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Title: Stability Issues in Ambient-Temperature Passive Magnetic Bearing Systems

The ambient-temperature passive magnetic bearing system developed at the Lawrence Livermore National Laboratory achieves rotor-dynamic stability by employing special combinations of levitating and stabilizing elements. These elements, energized by permanent magnet material, create the magnetic and electrodynamic forces that are required for the stable levitation of rotating systems, such as energy-storage flywheels. Stability criteria, derived from theory, describe the bearing element parameters, i.e., stiffnesses and damping coefficients, that are required both to assure stable levitation (''Earnshaw-stability''), and stability against whirl-type rotor-dynamic instabilities. The work described in this report concerns experimental measurements and computer simulations that address some critical aspects of this overall stability problem. Experimentally, a test device was built to measure the damping coefficient of dampers that employ eddy currents induced in a metallic disc. Another test device was constructed for the purpose of measuring the displacement-dependent drag coefficient of annular permanent magnet bearing elements. In the theoretical developments a computer code was written for the purpose of simulating the rotor-dynamics of our passive bearing systems. This code is capable of investigating rotor-dynamic stability effects for both small-amplitude transient displacements (i.e., those within the linear regime), and for large-amplitude displacements, where non-linear effects can become dominant. Under the lattermore » conditions a bearing system that is stable for small-amplitude displacements may undergo a rapidly growing rotor-dynamic instability once a critical displacement is exceeded. A new result of the study was to demonstrate that stiffness anisotropy of the bearing elements (which can be designed into our bearing system) is strongly stabilizing, not only in the linear regime, but also in the non-linear regime.« less
Authors:
Publication Date:
OSTI Identifier:
792426
Report Number(s):
UCRL-ID-137632
TRN: US200302%%44
DOE Contract Number:
W-7405-Eng-48
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 17 Feb 2000
Research Org:
Lawrence Livermore National Lab., CA (US)
Sponsoring Org:
USDOE Office of Defense Programs (DP) (US)
Country of Publication:
United States
Language:
English
Subject:
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION; AMBIENT TEMPERATURE; BEARINGS; COMPUTER CODES; EDDY CURRENTS; ELECTRODYNAMICS; ENERGY STORAGE; LAWRENCE LIVERMORE NATIONAL LABORATORY; MAGNETIC BEARINGS; PERMANENT MAGNETS; STABILITY