Zhang Yi-min

Synchronisation and general dynamic symmetry of a vibrating system with two exciters rotating in opposite directions

We derive the non-dimensional coupling equation of two exciters, including inertia coupling, stiffness coupling and load coupling. The concept of general dynamic symmetry is proposed to physically explain the synchronisation of the two exciters, which stems from the load coupling that produces the torque of general dynamic symmetry to force the phase difference between the two exciters close to the angle of general dynamic symmetry. The condition of implementing synchronisation is that the torque of general dynamic symmetry is greater than the asymmetric torque of the two motors. A general Lyapunov function is constructed to derive the stability condition of synchronisation that the non-dimensional inertia coupling matrix is positive definite and all its elements are positive. Numeric results show that the structure of the vibrating system can guarantee the stability of synchronisation of the two exciters, and that the greater the distances between the installation positions of the two exciters and the mass centre of the vibrating system are, the stronger the ability of general dynamic symmetry is.

A numerical method for structural uncertainty response computation

A novel numerical procedure, which realizes the stochastic analysis with dimensional reduction integration (DRI), C-type Gram-Charlier (CGC) series, and finite element (FE) model, is proposed to assess the probability distribution of structural performance. From the relationship between the weighting function of orthogonal polynomial and probability density function (PDF) of random variable, the numerical integration formulas are derived for moment computation. Then, distribution of structural uncertainty response can be approximated by the CGC series with the calculated moments. Three engineering applications for the distribution of, the maximum displacement of a ten-bar planer truss, natural frequency of an auto frame, and Von-Mises stress of a bending pipe, are employed to illustrate the computational efficiency and accuracy of the proposed methodology. As compared with plain Monte Carlo simulation (MCS), the method can obtain the accurate distribution of structural performance. Especially at the tail region of cumulative distribution function (CDF), results have shown the satisfying estimators for small probabilities, say, P ∈ [10−4, 10−3]. That implies the method could be trusted for structural failure probability prediction. As the computational efficiency is concerned, the procedure could save more than two orders of computational resources as compared with the direct numerical integration (NI) and MCS. Furthermore, realization of the procedure does not require computing the performance gradient or Hessian matrix with respect to random variables, or reshaping the finite element matrix as other stochastic finite element (SFE) codes. Therefore, it should be an efficient and reliable routine for uncertainty structural analysis.

Deflections of Nanowires with Consideration of Surface Effects

The elementary beam model is modified to include the surface effects and used to analyze the deflections of nanowires under different boundary conditions. The results show that compared to deflections of nanowires without consideration of surface effects, the surface effects can enlarge or reduce deflections of nanowires, and nanowire buckling occurs under certain conditions. This study might be helpful for design of nanowire-based nanoelectromechanical systems.

Gradual Reliability Sensitivity Analysis of Mechanical Part Considering Preventive Maintenance

A lot of mechanical parts are subject to failure due to the deterioration. Usually the preventive maintenance is taken to ensure the safety and reliability. Therefore, it is very important to study the gradual reliability design of the mechanical part for improving the gradual reliability of the mechanical system under the condition of considering the preventive maintenance. Beta distribution is employed to describe the randomness of the mechanical part state after the preventive maintenance. The deterioration process of the mechanical part is modeled using the nonstationary Gamma process. The gradual reliability model before the first preventive maintenance is proposed according to the gradual failure principle and using the initial state distribution and the properties of Gamma process. Then, the gradual reliability model between any two times of preventive maintenance is also derived. Subsequently, the sensitivity equations of the proposed gradual reliability model to each parameter are given. The application process and practicality of the proposed approach are described by a numerical example. This work solved the problem where the maintenance has not been well considered in the reliability design of the mechanical part and contributed to the theory and method of improving the safety and reliability operation of the mechanical system.

Study of B-Spline Interpolation, Correction and Inverse Algorithm

This paper aims to make a detail analysis of B-spline interpolation and inverse algorithm that are widely used in CAD/CAM. It points out the nature of two definitions of B-spline curve as well as five correction methods of one B-spline interpolation. In this paper, it explores B-spline inverse algorithm and gives the scope of the algorithm. In addition, it verifies this algorithm by writing a program using VB 6.0.

Development of the Analysis Software of Reliability Based on the Matlab

In this paper, the analysis of reliability software was developed using the MATLAB language. This software has the functions as following: creating sample data with the specify Probability distribution types and parameters, test sample data analysis, solving the reliability problem with 2 to 4 stochastic variable. Reliability function is input by user which enhances the applicability. The method of Monte Carlo is presented to verify the result. The development of this software is an application of computer to the engineering.

Structural Optimization Method of Key Part of High Speed Machining Center

Aimed at the dynamical design of the column for a high speed machining center, an optimization design is carried on under the restrain of mass and frequency. Dynamical stiffness is the optimization target. Using the Ansys Workbench, the optimal thickness of ribs in column is solved, and the increment of dynamical stiffness is also given. Optimal model is analysised to verify the optimization design. It is a method to dynamical design typical parts in machining tools.

Finite Element Analysis about Transmission Components in C Parts of Direct-drive Bi-Rotary Milling Head

In a direct-drive high-power A / C-axis bi-rotary milling head,torque is transferred by two parallel connected rotary direct drive motors in C-axis, therefore, the length of C axis is inevitable large, moreover, the transmission components of it are bearing high torque. Through analyzing the twist stiffness of the transmission components in C-axis by the finite element method, the result that the torsion deformation of the sleeve accounts for a large scale in transmission components of C parts is found. In the permitted extent structural design of C-axis, the stiffness of transmission components in C parts is increased effectively through shortening the sleeve and lengthening its external diameter.