A Miniature Couette to Generate Shear for Flow Cytometry: Studying Real-Time Modulation of Intracellular Calcium in Monocytic Cells

PubMed Central

Zwartz, Gordon J.; Chigaev, Alexandre; Foutz, Terry D.; Edwards, Bruce; Sklar, Larry A.

2013-01-01

Extracellular hydrodynamic forces may be transmitted to the interior of cells through the alteration of integrin conformation and affinity. Integrin activation regulates leukocyte recruitment, cell activation, and transmigration. The cellular and molecular mechanisms for integrin activation are not precisely known, although intracellular calcium signaling is involved. Flow cytometry offers a versatile way to study intracellular calcium signaling in real-time. We report a novel method to generate defined shear by using a miniature Couette. Testing involved measuring shear induced intracellular calcium signals of human monoblastoid U937 cells in suspension. The Couette was connected externally to a flow cytometer and pressurized at 6 PSI (4.1 N/m2). Cells were subjected to well-defined shear between 0 and 1000 s−1 and delivered continuously within 10 s to a FACScan at 1 μl/s. Intracellular calcium levels and the percentage of cells activated increased as shear increased in duration and intensity. PMID:22045643

Letter: The link between the Reynolds shear stress and the large structures of turbulent Couette-Poiseuille flow

NASA Astrophysics Data System (ADS)

Gandía-Barberá, Sergio; Hoyas, Sergio; Oberlack, Martin; Kraheberger, Stefanie

2018-04-01

The length and width of the long and wide structures appearing in turbulent Couette flows are studied by means of a new dataset of direct numerical simulation covering a stepped transition from pure Couette flow to pure Poiseuille one, at Reτ ≈ 130, based on the stationary wall. The existence of these structures is linked to the averaged Reynolds stress, u v ¯ : as soon as in any part of the channel u v ¯ changes its sign, the structures disappear. The length and width of the rolls are found to be, approximately, 50h and 2.5h, respectively. For this Reynolds number, simulations with a domain shorter than 100h cannot properly describe the behaviour of the longest structures of the flow.

Sensitivity analysis of hydrodynamic stability operators

NASA Technical Reports Server (NTRS)

Schmid, Peter J.; Henningson, Dan S.; Khorrami, Mehdi R.; Malik, Mujeeb R.

1992-01-01

The eigenvalue sensitivity for hydrodynamic stability operators is investigated. Classical matrix perturbation techniques as well as the concept of epsilon-pseudoeigenvalues are applied to show that parts of the spectrum are highly sensitive to small perturbations. Applications are drawn from incompressible plane Couette, trailing line vortex flow and compressible Blasius boundary layer flow. Parametric studies indicate a monotonically increasing effect of the Reynolds number on the sensitivity. The phenomenon of eigenvalue sensitivity is due to the non-normality of the operators and their discrete matrix analogs and may be associated with large transient growth of the corresponding initial value problem.

Linear instability of plane Couette and Poiseuille flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chefranov, S. G., E-mail: schefranov@mail.ru; Chefranov, A. G., E-mail: Alexander.chefranov@emu.edu.tr

2016-05-15

It is shown that linear instability of plane Couette flow can take place even at finite Reynolds numbers Re > Re{sub th} ≈ 139, which agrees with the experimental value of Re{sub th} ≈ 150 ± 5 [16, 17]. This new result of the linear theory of hydrodynamic stability is obtained by abandoning traditional assumption of the longitudinal periodicity of disturbances in the flow direction. It is established that previous notions about linear stability of this flow at arbitrarily large Reynolds numbers relied directly upon the assumed separation of spatial variables of the field of disturbances and their longitudinal periodicitymore » in the linear theory. By also abandoning these assumptions for plane Poiseuille flow, a new threshold Reynolds number Re{sub th} ≈ 1035 is obtained, which agrees to within 4% with experiment—in contrast to 500% discrepancy for the previous estimate of Re{sub th} ≈ 5772 obtained in the framework of the linear theory under assumption of the “normal” shape of disturbances [2].« less

Hydrodynamics beyond Navier-Stokes: the slip flow model.

PubMed

Yudistiawan, Wahyu P; Ansumali, Santosh; Karlin, Iliya V

2008-07-01

Recently, analytical solutions for the nonlinear Couette flow demonstrated the relevance of the lattice Boltzmann (LB) models to hydrodynamics beyond the continuum limit [S. Ansumali, Phys. Rev. Lett. 98, 124502 (2007)]. In this paper, we present a systematic study of the simplest LB kinetic equation-the nine-bit model in two dimensions--in order to quantify it as a slip flow approximation. Details of the aforementioned analytical solution are presented, and results are extended to include a general shear- and force-driven unidirectional flow in confined geometry. Exact solutions for the velocity, as well as for pertinent higher-order moments of the distribution functions, are obtained in both Couette and Poiseuille steady-state flows for all values of rarefaction parameter (Knudsen number). Results are compared with the slip flow solution by Cercignani, and a good quantitative agreement is found for both flow situations. Thus, the standard nine-bit LB model is characterized as a valid and self-consistent slip flow model for simulations beyond the Navier-Stokes approximation.

Nonlinear transport for a dilute gas in steady Couette flow

NASA Astrophysics Data System (ADS)

Garzó, V.; López de Haro, M.

1997-03-01

Transport properties of a dilute gas subjected to arbitrarily large velocity and temperature gradients (steady planar Couette flow) are determined. The results are obtained from the so-called ellipsoidal statistical (ES) kinetic model, which is an extension of the well-known BGK kinetic model to account for the correct Prandtl number. At a hydrodynamic level, the solution is characterized by constant pressure, and linear velocity and parabolic temperature profiles with respect to a scaled variable. The transport coefficients are explicitly evaluated as nonlinear functions of the shear rate. A comparison with previous results derived from a perturbative solution of the Boltzmann equation as well as from other kinetic models is carried out. Such a comparison shows that the ES predictions are in better agreement with the Boltzmann results than those of the other approximations. In addition, the velocity distribution function is also computed. Although the shear rates required for observing non-Newtonian effects are experimentally unrealizable, the conclusions obtained here may be relevant for analyzing computer results.

Channel-shoal morphodynamics in response to distinct hydrodynamic drivers at the outer Weser estuary

NASA Astrophysics Data System (ADS)

Herrling, Gerald; Benninghoff, Markus; Zorndt, Anna; Winter, Christian

2017-04-01

The interaction of tidal, wave and wind forces primarily governs the morphodynamics of intertidal channel-shoal systems. Typical morphological changes comprise tidal channel meandering and/or migration with related shoal erosion or accretion. These intertidal flat systems are likely to response to accelerated sea level rise and to potential changes in storm frequency and direction. The aim of the ongoing research project is an evaluation of outer estuarine channel-shoal dynamics by combining the analysis of morphological monitoring data with high-resolution morphodynamic modelling. A focus is set on their evolution in reaction to different hydrodynamic forcings like tides, wind driven currents, waves under fair-weather and high energy conditions, and variable upstream discharges. As an example the Outer Weser region was chosen, and a tidal channel system serves as a reference site: Availability of almost annual bathymetrical observations of an approx. 10 km long tidal channel (Fedderwarder Priel) and its morphological development largely independent from maintenance dredging of the main Weser navigational channel make this tributary an ideal study area. The numerical modelling system Delft3D (Deltares) is applied to run real-time annual scenario simulations aiming to evaluate and to differentiate the morphological responses to distinct hydrodynamic drivers. A comprehensive morphological analysis of available observations at the FWP showed that the channel migration trends and directions are persistent at particular channel bends and meanders for the considered period of 14 years. Migration trends and directions are well reproduced by one-year model simulations. Morphodynamic modelling is applied to interpolate between observations and relate sediment dynamics to different forcing scenarios in the outer Weser estuary as a whole and at the scale of local tributary channels and flats.

Effects of the computational domain on the secondary flow in turbulent plane Couette flow

NASA Astrophysics Data System (ADS)

Gai, Jie; Xia, Zhen-Hua; Cai, Qing-Dong

2015-10-01

A series of direct numerical simulations of the fully developed plane Couette flow at a Reynolds number of 6000 (based on the relative wall speed and half the channel height h) with different streamwise and spanwise lengths are conducted to investigate the effects of the computational box sizes on the secondary flow (SF). Our focuses are the number of counter-rotating vortex pairs and its relationship to the statistics of the mean flow and the SF in the small and moderate computational box sizes. Our results show that the number of vortex pairs is sensitive to the computational box size, and so are the slope parameter, the rate of the turbulent kinetic energy contributed by the SF, and the ratio of the kinetic energy of the SF to the total kinetic energy. However, the averaged spanwise width of each counter-rotating vortex pair in the plane Couette flow is found, for the first time, within 4(1 ± 0.25)h despite the domain sizes. Project supported by the National Natural Science Foundation of China (Grant Nos. 11221061, 11272013, and 11302006).

Zero absolute vorticity: insight from experiments in rotating laminar plane Couette flow.

PubMed

Suryadi, Alexandre; Segalini, Antonio; Alfredsson, P Henrik

2014-03-01

For pressure-driven turbulent channel flows undergoing spanwise system rotation, it has been observed that the absolute vorticity, i.e., the sum of the averaged spanwise flow vorticity and system rotation, tends to zero in the central region of the channel. This observation has so far eluded a convincing theoretical explanation, despite experimental and numerical evidence reported in the literature. Here we show experimentally that three-dimensional laminar structures in plane Couette flow, which appear under anticyclonic system rotation, give the same effect, namely, that the absolute vorticity tends to zero if the rotation rate is high enough. It is shown that this is equivalent to a local Richardson number of approximately zero, which would indicate a stable condition. We also offer an explanation based on Kelvin's circulation theorem to demonstrate that the absolute vorticity should remain constant and approximately equal to zero in the central region of the channel when going from the nonrotating fully turbulent state to any state with sufficiently high rotation.

Hydrodynamic Dispersion in Turbulent Open-Channel Flow Over an Irregular Bed

NASA Astrophysics Data System (ADS)

Stefan, D.; Iobst, B. R.; Furbish, D. J.

2007-05-01

Characterizing hydrodynamic dispersion in open-channel flow is a key element in environmental studies aimed at modeling the transport and cycling of nutrients and pollutants. We use a simple flow model together with a particle-tracking algorithm to explore first-order influences of bed topography on the hydrodynamic dispersion. The model is based on linearized versions of the shallow-water equations for flow over an irregular bed topography composed of alternate bars. Theoretical dispersion curves were generated by simultaneously releasing tracer particles across the channel at a fixed location and keeping track of their positions for various intervals of time and different channel geometries. Particles were subject to fluctuating motions mimicking effects of turbulence. The shape and length of the tail of the dispersion curve appears to depend primarily on the time elapsed since the particles were released. For short time intervals, the curve is characterized by a steep leading edge which later transforms into a peak with a less steeply sloping front. This transition occurs more rapidly with increasing bar amplitude, and also with increasing number of alternate bars in the section traveled - thus with shorter bar wavelengths. Rhodamine WT was used in a field dye test conducted on a 150 m straight reach of Panther Creek, KY. This section of the creek has an average channel width of 6.3m, and exhibits a loose alternate bar structure with wavelength of ~55 m and amplitude of ~0.1 m. The bed of the channel has an average slope of 0.01 and consists of coarse gravel with a D85 of 6 cm. Consistent with the modeling results, the tracer test revealed a relative steep leading front and slowing decaying tail. In both the simulated and field case, this tail is similar to the behavior predicted by "dead zone" models of dispersion, and is attributable mostly to spatial variations in the local flow (with superimposed fluctuating motions) associated with vertical velocity

Verification of the Hydrodynamic and Sediment Transport Hybrid Modeling System for Cumberland Sound and Kings Bay Navigation Channel, Georgia

DTIC Science & Technology

1989-07-01

TECHNICAL REPORT HL-89-14 VERIFICATION OF THE HYDRODYNAMIC AND Si SEDIMENT TRANSPORT HYBRID MODELING SYSTEM FOR CUMBERLAND SOUND AND I’) KINGS BAY...Hydrodynamic and Sediment Transport Hybrid Modeling System for Cumberland Sound and Kings Bay Navigation Channel, Georgia 12 PERSONAL AUTHOR(S) Granat...Hydrodynamic results from RMA-2V were used in the numerical sediment transport code STUDH in modeling the interaction of the flow transport and

High resolution multibeam and hydrodynamic datasets of tidal channels and inlets of the Venice Lagoon

NASA Astrophysics Data System (ADS)

Madricardo, Fantina; Foglini, Federica; Kruss, Aleksandra; Ferrarin, Christian; Pizzeghello, Nicola Marco; Murri, Chiara; Rossi, Monica; Bajo, Marco; Bellafiore, Debora; Campiani, Elisabetta; Fogarin, Stefano; Grande, Valentina; Janowski, Lukasz; Keppel, Erica; Leidi, Elisa; Lorenzetti, Giuliano; Maicu, Francesco; Maselli, Vittorio; Mercorella, Alessandra; Montereale Gavazzi, Giacomo; Minuzzo, Tiziano; Pellegrini, Claudio; Petrizzo, Antonio; Prampolini, Mariacristina; Remia, Alessandro; Rizzetto, Federica; Rovere, Marzia; Sarretta, Alessandro; Sigovini, Marco; Sinapi, Luigi; Umgiesser, Georg; Trincardi, Fabio

2017-09-01

Tidal channels are crucial for the functioning of wetlands, though their morphological properties, which are relevant for seafloor habitats and flow, have been understudied so far. Here, we release a dataset composed of Digital Terrain Models (DTMs) extracted from a total of 2,500 linear kilometres of high-resolution multibeam echosounder (MBES) data collected in 2013 covering the entire network of tidal channels and inlets of the Venice Lagoon, Italy. The dataset comprises also the backscatter (BS) data, which reflect the acoustic properties of the seafloor, and the tidal current fields simulated by means of a high-resolution three-dimensional unstructured hydrodynamic model. The DTMs and the current fields help define how morphological and benthic properties of tidal channels are affected by the action of currents. These data are of potential broad interest not only to geomorphologists, oceanographers and ecologists studying the morphology, hydrodynamics, sediment transport and benthic habitats of tidal environments, but also to coastal engineers and stakeholders for cost-effective monitoring and sustainable management of this peculiar shallow coastal system.

High resolution multibeam and hydrodynamic datasets of tidal channels and inlets of the Venice Lagoon

PubMed Central

Madricardo, Fantina; Foglini, Federica; Kruss, Aleksandra; Ferrarin, Christian; Pizzeghello, Nicola Marco; Murri, Chiara; Rossi, Monica; Bajo, Marco; Bellafiore, Debora; Campiani, Elisabetta; Fogarin, Stefano; Grande, Valentina; Janowski, Lukasz; Keppel, Erica; Leidi, Elisa; Lorenzetti, Giuliano; Maicu, Francesco; Maselli, Vittorio; Mercorella, Alessandra; Montereale Gavazzi, Giacomo; Minuzzo, Tiziano; Pellegrini, Claudio; Petrizzo, Antonio; Prampolini, Mariacristina; Remia, Alessandro; Rizzetto, Federica; Rovere, Marzia; Sarretta, Alessandro; Sigovini, Marco; Sinapi, Luigi; Umgiesser, Georg; Trincardi, Fabio

2017-01-01

Tidal channels are crucial for the functioning of wetlands, though their morphological properties, which are relevant for seafloor habitats and flow, have been understudied so far. Here, we release a dataset composed of Digital Terrain Models (DTMs) extracted from a total of 2,500 linear kilometres of high-resolution multibeam echosounder (MBES) data collected in 2013 covering the entire network of tidal channels and inlets of the Venice Lagoon, Italy. The dataset comprises also the backscatter (BS) data, which reflect the acoustic properties of the seafloor, and the tidal current fields simulated by means of a high-resolution three-dimensional unstructured hydrodynamic model. The DTMs and the current fields help define how morphological and benthic properties of tidal channels are affected by the action of currents. These data are of potential broad interest not only to geomorphologists, oceanographers and ecologists studying the morphology, hydrodynamics, sediment transport and benthic habitats of tidal environments, but also to coastal engineers and stakeholders for cost-effective monitoring and sustainable management of this peculiar shallow coastal system. PMID:28872636

High resolution multibeam and hydrodynamic datasets of tidal channels and inlets of the Venice Lagoon.

PubMed

Madricardo, Fantina; Foglini, Federica; Kruss, Aleksandra; Ferrarin, Christian; Pizzeghello, Nicola Marco; Murri, Chiara; Rossi, Monica; Bajo, Marco; Bellafiore, Debora; Campiani, Elisabetta; Fogarin, Stefano; Grande, Valentina; Janowski, Lukasz; Keppel, Erica; Leidi, Elisa; Lorenzetti, Giuliano; Maicu, Francesco; Maselli, Vittorio; Mercorella, Alessandra; Montereale Gavazzi, Giacomo; Minuzzo, Tiziano; Pellegrini, Claudio; Petrizzo, Antonio; Prampolini, Mariacristina; Remia, Alessandro; Rizzetto, Federica; Rovere, Marzia; Sarretta, Alessandro; Sigovini, Marco; Sinapi, Luigi; Umgiesser, Georg; Trincardi, Fabio

2017-09-05

Tidal channels are crucial for the functioning of wetlands, though their morphological properties, which are relevant for seafloor habitats and flow, have been understudied so far. Here, we release a dataset composed of Digital Terrain Models (DTMs) extracted from a total of 2,500 linear kilometres of high-resolution multibeam echosounder (MBES) data collected in 2013 covering the entire network of tidal channels and inlets of the Venice Lagoon, Italy. The dataset comprises also the backscatter (BS) data, which reflect the acoustic properties of the seafloor, and the tidal current fields simulated by means of a high-resolution three-dimensional unstructured hydrodynamic model. The DTMs and the current fields help define how morphological and benthic properties of tidal channels are affected by the action of currents. These data are of potential broad interest not only to geomorphologists, oceanographers and ecologists studying the morphology, hydrodynamics, sediment transport and benthic habitats of tidal environments, but also to coastal engineers and stakeholders for cost-effective monitoring and sustainable management of this peculiar shallow coastal system.

Population splitting of rodlike swimmers in Couette flow.

PubMed

Nili, Hossein; Kheyri, Masoud; Abazari, Javad; Fahimniya, Ali; Naji, Ali

2017-06-28

We present a quantitative analysis on the response of a dilute active suspension of self-propelled rods (swimmers) in a planar channel subjected to an imposed shear flow. To best capture the salient features of the shear-induced effects, we consider the case of an imposed Couette flow, providing a constant shear rate across the channel. We argue that the steady-state behavior of swimmers can be understood in the light of a population splitting phenomenon, occurring as the shear rate exceeds a certain threshold, initiating the reversal of the swimming direction for a finite fraction of swimmers from down- to upstream or vice versa, depending on the swimmer position within the channel. Swimmers thus split into two distinct, statistically significant and oppositely swimming majority and minority populations. The onset of population splitting translates into a transition from a self-propulsion-dominated regime to a shear-dominated regime, corresponding to a unimodal-to-bimodal change in the probability distribution function of the swimmer orientation. We present a phase diagram in terms of the swim and flow Péclet numbers showing the separation of these two regimes by a discontinuous transition line. Our results shed further light on the behavior of swimmers in a shear flow and provide an explanation for the previously reported non-monotonic behavior of the mean, near-wall, parallel-to-flow orientation of swimmers with increasing shear strength.

Couette flow of an incompressible fluid in a porous channel with mass transfer

NASA Astrophysics Data System (ADS)

Niranjana, N.; Vidhya, M.; Govindarajan, A.

2018-04-01

The present discussion deals with the study of couette flow through a porous medium of a viscous incompressible fluid between two infinite horizontal parallel porous flat plates with heat and mass transfer. The stationary plate and the plate in uniform motion are subjected to transverse sinusoidal injection and uniform suction of the fluid. Due to this type of injection velocity, the flow becomes three dimensional. The analytical solutions of the nonlinear partial differential equations of this problem are obtained by using perturbation technique. Expressions for the velocity, temperature fields and the rate of heat and mass transfers are obtained. Effects of the following parameters Schmidt number (Sc), Modified Grashof number (Gm) on the velocity, temperature and concentration fields are obtained numerically and depicted through graphs. The rate of heat and mass transfer are also analyzed.

Hydrodynamic and Sediment Responses of Open Channels to Exposed Pipe Encasements

PubMed Central

Mao, J. Q.; Zhang, H. Q.; Dai, H. C.; Yuan, B. H.; Hu, T. F.

2015-01-01

The effects of exposed pipe encasements on the local variation of hydrodynamic and sediment conditions in a river channel are examined. Laboratory experiments are performed to assess the response of water level, flow regime and bed deformation to several representative types of concrete encasements. The experimental conditions considered are: three types of exposed pipe encasements exposed on the bed, including trapezoidal shape, circular-arc shape and polygonal shape, and three sets of discharges, including annual discharge, once-in-3-year flood, and once-in-50-year flood. Our experiments show that: (1) the amount of backwater definitely depends on the encasement geometric shape and the background discharge; (2) smaller discharges generally tend to induce local scour of river bed downstream of the encasement, and the order of sensitivity of bed deformation to the encasement geometric shape is trapezoidal > circular-arc > polygonal; (3) comparatively speaking, the polygonal encasement may be considered as a suitable protective structure for pipelines across alluvial rivers, with relatively modest effects on the local hydrodynamic conditions and bed stabilization. PMID:26588840

Absolute versus convective helical magnetorotational instability in a Taylor-Couette flow.

PubMed

Priede, Jānis; Gerbeth, Gunter

2009-04-01

We analyze numerically the magnetorotational instability of a Taylor-Couette flow in a helical magnetic field [helical magnetorotational instability (HMRI)] using the inductionless approximation defined by a zero magnetic Prandtl number (Pr_{m}=0) . The Chebyshev collocation method is used to calculate the eigenvalue spectrum for small-amplitude perturbations. First, we carry out a detailed conventional linear stability analysis with respect to perturbations in the form of Fourier modes that corresponds to the convective instability which is not in general self-sustained. The helical magnetic field is found to extend the instability to a relatively narrow range beyond its purely hydrodynamic limit defined by the Rayleigh line. There is not only a lower critical threshold at which HMRI appears but also an upper one at which it disappears again. The latter distinguishes the HMRI from a magnetically modified Taylor vortex flow. Second, we find an absolute instability threshold as well. In the hydrodynamically unstable regime before the Rayleigh line, the threshold of absolute instability is just slightly above the convective one although the critical wavelength of the former is noticeably shorter than that of the latter. Beyond the Rayleigh line the lower threshold of absolute instability rises significantly above the corresponding convective one while the upper one descends significantly below its convective counterpart. As a result, the extension of the absolute HMRI beyond the Rayleigh line is considerably shorter than that of the convective instability. The absolute HMRI is supposed to be self-sustained and, thus, experimentally observable without any external excitation in a system of sufficiently large axial extension.

Hydrodynamic model of screen channel liquid acquisition devices for in-space cryogenic propellant management

NASA Astrophysics Data System (ADS)

Darr, S. R.; Camarotti, C. F.; Hartwig, J. W.; Chung, J. N.

2017-01-01

Technologies that enable the storage and transfer of cryogenic propellants in space will be needed for the next generation vehicles that will carry humans to Mars. One of the candidate technologies is the screen channel liquid acquisition device (LAD), which uses a metal woven wire mesh to separate the liquid and vapor phases so that single-phase liquid propellant can be transferred in microgravity. In this work, an experiment is carried out that provides measurements of the velocity and pressure fields in a screen channel LAD. These data are used to validate a new analytical solution of the liquid flow through a screen channel LAD. This hydrodynamic model, which accounts for non-uniform injection through the screen, is compared with the traditional pressure term summation model which assumes a constant, uniform injection velocity. Results show that the new model performs best against the new data and historical data. The velocity measurements inside the screen channel LAD are used to provide a more accurate velocity profile which further improves the new model. The result of this work is a predictive tool that will instill confidence in the design of screen channel LADs for future in-space propulsion systems.

Lattice Boltzmann simulations of liquid crystal particulate flow in a channel with finite anchoring boundary conditions

NASA Astrophysics Data System (ADS)

Zhang, Rui; Roberts, Tyler; de Pablo, Juan; dePablo Team

2014-11-01

Liquid crystals (LC) posses anisotropic viscoelastic properties, and, as such, LC flow can be incredibly complicated. Here we employ a hybrid lattice Boltzmann method (pioneered by Deniston, Yeomans and Cates) to systematically study the hydrodynamics of nematic liquid crystals (LCs) with and without solid particles. This method evolves the velocity field through lattice Boltzmann and the LC-order parameter via a finite-difference solver of the Beris-Edwards equation. The evolution equation of the boundary points with finite anchoring is obtained through Poisson bracket formulation. Our method has been validated by matching the Ericksen-Leslie theory. We demonstrate two applications in the flow alignment regime. We first investigate a hybrid channel flow in which the top and bottom walls have different anchoring directions. By measuring the apparent shear viscosity in terms of Couette flow, we achieve a viscosity inhomogeneous system which may be applicable to nano particle processing. In the other example, we introduce a homeotropic spherical particle to the channel, and focus on the deformations of the defect ring due to anchorings and flow. The results are then compared to the molecular dynamics simulations of a colloid particle in an LC modeled by a Gay-Berne potential.

Colloid-Colloid Hydrodynamic Interaction Around a Bend in a Quasi-One-Dimensional Channel

NASA Astrophysics Data System (ADS)

Liepold, Christopher; Zarcone, Ryan; Heumann, Tibor; Lin, Binhua; Rice, Stuart

We report a study of the correlation between a pair of particles in a colloid suspension in a bent quasi-one-dimensional (q1d) channel as a function of bend angle. As the bend angle becomes more acute, we observe an increasing depletion of particles in the vicinity of the bend and an increase in the nearest-neighbor separation in the pair correlation function for particles on opposite sides of the bend. Further, we observe that the peak value of D12, the coupling term in the pair diffusion tensor that characterizes the effect of the motion of particle 1 on particle 2, coincides with the first peak in the pair correlation function, and that the pair separation dependence of D12 mimics that of the pair correlation function. We show that the observed behavior is a consequence of the geometric constraints imposed by the single-file requirement that the particle centers lie on the centerline of the channel and the requirement that the hydrodynamic flow must follow the channel around the bend. We find that the correlation between a pair of particles in a colloidal suspension in a bent q1D channel has the same functional dependence on the pair correlation function as in a straight q1D channel when measured in a coordinate system that follows the centerline of the bent channel. NSF MRSEC (DMR-1420709), Dreyfus Foundation (SI-14-014).

A Molecular Dynamics Simulation of the Turbulent Couette Minimal Flow Unit

NASA Astrophysics Data System (ADS)

Smith, Edward

2016-11-01

What happens to turbulent motions below the Kolmogorov length scale? In order to explore this question, a 300 million molecule Molecular Dynamics (MD) simulation is presented for the minimal Couette channel in which turbulence can be sustained. The regeneration cycle and turbulent statistics show excellent agreement to continuum based computational fluid dynamics (CFD) at Re=400. As MD requires only Newton's laws and a form of inter-molecular potential, it captures a much greater range of phenomena without requiring the assumptions of Newton's law of viscosity, thermodynamic equilibrium, fluid isotropy or the limitation of grid resolution. The fundamental nature of MD means it is uniquely placed to explore the nature of turbulent transport. A number of unique insights from MD are presented, including energy budgets, sub-grid turbulent energy spectra, probability density functions, Lagrangian statistics and fluid wall interactions. EPSRC Post Doctoral Prize Fellowship.

Frictional Torque Reduction in Taylor-Couette Flows with Riblet-Textured Rotors

NASA Astrophysics Data System (ADS)

Raayai, Shabnam; McKinley, Gareth

2017-11-01

Inspired by the riblets on the denticles of fast swimming shark species, periodic surface microtextures of different shapes have been studied under laminar and turbulent flow conditions to understand their drag reduction mechanism and to offer guides for designing optimized low-friction bio-inspired surfaces. Various reports over the past four decades have suggested that riblet surfaces can reduce the frictional drag force in high Reynolds number laminar and turbulent flow regimes. Here, we investigate the effect of streamwise riblets on torque reduction in steady flow between concentric cylinders, known as Taylor-Couette Flow. Using 3D printed riblet-textured rotors and a custom-built Taylor-Couette cell which can be mounted on a rheometer we measure the torque on the inner rotor as a function of three different dimensionless parameters; the Reynolds number of the flow, the sharpness of the riblets, and the size of the riblets with respect to the scale of the Taylor-Couette cell. Our experimental results in the laminar viscous flow regime show a reduction in torque up to 10% over a wide range of Reynolds numbers, that is a non-monotonic function of the aspect ratio and independent of Re. However, after transition to the Taylor vortex regime, the modification in torque becomes a function of the Reynolds number, while remaining a non-monotonic function of the aspect ratio. Using finite volume modelling of the geometry we discuss the changes in the Taylor-Couette flow in presence of the riblets compared to the case of smooth rotors and the resulting torque reduction as a function of the parameter space defined above.

Tuning Shear Jamming by Basal Assisted Couette Shear

NASA Astrophysics Data System (ADS)

Zhao, Yiqiu; Barés, Jonathan; Behringer, Robert

Granular matter with packing fraction ϕS < ϕ <ϕJ can be jammed by applying shear strain. However, the stress-strain relation in shear jamming transition is not very well understood. Part of the difficulty is that the strain inside the granular system is very complicated and hard to control. In this work, by using a novel Couette shear apparatus capable of generating arbitrary shear profiles, we study the stress-strain relation during shear jamming transition for granular system under different kinds of controlled interior strain. The novel Couette shear apparatus consists of 21 independently movable rings and two circular boundaries. The apparatus can shear the granular sample not only from the boundaries but also from the bottom. The granular sample is made of about 2000 bi-disperse photo elastic disks, making it possible to extract force information. This work is supported by NSF-DMR1206351, DMS1248071, NASA NNX15AD38G.

Absolute and convective instabilities in combined Couette-Poiseuille flow past a neo-Hookean solid

NASA Astrophysics Data System (ADS)

Patne, Ramkarn; Shankar, V.

2017-12-01

Temporal and spatio-temporal stability analyses are carried out to characterize the occurrence of convective and absolute instabilities in combined Couette-Poiseuille flow of a Newtonian fluid past a deformable, neo-Hookean solid layer in the creeping-flow limit. Plane Couette flow of a Newtonian fluid past a neo-Hookean solid becomes temporally unstable in the inertia-less limit when the parameter Γ = V η/(GR) exceeds a critical value. Here, V is the velocity of the top plate, η is the fluid viscosity, G is the shear modulus of the solid layer, and R is the fluid layer thickness. The Kupfer-Bers method is employed to demarcate regions of absolute and convective instabilities in the Γ-H parameter space, where H is the ratio of solid to fluid thickness in the system. For certain ranges of the thickness ratio H, we find that the flow could be absolutely unstable, and the critical Γ required for absolute instability is very close to that for temporal instability, thus making the flow absolutely unstable at the onset of temporal instability. In some cases, there is a gap in the parameter Γ between the temporal and absolute instability boundaries. The present study thus shows that absolute instabilities are possible, even at very low Reynolds numbers in flow past deformable solid surfaces. The presence of absolute instabilities could potentially be exploited in the enhancement of mixing at low Reynolds numbers in flow through channels with deformable solid walls.

Stability of compressible Taylor-Couette flow

NASA Technical Reports Server (NTRS)

Kao, Kai-Hsiung; Chow, Chuen-Yen

1991-01-01

Compressible stability equations are solved using the spectral collocation method in an attempt to study the effects of temperature difference and compressibility on the stability of Taylor-Couette flow. It is found that the Chebyshev collocation spectral method yields highly accurate results using fewer grid points for solving stability problems. Comparisons are made between the result obtained by assuming small Mach number with a uniform temperature distribution and that based on fully incompressible analysis.

Hydrodynamic Behaviour of Fully and Partially Submerged Plants In Open Channel Flow: A Prototype Scale Experiment.

NASA Astrophysics Data System (ADS)

Armanini, A.; Bortoluzzi, D.; Grisenti, P.; Righetti, M.

The hydrodynamic behaviour of partially and fully submerged tall vegetation is of great interest in the river management. Only recently some researchers (Kouwen, 1999, Oplatka, 1998) analyzed the hydrodynamic resistance of bushes, taking into account also the plants elasticity in the classical Petryk & Bosmajian approach. In the present work, an experimental investigation is performed, where the hydrodynamic resistance of isolated and grouped salix alba bushes is measured, in a laboratory chan- nel at prototype scale. This kind of plants has particular interest because they are often used in bank stabilization and remediation works for mountain streams. The tests are performed using young plants, ranging from 1 m up to 2 m high, in a 100 m long, 2 m deep and 2 m large open channel flow, the discharge ranges up to 1,3 m3/sec. A suitable strain gauges system has been realized in order to directly measure the force exerted on the plant by the flow. The results are compared with analogous measure- ments of Oplatka and Kouwen, confirming the influence of elasticity and leaves on hydrodynamic resistance; in particular the effect of smaller branches bending and the influence of foliage on drag has been analyzed, comparing the drag of the same bush with and without leaves. Moreover an approach for drag evaluation, alternative to that of Oplatka and Kouwen is proposed.

Tuning strain of granular matter by basal assisted Couette shear

NASA Astrophysics Data System (ADS)

Zhao, Yiqiu; Barés, Jonathan; Zheng, Hu; Behringer, Robert

2017-06-01

We present a novel Couette shear apparatus capable of generating programmable azimuthal strain inside 2D granular matter under Couette shear. The apparatus consists of 21 independently movable concentric rings and two boundary wheels with frictional racks. This makes it possible to quasistatically shear the granular matter not only from the boundaries but also from the bottom. We show that, by specifying the collective motion of wheels and rings, the apparatus successfully generates the desired strain profile inside the sample granular system, which is composed of about 2000 photoelastic disks. The motion and stress of each particle is captured by an imaging system utilizing reflective photoelasticimetry. This apparatus provides a novel method to investigate shear jamming properties of granular matter with different interior strain profiles and unlimited strain amplitudes.

Rubber Bands as Model Polymers in Couette Flow

ERIC Educational Resources Information Center

Dunstan, Dave E.

2008-01-01

We present a simple device for demonstrating the essential aspects of polymers in flow in the classroom. Rubber bands are used as a macroscopic model of polymers to allow direct visual observation of the flow-induced changes in orientation and conformation. A transparent Perspex Couette cell, constructed from two sections of a tube, is used to…

Thermal and hydrodynamic studies for micro-channel cooling for large area silicon sensors in high energy physics experiments

NASA Astrophysics Data System (ADS)

Flaschel, Nils; Ariza, Dario; Díez, Sergio; Gerboles, Marta; Gregor, Ingrid-Maria; Jorda, Xavier; Mas, Roser; Quirion, David; Tackmann, Kerstin; Ullan, Miguel

2017-08-01

Micro-channel cooling initially aiming at small-sized high-power integrated circuits is being transferred to the field of high energy physics. Today's prospects of micro-fabricating silicon opens a door to a more direct cooling of detector modules. The challenge in high energy physics is to save material in the detector construction and to cool large areas. In this paper, we are investigating micro-channel cooling as a candidate for a future cooling system for silicon detectors in a generic research and development approach. The work presented in this paper includes the production and the hydrodynamic and thermal testing of a micro-channel equipped prototype optimized to achieve a homogeneous flow distribution. Furthermore, the device was simulated using finite element methods.

Brownsville Ship Channel Hydrodynamic Modeling

DTIC Science & Technology

2012-01-01

the Brownsville Ship Channel in Brownsville, Texas. These plans include possible deepening and widening of the ship channel from its connection to...LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR. ERDC/CHL TR-12-6 iii Table of Contents Abstract...Ship Channel, to include potential deepening and widening. In order to assess the impacts of these changes on both navigation and the ecosystem, it is

Traveling waves in a magnetized Taylor-Couette flow.

PubMed

Liu, Wei; Goodman, Jeremy; Ji, Hantao

2007-07-01

We investigate numerically a traveling wave pattern observed in experimental magnetized Taylor-Couette flow at low magnetic Reynolds number. By accurately modeling viscous and magnetic boundaries in all directions, we reproduce the experimentally measured wave patterns and their amplitudes. Contrary to previous claims, the waves are shown to be transiently amplified disturbances launched by viscous boundary layers, rather than globally unstable magnetorotational modes.

CFD Investigation of the effects of bubble aerator layouts on hydrodynamics of an activated sludge channel reactor.

PubMed

Hreiz, Rainier; Potier, Olivier; Wicks, Jim; Commenge, Jean-Marc

2018-03-08

In this paper, computational fluid dynamics (CFD) simulations are employed to characterize the effects of bubble aerator layouts (i.e. spatial arrangement) on the hydrodynamics in activated sludge (AS) reactors. The first configuration considered is a channel reactor with aerators placed alongside one lateral wall, for which velocity measurements are available in literature. CFD results were in good agreement with experimental data, which proves that the model is sufficiently accurate and predictive. Accordingly, simulations and numerical residence time distribution tests were conducted for different aerator layouts to determine their effects on the reactor hydrodynamics. The results revealed that the flow characteristics are extremely sensitive to the aerators arrangement given the high gas flow rates used in AS processes. Among the layouts investigated, the one where diffusers are placed all over the reactor floor has led to the least dispersive flow, i.e. which characteristics best tend toward that of an ideal plug flow reactor. Indeed, this flow field presented the lowest average turbulent diffusion and the most uniform axial velocity and turbulence fields. Such a flow behaviour is expected to be highly beneficial for biological treatment since it reduces pollutant dilution by axial diffusion and limits raw wastewater channelling to the outlet.

Hydrodynamics and Connectivity of Channelized Floodplains: Insights from the Meandering East Fork White River, Indiana, USA

NASA Astrophysics Data System (ADS)

Czuba, J. A.; David, S. R.; Edmonds, D. A.

2017-12-01

High resolution topography reveals that meandering river floodplains in Indiana commonly have networks of channels. These floodplain channel networks are most prevalent in agricultural, low-gradient, wide floodplains. It appears that these networks are formed when floodplain channels connect oxbows to each other and the main river channel. Collectively, the channels in the floodplain create an interconnected network of pathways that convey water beginning at flows less than bankfull, and as stage increases, more of the floodplain becomes dissected by floodplain channels. In this work, we quantify the hydrodynamics and connectivity of the flow on the floodplain and in the main channel of the East Fork White River near Seymour, Indiana, USA. We constructed a two-dimensional numerical model using HECRAS of the river-floodplain system from LiDAR data and from main-channel river bathymetry to elucidate the behaviour of these floodplain channels across a range of flows. Model calibration and verification data included stage from a USGS gage, high-water marks at a high and medium flow, and an aerial photograph of inundation in the floodplain channels. The numerical model simulated flow depth and velocity, which was used to quantify connectivity of the floodplain channels, exchange between the main channel and floodplain channels, and residence time of water on the floodplain. Model simulations suggest that the floodplain channels convey roughly 50% of the total flow at what is typically considered "bankfull" flow. Overall, we present a process-based approach for analyzing complex floodplain-river systems where an individual floodplain-river system can be distilled down to a set of characteristic curves. Notably, we map the East Fork White River system to exchange-residence time space and argue that this characterization forms the basis for thinking about morphologic evolution (e.g., sediment deposition and erosion) and biogeochemistry (e.g., nitrate removal) in floodplain

Transition to turbulence in Taylor-Couette ferrofluidic flow

PubMed Central

Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng

2015-01-01

It is known that in classical fluids turbulence typically occurs at high Reynolds numbers. But can turbulence occur at low Reynolds numbers? Here we investigate the transition to turbulence in the classic Taylor-Couette system in which the rotating fluids are manufactured ferrofluids with magnetized nanoparticles embedded in liquid carriers. We find that, in the presence of a magnetic field transverse to the symmetry axis of the system, turbulence can occur at Reynolds numbers that are at least one order of magnitude smaller than those in conventional fluids. This is established by extensive computational ferrohydrodynamics through a detailed investigation of transitions in the flow structure, and characterization of behaviors of physical quantities such as the energy, the wave number, and the angular momentum through the bifurcations. A finding is that, as the magnetic field is increased, onset of turbulence can be determined accurately and reliably. Our results imply that experimental investigation of turbulence may be feasible by using ferrofluids. Our study of transition to and evolution of turbulence in the Taylor-Couette ferrofluidic flow system provides insights into the challenging problem of turbulence control. PMID:26065572

Droplet motion in microfluidic networks: Hydrodynamic interactions and pressure-drop measurements

NASA Astrophysics Data System (ADS)

Sessoms, D. A.; Belloul, M.; Engl, W.; Roche, M.; Courbin, L.; Panizza, P.

2009-07-01

We present experimental, numerical, and theoretical studies of droplet flows in hydrodynamic networks. Using both millifluidic and microfluidic devices, we study the partitioning of monodisperse droplets in an asymmetric loop. In both cases, we show that droplet traffic results from the hydrodynamic feedback due to the presence of droplets in the outlet channels. We develop a recently-introduced phenomenological model [W. Engl , Phys. Rev. Lett. 95, 208304 (2005)] and successfully confront its predictions to our experimental results. This approach offers a simple way to measure the excess hydrodynamic resistance of a channel filled with droplets. We discuss the traffic behavior and the variations in the corresponding hydrodynamic resistance length Ld and of the droplet mobility β , as a function of droplet interdistance and confinement for channels having circular or rectangular cross sections.

Polymeric microchip for the simultaneous determination of anions and cations by hydrodynamic injection using a dual-channel sequential injection microchip electrophoresis system.

PubMed

Gaudry, Adam J; Nai, Yi Heng; Guijt, Rosanne M; Breadmore, Michael C

2014-04-01

A dual-channel sequential injection microchip capillary electrophoresis system with pressure-driven injection is demonstrated for simultaneous separations of anions and cations from a single sample. The poly(methyl methacrylate) (PMMA) microchips feature integral in-plane contactless conductivity detection electrodes. A novel, hydrodynamic "split-injection" method utilizes background electrolyte (BGE) sheathing to gate the sample flows, while control over the injection volume is achieved by balancing hydrodynamic resistances using external hydrodynamic resistors. Injection is realized by a unique flow-through interface, allowing for automated, continuous sampling for sequential injection analysis by microchip electrophoresis. The developed system was very robust, with individual microchips used for up to 2000 analyses with lifetimes limited by irreversible blockages of the microchannels. The unique dual-channel geometry was demonstrated by the simultaneous separation of three cations and three anions in individual microchannels in under 40 s with limits of detection (LODs) ranging from 1.5 to 24 μM. From a series of 100 sequential injections the %RSDs were determined for every fifth run, resulting in %RSDs for migration times that ranged from 0.3 to 0.7 (n = 20) and 2.3 to 4.5 for peak area (n = 20). This system offers low LODs and a high degree of reproducibility and robustness while the hydrodynamic injection eliminates electrokinetic bias during injection, making it attractive for a wide range of rapid, sensitive, and quantitative online analytical applications.

Velocity Inversion In Cylindrical Couette Gas Flows

NASA Astrophysics Data System (ADS)

Dongari, Nishanth; Barber, Robert W.; Emerson, David R.; Zhang, Yonghao; Reese, Jason M.

2012-05-01

We investigate a power-law probability distribution function to describe the mean free path of rarefied gas molecules in non-planar geometries. A new curvature-dependent model is derived by taking into account the boundary-limiting effects on the molecular mean free path for surfaces with both convex and concave curvatures. In comparison to a planar wall, we find that the mean free path for a convex surface is higher at the wall and exhibits a sharper gradient within the Knudsen layer. In contrast, a concave wall exhibits a lower mean free path near the surface and the gradients in the Knudsen layer are shallower. The Navier-Stokes constitutive relations and velocity-slip boundary conditions are modified based on a power-law scaling to describe the mean free path, in accordance with the kinetic theory of gases, i.e. transport properties can be described in terms of the mean free path. Velocity profiles for isothermal cylindrical Couette flow are obtained using the power-law model. We demonstrate that our model is more accurate than the classical slip solution, especially in the transition regime, and we are able to capture important non-linear trends associated with the non-equilibrium physics of the Knudsen layer. In addition, we establish a new criterion for the critical accommodation coefficient that leads to the non-intuitive phenomena of velocity-inversion. Our results are compared with conventional hydrodynamic models and direct simulation Monte Carlo data. The power-law model predicts that the critical accommodation coefficient is significantly lower than that calculated using the classical slip solution and is in good agreement with available DSMC data. Our proposed constitutive scaling for non-planar surfaces is based on simple physical arguments and can be readily implemented in conventional fluid dynamics codes for arbitrary geometric configurations.

Characterizing Strength of Chaotic Dynamics and Numerical Simulation Relevant to Modified Taylor-Couette Flow with Hourglass Geometry

NASA Astrophysics Data System (ADS)

Hou, Yu; Kowalski, Adam; Schroder, Kjell; Halmstad, Andrew; Olsen, Thomas; Wiener, Richard

2006-05-01

We characterize the strength of chaos in two different regimes of Modified Taylor-Couette flow with Hourglass Geometry: the formation of Taylor Vortices with laminar flow and with turbulent flow. We measure the strength of chaos by calculating the correlation dimension and the Kaplan-Yorke dimension based upon the Lyapunov Exponents of each system. We determine the reliability of our calculations by considering data from a chaotic electronic circuit. In order to predict the behavior of the Modified Taylor-Couette flow system, we employ simulations based upon an idealized Reaction-Diffusion model with a third order non-linearity in the reaction rate. Variation of reaction rate with length corresponds to variation of the effective Reynolds Number along the Taylor-Couette apparatus. We present preliminary results and compare to experimental data.

Hydrodynamics and sediment transport in a meandering channel with a model axial-flow hydrokinetic turbine

NASA Astrophysics Data System (ADS)

Hill, Craig; Kozarek, Jessica; Sotiropoulos, Fotis; Guala, Michele

2016-02-01

An investigation into the interactions between a model axial-flow hydrokinetic turbine (rotor diameter, dT = 0.15 m) and the complex hydrodynamics and sediment transport processes within a meandering channel was carried out in the Outdoor StreamLab research facility at the University of Minnesota St. Anthony Falls Laboratory. This field-scale meandering stream with bulk flow and sediment discharge control provided a location for high spatiotemporally resolved measurements of bed and water surface elevations around the model turbine. The device was installed within an asymmetric, erodible channel cross section under migrating bed form and fixed outer bank conditions. A comparative analysis between velocity and topographic measurements, with and without the turbine installed, highlights the local and nonlocal features of the turbine-induced scour and deposition patterns. In particular, it shows how the cross-section geometry changes, how the bed form characteristics are altered, and how the mean flow field is distorted both upstream and downstream of the turbine. We further compare and discuss how current energy conversion deployments in meander regions would result in different interactions between the turbine operation and the local and nonlocal bathymetry compared to straight channels.

Hydrodynamic model of screen channel liquid acquisition devices for in-space cryogenic propellant management

NASA Astrophysics Data System (ADS)

Darr, Samuel Ryan

Technologies that enable the storage and transfer of cryogenic propellants in space will be needed for the next generation vehicles that will carry humans to Mars. One of the candidate technologies is the screen channel liquid acquisition device (LAD), which uses a metal woven wire mesh to separate the liquid and vapor phases so that single-phase liquid propellant can be transferred in microgravity. The purpose of this work is to provide an accurate hydrodynamic model of the liquid flow through a screen channel LAD. Chapter 2 provides a derivation of the flow-through-screen (FTS) boundary condition. The final boundary condition more accurately represents the complex geometry of metal woven wire mesh than the current model used in the literature. The effect of thermal contraction on the screen geometry due to large temperature changes common in cryogenic systems is quantified in this chapter as well. Chapter 3 provides a two-dimensional (2-D) analytical solution of the velocity and pressure fields in a screen channel LAD. This solution, which accounts for non-uniform injection through the screen, is compared with the traditional 1-D model which assumes a constant, uniform injection velocity. Chapter 4 describes the setup and results of an experiment that measures both the velocity and pressure fields in a screen channel LAD in order to validate the 2-D model. Results show that the 2-D model performs best against the new data and historical data. With the improved FTS boundary condition and the 2-D model, the pressure drop of a screen channel LAD is described with excellent accuracy. The result of this work is a predictive tool that will instill confidence in the design of screen channel LADs for future in-space propulsion systems.

Identification of hydrodynamic forces around 3D surrogates using particle image velocimetry in a microfluidic channel

NASA Astrophysics Data System (ADS)

Afshar, Sepideh; Nath, Shubhankar; Demirci, Utkan; Hasan, Tayyaba; Scarcelli, Giuliano; Rizvi, Imran; Franco, Walfre

2018-02-01

Previous studies have demonstrated that flow-induced shear stress induces a motile and aggressive tumor phenotype in a microfluidic model of 3D ovarian cancer. However, the magnitude and distribution of the hydrodynamic forces that influence this biological modulation on the 3D cancer nodules are not known. We have developed a series of numerical and experimental tools to identify these forces within a 3D microchannel. In this work, we used particle image velocimetry (PIV) to find the velocity profile using fluorescent micro-spheres as surrogates and nano-particles as tracers, from which hydrodynamic forces can be derived. The fluid velocity is obtained by imaging the trajectory of a range of florescence nano-particles (500-800 μm) via confocal microscopy. Imaging was done at different horizontal planes and with a 50 μm bead as the surrogate. For an inlet current rate of 2 μl/s, the maximum velocity at the center of the channel was 51 μm/s. The velocity profile around the sphere was symmetric which is expected since the flow is dominated by viscous forces as opposed to inertial forces. The confocal PIV was successfully employed in finding the velocity profile in a microchannel with a nodule surrogate; therefore, it seems feasible to use PIV to investigate the hydrodynamic forces around 3D biological models.

Zombie Turbulence and More in Stratified Couette Flow

NASA Astrophysics Data System (ADS)

Marcus, Philip; Barranco, Joe; Pei, Suyang; Jiang, Chung-Hsiang

2016-11-01

Zombie turbulence occurs in rotating, shearing vertically-stratified flows such as stratified Couette flows. The turbulence is triggered by a neutrally-stable eigenmode with a critical layer receptive to finite-amplitude perturbations. Once excited, the critical layer becomes a vortex layer pair that rolls up into discrete vortices. Those vortices excite new critical layers, and the process repeats ad infinitum. When the vortex amplitudes become sufficiently large, the flow becomes turbulent. Although possessing a mid-range energy spectrum with E (k) k - 5 / 3 , the turbulence is non-Kolmogorov, highly anisotropic, and with large turbulent, but coherent, structures that retain the length scales of the spacing between the critical layers. The motivation for this study is protoplanetary disks (PPDs) where new stars form. In the PPD the Brunt-Vaisala frequency N increases as a function of distance from the midplane where it is zero. We cannot trigger the initial finite amplitude instability where N is small (close to the midplane). However, computations in PPDs and Couette flows show that zombie turbulence forms where N is large, and then a new type of turbulence, that is neither zombie nor Kolmogorov turbulence, fills in the remainder of the domain even where N = 0 .

Self-similar mixing in stratified plane Couette flow for varying Prandtl number

NASA Astrophysics Data System (ADS)

Caulfield, C. P.; Zhou, Qi; Taylor, John

2017-11-01

We investigate fully developed turbulence in statically stable stratified plane Couette flows (the flow between two horizontal plates a distance 2 h apart moving at velocities +/-U0 and held at densities ρa -/+ρ0) using direct numerical simulations at a range of Prandtl numbers Pr ≡ ν / κ ∈ { 0.7 , 7 , 70 } and Reynolds numbers Re ≡U0 h / ν ∈ [ 865 , 280000 ] . We observe significant effects of Pr on the heat and momentum fluxes across the channel gap and on the mean temperature and velocity profile, which can be described through a mixing length model using Monin-Obukhov (M-O) similarity theory. We employ M-O theory to formulate similarity scalings for various flow diagnostics in the gap interior. The mid-channel-gap gradient Richardson number Rig is determined by the length scale ratio h / L , where L is the Obukhov length scale. When h / L >> 1 , Rig asymptotes to a maximum characteristic value of approximately 0.2, for very high Re and for a range of Pr and bulk Richardson number Ri = gρ0 h /(ρaU02) . The flux Richardson number Rif = Rig , implying that such turbulent flows do not access the (strongly) `layered anisotropic stratified turbulence' regime, and that the turbulent Prandtl number is approximately one.

Simulation of Helical Flow Hydrodynamics in Meanders and Advection-Turbulent Diffusion Using Smoothed Particle Hydrodynamics

NASA Astrophysics Data System (ADS)

Gusti, T. P.; Hertanti, D. R.; Bahsan, E.; Soeryantono, H.

2013-12-01

Particle-based numerical methods, such as Smoothed Particle Hydrodynamics (SPH), may be able to simulate some hydrodynamic and morphodynamic behaviors better than grid-based numerical methods. This study simulates hydrodynamics in meanders and advection and turbulent diffusion in straight river channels using Microsoft Excel and Visual Basic. The simulators generate three-dimensional data for hydrodynamics and one-dimensional data for advection-turbulent diffusion. Fluid at rest, sloshing, and helical flow are simulated in the river meanders. Spill loading and step loading are done to simulate concentration patterns associated with advection-turbulent diffusion. Results indicate that helical flow is formed due to disturbance in morphology and particle velocity in the stream and the number of particles does not have a significant effect on the pattern of advection-turbulent diffusion concentration.

A numerical simulation of finite-length Taylor-Couette flow

NASA Technical Reports Server (NTRS)

Streett, C. L.; Hussaini, M. Y.

1988-01-01

Results from numerical simulations of finite-length Taylor-Couette flow are presented. Included are time-accurate and steady-state studies of the change in the nature of the symmetric two-cell/asymmetric one-cell bifurcation with varying aspect ratio and of the Reynolds number/aspect ratio locus of the two-cell/four-cell bifurcation. Preliminary results from wavy-vortex simulations at low aspect ratios are also presented.

Bifurcating fronts for the Taylor-Couette problem in infinite cylinders

NASA Astrophysics Data System (ADS)

Hărăguş-Courcelle, M.; Schneider, G.

We show the existence of bifurcating fronts for the weakly unstable Taylor-Couette problem in an infinite cylinder. These fronts connect a stationary bifurcating pattern, here the Taylor vortices, with the trivial ground state, here the Couette flow. In order to show the existence result we improve a method which was already used in establishing the existence of bifurcating fronts for the Swift-Hohenberg equation by Collet and Eckmann, 1986, and by Eckmann and Wayne, 1991. The existence proof is based on spatial dynamics and center manifold theory. One of the difficulties in applying center manifold theory comes from an infinite number of eigenvalues on the imaginary axis for vanishing bifurcation parameter. But nevertheless, a finite dimensional reduction is possible, since the eigenvalues leave the imaginary axis with different velocities, if the bifurcation parameter is increased. In contrast to previous work we have to use normalform methods and a non-standard cut-off function to obtain a center manifold which is large enough to contain the bifurcating fronts.

Global stability of plane Couette flow beyond the energy stability limit

NASA Astrophysics Data System (ADS)

Fuentes, Federico; Goluskin, David

2017-11-01

This talk will present computations verifying that the laminar state of plane Couette flow is nonlinearly stable to all perturbations. The Reynolds numbers up to which this globally stability is verified are larger than those at which stability can be proven by the energy method, which is the typical method for demonstrating nonlinear stability of a fluid flow. This improvement is achieved by constructing Lyapunov functions that are more general than the energy. These functions are not restricted to being quadratic, and they are allowed to depend explicitly on the spectrum of the velocity field in the eigenbasis of the energy stability operator. The optimal choice of such a Lyapunov function is a convex optimization problem, and it can be constructed with computer assistance by solving a semidefinite program. This general method will be described in a companion talk by David Goluskin; the present talk focuses on its application to plane Couette flow.

Split rheometer Couette attachment to enable sample extraction

NASA Astrophysics Data System (ADS)

Guthrie, Sarah E.; Idziak, Stefan H. J.

2005-02-01

We report on the development of a Couette attachment insert for a rheometer, which is designed to split in half, enabling intact sample extraction of cocoa butter crystallized from the melt under known dynamic stress conditions. This cell is capable of producing a sample 1mm thick. At shear rates of 90-720s-1 and final temperatures of 18-20°C it was shown that the sample will completely separate from the cell surface intact.

Dynamics of ferrofluidic flow in the Taylor-Couette system with a small aspect ratio

PubMed Central

Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng

2017-01-01

We investigate fundamental nonlinear dynamics of ferrofluidic Taylor-Couette flow - flow confined be-tween two concentric independently rotating cylinders - consider small aspect ratio by solving the ferro-hydrodynamical equations, carrying out systematic bifurcation analysis. Without magnetic field, we find steady flow patterns, previously observed with a simple fluid, such as those containing normal one- or two vortex cells, as well as anomalous one-cell and twin-cell flow states. However, when a symmetry-breaking transverse magnetic field is present, all flow states exhibit stimulated, finite two-fold mode. Various bifurcations between steady and unsteady states can occur, corresponding to the transitions between the two-cell and one-cell states. While unsteady, axially oscillating flow states can arise, we also detect the emergence of new unsteady flow states. In particular, we uncover two new states: one contains only the azimuthally oscillating solution in the configuration of the twin-cell flow state, and an-other a rotating flow state. Topologically, these flow states are a limit cycle and a quasiperiodic solution on a two-torus, respectively. Emergence of new flow states in addition to observed ones with classical fluid, indicates that richer but potentially more controllable dynamics in ferrofluidic flows, as such flow states depend on the external magnetic field. PMID:28059129

Short-time Lyapunov exponent analysis and the transition to chaos in Taylor-Couette flow

NASA Technical Reports Server (NTRS)

Vastano, John A.; Moser, Robert D.

1991-01-01

The physical mechanism driving the weakly chaotic Taylor-Couette flow is investigated using the short-time Liapunov exponent analysis. In this procedure, the transition from quasi-periodicity to chaos is studied using direct numerical 3D simulations of axially periodic Taylor-Couette flow, and a partial Liapunov exponent spectrum for the flow is computed by simultaneously advancing the full solution and a set of perturbations. It is shown that the short-time Liapunov exponent analysis yields more information on the exponents and dimension than that obtained from the common Liapunov exponent calculations. Results show that the chaotic state studied here is caused by a Kelvin-Helmholtz-type instability of the outflow boundary jet of Taylor vortices.

On new non-modal hydrodynamic stability modes and resulting non-exponential growth rates - a Lie symmetry approach

NASA Astrophysics Data System (ADS)

Oberlack, Martin; Nold, Andreas; Sanjon, Cedric Wilfried; Wang, Yongqi; Hau, Jan

2016-11-01

Classical hydrodynamic stability theory for laminar shear flows, no matter if considering long-term stability or transient growth, is based on the normal-mode ansatz, or, in other words, on an exponential function in space (stream-wise direction) and time. Recently, it became clear that the normal mode ansatz and the resulting Orr-Sommerfeld equation is based on essentially three fundamental symmetries of the linearized Euler and Navier-Stokes equations: translation in space and time and scaling of the dependent variable. Further, Kelvin-mode of linear shear flows seemed to be an exception in this context as it admits a fourth symmetry resulting in the classical Kelvin mode which is rather different from normal-mode. However, very recently it was discovered that most of the classical canonical shear flows such as linear shear, Couette, plane and round Poiseuille, Taylor-Couette, Lamb-Ossen vortex or asymptotic suction boundary layer admit more symmetries. This, in turn, led to new problem specific non-modal ansatz functions. In contrast to the exponential growth rate in time of the modal-ansatz, the new non-modal ansatz functions usually lead to an algebraic growth or decay rate, while for the asymptotic suction boundary layer a double-exponential growth or decay is observed.

Transport in Rayleigh-stable experimental Taylor-Couette flow and granular electrification in a shaking experiment

NASA Astrophysics Data System (ADS)

Nordsiek, Freja

This dissertation consists of two projects: Rayleigh-stable Taylor-Couette flow and granular electrification. Taylor-Couette flow is the fluid flow in the gap between two cylinders rotating at different rates. Azimuthal velocity profiles, dye visualization, and inner cylinder torques were measured on two geometrically similar Taylor-Couettes with axial boundaries attached to the outer cylinder, the Maryland and Twente T3C experiments. This was done in the Rayleigh stable regime, where the specific angular momentum increases radially, which is relevant to astrophysical and geophysical flows and in particular, stellar and planetary accretion disks. The flow substantially deviates from laminar Taylor-Couette flow beginning at moderate Reynolds number. Angular momentum is primarily transported to the axial boundaries instead of the outer cylinder due to Ekman pumping when the inner cylinder is rotating faster than the outer cylinder. A phase diagram was constructed from the transitions identified from torque measurements taken over four decades of the Reynolds number. Flow angular velocities larger and smaller than both cylinders were found. Together, these results indicate that experimental Taylor-Couette with axial boundaries attached to the outer cylinder is an imperfect model for accretion disk flows. Thunderstorms, thunder-snow, volcanic ash clouds, and dust storms all display lightning, which results from electrification of droplets and particles in the atmosphere. While lightning is fairly well understood (plasma discharge), the mechanisms that result in million-volt differences across the storm are not. A novel granular electrification experiment was upgraded and used to study some of these mechanisms in the lab. The relative importance of collective interactions between particles versus particle properties (material, size, etc.) on collisional electrification was investigated. While particle properties have an order of magnitude effect on the strength of

Inertial migration of particles in Taylor-Couette flows

NASA Astrophysics Data System (ADS)

Majji, Madhu V.; Morris, Jeffrey F.

2018-03-01

An experimental study of inertial migration of neutrally buoyant particles in the circular Couette flow (CCF), Taylor vortex flow (TVF) and wavy vortex flow (WVF) is reported. This work considers a concentric cylinder Taylor-Couette device with a stationary outer cylinder and rotating inner cylinder. The device has a radius ratio of η = ri/ro = 0.877, where ri and ro are the inner and outer radii of the flow annulus. The ratio of the annular width between the cylinders (δ = ro - ri) and the particle diameter (dp) is α = δ/dp = 20. For η = 0.877, the flow of a Newtonian fluid undergoes transitions from CCF to TVF and TVF to WVF at Reynolds numbers Re = 120 and 151, respectively, and for the dilute suspensions studied here, these critical Reynolds numbers are almost unchanged. In CCF, particles were observed to migrate, due to the competition between the shear gradient of the flow and the wall interactions, to an equilibrium location near the middle of the annulus with an offset toward the inner cylinder. In TVF, the vortex motion causes the particles to be exposed to the shear gradient and wall interactions in a different manner, resulting in a circular equilibrium region in each vortex. The radius of this circular region grows with increase in Re. In WVF, the azimuthal waviness results in fairly well-distributed particles across the annulus.

Assessing and Testing Hydrokinetic Turbine Performance and Effects on Open Channel Hydrodynamics: An Irrigation Canal Case Study.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gunawan, Budi; Neary, Vincent Sinclair; Mortensen, Josh

Hydrokinetic energy from flowing water in open channels has the potential to support local electricity needs with lower regulatory or capital investment than impounding water with more conventional means. MOU agencies involved in federal hydropower development have identified the need to better understand the opportunities for hydrokinetic (HK) energy development within existing canal systems that may already have integrated hydropower plants. This document provides an overview of the main considerations, tools, and assessment methods, for implementing field tests in an open-channel water system to characterize current energy converter (CEC) device performance and hydrodynamic effects. It describes open channel processes relevantmore » to their HK site and perform pertinent analyses to guide siting and CEC layout design, with the goal of streamlining the evaluation process and reducing the risk of interfering with existing uses of the site. This document outlines key site parameters of interest and effective tools and methods for measurement and analysis with examples drawn from the Roza Main Canal, in Yakima, WA to illustrate a site application.« less

Influence of bedrock on river hydrodynamics and channel geometry

NASA Astrophysics Data System (ADS)

Rennie, C. D.; Church, M. A.; Venditti, J. G.; Bomhof, J.; Adderley, C.

2013-12-01

We present an acoustic Doppler current profiler (aDcp) survey of a 524 km long reach of Fraser River, British Columbia, Canada, as it passes through the Fraser Canyons. The channel alternates between gravel-bedded reaches that are incised into semi-consolidated glacial deposits and bedrock-bound reaches (7.7% of the reach between the towns of Quesnel and Hope). A continuous centreline aDcp survey was employed to measure longitudinal variation in slope, depth, depth-averaged velocity, and shear velocity. A total of 71 aDcp sectional surveys throughout the reach provided section widths (w), section-averaged depths (d), velocity distributions, and discharge (Q). Finally, air photo analysis using Google imagery provided channel widths at 0.5 km spacing. The survey reach was subdivided into 10 morphological sub-reaches, which ranged from alluvial gravel-bed reaches with relatively moderate slope to steep non-alluvial rock-walled canyons. The resulting data provide a unique opportunity to evaluate the influence of bedrock confinement on river hydrodynamics and channel geometry. Continuous centreline longitudinal aDcp data and the widths from air photo analysis were grouped within each sub-reach based on presence of bedrock confinement on both banks, either bank, or neither bank. The results demonstrate that river widths decreased and water depths, flow velocities, and shear velocities increased from the alluvial sub-reaches to the semi-alluvial reaches to the canyon reaches. Within each sub-reach, locations with bedrock encroachment on both banks were also narrower and deeper, but had lower depth-averaged velocity and shear velocity. Sectional geometry data were homogenized along the river (to compensate increasing flows at tributary junctions) by computing w/Q^{1/2} and d/Q^{1/3}, following commonly observed scaling relations. Alluvial reaches are 2.3x wider than rock-bound reaches (from the more abundant imagery data) and 0.60x as deep (from aDcp sections), implying

The Weakly Nonlinear Magnetorotational Instability in a Global, Cylindrical Taylor–Couette Flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clark, S. E.; Oishi, Jeffrey S., E-mail: seclark@astro.columbia.edu

We conduct a global, weakly nonlinear analysis of the magnetorotational instability (MRI) in a Taylor–Couette flow. This is a multiscale, perturbative treatment of the nonideal, axisymmetric MRI near threshold, subject to realistic radial boundary conditions and cylindrical geometry. We analyze both the standard MRI, initialized by a constant vertical background magnetic field, and the helical MRI, with an azimuthal background field component. This is the first weakly nonlinear analysis of the MRI in a global Taylor–Couette geometry, as well as the first weakly nonlinear analysis of the helical MRI. We find that the evolution of the amplitude of the standardmore » MRI is described by a real Ginzburg–Landau equation (GLE), whereas the amplitude of the helical MRI takes the form of a complex GLE. This suggests that the saturated state of the helical MRI may itself be unstable on long spatial and temporal scales.« less

Ekman-Hartmann layer in a magnetohydrodynamic Taylor-Couette flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szklarski, Jacek; Ruediger, Guenther

2007-12-15

We study magnetic effects induced by rigidly rotating plates enclosing a cylindrical magnetohydrodynamic (MHD) Taylor-Couette flow at the finite aspect ratio H/D=10. The fluid confined between the cylinders is assumed to be liquid metal characterized by small magnetic Prandtl number, the cylinders are perfectly conducting, an axial magnetic field is imposed with Hartmann number Ha{approx_equal}10, and the rotation rates correspond to Reynolds numbers of order 10{sup 2}-10{sup 3}. We show that the end plates introduce, besides the well-known Ekman circulation, similar magnetic effects which arise for infinite, rotating plates, horizontally unbounded by any walls. In particular, there exists the Hartmannmore » current, which penetrates the fluid, turns in the radial direction, and together with the applied magnetic field gives rise to a force. Consequently, the flow can be compared with a Taylor-Dean flow driven by an azimuthal pressure gradient. We analyze the stability of such flows and show that the currents induced by the plates can give rise to instability for the considered parameters. When designing a MHD Taylor-Couette experiment, special care must be taken concerning the vertical magnetic boundaries so that they do not significantly alter the rotational profile.« less

Direct numerical simulation of turbulent plane Couette flow under neutral and stable stratification

NASA Astrophysics Data System (ADS)

Mortikov, Evgeny

2017-11-01

Direct numerical simulation (DNS) approach was used to study turbulence dynamics in plane Couette flow under conditions ranging from neutral stability to the case of extreme stable stratification, where intermittency is observed. Simulations were performed for Reynolds numbers, based on the channel height and relative wall speed, up to 2 ×105 . Using DNS data, which covers a wide range of stability conditions, parameterizations of pressure correlation terms used in second-order closure turbulence models are discussed. Particular attention is also paid to the sustainment of intermittent turbulence under strong stratification. Intermittent regime is found to be associated with the formation of secondary large-scale structures elongated in the spanwise direction, which define spatially confined alternating regions of laminar and turbulent flow. The spanwise length of this structures increases with the increase in the bulk Richardson number and defines and additional constraint on the computational box size. In this work DNS results are presented in extended computational domains, where the intermittent turbulence is sustained for sufficiently higher Richardson numbers than previously reported.

A hydrodynamic mechanism for spontaneous formation of ordered drop arrays in confined shear flow

NASA Astrophysics Data System (ADS)

Singha, Sagnik; Zurita-Gotor, Mauricio; Loewenberg, Michael; Migler, Kalman; Blawzdziewicz, Jerzy

2017-11-01

It has been experimentally demonstrated that a drop monolayer driven by a confined shear flow in a Couette device can spontaneously arrange into a flow-oriented parallel chain microstructure. However, the hydrodynamic mechanism of this puzzling self-assembly phenomenon has so far eluded explanation. In a recent publication we suggested that the observed spontaneous drop ordering may arise from hydrodynamic interparticle interactions via a far-field quadrupolar Hele-Shaw flow associated with drop deformation. To verify this conjecture we have developed a simple numerical-simulation model that includes the far-field Hele-Shaw flow quadrupoles and a near-field short-range repulsion. Our simulations show that an initially disordered particle configuration self-organizes into a system of particle chains, similar to the experimentally observed drop-chain structures. The initial stage of chain formation is fast; subsequently, microstructural defects in a partially ordered system are removed by slow annealing, leading to an array of equally spaced parallel chains with a small number of defects. The microstructure evolution is analyzed using angular and spatial order parameters and correlation functions. Supported by NSF Grants No. CBET 1603627 and CBET 1603806.

Zonal Flow Velocimetry in Spherical Couette Flow using Acoustic Modes

NASA Astrophysics Data System (ADS)

Adams, Matthew M.; Mautino, Anthony R.; Stone, Douglas R.; Triana, Santiago A.; Lekic, Vedran; Lathrop, Daniel P.

2015-11-01

We present studies of spherical Couette flows using the technique of acoustic mode Doppler velocimetry. This technique uses rotational splittings of acoustic modes to infer the azimuthal velocity profile of a rotating flow, and is of special interest in experiments where direct flow visualization is impractical. The primary experimental system consists of a 60 cm diameter outer spherical shell concentric with a 20 cm diameter sphere, with air or nitrogen gas serving as the working fluid. The geometry of the system approximates that of the Earth's core, making these studies geophysically relevant. A turbulent shear flow is established in the system by rotating the inner sphere and outer shell at different rates. Acoustic modes of the fluid volume are excited using a speaker and measured via microphones, allowingdetermination of rotational splittings. Preliminary results comparing observed splittings with those predicted by theory are presented. While the majority of these studies were performed in the 60 cm diameter device using nitrogen gas, some work has also been done looking at acoustic modes in the 3 m diameter liquid sodium spherical Couette experiment. Prospects for measuring zonal velocity profiles in a wide variety of experiments are discussed.

High pressure rheology of gas hydrate formed from multiphase systems using modified Couette rheometer.

PubMed

Pandey, Gaurav; Linga, Praveen; Sangwai, Jitendra S

2017-02-01

Conventional rheometers with concentric cylinder geometries do not enhance mixing in situ and thus are not suitable for rheological studies of multiphase systems under high pressure such as gas hydrates. In this study, we demonstrate the use of modified Couette concentric cylinder geometries for high pressure rheological studies during the formation and dissociation of methane hydrate formed from pure water and water-decane systems. Conventional concentric cylinder Couette geometry did not produce any hydrates in situ and thus failed to measure rheological properties during hydrate formation. The modified Couette geometries proposed in this work observed to provide enhanced mixing in situ, thus forming gas hydrate from the gas-water-decane system. This study also nullifies the use of separate external high pressure cell for such measurements. The modified geometry was observed to measure gas hydrate viscosity from an initial condition of 0.001 Pa s to about 25 Pa s. The proposed geometries also possess the capability to measure dynamic viscoelastic properties of hydrate slurries at the end of experiments. The modified geometries could also capture and mimic the viscosity profile during the hydrate dissociation as reported in the literature. The present study acts as a precursor for enhancing our understanding on the rheology of gas hydrate formed from various systems containing promoters and inhibitors in the context of flow assurance.

High pressure rheology of gas hydrate formed from multiphase systems using modified Couette rheometer

NASA Astrophysics Data System (ADS)

Pandey, Gaurav; Linga, Praveen; Sangwai, Jitendra S.

2017-02-01

Conventional rheometers with concentric cylinder geometries do not enhance mixing in situ and thus are not suitable for rheological studies of multiphase systems under high pressure such as gas hydrates. In this study, we demonstrate the use of modified Couette concentric cylinder geometries for high pressure rheological studies during the formation and dissociation of methane hydrate formed from pure water and water-decane systems. Conventional concentric cylinder Couette geometry did not produce any hydrates in situ and thus failed to measure rheological properties during hydrate formation. The modified Couette geometries proposed in this work observed to provide enhanced mixing in situ, thus forming gas hydrate from the gas-water-decane system. This study also nullifies the use of separate external high pressure cell for such measurements. The modified geometry was observed to measure gas hydrate viscosity from an initial condition of 0.001 Pa s to about 25 Pa s. The proposed geometries also possess the capability to measure dynamic viscoelastic properties of hydrate slurries at the end of experiments. The modified geometries could also capture and mimic the viscosity profile during the hydrate dissociation as reported in the literature. The present study acts as a precursor for enhancing our understanding on the rheology of gas hydrate formed from various systems containing promoters and inhibitors in the context of flow assurance.

Suppressing Taylor vortices in a Taylor-Couette flow system with free surface

NASA Astrophysics Data System (ADS)

Bouabdallah, A.; Oualli, H.; Mekadem, M.; Gad-El-Hak, M.

2016-11-01

Taylor-Couette flows have been extensively investigated due to their many industrial applications, such as catalytic reactors, electrochemistry, photochemistry, biochemistry, and polymerization. Mass transfer applications include extraction, tangential filtration, crystallization, and dialysis. A 3D study is carried out to simulate a Taylor-Couette flow with a rotating and pulsating inner cylinder. We utilize FLUENT to simulate the incompressible flow with a free surface. The study reveals that flow structuring is initiated with the development of an Ekman vortex at low Taylor number, Ta = 0 . 01 . For all encountered flow regimes, the Taylor vortices are systematically inhibited by the pulsatile motion of the inner cylinder. A spectral analysis shows that this pulsatile motion causes a rapid decay of the free surface oscillations, from a periodic wavy movement to a chaotic one, then to a fully turbulent motion. This degenerative free surface behavior is interpreted as the underlying mechanism responsible for the inhibition of the Taylor vortices.

The Hagen-Poiseuille, Plane Couette and Poiseuille Flows Linear Instability and Rogue Waves Excitation Mechanism

NASA Astrophysics Data System (ADS)

Chefranov, Sergey; Chefranov, Alexander

2016-04-01

Linear hydrodynamic stability theory for the Hagen-Poiseuille (HP) flow yields a conclusion of infinitely large threshold Reynolds number, Re, value. This contradiction to the observation data is bypassed using assumption of the HP flow instability having hard type and possible for sufficiently high-amplitude disturbances. HP flow disturbance evolution is considered by nonlinear hydrodynamic stability theory. Similar is the case of the plane Couette (PC) flow. For the plane Poiseuille (PP) flow, linear theory just quantitatively does not agree with experimental data defining the threshold Reynolds number Re= 5772 ( S. A. Orszag, 1971), more than five-fold exceeding however the value observed, Re=1080 (S. J. Davies, C. M. White, 1928). In the present work, we show that the linear stability theory conclusions for the HP and PC on stability for any Reynolds number and evidently too high threshold Reynolds number estimate for the PP flow are related with the traditional use of the disturbance representation assuming the possibility of separation of the longitudinal (along the flow direction) variable from the other spatial variables. We show that if to refuse from this traditional form, conclusions on the linear instability for the HP and PC flows may be obtained for finite Reynolds numbers (for the HP flow, for Re>704, and for the PC flow, for Re>139). Also, we fit the linear stability theory conclusion on the PP flow to the experimental data by getting an estimate of the minimal threshold Reynolds number as Re=1040. We also get agreement of the minimal threshold Reynolds number estimate for PC with the experimental data of S. Bottin, et.al., 1997, where the laminar PC flow stability threshold is Re = 150. Rogue waves excitation mechanism in oppositely directed currents due to the PC flow linear instability is discussed. Results of the new linear hydrodynamic stability theory for the HP, PP, and PC flows are published in the following papers: 1. S.G. Chefranov, A

An alternative method for calibration of flow field flow fractionation channels for hydrodynamic radius determination: The nanoemulsion method (featuring multi angle light scattering).

PubMed

Bolinsson, Hans; Lu, Yi; Hall, Stephen; Nilsson, Lars; Håkansson, Andreas

2018-01-19

This study suggests a novel method for determination of the channel height in asymmetrical flow field-flow fractionation (AF4), which can be used for calibration of the channel for hydrodynamic radius determinations. The novel method uses an oil-in-water nanoemulsion together with multi angle light scattering (MALS) and elution theory to determine channel height from an AF4 experiment. The method is validated using two orthogonal methods; first, by using standard particle elution experiments and, secondly, by imaging an assembled and carrier liquid filled channel by x-ray computed tomography (XCT). It is concluded that the channel height can be determined with approximately the same accuracy as with the traditional channel height determination technique. However, the nanoemulsion method can be used under more challenging conditions than standard particles, as the nanoemulsion remains stable in a wider pH range than the previously used standard particles. Moreover, the novel method is also more cost effective. Copyright © 2017 Elsevier B.V. All rights reserved.

Experimental Evidence for Magnetorotational Instability in a Taylor-Couette Flow under the Influence of a Helical Magnetic Field

NASA Astrophysics Data System (ADS)

Stefani, Frank; Gundrum, Thomas; Gerbeth, Gunter; Rüdiger, Günther; Schultz, Manfred; Szklarski, Jacek; Hollerbach, Rainer

2006-11-01

A recent Letter [R. Hollerbach and G. Rüdiger, Phys. Rev. Lett. 95, 124501 (2005)PRLTAO0031-900710.1103/PhysRevLett.95.124501] has shown that the threshold for the onset of the magnetorotational instability in a Taylor-Couette flow is dramatically reduced if both axial and azimuthal magnetic fields are imposed. In agreement with this prediction, we present results of a Taylor-Couette experiment with the liquid metal alloy GaInSn, showing evidence for the existence of the magnetorotational instability at Reynolds numbers of order 1000 and Hartmann numbers of order 10.

Spatial variation of a short-lived intermediate chemical species in a Couette reactor

NASA Astrophysics Data System (ADS)

Vigil, R. Dennis; Ouyang, Q.; Swinney, Harry L.

1992-04-01

We have conducted experiments and simulations of the spatial variation of a short-lived intermediate species (triiodide) in the autocatalytic oxidation of arsenite by iodate in a reactor that is essentially one dimensional—the Couette reactor. (This reactor consists of two concentric cylinders with the inner one rotating and the outer one at rest; reagents are continuously fed and removed at each end in such a way that there is no net axial flux and there are opposing arsenite and iodate gradients.) The predictions of a one-dimensional reaction-diffusion model, which has no adjustable parameters, are in good qualitative (and, in some cases, quantitative) agreement with experiments. Thus, the Couette reactor, which is used to deliberately create spatial inhomogeneities, can be exploited to enhance the recovery of short-lived intermediate species relative to that which can be obtained with either a batch or continuous-flow stirred-tank reactor.

On the compressible Taylor?Couette problem

NASA Astrophysics Data System (ADS)

Manela, A.; Frankel, I.

We consider the linear temporal stability of a Couette flow of a Maxwell gas within the gap between a rotating inner cylinder and a concentric stationary outer cylinder both maintained at the same temperature. The neutral curve is obtained for arbitrary Mach (Ma) and arbitrarily small Knudsen (Kn) numbers by use of a continuum model and is verified via comparison to direct simulation Monte Carlo results. At subsonic rotation speeds we find, for the radial ratios considered here, that the neutral curve nearly coincides with the constant-Reynolds-number curve pertaining to the critical value for the onset of instability in the corresponding incompressible-flow problem. With increasing Mach number, transition is deferred to larger Reynolds numbers. It is remarkable that for a fixed Reynolds number, instability is always eventually suppressed beyond some supersonic rotation speed. To clarify this we examine the variation with increasing (Ma) of the reference Couette flow and analyse the narrow-gap limit of the compressible TC problem. The results of these suggest that, as in the incompressible problem, the onset of instability at supersonic speeds is still essentially determined through the balance of inertial and viscous-dissipative effects. Suppression of instability is brought about by increased rates of dissipation associated with the elevated bulk-fluid temperatures occurring at supersonic speeds. A useful approximation is obtained for the neutral curve throughout the entire range of Mach numbers by an adaptation of the familiar incompressible stability criteria with the critical Reynolds (or Taylor) numbers now based on average fluid properties. The narrow-gap analysis further indicates that the resulting approximate neutral curve obtained in the (Ma, Kn) plane consists of two branches: (i) the subsonic part corresponding to a constant ratio (Ma/Kn) (i.e. a constant critical Reynolds number) and (ii) a supersonic branch which at large Ma values corresponds to a

Effect on Non-Newtonian Rheology on Mixing in Taylor-Couette Flow

NASA Astrophysics Data System (ADS)

Cagney, Neil; Balabani, Stavroula

2017-11-01

Mixing processes within many industry applications are strongly affected by the rheology of the working fluid. This is particularly relevant for pharmaceutical, food and waste treatment industries, where the working fluids are often strongly non-Newtonian, and significant variations in rheology between batches may occur. We approach the question of how rheology affects mixing by focussing on a the classical case of Taylor-Couette flow, which exhibits a number of instabilities and flow regimes as a function of Reynolds number. We examine Taylor-Couette flow generated for a range of aqueous solutions of xantham gum or corn starch, such that the rheology varies from shear-thinning to shear-thickening. For each case, we measure the power consumption using a torque meter and the flow field using high speed, time-resolved Particle-Image Velocimetry. The mixing characteristics are quantified using a number of Lagrangian and Eulerian approaches, including the coarse grained density method and vortex strength. By comparing these metrics to the power number, we discuss how the mixing efficiency (ratio of mixing effectiveness to power input) varies with the flow index of the fluid.

Couette-Poiseuille flow experiment with zero mean advection velocity: Subcritical transition to turbulence

NASA Astrophysics Data System (ADS)

Klotz, L.; Lemoult, G.; Frontczak, I.; Tuckerman, L. S.; Wesfreid, J. E.

2017-04-01

We present an experimental setup that creates a shear flow with zero mean advection velocity achieved by counterbalancing the nonzero streamwise pressure gradient by moving boundaries, which generates plane Couette-Poiseuille flow. We obtain experimental results in the transitional regime for this flow. Using flow visualization, we characterize the subcritical transition to turbulence in Couette-Poiseuille flow and show the existence of turbulent spots generated by a permanent perturbation. Due to the zero mean advection velocity of the base profile, these turbulent structures are nearly stationary. We distinguish two regions of the turbulent spot: the active turbulent core, which is characterized by waviness of the streaks similar to traveling waves, and the surrounding region, which includes in addition the weak undisturbed streaks and oblique waves at the laminar-turbulent interface. We also study the dependence of the size of these two regions on Reynolds number. Finally, we show that the traveling waves move in the downstream (Poiseuille) direction.

In situ and online monitoring of hydrodynamic flow profiles in microfluidic channels based upon microelectrochemistry: concept, theory, and validation.

PubMed

Amatore, Christian; Oleinick, Alexander; Klymenko, Oleksiy V; Svir, Irina

2005-08-12

Herein, we propose a method for reconstructing any plausible macroscopic hydrodynamic flow profile occurring locally within a rectangular microfluidic channel. The method is based on experimental currents measured at single or double microband electrodes embedded in one channel wall. A perfectly adequate quasiconformal mapping of spatial coordinates introduced in our previous work [Electrochem. Commun. 2004, 6, 1123] and an exponentially expanding time grid, initially proposed [J. Electroanal. Chem. 2003, 557, 75] in conjunction with the solution of the corresponding variational problem approached by the Ritz method are used for the numerical reconstruction of flow profiles. Herein, the concept of the method is presented and developed theoretically and its validity is tested on the basis of the use of pseudoexperimental currents emulated by simulation of the diffusion-convection problem in a channel flow cell, to which a random Gaussian current noise is added. The flow profiles reconstructed by our method compare successfully with those introduced a priori into the simulations, even when these include significant distortions compared with either classical Poiseuille or electro-osmotic flows.

Dynamic domains of the Derviche Tourneur sodium experiment: Simulations of a spherical magnetized Couette flow

NASA Astrophysics Data System (ADS)

Kaplan, E. J.; Nataf, H.-C.; Schaeffer, N.

2018-03-01

The Derviche Tourneur sodium experiment, a spherical Couette magnetohydrodynamics experiment with liquid sodium as the medium and a dipole magnetic field imposed from the inner sphere, recently underwent upgrades to its diagnostics to better characterize the flow and induced magnetic fields with global rotation. In tandem with the upgrades, a set of direct numerical simulations were run to give a more complete view of the fluid and magnetic dynamics at various rotation rates of the inner and outer spheres. These simulations reveal several dynamic regimes, determined by the Rossby number. At positive differential rotation there is a regime of quasigeostrophic flow, with low levels of fluctuations near the outer sphere. Negative differential rotation shows a regime of what appear to be saturated hydrodynamic instabilities at low negative differential rotation, followed by a regime where filamentary structures develop at low latitudes and persist over five to ten differential rotation periods as they drift poleward. We emphasize that all these coherent structures emerge from turbulent flows. At least some of them seem to be related to linear instabilities of the mean flow. The simulated flows can produce the same measurements as those that the physical experiment can take, with signatures akin to those found in the experiment. This paper discusses the relation between the internal velocity structures of the flow and their magnetic signatures at the surface.

Hydrodynamic dispersion within porous biofilms

NASA Astrophysics Data System (ADS)

Davit, Y.; Byrne, H.; Osborne, J.; Pitt-Francis, J.; Gavaghan, D.; Quintard, M.

2013-01-01

Many microorganisms live within surface-associated consortia, termed biofilms, that can form intricate porous structures interspersed with a network of fluid channels. In such systems, transport phenomena, including flow and advection, regulate various aspects of cell behavior by controlling nutrient supply, evacuation of waste products, and permeation of antimicrobial agents. This study presents multiscale analysis of solute transport in these porous biofilms. We start our analysis with a channel-scale description of mass transport and use the method of volume averaging to derive a set of homogenized equations at the biofilm-scale in the case where the width of the channels is significantly smaller than the thickness of the biofilm. We show that solute transport may be described via two coupled partial differential equations or telegrapher's equations for the averaged concentrations. These models are particularly relevant for chemicals, such as some antimicrobial agents, that penetrate cell clusters very slowly. In most cases, especially for nutrients, solute penetration is faster, and transport can be described via an advection-dispersion equation. In this simpler case, the effective diffusion is characterized by a second-order tensor whose components depend on (1) the topology of the channels' network; (2) the solute's diffusion coefficients in the fluid and the cell clusters; (3) hydrodynamic dispersion effects; and (4) an additional dispersion term intrinsic to the two-phase configuration. Although solute transport in biofilms is commonly thought to be diffusion dominated, this analysis shows that hydrodynamic dispersion effects may significantly contribute to transport.

Near-bed turbulence and sediment flux measurements in tidal channels

USGS Publications Warehouse

Wright, S.A.; Whealdon-Haught, D.R.

2012-01-01

Understanding the hydrodynamics and sediment transport dynamics in tidal channels is important for studies of estuary geomorphology, sediment supply to tidal wetlands, aquatic ecology and fish habitat, and dredging and navigation. Hydrodynamic and sediment transport data are essential for calibration and testing of numerical models that may be used to address management questions related to these topics. Herein we report preliminary analyses of near-bed turbulence and sediment flux measurements in the Sacramento-San Joaquin Delta, a large network of tidal channels and wetlands located at the confluence of the Sacramento and San Joaquin Rivers, California, USA (Figure 1). Measurements were made in 6 channels spanning a wide range of size and tidal conditions, from small channels that are primarily fluvial to large channels that are tidally dominated. The results of these measurements are summarized herein and the hydrodynamic and sediment transport characteristics of the channels are compared across this range of size and conditions.

Deformable cells in confined geometries: From hemolysis to hydrodynamic interactions

NASA Astrophysics Data System (ADS)

Abkarian, Manouk; Faivre, Magalie; Stone, Howard A.

2004-11-01

Recent developments in microfluidics allow a wide range of possibilities for studying cellular-scale hydrodynamics. Here we use microfluidic technology to address several open questions in the blood flow literature where cell deformation and hydrodynamic interactions are significant. In particular, we investigate the pressure-driven flow of a dilute suspension in a channel and characterize the transition from steady axisymmetric cell shapes (for which numerical calculations exist) to asymmetric, highly extended shapes, which are precursors to hemolysis (i.e. destruction of the cell). In addition, we examine the influence of geometry on hydrodynamic interactions of deformable cells by contrasting one-dimensional motion of a train of particles in a channel with two-dimensional motions in a Hele-Shaw cell. This study can help to understand flow of cells in microcirculation from the unidirectional flow in capillaries to the two-dimensional flow in the lung alveoli and provides the basic steps to understand certain aspects of microcirculatory deseases like sickle cell anemia for example.

Viscoelastic Taylor-Couette instability as analog of the magnetorotational instability.

PubMed

Bai, Yang; Crumeyrolle, Olivier; Mutabazi, Innocent

2015-09-01

A linear stability analysis and an experimental study of a viscoelastic Taylor-Couette flow corotating in the Keplerian ratio allow us to elucidate the analogy between the viscoelastic instability and the magnetorotational instability (MRI). A generalized Rayleigh criterion allows us to determine the potentially unstable zone to pure-elasticity-driven perturbations. Experiments with a viscoelastic polymer solution yield four modes: one pure-elasticity mode and three elastorotational instability (ERI) modes that represent the MRI-analog modes. The destabilization by the polymer viscosity is evidenced for the ERI modes.

Defect-mediated turbulence in ribbons of viscoelastic Taylor-Couette flow.

PubMed

Latrache, Noureddine; Abcha, Nizar; Crumeyrolle, Olivier; Mutabazi, Innocent

2016-04-01

Transition to defect-mediated turbulence in the ribbon patterns observed in a viscoelastic Taylor-Couette flow is investigated when the rotation rate of the inner cylinder is increased while the outer cylinder is fixed. In four polymer solutions with different values of the elasticity number, the defects appear just above the onset of the ribbon pattern and trigger the appearance of disordered oscillations when the rotation rate is increased. The flow structure around the defects is determined and the statistical properties of these defects are analyzed in the framework of the complex Ginzburg-Landau equation.

DSMC Simulations of High Mach Number Taylor-Couette Flow

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev

2017-11-01

The main focus of this work is to characterise the Taylor-Couette flow of an ideal gas between two coaxial cylinders at Mach number Ma =(Uw /√{ kbTw / m }) in the range 0.01 Couette flow using DSMC method, wall slip in the temperature and the velocities are found to be significant. Slip occurs because the temperature/velocity of the molecules incident on the wall could be very different from that of the wall, even though the temperature/velocity of the reflected molecules is equal to that of the wall. Due to the high surface speed of the inner cylinder, significant heating of the gas is taking place. The gas temperature increases until the heat transfer to the surface equals the work done in moving the surface. The highest temperature is obtained near the moving surface of the inner cylinder at a radius of about (1.26 r1).

Small scale exact coherent structures at large Reynolds numbers in plane Couette flow

NASA Astrophysics Data System (ADS)

Eckhardt, Bruno; Zammert, Stefan

2018-02-01

The transition to turbulence in plane Couette flow and several other shear flows is connected with saddle node bifurcations in which fully three-dimensional, nonlinear solutions to the Navier-Stokes equation, so-called exact coherent states (ECS), appear. As the Reynolds number increases, the states undergo secondary bifurcations and their time-evolution becomes increasingly more complex. Their spatial complexity, in contrast, remains limited so that these states cannot contribute to the spatial complexity and cascade to smaller scales expected for higher Reynolds numbers. We here present families of scaling ECS that exist on ever smaller scales as the Reynolds number is increased. We focus in particular on two such families for plane Couette flow, one centered near the midplane and the other close to a wall. We discuss their scaling and localization properties and the bifurcation diagrams. All solutions are localized in the wall-normal direction. In the spanwise and downstream direction, they are either periodic or localized as well. The family of scaling ECS localized near a wall is reminiscent of attached eddies, and indicates how self-similar ECS can contribute to the formation of boundary layer profiles.

Design of a High Viscosity Couette Flow Facility for Patterned Surface Drag Measurements

NASA Astrophysics Data System (ADS)

Johnson, Tyler; Lang, Amy

2009-11-01

Direct drag measurements can be difficult to obtain with low viscosity fluids such as air or water. In this facility, mineral oil is used as the working fluid to increase the shear stress across the surface of experimental models. A mounted conveyor creates a flow within a plexiglass tank. The experimental model of a flat or patterned surface is suspended above a moving belt. Within the gap between the model and moving belt a Couette flow with a linear velocity profile is created. PIV measurements are used to determine the exact velocities and the Reynolds numbers for each experiment. The model is suspended by bars that connect to the pillow block housing of each bearing. Drag is measured by a force gauge connected to linear roller bearings that slide along steel rods. The patterned surfaces, initially consisting of 2-D cavities, are embedded in a plexiglass plate so as to keep the total surface area constant for each experiment. First, the drag across a flat plate is measured and compared to theoretical values for laminar Couette flow. The drag for patterned surfaces is then measured and compared to a flat plate.

Semi-Numerical Studies of the Three-Meter Spherical Couette Experiment Utilizing Data Assimilation

NASA Astrophysics Data System (ADS)

Burnett, Sarah; Rojas, Ruben; Perevalov, Artur; Lathrop, Daniel; Ide, Kayo; Schaeffer, Nathanael

2017-11-01

The model of the Earth's magnetic field has been investigated in recent years through experiments and numerical models. At the University of Maryland, experimental studies are implemented in a three-meter spherical Couette device filled with liquid sodium. The inner and outer spheres of this apparatus mimic the planet's inner core and core-mantle boundary, respectively. These experiments incorporate high velocity flows with Reynolds numbers 108 . In spherical Couette geometry, the numerical scheme applied to this work features finite difference methods in the radial direction and pseudospectral spherical harmonic transforms elsewhere. Adding to the numerical model, data assimilation integrates the experimental outer-layer magnetic field measurements. This semi-numerical model can then be compared to the experimental results as well as forecasting magnetic field changes. Data assimilation makes it possible to get estimates of internal motions of the three-meter experiment that would otherwise be intrusive or impossible to obtain in experiments or too computationally expensive with a purely numerical code. If we can provide accurate models of the three-meter device, it is possible to attempt to model the geomagnetic field. We gratefully acknowledge the support of NSF Grant No. EAR1417148 & DGE1322106.

Identification and onset of inertial modes in the wide-gap spherical Couette system

NASA Astrophysics Data System (ADS)

Barik, A.; Wicht, J.; Triana, S. A.; Hoff, M.

2016-12-01

The spherical Couette system consists of two concentric rotating spheres with a fluid filling the shell in between. The system has been studied for a long time by fluid dynamicists and is ideal for studying flow instabilities due to differential rotation and the interaction of the same with magnetic fields - important for understanding dynamics of planetary and stellar interiors. The system is also a basis for a new generation of dynamo experiments because of its closer geometrical resemblance to real astrophysical objects as compared to past experiments. We simulate this system using the two different pseudo-spectral codes MagIC and XSHELLS. We focus here on a very interesting and general instability in this system - inertial modes. A rotating body of fluid is known to sustain oscillatory waves due to the restoring action of the Coriolis force. In a bounded container, these form a discrete spectrum called inertial modes. These modes have been analytically known for a rotating full sphere for over a century now. In a spherical shell, they cannot be formulated analytically. However, many of these inertial modes are observed in spherical Couette experiments as well as in simulations. Past studies have tried to explain the onset of these modes invoking wave over-reflection or critical layer instabilities on the cylinder tangent to the inner sphere. In this study, we present the inertial modes found in our simulations and try to explain their onset as secondary instabilities due to the destabilization of the fundamental non-axisymmetric instability, forming a triadic resonance with the fundamental instability. We run various simulations varying the rotation rate of the inner sphere, while keeping the rotation rate of the outer sphere constant. We track velocities and induced magnetic field and produce spectrograms similar to those of the experiments. Our results match very well the experimental data from spherical Couette set-ups at BTU Cottbus and the University of

Otto LaPorte Lecture: Ultimate Rayleigh-Bénard and Taylor-Couette turbulence

NASA Astrophysics Data System (ADS)

Lohse, Detlef

2017-11-01

Rayleigh-Bénard flow - the flow in a box heated from below and cooled from above - and Taylor-Couette flow - the flow between two coaxial co- or counter-rotating cylinders - are the two paradigmatic systems in physics of fluids and many new concepts have been tested with them. They are mathematically well defined, namely by the Navier-Stokes equations and the respective boundary conditions, and share many features. While the low Reynolds number regime (i.e., weakly driven systems) has been very well explored in the '80s and '90s of the last century, in the fully turbulent regime major research activity only developed in the last two decades. In this talk we will first briefly review this recent progress in our understanding of fully developed Rayleigh-Bénard (RB) and Taylor-Couette (TC) turbulence, from the experimental, theoretical, and numerical point of view. We will explain the parameter dependences of the global transport properties of the flow and the local flow organisation, including velocity profiles and boundary layers, which are closely connected to the global properties. Next, we will discuss transitions between different (turbulent) flow states. We will in particular focus on the so-called ultimate regime, in which the boundary layer has become turbulent, and which therefore has enhanced transport properties. In the mechanical driven TC flow this ultimate regime can also be achieved in our high-performance numerical simulations, showing excellent agreement with our experiments on the Twente Turbulent Taylor-Couette (T3 C) facility. In the last part of the talk we will discuss RB and TC turbulence with rough walls. There the results can be expressed in terms of the skin-friction factor, revealing analogy to turbulent flow in rough pipes. Finally, we will present our results on RB and TC flow with bubbles, focusing on bubbly drag reduction and its origin. This is joint work with many colleagues over the years, and I in particular would like to name

Identification of complex flows in Taylor-Couette counter-rotating cavities

NASA Technical Reports Server (NTRS)

Czarny, O.; Serre, E.; Bontoux, P.; Lueptow, R. M.

2001-01-01

The transition in confined rotating flows is a topical problem with many industrial and fundamental applications. The purpose of this study is to investigate the Taylor-Couette flow in a finite-length cavity with counter-rotating walls, for two aspect ratios L=5 or L=6. Two complex regimes of wavy vortex and spirals are emphasized for the first time via direct numerical simulation, by using a three-dimensional spectral method. The spatio-temporal behavior of the solutions is analyzed and compared to the few data actually available. c2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.

Analysis of activation energy in Couette-Poiseuille flow of nanofluid in the presence of chemical reaction and convective boundary conditions

NASA Astrophysics Data System (ADS)

Zeeshan, A.; Shehzad, N.; Ellahi, R.

2018-03-01

The motivation of the current article is to explore the energy activation in MHD radiative Couette-Poiseuille flow nanofluid in horizontal channel with convective boundary conditions. The mathematical model of Buongiorno [1] effectively describes the current flow analysis. Additionally, the impact of chemical reaction is also taken in account. The governing flow equations are simplified with the help of boundary layer approximations. Non-linear coupled equations for momentum, energy and mass transfer are tackled with analytical (HAM) technique. The influence of dimensionless convergence parameter like Brownian motion parameter, radiation parameter, buoyancy ratio parameter, dimensionless activation energy, thermophoresis parameter, temperature difference parameter, dimensionless reaction rate, Schmidt number, Brinkman number, Biot number and convection diffusion parameter on velocity, temperature and concentration profiles are discussed graphically and in tabular form. From the results, it is elaborate that the nanoparticle concentration is directly proportional to the chemical reaction with activation energy and the performance of Brownian motion on nanoparticle concentration gives reverse pattern to that of thermophoresis parameter.

Understanding the hydrodynamics of the Congo River

NASA Astrophysics Data System (ADS)

O'Loughlin, Fiachra; Bates, Paul

2014-05-01

We present the results of the first hydrodynamic model of the middle reach of the Congo Basin, which helps our understanding of the behaviour of the second largest river in the world. In data sparse area, hydrodynamic models, utilizing a mixture of limited in-situ measurements and remotely sensed datasets, can be used to understand and identify key features that control large river systems. Unlike previous hydrodynamic models for the Congo Basin, which concentrated on only a small area, we look at the entire length of the Congo's middle reach and its six main tributaries (Kasai, Ubangai, Sangha, Ruki, Lulonga and Lomami). This corresponds to: a drainage area of approximately two and a half million kilometres squared; over 5000 kilometres of river channels; and incorporates some of the largest and most important global wetlands. The hydrodynamic model is driven by a mixture of in-situ and modelled discharges. In situ measurements are available at five locations. Two were obtained from the Global River Discharge Centre (GRDC) at Kinshasa and Bangui, and data for Kisangani, Ouesso and Lediba were obtained from local agencies in the Democratic Republic of the Congo and the Republic of Congo. Using the gauging station at Kinshasa as the downstream boundary, the remaining in-situ measurements account for 61 percent of the discharge and represent 72 percent of the total drainage area. Modelled discharges are used to account for the missing discharge and corresponding area. Calibration and validation of the model was undertaken using a mixture of in-situ measurements, discharge and water level at Kinshasa, and water surface heights along the main reach obtained from both laser and radar altimeters. Through the hydrodynamic model we will investigate: how important constraints, identified by a previous study, are to the behaviour of the Congo; what impacts the wetlands have on the Congo Basin; how the wetlands and main channel interact with each other. Our results will

Momentum balance and stresses in a suspension of spherical particles in a plane Couette flow

NASA Astrophysics Data System (ADS)

Rahmani, Mona; Hammouti, Abdelkader; Wachs, Anthony

2018-04-01

Non-Brownian suspension of monodisperse spherical particles, with volume fractions ranging between ϕ = 0.05 and 0.38 and particle Reynolds numbers ranging between Rep = 0.002 and 20, in plane Couette shear flows is investigated using three-dimensional particle-resolved numerical simulations. We examine the effects of volume fraction and particle Reynolds number on the macroscopic and microscopic stresses in the fluid phase. The effective viscosity of the suspension is in a good agreement with the previous empirical and experimental studies. At Rep = 20, however, the effective viscosity increases significantly compared to the lower particle Reynolds number simulations in the Stokes flow regime. Examining the stresses over the depth of the Couette gap reveals that this increase in wall shear stresses at high particle Reynolds numbers is mainly due to the significantly higher particle phase stress contributions. Next, we examine the momentum balance in the fluid and particle phase for different regimes to assess the significance of particle/particle interaction and fluid and particle inertia. At the highest particle Reynolds number and volume fraction, the particle inertia plays a dominant role in the momentum balance and the fluid inertia is non-negligible, while the short-lived contact forces are negligible compared to these effects. For all other regimes, the fluid inertia is negligible, but the particle inertia and contact forces are important in the momentum balance. Reynolds stresses originated from velocity fluctuations do not contribute significantly to the suspension stresses in any of the regimes we have studied, while the reduction in the shear-induced particle rotation can be a reason for higher wall shear stress at Rep = 20. Finally, we study the kinematics of particles, including their velocity fluctuations, rotation, and diffusion over the depth of the Couette gap. The particle diffusion coefficients in the cross flow direction exhibit an abrupt

Experimental investigation of liquid-liquid system drop size distribution in Taylor-Couette flow and its application in the CFD simulation

NASA Astrophysics Data System (ADS)

Farzad, Reza; Puttinger, Stefan; Pirker, Stefan; Schneiderbauer, Simon

Liquid-liquid systems are widely used in the several industries such as food, pharmaceutical, cosmetic, chemical and petroleum. Drop size distribution (DSD) plays a key role as it strongly affects the overall mass and heat transfer in the liquid-liquid systems. To understand the underlying mechanisms single drop breakup experiments have been done by several researchers in the Taylor-Couette flow; however, most of those studies concentrate on the laminar flow regime and therefore, there is no sufficient amount of data in the case of in turbulent flows. The well-defined pattern of the Taylor-Couette flow enables the possibility to investigate DSD as a function of the local fluid dynamic properties, such as shear rate, which is in contrast to more complex devices such as stirred tank reactors. This paper deals with the experimental investigation of liquid-liquid DSD in Taylor-Couette flow. From high speed camera images we found a simple correlation for the Sauter mean diameter as a function of the local shear employing image processing. It is shown that this correlation holds for different oil-in-water emulsions. Finally, this empirical correlation for the DSD is used as an input data for a CFD simulation to compute the local breakup of individual droplets in a stirred tank reactor.

Transition of planar Couette flow at infinite Reynolds numbers.

PubMed

Itano, Tomoaki; Akinaga, Takeshi; Generalis, Sotos C; Sugihara-Seki, Masako

2013-11-01

An outline of the state space of planar Couette flow at high Reynolds numbers (Re<10^{5}) is investigated via a variety of efficient numerical techniques. It is verified from nonlinear analysis that the lower branch of the hairpin vortex state (HVS) asymptotically approaches the primary (laminar) state with increasing Re. It is also predicted that the lower branch of the HVS at high Re belongs to the stability boundary that initiates a transition to turbulence, and that one of the unstable manifolds of the lower branch of HVS lies on the boundary. These facts suggest HVS may provide a criterion to estimate a minimum perturbation arising transition to turbulent states at the infinite Re limit.

River channel morphology and hydraulics properties due to introduction of plant basket hydraulic structures for river channel management

NASA Astrophysics Data System (ADS)

Kałuża, Tomasz; Radecki-Pawlik, Artur; Plesiński, Karol; Walczak, Natalia; Szoszkiewicz, Krzysztof; Radecki-Pawlik, Bartosz

2016-04-01

In the present time integrated water management is directly connected with management and direct works in river channels themselves which are taking into account morphological processes in rivers and improve flow conditions. Our work focused on the hydraulic and hydrodynamic consequences upon the introduction of the concept of the improvement of the hydromorphological conditions of the Flinta River in a given reach following river channel management concept. Based on a comprehensive study of the hydromorphological state of the river, four sections were selected where restoration measures can efficiently improve river habitat conditions in the river. For each section a set of technical and biological measures were proposed and implemented in practice. One of the proposed solutions was to construct plant basket hydraulic structures (PBHS) within the river channel, which are essentially plant barriers working as sediment traps, changing river channel morphology and are in line with concepts of Water Framework Directive. These relatively small structures work as crested weirs and unquestionably change the channel morphology. Along our work we show the results of three-year long (2013-2015) systematic measurements that provided information on the morphological consequences of introducing such structures into a river channel. Our main conclusions are as follows: 1. Plant basket hydraulic structures cause changes in hydrodynamic conditions and result in sediment accumulation and the formation of river backwaters upstream and downstream the obstacle; 2. The introduced plant basket hydraulic structures cause plant debris accumulation which influences the hydrodynamic flow conditions; 3. The installation of plant basket hydraulic structures on the river bed changes flow pattern as well as flow hydrodynamic conditions causing river braiding process; 4. The erosion rate below the plant basket hydraulic structures is due to the hydraulic work conditions of the PBHS and its

Active and hibernating turbulence in drag-reducing plane Couette flows

NASA Astrophysics Data System (ADS)

Pereira, Anselmo S.; Mompean, Gilmar; Thais, Laurent; Soares, Edson J.; Thompson, Roney L.

2017-08-01

In this paper we analyze the active and hibernating turbulence in drag-reducing plane Couette flows using direct numerical simulations of the viscoelastic finitely extensible nonlinear elastic model with the Peterlin approximation fluids. The polymer-turbulence interactions are studied from an energetic standpoint for a range of Weissenberg numbers (from 2 up to 30), fixing the Reynolds number based on the plate velocities at 4000, the viscosity ratio at 0.9, and the maximum polymer molecule extensibility at 100. The qualitative picture that emerges from this investigation is a cyclic mechanism of energy exchange between the polymers and turbulence that drives the flow through an oscillatory behavior.

Fluid-structure interaction in Taylor-Couette flow

NASA Astrophysics Data System (ADS)

Kempf, Martin Horst Willi

1998-10-01

The linear stability of a viscous fluid between two concentric, rotating cylinders is considered. The inner cylinder is a rigid boundary and the outer cylinder has an elastic layer exposed to the fluid. The subject is motivated by flow between two adjoining rollers in a printing press. The governing equations of the fluid layer are the incompressible Navier-Stokes equations, and the governing equations of the elastic layer are Navier's equations. A narrow gap, neutral stability, and axisymmetric disturbances are assumed. The solution involves a novel technique for treating two layer stability problems, where an exact solution in the elastic layer is used to isolate the problem in the fluid layer. The results show that the presence of the elastic layer has only a slight effect on the critical Taylor numbers for the elastic parameters of modern printing presses. However, there are parameter values where the critical Taylor number is dramatically different than the classical Taylor-Couette problem.

The mechanism by which nonlinearity sustains turbulence in plane Couette flow

NASA Astrophysics Data System (ADS)

Nikolaidis, M.-A.; Farrell, B. F.; Ioannou, P. J.

2018-04-01

Turbulence in wall-bounded shear flow results from a synergistic interaction between linear non-normality and nonlinearity in which non-normal growth of a subset of perturbations configured to transfer energy from the externally forced component of the turbulent state to the perturbation component maintains the perturbation energy, while the subset of energy-transferring perturbations is replenished by nonlinearity. Although it is accepted that both linear non-normality mediated energy transfer from the forced component of the mean flow and nonlinear interactions among perturbations are required to maintain the turbulent state, the detailed physical mechanism by which these processes interact in maintaining turbulence has not been determined. In this work a statistical state dynamics based analysis is performed on turbulent Couette flow at R = 600 and a comparison to DNS is used to demonstrate that the perturbation component in Couette flow turbulence is replenished by a non-normality mediated parametric growth process in which the fluctuating streamwise mean flow has been adjusted to marginal Lyapunov stability. It is further shown that the alternative mechanism in which the subspace of non-normally growing perturbations is maintained directly by perturbation-perturbation nonlinearity does not contribute to maintaining the turbulent state. This work identifies parametric interaction between the fluctuating streamwise mean flow and the streamwise varying perturbations to be the mechanism of the nonlinear interaction maintaining the perturbation component of the turbulent state, and identifies the associated Lyapunov vectors with positive energetics as the structures of the perturbation subspace supporting the turbulence.

Irregular wall roughness in turbulent Taylor-Couette flow

NASA Astrophysics Data System (ADS)

Berghout, Pieter; Zhu, Xiaojue; Verzicco, Roberto; Lohse, Detlef; Stevens, Richard

2017-11-01

Many wall bounded flows in nature, engineering and transport are affected by surface roughness. Often, this has adverse effects, e.g. drag increase leading to higher energy costs. A major difficulty is the infinite number of roughness geometries, which makes it impossible to systematically investigate all possibilities. Here we present Direct Numerical Simulations (DNS) of turbulent Taylor-Couette flow. We focus on the transitionally rough regime, in which both viscous and pressure forces contribute to the total wall stress. We investigate the effect of the mean roughness height and the effective slope on the roughness function, ΔU+ . Also, we present simulations of varying Ta (Re) numbers for a constant mean roughness height (kmean+). Alongside, we show the behavior of the large scale structures (e.g. plume ejection, Taylor rolls) and flow structures in the vicinity of the wall.

Extreme-scale motions in turbulent plane Couette flows

NASA Astrophysics Data System (ADS)

Lee, Myoungkyu; Moser, Robert D.

2018-05-01

We study the size of large-scale motions in turbulent plane Couette flows at moderate Reynolds number up to $Re_\\tau$ = 500. Direct numerical simulation domains were as large as $100\\pi\\delta\\times2\\delta\\times5\\pi\\delta$, where $\\delta$ is half the distance between the walls. The results indicate that there are structures with streamwise extent, as measured by the wavelength, as long as 78$\\delta$ and at least 310$\\delta$ at $Re_\\tau$ = 220 and 500, respectively. The presence of these very long structures is apparent in the spectra of all three velocity components and the Reynolds stress. In DNS using a smaller domain, the large structures are constrained, eliminating the streamwise variations present in the larger domain. Effects of a smaller domain are also present in the mean velocity and the streamwise velocity variance in the outer flow.

Semi-Numerical Studies of the Three-Meter Spherical Couette Experiment Utilizing Data Assimilation

NASA Astrophysics Data System (ADS)

Burnett, S. C.; Rojas, R.; Perevalov, A.; Lathrop, D. P.

2017-12-01

The model of the Earth's magnetic field has been investigated in recent years through experiments and numerical models. At the University of Maryland, experimental studies are implemented in a three-meter spherical Couette device filled with liquid sodium. The inner and outer spheres of this apparatus mimic the planet's inner core and core-mantle boundary, respectively. These experiments incorporate high velocity flows with Reynolds numbers 108. In spherical Couette geometry, the numerical scheme applied to this work features finite difference methods in the radial direction and pseudospectral spherical harmonic transforms elsewhere [Schaeffer, N. G3 (2013)]. Adding to the numerical model, data assimilation integrates the experimental outer-layer magnetic field measurements. This semi-numerical model can then be compared to the experimental results as well as forecasting magnetic field changes. Data assimilation makes it possible to get estimates of internal motions of the three-meter experiment that would otherwise be intrusive or impossible to obtain in experiments or too computationally expensive with a purely numerical code. If we can provide accurate models of the three-meter device, it is possible to attempt to model the geomagnetic field. We gratefully acknowledge the support of NSF Grant No. EAR1417148 & DGE1322106.

Supraglacial channel inception: Modeling and processes

NASA Astrophysics Data System (ADS)

Mantelli, E.; Camporeale, C.; Ridolfi, L.

2015-09-01

Supraglacial drainage systems play a key role in glacial hydrology. Nevertheless, physical processes leading to spatial organization in supraglacial networks are still an open issue. In the present work we thus address from a quantitative point of view the question of what is the physics leading to widely observed patterns made up of evenly spaced channels. To this aim, we set up a novel mathematical model describing a condition antecedent channel formation, i.e., the down-glacier flow of a distributed meltwater film. We then perform a linear stability analysis to assess whether the ice-water interface undergoes a morphological instability compatible with observed patterns. The instability is detected, its features depending on glacier surface slope, ice friction factor, and water as well as ice thermal conditions. By contrast, in our model channel spacing is solely hydrodynamically driven and relies on the interplay between pressure perturbations, flow depth response, and Reynolds stresses. Geometrical features of the predicted pattern are quantitatively consistent with available field data. The hydrodynamic origin of supraglacial channel morphogenesis suggests that alluvial patterns might share the same physical controls.

Multi-dimensional computer simulation of MHD combustor hydrodynamics

NASA Astrophysics Data System (ADS)

Berry, G. F.; Chang, S. L.; Lottes, S. A.; Rimkus, W. A.

1991-04-01

Argonne National Laboratory is investigating the nonreacting jet gas mixing patterns in an MHD second stage combustor by using a 2-D multiphase hydrodynamics computer program and a 3-D single phase hydrodynamics computer program. The computer simulations are intended to enhance the understanding of flow and mixing patterns in the combustor, which in turn may lead to improvement of the downstream MHD channel performance. A 2-D steady state computer model, based on mass and momentum conservation laws for multiple gas species, is used to simulate the hydrodynamics of the combustor in which a jet of oxidizer is injected into an unconfined cross stream gas flow. A 3-D code is used to examine the effects of the side walls and the distributed jet flows on the non-reacting jet gas mixing patterns. The code solves the conservation equations of mass, momentum, and energy, and a transport equation of a turbulence parameter and allows permeable surfaces to be specified for any computational cell.

Dynamo Action in a Quasi-Keplerian Taylor-Couette Flow.

PubMed

Guseva, Anna; Hollerbach, Rainer; Willis, Ashley P; Avila, Marc

2017-10-20

We numerically compute the flow of an electrically conducting fluid in a Taylor-Couette geometry where the rotation rates of the inner and outer cylinders satisfy Ω_{o}/Ω_{i}=(r_{o}/r_{i})^{-3/2}. In this quasi-Keplerian regime, a nonmagnetic system would be Rayleigh stable for all Reynolds numbers Re, and the resulting purely azimuthal flow incapable of kinematic dynamo action for all magnetic Reynolds numbers Rm. For Re = 10^{4} and Rm=10^{5}, we demonstrate the existence of a finite-amplitude dynamo, whereby a suitable initial condition yields mutually sustaining turbulence and magnetic fields, even though neither could exist without the other. This dynamo solution results in significantly increased outward angular momentum transport, with the bulk of the transport being by Maxwell rather than Reynolds stresses.

Hydrodynamic and sedimentological controls governing formation of fluvial levees

NASA Astrophysics Data System (ADS)

Johnston, G. H.; Edmonds, D. A.; David, S. R.; Czuba, J. A.

2017-12-01

Fluvial levees are familiar features found on the margins of river channels, yet we know little about what controls their presence, height, and shape. These attributes of levees are important because they control sediment transfer from channel to floodplain and flooding patterns along a river system. Despite the familiarity and importance of levees, there is a surprising lack of basic geomorphic data on fluvial levees. Because of this we seek to understand: 1) where along rivers do levees tend to occur?; 2) what geomorphic and hydrodynamic variables control cross-sectional shape of levees? We address these questions by extracting levee shape from LiDAR data and by collecting hydrodynamic and sedimentological data from reaches of the Tippecanoe River, the White River, and the Muscatatuck River, Indiana, USA. Fluvial levees are extracted from a 1.5-m resolution LiDAR bare surface model and compared to hydrological, sedimentological, and geomorphological data from USGS stream gages. We digitized banklines and extracted levee cross-sections to calculate levee slope, taper, height, e-folding length, and e-folding width. To answer the research questions, we performed a multivariable regression between the independent variables—channel geometry, sediment grain size and concentration, flooding conditions, and slope—and the dependent levee variables. We find considerable variation in levee presence and shape in our field data. On the Muscatatuck River levees occur on 30% of the banks compared to 10% on the White River. Moreover, levees on the Muscatatuck are on average 3 times wider than the White River. This is consistent with the observation that the Muscatatuck is finer-grained compared to the White River and points to sedimentology being an important control on levee geomorphology. Future work includes building a morphodynamic model to understand how different hydrodynamic and geomorphic conditions control levee geometry.

Impact of intertidal area characteristics on estuarine tidal hydrodynamics: A modelling study for the Scheldt Estuary

NASA Astrophysics Data System (ADS)

Stark, J.; Smolders, S.; Meire, P.; Temmerman, S.

2017-11-01

Marsh restoration projects are nowadays being implemented as ecosystem-based strategies to reduce flood risks and to restore intertidal habitat along estuaries. Changes in estuarine tidal hydrodynamics are expected along with such intertidal area changes. A validated hydrodynamic model of the Scheldt Estuary is used to gain fundamental insights in the role of intertidal area characteristics on tidal hydrodynamics and tidal asymmetry in particular through several geomorphological scenarios in which intertidal area elevation and location along the estuary is varied. Model results indicate that the location of intertidal areas and their storage volume relative to the local tidal prism determine the intensity and reach along the estuary over which tidal hydrodynamics are affected. Our model results also suggest that intertidal storage areas that are located within the main estuarine channel system, and hence are part of the flow-carrying part of the estuary, may affect tidal hydrodynamics differently than intertidal areas that are side-basins of the main estuarine channel, and hence only contribute little to the flow-carrying cross-section of the estuary. If tidal flats contribute to the channel cross-section and exert frictional effects on the tidal propagation, the elevation of intertidal flats influences the magnitude and direction of tidal asymmetry along estuarine channels. Ebb-dominance is most strongly enhanced if tidal flats are around mean sea level or slightly above. Conversely, flood-dominance is enhanced if the tidal flats are situated low in the tidal frame. For intertidal storage areas at specific locations besides the main channel, flood-dominance in the estuary channel peaks in the vicinity of those areas and generally reduces upstream and downstream compared to a reference scenario. Finally, the model results indicate an along-estuary varying impact on the tidal prism as a result of adding intertidal storage at a specific location. In addition to known

Recent research on the hydrodynamics of the Sacramento - San Joaquin River Delta and north San Francisco Bay

USGS Publications Warehouse

Burau, J.R.; Monismith, S.G.; Stacey, M.T.; Oltmann, R.N.; Lacy, J.R.; Schoellhamer, D.H.

1999-01-01

This article presents an overview of recent findings from hydrodynamic research on circulation and mixing in the Sacramento-San Joaquin Delta (Delta) (Figure 1) and North San Francisco Bay (North Bay) (Figure 2). For the purposes of this article, North Bay includes San Pablo Bay, Carquinez Strait, and Suisun Bay. The findings presented are those gained from field studies carried out by the U.S. Geological Survey (USGS), as part of the Interagency Ecological Program (IEP), and Stanford University beginning about 1993. The premise behind these studies was that a basic understanding of circulation and mixing patterns in the Bay and Delta is an essential part of understanding how biota and water quality are affected by natural hydrologic variability, water appropriation, and development activities. Data collected for the field studies described in this article have significantly improved our understanding of Bay and Delta hydrodynamics. Measured flows ,in the Delta have provided valuable information on how water moves through the Delta's network of channels and how export pumping affects flows. Studies of the shallows and shallow-channel exchange processes conducted in Honker Bay have shown that the water residence time in Honker Bay is much shorter than previously reported (on the order of hours to several tidal cycles instead ofweeks). Suisun Bay studies have provided data on hydrodynamic transport and accumulation mechanisms that operate primarily in the channels. The Suisun Bay studies have caused us to revise our understanding of residual circulation in the channels of North Bay and of "entrapment" mechanisms in the low salinity zone. Finally, detailed tidal and residual (tidally averaged) time-scale studies of the mechanisms that control gravitational circulation in the estuary show that density-driven transport in the channels is governed by turbulence time-scale (seconds) interactions between the mean flow and stratification. The hydrodynamic research

Spontaneous electrorheological effect in nematic liquid crystals under Taylor-Couette flow configuration

NASA Astrophysics Data System (ADS)

Dhar, Jayabrata; Chakraborty, Suman

2017-09-01

Electrorheological (ER) characteristics of Nematic Liquid Crystals (NLCs) have been a topic of immense interest in the field of soft matter physics owing to its rheological modulation capabilities. Here we explore the augmentation in rheological characteristics of the nematic fluid confined within the annular region of the concentric cylindrical space with an Electrical Double Layer (EDL) induced at the fluid-substrate interface due to certain physico-chemical interactions. Using a Taylor-Couette flow configuration associated with an EDL induced at the inner cylinder wall, we show that a spontaneous electrorheological effect is generated owing to the intrinsic director anisotropy and structural order of complex nematic fluids. We seek to find the enhancement in torque transfer capability due to the inherent electrorheological nature of the nematic medium, apart from exploiting the innate nature of such homogeneous media to remain free of coagulation, a fact which makes it an excellent candidate for the applications in microfluidic environment. Our analysis reveals that with stronger induced charge density within the EDL, the apparent viscosity enhances, which, in turn, augments torque transfer across the concentric cylinder. The velocity profile tends to flatten in comparison to the classical circular Couette flow in annular geometry as one increases the surface charge density. We further observe a more pronounced ER effect for the nematic medium having larger electrical permittivity anisotropy. Besides the torque transfer qualifications, we also explore the distinct scenarios, wherein the same NLC medium exhibits shear thinning and shear thickening characteristics. The present configuration of the efficient torque transfer mechanism may be proficiently downscaled to micro-level and is relevant in the fabrication of micro-clutch and micro-dampers.

Magneto-hydrodynamic modeling of gas discharge switches

NASA Astrophysics Data System (ADS)

Doiphode, P.; Sakthivel, N.; Sarkar, P.; Chaturvedi, S.

2002-12-01

We have performed one-dimensional, time-dependent magneto-hydrodynamic modeling of fast gas-discharge switches. The model has been applied to both high- and low-pressure switches, involving a cylindrical argon-filled cavity. It is assumed that the discharge is initiated in a small channel near the axis of the cylinder. Joule heating in this channel rapidly raises its temperature and pressure. This drives a radial shock wave that heats and ionizes the surrounding low-temperature region, resulting in progressive expansion of the current channel. Our model is able to reproduce this expansion. However, significant difference of detail is observed, as compared with a simple model reported in the literature. In this paper, we present details of our simulations, a comparison with results from the simple model, and a physical interpretation for these differences. This is a first step towards development of a detailed 2-D model for such switches.

A hydrodynamic microchip for formation of continuous cell chains

NASA Astrophysics Data System (ADS)

Khoshmanesh, Khashayar; Zhang, Wei; Tang, Shi-Yang; Nasabi, Mahyar; Soffe, Rebecca; Tovar-Lopez, Francisco J.; Rajadas, Jayakumar; Mitchell, Arnan

2014-05-01

Here, we demonstrate the unique features of a hydrodynamic based microchip for creating continuous chains of model yeast cells. The system consists of a disk shaped microfluidic structure, containing narrow orifices that connect the main channel to an array of spoke channels. Negative pressure provided by a syringe pump draws fluid from the main channel through the narrow orifices. After cleaning process, a thin layer of water is left between the glass substrate and the polydimethylsiloxane microchip, enabling leakage beneath the channel walls. A mechanical clamp is used to adjust the operation of the microchip. Relaxing the clamp allows leakage of liquid beneath the walls in a controllable fashion, leading to formation of a long cell chain evenly distributed along the channel wall. The unique features of the microchip are demonstrated by creating long chains of yeast cells and model 15 μm polystyrene particles along the side wall and analysing the hydrogen peroxide induced death of patterned cells.

Improving Watershed-Scale Hydrodynamic Models by Incorporating Synthetic 3D River Bathymetry Network

NASA Astrophysics Data System (ADS)

Dey, S.; Saksena, S.; Merwade, V.

2017-12-01

Digital Elevation Models (DEMs) have an incomplete representation of river bathymetry, which is critical for simulating river hydrodynamics in flood modeling. Generally, DEMs are augmented with field collected bathymetry data, but such data are available only at individual reaches. Creating a hydrodynamic model covering an entire stream network in the basin requires bathymetry for all streams. This study extends a conceptual bathymetry model, River Channel Morphology Model (RCMM), to estimate the bathymetry for an entire stream network for application in hydrodynamic modeling using a DEM. It is implemented at two large watersheds with different relief and land use characterizations: coastal Guadalupe River basin in Texas with flat terrain and a relatively urban White River basin in Indiana with more relief. After bathymetry incorporation, both watersheds are modeled using HEC-RAS (1D hydraulic model) and Interconnected Pond and Channel Routing (ICPR), a 2-D integrated hydrologic and hydraulic model. A comparison of the streamflow estimated by ICPR at the outlet of the basins indicates that incorporating bathymetry influences streamflow estimates. The inundation maps show that bathymetry has a higher impact on flat terrains of Guadalupe River basin when compared to the White River basin.

Relativistic Gurzhi effect in channels of Dirac materials

NASA Astrophysics Data System (ADS)

Kashuba, Oleksiy; Trauzettel, Björn; Molenkamp, Laurens W.

2018-05-01

Charge transport in channel-shaped 2D Dirac systems is studied employing the Boltzmann equation. The dependence of the resistivity on temperature and chemical potential is investigated. An accurate understanding of the influence of electron-electron interaction and material disorder allows us to identify a parameter regime, where the system reveals hydrodynamic transport behavior. We point out the conditions for three Dirac fermion specific features: heat flow hydrodynamics, pseudodiffusive transport, and the electron-hole scattering dominated regime. It is demonstrated that for clean samples the relativistic Gurzhi effect, a definite indicator of hydrodynamic transport, can be observed.

Numerical modeling of hydrodynamics and sediment transport at diversions: why depth-averaged models are not able to capture the inherent physics

NASA Astrophysics Data System (ADS)

Dutta, S.; Tassi, P.; Fischer, P.; Wang, D.; Garcia, M. H.

2016-12-01

Diversions are a subset of asymmetric bifurcations, where one of the channels after bifurcation continues along the direction of the original channel, often referred to as the main-channel. Diversions are not only built for river-engineering purposes, e.g. navigational canals, channels to divert water and sediment to rebuild deltas etc.; they can also be formed naturally, e.g. chute cutoffs. Thus correct prediction of the hydrodynamics and sediment transport at a diversion is essential. One of the first extensive studies on diversion was conducted by Bulle [1926], where it was found that compared to discharge of water; a disproportionately higher amount of bed-load sediment entered the lateral-channel at the diversion. Hence, this phenomenon is known as the Bulle-Effect. Recent studies have used high-resolution Large Eddy Simulation (LES) [Dutta et al., 2016a] and Reynolds Averaged Navier-Stokes (RANS) based three-dimensional hydrodynamics model [Dutta et al., 2016b] to unravel the mechanism behind the aforementioned non-linear phenomenon. Such studies have shown that the Bulle-Effect is caused by a stark difference between the flow structure near the bottom of a channel, and near the top of a channel. These findings hint towards the possible failure of 2D shallow water based numerical models in simulating the hydrodynamics and the sediment transport at a diversion correctly. The current study analyzes the hydrodynamics and sediment transport at a 90-degree diversion across five different models of increasing complexity, starting from a 2D depth-averaged hydrodynamics model to a high-resolution LES. This comparative study will provide a clear indication of the minimum amount of complexity a model should inculcate in order to capture the Bulle-Effect relatively well. Bulle, (1926), Untersuchungen ber die geschiebeableitung bei der spaltung von wasserlufen, Technical Report, V.D.I. Verlag, Berlin, Germany Dutta et al., (2016), Large Eddy Simulation (LES) of flow and

Connections between centrifugal, stratorotational, and radiative instabilities in viscous Taylor-Couette flow

NASA Astrophysics Data System (ADS)

Leclercq, Colin; Nguyen, Florian; Kerswell, Rich R.

2016-10-01

The "Rayleigh line" μ =η2 , where μ =Ωo/Ωi and η =ri/ro are respectively the rotation and radius ratios between inner (subscript i ) and outer (subscript o ) cylinders, is regarded as marking the limit of centrifugal instability (CI) in unstratified inviscid Taylor-Couette flow, for both axisymmetric and nonaxisymmetric modes. Nonaxisymmetric stratorotational instability (SRI) is known to set in for anticyclonic rotation ratios beyond that line, i.e., η2<μ <1 for axially stably stratified Taylor-Couette flow, but the competition between CI and SRI in the range μ <η2 has not yet been addressed. In this paper, we establish continuous connections between the two instabilities at finite Reynolds number Re, as previously suggested by Le Bars and Le Gal [Phys. Rev. Lett. 99, 064502 (2007), 10.1103/PhysRevLett.99.064502], making them indistinguishable at onset. Both instabilities are also continuously connected to the radiative instability at finite Re. These results demonstrate the complex impact viscosity has on the linear stability properties of this flow. Several other qualitative differences with inviscid theory were found, among which are the instability of a nonaxisymmetric mode localized at the outer cylinder without stratification and the instability of a mode propagating against the inner cylinder rotation with stratification. The combination of viscosity and stratification can also lead to a "collision" between (axisymmetric) Taylor vortex branches, causing the axisymmetric oscillatory state already observed in past experiments. Perhaps more surprising is the instability of a centrifugal-like helical mode beyond the Rayleigh line, caused by the joint effects of stratification and viscosity. The threshold μ =η2 seems to remain, however, an impassable instability limit for axisymmetric modes, regardless of stratification, viscosity, and even disturbance amplitude.

Stochastic characteristics and Second Law violations of atomic fluids in Couette flow

NASA Astrophysics Data System (ADS)

Raghavan, Bharath V.; Karimi, Pouyan; Ostoja-Starzewski, Martin

2018-04-01

Using Non-equilibrium Molecular Dynamics (NEMD) simulations, we study the statistical properties of an atomic fluid undergoing planar Couette flow, in which particles interact via a Lennard-Jones potential. We draw a connection between local density contrast and temporal fluctuations in the shear stress, which arise naturally through the equivalence between the dissipation function and entropy production according to the fluctuation theorem. We focus on the shear stress and the spatio-temporal density fluctuations and study the autocorrelations and spectral densities of the shear stress. The bispectral density of the shear stress is used to measure the degree of departure from a Gaussian model and the degree of nonlinearity induced in the system owing to the applied strain rate. More evidence is provided by the probability density function of the shear stress. We use the Information Theory to account for the departure from Gaussian statistics and to develop a more general probability distribution function that captures this broad range of effects. By accounting for negative shear stress increments, we show how this distribution preserves the violations of the Second Law of Thermodynamics observed in planar Couette flow of atomic fluids, and also how it captures the non-Gaussian nature of the system by allowing for non-zero higher moments. We also demonstrate how the temperature affects the band-width of the shear-stress and how the density affects its Power Spectral Density, thus determining the conditions under which the shear-stress acts is a narrow-band or wide-band random process. We show that changes in the statistical characteristics of the parameters of interest occur at a critical strain rate at which an ordering transition occurs in the fluid causing shear thinning and affecting its stability. A critical strain rate of this kind is also predicted by the Loose-Hess stability criterion.

On the linear stability of compressible plane Couette flow

NASA Technical Reports Server (NTRS)

Duck, Peter W.; Erlebacher, Gordon; Hussaini, M. Yousuff

1991-01-01

The linear stability of compressible plane Couette flow is investigated. The correct and proper basic velocity and temperature distributions are perturbed by a small amplitude normal mode disturbance. The full small amplitude disturbance equations are solved numerically at finite Reynolds numbers, and the inviscid limit of these equations is then investigated in some detail. It is found that instability can occur, although the stability characteristics of the flow are quite different from unbounded flows. The effects of viscosity are also calculated, asymptotically, and shown to have a stabilizing role in all the cases investigated. Exceptional regimes to the problem occur when the wavespeed of the disturbances approaches the velocity of either of the walls, and these regimes are also analyzed in some detail. Finally, the effect of imposing radiation-type boundary conditions on the upper (moving) wall (in place of impermeability) is investigated, and shown to yield results common to both bounded and unbounded flows.

Protein fiber linear dichroism for structure determination and kinetics in a low-volume, low-wavelength couette flow cell.

PubMed

Dafforn, Timothy R; Rajendra, Jacindra; Halsall, David J; Serpell, Louise C; Rodger, Alison

2004-01-01

High-resolution structure determination of soluble globular proteins relies heavily on x-ray crystallography techniques. Such an approach is often ineffective for investigations into the structure of fibrous proteins as these proteins generally do not crystallize. Thus investigations into fibrous protein structure have relied on less direct methods such as x-ray fiber diffraction and circular dichroism. Ultraviolet linear dichroism has the potential to provide additional information on the structure of such biomolecular systems. However, existing systems are not optimized for the requirements of fibrous proteins. We have designed and built a low-volume (200 microL), low-wavelength (down to 180 nm), low-pathlength (100 microm), high-alignment flow-alignment system (couette) to perform ultraviolet linear dichroism studies on the fibers formed by a range of biomolecules. The apparatus has been tested using a number of proteins for which longer wavelength linear dichroism spectra had already been measured. The new couette cell has also been used to obtain data on two medically important protein fibers, the all-beta-sheet amyloid fibers of the Alzheimer's derived protein Abeta and the long-chain assemblies of alpha1-antitrypsin polymers.

State diagram of a three-sphere microswimmer in a channel

NASA Astrophysics Data System (ADS)

Daddi-Moussa-Ider, Abdallah; Lisicki, Maciej; Mathijssen, Arnold J. T. M.; Hoell, Christian; Goh, Segun; Bławzdziewicz, Jerzy; Menzel, Andreas M.; Löwen, Hartmut

2018-06-01

Geometric confinements are frequently encountered in soft matter systems and in particular significantly alter the dynamics of swimming microorganisms in viscous media. Surface-related effects on the motility of microswimmers can lead to important consequences in a large number of biological systems, such as biofilm formation, bacterial adhesion and microbial activity. On the basis of low-Reynolds-number hydrodynamics, we explore the state diagram of a three-sphere microswimmer under channel confinement in a slit geometry and fully characterize the swimming behavior and trajectories for neutral swimmers, puller- and pusher-type swimmers. While pushers always end up trapped at the channel walls, neutral swimmers and pullers may further perform a gliding motion and maintain a stable navigation along the channel. We find that the resulting dynamical system exhibits a supercritical pitchfork bifurcation in which swimming in the mid-plane becomes unstable beyond a transition channel height while two new stable limit cycles or fixed points that are symmetrically disposed with respect to the channel mid-height emerge. Additionally, we show that an accurate description of the averaged swimming velocity and rotation rate in a channel can be captured analytically using the method of hydrodynamic images, provided that the swimmer size is much smaller than the channel height.

Couette shear of an ideal 2D photo-elastic granular system

NASA Astrophysics Data System (ADS)

Wang, Meimei; Zheng, Hu; BaréS, Jonathan; Wang, Dong; Behringe, Robert

In this study, Couette shear experiments are conducted using 2D photoelastic granular particles, which allows us to apply infinite shear strain to the granular system. We obtain force information st the granular scale using the calibrated photo-elastic grain force response. The whole granular system is density matched in salt solution, which guarantees an ideal 2D system without basal friction between the particles and the table. The viscosity is negligible at the very small shear strain rate (0.017 rpm). This talk will address two main points: i) how does the system reach a jammed state; ii) how does system reach a long term stable state and what are the properties of that state. NSF Grant No. DMR1206351, NASA Grant No. NNX15AD38G and the W.M. Keck Foundation.

Characterising experimental time series using local intrinsic dimension

NASA Astrophysics Data System (ADS)

Buzug, Thorsten M.; von Stamm, Jens; Pfister, Gerd

1995-02-01

Experimental strange attractors are analysed with the averaged local intrinsic dimension proposed by A. Passamante et al. [Phys. Rev. A 39 (1989) 3640] which is based on singular value decomposition of local trajectory matrices. The results are compared to the values of Kaplan-Yorke and the correlation dimension. The attractors, reconstructed with Takens' delay time coordinates from scalar velocity time series, are measured in the hydrodynamic Taylor-Couette system. A period doubling route towards chaos obtained from a very short Taylor-Couette cylinder yields a sequence of experimental time series where the local intrinsic dimension is applied.

Lattice Boltzmann simulation of asymmetric flow in nematic liquid crystals with finite anchoring

NASA Astrophysics Data System (ADS)

Zhang, Rui; Roberts, Tyler; Aranson, Igor S.; de Pablo, Juan J.

2016-02-01

Liquid crystals (LCs) display many of the flow characteristics of liquids but exhibit long range orientational order. In the nematic phase, the coupling of structure and flow leads to complex hydrodynamic effects that remain to be fully elucidated. Here, we consider the hydrodynamics of a nematic LC in a hybrid cell, where opposite walls have conflicting anchoring boundary conditions, and we employ a 3D lattice Boltzmann method to simulate the time-dependent flow patterns that can arise. Due to the symmetry breaking of the director field within the hybrid cell, we observe that at low to moderate shear rates, the volumetric flow rate under Couette and Poiseuille flows is different for opposite flow directions. At high shear rates, the director field may undergo a topological transition which leads to symmetric flows. By applying an oscillatory pressure gradient to the channel, a net volumetric flow rate is found to depend on the magnitude and frequency of the oscillation, as well as the anchoring strength. Taken together, our findings suggest several intriguing new applications for LCs in microfluidic devices.

Field-flow fractionation and hydrodynamic chromatography on a microfluidic chip.

PubMed

Shendruk, Tyler N; Tahvildari, Radin; Catafard, Nicolas M; Andrzejewski, Lukasz; Gigault, Christian; Todd, Andrew; Gagne-Dumais, Laurent; Slater, Gary W; Godin, Michel

2013-06-18

We present gravitational field-flow fractionation and hydrodynamic chromatography of colloids eluting through 18 μm microchannels. Using video microscopy and mesoscopic simulations, we investigate the average retention ratio of colloids with both a large specific weight and neutral buoyancy. We consider the entire range of colloid sizes, including particles that barely fit in the microchannel and nanoscopic particles. Ideal theory predicts four operational modes, from hydrodynamic chromatography to Faxén-mode field-flow fractionation. We experimentally demonstrate, for the first time, the existence of the Faxén-mode field-flow fractionation and the transition from hydrodynamic chromatography to normal-mode field-flow fractionation. Furthermore, video microscopy and simulations show that the retention ratios are largely reduced above the steric-inversion point, causing the variation of the retention ratio in the steric- and Faxén-mode regimes to be suppressed due to increased drag. We demonstrate that theory can accurately predict retention ratios if hydrodynamic interactions with the microchannel walls (wall drag) are added to the ideal theory. Rather than limiting the applicability, these effects allow the microfluidic channel size to be tuned to ensure high selectivity. Our findings indicate that particle velocimetry methods must account for the wall-induced lag when determining flow rates in highly confining systems.

Screening effects in flow through rough channels.

PubMed

Andrade, J S; Araújo, A D; Filoche, M; Sapoval, B

2007-05-11

A surprising similarity is found between the distribution of hydrodynamic stress on the wall of an irregular channel and the distribution of flux from a purely Laplacian field on the same geometry. This finding is a direct outcome of numerical simulations of the Navier-Stokes equations for flow at low Reynolds numbers in two-dimensional channels with rough walls presenting either deterministic or random self-similar geometries. For high Reynolds numbers, the distribution of wall stresses on deterministic and random fractal rough channels becomes substantially dependent on the microscopic details of the walls geometry. Finally, the effects on the flow behavior of the channel symmetry and aspect ratio are also investigated.

Linear dichroism of DNA: Characterization of the orientation distribution function caused by hydrodynamic shear

DOE PAGES

Sutherland, John C.

2017-04-15

Linear dichroism provides information on the orientation of chromophores part of, or bound to, an orientable molecule such as DNA. For molecular alignment induced by hydrodynamic shear, the principal axes orthogonal to the direction of alignment are not equivalent. Thus, the magnitude of the flow-induced change in absorption for light polarized parallel to the direction of flow can be more than a factor of two greater than the corresponding change for light polarized perpendicular to both that direction and the shear axis. The ratio of the two flow-induced changes in absorption, the dichroic increment ratio, is characterized using the orthogonalmore » orientation model, which assumes that each absorbing unit is aligned parallel to one of the principal axes of the apparatus. The absorption of the alienable molecules is characterized by components parallel and perpendicular to the orientable axis of the molecule. The dichroic increment ratio indicates that for the alignment of DNA in rectangular flow cells, average alignment is not uniaxial, but for higher shear, as produced in a Couette cell, it can be. The results from the simple model are identical to tensor models for typical experimental configuration. Approaches for measuring the dichroic increment ratio with modern dichrometers are further discussed.« less

Linear dichroism of DNA: Characterization of the orientation distribution function caused by hydrodynamic shear

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sutherland, John C.

Linear dichroism provides information on the orientation of chromophores part of, or bound to, an orientable molecule such as DNA. For molecular alignment induced by hydrodynamic shear, the principal axes orthogonal to the direction of alignment are not equivalent. Thus, the magnitude of the flow-induced change in absorption for light polarized parallel to the direction of flow can be more than a factor of two greater than the corresponding change for light polarized perpendicular to both that direction and the shear axis. The ratio of the two flow-induced changes in absorption, the dichroic increment ratio, is characterized using the orthogonalmore » orientation model, which assumes that each absorbing unit is aligned parallel to one of the principal axes of the apparatus. The absorption of the alienable molecules is characterized by components parallel and perpendicular to the orientable axis of the molecule. The dichroic increment ratio indicates that for the alignment of DNA in rectangular flow cells, average alignment is not uniaxial, but for higher shear, as produced in a Couette cell, it can be. The results from the simple model are identical to tensor models for typical experimental configuration. Approaches for measuring the dichroic increment ratio with modern dichrometers are further discussed.« less

Linear dichroism of DNA: Characterization of the orientation distribution function caused by hydrodynamic shear.

PubMed

Sutherland, John C

2017-04-15

Linear dichroism provides information on the orientation of chromophores part of, or bound to, an orientable molecule such as DNA. For molecular alignment induced by hydrodynamic shear, the principal axes orthogonal to the direction of alignment are not equivalent. Thus, the magnitude of the flow-induced change in absorption for light polarized parallel to the direction of flow can be more than a factor of two greater than the corresponding change for light polarized perpendicular to both that direction and the shear axis. The ratio of the two flow-induced changes in absorption, the dichroic increment ratio, is characterized using the orthogonal orientation model, which assumes that each absorbing unit is aligned parallel to one of the principal axes of the apparatus. The absorption of the alienable molecules is characterized by components parallel and perpendicular to the orientable axis of the molecule. The dichroic increment ratio indicates that for the alignment of DNA in rectangular flow cells, average alignment is not uniaxial, but for higher shear, as produced in a Couette cell, it can be. The results from the simple model are identical to tensor models for typical experimental configurations. Approaches for measuring the dichroic increment ratio with modern dichrometers are discussed. Copyright © 2017. Published by Elsevier Inc.

Changing tidal hydrodynamics during different stages of eco-geomorphological development of a tidal marsh: A numerical modeling study

NASA Astrophysics Data System (ADS)

Stark, J.; Meire, P.; Temmerman, S.

2017-03-01

The eco-geomorphological development of tidal marshes, from initially low-elevated bare tidal flats up to a high-elevated marsh and its typical network of channels and creeks, induces long-term changes in tidal hydrodynamics in a marsh, which will have feedback effects on the marsh development. We use a two-dimensional hydrodynamic model of the Saeftinghe marsh (Netherlands) to study tidal hydrodynamics, and tidal asymmetry in particular, for model scenarios with different input bathymetries and vegetation coverages that represent different stages of eco-geomorphological marsh development, from a low elevation stage with low vegetation coverage to a high and fully vegetated marsh platform. Tidal asymmetry is quantified along a 4 km marsh channel by (1) the difference in peak flood and peak ebb velocities, (2) the ratio between duration of the rising tide and the falling tide and (3) the time-integrated dimensionless bed shear stress during flood and ebb. Although spatial variations in tidal asymmetry are large and the different indicators for tidal asymmetry do not always respond similarly to eco-geomorphological changes, some general trends can be obtained. Flood-dominance prevails during the initial bare stage of a low-lying tidal flat. Vegetation establishment and platform expansion lead to marsh-scale flow concentration to the bare channels, causing an increase in tidal prism in the channels along with a less flood-dominant asymmetry of the horizontal tide. The decrease in flood-dominance continues as the platform grows vertically and the sediment-demand of the platform decreases. However, when the platform elevation gets sufficiently high in the tidal frame and part of the spring-neap cycle is confined to the channels, the discharge in the channels decreases and tidal asymmetry becomes more flood-dominant again, indicating an infilling of the marsh channels. Furthermore, model results suggest that hydro-morphodynamic feedbacks based on tidal prism to channel

Superhydrophobic nanofluidic channels for enhanced electrokinetic conversion

NASA Astrophysics Data System (ADS)

Checco, Antonio; Al Hossain, Aktaruzzaman; Rahmani, Amir; Black, Charles; Doerk, Gregory; Colosqui, Carlos

2017-11-01

We present current efforts in the development of novel slit nanofluidic channels with superhydrophobic nanostructured surfaces designed to enhance hydrodynamic conductivity and improve selective transport and electrokinetic energy conversion efficiencies (mechanical-electrical energy conversion). The nanochannels are fabricated on silicon wafers using UV lithography, and their internal surface is patterned with conical nanostructures (feature size and spacing 30 nm) defined by block copolymer self-assembly and plasma etching. These nanostructures are rendered superhydrophobic by passivation with a hydrophobic silane monolayer. We experimentally characterize hydrodynamic conductivity, effective zeta potentials, and eletrokinetic flows for the patterned nanochannels, comparing against control channels with bare surfaces. Experimental observations are rationalized using both continuum-based modeling and molecular dynamics simulations. Scientific and technical knowledge produced by this work is particularly relevant for sustainable energy conversion and storage, separation processes and water treatment using nanoporous materials. The ONR Contract # N000141613178 and NSF-CBET award# 1605809.

Hydrodynamics, vegetation transition and geomorphology coevolution in a semi-arid floodplain wetland.

NASA Astrophysics Data System (ADS)

Sandi, Steven; Rodriguez, Jose F.; Saco, Patricia M.; Riccardi, Gerardo; Wen, Li; Saintilan, Neil

2016-04-01

The Macquarie Marshes is a complex system of marshes, swamps and lagoons interconnected by a network of streams in the semi-arid region in north western NSW, Australia. The low-gradient topography of the site leads to channel breakdown processes where the river network becomes practically non-existent. As a result, the flow extends over large areas of wetland that later re-join and reform channels exiting the system. Vegetation in semiarid wetlands are often water dependent and flood tolerant species that rely on periodical floods in order to maintain healthy conditions. The detrimental state of vegetation in the Macquarie Marshes over the past few decades has been linked to decreasing inundation frequencies. Spatial distribution of flood tolerant overstory species such as River Red Gum and Black Box has not greatly changed since early 1990's, however; the condition of the vegetation patches shows a clear deterioration evidenced by terrestrial species encroachment on the wetland understory. On the other hand, areas of flood dependent species such as Water Couch and Common Reed have undergone complete succession to terrestrial species and dryland. In order to simulate the complex dynamics of the marshes we have developed an ecogeomorphological modelling framework that combines hydrodynamic, vegetation and channel evolution modules and in this presentation we provide an update on the status of the model. The hydrodynamic simulation provides spatially distributed values of inundation extent, duration, depth and recurrence to drive a vegetation model based on species preference to hydraulic conditions. It also provides velocities and shear stresses to assess geomorphological changes. Regular updates of stream network, floodplain surface elevations and vegetation coverage provide feedbacks to the hydrodynamic model. We presents also the development and assessment of transitional rules to determine if the water conditions have been met for different vegetation

Couette shear of an ideal 2D photo-elastic granular system

NASA Astrophysics Data System (ADS)

Behringer, Robert; Zheng, Hu; Barés, Jonathan; Wang, Dong

2016-11-01

In this study, Couette shear experiments are conducted using 2D photoelastic granular particles, which allows us to apply infinite shear strain to the granular system. We obtain force information at the granular scale using the calibrated photo-elastic grain force response. The whole granular system is density matched in salt solution, which guarantees an ideal 2D system without basal friction between the particles and the table. The viscosity is negligible at the very small shear strain rate (0.017 rpm). This talk will address two main points: i) how does the system reach a jammed state; ii) how does system reach a long term stable state and what are the properties of that state. We acknowledge support from NSF Grant No. DMR1206351, NASA Grant No. NNX15AD38G and the W.M. Keck Foundation.

Instability-induced ordering, universal unfolding and the role of gravity in granular Couette flow

NASA Astrophysics Data System (ADS)

Alam, Meheboob; Arakeri, V. H.; Nott, P. R.; Goddard, J. D.; Herrmann, H. J.

2005-01-01

Linear stability theory and bifurcation analysis are used to investigate the role of gravity in shear-band formation in granular Couette flow, considering a kinetic-theory rheological model. We show that the only possible state, at low shear rates, corresponds to a "plug" near the bottom wall, in which the particles are densely packed and the shear rate is close to zero, and a uniformly sheared dilute region above it. The origin of such plugged states is shown to be tied to the spontaneous symmetry-breaking instabilities of the gravity-free uniform shear flow, leading to the formation of ordered bands of alternating dilute and dense regions in the transverse direction, via an infinite hierarchy of pitchfork bifurcations. Gravity plays the role of an "imperfection", thus destroying the "perfect" bifurcation structure of uniform shear. The present bifurcation problem admits universal unfolding of pitchfork bifurcations which subsequently leads to the formation of a sequence of a countably infinite number of "isolas", with the solution structures being a modulated version of their gravity-free counterpart. While the solution with a plug near the bottom wall looks remarkably similar to the shear-banding phenomenon in dense slow granular Couette flows, a "floating" plug near the top wall is also a solution of these equations at high shear rates. A two-dimensional linear stability analysis suggests that these floating plugged states are unstable to long-wave travelling disturbances.The unique solution having a bottom plug can also be unstable to long waves, but remains stable at sufficiently low shear rates. The implications and realizability of the present results are discussed in the light of shear-cell experiments under "microgravity" conditions.

Direct Simulation Monte Carlo Investigation of Noncontinuum Couette Flow

NASA Astrophysics Data System (ADS)

Torczynski, J. R.; Gallis, M. A.

2009-11-01

The Direct Simulation Monte Carlo (DSMC) method of molecular gas dynamics is used to study noncontinuum effects in Couette flow. The walls have equal temperatures and equal accommodation coefficients but unequal tangential velocities. Simulations are performed for near-free-molecular to near-continuum gas pressures with accommodation coefficients of 0.25, 0.5, and 1. Ten gases are examined: argon, helium, nitrogen, sea-level air, and six Inverse-Power-Law (IPL) gases with viscosity temperature exponents of 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0, as represented by the Variable Soft Sphere (VSS) interaction. In all cases, the wall shear stress is proportional to the slip velocity. The momentum transfer coefficient relating these two quantities can be accurately correlated in terms of the Knudsen number based on the wall separation. The two dimensionless parameters in the correlation are similar for all gases examined. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Hydrodynamic lift for single cell manipulation in a femtosecond laser fabricated optofluidic chip

NASA Astrophysics Data System (ADS)

Bragheri, Francesca; Osellame, Roberto

2017-08-01

Single cell sorting based either on fluorescence or on mechanical properties has been exploited in the last years in microfluidic devices. Hydrodynamic focusing allows increasing the efficiency of theses devices by improving the matching between the region of optical analysis and that of cell flow. Here we present a very simple solution fabricated by femtosecond laser micromachining that exploits flow laminarity in microfluidic channels to easily lift the sample flowing position to the channel portion illuminated by the optical waveguides used for single cell trapping and analysis.

Impacts of variable channel hydraulics on the stratigraphic record: an example provided from the Tullig Sandstone, Western Irish Namurian Basin

NASA Astrophysics Data System (ADS)

Wu, C.; Nittrouer, J. A.; Burmeister, K. C.

2017-12-01

River hydrodynamic conditions are modified where a system approaches its terminal basin, characterized by the onset of non-uniform "backwater" flow. A decrease in boundary shear stress in the backwater region reduces transport capacity and results in sediment deposition on the channel bed. Although such morphodynamic conditions are common in modern fluvial-deltaic channels, the extent to which these processes are prevalent in the stratigraphic record remains unclear. For example, a few studies documenting changes in fluvial sandstone channel dimensions and grain size distributions near a river terminus attributed this variability to backwater hydrodynamics. However, quantitative tests using morphodynamic models bolstered by a variety of field observations, which could then be linked to sediment depositional patterns and stratigraphy, have yet to be produced. Here we calibrate a one-dimensional river flow model with measurements of paleo-slope and channel depth, and use the output to constrain a sediment transport model, with data from the Tullig Sandstone in the Western Irish Namurian Basin. Based on the model results, our analyses indicate that: (1) backwater hydrodynamics influence the spatial variation of sandstone dimensions and grain size across the delta, and (2) backwater hydrodynamics drive channel bed aggradation and progradation of the river mouth for conditions of constant sea level. Field data indicate that the reach-average story thickness increases, and then decreases, progressing downstream over the backwater reach. Based on the inferred transport and depositional processes, the measured deltaic stratigraphy patterns shown here are assumed to be associated with backwater hydrodynamics, and are therefore largely autogenic in origin. These analyses indicate that non-uniform hydrodynamics can generate stratigraphic patterns that could be conflated as arising due to allogenic effects, based on traditional geometric or diffusion-based depositional models

Stabilization of Taylor-Couette flow due to time-periodic outer cylinder oscillation

NASA Technical Reports Server (NTRS)

Murray, B. T.; Mcfadden, G. B.; Coriell, S. R.

1990-01-01

The linear stability of circular Couette flow between concentric infinite cylinders is considered for the case when the inner cylinder is rotated at a constant angular velocity and the outer cylinder is driven sinusoidally in time with zero mean rotation. This configuration was studied experimentally by Walsh and Donnelly. The critical Reynolds numbers calculated from linear stability theory agree well with the experimental values, except at large modulation amplitudes and small frequencies. The theoretical values are obtained using Floquet theory implemented in two distinct approaches: a truncated Fourier series representation in time, and a fundamental solution matrix based on a Chebyshev pseudospectral representation in space. For large amplitude, low frequency modulation, the linear eigenfunctions are temporally complex, consisting of a quiescent region followed by rapid change in the perturbed flow velocities.

Model microswimmers in channels with varying cross section

NASA Astrophysics Data System (ADS)

Malgaretti, Paolo; Stark, Holger

2017-05-01

We study different types of microswimmers moving in channels with varying cross section and thereby interacting hydrodynamically with the channel walls. Starting from the Smoluchowski equation for a dilute suspension, for which interactions among swimmers can be neglected, we derive analytic expressions for the lateral probability distribution between plane channel walls. For weakly corrugated channels, we extend the Fick-Jacobs approach to microswimmers and thereby derive an effective equation for the probability distribution along the channel axis. Two regimes arise dominated either by entropic forces due to the geometrical confinement or by the active motion. In particular, our results show that the accumulation of microswimmers at channel walls is sensitive to both the underlying swimming mechanism and the geometry of the channels. Finally, for asymmetric channel corrugation, our model predicts a rectification of microswimmers along the channel, the strength and direction of which strongly depends on the swimmer type.

Helical magnetorotational instability in magnetized Taylor-Couette flow.

PubMed

Liu, Wei; Goodman, Jeremy; Herron, Isom; Ji, Hantao

2006-11-01

Hollerbach and Rüdiger have reported a new type of magnetorotational instability (MRI) in magnetized Taylor-Couette flow in the presence of combined axial and azimuthal magnetic fields. The salient advantage of this "helical" MRI (HMRI) is that marginal instability occurs at arbitrarily low magnetic Reynolds and Lundquist numbers, suggesting that HMRI might be easier to realize than standard MRI (axial field only), and that it might be relevant to cooler astrophysical disks, especially those around protostars, which may be quite resistive. We confirm previous results for marginal stability and calculate HMRI growth rates. We show that in the resistive limit, HMRI is a weakly destabilized inertial oscillation propagating in a unique direction along the axis. But we report other features of HMRI that make it less attractive for experiments and for resistive astrophysical disks. Large axial currents are required. More fundamentally, instability of highly resistive flow is peculiar to infinitely long or periodic cylinders: finite cylinders with insulating endcaps are shown to be stable in this limit, at least if viscosity is neglected. Also, Keplerian rotation profiles are stable in the resistive limit regardless of axial boundary conditions. Nevertheless, the addition of a toroidal field lowers thresholds for instability even in finite cylinders.

Propulsion and hydrodynamic particle transport of magnetically twisted colloidal ribbons

NASA Astrophysics Data System (ADS)

Massana-Cid, Helena; Martinez-Pedrero, Fernando; Navarro-Argemí, Eloy; Pagonabarraga, Ignacio; Tierno, Pietro

2017-10-01

We describe a method to trap, transport and release microscopic particles in a viscous fluid using the hydrodynamic flow field generated by a magnetically propelled colloidal ribbon. The ribbon is composed of ferromagnetic microellipsoids that arrange with their long axis parallel to each other, a configuration that is energetically favorable due to their permanent magnetic moments. We use an external precessing magnetic field to torque the anisotropic particles forming the ribbon, and to induce propulsion of the entire structure due to the hydrodynamic coupling with the close substrate. The propulsion speed of the ribbon can be controlled by varying the driving frequency, or the amplitude of the precessing field. The latter parameter is also used to reduce the average inter particle distance and to induce the twisting of the ribbon due to the increase in the attraction between the rotating ellipsoids. Furthermore, non magnetic particles are attracted or repelled with the hydrodynamic flow field generated by the propelling ribbon. The proposed method may be used in channel free microfluidic applications, where the precise trapping and transport of functionalized particles via non invasive magnetic fields is required.

Heat transport in Rayleigh-Bénard convection and angular momentum transport in Taylor-Couette flow: a comparative study

NASA Astrophysics Data System (ADS)

Brauckmann, Hannes J.; Eckhardt, Bruno; Schumacher, Jörg

2017-03-01

Rayleigh-Bénard convection and Taylor-Couette flow are two canonical flows that have many properties in common. We here compare the two flows in detail for parameter values where the Nusselt numbers, i.e. the thermal transport and the angular momentum transport normalized by the corresponding laminar values, coincide. We study turbulent Rayleigh-Bénard convection in air at Rayleigh number Ra=107 and Taylor-Couette flow at shear Reynolds number ReS=2×104 for two different mean rotation rates but the same Nusselt numbers. For individual pairwise related fields and convective currents, we compare the probability density functions normalized by the corresponding root mean square values and taken at different distances from the wall. We find one rotation number for which there is very good agreement between the mean profiles of the two corresponding quantities temperature and angular momentum. Similarly, there is good agreement between the fluctuations in temperature and velocity components. For the heat and angular momentum currents, there are differences in the fluctuations outside the boundary layers that increase with overall rotation and can be related to differences in the flow structures in the boundary layer and in the bulk. The study extends the similarities between the two flows from global quantities to local quantities and reveals the effects of rotation on the transport.

Relativistic anisotropic hydrodynamics

NASA Astrophysics Data System (ADS)

Alqahtani, Mubarak; Nopoush, Mohammad; Strickland, Michael

2018-07-01

In this paper we review recent progress in relativistic anisotropic hydrodynamics. We begin with a pedagogical introduction to the topic which takes into account the advances in our understanding of this topic since its inception. We consider both conformal and non-conformal systems and demonstrate how one can implement a realistic equation of state using a quasiparticle approach. We then consider the inclusion of non-spheroidal (non-ellipsoidal) corrections to leading-order anisotropic hydrodynamics and present the findings of the resulting second-order viscous anisotropic hydrodynamics framework. We compare the results obtained in both the conformal and non-conformal cases with exact solutions to the Boltzmann equation and demonstrate that, in all known cases, anisotropic hydrodynamics best reproduces the exact solutions. Based on this success, we then discuss the phenomenological application of anisotropic hydrodynamics. Along these lines, we review techniques which can be used to convert a momentum-space anisotropic fluid into hadronic degrees of freedom by generalizing the original idea of Cooper-Frye freeze-out to momentum-space anisotropic systems. And, finally, we present phenomenological results of 3 + 1 d quasiparticle anisotropic hydrodynamic simulations and compare them to experimental data produced in 2.76 TeV Pb-Pb collisions at the LHC. Our results indicate that anisotropic hydrodynamics provides a promising framework for describing the dynamics of the momentum-space anisotropic QGP created in heavy-ion collisions.

The Green's function in a channel with a sound-absorbing cover in the case of a uniform flow

NASA Astrophysics Data System (ADS)

Sobolev, A. F.

2012-07-01

We study the modal structure of an acoustic field of a point source as function of channel wall admittance in the case of a two-dimensional channel. The characteristic equation for determining the eigen-values corresponding to the boundary problem is studied in the form of this equation's dependence on the admittance, which varies in the entire complex plane. All modes, without exception, existing in the channel and forming the source field are classified based on the obtained topography of the characteristic equation. The expressions that describe the amplitudes and spatial distribution of the hydrodynamic modes, attenuation rate (for stable modes), or increment (for unstable modes) were obtained as functions of the wall admittance and flow velocity. It is shown that in addition to the hydrodynamic unstable modes existing downstream from the source, hydrodynamic unstable modes exist upstream from the source at any admittance. They appear only when the admittance has an elastic character. It is shown that hydrodynamic modes are induced only in the case when the source is located close to the wall or on the wall. The amplitude of these modes decreases exponentially with distance from the wall.

Numerical investigation of exact coherent structures in turbulent small-aspect-ratio Taylor-Couette flow

NASA Astrophysics Data System (ADS)

Krygier, Michael; Crowley, Christopher J.; Schatz, Michael F.; Grigoriev, Roman O.

2017-11-01

As suggested by recent theoretical and experimental studies, fluid turbulence can be described as a walk between neighborhoods of unstable nonchaotic solutions of the Navier-Stokes equation known as exact coherent structures (ECS). Finding ECS in an experimentally-accessible setting is the first step toward rigorous testing of the dynamical role of ECS in 3D turbulence. We found several ECS (both relative periodic orbits and relative equilibria) in a weakly turbulent regime of small-aspect-ratio Taylor-Couette flow with counter-rotating cylinders. This talk will discuss how the geometry of these solutions guides the evolution of turbulent flow in the simulations. This work is supported by the Army Research Office (Contract # W911NF-15-1-0471).

Molecular dynamics studies of polyethylene oxide and polyethylene glycol: hydrodynamic radius and shape anisotropy.

PubMed

Lee, Hwankyu; Venable, Richard M; Mackerell, Alexander D; Pastor, Richard W

2008-08-01

A revision (C35r) to the CHARMM ether force field is shown to reproduce experimentally observed conformational populations of dimethoxyethane. Molecular dynamics simulations of 9, 18, 27, and 36-mers of polyethylene oxide (PEO) and 27-mers of polyethylene glycol (PEG) in water based on C35r yield a persistence length lambda = 3.7 A, in quantitative agreement with experimentally obtained values of 3.7 A for PEO and 3.8 A for PEG; agreement with experimental values for hydrodynamic radii of comparably sized PEG is also excellent. The exponent upsilon relating the radius of gyration and molecular weight (R(g) proportional, variantM(w)(upsilon)) of PEO from the simulations equals 0.515 +/- 0.023, consistent with experimental observations that low molecular weight PEG behaves as an ideal chain. The shape anisotropy of hydrated PEO is 2.59:1.44:1.00. The dimension of the middle length for each of the polymers nearly equals the hydrodynamic radius R(h)obtained from diffusion measurements in solution. This explains the correspondence of R(h) and R(p), the pore radius of membrane channels: a polymer such as PEG diffuses with its long axis parallel to the membrane channel, and passes through the channel without substantial distortion.

The impact of channel capture on estuarine hydro-morphodynamics and water quality in the Amazon delta.

PubMed

Silva Dos Santos, Eldo; Pinheiro Lopes, Paula Patrícia; da Silva Pereira, Hyrla Herondina; de Oliveira Nascimento, Otávio; Rennie, Colin David; da Silveira Lobo O'Reilly Sternberg, Leonel; Cavalcanti da Cunha, Alan

2018-05-15

Due to progressive erosion of the new Urucurituba Channel, the Amazon River has recently captured almost all discharge from the lower Araguari River (Amapá-AP, Brazil), which previously flowed directly to the Atlantic Ocean. These recent geomorphological changes have caused strong impacts on the landscape and hydrodynamic patterns near the Araguari River mouth, especially the alteration of the riverine drainage system and its water quality. Landsat images were used to assess the estuarine landscape morphodynamic, particularly the expansion of the Urucurituba Channel, 80km from the Araguari River mouth, chronicling its connection to the Amazon River. The results suggest that the Urucurituba developed by headward migration across the Amazon delta; this is perhaps the first observation of estuarine distributary network development by headward channel erosion. The rate of Urucurituba Channel width increase has been ≈5m/month since 2011, increasing drainage capacity of the channel. We also collected in situ hydrodynamic measurements and analyzed 17 water quality parameters. Having 2011 as baseline, the flowrate of Araguari River has been diverted by up to 98% through Urucurituba Channel, with substantial changes in net discharge recorded at 3 monitoring stations. Statistically significant differences in water quality (p<0.05) were observed between 2011 and 2015, associated with the change in the flow pattern. Estuarine salinity and solids concentrations have increased. Overall, we demonstrate changes in landscape, hydrodynamics and water quality of the lower Araguari River. Copyright © 2017 Elsevier B.V. All rights reserved.

Modeling small-scale and large-scale flood wave processes as indicators of channel-floodplain connectivity

NASA Astrophysics Data System (ADS)

Byrne, C. F.; Stone, M. C.

2016-12-01

Anthropogenic alterations to rivers and floodplains, either in the context of river engineering or river restoration efforts, have no doubt impacted channel-floodplain connectivity in the majority of developed river systems. River management strategies now often strive to retain or improve ecological integrity of floodplains. Therefore, there is a need to quantify the hydrodynamic processes that have implications for river geomorphology and ecology within the channel-floodplain interface. Because field quantification of these processes is extremely difficult, new methods in hydrodynamic modeling can help to inform river science. This research focused on the assessment of channel-floodplain flow dynamics using two-dimensional hydrodynamic modeling and presents various methods of hydrodynamic process quantification in unsteady flow scenarios. The objectives of this research were to: (1) quantify the small-scale processes of mass and momentum transfer from the main channel to the floodplain; and (2) assess how these processes accrue to meaningful levels to affect the large-scale process of flood wave attenuation. This was achieved by modeling the heavily manipulated Albuquerque Reach of the Rio Grande in New Mexico. Results are presented as mass and momentum fluxes along the channel-floodplain boundaries with a focus on the application of these methods to unsteady flood wave modeling. In addition, quantification of downstream flood wave attenuation is presented as attenuation ratios of discharge and stage, as well as wave celerity. Mass and momentum fluxes during flood waves are shown to be highly variable over spatial and temporal scales and demonstrate the implications of lateral surface connectivity. Results from this research and further application of the methods presented here can help river scientists better understand the dynamics of flood processes especially in the context of process-based river restoration.

Rigid spherical particles in highly turbulent Taylor-Couette flow

NASA Astrophysics Data System (ADS)

Bakhuis, Dennis; Verschoof, Ruben A.; Mathai, Varghese; Huisman, Sander G.; Lohse, Detlef; Sun, Chao

2016-11-01

Many industrial and maritime processes are subject to enormous frictional losses. Reducing these losses even slightly will already lead to large financial and environmental benefits. The understanding of the underlying physical mechanism of frictional drag reduction is still limited, for example, in bubbly drag reduction there is an ongoing debate whether deformability and bubble size are the key parameters. In this experimental study we report high precision torque measurements using rigid non-deformable spherical particles in highly turbulent Taylor-Couette flow with Reynolds numbers up to 2 ×106 . The particles are made of polystyrene with an average density of 1.036 g cm-3 and three different diameters: 8mm, 4mm, and 1.5mm. Particle volume fractions of up to 6% were used. By varying the particle diameter, density ratio of the particles and the working fluid, and volume fraction of the particles, the effect on the torque is compared to the single phase case. These systematic measurements show that adding rigid spherical particles only results in very minor drag reduction. This work is financially supported by Netherlands Organisation for Scientific Research (NWO) by VIDI Grant Number 13477.

Hydrodynamic outcomes of planet scattering in transitional discs

NASA Astrophysics Data System (ADS)

Moeckel, Nickolas; Armitage, Philip J.

2012-01-01

A significant fraction of unstable multiple planet systems are likely to scatter during the transitional disc phase as gas damping becomes ineffectual. Using a large ensemble of FARGO hydrodynamic simulations and MERCURY N-body integrations, we directly follow the dynamics of planet-disc and planet-planet interactions through the clearing phase and through 50 Myr of planetary system evolution. Disc clearing is assumed to occur as a result of X-ray-driven photoevaporation. We find that the hydrodynamic evolution of individual scattering systems is complex, and can involve phases in which massive planets orbit within eccentric gaps, or accrete directly from the disc without a gap. Comparing the results to a reference gas-free model, we find that the N-body dynamics and hydrodynamics of scattering into one- and two-planet final states are almost identical. The eccentricity distributions in these channels are almost unaltered by the presence of gas. The hydrodynamic simulations, however, also form a population of low-eccentricity three-planet systems in long-term stable configurations, which are not found in N-body runs. The admixture of these systems results in modestly lower eccentricities in hydrodynamic as opposed to gas-free simulations. The precise incidence of these three-planet systems is likely a function of the initial conditions; different planet set-ups (number or spacing) may change the quantitative character of this result. We analyse the properties of surviving multiple planet systems, and show that only a small fraction (a few per cent) enter mean motion resonances after scattering, while a larger fraction form stable resonant chains and avoid scattering entirely. Our results remain consistent with the hypothesis that exoplanet eccentricity results from scattering, though the detailed agreement between observations and gas-free simulation results is likely coincidental. We discuss the prospects for further tests of scattering models by observing planets

Observation of chemiluminescence induced by hydrodynamic cavitation in microchannels.

PubMed

Podbevsek, D; Colombet, D; Ledoux, G; Ayela, F

2018-05-01

We have performed hydrodynamic cavitation experiments with an aqueous luminol solution as the working fluid. Light emission, together with the high frequency noise which characterizes cavitation, was emitted by the two-phase flow, whereas no light emission from luminol was recorded in the single phase liquid flow. Light emission occurs downstream transparent microdiaphragms. The maximum level of the recorded signal was around 180 photons per second with flow rates of 380 µl/s, that corresponds to a real order of magnitude of the chemiluminescence of 75,000 photons per second. The yield of emitted photons increases linearly with the pressure drop, which is proportional to the square of the total flow rate. Chemiluminescence of luminol is a direct and a quantitative demonstration of the presence of OH hydroxyl radicals created by hydrodynamic cavitation. The presented method could be a key to optimize channel geometry for processes where radical production is essential. Copyright © 2018 Elsevier B.V. All rights reserved.

Transient growth in Taylor-Couette flow of a Bingham fluid.

PubMed

Chen, Cheng; Wan, Zhen-Hua; Zhang, Wei-Guo

2015-04-01

In this paper we investigate linear transient growth of perturbation energy in Taylor-Couette flow of a Bingham fluid. The effects of yield stress on transient growth and the structure of the optimal perturbation are mainly considered for both the wide-gap case and the narrow-gap case. For this purpose we complement the linear stability of this flow subjected to axisymmetric disturbances, presented by Landry et al. [M. P. Landry, I. A. Frigaard, and D. M. Martinez, J. Fluid Mech. 560, 321 (2006)], with the transient growth characteristics of both axisymmetric and nonaxisymmetric perturbations. We obtain the variations of the relative amplitude of optimal perturbation with yield stress, analyze the roles played by the Coriolis force and the additional stress in the evolution of meridional perturbations for the axisymmetric modes, and give the explanations for the possible change of the optimal azimuthal mode (featured by the maximum optimal energy growth G(opt)) with yield stress. These results might help us in the understanding of the effect of fluid rheology on transient growth mechanism in vortex flows.

DIANA: A multi-phase, multi-component hydrodynamic model for the analysis of severe accidents in heavy water reactors with multiple-tube assemblies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tentner, A.M.

1994-03-01

A detailed hydrodynamic fuel relocation model has been developed for the analysis of severe accidents in Heavy Water Reactors with multiple-tube Assemblies. This model describes the Fuel Disruption and Relocation inside a nuclear fuel assembly and is designated by the acronym DIANA. DIANA solves the transient hydrodynamic equations for all the moving materials in the core and treats all the relevant flow regimes. The numerical solution techniques and some of the physical models included in DIANA have been developed taking advantage of the extensive experience accumulated in the development and validation of the LEVITATE (1) fuel relocation model of SAS4Amore » [2, 3]. The model is designed to handle the fuel and cladding relocation in both voided and partially voided channels. It is able to treat a wide range of thermal/ hydraulic/neutronic conditions and the presence of various flow regimes at different axial locations within the same hydrodynamic channel.« less

A mass-conservation-based approach to predicting river mouth channel bifurcations

NASA Astrophysics Data System (ADS)

Shaw, J.; McElroy, B. J.; Miller, K. L.

2015-12-01

Channel bifurcation is an important process in fluvio-deltaic morphodynamics and resulting stratigraphic architecture of prograding river deltas. We develop and test a new theory for the formation of channel bifurcations based on fluid mass conservation and system-averaged transport conditions rather than local hydrodynamics. We built 29 experimental deltas under a variety of boundary conditions to examine the inception and growth of bars and channel bifurcations. From the initial condition of water and sediment entering a still basin of uniform depth as a wall-bounded turbulent jet, delta growth begins with the formation of a lunate bar as predicted by the hydrodynamics of jet spreading. However, the lunate bar diverts water and sediment laterally causing the bar to widen into a radially symmetric sediment "apron" extending uniformly from the channel axis to the flume walls. This apron is stable to perturbations, and its distal limit progrades basinward while maintaining a roughly constant flow depth of ~10 times the median grain diameter (H=2-3 mm). Bar formation and channel bifurcation occur on top of the apron at the distance where shear stress applied by radially-averaged flow velocity falls below the threshold of sediment motion. Our model predicts that the distance to the first channel bifurcation should scale with water discharge, scale inversely with flow depth over the apron, and scale with median grain diameter to the negative one half.

Hydrodynamic trapping for rapid assembly and in situ electrical characterization of droplet interface bilayer arrays

DOE PAGES

Nguyen, Mary -Anne; Srijanto, Bernadeta; Collier, C. Patrick; ...

2016-08-02

The droplet interface bilayer (DIB) is a modular technique for assembling planar lipid membranes between water droplets in oil. The DIB method thus provides a unique capability for developing digital, droplet-based membrane platforms for rapid membrane characterization, drug screening and ion channel recordings. This paper demonstrates a new, low-volume microfluidic system that automates droplet generation, sorting, and sequential trapping in designated locations to enable the rapid assembly of arrays of DIBs. The channel layout of the device is guided by an equivalent circuit model, which predicts that a serial arrangement of hydrodynamic DIB traps enables sequential droplet placement and minimizesmore » the hydrodynamic pressure developed across filled traps to prevent squeeze-through of trapped droplets. Furthermore, the incorporation of thin-film electrodes fabricated via evaporation metal deposition onto the glass substrate beneath the channels allows for the first time in situ, simultaneous electrical interrogation of multiple DIBs within a sealed device. Combining electrical measurements with imaging enables measurements of membrane capacitance and resistance and bilayer area, and our data show that DIBs formed in different trap locations within the device exhibit similar sizes and transport properties. Simultaneous, single channel recordings of ion channel gating in multiple membranes are obtained when alamethicin peptides are incorporated into the captured droplets, qualifying the thin-film electrodes as a means for measuring stimuli-responsive functions of membrane-bound biomolecules. Furthermore, this novel microfluidic-electrophysiology platform provides a reproducible, high throughput method for performing electrical measurements to study transmembrane proteins and biomembranes in low-volume, droplet-based membranes.« less

Hydrodynamic trapping for rapid assembly and in situ electrical characterization of droplet interface bilayer arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Mary -Anne; Srijanto, Bernadeta; Collier, C. Patrick

The droplet interface bilayer (DIB) is a modular technique for assembling planar lipid membranes between water droplets in oil. The DIB method thus provides a unique capability for developing digital, droplet-based membrane platforms for rapid membrane characterization, drug screening and ion channel recordings. This paper demonstrates a new, low-volume microfluidic system that automates droplet generation, sorting, and sequential trapping in designated locations to enable the rapid assembly of arrays of DIBs. The channel layout of the device is guided by an equivalent circuit model, which predicts that a serial arrangement of hydrodynamic DIB traps enables sequential droplet placement and minimizesmore » the hydrodynamic pressure developed across filled traps to prevent squeeze-through of trapped droplets. Furthermore, the incorporation of thin-film electrodes fabricated via evaporation metal deposition onto the glass substrate beneath the channels allows for the first time in situ, simultaneous electrical interrogation of multiple DIBs within a sealed device. Combining electrical measurements with imaging enables measurements of membrane capacitance and resistance and bilayer area, and our data show that DIBs formed in different trap locations within the device exhibit similar sizes and transport properties. Simultaneous, single channel recordings of ion channel gating in multiple membranes are obtained when alamethicin peptides are incorporated into the captured droplets, qualifying the thin-film electrodes as a means for measuring stimuli-responsive functions of membrane-bound biomolecules. Furthermore, this novel microfluidic-electrophysiology platform provides a reproducible, high throughput method for performing electrical measurements to study transmembrane proteins and biomembranes in low-volume, droplet-based membranes.« less

Numerical investigations of passive scalar transport in Taylor-Couette flows: Counter-rotation effect

NASA Astrophysics Data System (ADS)

Ouazib, Nabila; Salhi, Yacine; Si-Ahmed, El-Khider; Legrand, Jack; Degrez, G.

2017-07-01

Numerical methods for solving convection-diffusion-reaction (CDR) scalar transport equation in three-dimensional flow are used in the present investigation. The flow is confined between two concentric cylinders both the inner cylinder and the outer one are allowed to rotate. Direct numerical simulations (DNS) have been achieved to study the effects of the gravitational and the centrifugal potentials on the stability of incompressible Taylor-Couette flow. The Navier-Stokes equations and the uncoupled convection-diffusion-reaction equation are solved using a spectral development in one direction combined together with a finite element discretization in the two remaining directions. The complexity of the patterns is highlighted. Since, it increases as the rotation rates of the cylinders increase. In addition, the effect of the counter-rotation of the cylinders on the mass transfer is pointed out.

Hydrodynamic flow in capillary-channel fiber columns for liquid chromatography.

PubMed

Stanelle, Rayman D; Sander, Lane C; Marcus, R Kenneth

2005-12-23

The flow characteristics of capillary-channel polymer (C-CP) fiber liquid chromatographic (LC) columns have been investigated. The C-CP fibers are manufactured with eight longitudinal grooves (capillary channels) extending the length of the fibers. Three C-CP fiber examples were studied, with fiber dimensions ranging from approximately 35 microm to 65 microm, and capillary-channel dimensions ranging from approximately 6 microm to 35 microm. The influence of fiber packing density and column inner diameter on peak asymmetry, peak width, and run-to-run reproducibility have been studied for stainless steel LC columns packed with polyester (PET) and polypropylene (PP) C-CP fibers. The van Deemter A-term was evaluated as a function of fiber packing density (approximately 0.3 g/cm(3)-0.75 g/cm(3)) for columns of 4.6 mm inner diameter (i.d.) and at constant packing densities for 1.5 mm, 3.2 mm, 4.6 mm, and 7.7 mm i.d. columns. Although column diameter had little influence on the eluting peak widths, peak asymmetry increased with increasing column diameter. The A-terms for the C-CP fiber packed columns are somewhat larger than current commercial, microparticulate-packed columns, and means for improvement are discussed. Applications in the area of protein (macromolecule) separations appear the most promising at this stage of the system development.

Electrokinetic sample preconcentration and hydrodynamic sample injection for microchip electrophoresis using a pneumatic microvalve.

PubMed

Cong, Yongzheng; Katipamula, Shanta; Geng, Tao; Prost, Spencer A; Tang, Keqi; Kelly, Ryan T

2016-02-01

A microfluidic platform was developed to perform online electrokinetic sample preconcentration and rapid hydrodynamic sample injection for zone electrophoresis using a single microvalve. The polydimethylsiloxane microchip comprises a separation channel, a side channel for sample introduction, and a control channel which is used as a pneumatic microvalve aligned at the intersection of the two flow channels. The closed microvalve, created by multilayer soft lithography, serves as a nanochannel preconcentrator under an applied electric potential, enabling current to pass through while preventing bulk flow. Once analytes are concentrated, the valve is briefly opened and the stacked sample is pressure injected into the separation channel for electrophoretic separation. Fluorescently labeled peptides were enriched by a factor of ∼450 in 230 s. This method enables both rapid analyte concentration and controlled injection volume for high sensitivity, high-resolution CE. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Heat transport in Rayleigh–Bénard convection and angular momentum transport in Taylor–Couette flow: a comparative study

PubMed Central

Brauckmann, Hannes J.

2017-01-01

Rayleigh–Bénard convection and Taylor–Couette flow are two canonical flows that have many properties in common. We here compare the two flows in detail for parameter values where the Nusselt numbers, i.e. the thermal transport and the angular momentum transport normalized by the corresponding laminar values, coincide. We study turbulent Rayleigh–Bénard convection in air at Rayleigh number Ra=107 and Taylor–Couette flow at shear Reynolds number ReS=2×104 for two different mean rotation rates but the same Nusselt numbers. For individual pairwise related fields and convective currents, we compare the probability density functions normalized by the corresponding root mean square values and taken at different distances from the wall. We find one rotation number for which there is very good agreement between the mean profiles of the two corresponding quantities temperature and angular momentum. Similarly, there is good agreement between the fluctuations in temperature and velocity components. For the heat and angular momentum currents, there are differences in the fluctuations outside the boundary layers that increase with overall rotation and can be related to differences in the flow structures in the boundary layer and in the bulk. The study extends the similarities between the two flows from global quantities to local quantities and reveals the effects of rotation on the transport. This article is part of the themed issue ‘Toward the development of high-fidelity models of wall turbulence at large Reynolds number’. PMID:28167575

Anisotropic particles in highly turbulent Taylor-Couette flow

NASA Astrophysics Data System (ADS)

Bakhuis, Dennis; Verschoof, Ruben A.; Mathai, Varghese; Huisman, Sander G.; Lohse, Detlef; Sun, Chao

2017-11-01

In industry and nature, particle-laden turbulent flows consist mostly, if not always, of anisotropic particles. Examples of such flows are plankton distributions in the oceans, and pumping of concrete. In these flows, the suspended particles often distribute inhomogeneously, thereby affecting the drag and the flow properties significantly. Despite their widespread occurrence, a good understanding of how such particles affect the flow is still missing. Here we performed Particle Tracking Velocimetry and global torque measurements for a suspension of rigid fibers (or rods) in the Twente Turbulent Taylor-Couette facility. The fibers are density matched with the fluid, and we used particle volume fractions up to α = 2 % of fibers with aspect ratio λ = L / d = 5 , where L = 5 mm is the length and d = 1 mm the diameter. The global torque measurements were performed for Reynolds numbers up to 2.5 ×105 and showed similar values of drag reduction as was obtained for spherical particles (λ = 1). Using PTV we have extracted the orientation, the rotation rate, and the translation velocity and acceleration for the fibers. The fibers do not show a clear alignment with the main velocity gradient. We do, however, observe occasional large rotation rates for the fibers. This work is financially supported by Netherlands Organisation for Scientific Research (NWO) by VIDI Grant Number 13477.

Poiseuille, thermal transpiration and Couette flows of a rarefied gas between plane parallel walls with nonuniform surface properties in the transverse direction and their reciprocity relations

NASA Astrophysics Data System (ADS)

Doi, Toshiyuki

2018-04-01

Slow flows of a rarefied gas between two plane parallel walls with nonuniform surface properties are studied based on kinetic theory. It is assumed that one wall is a diffuse reflection boundary and the other wall is a Maxwell-type boundary whose accommodation coefficient varies periodically in the direction perpendicular to the flow. The time-independent Poiseuille, thermal transpiration and Couette flows are considered. The flow behavior is numerically studied based on the linearized Bhatnagar-Gross-Krook-Welander model of the Boltzmann equation. The flow field, the mass and heat flow rates in the gas, and the tangential force acting on the wall surface are studied over a wide range of the gas rarefaction degree and the parameters characterizing the distribution of the accommodation coefficient. The locally convex velocity distribution is observed in Couette flow of a highly rarefied gas, similarly to Poiseuille flow and thermal transpiration. The reciprocity relations are numerically confirmed over a wide range of the flow parameters.

Stabilization of domain walls between traveling waves by nonlinear mode coupling in Taylor-Couette flow.

PubMed

Heise, M; Hoffmann, Ch; Abshagen, J; Pinter, A; Pfister, G; Lücke, M

2008-02-15

We present a new mechanism that allows the stable existence of domain walls between oppositely traveling waves in pattern-forming systems far from onset. It involves a nonlinear mode coupling that results directly from the nonlinearities in the underlying momentum balance. Our work provides the first observation and explanation of such strongly nonlinearly driven domain walls that separate structured states by a phase generating or annihilating defect. Furthermore, the influence of a symmetry breaking externally imposed flow on the wave domains and the domain walls is studied. The results are obtained for vortex waves in the Taylor-Couette system by combining numerical simulations of the full Navier-Stokes equations and experimental measurements.

Correspondence between the distribution of hydrodynamic time parameters and the distribution of biological and chemical variables in a semi-enclosed coral reef lagoon

NASA Astrophysics Data System (ADS)

Torréton, Jean-Pascal; Rochelle-Newall, Emma; Jouon, Aymeric; Faure, Vincent; Jacquet, Séverine; Douillet, Pascal

2007-09-01

Hydrodynamic modeling can be used to spatially characterize water renewal rates in coastal ecosystems. Using a hydrodynamic model implemented over the semi-enclosed Southwest coral lagoon of New Caledonia, a recent study computed the flushing lag as the minimum time required for a particle coming from outside the lagoon (open ocean) to reach a specific station [Jouon, A., Douillet, P., Ouillon, S., Fraunié, P., 2006. Calculations of hydrodynamic time parameters in a semi-opened coastal zone using a 3D hydrodynamic model. Continental Shelf Research 26, 1395-1415]. Local e -flushing time was calculated as the time requested to reach a local grid mesh concentration of 1/e from the precedent step. Here we present an attempt to connect physical forcing to biogeochemical functioning of this coastal ecosystem. An array of stations, located in the lagoonal channel as well as in several bays under anthropogenic influence, was sampled during three cruises. We then tested the statistical relationships between the distribution of flushing indices and those of biological and chemical variables. Among the variables tested, silicate, chlorophyll a and bacterial biomass production present the highest correlations with flushing indices. Correlations are higher with local e-flushing times than with flushing lags or the sum of these two indices. In the bays, these variables often deviate from the relationships determined in the main lagoon channel. In the three bays receiving significant riverine inputs, silicate is well above the regression line, whereas data from the bay receiving almost insignificant freshwater inputs generally fit the lagoon channel regressions. Moreover, in the three bays receiving important urban and industrial effluents, chlorophyll a and bacterial production of biomass generally display values exceeding the lagoon channel regression trends whereas in the bay under moderate anthropogenic influence values follow the regressions obtained in the lagoon channel

Electrokinetic Sample Preconcentration and Hydrodynamic Sample Injection for Microchip Electrophoresis Using a Pneumatic Microvalve

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cong, Yongzheng; Katipamula, Shanta; Geng, Tao

2016-02-01

A microfluidic platform was developed to perform online electrokinetic sample preconcentration and rapid hydrodynamic sample injection for electrophoresis using a single microvalve. The PDMS microchip consists of a separation channel, a side channel for sample introduction, and a control channel which is used as a pneumatic microvalve aligned at the intersection of the two flow channels. The closed microvalve, created by multilayer soft lithography, can serve as a preconcentrator under an applied electric potential, enabling current to pass through while blocking bulk flow. Once analytes are concentrated, the valve is briefly opened and the stacked sample is pressure injected intomore » the separation channel for electrophoretic separation. Fluorescently labeled peptides were enriched by a factor of ~450 in 230 s. The performance of the platform was validated by the online preconcentration, injection and electrophoretic separation of fluorescently labeled peptides. This method enables both rapid analyte concentration and controlled injection volume for high sensitivity, high resolution capillary electrophoresis.« less

A watershed scale spatially-distributed model for streambank erosion rate driven by channel curvature

NASA Astrophysics Data System (ADS)

McMillan, Mitchell; Hu, Zhiyong

2017-10-01

Streambank erosion is a major source of fluvial sediment, but few large-scale, spatially distributed models exist to quantify streambank erosion rates. We introduce a spatially distributed model for streambank erosion applicable to sinuous, single-thread channels. We argue that such a model can adequately characterize streambank erosion rates, measured at the outsides of bends over a 2-year time period, throughout a large region. The model is based on the widely-used excess-velocity equation and comprised three components: a physics-based hydrodynamic model, a large-scale 1-dimensional model of average monthly discharge, and an empirical bank erodibility parameterization. The hydrodynamic submodel requires inputs of channel centerline, slope, width, depth, friction factor, and a scour factor A; the large-scale watershed submodel utilizes watershed-averaged monthly outputs of the Noah-2.8 land surface model; bank erodibility is based on tree cover and bank height as proxies for root density. The model was calibrated with erosion rates measured in sand-bed streams throughout the northern Gulf of Mexico coastal plain. The calibrated model outperforms a purely empirical model, as well as a model based only on excess velocity, illustrating the utility of combining a physics-based hydrodynamic model with an empirical bank erodibility relationship. The model could be improved by incorporating spatial variability in channel roughness and the hydrodynamic scour factor, which are here assumed constant. A reach-scale application of the model is illustrated on ∼1 km of a medium-sized, mixed forest-pasture stream, where the model identifies streambank erosion hotspots on forested and non-forested bends.

Flow of quasi-two dimensional water in graphene channels

NASA Astrophysics Data System (ADS)

Fang, Chao; Wu, Xihui; Yang, Fengchang; Qiao, Rui

2018-02-01

When liquids confined in slit channels approach a monolayer, they become two-dimensional (2D) fluids. Using molecular dynamics simulations, we study the flow of quasi-2D water confined in slit channels featuring pristine graphene walls and graphene walls with hydroxyl groups. We focus on to what extent the flow of quasi-2D water can be described using classical hydrodynamics and what are the effective transport properties of the water and the channel. First, the in-plane shearing of quasi-2D water confined between pristine graphene can be described using the classical hydrodynamic equation, and the viscosity of the water is ˜50% higher than that of the bulk water in the channel studied here. Second, the flow of quasi-2D water around a single hydroxyl group is perturbed at a position of tens of cluster radius from its center, as expected for low Reynolds number flows. Even though water is not pinned at the edge of the hydroxyl group, the hydroxyl group screens the flow greatly, with a single, isolated hydroxyl group rendering drag similar to ˜90 nm2 pristine graphene walls. Finally, the flow of quasi-2D water through graphene channels featuring randomly distributed hydroxyl groups resembles the fluid flow through porous media. The effective friction factor of the channel increases linearly with the hydroxyl groups' area density up to 0.5 nm-2 but increases nonlinearly at higher densities. The effective friction factor of the channel can be fitted to a modified Carman equation at least up to a hydroxyl area density of 2.0 nm-2. These findings help understand the liquid transport in 2D material-based nanochannels for applications including desalination.

Hydrodynamics in Cell Studies

PubMed Central

2018-01-01

Hydrodynamic phenomena are ubiquitous in living organisms and can be used to manipulate cells or emulate physiological microenvironments experienced in vivo. Hydrodynamic effects influence multiple cellular properties and processes, including cell morphology, intracellular processes, cell–cell signaling cascades and reaction kinetics, and play an important role at the single-cell, multicellular, and organ level. Selected hydrodynamic effects can also be leveraged to control mechanical stresses, analyte transport, as well as local temperature within cellular microenvironments. With a better understanding of fluid mechanics at the micrometer-length scale and the advent of microfluidic technologies, a new generation of experimental tools that provide control over cellular microenvironments and emulate physiological conditions with exquisite accuracy is now emerging. Accordingly, we believe that it is timely to assess the concepts underlying hydrodynamic control of cellular microenvironments and their applications and provide some perspective on the future of such tools in in vitro cell-culture models. Generally, we describe the interplay between living cells, hydrodynamic stressors, and fluid flow-induced effects imposed on the cells. This interplay results in a broad range of chemical, biological, and physical phenomena in and around cells. More specifically, we describe and formulate the underlying physics of hydrodynamic phenomena affecting both adhered and suspended cells. Moreover, we provide an overview of representative studies that leverage hydrodynamic effects in the context of single-cell studies within microfluidic systems. PMID:29420889

Life stages of wall-bounded decay of Taylor-Couette turbulence

NASA Astrophysics Data System (ADS)

Ostilla-Mónico, Rodolfo; Zhu, Xiaojue; Spandan, Vamsi; Verzicco, Roberto; Lohse, Detlef

2017-11-01

The decay of Taylor-Couette turbulence, i.e., the flow between two coaxial and independently rotating cylinders, is numerically studied by instantaneously stopping the forcing from an initially statistically stationary flow field at a Reynolds number of Re=3.5 ×104 . The effect of wall friction is analyzed by comparing three separate cases, in which the cylinders are either suddenly made no-slip or stress-free. Different life stages are observed during the decay. In the first stage, the decay is dominated by large-scale rolls. Counterintuitively, when these rolls fade away, if the flow inertia is small a redistribution of energy occurs and the energy of the azimuthal velocity behaves nonmonotonically, first decreasing by almost two orders of magnitude and then increasing during the redistribution. The second stage is dominated by non-normal transient growth of perturbations in the axial (spanwise) direction. Once this mechanism is exhausted, the flow enters the final life stage, viscous decay, which is dominated by wall friction. We show that this stage can be modeled by a one-dimensional heat equation, and that self-similar velocity profiles collapse onto the theoretical solution.

Experimental search for Exact Coherent Structures in turbulent small aspect ratio Taylor-Couette flow

NASA Astrophysics Data System (ADS)

Crowley, Christopher J.; Krygier, Michael; Grigoriev, Roman O.; Schatz, Michael F.

2017-11-01

Recent theoretical and experimental work suggests that the dynamics of turbulent flows are guided by unstable nonchaotic solutions to the Navier-Stokes equations. These solutions, known as exact coherent structures (ECS), play a key role in a fundamentally deterministic description of turbulence. In order to quantitatively demonstrate that actual turbulence in 3D flows is guided by ECS, high resolution, 3D-3C experimental measurements of the velocity need to be compared to solutions from direct numerical simulation of the Navier-Stokes equations. In this talk, we will present experimental measurements of fully time resolved, velocity measurements in a volume of turbulence in a counter-rotating, small aspect ratio Taylor-Couette flow. This work is supported by the Army Research Office (Contract # W911NF-16-1-0281).

Ultrasonic velocity profiling rheometry based on a widened circular Couette flow

NASA Astrophysics Data System (ADS)

Shiratori, Takahisa; Tasaka, Yuji; Oishi, Yoshihiko; Murai, Yuichi

2015-08-01

We propose a new rheometry for characterizing the rheological properties of fluids. The technique produces flow curves, which represent the relationship between the fluid shear rate and shear stress. Flow curves are obtained by measuring the circumferential velocity distribution of tested fluids in a circular Couette system, using an ultrasonic velocity profiling technique. By adopting a widened gap of concentric cylinders, a designed range of the shear rate is obtained so that velocity profile measurement along a single line directly acquires flow curves. To reduce the effect of ultrasonic noise on resultant flow curves, several fitting functions and variable transforms are examined to best approximate the velocity profile without introducing a priori rheological models. Silicone oil, polyacrylamide solution, and yogurt were used to evaluate the applicability of this technique. These substances are purposely targeted as examples of Newtonian fluids, shear thinning fluids, and opaque fluids with unknown rheological properties, respectively. We find that fourth-order Chebyshev polynomials provide the most accurate representation of flow curves in the context of model-free rheometry enabled by ultrasonic velocity profiling.

Experimental study of mixing mechanisms in stably stratified Taylor-Couette flow

NASA Astrophysics Data System (ADS)

Augier, Pierre; Caulfield, Colm-Cille; Dalziel, Stuart

2014-11-01

We consider experimentally the mechanisms of mixing in stably stratified Taylor-Couette (TC) flow in a TC apparatus for which both cylinders can rotate independently. In the case for which only the inner cylinder rotates, centrifugal instability rapidly splits an initially linear density profile into an array of thin nearly homogeneous layers. Shadowgraph, PIV and density profiles measured by a moving conductivity probe allow us to characterise this process and the resulting flow. In particular, we observe turbulent intrusions of mixed fluid propagating relatively slowly around the tank at the interfaces between the layers, leading to a time-dependent variation in the sharpness and turbulent activity at these interfaces, whose period scales with (but is much larger than) the rotation period. Interestingly, the turbulent intrusions are anti-correlated between adjacent interfaces leading to snake-skin-like patterns in the spatio-temporal diagrams of the density profiles. We also explore how the presence of a density stratification modifies end effects at the top and bottom of the cylinders, in both the presence and absence of primary centrifugal instability.

GLOFRIM - A globally applicable framework for integrated hydrologic-hydrodynamic inundation modelling

NASA Astrophysics Data System (ADS)

Hoch, J. M.; Neal, J. C.; Baart, F.; Van Beek, L. P.; Winsemius, H.; Bates, P. D.; Bierkens, M. F.

2017-12-01

Currently, many approaches to provide detailed flood hazard and risk estimates are built upon specific hydrologic or hydrodynamic model routines. By applying these routines in stand-alone mode important processes can however not accurately be described. For instance, global hydrologic models run at coarse spatial resolution, not supporting the detailed simulation of flood hazard. Hydrodynamic models excel in the computations of open water flow dynamics, but dependent on specific runoff or observed discharge as input. In most cases hydrodynamic models are forced at the boundaries and thus cannot account for water sources within the model domain, limiting the simulation of inundation dynamics to reaches fed by upstream boundaries. Recently, Hoch et al. (HESS, 2017) coupled PCR-GLOBWB (PCR) with the hydrodynamic model Delft3D Flexible Mesh (DFM). By means of the Basic Model Interface both models were connected on a cell-by-cell basis, allowing for spatially explicit coupling. Model results showed that discharge simulations can profit from model coupling compared to stand-alone runs. As model results of a coupled simulation depend on the quality of the models, it would be worthwhile to allow a suite of models to be coupled. To facilitate this, we present GLOFRIM, a globally applicable framework for integrated hydrologic-hydrodynamic inundation modelling. In the current version coupling between PCR and both DFM and LISFLOOD-FP (LFP) can be established (Hoch et al., GMDD, 2017). First results show that differences between both hydrodynamic models are present in the timing of peak discharge which is most likely due to differences in channel-floodplain interactions and bathymetry processing. Having benchmarked inundation extent, LFP and DFM agree for around half of the inundated area which is attributable to variations in grid size. Results also indicate that, despite using identical boundary conditions and forcing, the schematization itself as well as internal processes

Heat transport in Rayleigh-Bénard convection and angular momentum transport in Taylor-Couette flow: a comparative study.

PubMed

Brauckmann, Hannes J; Eckhardt, Bruno; Schumacher, Jörg

2017-03-13

Rayleigh-Bénard convection and Taylor-Couette flow are two canonical flows that have many properties in common. We here compare the two flows in detail for parameter values where the Nusselt numbers, i.e. the thermal transport and the angular momentum transport normalized by the corresponding laminar values, coincide. We study turbulent Rayleigh-Bénard convection in air at Rayleigh number Ra=10 7 and Taylor-Couette flow at shear Reynolds number Re S =2×10 4 for two different mean rotation rates but the same Nusselt numbers. For individual pairwise related fields and convective currents, we compare the probability density functions normalized by the corresponding root mean square values and taken at different distances from the wall. We find one rotation number for which there is very good agreement between the mean profiles of the two corresponding quantities temperature and angular momentum. Similarly, there is good agreement between the fluctuations in temperature and velocity components. For the heat and angular momentum currents, there are differences in the fluctuations outside the boundary layers that increase with overall rotation and can be related to differences in the flow structures in the boundary layer and in the bulk. The study extends the similarities between the two flows from global quantities to local quantities and reveals the effects of rotation on the transport.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'. © 2017 The Author(s).

Bound of dissipation on a plane Couette dynamo

NASA Astrophysics Data System (ADS)

Alboussière, Thierry

2009-06-01

Variational turbulence is among the few approaches providing rigorous results in turbulence. In addition, it addresses a question of direct practical interest, namely, the rate of energy dissipation. Unfortunately, only an upper bound is obtained as a larger functional space than the space of solutions to the Navier-Stokes equations is searched. Yet, in some cases, this upper bound is in good agreement with experimental results in terms of order of magnitude and power law of the imposed Reynolds number. In this paper, the variational approach to turbulence is extended to the case of dynamo action and an upper bound is obtained for the global dissipation rate (viscous and Ohmic). A simple plane Couette flow is investigated. For low magnetic Prandtl number Pm fluids, the upper bound of energy dissipation is that of classical turbulence (i.e., proportional to the cubic power of the shear velocity) for magnetic Reynolds numbers below Pm-1 and follows a steeper evolution for magnetic Reynolds numbers above Pm-1 (i.e., proportional to the shear velocity to the power of 4) in the case of electrically insulating walls. However, the effect of wall conductance is crucial: for a given value of wall conductance, there is a value for the magnetic Reynolds number above which energy dissipation cannot be bounded. This limiting magnetic Reynolds number is inversely proportional to the square root of the conductance of the wall. Implications in terms of energy dissipation in experimental and natural dynamos are discussed.

Thermal analysis of a reactive generalized Couette flow of power law fluids between concentric cylindrical pipes

NASA Astrophysics Data System (ADS)

Makinde, O. D.

2014-12-01

In this paper, the steady generalized axial Couette flow of Ostwald-de Waele power law reactive fluids between concentric cylindrical pipes is investigated. It is assumed that the outer cylinder is stationary and exchanges heat with the ambient surrounding following Newton's law of cooling, while the inner cylinder with isothermal surface is set in motion in the axial direction. The model nonlinear differential equations for the momentum and energy balance are obtained and tackled numerically using the shooting method coupled with the Runge-Kutta-Fehlberg integration technique. The effects of various embedded thermophysical parameters on the velocity and temperature fields including skin friction, Nusselt number and thermal criticality conditions are presented graphically and discussed quantitatively.

Experimental investigation of thermal processes in the multi-ring Couette system with counter rotation of cylinders

NASA Astrophysics Data System (ADS)

Mamonov, V. N.; Nazarov, A. D.; Serov, A. F.; Terekhov, V. I.

2016-01-01

The effect of parameters of the multi-ring Couette system with counter rotating coaxial cylinders on the process of thermal energy release in a viscous liquid filling this system is considered with regard to the problem of determining the possibility of creating the high-performance wind heat generator. The multi-cylinder rotor design allows directly conversion of the mechanical power of a device consisting of two "rotor" wind turbines with a common axis normal to the air flow into the thermal energy in a wide range of rotational speed of the cylinders. Experimental results on the measurement of thermal power released in the pilot heat generator at different relative angular speeds of cylinder rotation are presented.

A numerical study of the axisymmetric Couette-Taylor problem using a fast high-resolution second-order central scheme

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kupferman, R.

The author presents a numerical study of the axisymmetric Couette-Taylor problem using a finite difference scheme. The scheme is based on a staggered version of a second-order central-differencing method combined with a discrete Hodge projection. The use of central-differencing operators obviates the need to trace the characteristic flow associated with the hyperbolic terms. The result is a simple and efficient scheme which is readily adaptable to other geometries and to more complicated flows. The scheme exhibits competitive performance in terms of accuracy, resolution, and robustness. The numerical results agree accurately with linear stability theory and with previous numerical studies.

Inertial and viscoelastic forces on rigid colloids in microfluidic channels.

PubMed

Howard, Michael P; Panagiotopoulos, Athanassios Z; Nikoubashman, Arash

2015-06-14

We perform hybrid molecular dynamics simulations to study the flow behavior of rigid colloids dispersed in a dilute polymer solution. The underlying Newtonian solvent and the ensuing hydrodynamic interactions are incorporated through multiparticle collision dynamics, while the constituent polymers are modeled as bead-spring chains, maintaining a description consistent with the colloidal nature of our system. We study the cross-stream migration of the solute particles in slit-like channels for various polymer lengths and colloid sizes and find a distinct focusing onto the channel center under specific solvent and flow conditions. To better understand this phenomenon, we systematically measure the effective forces exerted on the colloids. We find that the migration originates from a competition between viscoelastic forces from the polymer solution and hydrodynamically induced inertial forces. Our simulations reveal a significantly stronger fluctuation of the lateral colloid position than expected from thermal motion alone, which originates from the complex interplay between the colloid and polymer chains.

Comparison of new generation low-complexity flood inundation mapping tools with a hydrodynamic model

NASA Astrophysics Data System (ADS)

Afshari, Shahab; Tavakoly, Ahmad A.; Rajib, Mohammad Adnan; Zheng, Xing; Follum, Michael L.; Omranian, Ehsan; Fekete, Balázs M.

2018-01-01

The objective of this study is to compare two new generation low-complexity tools, AutoRoute and Height Above the Nearest Drainage (HAND), with a two-dimensional hydrodynamic model (Hydrologic Engineering Center-River Analysis System, HEC-RAS 2D). The assessment was conducted on two hydrologically different and geographically distant test-cases in the United States, including the 16,900 km2 Cedar River (CR) watershed in Iowa and a 62 km2 domain along the Black Warrior River (BWR) in Alabama. For BWR, twelve different configurations were set up for each of the models, including four different terrain setups (e.g. with and without channel bathymetry and a levee), and three flooding conditions representing moderate to extreme hazards at 10-, 100-, and 500-year return periods. For the CR watershed, models were compared with a simplistic terrain setup (without bathymetry and any form of hydraulic controls) and one flooding condition (100-year return period). Input streamflow forcing data representing these hypothetical events were constructed by applying a new fusion approach on National Water Model outputs. Simulated inundation extent and depth from AutoRoute, HAND, and HEC-RAS 2D were compared with one another and with the corresponding FEMA reference estimates. Irrespective of the configurations, the low-complexity models were able to produce inundation extents similar to HEC-RAS 2D, with AutoRoute showing slightly higher accuracy than the HAND model. Among four terrain setups, the one including both levee and channel bathymetry showed lowest fitness score on the spatial agreement of inundation extent, due to the weak physical representation of low-complexity models compared to a hydrodynamic model. For inundation depth, the low-complexity models showed an overestimating tendency, especially in the deeper segments of the channel. Based on such reasonably good prediction skills, low-complexity flood models can be considered as a suitable alternative for fast

Hydrodynamics of the Dirac spectrum

DOE PAGES

Liu, Yizhuang; Warchoł, Piotr; Zahed, Ismail

2015-12-15

We discuss a hydrodynamical description of the eigenvalues of the Dirac spectrum in even dimensions in the vacuum and in the large N (volume) limit. The linearized hydrodynamics supports sound waves. The hydrodynamical relaxation of the eigenvalues is captured by a hydrodynamical (tunneling) minimum configuration which follows from a pertinent form of Euler equation. As a result, the relaxation from a phase of unbroken chiral symmetry to a phase of broken chiral symmetry occurs over a time set by the speed of sound.

Log law of the wall revisited in Taylor-Couette flows at intermediate Reynolds numbers.

PubMed

Singh, Harminder; Suazo, Claudio Alberto Torres; Liné, Alain

2016-11-01

We provide Reynolds averaged azimuthal velocity profiles, measured in a Taylor-Couette system in turbulent flow, at medium Reynolds (7800 < Re < 18000) number with particle image velocimetry technique. We find that in the wall regions, close to the inner and outer cylinders, the azimuthal velocity profile reveals a significant deviation from classical logarithmic law. In order to propose a new law of the wall, the profile of turbulent mixing length was estimated from data processing; it was shown to behave nonlinearly with the radial wall distance. Based on this turbulent mixing length expression, a law of the wall was proposed for the Reynolds averaged azimuthal velocity, derived from momentum balance and validated by comparison to different data. In addition, the profile of viscous dissipation rate was investigated and compared to the global power needed to maintain the inner cylinder in rotation.

Multiplex Particle Focusing via Hydrodynamic Force in Viscoelastic Fluids

NASA Astrophysics Data System (ADS)

Lee, Doo Jin; Brenner, Howard; Youn, Jae Ryoun; Song, Young Seok

2013-11-01

We introduce a multiplex particle focusing phenomenon that arises from the hydrodynamic interaction between the viscoelastic force and the Dean drag force in a microfluidic device. In a confined microchannel, the first normal stress difference of viscoelastic fluids results in a lateral migration of suspended particles. Such a viscoelastic force was harnessed to focus different sized particles in the middle of a microchannel, and spiral channel geometry was also considered in order to take advantage of the counteracting force, Dean drag force that induces particle migration in the outward direction. For theoretical understanding, we performed a numerical analysis of viscoelastic fluids in the spiral microfluidic channel. From these results, a concept of the `Dean-coupled Elasto-inertial Focusing band (DEF)' was proposed. This study provides in-depth physical insight into the multiplex focusing of particles that can open a new venue for microfluidic particle dynamics for a concrete high throughput platform at microscale.

Evidence for hydrodynamic electron flow in PdCoO₂.

PubMed

Moll, Philip J W; Kushwaha, Pallavi; Nandi, Nabhanila; Schmidt, Burkhard; Mackenzie, Andrew P

2016-03-04

Electron transport is conventionally determined by the momentum-relaxing scattering of electrons by the host solid and its excitations. Hydrodynamic fluid flow through channels, in contrast, is determined partly by the viscosity of the fluid, which is governed by momentum-conserving internal collisions. A long-standing question in the physics of solids has been whether the viscosity of the electron fluid plays an observable role in determining the resistance. We report experimental evidence that the resistance of restricted channels of the ultrapure two-dimensional metal palladium cobaltate (PdCoO2) has a large viscous contribution. Comparison with theory allows an estimate of the electronic viscosity in the range between 6 × 10(-3) kg m(-1) s(-1) and 3 × 10(-4) kg m(-1) s(-1), versus 1 × 10(-3) kg m(-1) s(-1) for water at room temperature. Copyright © 2016, American Association for the Advancement of Science.

Coupled Electro-Hydrodynamic Effects of Electro-Osmosis from Pore Scale to Darcy Scale

NASA Astrophysics Data System (ADS)

Schotting, R.; Joekar-Niasar, V.; Leijnse, A.

2011-12-01

Electro-osmosis is "movement of a fluid under the effect of an electric field in a porous medium". This phenomenon has many applications in civil engineering (slope stabilization, dewatering), environmental engineering (soil remediation, sludge dewatering), chemical engineering (micro- or nano- mixers), medical engineering (drug delivery), etc. The key factor in electro-osmosis is the competition between the electrochemical and hydrodynamic forces as well as the coupling between the solid surface and the electrolyte properties. The objective of this research is to understand the influence of pore-scale heterogeneities of surface properties on the Darcy-scale behavior. We develop novel analytical solutions for the flow and transport of electrolyte including electro-hydrodynamic forces in a single micro-channel. We propose the complete analytical solution for monovalent electrolyte at full range overlapping double layers, and nonlinear electric field, including the Donan effect in transport of ions. These pore-scale formulations are numerically upscaled to obtain the Darcy-scale behavior. Our results show the contribution of electro-osmotic, chemical-osmotic and hydrodynamic components of the flow equation on pressure field evolution and multi-directional flow field at Darcy scale.

Two-dimensional hydrodynamic modeling to quantify effects of peak-flow management on channel morphology and salmon-spawning habitat in the Cedar River, Washington

USGS Publications Warehouse

Czuba, Christiana; Czuba, Jonathan A.; Gendaszek, Andrew S.; Magirl, Christopher S.

2010-01-01

The Cedar River in Washington State originates on the western slope of the Cascade Range and provides the City of Seattle with most of its drinking water, while also supporting a productive salmon habitat. Water-resource managers require detailed information on how best to manage high-flow releases from Chester Morse Lake, a large reservoir on the Cedar River, during periods of heavy precipitation to minimize flooding, while mitigating negative effects on fish populations. Instream flow-management practices include provisions for adaptive management to promote and maintain healthy aquatic habitat in the river system. The current study is designed to understand the linkages between peak flow characteristics, geomorphic processes, riverine habitat, and biological responses. Specifically, two-dimensional hydrodynamic modeling is used to simulate and quantify the effects of the peak-flow magnitude, duration, and frequency on the channel morphology and salmon-spawning habitat. Two study reaches, representative of the typical geomorphic and ecologic characteristics of the Cedar River, were selected for the modeling. Detailed bathymetric data, collected with a real-time kinematic global positioning system and an acoustic Doppler current profiler, were combined with a LiDAR-derived digital elevation model in the overbank area to develop a computational mesh. The model is used to simulate water velocity, benthic shear stress, flood inundation, and morphologic changes in the gravel-bedded river under the current and alternative flood-release strategies. Simulations of morphologic change and salmon-redd scour by floods of differing magnitude and duration enable water-resource managers to incorporate model simulation results into adaptive management of peak flows in the Cedar River. PDF version of a presentation on hydrodynamic modelling in the Cedar River in Washington state. Presented at the American Geophysical Union Fall Meeting 2010.

Development and application of hydraulic geometry equations for tidal channel restoration in Atlantic Canada

NASA Astrophysics Data System (ADS)

Graham, J.; van Proosdij, D.; Bowron, T.

2017-12-01

Tidal wetlands play a key role in our environment, particularly in the face of climate change and rising sea levels. Successful restoration of these coastal habitats requires a good understanding of the hydrology and morphology of the site. In Atlantic Canada, restoration design must consider significant variation in tidal range (1 to 16 m), sediment supply (50-70,000 mg/L) and winter conditions. In 2012 ground surveys, aerial photos and digital terrain data were used to conduct a morphometric analysis of representative tidal channels and to establish regional hydraulic geometry relationships to aid in restoration design. Channel morphology was strongly related to freshwater discharge and channel order while drainage density, channel length, and sinuosity were related to site history and maturity. Five years after the initial study, two restored salt marshes have been analyzed to assess the validity of the equations. At both marshes, tidal channels were excavated and erosion/accretion tracked for five years following restoration. Channels were found to experience rapid erosion in the first 2 years following restoration but to stabilize with dimensions on par with those predicted. Furthermore, both sites rapidly developed hybrid creek networks beyond the primary excavated channels when allowed to self design. The methodology has been used to design tidal channels for 2 additional sites. Although these sites have not been restored at present, hydrodynamic modeling supported channel dimension predictions, with acceptable in-channel velocities and flood extents simulated in the model. The authors conclude that the use of regional hydraulic geometry equations have been effective in salt marsh restoration design in Atlantic Canada, particularly when used in conjunction with other techniques such as hydrodynamic modeling and analysis of historic conditions.

A two-dimensional hydrodynamic model of a tidal estuary

USGS Publications Warehouse

Walters, Roy A.; Cheng, Ralph T.

1979-01-01

A finite element model is described which is used in the computation of tidal currents in an estuary. This numerical model is patterned after an existing algorithm and has been carefully tested in rectangular and curve-sided channels with constant and variable depth. One of the common uncertainties in this class of two-dimensional hydrodynamic models is the treatment of the lateral boundary conditions. Special attention is paid specifically to addressing this problem. To maintain continuity within the domain of interest, ‘smooth’ curve-sided elements must be used at all shoreline boundaries. The present model uses triangular, isoparametric elements with quadratic basis functions for the two velocity components and a linear basis function for water surface elevation. An implicit time integration is used and the model is unconditionally stable. The resultant governing equations are nonlinear owing to the advective and the bottom friction terms and are solved iteratively at each time step by the Newton-Raphson method. Model test runs have been made in the southern portion of San Francisco Bay, California (South Bay) as well as in the Bay west of Carquinez Strait. Owing to the complex bathymetry, the hydrodynamic characteristics of the Bay system are dictated by the generally shallow basins which contain deep, relict river channels. Great care must be exercised to ensure that the conservation equations remain locally as well as globally accurate. Simulations have been made over several representative tidal cycles using this finite element model, and the results compare favourably with existing data. In particular, the standing wave in South Bay and the progressive wave in the northern reach are well represented.

Superhydrophobic and polymer drag reduction in turbulent Taylor-Couette flow

NASA Astrophysics Data System (ADS)

Rajappan, Anoop; McKinley, Gareth H.

2017-11-01

We use a custom-built Taylor-Couette apparatus (radius ratio η = 0.75) to study frictional drag reduction by dilute polymer solutions and superhydrophobic (SH) surfaces in turbulent flows for 15000 < Re < 86000 . By monitoring the torque-speed scaling we show that the swirling flow becomes fully turbulent above Re = 15000 and we focus on measurements in this regime. By applying SH coatings on the inner cylinder, we can evaluate the drag reducing performance of the coating and calculate the effective slip length in turbulent flow using a suitably modified Prandtl-von Kármán analysis. We also investigate drag reduction by dilute polymer solutions, and show that natural biopolymers from plant mucilage can be an inexpensive and effective alternative to synthetic polymers in drag reduction applications, approaching the same maximum drag reduction asymptote. Finally we explore combinations of the two methods - one arising from wall slip and the other due to changes in turbulence dynamics in the bulk flow - and find that the two effects are not additive; interestingly, the effectiveness of polymer drag reduction is drastically reduced in the presence of an SH coating on the wall. This study was financially supported by the Office of Naval Research (ONR) through Contract No. 3002453814.

Surfactants and the Rayleigh-Taylor instability of Couette type flows

NASA Astrophysics Data System (ADS)

Frenkel, A. L.; Halpern, D.; Schweiger, A. S.

2011-11-01

We study the Rayleigh-Taylor instability of slow Couette- type flows in the presence of insoluble surfactants. It is known that with zero gravity, the surfactant makes the flow unstable to longwave disturbances in certain regions of the parameter space; while in other parametric regions, it reinforces the flow stability (Frenkel and Halpern 2002). Here, we show that in the latter parametric sectors, and when the (gravity) Bond number Bo is below a certain threshold value, the Rayleigh-Taylor instability is completely stabilized for a finite interval of Ma, the (surfactant) Marangoni number: MaL Ma2, and also for MaL

Hydrodynamic optical soliton tunneling

NASA Astrophysics Data System (ADS)

Sprenger, P.; Hoefer, M. A.; El, G. A.

2018-03-01

A notion of hydrodynamic optical soliton tunneling is introduced in which a dark soliton is incident upon an evolving, broad potential barrier that arises from an appropriate variation of the input signal. The barriers considered include smooth rarefaction waves and highly oscillatory dispersive shock waves. Both the soliton and the barrier satisfy the same one-dimensional defocusing nonlinear Schrödinger (NLS) equation, which admits a convenient dispersive hydrodynamic interpretation. Under the scale separation assumption of nonlinear wave (Whitham) modulation theory, the highly nontrivial nonlinear interaction between the soliton and the evolving hydrodynamic barrier is described in terms of self-similar, simple wave solutions to an asymptotic reduction of the Whitham-NLS partial differential equations. One of the Riemann invariants of the reduced modulation system determines the characteristics of a soliton interacting with a mean flow that results in soliton tunneling or trapping. Another Riemann invariant yields the tunneled soliton's phase shift due to hydrodynamic interaction. Soliton interaction with hydrodynamic barriers gives rise to effects that include reversal of the soliton propagation direction and spontaneous soliton cavitation, which further suggest possible methods of dark soliton control in optical fibers.

Hydrodynamic optical soliton tunneling.

PubMed

Sprenger, P; Hoefer, M A; El, G A

2018-03-01

A notion of hydrodynamic optical soliton tunneling is introduced in which a dark soliton is incident upon an evolving, broad potential barrier that arises from an appropriate variation of the input signal. The barriers considered include smooth rarefaction waves and highly oscillatory dispersive shock waves. Both the soliton and the barrier satisfy the same one-dimensional defocusing nonlinear Schrödinger (NLS) equation, which admits a convenient dispersive hydrodynamic interpretation. Under the scale separation assumption of nonlinear wave (Whitham) modulation theory, the highly nontrivial nonlinear interaction between the soliton and the evolving hydrodynamic barrier is described in terms of self-similar, simple wave solutions to an asymptotic reduction of the Whitham-NLS partial differential equations. One of the Riemann invariants of the reduced modulation system determines the characteristics of a soliton interacting with a mean flow that results in soliton tunneling or trapping. Another Riemann invariant yields the tunneled soliton's phase shift due to hydrodynamic interaction. Soliton interaction with hydrodynamic barriers gives rise to effects that include reversal of the soliton propagation direction and spontaneous soliton cavitation, which further suggest possible methods of dark soliton control in optical fibers.

Radiation Hydrodynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Castor, J I

2003-10-16

The discipline of radiation hydrodynamics is the branch of hydrodynamics in which the moving fluid absorbs and emits electromagnetic radiation, and in so doing modifies its dynamical behavior. That is, the net gain or loss of energy by parcels of the fluid material through absorption or emission of radiation are sufficient to change the pressure of the material, and therefore change its motion; alternatively, the net momentum exchange between radiation and matter may alter the motion of the matter directly. Ignoring the radiation contributions to energy and momentum will give a wrong prediction of the hydrodynamic motion when the correctmore » description is radiation hydrodynamics. Of course, there are circumstances when a large quantity of radiation is present, yet can be ignored without causing the model to be in error. This happens when radiation from an exterior source streams through the problem, but the latter is so transparent that the energy and momentum coupling is negligible. Everything we say about radiation hydrodynamics applies equally well to neutrinos and photons (apart from the Einstein relations, specific to bosons), but in almost every area of astrophysics neutrino hydrodynamics is ignored, simply because the systems are exceedingly transparent to neutrinos, even though the energy flux in neutrinos may be substantial. Another place where we can do ''radiation hydrodynamics'' without using any sophisticated theory is deep within stars or other bodies, where the material is so opaque to the radiation that the mean free path of photons is entirely negligible compared with the size of the system, the distance over which any fluid quantity varies, and so on. In this case we can suppose that the radiation is in equilibrium with the matter locally, and its energy, pressure and momentum can be lumped in with those of the rest of the fluid. That is, it is no more necessary to distinguish photons from atoms, nuclei and electrons, than it is to

Drag Measurements over Embedded Cavities in a Low Reynolds Number Couette Flow

NASA Astrophysics Data System (ADS)

Gilmer, Caleb; Lang, Amy; Jones, Robert

2010-11-01

Recent research has revealed that thin-walled, embedded cavities in low Reynolds number flow have the potential to reduce the net viscous drag force acting on the surface. This reduction is due to the formation of embedded vortices allowing the outer flow to pass over the surface via a roller bearing effect. It is also hypothesized that the scales found on butterfly wings may act in a similar manner to cause a net increase in flying efficiency. In this experimental study, rectangular embedded cavities were designed as a means of successfully reducing the net drag across surfaces in a low Reynolds number flow. A Couette flow was generated via a rotating conveyor belt immersed in a tank of high viscosity mineral oil above which the plates with embedded cavities were placed. Drag induced on the plate models was measured using a force gauge and compared directly to measurements acquired over a flat plate. Various cavity aspect ratios and gap heights were tested in order to determine the conditions under which the greatest drag reductions occurred.

Self-sustaining turbulence in a restricted nonlinear model of plane Couette flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, Vaughan L.; Gayme, Dennice F.; Lieu, Binh K.

2014-10-15

This paper demonstrates the maintenance of self-sustaining turbulence in a restricted nonlinear (RNL) model of plane Couette flow. The RNL system is derived directly from the Navier-Stokes equations and permits higher resolution studies of the dynamical system associated with the stochastic structural stability theory (S3T) model, which is a second order approximation of the statistical state dynamics of the flow. The RNL model shares the dynamical restrictions of the S3T model but can be easily implemented by reducing a DNS code so that it retains only the RNL dynamics. Comparisons of turbulence arising from DNS and RNL simulations demonstrate thatmore » the RNL system supports self-sustaining turbulence with a mean flow as well as structural and dynamical features that are consistent with DNS. These results demonstrate that the simplified RNL system captures fundamental aspects of fully developed turbulence in wall-bounded shear flows and motivate use of the RNL/S3T framework for further study of wall-turbulence.« less

Rotation of a spheroid in a Couette flow at moderate Reynolds numbers.

PubMed

Yu, Zhaosheng; Phan-Thien, Nhan; Tanner, Roger I

2007-08-01

The rotation of a single spheroid in a planar Couette flow as a model for simple shear flow is numerically simulated with the distributed Lagrangian multiplier based fictitious domain method. The study is focused on the effects of inertia on the orbital behavior of prolate and oblate spheroids. The numerical orbits are found to be well described by a simple empirical model, which states that the rate of the spheroid rotation about the vorticity axis is a sinusoidal function of the corresponding projection angle in the flow-gradient plane, and that the exponential growth rate of the orbit function is a constant. The following transitions in the steady state with increasing Reynolds number are identified: Jeffery orbit, tumbling, quasi-Jeffery orbit, log rolling, and inclined rolling for a prolate spheroid; and Jeffery orbit, log rolling, inclined rolling, and motionless state for an oblate spheroid. In addition, it is shown that the orbit behavior is sensitive to the initial orientation in the case of strong inertia and there exist different steady states for certain shear Reynolds number regimes.

Hydrodynamic cavitation for sonochemical effects.

PubMed

Moholkar, V S; Kumar, P S; Pandit, A B

1999-03-01

A comparative study of hydrodynamic and acoustic cavitation has been made on the basis of numerical solutions of the Rayleigh-Plesset equation. The bubble/cavity behaviour has been studied under both acoustic and hydrodynamic cavitation conditions. The effect of varying pressure fields on the collapse of the cavity (sinusoidal for acoustic and linear for hydrodynamic) and also on the latter's dynamic behaviour has been studied. The variations of parameters such as initial cavity size, intensity of the acoustic field and irradiation frequency in the case of acoustic cavitation, and initial cavity size, final recovery pressure and time for pressure recovery in the case of hydrodynamic cavitation, have been found to have significant effects on cavity/bubble dynamics. The simulations reveal that the bubble/cavity collapsing behaviour in the case of hydrodynamic cavitation is accompanied by a large number of pressure pulses of relatively smaller magnitude, compared with just one or two pulses under acoustic cavitation. It has been shown that hydrodynamic cavitation offers greater control over operating parameters and the resultant cavitation intensity. Finally, a brief summary of the experimental results on the oxidation of aqueous KI solution with a hydrodynamic cavitation set-up is given which supports the conclusion of this numerical study. The methodology presented allows one to manipulate and optimise of specific process, either physical or chemical.

Solitonic Dispersive Hydrodynamics: Theory and Observation

NASA Astrophysics Data System (ADS)

Maiden, Michelle D.; Anderson, Dalton V.; Franco, Nevil A.; El, Gennady A.; Hoefer, Mark A.

2018-04-01

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

Large-Scale Description of Interacting One-Dimensional Bose Gases: Generalized Hydrodynamics Supersedes Conventional Hydrodynamics

NASA Astrophysics Data System (ADS)

Doyon, Benjamin; Dubail, Jérôme; Konik, Robert; Yoshimura, Takato

2017-11-01

The theory of generalized hydrodynamics (GHD) was recently developed as a new tool for the study of inhomogeneous time evolution in many-body interacting systems with infinitely many conserved charges. In this Letter, we show that it supersedes the widely used conventional hydrodynamics (CHD) of one-dimensional Bose gases. We illustrate this by studying "nonlinear sound waves" emanating from initial density accumulations in the Lieb-Liniger model. We show that, at zero temperature and in the absence of shocks, GHD reduces to CHD, thus for the first time justifying its use from purely hydrodynamic principles. We show that sharp profiles, which appear in finite times in CHD, immediately dissolve into a higher hierarchy of reductions of GHD, with no sustained shock. CHD thereon fails to capture the correct hydrodynamics. We establish the correct hydrodynamic equations, which are finite-dimensional reductions of GHD characterized by multiple, disjoint Fermi seas. We further verify that at nonzero temperature, CHD fails at all nonzero times. Finally, we numerically confirm the emergence of hydrodynamics at zero temperature by comparing its predictions with a full quantum simulation performed using the NRG-TSA-abacus algorithm. The analysis is performed in the full interaction range, and is not restricted to either weak- or strong-repulsion regimes.

Hydrodynamic escape from planetary atmospheres

NASA Astrophysics Data System (ADS)

Tian, Feng

Hydrodynamic escape is an important process in the formation and evolution of planetary atmospheres. Due to the existence of a singularity point near the transonic point, it is difficult to find transonic steady state solutions by solving the time-independent hydrodynamic equations. In addition to that, most previous works assume that all energy driving the escape flow is deposited in one narrow layer. This assumption not only results in less accurate solutions to the hydrodynamic escape problem, but also makes it difficult to include other chemical and physical processes in the hydrodynamic escape models. In this work, a numerical model describing the transonic hydrodynamic escape from planetary atmospheres is developed. A robust solution technique is used to solve the time dependent hydrodynamic equations. The method has been validated in an isothermal atmosphere where an analytical solution is available. The hydrodynamic model is applied to 3 cases: hydrogen escape from small orbit extrasolar planets, hydrogen escape from a hydrogen rich early Earth's atmosphere, and nitrogen/methane escape from Pluto's atmosphere. Results of simulations on extrasolar planets are in good agreement with the observations of the transiting extrasolar planet HD209458b. Hydrodynamic escape of hydrogen from other hypothetical close-in extrasolar planets are simulated and the influence of hydrogen escape on the long-term evolution of these extrasolar planets are discussed. Simulations on early Earth suggest that hydrodynamic escape of hydrogen from a hydrogen rich early Earth's atmosphere is about two orders magnitude slower than the diffusion limited escape rate. A hydrogen rich early Earth's atmosphere could have been maintained by the balance between the hydrogen escape and the supply of hydrogen into the atmosphere by volcanic outgassing. Origin of life may have occurred in the organic soup ocean created by the efficient formation of prebiotic molecules in the hydrogen rich early

Water transport by the bacterial channel alpha-hemolysin

NASA Technical Reports Server (NTRS)

Paula, S.; Akeson, M.; Deamer, D.

1999-01-01

This study is an investigation of the ability of the bacterial channel alpha-hemolysin to facilitate water permeation across biological membranes. alpha-Hemolysin channels were incorporated into rabbit erythrocyte ghosts at varying concentrations, and water permeation was induced by mixing the ghosts with hypertonic sucrose solutions. The resulting volume decrease of the ghosts was followed by time-resolved optical absorption at pH 5, 6, and 7. The average single-channel permeability coefficient of alpha-hemolysin for water ranged between 1.3x10-12 cm/s and 1.5x10-12 cm/s, depending on pH. The slightly increased single-channel permeability coefficient at lower pH-values was attributed to an increase in the effective pore size. The activation energy of water transport through the channel was low (Ea=5.4 kcal/mol), suggesting that the properties of water inside the alpha-hemolysin channel resemble those of bulk water. This conclusion was supported by calculations based on macroscopic hydrodynamic laws of laminar water flow. Using the known three-dimensional structure of the channel, the calculations accurately predicted the rate of water flow through the channel. The latter finding also indicated that water permeation data can provide a good estimate of the pore size for large channels.

Hydrodynamic simulations with the Godunov smoothed particle hydrodynamics

NASA Astrophysics Data System (ADS)

Murante, G.; Borgani, S.; Brunino, R.; Cha, S.-H.

2011-10-01

We present results based on an implementation of the Godunov smoothed particle hydrodynamics (GSPH), originally developed by Inutsuka, in the GADGET-3 hydrodynamic code. We first review the derivation of the GSPH discretization of the equations of moment and energy conservation, starting from the convolution of these equations with the interpolating kernel. The two most important aspects of the numerical implementation of these equations are (a) the appearance of fluid velocity and pressure obtained from the solution of the Riemann problem between each pair of particles, and (b) the absence of an artificial viscosity term. We carry out three different controlled hydrodynamical three-dimensional tests, namely the Sod shock tube, the development of Kelvin-Helmholtz instabilities in a shear-flow test and the 'blob' test describing the evolution of a cold cloud moving against a hot wind. The results of our tests confirm and extend in a number of aspects those recently obtained by Cha, Inutsuka & Nayakshin: (i) GSPH provides a much improved description of contact discontinuities, with respect to smoothed particle hydrodynamics (SPH), thus avoiding the appearance of spurious pressure forces; (ii) GSPH is able to follow the development of gas-dynamical instabilities, such as the Kevin-Helmholtz and the Rayleigh-Taylor ones; (iii) as a result, GSPH describes the development of curl structures in the shear-flow test and the dissolution of the cold cloud in the 'blob' test. Besides comparing the results of GSPH with those from standard SPH implementations, we also discuss in detail the effect on the performances of GSPH of changing different aspects of its implementation: choice of the number of neighbours, accuracy of the interpolation procedure to locate the interface between two fluid elements (particles) for the solution of the Riemann problem, order of the reconstruction for the assignment of variables at the interface, choice of the limiter to prevent oscillations of

On the tidal prism-channel area relations

NASA Astrophysics Data System (ADS)

D'Alpaos, Andrea; Lanzoni, Stefano; Marani, Marco; Rinaldo, Andrea

2010-03-01

We verify the broad applicability of tidal prism cross-sectional area relationships, originally proposed to relate the total water volume entering a lagoon during a characteristic tidal cycle (the tidal prism) to the size of its inlet, to arbitrary sheltered cross sections within a tidal network. We suggest, with reasonable approximation defining a statistical tendency rather than a pointwise equivalence, that the regime of tidal channels may be anywhere related to local landscape-forming prisms embedded in a characteristic spring tide oscillation. The importance of the proposed extension stems from its potential for quantitative predictions of the long-term morphological evolution of whole tidal landforms, in response to forcings affecting tidal prisms. This is the case, in particular, for alterations of relative mean sea levels possibly driven by climate change. Various 1-D and 2-D morphodynamic and hydrodynamic models are employed to evaluate peak flow rates, bottom shear stresses, and the ensuing local tidal prisms. One-dimensional morphodynamic models describing both the longitudinal and cross-sectional evolution of tidal channels are used to verify the validity of the relationship for sheltered sections. Relevant hydrodynamic features determined through accurate 2-D numerical models are compared with those obtained through time-invariant equivalents, defining a mean watershed by an energy landscape from averaged free surface gradients. Empirical evidence gathered within the lagoon of Venice (Italy) supports the proposed extension. We conclude that the geomorphic law relating tidal prisms to channel cross-sectional areas anywhere within a tidal landscape is a valuable tool for studies on long-term tidal geomorphology.

Effects of human alterations on the hydrodynamics and sediment transport in the Sacramento-San Joaquin Delta, California

USGS Publications Warehouse

Marineau, Mathieu D.; Wright, Scott A.

2015-01-01

The Sacramento-San Joaquin Delta, California, (Delta) has been significantly altered since the mid-nineteenth century. Many existing channels have been widened or deepened and new channels have been created for navigation and water conveyance. Tidal marshes have been drained and leveed to form islands that have subsided, some of which have permanently flooded. To understand how these alterations have affected hydrodynamics and sediment transport in the Delta, we analysed measurements from 27 sites, along with other spatial data, and previous literature. Results show that: (a) the permanent flooding of islands results in an increase in the shear velocity of channels downstream, (b) artificial widening and deepening of channels generally results in a decrease in shear velocity except when the channel is also located downstream of a flooded island, (c) 1.5 Mt/year of sediment was deposited in the Delta (1997–2010), and of this deposited sediment, 0.31 Mt/year (21%) was removed through dredging.

What Controls the Hydrodynamics of the Central Congo River?

NASA Astrophysics Data System (ADS)

O'Loughlin, F.; Bates, P. D.

2014-12-01

Despite being the second largest river basin in the world, with a drainage area greater than 3.7 million square kilometres, little is known about the hydraulics of the Congo River. This lack of knowledge is mainly due to a mixture of conflicts and the difficulty of accessing existing data. We present results of studies which have focused primarily on the middle reach of the Congo River, located between Kisangani and Kinshasa, and its six main tributaries (Kasai, Ubangai, Sangha, Ruki, Lulonga and Lomami rivers). Through a combination of remotely sensed datasets and a hydrodynamic model we investigated what factors control the hydrodynamics of the middle reach. From the analysis of the remotely sensed datasets, we discover that variability in river width of the middle reach of the Congo is large and cannot be represented by empirical equations which relate channel geometry to basin area and discharge. Water surface slopes vary from 3.5 cm/km to 9 cm/km, which is far more than previous studies suggest. The remote datasets indicate that there exist 5 large constrictions in the river width which may result in backwater affecting between 11 and 33 percent of middle reach at low and high water respectively. These results were corroborated by the hydrodynamic model. In fact, when all constrictions caused by a narrowing in width of 1 km or more are considered, water levels along 43 percent of the middle reach change by at least 0.5 m. Using the hydrodynamic model we also investigated the importance of the wetlands to the attenuation of the flood wave through the system. Initial results suggest that for the Congo River, floodplains have far more impact on the peak magnitude than the timing of the flood wave. When the model was run with no floodplain interactions an increase in the magnitude of flood peak was observed, with the timing of the waves being consistent with observed measurements.

Luminescence and electrification in a flow of dielectric liquids through narrow channels

NASA Astrophysics Data System (ADS)

Margulis, M. A.; Pil'Gunov, V. N.

2009-08-01

Blue-violet luminescence was observed in a mineral oil, which appeared under hydrodynamic cavitation conditions in a channel orifice 1 mm in diameter in a transparent throttling device at inlet pressures higher than 2 MPa. The appearance of electric pulses when a dielectric liquid flew through a thin channel orifice was observed much earlier than luminescence arose. A device for continuously scanning electric potential along a flow without disturbing it was developed. According to the oscillograms obtained, the electric signal was high-frequency, could not be synchronized, and its separate peaks reached 1000 mV. Light emission flux decreased as the temperature of the liquid increased to 30-35°C and inlet pressure grew. The appearance of luminescence and its intensity depended on the sharpness of the entrance edge of the throttle. Studies of hydrodynamic luminescence revealed hysteresis of light emission. A mechanism of localized light emission based on an important role played by electrokinetic phenomena was suggested.

Skew resisting hydrodynamic seal

DOEpatents

Conroy, William T.; Dietle, Lannie L.; Gobeli, Jeffrey D.; Kalsi, Manmohan S.

2001-01-01

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.

A comparison of two finite element models of tidal hydrodynamics using a North Sea data set

USGS Publications Warehouse

Walters, R.A.; Werner, F.E.

1989-01-01

Using the region of the English Channel and the southern bight of the North Sea, we systematically compare the results of two independent finite element models of tidal hydrodynamics. The model intercomparison provides a means for increasing our understanding of the relevant physical processes in the region in question as well as a means for the evaluation of certain algorithmic procedures of the two models. ?? 1989.

Hydrodynamics of concordant and discordant fixed bed open-channel confluences

NASA Astrophysics Data System (ADS)

Birjukova Canelas, Olga; Lage Ferreira, Rui Miguel; Heleno Cardoso, António

2017-04-01

The detailed characterization of the flow field in river confluences constitutes a relevant step towards the understanding of the hydro-morpho-dynamics of these key zones of the fluvial system. With a few exceptions, existing works on this topic covered concordant bed scenarios, meaning that both confluent channels had the same elevation. This laboratory study aims to contribute to a detailed three-dimensional characterization of the flow field at a fixed bed confluence, as well as to shed light on how bed elevation discordance modifies the flow patterns of the converging flows. While the junction angle and the discharge ratio were kept fixed, two scenarios were studied on the basis of detailed water level and 3D ADV measurements at the denser mesh ever. The internal flow structure of the concordant bed scenario mostly complied with the classical conceptual models. A relevant difference concerns the size of the stagnation zone, much smaller close to the bed of the discordant bed confluence. A more significant difference is a horizontal flow structure, not previously identified in the literature, characterized by strong streamwise mean vorticity and strong secondary motion. It is observed for the discordant bed case, occurring along the inner wall of the main channel and downstream the junction corner. This structure is spatially well-correlated to a pronounced imbalance of cross-stream and vertical normal Reynolds stresses. This highlights the role of Reynolds stress anisotropy (RSA) that is generated in the shear layers than accompany the entrance of the tributary flow. Since this structure is not present in the concordant case, where RSA is also evident, it is argued that convective effects should also play a role in its formation, presumably due to deflection of the flow in the main channel by the tributary. The newly identified secondary motion should, thus, be a combination of Prandtĺs second kind and Prandtĺs first kind of secondary flow. The relative

Hydrodynamic controls on the long-term construction of large river floodplains and alluvial ridges

NASA Astrophysics Data System (ADS)

Nicholas, Andrew; Aalto, Rolf; Sambrook Smith, Gregory; Schwendel, Arved

2017-04-01

Floodplain construction involves the interplay between channel belt sedimentation and avulsion, overbank deposition of fines, and sediment reworking by channel migration. Each of these processes is controlled, in part, by within-channel and/or overbank hydraulics. However, while spatially-distributed hydrodynamic models are used routinely to simulate floodplain inundation and overbank sedimentation during individual floods, most existing models of long-term floodplain construction and alluvial architecture do not account for flood hydraulics explicitly. Instead, floodplain sedimentation is typically modelled as an exponential function of distance from the river, and avulsion thresholds are defined using topographic indices that quantify alluvial ridge morphology (e.g., lateral:downstream slope ratios or metrics of channel belt super-elevation). Herein, we apply a hydraulically driven model of floodplain evolution, in order to quantify the controls on alluvial ridge construction and avulsion likelihood in large lowland rivers. We combine a simple model of meander migration and cutoff with a 2D grid-based model of flood hydrodynamics and overbank sedimentation. The latter involves a finite volume solution of the shallow water equations and an advection-diffusion model for suspended sediment transport. The model is used to carry out a series of numerical experiments to investigate floodplain construction for a range of flood regimes and sediment supply scenarios, and results are compared to field data from the Rio Beni system, northern Bolivia. Model results, supported by field data, illustrate that floodplain sedimentation is characterised by a high degree of intermittency that is driven by autogenic mechanisms (i.e. even in the absence of temporal variations in flood magnitude and sediment supply). Intermittency in overbank deposits occurs over a range of temporal and spatial scales, and is associated with the interaction between channel migration dynamics and

Hydrodynamics beyond Navier-Stokes: exact solution to the lattice Boltzmann hierarchy.

PubMed

Ansumali, S; Karlin, I V; Arcidiacono, S; Abbas, A; Prasianakis, N I

2007-03-23

The exact solution to the hierarchy of nonlinear lattice Boltzmann (LB) kinetic equations in the stationary planar Couette flow is found at nonvanishing Knudsen numbers. A new method of solving LB kinetic equations which combines the method of moments with boundary conditions for populations enables us to derive closed-form solutions for all higher-order moments. A convergence of results suggests that the LB hierarchy with larger velocity sets is the novel way to approximate kinetic theory.

The use of hydro-dynamic models in the practice-oriented education of engineering students

NASA Astrophysics Data System (ADS)

Sziebert, J.; Zellei, L.; Tamás, E. A.

2009-04-01

Management tasks related to open channel flows became rather comprehensive and multi-disciplinary, particularly with the predominancy of nature management aspects. The water regime of our rivers has proven to reach extremities more and more frequently in the past decades. In order to develop and analyse alternative solutions and to handle and resolve conflicts of interests, we apply 1D hydro-dynamic models in education for the explanation of processes and to improve practical skills of our students.

Couette flow through a porous medium with heat and mass transfer in the presence of tranverse magnetic field

NASA Astrophysics Data System (ADS)

Lawanya, T.; Vidhya, M.; Govindarajan, A.

2018-04-01

This present paper deals with the investigation of couette flow of a viscous electrically conducting incompressible fluid three dimensionally through a porous medium in presence of transverse magnetic field. Approximate Solution of equations of motion and energy equations are derived using series solution method. Hartmann number, Schmidt number and Grashoff number (or) modified Grashoff number for mass transfer on the velocity and temperature distribution are numerically discussed and shown graphically. The Nusselt number and skin friction coefficients atthe plate are derived and their numerical values are shown graphically. It is seen that in the main flow direction the velocity profiles decreases due to either an increase in Schmidt number (Or) Hartmann number.

Identifying Levee Breach Hotspots via Fine Resolution 2D Hydrodynamic Modeling - a Case Study in the Obion River

NASA Astrophysics Data System (ADS)

Bhuyian, M. N. M.; Kalyanapu, A. J.; Dullo, T. T.; VandenBerge, D.

2017-12-01

The Obion River, located in North-West Tennessee was channelized in last century to increase flow capacity and reduce flooding. Upstream of the river mainly consists of multiple tributaries that merge near Rives. The lowest water level (LWL) downstream of Rives has increased about four feet since 1980. It is estimated that this phenomenon could reduce 20% of channel conveyance if water surface slope is assumed same as channel slope. Reduction in conveyance would result in a frequent exposure to flood stage and higher stage for a given flood. Bed level change and exposure to flood stage are critical to levee safety. In the Obion River, levee breach was responsible for flooding in instances even when flood stage was lower than the levee crest. In such a circumstance, accurate simulation of inundation extent via conventional flood model is challenging because, the flood models consider ground data as static and cannot accommodate breaching unless the location of breaching is specified. Therefore, the objective of this study is to propose an approach for determining hotspots of levee breach via fine resolution hydrodynamic modeling to reduce uncertainty in flood inundation modeling. A two-dimensional LiDAR based hydrodynamic model for the Obion River would be used to determine levee breach hotspots using simulated flow parameters (i.e. current velocity, change in stage, time of exposure to high stage etc.) for a design flood event. Identifying breaching hotspots would allow determining probabilistic flood extent under probable breaching conditions. This should reduce uncertainty in inundation mapping in a channelized riverine system.

Effect of the radial buoyancy on a circular Couette flow

NASA Astrophysics Data System (ADS)

Meyer, Antoine; Yoshikawa, Harunori N.; Mutabazi, Innocent

2015-11-01

The effect of a radial temperature gradient on the stability of a circular Couette flow is investigated when the gravitational acceleration is neglected. The induced radial stratification of the fluid density coupled with the centrifugal acceleration generates radial buoyancy which is centrifugal for inward heating and centripetal for outward heating. This radial buoyancy modifies the Rayleigh discriminant and induces the asymmetry between inward heating and outward heating in flow behavior. The critical modes are axisymmetric and stationary for inward heating while for outward heating, they can be oscillatory axisymmetric or nonaxisymmetric depending on fluid diffusion properties, i.e., on the Prandtl number Pr. The dependence of the critical modes on Pr is explored for different values of the radius ratio of the annulus. The power input of the radial buoyancy is compared with other power terms. The critical frequency of the oscillatory axisymmetric modes is linked to the Brunt-Väisälä frequency due to the density stratification in the radial gravity field induced by the rotation. These modes are associated with inertial waves. The dispersion relation of the oscillatory axisymmetric modes is derived in the vicinity of the critical conditions. A weakly nonlinear amplitude equation with a forcing term is proposed to explain the domination of these axisymmetric oscillatory modes over the stationary centrifugal mode.

The potential of hydrodynamic analysis for the interpretation of Martian fluvial activities

NASA Astrophysics Data System (ADS)

Kim, Jungrack; Schumann, Guy; Neal, Jeffrey; Lin, Shih-Yuan

2014-05-01

After liquid water was identified as the agent of ancient Martian fluvial activities, the valley and channels on the Martian surface were investigated by a number of remote sensing and in-situ measurements. In particular, the stereo DTMs and ortho images from various successful orbital sensors are being effectively used to trace the origin and consequences of Martian hydrological channels. For instance, to analyze the Martian fluvial activities more quantitatively using the topographic products, Burr et al. (2003) employed 1D hydrodynamic models such as HEC-RAS together with the topography by MOLA to derive water flow estimates for the Athabasca Valles area on Mars [1]. Where extensive floodplain flows or detailed 2D bathymetry for the river channel exist, it may be more accurate to simulate flows in two dimensions, especially if the direction of flow is unclear a priori. Thus in this study we demonstrated a quantitative modeling method utilizing multi-resolution Martian DTMs, constructed in line with Kim and Muller's (2009) [2] approach, and an advanced hydraulics model LISFLOOD-FP (Bates et al., 2010) [3], which simulates in-channel dynamic wave behavior by solving for 2D shallow water equations without advection. Martian gravitation and manning constants were adjusted in the hydraulic model and the inflow values were iteratively refined from the outputs of the coarser to the finer model. Then we chose the target areas among Martian fluvial geomorphologies and tested the effectiveness of high resolution hydraulic modeling to retrieve the characteristics of fluvial systems. Test sites were established in the Athabasca Valles, Bahram Vallis, and Naktong Vallis respectively. Since those sites are proposed to be originated by different fluvial mechanisms, it is expected that the outputs from hydraulics modeling will provide important clues about the evolution of each fluvial system. Hydraulics modeling in the test areas with terrestrial simulation parameters was also

Impacts of salt marsh plants on tidal channel initiation and inheritance

NASA Astrophysics Data System (ADS)

Schwarz, Christian; Ye, Qinghua; van der Wal, Daphne; Zhang, Liquan; Ysebaert, Tom; Herman, Peter MJ

2013-04-01

Tidal channel networks are the most prominent and striking features visible in tidal wetlands. They serve as major pathways for the exchange of water, sediments, nutrients and contaminants between the wetland and the adjacent open water body. Previous studies identified topography guided sheet flows, as the predominate process for tidal channel initiation. Guided through differences in local topography, sheet flows are able to locally exceed bottom shear stress thresholds, initiating scouring and incision of tidal channels, which then further grow through head ward erosion. The fate of these channels after plant colonization is described in literature as being inherited into the salt marsh through vegetation induced bank stabilization (further referred to as vegetation stabilized channel inheritance). In this study we present a combination of flume experiments and modelling simulations elucidating the impact of vegetation on tidal channel initiation. We first studied the impact of plant properties (stiff: Spartina alterniflora versus flexible: Scirpus mariqueter) on local sediment transport utilizing a flume experiment. Then a coupled hydrodynamic morphodynamic plant growth model was set up to simulate plant colonization by these two different species in the pioneer zone at the mudflat - salt marsh transition. Based on the model we investigated the ramifications of interactions between vegetation, sediment and flow on tidal channel initiation. We specifically compared the effect of vegetation properties (such as stiffness, growth velocity and stress tolerance) on emerging channel patterns, hypothesizing that vegetation mediated channel incision (vegetation induced flow routing and differential sedimentation/erosion patterns leading to tidal channel incision) plays an active role in intertidal landscape evolution. We finally extended our model simulation by imposing pre-existing mudflat channels with different maximum depths, to investigate the impact of existing

Hydrodynamic separator sediment retention testing.

DOT National Transportation Integrated Search

2010-03-01

Hydrodynamic separators are widely used in urban areas for removal of suspended sediments and floatables from : stormwater due to limited land availability for the installation of above ground stormwater best management : practices (BMPs). Hydrodynam...

Evaluation of in-channel amperometric detection using a dual-channel microchip electrophoresis device and a two-electrode potentiostat for reverse polarity separations

PubMed Central

Meneses, Diogenes; Gunasekara, Dulan B.; Pichetsurnthorn, Pann; da Silva, José A. F.; de Abreu, Fabiane C.; Lunte, Susan M.

2015-01-01

In-channel amperometric detection combined with dual-channel microchip electrophoresis is evaluated using a two-electrode isolated potentiostat for reverse polarity separations. The device consists of two separate channels with the working and reference electrodes placed at identical positions relative to the end of the channel, enabling noise subtraction. In previous reports of this configuration, normal polarity and a three-electrode detection system were used. In the two-electrode detection system described here, the electrode in the reference channel acts as both the counter and reference. The effect of electrode placement in the channels on noise and detector response was investigated using nitrite, tyrosine, and hydrogen peroxide as model compounds. The effects of electrode material and size and type of reference electrode on noise and the potential shift of hydrodynamic voltammograms for the model compounds were determined. In addition, the performance of two- and three-electrode configurations using Pt and Ag/AgCl reference electrodes was compared. Although the signal was attenuated with the Pt reference, the noise was also significantly reduced. It was found that lower LOD were obtained for all three compounds with the dual-channel configuration compared to single-channel, in-channel detection. The dual-channel method was then used for the detection of nitrite in a dermal microdialysis sample obtained from a sheep following nitroglycerin administration. PMID:25256669

Interfacial instability of wormlike micellar solutions sheared in a Taylor-Couette cell

NASA Astrophysics Data System (ADS)

Mohammadigoushki, Hadi; Muller, Susan J.

2014-11-01

We report experiments on wormlike micellar solutions sheared in a custom-made Taylor-Couette (TC) cell. The computer controlled TC cell allows us to rotate both cylinders independently. Wormlike micellar solutions containing water, CTAB, and NaNo3 with different compositions are highly elastic and exhibit shear banding. We visualized the flow field in the θ-z as well as r-z planes, using multiple cameras. When subject to low shear rates, the flow is stable and azimuthal, but becomes unstable above a certain threshold shear rate. This shear rate coincides with the onset of shear banding. Visualizing the θ-z plane shows that this instability is characterized by stationary bands equally spaced in the z direction. Increasing the shear rate results to larger wave lengths. Above a critical shear rate, experiments reveal a chaotic behavior reminiscent of elastic turbulence. We also studied the effect of ramp speed on the onset of instability and report an acceleration below which the critical Weissenberg number for onset of instability is unaffected. Moreover, visualizations in the r-z direction reveals that the interface between the two bands undulates with shear bands evolving towards the outer cylinder regardless of which cylinder is rotating.

Asymptotic behavior of modulated Taylor-Couette flows with a crystalline inner cylinder

NASA Technical Reports Server (NTRS)

Braun, R. J.; Mcfadden, G. B.; Murray, B. T.; Coriell, S. R.; Glicksman, M. E.; Selleck, M. E.

1993-01-01

The linear stability of a modulated Taylor-Couette system when the inner cylindrical boundary consists of a crystalline solid-liquid interface is considered. Both experimentally and in numerical calculations it is found that the two-phase system is significantly less stable than the analogous rigid-walled system for materials with moderately large Prandtl numbers. A numerical treatment based on Floquet theory is described, which gives results that are in good agreement with preliminary experimental findings. In addition, this instability is further examined by carrying out a formal asymptotic expansion of the solution in the limit of large Prandtl number. In this limit the Floquet analysis is considerably simplified, and the linear stability of the modulated system can be determined to leading order through a conventional stability analysis, without recourse to Floquet theory. The resulting simplified problem is then studied for both the narrow gap geometry and for the case of a finite gap. It is surprising that the determination of the linear stability of the two-phase system is considerably simpler than that of the rigid-walled system, despite the complications introduced by the presence of the crystal-melt interface.

Utilizing dimensional analysis with observed data to determine the significance of hydrodynamic solutions in coastal hydrology

USGS Publications Warehouse

Swain, Eric D.; Decker, Jeremy D.; Hughes, Joseph D.

2014-01-01

In this paper, the authors present an analysis of the magnitude of the temporal and spatial acceleration (inertial) terms in the surface-water flow equations and determine the conditions under which these inertial terms have sufficient magnitude to be required in the computations. Data from two South Florida field sites are examined and the relative magnitudes of temporal acceleration, spatial acceleration, and the gravity and friction terms are compared. Parameters are derived by using dimensionless numbers and applied to quantify the significance of the hydrodynamic effects. The time series of the ratio of the inertial and gravity terms from field sites are presented and compared with both a simplified indicator parameter and a more complex parameter called the Hydrodynamic Significance Number (HSN). Two test-case models were developed by using the SWIFT2D hydrodynamic simulator to examine flow behavior with and without the inertial terms and compute the HSN. The first model represented one of the previously-mentioned field sites during gate operations of a structure-managed coastal canal. The second model was a synthetic test case illustrating the drainage of water down a sloped surface from an initial stage while under constant flow. The analyses indicate that the times of substantial hydrodynamic effects are sporadic but significant. The simplified indicator parameter correlates much better with the hydrodynamic effect magnitude for a constant width channel such as Miami Canal than at the non-uniform North River. Higher HSN values indicate flow situations where the inertial terms are large and need to be taken into account.

Coarse-grained hydrodynamics from correlation functions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palmer, Bruce

This paper will describe a formalism for using correlation functions between different grid cells as the basis for determining coarse-grained hydrodynamic equations for modeling the behavior of mesoscopic fluid systems. Configuration from a molecular dynamics simulation are projected onto basis functions representing grid cells in a continuum hydrodynamic simulation. Equilbrium correlation functions between different grid cells are evaluated from the molecular simulation and used to determine the evolution operator for the coarse-grained hydrodynamic system. The formalism is applied to some simple hydrodynamic cases to determine the feasibility of applying this to realistic nanoscale systems.

Channel Bottom Morphology in the Deltaic Reach of the Song Hau (mekong) River Channel in Vietnam

NASA Astrophysics Data System (ADS)

Allison, M. A.; Weathers, H. D., III; Meselhe, E. A.

2016-02-01

Boat-based, channel bathymetry and bankline elevation studies were conducted in the tidal and estuarine Mekong River channel using multibeam bathymetry and LIDAR corrected for elevation by RTK satellite positioning. Two mapping campaigns, one at high discharge in October 2014 and one at low discharge in March 2015, were conducted in the lower 100 km reach of the Song Hau distributary channel to (1) examine bottom morphology and its relationship to sediment transport, and (2) to provide information to setup the grid for a multi-dimensional and reduced complexity models of channel hydrodynamics and sediment dynamics. Sand fields were identified in multibeam data by the presence of dunes that were as large as 2-4 m high and 40-80 m wavelength and by clean sands in bottom grabs. Extensive areas of sand at the head and toe of mid-channel islands displayed 10-25 m diameter circular pits that could be correlated with bucket dredge, sand mining activities observed at some of the sites. Large areas of the channel floor were relict (containing little or no modern sediment) in the high discharge campaign, identifiable by the presence of along channel erosional furrows and terraced outcrops along the channel floor and margins. Laterally extensive flat areas were also observed in the channel thalweg. Both these and the relict areas were sampled by bottom grab as stiff silty clays. Complex cross-channel combinations of these morphologies were observed in some transects, suggesting strong bottom steering of tidal and riverine currents. Relative to high discharge, transects above and below the salt penetration limit showed evidence of shallowing in the thalweg and adjacent sloping areas at low discharge in March 2015. This shallowing, combined with the reduced extent of sand fields and furrowed areas, and soft muds in grabs, suggests seasonal trapping of fine grained sediment is occurring by estuarine and tidal circulation.

Study of the Stability of Compressible Couette Flow.

NASA Astrophysics Data System (ADS)

Girard, Jeffrey John

This study is concerned with a two-dimensional disturbance of plane Couette flow. All reviewed analyses of the basic problem have led to the conclusion that the flow is unconditionally stable. All of the literature assumed the fluid was incompressible. The assumption that a fluid is incompressible neglects solutions to the problem. The motivation of the analysis presented herein is a hypothesis that some of the acoustic disturbances in the fluid, usually neglected, may interact with the mean vorticity to produce more sound. This hypothesis was discussed by Vaidya (1988). The fluid considered herein has been a viscous, heat-conducting, ideal gas. For the cases investigated in this study, most solutions exhibited stability. There were found, however, solutions at somewhat unrealistically high Mach numbers which exhibited unstable nature. Further, it was found that for even low Mach number flows, the sound solution was the least stable solution. It is thought that the interaction between the sound perturbation and the mean flow has fed energy to the disturbance from the mean flow. Enough energy was transferred to balance some of the viscous dissipation. At low Mach numbers, for the investigated cases, not enough energy was transferred to tip the flow to instability. The established theory has been challenged. All previous analysis of the basic infinitesimal perturbation problem has suggested unconditional stability. This work has shown some unstable regimes. This keeps the hope alive that analysis may one day explain the experimental evidence (which is at much lower Mach numbers). The future work should concentrate on the sound solution for this problem. It has been shown to be the least stable, though it is usually neglected. An attempt should be made to investigate the possibility of reducing the lowest Mach number for instability. Suggestions for this have been provided in Chapter 4.

Dispersive hydrodynamics: Preface

NASA Astrophysics Data System (ADS)

Biondini, G.; El, G. A.; Hoefer, M. A.; Miller, P. D.

2016-10-01

This Special Issue on Dispersive Hydrodynamics is dedicated to the memory and work of G.B. Whitham who was one of the pioneers in this field of physical applied mathematics. Some of the papers appearing here are related to work reported on at the workshop "Dispersive Hydrodynamics: The Mathematics of Dispersive Shock Waves and Applications" held in May 2015 at the Banff International Research Station. This Preface provides a broad overview of the field and summaries of the various contributions to the Special Issue, placing them in a unified context.

Hydrodynamics of electrons in graphene.

PubMed

Lucas, Andrew; Fong, Kin Chung

2018-02-07

Generic interacting many-body quantum systems are believed to behave as classical fluids on long time and length scales. Due to rapid progress in growing exceptionally pure crystals, we are now able to experimentally observe this collective motion of electrons in solid-state systems, including graphene. We present a review of recent progress in understanding the hydrodynamic limit of electronic motion in graphene, written for physicists from diverse communities. We begin by discussing the 'phase diagram' of graphene, and the inevitable presence of impurities and phonons in experimental systems. We derive hydrodynamics, both from a phenomenological perspective and using kinetic theory. We then describe how hydrodynamic electron flow is visible in electronic transport measurements. Although we focus on graphene in this review, the broader framework naturally generalizes to other materials. We assume only basic knowledge of condensed matter physics, and no prior knowledge of hydrodynamics.

Hydrodynamics of electrons in graphene

NASA Astrophysics Data System (ADS)

Lucas, Andrew; Chung Fong, Kin

2018-02-01

Generic interacting many-body quantum systems are believed to behave as classical fluids on long time and length scales. Due to rapid progress in growing exceptionally pure crystals, we are now able to experimentally observe this collective motion of electrons in solid-state systems, including graphene. We present a review of recent progress in understanding the hydrodynamic limit of electronic motion in graphene, written for physicists from diverse communities. We begin by discussing the ‘phase diagram’ of graphene, and the inevitable presence of impurities and phonons in experimental systems. We derive hydrodynamics, both from a phenomenological perspective and using kinetic theory. We then describe how hydrodynamic electron flow is visible in electronic transport measurements. Although we focus on graphene in this review, the broader framework naturally generalizes to other materials. We assume only basic knowledge of condensed matter physics, and no prior knowledge of hydrodynamics.

Hydrodynamic injection with pneumatic valving for microchip electrophoresis with total analyte utilization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Xuefei; Kelly, Ryan T.; Danielson, William F.

2011-04-26

A novel hydrodynamic injector that is directly controlled by a pneumatic valve has been developed for reproducible microchip capillary electrophoresis (CE) separations. The poly(dimethylsiloxane) (PDMS) devices used for evaluation comprise a separation channel, a side channel for sample introduction, and a pneumatic valve aligned at the intersection of the channels. A low pressure (≤ 3 psi) applied to the sample reservoir is sufficient to drive sample into the separation channel. The rapidly actuated pneumatic valve enables injection of discrete sample plugs as small as ~100 pL for CE separation. The injection volume can be easily controlled by adjusting the intersectionmore » geometry, the solution back pressure and the valve actuation time. Sample injection could be reliably operated at different frequencies (< 0.1 Hz to >2 Hz) with good reproducibility (peak height relative standard deviation ≤ 3.6%) and no sampling biases associated with the conventional electrokinetic injections. The separation channel was dynamically coated with a cationic polymer, and FITC-labeled amino acids were employed to evaluate the CE separation. Highly efficient (≥ 7.0 × 103 theoretical plates for the ~2.4 cm long channel) and reproducible CE separations were obtained. The demonstrated method has numerous advantages compared with the conventional techniques, including repeatable and unbiased injections, no sample waste, high duty cycle, controllable injected sample volume, and fewer electrodes with no need for voltage switching. The prospects of implementing this injection method for coupling multidimensional separations, for multiplexing CE separations and for sample-limited bioanalyses are discussed.« less

Hydrodynamic injection with pneumatic valving for microchip electrophoresis with total analyte utilization

PubMed Central

Sun, Xuefei; Kelly, Ryan T.; Danielson, William F.; Agrawal, Nitin; Tang, Keqi; Smith, Richard D.

2011-01-01

A novel hydrodynamic injector that is directly controlled by a pneumatic valve has been developed for reproducible microchip capillary electrophoresis (CE) separations. The poly(dimethylsiloxane) (PDMS) devices used for evaluation comprise a separation channel, a side channel for sample introduction, and a pneumatic valve aligned at the intersection of the channels. A low pressure (≤ 3 psi) applied to the sample reservoir is sufficient to drive sample into the separation channel. The rapidly actuated pneumatic valve enables injection of discrete sample plugs as small as ~100 pL for CE separation. The injection volume can be easily controlled by adjusting the intersection geometry, the solution back pressure and the valve actuation time. Sample injection could be reliably operated at different frequencies (< 0.1 Hz to >2 Hz) with good reproducibility (peak height relative standard deviation ≤ 3.6%) and no sampling biases associated with the conventional electrokinetic injections. The separation channel was dynamically coated with a cationic polymer, and FITC-labeled amino acids were employed to evaluate the CE separation. Highly efficient (≥ 7.0 × 103 theoretical plates for the ~2.4 cm long channel) and reproducible CE separations were obtained. The demonstrated method has numerous advantages compared with the conventional techniques, including repeatable and unbiased injections, little sample waste, high duty cycle, controllable injected sample volume, and fewer electrodes with no need for voltage switching. The prospects of implementing this injection method for coupling multidimensional separations, for multiplexing CE separations and for sample-limited bioanalyses are discussed. PMID:21520147

Relaxation of microparticles exposed to hydrodynamic forces in microfluidic conduits.

PubMed

Janča, Josef; Halabalová, Věra; Polášek, Vladimír; Vašina, Martin; Menshikova, Anastasia Yu

2011-02-01

The behavior of microparticles exposed to gravitational and lift forces and to the velocity gradient in flow velocity profile formed in microfluidic conduits is studied from the viewpoint of the transient period (the relaxation) between the moment at which a particle starts to be transported by the hydrodynamic flow and the time at which it reaches an equilibrium position, characterized by a balance of all active forces. The theoretical model allowing the calculation of the relaxation time is proposed. The numerical calculus based on the proposed model is compared with the experimental data obtained under different experimental conditions, namely, for different lengths of microfluidic channels, different average linear velocities of the carrier liquid, and different sizes and densities of the particles used in the study. The results are important for the optimization of microfluidic separation units such as microthermal field-flow fractionation channels in which the separation or manipulation of the microparticles of various origin, synthetic, natural, biological, etc., is performed under similar experimental conditions but by applying an additional thermodynamic force.

Drag reduction in plane Couette flow of dilute polymer solutions

NASA Astrophysics Data System (ADS)

Liu, Nansheng; Teng, Hao; Lu, Xiyun; Khomami, Bamin

2017-11-01

Drag reduction (DR) in the plane Couette flow (PCF) by the addition of flexible polymers has been studied by direct numerical simulation (DNS) in this work. Special interest has been directed to explore the similarity and difference in the DR features between the PCF and the plane Poiseuille flow (PPF), and to clarify the effects of large-scale structures (LSSs) on the near-wall turbulence. It has been demonstrated that in the near-wall region the drag-reduced PCF shares typical DR features similar to those reported for the drag-reduced PPF (White & Mungal 2008; Graham 2014), however in the core region intriguing differences are found between these two DR shear flows of polymeric solution. Specifically, in the core region of the drag-reduced PCF, the polymer chains are stretched substantial and absorb kinetic energy from the turbulent fluctuations. In commensurate, peak values of conformation tensor components Cyy and Czz occur in the core region. This finding is strikingly different from that of the drag-reduced PPF. For the drag-reduced PCF, the LSSs are found to have monotonically increasing effects on the near-wall flow as the Weissenberg number increases, and have their spanwise length scale unchanged. This work is supported by the NSFC Grants 11272306 and 11472268 and the NSF Grant CBET0755269. This research was also supported in part by allocation of advanced computational resources on DARTER by the National Institute for Computational Sciences (NICS).

Estimation of bathymetric depth and slope from data assimilation of swath altimetry into a hydrodynamic model

NASA Astrophysics Data System (ADS)

Durand, Michael; Andreadis, Konstantinos M.; Alsdorf, Douglas E.; Lettenmaier, Dennis P.; Moller, Delwyn; Wilson, Matthew

2008-10-01

The proposed Surface Water and Ocean Topography (SWOT) mission would provide measurements of water surface elevation (WSE) for characterization of storage change and discharge. River channel bathymetry is a significant source of uncertainty in estimating discharge from WSE measurements, however. In this paper, we demonstrate an ensemble-based data assimilation (DA) methodology for estimating bathymetric depth and slope from WSE measurements and the LISFLOOD-FP hydrodynamic model. We performed two proof-of-concept experiments using synthetically generated SWOT measurements. The experiments demonstrated that bathymetric depth and slope can be estimated to within 3.0 microradians or 50 cm, respectively, using SWOT WSE measurements, within the context of our DA and modeling framework. We found that channel bathymetry estimation accuracy is relatively insensitive to SWOT measurement error, because uncertainty in LISFLOOD-FP inputs (such as channel roughness and upstream boundary conditions) is likely to be of greater magnitude than measurement error.

Shear-induced crystallization of a dense rapid granular flow: hydrodynamics beyond the melting point.

PubMed

Khain, Evgeniy; Meerson, Baruch

2006-06-01

We investigate shear-induced crystallization in a very dense flow of monodisperse inelastic hard spheres. We consider a steady plane Couette flow under constant pressure and neglect gravity. We assume that the granular density is greater than the melting point of the equilibrium phase diagram of elastic hard spheres. We employ a Navier-Stokes hydrodynamics with constitutive relations all of which (except the shear viscosity) diverge at the crystal-packing density, while the shear viscosity diverges at a smaller density. The phase diagram of the steady flow is described by three parameters: an effective Mach number, a scaled energy loss parameter, and an integer number m: the number of half-oscillations in a mechanical analogy that appears in this problem. In a steady shear flow the viscous heating is balanced by energy dissipation via inelastic collisions. This balance can have different forms, producing either a uniform shear flow or a variety of more complicated, nonlinear density, velocity, and temperature profiles. In particular, the model predicts a variety of multilayer two-phase steady shear flows with sharp interphase boundaries. Such a flow may include a few zero-shear (solidlike) layers, each of which moving as a whole, separated by fluidlike regions. As we are dealing with a hard sphere model, the granulate is fluidized within the "solid" layers: the granular temperature is nonzero there, and there is energy flow through the boundaries of the solid layers. A linear stability analysis of the uniform steady shear flow is performed, and a plausible bifurcation diagram of the system, for a fixed m, is suggested. The problem of selection of m remains open.

Microscale hydrodynamics near moving contact lines

NASA Technical Reports Server (NTRS)

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

1994-01-01

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.

Pulsating flow and boundary layers in viscous electronic hydrodynamics

NASA Astrophysics Data System (ADS)

Moessner, Roderich; Surówka, Piotr; Witkowski, Piotr

2018-04-01

Motivated by experiments on a hydrodynamic regime in electron transport, we study the effect of an oscillating electric field in such a setting. We consider a long two-dimensional channel of width L , whose geometrical simplicity allows an analytical study as well as hopefully permitting an experimental realization. The response depends on viscosity ν , driving frequency ω , and ohmic heating coefficient γ via the dimensionless complex variable L/2ν (i ω +γ ) =i Ω +Σ . While at small Ω , we recover the static solution, a different regime appears at large Ω with the emergence of a boundary layer. This includes a splitting of the location of maximal flow velocity from the center towards the edges of the boundary layer, an increasingly reactive nature of the response, with the phase shift of the response varying across the channel. The scaling of the total optical conductance with L differs between the two regimes, while its frequency dependence resembles a Drude form throughout, even in the complete absence of ohmic heating, against which, at the same time, our results are stable. Current estimates for transport coefficients in graphene and delafossites suggest that the boundary-layer regime should be experimentally accessible.

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

PubMed

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

2010-07-01

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.

Cultivation of the photosynthesis microorganism in a Taylor-Couette Vortex Flow with a small aspect ratio

NASA Astrophysics Data System (ADS)

Kawai, H.; Yasui, S.; Takahashi, H.; Kikura, H.; Aritomi, M.

2009-02-01

This study focuses on the dynamics of the Taylor-Couette Vortex Flow (TVF) in a photo-bioreactor in which CO2 is changed to O2 with high efficiency by the photosynthesis ability of micro algae. Stirring by means of a screw propeller is generally used for a simple agitation. However, the problem is that there exists a very high shearing flow region just near the propeller, which causes the destruction of the alga cell by the shearing force. In contrast, the TVF mixing is expected to reduce such a local and random shearing force because of their column of steady and orderly vortices. In this study, the relationship between the microorganism growth rate and the flow structures in dilute suspensions of a TVF is investigated and the flow characteristics are measured by using an ultrasonic velocity profiler with a small aspect ratio of 3.

Anomalous hydrodynamics of Weyl materials

NASA Astrophysics Data System (ADS)

Monteiro, Gustavo; Abanov, Alexander

Kinetic theory is a useful tool to study transport in Weyl materials when the band-touching points are hidden inside a Fermi surface. It accounts, for example, for the negative magnetoresistance caused by the chiral magnetic effect and quantum oscillations (SdH effect) in the magnetoresistance together within the same framework. As an alternative approach to kinetic theory we also consider the regime of strong interactions where hydrodynamics can be applicable. A variational principle of these hydrodynamic equations can be found in and provide a natural framework to study hydrodynamic surface modes which correspond to the strongly-interacting physics signature of Fermi arcs. G.M. acknowledges the financial support from FAPESP.

Asymptotic theory of neutral stability of the Couette flow of a vibrationally excited gas

NASA Astrophysics Data System (ADS)

Grigor'ev, Yu. N.; Ershov, I. V.

2017-01-01

An asymptotic theory of the neutral stability curve for a supersonic plane Couette flow of a vibrationally excited gas is developed. The initial mathematical model consists of equations of two-temperature viscous gas dynamics, which are used to derive a spectral problem for a linear system of eighth-order ordinary differential equations within the framework of the classical linear stability theory. Unified transformations of the system for all shear flows are performed in accordance with the classical Lin scheme. The problem is reduced to an algebraic secular equation with separation into the "inviscid" and "viscous" parts, which is solved numerically. It is shown that the thus-calculated neutral stability curves agree well with the previously obtained results of the direct numerical solution of the original spectral problem. In particular, the critical Reynolds number increases with excitation enhancement, and the neutral stability curve is shifted toward the domain of higher wave numbers. This is also confirmed by means of solving an asymptotic equation for the critical Reynolds number at the Mach number M ≤ 4.

Bacterial Hydrodynamics

NASA Astrophysics Data System (ADS)

Lauga, Eric

2016-01-01

Bacteria predate plants and animals by billions of years. Today, they are the world's smallest cells, yet they represent the bulk of the world's biomass and the main reservoir of nutrients for higher organisms. Most bacteria can move on their own, and the majority of motile bacteria are able to swim in viscous fluids using slender helical appendages called flagella. Low-Reynolds number hydrodynamics is at the heart of the ability of flagella to generate propulsion at the micrometer scale. In fact, fluid dynamic forces impact many aspects of bacteriology, ranging from the ability of cells to reorient and search their surroundings to their interactions within mechanically and chemically complex environments. Using hydrodynamics as an organizing framework, I review the biomechanics of bacterial motility and look ahead to future challenges.

Validation of a Global Hydrodynamic Flood Inundation Model

NASA Astrophysics Data System (ADS)

Bates, P. D.; Smith, A.; Sampson, C. C.; Alfieri, L.; Neal, J. C.

2014-12-01

In this work we present first validation results for a hyper-resolution global flood inundation model. We use a true hydrodynamic model (LISFLOOD-FP) to simulate flood inundation at 1km resolution globally and then use downscaling algorithms to determine flood extent and depth at 90m spatial resolution. Terrain data are taken from a custom version of the SRTM data set that has been processed specifically for hydrodynamic modelling. Return periods of flood flows along the entire global river network are determined using: (1) empirical relationships between catchment characteristics and index flood magnitude in different hydroclimatic zones derived from global runoff data; and (2) an index flood growth curve, also empirically derived. Bankful return period flow is then used to set channel width and depth, and flood defence impacts are modelled using empirical relationships between GDP, urbanization and defence standard of protection. The results of these simulations are global flood hazard maps for a number of different return period events from 1 in 5 to 1 in 1000 years. We compare these predictions to flood hazard maps developed by national government agencies in the UK and Germany using similar methods but employing detailed local data, and to observed flood extent at a number of sites including St. Louis, USA and Bangkok in Thailand. Results show that global flood hazard models can have considerable skill given careful treatment to overcome errors in the publicly available data that are used as their input.

Interfacial instability of wormlike micellar solutions sheared in a Taylor-Couette cell

NASA Astrophysics Data System (ADS)

Mohammadigoushki, Hadi; Muller, Susan J.

2014-10-01

We report experiments on wormlike micellar solutions sheared in a custom-made Taylor-Couette (TC) cell. The computer controlled TC cell allows us to rotate both cylinders independently. Wormlike micellar solutions containing water, CTAB, and NaNo3 with different compositions are highly elastic and exhibit shear banding within a range of shear rate. We visualized the flow field in the θ-z as well as r-z planes, using multiple cameras. When subject to low shear rates, the flow is stable and azimuthal, but becomes unstable above a certain threshold shear rate. This shear rate coincides with the onset of shear banding. Visualizing the θ-z plane shows that this instability is characterized by stationary bands equally spaced in the z direction. Increasing the shear rate results to larger wave lengths. Above a critical shear rate, experiments reveal a chaotic behavior reminiscent of elastic turbulence. We also studied the effect of ramp speed on the onset of instability and report an acceleration below which the critical Weissenberg number for onset of instability is unaffected. Moreover, visualizations in the r-z direction reveals that the interface between the two bands undulates. The shear band evolves towards the outer cylinder upon increasing the shear rate, regardless of which cylinder is rotating.

Magnetic field induced flow pattern reversal in a ferrofluidic Taylor-Couette system

PubMed Central

Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng

2015-01-01

We investigate the dynamics of ferrofluidic wavy vortex flows in the counter-rotating Taylor-Couette system, with a focus on wavy flows with a mixture of the dominant azimuthal modes. Without external magnetic field flows are stable and pro-grade with respect to the rotation of the inner cylinder. More complex behaviors can arise when an axial or a transverse magnetic field is applied. Depending on the direction and strength of the field, multi-stable wavy states and bifurcations can occur. We uncover the phenomenon of flow pattern reversal as the strength of the magnetic field is increased through a critical value. In between the regimes of pro-grade and retrograde flow rotations, standing waves with zero angular velocities can emerge. A striking finding is that, under a transverse magnetic field, a second reversal in the flow pattern direction can occur, where the flow pattern evolves into pro-grade rotation again from a retrograde state. Flow reversal is relevant to intriguing phenomena in nature such as geomagnetic reversal. Our results suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which can be realized in laboratory experiments with potential applications in the development of modern fluid devices. PMID:26687638

Magnetic field induced flow pattern reversal in a ferrofluidic Taylor-Couette system.

PubMed

Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng

2015-12-21

We investigate the dynamics of ferrofluidic wavy vortex flows in the counter-rotating Taylor-Couette system, with a focus on wavy flows with a mixture of the dominant azimuthal modes. Without external magnetic field flows are stable and pro-grade with respect to the rotation of the inner cylinder. More complex behaviors can arise when an axial or a transverse magnetic field is applied. Depending on the direction and strength of the field, multi-stable wavy states and bifurcations can occur. We uncover the phenomenon of flow pattern reversal as the strength of the magnetic field is increased through a critical value. In between the regimes of pro-grade and retrograde flow rotations, standing waves with zero angular velocities can emerge. A striking finding is that, under a transverse magnetic field, a second reversal in the flow pattern direction can occur, where the flow pattern evolves into pro-grade rotation again from a retrograde state. Flow reversal is relevant to intriguing phenomena in nature such as geomagnetic reversal. Our results suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which can be realized in laboratory experiments with potential applications in the development of modern fluid devices.

Hydrodynamic characteristics of viscous fluid flow in screw channels formed by two ribs

NASA Astrophysics Data System (ADS)

Kadyirov, A. I.; Abaydullin, B. R.; Vachagina, E. K.

2018-03-01

The mathematical model of laminar viscous flows in screw channels, formed by two ribs, is developed using the helical coordinates. The numerical results of the flow with helical symmetry are presented.

Hydrodynamic interactions in active colloidal crystal microrheology.

PubMed

Weeber, R; Harting, J

2012-11-01

In dense colloids it is commonly assumed that hydrodynamic interactions do not play a role. However, a found theoretical quantification is often missing. We present computer simulations that are motivated by experiments where a large colloidal particle is dragged through a colloidal crystal. To qualify the influence of long-ranged hydrodynamics, we model the setup by conventional Langevin dynamics simulations and by an improved scheme with limited hydrodynamic interactions. This scheme significantly improves our results and allows to show that hydrodynamics strongly impacts the development of defects, the crystal regeneration, as well as the jamming behavior.

Numerical Hydrodynamics in General Relativity.

PubMed

Font, José A

2003-01-01

The current status of numerical solutions for the equations of ideal general relativistic hydrodynamics is reviewed. With respect to an earlier version of the article, the present update provides additional information on numerical schemes, and extends the discussion of astrophysical simulations in general relativistic hydrodynamics. Different formulations of the equations are presented, with special mention of conservative and hyperbolic formulations well-adapted to advanced numerical methods. A large sample of available numerical schemes is discussed, paying particular attention to solution procedures based on schemes exploiting the characteristic structure of the equations through linearized Riemann solvers. A comprehensive summary of astrophysical simulations in strong gravitational fields is presented. These include gravitational collapse, accretion onto black holes, and hydrodynamical evolutions of neutron stars. The material contained in these sections highlights the numerical challenges of various representative simulations. It also follows, to some extent, the chronological development of the field, concerning advances on the formulation of the gravitational field and hydrodynamic equations and the numerical methodology designed to solve them. Supplementary material is available for this article at 10.12942/lrr-2003-4.

Anthropogenic changes to the tidal channel network, sediment rerouting, and social implications in southwest Bangladesh

NASA Astrophysics Data System (ADS)

Wilson, C.; Goodbred, S. L., Jr.; Sams, S.; Small, C.

2015-12-01

The tidal channel network in southwest Bangladesh has been undergoing major adjustment in response to anthropogenic modification over the past few decades. Densely inhabited, agricultural islands that have been embanked to protect against inundation by tides, river flooding, and storm surges (i.e., polders) preclude tidal exchange and sedimentation. Studies reveal this results in elevation deficits relative to mean high water, endangering local communities when embankment failures occur (e.g., during storms, lateral channel erosion). In addition, many studies suggest that the decrease in tidal prism and associated change in hydrodynamics from poldering causes shoaling in remaining tidal channels, which can cause a disruption in transportation. The widespread closure and conversion of tidal channel areas to profitable shrimp aquaculture is also prevalent in this region. In this study, we quantify the direct closure of tidal channels due to poldering and shrimp aquaculture using historical Landsat and Google Earth imagery, and analyze the morphologic adjustment of the tidal channel network due to these perturbations. In the natural Sundarbans mangrove forest, the tidal channel network has remained relatively constant since the 1970s. In contrast, construction of polders removed >1000 km of primary tidal creeks and >90 km2 has been reclaimed outside of polders through infilling and closure of formerly-active, higher order conduit channels now used for shrimp aquaculture. Field validation confirm tidal restriction by large sluice gates is prevalent, favoring local channel siltation at rates up to 20cm/yr. With the impoundment of primary creeks and closure of 30-60% of conduit channels in the study area, an estimated 1,400 x 106 m3 of water has been removed from the tidal prism and potentially redirected within remaining channels. This has significant implications for tidal amplification in this region. Further, we estimate that 12.3 x 106 MT of sediment annually

Biased and flow driven Brownian motion in periodic channels

NASA Astrophysics Data System (ADS)

Martens, S.; Straube, A.; Schmid, G.; Schimansky-Geier, L.; Hänggi, P.

2012-02-01

In this talk we will present an expansion of the common Fick-Jacobs approximation to hydrodynamically as well as by external forces driven Brownian transport in two-dimensional channels exhibiting smoothly varying periodic cross-section. We employ an asymptotic analysis to the components of the flow field and to stationary probability density for finding the particles within the channel in a geometric parameter. We demonstrate that the problem of biased Brownian dynamics in a confined 2D geometry can be replaced by Brownian motion in an effective periodic one-dimensional potential ψ(x) which takes the external bias, the change of the local channel width, and the flow velocity component in longitudinal direction into account. In addition, we study the influence of the external force magnitude, respectively, the pressure drop of the fluid on the particle transport quantities like the averaged velocity and the effective diffusion coefficient. The critical ratio between the external force and pressure drop where the average velocity equals zero is identified and the dependence of the latter on the channel geometry is derived. Analytic findings are confirmed by numerical simulations of the particle dynamics in a reflection symmetric sinusoidal channel.

Hydrodynamic blade guide

DOEpatents

Blaedel, Kenneth L.; Davis, Pete J.; Landram, Charles S.

2000-01-01

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.

Influences of Altered River Geomorphology on Channel-Floodplain Mass and Momentum Transfer

NASA Astrophysics Data System (ADS)

Byrne, C. F.; Stone, M. C.

2017-12-01

River management strategies, including both river engineering and restoration, have altered river geomorphology and associated lateral channel-floodplain connectivity throughout the world. This altered connectivity is known to drive changes in ecologic and geomorphic processes during floods, however, quantification of altered connectivity is difficult due to the highly dynamic spatial and temporal nature of flood wave conditions. The objective of this research was to quantify the physical processes of lateral mass and momentum transfer at the channel-floodplain interface. The objective was achieved with the implementation of novel scripting and high-resolution, two-dimensional hydrodynamic modeling techniques under unsteady flow conditions. The process-based analysis focused on three geomorphic feature types within the Middle Rio Grande, New Mexico, USA: (1) historical floodplain surfaces, (2) inset floodplain surfaces formed as a result of channel training and hydrologic alteration, and (3) mechanically restored floodplain surfaces. Results suggest that inset floodplain feature types are not only subject to greater mass and momentum transfer magnitudes, but those connections are also more heterogeneous in nature compared with historical feature types. While restored floodplain feature types exhibit transfer magnitudes and heterogeneity comparable to inset feature types, the surfaces are not of great enough spatial extent to substantially influence total channel-floodplain mass and momentum transfer. Mass and momentum transfer also displayed differing characteristic changes as a result of increased flood magnitude, indicating that linked hydrodynamic processes can be altered differently as a result of geomorphic and hydrologic change. The results display the potential of high-resolution modeling strategies in capturing the spatial and temporal complexities of river processes. In addition, the results have implications for other fields of river science including

Influence of boundary conditions on the hydrodynamic forces of an oscillating sphere

NASA Astrophysics Data System (ADS)

Mirauda, Domenica; Negri, Marco; Martinelli, Luca; Malavasi, Stefano

2018-06-01

The design of submerged structures in sea currents presents certain problems that are not only connected to the shape of the obstacle but also to the number of acting forces as well as the correct modelling of the structures dynamic response. Currently, the common approach is that of integrated numerical modelling, which considers the contribution of both current and structure. The reliability of such an approach is better verified with experimental tests performed on models of simple geometry. On the basis of these considerations, the present work analyses the hydrodynamic forces acting on a sphere, which is characterised by a low mass ratio and damping. The sphere is immersed in a free surface flow and can oscillate along the streamwise and transverse flow direction. It is located at three different positions inside the current: close to the channel bottom, near the free surface and in the middle, and equally distant from both the bottom and free surface. The obtained results for different boundaries and flow kinematic conditions show a relevant influence of the free surface on the hydrodynamic forces along both the streamwise and transverse flow directions.

Changes of hydrodynamic parameters on mountain stream bed within the block ramp influence and possibility of their use for integrated river management

NASA Astrophysics Data System (ADS)

Radecki-Pawlik, Artur; Plesiński, Karol

2016-04-01

In modern river management practices and philosophy one can notice coming more into use ecological friendly hydraulic structures. Those, which are especially needed for river training works, as far as expectation of Water Framework Directive is concerned, are block ramps which are hydraulic structures working similar to riffles known very well from fluvial geomorphology studies and are natural features in streams and rivers. What is important well designed block ramps do not stop fish and invertebrates against migrating, provide natural and esthetical view being built within the river channel, still working as hydraulic engineering structures and might be used in river management in different river ecosystems. The main aim of the research was to describe changes of values of hydrodynamics parameters upstream and downstream of the block ramps and to find out their influence on hydrodynamics of the stream. The study was undertaken on the Porębianka River in the Gorce Mountains, Polish Carpathians. Observed hydrodynamic parameters within the reach of the block ramps depend on the location of measuring point and the influence of individual part of the structure. We concluded that: 1. Hydrodynamic parameters close to block ramps depend on the location of the measurement points in relation to particular elements of the structure; 2. The highest value of velocities don't cause the highest force values, which acting on the bed of the watercourse, because they are rather related to the water level of the channel; 3. The values of mean velocities, shear velocities and shear stresses were similar upstream and downstream the block ramps, which means that the structures stabilize the river bed. This study was performed within the scope of the Science Activity money from Ministry of High Education and Young Scientist's Activity Money of Department of Hydraulics Engineering and Geotechnique, University of Agriculture, Cracow, Poland

Nonlinear theory of nonstationary low Mach number channel flows of freely cooling nearly elastic granular gases.

PubMed

Meerson, Baruch; Fouxon, Itzhak; Vilenkin, Arkady

2008-02-01

We employ hydrodynamic equations to investigate nonstationary channel flows of freely cooling dilute gases of hard and smooth spheres with nearly elastic particle collisions. This work focuses on the regime where the sound travel time through the channel is much shorter than the characteristic cooling time of the gas. As a result, the gas pressure rapidly becomes almost homogeneous, while the typical Mach number of the flow drops well below unity. Eliminating the acoustic modes and employing Lagrangian coordinates, we reduce the hydrodynamic equations to a single nonlinear and nonlocal equation of a reaction-diffusion type. This equation describes a broad class of channel flows and, in particular, can follow the development of the clustering instability from a weakly perturbed homogeneous cooling state to strongly nonlinear states. If the heat diffusion is neglected, the reduced equation becomes exactly soluble, and the solution develops a finite-time density blowup. The blowup has the same local features at singularity as those exhibited by the recently found family of exact solutions of the full set of ideal hydrodynamic equations [I. Fouxon, Phys. Rev. E 75, 050301(R) (2007); I. Fouxon,Phys. Fluids 19, 093303 (2007)]. The heat diffusion, however, always becomes important near the attempted singularity. It arrests the density blowup and brings about previously unknown inhomogeneous cooling states (ICSs) of the gas, where the pressure continues to decay with time, while the density profile becomes time-independent. The ICSs represent exact solutions of the full set of granular hydrodynamic equations. Both the density profile of an ICS and the characteristic relaxation time toward it are determined by a single dimensionless parameter L that describes the relative role of the inelastic energy loss and heat diffusion. At L>1 the intermediate cooling dynamics proceeds as a competition between "holes": low-density regions of the gas. This competition resembles Ostwald

Three-dimensional couette flow of dusty fluid with heat transfer in the presence of magnetic field

NASA Astrophysics Data System (ADS)

Gayathri, R.; Govindarajan, A.; Sasikala, R.

2018-04-01

This paper is focused on the mathematical modelling of three-dimensional couette flow and heat transfer of a dusty fluid between two infinite horizontal parallel porous flat plates in the presence of an induced magnetic field. The problem is formulated using a continuum two-phase model and the resulting equations are solved analytically. The lower plate is stationary while the upper plate is undergoing uniform motion in its plane. These plates are, respectively subjected to transverse exponential injection and its corresponding removal by constant suction. Due to this type of injection velocity, the flow becomes three dimensional. The closed-form expressions for velocity and temperature fields of both the fluid and dust phase are obtained by solving the governing partial differentiation equations using the perturbation method. A selective set of graphical results is presented and discussed to show interesting features of the problem. It is found that the velocity profiles of both fluid and dust particles decrease due to the increase of (magnetic parameter) Hartmann number.

Multidimensional Simulations of Filament Channel Structure and Evolution

NASA Astrophysics Data System (ADS)

Karpen, J. T.

2007-10-01

Over the past decade, the NRL Solar Theory group has made steady progress toward formulating a comprehensive model of filament-channel structure and evolution, combining the results of our sheared 3D arcade model for the magnetic field with our thermal nonequilibrium model for the cool, dense material suspended in the corona. We have also discovered that, when a sheared arcade is embedded within the global dipolar field, the resulting stressed filament channel can erupt through the mechanism of magnetic breakout. Our progress has been largely enabled by the development and implementation of state-of-the-art 1D hydrodynamic and 3D magnetohydrodynamic (MHD) codes to simulate the field-aligned plasma thermodynamics and large-scale magnetic-field evolution, respectively. Significant questions remain, however, which could be answered with the advanced observations anticipated from Solar-B. In this review, we summarize what we have learned from our simulations about the magnetic and plasma structure, evolution, and eruption of filament channels, and suggest key observational objectives for Solar-B that will test our filament-channel and CME-initiation models and augment our understanding of the underlying physical processes.

D Hydrodynamics Simulation of Amazonian Seasonally Flooded Wetlands

NASA Astrophysics Data System (ADS)

Pinel, S. S.; Bonnet, M. P.; Da Silva, J. S.; Cavalcanti, R., Sr.; Calmant, S.

2016-12-01

In the low Amazonian basin, interactions between floodplains and river channels are important in terms of water exchanges, sediments, or nutrients. These wetlands are considered as hotspot of biodiversity and are among the most productive in the world. However, they are threatened by climatic changes and anthropic activities. Hence, considering the implications for predicting inundation status of floodplain habitats, the strong interactions between water circulation, energy fluxes, biogeochemical and ecological processes, detailed analyses of flooding dynamics are useful and needed. Numerical inundation models offer means to study the interactions among different water sources. Modeling floods events in this area is challenging because flows respond to dynamic hydraulic controls coming from several water sources, complex geomorphology, and vegetation. In addition, due to the difficulty of access, there is a lack of existing hydrological data. In this context, the use of monitoring systems by remote sensing is a good option. In this study, we simulated filling and drainage processes of an Amazon floodplain (Janauacá Lake, AM, Brazil) over a 6 years period (2006-2012). Common approaches of flow modeling in the Amazon region consist of coupling a 1D simulation of the main channel flood wave to a 2D simulation of the inundation of the floodplain. Here, our approach differs as the floodplain is fully simulated. Model used is the 3D model IPH-ECO, which consists of a three-dimensional hydrodynamic module coupled with an ecosystem module. The IPH-ECO hydrodynamic module solves the Reynolds-Averaged Navier-Stokes equations using a semi-implicit discretization. After having calibrated the simulation against roughness coefficients, we validated the model in terms of vertical accuracy against water levels (daily in situ and altimetrics data), in terms of flood extent against inundation maps deduced from available remote-sensed product imagery (ALOS-1/PALSAR.), and in terms

An updated Lagrangian particle hydrodynamics (ULPH) for Newtonian fluids

NASA Astrophysics Data System (ADS)

Tu, Qingsong; Li, Shaofan

2017-11-01

In this work, we have developed an updated Lagrangian particle hydrodynamics (ULPH) for Newtonian fluid. Unlike the smoothed particle hydrodynamics, the non-local particle hydrodynamics formulation proposed here is consistent and convergence. Unlike the state-based peridynamics, the discrete particle dynamics proposed here has no internal material bond between particles, and it is not formulated with respect to initial or a fixed referential configuration. In specific, we have shown that (1) the non-local update Lagrangian particle hydrodynamics formulation converges to the conventional local fluid mechanics formulation; (2) the non-local updated Lagrangian particle hydrodynamics can capture arbitrary flow discontinuities without any changes in the formulation, and (3) the proposed non-local particle hydrodynamics is computationally efficient and robust.

Hydrodynamic Modeling and Its Application in AUC.

PubMed

Rocco, Mattia; Byron, Olwyn

2015-01-01

The hydrodynamic parameters measured in an AUC experiment, s(20,w) and D(t)(20,w)(0), can be used to gain information on the solution structure of (bio)macromolecules and their assemblies. This entails comparing the measured parameters with those that can be computed from usually "dry" structures by "hydrodynamic modeling." In this chapter, we will first briefly put hydrodynamic modeling in perspective and present the basic physics behind it as implemented in the most commonly used methods. The important "hydration" issue is also touched upon, and the distinction between rigid bodies versus those for which flexibility must be considered in the modeling process is then made. The available hydrodynamic modeling/computation programs, HYDROPRO, BEST, SoMo, AtoB, and Zeno, the latter four all implemented within the US-SOMO suite, are described and their performance evaluated. Finally, some literature examples are presented to illustrate the potential applications of hydrodynamics in the expanding field of multiresolution modeling. © 2015 Elsevier Inc. All rights reserved.

A first computational framework for integrated hydrologic-hydrodynamic inundation modelling

NASA Astrophysics Data System (ADS)

Hoch, Jannis; Baart, Fedor; Neal, Jeffrey; van Beek, Rens; Winsemius, Hessel; Bates, Paul; Bierkens, Marc

2017-04-01

-FP. The coupling framework consists of a main script and a set of functions performing the actual model coupling as well as data processing. All that is required therefore are model schematizations of the models involved for the domain of interest. It is noteworthy that no adaptions to already existing schematizations have to be made. Within the framework, it is possible to distribute input volume from PCR-GLOBWB over the 2D hydrodynamic grid ("2D option"), or if available, directly into the 1D channels ("1D option"). Besides, it is possible to input the water volumes into the hydrodynamic models either as fluxes or states. With PCR-GLOBWB being a global model, it is possible to apply the coupling scheme anywhere, which reduces the dependency of observation data for discharge boundaries. Reducing this dependency is of particular benefit for areas where only a limited number of accurate measurements are available. First results of applying the coupling framework show that differences between both hydrodynamic models are mainly apparent in the timing of peak discharge when using the 1D option. Regarding inundation extent, applying LISFLOOD-FP with a regular grid outperforms the flexible mesh of Delft3D for those areas where a coarser spatial resolution is used in the flexible mesh. When using the 2D option, however, using Delft3D Flexible Mesh is more robust than LISFLOOD-FP due to the differences in the solver used in the models. With Delft3D Flexible Mesh solving the full Saint-Vernant equations, and LISFLOOD-FP solving the local inertial wave approximation which lacks the convective acceleration term, the framework hence allows for choosing the hydrodynamic parts based on the local characteristics of a chosen study area.

A coupled biophysical model for the distribution of the great scallop Pecten maximus in the English Channel

NASA Astrophysics Data System (ADS)

Le Goff, Clément; Lavaud, Romain; Cugier, Philippe; Jean, Fred; Flye-Sainte-Marie, Jonathan; Foucher, Eric; Desroy, Nicolas; Fifas, Spyros; Foveau, Aurélie

2017-03-01

In this paper we used a modelling approach integrating both physical and biological constraints to understand the biogeographical distribution of the great scallop Pecten maximus in the English Channel during its whole life cycle. A 3D bio-hydrodynamical model (ECO-MARS3D) providing environmental conditions was coupled to (i) a population dynamics model and (ii) an individual ecophysiological model (Dynamic Energy Budget model). We performed the coupling sequentially, which underlined the respective role of biological and physical factors in defining P. maximus distribution in the English Channel. Results show that larval dispersion by hydrodynamics explains most of the scallop distribution and enlighten the main known hotspots for the population, basically corresponding to the main fishing areas. The mechanistic description of individual bioenergetics shows that food availability and temperature control growth and reproduction and explain how populations may maintain themselves in particular locations. This last coupling leads to more realistic densities and distributions of adults in the English Channel. The results of this study improves our knowledge on the stock and distribution dynamics of P. maximus, and provides grounds for useful tools to support management strategies.

Transition regime analytical solution to gas mass flow rate in a rectangular micro channel

NASA Astrophysics Data System (ADS)

Dadzie, S. Kokou; Dongari, Nishanth

2012-11-01

We present an analytical model predicting the experimentally observed gas mass flow rate in rectangular micro channels over slip and transition regimes without the use of any fitting parameter. Previously, Sone reported a class of pure continuum regime flows that requires terms of Burnett order in constitutive equations of shear stress to be predicted appropriately. The corrective terms to the conventional Navier-Stokes equation were named the ghost effect. We demonstrate in this paper similarity between Sone ghost effect model and newly so-called 'volume diffusion hydrodynamic model'. A generic analytical solution to gas mass flow rate in a rectangular micro channel is then obtained. It is shown that the volume diffusion hydrodynamics allows to accurately predict the gas mass flow rate up to Knudsen number of 5. This can be achieved without necessitating the use of adjustable parameters in boundary conditions or parametric scaling laws for constitutive relations. The present model predicts the non-linear variation of pressure profile along the axial direction and also captures the change in curvature with increase in rarefaction.

Taming axial dispersion in hydrodynamic chromatography columns through wall patterning

NASA Astrophysics Data System (ADS)

Adrover, Alessandra; Cerbelli, Stefano; Giona, Massimiliano

2018-04-01

A well-known limitation of hydrodynamic chromatography arises from the synergistic interaction between transverse diffusion and streamwise convection, which enhances axial dispersion through the Taylor-Aris mechanism. We show that a periodic sequence of slip/no-slip conditions at the channel walls (e.g., representing wall indentations hosting stable air pockets) can significantly reduce axial dispersion, thus enhancing separation performance. The theoretical/numerical analysis is based on a generalization of Brenner's macrotransport approach to solute transport, here modified to account for the finite-size of the suspended particles. The most effective dispersion-taming outcome is observed when the alternating sequence of slip/no-slip conditions yields non-vanishing cross-sectional flow components. The combination of these components with the hindering interaction between the channel boundaries and the finite-sized particles gives rise to a non-trivial solution of Brenner's problem on the unit periodic cell, where the cross-sectional particle number density departs from the spatially homogeneous condition. In turn, this effect impacts upon the solution of the so-called b-field defining the large-scale dispersion tensor, with an overall decremental effect on the axial dispersion coefficient and on the Height Equivalent of a Theoretical Plate.

Stability and instability of hydromagnetic Taylor-Couette flows

NASA Astrophysics Data System (ADS)

Rüdiger, Günther; Gellert, Marcus; Hollerbach, Rainer; Schultz, Manfred; Stefani, Frank

2018-04-01

Decades ago S. Lundquist, S. Chandrasekhar, P. H. Roberts and R. J. Tayler first posed questions about the stability of Taylor-Couette flows of conducting material under the influence of large-scale magnetic fields. These and many new questions can now be answered numerically where the nonlinear simulations even provide the instability-induced values of several transport coefficients. The cylindrical containers are axially unbounded and penetrated by magnetic background fields with axial and/or azimuthal components. The influence of the magnetic Prandtl number Pm on the onset of the instabilities is shown to be substantial. The potential flow subject to axial fields becomes unstable against axisymmetric perturbations for a certain supercritical value of the averaged Reynolds number Rm bar =√{ Re ṡ Rm } (with Re the Reynolds number of rotation, Rm its magnetic Reynolds number). Rotation profiles as flat as the quasi-Keplerian rotation law scale similarly but only for Pm ≫ 1 while for Pm ≪ 1 the instability instead sets in for supercritical Rm at an optimal value of the magnetic field. Among the considered instabilities of azimuthal fields, those of the Chandrasekhar-type, where the background field and the background flow have identical radial profiles, are particularly interesting. They are unstable against nonaxisymmetric perturbations if at least one of the diffusivities is non-zero. For Pm ≪ 1 the onset of the instability scales with Re while it scales with Rm bar for Pm ≫ 1. Even superrotation can be destabilized by azimuthal and current-free magnetic fields; this recently discovered nonaxisymmetric instability is of a double-diffusive character, thus excluding Pm = 1. It scales with Re for Pm → 0 and with Rm for Pm → ∞. The presented results allow the construction of several new experiments with liquid metals as the conducting fluid. Some of them are described here and their results will be discussed together with relevant diversifications of

Generalized Couette Poiseuille flow with boundary mass transfer

NASA Astrophysics Data System (ADS)

Marques, F.; Sanchez, J.; Weidman, P. D.

1998-11-01

A generalized similarity formulation extending the work of Terrill (1967) for Couette Poiseuille flow in the annulus between concentric cylinders of infinite extent is given. Boundary conditions compatible with the formulation allow a study of the effects of inner and outer cylinder transpiration, rotation, translation, stretching and twisting, in addition to that of an externally imposed constant axial pressure gradient. The problem is governed by [eta], the ratio of inner to outer radii, a Poiseuille number, and nine Reynolds numbers. Single-cylinder and planar problems can be recovered in the limits [eta][rightward arrow]0 and [eta][rightward arrow]1, respectively. Two coupled primary nonlinear equations govern the meridional motion generated by uniform mass flux through the porous walls and the azimuthal motion generated by torsional movement of the cylinders; subsidiary equations linearly slaved to the primary flow govern the effects of cylinder translation, cylinder rotation, and an external pressure gradient. Steady solutions of the primary equations for uniform source/sink flow of strength F through the inner cylinder are reported for 0[less-than-or-eq, slant][eta][less-than-or-eq, slant]1. Asymptotic results corroborating the numerical solutions are found in different limiting cases. For F<0 fluid emitted through the inner cylinder fills the gap and flows uniaxially down the annulus; an asymptotic analysis leads to a scaling that removes the effect of [eta] in the pressure parameter [beta], namely [beta]=[pi]2R*2, where R*=F(1[minus sign][eta])/(1+[eta]). The case of sink flow for F>0 is more complex in that unique solutions are found at low Reynolds numbers, a region of triple solutions exists at moderate Reynolds numbers, and a two-cell solution prevails at large Reynolds numbers. The subsidiary linear equations are solved at [eta]=0.5 to exhibit the effects of cylinder translation, rotation, and an axial pressure gradient on the source/sink flows.

Relativistic Hydrodynamics for Heavy-Ion Collisions

ERIC Educational Resources Information Center

Ollitrault, Jean-Yves

2008-01-01

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…

Experimental investigation of head resistance reduction in bubbly Couette-Taylor flow

NASA Astrophysics Data System (ADS)

Maryami, R.; Javadpoor, M.; Farahat, S.

2016-12-01

Small bubble experiments are carried out in a circulating vertical Couette-Taylor flow system to investigate the effect of air bubbles on head resistance. In the system with inner rotating cylinder and circulating flow, flow is combined with circumferential and axial flow. Moreover, the variation range of rotational Reynolds number is 7 × 103 ≤ {Re}_{ω } ≤ 70 × 103 and small bubbles are dispersed into fully turbulent flow which consists of Taylor vortices. The modification of head resistance is examined by measuring the pressure difference between two certain holes along the cylinders axis. The results show that head resistance is decreased in the presence of small bubbles and a head resistance reduction greater than 60 % is achieved in low {Re}_{ω } s and in all {Re}_{ax} s changing from 299.15 to 396.27. The effect of air bubbles on vortices could be possible reason for head resistance reduction. Since Taylor vortices are stable in this regime, bubbles decrease the momentum transfer by elongating vortices along the axis of cylinders and decreasing their numbers. The positive effect of air bubbles on head resistance reduction is diminished when {Re}_{ω } is increased. Moreover, in certain ranges of {Re}_{ω }, small bubbles enhance head resistance when {Re}_{ax} is increased. It is predicted that negative effect of small bubbles on head resistance reduction is due to flow turbulence enhancement when {Re}_{ω } and {Re}_{ax} are increased.

Hydrodynamic simulations of mechanical stellar feedback in a molecular cloud formed by thermal instability

NASA Astrophysics Data System (ADS)

Wareing, C. J.; Pittard, J. M.; Falle, S. A. E. G.

2017-09-01

We have used the AMR hydrodynamic code, mg, to perform 3D hydrodynamic simulations with self-gravity of stellar feedback in a spherical clumpy molecular cloud formed through the action of thermal instability. We simulate the interaction of the mechanical energy input from 15, 40, 60 and 120 M⊙ stars into a 100 pc diameter 16 500 M⊙ cloud with a roughly spherical morphology with randomly distributed high-density condensations. The stellar winds are introduced using appropriate non-rotating Geneva stellar evolution models. In the 15 M⊙ star case, the wind has very little effect, spreading around a few neighbouring clumps before becoming overwhelmed by the cloud collapse. In contrast, in the 40, 60 and 120 M⊙ star cases, the more powerful stellar winds create large cavities and carve channels through the cloud, breaking out into the surrounding tenuous medium during the wind phase and considerably altering the cloud structure. After 4.97, 3.97 and 3.01 Myr, respectively, the massive stars explode as supernovae (SNe). The wind-sculpted surroundings considerably affect the evolution of these SN events as they both escape the cloud along wind-carved channels and sweep up remaining clumps of cloud/wind material. The 'cloud' as a coherent structure does not survive the SN from any of these stars, but only in the 120 M⊙ case is the cold molecular material completely destabilized and returned to the unstable thermal phase. In the 40 and 60 M⊙ cases, coherent clumps of cold material are ejected from the cloud by the SN, potentially capable of further star formation.

Sediment sorting at a side channel bifurcation

NASA Astrophysics Data System (ADS)

van Denderen, Pepijn; Schielen, Ralph; Hulscher, Suzanne

2017-04-01

Side channels have been constructed to reduce the flood risk and to increase the ecological value of the river. In various Dutch side channels large aggradation in these channels occurred after construction. Measurements show that the grain size of the deposited sediment in the side channel is smaller than the grain size found on the bed of the main channel. This suggest that sorting occurs at the bifurcation of the side channel. The objective is to reproduce with a 2D morphological model the fining of the bed in the side channel and to study the effect of the sediment sorting on morphodynamic development of the side channel. We use a 2D Delft3D model with two sediment fractions. The first fraction corresponds with the grain size that can be found on the bed of the main channel and the second fraction corresponds with the grain size found in the side channel. With the numerical model we compute several side channel configurations in which we vary the length and the width of the side channel, and the curvature of the upstream channel. From these computations we can derive the equilibrium state and the time scale of the morphodynamic development of the side channel. Preliminary results show that even when a simple sediment transport relation is used, like Engelund & Hansen, more fine sediment enters the side channel than coarse sediment. This is as expected, and is probably related to the bed slope effects which are a function of the Shields parameter. It is expected that by adding a sill at the entrance of the side channel the slope effect increases. This might reduce the amount of coarse sediment which enters the side channel even more. It is unclear whether the model used is able to reproduce the effect of such a sill correctly as modelling a sill and reproducing the correct hydrodynamic and morphodynamic behaviour is not straightforward in a 2D model. Acknowledgements: This research is funded by STW, part of the Dutch Organization for Scientific Research under

Instability of the roll-streak structure induced by background turbulence in pretransitional Couette flow

NASA Astrophysics Data System (ADS)

Farrell, Brian F.; Ioannou, Petros J.; Nikolaidis, Marios-Andreas

2017-03-01

Although the roll-streak structure is ubiquitous in both observations and simulations of pretransitional wall-bounded shear flow, this structure is linearly stable if the idealization of laminar flow is made. Lacking an instability, the large transient growth of the roll-streak structure has been invoked to explain its appearance as resulting from chance occurrence in the background turbulence of perturbations configured to optimally excite it. However, there is an alternative interpretation for the role of free-stream turbulence in the genesis of the roll-streak structure, which is that the background turbulence interacts with the roll-streak structure to destabilize it. Statistical state dynamics (SSD) provides analysis methods for studying instabilities of this type that arise from interaction between the coherent and incoherent components of turbulence. SSD in the form of a closure at second order is used in this work to analyze the cooperative eigenmodes arising from interaction between the coherent streamwise invariant component and the incoherent background component of turbulence. In pretransitional Couette flow a manifold of stable modes with roll-streak form is found to exist in the presence of low-intensity background turbulence. The least stable mode of this manifold is destabilized at a critical value of a parameter controlling the background turbulence intensity and a finite-amplitude roll-streak structure arises from this instability through a bifurcation in this parameter. Although this bifurcation has analytical expression only in the infinite ensemble formulation of second order SSD, referred in this work as the S3T system, it is closely reflected in numerical simulations of both the dynamically similar quasilinear system, referred to as the restricted nonlinear (RNL) system, as well as in the full Navier-Stokes equations. This correspondence is verified using ensemble implementations of the RNL system and the Navier-Stokes equations. The S3T

Entropy-limited hydrodynamics: a novel approach to relativistic hydrodynamics

NASA Astrophysics Data System (ADS)

Guercilena, Federico; Radice, David; Rezzolla, Luciano

2017-07-01

We present entropy-limited hydrodynamics (ELH): a new approach for the computation of numerical fluxes arising in the discretization of hyperbolic equations in conservation form. ELH is based on the hybridisation of an unfiltered high-order scheme with the first-order Lax-Friedrichs method. The activation of the low-order part of the scheme is driven by a measure of the locally generated entropy inspired by the artificial-viscosity method proposed by Guermond et al. (J. Comput. Phys. 230(11):4248-4267, 2011, doi: 10.1016/j.jcp.2010.11.043). Here, we present ELH in the context of high-order finite-differencing methods and of the equations of general-relativistic hydrodynamics. We study the performance of ELH in a series of classical astrophysical tests in general relativity involving isolated, rotating and nonrotating neutron stars, and including a case of gravitational collapse to black hole. We present a detailed comparison of ELH with the fifth-order monotonicity preserving method MP5 (Suresh and Huynh in J. Comput. Phys. 136(1):83-99, 1997, doi: 10.1006/jcph.1997.5745), one of the most common high-order schemes currently employed in numerical-relativity simulations. We find that ELH achieves comparable and, in many of the cases studied here, better accuracy than more traditional methods at a fraction of the computational cost (up to {˜}50% speedup). Given its accuracy and its simplicity of implementation, ELH is a promising framework for the development of new special- and general-relativistic hydrodynamics codes well adapted for massively parallel supercomputers.

Non-linear dynamics and alternating 'flip' solutions in ferrofluidic Taylor-Couette flow

NASA Astrophysics Data System (ADS)

Altmeyer, Sebastian

2018-04-01

This study treats with the influence of a symmetry-breaking transversal magnetic field on the nonlinear dynamics of ferrofluidic Taylor-Couette flow - flow confined between two concentric independently rotating cylinders. We detected alternating 'flip' solutions which are flow states featuring typical characteristics of slow-fast-dynamics in dynamical systems. The flip corresponds to a temporal change in the axial wavenumber and we find them to appear either as pure 2-fold axisymmetric (due to the symmetry-breaking nature of the applied transversal magnetic field) or involving non-axisymmetric, helical modes in its interim solution. The latter ones show features of typical ribbon solutions. In any case the flip solutions have a preferential first axial wavenumber which corresponds to the more stable state (slow dynamics) and second axial wavenumber, corresponding to the short appearing more unstable state (fast dynamics). However, in both cases the flip time grows exponential with increasing the magnetic field strength before the flip solutions, living on 2-tori invariant manifolds, cease to exist, with lifetime going to infinity. Further we show that ferrofluidic flow turbulence differ from the classical, ordinary (usually at high Reynolds number) turbulence. The applied magnetic field hinders the free motion of ferrofluid partials and therefore smoothen typical turbulent quantities and features so that speaking of mildly chaotic dynamics seems to be a more appropriate expression for the observed motion.

New Hydrodynamic Flows in Fluctuating Superconductors

NASA Astrophysics Data System (ADS)

Delacretaz, Luca; Lucas, Andy; Hartnoll, Sean; SITP Collaboration

Recent advances, both theoretical and experimental, have made it possible to observe hydrodynamic flow in electron systems such as graphene and extract hydrodynamic transport coefficients such as the shear viscosity. Following the same logic, I will show how certain flows in superconductors could show signatures of fluctuating superconductivity.

Hydrodynamic simulations of pulsar glitch recovery

NASA Astrophysics Data System (ADS)

Howitt, G.; Haskell, B.; Melatos, A.

2016-08-01

Glitches are sudden jumps in the spin frequency of pulsars believed to originate in the superfluid interior of neutron stars. Superfluid flow in a model neutron star is simulated by solving the equations of motion of a two-component superfluid consisting of a viscous proton-electron plasma and an inviscid neutron condensate in a spherical Couette geometry. We examine the response of the model to glitches induced in three different ways: by instantaneous changes of the spin frequency of the inner and outer boundaries, and by instantaneous recoupling of the fluid components in the bulk. All simulations are performed with strong and weak mutual friction. It is found that the maximum size of a glitch originating in the bulk decreases as the mutual friction strengthens. It is also found that mutual friction determines the fraction of the frequency jump which is later recovered, a quantity known as the `healing parameter'. These behaviours may explain some of the diversity in observed glitch recoveries.

Holographic constraints on Bjorken hydrodynamics at finite coupling

NASA Astrophysics Data System (ADS)

DiNunno, Brandon S.; Grozdanov, Sašo; Pedraza, Juan F.; Young, Steve

2017-10-01

In large- N c conformal field theories with classical holographic duals, inverse coupling constant corrections are obtained by considering higher-derivative terms in the corresponding gravity theory. In this work, we use type IIB supergravity and bottom-up Gauss-Bonnet gravity to study the dynamics of boost-invariant Bjorken hydrodynamics at finite coupling. We analyze the time-dependent decay properties of non-local observables (scalar two-point functions and Wilson loops) probing the different models of Bjorken flow and show that they can be expressed generically in terms of a few field theory parameters. In addition, our computations provide an analytically quantifiable probe of the coupling-dependent validity of hydrodynamics at early times in a simple model of heavy-ion collisions, which is an observable closely analogous to the hydrodynamization time of a quark-gluon plasma. We find that to third order in the hydrodynamic expansion, the convergence of hydrodynamics is improved and that generically, as expected from field theory considerations and recent holographic results, the applicability of hydrodynamics is delayed as the field theory coupling decreases.

Frequency-dependent hydrodynamic interaction between two solid spheres

NASA Astrophysics Data System (ADS)

Jung, Gerhard; Schmid, Friederike

2017-12-01

Hydrodynamic interactions play an important role in many areas of soft matter science. In simulations with implicit solvent, various techniques such as Brownian or Stokesian dynamics explicitly include hydrodynamic interactions a posteriori by using hydrodynamic diffusion tensors derived from the Stokes equation. However, this equation assumes the interaction to be instantaneous which is an idealized approximation and only valid on long time scales. In the present paper, we go one step further and analyze the time-dependence of hydrodynamic interactions between finite-sized particles in a compressible fluid on the basis of the linearized Navier-Stokes equation. The theoretical results show that at high frequencies, the compressibility of the fluid has a significant impact on the frequency-dependent pair interactions. The predictions of hydrodynamic theory are compared to molecular dynamics simulations of two nanocolloids in a Lennard-Jones fluid. For this system, we reconstruct memory functions by extending the inverse Volterra technique. The simulation data agree very well with the theory, therefore, the theory can be used to implement dynamically consistent hydrodynamic interactions in the increasingly popular field of non-Markovian modeling.

Elliptical, parabolic, and hyperbolic exchanges of energy in drag reducing plane Couette flows

NASA Astrophysics Data System (ADS)

Pereira, Anselmo S.; Mompean, Gilmar; Thompson, Roney L.; Soares, Edson J.

2017-11-01

In the present paper, we investigate the polymer-turbulence interaction by discriminating between the mechanical responses of this system to three different subdomains: elliptical, parabolic, and hyperbolic, corresponding to regions where the magnitude of vorticity is greater than, equal to, or less than the magnitude of the rate of strain, respectively, in accordance with the Q-criterion. Recently, it was recognized that hyperbolic structures play a crucial role in the drag reduction phenomenon of viscoelastic turbulent flows, thanks to the observation that hyperbolic structures, as well as vortical ones, are weakened by the action of polymers in turbulent flows in a process that can be referred to as flow parabolization. We employ direct numerical simulations of a viscoelastic finite extensible nonlinear elastic model with the Peterlin approximation to examine the transient evolution and statistically steady regimes of a plane Couette flow that has been perturbed from a laminar flow at an initial time and developed a turbulent regime as a result of this perturbation. We have found that even more activity is located within the confines of the hyperbolic structures than in the elliptical ones, which highlights the importance of considering the role of hyperbolic structures in the drag reduction mechanism.

Hydrodynamics of insect spermatozoa

NASA Astrophysics Data System (ADS)

Pak, On Shun; Lauga, Eric

2010-11-01

Microorganism motility plays important roles in many biological processes including reproduction. Many microorganisms propel themselves by propagating traveling waves along their flagella. Depending on the species, propagation of planar waves (e.g. Ceratium) and helical waves (e.g. Trichomonas) were observed in eukaryotic flagellar motion, and hydrodynamic models for both were proposed in the past. However, the motility of insect spermatozoa remains largely unexplored. An interesting morphological feature of such cells, first observed in Tenebrio molitor and Bacillus rossius, is the double helical deformation pattern along the flagella, which is characterized by the presence of two superimposed helical flagellar waves (one with a large amplitude and low frequency, and the other with a small amplitude and high frequency). Here we present the first hydrodynamic investigation of the locomotion of insect spermatozoa. The swimming kinematics, trajectories and hydrodynamic efficiency of the swimmer are computed based on the prescribed double helical deformation pattern. We then compare our theoretical predictions with experimental measurements, and explore the dependence of the swimming performance on the geometric and dynamical parameters.

Hydrodynamical processes in planet-forming accretion disks

NASA Astrophysics Data System (ADS)

Lin, Min-Kai

Understanding the physics of accretion flows in circumstellar disk provides the foundation to any theory of planet formation. The last few years have witnessed dramatic a revision in the fundamental fluid dynamics of protoplanetary accretion disks. There is growing evidence that the key to answering some of the most pressing questions, such as the origin of disk turbulence, mass transport, and planetesimal formation, may lie within, and intimately linked to, purely hydrodynamical processes in protoplanetary disks. Recent studies, including those from the proposal team, have discovered and highlighted the significance of several new hydrodynamical instabilities in the planet-forming regions of these disks. These include, but not limited to: the vertical shear instability, active between 10 to 100 AU; the zombie vortex instability, operating in regions interior to about 1AU; and the convective over-stability at intermediate radii. Secondary Rossbywave and elliptic instabilities may also be triggered, feeding off the structures that emerge from the above primary instabilities. The result of these hydrodynamic processes range from small-scale turbulence that transports angular momentum, to large-scale vortices that concentrate dust particles and enhance planetesimal formation. Hydrodynamic processes pertain to a wide range of disk conditions, meaning that at least one of these processes are active at any given disk location and evolutionary epoch. This remains true even after planet formation, which affects their subsequent orbital evolution. Hydrodynamical processes also have direct observable consequences. For example, vortices have being invoked to explain recent ALMA images of asymmetric `dust-traps' in transition disks. Hydrodynamic activities thus play a crucial role at every stage of planet formation and disk evolution. We propose to develop theoretical models of the above hydrodynamic processes under physical disk conditions by properly accounting for disk

Hydrodynamics based transfection in normal and fibrotic rats

PubMed Central

Yeikilis, Rita; Gal, Shunit; Kopeiko, Natalia; Paizi, Melia; Pines, Mark; Braet, Filip; Spira, Gadi

2006-01-01

AIM: Hydrodynamics based transfection (HBT), the injection of a large volume of naked plasmid DNA in a short time is a relatively simple, efficient and safe method for in vivo transfection of liver cells. Though used for quite some time, the mechanism of gene transfection has not yet been elucidated. METHODS: A luciferase encoding plasmid was injected using the hydrodynamics based procedure into normal and thioacetamide-induced fibrotic Sprague Dawley rats. Scanning and transmission electron microscopy images were taken. The consequence of a dual injection of Ringer solution and luciferase pDNA was followed. Halofuginone, an anti collagen type I inhibitor was used to reduce ECM load in fibrotic rats prior to the hydrodynamic injection. RESULTS: Large endothelial gaps formed as soon as 10’ following hydrodynamic injection; these gradually returned to normal 10 d post injection. Hydrodynamic administration of Ringer 10 or 30 m prior to moderate injection of plasmid did not result in efficient transfection suggesting that endothelial gaps by themselves are not sufficient for gene expression. Gene transfection following hydrodynamic injection in thioacetamide induced fibrotic rats was diminished coinciding with the level of fibrosis. Halofuginone, a specific collagen typeIinhibitor, alleviated this effect. CONCLUSION: The hydrodynamic pressure formed following HBT results in the formation of large endothelial gaps. These gaps, though important in the transfer of DNA molecules from the blood to the space of Disse are not enough to provide the appropriate conditions for hepatocyte transfection. Hydrodynamics based injection is applicable in fibrotic rats provided that ECM load is reduced. PMID:17036386

Improved Large-Scale Inundation Modelling by 1D-2D Coupling and Consideration of Hydrologic and Hydrodynamic Processes - a Case Study in the Amazon

NASA Astrophysics Data System (ADS)

Hoch, J. M.; Bierkens, M. F.; Van Beek, R.; Winsemius, H.; Haag, A.

2015-12-01

Understanding the dynamics of fluvial floods is paramount to accurate flood hazard and risk modeling. Currently, economic losses due to flooding constitute about one third of all damage resulting from natural hazards. Given future projections of climate change, the anticipated increase in the World's population and the associated implications, sound knowledge of flood hazard and related risk is crucial. Fluvial floods are cross-border phenomena that need to be addressed accordingly. Yet, only few studies model floods at the large-scale which is preferable to tiling the output of small-scale models. Most models cannot realistically model flood wave propagation due to a lack of either detailed channel and floodplain geometry or the absence of hydrologic processes. This study aims to develop a large-scale modeling tool that accounts for both hydrologic and hydrodynamic processes, to find and understand possible sources of errors and improvements and to assess how the added hydrodynamics affect flood wave propagation. Flood wave propagation is simulated by DELFT3D-FM (FM), a hydrodynamic model using a flexible mesh to schematize the study area. It is coupled to PCR-GLOBWB (PCR), a macro-scale hydrological model, that has its own simpler 1D routing scheme (DynRout) which has already been used for global inundation modeling and flood risk assessments (GLOFRIS; Winsemius et al., 2013). A number of model set-ups are compared and benchmarked for the simulation period 1986-1996: (0) PCR with DynRout; (1) using a FM 2D flexible mesh forced with PCR output and (2) as in (1) but discriminating between 1D channels and 2D floodplains, and, for comparison, (3) and (4) the same set-ups as (1) and (2) but forced with observed GRDC discharge values. Outputs are subsequently validated against observed GRDC data at Óbidos and flood extent maps from the Dartmouth Flood Observatory. The present research constitutes a first step into a globally applicable approach to fully couple

Hydrodynamic Limit of Multiple SLE

NASA Astrophysics Data System (ADS)

Hotta, Ikkei; Katori, Makoto

2018-04-01

Recently del Monaco and Schleißinger addressed an interesting problem whether one can take the limit of multiple Schramm-Loewner evolution (SLE) as the number of slits N goes to infinity. When the N slits grow from points on the real line R in a simultaneous way and go to infinity within the upper half plane H, an ordinary differential equation describing time evolution of the conformal map g_t(z) was derived in the N → ∞ limit, which is coupled with a complex Burgers equation in the inviscid limit. It is well known that the complex Burgers equation governs the hydrodynamic limit of the Dyson model defined on R studied in random matrix theory, and when all particles start from the origin, the solution of this Burgers equation is given by the Stieltjes transformation of the measure which follows a time-dependent version of Wigner's semicircle law. In the present paper, first we study the hydrodynamic limit of the multiple SLE in the case that all slits start from the origin. We show that the time-dependent version of Wigner's semicircle law determines the time evolution of the SLE hull, K_t \\subset H\\cup R, in this hydrodynamic limit. Next we consider the situation such that a half number of the slits start from a>0 and another half of slits start from -a < 0, and determine the multiple SLE in the hydrodynamic limit. After reporting these exact solutions, we will discuss the universal long-term behavior of the multiple SLE and its hull K_t in the hydrodynamic limit.

Electrochemistry in hollow-channel paper analytical devices.

PubMed

Renault, Christophe; Anderson, Morgan J; Crooks, Richard M

2014-03-26

In the present article we provide a detailed analysis of fundamental electrochemical processes in a new class of paper-based analytical devices (PADs) having hollow channels (HCs). Voltammetry and amperometry were applied under flow and no flow conditions yielding reproducible electrochemical signals that can be described by classical electrochemical theory as well as finite-element simulations. The results shown here provide new and quantitative insights into the flow within HC-PADs. The interesting new result is that despite their remarkable simplicity these HC-PADs exhibit electrochemical and hydrodynamic behavior similar to that of traditional microelectrochemical devices.

Nonlinear elastic instability in channel flows at low Reynolds numbers.

PubMed

Pan, L; Morozov, A; Wagner, C; Arratia, P E

2013-04-26

It is presently believed that flows of viscoelastic polymer solutions in geometries such as a straight pipe or channel are linearly stable. Here we present experimental evidence that such flows can be nonlinearly unstable and can exhibit a subcritical bifurcation. Velocimetry measurements are performed in a long, straight microchannel; flow disturbances are introduced at the entrance of the channel system by placing a variable number of obstacles. Above a critical flow rate and a critical size of the perturbation, a sudden onset of large velocity fluctuations indicates the presence of a nonlinear subcritical instability. Together with the previous observations of hydrodynamic instabilities in curved geometries, our results suggest that any flow of polymer solutions becomes unstable at sufficiently high flow rates.

Soliton Gases and Generalized Hydrodynamics

NASA Astrophysics Data System (ADS)

Doyon, Benjamin; Yoshimura, Takato; Caux, Jean-Sébastien

2018-01-01

We show that the equations of generalized hydrodynamics (GHD), a hydrodynamic theory for integrable quantum systems at the Euler scale, emerge in full generality in a family of classical gases, which generalize the gas of hard rods. In this family, the particles, upon colliding, jump forward or backward by a distance that depends on their velocities, reminiscent of classical soliton scattering. This provides a "molecular dynamics" for GHD: a numerical solver which is efficient, flexible, and which applies to the presence of external force fields. GHD also describes the hydrodynamics of classical soliton gases. We identify the GHD of any quantum model with that of the gas of its solitonlike wave packets, thus providing a remarkable quantum-classical equivalence. The theory is directly applicable, for instance, to integrable quantum chains and to the Lieb-Liniger model realized in cold-atom experiments.

Impact of hydrodynamic interactions on protein folding rates depends on temperature

NASA Astrophysics Data System (ADS)

Zegarra, Fabio C.; Homouz, Dirar; Eliaz, Yossi; Gasic, Andrei G.; Cheung, Margaret S.

2018-03-01

We investigated the impact of hydrodynamic interactions (HI) on protein folding using a coarse-grained model. The extent of the impact of hydrodynamic interactions, whether it accelerates, retards, or has no effect on protein folding, has been controversial. Together with a theoretical framework of the energy landscape theory (ELT) for protein folding that describes the dynamics of the collective motion with a single reaction coordinate across a folding barrier, we compared the kinetic effects of HI on the folding rates of two protein models that use a chain of single beads with distinctive topologies: a 64-residue α /β chymotrypsin inhibitor 2 (CI2) protein, and a 57-residue β -barrel α -spectrin Src-homology 3 domain (SH3) protein. When comparing the protein folding kinetics simulated with Brownian dynamics in the presence of HI to that in the absence of HI, we find that the effect of HI on protein folding appears to have a "crossover" behavior about the folding temperature. This means that at a temperature greater than the folding temperature, the enhanced friction from the hydrodynamic solvents between the beads in an unfolded configuration results in lowered folding rate; conversely, at a temperature lower than the folding temperature, HI accelerates folding by the backflow of solvent toward the folded configuration of a protein. Additionally, the extent of acceleration depends on the topology of a protein: for a protein like CI2, where its folding nucleus is rather diffuse in a transition state, HI channels the formation of contacts by favoring a major folding pathway in a complex free energy landscape, thus accelerating folding. For a protein like SH3, where its folding nucleus is already specific and less diffuse, HI matters less at a temperature lower than the folding temperature. Our findings provide further theoretical insight to protein folding kinetic experiments and simulations.

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

Federal Register 2010, 2011, 2012, 2013, 2014

2013-02-12

... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [ Project No. 13531-000] Hydrodynamics, Inc.; Notice Denying Late Intervention On June 24, 2010, Commission staff issued a three-year preliminary permit to Hydrodynamics, Inc. (Hydrodynamics) to study the feasibility of its proposed East...

A field study of the confluence between Negro and Solimões Rivers. Part 1: Hydrodynamics and sediment transport

NASA Astrophysics Data System (ADS)

Gualtieri, Carlo; Filizola, Naziano; de Oliveira, Marco; Santos, Andrè Martinelli; Ianniruberto, Marco

2018-01-01

Confluences are a common feature of riverine systems, where are located converging flow streamlines and potential mixing of separate flows. The confluence of the Negro and Solimões Rivers ranks among the largest on Earth and its study may provide some general insights into large confluence dynamics and processes. An investigation was recently conducted about that confluence in both low and high-flow conditions using acoustic Doppler velocity profiling (ADCP), water quality sampling and high-resolution seismic data. First, the study gained insights into the characterization of the basic hydrodynamics parameters about the confluence as well as of those affecting sediments transport. Second, the analysis of the results showed that common hydrodynamic features noted in previous confluence studies were herein observed. Finally, some differences between low-flow and relatively high-flow conditions about the transfer of momentum from the Solimões to the Negro side of the Amazon Channel were identified.

Determination of nitrite and nitrate in water samples by an automated hydrodynamic sequential injection method.

PubMed

Somnam, Sarawut; Jakmunee, Jaroon; Grudpan, Kate; Lenghor, Narong; Motomizu, Shoji

2008-12-01

An automated hydrodynamic sequential injection (HSI) system with spectrophotometric detection was developed. Thanks to the hydrodynamic injection principle, simple devices can be used for introducing reproducible microliter volumes of both sample and reagent into the flow channel to form stacked zones in a similar fashion to those in a sequential injection system. The zones were then pushed to the detector and a peak profile was recorded. The determination of nitrite and nitrate in water samples by employing the Griess reaction was chosen as a model. Calibration graphs with linearity in the range of 0.7 - 40 muM were obtained for both nitrite and nitrate. Detection limits were found to be 0.3 muM NO(2)(-) and 0.4 muM NO(3)(-), respectively, with a sample throughput of 20 h(-1) for consecutive determination of both the species. The developed system was successfully applied to the analysis of water samples, employing simple and cost-effective instrumentation and offering higher degrees of automation and low chemical consumption.

Hydrodynamic dispersion of microswimmers in suspension

NASA Astrophysics Data System (ADS)

Martin, Matthieu; Rafaï, Salima; Peyla, Philippe

2014-11-01

In our laboratory, we study hydrodynamics of suspensions of micro-swimmers. These micro-organisms are unicellular algae Chlamydomonas Rheinhardii which are able to swim by using their flagella. The swimming dynamics of these micro-swimmers can be seen as a random walk, in absence of any kind of interaction. In addition, these algae have the property of being phototactic, i.e. they swim towards the light. Combining this property with a hydrodynamic flow, we were able to reversibly separate algae from the rest of the fluid. But for sufficiently high volume fraction, these active particles interact with each other. We are now interested in how the coupling of hydrodynamic interactions between swimmers and phototaxis can modify the swimming dynamics at the scale of the suspension. To this aim, we conduct experiments in microfluidic devices to study the dispersion of the micro-organisms in a the liquid phase as a function of the volume fraction. We show that the dispersion of an assembly of puller type microswimmers is quantitatively affected by hydrodynamics interactions. Phd student.

Anisotropic hydrodynamics for conformal Gubser flow

NASA Astrophysics Data System (ADS)

Nopoush, Mohammad; Ryblewski, Radoslaw; Strickland, Michael

2015-02-01

We derive the equations of motion for a system undergoing boost-invariant longitudinal and azimuthally symmetric transverse "Gubser flow" using leading-order anisotropic hydrodynamics. This is accomplished by assuming that the one-particle distribution function is ellipsoidally symmetric in the momenta conjugate to the de Sitter coordinates used to parametrize the Gubser flow. We then demonstrate that the S O (3 )q symmetry in de Sitter space further constrains the anisotropy tensor to be of spheroidal form. The resulting system of two coupled ordinary differential equations for the de Sitter-space momentum scale and anisotropy parameter are solved numerically and compared to a recently obtained exact solution of the relaxation-time-approximation Boltzmann equation subject to the same flow. We show that anisotropic hydrodynamics describes the spatiotemporal evolution of the system better than all currently known dissipative hydrodynamics approaches. In addition, we prove that anisotropic hydrodynamics gives the exact solution of the relaxation-time approximation Boltzmann equation in the ideal, η /s →0 , and free-streaming, η /s →∞, limits.

Assessing hydrodynamic space use of brown trout, Salmo trutta, in a complex flow environment: a return to first principles.

PubMed

Kerr, James R; Manes, Costantino; Kemp, Paul S

2016-11-01

It is commonly assumed that stream-dwelling fish should select positions where they can reduce energetic costs relative to benefits gained and enhance fitness. However, the selection of appropriate hydrodynamic metrics that predict space use is the subject of recent debate and a cause of controversy. This is for three reasons: (1) flow characteristics are often oversimplified, (2) confounding variables are not always controlled and (3) there is limited understanding of the explanatory mechanisms that underpin the biophysical interactions between fish and their hydrodynamic environment. This study investigated the space use of brown trout, Salmo trutta, in a complex hydrodynamic flow field created using an array of different sized vertically oriented cylinders in a large open-channel flume in which confounding variables were controlled. A hydrodynamic drag function (D) based on single-point time-averaged velocity statistics that incorporates the influence of turbulent fluctuations was used to infer the energetic cost of steady swimming. Novel hydrodynamic preference curves were developed and used to assess the appropriateness of D as a descriptor of space use compared with other commonly used metrics. Zones in which performance-enhancing swimming behaviours (e.g. Kármán gaiting, entraining and bow riding) that enable fish to hold position while reducing energetic costs (termed 'specialised behaviours') were identified and occupancy was recorded. We demonstrate that energy conservation strategies play a key role in space use in an energetically taxing environment with the majority of trout groups choosing to frequently occupy areas in which specialised behaviours may be adopted or by selecting low-drag regions. © 2016. Published by The Company of Biologists Ltd.

Flow field induced particle accumulation inside droplets in rectangular channels.

PubMed

Hein, Michael; Moskopp, Michael; Seemann, Ralf

2015-07-07

Particle concentration is a basic operation needed to perform washing steps or to improve subsequent analysis in many (bio)-chemical assays. In this article we present field free, hydrodynamic accumulation of particles and cells in droplets flowing within rectangular micro-channels. Depending on droplet velocity, particles either accumulate at the rear of the droplet or are dispersed over the entire droplet cross-section. We show that the observed particle accumulation behavior can be understood by a coupling of particle sedimentation to the internal flow field of the droplet. The changing accumulation patterns are explained by a qualitative change of the internal flow field. The topological change of the internal flow field, however, is explained by the evolution of the droplet shape with increasing droplet velocity altering the friction with the channel walls. In addition, we demonstrate that accumulated particles can be concentrated, removing excess dispersed phase by splitting the droplet at a simple channel junction.

Hydrodynamics experiments with soap films and soap bubbles: A short review of recent experiments

NASA Astrophysics Data System (ADS)

Kellay, H.

2017-11-01

In this short review, I focus on recent experiments that benefit from the advantages offered by the two-dimensionality of the flow in suspended thin liquid films to reconsider hydrodynamics problems which have resisted a full understanding. The first problem discussed here concerns friction drag in channel flows. The use of turbulent channel flows, using thin liquid films, allows measurements of friction drag as well as mean velocity profiles for flows with different spectral exponents. Is there a link between the spectral properties of the turbulence and the mean velocity profiles or the frictional drag? This is the first question considered. The second issue examined considers the long time dynamics of large scale vortices. These are obtained in half bubbles rendered "turbulent" through thermal convection. These vortices, which live in a quasi two-dimensional environment, have a long time dynamics where their vorticity goes through what seems to be a well-defined cycle with generic features.

Tuning bacterial hydrodynamics with magnetic fields

NASA Astrophysics Data System (ADS)

Pierce, C. J.; Mumper, E.; Brown, E. E.; Brangham, J. T.; Lower, B. H.; Lower, S. K.; Yang, F. Y.; Sooryakumar, R.

2017-06-01

Magnetotactic bacteria are a group of motile prokaryotes that synthesize chains of lipid-bound, magnetic nanoparticles called magnetosomes. This study exploits their innate magnetism to investigate previously unexplored facets of bacterial hydrodynamics at surfaces. Through use of weak, uniform, external magnetic fields and local, micromagnetic surface patterns, the relative strength of hydrodynamic, magnetic, and flagellar force components is tuned through magnetic control of the bacteria's orientation. The resulting swimming behaviors provide a means to experimentally determine hydrodynamic parameters and offer a high degree of control over large numbers of living microscopic entities. The implications of this controlled motion for studies of bacterial motility near surfaces and for micro- and nanotechnology are discussed.

Coarse-grained hydrodynamics from correlation functions

NASA Astrophysics Data System (ADS)

Palmer, Bruce

2018-02-01

This paper will describe a formalism for using correlation functions between different grid cells as the basis for determining coarse-grained hydrodynamic equations for modeling the behavior of mesoscopic fluid systems. Configurations from a molecular dynamics simulation or other atomistic simulation are projected onto basis functions representing grid cells in a continuum hydrodynamic simulation. Equilibrium correlation functions between different grid cells are evaluated from the molecular simulation and used to determine the evolution operator for the coarse-grained hydrodynamic system. The formalism is demonstrated on a discrete particle simulation of diffusion with a spatially dependent diffusion coefficient. Correlation functions are calculated from the particle simulation and the spatially varying diffusion coefficient is recovered using a fitting procedure.

Hydrodynamics in a Degenerate, Strongly Attractive Fermi Gas

NASA Technical Reports Server (NTRS)

Thomas, John E.; Kinast, Joseph; Hemmer, Staci; Turlapov, Andrey; O'Hara, Ken; Gehm, Mike; Granade, Stephen

2004-01-01

In summary, we use all-optical methods with evaporative cooling near a Feshbach resonance to produce a strongly interacting degenerate Fermi gas. We observe hydrodynamic behavior in the expansion dynamics. At low temperatures, collisions may not explain the expansion dynamics. We observe hydrodynamics in the trapped gas. Our observations include collisionally-damped excitation spectra at high temperature which were not discussed above. In addition, we observe weakly damped breathing modes at low temperature. The observed temperature dependence of the damping time and hydrodynamic frequency are not consistent with collisional dynamics nor with collisionless mean field interactions. These observations constitute the first evidence for superfluid hydrodynamics in a Fermi gas.

A hydrodynamically suspended, magnetically sealed mechanically noncontact axial flow blood pump: design of a hydrodynamic bearing.

PubMed

Mitamura, Yoshinori; Kido, Kazuyuki; Yano, Tetsuya; Sakota, Daisuke; Yambe, Tomoyuki; Sekine, Kazumitsu; OKamoto, Eiji

2007-03-01

To overcome the drive shaft seal and bearing problem in rotary blood pumps, a hydrodynamic bearing, a magnetic fluid seal, and a brushless direct current (DC) motor were employed in an axial flow pump. This enabled contact-free rotation of the impeller without material wear. The axial flow pump consisted of a brushless DC motor, an impeller, and a guide vane. The motor rotor was directly connected to the impeller by a motor shaft. A hydrodynamic bearing was installed on the motor shaft. The motor and the hydrodynamic bearing were housed in a cylindrical casing and were waterproofed by a magnetic fluid seal, a mechanically noncontact seal. Impeller shaft displacement was measured using a laser sensor. Axial and radial displacements of the shaft were only a few micrometers for motor speed up to 8500 rpm. The shaft did not make contact with the bearing housing. A flow of 5 L/min was obtained at 8000 rpm at a pressure difference of 100 mm Hg. In conclusion, the axial flow blood pump consisting of a hydrodynamic bearing, a magnetic fluid seal, and a brushless DC motor provided contact-free rotation of the impeller without material wear.

Hyperscaling-violating Lifshitz hydrodynamics from black-holes: part II

NASA Astrophysics Data System (ADS)

Kiritsis, Elias; Matsuo, Yoshinori

2017-03-01

The derivation of Lifshitz-invariant hydrodynamics from holography, presented in [1] is generalized to arbitrary hyperscaling violating Lifshitz scaling theories with an unbroken U(1) symmetry. The hydrodynamics emerging is non-relativistic with scalar "forcing". By a redefinition of the pressure it becomes standard non-relativistic hydrodynamics in the presence of specific chemical potential for the mass current. The hydrodynamics is compatible with the scaling theory of Lifshitz invariance with hyperscaling violation. The bulk viscosity vanishes while the shear viscosity to entropy ratio is the same as in the relativistic case. We also consider the dimensional reduction ansatz for the hydrodynamics and clarify the difference with previous results suggesting a non-vanishing bulk viscosity.

Pinched-flow hydrodynamic stretching of single-cells.

PubMed

Dudani, Jaideep S; Gossett, Daniel R; Tse, Henry T K; Di Carlo, Dino

2013-09-21

Reorganization of cytoskeletal networks, condensation and decondensation of chromatin, and other whole cell structural changes often accompany changes in cell state and can reflect underlying disease processes. As such, the observable mechanical properties, or mechanophenotype, which is closely linked to intracellular architecture, can be a useful label-free biomarker of disease. In order to make use of this biomarker, a tool to measure cell mechanical properties should accurately characterize clinical specimens that consist of heterogeneous cell populations or contain small diseased subpopulations. Because of the heterogeneity and potential for rare populations in clinical samples, single-cell, high-throughput assays are ideally suited. Hydrodynamic stretching has recently emerged as a powerful method for carrying out mechanical phenotyping. Importantly, this method operates independently of molecular probes, reducing cost and sample preparation time, and yields information-rich signatures of cell populations through significant image analysis automation, promoting more widespread adoption. In this work, we present an alternative mode of hydrodynamic stretching where inertially-focused cells are squeezed in flow by perpendicular high-speed pinch flows that are extracted from the single inputted cell suspension. The pinched-flow stretching method reveals expected differences in cell deformability in two model systems. Furthermore, hydraulic circuit design is used to tune stretching forces and carry out multiple stretching modes (pinched-flow and extensional) in the same microfluidic channel with a single fluid input. The ability to create a self-sheathing flow from a single input solution should have general utility for other cytometry systems and the pinched-flow design enables an order of magnitude higher throughput (65,000 cells s(-1)) compared to our previously reported deformability cytometry method, which will be especially useful for identification of rare

Numerical Hydrodynamic Study of Hypothetical Levee Setback Scenarios

DTIC Science & Technology

2018-01-01

ER D C /C HL T R- 18 -1 Flood and Coastal Systems Research and Development Program Numerical Hydrodynamic Study of Hypothetical Levee...default. Flood and Coastal Systems Research and Development Program ERDC/CHL TR-18-1 January 2018 Numerical Hydrodynamic Study of Hypothetical...Reduction” ERDC/CHL TR-18-1 ii Abstract A numerical hydrodynamic study was conducted to compare multiple levee setback alternatives to the base

Hydrodynamics and inundation of a tidal saltmarsh in Kent County, Delaware

NASA Astrophysics Data System (ADS)

Pieterse, A.; Puleo, J. A.; McKenna, T. E.

2013-12-01

A 2-week field experiment was conducted in March and April 2013 in a tidal wetland in Kent County, Delaware. The study area was a tidal flat fed by a secondary channel of a small tributary of Delaware Bay. The goal of the field study was to investigate spatio-temporal variability in the hydrodynamics of the saltmarsh and tidal flat, over the period of one spring-neap tidal cycle. The experiment combined remotely-sensed imagery with high-frequency in-situ measurements. A tower with imagers (RGB, NIR, TIR) was deployed to quantify the spatial variations of inundation of the channels, flat and marsh. In-situ sensors that measured flow velocity, sediment concentration and water depth were deployed on the tidal flat and in the channels. At three locations, a Nortek Vectrino II - profiling velocimeter was deployed that measured a 30 mm velocity profile at 1 mm vertical increments at 100 Hz. These velocity profiles are used to compute turbulent kinetic energy, energy dissipation and stress profiles close to the bed. Preliminary results of the experiment show that peak velocities occur at the beginning of the rising and end of ebbing tide, when the water levels are low. At these instances, peaks in turbulence and bed stress also occur, which coincides with the largest sediment concentrations that were observed. During both rising and falling tide, flow velocities up to 0.4 m/s were observed in the main channel leading to the tidal flat. After these initial large flow velocities, the flat inundated very quickly, and flow velocities decreased. Furthermore, due to the large flow velocities, bed erosion often took place in the channel at the beginning of each high tide, while deposition occurred during ebbing tide, resulting in small net changes over the tidal cycle. The velocities in the channel relative to those on the adjacent flat were investigated. Furthermore, the relationship between near-bed turbulence and suspended sediment concentration and an analysis of the near

Manipulation of cells' position across a microfluidic channel using a series of continuously varying herringbone structures

NASA Astrophysics Data System (ADS)

Jung, Yugyung; Hyun, Ji-chul; Choi, Jongchan; Atajanov, Arslan; Yang, Sung

2017-12-01

Controlling cells' movement is an important technique in biological analysis that is performed within a microfluidic system. Many external forces are utilized for manipulation of cells, including their position in the channel. These forces can effectively control cells in a desired manner. Most of techniques used to manipulate cells require sophisticated set-ups and equipment to generate desired effect. The exception to this is the use of hydrodynamic force. In this study, a series of continuously varying herringbone structures is proposed for positioning cells in a microfluidic channel using hydrodynamic force. This structure was experimentally developed by changing parameters, such as the length of the herringbone's apex, the length of the herringbone's base and the ratio of the height of the flat channel to the height of the herringbone structure. Results of this study, have demonstrated that the length of the herringbone's apex and the ratio of the heights of the flat channel and the herringbone structure were crucial parameters influencing positioning of cells at 100 μl/h flow rate. The final design was fixed at 170 and 80 μm for the length of herringbone's apex and the length of herringbone's base, respectively. The average position of cells in this device was 34 μm away from the side wall in a 200 μm wide channel. Finally, to substantiate a practical application of the herringbone structure for positioning, cells were randomly introduced into a microfluidic device, containing an array of trapping structures together with a series of herringbone structures along the channel. The cells were moved toward the trapping structure by the herringbone structure and the trapping efficiency was increased. Therefore, it is anticipated that this device will be utilized to continuously control cells' position without application of external forces.

Ship Hydrodynamics

ERIC Educational Resources Information Center

Lafrance, Pierre

1978-01-01

Explores in a non-mathematical treatment some of the hydrodynamical phenomena and forces that affect the operation of ships, especially at high speeds. Discusses the major components of ship resistance such as the different types of drags and ways to reduce them and how to apply those principles for the hovercraft. (GA)

Vertical Ship Motion Study for Ambrose Entrance Channel, New York

DTIC Science & Technology

2014-05-01

channels, PIANC Bulletin 1971, Vol. 1, No. 7, 17-20. Hardy, T. A. 1993. The attenuation of spectral transformation of wind waves on a coral reef ...A80(12): 95 p. Hearn, C. J. 1999. Wave -breaking hydrodynamics within coral reef systems and the effect of changing relative sea level, Journal of...Values of cf applied for coral reefs range from 0.05 to 0.40 (Hardy 1993; Hearn 1999 and Lowe et al. 2005). CMS- Wave uses a default value of cf

Hydrodynamics of fossil fishes

PubMed Central

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

2014-01-01

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

Global hydrodynamic modelling of flood inundation in continental rivers: How can we achieve it?

NASA Astrophysics Data System (ADS)

Yamazaki, D.

2016-12-01

Global-scale modelling of river hydrodynamics is essential for understanding global hydrological cycle, and is also required in interdisciplinary research fields . Global river models have been developed continuously for more than two decades, but modelling river flow at a global scale is still a challenging topic because surface water movement in continental rivers is a multi-spatial-scale phenomena. We have to consider the basin-wide water balance (>1000km scale), while hydrodynamics in river channels and floodplains is regulated by much smaller-scale topography (<100m scale). For example, heavy precipitation in upstream regions may later cause flooding in farthest downstream reaches. In order to realistically simulate the timing and amplitude of flood wave propagation for a long distance, consideration of detailed local topography is unavoidable. I have developed the global hydrodynamic model CaMa-Flood to overcome this scale-discrepancy of continental river flow. The CaMa-Flood divides river basins into multiple "unit-catchments", and assumes the water level is uniform within each unit-catchment. One unit-catchment is assigned to each grid-box defined at the typical spatial resolution of global climate models (10 100 km scale). Adopting a uniform water level in a >10km river segment seems to be a big assumption, but it is actually a good approximation for hydrodynamic modelling of continental rivers. The number of grid points required for global hydrodynamic simulations is largely reduced by this "unit-catchment assumption". Alternative to calculating 2-dimensional floodplain flows as in regional flood models, the CaMa-Flood treats floodplain inundation in a unit-catchment as a sub-grid physics. The water level and inundated area in each unit-catchment are diagnosed from water volume using topography parameters derived from high-resolution digital elevation models. Thus, the CaMa-Flood is at least 1000 times computationally more efficient compared to regional

Dynamo efficiency controlled by hydrodynamic bistability.

PubMed

Miralles, Sophie; Herault, Johann; Herault, Johann; Fauve, Stephan; Gissinger, Christophe; Pétrélis, François; Daviaud, François; Dubrulle, Bérengère; Boisson, Jean; Bourgoin, Mickaël; Verhille, Gautier; Odier, Philippe; Pinton, Jean-François; Plihon, Nicolas

2014-06-01

Hydrodynamic and magnetic behaviors in a modified experimental setup of the von Kármán sodium flow-where one disk has been replaced by a propeller-are investigated. When the rotation frequencies of the disk and the propeller are different, we show that the fully turbulent hydrodynamic flow undergoes a global bifurcation between two configurations. The bistability of these flow configurations is associated with the dynamics of the central shear layer. The bistable flows are shown to have different dynamo efficiencies; thus for a given rotation rate of the soft-iron disk, two distinct magnetic behaviors are observed depending on the flow configuration. The hydrodynamic transition controls the magnetic field behavior, and bifurcations between high and low magnetic field branches are investigated.

Numerical Simulation of Sediment Plug Formation in Alluvial Channels

NASA Astrophysics Data System (ADS)

Posner, A. J.; Duan, J. G.

2011-12-01

A sediment plug is the aggregation of sediment in a river reach that completely blocks the original channel resulting in plug growth upstream by accretion and flooding in surrounding areas. Sediment plugs historically form over relatively short periods, in many cases a matter of weeks. Although sediment plugs are much more common in reach constrictions associated with large woody debris, the mouths of tributaries, and along coastal regions, this investigation focuses on sediment plug formation in an alluvial river. During high flows in the years 1991, 1995, 2005, and 2008, a sediment plug formed in the San Marcial reach of the Middle Rio Grande. The Bureau of Reclamation has had to spend millions of dollars dredging the channel to restore flows to Elephant Butte Reservoir. The hydrodynamic and sediment transport processes, associated with plug formation, occurring in this reach are driven by 1) a flow constriction associated with a rock outcrop, 2) a railroad bridge, and 3) the water level of the downstream reservoir. The three-dimensional hydrodynamic model, Delft3D, was implemented to determine the hydrodynamic and sediment transport parameters and variables required to simulate plug formation in an effort to identify hydro- and morphodynamic thresholds. Several variables were identified by previous studies as metrics for plug formation. These variables were used in our investigation to detect the relative magnitude of each process. Both duration and degree of high flow events were simulated, along with extent of cohesive sediment deposits, reservoir level, and percent of fines in suspended sediment distribution. Results of this analysis illustrate that this model is able to reproduce the sediment plug formation. Model calibration was based on measured water levels and changes in bathymetry using both sediment transport and morphologic change parameters. Changes to hydraulic and sediment parameters are not proportional to morphologic changes and are asymptotic in

Hydrodynamics and eutrophication in a mariculture site in the Philippines

NASA Astrophysics Data System (ADS)

Escobar, M. T.; San Diego-McGlone, M. L.; Martin, M.; Villanoy, C.

2014-12-01

Bolinao, Pangasinan in the Philippines is a site for extensive and intensive culture of Chanos chanos. The proliferation of fish farm structures coupled with excessive feeding caused the deterioration of water quality in the area that lead to hypoxic condition (<2mg/L) and fish kills. A hydrodynamic model of the area, developed using DELFT3D, showed a residence time of 5-15 days in the northern channel and 25 to 28 days in the southern end. The complex configuration of the coast, which includes narrow channels that serve as bottlenecks, result to the inefficient flushing of the area. This was further aggravated by the presence of fish farm structures that restricted the natural flow of water. Water quality was monitored in the mariculture site and a nearby seagrass reserve. Nitrate+nitrite concentration ranged from 0.34 - 4.1 µM, 0.13 - 2.7 µM for phosphate, and 1.7 - 8.8 µM for ammonia. Highest nutrient concentrations were seen near the fish farms. Analysis of nutrients, chlorophyll-a and tss for a tidal cycle showed that these substances were inadequately flushed from the coastal waters. Long residence times and high nutrient loading in the area were ideal conditions for the development of hypoxia.

Numerical Hydrodynamics in Special Relativity.

PubMed

Martí, José Maria; Müller, Ewald

2003-01-01

This review is concerned with a discussion of numerical methods for the solution of the equations of special relativistic hydrodynamics (SRHD). Particular emphasis is put on a comprehensive review of the application of high-resolution shock-capturing methods in SRHD. Results of a set of demanding test bench simulations obtained with different numerical SRHD methods are compared. Three applications (astrophysical jets, gamma-ray bursts and heavy ion collisions) of relativistic flows are discussed. An evaluation of various SRHD methods is presented, and future developments in SRHD are analyzed involving extension to general relativistic hydrodynamics and relativistic magneto-hydrodynamics. The review further provides FORTRAN programs to compute the exact solution of a 1D relativistic Riemann problem with zero and nonzero tangential velocities, and to simulate 1D relativistic flows in Cartesian Eulerian coordinates using the exact SRHD Riemann solver and PPM reconstruction. Supplementary material is available for this article at 10.12942/lrr-2003-7 and is accessible for authorized users.

Floodplain Hydrodynamics and Ecosystem Function in a Dryland Wetland

NASA Astrophysics Data System (ADS)

Rodriguez, J. F.; Sandi, S. G.; Saco, P. M.; Wen, L.; Saintilan, N.; Kuczera, G. A.

2017-12-01

The Macquarie Marshes is a floodplain wetland system located in the semiarid region of south-east Australia, regularly flooded by small channels and creeks that get their water from a regulated river system. Flood-dependent vegetation in the wetland includes semi-permanent wetland areas (reed beds, lagoons, and mixed marsh), and floodplain forests and woodlands mainly dominated by River Red Gum (Eucalyptus Camaldulensis). These plant communities support a rich ecosystem and provide sanctuary for birds, frogs and fish and their ecological importance has been recognized under the Ramsar convention. During droughts, wetland vegetation can deteriorate or transition to terrestrial vegetation. Most recently, during the Millennium drought (2001-2009) large areas of water couch and common reeds transitioned to terrestrial vegetation and many patches of River Red Gum reported up to an 80% mortality. Since then, a significant recovery has occurred after a few years of record or near record rainfall. In order to support management decisions regarding watering of the wetland from the upstream reservoir, we have developed an eco-hydraulic model that relates vegetation distribution to the inundation regime (present and past) determined by floodplain hydrodynamics. The model couples hydrodynamic simulations with a rules-based vegetation module that considers water requirements for different plant associations and transition rules accounting for patch dynamics and vegetation resilience. The model has been setup and calibrated with satellite-derived inundation and vegetation maps as well as fractional cover products during the period from 1991 to 2013. We use the model to predict short-term wetland evolution under dry and wet future conditions.

Fractionation of Magnetic Microspheres in a Microfluidic Spiral: Interplay between Magnetic and Hydrodynamic Forces

PubMed Central

Hayden, M. E.; Häfeli, U. O.

2017-01-01

Magnetic forces and curvature-induced hydrodynamic drag have both been studied and employed in continuous microfluidic particle separation and enrichment schemes. Here we combine the two. We investigate consequences of applying an outwardly directed magnetic force to a dilute suspension of magnetic microspheres circulating in a spiral microfluidic channel. This force is realized with an array of permanent magnets arranged to produce a magnetic field with octupolar symmetry about the spiral axis. At low flow rates particles cluster around an apparent streamline of the flow near the outer wall of the turn. At high flow rates this equilibrium is disrupted by the induced secondary (Dean) flow and a new equilibrium is established near the inner wall of the turn. A model incorporating key forces involved in establishing these equilibria is described, and is used to extract quantitative information about the magnitude of local Dean drag forces from experimental data. Steady-state fractionation of suspensions by particle size under the combined influence of magnetic and hydrodynamic forces is demonstrated. Extensions of this work could lead to new continuous microscale particle sorting and enrichment processes with improved fidelity and specificity. PMID:28107472

Boltzmann equation and hydrodynamics beyond Navier-Stokes.

PubMed

Bobylev, A V

2018-04-28

We consider in this paper the problem of derivation and regularization of higher (in Knudsen number) equations of hydrodynamics. The author's approach based on successive changes of hydrodynamic variables is presented in more detail for the Burnett level. The complete theory is briefly discussed for the linearized Boltzmann equation. It is shown that the best results in this case can be obtained by using the 'diagonal' equations of hydrodynamics. Rigorous estimates of accuracy of the Navier-Stokes and Burnett approximations are also presented.This article is part of the theme issue 'Hilbert's sixth problem'. © 2018 The Author(s).

Stabilizing geometry for hydrodynamic rotary seals

DOEpatents

Dietle, Lannie L.; Schroeder, John E.

2010-08-10

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.

Assessing vulnerability in stream channel evolution in relation with morphological transformations and hydrodynamic behavior. Case Study: the Subcarpathian Prahova Valley, Romania

NASA Astrophysics Data System (ADS)

Osaci-Costache, G.; Armas, I.; Gogoase Nistoran, D.; Gheorghe, D.

2010-05-01

The objective of the study is to analyze the relationship between morphological transformations observed during the last 200 years along a 20 km reach of Prahova river, and hydrodynamic behavior during high intensity flood periods, in the context of erosion-control works and environmental changes. Along this sub-Carpathian reach, Prahova is a typical mountain river, partially regulated, flowing under fluvial and torrential regime and having a mean thalweg slope of about 1%. Riverbed material consists in cobbles and boulders. Its valley has gradually been cut; therefore four terraces may clearly be identified in the subbasin areas of Breaza and Câmpina. The Holocene floodplain is asymmetrical, and during the last decades an incision of about 3-4 m has clearly been observed in the main channel. This also led to an evolution from an anabranching river aspect to a meandering one along the studied reach. Reasons to explain these changes are a positive neotectonic background coupled with an increased anthropic component (granular material extraction, channel regulation for construction purposes of roads, bridges, railways, layout of gas and oil pipelines, vegetation cutoff etc.). The data obtained from 1900-1980 topographical maps and 1997-2002 satellite images and orthophotos were coupled with topo-bathymetric surveys carried out in 57 cross-sections, in order to obtain the DTM of the studied area. These cross-sections were used to build up the geometry of a 1D hydraulic model by using the HEC-RAS software (USACE, version 3.1.3). Simulations were obtained under steady flow conditions for 1% and 2% return periods (360-400 mc/s and 450-500 mc/s). Calibration of Manning roughness factors was performed on stages measured at the two upstream and downstream gauging stations. High values of computed shear stresses and velocities show areas of potential erosion leading to morphological changes, bank collapsing and incision observed during the last decades and predicted for the

Acute hydrodynamic damage induced by SPLITT fractionation and centrifugation in red blood cells.

PubMed

Urbina, Adriana; Godoy-Silva, Ruben; Hoyos, Mauricio; Camacho, Marcela

2016-05-01

Though blood bank processing traditionally employs centrifugation, new separation techniques may be appealing for large scale processes. Split-flow fractionation (SPLITT) is a family of techniques that separates in absence of labelling and uses very low flow rates and force fields, and is therefore expected to minimize cell damage. However, the hydrodynamic stress and possible consequent damaging effects of SPLITT fractionation have not been yet examined. The aim of this study was to investigate the hydrodynamic damage of SPLITT fractionation to human red blood cells, and to compare these effects with those induced by centrifugation. Peripheral whole blood samples were collected from healthy volunteers. Samples were diluted in a buffered saline solution, and were exposed to SPLITT fractionation (flow rates 1-10 ml/min) or centrifugation (100-1500 g) for 10 min. Cell viability, shape, diameter, mean corpuscular hemoglobin, and membrane potential were measured. Under the operating conditions employed, both SPLITT and centrifugation maintained cell viability above 98%, but resulted in significant sublethal damage, including echinocyte formation, decreased cell diameter, decreased mean corpuscular hemoglobin, and membrane hyperpolarization which was inhibited by EGTA. Wall shear stress and maximum energy dissipation rate showed significant correlation with lethal and sublethal damage. Our data do not support the assumption that SPLITT fractionation induces very low shear stress and is innocuous to cell function. Some changes in SPLITT channel design are suggested to minimize cell damage. Measurement of membrane potential and cell diameter could provide a new, reliable and convenient basis for evaluation of hydrodynamic effects on different cell models, allowing identification of optimal operating conditions on different scales. Copyright © 2016 Elsevier B.V. All rights reserved.

Exploring the large-scale structure of Taylor–Couette turbulence through Large-Eddy Simulations

NASA Astrophysics Data System (ADS)

Ostilla-Mónico, Rodolfo; Zhu, Xiaojue; Verzicco, Roberto

2018-04-01

Large eddy simulations (LES) of Taylor-Couette (TC) flow, the flow between two co-axial and independently rotating cylinders are performed in an attempt to explore the large-scale axially-pinned structures seen in experiments and simulations. Both static and dynamic LES models are used. The Reynolds number is kept fixed at Re = 3.4 · 104, and the radius ratio η = ri /ro is set to η = 0.909, limiting the effects of curvature and resulting in frictional Reynolds numbers of around Re τ ≈ 500. Four rotation ratios from Rot = ‑0.0909 to Rot = 0.3 are simulated. First, the LES of TC is benchmarked for different rotation ratios. Both the Smagorinsky model with a constant of cs = 0.1 and the dynamic model are found to produce reasonable results for no mean rotation and cyclonic rotation, but deviations increase for increasing rotation. This is attributed to the increasing anisotropic character of the fluctuations. Second, “over-damped” LES, i.e. LES with a large Smagorinsky constant is performed and is shown to reproduce some features of the large-scale structures, even when the near-wall region is not adequately modeled. This shows the potential for using over-damped LES for fast explorations of the parameter space where large-scale structures are found.

Characterising the structure of quasi-periodic mixing events in stratified turbulent Taylor-Couette flow

NASA Astrophysics Data System (ADS)

Singh, Kanwar Nain; Partridge, Jamie; Dalziel, Stuart; Caulfield, C. P.; Mathematical Underpinnings of Stratified Turbulence (MUST) Team

2017-11-01

We present results from experiments conducted to study mixing in a two-layer stably-stratified turbulent Taylor-Couette flow. It has previously been observed that there is a quasi-periodic mixing event located at the interface separating the layers. We observe, through conductivity probe measurements, that the power of the mixing event in the frequency spectrum of the density data at the interface is higher when measured near the inner cylinder than in the middle of the annular gap. This is consistent with Oglethorpe's (2014) hypothesis that the mixing structure is triggered near the inner cylinder, and then advects and decays or disperses radially. We also observe that at Ri =g/'Ro (RiΩi)2 7 , where Ri, Ro are the inner and outer cylinder radius, respectively, g ' the reduced gravity characterising the density jump between the layers and Ωi is the rotation rate of the inner cylinder, the power drops significantly at all radial locations, which is reminiscent of the onset of the enhanced flux regime as observed by Oglethorpe et al. (2013). We perform experiments to characterise the spatial extent and dynamics of this mixing structure using particle image velocimetry (PIV) giving further insights into this important mixing process. EPSRC programme Grant EP/K034529/1 & SGPC-CCT Scholarship.

Wave propagation reversal for wavy vortices in wide-gap counter-rotating cylindrical Couette flow.

PubMed

Altmeyer, S; Lueptow, Richard M

2017-05-01

We present a numerical study of wavy supercritical cylindrical Couette flow between counter-rotating cylinders in which the wavy pattern propagates either prograde with the inner cylinder or retrograde opposite the rotation of the inner cylinder. The wave propagation reversals from prograde to retrograde and vice versa occur at distinct values of the inner cylinder Reynolds number when the associated frequency of the wavy instability vanishes. The reversal occurs for both twofold and threefold symmetric wavy vortices. Moreover, the wave propagation reversal only occurs for sufficiently strong counter-rotation. The flow pattern reversal appears to be intrinsic in the system as either periodic boundary conditions or fixed end wall boundary conditions for different system sizes always result in the wave propagation reversal. We present a detailed bifurcation sequence and parameter space diagram with respect to retrograde behavior of wavy flows. The retrograde propagation of the instability occurs when the inner Reynolds number is about two times the outer Reynolds number. The mechanism for the retrograde propagation is associated with the inviscidly unstable region near the inner cylinder and the direction of the global average azimuthal velocity. Flow dynamics, spatio-temporal behavior, global mean angular velocity, and torque of the flow with the wavy pattern are explored.

A numerical study on bow shocks around the lightning return stroke channel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Qiang, E-mail: cq0405@126.com; Chen, Bin, E-mail: emcchen@163.com; Yi, Yun

2015-03-15

Bow shock structures are important to various hydrodynamics and magnetohydrodynamics (MHD) phenomena in geophysics and astrophysics. The formation and propagation of bow shocks around the lightning return stroke channel are investigated based on the self-similar motion theory and simulated with a two-dimensional Eulerian finite volume resistive radiation MHD code. In this framework, as verification of theoretical models, the evolving structures of many quantities, such as the plasma density, temperature, pressure, shock velocity, and magnetic field, can be obtained, which present all the characteristics of bow shocks in the lightning return stroke processes. The evolution characteristics and the configuration of themore » curved return stroke channels, e.g., the non-ideal effects and the scaling laws, are discussed in detail. The results may have applications for some observed features of the return stroke channels and other phenomena in the lightning discharge plasmas.« less

Modelling hydrologic and hydrodynamic processes in basins with large semi-arid wetlands

NASA Astrophysics Data System (ADS)

Fleischmann, Ayan; Siqueira, Vinícius; Paris, Adrien; Collischonn, Walter; Paiva, Rodrigo; Pontes, Paulo; Crétaux, Jean-François; Bergé-Nguyen, Muriel; Biancamaria, Sylvain; Gosset, Marielle; Calmant, Stephane; Tanimoun, Bachir

2018-06-01

Hydrological and hydrodynamic models are core tools for simulation of large basins and complex river systems associated to wetlands. Recent studies have pointed towards the importance of online coupling strategies, representing feedbacks between floodplain inundation and vertical hydrology. Especially across semi-arid regions, soil-floodplain interactions can be strong. In this study, we included a two-way coupling scheme in a large scale hydrological-hydrodynamic model (MGB) and tested different model structures, in order to assess which processes are important to be simulated in large semi-arid wetlands and how these processes interact with water budget components. To demonstrate benefits from this coupling over a validation case, the model was applied to the Upper Niger River basin encompassing the Niger Inner Delta, a vast semi-arid wetland in the Sahel Desert. Simulation was carried out from 1999 to 2014 with daily TMPA 3B42 precipitation as forcing, using both in-situ and remotely sensed data for calibration and validation. Model outputs were in good agreement with discharge and water levels at stations both upstream and downstream of the Inner Delta (Nash-Sutcliffe Efficiency (NSE) >0.6 for most gauges), as well as for flooded areas within the Delta region (NSE = 0.6; r = 0.85). Model estimates of annual water losses across the Delta varied between 20.1 and 30.6 km3/yr, while annual evapotranspiration ranged between 760 mm/yr and 1130 mm/yr. Evaluation of model structure indicated that representation of both floodplain channels hydrodynamics (storage, bifurcations, lateral connections) and vertical hydrological processes (floodplain water infiltration into soil column; evapotranspiration from soil and vegetation and evaporation of open water) are necessary to correctly simulate flood wave attenuation and evapotranspiration along the basin. Two-way coupled models are necessary to better understand processes in large semi-arid wetlands. Finally, such coupled

Use of hydrodynamic cavitation in (waste)water treatment.

PubMed

Dular, Matevž; Griessler-Bulc, Tjaša; Gutierrez-Aguirre, Ion; Heath, Ester; Kosjek, Tina; Krivograd Klemenčič, Aleksandra; Oder, Martina; Petkovšek, Martin; Rački, Nejc; Ravnikar, Maja; Šarc, Andrej; Širok, Brane; Zupanc, Mojca; Žitnik, Miha; Kompare, Boris

2016-03-01

The use of acoustic cavitation for water and wastewater treatment (cleaning) is a well known procedure. Yet, the use of hydrodynamic cavitation as a sole technique or in combination with other techniques such as ultrasound has only recently been suggested and employed. In the first part of this paper a general overview of techniques that employ hydrodynamic cavitation for cleaning of water and wastewater is presented. In the second part of the paper the focus is on our own most recent work using hydrodynamic cavitation for removal of pharmaceuticals (clofibric acid, ibuprofen, ketoprofen, naproxen, diclofenac, carbamazepine), toxic cyanobacteria (Microcystis aeruginosa), green microalgae (Chlorella vulgaris), bacteria (Legionella pneumophila) and viruses (Rotavirus) from water and wastewater. As will be shown, hydrodynamic cavitation, like acoustic, can manifest itself in many different forms each having its own distinctive properties and mechanisms. This was until now neglected, which eventually led to poor performance of the technique. We will show that a different type of hydrodynamic cavitation (different removal mechanism) is required for successful removal of different pollutants. The path to use hydrodynamic cavitation as a routine water cleaning method is still long, but recent results have already shown great potential for optimisation, which could lead to a low energy tool for water and wastewater cleaning. Copyright © 2015 Elsevier B.V. All rights reserved.

Regeneration of near-wall turbulence structures

NASA Technical Reports Server (NTRS)

Hamilton, James M.; Kim, John J.; Waleffe, Fabian A.

1993-01-01

An examination of the regeneration mechanisms of near-wall turbulence and an attempt to investigate the critical Reynolds number conjecture of Waleffe & Kim is presented. The basis is an extension of the 'minimal channel' approach of Jimenez and Moin which emphasizes the near-wall region and further reduces the complexity of the turbulent flow. Reduction of the flow Reynolds number to the minimum value which will allow turbulence to be sustained has the effect of reducing the ratio of the largest scales to the smallest scales or, equivalently, of causing the near-wall region to fill more of the area between the channel walls. In addition, since each wall may have an active near-wall region, half of the channel is always somewhat redundant. If a plane Couette flow is instead chosen as the base flow, this redundancy is eliminated: the mean shear of a plane Couette flow has a single sign, and at low Reynolds numbers, the two wall regions share a single set of structures. A minimal flow with these modifications possesses, by construction, the strongest constraints which allow sustained turbulence, producing a greatly simplified flow in which the regeneration process can be examined.

Method based on the Laplace equations to reconstruct the river terrain for two-dimensional hydrodynamic numerical modeling

NASA Astrophysics Data System (ADS)

Lai, Ruixun; Wang, Min; Yang, Ming; Zhang, Chao

2018-02-01

The accuracy of the widely-used two-dimensional hydrodynamic numerical model depends on the quality of the river terrain model, particularly in the main channel. However, in most cases, the bathymetry of the river channel is difficult or expensive to obtain in the field, and there is a lack of available data to describe the geometry of the river channel. We introduce a method that originates from the grid generation with the elliptic equation to generate streamlines of the river channel. The streamlines are numerically solved with the Laplace equations. In the process, streamlines in the physical domain are first computed in a computational domain, and then transformed back to the physical domain. The interpolated streamlines are integrated with the surrounding topography to reconstruct the entire river terrain model. The approach was applied to a meandering reach in the Qinhe River, which is a tributary in the middle of the Yellow River, China. Cross-sectional validation and the two-dimensional shallow-water equations are used to test the performance of the river terrain generated. The results show that the approach can reconstruct the river terrain using the data from measured cross-sections. Furthermore, the created river terrain can maintain a geometrical shape consistent with the measurements, while generating a smooth main channel. Finally, several limitations and opportunities for future research are discussed.

Integral representation of channel flow with interacting particles

NASA Astrophysics Data System (ADS)

Fouxon, Itzhak; Ge, Zhouyang; Brandt, Luca; Leshansky, Alexander

2017-12-01

We construct a boundary integral representation for the low-Reynolds-number flow in a channel in the presence of freely suspended particles (or droplets) of arbitrary size and shape. We demonstrate that lubrication theory holds away from the particles at horizontal distances exceeding the channel height and derive a multipole expansion of the flow which is dipolar to the leading approximation. We show that the dipole moment of an arbitrary particle is a weighted integral of the stress and the flow at the particle surface, which can be determined numerically. We introduce the equation of motion that describes hydrodynamic interactions between arbitrary, possibly different, distant particles, with interactions determined by the product of the mobility matrix and the dipole moment. Further, the problem of three identical interacting spheres initially aligned in the streamwise direction is considered and the experimentally observed "pair exchange" phenomenon is derived analytically and confirmed numerically. For nonaligned particles, we demonstrate the formation of a configuration with one particle separating from a stable pair. Our results suggest that in a dilute initially homogenous particulate suspension flowing in a channel the particles will eventually separate into singlets and pairs.

Innovatively Continuous Mass Production Couette-taylor Flow: Pure Inorganic Green-Emitting Cs4PbBr6 Perovskite Microcrystal for display technology.

PubMed

Song, Young Hyun; Choi, Seung Hee; Park, Won Kyu; Yoo, Jin Sun; Kwon, Seok Bin; Kang, Bong Kyun; Park, Sang Ryul; Seo, Young Soo; Yang, Woo Seok; Yoon, Dae Ho

2018-01-31

We report for the first time the mass production of Cs 4 PbBr 6 perovskite microcrystal with a Couette-Taylor flow reactor in order to enhance the efficiency of the synthesis reaction. We obtained a pure Cs 4 PbBr 6 perovskite solid within 3 hrs that then realized a high photoluminescence quantum yield (PLQY) of 46%. Furthermore, the Cs 4 PbBr 6 perovskite microcrystal is applied with red emitting K 2 SiF 6 phosphor on a blue-emitting InGaN chip, achieving a high-performance luminescence characteristics of 9.79 lm/W, external quantum efficiency (EQE) of 2.9%, and correlated color temperature (CCT) of 2976 K; therefore, this perovskite is expected to be a promising candidate material for applications in optoelectronic devices.

Generating multiplex gradients of biomolecules for controlling cellular adhesion in parallel microfluidic channels.

PubMed

Didar, Tohid Fatanat; Tabrizian, Maryam

2012-11-07

Here we present a microfluidic platform to generate multiplex gradients of biomolecules within parallel microfluidic channels, in which a range of multiplex concentration gradients with different profile shapes are simultaneously produced. Nonlinear polynomial gradients were also generated using this device. The gradient generation principle is based on implementing parrallel channels with each providing a different hydrodynamic resistance. The generated biomolecule gradients were then covalently functionalized onto the microchannel surfaces. Surface gradients along the channel width were a result of covalent attachments of biomolecules to the surface, which remained functional under high shear stresses (50 dyn/cm(2)). An IgG antibody conjugated to three different fluorescence dyes (FITC, Cy5 and Cy3) was used to demonstrate the resulting multiplex concentration gradients of biomolecules. The device enabled generation of gradients with up to three different biomolecules in each channel with varying concentration profiles. We were also able to produce 2-dimensional gradients in which biomolecules were distributed along the length and width of the channel. To demonstrate the applicability of the developed design, three different multiplex concentration gradients of REDV and KRSR peptides were patterned along the width of three parallel channels and adhesion of primary human umbilical vein endothelial cell (HUVEC) in each channel was subsequently investigated using a single chip.

Appliance of Inertial Gas-Dynamic Separation of Gas-Dispersion Flows in the Curvilinear Convergent-Divergent Channels for Compressor Equipment Reliability Improvement

NASA Astrophysics Data System (ADS)

Liaposhchenko, O. O.; Sklabinskyi, V. I.; Zavialov, V. L.; Pavlenko, I. V.; Nastenko, O. V.; Demianenko, M. M.

2017-08-01

The new methods of vibration and inertial gas-dynamic separation of gas-condensate and dusty flows and the corresponding separation devices are proposed in order to avoid emergencies and premature wear of parts and components of the compressor equipment. The formation of the gas flow and disperse particles in the curvilinear convergent-divergent channels are investigated. The optimizing hydrodynamic profiling of a geometrical configuration of curvilinear separation channels with rigid and flexible walls of baffles is carried out.

Morphological and biomechanical response to eutrophication and hydrodynamic stresses.

PubMed

Zhu, Guorong; Yuan, Changbo; Di, Guilan; Zhang, Meng; Ni, Leyi; Cao, Te; Fang, Rongting; Wu, Gongguo

2018-05-01

Eutrophication and hydrodynamics determine the final distribution patterns of aquatic macrophytes; however, there is limited available knowledge regarding their interactive effects. Morphological and biomechanical responses to eutrophication and hydrodynamic stresses were assessed by sampling five abundant and dominant species, Potamogeton maackianus, P. pectinatus, P. lucens, Ceratophyllum demersum and Myriophyllum spicatum, in three macrophyte beds in Lake Erhai, Yunnan Province, China: one exposed to eutrophication and moderate southeast (SE) wind; one with mesotrophication, but sheltered by the lakeshore, with weak wind disturbance; and one with meso-eutrophication and strong SE wind. The results showed significant interactive effects of eutrophication and hydrodynamics on most biomechanical traits and some morphological traits, suggesting that aquatic macrophytes preferentially undergo biomechanical adjustments to resist the coexisting eutrophication and hydrodynamic stresses. In particular, hydrodynamics increased both the tensile force and tensile strain of P. maackianus under meso-eutrophication and dramatically decreased them in eutrophic areas, suggesting that eutrophication triggers mechanical failure in this species. Additionally, P. pectinatus, C. demersum and M. spicatum showed the lowest and highest values for the biomechanical variables (greater values for M. spicatum) in the most eutrophic and hydrodynamic areas, respectively, implying that increases in hydrodynamics primarily induce mechanical damage in eutrophic species. The plants generally exhibited greater tensile strain in both shallow and deep waters and the greatest tensile force at moderate depths. The stem cross-sectional area, plant height, stem length, internode length, and branch traits were all responsible for determining the biomechanical variables. This study reveals that hydrodynamic changes primarily induce mechanical damage in eutrophic species, whereas eutrophication triggers

The Gulf of Lions' hydrodynamics

NASA Astrophysics Data System (ADS)

Millot, Claude

1990-09-01

From an hydrodynamical point of view, the Gulf of Lions can be considered as a very complex region, because several intense and highly variable phenomena compete simultaneously. These processes include the powerful general circulation along the continental slope, the formation of dense water both on the shelf and offshore, a seasonal variation of stratification and the extreme energies associated with meteorological conditions. The cloudless atmospheric conditions encountered generally in the northwestern Mediterranean Sea have enabled us to make use of, over more than 10 years, large use of various satellite imageries. The large space and time variability of the hydrodynamical features, a complex topography and a noticeable fishing activity, represent certain difficulties to the collection of observations in situ. We have obtained, therefore, only a few current time series on the slope; those obtained on the shelf only cover the summer period. Models have been elaborated to help us understand the reasons for the general circulation. Observational programmes to be carried out in the forthcoming years will probably provide us with more definitive results on the Gulf of Lions' hydrodynamics.

Hydrodynamics of bacterial colonies: A model

NASA Astrophysics Data System (ADS)

Lega, J.; Passot, T.

2003-03-01

We propose a hydrodynamic model for the evolution of bacterial colonies growing on soft agar plates. This model consists of reaction-diffusion equations for the concentrations of nutrients, water, and bacteria, coupled to a single hydrodynamic equation for the velocity field of the bacteria-water mixture. It captures the dynamics inside the colony as well as on its boundary and allows us to identify a mechanism for collective motion towards fresh nutrients, which, in its modeling aspects, is similar to classical chemotaxis. As shown in numerical simulations, our model reproduces both usual colony shapes and typical hydrodynamic motions, such as the whirls and jets recently observed in wet colonies of Bacillus subtilis. The approach presented here could be extended to different experimental situations and provides a general framework for the use of advection-reaction-diffusion equations in modeling bacterial colonies.

A hydrodynamic approach to cosmology - Methodology

NASA Technical Reports Server (NTRS)

Cen, Renyue

1992-01-01

The present study describes an accurate and efficient hydrodynamic code for evolving self-gravitating cosmological systems. The hydrodynamic code is a flux-based mesh code originally designed for engineering hydrodynamical applications. A variety of checks were performed which indicate that the resolution of the code is a few cells, providing accuracy for integral energy quantities in the present simulations of 1-3 percent over the whole runs. Six species (H I, H II, He I, He II, He III) are tracked separately, and relevant ionization and recombination processes, as well as line and continuum heating and cooling, are computed. The background radiation field is simultaneously determined in the range 1 eV to 100 keV, allowing for absorption, emission, and cosmological effects. It is shown how the inevitable numerical inaccuracies can be estimated and to some extent overcome.

Interchange Method in Compressible Magnetized Couette Flow: Magnetorotational and Magnetoconvective Instabilities

NASA Astrophysics Data System (ADS)

Christodoulou, Dimitris M.; Contopoulos, John; Kazanas, Demosthenes

2003-03-01

We obtain the general forms of the axisymmetric stability criteria in a magnetized compressible Couette flow using an energy variational principle, the so-called interchange or Chandrasekhar's method, which we applied successfully in the incompressible case. This formulation accounts for the simultaneous presence of gravity, rotation, a toroidal magnetic field, a weak axial magnetic field, entropy gradients, and density gradients in the initial equilibrium state. The power of the method lies in its simplicity, which allows us to derive extremely compact and physically clear expressions for the relevant stability criteria despite the inclusion of so many physical effects. In the implementation of the method, all the applicable conservation laws are explicitly taken into account during the variations of a quantity with dimensions of energy that we call the ``free-energy function.'' As in the incompressible case, the presence of an axial field invalidates the conservation laws of angular momentum and azimuthal magnetic flux and introduces instead isorotation and axial current conservation along field lines. Our results are therefore markedly different depending on whether an axial magnetic field is present, and they generalize in two simple expressions all previously known, partial stability criteria for the appearance of magnetorotational instability. Furthermore, the coupling between magnetic tension and buoyancy and its influence to the dynamics of nonhomoentropic magnetized flows become quite clear from our results. In the limits of plane-parallel atmospheres and homoentropic flows, our formulation easily recovers the stability criteria for suppression of convective and Parker instabilities, as well as some related special cases studied over 40 years ago by Newcomb and Tserkovnikov via laborious variational techniques.

Hydrodynamic simulation and particle-tracking techniques for identification of source areas to public-water intakes on the St. Clair-Detroit river waterway in the Great Lakes Basin

USGS Publications Warehouse

Holtschlag, David J.; Koschik, John A.

2004-01-01

Source areas to public water intakes on the St. Clair-Detroit River Waterway were identified by use of hydrodynamic simulation and particle-tracking analyses to help protect public supplies from contaminant spills and discharges. This report describes techniques used to identify these areas and illustrates typical results using selected points on St. Clair River and Lake St. Clair. Parameterization of an existing two-dimensional hydrodynamic model (RMA2) of the St. Clair-Detroit River Waterway was enhanced to improve estimation of local flow velocities. Improvements in simulation accuracy were achieved by computing channel roughness coefficients as a function of flow depth, and determining eddy viscosity coefficients on the basis of velocity data. The enhanced parameterization was combined with refinements in the model mesh near 13 public water intakes on the St. Clair-Detroit River Waterway to improve the resolution of flow velocities while maintaining consistency with flow and water-level data. Scenarios representing a range of likely flow and wind conditions were developed for hydrodynamic simulation. Particle-tracking analyses combined advective movements described by hydrodynamic scenarios with random components associated with sub-grid-scale movement and turbulent mixing to identify source areas to public water intakes.

Hydrodynamics of bacterial colonies: Phase diagrams

NASA Astrophysics Data System (ADS)

Lega, J.; Passot, T.

2004-09-01

We present numerical simulations of a recent hydrodynamic model describing the growth of bacterial colonies on agar plates. We show that this model is able to qualitatively reproduce experimentally observed phase diagrams, which relate a colony shape to the initial quantity of nutrients on the plate and the initial wetness of the agar. We also discuss the principal features resulting from the interplay between hydrodynamic motions and colony growth, as described by our model.

Development and Calibration of Two-Dimensional Hydrodynamic Model of the Tanana River near Tok, Alaska

USGS Publications Warehouse

Conaway, Jeffrey S.; Moran, Edward H.

2004-01-01

Bathymetric and hydraulic data were collected by the U.S. Geological Survey on the Tanana River in proximity to Alaska Department of Transportation and Public Facilities' bridge number 505 at mile 80.5 of the Alaska Highway. Data were collected from August 7-9, 2002, over an approximate 5,000- foot reach of the river. These data were combined with topographic data provided by Alaska Department of Transportation and Public Facilities to generate a two-dimensional hydrodynamic model. The hydrodynamic model was calibrated with water-surface elevations, flow velocities, and flow directions collected at a discharge of 25,600 cubic feet per second. The calibrated model was then used for a simulation of the 100-year recurrence interval discharge of 51,900 cubic feet per second. The existing bridge piers were removed from the model geometry in a second simulation to model the hydraulic conditions in the channel without the piers' influence. The water-surface elevations, flow velocities, and flow directions from these simulations can be used to evaluate the influence of the piers on flow hydraulics and will assist the Alaska Department of Transportation and Public Facilities in the design of a replacement bridge.

Application of Hydrodynamic Cavitation for Food and Bioprocessing

NASA Astrophysics Data System (ADS)

Gogate, Parag R.

Hydrodynamic cavitation can be simply generated by the alterations in the flow field in high speed/high pressure devices and also by passage of the liquid through a constriction such as orifice plate, venturi, or throttling valve. Hydrodynamic cavitation results in the formation of local hot spots, release of highly reactive free radicals, and enhanced mass transfer rates due to turbulence generated as a result of liquid circulation currents. These conditions can be suitably applied for intensification of different bioprocessing applications in an energy-efficient manner as compared to conventionally used ultrasound-based reactors. The current chapter aims at highlighting different aspects related to hydrodynamic cavitation, including the theoretical aspects for optimization of operating parameters, reactor designs, and overview of applications relevant to food and bioprocessing. Some case studies highlighting the comparison of hydrodynamic cavitation and acoustic cavitation reactors will also be discussed.

Small systems and regulator dependence in relativistic hydrodynamics

NASA Astrophysics Data System (ADS)

Spaliński, Michał

2016-10-01

Consistent theories of hydrodynamics necessarily include nonhydrodynamic modes, which can be viewed as a regulator necessary to ensure causality. Under many circumstances the choice of regulator is not relevant, but this is not always the case. In particular, for sufficiently small systems (such as those arising in pA or pp collisions) such dependence may be inevitable. We address this issue in the context of the modern version of Müller-Israel-Stewart theory of relativistic hydrodynamics. In this case, by demanding that the nonhydrodynamic modes do not dominate, we find that regulator dependence becomes inevitable only for multiplicities d N /d Y of the order of a few. This conclusion supports earlier studies based on hydrodynamic simulations of small systems, at the same time providing a simple physical picture of how hydrodynamics can be reliable even in such seemingly extreme conditions.

Continuous cell introduction and rapid dynamic lysis for high-throughput single-cell analysis on microfludic chips with hydrodynamic focusing.

PubMed

Xu, Chun-Xiu; Yin, Xue-Feng

2011-02-04

A chip-based microfluidic system for high-throughput single-cell analysis is described. The system was integrated with continuous introduction of individual cells, rapid dynamic lysis, capillary electrophoretic (CE) separation and laser induced fluorescence (LIF) detection. A cross microfluidic chip with one sheath-flow channel located on each side of the sampling channel was designed. The labeled cells were hydrodynamically focused by sheath-flow streams and sequentially introduced into the cross section of the microchip under hydrostatic pressure generated by adjusting liquid levels in the reservoirs. Combined with the electric field applied on the separation channel, the aligned cells were driven into the separation channel and rapidly lysed within 33ms at the entry of the separation channel by Triton X-100 added in the sheath-flow solution. The maximum rate for introducing individual cells into the separation channel was about 150cells/min. The introduction of sheath-flow streams also significantly reduced the concentration of phosphate-buffered saline (PBS) injected into the separation channel along with single cells, thus reducing Joule heating during electrophoretic separation. The performance of this microfluidic system was evaluated by analysis of reduced glutathione (GSH) and reactive oxygen species (ROS) in single erythrocytes. A throughput of 38cells/min was obtained. The proposed method is simple and robust for high-throughput single-cell analysis, allowing for analysis of cell population with considerable size to generate results with statistical significance. Copyright © 2010 Elsevier B.V. All rights reserved.

Pilot-Wave Hydrodynamics

NASA Astrophysics Data System (ADS)

Bush, John W. M.

2015-01-01

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 reviews experimental evidence indicating that the walking droplets exhibit certain features previously thought to be exclusive to the microscopic, quantum realm. It then reviews theoretical descriptions of this hydrodynamic pilot-wave system that yield insight into the origins of its quantum-like behavior. Quantization arises from the dynamic constraint imposed on the droplet by its pilot-wave field, and multimodal statistics appear to be a feature of chaotic pilot-wave dynamics. I attempt to assess the potential and limitations of this hydrodynamic system as a quantum analog. This fluid system is compared to quantum pilot-wave theories, shown to be markedly different from Bohmian mechanics and more closely related to de Broglie's original conception of quantum dynamics, his double-solution theory, and its relatively recent extensions through researchers in stochastic electrodynamics.

Model of Collective Fish Behavior with Hydrodynamic Interactions

NASA Astrophysics Data System (ADS)

Filella, Audrey; Nadal, François; Sire, Clément; Kanso, Eva; Eloy, Christophe

2018-05-01

Fish schooling is often modeled with self-propelled particles subject to phenomenological behavioral rules. Although fish are known to sense and exploit flow features, these models usually neglect hydrodynamics. Here, we propose a novel model that couples behavioral rules with far-field hydrodynamic interactions. We show that (1) a new "collective turning" phase emerges, (2) on average, individuals swim faster thanks to the fluid, and (3) the flow enhances behavioral noise. The results of this model suggest that hydrodynamic effects should be considered to fully understand the collective dynamics of fish.

Molecular Dynamics Studies of Polyethylene Oxide and Polyethylene Glycol: Hydrodynamic Radius and Shape Anisotropy

PubMed Central

Lee, Hwankyu; Venable, Richard M.; MacKerell, Alexander D.; Pastor, Richard W.

2008-01-01

A revision (C35r) to the CHARMM ether force field is shown to reproduce experimentally observed conformational populations of dimethoxyethane. Molecular dynamics simulations of 9, 18, 27, and 36-mers of polyethylene oxide (PEO) and 27-mers of polyethylene glycol (PEG) in water based on C35r yield a persistence length λ = 3.7 Å, in quantitative agreement with experimentally obtained values of 3.7 Å for PEO and 3.8 Å for PEG; agreement with experimental values for hydrodynamic radii of comparably sized PEG is also excellent. The exponent υ relating the radius of gyration and molecular weight (\\documentclass[10pt]{article} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{pmc} \\usepackage[Euler]{upgreek} \\pagestyle{empty} \\oddsidemargin -1.0in \\begin{document} \\begin{equation*}R_{{\\mathrm{g}}}{\\propto}M_{{\\mathrm{w}}}^{{\\upsilon}}\\end{equation*}\\end{document}) of PEO from the simulations equals 0.515 ± 0.023, consistent with experimental observations that low molecular weight PEG behaves as an ideal chain. The shape anisotropy of hydrated PEO is 2.59:1.44:1.00. The dimension of the middle length for each of the polymers nearly equals the hydrodynamic radius \\documentclass[10pt]{article} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{pmc} \\usepackage[Euler]{upgreek} \\pagestyle{empty} \\oddsidemargin -1.0in \\begin{document} \\begin{equation*}R_{{\\mathrm{h}}}\\end{equation*}\\end{document}obtained from diffusion measurements in solution. This explains the correspondence of \\documentclass[10pt]{article} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{pmc} \\usepackage[Euler]{upgreek} \\pagestyle{empty} \\oddsidemargin -1.0in \\begin{document} \\begin

Exploiting an automated microfluidic hydrodynamic sequential injection system for determination of phosphate.

PubMed

Khongpet, Wanpen; Pencharee, Somkid; Puangpila, Chanida; Kradtap Hartwell, Supaporn; Lapanantnoppakhun, Somchai; Jakmunee, Jaroon

2018-01-15

A microfluidic hydrodynamic sequential injection (μHSI) spectrophotometric system was designed and fabricated. The system was built by laser engraving a manifold pattern on an acrylic block and sealing with another flat acrylic plate to form a microfluidic channel platform. The platform was incorporated with small solenoid valves to obtain a portable setup for programmable control of the liquid flow into the channel according to the HSI principle. The system was demonstrated for the determination of phosphate using a molybdenum blue method. An ascorbic acid, standard or sample, and acidic molybdate solutions were sequentially aspirated to fill the channel forming a stack zone before flowing to the detector. Under the optimum condition, a linear calibration graph in the range of 0.1-6mg P L -1 was obtained. The detection limit was 0.1mgL -1 . The system is compact (5.0mm thick, 80mm wide × 140mm long), durable, portable, cost-effective, and consumes little amount of chemicals (83μL each of molybdate and ascorbic acid, 133μL of the sample solution and 1.7mL of water carrier/run). It was applied for the determination of phosphate content in extracted soil samples. The percent recoveries of the analysis were obtained in the range of 91.2-107.3. The results obtained agreed well with those of the batch spectrophotometric method. Copyright © 2017 Elsevier B.V. All rights reserved.

Optical chromatographic sample separation of hydrodynamically focused mixtures

PubMed Central

Terray, A.; Hebert, C. G.; Hart, S. J.

2014-01-01

Optical chromatography relies on the balance between the opposing optical and fluid drag forces acting on a particle. A typical configuration involves a loosely focused laser directly counter to the flow of particle-laden fluid passing through a microfluidic device. This equilibrium depends on the intrinsic properties of the particle, including size, shape, and refractive index. As such, uniquely fine separations are possible using this technique. Here, we demonstrate how matching the diameter of a microfluidic flow channel to that of the focusing laser in concert with a unique microfluidic platform can be used as a method to fractionate closely related particles in a mixed sample. This microfluidic network allows for a monodisperse sample of both polystyrene and poly(methyl methacrylate) spheres to be injected, hydrodynamically focused, and completely separated. To test the limit of separation, a mixed polystyrene sample containing two particles varying in diameter by less than 0.5 μm was run in the system. The analysis of the resulting separation sets the framework for continued work to perform ultra-fine separations. PMID:25553179

Modelling of the hole-initiated impact ionization current in the framework of hydrodynamic equations

NASA Astrophysics Data System (ADS)

Lorenzini, Martino; Van Houdt, Jan

2002-02-01

Several research papers have shown the feasibility of the hydrodynamic transport model to investigate impact ionization in semiconductor devices by means of mean-energy-dependent generation rates. However, the analysis has been usually carried out for the case of the electron-initiated impact ionization process and less attention has been paid to the modelling of the generation rate due to impact ionization events initiated by holes. This paper therefore presents an original model for the hole-initiated impact ionization in silicon and validates it by comparing simulation results with substrate currents taken from p-channel transistors manufactured in a 0.35 μm CMOS technology having three different channel lengths. The experimental data are successfully reproduced over a wide range of applied voltages using only one fitting parameter. Since the impact ionization of holes triggers the mechanism responsible for the back-bias enhanced gate current in deep submicron nMOS devices, the model can be exploited in the development of non-volatile memories programmed by secondary electron injection.

A theoretical study of hydrodynamic cavitation.

PubMed

Arrojo, S; Benito, Y

2008-03-01

The optimization of hydrodynamic cavitation as an AOP requires identifying the key parameters and studying their effects on the process. Specific simulations of hydrodynamic bubbles reveal that time scales play a major role on the process. Rarefaction/compression periods generate a number of opposing effects which have demonstrated to be quantitatively different from those found in ultrasonic cavitation. Hydrodynamic cavitation can be upscaled and offers an energy efficient way of generating cavitation. On the other hand, the large characteristic time scales hinder bubble collapse and generate a low number of cavitation cycles per unit time. By controlling the pressure pulse through a flexible cavitation chamber design these limitations can be partially compensated. The chemical processes promoted by this technique are also different from those found in ultrasonic cavitation. Properties such as volatility or hydrophobicity determine the potential applicability of HC and therefore have to be taken into account.

Experiences and results multitasking a hydrodynamics code on global and local memory machines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mandell, D.

1987-01-01

A one-dimensional, time-dependent Lagrangian hydrodynamics code using a Godunov solution method has been multitasked for the Cray X-MP/48, the Intel iPSC hypercube, the Alliant FX series and the IBM RP3 computers. Actual multitasking results have been obtained for the Cray, Intel and Alliant computers and simulated results were obtained for the Cray and RP3 machines. The differences in the methods required to multitask on each of the machines is discussed. Results are presented for a sample problem involving a shock wave moving down a channel. Comparisons are made between theoretical speedups, predicted by Amdahl's law, and the actual speedups obtained.more » The problems of debugging on the different machines are also described.« less

Modeling the hydrodynamics of Phloem sieve plates.

PubMed

Jensen, Kaare Hartvig; Mullendore, Daniel Leroy; Holbrook, Noel Michele; Bohr, Tomas; Knoblauch, Michael; Bruus, Henrik

2012-01-01

Sieve plates have an enormous impact on the efficiency of the phloem vascular system of plants, responsible for the distribution of photosynthetic products. These thin plates, which separate neighboring phloem cells, are perforated by a large number of tiny sieve pores and are believed to play a crucial role in protecting the phloem sap from intruding animals by blocking flow when the phloem cell is damaged. The resistance to the flow of viscous sap in the phloem vascular system is strongly affected by the presence of the sieve plates, but the hydrodynamics of the flow through them remains poorly understood. We propose a theoretical model for quantifying the effect of sieve plates on the phloem in the plant, thus unifying and improving previous work in the field. Numerical simulations of the flow in real and idealized phloem channels verify our model, and anatomical data from 19 plant species are investigated. We find that the sieve plate resistance is correlated to the cell lumen resistance, and that the sieve plate and the lumen contribute almost equally to the total hydraulic resistance of the phloem translocation pathway.

Modeling the Hydrodynamics of Phloem Sieve Plates

PubMed Central

Jensen, Kaare Hartvig; Mullendore, Daniel Leroy; Holbrook, Noel Michele; Bohr, Tomas; Knoblauch, Michael; Bruus, Henrik

2012-01-01

Sieve plates have an enormous impact on the efficiency of the phloem vascular system of plants, responsible for the distribution of photosynthetic products. These thin plates, which separate neighboring phloem cells, are perforated by a large number of tiny sieve pores and are believed to play a crucial role in protecting the phloem sap from intruding animals by blocking flow when the phloem cell is damaged. The resistance to the flow of viscous sap in the phloem vascular system is strongly affected by the presence of the sieve plates, but the hydrodynamics of the flow through them remains poorly understood. We propose a theoretical model for quantifying the effect of sieve plates on the phloem in the plant, thus unifying and improving previous work in the field. Numerical simulations of the flow in real and idealized phloem channels verify our model, and anatomical data from 19 plant species are investigated. We find that the sieve plate resistance is correlated to the cell lumen resistance, and that the sieve plate and the lumen contribute almost equally to the total hydraulic resistance of the phloem translocation pathway. PMID:22811681

Collective Modes in a Trapped Gas from Second-Order Hydrodynamics

NASA Astrophysics Data System (ADS)

Lewis, William; Romatschke, Paul

Navier-Stokes equations are often used to analyze collective oscillations and expansion dynamics of strongly interacting quantum gases. However, their use, for example, in precision determination of transport properties such as the ratio shear viscosity to entropy density (η / s) in strongly interacting Fermi gases problematic. Second-order hydrodynamics addresses this by promoting the viscous stress tensor to a hydrodynamic variable relaxing to the Navier-Stokes form on a timescale τπ. We derive frequencies, damping rates, and spatial structure of collective oscillations up to the decapole mode of a harmonically trapped gas in this framework. We find damping of higher-order modes (i.e. beyond quadrupolar) exhibits greater sensitivity to shear viscosity. Thus measurement of the hexapolar mode, for example, may lead to a stronger experimental constraint on η / s . Additionally, we find ``non-hydrodynamic'' modes not contained in a Navier-Stokes description. We calculate excitation amplitudes of non-hydrodynamic modes demonstrating they should be observable. Non-hydrodynamic modes may have implications for the hydrodynamization timescale, the existence of quasi-particles, and universal transport behavior in strongly interacting quantum fluids.

Hydrodynamic suppression of phase separation in active suspensions.

PubMed

Matas-Navarro, Ricard; Golestanian, Ramin; Liverpool, Tanniemola B; Fielding, Suzanne M

2014-09-01

We simulate with hydrodynamics a suspension of active disks squirming through a Newtonian fluid. We explore numerically the full range of squirmer area fractions from dilute to close packed and show that "motility induced phase separation," which was recently proposed to arise generically in active matter, and which has been seen in simulations of active Brownian disks, is strongly suppressed by hydrodynamic interactions. We give an argument for why this should be the case and support it with counterpart simulations of active Brownian disks in a parameter regime that provides a closer counterpart to hydrodynamic suspensions than in previous studies.

Influence of mass transfer on bubble plume hydrodynamics.

PubMed

Lima Neto, Iran E; Parente, Priscila A B

2016-03-01

This paper presents an integral model to evaluate the impact of gas transfer on the hydrodynamics of bubble plumes. The model is based on the Gaussian type self-similarity and functional relationships for the entrainment coefficient and factor of momentum amplification due to turbulence. The impact of mass transfer on bubble plume hydrodynamics is investigated considering different bubble sizes, gas flow rates and water depths. The results revealed a relevant impact when fine bubbles are considered, even for moderate water depths. Additionally, model simulations indicate that for weak bubble plumes (i.e., with relatively low flow rates and large depths and slip velocities), both dissolution and turbulence can affect plume hydrodynamics, which demonstrates the importance of taking the momentum amplification factor relationship into account. For deeper water conditions, simulations of bubble dissolution/decompression using the present model and classical models available in the literature resulted in a very good agreement for both aeration and oxygenation processes. Sensitivity analysis showed that the water depth, followed by the bubble size and the flow rate are the most important parameters that affect plume hydrodynamics. Lastly, dimensionless correlations are proposed to assess the impact of mass transfer on plume hydrodynamics, including both the aeration and oxygenation modes.

Torque scaling in small-gap Taylor-Couette flow with smooth or grooved wall

NASA Astrophysics Data System (ADS)

Zhu, Bihai; Ji, Zengqi; Lou, Zhengkun; Qian, Pengcheng

2018-03-01

The torque in the Taylor-Couette flow for radius ratios η ≥0.97 , with smooth or grooved wall static outer cylinders, is studied experimentally, with the Reynolds number of the inner cylinder reaching up to Rei=2 ×105 , corresponding to the Taylor number up to Ta =5 ×1010 . The grooves are perpendicular to the mean flow, and similar to the structure of a submersible motor stator. It is found that the dimensionless torque G , at a given Rei and η , is significantly greater for grooved cases than smooth cases. We compare our experimental torques for the smooth cases to the fit proposed by Wendt [F. Wendt, Ing.-Arch. 4, 577 (1993), 10.1007/BF02084936] and the fit proposed by Bilgen and Boulos [E. Bilgen and R. Boulos, J Fluids Eng. 95, 122 (1973), 10.1115/1.3446944], which shows both fits are outside their range for small gaps. Furthermore, an additional dimensionless torque (angular velocity flux) N uω in the smooth cases exhibits an effective scaling of N uω˜T a0.39 in the ultimate regime, which occurs at a lower Taylor number, Ta ≈3.5 ×107 , than the well-explored η =0.714 case (at Ta ≈3 ×108 ). The same effective scaling exponent, 0.39, is also evident in the grooved cases, but for η =0.97 and 0.985, there is a peak before this exponent appears.

Hydrodynamic observations in support of Moored Autonomous pCO2 buoy efforts at La Parguera Marine Reserve

NASA Astrophysics Data System (ADS)

Rodriguez-Abudo, S.; Melendez, M.; Morell, J. M.; Padilla, A.; Salisbury, J.

2016-02-01

Time series of near-reef carbonate chemistry obtained through the National Coral Reef Monitoring Program (NCRMP) at La Parguera Marine Reserve, Puerto Rico exhibit seasonal and diurnal variations modulated by diverse processes including coral community metabolism, thermodynamics and hydrodynamics. While surface CO2 dynamics have been fairly well characterized with moored pCO2 efforts, detailed hydrodynamic information resulting from La Parguera's complex morphological, meteorological, and oceanographic processes is currently lacking. This project focuses on a one-month-long hydrodynamic assessment near a fore reef site located within 100 m of the NCRMP pCO2 buoy. Current profiles spanning 12 m of depth were resolved with a bottom-mounted ADCP. Preliminary results show that under no wind conditions, dominant currents are tidally driven and aligned with the reef channel. Depth-averaged currents exhibit diurnal and semidiurnal peaks, not inconsistent with tidal and wind forcing. The analysis also shows that at times surface current direction can differ from near-reef currents by as much as 200 degrees, suggesting a possible mismatch between carbonate chemistry resolved at the surface and that felt by the reef structure. Moreover, buoy measurements are potentially resolving carbonate chemistry from both, oceanic and inshore water masses. Our findings suggest that monitoring and potentially predicting near-reef CO2 dynamics require interdisciplinary expertise and integrated approaches. This project provides new insights into the effects of tidal and meteorological forcing on the carbonate chemistry of near-reef coral ecosystems.

Small aspect ratio Taylor-Couette flow: onset of a very-low-frequency three-torus state.

PubMed

Lopez, Juan M; Marques, Francisco

2003-09-01

The nonlinear dynamics of Taylor-Couette flow in a small aspect ratio annulus (where the length of the cylinders is half of the annular gap between them) is investigated by numerically solving the full three-dimensional Navier-Stokes equations. The system is invariant to arbitrary rotations about the annulus axis and to a reflection about the annulus half-height, so that the symmetry group is SO(2)xZ2. In this paper, we systematically investigate primary and subsequent bifurcations of the basic state, concentrating on a parameter regime where the basic state becomes unstable via Hopf bifurcations. We derive the four distinct cases for the symmetries of the bifurcated orbit, and numerically find two of these. In the parameter regime considered, we also locate the codimension-two double Hopf bifurcation where these two Hopf bifurcations coincide. Secondary Hopf bifurcations (Neimark-Sacker bifurcations), leading to modulated rotating waves, are subsequently found and a saddle-node-infinite-period bifurcation between a stable (node) and an unstable (saddle) modulated rotating wave is located, which gives rise to a very-low-frequency three-torus. This paper provides the computed example of such a state, along with a comprehensive bifurcation sequence leading to its onset.

Abnormal pressures as hydrodynamic phenomena

USGS Publications Warehouse

Neuzil, C.E.

1995-01-01

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

Hydrodynamic behavior in the outer shear layer of partly obstructed open channels

NASA Astrophysics Data System (ADS)

Ben Meftah, Mouldi; De Serio, Francesca; Mossa, Michele

2014-06-01

Despite the many studies on flow in partly obstructed open channels, this issue remains of fundamental importance in order to better understand the interaction between flow behavior and the canopy structure. In the first part of this study we suggest a new theoretical approach able to model the flow pattern within the shear layer in the unobstructed domain, adjacent to the canopy area. Differently from previous studies, the new analytical solution of flow momentum equations takes into account the transversal velocity component of the flow, which is modelled as a linear function of the streamwise velocity. The proposed theoretical model is validated by different experiments carried out on a physical model of a very large rectangular channel by the research group of the Department of Civil, Environmental, Building Engineering and Chemistry of the Technical University of Bari. An array of vertical, rigid, and circular steel cylinders was partially mounted on the bottom in the central part of the flume, leaving two lateral areas of free flow circulation near the walls. The three-dimensional flow velocity components were measured using a 3D Acoustic Doppler Velocimeter. A comparison of the measured and predicted data of the present study with those obtained in other previous studies, carried out with different canopy density, show a non-dependence of this analytical solution on the array density and the Reynolds number. In the second part of the paper, detailed observations of turbulent intensities and spanwise Reynolds stresses in the unobstructed flow are analyzed and discussed. Differently from some earlier studies, it was observed that the peak of the turbulence intensity and that of the spanwise Reynolds stress are significantly shifted toward the center of the shear layer.

Flow through a very porous obstacle in a shallow channel.

PubMed

Creed, M J; Draper, S; Nishino, T; Borthwick, A G L

2017-04-01

A theoretical model, informed by numerical simulations based on the shallow water equations, is developed to predict the flow passing through and around a uniform porous obstacle in a shallow channel, where background friction is important. This problem is relevant to a number of practical situations, including flow through aquatic vegetation, the performance of arrays of turbines in tidal channels and hydrodynamic forces on offshore structures. To demonstrate this relevance, the theoretical model is used to (i) reinterpret core flow velocities in existing laboratory-based data for an array of emergent cylinders in shallow water emulating aquatic vegetation and (ii) reassess the optimum arrangement of tidal turbines to generate power in a tidal channel. Comparison with laboratory-based data indicates a maximum obstacle resistance (or minimum porosity) for which the present theoretical model is valid. When the obstacle resistance is above this threshold the shallow water equations do not provide an adequate representation of the flow, and the theoretical model over-predicts the core flow passing through the obstacle. The second application of the model confirms that natural bed resistance increases the power extraction potential for a partial tidal fence in a shallow channel and alters the optimum arrangement of turbines within the fence.

The motion of a train of vesicles in channel flow

NASA Astrophysics Data System (ADS)

Barakat, Joseph; Shaqfeh, Eric

2017-11-01

The inertialess motion of a train of lipid-bilayer vesicles flowing through a channel is simulated using a 3D boundary integral equation method. Steady-state results are reported for vesicles positioned concentrically inside cylindrical channels of circular, square, and rectangular cross sections. The vesicle translational velocity U and excess channel pressure drop Δp+ depend strongly on the ratio of the vesicle radius to the hydraulic radius λ and the vesicle reduced volume υ. ``Deflated vesicles'' of lower reduced volume υ are more streamlined and translate with greater velocity U relative to the mean flow velocity V. Increasing the vesicle size (λ) increases the wall friction force and extra pressure drop Δp+, which in turn reduces the vesicle velocity U. Hydrodynamic interactions between vesicles in a periodic train are largely screened by the channel walls, in accordance with previous results for spheres and drops. The hydraulic resistance is compared across different cross sections, and a simple correction factor is proposed to unify the results. Nonlinear effects are observed when β - the ratio of membrane bending elasticity to viscous traction - is changed. The simulation results show excellent agreement with available experimental measurements as well as a previously reported ``small-gap theory'' valid for large values of λ. NSF CBET 1066263/1066334.

Flow through a very porous obstacle in a shallow channel

PubMed Central

Draper, S.; Nishino, T.; Borthwick, A. G. L.

2017-01-01

A theoretical model, informed by numerical simulations based on the shallow water equations, is developed to predict the flow passing through and around a uniform porous obstacle in a shallow channel, where background friction is important. This problem is relevant to a number of practical situations, including flow through aquatic vegetation, the performance of arrays of turbines in tidal channels and hydrodynamic forces on offshore structures. To demonstrate this relevance, the theoretical model is used to (i) reinterpret core flow velocities in existing laboratory-based data for an array of emergent cylinders in shallow water emulating aquatic vegetation and (ii) reassess the optimum arrangement of tidal turbines to generate power in a tidal channel. Comparison with laboratory-based data indicates a maximum obstacle resistance (or minimum porosity) for which the present theoretical model is valid. When the obstacle resistance is above this threshold the shallow water equations do not provide an adequate representation of the flow, and the theoretical model over-predicts the core flow passing through the obstacle. The second application of the model confirms that natural bed resistance increases the power extraction potential for a partial tidal fence in a shallow channel and alters the optimum arrangement of turbines within the fence. PMID:28484321

Porosity of spacer-filled channels in spiral-wound membrane systems: Quantification methods and impact on hydraulic characterization.

PubMed

Siddiqui, A; Lehmann, S; Haaksman, V; Ogier, J; Schellenberg, C; van Loosdrecht, M C M; Kruithof, J C; Vrouwenvelder, J S

2017-08-01

The porosity of spacer-filled feed channels influences the hydrodynamics of spiral-wound membrane systems and impacts the overall performance of the system. Therefore, an exact measurement and a detailed understanding of the impact of the feed channel porosity is required to understand and improve the hydrodynamics of spiral-wound membrane systems applied for desalination and wastewater reuse. The objectives of this study were to assess the accuracy of porosity measurement techniques for feed spacers differing in geometry and thickness and the consequences of using an inaccurate method on hydrodynamic predictions, which may affect permeate production. Six techniques were applied to measure the porosity namely, three volumetric techniques based on spacer strand count together with a cuboidal (SC), cylindrical (VCC) and ellipsoidal volume calculation (VCE) and three independent techniques based on volume displacement (VD), weight and density (WD) and computed tomography (CT) scanning. The CT method was introduced as an alternative for the other five already existing and applied methods in practice. Six feed spacers used for the porosity measurement differed in filament thickness, angle between the filaments and mesh-size. The results of the studies showed differences between the porosities, measured by the six methods. The results of the microscopic techniques SC, VCC and VCE deviated significantly from measurements by VD, WD and CT, which showed similar porosity values for all spacer types. Depending on the maximum deviation of the porosity measurement techniques from -6% to +6%, (i) the linear velocity deviations were -5.6% and +6.4% respectively and (ii) the pressure drop deviations were -31% and +43% respectively, illustrating the importance of an accurate porosity measurement. Because of the accuracy and standard deviation, the VD and WD method should be applied for the porosity determination of spacer-filled channels, while the CT method is recommended

Measurements of wall shear stress in a planar turbulent Couette flow with porous walls

NASA Astrophysics Data System (ADS)

Beuther, Paul

2013-11-01

Measurements of drag on a moving web in a multi-span festoon show a stronger than expected dependency on the porosity of the web. The experiments suggest a wall shear stress 3-4 times larger than non-porous webs or historical Couette flow data for solid walls. Previous DNS studies by Jimenez et al. (JFM Vol 442) of boundary layers with passive porous surfaces predict a much smaller increase in wall shear stress for a porous wall of only 40%. Other DNS studies by Quadrio et al. (JFM Vol 576) of porous walls with periodic transpiration do show a large increase in drag under certain periodic conditions of modest amplitude. Although those results are aligned in magnitude with this study, the exact reason for the observed high drag for porous webs in this present study is not understood because there was no external disturbance applied to the web. It can be hypothesized that natural flutter of the web results in a similar mechanism shown in the periodic DNS study, but when the natural flutter was reduced by increasing web tension, there was only a small decrease of the drag. A key difference in this study is that because of the multiple parallel spans in a festoon, any transpiration in one layer must act in the opposite manner on the adjacent span.

Heterogeneity of hydrodynamic properties and groundwater circulation of a coastal andesitic volcanic aquifer controlled by tectonic induced faults and rock fracturing - Martinique island (Lesser Antilles - FWI)

NASA Astrophysics Data System (ADS)

Vittecoq, B.; Reninger, P. A.; Violette, S.; Martelet, G.; Dewandel, B.; Audru, J. C.

2015-10-01

We conducted a multidisciplinary study to analyze the structure and the hydrogeological functioning of an andesitic coastal aquifer and to highlight the importance of faults and associated rock fracturing on groundwater flow. A helicopter-borne geophysical survey with an unprecedented resolution (SkyTEM) was flown over this aquifer in 2013. TDEM resistivity, total magnetic intensity, geological and hydrogeological data from 30 boreholes and two pumping tests were correlated, including one which lasted an exceptional 15 months. We demonstrate that heterogeneous hydrodynamic properties and channelized flows result from tectonically-controlled aquifer compartmentalization along the structural directions of successive tectonic phases. Significant fracturing of the central compartment results in enhanced hydrodynamic properties of the aquifer and an inverse relationship between electrical resistivity and transmissivity. Basalts within the fractured compartment have lower resistivity and higher permeability than basalts outside the compartment. Pumping tests demonstrate that the key factor is the hydraulic conductivity contrast between compartments rather than the hydrodynamic properties of the fault structure. In addition, compartmentalization and associated transmissivity contrasts protect the aquifer from seawater intrusion. Finally, unlike basaltic volcanic islands, the age of the volcanic formations is not the key factor that determines hydrodynamic properties of andesitic islands. Basalts that are several million years old (15 Ma here) have favorable hydrodynamic properties that are generated or maintained by earthquakes/faulting that result from active subduction beneath these islands, which is superimposed on their primary permeability.

Hydrodynamic mobility of a sphere moving on the centerline of an elastic tube

NASA Astrophysics Data System (ADS)

Daddi-Moussa-Ider, Abdallah; Lisicki, Maciej; Gekle, Stephan

2017-11-01

Elastic channels are an important component of many soft matter systems, in which hydrodynamic interactions with confining membranes determine the behavior of particles in flow. In this work, we derive analytical expressions for Green's functions associated with a point-force (Stokeslet) directed parallel or perpendicular to the axis of an elastic cylindrical channel exhibiting resistance against shear and bending. We then compute the leading order self- and pair mobility functions of particles on the cylinder axis, finding that the mobilities are primarily determined by membrane shear and that bending does not play a significant role. In the quasi-steady limit of vanishing frequency, the particle self- and pair mobilities near a no-slip hard cylinder are recovered only if the membrane possesses a non-vanishing shear rigidity. We further compute the membrane deformation, finding that deformation is generally more pronounced in the axial (radial) directions, for the motion along (perpendicular to) the cylinder centerline, respectively. Our analytical calculations for Green's functions in an elastic cylinder can serve as a fundamental building block for future studies and are verified by fully resolved boundary integral simulations where very good agreement is obtained.

A method to combine hydrodynamics and constructive design in the optimization of the runner blades of Kaplan turbines

NASA Astrophysics Data System (ADS)

Miclosina, C. O.; Balint, D. I.; Campian, C. V.; Frunzaverde, D.; Ion, I.

2012-11-01

This paper deals with the optimization of the axial hydraulic turbines of Kaplan type. The optimization of the runner blade is presented systematically from two points of view: hydrodynamic and constructive. Combining these aspects in order to gain a safer operation when unsteady effects occur in the runner of the turbine is attempted. The design and optimization of the runner blade is performed with QTurbo3D software developed at the Center for Research in Hydraulics, Automation and Thermal Processes (CCHAPT) from "Eftimie Murgu" University of Resita, Romania. QTurbo3D software offers possibilities to design the meridian channel of hydraulic turbines design the blades and optimize the runner blade. 3D modeling and motion analysis of the runner blade operating mechanism are accomplished using SolidWorks software. The purpose of motion study is to obtain forces, torques or stresses in the runner blade operating mechanism, necessary to estimate its lifetime. This paper clearly states the importance of combining the hydrodynamics with the structural design in the optimization procedure of the runner of hydraulic turbines.

A coupled hydrodynamic-hydrochemical modeling for predicting mineral transport in a natural acid drainage system.

NASA Astrophysics Data System (ADS)

Zegers Risopatron, G., Sr.; Navarro, L.; Montserrat, S., Sr.; McPhee, J. P.; Niño, Y.

2017-12-01

The geochemistry of water and sediments, coupled with hydrodynamic transport in mountainous channels, is of particular interest in central Chilean Andes due to natural occurrence of acid waters. In this paper, we present a coupled transport and geochemical model to estimate and understand transport processes and fate of minerals at the Yerba Loca Basin, located near Santiago, Chile. In the upper zone, water presentes low pH ( 3) and high concentrations of iron, aluminum, copper, manganese and zinc. Acidity and minerals are the consequence of water-rock interactions in hydrothermal alteration zones, rich in sulphides and sulphates, covered by seasonal snow and glaciers. Downstream, as a consequence of neutral to alkaline lateral water contributions (pH >7) along the river, pH increases and concentration of solutes decreases. The mineral transport model has three components: (i) a hydrodynamic model, where we use HEC-RAS to solve 1D Saint-Venant equations, (ii) a sediment transport model to estimate erosion and sedimentation rates, which quantify minerals transference between water and riverbed and (iii) a solute transport model, based on the 1D OTIS model which takes into account the temporal delay in solutes transport that typically is observed in natural channels (transient storage). Hydrochemistry is solved using PHREEQC, a software for speciation and batch reaction. Our results show that correlation between mineral precipitation and dissolution according to pH values changes along the river. Based on pH measurements (and according to literature) we inferred that main minerals in the water system are brochantite, ferrihydrite, hydrobasaluminite and schwertmannite. Results show that our model can predict the transport and fate of minerals and metals in the Yerba Loca Basin. Mineral dissolution and precipitation process occur for limited ranges of pH values. When pH values are increased, iron minerals (schwertmannite) are the first to precipitate ( 2.5

The influence of tributary flow density differences on the hydrodynamic behavior of a confluent meander bend and implications for flow mixing

NASA Astrophysics Data System (ADS)

Herrero, Horacio S.; Díaz Lozada, José M.; García, Carlos M.; Szupiany, Ricardo N.; Best, Jim; Pagot, Mariana

2018-03-01

The goal of this study is to evaluate the influence of tributary flow density differences on hydrodynamics and mixing at a confluent meander bend. A detailed field characterization is performed using an Acoustic Doppler Current Profiler (ADCP) for quantification of the 3D flow field, flow discharge and bathymetry, as well as CTD measurements (conductivity, temperature, depth) to characterize the patterns of mixing. Satellite images of the confluence taken at complementary times to the field surveys were analyzed to evaluate the confluence hydrodynamics at different flow conditions. The results illustrate the differences in hydrodynamics and mixing length in relation to confluences with equal density tributaries. At low-density differences, and higher discharge ratio (Qr) between the two rivers, the flow is similar to equi-density confluent meander bends. In contrast, at high-density differences (low Qr), the tributary flow is confined to near the confluence but the density difference causes the flow to move across channel. In this case, the density difference causes the lateral spread of the tributary flow to be greater than at a greater Qr when the density difference is less. These results illustrate the potential importance of density differences between tributaries in determining the rate and spatial extent of mixing and sediment dispersal at confluent meander bends.

Robust boundary treatment for open-channel flows in divergence-free incompressible SPH

NASA Astrophysics Data System (ADS)

Pahar, Gourabananda; Dhar, Anirban

2017-03-01

A robust Incompressible Smoothed Particle Hydrodynamics (ISPH) framework is developed to simulate specified inflow and outflow boundary conditions for open-channel flow. Being purely divergence-free, the framework offers smoothed and structured pressure distribution. An implicit treatment of Pressure Poison Equation and Dirichlet boundary condition is applied on free-surface to minimize error in velocity-divergence. Beyond inflow and outflow threshold, multiple layers of dummy particles are created according to specified boundary condition. Inflow boundary acts as a soluble wave-maker. Fluid particles beyond outflow threshold are removed and replaced with dummy particles with specified boundary velocity. The framework is validated against different cases of open channel flow with different boundary conditions. The model can efficiently capture flow evolution and vortex generation for random geometry and variable boundary conditions.

New theories of relativistic hydrodynamics in the LHC era

NASA Astrophysics Data System (ADS)

Florkowski, Wojciech; Heller, Michal P.; Spaliński, Michał

2018-04-01

The success of relativistic hydrodynamics as an essential part of the phenomenological description of heavy-ion collisions at RHIC and the LHC has motivated a significant body of theoretical work concerning its fundamental aspects. Our review presents these developments from the perspective of the underlying microscopic physics, using the language of quantum field theory, relativistic kinetic theory, and holography. We discuss the gradient expansion, the phenomenon of hydrodynamization, as well as several models of hydrodynamic evolution equations, highlighting the interplay between collective long-lived and transient modes in relativistic matter. Our aim to provide a unified presentation of this vast subject—which is naturally expressed in diverse mathematical languages—has also led us to include several new results on the large-order behaviour of the hydrodynamic gradient expansion.

Hydrodynamics of Turning Flocks.

PubMed

Yang, Xingbo; Marchetti, M Cristina

2015-12-18

We present a hydrodynamic model of flocking that generalizes the familiar Toner-Tu equations to incorporate turning inertia of well-polarized flocks. The continuum equations controlled by only two dimensionless parameters, orientational inertia and alignment strength, are derived by coarse-graining the inertial spin model recently proposed by Cavagna et al. The interplay between orientational inertia and bend elasticity of the flock yields anisotropic spin waves that mediate the propagation of turning information throughout the flock. The coupling between spin-current density to the local vorticity field through a nonlinear friction gives rise to a hydrodynamic mode with angular-dependent propagation speed at long wavelengths. This mode becomes unstable as a result of the growth of bend and splay deformations augmented by the spin wave, signaling the transition to complex spatiotemporal patterns of continuously turning and swirling flocks.

On streak spacing in wall-bounded turbulent flows

NASA Technical Reports Server (NTRS)

Hamilton, James M.; Kim, John J.

1993-01-01

The present study is a continuation of the examination by Hamilton et al. of the regeneration mechanisms of near-wall turbulence and an attempt to investigate the conjecture of Waleffe et al. The basis of this study is an extension of the 'minimal channel' approach of Jimenez and Moin that emphasizes the near-wall region and reduces the complexity of the turbulent flow by considering a plane Couette flow of near minimum Reynolds number and stream-wise and span-wise extent. Reduction of the flow Reynolds number to the minimum value which will allow turbulence to be sustained has the effect of reducing the ratio of the largest scales to the smallest scales or, equivalently, of causing the near-wall region to fill more of the area between the channel walls. A plane Couette flow was chosen for study since this type of flow has a mean shear of a single sign, and at low Reynolds numbers, the two wall regions are found to share a single set of structures.

Precipitation patterns during channel flow

NASA Astrophysics Data System (ADS)

Jamtveit, B.; Hawkins, C.; Benning, L. G.; Meier, D.; Hammer, O.; Angheluta, L.

2013-12-01

Mineral precipitation during channelized fluid flow is widespread in a wide variety of geological systems. It is also a common and costly phenomenon in many industrial processes that involve fluid flow in pipelines. It is often referred to as scale formation and encountered in a large number of industries, including paper production, chemical manufacturing, cement operations, food processing, as well as non-renewable (i.e. oil and gas) and renewable (i.e. geothermal) energy production. We have studied the incipient stages of growth of amorphous silica on steel plates emplaced into the central areas of the ca. 1 meter in diameter sized pipelines used at the hydrothermal power plant at Hellisheidi, Iceland (with a capacity of ca 300 MW electricity and 100 MW hot water). Silica precipitation takes place over a period of ca. 2 months at approximately 120°C and a flow rate around 1 m/s. The growth produces asymmetric ca. 1mm high dendritic structures ';leaning' towards the incoming fluid flow. A novel phase-field model combined with the lattice Boltzmann method is introduced to study how the growth morphologies vary under different hydrodynamic conditions, including non-laminar systems with turbulent mixing. The model accurately predicts the observed morphologies and is directly relevant for understanding the more general problem of precipitation influenced by turbulent mixing during flow in channels with rough walls and even for porous flow. Reference: Hawkins, C., Angheluta, L., Hammer, Ø., and Jamtveit, B., Precipitation dendrites in channel flow. Europhysics Letters, 102, 54001

Simulation of spiral instabilities in wide-gap spherical Couette flow

NASA Astrophysics Data System (ADS)

Abbas, Suhail; Yuan, Li; Shah, Abdullah

2018-04-01

We numerically study the wide-gap spherical Couette flow between two concentric spheres with the inner sphere rotating and the outer one stationary. Two wide-gap clearance ratios, β =({R}2-{R}1)/{R}1=0.33 and 0.50, are chosen to investigate the transition scenarios of the spiral instabilities with increasing Reynolds number ({{Re}}). For β =0.33, we first obtain the steady 1-vortex flow at {{Re}} = 700 by using the 1-vortex flow for a medium gap β =0.18 at {{Re}} = 700 as the initial condition. The 1-vortex flow for β =0.33 exists for {Re} \\in [450,2050] and it collapses back to the basic flow when {Re} > 2050. We then detect spiral instabilities by increasing the Reynolds number gradually. The basic flow becomes unstable at {{Re}}{{c}1} = 2900 where spiral waves of wavenumber m = 6 appear first. Increasing the Reynolds number further, the wavenumber decreases to 5 and 4 at {{Re}}{{c}2} = 3000 and {{Re}}{{c}3} = 4000 respectively. The flow becomes turbulent when {Re} > 4500. For β =0.50, no Taylor vortices are found. The basic flow becomes unstable at {{Re}}{{c}1} = 1280 where spiral waves of wavenumber m = 5 occur first. As the Reynolds number is increased, the wavenumber becomes 4 at {{Re}}{{c}2} = 1700, 5 again at {{Re}}{{c}3} = 1800, 4 at {{Re}}{{c}4} = 2000, and becomes 3 at {{Re}}{{c}5} = 2200 while the flow becomes turbulent for {Re} > 2200. The computed rotational frequencies as a function of the Reynolds number for spiral waves of wavenumber m = 5, 4 and 3 are in good agreement with previous experimental results. The present transition scenario of the spiral wavenumber with increasing Reynolds number for β =0.33 is the same as that of Egbers and Rath (1995 Acta Mech. 111 125-40), while for β =0.50, it is only partially similar to those of Wulf et al (1999 Phys. Fluids 11 1359-72) and Egbers and Rath (1995 Acta Mech. 111 125-40).

Validating Hydrodynamic Growth in National Ignition Facility Implosions

NASA Astrophysics Data System (ADS)

Peterson, J. Luc

2014-10-01

The hydrodynamic growth of capsule imperfections can threaten the success of inertial confinement fusion implosions. Therefore, it is important to design implosions that are robust to hydrodynamic instabilities. However, the numerical simulation of interacting Rayleigh-Taylor and Richtmyer-Meshkov growth in these implosions is sensitive to modeling uncertainties such as radiation drive and material equations of state, the effects of which are especially apparent at high mode number (small perturbation wavelength) and high convergence ratio (small capsule radius). A series of validation experiments were conducted at the National Ignition Facility to test the ability to model hydrodynamic growth in spherically converging ignition-relevant implosions. These experiments on the Hydro-Growth Radiography platform constituted direct measurements of the growth of pre-imposed imperfections up to Legendre mode 160 and a convergence ratio of greater than four using two different laser drives: a ``low-foot'' drive used during the National Ignition Campaign and a larger adiabat ``high-foot'' drive that is modeled to be relatively more robust to ablation front hydrodynamic growth. We will discuss these experiments and how their results compare to numerical simulations and analytic theories of hydrodynamic growth, as well as their implications for the modeling of future designs. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Hydrodynamics of the Dirac fluid in graphene

NASA Astrophysics Data System (ADS)

Lucas, Andrew

Recent advances in materials physics have allowed us to observe hydrodynamic electron flow in multiple materials. A uniquely interesting possibility is the emergence of a quasi-relativistic plasma of electrons and holes appearing in Dirac semimetals such as graphene. I will briefly review the unique features of the hydrodynamics of the Dirac fluid, and then discuss the theroetical signatures for the Dirac fluid, and its observation in experiment.

Littoral Hydrodynamics and Sediment Transport Around a Semi-Permeable Breakwater

DTIC Science & Technology

2015-09-18

Australasian Coasts & Ports Conference 2015 15 - 18 September 2015, Auckland , New Zealand Li, H et al. Littoral Hydrodynamics and Sediment...Coasts and Ports 2015, Auckland , New Zealand, 15-18 September, 2015, 7 pp. Littoral Hydrodynamics and Sediment Transport Around a Semi...Conference 2015 15 - 18 September 2015, Auckland , New Zealand Li, H et al. Littoral Hydrodynamics and Sediment Transport 2 The bathymetric and side

Stability investigations of relaxing molecular gas flows. Results and perspectives

NASA Astrophysics Data System (ADS)

Grigor'ev, Yurii N.; Ershov, Igor V.

2017-10-01

This article presents results of systematic investigations of a dissipative effect which manifests itself as the growth of hydrodynamic stability and suppression of turbulence in relaxing molecular gas flows. The effect can be a new way for control stability and laminar turbulent transition in aerodynamic flows. The consideration of suppression of inviscid acoustic waves in 2D shear flows is presented. Nonlinear evolution of large-scale vortices and Kelvin — Helmholtz waves in relaxing shear flows are studied. Critical Reynolds numbers in supersonic Couette flows are calculated analytically and numerically within the framework of both classical linear and nonlinear energy hydrodynamic stability theories. The calculations clearly show that the relaxation process can appreciably delay the laminar-turbulent transition. The aim of this article is to show the new dissipative effect, which can be used for flow control and laminarization.

The role of hydrodynamic processes on anchovy eggs and larvae distribution in the sicily channel (mediterranean sea): a case study for the 2004 data set.

PubMed

Falcini, Federico; Palatella, Luigi; Cuttitta, Angela; Buongiorno Nardelli, Bruno; Lacorata, Guglielmo; Lanotte, Alessandra S; Patti, Bernardino; Santoleri, Rosalia

2015-01-01

Knowledge of the link between ocean hydrodynamics and distribution of small pelagic fish species is fundamental for the sustainable management of fishery resources. Both commercial and scientific communities are indeed seeking to provide services that could "connect the dots" among in situ and remote observations, numerical ocean modelling, and fisheries. In the Mediterranean Sea and, in particular, in the Sicily Channel the reproductive strategy of the European Anchovy (Engraulis encrasicolus) is strongly influenced by the oceanographic patterns, which are often visible in sea surface temperature satellite data. Based on these experimental evidences, we propose here a more general approach where the role of ocean currents, wind effects, and mesoscale activity are tied together. To investigate how these features affect anchovy larvae distribution, we pair ichthyoplankton observations to a wide remote sensing data set, and to Lagrangian numerical simulations for larval transport. Our analysis shows that while the wind-induced coastal current is able to transport anchovy larvae from spawning areas to the recruiting area off the Sicilian south-eastern tip, significant cross-shore transport due to the combination of strong northwesterly mistral winds and topographic effects delivers larvae away from the coastal conveyor belt. We then use a potential vorticity approach to describe the occurrence of larvae cross-shore transport. We conclude that monitoring and quantifying the upwelling on the southern Sicilian coast during the spawning season allows to estimate the cross-shore transport of larvae and the consequent decrease of individuals within the recruiting area.

Combining Envisat type and CryoSat-2 altimetry to inform hydrodynamic models

NASA Astrophysics Data System (ADS)

Schneider, Raphael; Nygaard Godiksen, Peter; Villadsen, Heidi; Madsen, Henrik; Bauer-Gottwein, Peter

2015-04-01

good accordance with other products, such as the SRTM DEM. The adjusted hydrodynamic model reproduced the average water level profile along the river channel with a higher accuracy than a model based on the SRTM DEM. Furthermore, the amplitudes as observed in Envisat virtual station time series could be reproduced fitting simple triangular cross section shapes. A hydrodynamic model prepared in such a way provides water levels at any point along the river and any point in time, which are consistent with the multi-mission altimetric dataset. This means it can for example be updated by assimilation of near real-time water level measurements from CryoSat-2 improving its flood forecasting capability.

On Fully Developed Channel Flows: Some Solutions and Limitations, and Effects of Compressibility, Variable Properties, and Body Forces

NASA Technical Reports Server (NTRS)

Maslen, Stephen H.

1959-01-01

An examination of the effects of compressibility, variable properties, and body forces on fully developed laminar flow has indicated several limitations on such streams. In the absence of a pressure gradient, but presence of a body force (e.g., gravity), an exact fully developed gas flow results. For a liquid this follows also for the case of a constant streamwise pressure gradient. These motions are exact in the sense of a Couette flow. In the liquid case two solutions (not a new result) can occur for the same boundary conditions. An approximate analytic solution was found which agrees closely with machine calculations.In the case of approximately exact flows, it turns out that for large temperature variations across the channel the effects of convection (due to, say, a wall temperature gradient) and frictional heating must be negligible. In such a case the energy and momentum equations are separated, and the solutions are readily obtained. If the temperature variations are small, then both convection effects and frictional heating can consistently be considered. This case becomes the constant-property incompressible case (or quasi-incompressible case for free-convection flows) considered by many authors. Finally there is a brief discussion of cases wherein streamwise variations of all quantities are allowed but only a such form that independent variables are separable. For the case where the streamwise velocity varies inversely as the square root distance along the channel a solution is given.

Black Hole Scrambling from Hydrodynamics.

PubMed

Grozdanov, Sašo; Schalm, Koenraad; Scopelliti, Vincenzo

2018-06-08

We argue that the gravitational shock wave computation used to extract the scrambling rate in strongly coupled quantum theories with a holographic dual is directly related to probing the system's hydrodynamic sound modes. The information recovered from the shock wave can be reconstructed in terms of purely diffusionlike, linearized gravitational waves at the horizon of a single-sided black hole with specific regularity-enforced imaginary values of frequency and momentum. In two-derivative bulk theories, this horizon "diffusion" can be related to late-time momentum diffusion via a simple relation, which ceases to hold in higher-derivative theories. We then show that the same values of imaginary frequency and momentum follow from a dispersion relation of a hydrodynamic sound mode. The frequency, momentum, and group velocity give the holographic Lyapunov exponent and the butterfly velocity. Moreover, at this special point along the sound dispersion relation curve, the residue of the retarded longitudinal stress-energy tensor two-point function vanishes. This establishes a direct link between a hydrodynamic sound mode at an analytically continued, imaginary momentum and the holographic butterfly effect. Furthermore, our results imply that infinitely strongly coupled, large-N_{c} holographic theories exhibit properties similar to classical dilute gases; there, late-time equilibration and early-time scrambling are also controlled by the same dynamics.

Black Hole Scrambling from Hydrodynamics

NASA Astrophysics Data System (ADS)

Grozdanov, Sašo; Schalm, Koenraad; Scopelliti, Vincenzo

2018-06-01

We argue that the gravitational shock wave computation used to extract the scrambling rate in strongly coupled quantum theories with a holographic dual is directly related to probing the system's hydrodynamic sound modes. The information recovered from the shock wave can be reconstructed in terms of purely diffusionlike, linearized gravitational waves at the horizon of a single-sided black hole with specific regularity-enforced imaginary values of frequency and momentum. In two-derivative bulk theories, this horizon "diffusion" can be related to late-time momentum diffusion via a simple relation, which ceases to hold in higher-derivative theories. We then show that the same values of imaginary frequency and momentum follow from a dispersion relation of a hydrodynamic sound mode. The frequency, momentum, and group velocity give the holographic Lyapunov exponent and the butterfly velocity. Moreover, at this special point along the sound dispersion relation curve, the residue of the retarded longitudinal stress-energy tensor two-point function vanishes. This establishes a direct link between a hydrodynamic sound mode at an analytically continued, imaginary momentum and the holographic butterfly effect. Furthermore, our results imply that infinitely strongly coupled, large-Nc holographic theories exhibit properties similar to classical dilute gases; there, late-time equilibration and early-time scrambling are also controlled by the same dynamics.

Kinetic Equation for a Soliton Gas and Its Hydrodynamic Reductions

NASA Astrophysics Data System (ADS)

El, G. A.; Kamchatnov, A. M.; Pavlov, M. V.; Zykov, S. A.

2011-04-01

We introduce and study a new class of kinetic equations, which arise in the description of nonequilibrium macroscopic dynamics of soliton gases with elastic collisions between solitons. These equations represent nonlinear integro-differential systems and have a novel structure, which we investigate by studying in detail the class of N-component `cold-gas' hydrodynamic reductions. We prove that these reductions represent integrable linearly degenerate hydrodynamic type systems for arbitrary N which is a strong evidence in favour of integrability of the full kinetic equation. We derive compact explicit representations for the Riemann invariants and characteristic velocities of the hydrodynamic reductions in terms of the `cold-gas' component densities and construct a number of exact solutions having special properties (quasiperiodic, self-similar). Hydrodynamic symmetries are then derived and investigated. The obtained results shed light on the structure of a continuum limit for a large class of integrable systems of hydrodynamic type and are also relevant to the description of turbulent motion in conservative compressible flows.

Tidal Channel Dynamics and Muddy Substrates: A Comparison between a Wave Dominated and a Tidal Dominated System

DTIC Science & Technology

2012-09-30

standard linear wave theory. Suspended sediment concentration (SSC) was estimated using the backscatter signal of the ADCP and the turbidity value...measured by the OBS when present. The OBS turbidity signal was calibrated against SSC measured in a laboratory tank, using sediments collected on the...link the geotechnical properties of sediment substrates to the spatial and hydrodynamic characteristics of tidal channels • To develop new

Nucleation and chiral symmetry breaking under controlled hydrodynamic flows

NASA Technical Reports Server (NTRS)

Wu, Xiao-Lun; Martin, Brian; Tharrington, Arnold

1994-01-01

The effects of hydrodynamic convection on nucleation and broken chiral symmetry have been investigated for a simple inorganic molecule, sodium chlorate (NaClO3). Our experiment suggests that the symmetry breaking is a result of hydrodynamic amplification of rare nucleation events. The effect is more pronounced when the primary nucleation occurs on the solute-vapor interface, where mixing in the surface sublayer becomes important. The transition from the achiral to the chiral states appears to be smooth as the hydrodynamic parameters, such as flow rate, are varied.

Cavitation Generation and Usage Without Ultrasound: Hydrodynamic Cavitation

NASA Astrophysics Data System (ADS)

Gogate, Parag R.; Pandit, Aniruddha B.

Hydrodynamic Cavitation, which was and is still looked upon as an unavoidable nuisance in the flow systems, can be a serious contender as an alternative to acoustic cavitation for harnessing the spectacular effects of cavitation in physical and chemical processing. The present chapter covers the basics of hydrodynamic cavitation including the considerations for the bubble dynamics analysis, reactor designs and recommendations for optimum operating parameters. An overview of applications in different areas of physical, chemical and biological processing on scales ranging from few grams to several hundred kilograms has also been presented. Since hydrodynamic cavitation was initially proposed as an alternative to acoustic cavitation, it is necessary to compare the efficacy of both these modes of cavitations for a variety of applications and hence comparisons have been discussed either on the basis of energy efficiency or based on the scale of operation. Overall it appears that hydrodynamic cavitation results in conditions similar to those generated using acoustic cavitation but at comparatively much larger scale of operation and with better energy efficiencies.

Prototype Mixed Finite Element Hydrodynamics Capability in ARES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rieben, R N

This document describes work on a prototype Mixed Finite Element Method (MFEM) hydrodynamics algorithm in the ARES code, and its application to a set of standard test problems. This work is motivated by the need for improvements to the algorithms used in the Lagrange hydrodynamics step to make them more robust. We begin by identifying the outstanding issues with traditional numerical hydrodynamics algorithms followed by a description of the proposed method and how it may address several of these longstanding issues. We give a theoretical overview of the proposed MFEM algorithm as well as a summary of the coding additionsmore » and modifications that were made to add this capability to the ARES code. We present results obtained with the new method on a set of canonical hydrodynamics test problems and demonstrate significant improvement in comparison to results obtained with traditional methods. We conclude with a summary of the issues still at hand and motivate the need for continued research to develop the proposed method into maturity.« less

Structural, micro-structural and kinematic analyses of channel flow in the Karmostaj salt diapir in the Zagros foreland folded belt, Fars province, Iran

NASA Astrophysics Data System (ADS)

Sarkarinejad, Khalil; Sarshar, Maryam Asadi; Adineh, Sadegh

2018-02-01

One of the main characteristic of the Zagros foreland fold-and-thrust belt and the Zagros foreland folded belt are wide distributions of surface extrusion from the Hormuz salt diapirs. This study examines the structure and kinematic of channel flow in the Karmostaj salt diapir in the southwestern part of the Zagros foreland folded belt. This diapir has reached the surface as a result of the channel flow mechanism and has extruded in the southern limb of the Kuh-Gach anticline which is an asymmetric décollement fold with convergence to the south. Structural and microstructural studies and quantitative finite strain (Rs) and kinematic vorticity number (Wk) analyses were carried out within this salt diapir and its namakier. This was in order to investigate the structural evolution in the salt diapiric system, the characteristics and mechanism of the salt flow and the distribution of flow regimes within the salt diapir and interaction of regional tectonics and salt diaprism. The extruded salt has developed a flow foliation sub-parallel to the remnant bedding recorded by different colors, a variety of internal folds including symmetrical and asymmetrical folds and interference fold patterns, shear zones, and boudins. These structures were used to analyze mechanisms and history of diapiric flow and extrusion. The microstructures, reveal various deformation mechanisms in various parts of salt diapir. The measurements of finite strain show that Rs values in the margin of salt diapir are higher than within its namakier which is consistent with the results of structural studies. Mean kinematic vorticity number (Wm) measured in steady state deformation of diapir and namakier is Wm = 0.45-0.48 ± 0.13. The estimated mean finite deformation (Wm) values indicate that 67.8% pure shear and 32.2% simple shear deformation were involved; the implications of which are discussed. The vorticity of flow indicates that in the early stage of growth, Poiseuille flow was the dominate

Collisionless solar wind protons: A comparison of kinetic and hydrodynamic descriptions

NASA Technical Reports Server (NTRS)

Leer, E.; Holzer, T. E.

1971-01-01

Kinetic and hydrodynamic descriptions of a collisionless solar wind proton gas are compared. Heat conduction and viscosity are neglected in the hydrodynamic formulation but automatically included in the kinetic formulation. The results of the two models are very nearly the same, indicating that heat conduction and viscosity are not important in the solar wind proton gas beyond about 0.1 AU. It is concluded that the hydrodynamic equations provide a valid description of the collisionless solar wind protons, and hence that future models of the quiet solar wind should be based on a hydrodynamic formulation.

Two-dimensional fluid dynamics in a sharply bent channel: Laminar flow, separation bubble, and vortex dynamics

NASA Astrophysics Data System (ADS)

Matsumoto, Daichi; Fukudome, Koji; Wada, Hirofumi

2016-10-01

Understanding the hydrodynamic properties of fluid flow in a curving pipe and channel is important for controlling the flow behavior in technologies and biomechanics. The nature of the resulting flow in a bent pipe is extremely complicated because of the presence of a cross-stream secondary flow. In an attempt to disentangle this complexity, we investigate the fluid dynamics in a bent channel via the direct numerical simulation of the Navier-Stokes equation in two spatial dimensions. We exploit the absence of secondary flow from our model and systematically investigate the flow structure along the channel as a function of both the bend angle and Reynolds number of the laminar-to-turbulent regime. We numerically suggest a scaling relation between the shape of the separation bubble and the flow conductance, and construct an integrated phase diagram.

The role of seasonal sediment storage in tidal channels on a mesotidal delta

NASA Astrophysics Data System (ADS)

Hale, R. P.; Wilson, C.; Bomer, J.; Goodbred, S. L., Jr.; Bain, R. L.

2017-12-01

The Sundarbans National Forest (SNF), located on the modern topset of the Ganges-Brahmaputra-Meghna (GBM) Delta, is the world's largest mangrove stand ( 10,000 km2), and provides a wide range of cultural, environmental, and economic benefits to the nation of Bangladesh. At present, sediment accretion in the SNF occurs at a rate comparable to that of the locally accelerated sea-level rise ( 1.1 cm/yr), despite substantial modification of the regional hydrodynamics via the construction of channel embankments to prevent inundation of agricultural areas. Approximately 50% of the sediment deposited in the SNF each year is recently delivered (<6 mos) from the GBM. As such, reducing sediment supply by an estimated 60-80% as a result of sediment and water diversions associated with India's National River Linking Project raises serious concerns over the SNF's continued sustainability. Here, we examine: 1) the capacity for short-term sediment storage within tidal channels of varying dimensions, and 2) the hydrodynamic conditions responsible for resuspending this material and delivering it to the mangrove platform. We compare textural and radiochemical characteristics from short cores (<50 cm) collected along the intertidal channel banks, with those from the mangrove platform, to assess seasonal storage of GBM sediment within tidal channels, and the timeframe of its delivery to the SNF platform. We also present instrument data from multiple locations within a confined basin of the SNF, using an upward-looking acoustic Doppler current profiler, pressure sensors, and optical backscatter sensors, to document how transport conditions vary with distance away from the primary tidal inlet, and across the platform. This collection of physical and instrumental observations is then compared to an existing dataset of platform inundation hydroperiods and deposition rates, allowing us to address the threat of a reduced sediment supply to this region, as well as the capacity for this

Hydrodynamics of a Multistage Wet Scrubber Incineration Conditions

ERIC Educational Resources Information Center

Said, M. M.; Manyele, S. V.; Raphael, M. L.

2012-01-01

The objective of the study was to determine the hydrodynamics of the two stage counter-current cascade wet scrubbers used during incineration of medical waste. The dependence of the hydrodynamics on two main variables was studied: Inlet air flow rate and inlet liquid flow rate. This study introduces a new wet scrubber operating features, which are…

Cylindrical Couette flow of a rarefied gas: Effect of a boundary condition on the inverted velocity profile.

PubMed

Kosuge, Shingo

2015-07-01

The cylindrical Couette flow of a rarefied gas between a rotating inner cylinder and a stationary outer cylinder is investigated under the following two kinds of kinetic boundary conditions. One is the modified Maxwell-type boundary condition proposed by Dadzie and Méolans [J. Math. Phys. 45, 1804 (2004)] and the other is the Cercignani-Lampis condition, both of which have separate accommodation coefficients associated with the molecular velocity component normal to the boundary and with the tangential component. An asymptotic analysis of the Boltzmann equation for small Knudsen numbers and a numerical analysis of the Bhatnagar-Gross-Krook model equation for a wide range of the Knudsen number are performed to clarify the effect of each accommodation coefficient as well as of the boundary condition itself on the behavior of the gas, especially on the flow-velocity profile. As a result, the velocity-slip and temperature-jump conditions corresponding to the above kinetic boundary conditions are derived, which are necessary for the fluid-dynamic description of the problem for small Knudsen numbers. The parameter range for the onset of the velocity inversion phenomenon, which is related mainly to the decrease in the tangential momentum accommodation, is also obtained.

Hydrodynamic Stability of Multicomponent Droplet Gasification in Reduced Gravity

NASA Technical Reports Server (NTRS)

Aharon, I.; Shaw, B. D.

1995-01-01

This investigation addresses the problem of hydrodynamic stability of a two-component droplet undergoing spherically-symmetrical gasification. The droplet components are assumed to have characteristic liquid species diffusion times that are large relative to characteristic droplet surface regression times. The problem is formulated as a linear stability analysis, with a goal of predicting when spherically-symmetric droplet gasification can be expected to be hydrodynamically unstable from surface-tension gradients acting along the surface of a droplet which result from perturbations. It is found that for the conditions assumed in this paper (quasisteady gas phase, no initial droplet temperature gradients, diffusion-dominated gasification), surface tension gradients do not play a role in the stability characteristics. In addition, all perturbations are predicted to decay such that droplets were hydrodynamically stable. Conditions are identified, however, that deserve more analysis as they may lead to hydrodynamic instabilities driven by capillary effects.

Riemann Solvers in Relativistic Hydrodynamics: Basics and Astrophysical Applications

NASA Astrophysics Data System (ADS)

Ibanez, Jose M.

2001-12-01

My contribution to these proceedings summarizes a general overview on t High Resolution Shock Capturing methods (HRSC) in the field of relativistic hydrodynamics with special emphasis on Riemann solvers. HRSC techniques achieve highly accurate numerical approximations (formally second order or better) in smooth regions of the flow, and capture the motion of unresolved steep gradients without creating spurious oscillations. In the first part I will show how these techniques have been extended to relativistic hydrodynamics, making it possible to explore some challenging astrophysical scenarios. I will review recent literature concerning the main properties of different special relativistic Riemann solvers, and discuss several 1D and 2D test problems which are commonly used to evaluate the performance of numerical methods in relativistic hydrodynamics. In the second part I will illustrate the use of HRSC methods in several astrophysical applications where special and general relativistic hydrodynamical processes play a crucial role.

Shadowfax: Moving mesh hydrodynamical integration code

NASA Astrophysics Data System (ADS)

Vandenbroucke, Bert

2016-05-01

Shadowfax simulates galaxy evolution. Written in object-oriented modular C++, it evolves a mixture of gas, subject to the laws of hydrodynamics and gravity, and any collisionless fluid only subject to gravity, such as cold dark matter or stars. For the hydrodynamical integration, it makes use of a (co-) moving Lagrangian mesh. The code has a 2D and 3D version, contains utility programs to generate initial conditions and visualize simulation snapshots, and its input/output is compatible with a number of other simulation codes, e.g. Gadget2 (ascl:0003.001) and GIZMO (ascl:1410.003).

Influences of the separation distance, ship speed and channel dimension on ship maneuverability in a confined waterway

NASA Astrophysics Data System (ADS)

Du, Peng; Ouahsine, Abdellatif; Sergent, Philippe

2018-05-01

Ship maneuvering in the confined inland waterway is investigated using the system-based method, where a nonlinear transient hydrodynamic model is adopted and confinement models are implemented to account for the influence of the channel bank and bottom. The maneuvering model is validated using the turning circle test, and the confinement model is validated using the experimental data. The separation distance, ship speed, and channel width are then varied to investigate their influences on ship maneuverability. With smaller separation distances and higher speeds near the bank, the ship's trajectory deviates more from the original course and the bow is repelled with a larger yaw angle, which increase the difficulty of maneuvering. Smaller channel widths induce higher advancing resistances on the ship. The minimum distance to the bank are extracted and studied. It is suggested to navigate the ship in the middle of the channel and with a reasonable speed in the restricted waterway.

Blood-plasma separation in Y-shaped bifurcating microfluidic channels: A dissipative particle dynamics simulation study

PubMed Central

Li, Xuejin; Popel, Aleksander S.; Karniadakis, George Em

2012-01-01

The motion of a suspension of red blood cells (RBCs) flowing in a Y-shaped bifurcating microfluidic channel is investigated using a validated low-dimensional RBC (LD-RBC) model based on dissipative particle dynamics (DPD). Specifically, the RBC is represented as a closed torus-like ring of ten colloidal particles, which leads to efficient simulations of blood flow in microcirculation over a wide range of hematocrits. Adaptive no-slip wall boundary conditions were implemented to model hydrodynamic flow within a specific wall structure of diverging 3D microfluidic channels, paying attention to controlling density fluctuations. Plasma skimming and the all-or-nothing phenomenon of RBCs in a bifurcating microfluidic channel have been investigated in our simulations for healthy and diseased blood, including the size of cell-free layer on the daughter branches. The feed hematocrit level in the parent channel has considerable influence on blood-plasma separation. Compared to the blood-plasma separation efficiencies of healthy RBCs, malaria-infected stiff RBCs (iRBCs) have a tendency to travel into the low flowrate daughter branch because of their different initial distribution in the parent channel. Our simulation results are consistent with previously published experimental results and theoretical predictions. PMID:22476709

A Computational Study of the Hydrodynamics in the Nasal Region of a Hammerhead Shark (Sphyrna tudes): Implications for Olfaction

PubMed Central

Rygg, Alex D.; Cox, Jonathan P. L.; Abel, Richard; Webb, Andrew G.; Smith, Nadine B.; Craven, Brent A.

2013-01-01

The hammerhead shark possesses a unique head morphology that is thought to facilitate enhanced olfactory performance. The olfactory chambers, located at the distal ends of the cephalofoil, contain numerous lamellae that increase the surface area for olfaction. Functionally, for the shark to detect chemical stimuli, water-borne odors must reach the olfactory sensory epithelium that lines these lamellae. Thus, odorant transport from the aquatic environment to the sensory epithelium is the first critical step in olfaction. Here we investigate the hydrodynamics of olfaction in Sphyrna tudes based on an anatomically-accurate reconstruction of the head and olfactory chamber from high-resolution micro-CT and MRI scans of a cadaver specimen. Computational fluid dynamics simulations of water flow in the reconstructed model reveal the external and internal hydrodynamics of olfaction during swimming. Computed external flow patterns elucidate the occurrence of flow phenomena that result in high and low pressures at the incurrent and excurrent nostrils, respectively, which induces flow through the olfactory chamber. The major (prenarial) nasal groove along the cephalofoil is shown to facilitate sampling of a large spatial extent (i.e., an extended hydrodynamic “reach”) by directing oncoming flow towards the incurrent nostril. Further, both the major and minor nasal grooves redirect some flow away from the incurrent nostril, thereby limiting the amount of fluid that enters the olfactory chamber. Internal hydrodynamic flow patterns are also revealed, where we show that flow rates within the sensory channels between olfactory lamellae are passively regulated by the apical gap, which functions as a partial bypass for flow in the olfactory chamber. Consequently, the hammerhead shark appears to utilize external (major and minor nasal grooves) and internal (apical gap) flow regulation mechanisms to limit water flow between the olfactory lamellae, thus protecting these delicate

Transduction channels' gating can control friction on vibrating hair-cell bundles in the ear.

PubMed

Bormuth, Volker; Barral, Jérémie; Joanny, Jean-François; Jülicher, Frank; Martin, Pascal

2014-05-20

Hearing starts when sound-evoked mechanical vibrations of the hair-cell bundle activate mechanosensitive ion channels, giving birth to an electrical signal. As for any mechanical system, friction impedes movements of the hair bundle and thus constrains the sensitivity and frequency selectivity of auditory transduction. Friction is generally thought to result mainly from viscous drag by the surrounding fluid. We demonstrate here that the opening and closing of the transduction channels produce internal frictional forces that can dominate viscous drag on the micrometer-sized hair bundle. We characterized friction by analyzing hysteresis in the force-displacement relation of single hair-cell bundles in response to periodic triangular stimuli. For bundle velocities high enough to outrun adaptation, we found that frictional forces were maximal within the narrow region of deflections that elicited significant channel gating, plummeted upon application of a channel blocker, and displayed a sublinear growth for increasing bundle velocity. At low velocity, the slope of the relation between the frictional force and velocity was nearly fivefold larger than the hydrodynamic friction coefficient that was measured when the transduction machinery was decoupled from bundle motion by severing tip links. A theoretical analysis reveals that channel friction arises from coupling the dynamics of the conformational change associated with channel gating to tip-link tension. Varying channel properties affects friction, with faster channels producing smaller friction. We propose that this intrinsic source of friction may contribute to the process that sets the hair cell's characteristic frequency of responsiveness.

Hydrodynamic instabilities in miscible fluids

NASA Astrophysics Data System (ADS)

Truzzolillo, Domenico; Cipelletti, Luca

2018-01-01

Hydrodynamic instabilities in miscible fluids are ubiquitous, from natural phenomena up to geological scales, to industrial and technological applications, where they represent the only way to control and promote mixing at low Reynolds numbers, well below the transition from laminar to turbulent flow. As for immiscible fluids, the onset of hydrodynamic instabilities in miscible fluids is directly related to the physics of their interfaces. The focus of this review is therefore on the general mechanisms driving the growth of disturbances at the boundary between miscible fluids, under a variety of forcing conditions. In the absence of a regularizing mechanism, these disturbances would grow indefinitely. For immiscible fluids, interfacial tension provides such a regularizing mechanism, because of the energy cost associated to the creation of new interface by a growing disturbance. For miscible fluids, however, the very existence of interfacial stresses that mimic an effective surface tension is debated. Other mechanisms, however, may also be relevant, such as viscous dissipation. We shall review the stabilizing mechanisms that control the most common hydrodynamic instabilities, highlighting those cases for which the lack of an effective interfacial tension poses deep conceptual problems in the mathematical formulation of a linear stability analysis. Finally, we provide a short overview on the ongoing research on the effective, out of equilibrium interfacial tension between miscible fluids.

Macrobenthic Biomass Relations in the Faroe-Shetland Channel: An Arctic-Atlantic Boundary Environment

PubMed Central

Narayanaswamy, Bhavani E.; Bett, Brian J.

2011-01-01

The Faroe-Shetland Channel, located in the NE Atlantic, ranges in depth from 0–1700 m and is an unusual deep-sea environment because of its complex and dynamic hydrographic regime, as well as having numerous different seafloor habitats. Macrofaunal samples have been collected on a 0.5 mm mesh sieve from over 300 stations in a wide area survey and on nested 0.5 and 0.25 mm mesh sieves along a specific depth transect. Contrary to general expectation, macrofauanl biomass in the Channel did not decline with increasing depth. When examined at phylum level, two main biomass patterns with depth were apparent: (a) polychaetes showed little change in biomass on the upper slope then increased markedly below 500 m to a depth of 1100 m before declining; and (b) other phyla showed enhanced biomass between 300–500 m. The polychaete response may be linked with a seafloor environment change to relatively quiescent hydrodynamic conditions and an increasing sediment mud content that occurs at c. 500 m. In contrast, the mid-slope enhancement of other phyla biomass may reflect the hydrodynamically active interface between the warm and cold water masses present in the Channel at c. 300–500 m. Again contrary to expectation, mean macrofaunal body size did not decline with depth, and the relative contribution of smaller (>0.25 mm<0.5 mm) to total (>0.25 mm) macrobenthos did not increase with depth. Overall our total biomass and average individual biomass estimates appear to be greater than those predicted from global analyses. It is clear that global models of benthic biomass distribution may mask significant variations at the local and regional scale. PMID:21526171

Linearly resummed hydrodynamics in a weakly curved spacetime

NASA Astrophysics Data System (ADS)

Bu, Yanyan; Lublinsky, Michael

2015-04-01

We extend our study of all-order linearly resummed hydrodynamics in a flat space [1, 2] to fluids in weakly curved spaces. The underlying microscopic theory is a finite temperature super-Yang-Mills theory at strong coupling. The AdS/CFT correspondence relates black brane solutions of the Einstein gravity in asymptotically locally AdS5 geometry to relativistic conformal fluids in a weakly curved 4D background. To linear order in the amplitude of hydrodynamic variables and metric perturbations, the fluid's energy-momentum tensor is computed with derivatives of both the fluid velocity and background metric resummed to all orders. We extensively discuss the meaning of all order hydrodynamics by expressing it in terms of the memory function formalism, which is also suitable for practical simulations. In addition to two viscosity functions discussed at length in refs. [1, 2], we find four curvature induced structures coupled to the fluid via new transport coefficient functions. In ref. [3], the latter were referred to as gravitational susceptibilities of the fluid. We analytically compute these coefficients in the hydrodynamic limit, and then numerically up to large values of momenta.

Resurgence and hydrodynamic attractors in Gauss-Bonnet holography

NASA Astrophysics Data System (ADS)

Casalderrey-Solana, Jorge; Gushterov, Nikola I.; Meiring, Ben

2018-04-01

We study the convergence of the hydrodynamic series in the gravity dual of Gauss-Bonnet gravity in five dimensions with negative cosmological constant via holography. By imposing boost invariance symmetry, we find a solution to the Gauss-Bonnet equation of motion in inverse powers of the proper time, from which we can extract high order corrections to Bjorken flow for different values of the Gauss-Bonnet parameter λGB. As in all other known examples the gradient expansion is, at most, an asymptotic series which can be understood through applying the techniques of Borel-Padé summation. As expected from the behaviour of the quasi-normal modes in the theory, we observe that the singularities in the Borel plane of this series show qualitative features that interpolate between the infinitely strong coupling limit of N=4 Super Yang Mills theory and the expectation from kinetic theory. We further perform the Borel resummation to constrain the behaviour of hydrodynamic attractors beyond leading order in the hydrodynamic expansion. We find that for all values of λGB considered, the convergence of different initial conditions to the resummation and its hydrodynamization occur at large and comparable values of the pressure anisotropy.

Hydrodynamic electronic fluid instability in GaAs MESFETs at terahertz frequencies

NASA Astrophysics Data System (ADS)

Li, Kang; Hao, Yue; Jin, Xiaoqi; Lu, Wu

2018-01-01

III-V compound semiconductor field effect transistors (FETs) are potential candidates as solid state THz emitters and detectors due to plasma wave instability in these devices. Using a 2D hydrodynamic model, here we present the numerical studies of electron fluid instability in a FET structure. The model is implemented in a GaAs MESFET structure with a gate length of 0.2 µm as a testbed by taking into account the non-equilibrium transport and multi-valley non-parabolicity energy bands. The results show that the electronic density instability in the channel can produce stable periodic oscillations at THz frequencies. Along with stable oscillations, negative differential resistance in output characteristics is observed. The THz emission energy density increases monotonically with the drain bias. The emission frequency of electron density oscillations can be tuned by both gate and drain biases. The results suggest that III-V FETs can be a kind of versatile THz devices with good tunability on both radiative power and emission frequency.

High-order hydrodynamic algorithms for exascale computing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morgan, Nathaniel Ray

Hydrodynamic algorithms are at the core of many laboratory missions ranging from simulating ICF implosions to climate modeling. The hydrodynamic algorithms commonly employed at the laboratory and in industry (1) typically lack requisite accuracy for complex multi- material vortical flows and (2) are not well suited for exascale computing due to poor data locality and poor FLOP/memory ratios. Exascale computing requires advances in both computer science and numerical algorithms. We propose to research the second requirement and create a new high-order hydrodynamic algorithm that has superior accuracy, excellent data locality, and excellent FLOP/memory ratios. This proposal will impact a broadmore » range of research areas including numerical theory, discrete mathematics, vorticity evolution, gas dynamics, interface instability evolution, turbulent flows, fluid dynamics and shock driven flows. If successful, the proposed research has the potential to radically transform simulation capabilities and help position the laboratory for computing at the exascale.« less

Electrolysis Apparatus and a Method of Hydrodynamic Cavitation Protection.

DTIC Science & Technology

1974-09-17

AD-DO01 178 ELECTROLYSIS APPARATUS AND A METHOD OF HYDRODYNAMIC CAVITATION PROTECTION Earl Quandt, et al Department of the Navy Washington, D. C. 17...213" 261123 , Navy Case No. 57,238 ELECTROLYSIS APPARATUS AND A METHOD OF HYDRODYNAMIC CAVITATION PROTECTION 1 ABSTRACT Method of and apparatus for

Effective dynamical coupling of hydrodynamics and transport for heavy-ion collisions

NASA Astrophysics Data System (ADS)

Oliinychenko, Dmytro; Petersen, Hannah

2017-04-01

Present hydrodynamics-based simulations of heavy-ion collisions neglect the feedback from the frozen-out particles flying back into the hydrodynamical region. This causes an artefact called “negative Cooper-Frye contributions”, which is negligible for high collision energies, but becomes significant for lower RHIC BES energies and for event-by-event simulations. To avoid negative Cooper-Frye contributions, while still preserving hydrodynamical behavior, we propose a pure hadronic transport approach with forced thermalization in the regions of high energy density. It is demonstrated that this approach exhibits enhancement of strangeness and mean transverse momenta compared to conventional transport - an effect typical for hydrodynamical approaches.

Holography and hydrodynamics in small systems

NASA Astrophysics Data System (ADS)

Chesler, Paul M.

2016-12-01

Using holographic duality, we present results for the off-center collision of Gaussian wave packets in strongly coupled N = 4 supersymmetric Yang-Mills theory. The wave packets are thin along the collision axis and superficially at least resemble Lorentz contracted colliding protons. The collision results in the formation of a droplet of liquid of size R ∼ 1 /Teff where Teff is the effective temperature, which is the characteristic microscopic scale in strongly coupled plasma. These results demonstrate the applicability of hydrodynamics to microscopically small systems and bolster the notion that hydrodynamics can be applied to heavy-light ion collisions as well as proton-proton collisions.

Asymmetric (1+1)-dimensional hydrodynamics in high-energy collisions

NASA Astrophysics Data System (ADS)

Bialas, A.; Peschanski, R.

2011-05-01

The possibility that particle production in high-energy collisions is a result of two asymmetric hydrodynamic flows is investigated using the Khalatnikov form of the (1+1)-dimensional approximation of hydrodynamic equations. The general solution is discussed and applied to the physically appealing “generalized in-out cascade” where the space-time and energy-momentum rapidities are equal at initial temperature but boost invariance is not imposed. It is demonstrated that the two-bump structure of the entropy density, characteristic of the asymmetric input, changes easily into a single broad maximum compatible with data on particle production in symmetric processes. A possible microscopic QCD interpretation of asymmetric hydrodynamics is proposed.

Hydrodynamic limit of the Yukawa one-component plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salin, Gwenaeel

This paper presents a detailed mathematical analysis of the dynamical correlation of density fluctuations of the Yukawa one component plasma in the framework of linearized hydrodynamics. In particular, expressions for the hydrodynamic modes which hold both for the plasma and the neutral fluid are derived. This work constitutes an extension of the computation of the dynamical structure factor in the hydrodynamic limit done by Vieillefosse and Hansen [Phys. Rev. A 12, 1106 (1975)]. As a typical result of Yukawa plasma, a coupling appears between thermal and mechanical effects in the damping of the sound modes, which does not exist inmore » the classical one component plasma. Theoretical and numerical results obtained by means of equilibrium molecular-dynamic simulations in the microcanonical ensemble are compared and discussed.« less

Numerical modelling of channel processes and analysis of possible channel improvement measures on the Lena River near city Yakutsk

NASA Astrophysics Data System (ADS)

Krylenko, Inna; Belikov, Vitaly; Zavadskii, Aleksander; Borisova, Natalya; Golovlyov, Pavel; Rumyantsev, Alexey

2017-04-01

City Yakutsk (administrative, culture and industrial center of the North East of Russia) situated on the left bank of large Russian river Lena last decades has faced with many problems, concerning intensive channel processes. Most dramatic among them are sediment accumulation near main water intake structure, supplying city Yakutsk by the drinking water, and deterioration in conditions of the navigation roots to the main city ports. Hydrodynamic modelling has been chosen as the main tool for analyses of the modern tendencies in channel processes and for the evaluation of possible channel improvement measures efficiency. STREAM_2D program complex (authors V. Belikov et al.), which is based on the numerical solution of two-dimensional Saint-Venant equations on a hybrid curvilinear quadrangular and rectangular mesh and take into account sediment transport, was used for the simulations. Detailed field data about water regime of the Lena river, bathymetry of the channels and topography of the floodplains was collected for model developing. Model area has covered 75 km of the Lena river valley including branched channels and wide floodplain from Tabaga to Kangalassy gauge cites. Data of these stations were used for model boundary conditions assigning. Data of gauge station city Yakutsk as well as measured during field campaign water levels and flow velocities was taken into account for model calibration and validation. Results of modelling has demonstrated close correspondence with observed water levels and discharges distribution between channel branches for different hydrological situations. Different combinations of hydrographs of 1, 10, 50% exceedance probability was used as input for modelling of channel deformations. Simulation results has shown that in future 10 years aligning of water discharges distribution between main Lena river branches near Yakutsk is possible, that is a positive tendency from the point of view of water supply of the city. More than 15

Understanding cell passage through constricted microfluidic channels

NASA Astrophysics Data System (ADS)

Cartas-Ayala, Marco A.; Karnik, Rohit

2012-11-01

Recently, several microfluidic platforms have been proposed to characterize cells based on their behaviour during cell passage through constricted channels. Variables like transit time have been analyzed in disease states like sickle cell anemia, malaria and sepsis. Nevertheless, it is hard to make direct comparisons between different platforms and cell types. We present experimental results of the relationship between solid deformable particle properties, i.e. stiffness and relative particle size, and flow properties, i.e. particle's velocity. We measured the hydrodynamic variables during the flow of HL-60 cells, a white myeloid cell type, in narrow microfluidic square channels using a microfluidic differential manometer. We measured the flow force required to move cells of different sizes through microchannels and quantified friction forces opposing cell passage. We determined the non-dimensional parameters that influence the flow of cells and we used them to obtain a non dimensional expression that can be used to predict the forces needed to drive cells through microchannels. We found that the friction force needed to flow HL-60 through a microfluidic channel is the sum of two parts. The first part is a static friction force that is proportional to the force needed to keep the force compressed. The second part is a factor that is proportional to the cell velocity, hence a dynamic term, and slightly sensitive to the compressive force. We thank CONACYT (Mexican Science and Technology Council) for supporting this project, grant 205899.

The Role of Hydrodynamic Processes on Anchovy Eggs and Larvae Distribution in the Sicily Channel (Mediterranean Sea): A Case Study for the 2004 Data Set

PubMed Central

Falcini, Federico; Palatella, Luigi; Cuttitta, Angela; Buongiorno Nardelli, Bruno; Lacorata, Guglielmo; Lanotte, Alessandra S.; Patti, Bernardino; Santoleri, Rosalia

2015-01-01

Knowledge of the link between ocean hydrodynamics and distribution of small pelagic fish species is fundamental for the sustainable management of fishery resources. Both commercial and scientific communities are indeed seeking to provide services that could “connect the dots” among in situ and remote observations, numerical ocean modelling, and fisheries. In the Mediterranean Sea and, in particular, in the Sicily Channel the reproductive strategy of the European Anchovy (Engraulis encrasicolus) is strongly influenced by the oceanographic patterns, which are often visible in sea surface temperature satellite data. Based on these experimental evidences, we propose here a more general approach where the role of ocean currents, wind effects, and mesoscale activity are tied together. To investigate how these features affect anchovy larvae distribution, we pair ichthyoplankton observations to a wide remote sensing data set, and to Lagrangian numerical simulations for larval transport. Our analysis shows that while the wind-induced coastal current is able to transport anchovy larvae from spawning areas to the recruiting area off the Sicilian south-eastern tip, significant cross-shore transport due to the combination of strong northwesterly mistral winds and topographic effects delivers larvae away from the coastal conveyor belt. We then use a potential vorticity approach to describe the occurrence of larvae cross-shore transport. We conclude that monitoring and quantifying the upwelling on the southern Sicilian coast during the spawning season allows to estimate the cross-shore transport of larvae and the consequent decrease of individuals within the recruiting area. PMID:25915489

Tetrameric subunit structure of the native brain inwardly rectifying potassium channel Kir 2.2.

PubMed

Raab-Graham, K F; Vandenberg, C A

1998-07-31

Strongly inwardly rectifying potassium channels of the Kir 2 subfamily (IRK1, IRK2, and IRK3) are involved in maintenance and modulation of cell excitability in brain and heart. Electrophysiological studies of channels expressed in heterologous systems have suggested that the pore-conducting pathway contains four subunits. However, inferences from electrophysiological studies have not been tested on native channels and do not address the possibility of nonconducting auxiliary subunits. Here, we investigate the subunit stoichiometry of endogenous inwardly rectifying potassium channel Kir 2.2 (IRK2) from rat brain. Using chemical cross-linking, immunoprecipitiation, and velocity sedimentation, we report physical evidence demonstrating the tetrameric organization of the native channel. Kir 2.2 was sequentially cross-linked to produce bands on SDS-polyacrylamide gel electrophoresis corresponding in size to monomer, dimer, trimer, and three forms of tetramer. Fully cross-linked channel was present as a single band of tetrameric size. Immunoprecipitation of biotinylated membranes revealed a single band corresponding to Kir 2.2, suggesting that the channel is composed of a single type of subunit. Hydrodynamic properties of 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonic acid-solubilized channel were used to calculate the molecular mass of the channel. Velocity sedimentation in H2O or D2O gave a sharp peak with a sedimentation coefficient of 17.3 S. Gel filtration yielded a Stokes radius of 5.92 nm. These data indicate a multisubunit protein with a molecular mass of 193 kDa, calculated to contain 3.98 subunits. Together, these results demonstrate that Kir 2.2 channels are formed by the homotetrameric association of Kir 2.2 subunits and do not contain tightly associated auxiliary subunits. These studies suggest that Kir 2.2 channels differ in structure from related heterooctomeric ATP-sensitive K channels and heterotetrameric G-protein-regulated inward rectifier K

Cohesiveness and hydrodynamic properties of young drinking water biofilms.

PubMed

Abe, Yumiko; Skali-Lami, Salaheddine; Block, Jean-Claude; Francius, Grégory

2012-03-15

Drinking water biofilms are complex microbial systems mainly composed of clusters of different size and age. Atomic force microscopy (AFM) measurements were performed on 4, 8 and 12 weeks old biofilms in order to quantify the mechanical detachment shear stress of the clusters, to estimate the biofilm entanglement rate ξ. This AFM approach showed that the removal of the clusters occurred generally for mechanical shear stress of about 100 kPa only for clusters volumes greater than 200 μm3. This value appears 1000 times higher than hydrodynamic shear stress technically available meaning that the cleaning of pipe surfaces by water flushing remains always incomplete. To predict hydrodynamic detachment of biofilm clusters, a theoretical model has been developed regarding the averaging of elastic and viscous stresses in the cluster and by including the entanglement rate ξ. The results highlighted a slight increase of the detachment shear stress with age and also the dependence between the posting of clusters and their volume. Indeed, the experimental values of ξ allow predicting biofilm hydrodynamic detachment with same order of magnitude than was what reported in the literature. The apparent discrepancy between the mechanical and the hydrodynamic detachment is mainly due to the fact that AFM mechanical experiments are related to the clusters local properties whereas hydrodynamic measurements reflected the global properties of the whole biofilm. Copyright © 2011 Elsevier Ltd. All rights reserved.

Role of hydrodynamic viscosity on phonon transport in suspended graphene

NASA Astrophysics Data System (ADS)

Li, Xun; Lee, Sangyeop

2018-03-01

When phonon transport is in the hydrodynamic regime, the thermal conductivity exhibits peculiar dependences on temperatures (T ) and sample widths (W ). These features were used in the past to experimentally confirm the hydrodynamic phonon transport in three-dimensional bulk materials. Suspended graphene was recently predicted to exhibit strong hydrodynamic features in thermal transport at much higher temperature than the three-dimensional bulk materials, but its experimental confirmation requires quantitative guidance by theory and simulation. Here we quantitatively predict those peculiar dependences using the Monte Carlo solution of the Peierls-Boltzmann equation with an ab initio full three-phonon scattering matrix. Thermal conductivity is found to increase as Tα where α ranges from 1.89 to 2.49 depending on a sample width at low temperatures, much larger than 1.68 of the ballistic case. The thermal conductivity has a width dependence of W1.17 at 100 K, clearly distinguished from the sublinear dependence of the ballistic-diffusive regime. These peculiar features are explained with a phonon viscous damping effect of the hydrodynamic regime. We derive an expression for the phonon hydrodynamic viscosity from the Peierls-Boltzmann equation, and discuss the fact that the phonon viscous damping explains well those peculiar dependences of thermal conductivity at 100 K. The phonon viscous damping still causes significant thermal resistance when a temperature is 300 K and a sample width is around 1 µm, even though the hydrodynamic regime is not dominant over other regimes at this condition.

The Topographic Design of River Channels for Form-Process Linkages.

PubMed

Brown, Rocko A; Pasternack, Gregory B; Lin, Tin

2016-04-01

Scientists and engineers design river topography for a wide variety of uses, such as experimentation, site remediation, dam mitigation, flood management, and river restoration. A recent advancement has been the notion of topographical design to yield specific fluvial mechanisms in conjunction with natural or environmental flow releases. For example, the flow convergence routing mechanism, whereby shear stress and spatially convergent flow migrate or jump from the topographic high (riffle) to the low point (pool) from low to high discharge, is thought to be a key process able to maintain undular relief in gravel bedded rivers. This paper develops an approach to creating riffle-pool topography with a form-process linkage to the flow convergence routing mechanism using an adjustable, quasi equilibrium synthetic channel model. The link from form to process is made through conceptualizing form-process relationships for riffle-pool couplets into geomorphic covariance structures (GCSs) that are then quantitatively embedded in a synthetic channel model. Herein, GCSs were used to parameterize a geometric model to create five straight, synthetic river channels with varying combinations of bed and width undulations. Shear stress and flow direction predictions from 2D hydrodynamic modeling were used to determine if scenarios recreated aspects of the flow convergence routing mechanism. Results show that the creation of riffle-pool couplets that experience flow convergence in straight channels requires GCSs with covarying bed and width undulations in their topography as supported in the literature. This shows that GCSs are a useful way to translate conceptualizations of form-process linkages into quantitative models of channel form.

Non-equilibrium Stokes-Einstein relation via active microrheology of hydrodynamically interacting suspensions

NASA Astrophysics Data System (ADS)

Chu, Henry; Zia, Roseanna

In our recently developed non-equilibrium Stokes-Einstein relation, we showed that, in the absence of hydrodynamic interactions, the stress in a suspension is given by a balance between fluctuation and dissipation. Here, we generalize our theory for systems of hydrodynamically interacting colloids, via active microrheology, where motion of a Brownian probe through the medium reveals rheological properties. The strength of probe forcing compared to the entropic restoring force defines a Peclet number, Pe. In the absence of hydrodynamics, the first normal stress difference and the osmotic pressure scale as Pe4 and Pe2 respectively when probe forcing is weak, and uniformly as Pe for strong probe forcing. As hydrodynamics become important, interparticle forces give way to lubrication interactions. Hydrodynamic coupling leads to a new low-Pe scaling of the first normal stress difference and the osmotic pressure as Pe2, and high-Pe scaling as Peδ, where 0.799 <= δ <= 1 as hydrodynamics vary from strong to weak. For the entire range of the strength of hydrodynamic interactions and probe forcing, the new phenomenological theory is shown to agree with standard micromechanical definitions of the stress. We further draw a connection between the stress and the energy storage in a suspension, and the entropic nature of such storage is identified.

Nonlinear viscoelasticity of entangled wormlike micellar fluid under large-amplitude oscillatory shear: Role of elastic Taylor-Couette instability

NASA Astrophysics Data System (ADS)

Majumdar, Sayantan; Sood, A. K.

2014-06-01

The role of elastic Taylor-Couette flow instabilities in the dynamic nonlinear viscoelastic response of an entangled wormlike micellar fluid is studied by large-amplitude oscillatory shear (LAOS) rheology and in situ polarized light scattering over a wide range of strain and angular frequency values, both above and below the linear crossover point. Well inside the nonlinear regime, higher harmonic decomposition of the resulting stress signal reveals that the normalized third harmonic I3/I1 shows a power-law behavior with strain amplitude. In addition, I3/I1 and the elastic component of stress amplitude σ0E show a very prominent maximum at the strain value where the number density (nv) of the Taylor vortices is maximum. A subsequent increase in applied strain (γ) results in the distortions of the vortices and a concomitant decrease in nv, accompanied by a sharp drop in I3 and σ0E. The peak position of the spatial correlation function of the scattered intensity along the vorticity direction also captures the crossover. Lissajous plots indicate an intracycle strain hardening for the values of γ corresponding to the peak of I3, similar to that observed for hard-sphere glasses.

Statistical State Dynamics Based Study of the Role of Nonlinearity in the Maintenance of Turbulence in Couette Flow

NASA Astrophysics Data System (ADS)

Farrell, Brian; Ioannou, Petros; Nikolaidis, Marios-Andreas

2017-11-01

While linear non-normality underlies the mechanism of energy transfer from the externally driven flow to the perturbation field, nonlinearity is also known to play an essential role in sustaining turbulence. We report a study based on the statistical state dynamics of Couette flow turbulence with the goal of better understanding the role of nonlinearity in sustaining turbulence. The statistical state dynamics implementations used are ensemble closures at second order in a cumulant expansion of the Navier-Stokes equations in which the averaging operator is the streamwise mean. Two fundamentally non-normal mechanisms potentially contributing to maintaining the second cumulant are identified. These are essentially parametric perturbation growth arising from interaction of the perturbations with the fluctuating mean flow and transient growth of perturbations arising from nonlinear interaction between components of the perturbation field. By the method of selectively including these mechanisms parametric growth is found to maintain the perturbation field in the turbulent state while the more commonly invoked mechanism associated with transient growth of perturbations arising from scattering by nonlinear interaction is found to suppress perturbation variance. Funded by ERC Coturb Madrid Summer Program and NSF AGS-1246929.

On the ecogeomorphological feedbacks that control tidal channel network evolution in a sandy mangrove setting

PubMed Central

van Maanen, B.; Coco, G.; Bryan, K. R.

2015-01-01

An ecomorphodynamic model was developed to study how Avicennia marina mangroves influence channel network evolution in sandy tidal embayments. The model accounts for the effects of mangrove trees on tidal flow patterns and sediment dynamics. Mangrove growth is in turn controlled by hydrodynamic conditions. The presence of mangroves was found to enhance the initiation and branching of tidal channels, partly because the extra flow resistance in mangrove forests favours flow concentration, and thus sediment erosion in between vegetated areas. The enhanced branching of channels is also the result of a vegetation-induced increase in erosion threshold. On the other hand, this reduction in bed erodibility, together with the soil expansion driven by organic matter production, reduces the landward expansion of channels. The ongoing accretion in mangrove forests ultimately drives a reduction in tidal prism and an overall retreat of the channel network. During sea-level rise, mangroves can potentially enhance the ability of the soil surface to maintain an elevation within the upper portion of the intertidal zone, while hindering both the branching and headward erosion of the landward expanding channels. The modelling results presented here indicate the critical control exerted by ecogeomorphological interactions in driving landscape evolution. PMID:26339195

Hydrodynamic Properties of Planing Surfaces and Flying Boats

NASA Technical Reports Server (NTRS)

Sokolov, N. A.

1950-01-01

The study of the hydrodynamic properties of planing bottom of flying boats and seaplane floats is at the present time based exclusively on the curves of towing tests conducted in tanks. In order to provide a rational basis for the test procedure in tanks and practical design data, a theoretical study must be made of the flow at the step and relations derived that show not only qualitatively but quantitatively the inter-relations of the various factors involved. The general solution of the problem of the development of hydrodynamic forces during the motion of the seaplane float or flying boat is very difficult for it is necessary to give a three-dimensional solution, which does not always permit reducing the analysis to the form of workable computation formulas. On the other had, the problem is complicated by the fact that the object of the analysis is concerned with two fluid mediums, namely, air and water, which have a surface of density discontinuity between them. The theoretical and experimental investigations on the hydrodynamics of a ship cannot be completely carried over to the design of floats and flying-boat hulls, because of the difference in the shape of the contour lines of the bodies, and, because of the entirely different flow conditions from the hydrodynamic viewpoint.

High Efficiency Hydrodynamic DNA Fragmentation in a Bubbling System

PubMed Central

Li, Lanhui; Jin, Mingliang; Sun, Chenglong; Wang, Xiaoxue; Xie, Shuting; Zhou, Guofu; van den Berg, Albert; Eijkel, Jan C. T.; Shui, Lingling

2017-01-01

DNA fragmentation down to a precise fragment size is important for biomedical applications, disease determination, gene therapy and shotgun sequencing. In this work, a cheap, easy to operate and high efficiency DNA fragmentation method is demonstrated based on hydrodynamic shearing in a bubbling system. We expect that hydrodynamic forces generated during the bubbling process shear the DNA molecules, extending and breaking them at the points where shearing forces are larger than the strength of the phosphate backbone. Factors of applied pressure, bubbling time and temperature have been investigated. Genomic DNA could be fragmented down to controllable 1–10 Kbp fragment lengths with a yield of 75.30–91.60%. We demonstrate that the ends of the genomic DNAs generated from hydrodynamic shearing can be ligated by T4 ligase and the fragmented DNAs can be used as templates for polymerase chain reaction. Therefore, in the bubbling system, DNAs could be hydrodynamically sheared to achieve smaller pieces in dsDNAs available for further processes. It could potentially serve as a DNA sample pretreatment technique in the future. PMID:28098208

High Efficiency Hydrodynamic DNA Fragmentation in a Bubbling System.

PubMed

Li, Lanhui; Jin, Mingliang; Sun, Chenglong; Wang, Xiaoxue; Xie, Shuting; Zhou, Guofu; van den Berg, Albert; Eijkel, Jan C T; Shui, Lingling

2017-01-18

DNA fragmentation down to a precise fragment size is important for biomedical applications, disease determination, gene therapy and shotgun sequencing. In this work, a cheap, easy to operate and high efficiency DNA fragmentation method is demonstrated based on hydrodynamic shearing in a bubbling system. We expect that hydrodynamic forces generated during the bubbling process shear the DNA molecules, extending and breaking them at the points where shearing forces are larger than the strength of the phosphate backbone. Factors of applied pressure, bubbling time and temperature have been investigated. Genomic DNA could be fragmented down to controllable 1-10 Kbp fragment lengths with a yield of 75.30-91.60%. We demonstrate that the ends of the genomic DNAs generated from hydrodynamic shearing can be ligated by T4 ligase and the fragmented DNAs can be used as templates for polymerase chain reaction. Therefore, in the bubbling system, DNAs could be hydrodynamically sheared to achieve smaller pieces in dsDNAs available for further processes. It could potentially serve as a DNA sample pretreatment technique in the future.

Numerical Hydrodynamics and Magnetohydrodynamics in General Relativity.

PubMed

Font, José A

2008-01-01

This article presents a comprehensive overview of numerical hydrodynamics and magneto-hydrodynamics (MHD) in general relativity. Some significant additions have been incorporated with respect to the previous two versions of this review (2000, 2003), most notably the coverage of general-relativistic MHD, a field in which remarkable activity and progress has occurred in the last few years. Correspondingly, the discussion of astrophysical simulations in general-relativistic hydrodynamics is enlarged to account for recent relevant advances, while those dealing with general-relativistic MHD are amply covered in this review for the first time. The basic outline of this article is nevertheless similar to its earlier versions, save for the addition of MHD-related issues throughout. Hence, different formulations of both the hydrodynamics and MHD equations are presented, with special mention of conservative and hyperbolic formulations well adapted to advanced numerical methods. A large sample of numerical approaches for solving such hyperbolic systems of equations is discussed, paying particular attention to solution procedures based on schemes exploiting the characteristic structure of the equations through linearized Riemann solvers. As previously stated, a comprehensive summary of astrophysical simulations in strong gravitational fields is also presented. These are detailed in three basic sections, namely gravitational collapse, black-hole accretion, and neutron-star evolutions; despite the boundaries, these sections may (and in fact do) overlap throughout the discussion. The material contained in these sections highlights the numerical challenges of various representative simulations. It also follows, to some extent, the chronological development of the field, concerning advances in the formulation of the gravitational field, hydrodynamics and MHD equations and the numerical methodology designed to solve them. To keep the length of this article reasonable, an effort has

Hydrodynamics of confined active fluids.

PubMed

Brotto, Tommaso; Caussin, Jean-Baptiste; Lauga, Eric; Bartolo, Denis

2013-01-18

We theoretically describe the dynamics of swimmer populations in rigidly confined thin liquid films. We first demonstrate that hydrodynamic interactions between confined swimmers depend solely on their shape and are independent of their specific swimming mechanism. We also show that, due to friction with the nearby rigid walls, confined swimmers do not just reorient in flow gradients but also in uniform flows. We then quantify the consequences of these microscopic interaction rules on the large-scale hydrodynamics of isotropic populations. We investigate in detail their stability and the resulting phase behavior, highlighting the differences with conventional active, three-dimensional suspensions. Two classes of polar swimmers are distinguished depending on their geometrical polarity. The first class gives rise to coherent directed motion at all scales, whereas for the second class we predict the spontaneous formation of coherent clusters (swarms).

Advances in colloidal manipulation and transport via hydrodynamic interactions.

PubMed

Martínez-Pedrero, F; Tierno, P

2018-06-01

In this review article, we highlight many recent advances in the field of micromanipulation of colloidal particles using hydrodynamic interactions (HIs), namely solvent mediated long-range interactions. At the micrsocale, the hydrodynamic laws are time reversible and the flow becomes laminar, features that allow precise manipulation and control of colloidal matter. We focus on different strategies where externally operated microstructures generate local flow fields that induce the advection and motion of the surrounding components. In addition, we review cases where the induced flow gives rise to hydrodynamic bound states that may synchronize during the process, a phenomenon essential in different systems such as those that exhibit self-assembly and swarming. Copyright © 2018 Elsevier Inc. All rights reserved.

A study for bank effect on ship traffic in narrow water channels using cellular automata

NASA Astrophysics Data System (ADS)

Sun, Zhuo; Cong, Shuang; Pan, Junnan; Zheng, Jianfeng

2017-12-01

In narrow water channels, bank might affect nearby ships due to hydrodynamic forces (bank effect). To avoid accidents, different sailing rules (i.e., lane-changing, speed control) are required. In this paper, a two-lane cellular automata model is proposed to evaluate such phenomena. Numerical experiments show that ships will form a “slow-moving chunk” in the bank area, which will significantly block the flux. As further study demonstrated to alleviate bank effect, ship speed and bank length should be controlled.

SPH modelling of depth-limited turbulent open channel flows over rough boundaries.

PubMed

Kazemi, Ehsan; Nichols, Andrew; Tait, Simon; Shao, Songdong

2017-01-10

A numerical model based on the smoothed particle hydrodynamics method is developed to simulate depth-limited turbulent open channel flows over hydraulically rough beds. The 2D Lagrangian form of the Navier-Stokes equations is solved, in which a drag-based formulation is used based on an effective roughness zone near the bed to account for the roughness effect of bed spheres and an improved sub-particle-scale model is applied to account for the effect of turbulence. The sub-particle-scale model is constructed based on the mixing-length assumption rather than the standard Smagorinsky approach to compute the eddy-viscosity. A robust in/out-flow boundary technique is also proposed to achieve stable uniform flow conditions at the inlet and outlet boundaries where the flow characteristics are unknown. The model is applied to simulate uniform open channel flows over a rough bed composed of regular spheres and validated by experimental velocity data. To investigate the influence of the bed roughness on different flow conditions, data from 12 experimental tests with different bed slopes and uniform water depths are simulated, and a good agreement has been observed between the model and experimental results of the streamwise velocity and turbulent shear stress. This shows that both the roughness effect and flow turbulence should be addressed in order to simulate the correct mechanisms of turbulent flow over a rough bed boundary and that the presented smoothed particle hydrodynamics model accomplishes this successfully. © 2016 The Authors International Journal for Numerical Methods in Fluids Published by John Wiley & Sons Ltd.

Hydrodynamic Electron Flow and Hall Viscosity

NASA Astrophysics Data System (ADS)

Scaffidi, Thomas; Nandi, Nabhanila; Schmidt, Burkhard; Mackenzie, Andrew P.; Moore, Joel E.

2017-06-01

In metallic samples of small enough size and sufficiently strong momentum-conserving scattering, the viscosity of the electron gas can become the dominant process governing transport. In this regime, momentum is a long-lived quantity whose evolution is described by an emergent hydrodynamical theory. Furthermore, breaking time-reversal symmetry leads to the appearance of an odd component to the viscosity called the Hall viscosity, which has attracted considerable attention recently due to its quantized nature in gapped systems but still eludes experimental confirmation. Based on microscopic calculations, we discuss how to measure the effects of both the even and odd components of the viscosity using hydrodynamic electronic transport in mesoscopic samples under applied magnetic fields.

Hydrodynamic Electron Flow and Hall Viscosity.

PubMed

Scaffidi, Thomas; Nandi, Nabhanila; Schmidt, Burkhard; Mackenzie, Andrew P; Moore, Joel E

2017-06-02

In metallic samples of small enough size and sufficiently strong momentum-conserving scattering, the viscosity of the electron gas can become the dominant process governing transport. In this regime, momentum is a long-lived quantity whose evolution is described by an emergent hydrodynamical theory. Furthermore, breaking time-reversal symmetry leads to the appearance of an odd component to the viscosity called the Hall viscosity, which has attracted considerable attention recently due to its quantized nature in gapped systems but still eludes experimental confirmation. Based on microscopic calculations, we discuss how to measure the effects of both the even and odd components of the viscosity using hydrodynamic electronic transport in mesoscopic samples under applied magnetic fields.

pyro: Python-based tutorial for computational methods for hydrodynamics

NASA Astrophysics Data System (ADS)

Zingale, Michael

2015-07-01

pyro is a simple python-based tutorial on computational methods for hydrodynamics. It includes 2-d solvers for advection, compressible, incompressible, and low Mach number hydrodynamics, diffusion, and multigrid. It is written with ease of understanding in mind. An extensive set of notes that is part of the Open Astrophysics Bookshelf project provides details of the algorithms.

Hydrodynamic shrinkage of liquid CO2 Taylor drops in a straight microchannel

NASA Astrophysics Data System (ADS)

Qin, Ning; Wen, John Z.; Ren, Carolyn L.

2018-03-01

Hydrodynamic shrinkage of liquid CO2 drops in water under a Taylor flow regime is studied using a straight microchannel (length/width ~100). A general form of a mathematical model of the solvent-side mass transfer coefficient (k s) is developed first. Based on formulations of the surface area (A) and the volume (V) of a general Taylor drop in a rectangular microchannel, a specific form of k s is derived. Drop length and speed are experimentally measured at three specified positions of the straight channel, namely, immediately after drop generation (position 1), the midpoint of the channel (position 2) and the end of the channel (position 3). The reductions of drop length (L x , x  =  1, 2, 3) from position 1 to 2 and down to 3 are used to quantify the drop shrinkage. Using the specific model, k s is calculated mainly based on L x and drop flowing time (t). Results show that smaller CO2 drops produced by lower flow rate ratios ({{Q}LC{{O2}}}/{{Q}{{H2}O}} ) are generally characterized by higher (nearly three times) k s and Sherwood numbers than those produced by higher {{Q}LC{{O2}}}/{{Q}{{H2}O}} , which is essentially attributed to the larger effective portion of the smaller drop contributing in the mass transfer under same levels of the flowing time and the surface-to-volume ratio (~104 m-1) of all drops. Based on calculated pressure drops of the segmented flow in microchannel, the Peng-Robinson equation of state and initial pressures of drops at the T-junction in experiments, overall pressure drop (ΔP t) in the straight channel as well as the resulted drop volume change are quantified. ΔP t from position 1-3 is by average 3.175 kPa with a ~1.6% standard error, which only leads to relative drop volume changes of 0.3‰ to 0.52‰.

Simulation of confined magnetohydrodynamic flows with Dirichlet boundary conditions using a pseudo-spectral method with volume penalization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morales, Jorge A.; Leroy, Matthieu; Bos, Wouter J.T.

A volume penalization approach to simulate magnetohydrodynamic (MHD) flows in confined domains is presented. Here the incompressible visco-resistive MHD equations are solved using parallel pseudo-spectral solvers in Cartesian geometries. The volume penalization technique is an immersed boundary method which is characterized by a high flexibility for the geometry of the considered flow. In the present case, it allows to use other than periodic boundary conditions in a Fourier pseudo-spectral approach. The numerical method is validated and its convergence is assessed for two- and three-dimensional hydrodynamic (HD) and MHD flows, by comparing the numerical results with results from literature and analyticalmore » solutions. The test cases considered are two-dimensional Taylor–Couette flow, the z-pinch configuration, three dimensional Orszag–Tang flow, Ohmic-decay in a periodic cylinder, three-dimensional Taylor–Couette flow with and without axial magnetic field and three-dimensional Hartmann-instabilities in a cylinder with an imposed helical magnetic field. Finally, we present a magnetohydrodynamic flow simulation in toroidal geometry with non-symmetric cross section and imposing a helical magnetic field to illustrate the potential of the method.« less

Hydrodynamics of an electrochemical membrane bioreactor.

PubMed

Wang, Ya-Zhou; Wang, Yun-Kun; He, Chuan-Shu; Yang, Hou-Yun; Sheng, Guo-Ping; Shen, Jin-You; Mu, Yang; Yu, Han-Qing

2015-05-22

An electrochemical membrane bioreactor (EMBR) has recently been developed for energy recovery and wastewater treatment. The hydrodynamics of the EMBR would significantly affect the mass transfers and reaction kinetics, exerting a pronounced effect on reactor performance. However, only scarce information is available to date. In this study, the hydrodynamic characteristics of the EMBR were investigated through various approaches. Tracer tests were adopted to generate residence time distribution curves at various hydraulic residence times, and three hydraulic models were developed to simulate the results of tracer studies. In addition, the detailed flow patterns of the EMBR were acquired from a computational fluid dynamics (CFD) simulation. Compared to the tank-in-series and axial dispersion ones, the Martin model could describe hydraulic performance of the EBMR better. CFD simulation results clearly indicated the existence of a preferential or circuitous flow in the EMBR. Moreover, the possible locations of dead zones in the EMBR were visualized through the CFD simulation. Based on these results, the relationship between the reactor performance and the hydrodynamics of EMBR was further elucidated relative to the current generation. The results of this study would benefit the design, operation and optimization of the EMBR for simultaneous energy recovery and wastewater treatment.

Hydrodynamics of an Electrochemical Membrane Bioreactor

PubMed Central

Wang, Ya-Zhou; Wang, Yun-Kun; He, Chuan-Shu; Yang, Hou-Yun; Sheng, Guo-Ping; Shen, Jin-You; Mu, Yang; Yu, Han-Qing

2015-01-01

An electrochemical membrane bioreactor (EMBR) has recently been developed for energy recovery and wastewater treatment. The hydrodynamics of the EMBR would significantly affect the mass transfers and reaction kinetics, exerting a pronounced effect on reactor performance. However, only scarce information is available to date. In this study, the hydrodynamic characteristics of the EMBR were investigated through various approaches. Tracer tests were adopted to generate residence time distribution curves at various hydraulic residence times, and three hydraulic models were developed to simulate the results of tracer studies. In addition, the detailed flow patterns of the EMBR were acquired from a computational fluid dynamics (CFD) simulation. Compared to the tank-in-series and axial dispersion ones, the Martin model could describe hydraulic performance of the EBMR better. CFD simulation results clearly indicated the existence of a preferential or circuitous flow in the EMBR. Moreover, the possible locations of dead zones in the EMBR were visualized through the CFD simulation. Based on these results, the relationship between the reactor performance and the hydrodynamics of EMBR was further elucidated relative to the current generation. The results of this study would benefit the design, operation and optimization of the EMBR for simultaneous energy recovery and wastewater treatment. PMID:25997399

GIZMO: Multi-method magneto-hydrodynamics+gravity code

NASA Astrophysics Data System (ADS)

Hopkins, Philip F.

2014-10-01

GIZMO is a flexible, multi-method magneto-hydrodynamics+gravity code that solves the hydrodynamic equations using a variety of different methods. It introduces new Lagrangian Godunov-type methods that allow solving the fluid equations with a moving particle distribution that is automatically adaptive in resolution and avoids the advection errors, angular momentum conservation errors, and excessive diffusion problems that seriously limit the applicability of “adaptive mesh” (AMR) codes, while simultaneously avoiding the low-order errors inherent to simpler methods like smoothed-particle hydrodynamics (SPH). GIZMO also allows the use of SPH either in “traditional” form or “modern” (more accurate) forms, or use of a mesh. Self-gravity is solved quickly with a BH-Tree (optionally a hybrid PM-Tree for periodic boundaries) and on-the-fly adaptive gravitational softenings. The code is descended from P-GADGET, itself descended from GADGET-2 (ascl:0003.001), and many of the naming conventions remain (for the sake of compatibility with the large library of GADGET work and analysis software).

Hydrodynamic starvation in first-feeding larval fishes

PubMed Central

China, Victor; Holzman, Roi

2014-01-01

Larval fishes suffer prodigious mortality rates, eliminating 99% of the brood within a few days after first feeding. Hjort (1914) famously attributed this “critical period” of low survival to the larvae’s inability to obtain sufficient food [Hjort (1914) Rapp P-v Réun Cons Int Explor Mer 20:1–228]. However, the cause of this poor feeding success remains to be identified. Here, we show that hydrodynamic constraints on the ubiquitous suction mechanism in first-feeding larvae limit their ability to capture prey, thereby reducing their feeding rates. Dynamic-scaling experiments revealed that larval size is the primary determinant of feeding rate, independent of other ontogenetic effects. We conclude that first-feeding larvae experience “hydrodynamic starvation,” in which low Reynolds numbers mechanistically limit their feeding performance even under high prey densities. Our results provide a hydrodynamic perspective on feeding of larval fishes that focuses on the physical properties of the larvae and prey, rather than on prey concentration and the rate of encounters. PMID:24843180

Second-order (2 +1 ) -dimensional anisotropic hydrodynamics

NASA Astrophysics Data System (ADS)

Bazow, Dennis; Heinz, Ulrich; Strickland, Michael

2014-11-01

We present a complete formulation of second-order (2 +1 ) -dimensional anisotropic hydrodynamics. The resulting framework generalizes leading-order anisotropic hydrodynamics by allowing for deviations of the one-particle distribution function from the spheroidal form assumed at leading order. We derive complete second-order equations of motion for the additional terms in the macroscopic currents generated by these deviations from their kinetic definition using a Grad-Israel-Stewart 14-moment ansatz. The result is a set of coupled partial differential equations for the momentum-space anisotropy parameter, effective temperature, the transverse components of the fluid four-velocity, and the viscous tensor components generated by deviations of the distribution from spheroidal form. We then perform a quantitative test of our approach by applying it to the case of one-dimensional boost-invariant expansion in the relaxation time approximation (RTA) in which case it is possible to numerically solve the Boltzmann equation exactly. We demonstrate that the second-order anisotropic hydrodynamics approach provides an excellent approximation to the exact (0+1)-dimensional RTA solution for both small and large values of the shear viscosity.

Hydrodynamic perception in true seals (Phocidae) and eared seals (Otariidae).

PubMed

Hanke, Wolf; Wieskotten, Sven; Marshall, Christopher; Dehnhardt, Guido

2013-06-01

Pinnipeds, that is true seals (Phocidae), eared seals (Otariidae), and walruses (Odobenidae), possess highly developed vibrissal systems for mechanoreception. They can use their vibrissae to detect and discriminate objects by direct touch. At least in Phocidae and Otariidae, the vibrissae can also be used to detect and analyse water movements. Here, we review what is known about this ability, known as hydrodynamic perception, in pinnipeds. Hydrodynamic perception in pinnipeds developed convergently to the hydrodynamic perception with the lateral line system in fish and the sensory hairs in crustaceans. So far two species of pinnipeds, the harbour seal (Phoca vitulina) representing the Phocidae and the California sea lion (Zalophus californianus) representing the Otariidae, have been studied for their ability to detect local water movements (dipole stimuli) and to follow hydrodynamic trails, that is the water movements left behind by objects that have passed by at an earlier point in time. Both species are highly sensitive to dipole stimuli and can follow hydrodynamic trails accurately. In the individuals tested, California sea lions were clearly more sensitive to dipole stimuli than harbour seals, and harbour seals showed a superior trail following ability as compared to California sea lions. Harbour seals have also been shown to derive additional information from hydrodynamic trails, such as motion direction, size and shape of the object that caused the trail (California sea lions have not yet been tested). The peculiar undulated shape of the harbour seals' vibrissae appears to play a crucial role in trail following, as it suppresses self-generated noise while the animal is swimming.

Smoothed Particle Hydrodynamic Simulator

DOE Office of Scientific and Technical Information (OSTI.GOV)

2016-10-05

This code is a highly modular framework for developing smoothed particle hydrodynamic (SPH) simulations running on parallel platforms. The compartmentalization of the code allows for rapid development of new SPH applications and modifications of existing algorithms. The compartmentalization also allows changes in one part of the code used by many applications to instantly be made available to all applications.

In Vitro Effect of Laser-Induced Hydrodynamics on Cancer Cells.

PubMed

Elagin, V V; Pavlikov, A I; Yusupov, V I; Shirmanova, M V; Zagaynova, E V; Bagratashvili, V N

2015-11-01

We studied the effect of laser-induced hydrodynamic on viability of Colo-26 murine colon carcinoma cells in vitro. Laser-induced hydrodynamics was generated by a laser (λ=1.56 μ, power 3 W, 5 min exposure); to this end, the fiber end was submersed into a buffer above the cell monolayer. It was found that laser-induced hydrodynamics destructed the monolayer at standoff distances of between the working end of the laser fiber to cell monolayer of 1 and 5 mm and triggers apoptotic and necrotic death in remaining cells at a distance of 4 mm from the emitter.

Directed collective motion of bacteria under channel confinement

NASA Astrophysics Data System (ADS)

Wioland, H.; Lushi, E.; Goldstein, R. E.

2016-07-01

Dense suspensions of swimming bacteria are known to exhibit collective behaviour arising from the interplay of steric and hydrodynamic interactions. Unconfined suspensions exhibit transient, recurring vortices and jets, whereas those confined in circular domains may exhibit order in the form of a spiral vortex. Here we show that confinement into a long and narrow macroscopic ‘racetrack’ geometry stabilises bacterial motion to form a steady unidirectional circulation. This motion is reproduced in simulations of discrete swimmers that reveal the crucial role that bacteria-driven fluid flows play in the dynamics. In particular, cells close to the channel wall produce strong flows which advect cells in the bulk against their swimming direction. We examine in detail the transition from a disordered state to persistent directed motion as a function of the channel width, and show that the width at the crossover point is comparable to the typical correlation length of swirls seen in the unbounded system. Our results shed light on the mechanisms driving the collective behaviour of bacteria and other active matter systems, and stress the importance of the ubiquitous boundaries found in natural habitats.

The way from microscopic many-particle theory to macroscopic hydrodynamics.

PubMed

Haussmann, Rudolf

2016-03-23

Starting from the microscopic description of a normal fluid in terms of any kind of local interacting many-particle theory we present a well defined step by step procedure to derive the hydrodynamic equations for the macroscopic phenomena. We specify the densities of the conserved quantities as the relevant hydrodynamic variables and apply the methods of non-equilibrium statistical mechanics with projection operator techniques. As a result we obtain time-evolution equations for the hydrodynamic variables with three kinds of terms on the right-hand sides: reversible, dissipative and fluctuating terms. In their original form these equations are completely exact and contain nonlocal terms in space and time which describe nonlocal memory effects. Applying a few approximations the nonlocal properties and the memory effects are removed. As a result we find the well known hydrodynamic equations of a normal fluid with Gaussian fluctuating forces. In the following we investigate if and how the time-inversion invariance is broken and how the second law of thermodynamics comes about. Furthermore, we show that the hydrodynamic equations with fluctuating forces are equivalent to stochastic Langevin equations and the related Fokker-Planck equation. Finally, we investigate the fluctuation theorem and find a modification by an additional term.

Improved upper bounds on energy dissipation rates in plane Couette flow with boundary injection and suction

NASA Astrophysics Data System (ADS)

Lee, Harry; Wen, Baole; Doering, Charles

2017-11-01

The rate of viscous energy dissipation ɛ in incompressible Newtonian planar Couette flow (a horizontal shear layer) imposed with uniform boundary injection and suction is studied numerically. Specifically, fluid is steadily injected through the top plate with a constant rate at a constant angle of injection, and the same amount of fluid is sucked out vertically through the bottom plate at the same rate. This set-up leads to two control parameters, namely the angle of injection, θ, and the Reynolds number of the horizontal shear flow, Re . We numerically implement the `background field' variational problem formulated by Constantin and Doering with a one-dimensional unidirectional background field ϕ(z) , where z aligns with the distance between the plates. Computation is carried out at various levels of Re with θ = 0 , 0 .1° ,1° and 2°, respectively. The computed upper bounds on ɛ scale like Re0 as Re > 20 , 000 for each fixed θ, this agrees with Kolmogorov's hypothesis on isotropic turbulence. The outcome provides new upper bounds to ɛ among any solution to the underlying Navier-Stokes equations, and they are sharper than the analytical bounds presented in Doering et al. (2000). This research was partially supported by the NSF Award DMS-1515161, and the University of Michigan's Rackham Graduate Student Research Grant.

Warm Dense Matter: Another Application for Pulsed Power Hydrodynamics

DTIC Science & Technology

2009-06-01

Pulsed power hydrodynamic techniques, such as large convergence liner compression of a large volume, modest density, low temperature plasma to...controlled than are similar high explosively powered hydrodynamic experiments. While the precision and controllability of gas- gun experiments is...well established, pulsed power techniques using imploding liner offer access to convergent conditions, difficult to obtain with guns – and essential

Hydrodynamic interaction of swimming organisms in an inertial regime

NASA Astrophysics Data System (ADS)

Li, Gaojin; Ostace, Anca; Ardekani, Arezoo M.

2016-11-01

We numerically investigate the hydrodynamic interaction of swimming organisms at small to intermediate Reynolds number regimes, i.e., Re˜O (0.1 -100 ) , where inertial effects are important. The hydrodynamic interaction of swimming organisms in this regime is significantly different from the Stokes regime for microorganisms, as well as the high Reynolds number flows for fish and birds, which involves strong flow separation and detached vortex structures. Using an archetypal swimmer model, called a "squirmer," we find that the inertial effects change the contact time and dispersion dynamics of a pair of pusher swimmers, and trigger hydrodynamic attraction for two pullers. These results are potentially important in investigating predator-prey interactions, sexual reproduction, and the encounter rate of marine organisms such as copepods, ctenophora, and larvae.

Overview of the 9th International Conference on Hydrodynamics

NASA Astrophysics Data System (ADS)

Lu, Dong-qiang

2010-10-01

The 9th International Conference on Hydrodynamics (ICHD), held in Shanghai, China from 11 to 15 October, 2010, was briefly reviewed. More than 240 delegates from 23 countries and regions attended this Conference, at which three plenary lectures, two keynote lectures and more than 160 papers were delivered. A special symposium on hydrodynamics in honor of Prof. You-sheng He was jointly organized in this ICHD. The printed proceedings, edited by Y. S. Wu, S. Q. Dai, H. Liu et al. and published by China Ocean Press, collect 172 technical papers contributed from 26 countries and regions. The electronic proceedings are distributed by the Elsevier at the ScienceDirect website as "Journal of Hydrodynamics, 2010, Vol. 22, No. 5 (Supplement)".

Distant touch hydrodynamic imaging with an artificial lateral line.

PubMed

Yang, Yingchen; Chen, Jack; Engel, Jonathan; Pandya, Saunvit; Chen, Nannan; Tucker, Craig; Coombs, Sheryl; Jones, Douglas L; Liu, Chang

2006-12-12

Nearly all underwater vehicles and surface ships today use sonar and vision for imaging and navigation. However, sonar and vision systems face various limitations, e.g., sonar blind zones, dark or murky environments, etc. Evolved over millions of years, fish use the lateral line, a distributed linear array of flow sensing organs, for underwater hydrodynamic imaging and information extraction. We demonstrate here a proof-of-concept artificial lateral line system. It enables a distant touch hydrodynamic imaging capability to critically augment sonar and vision systems. We show that the artificial lateral line can successfully perform dipole source localization and hydrodynamic wake detection. The development of the artificial lateral line is aimed at fundamentally enhancing human ability to detect, navigate, and survive in the underwater environment.

Impact of hydrodynamic stresses on bacterial flagella

NASA Astrophysics Data System (ADS)

Das, Debasish; Riley, Emily; Lauga, Eric

2017-11-01

The locomotion of bacteria powered by helical filaments, such as Escherichia coli, critically involves the generation of flows and hydrodynamic stresses which lead to forces and moments balanced by the moment applied by the bacterial rotary motor (which is embedded in the cell wall) and the deformation of the short flexible hook. In this talk we use numerical computations to accurately compute these hydrodynamic stresses, to show how they critically lead to fluid-structure instabilities at the whole-cell level, and enquire if they can be used to rationalise experimental measurements of bacterial motor torques. ERC Consolidator Grant.

Hydrodynamic chromatography of macromolecules using polymer monolithic columns.

PubMed

Edam, Rob; Eeltink, Sebastiaan; Vanhoutte, Dominique J D; Kok, Wim Th; Schoenmakers, Peter J

2011-12-02

The selectivity window of size-based separations of macromolecules was tailored by tuning the macropore size of polymer monolithic columns. Monolithic materials with pore sizes ranging between 75 nm and 1.2 μm were prepared in situ in large I.D. columns. The dominant separation mechanism was hydrodynamic chromatography in the flow-through pores. The calibration curves for synthetic polymers matched with the elution behavior by HDC separations in packed columns with 'analyte-to-pore' aspect ratios (λ) up to 0.2. For large-macropore monoliths, a deviation in retention behavior was observed for small polystyrene polymers (M(r)<20 kDa), which may be explained by a combined HDC-SEC mechanism for λ<0.02. The availability of monoliths with very narrow pore sizes allowed investigation of separations at high λ values. For high-molecular weight polymers (M(r)>300,000 Da) confined in narrow channels, the separation strongly depended on flow rate. Flow-rate dependent elution behavior was evaluated by calculation of Deborah numbers and confirmed to be outside the scope of classic shear deformation or slalom chromatography. Shear-induced forces acting on the periphery of coiled polymers in solution may be responsible for flow-rate dependent elution. Copyright © 2011 Elsevier B.V. All rights reserved.

Activity-induced clustering in model dumbbell swimmers: the role of hydrodynamic interactions.

PubMed

Furukawa, Akira; Marenduzzo, Davide; Cates, Michael E

2014-08-01

Using a fluid-particle dynamics approach, we numerically study the effects of hydrodynamic interactions on the collective dynamics of active suspensions within a simple model for bacterial motility: each microorganism is modeled as a stroke-averaged dumbbell swimmer with prescribed dipolar force pairs. Using both simulations and qualitative arguments, we show that, when the separation between swimmers is comparable to their size, the swimmers' motions are strongly affected by activity-induced hydrodynamic forces. To further understand these effects, we investigate semidilute suspensions of swimmers in the presence of thermal fluctuations. A direct comparison between simulations with and without hydrodynamic interactions shows these to enhance the dynamic clustering at a relatively small volume fraction; with our chosen model the key ingredient for this clustering behavior is hydrodynamic trapping of one swimmer by another, induced by the active forces. Furthermore, the density dependence of the motility (of both the translational and rotational motions) exhibits distinctly different behaviors with and without hydrodynamic interactions; we argue that this is linked to the clustering tendency. Our study illustrates the fact that hydrodynamic interactions not only affect kinetic pathways in active suspensions, but also cause major changes in their steady state properties.

Activity-induced clustering in model dumbbell swimmers: The role of hydrodynamic interactions

NASA Astrophysics Data System (ADS)

Furukawa, Akira; Marenduzzo, Davide; Cates, Michael E.

2014-08-01

Using a fluid-particle dynamics approach, we numerically study the effects of hydrodynamic interactions on the collective dynamics of active suspensions within a simple model for bacterial motility: each microorganism is modeled as a stroke-averaged dumbbell swimmer with prescribed dipolar force pairs. Using both simulations and qualitative arguments, we show that, when the separation between swimmers is comparable to their size, the swimmers' motions are strongly affected by activity-induced hydrodynamic forces. To further understand these effects, we investigate semidilute suspensions of swimmers in the presence of thermal fluctuations. A direct comparison between simulations with and without hydrodynamic interactions shows these to enhance the dynamic clustering at a relatively small volume fraction; with our chosen model the key ingredient for this clustering behavior is hydrodynamic trapping of one swimmer by another, induced by the active forces. Furthermore, the density dependence of the motility (of both the translational and rotational motions) exhibits distinctly different behaviors with and without hydrodynamic interactions; we argue that this is linked to the clustering tendency. Our study illustrates the fact that hydrodynamic interactions not only affect kinetic pathways in active suspensions, but also cause major changes in their steady state properties.

Hydrodynamic Assists Magnetophoreses Rare Cancer cells Separation in Microchannel Simulation and Experimental Verifications

NASA Astrophysics Data System (ADS)

Saeed, O.; Duru, L.; Yulin, D.

2018-05-01

A proposed microfluidic design has been fabricated and simulated using COMSOL Multiphysics software, based on two physical models included in this design. The device’s ability to create a narrow stream of the core sample by controlling the sheath flow rates Qs1 and Qs2 in both peripheral channels was investigated. The main target of this paper is to study the possibility of combing the hydrodynamic and magnetic techniques, in order to achieve a high rate of cancer cells separation from a cell mixture and/or buffer sample. The study has been conducted in two stages, firstly, the effects of the sheath flow rates (Qs1 and Qs2) on the sample stream focusing were studied, to find the proposed device effectiveness optimal conditions and its capability in cell focusing, and then the magnetic mechanism has been utilized to finalize the pre-labelled cells separation process.

Metric anisotropies and emergent anisotropic hydrodynamics

NASA Astrophysics Data System (ADS)

Dash, Ashutosh; Jaiswal, Amaresh

2018-05-01

Expansion of a locally equilibrated fluid is considered in an anisotropic space-time given by the Bianchi type-I metric. Starting from the isotropic equilibrium phase-space distribution function in the local rest frame, we obtain expressions for components of the energy-momentum tensor and conserved current, such as number density, energy density, and pressure components. In the case of an axissymmetric Bianchi type-I metric, we show that they are identical to those obtained within the setup of anisotropic hydrodynamics. We further consider the case in which the Bianchi type-I metric is a vacuum solution of the Einstein equation: the Kasner metric. For the axissymmetric Kasner metric, we discuss the implications of our results in the context of anisotropic hydrodynamics.

Combined treatment technology based on synergism between hydrodynamic cavitation and advanced oxidation processes.

PubMed

Gogate, Parag R; Patil, Pankaj N

2015-07-01

The present work highlights the novel approach of combination of hydrodynamic cavitation and advanced oxidation processes for wastewater treatment. The initial part of the work concentrates on the critical analysis of the literature related to the combined approaches based on hydrodynamic cavitation followed by a case study of triazophos degradation using different approaches. The analysis of different combinations based on hydrodynamic cavitation with the Fenton chemistry, advanced Fenton chemistry, ozonation, photocatalytic oxidation, and use of hydrogen peroxide has been highlighted with recommendations for important design parameters. Subsequently degradation of triazophos pesticide in aqueous solution (20 ppm solution of commercially available triazophos pesticide) has been investigated using hydrodynamic cavitation and ozonation operated individually and in combination for the first time. Effect of different operating parameters like inlet pressure (1-8 bar) and initial pH (2.5-8) have been investigated initially. The effect of addition of Fenton's reagent at different loadings on the extent of degradation has also been investigated. The combined method of hydrodynamic cavitation and ozone has been studied using two approaches of injecting ozone in the solution tank and at the orifice (at the flow rate of 0.576 g/h and 1.95 g/h). About 50% degradation of triazophos was achieved by hydrodynamic cavitation alone under optimized operating parameters. About 80% degradation of triazophos was achieved by combination of hydrodynamic cavitation and Fenton's reagent whereas complete degradation was achieved using combination of hydrodynamic cavitation and ozonation. TOC removal of 96% was also obtained for the combination of ozone and hydrodynamic cavitation making it the best treatment strategy for removal of triazophos. Copyright © 2014 Elsevier B.V. All rights reserved.

Study on unsteady hydrodynamic performance of propeller in waves

NASA Astrophysics Data System (ADS)

Zhao, Qingxin; Guo, Chunyu; Su, Yumin; Liu, Tian; Meng, Xiangyin

2017-09-01

The speed of a ship sailing in waves always slows down due to the decrease in efficiency of the propeller. So it is necessary and essential to analyze the unsteady hydrodynamic performance of propeller in waves. This paper is based on the numerical simulation and experimental research of hydrodynamics performance when the propeller is under wave conditions. Open-water propeller performance in calm water is calculated by commercial codes and the results are compared to experimental values to evaluate the accuracy of the numerical simulation method. The first-order Volume of Fluid (VOF) wave method in STAR CCM+ is utilized to simulate the three-dimensional numerical wave. According to the above prerequisite, the numerical calculation of hydrodynamic performance of the propeller under wave conditions is conducted, and the results reveal that both thrust and torque of the propeller under wave conditions reveal intense unsteady behavior. With the periodic variation of waves, ventilation, and even an effluent phenomenon appears on the propeller. Calculation results indicate, when ventilation or effluent appears, the numerical calculation model can capture the dynamic characteristics of the propeller accurately, thus providing a significant theory foundation for further studying the hydrodynamic performance of a propeller in waves.

Augmenting two-dimensional hydrodynamic simulations with measured velocity data to identify flow paths as a function of depth on Upper St. Clair River in the Great Lakes basin

USGS Publications Warehouse

Holtschlag, D.J.; Koschik, J.A.

2005-01-01

Upper St. Clair River, which receives outflow from Lake Huron, is characterized by flow velocities that exceed 7 feet per second and significant channel curvature that creates complex flow patterns downstream from the Blue Water Bridge in the Port Huron, Michigan, and Sarnia, Ontario, area. Discrepancies were detected between depth-averaged velocities previously simulated by a two-dimensional (2D) hydrodynamic model and surface velocities determined from drifting buoy deployments. A detailed ADCP (acoustic Doppler current profiler) survey was done on Upper St. Clair River during July 1–3, 2003, to help resolve these discrepancies. As part of this study, a refined finite-element mesh of the hydrodynamic model used to identify source areas to public water intakes was developed for Upper St. Clair River. In addition, a numerical procedure was used to account for radial accelerations, which cause secondary flow patterns near channel bends. The refined model was recalibrated to better reproduce local velocities measured in the ADCP survey. ADCP data also were used to help resolve the remaining discrepancies between simulated and measured velocities and to describe variations in velocity with depth. Velocity data from ADCP surveys have significant local variability, and statistical processing is needed to compute reliable point estimates. In this study, velocity innovations were computed for seven depth layers posited within the river as the differences between measured and simulated velocities. For each layer, the spatial correlation of velocity innovations was characterized by use of variogram analysis. Results were used with kriging to compute expected innovations within each layer at applicable model nodes. Expected innovations were added to simulated velocities to form integrated velocities, which were used with reverse particle tracking to identify the expected flow path near a sewage outfall as a function of flow depth. Expected particle paths generated by use

Introduction to the Focus Issue: Chemo-Hydrodynamic Patterns and Instabilities

NASA Astrophysics Data System (ADS)

De Wit, A.; Eckert, K.; Kalliadasis, S.

2012-09-01

Pattern forming instabilities are often encountered in a wide variety of natural phenomena and technological applications, from self-organization in biological and chemical systems to oceanic or atmospheric circulation and heat and mass transport processes in engineering systems. Spatio-temporal structures are ubiquitous in hydrodynamics where numerous different convective instabilities generate pattern formation and complex spatiotemporal dynamics, which have been much studied both theoretically and experimentally. In parallel, reaction-diffusion processes provide another large family of pattern forming instabilities and spatio-temporal structures which have been analyzed for several decades. At the intersection of these two fields, "chemo-hydrodynamic patterns and instabilities" resulting from the coupling of hydrodynamic and reaction-diffusion processes have been less studied. The exploration of the new instability and symmetry-breaking scenarios emerging from the interplay between chemical reactions, diffusion and convective motions is a burgeoning field in which numerous exciting problems have emerged during the last few years. These problems range from fingering instabilities of chemical fronts and reactive fluid-fluid interfaces to the dynamics of reaction-diffusion systems in the presence of chaotic mixing. The questions to be addressed are at the interface of hydrodynamics, chemistry, engineering or environmental sciences to name a few and, as a consequence, they have started to draw the attention of several communities including both the nonlinear chemical dynamics and hydrodynamics communities. The collection of papers gathered in this Focus Issue sheds new light on a wide range of phenomena in the general area of chemo-hydrodynamic patterns and instabilities. It also serves as an overview of the current research and state-of-the-art in the field.

Automatization of hydrodynamic modelling in a Floreon+ system

NASA Astrophysics Data System (ADS)

Ronovsky, Ales; Kuchar, Stepan; Podhoranyi, Michal; Vojtek, David

2017-07-01

The paper describes fully automatized hydrodynamic modelling as a part of the Floreon+ system. The main purpose of hydrodynamic modelling in the disaster management is to provide an accurate overview of the hydrological situation in a given river catchment. Automatization of the process as a web service could provide us with immediate data based on extreme weather conditions, such as heavy rainfall, without the intervention of an expert. Such a service can be used by non scientific users such as fire-fighter operators or representatives of a military service organizing evacuation during floods or river dam breaks. The paper describes the whole process beginning with a definition of a schematization necessary for hydrodynamic model, gathering of necessary data and its processing for a simulation, the model itself and post processing of a result and visualization on a web service. The process is demonstrated on a real data collected during floods in our Moravian-Silesian region in 2010.

Origins of hydrodynamic forces on centrifugal pump impellers

NASA Technical Reports Server (NTRS)

Adkins, Douglas R.; Brennen, Christopher E.

1987-01-01

Hydrodynamic interactions that occur between a centrifugal pump impeller and volute are experimentally and theoretically investigated. The theoretical analysis considers the inability of the blades to perfectly guide the flow through the impeller, and also includes a quasi-one dimensional treatment of the flow in the volute. The disturbance at the impeller discharge and the resulting forces are determined by the theoretical model. The model is then extended to obtain the hydrodynamic force perturbations that are caused by the impeller whirling eccentrically in the volute. Under many operating conditions, these force perturbations were found to be destablizing. Comparisons are made between the theoretical model and the experimental measurements of pressure distributions and radial forces on the impeller. The theoretical model yields fairly accurate predictions of the radial forces caused by the flow through the impeller. However, it was found that the pressure acting on the front shroud of the impeller has a substantial effect on the destablizing hydrodynamic forces.

Channel Extension in Deep-Water Distributive Systems

NASA Astrophysics Data System (ADS)

Hoyal, D. C.; Sheets, B. A.

2007-12-01

The cyclic nature of channel and lobe formation in submarine fans is the result of the unstable and ephemeral nature of newly formed distributary channels. Avulsion cycles are initiated as unconfined sheet flow immediately following avulsion followed by stages of channel incision and extension, deposition of channel mouth deposits, and often channel backfilling. In contrast with those in alluvial and deltaic environments, avulsion cycles in submarine fans are relatively poorly understood due to the difficulty of observing deep ocean processes, either over short timescales needed to measure the hydrodynamics of active turbidity currents, or over longer timescales needed for the morphodynamic evolution of individual distributary channels and avulsion events. Here we report the results of over 80 experiments in a 5m x 3m x1m deep tank using saline (NaCl) density flows carrying low-density plastic sediment (SG 1.5) flowing down an inclined ramp. These experiments were designed to investigate trends observed in earlier self-organized experimental submarine fans with well-developed avulsion cycles, in which distributive lobes were observed to form on relatively high slopes. In particular, we were interested in investigating the relationship between channel extension length (distance from the inlet to the point where the flow becomes de-channelized, transitioning into a mouth-bar/lobe) and slope. The results of the experiments are clear but counter-intuitive. Channels appear to extend in discrete segments and channel extension length is inversely related to slope over a wide range of slopes (5-17 degrees). In addition, channel extension seems largely independent of inlet flow density (salt concentration) over the experimental range (10-24 g/cc). Measurements of densimetric Froude number (Fr') indicate Fr' increases downstream to near critical conditions at the channel lobe transition. Our preliminary interpretation is that distributary channels become unstable due to

Separability of electrostatic and hydrodynamic forces in particle electrophoresis

NASA Astrophysics Data System (ADS)

Todd, Brian A.; Cohen, Joel A.

2011-09-01

By use of optical tweezers we explicitly measure the electrostatic and hydrodynamic forces that determine the electrophoretic mobility of a charged colloidal particle. We test the ansatz of O'Brien and White [J. Chem. Soc. Faraday IIJCFTBS0300-923810.1039/f29787401607 74, 1607 (1978)] that the electrostatically and hydrodynamically coupled electrophoresis problem is separable into two simpler problems: (1) a particle held fixed in an applied electric field with no flow field and (2) a particle held fixed in a flow field with no applied electric field. For a system in the Helmholtz-Smoluchowski and Debye-Hückel regimes, we find that the electrostatic and hydrodynamic forces measured independently accurately predict the electrophoretic mobility within our measurement precision of 7%; the O'Brien and White ansatz holds under the conditions of our experiment.

Buoyancy-driven mean flow in a long channel with a hydraulically constrained exit condition

NASA Astrophysics Data System (ADS)

Grimm, Th.; Maxworthy, T.

1999-11-01

Convection plays a major role in a variety of natural hydrodynamic systems. Those in which convection drives exchange flows through a lateral contraction and/or over a sill form a special class with typical examples being the Red and Mediterranean Seas, the Persian Gulf, and the fjords that indent many coastlines. The present work focuses on the spatial distribution and scaling of the density difference between the inflowing and outflowing fluid layers. Using a long water-filled channel, fitted with buoyancy sources at its upper surface, experiments were conducted to investigate the influence of the geometry of the strait and the channel as well as the magnitude of the buoyancy flux. Two different scaling laws, one by Phillips (1966), and one by Maxworthy (1994, 1997) were compared with the experimental results. It has been shown that a scaling law for which g[prime prime or minute] = kB02/3x/h4/3 best describes the distribution of the observed density difference along the channel, where B0 is the buoyancy flux, x the distance from the closed end of the channel, h its height at the open end (sill) and k a constant that depends on the details of the channel geometry and flow conditions. This result holds for the experimental results and appears to be valid for a number of natural systems as well.

Hydrodynamics and long range correlations

NASA Astrophysics Data System (ADS)

Bialas, A.; Zalewski, K.

2011-04-01

It is shown that the recently proposed method of studying the long-range correlations in multiparticle production can be effectively used to verify the hydrodynamic nature of the longitudinal expansion of the partonic system created in the collision. The case of ALICE detector is explicitly considered.

Boreal tree hydrodynamics: asynchronous, diverging, yet complementary.

PubMed

Pappas, Christoforos; Matheny, Ashley M; Baltzer, Jennifer L; Barr, Alan G; Black, T Andrew; Bohrer, Gil; Detto, Matteo; Maillet, Jason; Roy, Alexandre; Sonnentag, Oliver; Stephens, Jilmarie

2018-05-08

Water stress has been identified as a key mechanism of the contemporary increase in tree mortality rates in northwestern North America. However, a detailed analysis of boreal tree hydrodynamics and their interspecific differences is still lacking. Here we examine the hydraulic behaviour of co-occurring larch (Larix laricina) and black spruce (Picea mariana), two characteristic boreal tree species, near the southern limit of the boreal ecozone in central Canada. Sap flux density (Js), concurrently recorded stem radius fluctuations and meteorological conditions are used to quantify tree hydraulic functioning and to scrutinize tree water-use strategies. Our analysis revealed asynchrony in the diel hydrodynamics of the two species with the initial rise in Js occurring 2 h earlier in larch than in black spruce. Interspecific differences in larch and black spruce crown architecture explained the observed asynchrony in their hydraulic functioning. Furthermore, the two species exhibited diverging stomatal regulation strategies with larch and black spruce employing relatively isohydric and anisohydric behaviour, respectively. Such asynchronous and diverging tree-level hydrodynamics provide new insights into the ecosystem-level complementarity in tree form and function, with implications for understanding boreal forests' water and carbon dynamics and their resilience to environmental stress.

Calibration of the 2D Hydrodynamic Model Floodos and Implications of Distributed Friction on Sediment Transport Capacity

NASA Astrophysics Data System (ADS)

Croissant, T.; Lague, D.; Davy, P.

2014-12-01

Numerical models of floodplain dynamics often use a simplified 1D description of flow hydraulics and sediment transport that cannot fully account for differential friction between vegetated banks and low friction in the main channel. Key parameters of such models are the friction coefficient and the description of the channel bathymetry which strongly influence predicted water depth and velocity, and therefore sediment transport capacity. In this study, we use a newly developed 2D hydrodynamic model, Floodos, whose efficiency is a major advantage for exploring channel morphodynamics from a flood event to millennial time scales. We evaluate the quality of Floodos predictions in the Whataroa river, New Zealand and assess the effect of a spatially distributed friction coefficient (SDFC) on long term sediment transport. Predictions from the model are compared to water depth data from a gauging station located on the Whataroa River in Southern Alps, New Zealand. The Digital Elevation Model (DEM) of the 2.5 km long studied reach is derived from a 2010 LiDAR acquisition with 2 m resolution and an interpolated bathymetry. The several large floods experienced by this river during 2010 allow us to access water depth for a wide range of possible river discharges and to retrieve the scaling between these two parameters. The high resolution DEM used has a non-negligible part of submerged bathymetry that airborne LiDAR was not able to capture. Bathymetry can be reconstructed by interpolation methods that introduce several uncertainties concerning water depth predictions. We address these uncertainties inherent to the interpolation using a simplified channel with a geometry (slope and width) similar to the Whataroa river. We then explore the effect of a SDFC on velocity pattern, water depth and sediment transport capacity and discuss its relevance on long term predictions of sediment transport and channel morphodynamics.

Py-SPHViewer: Cosmological simulations using Smoothed Particle Hydrodynamics

NASA Astrophysics Data System (ADS)

Benítez-Llambay, Alejandro

2017-12-01

Py-SPHViewer visualizes and explores N-body + Hydrodynamics simulations. The code interpolates the underlying density field (or any other property) traced by a set of particles, using the Smoothed Particle Hydrodynamics (SPH) interpolation scheme, thus producing not only beautiful but also useful scientific images. Py-SPHViewer enables the user to explore simulated volumes using different projections. Py-SPHViewer also provides a natural way to visualize (in a self-consistent fashion) gas dynamical simulations, which use the same technique to compute the interactions between particles.

Anisotropic nonequilibrium hydrodynamic attractor

NASA Astrophysics Data System (ADS)

Strickland, Michael; Noronha, Jorge; Denicol, Gabriel S.

2018-02-01

We determine the dynamical attractors associated with anisotropic hydrodynamics (aHydro) and the DNMR equations for a 0 +1 d conformal system using kinetic theory in the relaxation time approximation. We compare our results to the nonequilibrium attractor obtained from the exact solution of the 0 +1 d conformal Boltzmann equation, the Navier-Stokes theory, and the second-order Mueller-Israel-Stewart theory. We demonstrate that the aHydro attractor equation resums an infinite number of terms in the inverse Reynolds number. The resulting resummed aHydro attractor possesses a positive longitudinal-to-transverse pressure ratio and is virtually indistinguishable from the exact attractor. This suggests that an optimized hydrodynamic treatment of kinetic theory involves a resummation not only in gradients (Knudsen number) but also in the inverse Reynolds number. We also demonstrate that the DNMR result provides a better approximation of the exact kinetic theory attractor than the Mueller-Israel-Stewart theory. Finally, we introduce a new method for obtaining approximate aHydro equations which relies solely on an expansion in the inverse Reynolds number. We then carry this expansion out to the third order, and compare these third-order results to the exact kinetic theory solution.

Dissipative hydrodynamics for multi-component systems

NASA Astrophysics Data System (ADS)

El, Andrej; Bouras, Ioannis; Wesp, Christian; Xu, Zhe; Greiner, Carsten

2012-11-01

Second-order dissipative hydrodynamic equations for each component of a multi-component system are derived using the entropy principle. Comparison of the solutions with kinetic transport results demonstrates validity of the obtained equations. We demonstrate how the shear viscosity of the total system can be calculated in terms of the involved cross-sections and partial densities. The presence of the inter-species interactions leads to a characteristic time dependence of the shear viscosity of the mixture, which also means that the shear viscosity of a mixture cannot be calculated using the Green-Kubo formalism the way it has been done recently. This finding is of interest for understanding of the shear viscosity of a quark-gluon plasma extracted from comparisons of hydrodynamic simulations with experimental results from RHIC and LHC.

TORUS: Radiation transport and hydrodynamics code

NASA Astrophysics Data System (ADS)

Harries, Tim

2014-04-01

TORUS is a flexible radiation transfer and radiation-hydrodynamics code. The code has a basic infrastructure that includes the AMR mesh scheme that is used by several physics modules including atomic line transfer in a moving medium, molecular line transfer, photoionization, radiation hydrodynamics and radiative equilibrium. TORUS is useful for a variety of problems, including magnetospheric accretion onto T Tauri stars, spiral nebulae around Wolf-Rayet stars, discs around Herbig AeBe stars, structured winds of O supergiants and Raman-scattered line formation in symbiotic binaries, and dust emission and molecular line formation in star forming clusters. The code is written in Fortran 2003 and is compiled using a standard Gnu makefile. The code is parallelized using both MPI and OMP, and can use these parallel sections either separately or in a hybrid mode.

Hydrodynamic Electron Flow and Hall Viscosity

NASA Astrophysics Data System (ADS)

Scaffidi, Thomas; Moll, Philip; Kushwaha, Pallavi; Nandi, Nabhanila; Schmidt, Burkhard; MacKenzie, Andrew; Moore, Joel

In metallic samples of small enough size and sufficiently strong electron-electron scattering, the viscosity of the electron gas can become the dominant process governing transport. In this regime, momentum is a long-lived quantity whose evolution is described by an emergent hydrodynamical theory for which bounds on diffusion were conjectured based on an holographic correspondence. Furthermore, breaking time-reversal symmetry can lead to the appearance of an odd component to the viscosity called the Hall viscosity which has attracted a lot of attention recently due to its quantized nature in gapped systems but still eludes experimental confirmation. Based on microscopic calculations, we discuss how to measure the effects of both the even and odd components of the viscosity using hydrodynamic electronic transport in mesoscopic samples under applied magnetic fields. Gordon and Betty Moore Foundation.

Solvable Hydrodynamics of Quantum Integrable Systems

NASA Astrophysics Data System (ADS)

Bulchandani, Vir B.; Vasseur, Romain; Karrasch, Christoph; Moore, Joel E.

2017-12-01

The conventional theory of hydrodynamics describes the evolution in time of chaotic many-particle systems from local to global equilibrium. In a quantum integrable system, local equilibrium is characterized by a local generalized Gibbs ensemble or equivalently a local distribution of pseudomomenta. We study time evolution from local equilibria in such models by solving a certain kinetic equation, the "Bethe-Boltzmann" equation satisfied by the local pseudomomentum density. Explicit comparison with density matrix renormalization group time evolution of a thermal expansion in the XXZ model shows that hydrodynamical predictions from smooth initial conditions can be remarkably accurate, even for small system sizes. Solutions are also obtained in the Lieb-Liniger model for free expansion into vacuum and collisions between clouds of particles, which model experiments on ultracold one-dimensional Bose gases.

Young swimmers' classification based on kinematics, hydrodynamics, and anthropometrics.

PubMed

Barbosa, Tiago M; Morais, Jorge E; Costa, Mário J; Goncalves, José; Marinho, Daniel A; Silva, António J

2014-04-01

The aim of this article has been to classify swimmers based on kinematics, hydrodynamics, and anthropometrics. Sixty-seven young swimmers made a maximal 25 m front-crawl to measure with a speedometer the swimming velocity (v), speed-fluctuation (dv) and dv normalized to v (dv/v). Another two 25 m bouts with and without carrying a perturbation device were made to estimate active drag coefficient (CDa). Trunk transverse surface area (S) was measured with photogrammetric technique on land and in the hydrodynamic position. Cluster 1 was related to swimmers with a high speed fluctuation (ie, dv and dv/v), cluster 2 with anthropometrics (ie, S) and cluster 3 with a high hydrodynamic profile (ie, CDa). The variable that seems to discriminate better the clusters was the dv/v (F=53.680; P<.001), followed by the dv (F=28.506; P<.001), CDa (F=21.025; P<.001), S (F=6.297; P<.01) and v (F=5.375; P=.01). Stepwise discriminant analysis extracted 2 functions: Function 1 was mainly defined by dv/v and S (74.3% of variance), whereas function 2 was mainly defined by CDa (25.7% of variance). It can be concluded that kinematics, hydrodynamics and anthropometrics are determinant domains in which to classify and characterize young swimmers' profiles.

A weakly-compressible Cartesian grid approach for hydrodynamic flows

NASA Astrophysics Data System (ADS)

Bigay, P.; Oger, G.; Guilcher, P.-M.; Le Touzé, D.

2017-11-01

The present article aims at proposing an original strategy to solve hydrodynamic flows. In introduction, the motivations for this strategy are developed. It aims at modeling viscous and turbulent flows including complex moving geometries, while avoiding meshing constraints. The proposed approach relies on a weakly-compressible formulation of the Navier-Stokes equations. Unlike most hydrodynamic CFD (Computational Fluid Dynamics) solvers usually based on implicit incompressible formulations, a fully-explicit temporal scheme is used. A purely Cartesian grid is adopted for numerical accuracy and algorithmic simplicity purposes. This characteristic allows an easy use of Adaptive Mesh Refinement (AMR) methods embedded within a massively parallel framework. Geometries are automatically immersed within the Cartesian grid with an AMR compatible treatment. The method proposed uses an Immersed Boundary Method (IBM) adapted to the weakly-compressible formalism and imposed smoothly through a regularization function, which stands as another originality of this work. All these features have been implemented within an in-house solver based on this WCCH (Weakly-Compressible Cartesian Hydrodynamic) method which meets the above requirements whilst allowing the use of high-order (> 3) spatial schemes rarely used in existing hydrodynamic solvers. The details of this WCCH method are presented and validated in this article.

Progress and challenges in coupled hydrodynamic-ecological estuarine modeling.

PubMed

Ganju, Neil K; Brush, Mark J; Rashleigh, Brenda; Aretxabaleta, Alfredo L; Del Barrio, Pilar; Grear, Jason S; Harris, Lora A; Lake, Samuel J; McCardell, Grant; O'Donnell, James; Ralston, David K; Signell, Richard P; Testa, Jeremy M; Vaudrey, Jamie M P

2016-03-01

Numerical modeling has emerged over the last several decades as a widely accepted tool for investigations in environmental sciences. In estuarine research, hydrodynamic and ecological models have moved along parallel tracks with regard to complexity, refinement, computational power, and incorporation of uncertainty. Coupled hydrodynamic-ecological models have been used to assess ecosystem processes and interactions, simulate future scenarios, and evaluate remedial actions in response to eutrophication, habitat loss, and freshwater diversion. The need to couple hydrodynamic and ecological models to address research and management questions is clear, because dynamic feedbacks between biotic and physical processes are critical interactions within ecosystems. In this review we present historical and modern perspectives on estuarine hydrodynamic and ecological modeling, consider model limitations, and address aspects of model linkage, skill assessment, and complexity. We discuss the balance between spatial and temporal resolution and present examples using different spatiotemporal scales. Finally, we recommend future lines of inquiry, approaches to balance complexity and uncertainty, and model transparency and utility. It is idealistic to think we can pursue a "theory of everything" for estuarine models, but recent advances suggest that models for both scientific investigations and management applications will continue to improve in terms of realism, precision, and accuracy.

Progress and challenges in coupled hydrodynamic-ecological estuarine modeling

USGS Publications Warehouse

Ganju, Neil K.; Brush, Mark J.; Rashleigh, Brenda; Aretxabaleta, Alfredo L.; del Barrio, Pilar; Grear, Jason S.; Harris, Lora A.; Lake, Samuel J.; McCardell, Grant; O'Donnell, James; Ralston, David K.; Signell, Richard P.; Testa, Jeremy; Vaudrey, Jamie M. P.

2016-01-01

Numerical modeling has emerged over the last several decades as a widely accepted tool for investigations in environmental sciences. In estuarine research, hydrodynamic and ecological models have moved along parallel tracks with regard to complexity, refinement, computational power, and incorporation of uncertainty. Coupled hydrodynamic-ecological models have been used to assess ecosystem processes and interactions, simulate future scenarios, and evaluate remedial actions in response to eutrophication, habitat loss, and freshwater diversion. The need to couple hydrodynamic and ecological models to address research and management questions is clear because dynamic feedbacks between biotic and physical processes are critical interactions within ecosystems. In this review, we present historical and modern perspectives on estuarine hydrodynamic and ecological modeling, consider model limitations, and address aspects of model linkage, skill assessment, and complexity. We discuss the balance between spatial and temporal resolution and present examples using different spatiotemporal scales. Finally, we recommend future lines of inquiry, approaches to balance complexity and uncertainty, and model transparency and utility. It is idealistic to think we can pursue a “theory of everything” for estuarine models, but recent advances suggest that models for both scientific investigations and management applications will continue to improve in terms of realism, precision, and accuracy.

Progress and challenges in coupled hydrodynamic-ecological estuarine modeling

PubMed Central

Ganju, Neil K.; Brush, Mark J.; Rashleigh, Brenda; Aretxabaleta, Alfredo L.; del Barrio, Pilar; Grear, Jason S.; Harris, Lora A.; Lake, Samuel J.; McCardell, Grant; O’Donnell, James; Ralston, David K.; Signell, Richard P.; Testa, Jeremy M.; Vaudrey, Jamie M.P.

2016-01-01

Numerical modeling has emerged over the last several decades as a widely accepted tool for investigations in environmental sciences. In estuarine research, hydrodynamic and ecological models have moved along parallel tracks with regard to complexity, refinement, computational power, and incorporation of uncertainty. Coupled hydrodynamic-ecological models have been used to assess ecosystem processes and interactions, simulate future scenarios, and evaluate remedial actions in response to eutrophication, habitat loss, and freshwater diversion. The need to couple hydrodynamic and ecological models to address research and management questions is clear, because dynamic feedbacks between biotic and physical processes are critical interactions within ecosystems. In this review we present historical and modern perspectives on estuarine hydrodynamic and ecological modeling, consider model limitations, and address aspects of model linkage, skill assessment, and complexity. We discuss the balance between spatial and temporal resolution and present examples using different spatiotemporal scales. Finally, we recommend future lines of inquiry, approaches to balance complexity and uncertainty, and model transparency and utility. It is idealistic to think we can pursue a “theory of everything” for estuarine models, but recent advances suggest that models for both scientific investigations and management applications will continue to improve in terms of realism, precision, and accuracy. PMID:27721675

Application of the Geophysical Scale Multi-Block Transport Modeling System to Hydrodynamic Forcing of Dredged Material Placement Sediment Transport within the James River Estuary

NASA Astrophysics Data System (ADS)

Kim, S. C.; Hayter, E. J.; Pruhs, R.; Luong, P.; Lackey, T. C.

2016-12-01

The geophysical scale circulation of the Mid Atlantic Bight and hydrologic inputs from adjacent Chesapeake Bay watersheds and tributaries influences the hydrodynamics and transport of the James River estuary. Both barotropic and baroclinic transport govern the hydrodynamics of this partially stratified estuary. Modeling the placement of dredged sediment requires accommodating this wide spectrum of atmospheric and hydrodynamic scales. The Geophysical Scale Multi-Block (GSMB) Transport Modeling System is a collection of multiple well established and USACE approved process models. Taking advantage of the parallel computing capability of multi-block modeling, we performed one year three-dimensional modeling of hydrodynamics in supporting simulation of dredged sediment placements transport and morphology changes. Model forcing includes spatially and temporally varying meteorological conditions and hydrological inputs from the watershed. Surface heat flux estimates were derived from the National Solar Radiation Database (NSRDB). The open water boundary condition for water level was obtained from an ADCIRC model application of the U. S. East Coast. Temperature-salinity boundary conditions were obtained from the Environmental Protection Agency (EPA) Chesapeake Bay Program (CBP) long-term monitoring stations database. Simulated water levels were calibrated and verified by comparison with National Oceanic and Atmospheric Administration (NOAA) tide gage locations. A harmonic analysis of the modeled tides was performed and compared with NOAA tide prediction data. In addition, project specific circulation was verified using US Army Corps of Engineers (USACE) drogue data. Salinity and temperature transport was verified at seven CBP long term monitoring stations along the navigation channel. Simulation and analysis of model results suggest that GSMB is capable of resolving the long duration, multi-scale processes inherent to practical engineering problems such as dredged material

Three-dimensional investigations of the threading regime in a microfluidic flow-focusing channel

NASA Astrophysics Data System (ADS)

Gowda, Krishne; Brouzet, Christophe; Lefranc, Thibault; Soderberg, L. Daniel; Lundell, Fredrik

2017-11-01

We study the flow dynamics of the threading regime in a microfluidic flow-focusing channel through 3D numerical simulations and experiments. Making strong filaments from cellulose nano-fibrils (CNF) could potentially steer to new high-performance bio-based composites competing with conventional glass fibre composites. CNF filaments can be obtained through hydrodynamic alignment of dispersed CNF by using the concept of flow-focusing. The aligned structure is locked by diffusion of ions resulting in a dispersion-gel transition. Flow-focusing typically refers to a microfluidic channel system where the core fluid is focused by the two sheath fluids, thereby creating an extensional flow at the intersection. In this study, threading regime corresponds to an extensional flow field generated by the water sheath fluid stretching the dispersed CNF core fluid and leading to formation of long threads. The experimental measurements are performed using optical coherence tomography (OCT) and 3D numerical simulations with OpenFOAM. The prime focus is laid on the 3D characteristics of thread formation such as wetting length of core fluid, shape, aspect ratio of the thread and velocity flow-field in the microfluidic channel.

Swimming of Paramecium in confined channels

NASA Astrophysics Data System (ADS)

Jung, Sunghwan

2012-02-01

Many living organisms in nature have developed a few different swimming modes, presumably derived from hydrodynamic advantage. Paramecium is a ciliated protozoan covered by thousands of cilia with a few nanometers in diameter and tens of micro-meters in length and is able to exhibit both ballistic and meandering motions. First, we characterize ballistic swimming behaviors of ciliated microorganisms in glass capillaries of different diameters and explain the trajectories they trace out. We develop a theoretical model of an undulating sheet with a pressure gradient and discuss how it affects the swimming speed. Secondly, investigation into meandering swimmings within rectangular PDMS channels of dimension smaller than Paramecium length. We find that Paramecium executes a body-bend (an elastic buckling) using the cilia while it meanders. By considering an elastic beam model, we estimate and show the universal profile of forces it exerts on the walls. Finally, we discuss a few other locomotion of Paramecium in other extreme environments like gel.

Hemolysis in a laminar flow-through Couette shearing device: an experimental study.

PubMed

Boehning, Fiete; Mejia, Tzahiry; Schmitz-Rode, Thomas; Steinseifer, Ulrich

2014-09-01

Reducing hemolysis has been one of the major goals of rotary blood pump development and in the investigational phase, the capability of hemolysis estimation for areas of elevated shear stresses is valuable. The degree of hemolysis is determined by the amplitude of shear stress and the exposure time, but to date, the exact hemolytic behavior at elevated shear stresses and potential thresholds for subcritical shear exposure remain vague. This study provides experimental hemolysis data for a set of shear stresses and exposure times to allow better estimations of hemolysis for blood exposed to elevated shearing. Heparinized porcine blood with a hematocrit of 40% was mechanically damaged in a flow-through laminar Couette shear flow at a temperature of 23°C. Four levels of shear stress, 24, 592, 702, and 842 Pa, were replicated at two exposure times, 54 and 873 ms. For the calculation of the shear stresses, an apparent viscosity of 5 mPas was used, which was verified in an additional measurement of the blood viscosity. The hemolysis measurements were repeated four times, whereby all conditions were measured once within the same day and with blood from the same source. Samples were taken at the inlet and outlet of the shear region and an increase in plasma-free hemoglobin was measured. An index of hemolysis (IH) was thereby calculated giving the ratio of free to total hemoglobin. The results are compared with data from previously published studies using a similar shearing device. Hemolysis was found to increase exponentially with shear stress, but high standard deviations existed at measurements with elevated IH. At short exposure times, the IH remained low at under 0.5% for all shear stress levels. For high exposure times, the IH increased from 0.84% at 592 Pa up to 3.57% at the highest shear stress level. Hemolysis was significant for shear stresses above ∼600 Pa at the high exposure time of 873 ms. Copyright © 2014 International Center for Artificial

Hybrid methods for simulating hydrodynamics and heat transfer in multiscale (1D-3D) models

NASA Astrophysics Data System (ADS)

Filimonov, S. A.; Mikhienkova, E. I.; Dekterev, A. A.; Boykov, D. V.

2017-09-01

The work is devoted to application of different-scale models in the simulation of hydrodynamics and heat transfer of large and/or complex systems, which can be considered as a combination of extended and “compact” elements. The model consisting of simultaneously existing three-dimensional and network (one-dimensional) elements is called multiscale. The paper examines the relevance of building such models and considers three main options for their implementation: the spatial and the network parts of the model are calculated separately; spatial and network parts are calculated simultaneously (hydraulically unified model); network elements “penetrate” the spatial part and are connected through the integral characteristics at the tube/channel walls (hydraulically disconnected model). Each proposed method is analyzed in terms of advantages and disadvantages. The paper presents a number of practical examples demonstrating the application of multiscale models.

Three-Dimensional Hydrodynamic Simulations of OMEGA Implosions

NASA Astrophysics Data System (ADS)

Igumenshchev, I. V.

2016-10-01

The effects of large-scale (with Legendre modes less than 30) asymmetries in OMEGA direct-drive implosions caused by laser illumination nonuniformities (beam-power imbalance and beam mispointing and mistiming) and target offset, mount, and layers nonuniformities were investigated using three-dimensional (3-D) hydrodynamic simulations. Simulations indicate that the performance degradation in cryogenic implosions is caused mainly by the target offsets ( 10 to 20 μm), beampower imbalance (σrms 10 %), and initial target asymmetry ( 5% ρRvariation), which distort implosion cores, resulting in a reduced hot-spot confinement and an increased residual kinetic energy of the stagnated target. The ion temperature inferred from the width of simulated neutron spectra are influenced by bulk fuel motion in the distorted hot spot and can result in up to 2-keV apparent temperature increase. Similar temperature variations along different lines of sight are observed. Simulated x-ray images of implosion cores in the 4- to 8-keV energy range show good agreement with experiments. Demonstrating hydrodynamic equivalence to ignition designs on OMEGA requires reducing large-scale target and laser-imposed nonuniformities, minimizing target offset, and employing high-efficient mid-adiabat (α = 4) implosion designs that mitigate cross-beam energy transfer (CBET) and suppress short-wavelength Rayleigh-Taylor growth. These simulations use a new low-noise 3-D Eulerian hydrodynamic code ASTER. Existing 3-D hydrodynamic codes for direct-drive implosions currently miss CBET and noise-free ray-trace laser deposition algorithms. ASTER overcomes these limitations using a simplified 3-D laser-deposition model, which includes CBET and is capable of simulating the effects of beam-power imbalance, beam mispointing, mistiming, and target offset. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.