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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

A forester's look at the application of image manipulation techniques to multitemporal Landsat data

Registered, multitemporal Landsat data of a study area in central Pennsylvania were analyzed to detect and assess changes in the forest canopy resulting from insect defoliation. Images taken July 19, 1976, and June 27, 1977, were chosen specifically to represent forest canopy conditions before and after defoliation, respectively. Several image manipulation and data transformation techniques, developed primarily for estimating agricultural and rangeland standing green biomass, were applied to these data. The applicability of each technique for estimating the severity of forest canopy defoliation was then evaluated. All techniques tested had highly correlated results. In all cases, heavy defoliation was discriminated from healthy forest. Areas of moderate defoliation were confused with healthy forest on northwest (NW) aspects, but were distinct from healthy forest conditions on southeast (SE)-facing slopes.

Williams, D. L.↗
NASA NTRS1981

Experimental and analytical study of the longitudinal aerodynamic characteristics of analytically and empirically designed Strake-wing configurations at subcritical speeds

Sixteen analytically and empirically designed strakes have been tested experimentally on a wing-body at three subcritical speeds in such a way as to isolate the strake-forebody loads from the wing-afterbody loads. Analytical estimates for these longitudinal results are made using the suction analogy and the augmented vortex lift concepts. The synergistic data are reasonably well estimated or bracketed by the high- and low-angle-of-attack vortex lift theories over the Mach number range and up to maximum lift or strake-vortex breakdown over the wing. Also, the strake geometry is very important in the maximum lift value generated and the lift efficiency of a given additional area. Increasing size and slenderness ratios are important is generating lift efficiently, but similar efficiency can also be achieved by designing a strake with approximately half the area of the largest gothic strake tested. These results correlate well with strake-vortex-breakdown observations in the water tunnel.

Lamar, J. E.↗
NASA NTRS1980

Digital preprocessing of SEASAT imagery

A model for radar image data is derived for use in developing enhancement techniques. This model describes the image data as the result of a multiplicative-convolved noise process. This information is then used to design a minimum mean square error (MMSE) filter. The resulting filter is implemented adaptively to change with local statistics. A radar image processing technique which provides the MMSE estimate inside homogeneous areas and tends to preserve edge structure is thus developed. This technique has been implemented and tested using digitally correlated SEASAT-A synthetic aperture radar (SAR) imagery.

Frost, V. S.↗
NASA NTRS1981

The UTRC wind energy conversion system performance analysis for horizontal axis wind turbines (WECSPER)

The theory for the UTRC Energy Conversion System Performance Analysis (WECSPER) for the prediction of horizontal axis wind turbine performance is presented. Major features of the analysis are the ability to: (1) treat the wind turbine blades as lifting lines with a prescribed wake model; (2) solve for the wake-induced inflow and blade circulation using real nonlinear airfoil data; and (3) iterate internally to obtain a compatible wake transport velocity and blade loading solution. This analysis also provides an approximate treatment of wake distortions due to tower shadow or wind shear profiles. Finally, selected results of internal UTRC application of the analysis to existing wind turbines and correlation with limited test data are described.

Egolf, T. A.↗
NASA NTRS1980

Selection of some rotor parameters to reduce pitch-roll coupling of helicopter flight dynamics

The results of a study conducted to investigate further a means of choosing primary rotor parameters to reduce the coupling of longitudinal and lateral flapping in hover and in forward flight are presented. The rotor parameters included - flapping hinge offset, flapping hinge restraint, pitch-flap coupling, and blade Lock number - are known to influence the agility, stability, and operational safety of helicopters. Effects of the nonuniform downwash model of White and Blake on the blade flapping motion are examined, and the theoretical calculation is then correlated with experimental test data. The condition for achieving perfect decoupling of the flapping response due to aircraft pitch and roll rates, which was previously obtained for a hovering rotor, is evaluated in forward flight. The results show that negligible coupling is achieved in forward flight; moreover, there is the additional benefit of a slight reduction in the coupling of the roll rate to coning. It is also indicated that the values of the rotor parameters chosen according to the decoupling condition are moderate and that the flapping motion is stable with the parameters chosen.

Chen, R. T. N.↗
NASA NTRS1982

Dynamic structural aeroelastic stability testing of the XV-15 tilt rotor research aircraft

For the past 20 years, a significant effort has been made to understand and predict the structural aeroelastic stability characteristics of the tilt rotor concept. Beginning with the rotor-pylon oscillation of the XV-3 aircraft, the problem was identified and then subjected to a series of theoretical studies, plus model and full-scale wind tunnel tests. From this data base, methods were developed to predict the structural aeroelastic stability characteristics of the XV-15 Tilt Rotor Research Aircraft. The predicted aeroelastic characteristics are examined in light of the major parameters effecting rotor-pylon-wing stability. Flight test techniques used to obtain XV-15 aeroelastic stability are described. Flight test results are summarized and compared to the predicted values. Wind tunnel results are compared to flight test results and correlated with predicted values.

Schroers, L. G.↗
NASA NTRS1981

Remote sensing in West Virginia

Low altitude black and white aerial photography is the prinicipal remote sensing tool for geologic investigations in West Virginia, although side looking radar and color infrared photography are also used. The first land use/cover map for the state was produced in color infrared and is being digitized. Linear features in Cabell and Wayne Counties, as revealed by LANDSAT, were evaluated to test the possible correlations with rock fractures and gas production from shales. A LANDSAT linear features map (1:250,000) was prepared for the entire state, also. Presently investigations are being made to understand karst and to predict areas that should not be used for development. Aerial photography and field mapping is being conducted to detect the location and causes of landslides.

Lessing, P.↗
NASA NTRS1983

Image motion compensation by area correlation and centroid tracking of solar surface features

An experimental solar correlation tracker was tested and evaluated on a ground-based solar magnetograph. Using sunspots as fixed targets, tracking error signals were derived by which the telescope image was stabilized against wind induced perturbations. Two methods of stabilization were investigated; mechanical stabilization of the image by controlled two-axes motion of an active optical element in the telescope beam, and electronic stabilization by biasing of the electron scan in the recording camera. Both approaches have demonstrated telescope stability of about 0.6 arc sec under random perturbations which can cause the unstabilized image to move up to 120 arc sec at frequencies up to 30 Hz.

Nein, M. E.↗
NASA NTRS1982

Combined use of remote sensing and seismic observations to infer geologically recent crustal deformation, active faulting, and stress fields

Characteristic traits for earthquakes associated with strike-slip motion in Central California and the Salton Sea area, as revealed in ground based studies and LANDSAT imagery, were compared. The mapped lineaments are found to be oriented in several dominant directions. One direction is the same as the trend of the San Andreas fault. The other directions differ from area to area and may reflect the stresses of earlier geologic processes. The pattern of lineament orientations is significantly LANDSAT MSS data, SEASAT synthetic aperture radar data, and magnetic field data from the South Mountain area west of Gettysburg, Pennsylvania were registered to match each other in spatial position and merged. Pattern recognition techniques were applied to the composite data set to determine its utility in recognizing different rock types and structures in vegetated terrain around South Mountain. With the use of a texture algorithm to enhance geologic features, a classification of the entire area was made. A test of the correlation between SAR tone and texture, LANDSAT tone and texture, and magnetic field data revealed no tone or texture measures linking any two of the original data sets.

Alexander, S. S.↗
NASA NTRS1984

Thermal control surface experiment (S0069)

The objectives of this LDEF experiment are to determine the effects of the near Earth orbital environment and the Shuttle induced environment in spacecraft thermal control surfaces. Spectral reflectance measurements will be obtained and used to differentiate between different solid state damage mechanisms of environmental damage to separate the effects of contamination from those of natural environment damage, and for comparison and correlation with laboratory test data.

Donald R. Wilkes↗
NASA NTRS1984

A comparison of Wortmann airfoil computer-generated lift and drag polars with flight and wind tunnel results

Computations of drag polars for a low-speed Wortmann sailplane airfoil are compared with both wind tunnel and flight test results. Excellent correlation was shown to exist between computations and flight results except when separated flow regimes were encountered. Smoothness of the input coordinates to the PROFILE computer program was found to be essential to obtain accurate comparisons of drag polars or transition location to either the flight or wind tunnel flight results.

Bowers, A. H.↗
NASA NTRS1985

Transport Processes in the Upper Atmosphere

A proposed study to measure aerodynamic and heat transfer coefficients within the thermo-fluid-dynamic range experienced by a tethered satellite and to compare the coefficients with previous correlations is discussed. Tests are proposed on a satellite of existing design, on a satellite design consisting of models carried aboard, and on a newly designed satellite devoted to energy, mass, and momentum transfer studies on particular geometries.

Carlomagno, G. M.↗
NASA NTRS1983

Assessment of MSS spectral indexes for monitoring arid rangeland

The utility of MSS spectral indexes for monitoring arid rangeland vegetation was tested by determining correlations between spectral indexes and vegetation parameters and by examining retrospective MSS data to determine if vegetation change could be detected and measured using spectral indexes. MSS Band 5, albedo, and the Kauth-Thomas Brightness component appear to be useful for monitoring total vegetation cover. Multiseasonal green vegetation indexes could be used to estimate changes in the shrub/grass ratio. In retrospective monitoring, spectral index change appeared to be offset from true change, indicating that the methods used to standardize data sets for differences in solar elevation and sensor radiometric response were not completely successful.

Musick, H. B.↗
NASA NTRS1985

Prediction of HiMAT RPRV component interference effects at transonic speeds

Detailed surface flow field analyses of the NASA Highly Maneuverable Aircraft Technology Remotely Piloted Research Vehicle (HiMAT RPRV) are described. Computational predictions are provided by a nonlinear finite difference transonic wing-body code. Component interference effects are obtained through modifications in lifting surface twist and camber boundary conditions. Complex aircraft interactions created by wing-tip fins, landing gear, and lower surface wing actuator fairings are included. Lifting surface viscous flow effects are modeled using a two-dimensional 'strip' boundary layer method. Correlations with flight test data presented demonstrate the high degree of accuracy achieved for this realistic aircraft configuration. This methodology and approach appears to be generally applicable to other multisurface configurations.

Laiosa, J.↗
NASA NTRS1985

The infall velocity toward Virgo, the Hubble constant, and a search for motion toward the microwave background

The perturbation of the local velocity field due to the overdensity of the Virgo complex (VC) is investigated theoretically, using an idealized spherically symmetric Virgocentric flow model and testing for a correlation between cos theta (where theta is the angle from the VC direction to eight groups and clusters with velocity 800-2500 km/s) and the relevant velocity residuals. The data and results are presented in extensive tables, graphs, and a map in extragalactic coordinates. The infall of the Local Group (LG) toward the VC is estimated as 200 + or - 50 km/s, corresponding to a mean mass/light ratio M/L(B) = about 70 for a sphere centered at the VC core and extending to the LG. The rate of free expansion within the VC is estimated as 52 + or 2 km/s Mpc for a VC distance of 21.6 Mpc. It is pointed out that the LG infall toward the VC cannot account for observations of an apparent 630-km/s motion of the LG toward the microwave background.

Tammann, G. A.↗
NASA NTRS1985

Spacecraft heat transfer by two-phase flow method

A refrigerator/freezer has been designed with an oil-free compressor to provide an economical two-phase flow system for heat transfer. A computer simulation has been done for the condenser and evaporator to determine the design parameters, such as length, diameter, and flow regimes, for different refrigerants and load requirements. A large Reynolds number was considered to ensure annular flow (in order to maximize heat transfer coefficients) and large Froude number. The simulation was correlated with the test data of a vapor compression refrigerator/freezer flown on STS-4 (which provided information on vapor compression in a zero-gravity environment). The two-phase system will be used for the Spacelab mission SLS-1 and can be used in future spacecraft and high-speed aircraft, where weight, volume, and power requirements are critical.

Hye, A.↗
NASA NTRS1985

Implementation and verification of a comprehensive helicopter coupled rotor - Fuselage analysis

The analytical basis and the application of a Rotor/Airframe Comprehensive Aeroelastic Program (RACAP) are described in detail. The rationale behind each analytical choice is outlined and the modular procedure is described. The program is verified by application to the AH-1G helicopter. The applicability of various airload prediction models is examined, and both the steady and vibratory responses of the blade are compared with flight test data. Reasonable correlation is found between measured and calculated blade response, with excellent correlation for vibration amplitudes at various locations on the fuselage such as engine, pilot seat, and gunner. Within the analytical model, comparisons are drawn between an isolated blade analysis and a coupled rotor/fuselage model. The deficiency of the former in the context of the AH-1G is highlighted.

Wood, E. R.↗
NASA NTRS1986

Is OH abundance enhanced in tidally distorted galaxies?

An extensive survey of 240 galaxies for hydroxyl absorption has been completed using the Arecibo Observatory. These galaxies were used to compile a sample to test for statistical correlations between the optical depth of the 1667 MHz hydroxyl line and various parameters of the parent galaxy. To be included in the sample, the radio flux density of the galaxy at 1667 MHz had to be between 20 mjy and 1000 mjy and the galactic declination between 0 and 38 deg. Since this sample contains mainly non-detections, statistical methods for astronomical data with upper limits as previously described were used to obtain correlation and regression information. Preliminary studies indicate a strong correlation between OH optical depth and infrared to blue luminosity ratio (L sub IR/L sub B), where the infrared data were obtained from the Cataloged Galaxies and Quasars Observed in the IRAS Survey. A second correlation is seen between the optical depth of the 1667 MHz line and galactic type, where a number from 1 to 15 (Elliptical to peculiar, distorted, or interacting) has been assigned to each galaxy. So, stable, isolated galaxies tend not to have detectable hydroxyl. On the other hand, galaxies with more gas and dust, galaxies with a more peculiar or distorted appearance, and galaxies which are more tidally interacting tend to have much more detectable OH. These findings could indicate that these dusty, peculiar, distorted, and interacting galaxies could be the site of large amounts of shocked material where OH is likely to form. Hence, the hydroxyl abundance could be enhanced in these regions of shocked material making the detection of OH in these tidally distorted galaxies much more likely.

Schmelz, J. T.↗