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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Why a variable G

An attempt is made to put the possible time variability of G in a broader context. It is suggested that the variable G is a popular and incomplete representation of the problem of the validity of the strong equivalence principle (SEP). Particular reference is made to a reanalysis of Viking Mars data to study, in a model independent way, the influence of atomic clocks in recording purely gravitational phenomena. These data ought to provide the most reliable test of the variability of G and the validity of the SEP.

Canuto, V. M.↗
NASA NTRS1983

Large space structure damping design

Several FORTRAN subroutines and programs were developed which compute complex eigenvalues of a damped system using different approaches, and which rescale mode shapes to unit generalized mass and make rigid bodies orthogonal to each other. An analytical proof of a Minimum Constrained Frequency Criterion (MCFC) for a single damper is presented. A method to minimize the effect of control spill-over for large space structures is proposed. The characteristic equation of an undamped system with a generalized control law is derived using reanalysis theory. This equation can be implemented in computer programs for efficient eigenvalue analysis or control quasi synthesis. Methods to control vibrations in large space structure are reviewed and analyzed. The resulting prototype, using electromagnetic actuator, is described.

Pilkey, W. D.↗
NASA NTRS1982

Optimality criteria design and stress constraint processing

Methods for pre-screening stress constraints into either primary or side-constraint categories are reviewed; a projection method, which is developed from prior cycle stress resultant history, is introduced as an additional screening parameter. Stress resultant projections are also employed to modify the traditional stress-ratio, side-constraint boundary. A special application of structural modification reanalysis is applied to the critical stress constraints to provide feasible designs that are preferable to those obtained by conventional scaling. Sample problem executions show relatively short run times and fewer design cycle iterations to achieve low structural weights; those attained are comparable to the minimum values developed elsewhere.

Levy, R.↗
NASA NTRS1983

The Manicouagan impact structure - An analysis of its original dimensions and form

A reanalysis of the preerosional geology of the Canadian impact crater, Manicouagan, is presented. Although most of the current features of the annular moat are primarily a result of erosional processes, the original dimensions of the cavity have been determined to include a transient cavity 60 km in diam. The final floor of the crater was studied and found to be an impact melt-covered inner plateau 55 km in diam. Comparisons with similar crater bottoms on the moon are used to estimate a final crater rim diameter of 85-95 km. The inner plateau and relatively smooth deposits on the crater floor are noted to be most similar to the lunar crater Copernicus.

Grieve, R. A. F.↗
NASA NTRS1983

Variability of carbon monoxide in the Mars atmosphere

Recent measurements and reanalyses of past measurements are used to derive estimates of the variability of CO concentrations in the Martian atmosphere. The J = 1 - 2 rotational transition of CO in the microwave spectrum of Mars was observed in January, 1982, and abundances were calculated through surface and atmospheric temperature modeling. A column density of 4.6 + or - 2.0 x 10 to the 20th/sq cm is obtained, which is contrasted with values of 3.0 + or - 1.0 x 10 to the 20th/sq cm in 1980 and 1.7 x + or - 0.9 x 10 to the 20th/sq cm in 1975 obtained by reanalysis of the J = 0 - 1 transition observed by Good and Schloerb (1981) and Kakar et al. (1977), respectively. It is noted that due to the uncertainties in global atmospheric average temperatures, results are consistent with a CO variability of from 0 to 100 percent over a time scale of several years. It is suggested that simultaneous measurements of the J = 0 - 1 and J = 1 - 2 transitions may provide stronger constraints on the CO abundance and atmospheric temperature of Mars.

Clancy, R. T.↗
NASA NTRS1984

Selection of actuator locations for static shape control of large space structures by heuristic integer programing

Orbiting spacecraft such as large space antennas have to maintain a highly accurate space to operate satisfactorily. Such structures require active and passive controls to mantain an accurate shape under a variety of disturbances. Methods for the optimum placement of control actuators for correcting static deformations are described. In particular, attention is focused on the case were control locations have to be selected from a large set of available sites, so that integer programing methods are called for. The effectiveness of three heuristic techniques for obtaining a near-optimal site selection is compared. In addition, efficient reanalysis techniques for the rapid assessment of control effectiveness are presented. Two examples are used to demonstrate the methods: a simple beam structure and a 55m space-truss-parabolic antenna.

Haftka, R. T.↗
NASA NTRS1984

Large amplitude MHD waves upstream of the Jovian bow shock: Reinterpretation

Observations of large amplitude magnetohydrodynamic (MHD) waves upstream of the Jovian bow shock were previously interpreted as arising from a resonant electromagnetic ion beam instability. That interpretation was based on the conclusion that the observed fluctuations were predominantly right elliptically polarized in the solar wind rest frame. Because it was noted that the fluctuations are, in fact, left elliptically polarized, a reanalysis of the observations was necessary. Several mechanisms for producing left hand polarized MHD waves in the observed frequency range were investigated. Instabilities excited by protons appear unlikely to account for the observations. A resonant instability excited by relativistic electrons escaping from the Jovian magnetosphere is a likely source of free energy consistent with the observations. Evidence for the existence of such a population of electrons was found in both the Low Energy Charged Particle experiments and Cosmic Ray experiments on Voyager 2.

Goldstein, M. L.↗
NASA NTRS1984

Regional scale simulation of atmospheric structure using VAS data

Investigations with both Subsynoptic Scale Model (SSM) and Limited Area Mesoscale Prediction System (LAMPS) are directed at model static initializations using Visible Infrared Spin Scan Radiometer Atmospheric Sounder (VAS) derived temperatures and moistures and also satellite derived winds. The general approach for each day's case study is similar. A 12-hour control forecast (no satellite data) is made 12Z-OZ, using a radiosonde analysis at 12Z as the initial field. For the satellite data experiments, reanalyses are performed at intermediate times, using VAS soundings or VAS soundings in combination with satellite winds. Forecasts are subsequently made from the reanalysis time(s) to the same validation hour (OZ) as the control forecasts. Comparisons are then made between the control forecast and satellite experiments.

Disk, G.↗
NASA NTRS1983

Luminosity correlations in quasars

Simulations are conducted with and without flux thresholds in an investigation of quasar luminosity correlations by means of a Monte Carlo analysis, for various model distributions of quasars in X-rays and optical luminosity. For the case where the X-ray photons are primary, an anticorrelation between X-ray-to-optical luminosity ratio and optical luminosity arises as a natural consequence which resembles observations. The low optical luminosities of X-ray selected quasars can be understood as a consequence of the same effect, and similar conclusions may hold if the X-ray and optical luminosities are determined independently by a third parameter, although they do not hold if the optical photons are primary. The importance of such considerations is demonstrated through a reanalysis of the published X-ray-to-optical flux ratios for the 3CR sample.

Chanan, G. A.↗
NASA NTRS1985

A computer program for determining the electrophoretic mobility of cells in a rectangular chamber during asymmetric electroosmotic flow

In the field of cell electrophoresis, computer programs have been used for the estimation of zeta potential and surface charge density of specific charged chemical species from electrophoretic mobility data. The union of computer and microscope cell electrophoresis in the laboratory has yielded several satisfying results. The method organizes and error checks these data and stores them on permanent file for future reference or reanalysis. This computer analysis, accomplished in two steps by two main programs and a major subroutine, provides a quick, useful and realistic presentation of mobility data in histogram form, and is appropriate for any microelectrophoretic work using rectangular chambers. Computer program 1 is the first step of two in the analysis of mobility data. Program 2 consists of the main program, POLY2, which fits a least squares parabola to the apparent mobility data generated by Program 1, and the subroutine EXTRA which determines actual cell mobilities using the regression curve equation.

Source record↗
NASA NTRS1985

Large-amplitude MHD waves upstream of the Jovian bow shock Reinterpretation

Observations of large amplitude magnetohydrodynamic (MHD) waves upstream of the Jovian bow shock were previously interpreted as arising from a resonant electromagnetic ion beam instability. That interpretation was based on the conclusion that the observed fluctuations were predominantly right elliptically polarized in the solar wind rest frame. Because it was noted that the fluctuations are, in fact, left elliptically polarized, a reanalysis of the observations was necessary. Several mechanisms for producing left hand polarized MHD waves in the observed frequency range were investigated. Instabilities excited by protons appear unlikely to account for the observations. A resonant instability excited by relativistic electrons escaping from the Jovian magnetosphere is a likely source of free energy consistent with the observations. Evidence for the existence of such a population of electrons was found in both the Low Energy Charged Particle experiments and Cosmic Ray experiments on Voyager 2.

Goldstein, M. L.↗
NASA NTRS1985

Selection of actuator locations for static shape control of large space structures by heuristic integer programing

Orbiting spacecraft such as large space antennas have to maintain a highly accurate shape to operate satisfactorily. Such structures require active and passive controls to maintain an accurate shape under a variety of disturbances. Methods for the optimum placement of control actuators for correcting static deformations are described. In particular, attention is focused on the case were control locations have to be selected from a large set of available sites, so that integer programing methods are called for. The effectiveness of three heuristic techniques for obtaining a near-optimal site selection is compared. In addition, efficient reanalysis techniques for the rapid assessment of control effectiveness are presented. Two examples are used to demonstrate the methods: a simple beam structure and a 55m space-truss-parabolic antenna.

Haftka, R. T.↗
NASA NTRS1986

New models of Saturn's magnetic field using Pioneer 11 Vector Helium Magnetometer data

In a reanalysis of the Vector Helium Magnetometer data taken by Pioneer 11 during its Saturn encounter in 1979, using improvements in the data set and in the procedures, studies are made of a variety of models. The best is the P(11)84 model, an axisymmetric spherical harmonic model of Saturn's magnetic field within 8 Saturn radii of the planet. The appropriately weighted root mean square average of the difference between the observed and the modeled field is 1.13 percent. For the Voyager-based Z3 model of Connerney, Acuna, and Ness, this average difference from the Pioneer 11 data is 1.81 percent. The external source currents in the magnetopause, tail, bow shock, and perhaps ring currents vary with time and can only be crudely modeled. An algebraic formula is derived for calculating the L shells on which energetic charged particles drift in axisymmetric fields.

Davis, L., Jr.↗
NASA NTRS1984

Design enhancement tools in MSC/NASTRAN

Design sensitivity is the calculation of derivatives of constraint functions with respect to design variables. While a knowledge of these derivatives is useful in its own right, the derivatives are required in many efficient optimization methods. Constraint derivatives are also required in some reanalysis methods. It is shown where the sensitivity coefficients fit into the scheme of a basic organization of an optimization procedure. The analyzer is to be taken as MSC/NASTRAN. The terminator program monitors the termination criteria and ends the optimization procedure when the criteria are satisfied. This program can reside in several plances: in the optimizer itself, in a user written code, or as part of the MSC/EOS (Engineering Operating System) MSC/EOS currently under development. Since several excellent optimization codes exist and since they require such very specialized technical knowledge, the optimizer under the new MSC/EOS is considered to be selected and supplied by the user to meet his specific needs and preferences. The one exception to this is a fully stressed design (FSD) based on simple scaling. The gradients are currently supplied by various design sensitivity options now existing in MSC/NASTRAN's design sensitivity analysis (DSA).

Wallerstein, D. V.↗
NASA NTRS1987

On computing eigensolution sensitivity data using free vibration solutions

A simplified method of computing eigensolution sensitivity derivatives in structural dynamics is developed. It is shown that if the elements of stiffness and mass matrices associated with a design variable are homogeneous functions of that design variable, then eigenvalue derivatives can be computed from element strain and kinetic energies. Furthermore, if cross-mode energies are known, eigensolution derivatives of modified systems can be computed approximately using assume mode reanalysis formulation. A ten bar truss example is used to illustrate the present formulations.

Wang, B. P.↗
NASA NTRS1987

Sensitivity analysis for large-scale problems

The development of efficient techniques for calculating sensitivity derivatives is studied. The objective is to present a computational procedure for calculating sensitivity derivatives as part of performing structural reanalysis for large-scale problems. The scope is limited to framed type structures. Both linear static analysis and free-vibration eigenvalue problems are considered.

Noor, Ahmed K.↗
NASA NTRS1986

Cometary atmospheres: Modeling the spatial distribution of observed neutral radicals

Progress during the second year of a program of research on the modeling of the spatial distributions of cometary radicals is discussed herein in several major areas. New scale length laws for cometary C2 and CN were determined which explain that the previously-held apparent drop of the C2/CN ratio for large heliocentric distances does not exist and that there is no systematic variation. Monte Carlo particle trajectory model (MCPTM) analysis of sunward and anti-sunward brightness profiles of cometary C2 was completed. This analysis implies a lifetime of 31,000 seconds for the C2 parent and an ejection speed for C2 of approximately 0.5 km/sec upon dissociation from the parent. A systematic reanalysis of published C3 and OH data was begun. Preliminary results find a heliocentric distance dependence for C3 scale lengths with a much larger variation than for C2 and CN. Scale lengths for OH are generally somewhat larger than currently accepted values. The MCPTM was updated to include the coma temperature. Finally, the collaborative effort with the University of Arizona programs has yielded some preliminary CCD images of Comet P/Halley.

Combi, Michael R.↗
NASA NTRS1987

The role of plasma wave turbulence in the formation of shock waves in collisionless plasmas

A data set containing measurements for approximately 100 shock crossings was compiled, and plasma wave profiles were plotted in conjunction with magnetic field data. Three emissions analyzed include upstream electron plasma oscillations, ion acoustic noise, and low frequency electromagnetic noise. The data demonstrate that the observed waves are consistent with generation by the kinetic cross-field streaming instability. Reanalysis of shock overshoots prompted by the presence of plasma feet upstream of nominally subcritical shocks leads to the conclusion that no firm evidence exists for a sharp subcritical supercritical transition. Electron plasma oscillations persist up to the ramps of subcritical shocks and begin decaying at the front edge of the feet of supercritical shocks. Their intensity is anticorrelated with the amplitude of the foot ion acoustic noise. Wave measurements support the predicted predominance of lower hybrid-like modes over ion acoustic noise in the production of resistive (plasma) heating. Evidence for variable shock normal angles is seen upstream from nominally quasiparallel shocks. The first cases of very strong electron heating observed at the terrestrial bow shock were discovered.

Mellott, M. M.↗