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1

Hydrodynamic time-correlation functions of a Heisenberg ferrofluid

Using our previous results [Physica A 220 (1995) 325 and A 234 (1996) 129], where the generalized transport equations for a Heisenberg-like model of a ferrofluid were obtained and the hydrodynamic collective mode spectrum has been studied, we derive the analytical expressions for hydrodynamic time-correlation functions of a Heisenberg model ferrofluid in a homogeneous magnetic field and in the limit

I. Mryglod; R. Folk; S. Dubyk; Yu. Rudavskii

2000-01-01

2

Hydrodynamic time correlation functions of a Heisenberg ferrofluid

NASA Astrophysics Data System (ADS)

Using our previous results [Physica A 220 (1995) 325 and A 234 (1996) 129], where the generalized transport equations for a Heisenberg-like model of a ferrofluid were obtained and the hydrodynamic collective mode spectrum has been studied, we derive the analytical expressions for hydrodynamic time-correlation functions of a Heisenberg model ferrofluid in a homogeneous magnetic field and in the limit of small wave numbers k and frequencies ?. These results, being exact in the hydrodynamic limit, are presented in the form, where contributions from each of the hydrodynamic modes are separated. It is shown that the sound excitations contribute to the time-correlation function of ‘spin density-spin density’, and the weight of this contribution depends on the value of an external magnetic field. On the other side, the spin diffusive mode contributes to the central line of the dynamic structure factor. Both of these functions may be extracted from scattering experiments. The Landau-Placzek ratios for the dynamic structure factor S( k, ?) and the magnetic dynamic structure factor Sm( k, ?) are calculated.

Mryglod, I.; Folk, R.; Dubyk, S.; Rudavskii, Yu.

2000-03-01

3

Hydrodynamics of chains in ferrofluid-based magnetorheological fluids under rotating magnetic field.

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

Patel, Rajesh; Chudasama, Bhupendra

2009-07-01

4

Yves Couder, Emmanuel Fort, and coworkers recently discovered that a millimetric droplet sustained on the surface of a vibrating fluid bath may self-propel through a resonant interaction with its own wave field. This article ...

Bush, John W. M.

5

Efficiency of magnetic plane wave pumping of a ferrofluid through a planar duct

NASA Astrophysics Data System (ADS)

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.

Felderhof, B. U.

2011-09-01

6

NASA Technical Reports Server (NTRS)

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.

1993-01-01

7

Wave turbulence on the surface of a ferrofluid in a magnetic field.

We report the observation of wave turbulence on the surface of a ferrofluid mechanically forced and submitted to a static normal magnetic field. We show that magnetic surface waves arise only above a critical field. The power spectrum of their amplitudes displays a frequency-power law leading to the observation of a magnetic wave turbulence regime which is experimentally shown to involve a 4-wave interaction process. The existence of the regimes of gravity, magnetic and capillary wave turbulence is reported in the phase space parameters as well as a triple point of coexistence of these three regimes. Most of these features are understood using dimensional analysis or the dispersion relation of the ferrohydrodynamic surface waves. PMID:19113624

Boyer, François; Falcon, Eric

2008-12-12

8

Nonlinear waves in second order conformal hydrodynamics

NASA Astrophysics Data System (ADS)

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.

Fogaça, D. A.; Marrochio, H.; Navarra, F. S.; Noronha, J.

2015-02-01

9

Simple Waves in Ideal Radiation Hydrodynamics

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.

Johnson, B M

2008-09-03

10

Simple Waves in Ideal Radiation Hydrodynamics

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.

Bryan M. Johnson

2008-11-24

11

NASA Astrophysics Data System (ADS)

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 suspensions with properties clearly focused towards the need of the application. While such tailoring of fluids to certain well defined properties sounds like a straightforward approach one has to face the fact that it requires a clear definition of the required properties. This definition itself has to be based on a fundamental physical knowledge of the processes determining certain magnetically controlled phenomena in ferrofluids. To make this point concrete one can look into the detailed aims of the mentioned research program. The application areas identified for the future development of research and application of suspensions of magnetic nanoparticles have been on the one hand the biomedical application—especially with respect to cancer treatment—and on the other hand the use of magnetically controlled rheological properties of ferrofluids for new active technical devices. Both directions require, as mentioned, as a basis for success the synthesis of new ferrofluids with dedicated properties. While the medical applications have to rely on biocompatibility as well as on stability of the suspensions in a biomedical environment, the use of ferrofluids in technical devices employing their magnetically controlled rheological properties will depend on an enhancement of the changes of the fluid's viscous properties in the presence of moderate magnetic fields. For both requirements ferrofluids with a make up clearly different from the usual magnetite based fluids have to be synthesized. The question of how the detailed microscopic make up of the fluids would have to look has to be answered on the basis of basic research results defining the physics background of the respective phenomena. Taking these aspects together it becomes obvious that the aforementioned research program had goals aiming far beyond the state of the art of classical ferrofluid research. These goals as well as the basic strategy to achieve them is in a way reflected by the structure of this issue of Journal of Physics: Condensed Matter. The issue contains results emerging from the research pr

Odenbach, Professor Stefan

2006-09-01

12

Hydrodynamic Forces From Wave and Current Loads on Marine Pipelines

The weight coating requirements for assuring the on-bottom stability of several pipelines in the Arabian Gulf have been determined through an integrated design procedure including mathematical modelling for determining extreme wave conditions, field measurements of currents and physical model testing to establish the magnitude of the hydrodynamic forces. The paper describes in detail the hydro-dynamic model testing. By using the

M. B. Bryndum; Vagner Jacobsen; L. Brand

1983-01-01

13

NASA Astrophysics Data System (ADS)

The progress in the synthesis of new magnetic nanoparticles and agglomerates stimulates the development of novel ferrofluids with enhanced rheological properties. In the current work ferrofluids based on Co-nanoplatelets and clustered iron oxide nanoparticles have been considered. Steady-shear experiments and yield stress measurements of these ferrofluids have been performed using rotational rheometry.

Borin, Dmitry; Odenbach, Stefan

14

Wave attenuation by vegetation is a highly dynamic process and its quantification is important for accurately understanding and predicting coastal hydrodynamics. However, the influence of vegetation on wave dissipation is not yet fully established...

Anderson, Mary Elizabeth

2011-10-21

15

Nonlinear Generalized Hydrodynamic Wave Equations in Strongly Coupled Dusty Plasmas

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.

Veeresha, B. M.; Sen, A.; Kaw, P. K. [Institute for Plasma Research, Bhat, Gandhinagar-382428 (India)

2008-09-07

16

Transition to turbulence in ferrofluids

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 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 bifurcation analysis and characterization of behaviors of physical quantities such as the energy, the wave number, and the angular momentum through the bifurcations. A striking finding is that, as the magnetic field is increased, the onset of turbulence can be determined accurately and reliably. Our results imply that experimental investigation of turbulence can be greatly facilitated by using ferrofluids, opening up...

Altmeyer, Sebastian; Lai, Ying-Cheng

2015-01-01

17

Propagation of elastic waves in granular solid hydrodynamics

NASA Astrophysics Data System (ADS)

The anisotropic stress-dependent velocity of elastic waves in glass beads—as observed by Khidas and Jia [Phys. Rev. E 81, 021303 (2010)]10.1103/PhysRevE.81.021303—is shown to be well accounted for by “granular solid hydrodynamics,” a broad-range macroscopic theory of granular behavior. As the theory makes no reference to fabric anisotropy, the influence of which on sound is in doubt.

Mayer, Michael; Liu, Mario

2010-10-01

18

Hydrodynamic shock wave studies within a kinetic Monte Carlo approach

NASA Astrophysics Data System (ADS)

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.

Sagert, Irina; Bauer, Wolfgang; Colbry, Dirk; Howell, Jim; Pickett, Rodney; Staber, Alec; Strother, Terrance

2014-06-01

19

Modeling of Waves with Smoothed Particle Hydrodynamics on the GPU

NASA Astrophysics Data System (ADS)

Providing an accurate representation of breaking waves is extremely difficult due to the complexity of the free surface, splash-up, and the induced vortical flows in the water. Monaghan (1994) and Dalrymple and Rogers (2004) are examples of using the numerical method Smoothed Particle Hydrodynamics to model these breaking waves. Both of these studies accurately show the plunging jet and the splash-up of breaking plungers. However, full details of the flow requires highly resolved 3-D calculations. SPH is computational intensive, involving large numbers of computational particles and very small time steps. Recently Herault (2008) has shown that very high resolution and significant speed-ups in model calculation occurs by computing on the graphics card (GPU), rather than the CPU of computers. This use of the GPU is an on-going paradigm shift, which will be shown. Examples of breaking waves, along with a number of example free surface flows, will be shown.

Dalrymple, R. A.; Herault, A.

2008-12-01

20

The velocities and accelerations accompanying ocean waves can impose large hydrodynamic forces no guarantee, however, that these plants will not be broken. Indeed, wave forces imposed during storms tear (Koehl and Wainwright, 1977; Seymour et al. 1989). Despite the recognition of wave-induced hydrodynamic

Denny, Mark

21

Hydrodynamic Modes of a holographic $p-$ wave superfluid

In this work we analyze the hydrodynamics of a $p-$ wave superfluid on its strongly coupled regime by considering its holographic description. We obtain the poles of the retarded Green function through the computation of the quasi-normal modes of the dual AdS black hole background finding diffusive, pseudo-diffusive and sound modes. For the sound modes we compute the speed of sound and its attenuation as function of the temperature. For the diffusive and pseudo-diffusive modes we find that they acquire a non-zero real part at certain finite momentum.

Raul E. Arias; Ignacio Salazar Landea

2014-09-22

22

Hydrodynamic modes of a holographic p-wave superfluid

NASA Astrophysics Data System (ADS)

In this work we analyze the hydrodynamics of a p- wave superfluid on its strongly coupled regime by considering its holographic description. We obtain the poles of the retarded Green function through the computation of the quasi-normal modes of the dual AdS black hole background finding diffusive, pseudo-diffusive and sound modes. For the sound modes we compute the speed of sound and its attenuation as function of the temperature. For the diffusive and pseudo-diffusive modes we find that they acquire a non-zero real part at certain finite momentum.

Arias, Raúl E.; Landea, Ignacio Salazar

2014-11-01

23

Hydrodynamic Modes of a holographic $p-$ wave superfluid

In this work we analyze the hydrodynamics of a $p-$ wave superfluid on its strongly coupled regime by considering its holographic description. We obtain the poles of the retarded Green function through the computation of the quasi-normal modes of the dual AdS black hole background finding diffusive, pseudo-diffusive and sound modes. For the sound modes we compute the speed of sound and its attenuation as function of the temperature. For the diffusive and pseudo-diffusive modes we find that they acquire a non-zero real part at certain finite momentum.

Arias, Raul E

2014-01-01

24

Radiative Hydrodynamic Simulations of Acoustic Waves in Sunspots

NASA Astrophysics Data System (ADS)

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.

Bard, S.; Carlsson, M.

2010-10-01

25

RADIATIVE HYDRODYNAMIC SIMULATIONS OF ACOUSTIC WAVES IN SUNSPOTS

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.

Bard, S. [Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, N-0315 Oslo (Norway); Carlsson, M. [Also at Center of Mathematics for Applications, University of Oslo, P.O. Box 1053, Blindern, N-0316 Oslo, Norway. (Norway)

2010-10-10

26

Nanomagnets: Fun with Ferrofluid

NSDL National Science Digital Library

Ferrofluid provides an easy opportunity to introduce students to the fascinating properties of the nanoscale. It is essentially a liquid magnet made of nanosized magnetic particles suspended in water or oil. Not only does it demonstrate the strange and beautiful properties of the nanoscale, but it also illustrates a case where nanoparticles and their associated properties provide interesting opportunities for technological applications.

Amy R. Taylor

2007-01-01

27

Synthesis of ferrofluid with magnetic nanoparticles by sonochemical method for MRI contrast agent

NASA Astrophysics Data System (ADS)

Superparamagnetic iron oxide nanoparticles (SPIO) having high magnetization (83 emu/g) and crystallinity were synthesized by using a sonochemical method. Ferrofluids from these nanoparticles coated with oleic acid as a surfactant were prepared for magnetic resonance imaging (MRI) contrast agent. The coated SPIO could be easily dispersed in chitosan, and the hydrodynamic diameter of the coated SPIO in the chitosan solution was estimated to be 65 nm. The ferrofluids of various concentrations did not agglomerate for 30 days, indicating their good stability. The T1- and T2-weighted MR images of these ferrofluids were obtained and the MRI image contrasts were similar to those of Resovist ®.

Hee Kim, Eun; Sook Lee, Hyo; Kook Kwak, Byung; Kim, Byung-Kee

2005-03-01

28

Symmetry Breaking Via Global Bifurcations of Modulated Rotating Waves in Hydrodynamics Jan Abshagen experimental and numerical study finds a complex mechanism of Z2 symmetry breaking involving global bifurcations for the first time in hydrodynamics. In addition to symmetry breaking via pitchfork bifurcation

Marques, Francisco

29

Hydrodynamical simulations of penetrative convection and generation of internal gravity waves

Hydrodynamical simulations of penetrative convection and generation of internal gravity waves M investigate the generation of internal gravity waves in the stable region below a convective layer by means interiors that can be affected by internal gravity waves. Considered so far are: mixing of chemical elements

StÃªpieÃ±, Kazimierz

30

Experiments on wind-perturbed rogue wave hydrodynamics using the Peregrine breather model

on the surface that results in a flux of energy from the wind to the waves and (ii) it generates a rotationalExperiments on wind-perturbed rogue wave hydrodynamics using the Peregrine breather model A the evolu- tion of the Peregrine solution in the presence of wind forcing in the direction of wave

Boyer, Edmond

31

Hydrodynamics of the double-wave structure of insect spermatozoa flagella.

In addition to conventional planar and helical flagellar waves, insect sperm flagella have also been observed to display a double-wave structure characterized by the presence of two superimposed helical waves. In this paper, we present a hydrodynamic investigation of the locomotion of insect spermatozoa exhibiting the double-wave structure, idealized here as superhelical waves. Resolving the hydrodynamic interactions with a non-local slender body theory, we predict the swimming kinematics of these superhelical swimmers based on experimentally collected geometric and kinematic data. Our consideration provides insight into the relative contributions of the major and minor helical waves to swimming; namely, propulsion is owing primarily to the minor wave, with negligible contribution from the major wave. We also explore the dependence of the propulsion speed on geometric and kinematic parameters, revealing counterintuitive results, particularly for the case when the minor and major helical structures are of opposite chirality. PMID:22298815

Pak, On Shun; Spagnolie, Saverio E; Lauga, Eric

2012-08-01

32

Hydrodynamic forces and surface topography: Centimeter-scale spatial variation in wave forces

Hydrodynamic forces and surface topography: Centimeter-scale spatial variation in wave forces forces. The intertidal zone of wave-swept rocky shores is one of the most physically stressful (Denny et al. 2003). The high water velocities in the intertidal zone can impose large hydrody- namic

Denny, Mark

33

Ferrofluid Photonic Dipole Contours

NASA Astrophysics Data System (ADS)

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.

Snyder, Michael; Frederick, Jonathan

2008-03-01

34

COUPLING OF HYDRODYNAMIC AND WAVE MODELS FOR STORM TIDE SIMULATIONS: A CASE STUDY FOR HURRICANE for the simulation of storm tides. The hydrodynamic model employed for calculating tides and surges is ADCIRC-2DDI) astronomical tides, 2) inflows from tributaries, 3) meteorological effects (winds and pressure), and 4) waves

Central Florida, University of

35

Wake II model for hydrodynamic forces on marine pipelines including waves and currents

The Wake II model for the determination of the hydrodynamic forces on marine pipelines is extended to include currents and waves. There are two main differences between the Wake II and the traditional model. First, in the Wake II model the velocity is modified to include the pipe's encounter with the wake flow when the velocity reverses. Second, the model

Said R Sabag; Billy L Edge; Iwan Soedigdo

2000-01-01

36

Numerical simulation of wave scouring beneath marine pipeline using smoothed particle hydrodynamics

In this paper a smoothed particle hydrodynamics (SPH) approach is presented to simulate scouring due to wave around a marine pipeline on a sloping sea bed. The proposed method is similar to so-called SPH projection method and consists of three steps. The first two steps play the role of prediction, while in the third step a Poisson Equation is used

A. MIRMOHAMMADI; M. J. KETABDARI

2011-01-01

37

NO EFFECT OF HYDRODYNAMIC SHOCK WAVE ON PROTEIN FUNCTIONALITY OF BEEF MUSCLE

Technology Transfer Automated Retrieval System (TEKTRAN)

The protein functionality of meat proteins after treatment with hydrodynamic shock wave was determined. Frankfurters (cooked to 71 deg C) were evaluated for cooking yield, CIE L*a*b*, nitrosylhemochrome, Texture Profile Analysis (hardness, cohesiveness), and stress and strain (torsion testing). Comp...

38

A Dynamic Analysis of Hydrodynamic Wave Journal Bearings

NASA Technical Reports Server (NTRS)

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.

Ene, Nicoleta M.; Dimofte, Florin; Keith, Theo G.

2008-01-01

39

Synthesis of Hydrodynamic and Wave Models with Sediment Data in a Shallow Tidal Embayment.

NASA Astrophysics Data System (ADS)

Hydrodynamic and wave models have been established for Tampa Bay in Florida and the approaches to the Bay on the west Florida Shelf of the Gulf of Mexico. It uses an unstructured, bathymetry-following flexible mesh (bffm) which adapts to the complex coastline and inter-connected navigation channels. The model packages came from DHI Water & Environment. The hydrodynamics were calibrated against tidal currents in the main navigation channel supplied by the NOAA/NOS PORTS system operated by the University of South Florida. The model was validated for a period in September 2004 (including the passing of the hurricane Frances) using data from six tidal gauges in the Bay. Wave data were collected at several stations around the Bay in 2004 and from June 2005 to December 2006. These data were compared with both a full spectrum and parametric wave model. Production runs of all models were made for a 9 month period using measured surface elevation as boundary conditions extending from spring 2004 to winter 2005 and measured wind data at a station within the Bay. The results were used to derive exchange times and local wave climates around the Bay. The hydrodynamic and wave models were then used to determine sediment mobility. It is found that current is the most important influence on sediments in the deeper parts of the Bay but waves dominate sediment dynamics in the shallow regions of the Bay. Swell waves penetrate only a limited distance into the Bay. Comparisons are made with maps of bottom sediment and coastal habitat obtained from various data sources.

Jakobsen, N. G.; Kaergaard, K.; Jensen, J. H.

2006-12-01

40

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

Pu, Jaan Hui; Shao, Songdong

2012-01-01

41

Magnetization and susceptibility of ferrofluids.

A second-order Taylor series expansion of the free energy functional provides analytical expressions for the magnetic field dependence of the free energy and of the magnetization of ferrofluids, here modeled by dipolar Yukawa interaction potentials. The corresponding hard core dipolar Yukawa reference fluid is studied within the framework of the mean spherical approximation. Our findings for the magnetic and phase equilibrium properties are in quantitative agreement with previously published and new Monte Carlo simulation data. PMID:21694251

Szalai, I; Dietrich, S

2008-05-21

42

A Stability Analysis for a Hydrodynamic Three-Wave Journal Bearing

NASA Technical Reports Server (NTRS)

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.

Ene, Nicoleta M.; Dimofte, Florin; Keith, Theo G., Jr.

2007-01-01

43

Cyclone waves directly affect the density, structure and local distribution of coral assemblages by acting as agents of mortality and colony transport. Using the meteorological record, hydrodynamic formulations and risk analysis, we predict some demographic consequences of cyclones for massive corals growing in different regions of the Great Barrier Reef. Analysis of shear, compression and tension forces generated by waves

S. R. Massel; T. J. Done

1993-01-01

44

Hydrodynamics of the Oscillating Wave Surge Converter in the open ocean

A potential flow model is derived for a large flap-type oscillating wave energy converter in the open ocean. Application of the Green's integral theorem in the fluid domain yields a hypersingular integral equation for the jump in potential across the flap. Solution is found via a series expansion in terms of the Chebyshev polynomials of the second kind and even order. Several relationships are then derived between the hydrodynamic parameters of the system. Comparison is made between the behaviour of the converter in the open ocean and in a channel. The degree of accuracy of wave tank experiments aiming at reproducing the performance of the device in the open ocean is quantified. Parametric analysis of the system is then undertaken. It is shown that increasing the flap width has the beneficial effect of broadening the bandwidth of the capture factor curve. This phenomenon can be exploited in random seas to achieve high levels of efficiency.

Renzi, E

2012-01-01

45

Smoothed-particle-hydrodynamics modeling of dissipation mechanisms in gravity waves.

The smoothed-particle-hydrodynamics (SPH) method has been used to study the evolution of free-surface Newtonian viscous flows specifically focusing on dissipation mechanisms in gravity waves. The numerical results have been compared with an analytical solution of the linearized Navier-Stokes equations for Reynolds numbers in the range 50-5000. We found that a correct choice of the number of neighboring particles is of fundamental importance in order to obtain convergence towards the analytical solution. This number has to increase with higher Reynolds numbers in order to prevent the onset of spurious vorticity inside the bulk of the fluid, leading to an unphysical overdamping of the wave amplitude. This generation of spurious vorticity strongly depends on the specific kernel function used in the SPH model. PMID:23496634

Colagrossi, Andrea; Souto-Iglesias, Antonio; Antuono, Matteo; Marrone, Salvatore

2013-02-01

46

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.

Behdadfar, Behshid, E-mail: bbehdadfar@ma.iut.ac.ir [Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Kermanpur, Ahmad [Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Sadeghi-Aliabadi, Hojjat [School of Pharmacy, Isfahan Pharmaceutical Research Center, Isfahan University of Medical Sciences, Isfahan (Iran, Islamic Republic of); Morales, Maria del Puerto [Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco 28049, Madrid (Spain); Mozaffari, Morteza [Department of Physics, Razi University, Kermanshah (Iran, Islamic Republic of)

2012-03-15

47

Analysis of hydrodynamic behaviors of multiple net cages in combined wave-current flow

NASA Astrophysics Data System (ADS)

Numerical simulation is performed to analyze the hydrodynamic response of a net cage and submerged mooring grid system exposed to waves and current. A series of experiments are conducted to validate the numerical model of net cage and grid mooring system. The numerical results of this model correspond with those obtained from experimental observations. Then, the numerical simulation of a multi-cage and mooring system under the action of waves combined with current is conducted. The influence of waves and current directions and the length of grid lines on the cage responses are discussed. The twin mooring system and the orthogonal mooring system are compared. Results show that for the orthogonal mooring system, the maximum tension force on the anchor line of the four-cage system is less than four times of that of the single-cage system, when both waves and current travel along the x-axis. The minimum net cage volume holding coefficient of the single-cage system is smaller than that of the four-cage system. The amplitude of the mooring line tension force for the twin mooring system is larger than the orthogonal mooring system.

Xu, Tiao-Jian; Zhao, Yun-Peng; Dong, Guo-Hai; Li, Yu-Cheng; Gui, Fu-Kun

2013-05-01

48

Controlling ferrofluid permeability across the blood–brain barrier model.

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

Shi, Di; Sun, Linlin; Mi, Gujie; Sheikh, Lubna; Bhattacharya, Soumya; Nayar, Suprabha; Webster, Thomas J

2014-02-21

49

Controlling ferrofluid permeability across the blood-brain barrier model

NASA Astrophysics Data System (ADS)

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).

Shi, Di; Sun, Linlin; Mi, Gujie; Sheikh, Lubna; Bhattacharya, Soumya; Nayar, Suprabha; Webster, Thomas J.

2014-02-01

50

Viscoelastic properties of ferrofluids D. N. Chirikov,1

magnetic field. The first theories of the magnetorheological effects in ferrofluids 3,4 deal with very. 6Â14 . Both of them can induce strong magnetorheological effects in ferrofluids 8 . Unfortunately

Fedotov, Sergei

51

From AdS/CFT correspondence to hydrodynamics. II. Sound waves

As a non-trivial check of the non-supersymmetric gauge/gravity duality, we use a near-extremal black brane background to compute the retarded Green's functions of the stress-energy tensor in N=4 super-Yang-Mills (SYM) theory at finite temperature. For the long-distance, low-frequency modes of the diagonal components of the stress-energy tensor, hydrodynamics predicts the existence of a pole in the correlators corresponding to propagation of sound waves in the N=4 SYM plasma. The retarded Green's functions obtained from gravity do indeed exhibit this pole, with the correct values for the sound speed and the rate of attenuation.

G. Policastro; D. T. Son; A. O. Starinets

2002-10-22

52

Linear and nonlinear dust ion acoustic waves using the two-fluid quantum hydrodynamic model

NASA Astrophysics Data System (ADS)

The linear and nonlinear properties of a dust ion acoustic wave (DIAW) propagating in an electron-dust-ion plasma are investigated from both analytical and numerical perspectives by employing the two-fluid quantum hydrodynamic model. Ions and dust are assumed to be mobile while electrons are considered to be inertialess. Furthermore, quantum effects (diffraction as well as statistic) due to ions and electrons are incorporated. It is emphasized that the linear dispersion characteristics of the DIAW depend on the quantum diffraction effects of both ions and electrons as well as on the dust concentration. The one-dimensional Korteweg-deVries equation is derived for the quantum DIAW using the reductive perturbative technique. It is observed that the quantum electron diffraction term shrinks the width while the dust concentration enhances both the amplitude and width of the soliton.

Masood, W.; Mushtaq, A.; Khan, R.

2007-12-01

53

Linear and nonlinear dust ion acoustic waves using the two-fluid quantum hydrodynamic model

The linear and nonlinear properties of a dust ion acoustic wave (DIAW) propagating in an electron-dust-ion plasma are investigated from both analytical and numerical perspectives by employing the two-fluid quantum hydrodynamic model. Ions and dust are assumed to be mobile while electrons are considered to be inertialess. Furthermore, quantum effects (diffraction as well as statistic) due to ions and electrons are incorporated. It is emphasized that the linear dispersion characteristics of the DIAW depend on the quantum diffraction effects of both ions and electrons as well as on the dust concentration. The one-dimensional Korteweg-deVries equation is derived for the quantum DIAW using the reductive perturbative technique. It is observed that the quantum electron diffraction term shrinks the width while the dust concentration enhances both the amplitude and width of the soliton.

Masood, W.; Mushtaq, A.; Khan, R. [Theoretical Plasma Physics Division, P. O. Nilore, Islamabad (Pakistan)

2007-12-15

54

NASA Astrophysics Data System (ADS)

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.

Rablau, Corneliu; Vaishnava, Prem; Regmi, Rajesh; Sudakar, Chandran; Black, Correy; Lawes, Gavin; Naik, Ratna; Lavoie, Melissa; Kahn, David

2009-03-01

55

Magnetic Hyperthermia in ferrofluid-gel composites

NASA Astrophysics Data System (ADS)

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.

Nemala, Humeshkar; Wadehra, Anshu; Dixit, Ambesh; Regmi, Rajesh; Vaishnava, Prem; Lawes, Gavin; Naik, Ratna

2012-02-01

56

Magnetic pressure and shape of ferrofluid seals in cylindrical structures

NASA Astrophysics Data System (ADS)

This paper presents a three-dimensional analytical model for studying the shape and the pressure of ferrofluid seals in totally ironless structures. This three-dimensional analytical approach is based on the exact calculation of the magnetic field components created by ring permanent magnets whose polarizations are either radial or axial. We assume that the ferromagnetic particles of the ferrofluid are saturated. Moreover, the permanent magnets (neodymium iron boron) used in the considered applications create a magnetic field which is much higher than the magnetic field created by the magnetic particles in the ferrofluid so the latter is neglected. Nevertheless, the static behavior of the ferrofluid seal depends on both the magnetic field produced by the permanent magnets and the saturation magnetization of the ferrofluid particles. Furthermore, the accurate knowledge of the ferrofluid seal shape as well as the magnetic pressure inside the ferrofluid seal is very useful for the design of devices using both permanent magnets and ferrofluid seals. It is emphasized here that our structures are completely ironless and thus, there are no iron-base piston for these structures. Then, this paper makes a review of the main structures using ring permanent magnets and ferrofluid seals. For each ironless structure, the shape and the pressure of the ferrofluid seals are determined.

Ravaud, R.; Lemarquand, G.; Lemarquand, V.

2009-08-01

57

Measuring the magnetization of nano ferro-fluid with D.C electromagnetic application.

A new electromagnetic measuring technology of smaller size, simple structure and high efficiency was proposed in this study. Based on the ferrohydrodynamics (FHD) theory with the absence of viscous effect, the device, independent to the geometry of electro-magnetism, was set up to determine the magnetization of ferrofluid containing magnetite microcrystals of 10 approximately 100 nm size. To strengthen the magnetic intensity, a soft iron was placed across the solenoid of about 2,800 turns, and operated at a DC voltage of 10 V approximately 30 V. The magnetic intensity in this radial component had been found to be most active at this specific setting, which significantly influenced the hydrodynamics of the ferrofluid. With the rise of the liquid, caused by the action of the radial magnetic field, the permeability ratio of ferrofluid at about 1.32 approximately 1.24 could be successfully estimated by the FHD Bernoulli equation. If compared with the experimental data of 1.27, given by Matsumoto Yushi-Seiyaka Co., the relative errors are no more than 5%. PMID:19916445

Ho, Je-Ee; Young, Hong T

2009-07-01

58

The design of a ferrofluid magnetic pipette.

An electromagnetic pipette using a ferrofluid was designed to sample liquid volumes smaller than 0.2 microliter. Submicroliter sample sizes are desirable for reducing the amount of costly reagents and reducing sample requirement for large-scale analysis. The pipette consists of four electromagnets arranged such that air-gaps are aligned to accommodate a tube. A light-hydrocarbon-based ferrofluid is contained in the tube and acts as a plunger. The position of the ferrofluid in the tube was controlled to within 0.2 mm by combining adjacent air-gap magnetic fields. The position of the ferrofluid as a function of time and magnetic pressure as a function of position was measured in one electromagnet air-gap from the device. Maximum pressure measured was 770 Pa which corresponds to a maximum velocity of 0.9 cm/s. The assembled pipette weighs approximately 25 g, and it measures 4 cm long, 1 cm wide, and 3 cm high. PMID:9216126

Greivell, N E; Hannaford, B

1997-03-01

59

Passive Magnetic Bearing With Ferrofluid Stabilization

NASA Technical Reports Server (NTRS)

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.

Jansen, Ralph; DiRusso, Eliseo

1996-01-01

60

Pattern storage and recognition using ferrofluids

NASA Astrophysics Data System (ADS)

An implementation of an associative memory based on a ferromagnetic nanocolloid is proposed. The design contains inductive input and output units for training the ferrofluid as well as sensors incorporated into the output units for performing recall. Using Monte Carlo simulations of the system we demonstrate the possibility of creating nanoparticle configurations that can serve to associate input/output pattern pairs.

Ban, Shuai; Korenivski, V.

2006-04-01

61

NASA Astrophysics Data System (ADS)

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 implementations currently running, there is the need to: assess their forecast skill; quantitatively evaluate if the new, coupled systems provide better performances than the uncoupled ones; individuate weaknesses and eventual time trends in the forecasts quality, their causes, and actions to improve the systems. This work presents a first effort aimed to satisfy such need. We employ in situ and remote sensing data collected starting from November 2011, in particular: temperature and salinity data collected during several oceanographic cruises, sea surface temperature derived from satellite measurements, waves, sea level and currents measurements from oceanographic buoys and platforms; specific observational activities funded by the Italian Flagship project RITMARE allowed to collect new measurements in NA coastal areas. Data-model comparison is firstly performed with exploratory qualitative comparisons in order to highlight discrepancies between observed and forecasted data, then a quantitative comparison is performed through the computation of standard statistical scores (root mean square error, mean error, mean bias, standard deviation, cross-correlation). Results are plotted in Taylor diagrams for a rapid evaluation of the overall performances.

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

62

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.

Lacy, J.R.; Sherwood, C.R.; Wilson, D.J.; Chisholm, T.A.; Gelfenbaum, G.R.

2005-01-01

63

NASA Astrophysics Data System (ADS)

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.

Chabchoub, A.; Hoffmann, N.; Onorato, M.; Genty, G.; Dudley, J. M.; Akhmediev, N.

2013-08-01

64

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

Chabchoub, A; Hoffmann, N; Onorato, M; Genty, G; Dudley, J M; Akhmediev, N

2013-08-01

65

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 Sekiya et al. (2003). We found that the non-linear terms in the hydrodynamical equations neglected by Sekiya et al. (2003) 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.

Hitoshi Miura; Taishi Nakamoto

2006-11-09

66

Ferrofluid-based microchip pump and valve

Fluid control is a key element in the performance of microfluidic “lab-on-a-chip” devices. The development of integrated multi-function micro-chemical reactors and analysis platforms depends upon on-chip valving and pumping. In this work, microfluidic valves and pumps were fabricated from etched glass substrates each bonded to a second glass substrate lid that had ultrasonically drilled access holes. The devices contained ferrofluid

Herb Hartshorne; Christopher J. Backhouse; William E. Lee

2004-01-01

67

Measuring the transverse magnetization of rotating ferrofluids.

We report on measurements of the transverse magnetization of a ferrofluid rotating as a rigid body in a constant magnetic field, H0, applied perpendicular to the axis of rotation. The rotation of the fluid leads to a nonequilibrium situation, where the ferrofluid magnetization M and the magnetic field within the sample, H, are no longer parallel to each other. The off-axis magnetization perpendicular to H0 is measured as a function of both the applied magnetic field H0 and the angular frequency Omega. The latter ranges from a few hertz to frequencies well above a characteristic inverse Brownian relaxation time. Our experimental results strongly indicate that the transverse magnetization is caused only by a small fraction of the colloidal ferromagnetic particles. The effect of the polydispersity of the ferrofluid is discussed. Experimental results are compared to predictions based on several theoretical models. A single-time relaxation approach for the so-called effective field and a field-dependent Debye relaxation of M yield reasonably good shapes of the curves of transverse magnetization vs Omega. However, like the other models, they overestimate their magnitudes. PMID:16605646

Embs, J P; May, S; Wagner, C; Kityk, A V; Leschhorn, A; Lücke, M

2006-03-01

68

A seismic sensor based on IPMC combined with ferrofluids

In this paper preliminary results regarding a seismic sensor based on Ionic Polymer Metal Composite is presented. The device consists of a vial, filled with ferrofluid, in which an IPMC cantilever beam, used as a sensor, is encapsulated. External magnetic fields are imposed in order to modify the density of the ferrofluid in which the IPMC sensor is immersed. Considering

Bruno Ando; Salvatore Baglio; Angela Beninato; Salvatore Graziani; Francesco Pagano; Elena Umana

2012-01-01

69

Ferrofluid aggregates phase transitions in the planar magnetic field

The influence of the cyclic heating and cooling on properties of the aggregates (aka "ferrofluid clusters") in a ferrofluid, which made on the basis of magnetite nanoparticles, are investigated. The heating of the ferrofluid layer with such aggregates leads to equalization of the concentration between high- and low-concentrated phases. The temperature of the equalization of the phase concentrations was determined at different values of an external constant magnetic field, which was applied parallel to the layer of the ferrofluid. The temperature of the destruction of a periodic structure of the magnetic aggregates, which were formed during cooling of a homogeneous phase of the ferrofluid, was obtained at the different values of the applied external magnetic field.

V. F. Kovalenko; M. V. Petrychuk; B. M. Tanygin; S. I. Shulyma

2014-04-21

70

NASA Astrophysics Data System (ADS)

It is demonstrated that the method of smoothed particle hydrodynamics can be used to study the flow structure in a cavitating medium with a high concentration of the gas phase and to describe the process of inversion of the two-phase state of this medium: transition from a cavitating fluid to a system consisting of a gas and particles. A numerical analysis of the dynamics of the state of a hemispherical droplet under shock-wave loading shows that focusing of the shock wave reflected from the free surface of the droplet leads to the formation of a dense, but rapidly expanding cavitation cluster at the droplet center. By the time t = 500 µs, the bubbles at the cluster center not only coalesce and form a foam-type structure, but also transform to a gas-particle system, thus, forming an almost free rapidly expanding zone. The mechanism of this process defined previously as an internal "cavitation explosion" of the droplet is validated by means of mathematical modeling of the problem by the smoothed particle hydrodynamics method. The deformation of the cavitating droplet is finalized by its decomposition into individual fragments and particles.

Davydov, M. N.; Kedrinskii, V. K.

2013-11-01

71

Hydrodynamics of the double-wave structure of insect spermatozoa flagella

helical structures are of opposite chirality. Keywords: swimming micro-organisms; flagellar hydrodynamics into the fluid opposite to the direction of locomotion. Micro-organisms mean- while inhabit in a world of low stringent constraints on a micro-organism's locomotive capabilities. Many micro-organisms propel themselves

Lauga, Eric

72

Acoustic waves in a stratified atmosphere. II. Three-dimensional hydrodynamics

NASA Astrophysics Data System (ADS)

We investigate analytically the propagation of linear waves in a three-dimensional, nonmagnetic, isothermal atmosphere stratified in plane-parallel layers. The motivation is to study oscillations in the nonmagnetic chromosphere and to assess the limitations of one-dimensional simulations of the K_2v bright point phenomenon. We consider an impulsively excited acoustic disturbance, emanating from a point source, and propagating outward as a spherical acoustic wave accompanied by an internal gravity wave. The waves amplify exponentially in the upward direction. A significant wave amplitude is therefore found only in a relatively narrow cone about the vertical. The amplitude of the wave decreases with time. Because of the lateral spread, the wave amplitude decays faster in 2D and 3D simulations than in 1D. The initial pulse, which travels at the sound speed, carries most of the energy injected into the medium. Subsequent wave crests leave the source region at ever-increasing phase speed, but slow to the sound speed as they approach the head of the wave. Important conclusions from the 3D solution that were not anticipated from the plane-wave solution are: 1. The bulk of the energy is emitted in the upward (and downward) direction; much less goes into the horizontal direction. 2. The wave profile narrows from the initial pulse through the amplitude maxima in the wake of the pulse. As a consequence of both points, the shock-heated regions in the wake of the initial pulse would weaken in strength and shrink in size. 3. The height at which a given wave amplitude is reached spreads outward from the symmetry axis of the disturbance as the wave propagates upward. Thus the diameter of the shock-heated region would increase as the acoustic wave travels upward in the atmosphere.

Bodo, G.; Kalkofen, W.; Massaglia, S.; Rossi, P.

2000-02-01

73

From AdS\\/CFT correspondence to hydrodynamics. II. Sound waves

As a non-trivial check of the non-supersymmetric gauge\\/gravity duality, we use a near-extremal black brane background to compute the retarded Green's functions of the stress-energy tensor in = 4 super-Yang-Mills (SYM) theory at finite temperature. For the long-distance, low-frequency modes of the diagonal components of the stress-energy tensor, hydrodynamics predicts the existence of a pole in the correlators corresponding to

Giuseppe Policastro; Dam T. Son; Andrei O. Starinets

2002-01-01

74

We discuss 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 contribution of the annihilation interaction in the quantum hydrodynamic equations and in spectrum of waves in magnetized electron-positron plasmas. We consider propagation of waves parallel and perpendicular to an external magnetic field. We also consider oblique propagation of longitudinal waves. We derive set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory for the linear wave behavior in absence of external fields. We calculate contribution of the Darwin...

Andreev, Pavel A

2014-01-01

75

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.

Hoeke, R.; Storlazzi, C.; Ridd, P.

2011-01-01

76

Drops deformation and magnetic permeability of a ferrofluid emulsion

In the paper the novel soft magnetic composite system is investigated. A ferrofluid emulsion studied demonstrates the strong magnetic properties which are atypical for commonly known emulsions. Interaction of ferrofluid emulsions with a magnetic field is considered. Structural transformations in these media, such as deformation of emulsion microdroplets and emulsion inversion, are studied. The changes in the relative permeability of emulsion associated with structural transformations are investigated. The theory of the observed phenomena is developed, and the feasibility of effectively controlling the magnetic properties of ferrofluid emulsions by applying a magnetic field is demonstrated.

Arthur Zakinyan; Yury Dikansky

2011-04-17

77

Damping induced by ferrofluid seals in ironless loudspeaker

NASA Astrophysics Data System (ADS)

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.

Pinho, M.; Génevaux, J. M.; Dauchez, N.; Brouard, B.; Collas, P.; Mézière, H.

2014-04-01

78

Artificial viscosity in simulation of shock waves by smoothed particle hydrodynamics

NASA Astrophysics Data System (ADS)

This paper reconsiders artificial viscosity in smoothed particle hydrodynamics in order to prevent interparticle penetration, unwanted heating, and unphysical solutions. The coefficients in the Monaghan’s standard artificial viscosity are considered as a time variable, and we propose a restriction on them such that we avoid the undesired effects in the subsonic regions. We use the shock formation in adiabatic and isothermal cases to study the ability of this modified artificial viscosity recipe. Our computer experiments show that the proposal appears to work and the accuracy of this restriction is acceptable.

Nejad-Asghar, M.; Khesali, A. R.; Soltani, J.

2008-02-01

79

NASA Astrophysics Data System (ADS)

Based on rigid kinematics theory and lumped mass method, a mathematical model of the two net cages of grid mooring system under waves is developed. In order to verify the numerical model, a series of physical model tests have been carried out. According to the comparisons between the simulated and the experimental results, it can be found that the simulated and the experimental results agree well in each wave condition. Then, the forces on the mooring lines and the floating collar movement are calculated under different wave conditions. Numerical results show that under the same condition, the forces on the bridle ropes are the largest, followed by forces on the main ropes and the grid ropes. The horizontal and the vertical float collar motion amplitudes increase with the increase of wave height, while the relationship of the horizontal motion amplitude and the wave period is indistinct. The vertical motion amplitude of the two cages is almost the same, while on the respect of horizontal motion amplitude, cage B (behind cage A, as shown in Fig. 4) moves much farther than cage A under the same wave condition. The inclination angle of the floating system both in clockwise along y axis and the counter one enlarges a little with the increase of wave height.

Chen, Chang-ping; Zhao, Yun-peng; Li, Yu-cheng; Dong, Guo-hai; Zheng, Yan-na

2012-03-01

80

Waves in Radial Gravity Using Magnetic Fluid

NASA Technical Reports Server (NTRS)

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.

Ohlsen, Daniel R.; Hart, John E.; Weidman, Patrick D.

1996-01-01

81

NASA Astrophysics Data System (ADS)

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.

Dyer, Ashton; Blondin, J. M.; Reynolds, S. P.

2014-01-01

82

Elongational flow effects on the vortex growth out of Couette flow in ferrofluids.

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

Altmeyer, S; Leschhorn, A; Hoffmann, Ch; Lücke, M

2013-05-01

83

Magnetic-Field Induced Diffraction Patterns from Ferrofluids

NASA Astrophysics Data System (ADS)

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.

Rablau, Corneliu; Vaishnava, Prem; Lawes, Gavin; Naik, Ratna

2011-04-01

84

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 population of states with different spin direction is included in the spin density (magnetization). In this paper we derive a QHD model, which separately describes spin-up electrons and spin-down electrons. Hence we consider electrons with different projection of spin on the preferable direction as two different species of particles. We show that numbers of particles with different spin direction do not conserve. Hence the continuity equations contain sources of particles. These sources are caused by the interactions of spins with magnetic field. Terms of similar nature arise in the Euler equation. We have that z-projection of the spin density is no longer an independent variable. It is proportional to difference between concentrations of electrons with spin-up and electrons with spin-down. In terms of new model we consider propagation of waves in magnetized plasmas of degenerate electrons and motionless ions. We show that new form of QHD equations gives all solutions obtained from traditional form of QHD equations with no distinguish of spin-up and spin-down states. But it also reveals a sound-like solution we call the spin-electron acoustic wave. Coincidence of most solutions is expected since we started derivation with the same basic equation.

Pavel A. Andreev

2014-05-04

85

Gas response to the underlying stellar spirals is explored for M81 using unmagnetized hydrodynamic simulations. Constrained within the uncertainty of observations, 18 simulations are carried out to study the effects of selfgravity and to cover the parameter space comprising three different sound speeds and three different arm strengths. The results are confronted with those data observed at wavelengths of 8 $\\mu$m and 21 cm. In the outer disk, the ring-like structure observed in 8 $\\mu$m image is consistent with the response of cold neutral medium with an effective sound speed 7 km s$^{-1}$, while for the inner disk, the presence of spiral shocks can be understood as a result of 4:1 resonances associated with the warm neutral medium with an effective sound speed 19 km s$^{-1}$. Simulations with single effective sound speed alone cannot simultaneously explain the structures in the outer and inner disks. This justifies the coexistence of cold and warm neutral media in M81. The anomalously high streaming motions...

Wang, Hsiang-Hsu; Taam, Ronald E; Feng, Chien-Chang; Lin, Lien-Hsuan

2014-01-01

86

Ferrofluid spin-up flows from uniform and non-uniform rotating magnetic fields

When ferrofluid in a cylindrical container is subjected to a rotating azimuthally directed magnetic field, the fluid "spins up" into an almost rigid-body rotation where ferrofluid nanoparticles have both a linear and an ...

Khushrushahi, Shahriar Rohinton

2010-01-01

87

Wake II model for hydrodynamic forces on marine pipelines for the wave plus current case

's equation. In the Wake II model the velocity is modified to include the pipe's encounter with the wake flow when the velocity reverses. The model also uses time dependent drag and lift coefficients. For the wave plus current case, the flow field is assumed...

Ramirez Sabag, Said

1999-01-01

88

NASA Astrophysics Data System (ADS)

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 Hydrodynamics Front Fitting Artificial Dissipation The Adaptive Grid The TITAN Code References

Mihalas, Dimitri

89

Experimental investigation of magnetically driven flow of ferrofluids in porous media

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.

Borglin, S.E.; Moridis, G.J.; Oldenburg, C.M.

1998-08-01

90

NASA Astrophysics Data System (ADS)

Context. With the progress of observational constraints on stellar rotation and on the angular velocity profile in stars, it is necessary to understand how angular momentum is transported in stellar interiors during their whole evolution. In this context, more highly refined dynamical stellar evolution models have been built that take into account transport mechanisms. Aims: Internal gravity waves (IGWs) excited by convective regions constitute an efficient transport mechanism over long distances in stellar radiation zones. They are one of the mechanisms that are suspected of being responsible for the quasi-flat rotation profile of the solar radiative region up to 0.2 R?. Therefore, we include them in our detailed analysis started in Paper I of the main physical processes responsible for the transport of angular momentum and chemical species in stellar radiation zones. Here, we focus on the complete interaction between differential rotation, meridional circulation, shear-induced turbulence, and IGWs during the main sequence. Methods: We improved the diagnosis tools designed in Paper I to unravel angular momentum transport and chemical mixing in rotating stars by taking into account IGWs. The star's secular hydrodynamics is treated using projection on axisymmetric spherical harmonics and appropriate horizontal averages that allow the problem to be reduced to one dimension while preserving the non-diffusive character of angular momentum transport by the meridional circulation and IGWs. Wave excitation by convective zones is computed at each time-step of the evolution track. We choose here to analyse the evolution of a 1.1 M?, Z? star in which IGWs are known to be efficient. Results: We quantify the relative importance of the physical mechanisms that sustain meridional currents and that drive the transport of angular momentum, heat, and chemicals when IGWs are taken into account. First, angular momentum extraction, Reynolds stresses caused by IGWs, and viscous stresses sustain a large-scale multi-cellular meridional circulation. This circulation in turn advects entropy, which generates temperature fluctuations and a new rotation profile because of thermal wind. Conclusions: We have refined our diagnosis of secular transport processes in stellar interiors. We confirm that meridional circulation is sustained by applied torques, internal stresses, and structural readjustments, rather than by thermal imbalance, and we detail the impact of IGWs. These large-scale flows then modify the thermal structure of stars, their internal rotation profile, and their chemical stratification. The tools we developed in Paper I and generalised for the present analysis will be used in the near future to study secular hydrodynamics of rotating stars taking into account IGWs in the whole Hertzsprung-Russell diagram.

Mathis, S.; Decressin, T.; Eggenberger, P.; Charbonnel, C.

2013-10-01

91

Linear viscoelasticity of an inverse ferrofluid.

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

de Gans, B J; Blom, C; Philipse, A P; Mellema, J

1999-10-01

92

Viscoelasticity of mono- and polydisperse inverse ferrofluids.

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

Saldivar-Guerrero, Ruben; Richter, Reinhard; Rehberg, Ingo; Aksel, Nuri; Heymann, Lutz; Rodriguez-Fernández, Oliverio S

2006-08-28

93

The extrinsic hysteresis behavior of dilute binary ferrofluids.

We report on the magnetization behavior of dilute binary ferrofluids based on ?-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 ?(A) = 0.2% and B-particle volume fractions ?(B) = 0.1% and ?(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 ?-Fe(2)O(3)/Ni(2)O(3) ferrofluids with ?(A) = 0.2% and binary ferrofluids with ?(A) = 0.2% and ?(B) = 1.0%, the magnetization curves do not behave in this way. Additionally, at high field (750 kA/m), the binary ferrofluid with ?(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 ?(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

Lin, Lihua; Li, Jian; Lin, Yueqiang; Liu, Xiaodong; Chen, Longlong; Li, Junming; Li, Decai

2014-10-01

94

Magneto-optical and rheological behaviors of oil-based ferrofluids and magnetorheological fluids

NASA Astrophysics Data System (ADS)

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 behavior. Thus, using optical microscopy we were able to explain the magneto-optical and rheological behaviors of the ferrofluids and magnetorheological fluids investigated.

Getzie, Travis

95

Sink-float ferrofluid separator applicable to full scale nonferrous scrap separation

NASA Technical Reports Server (NTRS)

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.

1973-01-01

96

Stress relaxation in a ferrofluid with clustered nanoparticles.

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

Borin, Dmitry Yu; Zubarev, Andrey Yu; Chirikov, Dmitry N; Odenbach, Stefan

2014-10-01

97

We demonstrate experimentally multi-bound-soliton solutions of the Nonlinear Schr\\"odinger equation (NLS) in the context of surface gravity waves. In particular, the Satsuma-Yajima N-soliton solution with N=2,3,4 is investigated in detail. Such solutions, also known as breathers on zero background, lead to periodic self-focussing in the wave group dynamics, and the consequent generation of a steep localized carrier wave underneath the group envelope. Our experimental results are compared with predictions from the NLS for low steepness initial conditions where wave-breaking does not occur, with very good agreement. We also show the first detailed experimental study of irreversible massive spectral broadening of the water wave spectrum, which we refer to by analogy with optics as the first controlled observation of hydrodynamic supercontinuum a process which is shown to be associated with the fission of the initial multi-soliton bound state into individual fundamental solitons similar to what has been observe i...

Chabchoub, A; Onorato, M; Genty, G; Dudley, J M; Akhmediev, N

2013-01-01

98

NASA Astrophysics Data System (ADS)

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 models with the data recorded on SPEs. This long-term goal requires taking into account the 3D structure and thus a comprehensive characterization of the site.

Larmat, C. S.; Rougier, E.; Knight, E.; Yang, X.; Patton, H. J.

2013-12-01

99

Nonlinear hydrodynamic effects induced by Rayleigh surface acoustic wave in sessile droplets.

We report an experimental and numerical characterization of three-dimensional acoustic streaming behavior in small droplets of volumes (1-30 ?l) induced by surface acoustic wave (SAW). We provide a quantitative evidence of the existence of strong nonlinear nature of the flow inertia in this SAW-driven flow over a range of the newly defined acoustic parameter F{NA}=F?/(?/R_{d})?0.01, which is a measure of the strength of the acoustic force to surface tension, where F is the acoustic body force, ? is the SAW wavelength, ? is the surface tension, and R{d} is the droplet radius. In contrast to the widely used Stokes model of acoustic streaming, which generally ignores such a nonlinearity, we identify that the full Navier-Stokes equation must be applied to avoid errors up to 93% between the computed streaming velocities and those from experiments as in the nonlinear case. We suggest that the Stokes model is valid only for very small acoustic power of ?1 ?W (F{NA}<0.002). Furthermore, we demonstrate that the increase of F{NA} above 0.45 induces not only internal streaming, but also the deformation of droplets. PMID:23214873

Alghane, M; Chen, B X; Fu, Y Q; Li, Y; Desmulliez, M P Y; Mohammed, M I; Walton, A J

2012-11-01

100

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

Simard, J Marc; Pampori, Adam; Keledjian, Kaspar; Tosun, Cigdem; Schwartzbauer, Gary; Ivanova, Svetlana; Gerzanich, Volodymyr

2014-07-15

101

Magnetization behavior of ferrofluids with cryogenically imaged dipolar chains.

Theories and simulations have demonstrated that field-induced dipolar chains affect the static magnetic properties of ferrofluids. Experimental verification, however, has been complicated by the high polydispersity of the available ferrofluids, and the morphology of the dipolar chains was left to the imagination. We now present the concentration- and field-dependent magnetization of particularly well-defined ferrofluids, with a low polydispersity, three different average particle sizes, and with dipolar chains that were imaged with and without magnetic field using cryogenic transmission electron microscopy. At low concentrations, the magnetization curves obey the Langevin equation for noninteracting dipoles. Magnetization curves for the largest particles strongly deviate from the Langevin equation but quantitatively agree with a recently developed mean-field model that incorporates the field-dependent formation and alignment of flexible dipolar chains. The combination of magnetic results and in situ electron microscopy images provides original new evidence for the effect of dipolar chains on the field-dependent magnetization of ferrofluids. PMID:21694243

Klokkenburg, M; Erné, B H; Mendelev, V; Ivanov, A O

2008-05-21

102

Thermodynamics of ferrofluids in applied magnetic fields

NASA Astrophysics Data System (ADS)

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 (B2 and B3) are evaluated as functions of the dipolar coupling constant ?, and the Langevin parameter ?. The formula for B3 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 ? and ? are examined. Very good agreement between theory and computation is demonstrated for the realistic values ??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 is robust.

Elfimova, Ekaterina A.; Ivanov, Alexey O.; Camp, Philip J.

2013-10-01

103

We discuss 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 contribution of the annihilation interaction in the quantum hydrodynamic equations and in spectrum of waves in magnetized electron-positron plasmas. We consider propagation of waves parallel and perpendicular to an external magnetic field. We also consider oblique propagation of longitudinal waves. We derive set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory for the linear wave behavior in absence of external fields. We calculate 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 electron-positron plasmas including the Darwin and annihilation interactions. Existence of conserving helicity in electron-positron quantum plasmas of spinning particles with the Darwin and annihilation interactions is demonstrated. We show that annihilation interaction plays an important role in quantum electron-positron plasmas giving contribution of the same magnitude as the spin-spin interaction.

Pavel A. Andreev

2014-04-18

104

Dynamics of Single Chains of Suspended Ferrofluid Particles

NASA Technical Reports Server (NTRS)

We present an experimental study of the dynamics of isolated chains made of super-paramagnetic particles under the influence of a magnetic field. The motivation of this work is to understand if the chain fluctuations exist and, if it does, how does the fluctuation affect chain aggregation. We find that single chains strongly fluctuate and that the characteristic frequency of their fluctuations is inversely proportional to the magnetic field strength. The higher the field the lower the characteristic frequency of the chain fluctuations. In the high magnetic field limit, chains behave like rigid rods without any internal motions. In this work, we used ferrofluid particles suspended in water. These particles do not have any intrinsic magnetization. Once a magnetic field is applied, a dipole moment is induced in each particle, proportional to the magnetic field. A dipolar magnetic interaction then occurs between particles. If dipole-dipole magnetic energy is higher than the thermal energy, the result is a structure change inside the dipolar fluid. The ratio of these two energies is expressed by a coupling constant lambda as: lambda = (pi(a(exp 3))(chi(exp 2))(mu(sub 0))(H(sub 0))(exp 2))/18kT Where a is the particle radius, mu(sub 0) is the vacuum magnetic permeability, H(sub 0) the applied magnetic field, k the Boltzmann constant and T the absolute temperature. If lambda > 1, magnetic particles form chains along the field direction. The lateral coalescence of several chains may form bigger aggregates especially if the particle volume fraction is high. While many studies and applications deal with the rheological properties and the structural changes of these dipolar fluids, this work focuses on the understanding of the chain dynamics. In order to probe the chain dynamics, we used dynamic light scattering (DLS) in self-beating mode as our experimental technique. The experimental geometry is such that the scattering plane is perpendicular to the magnetic field. 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 particles per chain N(t) at a given time and to the diffusion coefficient of an isolated particle

Cutillas, S.; Liu, J.

1999-01-01

105

NASA Astrophysics Data System (ADS)

Pore fabric anisotropy is a common feature of many sedimentary rocks. In this paper we report results from a comparative study on the anisotropy of a porous sandstone (Crab Orchard) using anisotropy of magnetic susceptibility (AMS), acoustic wave velocity and fluid permeability techniques. Initially, we characterise the anisotropic pore fabric geometry by impregnating the sandstone with magnetic ferro-fluid and measuring its AMS. The results are used to guide subsequent measurements of the anisotropy of acoustic wave velocity and fluid permeability. These three independent measures of anisotropy are then directly compared. Results show strong positive correlation between the principal directions given from the AMS, velocity anisotropy and permeability anisotropy. Permeability parallel to the macroscopic crossbedding observed in the sandstone is 240% higher than that normal to it. P and S-wave velocity anisotropy and AMS show mean values of 19.1%, 4.8% and 3.8% respectively, reflecting the disparate physical properties measured.

Benson, Philip M.; Meredith, Philip G.; Platzman, Ellen S.

2003-10-01

106

Preparation of a biocompatible magnetic film from an aqueous ferrofluid

NASA Astrophysics Data System (ADS)

Very promising nanoparticles for biomedical applications or in medical drug targeting are superparamagnetic nanoparticles based on a core consisting of iron oxides (SPION) that can be targeted through external magnets. Polyvinyl alcohol (PVA) is a unique synthetic biocompatible polymer that can be chemically cross-linked to form a gel. Biotechnology applications of magnetic gels include biosensors, targeted drug delivery, artificial muscles and magnetic buckles. These gels are produced by incorporating magnetic materials in the polymer composites. In this paper we report the synthesis of an aqueous ferrofluid and the preparation of a biocompatible magnetic gel with polyvinyl alcohol and glutharaldehyde (GTA). HClO 4 was used to induce the peptization since this kind of ferrofluid does not have surfactant. The magnetic gel was dried to generate a biocompatible film.

Albornoz, Cecilia; Jacobo, Silvia E.

2006-10-01

107

Small-amplitude oscillatory shear magnetorheology of inverse ferrofluids.

A comprehensive investigation is performed on highly monodisperse silica-based inverse ferrofluids under small-amplitude oscillatory shear in the presence of external magnetic fields up to 1 T. The effect of particle volume fraction and continuous medium Newtonian viscosity is thoroughly investigated. Experimental results for storage modulus are used to validate existing micromechanical magnetorheological models assuming different particle-level field-induced structures. PMID:20345105

Ramos, Jose; de Vicente, Juan; Hidalgo-Alvarez, Roque

2010-06-15

108

Disclosed are processes for monitoring and control of underground contamination, which involve the application of ferrofluids. Two broad uses of ferrofluids are described: (1) to control liquid movement by the application of strong external magnetic fields; and (2) to image liquids by standard geophysical methods.

Moridis, George J. (Oakland, CA); Oldenburg, Curtis M. (Mill Valley, CA)

2001-01-01

109

NASA Astrophysics Data System (ADS)

Observations in all electromagnetic bands show that many supernova remnants (SNRs) have a very aspherical shape. This can be the result of asymmetries in the supernova explosion or a clumpy circumstellar medium. We study the generation of inhomogeneities and the mixing of elements arising from these two sources in multidimensional hydrodynamic simulations of the propagation of a supernova blast wave into a cloudy environment. We model a specific SNR, Vela Jr (RX J0852.0-4622). By comparing our results with recent observations, we can constrain the properties of the explosion. We find that a very energetic explosion of several 1051 erg occurring roughly about 800 years ago is consistent with the shape and emission of the SNR, as well as a supernova with an energy closer to the canonical value of 1051 erg a few thousand years ago.

Obergaulinger, M.; Iyudin, A. F.; Müller, E.; Smoot, G. F.

2014-01-01

110

The effect of suspended Fe3O4 nanoparticle size on magneto-optical properties of ferrofluids

NASA Astrophysics Data System (ADS)

We investigate the effect of hydrodynamic particle size on the magnetic field induced light transmission and transmitted speckle pattern in water based ferrofluids containing functionalized Fe3O4 nanoparticles of size ranging from 15 to 46 nm. Three water-based magnetic nanofluids, containing Fe3O4 nanoparticles functionalized with poly-acrylic acid (PAA), tetra-methyl ammonium hydroxide (TMAOH) and phosphate, are used in the present study. In all three cases, the transmitted light intensity starts decreasing above a certain magnetic field (called first critical field) and becomes a minimum at another field (second critical field). These two critical fields signify the onset of linear aggregation process and zippering transitions between fully grown chains, respectively. Both these critical fields shift towards a lower magnetic field with increasing hydrodynamic diameter, due to stronger magnetic dipolar interactions. The first and the second critical fields showed a power law dependence on the hydrodynamic diameters. The dipolar resonances occurring at certain values of the scatterer size, leads to the field induced extinction of light. Both the onset of chaining and zippering transitions were clearly evident in the time dependent transmitted light intensity. Above the first critical field, the lobe part of the transmitted intensity and the lobe speckle contrast values increase with increasing external magnetic field due to reduced Brownian motion of the field induced aggregates. The speckle contrast was highest for nanoparticle with the largest hydrodynamic diameter, due to reduced Brownian motion. These results provide better insight into field dependent light control in magnetic colloids, which may find interesting applications in magneto-optical devices.

Brojabasi, Surajit; Muthukumaran, T.; Laskar, J. M.; Philip, John

2015-02-01

111

In this paper, we develop a formalism in order to incorporate the contribution of internal gravity waves to the transport of angular momentum and chemicals over long time-scales in stars. We show that the development of a double peaked shear layer acts as a filter for waves, and how the asymmetry of this filter produces momentum extraction from the core when it is rotating faster than the surface. Using only this filtered flux, it is possible to follow the contribution of internal waves over long (evolutionary) time-scales. We then present the evolution of the internal rotation profile using this formalism for stars which are spun down via magnetic torquing. We show that waves tend to slow down the core, creating a "slow" front that may then propagate from the core to the surface. Further spin down of the surface leads to the formation of a new front. Finally we show how this momentum transport reduces rotational mixing in a 1.2Msun, Z=0.02 model, leading to a surface lithium abundance in agreement with observations in the Hyades.

S. Talon; C. Charbonnel

2005-05-11

112

Fluorimetric assay of interaction of protein with ferrofluids

NASA Astrophysics Data System (ADS)

Magnetic iron oxide nanoparticles are inherently biocompatible and are amenable to post synthesis surface modification, making them excellent candidates for many important applications. If the above can be achieved in a single-step i.e., in situ synthesis and functionalization, the results are expected to be more dramatic for sensitive detection of biomolecules. For any application, it is necessary to confer a high level of binding specificity through surface chemistry, which can be introduced by using biological moieties that possess lock-and-key interactions, like those observed in antibody-antigen and enzyme-substrate recognition. In this paper, we have synthesized water based ferrofluids with serum albumin, the major protein component of blood. A series of other ferrofluids using different biocompatible polymers have also been studied with respect to their size determined by transmission electron microscopy, magnetic behavior with the aid of vibrating sample magnetometry and binding capability to bovine serum albumin by quenching of its native fluorescence. From our results, it can be inferred that binding has taken place between magnetic particles and biomolecules, the binding constants of which indirectly reveal the efficiency of the interaction.

Mallik, Dhriti; Mir, Aparna; Bhattacharya, Soumya; Nayar, Suprabha

2011-01-01

113

Raman spectroscopy investigation of magnetite nanoparticles in ferrofluids

NASA Astrophysics Data System (ADS)

Raman spectroscopy is used to investigate magnetite nanoparticles dispersed in two types of ?-cyclodextrin suspensions. An approach is presented for characterization of the magnetic core in liquid surrounding at room temperature and atmospheric pressure. The effect of elevating laser power on the structural stability and chemical composition of magnetite in the ferrofluids is discussed. The data are compared with data from dry by-products from the fluids. Powder samples undergo total phase transition from magnetite to hematite at laser power of 1.95 mW. The same nanoparticles in the fluid undergo transformation at 9 mW, but no hematite positions appear throughout that investigation. The Raman spectra revealed that the main phase of the magnetic core in the fluids is magnetite. That is indicated by a strong and non-diminishing in intensity peak at 670 cm -1. A second phase is present at the nanoparticle's surface with Raman spectroscopy unveiling maghemite-like and small fractions of goethite-like structures. The Fourier transform infrared spectroscopy investigations confirm deviations in the surface structure and also point to the fact that the oxidation process starts at an early stage after formation of the nanoparticles. The analyses of the infrared data also show that ?-cyclodextrin molecules retain their cyclic character and the coating does not affect the oxidation process once the particles are evicted from the fluids. A Mössbauer spectroscopy measurement on a ferrofluidic sample is also presented.

Slavov, L.; Abrashev, M. V.; Merodiiska, T.; Gelev, Ch.; Vandenberghe, R. E.; Markova-Deneva, I.; Nedkov, I.

2010-07-01

114

A comparative study of different ferrofluid constitutive equations.

NASA Astrophysics Data System (ADS)

Ferrofluids are stable colloidal suspensions of fine ferromagnetic monodomain nanoparticles in a non-conducting carrier fluid.The particles are coated with a surfacant to avoid agglomeration and coagulation.Brownian motion keeps the nanoparticles from settling under gravity.In recent years these fluids have found several applications including in liquid seals in rotary shafts for vacuum system and in hard disk drives of personal computers,in cooling and damping of loud speakers, in shock absorbers and in biomedical applications. A continuum description of ferrofluids was initiated by Neuringer and Rosensweig [1] but the theory had some limitations. In subsequent years,several authors have proposed generalization of the above theory.Some of these are based upon the internal particle rotation concept, some are phemonological,some are based upon a thermodynamic framework,some employ statistical approach and some have used the dynamic mean field approach.The results based upon these theories ane in early stages and inconclusive. Our purpose is, first, to critically examine the basic foundations of these equations and then study the pedictions obtained in all the theories related to an experimental as well as a theoretical study. [1]J.L.Neuringer and R.E. Rosensweig, Physics Fluids,7.1727 (1964)..

Kaloni, Purna

2011-11-01

115

The mechanisms that lead to bulk flow within a ferrofluid-filled container subjected to a rotating uniform magnetic field are experimentally studied. There are two prevailing theories: spin diffusion theory and flow due ...

Snively, Michael John

2011-01-01

116

Design and manufacture of a modular cylindrical apparatus for ferrofluid experimentation

Ferrofluids, colloidal suspensions of coated magnetic nanoparticles inside a carrier fluid, respond to externally applied magnetic fields. This thesis addresses the behavior of these fluids when subjected to an azimuthally ...

Schoen, Katrina Leigh

2011-01-01

117

Motion of a droplet on a planar surface has applications in droplet-based lab on a chip technology. This paper reports the experimental results of the shape, contact angles, and motion of ferrofluid droplets driven by a permanent magnet on a planar homogeneous surface. The water-based ferrofluid in use is a colloidal suspension of single-domain magnetic nanoparticles. The effect of the magnetic field on the apparent contact angle of the ferrofluid droplet was first investigated. The results show that an increasing magnetic flux decreases the apparent contact angle of a sessile ferrofluid droplet. Next, the dynamic contact angle was investigated by observing the shape and the motion of a sessile ferrofluid droplet. The advancing and receding contact angles of the moving ferrofluid were measured at different moving speeds and magnetic field strengths. The measured contact angles were used to estimate the magnitude of the forces involved in the sliding motion. Scaling analysis was carried out to derive the critical velocity, beyond which the droplet is not able to catch up with the moving magnet. PMID:20608704

Nguyen, Nam-Trung; Zhu, Guiping; Chua, Yong-Chin; Phan, Vinh-Nguyen; Tan, Say-Hwa

2010-08-01

118

ERIC Educational Resources Information Center

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)

Lafrance, Pierre

1978-01-01

119

Field dependent Anisotropic Micro Rheological and Microstructrual properties of Ferrofluids

We have measured micro-rheological and micro-structural properties of a super paramagnetic ferrofluid made of Mn$_{0.75}$Zn$_{0.25}$Fe$_2$O$_4$ (MZF) nanoparticles, using passive microrheology in a home built inverted microscope. Thermal motion of a probe microsphere was measured for different values of an applied external magnetic field and analysed. The analysis shows anisotropy in magnetoviscous effect. Additional microrheological properties, such as storage modulus and loss modulus and their transition is seen. Following the analysis given in \\cite{Oliver Muller, Stefan Mahle}, we have obtained microstructural properties such as elongational flow coefficient $\\lambda_2$, relaxation time constant $\\tau$, coefficient of dissipative magnetization $\\alpha$ etc. From a single set of viscosity data, all the above parameters could be obtained. Our values for the above parameters are in agreement with earlier theoretical calculations and macro-rheological experimental measurements.

Balaji Yendeti; G. Thirupathi; Ashok Vudaygiri; R. Singh

2014-02-20

120

Development of magnetic chromatography to sort polydisperse nanoparticles in ferrofluids.

Whatever the strategy of synthesis, nanoparticles in magnetic fluids commonly feature a broad size distribution. However, the presence of several size populations in ferrofluids is often problematic because of the close relationship between the efficiency of the nanoparticles and their physicochemical properties. In this work, a magnetic size sorting procedure is developed in order to reduce this polydispersity, using the magnetic properties of the iron oxide nanoparticles. This magnetic sorting with an adjustable magnetic field allows isolation of the small superparamagnetic particles as well as the larger particles. Magnetometry, nuclear magnetic relaxation dispersion profiles and transmission electron microscopy were successfully used to check the efficiency of the magnetic sorting procedure, which was shown to work as a 'magnetic' chromatography. PMID:20586034

Forge, Delphine; Gossuin, Yves; Roch, Alain; Laurent, Sophie; Elst, Luce Vander; Muller, Robert N

2010-01-01

121

Magnetocoalescence of ferrofluid droplets in a flat microfluidic channel

NASA Astrophysics Data System (ADS)

In this work we present the numerical study of the deformation and the coalescence of two ferrofluid droplets in a uniform applied magnetic field. Employing the boundary element method (BEM), we numerically solve the Darcy equation in a flat microfluidic channel by applying the magnetic normal stress as a boundary condition at the interfaces of droplets. The occurrence of different numerical regimes is summarized in the two phase diagrams scanned by the distance between two droplets, magnetic capillary number, and magnetic permeability. We also show the existence of the critical separation of two droplets where the coalescence of the droplets is inhibited. This critical value is independent of the applied-magnetic-field intensity, although it depends on the permeability ratio of droplet and continuous phase.

Kadivar, Erfan

2014-04-01

122

Photonic Dipole Contours of Ferrofluid Hele-Shaw Cell

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. 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 dipole nature. A simple way of explaining this work is to think of the old magnetic iron filling experiments; but now each iron filling is a molecule floating in a liquid. Each molecule has the freedom to act as an independent lens that can be aligned by an external magnetic field. Because each lens directs light, the external field can be analyzed by following the light paths captured in the photographs.

Michael Snyder; Jonathan Frederick

2009-03-31

123

Coupling of blocking and melting in cobalt ferrofluids

NASA Astrophysics Data System (ADS)

Zero-field-cooling and field-cooling (FC) measurements were performed on ferrofluids of cobalt magnetic nanoparticles (MNPs) in various organic solvent. Two peaks, one broad peak corresponding to the blocking transition (TB), and one sharp peak corresponding to the melting of the solvent (TM), were observed. Furthermore, for a given MNP size, when the blocking and melting transitions were superposed by choosing an appropriate solvent, the strongest intensity of the sharp peak at the melting point of the organic solvent was obtained. This observation is explained by applying the M spectrum theory. Additionally, a first order, melting-induced magnetic phase transformation was observed at the melting point of the solvent. Associated with the first order phase transition and the supercooling effect, a thermal hysteresis loop in the FC curve was observed.

Wen, Tianlong; Liang, Wenkel; Krishnan, Kannan M.

2010-05-01

124

A circular ferrofluid driven microchip for rapid polymerase chain reaction.

In the past few years, much attention has been paid to the development of miniaturized polymerase chain reaction (PCR) devices. After a continuous flow (CF) PCR chip was introduced, several CFPCR systems employing various pumping mechanisms were reported. However, the use of pumps increases cost and imposes a high requirement on microchip bonding integrity due to the application of high pressure. Other significant limitations of CFPCR devices include the large footprint of the microchip and the fixed cycle number which is dictated by the channel layout. In this paper, we present a novel circular close-loop ferrofluid driven microchip for rapid PCR. A small ferrofluid plug, containing sub-domain magnetic particles in a liquid carrier, is driven by an external magnet along the circular microchannel, which in turn propels the PCR mixture through three temperature zones. Amplification of a 500 bp lambda DNA fragment has been demonstrated on the polymethyl methacrylate (PMMA) PCR microchip fabricated by CO(2) laser ablation and bonded by a low pressure, high temperature technique. Successful PCR was achieved in less than 4 min. Effects of cycle number and cycle time on PCR products were investigated. Using a magnet as the actuator eliminates the need for expensive pumps and provides advantages of low cost, small power consumption, low requirement on bonding strength and flexible number of PCR cycles. Furthermore, the microchip has a much simpler design and smaller footprint compared to the rectangular serpentine CFPCR devices. To demonstrate its application in forensics, a 16-loci short tandem repeat (STR) sample was successfully amplified using the PCR microchip. PMID:17653343

Sun, Y; Kwok, Y C; Nguyen, N T

2007-08-01

125

NSDL National Science Digital Library

We will review some basic properties of waves and then further explore sound and light. For a quick overview of some properties of all waves, click on this first site. Make sure you fill out your hand out as you work! Waves and Wave Motion : Describing Waves Practice what you've already learned about waves with this site: Waves This site will let you play around some more with transverse waves: Wave on a String Sound waves are mechanical waves, ...

Petersen, Mrs.

2014-05-27

126

The gap between two concentric rotating cylinders is filled with a ferrofluid. A homogeneous magnetic field is applied parallel to the cylinder axis. The stability of the circular Couette flow is analyzed with different models that take into account the polydispersity of the ferrofluid to a varying degree. Their results are compared and their merits are discussed. PMID:19392050

Leschhorn, A; Lücke, M; Hoffmann, C; Altmeyer, S

2009-03-01

127

NASA Astrophysics Data System (ADS)

Using a ferrofluid of cobalt-zinc ferrite nanoparticles (Co0.8Zn0.2Fe2O4) coated with oleic acid and suspended in ethanol, we have fabricated a 2D photonic crystal (PC) by the application of an external magnetic field perpendicular to the plane of the ferrofluid. The 2D PC is made by rods of nanoparticles organized in a hexagonal structure. By means of the plane-wave expansion method, we study its photonic band structure (PBS) which depends on the effective permittivity and on the area ratio of the liquid phase. Additionaly, taking into account the Maxwell-Garnett theory we calculated the effective permittivity of the rods. We have found that the effective refractive index of the ferrofluid increases with its magnetization. Using these results we calculate the band structure of the photonic crystal at different applied magnetic fields, finding that the increase of the applied magnetic field shifts the band structure to lower frequencies with the appearance of more band gaps.

López, J.; González, Luz E.; Quiñonez, M. F.; Porras-Montenegro, N.; Zambrano, G.; Gómez, M. E.

2014-04-01

128

Any single permanent or electro magnet will always attract a magnetic fluid. For this reason it is difficult to precisely position and manipulate ferrofluid at a distance from magnets. We develop and experimentally demonstrate optimal (minimum electrical power) 2-dimensional manipulation of a single droplet of ferrofluid by feedback control of 4 external electromagnets. The control algorithm we have developed takes into account, and is explicitly designed for, the nonlinear (fast decay in space, quadratic in magnet strength) nature of how the magnets actuate the ferrofluid, and it also corrects for electro-magnet charging time delays. With this control, we show that dynamic actuation of electro-magnets held outside a domain can be used to position a droplet of ferrofluid to any desired location and steer it along any desired path within that domain – an example of precision control of a ferrofluid by magnets acting at a distance. PMID:21218157

Probst, R.; Lin, J.; Komaee, A.; Nacev, A.; Cummins, Z.

2010-01-01

129

Mn Zn ferrite nanoparticles for ferrofluid preparation: Study on thermal magnetic properties

NASA Astrophysics Data System (ADS)

Mn 1-xZn xFe 2O 4 (with x varying from 0.1 to 0.5) ferrite nanoparticles used for ferrofluid preparation have been prepared by chemical co-precipitation method and characterized. Characterization techniques like elemental analysis by atomic absorption spectroscopy and spectrophotometry, thermal analysis using simultaneous TG-DTA, XRD, TEM, VSM and Mossbauer spectroscopy have been utilized. The final cation contents estimated agree with the initial degree of substitution. The Curie temperature ( T) and particle size decrease with the increase in zinc substitution. In the case of particles with higher zinc concentration, both ferrimagnetic nanoparticles and particles exhibiting superparamagnetic behavior at room temperature are present. In addition, some of the results obtained by slightly altering the preparation condition are also discussed. The precipitated particles were used for ferrofluid preparation. The fine particles were suitably dispersed in heptane using oleic acid as the surfactant. The volatile nature of the carrier chosen helps in altering the number concentration of the magnetic particles in a ferrofluid. Magnetic properties of the fine particles and ferrofluids are discussed. Ferrofluids having Mn 0.5Zn 0.5Fe 2O 4 particles can be used for the energy conversion application utilizing the magnetically induced convection for thermal dissipation.

Arulmurugan, R.; Vaidyanathan, G.; Sendhilnathan, S.; Jeyadevan, B.

2006-03-01

130

Interfacial stress balances in structured continua and free surface flows in ferrofluids

NASA Astrophysics Data System (ADS)

Interfacial linear and internal angular momentum balances are obtained for a structured continuum and for the special case of a ferrofluid, a suspension of magnetic nanoparticles in a Newtonian fluid. The interfacial balance equations account for the effects of surface tension and surface tension gradient, magnetic surface excess forces, antisymmetric stresses, and couple stresses in driving interfacial flows in ferrofluids. Application of the interfacial balance equations is illustrated by obtaining analytical expressions for the translational and spin velocity profiles in a thin film of ferrofluid on an infinite flat plate when a rotating magnetic field is applied with axis of rotation parallel to the ferrofluid/air interface. The cases of zero and non-zero spin viscosity are considered for small applied magnetic field amplitude. Expressions for the maximum translational velocity, slope of the translational velocity profile at the ferrofluid/air interface, and volumetric flow rate are obtained and their use to test the relevance of spin viscosity and couple stresses in the flow situation under consideration is discussed.

Chaves, Arlex; Rinaldi, Carlos

2014-04-01

131

Interfacial stress balances in structured continua and free surface flows in ferrofluids

Interfacial linear and internal angular momentum balances are obtained for a structured continuum and for the special case of a ferrofluid, a suspension of magnetic nanoparticles in a Newtonian fluid. The interfacial balance equations account for the effects of surface tension and surface tension gradient, magnetic surface excess forces, antisymmetric stresses, and couple stresses in driving interfacial flows in ferrofluids. Application of the interfacial balance equations is illustrated by obtaining analytical expressions for the translational and spin velocity profiles in a thin film of ferrofluid on an infinite flat plate when a rotating magnetic field is applied with axis of rotation parallel to the ferrofluid/air interface. The cases of zero and non-zero spin viscosity are considered for small applied magnetic field amplitude. Expressions for the maximum translational velocity, slope of the translational velocity profile at the ferrofluid/air interface, and volumetric flow rate are obtained and their use to test the relevance of spin viscosity and couple stresses in the flow situation under consideration is discussed.

Chaves, Arlex [School of Chemical Engineering, Universidad Industrial de Santander, Calle 9 Cra. 27, Edificio 24, Bucaramanga, Santander (Colombia)] [School of Chemical Engineering, Universidad Industrial de Santander, Calle 9 Cra. 27, Edificio 24, Bucaramanga, Santander (Colombia); Rinaldi, Carlos, E-mail: carlos.rinaldi@bme.ufl.edu [J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, Florida 32611, USA and Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611 (United States)] [J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, Florida 32611, USA and Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611 (United States)

2014-04-15

132

Ferrofluids based on magnetic Co{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} ferrite nanoparticles were prepared by co-precipitation method from aqueous salt solutions of Co (II), ZnSO{sub 4}, and Fe (III) in an alkaline medium. Ferrofluids placed in an external magnetic field show properties that make them interesting as magneto-controllable soft photonic crystals. Morphological and structural characterizations of the samples were obtained from Scanning Electron Microscopy and Transmission Electron Microscopy studies. Magnetic properties were investigated with the aid of a vibrating sample magnetometer at room temperature. Herein, the Co{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} samples showed superparamagnetic behavior, according to hysteresis loop results. Taking in mind that the Co-Zn ferrite hysteresis loop is very small, our magnetic nanoparticles can be considered soft magnetic material with interesting technological applications. In addition, by using the plane-wave expansion method, we studied the photonic band structure of 2D photonic crystals made of ferrofluids with the same nanoparticles. Previous experimental results show that a magnetic field applied perpendicular to the ferrofluid plane agglomerates the magnetic nanoparticles in parallel rods to form a hexagonal 2D photonic crystal. We calculated the photonic band structure of photonic crystals by means of the effective refractive index of the magnetic fluid, basing the study on the Maxwell-Garnett theory, finding that the photonic band structure does not present any band gaps under the action of applied magnetic field strengths used in our experimental conditions.

López, J., E-mail: javier.lopez@correounivalle.edu.co; González, Luz E.; Quiñonez, M. F.; Gómez, M. E.; Porras-Montenegro, N.; Zambrano, G. [Departamento de Física, Universidad del Valle, A.A. 25360, Cali (Colombia)

2014-05-21

133

NASA Astrophysics Data System (ADS)

Ferrofluids based on magnetic Co0.25Zn0.75Fe2O4 ferrite nanoparticles were prepared by co-precipitation method from aqueous salt solutions of Co (II), ZnSO4, and Fe (III) in an alkaline medium. Ferrofluids placed in an external magnetic field show properties that make them interesting as magneto-controllable soft photonic crystals. Morphological and structural characterizations of the samples were obtained from Scanning Electron Microscopy and Transmission Electron Microscopy studies. Magnetic properties were investigated with the aid of a vibrating sample magnetometer at room temperature. Herein, the Co0.25Zn0.75Fe2O4 samples showed superparamagnetic behavior, according to hysteresis loop results. Taking in mind that the Co-Zn ferrite hysteresis loop is very small, our magnetic nanoparticles can be considered soft magnetic material with interesting technological applications. In addition, by using the plane-wave expansion method, we studied the photonic band structure of 2D photonic crystals made of ferrofluids with the same nanoparticles. Previous experimental results show that a magnetic field applied perpendicular to the ferrofluid plane agglomerates the magnetic nanoparticles in parallel rods to form a hexagonal 2D photonic crystal. We calculated the photonic band structure of photonic crystals by means of the effective refractive index of the magnetic fluid, basing the study on the Maxwell-Garnett theory, finding that the photonic band structure does not present any band gaps under the action of applied magnetic field strengths used in our experimental conditions.

López, J.; González, Luz E.; Quiñonez, M. F.; Gómez, M. E.; Porras-Montenegro, N.; Zambrano, G.

2014-05-01

134

Investigating the energy harvesting potential of ferro-fluids sloshing in base-excited containers

NASA Astrophysics Data System (ADS)

This paper investigates the potential of designing a vibratory energy harvester which utilizes a ferrofluid sloshing in a seismically excited tank to generate electric power. Mechanical vibrations change the orientational order of the magnetic dipoles in the ferrofluid and create a varying magnetic flux which induces an electromotive force in a coil wound around the tank, thereby generating an electric current according to Faraday's law. Several experiments are performed on a cylindrical container of volume 5x10-5 m3 carrying a ferrofluid and subjected to different base excitation levels. Initial results illustrate that the proposed device can be excited at one or multiple modal frequencies depending on the container's size, can exhibit tunable characteristics by adjusting the external magnetic field, and currently produces 28 mV of open-circuit voltage using a base excitation of 2.5 m/s2 at a frequency of 5.5 Hz.

Bibo, A.; Masana, R.; King, A.; Li, G.; Daqaq, M. F.

2012-04-01

135

The influence of coating on interparticle interactions in ferrofluids has been investigated using various techniques such as Mossbauer spectroscopy, magnetometry, transmission electron microscopy, photon correlation spectroscopy, X-ray diffraction, X-ray photoelectron, and resonance micro-Raman spectroscopy. Aging and spin-glass-like behavior was investigated in frozen ferrofluids of various concentrations from dense, initial value of 40 mg of coated nanoparticles per 1 mL of water, to dilute 1:10 (4 mg/mL). The as-prepared nanoparticles, core size 7-8 nm, were subsequently coated with a gummic acid corona of 20 nm thickness, which was observed to prevent agglomeration and to delay aggregation even in dense ferrofluids. The resulting separation of magnetic cores due to the coating eliminated all magnetic interparticle interaction mechanisms, such as exchange and dipoledipole, thus ensuring no aging effects of the magnetic particle system, as manifested in particle agglomeration and precipitation. PMID:19206495

Rabias, Ioannis; Fardis, Michael; Devlin, Eamonn; Boukos, Nikos; Tsitrouli, Danai; Papavassiliou, George

2008-05-01

136

All-optical modulator based on a ferrofluid core metal cladding waveguide chip

NASA Astrophysics Data System (ADS)

We propose a novel optical intensity modulator based on the combination of a symmetrical metal cladding optical waveguide (SMCW) and ferrofluid, where the ferrofluid is sealed in the waveguide to act as a guiding layer. The light matter interaction in the ferrofluid film leads to the formation of a regular nanoparticle pattern, which changes the phase match condition of the ultrahigh order modes in return. When two lasers are incident on the same spot of the waveguide chip, experiments illustrate all-optical modulation of one laser beam by adjusting the intensity of the other laser. A possible theoretical explanation may be due to the optical trapping and Soret effect since the phenomenon is considerable only when the control laser is effectively coupled into the waveguide.

Han, Qing-Bang; Yin, Cheng; Li, Jian; Tang, Yi-Bin; Shan, Ming-Lei; Cao, Zhuang-Qi

2013-09-01

137

Simulation of the magnetization dynamics of diluted ferrofluids in medical applications.

Ferrofluids, which are stable, colloidal suspensions of single-domain magnetic nanoparticles, have a large impact on medical technologies like magnetic particle imaging (MPI), magnetic resonance imaging (MRI) and hyperthermia. Here, computer simulations promise to improve our understanding of the versatile magnetization dynamics of diluted ferrofluids. A detailed algorithmic introduction into the simulation of diluted ferrofluids will be presented. The algorithm is based on Langevin equations and resolves the internal and the external rotation of the magnetic moment of the nanoparticles, i.e., the Néel and Brown diffusion. The derived set of stochastic differential equations are solved by a combination of an Euler and a Heun integrator and tested with respect to Boltzmann statistics. PMID:24163220

Rogge, Henrik; Erbe, Marlitt; Buzug, Thorsten M; Lüdtke-Buzug, Kerstin

2013-12-01

138

We construct the hydrodynamics of quantum critical points with Lifshitz scaling. There are new dissipative effects allowed by the lack of boost invariance. The formulation is applicable, in general, to any fluid with an explicit breaking of boost symmetry. We use a Drude model of a strange metal to study the physical effects of the new transport coefficient. It can be measured using electric fields with non-zero gradients, or via the heat production when an external force is turned on. Scaling arguments fix the resistivity to be linear in the temperature.

Carlos Hoyos; Bom Soo Kim; Yaron Oz

2014-02-09

139

Co–Zn ferrite nanoparticles for ferrofluid preparation: Study on magnetic properties

Co–Zn substituted nanoferrites having stoichiometric composition Co1?xZnxFe2O4 with x ranging from 0.1 to 0.5 were prepared by chemical coprecipitation method. The precipitated particles were used for the preparation of ferrofluid. Ferrofluids having Co0.5Zn0.5Fe2O4 particles could be used for the energy conversion application utilizing the magnetically induced convection for thermal dissipation. The final estimated cation contents, agreed with the initial degree

R. Arulmurugan; G. Vaidyanathan; S. Sendhilnathan; B. Jeyadevan

2005-01-01

140

Elastic stability of silicone ferrofluid internal tamponade (SFIT) in retinal detachment surgery

NASA Astrophysics Data System (ADS)

It has been argued that silicone ferrofluid internal tamponade (SFIT) can provide (360°) tamponade of the retina in retinal detachment surgery. Provided that the produced SFIT is biocompatible, exact knowledge is needed of its elastic stability in the magnetic field produced by the semi-solid magnetic silicon band (MSB) used as a scleral buckle. We propose a quantitative, phenomenological model to estimate the critical magnetic field produced by the MSB that 'closes' retinal tears and results in the reattachment of the retina. The magnetic 'deformation' of SFIT is modeled in accordance with the deformation of a ferrofluid droplet in an external magnetic field.

Voltairas, P. A.; Fotiadis, D. I.; Massalas, C. V.

2001-01-01

141

Mössbauer evidence of 57Fe3O4 based ferrofluid biodegradation in the brain

NASA Astrophysics Data System (ADS)

The ferrofluid, based on 57Fe isotope enriched Fe3O4 nanoparticles, was synthesized, investigated by Mössbauer spectroscopy method and injected transcranially in the ventricle of the rat brain. The comparison of the Mössbauer spectra of the initial ferrofluid and the rat brain measured in two hours and one week after the transcranial injection allows us to state that the synthesized magnetic 57Fe3O4 nanoparticles undergo intensive biodegradation in live brain and, therefore, they can be regarded as a promising target for a new method of radionuclide-free Mössbauer brachytherapy.

Polikarpov, D.; Cherepanov, V.; Chuev, M.; Gabbasov, R.; Mischenko, I.; Nikitin, M.; Vereshagin, Y.; Yurenia, A.; Panchenko, V.

2014-04-01

142

Natural convection of ferrofluids in partially heated square enclosures

NASA Astrophysics Data System (ADS)

In this study, natural convection of ferrofluid in a partially heated square cavity is numerically investigated. The heater is located to the left vertical wall and the right vertical wall is kept at constant temperature lower than that of the heater. Other walls of the square enclosure are assumed to be adiabatic. Finite element method is utilized to solve the governing equations. The influence of the Rayleigh number (104?Ra?5×105), heater location (0.25H?yh?0.75H), strength of the magnetic dipole (0???2), horizontal and vertical location of the magnetic dipole (-2H?a?-0.5H, 0.2H?b?0.8H) on the fluid flow and heat transfer characteristics are investigated. It is observed that different velocity components within the square cavity are sensitive to the magnetic dipole source strength and its position. The length and size of the recirculation zones adjacent to the heater can be controlled with magnetic dipole strength. Averaged heat transfer increases with decreasing values of horizontal position of the magnetic dipole source. Averaged heat transfer value increases from middle towards both ends of the vertical wall when the vertical location of the dipole source is varied. When the heater location is changed, a symmetrical behavior in the averaged heat transfer plot is observed and the minimum value of the averaged heat transfer is attained when the heater is located at the mid of vertical wall.

Selimefendigil, Fatih; Öztop, Hakan F.; Al-Salem, Khaled

2014-12-01

143

NASA Astrophysics Data System (ADS)

Hydrodynamic chromatography (HDC) has experienced a resurgence in recent years for particle and polymer characterization, principally because of its coupling to a multiplicity of physical detection methods. When coupled to light scattering (both multiangle static and quasi-elastic), viscometric, and refractometric detectors, HDC can determine the molar mass, size, shape, and structure of colloidal analytes continuously and as a function of one another, all in a single analysis. In so doing, it exposes the analytes to less shear force (and, hence, less potential for flow-induced degradation) than in, for instance, size-exclusion chromatography. In this review, we discuss the fundamental chromatographic underpinnings of this technique in terms of retention, band broadening, and resolution, and we describe the power of multidetector HDC with examples from the recent literature.

Striegel, André M.; Brewer, Amandaa K.

2012-07-01

144

Characterization of a ferrofluid-based thermomagnetic pump for microfluidic applications

NASA Astrophysics Data System (ADS)

We experimentally characterize the performance of a miniature thermomagnetic pump, where suitably imposed temperature and magnetic field gradients are used to drive ferrofluid in a 2 mm diameter glass capillary tube, without application of any external pressure gradient. Such a pump can operate in a hermetically sealed micro electromechanical system configuration without any moving part, and is thus capable of handling microfluidic samples with little risk of contamination. In the experiment, the ferrofluid in the capillary is exposed to a magnetic field using a solenoid; a small resistive heater wrapped on the tube wall is used to create temperature gradient in such a way that the Kelvin body force in the medium produces a net unbalanced axial component. This causes a thermomagnetic pumping action, transporting the ferrofluid in the capillary tube from the colder end to the warmer end. Performance of the thermomagnetic pump is investigated experimentally to characterize the pump pressure head and discharge under different working conditions, namely, the magnetic field strength, heating power, and ferrofluid properties. A comparison with two other field actuation pumps at comparable length scales is also presented. The pump produces higher output at lower power supplies and magnetic field compared to the other two pumps.

Pal, Souvik; Datta, Amitava; Sen, Swarnendu; Mukhopdhyay, Achintya; Bandopadhyay, Kallol; Ganguly, Ranjan

2011-11-01

145

Ejection of ferrofluid grains using nonlinear acoustic impulses--A particle dynamical study

Photonic and Electronic Materials, State University of New York at Buffalo, Buffalo, New York 14260 with the grains suspended in water e.g., -Fe2O3 and subject the system to a strong, homogeneous magnetic field the ferrofluid grains can be suspended in water or oil and the system is subjected to a strong, homogeneous

Sen, Surajit

146

IDENTIFICATION OF MAGNETIC MINERALS BY SCANNING ELECTRON MICROSCOPE AND APPLICATION OF FERROFLUID

IDENTIFICATION OF MAGNETIC MINERALS BY SCANNING ELECTRON MICROSCOPE AND APPLICATION OF FERROFLUID G in combination with an optical microscope was applied during the last decades. But today, scanning electron are easily identifiable under the scanning electron microscope. The different mineralogy observed

Kletetschka, Gunther

147

A bio-inspired device to detect equilibrium variations using IPMCs and ferrofluids

This work describes a device designed and built to detect the inclination of a body, based on two emerging smart materials: ionic polymer–metal composites (IPMCs) and ferrofluids. The system is bio-inspired and simulates the behavior of the vestibular labyrinth, a biological component of living beings, situated in the inner ear and devoted to perception of the angular acceleration the head

B. Andò; C. Bonomo; L. Fortuna; P. Giannone; S. Graziani; L. Sparti; S. Strazzeri

2008-01-01

148

MAGNETOHYDRODYNAMICS Vol. 48 (2012), No. 4, pp. 615621 INSTABILITY OF THE FERROFLUID LAYER

MAGNETOHYDRODYNAMICS Vol. 48 (2012), No. 4, pp. 615Â621 INSTABILITY OF THE FERROFLUID LAYER. The paper presents an experimental study of the instability of a magnetic fluid layer of finite thickness. The surface structure development becomes specific when the fluid layer is of finite thickness, especially

Paris-Sud XI, UniversitÃ© de

149

Optical Negative Refraction in Ferrofluids with Magnetocontrollability J. P. Huang,1,* Y. M. Liu,3

Optical Negative Refraction in Ferrofluids with Magnetocontrollability Y. Gao,1,2 J. P. Huang,1,* Y October 2009; published 20 January 2010) We numerically demonstrate optical negative refraction of an external dc magnetic field H. The all-angle broadband optical negative refraction

Huang, Ji-Ping

150

Hydrodynamic compressibility of high-strength ceramics

In this study we have developed the techniques to investigate the hydrodynamic response of high-strength ceramics by mixing these powders with copper powder, preparing compacts, and performing shock compression tests on these mixtures. Hydrodynamics properties of silicon carbide, titanium diboride, and boron carbide to 30 GPa were examined by this method, and hydrodynamic compression data for these ceramics have been determined. We have concluded, however, that the measurement method is sensitive to sample preparation and uncertainties in shock wave measurements. Application of the experimental technique is difficult and further efforts are needed.

Grady, D.E.

1993-08-01

151

Hydrodynamic loading of tensegrity structures

NASA Astrophysics Data System (ADS)

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.

Wroldsen, Anders S.; Johansen, Vegar; Skelton, Robert E.; Sørensen, Asgeir J.

2006-03-01

152

Active surfaces: Ferrofluid-impregnated surfaces for active manipulation of droplets

NASA Astrophysics Data System (ADS)

Droplet manipulation and mobility on non-wetting surfaces is of practical importance for diverse applications ranging from micro-fluidic devices, anti-icing, dropwise condensation, and biomedical devices. The use of active external fields has been explored via electric, acoustic, and vibrational, yet moving highly conductive and viscous fluids remains a challenge. Magnetic fields have been used for droplet manipulation; however, usually, the fluid is functionalized to be magnetic, and requires enormous fields of superconducting magnets when transitioning to diamagnetic materials such as water. Here we present a class of active surfaces by stably impregnating active fluids such as ferrofluids into a textured surface. Droplets on such ferrofluid-impregnated surfaces have extremely low hysteresis and high mobility such that they can be propelled by applying relatively low magnetic fields. Our surface is able to manipulate a variety of materials including diamagnetic, conductive and highly viscous fluids, and additionally solid particles.

Khalil, Karim S.; Mahmoudi, Seyed Reza; Abu-dheir, Numan; Varanasi, Kripa K.

2014-07-01

153

Ferrofluid aggregation in chains under the influence of a magnetic field.

The theory of particle association in flexible chains in dilute ferrofluids is generalized to the case of an arbitrarily strengthened magnetic field. The chain distribution in dynamic equilibrium is obtained on the basis of free energy minimization method under the neglect of interchain interaction. The chain partition function is calculated analytically with the help of the rotation matrix technique under the condition when the interparticle dipole-dipole interaction between the nearest neighboring ferroparticles in each chain is taken into account. At weak fields, the chain distribution and the initial susceptibility are shown to be dependent on the value of the correlation coefficient describing the zero field mutual orientational correlations between the magnetic moments of two neighboring ferroparticles in a chain. The internal chain orientational correlations and the field dependent chain lengthening result in higher magnetization of the aggregated ferrofluid in comparison with the Langevin magnetization. PMID:15600619

Mendelev, Valentin S; Ivanov, Alexey O

2004-11-01

154

Magnetic characterization by SQUID and FMR of a biocompatible ferrofluid based on Fe3O4

NASA Astrophysics Data System (ADS)

Biocompatible superparamagnetic iron oxide nanoparticles of magnetite coated with dextran were magnetically characterized using the techniques of SQUID (superconducting quantum interference device) magnetometry and ferromagnetic resonance (FMR). The SQUID magnetometry characterization was performed by isothermal measurements under applied magnetic field using the methods of zero-field-cooling (ZFC) and field-cooling (FC). The magnetic behavior of the nanoparticles indicated their superparamagnetic nature and it was assumed that they consisted exclusively of monodomains. The transition to a blocked state was observed at the temperature TB = (43 ± 1) K for frozen ferrofluid and at (52 ± 1) K for the lyophilized ferrofluid samples. The FMR analysis showed that the derivative peak-to-peak linewidth (?HPP), gyromagnetic factor (g), number of spins (NS), and spin-spin relaxation time (T2) were strongly dependent on both temperature and super-exchange interaction. This information is important for possible nanotechnological applications, mainly those which are strongly dependent on the magnetic parameters.

Gamarra, L. F.; Pontuschka, W. M.; Mamani, J. B.; Cornejo, D. R.; Oliveira, T. R.; Vieira, E. D.; Costa-Filho, A. J.; Amaro, E., Jr.

2009-03-01

155

Rheological investigations on the theoretical predicted “Poisoning” effect in bidisperse ferrofluids

NASA Astrophysics Data System (ADS)

Interparticle interactions in ferrofluids especially the influence of small particles on the agglomeration behaviour of large particles were the topic of numerous theoretical predictions and simulations as well as of experimental investigations. In this context the "Poisoning" effect describes the decrease of the magnetoviscous effect in the presence of small particles in a bidisperse model fluid. In order to examine this effect rheological experiments have been carried out by means of a specially designed rheometer, which allows measurements under the influence of an applied magnetic field. We were able to synthesize ferrofluids with a narrow particle size distribution containing only small or large cobalt ferrite nanoparticles, which were mixed to receive various bidisperse fluid samples. With these fluids changes of the viscous behaviour in a magnetic field have been measured and compared according to their individual compositions.

Siebert, E.; Dupuis, V.; Neveu, S.; Odenbach, S.

2015-01-01

156

Ejection of ferrofluid grains using nonlinear acoustic impulses[emdash] A particle dynamical study

We consider a model dilute ferrofluid with the grains suspended in water (e.g.,[gamma]-Fe[sub 2]O[sub 3]) and subject the system to a strong, homogeneous magnetic field directed perpendicular to the surface such that there is chain formation along the field direction. We show that an appropriate impulse initiated at the base of the container might travel as a nondispersive soliton pulse with sufficient energy to overcome surface tension and eject the ferrofluid grain nearest to the liquid[endash]air interface. The proposed mechanism, if successfully realized in the laboratory, could help design a nozzle-free, ink-jet printer of unparalleled resolution. [copyright] [ital 1999 American Institute of Physics.

Sen, S.; Manciu, M.; Manciu, F.S. (Department of Physics and Center for Advanced Photonic and Electronic Materials, State University of New York at Buffalo, Buffalo, New York 14260 (United States))

1999-09-01

157

Magnetic guidance of ferrofluidic nanoparticles in an in vitro model of intraocular retinal repair

NASA Astrophysics Data System (ADS)

Agarose gel at a concentration of 0.6% was used to simulate the vitreous body of the eye during the infusion of a ferrofluid and the subsequent magnetic concentration of it onto a surrogate retinal surface. The 10 nm Fe3O4 particles in the ferrofluid served to mimic the cobalt particles in a silicone magnetic fluid that is being developed for use as a tamponading agent in magnetic fluid therapies designed to alleviate retinal detachments and other types of retinopathy. Magnetically guided interstitial diffusion of the nanoparticles through up to 20 mm of the gel over periods of 72 h was shown to be possible, thus demonstrating that essentially all points on the retinal surface are reachable from elsewhere in the ocular interior. The nanodynamics of the magnetic and viscous forces at work on the particles during movement through the gel are discussed; in particular the diffusion speeds of the particles are estimated and compared with observations.

Holligan, D. L.; Gillies, G. T.; Dailey, J. P.

2003-06-01

158

Hydrodynamic Simulations of Planetary Rings

NASA Astrophysics Data System (ADS)

Simulations of rings have traditionally been done using N-body methods, granting insight into the interactions of individual ring particles on varying scales. However, due to the scale of a typical ring system and the sheer number of particles involved, a global N-body simulation is too computationally expensive, unless particle collisions are replaced by stochastic forces (Bromley & Kenyon, 2013). Rings are extraordinarily flat systems and therefore are well-suited to existing geophysical shallow-water hydrodynamics models with well-established non-linear advection methods. By adopting a general relationship between pressure and surface density such as a polytropic equation of state, we can modify the shallow-water formula to treat a thin, compressible, self-gravitating, shearing fluid. Previous hydrodynamic simulations of planetary rings have been restricted to axisymmetric flows and therefore have not treated the response to nonaxisymmetric perturbations by moons (Schmidt & Tscharnuter 1999, Latter & Ogilvie 2010). We seek to expand on existing hydrodynamic methods and, by comparing our work with complementary N-body simulations and Cassini observations, confirm the veracity of our results at small scales before eventually moving to a global domain size. We will use non-Newtonian, dynamically variable viscosity to model the viscous transport caused by unresolved self-gravity wakes. Self-gravity will be added to model the dynamics of large-scale structures, such as density waves and edge waves. Support from NASA Outer Planets and Planetary Geology and Geophysics programs is gratefully acknowledged.

Miller, Jacob; Stewart, G. R.; Esposito, L. W.

2013-10-01

159

Mn–Zn ferrite nanoparticles for ferrofluid preparation: Study on thermal–magnetic properties

Mn1?xZnxFe2O4 (with x varying from 0.1 to 0.5) ferrite nanoparticles used for ferrofluid preparation have been prepared by chemical co-precipitation method and characterized. Characterization techniques like elemental analysis by atomic absorption spectroscopy and spectrophotometry, thermal analysis using simultaneous TG-DTA, XRD, TEM, VSM and Mossbauer spectroscopy have been utilized. The final cation contents estimated agree with the initial degree of substitution.

R. Arulmurugan; G. Vaidyanathan; S. Sendhilnathan; B. Jeyadevan

2006-01-01

160

Ferrofluids are colloidal systems composed of a single domain of magnetic nanoparticles with a mean diameter around 30 nm, dispersed in a liquid carrier. Magnetic Co(1-x)ZnxFe2O4 (x=0.25, 0.50, 0.75) ferrite nanoparticles were prepared via co-precipitation method from aqueous salt solutions in an alkaline medium. The composition and structure of the samples were characterized through Energy Dispersive X-ray Spectroscopy and X-ray

J. López; L. F. González-Bahamón; J. Prado; J. C. Caicedo; G. Zambrano; M. E. Gómez; J. Esteve; P. Prieto

2012-01-01

161

The purpose of this study was to compare the effects of magnetic thermal ablation in different porcine tissues using either a singular injection or a continuous infusion of superparamagnetic iron oxide nanoparticles. In the first setting samples of three ferrofluids containing different amounts of iron (1:171, 2:192, and 3:214 mg/ml) were singularly interstitially injected into specimens of porcine liver, kidney, and muscle (n = 5). Then the specimens were exposed to an alternating magnetic field (2.86 kA/m, 190 kHz) generated by a circular coil for 5 min. In the second experimental setup ferrofluid samples were continuously interstitially infused into the tissue specimens during the exposure to the magnetic field. To measure the temperature increase two fiber-optic temperature probes with a fixed distance of 0.5 cm were inserted into the specimens along the puncture tract of the injection needle and the temperature was measured every 15 s. Finally, the specimens were dissected, the diameters of the created thermal lesions were measured, and the volumes were calculated and compared. Compared to continuous infusion, a single injection of ferrofluids resulted in smaller coagulation volumes in all tissues. Significant differences regarding coagulation volume were found in kidney and muscle specimens. The continuous infusion technique led to more elliptically shaped coagulation volumes due to larger diameters along the puncture tract. Our data show the feasibility of magnetic thermal ablation using either a single interstitial injection or continuous infusion for therapy of lesions in muscle, kidney, and liver. Continuous infusion of ferrofluids results in larger zones of necrosis compared to a single injection technique.

Bruners, Philipp, E-mail: bruners@hia.rwth-aachen.de; Hodenius, Michael, E-mail: hodenius@hia.rwth-aachen.de; Baumann, Martin, E-mail: baumann@hia.rwth-aachen.de; Oversohl, Jessica, E-mail: jessy@oversohl.d [Helmholtz-Institute for Biomedical Engineering, RWTH Aachen University, Applied Medical Engineering (Germany); Guenther, Rolf W., E-mail: guenther@rad.rwth-aachen.d [RWTH Aachen University, Department of Diagnostic Radiology (Germany); Schmitz-Rode, Thomas, E-mail: smiro@hia.rwth-aachen.de; Mahnken, Andreas H., E-mail: mahnken@rad.rwth-aachen.d [Helmholtz-Institute for Biomedical Engineering, RWTH Aachen University, Applied Medical Engineering (Germany)

2008-11-15

162

Low-temperature magnetic susceptibility of concentrated ferrofluids: The influence of polydispersity

NASA Astrophysics Data System (ADS)

In this paper we address the question of theoretical explanation of extremely high low-temperature initial magnetic susceptibility of concentrated ferrofluids. These laboratory synthesized samples [A.F. Pshenichnikov, A.V. Lebedev, J. Chem. Phys. 121(11) (2004) 5455; Colloid J. 67(2) (2005) 189] demonstrated the record-breaking values ? ~ 120 - 150 at temperatures ~ 230-240 K. The existing models predict such high susceptibility only under the assumption of unreasonably large dipolar coupling constant, which is out of the range of applicability. Here we calculate the second virial contribution to susceptibility for polydisperse ferrofluid, modeled by the dipolar hard sphere fluid. In the resulting expression there exists the parameter, which plays a part of dipolar coupling constant and which is defined in a form of double averaging of high powers of particle sizes over the granulometric distribution. For real particle size distribution this effective parameter at least twice exceeds the commonly defined polydisperse dipolar coupling constant. We show that the low-temperature magnetic susceptibility of the record-breaking ferrofluids could be explained theoretically on the basis of the first terms of the polydisperse second virial contribution in combination with the second-order modified mean field model.

Ivanov, Alexey O.; Elfimova, Ekaterina A.

2015-01-01

163

Deformation of ferrofluid marbles in the presence of a permanent magnet.

This paper investigates the deformation of ferrofluid marbles in the presence of a permanent magnet. Ferrofluid marbles are formed using a water-based ferrofluid and 1 ?m hydrophobic polytetrafluoride particles. A marble placed on a Teflon coated glass plate deforms under gravity. In the presence of a permanent magnet, the marble is further deformed with a larger contact area. The geometric parameters are normalized by the radius of an undistorted spherical marble. The paper first discusses a scaling relationship between the dimensionless radius of the contact area as well as the dimensionless height and the magnetic Bond number. The dimensionless contact radius is proportional to the fourth root of the magnetic bond number. The dimensionless height scales with the inverse square root of the magnetic Bond number. In the case of a moving marble dragged by a permanent magnet, the deformation is evaluated as the difference between advancing and receding curvatures of the top view. The dimensionless height and the contact diameter of the marble do not significantly depend on the speed or the capillary number. The scaling analysis and experimental data show that the deformation is proportional to the capillary number. PMID:24164113

Nguyen, Nam-Trung

2013-11-12

164

NASA Astrophysics Data System (ADS)

The difference between success or failure of chemotherapy depends not only on the drug itself but also on how it is delivered to its target. Biocompatible ferrofluids (FF) are paramagnetic nanoparticles, that may be used as a delivery system for anticancer agents in locoregional tumor therapy, called "magnetic drug targeting". Bound to medical drugs, such magnetic nanoparticles can be enriched in a desired body compartment (tumor) using an external magnetic field, which is focused on the area of the tumor. Through this form of target directed drug application, one attempts to concentrate a pharmacological agent at its site of action in order to minimize unwanted side effects in the organism and to increase its locoregional effectiveness. Tumor bearing rabbits (VX2 squamous cell carcinoma) in the area of the hind limb, were treated by a single intra-arterial injection (A. femoralis) of mitoxantrone bound ferrofluids (FF-MTX), while focusing an external magnetic field (1.7 Tesla) onto the tumor for 60 minutes. Complete tumor remissions could be achieved in these animals in a dose related manner (20% and 50% of the systemic dose of mitoxantrone), without any negative side effects, like e.g. leucocytopenia, alopecia or gastrointestinal disorders. The strong and specific therapeutic efficacy in tumor treatment with mitoxantrone bound ferrofluids may indicate that this system could be used as a delivery system for anticancer agents, like radionuclids, cancer-specific antibodies, anti-angiogenetic factors, genes etc.

Alexiou, Ch.; Schmid, R.; Jurgons, R.; et al.

165

Algorithm refinement for fluctuating hydrodynamics

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.

Williams, Sarah A.; Bell, John B.; Garcia, Alejandro L.

2007-07-03

166

Hydrodynamics of coalescing binary neutron stars: Ellipsoidal treatment

We employ an approximate treatment of dissipative hydrodynamics in three dimensions to study the coalescence of binary neutron stars driven by the emission of gravitational waves. The stars are modeled as compressible ellipsoids obeying a polytropic equation of state; all internal fluid velocities are assumed to be linear functions of the coordinates. The hydrodynamics equations then reduce to a set

Dong Lai; Stuart L. Shapiro

1995-01-01

167

Viscoelastic Effect on Hydrodynamic Relaxation in Polymer Solutions

The viscoelastic effect on the hydrodynamic relaxation in semidilute polymer solutions is investigated. From the linearized two-fluid model equations, we predict that the dynamical asymmetry coupling between the velocity fluctuations and the viscoelastic stress influences on the hydrodynamic relaxation process, resulting in a wave-number-dependent shear viscosity.

Akira Furukawa

2002-12-11

168

Hydrodynamic instability in warped astrophysical discs

Warped astrophysical discs are usually treated as laminar viscous flows, which have anomalous properties when the disc is nearly Keplerian and the viscosity is small: fast horizontal shearing motions and large torques are generated, which cause the warp to evolve rapidly, in some cases at a rate that is inversely proportional to the viscosity. However, these flows are often subject to a linear hydrodynamic instability, which may produce small-scale turbulence and modify the large-scale dynamics of the disc. We use a warped shearing sheet to compute the oscillatory laminar flows in a warped disc and to analyse their linear stability by the Floquet method. We find widespread hydrodynamic instability deriving from the parametric resonance of inertial waves. Even very small, unobservable warps in nearly Keplerian discs of low viscosity can be expected to generate hydrodynamic turbulence, or at least wave activity, by this mechanism.

Ogilvie, Gordon I

2013-01-01

169

Ergoregion instability: The hydrodynamic vortex

Four-dimensional, asymptotically flat spacetimes with an ergoregion but no horizon have been shown to be linearly unstable against a superradiant-triggered mechanism. This result has wide implications in the search for astrophysically viable alternatives to black holes, but also in the understanding of black holes and Hawking evaporation. Here we investigate this instability in detail for a particular setup which can be realized in the laboratory: the {\\it hydrodynamic vortex}, an effective geometry for sound waves, with ergoregion and without an event horizon.

Leandro A. Oliveira; Vitor Cardoso; Luís C. B. Crispino

2014-05-16

170

Ergoregion instability: The hydrodynamic vortex

Four-dimensional, asymptotically flat spacetimes with an ergoregion but no horizon have been shown to be linearly unstable against a superradiant-triggered mechanism. This result has wide implications in the search for astrophysically viable alternatives to black holes, but also in the understanding of black holes and Hawking evaporation. Here we investigate this instability in detail for a particular setup which can be realized in the laboratory: the {\\it hydrodynamic vortex}, an effective geometry for sound waves, with ergoregion and without an event horizon.

Oliveira, Leandro A; Crispino, Luís C B

2014-01-01

171

NASA Astrophysics Data System (ADS)

Biocompatible, hydrophobic ferrofluids comprised of magnetite nanoparticles dispersed in polydimethylsiloxane show promise as materials for the treatment of retinal detachment. This paper focuses on the motion of hydrophobic ferrofluid droplets traveling through viscous aqueous media, whereby the movement is induced by gradients in external fields generated by small permanent magnets. A numerical method was utilized to predict the force on a spherical droplet, and then the calculated force was used to estimate the time required for the droplet to reach the permanent magnet. The calculated forces and travel times were verified experimentally.

Mefford, Olin T.; Woodward, Robert C.; Goff, Jonathan D.; Vadala, T. P.; St. Pierre, Tim G.; Dailey, James P.; Riffle, Judy S.

2007-04-01

172

We report an in-fiber magnetic field sensor based on magneto-driven optical loss effects, while being implemented in a ferrofluid infiltrated microstructured polymer optical fiber. We demonstrate that magnetic field flux changes up to 2000 gauss can be detected when the magnetic field is applied perpendicular to the fiber axis. In addition, the sensor exhibits high polarization sensitivity for the interrogated wavelengths, providing the possibility of both field flux and direction measurements. The underlying physical and guidance mechanisms of this sensing transduction are further investigated using spectrophotometric, light scattering measurements, and numerical simulations, suggesting photonic Hall effect as the dominant physical, transducing mechanism.

Candiani, A. [Foundation for Research and Technology-Hellas (FORTH), Institute of Electronic Structure and Laser (IESL), Heraklion 70013 Greece (Greece); Department of Information Engineering (DII), University of Parma, Parma 43124 (Italy); Argyros, A.; Leon-Saval, S. G.; Lwin, R. [Institute of Photonics and Optical Science (IPOS), School of Physics, The University of Sydney, Sydney (Australia); Selleri, S. [Department of Information Engineering (DII), University of Parma, Parma 43124 (Italy); Pissadakis, S., E-mail: pissas@iesl.forth.gr [Foundation for Research and Technology-Hellas (FORTH), Institute of Electronic Structure and Laser (IESL), Heraklion 70013 Greece (Greece)

2014-03-17

173

and magnetorheological fluids under external electric or magnetic fields. The columns can behave as different structures with nonmagnetic colloidal microparticles suspended in a host ferrofluid (also called magnetic fluid)1-3 have drawn-like structure, completing a phase transition process, which is similar to the cases of electrorheological fluids

Huang, Ji-Ping

174

of electrorheological fluids and magnetorheological fluids is body-centered tetragonal (bct) lattices.14,15 Because macromolecules.4 Ferrofluids, also known as magnetic fluids, are a colloidal suspension of single) lattices. Similar to electrorheological fluids,16 under appropriate conditions, such as by adjusting

Huang, Ji-Ping

175

Ferrofluid flow in cylindrical and annular geometries under the influence of a uniform rotating magnetic field was studied experimentally using aqueous ferrofluids consisting of low concentrations (<0.01 v/v) of cobalt ferrite nanoparticles with Brownian relaxation to test the ferrohydrodynamic equations, elucidate the existence of couple stresses, and determine the value of the spin viscosity in these fluids. An ultrasound technique was used to measure bulk velocity profiles in the spin-up (cylindrical) and annular geometries, varying the intensity and frequency of the rotating magnetic field generated by a two pole stator winding. Additionally, torque measurements in the cylindrical geometry were made. Results show rigid-body like velocity profiles in the bulk, and no dependence on the axial direction. Experimental velocity profiles were in quantitative agreement with the predictions of the spin diffusion theory, with a value of the spin viscosity of ?10{sup ?8} kg m/s, two orders of magnitude larger than the value estimated earlier for iron oxide based ferrofluids, and 12 orders of magnitude larger than estimated using dimensional arguments valid in the infinite dilution limit. These results provide further evidence of the existence of couple stresses in ferrofluids and their role in driving the spin-up flow phenomenon.

Torres-Diaz, I.; Cortes, A.; Rinaldi, C., E-mail: carlos.rinaldi@bme.ufl.edu [Department of Chemical Engineering, University of Puerto Rico, Mayagüez, Puerto Rico 00681-9000 (United States); Cedeño-Mattei, Y. [Department of Chemistry, University of Puerto Rico, Mayagüez, Puerto Rico 00681-9019 (United States)] [Department of Chemistry, University of Puerto Rico, Mayagüez, Puerto Rico 00681-9019 (United States); Perales-Perez, O. [Department of Engineering Science and Materials, University of Puerto Rico, Mayagüez, Puerto Rico 00681-9044 (United States)] [Department of Engineering Science and Materials, University of Puerto Rico, Mayagüez, Puerto Rico 00681-9044 (United States)

2014-01-15

176

We review the use of Monte Carlo simulations in the description of magnetic nanoparticles dispersed in a liquid carrier. Our main focus is the use of theory and simulation as tools for the description of the properties of ferrofluids. In particular, we report on the influence of polydispersity and short-range interaction on the self-organization of nanoparticles. Such contributions are shown to be extremely important for systems characterized by particles with diameters smaller than 10nm. A new 3D polydisperse Monte Carlo implementation for biocompatible magnetic colloids is proposed. As an example, theoretical and simulation results for an ionic-surfacted ferrofluid dispersed in a NaCl solution are directly compared to experimental data (transmission electron microscopy - TEM, magneto-transmissivity, and electron magnetic resonance - EMR). Our combined theoretical and experimental results suggest that during the aging process two possible mechanisms are likely to be observed: the nanoparticle's grafting decreases due to aggregate formation and the Hamaker constant increases due to oxidation. In addition, we also briefly discuss theoretical agglomerate formation models and compare them to experimental data. PMID:23360743

Bakuzis, Andris Figueiroa; Branquinho, Luis César; e Castro, Leonardo Luiz; e Eloi, Marcos Tiago de Amaral; Miotto, Ronei

2013-05-01

177

Ferrofluid based dispersive-solid phase extraction for spectrophotometric determination of dyes.

For the first time, ferrofluid based dispersive-solid phase extraction (D-SPE) has been applied for determination of trace levels of dyes in aqueous and fish samples. The contaminant used as a model compound was crystal violet (CV), a cationic dye, and was preconcentrated without any derivatization or ion-pair formation. The method is based on rapid injection of ferrofluid into the aqueous sample by a syringe. The sample preparation time is decreased by the fact that the sorbent dispersed in the bulk solution and extraction can be achieved very fast. In this way, the separation of sorbent from the aqueous bulk was achieved by a magnet, and no centrifugation is required. These significant features which obtained with this method are of key interest for routine trace laboratory analysis. The influence of different variables on D-SPE was investigated. Under optimum conditions, the calibration graph was linear over the range of 3.3-90 ?g L(-1), and the enrichment factor (EF) 267 was obtained. Detection limit was 1.51 ?g L(-1) (n=7), and the relative standard deviation of 5.6% at 50 ng mL(-1) was obtained (n=7). The proposed method was successfully applied for the determination of crystal violet in various samples. PMID:23849184

Davudabadi Farahani, Malihe; Shemirani, Farzaneh

2013-10-01

178

Magnetic and structural properties of ferrofluids based on Cobalt-Zinc ferrite nanoparticles

NASA Astrophysics Data System (ADS)

Ferrofluids are colloidal systems composed of a single domain of magnetic nanoparticles with a mean diameter around 10 nm, dispersed in a liquid carrier. Magnetic Co(1-x)ZnxFe2O4 ferrite nanoparticles were prepared via co-precipitation method from aqueous salt solutions in an alkaline medium. The composition and structure of the samples were characterized through EDX and XRD, respectively. Transmission Electron Microscopy studies permitted determining nanoparticle size. Grain size of nanoparticle conglomerates was established via Atomic Force Microscopy. The magnetic behavior of ferrofluids was characterized by Vibrating Sample Magnetometer; and finally, a Magnetic Force Microscope was used to visualize the magnetic domains of nanoparticles. The mean size of the crystallite of nanoparticles determined by using the Scherrer approximation diminished when the Zn concentration increases. The size of the nanoparticles obtained by TEM is in good agreement with the crystallite size calculated from XRD measures. The magnetic properties investigated at room temperature presented super-paramagnetic behavior, determined by the shape of the hysteresis loop. Finally, our magnetic nanoparticles are considered a soft magnetic material.

Prieto, P.; Lopez, J.; Gomez, M. E.; Prado, J.; Caicedo, J.; Zambrano, G.; Gonzalez, L.; Esteve, J.

2012-02-01

179

NASA Astrophysics Data System (ADS)

Ferrofluids containing nanoparticles of Mn0.5Zn0.5Fe2O4 (MZ5) and Fe3O4 (magnetite) have been examined as potential thermal transport media and energy harvesting materials. The ferrofluids were synthesized by chemical co-precipitation and characterized by EDX to determine composition and by TEM to determine particle size and agglomeration. A range of particle coatings and carrier fluids were used to complete the fluid preparation. Commercially available ferrofluids were tested in custom built rigs to demonstrate both thermal pumping (for waste heat removal applications) and power induction (for power conversion and energy harvesting applications). The results indicate that simple ferrofluids possess the necessary properties to remove waste heat, either into thermal storage or for conversion to electrical power.

Sansom, C. L.; Jones, P.; Dorey, R. A.; Beck, C.; Stanhope-Bosumpim, A.; Peterson, J.

2013-06-01

180

Hydrodynamics of vegetated channels

This paper highlights some recent trends in vegetation hydrodynamics, focusing on conditions within channels and spanning spatial scales from individual blades, to canopies or vegetation patches, to the channel reach. At ...

Nepf, Heidi

181

Ion holes in the hydrodynamic regime in ultracold neutral plasmas

We describe the creation of localized density perturbations, or ion holes, in an ultracold neutral plasma in the hydrodynamic regime, and show that the holes propagate at the local ion acoustic wave speed. We also observe the process of hole splitting, which results from the formation of a density depletion initially at rest in the plasma. One-dimensional, two-fluid hydrodynamic simulations describe the results well. Measurements of the ion velocity distribution also show the effects of the ion hole and confirm the hydrodynamic conditions in the plasma.

McQuillen, P.; Castro, J.; Strickler, T.; Bradshaw, S. J.; Killian, T. C. [Department of Physics and Astronomy, Rice University, Houston, Texas 77005 (United States)

2013-04-15

182

Influence of nanoparticle size on the nonlinear optical properties of magnetite ferrofluids

NASA Astrophysics Data System (ADS)

The nonlinear index of refraction (n2) and the two-photon absorption coefficient (?) of water-based ferrofluids made of magnetite nanocrystals of different sizes and with different coatings have been measured through the Z-scan technique, with ultrashort (femtoseconds) laser pulses. Their third-order susceptibility is calculated from the values of n2 and ?. The influence of different particles' coatings and sizes on these nonlinear optical properties are investigated. The values of n2 and ? depend more significantly on the nanoparticles' size than on the particular coating. We observe a decrease of ? as the nanoparticles' diameters decrease, although the optical gap is found to be the same for all samples. The results are interpreted considering modifications in the electronic orbital shape due to the particles' nanosize effect.

Espinosa, D.; Carlsson, L. B.; Neto, A. M. Figueiredo; Alves, S.

2013-09-01

183

NASA Astrophysics Data System (ADS)

Properties of ferrofluid bilayer (modeled as a system of two planar layers separated by a distance h and each layer carrying a soft sphere dipolar liquid) are calculated in the framework of inhomogeneous Ornstein-Zernike equations with reference hypernetted chain closure (RHNC). The bridge functions are taken from a soft sphere (1/r12) reference system in the pressure-consistent closure approximation. In order to make the RHNC problem tractable, the angular dependence of the correlation functions is expanded into special orthogonal polynomials according to Lado. The resulting equations are solved using the Newton-GRMES algorithm as implemented in the public-domain solver NITSOL. Orientational densities and pair distribution functions of dipoles are compared with Monte Carlo simulation results. A numerical algorithm for the Fourier-Hankel transform of any positive integer order on a uniform grid is presented.

Polyakov, Evgeny A.; Vorontsov-Velyaminov, Pavel N.

2014-08-01

184

Properties of ferrofluid bilayer (modeled as a system of two planar layers separated by a distance h and each layer carrying a soft sphere dipolar liquid) are calculated in the framework of inhomogeneous Ornstein-Zernike equations with reference hypernetted chain closure (RHNC). The bridge functions are taken from a soft sphere (1/r(12)) reference system in the pressure-consistent closure approximation. In order to make the RHNC problem tractable, the angular dependence of the correlation functions is expanded into special orthogonal polynomials according to Lado. The resulting equations are solved using the Newton-GRMES algorithm as implemented in the public-domain solver NITSOL. Orientational densities and pair distribution functions of dipoles are compared with Monte Carlo simulation results. A numerical algorithm for the Fourier-Hankel transform of any positive integer order on a uniform grid is presented. PMID:25173007

Polyakov, Evgeny A; Vorontsov-Velyaminov, Pavel N

2014-08-28

185

Hydrodynamics of spin-polarized transport and spin pendulum

The dynamics of a nonequilibrium spin system dominated by collisions preserving the total quasimomentum of the interacting electrons and quasiparticles is considered. An analysis of the derived hydrodynamic equations shows that weakly attenuated spin-polarization waves associated with an oscillating drift current can exist in a magnetically inhomogeneous conducting ring. Spin-polarized transport in a ballistic regime of wave propagation through a conductor is also considered, and a simple method is proposed for distinguishing these waves from spin and current oscillations that develop in the hydrodynamic regime. It is shown that a potential difference arises between the leads of an open nonuniformly spin-polarized conductor as a manifestation of spin polarization of electron density. This spin-mediated electrical phenomenon occurs in both hydrodynamic and diffusive limits.

Gurzhi, R. N., E-mail: gurzhi@ilt.kharkov.ua; Kalinenko, A. N.; Kopeliovich, A. I.; Pyshkin, P. V.; Yanovsky, A. V. [Verkin Institute for Low-Temperature Physics and Engineering (Ukraine)

2007-07-15

186

NASA Astrophysics Data System (ADS)

Cubic-like shaped ZnxFe3-xO4 particles with crystallite mean sizes D between 15 and 117 nm were obtained by co-precipitation. Particle size effects and preferential occupation of spinel tetrahedral site by Zn2+ ions led to noticeable changes of physical properties. D ? 30 nm particles displayed nearly bulk properties, which were dominated by Zn concentration. For D ? 30 nm, dominant magnetic relaxation effects were observed by Mössbauer spectroscopy, with the mean blocking size DB ˜ 13 to 15 nm. Saturation magnetization increased with x up to x ˜ 0.1-0.3 and decreased for larger x. Power absorbed by water and chitosan-based ferrofluids from a 260 kHz radio frequency field was measured as a function of x, field amplitude H0 and ferrofluid concentration. For H0 = 41 kA m-1 the maximum specific absorption rate was 367 W g-1 for D = 16 nm and x = 0.1. Absorption results are interpreted within the framework of the linear response theory for H0 ? 41 kA m-1. A departure towards a saturation regime was observed for higher fields. Simulations based on a two-level description of nanoparticle magnetic moment relaxation qualitatively agree with these observations. The frequency factor of the susceptibility dissipative component, derived from experimental results, showed a sharp maximum at D ˜ 16 nm. This behaviour was satisfactorily described by simulations based on moment relaxation processes, which furthermore indicated a crossover from Néel to Brown mechanisms at D ˜ 18 nm. Hints for further improvement of magnetite particles as nanocalefactors for magnetic hyperthermia are discussed.

Mendoza Zélis, P.; Pasquevich, G. A.; Stewart, S. J.; Fernández van Raap, M. B.; Aphesteguy, J.; Bruvera, I. J.; Laborde, C.; Pianciola, B.; Jacobo, S.; Sánchez, F. H.

2013-03-01

187

Smoothed particle hydrodynamics

In this review the theory and application of Smoothed particle hydrodynamics (SPH) since its inception in 1977 are discussed. Emphasis is placed on the strengths and weaknesses, the analogy with particle dynamics and the numerous areas where SPH has been successfully applied.

J. J. Monaghan

2005-01-01

188

Smoothed particle hydrodynamics

The fundamentals of the smoothed particle hydrodynamics (SPH) method and its applications in astrophysics are reviewed. The discussion covers equations of motion, viscosity amd thermal conduction, spatially varying resolution, kernels, magnetic fields, special relativity, and implementation. Applications of the SPH method are discussed with reference to gas dynamics, binary stars and stellar collisions, formation of the moon and impact problems,

J. J. Monaghan

1992-01-01

189

Skew resisting hydrodynamic seal

A novel hydrodynamically lubricated compression type rotary seal that is suitable for lubricant retention and environmental exclusion. Particularly, the seal geometry ensures constraint of a hydrodynamic seal in a manner preventing skew-induced wear and provides adequate room within the seal gland to accommodate thermal expansion. The seal accommodates large as-manufactured variations in the coefficient of thermal expansion of the sealing material, provides a relatively stiff integral spring effect to minimize pressure-induced shuttling of the seal within the gland, and also maintains interfacial contact pressure within the dynamic sealing interface in an optimum range for efficient hydrodynamic lubrication and environment exclusion. The seal geometry also provides for complete support about the circumference of the seal to receive environmental pressure, as compared the interrupted character of seal support set forth in U.S. Pat. Nos. 5,873,576 and 6,036,192 and provides a hydrodynamic seal which is suitable for use with non-Newtonian lubricants.

Conroy, William T. (Pearland, TX); Dietle, Lannie L. (Sugar Land, TX); Gobeli, Jeffrey D. (Houston, TX); Kalsi, Manmohan S. (Houston, TX)

2001-01-01

190

Hyperbolic metamaterial lens with hydrodynamic nonlocal response.

We investigate the effects of hydrodynamic nonlocal response in hyperbolic metamaterials (HMMs), focusing on the experimentally realizable parameter regime where unit cells are much smaller than an optical wavelength but much larger than the wavelengths of the longitudinal pressure waves of the free-electron plasma in the metal constituents. We derive the nonlocal corrections to the effective material parameters analytically, and illustrate the noticeable nonlocal effects on the dispersion curves numerically. As an application, we find that the focusing characteristics of a HMM lens in the local-response approximation and in the hydrodynamic Drude model can differ considerably. In particular, the optimal frequency for imaging in the nonlocal theory is blueshifted with respect to that in the local theory. Thus, to detect whether nonlocal response is at work in a hyperbolic metamaterial, we propose to measure the near-field distribution of a hyperbolic metamaterial lens. PMID:23787690

Yan, Wei; Mortensen, N Asger; Wubs, Martijn

2013-06-17

191

Temporal and spatial dependence of hydrodynamic correlations: Simulation and experiment

Time-dependent hydrodynamic interactions in a colloidal suspension of hard spheres are studied, both experimentally and through computer simulation. The focus is on the behavior at small wave vectors, which directly probes the temporal evolution of hydrodynamic interactions between nearby particles. The computer simulations show that the time-dependent diffusion coefficient has the same functional form for all wave vectors, with a single characteristic scaling time for each length scale and for each volume fraction. Wave-vector-averaged effective diffusion coefficients, measured experimentally using diffusing wave spectroscopy, also scale to the same functional form. In this case, the scaling time is dependent on both volume fraction and particle size; it decreases sharply with decreasing particle radius, reflecting the greater contribution from smaller wave vectors that is contained in the scattering from the smaller particles. For a direct comparison of simulation and experiment, we simulate the experimentally observed correlation functions, by averaging the wave-vector-dependent computer-simulation data with the weighting appropriate to the experimental technique. Although the overall scaling is similar, there are quantitative differences in the simulated and measured relaxation times. We suggest these differences are due to the compressibility of the suspension, and that the resultant pressure waves make an unexpectedly significant contribution to the hydrodynamic interactions. (c) 1995 The American Physical Society

Ladd, A.J.C. [Department of Theoretical and Applied Mechanics, Cornell University, Ithaca, New York 14853 (United States)] [Department of Theoretical and Applied Mechanics, Cornell University, Ithaca, New York 14853 (United States); Gang, H. [Exxon Research and Engineering Company, Route 22 East, Annandale, New Jersey 08801 (United States)] [Exxon Research and Engineering Company, Route 22 East, Annandale, New Jersey 08801 (United States); Zhu, J.X. [Department of Chemical Engineering, Princeton University, Princeton, New Jersey 07954 (United States)] [Department of Chemical Engineering, Princeton University, Princeton, New Jersey 07954 (United States); Weitz, D.A. [Exxon Research and Engineering Company, Route 22 East, Annandale, New Jersey 08801 (United States)] [Exxon Research and Engineering Company, Route 22 East, Annandale, New Jersey 08801 (United States)

1995-12-01

192

Hydrodynamic modeling of tsunamis from the Currituck landslide Eric L. Geist a,

Hydrodynamic modeling of tsunamis from the Currituck landslide Eric L. Geist a, , Patrick J. Lynett: Accepted 24 September 2008 Keywords: tsunami landslide hydrodynamic runup numerical model sensitivity analysis Tsunami generation from the Currituck landslide offshore North Carolina and propagation of waves

Lynett, Patrick

193

Evaluation of using ferrofluid as an interface material for a field-reversible thermal connector

NASA Astrophysics Data System (ADS)

The electrical functionality of an avionics chassis is limited due to heat dissipation limits. The limits arise due to the fact that components in an avionic computer boxes are packed very compactly, with the components mounted onto plug-in cards, and the harsh environment experienced by the chassis limits how heat can be dissipated from the cards. Convective and radiative heat transfer to the ambient are generally not possible. Therefore it is necessary to have heat transferred from the components conducted to the edge of the plug-in cards. The heat then needs to conduct from the card edge to a cold block that not only holds the card in place, but also removes the generated heat by some heat transfer fluid that is circulated through the cold block. The interface between the plug-in card and the cold block typically has a high thermal resistance since it is necessary for the card to have the capability to be re-workable, meaning that the card can be removed and then returned to the chassis. Reducing the thermal resistance of the interface is the objective of the current study and the topic of this thesis. The current design uses a pressure interface between the card and cold block. The contact pressure is increased through the addition of a wedgelock, which is a field-reversible mechanical connector. To use a wedgelock, the cold block has channels milled on the surface with widths that are larger than the thickness of the plug-in card and the un-expanded wedgelock. The card edge is placed in the channel and placed against one of the channel walls. A wedgelock is then placed between the card and the other channel wall. The wedgelock is then expanded by using either a screw or a lever. As the wedgelock expands it fills in the remaining channel gap and bears against the other face of the plug-in card. The majority of heat generated by the components on the plug-in card is forced to conduct from the card into the wall of the cold block, effectively a single sided, dry conduction heat transfer path. Having started as a student design competition named RevCon Challenge, work was performed to evaluate the use of new field-reversible thermal connectors. The new design proposed by the University of Missouri utilized oil based iron nanoparticles, commonly known as a ferrofluid, as a thermal interface material. By using a liquid type of interface material the channel gap can be reduced to a few micrometers, within machining tolerances, and heat can be dissipated off both sides of the card. The addition of nanoparticles improves the effective thermal conductivity of base fluid. The use of iron nanoparticles allows magnets to be used to hold the fluid in place, so the electronic cards may be easily inserted and removed while keeping the ferrofluid in the cold block channel. The ferrofluid-based design which was investigated has shown lower thermal resistance than the current wedgelock design. These results open the door for further development of electronic cards by using higher heat emitting components without compromising the simplicity of attaching/detaching cards from cooling plates.

Yousif, Ahmed S.

194

Onset of superradiant instabilities in the hydrodynamic vortex model

The hydrodynamic vortex, an effective spacetime geometry for propagating sound waves, is studied analytically. This acoustic geometry describes a horizonless spacetime which nevertheless possesses an ergoregion, a property which it shares with the familiar rotating Kerr black-hole spacetime. It has recently been shown numerically that this physical system is linearly unstable due to the superradiant scattering of sound waves in the ergoregion of the effective spacetime. In the present study we use analytical tools in order to explore the onset of these superradiant instabilities which characterize the effective spacetime geometry. In particular, we derive a simple analytical formula which describes the physical properties of the hydrodynamic vortex system in its critical (marginally-stable) state, the state which marks the boundary between stable and unstable fluid configurations. The analytically derived formula is shown to agree with the recently published numerical data for the hydrodynamic vortex system.

Hod, Shahar

2014-01-01

195

From Field Theory to the Hydrodynamics of Relativistic Superfluids

The hydrodynamic description of a superfluid is usually based on a two-fluid picture. In this thesis, basic properties of such a relativistic two-fluid system are derived from the underlying microscopic physics of a complex scalar quantum field theory. To obtain analytic results of all non-dissipative hydrodynamic quantities in terms of field theoretic variables, calculations are first carried out in a low-temperature and weak-coupling approximation. In a second step, the 2-particle-irreducible formalism is applied: This formalism allows for a numerical evaluation of the hydrodynamic parameters for all temperatures below the critical temperature. In addition, a system of two coupled superfluids is studied. As an application, the velocities of first and second sound in the presence of a superflow are calculated. The results show that first (second) sound evolves from a density (temperature) wave at low temperatures to a temperature (density) wave at high temperatures. This role reversal is investigated for ult...

Stetina, Stephan

2015-01-01

196

Nonlinear hydrodynamics. Lecture 9

A very sophisticated method for calculating the stability and pulsations of stars which make contact with actual observations of the stellar behavior, hydrodynamic calculations are very simple in principle. Conservation of mass can be accounted for by having mass shells that are fixed with their mass for all time. Motions of these shells can be calculated by taking the difference between the external force of gravity and that from the local pressure gradient. The conservation of energy can be coupled to this momentum conservation equation to give the current temperatures, densities, pressures, and opacities at the shell centers, as well as the positions, velocities, and accelerations of the mass shell interfaces. Energy flow across these interfaces can be calculated from the current conditions, and this energy is partitioned between internal energy and the work done on or by the mass shell. We discuss here only the purely radial case for hydrodynamics because it is very useful for stellar pulsation studies.

Cox, A.N.

1983-03-14

197

Nonlocal electron hydrodynamics

NASA Astrophysics Data System (ADS)

Analytical nonlocal theory of an electron transport in unmagnetized plasmas with arbitrary electron collisionality in the limit of large ion charge has been developed. We have found nonlocal expressions for electron transport coefficients: electric conductivity, thermoelectric coefficient, temperature and heat conductivities, electron-ion friction, and ion flux coefficients. We have shown that our theory properly describes a transition from strongly collisional, hydrodynamical regime into the collisionless, free-streaming limit. The thermoelectric coefficient changes its sign when the perturbation wavelength is comparable to the electron-ion mean free path. Electron and ion low frequency longitudinal and transversal susceptibilities are derived from our nonlocal hydrodynamics and the proper definition of the electron heat conductivity is also discussed.

Brantov, A. V.; Bychenkov, V. Yu.; Tikhonchuk, V. T.; Rozmus, W.

1996-11-01

198

Relativistic cosmological hydrodynamics

We investigate the relativistic cosmological hydrodynamic perturbations. We present the general large scale solutions of the perturbation variables valid for the general sign of three space curvature, the cosmological constant, and generally evolving background equation of state. The large scale evolution is characterized by a conserved gauge invariant quantity which is the same as a perturbed potential (or three-space curvature) in the comoving gauge.

J. Hwang; H. Noh

1997-11-29

199

NSDL National Science Digital Library

Hydrodynamics and viscosity: This site contains a complete description of fluid properties and fluid mechanics by defining the nature of a fluid, show where fluid mechanics concepts are common with those of solid mechanics and indicate some fundamental areas of difference, introduce viscosity and show what are Newtonian and non-Newtonian fluids and define the appropriate physical properties and show how these allow differentiation between solids and fluids as well as between liquids and gases.

2008-09-22

200

Ferrofluids consist of magnetic nanoparticles dispersed in a carrier liquid. Their strong thermodiffusive behaviour, characterised by the Soret coefficient, coupled with the dependency of the fluid's parameters on magnetic fields is dealt with in this work. It is known from former experimental investigations on the one hand that the Soret coefficient itself is magnetic field dependent and on the other hand that the accuracy of the coefficient's experimental determination highly depends on the volume concentration of the fluid. The thermally driven separation of particles and carrier liquid is carried out with a concentrated ferrofluid (? = 0.087) in a horizontal thermodiffusion cell and is compared to equally detected former measurement data. The temperature gradient (1 K/mm) is applied perpendicular to the separation layer. The magnetic field is either applied parallel or perpendicular to the temperature difference. For three different magnetic field strengths (40 kA/m, 100 kA/m, 320 kA/m) the diffusive separation is detected. It reveals a sign change of the Soret coefficient with rising field strength for both field directions which stands for a change in the direction of motion of the particles. This behaviour contradicts former experimental results with a dilute magnetic fluid, in which a change in the coefficient's sign could only be detected for the parallel setup. An anisotropic behaviour in the current data is measured referring to the intensity of the separation being more intense in the perpendicular position of the magnetic field: S{sub T?} = ?0.152 K{sup ?1} and S{sub T?} = ?0.257 K{sup ?1} at H = 320 kA/m. The ferrofluiddynamics-theory (FFD-theory) describes the thermodiffusive processes thermodynamically and a numerical simulation of the fluid's separation depending on the two transport parameters ?{sub ?} and ?{sub ?} used within the FFD-theory can be implemented. In the case of a parallel aligned magnetic field, the parameter can be determined to ?{sub ?} = (2.8;?9.1;?11.2)?×?10{sup ?11}?·?D{sub ?} kg/(A{sup 2}m) for the different field strengths and in dependence on the magnetic diffusion coefficient D{sub ?}. An adequate fit in the perpendicular case is not possible, by ?{sub ?} = 1?×?10{sup ?17} kg/(Am{sup 2}) a rather good agreement between numerical and experimental data can be found for a field strength of 40 kA/m, a change in the coefficient's sign in the perpendicular setup is not numerically determinable via this theory. The FFD-theory is only partly applicable to calculate the concentration profile in concentrated magnetic fluids established due to a temperature gradient and magnetic field applied.

Sprenger, Lisa, E-mail: Lisa.Sprenger@tu-dresden.de; Lange, Adrian; Odenbach, Stefan [Institute of Fluid Mechanics, Chair of Magnetofluiddynamics, Measuring and Automation Technology, TU Dresden, 01062 Dresden (Germany)] [Institute of Fluid Mechanics, Chair of Magnetofluiddynamics, Measuring and Automation Technology, TU Dresden, 01062 Dresden (Germany)

2014-02-15

201

NASA Astrophysics Data System (ADS)

Ferrofluids are colloidal systems composed of a single domain of magnetic nanoparticles with a mean diameter around 30 nm, dispersed in a liquid carrier. Magnetic Co(1-x)ZnxFe2O4 (x=0.25, 0.50, 0.75) ferrite nanoparticles were prepared via co-precipitation method from aqueous salt solutions in an alkaline medium. The composition and structure of the samples were characterized through Energy Dispersive X-ray Spectroscopy and X-ray diffraction, respectively. Transmission Electron Microscopy (TEM) studies permitted determining nanoparticle size; grain size of nanoparticle conglomerates was established via Atomic Force Microscopy. The magnetic behavior of ferrofluids was characterized by Vibrating Sample Magnetometer (VSM); and finally, a magnetic force microscope was used to visualize the magnetic domains of Co(1-x)ZnxFe2O4 nanoparticles. X-ray diffraction patterns of Co(1-x)ZnxFe2O4 show the presence of the most intense peak corresponding to the (311) crystallographic orientation of the spinel phase of CoFe2O4. Fourier Transform Infrared Spectroscopy confirmed the presence of the bonds associated to the spinel structures; particularly for ferrites. The mean size of the crystallite of nanoparticles determined from the full-width at half maximum of the strongest reflection of the (311) peak by using the Scherrer approximation diminished from (9.5±0.3) nm to (5.4±0.2) nm when the Zn concentration increases from 0.21 to 0.75. The size of the Co-Zn ferrite nanoparticles obtained by TEM is in good agreement with the crystallite size calculated from X-ray diffraction patterns, using Scherer's formula. The magnetic properties investigated with the aid of a VSM at room temperature presented super-paramagnetic behavior, determined by the shape of the hysteresis loop. In this study, we established that the coercive field of Co(1-x)ZnxFe2O4 magnetic nanoparticles, the crystal and nanoparticle sizes determined by X-ray Diffraction and TEM, respectively, decrease with the increase of the Zn at%. Finally, our magnetic nanoparticles are not very hard magnetic materials given that the hysteresis loop is small and for this reason Co(1-x)ZnxFe2O4 nanoparticles are considered as soft magnetic material.

López, J.; González-Bahamón, L. F.; Prado, J.; Caicedo, J. C.; Zambrano, G.; Gómez, M. E.; Esteve, J.; Prieto, P.

2012-02-01

202

Hydrodynamics of fossil fishes.

From their earliest origins, fishes have developed a suite of adaptations for locomotion in water, which determine performance and ultimately fitness. Even without data from behaviour, soft tissue and extant relatives, it is possible to infer a wealth of palaeobiological and palaeoecological information. As in extant species, aspects of gross morphology such as streamlining, fin position and tail type are optimized even in the earliest fishes, indicating similar life strategies have been present throughout their evolutionary history. As hydrodynamical studies become more sophisticated, increasingly complex fluid movement can be modelled, including vortex formation and boundary layer control. Drag-reducing riblets ornamenting the scales of fast-moving sharks have been subjected to particularly intense research, but this has not been extended to extinct forms. Riblets are a convergent adaptation seen in many Palaeozoic fishes, and probably served a similar hydrodynamic purpose. Conversely, structures which appear to increase skin friction may act as turbulisors, reducing overall drag while serving a protective function. Here, we examine the diverse adaptions that contribute to drag reduction in modern fishes and review the few attempts to elucidate the hydrodynamics of extinct forms. PMID:24943377

Fletcher, Thomas; Altringham, John; Peakall, Jeffrey; Wignall, Paul; Dorrell, Robert

2014-08-01

203

A saw having a self-pumped hydrodynamic blade guide or bearing for retaining the saw blade in a centered position in the saw kerf (width of cut made by the saw). The hydrodynamic blade guide or bearing utilizes pockets or grooves incorporated into the sides of the blade. The saw kerf in the workpiece provides the guide or bearing stator surface. Both sides of the blade entrain cutting fluid as the blade enters the kerf in the workpiece, and the trapped fluid provides pressure between the blade and the workpiece as an inverse function of the gap between the blade surface and the workpiece surface. If the blade wanders from the center of the kerf, then one gap will increase and one gap will decrease and the consequent pressure difference between the two sides of the blade will cause the blade to re-center itself in the kerf. Saws using the hydrodynamic blade guide or bearing have particular application in slicing slabs from boules of single crystal materials, for example, as well as for cutting other difficult to saw materials such as ceramics, glass, and brittle composite materials.

Blaedel, K.L.; Davis, P.J.; Landram, C.S.

2000-07-04

204

Hydrodynamics of fossil fishes

From their earliest origins, fishes have developed a suite of adaptations for locomotion in water, which determine performance and ultimately fitness. Even without data from behaviour, soft tissue and extant relatives, it is possible to infer a wealth of palaeobiological and palaeoecological information. As in extant species, aspects of gross morphology such as streamlining, fin position and tail type are optimized even in the earliest fishes, indicating similar life strategies have been present throughout their evolutionary history. As hydrodynamical studies become more sophisticated, increasingly complex fluid movement can be modelled, including vortex formation and boundary layer control. Drag-reducing riblets ornamenting the scales of fast-moving sharks have been subjected to particularly intense research, but this has not been extended to extinct forms. Riblets are a convergent adaptation seen in many Palaeozoic fishes, and probably served a similar hydrodynamic purpose. Conversely, structures which appear to increase skin friction may act as turbulisors, reducing overall drag while serving a protective function. Here, we examine the diverse adaptions that contribute to drag reduction in modern fishes and review the few attempts to elucidate the hydrodynamics of extinct forms. PMID:24943377

Fletcher, Thomas; Altringham, John; Peakall, Jeffrey; Wignall, Paul; Dorrell, Robert

2014-01-01

205

Building a Hydrodynamics Code with Kinetic Theory

NASA Astrophysics Data System (ADS)

We report on the development of a test-particle based kinetic Monte Carlo code for large systems and its application to simulate matter in the continuum regime. Our code combines advantages of the Direct Simulation Monte Carlo and the Point-of-Closest-Approach methods to solve the collision integral of the Boltzmann equation. With that, we achieve a high spatial accuracy in simulations while maintaining computational feasibility when applying a large number of test-particles. The hybrid setup of our approach allows us to study systems which move in and out of the hydrodynamic regime, with low and high particle densities. To demonstrate our code's ability to reproduce hydrodynamic behavior we perform shock wave simulations and focus here on the Sedov blast wave test. The blast wave problem describes the evolution of a spherical expanding shock front and is an important verification problem for codes which are applied in astrophysical simulation, especially for approaches which aim to study core-collapse supernovae.

Sagert, Irina; Bauer, Wolfgang; Colbry, Dirk; Pickett, Rodney; Strother, Terrance

2013-08-01

206

A new shock-capturing numerical scheme for ideal hydrodynamics

We present a new algorithm for solving ideal relativistic hydrodynamics based on Godunov method with an exact solution of Riemann problem for an arbitrary equation of state. Standard numerical tests are executed, such as the sound wave propagation and the shock tube problem. Low numerical viscosity and high precision are attained with proper discretization.

Feckova, Zuzana

2015-01-01

207

A new shock-capturing numerical scheme for ideal hydrodynamics

We present a new algorithm for solving ideal relativistic hydrodynamics based on Godunov method with an exact solution of Riemann problem for an arbitrary equation of state. Standard numerical tests are executed, such as the sound wave propagation and the shock tube problem. Low numerical viscosity and high precision are attained with proper discretization.

Zuzana Feckova; Boris Tomasik

2015-01-07

208

Hydrodynamic Phase Locking of Swimming Microorganisms

NASA Astrophysics Data System (ADS)

Some microorganisms, such as spermatozoa, synchronize their flagella when swimming in close proximity. Using a simplified model (two infinite, parallel, two-dimensional waving sheets), we show that phase locking arises from hydrodynamics forces alone, and has its origin in the front-back asymmetry of the geometry of their flagellar waveform. The time evolution of the phase difference between coswimming cells depends only on the nature of this geometrical asymmetry, and microorganisms can phase lock into conformations which minimize or maximize energy dissipation.

Elfring, Gwynn J.; Lauga, Eric

2009-08-01

209

Electric field distribution around the chain of composite nanoparticles in ferrofluids

NASA Astrophysics Data System (ADS)

Composite nanoparticles (NPs) have the ability of combining materials with different properties together, thus receiving extensive attention in many fields. Here we theoretically investigate the electric field distribution around core/shell NPs (a type of composite NPs) in ferrofluids under the influence of an external magnetic field. The NPs are made of cobalt (ferromagnetic) coated with gold (metallic). Under the influence of the external magnetic field, these NPs will align along the direction of this field, thus forming a chain of NPs. According to Laplace's equations, we obtain electric fields inside and outside the NPs as a function of the incident wavelength by taking into account the mutual interaction between the polarized NPs. Our calculation results show that the electric field distribution is closely related to the resonant incident wavelength, the metallic shell thickness, and the inter-particle distance. These analytical calculations agree well with our numerical simulation results. This kind of field-induced anisotropic soft-matter systems offers the possibility of obtaining an enhanced Raman scattering substrate due to enhanced electric fields.

Fan, Chun-Zhen; Wang, Jun-Qiao; Cheng, Yong-Guang; Ding, Pei; Liang, Er-Jun; Huang, Ji-Ping

2013-08-01

210

NASA Astrophysics Data System (ADS)

An experimental study of magnetic colloidal particles cluster formation induced by an external electric field in a ferrofluid based on transformer oil is presented. Using frequency domain isothermal dielectric spectroscopy, we study the influence of a test cell electrode separation distance on a low-frequency relaxation process. We consider the relaxation process to be associated with an electric double layer polarization taking place on the particle surface. It has been found that the relaxation maximum considerably shifts towards lower frequencies when conducting the measurements in the test cells with greater electrode separation distances. As the electric field intensity was always kept at a constant value, we propose that the particle cluster formation induced by the external ac electric field accounts for that phenomenon. The increase in the relaxation time is in accordance with the Schwarz theory of electric double layer polarization. In addition, we analyze the influence of a static electric field generated by dc bias voltage on a similar shift in the relaxation maximum position. The variation of the dc electric field for the hysteresis measurements purpose provides understanding of the development of the particle clusters and their decay. Following our results, we emphasize the utility of dielectric spectroscopy as a simple, complementary method for detection and study of clusters of colloidal particles induced by external electric field.

Rajnak, Michal; Kurimsky, Juraj; Dolnik, Bystrik; Kopcansky, Peter; Tomasovicova, Natalia; Taculescu-Moaca, Elena Alina; Timko, Milan

2014-09-01

211

An experimental study of magnetic colloidal particles cluster formation induced by an external electric field in a ferrofluid based on transformer oil is presented. Using frequency domain isothermal dielectric spectroscopy, we study the influence of a test cell electrode separation distance on a low-frequency relaxation process. We consider the relaxation process to be associated with an electric double layer polarization taking place on the particle surface. It has been found that the relaxation maximum considerably shifts towards lower frequencies when conducting the measurements in the test cells with greater electrode separation distances. As the electric field intensity was always kept at a constant value, we propose that the particle cluster formation induced by the external ac electric field accounts for that phenomenon. The increase in the relaxation time is in accordance with the Schwarz theory of electric double layer polarization. In addition, we analyze the influence of a static electric field generated by dc bias voltage on a similar shift in the relaxation maximum position. The variation of the dc electric field for the hysteresis measurements purpose provides understanding of the development of the particle clusters and their decay. Following our results, we emphasize the utility of dielectric spectroscopy as a simple, complementary method for detection and study of clusters of colloidal particles induced by external electric field. PMID:25314449

Rajnak, Michal; Kurimsky, Juraj; Dolnik, Bystrik; Kopcansky, Peter; Tomasovicova, Natalia; Taculescu-Moaca, Elena Alina; Timko, Milan

2014-09-01

212

NASA Astrophysics Data System (ADS)

Using light transmission experiments and optical microscope observations with a longitudinal gradient magnetic field configuration, the relationship between the behavior of the transmitted light relaxation and the microstructure evolution of ionic ferrofluids in the central region of an axisymmetric field is investigated. Under a low-gradient magnetic field, there are two types of relaxation process. When a field is applied, the transmitted light intensity decreases to a minimum within a time on the order of 101-102 s. It is then gradually restored, approaching its initial value within a time on the order of 102 s. This is type I relaxation, which corresponds to the formation of magnetic columns. After the transmission reaches this value, it either increases or decreases slowly, stabilizing within a time on the order of 103 s, according to the direction of the field gradient. This is a type II relaxation, which results from the shadowing effect, corresponding to the motion of the magnetic columns under the application of a gradient force. Under a magnetic field with a centripetal high-gradient (magnetic materials subjected to a force pointing toward the center of the axisymmetric field), the transmitted light intensity decreases monotonously and more slowly than that under a low-gradient field. Magnetic transport and separation resulted from magnetophoresis under high-gradient fields, changing the formation dynamics of the local columns and influencing the final state of the column system.

Huang, Yan; Li, Decai; Li, Feng; Zhu, Quanshui; Xie, Yu

2015-03-01

213

Modeling multiphase flow using fluctuating hydrodynamics

NASA Astrophysics Data System (ADS)

Fluctuating hydrodynamics provides a model for fluids at mesoscopic scales where thermal fluctuations can have a significant impact on the behavior of the system. Here we investigate a model for fluctuating hydrodynamics of a single-component, multiphase flow in the neighborhood of the critical point. The system is modeled using a compressible flow formulation with a van der Waals equation of state, incorporating a Korteweg stress term to treat interfacial tension. We present a numerical algorithm for modeling this system based on an extension of algorithms developed for fluctuating hydrodynamics for ideal fluids. The scheme is validated by comparison of measured structure factors and capillary wave spectra with equilibrium theory. We also present several nonequilibrium examples to illustrate the capability of the algorithm to model multiphase fluid phenomena in a neighborhood of the critical point. These examples include a study of the impact of fluctuations on the spinodal decomposition following a rapid quench, as well as the piston effect in a cavity with supercooled walls. The conclusion in both cases is that thermal fluctuations affect the size and growth of the domains in off-critical quenches.

Chaudhri, Anuj; Bell, John B.; Garcia, Alejandro L.; Donev, Aleksandar

2014-09-01

214

Smoothed Particle Hydrodynamics

Smoothed Particle Hydrodynamics (SPH) is a unique numerical method widely used for astrophysical problems since it involves no spatial grid. Rather, fluid quantities are carried by a set of Lagrangian `particles' which move with the flow, meaning that complicated dynamics and asymmetric phenomena are treated with ease. Since adaptivity is a built-in feature of the method there is no need to resort to complicated additional mesh refinement procedures. In this chapter we have undertaken a thorough review of the SPH method in order to develop a sufficiently accurate method which can be applied to MHD problems (Chapters 4-5). The review contains several results which have not been published elsewhere.

Daniel Price

2005-07-20

215

The Quantum Hydrodynamic Description of Tunneling

The quantum hydrodynamic approach is based on the de Broglie-Bohm formulation of quantum mechanics. The resulting fluid-like equations of motion describe the flow of probability and an accurate solution to these equations is equivalent to solving the time-dependent Schroedinger equation. Furthermore, the hydrodynamic approach provides new insight into the mechanisms as well as an alternative computational approach for treating tunneling phenomena. New concepts include well-defined 'quantum trajectories', 'quantum potential', and 'quantum force' all of which have classical analogues. The quantum potential and its associated force give rise to all quantum mechanical effects such as zero point energy, tunneling, and interference. A new numerical approach called the Iterative Finite Difference Method (IFDM) will be discussed. The IFDM is used to solve the set of non-linear coupled hydrodynamic equations. It is 2nd-order accurate in both space and time and exhibits exponential convergence with respect to the iteration count. The stability and computational efficiency of the IFDM is significantly improved by using a 'smart' Eulerian grid which has the same computational advantages as a Lagrangian or Arbitrary Lagrangian Eulerian (ALE) grid. The IFDM is also capable of treating anharmonic potentials. Example calculations using the IFDM will be presented which include: a one-dimensional Gaussian wave packet tunneling through an Eckart barrier, a one-dimensional bound-state Morse oscillator, and a two-dimensional (2D) model collinear reaction using an anharmonic potential energy surface. Approximate treatments of the quantum hydrodynamic equations will also be discussed which could allow scaling of the calculations to hundreds of degrees of freedom which is important for treating tunneling phenomena in condensed phase systems.

Kendrick, Brian K. [Los Alamos National Laboratory

2012-06-15

216

Hydrodynamics of spur and groove formations on a coral reef

NASA Astrophysics Data System (ADS)

Spur and groove (SAG) formations are found on the fore reefs of many coral reefs worldwide. Although these formations are primarily present in wave-dominated environments, their effect on wave-driven hydrodynamics is not well understood. A two-dimensional, depth-averaged, phase-resolving nonlinear Boussinesq model (funwaveC) was used to model hydrodynamics on a simplified SAG system. The modeling results show that the SAG formations together with shoaling waves induce a nearshore Lagrangian circulation pattern of counter-rotating circulation cells. The mechanism driving the modeled flow is an alongshore imbalance between the pressure gradient (PG) and nonlinear wave (NLW) terms in the momentum balance. Variations in model parameters suggest the strongest factors affecting circulation include spur-normal waves, increased wave height, weak alongshore currents, increased spur height, and decreased bottom drag. The modeled circulation is consistent with a simple scaling analysis based on the dynamical balance of NLW, PG, and bottom stress terms. Model results indicate that the SAG formations efficiently drive circulation cells when the alongshore SAG wavelength allows for the effects of diffraction to create alongshore differences in wave height without changing the mean wave angle.

Rogers, Justin S.; Monismith, Stephen G.; Feddersen, Falk; Storlazzi, Curt D.

2013-06-01

217

Load responsive hydrodynamic bearing

A load responsive hydrodynamic bearing is provided in the form of a thrust bearing or journal bearing for supporting, guiding and lubricating a relatively rotatable member to minimize wear thereof responsive to relative rotation under severe load. In the space between spaced relatively rotatable members and in the presence of a liquid or grease lubricant, one or more continuous ring shaped integral generally circular bearing bodies each define at least one dynamic surface and a plurality of support regions. Each of the support regions defines a static surface which is oriented in generally opposed relation with the dynamic surface for contact with one of the relatively rotatable members. A plurality of flexing regions are defined by the generally circular body of the bearing and are integral with and located between adjacent support regions. Each of the flexing regions has a first beam-like element being connected by an integral flexible hinge with one of the support regions and a second beam-like element having an integral flexible hinge connection with an adjacent support region. A least one local weakening geometry of the flexing region is located intermediate the first and second beam-like elements. In response to application of load from one of the relatively rotatable elements to the bearing, the beam-like elements and the local weakening geometry become flexed, causing the dynamic surface to deform and establish a hydrodynamic geometry for wedging lubricant into the dynamic interface.

Kalsi, Manmohan S. (Houston, TX); Somogyi, Dezso (Sugar Land, TX); Dietle, Lannie L. (Stafford, TX)

2002-01-01

218

Hydrodynamics of Bacterial Cooperation

NASA Astrophysics Data System (ADS)

Over the course of the last several decades, the study of microbial communities has identified countless examples of cooperation between microorganisms. Generally—as in the case of quorum sensing—cooperation is coordinated by a chemical signal that diffuses through the community. Less well understood is a second class of cooperation that is mediated through physical interactions between individuals. To better understand how the bacteria use hydrodynamics to manipulate their environment and coordinate their actions, we study the sulfur-oxidizing bacterium Thiovulum majus. These bacteria live in the diffusive boundary layer just above the muddy bottoms of ponds. As buried organic material decays, sulfide diffuses out of the mud. Oxygen from the pond diffuses into the boundary layer from above. These bacteria form communities—called veils— which are able to transport nutrients through the boundary layer faster than diffusion, thereby increasing their metabolic rate. In these communities, bacteria attach to surfaces and swim in place. As millions of bacteria beat their flagella, the community induces a macroscopic fluid flow, which mix the boundary layer. Here we present experimental observations and mathematical models that elucidate the hydrodynamics linking the behavior of an individual bacterium to the collective dynamics of the community. We begin by characterizing the flow of water around an individual bacterium swimming in place. We then discuss the flow of water and nutrients around a small number of individuals. Finally, we present observations and models detailing the macroscopic dynamics of a Thiovulum veil.

Petroff, A.; Libchaber, A.

2012-12-01

219

Study of Angular Momentum Transport in Hydrodynamic and Magnetohydrodynamic Experiments

NASA Astrophysics Data System (ADS)

Rapid angular momentum transport has been observed to occur in both laboratory fusion plasmas and astrophysical plasmas, but its physical mechanisms still remain illusive. In this paper, we describe a series of laboratory fluid experiments in order to investigate a variety of the proposed mechanisms either in hydrodynamics or magnetohydrodynamics (MHD). They include (1) hydrodynamic turbulence for Keplerian flows. (2) Magnetocoriolis (MC) waves, (3) Magnetorotational Instability (MRI), (4) Rossby waves, and (5) Magneto-Rossby waves. The first three mechanisms have been or are being investigated on the ongoing Princeton MRI experiment (http://mri.pppl.gov) while the last two mechanisms will be investigated on a newly built experiment, this mini-conference and on a further modified Princeton MRI experiments. Implications of these experimental results for the astrophysical problems will be discussed.

Ji, H.; Edlund, E.; Spence, E.; Roach, A.

2010-11-01

220

Analytical solutions of Landau (1+1)-dimensional hydrodynamics

NASA Astrophysics Data System (ADS)

To help guide our intuition, summarize important features, and point out essential elements, we review the analytical solutions of Landau (1+1)-dimensional hydrodynamics and discuss the full evolution of the dynamics from the very beginning. Special emphasis is placed on the matching and the interplay between the Khalatnikov solution and the Riemann simple wave solution, at the earliest times and in the edge regions at later times. These analytical solutions collected and developed here serve well as a useful guide and cross-check in the development of complicated numerically intensive relativistic hydrodynamical Monte Carlo simulations.

Wong, Cheuk-Yin; Sen, Abhisek; Gerhard, Jochen; Torrieri, Giorgio; Read, Kenneth

2014-12-01

221

Hydrodynamics of the turbulent point-spread function.

We derive hydrodynamic equations for the point-spread function of an imaging system looking through atmospheric turbulence at an incoherent object. These are derived from the hydrodynamics of the index of refraction of the air. We use the path integral representation of the paraxial approximation for wave propagation through turbulence. We then study the case of a frozen turbulent refractive index field being advected past the imaging system with a constant wind and discuss the implications for optical flow estimation. We conclude by discussing possible directions for future work. PMID:24323148

Potvin, Guy

2013-07-01

222

NASA Astrophysics Data System (ADS)

Co66Fe2Si13B15Cr4 based amorphous microwire was developed at the laboratory using in-water quenching apparatus. The field sensitivity of the wire was enhanced when coated with ferrofluids. The presence of coating also decreased the frequency of the magnetising field 5 MHz to 1 MHz at which the maximum GMI ratio observed.

Das, Tarun Kumar; Mandal, Sushil Kumar; Panda, Asish Kumar; Bhattacharya, Soumya; Banerji, Pallab; Mitra, Amitava

223

QGP Hydrodynamics for RHIC Energies

The relativistic hydrodynamic approach in this field became one of the best established theoretical and experimental methods [1]. The applicability of this method is vital, so we have to discuss the initial and final stages of heavy ion reactions in great detail, in addition to the middle stages of the reaction where the relativistic hydrodynamic description provides an adequate and

L. P. Csernai; C. Anderlik; A. Keranen

2003-01-01

224

Computational Ship Hydrodynamics MOERI Propeller

Computational Ship Hydrodynamics MOERI Propeller This area of research is coordinated by the ship of the Office of Naval Research for the past 20 years, with vast capabilities for ship hydrodynamics, enabling capabilities in CFDShip-Iowa were added under a grant from the Office of Naval Research for use in ship

Kusiak, Andrew

225

NASA Astrophysics Data System (ADS)

Rate of heat generated by magnetic nanoparticles in a ferrofluid is affected by their magnetic properties, temperature, and viscosity of the carrier liquid. We have investigated temperature dependent magnetic hyperthermia in ferrofluids, consisting of dextran coated superparamagnetic Fe3O4 nanoparticles, subjected to external magnetic fields of various frequencies (188-375 kHz) and amplitudes (140-235 Oe). Transmission electron microscopy measurements show that the nanoparticles are polydispersed with a mean diameter of 13.8 ± 3.1 nm. The fitting of experimental dc magnetization data to a standard Langevin function incorporating particle size distribution yields a mean diameter of 10.6 ± 1.2 nm, and a reduced saturation magnetization (˜65 emu/g) compared to the bulk value of Fe3O4 (˜95 emu/g). This is due to the presence of a finite surface layer (˜1 nm thickness) of non-aligned spins surrounding the ferromagnetically aligned Fe3O4 core. We found the specific absorption rate, measured as power absorbed per gram of iron oxide nanoparticles, decreases monotonically with increasing temperature for all values of magnetic field and frequency. Using the size distribution of magnetic nanoparticles estimated from the magnetization measurements, we have fitted the specific absorption rate versus temperature data using a linear response theory and relaxation dissipation mechanisms to determine the value of magnetic anisotropy constant (28 ± 2 kJ/m3) of Fe3O4 nanoparticles.

Nemala, H.; Thakur, J. S.; Naik, V. M.; Vaishnava, P. P.; Lawes, G.; Naik, R.

2014-07-01

226

Hydrodynamics of periodic breathers.

We report the first experimental observation of periodic breathers in water waves. One of them is Kuznetsov-Ma soliton and another one is Akhmediev breather. Each of them is a localized solution of the nonlinear Schrödinger equation (NLS) on a constant background. The difference is in localization which is either in time or in space. The experiments conducted in a water wave flume show results that are in good agreement with the NLS theory. Basic features of the breathers that include the maximal amplitudes and spectra are consistent with the theoretical predictions. PMID:25246673

Chabchoub, A; Kibler, B; Dudley, J M; Akhmediev, N

2014-10-28

227

The two-dimensional radiation-hydrodynamic code SN-YAQUI was used to calculate the evolution of a hypothetical nuclear fireball of 1-Mt yield at a burst altitude of 500 m. The ground-reflected shock wave interacts strongly with the fireball and induces the early formation of a rapidly rotating ring-shaped vortex. The hydrodynamic and radiation phenomena are discussed.

Horak, H.G.; Jones, E.M.; Sandford, M.T. II; Whitaker, R.W.; Anderson, R.C.; Kodis, J.W.

1982-03-01

228

Polarized seismic and solitary waves run-up at the sea bed

The polarization effects in hydrodynamics are studied. Hydrodynamic equation for the nonlinear wave is used along with the polarized solitary waves and seismic waves act as initial waves. The model is then solved by Fourier spectral and Runge-Kutta 4 methods, and the surface plot is drawn. The output demonstrates the inundation behaviors. Consequently, the polarized seismic waves along with the polarized solitary waves tend to generate dissimilar inundation which is more disastrous.

Dennis, L. C.C.; Zainal, A. A.; Faisal, S. Y. [Universiti Teknologi PETRONAS, 31750 Tronoh, Perak (Malaysia); Universiti Teknologi Malaysia, 81310 Johor Bahru (Malaysia)

2012-09-26

229

Onset of superradiant instabilities in the hydrodynamic vortex model

The hydrodynamic vortex, an effective spacetime geometry for propagating sound waves, is studied analytically. In contrast with the familiar Kerr black-hole spacetime, the hydrodynamic vortex model is described by an effective acoustic geometry which has no horizons. However, this acoustic spacetime possesses an ergoregion, a property which it shares with the rotating Kerr spacetime. It has recently been shown numerically that this physical system is linearly unstable due to the superradiant scattering of sound waves in the ergoregion of the effective spacetime. In the present study we use analytical tools in order to explore the onset of these superradiant instabilities which characterize the effective spacetime geometry. In particular, we derive a simple analytical formula which describes the physical properties of the hydrodynamic vortex system in its critical (marginally-stable) state, the state which marks the boundary between stable and unstable fluid configurations. The analytically derived formula is shown to agree with the recently published numerical data for the hydrodynamic vortex system.

Shahar Hod

2014-05-29

230

Sediment resuspension mechanisms associated with internal waves in coastal waters

Large-amplitude, vertically trapped internal waves can induce sizable velocities and trigger hydrodynamic instabilities in the bottom boundary layer, thereby contributing to the resuspension of sediments and the maintenance of sediment concentration in the water column. We discuss numerical simulations of several different situations in which the boundary layer in the wave footprint undergoes hydrodynamic instability, with a resultant increase in

M. Stastna; K. G. Lamb

2008-01-01

231

Hydrodynamic synchronization of colloidal oscillators

Two colloidal spheres are maintained in oscillation by switching the position of an optical trap when a sphere reaches a limit position, leading to oscillations that are bounded in amplitude but free in phase and period. The interaction between the oscillators is only through the hydrodynamic flow induced by their motion. We prove that in the absence of stochastic noise the antiphase dynamical state is stable, and we show how the period depends on coupling strength. Both features are observed experimentally. As the natural frequencies of the oscillators are made progressively different, the coordination is quickly lost. These results help one to understand the origin of hydrodynamic synchronization and how the dynamics can be tuned. Cilia and flagella are biological systems coupled hydrodynamically, exhibiting dramatic collective motions. We propose that weakly correlated phase fluctuations, with one of the oscillators typically precessing the other, are characteristic of hydrodynamically coupled systems in the presence of thermal noise. PMID:20385848

Kotar, Jurij; Leoni, Marco; Bassetti, Bruno; Lagomarsino, Marco Cosentino; Cicuta, Pietro

2010-01-01

232

Relativistic Hydrodynamics on Graphic Cards

We show how to accelerate relativistic hydrodynamics simulations using graphic cards (graphic processing units, GPUs). These improvements are of highest relevance e.g. to the field of high-energetic nucleus-nucleus collisions at RHIC and LHC where (ideal and dissipative) relativistic hydrodynamics is used to calculate the evolution of hot and dense QCD matter. The results reported here are based on the Sharp And Smooth Transport Algorithm (SHASTA), which is employed in many hydrodynamical models and hybrid simulation packages, e.g. the Ultrarelativistic Quantum Molecular Dynamics model (UrQMD). We have redesigned the SHASTA using the OpenCL computing framework to work on accelerators like graphic processing units (GPUs) as well as on multi-core processors. With the redesign of the algorithm the hydrodynamic calculations have been accelerated by a factor 160 allowing for event-by-event calculations and better statistics in hybrid calculations.

Jochen Gerhard; Volker Lindenstruth; Marcus Bleicher

2012-06-05

233

NASA Astrophysics Data System (ADS)

A wealth of low pT observables has been extracted from RHIC's year 2000 run with Au nuclei colliding at energies of 130 GeV per nucleon [1]. We summarize the indications given by the experimental particle spectra, their slope parameters, and anisotropies in the case of non-central collisions (elliptic flow), which suggest that the amount of transverse flow at RHIC is strongly increased compared to experiments at lower beam energies. In fact, we find that rescattering in the created fireball is strong enough that flow observables coincide with results given by an ideal hydrodynamic expansion [2]. This indicates that local thermal equilibrium is established at very short timescales after the collision with temperatures reaching well above the predicted QCD phase transition temperature - even in non-central collisions. We discuss the limitations and shortcomings of the idealized approach and give an outlook and expectations for results from the recent run at 200 AGeV. References: [1] Proceedings of 15th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions, 2001, Nucl. Phys. A, in press; Publications by the BRAHMS-, PHENIX-, PHOBOS-, and STAR-Collaborations. [2] P.F. Kolb et al., PLB 500 (2001) 232; P. Huovinen et al., PLB 503 (2001) 58; P.F. Kolb et al., NPA 696 (2001) 197.

Kolb, Peter

2002-04-01

234

Hydrodynamics of Holographic Superconductors

We study the poles of the retarded Green functions of a holographic superconductor. The model shows a second order phase transition where a charged scalar operator condenses and a U(1) symmetry is spontaneously broken. The poles of the holographic Green functions are the quasinormal modes in an AdS black hole background. We study the spectrum of quasinormal frequencies in the broken phase, where we establish the appearance of a massless or hydrodynamic mode at the critical temperature as expected for a second order phase transition. In the broken phase we find the pole representing second sound. We compute the speed of second sound and its attenuation length as function of the temperature. In addition we find a pseudo diffusion mode, whose frequencies are purely imaginary but with a non-zero gap at zero momentum. This gap goes to zero at the critical temperature. As a technical side result we explain how to calculate holographic Green functions and their quasinormal modes for a set of operators that mix under...

Amado, Irene; Landsteiner, Karl

2009-01-01

235

Hydrodynamics of Holographic Superconductors

We study the poles of the retarded Green functions of a holographic superconductor. The model shows a second order phase transition where a charged scalar operator condenses and a U(1) symmetry is spontaneously broken. The poles of the holographic Green functions are the quasinormal modes in an AdS black hole background. We study the spectrum of quasinormal frequencies in the broken phase, where we establish the appearance of a massless or hydrodynamic mode at the critical temperature as expected for a second order phase transition. In the broken phase we find the pole representing second sound. We compute the speed of second sound and its attenuation length as function of the temperature. In addition we find a pseudo diffusion mode, whose frequencies are purely imaginary but with a non-zero gap at zero momentum. This gap goes to zero at the critical temperature. As a technical side result we explain how to calculate holographic Green functions and their quasinormal modes for a set of operators that mix under the RG flow.

Irene Amado; Matthias Kaminski; Karl Landsteiner

2009-03-12

236

Perfusion effects and hydrodynamics.

Biological processes within living systems are significantly influenced by the motion of the liquids and gases to which those tissues are exposed. Accordingly, tissue engineers must not only understand hydrodynamic phenomena, but also appreciate the vital role of those phenomena in cellular and physiologic processes both in vitro and in vivo. In particular, understanding the fundamental principles of fluid flow underlying perfusion effects in the organ-level internal environment and their relation to the cellular microenvironment is essential to successfully mimicking tissue behavior. In this work, the major principles of hemodynamic flow and transport are summarized, to provide readers with a physical understanding of these important issues. In particular, since quantifying hemodynamic events through experiments can require expensive and invasive techniques, the benefits that can be derived from the use of computational fluid dynamics (CFD) packages and neural networking (NN) models are stressed. A capstone illustration based on analysis of the hemodynamics of aortic aneurysms is presented as a representative example of this approach, to stress the importance of tissue responses to flow-induced events. PMID:17195462

Peattie, Robert A; Fisher, Robert J

2007-01-01

237

Stability of pipeline under oblique waves

A marine pipeline laid on the ocean floor, without burial, is exposed to current and wave induced hydrodynamic forces. If the pipeline does not have enough submerged weight to resist the hydrodynamic forces, the pipeline will be unstable, moving up and down (due to lifting force) and back and forth (due to drag and inertia force). The excessive pipe movement

Jaeyoung Lee; Keh-Han Wang

2001-01-01

238

A hybrid Godunov method for radiation hydrodynamics

From a mathematical perspective, radiation hydrodynamics can be thought of as a system of hyperbolic balance laws with dual multiscale behavior (multiscale behavior associated with the hyperbolic wave speeds as well as multiscale behavior associated with source term relaxation). With this outlook in mind, this paper presents a hybrid Godunov method for one-dimensional radiation hydrodynamics that is uniformly well behaved from the photon free streaming (hyperbolic) limit through the weak equilibrium diffusion (parabolic) limit and to the strong equilibrium diffusion (hyperbolic) limit. Moreover, one finds that the technique preserves certain asymptotic limits. The method incorporates a backward Euler upwinding scheme for the radiation energy density E{sub r} and flux F{sub r} as well as a modified Godunov scheme for the material density {rho}, momentum density m, and energy density E. The backward Euler upwinding scheme is first-order accurate and uses an implicit HLLE flux function to temporally advance the radiation components according to the material flow scale. The modified Godunov scheme is second-order accurate and directly couples stiff source term effects to the hyperbolic structure of the system of balance laws. This Godunov technique is composed of a predictor step that is based on Duhamel's principle and a corrector step that is based on Picard iteration. The Godunov scheme is explicit on the material flow scale but is unsplit and fully couples matter and radiation without invoking a diffusion-type approximation for radiation hydrodynamics. This technique derives from earlier work by Miniati and Colella (2007) . Numerical tests demonstrate that the method is stable, robust, and accurate across various parameter regimes.

Sekora, Michael D., E-mail: sekora@math.princeton.ed [Program in Applied and Computational Mathematics, Princeton University, Princeton, NJ 08544 (United States); Stone, James M. [Program in Applied and Computational Mathematics, Princeton University, Princeton, NJ 08544 (United States); Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

2010-09-20

239

Waves and Instabilities in Magnetized Dusty Plasmas

The status of waves and instabilities in magnetized dusty plasmas is summarized. The effects of an external magnetic field on low-frequency electrostatic and electromagnetic waves in dusty plasmas are discussed. The kinetic and hydrodynamic instabilities are shown to excite magnetized dusty plasma waves. The presence of the latter can give rise to an oscillatory wake-potential which can be responsible for

Padma K. Shukla

1998-01-01

240

Waves and Instabilities in Magnetized Dusty Plasmas

The status of waves and instabilities in magnetized dusty plasmas is summarized. The effects of an external magnetic field on low-frequency electrostatic and electromagnetic waves in dusty plasmas are discussed. The kinetic and hydrodynamic instabilities are shown to excite magnetized dusty plasma waves. The presence of the latter can give rise to an oscillatory wake-potential which can be responsible for

Padma K. Shukla

1999-01-01

241

Multiscale temporal integrators for fluctuating hydrodynamics

NASA Astrophysics Data System (ADS)

Following on our previous work [S. Delong, B. E. Griffith, E. Vanden-Eijnden, and A. Donev, Phys. Rev. E 87, 033302 (2013), 10.1103/PhysRevE.87.033302], we develop temporal integrators for solving Langevin stochastic differential equations that arise in fluctuating hydrodynamics. Our simple predictor-corrector schemes add fluctuations to standard second-order deterministic solvers in a way that maintains second-order weak accuracy for linearized fluctuating hydrodynamics. We construct a general class of schemes and recommend two specific schemes: an explicit midpoint method and an implicit trapezoidal method. We also construct predictor-corrector methods for integrating the overdamped limit of systems of equations with a fast and slow variable in the limit of infinite separation of the fast and slow time scales. We propose using random finite differences to approximate some of the stochastic drift terms that arise because of the kinetic multiplicative noise in the limiting dynamics. We illustrate our integrators on two applications involving the development of giant nonequilibrium concentration fluctuations in diffusively mixing fluids. We first study the development of giant fluctuations in recent experiments performed in microgravity using an overdamped integrator. We then include the effects of gravity and find that we also need to include the effects of fluid inertia, which affects the dynamics of the concentration fluctuations greatly at small wave numbers.

Delong, Steven; Sun, Yifei; Griffith, Boyce E.; Vanden-Eijnden, Eric; Donev, Aleksandar

2014-12-01

242

Semi-relativistic hydrodynamics of three-dimensional and low-dimensional quantum plasma

Contributions of the current-current and Darwin interactions and weak-relativistic addition to kinetic energy in the quantum hydrodynamic equations are considered. Features of hydrodynamic equations for two-dimensional layer of plasma (two-dimensional electron gas for instance) are described. It is shown that the force fields caused by the Darwin interaction and weak-relativistic addition to kinetic energy are partially reduced. Dispersion of three- and two-dimensional semi-relativistic Langmuir waves is calculated.

Andreev, Pavel; Kuz'menkov, Leonid

2014-01-01

243

A new hydrodynamic analysis of double layers

NASA Technical Reports Server (NTRS)

A genuine two-fluid model of plasmas with collisions permits the calculation of dynamic (not necessarily static) electric fields and double layers inside of plasmas including oscillations and damping. For the first time a macroscopic model for coupling of electromagnetic and Langmuir waves was achieved with realistic damping. Starting points were laser-produced plasmas showing very high dynamic electric fields in nonlinear force-produced cavitous and inverted double layers in agreement with experiments. Applications for any inhomogeneous plasma as in laboratory or in astrophysical plasmas can then be followed up by a transparent hydrodynamic description. Results are the rotation of plasmas in magnetic fields and a new second harmonic resonance, explanation of the measured inverted double layers, explanation of the observed density-independent, second harmonics emission from laser-produced plasmas, and a laser acceleration scheme by the very high fields of the double layers.

Hora, Heinrich

1987-01-01

244

Preheat Measurements for Supernova Hydrodynamics Experiments

NASA Astrophysics Data System (ADS)

The use of multi-kilojoule, ns lasers to launch shock waves has become a standard method for initiating hydrodynamic experiments in the field of Laboratory Astrophysics. However, the intense laser ablation that creates moving plasma also leads to the production of unwanted energetic x-rays and suprathermal electrons, both of which can be sources of material preheating. In principle, this preheat can alter the conditions of the experimental setup prior to the desired experiment actually taking place. At the University of Michigan, ongoing Rayleigh-Taylor instability experiments are defined by precise initial conditions, and potential deformation due to preheat could greatly affect their accuracy. An experiment devised and executed in an attempt to assess the preheat in this specific case will be presented, along with the quantitative analysis of the data obtained.

Krauland, Christine; Kuranz, Carolyn; Drake, Paul; Grosskopf, Mike; Campbell, Duncan

2007-11-01

245

Polariton superfluids reveal quantum hydrodynamic solitons.

A quantum fluid passing an obstacle behaves differently from a classical one. When the flow is slow enough, the quantum gas enters a superfluid regime, and neither whirlpools nor waves form around the obstacle. For higher flow velocities, it has been predicted that the perturbation induced by the defect gives rise to the turbulent emission of quantized vortices and to the nucleation of solitons. Using an interacting Bose gas of exciton-polaritons in a semiconductor microcavity, we report the transition from superfluidity to the hydrodynamic formation of oblique dark solitons and vortex streets in the wake of a potential barrier. The direct observation of these topological excitations provides key information on the mechanisms of superflow and shows the potential of polariton condensates for quantum turbulence studies. PMID:21636766

Amo, A; Pigeon, S; Sanvitto, D; Sala, V G; Hivet, R; Carusotto, I; Pisanello, F; Leménager, G; Houdré, R; Giacobino, E; Ciuti, C; Bramati, A

2011-06-01

246

Hydrodynamic instability in eccentric astrophysical discs

Eccentric Keplerian discs are believed to be unstable to three-dimensional hydrodynamical instabilities driven by the time-dependence of fluid properties around an orbit. These instabilities could lead to small-scale turbulence, and ultimately modify the global disc properties. We use a local model of an eccentric disc, derived in a companion paper, to compute the nonlinear vertical ("breathing mode") oscillations of the disc. We then analyse their linear stability to locally axisymmetric disturbances for any disc eccentricity and eccentricity gradient using a numerical Floquet method. In the limit of small departures from a circular reference orbit, the instability of an isothermal disc is explained analytically. We also study analytically the small-scale instability of an eccentric neutrally stratified polytropic disc with any polytropic index using a WKB approximation. We find that eccentric discs are generically unstable to the parametric excitation of small-scale inertial waves. The nonlinear evolution o...

Barker, Adrian J

2014-01-01

247

Proportional Paths, Barodesy, and Granular Solid Hydrodynamics

Propotional paths as summed up by the Goldscheider Rule (GR) -- stating that given a constant strain rate, the evolution of the stress maintains the ratios of its components -- is a characteristics of elasto-plastic motion in granular media. Barodesy, a constitutive relation proposed recently by Kolymbas, is a model that, with GR as input, successfully accounts for data from soil mechanical experiments. Granular solid hydrodynamics (GSH), a theory derived from general principles of physics and two assumptions about the basic behavior of granular media, is constructed to qualitatively account for a wide range of observation -- from elastic waves over elasto-plastic motion to rapid dense flow. In this paper, showing the close resemblance of results from Barodesy and GSH, we further validate GSH and provide an understanding for GR.

Yimin Jiang; Mario Liu

2012-12-16

248

Hydrodynamics of coalescing binary neutron stars: Ellipsoidal treatment

NASA Technical Reports Server (NTRS)

We employ an approximate treatment of dissipative hydrodynamics in three dimensions to study the coalescence of binary neutron stars driven by the emission of gravitational waves. The stars are modeled as compressible ellipsoids obeying a polytropic equation of state; all internal fluid velocities are assumed to be linear functions of the coordinates. The hydrodynamics equations then reduce to a set of coupled ordinary differential equations for the evolution of the principal axes of the ellipsoids, the internal velocity parameters, and the binary orbital parameters. Gravitational radiation reaction and viscous dissipation are both incorporated. We set up exact initial binary equilibrium configurations and follow the transition from the quasi-static, secular decay of the orbit at large separation to the rapid dynamical evolution of the configurations just prior to contact. A hydrodynamical instability resulting from tidal interactions significantly accelerates the coalescence at small separation, leading to appreciable radial infall velocity and tidal lag angles near contact. This behavior is reflected in the gravitational waveforms and may be observable by gravitational wave detectors under construction. In cases where the neutron stars have spins which are not aligned with the orbital angular momentum, the spin-induced quadrupole moment can lead to precession of the orbital plane and therefore modulation of the gravitational wave amplitude even at large orbital radius. However, the amplitude of the modulation is small for typical neutron star binaries with spins much smaller than the orbital angular momentum.

Lai, Dong; Shapiro, Stuart L.

1995-01-01

249

Effect of Second-Order Hydrodynamics on a Floating Offshore Wind Turbine

The design of offshore floating wind turbines uses design codes that can simulate the entire coupled system behavior. At the present, most codes include only first-order hydrodynamics, which induce forces and motions varying with the same frequency as the incident waves. Effects due to second- and higher-order hydrodynamics are often ignored in the offshore industry, because the forces induced typically are smaller than the first-order forces. In this report, first- and second-order hydrodynamic analysis used in the offshore oil and gas industry is applied to two different wind turbine concepts--a spar and a tension leg platform.

Roald, L.; Jonkman, J.; Robertson, A.

2014-05-01

250

Influence of homogeneous magnetic fields on the flow of a ferrofluid in the Taylor-Couette system.

We investigate numerically the influence of a homogeneous magnetic field on a ferrofluid in the gap between two concentric, independently rotating cylinders. The full Navier-Stokes equations are solved with a combination of a finite difference method and a Galerkin method. Structure, dynamics, symmetry properties, bifurcation, and stability behavior of different vortex structures are investigated for axial and transversal magnetic fields, as well as combinations of them. We show that a transversal magnetic field modulates the Taylor vortex flow and the spiral vortex flow. Thus, a transversal magnetic field induces wavy structures: wavy Taylor vortex flow (wTVF) and wavy spiral vortex flow. In contrast to the classic wTVF, which is a secondarily bifurcating structure, these magnetically generated wavy Taylor vortices are pinned by the magnetic field, i.e., they are stationary and they appear via a primary forward bifurcation out of the basic state of circular Couette flow. PMID:20866739

Altmeyer, S; Hoffmann, Ch; Leschhorn, A; Lücke, M

2010-07-01

251

Hydrodynamic Stability of Liquid-Propellant Combustion: Landau's Problem Revisited

NASA Technical Reports Server (NTRS)

Hydrodynamic, or Landau, instability in combustion is typically associated with the onset of wrinkling of a flame surface, corresponding to the formation of steady cellular structures as the stability threshold is crossed. As its name suggests, it stems from hydrodynamic effects connected with thermal expansion across the reaction region. In the context of liquid-propellant combustion, the classical models that originally predicted this phenomenon have been extended to include the important effects that arise from a dynamic dependence of the burning rate on the local pressure and temperature fields. Thus, the onset of Landau instability has now been shown to occur for sufficiently small negative values of the pressure sensitivity of the burning rate, significantly generalizing previous classical results for this problem that assumed a constant normal burning rate. It has also been shown that the onset of instability occurs for decreasing values of the disturbance wave number as the gravitational-acceleration parameter decreases. Consequently, in an appropriate weak-gravity limit, Landau instability becomes a long-wave phenomena associated with the formation of large cells on the liquid-propellant surface. Additionally, a pulsating form of hydrodynamic instability has been shown to occur as well, corresponding to the onset of temporal oscillations in the location of the liquid/gas interface. This instability occurs for sufficiently large negative values of the pressure sensitivity, and is enhanced by increasing values of the burning-rate temperature sensitivity. It is further shown that for sufficiently small values of this parameter, there exists a stable range of pressure sensitivities for steady, planar burning such that the classical cellular form of hydrodynamic instability and the more recent pulsating form of hydrodynamic instability can each occur as the corresponding stability threshold is crossed. For larger thermal sensitivities, however, the pulsating stability boundary evolves into a C-shaped curve in the (disturbance-wave number, pressure-sensitivity) plane, indicating loss of stability to pulsating perturbations for all sufficiently large disturbance wavelengths. It is thus concluded, based on characteristic parameter values that an equally likely form of hydrodynamic instability in liquid-propellant combustion is of a nonsteady, long-wave nature, distinct from the steady, cellular form originally predicted by Landau.

Margolis, S. B.

2001-01-01

252

Investigation on the hydrodynamic performance of an ultra deep turret-moored FLNG system

NASA Astrophysics Data System (ADS)

Hydrodynamic performance of an ultra deep turret-moored Floating Liquefied Natural Gas (FLNG) system is investigated. Hydrodynamic modeling of a turret-moored FLNG system, in consideration of the coupling effects of the vessel and its mooring lines, has been addressed in details. Based on the boundary element method, a 3-D panel model of the FLNG vessel and the related free water surface model are established, and the first-order and second-order mean-drift wave loads and other hydrodynamic coefficients are calculated. A systematic model test program consisting of the white noise wave test, offset test and irregular wave test combined with current and wind, etc. is performed to verify the numerical model. Owing to the depth limit of the water basin, the model test is carried out for the hydrodynamics of the FLNG coupled with only the truncated mooring system. The numerical simulation model features well the hydrodynamic performance of the FLNG system obtained from the model tests. The hydrodynamic characteristics presented in both the numerical simulations and the physical model tests would serve as the guidance for the ongoing project of FLNG system.

Zhao, Wen-hua; Yang, Jian-min; Hu, Zhi-qiang; Xiao, Long-fei; Peng, Tao

2012-03-01

253

Granular hydrodynamics and pattern formation in vertically oscillated granular disk layers

NASA Astrophysics Data System (ADS)

The goal of this study is to demonstrate numerically that certain hydrodynamic systems, derived from inelastic kinetic theory, give fairly good descriptions of rapid granular flows even if they are way beyond their supposed validity limits. A numerical hydrodynamic solver is presented for a vibrated granular bed in two dimensions. It is based on a highly accurate shock capturing state-of-the-art numerical scheme applied to a compressible Navier-Stokes system for granular flow. The hydrodynamic simulation of granular flows is challenging, particularly in systems where dilute and dense regions occur at the same time and interact with each other. As a benchmark experiment, we investigate the formation of Faraday waves in a two-dimensional thin layer exposed to vertical vibration in the presence of gravity. The results of the hydrodynamic simulations are compared with those of event-driven molecular dynamics and the overall quantitative agreement is good at the level of the formation and structure of periodic patterns. The accurate numerical scheme for the hydrodynamic description improves the reproduction of the primary onset of patterns compared to previous literature. To our knowledge, these are the first hydrodynamic results for Faraday waves in two-dimensional granular beds that accurately predict the wavelengths of the two-dimensional standing waves as a function of the perturbation's amplitude. Movies are available with the online version of the paper.

Carrillo, Jos? A.; P?Schel, Thorsten; Salue?A, Clara

254

NASA Astrophysics Data System (ADS)

In this paper, we investigate the field-dependent T1-relaxation and T1-contrast imaging of ferrofluids using high-Tc superconducting quantum interference device (SQUID)-detected nuclear magnetic resonance and imaging in low magnetic fields, where T1 is the spin-lattice relaxation time. It was found that the 1/T1 of ferrofluids increases when the prepolarization field increases. We attribute this to the enhanced magnetic-field gradients generated from the induced magnetization that accelerates the T1-relaxation more in a high strength of fields in comparison to a low strength of fields. Using phantoms with different relaxation times, the T1-contrast images are demonstrated in low magnetic fields, which can be promising for discriminating tumors.

Liao, S. H.; Yang, Hong-Chang; Horng, H. E.; Liu, C. W.; Chen, H. H.; Chen, M. J.; Chen, K. L.; Liu, C. I.; Wang, L. M.

2012-12-01

255

NASA Astrophysics Data System (ADS)

This book gives a self-contained and up-to-date account of mathematical results in the linear theory of water waves. The study of waves has many applications, including the prediction of behavior of floating bodies (ships, submarines, tension-leg platforms etc.), the calculation of wave-making resistance in naval architecture, and the description of wave patterns over bottom topography in geophysical hydrodynamics. The first section deals with time-harmonic waves. Three linear boundary value problems serve as the approximate mathematical models for these types of water waves. The next section uses a plethora of mathematical techniques in the investigation of these three problems. The techniques used in the book include integral equations based on Green's functions, various inequalities between the kinetic and potential energy and integral identities which are indispensable for proving the uniqueness theorems. The so-called inverse procedure is applied to constructing examples of non-uniqueness, usually referred to as 'trapped nodes.'

Kuznetsov, N.; Maz'ya, V.; Vainberg, B.

2002-08-01

256

Axisymmetric solitary waves on the surface of a ferrofluid E. Bourdin, J.-C. Bacri, and E. Falcon

-carrying metallic tube. According to the ratio between the magnetic and capillary forces, both elevation through hollow waterproof screws. A dc electrical current, I, in the range 0Â100 A is applied

Paris-Sud XI, UniversitÃ© de

257

magnetic fluid layer surrounding a current-carrying metallic tube. According to the ratio between waterproof screws. A dc electri- cal current I in the range 0Â100 A is applied to the cylindrical conductor

Falcon, Eric

258

Black Brane Entropy and Hydrodynamics

A generalization of entropy to near-equilibrium phenomena is provided by the notion of a hydrodynamic entropy current. Recent advances in holography have lead to the formulation of fluid-gravity duality, a remarkable connection between the hydrodynamics of certain strongly coupled media and dynamics of higher dimensional black holes. This Letter introduces a correspondence between phenomenologically defined entropy currents in relativistic hydrodynamics and quasilocal horizons of near-equilibrium black objects in a dual gravitational description. A general formula is given, expressing the divergence of the entropy current in terms of geometric objects which appear naturally in the gravity dual geometry. The proposed definition is explicitly covariant with respect to boundary diffeomorphisms and reproduces known results when evaluated for the event horizon.

Ivan Booth; Michal P. Heller; Michal Spalinski

2011-03-27

259

RUN UP OF SURFACE AND INTERNAL WAVES H. Branger1

RUN UP OF SURFACE AND INTERNAL WAVES H. Branger1 , O. Kimmoun , N. Gavrilov , V. Liapidevskii3 , E as for internal waves is considered. The study is based on the laboratory run up experiments for surface waves in LIH (Lavrentyev Institute of Hydrodynamics) and on the field data describing the internal wave run up

Paris-Sud XI, UniversitÃ© de

260

Isogeometric analysis of Lagrangian hydrodynamics

NASA Astrophysics Data System (ADS)

Isogeometric analysis of Lagrangian shock hydrodynamics is proposed. The Euler equations of compressible hydrodynamics in the weak form are discretized using Non-Uniform Rational B-Splines (NURBS) in space. The discretization has all the advantages of a higher-order method, with the additional benefits of exact symmetry preservation and better per-degree-of-freedom accuracy. An explicit, second-order accurate time integration procedure, which conserves total energy, is developed and employed to advance the equations in time. The performance of the method is examined on a set of standard 2D and 3D benchmark examples, where good quality of the computational results is attained.

Bazilevs, Y.; Akkerman, I.; Benson, D. J.; Scovazzi, G.; Shashkov, M. J.

2013-06-01

261

Dissipation, hydrodynamics and the fireball

We investigate the hydrodynamics of the QCD plasma using dimensionless numbers built from the thermodynamics and transport theory of the plasma and characteristic dimensions of the fireball produced in heavy-ion collisions. We find that by the usual measures, dissipation is strong, and the fireball is on the borderline of equilibrium. As a result, the system is richer in phenomena than ideal hydrodynamics would predict. One general implication is that it may be possible to get a direct view of the QCD plasma phase rather than having to infer its existence indirectly from signals that come from the freezeout isotherm after the fireball has cooled into the hadronic phase.

Sourendu Gupta

2005-07-18

262

Black brane entropy and hydrodynamics

Recent advances in holography have led to the formulation of fluid-gravity duality, a remarkable connection between the hydrodynamics of certain strongly coupled media and dynamics of higher dimensional black holes. This paper introduces a correspondence between phenomenologically defined entropy currents in relativistic hydrodynamics and 'generalized horizons' of near-equilibrium black objects in a dual gravitational description. A general formula is given, expressing the divergence of the entropy current in terms of geometric objects which appear naturally in the gravity dual geometry. The proposed definition is explicitly covariant with respect to boundary diffeomorphisms and reproduces known results when evaluated for the event horizon.

Booth, Ivan; Heller, Michal P.; Spalinski, Michal [Department of Mathematics and Statistics, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, A1C 5S7 (Canada); Instituut voor Theoretische Fysica, Universiteit van Amsterdam, Science Park 904, 1090 GL Amsterdam (Netherlands); Soltan Institute for Nuclear Studies, Hoza 69, 00-681 Warsaw (Poland) and Physics Department, University of Bialystok, 15-424 Bialystok (Poland)

2011-03-15

263

Abnormal pressures as hydrodynamic phenomena

So-called abnormal pressures, subsurface fluid pressures significantly higher or lower than hydrostatic, have excited speculation about their origin since subsurface exploration first encountered them. Two distinct conceptual models for abnormal pressures have gained currency among earth scientists. The static model sees abnormal pressures generally as relict features preserved by a virtual absence of fluid flow over geologic time. The hydrodynamic model instead envisions abnormal pressures as phenomena in which flow usually plays an important role. This paper develops the theoretical framework for abnormal pressures as hydrodynamic phenomena, shows that it explains the manifold occurrences of abnormal pressures, and examines the implications of this approach. -from Author

Neuzil, C.E.

1995-01-01

264

From Field Theory to the Hydrodynamics of Relativistic Superfluids

The hydrodynamic description of a superfluid is usually based on a two-fluid picture. In this thesis, basic properties of such a relativistic two-fluid system are derived from the underlying microscopic physics of a complex scalar quantum field theory. To obtain analytic results of all non-dissipative hydrodynamic quantities in terms of field theoretic variables, calculations are first carried out in a low-temperature and weak-coupling approximation. In a second step, the 2-particle-irreducible formalism is applied: This formalism allows for a numerical evaluation of the hydrodynamic parameters for all temperatures below the critical temperature. In addition, a system of two coupled superfluids is studied. As an application, the velocities of first and second sound in the presence of a superflow are calculated. The results show that first (second) sound evolves from a density (temperature) wave at low temperatures to a temperature (density) wave at high temperatures. This role reversal is investigated for ultra-relativistic and near-nonrelativistic systems for zero and nonzero superflow. The studies carried out in this thesis are of a very general nature as one does not have to specify the system for which the microscopic field theory is an effective description. As a particular example, superfluidity in dense quark and nuclear matter in compact stars are discussed.

Stephan Stetina

2015-01-31

265

Hydrodynamically mediated macrophyte silica dynamics.

In most aquatic ecosystems, hydrodynamic conditions are a key abiotic factor determining species distributions and abundance of aquatic plants. Resisting stress and keeping an upright position often relies on investment in tissue reinforcement, which is costly to produce. Silica could provide a more economical alternative. Two laboratory experiments were conducted to measure the response of two submerged species, Egeria densa Planch. and Limnophila heterophylla (Roxb.) Benth., to dissolved silicic acid availability and exposure to hydrodynamic stress. The results were verified with a third species in a field study (Nuphar lutea (L.) Smith). Biogenic silica (BSi) concentration in both stems and leaves increases with increasing dissolved silica availability but also with the presence of hydrodynamic stress. We suggest that the inclusion of extra silica enables the plant to alternatively invest its energy in the production of lignin and cellulose. Although we found no significant effects of hydrodynamic stress on cellulose or lignin concentrations either in the laboratory or in the field, BSi was negatively correlated with cellulose concentration and positively correlated with lignin concentration in samples collected in the field study. This implies that the plant might perform with equal energy efficiency in both standing and running water environments. This could provide submerged species with a tool to respond to abiotic factors, to adapt to new ecological conditions and hence potentially colonise new environments. PMID:22512916

Schoelynck, J; Bal, K; Puijalon, S; Meire, P; Struyf, E

2012-11-01

266

Topological groundwater hydrodynamics Garrison Sposito

Topological groundwater hydrodynamics Garrison Sposito Department of Civil and Environmental; received in revised form 10 November 2000; accepted 15 November 2000 Abstract Topological groundwater, the topological characteristics of groundwater Â¯ows governed by the Darcy law are studied. It is demonstrated that

Chen, Yiling

267

Hydrodynamic instabilities in inertial fusion

This report discusses topics on hydrodynamics instabilities in inertial confinement: linear analysis of Rayleigh-Taylor instability; ablation-surface instability; bubble rise in late-stage Rayleigh-Taylor instability; and saturation and multimode interactions in intermediate-stage Rayleigh-Taylor instability.

Hoffman, N.M.

1994-09-01

268

Relativistic hydrodynamics with strangeness production

The relativistic hydrodynamic approach is used to describe production of strangeness and/or heavy quarks in ultrarelativistic heavy ion reactions. Production processes are important ingredients of dissipative effects in the hadronic liquid. Beyond viscosity also chemo- and thermo-diffusion processes are considered. This also allows to specify chemical and thermal freeze-out conditions.

L. Turko

2007-10-25

269

Hydrodynamic Damping in Trapped Bose Gases

Griffin, Wu and Stringari have derived the hydrodynamic equations of a trapped dilute Bose gas above the Bose-Einstein transition temperature. We give the extension which includes hydrodynamic damping, following the classic work of Uehling and Uhlenbeck based on the Chapman-Enskog procedure. Our final result is a closed equation for the velocity fluctuations dvwhich includes the hydrodynamic damping due to the

T. Nikuni; A. Griffin

1998-01-01

270

Axially symmetric pseudo-Newtonian hydrodynamics code

NASA Astrophysics Data System (ADS)

We develop a numerical hydrodynamics code using a pseudo-Newtonian formulation that uses the weak-field approximation for the geometry, and a generalized source term for the Poisson equation that takes into account relativistic effects. The code was designed to treat moderately relativistic systems such as rapidly rotating neutron stars. The hydrodynamic equations are solved using a finite volume method with high-resolution shock-capturing techniques. We implement several different slope limiters for second-order reconstruction schemes and also investigate higher order reconstructions such as the piecewise parabolic method, essentially non-oscillatory method (ENO) and weighted ENO. We use the method of lines to convert the mixed spatial-time partial differential equations into ordinary differential equations (ODEs) that depend only on time. These ODEs are solved using second- and third-order Runge-Kutta methods. The Poisson equation for the gravitational potential is solved with a multigrid method, and to simplify the boundary condition, we use compactified coordinates which map spatial infinity to a finite computational coordinate using a tangent function. In order to confirm the validity of our code, we carry out four different tests including one- and two-dimensional shock tube tests, stationary star tests of both non-rotating and rotating models, and radial oscillation mode tests for spherical stars. In the shock tube tests, the code shows good agreement with analytic solutions which include shocks, rarefaction waves and contact discontinuities. The code is found to be stable and accurate: for example, when solving a stationary stellar model the fractional changes in the maximum density, total mass, and total angular momentum per dynamical time are found to be 3 × 10-6, 5 × 10-7 and 2 × 10-6, respectively. We also find that the frequencies of the radial modes obtained by the numerical simulation of the steady-state star agree very well with those obtained by linear analysis.

Kim, Jinho; Kim, Hee Il; Choptuik, Matthew William; Lee, Hyung Mok

2012-08-01

271

Hydrodynamic model of Fukushima-Daiichi NPP Industrial site flooding

While the Fukushima-Daiichi was designed and constructed the maximal tsunami height estimate was about 3 m based on analysis of statistical data including Chile earthquake in 1960. The NPP project industrial site height was 10 m. The further deterministic estimates TPCO-JSCE confirmed the impossibility of the industrial site flooding by a tsunami and therefore confirmed ecological safety of the NPP. However, as a result of beyond design earthquake of 11 March 2011 the tsunami height at the shore near the Fukushima-Daiichi NPP reached 15 m. This led to flooding and severe emergencies having catastrophic environmental consequences. This paper proposes hydrodynamic model of tsunami emerging and traveling based on conservative assumptions. The possibility of a tsunami wave reaching 15 m height at the Fukushima-Daiichi NPP shore was confirmed for deduced hydrodynamic resistance coefficient of 1.8. According to the model developed a possibility of flooding is determined not only by the industrial site height, magni...

Vaschenko, V N; Gerasimenko, T V; Vachev, B

2014-01-01

272

Enhanced Heat Flow in the Hydrodynamic Collisionless Regime

We study the heat conduction of a cold, thermal cloud in a highly asymmetric trap. The cloud is axially hydrodynamic, but due to the asymmetric trap radially collisionless. By locally heating the cloud we excite a thermal dipole mode and measure its oscillation frequency and damping rate. We find an unexpectedly large heat conduction compared to the homogeneous case. The enhanced heat conduction in this regime is partially caused by atoms with a high angular momentum spiraling in trajectories around the core of the cloud. Since atoms in these trajectories are almost collisionless they strongly contribute to the heat transfer. We observe a second, oscillating hydrodynamic mode, which we identify as a standing wave sound mode.

Meppelink, R.; Rooij, R. van; Vogels, J. M.; Straten, P. van der [Atom Optics and Ultrafast Dynamics, Utrecht University, P.O. Box 80000, 3508 TA Utrecht (Netherlands)

2009-08-28

273

Hydrodynamical constraints on cosmic-ray acceleration in relativistic shocks

NASA Technical Reports Server (NTRS)

A two-fluid hydrodynamical model governing the transport of cosmic rays in a relativistically moving background plasma is developed. The equations are used to discuss the time asymptotic structure of a relativistic, plane-parallel shock wave significantly modified by first-order Fermi acceleration of cosmic rays. The model allows for an anisotropic cosmic-ray pressure tensor with pressure components parallel and perpendicular to the shock normal. It is surmised that the well-known energy threshold problem for diffusive shock acceleration that downstream particles have a large enough velocity to overtake the shock and subsequently scatter in the upstream medium before returning to the downstream medium may be expressed hydrodynamically by the condition V less than V(cr), where V is the fluid velocity relative to the shock and V(cr) is the relativistic cosmic-ray sound speed. Astrophysical implications of the results are briefly discussed.

Webb, G. M.

1987-01-01

274

Low Mach Number Fluctuating Hydrodynamics of Multispecies Liquid Mixtures

We develop a low Mach number formulation of the hydrodynamic equations describing transport of mass and momentum in a multispecies mixture of incompressible miscible liquids at specified temperature and pressure that generalizes our prior work on ideal mixtures of ideal gases and binary liquid mixtures. In this formulation we combine and extend a number of existing descriptions of multispecies transport available in the literature. The formulation applies to non-ideal mixtures of arbitrary number of species, without the need to single out a 'solvent' species, and includes contributions to the diffusive mass flux due to gradients of composition, temperature and pressure. Momentum transport and advective mass transport are handled using a low Mach number approach that eliminates fast sound waves (pressure fluctuations) from the full compressible system of equations and leads to a quasi-incompressible formulation. Thermal fluctuations are included in our fluctuating hydrodynamics description following the princi...

Donev, A; Bhattacharjee, A K; Garcia, A L; Bell, J B

2014-01-01

275

Hydrodynamics of maneuvering bodies: LDRD final report

The objective of the ``Hydrodynamics of Maneuvering Bodies`` LDRD project was to develop a Lagrangian, vorticity-based numerical simulation of the fluid dynamics associated with a maneuvering submarine. Three major tasks were completed. First, a vortex model to simulate the wake behind a maneuvering submarine was completed, assuming the flow to be inviscid and of constant density. Several simulations were performed for a dive maneuver, each requiring less than 20 cpu seconds on a workstation. The technical details of the model and the simulations are described in a separate document, but are reviewed herein. Second, a gridless method to simulate diffusion processes was developed that has significant advantages over previous Lagrangian diffusion models. In this model, viscous diffusion of vorticity is represented by moving vortices at a diffusion velocity, and expanding the vortices as specified by the kinematics for a compressible velocity field. This work has also been documented previously, and is only reviewed herein. The third major task completed was the development of a vortex model to describe inviscid internal wave phenomena, and is the focus of this document. Internal wave phenomena in the stratified ocean can affect an evolving wake, and thus must be considered for naval applications. The vortex model for internal wave phenomena includes a new formulation for the generation of vorticity due to fluid density variations, and a vortex adoption algorithm that allows solutions to be carried to much longer times than previous investigations. Since many practical problems require long-time solutions, this new adoption algorithm is a significant step toward making vortex methods applicable to practical problems. Several simulations are described and compared with previous results to validate and show the advantages of the new model. An overview of this project is also included.

Kempka, S.N.; Strickland, J.H.

1994-01-01

276

Lattice-Boltzmann modeling of phonon hydrodynamics.

Based on the phonon Boltzmann equation, a lattice-Boltzmann model for phonon hydrodynamics is developed. Both transverse and longitudinal polarized phonons that interact through normal and umklapp processes are considered in the model. The collision term is approximated by the relaxation time model where normal and umklapp processes tend to relax distributions of phonons to their corresponding equilibrium distribution functions-the displaced Planck distribution and the Planck distribution, respectively. A macroscopic phonon thermal wave equation (PTWE), valid for the second-sound mode, is derived through the technique of Chapman-Enskog expansion. Compared to the dual-phase-lag (DPL) -based thermal wave equation, the PTWE has an additional fourth-ordered spatial derivative term. The fundamental difference between the two models is discussed through examining a propagating thermal pulse in a single-phased medium and the transient and steady-state transport phenomena on a two-layered structure subjected to different temperatures at boundaries. Results show that transport phenomena are significantly different between the two models. The behavior exhibited by the DPL model, as thermal wave behavior goes over to diffusive behavior, tau_{T}-->tau_{q} is incompatible with any microscopic phonon propagating mode. Unlike the DPL model, in which tau_{T} only has an effect on the transient phenomena, in the PTWE model tau_{T} shows effects on phenomena at both transient and steady state. With the intrinsic compatibility to the microscopic state, discontinuous quantities, such as a jump of temperature at a boundary or at an interface, can be calculated naturally and straightforwardly with the present lattice-Boltzmann method. PMID:18643400

Jiaung, Wen-Shu; Ho, Jeng-Rong

2008-06-01

277

Formation Interuniversitaire de Physique Hydrodynamics

" . . . . . . . . . . . . . . . . . . . . 16 3.2 Rotating Frames . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.3 Manipulating Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.2.1 Hydraulic Jumps

Balbus, Steven

278

On theory of long-wave nonequilibrium fluctuations

NASA Astrophysics Data System (ADS)

The regular method for construction of kinetic equations of the long-wave fluctuation theory is developed in a microscopic approach on the base of generalization of the kinetic Bogolyubov theory. The transition to the hydrodynamic theory of long-wave fluctuations is investigated in detail. The derived hydrodynamical equations describe a turbulent liquid state. The stochastic interpretation of both kinetic equations and hydrodynamical equations of long-wave fluctuation is presented. The generalization of the local-equilibrium Maxwell distribution is obtained and the concept of nonequilibrium entropy for fluctuating systems is introduced. The H-theorem is proved.

Peletminsky, S. V.; Slusarenko, Yu. V.

1994-09-01

279

Computations of fully nonlinear three-dimensional wave-body interactions

Nonlinear effects in hydrodynamics of wave-body interaction problems become critically important when large-amplitude body motions and/or extreme surface waves are involved. Accurate prediction and understanding of these ...

Yan, Hongmei

2010-01-01

280

Analytic hydrodynamical simulation of the formation of tsunami using finite elements

NASA Astrophysics Data System (ADS)

An exact analytic solution of a Cauchy problem for a 2D-wave equation with a specific axially symmetric initial condition is considered. This solution is used to derive solutions of more complicated hydrodynamical problems simulating tsunami waves. Using these solutions, directivity diagrams and wave profiles are computed for initial conditions that are superpositions of axially symmetric ones, and these superpositions can excite waves of unusual directivity. A similar effect can be obtained by some successively activated symmetric initial conditions. An analytic hydrodynamicalal simulation of Sumatra tsunami on December 29, 2004 is carried out. The results are compared with some numerical simulation data obtained by other researchers.

Sekerzh-Zen'kovich, S.; Volkov, B.

2010-12-01

281

It is shown that the hydrodynamic interpretation of a charged quantum particle leads to a different theoretical prediction for low energy bremsstrahlung than does quantum electrodynamics (QED). In the calculations, the electromagnetic fields are treated classically in the hydrodynamic case, but are quantized in QED. Calculations show the hydrodynamic model to have a different and more sensitive dependence on the size and shape of the radiating particle's wave packet then does QED. In particular it is shown that bremsstrahlung is sometimes greatly reduced when the force acting on the particle is localized to a volume small compared to the particle's wave packet. QED exhibits no such reduction. Therefore it is possible to test this effect experimentally. An experiment is proposed. It involves an electron microscope with a Wien filter for producing monochromatic beam electrons and an accurate energy measurement of the particle after passing through a local force field.

Mark P. Davidson

2003-02-06

282

Aeroelastic simulation tools are routinely used to design and analyze onshore wind turbines, in order to obtain cost effective machines that achieve favorable performance while maintaining structural integrity. These tools employ sophisticated models of wind-inflow; aerodynamic, gravitational, and inertial loading of the rotor, nacelle, and tower; elastic effects within and between components; and mechanical actuation and electrical responses of the generator and of control and protection systems. For offshore wind turbines, additional models of the hydrodynamic loading in regular and irregular seas, the dynamic coupling between the support platform motions and wind turbine motions, and the dynamic characterization of mooring systems for compliant floating platforms are also important. Hydrodynamic loading includes contributions from hydrostatics, wave radiation, and wave scattering, including free surface memory effects. The integration of all of these models into comprehensive simulation tools, capable of modeling the fully coupled aeroelastic and hydrodynamic responses of floating offshore wind turbines, is presented.

Jonkman, J. M.; Sclavounos, P. D.

2006-01-01

283

Hydrodynamics of cold holographic matter

NASA Astrophysics Data System (ADS)

We show that at any temperature, the low-energy (with respect to the chemical potential) collective excitations of the transverse components of the energy-momentum tensor and the global U(1) current in the field theory dual to the planar RN-AdS4 black hole are simply those of hydrodynamics. That is, hydrodynamics is applicable even at energy scales much greater than the temperature. It is applicable even at zero temperature. Specifically, we find that there is always a diffusion mode with diffusion constant proportional to the ratio of entropy density to energy density. At low temperatures, the leading order momentum and temperature dependences of the dispersion relation of this mode are controlled by the dimension of an operator in the thermal CFT1 dual to the near-horizon Schwarzschild-AdS2 geometry.

Davison, Richard A.; Parnachev, Andrei

2013-06-01

284

Hydrodynamic interactions between rotating helices

NASA Astrophysics Data System (ADS)

Escherichia coli bacteria use rotating helical flagella to swim. At this scale, viscous effects dominate inertia, and there are significant hydrodynamic interactions between nearby helices. These interactions cause the flagella to bundle during the “runs” of bacterial chemotaxis. Here we use slender-body theory to solve for the flow fields generated by rigid helices rotated by stationary motors. We determine how the hydrodynamic forces and torques depend on phase and phase difference, show that rigid helices driven at constant torque do not synchronize, and solve for the flows. We also use symmetry arguments based on kinematic reversibility to show that for two rigid helices rotating with zero phase difference, there is no time-averaged attractive or repulsive force between the helices.

Kim, Munju; Powers, Thomas R.

2004-06-01

285

Interplay between hydrodynamics and jets

By combining the jet quenching Monte Carlo JEWEL with a realistic hydrodynamic model for the background we investigate the sensitivity of jet observables to details of the medium model and quantify the influence of the energy and momentum lost by jets on the background evolution. On the level of event averaged source terms the effects are small and are caused mainly by the momentum transfer.

Korinna C. Zapp; Stefan Floerchinger

2014-08-05

286

Wave drift forces on OTEC platforms

Analytical methods to determine the mean value of the slowly-varying second order drift forces due to waves on different types of OTEC platforms (a barge form and a spar) are described. The basic method used is via free surface hydrodynamics, in terms of the radiated and scattered waves for these platforms (including the deep cold water pipe) during their interaction

P. Kaplan

1979-01-01

287

Long Time Evolution of Unstable Bichromatic Waves

P, 31. For applications in hydrodynamic laboratories, the evolution and the resulting maximal wave heights are of practical interest. An experimental study by (4) in which the spatial evolution of a bichromatic wave group envelope is reported, motivated the research of this presentation. We numerically investigate with a nonlinear potential time domain method the long t,ime evolution and spatial distribution

J. H. Westhuis; E. van Groesen; R. H. M. Huijsmans; T. Miloh; G. Zilman

2000-01-01

288

Some open questions in hydrodynamics

When speaking of unsolved problems in physics, this is surprising at first glance to discuss the case of fluid mechanics. However, there are many deep open questions that come with the theory of fluid mechanics. In this paper, we discuss some of them that we classify in two categories, the long term behavior of solutions of equations of hydrodynamics and the definition of initial (boundary) conditions. The first set of questions come with the non-relativistic theory based on the Navier-Stokes equations. Starting from smooth initial conditions, the purpose is to understand if solutions of Navier-Stokes equations remain smooth with the time evolution. Existence for just a finite time would imply the evolution of finite time singularities, which would have a major influence on the development of turbulent phenomena. The second set of questions come with the relativistic theory of hydrodynamics. There is an accumulating evidence that this theory may be relevant for the description of the medium created in high energy heavy-ion collisions. However, this is not clear that the fundamental hypotheses of hydrodynamics are valid in this context. Also, the determination of initial conditions remains questionable. The purpose of this paper is to explore some ideas related to these questions, both in the non-relativistic and relativistic limits of fluid mechanics. We believe that these ideas do not concern only the theory side but can also be useful for interpreting results from experimental measurements.

Mateusz Dyndal; Laurent Schoeffel

2014-09-08

289

NASA Astrophysics Data System (ADS)

We investigate the influence of Coriolis force on the onset of thermomagnetic convection in ferrofluid saturating a porous layer in the presence of a uniform vertical magnetic field using both linear and weakly non-linear analyses. The modified Brinkman-Forchheimer-extended Darcy equation with Coriolis term has been used to describe the fluid flow. The linear theory based on normal mode method is considered to find the criteria for the onset of stationary thermomagnetic Convection and weakly non-linear analysis based on minimal representation of truncated Fourier series analysis containing only two terms has been used to find the Nusselt number Nu as functions of time. The range of thermal Rayleigh number R beyond which the bifurcation becomes subcritical increases with increasing ?, Da-1 and Ta. The global quantity of the heat transfer rate decreases by increasing the Taylor number Ta. The results obtained, during the above analyses, have been presented graphically and the effects of various parameters on heat and mass transfer have been discussed. Finally, we have drawn the steady streamlines for various parameters.

Nanjundappa, C. E.; Shivakumara, I. S.; Prakash, H. N.

2014-12-01

290

This paper presents a numerical method to evaluate the hydrodynamic forces of translating bodies under a free surface. Both steady and unsteady problems are considered. Analytical and numerical studies are carried out based on the Havelock wave-source function and the integral equation method. Two main problems arising inherently in the proposed solution method are overcome in order to facilitate the

S. A. Yang

2000-01-01

291

Direct Measurement of Wave-Induced Bottom Shear Stress Under Irregular Waves

\\u000a Wave-induced bottom shear stress is one of most important parameters in modelling of wave hydrodynamics and coastal sediment\\u000a transport, but has not been accurately estimated so far. A new type of shear plate is developed to measure instantaneous wave\\u000a bottom shear stress under both regular and irregular waves. The shear plate directly measures instantaneous horizontal force\\u000a by applying the Wheatstone

Zaijin You; Baoshu Yin; Guang Huo

292

Quantum positron acoustic waves

NASA Astrophysics Data System (ADS)

Nonlinear quantum positron-acoustic (QPA) waves are investigated for the first time, within the theoretical framework of the quantum hydrodynamic model. In the small but finite amplitude limit, both deformed Korteweg-de Vries and generalized Korteweg-de Vries equations governing, respectively, the dynamics of QPA solitary waves and double-layers are derived. Moreover, a full finite amplitude analysis is undertaken, and a numerical integration of the obtained highly nonlinear equations is carried out. The results complement our previously published results on this problem.

Metref, Hassina; Tribeche, Mouloud

2014-12-01

293

Advances in the hydrodynamics solver of CO5BOLD

NASA Astrophysics Data System (ADS)

Many features of the Roe solver used in the hydrodynamics module of CO5BOLD have recently been added or overhauled, including the reconstruction methods (by adding the new second-order ``Frankenstein's method''), the treatment of transversal velocities, energy-flux averaging and entropy-wave treatment at small Mach numbers, the CTU scheme to combine the one-dimensional fluxes, and additional safety measures. All this results in a significantly better behavior at low Mach number flows, and an improved stability at larger Mach numbers requiring less (or no) additional tensor viscosity, which then leads to a noticeable increase in effective resolution.

Freytag, Bernd

294

Hydrodynamic modeling of tsunamis from the Currituck landslide

Tsunami generation from the Currituck landslide offshore North Carolina and propagation of waves toward the U.S. coastline are modeled based on recent geotechnical analysis of slide movement. A long and intermediate wave modeling package (COULWAVE) based on the non-linear Boussinesq equations are used to simulate the tsunami. This model includes procedures to incorporate bottom friction, wave breaking, and overland flow during runup. Potential tsunamis generated from the Currituck landslide are analyzed using four approaches: (1) tsunami wave history is calculated from several different scenarios indicated by geotechnical stability and mobility analyses; (2) a sensitivity analysis is conducted to determine the effects of both landslide failure duration during generation and bottom friction along the continental shelf during propagation; (3) wave history is calculated over a regional area to determine the propagation of energy oblique to the slide axis; and (4) a high-resolution 1D model is developed to accurately model wave breaking and the combined influence of nonlinearity and dispersion during nearshore propagation and runup. The primary source parameter that affects tsunami severity for this case study is landslide volume, with failure duration having a secondary influence. Bottom friction during propagation across the continental shelf has a strong influence on the attenuation of the tsunami during propagation. The high-resolution 1D model also indicates that the tsunami undergoes nonlinear fission prior to wave breaking, generating independent, short-period waves. Wave breaking occurs approximately 40-50??km offshore where a tsunami bore is formed that persists during runup. These analyses illustrate the complex nature of landslide tsunamis, necessitating the use of detailed landslide stability/mobility models and higher-order hydrodynamic models to determine their hazard.

Geist, E.L.; Lynett, P.J.; Chaytor, J.D.

2009-01-01

295

A novel type of hybrid colloids is presented, based on the association of several polymeric systems and ferrofluids. On the one hand, we use inorganic nanoparticles made of magnetic iron oxide prepared at the LI2C, which response to a magnetic field of low intensity. On the other hand the organic part is made either of long linear polyacrylamide chains or of mesoscopic structures (vesicles and micelles) self-assembled from amphiphile polybutadiene-b-poly(glutamic acid) di-block copolymers, which conformation is pH-sensitive.

Delphine El Kharrat; Olivier Sandre; Régine Perzynski; Frédéric Chécot; Sébastien Lecommandoux

2007-09-21

296

Ocean waves, nearshore ecology, and natural selection Mark W. Denny*

-1 Ocean waves, nearshore ecology, and natural selection Mark W. Denny* Stanford University and Helmuth 2002). At high tide, ocean waves break on the shore, imposing large hydrodynamic forces, Intertidal communities, Lift, Wave theory Abstract Although they are subjected to one of the most stressful

Denny, Mark

297

Propagation of ionizing electron shock waves in electrical breakdown

A numerical solution of a hydrodynamic second-order model shows that the propagation of the first ionizing wave arises from an overgrowth of hot electrons in the wave front in a zone of a greatly disturbed electric field. This gives rise, in the electron shock zone ahead of the wave, to a precursor phenomenon, whose effect is to accelerate the channel

P. Bayle; B. Cornebois

1985-01-01

298

Combustion wave instability in the filtration combustion of gases

Theoretical and experimental approaches to the problem of combustion wave stability in gas filtration combustion are described. An approximate criterion of instability for an initially plane combustion wave front is suggested within the framework of a hydrodynamic model. It is shown that the wave instabiliry cannot be observed if the reactor diameter is under a critical value. The critical value

S. S. Minaev; S. I. Potytnyakov; V. S. Babkin

1994-01-01

299

Hydrodynamics of internal solitons and a comparison of SIR-A and SIR-B data with ocean measurements

NASA Technical Reports Server (NTRS)

Large internal solitary waves have been observed by Shuttle SIR-A and SIR-B at locations in the Andaman Sea and the New York Bight. Satellite imagery and oceanographic measurements are used in conjunction with hydrodynamic interaction and electromagnetic scattering models to estimate the expected SAR image intensity modulations associated with the internal waves. There is reasonable agreement between the predicted and observed internal wave signatures.

Apel, J. R.; Gasparovic, R. F.; Thompson, D. R.

1986-01-01

300

Hydrodynamic Instability and Coalescence of Binary Neutron Stars

We study the importance of hydrodynamic effects on the evolution of coalescing binary neutron stars. Using an approximate energy functional constructed from equilibrium solutions for polytropic binary configurations, we incorporate hydrodynamic effects into the calculation of the orbital decay driven by gravitational wave emission. In particular, we follow the transition between the quasi-static, secular decay of the orbit at large separation and the rapid dynamical evolution of configurations approaching contact. We show that a purely Newtonian hydrodynamic instability can significantly accelerate the coalescence at small separation. Such an instability occurs in all close binary configurations containing sufficiently incompressible stars. Calculations are performed for various neutron star masses, radii, spins, and effective polytropic indices. Typically, we find that the radial infall velocity just prior to contact is about 10\\% of the tangential orbital velocity. Post-Newtonian effects can move the stability limit to a larger binary separation, and may induce an even larger radial velocity. We also consider the possibility of mass transfer from one neutron star to the other. We show that stable mass transfer is impossible except when the mass of one of the components is very small (less than about 0.4 solar mass) and the viscosity is high enough to maintain corotation.

D. Lai; F. A. Rasio; S. L. Shapiro

1993-04-28

301

A hydrodynamic sensory antenna used by killifish for nocturnal hunting

SUMMARY The perception of sensory stimuli by an animal requires several steps, commencing with the capture of stimulus energy by an antenna that, as the interface between the physical world and the nervous system, modifies the stimulus in ways that enhance the animal's perception. The mammalian external ear, for example, collects sound and spectrally alters it to increase sensitivity and improve the detection of directionality. In view of the morphological diversity of the lateral-line system across species and its accessibility to observation and experimental intervention, we sought to investigate the role of antennal structures on the response characteristics of the lateral line. The surface-feeding killifish Aplocheilus lineatus is able to hunt in darkness by detecting surface capillary waves with the lateral-line system atop its head. This cephalic lateral line consists of a stereotyped array of 18 mechanosensitive neuromasts bordered by fleshy ridges. By recording microphonic potentials, we found that each neuromast has a unique receptive field defined by its sensitivity to stimulation of the water's surface. The ridges help determine these receptive fields by altering the flow of water over each neuromast. Modification of the hydrodynamic environment by the addition of a supplemental ridge changes the pattern of water movement, perturbs the receptive fields of adjacent neuromasts and impairs the fish's localization ability. On the basis of electrophysiological, hydrodynamic and behavioral evidence, we propose that the ridges constitute a hydrodynamic antenna for the cephalic lateral line. PMID:21562172

Schwarz, Jason S.; Reichenbach, Tobias; Hudspeth, A. J.

2011-01-01

302

Microscale hydrodynamics near moving contact lines

NASA Technical Reports Server (NTRS)

The hydrodynamics governing the fluid motions on a microscopic scale near moving contact lines are different from those governing motion far from the contact line. We explore these unique hydrodynamics by detailed measurement of the shape of a fluid meniscus very close to a moving contact line. The validity of present models of the hydrodynamics near moving contact lines as well as the dynamic wetting characteristics of a family of polymer liquids are discussed.

Garoff, Stephen; Chen, Q.; Rame, Enrique; Willson, K. R.

1994-01-01

303

Foundation of Hydrodynamics of Strongly Interacting Systems

Hydrodynamics and quantum mechanics have many elements in common, as the density field and velocity fields are common variables that can be constructed in both descriptions. Starting with the Schroedinger equation and the Klein-Gordon for a single particle in hydrodynamical form, we examine the basic assumptions under which a quantum system of particles interacting through their mean fields can be described by hydrodynamics.

Wong, Cheuk-Yin [ORNL] [ORNL

2014-01-01

304

The graphical simulation of a certain subset of hydrodynamics phenomena is examined. New algorithms for both modeling and rendering these complex phenomena are presented.The modeling algorithms deal with wave refraction in an ocean. Waves refract in much the same way as light. In both cases, the equation that controls the change in direction is Snell's law. Ocean waves are continuous

Pauline Y. Ts'o; Brian A. Barsky

1987-01-01

305

Annual Report: Hydrodynamics and Radiative Hydrodynamics with Astrophysical Applications

We report the ongoing work of our group in hydrodynamics and radiative hydrodynamics with astrophysical applications. During the period of the existing grant, we have carried out two types of experiments at the Omega laser. One set of experiments has studied radiatively collapsing shocks, obtaining high-quality scaling data using a backlit pinhole and obtaining the first (ever, anywhere) Thomson-scattering data from a radiative shock. Other experiments have studied the deeply nonlinear development of the Rayleigh-Taylor (RT) instability from complex initial conditions, obtaining the first (ever, anywhere) dual-axis radiographic data using backlit pinholes and ungated detectors. All these experiments have applications to astrophysics, discussed in the corresponding papers either in print or in preparation. We also have obtained preliminary radiographs of experimental targets using our x-ray source. The targets for the experiments have been assembled at Michigan, where we also prepare many of the simple components. The above activities, in addition to a variety of data analysis and design projects, provide good experience for graduate and undergraduates students. In the process of doing this research we have built a research group that uses such work to train junior scientists.

R. Paul Drake

2005-12-01

306

Hydrodynamics and Jets in Dialogue

Energy and momentum loss of jets in heavy ion collisions can affect the fluid dynamic evolution of the medium. We determine realistic event-by-event averages and correlation functions of the local energy-momentum transfer from hard particles to the soft sector using the jet-quenching Monte-Carlo code JEWEL combined with a hydrodynamic model for the background. The expectation values for source terms due to jets in a typical (minimum bias) event affect the fluid dynamic evolution mainly by their momentum transfer. This leads to a small increase in flow. The presence of hard jets in the event constitutes only a minor correction.

Stefan Floerchinger; Korinna C. Zapp

2014-07-07

307

Hydrodynamic characteristics of UASB bioreactors.

The hydrodynamic characteristics of UASB bioreactors operated under different organic loading and hydraulic loading rates were studied, using three laboratory scale models treating concocted sucrose wastewater. Residence time distribution (RTD) analysis using dispersion model and tanks-in-series model was directed towards the characterization of the fluid flow pattern in the reactors and correlation of the hydraulic regime with the biomass content and biogas production. Empty bed reactors followed a plug flow pattern and the flow pattern changed to a large dispersion mixing with biomass and gas production. Effect of increase in gas production on the overall hydraulics was insignificant. PMID:23505813

John, Siby; Tare, Vinod

2011-10-01

308

Hydrodynamics of post CHF region

Among various two-phase flow regimes, the inverted flow in the post-dryout region is relatively less well understood due to its special heat transfer conditions. The review of existing data indicates further research is needed in the areas of basic hydrodynamics related to liquid core disintegration mechanisms, slug and droplet formations, entrainment, and droplet size distributions. In view of this, the inverted flow is studied in detail both analytically and experimentally. Criteria for initial flow regimes in the post-dryout region are given. Preliminary models for subsequent flow regime transition criteria are derived together with correlations for a mean droplet diameter based on the adiabatic simulation data.

Ishii, M.; De Jarlais, G.

1984-04-01

309

Hydrodynamical models of young SNRs.

NASA Astrophysics Data System (ADS)

X-ray observations of the Tycho supernova (SN) remnant by XMM-Newton telescope present radial profiles of the remnant in emission lines from silicon and iron \\citep{decour}. To reproduce observed spectrum and X-ray profiles hydrodynamical modelling of the remnant was performed by \\citet{elka}. Standard computational SN models cannot reproduce observed spacial behavoir of the X-ray profiles of the remnant in the emission lines. We perform analysis of these numerical models and find conditions under which it is possible to reproduce observed profiles.

Kosenko, D. I.; Blinnikov, S. I.; Postnov, K. A.; Sorokina, E. I.

310

Disruptive Innovation in Numerical Hydrodynamics

We propose the research and development of a high-fidelity hydrodynamic algorithm for tetrahedral meshes that will lead to a disruptive innovation in the numerical modeling of Laboratory problems. Our proposed innovation has the potential to reduce turnaround time by orders of magnitude relative to Advanced Simulation and Computing (ASC) codes; reduce simulation setup costs by millions of dollars per year; and effectively leverage Graphics Processing Unit (GPU) and future Exascale computing hardware. If successful, this work will lead to a dramatic leap forward in the Laboratory's quest for a predictive simulation capability.

Waltz, Jacob I. [Los Alamos National Laboratory

2012-09-06

311

Numerical hydrodynamics of cloud implosion

NASA Astrophysics Data System (ADS)

The implosion of a spherical cloud under the action of an external shock is investigated by means of high-resolution 2D numerical hydrodynamics. The parabolic piecewise method (PPM) has been used to simulate numerically the cloud evolution. Numerical models have been computed setting two adimensional parameters: the density contrast of the cloud with respect to the ambient medium and the Mach number of the shock, for a cloud in pressure equilibrium with the unperturbed gas. Two models are computed and discussed for the same pairs of parameters in the cases of adiabatic and isothermal approximations.

Bedogni, R.; Woodward, P. R.

312

Hydrodynamic instability experiments and simulations

Richtmyer-Meshkov experiments are conducted on the Nova laser with strong radiatively driven shocks (Mach > 20) in planar, two-fluid targets with Atwood number A < 0. Single mode interfacial perturbations are used to test linear theory and 3D random perturbations are used to study turbulent mix. Rayleigh-Taylor experiments are conducted on a new facility called the Linear Electric Motor (LEM) in which macroscopic fluids are accelerated electromagnetically with arbitrary acceleration profiles. The initial experiments are described. Hydrodynamic simulations in 2D are in reasonable agreement with the experiments, but these studies show that simulations in 3D with good radiation transport and equation of state are needed.

Dimonte, G.; Schneider, M.; Frerking, C.E.

1995-07-01

313

Progress in smooth particle hydrodynamics

Smooth Particle Hydrodynamics (SPH) is a meshless, Lagrangian numerical method for hydrodynamics calculations where calculational elements are fuzzy particles which move according to the hydrodynamic equations of motion. Each particle carries local values of density, temperature, pressure and other hydrodynamic parameters. A major advantage of SPH is that it is meshless, thus large deformation calculations can be easily done with no connectivity complications. Interface positions are known and there are no problems with advecting quantities through a mesh that typical Eulerian codes have. These underlying SPH features make fracture physics easy and natural and in fact, much of the applications work revolves around simulating fracture. Debris particles from impacts can be easily transported across large voids with SPH. While SPH has considerable promise, there are some problems inherent in the technique that have so far limited its usefulness. The most serious problem is the well known instability in tension leading to particle clumping and numerical fracture. Another problem is that the SPH interpolation is only correct when particles are uniformly spaced a half particle apart leading to incorrect strain rates, accelerations and other quantities for general particle distributions. SPH calculations are also sensitive to particle locations. The standard artificial viscosity treatment in SPH leads to spurious viscosity in shear flows. This paper will demonstrate solutions for these problems that they and others have been developing. The most promising is to replace the SPH interpolant with the moving least squares (MLS) interpolant invented by Lancaster and Salkauskas in 1981. SPH and MLS are closely related with MLS being essentially SPH with corrected particle volumes. When formulated correctly, JLS is conservative, stable in both compression and tension, does not have the SPH boundary problems and is not sensitive to particle placement. The other approach to solving SPH problems, pioneered by Randles and Libersky, is to use a different SPH equation and to renormalize the kernel gradient sums. Finally the authors present results using the SPH statistical fracture model (SPHSFM). It has been applied to a series of ball on plate impacts performed by Grady and Kipp. A description of the model and comparison with the experiments will be given.

Wingate, C.A.; Dilts, G.A.; Mandell, D.A.; Crotzer, L.A.; Knapp, C.E.

1998-07-01

314

Effects of Second-Order Hydrodynamics on a Semisubmersible Floating Offshore Wind Turbine: Preprint

The objective of this paper is to assess the second-order hydrodynamic effects on a semisubmersible floating offshore wind turbine. Second-order hydrodynamics induce loads and motions at the sum- and difference-frequencies of the incident waves. These effects have often been ignored in offshore wind analysis, under the assumption that they are significantly smaller than first-order effects. The sum- and difference-frequency loads can, however, excite eigenfrequencies of the system, leading to large oscillations that strain the mooring system or vibrations that cause fatigue damage to the structure. Observations of supposed second-order responses in wave-tank tests performed by the DeepCwind consortium at the MARIN offshore basin suggest that these effects might be more important than originally expected. These observations inspired interest in investigating how second-order excitation affects floating offshore wind turbines and whether second-order hydrodynamics should be included in offshore wind simulation tools like FAST in the future. In this work, the effects of second-order hydrodynamics on a floating semisubmersible offshore wind turbine are investigated. Because FAST is currently unable to account for second-order effects, a method to assess these effects was applied in which linearized properties of the floating wind system derived from FAST (including the 6x6 mass and stiffness matrices) are used by WAMIT to solve the first- and second-order hydrodynamics problems in the frequency domain. The method has been applied to the OC4-DeepCwind semisubmersible platform, supporting the NREL 5-MW baseline wind turbine. The loads and response of the system due to the second-order hydrodynamics are analysed and compared to first-order hydrodynamic loads and induced motions in the frequency domain. Further, the second-order loads and induced response data are compared to the loads and motions induced by aerodynamic loading as solved by FAST.

Bayati, I.; Jonkman, J.; Robertson, A.; Platt, A.

2014-07-01

315

NSDL National Science Digital Library

This lab is an inquiry activity in that students do not know the answer and have probably never experienced this phenomenon. Most students have seen that water in U-tubes is always equal height on both sides. This lab will be both a discrepant event as we

Horton, Michael

2009-05-30

316

Waves and Instabilities in Magnetized Dusty Plasmas

The status of waves and instabilities in magnetized dusty plasmas is summarized. The effects of an external magnetic field\\u000a on low-frequency electrostatic and electromagnetic waves in dusty plasmas are discussed. The kinetic and hydrodynamic instabilities\\u000a are shown to excite magnetized dusty plasma waves. The presence of the latter can give rise to an oscillatory wake-potential\\u000a which can be responsible for

Padma K. Shukla

1998-01-01

317

Physics-Based Learning Models for Ship Hydrodynamics

We present the concepts of physics-based learning models (PBLM) and their relevance and application to the field of ship hydrodynamics. The utility of physics-based learning is motivated by contrasting generic learning models for regression predictions, which do not presume any knowledge of the system other than the training data provided with methods such as semi-empirical models, which incorporate physical insights along with data-fitting. PBLM provides a framework wherein intermediate models, which capture (some) physical aspects of the problem, are incorporated into modern generic learning tools to substantially improve the predictions of the latter, minimizing the reliance on costly experimental measurements or high-resolution high-fidelity numerical solutions. To illustrate the versatility and efficacy of PBLM, we present three wave-ship interaction problems: 1) at speed waterline profiles; 2) ship motions in head seas; and 3) three-dimensional breaking bow waves. PBLM is shown to be robust and produce ...

Weymouth, Gabriel D

2014-01-01

318

Hydrodynamic force characteristics of slender cylinders in the splash zone

This paper presents results from a pilot experimental program of research being performed on segmented vertical surface-piercing cylinders in the Department of Civil and Environmental Engineering at The University of Melbourne. The primary aim of this investigation is to determine the influence of the splash zone on the hydrodynamic force characteristics of such cylinders to wave loading in the Morison regime. This influence is assessed from a comparison of the observed force characteristics of instrumented segments located in the splash zone with the corresponding results obtained from similarly instrumented segments located in the fully submerged zone and from those obtained for the cylinder as a whole via measurements of the cylinder tip restraint force. Results to hand for uni-directional regular waves suggest that there appears to be a mild frequency dependence in the inertia force coefficient in the splash zone which only marginally exceeds the corresponding values observed for a submerged segment immediately below this zone.

Haritos, N.; Daliri, M.R. [Univ. of Melbourne, Parkville, Victoria (Australia). Dept. of Civil and Environmental Engineering

1995-12-31

319

On the low-frequency hydrodynamic damping forces acting on offshore moored vessels

Moored floating structures for drilling, production-storage-offloading or other purposes are being installed in ever increasing water depths and in areas where the environmental conditions are also more severe. Such structures, moored permanently in high seas, have to survive safely the most severe weather conditions. Therefore it is of importance to understand the mechanisms which govern the motions and the mooring forces of these facilities. In deep water the mooring systems inevitably have soft elasticity characteristics. With the increase in the elasticity of the mooring, the low frequency horizontal motions induced by low frequency second order wave drift forces also become larger. The low frequency resonant motion components completely dominate the horizontal motions and, consequently, also the mooring forces. In order to predict the amplitudes of the low frequency resonant motions the magnitude of the second order wave drift forces and the values of the low frequency hydrodynamic damping must be known. The low frequency hydrodynamic potential damping due to the radiated waves is negligibly small. In general the low frequency damping is determined by viscous effects and a damping caused by the presence of waves. The last mentioned damping is called the wave damping. Dependent on the wave spectra the wave damping can significantly dominate the viscous damping contributions. In this paper results are given of a study of the origin of the wave damping. For this purpose the second order wave drift forces acting on the moored vessel in head waves have been expanded to the low frequency surge displacement and surge velocity. The wave damping can be defined by taking into account the dependence on velocity of the second order wave drift forces. To verify the results, model experiments were carried out in which the velocity dependent second order wave drift forces were determined.

Wichers, J.E.W.; Huijsmans, R.M.H.

1984-05-01

320

Inducer Hydrodynamic Load Measurement Devices

NASA Technical Reports Server (NTRS)

Marshall Space Flight Center (MSFC) has demonstrated two measurement devices for sensing and resolving the hydrodynamic loads on fluid machinery. The first - a derivative of the six-component wind tunnel balance - senses the forces and moments on the rotating device through a weakened shaft section instrumented with a series of strain gauges. This rotating balance was designed to directly measure the steady and unsteady hydrodynamic loads on an inducer, thereby defining both the amplitude and frequency content associated with operating in various cavitation modes. The second device - a high frequency response pressure transducer surface mounted on a rotating component - was merely an extension of existing technology for application in water. MSFC has recently completed experimental evaluations of both the rotating balance and surface-mount transducers in a water test loop. The measurement bandwidth of the rotating balance was severely limited by the relative flexibility of the device itself, resulting in an unexpectedly low structural bending mode and invalidating the higher-frequency response data. Despite these limitations, measurements confirmed that the integrated loads on the four-bladed inducer respond to both cavitation intensity and cavitation phenomena. Likewise, the surface-mount pressure transducers were subjected to a range of temperatures and flow conditions in a non-rotating environment to record bias shifts and transfer functions between the transducers and a reference device. The pressure transducer static performance was within manufacturer's specifications and dynamic response accurately followed that of the reference.

Skelley, Stephen E.; Zoladz, Thomas F.; Turner, Jim (Technical Monitor)

2002-01-01

321

Inducer Hydrodynamic Load Measurement Devices

NASA Technical Reports Server (NTRS)

Marshall Space Flight Center (MSFC) has demonstrated two measurement devices for sensing and resolving the hydrodynamic loads on fluid machinery. The first - a derivative of the six component wind tunnel balance - senses the forces and moments on the rotating device through a weakened shaft section instrumented with a series of strain gauges. This "rotating balance" was designed to directly measure the steady and unsteady hydrodynamic loads on an inducer, thereby defining both the amplitude and frequency content associated with operating in various cavitation modes. The second device - a high frequency response pressure transducer surface mounted on a rotating component - was merely an extension of existing technology for application in water. MSFC has recently completed experimental evaluations of both the rotating balance and surface-mount transducers in a water test loop. The measurement bandwidth of the rotating balance was severely limited by the relative flexibility of the device itself, resulting in an unexpectedly low structural bending mode and invalidating the higher frequency response data. Despite these limitations, measurements confirmed that the integrated loads on the four-bladed inducer respond to both cavitation intensity and cavitation phenomena. Likewise, the surface-mount pressure transducers were subjected to a range of temperatures and flow conditions in a non-rotating environment to record bias shifts and transfer functions between the transducers and a reference device. The pressure transducer static performance was within manufacturer's specifications and dynamic response accurately followed that of the reference.

Skelley, Stephen E.; Zoladz, Thomas F.

2002-01-01

322

The hydrodynamics of lamprey locomotion

NASA Astrophysics Data System (ADS)

The lamprey, an anguilliform swimmer, propels itself by undulating most of its body. This type of swimming produces flow patterns that are highly three-dimensional in nature and not very well understood. However, substantial previous work has been done to understand two-dimensional unsteady propulsion, the possible wake structures and thrust performance. Limited studies of three-dimensional propulsors with simple geometries have displayed the importance of the third dimension in designing unsteady swimmers. Some of the results of those studies, primarily the ways in which vorticity is organized in the wake region, are seen in lamprey swimming as well. In the current work, the third dimension is not the only important factor, but complex geometry and body undulations also contribute to the hydrodynamics. Through dye flow visualization, particle induced velocimetry and pressure measurements, the hydrodynamics of anguilliform swimming are studied using a custom built robotic lamprey. These studies all indicate that the undulations of the body are not producing thrust. Instead, it is the tail which acts to propel the animal. This conclusion led to further investigation of the tail, specifically the role of varying tail flexibility on hydrodymnamics. It is found that by making the tail more flexible, one decreases the coherence of the vorticity in the lamprey's wake. Additional flexibility also yields less thrust.

Leftwich, Megan C.

323

NSDL National Science Digital Library

This web page provides an illustrated tutorial in wave motion and ocean waves. Topics include waves and wind, waves in shallow water, tsunamis, waves and environment, and more. Many drawings and photographs of waves and their effects complement the text.

2006-12-23

324

Quantum-relativistic hydrodynamic model for a spin-polarized electron gas interacting with light.

We develop a semirelativistic quantum fluid theory based on the expansion of the Dirac Hamiltonian to second order in 1/c. By making use of the Madelung representation of the wave function, we derive a set of hydrodynamic equations that comprises a continuity equation, an Euler equation for the mean velocity, and an evolution equation for the electron spin density. This hydrodynamic model is then applied to study the dynamics of a dense and weakly relativistic electron plasma. In particular, we investigate the impact of the quantum-relativistic spin effects on the Faraday rotation in a one-dimensional plasma slab irradiated by an x-ray laser source. PMID:25122397

Morandi, Omar; Zamanian, Jens; Manfredi, Giovanni; Hervieux, Paul-Antoine

2014-07-01

325

Weakly Nonlocal Hydrodynamics and the Origin of Viscosity in the Adhesion Model

We use the weakly nonlocal hydrodynamics approach to obtain a dynamical equation for the peculiar velocity field in which the viscosity term is physically motivated. Based on some properties of the Ginzburg-Landau equation and the wave mechanics analog of hydrodynamics we find the nonlocal adhesion approximation taking into account the internal structures of the Zeldovich pancakes. If the internal structures correspond to significant mesoscopic fluctuations, viscosity is probably driven by a stochastic force and dynamics is given by the noisy Burgers equation.

A. L. B. Ribeiro; J. G. Peixoto de Faria

2005-02-28

326

Hydrodynamic performance of the arc-shaped bottom-mounted breakwater

NASA Astrophysics Data System (ADS)

The problem of the hydrodynamic interaction with the arc-shaped bottom-mounted breakwaters is investigated theoretically. The breakwater is assumed to be rigid, thin, impermeable and vertically located in a finite water depth. The fluid domain is divided into two sub-regions of inner and outer by an auxiliary circular interface. Linear theory is assumed and the eigenfunction expansion approach is used to determine the wave field. In order to examine the validity of the theoretical model, the analytical solutions are compared to agree well with published results with the same parameters. Numerical results including wave amplitude, surge pressure, and wave force are presented with different model parameters. The major factors including wave parameters, structure configuration, and water depth that affect the surge pressure, wave forces, and wave amplitudes are discussed and illustrated by some graphs and cloud maps.

Chu, Yu-chuan; Cheng, Jian-sheng; Wang, Jing-quan; Li, Zhi-gang; Jiang, Ke-bin

2014-12-01

327

78 FR 9907 - Hydrodynamics, Inc.; Notice Denying Late Intervention

Federal Register 2010, 2011, 2012, 2013, 2014

...Regulatory Commission [ Project No. 13531-000] Hydrodynamics, Inc.; Notice Denying Late Intervention...issued a three-year preliminary permit to Hydrodynamics, Inc. (Hydrodynamics) to study the feasibility of its...

2013-02-12

328

A REVIEW OF HYDRODYNAMICAL MODELS FOR SEMICONDUCTORS: ASYMPTOTIC BEHAVIOR

A REVIEW OF HYDRODYNAMICAL MODELS FOR SEMICONDUCTORS: ASYMPTOTIC BEHAVIOR Hailiang Li , Peter results on the hydrodynamical model for semiconductors. The derivation of the mathematical model from on spatially bounded domain or whole space. Key words: Hydrodynamical models, semiconductors, asymptotic

Markowich, Peter A.

329

Extended Hydrodynamical Model of Carrier Transport in Semiconductors

Extended Hydrodynamical Model of Carrier Transport in Semiconductors Angelo Marcello Anile \\Lambda title: Extended Hydrodynamical Model in Semiconductors Abstract A hydrodynamical model based on the theory of Extended ThermoÂ dynamics is presented for carrier transport in semiconductors. Closure

Russo, Giovanni

330

A REVIEW OF HYDRODYNAMICAL MODELS FOR SEMICONDUCTORS: ASYMPTOTIC BEHAVIOR

A REVIEW OF HYDRODYNAMICAL MODELS FOR SEMICONDUCTORS: ASYMPTOTIC BEHAVIOR Hailiang Li # , Peter results on the hydrodynamical model for semiconductors. The derivation of the mathematical model from on spatially bounded domain or whole space. Key words: Hydrodynamical models, semiconductors, asymptotic

Markowich, Peter A.

331

Relativistic Hydrodynamics for Heavy-Ion Collisions

ERIC Educational Resources Information Center

Relativistic hydrodynamics is essential to our current understanding of nucleus-nucleus collisions at ultrarelativistic energies (current experiments at the Relativistic Heavy Ion Collider, forthcoming experiments at the CERN Large Hadron Collider). This is an introduction to relativistic hydrodynamics for graduate students. It includes a detailed…

Ollitrault, Jean-Yves

2008-01-01

332

Surmounting barriers: The benefit of hydrodynamic interactions

We experimentally and theoretically investigate the collective behavior of three colloidal particles that are driven by a constant force along a toroidal trap. Due to hydrodynamic interactions, a characteristic limit cycle is observed. When we additionally apply a periodic sawtooth potential, we find a novel caterpillar-like motional sequence that is dominated by hydrodynamic interactions and promotes the surmounting of potential

Christoph Lutz; Michael Reichert; Holger Stark; Clemens Bechinger

2006-01-01

333

Dynamic coupling of three hydrodynamic models

The need for integrated modelling is evidently present within the field of flood management and flood forecasting. Engineers, modellers and managers are faced with flood problems which transcend the classical hydrodynamic fields of urban, river and coastal flooding. Historically the modeller has been faced with having to select one hydrodynamic model to cover all the aspects of the potentially complex

J. N. Hartnack; G. T. Philip; M. Rungoe; G. Smith; G. Johann; O. Larsen; J. Gregersen; M. B. Butts

2008-01-01

334

Acceleration of hydrodynamic vortices in open systems

A new class of exact solutions of hydrodynamic equations for an incompressible fluid (gas) at the presence of a bulk sink and uprising vertical flows of matter is considered. The acceleration of the rotation velocity of classical non-stationary vortices is conditioned by the joint action of the convective and Coriolis hydrodynamic forces (accelerations), which appear due to the converging radial

E. A. PASHITSKII; V. N. MALNEV; R. A. NARYSHKIN

2007-01-01

335

Hydrodynamic Modeling and the QGP Shear Viscosity

In this article, we will briefly review the recent progress on hydrodynamic modeling and the extraction of the quark-gluon plasma (QGP) specific shear viscosity with an emphasis on results obtained from the hybrid model VISHNU that couples viscous hydrodynamics for the macroscopic expansion of the QGP to the hadron cascade model for the microscopic evolution of the late hadronic stage.

Huichao Song

2012-07-10

336

Hydrodynamic damping of microcantilevers near solid walls

The vibrations of microcantilevers in Atomic Force Microscopes (AFM) or Radio Frequency (RF) switches are strongly influenced by the viscous hydrodynamics of the surrounding fluid in the vicinity of a rigid wall. While prior efforts to model this hydrodynamic loading have focused on squeeze film damping effects at high Knudsen and squeeze numbers, the regime of low Knudsen and squeeze

Ryan C Tung

2008-01-01

337

Quantum Plasma Model with Hydrodynamical Phase Transition

Quantum Plasma Model with Hydrodynamical Phase Transition By Geoffrey L. Sewell* DepartmentÂhydrodynamics of the Jellium plasma model from its manyÂparticle SchrÂ¨odinger equation, subject to certain general initial Introduction The quantum Jellium model is a system of electrons, interacting via Coulomb forces both with one

338

Using pulsed power for hydrodynamic code validation

As part of ongoing hydrodynamic code verification and validation efforts, a series of near-term liner experiments (NTLX) was designed for the Shiva Star capacitor bank at the Air Force Research Laboratory . An aluminum liner that is magnetically imploded onto a central target by self-induced Lorentz forces drove the experiments. Target design utilized the adaptive mesh refinement Eulerian hydrodynamics code

Randall J. Kanzleiter; Walter L. Atchison; Richard L. Bowers; Richard L. Fortson; Joyce A. Guzik; Russell T. Olson; John L. Stokes; Peter J. Turchi

2002-01-01

339

Incompressible wave motion of compressible fluids.

We consider linear waves in compressible fluids in a uniform potential field, such as a gravity field, and demonstrate that a particular type of wave motion, in which pressure remains constant in each fluid parcel, is supported by inhomogeneous fluids occupying bounded or unbounded domains. We present elementary, exact solutions of linearized hydrodynamics equations, which describe the new type of waves in the coupled ocean-atmosphere system. The solutions provide an extension of surface gravity waves in an incompressible fluid half-space with a free boundary to waves in compressible, three-dimensionally inhomogeneous, rotating fluids. PMID:23003046

Godin, Oleg A

2012-05-11

340

Radiative Hydrodynamic Simulations of Acoustic Waves in Sunspots

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 \\

S. Bard; M. Carlsson

2010-01-01

341

Analogies and distinctions between hydrodynamic and optical nonlinear waves

NASA Astrophysics Data System (ADS)

We present the algorithm based on the Lax pair generalization to reveal some properties of nonautonomous KdV solitons. Starting from the general method of solution for the nonisospectral IST problem, we demonstrate how the varying-coefficient KdV equation can arise in nonuniformed and inhomogeneous media. We write down the one- and two-soliton solution of the nonautonomous varying-coefficient KdV with the time-dependent spectral parameter and consider some special cases of the isospectral solutions of the KdV equation with varying dispersion, nonlinearity, and gain. Finally, we compare these solutions with the nonautonomous solitons of the NLSE emphasizing their common features.

Mena-Contla, A.; Peña-Moreno, R.; Morales-Lara, L.; Serkin, V. N.; Belyaeva, T. L.

2015-01-01

342

Pilot-wave hydrodynamics in a rotating frame: Exotic orbits

NASA Astrophysics Data System (ADS)

We present the results of a numerical investigation of droplets walking on a rotating vibrating fluid bath. The drop's trajectory is described by an integro-differential equation, which is simulated numerically in various parameter regimes. As the forcing acceleration is progressively increased, stable circular orbits give way to wobbling orbits, which are succeeded in turn by instabilities of the orbital center characterized by steady drifting then discrete leaping. In the limit of large vibrational forcing, the walker's trajectory becomes chaotic, but its statistical behavior reflects the influence of the unstable orbital solutions. The study results in a complete regime diagram that summarizes the dependence of the walker's behavior on the system parameters. Our predictions compare favorably to the experimental observations of Harris and Bush ["Droplets walking in a rotating frame: from quantized orbits to multimodal statistics," J. Fluid Mech. 739, 444-464 (2014)].

Oza, Anand U.; Wind-Willassen, Øistein; Harris, Daniel M.; Rosales, Rodolfo R.; Bush, John W. M.

2014-08-01

343

Smoothed Particle Hydrodynamics Code Basics

NASA Astrophysics Data System (ADS)

SPH is the shorthand for Smoothed Particle Hydrodynamics. This method is a Lagrangian method which means that it involves following the motion of elements of fluid. These elements have the characteristics of particles and the method is called a particle method. A useful review of SPH (Monaghan 1992) gives the basic technique and how it can be applied to numerous problems relevant to astrophysics. You can get some basic SPH programs from http://www.maths.monash.edu.au/~jjm/sphlect. In the present lecture I will assume that the student has studied this review and therefore understands the basic principles. In today's lecture I plan to approach the equations from a different perspective by using a variational principle.

Monaghan, J. J.

2001-12-01

344

Radiation hydrodynamics in solar flares

Solar flares are rather violent and extremely complicated phenomena, and it should be made clear at the outset that a physically complete picture describing all aspects of flares does not exist. From the wealth of data which is available, it is apparent that many different types of physical processes are involved during flares: energetic particle acceleration, rapid magnetohydrodynamic motion of complex field structures, magnetic reconnection, violent mass motion along magnetic field lines, and the heating of plasma to tens of millions of degrees, to name a few. The goal of this paper is to explore just one aspect of solar flares, namely, the interaction of hydrodynamics and radiation processes in fluid being rapidly heated along closed magnetic field lines. The models discussed are therefore necessarily restrictive, and will address only a few of the observed or observable phenomena. 46 refs., 6 figs.

Fisher, G.H.

1985-10-18

345

The hydrodynamics of dolphin drafting

Background Drafting in cetaceans is defined as the transfer of forces between individuals without actual physical contact between them. This behavior has long been surmised to explain how young dolphin calves keep up with their rapidly moving mothers. It has recently been observed that a significant number of calves become permanently separated from their mothers during chases by tuna vessels. A study of the hydrodynamics of drafting, initiated in the hope of understanding the mechanisms causing the separation of mothers and calves during fishing-related activities, is reported here. Results Quantitative results are shown for the forces and moments around a pair of unequally sized dolphin-like slender bodies. These include two major effects. First, the so-called Bernoulli suction, which stems from the fact that the local pressure drops in areas of high speed, results in an attractive force between mother and calf. Second is the displacement effect, in which the motion of the mother causes the water in front to move forwards and radially outwards, and water behind the body to move forwards to replace the animal's mass. Thus, the calf can gain a 'free ride' in the forward-moving areas. Utilizing these effects, the neonate can gain up to 90% of the thrust needed to move alongside the mother at speeds of up to 2.4 m/sec. A comparison with observations of eastern spinner dolphins (Stenella longirostris) is presented, showing savings of up to 60% in the thrust that calves require if they are to keep up with their mothers. Conclusions A theoretical analysis, backed by observations of free-swimming dolphin schools, indicates that hydrodynamic interactions with mothers play an important role in enabling dolphin calves to keep up with rapidly moving adult school members. PMID:15132740

Weihs, Daniel

2004-01-01

346

Hydrodynamics of Euler incompressible fluid and the fractional quantum Hall effect

NASA Astrophysics Data System (ADS)

We show that the fractional quantum Hall effect can be phenomenologically described as a special flow of a quantum incompressible Euler liquid. This flow consists of a large number of vortices of the same chirality. In this approach each vortex is identified with an electron while the fluid is neutral. We show that the Laughlin wave function naturally emerges as a stationary flow of the system of vortices in quantum fluid dynamics. Here we develop the hydrodynamics of the vortex liquid and are able to consistently quantize it. As a demonstration of the efficiency of the hydrodynamics we show how subtle features of the fractional quantum Hall effect such as effects of Lorentz shear stress, the structure function, the Hall current in a nonuniform magnetic field, and Hall conductance in a curved spatial landscape naturally follow from the hydrodynamics approach.

Wiegmann, P. B.

2013-12-01

347

Hydrodynamic construction of the electromagnetic field

We present an alternative Eulerian hydrodynamic model for the electromagnetic field in which the discrete vector indices in Maxwell\\s equations are replaced by continuous angular freedoms, and develop the corresponding Lagrangian picture in which the fluid particles have rotational and translational freedoms. This enables us to extend to the electromagnetic field the exact method of state construction proposed previously for spin 0 systems, in which the time-dependent wavefunction is computed from a single-valued continuum of deterministic trajectories where two spacetime points are linked by at most a single orbit. The deduction of Maxwell\\s equations from continuum mechanics is achieved by generalizing the spin 0 theory to a general Riemannian manifold from which the electromagnetic construction is extracted as a special case. In particular, the flat-space Maxwell equations are represented as a curved-space Schr\\"odinger equation for a massive system. The Lorentz covariance of the Eulerian field theory is obtained from the non-covariant Lagrangian-coordinate model as a kind of collective effect. The method makes manifest the electromagnetic analogue of the quantum potential that is tacit in Maxwell\\s equations. This implies a novel definition of the \\classical limit\\ of Maxwell\\s equations that differs from geometrical optics. It is shown that Maxwell\\s equations may be obtained by canonical quantization of the classical model. Using the classical trajectories a novel expression is derived for the propagator of the electromagnetic field in the Eulerian picture. The trajectory and propagator methods of solution are illustrated for the case of a light wave.

Peter Holland

2014-10-03

348

Early Hydrodynamic Evolution of a Stellar Collision

NASA Astrophysics Data System (ADS)

The early phase of the hydrodynamic evolution following the collision of two stars is analyzed. Two strong shocks propagate from the contact surface and move toward the center of each star at a velocity that is a small fraction of the velocity of the approaching stars. The shocked region near the contact surface has a planar symmetry and a uniform pressure. The density vanishes at the (Lagrangian) surface of contact, and the speed of sound diverges there. The temperature, however, reaches a finite value, since as the density vanishes, the finite pressure is radiation dominated. For carbon-oxygen white dwarf (CO WD) collisions, this temperature is too low for any appreciable nuclear burning shortly after the collision, which allows for a significant fraction of the mass to be highly compressed to the density required for efficient 56Ni production in the detonation wave that follows. This property is crucial for the viability of collisions of typical CO WD as progenitors of type Ia supernovae, since otherwise only massive (>0.9 M ?) CO WDs would have led to such explosions (as required by all other progenitor models). The divergence of the speed of sound limits numerical studies of stellar collisions, as it makes convergence tests exceedingly expensive unless dedicated schemes are used. We provide a new one-dimensional Lagrangian numerical scheme to achieve this. A self-similar planar solution is derived for zero-impact parameter collisions between two identical stars, under some simplifying assumptions (including a power-law density profile), which is the planar version of previous piston problems that were studied in cylindrical and spherical symmetries.

Kushnir, Doron; Katz, Boaz

2014-04-01

349

Using CFD software to calculate hydrodynamic coefficients

NASA Astrophysics Data System (ADS)

Applications of computational fluid dynamic (CFD) to the maritime industry continue to grow with the increasing development of computers. Numerical approaches have evolved to a level of accuracy which allows them to be applied for hydrodynamic computations in industry areas. Hydrodynamic tests, especially planar-motion-mechanism (PMM) tests are simulated by CFD software -FLUENT, and all of the corresponding hydrodynamic coefficients are obtained, which satisfy the need of establishing the simulation system to evaluate maneuverability of vehicles during the autonomous underwater vehicle scheme design stage. The established simulation system performed well in tests.

Zhang, He; Xu, Yu-Ru; Cai, Hao-Peng

2010-06-01

350

Horava-Lifshitz black hole hydrodynamics

NASA Astrophysics Data System (ADS)

We consider the holographic hydrodynamics of black holes in generally covariant gravity theories with a preferred time foliation. Gravitational perturbations in these theories have spin two and spin zero helicity modes with generically different speeds. The black hole solutions possess a spacelike causal boundary called the universal horizon. We relate the flux of the spin zero perturbation across the universal horizon to the new dissipative transport in Lifshitz field theory hydrodynamics found in arXiv:1304.7481. We construct in detail the hydrodynamics of one such black hole solution, and calculate the ratio of the shear viscosity to the entropy density.

Eling, Christopher; Oz, Yaron

2014-11-01

351

Solving the viscous hydrodynamics order by order

In this paper, we propose a method of solving the viscous hydrodynamics order by order in a derivative expansion. In such method, the zero order solution is just the one of the ideal hydrodynamics. All the other higher order corrections satisfy the same first-order partial differential equations but with different inhomogeneous terms. We therefore argue that our method could be easily extended to any orders. The problem of causality and stability will be released if the gradient expansion is guaranteed. This method might be of great help to both theoretical and numerical calculations of relativistic hydrodynamics.

Jian-Hua Gao; Shi Pu

2014-09-02

352

Non abelian hydrodynamics and heavy ion collisions

The goal of the relativistic heavy ion collisions (RHIC) program is to create a state of matter where color degrees of freedom are deconfined. The dynamics of matter in this state, in spite of the complexities of quantum chromodynamics, is largely determined by the conservation laws of energy momentum and color currents. Therefore it is possible to describe its main features in hydrodynamic terms, the very short color neutralization time notwithstanding. In this lecture we shall give a simple derivation of the hydrodynamics of a color charged fluid, by generalizing the usual derivation of hydrodynamics from kinetic theory to the non abelian case.

Calzetta, E. [Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and IFIBA, CONICET, Ciudad Universitaria, Buenos Aires 1428 (Argentina)

2014-01-14

353

Building a Hydrodynamics Code with Kinetic Theory This article has been downloaded from IOPscience to the journal homepage for more Home Search Collections Journals About Contact us My IOPscience #12;Building simulations and focus here on the Sedov blast wave test. The blast wave problem describes the evolution

Bauer, Wolfgang

354

Hydrodynamic gradient expansion in gauge theory plasmas

We utilize the fluid-gravity duality to investigate the large order behavior of hydrodynamic gradient expansion of the dynamics of a gauge theory plasma system. This corresponds to the inclusion of dissipative terms and transport coefficients of very high order. Using the dual gravity description, we calculate numerically the form of the stress tensor for a boost-invariant flow in a hydrodynamic expansion up to terms with 240 derivatives. We observe a factorial growth of gradient contributions at large orders, which indicates a zero radius of convergence of the hydrodynamic series. Furthermore, we identify the leading singularity in the Borel transform of the hydrodynamic energy density with the lowest nonhydrodynamic excitation corresponding to a `nonhydrodynamic' quasinormal mode on the gravity side.

Michal P. Heller; Romuald A. Janik; Przemyslaw Witaszczyk

2013-05-24

355

Hydrodynamic phonon transport in suspended graphene.

Recent studies of thermal transport in nanomaterials have demonstrated the breakdown of Fourier's law through observations of ballistic transport. Despite its unique features, another instance of the breakdown of Fourier's law, hydrodynamic phonon transport, has drawn less attention because it has been observed only at extremely low temperatures and narrow temperature ranges in bulk materials. Here, we predict on the basis of first-principles calculations that the hydrodynamic phonon transport can occur in suspended graphene at significantly higher temperatures and wider temperature ranges than in bulk materials. The hydrodynamic transport is demonstrated through drift motion of phonons, phonon Poiseuille flow and second sound. The significant hydrodynamic phonon transport in graphene is associated with graphene's two-dimensional features. This work opens a new avenue for understanding and manipulating heat flow in two-dimensional materials. PMID:25693180

Lee, Sangyeop; Broido, David; Esfarjani, Keivan; Chen, Gang

2015-01-01

356

Temporal integrators for fluctuating hydrodynamics

NASA Astrophysics Data System (ADS)

Including the effect of thermal fluctuations in traditional computational fluid dynamics requires developing numerical techniques for solving the stochastic partial differential equations of fluctuating hydrodynamics. These Langevin equations possess a special fluctuation-dissipation structure that needs to be preserved by spatio-temporal discretizations in order for the computed solution to reproduce the correct long-time behavior. In particular, numerical solutions should approximate the Gibbs-Boltzmann equilibrium distribution, and ideally this will hold even for large time step sizes. We describe finite-volume spatial discretizations for the fluctuating Burgers and fluctuating incompressible Navier-Stokes equations that obey a discrete fluctuation-dissipation balance principle just like the continuum equations. We develop implicit-explicit predictor-corrector temporal integrators for the resulting stochastic method-of-lines discretization. These stochastic Runge-Kutta schemes treat diffusion implicitly and advection explicitly, are weakly second-order accurate for additive noise for small time steps, and give a good approximation to the equilibrium distribution even for very strong fluctuations. Numerical results demonstrate that a midpoint predictor-corrector scheme is very robust over a broad range of time step sizes.

Delong, Steven; Griffith, Boyce E.; Vanden-Eijnden, Eric; Donev, Aleksandar

2013-03-01

357

Hydrodynamic Simulations of Contact Binaries

NASA Astrophysics Data System (ADS)

The motivation for our project is the peculiar case of the 'red nova" V1309 Sco which erupted in September 2008. The progenitor was, in fact, a contact binary system. We are developing a simulation of contact binaries, so that their formation, structural, and merger properties could be studied using hydrodynamics codes. The observed transient event was the disruption of the secondary star by the primary, and their subsequent merger into one star; hence to replicate this behavior, we need a core-envelope structure for both the stars. We achieve this using a combination of Self Consistant Field (SCF) technique and composite polytropes, also known as bipolytropes. So far we have been able to generate close binaries with various mass ratios. Another consequence of using bipolytropes is that according to theoretical calculations, the radius of a star should expand when the core mass fraction exceeds a critical value, resulting in interesting consequences in a binary system. We present some initial results of these simulations.

Kadam, Kundan; Clayton, Geoffrey C.; Frank, Juhan; Marcello, Dominic; Motl, Patrick M.; Staff, Jan E.

2015-01-01

358

Numerical simulation of the hydrodynamic instability experiments and flow mixing

NASA Astrophysics Data System (ADS)

Based on the numerical methods of volume of fluid (VOF) and piecewise parabolic method (PPM) and parallel circumstance of Message Passing Interface (MPI), a parallel multi-viscosity-fluid hydrodynamic code MVPPM (Multi-Viscosity-Fluid Piecewise Parabolic Method) is developed and performed to study the hydrodynamic instability and flow mixing. Firstly, the MVPPM code is verified and validated by simulating three instability cases: The first one is a Riemann problem of viscous flow on the shock tube; the second one is the hydrodynamic instability and mixing of gaseous flows under re-shocks; the third one is a half height experiment of interfacial instability, which is conducted on the AWE’s shock tube. By comparing the numerical results with experimental data, good agreement is achieved. Then the MVPPM code is applied to simulate the two cases of the interfacial instabilities of jelly models accelerated by explosion products of a gaseous explosive mixture (GEM), which are adopted in our experiments. The first is implosive dynamic interfacial instability of cylindrical symmetry and mixing. The evolving process of inner and outer interfaces, and the late distribution of mixing mass caused by Rayleigh-Taylor (RT) instability in the center of different radius are given. The second is jelly layer experiment which is initialized with one periodic perturbation with different amplitude and wave length. It reveals the complex processes of evolution of interface, and presents the displacement of front face of jelly layer, bubble head and top of spike relative to initial equilibrium position vs. time. The numerical results are in excellent agreement with that experimental images, and show that the amplitude of initial perturbations affects the evolvement of fluid mixing zone (FMZ) growth rate extremely, especially at late times.

Bai, Jingsong; Wang, Tao; Li, Ping; Zou, Liyong; Liu, Cangli

2009-12-01

359

Numerical Hydrodynamics in Strong-Field General Relativity

NASA Astrophysics Data System (ADS)

In this thesis we develop and test methods for numerically evolving hydrodynamics coupled to the Einstein field equations, and then apply them to several problems in gravitational physics and astrophysics. The hydrodynamics scheme utilizes high-resolution shock-capturing techniques with flux corrections while the Einstein equations are evolved in the generalized harmonic formulation using finite difference methods. We construct initial data by solving the constraint equations using a multigrid algorithm with free data chosen based on superposing isolated compact objects. One application we consider is the merger of black hole-neutron star and neutron star-neutron star binaries that form through dynamical capture, as may occur in globular clusters or galactic nuclei. These systems can merge with non-negligible orbital eccentricity and display significant variability in dynamics and outcome as a function of initial impact parameter. We study the electromagnetic and gravitational-wave transients that these mergers may produce and their prospects for being detected with upcoming observations. We also introduce a numerical technique that allows solutions to the full Einstein equations to be obtained for extreme-mass-ratio systems where the spacetime is dominated by a known background solution. This technique is based on using the knowledge of a background solution to subtract off its contribution to the truncation error. We use this to study the tidal effects and gravitational radiation from a solar-type star falling into a supermassive black hole. Finally, we utilize general-relativistic hydrodynamics to study ultrarelativistic black hole formation. We study the head-on collision of fluid particles well within the kinetic energy dominated regime (Lorentz factors of 8-12). We find that black hole formation does occur at energies a factor of a few below simple hoop conjecture estimates. We also find that near the threshold for black hole formation, the collision leads to two separate apparent horizons which then merge. Both of these phenomena can be understood in terms of a gravitational focusing effect.

East, William Edward

360

Hydrodynamic instability and coalescence of binary neutron stars

NASA Technical Reports Server (NTRS)

We study the importance of hydrodynamic effects on the evolution of coalescing binary neutron stars. Using an approximate energy functional constructed from equilibrium solutions for polytropic binary configuration, we incorporate hydrodynamic effects into the calculation of the orbital decay driven by gravitational wave emission. In particular, we follow the transition between the quasi-static, secular decay of the orbit at large separation and the rapid dynamical evolution of confirgurations approaching contact. We show that a purely Newtonian hydrodynamic instability can significantly accelerate the coalescence at small separation. Such an instability occurs in all close binary configurations containing sufficiently incompressible stars. Calculations are performed for various neutron star masses, radii, and spins. The influence of the stiffness of the equation of state is also explored by varying the effective polytopic index. Typically, we find that the radial infall velocity just prior to contact is about 10% of the tangential orbital velocity. Once the stability limit is reached, the final evolution only takes another orbit. Post-Newtonian effects can move the stability limit to a larger binary separation, and may induce an even larger radial velocity. We also consider the possibiltiy of mass transfer form one neutron star to the other. We show that stable mass transfer is unlikely except when the mass of one of the components is very small (M is less than or approximately 0.4 solar mass) and the viscosity is high enough to maintain corotation. Otherwise, either the two stars come into contact or the dynamical instability sets in before a Roche limit can be reached.

Lai, Dong; Rasio, Frederic A.; Shapiro, Stuart L.

1994-01-01

361

Flagellar Synchronization Independent of Hydrodynamic Interactions

NASA Astrophysics Data System (ADS)

Inspired by the coordinated beating of the flagellar pair of the green algae Chlamydomonas, we study theoretically a simple, mirror-symmetric swimmer, which propels itself at low Reynolds number by a revolving motion of a pair of spheres. We show that perfect synchronization between these two driven spheres can occur due to the motion of the swimmer and local hydrodynamic friction forces. Hydrodynamic interactions, though crucial for net propulsion, contribute little to synchronization for this free-moving swimmer.

Friedrich, Benjamin M.; Jülicher, Frank

2012-09-01

362

Anomalous hydrodynamics and normal fluids in rapidly rotating Bose-Einstein condensates.

In rapidly rotating condensed Bose systems we show that there is a regime of anomalous hydrodynamics which coincides with the mean field quantum Hall regime. A consequence is the absence of a normal fluid in any conventional sense. However, even the superfluid hydrodynamics is not described by conventional Bernoulli and continuity equations. We show that there are constraints which connect spatial variations of density and phase and that the vortex positions are not the simplest description of the dynamics. We demonstrate, inter alia, a simple relation between vortices and surface waves. We show that the surface waves can emulate a "normal fluid," allowing dissipation by energy and angular momentum absorbtion from vortex motion in the trap. The time scale is sensitive to the initial configuration, which can lead to long-lived vortex patches--perhaps related to those observed at JILA. PMID:16907220

Bourne, A; Wilkin, N K; Gunn, J M F

2006-06-23

363

RICH: Numerical simulation of compressible hydrodynamics on a moving Voronoi mesh

NASA Astrophysics Data System (ADS)

RICH (Racah Institute Computational Hydrodynamics) is a 2D hydrodynamic code based on Godunov's method. The code, largely based on AREPO, acts on an unstructured moving mesh. It differs from AREPO in the interpolation and time advancement scheme as well as a novel parallelization scheme based on Voronoi tessellation. Though not universally true, in many cases a moving mesh gives better results than a static mesh: where matter moves one way and a sound wave is traveling in the other way (such that relative to the grid the wave is not moving), a static mesh gives better results than a moving mesh. RICH is designed in an object oriented, user friendly way that facilitates incorporation of new algorithms and physical processes.

Yalinewich, Almog; Steinberg, Elad; Sari, Re'em

2014-10-01

364

Adaptive Smoothed Particle Hydrodynamics: Methodology. II.

Further development and additional details and tests of adaptive smoothed particle hydrodynamics (ASPH), the new version of smoothed particle hydrodynamics (SPH) described in the first paper in this series (Shapiro et al.), are presented. The ASPH method replaces the isotropic smoothing algorithm of standard SPH, in which interpolation is performed with spherical kernels of radius given by a scalar smoothing length, with anisotropic smoothing involving ellipsoidal kernels and tensor smoothing lengths. In standard SPH, the smoothing length for each particle represents the spatial resolution scale in the vicinity of that particle and is typically allowed to vary in space and time so as to reflect the local value of the mean interparticle spacing. This isotropic approach is not optimal, however, in the presence of strongly anisotropic volume changes such as occur naturally in a wide range of astrophysical flows, including gravitational collapse, cosmological structure formation, cloud-cloud collisions, and radiative shocks. In such cases, the local mean interparticle spacing varies not only in time and space but also in {ital direction} as well. This problem is remedied in ASPH, where each axis of the ellipsoidal smoothing kernel for a given particle is adjusted so as to reflect the different mean interparticle spacings along different directions in the vicinity of that particle. By deforming and rotating these ellipsoidal kernels so as to follow the anisotropy of volume changes local to each particle, ASPH adapts its spatial resolution scale in time, space, and direction. This significantly improves the spatial resolving power of the method over that of standard SPH at fixed particle number per simulation. This paper presents an alternative formulation of the ASPH algorithm for evolving anisotropic smoothing kernels, in which the geometric approach of the first paper in this series, based upon the Lagrangian deformation of ellipsoidal fluid elements surrounding each particle, is replaced by an approach involving a local transformation of coordinates to those in which the underlying anisotropic volume changes appear to be isotropic. Using this formulation the ASPH method is presented in two and three dimensions, including a number of details not previously included in the earlier paper, some of which represent either advances or different choices with respect to the ASPH method detailed in the earlier paper. Among the advances included here are an asynchronous time-integration scheme with different time steps for different particles and the generalization of the ASPH method to three dimensions. In the category of different choices, the shock-tracking algorithm described in the earlier paper for locally adapting the artificial viscosity to restrict viscous heating just to particles encountering shocks is not included here. Instead, we adopt a different interpolation kernel for use with the artificial viscosity, which has the effect of spatially localizing effects of the artificial viscosity. This version of the ASPH method in two and three dimensions is then applied to a series of one-, two-, and three-dimensional test problems, and the results are compared to those of standard SPH applied to the same problems. These include the problem of cosmological pancake collapse, the Riemann shock tube, cylindrical and spherical Sedov blast waves, the collision of two strong shocks, and problems involving shearing disks intended to test the angular momentum conservation properties of the method. These results further support the idea that ASPH has significantly better resolving power than standard SPH for a wide range of problems, including that of cosmological structure formation. {copyright} {ital {copyright} 1998.} {ital The American Astronomical Society}

Owen, J.M. [LLNL, L-16, Livermore, California 94551 (United States)] [LLNL, L-16, Livermore, California 94551 (United States); Villumsen, J.V. [Max-Planck-Institut fuer Astrophysik, Karl Schwarzschild Strasse 1, 85740 Garching (Germany)] [Max-Planck-Institut fuer Astrophysik, Karl Schwarzschild Strasse 1, 85740 Garching (Germany); Shapiro, P.R.; Martel, H. [Department of Astronomy, University of Texas at Austin, Austin, Texas 78712 (United States)] [Department of Astronomy, University of Texas at Austin, Austin, Texas 78712 (United States)

1998-06-01

365

Adaptive Smoothed Particle Hydrodynamics: Methodology. II.

NASA Astrophysics Data System (ADS)

Further development and additional details and tests of adaptive smoothed particle hydrodynamics (ASPH), the new version of smoothed particle hydrodynamics (SPH) described in the first paper in this series (Shapiro et al.), are presented. The ASPH method replaces the isotropic smoothing algorithm of standard SPH, in which interpolation is performed with spherical kernels of radius given by a scalar smoothing length, with anisotropic smoothing involving ellipsoidal kernels and tensor smoothing lengths. In standard SPH, the smoothing length for each particle represents the spatial resolution scale in the vicinity of that particle and is typically allowed to vary in space and time so as to reflect the local value of the mean interparticle spacing. This isotropic approach is not optimal, however, in the presence of strongly anisotropic volume changes such as occur naturally in a wide range of astrophysical flows, including gravitational collapse, cosmological structure formation, cloud-cloud collisions, and radiative shocks. In such cases, the local mean interparticle spacing varies not only in time and space but also in direction as well. This problem is remedied in ASPH, where each axis of the ellipsoidal smoothing kernel for a given particle is adjusted so as to reflect the different mean interparticle spacings along different directions in the vicinity of that particle. By deforming and rotating these ellipsoidal kernels so as to follow the anisotropy of volume changes local to each particle, ASPH adapts its spatial resolution scale in time, space, and direction. This significantly improves the spatial resolving power of the method over that of standard SPH at fixed particle number per simulation. This paper presents an alternative formulation of the ASPH algorithm for evolving anisotropic smoothing kernels, in which the geometric approach of the first paper in this series, based upon the Lagrangian deformation of ellipsoidal fluid elements surrounding each particle, is replaced by an approach involving a local transformation of coordinates to those in which the underlying anisotropic volume changes appear to be isotropic. Using this formulation the ASPH method is presented in two and three dimensions, including a number of details not previously included in the earlier paper, some of which represent either advances or different choices with respect to the ASPH method detailed in the earlier paper. Among the advances included here are an asynchronous time-integration scheme with different time steps for different particles and the generalization of the ASPH method to three dimensions. In the category of different choices, the shock-tracking algorithm described in the earlier paper for locally adapting the artificial viscosity to restrict viscous heating just to particles encountering shocks is not included here. Instead, we adopt a different interpolation kernel for use with the artificial viscosity, which has the effect of spatially localizing effects of the artificial viscosity. This version of the ASPH method in two and three dimensions is then applied to a series of one-, two-, and three-dimensional test problems, and the results are compared to those of standard SPH applied to the same problems. These include the problem of cosmological pancake collapse, the Riemann shock tube, cylindrical and spherical Sedov blast waves, the collision of two strong shocks, and problems involving shearing disks intended to test the angular momentum conservation properties of the method. These results further support the idea that ASPH has significantly better resolving power than standard SPH for a wide range of problems, including that of cosmological structure formation.

Owen, J. Michael; Villumsen, Jens V.; Shapiro, Paul R.; Martel, Hugo

1998-05-01

366

Macrocystis pyrifera (Giant Kelp) forests form important habitats in temperate coastal regions. Hydrodynamics control the transport of nutrients, food particles, larvae and spores at scales ranging from boundary layers around individual blades to entire kelp forests. Our measurements include vertical profiles of current and temperature, and concurrent wave measurements, at a number of different locations in and around a kelp

Johanna H. Rosman; Jeffrey R. Koseff; Stephen G. Monismith; Jamie Grover

2007-01-01

367

Kinematics and hydrodynamics of linear acceleration in eels, Anguilla rostrata.

The kinematics and hydrodynamics of routine linear accelerations were studied in American eels, Anguilla rostrata, using high-speed video and particle image velocimetry. Eels were examined both during steady swimming at speeds from 0.6 to 1.9 body lengths (L) per second and during accelerations from -1.4 to 1.3 L s(-2). Multiple regression of the acceleration and steady swimming speed on the body kinematics suggests that eels primarily change their tail-tip velocity during acceleration. By contrast, the best predictor of steady swimming speed is body wave speed, keeping tail-tip velocity an approximately constant fraction of the swimming velocity. Thus, during steady swimming, Strouhal number does not vary with speed, remaining close to 0.32, but during acceleration, it deviates from the steady value. The kinematic changes during acceleration are indicated hydrodynamically by axial fluid momentum in the wake. During steady swimming, the wake consists of lateral jets of fluid and has minimal net axial momentum, which reflects a balance between thrust and drag. During acceleration, those jets rotate to point downstream, adding axial momentum to the fluid. The amount of added momentum correlates with the acceleration, but is greater than the necessary inertial force by 2.8+/-0.6 times, indicating a substantial acceleration reaction. PMID:15615678

Tytell, Eric D.

2004-01-01

368

Hydrodynamics of rapidly rotating superfluid neutron stars with mutual friction

We study time evolutions of superfluid neutron stars, focussing on the nature of the oscillation spectrum, the effect of mutual friction force on the oscillations and the hydrodynamical spin-up phase of pulsar glitches. We linearise the dynamical equations of a Newtonian two-fluid model for rapidly rotating backgrounds. In the axisymmetric equilibrium configurations, the two fluid components corotate and are in beta-equilibrium. We use analytical equations of state that generate stratified and non-stratified stellar models, which enable us to study the coupling between the dynamical degrees of freedom of the system. By means of time evolutions of the linearised dynamical equations, we determine the spectrum of axisymmetric and non-axisymmetric oscillation modes, accounting for the contribution of the gravitational potential perturbations, i.e. without adopting the Cowling approximation. We study the mutual friction damping of the superfluid oscillations and consider the effects of the non-dissipative part of the mutual friction force on the mode frequencies. We also provide technical details and relevant tests for the hydrodynamical model of pulsar glitches discussed by Sidery, Passamonti and Andersson (2010). In particular, we describe the method used to generate the initial data that mimic the pre-glitch state, and derive the equations that are used to extract the gravitational-wave signal.

A. Passamonti; N. Andersson

2010-04-26

369

A Variational approach to thin film hydrodynamics of binary mixtures.

In order to model the dynamics of thin films of mixtures, solutions, and suspensions, a thermodynamically consistent formulation is needed such that various coexisting dissipative processes with cross couplings can be correctly described in the presence of capillarity, wettability, and mixing effects. In the present work, we apply Onsager's variational principle to the formulation of thin film hydrodynamics for binary fluid mixtures. We first derive the dynamic equations in two spatial dimensions, one along the substrate and the other normal to the substrate. Then, using long-wave asymptotics, we derive the thin film equations in one spatial dimension along the substrate. This enables us to establish the connection between the present variational approach and the gradient dynamics formulation for thin films. It is shown that for the mobility matrix in the gradient dynamics description, Onsager's reciprocal symmetry is automatically preserved by the variational derivation. Furthermore, using local hydrodynamic variables, our variational approach is capable of introducing diffusive dissipation beyond the limit of dilute solute. Supplemented with a Flory-Huggins-type mixing free energy, our variational approach leads to a thin film model that treats solvent and solute in a symmetric manner. Our approach can be further generalized to include more complicated free energy and additional dissipative processes. PMID:25651053

Xu, Xinpeng; Thiele, Uwe; Qian, Tiezheng

2015-03-01

370

NSDL National Science Digital Library

In this activity, students learn about the different types of seismic waves in an environment they can control. Using an interactive, online wave generator, they will study P waves, S waves, Love waves, and Rayleigh waves, and examine a combination of P and S waves that crudely simulates the wave motion experienced during an earthquake. A tutorial is provided to show how the wave generator is used.

371

NASA Technical Reports Server (NTRS)

An analytical method is presented for calculating the hydrodynamic impact loads and motions experienced by seaplane floats and hulls with scalloped (fluted) bottoms. The analysis treats vertical impact at zero trim in addition to the more general problem of the step impact of a seaplane at positive trim where the flight path is oblique to the keel and to the water surface. Also considered are the transformations required to represent impacts into waves.

Milwitzky, Benjamin

1947-01-01

372

Calculation of heavy ion collisions within the framework of the modified hydrodynamic approach

NASA Astrophysics Data System (ADS)

We developed the hydrodynamic approach to describe heavy ion collisions of medium energy, allowing for the emission of secondary particles. The compression, decompression and freeze-out stages of the forming hot spot have been examined. The shock wave that appears in the compression stage has a time dependent front. The calculated spectra of protons have been compared with experimental data. Due to its simplicity, the model can be used for a convenient parameterization of the experimental data.

D'yachenko, A. T.; Gridnev, K. A.; Greiner, W.

2013-08-01

373

We have used a Lagrangian, hydrodynamic stellar-evolution computer code to evolve a thermonuclear runaway in the accreted hydrogen rich envelope of a 1.0M, 10-km neutron star. Our simulation produced an outburst which lasted about 2000 sec and peak effective temperature was 3 keV. The peak luminosity exceeded 2 x 10/sup 5/ L. A shock wave caused a precursor in the light curve which lasted 10/sup -5/ sec.

Starrfield, S.; Kenyon, S.; Truran, J.W.; Sparks, W.M.

1983-01-01

374

Analogy between stability of tangential discontinuities in an ideal liquid in conventional hydrodynamics and in collisionless nonisothermal plasma with T{sub e} >> T{sub i} is shown. The difference is due to specific features of dispersion of ion sound waves in nonisothermal plasma in the short-wavelength range, in which the lasma quasineutrality is violated and the dispersion curve tends to the ion Langmuir frequency.

Kirtshaliya, V. G.; Minaev, I. M.; Rukhadze, A. A.; Chogovadze, M. V. [Russian Academy of Sciences, Prokhorov Institute of General Physics (Russian Federation)

2010-12-15

375

Hydrodynamic Instability in an Extended Landau/Levich Model of Liquid-Propellant Combustion

NASA Technical Reports Server (NTRS)

The classical Landau/Levich models of liquid propellant combustion, which serve as seminal examples of hydrodynamic instability in reactive systems, have been combined and extended to account for a dynamic dependence, absent in the original formulations, of the local burning rate on the local pressure and/or temperature fields. The resulting model admits an extremely rich variety of both hydrodynamic and reactive/diffusive instabilities that can be analyzed in various limiting parameter regimes. In the present work, a formal asymptotic analysis, based on the realistic smallness of the gas-to-liquid density ratio, is developed to investigate the combined effects of gravity, surface tension and viscosity on the hydrodynamic instability of the propagating liquid/gas interface. In particular, a composite asymptotic expression, spanning three distinguished wavenumber regimes, is derived for both cellular and pulsating hydrodynamic neutral stability boundaries A(sub p)(k), where A(sub p) is the pressure sensitivity of the burning rate and k is the disturbance wavenumber. For the case of cellular (Landau) instability, the results demonstrate explicitly the stabilizing effect of gravity on long-wave disturbances, the stabilizing effect of viscosity and surface tension on short-wave perturbations, and the instability associated with intermediate wavenumbers for critical negative values of A(sub p). In the limiting case of weak gravity, it is shown that cellular hydrodynamic instability in this context is a long-wave instability phenomenon, whereas at normal gravity, this instability is first manifested through O(l) wavenumber disturbances. It is also demonstrated that, in the large wavenumber regime, surface tension and both liquid and gas viscosity all produce comparable stabilizing effects in the large-wavenumber regime, thereby providing significant modifications to previous analyses of Landau instability in which one or more of these effects were neglected. In contrast, the pulsating hydrodynamic stability boundary is found to be insensitive to gravitational and surface-tension effects, but is more sensitive to the effects of liquid viscosity, which is a significant stabilizing effect for O(l) and higher wavenumbers. Liquid-propellant combustion is predicted to be stable (i.e., steady and planar) only for a range of negative pressure sensitivities that lie between the two types of hydrodynamic stability boundaries.

Margolis, Stephen B.; Sackesteder, Kurt (Technical Monitor)

1998-01-01

376

Capturing shock waves in inelastic granular gases Susana Serna

Mach numbers and near close-packed limit, damping post-shock oscillations. We have performed several-dimensional reflecting shock wave generated when granular gas hits an angular obstacule through the acceleration are measured in cm/s. Hydrodynamical models are the most convenient and efficient ones to describe shock waves

Soatto, Stefano

377

The Action of Waving Cylindrical Tails in Propelling Microscopic Organisms

The action of the tail of a spermatozoon is discussed from the hydrodynamical point of view. The tail is assumed to be a flexible cylinder which is distorted by waves of lateral displacement propagated along its length. The resulting stress and motion in the surrounding fluid is analyzed mathematically. Waves propagated backwards along the tail give rise to a forward

Geoffrey Taylor

1952-01-01

378

Interaction of three-dimensional hydrodynamic and thermocapillary instabilities in film flows.

We study three-dimensional wave patterns on the surface of a film flowing down a uniformly heated wall. Our starting point is a model of four evolution equations for the film thickness h , the interfacial temperature theta , and the streamwise and spanwise flow rates, q and p , respectively, obtained by combining a gradient expansion with a weighted residual projection. This model is shown to be robust and accurate in describing the competition between hydrodynamic waves and thermocapillary Marangoni effects for a wide range of parameters. For small Reynolds numbers, i.e., in the "drag-gravity regime," we observe regularly spaced rivulets aligned with the flow and preventing the development of hydrodynamic waves. The wavelength of the developed rivulet structures is found to closely match the one of the most amplified mode predicted by linear theory. For larger Reynolds numbers, i.e., in the "drag-inertia regime," the situation is similar to the isothermal case and no rivulets are observed. Between these two regimes we observe a complex behavior for the hydrodynamic and thermocapillary modes with the presence of rivulets channeling quasi-two-dimensional waves of larger amplitude and phase speed than those observed in isothermal conditions, leading possibly to solitarylike waves. Two subregions are identified depending on the topology of the rivulet structures that can be either "ridgelike" or "groovelike." A regime map is further proposed that highlights the influence of the Reynolds and the Marangoni numbers on the rivulet structures. Interestingly, this map is found to be related to the variations of amplitude and speed of the two-dimensional solitary-wave solutions of the model. Finally, the heat transfer enhancement due to the increase of interfacial area in the presence of rivulet structures is shown to be significant. PMID:19256949

Scheid, Benoit; Kalliadasis, Serafim; Ruyer-Quil, Christian; Colinet, Pierre

2008-12-01

379

Hydrodynamics of soft active matter

NASA Astrophysics Data System (ADS)

This review summarizes theoretical progress in the field of active matter, placing it in the context of recent experiments. This approach offers a unified framework for the mechanical and statistical properties of living matter: biofilaments and molecular motors in vitro or in vivo, collections of motile microorganisms, animal flocks, and chemical or mechanical imitations. A major goal of this review is to integrate several approaches proposed in the literature, from semimicroscopic to phenomenological. In particular, first considered are “dry” systems, defined as those where momentum is not conserved due to friction with a substrate or an embedding porous medium. The differences and similarities between two types of orientationally ordered states, the nematic and the polar, are clarified. Next, the active hydrodynamics of suspensions or “wet” systems is discussed and the relation with and difference from the dry case, as well as various large-scale instabilities of these nonequilibrium states of matter, are highlighted. Further highlighted are various large-scale instabilities of these nonequilibrium states of matter. Various semimicroscopic derivations of the continuum theory are discussed and connected, highlighting the unifying and generic nature of the continuum model. Throughout the review, the experimental relevance of these theories for describing bacterial swarms and suspensions, the cytoskeleton of living cells, and vibrated granular material is discussed. Promising extensions toward greater realism in specific contexts from cell biology to animal behavior are suggested, and remarks are given on some exotic active-matter analogs. Last, the outlook for a quantitative understanding of active matter, through the interplay of detailed theory with controlled experiments on simplified systems, with living or artificial constituents, is summarized.

Marchetti, M. C.; Joanny, J. F.; Ramaswamy, S.; Liverpool, T. B.; Prost, J.; Rao, Madan; Simha, R. Aditi

2013-07-01

380

Hydrodynamic and magnetohydrodynamic computations inside a rotating sphere

Numerical solutions of the incompressible magnetohydrodynamic (MHD) equations are reported for the interior of a rotating, perfectly-conducting, rigid spherical shell that is insulator-coated on the inside. A previously-reported spectral method is used which relies on a Galerkin expansion in Chandrasekhar-Kendall vector eigenfunctions of the curl. The new ingredient in this set of computations is the rigid rotation of the sphere. After a few purely hydrodynamic examples are sampled (spin down, Ekman pumping, inertial waves), attention is focused on selective decay and the MHD dynamo problem. In dynamo runs, prescribed mechanical forcing excites a persistent velocity field, usually turbulent at modest Reynolds numbers, which in turn amplifies a small seed magnetic field that is introduced. A wide variety of dynamo activity is observed, all at unit magnetic Prandtl number. The code lacks the resolution to probe high Reynolds numbers, but nevertheless interesting dynamo regimes turn out to be plentiful in those ...

Mininni, P D; Turner, L; 10.1088/1367-2630/9/8/303

2009-01-01

381

An Implicit-Explicit Hybrid Method for Lagrangian Hydrodynamics

NASA Astrophysics Data System (ADS)

We describe a new implicit-explicit hybrid method for solving the equations of hydrodynamics. The scheme is an extension of the explicit second-order piecewise-parabolic method (PPM) which is unconditionally stable. The scheme is thus of the Godunov type. It is conservative, accurate to second order in both space and time, and makes use of a nonlinear Riemann solver to obtain fluxes of the conserved quantities. The hybrid character of the method provides increased accuracy and computational efficiency. Switching between implicit and explicit formulations occurs smoothly and in a natural way and is performed separately for each characteristic family of waves. The method provides high resolution with shocks spread over only one zone and can produce accurate answers to most reasonable problems without the use of an artificial viscosity. 1986 Academic Press, Inc.

Fryxell, Bruce A.; Woodward, Paul R.; Colella, Phillip; Winkler, Karl-Heinz

1986-04-01

382

From microscopic to macroscopic processes: hydrodynamical consequences of atomic diffusion

NASA Astrophysics Data System (ADS)

The atomic (microscopic) diffusion of individual elements in stellar interiors and atmospheres lead to their accumulation or depletion in specific layers. The selective radiative accelerations on individual elements, which work in opposition to the effects of the pressure and thermal gradients, have important consequences. When acting on elements like iron or nickel, which are important contributors to the opacity in some stellar layers, the resulting overabundance can lead to global macroscopic effects, like extra convective zones or wave excitation by kappa mechanism. The competition between atomic diffusion and independent hydrodynamical processes including turbulent (macroscopic) diffusion has been extensively studied in previous years using parametrized computations. An important macroscopic consequence of atomic diffusion was however ignored: the double-diffusive mixing, also referred to as fingering or thermohaline convection, directly induced by ?-gradient inversion created by local heavy element accumulation. Taking this process into account will modify the studies of the element abundance variations inside stars and in their atmospheres.

Vauclair, S.

2013-12-01

383

Oscillation of viscous drops with smoothed particle hydrodynamics.

We investigate the nonlinear oscillations of heat-conductive, viscous, liquid drops in vacuum with zero gravity, using smoothed particle hydrodynamics (SPH). The liquid drops are modeled as a van der Waals fluid in two dimensions so that the models apply to flat, disklike drops. Attention is focused on small- to large-amplitude oscillations of drops that are released from a static elliptic shape. We find that for small-amplitude motions the combined dissipative effects of finite viscosity and heat conduction induce rapid decay of the oscillations after a few periods, while for large-amplitude motions wave damping is governed by the action of both viscous dissipation and surface tension forces. The transition from periodic to aperiodic decay at Re approximately 1 as well as the quadratic decrease of the frequency with the initial aspect ratio at large Re are reproduced in good agreement with previous theoretical predictions and experimental results. PMID:16802922

López, Hender; Sigalotti, Leonardo Di G

2006-05-01

384

NASA Technical Reports Server (NTRS)

A pulsating form of hydrodynamic instability has recently been shown to arise during liquid-propellant deflagration in those parameter regimes where the pressure-dependent burning rate is characterized by a negative pressure sensitivity. This type of instability can coexist with the classical cellular, or Landau form of hydrodynamic instability, with the occurrence of either dependent on whether the pressure sensitivity is sufficiently large or small in magnitude. For the inviscid problem, it has been shown that, when the burning rate is realistically allowed to depend on temperature as well as pressure, sufficiently large values of the temperature sensitivity relative to the pressure sensitivity causes like pulsating form of hydrodynamic instability to become dominant. In that regime, steady, planar burning becomes intrinsically unstable to pulsating disturbances whose wave numbers are sufficiently small. This analysis is extended to the fully viscous case, where it is shown that although viscosity is stabilizing for intermediate and larger wave number perturbations, the intrinsic pulsating instability for small wave numbers remains. Under these conditions, liquid-propellant combustion is predicted to be characterized by large unsteady cells along the liquid/gas interface.

Margolis, Stephen B.; Sacksteder, Kurt (Technical Monitor)

2000-01-01

385

Relativistic Shock Waves in Viscous Gluon Matter

We solve the relativistic Riemann problem in viscous gluon matter employing a microscopic parton cascade. We demonstrate the transition from ideal to viscous shock waves by varying the shear viscosity to entropy density ratio eta/s from zero to infinity. We show that an eta/s ratio larger than 0.2 prevents the development of well-defined shock waves on time scales typical for ultrarelativistic heavy-ion collisions. Comparisons with viscous hydrodynamic calculations confirm our findings.

Bouras, I.; Xu, Z.; El, A.; Fochler, O.; Greiner, C. [Institut fuer Theoretische Physik, Johann Wolfgang Goethe-Universitaet, Max-von-Laue-Strasse 1, D-60438 Frankfurt am Main (Germany); Molnar, E.; Niemi, H. [Frankfurt Institute for Advanced Studies, Ruth-Moufang-Strasse 1, D-60438 Frankfurt am Main (Germany); Rischke, D. H. [Institut fuer Theoretische Physik, Johann Wolfgang Goethe-Universitaet, Max-von-Laue-Strasse 1, D-60438 Frankfurt am Main (Germany); Frankfurt Institute for Advanced Studies, Ruth-Moufang-Strasse 1, D-60438 Frankfurt am Main (Germany)

2009-07-17

386

Free wave propagation in binary gas mixtures

The problem concerning the propagation of free waves in binary mixtures of monatomic ideal gases is analyzed by using a kinetic model of the Boltzmann equation which is compatible with the two-fluid hydrodynamic theory. Comparison of the theoretical results with available experimental data shows that the two-fluid model equation can be used to describe the wave-vector dependence of the free

A. S. Fernandes; W. Marques Jr

2005-01-01

387

Hydrodynamic comparison between the north and south of Mallorca Island

NASA Astrophysics Data System (ADS)

A hydrodynamic comparison between two zones of fishing interest, one located to the north and the other to the south of Mallorca Island (Balearic Islands, Western Mediterranean) was done. The comparison was conducted using the data from two moorings, one placed in the middle of the Balearic Current, in the Balearic subbasin (herein, Sóller) and the other in the Mallorca Channel, near the Algerian subbasin (called Cabrera). The instruments moored, continuously recorded the temperature, salinity and currents at different depths, for over 15 months. The data analysis suggests that Sóller is hydrodynamically more active than Cabrera, at least during the time of recording the measurements. The mean currents were higher at Sóller than at Cabrera at all depths, also showing greater maximum speeds and variability. In addition, the presence of more mesoscale eddies in Sóller became evident from the altimetry data. These eddies were not only significantly more energetic near the surface, they also generally reached to greater depths, affecting the velocities of the seabed currents. Subsequent to each significant eddy episode, strong changes in temperature and/or salinity were observed, along the entire water column. Spectral analysis revealed the presence of high frequency oscillations with periods of a few hours. One energy peak, with a period around 3.7 h, was observed at both locations, probably related to trapped waves around Mallorca or the Balearic Islands, while others (3 h and 2 h) were reflected only in Sóller, suggesting they could be associated with some standing resonance waves between the Iberian Peninsula and Mallorca.

Amores, Angel; Monserrat, Sebastià

2014-10-01

388

Maneuvering hydrodynamics of fish and small underwater vehicles.

The understanding of fish maneuvering and its application to underwater rigid bodies are considered. The goal is to gain insight into stealth. The recent progress made in NUWC is reviewed. Fish morphology suggests that control fins for maneuverability have unique scalar relationships irrespective of their speed type. Maneuvering experiments are carried out with fish that are fast yet maneuverable. The gap in maneuverability between fish and small underwater vehicles is quantified. The hydrodynamics of a dorsal fin based brisk maneuvering device and a dual flapping foil device, as applied to rigid cylindrical bodies, are described. The role of pectoral wings in maneuvering and station keeping near surface waves is discussed. A pendulum model of dolphin swimming is presented to show that body length and tail flapping frequency are related. For nearly neutrally buoyant bodies, Froude number and maneuverability are related. Analysis of measurements indicates that the Strouhal number of dolphins is a constant. The mechanism of discrete and deterministic vortex shedding from oscillating control surfaces has the property of large amplitude unsteady forcing and an exquisite phase dependence, which makes it inherently amenable to active control for precision maneuvering. Theoretical control studies are carried out to demonstrate the feasibility of maneuverability of biologically inspired bodies under surface waves. The application of fish hydrodynamics to the silencing of propulsors is considered. Two strategies for the reduction of radiated noise are developed. The effects of a reduction of rotational rate are modeled. The active cambering of blades made of digitally programmable artificial muscles, and their thrust enhancement, are demonstrated. Next, wake momentum filling is carried out by artificial muscles at the trailing edge of a stator blade of an upstream stator propulsor, and articulating them like a fish tail. A reduction of radiated noise, called blade tonals, is demonstrated theoretically. PMID:21708699

Bandyopadhyay, Promode R

2002-02-01

389

NASA Astrophysics Data System (ADS)

We report on an experimental study of the hydrodynamic expansion following a nanosecond repetitively pulsed (NRP) discharge in atmospheric pressure air preheated up to 1000 K. Single-shot schlieren images starting from 50 ns after the discharge were recorded to show the shock-wave propagation and the expansion of the heated gas channel. The temporal evolution of the gas temperature behind the shock-front is estimated from the measured shock-wave velocity by using the Rankine-Hugoniot relationships. The results show that a gas temperature increase of up to 1100 K can be observed 50 ns after the nanosecond pulse.

Xu, Da A.; Lacoste, Deanna A.; Rusterholtz, Diane L.; Elias, Paul-Quentin; Stancu, Gabi D.; Laux, Christophe O.

2011-09-01

390

A Modern Code for Solving Magneto-hydrodynamic or Hydrodynamic Equations1

ABSTRACT We have developed a modern code to solve the magneto-hydrodynamic (MHD) or hydrodynamic (HD) equations. The code consists of several ap- proaches for solving the MHD (or HD) by high-resolution schemes to improve the parallel efficiency. Our code is designed in a way that existing codes for a single grid can

Kurien, Susan

391

Hydrodynamical Shear Instability in Accretion Disks?

NASA Astrophysics Data System (ADS)

For Keplerian disks to accrete a source of enhanced angular momentum transport must be present in the disk. A key issue is whether, in the absence of ``stirring'', hydrodynamic shear turbulence can be self-sustaining in Keplerian disks or has to be transient. Simulations by Hawley et al. (1999) with resolutions up to 2563 using two codes with different dispersion properties showed no evidence of a non-linear shear instability. These authors interpreted this result to mean that the stabilizing Coriolis force easily overcame the non-linear terms in the Navier-Stokes equation and led to the complete viscous decay of the turbulence. Recently, on the basis of phenomenological arguments, it has been claimed (Longaretti 2002) that this result stems from a lack of resolution of the numerical codes, which results in too low a Reynolds number for the non-linear instability to be observed. Even if true, however, the mechanism for sustaining turbulence remains to be elucidated. Kato and Yoshizawa (1997) took steps in this direction by treating non-linear pressure-strain fluctuating terms in a one-point Reynolds-stress closure model, and argued that these terms serve to re-distribute the energy of the fluctuations in shear-driven anisotropic flows, and can counter the effects of the energy sink due to the Coriolis term at sufficiently small scales, thus possibly resulting in self-sustaining shear turbulence. Yet, these authors did not model the dissipation of turbulence. More recently, Kassinos and Reynolds (2003, 2001) and Reynolds, Kassinos and Langer (2002) have greatly improved on prior one-point closure models of rotating shear flows by adding turbulent structure information to the modeling of the production and redistribution of turbulent kinetic energy, as well as explicitly including the effects of rotation in the dissipation of turbulence. In particular, the dissipation rate ? is obtained from a large-scale enstrophy equation, which differs from standard local treatments of the dissipation equation by incorporating the inhibition of the energy cascade from large to small scales due to the scrambling effects of inertial waves in rotating frames of reference (Cambon et al. 1997). Here we report on the results of direct numerical simulations with resolution of 5123 (and possibly 10243) conducted by Kassinos et al. We will also discuss structure-based modeling of unbounded turbulent shear flows rotated about a spanwise axis, the success in fitting low to medium Reynolds number numerical simulations, current indications as to the regime of stability in Keplerian flows, and the prospects for such modeling to provide reliable high Reynolds number results.

Mosqueira, I.; Kassinos, S.; Shariff, K.; Cuzzi, J. N.

2003-05-01

392

Hydrodynamic complexity in the Earth system

NASA Astrophysics Data System (ADS)

Geophysical fluid Dynamics (GFD), as a recognizably distinct subdiscipline in the geophysical sciences, was probably born in the continuing series of Summer Schools in GFD that began at the Woods Hole Oceanographic Institution over 20 years ago. The goal of these schools was to bring together relatively small groups of gifted graduate students with professional academics working in the areas of astrophysics, atmospheric science, geophysics, oceanography and other areas in which models based upon the concepts of classical hydrodynamics were coming to be seen as central to the understanding of a wide range of dynamical processes. The point of this effort was, and remains, to emphasize the commonality of physical process that underlies the behaviour of such apparently unrelated systems and thereby to stimulate the growth of a new group of theoretical geophysicists whose members are as comfortable in analyzing the behaviour of the infinite Reynold number flows that dominate the general circulation of the planetary atmosphere as they are in developing models of the zero Reynolds number flow associated with convection in the earth's mantle. The goal was, and remains, for example, to educate astrophysicists to understand that the double diffusive processes at work in magnetoconvection in the earth's core (say) have many similarities with the processes that operate in the oceanographically important heat-salt system; and similarly to educate oceanographers to understand that the process of Gulf Stream ring formation has everything to do with the process of occlusion of a frontal baroclinic wave in the atmosphere, etc. The summary of the present state and future promise of this young science, by Raymond Hyde, in the preceding paper of this volume, has provided an interesting view of some of the areas of present research that are liable to be most productive of new insights in the immediate future. By way of this invited response to what Dr. Hyde has written I thought I might amplify somewhat on this same general theme and provide a few further examples of what the future might have in store for those of us who are practitioners of the GFD art. I think I shall begin in the troposphere and work down!

Peltier, W. Richard

393

Kelvin-Helmholtz instabilities in smoothed particle hydrodynamics

NASA Astrophysics Data System (ADS)

In this paper we investigate whether smoothed particle hydrodynamics (SPH), equipped with artificial conductivity (AC), is able to capture the physics of density/energy discontinuities in the case of the so-called shearing layers test, a test for examining Kelvin-Helmholtz (KH) instabilities. We can trace back each failure of SPH to show KH rolls to two causes: (i) shock waves travelling in the simulation box and (ii) particle clumping, or more generally, particle noise. The probable cause of shock waves is the local mixing instability, previously identified in the literature. Particle noise on the other hand is a problem because it introduces a large error in the SPH momentum equation. The shocks are hard to avoid in SPH simulations with initial density gradients because the most straightforward way of removing them, i.e. relaxing the initial conditions, is not viable. Indeed, by the time sufficient relaxing has taken place the density and energy gradients have become prohibitively wide. The particle disorder introduced by the relaxation is also a problem. We show that setting up initial conditions with a suitably smoothed density gradient dramatically improves results: shock waves are reduced whilst retaining relatively sharp gradients and avoiding unnecessary particle disorder. Particle clumping is easy to overcome, the most straightforward method being the use of a suitable smoothing kernel with non-zero first central derivative. We present results to that effect using a new smoothing kernel: the linear quartic kernel. We also investigate the role of AC. Although AC is necessary in the simulations to avoid `oily' features in the gas due to artificial surface tension, we fail to find any relation between using AC and the appearance of seeded KH rolls. Including AC is necessary for the long-term behaviour of the simulation (e.g. to get ? = 1/2, 1 KH rolls). In sensitive hydrodynamical simulations great care is however needed in selecting the AC signal velocity, with the default formulation leading to too much energy diffusion. We present new signal velocities that lead to less diffusion. The effects of the shock waves and of particle disorder become less important as the time-scale of the physical problem (for the shearing layers problem: lower density contrast and higher Mach numbers) decreases. At the resolution of current galaxy formation simulations mixing is probably not important. However, mixing could become crucial for next-generation simulations.

Valcke, S.; de Rijcke, S.; Rödiger, E.; Dejonghe, H.

2010-10-01

394

Hydrodynamic lubrication in fully plastic asperity contacts

NASA Astrophysics Data System (ADS)

A line contact inlet zone analysis is carried out for the hydrodynamic lubrication in a fully plastic asperity contact. A governing equation of the central film thickness i.e. the film thickness in the fully plastic contact area is derived. An equation predicting this film thickness is also derived. It is found that for the fully plastic contact, under relatively light loads the prediction accuracy for the central film thickness is good, while at the load heavy enough the prediction equation greatly overestimates the central film thickness and the central film thickness solved from the analytical governing equation is significantly low showing the asperity in boundary layer lubrication. For the fully plastic contact, the central film thickness is nearly half of that obtained based on the elastic contact assumption for relatively light loads or even lower for heavier loads. The hydrodynamic lubrication is found difficult to form in the fully plastic asperity contact for the carried load heavy enough or the significantly low sliding speed between the asperities. To achieve a high hydrodynamic lubrication film thickness in the fully plastic asperity contact it is recommended to employ a high sliding speed or a high fluid viscosity. However, in the fully plastic asperity contact, the potential hydrodynamic load-carrying capacity is limited and much smaller than that based on the elastic contact assumption or predicted by conventional line contact elasto-hydrodynamic lubrication theory.

Zhang, Yongbin

2012-01-01

395

Hydrodynamic description of correlations in Quantum Fluids

NASA Astrophysics Data System (ADS)

We employ field theory methods to study correlation functions of Spin Chains. We derive asymptotic behaviors of the correlators through a hydrodynamic formulation of the problem. In particular, we are interested in a correlator known as Emptiness Formation Probability (EFP), which measures the probability P(n) of formation of an empty region of length n in the quantum fluid at low temperature. The EFP in the leading order is found as the action of the instanton solution of hydrodynamic equations of motion. This hydrodynamic approach has already been applied in the study of a number of systems, for instance the XXZ Spin Chain, a Bose gas with delta repulsion and free 1D fermions. The EFP for the XY Spin Chain is asymptotically Gaussian in n at the isotropic point and exponential in the anisotropic regime. We study the crossover between these two regimes by calculating the leading intermediate asymptotics of the EFP using a bosonization approach (linearized hydrodynamics). To study the subleading contributions to the EFP, we include gradient corrections to hydrodynamics and study quantum fluctuations around the saddle-point ``instanton'' solution.

Franchini, Fabio

2005-03-01

396

Retarded hydrodynamic properties of fractal clusters.

Fractal clusters are commonly encountered when working with the stability and the aggregation of colloidal suspensions. In spite of the number of studies that have focused on their stationary hydrodynamic properties, no information is currently known on their retarded hydrodynamic properties. The objective of this work is to close this gap. Clusters with a broad range of fractal dimension values, generated via Monte-Carlo simulations have been analyzed. A rigorous model based on multipole expansion of time-dependent Stokes equations has been developed, and then the full cluster resistance matrix as a function of the frequency has been computed. An attempt has been made to extend Basset, Boussinesque and Oseen equations to fractal clusters, but it was found that the corresponding hydrodynamic radius needs to be a function of frequency. In the case of translational motion, the cluster hydrodynamic radius loses any structural information at high frequencies, becoming independent of the fractal dimension, but depending only on its mass. A simplified model, based on an extension of Kirkwood-Rieseman approach has also been developed. This allows one to perform calculations for clusters with arbitrary masses and fractal dimensions, with good accuracy and very low computational time. It is the first time that the frequency dependence of hydrodynamic properties of complex non-spherical objects has been investigated. PMID:24935184

Lattuada, Marco

2014-09-01

397

Coastal Inundation due to Tide, Surge, Waves, and Sea Level Rise at Naval Station Norfolk

Coastal Inundation due to Tide, Surge, Waves, and Sea Level Rise at Naval Station Norfolk Honghai elevation and storm induced inundation for combined influence of tide, surge, waves, wind, and SLR Stresses CMS-Flow Hydrodynamics Tide, Wind, Waves Coriolis, River flux Sediment Transport Advection

US Army Corps of Engineers

398

A three-scale composite surface model for the ocean wave-radar modulation transfer function

An improved three-scale composite surface model for the modulation of the radar backscatter from the ocean surface by long ocean waves is presented. The model is based on Bragg scattering theory. In the conventional two-scale model, only the geometric modulation of the radar backscatter and the hydrodynamic modulation of the short Bragg waves by the long waves is considered. In

Roland Romeiser; Anke Schmidt; Werner Alpers

1994-01-01

399

This article analyzes the phase-averaged hydrodynamics induced by regular wave groups and the related long waves under reflective conditions outside of the wave-breaking zone. The solutions of the inviscid region and wave-group bottom boundary layer (WGBL) are analytically investigated for a regular wave group at a constant depth, impinging obliquely on an alongshore uniform reflective wall. The problem is formulated

E. Sánchez-Badorrey; M. A. Losada

2006-01-01

400

On Pulsating and Cellular Forms of Hydrodynamic Instability in Liquid-Propellant Combustion

NASA Technical Reports Server (NTRS)

An extended Landau-Levich model of liquid-propellant combustion, one that allows for a local dependence of the burning rate on the (gas) pressure at the liquid-gas interface, exhibits not only the classical hydrodynamic cellular instability attributed to Landau but also a pulsating hydrodynamic instability associated with sufficiently negative pressure sensitivities. Exploiting the realistic limit of small values of the gas-to-liquid density ratio p, analytical formulas for both neutral stability boundaries may be obtained by expanding all quantities in appropriate powers of p in each of three distinguished wave-number regimes. In particular, composite analytical expressions are derived for the neutral stability boundaries A(sub p)(k), where A, is the pressure sensitivity of the burning rate and k is the wave number of the disturbance. For the cellular boundary, the results demonstrate explicitly the stabilizing effect of gravity on long-wave disturbances, the stabilizing effect of viscosity (both liquid and gas) and surface tension on short-wave perturbations, and the instability associated with intermediate wave numbers for negative values of A(sub p), which is characteristic of many hydroxylammonium nitrate-based liquid propellants over certain pressure ranges. In contrast, the pulsating hydrodynamic stability boundary is insensitive to gravitational and surface-tension effects but is more sensitive to the effects of liquid viscosity because, for typical nonzero values of the latter, the pulsating boundary decreases to larger negative values of A(sub p) as k increases through O(l) values. Thus, liquid-propellant combustion is predicted to be stable (that is, steady and planar) only for a range of negative pressure sensitivities that lie below the cellular boundary that exists for sufficiently small negative values of A(sub p) and above the pulsating boundary that exists for larger negative values of this parameter.

Margolis, Stephen B.; Sacksteder, Kurt (Technical Monitor)

1998-01-01

401

Second-order diffraction loads on an array of vertical cylinders in bichromatic bidirectional waves

A complete second-order solution is presented for the Hydrodynamic forces due to the action of bichromatic, bidirectional, waves on an array of bottom-mounted, surface-piercing cylinders of arbitrary cross-section in water of uniform finite depth. Based on the constant structural cross-section, the first-order problem is solved utilizing a two-dimensional Green`s function approach while in assisting radiation potential approach is used to obtain the hydrodynamic loads due to the second-order potential. Results are presented which illustrate the influence of wave directionality on the second-order sum- and difference frequency hydrodynamic forces on a two cylinder array. It is found that wave directionality may have a significant influence on the second-order hydrodynamic loads on these arrays and that the assumption of unidirectional waves does not always lead to conservative estimates of the second-order loading.

Vazquez, J.H.; Williams, A.N. [Univ. of Houston, TX (United States). Dept. of Civil and Environmental Engineering

1994-12-31

402

Second-order diffraction forces on an array of vertical cylinders in bichromatic bidirectional waves

A complete second-order solution is presented for the hydrodynamic forces due to the action of bichromatic, bidirectional waves on an array of bottom-mounted, surface-piercing cylinders of arbitrary cross section in water of uniform finite depth. Based on the constant structural cross section, the first-order problem is solved utilizing a two-dimensional Green function approach, while an assisting radiation potential approach is used to obtain the hydrodynamic loads due to the second-order potential. Results are presented which illustrate the influence of wave directionality on the second-order sum and difference frequency hydrodynamic forces on a two-cylinder array. It is found that wave directionality may have a significant influence on the second-order hydrodynamic forces on these arrays and that the assumption of unidirectional waves does not always lead to conservative estimates of the second-order loading.

Vazquez, J.H. [Lamar Univ., Beaumont, TX (United States). Dept. of Civil Engineering; Williams, A.N. [Univ. of Houston, TX (United States). Dept. of Civil and Environmental Engineering

1995-02-01

403

1.138J / 2.062J / 18.376J Wave Propagation, Fall 2004

This course discusses the Linearized theory of wave phenomena in applied mechanics. Examples are chosen from elasticity, acoustics, geophysics, hydrodynamics and other subjects. The topics include: basic concepts, one ...

Akylas, Triantaphyllos R.

404

Radiation hydrodynamics integrated in the code PLUTO

The transport of energy through radiation is very important in many astrophysical phenomena. In dynamical problems the time-dependent equations of radiation hydrodynamics have to be solved. We present a newly developed radiation-hydrodynamics module specifically designed for the versatile MHD code PLUTO. The solver is based on the flux-limited diffusion approximation in the two-temperature approach. All equations are solved in the co-moving frame in the frequency independent (grey) approximation. The hydrodynamics is solved by the different Godunov schemes implemented in PLUTO, and for the radiation transport we use a fully implicit scheme. The resulting system of linear equations is solved either using the successive over-relaxation (SOR) method (for testing purposes), or matrix solvers that are available in the PETSc library. We state in detail the methodology and describe several test cases in order to verify the correctness of our implementation. The solver works in standard coordinate systems, such as Ca...

Kolb, Stefan M; Kley, Wilhelm; Mignone, Andrea

2013-01-01

405

Toward a Fully Consistent Radiation Hydrodynamics

Dimitri Mihalas set the standard for all work in radiation hydrodynamics since 1984. The present contribution builds on 'Foundations of Radiation Hydrodynamics' to explore the relativistic effects that have prevented having a consistent non-relativistic theory. Much of what I have to say is in FRH, but the 3-D development is new. Results are presented for the relativistic radiation transport equation in the frame obtained by a Lorentz boost with the fluid velocity, and the exact momentum-integrated moment equations. The special-relativistic hydrodynamic equations are summarized, including the radiation contributions, and it is shown that exact conservation is obtained, and certain puzzles in the non-relativistic radhydro equations are explained.

Castor, J I

2009-07-07

406

Cilia beating patterns are not hydrodynamically optimal

NASA Astrophysics Data System (ADS)

We examine the hydrodynamic performance of two cilia beating patterns reconstructed from experimental data. In their respective natural systems, the two beating patterns correspond to: (A) pumping-specialized cilia, and (B) swimming-specialized cilia. We compare the performance of these two cilia beating patterns as a function of the metachronal coordination in the context of two model systems: the swimming of a ciliated cylinder and the fluid pumping by a ciliated carpet. Three performance measures are used for this comparison: (i) average swimming speed/pumping flow rate; (ii) maximum internal moments generated by the cilia; and (iii) swimming/pumping efficiencies. We found that, in both models, pattern (B) outperforms pattern (A) in almost all three measures, including hydrodynamic efficiency. These results challenge the notion that hydrodynamic efficiency dictates the cilia beating kinematics, and suggest that other biological functions and constraints play a role in explaining the wide variety of cilia beating patterns observed in biological systems.

Guo, Hanliang; Nawroth, Janna; Ding, Yang; Kanso, Eva

2014-09-01

407

Hydrodynamic stellar interactions in dense star clusters

NASA Technical Reports Server (NTRS)

Highly detailed HST observations of globular-cluster cores and galactic nuclei motivate new theoretical studies of the violent dynamical processes which govern the evolution of these very dense stellar systems. These processes include close stellar encounters and direct physical collisions between stars. Such hydrodynamic stellar interactions are thought to explain the large populations of blue stragglers, millisecond pulsars, X-ray binaries, and other peculiar sources observed in globular clusters. Three-dimensional hydrodynamics techniques now make it possible to perform realistic numerical simulations of these interactions. The results, when combined with those of N-body simulations of stellar dynamics, should provide for the first time a realistic description of dense star clusters. Here I review briefly current theoretical work on hydrodynamic stellar interactions, emphasizing its relevance to recent observations.

Rasio, Frederic A.

1993-01-01

408

Bounce-free spherical hydrodynamic implosion

In a bounce-free spherical hydrodynamic implosion, the post-stagnation hot core plasma does not expand against the imploding flow. Such an implosion scheme has the advantage of improving the dwell time of the burning fuel, resulting in a higher fusion burn-up fraction. The existence of bounce-free spherical implosions is demonstrated by explicitly constructing a family of self-similar solutions to the spherically symmetric ideal hydrodynamic equations. When applied to a specific example of plasma liner driven magneto-inertial fusion, the bounce-free solution is found to produce at least a factor of four improvement in dwell time and fusion energy gain.

Kagan, Grigory; Tang Xianzhu; Hsu, Scott C.; Awe, Thomas J. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2011-12-15

409

Hydrodynamics, horizons, holography and black hole entropy

The usual discussions about black hole dynamics involve analogies with laws of thermodynamics especially in connection with black hole entropy and the associated holographic principle. We explore complementary aspects involving hydrodynamics of the horizon geometry through the membrane paradigm. New conceptual connections complementing usual thermodynamic arguments suggest deep links between diverse topics like black hole decay, quantum circulation and viscosity. Intriguing connections between turbulence cascades, quantum diffusion via quantum paths following Fokker- Planck equation and Hawking decay also result from this combination of thermodynamic and hydrodynamic analogies to black hole dynamics.

C. Sivaram

2011-05-20

410

Effect of Second-Order Hydrodynamics on Floating Offshore Wind Turbines: Preprint

Offshore winds are generally stronger and more consistent than winds on land, making the offshore environment attractive for wind energy development. A large part of the offshore wind resource is however located in deep water, where floating turbines are the only economical way of harvesting the energy. The design of offshore floating wind turbines relies on the use of modeling tools that can simulate the entire coupled system behavior. At present, most of these tools include only first-order hydrodynamic theory. However, observations of supposed second-order hydrodynamic responses in wave-tank tests performed by the DeepCwind consortium suggest that second-order effects might be critical. In this paper, the methodology used by the oil and gas industry has been modified to apply to the analysis of floating wind turbines, and is used to assess the effect of second-order hydrodynamics on floating offshore wind turbines. The method relies on combined use of the frequency-domain tool WAMIT and the time-domain tool FAST. The proposed assessment method has been applied to two different floating wind concepts, a spar and a tension-leg-platform (TLP), both supporting the NREL 5-MW baseline wind turbine. Results showing the hydrodynamic forces and motion response for these systems are presented and analysed, and compared to aerodynamic effects.

Roald, L.; Jonkman, J.; Robertson, A,; Chokani, N.

2013-07-01

411

Influence of cavity shape on hydrodynamic noise by a hybrid LES-FW-H method

NASA Astrophysics Data System (ADS)

The flow past various mechanical cavity, which is a common structure on the surface of the underwater vehicle, and generating hydrodynamic noise has attracted considerable attention in recent years. In this paper, a hybrid method is presented to investigate the hydrodynamic noise induced by mechanical cavities with various shapes. With this method, the noise sources in the near wall turbulences or in the wake are computed by the large eddy simulation (LES) and the generation and propagation of the acoustic waves are solved by the Ffowcs Williams-Hawkings (FW-H) acoustic analogy method with acoustic source terms extracted from the time-dependent solutions of the unsteady flow. The feasibility and reliability of the current method was verified by comparing with experimental data (Wang, 2009). The 2D cavity models with different cross-section shapes and 3D cavity models with different cavity mouth shapes (rectangular and circular) are developed to study the influence of cavity shape on the hydrodynamic noise. By comparing the flow mechanisms, wall pressure fluctuations, near-field and far-field sound propagation distributions, it is found that the quadrangular cavity with equal depths of leading-edge and trailing-edge is preferred for its inducing lower hydrodynamic noise than the cylindrical cavity does.

Wang, Yu; Wang, Shu-Xin; Liu, Yu-Hong; Chen, Chao-Ying

2011-09-01

412

Wave Climatology in Coastal Maine for Aquaculture and Other Applications

Wind waves represent a significant hydrodynamic factor affecting many oceanographic studies such as sediment transport, design\\u000a of structures, etc. In coastal Maine, wave information is needed, among other applications, for aquaculture-related activities.\\u000a As few data sources exist, a question that confronts scientists pertains to the magnitudes of typical and extreme wave conditions\\u000a at various times. To address this, numerical modeling

Vijay G. Panchang; Chankwon Jeong; Dongcheng Li

2008-01-01

413

NSDL National Science Digital Library

This demonstration elucidates the concept of propagation of compressional waves (primary or P waves) and shear waves (secondary or S waves), which constitute the seismic waves used in locating and modeling earthquakes and underground nuclear explosions, and for imaging the interior structure of the Earth. The demonstration uses a slinky, pushed along its axis to create a compressional (longitudinal) wave, and moved up and down on one end to create a shear (transverse) wave.

Jeffrey Barker

414

Wave Journal Bearing. Part 1: Analysis

NASA Technical Reports Server (NTRS)

A wave journal bearing concept features a waved inner bearing diameter of the non-rotating bearing side and it is an alternative to the plain journal bearing. The wave journal bearing has a significantly increased load capacity in comparison to the plain journal bearing operating at the same eccentricity. It also offers greater stability than the plain circular bearing under all operating conditions. The wave bearing's design is relatively simple and allows the shaft to rotate in either direction. Three wave bearings are sensitive to the direction of an applied stationary side load. Increasing the number of waves reduces the wave bearing's sensitivity to the direction of the applied load relative to the wave. However, the range in which the bearing performance can be varied decreases as the number of waves increases. Therefore, both the number and the amplitude of the waves must be properly selected to optimize the wave bearing design for a specific application. It is concluded that the stiffness of an air journal bearing, due to hydrodynamic effect, could be doubled and made to run stably by using a six or eight wave geometry with a wave amplitude approximately half of the bearing radial clearance.

Dimofte, Florin

1995-01-01

415

Backscatter characteristics of 2.3 m waves breaking in wave groups have been investigated with a C-band FMCW radar (7.5 cm range resolution) in the large wind-wave tank of the University of California, Santa Barbara. The purpose of these experiments was to determine the hydrodynamic sources of the sea spike and its structure. This paper covers the experimental subset of mechanically

Jorn Fuchs; Sam Welch; Takuji Waseda; Dominic Regas; Marshall P. Tulin

1997-01-01

416

Infragravity waves across the oceans

NASA Astrophysics Data System (ADS)

The propagation of transoceanic Infragravity (IG) wave was investigated using a global spectral wave model together with deep-ocean pressure recorders. IG waves are generated mostly at the shorelines due to non-linear hydrodynamic effects that transfer energy from the main windsea and swell band, with periods of 1 to 25 s, to periods up to 500 s. IG waves are important for the study of near-shore processes and harbor agitation, and can also be a potential source of errors in satellite altimetry measurements. Setting up a global IG model was motivated by the investigation of these errors for the future planned SWOT mission. Despite the fact that the infragravity waves exhibit much smaller vertical amplitudes than the usual high frequency wind-driven waves, of the order of 1 cm in the deep oceans, their propagation throughout the oceans and signature in the wave spectrum can be clearly observed. Using a simplified empirical parameterization of the nearshore source of free IG waves as a function of the incoming wave parameters we extended to WAVEWATCH III model, used so far for windseas and swell, to the IG band, up to periods of 300 s. The spatial and temporal variability of the modeled IG energy was well correlated to the DART station records, making it useful to interpret the records of IG waves. Open ocean IG wave records appear dominated by trans-oceanic events with well defined sources concentrated on a few days, usually on West coasts, and affecting the entire ocean basin, with amplitude patterns very similar to those of tsunamis. Three particular IG bursts during 2008 are studied, 2 in the Pacific Ocean and 1 in the North Atlantic. It was observed that the liberated IG waves can travel long distances often crossing whole oceans with negligible dissipation. The IG signatures are clearly observed at sensors along their propagation paths.

Rawat, Arshad; Ardhuin, Fabrice; Aucan, Jerome

2014-05-01

417

Passive hydrodynamic synchronization of two-dimensional swimming cells

NASA Astrophysics Data System (ADS)

Spermatozoa flagella are known to synchronize when swimming in close proximity. We use a model consisting of two-dimensional sheets propagating transverse waves of displacement to demonstrate that fluid forces lead to such synchronization passively. Using two distinct asymptotic descriptions (small amplitude and long wavelength), we derive the synchronizing dynamics analytically for arbitrarily shaped waveforms in Newtonian fluids, and show that phase-locking will always occur for sufficiently asymmetric shapes. We characterize the effect of the geometry of the waveforms and the separation between the swimmers on the synchronizing dynamics, the final stable conformations, and the energy dissipated by the cells. For two closely swimming cells, synchronization always occurs at the in-phase or opposite-phase conformation, depending solely on the geometry of the cells. In contrast, the work done by the swimmers is always minimized at the in-phase conformation. As the swimmers get further apart, additional fixed points arise at intermediate values of the relative phase. In addition, computations for large amplitude waves using the boundary integral method reveal that the two asymptotic limits capture all the relevant physics of the problem. Our results provide a theoretical framework to address other hydrodynamic interactions phenomena relevant to populations of self-propelled organisms.

Elfring, Gwynn J.; Lauga, Eric

2011-01-01

418

Hydrodynamic analysis of mooring lines based on optical tracking experiments

Due to the complexity of body-shape, the investigation of hydrodynamic forces on mooring lines, especially those comprised of chain segments, has not been conducted to a sufficient degree to properly characterize the hydrodynamic damping effect...

Yang, Woo Seuk

2009-05-15

419

NASA Astrophysics Data System (ADS)

We propose a new efficient and accurate numerical method based on harmonic polynomials to solve boundary value problems governed by 3D Laplace equation. The computational domain is discretized by overlapping cells. Within each cell, the velocity potential is represented by the linear superposition of a complete set of harmonic polynomials, which are the elementary solutions of Laplace equation. By its definition, the method is named as Harmonic Polynomial Cell (HPC) method. The characteristics of the accuracy and efficiency of the HPC method are demonstrated by studying analytical cases. Comparisons will be made with some other existing boundary element based methods, e.g. Quadratic Boundary Element Method (QBEM) and the Fast Multipole Accelerated QBEM (FMA-QBEM) and a fourth order Finite Difference Method (FDM). To demonstrate the applications of the method, it is applied to some studies relevant for marine hydrodynamics. Sloshing in 3D rectangular tanks, a fully-nonlinear numerical wave tank, fully-nonlinear wave focusing on a semi-circular shoal, and the nonlinear wave diffraction of a bottom-mounted cylinder in regular waves are studied. The comparisons with the experimental results and other numerical results are all in satisfactory agreement, indicating that the present HPC method is a promising method in solving potential-flow problems. The underlying procedure of the HPC method could also be useful in other fields than marine hydrodynamics involved with solving Laplace equation.

Shao, Yan-Lin; Faltinsen, Odd M.

2014-10-01

420

On pulsating and cellular forms of hydrodynamic instability in liquid-propellant combustion

An extended Landau/Levich model of liquid-propellant combustion, one that allows for a local dependence of the burning rate on the (gas) pressure at the liquid/gas interface, exhibits not only the classical hydrodynamic cellular instability attributed to Landau, but also a pulsating hydrodynamic instability associated with sufficiently negative pressure sensitivities. Exploiting the realistic limit of small values of the gas-to-liquid density ratio {rho}, analytical formulas for both neutral stability boundaries may be obtained by expanding all quantities in appropriate powers of {rho} in each of three distinguished wavenumber regimes. In particular, composite analytical expressions are derived for the neutral stability boundaries A{sub p}(k), where A{sub p} is the pressure sensitivity of the burning rate and k is the wavenumber of the disturbance. For the cellular boundary, the results demonstrate explicitly the stabilizing effect of gravity on long-wave disturbances, the stabilizing effect of viscosity and surface tension on short-wave perturbations, and the instability associated with intermediate wavenumbers for negative values of A{sub p}, which is characteristic of many hydroxylammonium nitrate-based liquid propellants over certain pressure ranges. In contrast, the pulsating hydrodynamic stability boundary is insensitive to gravitational and surface-tension effects, but is more sensitive to the effects of liquid viscosity since, for typical nonzero values of the latter, the pulsating boundary decreases to larger negative values of A{sub p} as k increases through O(1) values.

Margolis, S.B. [Sandia National Labs., Livermore, CA (United States). Combustion Research Facility

1997-11-01

421

Laser Plasmas for Underwater Shock Hydrodynamics Studies

A new facility, the Laser Laboratory for Underwater Hydrodynamics, is being built to produce and study underwater shocks using the Pharos laser at NRL. High energy density conditions are achieved by bringing a part of the laser energy, up 250 J in 5 ns, to a small focal volume. Hydrodyamics problems to be studied include underwater shock propagation and interaction

T. G. Jones; J. Grun; R. Burris; C. K. Manka

1998-01-01

422

Conduction Modelling Using Smoothed Particle Hydrodynamics

Heat transfer is very important in many industrial and geophysical problems. Because these problems often have complicated fluid dynamics, there are advantages in solving them using Lagrangian methods like smoothed particle hydrodynamics (SPH). Since SPH particles become disordered, the second derivative terms may be estimated poorly, especially when materials with different properties are adjacent. In this paper we show how

Paul W Cleary; Joseph J. Monaghan

1999-01-01

423

Boundary conditions in tunneling via quantum hydrodynamics

NASA Technical Reports Server (NTRS)

Via the hydrodynamical formulation of quantum mechanics, an approach to the problem of tunneling through sharp-edged potential barriers is developed. Above all, it is shown how more general boundary conditions follow from the continuity of mass, momentum, and energy.

Nassar, Antonio B.

1993-01-01

424

Hydrodynamic simulations of the core helium flash

NASA Astrophysics Data System (ADS)

We desribe and discuss hydrodynamic simulations of the core helium flash using an initial model of a 1.25 M? star with a metallicity of 0.02 near at its peak. Past research concerned with the dynamics of the core helium flash is inconclusive. Its results range from a confirmation of the standard picture, where the star remains in hydrostatic equilibrium during the flash (Deupree 1996), to a disruption or a significant mass loss of the star (Edwards 1969; Cole & Deupree 1980). However, the most recent multidimensional hydrodynamic study (Dearborn et al. 2006) suggests a quiescent behavior of the core helium flash and seems to rule out an explosive scenario. Here we present partial results of a new comprehensive study of the core helium flash, which seem to confirm this qualitative behavior and give a better insight into operation of the convection zone powered by helium burning during the flash. The hydrodynamic evolution is followed on a computational grid in spherical coordinates using our new version of the multi-dimensional hydrodynamic code HERAKLES, which is based on a direct Eulerian implementation of the piecewise parabolic method.

Mocák, Miroslav; Müller, Ewald; Weiss, Achim; Kifonidis, Konstantinos

2008-10-01

425

Canonical coordinates for plasma and hydrodynamic problems

Many nonlinear equations arising in plasma physics, hydrodynamics, and solid-state physics can be written in Hamiltonian form. The full advantage of this is achieved only when the existence of canonical coordinates and momenta is known. Here such coordinates are exhibited for three large classes of equations—which seem to include almost all known completely integrable Hamiltonian systems. PMID:16593126

Case, K. M.; Roos, A. M.

1981-01-01

426

Dilepton production in schematic causal viscous hydrodynamics

Assuming that in the hot dense matter produced in relativistic heavy-ion collisions, the energy density, entropy density, and pressure as well as the azimuthal and space-time rapidity components of the shear tensor are uniform in the direction transversal to the reaction plane, we derive a set of schematic equations from the Isreal-Stewart causal viscous hydrodynamics. These equations are then used to describe the evolution dynamics of relativistic heavy-ion collisions by taking the shear viscosity to entropy density ratio of 1/4{pi} for the initial quark-gluon plasma (QGP) phase and of 10 times this value for the later hadron-gas (HG) phase. Using the production rate evaluated with particle distributions that take into account the viscous effect, we study dilepton production in central heavy-ion collisions. Compared with results from the ideal hydrodynamics, we find that although the dilepton invariant mass spectra from the two approaches are similar, the transverse momentum spectra are significantly enhanced at high transverse momenta by the viscous effect. We also study the transverse momentum dependence of dileptons produced from QGP for a fixed transverse mass, which is essentially absent in the ideal hydrodynamics, and find that this so-called transverse mass scaling is violated in the viscous hydrodynamics, particularly at high transverse momenta.

Song, Taesoo [Cyclotron Institute, Texas A and M University, College Station, Texas 77843-3366 (United States); Han, Kyong Chol; Ko, Che Ming [Cyclotron Institute and Department of Physics and Astronomy, Texas A and M University, College Station, Texas 77843-3366 (United States)

2011-02-15

427

Vlasov hydrodynamics of a quantum mechanical model

We derive the Vlasov hydrodynamics from the microscopic equations of a quantum mechanical model, which simulates that of an assembly of gravitating particles. In addition we show that the local microscopic dynamics of the model corresponds, on a suitable time-scale, to that of an ideal Fermi gas.

Heide Narnhofer; Geoffrey L. Sewell

1981-01-01

428

Surmounting barriers: The benefit of hydrodynamic interactions

We experimentally and theoretically investigate the collective behavior of three colloidal particles that are driven by a constant force along a toroidal trap. Due to hydrody- namic interactions, a characteristic limit cycle is observed. When we additionally apply a peri- odic sawtooth potential, we find a novel caterpillar-like motional sequence that is dominated by hydrodynamic interactions and promotes the surmounting

429

Hydrodynamically induced crystallization of polymers from solution

Summary This paper deals with a study on the melting behaviour of polyethylene crystals showing a fibrillar morphology. These crystals were prepared by hydrodynamically induced crystallization from xylene solutions. Use was made of several techniques, such as differential scanning calorimetry, polarizing microscopy and infrared dichroism. The experimental observations indicate that the melting process of the fibrous crystals can only partly

A. J. Pennings; J. M. A. A. van der Mark

1971-01-01

430

(Non)-dissipative hydrodynamics on embedded surfaces

NASA Astrophysics Data System (ADS)

We construct the theory of dissipative hydrodynamics of uncharged fluids living on embedded space-time surfaces to first order in a derivative expansion in the case of codimension-1 surfaces (including fluid membranes) and the theory of non-dissipative hydrodynamics to second order in a derivative expansion in the case of codimension higher than one under the assumption of no angular momenta in transverse directions to the surface. This construction includes the elastic degrees of freedom, and hence the corresponding transport coefficients, that take into account transverse fluctuations of the geometry where the fluid lives. Requiring the second law of thermodynamics to be satisfied leads us to conclude that in the case of codimension-1 surfaces the stress-energy tensor is characterized by 2 hydrodynamic and 1 elastic independent transport coefficient to first order in the expansion while for codimension higher than one, and for non-dissipative flows, the stress-energy tensor is characterized by 7 hydrodynamic and 3 elastic independent transport coefficients to second order in the expansion. Furthermore, the constraints imposed between the stress-energy tensor, the bending moment and the entropy current of the fluid by these extra non-dissipative contributions are fully captured by equilibrium partition functions. This analysis constrains the Young modulus which can be measured from gravity by elastically perturbing black branes.

Armas, Jay

2014-09-01

431

Review of Dolphin Hydrodynamics and Swimming Performance

Abstract: This report describesinformation obtained from the available literature including published research and technical reportsfrom English-speaking and Russian sources. The project team specifically studied routine and maximumswimming speeds, morphological design related to hydrodynamic performance, drag reduction,swimming kinematics, thrust production and efficiency, behavioral strategies employed for energyeconomy when swimming, and maneuverability.SYNOPSISResearch into dolphin swimming...

J. J. Rohr

1999-01-01

432

Hydrodynamic and Water Quality Modeling Basics

Hydrodynamic and Water Quality Modeling Basics Jim Bowen, UNC Charlotte LCFRP Advisory Board to Numerical Water Quality Models Â·Introduction to Model Used - Environmental Fluid Dynamics Code (EFDC = flip a coin, since the choices are equally likely Choose a letter: k You won the prize 34% of the time

Bowen, James D.

433

Stabilizing geometry for hydrodynamic rotary seals

A hydrodynamic sealing assembly including a first component having first and second walls and a peripheral wall defining a seal groove, a second component having a rotatable surface relative to said first component, and a hydrodynamic seal comprising a seal body of generally ring-shaped configuration having a circumference. The seal body includes hydrodynamic and static sealing lips each having a cross-sectional area that substantially vary in time with each other about the circumference. In an uninstalled condition, the seal body has a length defined between first and second seal body ends which varies in time with the hydrodynamic sealing lip cross-sectional area. The first and second ends generally face the first and second walls, respectively. In the uninstalled condition, the first end is angulated relative to the first wall and the second end is angulated relative to the second wall. The seal body has a twist-limiting surface adjacent the static sealing lip. In the uninstalled condition, the twist-limiting surface is angulated relative to the peripheral wall and varies along the circumference. A seal body discontinuity and a first component discontinuity mate to prevent rotation of the seal body relative to the first component.

Dietle, Lannie L. (Houston, TX); Schroeder, John E. (Richmond, TX)

2010-08-10

434

Hydrodynamic implications for submarine launched underwater gliders

Underwater gliders are a type of long range unmanned vehicle that use bouyancy control and lifting surfaces to travel in a sawtooth trajectory through the water column. These vehicles are typically employed by oceanographers for environmental monitoring and also show promise as a sensor platform in military applications. This paper presents investigations of vehicle hydrodynamics relating to the deployment of

Joshua D. Rodgers; John M. Wharington

2010-01-01

435

Cosmological Simulations with Adaptive Smoothed Particles Hydrodynamics

We summarize the ideas that led to the Adaptive Smoothed Particle Hydrodynamics (ASPH) algorithm, with anisotropic smoothing and shock-tracking. We then identify a serious new problem for SPH simulations with shocks and radiative cooling --- false cooling --- and discuss a possible solution based on the shock-tracking ability of ASPH.

Hugo Martel; Paul R. Shapiro

2001-10-01

436

Microflow Cytometers with Integrated Hydrodynamic Focusing

This study demonstrates the suitability of microfluidic structures for high throughput blood cell analysis. The microfluidic chips exploit fully integrated hydrodynamic focusing based on two different concepts: Two-stage cascade focusing and spin focusing (vortex) principle. The sample—A suspension of micro particles or blood cells—is injected into a sheath fluid streaming at a substantially higher flow rate, which assures positioning of the particles in the center of the flow channel. Particle velocities of a few m/s are achieved as required for high throughput blood cell analysis. The stability of hydrodynamic particle positioning was evaluated by measuring the pulse heights distributions of fluorescence signals from calibration beads. Quantitative assessment based on coefficient of variation for the fluorescence intensity distributions resulted in a value of about 3% determined for the micro-device exploiting cascade hydrodynamic focusing. For the spin focusing approach similar values were achieved for sample flow rates being 1.5 times lower. Our results indicate that the performances of both variants of hydrodynamic focusing suit for blood cell differentiation and counting. The potential of the micro flow cytometer is demonstrated by detecting immunologically labeled CD3 positive and CD4 positive T-lymphocytes in blood. PMID:23571670

Frankowski, Marcin; Theisen, Janko; Kummrow, Andreas; Simon, Peter; Ragusch, Hülya; Bock, Nicole; Schmidt, Martin; Neukammer, Jörg

2013-01-01

437

Fast Calculation of Hydrodynamic Interaction among Particles

Fast Calculation of Hydrodynamic Interaction among Particles Kengo Ichiki Graduate School of Human is the number of particles. The iterative method is constructed only by the calculation of dotÂproduct between the mobility matrix and force moments and that calculation becomes a bottleneck in this case. Fast multipole

Ichiki, Kengo

438

Hydrodynamic model of an inhomogeneous electron gas

We present a simple hydrodynamic model for the ground state of an inhomogeneous electron gas. The profile relation and response are obtained explicitly. In the case of a uniform reference system the profile relation reduces to that of the Sjölander-Stott theory. We confirm their results using the most recent numerical data. We compare numerical results for a heavy impurity problem

Andrey Krakovsky; Jerome K. Percus

1995-01-01

439

Hydrodynamics of shear coaxial liquid rocket injectors

Hydrodynamic instabilities within injector passages can couple to chamber acoustic modes and lead to unacceptable levels of combustion instabilities inside liquid rocket engines. The instability of vena-contracta regions and mixing between fuel and oxidizer can serve as a fundamental source of unsteadiness produced by the injector, even in the absence of upstream or downstream pressure perturbations. This natural or \\

John Tsohas

2009-01-01

440

Using pulsed power for hydrodynamic code validation

As part of ongoing hydrodynamic code validation efforts, a series of Near Term Liner Experiments (NTLX) was designed for the Shiva Star capacitor bank at the Air Force Research Laboratory (AFRL). A cylindrical aluminum liner that is magnetically imploded onto a central target by self-induced radial Lorentz forces drove the experiments. The behavior of the target was simulated using the

Randall Kanzleiter; Walter Atchison; Richard Bowers; Michael Gittings; Joyce Guzik; D. Oro; J. Roberts; G. Rodriguez; J. Stokes; P. Turchi; S. Coffey; J. Degnan; G. Kiuttu

2001-01-01

441

NSDL National Science Digital Library

This webpage, from Hyperphysics, provides a detailed explanation of how waves form in the ocean. A series of diagrams show how the water moves as a wave passes by. The site shows how a water wave's speed depends on wavelength, and how the shape of a wave depends on its amplitude. A description of why waves break on a beach is included.

Nave, Carl R.

2010-07-13

442

Sound Waves in (2+1) Dimensional Holographic Magnetic Fluids

We use the AdS/CFT correspondence to study propagation of sound waves in strongly coupled (2+1) dimensional conformal magnetic fluids. Our computation provides a nontrivial consistency check of the viscous magneto-hydrodynamics of Hartnoll-Kovtun-Muller-Sachdev to leading order in the external field. Depending on the behavior of the magnetic field in the hydrodynamic limit, we show that it can lead to further attenuation of sound waves in the (2+1) dimensional conformal plasma, or reduce the speed of sound. We present both field theory and dual supergravity descriptions of these phenomena. While to the leading order in momenta the dispersion of the sound waves obtained from the dual supergravity description agrees with the one predicted from field theory, we find a discrepancy at higher order. This suggests that further corrections to HKMS magneto-hydrodynamics are necessary.

Evgeny I. Buchbinder; Alex Buchel; Samuel E. Vazquez

2008-10-22

443

Beat-wave experiments at Ecole Polytechnique

We summarize the results obtained in the context of the beat-wave experiments performed at Ecole Polytechnique in France. We first study the generation of long and homogeneous plasmas by multiphotoionization of low density gases and observe the density variation with time due to the ponderomotive force of the ionizing laser beam. In the Nd-laser beat-wave experiments we observe in the resonant conditions the generation of intense electron plasma waves. We also measure some daughter ion and electron waves generated by the decay of these primary electron waves by modulational instability (coupling with ion motions). These results show the importance of the ion hydrodynamic for the generation and the evolution of the accelerating electric fields in beat-wave experiments.

Amiranoff, F.; Dyson, A.; Laberge, M.; Marques, J.R.; Moulin, F.; Fabre, E. (Laboratoire d'Utilisation des Lasers Intenses, Ecole Polytechnique 9112, Palaiseau France (France)); Benkheiri, P.; Jacquet, F.; Meyer, J.; Mine, P. (Laboratoire de Physique Nucleaire des Hautes Energies, Ecole Polytechnique 9112, Palaiseau France (France)); Cros, B.; Matthieussent, G. (Laboratoire de Physique des Gaz et des Plasmas, Universite Paris-Sud, 9140, Orsay France (France)); Mora, P. (Centre de Physique Theorique, Ecole Polytechnique 9112, Palaiseau France (France)); Stenz, C. (Groupe de Recherche sur l'Energetique des Milieux Ionises, Universite d'Orleans 45000 Orleans (France))

1992-07-01

444

Modern Numerical Hydrodynamics and the Evolution of Dense Interstellar Medium

We discuss some typical problems related to numerical hydrodynamics of a dense interstellar medium. A newly developed hydrodynamical code based on adaptive mesh refinement technique is presented and applied to simulate the evolution of a supernova remnant in a high-density medium. Advantages of this new approach in comparison to commonly used hydrodynamical methods are briefly discussed.

Tomasz Plewa; Michal Rozyczka

1996-07-06

445

Modelling of Breaking Waves in Tsunami and Sloshing Waves by a New Particle Method

NASA Astrophysics Data System (ADS)

The recently developed Consistent Particle Method (CPM) is used to model breaking waves in tsunami and violent sloshing waves in a moving tank. Solving the Navier-Stokes equations in a semi-implicit time stepping scheme, the CPM eliminates the use of kernel function which is somewhat arbitrarily defined and used in other particle methods. It is demonstrated that the method is applicable to large amplitude free surface wave problems that involve breaking phenomenon. Tsunami wave impact on a fixed structure is modeled using CPM. The simulated results show fairly good agreement to the actual nonlinear wave motions including overturning and breaking of waves. Large amplitude sloshing waves in a moving tank are investigated with CPM. Experiment was conducted in the laboratory to verify the CPM solutions. The hydrodynamic pressure computed by the CPM agrees well with the experimental results.

Gao, Mimi; Koh, Chan Ghee; Luo, Min; Bai, Wei

2014-11-01

446

SRTM vegetation removal and hydrodynamic modeling accuracy

NASA Astrophysics Data System (ADS)

Hydrodynamic modeling of large remote forested floodplains, such as the Amazon, is hindered by the vegetation signal contained within Digital Elevation Models (DEMs) such as the Shuttle Radar Topography Mission (SRTM). Not removing the vegetation signal causes DEMs to be overelevated preventing the correct simulation of overbank inundation. Previous efforts to remove this vegetation signal have either not accounted for its spatial variability or relied upon single assumed error values. As a possible solution, a systematic approach to removing the vegetation signal which accounts for spatial variability using recently published estimates of global vegetation heights is proposed. The proposed approach is applied to a well-studied reach of the Amazon floodplain where previous hydrodynamic model applications were affected by the SRTM vegetation signal. Greatest improvements to hydrodynamic model accuracy were obtained by subtracting 50-60% of the vegetation height from the SRTM. The vegetation signal removal procedure improved the RMSE (Root-Mean-Square Error) accuracy of the hydrodynamic model than when using the original SRTM in three ways: (1) seasonal floodplain water elevation predictions against TOPEX/Poseidon observations improved from 6.61 to 1.84 m; (2) high water inundation extent prediction accuracy improved from 0.52 to 0.07 against a JERS (Japanese Earth Resources Satellite) observation; (3) low water inundation extent accuracy against a JERS observation improved from 0.22 to 0.12. The simple data requirements of this vegetation removal method enable it to be applied to any remote floodplain for which hydrodynamic model accuracy is hindered by vegetation present in the DEM.

Baugh, Calum A.; Bates, Paul D.; Schumann, Guy; Trigg, Mark A.

2013-09-01

447

Observation and control of shock waves in individual nanoplasmas.

Using an apparatus that images the momentum distribution of individual, isolated 100-nm-scale plasmas, we make the first experimental observation of shock waves in nanoplasmas. We demonstrate that the introduction of a heating pulse prior to the main laser pulse increases the intensity of the shock wave, producing a strong burst of quasimonoenergetic ions with an energy spread of less than 15%. Numerical hydrodynamic calculations confirm the appearance of accelerating shock waves and provide a mechanism for the generation and control of these shock waves. This observation of distinct shock waves in dense plasmas enables the control, study, and exploitation of nanoscale shock phenomena with tabletop-scale lasers. PMID:24702383

Hickstein, Daniel D; Dollar, Franklin; Gaffney, Jim A; Foord, Mark E; Petrov, George M; Palm, Brett B; Keister, K Ellen; Ellis, Jennifer L; Ding, Chengyuan; Libby, Stephen B; Jimenez, Jose L; Kapteyn, Henry C; Murnane, Margaret M; Xiong, Wei

2014-03-21

448

Finite-dimensional turbulence of planetary waves

NASA Astrophysics Data System (ADS)

Finite-dimensional wave turbulence refers to the chaotic dynamics of interacting wave “clusters” consisting of finite number of connected wave triads with exact three-wave resonances. We examine this phenomenon using the example of atmospheric planetary (Rossby) waves. It is shown that the dynamics of the clusters is determined by the types of connections between neighboring triads within a cluster; these correspond to substantially different scenarios of energy flux between different triads. All the possible cases of the energy cascade termination are classified. Free and forced chaotic dynamics in the clusters are investigated: due to the huge fluctuations of the energy exchange between resonant triads these two types of evolution have a lot in common. It is confirmed that finite-dimensional wave turbulence in finite wave systems is fundamentally different from kinetic wave turbulence in infinite systems; the latter is described by wave-kinetic equations that account for interactions with overlapping quasiresonances of finite amplitude waves. The present results are directly applicable to finite-dimensional wave turbulence in any wave system in finite domains with three-mode interactions as encountered in hydrodynamics, astronomy, plasma physics, chemistry, medicine, etc.

L'Vov, Victor S.; Pomyalov, Anna; Procaccia, Itamar; Rudenko, Oleksii

2009-12-01

449

NSDL National Science Digital Library

This is an activity about waves. Using marbles, paper clips and rubber bands, learners explore how waves behave. This is an excellent activity to use to lead into discussion of waves of all sorts (sound, ocean, light).

Cosi

2009-01-01

450

NSDL National Science Digital Library

This site from Carl Nave at Georgia State University presents a discussion of wave motion. The site explains the velocity of idealized ocean waves and details the measurement of large waves aboard the USS Ramapo.

Carl R. (Rod) Nave

451

Low torque hydrodynamic lip geometry for bi-directional rotation seals

A hydrodynamically lubricating geometry for the generally circular dynamic sealing lip of rotary seals that are employed to partition a lubricant from an environment. The dynamic sealing lip is provided for establishing compressed sealing engagement with a relatively rotatable surface, and for wedging a film of lubricating fluid into the interface between the dynamic sealing lip and the relatively rotatable surface in response to relative rotation that may occur in the clockwise or the counter-clockwise direction. A wave form incorporating an elongated dimple provides the gradual convergence, efficient impingement angle, and gradual interfacial contact pressure rise that are conducive to efficient hydrodynamic wedging. Skewed elevated contact pressure zones produced by compression edge effects provide for controlled lubricant movement within the dynamic sealing interface between the seal and the relatively rotatable surface, producing enhanced lubrication and low running torque.

Dietle, Lannie L. (Houston, TX); Schroeder, John E. (Richmond, TX)

2009-07-21

452

Low torque hydrodynamic lip geometry for bi-directional rotation seals

A hydrodynamically lubricating geometry for the generally circular dynamic sealing lip of rotary seals that are employed to partition a lubricant from an environment. The dynamic sealing lip is provided for establishing compressed sealing engagement with a relatively rotatable surface, and for wedging a film of lubricating fluid into the interface between the dynamic sealing lip and the relatively rotatable surface in response to relative rotation that may occur in the clockwise or the counter-clockwise direction. A wave form incorporating an elongated dimple provides the gradual convergence, efficient impingement angle, and gradual interfacial contact pressure rise that are conducive to efficient hydrodynamic wedging. Skewed elevated contact pressure zones produced by compression edge effects provide for controlled lubricant movement within the dynamic sealing interface between the seal and the relatively rotatable surface, producing enhanced lubrication and low running torque.

Dietle, Lannie L. (Houston, TX); Schroeder, John E. (Richmond, TX)

2011-11-15

453

An analysis of hydrodynamic phenomena in simulant experiments examining aspects of ex-vessel material interactions in a PWR re