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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Further analysis of field effects on liquids and solidification

Numerical calculations of the magnitude of external field effects on liquids are presented to describe how external fields can influence the substructure of the field. Quantitative estimates of magnetic and gravitational effects are reported on melts of metals and semiconductors. The results are condensed in tables which contain the input data for calculation of the field effects on diffusion coefficient, solidification rate and for calculation of field forces on individual molecules in the melt.

Seiler, R. F.↗
NASA NTRS1973

Liapunov stability analysis of hybrid dynamical systems in the neighborhood of nontrivial equilibrium

This paper is concerned with the stability of a hybrid dynamical system in the neighborhood of a nontrivial equilibrium, where the system consists of one rigid part and n elastic members. The body moves in a central-force field with its mass center describing a circular orbit. The nontrivial equilibrium is defined by steady rotation of the system at an angular velocity equal to the orbital velocity, with the elastic members being in deformed state. A Liapunov stability analysis is performed by assuming small perturbations about the nontrivial equilibrium, where the latter is generally defined by nonlinear differential equations. The theory is applied to a gravity-gradient stabilized satellite with flexible appendages.

Meirovitch, L.↗
NASA NTRS1974

Particle distribution functions in modulation theory

Development of a simple formulation of the cosmic ray modulation problem which involves the use of the omnidirectional part of the distribution function in phase space, and the magnitude of the momentum or the rigidity. It is shown that, by employing the proposed formulation, the Compton-Getting factor is greatly simplified, and the well-known force-field equation is reduced to a one-dimensional Vlasov equation. In addition, another Vlasov equation can be written for the very low energy galactic particles which are convected by the solar wind.

Forman, M. A.↗
NASA NTRS1974

Analytic approximations in the study of the solar modulation of electrons

Numerical solutions to the transport equation of galactic cosmic rays in the interplanetary medium have been used to investigate the applicability of commonly used approximate analytic solutions for electrons (10 MeV to 10 GeV). We find that for a given cosmic-ray diffusion coefficient the force-field approximation is in reasonable agreement with the numerical solution at energies above 200 MeV, but deviates significantly at lower energies, depending on the shape of the interstellar electron spectrum. The diffusion-convection approximation agrees generally with the numerical solution within a factor of 2 over the entire energy range.

Cummings, A. C.↗
NASA NTRS1974

Magnetic field and electric current structure in the chromosphere

The three-dimensional vector magnetic field structure in the chromosphere above an active region is deduced by using high-resolution H-alpha filtergrams together with a simultaneous digital magnetogram. An analog model of the field is made with 400 metal wires representing field lines that outline the H-alpha structure. The height extent of the field is determined from vertical field-gradient observations around sunspots, from observed fibril heights, and from an assumption that the sources of the field are largely local. The computed electric currents (typically 10 mA/sq m) are found to flow in patterns not similar to observed features and not parallel to magnetic fields. Force structures correspond to observed solar features; the dynamics to be expected include: downward motion in bipolar areas in the lower chromosphere, an outflow of the outer chromosphere into the corona with radially outward flow above bipolar plage regions, and motion of arch filament systems.

Dravins, D.↗
NASA NTRS1976

Studies of earth simulation experiments

The low gravity environment of earth orbit offers the potential for performing experiments involving baroclinic Geophysical Fluid Dynamics (GFD) on spherical surfaces. These experiments in turn have the potential for providing deeper understanding of large scale planetary and solar circulations. However, to perform these experiments, one requires an experimental technique whereby a radially directed body force can be generated to simulate a radial gravitational force field. One viable technique is the use of dielectric fluids with temperature dependent dielectric permittivity in a radially directed electric field. Application of the Boussinesq approximation to the equations of motion for this system and restrictions on the size of certain electrodynamic terms in the energy equations yields a set of equations which are analogous to the equations of motions of geophysical systems like the earth's atmosphere on term by term basis. The theoretical design of GFD experiments for performance in earth orbit are described along with results of preliminary tests of a prototype.

Hart, J. E.↗
NASA NTRS1976

Measured response of a complex structure to supersonic turbulent boundary layers

Measurements of the response of a large frame-stringer panel excited by supersonic turbulent boundary layer are reported. The statistical description of the wall pressure fluctuations in terms of the mean flow parameters governing the turbulent boundary layer is given. These results can be used in the development of design criteria on the response of sidewall structure of a large airplane in supersonic flight, since both forcing field and structure are realistic. Results indicate the significant importance of the modal coupling and the acoustic damping. The acoustic damping plays a major role in the response of the structure.

Maestrello, L.↗
NASA NTRS1975

IMP 6, 7 and 8 observations of the composition and time variations of low energy cosmic rays

The charge composition and time variations of quiet-time cosmic rays in the energy range 10 to 25 MeV/nucleon were studied to determine the source of the enhancement of quiet-time intensities of low energy nitrogen and oxygen nuclei observed by Pioneer 10. Time variations were established from data from IMPs 6, 7, and 8; the charge composition was obtained by summing data from IMP 7 and IMP 8. The neon to carbon ratio present in solar rays is too low to explain an observed enhancement of neon. Helium and oxygen have the same percentage modulation for a range of x5 in intensity. This can be explained within the framework of the field-force approximation and the selection mechanism based on the first ionization potential proposed by Fisk et al. (1974) if both oxygen and helium are singly charged.

Von Rosenvinge, T. T.↗
NASA NTRS1976

Dispersion of ensembles of non-interacting particles

The dynamics of an ensemble of noninteracting particles dispersing from a common origin and moving in a common force field with an initial distribution of momenta is analyzed using an approach where the particles are considered as a continuum described by a phase-space distribution function. General solutions are obtained for both the distribution function and the associated spatial density function. The linear case of small departures from circular orbits in an axisymmetric gravitational field is treated along with the specific case of particle dispersion from an object in a circular orbit in the same type of field. Numerical results are presented for the latter case, and consideration is given to the inverse problem of determining the initial time and velocity distribution from knowledge of the ensemble structure at a later time. Explicit results are provided for the case of an ellipsoidal distribution of initial momenta, and a numerical procedure is indicated for treating more general cases.

Heard, W. B.↗
NASA NTRS1977

Observations of galactic cosmic ray energy spectra between 1 and 9 AU

The variation of the 5 to 500 MeV/nuc cosmic ray helium component was studied between 1 and 9 A.U. using essentially identical detector systems on Pioneer 10 and 11 and Helios I. Between 100 and 200 MeV/nuc a radial gradient of 3.3?1.3%/A.U. is found. At 15 MeV/nuc this value increases to 20?4%/A.U. Between 4 and 9 A.U. a well defined intensity maximum is observed at approximately 17 MeV/nuc. The average adiabatic energy loss between 1 and 9 A.U. is approximately 4 MeV/nuc/A.U. The observed radial variation between 1 and 9 A.U. is well described by the Gleeson-Axford force field solution of the modulation equations over an energy range extending from 15 to 500 MeV/nuc and is in good agreement with the results reported by other Pioneer experiments. These values are much smaller than had been theoretically predicted.

Mcdonald, F. B.↗
NASA NTRS1977

Variational energy principle for compressible, baroclinic flow. 1: First and second variations of total kinetic action

The case of a cold gas in the absence of external force fields is considered. Since the only energy involved is kinetic energy, the total kinetic action (i.e., the space-time integral of the kinetic energy density) should serve as the total free-energy functional in this case, and as such should be a local minimum for all possible fluctuations about stable flow. This conjecture is tested by calculating explicit, manifestly covariant expressions for the first and second variations of the total kinetic action in the context of Lagrangian kinematics. The general question of the correlation between physical stability and the convexity of any action integral that can be interpreted as the total free-energy functional of the flow is discussed and illustrated for the cases of rectillinear and rotating shearing flows.

Schmid, L. A.↗
NASA NTRS1977

Electrostatic forces for personnel restraints

The feasibility of utilizing electrostatic forces for personnel retention devices on exterior spacecraft surfaces was analyzed. The investigation covered: (1) determination of the state of the art; (2) analysis of potential adhesion surfaces; (3) safety considerations for personnel; (4) electromagnetic force field determination and its effect on spacecraft instrumentation; and (5) proposed advances to current technology based on documentation review, analyses, and experimental test data.

Ashby, N.↗
NASA NTRS1977

Variational calculations of vibrational properties of ozone

A variational method is used to obtain vibrational-rotational properties for ozone from an experimental quartic force field. Band positions, average structures, matrix elements for calculating infrared intensities, and effective rotational constants are reported for (O-16)3 and its O-18 isotopic species. Also, the degree to which the vibrational energies and properties are converged is investigated as a function of the basis set parameters and basis set size, and of the method of obtaining the Hamiltonian matrix elements. A convenient procedure for assigning the vibrational states is developed for variational vibrational wavefunction expansions.

Carney, G. D.↗
NASA NTRS1977

The GEOS-20 m Cable Boom Mechanism

The GEOS Cable Boom Mechanism which allows the controlled deployment of a 20 m long cable in a centrifugal force field is described. In launch configuration the flat cable is reeled on a 240 mm diameter drum. The electrical connection between the rotating drum and the stationary housing is accomplished via a flexlead positioned inside the drum. Active motion control of this drum is achieved by a self locking worm gear, driven by a stepper motor. The deployment length of the cable is monitored by an optical length indicator, sensing black bars engraved on the cable surface.

Schmidt, G. K.↗
NASA NTRS1978

Dynamic MHD modeling of the solar wind disturbances during the August 1972 events

A time-dependent one-dimensional MHD theoretical model is tested by using plasma and magnetic field observations of Pioneer 9 and Pioneer 10 during the August 1972 events on the sun and in the interplanetary medium. These spacecraft were nearly aligned along a common heliocentric radius during these events, considered now to be the most spectacular and best-documented events during solar cycle 20. The observations of Pioneer 9 at 0.78 AU were used as input for the theoretical model. The plasma and magnetic field forcing functions were superimposed upon a preexisting ambient solar wind at this inner boundary, and the response was simulated as far as 8 AU. The simulated output at 2.2 AU is compared directly with the Pioneer 10 observations at 2.2 AU. Qualitative comparison is good, although several limitations of the one-dimensional theory are noted.

Dryer, M.↗
NASA NTRS1977

On Szebehely's equation for the potential of a prescribed family of orbits

In the present note we first give a simple proof of the Dainelli formulas for the force field generating a given family of orbits. We also show that the Szebehely partial differential equation for the potential can be derived from the Dainelli formulas if the energy integral is assumed. The Szebehely equation can be solved directly with the method of characteristics or indirectly with the Joukovsky formulas. Several examples are briefly described in the article. In particular we find some rather general potential functions corresponding to circular motion.

Broucke, R.↗
NASA NTRS1978

Plasma igniter for internal combustion engine

An igniter for the air/fuel mixture used in the cylinders of an internal combustion engine is described. A conventional spark is used to initiate the discharge of a large amount of energy stored in a capacitor. A high current discharge of the energy in the capacitor switched on by a spark discharge produces a plasma and a magnetic field. The resultant combined electromagnetic current and magnetic field force accelerates the plasma deep into the combustion chamber thereby providing an improved ignition of the air/fuel mixture in the chamber.

Fitzgerald, D. J.↗