In this work Abel inversion technique was used for radial measurements of the microplasma in Ar-2%H2 flow at open atmosphere. The gas discharge parameters were investigated using spatially resolved high resolution optical emission spectroscopy (OES) to allow acquisition of OH (A 2Σ+, ν = 0 →X 2Π, ν′ = 0) rotational bands at 306.357 nm, Ar I 603.213 nm line and N2(C3∏u, ν = 0 →B3∏g, ν′ = 0) second positive system with the band head at 337.13 nm. The nonthermal plasma was generated between microhollow anode (~500 μm inner diameter) and a cathode copper foil, fed by direct current source for a current ranging from 20 mA to 100 mA (Townsend discharge from 20 mA to 30 mA, normal glow discharge from 30 mA to 80 mA at 210 V and abnormal discharge beyond 90 mA). The 1.5 mm length cylindrical-shape plasma has an outspread bright disk (negative glow region) near the cathode surface. Besides the gas temperature, the excitation temperature was measured radially for a current ranging from 20 mA to 100 mA, either from Boltzmann-plot of Ar I 4p – 4s and 5p – 4s transitions of excited argon or from Cu I two lines method of excited cuprum atoms released from the cathode surface. The measurements showed a nearly bell-shaped distribution of these temperatures, peaked at 120 μm from the center with the minimum at the plasma border. The average excitation temperature was about ~8000 K (maximum ~10,000 K) and the average rotational temperature was about 650 K (maximum ~800 K) from 20 K to 100 K. For the N2 second positive system with Δν = -2 it was estimated the vibrational temperature for the bright disk (1500 K to 5000 K). Hβ line Stark broadening was employed to define the electron number density of the negative glow (1015 cm -3).
Resumo: Balanças aerodinâmicas são empregadas em túneis de vento para medir as cargas atuantes em modelos sob teste. Uma metodologia foi desenvolvida para a avaliação da incerteza de calibração da balança externa do Túnel de Vento Subsônico N.º 2, do Centro Técnico Aeroespacial de São José dos Campos. A fim de obter um modelo adequado para fornecer as cargas aerodinâmicas a partir das medições das células de carga da balança, anteriormente ao ensaio, realize-se uma calibração aplicando-se pesos na balança através de um sistema de cabos e roldanas. Dois procedimentos são empregados para relacionar as leituras das células de carga às cargas aerodinâmicas: ajuste de curva e Redes Neurais. A modelagem matemática para a regressão por mínimos quadrados é multivariada. A classe de Redes Neurais usada é a rede Multy-Layer Perceptrons (MLP) ou Perceptrons de Multicamadas. A análise de erro inclui o emprego da lei geral de Propagação de Incerteza à curva resultante da regressão multivariada e o método de Simulação Monte Carlo. Uma comparação dos métodos utilizados é destacada neste trabalho.
Palavras-chave: Incertezas, Calibração, Ensaios, Redes Neurais Artificiais.Abstract: Aerodynmic balances are employed in wind tunnels to measure the loads acting on the model under test. A methodology has been developed for the assessment of the calibration uncertainty of the external balance at the Subsonic Wind Tunnel No. 2 (TA-2), at the Aerodynamic Laboratory, (ASA-L), of the Centro Técnico Aeroespacial, (CTA), Brazil. In order to obtain a suitable model to provide aerodynamic loads from the balance load cell measurements, a balance calibration is performed prior to the tests, applying loads to the balance through a system of cables and pulleys. Two approaches are employed to relate the load cell readings and the areodynamic loads: curve fitting and neural networks. The mathematical model for the least-squares regression is the multivariate one. The class of neural networks used is the multilayer feedforward networks, commonly referred to as multilayer perceptrons. The error analysis includes the employment of the general law of 1 mluisareis@iae.cta.br, 2
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