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At least 433 records · Page 24

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NASA NTRS1975

Effect of compressibility on the nonlinear prediction of the aerodynamic loads on lifting surfaces

The vortex-lattice technique for incompressible flow which accounts for separation at sharp edges is modified to account for compressibility. This is accomplished by extending the Prandtl-Glauert transformation to moderate angles of attack. Thus, the aerodynamic characteristics for the compressible case are obtained from the solution of an equivalent incompressible problem. Numerical results are presented for parallelogram and delta wings to assess the effects of compressibility. The results are in good agreement with available experimental data.

Kandil, O. A.↗

NASA NTRS1975

Rheological properties of nondilute suspensions of deformable particles

The creeping flow equations have been solved to account for effects of shear on drop shape when the influence of neighboring drops is considered. A cell model is used to account for finite concentrations of the dispersed phase. From these results a constitutive equation is derived and implications for several flows are discussed. The shape and orientation of drops are computed and compared with existing data. Finally, dynamic viscosity and rigidity are obtained for nondilute suspensions of viscoelastic particles in an oscillatory shear flow.-

Choi, S. J.↗

NASA NTRS1975

Jupiter revisited - First results from the University of Chicago charged particle experiment on Pioneer 11

The data obtained by Pioneer 11 confirmed results from Pioneer 10 and provided new information for an understanding of the physics of the Jovian magnetosphere. Attention is given to the significance of Pioneer 11 data in relation to two fundamentally different models which have been proposed to account for the variations in the electron flux observed in Jupiter's outer magnetosphere. Proton flux characteristics are considered, taking into account the intensity profiles of energetic particles trapped in the dipole region of Jupiter's magnetic field.

Simpson, J. A.↗

NASA NTRS1975

Heavy element affinities in Apollo 17 samples

Pb-204, Bi, Tl, and Zn in samples from the Apollo 17 site exhibit relationships not found in samples from other sites. Pb-204, Tl, and Zn in residues remaining after dilute acid leaching are correlated with one another. Orange soil 74220, which is enriched in Pb-204, Tl, and Zn, is included in these relationships. In addition, the submicron metallic phase generally associated with agglutinate formation is correlated with all three of these elements; this relationship has already been reported for Pb-204 in other samples. Thus, orange soil and agglutinates appear to be involved in concentrating heavy volatile metals. A process other than mixing is required to account for this. As a consequence of the isolation of the landing site by the surrounding massifs, local supply and recycling of volatile trace elements in soils may account for some of the interelement relations.

Allen, R. O., Jr.↗

NASA NTRS1975

Conservation: Toward firmer ground

The following aspects of energy conservation were reviewed in order to place the problems in proper perspective: history and goals, conservation accounting-criteria, and a method to overcome obstacles. The effect of changing prices and available supplies of energy sources and their causes on consumption levels during the last few decades were described. Some examples of attainable conservation goals were listed and justified. A number of specific criteria applicable to conservation accounting were given. Finally, a discussion was presented to relate together the following aspects of energy conservation: widespread impact, involvement of government, industry, politics, moral and ethical aspects, urgency and time element.

Source record↗

NASA NTRS1975

Computation of output feedback gains for linear stochastic systems using the Zangnill-Powell Method

Because conventional optimal linear regulator theory results in a controller which requires the capability of measuring and/or estimating the entire state vector, it is of interest to consider procedures for computing controls which are restricted to be linear feedback functions of a lower dimensional output vector and which take into account the presence of measurement noise and process uncertainty. To this effect a stochastic linear model has been developed that accounts for process parameter and initial uncertainty, measurement noise, and a restricted number of measurable outputs. Optimization with respect to the corresponding output feedback gains was then performed for both finite and infinite time performance indices without gradient computation by using Zangwill's modification of a procedure originally proposed by Powell. Results using a seventh order process show the proposed procedures to be very effective.

Kaufman, H.↗

NASA NTRS1976

Approximate method for calculating transonic flow about lifting wing-body configurations

The three-dimensional problem of transonic flow about lifting wing-body configurations is reduced to a two-variable computational problem with the method of matched asymptotic expansions. The computational problem is solved with the method of relaxation. The method accounts for leading-edge separation, the presence of shock waves, and the presence of solid, slotted, or porous tunnel walls. The Mach number range of the method extends from zero to the supersonic value at which the wing leading edge becomes sonic. A modified form of the transonic area rule which accounts for the effect of lift is developed. This effect is explained from simple physical considerations.

Barnwell, R. W.↗

NASA NTRS1975

Conservation: Toward firmer ground

The following aspects of energy conservation were discussed: conservation history and goals, conservation modes, conservation accounting-criteria, and a method to overcome obstacles. The conservation modes tested fall into one of the following categories: reduced energy consumption, increased efficiency of energy utilization, or substitution of one or more forms of energy for another which is in shorter supply or in some sense thought to be of more value. The conservation accounting criteria include net energy reduction, economic, and technical criteria. A method to overcome obstacles includes (approaches such as: direct personal impact (life style, income, security, aspiration), an element of crisis, large scale involvement of environmental, safety, and health issues, connections to big government, big business, big politics, involvement of known and speculative science and technology, appeal to moral and ethical standards, the transient nature of opportunities to correct the system.

Source record↗

NASA NTRS1976

Partition function corrections

The vibration-rotation interaction coupling in diatomic molecules is analyzed and first-order expressions for the energy levels are deduced. Corrections to the partition function to account for this coupling are derived. The effects of long-range intermolecular forces due to induced dipole-induced dipole interactions, dipole-induced dipole interactions, charge-dipole interactions, and charge-charge interactions are considered. London's quantized oscillator model of the induced dipole-induced dipole interaction is developed. The partition function including effects of such dispersion forces is derived and is shown to lead to the virial equation of state. For a model combining the hard sphere and long-range attractive type potentials, this is found to lead to the van der Waals equation of state. The equation of state near the critical point is presented in reduced form (thermodynamic variables expressed in units of critical point values). Finally, approximate corrections to the electronic partition functions are derived to account for perturbations of excited electronic states induced by neighboring neutral particles, heavy ions, and fast electron collisions.

Source record↗

NASA NTRS1976

Arrangement of vortex lattices

A new method is developed for solving the lifting-surface equation for thin wings. The solution requires the downwash equation to be in the form of Cauchy integrals which can be interpreted as a vortex lattice with the positions of the vortices and control points dictated by the finite sum used to approximate the integrals involved. Lan's continuous loading method is employed for the chordwise integral since it properly accounts for the leading-edge singularity, Cauchy singularity, and Kutta condition. Unlike Lan, the spanwise loading is also continuous and the Cauchy singularity in the spanwise integral is also properly accounted for by using the midpoint trapezoidal rule and the theory of Chebyshev polynomials. This technique yields the exact classical solution to Prandtl's lifting-line equation.The solution to the lifting-surface equation for rectangular wings was found to compare well with other continuous loading methods, but with much smaller computational times, and to converge faster than other vortex lattice methods.

Dejarnette, F. R.↗

NASA NTRS1976

Reduced state feedback gain computation

Because application of conventional optimal linear regulator theory to flight controller design requires the capability of measuring and/or estimating the entire state vector, it is of interest to consider procedures for computing controls which are restricted to be linear feedback functions of a lower dimensional output vector and which take into account the presence of measurement noise and process uncertainty. Therefore, a stochastic linear model that was developed is presented which accounts for aircraft parameter and initial uncertainty, measurement noise, turbulence, pilot command and a restricted number of measurable outputs. Optimization with respect to the corresponding output feedback gains was performed for both finite and infinite time performance indices without gradient computation by using Zangwill's modification of a procedure originally proposed by Powell. Results using a seventh order process show the proposed procedures to be very effective.

Kaufman, H.↗

NASA NTRS1975

Numeric calculation of unsteady forces over thin pointed wings in sonic flow

A fast and reasonably accurate numerical procedure is proposed for the solution of a simplified unsteady transonic equation. The approach described takes into account many of the effects of the steady flow field. The resulting accuracy is within a few per cent and can be carried out on a computer in less than one minute per case (one frequency and one mode of oscillation). The problem concerns a rigid pointed wing which performs harmonic pitching oscillations of small amplitude in a steady uniform transonic flow. Wake influence is ignored and shocks must be weak. It is shown that the method is more flexible than the transonic box method proposed by Rodemich and Andrew (1965) in that it can easily account for variable local Mach number and rather arbitrary planform so long as the basic assumptions are fulfilled.

Kimble, K. R.↗

NASA NTRS1975

Mascons - A two-body solution

It is demonstrated that the mascon gravity anomalies are not produced simply by the occurrence of a superisostatic fill in mare basins. The fill alone is too thin to account for the large positive anomalies observed. The mascon anomaly can be explained if it is assumed that the mass excess occurs in two bodies rather than in a single body. The structure model discussed accounts for the gravity field so far observed at several heights over the central part of Mare Serenitatis.

Bowin, C.↗

NASA NTRS1975

Periodic variations in stratospheric-mesospheric temperature from 20-65 km at 80 N to 30 S

Results on large-scale periodic variations of the stratospheric-mesospheric temperature field based on Meteorological Rocket Network (MRN) measurements are reported for a long-term (12-year) mean, the quasi-biennial oscillation (QBO), and the first three harmonics of the annual wave (annual wave, semi-annual wave, and terannual wave or 4-month variation). Station-to-station comparisons are tabulated and charted for amplitude and phase of periodic variations in the temperature field. Masking and biasing factors, such as diurnal tides, solar radiation variations, mean monthly variations, instrument lag, aerodynamic heating, are singled out for attention. Models of the stratosphere will have to account for these oscillations of different periods in the thermal field and related properties of the wind fields, with multilayered horizontal stratification with height taken into account.-

Nastrom, G. D.↗

NASA NTRS1976

Perception of static orientation in a constant gravitoinertial environment

The illusions associated with the perception of static tilt in various specific force environments have been reviewed and then classified in such a way that a simple perceptual model could be developed to account for the experimental data. The fundamental conclusion to be drawn from this model is that these illusions can be accounted for by a simple nonlinear transformation of the information primarily from the saccule.

Ormsby, C. C.↗

NASA NTRS1976

The solar XUV spectrum of He II

OSO-7 observations of the first five Lyman lines and the Lyman continuum of He II are given for the quiet sun, a coronal hole, prominences, filaments, and the flare of August 7, 1972. These data are calibrated and given in specific intensity units together with color and brightness temperatures for the He II continuum. It is found that He II is overionized in all features except the flare and that the continuum is formed at temperatures near 14,000 K. The He II-He III ionization equilibrium appears to be dominated by photoionizations and radiative recombinations. Schematic calculations for realistic chromosphere and transition-region models can account for the observed intensities of Ly-beta through Ly-epsilon, the Lyman continuum, and its color temperature. To account for the intensity of Ly-alpha, either an implausible 100-km plateau at temperatures near 80,000 K is needed or, more likely, the diffusion-enhanced collisional excitation should be incorporated into the models.

Linsky, J. L.↗

NASA NTRS1975

The radio spectrum of Vela supernova and its implication on the propagation of cosmic rays from sources

A detailed analysis of the radio spectrum of the Vela supernova remnant has been carried out to show that the positive spectral shape below 80 MHz can be understood on the basis of Razin effect. This result requires most of the gas in the remnant to be stratified into high density clumps with intense magnetic fields and large cosmic ray densities. The free-free emission is found to be partly responsible for the observed flat radio spectrum. In order to account for both the gamma ray flux above 100 MeV and the radio spectrum, the equipartition between the cosmic ray density and magnetic field seems to break down. The total cosmic ray energy residing in the supernova is found to be about ten to the forty-ninth ergs, which is much smaller than the value obtained without taking into account the stratification of gas.

Stephens, S. A.↗

NASA NTRS1976

Effective defect density for MOS breakdown - Dependence on oxide thickness

A new procedure for measuring effective defect density takes time-dependent primary dielectric breakdown in MOS devices into account. A time-varying breakdown probability is obtained by applying a constant field stress to a statistically sufficient number of MOS capacitors. Effective defects are assumed distributed randomly in two dimensions, hence indistinguishable. The effective defect density is found to vary with oxide thickness; tentative explanations are ventured to account for this (interfacial tensile stress, ion patching enhanced by local trapping, breakdown in the form of filamentary discharges with release of stored electrostatic energy).

Li, S. P.↗