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  • 1
    Publication Date: 2011-08-24
    Description: The closely integrated design effort entailed by such prospective NASA-JPL project hardware as the Large Deployable Reflector, encompassing controls, dynamics, structures, optics, and thermal considerations, has prompted the development of the Figure Control Simulation, or 'FCSim' simulation program. This code is presently demonstrated for the case of a 7-segment, 3.65-m diameter primary mirror designed for 100-800 micron wavelengths. The optical component of the analysis can handle multispectral images, extended sources, image smear due to structural jitter, and mirror segment surface irregularities.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: In: Controls for optical systems; Proceedings of the Meeting, Orlando, FL, Apr. 21, 22, 1992 (A93-34276 13-74); p. 243-252.
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  • 2
    Publication Date: 2013-08-31
    Description: In this work, various parameter estimation techniques are investigated in the context of structural system identification utilizing distributed parameter models and 'measured' time-domain data. Distributed parameter models are formulated using the PDEMOD software developed by Taylor. Enhancements made to PDEMOD for this work include the following: (1) a Wittrick-Williams based root solving algorithm; (2) a time simulation capability; and (3) various parameter estimation algorithms. The parameter estimations schemes will be contrasted using the NASA Mini-Mast as the focus structure.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA. Langley Research Center, NASA Workshop on Distributed Parameter Modeling and Control of Flexible Aerospace Systems; p 215-239
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  • 3
    Publication Date: 2013-08-31
    Description: Thirty years of control systems research has produced an enormous body of theoretical results in feedback synthesis. Yet such results see relatively little practical application, and there remains an unsettling gap between classical single-loop techniques (Nyquist, Bode, root locus, pole placement) and modern multivariable approaches (LQG and H infinity theory). Large scale, complex systems, such as high performance aircraft and flexible space structures, now demand efficient, reliable design of multivariable feedback controllers which optimally tradeoff performance against modeling accuracy, bandwidth, sensor noise, actuator power, and control law complexity. A methodology is described which encompasses numerous practical design constraints within a single unified formulation. The approach, which is based upon coupled systems or modified Riccati and Lyapunov equations, encompasses time-domain linear-quadratic-Gaussian theory and frequency-domain H theory, as well as classical objectives such as gain and phase margin via the Nyquist circle criterion. In addition, this approach encompasses the optimal projection approach to reduced-order controller design. The current status of the overall theory will be reviewed including both continuous-time and discrete-time (sampled-data) formulations.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: JPL, Proceedings of the 3rd Annual Conference on Aerospace Computational Control, Volume 1; p 293
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  • 4
    Publication Date: 2019-06-28
    Description: We present a method for visualizing unsteady flow by displaying its vortices. The vortices are identified by using a vorticity-predictor pressure-corrector scheme that follows vortex cores. The cross-sections of a vortex at each point along the core can be represented by a Fourier series. A vortex can be faithfully reconstructed from the series as a simple quadrilateral mesh, or its reconstruction can be enhanced to indicate helical motion. The mesh can reduce the representation of the flow features by a factor of one thousand or more compared with the volumetric dataset. With this amount of reduction it is possible to implement an interactive system on a graphics workstation to permit a viewer to examine, in three dimensions, the evolution of the vortical structures in a complex, unsteady flow.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA-CR-198180 , NAS 1.26:198180 , ICASE-95-51
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  • 5
    Publication Date: 2019-06-28
    Description: We describe an interactive, immersive 3D system called Tracktur, which allows a viewer to track the development of a turbulent flow. Tracktur displays time-varying vortex structures extracted from a numerical flow simulation. The user navigates the space and probes the data within a windy 3D landscape. In order to sustain a constant frame rate, we enforce a fixed polygon budget on the geometry. We supplement the interactive system with interactive, hypertext documentation available on the World Wide Web. In actual use by a fluid dynamicist, the system has yielded new insights into the transition to turbulence in a laminar flow.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA-CR-198179 , NAS 1.26:198179 , ICASE-95-50
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  • 6
    Publication Date: 2019-06-28
    Description: An interactive adaptive remeshing algorithm utilizing a frontal grid generator and a variety of time integration schemes for the two-dimensional Euler equations on unstructured meshes is presented. Several device dependent interactive graphics interfaces have been developed along with a device independent DI-3000 interface which can be employed on any computer that has the supporting software including the Cray-2 supercomputers Voyager and Navier. The time integration methods available include: an explicit four stage Runge-Kutta and a fully implicit LU decomposition. A cell-centered finite volume upwind scheme utilizing Roe's approximate Riemann solver is developed. To obtain higher order accurate results a monotone linear reconstruction procedure proposed by Barth is utilized. Results for flow over a transonic circular arc and flow through a supersonic nozzle are examined.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: AIAA PAPER 90-0331
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  • 7
    Publication Date: 2019-01-25
    Description: A software architecture is described which facilitates the construction of distributed expert systems using Ada and selected knowledge based systems. This architecture was utilized in the development of a Knowledge-based Maintenance Expert System (KNOMES) prototype for the Space Station Mobile Service Center (MSC). The KNOMES prototype monitors a simulated data stream from MSC sensors and built-in test equipment. It detects anomalies in the data and performs diagnosis to determine the cause. The software architecture which supports the KNOMES prototype allows for the monitoring and diagnosis tasks to be performed concurrently. The basic concept of this software architecture is named ACTOR (Ada Cognitive Task ORganization Scheme). An individual ACTOR is a modular software unit which contains both standard data processing and artificial intelligence components. A generic ACTOR module contains Ada packages for communicating with other ACTORs and accessing various data sources. The knowledge based component of an ACTOR determines the role it will play in a system. In this prototype, an ACTOR will monitor the MSC data stream.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA, Lyndon B. Johnson Space Center, First International Conference on Ada (R) Programming Language Applications for the NASA Space Station, Volume 2; 1 p
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  • 8
    Publication Date: 2019-06-28
    Description: When surfaces intersect, one may desire to highlight the intersection curve in order to make the shape of the penetrating surfaces more visible. Highlighting the intersection is especially helpful when the surfaces become transparent, because transparency makes the intersections less evident. A technique for locating intersections in screen space using only the information locally available to a pixel is discussed. The technique is designed to exploit parallelism at the pixel level and was implemented on the Pixel-Planes 5 graphics supercomputer.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA-CR-191498 , NAS 1.26:191498 , ICASE-93-41 , AD-A269019
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  • 9
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    In:  CASI
    Publication Date: 2019-06-28
    Description: This paper derives a model of diffuse and specular illumination in arbitrarily large dimensions, based on a few characteristics of material and light in three-space. It then describes how to adjust for the anomaly of excess brightness in large codimensions. If a surface is grooved or furry, it can be illuminated with a hybrid model that incorporates both the one dimensional geometry (the grooves or fur) and the two dimensional geometry (the surface).
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: AD-A277602 , NASA-CR-191596 , NAS 1.26:191596 , ICASE-94-6
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  • 10
    Publication Date: 2019-06-28
    Description: The paper deals with the performance of two parallel variants of the simplex algorithm on a message-passing system. First, the simplex algorithm is reviewed, two possible parallelizations of the algorithm are discussed, and results of benchmark speedups of the alternatives are presented. Between column and row partitionings, the row partitioning method is found to be generally superior, while the column partitioning method is more efficient when the number of rows is small, and the number of columns is much greater that the number of rows. Various performance analysis tools are then applied to examine the reasons for relative performance differences, and communication idle time due to global minimization and load imbalances is noted as the main factor in execution slowdown.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
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