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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Effect of crosslinking density on biaxial relaxation of SBR by using reduced variables

The use of reduced variables to account for the effect of crosslinking density in a styrene-butadiene rubber (SBR) system is demonstrated for general biaxial stress states. Recently published results from stress relaxation tests on five SBR vulcanizates crosslinked to different degrees by tetramethylthiuram disulfide were superposed by using the crosslinking density as a reduction variable. The equilibrium shear modulus calculated from the master relaxation curve at long reduced times was in satisfactory agreement with other results for SBR. The time-axis shifts were related in a linear logarithmic manner to the crosslinking density but had a slope slightly less than values previously reported for elastomer systems.

Arenz, R. J.↗
NASA NTRS1975

Thresholds for the perception of angular acceleration as indicated by the oculogyral illusion

A motorized chair (with precise servo controls) accelerated the observer in a clockwise (CW) or counterclockwise (CCW) direction at rates that ranged in logarithmic progression from 0.02 to 6.00 deg/sq sec. The target, a narrow collimated line of light, was contained within a goggle device worn by the observer and therefore fixed in relative position to him. The illusion, appearing as rightward or leftward movement of the visual target in the direction of acceleration, was determined by a double staircase procedure among 300 normal and 4 labyrinthine-defective observers. None of the latter perceived the illusion. The majority of normal observers revealed no substantial directional difference (CW vs. CCW threshold). Threshold frequency distributions ranged in rate (deg/sq sec) from 0.020 to 0.950; the threshold of response in more than half the normal observers was less than 0.10, in over three-fourths was less than 0.20, in over 90% less than 0.30, and 100% less than 1.00.

Miller, E. F., II↗
NASA NTRS1974

Relation of solar wind fluctuations to differential flow between protons and alphas

An analysis is made of the difference between the alpha particle and proton flow velocities in the solar wind as observed by the OGO 5 satellite. The alpha and proton velocities from each of 962 spectral scans are compared with the variance of 32 solar wind flux measurements made during the scans. The average velocity difference is plotted for each of 10 logarithmic variance intervals and is seen to decrease and approach zero when the variance is high. It is shown that such an anticorrelation may be due to the fact the wave/particle interactions provide the drag force between two streams of different velocity in a collisionless plasma.

Neugebauer, M.↗
NASA NTRS1975

Variation in the number of meteoroid impacts on the moon with lunar phase

Data obtained with the Apollo 12 and 14 long-period seismometers in the period between December 1969 and January 1973 are used to determine the direction of approach and mass-distribution statistics of meteoroids in near-earth space. The total number of detected meteoroid impacts in this period is analyzed as a function of lunar phase with allowance for seismometer sensitivity and characteristics of lunar seismic-wave propagation. A logarithmic relation is derived which describes the mass-distribution statistics. It is concluded that most orbits for meteoroids with a mass in excess of 5 kg lie near the plane of the ecliptic with aphelia between 2 and 5 AU.

Dainty, A. M.↗
NASA NTRS1975

Shock tube measurements of specific reaction rates in the branched chain CH4-CO-O2 system

Growth constants, obtained by measuring the blue CO flame band emission behind incident shock waves, were obtained for two elementary bimolecular reactions involved in the oxidation of methane. Gas mixtures containing small amounts of CH4 with varying amounts of CO, O2, and in one case CO2, diluted with argon, were investigated, and exponential growth constants were derived from plots of the logarithm of observed light intensity versus gas time. The rate constant for the reaction O + CH4 yields CH3 + OH was found to be 1.9 times 10 to the 14th exp(-5900/T) cu cm per mole per sec in the range 1300-2000 K; for the reaction CH3 + O2 yields CH3O + O, the rate constant was determined to be 2.4 times 10 to the 13th exp(-14,500/T) cu cm per mole per sec in the range 1200 to 1900 K.

Brabbs, T. A.↗
NASA NTRS1977

Vacuum-ultraviolet reflectometer

Baffle, three-blade chopper, and split spherical mirror transmit alternating dual beam into integrating sphere. Alternating reference and sample beams are detected by high gain photomultiplier and modified logarithmic ratiometer. Device is useful in fusion research, high power laser work, and spectrometer or monochromator construction.

Allen, T. H.↗
NASA NTRS1975

Rough-to-smooth transition of an equilibrium neutral constant stress layer

Purpose of research on rough-to-smooth transition of an equilibrium neutral constant stress layer is to develop a model for low-level atmospheric flow over terrains of abruptly changing roughness, such as those occurring near the windward end of a landing strip, and to use the model to derive functions which define the extent of the region affected by the roughness change and allow adequate prediction of wind and shear stress profiles at all points within the region. A model consisting of two bounding logarithmic layers and an intermediate velocity defect layer is assumed, and dimensionless velocity and stress distribution functions which meet all boundary and matching conditions are hypothesized. The functions are used in an asymptotic form of the equation of motion to derive a relation which governs the growth of the internal boundary layer. The growth relation is used to predict variation of surface shear stress.

Logan, E., Jr.↗
NASA NTRS1975

Simulator studies and psychophysical ride comfort models

An elementary psychophysical model to predict ride comfort was developed using flight and simulator data where subjects were exposed to six degrees of freedom. The model presumes that the comfort response is proportional to the logarithm of the stimulus above some threshold stimulus. In order to verify this concept of comfort modeling, it was necessary to obtain ride comfort data for single degree of freedom random motions and for combinations of random motions. Accordingly, a simulator program was performed at the NASA Langley Research Center to measure subjective comfort response ratings using one degree of freedom, two degrees of freedom, three degrees of freedom, and six degrees of freedom. An analysis of the single degree of freedom and two degrees of freedom data is presented. Preliminary models of ride comfort response for single degree of freedom random motions and for certain combinations of two degrees of freedom random motions were developed.

Stone, R. W., Jr.↗
NASA NTRS1976

A simplified application of the method of operators to the calculation disturbed motions of an airplane

A simplified treatment of the application of Heaviside's operational methods to problems of airplane dynamics is given. Certain graphical methods and logarithmic formulas that lessen the amount of computation involved are explained. The problem of representing a gust disturbance or control manipulation is taken up and it is pointed out that in certain cases arbitrary control manipulations may be dealt with as though they imposed specific constraints on the airplane, thus avoiding the necessity of any integration whatever.

Jones, R. T.↗
NASA NTRS1976

Extended Conformal Mappings for Supersonic Aircraft Calculations

A gasdynamical analysis is presented for a three-dimensional, supersonic, inviscid, steady, shockless flow past an arbitrary airframe, using computational grids. The analysis, which includes special treatments for body points and bow-shock points, relies on the equations of motion written in terms of logarithm of pressure entropy and two angles reprising the velocity vector. A FORTRAN code was employed (sample geometry is shown). The flow analysis is considered reliable for aircraft cross-sections that are elliptical in shape.

Moretti, G.↗
NASA NTRS1975

Gravity shear waves atop the cirrus layer of intense convective storms

Recent visual satellite photographs of certain intense convective storms have revealed concentric wave patterns. A model for the generation and growth of these waves is proposed. The proposed initial generating mechanism is similar to the effect noticed when a pebble is dropped into a calm pond. The penetration of the tropopause by overshooting convection is analogous to the pebble's penetration of the water's surface. The model for wave growth involves instability due to the wind shear resulting from the cirrus outflow. This model is based on an equation for the waves' phase speed which is similar to the Helmholtz equation. It, however, does not assume an incompressible atmosphere, but rather assumes density is a logarithmic function of height. Finally, the model is evaluated on the two mid-latitude and three tropical cases. The data indicate that shearing instability may be a significant factor in the appearance of these waves.

Stobie, J. G.↗
NASA NTRS1976

An analog technique for the measurement of damping from transient decay signals

A tracking filter that includes an output that is logarithmically proportional to the amplitude of the filtered signal is used to measure the damping exponent of a transient decay. This method is analogous to the digital technique referred to as the moving-block or peak-plot method. The method is simple to use and quite accurate, avoids the numerical computations associated with similar digital techniques, but is constrained by the poor time-domain response characteristics of commercial tracking filters presently available.

Bousman, W. G.↗
NASA NTRS1976

Perturbation theory in thermosphere dynamics

It is shown that density and pressure throughout the thermosphere can be adequately described in a logarithmic expansion that provides a sound basis for the application of perturbation theory. This expansion eliminates most of the important nonlinearities associated with density variations. On the basis of this expansion, the validity of perturbation theory can be extended to cover a large variety of atmospheric conditions in which the relative temperature amplitude is less than 0.5 and wind velocities are significantly less than the speed of sound.

Mayr, H. G.↗
NASA NTRS1976

On the relation of J sub I to work done per unit uncracked area - Total, or component 'due to crack'

The J sub I relation, introduced by Rice (1968), expresses the work done on a quasiplanar specimen of specified width (or depth) for a fixed uniform crack length when the displacement of the load is increased from zero to some given value. The relation remains the same if the work done and its logarithmic derivative are calculated in terms of the component of the displacement that is 'due to the crack' rather than the total displacement. J sub I is studied as a function of displacement for a precracked, three-point-loaded bend specimen and also in the extremes of linear-elastic, and rigid/perfectly plastic behavior.

Srawley, J. E.↗
NASA NTRS1976

Resonance-line transfer with partial redistribution. VIII - Solution in the comoving frame for moving atmospheres

The effects of partial frequency redistribution in the scattering process for lines formed in moving atmospheres are analyzed using a general method that allows the transfer equation to be solved in the comoving frame of the gas. The same chromospheric and atomic model studied by Cannon and Vardavas (1974) is employed in the calculations, but a depth scale with logarithmically spaced points is adopted. It is found that in both static and moving atmospheres, the profiles obtained with complete and partial frequency redistribution are virtually identical. The large differences in profiles obtained by Cannon and Vardavas when they used complete and partial redistribution are shown to be spurious (and physically unreal) effects resulting from angle averaging in the observer's frame instead of the comoving frame.

Mihalas, D.↗
NASA NTRS1976

Optical computing with laser light

Linear and nonlinear optical processing techniques (Fourier transformation, convolution and correlation, arithmetic operations - addition and subtraction with gratings, generalized orthogonal transformations; theta modulation, half-tone screen process, optical feedback) for mathematical computations are reviewed. The use of gratings and computer holograms in addition, subtraction, differentiation, and application of generalized transformations is discussed. Use of nonlinear optical elements with or without optical coherent feedback in such nonlinear operations as taking logarithms and thresholding is described. Applications in hybrid systems incorporating digital computer and optical processor with real-time interface devices, or optical threshold and logic devices for parallel processing to apply digital techniques to optical information are considered.

Lee, S. H.↗
NASA NTRS1976

Analysis of neutrally stable atmospheric flow over a two-dimensional forward facing step

A mathematical model describing ground-wind induced flow fields around surface obstructions such as buildings, bridges or other man-made structures is presented. The Navier-Stokes equations with a two-equation turbulence model are used to analyze the flow over a two-dimensional forward facing step. A study of the assumed logarithmic approach velocity profile shows that an increase of surface roughness produces a rise to higher turbulence levels in the shear layer originating from the step corner. This rise leads to higher Reynolds stress and to faster reattachment of the separated flow.

Bitte, J.↗
NASA NTRS1976

Atmospheric flow over two-dimensional bluff surface obstructions

The phenomenon of atmospheric flow over a two-dimensional surface obstruction, such as a building (modeled as a rectangular block, a fence or a forward-facing step), is analyzed by three methods: (1) an inviscid free streamline approach, (2) a turbulent boundary layer approach using an eddy viscosity turbulence model and a horizontal pressure gradient determined by the inviscid model, and (3) an approach using the full Navier-Stokes equations with three turbulence models; i.e., an eddy viscosity model, a turbulence kinetic-energy model and a two-equation model with an additional transport equation for the turbulence length scale. A comparison of the performance of the different turbulence models is given, indicating that only the two-equation model adequately accounts for the convective character of turbulence. Turbulence flow property predictions obtained from the turbulence kinetic-energy model with prescribed length scale are only insignificantly better than those obtained from the eddy viscosity model. A parametric study includes the effects of the variation of the characteristics parameters of the assumed logarithmic approach velocity profile. For the case of the forward-facing step, it is shown that in the downstream flow region an increase of the surface roughness gives rise to higher turbulence levels in the shear layer originating from the step corner.

Bitte, J.↗