Journal of Vibroengineering
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Analysis of dynamics of a scaled PRT (personal rapid transit) vehicle
Get PDFThis publication provides a discussion concerning research aimed to analyse running properties of PRT vehicles. A PRT vehicle is guideway vehicle equipped with rubber-tyred wheels, running on a flat subgrade guideway of special design. The guideway cross-section is similar to that of a C-shaped beam with two outer limiting edges. This specific design characteristic of the running system of PRT vehicles distinguishes them from typical rail vehicles, where the latter can move along the track by the action of a unit referred to as the centring mechanism, operating at the contact of profiled wheels with the running rail head. In a PRT vehicle, the typical railway centring mechanism has been removed and substituted with a system of outer and inner rollers, forming what is referred to as a passive switch system, responsible for carrying the vehicle along the guideway and within the boundaries delimited by its edges by the action of the rollers’ contact forces. Compared to railway infrastructure, this system is characterised by different dynamic properties, and it has not been sufficiently researched yet. The goal of this article is to analyse motion stability of a PRT vehicle with a passive switch system and having the following structural features: wheel sets with beams turning against the vehicle body and independently revolving wheels, non-turning rubber-tyred and non-profiled wheels rolling on a flat surface, and a set of outer and inner rollers performing the passive switch system’s functions. The paper describes a PRT vehicle simulation model. It has been assumed that the model’s design and parameters describe a scaled vehicle/guideway system whose physical model is actually set at a laboratory testing station on premises of the Warsaw University of Technology. The article provides results of simulation studies of motion stability pertaining to the following characteristics: radial positioning, yawing, sticking to the guideway edge, self-excited vibrations of wheel sets as well as free vibrations. It also discusses results of an analysis of sensitivity of the model’s parameters against selected control parameters (model’s design parameters) and assessment indicators which describe the intensity of the yaw type torsional vibrations of wheel sets. The article closes with a discussion on the potential to use the results of the tests conducted under the study on the scaled vehicles in question for purposes of vehicles of real-life dimensions
A multi-fault diagnosis method for piston pump in construction machinery based on information fusion and PSO-SVM
Get PDFPiston pumps are key components in construction machinery, the failure of which may cause long delay of the construction work and even lead to serious accident. Because construction machines are exposed to poor working conditions, multiple faults of piston pumps are most likely to occur simultaneously. When multiple faults occur together, it is difficult to detect. A multi-fault diagnosis method for piston pump based on information fusion and PSO-SVM is proposed in this thesis. Information fusion is used as fault feature extraction and PSO-SVM is applied as the fault mode classifier. According to the method, vibration signal and pressure signal of piston pump in normal state, single fault state and multi-fault state are collected at first. Then the empirical mode decomposition (EMD) is used to decompose vibration signals into different frequency band and energy features are extracted. These energy features extracted from vibration signals and time-domain features extracted from pressure signal are information fused at the feature layer and constitute the eigenvectors. Finally, these eigenvectors are put into support vector machine (SVM) and the working conditions of piston pump were classified. Particle swarm optimization (PSO) is applied to optimize two parameters of SVM. The experimental results show that the recognition accuracy of the normal state, three single failure modes and multi-fault modes are 98.3 %, 97.6 % and 94 % respectively. These recognition accuracies are higher than which using vibration signal or pressure signal alone. So, the proposed method can not only identify the single fault, but also effectively identify the multi-fault of piston pump
Near-field acoustic holography for high-frequency weak sound sources under low signal-to-noise ratio
Get PDFThe mechanical noise in the cabin of the ship is so large that the leakage of high-pressure fluid is not easily noticed. In view of this situation, a near-field acoustic holography for high-frequency weak sound source under low signal-to-noise ratio is proposed. The method uses the empirical mode decomposition method to add weights to the time-domain sampling signals of each array element, and then uses the plane equivalent source near-field acoustic holography combined with compressive sensing to find the holographic surface acoustic pressure distribution. The simulation and experiment show that this method has certain feasibility under low signal-to-noise ratio, and the results are better than the method based on Fourier transform and the traditional boundary element method. It is of positive significance to apply it to engineering practice
Simulation and experimental research on dynamic characteristics of overrunning clutch
Get PDFBecause of the self-locking part inertia, deformation factors, and interspace between the driving and driven sides of the overrunning clutch, the existing dynamic models, which consider the rotational speed discrepancy or angle discrepancy as the only determinant to recognize the engaging state, have some difficulty in accurately describing and studying the dynamic characteristics of the overrunning clutch and its transmission system. In order to solve these problems, this paper proposed a modified method considering the influence of the dynamic characteristics of self-locking components through angle compensation. Four models were established on a MATLAB/Simulink platform, and an experiment was carried out on a transmission experimental platform under a stable driving torque and varying driving torque. Then, the comparison of the dynamic characteristic between the simulation and the experiment showed that under non-stationary excitation, taking the influence of the dynamic characteristic of the self-locking components into account through angle compensation can help to more accurately describe the dynamic characteristics of a transmission system with an overrunning clutch
The double Burgers model of fractured rock masses considering creep fracture damage
Get PDFCreep fracture of rock cracks is responsible for the creep failure of fractured rock masses. To capture creep fracture behaviors of fractured rock, we investigated the time-dependent characteristics of the rock crack propagation. The theoretical analysis shows that, similar to the rock creep process, the creep fracture of rock cracks includes the attenuation and steady creep stages. In addition, we established an equivalent Burgers model for creep fracture of rock cracks by introducing the equivalent stress and proposed a double Burgers model to study creep behaviors of fractured rock masses. Moreover, the proposed double Burgers model was embedding into FLAC3D, using FISH function. The numerical simulations on the specimens, containing ordered and random cracks, show that the creep fracture is responsible for the creep damage of fractured rock masses; moreover, the lateral creep damage is larger than the axial creep damage
An optimized bearing parameter identification approach from vibration response spectra
Get PDFIn the present work, an effective identification methodology bearing dynamic parameters using measured vibration responses at the bearing is proposed. The flexible rotor is analyzed by using finite element beam model with nonlinear hydrodynamic bearing forces due to floating ring bearing supports. The frequency domain responses at different operating speeds are initially obtained in both the lateral directions. The error function is formulated as an average difference in amplitudes of two lateral displacements at a bearing node with known reference signals over a frequency range. The design variables are the speed dependent direct and cross-coupled stiffness and damping parameters of the bearing. With the side constraints on the variables, the error is minimized by using a modified particle swarm optimization scheme. The accuracy of the approach is tested with noisy input signals
Complete results for free and forced vibrations of inerter-added one-degree-of-freedom systems
Get PDFA comprehensive study on the influence of an inerter on the response of single-degree-of-freedom systems is presented; therefore, complete and thorough results for free and forced vibrations of linear SDOF systems with inerter are obtained. The free response results are for damped and undamped systems; moreover, the forced response solutions are for harmonic and arbitrary excitations. The classical problems of rotating unbalanced mass and support vibration isolation are solved
Research on vibration suppression mode of sorting arm structure in high-frequency reciprocating motion
Get PDFThe sorting arm structure is under the inertia impact of high frequency reciprocating motion. The vibration characteristics are related to the operation process so that the precision of the chip sorting is uncertain. Thus, the accuracy of chips and efficiency of LED sorting machine are reduced. In the paper, the relationship between the vibration of the sorting arm and the positioning error of the chip has been studied. Besides, the correlation between the sorting arm structure’s vibration and the working precision of the separator are pointed out. The operation control is optimized based on the dynamics of the sorting arm and the operation parameters are optimized based on time sequence setting, in order to shorten the vibration attenuation time of the sorting arm for suppress vibration and provide efficiency. The incentives, which are introduced by variable structure and by the operation, can be effectively controlled. The array accuracy of chips and working efficiency of chip sorting machine are improved
Simulation and experiment research of vibration characteristic on star compressor
Get PDFAiming at the vibration defects of star compressor, simulation and experiment are carried out to investigate the compressor. By drilling holes in the valve stem, the pressure changes of each cylinder are measured without damaging the cylinder block. The dynamic model of crank-connecting rod mechanism is established. After the measured cylinder pressure loaded on the dynamic model, the force acting on the main motion pair is obtained. The finite element model of the compressor is established for the first time, the force of the motion pair is loaded on the finite element model by MPC coupling method, and the vibration acceleration of the machine base is tested. The result shows that the main modal shapes between 50-150 Hz are body deformation, modal shapes between 150-200 Hz are base deformation, the simulation acceleration of the base is higher than that of the experiment, and the main working frequency and frequency doubling can correspond. The conclusions provide reference for vibration isolation design of star compressor
A novel method of weakness imbalance fault identification and application in aero-hydraulic pump
Get PDFA method of combining auto-correlation and Hilbert envelope analysis is proposed and used to identify weakness imbalance fault of aero-hydraulic pump, the central part of hydraulic system of aircraft. Firstly, the integral and polynomial least square fitting is applied to convert acceleration signal to velocity one; secondly, the Hilbert envelope spectrum of auto-correlation function of velocity signal is obtained and used to identify the weakness imbalance fault of aero-hydraulic pump; finally, the energy ratio of velocity signal is calculated according to Hilbert envelope spectrum for identifying imbalance fault of aero-hydraulic pump by means of easier and more visual method. Meanwhile, the comparing analysis is carried out between traditional research method and proposed new one. The result shows that the weakness imbalance fault of aero-hydraulic pump can be identified and diagnosed effectively and correctly according to the velocity signal whether Hilbert envelope spectrum or calculation energy ratio while direct acceleration signal cannot