The R2O-SiO2-B2O3 glass has emerged as an important material due to its high performance. During the process of glass melting, copious amounts of bubbles can be produced. The bubbles are considered as serious defects of the R2O-SiO2-B2O3 glass and can induce negative effects on properties of glass, such as optical uniformity, mechanical property, etc. The influence of the fining agents on the properties of R2O-SiO2-B2O3 glass such as density, refractive index, and transmissivity were systematically studied. The results indicate that fining agents had influence on the density of the R2O-SiO2-B2O3 glass, fining agents do not have obvious impact on the refractive index and transmissivity of R2O-SiO2-B2O3 glass.
A high-precision ground microgravity simulation environment serves as the prerequisite and key to studying landing dynamics in microgravity environments. However, the microgravity level accuracy in traditional ground simulation tests is difficult to guarantee and fails to precisely depict the collision behavior of massive spacecraft. To solve such problems, this paper takes the microgravity simulation system based on quasi-zero stiffness (QZS) mechanism as the research object, and simulates a high-precision and high-level microgravity environment. Then, the collision contact force model of the planar foot and high elastic body rubber is established, the landing dynamics research under different microgravity environments is carried out, the influence of different microgravity environments on the landing behavior of large mass spacecraft is analyzed in depth, and ground microgravity simulation experiments are carried out. The results show that the microgravity simulation level reaches 10−4 g, the error of gravity compensation for each working condition is not more than 4.22%, and the error of sinking amount is not more than 4.61%, which verifies the superior compensation performance of the QZS mechanism and the accuracy of the dynamic model.
Abstract The driving mechanism of the microvibration of aerostatic bearings is still unclear. Although there are several interpretations, none of them is conclusive. The difficulty lies in the complicated information concealed beneath the turbulence flow. To this end, the proper orthogonal decomposition (POD) method was systematically implemented in the aerostatic bearing flow field analysis in the present study, and some new findings have been proposed. First, the accuracy of our large eddy simulation (LES) has been validated through quantitative comparison with the experimental reference. Then, the mode decomposition has been conducted at a circumferential symmetry plane and the influence of supply pressure has been uncovered. It turns out that the vortices within the recess dominate the flowfield when the supply energy Ps=3atm, while the shear flow in the vicinity of the recess inlet becomes intense and corresponding vortices become predominant in the case of Ps=5atm. Meanwhile, the 4atm case could be regarded as an intermediate state between the 3atm and 5atm cases and both of the above flow features could be observed. Eventually, the influences of film thickness have also been discussed when Ps=4atm. Different from the case of h=10μm, the vortices near the recess outlet could be detected when the film thickness is increased to 20μm. The control of corresponding flow structures might be helpful for the microvibration suppression.
With the development of space technology, the functions of lunar vehicles are constantly enriched, and the structure is constantly complicated, which puts forward more stringent requirements for its ground micro-low-gravity simulation test technology. This paper puts forward a high-precision and high-dynamic landing buffer test method based on the principle of magnetic quasi-zero stiffness. Firstly, the micro-low-gravity simulation system for the lunar vehicle was designed. The dynamic model of the system and a position control method based on fuzzy PID parameter tuning were established. Then, the dynamic characteristics of the system were analyzed through joint simulation. At last, a prototype of the lunar vehicle's vertical constant force support system was built, and a micro-low-gravity landing buffer test was carried out. The results show that the simulation results were in good agreement with the test results. The sensitivity of the system was better than 0.1%, and the constant force deviation was 0.1% under landing impact conditions. The new method and idea are put forward to improve the micro-low-gravity simulation technology of lunar vehicles.
Low-frequency vibration is the core problem that hinders high-precision equipment's positioning accuracy and control accuracy. However, the response of a nonlinear electrical-mechanical coupling system is nonlinear and quite complicated under the ambient random vibrating environment. This paper presents a vibration suppression method through NARX (Nonlinear autoregressive with external input) neural network and its controller. The experiment platform is designed, and its dynamic model is obtained through system identification. The Neural network direct dynamic inverse control system is established, and the controller is designed. Both the simulation and experimental results show that the NARX identification and the controller can effectively achieve vibration suppression, and the experiment's highest vibration rejection ratio is 90.8%. The vibration suppression technology can be extensively applied to low-frequency vibration systems, such as aerospace equipment and high-precision equipment.
This paper proposes a quasi-zero stiffness (QZS) isolator based on an inclined trapezoidal beam to explore its advantages in low-frequency passive vibration isolation. The nonlinear stiffness of the inclined trapezoidal beam due to the buckling effect is investigated through finite element simulation, and a linear positive stiffness spring is connected in parallel to form a QZS isolator with high-static and low-dynamic stiffness performance. The natural frequency of the isolator in the QZS region is simulated and analyzed, and the dynamic response of the QZS isolator under different damping ratios, excitation and load conditions is explored. The prototype of the QZS isolator was manufactured, and a static compression experiment was conducted to obtain its nonlinear stiffness. The dynamic experiment results verify the correctness of the simulation conclusions. The simulation and experimental data demonstrate that the QZS isolator has the characteristics of lower initial isolation frequency compared with the equivalent linear isolator. The proposed QZS isolator has an initial isolation frequency of 2.91 Hz and achieves a 90% isolation efficiency at 7.02 Hz. The proposed QZS isolator has great application prospects and can provide a reference for optimizing low-frequency or ultra-low-frequency isolators.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)