This paper presents a three-dimensional fully hydro-mechanical coupled distinct element study on fault reactivation and induced seismicity due to hydraulic fracturing injection and subsequent backflow process,based on...This paper presents a three-dimensional fully hydro-mechanical coupled distinct element study on fault reactivation and induced seismicity due to hydraulic fracturing injection and subsequent backflow process,based on the geological data in Horn River Basin,Northeast British Columbia,Canada.The modeling results indicate that the maximum magnitude of seismic events appears at the fracturing stage.The increment of fluid volume in the fault determines the cumulative moment and maximum fault slippage,both of which are essentially proportional to the fluid volume.After backflow starts,the fluid near the joint intersection keeps flowing into the critically stressed fault,rather than backflows to the wellbore.Although fault slippage is affected by the changes of both pore pressure and ambient rock stress,their contributions are different at fracturing and backflow stages.At fracturing stage,pore pressure change shows a dominant effect on induced fault slippage.While at backflow stage,because the fault plane is under a critical stress state,any minor disturbance would trigger a fault slippage.The energy analysis indicates that aseismic deformation takes up a majority of the total deformation energy during hydraulic fracturing.A common regularity is found in both fracturing-and backflow-induced seismicity that the cumulative moment and maximum fault slippage are nearly proportional to the injected fluid volume.This study shows some novel insights into interpreting fracturing-and backflowinduced seismicity,and provides useful information for controlling and mitigating seismic hazards due to hydraulic fracturing.展开更多
Backflow of migrant workers is an essential part of rural surplus labor transfer. 425 valid samples from Haicheng,Taian and Xiuyan cities of Liaoning Province were analyzed and place selection and influencing factors ...Backflow of migrant workers is an essential part of rural surplus labor transfer. 425 valid samples from Haicheng,Taian and Xiuyan cities of Liaoning Province were analyzed and place selection and influencing factors were discussed. The study indicated that in backflow migrant workers,43. 16% returned to counties and towns,while 56. 84% returned to rural areas. Place selection was significantly influenced by years of migrant work,training,times of migration,migration distance,age,land area in hometown,and living preference.展开更多
A novel variational wave function defined as a Jastrow factor multiplying a backflow transformed Slater determinant was developed for A=3 nuclei.The Jastrow factor and backflow transformation were represented by artif...A novel variational wave function defined as a Jastrow factor multiplying a backflow transformed Slater determinant was developed for A=3 nuclei.The Jastrow factor and backflow transformation were represented by artificial neural networks.With this newly developed wave function,variational Monte Carlo calculations were carried out for3H and3He nuclei starting from a nuclear Hamiltonian based on the leadingorder pionless effective field theory.The obtained ground-state energy and charge radii were successfully benchmarked against the results of the highly-accurate hypersphericalharmonics method.The backflow transformation plays a crucial role in improving the nodal surface of the Slater determinant and,thus,providing accurate ground-state energy.展开更多
It takes flavonoid extraction rate as indicator and adopts the method of orthogonal experiment to study process of total flavonoid in Trollius chinensis through ultrasonic wave assisted extraction, microwave assisted ...It takes flavonoid extraction rate as indicator and adopts the method of orthogonal experiment to study process of total flavonoid in Trollius chinensis through ultrasonic wave assisted extraction, microwave assisted extraction and backflow extraction, as well as optimization of process parameter. The result indicates that in terms of extraction efficiency, microwave extraction method is better than ultrasonic radiation extraction method, which is better than backflow extraction method. Optimal process parameter through backflow extraction is： backflow temperature 60℃, fluid material ratio 1：20, ethanol density 65%, backflow time 60min; optimal process parameter through ultrasonic wave assisted extraction is： ultrasonic radiation temperature 70℃, fluid material ratio 1：20, ethanol density 65%, ultrasonic wave radiation time 45rain; optimal process parameter of microwave assisted extraction is： microwave radiation temperature 60℃, fluid material ratio 1：20, ethanol density 75%, microwave radiation time 45min.展开更多
For mitigating the hazards of slurry flowing back into the casing after liner cementing,the deficiency of slurry backflow prevention structure of current liner hangers at home and aboard was analyzed in this paper.The...For mitigating the hazards of slurry flowing back into the casing after liner cementing,the deficiency of slurry backflow prevention structure of current liner hangers at home and aboard was analyzed in this paper.Then,a structurally new casing plug,i.e.,a semi-hollow casing plug was designed and developed.And it,combined with the hanger,was tested on site.And the following research results were obtained.First,the deficiency of the slurry backflow prevention structure of liner hanger,is that the locking mechanism on the drill pipe plug is damaged before it reaches the casing plug and matches with each other.Second,the inner bore of the semi-hollow casing plug is designed as a bend hole,which has a hollow round hole in its upper part and a solid column in its lower part.Third,during the cementing operation,the drill pipe plug enters into the semi-hollow casing plug once it gets to the position of hanger.And it is stuck at the bend and cannot go down anymore.Consequently it is integrated with the casing plug as a whole part.Fourth,when the shear pin goes down to the setting seat through the casing string under the force of drilling fluid,the solid column at the lower part of the semi-hollow casing plug is squeezed into the inner hole of the seat.In this situation,the backflow of cement slurry can be prevented only by using sealing elements and locking device on the casing plug instead of by using drill pipe plug.Fifth,field tests show that the cement top of test wells is only 24 m higher than the designed value while that of offset wells is 59 m higher.Obviously,the former is 50%less than the latter.In conclusion,this newly developed semi-hollow casing plug matches well with hangers,having no negative effects on cementing operation,so the cement top after cementing can be well controlled.展开更多
Backflow is a counterintuitive phenomenon that is widely predicted in the fields of quantum physics and optics.In contrast to quantum backflow,which is challenging to be observed,optical backflow is prevailing in stru...Backflow is a counterintuitive phenomenon that is widely predicted in the fields of quantum physics and optics.In contrast to quantum backflow,which is challenging to be observed,optical backflow is prevailing in structured lights.For instance,the azimuthal backflow has been recently observed experimentally in optics via the superposition of two beams carrying different orbital angular momentum topological charges.In this paper,we investigate the spin-momentum characteristics of the superimposed orbital angular momentum beams to confirm the optical azimuthal backflow,which is closely related to off-axis vortex flow and super-oscillations.Furthermore,we extend our study to axial backflow,characterized by a reversed axial energy flow in tightly focused cylindrical vector vortex beams.Then,we explore the application of optical backflow in the manipulation of dipolar nanoparticles.By optimizing material parameters,we achieve on-demand control of optical forces in both azimuthal and axial backflow scenarios.Our findings provide in-depth insights into the optical backflow phenomena with potential applications in optical manipulations.展开更多
Axial flow pumps are widely used in water conservancy,petrochemical and agricultural industries.Efficient operation is crucial for energy conservation and emission reduction.Improving efficiency under severe condition...Axial flow pumps are widely used in water conservancy,petrochemical and agricultural industries.Efficient operation is crucial for energy conservation and emission reduction.Improving efficiency under severe conditions requires studying the internal flow of axial-flow pumps,particularly at low flow rates where backflow vortices form near the impeller inlet.This study investigates the unsteady flow characteristics of backflow vortices at different flow rates in an axial-flow pump.Results show that backflow vortices form when the flow rate decreases to 0.59Q_(d).As the flow rate further declines,the backflow vortex progresses upstream,contracts,and rebounds.The flow rate range is divided into three stages:Stage Ⅰ with no backflow vortex,stage Ⅱ with initial vortex development extending upstream and relatively fragmented,and stage Ⅲ with vortex contraction and rebound forming a more coherent structure.Besides,backflow vortices induce significant pressure fluctuations and velocity oscillations with the primary frequency being 0.5 fb.They exhibit a three-dimensional spiral motion involving changes in axial length,self-rotation,and revolution around the pump axis,with an angular velocity of approximately half the impeller’s rotational speed.This work enhances insights into backflow vortex behaviors,which is essential for optimizing pump design and improving operational stability in challenging environments.展开更多
为解决传统双有源桥(dual active bridge,DAB)变换器在宽输入电压工况下无法同时实现零回流功率和全局软开关的问题,提出了一种基于LCL-T谐振型DAB变换器的改进三重移相(improved triple-phase-shift,ITPS)调制策略。首先,对LCL-T谐振型...为解决传统双有源桥(dual active bridge,DAB)变换器在宽输入电压工况下无法同时实现零回流功率和全局软开关的问题,提出了一种基于LCL-T谐振型DAB变换器的改进三重移相(improved triple-phase-shift,ITPS)调制策略。首先,对LCL-T谐振型DAB变换器的功率传输特性和软开关特性进行分析,推导出不同电压转换比下无回流功率的控制量表达式。然后,利用LCL谐振网络的对称特性和考虑开关管寄生电容影响下的零电压开关(zero voltage switching,ZVS)约束条件,推导出全工况连续、形式统一、计算量小的ITPS调制控制量表达式,并对调制轨迹进行优化。最后,设计了一台1 kW的实验样机进行调制策略有效性的验证。实验结果表明,与传统调制策略相比,ITPS调制策略具有较宽输入电压范围、无回流功率及全局软开关的优势。展开更多
提出1种基于LCL全-半桥谐振变换器的增强型扩展移相调制策略,在保证所有开关均实现零电压开关ZVS(zero voltage switching)的前提下,消除了一次侧回流功率;同时二次侧半桥结构使变换器在低功率条件下具有更高的性价比。利用基波近似法...提出1种基于LCL全-半桥谐振变换器的增强型扩展移相调制策略,在保证所有开关均实现零电压开关ZVS(zero voltage switching)的前提下,消除了一次侧回流功率;同时二次侧半桥结构使变换器在低功率条件下具有更高的性价比。利用基波近似法进行变换器的稳态分析,从而得到功率模型及ZVS条件。最后利用PSIM软件进行仿真,搭建1台300 W的实验样机,由实验结果验证上述理论的可行性。展开更多
基金supported by the Key Innovation Team Program of Innovation Talents Promotion Plan by Ministry of Science and Technology of China(Grant No.2016RA4059)National Natural Science Foundation of China(Grant Nos.41672268 and 41772286)。
文摘This paper presents a three-dimensional fully hydro-mechanical coupled distinct element study on fault reactivation and induced seismicity due to hydraulic fracturing injection and subsequent backflow process,based on the geological data in Horn River Basin,Northeast British Columbia,Canada.The modeling results indicate that the maximum magnitude of seismic events appears at the fracturing stage.The increment of fluid volume in the fault determines the cumulative moment and maximum fault slippage,both of which are essentially proportional to the fluid volume.After backflow starts,the fluid near the joint intersection keeps flowing into the critically stressed fault,rather than backflows to the wellbore.Although fault slippage is affected by the changes of both pore pressure and ambient rock stress,their contributions are different at fracturing and backflow stages.At fracturing stage,pore pressure change shows a dominant effect on induced fault slippage.While at backflow stage,because the fault plane is under a critical stress state,any minor disturbance would trigger a fault slippage.The energy analysis indicates that aseismic deformation takes up a majority of the total deformation energy during hydraulic fracturing.A common regularity is found in both fracturing-and backflow-induced seismicity that the cumulative moment and maximum fault slippage are nearly proportional to the injected fluid volume.This study shows some novel insights into interpreting fracturing-and backflowinduced seismicity,and provides useful information for controlling and mitigating seismic hazards due to hydraulic fracturing.
文摘Backflow of migrant workers is an essential part of rural surplus labor transfer. 425 valid samples from Haicheng,Taian and Xiuyan cities of Liaoning Province were analyzed and place selection and influencing factors were discussed. The study indicated that in backflow migrant workers,43. 16% returned to counties and towns,while 56. 84% returned to rural areas. Place selection was significantly influenced by years of migrant work,training,times of migration,migration distance,age,land area in hometown,and living preference.
基金Supported by National Key R&D Program of China (018YFA0404400)National Natural Science Foundation of China (12070131001,11875075,11935003,11975031,12141501)。
文摘A novel variational wave function defined as a Jastrow factor multiplying a backflow transformed Slater determinant was developed for A=3 nuclei.The Jastrow factor and backflow transformation were represented by artificial neural networks.With this newly developed wave function,variational Monte Carlo calculations were carried out for3H and3He nuclei starting from a nuclear Hamiltonian based on the leadingorder pionless effective field theory.The obtained ground-state energy and charge radii were successfully benchmarked against the results of the highly-accurate hypersphericalharmonics method.The backflow transformation plays a crucial role in improving the nodal surface of the Slater determinant and,thus,providing accurate ground-state energy.
文摘It takes flavonoid extraction rate as indicator and adopts the method of orthogonal experiment to study process of total flavonoid in Trollius chinensis through ultrasonic wave assisted extraction, microwave assisted extraction and backflow extraction, as well as optimization of process parameter. The result indicates that in terms of extraction efficiency, microwave extraction method is better than ultrasonic radiation extraction method, which is better than backflow extraction method. Optimal process parameter through backflow extraction is： backflow temperature 60℃, fluid material ratio 1：20, ethanol density 65%, backflow time 60min; optimal process parameter through ultrasonic wave assisted extraction is： ultrasonic radiation temperature 70℃, fluid material ratio 1：20, ethanol density 65%, ultrasonic wave radiation time 45rain; optimal process parameter of microwave assisted extraction is： microwave radiation temperature 60℃, fluid material ratio 1：20, ethanol density 75%, microwave radiation time 45min.
文摘For mitigating the hazards of slurry flowing back into the casing after liner cementing,the deficiency of slurry backflow prevention structure of current liner hangers at home and aboard was analyzed in this paper.Then,a structurally new casing plug,i.e.,a semi-hollow casing plug was designed and developed.And it,combined with the hanger,was tested on site.And the following research results were obtained.First,the deficiency of the slurry backflow prevention structure of liner hanger,is that the locking mechanism on the drill pipe plug is damaged before it reaches the casing plug and matches with each other.Second,the inner bore of the semi-hollow casing plug is designed as a bend hole,which has a hollow round hole in its upper part and a solid column in its lower part.Third,during the cementing operation,the drill pipe plug enters into the semi-hollow casing plug once it gets to the position of hanger.And it is stuck at the bend and cannot go down anymore.Consequently it is integrated with the casing plug as a whole part.Fourth,when the shear pin goes down to the setting seat through the casing string under the force of drilling fluid,the solid column at the lower part of the semi-hollow casing plug is squeezed into the inner hole of the seat.In this situation,the backflow of cement slurry can be prevented only by using sealing elements and locking device on the casing plug instead of by using drill pipe plug.Fifth,field tests show that the cement top of test wells is only 24 m higher than the designed value while that of offset wells is 59 m higher.Obviously,the former is 50%less than the latter.In conclusion,this newly developed semi-hollow casing plug matches well with hangers,having no negative effects on cementing operation,so the cement top after cementing can be well controlled.
基金National Natural Science Foundation of China(12174266,92250304,61935013)Basic and Applied Basic Research Foundation of Guangdong Province(2020B0301030009)Research Team Cultivation Program of Shenzhen University(2023QNT014)。
文摘Backflow is a counterintuitive phenomenon that is widely predicted in the fields of quantum physics and optics.In contrast to quantum backflow,which is challenging to be observed,optical backflow is prevailing in structured lights.For instance,the azimuthal backflow has been recently observed experimentally in optics via the superposition of two beams carrying different orbital angular momentum topological charges.In this paper,we investigate the spin-momentum characteristics of the superimposed orbital angular momentum beams to confirm the optical azimuthal backflow,which is closely related to off-axis vortex flow and super-oscillations.Furthermore,we extend our study to axial backflow,characterized by a reversed axial energy flow in tightly focused cylindrical vector vortex beams.Then,we explore the application of optical backflow in the manipulation of dipolar nanoparticles.By optimizing material parameters,we achieve on-demand control of optical forces in both azimuthal and axial backflow scenarios.Our findings provide in-depth insights into the optical backflow phenomena with potential applications in optical manipulations.
基金Project supported by the National Natural Science Foundation of China(Grant No.U22B6010)supported by the International Partnership Program of Chinese Academy of Sciences(Grant No.025GJHZ2022118FN)the Hainan Provincial Joint Project of Sanya Yazhou Bay Science and Technology City(Grant No.2021CXLH0003).
文摘Axial flow pumps are widely used in water conservancy,petrochemical and agricultural industries.Efficient operation is crucial for energy conservation and emission reduction.Improving efficiency under severe conditions requires studying the internal flow of axial-flow pumps,particularly at low flow rates where backflow vortices form near the impeller inlet.This study investigates the unsteady flow characteristics of backflow vortices at different flow rates in an axial-flow pump.Results show that backflow vortices form when the flow rate decreases to 0.59Q_(d).As the flow rate further declines,the backflow vortex progresses upstream,contracts,and rebounds.The flow rate range is divided into three stages:Stage Ⅰ with no backflow vortex,stage Ⅱ with initial vortex development extending upstream and relatively fragmented,and stage Ⅲ with vortex contraction and rebound forming a more coherent structure.Besides,backflow vortices induce significant pressure fluctuations and velocity oscillations with the primary frequency being 0.5 fb.They exhibit a three-dimensional spiral motion involving changes in axial length,self-rotation,and revolution around the pump axis,with an angular velocity of approximately half the impeller’s rotational speed.This work enhances insights into backflow vortex behaviors,which is essential for optimizing pump design and improving operational stability in challenging environments.
文摘为解决传统双有源桥(dual active bridge,DAB)变换器在宽输入电压工况下无法同时实现零回流功率和全局软开关的问题,提出了一种基于LCL-T谐振型DAB变换器的改进三重移相(improved triple-phase-shift,ITPS)调制策略。首先,对LCL-T谐振型DAB变换器的功率传输特性和软开关特性进行分析,推导出不同电压转换比下无回流功率的控制量表达式。然后,利用LCL谐振网络的对称特性和考虑开关管寄生电容影响下的零电压开关(zero voltage switching,ZVS)约束条件,推导出全工况连续、形式统一、计算量小的ITPS调制控制量表达式,并对调制轨迹进行优化。最后,设计了一台1 kW的实验样机进行调制策略有效性的验证。实验结果表明,与传统调制策略相比,ITPS调制策略具有较宽输入电压范围、无回流功率及全局软开关的优势。
文摘提出1种基于LCL全-半桥谐振变换器的增强型扩展移相调制策略,在保证所有开关均实现零电压开关ZVS(zero voltage switching)的前提下,消除了一次侧回流功率;同时二次侧半桥结构使变换器在低功率条件下具有更高的性价比。利用基波近似法进行变换器的稳态分析,从而得到功率模型及ZVS条件。最后利用PSIM软件进行仿真,搭建1台300 W的实验样机,由实验结果验证上述理论的可行性。
