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São José dos Campos, Brazil

Toneli D.A.,Techonological Institute of Aeronautics | Pessoa R.S.,Techonological Institute of Aeronautics | Pessoa R.S.,University of Paraiba Valley | Roberto M.,Techonological Institute of Aeronautics | And 2 more authors.
Journal of Physics D: Applied Physics | Year: 2015

We describe a volume averaged global model for an inductively coupled RF oxygen discharge that considers an extensive reaction set that includes the species: O2(X), O2(), O2(), O2(A, A', ), O, O, O(3P), O(1D), O+, O-, O3, O, O, and electrons. We propose revised rate coefficients for some of the reactions and explore the densities of various species as a function of discharge pressure, in the pressure range 1-100 mTorr. We find that the O2() density can be lower than the O2() density in the pressure range from 2.5 to 80 mTorr. The relative reaction rates for formation and annihilation of O2() and O2() are evaluated and the most important reactions are indicated. The O- loss process is also studied. The results show that O2() has only a small contribution to the loss of the negative ion O-, while electron impact detachment is a very effective loss process at low pressure (<2 mTorr) and detachment by the oxygen atom O(3P) and the metastable singlet O2() are the most effective loss process up to roughly 50 mTorr where charge exchange becomes the most effective process for O- loss. © 2015 IOP Publishing Ltd. Source


Toneli D.A.,Techonological Institute of Aeronautics | Pessoa R.S.,Techonological Institute of Aeronautics | Pessoa R.S.,University of Paraiba Valley | Roberto M.,Techonological Institute of Aeronautics | And 2 more authors.
Journal of Physics D: Applied Physics | Year: 2015

A low pressure high density oxygen discharge is studied through a global (volume averaged) model in the pressure range 0.5-100 mTorr. The goal of this work is to evaluate the dependence of collisional energy loss per electron-ion pair created, effective electron temperature, mean density of species, and mean electronegativity on the electron energy distribution function. Differences in the results for Maxwellian and non-Maxwellian distributions show the importance of using a proper electron energy distribution function in discharge modelling. We also explore the differences due to different reactor wall materials comparing the results for an anodized aluminium reactor with a stainless steel reactor. Due to the low recombination coefficient for oxygen atoms on the anodized aluminium walls, the yield of atomic oxygen in anodized aluminium reactors increases significantly as compared to stainless steel reactors. However, the difference of the yield of atomic oxygen in these reactors decreases as pressure increases. Thus, anodized aluminium reactors can be desired for applications where a high concentration of atomic oxygen is required. Finally, the importance of quenching coefficient for plasma modelling is stressed through the quenching coefficient at the walls for O2(b1Σ+g). Low quenching coefficients result in high densities of O2(b1Σ+g) affecting the mean electronegativity of the plasma due to the decrease in the density of O-2. © 2015 IOP Publishing Ltd. Source


Cunha-Filho A.G.,Federal University of Uberlandia | De Lima A.M.G.,Federal University of Uberlandia | Donadon M.V.,Techonological Institute of Aeronautics | Leao L.S.,Federal University of Uberlandia
Aerospace Science and Technology | Year: 2016

The present study involves the application of surface viscoelastic damping treatments to remedy panel flutter problems in existing aircraft components in which active control strategies cannot be easily performed. The rationale for such study is the fact that as the viscoelastic materials are often used to solve a variety of resonant noise and vibration problems in aerospace industry, it becomes important to quantify the increase of aeroelastic stability that can be obtained by the inclusion of viscoelastic treatments. The flutter boundaries of the aeroviscoelastic system accounting for the frequency- and temperature-dependent behavior of the viscoelastic material are computed by adopting the so-named Golla-Hughes-McTavish model. Since the inclusion of internal variables in the viscoelastic model leads to an augmented coupled system of equations of motion, a numerical pre-processing is found to be necessary prior to the resolution of the complex eigenvalue problem for the purposes of flutter analysis. After the theoretical foundations, the stability analysis of a three-layer sandwich plate under supersonic flow is addressed. The results show that it is possible to increase the critical flutter speeds of flat panels using surface viscoelastic damping treatments. However, the temperature and the thicknesses of the layers have significant effect on the flutter boundary. © 2016 Elsevier Masson SAS. All rights reserved. Source

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