Numerical prediction of temperature effect on propagation of rubbing acoustic emission waves in a thin-walled cylinder structure

Temperature field has serious effects on the accuracy of rubbing acoustic emission (AE) source localization in a thin-walled cylinder structure, but it is difficult to explore the functioning mechanism through experiments. This paper aims to propose a thermos-elastic coupling simulation procedure to reveal the effect of the uniform temperature and non-uniform temperature field on the propagation characteristics of AE waves. To obtain the behaviors of guiding wave in the thin-walled cylinder, an efficient numerical simulation tool for AE wave propagation modeling is explored. The numerical results of AE propagation in a plate are compared with the experimental data. Then the semi-analytical finite element method is introduced to calculate the characteristics of multi-modal and dispersion. To remove the unwanted reflections from boundaries generated by the numerical simulation, a methodology combined with the infinite element and Rayleigh damping is presented. Consequently, several AE wave propagation simulations are carried out respectively, including the model with the uniform temperature in a range of 20-700 °C, and the non-uniform temperature field with the temperature of the central region, 649 °C. On the basis of the modeling and evaluation results, both the peak-to-peak amplitude and arrival time versus temperatures are summarized and analyzed. The validation results demonstrate that the proposed approach could be used efficiently to research rubbing AE source localization applications with a high degree of accuracy

Design and analysis of a novel eddy current damper based on three-dimensional transient analysis

With advantages of no mechanical contact, vacuum compatibility, oil-free, and high reliability, an eddy current damper has a great potential use in space. In this paper, a passive magnetic damper system is developed by using the eddy current damping effect. The proposed eddy current damper utilizes a stationary permanent magnet and two conductive plates, and has significant performance than the model with only one plate. An accurate analytical model based on the electromagnetic theory for this novel eddy current damper is proposed, and the three-dimensional transient analysis based on finite element method is carried out to predict the magnetic field and current density. To optimize the design, simulations are conducted and the design parameters are evaluated from the thickness of magnet and two plates. Simulations for the optimized eddy current damper finite element model are conducted and the damping coefficient as high as 124.079 Ns/m is achieved. The results demonstrate that this novel eddy current damper has high damping performance but simple structure, which is applicable in some vibration isolation systems of spacecraft

Fault diagnosis of gears based on local mean decomposition combing with kurtosis

Local Mean Decomposition (LMD) is a new self-adaptive time frequency analysis method. In present paper, the effectiveness of LMD method to extract fault features of gears, which are multi-component amplitude modulation (AM) and frequency modulation (FM), is demonstrated. A series of tests on tooth wearing, breaking and spalling gears are conducted and analyzed by LMD. And the fault features extracted by LMD are compared with those obtained from conventional Hilbert transform (HT). Moreover, the gear faults are identified by kurtosis based on LMD decomposed signals. The results demonstrate that the scheme combining LMD method with kurtosis analysis is effective to extract the characteristics of fault gears and improve the accuracy of fault diagnosis of gears

Design, simulation and experiment of particle dampers attached to a precision instrument in spacecraft

Aiming at attenuating the vibration of a precision instrument in spacecraft, multiple particle dampers are designed and their damping performances are evaluated. Firstly, the vibrating table test for the primary system under sin-swept excitation is conducted to acquire the vibration characteristic. Then enclosures attached to the installing bracket are designed and fabricated elaborately. Using discrete element-finite element (DE-FE) coupling algorithm, the effects of some system parameters (such as: mass ratio, particle material, numbers of dampers and cavity depth) are investigated to optimize the damping capacity of particle dampers. Furthermore, a series of experiments are conducted to verify the performance of particle dampers under dynamic load. The results indicate that the transfer functions of acceleration in Y and Z direction decrease at 22.58 % and 77.38 % respectively, while only 3.1 % mass of the primary system is attached

Nonlinear dynamics modeling and analysis of disc brake squeal considering acting process of brake force

Disc brake squeal of automobile is one of the hottest and most difficult issues concerned by automobile manufacturers and researchers. Considering the acting process of brake force, a simplified nonlinear dynamics model is developed in this paper. The nonlinear dynamics equations are set up and solved by theoretical method and numerical calculation. By studying the effects of key parameters on the system’s behavior, the mechanism of brake squeal are analyzed and discussed. The results indicate that the state of system is more sensitive to the fluctuation of brake force than the variation of the negative slope of friction coefficient against the relative velocity between pad and disc. The dynamic characteristics of brake system are greatly connected with the components stiffness. The brake system may become weakly stable and easily produce brake squeal when tangential contact stiffness, normal contact stiffness and connection stiffness satisfy a certain relationship

Nonlinear behavior evolution and squeal analysis of disc brake based on different friction models

A four-degree-of-freedom model of disc brake with friction and contact loss nonlinearities is developed to investigate the mechanism and dynamic characteristics of brake squeal. The nonlinear equations of motion are presented, and Coulomb and Stribeck friction models are applied and compared in the analysis. The effects of key parameters on system stability are investigated based on the linear equations around the equilibrium point using the complex eigenvalue analysis method. Mode-coupling motion is found to be one significant mechanism to initiate the system instability and lead to brake squeal, and is exceptionally reliant on the parameter configurations of brake system. Numerical solutions of the nonlinear equations of motion are obtained to examine the dynamic behaviors and find the routes to squeal of the brake system with nonlinearities. Results demonstrate that the tangential stiffness of the pad and the rotating velocity of the disc play important roles on the occurrence of stick-slip vibration resulting from the falling characteristic of friction coefficient, and contact loss nonlinearity may make system become unstable even for constant friction coefficient. The separation between the brake pad and disc is dependent on the ratio of normal stiffness of pad/disc and contact stiffness. Strong nonlinear items of the brake system may lead to complicated quasi-periodic and chaotic motions, resulting in squeal problem

Impulsive noise cancellation of acoustic emission signal based on iterative mathematical morphology filter

This paper aims to propose an iterative mathematical morphology (IMM) filter methodology to de-noise the acoustic emission (AE) signal with impulsive noise. To develop the principle of IMM filter, a simulation signal is used to be de-noised by the conventional MM filter. Moreover, a novel approach is introduced to eliminate the end effect of MM filter by connecting the initial point with the end point of the time series. Therefore, the IMM filter can be realized based on the operations of MM filter and the elimination method of end effect. The noise elimination of a simulation signal indicates that the IMM filter can remove the impulsive noise more effectively than the MM filter and maintain useful information as much as possible. Two AE signals acquired from rock compression experiment, which are polluted by electromagnetic impulsive noise, are de-noised by the IMM filter, the conventional digital filter and the wavelet filter respectively. Compared with the other two methods, the IMM filter can preserve the essential information contained in AE signal better, especially the arrival time. These two experiments manifest the effectiveness of the IMM filter in de-noising issues of AE signals polluted by impulsive noise

Line bisection performance in patients with generalized anxiety disorder and treatment-resistant depression

Background and Objectives The line bisection error to the left of the true center has been interpreted as a relative right hemisphere activation, which might relate to the subject's emotional state. Considering that patients with generalized anxiety disorder (GAD) or treatment-resistant depression (TRD) often have negative emotions, we hypothesized that these patients would bisect lines significantly leftward. Methods We tried the line bisection task in the right-handed healthy volunteers (n = 56), GAD (n = 47) and TRD outpatients (n = 52). Subjects also completed the Zuckerman - Kuhlman Personality Questionnaire, the Zuckerman Sensation Seeking Scales, and the Plutchik-van Praag Depression Inventory. Results GAD patients scored highest on the Neuroticism-Anxiety trait, TRD patients scored highest on depression, and both patients scored lower on the Sociability trait. Patients with GAD also bisected lines significantly leftward compared to the healthy subjects. The Frequency of the bisection error was negatively correlated with Disinhibition-Seeking in the healthy subjects, and with Total sensation-seeking and Experience-Seeking in GAD patients, while the Magnitude of the line bisection error was negatively correlated with depression in TRD patients. Conclusions The study suggests a stronger right hemispheric activation, a weaker left activation, or both in the GAD, instead of TRD patients