The complex structure of the bottom of a high-speed train is an important source of train aerodynamic drag.Thus,improving the bottom structure is of great significance to reduce the aerodynamic drag of the train.In th...The complex structure of the bottom of a high-speed train is an important source of train aerodynamic drag.Thus,improving the bottom structure is of great significance to reduce the aerodynamic drag of the train.In this study,computational fluid dynamics(CFD)based on three-dimensional steady incompressible Reynolds-average Naiver-Stokes(RANS)equations and Realizable k-εturbulence model were utilized for numerical simulations.Inspired by the concept of streamlined design and the idea of bottom flow field control,this study iteratively designed the bogies in a streamlined shape and combined them with the bottom deflectors to investigate the joint drag reduction mechanism.Three models,i.e.,single-bogie model,simplified train model,and eight-car high-speed train model,were created and their aerodynamic characteristics were analyzed.The results show that the single-bogie model with streamlined design shows a noticeable drag reduction,whose power bogie and trailer bogie experience 13.92%and 7.63%drag reduction,respectively.The range of positive pressure area on the bogie is reduced.The aerodynamic drag can be further reduced to 15.01%by installing both the streamlined bogie and the deflector on the simplified train model.When the streamlined bogies and deflectors are used on the eight-car model together,the total drag reduction rate reaches 2.90%.Therefore,the proposed aerodynamic kit for the high-speed train bottom is capable to improve the flow structure around the bogie regions,reduce the bottom flow velocity,and narrow the scope of the train’s influence on the surrounding environment,achieving the appreciable reduction of aerodynamic drag.This paper can provide a new idea for the drag reduction of high-speed trains.展开更多
The streamlined nose length(SNL)plays a crucial role in determining the aerodynamic performance of high-speed trains.An appropriate SNL can not only effectively reduce the magnitude of aerodynamic drag and lift forces...The streamlined nose length(SNL)plays a crucial role in determining the aerodynamic performance of high-speed trains.An appropriate SNL can not only effectively reduce the magnitude of aerodynamic drag and lift forces,but also improve the performance of the high-speed train in tunnel passing and crosswind circumstances.In this study,a numerical simulation of the aerodynamic performance of high-speed trains at a speed of 400 km/h,with varying SNLs,is conducted using the k-ωshear stress transport(SST)turbulence model.The different SNLs include 6.0,7.0,8.0,9.0,9.8,12.0,15.0,and 18.0 m.In order to validate the accuracy of the numerical simulation,its results are compared with wind tunnel test data obtained from the literature.Numerical simulation is carried out using compressible and incompressible gases to determine the effect of gas compressibility on results.The impact of SNL on the aerodynamic performance of the trains is analyzed in terms of aerodynamic forces,velocity,and pressure distributions.In comparison to the original train,the train with a 6.0 m SNL experienced a 10.8%increase in overall aerodynamic resistance.Additionally,the lift forces on the head and tail cars increased by 35.7%and 75.5%,respectively.On the other hand,the train with an 18.0 m SNL exhibited a 16.5%decrease in aerodynamic drag.Furthermore,the lift forces on the head and tail cars decreased by 21.9%and 49.7%,respectively.The aerodynamic drag force of the entire train varies linearly with the SNL,while the aerodynamic lift of the tail car follows a quadratic function in relation to the SNL.展开更多
Purpose – The volume of passenger traffic at metro transfer stations serves as a pivotal metric for theorchestration of crowd flow management. Given the intricacies of crowd dynamics within these stations andthe recu...Purpose – The volume of passenger traffic at metro transfer stations serves as a pivotal metric for theorchestration of crowd flow management. Given the intricacies of crowd dynamics within these stations andthe recurrent instances of substantial passenger influxes, a methodology predicated on stochastic processesand the principle of user equilibrium is introduced to facilitate real-time traffic flow estimation within transferstation streamlines.Design/methodology/approach – The synthesis of stochastic process theory with streamline analysisengenders a probabilistic model of intra-station pedestrian traffic dynamics. Leveraging real-time passengerflow data procured from monitoring systems within the transfer station, a gradient descent optimizationtechnique is employed to minimize the cost function, thereby deducing the dynamic distribution of categorizedpassenger flows. Subsequently, adhering to the tenets of user equilibrium, the Frank–Wolfe algorithm isimplemented to allocate the intra-station categorized passenger flows across various streamlines, ascertainingthe traffic volume for each.Findings – Utilizing the Xiaozhai Station of the Xi’an Metro as a case study, the Anylogic simulation softwareis engaged to emulate the intra-station crowd dynamics, thereby substantiating the efficacy of the proposedpassenger flow estimation model. The derived solutions are instrumental in formulating a crowd controlstrategy for Xiaozhai Station during the peak interval from 17:30 to 18:00 on a designated day, yielding crowdmanagement interventions that offer insights for the orchestration of passenger flow and operationalgovernance within metro stations.Originality/value – The construction of an estimation methodology for the real-time streamline traffic flowaugments the model’s dataset, supplanting estimated values derived from surveys or historical datasets withreal-time computed traffic data, thereby enhancing the precision and immediacy of crowd flow managementwithin metro stations.展开更多
The mathematical model of a 3-element centripetal-turbine hydrodynamic torque converter and analytic description of fluid flow inside the hydrodynamic torque converter are investigated. A new torus coordinate system i...The mathematical model of a 3-element centripetal-turbine hydrodynamic torque converter and analytic description of fluid flow inside the hydrodynamic torque converter are investigated. A new torus coordinate system is proposed so as to quantitatively describe fluid movement inside the hydrodynamic torque converter. The particle movement inside the hydrodynamic torque converter is decomposed into meridional component movement and torus component movement, and a universal meridional streamline equation is derived. According to the relationship between the converter wheel velocity polygon and its blade angle, a torus streamline differential equation is established. The universal meridional streamline equation is approximated with square polynomials. The approximation error curve is given and the percentage error is not greater than 0.86%. Considered as a function of polar angle, the blade angle cotangent of each converter wheel varies linearly with polar angle. By using integral calculus, torus streamline equations are obtained. As a result, the problem of difficult flow description of the hydrodynamic torque converter is solved and a new analytic research system is established.展开更多
Well production optimization is a complex and time-consuming task in the oilfield development.The combination of reservoir numerical simulator with optimization algorithms is usually used to optimize well production.T...Well production optimization is a complex and time-consuming task in the oilfield development.The combination of reservoir numerical simulator with optimization algorithms is usually used to optimize well production.This method spends most of computing time in objective function evaluation by reservoir numerical simulator which limits its optimization efficiency.To improve optimization efficiency,a well production optimization method using streamline features-based objective function and Bayesian adaptive direct search optimization(BADS)algorithm is established.This new objective function,which represents the water flooding potential,is extracted from streamline features.It only needs to call the streamline simulator to run one time step,instead of calling the simulator to calculate the target value at the end of development,which greatly reduces the running time of the simulator.Then the well production optimization model is established and solved by the BADS algorithm.The feasibility of the new objective function and the efficiency of this optimization method are verified by three examples.Results demonstrate that the new objective function is positively correlated with the cumulative oil production.And the BADS algorithm is superior to other common algorithms in convergence speed,solution stability and optimization accuracy.Besides,this method can significantly accelerate the speed of well production optimization process compared with the objective function calculated by other conventional methods.It can provide a more effective basis for determining the optimal well production for actual oilfield development.展开更多
The aim of this investigation is to determine the effect of fluid leak-off (suction) and fluid injection (blowing) at the horizontal base on the two-dimensional spreading under the gravity of a thin film of viscous in...The aim of this investigation is to determine the effect of fluid leak-off (suction) and fluid injection (blowing) at the horizontal base on the two-dimensional spreading under the gravity of a thin film of viscous incompressible fluid by studying the evolution of the streamlines in the thin film. It is assumed that the normal component of the fluid velocity at the base is proportional to the spatial gradient of the height of the film. Lie symmetry methods for partial differential equations are applied. The invariant solution for the surface profile is derived. It is found that the thin fluid film approximation is satisfied for weak to moderate leak-off and for the whole range of fluid injection. The streamlines are derived and plotted by solving a cubic equation numerically. For fluid injection, there is a dividing streamline originating at the stagnation point at the base which separates the flow into two regions, a lower region consisting mainly of rising fluid and an upper region consisting mainly of descending fluid. An approximate analytical solution for the dividing streamline is derived. It generates an approximate V-shaped surface along the length of the two-dimensional film with the vertex of each section the stagnation point. It is concluded that the fluid flow inside the thin film can be visualised by plotting the streamlines. Other models relating the fluid velocity at the base to the height of the thin film can be expected to contain a dividing streamline originating at a stagnation point and dividing the flow into a lower region of rising fluid and an upper region of descending fluid.展开更多
In this paper, two finite difference streamline diffusion (FDSD) schemes for solving two-dimensional time-dependent convection-diffusion equations are constructed. Stability and optimal order error estimati-ions for c...In this paper, two finite difference streamline diffusion (FDSD) schemes for solving two-dimensional time-dependent convection-diffusion equations are constructed. Stability and optimal order error estimati-ions for considered schemes are derived in the norm stronger than L^2-norm.展开更多
Streamline box girders are widely applied in the design and construction of long-span bridges all over the world. In order to study the influence of modifications of aerodynamic configuration and accessory components ...Streamline box girders are widely applied in the design and construction of long-span bridges all over the world. In order to study the influence of modifications of aerodynamic configuration and accessory components on flutter and vortex-induced vibration （VIV）, more than 60 cases were tested through a 1：50 scale section model. The test results indicates that the aerodynamic configuration and accessory components of streamline box girders can signifi- cantly affect the wind-induced vibration of bridge, which is in good agreement with the experience of past researchers. From the tests carried out, it is observed that if the horizontal angle of the inclined web of the streamline box girder is below 16°, the critical flutter wind speed of bridge will increase remarkably, and the VIV will diminish. The test results also show that the 15° inclined web can restrain the formation of vortex near the tail, and consequently improve the performance of aerodynamic stability of long-span bridges. Finally, a new streamline box girder with 15° inclined web was presented and strongly recommended in the aerodynamic configuration design of long-span bridges.展开更多
Streamline simulation is developed to simulate waterflooding in fractured reservoirs. Conventional reservoir simulation methods for fluid flow simulation in large and complex reservoirs are very costly and time consum...Streamline simulation is developed to simulate waterflooding in fractured reservoirs. Conventional reservoir simulation methods for fluid flow simulation in large and complex reservoirs are very costly and time consuming. In streamline method, transport equations are solved on one-dimensional streamlines to reduce the computation time with less memory for simulation. First, pressure equation is solved on an Eulerian grid and streamlines are traced. Defining the "time of flight", saturation equations are mapped and solved on streamlines. Finally, the results are mapped back on Eulerian grid and the process is repeated until the simulation end time. The waterflooding process is considered in a fractured reservoir using the dual porosity model. Afterwards, a computational code is developed to solve the same problem by the IMPES method and the results of streamline simulation are compared to those of the IMPES and a commercial software. Finally, the accuracy and efficiency of streamline simulator for simulation of two-phase flow in fractured reservoirs has been proved.展开更多
The aerodynamic resistance of a train running in the open air limits the maximum speed that can be attained by the train.For this reason,evacuated tube trains(ETT)are being considered as valid alternatives to be imple...The aerodynamic resistance of a train running in the open air limits the maximum speed that can be attained by the train.For this reason,evacuated tube trains(ETT)are being considered as valid alternatives to be implemented in the future.The atmosphere in the tube,the so-called blocking ratio and the length of the streamlined nose are the key factors affecting the aerodynamic performances of these trains.In the present work,we investigate evacuated tube trains with different lengths of the streamline nose on the basis of computational fluid dynamics(CFD).The three-dimensional steady compressible Navier-Stokes equations are solved.The running speed of the ETT is 800 km/h and the blocking ratio is 0.2.Results show that with the increase of the streamlined nose length,the aerodynamic drag and lift forces of the head car decrease gradually,and the drag and lift forces of the middle car change slightly.For the tail car,the drag force decreases,whereas the absolute value of the lift force increases.At a speed of 800 km/h,a slight shock wave appears at the rear of the tail car,which affects the aerodynamic forces acting on the train.展开更多
Streamline-adjustment-assisted heterogeneous combination flooding is a new technology for enhanced oil recovery for post-polymer-flooded reservoirs.In this work,we first carried out a series of 2D visualization experi...Streamline-adjustment-assisted heterogeneous combination flooding is a new technology for enhanced oil recovery for post-polymer-flooded reservoirs.In this work,we first carried out a series of 2D visualization experiments for different chemical flooding scenarios after polymer flooding.Then,we explored the synergistic mechanisms of streamline-adjustment-assisted heterogeneous combination flooding for enhanced oil recovery and the contribution of each component.Test results show that for single heterogeneous combination flooding,the residual oil in the main streamline area after polymer flooding is ready to be driven,but it is difficult to be recovered in the non-main streamline area.Due to the effect of drainage and synergism,the streamline-adjustment-assisted heterogeneous combination flooding diverts the injected chemical agent from the main streamline area to the non-main streamline area,which consequently expands the active area of chemical flooding.Based on the results from the single-factor contribution of the quantitative analysis,the contribution of temporary plugging and profile control of branched preformed particle gels ranks in the first place and followed by the polymer profile control and the effect of streamline adjustment.On the contrary,the surfactant contributes the least to enhance the efficiency of oil displacement.展开更多
In this paper,a streamline diffusion F.E.M. for linear Sobolev equations with convection dominated term is given.According to the range of space time F.E mesh parameter h ,two choices for artifical diffusion par...In this paper,a streamline diffusion F.E.M. for linear Sobolev equations with convection dominated term is given.According to the range of space time F.E mesh parameter h ,two choices for artifical diffusion parameter δ are presented,and for the corresponding computation schemes the stability and error estimates in suitable norms are estabilished.展开更多
With continuous changes to energy-saving requirements,the task of train aerodynamic optimization becomes important.Traditional aerodynamic optimization of a high-speed train is carried out assuming the same shape of t...With continuous changes to energy-saving requirements,the task of train aerodynamic optimization becomes important.Traditional aerodynamic optimization of a high-speed train is carried out assuming the same shape of the head and tail cars,which ignores the combined effect of the two cars on aerodynamic forces.The streamlined structure of the train has different effects on the aerodynamics of the head and tail cars.In-depth study of these effects will help engineers improve their shape design capabilities.Based on the surrogate model method,this paper studies the influence of five shape parameters of the streamlined area on the resistance of the head and tail cars and the lift force of the tail car of CRH380A,and compares the aerodynamic performance of the two optimization schemes.The research results show that the optimization direction for reducing drag of the head car is opposite to that for reducing the drag and lift of the tail car,while the optimization directions for reducing both drag and lift for the tail car alone,are roughly the same.Therefore,the same shaped head and tail cars are problematic for improving aerodynamic performance.After optimization,the head car’s resistance,the tail car’s resistance,and the tail car’s lift of the train with the same shape of head and tail cars are reduced by 1.7%,0.5%,and 3.5%,respectively.The train with different shapes had values decreased by 5.6%,1.4%,and 7.5%,respectively.The optimization effect of the latter is more than twice that of the former.展开更多
The calculation precision and convergence speed of streamline strip element method are increased by (using) the method whose initial value of the exit lateral displacement is determined with strip element variation me...The calculation precision and convergence speed of streamline strip element method are increased by (using) the method whose initial value of the exit lateral displacement is determined with strip element variation method, and the accurate tension lateral distribution model is adopted based on the original third power spline function streamline strip element method. The basic theory of the strip element method is developed. The calculated results by the improved streamline strip element method and the original streamline strip element method are compared with the measured results, showing that the calculated results of the improved method are in good agreement with the measured results.展开更多
Valveless piezoelectric pump is widely used in the medical,however,there is a general and difficult problem to be solved:Low vortex and large flow rate are not compatible,resulting in the blood prone to thrombosis dur...Valveless piezoelectric pump is widely used in the medical,however,there is a general and difficult problem to be solved:Low vortex and large flow rate are not compatible,resulting in the blood prone to thrombosis during blood delivery.In this paper,a new valveless piezoelectric(PZT)pump with streamlined flow tubes(streamlined pump)is proposed.The design method and the working principle of the pump are analyzed.The velocity streamlines are simulated,and the results demonstrate that there are no obvious vortexes in the flow tube of the streamlined pump.Five prototype pumps(two cone pumps and three streamlined pumps)are designed and fabricated to perform flow rate and flow resistance experiments.The experimental results illustrate that the maximum flow rate of the streamlined pump is 142 mL/min,which is 179%higher than that of the cone piezoelectric pump,demonstrating that the streamlined pump has a large flow rate performance.This research provides an inspiration for future research on simple structure,low vortex and large flow rate volume-type pumps,and also provides a useful solution for thrombosis preventing.展开更多
We discuss the effects of the surface slip on streamline patterns and their bifurcations for the peristaltic transport of a Newtonian fluid. The flow is in a two-dimensional symmetric channel or an axisymmetric tube. ...We discuss the effects of the surface slip on streamline patterns and their bifurcations for the peristaltic transport of a Newtonian fluid. The flow is in a two-dimensional symmetric channel or an axisymmetric tube. An exact expression for the stream function is obtained in the wave frame under the assumptions of long wavelength and low Reynolds number for both cases. For the discussion of the particle path in the wave frame, a system of nonlinear autonomous differential equations is established and the methods of dynamical systems are used to discuss the local bifurcations and their topological changes. Moreover, all types of bifurcations and their topological changes are discussed graphically. Finally, the global bifurcation diagram is used to summarize the bifurcations.展开更多
Two strategies extended the single-cascade methods from a compressible three-dimensional inverse method for radial and mixed flow turbomachines to two three-dimensional multi-cascade co-design methods for single-stage...Two strategies extended the single-cascade methods from a compressible three-dimensional inverse method for radial and mixed flow turbomachines to two three-dimensional multi-cascade co-design methods for single-stage centrifugal compressors.These two three-dimensional methods and a typical quasi-threedimensional streamline curvature through-flow inverse method were employed to design the same subsonic high-speed single-stage centrifugal compressors.The compressor performances were simulated by a commercial Reynolds averaged Navier-Stokes(RANS) equations solver.The studies show that two three-dimensional codesign methods are reasonable and feasible.It was found that : firstly the blade camber angle designed by the three-dimensional methods was larger than that designed by the quasi-three-dimensional method;and secondly with regard to two three-dimensional methods with different boundary conditions,the co-design result differences between the diffusers were small,but those between the deswirlers were relatively large.展开更多
基金Project(2020YFA0710901)supported by the National Key Research and Development Program of ChinaProject(2023JJ30643)supported by the Natural Science Foundation of Hunan Province,China+1 种基金Project(12372204)supported by the National Natural Science Foundation of ChinaProject(2022ZZTS0725)supported by the Self-exploration and Innovation Project for Postgraduates of Central South University,China。
文摘The complex structure of the bottom of a high-speed train is an important source of train aerodynamic drag.Thus,improving the bottom structure is of great significance to reduce the aerodynamic drag of the train.In this study,computational fluid dynamics(CFD)based on three-dimensional steady incompressible Reynolds-average Naiver-Stokes(RANS)equations and Realizable k-εturbulence model were utilized for numerical simulations.Inspired by the concept of streamlined design and the idea of bottom flow field control,this study iteratively designed the bogies in a streamlined shape and combined them with the bottom deflectors to investigate the joint drag reduction mechanism.Three models,i.e.,single-bogie model,simplified train model,and eight-car high-speed train model,were created and their aerodynamic characteristics were analyzed.The results show that the single-bogie model with streamlined design shows a noticeable drag reduction,whose power bogie and trailer bogie experience 13.92%and 7.63%drag reduction,respectively.The range of positive pressure area on the bogie is reduced.The aerodynamic drag can be further reduced to 15.01%by installing both the streamlined bogie and the deflector on the simplified train model.When the streamlined bogies and deflectors are used on the eight-car model together,the total drag reduction rate reaches 2.90%.Therefore,the proposed aerodynamic kit for the high-speed train bottom is capable to improve the flow structure around the bogie regions,reduce the bottom flow velocity,and narrow the scope of the train’s influence on the surrounding environment,achieving the appreciable reduction of aerodynamic drag.This paper can provide a new idea for the drag reduction of high-speed trains.
基金supported by the National Natural Science Foundation of China(No.12372049)the Sichuan Science and Technology Program(No.2023JDRC0062)+1 种基金the Independent Project of State Key Laboratory of Rail Transit Vehicle System(No.2023TPL-T06)the Fundamental Research Funds for the Central Universities,China(No.2682023ZTPY036).
文摘The streamlined nose length(SNL)plays a crucial role in determining the aerodynamic performance of high-speed trains.An appropriate SNL can not only effectively reduce the magnitude of aerodynamic drag and lift forces,but also improve the performance of the high-speed train in tunnel passing and crosswind circumstances.In this study,a numerical simulation of the aerodynamic performance of high-speed trains at a speed of 400 km/h,with varying SNLs,is conducted using the k-ωshear stress transport(SST)turbulence model.The different SNLs include 6.0,7.0,8.0,9.0,9.8,12.0,15.0,and 18.0 m.In order to validate the accuracy of the numerical simulation,its results are compared with wind tunnel test data obtained from the literature.Numerical simulation is carried out using compressible and incompressible gases to determine the effect of gas compressibility on results.The impact of SNL on the aerodynamic performance of the trains is analyzed in terms of aerodynamic forces,velocity,and pressure distributions.In comparison to the original train,the train with a 6.0 m SNL experienced a 10.8%increase in overall aerodynamic resistance.Additionally,the lift forces on the head and tail cars increased by 35.7%and 75.5%,respectively.On the other hand,the train with an 18.0 m SNL exhibited a 16.5%decrease in aerodynamic drag.Furthermore,the lift forces on the head and tail cars decreased by 21.9%and 49.7%,respectively.The aerodynamic drag force of the entire train varies linearly with the SNL,while the aerodynamic lift of the tail car follows a quadratic function in relation to the SNL.
文摘Purpose – The volume of passenger traffic at metro transfer stations serves as a pivotal metric for theorchestration of crowd flow management. Given the intricacies of crowd dynamics within these stations andthe recurrent instances of substantial passenger influxes, a methodology predicated on stochastic processesand the principle of user equilibrium is introduced to facilitate real-time traffic flow estimation within transferstation streamlines.Design/methodology/approach – The synthesis of stochastic process theory with streamline analysisengenders a probabilistic model of intra-station pedestrian traffic dynamics. Leveraging real-time passengerflow data procured from monitoring systems within the transfer station, a gradient descent optimizationtechnique is employed to minimize the cost function, thereby deducing the dynamic distribution of categorizedpassenger flows. Subsequently, adhering to the tenets of user equilibrium, the Frank–Wolfe algorithm isimplemented to allocate the intra-station categorized passenger flows across various streamlines, ascertainingthe traffic volume for each.Findings – Utilizing the Xiaozhai Station of the Xi’an Metro as a case study, the Anylogic simulation softwareis engaged to emulate the intra-station crowd dynamics, thereby substantiating the efficacy of the proposedpassenger flow estimation model. The derived solutions are instrumental in formulating a crowd controlstrategy for Xiaozhai Station during the peak interval from 17:30 to 18:00 on a designated day, yielding crowdmanagement interventions that offer insights for the orchestration of passenger flow and operationalgovernance within metro stations.Originality/value – The construction of an estimation methodology for the real-time streamline traffic flowaugments the model’s dataset, supplanting estimated values derived from surveys or historical datasets withreal-time computed traffic data, thereby enhancing the precision and immediacy of crowd flow managementwithin metro stations.
基金supported by Henan Provincial Tackle Key Program of China (Grant No. 0424260038)
文摘The mathematical model of a 3-element centripetal-turbine hydrodynamic torque converter and analytic description of fluid flow inside the hydrodynamic torque converter are investigated. A new torus coordinate system is proposed so as to quantitatively describe fluid movement inside the hydrodynamic torque converter. The particle movement inside the hydrodynamic torque converter is decomposed into meridional component movement and torus component movement, and a universal meridional streamline equation is derived. According to the relationship between the converter wheel velocity polygon and its blade angle, a torus streamline differential equation is established. The universal meridional streamline equation is approximated with square polynomials. The approximation error curve is given and the percentage error is not greater than 0.86%. Considered as a function of polar angle, the blade angle cotangent of each converter wheel varies linearly with polar angle. By using integral calculus, torus streamline equations are obtained. As a result, the problem of difficult flow description of the hydrodynamic torque converter is solved and a new analytic research system is established.
基金supported partly by the National Science and Technology Major Project of China(Grant No.2016ZX05025-001006)Major Science and Technology Project of CNPC(Grant No.ZD2019-183-007)
文摘Well production optimization is a complex and time-consuming task in the oilfield development.The combination of reservoir numerical simulator with optimization algorithms is usually used to optimize well production.This method spends most of computing time in objective function evaluation by reservoir numerical simulator which limits its optimization efficiency.To improve optimization efficiency,a well production optimization method using streamline features-based objective function and Bayesian adaptive direct search optimization(BADS)algorithm is established.This new objective function,which represents the water flooding potential,is extracted from streamline features.It only needs to call the streamline simulator to run one time step,instead of calling the simulator to calculate the target value at the end of development,which greatly reduces the running time of the simulator.Then the well production optimization model is established and solved by the BADS algorithm.The feasibility of the new objective function and the efficiency of this optimization method are verified by three examples.Results demonstrate that the new objective function is positively correlated with the cumulative oil production.And the BADS algorithm is superior to other common algorithms in convergence speed,solution stability and optimization accuracy.Besides,this method can significantly accelerate the speed of well production optimization process compared with the objective function calculated by other conventional methods.It can provide a more effective basis for determining the optimal well production for actual oilfield development.
文摘The aim of this investigation is to determine the effect of fluid leak-off (suction) and fluid injection (blowing) at the horizontal base on the two-dimensional spreading under the gravity of a thin film of viscous incompressible fluid by studying the evolution of the streamlines in the thin film. It is assumed that the normal component of the fluid velocity at the base is proportional to the spatial gradient of the height of the film. Lie symmetry methods for partial differential equations are applied. The invariant solution for the surface profile is derived. It is found that the thin fluid film approximation is satisfied for weak to moderate leak-off and for the whole range of fluid injection. The streamlines are derived and plotted by solving a cubic equation numerically. For fluid injection, there is a dividing streamline originating at the stagnation point at the base which separates the flow into two regions, a lower region consisting mainly of rising fluid and an upper region consisting mainly of descending fluid. An approximate analytical solution for the dividing streamline is derived. It generates an approximate V-shaped surface along the length of the two-dimensional film with the vertex of each section the stagnation point. It is concluded that the fluid flow inside the thin film can be visualised by plotting the streamlines. Other models relating the fluid velocity at the base to the height of the thin film can be expected to contain a dividing streamline originating at a stagnation point and dividing the flow into a lower region of rising fluid and an upper region of descending fluid.
基金Project supported by National Natural Science Foundation of China and China State Key project for Basic Researchcs.
文摘In this paper, two finite difference streamline diffusion (FDSD) schemes for solving two-dimensional time-dependent convection-diffusion equations are constructed. Stability and optimal order error estimati-ions for considered schemes are derived in the norm stronger than L^2-norm.
文摘Streamline box girders are widely applied in the design and construction of long-span bridges all over the world. In order to study the influence of modifications of aerodynamic configuration and accessory components on flutter and vortex-induced vibration （VIV）, more than 60 cases were tested through a 1：50 scale section model. The test results indicates that the aerodynamic configuration and accessory components of streamline box girders can signifi- cantly affect the wind-induced vibration of bridge, which is in good agreement with the experience of past researchers. From the tests carried out, it is observed that if the horizontal angle of the inclined web of the streamline box girder is below 16°, the critical flutter wind speed of bridge will increase remarkably, and the VIV will diminish. The test results also show that the 15° inclined web can restrain the formation of vortex near the tail, and consequently improve the performance of aerodynamic stability of long-span bridges. Finally, a new streamline box girder with 15° inclined web was presented and strongly recommended in the aerodynamic configuration design of long-span bridges.
文摘Streamline simulation is developed to simulate waterflooding in fractured reservoirs. Conventional reservoir simulation methods for fluid flow simulation in large and complex reservoirs are very costly and time consuming. In streamline method, transport equations are solved on one-dimensional streamlines to reduce the computation time with less memory for simulation. First, pressure equation is solved on an Eulerian grid and streamlines are traced. Defining the "time of flight", saturation equations are mapped and solved on streamlines. Finally, the results are mapped back on Eulerian grid and the process is repeated until the simulation end time. The waterflooding process is considered in a fractured reservoir using the dual porosity model. Afterwards, a computational code is developed to solve the same problem by the IMPES method and the results of streamline simulation are compared to those of the IMPES and a commercial software. Finally, the accuracy and efficiency of streamline simulator for simulation of two-phase flow in fractured reservoirs has been proved.
基金supported by Sichuan Science and Technology Program(No.2019YJ0227)China Postdoctoral Science Foundation(No.2019M663550)+1 种基金National Natural Science Foundation of China(No.51605397)Science and Technolgoy program of China Railway Group Limited(No.2018-S-02).
文摘The aerodynamic resistance of a train running in the open air limits the maximum speed that can be attained by the train.For this reason,evacuated tube trains(ETT)are being considered as valid alternatives to be implemented in the future.The atmosphere in the tube,the so-called blocking ratio and the length of the streamlined nose are the key factors affecting the aerodynamic performances of these trains.In the present work,we investigate evacuated tube trains with different lengths of the streamline nose on the basis of computational fluid dynamics(CFD).The three-dimensional steady compressible Navier-Stokes equations are solved.The running speed of the ETT is 800 km/h and the blocking ratio is 0.2.Results show that with the increase of the streamlined nose length,the aerodynamic drag and lift forces of the head car decrease gradually,and the drag and lift forces of the middle car change slightly.For the tail car,the drag force decreases,whereas the absolute value of the lift force increases.At a speed of 800 km/h,a slight shock wave appears at the rear of the tail car,which affects the aerodynamic forces acting on the train.
基金financial support from the National Natural Science Foundation of China (Grant No. 51574269)the National Science Foundation for Distinguished Young Scholars of China (Grant No. 51625403)+3 种基金the Important National Science and Technology Specific Projects of China (Grant No. 2016ZX05025-003)the Fundamental Research Funds for the Central Universities (Grant No. 15CX08004A, 18CX02169A)China Postdoctoral Science Foundation (Grant No. 2017M622319)the Natural Science Foundation of Shandong Province (Grant No. ZR2018BEE004)
文摘Streamline-adjustment-assisted heterogeneous combination flooding is a new technology for enhanced oil recovery for post-polymer-flooded reservoirs.In this work,we first carried out a series of 2D visualization experiments for different chemical flooding scenarios after polymer flooding.Then,we explored the synergistic mechanisms of streamline-adjustment-assisted heterogeneous combination flooding for enhanced oil recovery and the contribution of each component.Test results show that for single heterogeneous combination flooding,the residual oil in the main streamline area after polymer flooding is ready to be driven,but it is difficult to be recovered in the non-main streamline area.Due to the effect of drainage and synergism,the streamline-adjustment-assisted heterogeneous combination flooding diverts the injected chemical agent from the main streamline area to the non-main streamline area,which consequently expands the active area of chemical flooding.Based on the results from the single-factor contribution of the quantitative analysis,the contribution of temporary plugging and profile control of branched preformed particle gels ranks in the first place and followed by the polymer profile control and the effect of streamline adjustment.On the contrary,the surfactant contributes the least to enhance the efficiency of oil displacement.
基金Supported by the National Natural Sciences Foundation of China(1 8971 0 51 )
文摘In this paper,a streamline diffusion F.E.M. for linear Sobolev equations with convection dominated term is given.According to the range of space time F.E mesh parameter h ,two choices for artifical diffusion parameter δ are presented,and for the corresponding computation schemes the stability and error estimates in suitable norms are estabilished.
基金supported by the National Key R&D Program of China(Nos.2020YFA0710902 and 2018YFB1201603-12)the National Natural Science Foundation of China(No.12172308)+1 种基金the Sichuan Provincial Science and Technology Program of China(No.2019YJ0227)the Foundation of the State Key Laboratory of Traction Power of China(No.2019TPL_T02)。
文摘With continuous changes to energy-saving requirements,the task of train aerodynamic optimization becomes important.Traditional aerodynamic optimization of a high-speed train is carried out assuming the same shape of the head and tail cars,which ignores the combined effect of the two cars on aerodynamic forces.The streamlined structure of the train has different effects on the aerodynamics of the head and tail cars.In-depth study of these effects will help engineers improve their shape design capabilities.Based on the surrogate model method,this paper studies the influence of five shape parameters of the streamlined area on the resistance of the head and tail cars and the lift force of the tail car of CRH380A,and compares the aerodynamic performance of the two optimization schemes.The research results show that the optimization direction for reducing drag of the head car is opposite to that for reducing the drag and lift of the tail car,while the optimization directions for reducing both drag and lift for the tail car alone,are roughly the same.Therefore,the same shaped head and tail cars are problematic for improving aerodynamic performance.After optimization,the head car’s resistance,the tail car’s resistance,and the tail car’s lift of the train with the same shape of head and tail cars are reduced by 1.7%,0.5%,and 3.5%,respectively.The train with different shapes had values decreased by 5.6%,1.4%,and 7.5%,respectively.The optimization effect of the latter is more than twice that of the former.
文摘The calculation precision and convergence speed of streamline strip element method are increased by (using) the method whose initial value of the exit lateral displacement is determined with strip element variation method, and the accurate tension lateral distribution model is adopted based on the original third power spline function streamline strip element method. The basic theory of the strip element method is developed. The calculated results by the improved streamline strip element method and the original streamline strip element method are compared with the measured results, showing that the calculated results of the improved method are in good agreement with the measured results.
基金supported by the National Natural Science Foundation of China (No. 51375227)the Introduction of Talent Research Start-up Fund of Nanjing Institute of Technology(No. YKJ201960).
文摘Valveless piezoelectric pump is widely used in the medical,however,there is a general and difficult problem to be solved:Low vortex and large flow rate are not compatible,resulting in the blood prone to thrombosis during blood delivery.In this paper,a new valveless piezoelectric(PZT)pump with streamlined flow tubes(streamlined pump)is proposed.The design method and the working principle of the pump are analyzed.The velocity streamlines are simulated,and the results demonstrate that there are no obvious vortexes in the flow tube of the streamlined pump.Five prototype pumps(two cone pumps and three streamlined pumps)are designed and fabricated to perform flow rate and flow resistance experiments.The experimental results illustrate that the maximum flow rate of the streamlined pump is 142 mL/min,which is 179%higher than that of the cone piezoelectric pump,demonstrating that the streamlined pump has a large flow rate performance.This research provides an inspiration for future research on simple structure,low vortex and large flow rate volume-type pumps,and also provides a useful solution for thrombosis preventing.
文摘We discuss the effects of the surface slip on streamline patterns and their bifurcations for the peristaltic transport of a Newtonian fluid. The flow is in a two-dimensional symmetric channel or an axisymmetric tube. An exact expression for the stream function is obtained in the wave frame under the assumptions of long wavelength and low Reynolds number for both cases. For the discussion of the particle path in the wave frame, a system of nonlinear autonomous differential equations is established and the methods of dynamical systems are used to discuss the local bifurcations and their topological changes. Moreover, all types of bifurcations and their topological changes are discussed graphically. Finally, the global bifurcation diagram is used to summarize the bifurcations.
基金Programme of Introducing Talents of Discipline to Universities(B08009)
文摘Two strategies extended the single-cascade methods from a compressible three-dimensional inverse method for radial and mixed flow turbomachines to two three-dimensional multi-cascade co-design methods for single-stage centrifugal compressors.These two three-dimensional methods and a typical quasi-threedimensional streamline curvature through-flow inverse method were employed to design the same subsonic high-speed single-stage centrifugal compressors.The compressor performances were simulated by a commercial Reynolds averaged Navier-Stokes(RANS) equations solver.The studies show that two three-dimensional codesign methods are reasonable and feasible.It was found that : firstly the blade camber angle designed by the three-dimensional methods was larger than that designed by the quasi-three-dimensional method;and secondly with regard to two three-dimensional methods with different boundary conditions,the co-design result differences between the diffusers were small,but those between the deswirlers were relatively large.
