Journal of Vibroengineering
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Shooting method for free vibration of FGM Reissner-Mindlin circular plates resting on elastic foundation in thermal environments
Get PDFThis paper presents a free vibration analysis of functionally graded Reissner-Mindlin circular plates with various supported boundaries in thermal environments. A FGM consisting of metal and ceramic was considered in the study. Based on the geometric equation, physical equation and equilibrium equation of thick plate, taking into account the transverse shearing deformation, the free vibration equation of the axisymmetric FGM moderately thick circular plates was derived in terms of the middle surface angles of rotation and lateral displacement. The material properties of the plate were assumed to vary continuously in the thickness direction according a power law. By using shooting method to solve the coupled ordinary differential equations with different boundary conditions, the natural frequencies of FGM thick circular plates were obtained numerically. The effects of material gradient property, thickness ratio and boundary conditions on the natural frequencies were discussed in detail
Multi-objective optimization for the aerodynamic noise of the high-speed train in the near and far field based on the improved NSGA-II algorithm
Get PDFWith the increased running speed of trains, the aerodynamic noise of trains becomes increasingly obvious. Reducing aerodynamic noises has become one of keys to controlling the noise of high-speed trains. This paper conducted a numerical simulation on the aerodynamic noise of head of the high-speed train. Firstly, this paper established a mathematical-physical model for the three-dimensional turbulent flow field of a high-speed train, adopted standard k-ε equation turbulent model and broadband noise source model to compute the aerodynamic noise sources of the high-speed train and applied three-dimensional transient large eddy simulation (LES) to compute the external unsteady flow field of the high-speed train after obtaining noise sources. Based on the unsteady flow field, then this paper applied FW-H equations to compute the far-field aerodynamic noise of the high-speed train. After obtaining the unsteady fluctuation pressure on the surface of the train, this paper computed the radiation characteristics of aerodynamic noises around the high-speed train based on the boundary element method (BEM). Researched results showed: The main aerodynamic noise sources of the high-speed train were at the nose tip of head train; fluid separation and recombination were main reasons for the aerodynamic noise of the high-speed train; vortexes in the position of head train were striped and horseshoe-shaped or hairpin vortexes were mainly in the area of tail train; in addition, vortexes were symmetrically distributed along the longitudinal symmetry plane of train; dipole noises were mainly distributed in the area of head train, whose main energy was decreased with the increased frequency; the quadrupole noise of aerodynamic noises of the high-speed train was mainly distributed in the wake flow area of tail train; when the high-speed train ran at the speed of 300 km/h, the maximum sound pressure level of far-field observation points was 76.8 dB; additionally, aerodynamic noises in the far field were mainly a broadband noise, whose main energy was within the frequency range of 1250 Hz to 3150 Hz. Finally, the improved NSGA-II algorithm was used to conduct a multi-objective optimization for the head shape. The aerodynamic drag of the high-speed train could be most reduced by 6.74 %, and the dipole aerodynamic noise source could be most reduced by 8.34 dB. The improved NSGA-II algorithm has an obvious effect on the multi-objective optimization of the head shape
Systematical research on the aerodynamic noise of the high-lift airfoil based on FW-H method
Get PDFIn numerical computation of aerodynamic noises, the solution accuracy of flow fields has an obvious impact on detailed computation of eddy turbulence and acoustic results. In this paper, LES (Large Eddy Simulation) was used to conduct numerical simulation of flow fields of three-dimensional high-lift L1T2 airfoil. Unsteady flow field data on the solid wall face was extracted as the noise source. The integration method FW-H (Ffowcs Williams-Hawkings) was used to compute far-field noises. The numerical computation method was verified by experiments. Results show that: the numerical computation method used in this paper can provide an accurate solution for computing far-field aerodynamic noises. Finally, based on the verified numerical model, contribution amounts made by each high-lift airfoil component to noises as well as major factors affecting aerodynamic noises were analyzed. Computational results show that: the leading edge slats generated aerodynamic noises mainly because of the unsteady waves which were caused by the grooves between the slat and main wing, as well as small wake eddies generated on the trailing edge of slats; flaps generated aerodynamic noises mainly because of mixing between high-frequency small-scale eddies and low-frequency large-scale eddies caused by flow separation around the wing flaps. Acoustic directivity of leading edge slats and trailing edge flaps showed an obvious dipole characteristic. For both of them, the sound pressure levels reached the maximum value in the direction perpendicular to the chord line
Application of the polynomial dimensional decomposition method in a class of random dynamical systems
Get PDFThe polynomial dimensional decomposition (PDD) method is applied to study the amplitude-frequency response behaviors of dynamical system model in this paper. The first two order moments of the steady-state response of a dynamical random system are determined via PDD and Monte Carlo simulation (MCS) method that provides the reference solution. The amplitude-frequency behaviors of the approximately exact solution obtained by MCS method can be retained by PDD method except the interval close to the resonant frequency, where the perturbations may occur. First, the results are shown on the two degrees of freedom (DOFs) spring system with uncertainties; the dynamic behaviors of the uncertainties for mass, damping, stiffness and hybrid cases are respectively studied. The effects of PDD order to amplitude-frequency behaviors are also discussed. Second, a simple rotor system model with four random variables is studied to further verify the accuracy of the PDD method. The results obtained in this paper show that the PDD method is accurate and efficient in the dynamical model, providing the theoretical guidance to complexly nonlinear rotor dynamics models
Detection of a transverse crack in a nonlinear rotor using non-stationary response
Get PDFTo accurately detect an early transverse crack in the rotating machinery caused by fatigue or creep, various kinds of diagnosis systems utilizing the steady-state responses of a cracked rotor were developed. The paper focuses on the non-stationary response of a rotor system such as the startup, the shutdown or the variable running speeds of a rotating machinery to detect a transverse crack and to overcome the defects of the diagnosis system utilizing steady-state responses. Non-stationary characteristics during passages through the major resonance and various kinds of resonances are studied numerically and experimentally. The results demonstrate that the changes of vibration characteristics in a non-stationary response can detect a crack in a wide rational speed range and also prevent the dangerous operation for detecting a crack
Dynamic response and limit analysis of buried gas pipeline under ground consolidation load
Get PDFCurrently, the significant dynamic plastic deformation of a buried gas pipeline frequently occurs due to the ground construction process that acts as a direct threat to the operation security of a buried gas transmission system. In this study, the pipe-soil interaction structure under a dynamic consolidation load, such as high energy dynamic compaction load, was considered as a non-conservative system in the work. Two parts of structure dissipation energy were introduced into the Lagrange function, and the elastoplastic dynamic equations of a non-conservative system based on the Hamilton Variation Principle (HVP) and the finite element (FE) theory were established. Implicit solution schemes were proposed based on the dynamic equations, and a steel weight-soil-buried pipeline finite element model was developed by performing a dynamic analysis in the LS-DYNA software with an explicit format. Vivid impact responses of an underground pipeline associated with the buried depth, wall thickness, and tamping energy were simulated. The plastic failure criterion of high toughness pipeline steel indicates that treated pipeline buried depth, wall thickness, and tamping energy corresponded to the generalized loads, and limit state of a specific case. So, they were recognized via the relationship of generalized load in relation to the total strain of pipelines. This was performed by using tangent intersection criteria, two elastic slope criteria, and zero curvature criteria. Additionally, the von Mises yield stress criterion was also applied as a traditional approach. The study potentially offers significant references on the quantitative pre-evaluation of a buried gas pipeline that poses as a threat due to the occurrence of third-party damage such as extreme strong ground interference
Direct calculation method of probability density from sampled vibration signal based on linear interpolation method
Get PDFIn order to monitor, analyze and diagnose the conditions of all kinds of machines, it is often necessary to calculate the probability density function of the sampled vibration signal. A new direct calculation method of probability density from sampled vibration signal based on the linear interpolation method (LIM) is presented in this paper. Two advantages are observed: 1) the time length of each amplitude segment obtained from a sampled vibration signal by the LIM is closer to the original continuous vibration signal, and 2) the calculation results of probability density got by calculating directly the ratio of time length of each amplitude segment to the total time of sampled vibration signal are more correct than those obtained by other existing methods. The applications to sampled simulation and actual vibration signals of a rolling bearing show that the probability density curves obtained by the new direct calculation method are more accurate and smoother than the curves got by other estimating methods used in a lot of famous software
Study on seismic behavior of a concrete elevated tank with frame shaped base using SMA damper
Get PDFShape memory alloys are considered as novel materials, and during the recent decades, these materials are increasingly used with different applications in various fields of science and engineering. Shaped memory alloys are extensively used in the field of structures and earthquake engineering. These alloys are so expensive, and they are not sufficiently economical to be used in structures, so scholars sought to find a combination usage of these materials along with steel in order to achieve the maximum efficiency. We can make any structure resistant enough against the dynamic loads and forces exerted due to earthquakes, by placing a new member in the structure, so called Damper, which is regarded as a factor with a capability of dissipating the energy. In the present paper, an elevated tank with a capacity of 1500 m3 and frame-shaped base of 37.5 m in height, equipped with SMA damper at the tank-to-beam connection has been analyzed. It should be noted that the SMA material was used on first and seventh storey of the frame-shaped base. A numerical model of the tank was developed using Abaqus software and it was analyzed by applying EL-Centro earthquake record. Then, the best placement states of the SMA dampers indicating a better seismic behaviour were proposed. The findings indicate that an elevated tank with SMA damper has a better seismic behaviour, especially in the upper section of the beam, compared to other models
A novel high-strength large vibrating screen with duplex statically indeterminate mesh beam structure
Get PDFScreening is an indispensable unit process for separation of materials. Large vibrating screen is extensively used in coal processing because of its large production capacity. In this study, a novel large vibrating screen with duplex statically indeterminate mesh beam structure (VSDSIMBS) was presented. The dynamic model of VSDSIMBS was proposed, and characteristic parameters were obtained by theoretical calculations. In order to obtain more reliable and believable research results, model of a traditional vibrating screen (TVS) with the same mass was also established for comparisons with VSDSIMBS. The finite element (FE) method was applied to study the performance of VSDSIMBS and FE analysis of VSDSIMBS and TVS was completed by using characteristic parameters. Modal analysis results indicated that VSDSIMBS could avoid the resonance and run more smoothly than TVS. Furthermore, harmonic response analysis results showed that VSDSIMBS could improve the entire stress distribution, reduce high stress areas, and increase the strength of vibrating screen. With DSIMBS, the maximum stress of vibrating screen decreased from 130.53 to 64.54 MPa. The full-scale experimental tests were performed to validate the credibility and accuracy of FE analysis results. The stress and displacements of VSDSIMBS were measured under working conditions. The test results obtained are in good agreement with simulation results, and accord with conclusions made from FE analysis
Hybrid residual fatigue life prediction approach for gear based on Paris law and particle filter with prior crack growth information
Get PDFGear has been widely used in the modern industry, and the gear reliability is important to the driving system, which makes the residual fatigue life prediction for a gear crucial. In order to realize the residual fatigue life of the gear accurately, a hybrid approach based on the Paris law and particle filter is proposed in this paper. The Paris law is usually applied to predict the residual fatigue life, and accurate model parameters allow a more realistic prediction. Therefore, a particle filtering model is utilized to assess both model parameters and gear crack size simultaneously. As a data-driven method, particle filter describes the dynamical behavior of model parameters updating and gear crack growth, whereas the Paris law, as a model-based method, characterizes the gear’s crack growth according to the physical properties. The integration of the Paris law and particle filter is proposed as a hybrid approach, which is suitable for nonlinear and non-Gaussian systems, and can update the parameters online and make full use of the prior information. Finally, case studies performed on gear tests indicate that the proposed approach is effective in tracking the degradation of gear and accurately predicts the residual gear fatigue life