Journal of Vibroengineering
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Study on creep mechanism of coral sand based on particle breakage evolution law
Get PDFThe time-dependent deformation property of backfill coral sand is of great important to the long-term stability of engineer facilities bulit on reefs and reclaimed land. In order to investigate the long-term deformation behavior, one-dimensional compression creep tests under different constant stresses were carried out for coral sand taken from a reef in the South China Sea by WG type high-pressure consolidation instrument. The test results show that under the action of constant stress, coral sand has a strong deformation timeliness and shows remarkable nonlinear attenuation creep characteristics. The creep of coral sand has obvious stages and has gone through three stages of instantaneous deformation, accelerated deformation and slow deformation phase tending to stability. The relationship of strain-time can be fitted with power function in mathematic. The particle breakage state of any single particle size group of coral sand after creep can be well described by using the two-parameter Weibull distribution function, Weibull parameters a and b have a good exponential relationship with stress, and have a negative linear relation with quantitative index Br of particle breakage, and have a negatively correlated with final total strain. Under the action of low stress level, the main cause of creep deformation is the movement and recombination of particles. At low stress level, the movement and recombination of particles are the main reason of creep deformation, while at high stress level, the slippage and filling pores of broken coral sand particles are the main reason of creep deformation
Research on vibration characteristics of a multi-barrel artillery
Get PDFThe vibration of the barrel, induced by the interaction with a high-speed moving projectile, has a considerable influence on the shooting accuracy of a weapon. The finite element model of a multi-barrel was established with the goal to investigate its vibration characteristics in this paper, and the natural frequency and mode shape were analyzed by finite element method. To verify the result of finite element modal analysis (FEMA), a modal testing system basis on SC310W multi-path data-collecting system and hammer hitting method was set up. Results show that the low order vibrations of the multi-barrel artillery were mainly vertical, horizontal and torsional vibration, but the local vibration at high orders. The error of natural frequencies between the results obtained by simulation and test was 8.82 % in the first mode frequency and 1.37 % in the eighth. The FEMA can effectively simulate the actual vibration of the multi-barrel artillery
Multi-objective optimization of active suspension predictive control based on improved PSO algorithm
Get PDFThe design and control for active suspension is of great significance for improving the vehicle performance, which requires considering simultaneously three indexes including ride comfort, packaging requirements and road adaptability. To find optimal suspension parameters and provide a better tradeoff among these three performances, this paper presents a novel multi-objective particle swarm optimization (MPSO) algorithm for the suspension design. The mathematical model of quarter-car suspension is first established, and it integrates the hydraulic servo actuator model. Further a model predictive controller is designed for the suspension by using the control strategies of multi-step forecast, rolling optimization and online correction of predictive control theory. To use vehicle body acceleration, tire deflection and suspension stroke to represent the above three performances respectively, a multi-objective optimization model is constructed to optimize the suspension stiffness and damping coefficients. The MPSO algorithm includes extra crossover operations, which are applied to find the Pareto optimal set. The rule to update the Pareto pool is that the newly selected solutions must have two better performances compared with at least one already existed in the Pareto pool, which ensures that each solution is non-dominated within the Pareto set. Finally, numerical simulations on a vehicle-type example are done under B-level road surface excitation. Simulation results show that the optimized suspension can effectively reduce the vertical vibrations and improve the road adaptability. The model predictive controller also shows high robustness with vehicle under null load, half load and full load. Therefore, the proposed MPSO algorithm provides a new valuable reference for the multi-objective optimization of active suspension control
Numerical investigation on rules of fracture propagation during hydraulic fracturing in heterogeneous coal-rock mass
Get PDFTo investigate rules of fracture propagation during hydraulic fracturing in heterogeneous coal-rock mass, a new mathematical model for hydraulic fracturing with seepage-damage coupling and its numerical algorithm are proposed. The rules of coal-rock mass heterogeneity, confining pressure, beforehand hydraulic slotting, and non-symmetric pressure gradient on fracture propagation are investigated. Numerical results show the following: (1) Compared to homogeneous coal-rock mass, the fracture propagation pattern exhibits a more zig-zag characteristic and the fracture initiation pressure is reduced in heterogeneous coal-rock mass. (2) Fracture propagation during borehole fracturing is mainly controlled by confining pressure ratio, and the fracture would propagate along the path with least resistance in coal-rock mass. (3) During hydraulic fracturing with beforehand hydraulic slotting, fracture propagation pattern would become more complex with slotting length increasing; the propagation direction of fracture is primarily controlled by principal stress difference, the larger of principal stress difference, the more difficult of oriented fracturing. (4) Non-symmetric pressure gradient can reduce breakdown pressure and influence fracture propagation pattern, which provides a beneficial guide for oriented fracturing. The simulation results are consistent with the theoretical solutions and experimental observations, which is promising to guide field operation of hydraulic fracturing to improve coalbed methane extraction
Fine-grained fault recognition method for shaft orbit of rotary machine based on convolutional neural network
Get PDFIn the fault diagnosis of the shaft orbit of rotating machinery, there are few prejudgments about the severity of the faults, which is very important for fault repair. Therefore, a fine-grained recognition method is proposed to detect different severity faults by shaft orbit. Since different shaft orbits represent different type and different severity of faults, the convolutional neural network (CNN) is applied for identifying the shaft orbits to recognize the type and severity of the fault. The recognition rate of proposed fine-grained fault identification method is 97.96 % on the simulated shaft orbit database, and it takes only 0.31 milliseconds for the recognition of single sample. Experimental result indicated that the classification performance of the proposed method are better than the traditional machine learning models. Moreover, the method is applied for the identification of the measured shaft orbits of rotor with different degree of imbalance faults, and the testing accuracy of the experiments in measured shaft orbits is 97.14 %, which has verified the effectiveness of the proposed fine-grained fault recognition method
Parameter optimization design of rotor dynamic vibration absorber
Get PDFThe dynamic vibration absorber, which is adopted to suppress the unbalanced vibration of rotor, is optimized for the optimal parameters in this paper. This paper proposes a parameter optimization method for dynamic vibration absorbers and seeks parameters of a dynamic vibration absorber with better vibration suppression performance. Firstly, the frequency response function of the dynamic vibration absorber-rotor coupling system is obtained by using the finite element method. Then, basing on the optimal mathematical model, the optimal design variables are solved with the adaptive particle swarm optimization algorithm. Also, an example is used to prove the validity of the optimization design method mentioned in this paper. Further, in order to master the influence of deviation from the optimal value on the suppressing vibration effect, the vibration suppression performance changes of the dynamic vibration absorber whose parameters deviate from the optimal value are analyzed. The results show that: compared with conventional design method, this method is more superior; The dynamic vibration absorber with optimal parameters has better vibration suppression performance; At the same degree deviated from the optimal value, the stiffness has a more remarkable influence on the vibration suppression performance than damping for suppressing the first resonance; For the dynamic vibration absorber which is adopted to suppress the fixed-frequency vibration, the influence of stiffness deviation on the vibration suppression performance appears an obvious interval which is related to working speed
Launching dynamic analysis for tank on the move based on dynamic simulation
Get PDFAchieving high firing accuracy of tank on the move is challenging. For improving firing accuracy, better understanding launching dynamic behavior of tank firing on the move is required. This study established a rigid-flexible coupling dynamic model of tank firing on the move. Thereinto, the barrel flexibility was considered based on the FFlex body technology, and the contact-impact algorithm was used to describe the projectile-barrel interaction. With the sinusoid superposition method, a three-dimensional road surface spectrum file considering the coherence of left and right tracks was created. Based on the results obtained in simulation, this study discussed the dynamic behaviors of a tank gun system such as the barrel curvature and the influence of projectile-barrel interaction on firing accuracy of tank firing on the move, in which the factors including projectile type, driving speed and road roughness were taken into consideration. The results indicated that the barrel curvature and the muzzle vibration do not increase simply with the increase of road roughness and driving speed as common sense
Dynamical processes in a multi-motor gear drive of heavy slabbing mill
Get PDFA real case study is represented of abrupt failures in a new multi-motor gear drive of vertical rolls in the heavy slabbing mill. Modal analysis is conducted, and the lowest torsional vibration modes are verified by the data from an industrial plant. Conditions of parametric resonances due to variable stiffness of teeth are determined within the range of working speed. The branched gear drive is investigated by the non-linear dynamical model with backlashes. It is shown that instantaneous dynamic loads in driveline are strongly dependent on the difference in gap sizes and phase shift between two intermediate gears in the output gear wheel coupling. Deviation in electrical parameters by 0.5 % is considered as the additional cause of not equal load sharing of parallel motors. Results of this research allowed preventing further failures of the gearbox and optimizing slabbing mill control. The proposed approach can be used in other multi-motor machines
Sensitivity analyses of resonant frequencies and modal strain energy of damaged beams by perturbation method
Get PDFA new perturbation method has been proposed to investigate the sensitivities of the eigen-parameters (frequencies and mode shapes) and the modal strain energy density of a damaged beam. The sensitivities were obtained via the Rayleigh quotient and Taylor series expansion. The damage was simulated by the reduction in the cross-sectional area of the beam. The theoretical relationships were established between the damage parameter and the variations of the frequency and modal strain energy. The analytical formulae explicitly reveal the underlying mechanism that, the frequency, which is closely related to the modal strain energy of the entire structure, is less sensitive to the local damage; the modal strain energy density, on the other hand, is able to reflect the local damage in a small region. The results of the perturbation analyses were validated with the finite element analyses and experimental tests of the beam models with 2 damage levels. The first resonant frequencies decrease slightly with the increases of the damage. When 30 % of the cross-sectional area is cut off in the damaged zone, the first resonant frequencies are still 95 % and 98 % those of the intact beam for the bending vibration around x-axis and around y-axis; meanwhile, the modal strain energy increases 94 % and 54 % in the damage zone, which closely correlates with the local damage parameters. The proposed perturbation method has the potential to assess the quality of damage indictors faster and more easily than FE and experimental methods
Experimental analysis on noise characteristics of surface-mounted permanent magnet synchronous motors
Get PDFStarting with the analysis on sound pressure level (SPL) spectrum of surface-mounted permanent magnet synchronous motors (SMPMSMs), the reasons for producing main peaks are investigated. According to different causes, different methods for reducing noise are proposed. Firstly, the SPL spectrum of SMPMSMs is obtained by experiment under the conditions of 2000 rpm rated speed, full load and 4 kHz switching frequency. Meanwhile, the frequencies corresponding to main peaks are found out. Secondly, the reasons for generating peaks in the SPL spectrum are researched from three aspects, namely, force sources, natural frequencies, coefficient of relative sound intensity. Then, on the basis of different causes for generating noise, different measures for decreasing noise are presented, namely, single cutting of two end rabbets of motor case in single clamping, waveform reconstruction of radial electromagnetic force density, enhancing of switching frequency, changing of natural frequency and decreasing of the length-diameter ratio of stator. Furthermore, the effectiveness for these methods is studied. Finally, a comprehensive method is proposed to decrease noise. The noise value of SMPMSMs is reduced by 4.7 dB(A) at the rated speed of 2000 rpm, full load and switching frequency of 4 kHz. In addition, the sharpness and loudness are respectively decreased by 0.522 acum and 6.97 sone at no load. The study provides references for the design of SMPMSMs with low noise