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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

On isostatic geoid anomalies

In regions of slowly varying lateral density changes, the gravity and geoid anomalies may be expressed as power series expansions in topography. Geoid anomalies in isostatically compensated regions can be directly related to the local dipole moment of the density-depth distribution. This relationship is used to obtain theoretical geoid anomalies for different models of isostatic compensation. The classical Pratt and Airy models give geoid height-elevation relationships differing in functional form but predicting geoid anomalies of comparable magnitude. The thermal cooling model explaining ocean floor subsidence away from mid-ocean ridges predicts a linear age-geoid height relationship of 0.16 m/m.y. Geos 3 altimetry profiles were examined to test these theoretical relationships. A profile over the mid-Atlantic ridge is closely matched by the geoid curve derived from the thermal cooling model. The observed geoid anomaly over the Atlantic margin of North America can be explained by Airy compensation. The relation between geoid anomaly and bathymetry across the Bermuda Swell is consistent with Pratt compensation with a 100-km depth of compensation.

Haxby, W. F.↗
NASA NTRS1991

Rate dependent stress-strain behavior of advanced polymer matrix composites

The formulation of an elastic/viscoplastic constitutive model which was used to predict the measured behavior of graphite/thermoplastic and graphite/bismaleimide composite materials at elevated temperature is described. The model incorporates the concepts of overstress and effective strain/strain to provide a simple formulation which was able to account for material behavior under monotonic tension or compression loads over a temperature range of 23 to 200 C. Observed behavior such as stress relaxation and steady state creep, in off-axis tension and compression tests, were predicted by the model. Material constants required by the model were extracted from simple off-axis test data.

Gates, Thomas S.↗
NASA NTRS2020

Very High Resolution, Altitude-Corrected, TMPA-Based Monthly Satellite Precipitation Product Over the CONUS

The Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) product provided over 17 years of gridded precipitation datasets. However, the accuracy and spatial resolution of TMPA limits the applicability in hydrometeorological applications. We present a dataset that enhances the accuracy and spatial resolution of the TMPA monthly product (3B43). We resample the TMPA data to a 1 km grid and apply a correction function derived from the Parameter-elevation Regressions on Independent Slopes Model (PRISM) to reduce bias in the data. We confirm a linear relationship between bias and elevation above 1,500 meters where TMPA underestimates measured precipitation, providing a proof-of-concept of how simple linear scaling can be used to augment existing satellite datasets. The result of the correction is the High-Resolution Altitude-Corrected Precipitation product (HRAC-Precip) for the CONUS. Using 9,200 precipitation stations from the Global Historical Climatology Network (GHCN), we compare the accuracy of TMPA 3B43 versus the new HRAC-Precip product. The results show an improvement of the mean absolute error of 12.98% on average.

Hossein Hashemi↗
DOE OSTI2021

Geophysical and Environmental Monitoring Data, Lower Watershed, Teller Road Mile Marker 27, Seward Peninsula, Alaska, 2017-2019

This data set contains geophysical and environmental monitoring data acquired between September 2017 and 2019 at the lower Teller watershed, Seward Peninsula, Alaska. Geophysical data comprises processed resistivity data, acquired daily between Spring and Fall of 2018 and 2019, and a baseline measurement of Fall 2017. The environmental monitoring data comprises depth resolved, distributed soil moisture and soil temperature data. These measurements were obtained used Decagon 5TE sensors placed at 0.1 m, 0.2 m , 0.3 m, and 0.4 m depth. In addition, temperature data at 0.5 m, 1.0 m, and 1.5 m were acquired using Hobo temperature sensors. Data were collected to improve our understanding of the hydrological response of discontinuous permafrost systems, in particular focusing on multi-annual dynamics and short term disturbances, such as snowmelt or precipitation events. The electrical resistivity tomography (ERT) monitoring data are included as processed resistivity models, with model cells x dimension equal to the distance along the profile, and model z dimension being elevation. The start and end point of the transect are (UTM Zone 3N): E 454881.66 m, N 7178949.45 m, and E 454772.60, N 7178885.81. Locations of the soil moisture and temperature sensors are provided in the data package. This dataset is discussed in detail in the Uhlemann, S. et al 2021 paper listed in the references. This dataset includes one *.pdf user guide and 315 *.csv data files included within four zipped files.The Next-Generation Ecosystem Experiments: Arctic (NGEE Arctic), was a research effort to reduce uncertainty in Earth System Models by developing a predictive understanding of carbon-rich Arctic ecosystems and feedbacks to climate. NGEE Arctic was supported by the Department of Energy's Office of Biological and Environmental Research.The NGEE Arctic project had two field research sites: 1) located within the Arctic polygonal tundra coastal region on the Barrow Environmental Observatory (BEO) and the North Slope near Utqiagvik (Barrow), Alaska and 2) multiple areas on the discontinuous permafrost region of the Seward Peninsula north of Nome, Alaska.Through observations, experiments, and synthesis with existing datasets, NGEE Arctic provided an enhanced knowledge base for multi-scale modeling and contributed to improved process representation at global pan-Arctic scales within the Department of Energy's Earth system Model (the Energy Exascale Earth System Model, or E3SM), and specifically within the E3SM Land Model component (ELM).

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1985

Magsat and POGO magnetic anomalies over the Lord Howe Rise Evidence against a simple continental crustal structure

Magsat average scalar and POGO reduced-to-pole magnetic anomaly data both show prominent positive signatures over the Lord Howe Rise. Although generally assumed to be continental in nature, the Lord Howe Rise cannot simply be submerged ordinary continental crust, which would produce a negative anomaly contrast with respect to the surrounding higher susceptibility oceanic crust. Three-dimensional modeling of the plateau, using the known crustal structure and assuming an induced origin for the satellite elevation anomaly, leads to a model in which the lowest crustal layer in an otherwise 'continental' crustal structure has an unusually high susceptibility in the range cgs 0.008-0.010 (SI 0.10-0.13). Replacement or alteration of the lowest layer by a high-susceptibility rock type may be related to the subsidence of the plateau.

Frey, H.↗
NASA NTRS1991

Modeling and simulations of the DSS 13 antenna control system

A model of the antenna control system for the azimuth and elevation axes of the Deep Space Station (DSS) 13 antenna is developed. This model is used for simulation of elevation and azimuth dynamics, cross-coupled dynamics, and radio-frequency pointing error due to both input commands and wind disturbances. This model also serves as a tool for the antenna controller design. A modal state-space model of the antenna structure was obtained from its finite-element model with a free-rotating tipping structure and alidade. Model reduction techniques applied separately for the antenna structure, elevation, and azimuth drives, and rate-loop model reduce the system order to one-third of that of the original, while preserving its significant dynamic properties. Extensive simulation results illustrate properties of the model.

Gawronski, W.↗
NASA NTRS1983

Assessment of two neglected effects in the analysis of an oil pumping ring seal

Many factors have been found to affect the performance of a pumping ring seal. In this paper, two effects (elevated reservoir temperature and rod deformation), both heretofore neglected, are assessed through the use of a thermoelastohydrodynamic numerical model of the pumping ring. Elevated reservoir temperatures are found to result in an increase in the amount of lubricant pumped while deformation of the translating rod is shown to cause a reduction in the lubricant pumped.

Keith, T. G.↗
DOE OSTI2020

Elevated temperature mechanical properties of Inconel 617 surface oxide using nanoindentation

Inconel 617 is a principal candidate material for helium gas cooled very-high-temperature reactors with outlet temperatures of 700–950 °C. Recent findings showed that this alloy develops unique surface oxide layers especially at high temperature (HT) helium environment with distinctive wear, friction and contact properties. This study investigates the elevated temperature mechanical properties of Inconel 617 top surface layers aged in HT helium environment. Nanoindentation technique is used to obtain load-displacement graphs of the alloy top surface oxide in temperatures ranging from 25 °C up to 600 °C. In addition, using finite element analysis along with an iterative regression technique, a semi-numerical method is developed to further measure and quantify the material parameters and, in particular, time-independent and creep characteristics of the oxide. Although Young's modulus of the oxide is found to be relatively close to the bulk for the tested temperatures, the yield strength and hardness, in comparison to the bulk material, increase significantly as the material is oxidized after aging. The oxide exhibits significant softening as the temperature increases to 600 °C. Unlike the bulk material, diffusion through the grains is found to be the dominant creep mechanism for the oxide. Considerable difference between the mechanical properties of the oxide and the bulk material shows the need for accurate measurements of near surface mechanical properties, if reliable predictive contact and tribological models are sought at elevated temperatures.

36 MATERIALS SCIENCE↗
NASA NTRS1999

Modeling Surface Structure Derived from Laser Altimeter Return Waveforms Using High-Resolution Elevation Data

The upcoming generation of operational spaceborne laser altimeters (i.e VCL and GLAS) record the interaction of emitted laser radiation with terrestrial surfaces in the form of a digitized waveform. We show that we can accurately model return laser altimeter waveforms as the sum of the reflections from individual surfaces within laser footprints. In one case, we predict return waveforms using high resolution elevation data generated by a small-footprint laser altimeter in a dense tropical forest. We compare over 3000 modeled and recorded waveform pairs using the Pearson correlation. The modeled and recorded waveforms are highly correlated, with a mean correlation of 0.90 and a median of 0.95. The mean correlation is highly dependent on the relative positions of the data sets. By shifting the relative locations of the two compared data sets, we infer that the data are colocated to within 0.4$\sim$m horizontally and 0.12$\sim$m vertically. The high degree of correlation shows that we can reliably synthesize the vertical structure information measured by medium-large footprint laser altimeters for complex, dense vegetation.

Blair, J. Bryan↗
NASA NTRS1990

Internal structure of Io and the global distribution of its topography

A global topography is presently calculated for two multilayer Io models in which dissipation occurs in a viscous asthenosphere and a solid mantle: (1) a 'thermal swell' model, in which topography and heat flow are positively correlated, and (2) a 'differentiated lithosphere' model, in which topography and heat flow are negatively correlated. Both the polar topography and the hypsometric distribution of elevations in the differentiated lithosphere model are better matched with observations than the thermal swell model. The shift of the equatorial basin-swell pattern indicates a recent zonal rotation of about 25 deg for Io's lithosphere.

Ross, M. N.↗
NASA NTRS2002

Performance of a Model Rich Burn-quick Mix-lean Burn Combustor at Elevated Temperature and Pressure

As interest in pollutant emission from stationary and aero-engine gas turbines increases, combustor engineers must consider various configurations. One configuration of increasing interest is the staged, rich burn - quick mix - lean burn (RQL) combustor. This report summarizes an investigation conducted in a recently developed high pressure gas turbine combustor facility. The model RQL combustor was plenum fed and modular in design. The fuel used for this study is Jet-A which was injected from a simplex atomizer. Emission (CO2, CO, O2, UHC, NOx) measurements were obtained using a stationary exit plane water-cooled probe and a traversing water-cooled probe which sampled from the rich zone exit and the lean zone entrance. The RQL combustor was operated at inlet temperatures ranging from 367 to 700 K, pressures ranging from 200 to 1000 kPa, and combustor reference velocities ranging from 10 to 20 m/s. Variations were also made in the rich zone and lean zone equivalence ratios. Several significant trends were observed. NOx production increased with reaction temperature, lean zone equivalence ratio and residence time and decreased with increased rich zone equivalence ratio. NOx production in the model RQL combustor increased to the 0.4 power with increased pressure. This correlation, compared to those obtained for non-staged combustors (0.5 to 0.7), suggests a reduced dependence on NOx on pressure for staged combustors. Emissions profiles suggest that rich zone mixing is not uniform and that the rich zone contributes on the order of 16 percent to the total NOx produced.

Peterson, Christopher O.↗
NASA NTRS1983

Monitoring tropical vegetation succession with LANDSAT data

The shadowing problem, which is endemic to the use of LANDSAT in tropical areas, and the ability to model changes over space and through time are problems to be addressed when monitoring tropical vegetation succession. Application of a trend surface analysis model to major land cover classes in a mountainous region of the Phillipines shows that the spatial modeling of radiance values can provide a useful approach to tropical rain forest succession monitoring. Results indicate shadowing effects may be due primarily to local variations in the spectral responses. These variations can be compensated for through the decomposition of the spatial variation in both elevation and MSS data. Using the model to estimate both elevation and spectral terrain surface as a posteriori inputs in the classification process leads to improved classification accuracy for vegetation of cover of this type. Spatial patterns depicted by the MSS data reflect the measurement of responses to spatial processes acting at several scales.

Robinson, V. B.↗
DOE OSTI2026

Dynamical Downscaling of Earth System Model Data for Energy System Analysis

Assessing energy resources (e.g., solar, wind, and hydro) under future scenarios requires datasets with sufficient spatial and temporal detail to capture variability and extreme events. While global-scale Earth System Model (ESM) projections are widely used, their coarse resolution limits direct application to regional energy system analyses. Dynamical downscaling offers a robust approach to generate physically consistent, fine-scale datasets that better represent local atmospheric processes impacting energy resources. In this work, we present a two-stage approach for producing high-resolution historical and future projections over the contiguous United States (CONUS). First, we optimize the Weather Research and Forecasting (WRF) model configuration for energy-relevant variables - solar irradiance, wind speed, and precipitation - by conducting ERA5-driven simulations at 8-km and 28-km resolution. Multiple physics schemes and model configurations within the WRF are evaluated against observational datasets including the National Solar Radiation Database (NSRDB), the Parameter-elevation Regressions on Independent Slopes Model (PRISM), and the Stage IV multi-radar/multi-sensor precipitation product for the CONUS domain. Using the best-performing configuration, we dynamically downscale MPI-ESM1-2-HR simulations for 2000-2060 under SSP2-4.5 and SSP5-8.5 scenarios at 4-km spatial and hourly temporal resolution. This presentation will provide a comprehensive analysis of the results from multiple numerical experiments and high-resolution ESM projections. In addition, we will discuss potential applications of our high-resolution datasets within the energy sector and outline future research avenues dedicated to evaluating how extreme weather events influence system performance and resilience.

24 POWER TRANSMISSION AND DISTRIBUTION↗
NASA NTRS1984

Diffusive equilibrium distributions of He(+) in the plasmasphere

Recent satellite observations of thermal ion composition in the near-equatorial plasmasphere have shown that He(+) comprises 5-10 percent typically and occasionally 25 percent or more of the total thermal ion density. A steady state diffusive equillibrium model for the distributions of H(+), He(+) and O(+) along a plasmaspheric flux tube is used to elicit effects that may help explain these observed high He(+) fractional concentrations. The model indicates that both the ionospheric composition and the temperature distribution along the flux tubes are important factors controlling the equatorial He(+) composition, through the phlasma scale height and thermal diffusion effects. Direct comparison of the model results with thermal ion observations by ISEE-1 indicates that the effects incorporated into the model may explain some of the elevated He(+) concentrations. In some instances, however, effects not included in the model may be of importance.

Waite, J. H., Jr.↗
NASA NTRS1988

An automated procedure for material parameter evaluation for viscoplastic constitutive models

An automated procedure is presented for evaluating the material parameters in Walker's exponential viscoplastic constitutive model for metals at elevated temperature. Both physical and numerical approximations are utilized to compute the constants for Inconel 718 at 1100 F. When intermediate results are carefully scrutinized and engineering judgement applied, parameters may be computed which yield stress output histories that are in agreement with experimental results. A qualitative assessment of the theta-plot method for predicting the limiting value of stress is also presented. The procedure may also be used as a basis to develop evaluation schemes for other viscoplastic constitutive theories of this type.

Imbrie, P. K.↗
NASA NTRS1990

Topographic distribution of clear-sky radiation over the Konza Prairie, Kansas

A method for exploring the topographic modulation of clear-sky incoming radiation using a two-stream atmospheric model together with digital elevation data is presented to obtain the temporal and spatial distribution of this energy. Utilizing this methodology for the Konza Prairie, it is observed that the variance and spatial autocorrelation of the simulated radiation data changed with sun angle and elevation grid spacing. An analytical formula that describes the behavior of the variance as a function of optical depth, sun angle, and mean terrain slope can be developed by considering direct solar radiation variability on a constant-slope terrain which has a uniform albedo and a uniform distribution of slopes. The decrease in mean slope and the increase in slope and autocorrelation is attributed to a loss of some of the shorter-wavelength terrain features at coarser grid spacings.

Dubayah, Ralph↗
NASA NTRS1991

Critical experiments of the self-consistent model for polycrystalline Hastelloy-X

A viscoplastic constitutive model is presented for the estimation of the overall mechanical response of Hastelloy-X polycrystalline metals from a knowledge of single crystal behavior. The behavior of polycrystal is derived from that of single crystals using a self-consistent formulation. The single crystal behavior which has been used was developed by summing postulated slip on crystallographic slip systems. The plasticity and creep are treated coupledly using unified viscoplastic model which includes the interaction effects between rapid and slow deformation at elevated temperature. The validity of the model is directly tested by experiments on Hastelloy-X in both single crystal and polycrystalline versions.

Shi, Shixiang↗
NASA NTRS1992

Fracture and damage; Winter Annual Meeting of the American Society of Mechanical Engineers, Anaheim, CA, Nov. 8-13, 1992

The latest developments in the area of fracture and damage at high temperatures are discussed, in particular: modeling; analysis and experimental techniques for interface damage in composites including the effects of residual stresses and temperatures; and crack growth, inelastic deformation and fracture parameters for isotropic materials. Also included are damage modeling and experiments at elevated temperatures.

Nagar, Arvind↗