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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 1,639 records · Page 91

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NASA NTRS1981

Experience with high performance V/STOL fighter projects at MBB

Flight control systems and aerodynamic aspects of experimental V/STOL aircraft are discussed. The VJ 101 C featured tilting engines for increased thrust, reheat for takeoff, simple translation, triangular decentralization of the engines for thrust modulation, and moderate ground effects. Two experimental aircraft were built, with and without reheat, capable of Mach 2 and Mach 1.04, respectively. The mechanical flight control system and tests are outlined, both for hover rig and flight configurations. Ground suction, acoustic and thermal loading, sodium silicate coatings to avoid ground corrosion, and recirculation are considered. Results of the follow-on project to the VJ 101 C, the AVS, which was developed by NASA, are reviewed, and it is noted that trends toward thrust-to-weight ratios exceeding one, in concert with low wing loading, favor the development of V/STOL aircraft.

Aulehla, F.↗

NASA NTRS1981

Orbits of the Tethys Lagrangian bodies

Preliminary libration parameters are derived for the objects found in 1980 at the triangular libration points of Tethys. The parameters are obtained from an orbit analysis of ground-based and Voyager I data obtained in 1980 for the separation from Saturn along the ring major axis, the projected separations from the Tethys L4 and L5 points and the separations from Tethys in orbital longitude. The best fitting libration parameters indicate a small (approximately 2 deg) libration amplitude for the L4 body. Data for the object at the L5 point may be fit either by orbits with libration amplitudes greater than 50 deg, or with small libration amplitudes, which are in agreement with recent Voyager II observations.

Reitsema, H. J.↗

NASA NTRS1982

Dissipation of ionospheric irregularities by wave-particle and collisional interactions

The nonlinear dissipation of plasma irregularities aligned parallel to an ambient magnetic field is studied numerically using a model which employs both wave-particle and collisional diffusion. A wave-particle diffusion coefficient derived from a local theory of the universal drift instability is used. This coefficient is effective in regions of nonzero plasma gradients and produces triangular-shaped irregularities with spectra which vary as f to the -4th, where f is the spatial frequency. Collisional diffusion acts rapidly on the vertices of the irregularities to reduce their amplitude. The simultaneous action of the two dissipative processes is more efficient than collisions acting alone. In this model, wave-particle diffusion mimics the forward cascade process of wave-wave coupling.

Bernhardt, P. A.↗

NASA NTRS1982

Programmable controller system for wind tunnel diversion vanes

A programmable controller (PC) system automatic sequence control, which acts as a supervisory controller for the servos, selects the proper drives, and automatically sequences the vanes, was developed for use in a subsonic wind tunnel. Tunnel modifications include a new second test section (80 ft x 100 ft with a maximum air speed capability of 110 knots) and an increase in maximum velocity flow from 200 knots to 300 knots. A completely automatic sequence control is necessary in order to allow intricate motion of the 14 triangularly arranged vanes which can be as large as 70 ft high x 35 ft wide and which require precise acceleration and deceleration control. Rate servos on each drive aid in this control, and servo cost was minimized by using four silicon controlled rectifier controllers to control the 20 dc drives. The PC has a programming capacity which facilitated the implementation of extensive logic design. A series of diagrams sequencing the vanes and a block diagram of the system are included.

King, R. F.↗

NASA NTRS1983

Estimating Waveguide Feed Directivity and Spacing

Approximate curves simplify initial steps of antenna design. Maximum achievable directivity exponents plotted as functions of element spacing in wavelengths for equilateral triangular array of rectangular waveguides. Directivities and exponents calculated for circular waveguides, pyramidal horns, and other standard feeds. Designer quickly estimates element spacing necessary to achieve required directivity or directivity achievable.

Rahmat-Samii, Y.↗

NASA NTRS1984

General-Purpose Icosahedral Structure

Scheme based on geodesic sphere approximated by regular icosahedron. Structure rigid and lightweight. Allows access to all subsystems and equipment from outside. Regular icosahedron constructed from triangular panels. Five panels meeting at each corner all rigidly attached to fivesided adapter. Strengthened version useful on Earth for rapidly-erectable temporary shelters, industrial structures, or playground equipment.

Evans, J.↗

NASA NTRS1984

Microyield Stress in Composite Materials

New interferometric method for measuring microyield stress faster and more accurate than previous strain-gage method. Multiple laser beams reflected from corner-cube reflectors arranged in triangular patterns yielding data sufficient to separate length changes from rigid-body motion and bending.

Mcmahan, L.↗

NASA NTRS1982

Surfaces: Representation and approximation

Schemes for the representation and approximation of surfaces, based on Coon's and triangular patches and blending are discussed. The necessary criteria/characteristics for resulting spaces are outlined.

Barnhill, R. E.↗

NASA NTRS1982

A recursive algorithm for Zernike polynomials

The analysis of a function defined on a rotationally symmetric system, with either a circular or annular pupil is discussed. In order to numerically analyze such systems it is typical to expand the given function in terms of a class of orthogonal polynomials. Because of their particular properties, the Zernike polynomials are especially suited for numerical calculations. Developed is a recursive algorithm that can be used to generate the Zernike polynomials up to a given order. The algorithm is recursively defined over J where R(J,N) is the Zernike polynomial of degree N obtained by orthogonalizing the sequence R(J), R(J+2), ..., R(J+2N) over (epsilon, 1). The terms in the preceding row - the (J-1) row - up to the N+1 term is needed for generating the (J,N)th term. Thus, the algorith generates an upper left-triangular table. This algorithm was placed in the computer with the necessary support program also included.

Davenport, J. W.↗

NASA NTRS1982

Efficient structures for geosynchronous spacecraft solar arrays, phase 4

Efficient structures for geosynchronous spacecraft solar arrays were investigated. The STACBEAM (stacking triangular articulated compact beam) concept was selected. The primary component, the solar array blanket, is stored in a folded configuration and is deployed by controlled linear extension. Blanket stiffness is attained by axially tensioning the blanket and by providing periodic lateral ribs and standoffs which attach the blanket to the beam at several places along its length. The STACBEAM deploys sequentially (one bay at a time) using a deployer of sufficient rigidity so that beam stiffness is not degraded during deployment. The beam does not rotate during deployment, thus making blanket beam attachment possible in the packaged condition. In addition to high bending stiffness, the STACBEAM possesses high torsional rigidity due to nonflexible diagonals. The concept is adaptable to various size and loading requirements by changing member diameter and baylength, thus affecting the ratio of packaged and deployed length.

Adams, L. R.↗

NASA NTRS1982

Description of the 3 MW SWT-3 wind turbine at San Gorgonio Pass, California

The SWT-3 wind turbine, a microprocessor controlled three bladed variable speed upwind machine with a 3MW rating that is presently operational and undergoing system testing, is discussed. The tower, a rigid triangular truss configuration, is rotated about its vertical axis to position the wind turbine into the prevailing wind. The blades rotate at variable speed in order to maintain an optimum 6 to 1 tip speed ratio between cut in and fated wind velocity, thereby maximizing power extraction from the wind. Rotor variable speed is implemented by the use of a hydrostatic transmission consisting of fourteen fixed displacement pumps operating in conjunction with eighteen variable displacement motors. Full blade pitch with on-off hydraulic actuation is used to maintain 3MW of output power.

Rybak, S. C.↗

NASA NTRS1983

Numerical Simulation for Droplet Combustion Using Lagrangian Hydrodynamics

A predictive model of spray combustion must incorporate models for the wide variety of physical environments in a practical combustor. In regions where droplets are closely spaced, combustion resembles a diffusion flame; where they are well separated, an envelope or wake flame results. The relative velocity field between the fuel droplets and oxidizer in influences boundary layer development about the droplet, recirculating flow patterns, and droplet shape and stability. A model must encompass these interacting temporal and spatial effects as well as complicated combustor boundaries. The objective of the current work is to develop the triangular gridding method for describing the individual and collective properties of vaporizing and burning fuel droplets.

Fritts, M. J.↗

NASA NTRS1982

A multiple beam antenna concept for a 30/20 GHz satellite communications system

Design and operational performance features of a NASA planned 30/30 GHz flight experiment communications system multiple-beam antenna (MBA) are described. The MBA is a shared aperture offset Cassegrain type with a main reflector diameter of 3 m and physically separated transmit and receive feeds. A planar frequency selective surface is employed which is transmissive to the receive signals and reflective to the transmit signals. Trade-offs and constraints in the MBA feed design are explored, noting the higher feed loss and complexity due to choosing variable power dividers for the beam forming network. Doublet beam coverage of the east coast of the continental U.S. is shown to be possible with a triangular lattice array of feed horns with aperture diameters and element spacings of two wavelengths. The doublet configuration requires ten times the components as a singlet array.

Forman, B. J.↗

NASA NTRS1982

Global sensitivity to velocity errors at the libration points

The global effects on non-linear stability are investigated at and around the triangular libration points. The model of the circular restricted problem of three bodies is used, considering the earth and the moon as the primaries. Areas of the initial conditions in the configuration space leading to stability with zero initial velocity around the equilibrium points are compared to stable areas in the phase space with variable initial velocity and zero initial deviations at the equilibrium points. The behavior of the system concerning errors due to initial conditions in the configuration space is studied for 6 years and the effects of initial velocity errors are considered for 7.73 years.

Szebehely, V.↗

NASA NTRS1982

Petrologic variations in Apollo 16 surface soils

Source rock, maturation history and intrasite variation data are derived for the Apollo 16 regolith by comparing modal analyses of 15 surface soils with rake and rock sample data. Triangular source rock component plots show that Apollo 16 soils have similar source rocks that are well homogenized throughout the site. The site can be divided into three soil petrographic provinces. Central site soils are mature, well homogenized, and enriched in glass. They are probably the most typical Cayley Plains materials present. North Ray soils are immature to submature, containing North Ray ejecta. South Ray soils are mature, but contain small amounts of fresh impact melts and plagioclase, due perhaps to the breakdown of blocky South Ray ejecta. The different compositions and physical properties of North and South Ray ejecta support the hypothesis that the latter event excavated Cayley material, while the former excavated Descartes materials.

Houck, K. J.↗

NASA NTRS1983

An experimental study of changes in the structure of a turbulent boundary layer due to surface geometry changes

This investigation attempts to observe changes in the flow structure of a nominally zero pressure gradient turbulent boundary layer by altering the surface of a smooth plate with small triangular riblets oriented in the direction of flow and protruding just above the viscous sublayer. Hot-wire measurements show a reduction in the local skin friction over the riblet valleys by about 40% compared to the smooth surface near the end of the plate. Local skin friction increases by about 10% over the riblet peaks. Results showing the effects of the riblets on the mean, root-mean-square and skewness factor distributions of the streamwise velocity are presented. The mean profile displays characteristics similar to those of drag reducing additives; the streamwise turbulence intensity is reduced by approximately 10-15% near the surface by the riblets; the skewness factor distribution is virtually unchanged. A comparison of results from an application of the VITA 'burst' detection technique to smooth and riblet surface data is also presented although the results are rather inconclusive. Flow visualization of 'bursting' over both surfaces, while dramatically revealing the structure, reveals little difference resulting from the presence of the riblet.

Source record↗

NASA NTRS1983

The nonlocal theory of periodic density drift instabilities

The nonlocal theory of electrostatic density drift instabilities is developed for an arbitrary, periodic variation in plasma density. Linear Vlasov theory is applied to Fourier series representations of the plasma density, and the resulting equations are solved numerically. The growth rates of the universal drift instability are compared by using local and nonlocal theories. It is demonstrated that the local theory is inadequate if the nonlocal eigenfunctions of the electrostatic modes have significant amplitude over spatial regions wider than the regions of large plasma density gradients. Nonlocal effects can enhance wave-particle diffusion of a triangular-shaped variation and reduce wave-particle dissipation of a square-shaped irregularity.

Bernhardt, P. A.↗

NASA NTRS1983

Reduction of rms-error in shallow faceted large space antennas

This paper examines the potential for reducing root-mean-square surface error in shallow faceted reflectors by replacing flat facets with membrane facets. Exact solutions are obtained for the small lateral deflections of equilateral triangular and rectangular membranes subject to isotropic tension and parabolic edge deflections. These solutions are used to minimize the rms-error between a facet of a shallow paraboloidal surface and its approximating membrane facet. The resulting optimum placements and edge curvatures yield membrane facets which have significantly lower rms-errors than the corresponding best-fit flat facets. The rms-error reductions are about 55 percent for equilateral triangles and 25 percent to 93 percent for rectangles, depending on aspect ratio. The results suggest that the use of membrane facets conforming to curved structural members could yield reflectors with lower rms-error, or comparable error with larger facets and, hence, fewer structural members.

Fichter, W. B.↗