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NASA NTRS1989

Normal mode energetics and error analysis of GLA GCM simulations with different horizontal resolutions during a winter month

Comparative energetics is presented for a series of four general circulation model simulations for January 1979 conducted by the Goddard Laboratory for Atmospheres. The simulations include cases of coarse and fine horizontal model resolutions with two slightly different initial conditions. Using a three-dimensional normal mode expansion, it is found that the gravity-mode energy levels are significantly reduced in the higher wavenumbers and in the higher-order internal vertical modes by the increase of horizontal model resolution.

Tanaka, H. L.↗

NASA NTRS1989

The proton temperature and the total hourly variance of the magnetic field components in different solar wind speed regions

A comparison has been made between the predictions of the theory for radial variations of both Alfvenic fluctuations and solar wind proton temperatures proposed by Tu (1987, 1988) and the statistical results of hourly averaged plasma and magnetic field data observed by Helios 1 and 2 from launch through 1980 for different solar wind speed regimes. The comparison shows that for speed ranges between 500-800 km/s, the radial variation of the proton temperature between 0.3 and 1 AU can be explained by heating from the cascade energy which is determined by the radial variation of the total variance of magnetic field vector.

Tu, Chuan-Yi↗

NASA NTRS1990

Two-Wavelength Optical-Path-Difference Mapping

Proposed technique for measuring shapes and alignments of reflectors based on use of two-wavelength absolute-distance interferometer to generate optical-path-difference maps of reflecting or refracting surfaces. Facilitates such tasks as determining manufacturing and alignment errors of off-axis segment of large-aperture paraboloidal telescope mirror, or aligning all segments of such mirror. Suitable for use where reflecting surfaces highly aspherical, initial misalignments large, and/or surface errors exceed optical wavelengths.

Manhart, Paul K.↗

NASA NTRS1989

Quotient-difference type generalizations of the power method and their analysis

The recursion relations that were proposed by W. F. Ford and A. Sidi (Appl. Numer. Math, 4 (1988), pp. 477-489) for implementing vector extrapolation methods are used for devising generalizations of the power method for linear operators. These generalizations are shown to produce approximations to largest eigenvalues of a linear operator under certain conditions. They are similar in form to the quotient-difference algorithm and share similar convergence properties with the latter. These convergence properties also resemble those obtained for the basic LR and QR algorithms. Finally, it is shown that the convergence rate produced by one fo these generalizations is twice as fast for normal operators as it is for nonnormal operators.

Sidi, Avram↗

NASA NTRS1989

An Eigenvalue Analysis of finite-difference approximations for hyperbolic IBVPs

The eigenvalue spectrum associated with a linear finite-difference approximation plays a crucial role in the stability analysis and in the actual computational performance of the discrete approximation. The eigenvalue spectrum associated with the Lax-Wendroff scheme applied to a model hyperbolic equation was investigated. For an initial-boundary-value problem (IBVP) on a finite domain, the eigenvalue or normal mode analysis is analytically intractable. A study of auxiliary problems (Dirichlet and quarter-plane) leads to asymptotic estimates of the eigenvalue spectrum and to an identification of individual modes as either benign or unstable. The asymptotic analysis establishes an intuitive as well as quantitative connection between the algebraic tests in the theory of Gustafsson, Kreiss, and Sundstrom and Lax-Richtmyer L(sub 2) stability on a finite domain.

Warming, Robert F.↗

NASA NTRS1990

Galerkin finite difference Laplacian operators on isolated unstructured triangular meshes by linear combinations

The Galerkin weighted residual technique using linear triangular weight functions is employed to develop finite difference formulae in Cartesian coordinates for the Laplacian operator on isolated unstructured triangular grids. The weighted residual coefficients associated with the weak formulation of the Laplacian operator along with linear combinations of the residual equations are used to develop the algorithm. The algorithm was tested for a wide variety of unstructured meshes and found to give satisfactory results.

Baumeister, Kenneth J.↗

NASA NTRS1989

On the relationship between the phases of 27-day total ozone and solar activity indices in different latitudinal zones

The dynamics of 27 day total ozone variations during and 11 year solar activity cycle at high and low latitudes was analyzed. The calculations were made using a specially worked out program permitting, besides the determination of the amplitudes and phases, the observation of the coherence of phases in any time interval. To characterize solar activity, solar radio-flux at 10.7 cm was used. The results of the calculation of total ozone phases difference and those of the index F(sub 10.7), as well as the amplitudes of the 27 day variations of these parameters are presented.

Ivanova, I. N.↗

NASA NTRS1990

Parallelization of implicit finite difference schemes in computational fluid dynamics

Implicit finite difference schemes are often the preferred numerical schemes in computational fluid dynamics, requiring less stringent stability bounds than the explicit schemes. Each iteration in an implicit scheme involves global data dependencies in the form of second and higher order recurrences. Efficient parallel implementations of such iterative methods are considerably more difficult and non-intuitive. The parallelization of the implicit schemes that are used for solving the Euler and the thin layer Navier-Stokes equations and that require inversions of large linear systems in the form of block tri-diagonal and/or block penta-diagonal matrices is discussed. Three-dimensional cases are emphasized and schemes that minimize the total execution time are presented. Partitioning and scheduling schemes for alleviating the effects of the global data dependencies are described. An analysis of the communication and the computation aspects of these methods is presented. The effect of the boundary conditions on the parallel schemes is also discussed.

Decker, Naomi H.↗

NASA NTRS1989

What kind of computation is intelligence. A framework for integrating different kinds of expertise

The view that the deliberative aspect of intelligent behavior is a distinct type of algorithm; in particular, a goal-seeking exploratory process using qualitative representations of knowledge and inference is elaborated. There are other kinds of algorithms that also embody expertise in domains. The different types of expertise and how they can and should be integrated to give full account of expert behavior are discussed.

Chandrasekaran, B.↗

NASA NTRS1989

Time-dependent viscous incompressible Navier-Stokes equations - The finite difference Galerkin formulation and streamfunction algorithms

Numerical techniques are developed to solve the Navier-Stokes equations for unsteady incompressible flow. The extension of the finite-difference Galerkin (FDG) method of Stephens et al. (1984) to the continuous-time case in two or three space dimensions is explained, and the numerical implementation of the method is discussed with particular attention to the staggered-MAC-grid primitive-variable discretization, the application of discrete mass balance to avoid problems inherent in FDG schemes, the direct interpretation of the FDG expansion variables as a discrete streamfunction, and a mass-balance approach to two-dimensional problems with throughflow or obstacles. Numerical results are presented graphically for the evolution of asymptotic steady flow in a driven cavity at Reynolds number 400, 1000, or 3200; good agreement with published experimental data is demonstrated, with accurate predictions of secondary-vortex formation from wall bubble recirculations at Reynolds number 1000.

Goodrich, John W.↗

NASA NTRS1989

Constructing space difference schemes which satisfy a cell entropy inequality

A numerical methodology for solving convection problems is presented, using finite difference schemes which satisfy the second law of thermodynamics on a cell-by-cell basis in addition to the usual conservation laws. It is shown that satisfaction of a cell entropy inequality is sufficient, in some cases, to guarantee nonlinear stability. Some details are given for several one-dimensional problems, including the quasi-one-dimensional Euler equations applied to flow in a nozzle.

Merriam, Marshal L.↗

NASA NTRS1989

A parallel finite-difference method for computational aerodynamics

A finite-difference scheme for solving complex three-dimensional aerodynamic flow on parallel-processing supercomputers is presented. The method consists of a basic flow solver with multigrid convergence acceleration, embedded grid refinements, and a zonal equation scheme. Multitasking and vectorization have been incorporated into the algorithm. Results obtained include multiprocessed flow simulations from the Cray X-MP and Cray-2. Speedups as high as 3.3 for the two-dimensional case and 3.5 for segments of the three-dimensional case have been achieved on the Cray-2. The entire solver attained a factor of 2.7 improvement over its unitasked version on the Cray-2. The performance of the parallel algorithm on each machine is analyzed.

Swisshelm, Julie M.↗

NASA NTRS1990

Finite-difference models of ordinary differential equations - Influence of denominator functions

This paper discusses the influence on the solutions of finite-difference schemes of using a variety of denominator functions in the discrete modeling of the derivative for any ordinary differential equation. The results obtained are a consequence of using a generalized definition of the first derivative. A particular example of the linear decay equation is used to illustrate in detail the various solution possibilities that can occur.

Mickens, Ronald E.↗

NASA NTRS1990

Trends and individual differences in response to short-haul flight operations

A survey of airline pilots was undertaken to determine normative patterns and individual differences in mood and sleep during short-haul flight operations. The results revealed that over the course of a typical 2-d trip, pilots experience a decline in positive mood, or activity, and an increase in negative mood, or tension. On layovers, pilots report experiencing sleep of shorter duration and poorer quality than at home. These patterns are very similar to those reported by Gander and Graeber (1987) and by Gander et al. (1988), using high-fidelity sleep and activity monitoring equipment. Examination of the impact of two personality dimensions extracted from the Jenkins Activity Survey measure of the Type A personality, Achievement Striving and Impatience/Irritability, suggested that Impatience/Irritability may serve as a marker of individuals most likely to experience health-related problems on trips. Achievement Striving may serve as a predictor of performance in crew settings.

Chidester, Thomas R.↗

NASA NTRS1990

On the sensitivity of a residual circulation model to differences in input temperature data

The residual mean circulation (RMC) formulation of zonally averaged transport in the middle atmosphere produces a circulation which depends on the distributions of net diabatic heating and temperature. Such circulations are from two temperature data sets, using the same radiative transfer code (Rosenfield et al. 1987). These circulations are then used to transport N2O in a photochemical model. The circulations and the resulting N2O distributions are notably different during the Northern Hemisphere winter, with that based on the NMC temperatures producing too much upward transport in the tropical stratosphere, as judged by comparison with the stratospheric and mesoscale sounder data. The experiment demonstrates that model calculations, in general, and perturbation assessments, in particular, are likely to be quite sensitive to the choice of input temperature data (where this is not computed self-consistently). It also reveals what appears to be a seasonally dependent bias in NMC zonally averaged temperatures with respect to those obtained from the LIMS instrument during 1978/1979.

Guthrie, Paul D.↗

NASA NTRS1990

Characterization of two germania gels of different coordination

Two germania gels were synthesized by hydrolytic condensation of germanium ethoxide and by dissolution of germanium dioxide powder in ammonium hydroxide solution. The two gels were characterized using differential scanning calorimetry, X-ray powder diffraction, surface area and weight loss data, and infrared spectroscopy. The results indicate that, in gels, germanium is capable of tetragonal as well as hexagonal coordination, resulting in different crystallization behaviors.

Mukherjee, Shyama P.↗

NASA NTRS1990

Venus mantle-Mars planetosphere - What are the similarities and differences?

An overview of data concerning the mantle and planetosphere regions of Mars and Venus is presented, emphasizing data from the Phobos 2 mission. It is shown that there are significant similarities between the mantle/planetosphere regions on the two planets. These similarities include a transition region between the magnetosheath and the ionosphere dominated by heavy, planetary ions, and a transition region in which the electron population is different from both the shock solar wind and the photoelectron populations. Also, on both planets, a magnetic signature near the transition boundary and the presence of low frequency electric waves within the transition region are observed.

Nagy, Andrew F.↗

NASA NTRS1990

A comparison of different models for beam vibrations from the standpoint of control design

Different models for beam vibrations are analyzed from the standpoint of designing finite-dimensional controllers to stabilize the beam vibrations. A distributed system described by an undamped Euler-Bernoulli equation cannot be stabilized by any finite-dimensional controller, i.e., any controller which can be described an ordinary differential equation with constant coefficients. If viscous damping is included, a similar problem occurs in that all the poles can not be moved to the left of a given vertical line. These negative results should be interpreted as a commentary on the limitations of these models, rather than on the control of real beams. If a Rayleigh damping model is used, a finite-dimensional controller may be designed to move the closed loop system poles essentially as far to the left in the complex plane as desired. This result will also hold for certain hysteresis damping models. This has implications for the settling time of the vibrations.

Morris, K. A.↗