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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 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Pterodactyl: Effects of 3D Thermal Analysis on Thermal Protection System Design for a Flap Control System

NASA’s Pterodactyl project has investigated the use of a novel multi-flap control system to facilitate precision targeting of Deployable Entry Vehicles (DEVs) during atmospheric re-entry [1]. DEVs can be folded to fit within the limiting cross-sectional area of current launch systems. Once deployed, the vehicle expands and settles into a pre-determined blunt body shape. While DEVs provide a more efficient solution to increased payload sizes, the absence of a back shell does not allow for easy integration of reaction control systems, which have historically been used for guidance and control (G&C) of rigid aeroshells during entry. One DEV solution, called the Adaptable, Deployable Entry Placement Technology (ADEPT), employs mechanically deployed gores. This provided the Pterodactyl project with the opportunity to incorporate a rib-mounted, 8-flap control system for G&C. Each flap can deflect independently in and out of the hypersonic flow, requiring TPS for the flaps. Previous work within the Pterodactyl project utilized 1D thermal analysis to design the TPS. However, the Pterodactyl project was concerned that the base level tools for 1D thermal analysis were not accounting for the 3D effects of the large heating gradients along and across the flaps, the in-depth in-plane conductivity of the TPS and internal structure, and the effects of the small edge radii at the neck of the flaps. This paper discusses the methodology and results of a 3D thermal analysis of the flap control system. Additionally, the results from the 1D and 3D thermal analyses are compared. It is found that elements of the original design that resulted from the 1D analysis may be overly conservative, and implementation of a 3D thermal analysis indicated a reduction in TPS thickness is feasible. This result helps to reduce the mechanical integration complexity of the flap at the rib tip and realizes potential mass savings.

Sarah N D'Souza↗
NASA NTRS2023

Large Photospheric Doppler Shift in Solar Active Region 12673: I. Field-Aligned Flows

Delta (δ) sunspots sometimes host fast photospheric flows along the central magnetic polarity inversion line (PIL). Here we study the strong Doppler shift signature in the central penumbral light bridge of solar active region NOAA 12673. Observations from the Helioseismic and Magnetic Imager (HMI) indicate highly sheared, strong magnetic fields. Large Doppler shifts up to 3.2 km s −1 appeared during the formation of the light bridge and persisted for about 16 hours. A new velocity estimator, called DAVE4VMwDV, reveals fast converging and shearing motion along the PIL from HMI vector magnetograms, and recovers the observed Doppler signal much better than an old version of the algorithm. The inferred velocity vectors are largely (anti-)parallel to the inclined magnetic fields, suggesting that the observed Doppler shift contains significant contribution from the projected, field-aligned flows. High-resolution observations from the Hinode/Spectro-Polarimeter (SP) further exhibit a clear correlation between the Doppler velocity and the cosine of the magnetic inclination, which is in agreement with HMI results and consistent with a field-aligned flow of about 9.6 km s −1 . The complex Stokes profiles suggest significant gradients of physical variables along the line of sight. We discuss the implications on the δ-spot magnetic structure and the flow-driving mechanism.

Solar active region magnetic fields↗
DOE OSTI2021

Unsupervised Resource Allocation with Graph Neural Networks

We present an approach for maximizing a global utility function by learning how to allocate resources in an unsupervised way. We expect interactions between allocation targets to be important and therefore propose to learn the reward structure for near-optimal allocation policies with a GNN. By relaxing the resource constraint, we can employ gradient-based optimization in contrast to more standard evolutionary algorithms. Our algorithm is motivated by a problem in modern astronomy, where one needs to select-based on limited initial information-among $10^9$ galaxies those whose detailed measurement will lead to optimal inference of the composition of the universe. Our technique presents a way of flexibly learning an allocation strategy by only requiring forward simulators for the physics of interest and the measurement process. We anticipate that our technique will also find applications in a range of resource allocation problems.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Characterizing Stress Roughness at Utah FORGE Through Simulation of Hydraulic Fracture Growth During 16A Stage 3 Stimulation

In most geologic formations, the vertical gradient of the minimum horizontal stress (𝜎 h ) exceeds the hydrostatic gradient, often driving hydraulic fractures to propagate upward. However, observations indicate that the upward growth of real hydraulic fractures is less pronounced than theoretical predictions based on smoothly varying 𝜎 h fields. In fact, the layered structure of sedimentary rocks hinders fracture propagation across layers, partially explaining the limited height growth observed in practice (Zoback et al., 2022). While crystalline rocks lack the pervasive layered fabric of sedimentary formations, they still possess structural fabric formed over their geologic history, resulting in inherently "rough" in situ stress fields. Recent studies have identified another key factor: the "roughness" of in situ stress, characterized by temporal, relatively short-wavelength fluctuations superimposed on the overall stress gradient. This stress roughness leads to apparent toughness anisotropy, where the vertical toughness appears significantly larger than the horizontal toughness (P. Fu et al., 2019; Dontsov & Suarez-Rivera, 2021). Neglecting the effects of rock fabric and stress roughness can yield inaccurate predictions of hydraulic fracture geometry and growth rates at larger length scales.

58 GEOSCIENCES↗
DOE OSTI2022

Training neural networks using Metropolis Monte Carlo and an adaptive variant

Abstract We examine the zero-temperature Metropolis Monte Carlo (MC) algorithm as a tool for training a neural network by minimizing a loss function. We find that, as expected on theoretical grounds and shown empirically by other authors, Metropolis MC can train a neural net with an accuracy comparable to that of gradient descent (GD), if not necessarily as quickly. The Metropolis algorithm does not fail automatically when the number of parameters of a neural network is large. It can fail when a neural network’s structure or neuron activations are strongly heterogenous, and we introduce an adaptive Monte Carlo algorithm (aMC) to overcome these limitations. The intrinsic stochasticity and numerical stability of the MC method allow aMC to train deep neural networks and recurrent neural networks in which the gradient is too small or too large to allow training by GD. MC methods offer a complement to gradient-based methods for training neural networks, allowing access to a distinct set of network architectures and principles.

97 MATHEMATICS AND COMPUTING↗
NASA NTRSDate not supplied

Nonlinear Homogenization of Finitely Deformed Viscoelastic-Viscoplastic Composites Using Mechanics of Structure Genome

The objective of this paper is to develop a micromechanics approach to homogenizing finitely deformed viscoelastic-viscoplastic composites using the mechanics of structure genome. The incremental constitutive relation for glassy polymers, formulated in the spatial configuration, is implemented in the present approach.This involves (1) pulling-back the constitutive model to the material configuration and (2)choosing the deformation gradient tensor and the first Piola–Kirchhoff stress tensor as the strain and the stress measures during homogenization, respectively. An Euler–Newton predictor–corrector method is developed for homogenization. Each step involves formulating a variational statement using the mechanics of structure genome, discretizing the statement in a finite-dimensional space, and solving the problem using an Euler/multilevel Newton method. The present approach is demonstrated by homogenizing fiber- and particle-reinforced composites undergoing uniaxial, biaxial, or shear deformation, at different stain rates.

Multi-scale modeling, High Strain Composites, Visc↗
NASA NTRS1984

The structures and energetics of fully nonlinear symmetric baroclinic waves

Rotating baroclinic flow for Richardson number lower than about 1 is studied by means of a finite difference Navier-Stokes model assuming no variations except in the vertical plane that completely contains the density gradient vector. The horizontally infinite channel to which attention is given further assumes periodic boundary conditions at the vertical computational boundaries and no-slip conducting horizontal boundaries. Two configurations are considered. Symmetric baroclinic waves developed in the flows in a manner consistent with linear theory, and it is noted that the structures and energetics of the fully developed waves were dependent on the Prandtl number Pr. For Pr greater than 1, the conversion from potential energy to wave kinetic energy was direct, via temperature and vertical motion correlation, while for Pr of less than 1, conversion proceeded from potential energy to average kinetic energy by means of an induced meridional flow, and then to wave kinetic energy.

Miller, T. L.↗
DOE OSTI2024

Soil microenvironmental variation drives below‐ground trait variation and interacts with macroclimate to structure above‐ground trait variation of arctic shrubs

Abstract Intraspecific trait variation can influence plant performance in different environments and may thereby determine the ability of individual plants to respond to climate change. However, our understanding of its patterns and environmental drivers across different spatial scales is incomplete, especially in understudied regions like the Arctic. To fill this knowledge gap, we examined above‐ground and below‐ground traits from three shrub taxa expanding across the tundra biome and evaluated their relationships with multiple microenvironmental and macroclimatic factors. The traits reflected plant size and structure (plant height, leaf area and root to shoot ratio), leaf economics (specific leaf area, nitrogen content), and root economics and collaboration with mycorrhizal fungi (specific root length, root tissue density, nitrogen content, and ectomycorrhizal colonisation intensity). We also measured leaf and root δ 15 N and leaf δ 13 C to characterise nitrogen source and acquisition pathways and plant water stress. Traits were measured in replicated plots ( N = 135) varying in soil microclimate, thaw depth and organic layer thickness established across five sites spanning a macroclimate gradient in northern Alaska. This hierarchical design allowed us to disentangle the independent and combined effects of fine‐scale and broad‐scale factors on intraspecific trait variation. We found substantial intraspecific variation at fine spatial scales for most traits and less variation along the macroclimate gradient and between shrub taxa. Consistent with these patterns, microenvironmental factors, mainly soil moisture and thaw depth, interacted with macroclimate, mainly climatic water deficit, to structure size‐structural and leaf trait variation. In contrast, most root traits responded additively to thaw depth and macroclimate. Synthesis . Our results demonstrate that above‐ground and below‐ground tundra shrub traits respond differently to microenvironmental and macroclimatic variation. These differing responses contribute to substantial trait variation at fine spatial scales and may decouple above‐ground and below‐ground trait responses to climate change.

Environmental Sciences & Ecology↗
NASA NTRS1981

Solutal convection induced macrosegregation and the dendrite to composite transition in off-eutectic alloys

The effect of solute gradient induced convection during vertical solidification on the macrosegregation of Pb-rich Pb-Sn off-eutectic alloys is determined experimentally as a function of composition and growth rate. In many cases macrosegregation is sufficient to prevent the plane front solidification of the alloy. The transition from dendritic to composite structure is found to occur when the composition of the solid is close enough to the eutectic composition to satisfy a stability criterion based on the ratio of the liquid temperature gradient to growth rate. A vertical or horizontal magnetic field of 0.1 T (1 kilogauss) does not reduce macrosegregation, but downward solidification (liquid below solid) virtually eliminates macrosegregation in small (3 mm) diameter samples.

Boettinger, W. J.↗
NASA NTRS1984

Structure and polarization of active region microwave emission

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

Kundu, M. R.↗
DOE OSTI2020

Formulation and solution approach for calibrating activity-based travel demand model-system via microsimulation

This study addresses the problem of calibrating utility-maximizing nested logit activity-based travel demand model-systems. After estimation, it is common practice to use aggregate measurements to calibrate the estimated model-system’s parameters prior to their application in transportation planning, policy making, and operations. However, calibration of activity-based model-systems has received much less attention. Existing calibration approaches are myopic heuristics in the sense that they do not consider the fundamental inter-dependencies among choice-models and do not have a systematic way to adjust model parameters. Also, other purely simulation-based approaches do not perform well in large-scale applications. In this study, we focus on utility-maximizing nested logit activity-based model-systems and calibrating aggregate statistics such as activity shares, mode shares, time-dependent & mode-specific OD flows, and time-dependent & mode-specific sensor counts. We formulate the calibration problem as a simulation-based optimization problem and propose a stochastic gradient-based solution procedure to solve it. The solution procedure relies on microsimulation to calculate expectations of the aggregate statistics of interest to the calibration problem. Additionally, we derive approximate analytical expressions for the gradient of the objective function —that are evaluated through microsimulation on mini-batches of the population. The proposed solution procedure is sensitive to the fundamental structure of the activity-based model-system and is non-myopic in considering the dependencies across its model components. The formulated optimization problem is non-convex, highly nonlinear, and potentially has multiple-minima. Lastly, we show —through a real-world application— that the proposed solution procedure outperforms other state-of-the-art purely simulation-based optimization approaches in terms of computational efficiency, stability, and convergence. We also compare various gradient-based solution algorithms to determine the best algorithm to update the parameters. This work has the potential to facilitate wider and easier application of activity-based model-systems.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1977

Surface temperatures and temperature gradient features of the US Gulf Coast waters

Satellite thermal infrared data on the Gulf of Mexico show that a seasonal cycle exists in the horizontal surface temperature structure. In the fall, the surface temperatures of both coastal and deep waters are nearly uniform. With the onset of winter, atmospheric cold fronts, which are accompanied by dry, low temperature air and strong winds, draw heat from the sea. A band of cooler water forming on the inner shelf expands, until a thermal front develops seaward along the shelf break between the cold shelf waters and the warmer deep waters of the Gulf. Digital analysis of the satellite data was carried out in an interactive mode using a minicomputer and software. A time series of temperature profiles illustrates the temporal and spatial changes in the sea-surface temperature field.

Huh, O. K.↗
NASA NTRS1979

The dynamics and control of large flexible space structures, 2. Part A: Shape and orientation control using point actuators

The equations of planar motion for a flexible beam in orbit which includes the effects of gravity gradient torques and control torques from point actuators located along the beam was developed. Two classes of theorems are applied to the linearized form of these equations to establish necessary conditions for controlability for preselected actuator configurations. The feedback gains are selected: (1) based on the decoupling of the original coordinates and to obtain proper damping, and (2) by applying the linear regulator problem to the individual model coordinates separately. The linear control laws obtained using both techniques were evaluated by numerical integration of the nonlinear system equations. Numerical examples considering pitch and various number of modes with different combination of actuator numbers and locations are presented. The independent model control concept used earlier with a discretized model of the thin beam in orbit was reviewed for the case where the number of actuators is less than the number of modes. Results indicate that although the system is controllable it is not stable about the nominal (local vertical) orientation when the control is based on modal decoupling. An alternate control law not based on modal decoupling ensures stability of all the modes.

Bainum, P. M.↗
NASA NTRS1992

Design of a high-temperature experiment for evaluating advanced structural materials

This report describes the design of an experiment for evaluating monolithic and composite material specimens in a high-temperature environment and subject to big thermal gradients. The material specimens will be exposed to aerothermal loads that correspond to thermally similar engine operating conditions. Materials evaluated in this study were monolithic nickel alloys and silicon carbide. In addition, composites such as tungsten/copper were evaluated. A facility to provide the test environment has been assembled in the Engine Research Building at the Lewis Research Center. The test section of the facility will permit both regular and Schlieren photography, thermal imaging, and laser Doppler anemometry. The test environment will be products of hydrogen-air combustion at temperatures from about 1200 F to as high as 4000 F. The test chamber pressure will vary up to 60 psia, and the free-stream flow velocity can reach Mach 0.9. The data collected will be used to validate thermal and stress analysis models of the specimen. This process of modeling, testing, and validation is expected to yield enhancements to existing analysis tools and techniques.

Mockler, Theodore T.↗
DOE OSTI2020

ABINIT: Overview and focus on selected capabilities

ABINIT is probably the first electronic-structure package to have been released under an open-source license about 20 years ago. It implements density functional theory, density-functional perturbation theory (DFPT), many-body perturbation theory (GW approximation and Bethe–Salpeter equation), and more specific or advanced formalisms, such as dynamical mean-field theory (DMFT) and the “temperature-dependent effective potential” approach for anharmonic effects. Relying on planewaves for the representation of wavefunctions, density, and other space-dependent quantities, with pseudopotentials or projector-augmented waves (PAWs), it is well suited for the study of periodic materials, although nanostructures and molecules can be treated with the supercell technique. The present article starts with a brief description of the project, a summary of the theories upon which ABINIT relies, and a list of the associated capabilities. It then focuses on selected capabilities that might not be present in the majority of electronic structure packages either among planewave codes or, in general, treatment of strongly correlated materials using DMFT; materials under finite electric fields; properties at nuclei (electric field gradient, Mössbauer shifts, and orbital magnetization); positron annihilation; Raman intensities and electro-optic effect; and DFPT calculations of response to strain perturbation (elastic constants and piezoelectricity), spatial dispersion (flexoelectricity), electronic mobility, temperature dependence of the gap, and spin-magnetic-field perturbation. The ABINIT DFPT implementation is very general, including systems with van der Waals interaction or with noncollinear magnetism. Community projects are also described: generation of pseudopotential and PAW datasets, high-throughput calculations (databases of phonon band structure, second-harmonic generation, and GW computations of bandgaps), and the library libpaw. ABINIT has strong links with many other software projects that are briefly mentioned.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2010

Transparent Large Strain Thermoplastic Polyurethane Magneto-Active Nanocomposites

Smart adaptive materials are an important class of materials which can be used in space deployable structures, morphing wings, and structural air vehicle components where remote actuation can improve fuel efficiency. Adaptive materials can undergo deformation when exposed to external stimuli such as electric fields, thermal gradients, radiation (IR, UV, etc.), chemical and electrochemical actuation, and magnetic field. Large strain, controlled and repetitive actuation are important characteristics of smart adaptive materials. Polymer nanocomposites can be tailored as shape memory polymers and actuators. Magnetic actuation of polymer nanocomposites using a range of iron, iron cobalt, and iron manganese nanoparticles is presented. The iron-based nanoparticles were synthesized using the soft template (1) and Sun's (2) methods. The nanoparticles shape and size were examined using TEM. The crystalline structure and domain size were evaluated using WAXS. Surface modifications of the nanoparticles were performed to improve dispersion, and were characterized with IR and TGA. TPU nanocomposites exhibited actuation for approximately 2wt% nanoparticle loading in an applied magnetic field. Large deformation and fast recovery were observed. These nanocomposites represent a promising potential for new generation of smart materials.

Yoonessi, Mitra↗
NASA NTRS1984

Observations of frontal zone structures with a VHF Doppler radar and radiosondes, part 1.2A

The SOUSY-VHF-Radar is a pulsed coherent radar operating at 53.5 MHz and located near Bad Lauterbert, West Germany. Since 1977, the facility, operated by the Max-Planck-Institut fur Aeronomie, has been used to make a series of frontal passage observations in the spring and fall. Experiments in winter have been difficult because part of the transmitting and receiving array is usually covered by snow during that part of the year. Wavelengths around 6 m are known to be sensitive to the vertical temperature structure of the atmosphere (GREEN and GAGE, 1980; RASTOGI and ROTTGER, 1982). Thus, it has been possible to use radars operating at frequencies near 500 MHz to locate the tropopause. Comparisons between radar data and radiosonde data have shown that there is a large gradient in the radar reflectivity at the height where the radiosonde tropopause occurs. An experiment carried out by ROTTGER (1979) on March 15 to 16, 1977, showed that the radar's sensitivity to the vertical temperature structure could also be used to locate the position of fronts. The SOUSY-VHF-Radar consists of a transmitting array, also used for receiving in some configurations, that can be scanned in the off-vertical direction but not at sufficiently low elevation angles to study the horizontal extent of structures.

Larsen, M. F.↗
NASA NTRS1975

Lunar shear velocity structure at Apollo sites 12, 14, and 15

Spectral amplitude ratios of horizontal-to-vertical motion produced on seismograms of meteoroid impacts at the Apollo 12, 14, and 15 sites, the Apollo 14 and 15 lunar-module impacts, and the Apollo 15 S4B impact show consistent differences among the recording sites. On the assumption that the motion represents predominantly fundamental-mode Reyleigh waves and that the compressional-wave velocity structure is similar to that derived in other investigations involving the Apollo seismic experiments, estimates are made of the shear-wave velocity structure under the three sites. Near-surface velocities are about 35 m/s at the three sites. The results for site 14 indicate an increase to about 100 m/s near the 8-m depth and to 200 m/s at the 38-m depth. Results for sites 12 and 15 show a smoother gradient and generally a greater velocity at a given depth than that indicated at site 14, reaching velocities of about 400 m/s near the 120-m depth. If the assumed P velocity structures are correct and if changes in S velocity coincide with changes in P velocity, then the ratio of these velocities decreases from 2.9 to 2.0 in the upper 19 meters at site 12, in the upper 38 meters at site 14, and in the upper 21 meters at site 15.

Mark, N.↗