Search NASA⌕ Search

SEARCH · Search NASA

Results for “rotation”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Rotation of dwarf star chromospheres in the ultraviolet

Periodic variations in the ultraviolet fluxes of chromospheric emission line multiplets are investigated for F, G and K stars as evidence of rotational modulation. Vacuum ultraviolet spectra were obtained with the IUE spacecraft for six stars as many as 11 times over the period April 23 to December 3, 1980. Variations in the emission fluxes of the hydrogen Lyman-alpha, Si II and Mg II lines are observed with periods up to 47 days. The periodicity, which is identified with rotational modulation, is found to persist over many rotational cycles, although the periods and time dependences of the fluxes from the different ionic species are not identical, probably due to differential rotation and global distributions. The spread of the UV periods is observed to be within 10%, with one or two peaks per cycle and a ratio of modulated to umodulated flux ranging from 1.1 to 3.0, analogous to solar behavior.

Hallam, K. L.↗
NASA NTRS1953

Preliminary Results of Heat Transfer from a Stationary and Rotating Ellipsoidal Spinner

Convective heat-transfer coefficients in dry air were obtained for an ellipsoidal spinner of 30-inch maximum diameter for both stationary and rotating operation over a range of conditions including airspeeds up to 275 miles per hour, rotational speeds up to 1200 rpm, and angles of attack of zero and 40 The results are presented in terms of Nusselt numbers, Reynolds numbers, and convective heat-transfer coefficients. The studies included both uniform heating densities over the spinner and uniform surface temperatures.. In general, the results showed that rotation will increase the convective heat transfer from a spinner, especially in the turbulent-flow regions. Rotation of the spinner at 1200 rpm and at a free-stream velocity of 275 miles per hour increased the Nusselt number parameter in the turbulent-flow region by 32 percent over that obtained with a stationary spinner; whereas in the nose region, where the flow was laminar, an increase of only 18 percent was observed. Transition from laminar to turbulent flow occurred over a large range of Reynolds numbers primarily because of surface roughness of the spinner. Operation at an angle of attack of 40 had only small effects on the local convective heat transfer for the model studied.

vonGlahn, U.↗
NASA NTRS1981

Faraday rotation measurement method and apparatus

A method and device for measuring Faraday rotation of a received RF signal is described. A simultaneous orthogonal polarization receiver compensates for a 3 db loss due to splitting of a received signal into left circular and right circular polarization channels. The compensation is achieved by RF and modulation arraying utilizing a specific receiver array which also detects and measures Faraday rotation in the presence or absence of spin stabilization effects on a linear polarization vector. Either up-link or down-link measurement of Faraday rotation is possible. Specifically, the Faraday measurement apparatus utilized in conjunction with the specific receiver array provides a means for comparing the phase of a reference signal in the receiver array to the phase of a tracking loop signal related to the incoming signal, and comparing the phase of the reference signal to the phase of the tracking signal shifted in phase by 90 degrees. The averaged and unaveraged signals, are compared, the phase changes between the two signals being related to Faraday rotation.

Brockman, M. H.↗
NASA NTRS1981

Development of rotation sample designs for the estimation of crop acreages

The idea behind the use of rotation sample designs is that the variation of the crop acreage of a particular sample unit from year to year is usually less than the variation of crop acreage between units within a particular year. The estimation theory is based on an additive mixed analysis of variance model with years as fixed effects, (a sub t), and sample units as a variable factor. The rotation patterns are decided upon according to: (1) the number of sample units in the design each year; (2) the number of units retained in the following years; and (3) the number of years to complete the rotation pattern. Different analytic formulae for the variance of (a sub t) and the variance comparisons in using a complete survey of the rotation patterns.

Lycthuan-Lee, T. G.↗
NASA NTRS1982

Acoustically induced oscillation and rotation of a large drop in space

A 2.5 cm diameter water drop was successfully deployed and manipulated in a triaxial acoustic resonance chamber during a 240 sec low-gravity SPAR rocket flight. Oscillation and rotation were induced by modulating and phase shifting the signals to the speakers. Portions of the film record were digitized and analyzed. Spectral analysis brought out the n = 2, 3, 4 free oscillation modes of the drop, its very low-frequency center-of-mass motion in the acoustic potential well, and the forced oscillation frequency. The drop boundaries were least-square fitted to general ellipses, providing eccentricities of the distorted drop. The normalized equatorial area of the rotating drop was plotted vs a rotational parameter, and was in excellent agreement with values derived from the theory of equilibrium shapes of rotating liquid drops.

Jacobi, N.↗
NASA NTRS1982

The numerical analysis of the rotational theory for the formation of lunar globules

The morphology of lunar globules is studied through the application of a numerical analysis of their rotation in space during cooling. It is assumed that molten rock is shot from the surface of the moon, solidifies in space above the moon and then falls back to the surface. The rotational theory studied makes the following assumptions: the volume of the molten rock does not change during cooling; the angular momentum is conserved; there are no internal motions because of the high viscosity of the molten rock, i.e., in equilibrium the globule is rotating as a rigid body; finally, the kinetic reaction of the globule to the forces is fast relative to the rate of cooling, i.e., the globule reaches equilibrium at constant energy. These assumptions are subjected to numerical analysis yielding good agreement between the actual globule shapes and the numerical results, but leaving some doubt as to the validity of the rotational theory due to the failure to establish the existence of true local minima and an incomplete understanding of the thermokentics.

Ross, J.↗
NASA NTRS1982

The chromospheric rotation activity relation in late type close binary systems

The IUE data on 36 late type close binary stars are presented. It is shown that the chromospheric and TR line fluxes increase with decreasing stellar rotation period, though not as rapidly as does the X-ray flux. There is an increasing dependence upon rotation with increasing line temperature. The data are consistent with the hypothesis that there exists a critical rotation rate, which depends on temperature, below which the emission flux is independent of rotation and above which it increases linearly with increasing angular velocity omega.

Walter, F. M.↗
NASA NTRS1981

Earth rotation from lunar laser ranging

Since the time when the first laser retroreflector was placed on the lunar surface by the Apollo 11 astronauts, lunar laser ranging (LLR) has led to advances in a wide range of disciplines, including the study of variations in the rotation of the earth. The conventional techniques used to monitor earth rotation suffer from lack of precision on time scales of a few months and less. LLR, by contrast, makes it possible to monitor small changes in earth rotation with a temporal resolution of the order of 1 day. Studies of earth rotation by LLR are discussed, taking into account data sensitivity, aspects of data analysis, the variation of latitude, and UTO, the mean solar time at the site as affected by polar motion.

Langley, R. B.↗
NASA NTRS1982

Radiative lifetimes and quenching rate coefficients for directly excited rotational levels of OH/A 2Sigma +, v-prime = 0/

A narrow-bandwidth pulsed dye laser was used to excite OH X 2Pi i radicals to the A 2Sigma(+) state by pumping in the (0, 0) vibrational band around 308 nm. The radiative lifetimes of specific (K-prime, J-prime) rotational levels in v-prime = 0 were measured at low pressures (not greater than 1 mtorr), which yielded a mean lifetime of 0.71 + or - 0.009 microsec (2 sigma). Electronic quenching rate constants for N2, O2, H2O, and H2 were measured for a range of initially excited rotational levels. A strong dependence of this rate constant on the initially excited rotational level was found for N2, and less markedly for O2, with the rate constant tending to increase for the lowest rotational levels K-prime not greater than 3. The implications of these results for the laser-induced fluorescence detection of atmospheric OH are discussed.

Mcdermid, I. S.↗
NASA NTRS1982

The rotation of Uranus

The determination of the rotation rate of Uranus based on available observational evidence is discussed. Previous determinations of the rotation rate since the work of Lowell and Slipher (1912), which tended to converge on a period of 10.8 days until the mid 1970s, most likely due to mutual reinforcement between unreliable results, are reviewed. Recent independent determinations based on (1) the use of theoretical interior models together with observations of oblateness and the gravitational moment J2; (2) periodic brightness fluctuations; and (3) spectrographic measurements of Doppler shifts are then presented which yield a weighted mean value of 16.31 + or - 0.27 h for the rotational period of Uranus. It is noted that the detection of the motion of surface features across the disk by future high-resolution imaging and Voyager 2 observations may allow a direct determination of the rotational period of Uranus.

Goody, R. M.↗
NASA NTRS1982

The rotational spectra of HOCO/plus/, HOCN, HN3, and HNCO from quantum mechanical calculations

Ab initio molecular orbital theory has been used to determine the equilibrium geometries, rotational constants, and rotational spectra of four isoelectronic molecules. Two of these, HOCO(plus) and HOCN, are candidate interstellar molecules. The other two, HNCO and HN3, have known rotational constants. Theoretical rotational constants and spectra for the two unknown species were corrected with the mean experimental to theoretical ratios from the two known species. This procedure resulted in predicted frequencies of 83.75 plus or minus 0.2 GHz for the 4(04) to 3(03) transition in HOCN and 85.08 plus or minus 0.2 GHz for the same transition in HOCO(plus). These are the central lines of triplets whose other members are the 4(14) to 3(13) and 4(13) to 3(12) transitions. The triplet splittings were predicted to be 0.36 plus or minus 0.01 GHz for HOCN and 0.33 plus or minus 0.01 GHz for HOCO(plus). These results indicate that HOCO(plus) is a better candidate for the source of a series of lines reported by Thaddeus, Guelin, and Linke than is HOCN.

Defrees, D. J.↗
NASA NTRS1982

Axisymmetric collapse of rotating, isothermal clouds

The results of over 50 new models of the axisymmetric collapse of rotating, isothermal clouds are presented, with the following objectives: (1) to fully explore the initial conditions necessary for collapse from uniform density and uniform rotation, subject to constant volume and constant pressure boundary conditions; (2) to catalog the possible end states for cloud collapse from these initial conditions; and (3) to determine if there is a critical value of rotational energy/gravitational energy associated with ring formation, as appears to be the case for adiabatic clouds. Three end states are obtained: Bonnor-Ebert spheroids, rings and collapsing disks. The rings are formed with values of the ratio of rotational energy to the absolute value of the gravitational energy typically less than the Maclaurin spheroid value for dynamic instability to ring formation.

Boss, A. P.↗
NASA NTRS1982

The Mg II resonance line emission at 2800 A in stars with different rotational velocities and different metal abundances

In many investigations, a study of the Mg II 2800 A emission was conducted in order to derive more information about the correlation of chromospheric emission with the properties of the convection zone. It has been suggested by Ayres and Linsky (1980) that there is a positive correlation between rotation and chromospheric emission at least for binary stars. The present investigation is concerned with such a correlation between rotation and chromospheric emission. Since large differences in rotational velocities are observed for F stars for which also strong chromospheric emission is observable, this particular study deals mainly with F stars. On the basis of observations of the Mg II emission in F and G stars, it is found that the emission is abnormally strong in close binary F stars. This may be explained by the generation of a large differential rotation due to tidal effects which may give very efficient dynamo generation of a surface magnetic field.

Boehm-Vitense, E.↗
NASA NTRS1982

Bubble migration in a rotating, liquid-filled sphere

Results and analysis of ground-based experiments performed to aid in designing experiments on the behavior of bubbles in a rotating liquid body on board the Shuttle in free fall are presented. Spherical shells filled with silicone oil containing a small gas bubble were spun and filmed by high speed motion picture photography. The rotation of the shell and the trajectory of the bubble motion were recorded and the film was exposed to a motion analyzer connected to a keypunch. The analyzer measured Cartesian coordinates as well as angle, frame number, and rotation rate. Optical correction equations were employed to determine the apparent bubble trajectory relative to an inertial frame of reference. An analytical model for the bubble motion was defined, yielding predictions of velocity and position at different times. Rotation of the fluid container is concluded to aid in centering the bubbles.

Annamalai, P.↗
NASA NTRS1982

Rhomboid prism pair for rotating the plane of parallel light beams

An optical system is described for rotating the plane defined by a pair of parallel light beams. In one embodiment a single pair of rhomboid prisms have their respective input faces disposed to receive the respective input beams. Each prism is rotated about an axis of revolution coaxial with each of the respective input beams by means of a suitable motor and gear arrangement to cause the plane of the parallel output beams to be rotated relative to the plane of the input beams. In a second embodiment, two pairs of rhomboid prisms are provided. In a first angular orientation of the output beams, the prisms merely decrease the lateral displacement of the output beams in order to keep in the same plane as the input beams. In a second angular orientation of the prisms, the input faces of the second pair of prisms are brought into coincidence with the input beams for rotating the plane of the output beams by a substantial angle such as 90 deg.

Orloff, K. L.↗
NASA NTRS1983

A turbulence model for three dimensional turbulent shear flows over curved rotating bodies

There exists currently considerable interest in the development of numerical procedures for solving the equations governing three-dimensional fluid flows. In particular, improved calculations of viscous flows on rotating bodies such a turbomachinery rotors are of great importance. The present investigation is mainly concerned with the analysis of the effect of rotation on the dissipation rate equation and the Reynolds stress equations. Attention is given to governing equations and modelling, algebraic Reynolds stress equations, a procedure for implementing the turbulence closure scheme, results for a model representative of centrifugal turbomachinery, and results for axial turbomachinery. The proposed turbulence model is valid for three-dimensional, rotating, and curved flows. The model has all the essential physics of turbulence, mean flow, rotation, and the curvature.

Galmes, J. M.↗
NASA NTRS1983

Collisional rates for vibrational-rotational transitions in circumstellar SiO masers

Calculations for rotational population inversion in circumstellar SiO masers require collisional rates for vibrational-rotational transitions. This paper reports quantum mechanical, state-to-state collisional rate coefficients for pure rotational and vibrational-rotational transitions among the first three vibrational states of SiO. These are expressed in terms of simple two-parameter power-law fits accurate in the temperature range 1000-3000 K.

Bieniek, R. J.↗
NASA NTRS1983

Polar motion and earth rotation

New observational techniques and studies of relationships between observed polar motions and the earth rotation and geophysical phenomena developed in the period 1979-1982 are reviewed. The MERIT campaign was performed to characterize the accuracy of and operational procedures for Doppler satellite measurements, lunar laser ranging, laser ranging to the Lageos satellite, and the use of extragalactic radio sources for examining earth rotation and polar motion. Only the new U.S. Naval Observatory 26 in. aperture telescope with photographic zenith tubes will be operated from the former classical earth rotation ILS network. Earth orientation parameters are presently determined each week by NASA JPL using two single baseline VLBI 64 m radio telescopes of the Deep Space Network. Studies are also proceeding to relate fluctuations in the atmospheric angular momentum to changes in earth's rotational rate.

Tapley, B. D.↗