| Summary: | 碩士 === 國立中央大學 === 機械工程研究所 === 100 === The fluid-induced instability are usually vexing when rotating machines, which are equipped with fluid-film bearings, operate during start up or lightly loaded. Several factors may influence the dynamic performance of a rotor system on the elimination of instability, and the factors sometimes interact each other. Typically the importance and weighting of an influencing factor is not clear through traditional experiments; especially, the interactions between factors change the result. Therefore, this thesis builds the experiment by Taguchi method with the least runs of experiment to evaluate the weightings of factors on the occurrences of fluid-induced instability.
The rotational speed at which the instability onset occurs is called the threshold of instability. The important parameters of the instability threshold are fluid circumferential average velocity ratio and fluid radial stiffness. Disk unbalance, oil circulation blocking, oil pressure, and oil temperature are classified as control factors and two levels are selected in this thesis. Then, the appropriate orthogonal array L8 for the experiment is determined. When the operation conditions of machinery are changed, the threshold of instability can be figured out through the analysis of the machinery vibration signal. As a result, there is an interaction between oil circulation blocking and oil pressure. Disk unbalance and oil temperature are significant factors for fluid-induced instability, but the effect of unbalance with any factors cause the instability occur early. Thus, unbalance must singly work on eliminating instability. In summary, the raising of oil temperature can increase the threshold of instability the most effectively. The results of this thesis may provide engineers to develop a process on eliminating instability.
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