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  • 1
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    Modeling and Identification of a Large Gap Magnetic Suspension System (1996)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: This paper presents the results of modeling and system identification efforts on the NASA Large-Angle Magnetic Suspension Test Fixture (LAMSTF). The LAMSTF consists of a cylindrical permanent magnet which is levitated above a planar array of five electromagnets mounted in a circular configuration. The analytical model is first developed and open-loop characteristics are described. The system is shown to be highly unstable and requires feedback control in order to apply system identification. Limitations on modeling accuracy due to the effect of eddy-currents on the system are discussed. An algorithm is derived to identify a state-space model for the system from input/output data acquired during closed-loop operation. The algorithm is tested on both the baseline system and a perturbed system which has an increased presence of eddy currents. It is found that for the baseline system the analytic model adequately captures the dynamics, although the identified model improves the simulation accuracy. For the system perturbed by additional unmodeled eddy-currents the analytic model is no longer adequate and a higher-order model, determined through system identification, is required to accurately predict the system's time response.
    Keywords: Mechanical Engineering
    Type: Third International Symposium on Magnetic Suspension Technology; Part 2; 403-419; NASA-CP-3336-Pt-2
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Numerical Investigation of the ARMSEF Arc-Jet (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The NASA/JSC 10 MW Atmospheric Reentry Materials and Structures Evaluation Facility (ARMSEF) is used for the development and evaluation of thermal protection systems for manned reentry vehicles. In an effort at better understanding the flow characteristics of an arc-jet wind tunnel and hence the correlation between simulation and actual flight conditions, preliminary numerical analyses have been made. Difficulties in defining inlet boundary conditions to the plenum chamber, where there is very little usable experimental data, are discussed. Two different boundary conditions for the plenum, a straight profile and parabolic profile, are employed to describe the conditions in this very important flow defining region. Comparisons are made to experimental data with the results showing that some type of parabolic or step profile is needed to adequately resolve the strong core flow that is present in the nozzle and plume region. Recommendations are made regarding future efforts in analyzing this challenging flow field.
    Keywords: Mechanical Engineering
    Type: National Aeronautics and Space Administration (NASA)/American Society for Engineering Education (ASEE) Summer Faculty Fellowship Program, 1998; 1; 6-1 - 6-12; NASA/CR-1999-208923/VOL1
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Nondestructive Evaluation of the Friction Weld Process on 2195/2219 Grade Aluminum (1999)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: In 1996, NASA's Marshall Space Flight Center began an ambitious program designed to find alternative methods of repairing conventional TIG (Tungsten Inert Gas) welds and VPPA (Variable Polarity Plasma Arc) welds on the Space Shuttle External Tank without producing additional heat-related anomalies or conditions. Therefore, a relatively new method, invented by The Welding Institute (TWI) in Cambridge, England, called Friction Stir Welding (FSW), was investigated for use in this application, as well as being used potentially as an initial weld process. As with the conventional repair welding processes, nondestructive evaluation (NDE) plays a crucial role in the verification of these repairs. Since it was feared that conventional NDE might have trouble with this type of weld structure (due to shape of nugget, grain structure, etc.) it was imperative that a complete study be performed to address the adequacy of the NDE process. This paper summarizes that process.
    Keywords: Mechanical Engineering
    Type: Mar 23, 1999 - Mar 25, 1999; Orlando, FL; United States
    Format: text
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    NASA TECHNICAL REPORTS
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