Search NASA⌕ Search

SEARCH · Search NASA

Results for “simultaneous operations”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Telerobotic control of a dextrous manipulator using master and six-DOF hand-controllers for space assembly and servicing tasks

Two studies were conducted evaluating methods of controlling a telerobot; bilateral force reflecting master controllers and proportional rate six degrees of freedom (DOF) hand controllers. The first study compared the controllers on performance of single manipulator arm tasks, a peg-in-the-hole task, and simulated satellite orbital replacement unit changeout. The second study, a Space Station truss assembly task, required simultaneous operation of both manipulator arms (all 12 DOFs) and complex multiaxis slave arm movements. Task times were significantly longer and fewer errors were committed with the hand controllers. The hand controllers were also rated significantly higher in cognitive and manual control workload on the two-arm task. The master controllers were rated significantly higher in physical workload. There were no significant differences in ratings of manipulator control quality.

O'Hara, John M.↗
NASA NTRS1987

Time-partitioning simulation models for calculation of parallel computers

A technique allowing time-staggered solution of partial differential equations is presented in this report. Using this technique, called time-partitioning, simulation execution speedup is proportional to the number of processors used because all processors operate simultaneously, with each updating of the solution grid at a different time point. The technique is limited by neither the number of processors available nor by the dimension of the solution grid. Time-partitioning was used to obtain the flow pattern through a cascade of airfoils, modeled by the Euler partial differential equations. An execution speedup factor of 1.77 was achieved using a two processor Cray X-MP/24 computer.

Milner, Edward J.↗
NASA NTRS1988

Three component laser anemometer measurements in an annular cascade of core turbine vanes with contoured end wall

The three mean velocity components were measured in a full-scale annular turbine stator cascade with contoured hub end wall using a newly developed laser anemometer system. The anemometer consists of a standard fringe configuration using fluorescent seed particles to measure the axial and tangential components. The radial component is measured with a scanning confocal Fabry-Perot interferometer. These two configurations are combined in a single optical system that can operate simultaneously in a backscatter mode through a single optical access port. Experimental measurements were obtained both within and downstream of the stator vane row and compared with calculations from a three-dimensional inviscid computer program. In addition, detailed calibration procedures are described that were used, prior to the experiment, to accurately determine the laser beam probe volume location relative to the cascade hardware.

Goldman, Louis J.↗
NASA NTRS1988

Infrared measurements in the spring 1987 ozone hole

Solar spectra were recorded from Arrival Heights (McMurdo), Antartica, with a FTIR system during the austral spring of 1987. Spectra were recorded on 22 days from September 13 through October 28. The instrument was setup with 2 detectors for simultaneous operation in 2 wavelength regions. Several stratospheric gases have measurable absorptions in these regions including HCl, HNO3, O3, ClONO2, and NO2. The system is equipped with an automatic solar tracking system and records data on tape cartridges. A portable personal computer allows Fourier transforming and initial processing of some of the data. The HNO3 gas column amount shows large variations, but no apparent correlation with stratospheric temperature. The HCl column shows a steady increase from 0.9 x 10 to the 15th power molecules/sq.cm. on September 13 to 1.5 x 10 to the 15th power on October 6. McMurdo moved out of the polar vortex for a few days, and the HCl column jumped to 2.9 x 10 to the 15th power by October 11. Although McMurdo moved back under the vortex, the HCl continued to increase, reaching 3.4 x 10 to the 15th power at the end of the period.

Murcray, F. J.↗
NASA NTRS1990

Selecting Modulation Indices For Telemetry And Ranging

Report describes algorithm for selection of optimum modulation indices in system for communication between ground station and spacecraft, in which ranging channel operated simultaneously with data (command and telemetry) channel. Provides for optimum division of power among data, ranging, and carrier channels and reduces degradation of performance by undesired interferences among signals.

Nguyen, Tien M.↗
NASA NTRS1990

Microgravity acoustic mixing for particle cloud combustors

Experimental and theoretical investigations of acoustic mixing procedures designed to uniformly distribute fuel particles in a combustion tube for application in the proposed Particle Cloud Combustion Experiment (PCCE) are described. Two acoustic mixing methods are investigated: mixing in a cylindrical tube using high frequency spinning modes generated by suitably phased, or quadrature speakers, and acoustic premixing in a sphere. Quadrature mixing leads to rapid circumferential circulation of the powder around the tube. Good mixing is observed in the circulating regions. However, because axial inhomogeneities are necessarily present in the acoustic field, this circulation does not extend throughout the tube. Simultaneous operation of the quadrature-speaker set and the axial-speaker was observed to produce considerably enhanced mixing compared to operation of the quadrature-speaker set alone. Mixing experiments using both types of speakers were free of the longitudinal powder drift observed using axial-speakers alone. Vigorous powder mixing was obtained in the sphere for many normal modes: however, in no case was the powder observed to fill the sphere entirely. Theoretical analysis indicated that mixing under steady conditions cannot fill more than a hemisphere except under very unusual conditions. Premixing in a hemisphere may be satisfactory; otherwise, complete mixing in microgravity might be possible by operating the speaker in short bursts. A general conclusion is that acoustic transients are more likely to produce good mixing than steady state conditions. The reason is that in steady conditions, flow structures like nodal planes are possible and often even unavoidable. These tend to separate the mixing region into cells across which powder cannot be transferred. In contrast, transients not only are free of such structures, they also have the characteristics, desirable for mixing, of randomness and disorder. This conclusion is corroborated by mixing experiments using axial waves.

Pla, Frederic↗
NASA NTRS1990

A novel demodulator/detector for digital and analog signals on LMR channels

The design, implementation, and performance of an all-digital demodulator/detector suitable for differentially encoded phase-shift keying (DPSK), continuous-phase frequency-shift keying (CPFSK), frequency-shift keying (FSK), and analog FM are discussed. In this demodulator/detector, two detectors, one noncoherent and another differentially coherent, operate simultaneously to provide data detection and automatic frequency control (AFC). Test results indicate that the system provides improved performance over the conventional analog quadrature detector for two-period raised-cosine (2RC) CPFSK modulation in additive white Gaussian noise (AWGN) and Rayleigh fading channels. Being all-digital, the demodulator/detector is well suited for integrated circuit implementation. In addition, the system performs as well as the analog quadrature detector for analog FM voice transmissions, thereby maintaining full compatibility with analog land mobile radio (LMR) transmissions.

Saulnier, Gary J.↗
NASA NTRS1991

Parallel Inferencing For Rule-Based Expert Systems

Improved approach to development of expert-system computer programs increases speed of execution on parallel processors; that is, on multiple coordinated computers operating simultaneously, each on different part of problem. Based on detection and analysis of hidden parallelism in knowledge bases (collections of "if...then..." rules) and exploitation of this parallelism to maximize speed of execution on parallel processors connected to each other in hypercube configuration.

Schwuttke, Ursula M.↗
NASA NTRS1989

Mission to Planet Earth - The Earth Observing System

The Earth Observing System (EOS) is a major component of NASA's Mission to Planet Earth initiative. It seeks to achieve a comprehensive understanding of the earth as a system, including its various components (solid earth, atmosphere, hydrosphere, and biosphere) and its various processes (hydrologic cycle, biogeochemical cycles, and climatic processes). This is to be achieved by space-based remote sensing, using a variety of instrumentation and observing techniques, operating simultaneously, and providing continuous and complete global coverage over a long time period. A few of the investigations to be carried out with EOS, in areas of (1) imagery of the earth from space, and (2) investigations of the earth's radiation budget are described. EOS is expected to make major contributions to the basic earth sciences (geology, meteorology, etc.), but its results also will have important immediate or near-term practical applications which will improve the quality of life on earth.

Carruthers, George R.↗
NASA NTRS1990

Thermal management of advanced fuel cell power systems

It is shown that fuel cell devices are particularly attractive for the high-efficiency, high-reliability space hardware necessary to support upcoming space missions. These low-temperature hydrogen-oxygen systems necessarily operate with two-phase water. In either PEMFCs (proton exchange membrane fuel cells) or AFCs (alkaline fuel cells), engineering design must be critically focused on both stack temperature control and on the relative humidity control necessary to sustain appropriate conductivity within the ionic conductor. Water must also be removed promptly from the hardware. Present designs for AFC space hardware accomplish thermal management through two coupled cooling loops, both driven by a heat transfer fluid, and involve a recirculation fan to remove water and heat from the stack. There appears to be a certain advantage in using product water for these purposes within PEM hardware, because in that case a single fluid can serve both to control stack temperature, operating simultaneously as a heat transfer medium and through evaporation, and to provide the gas-phase moisture levels necessary to set the ionic conductor at appropriate performance levels. Moreover, the humidification cooling process automatically follows current loads. This design may remove the necessity for recirculation gas fans, thus demonstrating the long-term reliability essential for future space power hardware.

Vanderborgh, N. E.↗
NASA NTRS1991

Doppler detection of decompression bubbles with computer assisted digitization of ultrasonic signals

The use of an inexpensive, commercially available audio digitizer in conjunction with a PC to digitize Doppler bubble signals for visual and electronic evaluation is reported. This device can be operated simultaneously with Doppler audio monitoring. Precordial and arterial Doppler recordings of gas bubbles were obtained from anesthetized dogs after intravascular infusion or following decompression. Additional evaluations were conducted on Doppler bubble recordings obtained from human decompression studies. The device can be used in real-time or for later signal analysis. Accompanying menu-driven software provides for numerous signal modification options and visual displays. This device can provide a simultaneous visual display of Doppler signals normally available only for audio evaluation.

Butler, B. D.↗
NASA NTRS1992

A Multi-wavelength Ozone Lidar for the EASOE Experiment

The study of the ozone layer during winter and springtime in high latitude regions is a major issue in atmospheric research. For a better understanding of these problems, an important experimental campaign called EASOE (European Arctic Stratospheric Ozone Experiment) was organized by the European Community during the winter 1991-1992. Its main objective was to establish a budget of the ozone destruction processes on the whole northern hemisphere. This implied the simultaneous operation of different types of instruments located in both high and mid-latitude regions in order to study the destruction processes as well as the evolution of the ozone layer during the period of the campaign. A description will be given here of a mobile ozone lidar instrument specially designed for operation during the EASOE campaign. This system, which performs ozone measurements in the 5 to 40 km altitude range was located in Sodankyla, Finland as part of the ELSA experiment which also includes operation of another multi-wavelength lidar designed for polar stratospheric cloud measurements.

Godin, S.↗
NASA NTRS1992

Rolling maneuver load alleviation using active controls

Rolling Maneuver Load Alleviation (RMLA) was demonstrated on the Active Flexible Wing (AFW) wind tunnel model in the LaRC Transonic Dynamics Tunnel. The design objective was to develop a systematic approach for developing active control laws to alleviate wing incremental loads during roll maneuvers. Using linear load models for the AFW wind-tunnel model which were based on experimental measurements, two RMLA control laws were developed based on a single-degree-of-freedom roll model. The RMLA control laws utilized actuation of outboard control surface pairs to counteract incremental loads generated during rolling maneuvers and roll performance. To evaluate the RMLA control laws, roll maneuvers were performed in the wind tunnel at dynamic pressures of 150, 200, and 250 psf and Mach numbers of .33, .38, and .44, respectively. Loads obtained during these maneuvers were compared to baseline maneuver loads. For both RMLA controllers, the incremental torsion moments were reduced by up to 60 percent at all dynamic pressures and performance times. Results for bending moment load reductions during roll maneuvers varied. In addition, in a multiple function test, RMLA and flutter suppression system control laws were operated simultaneously during roll maneuvers at dynamic pressures 11 percent above the open-loop flutter dynamic pressure.

Woods-Vedeler, Jessica A.↗
NASA NTRS1991

Damping and structural control of the JPL phase 0 testbed structure

This paper describes recent advances in structural quieting technology as applied to active truss structures intended for high precision space based optics applications. The active structure incorporates piezoelectric active members which exert control forces internal to the structure and thereby improve the structure's dimensional stability. The control architecture involves two layers of feedback control. The first utilizes collocated measurements of force and velocity at the active member to achieve active damping, the second utilizes noncollocated measurements of acceleration at the location of a simulated optical component to achieve structural stabilization. The local control loops are based on the concept of impedance matching, the global control loops are designed using robust control methods. These two levels of control are intended to operate simultaneously; however, in this paper each approach is applied individually. The combined implementation is left for future work.

Fanson, James L.↗
NASA NTRS1992

Rolling Maneuver Load Alleviation using active controls

Rolling Maneuver Load Alleviation (RMLA) has been demonstrated on the Active Flexible Wing (AFW) wind tunnel model in the NASA Langley Transonic Dynamics Tunnel. The design objective was to develop a systematic approach for developing active control laws to alleviate wing incremental loads during roll maneuvers. Using linear load models for the AFW wind-tunnel model which were based on experimental measurements, two RMLA control laws were developed based on a single-degree-of-freedom roll model. The RMLA control laws utilized actuation of outboard control surface pairs to counteract incremental loads generated during rolling maneuvers and actuation of the trailing edge inboard control surface pairs to maintain roll performance. To evaluate the RMLA control laws, roll maneuvers were performed in the wind tunnel at dynamic pressures of 150, 200, and 250 psf and Mach numbers of 0.33, .38 and .44, respectively. Loads obtained during these maneuvers were compared to baseline maneuver loads. For both RMLA controllers, the incremental torsion moments were reduced by up to 60 percent at all dynamic pressures and performance times. Results for bending moment load reductions during roll maneuvers varied. In addition, in a multiple function test, RMLA and flutter suppression system control laws were operated simultaneously during roll maneuvers at dynamic pressures 11 percent above the open-loop flutter dynamic pressure.

Woods-Vedeler, Jessica A.↗
NASA NTRS1991

An algorithm to design a multiple-channel communications system

The authors present a novel algorithm to design a phase-modulated residual carrier communications system for optimum performance. The algorithm has been developed as an aid in the design of two telemetry data channels operating simultaneously with a turn-around ranging signal. The algorithm provides the selection of an optimum subcarrier frequency and modulation indices for minimizing the mutual interferences among the channels to achieve desired link performance margins. The set of modulation indices provided by this algorithm will also achieve an optimum power division between the carrier, the ranging and the high data rate and low data rate channels. Finally, a software program using this algorithm has been developed for use with personal computers. This program provides the computation of the optimum subcarrier frequencies and modulation indices for a standard case that is recommended by the international Consultative Committee for Space Data Systems.

Nguyen, Tien M.↗
NASA NTRS1993

The electrodynamic and hydrodynamic phenomena in magnetically-levitated molten droplets. II - Transient behavior and heat transfer considerations

Computed results are presented describing the transient evolution of the velocity and the temperature fields in a levitation-melted, electromagnetically-positioned metallic sample under microgravity, for conditions, when the heating current is switched off. Thus the calculations trace the evolution from one steady state corresponding to the simultaneous operation of both the heating and the positioning coils to that corresponding to the operation of the positioning coils only. The calculations have shown that the velocity field will decay much more rapidly than the temperature field, so that the cooling and subsequent undercooling and recalescence of the samples should take place from an essentially stagnant melt, meeting the original objectives of the experiment. The computed results for the velocity decay appear to agree with asymptotic calculations and also appear to follow the scaling laws.

Zong, Jin-Ho↗
NASA NTRS1993

Surface hot-film method for the measurement of transition, separation and reattachment points

A real-time method of determining positions of laminar-to-turbulent transition region, separation and reattachment points and stagnation points using an array of simultaneously operated surface-mounted hot-film sensors has been developed and applied to a wind-tunnel test of a multielement airfoil model. Determination of various types of transitions and flow directions in various regimes of flows seen on multielement airfoils are possible without precise sensor calibration or laborious post-test data analysis. The results agree with established method and theoretical methods, but determination of turbulent reattachment points are not yet satisfactory.

Nakayama, Akihiko↗