferrofluid, exhibits 2+1 dimensional Lorentz symmetry. The role of time in the corresponding effective three-dimensional Minkowski space-time is played by the spatial coordinate directed along the periodic nanoparticle chains aligned by the magnetic field. Here, we present a microscopic study of point, linear, planar and volume defects of the nanoparticle chain structure and demonstrate that they may exhibit strong similarities with such Minkowski space-time defects as magnetic monopoles, cosmic strings and the recently proposed space-time cloaks. Experimental observations of such defects are described. PMID:26217055
Smolyaninov, Igor I.; Smolyaninova, Vera N.; Smolyaninov, Alexei I.
2015-01-01
In the presence of an external magnetic field, cobalt nanoparticle-based ferrofluid forms a self-assembled hyperbolic metamaterial. The wave equation, which describes propagation of extraordinary light inside the ferrofluid, exhibits 2+1 dimensional Lorentz symmetry. The role of time in the corresponding effective three-dimensional Minkowski space–time is played by the spatial coordinate directed along the periodic nanoparticle chains aligned by the magnetic field. Here, we present a microscopic study of point, linear, planar and volume defects of the nanoparticle chain structure and demonstrate that they may exhibit strong similarities with such Minkowski space–time defects as magnetic monopoles, cosmic strings and the recently proposed space–time cloaks. Experimental observations of such defects are described. PMID:26217055
Dynamics of Single Chains of Suspended Ferrofluid Particles
NASA Technical Reports Server (NTRS)
Cutillas, S.; Liu, J.
1999-01-01
. Therefore, only motions in this plane are probed. A very dilute sample of a ferrofluid emulsion with a particle volume fraction of 10(exp -5) is used in this experiment. We chose such a low volume fraction to avoid multiple light scattering as well as lateral chain-chain aggregation. DLS measures the dynamic structure factor S(q,t) of the sample (q is the scattering wave vector, t is the time). In the absence of the magnetic field, identical particles of ferrofluid droplets are randomly distributed and S(q,t) reduces to exp(-q(exp 2)2D(sub 0)t). D(sub 0)=(kT/(6(pi)(eta)(a)) is the diffusion coefficient of Brownian particles (where Xi = (6(pi)(eta)(a)) is the Stokes frictional coefficient of a spherical particle in a fluid of viscosity eta). If interactions or polydispersity can not be ignored, an effective diffusion coefficient is introduced. Formally, D(sub eff) is defined as: D(sub eff) = - q(exp -2) partial derivative of (ln(S(q,t)) with respect to time, as t goes to 0. D(sub eff) reduces to D(sub 0) if no interactions and only a few particles size are present. Therefore, we can use DLS to measure particle size. The particle radius was found to be a=0.23 mu m with 7% of polydispersity. In this case, if we vary the scattering angle theta (and so q) we do not have any change in the measured diffusion coefficient: it is q-independent. When a magnetic field is applied, particles aggregate into chains if lambda > 1. We first studied the kinetics of the chain formation when lambda = 406. At a fixed scattering angle, we measured diffusion coefficient D(sub eff) as a function of time. Experimentally, we find that D(sub eff) decreases monotonously with time. Physically, this means that chains are becoming longer and longer. Since we are only sensitive to motions in the scattering plane and since chains have their main axis perpendicular to this plane, the measured diffusion coefficient is the trans-verse diffusion coefficient. We can relate D(sub eff) to the mean number of
Thermodynamics of ferrofluids in applied magnetic fields.
Elfimova, Ekaterina A; Ivanov, Alexey O; Camp, Philip J
2013-10-01
The thermodynamic properties of ferrofluids in applied magnetic fields are examined using theory and computer simulation. The dipolar hard sphere model is used. The second and third virial coefficients (B(2) and B(3)) are evaluated as functions of the dipolar coupling constant λ, and the Langevin parameter α. The formula for B(3) for a system in an applied field is different from that in the zero-field case, and a derivation is presented. The formulas are compared to results from Mayer-sampling calculations, and the trends with increasing λ and α are examined. Very good agreement between theory and computation is demonstrated for the realistic values λ≤2. The analytical formulas for the virial coefficients are incorporated in to various forms of virial expansion, designed to minimize the effects of truncation. The theoretical results for the equation of state are compared against results from Monte Carlo simulations. In all cases, the so-called logarithmic free energy theory is seen to be superior. In this theory, the virial expansion of the Helmholtz free energy is re-summed in to a logarithmic function. Its success is due to the approximate representation of high-order terms in the virial expansion, while retaining the exact low-concentration behavior. The theory also yields the magnetization, and a comparison with simulation results and a competing modified mean-field theory shows excellent agreement. Finally, the putative field-dependent critical parameters for the condensation transition are obtained and compared against existing simulation results for the Stockmayer fluid. Dipolar hard spheres do not undergo the transition, but the presence of isotropic attractions, as in the Stockmayer fluid, gives rise to condensation even in zero field. A comparison of the relative changes in critical parameters with increasing field strength shows excellent agreement between theory and simulation, showing that the theoretical treatment of the dipolar interactions
Oscillatory-like relaxation behavior of light transmitted through ferrofluids.
Li, Jian; Qiu, Xiaoyan; Lin, Yueqiang; Liu, Xiaodong; Fu, Jun; Miao, Hua; Zhang, Qingmei; Zhang, Tingzhen
2011-10-20
An oscillatory-like relaxation process in which there are two valleys in the T-t curve is observed when light is transmitted through binary ferrofluids composed of both ferrimagnetic CoFe(2)O(4) nanoparticles and paramagnetic p-MgFe(2)O(4) nanoparticles in the presence of a high magnetic field and through pure (single) CoFe(2)O(4) ferrofluids in a low magnetic field. This relaxation behavior is explained using a model of a bidispersed system based on both chained and unchained particles. In such a bidispersed system, the variation of the transmitted light results mainly from the motion of the chains, with the polarized unchained particles' gas producing the modulation effect. The oscillatory-like relaxation phenomenon depends on the features of both the chained and unchained particle systems. If either the particle volume fraction of chained particles or of unchained particles is very low, or the degree of polarization of the unchained particles gas is very weak, a simple nonlinear relaxation process, giving only a valley in the T-t curve, will appear for the transmitted light. For pure CoFe(2)O(4) ferrofluids, the number of chained and unchained particles does not remain constant under different values of the magnetic field. According to the analysis of the relaxation behavior of transmitted light, it is known that binary ferrofluids based on strong magnetic CoFe(2)O(4) particles and weak magnetic p-MgFe(2)O(4) particles can be much closer to the theoretical bidispersed system than single ferrofluids containing only strong magnetic particles. PMID:22015404
Rheological characterization of a magnetorheological ferrofluid using iron nitride nanoparticles
NASA Astrophysics Data System (ADS)
Armijo, Leisha M.; Ahuré-Powell, Louise A.; Wereley, Norman M.
2015-05-01
Magnetorheology of a magnetorheological ferrofluid (MRFF) was investigated to study the role of a ferromagnetic nanoparticle (NP) additive in magnetorheological fluids (MRFs). Iron nitride (Fe16N2) NPs, nominally within the diameter range of ˜16-45 nm (spherical NPs) and ˜30-66 nm (cubic NPs), were coated with carboxy-polyethylene glycol (carboxy-PEG) and dispersed in silicone oil in order to produce a magnetic carrier fluid or ferrofluid for two solids loadings: 2 vol. % and 5 vol. %. Conventional spherical carbonyl iron (CI) particles, varying in diameter from 6 to 10 μm, were suspended in the ferrofluid at 25 vol. % solids loading. Rheological properties of the MRFF synthesized with the carboxy-PEG-based ferromagnetic carrier fluid were compared to the MRF synthesized with silicone oil to determine how ferrofluid can influence dynamic viscosity and yield stress. Rheological measurements of both MRF and MRFF samples were carried out using a Paar Physica 300 rheometer to estimate the field-off viscosity and to measure flow curves (i.e., shear stress vs. shear rate) as a function of magnetic field. A Bingham-plastic model was used to characterize the flow curves, and results show that there is an increase in the dynamic viscosity of the MRFF over the MRF. The ferromagnetic carrier fluid greatly increases yield stress as only 2 vol. % of added carboxy-PEG NPs improves the yield stress performance by almost 5%. A second MRFF sample synthesized with 5 vol. % of added carboxy-PEG NPs contained in the ferrofluid significantly enhanced the yield stress performance by 13% over the MRF at the same CI solids loading (25 vol. %).