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  • 1
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    New stopping criteria for iterative root finding (2014)
    The Royal Society
    Details
    Publication Date: 2014-10-01
    Description: A set of simple stopping criteria is presented, which improve the efficiency of iterative root finding by terminating the iterations immediately when no further improvement of the roots is possible. The criteria use only the function evaluations already needed by the root finding procedure to which they are applied. The improved efficiency is achieved by formulating the stopping criteria in terms of fractional significant digits. Test results show that the new stopping criteria reduce the iteration work load by about one-third compared with the most efficient stopping criteria currently available. This is achieved without compromising the accuracy of the extracted roots.
    Electronic ISSN: 2054-5703
    Topics: Natural Sciences in General
    Published by The Royal Society
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    PAPER CURRENT
  • 2
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    Experimental verification of an eddy-current bearing (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A new type of electromagnetic bearing was built and tested. It consists of fixed AC-electromagnets in a star formation surrounding a conducting rotor. The bearing works by repulsion due to eddy-currents induced in the rotor. A single bearing is able to fully support a short rotor. The rotor support is inherently stable in all five degrees of freedom. No feedback control is needed. The bearing is also able to accelerate the rotor up to speed and decelerate the rotor back to standstill. The bearing design and the experimentation to verify its capabilities are described.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA, Lewis Research Center, Rotordynamic Instability Problems in High-Performance Turbomachinery, 1988; p 389-394
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    An electroviscous damper (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A new type of vibration damper for rotor systems was developed and tested. The damper contains electroviscous fluid which solidifies and provides Coulomb damping when an electric voltage is imposed across the fluid. The damping capacity is controlled by the voltage. The damper was incorporated in a flexible rotor system and found to be able to damp out high levels of unbalanced excitation. Other proven advantages include controllability, simplicity, and no requirement for oil supply. Still unconfirmed are the capabilities to eliminate critical speeds and to suppress rotor instabilities.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA, Lewis Research Center, Rotordynamic Instability Problems in High-Performance Turbomachinery, 1988; p 133-141
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    An AC-electromagnetic bearing for flywheel energy storage in space (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A repulsive type AC-electromagnetic bearing was developed and tested. It was conceived on the basis of the so-called Magnetic River suspension for high-speed trains. The appearance of the bearing is similar to the traditional DC-type electromagnetic bearing but the operating principle is different. The magnets are fed with alternating current instead of direct current and the rotor is fitted with a conducting sleeve (e.g. aluminum) instead of a ferromagnetic sleeve. The repulsion is due to induction of eddy-currents in the conducting sleeve. The bearing is inherently stable and requires no feedback control. It provides support in five degrees of freedom such that a short rotor may be fully supported by a single bearing. These capabilities were demonstrated experimentally. On the down side, the load carrying capacity and the damping obtained so far were quite low compared to the DC-type bearing. Also, significant heating of the conducting sleeve was experienced. The AC-bearing is essentially a modified induction motor and there are strong indications that it can be run both as a motor and as a generator with no commutator requirements. It is therefore considered to be a good candidate for support of energy storage flywheels in space.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Langley Research Center, Magnetic Suspension Technology Workshop; p 317-323
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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