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## ‣ Swirling motion of a second-order viscous fluid in a straight tube

Fonte: Carapau, F., Sequeira, A., "Swirling motion of a second-order viscous fluid in a straight tube", Proceedings of the International Conference on Topical Problems of Fluid Mechanics, Institute of Thermomechanics AS CR, Prague, Czech Republic, February 28 – March 2, 2007, pp. 21-24. Publicador: Carapau, F., Sequeira, A., "Swirling motion of a second-order viscous fluid in a straight tube", Proceedings of the International Conference on Topical Problems of Fluid Mechanics, Institute of Thermomechanics AS CR, Prague, Czech Republic, February 28 – March 2, 2007, pp. 21-24.
Tipo: Artigo de Revista Científica
Português
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We consider a second-order viscous fluid with swirling motion flowing in a circular straight tube with constant radius. Integrating the equation of conservation of linear momentum over the tube cross section with the velocity field approximated by the Cosserat theory, we obtain a one-dimensional system depending only on time and on a single spatial variable. From this 1D model, we derive the relationship between mean pressure gradient and volume flow rate over a finite section of the tube as well the wall shear stress.

## ‣ Theory and validation of magnetic resonance fluid motion estimation using intensity flow data

Wong, K.; Kelso, R.; Worthley, S.; Sanders, P.; Mazumdar, J.; Abbott, D.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
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Background Motion tracking based on spatial-temporal radio-frequency signals from the pixel representation of magnetic resonance (MR) imaging of a non-stationary fluid is able to provide two dimensional vector field maps. This supports the underlying fundamentals of magnetic resonance fluid motion estimation and generates a new methodology for flow measurement that is based on registration of nuclear signals from moving hydrogen nuclei in fluid. However, there is a need to validate the computational aspect of the approach by using velocity flow field data that we will assume as the true reference information or ground truth. Methodology/Principal Findings In this study, we create flow vectors based on an ideal analytical vortex, and generate artificial signal-motion image data to verify our computational approach. The analytical and computed flow fields are compared to provide an error estimate of our methodology. The comparison shows that the fluid motion estimation approach using simulated MR data is accurate and robust enough for flow field mapping. To verify our methodology, we have tested the computational configuration on magnetic resonance images of cardiac blood and proved that the theory of magnetic resonance fluid motion estimation can be applicable practically. Conclusions/Significance The results of this work will allow us to progress further in the investigation of fluid motion prediction based on imaging modalities that do not require velocity encoding. This article describes a novel theory of motion estimation based on magnetic resonating blood...

## ‣ Flow imaging and validation of MR fluid motion tracking

Wong, K.; Kelso, R.; Worthley, S.; Sanders, P.; Mazumdar, J.; Abbott, D.
Fonte: Springer; Germany Publicador: Springer; Germany
Tipo: Conference paper
Relevância na Pesquisa
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This paper presents flow results of a magnetic resonance imaging velocimetry system which relies on fluid motion estimation, and uses vorticity map differencing for calibrating its reliability. To validate this new concept, phase contrast magnetic resonance imaging on the right atrium of a healthy subject has been suggested. The study has demonstrated the state of change in blood flow patterns within a cardiac chamber using our implemented system and a well established flow imaging modality. Based on the gold standard imaging technique, flow fields can be used to establish a set of reference data to compare against magnetic resonance fluid motion tracking results. We conclude that our validated technique can be reliable enough for establishing a cardiac based velocimetry system.; K.K.L. Wong, R.M. Kelso, S.G. Worthley, P. Sanders, J. Mazumdar and D. Abbott

## ‣ Bayesian Estimation of Turbulent Motion

Héas, Patrick; Herzet, Cédric; Mémin, Etienne; Heitz, Dominique; Mininni, Pablo Daniel
Fonte: IEEE Computer Society Publicador: IEEE Computer Society
Tipo: info:eu-repo/semantics/article; info:ar-repo/semantics/artículo; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Português
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Based on physical laws describing the multiscale structure of turbulent flows, this paper proposes a regularizer for fluid motion estimation from an image sequence. Regularization is achieved by imposing some scale invariance property between histograms of motion increments computed at different scales. By reformulating this problem from a Bayesian perspective, an algorithm is proposed to jointly estimate motion, regularization hyperparameters, and to select the most likely physical prior among a set of models. Hyperparameter and model inference are conducted by posterior maximization, obtained by marginalizing out non-Gaussian motion variables. The Bayesian estimator is assessed on several image sequences depicting synthetic and real turbulent fluid flows. Results obtained with the proposed approach exceed the state-of-the-art results in fluid flow estimation.; Fil: Héas, Patrick. Rennes Bretagne Atlantique. Institut National de Recherche en Informatique et en Automatique; Francia;; Fil: Herzet, Cédric. Rennes Bretagne Atlantique. Institut National de Recherche en Informatique et en Automatique; Francia;; Fil: Mémin, Etienne. Rennes Bretagne Atlantique. Institut National de Recherche en Informatique et en Automatique; Francia;; Fil: Heitz...

## ‣ Computation of Fluid Flows in Non-inertial Contracting, Expanding, and Rotating Reference Frames

Poludnenko, A. Y.; Khokhlov, A. M.
Tipo: Artigo de Revista Científica
Português
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We present the method for computation of fluid flows that are characterized by the large degree of expansion/contraction and in which the fluid velocity is dominated by the bulk component associated with the expansion/contraction and/or rotation of the flow. We consider the formulation of Euler equations of fluid dynamics in a homologously expanding/contracting and/or rotating reference frame. The frame motion is adjusted to minimize local fluid velocities. Such approach allows to accommodate very efficiently large degrees of change in the flow extent. Moreover, by excluding the contribution of the bulk flow to the total energy the method eliminates the high Mach number problem in the flows of interest. An important practical advantage of the method is that it can be easily implemented with virtually any implicit or explicit Eulerian hydrodynamic scheme and adaptive mesh refinement (AMR) strategy. We also consider in detail equation invariance and existence of conservative formulation of equations for special classes of expanding/contracting reference frames. Special emphasis is placed on extensive numerical testing of the method for a variety of reference frame motions, which are representative of the realistic applications of the method. We study accuracy...

## ‣ Generalized squirming motion of a sphere

Pak, On Shun; Lauga, Eric
Tipo: Artigo de Revista Científica
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47.15669%
A number of swimming microorganisms such as ciliates ($\textit{Opalina}$) and multicellular colonies of flagellates ($\textit{Volvox}$) are approximately spherical in shape and swim using beating arrays of cilia or short flagella covering their surfaces. Their physical actuation on the fluid may be mathematically modeled as the generation of surface velocities on a continuous spherical surface -- a model known in the literature as squirming, which has been used to address various aspects of the biological physics of locomotion. Previous analyses of squirming assumed axisymmetric fluid motion and hence restricted all swimming kinematics to take place along a line. In this paper we generalize squirming to three spatial dimensions. We derive analytically the flow field surrounding a spherical squirmer with arbitrary surface motion, and use it to derive its three-dimensional translational and rotational swimming kinematics. We then use our results to physically interpret the flow field induced by the swimmer in terms of fundamental flow singularities up to terms decaying spatially as $\sim 1/r^3$. Our results will enable to develop new models in biological physics, in particular in the area of hydrodynamic interactions and collective locomotion.

## ‣ Fluid fragmentation from hospital toilets

Traverso, G.; Laken, S.; Lu, C. -C.; Maa, R.; Langer, R.; Bourouiba, L.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Hospital-acquired infections represent significant health and financial burdens to society. Clostridium difficile (C. difficile) is a particularly challenging bacteria with the potential to cause severe diarrhea and death. One mode of transmission for C. difficile, as well as other pathogens, which has received little attention is the potential air contamination by pathogen-bearing droplets emanating from toilets. In the fluid dynamics video submitted to the APS DFD Gallery of Fluid Motion 2013, we present flow visualizations via high-speed recordings showing the capture of the product of the fluid fragmentation generated by hospital toilet high-pressure flushes. Important quantities of both large and small droplets are observed. We illustrate how high-pressure flushes and cleaning products currently used in hospital toilets result in aggravating, rather than alleviating, the suspension and recirculation of tenacious airborne pathogen-bearing droplets.; Comment: The full results on the fluid dynamics of hospital flush ejecta will be published elsewhere. The Gallery of Fluid Motion is showcase of fluid dynamics videos

## ‣ A New Continuum Formulation for Materials--Part I. The Equations of Motion for a Single-Component Fluid

Morris, Melissa
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The continuum equations of fluid mechanics are rederived with the intention of keeping certain mechanical and thermodynamic concepts separate. A new "mechanical" mass density is created to be used in computing inertial quantities, whereas the actual mass density is treated as a thermodynamic variable. A new set of balance laws is proposed, including a mass balance equation with a non-convective flux. The basic principles of irreversible thermodynamics are used to obtain linear constitutive equations that are expansions of--not only the usual affinities involving gradients of temperature and velocity--but also the gradient of the chemical potential. Transport coefficients are then chosen based on an elementary diffusion model, which yields simple constitutive laws featuring just one diffusion transport parameter. The resulting formulation differs from the Navier-Stokes-Fourier equations of fluid motion. In order to highlight key similarities and differences between the two formulations, several fluid mechanics problems are examined, including sound propagation, light scattering, steady-state shock waves, and thermophoresis.; Comment: 63 pages, 7 figures

## ‣ Intrinsic Geometric Structure of Turbulent Flow for Newton Fluid

Xiao, Jianhua
Tipo: Artigo de Revista Científica
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Many researches show that the complicated motion of fluid, such as turbulence, cannot be well solved by the Navier-Stokes equation. Chen Zida has founded that the definition of vortex, based on the Stokes decomposition, cannot well describe the local rotation when the velocity gradient is highly asymmetric. Chen reformulates the Stokes S+R decomposition into a general S+R decomposition. By further extending Chen results, this research studies the motion equation of fluid for the case where highly asymmetric velocity gradient is exhibited. The result shows that the classical NS equation does not meet the requirement of angular momentum conservation, which is apparently ignored for infinitesimal velocity gradient of fluid. This paper reformulates the intrinsic geometric description of fluid motion and two additional equations are introduced. Combining with the classical NS equation, the reformulated motion equations are in closed-form. The research shows that the NS equation is good approximation for average flow, so it can not solve the turbulent problem in essential sense. However, this conclusion does not deny that with suitable additional condition for special engineering problem it is still a would-be acceptable approximation.; Comment: 16 pages...

## ‣ On the limit of large surface tension for a fluid motion with free boundary

Disconzi, Marcelo M.; Ebin, David G.
Tipo: Artigo de Revista Científica
Português
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We study the free boundary Euler equations in two spatial dimensions. We prove that if the boundary is sufficiently regular, then solutions of the free boundary fluid motion converge to solutions of the Euler equations in a fixed domain when the coefficient of surface tension tends to infinity.

## ‣ Sedimentation of a dilute suspension of rigid spheres at intermediate Galileo numbers: the effect of clustering upon the particle motion

Uhlmann, Markus; Doychev, Todor
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Direct numerical simulation of the gravity-induced settling of finite-size particles in triply-periodic domains has been performed under dilute conditions. For a single solid-to-fluid density ratio of 1.5 we have considered two values of the Galileo number corresponding to steady vertical motion (Ga=121) and to steady oblique motion (Ga=178) in the case of one isolated sphere. For the multi-particle system we observe strong particle clustering only in the latter case. The geometry and time scales related to clustering are determined from Voronoi tesselation and particle-conditioned averaging. As a consequence of clustering, the average particle settling velocity is increased by 12% as compared to the value of an isolated sphere; such a collective effect is not observed in the non-clustering case. By defining a local (instantaneous) fluid velocity average in the vicinity of the finite-size particles it is shown that the observed enhancement of the settling velocity is due to the fact that the downward fluid motion (with respect to the global average) which is induced in the cluster regions is preferentially sampled by the particles. It is further observed that the variance of the particle velocity is strongly enhanced in the clustering case. With the aid of a decomposition of the particle velocity it is shown that this increase is due to enhanced fluid velocity fluctuations (due to clustering) in the vicinity of the particles. Finally...

## ‣ Droplets bouncing over a vibrating fluid layer

Cabrera-Garcia, Pablo; Zenit, Roberto
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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This is an entry for the Gallery of Fluid Motion of the 65st Annual Meeting of the APS-DFD (fluid dynamics video). This video shows the motion of levitated liquid droplets. The levitation is produced by the vertical vibration of a liquid container. We made visualizations of the motion of many droplets to study the formation of clusters and their stability.; Comment: This entry contains videos for the Gallery of Fluid Motion of the 65st Annual Meeting of the APS-DFD

## ‣ On the Motion of a Self-Gravitating Incompressible Fluid with Free Boundary

Bieri, Lydia; Miao, Shuang; Shahshahani, Sohrab; Wu, Sijue
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We consider the motion of the interface separating a vacuum from an inviscid, incompressible, and irrotational fluid, subject to the self-gravitational force and neglecting surface tension, in two space dimensions. The fluid motion is described by the Euler-Poission system in moving bounded simply connected domains. A family of equilibrium solutions of the system are the perfect balls moving at constant velocity. We show that for smooth data which are small perturbations of size $\epsilon$ of these static states, measured in appropriate Sobolev spaces, the solution exists and remains of size $\epsilon$ on a time interval of length at least $c\epsilon^{-2},$ where $c$ is a constant independent of $\epsilon.$ This should be compared with the lifespan $O(\epsilon^{-1})$ provided by local well-posdness. The key ingredient of our proof is finding a nonlinear transformation which removes quadratic terms from the nonlinearity. An important difference with the related gravity water waves problem is that unlike the constant gravity for water waves, the self-gravity in the Euler-Poisson system is nonlinear. As a first step in our analysis we also show that the Taylor sign condition always holds and establish local well-posedness for this system.; Comment: 73 pages

## ‣ On the flow of Oldroyd-B fluids with fractional derivatives over a plate that applies shear to the fluid

Zafar, Azhar Ali; Fetecau, Constantin; Mirza, Itrat Abbas
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The motion of incompressible fractional Oldroyd-B fluids between two parallel walls perpendicular to a plate that applies time-dependent shear stresses to the fluid is studied by means of integral transforms. In the special cases of Newtonian and second grade fluids, these shear stresses reduces to fH(t)sin(wt) or fH(t)cos(wt). General solutions for velocity are presented as a sum of Newtonian solutions and the corresponding non-Newtonian contributions. They reduce to the similar solutions corresponding to the motion over an infinite plate if the distance between walls tend to infinity and can be easy particularized to give the similar solutions for ordinary and fractional Maxwell or second grade fluids performing the same motions. As a check of general results some known solutions from the literature are recovered as limiting cases. Finally, the influence of fractional parameters on the fluid motion and the distance between walls for which the measured value of the velocity in the middle of the channel is unaffected by their presence (more exactly, it is equal to the velocity corresponding to the motion over an infinite plate) are graphically determined.; Comment: 23 pages, 9 figures

## ‣ To the Fluid Motion Dynamics

Arsenjev, S. L.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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A fluid motion through the flow element is presented in the kind of an autooscillating system with the distributed parameters: mass, elasticity, viscosity. The system contains a self-excited oscillator and possesses a self-regulation on base of the intrinsic voluntary negative servo output feedback. The interaction dynamics of the submerged jet, out-flowing out of a flow element, with the homogeneous for it surrounding medium as well as dynamics of evolution of the spiral-vortex structures, appearing at the relative motion of fluids, are described for the first time. The conceptual model of a flow in the kind of the completed system of the cause and effect relationship, that presents the fluid motion process as a result in interaction of the motive power, applied from without, and the internal wave mechanism, selfregulating the flow structure and its intensity, is created.; Comment: 20 pages, 15 figures

## ‣ Rheological fluid motion in tube by metachronal wave of cilia

Maiti, S.; Pandey, S. K.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The purpose of this paper is a theoretical study of a non-linear problem of rheological fluid transport in an axisymmetric tube by cilium. However, an attempt has been made to explain the role of cilia motion on the transport of fluid through the ductus efferentes of the male reproductive tract. Ostwald-de Waele power law viscous fluid has been considered to represent the rheological fluid to analyze pumping by means of a sequence of beat of cilia from row to row of cilia in a given row of cells and from one row of cells to the next (metachronal wave movement) under conditions for which the corresponding Reynolds number is small enough for inertial effects to be negligible and the wavelength to diameter ratio is large enough for the pressure to be considered uniform over the cross-section. Analyses and computations of the detailed fluid motions reveal that the time-averaged flow rates are directly dependent on epsilon, a non-dimensional measure involving the mean radius R of the tube and the cilia length. Thus, flow rate significantly varies with the cilia length. Moreover, the flow rate has been reported close to the estimated value 0.006 ml/h in human ductus efferentes when epsilon is near by 0.5. The estimated value was suggested by Lardner and Shack [4] in human based on the experimental observations on the flow rates in the ductus efferentes in the other animals...

## ‣ Fluid Motion Physics: The Total Head Vector of the Real Fluid Stream

Arsenjev, S. L.
Tipo: Artigo de Revista Científica
Português
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The overcoming of a mechanics problem on origin of secondary jet flows, on dynamics of its development and interaction with the main stream of the viscous fluid is reached by means of elucidation of the energy distribution in the stream at its interaction with the flow system walls and a body surface. In contrast to a traditional conception on a total head of a fluid stream in a pipe as a sum of a velocity head and a static pressure, it is ascertained that this sum is only longitudinal component of the stream total head vector. It is stated a new conception and it is produced the expressions for quantitative evaluation of radial and tangential components of the stream total head vector and for angle of its deflection from the stream axis. The new approach has allowed rationally to explain the causes of origin of the secondary jet flows and dynamics of its interaction with the main stream in various cases. Thereby with the taking into account of previous articles of the author the necessary theoretical preconditions has been created for a working out of the modern physically valuable apparatus for mathematical modeling of the real - viscous - fluid motion in any problems of hydromechanics and gas dynamics.; Comment: 14 pages, 1 figure

## ‣ Three-dimensional fluid motion in Faraday waves: creation of vorticity and generation of two-dimensional turbulence

Francois, N.; Xia, H.; Punzmann, H.; Ramsden, S.; Shats, M.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We study the generation of 2D turbulence in Faraday waves by investigating the creation of spatially periodic vortices in this system. Measurements which couple a diffusing light imaging technique and particle tracking algorithms allow the simultaneous observation of the three-dimensional fluid motion and of the temporal changes in the wave field topography. Quasi-standing waves are found to coexist with a spatially extended fluid transport. More specifically, the destruction of regular patterns of oscillons coincides with the emergence of a complex fluid motion whose statistics are similar to that of two-dimensional turbulence. We reveal that a lattice of oscillons generates vorticity at the oscillon scale in the horizontal flow. The interaction of these vortices explain how 2D turbulence is fueled by almost standing waves. Remarkably, the curvature of Lagrangian trajectories reveals a "footprint" of the forcing scale vortices in fully developed turbulence. 2D Navier-Stokes turbulence should be considered a source of disorder in Faraday waves. These findings also provide a new paradigm for vorticity creation in 2D flows.

## ‣ Volumetric 3-component velocimetry measurements of the flow around a Rushton turbine: A fluid dynamics video

Sharp, K. V.; Hill, D. F.; Troolin, D.; Walters, G.; Lai, W.
Tipo: Artigo de Revista Científica