Journal of Vibroengineering
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Narrowbandness of seismic ground displacement on a broader area of the lithosphere and importance on base motion in isolated structures
Full text linkPower spectral density of horizontal ground displacement of large and recent events in earthquake-prone Latin America is analyzed. The results confirm -in a larger region of the world- that strong motion horizontal displacement is a narrowband process, which was previously demonstrated solely on a very limited area: the State of California. Nonetheless, those limited and previous results proved to be important in seismic base isolation; particularly, in the solution of the problem of large displacements at the structure base. This is a current problem for which more expensive techniques than passive control are presently being implemented, as active or hybrid control; therefore, it is emphasized that a solution exists within simple base isolation, and it is based on ground displacement narrowbandness
A two-way linear piezoelectric vibratory conveyor actuated by a composite sinusoidal voltage input
Full text linkPiezoelectric vibratory conveyors are widely used in many industrial fields such as factory automation. However, there is still a limitation for most cases that the vibratory conveyor can only feed in the designed direction. In today's multitasking intelligent machinery, how to sort different parts from the same feed source and convey them efficiently in different directions remains a challenge to be overcome. This study proposes an innovative design that uses a composite sinusoidal control signal to drive a linear two-stage piezoelectric vibratory feeder. By simply tuning the amplitude and phase of the input composite signal, the conveying velocity and direction can be altered easily. The dynamic characteristics of this feeder were both investigated by theoretical formulation and experimental measurement. It is found that the conveying performance of this feeder is better suited for using the composite signal with two sinusoidal components of double frequency. With the composite control signal synthesized by two sinusoidal components of 237.5 Hz and 475.0 Hz, which were close to the feeder’s first two resonance frequencies to increase the response gain of the structure, and the input voltage of 60 V, which corresponded to the trough’s displacement amplitude of 54.5 m, the measured conveying speeds were +30.8 mm/s and –33.3 mm/s for setting the phase angles 180° and 0°, respectively. The result demonstrates the feasibility of the proposed two-way vibratory feeder design
Research on seismic response of new lining structured of shallow double-arch tunnels under unsymmetrical pressure
Full text linkA physical test model of a new lining structure for a shallow double-arch tunnels under unsymmetrical pressure with a scale of 1:20 was designed and manufactured. Kobe seismic waves and EI seismic waves were selected as the loading waves and a large-scale shaking table test was carried out. The acceleration and dynamic strain response of shallow double-arch tunnels under unsymmetrical pressure under different seismic wave types and seismic intensities are studied. The results show: Under different seismic wave excitations, only the horizontal acceleration amplification factor of the left-hole vault, right-hole invert and the top right of the mid-partition is less than 1, and the horizontal acceleration amplification factors of other measurement points are all greater than 1. The measurement points with relatively large horizontal acceleration response are the left-hole shoulder, the top left of the mid-partition, the right-hole vault and shoulder; The overall response of the right half-arch of the left-hole is greater than the left half-arch of the left-hole, and the overall response of the left half-arch of the right-hole is greater than the right half-arch of the right-hole. The measured points in the left half-arch of the left-hole and the right half-arch of the right-hole have small differences in acceleration response; The effects of Kobe wave on horizontal acceleration and vertical acceleration are greater than EI wave, and the average value of the vertical acceleration response of the lining is greater than the average value of the horizontal acceleration response. With the increase of seismic intensity, the larger the acceleration amplification factor is, the greater the increase is; Under the action of different seismic waves, the seismic wave excitation has a greater impact on the dynamic strain response of the left-hole, and less impact on the right-hole. Among them, the strain value of the left-hole shoulder, left-hole invert and the top left of the mid-partition is much larger than the other measurement points, the trend of the right-hole is relatively gentle, and the strain values of the shoulder are slightly larger. The research conclusions have certain guidance and reference value for the seismic design of shallow double-arch tunnels under unsymmetrical pressure
Adaptive fuzzy control of nonlinear aeroelastic system with measurement noise
Full text linkThis paper presents a limit cycle oscillation (LCO) suppression method of nonlinear aeroelastic system based on adaptive neuro-fuzzy control. A prototypical 2D wing section with a single control surface at the trailing edge of the main wing, which contains a symmetrical freeplay nonlinearity in the pitch degree of freedom, is modelled by SIMULINK (Matlab 2016R) to illustrate the proposed method. Proportional integral differential (PID) controller is used to suppression the LCO of nonlinear aeroelastic system. The control law of the PID controller is identified by neural network. A new fuzzy control law of the nonlinear aeroelastic system is obtained by adjusting the parameters of the fuzzy control system. A nonlinear aeroelastic system with measurement noise in the measurement feedback loop is conducted to verify the effectiveness of the proposed method
Fault recognition of rolling bearing with small-scale dataset based on transfer learning
Full text linkAlthough, deep learning has been successfully used for fault diagnosis of rolling bearing by training large-scale data, the acquisition of large-scale fault data requires a high cost. For small-scale data, the precision of network model will decrease with the deepening of network layers. Aiming at above issue, a convolutional neural network algorithm based on transfer learning model is proposed. First, the overlap sampling of rolling bearing fault signals are used to enhance the datasets, and the transfer learning model is pre-trained on standard-scale dataset to obtain the initial network parameters, that will be used to extract bearing fault features from small-scale dataset. The effects of data scale and fault categories on model accuracy are discussed based on the comparison and verification on public bearing fault dataset. The results show that the proposed method in this paper can achieve high-precision with a small computational cost on fault identification of small-scale fault data, and the method shows popularization value for the analysis of small-scale datasets in other areas
The multi-harmonic excitation characteristic of airflow piezoelectric generator
Full text linkIn order to improve the adaptive range of airflow velocity, an airflow piezoelectric generator based on multi-harmonic excitation is proposed. The flow field characteristics are obtained by CFD method, the acoustic vibration characteristics and variation with velocity of the excitation frequency are studied. The result shows that periodic compression and expansion of air are presented and a standing wave is formed inside the resonator, which can provide stable excitation source. The excitation frequencies are distributed on the acoustic modes of the resonator and captured. With different velocity segment, the excitation frequencies are different, and frequency conversion is presented from the first-order to the third-order and from the third-order to the first-order. The conclusions verify the feasibility of the multi-harmonic excitation energy exchange scheme, which is helpful to improve the flow velocity adaptive range of the airflow-induced vibration piezoelectric generator
Review on engine vibration fault analysis based on data mining
Full text linkThrough equipment monitoring, the uptimes of machines are enhanced in the industrial applications. The unpredicted failures risks are minimized by the proper equipment monitoring. The machine vibrations are increased caused by the failure modes. The vibration data requires effective analysis by the accurate assessment of the machine equipment. For fault feature selection and detection of faults in rotating equipment, the empirical knowledge is required. Low efficiency of the methods and motor speed control are the main drawbacks of the existing techniques. So the basic aim of this paper is the detection of rotating equipment faults by utilizing the vibration analysis. The motor vibration is analyzed and monitored using spectrum analysis. The spectral content are extracted and fed into the classifier like k-Nearest neighbors (KNN), back-propagation neural network BPNN, Sparse Representation Classifier (SRC), Support vector machine (SVM) and Random Forest (RF) for the type of failure prediction and analyze the unbalance condition (UNB), bearing faults (BDF), and broken rotor bars (BRB) faults. The RF classifier is better as compared to other classifiers in terms of accuracy, precision and recalls values by approximately 10.92 %, 11.03 % and 20.13 % respectively
Dynamical analysis and validation of motion control by filtering performance for aerial robotic system
Full text linkAlthough drone appears in different applications, such as environmental inspection, agriculture or transportation, some aspects require more studies to clarify the efficient outcomes. One of them is to investigate the filtering performance such as Kalman and Complementary filters when the autonomous aerial system (AAS) handles its mission. However, it lacks the systematic research about these filters to provide the proper evaluation. Therefore, in this paper, the research topic related to AAS model to indicate the filtering effects in the agricultural application for making an alternative solution is presented. Firstly, the mathematical representation of system model is established in order to describe the dynamical performance and motion constraints. Then, the theory of filter structure is implemented to estimate the system state. The proposed design is validated in both numerical simulation and experiments. The system parameters that are monitored, include angular values of roll, pitch and yaw in three axes, motion parameters and its trajectories. By utilizing various sensing devices such as gyroscope, accelerometer and compass in real-world hardware, the experimental results could evaluate more precise and efficient design. The findings of this study are to (1) propose the model of AAS and proper filters, (2) launch the verified process and calibration, and (3) demonstrate the competitive performance among filters. From these results of our work, it could be clearly seen that the AAS plays an important role in daily applications and the related topics are still attractive
The PWM rectifier with LCL filter direct power control based on power damping feedback
Full text linkBased on the topology and mathematical model of the three-phase voltage source PWM rectifier with LCL filter, the resonance produced by the LCL filter and the design method of filter parameters is analyzed. For the resonance problem of the LCL filter, a direct power control strategy of the LCL PWM rectifier based on power damping feedback is proposed. The double-loop control structure is constructed for the inner loop power and outer loop current. The virtual voltage source is constructed as equivalent to power damping in the power loop. The power loop of the output is adopted as a command value in the input current loop, and the current loop is designed to use deadbeat control to ensure the accuracy of current tracking. SVPWM is introduced in this novel direct power control method to generate PWM signals to drive the rectifier power switch and achieve a fixed switching frequency. The experimental results show that this proposed control method can achieve the unit power factor operation of the rectifier while it’s suppressing the resonance, and the system has a better dynamic and static performance
Study on longitudinal vibrations in turbomachinery coupled with skewed slotted bar cage induction motors
Full text linkThe present paper discusses the study of longitudinal vibrations in turbomachines coupled with skewed slotted bar cage induction motors and which are of the typical configurations in refinery industries. Based on vibration data, the severe longitudinal vibrations in tilting pad thrust bearing assembly and its failure mechanism during start up transient and steady-state operations has been observed. The excitation sources for these longitudinal vibrations originates from asymmetric air gaps in cage induction motors. Hereby, the study of longitudinal vibrations in turbomachines with thrust bearing is found to be necessary. A simplified Single degree freedom (SDOF) analytical model is proposed to estimate the peak response based on tuned variable stiffness method. Uniform air gap with rotor skew causes fixed thrust and is proportion to square of the load current. Static eccentricity across the rotor motor air gap causes variations in gap length and intern creates the torque fluctuations. This value is proportional to variance in square of the load current. In the proposed model evaluates the cascade effect of preloaded thrust due to rotor motor skewness and followed by compressor thrust due to differential pressure across the impeller in the form of the variable stiffness. This model has advantage in analysing the coupled motor and turbomachinery system response in longitudinal direction in a simple manner. The longitudinal vibrations estimate at thrust bearing and compared with experimental vibration data obtained from the field machinery. There is a good convergence between results of the analytical model and experimental field vibration data