•A versatile intelligent MR suspension system for high-speed trains is investigated.•A scaled train model is built to evaluate the new suspension system experimentally.•The train with the new ...suspension avoids resonance and dampens energy efficiently.•The new suspension improves the ride comfort by 55% compared to passive suspensions.
With the increase in speed of high-speed trains, their vibration will become fiercer and fiercer, especially when the lateral resonance of the car body occurs. This paper develops a versatile semi-active suspension system with variable stiffness (VS) magnetorheological elastomer (MRE) isolators and variable damping (VD) magnetorheological (MR) dampers for high-speed trains, aiming to improve ride comfort by avoiding car body resonance and dissipating vibration energy. As the first step, a multifunction VSVD semi-active suspension system for high-speed railway vehicles was designed and prototyped, including four VS-MRE isolators and two VD-MR dampers. After that, a scaled train model, composing of a car body and a secondary lateral suspension system was designed and built to evaluate the performance of the new VSVD suspension system; a control strategy based on short-time Fourier transform (STFT) and sky-hook was proposed to control the new suspension system. Two different excitations, harmonic excitation and random excitation, were applied to evaluate the train’s VSVD suspension. As a comparison, four alternative suspension systems, including passive-off suspension, passive-on suspension, pure VS suspension, and pure VD suspension were also evaluated. The evaluation results verified that the VSVD suspension of the train can avoid lateral resonance of car body and dissipate the vibration energy efficiently. The comparison verified that the VSVD suspension system outperforms the passive-off suspension, passive-on suspension, pure VS suspension, and pure VD suspension.
•Tribofilm-asperity interaction for resonant vibration of journal bearings is analysed.•TAI model regarding spatial power spectral density of rough surface is derived.•The effect of wears and ...operating conditions on the random excitation is evaluated.•Frequency bandwidth depending on the rotational frequency and wavenumbers is verified.•Resonant responds from tests with worn journal surface is explained by TAI model.
Vibration analysis is an effective approach to condition monitoring of hydrodynamic journal bearings. However, the analysis is largely based on the understanding of asperity-asperity interactions due to severe wears in the late phase of bearing lifetime. It often provides very tight leading time for maintenance actions. Aiming at developing effective techniques for early wear monitoring, this paper investigates the excitation mechanisms and contributions of Tribofilm-Asperity Interaction (TAI) that occurs in the hydrodynamic lubrication regime of journal bearings. Analytical expressions for the microscopic pressure fluctuations with respect to the surface topography are derived using the perturbation techniques. The Spatial Power Spectral Density (SPSD), a feature of the non-Gaussian roughness surfaces for early wear, is used to analyse the microscopic pressure fluctuations. The effect of the SPSD and operating conditions on the random excitation are evaluated through numerical simulations. The bandwidth of such random excitation depends on the SPSD of dynamic asperities and rotational speeds simultaneously. The excitation intensity increases when the standard deviation or correlation length of the surface parameters increases. These agree well with the measurements for wide bearing conditions including different degrees of wears. This new efficient analysis and insightful findings provide new understanding for characterising noisy vibration signals for early wear monitoring of journal bearings.
•Vertical random vibration is suppressed by a nonlinear energy sink.•The suppression performance increases with the NES cubic stiffness coefficient.•The account for the NES weight increases the peak ...values of probability density.•The account for the NES weight increases the suppression performance.
A primary structure attached by a nonlinear energy sink (NES) moving vertically under a Gaussian white noise excitation is investigated. This paper demonstrates the stochastic responses and vibration suppression with emphasis on the effects of the weights. Four-dimensional state space equations which consider or ignore the weights in the vertical direction are given. Numerical probability density functions computed via the path integration method based on the Gauss-Legendre scheme are confirmed by Monte Carlo simulations. Probability density functions of the structure’s responses are compared between two cases under various random excitation intensities. The root-mean-square (RMS) displacement of the primary structure or random vibration suppression is estimated through the path integration method. Results reveal that the NES is able to suppress broadband random vibration of the structure. As the stochastic excitation decreases, the NES weight has significant effects on both probability density functions of the structure’s responses and RMS displacements of the primary structure. The NES parameters are discussed to explore random vibration suppression. For purpose of more accurate predictions, the effects of weights should be taken into consideration when the primary structure is excited by small random excitations or coupled with a large and reasonable NES mass. Simulations and discussions in this work provide theorical meanings to predict vibration suppression via a NES in stochastic environment.
In linear vibration studies, the statistical description of multipoint random excitations is sufficient to calculate the vibration response of a structure. For nonlinear vibrations, it is necessary ...to model each excitation point separately, taking into account the correlation between each excitation point. The objective of this paper is to show how to reduce the number of excitation terms while remaining in a formalism compatible with nonlinear vibration studies.
The reduction of the number of stochastic excitation terms can be achieved by Galerkin methods (such as the Karhunen–Loève decomposition). This paper presents an original method which consists of projecting the excitation terms on the eigenmodes of the structure. These two methods are illustrated in the concrete case of a benchmark structure developed by the Commissariat à l’Energie Atomique (CEA), i.e., the mechanical beam system called the CEA-beam benchmark structure, previously studied in Talik et al. (2022), restrained to its first vibration mode and seen as a Duffing oscillator. A random excitation, composed of a consequent number of points of excitation distributed spatially along the structure (more exactly 101 points) and partially correlated, is used to illustrate the effectiveness of the proposed methodology. The proposed method makes it possible to reduce the number of random excitation signals to a single modal excitation term.
•Modeling of multipoint correlated random excitation.•Reducting the number of random excitation signals to a single modal excitation term.•Predicting the nonlinear response of a system subjected to complex excitation.•Application on a beam system subjected to multipoint correlated random excitation.
•A quad-stable piezoelectric energy harvester (QEH) is thoroughly investigated.•Bifurcation analysis proves the quad-stable characteristics of the QEH.•The QEH’s coherence resonance can generate high ...voltages in experiments.•There exist the optimum magnet distances for given random excitations.
To overcome the defects of bi-stable energy harvester (BEH) and improve the energy conversion ability under weak stochastic excitation, we developed a novel quad-stable energy harvester (QEH). This configuration is composed of a piezoelectric cantilever beam with a tip magnet and three external fixed magnets. By adjusting positions of the fixed magnets and altering the distances between the tip and the fixed magnets, four stable equilibrium positions (SEPs) can be realized in the static state of QEH. The diagram of potential energy illustrates that QEH has shallower and wider potential wells than BEH at the same separation distance, implying that it can execute jumping across the potential barrier easily. Validation experiment was carried out and the experimental results showed that QEH could create larger deflection and generate higher output voltage than BEH nearly over the whole range of excitation intensity. Furthermore, by controlling the gap and separation distances, the QEH can be optimized to reach the maximum output power for a certain excitation intensity.
The combination of nonlinear bistable and flextensional mechanisms has the advantages of wide operating frequency and high equivalent piezoelectric constant. In this paper, three magnetically coupled ...flextensional vibration energy harvesters (MF-VEHs) are designed from three magnetically coupled vibration systems which utilize a magnetic repulsion, two symmetrical magnetic attractions and multi-magnetic repulsions, respectively. The coupled dynamic models are developed to describe the electromechanical transitions. Simulations under harmonic excitation and random excitation are carried out to investigate the performance of the MF-VEHs with different parameters. Experimental validations of the MF-VEHs are performed under different excitation levels. The experimental results verify that the developed mathematical models can be used to accurately characterize the MF-VEHs for various magnetic coupling modes. A comparison of three MF-VEHs is provided and the results illustrate that a reasonable arrangement of multiple magnets can reduce the threshold excitation intensity and increase the harvested energy.
•A continuum dynamic model of blade disk shaft system is established.•A method for the monitoring of blade damage is proposed based on random vibration.•The proposed statistical based method can ...extract the blade damage features.•The experiment verified the effectiveness of the proposed statistical index.
The shaft vibration based blade damage monitoring method has become another research focus in addition to tip timing technology because of its simple testing system. However, how to extract the accurate and effective blade damage information from the vibration response of the shaft is the key to the implementation of this method. In this paper, a blade damage monitoring method based on the frequency domain statistical index of shaft’s random vibration is proposed. Firstly, a continuum dynamic model of blade disk shaft system is established and verified for the statistical feature analysis of rotor system with blade damages, in which the coupling among shaft’s bending, torsion and blade’s bending is considered. Then, base on the vibration response from the dynamic model, a blade damage monitoring method is constructed, in which the harmonic components of forced vibrations are removed, the random vibration component is retained, and the mean frequency and bandwidth index in the resonance frequency band of the random torsional vibration is adopted as the blade damage monitoring index. After that, a blade-disk-rotor system test bed is designed and the vibration measurement system is constructed. The experimental results verify the effectiveness of the proposed methods and indicators. To sum up, the verified dynamic model can provide abundant simulation data under various working conditions and various fault parameters for the research of diagnosis index and methods. The random excitation is inherent in the running rotor system, so the random vibration based blade damage monitoring method is easy to implement. The statistical index based method is a simple and effective way to extract the damage information of blade in random vibration. Therefore, the research results of this paper can provide important supplements to the blade damage monitoring.
•A novel magnetically modulated sliding structure (MMSS) vibration isolator is proposed.•Magnetic positive stiffness is employed to lower the resonant frequency.•The nonlinear modulation mechanism is ...investigated for realizing QZS.•Analysis and experiment verify the excellent vibration isolation performance.
Magnetically modulated sliding structure (MMSS) is proposed and systematically investigated in this paper. The MMSS consists of the sliding beam and a pair of repulsive magnets. The sliding beam can provide negative stiffness, which can be modulated by a pair of repulsive magnets (hardening positive stiffness). The static analysis is completed to fully clarify the modulation mechanism. With the modulation of magnets, the sliding beam can exhibit favorable high-static-low-dynamic stiffness (HSLDS). The dynamic model of the MMSS is developed to evaluate its response when subject to base excitation. The displacement transmissibility is derived by the harmonic balance method (HBM). Transmissibility curves show that the MMSS isolator possesses a low resonant frequency and can isolate vibration in a wide frequency range. The principle prototype is fabricated and tested. The effectiveness of the modulation mechanism in realizing quasi-zero stiffness (QZS) is verified by static experiment. Dynamic tests under periodic, sweep and random excitation demonstrate that the isolator exhibits excellent low frequency isolation performance and the vibration exceeding 4 Hz can be effectively isolated. The MMSS system provides a new approach to solve the problem of low frequency vibration isolation. The modulation mechanism, that is, utilizing hardening stiffness to modulate negative stiffness, is of reference significance for the design of HSLDS isolators.
This paper presents a comparative study on the applicability of existing popular wear models in simulation of railway wheel polygonization. Four representative wear models developed by BRR (British ...Rail Research), KTH (Royal Institute of Technology), USFD (University of Sheffield), and Professor Zobory respectively, are selected for the comparison with consideration of global and local methods. All the wear models are converted to calculate the instantaneous wear of one contact patch. Uniform expression of the converted wear functions is derived analytically with the equivalent wear coefficient as a useful index to identify the proportional relationship among the wear models quantitatively. Several scenarios grouped by harmonic excitation and random excitation are adopted to assess the fluctuation of the instantaneous wear depth calculated by different wear models. The evolved polygonal wear around the wheel circumference is also compared among the wear models based on a developed prediction program. Simulation results show that all the wear models being investigated in this paper present a similar ability to reflect the fluctuation of the instantaneous wear under various circumstances. Specifically, all wear models can correctly reflect the frequency characteristics of the excitation in a general sense, and the fluctuation phase of the instantaneous wear is obtained with almost the same result among the wear models. There is a very good consistency of trend for all local wear models to simulate the evolved polygonal wear. The mean value and the fluctuation amplitude of the instantaneous wear, as well as the roughness level of the evolved polygonal wear, are all determined by the original wear coefficients used. Besides, the global method is not suitable for calculating the polygonal wear of railway wheels as some sharp points might be generated by the absolute operation for the global WI (Wear Index).
•A uniform expression is analytically derived for four widely used wear models developed by BRR, KTH, USFD, and Professor Zobory respectively.•The derived equivalent wear coefficient is a useful index to identify the quantitative relationship among the wear models.•All of the wear models present a similar ability to reflect the fluctuation of the instantaneous wear depths under various circumstances.•The global method is not suitable for calculation of instantaneous wear depth of railway wheels.
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