The effect of gradient exhaust strategy and blind plate installation on the inhibition of backflow and thermal stratification in data center cabinets is systematically investigated in this study through numericalmetho...The effect of gradient exhaust strategy and blind plate installation on the inhibition of backflow and thermal stratification in data center cabinets is systematically investigated in this study through numericalmethods.The validated Re-Normalization Group(RNG)k-ε turbulence model was used to analyze airflow patterns within cabinet structures equipped with backplane air conditioning.Key findings reveal that server-generated thermal plumes induce hot air accumulation at the cabinet apex,creating a 0.8℃ temperature elevation at the top server’s inlet compared to the ideal situation(23℃).Strategic increases in backplane fan exhaust airflow rates reduce server 1’s inlet temperature from 26.1℃(0%redundancy case)to 23.1℃(40%redundancy case).Gradient exhaust strategies achieve equivalent server temperature performance to uniform exhaust distributions while requiring 25%less redundant airflow.This approach decreases the recirculation ratio from1.52%(uniformexhaust at 15%redundancy)to 0.57%(gradient exhaust at equivalent redundancy).Comparative analyses demonstrate divergent thermal behaviors:in bottom-server-absent configurations,gradient exhaust reduces top server inlet temperatures by 1.6℃vs.uniformexhaust,whereas top-serverabsent configurations exhibit a 1.8℃ temperature increase under gradient conditions.The blind plate implementation achieves a 0.4℃ top server temperature reduction compared to 15%-redundancy uniform exhaust systems without requiring additional airflow redundancy.Partially installed server arrangements with blind plates maintain thermal characteristics comparable to fully populated cabinets.This study validates gradient exhaust and blind plate technologies as effective countermeasures against cabinet-scale thermal recirculation,providing actionable insights for optimizing backplane air conditioning systems in mission-critical data center environments.展开更多
This contribution presents a novel wear dependent virtual flow rate sensor for single stage single lobe progressing cavity pumps. We study the wear-induced material loss of the pump components and the impact of this m...This contribution presents a novel wear dependent virtual flow rate sensor for single stage single lobe progressing cavity pumps. We study the wear-induced material loss of the pump components and the impact of this material loss on the volumetric efficiency. The results are combined with an established backflow model to implement a backflow calculation procedure that is adaptive to wear. We use a laboratory test setup with a highly abrasive fluid and operate a pump from new to worn condition to validate our approach. The obtained measurement data show that the presented virtual sensor is capable of calculating the flow rate of a pump being subject to wear during its regular operation.展开更多
Fiber is highly escapable in conventional slickwater,making it difficult to form fiber-proppant agglomerate with proppant and exhibit limited effectiveness.To solve these problems,a novel structure stabilizer(SS)is de...Fiber is highly escapable in conventional slickwater,making it difficult to form fiber-proppant agglomerate with proppant and exhibit limited effectiveness.To solve these problems,a novel structure stabilizer(SS)is developed.Through microscopic structural observations and performance evaluations in indoor experiments,the mechanism of proppant placement under the action of the SS and the effects of the SS on proppant placement dimensions and fracture conductivity were elucidated.The SS facilitates the formation of robust fiber-proppant agglomerates by polymer,fiber,and quartz sand.Compared to bare proppants,these agglomerates exhibit reduced density,increased volume,and enlarged contact area with the fluid during settlement,leading to heightened buoyancy and drag forces,ultimately resulting in slower settling velocities and enhanced transportability into deeper regions of the fracture.Co-injecting the fiber and the SS alongside the proppant into the reservoir effectively reduces the fiber escape rate,increases the proppant volume in the slickwater,and boosts the proppant placement height,conveyance distance and fracture conductivity,while also decreasing the proppant backflow.Experimental results indicate an optimal SS mass fraction of 0.3%.The application of this SS in over 80 wells targeting tight gas,shale oil,and shale gas reservoirs has substantiated its strong adaptability and general suitability for meeting the production enhancement,cost reduction,and sand control requirements of such wells.展开更多
This paper discusses the tectonic divisions of the Himalayan collision belt anddeals with the tectonic evolution of the collision belt in the context of crustal accretion in thefront of the collision belt, deep diapir...This paper discusses the tectonic divisions of the Himalayan collision belt anddeals with the tectonic evolution of the collision belt in the context of crustal accretion in thefront of the collision belt, deep diapirism and thermal-uplift extension and deep material flow-ing of the lithosphere-backflowing. Finally it proposes a model of the tectonic evolution-progressive intracontinental deformation model-of the Himalayan belt.展开更多
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
On basis of bond dissociation energies （BDEs） for BH2, B（OH）2, BCl2, and BCl, the diffusion Monte Carlo （DMC） method is applied to explore the BDEs of HB-H, HOB-OH, ClB-Cl, and B-Cl. The effect of the choice of ...On basis of bond dissociation energies （BDEs） for BH2, B（OH）2, BCl2, and BCl, the diffusion Monte Carlo （DMC） method is applied to explore the BDEs of HB-H, HOB-OH, ClB-Cl, and B-Cl. The effect of the choice of orbitals, as well as the backflow transformation, is studied. The Slater-Jastrow DMC algorithm gives BDEs of 359.1±0.12 kJ/mol for HB-H, 410.5±0.50 kJ/mol for HOB-OH, 357.8±1.46 kJ/mol for ClB-Cl, and 504.5±0.96 kJ/mol for B-Cl using B3PW91 orbitals and similar BDEs when B3LYP orbitals are used. DMC with backflow corrections （BF-DMC） gives a HB-H BDE of 369.9±0.12 kJ/mol which is close to one of the available experimental value （375.8 kJ/mol）. In the case of HOB-OH BDE, the BF-DMC calculation is 446.04-1.84 k J/mol that is closer to the experimental BDE. The BF-DMC BDE for ClB-Cl is 343.2±2.34 kJ/mol and the BF-DMC B-Cl BDE is 523.3±0.33 kJ/mol, which are close to the experimental BDEs, 341.9 and 530.0 kJ/mol, respectively.展开更多
Orifice plate energy dissipater as well as plug energy dissipater, as a kind of effective energy dissipater with characteristics of simple structure, convenient construction and high energy dissipation ratio, has beco...Orifice plate energy dissipater as well as plug energy dissipater, as a kind of effective energy dissipater with characteristics of simple structure, convenient construction and high energy dissipation ratio, has become welcomed more and more by hydraulics researchers. The two kinds of energy dissipaters with sudden reduction and sudden enlargement forms are similar in energy dissipation mechanism, but there are differences in energy dissipation characteristics and cavitation characteristics. In the present paper, the differences between orifice plate and plug in energy loss coefficient, relating to their energy dissipation ratio, in the backflow region length, relating to their energy loss coefficient, and in the lowest wall pressure coefficient, relating to their cavitations risk, were analyzed by numerical simulations and physical experiment, and their features in above three aspects were also revealed. The results of research in the present paper demonstrate that the backflow region length of orifice plate is longer than that of plug at the same contraction ratio, the lowest wall pressure coefficient of plug is smaller than that of orifice plate at the same contraction ratio, and the energy loss coefficient of orifice plate is bigger than that of plug, which illustrates that plug is superior to orifice plate in resistance cavitation damage at the same contraction ratio.展开更多
Three-dimensional simulations of diesel particulate matter （DPM） distribution inside a single straight entry for the Load-Haul-Dump loader （LHD）-truck loading and truck hauling operations were conducted by using A...Three-dimensional simulations of diesel particulate matter （DPM） distribution inside a single straight entry for the Load-Haul-Dump loader （LHD）-truck loading and truck hauling operations were conducted by using ANSYS FLUENT computational fluid dynamics software. The loading operation was performed for a fixed period of 3 min. The dynamic mesh technique in FLUENT was used to study the impact of truck motion on DPM distribution. The resultant DPM distributions are presented for the cases when the truck were driving upstream and downstream of the loading face. Interesting phenomena were revealed in the study including the piston effect, layering of DPM in the roof region, and backflow of diesel exhaust against ventilation. The results from the simulation can be used to determine if the areas inside the face area and straight entry exceed the current U.S. regulatory requirement for DPM concentration （〉160 pg/m3）. This research can guide the selection of DPM reduction strategies and improve the working practices for the underground miners.展开更多
This paper presents an improved three-dimensional non-equilibrium mixing pool model.It is a simplified form of the original model and is more practical for applications.The simulation re-sults show that the industrial...This paper presents an improved three-dimensional non-equilibrium mixing pool model.It is a simplified form of the original model and is more practical for applications.The simulation re-sults show that the industrial scale distillation tray columns can be described closely by the improvedmodel.The effects of model parameters,such as the number of mixing pools,the point efficiencyand flow pattern,on separation are analyzed quantitatively.展开更多
In order to solve the problem of the original residual energy release strategy being unsuitable for high-energy and fast-firing electromagnetic rail launch,this work has explored the applicability of active arc-igniti...In order to solve the problem of the original residual energy release strategy being unsuitable for high-energy and fast-firing electromagnetic rail launch,this work has explored the applicability of active arc-ignition technology(AAT).The results obtained from the comparison of launching experiments show that AAT has no influence on the acceleration of the armature and is capable of quickly releasing the residual energy.Based on the theory of magnetohydrodynamics,this work has also made numerical simulation of the muzzle arc,analyzed the influence of AAT on the muzzle arc flow field,electromagnetic(EM)field and temperature field,and evaluated the performance of AAT according to the projectile initial disturbance,the EM impact on guidance devices and the rail ablation.The results show that AAT is now one of the most practicable strategies for residual energy release.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
A theoretical calculation method of off-design performance is developed for an axial flow fan of oil cooling system in helicopter,including calculation of aerodynamic parameters and performance parameters.When calcula...A theoretical calculation method of off-design performance is developed for an axial flow fan of oil cooling system in helicopter,including calculation of aerodynamic parameters and performance parameters.When calculating inlet shock loss,the shock loss coefficient is obtained by comparing results of theoretical calculation,experimental and numerical calculation.The theoretical results and numerical results show that all air velocity components increase from hub to shroud in main flow area at rated condition.Tip leakage vortex moves downstream as flow rate increases.When flow rate decreases,Re decreases,and boundary layer thickness from hub to shroud area all increases gradually.Tip leakage vortex moves upstream,and secondary loss increases.Low speed area in the passage is widened along with high speed area moving to hub area,influenced by boundary layer separation.Consequently wake area and jet area at fan outlet are both larger than rated condition.Therefore optimization design for off-design performance of the fan is required on aerodynamic parameters influencing fan loss.A reliable method is supplied for estimating altitude performance of lubricating system in helicopter.展开更多
Thin-slab continuous casting and rolling technology is a process integrating casting and plastic deformation. In this study,targeting actions such as slab deformation and liquid core flows during the process of liquid...Thin-slab continuous casting and rolling technology is a process integrating casting and plastic deformation. In this study,targeting actions such as slab deformation and liquid core flows during the process of liquid core reduction on thin-slab continuous casting, suggests the fluid-solid coupling method should be used to research the characteristic and patterns of slab deformation during the liquid core reduction process, as well as research liquid core backflows. A material model of the slab shell was obtained through the high-temperature compression test of the cast steel. The analysis of the fluid-solid coupling simulation for liquid core reduction shows that slab deformation concentrates on the narrow side due to the existence of the liquid core. Meanwhile,the stress and strain increases with the increase of the reduction rate and slab thickness. The changing trends of stress and strain are identical under various conditions. The results demonstrate that using greater reduction at the upper part of the slab, which has a higher temperature and thinner slab,is beneficial to the quality of the slab. Moreover,the liquid core is extruded as the reduction is implemented. The quantity of the extrusion increases with the increase of reduction rate and the thickness of thinner shell, which leads to fluctuation of the mould level, making the operation more difficult.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
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
In liner cementing,the upper cement plug and inner components of a common hanger needs to be drilled out after cementing,which will result in a poor cementing quality or even gas leakage at the flare opening.Therefore...In liner cementing,the upper cement plug and inner components of a common hanger needs to be drilled out after cementing,which will result in a poor cementing quality or even gas leakage at the flare opening.Therefore,a new packer-type drilling-free liner hanger has been developed,and a hydraulic setting-control packer,a flexible drilling-free seal box,and an auxiliary bearing back-off mechanism that go with the line hanger have been designed at the same time.Specific operation procedures include:(1)run in the liner string to the designed depth,then fully circulate the drilling fluid,finally drop the ball.When the tripping ball gets into the seat,the pressure will go up to cut off the hanging control pin and set the hanger;(2)continue to hold the pressure and cut off the ball seat pin to form circulation;(3)trip in the drill pipe to exert pressure on the hanger,back off to release the hanger from the running tool;(4)lower the drill pipe plug upon the completion of cement in-jection,cut off the releasing control pin of hollow casing plug,and run down further to bump with the bumping assembly;(5)remove the cementing head and connect the kelly driver,hold pressure again,then slowly pull up the drill tools,exert hydraulic pressure on the setting hydraulic cylinder of the packer assembly to cut off the setting control pin and set the packer;and(6)pull up the tools to the flare opening and wash out excessive cement slurry by circulating to realize free drilling of the whole hole.The successful application of the liner hanger in 127 mm diameter liner in Well BQ203-H1 indicates that the packer-type liner hanger has such advantages as easy hanging and back-off,accurate bumping,simple setting,and sound sealing performance.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
A runaway transition after the pump power interruption and the simultaneous guide vane servomotor failure is one of the most dangerous and complex transitions for a pumped storage power system(PSPS).This paper analyze...A runaway transition after the pump power interruption and the simultaneous guide vane servomotor failure is one of the most dangerous and complex transitions for a pumped storage power system(PSPS).This paper analyzes the fluctuation behavior and mechanism of a PSPS during a runaway transition caused by the pump power interruption.The transient cavitation flow in the PSPS is simulated by using a one-dimensional and three-dimensional coupling flow simulation method for the runaway transition.Subsequently,the effects of the transient fluctuation of the radial hydraulic thrust on the runner and transient pressures are analyzed using the short-time Fourier transform method.Finally,the mechanisms are analyzed based on the analysis of the internal flow field.This study suggests that the extreme fluctuation generally occurs near the critical transformation points between the two operation modes.In addition,the extreme fluctuation behavior is primarily related to the local backflow near the runner inlet and the unstable cavitation phenomena in the runner and the draft tube.This finding helps for optimizing the runner design to resolve the instability problems of a PSPS.展开更多
基金financially supported by the Basic Research Funds for the Central Government“Innovative Team of Zhejiang University”under contract number(2022FZZX01-09).
文摘The effect of gradient exhaust strategy and blind plate installation on the inhibition of backflow and thermal stratification in data center cabinets is systematically investigated in this study through numericalmethods.The validated Re-Normalization Group(RNG)k-ε turbulence model was used to analyze airflow patterns within cabinet structures equipped with backplane air conditioning.Key findings reveal that server-generated thermal plumes induce hot air accumulation at the cabinet apex,creating a 0.8℃ temperature elevation at the top server’s inlet compared to the ideal situation(23℃).Strategic increases in backplane fan exhaust airflow rates reduce server 1’s inlet temperature from 26.1℃(0%redundancy case)to 23.1℃(40%redundancy case).Gradient exhaust strategies achieve equivalent server temperature performance to uniform exhaust distributions while requiring 25%less redundant airflow.This approach decreases the recirculation ratio from1.52%(uniformexhaust at 15%redundancy)to 0.57%(gradient exhaust at equivalent redundancy).Comparative analyses demonstrate divergent thermal behaviors:in bottom-server-absent configurations,gradient exhaust reduces top server inlet temperatures by 1.6℃vs.uniformexhaust,whereas top-serverabsent configurations exhibit a 1.8℃ temperature increase under gradient conditions.The blind plate implementation achieves a 0.4℃ top server temperature reduction compared to 15%-redundancy uniform exhaust systems without requiring additional airflow redundancy.Partially installed server arrangements with blind plates maintain thermal characteristics comparable to fully populated cabinets.This study validates gradient exhaust and blind plate technologies as effective countermeasures against cabinet-scale thermal recirculation,providing actionable insights for optimizing backplane air conditioning systems in mission-critical data center environments.
基金Funding by Ministerium für Wirtschaft,Innovation,Digitalisierung und Energie des Landes Nordrhein-Westfalen。
文摘This contribution presents a novel wear dependent virtual flow rate sensor for single stage single lobe progressing cavity pumps. We study the wear-induced material loss of the pump components and the impact of this material loss on the volumetric efficiency. The results are combined with an established backflow model to implement a backflow calculation procedure that is adaptive to wear. We use a laboratory test setup with a highly abrasive fluid and operate a pump from new to worn condition to validate our approach. The obtained measurement data show that the presented virtual sensor is capable of calculating the flow rate of a pump being subject to wear during its regular operation.
文摘Fiber is highly escapable in conventional slickwater,making it difficult to form fiber-proppant agglomerate with proppant and exhibit limited effectiveness.To solve these problems,a novel structure stabilizer(SS)is developed.Through microscopic structural observations and performance evaluations in indoor experiments,the mechanism of proppant placement under the action of the SS and the effects of the SS on proppant placement dimensions and fracture conductivity were elucidated.The SS facilitates the formation of robust fiber-proppant agglomerates by polymer,fiber,and quartz sand.Compared to bare proppants,these agglomerates exhibit reduced density,increased volume,and enlarged contact area with the fluid during settlement,leading to heightened buoyancy and drag forces,ultimately resulting in slower settling velocities and enhanced transportability into deeper regions of the fracture.Co-injecting the fiber and the SS alongside the proppant into the reservoir effectively reduces the fiber escape rate,increases the proppant volume in the slickwater,and boosts the proppant placement height,conveyance distance and fracture conductivity,while also decreasing the proppant backflow.Experimental results indicate an optimal SS mass fraction of 0.3%.The application of this SS in over 80 wells targeting tight gas,shale oil,and shale gas reservoirs has substantiated its strong adaptability and general suitability for meeting the production enhancement,cost reduction,and sand control requirements of such wells.
基金This study was a part of the Project Research on Deformation Dynamics on the North Margin of the Qinghai-Tibet Plateau(No,86-06-207)- a key Project of deep geology of the Ministry of Geology and Mineral Resources in the Eighth Five-Year Plan period(1991
文摘This paper discusses the tectonic divisions of the Himalayan collision belt anddeals with the tectonic evolution of the collision belt in the context of crustal accretion in thefront of the collision belt, deep diapirism and thermal-uplift extension and deep material flow-ing of the lithosphere-backflowing. Finally it proposes a model of the tectonic evolution-progressive intracontinental deformation model-of the Himalayan belt.
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On basis of bond dissociation energies （BDEs） for BH2, B（OH）2, BCl2, and BCl, the diffusion Monte Carlo （DMC） method is applied to explore the BDEs of HB-H, HOB-OH, ClB-Cl, and B-Cl. The effect of the choice of orbitals, as well as the backflow transformation, is studied. The Slater-Jastrow DMC algorithm gives BDEs of 359.1±0.12 kJ/mol for HB-H, 410.5±0.50 kJ/mol for HOB-OH, 357.8±1.46 kJ/mol for ClB-Cl, and 504.5±0.96 kJ/mol for B-Cl using B3PW91 orbitals and similar BDEs when B3LYP orbitals are used. DMC with backflow corrections （BF-DMC） gives a HB-H BDE of 369.9±0.12 kJ/mol which is close to one of the available experimental value （375.8 kJ/mol）. In the case of HOB-OH BDE, the BF-DMC calculation is 446.04-1.84 k J/mol that is closer to the experimental BDE. The BF-DMC BDE for ClB-Cl is 343.2±2.34 kJ/mol and the BF-DMC B-Cl BDE is 523.3±0.33 kJ/mol, which are close to the experimental BDEs, 341.9 and 530.0 kJ/mol, respectively.
文摘Orifice plate energy dissipater as well as plug energy dissipater, as a kind of effective energy dissipater with characteristics of simple structure, convenient construction and high energy dissipation ratio, has become welcomed more and more by hydraulics researchers. The two kinds of energy dissipaters with sudden reduction and sudden enlargement forms are similar in energy dissipation mechanism, but there are differences in energy dissipation characteristics and cavitation characteristics. In the present paper, the differences between orifice plate and plug in energy loss coefficient, relating to their energy dissipation ratio, in the backflow region length, relating to their energy loss coefficient, and in the lowest wall pressure coefficient, relating to their cavitations risk, were analyzed by numerical simulations and physical experiment, and their features in above three aspects were also revealed. The results of research in the present paper demonstrate that the backflow region length of orifice plate is longer than that of plug at the same contraction ratio, the lowest wall pressure coefficient of plug is smaller than that of orifice plate at the same contraction ratio, and the energy loss coefficient of orifice plate is bigger than that of plug, which illustrates that plug is superior to orifice plate in resistance cavitation damage at the same contraction ratio.
文摘Three-dimensional simulations of diesel particulate matter （DPM） distribution inside a single straight entry for the Load-Haul-Dump loader （LHD）-truck loading and truck hauling operations were conducted by using ANSYS FLUENT computational fluid dynamics software. The loading operation was performed for a fixed period of 3 min. The dynamic mesh technique in FLUENT was used to study the impact of truck motion on DPM distribution. The resultant DPM distributions are presented for the cases when the truck were driving upstream and downstream of the loading face. Interesting phenomena were revealed in the study including the piston effect, layering of DPM in the roof region, and backflow of diesel exhaust against ventilation. The results from the simulation can be used to determine if the areas inside the face area and straight entry exceed the current U.S. regulatory requirement for DPM concentration （〉160 pg/m3）. This research can guide the selection of DPM reduction strategies and improve the working practices for the underground miners.
基金Supported by the National Natural Science Foundation of China.
文摘This paper presents an improved three-dimensional non-equilibrium mixing pool model.It is a simplified form of the original model and is more practical for applications.The simulation re-sults show that the industrial scale distillation tray columns can be described closely by the improvedmodel.The effects of model parameters,such as the number of mixing pools,the point efficiencyand flow pattern,on separation are analyzed quantitatively.
基金supported in part by National Natural Science Foundation of China(Nos.51522706,51877214,51607187)in part by the National Basic Research Program of China(973 Program)(No.613262)。
文摘In order to solve the problem of the original residual energy release strategy being unsuitable for high-energy and fast-firing electromagnetic rail launch,this work has explored the applicability of active arc-ignition technology(AAT).The results obtained from the comparison of launching experiments show that AAT has no influence on the acceleration of the armature and is capable of quickly releasing the residual energy.Based on the theory of magnetohydrodynamics,this work has also made numerical simulation of the muzzle arc,analyzed the influence of AAT on the muzzle arc flow field,electromagnetic(EM)field and temperature field,and evaluated the performance of AAT according to the projectile initial disturbance,the EM impact on guidance devices and the rail ablation.The results show that AAT is now one of the most practicable strategies for residual energy release.
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.
基金National Aviation Science Foundation of China (No. 20080451014)
文摘A theoretical calculation method of off-design performance is developed for an axial flow fan of oil cooling system in helicopter,including calculation of aerodynamic parameters and performance parameters.When calculating inlet shock loss,the shock loss coefficient is obtained by comparing results of theoretical calculation,experimental and numerical calculation.The theoretical results and numerical results show that all air velocity components increase from hub to shroud in main flow area at rated condition.Tip leakage vortex moves downstream as flow rate increases.When flow rate decreases,Re decreases,and boundary layer thickness from hub to shroud area all increases gradually.Tip leakage vortex moves upstream,and secondary loss increases.Low speed area in the passage is widened along with high speed area moving to hub area,influenced by boundary layer separation.Consequently wake area and jet area at fan outlet are both larger than rated condition.Therefore optimization design for off-design performance of the fan is required on aerodynamic parameters influencing fan loss.A reliable method is supplied for estimating altitude performance of lubricating system in helicopter.
文摘Thin-slab continuous casting and rolling technology is a process integrating casting and plastic deformation. In this study,targeting actions such as slab deformation and liquid core flows during the process of liquid core reduction on thin-slab continuous casting, suggests the fluid-solid coupling method should be used to research the characteristic and patterns of slab deformation during the liquid core reduction process, as well as research liquid core backflows. A material model of the slab shell was obtained through the high-temperature compression test of the cast steel. The analysis of the fluid-solid coupling simulation for liquid core reduction shows that slab deformation concentrates on the narrow side due to the existence of the liquid core. Meanwhile,the stress and strain increases with the increase of the reduction rate and slab thickness. The changing trends of stress and strain are identical under various conditions. The results demonstrate that using greater reduction at the upper part of the slab, which has a higher temperature and thinner slab,is beneficial to the quality of the slab. Moreover,the liquid core is extruded as the reduction is implemented. The quantity of the extrusion increases with the increase of reduction rate and the thickness of thinner shell, which leads to fluctuation of the mould level, making the operation more difficult.
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.
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.
基金2011 Overall Project of China National Petroleum Corpo-ration(No.2011T-0501).
文摘In liner cementing,the upper cement plug and inner components of a common hanger needs to be drilled out after cementing,which will result in a poor cementing quality or even gas leakage at the flare opening.Therefore,a new packer-type drilling-free liner hanger has been developed,and a hydraulic setting-control packer,a flexible drilling-free seal box,and an auxiliary bearing back-off mechanism that go with the line hanger have been designed at the same time.Specific operation procedures include:(1)run in the liner string to the designed depth,then fully circulate the drilling fluid,finally drop the ball.When the tripping ball gets into the seat,the pressure will go up to cut off the hanging control pin and set the hanger;(2)continue to hold the pressure and cut off the ball seat pin to form circulation;(3)trip in the drill pipe to exert pressure on the hanger,back off to release the hanger from the running tool;(4)lower the drill pipe plug upon the completion of cement in-jection,cut off the releasing control pin of hollow casing plug,and run down further to bump with the bumping assembly;(5)remove the cementing head and connect the kelly driver,hold pressure again,then slowly pull up the drill tools,exert hydraulic pressure on the setting hydraulic cylinder of the packer assembly to cut off the setting control pin and set the packer;and(6)pull up the tools to the flare opening and wash out excessive cement slurry by circulating to realize free drilling of the whole hole.The successful application of the liner hanger in 127 mm diameter liner in Well BQ203-H1 indicates that the packer-type liner hanger has such advantages as easy hanging and back-off,accurate bumping,simple setting,and sound sealing performance.
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.
基金Projects supported by the National Natural Science Foundation of China(Grant No.52079034).
文摘A runaway transition after the pump power interruption and the simultaneous guide vane servomotor failure is one of the most dangerous and complex transitions for a pumped storage power system(PSPS).This paper analyzes the fluctuation behavior and mechanism of a PSPS during a runaway transition caused by the pump power interruption.The transient cavitation flow in the PSPS is simulated by using a one-dimensional and three-dimensional coupling flow simulation method for the runaway transition.Subsequently,the effects of the transient fluctuation of the radial hydraulic thrust on the runner and transient pressures are analyzed using the short-time Fourier transform method.Finally,the mechanisms are analyzed based on the analysis of the internal flow field.This study suggests that the extreme fluctuation generally occurs near the critical transformation points between the two operation modes.In addition,the extreme fluctuation behavior is primarily related to the local backflow near the runner inlet and the unstable cavitation phenomena in the runner and the draft tube.This finding helps for optimizing the runner design to resolve the instability problems of a PSPS.
