The two-rotational-degrees-of-freedom（2R） parallel mechanism（PM） with two continuous rotational axes（CRAs） has a simple kinematic model.It is therefore easy to implement trajectory planning,parameter calibration...The two-rotational-degrees-of-freedom（2R） parallel mechanism（PM） with two continuous rotational axes（CRAs） has a simple kinematic model.It is therefore easy to implement trajectory planning,parameter calibration,and motion control,which allows for a variety of application prospects.However,no systematic analysis on structural constraints of the 2R-PM with two CRAs has been performed,and there are only a few types of 2R-PM with two CRAs.Thus,a theory regarding the type synthesis of the 2R-PM with two CRAs is systematically established.First,combining the theories of reciprocal screw and space geometry,the spatial arrangement relationships of the constraint forces applied to the moving platform by the branches are explored,which give the 2R-PM two CRAs.The different distributions of the constraint forces in each branch are also studied.On the basis of the obtained structural constraints of branches,and considering the geometric relationships of constraint forces in each branch,the appropriate kinematic chains are constructed.Through the reasonable configuration of branch kinematic chains corresponding to every structural constraint,a series of new 2R-PMs with two CRAs are finally obtained.展开更多
Ball-drop fracturing is a kind of technology that is commonly used for multistage fracturing of shale gas horizontal wells.At present,the ball injector cannot satisfy the operation demands of large bore and small spac...Ball-drop fracturing is a kind of technology that is commonly used for multistage fracturing of shale gas horizontal wells.At present,the ball injector cannot satisfy the operation demands of large bore and small spacing fracturing of shale gas wells due to its disadvantages,such as a small size of fracturing ball,a limited number of balls,complicated structure and poor applicability.In this paper,a new type of automatic ball injector with rotating plate and large bore was designed.There is a ball storage at the upper part of the ball injector and a ball injecting mechanism inside the pedestal at the lower part.And the ball injecting mechanism is controlled by the drive motor to inject the balls one by one.Then,collision analysis was carried out on its ball injecting process by using finite element method(FEM).Finally,simulation and prototype tests were conducted by using the arbitrary Lagrangian-Eulerian(ALE)mesh adaption method and the coupled smoothed particle hydrodynamics method(FEM-SPH).And the following research results were obtained.First,in the process of ball collision,the maximum equivalent stress,equivalent plastic strain and displacement are generated at the edge of the rotating plate.The maximum stress is about 600 MPa,which is less than the yield strength of 42CrMo(930 MPa),so the strength requirement is satisfied with a certain safety margin.Second,the prototype successfully passes the continuous ball injecting test of 12-stage fracturing process with the ball diameter of 64-108 mm and the ball contrast of 4 mm.In conclusion,this automatic ball injector with rotating plate and large bore is advantageous with simple operation and wide applicability and can effectively address the needs of multistage fracturing of shale gas horizontal wells.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.51405425)Hebei Provincial Natural Science Foundation of China(Grant No.E2014203255)Independent Research Program Topics of Young Teachers in Yanshan University,China(Grant No.13LGA001)
文摘The two-rotational-degrees-of-freedom（2R） parallel mechanism（PM） with two continuous rotational axes（CRAs） has a simple kinematic model.It is therefore easy to implement trajectory planning,parameter calibration,and motion control,which allows for a variety of application prospects.However,no systematic analysis on structural constraints of the 2R-PM with two CRAs has been performed,and there are only a few types of 2R-PM with two CRAs.Thus,a theory regarding the type synthesis of the 2R-PM with two CRAs is systematically established.First,combining the theories of reciprocal screw and space geometry,the spatial arrangement relationships of the constraint forces applied to the moving platform by the branches are explored,which give the 2R-PM two CRAs.The different distributions of the constraint forces in each branch are also studied.On the basis of the obtained structural constraints of branches,and considering the geometric relationships of constraint forces in each branch,the appropriate kinematic chains are constructed.Through the reasonable configuration of branch kinematic chains corresponding to every structural constraint,a series of new 2R-PMs with two CRAs are finally obtained.
基金supported by the National Major Science and Technology Project“Study on coalbed methane recovery equipment and technologies”(No.2016ZX05042-004)Graduate Student Innovation Project Funding Project“Study on the design of pneumatic technologies and equipment for unloading liquids and producing gas through a preset pipe string”(No.YCX2018058).
文摘Ball-drop fracturing is a kind of technology that is commonly used for multistage fracturing of shale gas horizontal wells.At present,the ball injector cannot satisfy the operation demands of large bore and small spacing fracturing of shale gas wells due to its disadvantages,such as a small size of fracturing ball,a limited number of balls,complicated structure and poor applicability.In this paper,a new type of automatic ball injector with rotating plate and large bore was designed.There is a ball storage at the upper part of the ball injector and a ball injecting mechanism inside the pedestal at the lower part.And the ball injecting mechanism is controlled by the drive motor to inject the balls one by one.Then,collision analysis was carried out on its ball injecting process by using finite element method(FEM).Finally,simulation and prototype tests were conducted by using the arbitrary Lagrangian-Eulerian(ALE)mesh adaption method and the coupled smoothed particle hydrodynamics method(FEM-SPH).And the following research results were obtained.First,in the process of ball collision,the maximum equivalent stress,equivalent plastic strain and displacement are generated at the edge of the rotating plate.The maximum stress is about 600 MPa,which is less than the yield strength of 42CrMo(930 MPa),so the strength requirement is satisfied with a certain safety margin.Second,the prototype successfully passes the continuous ball injecting test of 12-stage fracturing process with the ball diameter of 64-108 mm and the ball contrast of 4 mm.In conclusion,this automatic ball injector with rotating plate and large bore is advantageous with simple operation and wide applicability and can effectively address the needs of multistage fracturing of shale gas horizontal wells.
