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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 181 records · Page 10
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NASA NTRS2008

Energetic Consistency and Coupling of the Mean and Covariance Dynamics

The dynamical state of the ocean and atmosphere is taken to be a large dimensional random vector in a range of large-scale computational applications, including data assimilation, ensemble prediction, sensitivity analysis, and predictability studies. In each of these applications, numerical evolution of the covariance matrix of the random state plays a central role, because this matrix is used to quantify uncertainty in the state of the dynamical system. Since atmospheric and ocean dynamics are nonlinear, there is no closed evolution equation for the covariance matrix, nor for the mean state. Therefore approximate evolution equations must be used. This article studies theoretical properties of the evolution equations for the mean state and covariance matrix that arise in the second-moment closure approximation (third- and higher-order moment discard). This approximation was introduced by EPSTEIN [1969] in an early effort to introduce a stochastic element into deterministic weather forecasting, and was studied further by FLEMING [1971a,b], EPSTEIN and PITCHER [1972], and PITCHER [1977], also in the context of atmospheric predictability. It has since fallen into disuse, with a simpler one being used in current large-scale applications. The theoretical results of this article make a case that this approximation should be reconsidered for use in large-scale applications, however, because the second moment closure equations possess a property of energetic consistency that the approximate equations now in common use do not possess. A number of properties of solutions of the second-moment closure equations that result from this energetic consistency will be established.

Cohn, Stephen E.↗
NASA NTRS1990

A study of the evolution of the surface heat flux off the southeast coast of the United States during a cold air outbreak using satellite remote sensing data

Attention is given to the contribution of the marine boundary layer to storm development via a study of the evolution of the spatial distribution of the heat flux during a cold-air outburst (CAO) which occurred during the GALE Field Program period in a 550,000-sq-km area off the southeast coast of the United States. The study focuses on a CAO that occurred in the period February 24-26, 1986. During the CAO, the area averaged total surface heat flux ranged from 190 W/sq m to 1114 W/sq m. The high value was characterized by a lower average surface air and dew-point temperatures and a higher average surface wind speed. In general, the surface heat flux increased as the sea-surface temperatures on the continental shelf increased. It reached the maximum over the Gulf Stream, and then decreased over the eastern portions of the Gulf Stream and over the Sargasso Sea. The configuration conforms with some of the earlier findings of Bane and Osgoode (1989) and Blanton et al. (1989).

Vukovich, Fred M.↗
NASA NTRS2005

Lidar Applications in Atmospheric Dynamics: Measurements of Wind, Moisture and Boundary Layer Evolution

A large array of state-of-the-art ground-based and airborne remote and in-situ sensors were deployed during the International H2O Project (THOP), a field experiment that took place over the Southern Great Plains (SGP) of the United States from 13 May to 30 June 2002. These instruments provided extensive measurements of water vapor mixing ratio in order to better understand the influence of its variability on convection and on the skill of quantitative precipitation prediction (Weckwerth et all, 2004). Among the instrument deployed were ground based lidars from NASA/GSFC that included the Scanning Raman Lidar (SRL), the Goddard Laboratory for Observing Winds (GLOW), and the Holographic Airborne Rotating Lidar Instrument Experiment (HARLIE). A brief description of the three lidars is given below. This study presents ground-based measurements of wind, boundary layer structure and water vapor mixing ratio measurements observed by three co-located lidars during MOP at the MOP ground profiling site in the Oklahoma Panhandle (hereafter referred as Homestead). This presentation will focus on the evolution and variability of moisture and wind in the boundary layer when frontal and/or convergence boundaries (e.g. bores, dry lines, thunderstorm outflows etc) were observed.

Demoz, Belay↗
NASA NTRS1985

Molecular cloud evolution and star formation

The present state of knowledge of the relationship between molecular clouds and young stars is reviewed. The determination of physical parameters from molecular line observations is summarized, and evidence for fragmentation of molecular clouds is discussed. Hierarchical fragmentation is reviewed, minimum fragment scales are derived, and the stability against fragmentation of both spherically and anisotropically collapsing clouds is discussed. Observational evidence for high-velocity flows in clouds is summarized, and the effects of winds from pre-main sequence stars on molecular gas are discussed. The triggering of cloud collapse by enhanced pressure is addressed, as is the formation of dense shells by spherical outflows and their subsequent breakup. A model for low-mass star formation is presented, and constraints on star formation from the initial mass function are examined. The properties of giant molecular clouds and massive star formation are described. The implications of magnetic fields for cloud evolution and star formation are addressed.

Silk, J.↗
NASA NTRS1979

Status of the Space Telescope project in the United States

A general description of the evolution of the Large Space Telescope project is given, including mirror construction, interface requirements, and the review cycle for the scientific instruments. The anticipated participation of ESA scientists through the means of the Science Institute is discussed.

Odell, C. R.↗
NASA NTRS2000

Thermal and Driven Stochastic Growth of Langmuir Waves in the Solar Wind and Earth's Foreshock

Statistical distributions of Langmuir wave fields in the solar wind and the edge of Earth's foreshock are analyzed and compared with predictions for stochastic growth theory (SGT). SGT quantitatively explains the solar wind, edge, and deep foreshock data as pure thermal waves, driven thermal waves subject to net linear growth and stochastic effects, and as waves in a pure SGT state, respectively, plus radiation near the plasma frequency f(sub p). These changes are interpreted in terms of spatial variations in the beam instability's growth rate and evolution toward a pure SGT state. SGT analyses of field distributions are shown to provide a viable alternative to thermal noise spectroscopy for wave instruments with coarse frequency resolution, and to separate f(sub p) radiation from Langmuir waves.

Cairns, Iver H.↗
NASA NTRS1986

Generalized energetics for linear and nonlinear symmetric instabilities

The generalized energy conservation integral is applied to linear and nonlinear symmetric instabilities (SIs) and conditional symmetric instabilities (CSIs) in uniform and nonuniform basic states. The generalized energy conservation integral for linear SI in nonuniform basic state is refined to include initial thermal-inertial perturbations. A generalized conservation integral is derived for a nonlinear SI with uniform and nonuniform basic states. The integral reveals that: (1) the stability conditions of nonlinear and linear SI are not the same; (2) when the basic state is symmetrically stable the nonlinear evolution of a symmetric disturbance is energetically bounded by its initial energy; and (3) when the basic state is symmetrically unstable the growth of the symmetric perturbation is approximated by the linear SI theory. Precipitative heating is incorporated into the generalized energy integral for nonlinear CSI; the relation between nonlinear evolution of a CSI circulation and precipitative heating is examined.

Xu, Q.↗
NASA NTRSDate not supplied

AEGIS: Autonomous Entity Global Intelligence System for Urban Air Mobility

This paper presents a global intelligence system that synthesizes aerial vehicles’ real-time physical data, planned actions, and historical behavior into engineered data frames representing the collective state of the airspace and suitable for efficient machine learning consumption. These data frames are then learnt by a deep neural net to build a prediction model that estimates the expected evolution path of the current state, thereby identifying potential future conflicts. This approach lends itself to an automated early warning system that the aerial vehicles can implement onboard with a suitable edge computing module more efficiently and effectively than non-AI methods, and eventually take preventive or corrective measures towards self/collaborative resolution of the issues. Contrary to a centralized early warning system where all vehicles’ task-space eventually converges to a global optimum state, the presented distributed global intelligence system brings in a balance between local utility functions of each vehicle and the global operating framework. This contributes to effectively handle the potential massive scaling in urban air mobility in the near future.

Artificial Intelligence↗
NASA NTRS2018

Payload Operations Center - Lessons from Commercial Engagement

The International Space Station (ISS) Payload Operations and Integration Center (POIC) at NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama, United States, has gone through an evolution from supporting exclusively government ISS users to providing 50% (or more) of their support to commercial users. At the same time, they have expanded ground and facility operations to support a United States Orbital Segment crew expansion from three to four astronauts allowing an additional of 34 hours crew time per week. These additional hours are dedicated to utilization and have already surpassed the 100 hour peak weekly milestone in July 2018. This paper discusses the Center's changes in planning, staffing, coordination, and operations while addressing topics from the addition of secondary flight control positions to dynamic operations product reviews. MSFC's Human Exploration and Development Operations Office, which manages payload operations, seeks through this paper to highlight the higher priority commercial users now receive in replanning and in additional crew time.

Watkins, Bobby J.↗
NASA NTRS1979

On the effects of higher convection modes on the thermal evolution of small planetary bodies

The effects of higher modes of convection on the thermal evolution of a small planetary body is investigated. Three sets of models are designed to specify an initially cold and differentiated, an initially hot and differentiated, and an initially cold and undifferentiated Moon-type body. The strong temperature dependence of viscosity enhances the thickening of lithosphere so that a lithosphere of about 400 km thickness is developed within the first billion years of the evolution of a Moon-type body. The thermally isolating effect of such a lithosphere hampers the heat flux out of the body and increases the temperature of the interior, causing the solid-state convection to occur with high velocity so that even the lower modes of convection can maintain an adiabatic temperature gradient there. It is demonstrated that the effect of solid-state convection on the thermal evolution of the models may be adequately determined by a combination of convection modes up to the third or the fourth order harmonic. The inclusion of higher modes does not affect the results significantly.

Arkani-Hamed, J.↗
NASA NTRS2020

Projection-Based Inter-Agent Collision Avoidance in Dual Agent Systems

Inter-agent collisions can occur in otherwise dynamically-stable (i.e., Lyapunov stable) dual-agent leaderfollower systems. These inter-agent collisions between the leader and the follower happen during the transient phase of the system’s evolution, although the steady-state behavior of the system is asymptotically/exponentially stable. Therefore, to avoid such inter-agent collisions, it is essential to control the relative error trajectory between the leader and the follower during the transient phase of the system’s evolution. In this paper, we introduce a novel projection operator based modelreference control architecture that can mitigate impending inter-agent collisions by modifying the transient dynamics of relative trajectories. This controller augments the follower’s baseline controller and consists of two essential components: a collision-free reference model based on the projection operator and a model reference tracking controller to guide the follower to follow the reference-model. This paper defines the concept of transient-instability in leader-follower systems, introduces collision mitigation controller architecture, and presents an illustrative example demonstrating its effectiveness.

Bayard, David S.↗
NASA NTRS2014

Numerical Modeling of Ocular Dysfunction in Space

Upon introduction to microgravity, the near-loss of hydrostatic pressure causes a marked cephalic (headward) shift of fluid in an astronaut's body. The fluid shift, along with other factors of spaceflight, induces a cascade of interdependent physiological responses which occur at varying time scales. Long-duration missions carry an increased risk for the development of the Visual Impairment and Intracranial Pressure (VIIP) syndrome, a spectrum of ophthalmic changes including posterior globe flattening, choroidal folds, distension of the optic nerve sheath, kinking of the optic nerve and potentially permanent degradation of visual function. In the cases of VIIP found to date, the initial onset of symptoms occurred after several weeks to several months of spaceflight, by which time the gross bodily fluid distribution is well established. We are developing a suite of numerical models to simulate the effects of fluid shift on the cardiovascular, central nervous and ocular systems. These models calculate the modified mean volumes, flow rates and pressures that are characteristic of the altered quasi-homeostatic state in microgravity, including intracranial and intraocular pressures. The results of the lumped models provide initial and boundary data to a 3D finite element biomechanics simulation of the globe, optic nerve head and retrobulbar subarachnoid space. The integrated set of models will be used to investigate the evolution of the biomechanical stress state in the ocular tissues due to long-term exposure to microgravity.

intraocular pressure↗
NASA NTRS1981

Hydrogen partitioning in pure cast aluminum as determined by dynamic evolution rate measurements

Hydrogen in pure aluminum can be found in two different states. One is related to a presence in gas-filled pores, while the other state involves the formation of a solid solution between hydrogen and aluminum. The considered investigation is concerned with the distribution of the hydrogen between various states. A dynamic technique is employed to measure the evolution of hydrogen from commercially available samples of polycrystalline pure aluminum under ultrahigh vacuum conditions. The obtained data are compared with the results of a statistical analysis concerning the porosity in the cast aluminum. It was found that more than 99 pct of the hydrogen in the aluminum is located in large pores. Less than 1 pct of the hydrogen is partitioned between the solid solution and the small pores.

Outlaw, R. A.↗
NASA NTRS1999

Evolution of the Iron K-Alpha Emission Line in the Black Hole Candidate GX339-4 During and Outburst Decay Phase

The evolution of the iron K-alpha line emission feature was found from the black hole candidate GX339-4 when its X-ray flux (2 to 10 keV) decreased significantly. With RXTE observations, a broad line emission feature around 7 keV was detected in its quiescent and low flux state; while in the high flux state, an emission line feature around 6.4 keV was detected. A similar 6.4 keV line feature was also detected with previous ASCA observations in a high flux state. We consider that the evolution could be the evidence of the variations in the geometric structure and the physical properties of the accretion flow when the accretion rate changed. This is because that the 7 keV line feature can be produced by the radiative recombination cascade, collisional excitation, and fluorescence of Fe XXVI and Fe XXV, which can exist in a very high temperature plasma; while the 6.4 keV line feature can be produced by fluorescent K-alpha line emission of neutral iron atoms in the cold accretion disk. (copyright) 1999 American Astronomical Society. All rights reserved.

Feng, Y.↗
NASA NTRS1985

A ray tracing model of gravity wave propagation and breakdown in the middle atmosphere

Gravity wave ray tracing and wave packet theory is used to parameterize wave breaking in the mesosphere. Rays are tracked by solving the group velocity equations, and the interaction with the basic state is determined by considering the evolution of the packet wave action density. The ray tracing approach has a number of advantages over the steady state parameterization as the effects of gravity wave focussing and refraction, local dissipation, and wave response to rapid changes in the mean flow are more realistically considered; however, if steady state conditions prevail, the method gives identical results. The ray tracing algorithm is tested using both interactive and noninteractive models of the basic state. In the interactive model, gravity wave interaction with the polar night jet on a beta-plane is considered. The algorithm produces realistic polar night jet closure for weak topographic forcing of gravity waves. Planetary scale waves forced by local transfer of wave action into the basic flow in turn transfer their wave action into the zonal mean flow. Highly refracted rays are also found not to contribute greatly to the climatology of the mesosphere, as their wave action is severely reduced by dissipation during their lateral travel.

Schoeberl, M. R.↗
NASA NTRS1996

Collisional Removal of O2 (c(sup 1) Sigma(sup-)(sub u), nu=9) by O2, N2, and He

The collisional removal Of 02 molecules in selected vibrational levels of the c state is studied using a two-laser double-resonance technique. The output of the first laser excites the 02 to nu = 9 or 10 of the c Sigma - state, and the ultraviolet output of the second laser monitors specific rovibrational levels via resonance-enhanced ionization. The temporal evolution of the c Sigma u state vibrational level is observed by scanning the time delay between the two pulsed lasers. As the rate constants for 02 and N2 are similar in magnitude, N2 collisions dominate the removal rate in the earth's atmosphere. For v= 10 colliding with 02, we find a removal rate constant that is 2-5 times that for v=9 and that single quantum collision cascade is an important pathway for removal.

Copeland, Richard A.↗