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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 649 records · Page 36

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NASA NTRS1982

Fluid dynamical description of relativistic nuclear collisions

On the basis of both a conventional relativistic nuclear fluid dynamic model and a two fluid generalization that takes into account the interpenetration of the target and projectile upon contact, collisions between heavy nuclei moving at relativistic speeds are calculated. This is done by solving the relevant equations of motion numerically in three spatial dimensions by use of particle in cell finite difference computing techniques. The effect of incorporating a density isomer, or quasistable state, in the nuclear equation of state at three times normal nuclear density, and the effect of doubling the nuclear compressibility coefficient are studied. For the reaction 20Ne + 238U at a laboratory bombarding energy per nucleon of 393 MeV, the calculated distributions in energy and angle of outgoing charged particles are compared with recent experimental data both integrated over all impact parameters and for nearly central collisions.

Nix, J. R.↗

NASA NTRS1989

The role of shock induced trailing-edge separation in limit cycle oscillations

The potential role of shock induced trailing edge separation (SITES) in limit cycle oscillations (LCO) was established. It was shown that the flip-flop characteristics of transition to and from SITES as well as its hysteresis could couple with wing modes with torsional motion and low damping. This connection led to the formulation of a very simple nonlinear math model using the linear equations of motion with a nonlinear step forcing function with hysteresis. A finite difference solution with time was developed and calculations were made for the F-111 TACT were used to determine the step forcing function due to SITES transition. Since no data were available for the hysteresis, a parameter study was conducted allowing the hysteresis effect to vary. Very small hysteresis effects, which were within expected bounds, were required to obtain reasonable response levels that essentially agreed with flight test results. Also in agreement with wind tunnel tests, LCO calculations for the 1/6 scale F-111 model showed that the model should have not experienced LCO.

Cunningham, Atlee M., Jr.↗

NASA NTRS1988

Aeroelastic effects on stability and control of hingeless rotor helicopters

The combined effect of torsional flexibility and offset of the aerodynamic center relative to the elastic axis on the stability and control of a hingeless rotor helicopter in forward flight is studied in this paper. The aeroelastic model of the blade is based on fully coupled flap-lag-torsion equations of motion, which include kinematic nonlinearities due to moderate deflections. The equations are discretized using a finite element Galerkin method in space, and a classical Galerkin method in time. The vehicle trim calculations are coupled to the blade aeroelastic response calculations. Quasilinearization is used to compute aeroelastic stability. Reducing torsional stiffness and moving the elastic axis ahead of the aerodynamic center strongly stabilizes the phugoid mode without reducing control sensitivity. Aeroelastic stability calculations must accompany flight dynamics calculations to prevent aeroelastic instabilities that might easily go undetected.

Celi, Roberto↗

NASA NTRS1992

Input shaped control of 3-dimensional maneuvers of flexible spacecraft

This paper deals with the control of three dimensional rotational maneuvers of flexible spacecraft. A spacecraft with a spherical hub and six symmetric appendages is considered here as a model. The appendages are long and flexible leading to low frequency vibration under any control action. To provide a comprehensive treatment of input shaped controllers, both open loop and closed loop controllers are considered. The minimum-time bang-bang and the near-minimum-time controller, used in conjunction with the shaped input technique are studied. In addition, a combination of a Liapunov controller with the shaped input control technique is proposed to take advantage of the simple feedback control strategy and augment it with a technique that can eliminate the vibratory motion of the flexible appendages more efficiently.

Singh, T.↗

NASA NTRS1994

Ionospheric dynamics instrument investigation for the Timed Mission

The primary science objectives for the Ionospheric Dynamics Instrument (IDI) investigation are related to the global response of the ITM to energy inputs from the magnetosphere and an understanding of the ways in which electric fields are internally generated by neutral atmosphere motions in the lower thermosphere and mesosphere. At low and mid latitudes the electric fields are generated by neutral atmosphere motions and temporal resolution on time scales of a second will adequately describe the global field and allow its relationship to neutral wind motion to be established. However, the redistribution of current systems and the electrodynamics associated with plasma structures requires temporal sampling rates at the highest possible frequencies. The results of these studies are presented graphically.

Heelis, R. A.↗

NASA NTRS1995

Radial alignment simulation of solar wind streams observed by Pioneers 10 and 11 in 1974

A particularly favorable radial lineup between spacecraft in Earth orbit and Pioneers 10 and 11 (near the ecliptic plane at approximately 5.5 AU and approximately 4.5 AU, respectively) occurred in mid-1974, when the solar corona was in a stable and well-defined warped-dipole configuration. The radial alignment study reported here differs from previous applications of the technique in two respects: (1) It is the first time a two-dimensional (2-D) MHD model has been tested over such a lengthy propagation interval; the 2-D capability is crucial for treatment of the nonradial shearing motions occurring across the stream interface. (2) The three-dimensional (3-D) structure observed in the white light corona at that time is related to the systematic patterns of nonradial flow deflections appearing at the Pioneer corotating interaction region (CIR) fronts. Comparison of predicted and observed flows for pairs of streams in two successive rotations reveals that when the parent coronal hole projects far across the solar equator in a predominantly north-south orientation (i.e., nearest the 2-D idealization), the mapping is accurate down to details of the flow structures. But where the spacecraft tracks along a latitudinal boundary of a hole or the associated stream front is inclined at a shallow angle to the equator, the numerical projections deviate systematically from the observations. Among the sources of error are 3-D dynamical interactions neglected in the model, differential rotation effects, and slow temporal evolution of the coronal structures. A characteristic pattern of north-south and east-west deflections indicative of the 3-D geometry appears across the CIRs, but these patterns evidently reflect primarily the local, as opposed to global, orientation of the 3-D stream fronts. Such patterns appear common in CIRs observed by Pioneer during this period. These findings thus hold special relevance for the analysis of Ulysses observations, since the present coronal configuration is similar to that of 1974.

Pizzo, V. J.↗

NASA NTRS2001

EUNIS: An Extreme-Ultraviolet Normal-Incidence Spectrometer

GSFC is in the process of assembling an Extreme-Ultraviolet Normal-Incidence Spectrometer called EUNIS, to be flown as a sounding rocket payload. This instrument builds on the many technical innovations pioneered by our highly successful SERTS experiment over its past ten flights. The new design will have somewhat improved spatial and spectral resolutions, as well as 100 times greater sensitivity, permitting EUV spectroscopy with a temporal resolution near 1-second for the first time ever. To achieve such high time cadence, a novel Active-Pixel-Sensor detector is being developed as a key component of our design. The high sensitivity of EUNIS will allow entirely new studies of transient coronal phenomena, such as the rapid loop dynamics seen by TRACE, and searches for non-thermal motions indicative of magnetic reconnection or wave heating. The increased sensitivity will also permit useful EUV spectra at heights of 2-3-R$ \odot$ above the limb, where the transition between the static corona and the solar wind might occur. In addition, the new design features two independent optical systems, more than doubling the spectral bandwidth covered on each flight. Its 300-370\AA\ bandpass includes He-II 304\AA\ and strong lines from Fe-XI-XVI, extending the current SERTS range of 300-355\AA\ to further improve our ongoing series of calibration under-flights for SOHO/CDS and EIT. The second bandpass of 170-230\AA\ has a sequence of very strong Fe-IX-XIV lines, and will allow under-flight support for two more channels on SOHO/EIT, two channels on TRACE, one on Solar-B/EIS, and all four channels on the STEREO/EUVI instrument. First flight of the new EUNIS payload is scheduled for 2002 October.

Thomas, Roger J.↗

NASA NTRS2002

Using Kalman Filter Chemical Data Assimilation to Study Ozone Catalytic Loss Cycles in January 1992

This paper presents for the first time a global study of the ozone catalytic destruction cycles operating in the stratosphere using a stratospheric analyses for January 1992. The chemical analyses were produced using a Kalman filter data assimilation system. Because a major component of the variability of trace gases is due to the atmospheric motions the analyses have been cast in a flow-tracking coordinate system that moves with the large scale flow pattern. Particular attention is paid to the kinetic aspects of these cycles such as the rate limiting step and chain length. Although it is an important kinetic parameter, the chain length of the various cycles is seldom considered when the various catalytic cycles are discussed. This survey highlights that in the low stratosphere the cycles involving HO2 and halogens (notably bromine) are particularly important. In approximate order of effectiveness the most important ozone loss cycles in the polar lower stratosphere are the BrO/ClO, HO2/BrO, and OH/HO2 cycles. The ClO/ClO cycle clearly delineates the regions of chlorine activation. The chain length of the HO2/ClO, OH/HO2, Br/BrO, and ClO/NO2, clearly delineate the vortex edge region. The chain length of the BrO/NO2 and Cl/NO2 cycles highlight the regions of chemical processing outside the vortex where streamers of chemically processed air are stripped-off and transported away from the vortex. This is also true in the very low stratosphere for the Cl/ClO and BrO/ClO cycles.

Lary, David J.↗

NASA NTRS2017

Decadal Polar Motion of the Earth Excited by the Convective Outer Core From Geodynamo Simulations

Long time geodetic observation records show that the orientation of the Earth's rotation axis with respect to the terrestrial reference frame, or polar motion, changes on a broad range of timescales. Apart from external torques from the luni-solar tides, these changes are excited by interactions among different components of the Earth system. The convective fluid outer core has long been conjectured a likely contributor to the observed polar motion on timescales upward of decades, such as the 30 year Markowitz wobble. We investigated the electromagnetic coupling scenario across the core-mantle boundary via numerical geodynamo simulation for different geodynamo parameters (Rayleigh numbers and magnetic Rossby numbers). Our simulated polar motion varies strongly with the dynamo parameters, while its excitation on decadal timescales appear to converge asymptotically within the adopted range of numerical Rossby numbers. Three strongest asymptotic modes emerge from numerical results, with periods around 30, 40, and 60 years for the prograde excitation and around 24, 30, and 60 years for the retrograde excitation. Their amplitudes are all larger than 5 times 10 (sup minus 8), or approximately 10 milliseconds of arc.The results suggest that the electromagnetic core-mantle coupling could explain a substantial portion, if not all, of the observed decadal polar motion. In particular, the predicted 60 year polar motion deserves special attention for future observations and studies.

Kuang, W.↗

NASA NTRS2000

Satellite-Derived Dynamics of Southern Ocean Sea Ice

Antarctic ERS-2, RADARSAT Synthetic Aperture Radar and ERS-1/2 Scatterometer images were analyzed with SMMI radiometer image time-series data to investigate seasonal variability in satellite-tracked sea-ice dynamics in the Southern Ocean during 1992. Supporting field data were acquired during 'in-situ' experiments including the winter 1992 Ice Station Weddell and Winter Weddell Gyre studies. A variety of surface measurements were made during these experiments including Argos-buoy deployment and GPS drift measurements. These are used in conjunction with International Program for Antarctic Buoys drift trajectories for ice-motion tracking validation. Comparisons between gridded Special Sensor Microwave Imager (SSMI) ice-motion vectors and European Center for Medium Range Weather Forecasts/National Centers for Environmental Prediction (ECMWF/NCEP) analyses indicate that large-scale drift is forced predominantly by the long-term mean, large-scale synoptic pressure field. Only sub-daily SAR sea-ice tracking can capture high-frequency fluctuations, driven by polar lows or tidal forcing. In these cases, sea-ice drift can respond rapidly to changes in forcing on semi-diurnal time scales depending on the location with respect to the coastline. Seasonality of ice drift, particularly in the Weddell and Ross Seas, is linked to ice extent and compactness, and internal ice stresses transmitted through the pack ice from the coast. Three-monthly seasonal climatologies are presented of austral winter of ice drift in the Southern Ocean. The large Weddell and Ross Sea gyres are clearly resolved along with key seasonal and spatial attributes of their cyclonic circulation. Regional time series of ice dynamics parameters are used to illustrate correlations with meteorological forcing. Persistent divergence such as that occurring in the Ronne-Filchner polynya system results in large fractions of new ice. Similarly, convergence zones produce large fractions of deformed ice and characterize the dynamics of regions where perennial ice is observed. High shear strains also help delineate the axis of the Antarctic divergence in many places in the ice cover. In these regions, the separation between the coastal 'east wind drift'and ACC-dominated drift regimes is characterized by zonally extended regions of intense shear.

Drinkwater, Mark R.↗

DOE OSTI2021

Phase Modeling of the TRAPPIST-1 Planetary Atmospheres

Transiting compact multiplanet systems provide many unique opportunities to characterize the planets, including studies of size distributions, mean densities, orbital dynamics, and atmospheric compositions. The relatively short orbital periods in these systems ensure that events requiring specific orbital locations of the planets (such as primary transit and secondary eclipse points) occur with high frequency. The orbital motion and associated phase variations of the planets provide a means to constrain the atmospheric compositions through measurement of their albedos. Here we describe the expected phase variations of the TRAPPIST-1 system and times of superior conjunction when the summation of phase effects produce maximum amplitudes. We also describe the infrared flux emitted by the TRAPPIST-1 planets and the influence on the overall phase amplitudes. We further present the results from using the global circulation model ROCKE-3D to model the atmospheres of TRAPPIST-1e and TRAPPIST-1f assuming modern Earth and Archean atmospheric compositions. These simulations are used to calculate predicted phase curves for both reflected light and thermal emission components. We discuss the detectability of these signatures and the future prospects for similar studies of phase variations for relatively faint M stars.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2023

Accelerating discrete dislocation dynamics simulations with graph neural networks

Discrete dislocation dynamics (DDD) is a widely employed computational method to study plasticity at the mesoscale that connects the motion of dislocation lines to the macroscopic response of crystalline materials. However, the computational cost of DDD simulations remains a bottleneck that limits its range of applicability. Here, we introduce a new DDD-GNN framework in which the expensive time-integration of dislocation motion is entirely substituted by a graph neural network (GNN) model trained on DDD trajectories. As a first application, we demonstrate the feasibility and potential of our method on a simple yet relevant model of a dislocation line gliding through an array of obstacles. We show that the DDD-GNN model is stable and reproduces very well unseen ground-truth DDD simulation responses for a range of straining rates and obstacle densities, without the need to explicitly compute nodal forces or dislocation mobilities during time-integration. Our approach opens new promising avenues to accelerate DDD simulations and to incorporate more complex dislocation motion behaviors.

36 MATERIALS SCIENCE↗

NASA NTRS1973

Parametric instability of a relativistically strong electromagnetic wave.

The stability of a circularly polarized electromagnetic wave that is strong enough to make plasma electrons, but not ions, relativistic is studied. Small perturbations are considered which propagate parallel to the large-amplitude driver. A relativistically strong wave can be unstable on time scales as short as twice its own oscillation period, and decays into a forward-going plasma oscillation and either one or two electromagnetic waves. Ion motion introduces an additional instability which can be important at short perturbation wavelengths, where the driver would otherwise be stable. The unstable ion and electron modes both have potential for producing anomalously large acceleration of relativistic particles, as well as significant amounts of backscattered light. These effects may be important in two applications: (1) the use of intense lasers to heat or compress plasma, and (2) the plasma surrounding a pulsar, if the pulsar is losing energy by radiation of electromagnetic waves at its rotation frequency. Instability persists in the nonrelativistic regime, reducing to stimulated Raman scattering as a special case.

Max, C. E.↗

NASA NTRS1976

An analytical study of reduced-gravity flow dynamics

Addition of surface tension forces to a marker-and-cell code and the performance of four incompressible fluid simulations in reduced gravity, were studied. This marker-and-cell code has a variable grid capability with arbitrary curved boundaries and time dependent acceleration fields. The surface tension logic includes a spline fit of surface marker particles as well as contact angle logic for straight and curved wall boundaries. Three types of flow motion were simulated with the improved code: impulsive settling in a model Centaur LH2 tank, continuous settling in a model and full scale Centaur LO2 tank and mixing in a Centaur LH2 tank. The impulsive settling case confirmed a drop tower analysis which indicated more orderly fluid collection flow patterns with this method providing a potential savings in settling propellants. In the LO2 tank, fluid collection and flow simulation into the thrust barrel were achieved. The mixing simulation produced good results indicating both the development of the flow field and fluid interface behavior.

Bradshaw, R. D.↗

NASA NTRS1984

Temporal evolution of the solar wind and the formation of a standing shock

The temporal evolution of the solar wind from one steady state to another is explored when momentum deposition produces multiple critical points in the flow. It is shown that the wind always evolves in time to a new steady state compatible with the solution of the steady state equation of motion. However, for the same initial state and identical asymptotic momentum deposition rate, the temporal evolution pattern of the wind depends on the detailed time history of momentum addition and is therefore not unique. This feature plays an important role in the particular case when multiple (three in this study) steady states exist for identical boundary conditions; each one of these solutions is thus shown to be physically accessible. The details of the temporal evolution pattern of the wind reveal the formation of a shock discontinuity whenever the flow becomes supersonic at a critical point upstream from the initial critical point. If the flow remains supersonic at that inner critical point, the shock can become a standing one, depending on the strength and the temporal history of momentum addition. The results of this study indicate that the time scale required for the solar wind to evolve between steady states is of the order of 30-60 hours. Furthermore, the results also reveal the interesting and novel phenomenon that a standing shock is likely to develop in the inner solar wind flow within this time frame, in particular, in coronal hole regions with rapidly diverging geometries.

Habbal, S. R.↗

NASA NTRS1985

Short-interval estimations of trigonometric parallaxes

A technique for estimating trigonometric parallaxes in a matter of days or weeks is presented. The technique relies on the discrepancy between the instantaneous proper motion and the proper motion of a star. The main sources of error in the method are the standard error of the individual observations (0.004 arcsec) and the arbitrary limit placed on the observation interval. The parallactic motion of an MO dwarf of known parallax and a blue magnitude of 11.2 is determined. The slope inferred is within 10 percent of the value (0.555 arcsec) derived from a 1.5-year study of Barnard's star. It is concluded that the technique, if used on the same time scale as conventional techniques, would yield results of much higher accuracy.

Gatewood, G.↗

NASA NTRS1990

Numerical simulations of solar disturbances and their interplanetary consequences

Time-dependent MHD numerical simulations are used to study responses of the solar atmosphere and interplanetary medium to simulated solar disturbances. A number of 2D and 3D examples of coronal mass ejection (CME) simulations and some current controversies concerning the basic processes of CME initiation are discussed. Footpoint shearing motion is tested to determine whether it can provide a reasonable mechanism for CME development from arch filament configurations. Possible interplanetary consequences to CME-like disturbances are demonstrated by using 3D simulations to determine the dynamic response of the solar wind to a plasmoid injection from an eruptive filament or prominence. The possibility that a plasmoid may be generated in the interplanetary medium by a solar-generated shock that propagates through a heliospheric current sheet is discussed. Application of the 3D model for the interpretation of interplanetary scintillation observations is addressed.

Dryer, M.↗

NASA NTRS1991

A computer architecture for intelligent machines

The Theory of Intelligent Machines proposes a hierarchical organization for the functions of an autonomous robot based on the Principle of Increasing Precision With Decreasing Intelligence. An analytic formulation of this theory using information-theoretic measures of uncertainty for each level of the intelligent machine has been developed in recent years. A computer architecture that implements the lower two levels of the intelligent machine is presented. The architecture supports an event-driven programming paradigm that is independent of the underlying computer architecture and operating system. Details of Execution Level controllers for motion and vision systems are addressed, as well as the Petri net transducer software used to implement Coordination Level functions. Extensions to UNIX and VxWorks operating systems which enable the development of a heterogeneous, distributed application are described. A case study illustrates how this computer architecture integrates real-time and higher-level control of manipulator and vision systems.

Lefebvre, D. R.↗