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  • 1
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    The prediction of nonlinear dynamic loads on helicopters from flight variables using artificial neural networks (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A method of indirectly monitoring component loads through common flight variables is proposed which requires an accurate model of the underlying nonlinear relationships. An artificial neural network (ANN) model learns relationships through exposure to a database of flight variable records and corresponding load histories from an instrumented military helicopter undergoing standard maneuvers. The ANN model, utilizing eight standard flight variables as inputs, is trained to predict normalized time-varying mean and oscillatory loads on two critical components over a range of seven maneuvers. Both interpolative and extrapolative capabilities are demonstrated with agreement between predicted and measured loads on the order of 90 percent to 95 percent. This work justifies pursuing the ANN method of predicting loads from flight variables.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: In: DGLR(AIAA Aeroacoustics Conference, 14th, Aachen, Germany, May 11-14, 1992, Proceedings. Vol. 2 (A93-19126 05-71); p. 971-979.
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  • 2
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    Identification of aerospace acoustic sources using sparse distributed associative memory (1990)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A pattern recognition system has been developed to classify five different aerospace acoustic sources. In this paper the performance of two new classifiers, an associative memory classifier and a neural network classifier, is compared to the performance of a previously designed system. Sources are classified using features calculated from the time and frequency domain. Each classifier undergoes a training period where it learns to classify sources correctly based on a set of known sources. After training the classifier is tested with unknown sources. Results show that over 96 percent of sources were identified correctly with the new associative memory classifier. The neural network classifier identified over 81 percent of the sources correctly.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 90-3992
    Format: text
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  • 3
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    Improved plasma torch for ignition and flame holding in supersonic combustion (1989)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A plasma torch system designed for ignition and flame-holding in supersonic combustion studies has been modified, in order to decrease electrode wear and increase stability, through the incorporation of a flow swirler in the gas inlet that adds vortex-stabilization to the arc. The torch body was redesigned in order to achieve superior alignment of the electrodes; the electrode gap was made continuously adjustable, thereby allowing fine tuning during torch operation. Table operation of the improved torch has been demonstrated in pure nitrogen, eliminating the requirement of argon gas for arc stabilization.
    Keywords: MECHANICAL ENGINEERING
    Type: AIAA PAPER 89-2945
    Format: text
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  • 4
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    Operating characteristics of a hydrogen-argon plasma torch for supersonic combustion applications (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The residence time of the combustible mixture in the combustion chamber of a scramjet engine is much less than the time normally required for complete combustion. Hydrogen and hydrocarbon fuels require an ignition source under conditions typically found in a scramjet combustor. Analytical studies indicate that the presence of hydrogen atoms should greatly reduce the ignition delay in this environment. Because hydrogen plasmas are prolific sources of hydrogen atoms, a low-power, uncooled hydrogen plasma torch has been built and tested to evaluate its potential as a possible flame holder for supersonic combustion. The torch was found to be unstable when operated on pure hydrogen; however, stable operation could be obtained by using argon as a body gas and mixing in the desired amount of hydrogen. The stability limits of the torch are delineated and its electrical and thermal behavior documented. An average torch thermal efficiency of around 88 percent is demonstrated.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: Journal of Propulsion and Power (ISSN 0748-4658); 5; 129-133
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  • 5
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    Application of the complex cepstrum to locate acoustic sources near reflective surfaces (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Keywords: ACOUSTICS
    Type: AIAA Journal (ISSN 0001-1452); 26; 905-910
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  • 6
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    Preliminary experiments on active control of fan noise from a turbofan engine (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: In the preliminary experiments reported here, active acoustic sources positioned around the circumference of a turbofan engine were used to control the fan noise radiated forward through the inlet. The main objective was to demonstrate the potential of active techniques to alleviate the noise pollution that will be produced by the next generation of larger engines. A reduction of up to 19 dB in the radiation directivity was demonstrated in a zone that encompasses a 30-deg angle, near the error sensor, while spillover effects were observed toward the lateral direction. The simultaneous control of two tones was also demonstrated using two identical controllers in a parallel control configuration.
    Keywords: ACOUSTICS
    Type: Journal of Sound and Vibration (ISSN 0022-460X); 161; 3; p. 532-537.
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  • 7
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    A neural network for the identification of measured helicopter noise (1991)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The results of a preliminary study of the components of a novel acoustic helicopter identification system are described. The identification system uses the relationship between the amplitudes of the first eight harmonics in the main rotor noise spectrum to distinguish between helicopter types. Two classification algorithms are tested; a statistically optimal Bayes classifier, and a neural network adaptive classifier. The performance of these classifiers is tested using measured noise of three helicopters. The statistical classifier can correctly identify the helicopter an average of 67 percent of the time, while the neural network is correct an average of 65 percent of the time. These results indicate the need for additional study of the envelope of harmonic amplitudes as a component of a helicopter identification system. Issues concerning the implementation of the neural network classifier, such as training time and structure of the network, are discussed.
    Keywords: CYBERNETICS
    Type: AHS Annual Forum; May 06, 1991 - May 08, 1991; Phoenix, AZ; United States
    Format: text
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  • 8
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    Sparse distributed associative memory for the identification of aerospace acoustic sources (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Keywords: ACOUSTICS
    Type: AIAA Journal (ISSN 0001-1452); 31; 9; p. 1583-1589.
    Format: text
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