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  • 1
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    Experience with a Genetic Algorithm Implemented on a Multiprocessor Computer (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Numerical experiments were conducted to find out the extent to which a Genetic Algorithm (GA) may benefit from a multiprocessor implementation, considering, on one hand, that analyses of individual designs in a population are independent of each other so that they may be executed concurrently on separate processors, and, on the other hand, that there are some operations in a GA that cannot be so distributed. The algorithm experimented with was based on a gaussian distribution rather than bit exchange in the GA reproductive mechanism, and the test case was a hub frame structure of up to 1080 design variables. The experimentation engaging up to 128 processors confirmed expectations of radical elapsed time reductions comparing to a conventional single processor implementation. It also demonstrated that the time spent in the non-distributable parts of the algorithm and the attendant cross-processor communication may have a very detrimental effect on the efficient utilization of the multiprocessor machine and on the number of processors that can be used effectively in a concurrent manner. Three techniques were devised and tested to mitigate that effect, resulting in efficiency increasing to exceed 99 percent.
    Keywords: Computer Programming and Software
    Type: AIAA Paper 2000-4844 , Multidisciplinary Analysis and Optimization; Sep 06, 2000 - Sep 08, 2000; Long Beach, CA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    NASA Hybrid Wing Aircraft Aeroacoustic Test Documentation Report (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: This report summarizes results of the Hybrid Wing Body (HWB) N2A-EXTE model aeroacoustic test. The N2A-EXTE model was tested in the NASA Langley 14- by 22-Foot Subsonic Tunnel (14x22 Tunnel) from September 12, 2012 until January 28, 2013 and was designated as test T598. This document contains the following main sections: Section 1 - Introduction, Section 2 - Main Personnel, Section 3 - Test Equipment, Section 4 - Data Acquisition Systems, Section 5 - Instrumentation and Calibration, Section 6 - Test Matrix, Section 7 - Data Processing, and Section 8 - Summary. Due to the amount of material to be documented, this HWB test documentation report does not cover analysis of acquired data, which is to be presented separately by the principal investigators. Also, no attempt was made to include preliminary risk reduction tests (such as Broadband Engine Noise Simulator and Compact Jet Engine Simulator characterization tests, shielding measurement technique studies, and speaker calibration method studies), which were performed in support of this HWB test. Separate reports containing these preliminary tests are referenced where applicable.
    Keywords: Acoustics
    Type: NASA/TM-2016-219185 , L-20425 , NF1676L-19028
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    A Survey of Singular Value Decomposition Methods and Performance Comparison of Some Available Serial Codes (2005)
    In:  CASI
    Details
    Publication Date: 2019-08-17
    Description: This contractor report describes a performance comparison of available alternative complete Singular Value Decomposition (SVD) methods and implementations which are suitable for incorporation into point spread function deconvolution algorithms. The report also presents a survey of alternative algorithms, including partial SVD's special case SVD's, and others developed for concurrent processing systems.
    Keywords: Acoustics
    Type: NASA/CR-2005-213500
    Format: application/pdf
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  • 4
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    Experience with a Genetic Algorithm Implemented on a Multiprocessor Computer (2000)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: Numerical experiments were conducted to find out the extent to which a Genetic Algorithm (GA) may benefit from a multiprocessor implementation, considering, on one hand, that analyses of individual designs in a population are independent of each other so that they may be executed concurrently on separate processors, and, on the other hand, that there are some operations in a GA that cannot be so distributed. The algorithm experimented with was based on a gaussian distribution rather than bit exchange in the GA reproductive mechanism, and the test case was a hub frame structure of up to 1080 design variables. The experimentation engaging up to 128 processors confirmed expectations of radical elapsed time reductions comparing to a conventional single processor implementation. It also demonstrated that the time spent in the non-distributable parts of the algorithm and the attendant cross-processor communication may have a very detrimental effect on the efficient utilization of the multiprocessor machine and on the number of processors that can be used effectively in a concurrent manner. Three techniques were devised and tested to mitigate that effect, resulting in efficiency increasing to exceed 99 percent.
    Keywords: Computer Programming and Software
    Type: AIAA Paper 2000-4844 , Multidisciplinary Analysis and Optimization; Sep 06, 2000 - Sep 08, 2000; Long Beach, CA; United States
    Format: text
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  • 5
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    Linear Multivariable Regression Models for Prediction of Eddy Dissipation Rate from Available Meteorological Data (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-11
    Description: Linear multivariable regression models for predicting day and night Eddy Dissipation Rate (EDR) from available meteorological data sources are defined and validated. Model definition is based on a combination of 1997-2000 Dallas/Fort Worth (DFW) data sources, EDR from Aircraft Vortex Spacing System (AVOSS) deployment data, and regression variables primarily from corresponding Automated Surface Observation System (ASOS) data. Model validation is accomplished through EDR predictions on a similar combination of 1994-1995 Memphis (MEM) AVOSS and ASOS data. Model forms include an intercept plus a single term of fixed optimal power for each of these regression variables; 30-minute forward averaged mean and variance of near-surface wind speed and temperature, variance of wind direction, and a discrete cloud cover metric. Distinct day and night models, regressing on EDR and the natural log of EDR respectively, yield best performance and avoid model discontinuity over day/night data boundaries.
    Keywords: Air Transportation and Safety
    Type: NASA/CR-2005-213504
    Format: application/pdf
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  • 6
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    Airframe Noise from a Hybrid Wing Body Aircraft Configuration (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A high fidelity aeroacoustic test was conducted in the NASA Langley 14- by 22-Foot Subsonic Tunnel to establish a detailed database of component noise for a 5.8% scale HWB aircraft configuration. The model has a modular design, which includes a drooped and a stowed wing leading edge, deflectable elevons, twin verticals, and a landing gear system with geometrically scaled wheel-wells. The model is mounted inverted in the test section and noise measurements are acquired at different streamwise stations from an overhead microphone phased array and from overhead and sideline microphones. Noise source distribution maps and component noise spectra are presented for airframe configurations representing two different approach flight conditions. Array measurements performed along the aircraft flyover line show the main landing gear to be the dominant contributor to the total airframe noise, followed by the nose gear, the inboard side-edges of the LE droop, the wing tip/LE droop outboard side-edges, and the side-edges of deployed elevons. Velocity dependence and flyover directivity are presented for the main noise components. Decorrelation effects from turbulence scattering on spectral levels measured with the microphone phased array are discussed. Finally, noise directivity maps obtained from the overhead and sideline microphone measurements for the landing gear system are provided for a broad range of observer locations.
    Keywords: Acoustics
    Type: NF1676L-22760 , AIAA/CEAS Aeroacoustics Conference; May 30, 2016 - Jun 01, 2016; Lyon; France
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Experimental Study of Wake / Flap Interaction Noise and the Reduction of Flap Side Edge Noise (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The effects of the interaction of a wake with a half-span flap on radiated noise are examined. The incident wake is generated by bars of various widths and lengths or by a simplified landing gear model. Single microphone and phased array measurements are used to isolate the effects of the wake interaction on the noise radiating from the flap side edge and flap cove regions. The effects on noise of the wake generator's geometry and relative placement with respect to the flap are assessed. Placement of the wake generators upstream of the flap side edge is shown to lead to the reduction of flap side edge noise by introducing a velocity deficit and likely altering the instabilities in the flap side edge vortex system. Significant reduction in flap side edge noise is achieved with a bar positioned directly upstream of the flap side edge. The noise reduction benefit is seen to improve with increased bar width, length and proximity to the flap edge. Positioning of the landing gear model upstream of the flap side edge also leads to decreased flap side edge noise. In addition, flap cove noise levels are significantly lower than when the landing gear is positioned upstream of the flap mid-span. The impact of the local flow velocity on the noise radiating directly from the landing gear is discussed. The effects of the landing gear side-braces on flap side edge, flap cove and landing gear noise are shown.
    Keywords: Acoustics; Aerodynamics
    Type: NF1676L-22656 , AIAA/CEAS Aeroacoustics Conference; May 30, 2016 - Jul 01, 2016; Lyon; France
    Format: application/pdf
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  • 8
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    DAMAS Processing for a Phased Array Study in the NASA Langley Jet Noise Laboratory (2010)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A jet noise measurement study was conducted using a phased microphone array system for a range of jet nozzle configurations and flow conditions. The test effort included convergent and convergent/divergent single flow nozzles, as well as conventional and chevron dual-flow core and fan configurations. Cold jets were tested with and without wind tunnel co-flow, whereas, hot jets were tested only with co-flow. The intent of the measurement effort was to allow evaluation of new phased array technologies for their ability to separate and quantify distributions of jet noise sources. In the present paper, the array post-processing method focused upon is DAMAS (Deconvolution Approach for the Mapping of Acoustic Sources) for the quantitative determination of spatial distributions of noise sources. Jet noise is highly complex with stationary and convecting noise sources, convecting flows that are the sources themselves, and shock-related and screech noise for supersonic flow. The analysis presented in this paper addresses some processing details with DAMAS, for the array positioned at 90 (normal) to the jet. The paper demonstrates the applicability of DAMAS and how it indicates when strong coherence is present. Also, a new approach to calibrating the array focus and position is introduced and demonstrated.
    Keywords: Acoustics
    Type: AIAA Paper 2010-3780 , NF1676L-9668 , 16th AIAA/CEAS Aeroacoustics Conference; Jun 07, 2010 - Jun 09, 2010; Stockholm; Sweden
    Format: application/pdf
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