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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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NASA NTRS1987

Progress in compilation of the 1:2,000,000-scale topographic map

The application of special photogrammetric techniques has enabled the systematic mapping of Mars' topography at a scale of 1:2,000,000, using high-altitude Viking Orbiter pictures. In fiscal 86, compilation was completed of the 24 subquadrangles that make up the quadrangles MC-12, MC-13, MC-14, MC-15, MC-20, and MC-21. This work completes compilation of the 60 topographic maps covering the equatorial belt (lat. + or - 30 deg). The remaining 80 subquadrangles of Mars are planned to be completed within 3 years (27, 27 and 26 subquadrangles, in fiscal 87, 88, and 89, respectively). Elevations on all topographic maps are relative to the Mars topographic datum. The maps have a contour interval of 1 km and a precision of + or - 1 km. The equatorial-belt maps are Mercator projections having true scale at lat. + or - 27.476 deg. These maps provide more precise information than do those previously available and they will help in understanding the geologic processes that have shaped the Martian surface.

Wu, Sherman S. C.↗

NASA NTRS1987

Aeroelasticity and mechanical stability report, 0.27 Mach scale model of the YAH-64 advanced attack helicopter

A 27% dynamically scaled model of the YAH-64 Advanced Attack Helicopter main rotor and hub has been designed and fabricated. The model will be tested in the NASA Langley Research Center V/STOL wind tunnel using the General Rotor Model System (GRMS). This report documents the studies performed to ensure dynamic similarity of the model with its full scale parent. It also contains a preliminary aeroelastic and aeromechanical substantiation for the rotor installation in the wind tunnel. From the limited studies performed no aeroelastic stability or load problems are projected. To alleviate a projected ground resonance problem, a modification of the roll characteristics of the GRMS is recommended.

Straub, F. K.↗

NASA NTRS1987

Experimental evaluation of small-scale erectable truss hardware

To aid in the prediction of the dynamic behavior of the space station, a one-tenth scale dynamic test model is to be constructed of commercially available, small scale truss hardware. Tests have been performed to determine the axial stiffness characteristics and failure loads of the truss joint. A parametric study has shown that the stiffness of the joint increases as the attachment bolt torque value is increased. Furthermore, at torque values equal to or higher than 250 in-lbs, hysteresis in the load-deflection curve is essentially eliminated. Also, the joint stiffness remained relatively constant between specimens. The effective stiffness of a joint subassembly tested is 76 percent that of the strut. Tensile and compressive failure occurred in the region of the bonded plug, with lower failure loads corresponding to compressive loadings.

Mcgowan, David M.↗

NASA NTRS1986

Time scale analysis of a digital flight control system

In this paper, consideration is given to the fifth order discrete model of an aircraft (longitudinal) control system which possesses three slow (velocity, pitch angle and altitude) and two fast (angle of attack and pitch angular velocity) modes and exhibits a two-time scale property. Using the recent results of the time scale analysis of discrete control systems, the high-order discrete model is decoupled into low-order slow and fast subsystems. The results of the decoupled system are found to be in excellent agreement with those of the original system.

Naidu, D. S.↗

NASA NTRS1986

The topology of the large-scale structure of the universe

It has been suggested recently that the topology of a distribution of galaxies can be characterized by the mean Gaussian curvature per unit volume of surfaces of constant density. An expression is derived which relates the mean curvature of isodensity surfaces to the power spectrum of density fluctuations in the linear regime of Gaussian fluctuations with random phases. The result may be compared to real galaxy catalogs if the galaxy density is smoothed over scales larger than a correlation length. The implications of the result for understanding the large-scale structure of the universe are discussed.

Hamilton, A. J. S.↗

NASA NTRS1987

A prediction of helicopter rotor discrete frequency noise for three scale models using a new acoustics program

A new computer program which uses Farassat's most advanced subsonic time domain formulation has been written to predict helicopter rotor discrete frequency noise. A brief description of the program, WOPWOP, is followed by a comparison of predicted and experimentally measured acoustic pressure and spectra for a 1/4 scale UH-1 model rotor blade and a 1/7 scale OLS (AH-1G) model rotor blade. The C81 computer program was used to predict the spanwise loading on the rotor for aerodynamic input into the acoustic prediction. Comparisons are made for different flight conditions and microphone locations with good results. In general the acoustic pressure is underpredicted. The acoustic predictions for a tapered rotor blade and predictions for microphones well below the tip path plane show less underprediction. Finally, in-plane motion of the rotor blade is shown to significantly affect the peak-to-peak amplitude of the acoustic pressure for high advancing tip Mach numbers.

Brentner, Kenneth S.↗

NASA NTRS1986

A global-scale model of aerosol backscatter at CO2 wavelengths for satellite-based lidar sensors

The status of a global-scale model of background aerosol backscatter cross-sections at CO2 wavelengths is described. The model needs, strategy, concept, parameters, and capabilities are addressed, and the data base is discussed, concluding data selection, CO2 backscatter measurements, aerosol optical measurements, aerosol microphysical measurements, water vapor measurements, and data analysis. Strong evidence is reported for a 'universal' background tropospheric aerosol population. Typical background backscatter values at CO2 wavelengths appear to be about 3 x 10 to the -11th to 8 x 10 to the -11th/m/sr. Background signatures are evident in most aerosol data sets which have global-scale coverage in space or time.

Bowdle, David A.↗

NASA NTRS1986

An observational view of large scale structure

A summary of recent observations of galaxy clustering is presented, including a brief review of redshift maps and galaxy clustering statistics. Simple arguments are presented that argue the underlying mass fluctuations are most likely associated with a clustering scale no larger than that of individual galaxies. The acceleration of the local group from the comoving frame of the universe and its connection to the microwave dipole anisotropy are also discussed. A final topic for consideration is the existence of large voids and clusters, and whether they are consistent with Gaussian initial conditions. The extreme size and depth of the Bootes void, if real, do present a puzzle. Finally, future directions for observational study of large scale structure are discussed.

Davis, Marc↗

NASA NTRS1986

Large-scale short-period sea ice atmosphere interaction

Changes in the microwave brightness temperature measured by the Electrically Scanning Microwave Radiometer (ESMR) flown on board the Nimbus V satellite reveal large-scale sea ice fluctuations in the Antarctic marginal ice zone. These ice margin fluctuations arre predominantly wave numbers 1-4, with phase speeds of about 3 m/s independent of wave number. The spatial pattern and eastward advection of the sea ice anomalies match those of the atmospheric sea level pressure, and are consistent with sea ice displacement due to surface wind stress. Examination of the outgoing longwave radiation indicates that suppression of high clouds in regions of increased sea ice inc reases the radiative cooling which contributes to maintaining the ice. Data from three winter seasons indicate about a one-third probability of occurence of this large scale high frequency sea ice atmosphere interaction during any given 2-week period in winter.

Cahalan, Robert F.↗

NASA NTRS1986

Multiply scaled constrained nonlinear equation solvers

To improve the numerical stability of nonlinear equation solvers, a partitioned multiply scaled constraint scheme is developed. This scheme enables hierarchical levels of control for nonlinear equation solvers. To complement the procedure, partitioned convergence checks are established along with self-adaptive partitioning schemes. Overall, such procedures greatly enhance the numerical stability of the original solvers. To demonstrate and motivate the development of the scheme, the problem of nonlinear heat conduction is considered. In this context the main emphasis is given to successive substitution-type schemes. To verify the improved numerical characteristics associated with partitioned multiply scaled solvers, results are presented for several benchmark examples.

Padovan, Joe↗

NASA NTRS1987

Analysis of subgrid-scale eddy viscosity with use of results from direct numerical simulations

Without resort to any modeling, subgrid-scale eddy viscosity is computed from the results of high-resolution (64 cubed and 128 cubed grid points) direct numerical simulations of three-dimensional homogeneous isotropic decaying turbulence. In these simulations the eddy viscosity peaks sharply at the cutoff wavenumber, in rough agreement with the results of Kraichnan (1976). In addition, in the low-wavenumber range the eddy viscosity may be negative, contrary to the generally accepted concept of subgrid-scale eddy viscosity. Some possible explanations of this behavior are discussed.

Domaradzki, J. Andrzej↗

NASA NTRS1987

Large-scale fluctuations in the interplanetary medium

Power spectra of measurements of the magnetic field strength in the heliosphere obtained by Voyager 1 between 1 AU and 9 AU have the form of a power law f exp -a from periods of several hours to at least 6 days. The exponent was a = 2.0 + or - 0.05 for all of the spectra considered, which is the exponent for a series of steps and for Burgers' (1971) turbulence. Spectra of large-scale speed fluctuations also have the form f exp - b from a period of a few hours to periods greater than 13 days in the region from 1 AU to 8.9 AU. The exponent b is generally somewhat larger than b = 2, implying some 'persistence' of the speed fluctuations. The low-frequency cutoff (outer cutoff) of the power law increases from a period of 6.5 days at 1 AU to 26 days at (6.1-8.9) AU, which can be attributed to: (1) the coalescence of interaction regions and (2) a transfer of energy from the spectrum of large-scale speed fluctuations. The outer cutoff of the spectrum of speed fluctuations increases from a period of 13 days at 1 AU to 26 days between a few AU and 8.9 AU. Both the magnetic field strength fluctuations and the speed fluctuations have fractal behavior, suggesting that they are self affine rather than dominated by a few large discontinuities.

Burlaga, L. F.↗

NASA NTRS1986

Temporal variations of cosmic rays over a variety of time scales

The variation of the intensity of Galactic cosmic rays in the inner solar system over a wide variety of time scales is discussed, and the generally accepted physical model which can account quantitatively for these modulations is reviewed. The use of direct measurements and of nuclear reactions to study the temporal intensity variations is summarized. It is demonstrated that all of the observed variations could easily be the result of solar variations on long and short time scales.

Jokipii, J. R.↗

NASA NTRS1987

Molecular clouds in the Carina arm - Large-scale properties of molecular gas and comparison with H I

Results from the first large-scale survey in the CO (J = 1 - 0) line of the Vela-Carina-Centaurus region of the southern Milky Way are reported. The results demonstrate that molecular clouds in the Galaxy are largely confined to the spiral arms and that CO is therefore an extremely good tracer of the large-scale structure of the system. The Carina arm is the dominant feature in the data. Its abrupt tangent at l of roughly 280 deg and characteristic loop in the (l, v) diagram are unmistakable evidence for CO spiral structure. When the emission is integrated over velocity and latitude, the height of the step seen in the tangent direction indicate that the arm-interarm contrast is at least 13:1.

Grabelsky, D. A.↗

NASA NTRS1987

Tropical and extratropical forcing of the large-scale circulation - A diagnostic study

Seasonal anomalies in the large-scale circulation are studied in relation to seasonal-mean tropical forcing and extratropical transient-eddy forcing using nine years of tropical-wind and outgoing-longwave-radiation (OLR) data. Results show that in the interannual time scale, extreme swings in anomalous convection over the maritime continent of Indonesia/Borneo and the equatorial central Pacific are linked, respectively, by an east-west seesaw or a dipole pattern, identified with major fluctuations of the Pacific Walker circulation. It is found that extratropical circulation anomalies are related to the fluctuation of this dipole heat source. The overall extratropical circulation seems to be more responsive to the dipole heating with enhanced convection over the maritime continent. While the characteristics of the transient eddies, especially near the exit region of the East Asia jet stream, change substantially between maximum or minimum convection episodes, these transient eddies (defined as transients from the seasonal mean) appear to be unimportant in forcing the seasonal mean circulation anomalies.

Lau, K. M.↗

NASA NTRS1987

Small-scale physics of the ocean

Observations and theoretical models of small-scale phenomena in the oceans are reviewed, with a focus on progress during the period 1983-1986. Topics examined include surface layers, equatorial turbulence, off-equator mixed layers, the scaling of mixing, turbulence concepts, laboratory results, internal waves and mixing, rings, the nature of the bottom layer, double diffusion and intrusions, salt fingers, and biological interactions. Also discussed are developments in instrumentation (fast sampling profilers with upward-profiling capability, deep profilers, ship-motion correction, horizontal samplers, small submersibles, submarines, towed packages, conductivity sensors, dissolved-oxygen sensors, and acoustic Doppler current profilers) and goals for future research.

Caldwell, Douglas R.↗

NASA NTRS1987

The large-scale peculiar velocity field in flat models of the universe

The inflationary universe scenario predicts a flat universe and both adiabatic and isocurvature primordial density perturbations with the Zel'dovich spectrum. The two simplest realizations, models dominated by hot or cold dark matter, seem to be in conflict with observations. Flat models with two components of mass density, where one of the components of mass density is smoothly distributed, are examined, and the large-scale peculiar velocity field for these models is computed. For the smooth component the authors consider relativistic particles, a relic cosmological term, and light strings. At present the observational situation is unsettled, but, in principle, the large-scale peculiar velocity field is a very powerful discriminator between these different models.

Vittorio, Nicola↗

NASA NTRS1987

A preliminary investigation of large-scale organized motions in a supersonic turbulent boundary layer on a curved surface

An experimental investigation concentrating on the change in the large-scale organized motions of a supersonic turbulent boundary layer subjected to a short region of concave surface curvature is presented. Two flows were studied, a relatively weak and a relatively strong perturbation. In both flows the freestream Mach number was 2.89 and the Reynolds number based on momentum thickness was 81,900. Hot-wire anemometry and schlieren photography provided the principle tools for this investigation. Hot-wire data were analyzed using spectral and correlation methods and conditional sampling techniques. Changes in structure angle and results of conditionally sampled velocity signals are discussed. The strong perturbation is found to increase the structure angle, and in both flows the length scales of the organized motions are altered.

Donovan, J. F.↗