Journal of Vibroengineering
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Numerical simulation on the aerodynamic performance of the high-speed train under crosswinds
Get PDFWith the continuously increased speed of the high-speed train, the lateral aerodynamic performance of high-speed trains has attracted more and more attention. Under strong crosswinds, the aerodynamic performance of trains deteriorate and air drag, lift and lateral forces borne by trains quickly increase, which has an impact on the lateral stability of trains and even leads to train derailment. This paper adopted computational fluid dynamics theory to establish an aerodynamic model for a high-speed train, computed aerodynamic forces and moments acting on the high-speed train and obtained the unsteady flow field of the high-speed train. In the meanwhile, this paper combined with multi-body system dynamics theory to establish a system dynamics model for the train and analyzed the safe aerodynamic performance of the high-speed train under cross winds. Computational results showed: Under cross winds, the aerodynamic performance of the high-speed train had a random fluctuation. When wind direction angle was 90°, aerodynamic forces (drag, lift and lateral forces) and moments (overturning moment, shaking moment and nodding moment) borne by the high-speed train were the largest; train speed was a main factor affecting the size of positive pressures of train and cross wind velocity had no obvious impacts on the positive and negative pressures of train body; the aerodynamic forces and moments of the high-speed train had a random fluctuation within a certain range with time; the frequency for the peak value of power spectral density of lateral forces of head train was within 25 Hz and the peak value of power spectral density was the largest when the main frequency was 1.6 Hz; the frequency for the peak value of power spectral density of overturning moment of head train was within 20 Hz and main frequency was 0.57 Hz. When the cross wind speed was 15 m/s, all safety indexes of the high-speed train running at the speed of 250 km/h were within the range of limited values and satisfied design requirements. Aerodynamic performance of the high-speed train with the suction chamber under the cross wind was computed and compared with original results. Aerodynamic force and force moments of the high-speed train under cross wind will be reduced obviously and running safety of the high-speed train can be improved through application of the suction chamber
Dynamic instability analysis of U-shaped electromechanical nano-sensor operated in vdW regime
Get PDFU-shape nanoelectromechanical systems (NEMS) are potential for developing miniature sensors. While the electro-mechanical performance of conventional beam-type NEMS has been exclusively addressed in the literature, few works have considered this phenomenon in U-shaped systems. Herein, the static and dynamic pull-in instability of the U-shaped NEMS is investigated under the presence of vdW force. Based on the recently developed consistent couple stress theory (CCST), the size-dependent constitutive equation is derived. Two types of the beam cross-sections including rectangular and circular geometries are considered. The nonlinear equations are solved by employing Ray-leigh-Ritz solution method. The developed model is validated by comparison with the results presented in literature. The effect of various parameters on the static and dynamic pull-in parameters, phase plans and stability threshold of the system is discussed. The obtained results reveal that the vdW attraction decreases the pull-in voltage while the size dependency enhances the instability voltage. On the other hand, the presented model demonstrates that characteristics of the tip-plate can change the pull-in parameters significantly
Bifurcation and chaotic behaviors of 4-UPS-RPS high-speed parallel mechanism
Get PDFIn order to grasp the nonlinear characteristics of high-speed spatial parallel mechanism, the bifurcation and chaotic behaviors of 4-UPS-RPS mechanism are analyzed. Firstly, the nonlinear elastic dynamic model of the mechanism is established by using the Lagrange equation and the finite element method. Then the effects of parameters including driving angular velocity, the radius of motion trajectory, the material of driving limbs, the diameter of driving limbs, and the mass of moving platform, on the bifurcation and chaotic behaviors of high-speed spatial parallel mechanism are studied. The results show that the above parameters all have a certain influence on nonlinear characteristics of the 4-UPS-RPS high-speed spatial parallel mechanism. The research can provide important theoretical basis for the further research on the non-linear dynamics of spatial parallel mechanism
Republished Paper. Numerical study for single and multiple damage detection and localization in beam-like structures using BAT algorithm
Get PDFThis paper presents a new damage detection and localization technique based on the changes in vibration parameters using BAT and Particle Swarm Optimization algorithm. The finite element method is used to apply damage at specific element(s) of the considered beams. The damage is represented by a reduction in Young’s modulus and the identification of damage is formulated as an optimization problem using objective function based on Modal Scale Factor and changes in natural frequencies. A procedure for detecting and locating damage of beam-like structures based on BAT algorithm is used. This approach presents a method that can be used to detect the single and multiple-damage positions and the rate of damage in structural elements with high accuracy after the first iteration. The results obtained using BAT algorithm are compared to those obtained using Particle Swarm Optimization Algorithm. By taking noise into account in the damage detection and localization problem, it is shown that our approach based on BAT algorithm can detect the damage locations with high accuracy
Thickness shear vibration of a ZnO film structure covered with magnetic fluid
Get PDFThis paper aims to reveal the effect of magnetic liquid on the resonant frequency shift and the output impedance. For this purpose, a thin film sensor was designed with a finite-thickness layer of magnetic fluid, and the thickness shear vibration of the film was analysed in details. The main findings are as follows. First, the relative resonance frequency is positively correlated with the intensity of magnetic field, and the viscosity coefficient, density and volume fraction of magnetic fluid. The effect of magnetic field on the shift of the relative resonant frequency depends on various parameters of magnetic liquid. With the increase of the volume fraction, density and viscosity coefficient, the resonant frequency plunges, but the output impedance peak grows in size. Therefore, the relative resonant frequency shift and the output impedance are sensitive to various parameters in the design. The research findings shed new light on the application of thin piezoelectric film in sensors
A novel classification method combining adaptive local iterative filtering with singular value decomposition for fault diagnosis
Get PDFAs a novel time-frequency analysis method, adaptive local iterative filtering (ALIF) can decompose the time series into several stable components which contain the main fault information. In addition, the amplitude of singular value obtained by singular value decomposition (SVD) can reflect the energy distribution. Naturally, there are certain differences in the energy produced by different faults such as the broken tooth, wearing and normal. Thus, a novel method of mechanical fault classification method based on adaptive local iterative filtering and singular value decomposition is proposed in this paper. Firstly, ALIF method decomposed the original vibration signal into a number of stable components to establish an initial feature vector matrix. Then, the singular values energy corresponding to the feature matrix is employed as a criterion to identify various faults. Compared with the conventional EMD method by simulation experiments, ALIF method has obvious superiority in solving modal aliasing, which is more conducive to the advanced analysis. In this paper, the proposed method is employed to extract the fault information of rolling bearing fault signals from Case Western Reserve University Bearing Data Center. To further verify the effectiveness of the method, the case study is conducted at Drivetrain Diagnostics Simulator. To further illustrate the effectiveness of the method, the results obtained by this method are compared with EMD and EEMD. The results indicated the proposed method performs better in the classification of different mechanical faulty modes
Combined effects of penetration and explosion on damage characteristics of a mass concrete target
Get PDFWith the development of the precision guidance technology, the earth-penetrating weapon (EPW) is a huge threat to infrastructures. The objective of this research is to investigate the damage characteristics of mass concrete targets under the combined action of penetration and explosion. The validity of the penetration model is discussed by reproducing a previous experimental test reported in the literature. Meanwhile, a field test about the internal explosion in a concrete cube is conducted to verify the validity of the internal explosion model. Subsequently, damage characteristics of a mass concrete target from the upper part of a concrete gravity dam are discussed when subjected to the combined action of the penetration and explosion. In order to improve the structural performance of the mass concrete target to penetration and explosion loadings, high strength concrete material is selected as a preventive measure. Penetration processes and damage patterns of the mass target with normal and high strength concrete material are compared. Then, three internal explosion models are presented to investigate the influence of the initial penetration damage on the failure characteristics of the mass concrete target. The results show that the resistance of the mass target to the combined action of the penetration and explosion can be enhanced significantly by using the high strength concrete material. The initial penetration damage has a significant influence on the damage processes of the mass concrete target subjected to internal blast loading
Research on unbalance response characteristics of gas turbine blade-disk rotor system
Get PDFTaken a gas turbine rotor system as the research object, this paper has established dynamical model based on transfer matrix method. Natural vibration characteristics are solved with different transfer matrix models, and are compared with that gotten by finite element method. Then unbalanced response is researched. The effects of eccentric factors are discussed on unbalanced vibration. Furthermore, the application is explored in rotor dynamic balancing. The results show there is much minor deviation between natural frequencies of transfer matrix method and finite element method, and vibration modes of two methods coincide quite well. It illustrates the model established in the research is reliable. For input side of blade-disk rotor, unbalanced vibration occurs more easily in lower frequency. While unbalanced vibration of output side is more sensitive at higher frequency. With the increase of eccentric mass, unbalanced vibration of blade-disk rotor is more heavily, and the displacement rotates around a fixed node. The application of opposite unbalanced mass can decrease the amplitude of vibration in lower frequency. Hence, it can be used to achieve the balance of rotor dynamics. This research provides the theoretical basis and technological fundament for gas turbine rotor dynamics design
Research on dynamics of sorting arms with high frequency reciprocating motion
Get PDFThe characters of high frequency reciprocating equipment are quick starting and stopping, short range, high frequency and multi-freedom reciprocating motion. The inertia introduced by the high frequency reciprocating motion of a LED chip sorter has complicated effects on the positional accuracy. It is necessary to obtain dynamics of the sorting arm to suppress the vibration of the high frequency operation. The positioning precision and positioning time are affected by the natural vibration of the sorting arm by analyzing the displacement response. The paper verifies that the inherent vibration of the sorting arm has a crucial effect on its positioning precision and positioning time. Under static condition, due to the additional mass of the accelerometers, the research results show that there is no obvious difference in the experimental modal analysis (EMA) based on multi-type sensors. The modal parameters identified by accelerometers and strain gauges are very close. The modal parameters are obtained through the modal analysis method, which combines the strain modal analysis and operational modal analysis (OMA), under high frequency reciprocating motion. The paper verifies that the modal parameters of lightweight structure are very different in the static and operation. The key points of each mode are found by analyzing the modal amplitudes at different speeds which provide the guiding principle and basis for the dynamic optimization of the sorting arm mechanism
Literature review of tire-pavement interaction noise and reduction approaches
Get PDFTire-pavement interaction noise (TPIN) dominates for passenger vehicles with the speed of above 40 km/h and for trucks with the speed of 70 km/h. With the prevailing trend of electric vehicles, TPIN can become more NVH (Noise, Vibration, and Harshness) issue in the future. In this paper, the vehicle noise and tire noise were briefly reviewed in the background introduction. Then the motivation of and approaches to reducing tire noise was reviewed from open literature. It was found that the tire industry and the pavement industry have been working individually on designing and building quiet tire and quiet pavement for many decades. However, the interaction between tire and pavement was less investigated. The future research on reducing TPIN can be the combined consideration of both tire and pavement characteristics while maintaining other performances, such as traction, handling, rolling resistance, hydroplaning, and durability