Yi Lun Liu

Degradation assessment and fault diagnosis for roller bearing based on AR model and fuzzy cluster analysis

This paper proposes a new approach combining autoregressive (AR) model and fuzzy cluster analysis for bearing fault diagnosis and degradation assessment. AR model is an effective approach to extract the fault feature, and is generally a pplied to stationary signals. However, the fault vibration signal s of a roller bearing are non-stationary and non-Gaussian. Aiming at this problem, the set of parameters of the AR model is estimated based on higher-order cumulants. Consequently, the AR parameters are taken as the feature vectors, and fuzzy cluster analysis is applied to perform classification and pattern recognition. Experiments analysis results show that the proposed method can be used to identify various types and severities of fault bearings. This study is significant for non-stationary and non-Gaussi an signal analysis, fault diagnosis and degradation assess ment.

Radial mixing and segregation of granular bed bi-dispersed both in particle size and density within horizontal rotating drum

Abstract Taking simultaneous variations in both particle volume and density into account, the radial mixing and segregation of binary granular bed in a rotating drum half loaded were investigated by a 3D discrete element method. Then, based on the competition theory of condensation and percolation, radial segregation due to differences in particle volume and/or density was analyzed. The results show that if either percolation effect induced by volume difference or condensation effect induced by density difference dominates in the active layer of moving bed, separation will occur. Controlling the volume ratio or density ratio of the two types of particles can achieve an equilibrium state between percolation and condensation, and then homogenous mixture can be obtained. When the percolation balances with the condensation, the relationship between volume ratio and density ratio presents nearly a power function. Scaling up a rotating drum will not affect the mixing degree of the granular bed so long as the volume ratio and density ratio are predefined.

Optimization Design of the Web Press’s Fold Mechanism Based on Robustness

With the increasing of printing machine’s working speed, the minor changes of design variables will decrease mechanical precision and stability in working state. So, high-speed and high stability are the tow mutual restraint aspects in modern printing machine design. The web press is the highest printing speed and large-scale with, but the stability of fold mechanism is the most significant constraints to speed. In order to increase the mechanism speed and stability, the two robust criterions, kinematics and dynamics precision, has been proposed. Through the kinetic analysis to the fold mechanism of web press, the dynamic model of the mechanism response to design variables has been established. By the model, the optimization model has been established based on robust analysis. Through the robust model, seeking the design variables with the best robustness，the goal of increasing the mechanical long-term stability in high speed can be attached in the condition of ensuring the fold precision. The design example shows that in the case of the stable design variables, the kinematics performances of robust design and trace optimization design are slightly different , but the dynamic performances of robust design are much better than that of trace optimization, and in the case of the design variables’ slight changes, robust design can make the mechanism’s dynamic performances still maintain, but the trace optimization doesn’t. In short, robust design is a good way to increase the stability of machine.

Fault Diagnosis of Roller Bearing Based on Bispectrum Estimation and Fuzzy Cluster Analysis

Performing bispectrum analysis on the actual measured vibration signals of the roller bearing with different failure modes, it developed that the spectrum distribution regions are similar among the same failure modes, and distinguishable among the different failure modes, thus this character can be used to classify fault types. The binary images extracted from the bispectra are taken as the feature vectors. The fuzzy clustering analysis based on objective function is applied for pattern recognition, which makes use of the binary image to construct a core and a domain representing the common and scope of bispectrum distribution, respectively, then constructs the objective function as the classify to achieve pattern recognition and diagnosis. The roller bearing fault diagnosis is performed as an example to verify the feasibility of the proposed method.

Effects of aging temperature on microstructure and high cycle fatigue performance of 7075 aluminum alloy

The hardness, the tensile and the high-cycle fatigue (HCF) performances of 7075 aluminum alloy were investigated under temper T651, solution treated at 380 °C for 0.5 h and aged at different temperatures (150, 170, 190 °C) for 10 hours. The optimal microstructures and the fatigue fracture surfaces were observed. The results show that the hardness and the tensile performances are at their optimum at T651, but the fatigue life is the shortest. The hardness and the elongation are the lowest after solution treatment. With the aging temperature increasing (150-190 °C), the HCF is improved. The crack is initiated from the impurity particles on the subsurface. Treated at 170 °C,the area of the quasi-cleavage plane and the width of parallel serrated sections of the crack propagation are the largest. With increasing aging temperature, the dimple size of finally fracture surfaces becomes larger and the depth deeper.

Finite element method and experimental modal analysis of PMLSM for ropeless elevator

Modal analysis is a technology for vibration characteristic research. It is the foundation for structural dynamics analysis. Natural frequency is a very important performance in dynamics analysis. Modal characteristics of the Permanent Magnet Linear Synchronous Motor (PMLSM) for ropeless elevator were investigated by finite element method (FEM). FEM models for modal analysis were built for the primary winding, iron core, fixed block, secondary back iron and permanent block by appropriate structure simplification. The influences on natural frequencies of the PMLSM were analyzed. Natural frequencies and mode shapes were simulated by FEM. The accuracy of the FEM analysis is validated by the modal analysis experiment of hammering method.

The Robust Design of Four-Bar Linkage with Clearance Based on Sensitivity Analysis

Clearance is inevitable，so, with the increasing of machine’s speed, nonlinear vibration phenomenon caused by clearance is more apparent, which influences the precision and stability of mechanical system. For increasing the stability of mechanical system, a robust design method based on sensitivity analysis is studied, by using four-bar linkage as the research object, deducing the nonlinear dynamic model with clearance and the sensitivity of dynamic response, based on the rational planning to the tracks and control the sensitivities. In the design example, it shows that although the track deviation of robust design is slightly bigger than that of optimization design, the comprehensive dynamic performance of the mechanical system is much better than the latter, which means the stability of mechanical system is improved greatly. Thus, the robust design based on sensitivity analysis is an effective way to improve the stability of the mechanical system.

Fatigue crack growth prediction of 7075 aluminum alloy based on the GMSVR model optimized by the artificial bee colony algorithm

Purpose The aim of this paper is to solve the problem of low accuracy of traditional fatigue crack growth (FCG) prediction methods. Design/methodology/approach The GMSVR model was proposed by combining the grey modeling (GM) and the support vector regression (SVR). Meanwhile, the GMSVR model parameter optimal selection method based on the artificial bee colony (ABC) algorithm was presented. The FCG prediction of 7075 aluminum alloy under different conditions were taken as the study objects, and the performance of the genetic algorithm, the particle swarm optimization algorithm, the n-fold cross validation and the ABC algorithm were compared and analyzed. Findings The results show that the speed of the ABC algorithm is the fastest and the accuracy of the ABC algorithm is the highest too. The prediction performances of the GM (1, 1) model, the SVR model and the GMSVR model were compared, the results show that the GMSVR model has the best prediction ability, it can improve the FCG prediction accuracy of 7075 aluminum alloy greatly. Originality/value A new prediction model is proposed for FCG combined the non-equidistant grey model and the SVR model. Aiming at the problem of the model parameters are difficult to select, the GMSVR model parameter optimization method based on the ABC algorithm was presented. the results show that the GMSVR model has better prediction ability, which increase the FCG prediction accuracy of 7075 aluminum alloy greatly.

Transmission Efficiency Analysis and Experiment Research on Screw Oscillating Hydraulic Cylinder

This paper introduces working principle of screw oscillating hydraulic cylinder. Structure parameters and process parameters influence on mechanical efficiency is analyzed, simultaneously, structure parameters and process parameters influence on volumetric efficiency is also analyzed. the maximum mechanical efficiency and optimal spiral angle are acquired. Total transmission efficiency model is established. Transmission efficiency experimental test is carried out, experiment test efficiency is basically in accordance with calculated efficiency.

Finite Element Analysis of Contact between Laying Head Pipe and High-Speed Wire Rod

Wire spinning, which is a deformation process of great complexity in laying head pipe, was simulated using MSC. Marc, a software for finite element analysis, with the aid of production data collected in a high-speed wire spinning production line. The stress condition and the temperature distribution of the laying head inner wall, under the condition of high speed dry sliding friction, were obtained. The effects of different feed speeds on the contact stress and the transient temperature of the easily-wear part were analyzed. The simulation result coincides with the actual wear condition in the laying head pipe, indicating the soundness of the finite element model and making a contribution to optimizing the special curve of the laying head pipe and the finished rolling speed.