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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Observational evidence of continual heating in X-ray emitting coronal loops

A 90 s time resolution study of the soft X-ray emission from three active region loops shows the emission to be constant to about two percent over the half hour period of observation. Soft X-ray observations in two wavebands are used to deduce the temperature and density of these loops. The data unambiguously demonstrate that energy is supplied to each loop during the observations. If heating is due to discrete events, the time interval between events is shown to be less than 10 min, which is short relative to the radiative cooling time of the loops.

Gerassimenko, M.↗
NASA NTRS1997

Method for neural network control of motion using real-time environmental feedback

A method of motion control for robotics and other automatically controlled machinery using a neural network controller with real-time environmental feedback. The method is illustrated with a two-finger robotic hand having proximity sensors and force sensors that provide environmental feedback signals. The neural network controller is taught to control the robotic hand through training sets using back- propagation methods. The training sets are created by recording the control signals and the feedback signal as the robotic hand or a simulation of the robotic hand is moved through a representative grasping motion. The data recorded is divided into discrete increments of time and the feedback data is shifted out of phase with the control signal data so that the feedback signal data lag one time increment behind the control signal data. The modified data is presented to the neural network controller as a training set. The time lag introduced into the data allows the neural network controller to account for the temporal component of the robotic motion. Thus trained, the neural network controlled robotic hand is able to grasp a wide variety of different objects by generalizing from the training sets.

Buckley, Theresa M.↗
NASA NTRS1984

Electromyographic Patterns Associated with Discrete Limb Movements

The relationship between the movement time (MT) for accurate and rapid discrete movements of distance A to a target of width W was quantified by Fitts and is given by the equation: MT = a + b log sub 2 (2A/W). This relationship, known as Fitt's Law, received considerable support for many types of movements. It also raises the interesting question: if MT is affected by distance moved and accuracy, then how do the patterns of muscle activation alter? It is suggested that it is unlikely that all movements are initiated by a pulse of constant duration. Instead, it seems that movements are initiated by an agonist burst which is scaled both in the amount of activation and the duration of activation according to either distance, target size, velocity, or a combination of factors. The number of bursts varies considerably and further research is required to establish: (1) which factors affect the pattern of the signal and (2) how different patterns produce movement trajectories.

Corcos, D. M.↗
NASA NTRS2014

The Cassini Solstice Mission: Streamlining Operations by Sequencing with PIEs

The Cassini Solstice Mission (CSM) is the second extended mission phase of the highly successful Cassini/Huygens mission to Saturn. Conducted at a much-reduced funding level, operations for the CSM have been streamlined and simplified significantly. Integration of the science timeline, which involves allocating observation time in a balanced manner to each of the five different science disciplines (with representatives from the twelve different science instruments), has long been a labor-intensive endeavor. Lessons learned from the prime mission (2004-2008) and first extended mission (Equinox mission, 2008-2010) were utilized to design a new process involving PIEs (Pre-Integrated Events) to ensure the highest priority observations for each discipline could be accomplished despite reduced work force and overall simplification of processes. Discipline-level PIE lists were managed by the Science Planning team and graphically mapped to aid timeline deconfliction meetings prior to assigning discrete segments of time to the various disciplines. Periapse segments are generally discipline-focused, with the exception of a handful of PIEs. In addition to all PIEs being documented in a spreadsheet, allocated out-of-discipline PIEs were entered into the Cassini Information Management System (CIMS) well in advance of timeline integration. The disciplines were then free to work the rest of the timeline internally, without the need for frequent interaction, debate, and negotiation with representatives from other disciplines. As a result, the number of integration meetings has been cut back extensively, freeing up workforce. The sequence implementation process was streamlined as well, combining two previous processes (and teams) into one. The new Sequence Implementation Process (SIP) schedules 22 weeks to build each 10-week-long sequence, and only 3 sequence processes overlap. This differs significantly from prime mission during which 5-week-long sequences were built in 24 weeks, with 6 overlapping processes.

Vandermey, Nancy↗
NASA NTRS1992

User's manual for three dimensional FDTD version D code for scattering from frequency-dependent dielectric and magnetic materials

The Penn State Finite Difference Time Domain Electromagnetic Scattering Code version D is a 3-D numerical electromagnetic scattering code based upon the finite difference time domain technique (FDTD). The manual provides a description of the code and corresponding results for several scattering problems. The manual is organized into 14 sections: introduction; description of the FDTD method; operation; resource requirements; version D code capabilities; a brief description of the default scattering geometry; a brief description of each subroutine; a description of the include file; a section briefly discussing Radar Cross Section computations; a section discussing some scattering results; a sample problem setup section; a new problem checklist; references and figure titles. The FDTD technique models transient electromagnetic scattering and interactions with objects of arbitrary shape and/or material composition. In the FDTD method, Maxwell's curl equations are discretized in time-space and all derivatives (temporal and spatial) are approximated by central differences.

Beggs, John H.↗
NASA NTRS2000

Numerical Solutions to the Third CAA Workshop Benchmark Problems

This paper presents numerical solutions to the problems of propagation of sound waves through a transonic nozzle, shock-sound interactions, and automobile noise involving feedback of the third NASA Computational Aeroacoustics (CAA) Workshop on benchmark problems. The numerical algorithm is based on a dual time scheme for temporal discretization and a third-order finite volume scheme for spatial discretization. The aims of this study are to apply a dual time stepping scheme to treat aeroacoustic problems of sound propagation and to validate our CAA solver with the benchmark problems for developing a numerical tool for noise analysis and control.

Loh, Roy H.↗
NASA NTRS1974

Discrete optimal control approach to a four-dimensional guidance problem near terminal areas

Description of a computer-oriented technique to generate the necessary control inputs to guide an aircraft in a given time from a given initial state to a prescribed final state subject to the constraints on airspeed, acceleration, and pitch and bank angles of the aircraft. A discrete-time mathematical model requiring five state variables and three control variables is obtained, assuming steady wind and zero sideslip. The guidance problem is posed as a discrete nonlinear optimal control problem with a cost functional of Bolza form. A solution technique for the control problem is investigated, and numerical examples are presented. It is believed that this approach should prove to be useful in automated air traffic control schemes near large terminal areas.

Nagarajan, N.↗
NASA NTRS1972

Mapping an operator's perception of a parameter space

Operators monitored the output of two versions of the crossover model having a common random input. Their task was to make discrete, real-time adjustments of the parameters k and tau of one of the models to make its output time history converge to that of the other, fixed model. A plot was obtained of the direction of parameter change as a function of position in the (tau, k) parameter space relative to the nominal value. The plot has a great deal of structure and serves as one form of representation of the operator's perception of the parameter space.

Pew, R. W.↗
NASA NTRS1973

Use of ERTS-1 data for regional planning in the Metropolitan Washington Council of Governments: A short brief

Land use and land use activity changes over discrete intervals of time represent basic data requirements in regional planning studies. Two examples of land use analysis required by the Council of Governments' transportation planning staff are described. Both were undertaken utilizing remote sensing imagery analysis. One study using large scale aircraft imagery developed a high degree of analytical detail and functional identification. The other, to support further detailed data base evaluation, utilizing ERTS-1 and small scale aircraft imagery, developed data identifying in more general detail major activity changes within the metropolitan region.

Mallon, H. J.↗
NASA NTRS1975

Uniform sampling analysis of a hybrid phase-locked loop with a sample-and-hold phase detector

Phase-locked-loop (PLL) bit synchronizers often employ integrate-and-dump type phase detectors that provide phase error information only at discrete points in time. Usually these phase detectors are followed by sample-and-hold circuits to produce a stairstep error voltage as the input to a standard analog circuit loop filter. When the loop is configured in this manner, it is referred to as a hybrid PLL. Sampled-data analysis methods (Z transforms) are used to determine the stability and transient response of this loop.

Barab, S.↗
NASA NTRS1978

The UCSD/MIT hard X-ray and low energy gamma-ray experiment for HEAO-1 - Design and early results

Primary scientific objectives of the experiment are the measurement of the spectra and time variations of discrete sources and the spectrum and isotropy of the diffuse background, all in the 10 keV to 10 MeV energy range. The instrument consists of an array of 7 NaI(Tl)/CsI(Na) phoswich-type detectors and 8 large CsI(Na) shields. In order to achieve the maximum sensitivity allowed by weight, data rate and funding constraints of the mission, three detector and aperture geometries were selected. The instrument's total sensitive area is 494 sq cm. The fields of view vary from 1.7 deg x 20 deg FWHM at low energies to 43 deg FWHM at high energies. The basic instrument concepts, details of the mechanical and electrical design, and pre-launch calibrations are presented. In-orbit performance is described and background measurements are analyzed and used to estimate the experiment's ultimate sensitivity.

Matteson, J. L.↗
NASA NTRS1982

Infrared array detectors

Arrays of detectors sensitive to infrared radiation will enable astronomical observations to be made with shorter observing times than with discrete detectors and with good relative spatial accuracy. Systems using such arrays are being developed for astronomy in several regions of the electromagnetic spectrum. An example of an infrared system is given here consisting of a 32x32 element bismuth doped silicon charge injection device array that has been used in an astronomical camera.

Arens, J. F.↗
NASA NTRS1985

Accuracy of schemes with nonuniform meshes for compressible fluid flows

The accuracy of the space discretization for time-dependent problems when a nonuniform mesh is used is considered. Many schemes reduce to first-order accuracy while a popular finite volume scheme is even inconsistent for general grids. This accuracy is based on physical variables. However, when accuracy is measured in computational variables then second-order accuracy can be obtained. This is meaningful only if the mesh accurately reflects the properties of the solution. In addition, the stability properties of some improved accurate schemes are analyzed and it can be shown that they also allow for larger time steps when Runge-Kutta type methods are used to advance in time.

Turkel, E.↗
NASA NTRS1986

Accuracy of schemes with nonuniform meshes for compressible fluid flows

The accuracy of the space discretization for time-dependent problems when a nonuniform mesh is used is considered. Many schemes reduce to first-order accuracy while a popular finite volume scheme is even inconsistent for general grids. This accuracy is based on physical variables. However, when accuracy is measured in computational variables then second-order accuracy can be obtained. This is meaningful only if the mesh accurately reflects the properties of the solution. In addition, the stability properties of some improved accurate schemes are analyzed and it can be shown that they also allow for larger time steps when Runge-Kutta type methods are used to advance in time.

Turkel, Eli↗
NASA NTRS1990

On the continuous dependence with respect to sampling of the linear quadratic regulator problem for distributed parameter systems

The convergence of solutions to the discrete or sampled time linear quadratic regulator problem and associated Riccati equation for infinite dimensional systems to the solutions to the corresponding continuous time problem and equation, as the length of the sampling interval (the sampling rate) tends toward zero (infinity) is established. Both the finite and infinite time horizon problems are studied. In the finite time horizon case, strong continuity of the operators which define the control system and performance index together with a stability and consistency condition on the sampling scheme are required. For the infinite time horizon problem, in addition, the sampled systems must be stabilizable and detectable, uniformly with respect to the sampling rate. Classes of systems for which this condition can be verified are discussed. Results of numerical studies involving the control of a heat/diffusion equation, a hereditary of delay system, and a flexible beam are presented and discussed.

Rosen, I. G.↗
NASA NTRS1990

Quiet mode for nonlinear rotor models

High frequency harmonics are generated by helicopter rotor systems, and nonlinear blade-element models of these systems create the same harmonics. In discrete real-time rotorcraft simulation, however, especially for handling qualities research, they are more of a nuisance than a benefit. The cycle times required to adequately represent them are rarely obtainable. The result is that distinct frequencies alias into the pilot and simulator bandwidths, thereby decreasing simulation fidelity. However, use of an interpolation procedure permits the observation of harmonics at their proper frequency locations, and an accompanying notch filter may then be used to attenuate the harmonics prior to decimation. Rotorcraft simulations using these techniques are not contaminated with the spurious frequencies that create variable trim points, produce erroneous stability and control derivative data, and obscure time histories.

Mcfarland, R. E.↗