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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Multicolor laser altimeter for barometric measurements over the ocean - Experimental

Measurement theory and results from testing a breadboard multiwavelength (355-, 532- and 1064-nm) laser altimeter over horizontal paths are presented. They show that pressure accuracies of 3 mbar can be achieved when ranging at nadir to cube corner targets when using a 500-psec resolution waveform digitizer and utilizing new calibration techniques. Streak camera-based receivers will be required for the same or higher accuracies when ranging to the ocean surface. System design calculations for aircraft and spaceborne experiments are presented.

Abshire, J. B.↗
NASA NTRS1984

Numerical simulation of the tip vortex off a low-aspect-ratio wing at transonic speed

The viscous transonic flow around a low aspect ratio wing was computed by an implicit, three dimensional, thin-layer Navier-Stokes solver. The grid around the geometry of interest is obtained numerically as a solution to a Dirichlet problem for the cube. A low aspect ratio wing with large sweep, twist, taper, and camber is the chosen geometry. The topology chosen to wrap the mesh around the wing with good tip resolution is a C-O type mesh. The flow around the wing was computed for a free stream Mach number of 0.82 at an angle of attack of 5 deg. At this Mach number, an oblique shock forms on the upper surface of the wing, and a tip vortex and three dimensional flow separation off the wind surface are observed. Particle path lines indicate that the three dimensional flow separation on the wing surface is part of the roots of the tip vortex formation. The lifting of the tip vortex before the wing trailing edge is observed by following the trajectory of particles release around the wing tip.

Mansour, N. N.↗
NASA NTRS1983

Effects of preprocessing Landsat MSS data on derived features

Important to the use of multitemporal Landsat MSS data for earth resources monitoring, such as agricultural inventories, is the ability to minimize the effects of varying atmospheric and satellite viewing conditions, while extracting physically meaningful features from the data. In general, the approaches to the preprocessing problem have been derived from either physical or statistical models. This paper compares three proposed algorithms; XSTAR haze correction, Color Normalization, and Multiple Acquisition Mean Level Adjustment. These techniques represent physical, statistical, and hybrid physical-statistical models, respectively. The comparisons are made in the context of three feature extraction techniques; the Tasseled Cap, the Cate Color Cube. and Normalized Difference.

Parris, T. M.↗
NASA NTRS1984

Algebraic grid generation for wing-fuselage bodies

An algebraic procedure for the generation of boundary-fitted grids about wing-fuselage configurations is presented. A wing-fuselage configuration is specified by cross sections and mathematically represented by Coons' patches. A configuration is divided into sections so that several grid blocks that either adjoin each other or partially overlap each other can be generated, and each grid has six surfaces that map into a computational cube. Grids are first determined on the six boundary surfaces and then in the interior. Grid curves that are on the surface of the configuration are derived using plane-patch intersections, and single-valued functions relating approximate arc lengths along the curves to computational coordinates define the distribution of grid points. The two-boundary technique and transfinite interpolation are used to determine the boundary surface grids that are not on the configuration, and transfinite interpolation with linear blending functions is used to determine the interior grids.

Smith, R. E.↗
NASA NTRS1984

Numerical simulation of the tip vortex off a low-aspect-ratio wing at transonic speed

The viscous transonic flow around a low-aspect-ratio wing has been computed using an implicit, three-dimensional, 'thin-layer' Navier-Stokes solver. The grid around the geometry of interest is obtained numerically as a solution to a Dirichlet problem for the cube. The geometry chosen for this study is a low-aspect-ratio wing with large sweep, twist, taper, and camber. The topology chosen to wrap the mesh around the wing with good tip resolution is a C-O type mesh. Using this grid, the flow around the wing was computed for a free-stream Mach number of 0.82 at an angle of attack of 5 deg. At this Mach number, an oblique shock forms on the upper surface of the wing, and a tip vortex and three-dimensional flow separation off the wing surface are observed. Particle path lines indicate that the three-dimensional flow separation on the wing surface is part of the roots of the tip-vortex formation. The lifting of the tip vortex before the wing trailing edge is clearly observed by following the trajectory of particles released around the wing tip.

Mansour, N. N.↗
NASA NTRS1984

The Effect of Part-simulation of Weightlessness on Human Control of Bilateral Teleoperation: Neuromotor Considerations

The effect of weightlessness on the human operator's performance in force reflecting position control of remote manipulators was investigated. A gravity compensation system was developed to simulate the effect of weightlessness on the operator's arm. A universal force reflecting hand controller (FRHC) and task simulation software were employed. Two experiments were performed because of anticipated disturbances in neuromotor control specification on the human operator in an orbital control environment to investigate: (1) the effect of controller stiffness on the attainment of a learned terminal position in the three dimensional controller space, and (2) the effect of controller stiffness and damping on force tracking of the contour of a simulated three dimensional cube using the part simulation of weightless conditions. The results support the extension of neuromotor control models, which postulate a stiffness balance encoding of terminal position, to three dimensional motion of a multilink system, confirm the existence of a disturbance in human manual control performance under gravity compensated conditions, and suggest techniques for compensation of weightlessness induced performance decrement through appropriate specification of hand controller response characteristics. These techniques are based on the human control model.

Corker, K.↗
NASA NTRS1984

Light Scattered from Polished Optical Surfaces: Wings of the Point Spread Function

Random figure errors from the polishing process plus particles on the main mirrors in a telescope cause an extended point spread function (PSF) declining approximately as the inverse square of the sine of the angle from a star from about 100 micro-rad to a right angle. The decline in at least one case, and probably in general, proceeds as the inverse cube at smaller angles where the usual focal plane aperture radius is chosen. The photometric error due to misalignment by one Airy ring spacing with an aperture of n rings depends on the net variance in the figure. It is approximately 60/(n+1)(3) when using the data of Kormendy (1973). A typical value is 6 x 10 to the -5th power per ring of misalignment with n = 100 rings. The encircled power may be modulated on a time scale of hours by parts per thousand in a wavelength dependent manner due to relative humidity effects on mirror dust. The scattering according to an inverse power law is due to a random walk in aberration height caused by a multitude of facets and slope errors left by the polishing process. A deviation from such a law at grazing emergence may permit monitoring the dust effects.

Kenknight, C. E.↗
NASA NTRS1984

Low cycle fatigue of MAR-M 200 single crystals at 760 and 870 deg C

Fully reversed low cycle fatigue tests were conducted on single crystals of the nickel-base superalloys Mar-M 200 at 760 C and 870 C. At 760 C, planar slip (octahedral) lead to orientation-dependent strain hardening and cyclic lives. Multiple slip crystals strain hardened the most, resulting in relatively high stress ranges and low lives. Single slip crystals strain hardened the least, resulting in relatively low stress ranges and higher lives. A preferential crack initiation site which was related to slip plane geometry was observed in single slip orientated crystals. At 870 C, the trends were quite different, and the slip character was much more homogeneous. As the tensile axis orientation deviated from 001 , the stress ranges increased and the cyclic lives decreased. Two possible mechanisms were proposed to explain the behavior: one is based on Takeuchi and Kuramoto's cube cross-slip model, and the other is based on orientation-dependent creep rates.

Milligan, W. W.↗
NASA NTRS1985

The Search for Igneous Materials at the Viking Landing Sites

The use of Viking Lander 6 channel (0.4 to 1.1 microns) images to identify igneous materials is discussed. Movies of synthetic image cubes demonstrate that there are a number of contrast reversals between soils and certain rocks. Typically, large, angular rocks are brighter than the surrounding soils in the shortest wavelengths, and much darker than the soils at longest wavelengths. These results, which seem difficult to explain solely on the basis of photometric effects related to local lighting and viewing, are consistent with the presence of Fe+2 bearing silicates at the rock surfaces, producing relatively moderate absorptions in the blue and green parts of the spectrum, but more significant absorptions near about 1.0 micrometer (e.g., Fe+2 bearing pyroxenes). The soils, on the other hand, have signatures consistent with strong Fe+3 related absorptions at shorter wavelengths (e.g., Fe+3 bearing oxides or hydroxides).

Arvidson, R. E.↗
NASA NTRS1985

Importance of Gravity for Plant Growth and Behavior

Flight experiments on the importance of gravity to plant growth and behavior are reported. The following studies were undertaken: (1) hyperastic responses to incremental changes of an axially imposed centripetal force; (2) Spacelab-1 experiments, methods for preparing soil in flight hardware containers were impound, to ensure desired moisture content and minimal contamination probability; (3) mesocotyl growth patterns were established by Avena lore exposure to red light during early seedling outogency; (4) the development of flight hardware; (5) choice of member of seedlings in each cube; (6) data processing and reduction; (7) clinostat validation; circummutation in space was more vigorous than on Earth based clinostat.

Brown, A. H.↗
NASA NTRS1985

Triangular Berstein-bezier Patches, a Survey and New Results

Triangular Bernstein-Bezier patches are an alternative to the standard rectangular ones. They are maps of triangular domains into R cubed, where the patches are described by control nets similar to the rectangular case. One difference in the definition of surface normals at the patch corners: rectangular patches have inherent problems with so-called degenerate corners, i.e., edges collapsing into one point. Triangular patches do not have these problems. Since triangular shapes arise rather frequently in the design of complicated surfaces (e.g., interior car body panels), it seems that for such surfaces triangular patches are a promising addition to the usually employed rectangular patches. Another major application is the formulation of interpolants to solve the scattered data problem: here Bernstein-Bezier patches provide a very powerful tool; they can be used to discover new schemes as well as to discover new properties of existing methods.

Farin, G.↗
NASA NTRS1985

Application of the ADAMS program to deployable space truss structures

The need for a computer program to perform kinematic and dynamic analyses of large truss structures while deploying from a packaged configuration in space led to the evaluation of several existing programs. ADAMS (automatic dynamic analysis of mechanical systems), a generalized program from performing the dynamic simulation of mechanical systems undergoing large displacements, is applied to two concepts of deployable space antenna units. One concept is a one cube folding unit of Martin Marietta's Box Truss Antenna and the other is a tetrahedral truss unit of a Tetrahedral Truss Antenna. Adequate evaluation of dynamic forces during member latch-up into the deployed configuration is not yet available from the present version of ADAMS since it is limited to the assembly of rigid bodies. Included is a method for estimating the maximum bending stress in a surface member at latch-up. Results include member displacement and velocity responses during extension and an example of member bending stresses at latch-up.

Calleson, R. E.↗
NASA NTRS1985

Numerical techniques for large cosmological N-body simulations

Techniques for carrying out large N-body simulations of the gravitational evolution of clustering in the fundamental cube of an infinite periodic universe are described and compared. The accuracy of the forces derived from several commonly used particle mesh schemes is examined, showing how submesh resolution can be achieved by including short-range forces between particles by direct summation techniques. The time integration of the equations of motion is discussed, and the accuracy of the codes for various choices of 'time' variable and time step is tested by considering energy conservation as well as by direct analysis of particle trajectories. Methods for generating initial particle positions and velocities corresponding to a growing mode representation of a specified power spectrum of linear density fluctuations are described. The effects of force resolution are studied and different simulation schemes are compared. An algorithm is implemented for generating initial conditions by varying the number of particles, the initial amplitude of density fluctuations, and the initial peculiar velocity field.

Efstathiou, G.↗
NASA NTRS1985

Quantification of the effects of generation volume, surface recombination velocity, and diffusion length on the electron-beam-induced current and its derivative Determination of diffusion lengths in the low micron and submicron ranges

A systematic and quantitative analysis is carried out to investigate the effects of the shape (point, cube, Gaussian) and size of the generation volume, the surface recombination velocity, and the diffusion length on the electron-beam-induced current (EBIC) and its derivative (DEIC). Thick homogeneously doped samples exhibiting diffusion lengths in the low micron and submicron range are considered. The results are presented in computed EBIC curves as a function of scanning distance and of the ratio true diffusion length/effective diffusion length. Shown using these curves are: (1) a simple and yet rigorous method for the determination of the true diffusion length, taking into consideration all of the factors cited above, (2) a method for the rapid determination of the surface recombination velocity, (3) the condition under which the source shape becomes insignificant, and (4) a new value for the lower limit of the diffusion length which can be determined by the EBOC technique.

Luke, K. L.↗
NASA NTRS1985

Satellite geodynamics

The application of space technology to the study of solid-earth geophysics are reviewed. Attention is given to the major experiments in the field of space-based geodynamics research including early satellite laser ranging (SLR) measurements, the GEOS-3 satellite observations, and the installation of corner cube reflectors on the moon. The contribution of VLBI techniques to terrestriral positioning measurements is also discussed. Prospects for future advances with the development of the Global Positioning System (GPS) and observations from on board the Space Station are also assessed.

Walter, L. S.↗
NASA NTRS1985

Radio occultation by Saturn's rings - Observations of structure and particle size with Voyager 1

Voyager 1 radio occultation study of Saturn's rings gives detailed information regarding the rings' radial structure and particle sizes. Structure within the rings is mapped to a radial resolution of few hundred m in the tenuous parts of ring C and the Cassini Division, and few km over most of ring A. Fine resolution profiles reveal extremely sharp edges, very narrow gaps, and a host of wave phenomena. Particle size distributions obtained from occultation data within several ring regions are roughly consistent with an inverse cube power law with upper size cutoff in the 5 to 10 m radius range.

Marouf, E. A.↗
NASA NTRS1985

A remark about pointed bubbles

The polymer expansion is a formal algebraic identity between a partition function and logarithm in statistical physics problems. The expansion gives a systematic method to control the free energy or to establish exponential tree-graph decay of connected correlations. Here, the convergence properties of the polymer expansion are analyzed in connection with three practical examples, including: intersecting bonds in chemical polymer chains; a connected closed hypersurface built from the (d-1)-faces of the d-dimensional unit cubes; and the set of Feynamn diagrams in the perturbation series of the Euclidean field theory partition function Z. The example of connected polymer chains is generalized to apply to other lattice models, including n-state Ising models at high temperature; short range lattice gases at high temperature; and weak coupling lattice field and gauge theories.

Garabedian, P. R.↗
NASA NTRS1985

Particle generation experience in Langley's 16-foot transonic tunnel

The Langley 16-Foot Transonic Tunnel is a single-return, continuous-flow, atmospheric tunnel which uses air exchange for cooling. The tunnel speed is continuously variable from Mach 0 to 1.30. The test section is a regular octagon in cross-section with slots at the corners of the octagon. The laser velocimeter optics, laser, photomultipliers, etc. are mounted in the test section plenum chamber which surrounds the test section. The test volume is approximately a 1-meter cube about the tunnel center line centered on tunnel station 40.84 meters. The seeding system particle generators are mounted on the upstream side of the fourth set of turning vanes approximately 49 meters upstream of the test volume. At this point the tunnel has a diameter of 17.68 meters which meant that installation of the generators was a difficult procedure. It might be noted that particle generation had to be continuous as when the generators were turned off the data rate rapidly deteriorated to zero.

Reubush, D. E.↗