scholarly journals Time Frequency Features of Rotor Systems with Slowly Varying Mass

2011 ◽  
Vol 18 (1-2) ◽  
pp. 29-44
Author(s):  
Tao Yu ◽  
Qingkai Han
Keyword(s):  
Numerical Method ◽  
Element Model ◽  
Rotor System ◽  
Analytic Method ◽  
Rotor Systems ◽  
Time Frequency ◽  
First Order ◽  
General Rules ◽  
Frequency Features ◽  
Varying Mass

With the analytic method and numerical method respectively, the asymptotic solutions and finite element model of rotor system with single slowly varying mass is obtained to investigate the time frequency features of such rotor system; furthermore, with given model of slowly varying mass, the rotor system with dual slowly varying mass is studied. For the first order approximate solution is used, there exists difference between the results with analytic method and numerical method. On the base of common characteristics of rotor system with dual slowly varying mass, the general rules and formula describing the frequency distribution of rotor system with multiple slowly varying mass are proposed.

scholarly journals The Influence of Slowly Varying Mass on Severity of Dynamics Nonlinearity of Bearing-Rotor Systems with Pedestal Looseness

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Mian Jiang ◽  
Jigang Wu ◽  
Shuangqi Liu
Keyword(s):  
Mathematical Model ◽  
Control Parameter ◽  
Rotor System ◽  
Cosine Function ◽  
Nonlinear Mathematical Model ◽  
Rotor Systems ◽  
Disk Mass ◽  
Amplitude Coefficient ◽  
Varying Mass

Nonlinearity measure is proposed to investigate the influence of slowly varying mass on severity of dynamics nonlinearity of bearing-rotor systems with pedestal looseness. A nonlinear mathematical model including the effect of slowly varying disk mass is developed for a bearing-rotor system with pedestal looseness. The varying of equivalent disk mass is described by a cosine function, and the amplitude coefficient is used as a control parameter. Then, nonlinearity measure is employed to quantify the severity of dynamics nonlinearity of bearing-rotor systems. With the increasing of looseness clearances, the curves that denote the trend of nonlinearity degree are plotted for each amplitude coefficient of mass varying. It can be concluded that larger amplitude coefficients of the disk mass varying will have more influence on the severity of dynamics nonlinearity and generation of chaotic behaviors in rotor systems with pedestal looseness.

The Gearbox Fault Detection of Machine Center by Using Time Frequency Order Spectrum

2012 ◽  
Vol 452-453 ◽  
pp. 1329-1333 ◽  
Author(s):  
C.C. Wang ◽  
Y. Kang ◽  
Y.L. Chung
Keyword(s):  
Fault Detection ◽  
Back Propagation ◽  
Machine Center ◽  
Rotor Systems ◽  
Time Frequency ◽  
Order Spectrum ◽  
Signal Features ◽  
Stationary Signals ◽  
Short Time ◽  
Frequency Features

Previously, for the case of fixed or steady state rotation rate, spectrum analysis can be used to extract the frequency features as the basis for the gearbox fault detection of machine center. However, the gearbox of machine center for increasingly instant speed variations mostly generate non-stationary signals, and the signal features must be averaged with analysis time which makes it difficult to identify the causes of failures. This study proposes a time frequency order spectrum method combining the short-time Fourier transform (STFT) and speed frequency order method to capture the order features of non-stationary signals. Such signal features do not change with speed, and are thus effective in identifying faults in mechanical components under non-stationary conditions. In this study, back propagation neural networks (BPNN) and time frequency order spectrum methods were used to verify faults diagnosis and obtained superior diagnosis results in non-stationary signals of gear-rotor systems in machine center.

Time–frequency features of two types of coupled rub-impact faults in rotor systems

2009 ◽  
Vol 321 (3-5) ◽  
pp. 1109-1128 ◽  
Author(s):  
Hui Ma ◽  
Tao Yu ◽  
Qingkai Han ◽  
Yimin Zhang ◽  
Bangchun Wen ◽  
...  
Keyword(s):  
Rotor Systems ◽  
Time Frequency ◽  
Frequency Features

scholarly journals Dynamics of Flexible Rotor Systems with an Interim Mass Unbalanced Disk Using a Spectral Element Model

2014 ◽  
Vol 2014 ◽  
pp. 1-14
Author(s):  
Sangkyu Choi ◽  
Usik Lee
Keyword(s):  
Natural Frequencies ◽  
Equations Of Motion ◽  
Element Model ◽  
Spectral Element ◽  
Rotor System ◽  
Dynamic Responses ◽  
Disk System ◽  
Unbalanced Mass ◽  
Rotor Systems ◽  
Blade System

A frequency domain spectral element model is developed for a rotor system that consists of two spinning shafts and an interim disk or blade system. In this study, the shafts are represented by spinning Timoshenko beam models, and the interim disk system is represented by a uniform thick rigid disk with an unbalanced mass. In our derivation of the governing equations of motion of the disk system, the disk is considered to be wobbling about the geometric center of the disk at which the spinning shafts are attached. The high accuracy of the proposed spectral element model is evaluated by comparison with the natural frequencies obtained using the conventional finite element method (FEM). The spectral element model is then used to investigate the effects of the unbalanced mass on the natural frequencies and dynamic responses of an example rotor system.

Mitigation of nonlinear rub-impact of a rotor system with magnetorheological damper

2019 ◽  
Vol 31 (3) ◽  
pp. 321-338
Author(s):  
Jun Wang ◽  
Liang Ma ◽  
Junhong Zhang ◽  
Xin Lu ◽  
YangYang Yu
Keyword(s):  
Magnetic Field Intensity ◽  
Element Model ◽  
Considerable Effect ◽  
Rotor System ◽  
Magnetorheological Damper ◽  
Self Healing ◽  
Nonlinear Dynamic Response ◽  
Rotor Systems ◽  
Adaptive Ability ◽  
The Relationship

In this work, a new method of using a magnetorheological damper to improve the self-adaptive ability of a rotor system to rub-impact is developed. To validate the feasibility of this method, a finite element model of the rub-impact rotor system with magnetorheological damper is investigated. A revised formula describing the relationship between the yielding shear stress and magnetic field intensity is proposed. Focusing on the mitigation effect of magnetorheological damper on the nonlinear dynamic response of the rotor system, numerical simulation is conducted. The results show that magnetorheological damper has a considerable effect on the vibration and stability of a rub-impact rotor system. When a suitable current is applied, magnetorheological damper can effectively mitigate the vibration of the rotor system to prevent rub-impact. If contact of the rotor/stator is inevitable, magnetorheological damper can further stabilize heavy rub-impact to slight rub-impact by adjusting the current to an appropriate value. This research reveals the influence mechanisms of magnetorheological damper on normal and rub-impact rotor systems and is helpful for vibration control and fault self-healing of rotating machinery.

Simulation of Rotor System Vibrations Using Experimentally Verified Super Elements

2016 ◽  
Author(s):  
Sergei Semenov ◽  
Mikhail Nikhamkin ◽  
Nikolai Sazhenkov ◽  
Irina Semenova ◽  
Grigorii Mekhonoshin
Keyword(s):  
Numerical Technique ◽  
Element Model ◽  
3D Models ◽  
Rotor System ◽  
Vibration Modes ◽  
Frequency Range ◽  
Test Rig ◽  
Rotor Systems ◽  
Operating Frequency Range ◽  
Analysis Of Results

A numerical technique based on finite element model reduced by using experimentally verified superelements is presented in the paper. This method can be used for modelling of rotor systems with elements which can produce nonaxisymmetrical vibration modes (fan, flexible disks and etc.) in operating frequency range thus forcing to calculate 3D models without cycle symmetry. Testing of proposed mathematical modeling method is produced using special rotor test rig. The procedure of superelements creation and verification is provided. Critical speeds of test rotor system were determined numerically and experimentally. Comparative analysis of results is provided.

A Lower Pad Adjustable Bearing Reducing Vibration Response of Rotor Systems During Acceleration

2019 ◽  
Author(s):  
Lei Zhang ◽  
Hua Xu ◽  
Shenglun Zhang ◽  
Shiyuan Pei
Keyword(s):  
Critical Speed ◽  
Vibration Suppression ◽  
Load Condition ◽  
Element Model ◽  
Rotor System ◽  
Vibration Response ◽  
Resonance Amplitude ◽  
Suppression Effect ◽  
Rotor Systems ◽  
Light Load

Abstract A lower pad movable bearing is proposed which has the ability to change the lubricating performance of the journal bearing. The structure and working principle of the adjustable bearing are introduced. This bearing can adjust the working status of the rotor system by changing the position of the bearing pad and reduces the vibration amplitude of rotor. In this paper, a simple rotor bearing finite element model is used to study the vibration response of the rotor system. Through research, it is found that larger ellipticity can effectively reduce the amplitude of the rotor when the rotor speed is running at a certain speed away from the critical speed, and the vibration suppression effect can reach 67%. When the rotor passes the critical speed, reducing the ellipticity can significantly reduce the resonance amplitude of the rotor, and the vibration suppression effect reaches about 37%. In addition, when the rotational speed increases to twice the critical speed, the oil film oscillation occurs under light load condition, which can be suppressed by reducing the ellipticity. Adjustable bearing can then be proposed to adaptively improve the vibration of the rotor system based on the rotor speeds.

Rub-Impact Detection of Rotor Systems Using Time-Frequency Techniques

2016 ◽  
Author(s):  
Laihao Yang ◽  
Xuefeng Chen ◽  
Shibin Wang ◽  
Hao Zuo
Keyword(s):  
Contact Force ◽  
High Speed ◽  
High Efficiency ◽  
Rotor System ◽  
Fast Time ◽  
Time Varying ◽  
Rotor Systems ◽  
Time Frequency ◽  
Jeffcott Rotor ◽  
Vibration Responses

Since increasing demands for high efficiency of high speed rotating machines in recent years, the clearance between rotor and stator becomes smaller and smaller. Consequently, rub-impact fault is more likely to occur. It has become one of the most common and serious malfunctions for rotor system in practical engineering. Because the rub-impact severely induces the rotor dynamic instability, it will finally result in catastrophic failures and great economic loss if undetected in time. The occurrence of the rub-impact leads to a contact force between rotating shaft and stator which can be regarded as an additional support on the rotor system. The contact force will further result in the stiffening effect. As a result, some fast time-varying phenomena of vibration responses including the fast time-varying transient stiffness and the fast oscillated instantaneous frequency (IF) may appear. These phenomena may offer abundant characteristics to diagnose the rub-impact fault of rotor system. In this paper, an effective method based on the fast oscillated characteristics of IF for vibration responses is proposed to detect rub-impact fault of rotor bearing system. First of all, the fast time-varying transient stiffness of rub-impact rotor system is qualitatively formulated based on the Jeffcott rotor model and the fast oscillated characteristics of IF is presented and theoretically analyzed. Second, a time-frequency technique called nonlinear squeezing time-frequency transform (NSTFT) is introduced to extract the fast oscillated IF resulting from the rub-impact fault of rotor systems. Numerical simulations are respectively conducted on the Jeffcott rotor system with linear stiffness and oil film bearings. And then the oscillated characteristics of the IF are analyzed. The analysis results suggest that the IF of the vibration responses remains constant at the rotating frequency if there is no rub-impact fault. However, if rub-impact fault occurs, the IF of the vibration responses will oscillate periodically around the basic harmonic frequency. Furthermore, the oscillation law of the IF of vibration responses for rub-impact rotor systems is also numerically investigated. It is found that the oscillation frequency is the 1/k (k = 1, 2, 3, ...) of the rotating frequency if the rotor system operates at periodic-k motion. Finally, rub-impact fault experiments are performed under different operating regimes. The experimental results are consistent with the numerical results, thus demonstrating the validity and the practicability of the proposed method.

scholarly journals Numerical Investigation on the Gravity Response of a Two-Pole Generator Rotor System with Interval Uncertainties

2019 ◽  
Vol 9 (15) ◽  
pp. 3036 ◽  
Author(s):  
Zhaoli Zheng ◽  
Yonghui Xie ◽  
Di Zhang
Keyword(s):  
Material Properties ◽  
Equations Of Motion ◽  
Deep Understanding ◽  
Element Model ◽  
Rotor System ◽  
Scanning Method ◽  
Rotor Systems ◽  
Generator Rotor ◽  
Gravity Response ◽  
Asymmetric Rotor

Asymmetric rotor systems widely exist in commercial plants. In the previous studies about asymmetric rotor systems, parameters such as material properties and boundary conditions are deterministic. To obtain a deep understanding of the dynamics of asymmetric rotor systems, a generator rotor system considering uncertain factors is studied in this paper. The equations of motion of the three-dimensional finite element model are solved in the rotating frame. The component mode synthesis is used to reduce the degrees of freedom. By employing the Chebyshev interval method (CIM), the uncertain gravity responses of the generator rotor system are investigated. The influences of the uncertainties in the bearing’s properties and the rotor’s material properties on the gravity response are studied in cases with a single uncertainty and double uncertainties. The accuracy and the efficiency of CIM are validated by comparing with the results of the scanning method. The results show that uncertainties have remarkable influences on the gravity response, and that these influences are different from each other. The proposed method and the results can provide guidance to the design and optimization of the rotary machinery.

Finite Element Analysis for Vibration Characteristic on Gear Rotors

2013 ◽  
Vol 273 ◽  
pp. 193-197
Author(s):  
Hong Yu Qi ◽  
Lei Liu
Keyword(s):  
Finite Element ◽  
Element Model ◽  
Helix Angle ◽  
Forced Response ◽  
Rotor System ◽  
Ansys Software ◽  
Element Analysis ◽  
Rotor Systems ◽  
Rotational Motions ◽  
Marine Applications

Gear rotor systems are widely used in many automotive, aerospace and marine applications. Dynamic analysis of gear rotor systems is essential in describing noise and durability characteristics. Using ANSYS software, a finite-element model for a gear rotor system on flexible bearing has been developed, with MARTIX element, beam element and mass element simulating mesh-couple relation and support bearing, shaft and gear individually. The dynamic coupling among the axial, transverse, tensional and rotational motions of gears are considered in the model. The harmonic analysis and forced response of the system were analyzed. The effect of bearing compliances, shaft compliances and helix angle on system dynamics were investigated. The feasibility of the method was verified, the model and result can be used for dynamic design of gear rotor system.

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