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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

A reversible phase transition for sodium insertion in anatase TiO 2

Anatase TiO 2 is a potential negative electrode for sodium-ion batteries. The sodium storage mechanism is, however, still under debate, yet its comprehension is required to optimize the electrochemical properties. To clarify the sodium storage mechanism occurring in anatase, we have used both electrochemical and chemical routes from which we obtained similar trends. During the first discharge, an irreversible plateau region is observed which corresponds to the insertion of Na+ within the interstitial sites of anatase and is accompanied by a drastic loss of the long-range order as revealed by X-ray diffraction, high resolution of high angle annular dark-field scanning transmission electron microscope (HAADF-STEM), and pair distribution function (PDF) analysis. Further structural analysis of the total scattering data indicates that the sodiated phase displays a layered-like rhombohedral R3m structure built from the stacking of Ti and Na slabs. Because of the initial 3D network of anatase, the reduced phase shows strong disorder due to cationic intermixing between the Ti and Na slabs and the refined chemical formula is (Na 0.43 Ti 0.57 ) 3a 0.22 Na 0.39 Ti 0.39 ) 3b O 2 , where refers to vacancy. The presence of high valence Ti ions in the Na layers induces a contraction of the c-parameter as compared to the ordered phase. Upon desodiation, the structure further amorphized and the local structure probed by PDF is shown to be similar to the anatase TiO 2 , suggesting that the 3D network is recovered. The reversible sodium insertion/deinsertion is thus attributed to the rhombohedral active phase formed during the first discharge, and an oxidized phase featuring the local structure of anatase. Due to the amorphous nature of the two phases, the potential-composition curves are characterized by a sloping curve. Lastly, a comparison between the intercalation of lithium and sodium into anatase TiO 2 performed by DFT calculations confirmed that, for the sodiated phase, the rhombohedral structure is more stable than the tetragonal phase observed during the lithiation of nanoparticles.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Local Decomposition of Hexahedral Singular Nodes into Singular Curves

Hexahedral (hex) meshing is a long studied topic in geometry processing with many challenging associated problems. Hex meshes vary from structured to unstructured depending on application or domain of interest. Fully structured meshes require that all interior mesh edges be adjacent to four hexes each. Edges failing this criteria are singular and indicate an unstructured hex mesh. Singular edges join together into singular curves that either form closed cycles, end on the mesh boundary, or end at a singular node, a complex junction of more than two singular curves. Hex meshes with more complex singular nodes tend to have more distorted elements and smaller scaled Jacobian values. In this work, we study the topology of singular nodes. We show that all eight of the most common singular nodes are decomposable into just singular curves. We further show that all singular nodes, regardless of edge valence, are locally decomposable. Finally we demonstrate these decompositions on hex meshes, thereby decreasing their distortion and converting all singular nodes into singular curves. In conclusion, with this decomposition, the enigmatic complexity of 3D singular nodes becomes effectively 2D.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1991

Vibration suppression using a proofmass actuator operating in stroke/force saturation

The design of the control-loop structure for a feedback control system which contains a proofmass actuator for suppressing vibration is discussed. The loop structure is composed of inner control loops, which determine the frequency of the actuator and which are directly related to the actuator and the outer loops which add damping to the structure. When the frequency response of the actuator is matched to the stroke/force saturation curve, the actuator is most effective in the vibration suppression loops, and, since the stroke/force saturation curve is characterized by the stroke length, the mass of the proofmass, and the maximum current delivered by the motor electronics, the size of the actuator can be easily determined. The results of the loop-structure model calculations are verified by examining linear DC motors as proofmass actuators for the Mast in NASA's Control of Flexible Structures program.

Lindner, D. K.↗
DOE OSTI2017

Boxy/Peanut/X-Shaped Bulges: Steep Inner Rotation Curve Leads to Barlens Face-on Morphology

We use stellar dynamical bulge/disk/halo simulations to study whether barlenses (lens-like structures embedded in the narrow bar component) are only the face-on counterparts of Boxy/Peanut/X-shapes (B/P/X) seen in edge-on bars, or if some additional physical parameter affects that morphology. A range of bulge-to-disk mass and size ratios are explored: our nominal parameters (B/D=0.08, r{sub eff}/h{sub r}=0.07, disk comprising two-thirds of total force at 2.2h{sub r}) correspond to typical Milky Way mass galaxies. In all models, a bar with pronounced B/P/X forms in a few Gyr, visible in the edge-on view. However, the pure barlens morphology forms only in models with sufficiently steep inner rotation curves, dV{sub cir}/dr≳5V{sub max}/h{sub r}, achieved when including a small classical bulge with B/D≳0.02 and r{sub eff}/h{sub r}≲0.1. For shallower slopes, the central structure still resembles a barlens, but shows a clear X signature even in low inclinations. A similar result holds for bulge-less simulations, where the central slope is modified by changing the halo concentration. The predicted sensitivity on the inner rotation curve is consistent with the slopes that are estimated from gravitational potentials calculated from the 3.6 μm images, for the observed barlens and X-shaped galaxies in the Spitzer Survey of Stellar Structure in Galaxies (S{sup 4}G). For inclinations <60° the galaxies with barlenses have on average twice steeper inner rotation curves than galaxies with X shapes: the limiting slope is ∼250 km s{sup −1} kpc{sup −1}. Among barred galaxies, those with barlenses have both the strongest bars and the largest relative excess of inner surface density, both in barlens regions (≲0.5h{sub r}) and near the center (≲0.1h{sub r}); this provides evidence for bar-driven secular evolution in galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1982

A nonlinear structural concept for compliant walls

Two mechanisms of drag reduction for flow over flat plates were investigated. The first mechanism employs Bushnell's hypothesis that compliant walls produce drag reduction by interfering with the formation of the turbulent spots in a turbulent boundary layer. It is shown that the amplitudes and frequencies of compliant wall motions for drag reduction might be achieved by using slightly curved walls and the resulting large amplitude motions of snap buckling. A simple structural model of an arch is used in the analysis, and an asymptotic method is developed. The required wall motions can be obtained by using materials like mylar. In addition, the delay of transition from laminar to turbulent flow by driven walls was studied for Poiseuille channel flow. The walls are driven by a periodic traveling wave. A significant increase in the transitional Reynolds number is obtained by appropriately prescibing the wavelength and phase velocity of the wall motion. Previously developed asymptotic methods are used in the analysis.

Reiss, E. L.↗
DOE OSTI2017

Structure and Phase Transformation in the Giant Magnetostriction Laves-Phase SmFe 2

As one class of the most important intermetallic compounds, the binary Laves-phase is well-known for their abundant magnetic properties. Samarium-iron alloy system, SmFe 2 , is a prototypical Laves compound that shows strong negative magnetostriction but relatively weak magnetocrystalline anisotropy. SmFe 2 has been identified as a cubic Fd$ \overline{3}\ $m structure at room temperature, however, the cubic symmetry does not match the spontaneous magnetization along the [111] cubic direction. Here we studied the crystal structure of SmFe 2 by high-resolution synchrotron X-ray powder diffraction and X-ray total scattering methods. SmFe 2 is found to adopt a centrosymmetric trigonal R$ \overline{3}\ $m structure at room temperature, which transforms to an orthorhombic Imma structure at 200 K. This transition is in agreement with the changes of easy magnetization direction from [111] cubic to [110] cubic direction, and is further evidenced by the inflexion of thermal expansion behavior, the sharp decline of the magnetic susceptibility in the FC-ZFC curve, and the anomaly in the specific heat capacity measurement. Lastly, the revised structure and phase transformation of SmFe 2 could be useful to understand the magnetostriction and related physical properties of other RM 2 -type pseudo-cubic Laves-phase intermetallic compounds.

36 MATERIALS SCIENCE↗
NASA NTRS1979

The dispersed fluorescence spectrum of NaAr - Ground and excited state potential curves

Potential curves for the ground state and the first excited state of NaAr were determined. The van der Waals molecule NaAr was prepared by supersonic free jet expansion of a mixture of sodium, argon, and helium. The electronic transition from the ground state to the first excited state A2pi was excited by a tunable dye laser and the resulting fluorescence was studied. The dispersed fluorescence spectra show discrete and diffuse features, corresponding to transitions from excited vibrational levels of the A state to bound and unbound levels of the x state. The characteristic reflection structure in the bound-free spectra permits an unambiguous assignment of the vibrational numbering in the A state, and this assignment together with previously measured spectroscopic constants are used to calculate the potential curve of the A state. The discrete structure in the fluorescence spectra is used to determine the potential curve of the x state in the well region, and the repulsive part of the X curve is then deduced through trial-and-error simulation of the bound-free spectra.

Tellinghuisen, J.↗
NASA NTRS1984

A nonlinear structural concept for drag-reducing compliant walls

Two mechanisms of drag reduction for flow over flat plates were investigated. The first mechanism employs Bushnell's hypothesis that compliant walls produce drag reduction by interfering with the formation of the turbulent spots in a turbulent boundary layer. It is shown that the amplitudes and frequencies of compliant wall motions for drag reduction might be achieved by using slightly curved walls and the resulting large amplitude motions of snap buckling. A simple structural model of an arch is used in the analysis, and an asymptotic method is developed. The required wall motions can be obtained by using materials like mylar. In addition, the delay of transition from laminar to turbulent flow by driven walls was studied for Poiseuille channel flow. The walls are driven by a periodic traveling wave. A significant increase in the transitional Reynolds number is obtained by appropriately prescribing the wavelength and phase velocity of the wall motion. Previously developed asymptotic methods are used in the analysis. Previously announced in STAR as N83-11061

Reiss, E. L.↗
NASA NTRS2012

Gamma-Ray Light Curves from Pulsar Magnetospheres with Finite Conductivity

The Fermi Large Area Telescope has provided an unprecedented database for pulsar emission studies that includes gamma-ray light curves for over 100 pulsars. Modeling these light curves can reveal and constrain the geometry of the particle accelerator, as well as the pulsar magnetic field structure. We have constructed 3D magnetosphere models with finite conductivity, that bridge the extreme vacuum and force-free solutions used in previous light curves modeling. We are investigating the shapes of pulsar gamma-ray light curves using these dissipative solutions with two different approaches: (l) assuming geometric emission patterns of the slot gap and outer gap, and (2) using the parallel electric field provided by the resistive models to compute the trajectories and . emission of the radiating particles. The light curves using geometric emission patterns show a systematic increase in gamma-ray peak phase with increasing conductivity, introducing a new diagnostic of these solutions. The light curves using the model electric fields are very sensitive to the conductivity but do not resemble the observed Fermi light curves, suggesting that some screening of the parallel electric field, by pair cascades not included in the models, is necessary

Harding, A. K.↗
DOE OSTI2017

First-principles simulations of warm dense lithium fluoride

Here we perform first-principles path integral Monte Carlo (PIMC) and density functional theory molecular dynamics (DFT-MD) calculations to explore warm dense matter states of LiF. Our simulations cover a wide density-temperature range of 2.08–15.70g cm -3 and 10 4 –10 9 K. Since PIMC and DFT-MD accurately treat effects of atomic shell structure, we find a pronounced compression maximum and a shoulder on the principal Hugoniot curve attributed to K-shell and L-shell ionization. The results provide a benchmark for widely used EOS tables, such as SESAME, LEOS, and models. In addition, we compute pair-correlation functions that reveal an evolving plasma structure and ionization process that is driven by thermal and pressure ionization. Finally, we compute electronic density of states of liquid LiF from DFT-MD simulations and find that the electronic gap can remain open with increasing density and temperature to at least 15.7 g cm -3 .

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2005

Structural Analysis of an Inflation-Deployed Solar Sail With Experimental Validation

Under the direction of the NASA In-Space Propulsion Technology Office, the team of L Garde, NASA Jet Propulsion Laboratory, Ball Aerospace, and NASA Langley Research Center has been developing a scalable solar sail configuration to address NASA s future space propulsion needs. Prior to a flight experiment of a full-scale solar sail, a comprehensive phased test plan is currently being implemented to advance the technology readiness level of the solar sail design. These tests consist of solar sail component, subsystem, and sub-scale system ground tests that simulate the vacuum and thermal conditions of the space environment. Recently, two solar sail test articles, a 7.4-m beam assembly subsystem test article and a 10-m four-quadrant solar sail system test article, were tested in vacuum conditions with a gravity-offload system to mitigate the effects of gravity. This paper presents the structural analyses simulating the ground tests and the correlation of the analyses with the test results. For programmatic risk reduction, a two-prong analysis approach was undertaken in which two separate teams independently developed computational models of the solar sail test articles using the finite element analysis software packages: NEiNastran and ABAQUS. This paper compares the pre-test and post-test analysis predictions from both software packages with the test data including load-deflection curves from static load tests, and vibration frequencies and mode shapes from structural dynamics tests. The analysis predictions were in reasonable agreement with the test data. Factors that precluded better correlation of the analyses and the tests were uncertainties in the material properties, test conditions, and modeling assumptions used in the analyses.

Sleight, David W.↗
NASA NTRS1975

Aluminum under high pressure. I - Equation of state

A curve of applied pressure versus lattice constant is calculated for single-crystal aluminum. It results from an application of the method of structural expansions for deriving the energies of simple metals, a method known to give reasonable results for the elastic constants even at second order in the effective electron-ion interaction. The latter is taken from Fermi-surface analysis, and it is verified that the extant face-centered cubic structure remains the preferred crystalline phase up to the highest pressures considered. Arguments are given to suggest that the curve should have reasonable a priori accuracy and can admit possible improvement if experimental data in the intermediate-pressure region can be provided to refine the (in principle) energy-dependent pseudopotential. At three megabars, the lattice constant is reduced by only 22 per cent; the ion cores at this pressure are still very well separated.

Friedli, C.↗
NASA NTRS1991

Long discontinuous fiber composite structure: Forming and structural mechanics

Cost effective composite structure has motivated the investigation of several new approaches to develop composite structure from innovative material forms. Among the promising new approaches is the conversion of planar sheet to components of complex curvature through sheet forming or stretch forming. In both cases, the potential for material stretch in the fiber direction appears to offer a clear advantage in formability over continuous fiber systems. In the present study, the authors have established a framework which allows the simulation of the anisotropic mechanisms of deformation of long discontinuous fiber laminates wherein the matrix phase is a viscous fluid. The initial study focuses upon the establishment of micromechanics models for prediction of the effective anisotropic viscosities of the oriented fiber assembly in a viscous matrix. Next, the developed constitutive relation is employed through an analogy with incompressible elasticity to exercise the finite element technique for determination of local fiber orientation and laminate thickness after forming. Results are presented for the stretch bending of a curved beam from an arbitrary composite laminate and the bulging of a clamped sheet. Structural analyses are conducted to determine the effect of microstructure on the performance of curved beams manufactured from long discontinuous fiber composites. For the purposes of this study, several curved beams with ideal and non-ideal microstructures are compared for response under pure bending. Material parameters are determined from a separate microstructural analysis.

Pipes, R. B.↗
DOE OSTI2022

Surface fluctuating hydrodynamics methods for the drift-diffusion dynamics of particles and microstructures within curved fluid interfaces

Here we introduce fluctuating hydrodynamics approaches on surfaces for capturing the drift-diffusion dynamics of particles and microstructures immersed within curved fluid interfaces of spherical shape. We take into account the interfacial hydrodynamic coupling, traction coupling with the surrounding bulk fluid, and thermal fluctuations. For fluid-structure interactions, we introduce Immersed Boundary Methods (IBM) and related Stochastic Eulerian-Lagrangian Methods (SELM) for curved surfaces. We use these approaches to investigate the statistics of surface fluctuating hydrodynamics and microstructures. For velocity autocorrelations, we find characteristic power-law scalings $τ^{-1}, τ^{-2}$, and plateaus can emerge. This depends on the physical regime associated with the geometry, surface viscosity, and bulk viscosity. This differs from the characteristic $τ^{-3/2}$ scaling for bulk three dimensional fluids. We develop theory explaining these observed power-laws associated with time-scales for dissipation within the fluid interface and coupling to the surrounding fluid. We then use our introduced methods to investigate a few example systems and roles of hydrodynamic coupling and thermal fluctuations including for the kinetics of passive particles and active microswimmers in curved fluid interfaces.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

Assessment of structural, thermal, and mechanical properties of portlandite through molecular dynamics simulations

The structural, thermal, and mechanical properties of portlandite, the primary solid phase of ordinary hydrated cement paste, are investigated using the molecular dynamics method. To understand the effects of temperature on the structural properties of portlandite, the coefficients of thermal expansion of portlandite are determined in the current study and validated with what reported from the experimental tests. The atomic structure of portlandite equilibrated at various temperatures is then subjected to uniaxial tensile strains in the three orthogonal directions and the stress-strain curves are developed. Based on the obtained results, the effect of the direction of straining on the mechanical properties of portlandite is investigated in detail. Structural damage analysis is performed to reveal the failure mechanisms in different directions. The energies of the fractured surfaces are calculated in different directions and compared to those of the ideal surfaces available in the literature. The key mechanical properties, including tensile strength, Young's modulus, and fracture strain, are extracted from the stress-strain curves. The sensitivity of the obtained mechanical properties to temperature and strain rate is then explored in a systematic way. This leads to valuable information on how the structural and mechanical properties of portlandite are affected under various exposure conditions and loading rates. - Graphical abstract: Fracture mechanism of portlandite under uniaxial strain in the z-direction. - Highlights: • The structural, thermal, and mechanical properties of portlandite are investigated. • The coefficients of thermal expansion are determined. • The stress-strain relationships are studied in three orthogonal directions. • The effects of temperature and strain rate on mechanical properties are examined. • The plastic energy required for fracture in the crystalline structure is reported.

36 MATERIALS SCIENCE↗
NASA NTRS1985

Curved Finite Elements and Curve Approximation

The approximation of parameterized curves by segments of parabolas that pass through the endpoints of each curve segment arises naturally in all quadratic isoparametric transformations. While not as popular as cubics in curve design problems, the use of parabolas allows the introduction of a geometric measure of the discrepancy between given and approximating curves. The free parameters of the parabola may be used to optimize the fit, and constraints that prevent overspill and curve degeneracy are introduced. This leads to a constrained optimization problem in two varibles that can be solved quickly and reliably by a simple method that takes advantage of the special structure of the problem. For applications in the field of computer-aided design, the given curves are often cubic polynomials, and the coefficient may be calculated in closed form in terms of polynomial coefficients by using a symbolic machine language so that families of curves can be approximated with no further integration. For general curves, numerical quadrature may be used, as in the implementation where the Romberg quadrature is applied. The coefficient functions C sub 1 (gamma) and C sub 2 (gamma) are expanded as polynomials in gamma, so that for given A(s) and B(s) the integrations need only be done once. The method was used to find optimal constrained parabolic approximation to a wide variety of given curves.

Baart, M. L.↗
DOE OSTI2025

Wind Turbine Sound Setbacks and Supply Curves: Ordinances and Extrapolated Trends, 110 Hub Height, 130 Rotor Diameter

This dataset provides a comprehensive set of wind turbine sound setbacks from every residential structure in the contiguous United States (CONUS). A sound setback is defined as the minimum required distance between a residential structure and a hypothetical turbine installation site to ensure that modeled sound levels received at the residence do not exceed local sound ordinances, which are commonly expressed in A-weighted decibels (dBA). Therefore, sound setbacks are a local spatial assessment combining multiple factors, including the sound pressure curve as a function of the observer location (distance and direction) relative to the turbine, local sound regulations, and the geographical distribution of residential structures. The dataset is organized into multiple scenario-based products, detailed as follows: 1. Existing and extrapolated sound setbacks. An existing scenario characterizes sound setbacks only in states or counties that have implemented sound regulations as of 2022. The extrapolated scenarios extend a constant sound threshold to counties that lack explicit sound regulations, with thresholds ranging from 35 to 60 dBA, in 5-dBA increments reflecting the variation observed in current sound ordinances. 2. Sound setbacks in directional and worst scenarios. The directional scenario accounts for the distance and orientation of residential structures relative to a hypothetical turbine location, utilizing the turbine's sound emissions in that specific direction. In contrast, the worst scenario takes loudest sound level at each distance step from the turbine, irrespective of directional considerations, which aligns with current industry practice. 3. Supply curves for Open and Reference Access scenarios. This dataset includes supply curves generated by the reV model, which integrates each of the above sound setbacks into both Open and Reference siting scenarios. In addition, two Open and Reference baselines scenarios were included which do not consider sound setbacks for comparative analysis. All sound setback data are stored in TIF files, with partial maps of the data provided in PNG format. The values in the sound setback raster range from 0 to 1, representing the fraction of developable land within a 90 meter by 90 meter pixel due to sound ordinances. A value of 0 indicates areas where wind energy development is prohibited, while a value of 1 signifies areas fully permissible. The wind turbine parameters used in the sound modeling are based on the land-based turbine from International Energy Agency (IEA), featuring a rated electrical power of 3.4 MW, a rotor diameter of 130 meters, and a hub height of 110 meters. The atmospheric conditions, including wind speed/direction, turbulence, air temperature, relative humidity, and air pressure, that drive the sound generation are obtained from the WIND Toolkit dataset.

Array↗
NASA NTRSDate not supplied

Integration of Fatigue R-Curve Effects into VCCT for Durability Predictions, Part 1: Buckled Composite Single-Stringer Stiffened Panels

Composite structures have become popular in modern aircraft because they help reduce weight and increase durability. In addition, hat-stiffened panels provide the stability that the airframe skin needs. However, they can be subject to delamination in the post-buckling regime. Progressive damage analysis (PDA) methods can help predict interlaminar and intralaminar failure events. Many aircraft structures are subject to cyclic loading in the post-buckling regime. Hence, fatigue life prediction becomes essential for design and sustainment purposes. Under the NASA Advanced Composites Project (ACP), composite panels stiffened with single hat-stringers were subject to a cyclic loading sequence from a pre-buckling state to a post-buckling state. This test campaign aimed to provide damage initiation and growth data for three initial damage scenarios: nominally pristine, initial Teflon inserts representing manufacturing defects, and impact-induced damage. This work uses the Abaqus FEA Virtual Crack Closure Technique (VCCT), capabilities enhanced through a novel empirical method integrating fatigue R-curve effects (different from R-ratio) into the Paris Law via user-defined subroutine to simulate the fatigue response of the panels with single hat-stringers. The analysis predictions were within 5% of the test results using this novel method.

single hat↗