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Results for “Time-varying data”

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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Research on regional numerical weather prediction

Extension of the predictive power of dynamic weather forecasting to scales below the conventional synoptic or cyclonic scales in the near future is assessed. Lower costs per computation, more powerful computers, and a 100 km mesh over the North American area (with coarser mesh extending beyond it) are noted at present. Doubling the resolution even locally (to 50 km mesh) would entail a 16-fold increase in costs (including vertical resolution and halving the time interval), and constraints on domain size and length of forecast. Boundary conditions would be provided by the surrounding 100 km mesh, and time-varying lateral boundary conditions can be considered to handle moving phenomena. More physical processes to treat, more efficient numerical techniques, and faster computers (improved software and hardware) backing up satellite and radar data could produce further improvements in forecasting in the 1980s. Boundary layer modeling, initialization techniques, and quantitative precipitation forecasting are singled out among key tasks.

Kreitzberg, C. W.↗
NASA NTRS1972

Nonlinear and adaptive estimation in reentry.

The problem of real-time estimation of a lifting reentry vehicle trajectory of the shuttle orbiter type is considered. Simulations feature large position and velocity uncertainties at radar acquisition and realistic model errors in lift, drag and other model parameters. Radar tracking and accelerometer data are simulated. Significant nonlinearities are found to exist on spacecraft acquisition. An iterated nonlinear filter is shown to perform optimally during the radar acquisition phase. An adaptive filter is shown to track time-varying model errors, such as errors in the lift and drag coefficients, down to the noise level. Such real-time model tracking (identification) is frequently required for guidance and control implementation.

Jazwinski, A. H.↗
NASA NTRS1975

A review and preliminary evaluation of methodological factors in performance assessments of time-varying aircraft noise effects

The effects of aircraft noise on human performance is considered. Progress is reported in the following areas: (1) review of the literature to identify the methodological and stimulus parameters involved in the study of noise effects on human performance; (2) development of a theoretical framework to provide working hypotheses as to the effects of noise on complex human performance; and (3) data collection on the first of several experimental investigations designed to provide tests of the hypotheses.

Coates, G. D.↗
NASA NTRS1973

A Real-Time Phase Vector Display for EEG Monitoring

A real-time, computer-based, phase vector display system has been developed which will output a vector whose phase is equal to the delay between a trigger and the peak of a function which is quasi-coherent with respect to the trigger. The system also contains a sliding averager which enables the operator to average successive trials before calculating the phase vector. Data collection, averaging and display generation are performed on a LINC-8 computer. Output displays appear on several X-Y CRT display units and on a kymograph camera/oscilloscope unit which is used to generate photographs of time-varying phase vectors or contourograms of time-varying averages of input functions.

Finger, Herbert J.↗
NASA NTRS1978

Bayesian classification in a time-varying environment

The problem of classifying a pattern based on multiple observation made in a time-varying environment is analyzed. The identity of the pattern may itself change. A Bayesian solution is derived, after which the conditions of the physical situation are invoked to produce a cascade classifier model. Experimental results based on remote sensing data demonstrate the effectiveness of the classifier.

Swain, P. H.↗
NASA NTRS1973

Transient characteristics of simple systems to modulated random noise.

Discussed are the mean-square response exceedance characteristics of a single-tuned system to amplitude modulated noise. The results bear on the accuracy of spectral estimates of nonstationary data, and subsequently, relate directly to the design, analysis, and testing of structural systems in environments as gusts, earthquakes, and ignition transients. For noise correlated as an exponentially damped cosine, the nonstationary response may exceed its stationary value by a factor in excess of two. A time-varying shaping filter explanation is offered for this behavior. For white noise, such exceedances do not occur.

Barnoski, R. L.↗
NASA NTRS1977

Thermal inertia mapping - A new view of the earth

The thermal response of a substance to a time-varying surface power input is determined by its thermal inertia. Remote sensing (e.g., from satellites) can be utilized to measure this property, which is related to surface composition or to near-surface soil moisture. An algorithm is developed which relates thermal inertia to remote measurements of surface temperature and reflectance. Application to geosynchronous satellite data illustrates the contrast between irrigated and desert areas in the region north of the Gulf of California. The effect of local weather conditions (latent and sensible heat transfer to the atmosphere) must be estimated before precise values for thermal inertia can be specified.

Price, J. C.↗
NASA NTRS1973

Effects of changing canopy directional reflectance on feature selection

The use of a Monte Carlo model for generating sample directional reflectance data for two simplified target canopies at two different solar positions is reported. Successive iterations through the model permit the calculation of a mean vector and covariance matrix for canopy reflectance for varied sensor view angles. These data may then be used to calculate the divergence between the target distributions for various wavelength combinations and for these view angles. Results of a feature selection analysis indicate that different sets of wavelengths are optimum for target discrimination depending on sensor view angle and that the targets may be more easily discriminated for some scan angles than others. The time-varying behavior of these results is also pointed out.

Smith, J. A.↗
NASA NTRS1978

Time-varying oscillations in the solar soft X-ray flux as observed from Skylab

Observations obtained by the Skylab/Apollo telescope S-056 X-ray experiment were used to study the time-varying oscillations in the solar soft X-ray flux during a flare. The observations consisted of count rates measured every 2.5 s by sealed, gas-filled counters operating over the 2.5-7.25-A and 6.1-20.0-A wavelength ranges. The power spectra for two other intervals were computed to determine whether the observed oscillations were flare-associated or instrumental in origin. The data indicate that the oscillations in the flare-associated X-ray flux are caused by waves which are generated during the flare and which periodically increase the electron density. No oscillations were observed during quiet periods.

Teuber, D. L.↗
NASA NTRS1975

Kinetics of the reaction of nitric oxide with hydrogen

The reaction of nitric oxide with hydrogen has been studied in the temperature range 2400-4500 K using a shock-tube technique. Mixtures of NO and H2 diluted in argon or krypton were heated by incident shock waves, and the infrared emission from the fundamental vibration-rotation band of NO at 5.3 microns was used to monitor the time-varying NO concentration. The decomposition of nitric oxide behind the shock was found to be modeled well by a fifteen-reaction system. A principal result of the study was the determination of the rate constant k1 for the reaction H + NO yields N + OH, which may be the rate-limiting step for NO removal in some combustion systems. Experimental values of k1 were obtained for each test through comparisons of measured and numerically predicted NO profiles. The data are fit closely by the expression k1 = 1.34 times 10 to the fourteenth power exp(-49 200/RT) cu cm/mole-sec. These data appear to be the first available for this rate constant.

Flower, W. L.↗
NASA NTRS1974

Influence of solar wind variability on geomagnetic activity

A statistical study of solar wind data from the Explorer 33 satellite shows that interplanetary magnetic field irregularities are enhanced in the interaction region where a fast solar wind stream overtakes a slower solar wind stream. Comparison with geomagnetic AE and ap indexes further shows that these interplanetary irregularities enhance the level of geomagnetic disturbances. Thus while substorm occurrence is highly correlated with the dawn-dusk component of the solar wind electric field, the amplitude of the substorms is an increasing function of the variance in the interplanetary field. This result can be interpreted as a capacitative effect of the magnetopause that allows a time-varying solar wind electric field to penetrate the magnetosphere more effectively than a static solar wind electric field.

Garrett, H. B.↗
NASA NTRS1971

Lunar conductivity models from the Apollo 12 magnetometer experiment

A number of conductivity models were investigated for compatibility with Apollo 12 magnetometer data. Except at the highest frequencies, a simple core-crust model is compatible with the observed dayside transfer function, which is expressed as the ratio of the lunar surface field spectrum to the interplanetary magnetic field spectrum. All conductivity profiles exhibit a peak near 1500 km, when the models are constrained to conform to the observed flat response at the higher frequencies. However, at frequencies above .01 Hz the long wavelength limitation of the theoretical model is no longer valid. A plausible explanation for the difference between the north-south and east-west transfer functions is that it is due to a time-varying compression of the remanent (dc) field at the Apollo 12 site by fluctuations in the solar wind plasma.

Sill, W. R.↗
NASA NTRS1978

Computed and observed ocean topography - A comparison

The Goddard Space Flight Center's latest Gravity Earth Model, GEM-8, was used to construct a static sea surface. Such a surface corresponds to the surface of an ocean without the time-varying effects of atmospheric pressure, surface wind friction, tides, and currents. It conforms to a surface dictated by the earth's gravitational and rotational forces. The sea surface model is the result of analyzing more than 500,000 satellite observations together with about 1600 5 deg x 5 deg and about 38,000 1 deg x 1 deg surface gravity anomalies. Preliminary comparisons between the computed and measured sea surface topography indicate that they agree quite well and differ by less than 1 m in many places including the Atlantic test area. Sea-surface features such as undulations caused by trenches and ridges are clearly and accurately detectable. The use of altimeter data for orbit computation reduces the uncertainty of the spacecraft height and thus the errors of the sea-surface topography.

Vonbun, F. O.↗
NASA NTRS1973

Marshall system for aerospace system simulation (MARSYAS), user's manual

The capabilities of the Marshall system for aerospace system simulation (MARSYAS) and how to use it are described. MARSYAS is a software system that allows easy setup and control of the simulation of the dynamics of large physical systems on a digital computer. The physical systems are modeled in the form of block diagrams or equations. The blocks can have multiple inputs and multiple outputs, and they can be nested to form hierarchies. The block diagrams can contain transfer functions, nonlinear and logical functions, equations, analog computer elements and FORTRAN programs. The input format of the equations can be combinations of nonlinear, time-varying differential equations and algebraic equations in their original format. MARSYAS could also serve as a storage and retrieval system for models as a basis for a model configuration control system on a central time-shared computer. The outputs of the simulation system can be not only time-responses but also other analysis data such as frequency response, power spectrum and stability parameters. The MARSYAS translator is written in FORTRAN running on the Univac 1108 computer under the EXEC 8 operating system.

Ventre, A.↗
NASA NTRS1973

Time variation in the reaction-zone structure of two-phase spray detonations.

A detailed theoretical analysis of the time-varying detonation structure in a monodisperse spray is presented. The theory identifies experimentally observed reaction-zone overpressures as deriving from blast waves formed therein by the explosive ignition of the spray droplets, and follows in time the motion, change in strength, and interactions of these blast waves with one another, and with the leading shock. The results are compared with experimental data by modeling the motion of a finite-size circular pressure transducer through the theoretical data field in an x-t space.

Pierce, T. H.↗
NASA NTRS1974

Investigation of nitric oxide decomposition in the temperature range 2500-4100 K

The decomposition of nitric oxide has been studied in the temperature range 2500-4100 K using a shock-tube technique. The principle result of the study was the determination of the rate constant (k) for the reaction O + NO yields N + O2. Mixtures of NO and N2O diluted in argon or krypton were heated by incident shock waves and the infrared emission from the fundamental vibration-rotation band of NO at 5.3 microns was used to monitor the time-varying NO concentration. The experimental values of k are fit closely by the expression k = (2.36 times 10 to the 9th power) x T x exp(-38,640/RT) cm cu/mole-sec, which also provides a good fit to previous data at higher and lower temperatures.

Flower, W. L.↗