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  • ACOUSTICS  (2)
  • CYBERNETICS  (2)
  • 2005-2009
  • 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
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 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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    NASA TECHNICAL REPORTS
  • 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
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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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
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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