油漩與油顫這一類因油膜軸承中流體所引發之不穩定現象，經常困擾著工程人員。此不穩定現象主要發生在轉動機械剛啟動時，以及運轉中負載條件突然改變。能影響流體引發不穩定的因子有很多，而且部分因子間存在著交互作用；往往並不知道各影響因子所佔的權重，尤其是當彼此有交互作用時。本研究藉由田口實驗計畫法設計實驗，以最少的實驗次數來評估相關因子對發生不穩定的權重。
流體引發不穩定門檻之重要參數:其一為動壓軸承中油膜的流體平均速度，其二是油膜的勁度。在本研究中以不平衡量、堵塞、油壓及油溫來當作控制因子，每一因子皆選擇二個水準，所以實驗設計採用L8直交表。不同因子均會影響轉子系統狀態，系統狀態訊息會蘊藏在轉速從零上升到額定轉速的訊號之中，經由分析振動訊號可得知流體引發不穩定在不同因子影響下發生時的轉速大小，此時的轉速稱之為不穩定門檻。結果顯示，堵塞和油壓彼此有交互作用，而且不平衡量和油溫都是影響流體引發不穩定的顯著因子，只是不平衡量和其他任一因子共同使用，反而會提早引發不穩定，所以對於消除不穩定來說不平衡量只能單獨作用，也就是說增加油溫能有效延後不穩定發生。本研究可提供工程師一套消除不穩定的流程，當作參考。

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.

[1] D.E. Bently and C.T. Hatch, 2002, “Fundamentals of rotating machinery diagnostics,” Bently Pressurized Bearing Company.
[2] A. Muszynska, 2005, “Rotordynamics,” CRC Taylor & Francis Group.
[3] R. Gasch, R. Nordmann and H. Pfutzner, 2002, “Rotordynamic,” Springer.
[4] J. Vance, 1988, “Rotordynamics of Turbomachinery,” John Wiley.
[5] D. Childs, 1993, “Turbomachinery Rotordynamics,” Wiley-Intersciences.
[6] G. Genta, 2005, “Dynamics of rotating systems,” Springer.
[7] C. Hearn, W. Maddox, Y. Kim, V. Gupta, D. Masser, P. Koenemant, C. Chu, I. Busch-Vishniac, D. Neikirk, W. Weldon, and K. Wood, 1995, “Smart mechanical bearings using MEMS technology,” American Society of Mechanical Engineers, Petroleum Division (Publication) PD, Tribology Symposium 1995, Vol. 72, pp. 1-10.
[8] I.E. Santos, and R. Nicoletti, 1996, “Self-excited vibrations in active hydrodynamic bearings,” Journal of the Brazilian Society of Mechanical Sciences and Engineering, Vol. 18, pp. 263-272.
[9] D.E. Bently, and C.T. Hatch, 2006, “Shaft levitation made simple,” Turbomachinery International, Vol. 47, pp. 30-32.
[10] K. Cheng and W.B. Rowe, 1995, “A selection strategy for the design of externally pressurized journal bearings,” Tribology International, Vol. 28, pp. 465–474.
[11] A. Muszynska, W.D. Franklin and D.E. Bently, 1988, “Rotor active ‘anti-swirl’ control,” Journal of Vibration, Acoustics, Stress, and Reliability in Design, Vol. 110, pp. 143–150.
[12] C.C. Fan and M.C. Pan, 2010, “Fluid-induced instability elimination of rotor-bearing system with an electromagnetic exciter,” International Journal of Mechanical Sciences, Vol. 52, pp. 581–589.
[13] C.C. Fan and M.C. Pan, 2011, “Experimental study on the whip elimination of rotor-bearing systems with electromagnetic exciters,” Mechanism and Machine Theory, Vol. 46, pp. 290–304.
[14] C.C. Fan and M.C. Pan, 2011, “Active elimination of fluid and dry whips in a rotating machine with an electromagnetic actuator,” International Journal of Mechanical Sciences, Vol. 53, pp. 126–134.
[15] A. EI-Shafei, S.H. Tawfick, M.S. Raafat and G.M. Aziz, 2007, “Some experiments on oil whirl and oil whip,” American Society Mechanical Engineers Standards, Vol. 129, pp.144-153.
[16] L.J. Read and R.D. Flack, 1987, “Temperature, pressure and film thickness measurements for an offset half bearing,” Wear, Vol. 117, pp. 197-210.
[17] S.B. Glavatskih, Osten Uusitalo and D.J. Spohn, 2001, “Simultaneous monitoring of oil film thickness and temperature in fluid film bearings,” Tribology International, Vol. 34, pp. 853-857.
[18] S.B. Glavatskih, 2004, “A method of temperature monitoring in fluid film bearings,” Tribology International, Vol. 37, pp. 143-148.
[19] C.M. Wang, 2008, “The oil-film temperature field analysis of oil-film bearing based on ANSYS,” Mechanical Management and Development, Vol. 23, No. 5, pp. 101-104.
[20] J. Durany, J. Pereira and F. Varas, 2010, “Dynamical stability of journal-bearing devices through numerical simulation of thermohydrodynamic models,” Tribology International, Vol. 43, pp. 1703-1718.
[21] W.H. Yang and Y.S. Tarng, 1998, “Design optimization of cutting parameters for turning operations based on the Taguchi method,” Journal of Materials Processing Technology, Vol. 84, pp. 122-129.
[22] J.A. Ghani, I.A. Choudhury and H.H. Hassan, 2004, “Application of Taguchi method in the optimization of end milling parameters,” Journal of Materials Processing Technology, Vol. 145, pp. 84-92.
[23] C.C. Tsao and H. Hocheng, 2004, “Taguchi analysis of delamination associated with various drill bits in drilling of composite material,” International Journal of Machine Tools & Manufacture, Vol. 44, pp. 1085-1090.
[24] B.M. Gopalsamy, B. Mondal and S. Ghosh, 2009, “Taguchi method and ANOVA: An approach for process parameters optimization of hard machining while machining hardened steel,” Journal of Scientific & Industrial Research, Vol. 68, pp. 686-695.
[25] C. Manoharan and V.P, Arunachalam, 2008, “Dynamic analysis of hydrodynamic bearing performance in ic engines by using Taguchi technique and Response Surface Methodology,” International Journal of Advanced Manufacturing Technology, Vol. 36, pp. 1061-1071.
[26] A. Muszynska and D.E. Bently, 1996, “Fluid-induced instabilities of rotors: whirl and whip – summary of result,” Bently Nevada Corporation ORBIT, pp. 6–14.
[27] A. Muszynska, 1986, “Whirl and whip-rotor bearing stability problems,” Journal of Sound and Vibration, Vol. 110, pp. 443–462.
[28] A. Muszynska, 1988, “Stability of whirl and whip in rotor bearing system,” Journal of Sound and Vibration, Vol. 127, pp. 49–64.
[29] A. Muszynska and D.E. Bently, 1994, “Fluid dynamic force model for rotors with seals or lightly-loaded bearings,” Bently Nevada Corporation ORBIT, pp. 5–7.
[30] P.J. Ross, G., 1988, “Taguchi Techniques for Quality Engineering,” McGraw-Hill.
[31] R.K. Roy, 1990, “A primer on the Taguchi Method,” Van Norstrand Reinhold, New York.
[32] J.W. Syu, 2010, “Study of Start-up Vibration Response for Oil Whirl, Oil Whip and Dry Whip,” Master Thesis of Nation Central University, Taiwan, Republic of China.
[33] C.K. Tsuei, 2011, “LQR Method Used in Fluid-Induced Instability Prevention for Rotating Machinery with Fluid-Film Bearings,” Master Thesis of Nation Central University, Taiwan, Republic of China.