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On the identification of a flexibly supported rigid foundation with unknown location of the principal axes of inertia
Satisfactory means for evaluating vibrations in turbomachinery installations where the foundation has natural frequencies in the operating range are not yet available. Required is a means of providing an equivalent foundation whereby one can predict the unbalance response of the rotor over the speed range of interest. Attempts to identify such an equivalent foundation by mass and stiffness matrices, using rotor and foundation motion measurements consequent upon unbalance excitation proved too susceptible to measurement accuracy to be of practical use. A more promising approach has been to identify relevant modal parameters of the equivalent foundation and in earlier work excellent identification was achieved for a flexibly supported rigid foundation, provided the location of its principal axes of inertia were known. This paper relaxes this assumption. It is shown that very good identification is attainable even if the directions of the principal axes of the foundation are unknown, provided the mass centre location is known. Though proper identification was not possible if the mass centre location and the foundation mass were also unknown, sensitivity studies show that with a reasonable estimate of the mass centre location, approximate identification results can still be achieved. Numerical experiments demonstrate that two digit measurement accuracy is adequate, rendering the technique suitable for practical implementation.
On the identification of a flexibly supported rigid foundation with unknown location of the principal axes of inertia
Satisfactory means for evaluating vibrations in turbomachinery installations where the foundation has natural frequencies in the operating range are not yet available. Required is a means of providing an equivalent foundation whereby one can predict the unbalance response of the rotor over the speed range of interest. Attempts to identify such an equivalent foundation by mass and stiffness matrices, using rotor and foundation motion measurements consequent upon unbalance excitation proved too susceptible to measurement accuracy to be of practical use. A more promising approach has been to identify relevant modal parameters of the equivalent foundation and in earlier work excellent identification was achieved for a flexibly supported rigid foundation, provided the location of its principal axes of inertia were known. This paper relaxes this assumption. It is shown that very good identification is attainable even if the directions of the principal axes of the foundation are unknown, provided the mass centre location is known. Though proper identification was not possible if the mass centre location and the foundation mass were also unknown, sensitivity studies show that with a reasonable estimate of the mass centre location, approximate identification results can still be achieved. Numerical experiments demonstrate that two digit measurement accuracy is adequate, rendering the technique suitable for practical implementation.
On the identification of a flexibly supported rigid foundation with unknown location of the principal axes of inertia
Über die Identifizierung eines elastisch gelagerten, biegesteifen Fundamentes mit unbekannter Position der Hauptträgheitsachsen
Feng, N.S. (author) / Hahn, E.J. (author)
1998
10 Seiten, 7 Bilder, 3 Tabellen, 10 Quellen
Conference paper
English
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