Journal of Vibroengineering
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Numerical simulation of aerodynamic noises in the far field of the high-speed train with considering bogies and connection windshields
Get PDFThe paper established a computational model of aerodynamic noises for 3-train formation including 3 trains, 6 bogies and 2 windshields. Based on Lighthill acoustic theories, a wideband noise source model was used to recognize the aerodynamic noise source of the high-speed train. Aerodynamic pressures of the high-speed train were extracted and compared with experimental results. The change trends and values presented a good consistency, which indicated that the computational model in this paper was effective. Large Eddy Simulation (LES) and FW-H acoustic model was then used to conduct numerical simulation of aerodynamic noises of the high-speed train. Aerodynamic noise characteristics in the far field of the high-speed train were analyzed. Analyzed results showed that when the high-speed train was running at the speed of 250 km/h, main energy was concentrated within 1250-3150 Hz, and the noise was a wideband noise in the analyzed frequency. The longitudinal observation point was 25 m away from the track center line and 25 m away from the nose tip, and its sound pressure level reached the maximum value of 89.7 dBA, while the sound pressure level around six bogies reached local maximum. With the larger distance from the track center line, the sound pressure level at horizontal observation points presented a smaller attenuation. Incoming flow had a larger impact on aerodynamic noises around the train than the tail flow. The main noise sources of a high-speed train were located at nose tip and pilot of head train, the second noise source was bogies, and the third noise source was located at train connections
A semi-analytical method for vibration analysis of thin spherical shells with elastic boundary conditions
Get PDFA semi-analytical method is proposed to analyze both axisymmetric and asymmetric vibrations of thin opened spherical shells with elastic boundary conditions and discontinuity in thickness. To establish the governing equation, the method is involved in dividing the shell into many narrow strips in meridional direction, and those strips are approximately treated as conical ones with uniform thickness. Flügge shell theory is used to describe the motions of strips and displacement functions are expanded as power series. Artificial springs are employed to restrain displacements at edges so that arbitrary boundary conditions can be analyzed. By assembling all continuity conditions of adjacent strips and boundary conditions, the governing equation is established. In numerical results discussion, many comparisons of frequency parameters of present method and those in literature are firstly presented and they illustrate high accuracy and wide application of present method. Furthermore, influences of elastic boundary conditions, open angle, ratio of thickness to radius and thickness discontinuity on natural frequencies of spherical shells are investigated. Results show that meridinoal and circumferential displacements have obvious effects on natural frequencies, and the influence of thickness discontinuity seriously depends on the location of discontinuity
Development of online detection system for natural frequency of brake discs based on the improved least squares complex frequency domain method
Get PDFThis paper firstly introduced the theory and implementation of the least squares complex frequency domain (LSCF) method based on the truncated singular value decomposition (SVD) for noise reduction. The simulation results of signals with different signal noise ratios (SNR) show that this algorithm is stable and has excellent capacity of resisting noise disturbance. On this basis, an online detection system for natural frequency of brake discs is developed. This system takes the LAN-XI date acquisition module and LABSHOP software of B&K as platform and uses Visual Basic (VB) and MATLAB mixed programming technique for its secondary development. The LSCF method based on the truncated SVD is applied for curve fitting and modal parameter extracting. The qualified criterion is that the stably appearing natural frequencies are in the tolerance ranges. The practical application shows that this system intuitively and accurately displays the detection results and performs stably and efficiently
Free vibration of basalt fiber reinforced polymer (FRP) laminated variable thickness plates with intermediate elastic support using finite strip transition matrix (FSTM) method
Get PDFThis paper presents a semi-analytical method to investigate the effect of intermediate elastic support on the natural frequencies of basalt fiber reinforced polymer (FRP) laminated, variable thickness plates based on the finite strip transition matrix (FSTM) method. The plate has a uniform thickness in x direction and varying thickness hy in y direction. A singular value decomposition algorithm is employed at the intermediate support to eliminate the dependence of the solution of the first span on another span. By a new treatment of the intermediate line support, the dimension of the final matrix of the general solution will be the same as that of plates without intermediate support. Numerical results for different combinations of classical boundary conditions at the plate edges with different elastic restraint coefficients (KT) for intermediate elastic support are presented to obtain the first six frequency parameters. The illustrated results are in excellent agreement with solutions available in the literature, thus validating the accuracy and reliability of the proposed technique
Dynamics analysis and simulation verification of a novel knee joint exoskeleton
Get PDFA novel knee joint exoskeleton, is designed in this paper, including the mechanical structure and hydraulic damper. To determine the spring parameters of knee joint exoskeleton and verify its effectiveness, we conduct the following studies. Firstly, forward kinematics analysis of the swing phase is obtained and Lagrange dynamics analysis is carried out. Secondly, the 3D model of exoskeleton is set up and ADAMS simulation is conducted. Then the spring parameters of knee joint exoskeleton are selected, including the spring force, the spring stiffness coefficient and the spring expansion, according to the simulation results. Finally, there are three sets of moments on the non-wearable side, the moments resulted from ADAMS simulations, the moments from the CGA (Clinical gait analysis) and the moments calculated from the Lagrange equation are compared, results show they are in good agreement. The effectiveness of the ADAMS simulation proves that the parameters of the hydraulic damper can meet the actual requirements. The simulation analysis of the exoskeleton provides important parameters for the manufacture and it also provides theoretical basis for the later control theory
Modeling of a magneto-rheological (MR) damper using genetic programming
Get PDFThis paper is based on the experimental study for design and control of vibrations in automotive vehicles. The objective of this paper is to develop a model for the highly nonlinear Magneto-Rheological (MR) damper to maximize passenger comfort in an automotive vehicle. The behavior of the MR damper is studied under different loading conditions and current values in the system. The input and output parameters of the system are used as a training data to develop a suitable model using Genetic Algorithm. To generate the training data, a test rig similar to a quarter car model was fabricated to load the MR damper with a mechanical shaker to excite it externally. With the help of the test rig the input and output parameter data points are acquired by measuring the acceleration and force of the system at different points with the help of an impedance head and accelerometers. The model is validated by measuring the error for the testing and validation data points. The output of the model is the optimum current that is supplied to the MR Damper, using a controller, to increase the passenger comfort by minimizing the amplitude of vibrations transmitted to the passenger. Besides using this model for cars, bikes and other automotive vehicles it can also be modified by re-training the algorithm and used for civil structures to make them earthquake resistant
Reliability sequential compliance method for a partially observable gear system subject to vibration monitoring
Get PDFAssumptions accompanying exponential failure models are often not met in the standard sequential probability ratio test (SPRT) of many products. However, for most of the mechanical products, Weibull distribution conforms to their life distributions better compared to other techniques. The SPRT method for Weibull life distribution is derived in this paper, which enables the implementation of reliability compliance tests for gearboxes. Using historical failure data and condition monitoring data, a life prediction model based on hidden Markov model (HMM) is established to describe the deterioration process of gearboxes, then the predicted remaining useful life (RUL) is transformed into failure data that is used in SPRT for further analysis, which can significantly save on testing time and reduce costs. Explicit expression for the distribution of RUL is derived in terms of the posterior probability that the system is in the unhealthy state. The predicted and actual values of the residual life are compared, and the average relative error is 3.90 %, which verifies the validity of the proposed residual life prediction approach. A comparison with other life prediction and SPRT methods is given to elucidate the efficacy of the proposed approach
Bearing fault diagnosis via kernel matrix construction based support vector machine
Get PDFA novel approach on kernel matrix construction for support vector machine (SVM) is proposed to detect rolling element bearing fault efficiently. First, multi-scale coefficient matrix is achieved by processing vibration sample signal with continuous wavelet transform (CWT). Next, singular value decomposition (SVD) is applied to calculate eigenvector from wavelet coefficient matrix as sample signal feature vector. Two kernel matrices i.e. training kernel and predicting kernel, are then constructed in a novel way, which can reveal intrinsic similarity among samples and make it feasible to solve nonlinear classification problems in a high dimensional feature space. To validate its diagnosis performance, kernel matrix construction based SVM (KMCSVM) classifier is compared with three SVM classifiers i.e. classification tree kernel based SVM (CTKSVM), linear kernel based SVM (L-SVM) and radial basis function based SVM (RBFSVM), to identify different locations and severities of bearing fault. The experimental results indicate that KMCSVM has better classification capability than other methods
Simultaneous excitation and parameter identification for non-linear structural systems
Get PDFIn this paper, an algorithm is proposed for simultaneous excitation and parameter identification for non-linear system in state space. The algorithm is based on the sequential application of extended Kalman estimator for non-linear structural parameters and the weighted least squares estimation for unknown excitations. The state and parameter are reformed into the augmented state, and the state space equations are non-linear associated with the augmented state. With the first-order Taylor expansion for nonlinear system and approximately linear minimum-variance unbiased estimation, a recursive algorithm is derived where the identification of the augmented state and the excitation are interconnected. Two numerical examples which identify uncertain parameters of a 3-DOF Duffing-type system and a four-story hysteretic shear-beam building subject to unknown random excitation respectively, are conducted to demonstrate the effectiveness of the proposed approach
Time-frequency analysis method of bearing fault diagnosis based on the generalized S transformation
Get PDFThe generalized S transform (GST) can flexibly adjust the change trend of the fundamental window function according to the frequency distribution characteristics and the time-frequency emphasis of vibration signal. Also, this transform can accelerate or slow down the time-band width change along with the frequency, in order to make the amplitude of the fundamental window function present the various nonlinear changes. These features are very constructive significance for signal analysis and processing. A time-frequency analysis method based on the generalized S transformation is introduced to the fault diagnosis of bearing. And the application principle and the steps of method applied in fault diagnosis are given. Simulated signals and the actual bearing fault signals from inner race, outer race and rolling body are processed to verify the validity of the proposed method. Results show that the method can effectively enhance the resolution of vibration signal not only in time domain but also in frequency domain. The fault characteristic frequency can be extracted from the reconstructed signal, and the status of bearing and the fault type of bearing can be obviously distinguished. The presented time-frequency method effectively improves the accuracy of the fault diagnosis of bearings