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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 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Observation and modeling of energetic particles at synchronous orbit on July 29, 1977

In the 12 hours immediately after a worldwide storm sudden commencement at 0027 UT on July 29, there was a series of at least four magnetospheric substorms, the last and largest of which exhibited an expansion phase onset at approximately 1200 UT. Data from six spacecraft in three general local time groupings (0300, 0700, and 1300 LT) are examined, and vector magnetic field data and energetic electron and ion data from approximately 15 keV to more than 2MeV are employed. Four primary types of studies are carried out: (1) timing and morphology of energetic particle injections; (2) variation of particle phase space densities, using local magnetic field and particle flux data; (3) measurement of boundary motions, using high-energy ion gradient anisotropies; and (4) adiabatic modeling, which included injection, large-scale convection, corotation, and gradient drifts. For the 1200 UT substorms, it is concluded that there was a substantial flux dropout in a broad sector near local midnight because of a large-scale boundary motion, followed by a recovery to a predropout configuration.

Baker, D. N.↗
NASA NTRS1984

Structure and polarization of active region microwave emission

Active region radio emission observations made at 6.16 cm wavelength during May 20-27, 1980, are the bases of maps of total intensity and circular polarization presented for the three regions whose Hale numbers are 16850, 16863, and 16864. A detailed comparison is made between these maps and on- and off-band H-alpha pictures and magnetograms. The neutral lines with which the strongest sources were associated have their two opposite polarities close to each other, implying a high magnetic field gradient, and are also associated with arch filament systems. A detailed analysis is undertaken of observations of the circular polarization sense inversion in region 16863. The large scale structure of the magnetic field can be approximated by a dipole with its axis inclined by 11 deg with respect to the photosphere, and with a dipole moment of about 2 x 10 to the 31 power cgs units.

Kundu, M. R.↗
NASA NTRS1987

Stochastic and hybrid-stress plate/shell finite elements for hot-section components

The research effort in the Center for the Advancement of Computational Mechanics at Georgia Tech has two main thrusts. The first of these is the development of special approaches for the numerical stress analysis of solids and structures whose material and geometric properties are uncertain. The second seeks to develop and implement high-efficiency plate and shell elements. The stochastic element method, currently being implemented, will be able to more accurately portray the probabilistic nature of stress, strain, and displacement in actual structures. Current research has provided a hybrid-stress shell element whose behavior is acceptable for aspect ratios as high as 30 to 1. Thus, substantially more complex analyses will be practicable as soon as this element is fully implemented. An additional advantage of the hybrid approach is that it permits more accurate stress-recovery at the upper and lower surfaces of the shell, an important consideration in high thickness-gradient applications. The software associated with the above research is being implemented in the form of extensions to the Nessus code. The hybrid shell element has been successfully tested in several small-deformation elastic analyses. The theoretical formulation of the stochastic elements is essentially complete; its implementation is just beginning.

Atluri, S. N.↗
NASA NTRS1988

Estimates of solar wind heating inside 0.3 AU

Helios 1 proton temperature data have been normalized in order to determine a base temperature-velocity curve at 0.3 AU and to provide quantitative estimates on the close-in heating at different solar wind velocities. The results suggest that the slope of the solar wind temperature gradients for high-speed streams inside 0.3 AU is about half of that found beyond it. The very-low-speed wind is shown to expand adiabatically all the way out. It is also found that intermediate speed winds have enhanced heating rates in proportion to their velocities.

Freeman, John W.↗
NASA NTRS1988

Color and population gradients in the core of the postcollapse globular cluster M30

A new technique has been developed for seeking color gradients in multicolor CCD images of a globular cluster. Application of this technique to M30 confirms the radial color gradient reported by others. The B - V and V - R colors show linear gradients, when plotted against log r, that are many times their statistical errors. In the radial range 3-100 arcsec, the B - V and V - R colors increase outwards by about (0.18 + or - 0.015) mag/dex and (0.09 + or - 0.01) mag/dex, respectively. Color-magnitude arrays of the central region show that the Balmer-line strength that accompanies the central blueness is due to an increased proportion of blue-horizontal-branch starlight in the center. This excess does not appear to be statistically significant in terms of star numbers, even though the color gradient is so highly significant.

Piotto, Giampaolo↗
NASA NTRS1992

Solar wind temperature observations in the outer heliosphere

The Pioneer 10, Pioneer 11, and Voyager 2 spacecraft are now at heliocentric distances of 50, 32 and 33 AU, and heliographic latitudes of 3.5 deg N, 17 deg N, and 0 deg N, respectively. Pioneer 11 and Voyager 2 are at similar celestial longitudes, while Pioneer l0 is on the opposite side of the sun. The baselines defined by these spacecraft make it possible to resolve radial, longitudinal, and latitudinal variations of solar wind parameters. The solar wind temperature decreases with increasing heliocentric distance out to a distance of 10-15 AU. At larger heliocentric distances, this gradient disappears. These high solar wind temperatures in the outer heliosphere have persisted for at least 10 years, which suggests that they are not a solar cycle effect. The solar wind temperature varied with heliographic latitude during the most recent solar minimum. The solar wind temperature at Pioneer 11 and Voyager 2 was higher than that seen at Pioneer 10 for an extended period of time, which suggests the existence of a large-scale variation of temperature with celestial longitude, but the contribution of transient phenomena is yet to be clarified.

Gazis, P. R.↗
NASA NTRS1990

Thermal Conductivity and Temperature Limits of Electron-Beam Physical-Vapor-Deposited ZrO2-7wt%Y2O3 Thermal Barrier Coating

The electron-beam physical-vapor-deposited (EB-PVD) ZrO2-7wt%Y2O3 thermal barrier coating has been widely used to protect engine hot section components in modem aircraft engines. Thermal conductivity and the conductivity increases due to sintering and phase changes are important coating design parameters. There is a need to characterize the coating thermal conductivity behavior and temperature limits, in order to potentially take full advantage of the coating capability. In addition, since the ZrO2-7wt%Y2O3 coating is often used as a baseline coating for the development of advanced lower thermal conductivity and higher temperature capability coatings, a thorough evaluation of the coating conductivity behavior at future higher engine operating temperatures will be useful for more accurately assessing the benefit gained from the new coating systems. In this study, thermal conductivity behavior of EB-PVD ZrO2-7wt%Y2O3 coating has been systematically investigated as a function of temperature (up to 2600 F) and time under steady-state and cyclic test conditions using a laser heat-flux technique. Thermal conductivity change kinetics were determined under realistic engine high temperature thermal gradient conditions, and correlated to the coating microstructural and phase changes. The thermal conductivity prediction models have been established in terms of heat flux, time, and testing temperatures.

Zhu, Dongming↗
NASA NTRS2007

Simple and Efficient Numerical Evaluation of Near-Hypersingular Integrals

Recently, significant progress has been made in the handling of singular and nearly-singular potential integrals that commonly arise in the Boundary Element Method (BEM). To facilitate object-oriented programming and handling of higher order basis functions, cancellation techniques are favored over techniques involving singularity subtraction. However, gradients of the Newton-type potentials, which produce hypersingular kernels, are also frequently required in BEM formulations. As is the case with the potentials, treatment of the near-hypersingular integrals has proven more challenging than treating the limiting case in which the observation point approaches the surface. Historically, numerical evaluation of these near-hypersingularities has often involved a two-step procedure: a singularity subtraction to reduce the order of the singularity, followed by a boundary contour integral evaluation of the extracted part. Since this evaluation necessarily links basis function, Green s function, and the integration domain (element shape), the approach ill fits object-oriented programming concepts. Thus, there is a need for cancellation-type techniques for efficient numerical evaluation of the gradient of the potential. Progress in the development of efficient cancellation-type procedures for the gradient potentials was recently presented. To the extent possible, a change of variables is chosen such that the Jacobian of the transformation cancels the singularity. However, since the gradient kernel involves singularities of different orders, we also require that the transformation leaves remaining terms that are analytic. The terms "normal" and "tangential" are used herein with reference to the source element. Also, since computational formulations often involve the numerical evaluation of both potentials and their gradients, it is highly desirable that a single integration procedure efficiently handles both.

Fink, Patrick W.↗
NASA NTRS2003

Solution-Adaptive Program for Computing 2D/Axi Viscous Flow

A computer program solves the Navier- Stokes equations governing the flow of a viscous, compressible fluid in an axisymmetric or two-dimensional (2D) setting. To obtain solutions more accurate than those generated by prior such programs that utilize regular and/or fixed computational meshes, this program utilizes unstructured (that is, irregular triangular) computational meshes that are automatically adapted to solutions. The adaptation can refine to regions of high change in gradient or can be driven by a novel residual minimization technique. Starting from an initial mesh and a corresponding data structure, the adaptation of the mesh is controlled by use of minimization functional. Other improvements over prior such programs include the following: (1) Boundary conditions are imposed weakly; that is, following initial specification of solution values at boundary nodes, these values are relaxed in time by means of the same formulations as those used for interior nodes. (2) Eigenvalues are limited in order to suppress expansion shocks. (3) An upwind fluctuation-splitting distribution scheme applied to inviscid flux requires fewer operations and produces less artificial dissipation than does a finite-volume scheme, leading to greater accuracy of solutions.

Wood, William A.↗
NASA NTRS2015

RACORO Continental Boundary Layer Cloud Investigations: 1. Case Study Development and Ensemble Large-Scale Forcings

Observation-based modeling case studies of continental boundary layer clouds have been developed to study cloudy boundary layers, aerosol influences upon them, and their representation in cloud- and global-scale models. Three 60 h case study periods span the temporal evolution of cumulus, stratiform, and drizzling boundary layer cloud systems, representing mixed and transitional states rather than idealized or canonical cases. Based on in situ measurements from the Routine AAF (Atmospheric Radiation Measurement (ARM) Aerial Facility) CLOWD (Clouds with Low Optical Water Depth) Optical Radiative Observations (RACORO) field campaign and remote sensing observations, the cases are designed with a modular configuration to simplify use in large-eddy simulations (LES) and single-column models. Aircraft measurements of aerosol number size distribution are fit to lognormal functions for concise representation in models. Values of the aerosol hygroscopicity parameter, kappa, are derived from observations to be approximately 0.10, which are lower than the 0.3 typical over continents and suggestive of a large aerosol organic fraction. Ensemble large-scale forcing data sets are derived from the ARM variational analysis, European Centre for Medium-Range Weather Forecasts, and a multiscale data assimilation system. The forcings are assessed through comparison of measured bulk atmospheric and cloud properties to those computed in "trial" large-eddy simulations, where more efficient run times are enabled through modest reductions in grid resolution and domain size compared to the full-sized LES grid. Simulations capture many of the general features observed, but the state-of-the-art forcings were limited at representing details of cloud onset, and tight gradients and high-resolution transients of importance. Methods for improving the initial conditions and forcings are discussed. The cases developed are available to the general modeling community for studying continental boundary clouds.

Boundary layers↗
NASA NTRS2019

Micro-scale Artificial Weave Generation Capabilities for Thermal Protection System Material Modeling

Thermal Protection System (TPS) modeling requires accurate representation and prediction of the thermomechanical behavior of ablative materials. State-of-the-art TPS materials such as Phenolic Impregnated Carbon Ablator (PICA) have a proven flight record and demonstrate exceptional capabilities for handling extreme aerothermal heating conditions. The constant push for lightweight materials that are flexible in their design and performance, and hence allow for a wide range of mission profiles, has led NASA over the past years to develop its Heatshield for Extreme Entry Environment Technology (HEEET). HEEET is based primarily on a dual layer woven carbon fiber architecture and the technology has successfully been tested in arc-jet facilities. These recent developments have sparked interest in the accurate micro-scale modeling of composite weave architectures, to predict the structural response of macro-scale heatshields upon atmospheric entry. This effort can be extended to incorporate in-depth failure mechanics analyses as a result of local thermal gradients or high-velocity particle impact.

Visser, Sander J.↗
NASA NTRSDate not supplied

Validation of Cryogenic Propellant Tank Self-Pressurization by Leveraging Reduced Order Modeling within Computational Fluid Dynamics Simulation

Validation of cryogenic propellant tank self-pressurization was performed using a hybrid Computational Fluid Dynamics (CFD) and reduced order modeling methodology. Data from a liquid hydrogen ground test conducted at the K-site facility at the National Aeronautics and Space Administration (NASA) Glenn Research Center was used for the validation effort. Liquid phase dynamics were explicitly resolved with a CFD tool. Vapor phase dynamics were modeled as a point mass that communicated heat from the tank wall to the liquid phase via a boundary condition used at the gas-liquid interface. The method proved to be more accurate, robust, and efficient than explicit resolution of the dynamics using a standard Volume of Fluid (VOF) methodology. The subject pressurization process was found to be heavily dependent upon both the relatively high liquid temperature gradient near the gas-liquid interface and the natural convection flow path. Modeling the gas-liquid interface as an immovable surface eliminated temperature gradient destroying gas-liquid interface velocities observed in VOF simulations, and correspondingly enabled more rapid simulation since interface advection was not allowed. The single phase computational domain also facilitated the ability to demonstrate spatial resolution convergence of natural convection cells within the liquid which significantly impacted the tank pressurization rate. This work was used to demonstrate the critical physics for tank self-pressurization and numerical methodologies that may be used to best resolve those physics. The findings informed development and operation of production level CFD tools used in the Fluid Dynamics Branch at NASA Marshall Space Flight Center.

J. M. Brodnick↗
DOE OSTI2015

MAGNET DESIGNS FOR THE MULTI-BEND ACHROMAT LATTICE AT THE ADVANCED PHOTON SOURCE

The Advanced Photon Source (APS) is currently investigating replacing the existing two-bend 7 GeV lattice with a 6 GeV seven-bend achromat magnet lattice in order to achieve a low electron beam emittance [1]. This new lattice requires 1320 magnets, of which there are nine types. These include high strength quadrupoles (gradient up to ~97 T/m), sextupoles with second derivative of field up to ~7000 T/m2, longitudinal gradient dipoles with field ratio of up to 5, and transverse gradient dipoles with gradients of ~50 T/m and central field of ~0.6 T. These field requirements and the limited space available pose several design challenges. This paper presents a summary of magnet designs for the various magnet types developed through a collaboration of APS with FNAL and BNL.

Jaski, M.↗
DOE OSTI2019

Simulations for Field-Enhanced Conduction-Cooled Superconducting RF Electron Source

We present a novel RF design for a field enhanced electron source driven by field emission cathodes. The proposed electron source relies on the enhanced high electric field gradients at the cathode to simultaneously extract and accelerate electrons. The system will be tested in a conduction-cooled superconducting radiofrequency cavity recently demonstrated at Fermilab. In this work, we present electromagnetic and thermal simulations of the setup that support the feasibility of the design.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Why Are There so Few Reports of High-Energy Electron Drift Resonances? Role of Radial Phase Space Density Gradients

Models of monochromatic Pc5 (2–7 mHz) ultralow frequency (ULF) wave interactions with high energy (greater than ~1 MeV) electrons predict drift resonant interactions that can cause rapid radial transport and acceleration. There are few reports of electron drift resonance at energies greater than ~1 MeV, in contrast to lower energies; moreover, all previous reports occur in the aftermath of interplanetary shocks. These two facts are difficult to reconcile with theory and numerical simulations predicting that greater than ~1 MeV drift resonances should occur more often and in a wider variety of driving conditions. In this study, we show that a combination of observational sampling biases and nominal radial phase space density gradients is one explanation for this discrepancy between theory and observations. In particular, we examine electron dynamics in two case studies with very similar satellite coverage, solar wind conditions, and Pc5 wave properties, yet with different radial phase space density profiles. Using global wave and particle observations, we show that the events have vastly different particle responses despite having similar wave properties. Placing these results in context with past studies, we further show here that nominal radial PSD gradients near geostationary orbit can mask the expected drift resonance particle response and explain (1) the small number of past greater than ~1 MeV drift resonance reports and (2) the restriction of these reports to interplanetary shock events. We argue that future observational studies characterizing radial transport via drift resonance should examine global particle dynamics, including observations of the radial phase space density profile.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1999

Thermal Conductivity and Elastic Modulus Evolution of Thermal Barrier Coatings under High Heat Flux Conditions

Laser high heat flux test approaches have been established to obtain critical properties of ceramic thermal barrier coatings (TBCs) under near-realistic temperature and thermal gradients that may he encountered in advanced engine systems. Thermal conductivity change kinetics of a thin ceramic coating were continuously monitored in real time at various test temperatures. A significant thermal conductivity increase was observed during the laser simulated engine heat flux tests. For a 0.25 mm thick ZrO2-8%Y2O3 coating system, the overall thermal conductivity increased from the initial value of 1.0 W/m-K to 1. 15 W/m-K, 1. 19 W/m-K and 1.5 W/m-K after 30 hour testing at surface temperatures of 990C, 1100C, and 1320C. respectively. Hardness and modulus gradients across a 1.5 mm thick TBC system were also determined as a function of laser testing time using the laser sintering/creep and micro-indentation techniques. The coating Knoop hardness values increased from the initial hardness value of 4 GPa to 5 GPa near the ceramic/bond coat interface, and to 7.5 GPa at the ceramic coating surface after 120 hour testing. The ceramic surface modulus increased from an initial value of about 70 GPa to a final value of 125 GPa. The increase in thermal conductivity and the evolution of significant hardness and modulus gradients in the TBC systems are attributed to sintering-induced micro-porosity gradients under the laser-imposed high thermal gradient conditions. The test techniques provide a viable means for obtaining coating data for use in design, development, stress modeling, and life prediction for various thermal barrier coating applications.

Zhu, Dongming↗
DOE OSTI2016

A Keck adaptive optics survey of a representative sample of gravitationally lensed star-forming galaxies: High spatial resolution studies of kinematics and metallicity gradients

We discuss spatially resolved emission line spectroscopy secured for a total sample of 15 gravitationally lensed star-forming galaxies at a mean redshift of z≃2 based on Keck laser-assisted adaptive optics observations undertaken with the recently improved OSIRIS integral field unit (IFU) spectrograph. By exploiting gravitationally lensed sources drawn primarily from the CASSOWARY survey, we sample these sub-L{sup ∗} galaxies with source-plane resolutions of a few hundred parsecs ensuring well-sampled 2D velocity data and resolved variations in the gas-phase metallicity. Such high spatial resolution data offer a critical check on the structural properties of larger samples derived with coarser sampling using multiple-IFU instruments. We demonstrate how kinematic complexities essential to understanding the maturity of an early star-forming galaxy can often only be revealed with better sampled data. Although we include four sources from our earlier work, the present study provides a more representative sample unbiased with respect to emission line strength. Contrary to earlier suggestions, our data indicate a more diverse range of kinematic and metal gradient behavior inconsistent with a simple picture of well-ordered rotation developing concurrently with established steep metal gradients in all but merging systems. Comparing our observations with the predictions of hydrodynamical simulations suggests that gas and metals have been mixed by outflows or other strong feedback processes, flattening the metal gradients in early star-forming galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Breakdown insensitive acceleration regime in a metamaterial accelerating structure

A new regime in radiofrequency (rf) breakdown, named the breakdown insensitive acceleration regime (BIAR), was observed in an 11.7 GHz metamaterial structure for wakefield acceleration driven by rf pulses with a duration of a few nanoseconds. In the BIAR, rf breakdown occurs without interrupting potential beam acceleration, resulting in greater resilience to breakdown. We have investigated the possibility that BIAR can support higher gradients by characterizing the breakdown in a high-power test. The peak gradient reached 190 MV / m when the structure was powered by 6 ns long rf pulses with 115 MW peak power. The short rf pulses were extracted from 65 MeV electron bunch trains with a total charge of up to 210 nC. This work has revealed the benefits of short-pulse acceleration by characterizing rf breakdown in the previously unexplored parameter space. Published by the American Physical Society 2024

43 PARTICLE ACCELERATORS↗