Journal of Vibroengineering
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Nonlinear dynamics of planetary gear wear in multistage gear transmission system
Get PDFWith the increasing service life of a gear transmission system, the gear teeth become constantly worn, and the gear clearance increases. The increase in the clearance will produce a series of nonlinear changes that change the stability of the system and can even result in loss of stability. In this paper, dimensionless dynamic equations of a multistage gear transmission system that contains a two-stage fixed-axis gear and a one-stage planetary gear were established. Planetary wear fault was simulated by changes in the gear clearance. System bifurcation diagrams with an increase in the clearance were studied. The frequency characteristics of planetary gears under different excitation frequencies and different degrees of wear were studied. The influence of planetary gear wear on the fixed-axis was discovered. The vibration mechanism and a fault diagnostic method in a multistage gear transmission system were obtained
Coupling vibration model for hot rolling mills and its application
Get PDFIn this paper, we propose an effective mechanical-electrical-hydraulic-interfacial coupling vibration model for hot rolling mills and obtain a practical measure to relieve mill vibration. First, an experiment related to mill modulus control gain in automatic gauge control (AGC) is carried out during manufacturing. Rolling mill vibration is observed to gradually be enhanced with increasing mill modulus control gain. Then, to explain this phenomenon, the mechanical-electrical-hydraulic-interface coupling dynamic model is modeled based on Sims’ rolling force method. Finally, we analyze the influence of mill modulus control gain on the vibration numerically on the basis of the coupling dynamic model. Moreover, the agreement between the experiment result and the simulation result is confirmed and the measure reducing the mill modulus control gain is obtained to relieve mill vibration
Dynamics research of a flywheel shafting with PMB and a single point flexible support
Get PDFFlywheel energy storage system (FESS) is new advanced machinery which is intended for electric power storage and release. A FESS, which is suitable for the small flywheel, was developed with a permanent magnet bearing (PMB) and a single point flexible support, and its friction loss is very low. By means of the Lagrange theory, a dynamic model was established. The Campbell diagram, mode shapes, modal damping ratios and critical speeds were designed after the flywheel data at different operating speeds was obtained by numerical simulation. Based on the excitation test and single freedom vibration theory, the stiffness and damping coefficient of the upper and lower damper was measured. The influences of damper dynamic parameters on modes of flywheel rotor bearing system were discussed in detail. The comparison between the calculated unbalance response and the experimental response indicates that the dynamic model is appropriate. The results showed that the lower damper absorbed vibration energy of the flywheel rotor, which increased vibration of the damping body. And the bigger damping coefficient had better vibration absorption effect. The developed FESS is simple, stable and efficient in structure
Stability of stope structure under different mining methods
Get PDFThe ore body has a great influence on the stability of surrounding rock and mining safety under different mining modes, and the reasonable selection of mining mode depends on other characteristics, such as ore structure surface feature, rock mass mechanical property, and ground stress distribution. Given the insufficient mining research data, this study establishes a 3D model by using the FLAC3D calculation program. Through numerical simulation and other technical means, a preliminary study on plastic and minimum stress changes during horizontal pillar mining, stress changes under different mining modes, and the effect comparison of full filling mining modes is conducted. Results show that the surrounding rock at the corner of pillar 1 is damaged, the plastic zone decreases, and the minimum stress in each working procedure increases slightly. The area of the plastic zone in alternate mining is smaller to that in continuous mining. This study provides a theoretical basis for ore body mining
Experimental study on secondary bearing mechanism of weakly cemented broken rock mass
Get PDFIn order to study the secondary bearing mechanism of weakly cemented broken surrounding rock, the surface of granite, limestone and mudstone broken rock samples were poured by cement slurry, and the weakly cemented rock mass was formed by static pressure infiltration method, and then an uniaxial loading test was carried out. The results show that the weakly cemented broken rock mass has a certain bearing capacity, but the bearing capacity is low, and the dispersion is high. The secondary bearing capacity of weakly cemented rock mass is affected by factors such as broken rock strength, rock particle size and rock gradation. The larger the rock particle size and strength are, the higher the secondary bearing capacity of the weakly cemented rock mass is. The average bearing capacity of the mudstone weak cementation specimen is 18.77 kN, and the residual bearing capacity is 1.46 kN, and a dispersion coefficient is 0.34. The average bearing capacity of granite is 343.65 kN, and the residual carrying capacity is 25.81 kN, and a dispersion coefficient is 0.11. The average bearing capacity of limestone is 367.22 kN, and the residual carrying capacity is 22.78 kN, and a dispersion coefficient is 0.3. After a certain grading, the average residual secondary bearing capacity of the weakly cemented rock mass is obviously improved, and the dispersion coefficient of peak bearing capacity is reduced. The grading scheme 1 has an average peak carrying capacity of 330.06 kN, a residual carrying capacity of 34.56 kN, and a dispersion coefficient is 0.07. The averaging scheme 2 has an average peak carrying capacity of 297.8 kN, a residual carrying capacity of 29.86 kN, and a dispersion coefficient is 0.14. The cementation regeneration mechanism of the broken rock mass mainly includes the cement-bonding effect of the cement slurry inside and on the broken rock mass. Under the loaded condition, the internal load-bearing network of the broken rock mass is the main mechanism for the secondary load of the broken rock mass, and the stability of the force-chain network is affected by the constraint. After the loss of the confinement, the force chain network fails, and the residual secondary bearing mechanism of the weakly cemented broken rock mass is transformed into the friction between the broken rock masses in the residual core rock pillar
Efficiency of near-fault ground motion pulses to evaluate seismic performance of the SMRF Systems
Get PDFEarthquake accelerograms recorded in the near-fault regions have special characteristics including the long-period pulse in velocity records as well as high frequency content in acceleration records. In the present study, by using a wavelet analysis, the long period pulses exist in the velocity records of 28 near-fault ground motions, selected from the PEER NGA database, were first separated from the original records. Subsequently, an incremental non-linear dynamic analysis (IDA) was conducted to evaluate the non-elastic response of an example frame subjected to these original records and their extracted pulses to examine the efficiency of the extracted pulse of the records instead of the original accelerograms in dynamic analysis. The results of this study revealed that the efficiency of the extracted pulses to estimate the structure capacity depends on the structural performance levels. From the numerical analysis performed in the present study, it is found that if a given structure is designed for immediate occupancy (IO) performance level (low drift), the application of the extracted pulses overestimates the structure capacity, which is in the unsafe side. Nevertheless, if the structure is designed for collapse prevention (CP) performance level and experiences high level of non-elastic displacements, the extracted pulses provide a conservative estimation of the collapse capacity, which is in the safe side
Finite element simulation on the reflection and transmission of the lamb waves across a micro defect of plates
Get PDFThis paper presents a theoretical and finite element (FE) investigation of the generation and propagation characteristics of the fundamental Lamb waves symmetrical mode S0 and anti-symmetrical mode A0 after testing with different types of defects in the plates. The reflection and transmission of Lamb waves at a micro symmetry defect and asymmetry defect are analyzed numerically in the two-dimension (2D) model. Mode conversion of Lamb waves can occur upon encountering the asymmetry discontinuities leading to newly-converted modes apart from wave reflection and transmission. When testing the symmetry defects, the reflection and transmission waves have no modal separation phenomenon. To describe the mode conversion and reflection and transmission degree, and evaluate the micro defect severity, a series of defects are simulated to explore the relationships of defect reflection and transmission with the length and depth of a defect in the 2D FE model. In the three-dimension (3D) FE model, the straight-crest Lamb waves and circular-crest Lamb waves are simulated and researched by contrast analysis. Then the straight-crest Lamb waves are motivated to study the scattering laws of Lamb waves interacting with the circle hole defects and rectangular hole defects. S0 mode and SH0 mode are contained in the scattering waves after S0 mode testing the through holes defects. Corresponding mode energy percentages were analyzed at different micro defect severities changed in different ways. Simulation results illustrated that the modal energy percentages varied in a different character and provided support for the analytically determined results of Lamb waves in the non-destructive testing and evaluation
Experimental diagnosis of multiple faults on a rotor-stator system by fast Fourier transform and wavelet scalogram
Get PDFThis paper presents the recent application of the scalogram of Continuous Wavelet Transform (CWT) as a vibration monitoring and signal processing tool for a rotor dynamic response under parametric excitation. The experimental test data of coupled lateral-torsional vibrations of a rotor-stator system with transverse crack was obtained through a data acquisition set-up interfaced with Rotor-Kit-4 (RK-4). Analysis was executed on rotor deflection, orbit, frequency and time-frequency spectrum of the RK-4 experimental data. The scalograms of CWT were used experimentally to represent the aperiodic occurrence of rub between the rotor-stator and crack features. Variation in 3-D scalogram peaks in the presence of rub and crack were unique and were used to distinguish quasi-periodic motion from other types of motion. An unbalanced cracked rotor gave a higher frequency amplitude response compared to an unbalanced rotor with rub under the same conditions. Irregularities in orbit orientation near sub-harmonic resonances were observed in the test data. Multiple rebounds inside the orbit loop were unique rub indicators. Conspicuous horizontal components of the higher harmonics were observed near the critical speed when a crack existed. CWT established inherent feature patterns that discriminated unbalance, rub and a crack
Experimental study on failure characteristics of jointed rock mass under staged unloading conditions
Get PDFStrength and deformability characteristics of rock with pre-existing fissure are governed by cracking behavior. To further research the effects of pre-existing fissures on the mechanical properties and crack coalescence process under staged unloading conditions, a series of uniaxial compression tests were carried out. In this study, cement, fine sand, and water were used to fabricate a kind of brittle rock-like material rectangular model specimen. The mechanical properties of rock-like material specimen used in this research were all in good agreement with the brittle rock materials. The pre-existing fissure was created by mica sheets and the unloading zone was created by pre-filling Polylactic acid (PLA) resin material during the molding processes the model specimen. And the staged unloading test was conducted based on polylactic acid’s hot-melt characteristics. In order to investigate the crack initiation, propagation and coalescence process, inclination angle of pre-existing fissure was set to change from 0° to 90°. The mechanism of crack propagation and coalescence under photographic monitoring was discussed. And these experimental results indicate that the failure modes in the zone above unloading zone mainly consist of four modes: separation failure, shear-slip failure, mixed shear-separation failure and compression-shear failure. The experimental results are also expected to increase the understanding of the strength failure behavior and the cracking mechanism of rock under staged unloading
Flow-thermo-elastic coupled vibration characteristics of aeroengine high pressure rotor at the typical start and stop conditions
Get PDFBased on the typical start and stop conditions of aeroengine high pressure rotor, the problem of flow-thermo-elastic coupling is solved in this research. Applying basic theory and control equation, it is analyzed the fields of transient temperature, thermal stress and thermal deformation in the start and stop process. Then the temperature at last stopping moment is selected as the boundary condition. With the flow-thermo-elastic coupling method, the distributions of air flow, heat transfer and temperature are discussed in high pressure rotor cavity. The results show the rotor has a higher temperature, and the density of temperature contour is much larger at the beginning of stop period. The temperature of each node gradually decreases as stop time increases. When the stop time is within 40-90 minutes, temperature difference between the upper and lower surfaces is larger than 20 °C. The distribution of transient temperature is different when restart process is taken at different stop moments. If the stop time is short, temperature distribution of the rotor is decreased firstly, then increased, and finally decreased. The time corresponding to the lowest temperature is also different in each node. It is the longest in the 3rd disk, and the shortest in the 8th disk