Journal of Vibroengineering
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Model reaching adaptive-robust control law for vibration isolation systems with parametric uncertainty
Get PDFAdaptive control has been used for active vibration isolation and vehicle suspensions systems. A model reference adaptive control law is used for the plant to track the ideal reference model. In a model reaching adaptive control approach, the ideal of a skyhook target without using a reference model is achieved. In this paper, a novel approach, a model reaching adaptive-robust control law is studied for active vibration isolation systems. A dynamic manifold for ideal system is defined using the ideal of a skyhook target model system parameters. First, a new Lyapunov function is defined. Based on the Lyapunov stability theory, a model reaching adaptive and a robust control laws are derived for the uncertain system to reach the ideal manifold. Parameters and upper bounding functions are estimated as a trigonometric function depending on the relative displacements, velocities and the defined manifold. The developed adaptive and the robust compensators are combined and this combination is proposed as an adaptive-robust control law. After that, the controller is applied to a vehicle suspension system and the ideal of a skyhook target without using a reference model is achieved. The results also show that the proposed robust control law can increase the comfort of the vehicle active suspension systems and the ride comfort is remarkably increased
A three-DOF ultrasonic motor using four piezoelectric ceramic plates in bonded-type structure
Get PDFA three-DOF ultrasonic motor is presented in this paper. The proposed motor consists of four piezoelectric ceramic plates and a mental base with a flange that can fix the motor on a rack. The proposed motor takes advantage of a longitudinal mode and two bending modes, different hybrids of which can realize three-DOF actuation. Because of symmetric structure of the proposed motor, the resonance frequencies of the two bending modes are identical. And the resonance frequency of the longitudinal mode was tuned closed to the ones of the bending modes by adjusting the structural parameters in modal analysis. Then trajectories of nodes on the driving foot were obtained by the transient analysis to verify the feasibility of driving principle. Experiments including vibration shape test and output characteristic test were executed. The starting voltages of the rotation along horizontal axes are about 10 Vp-p. Under driving voltages of 200 Vp-p, the output velocities of three DOF can reach 280 rpm, 277 rpm and 327 rpm, respectively. The results of the experiments indicate that the proposed motor is characterized by low starting voltages and high output velocities
Stiffness and vibration isolation characteristics of a torsional isolator with negative stiffness structure
Get PDFThis paper proposes a novel design torsional vibration isolator with negative stiffness structures. It consists of two shafts that are linked by positive springs and negative stiffness structures. The connection position of the two shafts has been designed into disc structure, which is the installation position of the positive springs and negative stiffness structures. The task of positive springs is to transmit the designed torque. In this paper, the nonlinear stiffness characteristics of the isolator are presented. The nonlinear mathematical model is presented, and its dynamic behaviors are investigated using the averaging method, and compared with that of the corresponding linear torsion isolator without negative stiffness structures. The study shows that the torsion isolator has a wider isolation region than that of the linear isolator. Furthermore, the performance of the isolator is sensitive to the damping of the system and the amplitude of vibration excitation. Choosing a suitable damping and vibration environment will be important for the stable application of this isolator
Editorial Note regarding the republication of the retracted papers No. 1884, No. 2211 and No. 2254
Get PDFRepublished Paper. Rapid early damage detection using transmissibility with distance measure analysis under unknown excitation in long-term health monitoring
Get PDFAccurate and efficient damage detection in long-term health monitoring for structures still encounters many difficulties due to the effect of environment. Furthermore, recorded big data requires efficient damage detection algorithm. In this study, an efficient and effective damage detection algorithm is proposed using transmissibility along with Mahalanobis distance and Hotelling T-square. A numerically simulated beam and an experimentally tested laboratory structure are used to validate the proposed algorithm. Results demonstrate good performance of the proposed technique in damage detection
Measurement method of torsional vibration signal to extract gear meshing characteristics
Get PDFA technique in measuring torsional vibration signal based on an optical encoder and a discrete wavelet transform is proposed for the extraction of gear meshing characteristics. The method measures the rotation angles of the input and output shafts of a gear pair by using two optical encoders and obtains the time interval sequences of the two shafts. By spline interpolation, the time interval sequences based on uniform angle sampling can be converted into angle interval sequences on the basis of uniform time sampling. The curve of the relative displacement of the gear pair on the meshing line (initial torsional vibration signal) can then be obtained by comparing the rotation angles of the input and output shafts at the interpolated time series. The initial torsional vibration signal is often disturbed by noise. Therefore, a discrete wavelet transform is used to decompose the signal at certain scales; the torsional vibration signal of the gear can then be obtained after filtering. The proposed method was verified by simulation and experimentation, and the results showed that the method could successfully obtain the torsional vibration signal of the gear at a high frequency. The waveforms of the torsional vibration could reflect the meshing characteristics of the teeth. These findings could provide a basis for fault diagnosis of gears
Numerical analysis on aerodynamic behavior of high-speed trains in the tunnel and open air based on the virtual reality technology
Get PDFThis paper numerically computed the problem of pressure fluctuations in the open air and tunnel based on the virtual computer technology, and experimentally verified the correctness of the numerically computational model. In the open air, pressure fluctuation at the nose tip of train head was serious and presented two obvious valley and peak values. Pressure at the nose tip of train tail did not present obvious fluctuations. Pressure at the train head was obviously more than that at the train tail. For different observation points, the peak and valley values of far-field pressures only showed translation with the increased running time. In the tunnel, pressures at the nose tip of train head had obvious peak and valley values and were far more than those in the open air. For different observation points, the peak and valley values of far-field pressures did not simply present translation with the increased running time, which indicated that there was wall effect in the tunnel. In addition, the absolute values of the maximum positive and negative pressures of the high-speed train in the near and far fields obviously increased with the increased running time. The pressure fluctuation caused by the high-speed train in the tunnel was the superposition of the inlet pressure wave and air disturbance caused by the passing train. The size of local air pressure was related to tunnel length, train length and speed. The peak value of positive pressures in the tunnel appeared when the train entered the tunnel. The valley value of negative pressures in the tunnel would appear in the area where the expansion wave of train head was superimposed with the compression wave of train tail. According to tunnel length, train length and speed, the specific positions where the peak and valley values of positive and negative pressures appeared could be approximately obtained. If the tunnel was very long, it was possible to present the peak value of positive pressures caused by the superposition of more continuous compression waves or the valley value of negative pressures caused by the superposition of more continuous expansion waves
FPGA based quasi z-source cascaded multilevel inverter using multicarrier PWM techniques
Get PDFFPGA based Quasi Z-Source Cascaded Multilevel Inverter (Quasi Zs-CMLI) using multicarrier PluseWidth Modulation (PWM) techniques are presented in this paper. Multicarrier based PWM techniques have been proposed for seven level Quasi Zs-CMLI and implemented using Field Programmable Gate Array (FPGA). For generating gating pulses to the inverter switches, Phase Disposition (PD), Inverted Phase Disposition (IPD), Phase Opposition Disposition (POD) and Alternative Phase Opposition Disposition (APOD) techniques are programmed on FPGA. In the proposed system, three solar PV emulator modules are used. These are acting as input source to the inverter. Finally, THD comparison made between different carrier based modulation with shoot through and non-shoot through the states. The proposed quasi Zs-CMLI and PWM techniques are verified through MATLAB/Simulink. For confirmation of simulation results, A laboratory prototype model have been implemented using FPGA. The capture hardware results are matched with simulation results
Modeling and analysis of a high-static-low-dynamic stiffness vibration isolator with experimental investigation
Get PDFIn order to attenuate low-frequency vibration, a novel nonlinear vibration isolator with high-static-low-dynamic stiffness (HSLDS) is developed in this paper by combining the negative stiffness corrector in parallel with a vertical linear spring. The force and stiffness characteristics are first derived by the static analysis. Then, the displacement transmissibility of the HSLDS system is obtained to evaluate the isolation performance using the harmonic balance method. The parametric analysis shows that the proposed HSLDS system can outperform the equivalent linear one in some aspects. Besides, the initial isolation frequency is defined and further investigated with the purpose of providing some useful guidelines for choosing parameter combinations conveniently. Finally, a prototype is developed and the experimental test is conducted to verify the isolation performance of the proposed HSLDS system
Gear fault feature extraction and classification of singular value decomposition based on Hilbert empirical wavelet transform
Get PDFVibration signal of gearbox systems carries the important dynamic information for fault diagnosis. However, vibration signals always show non stationary behavior and overwhelmed by a large amount of noise make this task challenging in many cases. Thus, a new fault diagnosis method combining the Hilbert empirical wavelet transform (HEWT), the singular value decomposition (SVD) and Elman neural network is proposed in this paper. Vibration signals of normal gear, gear with tooth root crack, gear with chipped tooth in width, gear with chipped tooth in length, gear with missing tooth and gear with general surface wear are collected in different speed and load conditions. HEWT, a new self-adaptive time-frequency analysis, was applied to the vibration signals to obtain the instantaneous amplitude matrices. Singular value vectors, as the fault feature vectors were then acquired by applying the SVD. Last, the Elman neural network was used for automatic gearbox fault identification and classification. Through experimental results, it was concluded that the proposed method can accurately extract and classify the gear fault features under variable conditions. Moreover, the performance of the proposed HEWT-SVD method has an advantage over that of Hilbert-Huang transform (HHT)-SVD, local mean decomposition (LMD)-SVD or wavelet packet transform (WPT)-PCA for feature extraction