In this paper, analytical and numerical studies are carried out on the full annular rub motions of a nonlinear Jeffcott rotor. Transition sets of the synchronous full annular rub are given with the help of averaging m...In this paper, analytical and numerical studies are carried out on the full annular rub motions of a nonlinear Jeffcott rotor. Transition sets of the synchronous full annular rub are given with the help of averaging method and constraint bifurcation theory to discuss the effects of system parameters on jump phenomena. Routh-Hurwitz criteria are employed to analyze the stability of synchronous full annular rub solution and determine the boundaries of static and Hopf bifurcations. Finally, the response and onset condition of reverse dry whip are investigated numerically, and at the same time, the influences of rotor parameters and rotation speed on the characteristics of the rotor response are investigated.展开更多
A new method to eliminate the oil whip online is put forward by use ofpassive electromagnetic damper. The damper works contactless and with DC current. Neither sensor norclosed loop control is needed. The dynamic equa...A new method to eliminate the oil whip online is put forward by use ofpassive electromagnetic damper. The damper works contactless and with DC current. Neither sensor norclosed loop control is needed. The dynamic equations of rotor-bearing system are built up bycombining d'Alemdert principle with Rize way, and the nonlinear oil film forces based on unsteadyshort bearing model are coupled to system. Such nonlinear equations are numerically solved byNewmark integration method. The calculated results show that the bifurcation behavior of the systemcan be. changed and the oil whip of the rotor may be well damped by external damping. Thebifurcation diagrams also show that the subharmonic vibration amplitude decreases in motion and thespeed at which the system losses its stability increases obviously by exerting external damping.Then experiments are carried out to demonstrate this phenomenon. It is observed that the complextrajectories of the journal motion are disappeared and the rotor-bearing system became stable whenthe power of passive electromagnetic damper is turned on. The experiments have good repeatability.展开更多
Many industrial applications and experiments have shown that sliding bearings often experience fluid film whip due to nonlinear fluid film forces which can cause rotor-stator rub-impact failures. The oil-film whips ha...Many industrial applications and experiments have shown that sliding bearings often experience fluid film whip due to nonlinear fluid film forces which can cause rotor-stator rub-impact failures. The oil-film whips have attracted many studies while the water-film whips in the water lubricated sliding bearing have been little researched with the mechanism still an open problem. The dynamic fluid film forces in a water sliding bearing are investigated numerically with rotational, whirling and squeezing motions of the journal using a nonlinear model to identify the relationships between the three motions. Rotor speed-up and slow-down experiments are then conducted with the rotor system supported by a water lubricated sliding bearing to induce the water-film whirl/whip and verify the relationship. The experimental results show that the vibrations of the journal alternated between increasing and decreasing rather than continuously increasing as the rotational speed increased to twice the first critical speed, which can be explained well by the nonlinear model. The radial growth rate of the whirl motion greatly affects the whirl frequency of the journal and is responsible for the frequency lock in the water-film whip. Further analysis shows that increasing the lubricating water flow rate changes the water-film whirl/whip characteristics, reduces the first critical speed, advances the time when significant water-film whirling motion occurs, and also increases the vibration amplitude at the bearing center which may lead to the rotor-stator rub-impact. The study gives the insight into the water-film whirl and whip in the water lubricated sliding bearing.展开更多
Dry whip motion is an instability of rubbing rotor system and may cause catastrophic failures of rotating machinery.Up to now,the related mechanisms of the dry whip is still not well understood.This paper aims to buil...Dry whip motion is an instability of rubbing rotor system and may cause catastrophic failures of rotating machinery.Up to now,the related mechanisms of the dry whip is still not well understood.This paper aims to build the relationship between the complex nonlinear modes and the dry whip motion,and propose an effective method to predict the response characteristics and existence boundary of the dry whip through complex nonlinear modes.For the first time,the paper discusses how to use the complex nonlinear modes to predict the dry whip systematically,and as a consequence,the mechanism of the relationship between the complex nonlinear mode and the dry whip is revealed.The results show that the Backward Whirl(BW)mode motion of the rubbing rotor system dominates the response characteristics and the existence boundary of dry whip.The whirl amplitude and whirl frequency of dry whip are equal to the modal amplitude and modal frequency of the BW mode at the jump up point where the modal damping is equal to zero.The existence boundary corresponds to the critical rotation speed where the minimum of the modal damping of the BW mode motion is exactly equal to zero.Moreover,the proposed nonlinear modal method in this article is very effective for the prediction of dry whip of the more complicated practical rotor system,which has been verified by applying the predicted method into a rubbing rotor test rig.展开更多
Influence of bearing misalignment on stability of a rotor-journal bearing system has been investigated through analysis and experiment on a test rig, mode component synthesis technique based on finite element method h...Influence of bearing misalignment on stability of a rotor-journal bearing system has been investigated through analysis and experiment on a test rig, mode component synthesis technique based on finite element method has been applied to model the system, sensitivity of stability behavious and bearing load to bearing characteristics and position have also been analyzed.展开更多
The vibration and control of pipes conveying fluid is studied. The solid-liquid coupling vibration equations of the pipe conveying fluid are deduced by Hamilton principle.The direct velocity feedback is used to contro...The vibration and control of pipes conveying fluid is studied. The solid-liquid coupling vibration equations of the pipe conveying fluid are deduced by Hamilton principle.The direct velocity feedback is used to control the pipe vibration. The whip response and control are discussed.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 10632040)
文摘In this paper, analytical and numerical studies are carried out on the full annular rub motions of a nonlinear Jeffcott rotor. Transition sets of the synchronous full annular rub are given with the help of averaging method and constraint bifurcation theory to discuss the effects of system parameters on jump phenomena. Routh-Hurwitz criteria are employed to analyze the stability of synchronous full annular rub solution and determine the boundaries of static and Hopf bifurcations. Finally, the response and onset condition of reverse dry whip are investigated numerically, and at the same time, the influences of rotor parameters and rotation speed on the characteristics of the rotor response are investigated.
基金This project is supported by National Natural Science Foundation of China (No.50375140).
文摘A new method to eliminate the oil whip online is put forward by use ofpassive electromagnetic damper. The damper works contactless and with DC current. Neither sensor norclosed loop control is needed. The dynamic equations of rotor-bearing system are built up bycombining d'Alemdert principle with Rize way, and the nonlinear oil film forces based on unsteadyshort bearing model are coupled to system. Such nonlinear equations are numerically solved byNewmark integration method. The calculated results show that the bifurcation behavior of the systemcan be. changed and the oil whip of the rotor may be well damped by external damping. Thebifurcation diagrams also show that the subharmonic vibration amplitude decreases in motion and thespeed at which the system losses its stability increases obviously by exerting external damping.Then experiments are carried out to demonstrate this phenomenon. It is observed that the complextrajectories of the journal motion are disappeared and the rotor-bearing system became stable whenthe power of passive electromagnetic damper is turned on. The experiments have good repeatability.
基金Supported by Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20120002110011)State Key Laboratory of Hydroscience and Engineering(Grant No.2014-KY-05)+1 种基金Tsinghua Scholarship for Overseas Graduate Studies,China(Grant No.2013128)Special Funds for Marine Renewable Engergy Projects(Grant No.GHME2012GC02)
文摘Many industrial applications and experiments have shown that sliding bearings often experience fluid film whip due to nonlinear fluid film forces which can cause rotor-stator rub-impact failures. The oil-film whips have attracted many studies while the water-film whips in the water lubricated sliding bearing have been little researched with the mechanism still an open problem. The dynamic fluid film forces in a water sliding bearing are investigated numerically with rotational, whirling and squeezing motions of the journal using a nonlinear model to identify the relationships between the three motions. Rotor speed-up and slow-down experiments are then conducted with the rotor system supported by a water lubricated sliding bearing to induce the water-film whirl/whip and verify the relationship. The experimental results show that the vibrations of the journal alternated between increasing and decreasing rather than continuously increasing as the rotational speed increased to twice the first critical speed, which can be explained well by the nonlinear model. The radial growth rate of the whirl motion greatly affects the whirl frequency of the journal and is responsible for the frequency lock in the water-film whip. Further analysis shows that increasing the lubricating water flow rate changes the water-film whirl/whip characteristics, reduces the first critical speed, advances the time when significant water-film whirling motion occurs, and also increases the vibration amplitude at the bearing center which may lead to the rotor-stator rub-impact. The study gives the insight into the water-film whirl and whip in the water lubricated sliding bearing.
基金the financial support from the National Natural Science Foundation of China(No.52005252)the Fundamental Research Funds for the Central Universities(No.NT2020018)the National Science and Technology Major Project(2017-IV-0008-0045)。
文摘Dry whip motion is an instability of rubbing rotor system and may cause catastrophic failures of rotating machinery.Up to now,the related mechanisms of the dry whip is still not well understood.This paper aims to build the relationship between the complex nonlinear modes and the dry whip motion,and propose an effective method to predict the response characteristics and existence boundary of the dry whip through complex nonlinear modes.For the first time,the paper discusses how to use the complex nonlinear modes to predict the dry whip systematically,and as a consequence,the mechanism of the relationship between the complex nonlinear mode and the dry whip is revealed.The results show that the Backward Whirl(BW)mode motion of the rubbing rotor system dominates the response characteristics and the existence boundary of dry whip.The whirl amplitude and whirl frequency of dry whip are equal to the modal amplitude and modal frequency of the BW mode at the jump up point where the modal damping is equal to zero.The existence boundary corresponds to the critical rotation speed where the minimum of the modal damping of the BW mode motion is exactly equal to zero.Moreover,the proposed nonlinear modal method in this article is very effective for the prediction of dry whip of the more complicated practical rotor system,which has been verified by applying the predicted method into a rubbing rotor test rig.
文摘Influence of bearing misalignment on stability of a rotor-journal bearing system has been investigated through analysis and experiment on a test rig, mode component synthesis technique based on finite element method has been applied to model the system, sensitivity of stability behavious and bearing load to bearing characteristics and position have also been analyzed.
文摘The vibration and control of pipes conveying fluid is studied. The solid-liquid coupling vibration equations of the pipe conveying fluid are deduced by Hamilton principle.The direct velocity feedback is used to control the pipe vibration. The whip response and control are discussed.
