In this study,a fully coupled hydromechanical model within the extended finite element method(XFEM)-based cohesive zone method(CZM)is employed to investigate the simultaneous height growth behavior of multi-cluster hy...In this study,a fully coupled hydromechanical model within the extended finite element method(XFEM)-based cohesive zone method(CZM)is employed to investigate the simultaneous height growth behavior of multi-cluster hydraulic fractures in layered porous reservoirs with modulus contrast.The coupled hydromechanical model is first verified against an analytical solution and a laboratory experiment.Then,the fracture geometry(e.g.height,aperture,and area)and fluid pressure evolutions of multiple hydraulic fractures placed in a porous reservoir interbedded with alternating stiff and soft layers are investigated using the model.The stress and pore pressure distributions within the layered reservoir during fluid injection are also presented.The simulation results reveal that stress umbrellas are easily to form among multiple hydraulic fractures’tips when propagating in soft layers,which impedes the simultaneous height growth.It is also observed that the impediment effect of soft layer is much more significant in the fractures suppressed by the preferential growth of adjoining fractures.After that,the combined effect of in situ stress ratio and fracturing spacing on the multi-fracture height growth is presented,and the results elucidate the influence of in situ stress ratio on the height growth behavior depending on the fracture spacing.Finally,it is found that the inclusion of soft layers changes the aperture distribution of outmost and interior hydraulic fractures.The results obtained from this study may provide some insights on the understanding of hydraulic fracture height containment observed in filed.展开更多
The gradual increase in shipping and drilling activities in the Arctic regions has resulted in the increased importance of studying the structural safety of polar ships in various ice conditions.Rafted ice refers to a...The gradual increase in shipping and drilling activities in the Arctic regions has resulted in the increased importance of studying the structural safety of polar ships in various ice conditions.Rafted ice refers to a type of accumulated and overlapped sea ice;it is driven by external forces,such as wind and waves,and may exert high loads on ships and threaten their structural safety.Therefore,the properties of rafted ice and the construction of numerical models should be studied before exploring the interaction and collision between ships and rafted ice.Based on the nonlinear finite-element method,this paper introduces the cohesive element model for the simulation of rafted ice.The interaction between ships and rafted ice is studied,and the ice force of the hull is obtained.Numerical simulation results are compared with model test findings,and the effectiveness of the cohesive element method in the construction of the model of rafted ice materials is verified.On this basis,a multilayer rafted ice model is constructed,and its interaction with the ship is studied.The research unveils that rafted ice parts impede crack generation and slow down crack propagation to a certain extent.展开更多
Reduced graphene oxide(rGO)enhanced B_(4)C ceramics was prepared by SPS sintering,the enhancement effect of rGO on the microstructure and mechanical properties of composites was studied through experiments and numeric...Reduced graphene oxide(rGO)enhanced B_(4)C ceramics was prepared by SPS sintering,the enhancement effect of rGO on the microstructure and mechanical properties of composites was studied through experiments and numerical simulation.The results show that the composite with 2wt%rGO has the best comprehensive mechanical properties.Compared with pure boron carbide,vickers hardness and bending strength are increased by 4.8%and 21.96%,respectively.The fracture toughness is improved by 25.71%.The microstructure observation shows that the improvement of mechanical properties is mainly attributed to the pullout and bridge mechanism of rGO and the crack deflection.Based on the cohesive force finite element method,the dynamic crack growth process of composites was simulated.The energy dissipation of B_(4)C/rGO multiphase ceramics during crack propagation was calculated and compared with that of pure boron carbide ceramics.The results show that the fracture energy dissipation can be effectively increased by adding graphene.展开更多
Fracture geometry is important when stimulating low-permeability reservoirs for natural gas or oil production. The geological layer(GL) properties and contrasts in in-situ stress are the two most important parameters ...Fracture geometry is important when stimulating low-permeability reservoirs for natural gas or oil production. The geological layer(GL) properties and contrasts in in-situ stress are the two most important parameters for determination of the vertical fracture growth extent and containment in layered rocks. However, the method for assessing the cumulative impact on growth in height remains ambiguous. In this research, a 3D model based on the cohesive zone method is used to simulate the evolution of hydraulic fracture(HF) height in layered reservoirs. The model incorporates fluid flow and elastic deformation, considering the friction between the contacting fracture surfaces and the interaction between fracture components. First, an analytical solution that was readily available was used to validate the model. Afterwards, a quantitative analysis was performed on the combined impacts of the layer interface strength, coefficient of interlayer stress difference, and coefficient of vertical stress difference.The results indicate that the observed fracture height geometries can be categorized into three distinct regions within the parametric space: blunted fracture, crossed fracture, and T-shaped fracture.Furthermore, the results explained the formation mechanism of the low fracture height in the deep shale reservoir of the Sichuan Basin, China, as well as the distinction between fracture network patterns in mid-depth and deep shale reservoirs.展开更多
Indirect fracturing in the roof of broken soft coal seams has been demonstrated to be a feasible technology.In this work,the No.5 coal seam in the Hancheng block was taken as the research object.Based on the findings ...Indirect fracturing in the roof of broken soft coal seams has been demonstrated to be a feasible technology.In this work,the No.5 coal seam in the Hancheng block was taken as the research object.Based on the findings of true triaxial hydraulic fracturing experiments and field pilot under this technology and the cohesive element method,a 3D numerical model of indirect fracturing in the roof of broken soft coal seams was established,the fracture morphology propagation and evolution law under different conditions was investigated,and analysis of main controlling factors of fracture parameters was conducted with the combination weight method,which was based on grey incidence,analytic hierarchy process and entropy weight method.The results show that“士”-shaped fractures,T-shaped fractures,cross fractures,H-shaped fractures,and“干”-shaped fractures dominated by horizontal fractures were formed.Different parameter combinations can form different fracture morphologies.When the coal seam permeability is lower and the minimum horizontal principal stress difference between layers and fracturing fluid injection rate are both larger,it tends to form“士”-shaped fractures.When the coal seam permeability and minimum horizontal principal stress between layers and perforation position are moderate,cross fractures are easily generated.Different fracture parameters have different main controlling factors.Engineering factors of perforation location,fracturing fluid injection rate and viscosity are the dominant factors of hydraulic fracture shape parameters.This study can provide a reference for the design of indirect fracturing in the roof of broken soft coal seams.展开更多
As the first safety barrier of nuclear reactors,zirconium alloy cladding tubes have attracted extensive attention because of its good mechanical properties.The strength and ductility of zirconium alloy are of great si...As the first safety barrier of nuclear reactors,zirconium alloy cladding tubes have attracted extensive attention because of its good mechanical properties.The strength and ductility of zirconium alloy are of great significance to the service process of cladding tubes,while brittle hydrides precipitate and thus deteriorate the overall performance.Based on the cohesive finite element method,the effects of cohesive strength,interfacial characteristics,and hydrides geometric characteristics on the strength and ductility of two-phase material(zirconium alloy with hydrides)are numerically simulated.The results show that the fracture behavior is significantly affected by the cohesive strength and that the overall strength and ductility are sensitive to the cohesive strength of the zirconium alloy.Furthermore,the interface is revealed to have prominent effects on the overall fracture behavior.When the cohesive strength and fracture energy of the interface are higher than those of the hydride phase,fracture initiates in the hydrides,which is consistent with the experimental phenomena.In addition,it is found that the number density and arrangement of hydrides play important roles in the overall strength and ductility.Our simulation provides theoretical support for the performance analysis of hydrogenated zirconium alloys during nuclear reactor operation.展开更多
文摘In this study,a fully coupled hydromechanical model within the extended finite element method(XFEM)-based cohesive zone method(CZM)is employed to investigate the simultaneous height growth behavior of multi-cluster hydraulic fractures in layered porous reservoirs with modulus contrast.The coupled hydromechanical model is first verified against an analytical solution and a laboratory experiment.Then,the fracture geometry(e.g.height,aperture,and area)and fluid pressure evolutions of multiple hydraulic fractures placed in a porous reservoir interbedded with alternating stiff and soft layers are investigated using the model.The stress and pore pressure distributions within the layered reservoir during fluid injection are also presented.The simulation results reveal that stress umbrellas are easily to form among multiple hydraulic fractures’tips when propagating in soft layers,which impedes the simultaneous height growth.It is also observed that the impediment effect of soft layer is much more significant in the fractures suppressed by the preferential growth of adjoining fractures.After that,the combined effect of in situ stress ratio and fracturing spacing on the multi-fracture height growth is presented,and the results elucidate the influence of in situ stress ratio on the height growth behavior depending on the fracture spacing.Finally,it is found that the inclusion of soft layers changes the aperture distribution of outmost and interior hydraulic fractures.The results obtained from this study may provide some insights on the understanding of hydraulic fracture height containment observed in filed.
基金The National Natural Science Foundation of China(Grant Nos.52192693,52192690,51979051,51979056 and U20A20327)the National Key Research and Development Program of China(Grant No.2021YFC2803400)。
文摘The gradual increase in shipping and drilling activities in the Arctic regions has resulted in the increased importance of studying the structural safety of polar ships in various ice conditions.Rafted ice refers to a type of accumulated and overlapped sea ice;it is driven by external forces,such as wind and waves,and may exert high loads on ships and threaten their structural safety.Therefore,the properties of rafted ice and the construction of numerical models should be studied before exploring the interaction and collision between ships and rafted ice.Based on the nonlinear finite-element method,this paper introduces the cohesive element model for the simulation of rafted ice.The interaction between ships and rafted ice is studied,and the ice force of the hull is obtained.Numerical simulation results are compared with model test findings,and the effectiveness of the cohesive element method in the construction of the model of rafted ice materials is verified.On this basis,a multilayer rafted ice model is constructed,and its interaction with the ship is studied.The research unveils that rafted ice parts impede crack generation and slow down crack propagation to a certain extent.
基金by the National Natural Science Foundation of China(52002299)。
文摘Reduced graphene oxide(rGO)enhanced B_(4)C ceramics was prepared by SPS sintering,the enhancement effect of rGO on the microstructure and mechanical properties of composites was studied through experiments and numerical simulation.The results show that the composite with 2wt%rGO has the best comprehensive mechanical properties.Compared with pure boron carbide,vickers hardness and bending strength are increased by 4.8%and 21.96%,respectively.The fracture toughness is improved by 25.71%.The microstructure observation shows that the improvement of mechanical properties is mainly attributed to the pullout and bridge mechanism of rGO and the crack deflection.Based on the cohesive force finite element method,the dynamic crack growth process of composites was simulated.The energy dissipation of B_(4)C/rGO multiphase ceramics during crack propagation was calculated and compared with that of pure boron carbide ceramics.The results show that the fracture energy dissipation can be effectively increased by adding graphene.
基金the funding provided by the National Natural Science Foundation of China (No. 52334001, No. 42372337)National Key Research and Development Program of China (No. SQ2023YFE0100562)+1 种基金CPET Industrialization Fund Project (No. CPETCY202417)Natural Science Starting Project of SWPU (No. 2022QHZ009)。
文摘Fracture geometry is important when stimulating low-permeability reservoirs for natural gas or oil production. The geological layer(GL) properties and contrasts in in-situ stress are the two most important parameters for determination of the vertical fracture growth extent and containment in layered rocks. However, the method for assessing the cumulative impact on growth in height remains ambiguous. In this research, a 3D model based on the cohesive zone method is used to simulate the evolution of hydraulic fracture(HF) height in layered reservoirs. The model incorporates fluid flow and elastic deformation, considering the friction between the contacting fracture surfaces and the interaction between fracture components. First, an analytical solution that was readily available was used to validate the model. Afterwards, a quantitative analysis was performed on the combined impacts of the layer interface strength, coefficient of interlayer stress difference, and coefficient of vertical stress difference.The results indicate that the observed fracture height geometries can be categorized into three distinct regions within the parametric space: blunted fracture, crossed fracture, and T-shaped fracture.Furthermore, the results explained the formation mechanism of the low fracture height in the deep shale reservoir of the Sichuan Basin, China, as well as the distinction between fracture network patterns in mid-depth and deep shale reservoirs.
基金National Natural Science Foundation of China(11672333).
文摘Indirect fracturing in the roof of broken soft coal seams has been demonstrated to be a feasible technology.In this work,the No.5 coal seam in the Hancheng block was taken as the research object.Based on the findings of true triaxial hydraulic fracturing experiments and field pilot under this technology and the cohesive element method,a 3D numerical model of indirect fracturing in the roof of broken soft coal seams was established,the fracture morphology propagation and evolution law under different conditions was investigated,and analysis of main controlling factors of fracture parameters was conducted with the combination weight method,which was based on grey incidence,analytic hierarchy process and entropy weight method.The results show that“士”-shaped fractures,T-shaped fractures,cross fractures,H-shaped fractures,and“干”-shaped fractures dominated by horizontal fractures were formed.Different parameter combinations can form different fracture morphologies.When the coal seam permeability is lower and the minimum horizontal principal stress difference between layers and fracturing fluid injection rate are both larger,it tends to form“士”-shaped fractures.When the coal seam permeability and minimum horizontal principal stress between layers and perforation position are moderate,cross fractures are easily generated.Different fracture parameters have different main controlling factors.Engineering factors of perforation location,fracturing fluid injection rate and viscosity are the dominant factors of hydraulic fracture shape parameters.This study can provide a reference for the design of indirect fracturing in the roof of broken soft coal seams.
基金Supported by National Key Research and Development Plan of China(Grant No.2018YFC0808800)National Natural Science Foundation of China(Grant No.51875398)China Postdoctoral Science Foundation(Grant No.2021M693240).
文摘As the first safety barrier of nuclear reactors,zirconium alloy cladding tubes have attracted extensive attention because of its good mechanical properties.The strength and ductility of zirconium alloy are of great significance to the service process of cladding tubes,while brittle hydrides precipitate and thus deteriorate the overall performance.Based on the cohesive finite element method,the effects of cohesive strength,interfacial characteristics,and hydrides geometric characteristics on the strength and ductility of two-phase material(zirconium alloy with hydrides)are numerically simulated.The results show that the fracture behavior is significantly affected by the cohesive strength and that the overall strength and ductility are sensitive to the cohesive strength of the zirconium alloy.Furthermore,the interface is revealed to have prominent effects on the overall fracture behavior.When the cohesive strength and fracture energy of the interface are higher than those of the hydride phase,fracture initiates in the hydrides,which is consistent with the experimental phenomena.In addition,it is found that the number density and arrangement of hydrides play important roles in the overall strength and ductility.Our simulation provides theoretical support for the performance analysis of hydrogenated zirconium alloys during nuclear reactor operation.
