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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 1,063 records · Page 59
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NASA NTRS1989

Corotation torques in the solar nebula - The cutoff function

The behavior of high-order corotation resonances in a disk of finite thickness is examined. The torque exerted at an mth-order resonance is determined by employing a vertically averaged disturbing function, and the ratio of this torque to that exerted on a cold, two-dimensional disk is identified as the so-called torque cutoff function. This function is then used to calculate contributions from the corotation torques to eccentricity variations of a perturber's orbit assumed orbiting in the disk.

Ward, William R.↗
NASA NTRS1989

The Shane Wirtanen counts - Observability of the galaxy correlation function

An explicit test of the ability of the galaxy two-point correlation function to be recovered from the Lick counts of galaxies (Shane and Wirtanen, 1967) is reported. High-fidelity simulations are created, starting with the distribution of galaxies in space. These distributions are projected onto a set of simulated Lick plates which are reduced to a uniform limiting magnitude with the method of Seldner et al. (1977). The simulated catalogs are then analyzed with the methods of Groth and Peebles (1977). The resulting correlation functions are found to reproduce accurately the correlation functions that were built in during the first step of the simulations.

Brown, Michael E.↗
NASA NTRS1989

Spline function approximation for velocimeter Doppler frequency measurement

A spline function approximation approach for measuring the Doppler spectral peak frequency in a laser Doppler velocimeter system is presented. The processor is designed for signal bursts with mean Doppler shift frequencies up to 100 MHz, input turbulence up to 20 percent, and photon counts as low as 300. The frequency-domain processor uses a bank of digital bandpass filters for the capture of the energy spectrum of each signal burst. The average values of the filter output energies, as a function of normalized frequency, are modeled as deterministic spline functions which are linearly weighted to evaluate the spectral peak location associated with the Doppler shift. The weighting coefficients are chosen to minimize the mean square error. Performance evaluation by simulation yields average errors in estimating mean Doppler frequencies within 0.5 percent for poor signal-to-noise conditions associated with a low photon count of 300 photons/burst.

Savakis, Andreas E.↗
NASA NTRS1989

Numerical optimization in Hilbert space using inexact function and gradient evaluations

Trust region algorithms provide a robust iterative technique for solving non-convex unstrained optimization problems, but in many instances it is prohibitively expensive to compute high accuracy function and gradient values for the method. Of particular interest are inverse and parameter estimation problems, since function and gradient evaluations involve numerically solving large systems of differential equations. A global convergence theory is presented for trust region algorithms in which neither function nor gradient values are known exactly. The theory is formulated in a Hilbert space setting so that it can be applied to variational problems as well as the finite dimensional problems normally seen in trust region literature. The conditions concerning allowable error are remarkably relaxed: relative errors in the gradient error condition is automatically satisfied if the error is orthogonal to the gradient approximation. A technique for estimating gradient error and improving the approximation is also presented.

Carter, Richard G.↗
NASA NTRS1989

Generation and tooth contact analysis of spiral bevel gears with predesigned parabolic functions of transmission errors

A new approach for determination of machine-tool settings for spiral bevel gears is proposed. The proposed settings provide a predesigned parabolic function of transmission errors and the desired location and orientation of the bearing contact. The predesigned parabolic function of transmission errors is able to absorb piece-wise linear functions of transmission errors that are caused by the gear misalignment and reduce gear noise. The gears are face-milled by head cutters with conical surfaces or surfaces of revolution. A computer program for simulation of meshing, bearing contact and determination of transmission errors for misaligned gear has been developed.

Litvin, Faydor L.↗
NASA NTRS1989

Automation of orbit determination functions for National Aeronautics and Space Administration (NASA)-supported satellite missions

The Flight Dynamics Facility (FDF) at Goddard Space Flight Center (GSFC) provides spacecraft trajectory determination for a wide variety of National Aeronautics and Space Administration (NASA)-supported satellite missions, using the Tracking Data Relay Satellite System (TDRSS) and Ground Spaceflight and Tracking Data Network (GSTDN). To take advantage of computerized decision making processes that can be used in spacecraft navigation, the Orbit Determination Automation System (ODAS) was designed, developed, and implemented as a prototype system to automate orbit determination (OD) and orbit quality assurance (QA) functions performed by orbit operations. Based on a machine-resident generic schedule and predetermined mission-dependent QA criteria, ODAS autonomously activates an interface with the existing trajectory determination system using a batch least-squares differential correction algorithm to perform the basic OD functions. The computational parameters determined during the OD are processed to make computerized decisions regarding QA, and a controlled recovery process isactivated when the criteria are not satisfied. The complete cycle is autonomous and continuous. ODAS was extensively tested for performance under conditions resembling actual operational conditions and found to be effective and reliable for extended autonomous OD. Details of the system structure and function are discussed, and test results are presented.

Mardirossian, H.↗
NASA NTRS1988

Effect of central obscuration on the LDR point spread function

It is well known that Gaussian apodization of an aperture reduces the sidelobe levels of its point spread function (PSF). In the limit where the standard deviation of the Gaussian function is much smaller than the diameter of the aperture, the sidelobes completely disappear. However, when Gaussian apodization is applied to the Large Deployable Reflector (LDR) array consisting of 84 hexagonal panels, it is found that the sidelobe level only decreases by about 2.5 dB. The reason for this is explained. The PSF is shown for an array consisting of 91 uniformly illuminated hexagonal apertures; this array is identical to the LDR array, except that the central hole in the LDR array is filled with seven additional panels. For comparison, the PSF of the uniformly illuminated LDR array is shown. Notice that it is already evident that the sidelobe structure of the LDR array is different from that of the full array of 91 panels. The PSF's of the same two arrays are shown, but with the illumination apodized with a Gaussian function to have 20 dB tapering at the edges of the arrays. While the sidelobes of the full array have decreased dramatically, those of the LDR array changed in structure, but stayed at almost the same level. This result is not completely surprising, since the Gaussian apodization tends to emphasize the contributions from the central portion of the array; exactly where the hole in the LDR array is located. The two most important conclusions are: the size of the central hole should be minimized, and a simple Gaussian apodization scheme to suppress the sidelobes in the PSF should not be used. A more suitable apodization scheme would be a Gaussian annular ring.

Vanzyl, Jakob J.↗
NASA NTRS1989

The influence of a wall function on turbine blade heat transfer prediction

The second phase of a continuing investigation to improve the prediction of turbine blade heat transfer coefficients was completed. The present study specifically investigated how a numeric wall function in the turbulence model of a two-dimensional boundary layer code, STAN5, affected heat transfer prediction capabilities. Several sources of inaccuracy in the wall function were identified and then corrected or improved. Heat transfer coefficient predictions were then obtained using each one of the modifications to determine its effect. Results indicated that the modifications made to the wall function can significantly affect the prediction of heat transfer coefficients on turbine blades. The improvement in accuracy due the modifications is still inconclusive and is still being investigated.

Whitaker, Kevin W.↗
NASA NTRS1990

A functional description of the advanced receiver

The breadboard Advanced Receiver 2 (ARX 2) that is currently being built for future use in NASA's Deep Space Network (DSN) is described. The hybrid analog/digital receiver performs multiple functions including carrier, subcarrier, and symbol synchronization. Tracking can be achieved for residual, suppressed, or hybrid carriers and for both sinusoidal and square-wave subcarriers. Other functions such as time-tagged Doppler extraction and monitor/control are also discussed, including acquisition algorithms and lock-detection schemes. System requirements are specified and a functional description of the ARX 2 is presented. The various digital signal-processing algorithms used are also discussed and illustrated with block diagrams.

Hinedi, S.↗
NASA NTRS1990

Experiment K-6-14. Hepatic function in rats after spaceflight

To determine the possible biochemical consequences of prolonged weightlessness on liver function, tissue samples from rats that had flown aboard Cosmos 1887 were analyzed for hepatic protein, glycogen and lipids as well as the activities of a number of key enzymes involved in metabolism of these compounds and xenobiotics. Among the parameters measured, the major differences were elevations in the hepatic glycogen content and HMG-CoA reductase activities of the rats flown on Cosmos 1887, and a decrease in the amount of microsomal cytochrome P sub 450 and the activity of aniline hydroxylase, a cytochrome P sub 450-dependent enzyme. Decreases in these two indices of the microsomal mixed-function oxidase system indicated that spaceflight may compromise the ability of liver to metabolize drugs and toxins. The higher HMG-CoA reductase correlated with elevated levels of serum cholestrol. Other changes included somewhat higher blood glucose, creatinine, SGOT, and much greater alkaline phosphatase and BUN. These results generally support the earlier observation of changes in these parameters (Merrill et al., Am. J. Physiol. 252:R22-R226, 1987). The importance of these alterations in liver function is not known; however, they have the potential to complicate long-term spaceflight.

Merrill, A., Jr.↗
NASA NTRS1990

Frequency analysis via the method of moment functionals

Several variants are presented of a linear-in-parameters least squares formulation for determining the transfer function of a stable linear system at specified frequencies given a finite set of Fourier series coefficients calculated from transient nonstationary input-output data. The basis of the technique is Shinbrot's classical method of moment functionals using complex Fourier based modulating functions to convert a differential equation model on a finite time interval into an algebraic equation which depends linearly on frequency-related parameters.

Pearson, A. E.↗
NASA NTRS1989

Design of a structural and functional hierarchy for planning and control of telerobotic systems

Hierarchical structures offer numerous advantages over conventional structures for the control of telerobotic systems. A hierarchically organized system can be controlled via undetailed task assignments and can easily adapt to changing circumstances. The distributed and modular structure of these systems also enables fast response needed in most telerobotic applications. On the other hand, most of the hierarchical structures proposed in the literature are based on functional properties of a system. These structures work best for a few given functions of a large class of systems. In telerobotic applications, all functions of a single system needed to be explored. This approach requires a hierarchical organization based on physical properties of a system and such a hierarchical organization is introduced. The decomposition, organization, and control of the hierarchical structure are considered, and a system with two robot arms and a camera is presented.

Acar, Levent↗
NASA NTRS1989

Irregular wave functions of a hydrogen atom in a uniform magnetic field

The highly excited irregular wave functions of a hydrogen atom in a uniform magnetic field are investigated analytically, with wave function scarring by periodic orbits considered quantitatively. The results obtained confirm that the contributions of closed classical orbits to the spatial wave functions vanish in the semiclassical limit. Their disappearance, however, is slow. This discussion is illustrated by numerical examples.

Wintgen, D.↗
NASA NTRS1989

Some elements of a theory of multidimensional complex variables. I - General theory. II - Expansions of analytic functions and application to fluid flows

The paper introduces a new theory of N-dimensional complex variables and analytic functions which, for N greater than 2, is both a direct generalization and a close analog of the theory of ordinary complex variables. The algebra in the present theory is a commutative ring, not a field. Functions of a three-dimensional variable were defined and the definition of the derivative then led to analytic functions.

Martin, E. Dale↗
NASA NTRS1989

The nearby Abell clusters. III - Luminosity functions for eight rich clusters

Red photographic data on eight rich Abell clusters are combined with previous results on four other Abell clusters to study the luminosity functions of the clusters. The results produce a mean value of the characteristic galaxy magnitude (M asterisk) that is consistent with previous results. No relation is found between the magnitude of the first-ranked cluster galaxy and M asterisk, suggesting that the value of M asterisk is not changed by dynamical evolution. The faint ends of the luminosity functions for many of the clusters are quite flat, validating the nonuniversality in the parametrization of Schechter (1976) functions for rich clusters of galaxies.

Oegerle, William R.↗
NASA NTRS1989

Theoretical study of the dipole moment function of OH(X2Pi)

A theoretical study of the sensitivity of the dipole moment function (DMF) of the X2Pi ground state of OH to basis-set saturation and to refinements in the correlation treatment is presented. Emphasis is placed on determining the slope of the DMF at r(e) and the r value at which the maximum occurs. Consideration is given to the effect of oxygen polarization functions up through h type, expansion of the active orbital space to include the O 3d-delta orbital, the effect of higher excitations using the averaged coupled-pair functional method, and the effect of evaluating the dipole moment as an energy derivative rather than as an expectation value. The theoretical DMFs obtained here, which should be the most accurate to date, differ markedly from an empirical DMF of Turnbull and Lowe that is based on experimentally derived intensity ratios. The theoretical DMFs agree better with a recently published DMF of Nelson et al., but suggest that this empirical DMF is also inaccurate for r greater than 2.3 a0.

Langhoff, Stephen R.↗
NASA NTRS1989

Liquid alkali metals - Equation of state and reduced-pressure, bulk-modulus, sound-velocity, and specific-heat functions

The previous work of Schlosser and Ferrante (1988) on universality in solids is extended to the study of liquid metals. As in the case of solids, to a good approximation, in the absence of phase transitions, plots of the logarithm of the reduced-pressure function H, of the reduced-isothermal-bulk-modulus function b, and of the reduced-sound-velocity function v are all linear in 1-X. Finally, it is demonstrated that ln(Cp/C/v) is also linear in 1-X, where X = (V/V/0/)exp 1/3), and V(0) is the volume at zero pressure.

Schlosser, Herbert↗
NASA NTRS1990

Embedded function methods for supersonic turbulent boundary layers

The development of embedded functions to represent the mean velocity and total enthalpy distributions in the wall layer of a supersonic turbulent boundary layer is considered. The asymptotic scaling laws (in the limit of large Reynolds number) for high speed compressible flows are obtained to facilitate eventual implementation of the embedded functions in a general prediction method. A self-consistent asymptotic structure is derived, as well as a compressible law of the wall in which the velocity and total enthalpy are logarithmic within the overlap zone, but in the Howarth-Dorodnitsyn variable. Simple outer region turbulence models are proposed (some of which are modifications of existing incompressible models) to reflect the effects of compressibility. As a test of the methodology and the new turbulence models, a set of self-similar outer region profiles is obtained for constant pressure flow; these are then coupled with embedded functions in the wall layer. The composite profiles thus obtained are compared directly with experimental data and good agreement is obtained for flows with Mach numbers up to 10.

He, J.↗