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NASA NTRS1980

Calculations of the spectral nature of the microwave emission from soils

The brightness temperatures for a set of soil profiles observed at USDA facilities in Arizona and Georgia were calculated at the wavelengths of 2.8, 6, 11, 21, and 49 cm using a coherent radiative transfer model. The soil moisture sampling depth is found to be a function of wavelength and is in the range 0.06 to 0.1 of a wavelength. The thermal sampling depth also depends on wavelength and is approximately equal to one wavelength at dry soil condition and 0.1 - 0.5 wavelengths at wet soil conditions. Calculated values of emissivity show strong diurnal variations when the soils are wet, while there is little diurnal change when the soil is dry. The soil moistures within the four depth intervals of 0-2, 0-5, 0-9, and 0-15 cm were parameterized as function of the calculated emissivity and brightness temperature. Best-fit parameters and correlation coefficients are presented for five wavelengths. Interrelationships among the effective temperature, surface temperature, and emissivity are displayed.

Mo, T.↗

NASA NTRS1980

Calculation of power spectrums from digital time series with missing data points

Two algorithms are developed for calculating power spectrums from the autocorrelation function when there are missing data points in the time series. Both methods use an average sampling interval to compute lagged products. One method, the correlation function power spectrum, takes the discrete Fourier transform of the lagged products directly to obtain the spectrum, while the other, the modified Blackman-Tukey power spectrum, takes the Fourier transform of the mean lagged products. Both techniques require fewer calculations than other procedures since only 50% to 80% of the maximum lags need be calculated. The algorithms are compared with the Fourier transform power spectrum and two least squares procedures (all for an arbitrary data spacing). Examples are given showing recovery of frequency components from simulated periodic data where portions of the time series are missing and random noise has been added to both the time points and to values of the function. In addition the methods are compared using real data. All procedures performed equally well in detecting periodicities in the data.

Murray, C. W., Jr.↗

NASA NTRS1981

Quantum chemical calculation of the equilibrium structures of small metal atom clusters

The application of ab initio quantum mechanical approaches in the study of metal atom clusters requires simplifying techniques that do not compromise the reliability of the calculations. Various aspects of the implementation of the effective core potential (ECP) technique for the removal of the metal atom core electrons from the calculation were examined. The ECP molecular integral formulae were modified to bring out the shell characteristics as a first step towards fulfilling the increasing need to speed up the computation of the ECP integrals. Work on the relationships among the derivatives of the molecular integrals that extends some of the techniques pioneered by Komornicki for the calculation of the gradients of the electronic energy was completed and a formulation of the ECP approach that quite naturally unifies the various state-of-the-art "shape- and Hamiltonian-consistent" techniques was discovered.

Kahn, L. R.↗

NASA NTRS1980

Ab initio projected-unrestricted Hartree-Fock calculation of some potential energy curves for carbonyl fluoride

Some potential energy curves for CF2O were calculated using projected-unrestricted Hartree-Fock (PUHF) theory. The calculations employed a contracted (4s 3p) Gaussian-type atomic orbital basis set. Bound states were found for the X-tilde 1A1 and 1,3A2 states while the 1,3B1 and 1,3B2 states were repulsive in the valence representation. The merits of the PUHF treatment for excited states are discussed. The results are discussed in terms of available experimental information and previous calculations with particular emphasis on the question of the photolysis channels open in the solar spectral region.

Brewer, D. A.↗

NASA NTRS1981

A vortex-lattice method for calculating lifting-surface interference

The interference effect of closely coupled lifting surfaces was investigated. A nonsteady vortex-lattice method was applied to calculate the steady-state and nonsteady lift characteristics of configurations having interference effects. The configurations consist of low-aspect-ratio delta wings, at low and high angles of attack. Leading-edge separation and wake roll-up are simulated by a time-dependent wake-shedding procedure. For steady-state flow conditions, this numerical procedure saves a considerable amount of computer time, compared with iterative methods, and yields the same results. A better understanding of the interference effect can be gained by using the method to study the transient behavior. The nonsteady approach also offers the capability of calculating various nonsteady motions, as is demonstrated in the calculation of the longitudinal damping.

Levin, D.↗

NASA NTRS1983

Calculating Clearances for Manipulators

Set of algorithms rapidly calculates minimum safe clearances for remote manipulators. Such calculations are used in design of trajectories for manipulators to ensure they do not accidentally strike surrounding objects. Structural parts are considered as cylindrical shells having circular plane areas for ends. Clearance calculation method offers special benefits in industrial robotics, particularly in automated machining.

Copeland, E. L.↗

NASA NTRS1982

A FORTRAN program for calculating three dimensional, inviscid and rotational flows with shock waves in axial compressor blade rows: User's manual

A FORTRAN-IV computer program was developed for the calculation of the inviscid transonic/supersonic flow field in a fully three dimensional blade passage of an axial compressor rotor or stator. Rotors may have dampers (part span shrouds). MacCormack's explicit time marching method is used to solve the unsteady Euler equations on a finite difference mesh. This technique captures shocks and smears them over several grid points. Input quantities are blade row geometry, operating conditions and thermodynamic quanities. Output quantities are three velocity components, density and internal energy at each mesh point. Other flow quanities are calculated from these variables. A short graphics package is included with the code, and may be used to display the finite difference grid, blade geometry and static pressure contour plots on blade to blade calculation surfaces or blade suction and pressure surfaces. The flow in a low aspect ratio transonic compressor was analyzed and compared with high response total pressure probe measurements and gas fluorescence static density measurements made in the MIT blowdown wind tunnel. These comparisons show that the computed flow fields accurately model the measured shock wave locations and overall aerodynamic performance.

Thompkins, W. T., Jr.↗

NASA NTRS1982

Solar radiation at the Earth's surface: Its calculation and inference from satellite imagery

Physical and empirical models for calculation of insolation on a horizontal surface are described. Calculation of the spectral components of insolation and the calculation of the integrated values using wavelength-averaged values, ignoring aerosol effects, are discussed. Empirical models for determining insolation from meteorological data under clear and cloudy skies are described. The influence of hourly and daily global solar radiation from GOES satellite images is illustrated. Data acquisition methods for the Great Plains experiment, the determination of cloud free brightness levels, and determination of cloud parameters and target brightness are considered. The use of two and seven satellite images per day resulted in insolation determinations having a standard error of less then 10% of the mean. Use of only one image per day resulted in a standard error of about 20% of the mean.

Bartman, F. L.↗

NASA NTRS1982

Quantum chemical calculations for polymers and organic compounds

The relativistic effects of the orbiting electrons on a model compound were calculated. The computational method used was based on 'Modified Neglect of Differential Overlap' (MNDO). The compound tetracyanoplatinate was used since empirical measurement and calculations along "classical" lines had yielded many known properties. The purpose was to show that for large molecules relativity effects could not be ignored and that these effects could be calculated and yield data in closer agreement to empirical measurements. Both the energy band structure and molecular orbitals are depicted.

Lopez, J.↗

NASA NTRS1980

Calculation of multiple scattered radiation in clean atmospheres

Calculations of the multiple-scattered solar radiation in the earth's atmosphere are compared with telephotometer measurements of the sky intensity obtained during the EPA-sponsored Visibility Impairment by Sulfate Transport and Transformation in the Atmosphere experiment. The doubling and adding calculation technique, in which the reflection and transmission properties of the atmosphere are computed by initially calculating such properties for the case of very thin layers and then adding adjacent layers together, is described and compared with data for two cloudless sky conditions. The first is typical of clean tropospheric conditions, and the second represents an ultraclean atmosphere in which surface aerosol scattering is much lower than molecular scattering. Good agreement is found between the computations and the measurement data.

Bergstrom, R. W.↗

NASA NTRS1980

Computer code simulations of the formation of Meteor Crater, Arizona - Calculations MC-1 and MC-2

It has been widely accepted that hypervelocity impact processes play a major role in the evolution of the terrestrial planets and satellites. In connection with the development of quantitative methods for the description of impact cratering, it was found that the results provided by two-dimensional finite difference, computer codes is greatly improved when initial impact conditions can be defined and when the numerical results can be tested against field and laboratory data. In order to address this problem, a numerical code study of the formation of Meteor (Barringer) Crater, Arizona, has been undertaken. A description is presented of the major results from the first two code calculations, MC-1 and MC-2, that have been completed for Meteor Crater. Both calculations used an iron meteorite with a kinetic energy of 3.8 Megatons. Calculation MC-1 had an impact velocity of 25 km/sec and MC-2 had an impact velocity of 15 km/sec.

Roddy, D. J.↗

NASA NTRS1982

Ab initio calculation of infrared intensities for hydrogen peroxide

Results of an ab initio SCF quantum mechanical study are used to derive estimates for the infrared intensities of the fundamental vibrations of hydrogen peroxide. Atomic polar tensors (APTs) were calculated on the basis of a 4-31G basis set, and used to derive absolute intensities for the vibrational transitions. Comparison of the APTs calculated for H2O2 with those previously obtained for H2O and CH3OH, and of the absolute intensities derived from the H2O2 APTs with those derived from APTs transferred from H2O and CH3OH, reveals the sets of values to differ by no more than a factor of two, supporting the validity of the theoretical calculation. Values of the infrared intensities obtained correspond to A1 = 14.5 km/mol, A2 = 0.91 km/mol, A3 = 0.058 km/mol, A4 = 123 km/mol, A5 = 46.2 km/mol, and A6 = 101 km/mol. Charge, charge flux and overlap contributions to the dipole moment derivatives are also computed.

Rogers, J. D.↗

NASA NTRS1982

Implementation of structural response sensitivity calculations in a large-scale finite-element analysis system

The methodology used to implement structural sensitivity calculations into a major, general-purpose finite-element analysis system (SPAR) is described. This implementation includes a generalized method for specifying element cross-sectional dimensions as design variables that can be used in analytically calculating derivatives of output quantities from static stress, vibration, and buckling analyses for both membrane and bending elements. Limited sample results for static displacements and stresses are presented to indicate the advantages of analytically calculating response derivatives compared to finite difference methods. Continuing developments to implement these procedures into an enhanced version of SPAR are also discussed.

Giles, G. L.↗

NASA NTRS1982

Finite volume calculation of three-dimensional potential flow around a propeller

The finite volume scheme of Jameson (1977) is used to calculate potential flow around a propeller rotating at high speed. An H-type mesh is generated and used successfully in the calculations. A test calculation with a thick blade cross section shows that the present code is capable of computing the propeller flow at the advance Mach number 0.8. The possible physical mechanisms which may play an important role in the propeller aerodynamics are discussed.

Jou, W.-H.↗

NASA NTRS1981

Multi-ring basin formation - Possible clues from impact cratering calculations

Finite difference continuum mechanics code calculations make it possible to vary the controlling variables in an impact event and to determine basic trends at scales unavailable to experimental analysis. Orphal et al. (1980) have summarized the results of a pair of such calculations for identical projectile/target characteristics but different impact velocities. One calculation considered a relatively low velocity iron impactor (5 km/s); the other, a high velocity iron impactor (15.8 km/s). The primary purpose was to investigate the generation and transport of impact melt for the two impact energies. Attention is given to crater growth, crater ejecta, and possible implications for basin-size events. Based on extrapolations, a new scenario is proposed. The scenario incorporates elements of several existing basin models.

Schultz, P. H.↗

NASA NTRS1982

Calculation of vortex flows on complex configurations

The calculation of aerodynamic characteristics of complex configurations having strongly coupled vortex flows is a non-linear problem requiring iterative solution techniques. This paper discusses the use of a low-order panel method as a means of obtaining practical solutions to such problems. The panel method is based on piecewise constant source and doublet quadrilateral panels and uses the internal Dirichlet boundary condition of zero perturbation potential. The problems of predicting vortex/surface interaction and vortex separation are discussed. Some example calculations are included but further test cases have yet to be carried out, in particular for comparisons with experimental data. The problem of convergence on the iterative calculation for the shape of the free vortex sheet is addressed and a preprocessor routine, based on an unsteady, two-dimensional version of the panel method, is put forward as a cost-effective way of generating an initial vortex structure for use as a starting solution for general configurations.

Maskew, B.↗

NASA NTRS1982

Ab initio calculation of infrared intensities for the linear isoelectronic series HCN, HNC, CO, HCO/+/, and HOC/+/

Ab initio infrared intensities and dipole moment derivatives expressed in atomic polar tensor form are calculated using the 4-31 and 6-31G(double asterisk) basis sets for the isoelectronic HCN, HNC, CO, HCO(+), and HOC(+) series of molecules. The calculated atomic polar tensors are analyzed in terms of the charge-charge flux-overlap model, which is found to be useful in explaining some of the trends observed in the dipole moment derivatives for this series of molecules. A detailed examination of the dipole moment derivatives for the structural isomers indicates some of the ways in which experimental atomic polar tensors for one isomer should be modified to predict infrared intensities for the other isomer. The absolute intensities calculated for the HCO(+) and HOC(+) ions are believed to be accurate to within a factor of 2 and thus should be useful in astrophysical applications.

Rogers, J. D.↗

NASA NTRS1982

Approximate Method of Calculating Heating Rates at General Three-Dimensional Stagnation Points During Atmospheric Entry

An approximate method for calculating heating rates at general three dimensional stagnation points is presented. The application of the method for making stagnation point heating calculations during atmospheric entry is described. Comparisons with results from boundary layer calculations indicate that the method should provide an accurate method for engineering type design and analysis applications.

Hamilton, H. H., II↗