| Summary: | 博士 === 國立中央大學 === 機械工程學系 === 104 === The phenomenon of fluid-induced instability existing in fluid-film bearing systems has been addressed for years. The revolution 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. The study proposes to construct experimentation based on Taguchi method with the least runs of experiment to evaluate the influence of factors on the occurrence of fluid-induced instability. Disk unbalance, oil circulation blocking, oil pressure, and oil temperature classified as control factors with two levels are selected to conduct the experiments. Then, the appropriate orthogonal array L8 is determined. When the operation conditions of machinery change, the threshold of instability can be evaluated through the analysis of machinery vibration signals. Observed from the results, disk unbalance and oil temperature are the significant factors for fluid-induced instability. However, due to interaction between each factors, the instability occurred earlier when disk unbalance and any other instability factors are performed together. Thus, disk unbalance should be dealt with solely for the elimination of instability. As a result, the threshold of instability can be most effectively increased by raising oil temperature. Since the fluid circumferential average velocity associated with journal speed generally is a key factor to cause the instability, thus the research also aims to soothe and even eliminate the occurrence of whirl in rotary machinery by increasing the threshold of instability through the anti-swirl injection using the linear quadratic regulator based optimal control. An acceptance region was established in order to decide starting up the control process. Three case studies were carried out to illustrate the effectiveness of the control scheme. The research results demonstrate that the control scheme incorporating with the acceptance region enables to avoid the occurrence of fluid-induced instability in rotary machinery. Moreover, the developed techniques can also be applied in other fluid-induced instability problems such as whip and rub, etc.
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