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At least 307 records · Page 17

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NASA NTRS1981

Products of multiple Fourier series with application to the multiblade transformation

A relatively simple and systematic method for forming the products of multiple Fourier series using tensor like operations is demonstrated. This symbolic multiplication can be performed for any arbitrary number of series, and the coefficients of a set of linear differential equations with periodic coefficients from a rotating coordinate system to a nonrotating system is also demonstrated. It is shown that using Fourier operations to perform this transformation make it easily understood, simple to apply, and generally applicable.

Kunz, D. L.↗

NASA NTRS1982

Radio frequency verification tasks related to a multiple aperture reflector system

The establishment of analytical methods for predicting the electromagnetic performance of multiple offset fed apertures for multiple beam large space antenna systems is highlighted. The development of experimental modeling techniques for verifying the analytical methods used in predicting the effects of surface roughness (pillows), scattering, and aperture coupling on RF performance is discussed.

Campbell, T. G.↗

NASA NTRS1982

Design and use of multiple blade slurry sawing in a production atmosphere

The technique and uses of the multiple blade slurry (MBS) saw are considered. Multiple bands of steel are arranged in a frame and the frame is reciprocated with the steel bands to a workpiece, while simultaneously applying abrasive at the point of contact. The blades wear slots in the workpiece and progress through the piece resulting in several parts of wafers. The transition to MBA from diamond slicing is justified by savings resulting from minimized kerf losses, minimized subsurface damage, and improved surface quality off the saw. This allows wafering much closer to finished thickness specifications. The current state of the art MBS technology must be significantly improved if the low cost solar array (LSA) goals are to be attained. It is concluded that although MBS will never be the answer to every wafering requirement, the economical production of wafers to LSA project specifications will be achieved.

Lynah, F. P., Jr.↗

NASA NTRS1981

Multiple EFG silicon ribbon technology as the basis for manufacturing low-cost terrestrial solar cells

Mackintosh et al. (1978) have reported on the development of a multiple ribbon furnace based on the 'edge defined film fed growth' (EFG) process for the fabrication of silicon ribbon. It has been demonstrated that this technology can meet the requirements for a silicon substrate material to be used in the manufacture of solar panels which can meet requirements regarding a selling price of $0.70/Wp when certain goals in terms of throughput and quality are achieved. These goals for the multiple ribbon technology using 10 cm wide ribbon require simultaneous growth of 12 ribbons by one operator at average speeds of 4 to 4.5 cm/min, and 13% efficient solar cells. A description is presented of the progress made toward achieving these goals. It is concluded that the required performance levels have now been achieved. The separate aspects of technology must now be integrated into a single prototype furnace.

Mackintosh, B.↗

NASA NTRS1982

Lidar clear atmosphere multiple scattering dependence on receiver range

The degree of multiple scattering encountered by nadir-directed lidar in clear atmosphere conditions was assessed by the Monte Carlo method based on a model of the vertical distribution of aerosol scattering in the atmosphere. The lowest 3 km of the atmosphere were regarded as containing 90% of the aerosol optical thickness, with the unity normalized value for the forward peak of the aerosol phase function being 4.38 at a 694.3 nm laser wavelength. Results were obtained for two lidar receiver heights for three receiver field of view (FOV) angular halfwidths. An increase in receiver height was determined to cause a significant increase in the amount of angular scattering of the lidar signal. A factor of 20 change in receiver height produced an order of magnitude change in the single to multiple scattering ratio.

Spinhirne, J. D.↗

NASA NTRS1982

Backscattered UV radiation - Effects of multiple scattering and the lower boundary of the atmosphere

A method is proposed for the calculation of a multiple-scattering correction to the single-scattering calculation of the radiance of the terrestrial atmosphere resulting from backscattered ultraviolet solar radiation in the spectral region used in the ozone profile inversion. This method uses jointly the usual analytical and Monte Carlo methods. Effects of the lower boundary of the atmosphere, cloud tops, and ground surface are investigated both qualitatively and quantitatively. The ratio of multiple to single scattering is determined, and its importance in ozone profile inversion of backscattered UV solar radiation from the terrestrial atmosphere is evaluated. The polarization of the atmospheric radiance is treated briefly.

Aruga, T.↗

NASA NTRS1983

Development of a multiple-parameter nonlinear perturbation procedure for transonic turbomachinery flows: Preliminary application to design/optimization problems

An investigation was conducted to continue the development of perturbation procedures and associated computational codes for rapidly determining approximations to nonlinear flow solutions, with the purpose of establishing a method for minimizing computational requirements associated with parametric design studies of transonic flows in turbomachines. The results reported here concern the extension of the previously developed successful method for single parameter perturbations to simultaneous multiple-parameter perturbations, and the preliminary application of the multiple-parameter procedure in combination with an optimization method to blade design/optimization problem. In order to provide as severe a test as possible of the method, attention is focused in particular on transonic flows which are highly supercritical. Flows past both isolated blades and compressor cascades, involving simultaneous changes in both flow and geometric parameters, are considered. Comparisons with the corresponding exact nonlinear solutions display remarkable accuracy and range of validity, in direct correspondence with previous results for single-parameter perturbations.

Stahara, S. S.↗

NASA NTRS1983

Multiple-grid convergence acceleration of viscous and inviscid flow computations

A multiple-grid algorithm for use in efficiently obtaining steady solution to the Euler and Navier-Stokes equations is presented. The convergence of a simple, explicit fine-grid solution procedure is accelerated on a sequence of successively coarser grids by a coarse-grid information propagation method which rapidly eliminates transients from the computational domain. This use of multiple-gridding to increase the convergence rate results in substantially reduced work requirements for the numerical solution of a wide range of flow problems. Computational results are presented for subsonic and transonic inviscid flows and for laminar and turbulent, attached and separated, subsonic viscous flows. Work reduction factors as large as eight, in comparison to the basic fine-grid algorithm, were obtained. Possibilities for further performance improvement are discussed.

Johnson, G. M.↗

NASA NTRS1982

Multiple scattering calculations of rain effects

The multiple scattering calculations of rain effects are studied on the basis of calculating the incoherent intensity at 30, 60, 90, and 120 GHz. The Mie solution and the Laws-Parsons distribution are used to determine scattering and absorption characteristics. The equation of transfer and the Stokes parameters are used to determine incoherent intensities for the horizontal and vertical polarizations. The ratio of the copolarized incoherent intensity to the copolarized coherent intensity is defined as the incoherent copolarized discrimination. The ratio of the cross-polarized incoherent intensity is defined as the incoherent cross-polarized discrimination. These ratios are calculated in terms of copolarized attenuation, rain rate, and field of view. The results show that multiple scattering effects may become significant during heavy rains.

Ishimaru, A.↗

NASA NTRS1983

Extremely high multiplicities in high-energy nucleus-nucleus collisions

Two unusually-high-multiplicity interactions of high-energy heavy nuclei were observed in a balloon-borne emulsion chamber: an Si(+)AgBr event (4 TeV/nucleon) and a Ca(+)C event (100 TeV/nucleon), with 1015 and 760 charged particles, respectively. The multiplicities and rapidity distributions favor the multichain model but not the wounded-nucleon superposition model. The high average transverse momentum (550-700 MeV/c) and the rapid fluctuations of the events are not readily understood in terms of any superposition models.

Burnett, T. H.↗

NASA NTRS1983

Efficient solution of the Euler and Navier-Stokes equations with a vectorized multiple-grid algorithm

A multiple-grid algorithm for use in efficiently obtaining steady solutions to the Euler and Navier-Stokes equations is presented. The convergence of the explicit MacCormack algorithm on a fine grid is accelerated by propagating transients from the domain using a sequence of successively coarser grids. Both the fine and coarse grid schemes are readily vectorizable. The combination of multiple-gridding and vectorization results in substantially reduced computational times for the numerical solution of a wide range of flow problems. Results are presented for subsonic, transonic, and supersonic inviscid flows and for subsonic attached and separated laminar viscous flows. Work reduction factors over a scalar, single-grid algorithm range as high as 76.8. Previously announced in STAR as N83-24467

Chima, R. V.↗

NASA NTRS1983

Comparison of several techniques to obtain multiple-look SAR imagery

In order to improve image interpretability when SAR imagery is contaminated by coherent speckle noise, multiple look images are often generated. The performance levels of techniques for the generation of such multiple look imagery are presently assessed, with attention to the detailed impulse responses and signal-to-speckle noise ratios obtainable. The speckle-reduction technique considered are those of the discrete mixed integrator and the image domain filter. It is found that, by using several types of image domain filters, the signal-to-speckle noise ratio can be improved over the conventional discrete mixed integrator method's results while maintaining the equivalent rectangular resolution constant.

Li, F.-K.↗

NASA NTRS1983

VLSI architectures for computing multiplications and inverses in GF(2-m)

Finite field arithmetic logic is central in the implementation of Reed-Solomon coders and in some cryptographic algorithms. There is a need for good multiplication and inversion algorithms that are easily realized on VLSI chips. Massey and Omura recently developed a new multiplication algorithm for Galois fields based on a normal basis representation. A pipeline structure is developed to realize the Massey-Omura multiplier in the finite field GF(2m). With the simple squaring property of the normal-basis representation used together with this multiplier, a pipeline architecture is also developed for computing inverse elements in GF(2m). The designs developed for the Massey-Omura multiplier and the computation of inverse elements are regular, simple, expandable and, therefore, naturally suitable for VLSI implementation.

Wang, C. C.↗

NASA NTRS1984

Algorithms for output feedback, multiple-model, and decentralized control problems

The optimal stochastic output feedback, multiple-model, and decentralized control problems with dynamic compensation are formulated and discussed. Algorithms for each problem are presented, and their relationship to a basic output feedback algorithm is discussed. An aircraft control design problem is posed as a combined decentralized, multiple-model, output feedback problem. A control design is obtained using the combined algorithm. An analysis of the design is presented.

Halyo, N.↗

NASA NTRS1984

Photometry of icy satellites: How important is multiple scattering in diluting shadows?

Voyager observations have shown that the photometric properties of icy satellites are influenced significantly by large-scale roughness elements on the surfaces. While recent progress was made in treating the photometric effects of macroscopic roughness, it is still the case that even the most complete models do not account for the effects of multiple scattering fully. Multiple scattering dilutes shadows caused by large-scale features, yet for any specific model it is difficult to calculate the amount of dilution as a function of albedo. Accordingly, laboratory measurements were undertaken using the Cornell Goniometer to evaluate the magnitude of the effect.

Buratti, B.↗

NASA NTRS1983

Multiple buoyancy driven flows in a vertical cylinder heated from below

The structure of axisymmetric buoyancy-driven convection in a vertical cylinder heated from below is probed by finite element solution of the Boussinesq equations coupled with computed-implemented perturbation techniques for detecting and tracking multiple flows and for determining flow stability. Results are reported for fluids with Prandtl number of one and for cylinders with aspect ratio (Lambda) (defined as the height to radius of the cylinder) between 0.5 and 2.25. Extensive calculations of the neutral stability curve for the static solution and of the nonlinear motions along the bifurcating flow families show a continuous evolution of the primary cellular motion from a single toroidal cell to two and three cells nested radially in the cylinder, instead of the sharp transitions found for a cylinder with shear-free sidewalls. The smooth transitions in flow structure with Rayleigh number and lambda are explained by nonlinear connectivity between the first two bifurcating flow families formed either by a secondary bifurcation point for Lambda or = Lambda * approximately 0.80 or by a limit point for Lambda Lambda *. The transition between these two modes may be described by the theory of multiple limit point bifurcation.

Yamaguchi, Y.↗

NASA NTRS1983

Multiple origins of life

There is some indication that life may have originated readily under primitive earth conditions. If there were multiple origins of life, the result could have been a polyphyletic biota today. Using simple stochastic models for diversification and extinction, we conclude: (1) the probability of survival of life is low unless there are multiple origins, and (2) given survival of life and given as many as 10 independent origins of life, the odds are that all but one would have gone extinct, yielding the monophyletic biota we have now. The fact of the survival of our particular form of life does not imply that it was unique or superior.

Raup, D. M.↗

NASA NTRS1983

Multiple-grid convergence acceleration of viscous and inviscid flow computations

A multiple-grid algorithm for use in efficiently obtaining steady solution to the Euler and Navier-Stokes equations is presented. The convergence of a simple, explicit fine-grid solution procedure is accelerated on a sequence of successively coarser grids by a coarse-grid information propagation method which rapidly eliminates transients from the computational domain. This use of multiple-gridding to increase the convergence rate results is substantially reduced work requirements for the numerical solution of a wide range of flow problems. Computational results are presented for subsonic and transonic inviscid flows and for laminar and turbulent, attached and separated, subsonic viscous flows. Work reduction factors as large as eight, in comparison to the basic fine-grid algorithm, were obtained. Possibilities for further performance improvement are discussed. Previously announced in STAR as N83-21847

Johnson, G. M.↗