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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

Experimental Constraints on Ureilite Petrogenesis

This experimental study explores the petrogenesis of ureilites by a partial melting/smelting process. Experiments have been performed over temperature (1150-1280 C), pressure (5-12.5 MPa), and low oxygen fugacity (graphite-CO gas) conditions appropriate for a hypothetical ureilite parent body approximately 200 km in size. Experimental and modeling results indicate that a partial melting/smelting model of ureilite petrogenesis can explain many of the unique characteristics displayed by this meteorite group. Compositional information preserved in the pigeonite-olivine ureilites was used to estimate the composition of melts in equilibrium with the ureilites. The results of 20 experiments saturated with olivine, pyroxene, metal, and liquid with appropriate ureilite compositions are used to calibrate the phase coefficients and pressure-temperature dependence of the smelting reaction. The calibrated coefficients are used to model the behavior of a hypothetical residue that is experiencing fractional smelting. The residue is initially olivine-rich and smelting progressively depletes the olivine content and enriches the pyroxene and metal contents of the residues. The modeled residue composition at 1260 C best reproduces the trend of ureilite bulk compositions. The model results also indicate that as a ureilite residue undergoes isothermal decompression smelting over a range of temperatures, Ca/Al values and Cr203 contents are enriched at lower temperatures (below about 1240 C) and tend to decrease at higher temperatures. Therefore, fractional smelting can account for the high Ca/A1 and Cr203 wt% values observed in ureilites. We propose that ureilites were generated from an olivine-rich, cpx-bearing residue. Smelting began when the residue was partially melted and contained liquid, olivine, and carbon. These residues experienced varying degrees of fractional smelting to produce the compositional variability observed within the pigeonite-bearing ureilites. Variations in mineral composition, modal proportions, and isotopic signatures are best described by heterogeneous accretion of the ureilite parent body followed by minimal and variable degrees of igneous processing.

Singletary, Steven↗
NASA NTRS1987

Investigation of turbulent flow in highly curved ducts with application to turbomachinery components

Numerical predictions were performed using a semi-elliptic calculation procedure for the case of turbulent flow in passage through a 90 deg bend of square cross section. Two versions of the isotropic turbulent viscosity two equation k-epsilon model were used. The first, the wall function model (WFM), employs the logarithmic law-of-the-wall relation and the notion of equilibrium flow to set all the necessary boundary conditions at the first grid point adjacent to a solid wall. The second model, the Van Driest model (VDM), employs Prandtl's original mixing length formulation, in conjunction with Van Driest's semi-empirical relation for the mixing length, to calculate the turbulent viscosity in the near wall regions of the flow. In this case, boundary conditions for k and epsilon, required to calculate these quantities in the core of the flow, are obtained by matching the mixing length and Reynolds number model formulations in an overlapping region of the flow near the walls. In both cases the results obtained show an improvement over earlier calculations using an elliptic numerical procedure. This is attributed to the finer grids possible in the present work. Of the two models, the VDM formulation shows better overall conformity with the mean flow measurements. Neither model reproduces well the details of the stress distribution as a result of the implied isotropic turbulent viscosity.

Humphrey, J. A. C.↗
NASA NTRS1989

LIMEX '87 ice surface characteristics - Implications for C-band SAR backscatter signatures

Ice surface characterization data collected in 1987, during the Labrador Sea Ice Margin Experiment, are analyzed to estimate the changes in snow and ice properties at the onset of melt. Surface measurements were made from an ice research vessel on several days (some of which had coincident remote-sensing flights) at a number of locations in the marginal ice zone. These data are used as input parameters in a simple scattering model to simulate the effects of variations in material properties upon C-band scattering signatures. Snow moisture and large-scale surface roughness are demonstrated to have the largest effect upon HH polarization scattering cross-section sigma(HH)(O) and large differences are predicted between undeformed floe surfaces and deformed or undulating rough ice surfaces. Using a parametric approach, an approximate picture of rough and smooth ice signatures and their relative contrast are provided. The models reproduce a trend observed in synthetic aperture radar (SAR) images of increasing backscatter contrast between deformed and underformed ice over an early period of warning: such observations are consistent with the results of analysis of SAR images to date. The model also reproduces a calibrated SAR-derived signature with a reasonable degree of accuracy.

Drinkwater, Mark R.↗
NASA NTRS1986

Oxygen index: An approximate value for the evaluation of combustion characteristics

The oxygen index has gained international recognition for the determination of combustion characteristics of plastic material. The amounts of oxygen and nitrogen were more accurately determined for existing test equipment in order to specify the oxygen index as precisely and as reproducible as possible. Parameters are outlined such as the size of the ignition flame, ignition of test pieces, test piece sizes and test temperature. The minimum oxygen index was determined by the dimension and duration of the fire. The results are sufficiently accurate for factory operating conditions and are also reproducible.

Zartmann, I.↗
NASA NTRS2000

Analysis of the NASA White Sands Test Facility (WSTF) Test System for Friction-Ignition of Metallic Materials

Friction is a known ignition source for metals in oxygen-enriched atmospheres. The test system developed by the NASA White Sands Test Facility in response to ASTM G-94 has been used successfully to determine the relative ignition from friction of numerous metallic materials and metallic materials pairs. These results have been ranked in terms of a pressure-velocity product (PV) as measured under the prescribed test conditions. A high value of 4.1(exp 8) watts per square meter for Inconel MA 754 is used to imply resistance to friction ignition, whereas a low value of 1.04(exp 8) watts per square meter for stainless steel 304 is taken as indicating material susceptible to friction ignition. No attempt has been made to relate PV values to other material properties. This work reports the analysis of the WSTF friction-ignition test system for producing fundamental properties of metallic materials relating to ignition through friction. Three materials, aluminum, titanium, and nickel were tested in the WSTF frictional ignition instrument system under atmospheres of oxygen or nitrogen. Test conditions were modified to reach a steady state of operation, that is applied, the force was reduced and the rotational speed was reduced. Additional temperature measurements were made on the stator sample. The aluminum immediately galled on contact (reproducible) and the test was stopped. Titanium immediately ignited as a result of non-uniform contact of the stator and rotor. This was reproducible. A portion of the stator sampled burned, but the test continued. Temperature measurements on the stator were used to validate the mathematical model used for estimating the interface (stator/rotor) temperature. These interface temperature measurements and the associate thermal flux into the stator were used to distinguish material-phase transitions, chemical reaction, and mechanical work. The mechanical work was used to analyze surface asperities in the materials and to estimate a coefficient of fiction. The coefficient of fiction was analyzed in terms of material properties that is, hardness, Young's modulus and elasticity/plasticity of the material.

Shoffstall, Michael S.↗
NASA NTRS2005

Simulations of Dynamics and Transport during the September 2002 Antarctic Major Warming

A mechanistic model simulation initialized on 14 September 2002, forced by 100-hPa geopotential heights from Met Office analyses, reproduced the dynamical features of the 2002 Antarctic major warming. The vortex split on approx.25 September; recovery after the warming, westward and equatorward tilting vortices, and strong baroclinic zones in temperature associated with a dipole pattern of upward and downward vertical velocities were all captured in the simulation. Model results and analyses show a pattern of strong upward wave propagation throughout the warming, with zonal wind deceleration throughout the stratosphere at high latitudes before the vortex split, continuing in the middle and upper stratosphere and spreading to lower latitudes after the split. Three-dimensional Eliassen-Palm fluxes show the largest upward and poleward wave propagation in the 0(deg)-90(deg)E sector prior to the vortex split (coincident with the location of strongest cyclogenesis at the model's lower boundary), with an additional region of strong upward propagation developing near 180(deg)-270(deg)E. These characteristics are similar to those of Arctic wave-2 major warmings, except that during this warming, the vortex did not split below approx.600 K. The effects of poleward transport and mixing dominate modeled trace gas evolution through most of the mid- to high-latitude stratosphere, with a core region in the lower-stratospheric vortex where enhanced descent dominates and the vortex remains isolated. Strongly tilted vortices led to low-latitude air overlying vortex air, resulting in highly unusual trace gas profiles. Simulations driven with several meteorological datasets reproduced the major warming, but in others, stronger latitudinal gradients at high latitudes at the model boundary resulted in simulations without a complete vortex split in the midstratosphere. Numerous tests indicate very high sensitivity to the boundary fields, especially the wave-2 amplitude. Major warmings occurred for initial fields with stronger winds and larger vortices, but not smaller vortices, consistent with the initiation of wind-deceleration by upward-propagating waves near the poleward edge of the region where wave 2 can propagate above the jet core. Thus, given the observed 100-hPa boundary forcing, stratospheric preconditioning is not needed to reproduce a major warming similar to that observed. The anomalously strong forcing in the lower stratosphere can be viewed as the primary direct cause of the major warming.

winds↗
NASA NTRS2002

Reproducibility and Repeatability of Tensile and Low-Cycle Fatigue Properties in Propulsion Grade Hydrogen

Hydrogen has the potential of increased use in the future as an environmentally friendly fuel. It has, however, shown a tendency to embrittle some materials. To be used in a safe manner and to exploit its full potential, it will be necessary to develop a database of material properties in hydrogen environment. The tests needed to produce this data are costly to perform (tensile test cost 25 times more and low cycle fatigue test are 55 times as expensive). Moreover, there is presently a lack of universal test methods to ensure standardized data within the hydrogen community. Each of the industries that work with hydrogen (aerospace, petroleum, fuel cells, etc.) performs tests by their own laboratory-developed methods, thus rendering cross- comparisons of material property data highly questionable. It is extremely important that data generated in a hydrogen environment be done to a standard that reduces variance to a minimum and allows direct comparison of test results from different laboratories. Doing so will assure that all data generated can be used to further our understanding of the hydrogen effects and to make sure components/products designed for hydrogen are the safest and most reliable possible. This paper reviews the results of two 'round-robin' programs conducted by NASA-MSFC. These two programs examined the reproducibility and repeatability of tensile and low-cycle fatigue test results in high-pressure hydrogen environments. The studies indicated that even with the tightest controls available from current commercial standards, the reproducibility (between different laboratories) and repeatability (within a laboratory) results of the tensile tests exhibited five times the variance as in standard ambient air tests. The variance with the LCF tests were on the same order as with air tests, but that was due to the large variation present in the last Interlaboratory air program. The paper concludes with a recommendation for a program that would allow the development of improved test methods, leading to lower variance in the generation of mechanical property data in the future.

Vesely, E. J.↗
NASA NTRS2022

The Simulation and Subseasonal Forecasting of Hydrological Variables: Insights from a Simple Water Balance Model

Past work has shown that a land surface model’s (LSM’s) implicit (not explicitly coded) relationships between soil moisture and both evapotranspiration (ET) and runoff largely determine the LSM’s hydrological behavior. Here we estimate the relationships that appear to be operating in the real world and compare them to those of the LSM component of a state-of-the-art Earth system model (ESM). The two sets of relationships are determined by calibrating them within a simple water balance model (WBM): once using stream gauge observations from small, unregulated rivers over the eastern half of the U.S., and once using the runoffs generated by the LSM as part of a state-of-the-art atmospheric reanalysis. Hydrological simulations and subseasonal hydrological forecasts performed with the two calibrated versions of the WBM provide two key results. First, the version calibrated to the LSM-generated runoffs does successfully reproduce, to first order, the hydrological behavior of the full LSM within its ESM environment. Second, of the two WBM versions, the one calibrated to the observations reproduces more accurately a broad collection of fully independent streamflow observations as well as a similarly broad collection of in-situ soil moisture measurements. Taken together, the two results suggest that the observations-calibrated ET and runoff efficiency functions do successfully represent, at least to some degree, soil moisture controls over hydrological variability in Nature and can serve as potentially useful targets for further LSM development.

Water Balance Model↗
NASA NTRS1978

Remote sensing of the ozone profile in the lower stratosphere using UV and IR measurements from Nimbus-4

A method of combining the information from the infrared interferometer spectrometer (IRIS) and the backscatter ultraviolet spectrometer (BUV) on board the Nimbus-4 satellite to derive the ozone profile from 10 mb to surface is described. The radiance in the IRIS 9-micron band can be related to the ozone profile by the radiative transfer equation. The IR intensity due to ozone is dependent on the pressure broadening of spectral lines, and an estimate of a weighted mean pressure of the ozone layer can be obtained from total ozone supplied by BUV long wave intensity measurements. With the aid of the Chapman function, a model of the ozone concentration profile described by three parameters is obtained. Given the ozone concentration at 10 mb one calculates several possible combinations of the three parameters that can produce the required total ozone, and the final choice of parameter is determined from IR measurements. An ozone profile calculated in this way reproduces well the gross features of balloon ozone sounding results. Meridional cross sections of ozone concentration have also been derived which are in reasonably good agreement with balloon-derived cross-section for the northern latitudes and tropics.

Prabhakara, C.↗
NASA NTRS1982

The seasonal CO2 cycle on Mars - An application of an energy balance climate model

Energy balance climate models of the Budyko-Sellers variety are applied to the carbon-dioxide cycle on Mars. Recent data available from the Viking mission, in particular the seasonal pressure variations measured by Viking landers, are used to constrain the models. No set of parameters was found for which a one-dimensional model parameterized in terms of ground temperature gave an adequate fit to the observed pressure variations. A modified, two-dimensional model including the effects of dust storms and the polar hood reasonably reproduces the pressure curve, however. The implications of these results for Martian climate changes are discussed.

James, P. B.↗
NASA NTRS1986

Simulation of the thermospheric tides by use of the NCAR thermospheric general circulation model

Numerical calculations of the thermospheric tidal winds and temperatures at equinox are presented. The calculations were made using the National Center for Atmospheric Research Thermospheric General Circulation Model (TGCM), which includes the effects of viscosity, conductivity, diffusion, ion drag, winds, and temperature gradients. The thermospheric diurnal and semidiurnal tides are excited in situ by solar heating and by ion-neutral momentum coupling. The semidiurnal tidal calculations also include the effects of upward propagating waves generated by heating in the lower atmosphere. This semidiurnal propagating component is modeled by use of the classical tidal perturbations as lower boundary conditions. The model is tuned by adjusting the propagating tidal forcing term until calculated semidiurnal wind and temperature fields best approximate incoherent scatter observations. The tidal TGCM results are consistent with previous theoretical work and successfully reproduce high altitude temperature and meridional velocity data, but they give significantly lower magnitudes for velocities and temperatures near 160 km than are seen by observations.

Fensen, C. G.↗
NASA NTRS1985

Numerical simulations of large-scale solar magnetic fields

A transport equation which describes the evolution of the large-scale magnetic field of the sun was solved numerically. Data derived from solar magnetic observations are used to initialize the computations and to account for the emergence of new magnetic flux during the sunspot cycle. The objective is to assess the ability of the model to reproduce the observed evolution of the field patterns. Recent results from simulations of individual active regions over a few solar rotations and of the magnetic field of the sun over sunspot cycle 21 are discussed.

Devore, C. R.↗
NASA NTRS1988

Anharmonic and screening corrections to the melting of a two-dimensional charged colloidal crystal

The Kosterlitz-Thouless-Halperin-Nelson-Young theory of melting is applied to a two-dimensional charged colloidal crystal. The renormalization of elastic constants due to anharmonic and dislocation pair-screening effects is calculated. For colloidal spheres ('polyballs') suspended in a thin film of water confined between two glass plates whose surfaces are highly charged, as in recent experimental configurations, the corrections to the harmonic results simply require an altered effective polyball charge to reproduce virtually the identical melting curve of the harmonic approximation (which agrees well with experiment). The effect on the melting curve of added salt is also calculated; the corresponding experiments have yet to be performed. For a film between uncharged surfaces the anharmonic correction again softens the lattice significantly. Dislocation pair screening causes an additional but minor reduction of the elastic constants. Neither correction eliminates a nonmelting behavior characteristic of the two-dimensional screened Coulomb system in this configuration.

Chang, Enson↗
NASA NTRS1990

Vibration responses of two house structures during the Edwards Air Force Base phase of the national sonic boom program

The data are reproduced from NSBEO-1-67, which contains some preliminary results of the test program, and from NASA-Langley working papers 259 and 288 which are now out of print. Included are sample acceleration and strain recordings from F-104, B-58, and XB-70 sonic boom exposures, along with tabulations of the maximum acceleration and strain values measured for each one of about 130 flight tests. These data are compared with similar measurements for engine noise exposures of the building during simulated landing approaches and takeoffs of KC-135 aircraft.

Hubbard, Harvey H.↗
NASA NTRS1989

An opacity-sampled treatment of water vapor

Although the bands of H2O are strong in the spectra of cool stars and calculations have repeatedly demonstrated their significance as opacity sources, only approximate opacities are currently available, due both to the difficulty of accounting for the millions of lines involved and to the inadequacy of laboratory and theoretical data. To overcome these obstacles, a new treatment is presented, based upon a statistical representation of the water vapor spectrum derived from available laboratory data. This statistical spectrum of water vapor employs an exponential distribution of line strengths and random positions of lines whose overall properties are forced to reproduce the mean opacities observed in the laboratory. The resultant data set is then treated by the opacity-sampling method exactly as are all other lines, both molecular and atomic. Significant differences are found between the results of this improved treatment and the results obtained with previous treatments of water-vapor opacity.

Alexander, David R.↗
NASA NTRS1992

An assay for intermolecular exchange of alpha crystallin

An affinity column of alpha crystallin linked to cyanogen bromide-activated Sepharose was developed to study the exchange of alpha subunits. Alpha crystallin bound to the Sepharose-alpha complex was dissociated with 8 mol/l urea, followed by quantitation using high-performance reverse-phase liquid chromatography. The time course of binding at 37 degrees C showed a hyperbolic binding pattern reaching equilibrium between 6-18 hr. Under these conditions, binding of beta and gamma crystallins to the same matrix was less than 10% of the alpha values, as was binding of alpha to glycine-coupled Sepharose. This assay was used to demonstrate changes in the subunit exchange of alpha crystallins present in high molecular weight versus lower molecular weight aggregates of the human lens. These results show that this binding procedure was a specific reproducible assay that might be used to study intermolecular interactions of the alpha crystallins.

NASA Discipline Cell Biology↗
NASA NTRS2006

Experimental Validation of a Closed Brayton Cycle System Transient Simulation

The Brayton Power Conversion Unit (BPCU) is a closed cycle system with an inert gas working fluid. It is located in Vacuum Facility 6 at NASA Glenn Research Center. Was used in previous solar dynamic technology efforts (SDGTD). Modified to its present configuration by replacing the solar receiver with an electrical resistance heater. The first closed-Brayton-cycle to be coupled with an ion propulsion system. Used to examine mechanical dynamic characteristics and responses. The focus of this work was the validation of a computer model of the BPCU. Model was built using the Closed Cycle System Simulation (CCSS) design and analysis tool. Test conditions were then duplicated in CCSS. Various steady-state points. Transients involving changes in shaft rotational speed and heat input. Testing to date has shown that the BPCU is able to generate meaningful, repeatable data that can be used for computer model validation. Results generated by CCSS demonstrated that the model sufficiently reproduced the thermal transients exhibited by the BPCU system. CCSS was also used to match BPCU steady-state operating points. Cycle temperatures were within 4.1% of the data (most were within 1%). Cycle pressures were all within 3.2%. Error in alternator power (as much as 13.5%) was attributed to uncertainties in the compressor and turbine maps and alternator and bearing loss models. The acquired understanding of the BPCU behavior gives useful insight for improvements to be made to the CCSS model as well as ideas for future testing and possible system modifications.

Johnson, Paul K.↗