Search results for "VISCOSITY"
showing 10 items of 542 documents
Azimuthal anisotropy ofπ0andηmesons in Au + Au collisions atsNN=200GeV
2013
The azimuthal anisotropy coefficients v2 and v4 of p 0 and. mesons are measured in Au + Au collisions at root s(NN) = 200 GeV as a function of transverse momentum p(T) (1-14 GeV/c) and centrality. The extracted v(2) coefficients are found to be consistent between the two meson species over the measured p(T) range. The ratio of v(4)/v(2)(2) for pi(0) mesons is found to be independent of p(T) for 1- 9 GeV/c, implying a lack of sensitivity of the ratio to the change of underlying physics with p(T). Furthermore, the ratio of v(4)/v(2)(2) is systematically larger in central collisions, which may reflect the combined effects of fluctuations in the initial collision geometry and finite viscosity i…
Temperature dependence of η/s : uncertainties from the equation of state
2018
We perform a global model-to-data comparison on Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV and Pb+Pb collisions at $2.76$ TeV and $5.02$ TeV, using a 2+1D hydrodynamics model with the EKRT initial state and a shear viscosity over entropy density ratio $(\eta/s)(T)$ with a linear $T$ dependence. To quantify the amount of uncertainty due to the choice of the equation of state (EoS), we compare analysis results based on four different EoSs: the well known $s95p$ parametrisation, an updated parametrisation based on the same list of particles in hadron resonance gas, but using recent lattice results for the partonic part of the EoS, and two new parametrisations based on the Particle Data Group …
Digital rock physics: Effect of fluid viscosity on effective elastic properties
2011
Abstract This paper is concerned with the effect of pore fluid viscosity on effective elastic properties using digitized rocks. We determine a significant velocity dispersion in wave propagation simulations by the variation of the pore fluid viscosity. Several attenuation regimes are considered which may contribute to this observation. Starting point is a virtual rock physics approach. Numerical simulations of effective transport and effective mechanical properties are applied to statistically representative rock samples. The rock microstructure is imaged by 3D X-ray tomography. Permeability values were estimated through Lattice-Boltzmann flow simulations. The dry rock moduli and the tortuo…
High Reynolds number Navier-Stokes solutions and boundary layer separation induced by a rectilinear vortex array
2008
Numerical solutions of Prandtl’s equation and Navier Stokes equations are considered for the two dimensional flow induced by an array of periodic rec- tilinear vortices interacting with an infinite plane. We show how this initial datum develops a separation singularity for Prandtl equation. We investigate the asymptotic validity of boundary layer theory considering numerical solu- tions for the full Navier Stokes equations at high Reynolds numbers.
Magnetic micro-droplet in rotating field: numerical simulation and comparison with experiment
2017
Magnetic droplets obtained by induced phase separation in a magnetic colloid show a large variety of shapes when exposed to an external field. However, the description of shapes is often limited. Here we formulate an algorithm based on three dimensional boundary-integral equations for strongly magnetic droplets in a high-frequency rotating magnetic field, allowing us to find their figures of equilibrium in three dimensions. The algorithm is justified by a series of comparisons with known analytical results. We compare the calculated equilibrium shapes with experimental observations and find a good agreement. The main features of these observations are the oblate-prolate transition, the flat…
Bending of ferrofluid droplet in rotating magnetic field
1999
Abstract This paper presents results concerning 2D ferrofluid droplet motion at high values of magnetic field and frequencies above a critical one with respect to droplet ability to follow field rotation. The boundary element method is used to solve 2D equations of a magnetic field and Stokes flow problems. If the viscosity of the ferrofluid is larger than that of the surrounding fluid, droplet exhibits bending, forming “S-shape”. Fluid flow inside the droplet is analyzed and the main stages of periodical rotation of a droplet are reported.
Two experiments to approach the Boltzmann factor: chemical reaction and viscous flow
2012
In this paper we discuss a pedagogical approach aimed at pointing out the role played by the Boltzmann factor in describing phenomena usually perceived as regulated by different mechanisms of functioning. Experimental results regarding some aspects of a chemical reaction and of the viscous flow of some liquids are analysed and described in terms of macroscopic variables whose temperature dependence is proportional to the Boltzmann factor. A description of a workshop implementing the approach in the framework of an undergraduate course for engineering education and some preliminary results about its pedagogical relevance are then reported.
Numerical study of the primitive equations in the small viscosity regime
2018
In this paper we study the flow dynamics governed by the primitive equations in the small viscosity regime. We consider an initial setup consisting on two dipolar structures interacting with a no slip boundary at the bottom of the domain. The generated boundary layer is analyzed in terms of the complex singularities of the horizontal pressure gradient and of the vorticity generated at the boundary. The presence of complex singularities is correlated with the appearance of secondary recirculation regions. Two viscosity regimes, with different qualitative properties, can be distinguished in the flow dynamics.
Theoretical and experimental behaviour of the muscle viscosity coefficient during maximal concentric actions
1994
The aim of this study was to calculate the theoretical variation of the nonlinear damping factor (B) as a function of the muscle shortening velocity, and then to compare the theoretical values with the experimental data obtained on both the elbow flexor and the ankle extensor muscles. The theoretical variation of the B factor was determined from a muscle model consisting of a contractile component in parallel with a viscous damper both in series with an elastic component, and by using, the characteristic equation of the force velocity curve. In this muscle model, the viscous element modelled the inability of the muscle to generate as big a contracting force (while shortening) as possible un…
Initial state anisotropies in ultrarelativistic heavy-ion collisions from the Monte Carlo Glauber model
2012
In hydrodynamicalmodeling of heavy-ion collisions the initial state spatial anisotropies translate into momentum anisotropies of the final state particle distributions. Thus, understanding the origin of the initial anisotropies and quantifying their uncertainties is important for the extraction of specific QCD matter properties, such as viscosity, from the experimental data. In this work we study the wounded nucleon approach in the Monte Carlo Glauber model framework, focusing especially on the uncertainties which arise from the modeling of the nucleon-nucleon interactions between the colliding nucleon pairs and nucleon-nucleon correlations inside the colliding nuclei. We compare the black …