To obtain the best geometric size of VL sealing ring and improve its sealing performance, this paper carried out multi-objective optimization research on VL sealing ring by Isight software. Firstly, according to the working principle and geometric size of the VL seal ring, determined the constraint conditions, established the optimization objective equation, and given the value range of the structural parameters was. Then, verified the validity of the approximate model by fitting the radial basis neural network model provided. Finally, analyzed the sensitivity of influencing factors of oil film thickness at lip, and established the optimization module by NSGA-II multi-objective optimization algorithm. As a result, the best geometric size is obtained from multi-objective optimization, and the structure of VL seal ring has achieved the goal of more suitable high speed dynamic seal and longer service life.
The surrounding rock of roadways in underground coal mines will lose its stability or even collapse under gas explosions, especially roadways surrounded by coals. The dynamic mechanical properties of coals were tested in order to investigate the dynamic response of coals under gas explosions. The static mechanical properties of coals were also tested as comparison. It is found that the dynamic stress-strain curves showed no obvious pore compaction stage comparing with uniaxial loading. The dynamic compression strength and the elastic modulus are obviously larger than those obtained in the static mechanical properties test, and the dynamic strain shows an obvious hysteresis phenomenon. The ultimate strain and absorbed energy increased linearly with increase of the strain rate. With the increase of dynamic loading, the fragment size of coal cores decreased obviously. The results could provide a reference for the antiexplosion design of the coal roadway.
Abstract. In order to evaluate the teaching quality of the badminton teachers and improve the teaching quality, in this article, the fuzzy analytic hierarchy process is used to establish badminton teaching quality evaluation system. We evaluate the teaching quality from four aspects such as teaching attitude, teaching content, teaching method and teaching effect and establish a three layer hierarchical structure. After constructing a fuzzy consistency matrix, we obtain the weights of the indicators in all layers and the combined weights of the indicators in the bottom layer. The comprehensive indicator calculated from the combined weight can reflect the teaching quality of the badminton teacher. By using the theory of fuzzy sets, the weights of the indicators can be determined so that the evaluation result can be more scientific. This system offsets the shortage of the badminton education teaching quality evaluation, which can improve the badminton education and its teaching quality.
Gas explosions or coal and gas outbursts can cause transient destruction of combined coal–rock, and the dynamic mechanical response of combined coal–rock masses plays a key role in accident failure, but we now know little about the dynamic mechanical responses of combined coal–rock. In this article, we selected three rocks (limestone, shale, sandstone) and two coals (bituminous coal and anthracite coal) to form combined coal–rock, and analyze their dynamic mechanical properties by using the SHPB system. We find that the dynamic compressive strength and elastic modulus of combined rock–coal are lower than the average value of single rock and coal, while the ultimate strain and strain rate of combined coal–rock are higher than the average values of single rock and coal. Compressive strength and elastic modulus of the combined body increase gradually with increasing confining pressure, and the strain decreases accordingly. The dynamic stress–strain curve demonstrates an obvious double-peak at high strain rate (85.55 s−1 and above in the present work), while there is no obvious double-peak of the curve at low strain rate. Dynamic compressive strength of combined coal–rock body increases significantly with increasing confining pressure at low strain rate, but it increases more smoothly at higher strain rate. The elastic modulus also increases with increasing confining pressure, and it seems to be stable as confining pressure increases at low strain rate. The ultimate strain decreases gradually with increasing confining pressure but more gently compared with that at low strain rate. Besides, longitudinal fractures of combined coal–rock bodies include penetrating fractures, partially penetrating fractures, and interrupted fractures stopped at the coal–rock interface. The dynamic mechanical response of combined coal–rock is of guiding significance for maintaining the stability of the roadway and formulating the support measures for the roadway.
The fragile cover of rocket not only has the characteristics of sealing and high-temperature resistance, but also can break according to preset scratches when hited by the rocket’s head. In this paper, a penetrating glass fiber fragile cover with scratches is designed, and six structural types are set up with the number of layers laid by glass fiber as independent variables. Based on Hashin failure criterion and damage evolution law, the finite element method is used to simulate the process of rocket breaking through fragile cover and gas flow impinging fragile cover. The results show that the fragile cover will break along the preset scratches, which does not produce debris to interfere with rocket launch. As the number of glass fiber cloth layers increases, the Mises stress of the rocket’s head increased when the fragile cover broken. The impact of the gas flow on the fragile cover of the adjacent pipe is not uniformly distributed, and the maximum value of the Mises stress appears at the scratches of the cover body. As the number of glass layers decreases, the failure index value of the fragile cover under the impact of gas flow increases. The research provides a reference for the design of rocket glass fiber fragile cover.
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