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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Polar motion and length of day determination from satellite laser ranging

The kinematic and dynamic models used in obtaining the GSFC MERIT solution (using data from satellite laser ranging) for the x and y coordinates of the earth's rotation pole and the excess length-of-day (LOD) are discussed together with the analysis technique. Comparisons of the GSFC polar motion time series with the time series from the Bureau International de l'Heure shows small but consistent systematic differences (4.6 milliarcsec rms about a mean offset of 1 milliarcsec in the x component, and 2.9 milliarcsec rms about a 21 milliarcsec offset in the y component). A comparison with the data of the National Geodetic Survey's IRIS network shows departures of 2.5 milliarcsec rms about the mean for the x component and 2.0 milliarcsec rms for the y component. The precision of the GSFC earth orientation is estimated to be better than 1 milliarcsec for polar motion and 0.1 msec for excess LOD.

Smith, David E.↗
NASA NTRS1987

The effect of along-front temperature variation in a two-dimensional primitive equation model of a surface frontogenesis

The effects of along-front temperature variations on the structure and evolution of surface fronts are investigated using a two-dimensional frontogenesis model. The formulation and characteristics of the confluence-horizontal shear model are described. The structures of three frontal zones forced by confluence and characterized by zero, negative, and positive along-front potential temperature variations are analyzed; particular attention is given to the ageostrophic vertical circulation and their forcings. The temporal evolution of the model frontal zones is examined in terms of the low-level maxima of vorticity, cross-front potential temperature gradient, and convergence. The kinematic and dynamic processes influencing the frontogenesis are discussed. It is noted that the two-dimensional model is applicable to the study of the dynamical properties of frontogenesis.

Keyser, Daniel↗
NASA NTRS1987

Proceedings of the Goddard Space Flight Center Workshop on Robotics for Commercial Microelectronic Processes in Space

Potential applications of robots for cost effective commercial microelectronic processes in space were studied and the associated robotic requirements were defined. Potential space application areas include advanced materials processing, bulk crystal growth, and epitaxial thin film growth and related processes. All possible automation of these processes was considered, along with energy and environmental requirements. Aspects of robot capabilities considered include system intelligence, ROM requirements, kinematic and dynamic specifications, sensor design and configuration, flexibility and maintainability. Support elements discussed included facilities, logistics, ground support, launch and recovery, and management systems.

Source record↗
NASA NTRS1988

Eddies, streams, and convergence zones in turbulent flows

Recent studies of turbulent shear flows have shown that many of their important kinematical and dynamical properties can be more clearly understood by describing the flows in terms of individual events or streamline patterns. These events or flow regions are studied because they are associated with relatively large contributions to certain average properties of the flow, for example kinetic energy, Reynolds stress, or to particular processes in the flow, such as mixing and chemical reactions, which may be concentrated at locations where streamlines converge for fast chemical reactions (referred to as convergence or C regions), or in recirculating eddying regions for slow chemical reactions. The aim of this project was to use the numerical simulations to develop suitable criteria for defining these eddying or vortical zones. The C and streaming (S) zones were defined in order to define the whole flow field. It is concluded that homogeneous and sheared turbulent flow fields are made up of characteristic flow zones: eddy, C, and S zones. A set of objective criteria were found which describe regions in which the streamlines circulate, converge or diverge, and form high streams of high velocity flow.

Hunt, J. C. R.↗
NASA NTRS1989

A spatial operator algebra for manipulator modeling and control

A spatial operator algebra for modeling the control and trajectory design of manipulation is discussed, with emphasis on its analytical formulation and implementation in the Ada programming language. The elements of this algebra are linear operators whose domain and range spaces consist of forces, moments, velocities, and accelerations. The effect of these operators is equivalent to a spatial recursion along the span of the manipulator. Inversion is obtained using techniques of recursive filtering and smoothing. The operator alegbra provides a high-level framework for describing the dynamic and kinematic behavior of a manipulator and control and trajectory design algorithms. Implementable recursive algorithms can be immediately derived from the abstract operator expressions by inspection, thus greatly simplifying the transition from an abstract problem formulation and solution to the detailed mechanization of a specific algorithm.

Rodriguez, G.↗
NASA NTRS1990

Parallel Architecture For Robotics Computation

Universal Real-Time Robotic Controller and Simulator (URRCS) is highly parallel computing architecture for control and simulation of robot motion. Result of extensive algorithmic study of different kinematic and dynamic computational problems arising in control and simulation of robot motion. Study led to development of class of efficient parallel algorithms for these problems. Represents algorithmically specialized architecture, in sense capable of exploiting common properties of this class of parallel algorithms. System with both MIMD and SIMD capabilities. Regarded as processor attached to bus of external host processor, as part of bus memory.

Fijany, Amir↗
NASA NTRS1990

Simulating A Massive, Mobile Structure

Simulator replicates, kinematically and dynamically, mating of large, massive mobile structure with similarly large and massive fixed structure. Developed for testing berthing-and-latching mechanism. Fixed section holds active berthing-and-latching mechanism and its motor control system with optical encoder to maintain synchronization among four latches in mechanism. Tripodal load-cell network gathers data on load history of berthing operation, and infrared tracking system including light-emitting diodes produces data for position history.

Fantasia, Peter M.↗
NASA NTRS1990

Quantitative assessment of human motion using video motion analysis

In the study of the dynamics and kinematics of the human body, a wide variety of technologies was developed. Photogrammetric techniques are well documented and are known to provide reliable positional data from recorded images. Often these techniques are used in conjunction with cinematography and videography for analysis of planar motion, and to a lesser degree three-dimensional motion. Cinematography has been the most widely used medium for movement analysis. Excessive operating costs and the lag time required for film development coupled with recent advances in video technology have allowed video based motion analysis systems to emerge as a cost effective method of collecting and analyzing human movement. The Anthropometric and Biomechanics Lab at Johnson Space Center utilizes the video based Ariel Performance Analysis System to develop data on shirt-sleeved and space-suited human performance in order to plan efficient on orbit intravehicular and extravehicular activities. The system is described.

Probe, John D.↗
NASA NTRS1989

Controlling multiple manipulators using RIPS

A prototype of the RIPS architecture (Robotic Instruction Processing System) was developed. A two arm robot control experiment is underway to characterize the architecture as well as research multi-arm control. This experiment uses two manipulators to cooperatively position an object. The location of the object is specified by the host computer's mouse. Consequently, real time kinematics and dynamics are necessary. The RIPS architecture is specialized so that it can satisfy these real time constraints. The two arm experimental set-up is discussed. A major part of this work is the continued development of a good programming environment for RIPS. The C++ language is employed and favorable results exist in the targeting of this language to the RIPS hardware.

Wang, Yulun↗
NASA NTRS1990

Vorticity-dilatation boundary conditions for viscous compressible flows

The theoretical generalization, synthesis, and classification of various relevant formulations of the vorticity-dilatation conditioning problem is presented. Kinematic and dynamic conditions as well as differential and integral forms are considered. The possibility of using various variables that relate directly to vorticity and dilatation to construct the desired boundary conditions is examined. Some new formulations are given and previously proposed ones are located properly in the classification, and their interrelations are clarified.

Wu, J. Z.↗
NASA NTRS1990

The extragalactic radiation field and sharp edges to HI disks in galaxies

Observations of neutral hydrogen (HI) are widely used as a probe of the interstellar medium in galaxies and of galactic kinematics and dynamics. The 21-cm line can be used to determine galactic rotation curves far beyond the optical disk, and is one of the prime sources of evidence for the existence of dark haloes in spiral galaxies. However, a recent attempt to measure the 21-cm emission from NGC 3198 to very low column densities (N sub H approx. equals 5 times 10 to the 18th power) found that the HI disk is very sharply truncated at a column density of a few times 10 to the 19th power (Sancisi 1989, private communication). This discovery reinforces the earlier suggestion (Briggs et al. 1980) that extended, low-column density envelopes of neutral hydrogen are not common around galaxies. Here the author suggests that the sharp edge seen in the HI disk in NGC 3198 is consistent with a model in which a self-gravitating neutral HI disk is photoionized by the extragalactic radiation field. The possibility that the extragalactic background would produce sharp edges to HI disks was first suggested by Silk and Sunyaev (1976).

Maloney, Philip Richard↗
NASA NTRS1990

High resolution CO images of Seyfert Galaxies

The CO (J = 1-0) emission of three Seyfert galaxies, NGC 3227, NGC 7469, and NGC 5033 was imaged. The CO emission in NGC 3227 and NGC 7469 appears as compact structures centered on the active nuclei, containing substantial fractions of the single-dish flux. In NGC 3227, 10 percent of the CO flux detected by the interferometer is contained within the ionized narrow-line region. The unresolved molecular gas concentrations in the nucleus of NGC 3227 imply a CO mass of 65 million solar masses concentrated within a diameter less than 50 pc. The CO emission in NGC 5033 is not detected at this resolution, implying a CO structure size of 20 to 60 arcsec. Continuum emission at 2.7 mm is not detected in any of the three galaxies. In the center of NGC 7469, the H2 mass is comparable to the dynamical mass. Kinematic studies of the detected gas reveal a rotational motion of the gas in NGC 3227 and NGC 7469, allowing identification of the gas in NGC 7469 with a nuclear starburst. These data are consistent with the idea that interactions between galaxies cause gas to concentrate in their nuclei thereby feeding starburst and Seyfert activity.

Meixner, M.↗
NASA NTRS1990

Global variability of water vapor and condensate from SSM/I

In the three years since its launch, the Special Sensor Microwave Imager (SSM/I) provided the beginnings of a data set crucial to the study of the Earth's global hydrologic cycle. Investigations with SSM/I centered largely on two themes: (1) an analysis of the variability in atmospheric moisture as a signature of dynamic and kinematic processes, and (2) development of high quality data sets for determining moisture balance and, eventually, diabatic heating on regional and planetary scales. To date, most of the emphasis has been on the precipitable water field since algorithms for this quantity appear to be the most mature. In addition, researchers began work with liquid water, precipitating ice and ocean surface wind stress fields. The retrievals used in these studies are from algorithms developed by Wentz (RSS Tech Rpt. 1989) and Spencer (1988 JTECH).

Robertson, Franklin R.↗
NASA NTRS1991

Development of the wake behind a circular cylinder impulsively started into rotatory and rectilinear motion: Intermediate rotation rates

The temporal development of two-dimensional viscous incompressible flow generated by a circular cylinder started impulsively into steady rotatory and rectilinear motion is studied by integration of a velocity/vorticity formulation of the governing equations, using an explicit finite-difference/pseudo-spectral technique and an implementation of the Biot-Savart law. Results are presented for a Reynolds number of 200 (based on the cylinder diameter 2a and the magnitude U of the rectilinear velocity) for several values of the angular/rectilinear speed ratio alpha = (omega x a)/U (where omega is the angular speed) up to 3.25. Several aspects of the kinematics and dynamics of the flow not considered earlier are discussed. For higher values of alpha, the results indicate that for Re = 200, vortex shedding does indeed occur for alpha = 3.25. The shedding process is; however, very different from that which gives rise to the usual Karman vortex street for alpha = 0. In particular, consecutive vortices shed by the body can be shed from the same side and be of the same sense, in contrast to the nonrotating case, in which mirror-image vortices of opposite sense are shed alternately on opposite sides of the body. The implications of the results are discussed in relation to the possibility of suppressing vortex shedding by open or closed-loop control of the rotation rate.

Chen, Yen-Ming↗
NASA NTRS1990

Some aspects of robotics calibration, design and control

The main objective is to introduce techniques in the areas of testing and calibration, design, and control of robotic systems. A statistical technique is described that analyzes a robot's performance and provides quantitative three-dimensional evaluation of its repeatability, accuracy, and linearity. Based on this analysis, a corrective action should be taken to compensate for any existing errors and enhance the robot's overall accuracy and performance. A comparison between robotics simulation software packages that were commercially available (SILMA, IGRIP) and that of Kennedy Space Center (ROBSIM) is also included. These computer codes simulate the kinematics and dynamics patterns of various robot arm geometries to help the design engineer in sizing and building the robot manipulator and control system. A brief discussion on an adaptive control algorithm is provided.

Tawfik, Hazem↗
NASA NTRS1990

Statistical mechanics models for motion and force planning

The models of statistical mechanics provide an alternative to the methods of classical mechanics more traditionally used in robotics. They have a potential to: improve analysis of object collisions; handle kinematic and dynamic contact interactions within the same frmework; and reduce the need for perfect deterministic world model information. The statistical mechanics models characterize the state of the system as a probability density function (p.d.f.) whose time evolution is governed by a partial differential equation subject to boundary and initial conditions. The boundary conditions when rigid objects collide reflect the conservation of momentum. The models are being developed to embedd in remote semi-autonomous systems with a need to reason and interact with a multiobject environment.

Rodriguez, G.↗
NASA NTRS1990

On the nature of control algorithms for space manipulators

A study of the characteristics of control algorithms that can be applied to the motion control of space manipulators is reported. The results obtained show that nearly any control algorithm that can be applied to conventional terrestrial fixed-base manipulators, with a few additional conditions, can be directly applied to free-floating space manipulators. Barycenters are used to formulate efficiently the kinematic and dynamic equations of free-floating space manipulators. A control algorithm for a space manipulator system is designed to demonstrate the value of the analysis.

Papadopoulos, Evangelos↗
NASA NTRS1992

Robot Control Based On Spatial-Operator Algebra

Method for mathematical modeling and control of robotic manipulators based on spatial-operator algebra providing concise representation and simple, high-level theoretical frame-work for solution of kinematical and dynamical problems involving complicated temporal and spatial relationships. Recursive algorithms derived immediately from abstract spatial-operator expressions by inspection. Transition from abstract formulation through abstract solution to detailed implementation of specific algorithms to compute solution greatly simplified. Complicated dynamical problems like two cooperating robot arms solved more easily.

Rodriguez, Guillermo↗