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The hydraulic support equipment is usually used to support the roof in underground mining. During this process, the support bears frequent impact load, which greatly weakens its dynamic stability. To study the dynamic response characteristics of the support, when it bears the impact load at the top beam and shield beam, the numerical model of the support is established using ADAMS and the equivalent variable stiffness damping system was used to replace the column system. An active static load is applied vertically above the top beam to simulate the roof gravity force, and the impact load is applied downward perpendicular to the top beam and shield beam. Based on the above model, the dynamic response of the key parts of the support, when different impact loads are applied to the top beam and shield beam, and the influence of offset loading on the stability of the support are analyzed. Then, when considering asymmetric bracing conditions, the dynamic characteristics of hydraulic support under impact load are discussed by setting different initial support forces. The results show that when under a single impact load, the load variation coefficient of the front column reaches 1.41, which is the most sensitive to the impact load at the front end of the top beam. When the top beam and shield beam bear the impact load at the same time, the support hinge joint response more violently to the impact load acting on the top beam end and the upper area of the shield beam, and the maximum load change coefficient is 0.64, which greatly affects the overall stability of the hydraulic support. When the support bears to lateral torque, the weakening effect of offset load acting on different positions on the bearing performance of the support is the same, and the magnitude of offset load is positively correlated with the weakening effect. When considering the different initial load ratios (ILR) of the column, it is found that the hinge joint of top beam and shield beam is the most sensitive to the change of ILR, and the insufficient initial support of the front column has the greatest weakening effect on the bearing performance of the support. The research results can help to optimize the structure of the support shield support and improve the bearing reliability of the hydraulic support.

Spherical and flaky particles are mixed during hard rock tunneling. In particular, flakey particles are difficult to load, resulting in conveying machines that have difficultly operating efficiently. Based on the characteristics of flakey particles and the present conveying structures, such as star wheels, three new conveying structures are introduced in this paper, and the parameters related to the conveying ability are evaluated with theoretical analysis. Then, the flow and trajectory of particles under different conveying structures and the difference in their working capabilities were investigated with the help of the discrete element method (DEM). Finally, conveying machines with different conveying structures are made with 3D printing technology and experiments for validation of the conveying ability are performed. The results show that the conveying structures can be divided into two categories: those with a rotational speed proportional to the loading rate and those with the opposite condition. The propulsion status has a stable loading phase with a long time period relative to the non-propulsion status. The findings can be used to guide conveying machine designs, and they can be helpful for the enhancement of the working ability in conveying particles with flakey shapes. [ABSTRACT FROM AUTHOR]

The selective catalytic oxidation (SCO) is an effective method for removing slipped high-concentration ammonia from NH3-fueled engine exhaust gas. Herein a novel bifunctional catalyst was synthesized by mechanically mixing sulfated Ce/ZrO2 (Ce/ZrO2-S) with a small fraction of Pt/Al2O3 (Pt 0.1 wt.%) for SCO of NH3. As expected, the introduction of a small amount of Pt/Al2O3 significantly improved NH3 conversion ability of Ce/ZrO2-S catalysts toward low-temperature direction. When the mass ratio of Pt/Al2O3 to Ce/ZrO2-S was 7.5% (the corresponding mixed catalyst was denoted as P@CZS-7.5), T90 temperature was 312 °C. More importantly, P@CZS-7.5 catalyst exhibited a much better N2 selectivity (> 96%) in a wide temperature range (320 ~ 450 °C). H2-TPR results revealed that the addition of a trace amount of Pt/Al2O3 significantly led to a distinct shift of reduction temperature peak toward low-temperature direction, thereby greatly improved the low-temperature redox performance of mixed catalysts. Furthermore, NH3-TPD and BET results showed that P@CZS-7.5 catalyst exhibited a similar NH3 adsorption capacity to Ce/ZrO2-S catalyst, while the former had a relatively higher specific surface area than the latter. It was considered as a crucial factor for P@CZS-7.5 catalyst maintaining superior N2 selectivity in high-concentration NH3 (5000 ppm) removal processes. In situ DRIFTS results indicated that P@CZS-7.5 catalyst followed the internal selective catalytic reduction (i-SCR) mechanism in NH3-SCO reactions. [ABSTRACT FROM AUTHOR]

In view of the problem of poor coupling adaptability and easy rib spalling of coal wall in large mining height comprehensive mining, based on the effective inhibition effect of face guard mechanism on coal wall spalling, the structural characteristics and bearing capacity of different structural forms of the face guard mechanism are compared and analyzed. According to the surrounding rock adaptability of the face guard mechanism, established a numerical analysis model for rigid-flexible coupling of the face guard mechanism under different spalling forms. In order to accurately simulate the stress state of the protective mechanism, a variable stiffness spring damping system is used to replace the hydraulic cylinder. The load-bearing performance and response characteristics of the face guard mechanism under rib spalling coupling conditions were analyzed by applying uniform normal load and impact load to the face guard. The findings indicated that, the integral-type face guard mechanism has a better effect on suppressing rib spalling. When the face guard mechanism bears the static load of the coal wall, the entire response process of the face guard jack can be divided into three stages: initial support, increasing resistance bearing, constant resistance bearing; both the impact load position and the coupling state of the rib spalling will affect the characteristics of force transmission at the face guard mechanism's hinge point, the hinge point between the extensible canopy and the primary face guard is most sensitive to biased load. The research results can provide reference for optimizing the face guard mechanism of large mining height hydraulic support and improving the reliability of coal wall support. [ABSTRACT FROM AUTHOR]