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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Internal performance of two nozzles utilizing gimbal concepts for thrust vectoring

The internal performance of an axisymmetric convergent-divergent nozzle and a nonaxisymmetric convergent-divergent nozzle, both of which utilized a gimbal type mechanism for thrust vectoring was evaluated in the Static Test Facility of the Langley 16-Foot Transonic Tunnel. The nonaxisymmetric nozzle used the gimbal concept for yaw thrust vectoring only; pitch thrust vectoring was accomplished by simultaneous deflection of the upper and lower divergent flaps. The model geometric parameters investigated were pitch vector angle for the axisymmetric nozzle and pitch vector angle, yaw vector angle, nozzle throat aspect ratio, and nozzle expansion ratio for the nonaxisymmetric nozzle. All tests were conducted with no external flow, and nozzle pressure ratio was varied from 2.0 to approximately 12.0.

Berrier, Bobby L.↗
NASA NTRS1989

Robot Acting on Moving Bodies (RAMBO): Interaction with tumbling objects

Interaction with tumbling objects will become more common as human activities in space expand. Attempting to interact with a large complex object translating and rotating in space, a human operator using only his visual and mental capacities may not be able to estimate the object motion, plan actions or control those actions. A robot system (RAMBO) equipped with a camera, which, given a sequence of simple tasks, can perform these tasks on a tumbling object, is being developed. RAMBO is given a complete geometric model of the object. A low level vision module extracts and groups characteristic features in images of the object. The positions of the object are determined in a sequence of images, and a motion estimate of the object is obtained. This motion estimate is used to plan trajectories of the robot tool to relative locations rearby the object sufficient for achieving the tasks. More specifically, low level vision uses parallel algorithms for image enhancement by symmetric nearest neighbor filtering, edge detection by local gradient operators, and corner extraction by sector filtering. The object pose estimation is a Hough transform method accumulating position hypotheses obtained by matching triples of image features (corners) to triples of model features. To maximize computing speed, the estimate of the position in space of a triple of features is obtained by decomposing its perspective view into a product of rotations and a scaled orthographic projection. This allows use of 2-D lookup tables at each stage of the decomposition. The position hypotheses for each possible match of model feature triples and image feature triples are calculated in parallel. Trajectory planning combines heuristic and dynamic programming techniques. Then trajectories are created using dynamic interpolations between initial and goal trajectories. All the parallel algorithms run on a Connection Machine CM-2 with 16K processors.

Davis, Larry S.↗
NASA NTRS1989

A tesselated probabilistic representation for spatial robot perception and navigation

The ability to recover robust spatial descriptions from sensory information and to efficiently utilize these descriptions in appropriate planning and problem-solving activities are crucial requirements for the development of more powerful robotic systems. Traditional approaches to sensor interpretation, with their emphasis on geometric models, are of limited use for autonomous mobile robots operating in and exploring unknown and unstructured environments. Here, researchers present a new approach to robot perception that addresses such scenarios using a probabilistic tesselated representation of spatial information called the Occupancy Grid. The Occupancy Grid is a multi-dimensional random field that maintains stochastic estimates of the occupancy state of each cell in the grid. The cell estimates are obtained by interpreting incoming range readings using probabilistic models that capture the uncertainty in the spatial information provided by the sensor. A Bayesian estimation procedure allows the incremental updating of the map using readings taken from several sensors over multiple points of view. An overview of the Occupancy Grid framework is given, and its application to a number of problems in mobile robot mapping and navigation are illustrated. It is argued that a number of robotic problem-solving activities can be performed directly on the Occupancy Grid representation. Some parallels are drawn between operations on Occupancy Grids and related image processing operations.

Elfes, Alberto↗
NASA NTRS1989

On the radio variability of V410 Tauri

The radio flux density of the star V410 Tauri has been monitored at 6 and 2 cm wavelengths at monthly intervals over a one-year period with the VLA. In contrast to earlier observations, the radio emission was typically at the level of roughly 1 mJy with flat or negative spectral indices. No large radio 'flare' events were detected. However, a periodicity analysis of the quiescent data shows statistically significant evidence for a modulation of the radio emission, with a period of 0.933 days, or one-half the optical period reported by Vrba, et al. (1988). If the modulation is real, it would imply that (1) the radio emission is produced either in localized zones on two opposite hemispheres of the star, or in a single, presumably high-latitude, structure that remains visible for an entire rotation period; (2) this zone or zones must be comparable to the stellar radius in size; (3) the energy spectrum of the radiating electrons is stable over long times (greater than 1 yr) but the absolute intensity level in the quiescent state may vary by factors of a few; and (4) the emission solid angle varies with viewing angle of the emission zone. It is suggested that gyrosynchrotron radiation from closed-loop magnetic structures may be responsible for the quasisteady low-level radio emission reported here. A geometric model for the radio emission structure may explain qualitatively the modulation of the radio emission. By analogy with the premain-sequence star DoAr 21, this same physical mechanism may produce both the 'quiescent' and 'flaring' radio emission. The monitoring results suggest that strong radio outbursts, such as were previously observed for V410 Tau, are relatively rare.

Bieging, John H.↗
NASA NTRS1991

Zodiacal emission. II - Dust near ecliptic

The location and brightness of the peak zodiacal emission are derived from IRAS observations of the diffuse infrared background radiation. A uniform ellipsoid geometrical model is fitted to the latitudes of peak brightness, from which the orientation of the surface of maximum dust density near the earth's orbit is derived. Deviations from the uniform ellipsoid indicate that this surface bends toward the invariable plane of the solar system beyond 2.5 AU from the sun. The variations of the peak zodiacal emission brightness with solar elongation and observation date allow two independent determinations of the gradient of the volume emissivity of interplanetary dust. Combined with theoretical calculations of the infrared emission from silicate and graphite grains heated by the sun, the gradient of the dust density is found to be n proportional to r exp (-1.1 + or - 0.2). Systematic brightness variations with ecliptic longitude reveal two potential asymmetries in the dust complex: excess emission following the earth in its orbit, and excess emission along lines of sight with ecliptic longitude lambda = 190 + or - 20 deg and solar lambda about 100 deg.

Reach, William T.↗
NASA NTRS1991

Multimission observations of 4U 1538 - 52

Archival data from the eclipsing binary X-ray pulsar 4U 1538 - 52 have been analyzed. These data were obtained from four different X-ray missions and span a baseline of 12 yr. Scanning observations were made using the Uhuru satellite during May 9-15, 1972 and using HEAO A1 during August 26-31, 1977 and February 22-28, 1978. Pointed observations were made using the Einstein Observatory during March 2, 1979 and Exosat during March 17, August 7-8 and 10-11, 1984. These data are used to improve the orbital period determination, to set a limit to the change in orbital period, and to improve the knowledge of the pulse period as a function of time. Exosat pulse profiles are presented and pulse-phase spectroscopy is performed. The pulsation observations of 4U 1538 - 52 are modeled geometrically, and parameters for magnetic beaming of the accretion column are derived.

Cominsky, L. R.↗
NASA NTRS1991

IRAS detection of very cold dust in the Lynds 134 cloud complex

IRAS maps at 60 and 100 microns of the complex of dark clouds containing L1345, L183, and L1780 are presented and discussed. Extended regions are apparent where the 60 micron emission is very low compared to the 100 micron emission. The 60-100 micron flux ratio has a constant value of 0.2 in the outer diffuse parts of the clouds but suddenly drops to less than 0.03 in the opaque cloud centers. A geometrical model is used to show that the drop occurs in a narrow transition layer that has not been resolved by IRAS. The observations provide direct evidence for dust temperatures colder than 15 K in dark clouds. A number of 60 micron-deficient regions are defined using the quantity Delta I(100) = I(60)/Theta, where Theta is the ratio I(60)/I(100) in the diffuse parts of the complex. Delta I(100) is highly proportional to extinction and (C-13)O column density. The relationships indicate that the dust temperature must be constant over a large fraction of the volume sampled by Delta I(100). An upper limit of 4.8 g/sq cm is obtained for the mass absorption coefficient of dust at 100 microns.

Laureijs, R. J.↗
NASA NTRS1990

Optical neural network system for pose determination of spinning satellites

An optical neural network architecture and algorithm based on a Hopfield optimization network are presented for multitarget tracking. This tracker utilizes a neuron for every possible target track, and a quadratic energy function of neural activities which is minimized using gradient descent neural evolution. The neural net tracker is demonstrated as part of a system for determining position and orientation (pose) of spinning satellites with respect to a robotic spacecraft. The input to the system is time sequence video from a single camera. Novelty detection and filtering are utilized to locate and segment novel regions from the input images. The neural net multitarget tracker determines the correspondences (or tracks) of the novel regions as a function of time, and hence the paths of object (satellite) parts. The path traced out by a given part or region is approximately elliptical in image space, and the position, shape and orientation of the ellipse are functions of the satellite geometry and its pose. Having a geometric model of the satellite, and the elliptical path of a part in image space, the three-dimensional pose of the satellite is determined. Digital simulation results using this algorithm are presented for various satellite poses and lighting conditions.

Lee, Andrew↗
NASA NTRS1990

Prospects for drag prediction using computational fluid dynamics

An account is given of CFD methods deemed likely to yield aerodynamic drag prediction improvements. Improvements in drag prediction are noted to largely proceed from improvements in viscous-layer resolution. Geometric modeling and grid generation are acknowledged to be major pacing items, and may be more important than turbulence modeling. The use of upwind differencing has led to improved solution accuracy due to the nature of the artificial viscosity in cases involving shocks and nonphysical dissipation across viscous layers. Multiblock algorithms will allow more complex geometries to be treated.

Roberts, Thomas W.↗
NASA NTRS1991

The eclipsing AM Herculis variable H1907 + 690

The discovery is reported of an eclipsing cataclysmic variable that exhibits up to 10 percent circular polarization at optical wavelengths, securing its classification as an AM Herculis type binary. The object, H1907 + 609, was located with the guidance of X-ray positions from the HEAO 1 survey. Optical CCD photometry exhibits deep eclipses, from which is derived a precise orbital period of 1.743750 hr. The eclipse duration suggests an inclination angle about 80 deg for a main-sequence secondary star. The optical flux has been persistently faint during observations spanning 1987-1990, while the X-ray measurements suggest long-term X-ray variability. The polarization and photometric light curves can be interpreted with a geometric model in which most of the accretion is directed toward a single magnetic pole, with an accretion spot displaced about 17 deg in longitude from the projection of the secondary star on the white dwarf surface.

Remillard, R. A.↗
NASA NTRS1989

Microwave remote sensing and radar polarization signatures of natural fields

Theoretical models developed for simulation of microwave remote sensing of the Earth surface from airborne/spaceborne sensors are described. Theoretical model calculations were performed and the results were compared with data of field measurements. Data studied included polarimetric images at the frequencies of P band, L band, and C band, acquired with airborne polarimeters over a agricultural field test site. Radar polarization signatures from bare soil surfaces and from tree covered fields were obtained from the data. The models developed in this report include: (1) Small perturbation model of wave scatterings from randomly rough surfaces, (2) Physical optics model, (3) Geometrical optics model, and (4) Electromagnetic wave scattering from dielectric cylinders of finite lengths, which replace the trees and branches in the modeling of tree covered field. Additionally, a three-layer emissivity model for passive sensing of a vegetation covered soil surface is also developed. The effects of surface roughness, soil moisture contents, and tree parameters on the polarization signatures were investigated.

Mo, Tsan↗
NASA NTRS1992

Influence of airfoil geometry on delta wing leading-edge vortices and vortex-induced aerodynamics at supersonic speeds

An assessment of the influence of airfoil geometry on delta wing leading edge vortex flow and vortex induced aerodynamics at supersonic speeds is discussed. A series of delta wing wind tunnel models were tested over a Mach number range from 1.7 to 2.0. The model geometric variables included leading edge sweep and airfoil shape. Surface pressure data, vapor screen, and oil flow photograph data were taken to evaluate the complex structure of the vortices and shocks on the family of wings tested. The data show that airfoil shape has a significant impact on the wing upper surface flow structure and pressure distribution, but has a minimal impact on the integrated upper surface pressure increments.

Wood, Richard M.↗
NASA NTRS1992

Numerical studies of the fluid and optical fields associated with complex cavity flows

Numerical solutions for the flowfield about several cavity configurations have been computed using the Reynolds averaged Navier-Stokes equations. Comparisons between numerical and experimental results are made in two dimensions for free shear layers and a rectangular cavity, and in three dimensions for the transonic aero-window problem of the Stratospheric Observatory for Infrared Astronomy (SOFIA). Results show that dominant acoustic frequencies and magnitudes of the self excited resonant cavity flows compare well with the experiment. In addition, solution sensitivity to artificial dissipation and grid resolution levels are determined. Optical path distortion due to the flow field is modelled geometrically and is found to match the experiment. The fluid field was computed using a diagonalized scheme within an overset mesh framework. An existing code, OVERFLOW, was utilized with the additions of characteristic boundary condition and output routines required for reduction of the unsteady data. The newly developed code is directly applicable to a generalized three dimensional structured grid zone. Details are provided in a paper included in Appendix A.

Atwood, Christopher A.↗
NASA NTRS1991

Structural mechanics of 3-D braided preforms for composites. IV - The 4-step tubular braiding

This paper presents the fundamentals of the 4-step 3D tubular braiding process and the structure of the preforms produced. Based on an idealized structural model, geometric relations between the structural parameters of the preform are analytically established. The effects of machine arrangement and operating conditions are discussed. Yarn retraction, yarn surface angle, outside diameter, and yarn volume fraction of the preform in terms of the pitch length, the inner diameter, and the machine arrangement are theoretically predicted and experimentally verified.

Hammad, M.↗
NASA NTRS1991

Effect of an arcjet plume on satellite reflector performance

The effect of an arcjet plume on the performance of satellite reflector antennas is studied. The arcjet plume is modeled as a weakly ionized plasma. The spatial permittivity distribution of the plume is approximated using the measured electron density profile and a cold plasma model. Geometrical optics is applied to determine the ray paths as well as the transmitted fields through the inhomogeneous plume. The ray optics results are compared against several exact solutions for scattering from inhomogeneous dielectrics, and good agreement is observed for sufficiently large scatterer size. The far-field antenna patterns of the reflector in the presence of the plume are calculated from the transmitted ray fields using a ray-tube integration scheme. For arcjet prototypes in the 1-kW class, the plume effect on the antenna performance is small. As the electron density increases, the main beam and sidelobe level gradually degrade. The main beam also tends to squint away from the plume region.

Ling, Hao↗
NASA NTRS1992

Anisotropic ionizing radiation in Seyfert galaxies. I - The extended narrow-line region in Markarian 573

The morphology, kinematics, and ionization state of the nuclear extended narrow-line region (ENLR) of the Seyfert 2 galaxy Mrk 573 are studied using narrow-band images of a grid of long-slit spectra. The entire ENLR is mapped spectroscopically, and velocity structure is studied. The velocity field map shows a typical galactic rotation picture with some important deviations. A simple geometric model, in accordance with the 'unified schemes', is employed to study the effects of various parameters of the observed picture. The best match is achieved when a biconical radiation field illuminates the ISM of the host galaxy that takes part in a normal galaxy rotation but also has radial motions close to the nucleus. The emission-line images reveal an ENLR elongated along the radio axis in the northwest-southeast direction, but a map of the flux ratio forbidden O III 5007/(H-alpha + forbidden N II) shows a different structure, with the highest excitation peak offset by about 4 arcsec along the radio axis to the southeast.

Tsvetanov, Zlatan↗
NASA NTRS1984

AWT Modeling Status

The NASA Altitude Wind Tunnel (AWT) modeling status is presented through analytical and physical performance assessments. Topics covered in viewgraph format include: performance assessment and modeling, geometric dimensions, organization of task force, and schedule of events.

Abbott, John M.↗
NASA NTRS1993

Dynamic analysis of spur gears using computer program DANST

DANST is a computer program for static and dynamic analysis of spur gear systems. The program can be used for parametric studies to predict the effect on dynamic load and tooth bending stress of spur gears due to operating speed, torque, stiffness, damping, inertia, and tooth profile. DANST performs geometric modeling and dynamic analysis for low- or high-contact-ratio spur gears. DANST can simulate gear systems with contact ratio ranging from one to three. It was designed to be easy to use, and it is extensively documented by comments in the source code. This report describes the installation and use of DANST. It covers input data requirements and presents examples. The report also compares DANST predictions for gear tooth loads and bending stress to experimental and finite element results.

Oswald, Fred B.↗