scholarly journals A Simple Gas-Kinetic Model For Dilute and Weakly Charged Plasma Micro-Jet Flows

Fluids ◽  
2021 ◽  
Vol 6 (7) ◽  
pp. 250
Author(s):  
Shiying Cai ◽  
Chunpei Cai
Keyword(s):  
Simple Model ◽  
Electric Fields ◽  
Neutral Condition ◽  
Jet Flows ◽  
Far Field ◽  
Convection Term ◽  
Number Density ◽  
Simulation Based ◽  
Analytical Formulas ◽  
Electric Field Force

This paper presents a simple model for slightly charged gas expanding into a vacuum from a planar exit. The number density, bulk velocity, temperature, and potential at the exit are given. The electric field force is assumed weaker than the convection term and is neglected in the analysis. As such, the quasi-neutral condition is naturally adopted and the potential field is computed with the Boltzmann relation. At far field, the exit degenerates as a point source, and simplified analytical formulas for flow and electric fields are obtained. The results are generic and offer insights on many existing models in the literature. They can be used to quickly approximate the flowfield and potential distributions without numerical simulations. They can also be used to initialize a simulation. Based on these results, more advanced models may be further developed.

Simulation-based assessment of coupled frequency response of magneto-electro-elastic auxetic multifunctional structures subjected to various electromagnetic circuits

2021 ◽  
pp. 146442072110219
Author(s):  
Vinyas Mahesh ◽  
Vishwas Mahesh ◽  
Dineshkumar Harursampath ◽  
Ahmed E Abouelregal
Keyword(s):  
Electric Fields ◽  
Solid Mechanics ◽  
Natural Frequencies ◽  
Comsol Multiphysics ◽  
Simulation Based ◽  
Electric And Magnetic Fields ◽  
Auxetic Structures ◽  
Triangular Elements ◽  
Benchmark Solutions ◽  
Free Vibration Response

This article deals with the modeling of magneto-electro-elastic auxetic structures and developing a methodology in COMSOL Multiphysics® to assess the free vibration response of such structures when subjected to various electromagnetic circuit conditions. The triple energy interaction between elastic, magnetic, and electric fields are established in the COMSOL Multiphysics® using structural mechanics and electromagnetic modules. The multiphase magneto-electro-elastic material with different percentages of piezoelectric and piezomagnetic phases are used as the material. In the solid mechanics module, the piezoelectric and piezomagnetic materials were created in stress-charge and stress-magnetization forms, respectively. The electric and magnetic fields are defined in COMSOL Multiphysics® through electromagnetic equations. Further, the customized controlled meshing constituted of free tetrahedral and triangular elements is adapted to trade-off between the accuracy and the computational expenses. The eigenvalue analysis is performed to obtain the natural frequencies of the MEE re-entrant auxetic structures. Also, the efficiency of smart auxetic structures over conventional honeycomb structures is presented throughout the manuscript. In addition, the discrepancy in the natural frequencies of the structures considering coupled and uncoupled state is also illustrated. It is believed that the modeling procedure and its outcomes serve as benchmark solutions for further design and analysis of smart auxetic magneto-electro-elastic structures.

WAVELET-BASED POSTPROCESSING OF JET LES DATA FOR ACOUSTIC FAR-FIELD EXTRAPOLATIONS

2013 ◽  
Vol 21 (04) ◽  
pp. 1350017
Author(s):  
RAMIN KAVIANI ◽  
VAHID ESFAHANIAN ◽  
MOHAMMAD EBRAHIMI
Keyword(s):  
Large Scale ◽  
Stokes Equations ◽  
Near Field ◽  
Flow Simulation ◽  
Computational Time ◽  
Jet Flows ◽  
Small Scale ◽  
Frequency Noise ◽  
Far Field ◽  
Noise Sources

The affordable grid resolutions in conventional large-eddy simulations (LESs) of high Reynolds jet flows are unable to capture the sound generated by fluid motions near and beyond the grid cut-off scale. As a result, the frequency spectrum of the extrapolated sound field is artificially truncated at high frequencies. In this paper, a new method is proposed to account for the high frequency noise sources beyond the resolution of a compressible flow simulation. The large-scale turbulent structures as dominant radiators of sound are captured in LES, satisfying filtered Navier–Stokes equations, while for small-scale turbulence, a Kolmogorov's turbulence spectrum is imposed. The latter is performed via a wavelet-based extrapolation to add randomly generated small-scale noise sources to the LES near-field data. Further, the vorticity and instability waves are filtered out via a passive wavelet-based masking and the whole spectrum of filtered data are captured on a Ffowcs-Williams/Hawkings (FW-H) surface surrounding the near-field region and are projected to acoustic far-field. The algorithm can be implemented as a separate postprocessing stage and it is observed that the computational time is considerably reduced utilizing a hybrid of many-core and multi-core framework, i.e. MPI-CUDA programming. The comparison of the results obtained from this procedure and those from experiments for high subsonic and transonic jets, shows that the far-field noise spectrum agree well up to 2 times of the grid cut-off frequency.

scholarly journals Analysis of Circular Polarization of Cylindrically Bent Microstrip Antennas

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Tiiti Kellomäki
Keyword(s):  
Simple Model ◽  
Circular Polarization ◽  
Axial Ratio ◽  
Microstrip Antennas ◽  
Far Field ◽  
Circularly Polarized ◽  
Wearable Antennas ◽  
Linearly Polarized ◽  
Frequency Shifting

When circularly polarized (CP) microstrip antennas are bent, the polarization becomes elliptical. We present a simple model that describes the phenomenon. The two linear modes present in a CP patch are modeled separately and added together to produce CP. Bending distorts the almost-spherical equiphase surface of a linearly polarized patch, which leads to phase imbalance in the far-field of a CP patch. The model predicts both the frequency shifting of the axial ratio band as well as the narrowing of the axial ratio beam. Uncontrolled bending is a problem associated especially with flexible textile antennas, and wearable antennas should therefore be designed somewhat conformal.

scholarly journals Comparative study of photo-produced ionosphere in the close environment of comets

2019 ◽  
Vol 630 ◽  
pp. A47 ◽  
Author(s):  
A. Beth ◽  
M. Galand ◽  
K. L. Heritier
Keyword(s):  
Comparative Study ◽  
Density Profile ◽  
Heliocentric Distance ◽  
Dissociative Recombination ◽  
Cometary Nucleus ◽  
Number Density ◽  
Loss Process ◽  
Plasma Loss ◽  
Relative Contribution ◽  
Analytical Formulas

Context. The Giotto and Rosetta missions gave us the unique opportunity of probing the close environment of cometary ionospheres of 1P/Halley (1P) and 67P/Churyumov-Gerasimenko (67P). The plasma conditions encountered at these two comets were very different from each other, which mainly stem from the different heliocentric distances, which drive photoionization rates, and from the outgassing activities, which drive the neutral densities. Aims. We asses the relative contribution of different plasma processes that are ongoing in the inner coma: photoionization, transport, photoabsorption, and electron–ion dissociative recombination. The main goal is to identify which processes are at play to then quantitatively assess the ionospheric density. Methods. We provide a set of analytical formulas to describe the ionospheric number density profile for cometary environments that take into account some of these processes. We discuss the validity of each model in the context of the Rosetta and Giotto missions. Results. We show that transport is the dominant loss process at large cometocentric distances and low outgassing rates. Chemical plasma loss through e−-ion dissociative recombination matters around 67P near perihelion and at 1P during the Giotto flyby: its effects increase as the heliocentric distance decreases, that is, at higher outgassing activity and higher photoionization frequency. Photoabsorption is of importance for outgassing rates higher than 1028 s−1 and only close to the cometary nucleus, well below the location of both spacecraft. Finally, regardless of the processes we considered, the ion number density profile always follows a 1∕r law at large cometocentric distances.

The structure of the impulse corona in a rod/plane gap. II. The negative corona: propagation and streamer/anode interaction

1979 ◽  
Vol 367 (1730) ◽  
pp. 321-342 ◽  
Keyword(s):  
Simple Model ◽  
Electric Field ◽  
Space Charge ◽  
Electric Fields ◽  
Electric Field Distribution ◽  
Electron Lifetime ◽  
Gas Temperature ◽  
Negative Corona ◽  
Negative Impulse ◽  
Total Electric Field

The electric fields due to negative impulse corona space charge in a 0.5 m rod/plane gap have been investigated with a rotating fluxmeter probe. Spatial development has also been studied by simultaneous photography. The results indicate that a total electric field of about 1.8 MV m-1 is required near the head of the streamer for propagation, and a simple model is proposed of the electric field distribution in the gap at various stages of development. Measurements of transfer charge, due to interaction of streamers with the plane, yield estimates of the free electron lifetime and the gas temperature in the streamer. Possible models of the charge distribution in streamers are considered, with their associated electric fields, and best agreement with the data is obtained when most of the space charge is assumed to be concentrated at the tip. Comparison is made with earlier work on positive coronas.

scholarly journals Response of personal exposimeters for exposure assessment in the GSM900 downlink band

2015 ◽  
Vol 34 (4) ◽  
pp. 1076-1084 ◽  
Author(s):  
Arno Thielens ◽  
Sam Agneessens ◽  
Günter Vermeeren ◽  
Leen Verloock ◽  
Hendrik Rogier ◽  
...  
Keyword(s):  
Confidence Interval ◽  
Numerical Simulations ◽  
Electric Fields ◽  
Mobile Communications ◽  
Design Methodology ◽  
Human Subjects ◽  
Far Field ◽  
Percent Confidence Interval ◽  
Global System ◽  
Content Type

Purpose – The purpose of this paper is to numerically determine the distribution of electric fields registered by a personal exposimeter (PEM) used for the Global System for Mobile Communications (GSM) around 900 MHz (GSM900) downlink (DL) band and compare these with calibration measurements of PEMs worn by real human subjects. Design/methodology/approach – Numerical simulations using the Virtual Family Male (VFM) are carried out at 950 MHz in order to determine the electric fields surrounding the phantom in realistic, far-field environments. These electric fields can be used to determine the distribution of a PEM’s response when worn by the VFM. Simultaneously, calibration measurements in an anechoic chamber are carried out using a real PEM worn by two different subjects, in order to determine the PEM’s response experimentally. Findings – Both the numerical simulations and the measurements show that a PEM will on average underestimate the incident electric fields in the GSM900 DL band and that the variation (expressed in terms of the 95 percent confidence interval and the interquartile distance) on its response is relatively large: a 95 percent confidence interval of 22 dB and an interquartile distance of 7.3 dB are found in a realistic environment using numerical simulations, while the calibration measurements show interquartile distances up to 12 dB. In terms of variation there is an excellent agreement between simulations and measurements. Originality/value – This paper proves that numerical simulations may be used as a replacement for the more time- and work-consuming calibration measurements if the variation of a PEM’s response is studied.

scholarly journals Experiments on jet flows and jet noise far-field spectra and directivity patterns

1964 ◽  
Vol 18 (02) ◽  
pp. 285 ◽  
Author(s):  
Erik Mollo-Christensen ◽  
Marc A. Kolpin ◽  
John R. Martuccelli
Keyword(s):  
Jet Noise ◽  
Jet Flows ◽  
Far Field ◽  
Directivity Patterns
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