Vibration Of Rotor-bearing System Research Articles

An experimental and FEA approach to investigate effect of cracks on a rotor bearing system

The field of rotordynamics primarily focuses on the analysis and characterization of lateral and torsional vibrations of rotor bearing system. In this study, the lateral vibrations of a single disc rotor bearing system are studied. The effect of crack location, crack depth, and number of cracks has been studied for structural health monitoring of shafts. For the finite element approach, Ansys version 19.0 is used, and a modal analysis was conducted in order to determine the participation factor and bending modal frequencies. Also, a Campbell diagram for critical speeds and whirl direction is plotted. A single-disc rotor bearing system is treated as a simply supported case. Experimental performance has been carried out on a self-designed testbed, and results are obtained using a DEWEsoft FFT Analyzer. A plot of the frequency spectrum is plotted for all shaft cases. After comparing FEA and Experimental results, a maximum variation of 5 percent was found. The investigational results are corelated; hence, the above methodology for rotordynamic analysis may be suggested.

The Study of Effect of Imbalance on Vibration of Rotor Bearing System

The Study of Effect of Imbalance on Vibration of Rotor Bearing System

Nonlinear Vibration Signature Analysis of a High Speed Rotor Bearing System Due to Race Imperfection

In this paper the nonlinear dynamic responses of a rigid rotor supported by ball bearings due to surface waviness of bearing races are analyzed. A mathematical formulation has been derived with consideration of the nonlinear springs and nonlinear damping at the contact points of rolling elements and races, whose stiffnesses are obtained by using Hertzian elastic contact deformation theory. The numerical integration technique Newmark-β with the Newton–Raphson method is used to solve the nonlinear differential equations, iteratively. The effect of bearing running surface waviness on the nonlinear vibrations of rotor bearing system is investigated. The results are mainly presented in time and frequency domains are shown in time-displacement, fast Fourier transformation, and Poincaré maps. The results predict discrete spectrum with specific frequency components for each order of waviness at the inner and outer races, also the excited frequency and waviness order relationships have been set up to prognosis the race defect on these bearing components. Numerical results obtained from the simulation are validated with respect to those of prior researchers.

The field test and calculation analysis for unstable vibration of 320MW turbomachinery rotor-bearing systems

Unstable vibration of rotor-bearing systems often occurs on large turbomachineries, which affects the normal operation and the equipment safety. However, the diagnosis for this defect is sometimes difficult in the field. This paper presents some examples of this unstable vibration concerning 320MW units, and introduces the field test procedure and calculation analysis for investigating the instability characteristics and detecting the causes of this fault. The results show that this vibration is induced by steam flow, and the causes of the fault is the improper construction design, operational parameters and others. This paper can be a reference to diagnose similar defects on large turbomachineries and troubleshooting.

Estimation of Distributed Unbalance of Rotors

Mass unbalance commonly causes vibration of rotor-bearing systems. Lumped mass modeling of unbalance was adapted in most previous research. The lumped unbalance assumption is adequate for thin disks or impellers, but not for thick disks or shafts. Lee et al. (Lee, A. C., et al., 1993, “The Analysis of Linear Rotor-Bearing Systems: A General Transfer Matrix Method,” ASME J. Vib. Acoust., 115, pp. 490–497) proposed that the unbalance of shafts should be continuously distributed. Balancing methods based on discrete unbalance models may not be very appropriate for rotors with distributed unbalance. A better alternative is to identify the distributed unbalance of shafts before balancing. In this study, the eccentricity distribution of the shaft is assumed in piecewise polynomials. A finite element model for the distributed unbalance is provided. Singular value decomposition is used to identify the eccentricity curves of the rotor. Numerical validation of this method is presented and examples are given to show the effectiveness of the identification method.

On the vibration of rotor-bearing system with squeeze film damper in an energy storage flywheel

The permanent magnetic bearing and the small-sized hydrodynamic spiral groove bearing are utilized as supports for the rotor of the energy storage flywheel system. The hydrodynamic bearing and the squeeze film damper do not need the oil cycle to remove the heat caused by friction because the friction loss is small. The linear dynamics model with four degrees of freedom is built to describe the vibration of the flywheel rotor-bearing system. The squeeze film dampers show good behavior in suppressing the vibration and improving the stability of the rotor-bearing system. The analytical solution of the dynamic characteristic coefficients of the squeeze film is achieved from Reynolds equation after some simplifications are taken. The numerical computation shows that the moment unbalance excites larger vibration of the rotor than the force unbalance. The upper damper plays an important role in helping the rotor pass its critical speed. The damping coefficient of the squeeze film dampers should be selected carefully. The flywheel arrived at the speed of 39,000 rpm and stored the energy of 308 Wh in the experiment. The calculated unbalance response is compared to the test response of the rotor storing quantities of kinetic energy. The comparison indicates that the dynamics model of the rotor-bearing-damper system is appropriate.

Dynamic Response of Rotor-Bearing Systems With Time-Dependent Spin Rates

This paper presents an investigation into the vibration of rotor-bearing systems with time-dependent spin rates. Due to this spin rate, parametric instability may take place in certain situations. In this work, the Galerkin method is used to eliminate the dependence on the spatial coordinates, and then the method of multiple scales is applied to derive periodic solutions and expressions for the boundaries of unstable regions analytically. Numerical results are given for the case where the spin rate is characterized as a small, harmonic perturbation superimposed on a constant rate. The effects of system parameters on the changes of the boundaries of unstable regions are shown.

Influence of Errors on the Vibration of Rotor-Bearing System

Influence of Errors on the Vibration of Rotor-Bearing System