Misalignment in Combi-Bearing: A Cause of Parametric Instability in Vertical Rotor Systems

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Jean-Claude Luneno ◽  
Jan-Olov Aidanpää ◽  
Rolf Gustavsson
Keyword(s):  
Journal Bearing ◽  
Contact Point ◽  
Parametric Instability ◽  
Rotor Speed ◽  
Angular Misalignment ◽  
Rotor Systems ◽  
Asymmetric Structures ◽  
Rotating Systems ◽  
Vertical Rotor ◽  
Stationary Frame

The dynamic characteristics of the combi-bearing (combined thrust-journal bearing) in vertical rotor systems were analytically modeled and experimentally verified in the authors’ previous publications. An angular misalignment, which may be caused by a possible manufacturing or assembling error, is introduced in the combi-bearing’s rotating collar. A new model of the defective combi-bearing has been derived. The derived model shows that the angular misalignment in the combi-bearing’s rotating collar generates an asymmetry in the rotor system at the combi-bearing’s location. The rotor system’s stiffness in its two translational X and Y directions differ at the combi-bearing’s location. Constant parameters and/or coefficients in rotating asymmetric structures appear to change with time when observed in the stationary frame. These time dependent parameters (coefficients) are the source of the so-called parametric instability in rotating systems. If the collar angular misalignment is located in the X-Z plane all rotor motions in this plane at the contact point between the combi-bearing and the rotor will be coupled. A parametric instability is observed within certain ranges of the rotor speed, depending on the magnitude of the angular misalignment.

Experimental Verification of a Combi-Bearing Model for Vertical Rotor Systems

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Jean-Claude Luneno ◽  
Jan-Olov Aidanpää ◽  
Rolf Gustavsson
Keyword(s):  
Dynamic Models ◽  
Contact Point ◽  
Element Model ◽  
Experimental Results ◽  
Small Scale ◽  
Rotor Systems ◽  
Vertical Rotor ◽  
Bearing Design ◽  
Rotor Bearings ◽  
Rotor Dynamic

Combi-bearing is a combined thrust-journal bearing design used in vertical hydropower rotors. The dynamic characteristics of this component (combi-bearing) were analytically modeled by Luneno et al. (2011, “Model Based Analysis of Coupled Vibrations Due to the Combi-Bearing in Vertical Hydroturbogenerator Rotors,” ASME J. Vib. Acoust., 133, p. 061012). This analytic model was inserted into a finite element model of a vertical rotor rig and numerically simulated. In this paper, the simulated vertical rotor-bearings system is a small-scale vertical machine constructed to validate the analytically derived combi-bearing model. Good agreement was found between the simulation and experimental results. The simulation and experimental results showed that the journal (radial) bearing's position relative to the contact point between the combi-bearing's collar and the rotor influences the rotor system's fundamental natural frequencies. Therefore, the combi-bearing model needs to be included into rotor dynamic models. Neglecting the effect of this component may cause significant errors in the predicted results.

scholarly journals Nonlinear Coupled Torsion/Lateral Vibration and Sommerfeld Behavior in a Double U-Joint Driveshaft

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Wei Yao ◽  
Hans DeSmidt
Keyword(s):  
Nonlinear Phenomenon ◽  
Shaft Speed ◽  
Rotor Speed ◽  
Load Torque ◽  
Angular Misalignment ◽  
Motor Torque ◽  
Rotor Systems ◽  
Rotor Imbalance ◽  
Pass Through ◽  
First Time

Abstract Many driveline systems are designed to accommodate angular misalignment by the use of flexible couplings or Universal Joints (U-Joints) which link individual shaft segments. The Sommerfeld effect is a nonlinear phenomenon observed in some rotor systems being driven through a critical speed when there is not enough power to accelerate the rotor through resonance. Previous studies have shown that rotor speed can become captured when transitioning through natural frequencies due to nonlinear interactions between a non-ideal driving input and rotor imbalance. This paper, for the first time, shows that this type of rotor speed capture phenomena can also be induced by driveline misalignment. During rotor spinup under constant motor torque, it is found that misalignment-induced rotor speed capture phenomena can occur as the shaft speed approaches ½ the first elastic torsional natural frequency. Depending on misalignment level and motor torque, the shaft speed will either dwell near this speed and then pass through, or the speed will become trapped. Here, a nonlinear rotordynamics model of a segmented driveshaft connected by two U-joints including effects of angular misalignment and load torque is developed for the study. This analysis also determines the minimum driveline misalignment angle for which the shaft speed capture phenomena will occur for a given motor torque and load torque condition.

A method to obtain the linear dynamic coefficients for journal bearing in vertical rotors

2019 ◽  
Vol 72 (1) ◽  
pp. 38-45 ◽  
Author(s):  
Changmin Chen ◽  
Jianping Jing ◽  
Jiqing Cong
Keyword(s):  
Coordinate System ◽  
Linear Models ◽  
Journal Bearing ◽  
Leading Edge ◽  
Content Type ◽  
Linear Dynamic ◽  
Dynamic Coefficients ◽  
Vertical Rotor ◽  
Rotor Bearing ◽  
Stiffness And Damping

Purpose The infinitesimal perturbation (IP) method is commonly used in calculating stiffness and damping of journal bearing in horizon rotor systems. The boundary condition (BC) for the perturbed pressure is assumed being zero at leading edge of film, although it is usually not zero because of nonzero pressure gradient. This assumption is sufficiently accurate for most purpose in horizon rotors. However, for journal bearing in vertical rotor-bearing systems, the BC with the assumption in IP method will bring in significant errors in calculating linear dynamic coefficients. This paper aims to propose a method to obtain the dynamic coefficients of journal bearing in vertical rotors. Design/methodology/approach The stiffness and damping are approached based on IP method and the modified BC of perturbed pressure. As it is difficult to predict perturbed pressure at leading edge at a fixed coordinate system using IP method, a dynamic coordinate system is introduced in this method, of which the origin on circumferential direction is defined as the leading edge of film. Findings The effectiveness and accuracy of proposed IP method in dynamic coordinate (IPMDC) system are verified by comparing the obtained results with analytical solutions. The comparison shows that the results from IPMDC present a good agreement with the analytic solutions. Originality/value The proposed method can be applied in obtaining linear dynamic coefficients of journal bearing in vertical rotors with high precisions. Instead of the usual nonlinear analysis of vertical rotors, this method provides a feasibility of predicting the instability threshold of vertical rotor-bearing systems via linear models.

Research on the Complete Dynamic Model of Tilting-Pad Journal Bearings Including Fluid Film Temperature Effect

2012 ◽  
Vol 157-158 ◽  
pp. 589-594
Author(s):  
Zhen Shan Zhang ◽  
Xu Dong Dai
Keyword(s):  
Journal Bearing ◽  
Dynamic Properties ◽  
Fluid Film ◽  
Effect Of Temperature ◽  
Rotor Systems ◽  
Dynamic Coefficients ◽  
Tilting Pad ◽  
Precise Prediction ◽  
Tilting Pad Journal Bearing ◽  
Tilting Pad Journal Bearings

Considering the coupling moving of shaft and pads, a theoretical model for calculating the complete dynamic coefficients (CDCs) of tilting-pad journal bearing (TPJB) is described in this paper. The model includes the influence of fluid film temperature. Based on this model, the effect of fluid film temperature on journal equilibrium position, pads inclinations, and complete dynamic coefficients is investigated for given load cases. The numerical results indicate that the effect of temperature is not neglected for the dynamic properties of TPJB. The solution will provide useful tool for precise prediction of dynamic behavior of the rotor systems supported by TPJB.

Vibration Analysis and Health Monitoring of Cracks in Composite Disk Rotor Systems

2005 ◽  
Author(s):  
Xin Hai ◽  
George Flowers ◽  
Roland Horvath ◽  
Jerry Fausz
Keyword(s):  
Health Monitoring ◽  
Natural Frequencies ◽  
Experimental Testing ◽  
Vibration Characteristics ◽  
Rotor Systems ◽  
Plane Vibration ◽  
Fea Model ◽  
Rotating Systems ◽  
Out Of Plane ◽  
Composite Disk

Cracks and voids are common defects in rotating systems and are a precursor to fatigue-induced failure. Identifying the presence and growth of cracks is a critical concept for the health monitoring and diagnostics of such systems. A combined computational and experimental study of the vibration characteristics of a composite hub flywheel rotor system with a cracked hub disk is presented. First, experimental testing of both in-plane and out-of-plane vibration characteristics using a rotor with a composite disk hub supporting a relatively massive rim was conducted. A crack was deliberately introduced into the hub disk during fabrication. Based upon these results, a finite element (FEA) model was developed to further explore the relationship between natural frequencies and crack properties. Finally, a simplified theoretical model for the primary in-plane vibration mode was developed and used in a series of parametric studies. Good agreement was found between the model predictions and the experimental results. It was observed that the presence of a crack tends to affect both the magnitudes and distribution of the rotor natural frequencies. Certain primary frequencies for rotors with a crack are smaller than for those without a crack. In addition, the frequency values of associated with the “in-crack” direction are generally smaller than those associated with the “off-crack” direction, introducing a non-symmetry into the rotordynamics which can serve as an indicator for rotor health monitoring.

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