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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Aeroelastic modeling for the FIT team F/A-18 simulation

Some details of the aeroelastic modeling of the F/A-18 aircraft done for the Functional Integration Technology (FIT) team's research in integrated dynamics modeling and how these are combined with the FIT team's integrated dynamics model are described. Also described are mean axis corrections to elastic modes, the addition of nonlinear inertial coupling terms into the equations of motion, and the calculation of internal loads time histories using the integrated dynamics model in a batch simulation program. A video tape made of a loads time history animation was included as a part of the oral presentation. Also discussed is work done in one of the areas of unsteady aerodynamic modeling identified as needing improvement, specifically, in correction factor methodologies for improving the accuracy of stability derivatives calculated with a doublet lattice code.

Zeiler, Thomas A.↗
NASA NTRS1989

Rapid fitting of particle cascade development data from X-ray film densitometry measurements

A semiautomatic method of fitting transition curves to X-ray film optical density measurements of electromagnetic particle cascades is described. Several hundred singly and multiple interacting cosmic ray events from the JACEE 8 balloon flights were analyzed using this procedure. In addition to greatly increased speed compared to the previous manual method, the semiautomatic method offers increased accuracy through maximum likelihood fitting.

Roberts, E.↗
NASA NTRS1989

Aeroelastic modeling for the FIT (Functional Integration Technology) team F/A-18 simulation

As part of Langley Research Center's commitment to developing multidisciplinary integration methods to improve aerospace systems, the Functional Integration Technology (FIT) team was established to perform dynamics integration research using an existing aircraft configuration, the F/A-18. An essential part of this effort has been the development of a comprehensive simulation modeling capability that includes structural, control, and propulsion dynamics as well as steady and unsteady aerodynamics. The structural and unsteady aerodynamics contributions come from an aeroelastic mode. Some details of the aeroelastic modeling done for the Functional Integration Technology (FIT) team research are presented. Particular attention is given to work done in the area of correction factors to unsteady aerodynamics data.

Zeiler, Thomas A.↗
NASA NTRS1991

Bonding Aramid Rope To Metal Fitting

Method for joining Kevlar (or equivalent) aramid rope to tubular corrosion-resistant steel end fitting increases strength of joint under tension to approximately three-fourths that of rope itself. End fitting contains internal thread, which provides good bonding surface. Small radial hole enables injection of adhesive into bore.

To, Dung T.↗
NASA NTRS1990

Determination of total column water vapor in the atmosphere at high spatial resolution from AVIRIS data using spectral curve fitting and band ratioing techniques

Techniques are developed for quantitative retrievals of high spatial resolution column atmospheric water vapor that is largely contained in the lower portion of the troposphere. One method consists of curve fitting observed spectra with simulated spectra in the 1.14 microns or the 0.94 micron water vapor band absorption region. The other method is a simple band ratioing technique, which requires less computer time than the curve fitting method. The advantage of the technique over humidity sounding by IR emission measurements is that the retrieved column water vapor amounts over land surfaces have significantly higher precision.

Gao, Bo-Cai↗
NASA NTRS1992

Toroid Joining Gun For Fittings And Couplings

Hand-held gun used to join metal heat-to-shrink couplings. Uses magnetic induction (eddy currents) to produce heat in metal coupling, and thermocouple to measure temperature and signals end of process. Gun, called "toroid joining gun" concentrates high levels of heat in localized areas. Reconfigured for use on metal heat-to-shrink fitting and coupling applications. Provides rapid heating, operates on low power, lightweight and portable. Safe for use around aircraft fuel and has no detrimental effects on surrounding surfaces or objects. Reliable in any environment and under all weather conditions. Gun logical device for taking full advantage of capabilities of new metal heat-to-shrink couplings and fittings.

Fox, Robert L.↗
NASA NTRS1991

Calculations and curve fits of thermodynamic and transport properties for equilibrium air to 30000 K

A self-consistent set of equilibrium air values were computed for enthalpy, total specific heat at constant pressure, compressibility factor, viscosity, total thermal conductivity, and total Prandtl number from 500 to 30,000 K over a range of 10(exp -4) atm to 10(exp 2) atm. The mixture values are calculated from the transport and thermodynamic properties of the individual species provided in a recent study by the authors. The concentrations of the individual species, required in the mixture relations, are obtained from a free energy minimization calculation procedure. Present calculations are based on an 11-species air model. For pressures less than 10(exp -2) atm and temperatures of about 15,000 K and greater, the concentrations of N(++) and O(++) become important, and consequently, they are included in the calculations determining the various properties. The computed properties are curve fitted as a function of temperature at a constant value of pressure. These curve fits reproduce the computed values within 5 percent for the entire temperature range considered here at specific pressures and provide an efficient means for computing the flowfield properties of equilibrium air, provided the elemental composition remains constant at 0.24 for oxygen and 0.76 for nitrogen by mass.

Gupta, Roop N.↗
NASA NTRS1992

Computer program for calculating and fitting thermodynamic functions

A computer program is described which (1) calculates thermodynamic functions (heat capacity, enthalpy, entropy, and free energy) for several optional forms of the partition function, (2) fits these functions to empirical equations by means of a least-squares fit, and (3) calculates, as a function of temperture, heats of formation and equilibrium constants. The program provides several methods for calculating ideal gas properties. For monatomic gases, three methods are given which differ in the technique used for truncating the partition function. For diatomic and polyatomic molecules, five methods are given which differ in the corrections to the rigid-rotator harmonic-oscillator approximation. A method for estimating thermodynamic functions for some species is also given.

Mcbride, Bonnie J.↗
NASA NTRS1993

M dwarf spectra from 0.6 to 1.5 micron - A spectral sequence, model atmosphere fitting, and the temperature scale

Red/infrared (0.6-1.5 micron) spectra are presented for a sequence of well-studied M dwarfs ranging from M2 through M9. A variety of temperature-sensitive features useful for spectral classification are identified. Using these features, the spectral data are compared to recent theoretical models, from which a temperature scale is assigned. The red portion of the model spectra provide reasonably good fits for dwarfs earlier than M6. For layer types, the infrared region provides a more reliable fit to the observations. In each case, the wavelength region used includes the broad peak of the energy distribution. For a given spectral type, the derived temperature sequence assigns higher temperatures than have earlier studies - the difference becoming more pronounced at lower luminosities. The positions of M dwarfs on the H-R diagram are, as a result, in closer agreement with theoretical tracks of the lower main sequence.

Kirkpatrick, J. D.↗
NASA NTRS1992

High-order wide-band frequency domain identification using composite curve fitting

A method is presented for curve fitting nonparametric frequency domain data so as to identify a parametric model composed of two models in parallel, where each model has dynamics in a specified portion of the frequency band. This decomposition overcomes the problem of numerical sensitivity since lower order polynomials can be used compared to existing methods which estimate the model as a single entity. Consequently, composite curve fitting is useful for frequency domain identification of high-order systems and/or systems whose dynamics are spread over a large bandwidth. The approach can be extended to identify an arbitrary number of parallel subsystems in specified frequency regimes.

Bayard, D. S.↗
NASA NTRS1993

Quasi-random narrow-band model fits to near-infrared low-temperature laboratory methane spectra and derived exponential-sum absorption coefficients

Near-infrared 10/cm resolution spectra of methane obtained at various temperatures, pressures, and abundances are fit to a quasi-random narrow-band model. Exponential-sum absorption coefficients for three temperatures (112, 188, and 295 K), and 20 pressures from 0.0001 to 5.6 bars, applicable to the cold environments of the major planets, are then derived from the band model for the 230 wavelengths measured from 1.6 to 2.5 microns. RMS deviations between the laboratory and the exponential-sum synthetic transmissions are reported for the best fitting 50 wavelengths. Deviations relevant to broadband, 1-percent spectral resolution observations are also presented. The validity of exponential-sum coefficients derived from broadband (10/cm) transmission data is demonstrated via direct comparison with line-by-line calculations. The complete atlas of coefficients is available from the Planetary Data System-Planetary Atmospheres Discipline Node.

Baines, Kevin H.↗
NASA NTRS1993

One-parameter scaling and exponential-sum fitting for water vapor and CO2 infrared transmission functions

A medium-sized band model for water vapor and CO2 absorption is developed using the one-parameter scaling approximation. The infrared spectrum is divided into 10 bands. The Planck-weighted diffuse transmittance is reduced to a function dependent only upon the scaled absorber amount and fit by an exponential sum. By selecting specific sets of absorption coefficients for exponential-sum fitting, computations of fluxes and cooling rate are made very fast. Compared to a broadband model, the accuracy, speed, and versatility are all enhanced. With absorption due to water vapor line, continuum, CO2 as well as O3 included, the parameterization introduces an error of less than 1.5 W/sq m in fluxes and less than 0.15 C/day in the tropospheric and lower stratospheric cooling rates.

Chou, Ming-Dah↗
NASA NTRS1993

Vector formulation for interferogram surface fitting

Interferometry is an optical testing technique that quantifies the optical path difference (OPD) between a reference wave front and a test wave front based on the interference of light. Fringes are formed when the OPD is an integral multiple of the illuminating wavelength. The resultant two-dimensional pattern is called an interferogram. The function of any interferogram analysis program is to extract this OPD and to produce a representation of the test wave front (or surface). This is accomplished through a three-step process of sampling, ordering, and fitting. We develop a generalized linear-algebra vector-notation model of the interferogram sampling and fitting process.

Fischer, David J.↗
NASA NTRS1994

Self-Sealing Cryogenic Fitting

Self-sealing fitting for cryogenic tubes remains free of leakage from room temperature to liquid-helium temperature even at internal pressure as high as 2.7 MPa. Fitting comprises parts made of materials with different coefficients of thermal expansion to prevent leakage gaps from forming as temperature decreases. Consists of coupling nut, two flared tube ends, and flared O-ring spacer. Spacer contracts more than tube ends do as temperature decreases. This greater contraction seals tube ends more tightly, preventing leakage.

Jia, Lin Xiang↗
NASA NTRS1993

The Langley Fitness Center

NASA Langley recognizes the importance of healthy employees by committing itself to offering a complete fitness program. The scope of the program focuses on promoting overall health and wellness in an effort to reduce the risks of illness and disease and to increase productivity. This is accomplished through a comprehensive Health and Fitness Program offered to all NASA employees. Various aspects of the program are discussed.

Source record↗
NASA NTRS1994

Numerical simulation of shock-induced combustion past blunt bodies using shock-fitting technique

Two-dimensional axisymmetric, reacting viscous flow over blunt projectiles is computed to study shock-induced combustion at Mach 5.11 and Mach 6.46 in hydrogen-air mixture. A finite-difference, shock-fitting method is used to solve the complete set of Navier-Stokes and species conservation equations. In this approach, the bow shock represents a boundary of the computational domain and is treated as a discontinuity across which Rankine-Hugoniot conditions are applied. All interior details of the flow such as compression waves, reaction front, and the wall boundary layer are captured automatically in the solution. Since shock-fitting approach reduces the amount of artificial dissipation, all the intricate details of the flow are captured much more clearly than has been possible with the shock-capturing approach. This has allowed an improved understanding of the physics of shock-induced combustion over blunt projectiles and the numerical results can now be explained more readily with one-dimensional wave-interaction model than before.

Ahuja, J. K.↗
NASA NTRS1994

Analysis of helium-rich subdwarf O stars. 1: NLTE models, methods, and fits for 21 Palomar Green survey sdOs

Atmospheric parameters for 21 helium-rich hot subdwarf O stars from the Palomar Green survey are found from fits of non-local thermodynamic equilibrium (NLTE) models to optical spectra. About 250 new NLTE models in the parameter range T(sub eff) from 35,000 to 65,000 K, log (g) from 4.0 to 6.5, and epsilon(He) from 50% He to 99% He have been calculated. A fit for each object is presented. Estimated distances and luminosities are calculated, assuming a mass of 0.5 solar masses. Large distances above the Galactic plane are found, and this implies that the majority of the sdO stars belong to a different stellar population than the sdB, planetary nebulae and white dwarf stars. Possibilities may include the halo and a 'thick disk.' Kinematical data from the literature are also discussed in view of the found distances. Five of the stars have been observed, modeled, and analyzed by Dreizler et al., and significant differences exist between their results and ours for these stars. The reason for these differences is not yet known, but the problem does not alter the conclusions about population membership that we present.

Thejll, P.↗
NASA NTRS1995

Geometry and pulse profiles of x-ray pulsars: Asymmetric relativistic fits to 4U1538 - 52 and vela x-1

Model calculation of inhomogenuous magnetized neutron star atmospheres are used to analyze the phase-dependent spectra of 4U 1538-52 and Vela X-1 taking into account general relativistic effects. A chi (exp 2) fitting procedure is used on the Ginga data for these objects to determine the geometry and the magnetic structure of the polar caps, as well as their size and location on the surface of the stars. Other parameters determined by the fit are the masses and radii of neutron stars, the accretion rates, and the rotation and magnetic inclination angles including an azimuthal offset to reproduce the asymmetry of the pulse shapes. We find that general relativistic effects play a significant role in determining the derived cap sizes, the fluxes, and the observational appearance of the pulses. There is evidence that the polar caps are unequal and nonantipodal, suggesting either an off-center or bent magnetic axis, or a strong nondipole component. The magnetic field structure is approximated by a two-component model. The rotation axes are inferred to be moderately close to the mean magnetic axes and seen at large inclinations with respect to the line of sight.

Bulik, T.↗