Static and dynamic force performance of two types of space truss structures i.e. square pyramid space truss（SPST） and diagonal on square pyramid space truss（DSPST）, are studied to determine the effect of stiffness...Static and dynamic force performance of two types of space truss structures i.e. square pyramid space truss（SPST） and diagonal on square pyramid space truss（DSPST）, are studied to determine the effect of stiffness of their lower supporting members. A simplified model for the supporting columns and the equivalent spring mass system are presented. Furthermore, the feasibility of the simplified model is demonstrated through theoretical analysis and examples of comparative analysis of the simplified model with the entire model. Meanwhile, from the elastic analysis under frequently occurring earthquakes and elasto-plastic analysis under seldom occurring earthquakes subjected to TAFT and EL-Centro seismic oscillation it is shown that the simplified method can be encompassed in the results from the normal model. It also showed good agreement between the two methods, as well as greatly improved the computational efficiency. This study verified that the dynamic effect of the supporting structures was under considered in space truss design in the past. The method proposed in the paper has important significance for other space truss structures.展开更多
During molten salt cleaning of remanufactured 27SiMn hydraulic support column,oxidation occurs on the surface of metal substrate.This results in a change of the surface roughness of metal substrate after cleaning,whic...During molten salt cleaning of remanufactured 27SiMn hydraulic support column,oxidation occurs on the surface of metal substrate.This results in a change of the surface roughness of metal substrate after cleaning,which affects subsequent remanufacturing process.To decrease the effect is very important.This paper analyzed the oxidation mechanism of molten salt cleaning,explored the oxidation reaction that occurred during cleaning,and determined the key process parameters of cleaning that affecting oxidation reaction.By using central composite experimental design method and taking surface roughness variation of 27SiMn steel samples before and after molten salt cleaning as response variable to optimize the key process parameters,the optimal parameters of molten salt for cleaning remanufactured 27SiMn hydraulic support column could be obtained.The results show that the oxidation reaction of cleaning paint dirt can protect metal substrate from oxidation to a certain extent,and cleaning temperature and placement depth of metal substrate have a direct impact on the degree of oxidation reaction.When the cleaning temperature is 300℃and the distance between paint dirt and free surface of molten salt is 0.5 times the height of the parts,the surface roughness variation is minimal.Therefore,the cleaning quality will be improved under such parameters.展开更多
The abandoned roadways(ARs)in front of the longwall face catastrophic instability will seriously hamper mining progress,which is a complicated process related to the stress environment,the roadway section,and the mech...The abandoned roadways(ARs)in front of the longwall face catastrophic instability will seriously hamper mining progress,which is a complicated process related to the stress environment,the roadway section,and the mechanical properties of the surrounding rock.The cusp catastrophe theory is employed to establish a state identification model for the irregular coal pillar-roof system(CPRS)formed by the ARs and re-mining entries.To begin,the state discrimination equation(4p)for the gradual CPRS is derived,and the critical value at which the system transitions into an unstable state under quasi-static conditions is determined.The results indicated that when 16.49 m≤L≤22.63 m(L denotes the equivalent span of the intersection roof)and 0<R_(e)≤2.61 m(Re denotes the width of the elastic zone within the triangular coal pillar),the triangular CPRS is inherently unstable.Similarly,for trapezoidal CPRS configurations where the length Lm(the span of the right-angled trapezoid roof in the propulsion direction)varies from 4.0 to 12.60 m,the system is unstable as well.Subsequently,the model was further enhanced by accounting for the impact of the P.(advance stress increment load),where a critical criterion for the catastrophic instability of the CPRS was proposed,which represented the external energy required to transition the CPRS from an unstable state to catastrophic instability in diferent mining stages.After that,the stability degree of the irregular coal pillar was categorized,and a coupling zoning control technology was applied to CPR operations.Field monitoring results demonstrated the effectiveness of the zoning control technology,providing valuable guidance for similar mining practices.展开更多
基金National Technology Research and Development Program of the Ministry of Science and Technology of China under Grant No.2015BAK17B03National Natural Science Foundation of China(General Program)under Grant No.51278152
文摘Static and dynamic force performance of two types of space truss structures i.e. square pyramid space truss（SPST） and diagonal on square pyramid space truss（DSPST）, are studied to determine the effect of stiffness of their lower supporting members. A simplified model for the supporting columns and the equivalent spring mass system are presented. Furthermore, the feasibility of the simplified model is demonstrated through theoretical analysis and examples of comparative analysis of the simplified model with the entire model. Meanwhile, from the elastic analysis under frequently occurring earthquakes and elasto-plastic analysis under seldom occurring earthquakes subjected to TAFT and EL-Centro seismic oscillation it is shown that the simplified method can be encompassed in the results from the normal model. It also showed good agreement between the two methods, as well as greatly improved the computational efficiency. This study verified that the dynamic effect of the supporting structures was under considered in space truss design in the past. The method proposed in the paper has important significance for other space truss structures.
基金supported by the National Natural Science Foundation of China(No.51375278)。
文摘During molten salt cleaning of remanufactured 27SiMn hydraulic support column,oxidation occurs on the surface of metal substrate.This results in a change of the surface roughness of metal substrate after cleaning,which affects subsequent remanufacturing process.To decrease the effect is very important.This paper analyzed the oxidation mechanism of molten salt cleaning,explored the oxidation reaction that occurred during cleaning,and determined the key process parameters of cleaning that affecting oxidation reaction.By using central composite experimental design method and taking surface roughness variation of 27SiMn steel samples before and after molten salt cleaning as response variable to optimize the key process parameters,the optimal parameters of molten salt for cleaning remanufactured 27SiMn hydraulic support column could be obtained.The results show that the oxidation reaction of cleaning paint dirt can protect metal substrate from oxidation to a certain extent,and cleaning temperature and placement depth of metal substrate have a direct impact on the degree of oxidation reaction.When the cleaning temperature is 300℃and the distance between paint dirt and free surface of molten salt is 0.5 times the height of the parts,the surface roughness variation is minimal.Therefore,the cleaning quality will be improved under such parameters.
基金support from the Major Project of Regional Joint Foundation of China(Grant No.U21A20107)the Natural Science Foundation of China(Grant No.52074239)+1 种基金Xinjiang Uygur Autono-mous Region Key R&D Project Task Special-Department and Department Linkage Project(Grant No.2022B01051)the Xinjiang Uygur Autonomous Region Tianchi Introduction Plan(Grant No.2024XGYTCYC03).
文摘The abandoned roadways(ARs)in front of the longwall face catastrophic instability will seriously hamper mining progress,which is a complicated process related to the stress environment,the roadway section,and the mechanical properties of the surrounding rock.The cusp catastrophe theory is employed to establish a state identification model for the irregular coal pillar-roof system(CPRS)formed by the ARs and re-mining entries.To begin,the state discrimination equation(4p)for the gradual CPRS is derived,and the critical value at which the system transitions into an unstable state under quasi-static conditions is determined.The results indicated that when 16.49 m≤L≤22.63 m(L denotes the equivalent span of the intersection roof)and 0<R_(e)≤2.61 m(Re denotes the width of the elastic zone within the triangular coal pillar),the triangular CPRS is inherently unstable.Similarly,for trapezoidal CPRS configurations where the length Lm(the span of the right-angled trapezoid roof in the propulsion direction)varies from 4.0 to 12.60 m,the system is unstable as well.Subsequently,the model was further enhanced by accounting for the impact of the P.(advance stress increment load),where a critical criterion for the catastrophic instability of the CPRS was proposed,which represented the external energy required to transition the CPRS from an unstable state to catastrophic instability in diferent mining stages.After that,the stability degree of the irregular coal pillar was categorized,and a coupling zoning control technology was applied to CPR operations.Field monitoring results demonstrated the effectiveness of the zoning control technology,providing valuable guidance for similar mining practices.
