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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Equipotential doming in flooded circular basins on the moon

A procedure is presented that permits determination of the shape of the gravity field due to an arbitrary mass configuration with circular symmetry. The procedure is used to model the shape of the field associated with the lunar circular basins. The mean slopes of the equipotential surfaces generated by a superisostatic deposit corresponding to a near-surface Crisium-size mascon are calculated to fall within the range from 1:700 to 1:1000; those generated by a mantle rebound of the same excess mass, at 60 km below the lunar surface, cluster around the value of 1:1500.

Roth, L. E.↗
NASA NTRS2010

Why Income Comparison is Rational

A major factor affecting a person s happiness is the gap between their income and their neighbors , independent of their own income. This effect is strongest when the neighbor has moderately higher income. In addition a person s lifetime happiness often follows a "U" shape. Previous models have explained subsets of these phenomena, typically assuming the person has limited ability to assess their own (hedonic) utility. Here I present a model that explains all the phenomena, without such assumptions. In this model greater income of your neighbor is statistical data that, if carefully analyzed, would recommend that you explore for a new income-generating strategy. This explains unhappiness that your neighbor has greater income, as an emotional "prod" that induces you to explore, in accord with careful statistical analysis. It explains the "U" shape of happiness similarly. Another benefit of this model is that it makes many falsifiable predictions.

Wolpert, David H.↗
NASA NTRS2005

Measurement and Prediction of the Thermomechanical Response of Shape Memory Alloy Hybrid Composite Beams

Previous work at NASA Langley Research Center (LaRC) involved fabrication and testing of composite beams with embedded, pre-strained shape memory alloy (SMA) ribbons within the beam structures. That study also provided comparison of experimental results with numerical predictions from a research code making use of a new thermoelastic model for shape memory alloy hybrid composite (SMAHC) structures. The previous work showed qualitative validation of the numerical model. However, deficiencies in the experimental-numerical correlation were noted and hypotheses for the discrepancies were given for further investigation. The goal of this work is to refine the experimental measurement and numerical modeling approaches in order to better understand the discrepancies, improve the correlation between prediction and measurement, and provide rigorous quantitative validation of the numerical analysis/design tool. The experimental investigation is refined by a more thorough test procedure and incorporation of higher fidelity measurements such as infrared thermography and projection moire interferometry. The numerical results are produced by a recently commercialized version of the constitutive model as implemented in ABAQUS and are refined by incorporation of additional measured parameters such as geometric imperfection. Thermal buckling, post-buckling, and random responses to thermal and inertial (base acceleration) loads are studied. The results demonstrate the effectiveness of SMAHC structures in controlling static and dynamic responses by adaptive stiffening. Excellent agreement is achieved between the predicted and measured results of the static and dynamic thermomechanical response, thereby providing quantitative validation of the numerical tool.

Davis, Brian↗
NASA NTRS1997

Wind Tunnel Measured Effects on a Twin-Engine Short-Haul Transport Caused by Simulated Ice Accretions: Data Report

The purpose of this report is to release the data from the NASA Langley/Lewis 14 by 22 foot wind tunnel test that examined icing effects on a 1/8 scale twin-engine short-haul jet transport model. Presented in this document are summary data from the major configurations tested. The entire test database in addition to ice shape and model measurements is available as a data supplement in CD-ROM form. Data measured and presented are: wing pressure distributions, model force and moment, and wing surface flow visualization.

Reehorst, Andrew↗
NASA NTRS1997

Wind Tunnel Measured Effects on a Twin-Engine Short-Haul Transport Caused by Simulated Ice Accretions: Data Report

The purpose of this report is to release the data from the NASA Langley/Lewis 14 by 22 foot wind tunnel test that examined icing effects on a 1/8 scale twin-engine short-haul jet transport model. Presented in this document are summary data from the major configurations tested. The entire test database in addition to ice shape and model measurements is available as a data supplement in CD-ROM form. Data measured and presented are: wing pressure distributions, model force and moment, and wing surface flow visualization.

Reehorst, Andrew↗
NASA NTRSDate not supplied

Bimodal SLD Ice Accretion on a CRM Midspan Wing Section Model

An ice shape database has been created to document ice accretions on a 65 per cent scale version of the mid-span section of the Common Research Model resulting from an exposure to a Supercooled Large Drop (SLD) icing cloud with a bimodal drop size distribution. The ice shapes created were documented with photographs, laser scanned surface measurements over a section of the model span, and measurement of the ice mass over the same section of each accretion. Drop distribution effects were evaluated by using the same IRT icing conditions except with either monomodal or bimodal drop distributions. Ice shapes resulting from the bimodal distribution as well as from equivalent monomodal drop size distributions were obtained and compared. Results indicate that the ice shapes resulting from the monomodal and bimodal drop size distributions had equivalent mass and volume, as expected with this approach. Note: No audio portion for this record, additionally slide 9 has a playable video but must be downed in order to view.

Icing↗
DOE OSTI2015

Perturbations of the optical properties of mineral dust particles by mixing with black carbon: a numerical simulation study

Field observations show that individual aerosol particles are a complex mixture of a wide variety of species, reflecting different sources and physico-chemical transformations. The impacts of individual aerosol morphology and mixing characteristics on the Earth system are not yet fully understood. Here we present a sensitivity study on climate-relevant aerosols optical properties to various approximations. Based on aerosol samples collected in various geographical locations, we have observationally constrained size, morphology and mixing, and accordingly simulated, using the discrete dipole approximation model (DDSCAT), optical properties of three aerosols types: (1) bare black carbon (BC) aggregates, (2) bare mineral dust, and (3) an internal mixture of a BC aggregate laying on top of a mineral dust particle, also referred to as polluted dust. DDSCAT predicts optical properties and their spectral dependence consistently with observations for all the studied cases. Predicted values of mass absorption, scattering and extinction coefficients (MAC, MSC, MEC) for bare BC show a weak dependence on the BC aggregate size, while the asymmetry parameter ( g ) shows the opposite behavior. The simulated optical properties of bare mineral dust present a large variability depending on the modeled dust shape, confirming the limited range of applicability of spheroids over different types and size of mineral dust aerosols, in agreement with previous modeling studies. The polluted dust cases show a strong decrease in MAC values with the increase in dust particle size (for the same BC size) and an increase of the single scattering albedo (SSA). Furthermore, particles with a radius between 180 and 300 nm are characterized by a decrease in SSA values compared to bare dust, in agreement with field observations.This paper demonstrates that observationally constrained DDSCAT simulations allow one to better understand the variability of the measured aerosol optical properties in ambient air and to define benchmark biases due to different approximations in aerosol parametrization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2000

BOREAS TE-18 GeoSail Canopy Reflectance Model

The SAIL (Scattering from Arbitrarily Inclined Leaves) model was combined with the Jasinski geo metric model to simulate canopy spectral reflectance and absorption of photosynthetically active radiation for discontinuous canopies. This model is called the GeoSail model. Tree shapes are described by cylinders or cones distributed over a plane. Spectral reflectance and transmittance of trees are calculated from the SAIL model to determine the reflectance of the three components used in the geometric model: illuminated canopy, illuminated background, shadowed canopy, and shadowed background. The model code is Fortran. sample input and output data are provided in ASCII text files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Activity Archive Center (DAAC).

Hall, Forrest G.↗
DOE OSTI2022

Hydrogen Line Shape Uncertainties in White Dwarf Model Atmospheres

For isolated white dwarf (WD) stars, fits to their observed spectra provide the most precise estimates of their effective temperatures and surface gravities. Even so, recent studies have shown that systematic offsets exist between such spectroscopic parameter determinations and those based on broadband photometry. These large discrepancies (10% in T eff , 0.1 M ⊙ in mass) provide scientific motivation for reconsidering the atomic physics employed in the model atmospheres of these stars. Recent simulation work of ours suggests that the most important remaining uncertainties in simulation-based calculations of line shapes are the treatment of 1) the electric field distribution and 2) the occupation probability (OP) prescription. We review the work that has been done in these areas and outline possible avenues for progress.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2005

Comparison of Two IRI Plasmasphere Extensions with GPS-TEC Observations

Two plasmasphere extensions of the International Reference Ionosphere are made available for the users. It is aimed to estimate the effect of charged particles on technical devices in the Earth's environment and to define the ionosphere-plasmasphere operational conditions compatible with existing and future systems of radio communication, radio navigation and other relevant radio technologies in the ranges of medium and higher frequencies. The Global Core Plasma Model (GCPM-2000) of Gallagher et al. (2000) is an empirical description of thermal plasma densities in the plasmasphere, plasmapause, magnetospheric trough, and polar cap. GCPM-2000 uses the Kp index and is coupled to IRI in the transition region 500-600 km. The IZMIRAN plasmasphere model (Chasovitin et al., 1998; Gulyaeva et al., 2002) is an empirical model based on whistler and satellite observations. It presents global vertical analytical profiles of electron density smoothly fitted to IRI electron density profile at 1000 km altitude and extended towards the plasmapause (up to 36,000 km). For the smooth fitting of the two models, the shape of the IRI topside electron density profile is improved using ISIS 1, ISIS 2, and IK19 satellite inputs (Gulyaeva, 2003). The plasmasphere model depends on solar activity and magnetic activity (kp-index). The two IRI plasmasphere extensions are compared in the present study with the total electron content derived from records of Global Positioning Satellites (GPS-TEC) observations for different latitudinal, solar activity, magnetic activity, diurnal and seasonal conditions. The differences of model TEC with observed TEC in the topside ionosphere and plasmasphere are discussed.

Gulyacva, Tamara↗
NASA NTRS2004

Constructing an Educational Mars Simulation

Working in the Educational Programs Office, my task this summer is to model a 3D habitat that will be part of a future Mars base. With the President's charge to further explore mars by way of robotic-led and human-led missions, there has been a surge in the activity regarding the "red planet". Since all present designs are merely conjecture, I have some creative freedom in deciding what the habitat will look like. To get ideas for what a Mars habitat might be like, I looked at several references including websites and NASA documents. One of these was a NASA Technical Memorandum about Space Transportation Systems that I looked at to get insight on spaceship design. Information about the planet's environment, such as the gravity and the weather, is useful as well when designing the structure. The main software that I am using is Lightwave 3D and Modeler 7.5 that comes along with it. Lightwave is very complex in that it lets you model, surface, and animate so there was a lot to learn. To learn the software I watched a series of instructional videos, looked at online tutorials, and referenced several books. Modeling is like shaping clay with a computer. Every item modeled is made of smaller shapes called polygons. For example, each side of a box would be a different polygon. Modelers must be careful to design with users' systems in mind. Having a model made with too many polygons can slow down a walk-through, but it usually improves the small details on a model. Getting speed and quality proved tricky. An important thing for me to remember when modeling the habitat was to save space. Also, I must consider that technology in the future will be much different than now, so I must be especially creative. My project will be used in an educational walkthough simulation in which users can interact with the environment. I worked closely with intern Stephen Henke who built a Mars Rover, terrain and programmed code for the simulation. This summer's project will help me with future aspirations in computer graphics. Modeling is a valuable skill that I appreciate having the chance to learn and practice.

Henke, Stephen A.↗
DOE OSTI2014

Geometric and dynamic distortions in anisotropic galaxy clustering

We examine the signature of dynamic (redshift-space) distortions and geometric distortions (including the Alcock-Paczynski effect) in the context of the galaxy power spectrum measured in upcoming galaxy redshift surveys. Information comes from both the baryon acoustic oscillation (BAO) feature and the broadband power spectrum shape. Accurate modeling is required to extract this information without systematically biasing the result. We consider an analytic model for the power spectrum of dark matter halos in redshift space, based on the distribution function expansion, and compare with halo clustering measured in N-body simulations. We forecast that the distribution function model is sufficiently accurate to allow the inclusion of broadband information on scales down to k ∼ 0.2h Mpc{sup −1}, with somewhat better accuracy for higher bias halos. Compared with a BAO-only analysis with reconstruction, including broadband shape information can improve unbiased constraints on distance measures H(z) and D{sub A}(z) by ∼ 30% and 20%, respectively, for a galaxy sample similar to the DESI luminous red galaxies. The gains in precision are larger in the absence of BAO reconstruction. Furthermore, including broadband shape information allows the measurement of structure growth, through redshift-space distortions. For the same galaxy sample, the distribution function model is able to constrain fσ{sub 8} to ∼ 2%, when simultaneously fitting for H(z) and D{sub A}(z). We discuss techniques to optimize the analysis of the power spectrum, including removing modes near the line-of-sight that are particularly challenging to model, and whether these approaches can improve parameter constraints. We find that such techniques are unlikely to significantly improve constraints on geometry, although they may allow higher precision measurements of redshift-space distortions.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1981

An investigation of drag reduction for a box-shaped vehicle with various modifications

The influence of physical variables on the aerodynamic drag of a box shaped vehicle model was studied. The physical variables included built-in rounded front corners, and two different designs of add on flow vanes for the front of box shaped vehicle with 67 deg and 90 deg of arc. For a diesel powered vehicle, only slightly larger than a family van, the built in rounded front corners provide a calculated fuel saving of about 6.0 liters per hour of driving (1.6 gallons per hour) at 88.6 km per hour (55 mph) in national average winds, as compared to the baseline vehicle having all square corners. The corresponding savings for a baseline vehicle to which front mounted flow vanes were added is competitive. For a gasoline powered vehicle the volumetric fuel savings would be larger by a factor of about 1.7. The fuel savings for a standard size motor home would be greater for the diesel or gasoline powered vehicles by from 30 to 35 percent because of the larger frontal area. Thus projected fuel savings for a standard size motor home powered by gasoline can approach 12.5 to 13.5 liters (3.3 to 3.6 gallons) for each hour driving at highway speeds.

Muirhead, V. U.↗
DOE OSTI2024

A crystal-plasticity-informed Gaussian Process Regression model to capture anisotropy in single crystal shape memory alloys

This work presents a machine learning (ML) framework that model the anisotropic actuation responses in a shape memory alloy. A Gaussian Process Regression (GPR) based ML model is trained on a set of different crystal orientations subjected to different actuation conditions. The training employed thermo-mechanical responses from a crystal-plasticity model that captures phase-transformation, stress-induced plasticity, and transformation-induced plasticity. Further, on training the GPR-ML model at fixed stress level for different orientations, it captured the thermo-mechanical responses accounting for the anisotropy, and predicted responses for new orientations with good accuracy. The GPR-ML model is able to capture the transformation temperature variations even when trained using multiple stress levels, and the transformation strain showed significant deviations. The developed GPR-ML model gave reasonable predictions for an unexplored sample set of orientations and loading conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2016

ELECTRON ACCELERATION IN PULSAR-WIND TERMINATION SHOCKS: AN APPLICATION TO THE CRAB NEBULA GAMMA-RAY FLARES

The γ -ray flares from the Crab Nebula observed by AGILE and Fermi -LAT reaching GeV energies and lasting several days challenge the standard models for particle acceleration in pulsar-wind nebulae because the radiating electrons have energies exceeding the classical radiation-reaction limit for synchrotron. Previous modeling has suggested that the synchrotron limit can be exceeded if the electrons experience electrostatic acceleration, but the resulting spectra do not agree very well with the data. As a result, there are still some important unanswered questions about the detailed particle acceleration and emission processes occurring during the flares. We revisit the problem using a new analytical approach based on an electron transport equation that includes terms describing electrostatic acceleration, stochastic wave-particle acceleration, shock acceleration, synchrotron losses, and particle escape. An exact solution is obtained for the electron distribution, which is used to compute the associated γ -ray synchrotron spectrum. We find that in our model the γ -ray flares are mainly powered by electrostatic acceleration, but the contributions from stochastic and shock acceleration play an important role in producing the observed spectral shapes. Our model can reproduce the spectra of all the Fermi -LAT and AGILE flares from the Crab Nebula, using magnetic field strengths in agreement with the multi-wavelength observational constraints. We also compute the spectrum and duration of the synchrotron afterglow created by the accelerated electrons, after they escape into the region on the downstream side of the pulsar-wind termination shock. The afterglow is expected to fade over a maximum period of about three weeks after the γ -ray flare.

79 ASTRONOMY AND ASTROPHYSICS↗