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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 1,693 records · Page 94
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Improving impact resistance of ceramic materials by energy absorbing surface layers

Energy absorbing surface layers were used to improve the impact resistance of silicon nitride and silicon carbide ceramics. Low elastic modulus materials were used. In some cases, the low elastic modulus was achieved using materials that form localized microcracks as a result of thermal expansion anisotropy, thermal expansion differences between phases, or phase transformations. In other cases, semi-vitreous or vitreous materials were used. Substantial improvements in impact resistance were observed at room and elevated temperatures.

Kirchner, H. P.↗
NASA NTRS1974

A theory of wave scatter from an inhomogeneous medium with a slightly rough boundary and its application to sea ice

An analytical theory of electromagnetic wave scattering from an inhomogeneous medium with a slightly rough boundary surface is formulated. The inhomogeneity in the medium is assumed to vary continuously in the vertical direction and to have a small random variation in the horizontal direction. The medium is assumed to consist of two layers. Maxwell's equations are solved by using the small perturbation method together with Fourier transform technique. The resulting differential equations are solved by using WKB and variation of parameter methods. Field amplitudes in each medium are determined by taking boundary conditions into account. The expressions for first order polarized radar backscatter cross-section are obtained. An attempt is made to apply the developed theory to compute sea ice scatter. Numerical calculations are performed for polarized radar backscatter cross-section at two frequencies, 13.3 GHz and 400 MHz. It is shown that WKB method is applicable at both of these frequencies. Theoretical results are compared with the experimental results obtained from NASA Earth Resources Program mission 126. Theoretical results and experimental results are in good agreement.

Parashar, S. K.↗
NASA NTRS1981

Heat transfer in cooled porous region with curved boundary

Heat transfer characteristics are analyzed for a cooled two-dimensional porous medium having a curved boundary. A general analytical procedure is given in combination with a numerical conformal mapping method used to transform the porous region into an upper half plane. To illustrate the method, results are evaluated for a cosine shaped boundary subjected to uniform external heating. The results show the effects of coolant starvation in the thick regions of the medium, and the extent that internal heat conduction causes the heated surface to have a more uniform temperature.

Siegel, R.↗
NASA NTRS1986

A generalized theory for eccentric and misalignment effects in high-pressure annular seals

High-pressure annular seal leakage and dynamic coefficients vary with eccentricity and misalignment. Recent seal leakage data with both concentric and fully eccentric alignments support the seal leakage model with surface roughness and eccentricity effects included. In this paper, the seal dynamic coefficient calculation has been generalized and allows direct calculation of the seal dynamic coefficients at any circumferential location. The generalized solution agrees with the results obtained by using the calculated values of an earlier paper and performing a coordinate transformation. The analysis results coincide with the measured data in showing that the stiffness and damping matrices of seal coefficients are not skew symmetric, and the main diagonal seal coefficients are not equal. The measured direct stiffnesses were found higher than predicted by the concentric seal theory, but this may be explained by the presence of eccentricity in the test operating mode.

Chen, W. C.↗
NASA NTRS1987

Cartography of irregularly shaped satellites

Irregularly shaped satellites, such as Phobos and Amalthea, do not lend themselves to mapping by conventional methods because mathematical projections of their surfaces fail to convey an accurate visual impression of the landforms, and because large and irregular scale changes make their features difficult to measure on maps. A digital mapping technique has therefore been developed by which maps are compiled from digital topographic and spacecraft image files. The digital file is geometrically transformed as desired for human viewing, either on video screens or on hard copy. Digital files of this kind consist of digital images superimposed on another digital file representing the three-dimensional form of a body.

Batson, R. M.↗
NASA NTRS1988

Modeling of wave-coherent pressures in the turbulent boundary layer above water waves

The behavior of air pressure fluctuations induced by progressive water waves generated mechanically in a laboratory tank was simulated by solving a modified Orr-Sommerfeld equation in a transformed Eulerian wave-following frame of reference. Solution is obtained by modeling the mean and wave-coherent turbulent Reynolds stresses, the behavior of which in the turbulent boundary layer above the waves was simulated using a turbulent kinetic energy-dissipation model, properly modified to account for free-surface proximity and favorable pressure gradient effects. The distribution of both the wave-coherent turbulent Reynolds stress and pressure amplitudes and their corresponding phase lags was found to agree reasonably well with available laboratory data.

Papadimitrakis, Yiannis ALEX.↗
NASA NTRS1990

The observational basis for JPL's DE 200, the planetary ephemerides of the Astronomical Almanac

This paper documents the planetary observational data used in a series of ephemerides produced at JPL over six years preceding the creation of DE118/LE62, the set which transformed directly into the JD2000-based set, DE200/LE200. Details of the data reduction procedures are presented, and techniques to overcome the uncertainties due to planetary topography are described. For the spacecraft data, the basic reductions are augmented by formulations for locating the transponder, whether in orbit or landed on the surface of a planet.

Standish, E. M., Jr.↗
NASA NTRS1943

On a new method for calculating the potential flow past a body of revolution

A new method is presented for obtaining the velocity potential of the flow about a body of revolution moving uniformly in the direction of its axis of symmetry in a fluid otherwise at rest. This method is based essentially on the fact that the form of the differential equation for the velocity potential is invariant with regard to conformal transformation of the meridian plane. By means of the conformal transformation of the meridian profile into a circle a system of orthogonal curvilinear coordinates is obtained, the main feature of which is that one of the coordinate lines is the meridian profile itself. The use of this type of coordinate system yields a simple expression of the boundary condition at the surface of the solid and leads to a rational process of iteration for the solution of the differential equation for the velocity potential. It is shown that the velocity potential for an arbitrary body of revolution may be expressed in terms of universal functions which, although not normal, are obtainable by means of simple quadratures. The general results are applied to a body of revolution obtained by revolving a symmetrical Joukowski profile about its axis of symmetry. A numerical example further serves to illustrate the theory.

Kaplan, Carl↗
NASA NTRS2005

Advanced Electrical Materials and Components Development: An Update

The primary means to develop advanced electrical components is to develop new and improved materials for magnetic components (transformers, inductors, etc.), capacitors, and semiconductor switches and diodes. This paper will give an update of the Advanced Power Electronics and Components Technology being developed by the NASA Glenn Research Center for use in future Power Management and Distribution subsystems used in space power systems for spacecraft and lunar and planetary surface power. The initial description and status of this technology program was presented two years ago at the First International Energy Conversion Engineering Conference held at Portsmouth, Virginia, August 2003. The present paper will give a brief background of the previous work reported and a summary of research performed the past several years on soft magnetic materials characterization, dielectric materials and capacitor developments, high quality silicon carbide atomically smooth substrates, and SiC static and dynamic device characterization under elevated temperature conditions. The rationale for and the benefits of developing advanced electrical materials and components for the PMAD subsystem and also for the total power system will also be briefly discussed.

Schwarze, Gene E.↗
NASA NTRS2003

Global navigation satellite sounding of the atmosphere and GNSS altimetry : prospects for geosciences

The vast illuminating power of the Global Positioning System (GPS), which transformed space geodesy in the 199Os, is now serving to probe the earth's fluid envelope in unique ways. Three distinct techniques have emerged: ground-based sensing of the integrated atmospheric moisture; space-based profiling of atmospheric refractivity, pressure, temperature, moisture, and other properties by active limb sounding; and surface (ocean and ice) altimetry and scatterometry with reflected signals detected from space. Ground-based GPS moisture sensing is already in provisional use for numerical weather prediction. Limb sounding, while less mature, offers a bevy of attractions, including high accuracy, stability, and vertical resolution; all-weather operation; and exceptionally low cost. GPS bistatic radar, r 'reflectometry,' is the least advanced but shows promise for a number of niche applications.

occultation↗
NASA NTRS2009

First Measurements of the HCFC-142b Trend from Atmospheric Chemistry Experiment (ACE) Solar Occultation Spectra

The first measurement of the HCFC-142b (CH3CClF2) trend near the tropopause has been derived from volume mixing ratio (VMR) measurements at northern and southern hemisphere mid-latitudes for the 2004-2008 time period from spaceborne solar occultation observations recorded at 0.02/cm resolution with the ACE (atmospheric chemistry experiment) Fourier transform spectrometer. The HCFC-142b molecule is currently the third most abundant HCFC (hydrochlorofluorocarbon) in the atmosphere and ACE measurements over this time span show a continuous rise in its volume mixing ratio. Monthly average measurements at northern and southern hemisphere midlatitudes have similar increase rates that are consistent with surface trend measurements for a similar time span. A mean northern hemisphere profile for the time span shows a near constant VMR at 8-20km altitude range, consistent on average for the same time span with in situ results. The nearly constant vertical VMR profile also agrees with model predictions of a long lifetime in the lower atmosphere.

Rinsland, Curtis P.↗
NASA NTRS2017

A Dose of Reality: Radiation Analysis for Realistic Human Spacecraft

INTRODUCTION As with most computational analyses, a tradeoff exists between problem complexity, resource availability and response accuracy when modeling radiation transport from the source to a detector. The largest amount of analyst time for setting up an analysis is often spent ensuring that any simplifications made have minimal impact on the results. The vehicle shield geometry of interest is typically simplified from the original CAD design in order to reduce computation time, but this simplification requires the analyst to "re-draw" the geometry with a limited set of volumes in order to accommodate a specific radiation transport software package. The resulting low-fidelity geometry model cannot be shared with or compared to other radiation transport software packages, and the process can be error prone with increased model complexity. The work presented here demonstrates the use of the DAGMC (Direct Accelerated Geometry for Monte Carlo) Toolkit from the University of Wisconsin, to model the impacts of several space radiation sources on a CAD drawing of the US Lab module. METHODS The DAGMC toolkit workflow begins with the export of an existing CAD geometry from the native CAD to the ACIS format. The ACIS format file is then cleaned using SpaceClaim to remove small holes and component overlaps. Metadata is then assigned to the cleaned geometry file using CUBIT/Trelis from csimsoft (Registered Trademark). The DAGMC plugin script removes duplicate shared surfaces, facets the geometry to a specified tolerance, and ensures that the faceted geometry is water tight. This step also writes the material and scoring information to a standard input file format that the analyst can alter as desired prior to running the radiation transport program. The scoring results can be transformed, via python script, into a 3D format that is viewable in a standard graphics program. RESULTS The CAD model of the US Lab module of the International Space Station, inclusive of all the racks and components, was simplified to remove holes and volume overlaps. Problematic features within the drawing were also removed or repaired to prevent runtime issues. The cleaned drawing was then run through the DAGMC workflow to prepare for analysis. Pilot tests modeling transport of 1GeV proton and 800MeV/A oxygen sources show that reasonable results are converged upon in an acceptable amount of overall computation time from drawing preparation to data analysis. The FLUKA radiation transport code will next be used to model both a GCR and a trapped radiation source. These results will then be compared with measurements that have been made by the radiation instrumentation deployed inside the US Lab module. DISCUSSION Early analyses have indicated that the DAGMC workflow is a promising toolkit for running vehicle geometries of interest to NASA through multiple radiation transport codes. In addition, recent work has shown that a realistic human phantom, provided via a subcontract with the University of Florida, can be placed inside any vehicle geometry for a combinatorial analysis. This added functionality gives the user the ability to score various parameters at the organ level, and the results can then be used as input for cancer risk models.

Barzilla, J. E.↗
NASA NTRSDate not supplied

TPSAS-NF1676L-33433-DND

Reducing aircraft noise is a major objective in the field of computational aeroacoustics. When designing next generation quiet aircraft, it is important to be able to accurately and efficiently predict the acoustic scattering by an aircraft body from a given noise source. Acoustic liners are an effective tool for aircraft noise reduction, and are characterized by a complex valued frequency-dependent impedance. Converted into the time-domain using Fourier transforms, an impedance boundary condition can be used to simulate the acoustic scattering of geometric bodies treated with acoustic liners. This work considers using either an impedance boundary condition or admittance boundary condition to allow acoustic scattering problems to be modeled with geometries consisting of both un-lined and lined surfaces; admittance is defined to be the inverse of impedance. Three different acoustic liner models will be discussed: the Extended Helmholtz Resonator Model, the Three-Parameter Impedance Model, and a Broadband Model. In the Extended Helmholtz Resonator Model and Three-Parameter Impedance Model, the liner impedance is specified at a single frequency; the Broadband Model allows for the investigation of multiple frequencies simultaneously. The impedance and admittance boundary conditions for each model will be derived and coupled with a time-domain boundary integral equation. The scattering solution will be obtained iteratively using spatial and temporal basis functions. Stability will be demonstrated through eigenvalue analysis. Moreover, fast algorithms and high performance computing are considered to both assess and reduce the computational cost of the simulation.

Michelle E Rodio↗
DOE OSTI2020

FFT-based solver for higher-order and multi-phase-field fracture models applied to strongly anisotropic brittle materials

This paper presents the application of a fast Fourier transform (FFT) based method to solve two phase field models designed to simulate crack growth of strongly anisotropic materials in the brittle regime. By leveraging the ability of the FFT-based solver to generate solutions with higher-order and global continuities, we design two simple algorithms to capture the complex fracture patterns (e.g. sawtooth, and curved crack growth) common in materials with strongly anisotropic surface energy via the multi-phase-field and high-order phase-field frameworks. A staggered operator-split solver is used where both the balance of linear momentum and the phase field governing equations are formulated in the periodic domain. The unit phase field of the initial failure region is prescribed by the penalty method to alleviate the sharp material contrast between the initial failure region and the base material. The discrete frequency vectors are generalized to estimate the second and fourth order gradients such that the Gibbs effect near shape interfaces or jump conditions can be suppressed. Furthermore, a preconditioner is adopted to improve the convergence rate of the iterative linear solver. Three numerical experiments are used to systematically compare the performance of the FFT-based method in the multi-phase-field and high-order phase-field frameworks.

42 ENGINEERING↗
DOE OSTI2024

Underlying mechanism of structural transformation between GaSb and GaAs response to intense electronic excitation

Ion irradiation of semiconductors has emerged as a promising approach for fabricating self-organized nanosystems with high atomic precision, despite often being accompanied by undesirable phenomena. Exploring the mechanisms underlying structural transformations is crucial for assessing nanostructure array types under complex irradiation environments. By quantitatively calculating the thermodynamically driven processes and analyzing the impact of intrinsic structural parameters, distinct structural transformations in response to intense electronic excitation are systematically investigated in gallium antimonide (GaSb) and gallium arsenide (GaAs) systems. In high-energy regimes, the nanofibers layer of GaSb exhibits intriguing structural discrepancy, characterized by partial nanofibers with coherent boundaries, interspersed nanopores accompanied by antisite defects and Ga precipitates, distinguishing to a series of discontinuous latent tracks that emerged within cylindrical trajectories in GaAs. Furthermore, significant diffusion behaviors of the nanohillocks are discovered in GaAs, with higher average roughness than GaSb, driven by the gradient stress distribution influenced by the free-surface effects. The deposition energy for melting phase formation, Gibbs free energy, and Ga diffusion coefficients contribute to the distinctive structural features, evidencing relatively stable morphological configurations and higher irradiation resistance in GaAs. Consequently, special optoelectronic properties associated with structural discrepancies facilitate the design and optimization of material functionalities by irradiation technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Supported Electrophilic Organoruthenium Catalyst for the Hydrosilylation of Olefins

A series of supported electrophilic organoruthenium complexes has been synthesized via surface organometallic chemistry (SOMC) techniques and applied to the selective hydrosilylation of olefins. The air-sensitive 16e - complex Cp*RuMes(PCy 3 ) (1) (Cp* = pentamethylcyclopentadienyl, Mes = mesityl) was synthesized by the treatment of Cp*RuCl(PCy 3 ) with mesityl Grignard MesMgBr. This species was chemisorbed onto sulfated zirconia SO 4 /ZrO 2 , but the resulting material was inactive toward cyclohexene hydrosilylation with phenylsilane. Instead, Cp*RuMes(PCy 3 ) was treated with phenylsilane (PhSiH 3 ) to provide a ruthenium disilyl hydride complex Cp*RuH(SiH 2 Ph) 2 (PCy 3 ) (3), which was fully characterized by NMR spectroscopy and single-crystal X-ray diffraction. Grafting this species onto SO 4 /ZrO 2 resulted in the formation of phenylsilane along with the surface electrophilic species [Cp*RuH(R)(X-SiHPh)(PCy 3 )] (R = H, O 3 S-O or O 3 Zr-O; 4a, 4b, X = O 3 S-O, and O 3 Zr-O, respectively) as the major species. Material 4 was characterized via a combination of spectroscopic techniques including dynamic nuclear polarization (DNP)-enhanced solid-state NMR spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray absorption spectroscopy (XAS), and density function theory (DFT) calculations. Further, capping the remaining acid sites on 4 with Me 3 Si-SiMe 3 provides 5, which significantly reduces side reactions, such as olefin isomerization and silane redistribution. Catalyst 5 is a highly robust and selective hydrosilylation catalyst and can be recycled up to 5 times without significant diminishment of activity. Exclusive anti-Markovnikov regiochemistry, cis-addition selectivity, and the inactivity of secondary and tertiary silanes provide support for the proposed Glaser-Tilley mechanism involving cationic ruthenium silylene species analogous to homogeneous systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1984

Utilization of satellite cloud information to diagnose the energy state and transformations in extratropical cyclones

A study of the contribution of latent heat release to the synoptic scale vertical motions in the Jan. 9-11, 1975 extratropical cyclone case study was completed. Results indicate that early cyclone development was dominated by dry dynamical forcing. However, as the cyclone matured, the influence of latent heating became more significant. This influence appeared to be of two types, (1) the direct impact of heating causing a lowering of surface pressures, and (2) an indirect role in which the heating altered thermal and vorticity gradients and lead to subsequent increases in dry dynamical forcing. The kinetic energy budget was completed and extended to include an available potential energy budget. Focusing on the eddy component of the budgets, results indicate that kinetic energy increased throughout the cyclone's development, with the increase being most pronounced after the onset of significant latent heat release. Latent heating played a strong role not only in generating available potential energy, but also in forcing baroclinic release of potential energy.

Smith, P. J.↗
DOE OSTI2021

Assessment and comparison of ordered & non-ordered supported metal oxide catalysts for upgrading propane to propylene

Propylene is an important chemical feedstock that is largely produced via cracking of oil-derived naphtha. Direct conversion of propane into propylene may be a more attractive alternative. Specifically, propane dehydrogenation (DH) and oxidative dehydrogenation (ODH) are promising for this transformation, albeit only DH has been industrially implemented. However, even the best DH catalysts (Pt-based) still suffer from deactivation. VO x - and BO x -based ODH catalysts result in significant over-oxidation and lack a mechanistic understanding. A common challenge in developing these catalysts is the broad distribution of surface species caused by the use of non-ordered catalyst supports. This hampers clear structure-performance correlations. Recent progress in the preparation of well-defined active sites on ordered supports has brought about improved catalysts, as well as fundamental insight into the working mechanism. This review will highlight recent advancements in the development of these catalysts and provide direction on the use of ordered supports for propane upgrading.

03 NATURAL GAS↗