Journal of Vibroengineering
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Based on lacing wires influence of coupling vibration of a multi flexible disks turbine rotor system by two methods
Get PDFThis paper explored the blade-bending, disk-transverse and shaft-torsion coupling vibrations phenomenon of a multi flexible disc rotor system, whose blades subsystem was grouped with spring. Being different from the author’s previous researches, here we used two methods: one is the assumed mode method (AMM) and the other is the finite element method (FEM), the proposed former one is main, and the latter one is complementary. Then compared the two results generated from them. According to the authors’ previous definition, a flexible disc rotor system displays three coupling vibrations’ types, inter-blade (BB), shaft-disk-blade (SDB) and disk-blade (DB) modes. In this paper, the authors additionally defined two new types, which were called lacing wires-blade (LB) and lacing wires-disk-blade (LDB) mode. The system change rules of natural frequencies and that of mode shapes would be discussed. Some interesting results are shown in this paper. Firstly, the author pointed out the change rules of the mode shapes and natural frequencies by using the AMM and FEM (including three kinds of softwares). Secondly, numerical calculation results also showed that the distance of disk, the disk with flexible, the constant of spring, and location of spring four phenomena would affect the natural frequencies
Design and the main parameters of tube-shaped ultrasound wave guide wire
Get PDFCardiovascular diseases are the leading cause of death among people up to 65 years old. One of the most common cardiovascular diseases is arterothrombosis. For recanalization of arteries usage of advanced invasive mechanical devices is required. The tube-shaped ultrasound waveguide wire was designed, investigated and validated by computational finite element method and experimental techniques
Analytical analysis on damping characteristics of rotor system
Get PDFA general vibration model of a flexible rotor system is established to investigate the influences of the damping characteristics on vibration behaviors. Based on the multi-scale method, the analytical solutions of steady-state and transient-state are derived under the positive and negative conditions of nonlinear damping. The physical significance of the coefficients and their influences on rotor behaviors are analyzed through theoretical analysis and numerical calculation. The experimental results elaborate the damping effect and verify the rationality of the model
Feature extraction of vibration signal using OMP-NWE method
Get PDFFeature extraction is one of the core problems in condition monitoring and fault diagnosis of mechanical equipment. In this study, an OMP-NWE method of feature extraction is proposed, aiming at the problem of low accuracy of existing feature extraction method. The OMP-NWE method integrates the strengths of orthogonal matching pursuit (OMP) algorithm with the benefits of nonparametric waveform estimation (NWE). Signal feature extraction model is constructed by design of filter bank and adaptive template signal. Then the vibration signal is linearly decomposed into a set of best matching waveform, which solves the problem that the basis function must be chosen in advance in OMP algorithm. The OMP-NWE method is applied to the feature extraction of the simulation and experimental vibration signal of rolling bearing, compared with the traditional OMP algorithm. Results show that the SNR of the extracted feature signal using OMP-NWE method increased by 19.22 % compared with that using the OMP method, which illustrates that OMP-NWE method has a higher accuracy in the feature extraction of unknown complex vibration signals. This work provides a new idea and a successful example for the feature extraction of vibration signal in the condition monitoring and fault diagnosis of mechanical equipment
Fault diagnosis for the gearbox of wind turbine combining ensemble intrinsic time-scale decomposition with Wigner bi-spectrum entropy
Get PDFThe complex dynamic working conditions of wind turbine make it a challenge to identify work status and fault type of wind turbine gearbox. In this paper, a novel method is presented to decompose non-stationary vibration signal and identify wind turbine faults applying ensemble intrinsic time-scale decomposition (EITD) with Wigner bi-spectrum entropy (WBE). Ensemble intrinsic time-scale decomposition (EITD) is able to restrict the end effect and to prevent the signal distortion. Wigner bi-spectrum entropy (WBE) has perfect energy aggregation and can extract the signal feature effectively. The advantage of method is that it does extract the fault features and recognize the gearbox fault types when two or more fault features are close to each other. This proposed approach based on EITD and WBE is applied in the fault diagnosis of wind turbine gearbox
Experimental and numerical investigation on dynamic behaviors of the concrete wall in underground coal mine with hydraulic blasting demolition
Get PDFIn order to investigate the dynamic response and failure modes of concrete wall under hydraulic blasting load in underground tunnels, the fracture mechanism and zoning characteristics of hydraulic blasting of concrete wall was analyzed theoretically. Stress field, displacement field and energy variation laws of concrete wall has been simulated based on the finite element dynamic program LS/dyna. Meanwhile, different experimental conditions on the dynamite, reserved hole parameters such as demolition parameters are designed studied according to the blasting fracturing principle. The effects of stress wave, high pressure gas expansion effect in the dismantling process, application of line of least resistance principle and directional blasting effect control principle are analyzed. Results reveal the FSI effect between concrete wall and the water-dynamite-pore wall and the relationship between parameters of the structure and the dynamite dynamite, the concrete dynamic compressive strength and dynamic tensile strength. Numerical and experimental methods as well as conclusions will provide basis for the blasting demolition of brick concrete wall under similar conditions
Numerical computation for vibration characteristics of long-span bridges with considering vehicle-wind coupling excitations based on finite element and neural network models
Get PDFCA (Cellular Automaton) model was applied to the simulation of random traffic flow to develop a model considering the randomness of traffic flow and apply it to wind-vehicle-bridge coupling vibration. Finite element and neural network models were adopted respectively to numerically compute the vibration characteristics of bridges under wind and vehicle loads, verify the correctness of model. Subspace iteration method was used for the modal analysis of bridges. Natural frequencies of the top 8 orders were 0.21 Hz, 0.27 Hz, 0.36 Hz, 0.45 Hz, 0.56 Hz, 0.66 Hz, 0.87 Hz and 1.02 Hz respectively. The vibration frequency of the long-span bridge was consistent with the vibration characteristics of large-scale complex structures. Natural modes mainly reflected the torsion and bending of main beam and the swinging vibration of side and main towers. Fluctuation wind time-history presented periodic characteristics. The maximum and minimum values of fluctuation wind were about 20 m/s and –20 m/s respectively. The target and simulation values of power spectral density of wind speed were basically the same in change trend, which indicated that the fluctuation wind time-history computed in this paper was reliable. The model of dense traffic flow based on CA more truly described the running status like accelerating, decelerating and changing lanes of vehicles on the bridge, also contained the density information of vehicles and more truly reflected traffic characteristics. Vibration accelerations of the long-span bridge were symmetrically distributed. Vibration acceleration of central position in the left main span was the largest and near 50 cm/s2; vibration acceleration on the main tower was the smallest. The curve of vibration displacement with considering wind loads presented some fluctuations, while the vibration displacement of bridges without considering wind loads was very smooth. In addition, the amplitude of vibration displacement without considering wind loads moved laterally towards the left compared with that with considering wind loads. Therefore, wind loads must be considered when the vibration characteristics of the long-span bridge were computed. Otherwise, the accuracy of computational results would be reduced. It only took 0.5 hours to use neural network to predict the vibration acceleration of the long-span bridge. In the case of the same computer performance, it took 5 hours to use finite element model to predict the vibration acceleration of the long-span bridge. The advantage of neural network model in predicting the performance of large-scale complex structures like a long-span bridge could be obviously found. In the future, we will consider using neural network model to systematically study and optimize the long-span bridge
Experimental research and numerical analysis on vibroacoustic characteristics of the laminated composite plate and its application in high-speed trains
Get PDFThis paper firstly used the finite element method to study the impact of air coupling on the structural radiation noise of thin plates and conducted a comparative analysis on the vibration noise of thin plates in the water and air. Results showed that coupling effect and medium property had an obvious influence on the radiation noise of thin plates, and these factors must be considered. Secondly, this paper proposed laminated plates based on the single-layered thin plate. The related experiment of laminated plates was conducted and compared with the computational result to verify its reliability. As an important parameter of laminated plates, laying angle can change the structural stiffness of laminated plates and mechanical properties. Therefore, based on the verified computation model, this paper studied the radiation noise of laminated plates through changing the laying angle of laminated plates, improved the vibration noise of laminated plates through applying control forces. As a result, a laminated plate with the optimal performance can be obtained. Finally, laminated composite plates were applied to the inner surface of panels which had made greater acoustic contributions to high-speed trains and controlled the vibration noise of high-speed trains through applying control forces. Results showed that the peak noise of high-speed trains was obviously improved at multiple frequencies and total sound power levels reduced by 23.1 dB
Silage production technology using grass thickening vibratory method
Get PDFThe article presents silage production technology using vibratory method. The objective of this research was to quantify the selected theoretical model by comparison to experimental results and to determine more reasonable calculations methods for practical issues. Based on the classical theory of mechanical oscillations a numerical analysis of silages thickening by vibrator was developed. Using the developed numerical model, the vibrator operational characteristics were obtained. Numerical and experimental investigation was performed using a direct-action vibrator to compact chopped maize. A comparison between the experimental and numerical results is presented. The results can be used to determine technical characteristics of the vibrator for silage thickening dynamics. The obtained system parameters can be used to prepare technical tasks for selection of vibratory silages thickening equipment
Non-orthogonal joint block diagonalization based on the LU or QR factorizations for convolutive blind source separation
Get PDFThis article addresses the problem of blind source separation, in which the source signals are most often of the convolutive mixtures, and moreover, the source signals cannot satisfy independent identical distribution generally. One kind of prevailing and representative approaches for overcoming these difficulties is joint block diagonalization (JBD) method. To improve present JBD methods, we present a class of simple Jacobi-type JBD algorithms based on the LU or QR factorizations. Using Jacobi-type matrices we can replace high dimensional minimization problems with a sequence of simple one-dimensional problems. The novel methods are more general i.e. the orthogonal, positive definite or symmetric matrices and a preliminary whitening stage is no more compulsorily required, and further, the convergence is also guaranteed. The performance of the proposed algorithms, compared with the existing state-of-the-art JBD algorithms, is evaluated with computer simulations and vibration experimental. The results of numerical examples demonstrate that the robustness and effectiveness of the two novel algorithms provide a significant improvement i.e., yield less convergence time, higher precision of convergence, better success rate of block diagonalization. And the proposed algorithms are effective in separating the vibration signals of convolutive mixtures