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  • Computer Systems  (4)
  • ACOUSTICS  (2)
  • CYBERNETICS  (2)
  • 2005-2009  (4)
  • 1990-1994  (4)
  • 1950-1954
  • 1935-1939
  • 1
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    Optimal disturbance rejecting control of hyperbolic systems (1994)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Optimal regulation of hyperbolic systems in the presence of unknown disturbances is considered. Necessary conditions for determining the optimal control that tracks a desired trajectory in the presence of the worst possible perturbations are developed. The results also characterize the worst possible disturbance that the system will be able to tolerate before any degradation of the system performance. Numerical results on the control of a vibrating beam are presented.
    Keywords: CYBERNETICS
    Type: NASA. Langley Research Center, NASA Workshop on Distributed Parameter Modeling and Control of Flexible Aerospace Systems; p 317-322
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  • 2
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    An intelligent control system for failure detection and controller reconfiguration (1994)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: We present an architecture of an intelligent restructurable control system to automatically detect failure of system components, assess its impact on system performance and safety, and reconfigure the controller for performance recovery. Fault detection is based on neural network associative memories and pattern classifiers, and is implemented using a multilayer feedforward network. Details of the fault detection network along with simulation results on health monitoring of a dc motor have been presented. Conceptual developments for fault assessment using an expert system and controller reconfiguration using a neural network are outlined.
    Keywords: CYBERNETICS
    Type: NASA. Goddard Space Flight Center, The 1994 Goddard Conference on Space Applications of Artificial Intelligence; p 285-291
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  • 3
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    Computation of helicopter rotor acoustics in forward flight (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper presents a new method for computing acoustic signals from helicopter rotors in forward flight. The aerodynamic and acoustic solutions in the near field are computed with a finite-difference solver for the Euler equations. A nonrotating cylindrical Kirchhoff surface is then placed around the entire rotor system. This Kirchhoff surface moves subsonically with the rotor in forward flight. The finite-difference solution is interpolated onto this cylindrical surface at each time step and a Kirchhoff integration is used to carry the acoustic signal to the far field. Computed values for high-speed impulsive noise show excellent agreement with model-rotor and flight-test experimental data. Results from the new method offer high accuracy with reasonable computer resource requirements.
    Keywords: ACOUSTICS
    Type: NASA-CR-196132 , NAS 1.26:196132 , RIACS-TR-94-06 , Army Science Conference; Jun 20, 1994 - Jun 24, 1994; Orlando, FL; United States
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  • 4
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    Role of High-End Computing in Meeting NASA's Science and Engineering Challenges (2006)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: High-End Computing (HEC) has always played a major role in meeting the modeling and simulation needs of various NASA missions. With NASA's newest 62 teraflops Columbia supercomputer, HEC is having an even greater impact within the Agency and beyond. Significant cutting-edge science and engineering simulations in the areas of space exploration, Shuttle operations, Earth sciences, and aeronautics research, are already occurring on Columbia, demonstrating its ability to accelerate NASA s exploration vision. The talk will describe how the integrated supercomputing production environment is being used to reduce design cycle time, accelerate scientific discovery, conduct parametric analysis of multiple scenarios, and enhance safety during the life cycle of NASA missions.
    Keywords: Computer Systems
    Type: International Supercomputer Conference (ISC 2006); Jun 27, 2006 - Jun 30, 2006; Dresden; Germany
    Format: text
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  • 5
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    Unstructured adaptive mesh computations of rotorcraft high-speed impulsive noise (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A new method is developed for modeling helicopter high-speed impulsive (HSI) noise. The aerodynamics and acoustics near the rotor blade tip are computed by solving the Euler equations on an unstructured grid. A stationary Kirchhoff surface integral is then used to propagate these acoustic signals to the far field. The near-field Euler solver uses a solution-adaptive grid scheme to improve the resolution of the acoustic signal. Grid points are locally added and/or deleted from the mesh at each adaptive step. An important part of this procedure is the choice of an appropriate error indicator. The error indicator is computed from the flow field solution and determines the regions for mesh coarsening and refinement. Computed results for HSI noise compare favorably with experimental data for three different hovering rotor cases.
    Keywords: ACOUSTICS
    Type: NASA-CR-195090 , NAS 1.26:195090 , RIACS-TR-93-10 , AIAA PAPER 93-4359 , AIAA Aeroacoustics Conference; Oct 25, 1993 - Oct 27, 1993; Long Beach, CA; United States
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  • 6
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    Hybrid Systems Diagnosis (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-11
    Description: This paper reports on an on-going Project to investigate techniques to diagnose complex dynamical systems that are modeled as hybrid systems. In particular, we examine continuous systems with embedded supervisory controllers that experience abrupt, partial or full failure of component devices. We cast the diagnosis problem as a model selection problem. To reduce the space of potential models under consideration, we exploit techniques from qualitative reasoning to conjecture an initial set of qualitative candidate diagnoses, which induce a smaller set of models. We refine these diagnoses using parameter estimation and model fitting techniques. As a motivating case study, we have examined the problem of diagnosing NASA's Sprint AERCam, a small spherical robotic camera unit with 12 thrusters that enable both linear and rotational motion.
    Keywords: Computer Systems
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  • 7
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    Impact of the Columbia Supercomputer on NASA Space and Exploration Mission (2006)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: NASA's 10,240-processor Columbia supercomputer gained worldwide recognition in 2004 for increasing the space agency's computing capability ten-fold, and enabling U.S. scientists and engineers to perform significant, breakthrough simulations. Columbia has amply demonstrated its capability to accelerate NASA's key missions, including space operations, exploration systems, science, and aeronautics. Columbia is part of an integrated high-end computing (HEC) environment comprised of massive storage and archive systems, high-speed networking, high-fidelity modeling and simulation tools, application performance optimization, and advanced data analysis and visualization. In this paper, we illustrate the impact Columbia is having on NASA's numerous space and exploration applications, such as the development of the Crew Exploration and Launch Vehicles (CEV/CLV), effects of long-duration human presence in space, and damage assessment and repair recommendations for remaining shuttle flights. We conclude by discussing HEC challenges that must be overcome to solve space-related science problems in the future.
    Keywords: Computer Systems
    Type: Second International Conference on Space Mission Challenges for Information Technology 2006; Jul 17, 2006 - Jul 21, 2006; Pasadena, CA; United States
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  • 8
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    An Application-Based Performance Characterization of the Columbia Supercluster (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Columbia is a 10,240-processor supercluster consisting of 20 Altix nodes with 512 processors each, and currently ranked as the second-fastest computer in the world. In this paper, we present the performance characteristics of Columbia obtained on up to four computing nodes interconnected via the InfiniBand and/or NUMAlink4 communication fabrics. We evaluate floating-point performance, memory bandwidth, message passing communication speeds, and compilers using a subset of the HPC Challenge benchmarks, and some of the NAS Parallel Benchmarks including the multi-zone versions. We present detailed performance results for three scientific applications of interest to NASA, one from molecular dynamics, and two from computational fluid dynamics. Our results show that both the NUMAlink4 and the InfiniBand hold promise for application scaling to a large number of processors.
    Keywords: Computer Systems
    Type: Supercomputing Conference 2005; Nov 12, 2005 - Nov 18, 2005; Seattle, WA; United States
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