Search NASA⌕ Search

SEARCH · Search NASA

Results for “geometric”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Preliminary Nonlinear Structural Analysis of Advanced Composite Tow-Steered Shells with Large Geometric Imperfections

The structural performance of two advanced composite tow-steered shells with and without tow overlaps, and with large geometric imperfections, are predicted using linear and geometrically nonlinear finite element analyses. These shells, 35 in. long and approximately 16.3 in. diameter, are fabricated using automated fiber placement from IM7/8552 graphite/epoxy prepreg. The 8-ply,[±45/±Θ]s. shell layup incorporates a steered fiber angle Θ that varies from 10 deg. to 45 deg. periodically over the shell circumference. Shell analysis models are evaluated using geometric imperfections normalized to ±1 shell wall thickness (±0.040 in.), which are then superposed and rotated incrementally around the shell longitudinal axis. Using these nominal imperfections, the shell prebuckling axial stiffnesses and buckling loads predicted with linear and nonlinear analyses are close to reference values from linear analyses with no imperfections. The linear and nonlinear analyses are then repeated for scaled imperfections that are larger by up to a factor of 10. For these larger imperfections, linear analyses predict reductions in axial stiffnesses and buckling loads of up to 5 and 30 percent, respectively, from reference values. The nonlinear analyses predict even larger reductions in axial stiffnesses and buckling loads of up to 10 and 55 percent, respectively.

Dobrin, Calvin P.↗
NASA NTRS1994

Ultraviolet Spectra and Geometric Albedos of 45 Asteroids

Spectral reflectances and geometric albedos between 2300 and 3250 Angstroms are determined for 45 asteroids from data acquired by the International Ultraviolet Explorer satellite. The geometric albedos are consistently low, ranging from ~0.02 for C-type asteroids to ~0.08 for M-type asteroids. An exception is the single E-type asteriod (44 Nysa) with a geometric albedo of 0.3 at 2950 Angstroms. We find that the three major asteroid taxonomic classes persist into the UV. The taxonomic classes are distinguished primarily by their albedos, but S-types are generally redder than C- or M-types. The first ultraviolet phase curves of asteroids are presented.

International↗
NASA NTRS2024

NASA HECC Geometry and Performance Review Part 2: Geometric Differences Between the As-Manufactured and Design-Intent Impeller Geometry and their Effects on the Vaneless Diffuser Configuration Performance

An investigation of the NASA High Efficiency Centrifugal Compressor (HECC) vaneless diffuser configuration was performed. This multipart investigation focused on validating the computational model against experimental data. The validated model was then used to explore the effects of observed geometric differences between the As-Manufactured and Design-Intent impellers. Lastly, the validated model was used for comparison against an experimental tip clearance study. Part II of the investigation of the NASA HECC vaneless diffuser configuration focused on understanding the differences in geometry and performance between the As-Manufactured impeller and the Design-Intent impeller. This was achieved through comparison of the As-Manufactured HECC vaneless computational model, developed from the solid model of the impeller and validated in Part I, against a new model developed from the Design-Intent blade sections published in NASA/CR-2014-218114/Rev1. The 1D performance values showed that the As-Manufactured impeller underperformed compared to the Design-Intent for all four speedlines that were simulated. Further investigation of profiles, loading and contours showed consistent underperformance of the As-Manufactured relative to the Design-Intent. An investigation into the source of the performance differences led to the discovery of several significant variations in the impeller geometries. The differences that were observed can be summarized into four categories: fillets, trailing-edge exit radii variation, dissimilarity in the splitter leading-edge geometry and main blade thickness differences. The investigation then shifted its effort to quantify the performance effects caused by geometric differences. The investigation showed that out of the four geometric differences that were explored, the differences in the splitter blade had the largest impact. These differences most notably changed flow physics near the splitter leading edge, especially near the tip of the impeller.

centrifugal compressor↗
NASA NTRSDate not supplied

Advancement of Deep Learning and Geometric Methods for Active Terrain Relative Navigation

To enhance NASA’s precision landing capabilities, in conjunction with the development of a novel active terrain relative navigation (ATRN) and terrain mapping system, denoted SHERIF, this work performed a comparative analysis between both deep-learning (DL) based and geometric approaches to hazard detection (HD) and safe-site-identification (SSI) through hardware-in-the loop testing on the Six degree-of-freedom Tendon Actuated Robot (STAR). The Standalone Hazard Evaluation and Refinement using Instrument Findings (SHERIF) system is capable of ingesting sensor data at an asynchronous rate, stitching successive terrain scans together to yield a high-resolution digital elevation map (DEM), performing absolute and relative localization using novel 3D feature extraction and matching methods, and HD/SSI activities. The DL-based HD/SSI algorithm provides a modular alternative to classical geometric approaches which have performance times that scale with map resolution. As the adoption of AI solutions become more prevalent for autonomous system decision making, it is prudent to explore the utility of such solutions in applications where they traditionally excel, such as image classification. Along with the development of a DL-based HD system, this work performed the first comparative analysis between DL and geometric approaches to HD/SSI using real sensor data from real-time testing in a relevant environment.

Davis Adams↗
NASA NTRS1997

Locating Geometric Primitives by Pruning the Parameter Space

This paper examines the extraction of geometric primitives from two- and three-dimensional image data. The geometric primitives are represented by parametric manifolds in the image space, such as circles, planes, and cylinders.

geometric primitives image data parameter space im↗
NASA NTRS1963

Lunar Flight Study Series: Volume 6. A Study of Geometrical and Terminal Characteristics of Earth-Moon Transits Embedded in the Earth-Moon Plane

This report represents the results of a study of coplanar earth-moon transits. The study was initiated to provide information concerning coplanar geometrical characteristics of earth-moon trnasits. The geometrical aspects of transit behavior are related to variations injection conditions. The model of the earth-moon system used in this investigation is the Jacobian model of the restricted three body problem. All transits considered in this study are restricted to the moon-earth plane (MEP).

TRAJECTORY MEASURING SYSTEM↗
NASA NTRS2017

Path Profiles of Cn2 Derived from Radiometer Temperature Measurements and Geometrical Ray Tracing

Atmospheric turbulence has significant impairments on the operation of Free-Space Optical (FSO) communication systems, in particular temporal and spatial intensity fluctuations at the receiving aperture resulting in power surges and fades, changes in angle of arrival, spatial coherence degradation, etc. The refractive index structure parameter Cn2 is a statistical measure of the strength of turbulence in the atmosphere and is highly dependent upon vertical height. Therefore to understand atmospheric turbulence effects on vertical FSO communication links such as space-to-ground links, it is necessary to specify Cn2 profiles along the atmospheric propagation path. To avoid the limitations on the applicability of classical approaches, propagation simulation through geometrical ray tracing is applied. This is achieved by considering the atmosphere along the optical propagation path as a spatial distribution of spherical bubbles with varying relative refractive index deviations representing turbulent eddies. The relative deviations of the refractive index are statistically determined from altitude-dependent and time-varying temperature fluctuations, as measured by a microwave profiling radiometer. For each representative atmosphere ray paths are analyzed using geometrical optics, which is particularly advantageous in situations of strong turbulence where there is severe wavefront distortion and discontinuity. The refractive index structure parameter is then determined as a function of height and time.

Atmospheric turbulence↗
NASA NTRS2020

Identify the Limits of Geometric Optics Ray Tracing by Numerically Solving the Vector Kirchhoff Integral

The properties of a pencil of light as defined approximately in the geometric optics ray tracing method are investigated. The vector Kirchhoff integral is utilized to accurately compute the electromagnetic near field in and around the pencil of light with various beam base sizes, shapes, propagation directions and medium refractive indices. If a pencil of light has geometric mean cross section size of the order p times the wavelength, it can propagate independently to a distance p2 times the wavelength, where most of the beam energy diffuses out of the beam region. This is consistent with a statement that van de Hulst made in a classical text on light scattering. The electromagnetic near fields in the pencil of light are not uniform, have complicated patterns within short distances from the beam base, and the fields tend to converge to Fraunhofer diffraction fields far away from the base.

Far field diffraction↗
NASA NTRS1971

Digital correction of geometric and radiometric errors in ERTS data.

The sensor systems of the ERTS-A satellite are discussed and sources of geometric and radiometric errors in the received images are identified. Digital algorithms are presented for detection of reseau and ground control points, for rapid implementation of geometric corrections, and for radiometric correction of errors caused by shading, image motion, modulation transfer function, and quantum and systematic noise.

Bakis, R.↗
NASA NTRS1974

Geometrical geodesy techniques in Goddard earth models

The method for combining geometrical data with satellite dynamical and gravimetry data for the solution of geopotential and station location parameters is discussed. Geometrical tracking data (simultaneous events) from the global network of BC-4 stations are currently being processed in a solution that will greatly enhance of geodetic world system of stations. Previously the stations in Goddard earth models have been derived only from dynamical tracking data. A linear regression model is formulated from combining the data, based upon the statistical technique of weighted least squares. Reduced normal equations, independent of satellite and instrumental parameters, are derived for the solution of the geodetic parameters. Exterior standards for the evaluation of the solution and for the scale of the earth's figure are discussed.

Lerch, F. J.↗
NASA NTRS1974

A system to geometrically rectify and map airborne scanner imagery and to estimate ground area

A system of computer programs were developed which performs geometric rectification and line-by-line mapping of airborne multispectral scanner data to ground coordinates and estimates ground area. The system requires aircraft attitude and positional information furnished by ancillary aircraft equipment, as well as ground control points. The geometric correction and mapping procedure locates the scan lines, or the pixels on each line, in terms of map grid coordinates. The area estimation procedure gives ground area for each pixel or for a predesignated parcel specified in map grid coordinates. The results of exercising the system with simulated data showed the uncorrected video and corrected imagery and produced area estimates accurate to better than 99.7%.

Spencer, M. M.↗
NASA NTRS1973

Ultraviolet reflectivity and geometrical albedo of Titan

Titan's geometrical albedo of 0.094 plus or minus 0.012 was measured at 4255 A with a 50-A bandpass. From this and the spectral measurements, the geometrical albedo was derived as a function of wavelength. It is found that the wavelength dependences of Titan's UV spectrum and of the spectrum of Saturn's Rings are remarkably similar. No trace of any absorption bands is apparent. These results imply that UV gaseous absorption and Rayleigh scattering play a strongly subdued role in Titan's atmosphere. Any homogeneous atmospheric model implies that the absorber responsible for Titan's UV spectral albedo varies strongly with wavelength. On the other hand, it is found that the UV observations can be satisfied by an absorber having a relatively weak dependence upon wavelength if an inhomogeneous atmospheric model is employed. In particular, a fine dust, which absorbs as the reciprocal of the wavelength, can explain the UV observations, provided that it is preferentially distributed high up in Titan's atmosphere where the optical depth from Rayleigh scattering is low.

Barker, E. S.↗
NASA NTRS1973

Finite element analysis of geometrically nonlinear problems

Recent developments in geometrically nonlinear finite element analysis are reviewed. Following a discussion of the theoretical bases for the construction of finite element equations for geometrically nonlinear analysis, the algorithmic tools for solving the resulting nonlinear equations of the complete system are described. Separate consideration is given to preinstability nonlinear analysis, the calculation of limit points, bifurcation points, and to postbifurcation analysis.

Gallagher, R. H.↗
NASA NTRS1974

Geometric distortions of opticommercial panoramic television systems

One of the problems solvable by the spaceborne television system, topographical surveying, makes high demands on image quality, particularly on the geometric distortions introduced by the television camera. It is the geometric distortions which determine measurement accuracy and, consequently, the possibility of creating reliable planetary surface maps. Comparative analysis of the different television systems capable of solving the problem showed that the requirements on quality of the transmitted images are best satisfied by television cameras with opticomechanical scanning. The design of panoramic television systems and the process of image construction by the opticomechanical camera are discussed. Results indicate that panoramic television cameras have the necessary instrumental accuracy and permit determination of the direction to objects with an error practically equal to the resolution.

Govorov, V. M.↗
NASA NTRS1975

The geometric approach to sets of ordinary differential equations and Hamiltonian dynamics

The calculus of differential forms is used to discuss the local integration theory of a general set of autonomous first order ordinary differential equations. Geometrically, such a set is a vector field V in the space of dependent variables. Integration consists of seeking associated geometric structures invariant along V: scalar fields, forms, vectors, and integrals over subspaces. It is shown that to any field V can be associated a Hamiltonian structure of forms if, when dealing with an odd number of dependent variables, an arbitrary equation of constraint is also added. Families of integral invariants are an immediate consequence. Poisson brackets are isomorphic to Lie products of associated CT-generating vector fields. Hamilton's variational principle follows from the fact that the maximal regular integral manifolds of a closed set of forms must include the characteristics of the set.

Estabrook, F. B.↗
NASA NTRS1976

On the surface brightness and geometric albedo of some Martian areas

High-quality photographs of Mars (red, yellow, green, and blue) are used to analyze the surface, limb, and south-polar-cap brightness of Mars. The surface brightness can be fitted with the Lommel-Seeliger reflection law. For the limb and polar-cap brightness, the method suggested by Lumme (1974) has been used to correct for smearing effects. It is found that the brightness increases noticeably when approaching the limb, that the upper limit to optical thickness of the atmosphere in the blue is 0.16, and that the corresponding single-scattering albedo is 0.55, both with uncertainties of about 15%. Values for the geometric albedo and the phase function (at 37-deg phase angle) are also obtained for both the atmosphere and the ground for a central meridian of 0 deg. The south polar cap in September 1973 was nearly circular, with a radius of about 8 deg (heliocentric longitude of 0 deg) and geometric albedos of 0.68 (red), 0.68 (yellow), 0.60 (green), and 0.53 (blue).

Lumme, K.↗
NASA NTRS1976

Computer modeling of electromagnetic problems using the geometrical theory of diffraction

Some applications of the geometrical theory of diffraction (GTD), a high frequency ray optical solution to electromagnetic problems, are presented. GTD extends geometric optics, which does not take into account the diffractions occurring at edges, vertices, and various other discontinuities. Diffraction solutions, analysis of basic structures, construction of more complex structures, and coupling using GTD are discussed.

Burnside, W. D.↗
NASA NTRS1977

Geometrical meaning of the curl operation when A dot curl A does not equal 0

We examine the geometrical interpretation of the vector operation curl for vector fields A such that A dot curl A does not equal 0. It is not possible to construct even locally a surface normal to field lines of A at all points; an explicit geometrical demonstration of this fact is given. Such fields do not admit the construction of orthogonal curvilinear coordinates in which one set of coordinate curves lies along field lines of A.

Barnes, A.↗