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At least 1,405 records · Page 78
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NASA NTRS1978

A ring-source model for jet noise

A model consisting of two ring sources was developed to study the direct radiation of jet noise in terms of correlation, coherence, and phase and also to aid in solving the inverse radiation problem of determining the noise source in terms of far-field measurements. The rings consist of discrete sources which are either monopoles or quadrupoles with Gaussian profiles. Only adjacent sources, both within the rings and between rings, are correlated. Results show that from the far-field information can be used to determine when the sources are compact or noncompact with respect to the acoustic wavelength and to distinguish between the types of sources. In addition, from the inverse radiation approach, the center of mass, the location and separation distance of the ring, and the diameters can be recovered.

Maestrello, L.↗
NASA NTRS1977

Diagonal dominance using function minimization algorithms

A new approach to the design of multivariable control systems using the inverse Nyquist array method is proposed. The technique utilizes a conjugate direction function minimization algorithm to achieve dominance over a specified frequency range by minimizing the ratio of the moduli of the off-diagonal terms to the moduli of the diagonal term of the inverse open loop transfer function matrix. The technique is easily implemented in either a batch or interactive computer mode and will yield diagonalization when previously suggested methods fail. The proposed method has been successfully applied to design a control system for a sixteenth order state model of the F-100 turbofan engine with three inputs.

Leininger, G. G.↗
NASA NTRS1977

Pioneer 10 and 11 radio occultations by Jupiter

Results on the temperature structure of the Jovian atmosphere are reviewed which were obtained by applying an integral inversion technique combined with a model for the planet's shape based on gravity data to Pioneer 10 and 11 radio-occultation data. The technique applied to obtain temperature profiles from the Pioneer data consisted of defining a center of refraction based on a computation of the radius of curvature in the plane of refraction and the normal direction to the equipotential surface at the closest approach point of a ray. Observations performed during the Pioneer 10 entry and exit and the Pioneer 11 exit are analyzed, sources of uncertainty are identified, and representative pressure-temperature profiles are presented which clearly show a temperature inversion between 10 and 100 mb. Effects of zonal winds on the reliability of radio-occultation temperature profiles are briefly discussed.

Kliore, A. J.↗
NASA NTRS1977

5-20 micron observations of Uranus and Neptune

Emission features at 8 and 12 microns indicate a strong temperature inversion in the upper atmosphere of Neptune. The presence of only a weak inversion on Uranus is confirmed.

Gillett, F. C.↗
NASA NTRS1978

Cometary brightness variation and nucleus structure

The Bobrovnikoff and Beyer photometric data for more than 100 comets analyzed for intrinsic brightness variations, before and after perihelion, according to some inverse power law of solar distance. The Oort and Schmidt classification of comet age is extended and applied with Marsden's new determinations of inverse semimajor axis. A physical interpretation of the data involves the quick loss of a frosting of supervolatile materials from new comets, and for all comets, the development of an insulating crust after perihelion. The orientation of the axes of rotating comets is shown to be an important factor in cometary brightness variations. A speculation is made concerning the axis of rotation of Comet Kohoutek.

Whipple, F. L.↗
NASA NTRS1977

C-14 in lunar soil - Temperature-release and grain-size dependence

C-14 is released from surface soils by heatings between 600 and 1000 C. The amounts of 600-1000-C C-14 obtained increase inversely with grain diameter for the 10-30 and 74-125-micron size fractions. The inverse relation shows that the 600-1000-C C-14 is located on the surface of grains and probably is of solar-wind origin. The amount released at these temperatures gives 0.002 C-14 ions per sq cm/sec for the implantation rate and corresponds to a C-14/H ratio of the order of 4 hundred-billionths for the solar wind. This result from the grain-size dependence is in accord with C-14 depth-variation studies. The C-14 released above melting temperatures can be attributed to spallation production.

Fireman, E. L.↗
NASA NTRS1978

Calculation of far-field jet noise spectra from near-field measurements using true source location

Jet mixing noise data at different measurement distances are compared with values calculated from the Lockheed prediction method. Although the method does not include any acoustic near-field effects, the measured and predicted results agree well where the measured data deviates from the inverse square law. It is therefore suggested that departures from the inverse square law are primarily the result of (1) the non-negligible distance between the nozzle exit plane and the true axial source location and (2) the jet mixing noise directionality, as modeled in the prediction method. Allowing for these effects, jet noise data at 8 and 96 diameters over a wide range of frequencies, angles and jet conditions are shown to collapse with reasonable accuracy.

Ahuja, K. K.↗
NASA NTRS1975

Sulfur abundances and distributions in mare basalts and their source magmas

An inverse correlation between metallic iron content and total sulfur abundances was observed by Gibson and Moore (1974) for five Apollo 17 and six Apollo 15 basalts. An investigation was conducted with the objective to distinguish between two processes leading to the inverse metallic iron and total sulfur correlation. The investigation included analyses of ten Apollo 15 and five Apollo 17 basalts for their sulfur and metallic iron abundances along with carbon and hydrogen. The sulfur isotopic compositions were measured for a possible identification of the fractionation processes which might have occurred during volatilization of the basalts.

Gibson, E. K., Jr.↗
NASA NTRS1975

Lunar electromagnetic scattering. IV - Transfer functions in the long-wavelength limit

The theory for asymmetric lunar magnetic induction in the long-wavelength limit, applicable to induction in the solar wind and magnetosheath plasmas at frequencies no higher than about 0.01 Hz, is presented. The lunar response to arbitrary ambient field orientations can be synthesized from the responses to field fluctuations parallel and perpendicular to the cavity axis. Radial and tangential transfer functions for a particular lunar electrical conductivity model are shown as functions of frequency and angular distance from the cavity axis for parallel and perpendicular field directions. Transfer functions based on asymmetric theory are significantly different from those based on symmetric approximations. Conductivity profiles from inversions of a given data set are strongly dependent on the theory incorporated in the inversions, the nature of the driving field, and the assumed location of the observer. Thus lunar conductivity models from surface and orbital magnetometer data, obtained either on the dayside or the nightside of the moon, must be determined using asymmetric theory.

Schwartz, K.↗
NASA NTRS1977

Implications of Navier-Stokes turbulence theory for plasma turbulence

Plasma turbulence is considered within the framework of the Navier-Stokes turbulence theory. Two-dimensional turbulence is discussed, noting inverse cascades, and compared to three-dimensional turbulence. MHD turbulence is described with reference to applications of the Navier-Stokes theory and the possibility of inverse magnetic cascades. Turbulence in Vlasov plasmas is outlined on the basis of the direct interaction approximation developed for Navier-Stokes fluids (Kraichnan, 1958-1959).

Montgomery, D.↗
NASA NTRS1978

A new boundary-layer interaction techniques for separated flows

A new viscous-inviscid interation procedure is presented which is applicable to separated flows. The new procedure is simple, converges rapidly, and does not require numerical smoothing and underrelaxation at least in the cases computer thus far. Calculations are presented for the low-speed separated flow in the juncture region between an axisymmetric body and ting. The viscous computation is done with an inverse boundary-layer procedure which was previously developed. The inviscid computation is made with an axisymmetric transonic code called RAXBOD. The main advantage of the new interaction procedure is that it combines an inverse boundary-layer technique, which is applicable to separated flows, with an existing inviscid analysis code with only a slight boundary condition change required in the inviscid code.

Carter, J. E.↗
NASA NTRS1979

Nonlinear wave choked inlets

The quasi-one dimensional flow program was modified in two ways. The Runge-Kutta subroutine was replaced with a subroutine which used a modified divided difference form of the Adams Pece method and the matrix inversion routine was replaced with a pseudo inverse routine. Calculations were run using both the original and modified programs. Comparison of the calculations showed that the original Runge-Kutta routine could not detect singularity near the throat and was integrating across it. The modified version was able to detect the singularity and therefore gave more valid calculations.

Source record↗
NASA NTRS1978

Correlations of catalytic combustor performance parameters

A 12-cm-diameter catalytic combustor test rig using propane fuel at an inlet temperature of 800 K, a pressure of 300,000 Pa, and reference velocities from 10 to 20 m/s was studied. Combustion efficiency at the test conditions is a function of the catalyst bed cell density, cell circumference, reactor length, and the reference velocity; the efficiency was also dependent on the adiabatic reaction temperature to the tenth power. The percentage pressure drop is proportional to the reference velocity to the 1.5 power and is also proportional to the reactor length and inversely proportional to the cell hydraulic diameter, fractional open area, and the pressure. The minimum adiabatic reaction temperature required to meet the emissions goals is proportional to the reference velocity to the 0.1 power and inversely proportional to the cell circumference, cell density, and reactor length to the 0.1 power. The parameters which are a function of a catalyst factor are reported.

Bulzan, D. L.↗
NASA NTRS1978

Remote sensing of environmental particulate pollutants - Optical methods for determinations of size distribution and complex refractive index

A unifying approach, based on a generalization of Pearson's differential equation of statistical theory, is proposed for both the representation of particulate size distribution and the interpretation of radiometric measurements in terms of this parameter. A single-parameter gamma-type distribution is introduced, and it is shown that inversion can only provide the dimensionless parameter, r/ab (where r = particle radius, a = effective radius, b = effective variance), at least when the distribution vanishes at both ends. The basic inversion problem in reconstructing the particle size distribution is analyzed, and the existing methods are reviewed (with emphasis on their capabilities) and classified. A two-step strategy is proposed for simultaneously determining the complex refractive index and reconstructing the size distribution of atmospheric particulates.

Fymat, A. L.↗
NASA NTRS1978

Procedures utilized for obtaining direct and remote atmospheric carbon monoxide measurements over the lower Lake Michigan Basin in August of 1976

In order to establish the applicability of a gas filter correlation radiometer, GFCR, to remote carbon monoxide, CO, measurements on a regional and worldwide basis, Old Dominion University has been engaged in the development of accurate and cost effective techniques for inversion of GFCR CO data and in the development of an independent gas chromatographic technique for measuring CO. This independent method is used to verify the results and the associated inversion method obtained from the GFCR. A description of both methods (direct and remote) will be presented. Data obtained by both techniques during a flight test over the lower Lake Michigan Basin in August of 1976 will also be discussed.

Casas, J. C.↗
NASA NTRS1978

Simulation gravity modeling to spacecraft-tracking data - Analysis and application

It is proposed that line-of-sight gravity measurements derived from spacecraft-tracking data can be used for quantitative subsurface density modeling by suitable orbit simulation procedures. Such an approach avoids complex dynamic reductions and is analogous to the modeling of conventional surface gravity data. This procedure utilizes the vector calculations of a given gravity model in a simplified trajectory integration program that simulates the line-of-sight gravity. Solutions from an orbit simulation inversion and a dynamic inversion on Doppler observables compare well (within 1% in mass and size), and the error sources in the simulation approximation are shown to be quite small. An application of this technique is made to lunar crater gravity anomalies by simulating the complete Bouguer correction to several large young lunar craters. It is shown that the craters all have negative Bouguer anomalies.

Phillips, R. J.↗
NASA NTRS1979

Scattering of emitted radiation from inhomogeneous and nonisothermal layers

A parametric study is performed for the exiting monochromatic intensities scattered from finite plane-parallel inhomogeneous layers that are driven solely by a distribution of thermal sources. Intensities are obtained by invariantly imbedding the standard and thermal scattering functions. The single-scattering albedo and the Henyey-Greenstein phase-function parameter are varied independently, and both linear and exponential profiles are considered. Linear temperature profiles are used, including temperature inversions. The resulting intensities, as a function of the direction cosine of propagation, are discussed from a remote-sensing point of view. For an isothermal and homogeneous medium, the gross characteristics of the exiting intensity, represented by its overall slope, mean value (magnitude), and an interior maximum value, can be related to the total optical depth, single-scattering albedo, and phase function, respectively. For a homogeneous medium, linearly decreasing (in the line of sight) temperature profiles tend to obscure the phase-function information and decrease the apparent optical depth. On the other hand, linearly increasing temperature profiles tend to retain phase-function information and increase the apparent optical depth. Temperature inversion profiles give intensities very similar to those for purely linear profiles.

Bergstrom, R. W.↗
NASA NTRS1979

Stratospheric sounding by infrared heterodyne spectroscopy

Intensity profiles of infrared spectral lines of stratospheric constituents can be fully resolved with a heterodyne spectrometer of sufficiently high resolution (approximately 5 MHz = 0.000167 kaysers at 10 microns). The constituents' vertical distributions can then be evaluated accurately by analytic inversion of the measured line profiles. Estimates of the detection sensitivity of a heterodyne receiver are given in terms of minimum detectable volume mixing ratios of stratospheric constituents, indicating a large number of minor constituents which can be studied. Stratospheric spectral line shapes and the resolution required to measure them are discussed in light of calculated synthetic line profiles for some stratospheric molecules in a model atmosphere. The inversion technique for evaluation of gas concentration profiles is briefly described, and applications to synthetic lines of O3, CO2, CH4, and N2O are given. Some recent heterodyne measurements of CO2 and O3 absorption lines are analytically inverted, and the vertical distributions of the two gases are determined.

Abbas, M. M.↗