Abstract: A real time and effective axlebox bearing fault diagnostic method is significant in the condition-based maintenance. In the axlebox bearing fault diagnostic system, fault features extraction and fault patterns classification are two important aspects to identify whether a axlebox bearing is failure or not. This paper presents a method of axlebox bearing fault diagnosis based on wavelet packet decomposition and BP neural network. First decompose the vibration signal into a finite number of coefficients by wavelet packet decomposition. Then calculate energy moment of each coefficient and take the energy moment as an eigenvector to effectively express the failure feature. Finally BP neural network is used for fault classification. The experimental results show that combining wavelet packet decomposition with BP neural network could identify the axlebox bearing fault effectively. The average diagnosis accuracy rate is 96.67%.
Abstract: Working condition of large rotating machine is varying. The collected vibration signals contain fault information as well as non-fault information, like load change and noise. The traditional fault feature extraction method which based on energy changing has certain limitations; therefore, new fault feature extraction method based on Fast ICA will be researched. Separating independent signals from blind signals by adopting Independent Component Analysis(ICA), purifying fault information and suppressing interference information; and the lifting wavelet packet is used for acquiring time frequency domain feature band from signals, so as to solve the difficulty that the fault information of the variable working condition rotating machine is always submerged by irregular working condition changing information such that effective fault prediction is hard to carry out.
Abstract: Blind source separation (BSS) has been successfully used to extract undetected fault vibration sources from mixed observation signals by assuming that each unknown vibration source is mutually independent. However, conventional BSS algorithms cannot address the situation in which the fault source could be partially dependent on or correlated to other sources. For this, a new matrix decomposition method, called Non-negative Matrix Factorization (NMF), is introduced to separate these partially correlated signals. In this paper, the observed temporal signals are transformed into the frequency domain to satisfy the non-negative limit of NMF. The constraint of the least correlation between the separated sources is added into the cost function of NMF to enhance the stability of NMF, and the constrained non-negative matrix factorization (CNMF) is proposed. The simulation results show that the separation performance of CNMF is superior to the common BSS algorithms and the experiment result verifies the practical performance of CNMF.
Abstract: Compound fault feature separation is a difficult problem in diagnosis field of mechanical system. For the rolling bearing with compound fault on outer and inner race, feature separation technology based on complex wavelet transform and energy operator demodulation is introduced. Through continuous wavelet transform, coefficients of mixed fault signal can be achieved in different wavelet transform domain (i.e. real, imaginary, modulus and phase domain). Furthermore, wavelet power spectrum contours and time average wavelet energy spectrum are applied to extract the scales which hold rich fault information, and the wavelet coefficient slice of specific scale is also drawn. For wavelet coefficients in different domain, spectrum analysis and energy operator demodulation can be used successfully to separate mixed fault. The comparison of feature extraction effect between complex wavelet and real wavelet transform shows that complex wavelet transform is obviously better than the latter.
Abstract: Offshore wind turbine is a novel approach in the field of wind energy technology. With the rapid development of coastal wind farms, it is the trend to move them outward to deep-water district. However, the cost of construction rises significantly with the increase in water depth. Floating wind turbine is one of the efficient methods to solve this problem. The early history, current status and cutting-edge improvements of overseas offshore floating wind turbine as well as the shortcomings shall be presented. The concept designs, international standards, fully coupled model simulations and hydrodynamic experiments will be illustrated and discussed together with the development of the theory and the related software modules. Thus a novel researching method and concept shall be presented to provide reference for future researches
Abstract: One stage light gas gun is an important device for experiments of low-speed supercavitation projectiles. After a reasonable simplification to the gas gun, movements of the projectile in the barrel have been analyzed and the relationships between the initial pressure of the gas gun and the exit velocity of the projectile were obtained. For meeting the velocity difference between at the gun exit and water-entry, a speed impairment factor was employed. The results of the adiabatic analysis of the simplified gun show that the best ratio between gun chamber volume and the barrel length is related to the gas thermodynamic process and the gas residual pressure has relation to the gas thermodynamic process. The low-speed supercavitation projectile experiments have been carried out. The movements of the projectile in the gas gun and the supercavitation shape and projectile speed after water-entry have been numerically simulated.
Abstract: Some key components’ failure often occurs in the process of the use of large-scale mining coal machine, and seriously affects the production of the enterprise. So it is necessary that analysis on the failure mechanical reason of guide shoes with the coal-winning machine by the modern mechanics analysis method. The stress diagram of guide shoes could be got by static analysis with MATLAB, and the dangerous parts of the finite element model with guide shoes appeared after loading. Finally, analysis on the fatigue strength and fatigue life of components under various complex condition, which provide some reference theory basis for the future related product designing, Manufacturing and maintenance.
Abstract: An effective optimization method using Kriging model and parametric sampling evaluation strategy is proposed to solve dynamic optimization design. The optimization problem is to find the design variables such that the structural weight is minimum and dynamic displacement of the points concerned plus certain side constraints are satisfied. The types of design variables are considered as the sizing variables of the beams and columns. Kriging model is used to build the approximate mapping relationship between the forced vibration amplitude and design variables, reducing expensive dynamic reanalysis. A dynamic analysis program is used as black-box to obtain dynamic response. Numerical examples show that the method has good accuracy and efficiency. Versatility of this method can be expected to play an important role in future engineering optimization problems.
Abstract: This paper describes a multidisciplinary computational study undertaken to compute the flight trajectories and simultaneously predict the unsteady free flight aerodynamics of aircraft in time domain using an advanced coupled computational fluid dynamics (CFD)/rigid body dynamics (RBD) technique. This incorporation of the flight mechanics equations and controller into the CFD solver loop and the treatment of the mesh, which must move with both the control surface deflections and the rigid motion of the aircraft, are illustrated. This work is a contribution to a wider effort towards the simulation of aeroelastic and flight stability in regions where nonlinear aerodynamics, and hence potentially CFD, can play a key role. Results demonstrating the coupled solution are presented.
Abstract: In order to explore micro-beam relaxation dynamics of MEMS, the beam deflection relaxation expression considering air slide-film damping effect was educed based on Euler–Bernoulli equation with boundary conditions of two hinged ends. The beam deflection relaxation process under over damping, critical damping and under damping was calculated used Maple. The relaxation simulation data of micro-beam with two hinged ends used ANSYS demonstrate that relaxation process conform to theoretical calculation and relaxation period of under damping relaxation approximate constant when damping coefficient is small, but increase significantly when damping coefficient is large.