Insight into the stick-slip characteristics of dry friction backward whirl in rotor/stator rubbing systems

Significance 

In some extensive engineering systems, self-excited stick-slip oscillations are induced by dry friction. This friction is also widely known for the destructive response of rotor/stator rubbing especially when the clearances between the rotor and stator have to be kept smaller to maximize the machine efficiency. Consequently, self-excited dry friction backward whirl has been experimentally observed to occur when the friction coefficient at the contact points exceeds a certain critical value. Due to its destructive effects, the dry friction backward whirl boundaries have been investigated for various rotor/stator rubbing models to determine its intrinsic characteristics influencing the existence of the response. Numerical simulations and analytical estimates have been used to investigate the transition between the stick-slip and pure stick motions. Nonetheless, these methods have not provided enough detection of dry friction backward whirl in different systems. For instance, the response of the dry friction backward whirl is not taken into account or cannot be correctly captured when the non-smooth effects are neglected.

In a recent study published in the journal- Mechanical Systems and Signal Processing, Shunzeng Wang (graduate student), Professor Ling Hong and Professor Jun Jiang from the Xi’an Jiaotong University investigated the intrinsic characteristics of the stick-slip oscillations exhibited in the response self-excited dry friction backward whirl, particularly, taking into consideration the sliding bifurcations. A four-dimensional piecewise smooth rotor/stator rubbing system was investigated. This system had a switching manifold defined by zero relative velocity on the rubbing point, which helped in the identification of the different sliding regions of the switching manifold surface based on the characteristics of the two discontinuous vector fields near it.

Results showed accurate detection of the sliding regions with the help of event-driven algorithms for the Filippov system approach. Practically, three different sliding regions were identified on the curved hypersurface of the switching manifold based on the derived conditions of the sliding regions and their boundaries. This confirmed the validity of the results. Pure rolling, whose ratio varied depending on the system parameters, was observed to exist in the one-period oscillation of dry friction backward whirl. This explained the underlying difficulty in experimental detection of existing pure rolling in cases comprising of both pure rolling and slipping in one period of oscillation.

By exploring the influence of the system parameters on the stick-slip transition of the dry friction backward whirl, the authors noted the interplay between the different parameters as revealed in the experimental observations. For example, increasing the rotor radius at contact for a given friction coefficient and increasing the friction coefficient at a given rotor radius exhibited the same effects. Besides, it was worth noting that for all the system parameters at their existence boundaries, dry friction backward whirl oscillated in a pure rolling manner and can serve as a given condition to predict the existence boundary in the rotor/stator rubbing models.

In a nutshell, the Xi’an Jiaotong University scientists studied the characteristics of stick-slip oscillations in dry friction backward whirl of piecewise smooth rotor/stator rubbing systems focusing mostly on sliding bifurcations. Filippov systems-based algorithms were used to accurately detect sliding regions. Furthermore, by analyzing the characters of the sliding motion at the existing boundary of the dry friction backward whirl, a summary of analytical relations was derived and observed to agree well with that in the literature. The study by Professor Jun Jiang and his colleagues will provide more insights into the detailed response features in self-excited dry friction backward whirl of rotor/stator rubbing systems.

Insight into the stick-slip characteristics of dry friction backward whirl in rotor/stator rubbing systems - Advances in Engineering

About the author

Shunzeng Wang is a doctoral candidate of mechanics from Xi’an Jiaotong University, China. He studied Mechanical Manufacture and Automation during his master degree at Lanzhou University of Technology. Since 2015, he is a Ph.D. student in Xi’an Jiaotong University. He participated in the research and development of a novel instrument for characterizing comprehensive physical properties based on multi-body dynamics , structural dynamics and rotor dynamics. Currently, his research focuses on the study of complex dynamical behaviors in rotor/stator rubbing systems with the help of the developed characterization instrument.

About the author

Ling Hong is a professor in the School of Aerospace at Xi’an Jiaotong University. She serves the Associate Editor of International Journal of Dynamics and Control published by Springer. She earned her PhD from Xi’an Jiaotong University in 2001. She worked as a postdoctoral fellow at the University of Delaware in USA from 2004 to 2006. She was awarded the National Nature Science Award in 2003 and nominated for ‘The Best 100 PhD Theses of China’ in 2004. Her research area is nonlinear dynamics and control focusing on global dynamics, bifurcations and chaos.

The following are her research projects from NSFC that she has currently been working: (1) Study on Evolutionary Dynamics of Transient Responses and Membership Distribution Functions for Fuzzy Nonlinear Systems (PI from 2017 to 2020) (2) Study on Analysis Methods and Phenomena Mechanisms for Dynamics of Fuzzy Non-smooth Systems (PI from 2020 to 2023). More information about her research contribution can be found from http://gr.xjtu.edu.cn/web/hongling

About the author

Jun Jiang is a full professor in The State Key Laboratory of Strength and Vibration, Xi’an Jiaotong University, China. He has worked shortly as a visiting professor in Germany and Belgium. His research areas focus on nonlinear and non-smooth dynamics with uncertainty, chaos and complex networks, numerical methods for nonlinear global analysis; Nonlinear modes and application; Rotor and multibody dynamics; Adaptive structure and vibration control; Fluid induced vibration and fluid-elasticity coupling, etc. He is, and has been, project leader in several NSFC research projects, and author of more than one hundred peer reviewed journal papers and chapters.

Jiang is now a Member of Dynamics and Control Committee in Chinese Society of Theoretical and Applied Mechanics; A vice-director of the Nonlinear Vibration Committee in Chinese Society of Vibration Engineering; and serves as a member of editor boards of International Journal of Dynamics and Control and several domestic journals.

Reference

Wang, S., Hong, L., & Jiang, J. (2020). Characteristics of stick-slip oscillations in dry friction backward whirl of piecewise smooth rotor/stator rubbing systems. Mechanical Systems and Signal Processing, 135, 106387.

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