| Summary: | 博士 === 國立成功大學 === 機械工程學系 === 86 === The objective of this dissertation is to study the dynamic
behavior of a composite shaft-disk system and an asymmetric
shaft system. A finite element model of a Timoshenko beam, based
upon the equivalent modulus beam theory, is adopted to
approximate the composite shaft. Numerical analyses are
validated by comparing flexural frequencies of the present shaft
model with those of ANSYS. This approach provides accurate
results for symmetric configurations and is easily extended
torotor dynamic analysis. The stability behavior of a rotating
shaft-disk subjected, respectively, to axial loads and follower
forces are studied. Numerical results show that the critical
speed of a thin-walled composite shaft is dependent on the
stacking sequence, the length-radius ratio (L/R) and the
boundary conditions. In addition, the dynamic stability of a
rotating composite shaft-disk system subjected to axial or
follower periodic forces, are also interesting. Effects of the
spin speed and the static component of the applied force on the
stability of the composite shaft are discussed. The numerical
results show that for the same geometric parameters, a steel
shaft has a lower frequency than that of the composite shafts.
However, the steel shaft is more stable than composite shafts
because the shaft-disk system is subjected to axial periodic
forces at lower rotational speeds. Also, the effect of the
gyroscopicmoments makes the steel shaft more sensitive to the
periodic axial load than the composite one. Finally, the dynamic
stability behaviors of a rotating shaft with dissimilar
stiffness are investigated. A finite element model of Timoshenko
beam is adopted to approximate the shaft, and the effects of the
rotatory inertia, shear deformations, gyroscopic moments and
torsional rigidities are taken into account. In studying the
whirl properties of such shafts, it is convenient to use
rotating co-ordinates to formulate the equations of motion. The
results reveal that the unstable zones will occur with the
existence of the dissimilar stiffness. If the stiffness ratio is
decreased or the axial compressive loads increase, the critical
speeds will decrease and the instability regions will enlarge.
The decrease of the stiffness ratio or the increase of the axial
loads consequently makes the rotating shaft more unstable.
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