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  • 1
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    Chemistry Experiments (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The purpose of the chemistry component of the model comparison is to assess to what extent differences in the formulation of chemical processes explain the variance between model results. Observed concentrations of chemical compounds are used to estimate to what degree the various models represent realistic situations. For readability, the materials for the chemistry experiment are reported in three separate sections. This section discussed the data used to evaluate the models in their simulation of the source gases and the Nitrogen compounds (NO(y)) and Chlorine compounds (Cl(y)) species.
    Keywords: Geophysics
    Type: Models and Measurements Intercomparison 2; 190-306; NASA/TM-1999-209554
    Format: text
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  • 2
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    The WCRP/GEWEX Surface Radiation Budget Project Release 2: First Results at 1 Degree Resolution (1999)
    In:  CASI
    Details
    Publication Date: 2018-06-05
    Description: The earth s surface radiative budget in the solar wavelengths (i.e., shortwave) and thermal infrared wavelengths (i.e., longwave) is an important component of Earth s global energy balance and climate. As such, it was identified as a priority need by the World Climate Research Programme (WCRP) and thus a program was instituted at NASA to estimate the radiative flux quantities at the surface from space observations. The Surface Radiation Budget (SRB) Project was created and later included as a component of the Global Energy and Water Cycle Experiment (GEWEX) under the auspices of the WCRP.
    Keywords: Geophysics
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  • 3
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    A simulation-based test bed for data-association algorithms (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A modular All-Source System-evaluation Test bed (ASSET) designed and developed for aiding in the testing and evaluation of advanced data-acquisition algorithms is described, with focus placed on the problem of integrating surveillance information in supporting command decision making. The evaluation procedure employed is based on a measure of the distance between a baseline representation and the representation produced by the association algorithm at some time instant. Choices for the baseline representation are presented, and scores are defined between these baselines and an algorithm representation. The test-bed architecture implementing the evaluation procedure is described, and sample outputs from performing algorithm evaluations in the test bed are outlined.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
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  • 4
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    Nonlinear vibration and radiation from a panel with transition to chaos induced by acoustic waves (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The dynamic response of an aircraft panel forced at resonance and off-resonance by plane acoustic waves at normal incidence is investigated experimentally and numerically. Linear, nonlinear (period doubling) and chaotic responses are obtained by increasing the sound pressure level of the excitation. The response time history is sensitive to the input level and to the frequency of excitation. The change in response behavior is due to a change in input conditions, triggered either naturally or by modulation of the bandwidth of the incident waves. Off-resonance, bifurcation is diffused and difficult to maintain, thus the panel response drifts into a linear behavior. The acoustic pressure emanated by the panel is either linear or nonlinear as is the vibration response. The nonlinear effects accumulate during the propagation with distance. Results are also obtained on the control of the panel response using damping tape on aluminum panel and using a graphite epoxy panel having the same size and weight. Good agreement is obtained between the experimental and numerical results.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: In: DGLR(AIAA Aeroacoustics Conference, 14th, Aachen, Germany, May 11-14, 1992, Proceedings. Vol. 1 (A93-19126 05-71); p. 409-420.
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  • 5
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    Vibration Pattern Imager (VPI): A control and data acquisition system for scanning laser vibrometers (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The Vibration Pattern Imager (VPI) system was designed to control and acquire data from scanning laser vibrometer sensors. The PC computer based system uses a digital signal processing (DSP) board and an analog I/O board to control the sensor and to process the data. The VPI system was originally developed for use with the Ometron VPI Sensor, but can be readily adapted to any commercially available sensor which provides an analog output signal and requires analog inputs for control of mirror positioning. The sensor itself is not part of the VPI system. A graphical interface program, which runs on a PC under the MS-DOS operating system, functions in an interactive mode and communicates with the DSP and I/O boards in a user-friendly fashion through the aid of pop-up menus. Two types of data may be acquired with the VPI system: single point or 'full field.' In the single point mode, time series data is sampled by the A/D converter on the I/O board (at a user-defined sampling rate for a selectable number of samples) and is stored by the PC. The position of the measuring point (adjusted by mirrors in the sensor) is controlled via a mouse input. The mouse input is translated to output voltages by the D/A converter on the I/O board to control the mirror servos. In the 'full field' mode, the measurement point is moved over a user-selectable rectangular area. The time series data is sampled by the A/D converter on the I/O board (at a user-defined sampling rate for a selectable number of samples) and converted to a root-mean-square (rms) value by the DSP board. The rms 'full field' velocity distribution is then uploaded for display and storage on the PC.
    Keywords: ACOUSTICS
    Type: NASA-TM-107721 , NAS 1.15:107721
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  • 6
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    Software For A Laser Vibrometer (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Vibration Pattern Imager (VPI) system and software designed to control and acquire data from laser vibrometer sensors. Based on personal computer, includes digital signal-processing (DSP) board and analog input/output (I/O) circuit board to control sensors and process data. Originally developed for use with Ometron VPI Sensor, adapted to any commercially available sensor that provides analog output signal and requires analog inputs for control of mirror position. VPI system includes graphical user interface providing for interactive control through keyboard and mouse-selected menu options. Main menu controls all functions for setup, acquisition of data, display, file operations, and leaving program. Two types of data acquired with system: single point or "full field". Written in C language and Texas Instrument' TMS320C30 assembly language.
    Keywords: ELECTRONIC SYSTEMS
    Type: LAR-14897 , Laser Tech. Brief.; 2; 4; P. 106
    Format: text
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  • 7
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    Neural network implementations of data association algorithms for sensor fusion (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The paper is concerned with locating a time varying set of entities in a fixed field when the entities are sensed at discrete time instances. At a given time instant a collection of bivariate Gaussian sensor reports is produced, and these reports estimate the location of a subset of the entities present in the field. A database of reports is maintained, which ideally should contain one report for each entity sensed. Whenever a collection of sensor reports is received, the database must be updated to reflect the new information. This updating requires association processing between the database reports and the new sensor reports to determine which pairs of sensor and database reports correspond to the same entity. Algorithms for performing this association processing are presented. Neural network implementation of the algorithms, along with simulation results comparing the approaches are provided.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: Sensor Fusion II; Mar 28, 1989 - Mar 29, 1989; Orlando, FL; United States
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  • 8
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    Generation of Higher Order Modes in a Rectangular Duct (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Advanced noise control methodologies to reduce sound emission from aircraft engines take advantage of the modal structure of the noise in the duct. This noise is caused by the interaction of rotor wakes with downstream obstructions such as exit guide vanes. Mode synthesis has been accomplished in circular ducts and current active noise control work has made use of this capability to cancel fan noise. The goal of the current effort is to examine the fundamental process of higher order mode propagation through an acoustically treated, curved duct. The duct cross-section is rectangular to permit greater flexibility in representation of a range of duct curvatures. The work presented is the development of a feedforward control system to generate a user-specified modal pattern in the duct. The multiple-error, filtered-x LMS algorithm is used to determine the magnitude and phase of signal input to the loudspeakers to produce a desired modal pattern at a set of error microphones. Implementation issues, including loudspeaker placement and error microphone placement, are discussed. Preliminary results from a 9-3/8 inch by 21 inch duct, using 12 loudspeakers and 24 microphones, are presented. These results demonstrate the ability of the control system to generate a user-specified mode while suppressing undesired modes.
    Keywords: Aircraft Design, Testing and Performance
    Type: ACTIVE 04: 2004 International Symposium on Active Control of Sound and Vibration; Sep 20, 2004 - Sep 22, 2004; Williamsburg, VA; United States
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  • 9
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    Nonlinear vibration and radiation from a panel with transition to chaos (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The dynamic response of an aircraft panel forced at resonance and off-resonance by plane acoustic waves at normal incidence is investigated experimentally and numerically. Linear, nonlinear (period doubling), and chaotic responses are obtained by increasing the sound pressure level of the excitation. The response time history is sensitive to the input level and to the frequency of excitation. The change in response behavior is due to a change in input conditions, triggered either naturally or by modulation of the bandwidth of the incident waves. Off-resonance bifurcation is diffused and difficult to maintain; thus the panel response drifts into a linear behavior. The acoustic pressure emanated by the panel is either linear or nonlinear as is the vibration response. The nonlinear effects accumulate during the propagation with distance. Results are also obtained on the control of the panel response using damping tape on an aluminum panel and a graphite epoxy panel having the same size and weight. Good agreement is obtained betwen the experimental and numerical results.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 30; 11; p. 2632-2638.
    Format: text
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  • 10
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    Closed-loop Separation Control Using Oscillatory Flow Excitation (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: Design and implementation of a digital feedback controller for a flow control experiment was performed. The experiment was conducted in a cryogenic pressurized wind tunnel on a generic separated configuration at a chord Reynolds number of 16 million and a Mach number of 0.25. The model simulates the upper surface of a 20% thick airfoil at zero angle-of-attack. A moderate favorable pressure gradient, up to 55% of the chord, is followed by a severe adverse pressure gradient which is relaxed towards the trailing edge. The turbulent separation bubble, behind the adverse pressure gradient, is then reduced by introducing oscillatory flow excitation just upstream of the point of flow separation. The degree of reduction in the separation region can be controlled by the amplitude of the oscillatory excitation. A feedback controller was designed to track a given trajectory for the desired degree of flow reattachment and to improve the transient behavior of the flow system. Closed-loop experiments demonstrated that the feedback controller was able to track step input commands and improve the transient behavior of the open-loop response.
    Keywords: Numerical Analysis
    Type: NASA/CR-2000-210324 , ICASE-2000-32 , NAS 1.26:210324
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