A numerical model of non-equilibrium thermal plasmas. II. Governing equations

2013 ◽  
Vol 20 (3) ◽  
pp. 033509 ◽  
Author(s):  
He-Ping Li ◽  
Xiao-Ning Zhang ◽  
Wei-Dong Xia
Keyword(s):  
Numerical Model ◽  
Thermal Plasmas ◽  
Governing Equations ◽  
Non Equilibrium

A numerical model of non-equilibrium thermal plasmas. I. Transport properties

2013 ◽  
Vol 20 (3) ◽  
pp. 033508 ◽  
Author(s):  
Xiao-Ning Zhang ◽  
He-Ping Li ◽  
Anthony B. Murphy ◽  
Wei-Dong Xia
Keyword(s):  
Numerical Model ◽  
Transport Properties ◽  
Thermal Plasmas ◽  
Non Equilibrium

Investigations on thermodynamic processes of a novel pneumatic drive asymmetric Gifford-McMahon cycle cryorefrigerator

2021 ◽  
pp. 1-21
Author(s):  
Debashis Panda ◽  
Suraj Kumar Behera ◽  
Ashok Kumar Satapathy ◽  
Sunil K. Sarangi
Keyword(s):  
Numerical Model ◽  
Performance Parameters ◽  
Pneumatic Drive ◽  
Governing Equations ◽  
Expansion Process ◽  
Intake Process ◽  
The Impact ◽  
First Time ◽  
Thermodynamic Processes ◽  
Dead Centre

Abstract In this paper, a numerical and experimental investigation is conducted on a novel pneumatic-drive asymmetric Gifford-McMahon cycle cryorefrigerator for the first time. In the pneumatic-drive asymmetric Gifford-McMahon cycle cryorefrigerator, the duration of the assistance space exhaust process is kept higher than that of the assistance space intake process. Therefore, the displacer moves faster at the lower dead centre and slower at the upper dead centre inside the expander cylinder, which makes the duration of expansion process longer. The numerical model solves the governing equations of the refrigerant and dynamics of free-floating displacer iteratively to illustrate the refrigeration mechanisms. Additionally, the model computes the performance parameters of the cryorefrigerator, like refrigerating capacity, and specific refrigerating capacity. By adopting the numerical model, the impact of the loitering time on the thermodynamic processes is elaborated. It is perceived that, both refrigerating capacity and specific refrigerating capacity reduces with an increase in the loitering time. The experimental cooling characteristics are studied for different values of discharge to suction pressure ratios of helium compressor.

Reply to ‘Comment on “Collective effects in bremsstrahlung in plasmas” ’

1998 ◽  
Vol 60 (2) ◽  
pp. 447-448 ◽  
Author(s):  
V. N. TSYTOVICH ◽  
R. BINGHAM ◽  
U. de ANGELIS ◽  
A. FORLANI
Keyword(s):  
Particle Distribution ◽  
Thermal Plasmas ◽  
Solar Interior ◽  
The Other ◽  
Standard Approach ◽  
Collective Effects ◽  
Fluctuation Dissipation ◽  
Fluctuation Dissipation Theorem ◽  
Electron Bremsstrahlung ◽  
Non Equilibrium

We reply here to a criticism of our paper (Tsytovich et al. 1996) by Iglesias (1997).In our paper we present a very general formulation of collective effects in bremsstrahlung that is valid for any non-equilibrium non-Maxwellian particle distribution. This result is given in (2.20) early in the paper. The standard treatments of bremsstrahlung found in books like Bekefi (1966) are only for thermal plasmas, where the fluctuation–dissipation theorem is valid. Note that the fluctuation–dissipation theorem cannot be used for non-thermal or non-dipole fields, and in this respect the method we use is more general. Our method is the more complex of the approaches used, but, as stated, it can handle situations that cannot be treated by the standard approach. Our main result is the formula (2.20), which is valid for any non-equilibrium non-Maxwellian particle distribution, and which cannot be found anywhere else in the literature. Furthermore, we find new qualitative effects indicating that the ion–ion bremsstrahlung (which is always neglected in the literature) is not small in the case where the collective effects are taken into account, and is in fact, for certain frequencies, of the order of the electron–electron bremsstrahlung. The other qualitatively new result is that, where collective effects are important, the electron–electron bremsstrahlung is not of the order v2Te/c2, as it is for the case in the absence of collective effects, but of the order ω2pe/ω2 times less – which, for example in the solar interior, where ω2pe/ω2 is of the order of v2Te/c2, is then of the order of v4Te/c4.

The Numerical Simulation of the Water Jet in Hydroentanglement

2011 ◽  
Vol 189-193 ◽  
pp. 2181-2184
Author(s):  
Heng Zhang ◽  
Xiao Ming Qian ◽  
Zhi Min Lu ◽  
Yuan Bai
Keyword(s):  
Numerical Simulation ◽  
Numerical Model ◽  
Multiphase Flow ◽  
Flow Model ◽  
Two Phase Flow ◽  
Water Jet ◽  
Phase Flow ◽  
Governing Equations ◽  
Two Phase ◽  
Set Up

The functions of hydroentangled nonwovens are determined by the degree of the fiber entanglement, which depend mainly on parameters of the water jet. According to the spun lacing technology, this paper set up the numerical model based on the simplified water jetting model, establishing the governing equations, and the blended two-phase flow as the multiphase flow model. This paper simulation the water needle after the water jetting from the water needle plate in the different pressure (100bar, 60bar, 45bar, 35bar).

scholarly journals Numerical Investigations of Tsunami Run-Up and Flow Structure on Coastal Vegetated Beaches

Water ◽  
2018 ◽  
Vol 10 (12) ◽  
pp. 1776 ◽  
Author(s):  
Hongxing Zhang ◽  
Mingliang Zhang ◽  
Tianping Xu ◽  
Jun Tang
Keyword(s):  
Wave Propagation ◽  
Numerical Model ◽  
Peak Flow ◽  
Tsunami Wave ◽  
Coastal Vegetation ◽  
Coastal Forest ◽  
Governing Equations ◽  
Tsunami Waves ◽  
Run Up ◽  
Sloping Beach

Tsunami waves become hazardous when they reach the coast. In South and Southeast Asian countries, coastal forest is widely utilized as a natural approach to mitigate tsunami damage. In this study, a depth-integrated numerical model was established to simulate wave propagation in a coastal region with and without forest cover. This numerical model was based on a finite volume Roe-type scheme, and was developed to solve the governing equations with the option of treating either a wet or dry wave front boundary. The governing equations were modified by adding a drag force term caused by vegetation. First, the model was validated for the case of solitary wave (breaking and non-breaking) run-up and run-down on a sloping beach, and long periodic wave propagation was investigated on a partially vegetated beach. The simulated results agree well with the measured data. Further, tsunami wave propagation on an actual-scale slope covered by coastal forest Pandanus odoratissimus (P. odoratissimus) and Casuarina equisetifolia (C. equisetifolia) was simulated to elucidate the influence of vegetation on tsunami mitigation with a different forest open gap. The numerical results revealed that coastal vegetation on sloping beach has significant potential to mitigate the impacts from tsunami waves by acting as a buffer zone. Coastal vegetation with open gaps causes the peak flow velocity at the exit of the gap to increase, and reduces the peak flow velocity behind the forest. Compared to a forest with open gaps in a linear arrangement, specific arrangements of gaps in the forest can increase the energy attenuation from tsunami wave. The results also showed that different cost-effective natural strategies in varying forest parameters including vegetation collocations, densities, and growth stages had significant impacts in reducing the severity of tsunami damage.

scholarly journals NUMERICAL MODELLING OF NEARSHORE CIRCULATION

1980 ◽  
Vol 1 (17) ◽  
pp. 160 ◽  
Author(s):  
Bruce A. Ebersole ◽  
Robert A. Dalrymple
Keyword(s):  
Numerical Model ◽  
Finite Difference ◽  
Numerical Models ◽  
Bottom Topography ◽  
Rip Currents ◽  
Time Dependency ◽  
Longshore Current ◽  
Governing Equations ◽  
Nearshore Circulation ◽  
Lateral Mixing

Waves impinging on beaches induce mean flows, such as longshore and rip currents. This nearshore circulation is of fundamental importance in the study of the transport of nearshore contaminants as well as littoral materials. Analytic models of this nearshore flow {see, e.g. 4, 9, 11, 12) have been constrained to be linear (in the governing equations) and simplistic in the bottom topography. Only recently have numerical models been developed to examine more complex situations. Steady state, finite difference models (1, 14), as well as a finite element model (10), have been proposed. The numerical model, developed by Birkemeier and Dalrymple (1), allowed for time dependency. Yet, in all of these cases, the governing equations have not included the nonlinear convective accelerations or lateral mixing terms. In this study, a nonlinear numerical model is presented based on a leapfrog finite difference scheme, which includes time dependency and eddy viscosity terms. Results are shown for a planar beach showing a comparison with the analytical longshore current models (with and without lateral mixing) of Longuet-Higgins (11, 12). The longshore current over a prismatic beach profile including an offshore bar is presented next, showing the effects of the bar on the velocity profile. The circulation set-up by a rip channel inset into a plane beach is then computed. A comparison is made to the linear model of Birkemeier and Dalrymple. Finally the model is applied to the case of synchronous intersecting wave trains (4). An interesting result occurs when the waves are of different amplitudes, which could provide an explanation of the formation of finger bars on a beach.

Parametric Studies on a Numerical, Nonlinear Pulse Tube Flow

1997 ◽  
Vol 119 (4) ◽  
pp. 831-837 ◽  
Author(s):  
C. S. Kirkconnell ◽  
G. T. Colwell
Keyword(s):  
Numerical Model ◽  
High Reliability ◽  
Low Cost ◽  
Method Of Lines ◽  
Pulse Tube ◽  
Governing Equations ◽  
Modeling Tools ◽  
The Method Of Lines ◽  
Commercial Applications ◽  
The One

The need for high reliability, low cost, low vibration cryocoolers, for both military and commercial applications, has spawned and continues to drive the development of pulse tube cryogenic refrigerators. The expander contains no moving parts, yielding the potential for marked improvements in these areas. Though pulse tube refrigeration has been thoroughly studied, more accurate analytic and numerical modeling tools are needed to facilitate the development of thermodynamically efficient pulse tube cryocoolers to meet the needs of the user community. At present, one of the primary areas of modeling uncertainty is in the calculation of the dissipative losses occurring within the pulse tube itself. Toward this end, a numerical model was developed to solve the one-dimensional, nonlinear governing equations for heat and mass flow in a pulse tube. The governing equations are scaled for high-frequency (>60 Hz) pulse lube operation. The resulting system of nonlinear, time-dependent equations was solved directly using the method of lines. The numerical model was verified analytically using a representative set of equations with a known solution. A sensitivity analysis was performed to investigate the influence of different parameters on the solution.

A Three Dimensional Non-Hydrostatic Numerical Model for Free Surface Flow and Mass Transportation

2013 ◽  
Vol 353-356 ◽  
pp. 2496-2501
Author(s):  
Biao Lv
Keyword(s):  
Numerical Model ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Navier Stokes ◽  
Mass Transportation ◽  
Governing Equations ◽  
Navier Stokes Equations ◽  
Good Agreement

A three dimensional non-hydrostatic numerical model is presented based on the incompressible Navier-Stokes equations and mass transport equations. An unstructured finite-volume technique is used to discretized the governing equations with good adaptable to complicated boundary. A conservative scalar transport algorithm is also applied in this model. An integral method of the top- layer pressure is applied to reduce the number of vertical layers. Three classical examples including periodic waves propagating over a submerged bar and non-hydrostatic lock exchange are used to demonstrate the capability and efficiency of the model. The simulation results are in good agreement with the analytical solution and experimental data.

Sign in / Sign up

Export Citation Format

Share Document