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نتیجه جستجو - Pressure wave

تعداد مقالات یافته شده: 2
ردیف عنوان نوع
1 Prediction of BLEVE mechanical energy by implementation of artificial neural network
پیش بینی انرژی مکانیکی BLEVE با اجرای شبکه عصبی مصنوعی-2020
In the event of a BLEVE, the overpressure wave can cause important effects over a certain area. Several thermodynamic assumptions have been proposed as the basis for developing methodologies to predict both the mechanical energy associated to such a wave and the peak overpressure. According to a recent comparative analysis, methods based on real gas behavior and adiabatic irreversible expansion assumptions can give a good estimation of this energy. In this communication, the Artificial Neural Network (ANN) approach has been implemented to predict the BLEVE mechanical energy for the case of propane and butane. Temperature and vessel filling degree at failure have been considered as input parameters (plus vessel volume), and the BLEVE blast energy has been estimated as output data by the ANN model. A Bayesian Regularization algorithm was chosen as the three-layer backpropagation training algorithm. Based on the neurons optimization process, the number of neurons at the hidden layer was five in the case of propane and four in the case of butane. The transfer function applied in this layer was a sigmoid, because it had an easy and straightforward differentiation for using in the backpropagation algorithm. For the output layer, the number of neurons had to be one in both cases, and the transfer function was purelin (linear). The model performance has been compared with experimental values, proving that the mechanical energy of a BLEVE explosion can be adequately predicted with the Artificial Neural Network approach.
Keywords: BLEVE | Vessel explosion | Explosion energy | Blast overpressure | Pressure wave | Artificial neural network
مقاله انگلیسی
2 Engine hot spots: Modes of auto-ignition and reaction propagation
نقاط داغ موتور: حالت خودکار سیستم جرقه زنی و انتشار واکنش-2016
Article history:Received 15 August 2015Revised 4 January 2016Accepted 5 January 2016Available online 6 February 2016Keywords:Ignition delay time Excitation time Hot spotsDetonation peninsula Auto-ignitive propagation Super-knockMany direct numerical simulations of spherical hot spot auto-ignitions, with different fuels, have identi- fied different auto-ignitive regimes. These range from benign auto-ignition, with pressure waves of small amplitude, to super-knock with the generation of damaging over-pressures. Results of such simulations are generalised diagrammatically, by plotting boundary values of ξ , the ratio of acoustic to auto-ignition velocity, against ε. This latter parameter is the residence time of the developing acoustic wave in the hot spot of radius ro , namely ro /a, normalised by the excitation time for the chemical heat release, τe . This ratio controls the energy transfer into the developing acoustic front. A third relevant parameter involves the product of the activation temperature, E/R, for the auto-ignition delay time, τi , normalised by the mixture temperature. T, the ratio, τi /τe , and the dimensionless hot spot temperature gradient, (∂ ln T /∂r¯), where r¯ is a dimensionless radius. These parameters define the boundaries of regimes of thermal ex- plosion, subsonic auto-ignition, developing detonations, and non-auto-ignitive deflagrations, in plots of ξ against ε.The regime of developing detonation forms a peninsula and contours, throughout the field. The product parameter (E/RT )(τi /τe )/∂ ln T /∂r¯ expresses the influences of hot spot temperature gradient and fuel characteristics, and a unique value of it might serve as a boundary between auto-ignitive and deflagrative regimes. Other combustion regimes can also be identified, including a mixed regime of both auto-ignitive and “normal” deflagrative burning. The paper explores the performances of a number of different engines in the regimes of controlled auto-ignition, normal combustion, combustion with mild knock and, ultimately, super-knock. The possible origins of hot spots are discussed and it is shown that the dissipation of turbulent energy alone is unlikely to lead directly to sufficiently energetic hot pots. The knocking characterisation of fuels also is discussed.© 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
مقاله انگلیسی
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