tailieunhanh - Hydrodynamic Lubrication 2011 Part 7

Tham khảo tài liệu 'hydrodynamic lubrication 2011 part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 112 5 Stability of a Rotating Shaft Oil Whip Fig. . Stability charts for a shaft in porous bearings 36 . a 10 2 b 10 4 c 0 nonporous bush such as an earthquake. This was confirmed experimentally also by simulating an artificial miniearthquake with a hammer by hitting the pedestal which carries the rotating shaft Adams 63 . Further if an imbalance and the bearing load of a rotor are changed variously while it is running in the hysteresis domain it has been shown that all kinds of rotor responses can occur . periodic quasiperiodic and chaotic 63 . These examples are shown in Fig. . Which one of these three actually occurs and when the transition from one state to another occurs is very sensitively related to the operating conditions of the rotor. Thus it has been reported that chaotic phenomena are useful Prevention of Oil Whip 113 Fig. . Chaos in rotor-bearing system 63 as safe diagnostic tools in assessing risks associated with the stable limit cycle within the hysteresis loop. 63 . Prevention of Oil Whip It is very important to prevent oil whip in rotating machines. Some common methods are listed below 1. Raise the critical speed of the shaft. The stable region in the stability chart is thereby expanded. Further even if the shaft becomes unstable if the rotating speed is lower than twice the critical speed the shaft will not start a violent oil whip. The stable region can also be expanded by lowering the length diameter ratio of the bearing. 2. Increase the eccentricity ratio of the journal to reduce the floating height of the journal . The operation point of the shaft moves thereby into the stable region of the stability chart. The shaft is stable whenever the eccentricity ratio is larger than . To increase the eccentricity ratio lowering the coefficient of viscousity of the oil reducing the bearing length increasing the bearing pressure and increasing the bearing clearance are useful. While the above-mentioned methods are effective

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