Numerical modeling of cathode-directed streamers branching in strong electric fields

2016 ◽  
Author(s):  
Белогловский ◽  
Andrey Beloglovskiy ◽  
Федорова ◽  
A. Fedorova
Keyword(s):  
Numerical Modeling ◽  
Numerical Model ◽  
Electric Fields ◽  
Strong Field ◽  
Strong Electric Field ◽  
Three Dimensional ◽  
Strong Electric Fields ◽  
Electron Avalanches ◽  
Discharge Gap ◽  
Positive Streamer

A research of conditions of the branching of positive streamer in air in a strong electric field by the use a three-dimensional numerical model is presented. This model is based on the assumption that the development of large electron avalanches in the strong field in front of the streamer head leads to branching. Tendency for branching has been observed, if the ratio of the diameters of the streamer heads to the distance between them is not greater than 0.55. If this ratio is more than 0,55, merger of originally formed streamer heads has been observed, and then only one streamer develops in the discharge gap.

scholarly journals The Dispersion of Strong Field Dielectric Permittivity in (1-x)PMN-(x)PT Ceramics

2011 ◽  
Vol 56 (4) ◽  
pp. 1199-1203 ◽  
Author(s):  
P. Wawrzała ◽  
R. Skulski
Keyword(s):  
Dielectric Permittivity ◽  
Hysteresis Loop ◽  
Electric Fields ◽  
Strong Field ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Strong Electric Fields

The Dispersion of Strong Field Dielectric Permittivity in (1-x)PMN-(x)PT CeramicsWe propose the method of analysis of the dielectric permittivity measured in very strong electric fields. The method is based on the numeric calculations of derivative fromP - Ehysteresis loop. Such investigations have been performed for PMN-PT ceramics at various temperatures and frequencies. As a result we analyze the low frequency dispersion of the strong field dielectric permittivity.

Comparison of Cable Insulation Control in Weak and Strong Electric Fields

2015 ◽  
Vol 756 ◽  
pp. 486-490 ◽  
Author(s):  
Nadezda S. Starikova ◽  
Vitaly V. Redko ◽  
G.V. Vavilova
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Strong Electric Field ◽  
Weak Electric Field ◽  
Cable Insulation ◽  
Modern Methods ◽  
Insulation Thickness ◽  
Defect Dimension ◽  
Cylindrical Capacitor ◽  
Strong Electric Fields

In this paper the modern methods of cable products insulation control are referred. A comparison of efficiency of the cable insulation defects control by changing in cable area capacitance is carried out in the strong and weak electric fields. The electric cable can be represented as a cylindrical capacitor, but to simplify the issue the insulation area is represented as a plate capacitor with anisotropic dielectric. The cable insulation model is created in the software Comsol Multyphysic. The effect of the defect dimension on the cable area electric capacitance in a strong and weak electric field is described. Also, the control sensitivity of both methods was assessed and compared with each other. The control sensitivity in a weak electric field is slightly higher for the defects with small size (less than 70% from insulation thickness). The control sensitivity in a strong electric field is considerably higher for the defects with big size (more than 70% from insulation thickness).

scholarly journals Generation of sequences of strong electric monopulses in nitride films

2021 ◽  
Vol 34 (2) ◽  
pp. 187-201
Author(s):  
Volodymyr Grimalsky ◽  
Svetlana Koshevaya ◽  
Jesus Escobedo-Alatorre ◽  
Anatoliy Kotsarenko
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Strong Electric Field ◽  
Numerical Algorithms ◽  
Negative Differential Conductivity ◽  
Differential Conductivity ◽  
Threshold Values ◽  
Bias Electric Field ◽  
Bulk Semiconductors ◽  
Strong Electric Fields

This paper presents theoretical investigation of the excitation of the sequences of strong nonlinear monopulses of space charge waves from input small envelope pulses with microwave carrier frequencies due to the negative differential conductivity in n-GaN and n-InN films. The stable numerical algorithms have been used for nonlinear 3D simulations. The sequences of the monopulses of the strong electric field of 3 - 10 ps durations each can be excited. The bias electric field should be chosen slightly higher than the threshold values for observing the negative differential conductivity. The doping levels should be moderate 1016 -1017 cm-3in the films of ? 2 mm thicknesses. The input microwave carrier frequencies of the exciting pulses of small amplitudes are up to 30 GHz in n-GaN films, whereas in n-InN films they are lower, up to 20 GHz. The sequences of the electric monopulses of high peak values are excited both in the uniform nitride films and in films with non-uniform conductivity. These nonlinear monopulses in the films differ from the domains of strong electric fields in the bulk semiconductors. In the films with non-uniform doping the nonlinear pulses are excited due to the inhomogeneity of the electric field near the input end of the film and the output nonlinear pulses are rather domains.

scholarly journals Observations by the LOFAR radio telescope of a fast negative leader propagation mode

2021 ◽  
Author(s):  
Olaf Scholten ◽  
Keyword(s):  
Electric Fields ◽  
Radio Telescope ◽  
Strong Field ◽  
Strong Electric Field ◽  
Broad Band ◽  
Propagation Mode ◽  
Lightning Flash ◽  
Strong Broad Band ◽  
Initial Stage ◽  
Reduced Density

<p>We report on recent observations made by the LOFAR radio-telescope of a fast propagation mode in negative leaders we named Rapid Negative Leader (RNL).<br>The RNL has a variety of properties that make them clearly distinct from negative leaders or dart leaders, such as -- fast propagation, -- emission of strong broad-band pulses, -- emission of very high VHF power, -- a reduced density of located sources, and -- terminating with the spawning of a large number of negative leaders in a small area. RNLs are almost always observed in the initial stage of a lightning flash, but may also occur much later. They may occur repeatedly in a certain part of the cloud.</p><p>We interpret a RNL as negative leader developing in strong electric field due to a relatively small highly-charged cloud, probably created by a local turbulence, with a typical size of order 5 km<sup>2</sup>.  The strong field will lead to a larger than usual charge at the leader tip resulting in an increased propagation velocity as well as a strongly enhanced emission of VHF power.<br>Since for the initiation of a lightning flash strong ambient electric fields are required, it is thus no surprise that the initial leader is in fact a RNL. </p><div> <div> <div></div> <div>What do you want to do ?</div> New mail</div> </div><div> <div> <div></div> <div>What do you want to do ?</div> New mail</div> </div>

scholarly journals Three-dimensional wave evolution on electrified falling films

2017 ◽  
Vol 822 ◽  
pp. 54-79 ◽  
Author(s):  
R. J. Tomlin ◽  
D. T. Papageorgiou ◽  
G. A. Pavliotis
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Stokes Equations ◽  
Strong Electric Field ◽  
Three Dimensional ◽  
Domain Size ◽  
Spatiotemporal Chaos ◽  
Electric Field Effect ◽  
Two Dimensional ◽  
Weakly Nonlinear

We consider the full three-dimensional dynamics of a thin falling liquid film on a flat plate inclined at some non-zero angle to the horizontal. In addition to gravitational effects, the flow is driven by an electric field which is normal to the substrate far from the flow. This extends the work of Tseluiko & Papageorgiou (J. Fluid Mech., vol. 556, 2006b, pp. 361–386) by including transverse dynamics. We study both the cases of overlying and hanging films, where the liquid lies above or below the substrate, respectively. Starting with the Navier–Stokes equations coupled with electrostatics, a fully nonlinear two-dimensional Benney equation for the interfacial dynamics is derived, valid for waves that are long compared to the film thickness. The weakly nonlinear evolution is governed by a Kuramoto–Sivashinsky equation with a non-local term due to the electric field effect. The electric field term is linearly destabilising and produces growth rates proportional to $|\unicode[STIX]{x1D743}|^{3}$, where $\unicode[STIX]{x1D743}$ is the wavenumber vector of the perturbations. It is found that transverse gravitational instabilities are always present for hanging films, and this leads to unboundedness of nonlinear solutions even in the absence of electric fields – this is due to the anisotropy of the nonlinearity. For overlying films and a restriction on the strength of the electric field, the equation is well-posed in the sense that it possesses bounded solutions. This two-dimensional equation is studied numerically for the case of periodic boundary conditions in order to assess the effects of inertia, electric field strength and the size of the periodic domain. Rich dynamical behaviours are observed and reported. For subcritical Reynolds number flows, a sufficiently strong electric field can promote non-trivial dynamics for some choices of domain size, leading to fully two-dimensional evolutions of the interface. We also observe two-dimensional spatiotemporal chaos on sufficiently large domains. For supercritical flows, such two-dimensional chaotic dynamics emerges in the absence of a field, and its presence enhances the amplitude of the fluctuations and broadens their spectrum.

scholarly journals Numerical Modeling of Multiple Inclined Dense Jets Discharged from Moderately Spaced Ports

Water ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 2077 ◽  
Author(s):  
Yan ◽  
Mohammadian
Keyword(s):  
Numerical Modeling ◽  
Numerical Model ◽  
Three Dimensional ◽  
Mixing Processes ◽  
Computational Costs ◽  
Promising Tool ◽  
Modeling Techniques ◽  
Turbulence Closures ◽  
Inclined Dense Jets ◽  
Better Than

Wastewaters are often discharged into water bodies from multiport diffusers in the form of inclined dense jets, and it is important to predict their mixing characteristics for a sound sustainable design for seawater desalination. Compared with single jets and multiple horizontal or vertical jets, the mixing processes of multiple inclined dense jets are more complicated, and thus the existing theoretical, analytical, or simplified numerical methods cannot effectively predict their dilution properties. Recent advances in numerical modeling techniques have provided a new avenue of simulating wastewater jets as three-dimensional phenomena, but their application to multiple inclined dense jets has rarely been reported. In this study, a fully three-dimensional numerical model is employed to simulate multiple inclined brine discharges from diffusers with moderately spaced ports, with the standard and re-normalization group (RNG) k-ε turbulence closures being tested. The simulated characteristic variables are compared to experimental data, and the results show that the simulations match very well with the experiments, demonstrating that the numerical model is a promising tool for simulating inclined dense jets discharged from multiport diffusers. The study also found that the RNG k-ε model performs better than the standard k-ε model without significantly increasing the computational costs.

scholarly journals Spontaneous generation of spin current from the vacuum by strong electric fields

2019 ◽  
Vol 2019 (11) ◽  
Author(s):  
Xu-Guang Huang ◽  
Mamoru Matsuo ◽  
Hidetoshi Taya
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Strong Electric Field ◽  
Spin Current ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
Longitudinal Direction ◽  
Spontaneous Generation ◽  
Strong Electric Fields ◽  
Schwinger Mechanism

Abstract We discuss spontaneous spin current generation from the vacuum by strong electric fields as a result of interplay between the Schwinger mechanism and a spin–orbit coupling. By considering a homogeneous slow strong electric field superimposed by a fast weak transverse electric field, we explicitly evaluate the vacuum expectation value of a spin current (the Bargmann–Wigner spin current) by numerically solving the Dirac equation. We show that a non-vanishing spin current polarized in the direction perpendicular to the electric fields flows mostly in the longitudinal direction. We also find that a relativistic effect due to helicity conservation affects the direction/polarization of a spin current.

Three-Dimensional Numerical Model of Wind-Driven Current in a Lake Based on POM Model

2009 ◽  
Author(s):  
Jialing Hao ◽  
Xiaoxin Jiang ◽  
Juan Yang
Keyword(s):  
Numerical Modeling ◽  
Numerical Model ◽  
Flow Direction ◽  
Tidal Flow ◽  
Three Dimensional ◽  
Vertical Direction ◽  
Ocean Model ◽  
Curvilinear Grid ◽  
Hydrodynamic Processes ◽  
Contaminant Transport Modeling

Lake current is the cause for the transport of many matters such as suspended sediment, algae, contaminant, therefore, it must be estimated fairly accurately. Generally speaking, the flow in many lakes is weak and the flow direction is follows dominated mainly by the wind direction on lake surface. Correct simulation of the wind-driven current in a lake requires using a three-dimensional hydrodynamic numerical model. The main factor affecting the lake hydrodynamic processes is wind. Because wind-driven current have important influence for the matter exchange and energy transform in a lake, and field observations are comparatively difficult, numerical modeling is the main method to estimate the wind-driven current nowadays. The numerical modeling of 3D tidal flow and mass transportation in this study was performed using the Princeton Ocean Model (POM). The model is validated by calculating wind-driven current in a rectangular flume [1][2]. The contaminant transport modeling in the Yangchenghu Lake is performed with POM using an orthogonal curvilinear grid in horizontal direction and sigma coordinate variation in vertical direction. An analysis of model results is presented.

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