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  • ELECTRONICS AND ELECTRICAL ENGINEERING  (3)
  • STRUCTURAL MECHANICS  (2)
  • 1
    Publication Date: 2013-08-31
    Description: The effectiveness of viscous elements in introducing damping in a structure is a function of several variables including their number, their location in the structure, and their physical properties. In this paper, the optimal damper placement and tuning problem is posed to optimize these variables. Both discrete and continuous optimization problems are formulated and solved corresponding, respectively, to the problems of placement of passive elements and to the tuning of their parameters. The paper particularly emphasizes the critical computational issues resulting from the optimization formulations. Numerical results involving a lightly damped testbed structure are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: Proceedings of the Fifth NASA(NSF)DOD Workshop on Aerospace Computational Control; p 479-490
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  • 2
    Publication Date: 2019-06-28
    Description: High temperature superconductors (HTS) hold the promise for applications in magnetic levitation bearings, vibration damping, and torque coupling. Traditional magnetic suspension systems require active feedback and vibration controls in which power consumption and low frequency vibration are among the major engineering concerns. HTS materials have been demonstrated to be an enabling approach towards such problems due to their flux trapping properties. In our laboratory at TCSUH, we have been conducting a series of experiments to explore various mechanical applications using HTS. We have constructed a 30 lb. model flywheel levitated by a hybrid superconducting magnetic bearing (HSMB). We are also developing a levitated and vibration-dampled platform for high precision instrumentation. These applications would be ideal for space usages where ambient temperature is adequate for HTS to operate properly under greatly reduced cryogenic requirements. We will give a general overview of these potential applications and discuss the operating principles of the HTS devices we have developed.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: NASA. Langley Research Center, Second International Symposium on Magnetic Suspension Technology, Part 1; p 111-118
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  • 3
    Publication Date: 2019-06-27
    Description: A new class of high-voltage power transistors has been achieved by adapting present interdigitated thyristor processing techniques to the fabrication of NPN Si transistors. Present devices are 2.3 cm in diameter. The electrical performance obtained is consistent with the predictions of an optimum design theory specifically developed for power switching transistors. The forward safe operating area of the experimental transistors shows a significant improvement over commercially available devices. The report describes device design, wafer processing, and various measurements which include dc characteristics, forward and reverse second breakdown limits, and switching times.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: NASA-CR-135013
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  • 4
    Publication Date: 2019-06-27
    Description: A two dimensional orthotropic sheet with through-the-thickness cracks and temperature gradient was analyzed. The program includes special crack tip elements that account for singular stress fields associated with crack opening and crack sliding displacements at the crack tip. The program also includes a linear spring element and a constant strain, triangular element. A number of problems for which closed form solutions exist were analyzed to demonstrate the capabilities of the program.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-2698
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  • 5
    Publication Date: 2019-06-27
    Description: A new class of high-voltage power transistors was achieved by adapting present interdigitated thyristor processing techniques to the fabrication of npn Si transistors. Present devices are 2.3 cm in diameter and have V sub CEO (sus) in the range of 400 to 600V. V sub CEO (sus) = 450V devices were made with an (h sub FE)(I sub C) product of 900A at V sub CE = 2.5V. The electrical performance obtained was consistent with the predictions of an optimum design theory specifically developed for power switching transistors. The device design, wafer processing, and assembly techniques are described. Experimental measurements of the dc characteristics, forward SOA, and switching times are included. A new method of characterizing the switching performance of power transistors is proposed.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: NASA-CR-159524
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