A frequency-weighted energy operator and swarm decomposition for bearing fault diagnosis

The weak fault characteristics of rolling bearings are difficult to identify due to strong background noise. To address this issue, a bearing fault detection scheme combining swarm decomposition (SWD) and frequency-weighted energy operator (FWEO) is presented. First, SWD is applied to decompose the bearing fault signal into single mode components. Then, a new evaluation index termed LEP is constructed by combining the advantages of envelope entropy, Pearson correlation coefficient and L-kurtosis, and it is utilized to choose the sensitive component containing the richest bearing fault characteristics. Finally, FWEO is employed for extracting the bearing fault features from the sensitive component. Simulation and experimental analyses indicate that the LEP index has better performance than the L-kurtosis index in determining the sensitive component. The method has the effect of suppressing noise and enhancing impulse characteristics, which is superior to the SWD-based envelope demodulation method.

Modelling of voltage changes in the n-p junction in the pulse mode

The article presents the results of modeling the effect of the effective lifetime in the space charge region (SCR) of the n+-p junction on the impulse characteristics of silicon structures. The model is based on solving the fundamental system of differential equations for the transport of charge carriers in inhomogeneous semiconductors. The calculated time dependences of the voltage change in the SCR for a pulse voltage change on the n+-p-p+ structure correspond to the experimental data.

Analysis on impulse characteristics of pulse detonation engine with nozzles

In order to study the influence of different nozzle configurations on the gas–liquid two-phase pulse detonation engine (PDE) propulsion performance, the measurement system based on the tunable diode laser absorption spectroscopy (TDLAS) technology is built to measure the velocity and the temperature, while the high frequency dynamic pressure sensor is used to measure the nozzle gas pressure. Based on the momentum principle, the contribution mechanism of unsteady gas jet on thrust is obtained indirectly by TDLAS data. The results show that the impulses of PDE with non-nozzle, convergent nozzle, divergent nozzle and convergent–divergent nozzle are 1.95, 2.08, 1.85 and 2.16 N∙s within 20 ms of the exhaust period, respectively. The analysis reveals that the impulses of PDE with convergent and convergent–divergent nozzles are larger than that with non-nozzle, while the impulse of PDE with divergent nozzle is smaller than that with non-nozzle. The research results in this paper can provide reference for the design of nozzles for PDE.

INFLUENCE OF THE INLET PRESSURE ON IMPULSE CHARACTERISTICS OF ALUMINUM SAMPLES

In this work, the cavitation water jet technique was used to clean the inner walls of oil pipes after tertiary oil recovery. The surface morphology, depth of impinging pits, and corrosion resistance of aluminum samples after impingement with the cavitation water jet were examined using scanning electron microscopy (SEM), 3D microscopy, and an electrochemical workstation. When the inlet pressure was higher than 3[Formula: see text]MPa, the number of cavitation bubbles generated by the cavitation nozzle increased with an increase in inlet pressure. Moreover, the cleaning effect that the cavitation water jet had on the aluminum samples was higher than that of general water jet technology. There were no obvious changes to the surface of the aluminum samples when the inlet pressure was decreased to 13[Formula: see text]MPa. Meanwhile, the mass loss of aluminum samples also increased. However, the internal corrosion resistance of the pipe wall after impact was relatively low. These results indicate that the impinging efficiency of the cavitation water jet was obviously enhanced and the degree of damage to the oil pipe wall was low at an inlet pressure of 15[Formula: see text]MPa. The best target distance was 8–12[Formula: see text]mm, and at this point, the jet flushing effect was the best. Moreover, the jet velocity at the outlet cavity was 184[Formula: see text]m/s, and the jet strike area was 250[Formula: see text]mm2.

The active dynamic vibration damper in non-stationary operation of a vibroactive unit

The paper considers a vibration isolation system, in which a force is applied to the moving mass of the active dynamic vibration damper by an actuator in proportion to the measured value of the base response. The amplitude-frequency and impulse characteristics are plotted depending on the parameters of the system, assuming the actuator without distortion generates the force proportional to the base response. It is shown that the considered vibration isolation system is quite effective in the low-frequency region, including in the resonance region of the passive system, both in stationary and nonstationary modes of vibroactive forces