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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 289 records · Page 16
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NASA NTRS1981

Rotating blade vibration analysis using shells

Shallow shell theory and the Ritz method are employed to determine the frequencies and mode shapes of turbomachinery blades having both camber and twist, rotating with non-zero angles of attack. Frequencies obtained for different degrees of shallowness and thickness are compared with results available in the literature, obtained from finite element analyses of nonrotating blades. Frequencies are also determined for a rotating blade, showing the effects of changing the (1) angular velocity of rotation, (2) disk radius and (3) angle of attack, as well as the significance of the most important body force terms.

Leissa, A. W.↗
NASA NTRS1981

Periodic solutions about the collinear Lagrangian solution in the general problem of three bodies

The article describes the solutions near Lagrange's circular collinear configuration in the planar problem of three bodies with three finite masses. The article begins with a detailed review of the properties of Lagrange's collinear solution. Lagrange's quintic equation is derived and several expressions are given for the angular velocity of the rotating frame. The equations of motion are then linearized near the circular collinear solution, and the characteristic equation is also derived in detail. The different types of roots and their corresponding solutions are discussed. The special case of two equal outer masses receives special attention, as well as the special case of two small outer masses. Finally, the fundamental family of periodic solutions is extended by numerical integration all the way up to and past a binary collision orbit. The stability and the bifurcations of this family are briefly enumerated.

Broucke, R.↗
NASA NTRS1981

How fast can an asteroid spin

Many large asteroids are probably gravitationally bound 'rubble piles', which should approximate figures of hydrostatic equilibrium. The maximum angular velocity of such bodies is limited by formation of Jacobi ellipsoids or binary fission at about half the surface orbit frequency. The observed limiting rotation period of approximately 4 hr implies asteroidal densities of about 2-3 g/cu cm.

Weidenschilling, S. J.↗
NASA NTRS1981

Analytical techniques for the analysis of stall/spin flight test data

Analytical techniques for the analysis of stall/spin flight test data are reviewed by discussing (1) certain special flight instrumentation issues, (2) the mathematical modeling techniques, and (3) the analysis of post stall and spinning flight of general aviation airplanes. The angles of attack, sideslip, roll, pitch, and yaw are derived from measurements of angular velocity and linear acceleration. The key to the success of this approach is to simultaneously estimate both the biases in the instrumentation and the initial conditions. Techniques for determining stability derivatives from flight data are applied to angles of attack too high for stabilized flight. This practice greatly expands the range over which aerodynamic characteristics can be determined from flight test. Nonlinear terms in certain aerodynamic functions are shown to be valid by comparing them with the trends of results at different angles of attack. A very old technique of studying spins is extended and applied to some modern light airplanes. Airplanes for which the wing provides the dominant moments during spins, offer the possibility of linking spin characteristics to longitudinal data.

Taylor, L. W., Jr.↗
NASA NTRS1983

Flexible Coupling Corrects Shaft Misalinements

Proposed flexible coupling provides nearly error free measurements of shaft rotation in presence of misalinements between shaft and position sensing transducer. Intended to be used in situations in which input or output shaft is mounted on flexible joint. Its function is to insure equal input and output angular velocities by forcing input and output shafts to remain parallel.

Mayo, R. A.↗
NASA NTRS1982

Hydrogen two photon emission in the UV spectrum of type 2 supernovae

The continuum emission of Type 2 supernovae demonstrates an ultraviolet (UV) excess when fit by black body emission is attempted. The H two photon emission is advanced as an explanation of the UV excess. A function by which the UV spectra of two Type 2 supernovae (SN 1979c in NGC 4321 and SN 1980k in NGC 6946) are fitted with U,B,V photometric data is presented. The angular velocity of expansion of the supernovae envelope is derived. From this, the linear velocity of expansion and the distances of the parent galaxies are derived. A distance of 17.3 Mpc is obtained for NGC 4321, and a distance of 7.1 Mpc for NGC 6946.

Benvenuti, P.↗
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

Magnetic fields in late-type stars

Observations show that magnetic activity in late-type stars is correlated with rotation rates and that there is a discontinuous change in behavior at a critical rotation period. This can be explained as a consequence of a transition from convection in rolls parallel to the rotation axis to normal convection cells as the angular velocity is decreased.

Knobloch, E.↗
NASA NTRS1981

On rotational forces in the solar wind

Solar rotational forces affecting the flow of minor ions in the solar wind are considered as corotating with the sun. Cold, noninteracting charged particles in the magnetic and gravitational fields of the sun rotate with the angular velocity of the sun, and calculations of lowest bulk order velocities show that differences in particle velocities decrease with increasing distance from the sun. A centrifugal potential in the corotating frame implies that ion motion is independent of protons, with velocities determined by the potential, which monotonically decreases without limit. The potential dominates the initial kinetic energy of the particles, and the equality of velocities within the potential is not due to interactions between particles as claimed by Mackenzie et al. (1979).

Hollweg, J. V.↗
NASA NTRS1982

On the nature of particles in Saturn's spokes

It is noted that an observed deviation of the angular velocity of spoke features from the Keplerian value can yield the charge to mass (q/m) ratio of spoke particles. Observations in the literature of spoke motion are consistent with q/m in the neighborhood of -10 coul/kg. Since a lower limit on q is one electronic charge, this value yields a lower limit to the size of spoke particles of approximately 0.01 micron. The criteria for electrostatically ejecting small particles from larger parent bodies suggest an upper limit of approximately 1,000 m for the parent bodies. The stability of the grains to electrostatic disruption or field emission yields an upper limit of approximately 3 microns for the spoke particle size. It also leads to the conclusion that the spoke particles must consist of material that is stronger than loose dust balls.

Thomsen, M. F.↗
NASA NTRS1982

Utilization of normal mode initial conditions for detecting errors in the dynamics part of primitive equation global models

When a global atmospheric basic state has constant angular velocity and its temperature varies with altitude only, there exist normal mode solutions to the linearized global primitive equations. The use of these normal modes, which have known behavior in time, is superior to the use of the Rossby-Haurwitz wave as initial conditions for detecting errors in the dynamics part of primitive equation global models. With these initial conditions, integration through only one time step is sufficient to detect many formulation and coding errors. Other tests are still required for detecting problems of nonlinear instability and conservation of integral properties, however.

Chao, W. C.↗
NASA NTRS1982

Applications of parameter estimation in the study of spinning airplanes

Spinning airplanes offer challenges to estimating dynamic parameters because of the nonlinear nature of the dynamics. In this paper, parameter estimation techniques are applied to spin flight test data for estimating the error in measuring post-stall angles of attack, deriving Euler angles from angular velocity data, and estimating nonlinear aerodynamic characteristics. The value of the scale factor for post-stall angles of attack agrees closely with that obtained from special wind-tunnel tests. The independently derived Euler angles are seen to be valid in spite of steep pitch angles. Estimates of flight derived nonlinear aerodynamic parameters are evaluated in terms of the expected fit error.

W Taylor, L., Jr.↗
NASA NTRS1982

Scaling from Jupiter to pulsars and mass spectrum of pulsars

Following the principle of similitude, the energy loss of Jupiter was scaled through the acceleration of high energy particles to that of Crab pulsar. The agreement suggests a classification scheme for all pulsars in which the pulsar angular velocity and its decrease with time are related to the pulsar moment of inertia divided by its radius and its mass is determined according to neutron star models. The mass spectrum of 194 pulsars is found to be approximately 1/sq m.

Fan, C. Y.↗
NASA NTRS1982

The dynamical evolution of the Saturnian ring spokes

It is suggested that the radial spokes observed in rotation across Saturn's B ring are composed of fine, charged dust levitated off the surfaces of larger bodies by electrostatic forces when the latter are sporadically charged to high electrostatic potentials. The time evolution of a spoke is likened to the continuous unfolding of a fan whose vertex is at the synchronous orbit, and whose corotating edge is fixed in the radial direction. According to the present model, the angular velocity of the fan leading edge depends on the age of the spoke, and it is anticipated that the observed scatter of the measured velocities about the Kepler value is real, rather than due to measurement errors, despite their presence inside the expected error bars. It is also shown that the resettling of the grains of dust on the larger bodies in the ring plane, following their initial levitation, results in a differential transport of grains across the ring plane, establishing different multimodal size distributions of dust within the spokes at different planetocentric distances.

Hill, J. R.↗
NASA NTRS1981

A flare event in the peculiar giant FK Comae

Observations are presented of a very energetic flare event in the peculiar rapidly rotating star FK Comae. During this event on June 18th 1981 the usual asymmetrical double peaked H alpha emission feature with an equivalent width (EW) approx 3-4 A changed to a broad emission feature with EW approx 13 A. Sixteen spectra were obtained over 2 hours. Some changes in the emission profile are apparent on this time scale. The following night the enhanced emission persisted but at lower levels and it was substantially redshifted. This event is interpreted in terms of a model where material is injected into a disk co-rotating with the angular velocity of the stellar surface. A localized region of surface activity is conjectured to be the source of the event.

Ramsey, L. W.↗
NASA NTRS1982

Effects of differential rotation on the gravitational figures of Jupiter and Saturn

It is assumed that observed zonal currents in the atmospheres of Jupiter and Saturn correspond to a state of permanent rotation, and that the angular velocity is constant on cylindrical surfaces parallel to the rotation axis. The equation of hydrostatic equilibrium for a rotating planet is solved under these restrictive assumptions, and the effect of the hypothesized rotation state on the planet's gravity harmonics and external shape is investigated. Spacecraft data on zonal currents are used to derive nearly model-independent corrections to the first four zonal gravity harmonic coefficients, which can be used to correct observed gravity harmonics to values appropriate for solid-body rotation. If the assumed rotation state is applicable, then zonal currents lead to measurable topography of isopycnic surfaces with respect to the reference figure defined by the magnetospheric rotation period and the gravity harmonics. The amplitude of the topography is on the order of 5 km for Jupiter and 60 km for Saturn.

Hubbard, W. B.↗
NASA NTRS1983

On-board estimation technology for space station - Current status and future developments.

Design considerations and projected solutions to on-board automated estimation techniques for advanced technology controls on a space station are described, with emphasis on the state estimator. The space station is modelled as a collection of rigid and flexible bodies connected at a finite number of hinges. The systems dynamics are characterized by angular velocities of the base body, gimbal angles, and deflections of the flexible appendages. The state estimator evolution is projected to occur in four generations, with the first being control logic in the Viking and Voyager spacecraft, the second in the Shuttle and Galileo probe, the third being large antennas and the prototype space station, the last, around the year 2000, for the actual space station. Considerations for attitude, ephemeris, shape determination, and position estimation through each generation are discussed.

Rodriguez, G.↗
NASA NTRS1983

Periods of activity cycles in late-type stars

The mean magnetic field dynamo theory is utilized to obtain the qualitative dependence of the period of activity on the angular velocity of rotation for stars with sufficiently extensive convective shells. The dependence of the cycle period on the spectral class is also discussed.

Kliorin, N. I.↗