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At least 667 records · Page 37

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NASA NTRS2008

Potential Use of a Bayesian Network for Discriminating Flash Type from Future GOES-R Geostationary Lightning Mapper (GLM) data

Continuous monitoring of the ratio of cloud flashes to ground flashes may provide a better understanding of thunderstorm dynamics, intensification, and evolution, and it may be useful in severe weather warning. The National Lighting Detection Network TM (NLDN) senses ground flashes with exceptional detection efficiency and accuracy over most of the continental United States. A proposed Geostationary Lightning Mapper (GLM) aboard the Geostationary Operational Environmental Satellite (GOES-R) will look at the western hemisphere, and among the lightning data products to be made available will be the fundamental optical flash parameters for both cloud and ground flashes: radiance, area, duration, number of optical groups, and number of optical events. Previous studies have demonstrated that the optical flash parameter statistics of ground and cloud lightning, which are observable from space, are significantly different. This study investigates a Bayesian network methodology for discriminating lightning flash type (ground or cloud) using the lightning optical data and ancillary GOES-R data. A Directed Acyclic Graph (DAG) is set up with lightning as a "root" and data observed by GLM as the "leaves." This allows for a direct calculation of the joint probability distribution function for the lighting type and radiance, area, etc. Initially, the conditional probabilities that will be required can be estimated from the Lightning Imaging Sensor (LIS) and the Optical Transient Detector (OTD) together with NLDN data. Directly manipulating the joint distribution will yield the conditional probability that a lightning flash is a ground flash given the evidence, which consists of the observed lightning optical data [and possibly cloud data retrieved from the GOES-R Advanced Baseline Imager (ABI) in a more mature Bayesian network configuration]. Later, actual GLM and NLDN data can be used to refine the estimates of the conditional probabilities used in the model; i.e., the Bayesian network is a learning network. Methods for efficient calculation of the conditional probabilities (e.g., an algorithm using junction trees), finding data conflicts, goodness of fit, and dealing with missing data will also be addressed.

Solakiewiz, Richard↗

NASA NTRS1985

Measurements in liquid fuel sprays

A ground test facility is being established at NASA Lewis Research Center to simulate the environmental and flight conditions needed to study adverse weather effects. One of the most important components is the water spray system which consists of many nozzles fitted on spray bars. Water is injected through air-assisted atomizers to generate uniform size drops to simulate icing in clouds. The primary objective is to provide experimental data on drop size distribution over a wide range of operating conditions. Correlation equations for mean drop size and initial injection parameters are being determined to assist in the design and modification of the Altitude Wind Tunnel. Special emphasis is being placed on the study of the aerodynamic structure of the air-assisted atomizer sprays. Detailed measurements of the variation of drop size distribution and velocity as a function of time and space are being made. Accurate initial and boundary conditions are being provided for computer model evaluation.

Chigier, N.↗

NASA NTRS1988

Imaging and spectroscopy of Comet P/Halley

The goals of this investigation are the analysis of a large set of high-resolution echelle/reticon spectra, and the reduction and analysis of a set of narrow-band-filtered charge coupled device (CCD) images of Comet Halley taken during the preperihelion period at Oak Ridge Observatory by Dr. R. E. McCrosky. The scientific objectives associated with these goals are the determination of the spatial distributions of several important radicals, atoms and ions in the coma. These include C2, CN, C3, H2O(+) and CO(+) from the image data. The analysis of the neutral species distribution with Monte Carlo models will aid in the understanding of their production and decay mechanisms as well as serve as an important indicator of the physical conditions in the inner coma. The spatial distributions of the ions will serve as a guide to constrain the complex model necessary for understanding the interaction of the solar wind and the cometary ions. Work during this past year has been devoted largely to the reduction of the standard star photometry for the CCD image data set, as well as the re-flat-fielding of a number of the comet images. We are pleased to report that despite a number of setbacks and the small effort devoted to this work (2 1/2 months for the PI and a generous share of completely unsupported time by Dr. McCrosky) that this portion of the work has been successfully completed. The goals for the upcoming final year of this project (under a new project number) are to complete the calibration of the CCD image data for inclusion in the IHW archive, to analyze a select portion of the neutral radical images with our Monte Carlo models, and to present the results of the 6300/region spectra as a guide to low-resolution spectral observers in order to yield the unambiguous separation of the contributions of cometary O(1D), airglow O(1D), and the numerous NH2 lines in that region of the spectrum.

Combi, Michael R.↗

NASA NTRS1992

Fast adaptive composite grid methods on distributed parallel architectures

The fast adaptive composite (FAC) grid method is compared with the adaptive composite method (AFAC) under variety of conditions including vectorization and parallelization. Results are given for distributed memory multiprocessor architectures (SUPRENUM, Intel iPSC/2 and iPSC/860). It is shown that the good performance of AFAC and its superiority over FAC in a parallel environment is a property of the algorithm and not dependent on peculiarities of any machine.

Lemke, Max↗

NASA NTRS2005

Discontinuous pore fluid distribution under microgravity--KC-135 flight investigations

Designing a reliable plant growth system for crop production in space requires the understanding of pore fluid distribution in porous media under microgravity. The objective of this experimental investigation, which was conducted aboard NASA KC-135 reduced gravity flight, is to study possible particle separation and the distribution of discontinuous wetting fluid in porous media under microgravity. KC-135 aircraft provided gravity conditions of 1, 1.8, and 10(-2) g. Glass beads of a known size distribution were used as porous media; and Hexadecane, a petroleum compound immiscible with and lighter than water, was used as wetting fluid at residual saturation. Nitrogen freezer was used to solidify the discontinuous Hexadecane ganglia in glass beads to preserve the ganglia size changes during different gravity conditions, so that the blob-size distributions (BSDs) could be measured after flight. It was concluded from this study that microgravity has little effect on the size distribution of pore fluid blobs corresponding to residual saturation of wetting fluids in porous media. The blobs showed no noticeable breakup or coalescence during microgravity. However, based on the increase in bulk volume of samples due to particle separation under microgravity, groups of particles, within which pore fluid blobs were encapsulated, appeared to have rearranged themselves under microgravity.

manned↗

NASA NTRS1975

Comparison of experimental and theoretical boundary-layer separation for inlets at incidence angle at low-speed conditions

Comparisons between experimental and theoretical Mach number distributions and separation locations are presented for the internal surfaces of four different subsonic inlet geometries with exit diameters of 13.97 centimeters. The free stream Mach number was held constant at 0.127, the one-dimensional throat Mach number ranged from 0.49 to 0.71, and the incidence angle ranged from 0 deg to 50 deg. Generally good agreement was found between the theoretical and experimental surface Mach number distributions as long as no flow separation existed. At high incidence angles, where separation was obvious in the experimental data, the theory predicted separation on the lip. At lower incidence angles, the theoretical results indicated diffuser separation which was not obvious from the experimental surface Mach number distributions. As incidence angle was varied from 0 deg to 50 deg, the predicted separation location shifted from the diffuser region to the inlet highlight. Relatively small total pressure losses were obtained when the predicted separation location was greater than 0.6 of the distance between the highlight and the diffuser exit.

Felderman, E. J.↗

NASA NTRS1979

Collisional evolution of the mass-distribution spectrum of planetesimals. II

An investigation of conditions for the early growth of planetesimals through their mutual collisions using Monte Carlo technique is presented. Rebound, erosion, catastrophic breakup, and coagulation are considered, mean random velocity is assumed to vary with time, and growth of km-sized planetesimals is shown to occur only when they have the mechanical properties similar to iron meteorites. The formation time of several hundred-km sized planetesimals is much longer than previously reported by Greenberg (1978), and an expression was derived for the temporal variation of the mean mass.

Matsui, T.↗

NASA NTRS1975

Analysis of organic matter in sediments and meteorites and paleochemical studies of extinct and contemporary life forms

The insoluble organic materials present in the algal mats at Laguna Mormona, Baja California were studied. A series of six identical sediments collected from Mono lake which were stored under different conditions was investigated to see if any changes are observed in the lipid distribution patterns as a result of differences in sample storage conditions. Bacteria strains from Mono Lake sediments were cultured in bulk quantities and the sterol fractions from them were isolated and analyzed. Results add further support to the utility of the sterols as a chemotaxonomical tool in distinguishing and classifying these bacteria.

Calvin, M.↗

NASA NTRS1989

Aerosol in the Pacific troposphere

The use of near real-time optical techniques is emphasized for the measurement of mid-tropospheric aerosol over the Central Pacific. The primary focus is on measurement of the aerosol size distribution over the range of particle diameters from 0.15 to 5.0 microns that are essential for modeling CO2 backscatter values in support of the laser atmospheric wind sounder (LAWS) program. The measurement system employs a LAS-X (Laser Aerosol Spectrometer-PMS, Boulder, CO) with a custom 256 channel pulse height analyzer and software for detailed measurement and analysis of aerosol size distributions. A thermal preheater system (Thermo Optic Aerosol Descriminator (TOAD) conditions the aerosol in a manner that allows the discrimination of the size distribution of individual aerosol components such as sulfuric acid, sulfates and refractory species. This allows assessment of the relative contribution of each component to the BCO2 signal. This is necessary since the different components have different sources, exhibit independent variability and provide different BCO2 signals for a given mass and particle size. Field activities involve experiments designed to examine both temporal and spatial variability of these aerosol components from ground based and aircraft platforms.

Clarke, Antony D.↗

NASA NTRS1993

Influence of ambient air pressure on effervescent atomization

The influence of ambient air pressure on the drop-size distributions produced in effervescent atomization is examined in this article. Also investigated are the effects on spray characteristics of variations in air/liquid mass ratio, liquid-injection pressure, and atomizer discharge-orifice diameter at different levels of ambient air pressure. It is found that continuous increase in air pressure above the normal atmospheric value causes the mean drop-size to first increase up to a maximum value and then decline. An explanation for this characteristic is provided in terms of the various contributing factors to the overall atomization process. It is also observed that changes in atomizer geometry and operating conditions have little effect on the distribution of drop-sizes in the spray.

Chen, S. K.↗

DOE OSTI2024

Data-driven nonlocal model for fragmentation in the crushing of solids

A technique is proposed for reproducing particle size distributions in three-dimensional simulations of the crushing and comminution of solid materials. The method is designed to produce realistic distributions over a wide range of loading conditions, especially for small fragments. In contrast to most existing methods, the new model does not explicitly treat the small-scale process of fracture. Instead, it uses measured fragment distributions from laboratory tests as the basic material property that is incorporated into the algorithm, providing a data-driven approach. The algorithm is implemented within a nonlocal peridynamic solver, which simulates the underlying continuum mechanics and contact interactions between fragments after they are formed. Finally, the technique is illustrated in reproducing fragmentation data from drop weight testing on sandstone samples.

58 GEOSCIENCES↗

NASA NTRS1979

A passive microwave technique for profiling of atmospheric water vapor

There is considerable interest in remote measurements of the vertical distribution of water vapor, particularly under cloud conditions. The net integrated amount of water vapor has been measured using the 22.235-GHz water vapor line (Staelin et al., 1975). Attempts to use this line for obtaining vertical distribution information have not been fruitful because of the weakness of absorption even at line center. The 183.310-GHz line is much stronger and thus provides a possibility of profiling water vapor. The paper presents a preliminary analysis of this possibility. A technique is described for retrieval of water vapor profiles from microwave radiometric measurements near the 183-GHz water vapor line, and weighting functions useful in the retrievals are developed. The results suggest that microwave radiometry near the 183-GHz water vapor line could yield interesting water vapor profiles, at least over oceans.

Schaerer, G.↗

NASA NTRS2015

System and Method for Monitoring Distributed Asset Data

A computer-based monitoring system and monitoring method implemented in computer software for detecting, estimating, and reporting the condition states, their changes, and anomalies for many assets. The assets are of same type, are operated over a period of time, and outfitted with data collection systems. The proposed monitoring method accounts for variability of working conditions for each asset by using regression model that characterizes asset performance. The assets are of the same type but not identical. The proposed monitoring method accounts for asset-to-asset variability; it also accounts for drifts and trends in the asset condition and data. The proposed monitoring system can perform distributed processing of massive amounts of historical data without discarding any useful information where moving all the asset data into one central computing system might be infeasible. The overall processing is includes distributed preprocessing data records from each asset to produce compressed data.

Gorinevsky, Dimitry↗

NASA NTRS1993

Dynamic of Langmuir and Ion-Sound Waves in Type 3 Solar Radio Sources

The evolution of Langmuir and ion-sound waves in type 3 sources is investigated, incorporating linear growth, linear damping, and nonlinear electrostatic decay. Improved estimates are obtained for the wavenumber range of growing waves and the nonlinear coupling coefficient for the decay process. The resulting prediction for the electrostatic decay threshold is consistent with the observed high-field cutoff in the Langmuir field distribution. It is shown that the conditions in the solar wind do not allow a steady state to be attained; rather, bursty linear and nonlinear interactions take place, consistent with the highly inhomogeneous and impulsive waves actually observed. Nonlinear growth is found to be fast enough to saturate the growth of the parent Langmuir waves in the available interaction time. The resulting levels of product Langmuir and ion-sound waves are estimated theoretically and shown to be consistent with in situ ISEE 3 observations of type 3 events at 1 AU. Nonlinear interactions slave the growth and decay of product sound waves to that of the product Langmuir waves. The resulting probability distribution of ion-sound field strengths is predicted to have a flat tail extending to a high-field cutoff. This prediction is consistent with statistics derived here from ISEE 3 observations. Agreement is also found between the frequencies of the observed waves and predictions for the product S waves. The competing processes of nonlinear wave collapse and quasilinear relaxation are discussed, and it is concluded that neither is responsible for the saturation of Langmuir growth. When wave and beam inhomogeneities are accounted for, arguments from quasi-linear relaxation yield an upper bound on the Langmuir fields that is too high to be relevant. Nor are the criteria for direct wave collapse of the beam-driven waves met, consistent with earlier simulation results that imply that this process is not responsible for saturation of the beam instability. Indeed, even if the highest observed Langmuir fields are assumed to he part of a long-wavelength 'condensate' produced via electrostatic decay, they still fall short of the relevant requirements for wave collapse. The most stringent requirement for collapse is that collapsing wave packets not be disrupted by ambient density fluctuations in the solar wind. Fields of several mV m(exp -1) extending over several hundred km would be needed to satisfy this requirement; at 1 AU such fields are rare at best.

Robinson, P. A.↗

NASA NTRS1978

Characterization of a swept-strut hydrogen fuel-injector for scramjet applications

Results of an experimental investigation of a swept-strut hydrogen fuel-injector simulating the center strut of a three strut scramjet module at Mach 6 flight conditions are presented. Detailed wall pressure distributions from over 100 separate tests with overall fuel flow from 0.1 to 1.3 times stoichiometric and test gas stagnation temperature from 1100 to 2400 K were recorded. The distance for pressure rise from the point of injection was found to increase with increasing test stagnation temperature. This trend indicates that chemical kinetics in the immediate region of perpendicular injection are not likely to be the mechanism controlling the onset of pressure rise. A fluid dynamic mechanism is suggested involving separation of the boundary layer downstream of injection which is forced upstream from the trailing edge by pressure rise due to combustion occurring in the base region of the strut. The results obtained indicate that the swept-strut fuel-injector concept can be adapted to a wide range of flight conditions by varying the amount of perpendicular fuel injection.

Northam, G. B.↗

NASA NTRS1989

Laboratory measurements of the 7.5-9.38-mm absorption of gaseous ammonia (NH3) under simulated Jovian conditions

An attempt is made to infer the abundance and distribution of ammonia from RF emission measurements more accurately than heretofore, on the basis of the results of laboratory measurements for the mm-wave opacity of gaseous ammonia under simulated Jovian atmosphere conditions. The measurements were conducted at various frequencies in the 32-40 GHz range at 2 atm and 203 K; the atmospheric mixture was 88.34 percent H2, 9.81 percent He, and 1.85 percent NH3. Experimental results are found to be readily modeled by the Gross (1955) line-shape factor, rather than that of Van Vleck and Weisskopf (1945).

Joiner, Joanna↗

NASA NTRS1979

Improvements in surface singularity analysis and design methods

The coupling of the combined source vortex distribution of Green's potential flow function with contemporary numerical techniques is shown to provide accurate, efficient, and stable solutions to subsonic inviscid analysis and design problems for multi-element airfoils. The analysis problem is solved by direct calculation of the surface singularity distribution required to satisfy the flow tangency boundary condition. The design or inverse problem is solved by an iteration process. In this process, the geometry and the associated pressure distribution are iterated until the pressure distribution most nearly corresponding to the prescribed design distribution is obtained. Typically, five iteration cycles are required for convergence. A description of the analysis and design method is presented, along with supporting examples.

Bristow, D. R.↗

NASA NTRS1975

Technology survey of electrical power generation and distribution for MIUS application

Candidate electrical generation power systems for the modular integrated utility systems (MIUS) program are described. Literature surveys were conducted to cover both conventional and exotic generators. Heat-recovery equipment associated with conventional power systems and supporting equipment are also discussed. Typical ranges of operating conditions and generating efficiencies are described. Power distribution is discussed briefly. Those systems that appear to be applicable to MIUS have been indicated, and the criteria for equipment selection are discussed.

Gill, W. L.↗