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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

A satellite interpretation of the dynamics of a severe local storms area using 5 minute interval SMS data

Wind fields derived from cloud-tracking on the visible digital data of the Synchronous Meteorological Satellite-2 are used to study the onset of local severe storms. The study is based on an assessment of several dynamic parameters of lower tropospheric wind fields, including the divergence, relative vorticity, and deformation. The automated cloud-tracking proves capable of detecting a preferred area of flow convergence located ahead of a dry line; the detection of this convergence aids in monitoring the onset of a hail-producing thunderstorm.

Peslen, C. A.↗
NASA NTRS1979

Propellant grain dynamics in aft attach ring of shuttle solid rocket booster

An analytical technique for implementing simultaneously the temperature, dynamic strain, real modulus, and frequency properties of solid propellant in an unsymmetrical vibrating ring mode is presented. All dynamic parameters and sources are defined for a free vibrating ring-grain structure with initial displacement and related to a forced vibrating system to determine the change in real modulus. Propellant test data application is discussed. The technique was developed to determine the aft attach ring stiffness of the shuttle booster at lift-off.

Verderaime, V.↗
NASA NTRS1978

Heave-pitch-roll analysis and testing of air cushion landing systems

The analytical tools (analysis and computer simulation) needed to explain and predict the dynamic operation of air cushion landing systems (ACLS) is described. The following tasks were performed: the development of improved analytical models for the fan and the trunk; formulation of a heave pitch roll analysis for the complete ACLS; development of a general purpose computer simulation to evaluate landing and taxi performance of an ACLS equipped aircraft; and the verification and refinement of the analysis by comparison with test data obtained through lab testing of a prototype cushion. Demonstration of simulation capabilities through typical landing and taxi simulation of an ACLS aircraft are given. Initial results show that fan dynamics have a major effect on system performance. Comparison with lab test data (zero forward speed) indicates that the analysis can predict most of the key static and dynamic parameters (pressure, deflection, acceleration, etc.) within a margin of a 10 to 25 percent.

Boghani, A. B.↗
NASA NTRS1977

Time determination for spacecraft users of the Navstar Global Positioning System /GPS/

Global Positioning System (GPS) navigation is performed by time measurements. A description is presented of a two body model of spacecraft motion. Orbit determination is the process of inferring the position, velocity, and clock offset of the user from measurements made of the user motion in the Newtonian coordinate system. To illustrate the effect of clock errors and the accuracy with which the user spacecraft time and orbit may be determined, a low-earth-orbit spacecraft (Seasat) as tracked by six Phase I GPS space vehicles is considered. The obtained results indicate that in the absence of unmodeled dynamic parameter errors clock biases may be determined to the nanosecond level. There is, however, a high correlation between the clock bias and the uncertainty in the gravitational parameter GM, i.e., the product of the universal gravitational constant and the total mass of the earth. It is, therefore, not possible to determine clock bias to better than 25 nanosecond accuracy in the presence of a gravitational error of one part per million.

Grenchik, T. J.↗
NASA NTRS1979

Planetary geodesy

The results of investigations of the geodesy of the planets and their satellites conducted during the period 1975 - 1978 are surveyed. Analysis of the photographic data of Mercury taken by Mariner 10 have revealed the mass, oblateness, radius rotation period and density of the panet, and allowed the high-resolution mapping of the surface. Earth-based radar imagery has permitted the identification of large-scale topographic features on Venus. Knowledge of the gravitational field of Mars has been improved by Mariner 9 and Viking tracking data, and the global topography and geometric figure of Mars have been derived. Doppler and ranging tracking data from the Viking landers have provided data for the precise determination of Martian rotational dynamics and the topographic features and figures of Phobos and Deimos have been observed. Pioneer 10 and 11 data have yielded information on the mass, gravitational field and dynamic parameters of Jupiter. Discoveries of a satellite of Pluto and a set of rings around Uranus have been made, the rotation of Uranus and Neptune have been measured, and the geodetic properties of the rings and satellites of Saturn have been investigated. Future developments in planetary geodesy are expected from continued Viking data and the Pioneer Venus probe and Voyager probes to Jupiter and Saturn.

Michael, W. H., Jr.↗
NASA NTRS1982

Sled Control and Safety System

Computerized system for controlling motion of linear-track accelerator applied to other automated equipment, such as numerically-controlled machine tools and robot manipulators on assembly lines. System controls motions of sled with sine-wave signal created digitally by microprocessor. Dynamic parameters of sled motion are monitored so sled may be stopped safely if malfunction occurs. Sled is capable of sinusoidal accelerations up to 0.5 g with 125-kg load.

Forrest, L. J.↗
NASA NTRS1982

Damping seals for turbomachinery

A rotor seal is proposed that restricts leakage like a labyrinth seal, but extends the stabilizing speed range beyond twice the first critical speed. The dynamic parameters were derived from bulk flow equations without requiring a dominant axial flow. The flow is considered incompressible and turbulent. Damping seals are shown to be feasible for extending the speed range of high performance turbomachinery beyond the limit imposed by conventional seals.

Vonpragenau, G. L.↗
NASA NTRS1981

First results from the Nimbus 7 total ozone mapping spectrometer

The Total Ozone Mapping Spectrometer (TOMS) instrument was launched on the Nimbus 7 satellite in October 1978. This instrument is designed to measure spatial variations in the total ozone field. The employed technique is an extension of the Backscattered Ultraviolet (BUV) total ozone method. The TOMS instrument has an improved capability for detailed monitoring of total ozone. The obtained data appear to contain information about dynamical processes in the upper troposphere and the lower stratosphere. Investigations are being conducted to determine qualitatively the conditions, if any, where total ozone fails as a predictor for tropopause height. Quantitative relations between the dynamic parameters and total ozone are also being studied.

Krueger, A. J.↗
NASA NTRS1982

A parametric study of the behavior of the angular momentum vector during spin rate changes of rigid body spacecraft

During a spin-up or spin-down maneuver of a spinning spacecraft, it is usual to have not only a constant body-fixed torque about the desired spin axis, but also small undesired constant torques about the transverse axes. This causes the orientation of the angular momentum vector to change in inertial space. Since an analytic solution is available for the angular momentum vector as a function of time, this behavior can be studied for large variations of the dynamic parameters, such as the initial spin rate, the inertial properties and the torques. As an example, the spin-up and spin-down maneuvers of the Galileo spacecraft was studied and as a result, very simple heuristic solutions were discovered which provide very good approximations to the parametric behavior of the angular momentum vector orientation.

Longuski, J. M.↗
NASA NTRS1983

Preconditioned Minimal Residual Methods for Chebyshev Spectral Caluclations

The problem of preconditioning the pseudospectral Chebyshev approximation of an elliptic operator is considered. The numerical sensitiveness to variations of the coefficients of the operator are investigated for two classes of preconditioning matrices: one arising from finite differences, the other from finite elements. The preconditioned system is solved by a conjugate gradient type method, and by a DuFort-Frankel method with dynamical parameters. The methods are compared on some test problems with the Richardson method and with the minimal residual Richardson method.

Canuto, C.↗
NASA NTRS1981

Model error estimation for large flexible spacecraft

The basic model obtained for spacecraft control system design applications is used to develop the control and estimation algorithms which constitute integral elements of the control system. The performance of this system is limited on account of modeling errors. The presence of such errors is inevitable in connection with truncated dynamics, parameter uncertainties, neglected nonlinearities, and external disturbances. In many cases, an approximate knowledge of the model errors can only be established by means of an estimation procedure. The present investigation has the objective to outline an approach to estimate errors inherent in a reduced-order model and to illustrate its application to modeling problems arising in spacecraft control system design. The considered procedure makes use of the principle of least-squares. In the discussed application this principle is employed to minimize a quadratic functional of the model errors.

Rodriguez, G.↗
NASA NTRS1985

Response of double wall composite shells

This paper presents an analytical study of double wall laminate cylindrical shell response to random loads. A soft viscoelastic core with dilatational modes included is used. The theory of laminate shells is simplified by assumptions similar to those in the Donnell-Mushtari development for isotropic shells. Modal solutions of simply supported shells are obtained. Modal frequencies and deflection response spectral densities are determined. It is found that this approach allows for easy parametric evaluation and that by proper selection of dynamic parameters, viscoelastic core characteristics and fiber reinforcement orientation, vibration response can be reduced.

Vaicaitis, R.↗
NASA NTRS1985

Fluid Dynamics and Thermodynamics of Vapor Phase Crystal Growth

The ground-based research effort under this program is concerned with systematic studies of the effects of variations: (1) of the relative importance of buoyancy-driven convection, and (2) of diffusion and viscosity conditions on crystal properties. These experimental studies are supported by thermodynamic characterizations of the systems, based on which fluid dynamic parameters can be determined. The specific materials under investigation include: the GeSe-GeI4, Ge-GeI4, HgTe-HgI2, and Hg sub (1-x)Cd sub (x) Te-HgI2 systems. Mass transport rate studies of the GeSe-GeI system as a function of orientation of the density gradient relative to the gravity vector demonstrated the validity of flux anomalies observed in earlier space experiments. The investigation of the effects of inert gases on mass flux yielded the first experimental evidence for the existence of a boundary layer in closed ampoules. Combined with a thorough thermodynamic analysis, a transport model for diffusive flow including chemical vapor transport, sublimation, and Stefan flow was developed.

Wiedemeier, H.↗
NASA NTRS1985

Discrimination of a major stratospheric warming event in February-March 1984 from earlier minor warmings

As part of its responsibility for stratospheric monitoring, the Climate Analysis Center derives time trends of various dynamic parameters from NMC stratospheric analyses. Selected figures from this stratospheric monitoring data base are published in Climate Diagnostics Bulletin in March and October, after each hemispheric winter. During the Northern Hemisphere winter of December 1983-February 1984 several warming events may be seen in the plot of 60 deg. N zonal mean temperatures for 10 mb. Minor warmings may be noted in early December, late December, mid January and early February. A major warming with the 60 deg. N zonal mean temperatures reaching -40C is observed in late February, associated with a circulation reversal. In all of the minor warming episodes, there is a polarward movement of the Aleutian anticyclone; however, at 10 mb the North Pole remains in the cyclonic circulation of the stratospheric vortex which is not displaced far from its usual position. In the case of the later February major warming, the 10 mb circulation pattern over the North Pole is anticyclonic, and the cyclonic circulation has moved to the south and east with a considerable elongation. Cross sections of heat transport and momentum transport are not dramatically different for the minor and major warming episodes.

Johnson, K. W.↗
NASA NTRS1985

Preconditioned minimal residual methods for Chebyshev spectral calculations

The problem of preconditioning the pseudospectral Chebyshev approximation of an elliptic operator is considered. The numerical sensitiveness to variations of the coefficients of the operator are investigated for two classes of preconditioning matrices: one arising from finite differences, the other from finite elements. The preconditioned system is solved by a conjugate gradient type method, and by a Dufort-Frankel method with dynamical parameters. The methods are compared on some test problems with the Richardson method and with the minimal residual Richardson method.

Canuto, C.↗
NASA NTRS1986

Determination of U, V, and W from single station Doppler radar radial velocities

The ST/MST (stratosphere troposphere/mesosphere stratosphere troposphere) clear air Doppler radar, or wind profiler, is an important tool in observational meteorology because of its capability to remote observe dynamic parameters of the atmosphere. There are difficulties in transforming the observed radial velocities into meteorological wind components. How this problem has been treated in the past is reviewed, and some of the analysis is recast to a form more suited to the high diagnostic abilities of a number of fixed beam configurations with reference to a linear wind field. The results, in conjunction with other works which treats problems such as the effects of finite sample volumes in the presence of nonhomogeneous atmospheric reflectivity, have implications important to the design of both individual MST/ST radars and MST/ST radar networks. The key parameters to uncoupling terms in the scaling equations are w sub x and w sub y. Whenever the stratiform condition, which states that these two parameters are negligible, is satisfied, a five beam ST radar may determine unbiased values of u, v, and w for sample volumes directly above the radar. The divergence and partial deformation of the flow may also be determined. Three beam systems can determine w and w sub z, but are unable to obtain u and v wind components uncontaminated by vertical sheer terms, even when the stratiform condition is satisfied.

Clark, W. L.↗
NASA NTRS1986

Radiation fluctuation statistics in satellites and GCM's Cross correlations of albedo and IR with temperature, moisture, and dynamics

Cross-correlations were calculated between the radiation emitted and reflected from the top of the atmosphere and the temperature, horizontal wind and precipitable water in the middle troposphere. The study was extended to the time domain by filtering data for 1-2 and 2.5-6 day periods. The effects of cloud radiation were quantified by comparisons of IR full-sky and clear-sky values. Significant correlations were obtained between the middle atmospheric physical and dynamical parameters and the top of the atmosphere radiation.

Charlock, T. P.↗
NASA NTRS1987

The cooling time scales of growing sunspots

The evolution of brightness and magnetic fields of growing sunspots is studied. Growing sunspots are found to be brighter (or less dark) than stable sunspots with the same magnetic field strength. From comparison of brightness and magnetic fields of a growing sunspot with those of stable sunspots, a dynamical parameter, the cooling time, of the growing sunspot is obtained. Ten growing sunspots are studied, and cooling times of 0.5 to 9 hr are found. Two models, the inhibition model and the Alfven wave model, give cooling times of about 0.05 hr, based on linear theory. The discrepancy between theory and observation may be due to the fact that the observed sunspots are in the nonlinear regime.

Chou, Dean-Yi↗