The goaf may face a series of deformation and settlement problems when the room-pillar mining method is used to excavate ore and pillars in the deep strata.To this end,a deep room-pillar model with two levels was made...The goaf may face a series of deformation and settlement problems when the room-pillar mining method is used to excavate ore and pillars in the deep strata.To this end,a deep room-pillar model with two levels was made,and the pillar recovery was carried out.The instantaneous deformation responses during the pillars recovery and the long-term settlements after the pillar recovery were analyzed.During the pillar recovery,different regions of surrounding rocks suffer from different dynamic disturbances which can be divided into three types,including(I)the combined action of blasting disturbance and unloading disturbance,(II)the sequential action of blasting disturbance and unloading disturbance,and(III)the action of unloading disturbance.After the pillar recovery,the settlement above the first recovering pillar is the largest,which has a traction effect on the settlement in other areas.The settlement process can be divided into two stages,stable displacement stage and unstable displacement stage.When the pillar-room system undergoes the unstable displacement stage,rock spalling and further cascading collapse will occur.展开更多
Step motors, compared to other drive systems, are low-cost and easy to use devices. However, despite these undeniable advantages, they are characterized by some critical running conditions, due to the loss of synchron...Step motors, compared to other drive systems, are low-cost and easy to use devices. However, despite these undeniable advantages, they are characterized by some critical running conditions, due to the loss of synchronization between the stator＇s magnetic field and the rotor. In order to theoretically investigate such a behavior, several complex mathematical models have been developed, which require several parameters to be defined. For most step motors, such parameters cannot be easily drawn from their data-sheets; on the contrary, in this paper the authors refer to a simplified electro-mechanical model where the most of the parameters are known from data-sheets. The dependence between electrical and mechanical quantities can be investigated by an experimental point of view. At this aim, a specific novel test rig has been designed and developed for either static or dynamic characteristics measurement of small size step motors. In particular, the test rig allow to measure rotor＇s angular position, motor＇s torque, currents flowing in the motor＇s phases. The paper ends with the report of the results of several experimental tests, carried-out on a small-size motor in different running conditions, and with some preliminary remarks on the basis of the measures analysis.展开更多
Herein symmetrical four-legged suspension lunar lander was used as the research object, the six-degree-of-freedom dynamic model was built and the model of the lunar soil friction coefficient was improved. For the low-...Herein symmetrical four-legged suspension lunar lander was used as the research object, the six-degree-of-freedom dynamic model was built and the model of the lunar soil friction coefficient was improved. For the low-gravity simulation on objects outside earth for future work, the law of dynamic similarity for detectors was deduced. A new method was proposed for simulating the low-gravity field on the surface of objects outside earth, which was achieved by changing initial conditions of the landing by the probe and by subsequent treatment of experimental data. The prototype tested the limitation of this method was verified. It is shown that the prototypes of detectors can be used in detectors low-gravity simulation test with this method, and equipments are simple and operationally effective. This method can be used for later lunar exploration, and low-gravity simulations on extraterrestrial objects.展开更多
The semi-circular bend(SCB) dynamic fracture toughness test is simulated using discrete element models. The influence of the frictional boundary condition, constitutive law and specimen thickness on the test measureme...The semi-circular bend(SCB) dynamic fracture toughness test is simulated using discrete element models. The influence of the frictional boundary condition, constitutive law and specimen thickness on the test measurements is investigated. It is found that friction between loading plates and the rock specimen affects the test results. Therefore, friction must be carefully considered to obtain accurate measurements. The simulation results also show that in contrast to the 2D model in which a rate-dependent cohesive law must be introduced, 3D models with a rate-independent law can produce good results. Furthermore, the study suggests that test measurements are seriously affected by specimen thickness; thus, full 3D modeling is required for simulation of the SCB test.展开更多
基金Projects(11972378,41630642)supported by the National Natural Science Foundation of China。
文摘The goaf may face a series of deformation and settlement problems when the room-pillar mining method is used to excavate ore and pillars in the deep strata.To this end,a deep room-pillar model with two levels was made,and the pillar recovery was carried out.The instantaneous deformation responses during the pillars recovery and the long-term settlements after the pillar recovery were analyzed.During the pillar recovery,different regions of surrounding rocks suffer from different dynamic disturbances which can be divided into three types,including(I)the combined action of blasting disturbance and unloading disturbance,(II)the sequential action of blasting disturbance and unloading disturbance,and(III)the action of unloading disturbance.After the pillar recovery,the settlement above the first recovering pillar is the largest,which has a traction effect on the settlement in other areas.The settlement process can be divided into two stages,stable displacement stage and unstable displacement stage.When the pillar-room system undergoes the unstable displacement stage,rock spalling and further cascading collapse will occur.
文摘Step motors, compared to other drive systems, are low-cost and easy to use devices. However, despite these undeniable advantages, they are characterized by some critical running conditions, due to the loss of synchronization between the stator＇s magnetic field and the rotor. In order to theoretically investigate such a behavior, several complex mathematical models have been developed, which require several parameters to be defined. For most step motors, such parameters cannot be easily drawn from their data-sheets; on the contrary, in this paper the authors refer to a simplified electro-mechanical model where the most of the parameters are known from data-sheets. The dependence between electrical and mechanical quantities can be investigated by an experimental point of view. At this aim, a specific novel test rig has been designed and developed for either static or dynamic characteristics measurement of small size step motors. In particular, the test rig allow to measure rotor＇s angular position, motor＇s torque, currents flowing in the motor＇s phases. The paper ends with the report of the results of several experimental tests, carried-out on a small-size motor in different running conditions, and with some preliminary remarks on the basis of the measures analysis.
基金supported by the National Natural Science Foundation of China(Grant No.51105196)Natural Science Foundation of Jiangsu Province(Grant No.BK2011733)
文摘Herein symmetrical four-legged suspension lunar lander was used as the research object, the six-degree-of-freedom dynamic model was built and the model of the lunar soil friction coefficient was improved. For the low-gravity simulation on objects outside earth for future work, the law of dynamic similarity for detectors was deduced. A new method was proposed for simulating the low-gravity field on the surface of objects outside earth, which was achieved by changing initial conditions of the landing by the probe and by subsequent treatment of experimental data. The prototype tested the limitation of this method was verified. It is shown that the prototypes of detectors can be used in detectors low-gravity simulation test with this method, and equipments are simple and operationally effective. This method can be used for later lunar exploration, and low-gravity simulations on extraterrestrial objects.
基金supported by the Australian Research Council(Grant No.DE130100457)State Key Laboratory of Hydraulics and Mountain River Engineering(SKHL)(Grant No.SKHL1407)the National Natural Science Foundation of China(Grant Nos.41202207,51204112 and 2015JY0045)
文摘The semi-circular bend(SCB) dynamic fracture toughness test is simulated using discrete element models. The influence of the frictional boundary condition, constitutive law and specimen thickness on the test measurements is investigated. It is found that friction between loading plates and the rock specimen affects the test results. Therefore, friction must be carefully considered to obtain accurate measurements. The simulation results also show that in contrast to the 2D model in which a rate-dependent cohesive law must be introduced, 3D models with a rate-independent law can produce good results. Furthermore, the study suggests that test measurements are seriously affected by specimen thickness; thus, full 3D modeling is required for simulation of the SCB test.
