Journal of Vibroengineering
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Transform-domain sparse representation based classification for machinery vibration signals
Get PDFThe working state of machinery can be reflected by vibration signals. Accurate classification of these vibration signals is helpful for the machinery fault diagnosis. A novel classification method for vibration signals, named Transform Domain Sparse Representation-based Classification (TDSRC), is proposed. The method achieves high classification accuracy by three steps. Firstly, time-domain vibration signals, including training samples and test samples, are transformed to another domain, e.g. frequency-domain, wavelet-domain etc. Then, the transform coefficients of the training samples are combined as a dictionary and the transform coefficients of the test samples are sparsely coded on the dictionary. Finally, the class label of the test samples is identified by their minimal reconstruction errors. Although the proposed method is very similar to the Sparse Representation-based Classification (SRC), experimental results illustrates its performance is far superior to SRC in the classification of vibration signals. These experiments include: frequency-domain classification of bearing vibration data from the Case Western Reserve University (CWRU) Bearing Data Center and wavelet-domain classification of six fault-types gearbox vibration data from our rotating machinery experimental platform
Design and dynamic testing of a roller coaster running wheel with a passive vibration damping system
Get PDFThis paper presents a design, a numerical analysis, a build-up and dynamic testing of an engineered and fabricated wheel with a passive vibration damping system designed for a roller coaster system. Taking into account the limited amount of space for fixing a wheel to a roller-coaster, this study shows an approach in which a special wheel design and viscoelastic inserts are used to reduce vibrations. A wheel comprises a rim and hub separated by a viscoelastic material and simultaneously connected by using spring steel fasteners with contractions ensuring elasticity. The dynamic tests of the wheel with a passive vibration damping system were completed with an assessment of the vibration reduction ratio in comparison to conventional roller coaster wheel types currently operated at the amusement park Energylandia located in Zator, Poland. Laboratory test results show reduction of vibrations by 36 % in the low frequency range, by 63 % in the medium frequency range and by 45 % in the high frequency range
Numerical optimization for aerodynamic noises of rear view mirrors of vehicles based on rectangular cavity structures
Get PDFThe rectangular cavity structure was applied to edges of the rear view mirror, numerical computation was conducted for aerodynamic noises of the rear view mirror, and the results of optimized structure were compared with those of the original structure to verify optimized effects. Wind tunnel test was then conducted on the rear view mirror to verify correctness of the computational model. Sound pressure levels of each observation point between experimental test and numerical simulation were basically consistent, where only parts of the peak frequency points were different. The computational accuracy was very high. Two large-size vortexes were in this region behind the common rear view mirror. Vortexes above the rear part of the rear view mirror rotated anticlockwise, while vortexes under it rotated clockwise. There were two vortexes in the region behind the optimized rear view mirror, but the energy intensity of this vortex near the side window panel was very weak. Pressures on the front part of the optimized rear view mirror were also smaller than those of the original structure. In addition, it could be found that radiation noise distribution of the rear view mirror on the lateral window presented symmetry. When lateral window effects were considered, the aerodynamic noise was more than results without considering the lateral window effects. Total noises of each observation point without considering the lateral window effects were 56.7 dB, 59.2 dB, 58.6 dB, 58.9 dB, 62.3 dB and 63.1 dB, respectively. Total noises at each observation point with consideration of the lateral window effects were 65.3 dB, 66.5 dB, 68.7 dB, 69.2 dB, 70.1 dB and 70.8 dB, respectively. Therefore, when aerodynamic noises of the rear view mirror were computed, impacts of lateral window effects must be considered, otherwise the computation would be seriously deviated from actual situations. The frequency corresponding to maximum peaks of the aerodynamic noise after optimization approached the self-oscillation frequency of the rectangular cavity. The result indicates that aerodynamic noises in the rectangular cavity were fluid self-oscillation caused by the cavity structure. In addition, within the analyzed frequency band, the aerodynamic noises of the optimized rear view mirror were smaller than those of the original structure. The maximum decrease rate of total noises of the optimized rear view mirror was 15.62 %, and minimum decrease rate was 8.90 %. Optimized effects were very significant, especially in the low frequency bands
A DPCA-based online fault indicator for gear faults using three-direction vibration signals
Get PDFFor online monitoring and identifying gear faults, a new fault indicator is proposed based on a multivariate statistical technique, dynamic principal component analysis (DPCA), under variable load conditions. In this method, a tri-axial vibration sensor is used to acquire the 3-direction vibration signals of gear in the gear box because it can pick up more abundant fault information than a single axis sensor does. By monitoring the value of the fault indicator, the running state of the gear (normal condition or faults) can be directly identified according to the set thresholds without using any other fault classification methods. To verify the effectiveness, the proposed method is applied on the QPZZ-II rotating machinery fault simulation rig in which the root crack and the tooth broken faults are introduced into the gearbox’s driving gear. Experimental results show that the fault indicator not only can effectively reveal the health state of the gear, but also is without being influenced by the load fluctuation. And, the accuracy rate of fault diagnosis is over 96 %
The development of a dynamic fracture propagation model for FRP-strengthened beam-column joints
Get PDFAccurate modeling is required to investigate the behavior of concrete structures strengthened by carbon fiber-reinforced polymer (CFRP). There is, however, limited knowledge on the use of dynamic modeling to study the crack propagation in the beam-column joints strengthened by CFRP. A finite element model is developed to study crack propagation in the CFRP-strengthened joints under dynamic loads. A three-dimensional model is developed to predict the crack propagation under cyclic loading in the ABAQUS software. In this study, dynamic fracture analysis is used to model the crack propagation in the concrete material. Furthermore, the model is used to predict dynamic debonding in CFRP strengthened with the fracture mechanics approach. The results of the present study showed a good agreement with previous experimental results by about 7.1-11.6 %. The proposed model indicates that the crack propagation is controlled by using CFRP composites in the beam-column joint. Furthermore, it is observed that the width of strut zone in the joint increases by the using of FRP strengthening
Analysis of dynamic characteristic for misalignment-spline gear shaft based on whole transfer matrix method
Get PDFSpline-gear-shaft (SGF), which is mainly composed of gear and spline shaft, is an important transmission system of RAT (driving the generator to output power with ram air). And its dynamic characteristics affect performance of RAT greatly. In this situation, gear coupling and spline coupling, must be taken into account when analyzing dynamics characteristics of SGF. The misalignment of axis for internal and external spline is inevitable owing to mass eccentricity and unconstrained in axial direction in a high-speed operation. Consequently, the dynamic model of SGF is established considering gear coupling and spline coupling based on whole transfer matrix method (WTMM) in this paper. In addition, numerical calculation method of meshing force for spline teeth under the condition of misalignment is presented considering the distribution force on contact surface of spline teeth in this paper, based on this, the coupled transfer matrix of misaligned spline coupling is established and the dynamic characteristics of SGF is analyzed using whole transfer matrix method with Riccati (WTMMR). The test experiments of dynamic characteristics for SGF are carried out by using portable vibration monitoring analyzer in this paper, furthermore, the time-frequency characteristics of SGF are analyzed through the analysis and processing of acceleration signal. The orders of magnitude for the first four natural frequencies with WTMMR are respectively consistent with experiment results, and the relative error is in the accepted range. Therefore, the correctness of solving meshing force and WTMMR for SGF are all verified. Moreover, it also shows that WTMMR is suitable for the analysis of complex coupled systems SGF and provides a new thought for dynamic analysis of complex shafting and promotes dynamic analysis to efficient and streamlined development
Numerical analysis on longitudinal seismic responses of high-speed railway bridges isolated by friction pendulum bearings
Get PDFAs to analyze the effects of friction pendulum bearings (FPB) on the responses of simply supported bridges on a high-speed railway under longitudinal earthquakes, a spatially integrated track-bridge model with a CRTS II slab ballastless track and FPB was established by using the OpenSEES software. The seismic responses under different ground motions were calculated and compared with those using common spherical steel bearings. The comparison results show that the combination of FPB and the CRTS II slab ballastless track is more reasonable. Namely, using FPB can effectively protect the bridge and track structures. Moreover, the rails, fasteners, CA layer and piers are perfectly protected by multi-layer isolation mechanics, induced by FPB and sliding layer, even under strong earthquakes. Finally, 0.05 is identified to be the best value for the friction coefficient of FPB under longitudinal earthquakes
Bispectral dynamics features for characterizing structural fatigue damage
Get PDFFatigue damage is a type of damage usually occurring to repeatedly loaded elements of structures in various engineering fields. Accumulation of fatigue damage may cause failure of structural elements. Identification of incipient fatigue damage is essential to ensure safety of structures. Fatigue crack under repeated loads commonly behaves in a nonlinear dynamic manner, typically manifested by both occurrence of higher harmonic components and interaction of harmonic components. Interrogation of nonlinear dynamic manner provides a promising way to characterize structural fatigue damage. This study aims at developing a new method to interrogate nonlinear dynamic manner for fatigue damage identification. This method is based on bispectral analysis of structural vibrational responses. This method portrays fatigue damage by inspecting the presence of higher harmonic components and quantifying the interaction of these harmonic components. The method can precisely locate and quantify a small-sized fatigue damage in a cantilever beam, presenting great accuracy in fatigue damage identification
Bifurcation and singularity analysis of HSLDS vibration isolation system with elastic base
Get PDFIn order to reveal the bifurcation mechanism and optimize the system design for high-static-low-dynamic-stiffness (HSLDS) vibration isolation system (VIS) with elastic base, the local bifurcation analyses both in unfolding parameter space and physical parameter space were carried out theoretically and numerically. Firstly, the restoring force of the HSLDS-VIS was approximated to linear and cubic stiffness by applying the Maclaurin series expansion and the motion equations of HSLDS-VIS with elastic base were established. Subsequently, the motion equations of HSLDS-VIS with elastic base were formulated to transform the system into a standard form and the averaging method was applied to obtain the single-variable bifurcation equation for the HSLDS-VIS with elastic base in case of primary resonance and 1:2 internal resonance. Furthermore, the transition sets and bifurcation diagrams in the unfolding parameter space were studied by means of singularity theory. Finally, for the engineering application, the transition sets were transferred back to the physical parameter space, thus to obtain the bifurcation diagrams of the amplitude with respect to the external force. The numerical simulation results show that the local bifurcations of HSLDS-VIS with elastic base in case of 1:2 internal resonance are considerable complex and need to be analyzed in six two-parameters spaces, meanwhile, the necessary condition of multiple solutions lies in some physical parameters, which can provide a theoretical basis and reference for design and application of the HSLDS-VIS with elastic base
Interior noise and vibration prediction of permanent magnet synchronous motor
Get PDFElectric vehicles (EV) are considerably quieter than internal combustion engine (ICE) powered vehicles, because noise of ICE is eliminated. However, the interior noise of an EV usually contains significant high-frequency noise components caused by electrical motor, which can be subjectively perceived as annoying and unpleasant. This paper describes a numerical model to predict interior acoustic noise caused by electromagnetic forces in permanent magnet synchronous motor (PMSM) for electric vehicles. Firstly, the principle of the multiphysics method is to establish a complete 3Dstructural finite element model (FEM) of motor. Based on FEM, natural frequency and modal shape were calculated by modal analysis. Secondly, using an electromagnetic finite element solver, the excitation due to electromagnetic phenomena is obtained. This excitation is then projected onto the structure mesh of motor in order to calculate the dynamic response. Thirdly, radiated electromagnetic vibration acceleration on the surface of the motor is calculated with modal superposition method. Compared with experimental test results, the creditability of motor electromagnetic vibration simulation is proved. Finally, by combining with transfer path analysis (TPA) techniques, interior electromagnetic noise of electric vehicles is accurately predicted. According to contribution analysis, motor surface zones and transfer paths contributing largely to the interior motor electromagnetic noise are identified. The results play a significant guiding role in both electric vehicle and permanent magnet synchronous motor for noise control and analysis