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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Improved design of subcritical and supercritical cascades using complex characteristics and boundary layer correction

The method of complex characteristics and hodograph transformation for the design of shockless airfoils was extended to design supercritical cascades with high solidities and large inlet angles. This capability was achieved by introducing a conformal mapping of the hodograph domain onto an ellipse and expanding the solution in terms of Tchebycheff polynomials. A computer code was developd based on this idea. A number of airfoils designed with the code are presented. Various supercritical and subcritical compressor, turbine and propeller sections are shown. The lag-entrainment method for the calculation of a turbulent boundary layer was incorporated to the inviscid design code. The results of this calculation are shown for the airfoils described. The elliptic conformal transformation developed to map the hodograph domain onto an ellipse can be used to generate a conformal grid in the physical domain of a cascade of airfoils with open trailing edges with a single transformation. A grid generated with this transformation is shown for the Korn airfoil.

Sanz, J. M.↗
NASA NTRS1984

Improved design of subcritical and supercritical cascades using complex characteristics and boundary-layer correction

The method of complex characteristics and hodograph transformation for the design of shockless airfoils was extended to design supercritical cascades with high solidities and large inlet angles. This capability was achieved by introducing a conformal mapping of the hodograph domain onto an ellipse and expanding the solution in terms of Tchebycheff polynomials. A computer code was developed based on this idea. A number of airfoils designed with the code are presented. Various supercritical and subcritical compressor, turbine and propeller sections are shown. The lag-entrainment method for the calculation of a turbulent boundary layer was incorporated to the inviscid design code. The results of this calculation are shown for the airfoils described. The elliptic conformal transformation developed to map the hodograph domain onto an ellipse can be used to generate a conformal grid in the physical domain of a cascade of airfoils with open trailing edges with a single transformation. A grid generated with this transformation is shown for the Korn airfoil. Previously announced in STAR as N83-24474

Sanz, J. M.↗
NASA NTRS2021

A Chlorophyll-a Algorithm for Landsat-8 Based on Mixture Density Networks

Retrieval of aquatic biogeochemical variables, such as the near-surface concentration of chlorophyll-a (Chla) in inland and coastal waters via remote observations, has long been regarded as a challenging task. This manuscript applies Mixture Density Networks (MDN) that use the visible spectral bands available by the Operational Land Imager (OLI) aboard Landsat-8 to estimate Chla. We utilize a database of co-located in situ radiometric and Chla measurements (N = 4,354), referred to as Type A data, to train and test an MDN model (MDN(A)). This algorithm’s performance, having been proven for other satellite missions, is further evaluated against other widely used machine learning models (e.g., support vector machines), as well as other domain-specific solutions (OC3), and shown to offer significant advancements in the field. Our performance assessment using a held-out test data set suggests that a 49% (median) accuracy with near-zero bias can be achieved via the MDN(A) model, offering improvements of 20 to 100% in retrievals with respect to other models. The sensitivity of the MDN(A) model and benchmarking methods to uncertainties from atmospheric correction (AC) methods, is further quantified through a semi-global matchup dataset (N = 3,337), referred to as Type B data. To tackle the increased uncertainties, alternative MDN models (MDN(B)) are developed through various features of the Type B data (e.g., Rayleigh-corrected reflectance spectra ρ(s)). Using held-out data, along with spatial and temporal analyses, we demonstrate that these alternative models show promise in enhancing the retrieval accuracy adversely influenced by the AC process. Results lend support for the adoption of MDN(B) models for regional and potentially global processing of OLI imagery, until a more robust AC method is developed. Index Terms—Chlorophyll-a, coastal water, inland water, Landsat-8, machine learning, ocean color, aquatic remote sensing.

Brandon Smith↗
NASA NTRS1992

Blockage correction in three-dimensional wind tunnel testing based on the wall signature method

An improved wall interference assessment and correction method for three-dimensional wind tunnel testing is presented. Blockage corrections on the surface of a test article are calculated based on a limited number of wall pressure measurements. These measurements are combined with a signature analysis procedure and influence functions to determine an equivalent test article and wake representation. Pressure coefficient corrections are calculated based on this equivalent body. The signature analysis procedure is modified to improve the on-line operation of the wall signature method. A new geometry of the equivalent body is introduced which can be combined with existing panel codes more effectively. The calculation of influence functions and the determination of pressure coefficient corrections are based on a panel code. Therefore it is possible to apply the present method to any closed tunnel cross section. A numerical simulation of the idealized flow field of a wing and its wake in a rectangular wind tunnel is used to verify the improved wall signature method. The present method is considered to calculate blockage corrections in the NASA/ARC 12ft Pressure Wind Tunnel.

Ulbrich, N.↗
NASA NTRS1986

Paneling methods with vorticity effects and corrections for nonlinear compressibility

The prediction of missile aerodynamic characteristics is presently undertaken through the application of supersonic paneling methods and nonlinear corrections to the prediction of missile aerodynamic characteristics. Attention is given to supersonic panel methods and line-singularity methods for the modeling of axisymmetric bodies, in combination with corrections for nonlinear flow phenomena, which are applied to complete missile, inlets, and wing-body combinations. The LRCDM2 computer program is used as an example of the methods presented.

Dillenius, Marnix F. E.↗
NASA NTRS2013

The Intercalibration of Geostationary Visible Imagers Using Operational Hyperspectral SCIAMACHY Radiances

Spectral band differences between sensors can complicate the process of intercalibration of a visible sensor against a reference sensor. This can be best addressed by using a hyperspectral reference sensor whenever possible because they can be used to accurately mitigate the band differences. This paper demonstrates the feasibility of using operational Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) large-footprint hyperspectral radiances to calibrate geostationary Earth-observing (GEO) sensors. Near simultaneous nadir overpass measurements were used to compare the temporal calibration of SCIAMACHY with Aqua Moderate Resolution Imaging Spectroradiometer band radiances, which were found to be consistent to within 0.44% over seven years. An operational SCIAMACHY/GEO ray-matching technique was presented, along with enhancements to improve radiance pair sampling. These enhancements did not bias the underlying intercalibration and provided enough sampling to allow up to monthly monitoring of the GEO sensor degradation. The results of the SCIAMACHY/GEO intercalibration were compared with other operational four-year Meteosat-9 0.65-μm calibration coefficients and were found to be within 1% of the gain, and more importantly, it had one of the lowest temporal standard errors of all the methods. This is more than likely that the GEO spectral response function could be directly applied to the SCIAMACHY radiances, whereas the other operational methods inferred a spectral correction factor. This method allows the validation of the spectral corrections required by other methods.

Doelling, David R.↗
NASA NTRS2001

Method for beam hardening correction in quantitative computed X-ray tomography

Each voxel is assumed to contain exactly two distinct materials, with the volume fraction of each material being iteratively calculated. According to the method, the spectrum of the X-ray beam must be known, and the attenuation spectra of the materials in the object must be known, and be monotonically decreasing with increasing X-ray photon energy. Then, a volume fraction is estimated for the voxel, and the spectrum is iteratively calculated.

Yan, Chye Hwang↗
NASA NTRS1987

Integral method of wall interference correction in low-speed wind tunnels

The analytical solution of Poisson's equation, derived form the definition of vortex, was applied to the calculation of interference velocities due to the presence of wind tunnel walls. This approach, called the Integral Method, allows an accurate evaluation of wall interference for separated or more complicated flows without the need for considering any features of the model. All the information necessary for obtaining the wall correction is contained in wall pressure measurements. The correction is not sensitive to normal data-scatter, and the computations are fast enough for on-line data processing.

Zhou, Changhai↗
NASA NTRS1977

On the logarithmic-singularity correction in the kernel function method of subsonic lifting-surface theory

A logarithmic-singularity correction factor is derived for use in kernel function methods associated with Multhopp's subsonic lifting-surface theory. Because of the form of the factor, a relation was formulated between the numbers of chordwise and spanwise control points needed for good accuracy. This formulation is developed and discussed. Numerical results are given to show the improvement of the computation with the new correction factor.

Lan, C. E.↗
NASA NTRS1984

Asymptotic methods for wind tunnel wall corrections at transonic speed

The effort to develop classical methods to compute wall interference at transonic speeds is outlined. The two-dimensional theory and three-dimensional development are discussed. Also, some numerical application of the two-dimensional work are indicated. The basic advantages of the asymptotic theory are noted.

Malmuth, N. D.↗
NASA NTRS2007

Ground-Based Correction of Remote-Sensing Spectral Imagery

Software has been developed for an improved method of correcting for the atmospheric optical effects (primarily, effects of aerosols and water vapor) in spectral images of the surface of the Earth acquired by airborne and spaceborne remote-sensing instruments. In this method, the variables needed for the corrections are extracted from the readings of a radiometer located on the ground in the vicinity of the scene of interest. The software includes algorithms that analyze measurement data acquired from a shadow-band radiometer. These algorithms are based on a prior radiation transport software model, called MODTRAN, that has been developed through several versions up to what are now known as MODTRAN4 and MODTRAN5 . These components have been integrated with a user-friendly Interactive Data Language (IDL) front end and an advanced version of MODTRAN4. Software tools for handling general data formats, performing a Langley-type calibration, and generating an output file of retrieved atmospheric parameters for use in another atmospheric-correction computer program known as FLAASH have also been incorporated into the present soft-ware. Concomitantly with the soft-ware described thus far, there has been developed a version of FLAASH that utilizes the retrieved atmospheric parameters to process spectral image data.

Alder-Golden, Steven M.↗
NASA NTRS1976

Multistep methods of numerical integration using back-corrections

A class of linear multistep methods is proposed for the solution of the equations of motion of certain dynamical systems encountered in celestial mechanics and astrodynamics. These methods are distinguished from the classical predictor-corrector methods in that they permit 'back-corrections' of the solution to be made. As the integration advances in time, the numerical solution is corrected or improved at certain points in the past. The enhanced numerical stability of these methods allows the meaningful application of high-order algorithms. Consequently, step sizes larger than those attainable with the classical methods may be adopted, and greater overall efficiency may be realized. These methods are applied to the problem of determining the orbit of an artificial satellite, and the results are compared with those obtained using classical methods.

Feagin, T.↗
NASA NTRS1972

Spectrofluorometer techniques applicable to sample surfaces

Methods for correcting fluorescence spectra to remove instrumental artifacts are described, including computational and graphical procedures for rapid manual correction by nomographs and similar techniques. Expedient methods for the selection and use of optical filters, the evaluation of filter effectiveness, and the selection of optimum wavelength settings in spectrofluorometry are outlined.

Stoertz, G. E.↗
NASA NTRS2003

Correcting for Beam Aberrations in a Beam-Waveguide Antenna

A method for correcting the aim of a beam-waveguide microwave antenna compensates for the beam aberration that occurs during radio tracking of a target that has a component of velocity transverse to the line of sight from the tracking station. The method was devised primarily for use in tracking of distant target spacecraft by large terrestrial beam-waveguide antennas of NASA's Deep Space Network (DSN). The method should also be adaptable to tracking, by other beam-waveguide antennas, of targets that move with large transverse velocities at large distances from the antennas.

Franco, Manuel↗
NASA NTRS2012

Methods for Detection and Correction of Sudden Pixel Sensitivity Drops

PDC 8.0 includes implementation of a new algorithm to detect and correct step discontinuities appearing in roughly one of every twenty stellar light curves during a given quarter. An example of such a discontinuity in an actual light curve is shown in fig. 1. The majority of such discontinuities are believed to result from high-energy particles (either cosmic or solar in origin) striking the photometer and causing permanent local changes (typically -0.5% in summed apertures) in quantum efficiency, though a partial exponential recovery is often observed. Since these features, dubbed sudden pixel sensitivity dropouts (SPSDs), are uncorrelated across targets they cannot be properly accounted for by the current detrending algorithm. PDC de-trending is based on the assumption that features in flux time series are due either to intrinsic stellar phenomena or to systematic errors and that systematics will exhibit measurable correlations across targets. SPSD events violate these assumptions and their successful removal not only rectifies the flux values of affected targets, but demonstrably improves the overall performance of PDC de-trending.

Kolodziejczak, Jeffery↗
NASA NTRS2014

A New Global Regression Analysis Method for the Prediction of Wind Tunnel Model Weight Corrections

A new global regression analysis method is discussed that predicts wind tunnel model weight corrections for strain-gage balance loads during a wind tunnel test. The method determines corrections by combining "wind-on" model attitude measurements with least squares estimates of the model weight and center of gravity coordinates that are obtained from "wind-off" data points. The method treats the least squares fit of the model weight separate from the fit of the center of gravity coordinates. Therefore, it performs two fits of "wind- off" data points and uses the least squares estimator of the model weight as an input for the fit of the center of gravity coordinates. Explicit equations for the least squares estimators of the weight and center of gravity coordinates are derived that simplify the implementation of the method in the data system software of a wind tunnel. In addition, recommendations for sets of "wind-off" data points are made that take typical model support system constraints into account. Explicit equations of the confidence intervals on the model weight and center of gravity coordinates and two different error analyses of the model weight prediction are also discussed in the appendices of the paper.

strain-gage balance↗
NASA NTRS1983

Techniques for the correction of topographical effects in scanning Auger electron microscopy

A number of ratioing methods for correcting Auger images and linescans for topographical contrast are tested using anisotropically etched silicon substrates covered with Au or Ag. Thirteen well-defined angles of incidence are present on each polyhedron produced on the Si by this etching. If N1 electrons are counted at the energy of an Auger peak and N2 are counted in the background above the peak, then N1, N1 - N2, (N1 - N2)/(N1 + N2) are measured and compared as methods of eliminating topographical contrast. The latter method gives the best compensation but can be further improved by using a measurement of the sample absorption current. Various other improvements are discussed.

Prutton, M.↗