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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Observations of geographically correlated orbit errors for TOPEX/Poseidon using the global positioning system

We have compared Global Positioning System (GPS)-based dynamic and reduced-dynamic TOPEX/Poseidon orbits over three 10-day repeat cycles of the ground-track. The results suggest that the prelaunch joint gravity model (JGM-1) introduces geographically correlated errors (GCEs) which have a strong meridional dependence. The global distribution and magnitude of these GCEs are consistent with a prelaunch covariance analysis, with estimated and predicted global rms error statistics of 2.3 and 2.4 cm rms, respectively. Repeating the analysis with the post-launch joint gravity model (JGM-2) suggests that a portion of the meridional dependence observed in JGM-1 still remains, with global rms error of 1.2 cm.

Christensen, E. J.↗
NASA NTRS1994

Coherent variations of monthly mean total ozone and lower stratospheric temperature

Space-time patterns of correlation between total ozone and lower stratospheric temperature are documented, based on 14 years (1979-1992) of global monthly mean observations. Data are obtained from the total ozone mapping spectrometer (TOMS) and microwave sounding unit (MSU) channel 4, the latter being a weighted mean temperature of the 150- to 50-mbar layer. These data are analyzed (separately) for linear trend, solar cycle, quasi-biennial oscillation (QBO), and El Nino-Southern Oscillation (ENSO) variations via linear regression: significant signals are identified for each term, and the corresponding structures in ozone and temperature are found to be highly coherent. The temperature trends derived here show significant cooling of the lower stratosphere over Northern Hemisphere (NH) midlatitudes in winter-spring and over Antarctica in Southern Hemisphere (SH) spring; the overall space-time patterns are similar to those determined for ozone trends. Interestingly, temperatures do not decrease over SH midlatitudes during midwinter, in spite of large ozone losses. These data furthermore show globally coherent ozone and temperature perturbations associated with both QBO and ENSO variations; a new result here show large total ozone anomalies in middle-to-high latitudes of both hemispheres associated with ENSO events. Residuals from the ozone and temperature time series (defined as the deseasonalized total minus the regression fits) show strong positive correlation in middle-to-high latitudes but weak correlations in the trop ics. Time periods following the volcanic eruptions of El Chichon and Pinatubo are clearly identified from the coupled signatures of decreased ozone and increased temperature, opposite to the positive ozone-temperature correlations observed at other times. The ratios of ozone to temperature anomalies derived here show quantitative signatures indicating that either radiative (trend, solar, and QBO) or dynamical (ENSO and residuals) processes are responsible for the strong ozone-temperature correlations.

Randel, William J.↗
NASA NTRS1982

Correlation and assessment of structural airplane crash data with flight parameters at impact

Crash deceleration pulse data from a crash dynamics program on general aviation airplanes and from transport crash data were analyzed. Structural airplane crash data and flight parameters at impact were correlated. Uncoupled equations for the normal and longitudinal floor impulses in the cabin area of the airplane were derived, and analytical expressions for structural crushing during impact and horizontal slide out were also determined. Agreement was found between experimental and analytical data for general aviation and transport airplanes over a relatively wide range of impact parameter. Two possible applications of the impulse data are presented: a postcrash evaluation of crash test parameters and an assumed crash scenario.

Carden, H. D.↗
NASA NTRS1985

Estimating unsteady aerodynamic forces on a cascade in a three-dimensional turbulence field

An analytical method has been developed to estimate the unsteady aerodynamic forces caused by flow field turbulence on a wind tunnel turning vane cascade system (vane set). This method approximates dynamic lift and drag by linearly perturbing the appropriate steady state force equations, assuming that the dynamic loads are due only to free stream turbulence and that this turbulence is homogeneous, isotropic, and Gaussian. Correlation and unsteady aerodynamic effects are also incorporated into the analytical model. Using these assumptions, equations relating dynamic lift and drag to flow turbulence, mean velocity, and vane set geometry are derived. From these equations, estimates for the power spectra and rms (root mean squared value, delta) loading of both lift and drag can be determined.

Norman, T.↗
NASA NTRS1986

Estimating unsteady aerodynamic forces on a cascade in a three-dimensional turbulence field

An analytical method has been developed to estimate tne unsteady aerodynamic forces caused by flow field turbulence on a wind tunnel turning vane cascade system (vane set). This method approximates dynamic lift and drag by linearly perturbing the appropriate steady state force equations, assuming that the dynamic loads are due only to free stream turbulence and that this turbulence is homogeneous, isotropic, and Gaussian. Correlation and unsteady aerodynamic effects are also incorporated into the analytical model. Using these assumptions, equations relating dynamic lift and drag to flow turbulence, mean velocity, and vane set geometry are derived. From these equations, estimates for the power spectra and rms (root mean squared value, delta) loading of both lift and drag can be determined.

Norman, T. R.↗
NASA NTRS2011

The Radio/Gamma-Ray Connection in Active Galactic Nuclei in the Era of the Fermi Large Area Telescope

We present a detailed statistical analysis of the correlation between radio and gamma-ray emission of the active galactic nuclei (AGNs) detected by Fermi during its first year of operation, with the largest data sets ever used for this purpose.We use both archival interferometric 8.4 GHz data (from the Very Large Array and ATCA, for the full sample of 599 sources) and concurrent single-dish 15 GHz measurements from the OwensValley RadioObservatory (OVRO, for a sub sample of 199 objects). Our unprecedentedly large sample permits us to assess with high accuracy the statistical significance of the correlation, using a surrogate data method designed to simultaneously account for common-distance bias and the effect of a limited dynamical range in the observed quantities. We find that the statistical significance of a positive correlation between the centimeter radio and the broadband (E > 100 MeV) gamma-ray energy flux is very high for the whole AGN sample, with a probability of <10(exp -7) for the correlation appearing by chance. Using the OVRO data, we find that concurrent data improve the significance of the correlation from 1.6 10(exp -6) to 9.0 10(exp -8). Our large sample size allows us to study the dependence of correlation strength and significance on specific source types and gamma-ray energy band. We find that the correlation is very significant (chance probability < 10(exp -7)) for both flat spectrum radio quasars and BL Lac objects separately; a dependence of the correlation strength on the considered gamma-ray energy band is also present, but additional data will be necessary to constrain its significance.

Ackermann, M.↗
NASA NTRS2001

Evaluation of Test/Analysis Correlation Methods for Crash Applications

A project has been initiated to improve crash test and analysis correlation. The work in this paper concentrated on the test and simulation results for a fuselage section. Two drop tests of the section were conducted. The first test was designed to excite the linear structural response for comparison with finite element modal analysis results. The second test was designed to provide data for correlation with crash simulations. An MSC.Dytran model was developed to generate nonlinear transient dynamic results. Following minor modifications, the same model was executed in MSC.Nastran to generate modal analysis results. The results presented in this paper concentrate on evaluation of correlation methodologies for crash test data and finite element simulation results.

Lyle, Karen H.↗
NASA NTRS1988

Precise orbit determination for NASA's earth observing system using GPS (Global Positioning System)

An application of a precision orbit determination technique for NASA's Earth Observing System (EOS) using the Global Positioning System (GPS) is described. This technique allows the geometric information from measurements of GPS carrier phase and P-code pseudo-range to be exploited while minimizing requirements for precision dynamical modeling. The method combines geometric and dynamic information to determine the spacecraft trajectory; the weight on the dynamic information is controlled by adjusting fictitious spacecraft accelerations in three dimensions which are treated as first order exponentially time correlated stochastic processes. By varying the time correlation and uncertainty of the stochastic accelerations, the technique can range from purely geometric to purely dynamic. Performance estimates for this technique as applied to the orbit geometry planned for the EOS platforms indicate that decimeter accuracies for EOS orbit position may be obtainable. The sensitivity of the predicted orbit uncertainties to model errors for station locations, nongravitational platform accelerations, and Earth gravity is also presented.

Williams, B. G.↗
NASA NTRS2016

Application of High Speed Digital Image Correlation in Rocket Engine Hot Fire Testing

Hot fire testing of rocket engine components and rocket engine systems is a critical aspect of the development process to understand performance, reliability and system interactions. Ground testing provides the opportunity for highly instrumented development testing to validate analytical model predictions and determine necessary design changes and process improvements. To properly obtain discrete measurements for model validation, instrumentation must survive in the highly dynamic and extreme temperature application of hot fire testing. Digital Image Correlation has been investigated and being evaluated as a technique to augment traditional instrumentation during component and engine testing providing further data for additional performance improvements and cost savings. The feasibility of digital image correlation techniques were demonstrated in subscale and full scale hotfire testing. This incorporated a pair of high speed cameras to measure three-dimensional, real-time displacements and strains installed and operated under the extreme environments present on the test stand. The development process, setup and calibrations, data collection, hotfire test data collection and post-test analysis and results are presented in this paper.

Gradl, Paul R.↗
NASA NTRS2014

Physical and Dynamical Linkages Between Lightning Jumps and Storm Conceptual Models

The presence and rates of total lightning are both correlated to and physically dependent upon storm updraft strength, mixed phase precipitation volume and the size of the charging zone. The updraft modulates the ingredients necessary for electrification within a thunderstorm, while the updraft also plays a critical role in the development of severe and hazardous weather. Therefore utilizing this relationship, the monitoring of lightning rates and jumps provides an additional piece of information on the evolution of a thunderstorm, more often than not, at higher temporal resolution than current operational radar systems. This correlation is the basis for the total lightning jump algorithm that has been developed in recent years. Currently, the lightning jump algorithm is being tested in two separate but important efforts. Schultz et al. (2014; this conference) is exploring the transition of the algorithm from its research based formulation to a fully objective algorithm that includes storm tracking, Geostationary Lightning Mapper (GLM) Proxy data and the lightning jump algorithm. Chronis et al. (2014) provides context for the transition to current operational forecasting using lightning mapping array based products. However, what remains is an end-to-end physical and dynamical basis for coupling total lightning flash rates to severe storm manifestation, so the forecaster has a reason beyond simple correlation to utilize the lightning jump algorithm within their severe storm conceptual models. Therefore, the physical basis for the lightning jump algorithm in relation to severe storm dynamics and microphysics is a key component that must be further explored. Many radar studies have examined flash rates and their relationship to updraft strength, updraft volume, precipitation-sized ice mass, etc.; however, their relationship specifically to lightning jumps is fragmented within the literature. Thus the goal of this study is to use multiple Doppler and polarimetric radar techniques to resolve the physical and dynamical storm characteristics specifically around the time of the lightning jump. This information will help forecasters anticipate lightning jump occurrence, or even be of use to determine future characteristics of a given storm (e.g., development of a mesocyclone, downdraft, or hail signature on radar), providing additional lead time/confidence in the severe storm warning paradigm.

Schultz, Christopher J.↗
NASA NTRS1972

Derivation of mass and stiffness matrices from dynamic test data.

A technique is described by which orthonormal modal vectors, computed from dynamic test response data, are used to derive mass, stiffness, and damping matrices for a discrete model of the distributed elastic system. Matrices thus computed from subsystems tests may be readily incorporated into larger system models. The method has been applied to a test of the Saturn V S-II stage LOX tank-engine support system. The dynamic responses of the discrete model are shown to correlate well with test data throughout the frequency range tested.

Thoren, A. R.↗
NASA NTRS1976

The stellar content of the nuclear regions of Sc galaxies

Stellar-population syntheses based on absolute spectral energy distributions over the wavelength range from 3300 to 10,400 A are used to determine the stellar content of the nuclear regions of seven nearby Sc galaxies (NGC 628, 1073, 1084, 1637, 2903, 4321, and 5194). A linear-programming procedure is employed to construct models of the overall stellar populations whose spectra closely match those of the seven galaxies. Absolute measurements of the emission-line spectra of the nuclear regions are also provided. It is found that: (1) intrinsic reddening is probably present in each nuclear region; (2) the upper main sequence is substantially populated in most of the models; (3) the lower main sequence contributes insignificantly to the luminosity in all optimal solutions; (4) substantial contributions are made by evolved M stars at long wavelengths in all the models; (5) the model photometric M/L ratios are low, of the order of unity; and (6) the O-B stars arising naturally in the population models are just sufficient to provide the observed nuclear ionization in all the galaxies except NGC 5194, which may be collisionally ionized. The properties of the nuclear regions are shown to be consistent with the existence of a common initial mass function for star formation and a variety of time dependences for the star-formation process. A possibly significant correlation is noted between nuclear stellar content and overall dynamical properties in four of the galaxies.

Turnrose, B. E.↗
NASA NTRS1982

The residue-measure criterion for model reduction in the analysis of the NASA Space Shuttle's digital flight control system

A residue-measure criterion model reduction technique is applied to the vehicle dynamics model used in the design and analysis of the NASA Space Shuttle's digital flight control system. As implemented in this study the residue-measure technique involved an a priori residue calculation with control system biasing. The predictions of the reduced model are compared to vehicle level dynamic stability test data. These comparisons show an excellent correlation of the dominant spectral and response features between the model and test data. In addition, the application of the reduction technique to various Shuttle mission flight phases is demonstrated.

Gluch, D. P.↗
NASA NTRS1984

Hover test of a full-scale hingeless rotor

The performance and aeroelastic stability in hover of a 9.8-m diameter, hingeless helicopter rotor system was evaluated. Rotor performance and inplane damping data were obtained for rotor operation between 350 and 425 rpm for thrust coefficients (CT/sigma) between 0.0 and 0.12. At constant rotor thrust, a minimum in rotor inplane damping was measured at 400 rpm. Good agreement is shown between experimental performance data and predicted performance. The influence of different aerodynamic inflow models on predicting damping levels is also shown. The best correlation with experimental stability data was obtained when a dynamic inflow model was used instead of static or quasistatic inflow models. Comparison with other full scale, hingeless rotor data in hover is presented. The hingeless rotor data and data from a full scale, bearingless main rotor test performed on the same general purpose test apparatus were compared. Although the bearingless rotor was more highly damped at design tip speed and 1-g thrust operation, greater sensitivity to operating conditions is shown. At low thrust levels the bearingless main rotor is less damped than the hingeless rotor.

Warmbrodt, W.↗
NASA NTRS1984

Hover test of a full-scale hingeless rotor

The performance and aeroelastic stability in hover of a 9.8-m diameter, hingeless helicopter rotor system was evaluated. Rotor performance and inplane damping data were obtained for rotor operation beteen 350 and 425 rpm for thrust coefficients (CT/sigma) between 0.0 and 0.12. At constant rotor thrust, a minimum in rotor inplane damping was measured at 400 rpm. Good agreement is shown between experimental performance data and predicted performance. The influence of different aerodynamic inflow models on predicting damping levels is also shown. The best correlation with experimental stability data was obtained when a dynamic inflow model was used instead of static or quasistatic inflow models. Comparison with other full scale, hingeless rotor data in hover is presented. The hingeless rotor data and data from a full scale, bearingless main rotor test performed on the same general purpose test apparatus were compared. Although the bearingless rotor was more highly damped at design tip speed and 1-g thrust operation, greater sensitivity to operating conditions is shown. At low thrust levels the bearingless main rotor is less damped than the hingeless rotor.

Warmbrodt, W.↗
NASA NTRS1987

Approximating SIR-B response characteristics and estimating wave height and wavelength for ocean imagery

NASA Space Shuttle Challenger SIR-B ocean scenes are used to derive directional wave spectra for which speckle noise is modeled as a function of Rayleigh random phase coherence downrange and Poisson random amplitude errors inherent in the Doppler measurement of along-track position. A Fourier filter that preserves SIR-B image phase relations is used to correct the stationary and dynamic response characteristics of the remote sensor and scene correlator, as well as to subtract an estimate of the speckle noise component. A two-dimensional map of sea surface elevation is obtained after the filtered image is corrected for both random and deterministic motions.

Tilley, David G.↗
NASA NTRS1988

Strain Elements For STARDYNE Computer Program

Program "tricked" into calculation of compatible strains. Simple mathematical substitution causes STARDYNE finite-element computer program to put out compatible static or dynamic strains for elements. Strains helpful in effort to correlate strain-guage data with finite-element mathematical models.

Cipra, Dale O.↗
NASA NTRS1988

On the dynamic estimation of relative weights for observation and forecast in numerical weather prediction

The problem of merging direct and remotely sensed (indirect) data with forecast data to get an estimate of the present state of the atmosphere for the purpose of numerical weather prediction is examined. To carry out this merging optimally, it is necessary to provide an estimate of the relative weights to be given to the observations and forecast. It is possible to do this dynamically from the information to be merged, if the correlation structure of the errors from the various sources is sufficiently different. Some new statistical approaches to doing this are described, and conditions quantified in which such estimates are likely to be good.

Wahba, Grace↗