Stability of Anisotropic Rotor Systems

• Main Authors: Peng, Wen-Kung, 彭文寬
• Other Authors: Chen Lien-Wen
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/73625704944693433896

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.