Handbook of Turbomachinery Second Edition Revised - Ventech!

Examples of structure modes coupling with a rotor mode include (1)
‘‘back-bone bending mode’’ of the entire engine case, and (2) lateral natural
frequency of a bearing support housing. Their natural frequencies should be
estimated before making the decision to exclude or include these factors in
the rotor dynamics analysis.
BALANCING PROCEDURES
The process of ‘‘balancing’’ a high-speed rotating machine is an inverse
engineering problem. The response (amplitude and phase of various system
outputs) of the machine may be measured at specific rotor speeds. Based on
this measured information, a balance procedure identifies, in some
equivalent sense, the unbalance distribution that is present in the rotor
assembly(s). A balance correction is then imposed with the intent of
effectively canceling the effects of the residual unbalance.
Many different strategies have been developed for balancing, and the
specific strategy to be used generally differs depending on the application.
Numerous publications discuss this important area of rotordynamics. An
excellent source is the book by Darlow [2] that discusses the balancing of
high-speed machinery in considerable detail and also provides an important
list of references.
NOMENCLATURE
c ¼ viscous damping coefficient.
cgx ¼ center of gravity eccentricity.
C ¼ radial clearance.
d ¼ deci.
d(O) ¼ damping exponent.
e ¼ cg eccentricity in x-direction.
EI ¼ bending stiffness.
f, g ¼ elliptic whirl components.
F ¼ force, dynamic flexibility coefficient.
I ¼ mass moment of inertia.
k ¼ stiffness coefficient.
L ¼ length.
m ¼ mass.
n ¼ critical spin-speed, subharmonic order.
q ¼ typical displacement component.
r ¼ radial displacement.
Copyright © 2003 Marcel Dekker, Inc.