Journal of Vibroengineering
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Characteristic extraction of rolling bearing compound faults of aero-engine
Get PDFRolling bearing’s fault mode usually shows compound faults in aero-engine. The compound faults characteristics are more complex than single one, and many signal analysis methods have rather great limitation for compound fault characteristic extraction which leads to the difficulty to monitor the running state of rolling bearing in aero-engine. Based on above analysis, a method of combining wavelet transform with cyclostationary theory, autocorrelation function and Hilbert transform is proposed and applied to extract characteristic frequency of rolling bearing from compound faults mode only according to single-channel vibration acceleration signal of aero-engine. Meanwhile, a consideration is given to the influence of sensor installation position, compound fault types in the extraction of compound faults characteristics. The result indicates that the proposed new method can effectively monitor rolling bearing running state in four different compound fault modes just according to single-channel vibration acceleration signal no matter sensors are installed in horizontal or vertical direction
Separation of motion techniques for trajectory optimization in flexible redundant robot manipulators
Get PDFThis paper presents a computational method for optimization of trajectory in redundant robot manipulators. For this purpose, all possible answers are acquired based on rigid conditions and redundancy of the robot. Using open loop optimal control method, the trajectory which minimizes the objective function will be obtained. The objective function is considered as an integral index that will be minimized in the entire trajectory. The objective function and constraints of optimization problem will be selected based on conditions of motion. Dynamic equations of the system are constraints of optimization problem in point-to-point motion. For motion conditions in the specified path, kinematic equations will be added. Also, unequal constraints are applied for limiting the velocity and torque. By selecting the state and control signal vectors which are obtained by assuming rigid motion of the robot, the objective function and constraints will be changed to standard form of an optimization problem. Pontryagin’s maximum principle is used to solve equations. So, the equations of classical form will be changed into two-point boundary value problem. Suggested method is applied to point-to-point motion and movement in the specified path. Results demonstrate accuracy and efficiency of suggested method
Seismic behavior of lightweight aggregate concrete frame
Get PDFA one-fifth scale, two-story, two-bay reinforced lightweight aggregate concrete (LWAC) frame subjected to quasi-static cyclical loading was analyzed to investigate the seismic behavior of this innovative system, primarily focusing on the failure modes, plastic hinge mechanism, load-deformation response, skeleton curves, stiffness degradation and energy dissipation capability. Overall, the test demonstrates that the LWAC frame meets the requirement of a “strong-column and weak-beam, strong-joint and weak-member” design criteria, exhibiting a mixed failure mechanisms consisting of both the beam hinge mechanism and column hinge mechanism. The former was the predominant failure mechanism and was fully developed after reaching the peak load point, while the latter was the inevitable result in the final failure of the LWAC frame. The fatter hysteretic loop and the displacement ductility factor Δu/Δy of 3.49 observed from LWAC frame indicate excellent energy dissipation and reliable displacement ductility capability, which are comparable to those of NWC frames. The test data observed in this study can provide theoretical guidance for the application of LWAC frames in seismic regions
Theoretical model and characteristics analysis of deflector-jet servo valve’s pilot stage
Get PDFTo analyze the deflector-jet servo valve’s internal flow characteristics, a theoretical model of the complicated flow distribution in the deflector plate is established based on the offset jet attachment theory. When the deflector plate offsets, jet attachment parameters are attained to figure out the jet’s bending and colliding process. On this basis, an analytical method of acquiring the pilot valve’s pressure gain is derived. According to an actual pilot stage’s structure, pressure gain calculations are carried out. Meanwhile, the pilot valve’s mesh model is established for numerical simulation in order to examine the accuracy of the theoretical model. Calculation and numerical simulation show that the final oil jet is not sensitive to the deflector plate’s movement, which directly reveals the pressure stabilizing effect of the V-shaped structure on the deflector plate. Moreover, the experiment on the pressure gain is accomplished and experiment results verify the accuracy of the analytical calculation
Numerical investigation and experimental test on aerodynamic noises of the bionic rear view mirror in vehicles
Get PDFAt present, there are some researches focusing on optimization of aerodynamic noises on rear view mirrors, but researches on bionic noise reduction of rear view mirrors are rarely reported. Therefore, with an original rear view mirror as the basic model, the paper applied a head convex hull of a dung beetle to the original rear view mirror cover to obtain a bionic rear view mirror, then conducted numerical computation for aerodynamic noises of the bionic rear view mirror and compared the computational results with the original model. Finally, in order to verify correctness of computational results of aerodynamic noises of the rear view mirror, wind tunnel test was conducted on the rear view mirror. Experimental and numerical simulation results were highly consistent in the whole frequency band, so the wind tunnel test could be replaced by numerical simulation. Only one obvious vortex was behind the bionic rear view mirror, but two obvious vortexes with the opposite rotation directions were behind the original rear view mirror. The bionic rear view mirror did not present vortexes near the lateral window, so impacts of vortexes on noises in the vehicle could be eliminated effectively. Pressure difference in front of and behind the bionic view mirror was smaller than the pressure difference in front of and behind the original rear view mirror. Pressure resistance caused by the convex structure outside the rear view mirror was reduced, so noise reduction could be promoted. The convex structure mainly affected the aerodynamic noise in mid-high frequency regions. Compared with the original rear view mirror, noise reduction effects of the bionic rear view mirror were obvious, where the noise reduction amplitude reached 10dB. Noise source size and intensity of the bionic rear view mirror were reduced obviously
Damage localization and quantification of composite beam structures using residual force and optimization
Get PDFStructural Health Monitoring (SHM) and impact monitoring of composite structures have become important research topics in the recent year. In this research, a non-destructive vibration-based damage detection method is formulated using Genetic Algorithm (GA) and compared with classical method. The robustness and reliability of the capability to locate and to estimate the severity of damage, based on changes in dynamic characteristics of a structure, is investigated. The objective function for the damage identification problem is established by using the residual force method (FRM). Numerical experiments using finite element analysis are performed on composite beams with different damage scenarios in order to clarify the validity of the developed technique. The comparison between estimated and real damage illustrates the efficiency of the algorithm in damage detection. The results show that the present approach is correct and efficient for detecting structural local damages in composite beam structures
Feature reconstruction based on t-SNE: an approach for fault diagnosis of rotating machinery
Get PDFIt is crucial to effectively and accurately diagnose the faults of rotating machinery. However, the high-dimensional characteristic of the features, which are extracted from the vibration signals of rotating machinery, makes it difficult to accurately recognize the fault mode. To resolve this problem, t-distributed stochastic neighbor embedding (t-SNE) is introduced to reduce the dimensionality of the feature vector in this paper. Therefore, the article describes a proposed method for fault diagnosis of rotating machinery based on local characteristic decomposition-sample entropy (LCD-SampEn), t-SNE and random forest (RF). First, the original vibration signals of rotating machinery are decomposed to a number of intrinsic scale components (ISCs) by the LCD. Next, the feature vector is obtained through calculating SampEn of each ISC. Subsequently, t-SNE is used to reduce the dimension of the feature vectors. Finally, the reconstructed feature vectors are applied to the RF for implementing the classification of the fault patterns. Two cases are studied based on the experimental data of the fault diagnoses of a bearing and a hydraulic pump. The proposed method can achieve a diagnosis rate of 98.22 % and 98.75 % for the bearing and the hydraulic pump, respectively. Compared with the other methods, the proposed approach exhibits the best performance. The results validate the effectiveness and superiority of the proposed method
Seismic evaluation and collapse prediction of RC moment frame structures by using energy balance concept
Get PDFSeismic evaluation and collapse prediction of structures mostly includes determination of story displacement demands, and member forces and deformations for certain hazard levels. A few methods have been developed in the decades, such as modal pushover analysis (MPA), FEMA 440, and capacity spectrum. In general, non-linear pushover analyses are applied in these methods. This paper presents a seismic evaluation and collapse prediction method based on energy balance concept. In this method, the design base shear for any given hazard level can be obtained by associating the work necessary to push the structure to the design target drift with the energy needed in a structure of an equivalent SDOF oscillator. This work energy equation can be further applied to estimate responses of existing structures under certain earthquake excitations. In this procedure, an energy-displacement plot (Ec) can be converted with the force-displacement curve (capacity) of the structure obtained by static pushover analysis. This curve is then overlaid over the energy demand plot (Ed) for the specified hazard level to determine the ultimate displacement demand. This method can be also used to obtain the collapse margin ratio (CMR) without cumbersome time-history analyses, such as incremental dynamic analysis (IDA). The drift estimations and collapse predictions of two 20-story RC moment frame structures by applying this energy balance concept were in good agreement with those obtained from inelastic dynamic analyses and IDA using a set of representative ground motion records
Prediction of dynamic characteristics of a pantograph-catenary system using the displacement compatibility
Get PDFUsing the equation of displacement compatibility, a novel method for describing the contact between pantograph and catenary is proposed in this paper. Then an interaction catenary-pantograph system capable of describing vertical vibration is established. Taking into account the frictional characteristic between pantograph and catenary, the Coulomb model is applied. Based on the continuum mechanics, the partial differential equations of the coupling system are set up. For facilitating numerical simulation, the dynamic equations are further discretized by the Galerkin method, in which the modes of the complicated system are obtained by the finite element method. Therefore, the ordinary differential equations of the coupling system are numerically solved and the corresponding dynamic behaviors at different running speeds are analyzed in terms of waveform. Moreover, the effects of the frictional characteristic on the contact force between pantograph and catenary are discussed in detail. By comparing the results with European standard EN50318, the novel contact method is proved to be valid and accurate
The evaluation of the sustainable transport system development with the scenario analyses procedure
Get PDFThe problem of sustainable transport system development is currently very important and frequently analysed. It concerns promotion of such transport, which is efficient, cost effective and meets the expectations of the society. At the same time, such transport should minimize its negative impact on public health, environment, and economy or urban planning. This paper deals with selected aspects of developing sustainable transport systems and assessing them based on their negative impact on society (amount of pollution and noise emissions). A number of different scenarios for the sustainable transport system development were presented. In addition, a procedure for evaluating these scenarios was proposed (using appropriate evaluation criteria and indicators, including noise and pollutant emissions from road transport). The studies presented in this paper were carried out using the PTV Visum tool and transport models developed in it (e.g. EMITRANSYS or MTAW 2015)