Thermal shock damage in deep shale hydraulic fracturing can impact fracture propagation behaviors,potentially leading to the formation of complex fractures and enhancing gas recovery.This study introduces a thermalhyd...Thermal shock damage in deep shale hydraulic fracturing can impact fracture propagation behaviors,potentially leading to the formation of complex fractures and enhancing gas recovery.This study introduces a thermalhydraulic-mechnical(THM)coupled fracture propagation model relying on the phase field method to simulate thermal shock-induced fracturing in the deep shale considering dynamic temperature conditions.The validity of this model is confirmed through comparison of experimental and numerical results concerning the THM-coupled stress field and thermal cracking.Special attention is paid to the interaction of thermal shock-induced fractures in deep shale that contains weak planes.The results indicate that thermal shock-induced stress significantly amplifies the tensile stress range and deteriorates rock strength,resulting in a multi-point failure pattern within a fracture.The thermal shock damage degree is closely related to the fracture cooling efficiency,suggesting that considering downhole temperature conditions in THM-coupled fracture stress field calculations is advisable.Thermal shock can activate pre-existing natural fractures and enhance the penetration ability of hydraulic fractures,thereby leading to a fracture network.展开更多
Study on crack propagation process of brittle rock is of most significance for cracking-arrest design and cracking-network optimization in rock engineering.Phase-field model(PFM)has advantages of simplicity and high c...Study on crack propagation process of brittle rock is of most significance for cracking-arrest design and cracking-network optimization in rock engineering.Phase-field model(PFM)has advantages of simplicity and high convergence over the common numerical methods(e.g.finite element method,discrete element method,and particle manifold method)in dealing with three-dimensional and multicrack problems.However,current PFMs are mainly used to simulate mode-I(tensile)crack propagation but difficult to effectively simulate mode-II(shear)crack propagation.In this paper,a new mixed-mode PFM is established to simulate both mode-I and mode-II crack propagation of brittle rock by distinguishing the volumetric elastic strain energy and deviatoric elastic strain energy in the total elastic strain energy and considering the effect of compressive stress on mode-II crack propagation.Numerical solution method of the new mixed-mode PFM is proposed based on the staggered solution method with self-programmed subroutines UMAT and HETVAL of ABAQUS software.Three examples calculated using different PFMs as well as test results are presented for comparison.The results show that compared with the conventional PFM(which only simulates the tensile wing crack but not mode-II crack propagation)and the modified mixed-mode PFM(which has difficulty in simulating the shear anti-wing crack),the new mixed-mode PFM can successfully simulate the whole trajectories of mixed-mode crack propagation(including the tensile wing crack,shear secondary crack,and shear anti-wing crack)and mode-II crack propagation,which are close to the test results.It can be further extended to simulate multicrack propagation of anisotropic rock under multi-field coupling loads.展开更多
A phase-field model(PFM)coupling with phase field,flow field and diffuse equation is presented for simulating isothermal dendrite growth of a nickel-copper alloy under a forced flow.Based on the finite difference meth...A phase-field model(PFM)coupling with phase field,flow field and diffuse equation is presented for simulating isothermal dendrite growth of a nickel-copper alloy under a forced flow.Based on the finite difference method with uniform grid,the C programming code is implemented to complete the phase-field simulations.The simulation results indicate that the interfacial morphology,the symmetry of dendrite formation,the tip growth velocity and the concentration distribution are strongly influenced by the fluid flow.展开更多
A novel method is proposed to dynamically control the path following of a ground Ackerman steering robot to avoid a collision.The method consists of collision prediction module,collision avoidance module and global pa...A novel method is proposed to dynamically control the path following of a ground Ackerman steering robot to avoid a collision.The method consists of collision prediction module,collision avoidance module and global path following module.The elliptic repulsive potential field method（ER-PFM）and the enhanced vector polar histogram method（VPH＋）based on the Ackerman steering model are proposed to predict the collision in a dynamic environment.The collision avoidance is realized by the proposed cost function and speed control law.The global path following process is achieved by pure pursuit.Experiments show that the robot can fulfill the dynamic path following task safely and efficiently using the proposed method.展开更多
基金paper is funded by the CNOOC Science and Technology Project(KJGG2022-0701)the National Natural Science Foundation of China(51904258,51874250).
文摘Thermal shock damage in deep shale hydraulic fracturing can impact fracture propagation behaviors,potentially leading to the formation of complex fractures and enhancing gas recovery.This study introduces a thermalhydraulic-mechnical(THM)coupled fracture propagation model relying on the phase field method to simulate thermal shock-induced fracturing in the deep shale considering dynamic temperature conditions.The validity of this model is confirmed through comparison of experimental and numerical results concerning the THM-coupled stress field and thermal cracking.Special attention is paid to the interaction of thermal shock-induced fractures in deep shale that contains weak planes.The results indicate that thermal shock-induced stress significantly amplifies the tensile stress range and deteriorates rock strength,resulting in a multi-point failure pattern within a fracture.The thermal shock damage degree is closely related to the fracture cooling efficiency,suggesting that considering downhole temperature conditions in THM-coupled fracture stress field calculations is advisable.Thermal shock can activate pre-existing natural fractures and enhance the penetration ability of hydraulic fractures,thereby leading to a fracture network.
基金supports by National Natural Science Foundation of China(Grant Nos.51874351 and 52078495)Excellent Postdoctoral Innovative Talents Project of Hunan Province,China(Grant No.2020RC2001).
文摘Study on crack propagation process of brittle rock is of most significance for cracking-arrest design and cracking-network optimization in rock engineering.Phase-field model(PFM)has advantages of simplicity and high convergence over the common numerical methods(e.g.finite element method,discrete element method,and particle manifold method)in dealing with three-dimensional and multicrack problems.However,current PFMs are mainly used to simulate mode-I(tensile)crack propagation but difficult to effectively simulate mode-II(shear)crack propagation.In this paper,a new mixed-mode PFM is established to simulate both mode-I and mode-II crack propagation of brittle rock by distinguishing the volumetric elastic strain energy and deviatoric elastic strain energy in the total elastic strain energy and considering the effect of compressive stress on mode-II crack propagation.Numerical solution method of the new mixed-mode PFM is proposed based on the staggered solution method with self-programmed subroutines UMAT and HETVAL of ABAQUS software.Three examples calculated using different PFMs as well as test results are presented for comparison.The results show that compared with the conventional PFM(which only simulates the tensile wing crack but not mode-II crack propagation)and the modified mixed-mode PFM(which has difficulty in simulating the shear anti-wing crack),the new mixed-mode PFM can successfully simulate the whole trajectories of mixed-mode crack propagation(including the tensile wing crack,shear secondary crack,and shear anti-wing crack)and mode-II crack propagation,which are close to the test results.It can be further extended to simulate multicrack propagation of anisotropic rock under multi-field coupling loads.
基金the National Natural Science Foundation of China(Nos.10964004 and 50804019)the Natural Science Foundation of Gansu Province (No.1014RJZA003)
文摘A phase-field model(PFM)coupling with phase field,flow field and diffuse equation is presented for simulating isothermal dendrite growth of a nickel-copper alloy under a forced flow.Based on the finite difference method with uniform grid,the C programming code is implemented to complete the phase-field simulations.The simulation results indicate that the interfacial morphology,the symmetry of dendrite formation,the tip growth velocity and the concentration distribution are strongly influenced by the fluid flow.
基金Supported by the National Natural Science Foundation of China(91420203)
文摘A novel method is proposed to dynamically control the path following of a ground Ackerman steering robot to avoid a collision.The method consists of collision prediction module,collision avoidance module and global path following module.The elliptic repulsive potential field method（ER-PFM）and the enhanced vector polar histogram method（VPH＋）based on the Ackerman steering model are proposed to predict the collision in a dynamic environment.The collision avoidance is realized by the proposed cost function and speed control law.The global path following process is achieved by pure pursuit.Experiments show that the robot can fulfill the dynamic path following task safely and efficiently using the proposed method.
