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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 NTRS1988

Time-dependent dynamical behavior of surface tension on rotating fluids under microgravity environment

Time dependent evolutions of the profile of free surface (bubble shapes) for a cylindrical container partially filled with a Newtonian fluid of constant density, rotating about its axis of symmetry, have been studied. Numerical computations of the dynamics of bubble shapes have been carried out with the following situations: (1) linear functions of spin-up and spin-down in low and microgravity environments, (2) step functions of spin-up and spin-down in a low gravity environment, and (3) sinusoidal function oscillation of gravity environment in high and low rotating cylinder speeds.

Hung, R. J.↗
NASA NTRS1991

'Self-consistent' production of ion conics on return current region auroral field lines - A time-dependent, semi-kinetic model

We describe initial results from a time-dependent, semi-kinetic model of plasma outflow incorporating wave-particle interactions along current-carrying auroral field lines. Electrostatic waves are generated by the current driven ion cyclotron instability (CDICI), causing perpendicular velocity diffusion of ions plus electron heating via anomalous resistivity when and where the relative drift between electrons and ions exceeds certain critical velocities. Using the local bulk parameters we calculate these critical velocities, and so are able to self-consistently switch on and off the heating of the various particle species. Due to the dependence of these critical velocities on the bulk parameters of the species the heating effects exhibit quite complex spatial and temporal variations. A wide range of ion distribution functions are observed in these simulations, including conics with energies of a few electron volts and 'ring' distributions. The rings are seen to be a natural result of transverse heating and velocity filter effects and do not require coherent acceleration processes. We also observe the formation of a density depletion in hydrogen and enhanced oxygen densities at high altitudes.

Brown, David G.↗
NASA NTRS1994

Spatial organization and time dependence of Jupiter's tropospheric temperatures, 1980-1993

The spatial organization and time dependence of Jupiter's temperature near 250-millibar pressure were measured through a jovian year by imaging thermal emission at 18 micrometers. The temperature field is influenced by seasonal radiative forcing, and its banded organization is closely correlated with the visible cloud field. Evidence was found for a quasi-periodic oscillation of temperatures in the Equatorial Zone, a correlation between tropospheric and stratospheric waves in the North Equatorial Belt, and slowly moving thermal features in the North and South Equatorial Belts. There appears to be no common relation between temporal changes of temperature and changes in the visual albedo of the various axisymmetric bands.

Orton, Glenn S.↗
NASA NTRS1979

Prediction of field-time-dependent gate-oxide breakdown in MOS devices

The model for field-time-dependent breakdown in the gate oxide of MOS devices is extended and verified with experimental data. The model permits accelerated tests at high fields which can be used to predict gate-oxide breakdowns at much longer times at normal operating fields.

Li, S. P.↗
NASA NTRS1991

A two-dimensional, time-dependent, near-earth magnetotail

A kinetic approach is presented for obtaining slowly time-dependent, self-consistent plasma, and magnetic field configurations for this region, using anisotropic particle distributions. At present, a 2D configuration is used. The time variation of the plasma/field configuration is assumed to be driven by a slowly varying, externally imposed electric field (representing, for example, a change in solar wind conditions). The numerical approach involves solving a 2D nonlinear Poisson equation for the magnetic vector potential at each time step. The local current density is calculated from particle velocity distributions under the assumption of adiabatic particle motion. The obtained equations of state are compared with those of double-adiabatic theory. Numerical examples of self-consistent responses of the near-earth plasma and field to an externally imposed electric field pulse are presented.

Whipple, Elden↗
NASA NTRS1983

Solar modulation of galactic cosmic rays. V - Time-dependent modulation

A numerical technique is introduced for the solution of the time-dependent equation for the solar modulation of galactic cosmic rays, in which transport in heliographic latitude is ignored. We illustrate this method with a model for the solar cycle variation in cosmic ray intensity. The variation is assumed to result from changes in the number of enhanced cosmic ray scattering regions, which are produced by flare-generated shock waves in the solar wind. The model can account for the observed solar cycle variation in intensity at different energies as well as the observed spatial gradients. This model also provides a natural explanation for the cosmic ray hysteresis effect.

Perko, J. S.↗
NASA NTRS1993

Response-coefficient method for heat-conduction transients with time-dependent inputs

A theoretical overview of the response coefficient method for heat conduction transients with time-dependent input forcing functions is presented with a number of illustrative applications. The method may be the most convenient and economical if the same problem is to be solved many times with different input-time histories or if the solution time is relatively long. The method is applicable to a wide variety of problems, including irregular geometries, position-dependent boundary conditions, position-dependent physical properties, and nonperiodic irregular input histories. Nonuniform internal energy generation rates within the structure can also be handled by the method. The area of interest is long-time solutions, in which initial condition is unimportant, and not the early transient period. The method can be applied to one dimensional problems in cartesian, cylindrical, and spherical coordinates as well as to two dimensional problems in cartesian and cylindrical coordinates.

Ceylan, Tamer↗
NASA NTRS1973

Cosmic Ray Hysteresis as Evidence for Time-dependent Diffusive Processes in the Long Term Solar Modulation

A simple one-dimensional time-dependent diffusion-convection model for the modulation of cosmic rays is presented. This model predicts that the observed intensity at a given time is approximately equal to the intensity given by the time independent diffusion convection solution under interplanetary conditions which existed a time iota in the past, (U(t sub o) = U sub s(t sub o - tau)) where iota is the average time spent by a particle inside the modulating cavity. Delay times in excess of several hundred days are possible with reasonable modulation parameters. Interpretation of phase lags observed during the 1969 to 1970 solar maximum in terms of this model suggests that the modulating region is probably not less than 10 a.u. and maybe as much as 35 a.u. in extent.

Ogallagher, J. J.↗
NASA NTRS1990

Stabilization and control of distributed systems with time-dependent spatial domains

This paper considers the problem of the stabilization and control of distributed systems with time-dependent spatial domains. The evolution of the spatial domains with time is described by a finite-dimensional system of ordinary differential equations, while the distributed systems are described by first-order or second-order linear evolution equations defined on appropriate Hilbert spaces. First, results pertaining to the existence and uniqueness of solutions of the system equations are presented. Then, various optimal control and stabilization problems are considered. The paper concludes with some examples which illustrate the application of the main results.

Wang, P. K. C.↗
NASA NTRS1973

Brownian motion of electrons in time-dependent magnetic fields.

The behavior of a weakly ionized plasma in slowly varying time-dependent magnetic fields is studied through an extension of Williamson's stochastic theory. In particular, attention is focused on the properties of electron diffusion in the plane perpendicular to the direction of the magnetic field, when the field strength is large. It is shown that, in the strong field limit, the classical 1/B-squared dependence of the perpendicular diffusion coefficient is obtained for two models in which the field B(t) is monotonic in t and for two models in which B(t) possesses at least one turning point.

Iverson, G. J.↗
NASA NTRS1980

Grid generation for time dependent problems: Criteria and methods

The problem of generating local mesh refinements when solving time dependent partial differential equations was examined. The problem of creating an appropriate grid, given a mesh function h defined over the spatial domain is discussed. A data structure which permits efficient use of the resulting grid is described. A good choice for h is an estimate of the local truncation error, and several ways to estimate it are discussed. The efficiency and implementation problems of these error estimates were compared.

Berger, M.↗
NASA NTRS1988

Time dependent temperature distribution in pulsed Ti:sapphire lasers

An expression is derived for the time dependent temperature distribution in a finite solid state laser rod for an end-pumped beam of arbitrary shape. The specific case of end pumping by circular (constant) or Gaussian beam is described. The temperature profile for a single pump pulse and for repetitive pulse operation is discussed. The particular case of the temperature distribution in a pulsed titanium:sapphire rod is considered.

Buoncristiani, A. Martin↗
NASA NTRS1989

Three-dimensional, time-dependent MHD simulations of interplanetary plasmoids

The paper presents a three-dimensional time-dependent simulation of a solar-ejected diamagnetic plasmoid that retains its closed topology to and beyond earth. It is assumed in this case that, before entering the computational domain, the plasmoid already exists at or near the sun. A simulation is also presented for a plasmoid that is formed in the corona near the sun or in the interplanetary medium as a consequence of the reconnection of opposite-directed IMF lines. The plasma and magnetic properties of the expanding plasmoid as it moves toward an observer at 1 AU are described.

Dryer, M.↗