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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Static and free-vibrational response of semi-circular graphite-epoxy frames with thin-walled open sections

Experiments were conducted to measure the three-dimensional static and free vibrational response of two graphite-epoxy, thin-walled, open section frames. The frames are semi-circular with a radius of three feet, and one specimen has an I cross section and the other has a channel cross section. The flexibility influence coefficients were measured in static tests for loads applied at midspan with the ends of the specimens clamped. Natural frequencies and modes were determined from vibrational tests for free and clamped end conditions. The experimental data is used to evaluate a new finite element which was developed specifically for the analysis of curved, thin-walled structures. The formulation of the element is based on a Vlasov-type, thin-walled, curved beam theory. The predictions from the finite element program generally correlated well with the experimental data for the symmetric I-specimen. Discrepancies in some of the data were found to be due to flexibility in the clamped end conditions. With respect to the data for the channel specimen, the correlation was less satisfactory. The finite element analysis predicted the out-of-plane response of the channel specimen reasonably well, but large discrepancies occurred between the predicted in-plane response and the experimental data. The analysis predicted a much more compliant in-plane response than was observed in the experiments.

Collins, J. Scott↗
NASA NTRS1977

Doubly-curved variable-thickness isoparametric heterogeneous finite element

This paper describes an element streamlined for the analysis of doubly-curved, variable-thickness structural components and illustrates its effective application to vibration and static problems. The element is isoparametric, doubly-curved, thin-shell and triangular with variable thickness and accounts for anisotropic, inhomogeneous elastic material behavior. The element has six nodes (three corner and three mid-side) with five degrees-of-freedom (DOF) per node - three translations and two rotations. Quadratic isoparametric interpolation polynomials are used to express the element geometry and displacement variables in terms of corresponding nodal variables.

Minich, M. D.↗
DOE OSTI2023

Inferring assembly-curving trends of bacterial micro-compartment shell hexamers from crystal structure arrangements

Bacterial microcompartments (BMC) are complex macromolecular assemblies that participate in varied chemical processes in about one fourth of bacterial species. BMC-encapsulated enzymatic activities are segregated from other cell contents by means of semipermeable shells, justifying why BMC are viewed as prototype nano-reactors for biotechnological applications. Herein, we undertook a comparative study of bending propensities of BMC hexamers (BMC-H), the most abundant shell constituents. Published data show that some BMC-H, like β -carboxysomal CcmK, tend to assemble flat whereas other BMC-H often build curved objects. Inspection of available crystal structures presenting BMC-H in tiled arrangements permitted us to identify two major assembly modes with a striking connection with experimental trends. All-atom molecular dynamics (MD) supported that BMC-H bending is triggered robustly only from the arrangement adopted in crystals by BMC-H that experimentally form curved objects, leading to very similar arrangements to those found in structures of recomposed BMC shells. Simulations on triplets of planar-behaving hexamers, which were previously reconfigured to comply with such organization, confirmed that bending propensity is mostly defined by the precise lateral positioning of hexamers, rather than by BMC-H identity. Finally, an interfacial lysine was pinpointed as the most decisive residue in controlling PduA spontaneous curvature. Globally, results presented herein should contribute to improve our understanding of the variable mechanisms of biogenesis characterized for BMC, and of possible strategies to regulate BMC size and shape.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1985

History and current understanding of the Suess abundance curve

By means of a gamma ray sum spectrometer currently under development, many neutron capture cross sections will be determined with high accuracy, thereby facilitating the inferrence of the abundance ratios of neighboring elements with the same accuracy. Attention is presently given to this and other prospects emerging in the study of nuclide abundances and the data base for theories of element synthesis. Poorly understood structures in the abundance curve are discussed in view of recent models on nuclear structure and stability.

Marti, K.↗
NASA NTRS1993

Photometric and spectroscopic observations of 5145 Pholus

Light curve observations carried out in January and February 1992 are presented. We find an amplitude of 0.2 magnitude and a period of 0.4157 day. Fine structures of the light curve and their variability with time are discussed in terms of the changing phase angle and deviations of the object's shape from a regular ellipsoid. The present orbital and physical properties alone for 5145 Pholus do not provide a clue for either a cometary or an asteroidal origin. It seems to have properties in common with both and thus could form a bridge between these two groups.

Hoffmann, Martin↗
NASA NTRS1980

Buckling and postbuckling research on flat and curved composite panels

Progress in the development of verified design technology for generic advanced-composite structural components loaded in compression is reported. Generic structural configurations material systems and load ranges of interest for a given application were investigated using structural procedures, structural analysis procedures, and laboratory testing of structural specimens. Both flat and curved composite compression panels that are designed either to be buckling resistant or to have postbuckling strength depending on the expected application of the panels were considered.

Starnes, J. H., Jr.↗
NASA NTRS1976

Analytical structural efficiency studies of borsic/aluminum compression panels

Analytically determined mass-strength curves, strain-strength curves, and dimensions are presented for structurally efficient hat-stiffened panels, corrugation-stiffened panels, hat-stiffened honeycomb-core sandwich panels, open-section corrugation panels, and honeycomb-core sandwich panels. The panels were assumed to be fabricated from either titanium, borsic/aluminum, or a combination of these materials. Borsic/aluminum panels and titanium panels reinforced with borsic/aluminum were lighter and stiffer than comparably designed titanium panels. Reinforced titanium panels had the same extensional stiffness as comparably designed Borsic/aluminum panels. For a given load, the structural efficiency of the hat-stiffened honeycomb-core sandwich panel was higher than the structural efficiency of the other stiffened panels.

Mcwithey, R. R.↗
DOE OSTI2017

First-principles equation of state and shock compression predictions of warm dense hydrocarbons

We use path integral Monte Carlo and density functional molecular dynamics to construct a coherent set of equations of state (EOS) for a series of hydrocarbon materials with various C:H ratios (2:1, 1:1, 2:3, 1:2, and 1:4) over the range of 0.07–22.4gcm –3 and 6.7 × 10 3 – 1.29 × 10 8 K. The shock Hugoniot curve derived for each material displays a single compression maximum corresponding to K-shell ionization. For C:H = 1:1, the compression maximum occurs at 4.7-fold of the initial density and we show radiation effects significantly increase the shock compression ratio above 2 Gbar, surpassing relativistic effects. The single-peaked structure of the Hugoniot curves contrasts with previous work on higher-Z plasmas, which exhibit a two-peak structure corresponding to both K- and L-shell ionization. Analysis of the electronic density of states reveals that the change in Hugoniot structure is due to merging of the L-shell eigenstates in carbon, while they remain distinct for higher-Z elements. Lastly, we show that the isobaric-isothermal linear mixing rule for carbon and hydrogen EOS is a reasonable approximation with errors better than 1% for stellar-core conditions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1994

R(sub nu)-dependent optical and near-ultraviolet extinction

We have derived extinctions A(lambda)/A(V) at the wavelengths of the uvby filters for 22 stars, with a range of values of R(sub nu), from the sample of Cardelli, Clayton, & Mathis (1989, hereafter CCM). We have fit these extinctions, and also UBVRIJHKL, IUE and ANS extinction measurements, with linear relations A(lambda)/A/(V) = a+b/R(sub nu) and fit a and b as a function of x(=1/lambda) with polynomials to obtain an R(sub nu)-dependent mean extinction law (A(x)/A(V) = a(x) + b(x)/R(sub nu))in the optical and near-ultraviolet (1.1/micrometer less than or equal to 3.3/micrometer). This law is virtually identical to the CCM extinction law for large values of R(sub nu)(R(sub nu) approximately 5) but is slightly lower in the near-ultraviolet for smaller R(sub nu) (R(sub nu) approximately 3). The extinction law presented here agrees much better with a high-resolution extinction curve for the diffuse interstellar medium (R(sub nu) approximately 3.1), presented by Bastiaansen (1992), than CCM. The deviations of individual extinction curves from the mean are dominated by observational errors. The wavelength resolution of this work is not high enough to show evidence for or against the existence of very broad structure in optical extinction curves.

O'Donnell, James E.↗
DOE OSTI2017

Theoretical Prediction of Si 2 –Si 33 Absorption Spectra

Here, the optical absorption spectra of Si 2 –Si 33 clusters were systematically studied by a time-dependent density functional theory approach. The calculations revealed that the absorption spectrum becomes significantly broad with increasing cluster size, stretching from ultraviolet to the infrared region. The absorption spectra are closely related to the structural motifs. With increasing cluster size, the absorption intensity of cage structures gradually increases, but the absorption curves of the prolate and the Y-shaped structures are very sensitive to cluster size. If the transition energy reaches ~12 eV, it is noted that all the clusters have remarkable absorption in deep ultraviolet region of 100–200 nm, and the maximum absorption intensity is ~100 times that in the visible region. Further, the optical responses to doping in the Si clusters were studied.

36 MATERIALS SCIENCE↗
NASA NTRS1996

Five X-ray observations of the intermediate polar FO Aqr spanning ten years

The comparison of five X-ray observations of FO Aqr reveals that the morphology of the X-ray light curve changes considerably with time. Power spectra from 1988 and 1993 reveal a sideband component, while power spectra from 1990 do not. This suggests that the amount of disk overflow accretion varies as a function of time. From structured spin folded light curves, the presence of complex, multicomponent emitting regions near the white dwarf's surface can be inferred.

Beardmore, A. P.↗
NASA NTRS1952

Structural Vulnerability of the Boeing B-29 Aircraft Wing to Damage by Warhead Fragments

An elementary type of analysis has been used to determine the amount of wing tip that must be severed to produce irrevocable loss of control of a B-29 airplane. The remaining inboard structure of the Boeing B-29 wing has then been analyzed and curves are presented for the estimated reduction in structural strength due to four general types of damage produced by rod-type warhead fragments. The curves indicate the extent of structural damage required to produce a kill of the aircraft within 10 seconds.

Kordes, Eldon E.↗
NASA NTRS1993

Direct simulations of premixed turbulent flames with nonunity Lewis numbers

A principal effect of turbulence on premixed flames in the flamelet regime is to wrinkle the flame fronts. For nonunity Lewis numbers, Le is not equal to 1, the local flame structure is altered in curved regions. This effect is examined using direct numerical simulations of 3D isotropic turbulence with constant density, single-step Arrhenius kinetics chemistry. Simulations of Lewis numbers 0.8, 1.0, and 1.2 are compared. At the local level, curvature effects dominated changes to the flame structure while strain effects were insignificant. A strong Lewis-number-dependent correlation was found between surface curvature and the local flame speed. The correlation was positive for Le less than 1 and negative for Le greater than 1. At the global level, strain-related effects were more significant than curvature effects. The turbulent flame speed changed significantly with Lewis number, increasing as Le decreased. This was found to be due to strain effects that have a nonzero mean over the flame surface, rather than to curvature effects that have a nearly zero mean. The mean product temperature was also found to vary with Lewis number, being higher for Le greater than 1 and lower for Le less than 1.

Rutland, C. J.↗
DOE OSTI2023

R -Nb 2 O 5 has an ‘idealized’ V 2 O 5 structure and Wadsley–Roth-like structural stability during Li-ion battery cycling

The adoption of batteries across diverse applications requires electrode materials with a wider range of performance metrics, such as cost, safety, and material availability. Along the path to discovering new commercially viable materials, a fundamental understanding of chemical and atomic structure features that provide structural stability and effective ion transport is essential. In support of new understanding, we report the cycling behavior of metastable R-Nb 2 O 5 . R-Nb 2 O 5 adopts an ‘idealized’ V 2 O 5 structure, in which [NbO 6 ] octahedra alternate in edge- and corner-sharing resulting in ReO 3 -like slabs, whereas Wadsley–Roth materials have ReO 3 -like blocks, linked through edge-sharing octahedra at intersecting crystallographic shear planes. We find that this slab structure is stable during cycling, with minor atomic structure changes and cycling curves that are symmetric on discharge and charge, resembling the behavior of Wadsley–Roth materials more than other related materials, such as ReO 3 , V 2 O 5 , or Nb 3 O 7 F. Based on our findings, R-Nb 2 O 5 can serve as a ‘structural bridge’ between Wadsley–Roth block structures and V 2 O 5 , through which we can relate inter- and intra-polyhedral structures to cycling behavior and structural stability during cycling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1985

Strong, Lighweight Curved Panels

Sandwich construction gives panels structural efficiency. Large panels with compound curvatures are formed from a honeycomb core faced with sheets of graphite/epoxy cloth and tape. Developed for pod on Space Shuttle, construction readily adapted to curved skin panels on cars, trucks, and airplanes.

Molho, R.↗