scholarly journals Incorporation of Fluid Compressibility into the Calculation of the Stationary Mode of Operation of a Hydraulic Device at High Fluid Pressures

2021 ◽  
Vol 17 (2) ◽  
pp. 195-209
Author(s):  
V. A. Tenenev ◽  
◽  
T. Raeder ◽  
A. A. Chernova ◽  
◽  
...  
Keyword(s):  
Equation Of State ◽  
Incompressible Fluid ◽  
Numerical Method ◽  
Fluid Model ◽  
Local Approximation ◽  
Critical Parameters ◽  
Stationary Mode ◽  
High Fluid ◽  
Comparison Of The Results ◽  
Valve Operation

This paper is concerned with assessing the correctness of applying various mathematical models for the calculation of the hydroshock phenomena in technical devices for modes close to critical parameters of the fluid. We study the applicability limits of the equation of state for an incompressible fluid (the assumption of constancy of the medium density) to the simulation of processes of the safety valve operation for high values of pressures in the valve. We present a scheme for adapting the numerical method of S. K. Godunov for calculation of flows of incompressible fluids. A generalization of the method for the Mie – Grüneisen equation of state is made using an algorithm of local approximation. A detailed validation and verification of the developed numerical method is provided, and relevant schemes and algorithms are given. Modeling of the hydroshock phenomenon under the valve actuation within the incompressible fluid model is carried out by the openFoam software. The comparison of the results for the weakly compressible

scholarly journals The I-Love-Q Relations for Superfluid Neutron Stars

Universe ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. 111
Author(s):  
Cheung-Hei Yeung ◽  
Lap-Ming Lin ◽  
Nils Andersson ◽  
Greg Comer
Keyword(s):  
Fluid Dynamics ◽  
Equation Of State ◽  
Neutron Stars ◽  
Quadrupole Moment ◽  
Fluid Model ◽  
Normal Component ◽  
Approximate Equation ◽  
Mean Field Model ◽  
Polytropic Model ◽  
Two Fluid

The I-Love-Q relations are approximate equation-of-state independent relations that connect the moment of inertia, the spin-induced quadrupole moment, and the tidal deformability of neutron stars. In this paper, we study the I-Love-Q relations for superfluid neutron stars for a general relativistic two-fluid model: one fluid being the neutron superfluid and the other a conglomerate of all charged components. We study to what extent the two-fluid dynamics might affect the robustness of the I-Love-Q relations by using a simple two-component polytropic model and a relativistic mean field model with entrainment for the equation-of-state. Our results depend crucially on the spin ratio Ωn/Ωp between the angular velocities of the neutron superfluid and the normal component. We find that the I-Love-Q relations can still be satisfied to high accuracy for superfluid neutron stars as long as the two fluids are nearly co-rotating Ωn/Ωp≈1. However, the deviations from the I-Love-Q relations increase as the spin ratio deviates from unity. In particular, the deviation of the Q-Love relation can be as large as O(10%) if Ωn/Ωp differ from unity by a few tens of percent. As Ωn/Ωp≈1 is expected for realistic neutron stars, our results suggest that the two-fluid dynamics should not affect the accuracy of any gravitational waveform models for neutron star binaries that employ the relation to connect the spin-induced quadrupole moment and the tidal deformability.

scholarly journals Nonlinear Processes in Safety Systems for Substances with Parameters Close to a Critical State

2021 ◽  
Vol 17 (1) ◽  
pp. 119-138
Author(s):  
M. R. Koroleva ◽  
◽  
O. V. Mishchenkova ◽  
V. A. Tenenev ◽  
T. Raeder ◽  
...  
Keyword(s):  
Equation Of State ◽  
Critical State ◽  
Stokes Equations ◽  
Safety Valve ◽  
Van Der Waals ◽  
Local Approximation ◽  
Critical Conditions ◽  
Nonlinear Processes ◽  
Real Gas ◽  
Van Der Waals Equation

The paper presents a modification of the digital method by S. K. Godunov for calculating real gas flows under conditions close to a critical state. The method is generalized to the case of the Van der Waals equation of state using the local approximation algorithm. Test calculations of flows in a shock tube have shown the validity of this approach for the mathematical description of gas-dynamic processes in real gases with shock waves and contact discontinuity both in areas with classical and nonclassical behavior patterns. The modified digital scheme by Godunov with local approximation of the Van der Waals equation by a two-term equation of state was used for simulating a spatial flow of real gas based on Navier – Stokes equations in the area of a complex shape, which is characteristic of the internal space of a safety valve. We have demonstrated that, under near-critical conditions, areas of nonclassical gas behavior may appear, which affects the nature of flows. We have studied nonlinear processes in a safety valve arising from the movement of the shut-off element, which are also determined by the device design features and the gas flow conditions.

INFLATIONARY SCENARIO IN BRANS–DICKE THEORY FOR BIANCHI VI0 SPACE–TIME MODEL

2003 ◽  
Vol 12 (01) ◽  
pp. 129-143 ◽  
Author(s):  
SUBENOY CHAKRABORTY ◽  
ARABINDA GHOSH
Keyword(s):  
Equation Of State ◽  
Perfect Fluid ◽  
Analytical Solutions ◽  
Fluid Model ◽  
Space Time ◽  
Time Model ◽  
Exact Analytical Solutions ◽  
Exponential Expansion ◽  
Barotropic Equation ◽  
Space Time Model

We have investigated perfect fluid model in Brans–Dicke theory for Bianchi VI 0 space–time and have obtained exact analytical solutions considering barotropic equation of state. These solutions have been analyzed for different values of the parameters involved and some of them have shown a period of exponential expansion.

An Upwind Numerical Method for a Hyperbolic One-Dimensional Two-Fluid Model

2011 ◽  
Author(s):  
Youn-Gyu Jung ◽  
Moon-Sun Chung ◽  
Sung-Jae Yi
Keyword(s):  
Numerical Method ◽  
Fluid Model ◽  
Equation System ◽  
Benchmark Problems ◽  
Two Phase ◽  
One Dimensional ◽  
Flow Problems ◽  
Complete Set ◽  
Two Fluid Model ◽  
Two Fluid

This study discusses on the implementation of an upwind method for a one-dimensional two-fluid model including the surface tension effect in the momentum equations. This model consists of a complete set of six equations including two-mass, two-momentum, and two-internal energy conservation equations having all real eigenvalues. Based on this equation system with upwind numerical method, the present authors first make a pilot code and then solve some benchmark problems to verify whether this model and numerical method is able to properly solve some fundamental one-dimensional two-phase flow problems or not.

MODEL EQUATION OF STATE OF LIQUID C60 BASED ON HARD SPHERE–YUKAWA POTENTIAL

2006 ◽  
Vol 20 (23) ◽  
pp. 3373-3382 ◽  
Author(s):  
M. BAHAA KHEDR
Keyword(s):  
Computer Simulation ◽  
Equation Of State ◽  
Hard Sphere ◽  
Yukawa Potential ◽  
Coexistence Curve ◽  
Critical Parameters ◽  
Spherical Approximation ◽  
Mean Spherical Approximation ◽  
The Fourier Transform ◽  
New Equation

The series mean spherical approximation (SMSA) for the hard sphere–Yukawa (HSYK) fluid is applied to C 60. The energy and range parameters of HSYK potential have been reduced to one parameter by forcing the q→0 limit of the Fourier transform of the potential to be identical to that of the empirical potential of C 60. The new equation of state (EOS) allows us to investigate the liquid–vapor coexistence curve and calculate the thermodynamic properties of liquid C 60. The comparisons with computer simulation results suggest the importance of treating the attractive tail of the potential accurately. The estimated critical parameters Tc=1984.8 K , ρc=0.464 nm -3 and Pc=36.3 bar , which are in good agreement with NVT-Monte Carlo computer simulation predictions. The results are discussed by making reference to previous studies.

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