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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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Distributed computer system enhances productivity for SRB joint optimization

Initial calculations of a redesign of the solid rocket booster joint that failed during the shuttle tragedy showed that the design had a weight penalty associated with it. Optimization techniques were to be applied to determine if there was any way to reduce the weight while keeping the joint opening closed and limiting the stresses. To allow engineers to examine as many alternatives as possible, a system was developed consisting of existing software that coupled structural analysis with optimization which would execute on a network of computer workstations. To increase turnaround, this system took advantage of the parallelism offered by the finite difference technique of computing gradients to allow several workstations to contribute to the solution of the problem simultaneously. The resulting system reduced the amount of time to complete one optimization cycle from two hours to one-half hour with a potential of reducing it to 15 minutes. The current distributed system, which contains numerous extensions, requires one hour turnaround per optimization cycle. This would take four hours for the sequential system.

Rogers, James L., Jr.↗
NASA NTRS1983

Flow Distribution in Hydraulic Systems

General Flow Distribution Program analyzes pressure drops and flow distribution in closed and open hydraulic systems. Analyzes system on basis of incompressible flow though system may contain either compressible or incompressible fluid. Program solves fixed or variable flow problems for series, parallel, or series/parallel systems.

Nguyen, S. N.↗
NASA NTRS1984

Interactive computer modeling of combustion chemistry and coalescence-dispersion modeling of turbulent combustion

An interactive computer code for simulation of a high-intensity turbulent combustor as a single point inhomogeneous stirred reactor was developed from an existing batch processing computer code CDPSR. The interactive CDPSR code was used as a guide for interpretation and direction of DOE-sponsored companion experiments utilizing Xenon tracer with optical laser diagnostic techniques to experimentally determine the appropriate mixing frequency, and for validation of CDPSR as a mixing-chemistry model for a laboratory jet-stirred reactor. The coalescence-dispersion model for finite rate mixing was incorporated into an existing interactive code AVCO-MARK I, to enable simulation of a combustor as a modular array of stirred flow and plug flow elements, each having a prescribed finite mixing frequency, or axial distribution of mixing frequency, as appropriate. Further increase the speed and reliability of the batch kinetics integrator code CREKID was increased by rewriting in vectorized form for execution on a vector or parallel processor, and by incorporating numerical techniques which enhance execution speed by permitting specification of a very low accuracy tolerance.

Pratt, D. T.↗
NASA NTRS1986

Field-aligned electron precipitation at the edge of an arc

Measurements of field-aligned electrons at the edge of an arc are presented from a sounding rocket flight through a quiet afternoon auroral arc. High time resolution measurements show the evolution of the electron distribution function over the 2.3-km width of field-aligned precipitation. A nearly constant 1.2-eV perpendicular temperature was found for these field-aligned fluxes over a broad range of parallel energies (100 - 900 eV). The small perpendicular temperature indicates that the acceleration region is located at a low altitude. Two models of cold plasma convection into the edge of a V-shaped potential structure are examined and found to be consistent with both the observed fluxes and spatial width of the edge precipitation. Both models predict an average source plasma density less than 130/cu cm to account for the observed field-aligned fluxes and thus an acceleration region well above 1000 km.

Mcfadden, J. P.↗
NASA NTRS1986

A laboratory study of ion energization by EIC waves and subsequent upstreaming along diverging magnetic field lines

A laboratory study related to energetic upstreaming ions in the ionosphere-magnetosphere system is described. The experiment was carried out in a cesium Q machine plasma with a region of nonuniform magnetic field. Electrostatic ion cyclotron waves were excited by drawing an electron current to a small biased exciter electrode. In the presence of the instability, ions are heated in the direction perpendicular to B. Using a gridded retarding potential ion energy analyzer, the evolution of the ion velocity distribution was followed as the ions passed through the heating region and subsequently flowed out along the diverging B field lines. As expected, the heated ions transfer their energy from perpendicular to parallel motion as they move through the region of diverging B field. Both their parallel thermal energy and the parallel drift energy increase at the expense of the perpendicular energy.

Cartier, S. L.↗
NASA NTRS1985

Comparative magnetospheric/ionospheric studies using Dynamics Explorer spacecraft and ground-based radars

Coincident magnetosphere-ionosphere observations between the Dynamics Explorer 1 and 2 spacecraft with ground-based radar are reviewed. Ionospheric-magnetospheric coupling processes in the plasmasphere, main trough, auroral zone, and polar cap are inferred from the density, temperature, composition, and angular distributions of the low-energy plasma observed from the E-region ionosphere out into the magnetosphere to an altitude of 2.5 Re. From the polar cap to the inner plasmasphere, parallel and perpendicular electric fields, polar wind flow, and equilibrium diffusion appear to be involved in the ionospheric-magnetospheric coupling of the low energy plasma.

Green, J. L.↗
NASA NTRS1986

Earth's compressional foreshock boundary revisited Observations by the ISEE 1 magnetometer

A 'solar foreshock coordinate' (SFC) system is introduced in which the positions of foreshock components can be collated with a minimum of assumptions about the physical processes involved. Location behind the interplanetary magnetic field (IMF) tangent surface to the bow shock and rotational symmetry around the solar wind flow (X) axis are the only presuppositions. The SFC system has been applied to over 300 observations of the boundary of the ULF compressional waves recorded by ISEE 1's magnetometer in 1978 and 1979. The boundary locations form a coherent pattern in the SFC frame. A selection of those cases for which the cone angle of the IMF was between 40 and 50 deg, corresponding to the average stream angle, yields a least square line whose mapping back to the solar ecliptic coordinates frame has slope of about 85 deg, very close to that of the tangent ULF boundary deduced earlier from more primitive methods with entirely different data sets. The line, being parallel to neither the IMF, the typical reflected beam, nor the shock, cannot be compatible with any model of wave production by beam-solar wind interaction that depends on uniform beam distribution or fixed growth rate. Rather, its tangency suggests the influence of a separate, escaping ion population.

Greenstadt, E. W.↗
NASA NTRS1992

Particle acceleration at comets

This paper compares calculated and measured energy spectra of implanted H(+) and O(+) ions on the assumption that the pickup geometry is quasi-parallel and about 1 percent of the waves generated by the cometary pickup process propagates backward (towards the comet). The model provides a good description of the implanted O(+) and H(+) energy distribution near the pickup energies.

Gombosi, Tamas I.↗
NASA NTRS1993

On the dynamical buoyancy of vortices

In this paper we consider the effect of dynamical buoyancy (Parker) on the motion of stratified fluid vortex tubes. We find that the dynamical buoyancy force does not necessarily lead to a buoyant rise if there exists a flow field external to a tube. In particular, the vortex tubes presented in our previous work are shown to have a pressure force exactly canceling the buoyancy force so that they do not move vertically (i.e., parallel to gravity) at all. Moreover, we construct a more general class of vortex tubes and find that their vertical motion can be either up or down, depending on the detailed vorticity distribution, regardless of the fact that they are all dynamically buoyant. We find that the vertical motion is intimately related to the horizontal self-motion of stratified fluid vortex tubes. Finally, we note that the presence of dynamical buoyancy implies that steady state compressible flow solutions for isolated fluid regions in a gravitational field do not exist. These results may have relevance to astrophysical convection.

Arendt, Steve↗
NASA NTRS1994

Efficient massively parallel simulation of dynamic channel assignment schemes for wireless cellular communications

Fast, efficient parallel algorithms are presented for discrete event simulations of dynamic channel assignment schemes for wireless cellular communication networks. The driving events are call arrivals and departures, in continuous time, to cells geographically distributed across the service area. A dynamic channel assignment scheme decides which call arrivals to accept, and which channels to allocate to the accepted calls, attempting to minimize call blocking while ensuring co-channel interference is tolerably low. Specifically, the scheme ensures that the same channel is used concurrently at different cells only if the pairwise distances between those cells are sufficiently large. Much of the complexity of the system comes from ensuring this separation. The network is modeled as a system of interacting continuous time automata, each corresponding to a cell. To simulate the model, conservative methods are used; i.e., methods in which no errors occur in the course of the simulation and so no rollback or relaxation is needed. Implemented on a 16K processor MasPar MP-1, an elegant and simple technique provides speedups of about 15 times over an optimized serial simulation running on a high speed workstation. A drawback of this technique, typical of conservative methods, is that processor utilization is rather low. To overcome this, new methods were developed that exploit slackness in event dependencies over short intervals of time, thereby raising the utilization to above 50 percent and the speedup over the optimized serial code to about 120 times.

Greenberg, Albert G.↗
NASA NTRS2017

Column Number Density Expressions Through M = 0 and M = 1 Point Source Plumes Along Any Straight Path

Providers of payloads carried aboard the International Space Station must conduct analyses to demonstrate that any planned gaseous venting events generate no more than a certain level of material that may interfere with optical measurements from other experiments or payloads located nearby. This requirement is expressed in terms of a maximum column number density (CND). Depending on the level of rarefaction, such venting may be characterized by effusion for low flow rates, or by a sonic distribution at higher levels. Since the relative locations of other sensitive payloads are often unknown because they may refer to future projects, this requirement becomes a search for the maximum CND along any path.In another application, certain astronomical observations make use of CND to estimate light attenuation from a distant star through gaseous plumes, such as the Fermi Bubbles emanating from the vicinity of the black hole at the center of our Milky Way galaxy, in order to infer the amount of material being expelled via those plumes.This paper presents analytical CND expressions developed for general straight paths based upon a free molecule point source model for steady effusive flow and for a distribution fitted to model flows from a sonic orifice. Among other things, in this Mach number range it is demonstrated that the maximum CND from a distant location occurs along the path parallel to the source plane that intersects the plume axis. For effusive flows this value is exactly twice the CND found along the ray originating from that point of intersection and extending to infinity along the plumes axis. For sonic plumes this ratio is reduced to about 43.

Venting↗
NASA NTRS1995

Parameterized spectral distributions for meson production in proton-proton collisions

Accurate semiempirical parameterizations of the energy-differential cross sections for charged pion and kaon production from proton-proton collisions are presented at energies relevant to cosmic rays. The parameterizations, which depend on both the outgoing meson parallel momentum and the incident proton kinetic energy, are able to be reduced to very simple analytical formulas suitable for cosmic ray transport through spacecraft walls, interstellar space, the atmosphere, and meteorites.

Schneider, John P.↗
NASA NTRS1991

Mesoscale and large-scale variability of the Antarctic circumpolar current

This investigation of the physical oceanography of the Southern Ocean will carry out two parallel efforts during the years preceding the launch of TOPEX/POSEIDON. First, the Geosat data will be used to develop a preliminary descriptive picture of the mesoscale and large-scale, low-frequency surface circulation of the Southern Ocean. Some of this analysis of Geosat data has already begun. For example, as a measure of the geographical distribution of mesoscale variability, a color-coded map of the standard deviation of sea level from two years of Geosat data is shown. Efforts are presently under way to investigate the seasonal and year-to-year variability of this mesoscale energy. The data are also being used to generate low-pass filtered fields of sea level from which the temporal evolution of large-scale variability in the Southern Ocean may be investigated. The second parallel effort is the development and test of modeling and data assimilation techniques that will later be applied to TOPEX/POSEIDON data during the postlaunch phase. One objective of the modeling and data assimilation is to investigate the relation between mesoscale sea level variations and eddy flux in the Southern Ocean. Uncertainties in present estimates of the various components of meridional oceanic heat transport are large. The evidence presented indicates that the very energetic mesoscale variability in the ACC apparently accounts for much of the estimated 0.45x10(exp 15) watts of poleward heat transport across the ACC required to balance the heat budget. Eddy variability is strongly coherent vertically in the ACC, at least in the vicinity of Drake Passage where nearly all of the historical in situ data have been collected.

Chelton, Dudley B.↗
NASA NTRS1986

Theory and simulations of broadband electrostatic noise in the geomagnetic tail

The excitation mechanism for broadband electrostatic noise (BEN) and the effects of BEN particles in the geomagnetic tail are examined using the linear analysis theory and particle simulations. The linear theory for electrostatic instabilities is discussed. The plasma sheet particle population is simulated using counter-streaming cold ion beams, and warm ions and electrons. The ion-ion instability, ion-acoustic mode, and the electrostatic ion cyclotron harmonic waves are studied. The velocity distributions, electric field intensity, and electron plasma waves for the plasma sheet boundary layer are evaluated. The frequency wave spectrum and particle distributions are computed and analyzed. The conditions for the two simulations, which differ only in beam ion drift speed, are described; it is observed that in the first simulation the dominate modes propagate parallel to the magnetic field and in the second simulation the propagation modes are oblique. The simulation data reveal that when beam temperature is smaller than plasma sheet temperature ion-acoustic and ion-ion instabilities grow to large amplitudes heating both electrons and ions. The data are compared to ISEE-1 observations and good correlation is obtained.

Ashour-Abdalla, M.↗
NASA NTRS1988

Generalized adiabatic theory applied to the magnetotail current sheet

The generalized first adiabatic invariant, an extension of the magnetic moment for regions of large field gradients, has been applied to the study of particles in the magnetotail current sheet. Boundaries in phase space are obtained which form a generalized loss cone and separate particles drifting into and out of the layer from particles trapped within the layer, and the boundaries can be employed in the moment integrals for densities and currents when the drifting particles differ in temperature. It is shown that the parallel pressure of the drifting particles must exceed the transverse pressure for self-consistent solutions to exist. Fully self-consistent solutions are obtained using bi-Maxwellian ion and Maxwellian electron distributions.

Rogers, Shelley H.↗
NASA NTRS1988

Modeling and control of flexible structures

This monograph presents integrated modeling and controller design methods for flexible structures. The controllers, or compensators, developed are optimal in the linear-quadratic-Gaussian sense. The performance objectives, sensor and actuator locations and external disturbances influence both the construction of the model and the design of the finite dimensional compensator. The modeling and controller design procedures are carried out in parallel to ensure compatibility of these two aspects of the design problem. Model reduction techniques are introduced to keep both the model order and the controller order as small as possible. A linear distributed, or infinite dimensional, model is the theoretical basis for most of the text, but finite dimensional models arising from both lumped-mass and finite element approximations also play an important role. A central purpose of the approach here is to approximate an optimal infinite dimensional controller with an implementable finite dimensional compensator. Both convergence theory and numerical approximation methods are given. Simple examples are used to illustrate the theory.

Gibson, J. S.↗
NASA NTRS1990

Electromagnetic fire-hose instability in a fully relativistic bi-Maxwellian plasma

Detailed properties of the classical hydromagnetic Alfven wave and the fire-hose instability, driven by an excess in the parallel energy are well understood in the nonrelativistic regime. In this brief communication, the analysis is extended to the fully relativistic regime. The analysis is carried out for fully relativistic bi-Maxwellian distributions of electrons and ions (or positrons). It is shown that the relativistic effect has a nonnegligible effect on the wave and stability properties of the low-frequency modes under certain conditions.

Yoon, Peter H.↗
NASA NTRS1990

Theory of electromagnetic cyclotron wave growth in a time-varying magnetoplasma

The effect of a time-dependent perturbation in the magnetoplasma on the wave and particle populations is investigated using the Kennel-Petchek (1966) approach. Perturbations in the cold plasma density, energetic particle distribution, and resonance condition are calculated on the basis of the ideal MHD assumption given an arbitrary compressional magnetic field perturbation. An equation is derived describing the time-dependent growth rate for parallel propagating electromagnetic cyclotron waves in a time-varying magnetoplasma with perturbations superimposed on an equilibrium configuration.

Gail, William B.↗