Journal of Vibroengineering
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Seismic dynamic responses of earth-rock dam considering wave and seepage
Full text linkEarth-rock dam plays an important role in water conservancy project, but there were many damage cases caused by earthquakes, so it is necessary to investigate dynamic responses of earth-rock dams under combined action of earthquake and wave. Considering material nonlinearity, seepage, wave action, fluid-solid interaction, liquid sloshing, a numerical calculation model is established, and Arbitrary Lagrange Eulerian method is used to solve the nonlinear dynamic coupling problem. Dynamic responses under wave, earthquake and wave+earthquake are studied comparatively, and influences of near and far field earthquakes and PGA on dynamic responses are investigated. Results show that values and distributions of dynamic responses under wave and earthquake are quite different, and dynamic responses were further increased considering combination of earthquake and wave. Dynamic responses under far field long period earthquake is significantly larger than that under near field earthquake. With the increase of PGA, increase trends of horizontal displacement, vertical displacement and plastic strain are increased, while increase trend of maximum shear stress is slowed down. It can be obtained that when earthquake intensity is large, earth-rock dam will be easily damaged due to excessive deformation
Numerical simulation analysis of hybrid impact cutting and its comparison with torsional impact cutting
Full text linkHybrid impact drilling is a new drilling method proposed in recent years, the PDC (polycrystalline diamond compact) bit impacts the rock in torsional and axial directions during its rotation. From the perspective of field application, hybrid impact drilling can increase the rate of penetration (ROP), especially in hard heterogeneous formations. However, its rock breaking mechanism and difference from torsional impact drilling are not clear, this leads to aimless in choosing these two drilling methods. In this paper, the quasi-3D numerical simulation model of hybrid impact cutting is carried out to investigate the rock breaking mechanism, including the chip formation, mechanical specific energy (MSE) etc. moreover, its comparison with torsional impact cutting is also conducted for evaluating the applicability of these two methods for the same formation. The results show that, the rock breaking efficiency of hybrid impact cutting is higher than torsional impact cutting for shallow depth of cut (DOC), on the contrary, the rock breaking efficiency of hybrid impact cutting is more lower for the medium DOC; but for the deep DOC, both of these two cutting methods cannot improve the rock breaking efficiency. The axial impact amplitude and frequency have large influence on rock breaking efficiency, the optimal axial impact amplitude and frequency exist for specific formation. Both of these drilling methods are not applicable to soft formations. This study leads to an enhanced understanding of rock breaking mechanisms in hybrid impact drilling, and contributes to the improvement in the design of impact tools and determination of the related parameters
Analysis of vibroexciters working process of the improved efficiency for ice breaking, construction and road machines
Full text linkIn the drives of the working bodies of ice breaking, road, construction and other technological machines the use of asymmetric planetary vibration exciters becomes promising. Where rotation carrier axis of the inertial runner is shifted relative to the treadmill center. Vibro-exciters of this type as a result of the joint action of the centrifugal and Coriolis forces on the inertial slider provide a significant increase in the integral value of the directional driving force. The momentum is proportional to the eccentricity of the carrier and directed towards the specified displacement of the carrier axis. The article presents the original mathematical and graphical dependencies characterizing the workflow of these vibration exciters and confirming their effectiveness
Dynamics modeling and experimental modal analysis of bolt loosening for lightning rod
Full text linkLightning rods are effective to prevent lightning damage in power systems. However, under the influence of severe weather conditions, they often face failure problems, mainly manifested as tilt and fracture caused by bolt loosening which can result in significant economic losses. Therefore, it is very meaningful to detect the loosening of the lightning rod. The vibration-based method is an effective method for bolt loosening detection and is suitable for use on large lightning rods. This paper built a finite element model of the lightning rod Flange-Bolt Structure Unit (FBSU) based on the virtual material method, designed an effective acquisition test of the vibration signal under different loosening conditions of the lightning rod FBSU. The experimental results showed that it was effective to establish the dynamic model of the lightning rod FBSU by using the virtual material method. According to the measured vibration signal, the frequency response function was obtained by TIME MDOF method, and the preliminary judgment of bolt loosening can be realized. This study lays the foundation for the precise positioning and the extent of loosening detection of lightning rod bolt loosening, and also provides a guideline for the vibration test design of large bolted structures similar to lightning rods
Causes and development characteristics of corrugation on tangential track of metro
Full text linkIn order to investigate the causes and development characteristics of rail corrugation on the tangential section, based on the finite element model of track structure and the vehicle-track space coupled dynamic model, modal analysis and dynamic analysis were carried out for detailed analysis. The results show that the line condition and passing frequency range of measured corrugation are close to those of roaring rail corrugation caused by Pinned-Pinned resonance of track structure, so it is preliminarily considered that corrugation occurring on this section is roaring rail corrugation. The modal analysis of track structure model shows that the vibration mode at the frequency of 513.7 Hz is the transverse Pinned-Pinned resonance of track structure and the vibration mode at the frequency of 1050.0 Hz is the vertical Pinned-Pinned resonance of track structure. The dynamic analysis of vehicle-track space coupled model shows that the amplitudes of rail vertical vibration acceleration levels are higher at the center frequencies of 500 Hz and 1000 Hz, and the one-third octave band widths corresponding to above center frequencies are in the frequency range of Pinned-Pinned resonance of track structure. Therefore, it can be determined that rail corrugation on the measured line is roaring rail corrugation. The changing trends of rail vertical vibration acceleration levels under different sleeper spacings and operating speeds are basically the same and amplitudes of rail vertical vibration acceleration levels at the center frequencies of 500 Hz and 1000 Hz are higher. With the increase of the sleeper spacing and operating speed, the variation trends of rail vertical vibration acceleration levels at 500 Hz and 1000 Hz are almost unanimous. By changing the sleeper spacing and operating speed, the rail vertical vibration acceleration levels can be changed significantly, which shows that the appropriate sleeper spacing (about 700 mm) and operating speed (about 80 km/h) can effectively control the occurrence and development of rail corrugation
Vibration reduction optimization for mistuned bladed disk based on reduced order modeling technique
Full text linkThe arrangement optimization algorithm of blades can reduce the vibration localization of mistuned bladed disk in a compressor of aero-engine, however, it will destroy the dynamic balance of bladed disk. A new arrangement optimization method of isolation zone on bladed disk system considering unbalance moment is proposed, on the basis the reduced order modeling technology. This method is based on the finite element model and can be implemented as fast and accurate vibration reduction optimization without destroying the mass balance of the bladed disk system, the method considers both mass and stiffness mistuning. Firstly, the discrete particle swarm optimization algorithm is used to sort the mass-mistuned blades according to unbalanced moment, then, the arranged bladed disk is divided into 6 isolation zones, then, in each isolation zone, the stiffness mistuned bladed disk is arranged optimally by the stiffness mistuning optimization algorithm. Under the premise of satisfying the dynamic balance of bladed disk, this algorithm optimizes the arrangement of blades with mass mistuning and stiffness mistuning, and achieves the purpose of vibration reduction optimization of mistuned bladed disk. The results show that, the maximum amplitude of the bladed disk system is reduced by 23.9 %. The vibration localization degree of the optimized blade are reduced by 46.3 %
A novel semi-active regenerative snubber
Full text linkA flyback topology has advantages like simplicity, better reliability and low cost, but comes with voltage stresses on semiconductor switches caused by the transformer leakage inductance. An improved regenerative snubber has been proposed to meet ever growing demand for higher efficiency. The proposed snubber topology is a modified LCD flying capacitor snubber and has advantages over conventional prototypes promising high efficiency of leakage energy recovery in high power applications. The beneficial features include: reduced circulating currents in snubber circuits; reduced current RMS on the secondary side; the possibility of recovering part of the leakage energy directly to the secondary output. The operation of the proposed snubber is analyzed to reveal benefits and simulation results are presented to verify performance. The stage by stage analysis with governing formulas has been provided. Design considerations are discussed
Study on natural characteristics of fiber metal laminates thin plates under cantilever boundary
Full text linkThrough the combination of theory and experiment, the natural characteristics of the fiber metal laminates thin plates under cantilever boundary are analyzed and verified. Based on the mechanics of composites and classical laminated plate theory, the theoretical model is established. The orthogonal polynomial method and the energy method are used to solve the natural characteristics. Meanwhile the calculation process is proposed. And then, the natural characteristics of a TA2/TC500 fiber metal laminates thin plate are tested. It is found that comparing the calculation results of the frequencies with the test ones, the errors are within the range of 3.4 % to 4.5 %, the trends of modal shapes are consistent as well, thus the effectiveness of above method has been verified
Local coordinate weight reconstruction for rolling bearing fault diagnosis
Full text linkThe high dimensionality data originating from rolling bearing measuring signals with non-linearity and low signal to noise ratio often contains too much disturbance like interference and redundancy for accurate condition identification. A novel manifold learning named Local coordinate weight reconstruction (LCWR) is proposed to remove such disturbance. Due to the different contribution of samples to their manifold structure, weight value is used for the contribution difference. By reconstructing local low-dimensional coordinates according to its weight function about geodesic distance in neighborhood, LCWR targets to reduce reconstruction error, preserve intrinsic structure of the high dimensionality data, eradicate disturbance and extract sensitive features as global low-dimensional coordinates. The experimental results show that the intraclass aggregation and interclass differences of global low-dimensional coordinates extracted via LCWR are better than those of local tangent space alignment (LTSA), locally linear embedding (LLE) and principal component analysis (PCA). The accuracy reaches the highest 96.43 % using SVM to identify LCWR based global low-dimensional coordinates, and its effectiveness is testified in diagnosis of rolling bearing fault
Vibration analysis of three-DOF motor with liquid suspension based on fluid-solid coupling
Full text linkBased on the combination of elastohydrodynamic lubrication and contact deformation theory, i.e. fluid-solid coupling theory, and considering the surface roughness of stator and rotor, a three-degree-of-freedom vibration model of spherical bearings with spiral grooves is established. The finite difference method is used to calculate and analyze the distribution of lubricating film pressure, film thickness and the influence of eccentricity of rotor on film pressure. Combining the stiffness of lubricating oil film with the finite element method, the displacement, stator vibration speed, acceleration and displacement of lubricating oil film are calculated from the angle of elastic boundary, and compared with the slotless structure. The results show that the bearing capacity of lubricating oil film of spherical bearing is improved and the stability of continuous oil film is improved by adding spiral groove. Secondly, the vibration characteristics of stator and rotor with spiral groove structure are more in line with the viscoelastic periodic distribution law. The vibration stability of the system is improved. In order to further optimize the vibration stability of the motor, the theoretical basis is provided