Oil Whip and Unstable Whirling in Anisotropic Rotors on Lubricated Bearings

2006 ◽  
Author(s):  
Giancarlo Genta ◽  
Nicola Amati
Keyword(s):  
Time Domain ◽  
Real World ◽  
Chaotic Motion ◽  
Dynamic Behaviour ◽  
Simplified Models ◽  
Complex Behaviour ◽  
Oil Whip ◽  
Oil Whirl ◽  
The Stability ◽  
Rotor Model

The dynamics of rotors running on lubricated bearings is complex. While the linearized analysis allows to study the stability in the small and phenomena like oil whirl and oil whip, more complex behaviour, that may include chaotic motion, requires a fully nonlinear analysis. Since lubricated bearings behave like anisotropic supports, complex whirling pattern can be expected when the rotor is anisotropic. The aim of the present paper is to investigate to what extent the anisotropy of the rotor affects its dynamic behaviour. In particular, the interactions between the instability ranges due to rotating anisotropy and to oil whip are searched. The rotor models are built using DYNROT FEM code to build the basic rotor model and to obtain linearized solutions. The linear model of the rotor is then mated to nonlinerar bearing models and integrated numerically in time. Time domain results allow to draw some general conclusions applicable to simplified models as well as to real-world rotors.

scholarly journals On the Role of Nonsynchronous Rotating Damping in Rotordynamics

2000 ◽  
Vol 6 (6) ◽  
pp. 467-475 ◽  
Author(s):  
Giancarlo Genta ◽  
Eugenio Brusa
Keyword(s):  
General Model ◽  
Degrees Of Freedom ◽  
Dynamic Behaviour ◽  
System Parameters ◽  
Spin Speed ◽  
Rotating Systems ◽  
Jeffcott Rotor ◽  
The Stability ◽  
Rotor Model

Nonsynchronous rotating damping, i.e. energy dissipations occurring in elements rotating at a speed different from the spin speed of a rotor, can have substantial effects on the dynamic behaviour and above all on the stability of rotating systems.The free whirling and unbalance response for systems with nonsynchronous damping are studied using Jeffcott rotor model. The system parameters affecting stability are identified and the threshold of instability is computed. A general model for a multi-degrees of freedom model for a general isotropic machine is then presented. The possibility of synthesizing nonsynchronous rotating and nonrotating damping using rotor- and stator-fixed active dampers is then discussed for the general case of rotors with many degrees of freedom.

Analysis and Control of Chaos in Sheppard-Taylor DC-DC Converter

2013 ◽  
Vol 401-403 ◽  
pp. 1596-1599 ◽  
Author(s):  
Chuang Bi ◽  
Zheng Hang Fan ◽  
Yong Xiang ◽  
Jin Gang Hu
Keyword(s):  
Nonlinear Dynamics ◽  
Bifurcation Diagram ◽  
Time Domain ◽  
Chaos Control ◽  
Phase Portraits ◽  
Control Of Chaos ◽  
Complex Behaviour ◽  
Power Spectral ◽  
The Stability ◽  
And Control

This paper addresses the nonlinear dynamics of the Sheppard-Taylor converter to explain the complex behaviour exhibited in the converter under different practical conditions. The bifurcation diagram of the converter is generated to analyze the stability of the system. Several representative waveforms are captured from simulation to illustrate the chaos control of the converter, such as time-domain waveforms, phase portraits, Poincaré section diagrams, and power spectral diagrams.

scholarly journals Asymmetry underlies stability in power grids

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Ferenc Molnar ◽  
Takashi Nishikawa ◽  
Adilson E. Motter
Keyword(s):  
Symmetry Breaking ◽  
Real World ◽  
Power Grids ◽  
Stable Operation ◽  
World Systems ◽  
Symmetric State ◽  
Network Systems ◽  
Additional Improvement ◽  
The Stability ◽  
General Method

AbstractBehavioral homogeneity is often critical for the functioning of network systems of interacting entities. In power grids, whose stable operation requires generator frequencies to be synchronized—and thus homogeneous—across the network, previous work suggests that the stability of synchronous states can be improved by making the generators homogeneous. Here, we show that a substantial additional improvement is possible by instead making the generators suitably heterogeneous. We develop a general method for attributing this counterintuitive effect to converse symmetry breaking, a recently established phenomenon in which the system must be asymmetric to maintain a stable symmetric state. These findings constitute the first demonstration of converse symmetry breaking in real-world systems, and our method promises to enable identification of this phenomenon in other networks whose functions rely on behavioral homogeneity.

Stability of Milling Operations With Asymmetric Cutter Dynamics in Rotating Coordinates

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Alptunc Comak ◽  
Orkun Ozsahin ◽  
Yusuf Altintas
Keyword(s):  
Time Domain ◽  
Machine Tools ◽  
High Speed ◽  
End Mill ◽  
Spindle Shaft ◽  
Milling Operations ◽  
Stability Model ◽  
Principal Directions ◽  
The Stability ◽  
Rotating Coordinates

High-speed machine tools have parts with both stationary and rotating dynamics. While spindle housing, column, and table have stationary dynamics, rotating parts may have both symmetric (i.e., spindle shaft and tool holder) and asymmetric dynamics (i.e., two-fluted end mill) due to uneven geometry in two principal directions. This paper presents a stability model of dynamic milling operations with combined stationary and rotating dynamics. The stationary modes are superposed to two orthogonal directions in rotating frame by considering the time- and speed-dependent, periodic dynamic milling system. The stability of the system is solved in both frequency and semidiscrete time domain. It is shown that the stability pockets differ significantly when the rotating dynamics of the asymmetric tools are considered. The proposed stability model has been experimentally validated in high-speed milling of an aluminum alloy with a two-fluted, asymmetric helical end mill.

Predictive Value of Assessing Vehicle Interior Design Ergonomics in a Virtual Environment

2004 ◽  
Vol 4 (2) ◽  
pp. 109-113 ◽  
Author(s):  
Thomas Reuding ◽  
Pamela Meil
Keyword(s):  
Virtual Environments ◽  
Interior Design ◽  
Real World ◽  
Predictive Value ◽  
Work Processes ◽  
Complex Activity ◽  
Vehicle Interior ◽  
Design Work ◽  
The Real ◽  
The Stability

The predictive value and the reliability of evaluations made in immersive projection environments are limited when compared to the real world. As in other applications of numerical simulations, the acceptance of such techniques does not only depend on the stability of the methods, but also on the quality and credibility of the results obtained. In this paper, we investigate the predictive value of virtual reality and virtual environments when used for engineering assessment tasks. We examine the ergonomics evaluation of a vehicle interior, which is a complex activity relying heavily on know-how gained from personal experience, and compare performance in a VE with performance in the real world. If one assumes that within complex engineering processes certain types of work will be performed by more or less the same personnel, one can infer that a fairly consistent base of experience-based knowledge exists. Under such premises and if evaluations are conducted as comparisons within the VE, we believe that the reliability of the assessments is suitable for conceptual design work. Despite a number of unanswered questions at this time we believe this study leads to a better understanding of what determines the reliability of results obtained in virtual environments, thus making it useful for optimizing virtual prototyping processes and better utilization of the potential of VR and VEs in company work processes.

Visual Memory for Objects in Natural Scenes: From Fixations to Object Files

2005 ◽  
Vol 58 (5) ◽  
pp. 931-960 ◽  
Author(s):  
Benjamin W. Tatler ◽  
Iain D. Gilchrist ◽  
Michael F. Land
Keyword(s):  
Real World ◽  
Visual Memory ◽  
Natural Scenes ◽  
Position Information ◽  
Object Property ◽  
Immediate Recall ◽  
Object Files ◽  
Stability Data ◽  
The Stability ◽  
Types Of Information

Object descriptions are extracted and retained across saccades when observers view natural scenes. We investigated whether particular object properties are encoded and the stability of the resulting memories. We tested immediate recall of multiple types of information from real-world scenes and from computer-presented images of the same scenes. The relationship between fixations and properties of object memory was investigated. Position information was encoded and accumulated from multiple fixations. In contrast, identity and colour were encoded but did not require direct fixation and did not accumulate. In the current experiments, participants were unable to recall any information about shape or relative distances between objects. In addition, where information was encoded we found differential patterns of stability. Data from viewing real scenes and images were highly consistent, with stronger effects in the real-world conditions. Our findings imply that object files are not dependent upon the encoding of any particular object property and so are robust to dynamic visual environments.

Non-linear dynamic analysis of bearing—rotor system lubricating with couple stress fluid

2008 ◽  
Vol 222 (4) ◽  
pp. 599-616 ◽  
Author(s):  
C-W Chang-Jian ◽  
C-K Chen
Keyword(s):  
Dynamic Analysis ◽  
Chaotic Motion ◽  
Couple Stress ◽  
Couple Stress Fluid ◽  
Speed Ratio ◽  
Non Linear ◽  
System Life ◽  
The Stability ◽  
Suitable System ◽  
Bearing System

The current study performs a dynamic analysis of a rotor supported by two couple stress fluid film journal bearings with non-linear suspension. The dynamics of the rotor centre and bearing centre are studied. The analysis of the rotor—bearing system is investigated under the assumptions of a couple-stress lubricant and a short journal bearing approximation. The displacements in the horizontal and vertical directions are considered for various non-dimensional speed ratios. The analysis methods employed in this study include the dynamic trajectories of the rotor centre and the bearing centre, Poincaré maps, and bifurcation diagrams. The Lyapunov exponent analysis is also used to identify the onset of chaotic motion. Numerical results show that the stability of the system varies with the non-dimensional speed ratios. Specifically, it is found that the system is quasi-periodic at a small speed ratio ( s = 0.5). At speed ratios of s = 0.6–0.7, the system is periodic. At s = 0.8–1.9, the system is quasi-periodic, but the system is periodic at s = 2.0–2.6. However, the system exhibits chaotic motion at the speed ratios s = 2.7–2.74. At the speed ratios s = 2.75–3.16, the system becomes periodic. At s = 3.17–3.30, the system is unstable. The Poincaré map has a particular form at s = 3.17, indicative of a chaotic motion. At s = 3.31–6.0, the system finally becomes periodic. The results also confirm that the stability of the system varies with the non-dimensional speed ratios s and l∗. The results of this study allow suitable system parameters to be defined such that undesirable behaviour of the rotor centre can be avoided and the bearing system life extended as a result.

scholarly journals A Finite-Difference Wavenumber-Time Domain Method for Sound Field Prediction in a Uniformly Moving Medium

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Bichun Dong ◽  
Runmei Zhang ◽  
Chuanyang Yu ◽  
Huan Li
Keyword(s):  
Finite Difference ◽  
Time Domain ◽  
Sound Pressure ◽  
Sound Field ◽  
Time Domain Method ◽  
Practical Significance ◽  
Moving Medium ◽  
Domain Method ◽  
Aero Engines ◽  
The Stability

Sound field prediction has practical significance in the control of noise generated by sources in a flow, for example, the noise in aero-engines and ventilation systems. Aiming at accurate and flexible prediction of time-dependent sound field, a finite-difference wavenumber-time domain method for sound field prediction in a uniformly moving medium is proposed. The method is based on the second-order convective wave equation, and the wavenumber-time domain representation of the sound pressure field on one plane is forward propagated via a derived recursive expression. In this paper, the recursive expression is first deduced, and then numerical stability and dispersion of the proposed method are analyzed, based on which the stability condition is given and the correction of dispersion related to the transition frequency is made. Numerical simulations are conducted to test the performance of the proposed method, and the results show that the method is valid and robust at different Mach numbers.

Acoustic Information Acquisition and Time Domain Analysis on Alternating Current Rail Flash Butt Welding

2012 ◽  
Vol 239-240 ◽  
pp. 16-20
Author(s):  
Qi Bing Lv ◽  
Ke Li Tan ◽  
Xi Zhang ◽  
Jian Chen ◽  
Guo Qing Liu
Keyword(s):  
Time Domain ◽  
Acoustic Signal ◽  
Information Acquisition ◽  
Welding Process ◽  
Welding Current ◽  
Time Domain Analysis ◽  
Mean Square ◽  
Butt Welding ◽  
The Mean ◽  
The Stability

Based on the mobile rail flash butt welding machine UN5-150ZB, the synchronous data acquisition hardware system was designed to collect welding current, welding voltage and flash acoustic signal in welding process, and the software platform with the functions of signal collecting, waveform display and data operation was developed by higher-level programming language LabVIEW. After the welding current, welding voltage and flash acoustic signal in welding process had been collected, the mean, variance and mean square value of flash acoustic signal in time-domain were analyzed. Through comparison, the relationship between these characteristics and the stability of flash was analyzed. The result shows that the changes of mean and variance of flash acoustic signal are not obvious, and do not correlate with stability of flash, but the mean square value in time domain is closely associated with the stability of flash, and the stability of flash can be indicated by the mean square value.

Dynamics and Stability of Turn-Milling Operations With Varying Time Delay in Discrete Time Domain

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Alptunc Comak ◽  
Yusuf Altintas
Keyword(s):  
Time Domain ◽  
Chip Thickness ◽  
Body Motion ◽  
Depth Of Cut ◽  
Time Varying Delay ◽  
Milling Operations ◽  
Varying Time Delay ◽  
The Stability ◽  
Five Axis ◽  
Turn Milling

Turn-milling machines are widely used in industry because of their multifunctional capabilities in producing complex parts in one setup. Both milling cutter and workpiece rotate simultaneously while the machine travels in three Cartesian directions leading to five axis kinematics with complex chip generation mechanism. This paper presents a general mathematical model to predict the chip thickness, cutting force, and chatter stability of turn milling operations. The dynamic chip thickness is modeled by considering the rigid body motion, relative vibrations between the tool and workpiece, and cutter-workpiece engagement geometry. The dynamics of the process are governed by delayed differential equations by time periodic coefficients with a time varying delay contributed by two simultaneously rotating spindles and kinematics of the machine. The stability of the system has been solved in semidiscrete time domain as a function of depth of cut, feed, tool spindle speed, and workpiece speed. The stability model has been experimentally verified in turn milling of Aluminum alloy cut with a helical cylindrical end mill.

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