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Handbook of Turbomachinery Second Edition Revised - Ventech!

Handbook of Turbomachinery Second Edition Revised - Ventech!

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LARGE-ORDER FLEXIBLE SYSTEMS<br />

A typical rotor dynamic system consists <strong>of</strong> a large number <strong>of</strong> interconnected<br />

and interacting components with various structural, thermal, and/or<br />

electrical functions. From a structural viewpoint a system includes three<br />

primary component groups: a rotating assembly, (or assemblies); a support<br />

structure (also referred to as a casing, frame, housing or stator); and a set <strong>of</strong><br />

interconnection components that provide physical links between a rotating<br />

assembly and the support structure or another rotating assembly.<br />

Interconnecting Mechanisms<br />

Typical interconnection components include rolling element bearings, fluidfilm<br />

(journal) bearings, magnetic bearings (passive and active), fluid-film<br />

(squeeze film) dampers, solid dampers, seals, couplings, gearing systems,<br />

and a variety <strong>of</strong> working fluid interactions. A brief description <strong>of</strong> the forces<br />

associated with some <strong>of</strong> these interconnection mechanisms is provided<br />

below. More detailed information may be found in references such as Childs<br />

[1], Ehrich [6], and Vance [21].<br />

Rolling Element Bearings<br />

Rolling element bearings are widely used in situations where large loads<br />

exist and where impacts due to various shock conditions are prevalent.<br />

These bearings exist in a variety <strong>of</strong> forms, including spherical ball,<br />

cylindrical roller, and tapered roller. They may be designed to carry<br />

transverse and/or axial thrust loads. The force–deformation relation <strong>of</strong> these<br />

types <strong>of</strong> bearings is approximately linear under normal operating conditions.<br />

General information on determining the stiffness <strong>of</strong> a rolling element<br />

bearing and other design information may be found in references such as<br />

Shaw and Macks [18] and Ehrich [6]. More detailed information about<br />

specific designs is usually available from the bearing manufacturer. The<br />

damping forces in rolling element bearings are quite low, and other damping<br />

mechanisms must generally be included in a system design to assist in<br />

attenuating high-amplitude response and/or controlling system instabilities.<br />

Fluid-Film Bearings<br />

Fluid-film bearings (journal bearings) have been successfully utilized in<br />

rotating machinery for a long period <strong>of</strong> time. These bearings are capable <strong>of</strong><br />

generating high fluid pressure and thereby can carry relatively large<br />

transverse loads. In addition, they inherently possess the ability to provide<br />

large damping forces that can, if suitably located on the rotating assembly,<br />

Copyright © 2003 Marcel Dekker, Inc.

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