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Handbook of Turbomachinery Second Edition Revised - Ventech!

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Figure 29 Steady unbalance response: straddle-mount rotor. (a) Case (1)<br />

unbalance.<br />

amplitude responses for Case (1) unbalance distribution. The unbalance<br />

distribution <strong>of</strong> Case (2), however, does not provide a significant excitation <strong>of</strong><br />

either the first mode (cylindrical rigid-body mode) or the second mode<br />

(conical rigid-body mode). It does, however, strongly excite the third mode<br />

(flexible). This situation is also illustrated by the response shown in Fig. 29.<br />

In general, if the unbalance distribution is similar in shape to a forward<br />

critical speed mode, the associated modal unbalance force will tend to be<br />

high.<br />

Figure 29 (b) Case (2) unbalance.<br />

Copyright © 2003 Marcel Dekker, Inc.

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