Structure design and performance analysis of aerostatic thrust bearing with compound restrictors

Aerostatic thrust bearing compensated by multi-orifices and porous material restrictor simultaneously is proposed to improve the static performance of the bearing. Load Carrying Capacity (LCC), stiffness and the flow field characteristics of the bearing are obtained by Computational Fluid Dynamic (CFD) simulation. The influences of supply pressure, orifice number, orifice diameter, orifice distribution, porous material thickness and permeability coefficient on the bearing performance are analysed. It is indicated that LCC and stiffness of the bearing with compound restrictors are much higher than those of the bearing with porous material restrictor or multi-orifice restrictor if gas film thickness is in rational range. The bearing with compound restrictors has better stability than that of the bearing with multi-orifice restrictor. Moreover, the optimum bearing parameters with compound restrictors are given to improving the performance of aerostatic thrust bearing.

Effects of Texture Bottom Profile on Static and Dynamic Characteristics of Journal Bearings

The purpose of this paper is to numerically study the effect of texture bottom profile on static, dynamic, and stability performance parameters of hydrodynamic journal bearings. The different performance parameters of square textured journal bearings with different bottom profiles are numerically investigated and compared with those of smooth journal bearing. There are five bottom profiles of this square texture: flat, curved, isosceles triangle (T1), oblique triangle (T2), and oblique triangle (T3). The static and dynamic coefficients are calculated by solving the steady-state Reynolds equation and the perturbation equations with FDM numerical technique. The performance characteristics under different texture distribution, depth, and bottom profiles are studied, and the current numerical results show that the selection of texture parameters is crucial to improve the static, dynamic, and stability performances of hydrodynamic journal bearing. Meanwhile, it is also found that the square texture with a flat bottom profile has a higher improvement in the values of static performance parameters in comparison to those other bottom profiles. Moreover, the simulation results indicate that the dynamic and stability performances improvement of textured journal bearing is also significant, especially when the eccentricity ratio is smaller.

High-performance SiC MOSFET embedded heterojunction diode with electric field protection region

In this study, we proposed high-performance SiC MOSFET embedded heterojunction diode (HJD) with an electric field protection (EFP) region and analyzed it using a Sentaurus TCAD simulation. The proposed device features an HJD positioned at the trench side wall in the middle of the JFET region and a highly doped EFP region under the P+ polysilicon to features excellent static performance and high reliability. The simulation results revealed that the maximum oxide electric field (EMOX) and the Baliga’s figure-of-merit (BFOM) improved by 54% and 12%, respectively, compared with those of conventional SiC MOSFETs (C-MOSFETs). In addition, the EFP region suppressed the DIBL effect and leakage current in the HJD interface sufficiently. The HJD suppressed the bipolar degradation of the PiN body diode effectively due to its low VF (1.75 V). In addition, the proposed device demonstrated superior reverse-recovery characteristics, thereby improving trr and Qrr by 35% and 57%, respectively, compared to the corresponding values in C-MOSFET. Moreover, the input capacitance (CISS) was reduced by 17.5%, and CGD was reduced by 96%. Therefore, the high-frequency figure-of-merit (HFOM) improved by a factor of 25.8 in terms of RON × CGD. As a result, the proposed device is a promising structure for high-frequency and high-reliability applications.

Experimental Study on Static Performance of Deployable Bridge Based on Cable-Strengthened Scissor Structures

The deployable bridge based on scissor structures is one of the effective methods to quickly restore traffic after natural and man-made disasters. Scissor structures have the advantages of high storage rate, lightweight, and convenient storage and transportation. However, when scissor structures are used as load-bearing structures, their stiffness and bearing capacity are low. In this study, a three-dimensional deployable bridge based on the cable-strengthened scissor structures was proposed. In addition to rapid expansion, steel cables were used to strengthen scissor structures to improve the stiffness and bearing capacity. Besides, the static loading comparative tests on cable-strengthened scissor structures and traditional scissor structures (cable-free scissor structures) were performed. The results show that the stiffness of the cable-free scissor structure is small, the bending moment of members is large, and the stress distribution is uneven. The stiffness of cable-strengthened scissor structure is significantly improved; the bending moment of members is significantly reduced; and the stress distribution in the member section is more uniform. It is proved that cables can be used to improve the stiffness and load-bearing capacity of scissor structures without affecting the deployability.

Numerical and experimental study on the static performance of externally pressurized thrust bearings lubricated with refrigerant gases

Purpose Oil-free heat pumps that use the system refrigerant gases as lubricants are preferred for thermal management in future space applications. This study aims to numerically and experimentally investigate the static performance of externally pressurized thrust bearings lubricated with refrigerant gases. Design/methodology/approach The refrigerant gases R22, R410A and CO2 were chosen as the research objects, while N2 was used for comparison. Computational fluid dynamics was used to solve the full 3 D Navier–Stokes equations to determine the load capacity, static stiffness and static pressure distribution in the bearing film. The numerical results were experimentally verified. Findings The results showed that the refrigerant-gas-lubricated thrust bearings had a lower load capacity than the N2-lubricated bearings, but they presented a higher static stiffness when the bearing clearance was less than 9 µm. Compared with the N2-lubricated bearings, the optimal static stiffness of the R22- and CO2-lubricated bearings increased by more than 46% and more than 21%, respectively. The numerical and experimental results indicate that a small bearing clearance would be preferable when designing externally pressurized gas thrust bearings lubricated with the working medium of heat pump systems for space applications. Originality/value The findings of this study can serve as a basis for the further investigation of refrigerant gases as lubricants in heat pump systems, as well as for the future design of such gas bearings in heat pump systems for space applications.