The Experts below are selected from a list of 50343 Experts worldwide ranked by ideXlab platform
George V Lauder - One of the best experts on this subject based on the ideXlab platform.
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Hydrodynamic function of dorsal fins in spiny dogfish and bamboo sharks during steady swimming.
The Journal of Experimental Biology, 2017Co-Authors: Anabela Maia, George V Lauder, Cheryl D. WilgaAbstract:A key feature of fish functional design is the presence of multiple fins that allow thrust vectoring and redirection of Fluid Momentum to contribute to both steady swimming and maneuvering. A number of previous studies have analyzed the function of dorsal fins in teleost fishes in this context, but the hydrodynamic function of dorsal fins in freely-swimming sharks has not been analyzed, despite the potential for differential functional roles between the anterior and posterior dorsal fins. Previous anatomical research has suggested a primarily stabilizing role for shark dorsal fins. We evaluated the generality of this hypothesis by using time-resolved particle image velocimetry to record water flow patterns in the wake of both the anterior and posterior dorsal fins in two species of freely-swimming sharks: bamboo sharks ( Chiloscyllium plagiosum ) and spiny dogfish ( Squalus acanthias ). Cross correlation analysis of consecutive images was used to calculate stroke-averaged mean, longitudinal and lateral velocity components, and vorticity. In spiny dogfish, we observed a velocity deficit in the wake of the first dorsal fin and flow acceleration behind the second dorsal fin, indicating that the first dorsal experiences net drag while the second dorsal fin can aid in propulsion. In contrast, the wake of both dorsal fins in bamboo sharks displayed increased net flow velocity in the majority of trials, reflecting a thrust contribution to steady swimming. In bamboo sharks, Fluid flow in the wake of the second dorsal fin had higher absolute average velocity than the first dorsal fin, and this may result from a positive vortex interaction between the first and second dorsal fins. These data suggest that the first dorsal fin in spiny dogfish has primarily a stabilizing function, while the second dorsal fin has a propulsive function. In bamboo sharks both dorsal fins can contribute thrust and should be considered as propulsive adjuncts to the body during steady swimming. The function of shark dorsal fins can thus differ considerably among fins and species, and is not limited to a stabilizing role.
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hydrodynamics of the escape response in bluegill sunfish lepomis macrochirus
The Journal of Experimental Biology, 2008Co-Authors: Eric D Tytell, George V LauderAbstract:SUMMARY Escape responses of fishes are one of the best characterized vertebrate behaviors, with extensive previous research on both the neural control and biomechanics of startle response performance. However, very little is known about the hydrodynamics of escape responses, despite the fact that understanding Fluid flow patterns during the escape is critical for evaluating how body movement transfers power to the Fluid, for defining the time course of power generation, and for characterizing the wake signature left by escaping fishes, which may provide information to predators. In this paper, we present an experimental hydrodynamic analysis of the C-start escape response in bluegill sunfish ( Lepomis macrochirus ). We used time-resolved digital particle image velocimetry at 1000 frames s –1 (fps) to image flow patterns during the escape response. We analyzed flow patterns generated by the body separately from those generated by the dorsal and anal fins to assess the contribution of these median fins to escape Momentum. Each escape response produced three distinct jets of Fluid. Summing the components of Fluid Momentum in the jets provided an estimate of fish Momentum that did not differ significantly from Momentum measured from the escaping fish body. In contrast to conclusions drawn from previous kinematic analyses and theoretical models, the caudal fin generated Momentum that opposes the escape during stage one, whereas the body bending during stage one contributed substantial propulsive Momentum. Additionally, the dorsal and anal fins each contributed substantial Momentum. The results underscore the importance of the dorsal and anal fins as propulsors and suggest that the size and placement of these fins may be a key determinant of fast start performance.
Eric D Tytell - One of the best experts on this subject based on the ideXlab platform.
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hydrodynamics of the escape response in bluegill sunfish lepomis macrochirus
The Journal of Experimental Biology, 2008Co-Authors: Eric D Tytell, George V LauderAbstract:SUMMARY Escape responses of fishes are one of the best characterized vertebrate behaviors, with extensive previous research on both the neural control and biomechanics of startle response performance. However, very little is known about the hydrodynamics of escape responses, despite the fact that understanding Fluid flow patterns during the escape is critical for evaluating how body movement transfers power to the Fluid, for defining the time course of power generation, and for characterizing the wake signature left by escaping fishes, which may provide information to predators. In this paper, we present an experimental hydrodynamic analysis of the C-start escape response in bluegill sunfish ( Lepomis macrochirus ). We used time-resolved digital particle image velocimetry at 1000 frames s –1 (fps) to image flow patterns during the escape response. We analyzed flow patterns generated by the body separately from those generated by the dorsal and anal fins to assess the contribution of these median fins to escape Momentum. Each escape response produced three distinct jets of Fluid. Summing the components of Fluid Momentum in the jets provided an estimate of fish Momentum that did not differ significantly from Momentum measured from the escaping fish body. In contrast to conclusions drawn from previous kinematic analyses and theoretical models, the caudal fin generated Momentum that opposes the escape during stage one, whereas the body bending during stage one contributed substantial propulsive Momentum. Additionally, the dorsal and anal fins each contributed substantial Momentum. The results underscore the importance of the dorsal and anal fins as propulsors and suggest that the size and placement of these fins may be a key determinant of fast start performance.
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kinematics and hydrodynamics of linear acceleration in eels anguilla rostrata
Proceedings of The Royal Society B: Biological Sciences, 2004Co-Authors: Eric D TytellAbstract:The kinematics and hydrodynamics of routine linear accelerations were studied in American eels, Anguilla rostrata, using high-speed video and particle image velocimetry. Eels were examined both during steady swimming at speeds from 0.6 to 1.9 body lengths (L) per second and during accelerations from -1.4 to 1.3 L s(-2). Multiple regression of the acceleration and steady swimming speed on the body kinematics suggests that eels primarily change their tail-tip velocity during acceleration. By contrast, the best predictor of steady swimming speed is body wave speed, keeping tail-tip velocity an approximately constant fraction of the swimming velocity. Thus, during steady swimming, Strouhal number does not vary with speed, remaining close to 0.32, but during acceleration, it deviates from the steady value. The kinematic changes during acceleration are indicated hydrodynamically by axial Fluid Momentum in the wake. During steady swimming, the wake consists of lateral jets of Fluid and has minimal net axial Momentum, which reflects a balance between thrust and drag. During acceleration, those jets rotate to point downstream, adding axial Momentum to the Fluid. The amount of added Momentum correlates with the acceleration, but is greater than the necessary inertial force by 2.8+/-0.6 times, indicating a substantial acceleration reaction.
B U Felderhof - One of the best experts on this subject based on the ideXlab platform.
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time dependent poiseuille flow of a viscous compressible Fluid confined between two planar walls with dynamic partial slip boundary condition
Physical Review E, 2012Co-Authors: B U FelderhofAbstract:: Time-dependent Poiseuille flow of a viscous compressible Fluid confined between two planar walls is studied for a partial slip boundary condition with frequency-dependent slip length. After an initial uniform impulse parallel to the walls, the flow pattern quickly becomes nearly parabolic. For a narrow gap, a dynamic slip length can lead to damped oscillations of total Fluid Momentum.
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Loss of Momentum in a viscous compressible Fluid due to no-slip boundary condition at one or two planar walls
The Journal of chemical physics, 2010Co-Authors: B U FelderhofAbstract:The loss of Fluid Momentum due to friction at one or two planar walls bounding a viscous compressible Fluid is studied as a function of time for the situation where the flow is due to a sudden impulse applied at a selected point in initially quiescent Fluid. The no-slip condition is assumed to hold at the walls, and the initial impulse is assumed to be sufficiently small, so that the linearized Navier–Stokes equations may be used. When the initial impulse is directed parallel to the walls the time-dependent total Fluid Momentum is independent of compressibility and volume viscosity. For initial impulse directed perpendicular to the walls an echoing effect, corresponding to sound bouncing between the two walls, is observed.
Aleksandar Donev - One of the best experts on this subject based on the ideXlab platform.
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fluctuation enhanced electric conductivity in electrolyte solutions
Proceedings of the National Academy of Sciences of the United States of America, 2017Co-Authors: Jean-philippe M. Péraud, Andrew Nonaka, John B. Bell, Aleksandar Donev, Alejandro L. GarciaAbstract:We analyze the effects of an externally applied electric field on thermal fluctuations for a binary electrolyte Fluid. We show that the fluctuating Poisson-Nernst-Planck (PNP) equations for charged multispecies diffusion coupled with the fluctuating Fluid Momentum equation result in enhanced charge transport via a mechanism distinct from the well-known enhancement of mass transport that accompanies giant fluctuations. Although the mass and charge transport occurs by advection by thermal velocity fluctuations, it can macroscopically be represented as electrodiffusion with renormalized electric conductivity and a nonzero cation-anion diffusion coefficient. Specifically, we predict a nonzero cation-anion Maxwell-Stefan coefficient proportional to the square root of the salt concentration, a prediction that agrees quantitatively with experimental measurements. The renormalized or effective macroscopic equations are different from the starting PNP equations, which contain no cross-diffusion terms, even for rather dilute binary electrolytes. At the same time, for infinitely dilute solutions the renormalized electric conductivity and renormalized diffusion coefficients are consistent and the classical PNP equations with renormalized coefficients are recovered, demonstrating the self-consistency of the fluctuating hydrodynamics equations. Our calculations show that the fluctuating hydrodynamics approach recovers the electrophoretic and relaxation corrections obtained by Debye-Huckel-Onsager theory, while elucidating the physical origins of these corrections and generalizing straightforwardly to more complex multispecies electrolytes. Finally, we show that strong applied electric fields result in anisotropically enhanced "giant" velocity fluctuations and reduced fluctuations of salt concentration.
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inertial coupling method for particles in an incompressible fluctuating Fluid
Computer Methods in Applied Mechanics and Engineering, 2014Co-Authors: Florencio Balboa Usabiaga, Rafael Delgadobuscalioni, Boyce E Griffith, Aleksandar DonevAbstract:Abstract We develop an inertial coupling method for modeling the dynamics of point-like “blob” particles immersed in an incompressible Fluid, generalizing previous work for compressible Fluids (Balboa Usabiaga et al., 2013 [42]). The coupling consistently includes excess (positive or negative) inertia of the particles relative to the displaced Fluid, and accounts for thermal fluctuations in the Fluid Momentum equation. The coupling between the Fluid and the blob is based on a no-slip constraint equating the particle velocity with the local average of the Fluid velocity, and conserves Momentum and energy. We demonstrate that the formulation obeys a fluctuation–dissipation balance, owing to the non-dissipative nature of the no-slip coupling. We develop a spatio-temporal discretization that preserves, as best as possible, these properties of the continuum formulation. In the spatial discretization, the local averaging and spreading operations are accomplished using compact kernels commonly used in immersed boundary methods. We find that the special properties of these kernels allow the blob to provide an effective model of a particle; specifically, the volume, mass, and hydrodynamic properties of the blob are remarkably grid-independent. We develop a second-order semi-implicit temporal integrator that maintains discrete fluctuation–dissipation balance, and is not limited in stability by viscosity. Furthermore, the temporal scheme requires only constant-coefficient Poisson and Helmholtz linear solvers, enabling a very efficient and simple FFT-based implementation on GPUs. We numerically investigate the performance of the method on several standard test problems. In the deterministic setting, we find the blob to be a remarkably robust approximation to a rigid sphere, at both low and high Reynolds numbers. In the stochastic setting, we study in detail the short and long-time behavior of the velocity autocorrelation function and observe agreement with all of the known behavior for rigid sphere immersed in a fluctuating Fluid. The proposed inertial coupling method provides a low-cost coarse-grained (minimal resolution) model of particulate flows over a wide range of time-scales ranging from Brownian to convection-driven motion.
Kannan N Premnath - One of the best experts on this subject based on the ideXlab platform.
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symmetrized operator split schemes for force and source modeling in cascaded lattice boltzmann methods for flow and scalar transport
Physical Review E, 2018Co-Authors: Farzaneh Hajabdollahi, Kannan N PremnathAbstract:Operator split forcing schemes exploiting a symmetrization principle, i.e., Strang splitting, for cascaded lattice Boltzmann (LB) methods in two- and three-dimensions for Fluid flows with impressed local forces are presented. Analogous scheme for the passive scalar transport represented by a convection-diffusion equation with a source term in a novel cascaded LB formulation is also derived. They are based on symmetric applications of the split solutions of the changes on the scalar field or Fluid Momentum due to the sources or forces over half time steps before and after the collision step. The latter step is effectively represented in terms of the post-collision change of moments at zeroth and first orders, respectively, to represent the effect of the sources on the scalar transport and forces on the Fluid flow. Such symmetrized operator split cascaded LB schemes are consistent with the second-order Strang splitting and naturally avoid any discrete effects due to forces or sources by appropriately projecting their effects for higher-order moments. All the force or source implementation steps are performed only in the moment space and they do not require formulations as extra terms and their additional transformations to the velocity space. These result in particularly simpler and efficient schemes to incorporate forces or sources in the cascaded LB methods unlike those considered previously. Numerical study for various benchmark problems in 2D and 3D for Fluid flow problems with body forces and scalar transport with sources demonstrate the validity and accuracy, as well as the second-order convergence rate of the symmetrized operator split forcing or source schemes for the cascaded LB methods.