scholarly journals Temperature variation in the dark cosmic fluid in the late universe

2016 ◽  
Vol 31 (08) ◽  
pp. 1650050 ◽  
Author(s):  
Iver Brevik
Keyword(s):  
Dark Energy ◽  
Time Dependence ◽  
Entropy Production ◽  
Temperature Variation ◽  
Temperature Jump ◽  
Fluid Model ◽  
Maxwell Fluid ◽  
Positive Temperature ◽  
Turbulent Transition ◽  
Big Rip

A one-component dark energy fluid model of the late universe is considered [Formula: see text] when the fluid, initially assumed laminar, makes a transition into a turbulent state of motion. Spatial isotropy is assumed so that only the bulk viscosities are included ([Formula: see text] in the laminar epoch and [Formula: see text] in the turbulent epoch). Both viscosities are assumed to be constants. We derive a formula, new as far as we know, for the time dependence of the temperature [Formula: see text] in the laminar case when viscosity is included. Assuming that the laminar/turbulent transition takes place at some time [Formula: see text] before the big rip is reached, we then analyze the positive temperature jump experienced by the fluid at [Formula: see text] if [Formula: see text]. This is just as one would expect physically. The corresponding entropy production is also considered. A special point emphasized in the paper is the analogy that exists between the cosmic fluid and a so-called Maxwell fluid in viscoelasticity.

scholarly journals On the flow of MHD generalized maxwell fluid via porous rectangular duct

Open Physics ◽  
2020 ◽  
Vol 18 (1) ◽  
pp. 989-1002
Author(s):  
Aamir Farooq ◽  
Muhammad Kamran ◽  
Yasir Bashir ◽  
Hijaz Ahmad ◽  
Azeem Shahzad ◽  
...  
Keyword(s):  
Fluid Model ◽  
Maxwell Fluid ◽  
Initial Boundary ◽  
Initial Boundary Value Problem ◽  
Rectangular Duct ◽  
Modified Darcy’S Law ◽  
Initial Boundary Value ◽  
Generalized Maxwell Fluid ◽  
Limiting Case ◽  
The Impact

Abstract The purpose of this proposed investigation is to study unsteady magneto hydrodynamic (MHD) mixed initial-boundary value problem for incompressible fractional Maxwell fluid model via oscillatory porous rectangular duct. Considering the modified Darcy’s law, the problem is simplified by using the method of the double finite Fourier sine and Laplace transforms. As a limiting case of the general solutions, the same results can be obtained for the classical Maxwell fluid. Also, the impact of magnetic parameter, porosity of medium, and the impact of various material parameters on the velocity profile and the corresponding tangential tensions are illuminated graphically. At the end, we will give the conclusion of the whole paper.

scholarly journals A MATHEMATICAL MODEL OF NONSTATIONARY MOTION OF A VISCOELASTIC FLUID IN ROLLER BEARINGS

2019 ◽  
Vol 81 (4) ◽  
pp. 501-512
Author(s):  
I.A. Zhurba Eremeeva ◽  
D. Scerrato ◽  
C. Cardillo ◽  
A. Tran
Keyword(s):  
Mathematical Model ◽  
Viscoelastic Fluid ◽  
Viscoelastic Properties ◽  
Fluid Model ◽  
Maxwell Fluid ◽  
Initial Boundary ◽  
Deborah Number ◽  
Nonstationary Motion ◽  
Friction Forces ◽  
Roller Bearings

Nowadays, the emergence of new lubricants requires an enhancement of the rheological models and methods used for solution of corresponding initial boundary-value problems. In particular, models that take into account viscoelastic properties are of great interest. In the present paper we consider the mathematical model of nonstationary motion of a viscoelastic fluid in roller bearings. We used the Maxwell fluid model for the modeling of fluid properties. The viscoelastic properties are exhibited by many lubricants that use polymer additives. In addition, viscoelastic properties can be essential at high fluid speeds. Also, viscoelastic properties can be significant in the case of thin gaps. Maxwell's model is one of the most common models of viscoelastic materials. It combines the relative simplicity of constitutive equations with the ability to describe a stress relaxation. In addition, viscoelastic fluids also allow us to describe some effects that are missing in the case of viscous fluid. An example it is worth to mention the Weissenberg effect and a number of others. In particular, such effects can be used to increase the efficiency of the film carrier in the sliding bearings. Here we introduced characteristic assumptions on the form of the flow, allowing to significantly simplify the solution of the problem. We consider so-called self-similar solutions, which allows us to get a solution in an analytical form. As a result these assumptions, the formulae for pressure and friction forces are derived. Their dependency on time and Deborah number is analyzed. The limiting values of the flow characteristics were obtained. The latter can be used for steady state of the flow regime. Differences from the case of Newtonian fluid are discussed. It is shown that viscoelastic properties are most evident at the initial stage of flow, when the effects of non-stationarity are most important.

On the Flow of a Polymer Melt Passing Over a Transverse Slot

1999 ◽  
Vol 19 (3) ◽  
pp. 175-196 ◽  
Author(s):  
G.H. Wu ◽  
C.K. Chen ◽  
S.H. Ju
Keyword(s):  
Fluid Model ◽  
Polymer Melt ◽  
Maxwell Fluid ◽  
Creeping Flow ◽  
Analytical Prediction ◽  
Hole Pressure ◽  
Fluid Elasticity ◽  
Conduit Wall ◽  
Liquid Flows ◽  
Transverse Slot

Abstract The phenomenon of hole pressure occurs whenever a polymeric or viscoelastic liquid flows over a depression in a conduit wall. Numerical simulations undertaken for the flow of an aqueous polyacrylamide melt passing over a transverse slot arc considered here. The fluid model used for this study is a White-Metzner constitutive equation describing the non-Newtonian behavior of the melt. The results were computed by an elastic-viscous split-stress finite clement method (EVSS-FEM). a mixed finite clement method incorporating the non-consistent streamline upwind scheme. For verification, the numerical algorithm was first applied to compute the corresponding flow of the upper-convected Maxwell fluid model, a special case of the Whitc-Metzner model characterized by constant viscosity and relation time. The resulting hole pressure (Ph) was evaluated for various Deborah numbers (De) and compared with the analytical prediction derived from the Higashitani-Pritchard (HP) theory. The agreement was found to be satisfactory for creeping flow in the low De range, for which the HP theory is valid. Subsequently, the hole pressure of this flow problem was predicted. The streamlines and pressure distribution along the channel walls arc also presented. Furthermore, the effects of fluid elasticity, shear thinning, the exponent in the viscosity function and the relaxation-time function, and slot geometry on the hole pressure were investigated.

scholarly journals Astronomical bounds on the modified Chaplygin gas as a unified dark fluid model

2019 ◽  
Vol 623 ◽  
pp. A28
Author(s):  
Hang Li ◽  
Weiqiang Yang ◽  
Liping Gai
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Fluid Model ◽  
Chaplygin Gas ◽  
Linear Perturbation ◽  
Model Parameters ◽  
Modified Chaplygin Gas ◽  
Dark Fluid ◽  
Type Ia ◽  
Linear Perturbation Theory

The modified Chaplygin gas could be considered to abide by the unified dark fluid model because the model might describe the past decelerating matter dominated era and at present time it provides an accelerating expansion of the Universe. In this paper, we have employed the Planck 2015 cosmic microwave background anisotropy, type-Ia supernovae, observed Hubble parameter data sets to measure the full parameter space of the modified Chaplygin gas as a unified dark matter and dark energy model. The model parameters Bs, α, and B determine the evolutional history of this unified dark fluid model by influencing the energy density ρMCG = ρMCG0[Bs + (1 − Bs)a−3(1 + B)(1 + α)]1/(1 + α). We assumed the pure adiabatic perturbation of unified modified Chaplygin gas in the linear perturbation theory. In the light of Markov chain Monte Carlo method, we find that Bs = 0.727+0.040+0.075−0.039−0.079, α = −0.0156+0.0982+0.2346−0.1380−0.2180, B = 0.0009+0.0018+0.0030−0.0017−0.0030 at 2σ level. The model parameters α and B are very close to zero and the nature of unified dark energy and dark matter model is very similar to cosmological standard model ΛCDM.

scholarly journals Dissipative unified dark fluid model

2019 ◽  
Vol 28 (09) ◽  
pp. 1950110
Author(s):  
Esraa Elkhateeb
Keyword(s):  
Dark Energy ◽  
Fluid Model ◽  
Dynamical Behavior ◽  
Power Laws ◽  
Viscosity Coefficient ◽  
Distance Modulus ◽  
Effective Equation ◽  
Dark Fluid ◽  
System Solution ◽  
The Universe

We consider a unified barotropic dark fluid model with dissipation. Our fluid asymptotes between two power laws and so can interpolate between the dust and dark energy (DE) equations-of-state at early and late times. The dissipative part is a bulk viscous part with constant viscosity coefficient. The model is analyzed using the phase-space methodology which helps to understand the dynamical behavior of the model in a robust manner without reference to the system solution. The parameters of the model are constrained through many observational constraints. The model is tested through many physical and observational tests. We first considered the model independent [Formula: see text] test. Results for [Formula: see text] are plotted against the BAO data for this quantity from different authors, which shows that the model is consistent with the data points for the full redshift range. The [Formula: see text] statistics results in the value of [Formula: see text] with a [Formula: see text]-value of [Formula: see text]. The Hubble parameter equation is solved numerically and results are plotted against the recent set of Hubble data. The [Formula: see text] test with the Hubble data resulted in the [Formula: see text] value of [Formula: see text] with a [Formula: see text]-value of [Formula: see text]. The distance modulus at different values of redshift is calculated numerically and results are compared to the newest set of SNe Ia data, the Pantheon Sample. We obtained a [Formula: see text] value of [Formula: see text] with a [Formula: see text]-value of [Formula: see text]. These results show that our model is efficiently consistent with observations. The model expectations for the evolution of the universe are also studied by testing the evolution of the deceleration parameter, the density of the universe, and the effective equation-of-state parameter of the model and of its underlying dark energy candidate. The value of the present day viscosity coefficient of the cosmic fluid, [Formula: see text], is estimated. It is found to be [Formula: see text][Formula: see text]Pa[Formula: see text]s. We argue that this model is able to explain the behavior of the universe evolution.

scholarly journals ATTRACTOR SOLUTION IN COUPLED YANG–MILLS FIELD DARK ENERGY MODELS

2009 ◽  
Vol 18 (09) ◽  
pp. 1331-1342 ◽  
Author(s):  
WEN ZHAO
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
De Sitter ◽  
Yang Mills ◽  
Constraint Equations ◽  
Energy Models ◽  
Big Rip ◽  
Attractor Solution ◽  
The Universe ◽  
Mills Field

We investigate the attractor solution in the coupled Yang–Mills field dark energy models with the general interaction term, and obtain the constraint equations for the interaction if the attractor solution exists. The research also shows that, if the attractor solution exists, the equation of state of dark energy must evolve from wy > 0 to wy ≤ -1, which is slightly suggested by the observation. At the same time, the total equation of state in the attractor solution is w tot = -1, the universe is a de Sitter expansion, and the cosmic big rip is naturally avoided. These features are all independent of the interacting forms.

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