Dawei Guo

The monitoring and fault diagnosis of axle-box bearings in high-speed trains is crucial for ensuring safe train operations. The vibration signals of these bearings exhibit non-stationary and non-linear characteristics. To further enhance the accuracy of identifying rolling bearing faults, a fault diagnosis method is proposed. This method is based on the improved Dung Beetle Optimization (DBO) algorithm for optimizing Variational Mode Decomposition (VMD) combined with Stacked Sparse Autoencoder (SSAE). Firstly, the DBO algorithm is enhanced to improve its optimization precision and global optimization capability. It is then utilized for the adaptive selection of two parameters: the number of decomposition modes and the penalty factor in VMD. These improvements address issues such as mode mixing, signal loss, and excessive decomposition, which arise from poor parameter selection in the traditional VMD method. Subsequently, components of intrinsic mode functions (IMFs) that are highly correlated with the original signal are selected. The time-domain and frequency-domain features of these IMF components are used to construct the dataset. The feature set is then inputted into the deep machine learning model SSAE for training and testing. Through diagnostic experiments on various types and levels of rolling bearing faults, the model demonstrates a higher rate of fault diagnosis recognition.

The ion velocities within the discharge channel of the 600 W magnetically shielded and unshielded Hall thrusters are measured by the laser-induced fluorescence technique to quantitatively evaluate the erosion of the channel walls. Visual inspection of the magnetically shielded Hall thruster has qualitatively indicated that the discharge channel has been successfully shielded from the bombarding of the plasma, while the erosion occurs in the unshielded counterpart. In addition, the ion velocities along the thruster centerline indicate that the voltage utilization efficiency of MSHT-600 is higher than that of USHT-600 and comparable to the state-of-the-art BHT-600 thruster. Furthermore, measurements performed inside the discharge channel show that the ions deep inside the channel impact the channel walls backward in the shielded thruster, while forward in the unshielded one. Moreover, the plasma potential along the channel walls remains as high as the anode potential in the shielded thruster, while it dramatically decreases in the unshielded one. When accounting for the sheath potential acceleration, the maximum erosion rate of the inner and outer walls of USHT-600 is 1.3 and 3.1 μm/h, respectively, based on the plasma parameters of SPT-100, while the maximum value of the weighted average erosion rate of MSHT-600 is 0.08 and 0.04 μm/h, respectively, for two cases of the ion number density. Compared to the erosion rate of SPT-100, it is qualitatively and quantitatively confirmed that strong shielding of the discharge channel is realized and high performance is maintained in the designed thruster with a magnetically shielded configuration.

Non-intrusive characterization of the ion velocity distribution functions at several points of interest in 600 W magnetically shielded MSHT-600 and unshielded USHT-600 Hall thrusters plume by laser-induced fluorescence was conducted. Several visual clues supporting the magnetic shielding effect of MSHT-600 were presented. The measured ion axial velocity distribution functions show that the ion axial velocity is higher and observed to reach the maximum at nearer location to the exit plane on the centerline in the magnetically shielded Hall thruster than that in the unshielded one under the same operating conditions but uniformly distributed in the radial direction when ignoring the slower population for both thrusters. These results are in accordance with the higher specific impulse measured in several other shielded Hall thrusters. Moreover, the ion axial velocity on the centerline is higher than the average axial velocity at other radial locations for the same axial distance downstream of the exit plane in USHT-600, while the higher plume divergence or the inner pole erosion causes the velocity on the centerline to decrease in MSHT-600. The downstream shift of the accelerating potential and electric field distribution are also the typical features in magnetically shielded Hall thrusters as reported in other studies. Finally, the xenon ion velocity vector fields show that the ion population starts to meet and diverge further downstream of the exit plane in MSHT-600 than that in USHT-600, which may be associated with the difference of the plume divergence.

The porous-media-based electrospray thruster is a cutting-edge micropropulsion technology that can revolutionize the capabilities of microsatellites. This paper reports the design, fabrication, and characterization of a novel porous-media borosilicate glass electrospray thruster. The porous glass used here is integrally formed by the phase separation method, which make it display outstanding pore uniformity and processability. The picosecond ultraviolet laser processing technique is applied to machine 361 emitters out of glass. Performance characteristic experiments are conducted with the thruster passively fed with ionic EMI-BF4 liquid. The results reveal that the per-emitter can emit up to 200.46 nA of ion current at 2 kV. The novel porous glass and the corresponding machine method present an opportunity to attain more-controllable emitter shapes, which has a positive impact on thruster lifetime and performance improvement.

In support of our planar pulsed inductive plasma thruster research, a fast electromagnetic inductive valve for a gas propellant injection system has been built and tested. A new and important design feature is the use of a conical diaphragm as the action part, which greatly contributes to the virtue of simplicity for adopting the resultant force of the diaphragm deformation as the closing force. An optical transmission technique is adopted to measure the opening and closing characters of the valve while the gas throughput is determined by measuring the pressure change per pulse in a test chamber with a capacitance manometer. The experimental results revealed that the delay time before the valve reaction is less than 40 μs, and the valve pulse width is no longer than 160 μs full width at half maximum. The valve delivers 0-2.5 mg of argon gas per pulse varied by adjusting the drive voltage and gas pressure.