Xingmin Ren

Bio: Xingmin Ren is an academic researcher from Northwestern Polytechnical University. The author has contributed to research in topics: Rotor (electric) & Helicopter rotor. The author has an hindex of 11, co-authored 29 publications receiving 262 citations.

An interval precise integration method for transient unbalance response analysis of rotor system with uncertainty

Abstract: A non-intrusive interval precise integration method (IPIM) is proposed in this paper to analyze the transient unbalance response of uncertain rotor systems. The transfer matrix method (TMM) is used to derive the deterministic equations of motion of a hollow-shaft overhung rotor. The uncertain transient dynamic problem is solved by combing the Chebyshev approximation theory with the modified precise integration method (PIM). Transient response bounds are calculated by interval arithmetic of the expansion coefficients. Theoretical error analysis of the proposed method is provided briefly, and its accuracy is further validated by comparing with the scanning method in simulations. Numerical results show that the IPIM can keep good accuracy in vibration prediction of the start-up transient process. Furthermore, the proposed method can also provide theoretical guidance to other transient dynamic mechanical systems with uncertainties.

Dynamic response analysis of an overhung rotor with interval uncertainties

Abstract: Rotor system is an important part in rotating machineries. As a matter of fact, rotors are subject to uncertainties inevitably due to occasions such as assembling errors, material properties dispersion and variable working conditions. In order to obtain more reasonable evaluations of dynamic response of rotor systems, uncertainties are recommended to be taken into consideration. In this paper, the dynamic responses of an elastically supported uncertain overhung rotor are studied in which uncertain parameters are treated as unknown-but-bounded interval variables. The finite element method is used to derive the deterministic analysis model. A non-intrusive interval method based on Chebyshev polynomial approximation is proposed to evaluate the uncertain dynamic response of the rotor system. Comparative study of the interval method, the scanning method and the Monte Carlo simulation is carried out to illustrate the effectiveness and accuracy. Deflection upper bounds and lower bounds of the disc are obtained with respect to rotating speed in several typical uncertain cases. Results show that the uncertainties have significant effects on the dynamic behaviours of the rotor system and multiple source small uncertainties can lead to large fluctuations in the dynamic responses.

Analysis on the nonlinear response of cracked rotor in hover flight

Abstract: The motion equations for a Jeffcott rotor in hover flight are derived. A periodically sampled peak-to-peak value diagram is used for characterizing and distinguishing different types of nonlinear responses in hovering state. The nonlinear responses become more apparent when the rotor is running above the critical speed in flat flight. There are three ways for rotor responses going to chaos, namely through quasi-periodic, intermittence, or period-3 bifurcation to chaos. The hover flight might suppress some nonlinear responses. However, the position of axis center might obviously deflect, leading to either nonlinear response or peak-to-peak value jump near the fraction frequency of swing critical speed.

Steady-state response analysis of cracked rotors with uncertain‑but‑bounded parameters using a polynomial surrogate method

Abstract: Uncertain‑but‑bounded (UBB) parameters are used to describe the non-probabilistic uncertainties in rotor systems. A general non-intrusive polynomial surrogate is constructed to quantify the uncertain effects of the UBB quantities on the dynamic responses. The surrogate is convenient to establish and able to deal with a large number of uncertain variables. The zeros of the Chebyshev series are used as sample points and the least square method (LSM) is employed to evaluate the coefficients. At the sample points of the polynomial surrogate, the harmonic balance method is applied to obtain the sample responses (PS-HBM). During the surrogate modeling, the deterministic rotor system with a breathing crack is treated as a black box and no modifications should be made to the deterministic finite element (FE) analysis process. It needs no distribution laws and is especially helpful in small sample sized problems. Numerical simulations of the rotor system with various UBB parameters are carried out to demonstrate the effectiveness of the surrogate. Moreover, its accuracy and efficiency are verified by comparisons with other classic sampling methods.

Improving energy harvesting in a tri-stable piezomagnetoelastic beam with two attractive external magnets subjected to random excitation

Abstract: A novel tri-stable energy harvester (TEH) is developed to improve the efficiency of harvesting vibration energy. The corresponding dynamical model was established, and its motion equations were derived. The potential energy shows that the TEH owns shallower and wider potential wells than bi-stable energy harvester (BEH). The bifurcation diagrams of stable equilibrium positions show that the TEH can experience mono-stable, bi-stable, and tri-stable states by altering the separation and gap distances. The simulations were carried out. Validate experiments were performed for several random excitation levels. The results verify that the TEH can realize interwell oscillation easier and generate a dense of high output voltages. So the presented TEH is a promising alternative for improving the energy harvesting performance.

Review for order reduction based on proper orthogonal decomposition and outlooks of applications in mechanical systems

Abstract: This paper presents a review of proper orthogonal decomposition (POD) methods for order reduction in a variety of research areas. The historical development and basic mathematical formulation of the POD method are introduced. POD for parametric dynamic systems is introduced, and a physical interpretation of the POD approach based on the proper orthogonal modes (POMs) is presented. The equivalence between POD and three other order reduction methods is discussed: the first alternative method is singular value decomposition (SVD), the second is principal component analysis (PCA), and the third is Karhunen-Loeve decomposition (KLD). A classification of POD methods is described based on the parameter adaptation and sampling. Actual applications of POD methods for order reduction in engineering systems are illustrated. Finally, outlooks on the use of POD methods in high-dimensional nonlinear dynamic systems are presented in more detail to provide direct guidance for researchers in various areas of engineering.

Influence of crack breathing model on nonlinear dynamics of a cracked rotor

Abstract: Fatigue cracking of the rotor shaft is an important fault observed in the rotating machinery, which can lead to catastrophic failure. The paper addresses the influence of the crack breathing models on the nonlinear vibration characteristics of the cracked rotors. Nonlinear dynamics of the cracked rotor is investigated using two well-known crack models, i.e. switching crack model and response-dependent breathing crack model. Equations of motion for the cracked rotor are systematically presented for both the models. Through numerical simulations, the dynamic response for both the crack models is compared for the subcritical speed region for the rotor. Distinct differences have been found in bifurcation, amplitude, orbit and Poincare map when carrying out the comparison between two models for the assumed rotor parameters. Switching crack modelling reveals chaotic, quasi-periodic and subharmonic vibration response for deeper cracks. Rotor system enters into chaos or quasi-periodic motion directly from periodic motion, and leaves the chaos via route of quasi-period. Transient chaos behaviour is also observed for the first time in the case of cracked rotor. Contrary to this, more realistic breathing crack model reveals no evidence of chaotic, quasi-periodic and subsynchronous vibrations in the response. Unbalance eccentricity level and its phase, crack depth and damping are found to have considerable influence on the bifurcation phenomena of the cracked rotor modelled using switching crack model.

Multistability phenomenon in signal processing, energy harvesting, composite structures, and metamaterials: A review

Abstract: Multistability is the phenomenon of multiple coexistent stable states, which are highly sensitive to perturbations, initial conditions, system parameters, etc. Multistability has been widely found in various scientific areas including biology, physics, chemistry, climatology, sociology, and ecology. In a number of systems where multistability naturally exists, it is found to be undesirable because of the involuntary interwell or chaotic switching among dynamical states that disorder the systems and cause instability. However, in recent decades, researchers have identified numerous benefits of multistability and have devoted research efforts to artificially creating it for a wide range of applications, including signal processing, energy harvesting, composite structures and metamaterials, and micro-/nano-electromechanical actuators. This is because of the unique characteristics of multistability, such as rich potential structure, interwell dynamics, broadband nature, and alleviation of the input energy to sustain stable states, which may play different advantageous roles depending on their applications. In this review, we introduce how researchers create the key of multistability and utilize it to open a new world of theories, materials, and structures. We concentrate on developing histories from bistability to multistability in several potential applications. Different designs of digital and physical multistable systems, and their modeling, performance quantifiers, advantageous mechanisms, and improved techniques are reviewed and discussed in depth. Furthermore, we summarize the key issues and challenges of application-oriented multistability and the corresponding possible solutions, from the phenomenon itself to its realistic implementation. Finally, we provide the prospects for future studies on multistability in more developing research fields.

Dynamic characteristics of cracked uncertain hollow-shaft

Abstract: Considering the parametric uncertainties, the model of a rotor system with transverse crack is investigated. Polynomial Chaos Expansion is used to describe the uncertainties. The Harmonic Balance method is employed to solve the dynamic equations of cracked uncertain hollow-shaft system. The application of the PCE in hollow shaft structures will be tested and the results can provide practical reference for engineering context. Validation of present method is verified by comparing with Monte Carlo simulations. From the simulation results, the multi-vibration peaks near the first critical speed and the sub-critical speeds are sensitive to the uncertain parameters. When considering the uncertain parameters, the non-linear responses in harmonic components of the rotor system are key indicators for the detection of transverse crack.

Multistability phenomenon in signal processing, energy harvesting, composite structures, and metamaterials: A review

Abstract: Multistability is the phenomenon of multiple coexistent stable states, which are highly sensitive to perturbations, initial conditions, system parameters, etc. Multistability has been widely found in various scientific areas including biology, physics, chemistry, climatology, sociology, and ecology. In a number of systems where multistability naturally exists, it is found to be undesirable because of the involuntary interwell or chaotic switching among dynamical states that disorder the systems and cause instability. However, in recent decades, researchers have identified numerous benefits of multistability and have devoted research efforts to artificially creating it for a wide range of applications, including signal processing, energy harvesting, composite structures and metamaterials, and micro-/nano-electromechanical actuators. This is because of the unique characteristics of multistability, such as rich potential structure, interwell dynamics, broadband nature, and alleviation of the input energy to sustain stable states, which may play different advantageous roles depending on their applications. In this review, we introduce how researchers create the key of multistability and utilize it to open a new world of theories, materials, and structures. We concentrate on developing histories from bistability to multistability in several potential applications. Different designs of digital and physical multistable systems, and their modeling, performance quantifiers, advantageous mechanisms, and improved techniques are reviewed and discussed in depth. Furthermore, we summarize the key issues and challenges of application-oriented multistability and the corresponding possible solutions, from the phenomenon itself to its realistic implementation. Finally, we provide the prospects for future studies on multistability in more developing research fields.