Search NASA⌕ Search

SEARCH · Search NASA

Results for “rapid evolution”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Initial results from the High Altitude Observatory white light coronagraph on Skylab - A progress report

Frequent periodic observations by the white-light coronagraph allow an examination of coronal variations over a broad range of temporal scales. Examples of the slowest and most rapid variations are presented. An example of extremely slow coronal variations is the gradual evolution - to a large equatorial streamer - in association with a marked decrease in solar activity, as the total magnetic flux in one hemisphere decreased. Another example is given of a long-lived quasi-stable coronal streamer, apparently associated with a stable filament channel; comparison of this streamer with coronal potential-magnetic-field computations show little correlation. Some results on coronal transients - the most rapid variations observed - are summarized. Characteristic masses and energies involved in mass-ejection transients, their temporal and spatial distributions, their associations with surface phenomena and possible interplanetary signatures, and their role in coronal evolution are briefly noted.

Macqueen, R. M.↗
NASA NTRS2003

Dynamical Evolution of the Inner Heliosphere Approaching Solar Activity Maximum: Interpreting Ulysses Observations Using a Global MHD Model

In this study we describe a series of MHD simulations covering the time period from 12 January 1999 to 19 September 2001 (Carrington Rotation 1945 to 1980). This interval coincided with: (1) the Sun s approach toward solar maximum; and (2) Ulysses second descent to the southern polar regions, rapid latitude scan, and arrival into the northern polar regions. We focus on the evolution of several key parameters during this time, including the photospheric magnetic field, the computed coronal hole boundaries, the computed velocity profile near the Sun, and the plasma and magnetic field parameters at the location of Ulysses. The model results provide a global context for interpreting the often complex in situ measurements. We also present a heuristic explanation of stream dynamics to describe the morphology of interaction regions at solar maximum and contrast it with the picture that resulted from Ulysses first orbit, which occurred during more quiescent solar conditions. The simulation results described here are available at: http://sun.saic.com.

Riley, Pete↗
NASA NTRS1990

Three-dimensional simulation study of ionospheric plasma clouds

The results of fully three-dimensional numerical simulations of ionospheric plasma cloud evolution are presented. The evolution of the plasma cloud considered by Drake and Huba (1987) in the limit of vanishingly small ion compressibility is discussed. Simulations support the results of the analytical theory: finite plasma temperature, combined with fully three-dimensional plasma dynamics, is a stabilizing influence on plasma cloud evolution. This stability is associated with sheared azimuthal ion flows in the vicinity of the cloud surface. Cloud evolution using realistic values of ion compressibility show that the cloud rapidly diffuses to a state in which the sheared azimuthal flow is substantially reduced; subsequently, the cloud becomes unstable and structures.

Zalesak, S. T.↗
NASA NTRS1990

Numerical simulation of solar coronal magnetic fields

Many aspects of solar activity are believed to be due to the stressing of the coronal magnetic field by footpoint motions at the photosphere. The results are presented of a fully spectral numerical simulation which is the first 3-D time dependent simulation of footpoint stressing in a geometry appropriate for the corona. An arcade is considered that is initially current-free and impose a smooth footpoint motion that produces a twist in the field of approx 2 pi. The footprints were fixed and the evolution was followed until the field relaxes to another current-free state. No evidence was seen for any instability, either ideal or resistive and no evidence for current sheet formation. The most striking feature of the evolution is that in response to photospheric motions, the field expands rapidly upward to minimize the stress. The expansion has two important effects. First, it suppresses the development of dips in the field that could support dense, cool material. For the motions assumed, the magnetic field does not develop a geometry suitable for prominence formation. Second, the expansion inhibits ideal instabilities such as kinking. The results indicate that simple stearing of a single arcade is unlikely to lead to solar activity such as flares or prominences. Effects are discussed that might possibly lead to such activity.

Dahlburg, Russell B.↗
NASA NTRS2002

Spectroscopic Detection of a Stellar-like Photosphere in an Accreting Protostar

We present high-resolution (R is approximately equal to 18,000), high signal-to-noise 2 micron spectra of two luminous, X-ray flaring Class I protostars in the rho Ophiuchi cloud acquired with the NIRSPEC (near infrared spectrograph) of the Keck II telescope. We present the first spectrum of a highly veiled, strongly accreting protostar which shows photospheric absorption features and demonstrates the stellar nature of its central core. We find the spectrum of the luminous (L (sub bol) = 10 solar luminosity) protostellar source, YLW 15, to be stellar-like with numerous atomic and molecular absorption features, indicative of a K5 IV/V spectral type and a continuum veiling r(sub k) = 3.0. Its derived stellar luminosity (3 stellar luminosity) and stellar radius (3.1 solar radius) are consistent with those of a 0.5 solar mass pre-main-sequence star. However, 70% of its bolometric luminosity is due to mass accretion, whose rate we estimate to be 1.7 x 10(exp -6) solar masses yr(exp -1). We determine that excess infrared emission produced by the circumstellar accretion disk, the inner infalling envelope, and accretion shocks at the surface of the stellar core of YLW 15 all contribute significantly to its near-IR (infrared) continuum veiling. Its rotational velocity v sin i = 50 km s(exp -1) is comparable to those of flat-spectrum protostars but considerably higher than those of classical T Tauri stars in the rho Oph cloud. The protostar may be magnetically coupled to its circumstellar disk at a radius of 2 - 3 R(sub *). It is also plausible that this protostar can shed over half its angular momentum and evolve into a more slowly rotating classical T Tauri star by remaining coupled to its circumstellar disk (at increasing radius) as its accretion rate drops by an order of magnitude during the rapid transition between the Class I and Class II phases of evolution. The spectrum of WL 6 does not show any photospheric absorption features, and we estimate that its continuum veiling is r(sub k) is greater than or equal to 4.6. Its low luminosity (2 solar masses) and high veiling dictate that its central protostar is very low mass, M is approx. 0.1 solar masses. We also evaluate multi-epoch X ray data along with these spectra and conclude that the X ray variabilities of these sources are not directly related to their protostellar rotation velocities.

Greene, Thomas P.↗
NASA NTRS2011

Observational Evidence of How Magnetofluid Turbulence in the Solar Wind Dissipates

The solar wind appears to be a fully developed turbulent magnetofluid. As this magnetofluid expands into the heliosphere, it cools significantly less rapidly than would be expected of an adiabatically expanding gas. The evolution of the temperature with distance is roughly what would be expected if the turbulence dissipated by heating the thermal plasma. Several physical mechanisms have been proposed, including resonance absorption of waves and Landau damping. Recently, high-time resolution magnetic field data from the four Cluster spacecraft have illustrated damping of the fluctuations out to the electron inertial scale. Use of the wave telescope/k-filtering technique during two intervals of busrt mode data suggests that dissipation of the fluctuations is due to Landau damping, first on protons, then on electrons.

Goldstein, Melvyn L.↗
NASA NTRS2021

Effects of Spin-Orbit Resonances and Tidal Heating on the Inner Edge of the Habitable Zone

Much attention has been given to the climate dynamics and habitable boundaries of synchronously rotating planets around low mass stars. However, other rotational states are possible, including spin–orbit resonant configurations, particularly when higher eccentricity orbits can be maintained in a system. Additionally, the oscillating strain as a planet moves from periastron to apoastron results in friction and tidal heating, which can be an important energy source. Here, we simulate the climate of ocean-covered planets near the inner edge of the habitable zone around M to solar stars with the NASA GISS ROCKE-3D general circulation model, and leverage the planetary evolution software package, VPLanet, to calculate tidal heating rates for Earth-sized planets orbiting 2600 and 3000 K stars. This study is the first to use a 3D general circulation model that implements tidal heating to investigate habitability for multiple resonant states. We find that for reference experiments without tidal heating, the resonant state has little impact on the radial position of the inner edge because for a given stellar flux, higher-order states tend to be warmer than synchronous rotators, but for a given temperature, have drier upper atmospheres. However, when strong tidal heating is present, the rotational component implies a strong dependence of habitable conditions on the system evolution and rotational state. Since tidal and stellar heating both decrease rapidly with orbital distance, this results in a compact orbital width separating temperate and uninhabitable climates. We summarize these results and also compare ROCKE-3D to previously published simulations of the inner edge.

Spin-Orbit Resonances↗
NASA NTRS1986

Greenstone belts: Their boundaries, surrounding rock terrains and interrelationships

Greenstone belts are an important part of the fragmented record of crustal evolution, representing samples of the magmatic activity that formed much of the Earth's crust. Most belts developed rapidly, in less than 100 Ma, leaving large gaps in the geological record. Surrounding terrains provide information on the context of greenstone belts. The effects of tectonic setting, structural geometry and evolution, associated plutonic activity and sedimentation are discussed.

Percival, J. A.↗
NASA NTRS2007

Development of Hairpin Vortices in Turbulent Spots and End-Wall Transition

The end-stage phase of boundary layer transition is characterized by the development of hairpin-like vortices which evolve rapidly into patches of turbulent behavior. In general, the characteristics of the evolution form this hairpin stage to the turbulent stage is poorly understood, which has prompted the present experimental examination of hairpin vortex development and growth processes. Two topics of particular relevance to the workshop focus will be covered: 1) the growth of turbulent spots through the generatio and amalgamation of hairpin-like vortices, and 2) the development of hairpin vortices during transition in an end-wall junction flow. Brief summaries of these studies are described below. Using controlled generation of hairpin vortices by surface injection in a critical laminar boundary layer, detailed flow visualization studies have been done of the phases of growth of single hairpin vortices, from the initial hairgin generation, through the systematic generation of secondary hairpin-like flow structures, culminating in the evolution to a turbulent spot. The key to the growth process is strong vortex-surface interactions, which give rise to strong eruptive events adjacent to the surface, which results in the generation of subsequent hairpin vortex structures due to inviscid-viscuous interactions between the eruptive events and the free steam fluid. The general process of vortex-surface fluid interaction, coupled with subsequent interactions and amalgamation of the generated multiple hairpin-type vortices, is demonstrated as a physical mechanism for the growth and development of turbulent spots. When a boundary layer flow along a surface encounters a bluff body obstruction extending from the surface (such as cylinder or wing), the strong adverse pressure gradients generated by these types of flows result in the concentration of the impinging vorticity into a system of discrete vortices near the end-wall juncture of the obstruction, with the extensions of the vortices engirdling the obstruction to form "necklace" or "horseshoe" vortices. Recent hydrogen bubble and particle image visualization have shown that as Reynolds number is increased for a laminar approach flow, the flow will become critical, and a destabilization of the necklace vortices results in the development of an azimuthal waviness, or "kinks", in the vortices. These vortex kinks are accentuated by Biot-Savart effects, causing portions of a distorted necklace vortex to make a rapid approach to the surface, precipitating processes of localized, three-dimensional surface interactions. These interactions result in the rapid generation, focussing, and ejection of thin tongues of surface fluid, which rapidly roll-over and appear as hairpin vortices in the junction region. Subsequent amalgamation of these hairpin vortices with the necklace vortices produces a complex transitional-type flow. A presentation of key results from both these studies will be done, emphasizing both the ubiquity of such hairpin-type flow structures in manifold transitional-type flows, and the importance of vortex-surface interactions n the development of hairpin vortices.

Smith, Charles R.↗
NASA NTRSDate not supplied

Technology Gaps for Rapid Response Missions to Near-Earth Objects, Interstellar Objects, and Long-Period Comets

The last several years has seen the discovery of the first two interstellar objects, the first ever planetary defense mission, recommendation for a rapid reconnaissance planetary defense demonstration, and the continued emergence of a robust commercial small satellite industry. The present and near future also consist of emerging next-generation observatories including Vera Rubin and NEO Surveyor. These seemingly disparate events converge in the context of rapid response: a cross-cutting capability that would enable NASA and the international community to quickly discover and respond to an emerging target such as a near-Earth object (NEO), interstellar object (ISO), or long-period comet (LPC) either for rapid characterization of a potential threat, or revolutionary science that would inform early solar system formation and evolution. In late October 2022, subject matter experts gathered at the California Institute of Technology in a week-long workshop sponsored by the Keck Institute for Space Studies (KISS) to address enabling mission concepts for rapid response and key technology gaps (final report in progress). These experts concurred that the ability to respond on the order of a few months is necessary for rapid in-situ characterization of a NEO, ISO, or LPC, and that while there are several technology gaps, this capability could be realized in the near future.

Technology gaps↗
NASA NTRS1993

The microstructural evolution, crystallography, and thermal processing of ultrahigh carbon Fe-1.85 pct C melt-spun ribbon

A study is presented to determine if fine microstructures could be achieved using rapid solidification to produce a fine-grained fully austenitic starting structure and then using thermal processing cycles to produce an even finer ferrite-cementite structure. The evolution, mechanisms of grain refinement, and crystallography of the resultant microstructures were examined by TEM. A thermal processing cycle consisted of quenching the ribbon in liquid nitrogen, tempering at 600 C for 10 sec, 'upquenching' to 750 C for 10 sec, and subsequently quenching again in liquid nitrogen. The heat-treatment resulted in martensite grains with sizes of about 1 micron or less in both length and thickness and cementite particles of 0.4 micron or less. It is concluded that these microstructures could be used for producing fine-grained ultrahigh carbon steels of very high strength without the brittleness associated with the formation of coarse carbide particles of the loss of strength due to graphite formation.

Spanos, G.↗
NASA NTRS2022

The Effects of Surface Fossil Magnetic Fields on Massive Star Evolution: IV. Grids of Models at Solar, LMC, and SMC Metallicities

Magnetic fields can drastically change predictions of evolutionary models of massive stars via mass-loss quenching, magnetic braking, and efficient angular momentum transport, which we aim to quantify in this work. We use the MESA software instrument to compute an e xtensiv e main-sequence grid of stellar structure and evolution models, as well as isochrones, accounting for the effects attributed to a surface fossil magnetic field. The grid is densely populated in initial mass (3–60 M ), surface equatorial magnetic field strength (0–50 kG), and metallicity (representative of the Solar neighbourhood and the Magellanic Clouds). We use two magnetic braking and two chemical mixing schemes and compare the model predictions for slowly rotating, nitrogen- enriched (‘Group 2’) stars with observations in the Large Magellanic Cloud. We quantify a range of initial field strengths that allow for producing Group 2 stars and find that typical values (up to a few kG) lead to solutions. Between the subgrids, we find notable departures in surface abundances and evolutionary paths. In our magnetic models, chemical mixing is al w ays less efficient compared to non-magnetic models due to the rapid spin-down. We identify that quasi-chemically homogeneous main sequence evolution by efficient mixing could be prevented by fossil magnetic fields. We recommend comparing this grid of evolutionary models with spectropolarimetric and spectroscopic observations with the goals of (i) revisiting the derived stellar parameters of known magnetic stars, and (ii) observationally constraining the uncertain magnetic braking and chemical mixing schemes.

stars: abundances↗
NASA NTRS1993

Was Martian mantle wet? A possible consequence of rapid core formation

Degassing of H2O in the planetary interior possibly plays an important role in the evolution of surface environment as well as geologic activity on the terrestrial planets. Mars may be such a planet that well preserves the materials and the geologic features directly related to early evolution of H2O. H2O content in the interior of proto-Mars during accretion and also core formation were investigated. Geodetic data shows that Mars has a dense core. The existence of iron-rich core on Mars may be also supported by the depletion of siderophile elements in SNC meteorites assuming that these samples came from Mars. Isotope systematics of these meteorites indicate that the core formation occurred very early, probably concurrently with Mars formation. Considering the kinetics of metal segregation from silicate, the melting of silicate is likely to precede the core formation. Once the core formation occurs, substantial amount of gravitational energy is released and thus the planetary interior is heated. This energy may be large enough to keep the silicate material in partially molten state along with the accretional heating. Under such circumstances, the silicate melt probably migrates to the surface. Early crustal formation, therefore, is also likely to be associated with the core formation.

Kuramoto, Kiyoshi↗
NASA NTRS1986

The life cycles of persistent anomalies and blocking over the North Pacific

The evolution of persistent anomaly patterns over the central North Pacific is investigated. Composite time evolution fields of the 500-mbar anomaly patterns are constructed from low-pass and unfiltered height anomaly data; the time scales for the development and decay of these persistent anomalies are analyzed. The relationship between zonal flow in the Pacific jet region and the development of the anomaly patterns is examined. The effect of baroclinic instabilities on the development of the anomalies is studied. The vertical structure and synoptic characteristics of the evolution of the anomalies are described. It is noted that the initial rapid growth of the main center may be associated with a propagating, intensifying, synoptic-scale disturbance which originates in the midlatitudes over eastern Asia.

Dole, Randall M.↗
NASA NTRS1992

Phase-field model for isothermal phase transitions in binary alloys

A new phase field model is described which models isothermal phase transitions between ideal binary alloy solution phases. Equations are developed for the temporal and spatial variation of the phase field, which describes the identity of the phase, and of the composition. An asymptotic analysis, as the gradient energy coefficient of the phase field becomes small, was conducted. From the analysis, it is shown that the model recovers classical sharp interface models of this situation when the interfacial layers are thin, and they show how to relate the parameters appearing in the phase field model to material and growth parameters in real systems. Further, three stages of temporal evolution are identified: the first corresponding to interfacial genesis which occurs very rapidly; the second to interfacial motion controlled by the local energy difference across the interface and diffusion; the last taking place on a long time scale in which curvature effects are important and which correspond to Ostwald ripening. The results of the numerical calculations are presented.

Wheeler, A. A.↗
NASA NTRS1993

Integrated Intelligent training and job aiding for combustion turbine engines

This paper describes an ongoing program to augment such an expert system gas turbine startup advisor, known as the EPRI SA VANT System, by including an intelligent training package. It will give a brief background on the SA VANT development and an overview of its evolution into a full-blown Gas Turbine Information System (GTIS) for rapid access of on-line documentation, diagnostics, and training. In particular, the paper will address: (1) the conversion of the knowledge base used by the SA VANT startup advisor so that it can be used for both training and job aiding; and (2) the hypertext-oriented user manuals being incorporated into the system for rapidly accessing on-line documentation at the job site.

Mckeithan, Clifford M., Jr.↗
NASA NTRS2003

Investigation of Dynamic Oxygen Adsorption in Molten Solder Jetting Technology

Surface tension forces play a critical role in fluid dynamic phenomena that are important in materials processing. The surface tension of liquid metals has been shown to be very susceptible to small amounts of adsorbed oxygen. Consequently, the kinetics of oxygen adsorption can influence the capillary breakup of liquid-metal jets targeted for use in electronics assembly applications, where low-melting-point metals (such as tin-containing solders) are utilized as an attachment material for mounting of electronic components to substrates. By interpreting values of surface tension measured at various surface ages, adsorption and diffusion rates of oxygen on the surface of the melt can be estimated. This research program investigates the adsorption kinetics of oxygen on the surface of an atomizing molten-metal jet. A novel oscillating capillary jet method has been developed for the measurement of dynamic surface tension of liquids, and in particular, metal melts which are susceptible to rapid surface degradation caused by oxygen adsorption. The experimental technique captures the evolution of jet swells and necks continuously along the jet propagation axis and is used in conjunction with an existing linear, axisymmetric, constant-property model to determine the variation of the instability growth rate, and, in turn, surface tension of the liquid as a function of surface age measured from the exit orifice. The conditions investigated so far focus on a time window of 2-4ms from the jet orifice. The surface properties of the eutectic 63%Sn-37%Pb solder alloy have been investigated in terms of their variation due to O2 adsorption from a N2 atmosphere containing controlled amounts of oxygen (from 8 ppm to 1000 ppm). The method performed well for situations where the oxygen adsorption was low in that time window. The value of surface tension for the 63Sn-37Pb solder in pure nitrogen was found to be 0.49 N/m, in good agreement with previously published work. A characteristic time of O(1ms) or less was determined for the molten-metal surface to be saturated by oxygen at 1000 ppm concentration in N2.

Megaridis, Constantine M.↗
NASA NTRS1991

Naturally occurring and forced azimuthal modes in a turbulent jet

Naturally occurring instability modes in an axisymmetric jet were studied using the modal frequency technique. The evolution of the modal spectrum was obtained for a jet with a Reynolds number based on a diameter of 400,000 for both laminar and turbulent nozzle boundary layers. In the early evolution of the jet the axisymmetric mode was predominant, with the azimuthal modes growing rapidly but dominating only the end of the potential core. The growth of the azimuthal was observed closer to the nozzle exit for the jet in the laminar boundary layer case than for the turbulent. Target modes for efficient excitation of the jet were determined and two cases of excitation were studied. First, a jet was excited simultaneously by two helical modes, m equals plus 1 and m equals minus 1 at a Strouhal number based on jet diameter of 0.15 and the axisymmetric mode, m equals 0 at a jet diameter of 0.6. Second, m equals plus one and m equals minus 1 at jet diameter equals 0.3 and m equals 0 at jet diameter equals 0.6 were excited simultaneously. The downstream evolution of the hydrodynamic modes and the spreading rate of the jet were documented for each case. Higher jet spreading rates, accompanied by distorted jet cross sections were observed for the cases where combinations of axisymmetric and helical forcings were applied.

Raman, Ganesh↗