Xingmin Ren

Grazing Bifurcation in the Response of Cracked Jeffcott Rotor

A cracked rotor is modeled by a piecewise linear system due to thebreath of crack in a rotating shaft. The differential equations ofmotion for the nonsmooth system are derived and solved with thenumerical integration method. From the simulation results, it isobserved that a grazing bifurcation exists in the response. Thegrazing bifurcation can give rise to jumps between periodic motions,quasi-periodic motions from the periodic ones, chaos, and intermittentchaos.

Stick–slip vibration of a friction damper for energy dissipation

This article studies energy dissipation of a friction damper (due to stick–slip vibration) in the context of harmonic excitation. There are numerous applications of such friction dampers in engineering. One particular example is a new kind of under-platform dry friction dampers for aero engines. The model consists of a clamped cross-like beam structure and two masses (friction dampers) in contact with the short beam of the cross. The two masses are allowed to slide along two extra short vertical clamped beams. They can exhibit three distinct dynamic regimes: pure slip, pure stick and a mixture of stick–slip relative to the short horizontal beam. The finite element method is used to obtain the numerical modes of the structure. The friction at the contact interface between the short horizontal beam and the friction dampers is assumed to follow the classical discontinuous Coulomb friction law in which the static coefficient of friction is greater than the kinetic coefficient. Modal superposition method is applied to solve the dynamic response of the structure with numerical modes. One major finding of this investigation is that there is an intermediate range of the normal contact forces (in stick–slip regime) that provides the best energy dissipation performance.

Unbalance Identification of Speed-Variant Rotary Machinery without Phase Angle Measurement

As rotary mechanical structure becomes more complicated, difficulty arises in receiving prime correction mass and optimum balancing plane efficiently. An innovative modal balancing process for estimating the residual unbalance from different equilibrium plane of complex flexible rotor system is presented. The method is based on a numerical approach with modal ratio among measurement points (MRMP) coefficient and triple phase method (TPM). The veracity of calculation result is verified by an academic rotor model. The latter study in this paper is subsequently put forward through a power turbine rotor modeled by finite element method. Simulation results show that proper equilibrium plane performs commendably in recognizing residual unbalance and reducing the vibration effect through the critical region. Moreover, the inherent unbalance recognized by experimental data from a turbine rotor with slender shaft is found to be in certain difference under different counterweight combination. Choosing suitable balancing planes will improve the accuracy of unbalance identification.

Rotating machine fault diagnosis based on denoising source separation

The application of denoising source separation (DSS) technology to the mechanical vibration signal processing provides a new technique of mechanical fault diagnosis. The DSS theory is investigated in this paper. The analog signals of the rotating machine are separated and the performance index and correlation coefficient of DSS are better than those of the joint approximate diagonalization of eigen-matrices (JADE). Applying the DSS method to rotating machine fault diagnosis, the measured fault signals are analyzed and the results are found to be in agreement with practice. The results show that the DSS method is efficient in analyzing the fault diagnosis of rotating machine.

Investigation of dynamical characteristic of shrouded blade of aero-engine subjected to impact and friction

The effect of combination of impact and friction on the dynamic characteristics of shrouded blade of aero-engine is investigated in this paper. Adding shroud to blade of aero-engine is an effective method of vibration reduction for blade subjected to centrifugal forces and gas forces which can lead to high cyclic fatigue (HCF). Approximate mass-springs model for shrouded blade is developed so as to predict vibration amplitudes and to study nonlinear characteristics. The dynamical equations of a shrouded blade system can be derived and solved to get numerical results. Parameters such as ratio of stiffness, friction coefficient and contact angle of shrouded blade are detailed. Nonlinear characteristics for the combination of impact and friction are also studied through bifurcation diagram with non-dimensional rotating speed and amplitude of gas excitation force as parameters. Numerical results indicate that the dynamical characteristics of the shrouded blade are varied with the parameters of the shrouds. Based on the numerical study, some practical suggestions for choosing parameters of shrouded blade are made.