Grid fin translation mechanism is the key actuator of trajectory and attitude control in reentry flight of the reusable launch vehicle. The kinetic characteristic of translation mechanism is investigated experimentally. An experimental device and experimental schemes comprise position test, transient state test and frequency test are set up. The linear displacement of servo piston rod and the angle displacement of rudder shaft are measured by the displacement sensors. Firstly, the cause of linear displacement abrupt change in position test and angle displacement vibration in transient state test is studied. Furthermore, small shaft turning angle frequency test in low, mid and high frequency are tested and the angle displacement signal delay are comparativly analyzed. The clearances in kinematic pairs are considered as the important affecting factor of kinetic characteristic of translation mechanism and its influencing mechanism is preliminarily proposed. The results provide research object and experimental fundament for farther dynamic analysis and optimal design of transmission mechanism.
An experimental apparatus was designed to test the pivoting friction moment of annular friction disc under either constant normal force and variable normal force. The experimental results demonstrated the applicability of the classical pivoting friction model under the continuous variable normal contact force, and showed that the rotary velocity affects the properties of the pivoting friction. By considering the Stribeck effect of the local friction at a contact point, a theoretical model was proposed for the pivoting friction. Good agreement between proposed theoretical and experimental results sheds light on the physical mechanism underlying the pivoting friction.
The turbulence data observed by eddy covariance system combined with soil temperature and soil volumetric water content (VWC) data from Xilinhot National Climate Observatory were used to analyze respiration process and its key climatic influencing factors of the semi-arid stipa grassland ecosystem in Xilin Gol during the growing season from 2010 to 2012. The applicability of four different ecosystem respiration models over this ecosystem was compared, including three multiplication models and a Q10 model. Based on this research, the interannual variability of net ecosystem exchange (NEE), ecosystem respiration (Reco) and gross primary productivity (GPP) were discussed. The respiration was affected by soil temperature and soil water content, in which soil water content was an important limiting factor. The precipitation in 2010 and 2011 was less than normal, so this ecosystem suffered from different degrees of drought stress. The respiration rate increased significantly with soil water content in the range of 12%?20%, while it was not sensitive to the change of soil water content in the range of <12% and >20%. In 2012, when the precipitation was abundant, respiration rate was more correlated with the trend of soil temperature. The fitting results indicated that Q10 model had better performance (R2 = 0.64) than other three models, and the cumulative total ecosystem respiration during growing season in these three years simulated by the Q10 model was 157.32, 138.75 and 246.32 gC/m2. The total amount of NEE was −110.28, −68.79 and −310.05 gC/m2, while the total amount of GPP was 267.52, 207.57 and 555.85 gC/m2. The effect of drought stress on photosynthesis was greater than that of respiration. Therefore, the inter-annual difference of net carbon exchange due to drought stress was more obvious than that of total primary productivity and respiration.
