As the proportion of newenergy increases,the traditional cumulant method(CM)produces significant errorswhen performing probabilistic load flow(PLF)calculations with large-scale wind power integrated.Considering the wi...As the proportion of newenergy increases,the traditional cumulant method(CM)produces significant errorswhen performing probabilistic load flow(PLF)calculations with large-scale wind power integrated.Considering the wind speed correlation,a multi-scenario PLF calculation method that combines random sampling and segmented discrete wind farm power was proposed.Firstly,based on constructing discrete scenes of wind farms,the Nataf transform is used to handle the correlation between wind speeds.Then,the random sampling method determines the output probability of discrete wind power scenarios when wind speed exhibits correlation.Finally,the PLF calculation results of each scenario areweighted and superimposed following the total probability formula to obtain the final power flow calculation result.Verified in the IEEE standard node system,the absolute percent error(APE)for the mean and standard deviation(SD)of the node voltages and branch active power are all within 1%,and the average root mean square(AMSR)values of the probability curves are all less than 1%.展开更多
This paper investigates the influence of the spanwise-distributed trailing-edge camber morphing on the dynamic stall characteristics of a finite-span wing at Re=2×10^(5).The mathematical model of the spanwise-dis...This paper investigates the influence of the spanwise-distributed trailing-edge camber morphing on the dynamic stall characteristics of a finite-span wing at Re=2×10^(5).The mathematical model of the spanwise-distributed trailing-edge camber morphing is established based on Chebyshev polynomials,and the deformed wing surface is modeled by a spline surface according to the rib's morphing in the chordwise direction.The Computational Fluid Dynamics(CFD)method is adopted to obtain flow-field results and aerodynamic forces.The SST-γmodel is introduced and the overset mesh technique is adopted.The numerical results show that the spanwisedistributed trailing-edge morphing obviously changes the aerodynamic and energy transfer characteristics of the dynamic stall.Especially when the phase difference between the trailing-edge motion and the wing pitch is-π/2,the interaction between the three-dimensional(3-D)Leading-Edge Vortex(LEV)and Trailing-Edge Vortex(TEV)is strengthened,and the work done by the aerodynamic force turns negative.This indicates that the trailing-edge deformation has the potential to suppress the oscillation amplitude of stall flutter.We also found that as the trailing-edge camber morphing varies more complexly along the spanwise direction,the suppression effect decreases accordingly.展开更多
Two actual rocks drilled from a typical ultra-deep hydrocarbon reservoir in the Tarim Basin are selected to conduct in-situ stress-loading micro-focus CT scanning experiments.The gray images of rock microstructure at ...Two actual rocks drilled from a typical ultra-deep hydrocarbon reservoir in the Tarim Basin are selected to conduct in-situ stress-loading micro-focus CT scanning experiments.The gray images of rock microstructure at different stress loading stages are obtained.The U-Net fully convolutional neural network is utilized to achieve fine semantic segmentation of rock skeleton,pore space,and microfractures based on CT slice images of deep rocks.The three-dimensional digital rock models of deformed multiscale fractured-porous media at different stress loading stages are thereafter reconstructed,and the equivalent fracture-pore network models are finally extracted to explore the underlying mechanisms of gas-water two-phase flow at the pore-scale.Results indicate that,in the process of insitu stress loading,both the deep rocks have experienced three stages:linear elastic deformation,nonlinear plastic deformation,and shear failure.The micro-mechanical behavior greatly affects the dynamic deformation of rock microstructure and gas-water two-phase flow.In the linear elastic deformation stage,with the increase in in-situ stress,both the deep rocks are gradually compacted,leading to decreases in average pore radius,pore throat ratio,tortuosity,and water-phase relative permeability,while the coordination number nearly remains unchanged.In the plastic deformation stage,the synergistic influence of rock compaction and existence of micro-fractures typically exert a great effect on pore-throat topological properties and gas-water relative permeability.In the shear failure stage,due to the generation and propagation of micro-fractures inside the deep rock,the topological connectivity becomes better,fluid flow paths increase,and flow conductivity is promoted,thus leading to sharp increases in average pore radius and coordination number,rapid decreases in pore throat ratio and tortuosity,as well as remarkable improvement in relative permeability of gas phase and waterphase.展开更多
The current research on the manufacturing of large-scale and complex components focuses mainly on the casting processes.Compared with casting,plastic forming has significant advantages in terms of performance.However,...The current research on the manufacturing of large-scale and complex components focuses mainly on the casting processes.Compared with casting,plastic forming has significant advantages in terms of performance.However,effectively controlling the material flow to achieve a reduced loading force and near-uniformity in the isothermal plastic forming process of large-scale asymmetric magnesium alloy complex housings(LSMACHs)is challenging.This study proposes a material flow control method based on the diffluence upsetting-extrusion forming(DUEF)process by dividing different forging deformation regions,combining these with the principal stress method,and establishing an efficient and accurate design procedure.A rational preformed billet was designed successfully using this method.Subsequently,a finite element simulation was employed to analyze the multiphysics fields of the DUEF process.The results indicated that compared with the traditional closed-die forging(TCDF)process,the DUEF process could control the orderly flow of materials,achieve short-distance filling of materials,and reduce hydrostatic stress.Simultaneously,it improved the deformation uniformity by 20.3%and reduced the loading force by 22.6%.Finally,the rationality of the proposed method was validated through physical experiments.Compared with the TCDF process,the DUEF process exhibited a low loading force and uniform mechanical properties.The proposed material flow control method based on the DUEF process provides a new technological approach for the plastic formation of LSMACH and similar components.展开更多
[Objective] The aim was to al eviate the constructed wetland clogging problems and to explore to the effects of hydraulic loading on wetland clogging. [Method] The experiment, through artificial soil columns, simulate...[Objective] The aim was to al eviate the constructed wetland clogging problems and to explore to the effects of hydraulic loading on wetland clogging. [Method] The experiment, through artificial soil columns, simulated vertical flow arti-ficial wetland, set four hydraulic load level at 50, 100, 150 and 200 cm/d, to identify the impact of hydraulic loading on wetland clogging and to explore the factors run-ning threshold. [Result] The results show that the different levels of hydraulic loading have greater impact; in the constructed wetland clogging process under high hy-draulic loading of 200 cm/d, the effective life was only six months, and the single factor can be speculated that the threshold of the hydraulic load should be at 100-150 cm/d; system can last for six months at low hydraulic loading and last for three months at medium hydraulic load. [Conclusion] The research provides references for wetland clogging experiments in future.展开更多
In this paper, a synthetic mathematical model of load flow for flexible AC transmission systems (FACTS) with unified power flow controller (UPFC) is presented based on the analysis of basic principle and operation sta...In this paper, a synthetic mathematical model of load flow for flexible AC transmission systems (FACTS) with unified power flow controller (UPFC) is presented based on the analysis of basic principle and operation state of UPFC. The model can use the fast P Q decoupled load flow method. Examples of test systems show that the proposed model and method have good convergence. An effective tool is provided by the load flow computer program to analyze the load flow and initial valve calculation of the dynamic state of FACTS.展开更多
Polyurethane polymer grouting materials were studied with conventional triaxial tests via the particle flow code in two dimensions（PFC^（2D）） method, and the simulation results agreed with the experimental data. Th...Polyurethane polymer grouting materials were studied with conventional triaxial tests via the particle flow code in two dimensions（PFC^（2D）） method, and the simulation results agreed with the experimental data. The particle flow code method can simulate the mechanical properties of the polymer. The triaxial cyclic loading tests of the polymer material under different confining pressures were carried out via PFC^（2D） to analyze its mechanical performance. The PFC^（2D） simulation results show that the value of the elastic modulus of the polymer decreases slowly at first and fluctuated within a narrow range near the value of the peak strength; the cumulative plastic strain increases slowly at first and then increases rapidly; the peak strength and elastic modulus of polymer increase with the confining pressure; the PFC^（2D） method can be used to quantitatively evaluate the damage behavior of the polymer material and estimate the fatigue life of the materials under fatigue load based on the number and the location of micro-cracks. Thus, the PFC^（2D） method is an effective tool to study polymers.展开更多
The breakdown of soil aggregates under rainfall and their abrasion in overland flow are important processes in water erosion due to the production of more fine and transportable particles and,the subsequent significan...The breakdown of soil aggregates under rainfall and their abrasion in overland flow are important processes in water erosion due to the production of more fine and transportable particles and,the subsequent significant effect on the erosion intensity.Currently,little is known about the effects of sediment load on the soil aggregate abrasion and the relationship of this abrasion with some related hydraulic parameters.Here,the potential effects of sediment load on soil aggregate abrasion and hydraulic parameters in overland flow were investigated through a series of experiments in a 3.8-m-long hydraulic flume at the slope gradients of 8.7 and 26.8%,unit flow discharges from 2×10^-3 to 6×10^-3 m^2 s^-1,and the sediment concentration from 0 to 110 kg m-3.All the aggregates from Ultisols developed Quaternary red clay,Central China.The results indicated that discharge had the most significant(P<0.01)effect on the aggregates abrasion with the contributions of 58.76 and 60.34%,followed by sediment feed rate,with contributions of 39.66 and 34.12%at the slope gradients of 8.7 and 26.8%,respectively.The abrasion degree of aggregates was found to increase as a power function of the sediment concentration.Meanwhile,the flow depth,friction factor,and shear stress increased as a power function along with the increase of sediment concentration at different slope gradients and discharges.Reynolds number was obviously affected by sediment concentration and it decreased as sediment concentration increased.The ratio of the residual weight to the initial weight of soil aggregates(Wr/Wi)was found to increase as the linear function with an increasing flow depth(P=0.008)or Reynolds number(P=0.002)in the sediment-laden flow.The Wr/Wi values followed a power function decrease with increasing friction factor or shear stress in the sediment-laden flow,indicating that friction factor is the best hydraulic parameter for prediction of soil aggregate abrasion under different sediment load conditions.The information regarding the soil aggregate abrasion under various sediment load conditions can facilitate soil process-based erosion modeling.展开更多
Load flow is an important tool used by power engineers for planning, to determine the best operation for a power system and exchange of power between utility companies. In order to have an efficient operating power sy...Load flow is an important tool used by power engineers for planning, to determine the best operation for a power system and exchange of power between utility companies. In order to have an efficient operating power system, it is necessary to determine which method is suitable and efficient for the system’s load flow analysis. A power flow analysis method may take a long time and therefore prevent achieving an accurate result to a power flow solution because of continuous changes in power demand and generations. This paper presents analysis of the load flow problem in power system planning studies. The numerical methods: Gauss-Seidel, Newton-Raphson and Fast Decoupled methods were compared for a power flow analysis solution. Simulation is carried out using Matlab for test cases of IEEE 9-Bus, IEEE 30-Bus and IEEE 57-Bus system. The simulation results were compared for number of iteration, computational time, tolerance value and convergence. The compared results show that Newton-Raphson is the most reliable method because it has the least number of iteration and converges faster.展开更多
For the low price of coal and ineffective environmental management in mining area, China is in the dilemma of the increasing coal demand and the serious environmental issues in mining area. The more coal that is expor...For the low price of coal and ineffective environmental management in mining area, China is in the dilemma of the increasing coal demand and the serious environmental issues in mining area. The more coal that is exported from a region, the more heavily it suffers from the environmental impacts of coal export. In this paper, the temporal and spatial process of exporting coal from Shanxi to other provinces of China is traced between 1975 and 2005. The coal net export of Shanxi increased to 370.69 million tonnes in 2005, representing an average annual growth rate of 7.5% from 1975 to 2005. With the increase of the amount of coal export from Shanxi, the Environmental Loads Transfer （ELT） that import provinces input to mining areas of Shanxi are rising. Effective means of internalizing the environmental externality of ELT lie in： 1） setting up a coal sustainable development fund to restore environment of coal mining area; 2） enforcing environment tax, financial transfer payment and transferring advantage technology of pollution reduction to coal export area; and 3） reducing coal regional flow by reducing coal demand from power generation and heating and other industries.展开更多
A filtering method of aero-engine load spectrum based on the rain flow counting is proposed in this paper.Firstly,the original load spectrum is counted through the rain flow method to get the peak and valley values.Th...A filtering method of aero-engine load spectrum based on the rain flow counting is proposed in this paper.Firstly,the original load spectrum is counted through the rain flow method to get the peak and valley values.Then,some data points in the original load spectrum are added between the peak and valley values.Finally,the filtering spectrum is obtained.The proposed method can reflect the path information of the original load spectrum.In addition,it can also eliminate the noise in the signal and improve the efficiency of signal processing,which is of practical significance for the research of aero-engine.展开更多
In today’s datacenter network,the quantity growth and complexity increment of traffic is unprecedented,which brings not only the booming of network development,but also the problem of network performance degradation,...In today’s datacenter network,the quantity growth and complexity increment of traffic is unprecedented,which brings not only the booming of network development,but also the problem of network performance degradation,such as more chance of network congestion and serious load imbalance.Due to the dynamically changing traffic patterns,the state-of the-art approaches that do this all require forklift changes to data center networking gear.The root of problem is lack of distinct strategies for elephant and mice flows.Under this condition,it is essential to enforce accurate elephant flow detection and come up with a novel load balancing solution to alleviate the network congestion and achieve high bandwidth utilization.This paper proposed an OpenFlow-based load balancing strategy for datacenter networks that accurately detect elephant flows and enforce distinct routing schemes with different flow types so as to achieve high usage of network capacity.The prototype implemented in Mininet testbed with POX controller and verify the feasibility of our load-balancing strategy when dealing with flow confliction and network degradation.The results show the proposed strategy can adequately generate flow rules and significantly enhance the performance of the bandwidth usage compared against other solutions from the literature in terms of load balancing.展开更多
Previous studies showed that an axisymmetric hub-initiated disturbance defined as partial surge may initiate the stall of a transonic compressor; to reveal the instability evolution under full-span incompressible flow...Previous studies showed that an axisymmetric hub-initiated disturbance defined as partial surge may initiate the stall of a transonic compressor; to reveal the instability evolution under full-span incompressible flow for different levels of hub loading and B parameter, an experimental investigation is conducted on a single-stage low-speed compressor. Experimental results show that under a uniform inflow condition without inlet flow distortion, a modal-type stall inception dominates in this low-speed compressor. When an inlet screen introducing hub distortion is used to increase the hub loading, a compressor stall is initiated by a modal wave, but large disturbances are present in the hub region before the compressor stall, which become stronger as the hub loading increases. Under high hub loading and large B parameter（implemented by adding hub distortion through an inlet screen and enlarging the outlet plenum volume, respectively）, a compressor stall is triggered by an axisymmetric hub-initiated disturbance, which is much different from the modal-like disturbances. The beginning of this axisymmetric disturbance may be captured over 800 rotor revolutions prior to the onset of stall, and the amplitude grows with time. The disturbance is hub-initiated because the disturbance signal at the hub is detected much earlier than that at the tip; meanwhile, the frequency of this axisymmetric disturbance changes with the length of the inlet duct. The characteristics of instability evolution in the low-speed compressor are also compared with those in a transonic compressor.展开更多
In coal mining,rock strata are fractured under cyclic loading and unloading to form fracture channels.Fracture channels are the main flow narrows for gas.Therefore,expounding the flow conductivity of fracture channels...In coal mining,rock strata are fractured under cyclic loading and unloading to form fracture channels.Fracture channels are the main flow narrows for gas.Therefore,expounding the flow conductivity of fracture channels in rocks on fluids is significant for gas flow in rock strata.In this regard,graded incremental cyclic loading and unloading experiments were conducted on sandstones with different initial stress levels.Then,the three-dimensional models for fracture channels in sandstones were established.Finally,the fracture channel percentages were used to reflect the flow conductivity of fracture channels.The study revealed how the particle size distribution of fractured sandstone affects the formation and expansion of fracture channels.It was found that a smaller proportion of large blocks and a higher proportion of small blocks after sandstone fails contribute more to the formation of fracture channels.The proportion of fracture channels in fractured rock can indicate the flow conductivity of those channels.When the proportion of fracture channels varies gently,fluids flow evenly through those channels.However,if the proportion of fracture channels varies significantly,it can greatly affect the flow rate of fluids.The research results contribute to revealing the morphological evolution and flow conductivity of fracture channels in sandstone and then provide a theoretical basis for clarifying the gas flow pattern in the rock strata of coal mines.展开更多
Ecosystem conservation has become one of the purposes in river management as well as flood mitigation and water resources management, and understanding of river flow and morphology in a stream with vegetation becomes ...Ecosystem conservation has become one of the purposes in river management as well as flood mitigation and water resources management, and understanding of river flow and morphology in a stream with vegetation becomes important. Recently 2D depth averaged analysis is familiar even in a stream with vegetation by taking account of form drag due to vegetation. However, the shear stress in vegetated area is not properly described because the resistance law due to bed roughness is not reasonably modified in vegetated area. In this study, we discussed the bed roughness boundary layer in flow with non-submerged vegetation to deduce a reasonable relation between U and u* in vegetated area toward improving the analysis of sediment transport. The results show that the modification of resistance law using by thickness, velocity distribution in that layer was found to bring significant improvement of accurate estimation of shear velocity and subsequently the sediment transport. The proposed modification is improved by 2D depth averaged analysis based on this concept, and its application is certificated through flume experiment.展开更多
In this paper a procedure is established for solving the Probabilistic Load Flow in an electrical power network, considering correlation between power generated by power plants, loads demanded on each bus and power in...In this paper a procedure is established for solving the Probabilistic Load Flow in an electrical power network, considering correlation between power generated by power plants, loads demanded on each bus and power injected by wind farms. The method proposed is based on the generation of correlated series of power values, which can be used in a MonteCarlo simulation, to obtain the probability density function of the power through branches of an electrical network.展开更多
Load sensing pumps have been widely used in diverse hydraulic systems.Studies show that structural parameters have undeniable impacts on the characteristics and efficiency of the load sensing pump.The main purpose of ...Load sensing pumps have been widely used in diverse hydraulic systems.Studies show that structural parameters have undeniable impacts on the characteristics and efficiency of the load sensing pump.The main purpose of this article is to study the influence of load sensing pump structure parameters on flow characteristics.In the present study,a nonlinear multi-parameter model is proposed for this type of pump.In this model,different parameters,including spool clearance,spool covering amount,internal leakage are considered to reflect the displacement adjustment process of the load sensing pump.Moreover,a frequency sweep method is proposed to analyze the frequency domain of the nonlinear mathematical model.An experiment rig was built to study the influence of key structural parameters on the dynamic follow-up characteristics of the pump flow.The obtained results show that the diameter of the orifice d can significantly affect the working characteristics of the pump.It is found that a large diameter of the orifice d can improve the phase following ability of the system,while a small diameter of the orifice d can reduce the bypass flow rate and increase the amplitude following ability.This paper provides a new consideration to study the dynamic follow-up characteristics of the load sensing pump.展开更多
Correlations among random variables make significant impacts on probabilistic load flow(PLF)calculation results.In the existing studies,correlation coefficients or Gaussian copula are usually used to model the correla...Correlations among random variables make significant impacts on probabilistic load flow(PLF)calculation results.In the existing studies,correlation coefficients or Gaussian copula are usually used to model the correlations,while vine copula,which describes the complex dependence structure(DS)of random variables,is seldom discussed since it brings in much heavier computational burdens.To overcome this problem,this paper proposes an efficient PLF method considering input random variables with complex DS.Specifically,the Rosenblatt transformation(RT)is used to transform vine copula⁃based correlated variables into independent ones;and then the sparse polynomial chaos expansion(SPCE)evaluates output random variables of PLF calculation.The effectiveness of the proposed method is verified using the IEEE 123⁃bus system.展开更多
Heat transfer between gas-solid multiphase flow and tubes occurs in many industry processes, such as circulating fluidized bed process, pneumatic conveying process, chemical process, drying process, etc. This paper fo...Heat transfer between gas-solid multiphase flow and tubes occurs in many industry processes, such as circulating fluidized bed process, pneumatic conveying process, chemical process, drying process, etc. This paper focuses on the influence of the presence of particles on the heat transfer between a tube and gas-solid suspension. The presence of particles causes positive enhancement of heat transfer in the case of high solid loading ratio, but heat transfer reduction has been found for in the case of very low solid loading ratio (M s of less than 0.05 kg/kg). A useful correlation incorporating solid loading ratio, particle size and flow Reynolds number was derived from experimental data. In addition, the k-ε two-equation model and the Fluctuation-Spectrum- Random-Trajectory Model (FSRT Model) are used to simulate the flow field and heat transfer of the gas-phase and the solid-phase, respectively. Through coupling of the two phases the model can predict the local and total heat transfer characteristics of tube in gas-solid cross flow. For the total heat transfer enhancement due to particles loading the model predictions agreed well with experimental data.展开更多
Because of the randomness and uncertainty,integration of large-scale wind farms in a power system will exert significant influences on the distribution of power flow.This paper uses polynomial normal transformation me...Because of the randomness and uncertainty,integration of large-scale wind farms in a power system will exert significant influences on the distribution of power flow.This paper uses polynomial normal transformation method to deal with non-normal random variable correlation,and solves probabilistic load flow based on Kriging method.This method is a kind of smallest unbiased variance estimation method which estimates unknown information via employing a point within the confidence scope of weighted linear combination.Compared with traditional approaches which need a greater number of calculation times,long simulation time,and large memory space,Kriging method can rapidly estimate node state variables and branch current power distribution situation.As one of the generator nodes in the western Yunnan power grid,a certain wind farm is chosen for empirical analysis.Results are used to compare with those by Monte Carlo-based accurate solution,which proves the validity and veracity of the model in wind farm power modeling as output of the actual turbine through PSD-BPA.展开更多
基金supported by Basic Science Research Program through the National Natural Science Foundation of China(Grant No.61867003).
文摘As the proportion of newenergy increases,the traditional cumulant method(CM)produces significant errorswhen performing probabilistic load flow(PLF)calculations with large-scale wind power integrated.Considering the wind speed correlation,a multi-scenario PLF calculation method that combines random sampling and segmented discrete wind farm power was proposed.Firstly,based on constructing discrete scenes of wind farms,the Nataf transform is used to handle the correlation between wind speeds.Then,the random sampling method determines the output probability of discrete wind power scenarios when wind speed exhibits correlation.Finally,the PLF calculation results of each scenario areweighted and superimposed following the total probability formula to obtain the final power flow calculation result.Verified in the IEEE standard node system,the absolute percent error(APE)for the mean and standard deviation(SD)of the node voltages and branch active power are all within 1%,and the average root mean square(AMSR)values of the probability curves are all less than 1%.
基金co-supported by the National Natural Science Foundation of China(No.12472332)。
文摘This paper investigates the influence of the spanwise-distributed trailing-edge camber morphing on the dynamic stall characteristics of a finite-span wing at Re=2×10^(5).The mathematical model of the spanwise-distributed trailing-edge camber morphing is established based on Chebyshev polynomials,and the deformed wing surface is modeled by a spline surface according to the rib's morphing in the chordwise direction.The Computational Fluid Dynamics(CFD)method is adopted to obtain flow-field results and aerodynamic forces.The SST-γmodel is introduced and the overset mesh technique is adopted.The numerical results show that the spanwisedistributed trailing-edge morphing obviously changes the aerodynamic and energy transfer characteristics of the dynamic stall.Especially when the phase difference between the trailing-edge motion and the wing pitch is-π/2,the interaction between the three-dimensional(3-D)Leading-Edge Vortex(LEV)and Trailing-Edge Vortex(TEV)is strengthened,and the work done by the aerodynamic force turns negative.This indicates that the trailing-edge deformation has the potential to suppress the oscillation amplitude of stall flutter.We also found that as the trailing-edge camber morphing varies more complexly along the spanwise direction,the suppression effect decreases accordingly.
基金supported by the National Natural Science Foundation of China(No.52174043)the Beijing Natural Science Foundation(No.3242019)+1 种基金the CNPC Innovation Foundation(No.2022DQ02-0208)the State Key Laboratory of Deep Oil and Gas(No.SKLD0G2024-KFZD-06).
文摘Two actual rocks drilled from a typical ultra-deep hydrocarbon reservoir in the Tarim Basin are selected to conduct in-situ stress-loading micro-focus CT scanning experiments.The gray images of rock microstructure at different stress loading stages are obtained.The U-Net fully convolutional neural network is utilized to achieve fine semantic segmentation of rock skeleton,pore space,and microfractures based on CT slice images of deep rocks.The three-dimensional digital rock models of deformed multiscale fractured-porous media at different stress loading stages are thereafter reconstructed,and the equivalent fracture-pore network models are finally extracted to explore the underlying mechanisms of gas-water two-phase flow at the pore-scale.Results indicate that,in the process of insitu stress loading,both the deep rocks have experienced three stages:linear elastic deformation,nonlinear plastic deformation,and shear failure.The micro-mechanical behavior greatly affects the dynamic deformation of rock microstructure and gas-water two-phase flow.In the linear elastic deformation stage,with the increase in in-situ stress,both the deep rocks are gradually compacted,leading to decreases in average pore radius,pore throat ratio,tortuosity,and water-phase relative permeability,while the coordination number nearly remains unchanged.In the plastic deformation stage,the synergistic influence of rock compaction and existence of micro-fractures typically exert a great effect on pore-throat topological properties and gas-water relative permeability.In the shear failure stage,due to the generation and propagation of micro-fractures inside the deep rock,the topological connectivity becomes better,fluid flow paths increase,and flow conductivity is promoted,thus leading to sharp increases in average pore radius and coordination number,rapid decreases in pore throat ratio and tortuosity,as well as remarkable improvement in relative permeability of gas phase and waterphase.
基金Supported by National Natural Science Foundation of China(Grant No.52075501).
文摘The current research on the manufacturing of large-scale and complex components focuses mainly on the casting processes.Compared with casting,plastic forming has significant advantages in terms of performance.However,effectively controlling the material flow to achieve a reduced loading force and near-uniformity in the isothermal plastic forming process of large-scale asymmetric magnesium alloy complex housings(LSMACHs)is challenging.This study proposes a material flow control method based on the diffluence upsetting-extrusion forming(DUEF)process by dividing different forging deformation regions,combining these with the principal stress method,and establishing an efficient and accurate design procedure.A rational preformed billet was designed successfully using this method.Subsequently,a finite element simulation was employed to analyze the multiphysics fields of the DUEF process.The results indicated that compared with the traditional closed-die forging(TCDF)process,the DUEF process could control the orderly flow of materials,achieve short-distance filling of materials,and reduce hydrostatic stress.Simultaneously,it improved the deformation uniformity by 20.3%and reduced the loading force by 22.6%.Finally,the rationality of the proposed method was validated through physical experiments.Compared with the TCDF process,the DUEF process exhibited a low loading force and uniform mechanical properties.The proposed material flow control method based on the DUEF process provides a new technological approach for the plastic formation of LSMACH and similar components.
基金Supported by National Natural Science Foundation of China(41071214)~~
文摘[Objective] The aim was to al eviate the constructed wetland clogging problems and to explore to the effects of hydraulic loading on wetland clogging. [Method] The experiment, through artificial soil columns, simulated vertical flow arti-ficial wetland, set four hydraulic load level at 50, 100, 150 and 200 cm/d, to identify the impact of hydraulic loading on wetland clogging and to explore the factors run-ning threshold. [Result] The results show that the different levels of hydraulic loading have greater impact; in the constructed wetland clogging process under high hy-draulic loading of 200 cm/d, the effective life was only six months, and the single factor can be speculated that the threshold of the hydraulic load should be at 100-150 cm/d; system can last for six months at low hydraulic loading and last for three months at medium hydraulic load. [Conclusion] The research provides references for wetland clogging experiments in future.
文摘In this paper, a synthetic mathematical model of load flow for flexible AC transmission systems (FACTS) with unified power flow controller (UPFC) is presented based on the analysis of basic principle and operation state of UPFC. The model can use the fast P Q decoupled load flow method. Examples of test systems show that the proposed model and method have good convergence. An effective tool is provided by the load flow computer program to analyze the load flow and initial valve calculation of the dynamic state of FACTS.
基金the National Key R&D Program of China(No.2017YFC0405002)
文摘Polyurethane polymer grouting materials were studied with conventional triaxial tests via the particle flow code in two dimensions（PFC^（2D）） method, and the simulation results agreed with the experimental data. The particle flow code method can simulate the mechanical properties of the polymer. The triaxial cyclic loading tests of the polymer material under different confining pressures were carried out via PFC^（2D） to analyze its mechanical performance. The PFC^（2D） simulation results show that the value of the elastic modulus of the polymer decreases slowly at first and fluctuated within a narrow range near the value of the peak strength; the cumulative plastic strain increases slowly at first and then increases rapidly; the peak strength and elastic modulus of polymer increase with the confining pressure; the PFC^（2D） method can be used to quantitatively evaluate the damage behavior of the polymer material and estimate the fatigue life of the materials under fatigue load based on the number and the location of micro-cracks. Thus, the PFC^（2D） method is an effective tool to study polymers.
基金financially supported by the National Natural Science Foundation of China(41771304)the National Key Research and Development Program of China(2017YFC0505404)。
文摘The breakdown of soil aggregates under rainfall and their abrasion in overland flow are important processes in water erosion due to the production of more fine and transportable particles and,the subsequent significant effect on the erosion intensity.Currently,little is known about the effects of sediment load on the soil aggregate abrasion and the relationship of this abrasion with some related hydraulic parameters.Here,the potential effects of sediment load on soil aggregate abrasion and hydraulic parameters in overland flow were investigated through a series of experiments in a 3.8-m-long hydraulic flume at the slope gradients of 8.7 and 26.8%,unit flow discharges from 2×10^-3 to 6×10^-3 m^2 s^-1,and the sediment concentration from 0 to 110 kg m-3.All the aggregates from Ultisols developed Quaternary red clay,Central China.The results indicated that discharge had the most significant(P<0.01)effect on the aggregates abrasion with the contributions of 58.76 and 60.34%,followed by sediment feed rate,with contributions of 39.66 and 34.12%at the slope gradients of 8.7 and 26.8%,respectively.The abrasion degree of aggregates was found to increase as a power function of the sediment concentration.Meanwhile,the flow depth,friction factor,and shear stress increased as a power function along with the increase of sediment concentration at different slope gradients and discharges.Reynolds number was obviously affected by sediment concentration and it decreased as sediment concentration increased.The ratio of the residual weight to the initial weight of soil aggregates(Wr/Wi)was found to increase as the linear function with an increasing flow depth(P=0.008)or Reynolds number(P=0.002)in the sediment-laden flow.The Wr/Wi values followed a power function decrease with increasing friction factor or shear stress in the sediment-laden flow,indicating that friction factor is the best hydraulic parameter for prediction of soil aggregate abrasion under different sediment load conditions.The information regarding the soil aggregate abrasion under various sediment load conditions can facilitate soil process-based erosion modeling.
文摘Load flow is an important tool used by power engineers for planning, to determine the best operation for a power system and exchange of power between utility companies. In order to have an efficient operating power system, it is necessary to determine which method is suitable and efficient for the system’s load flow analysis. A power flow analysis method may take a long time and therefore prevent achieving an accurate result to a power flow solution because of continuous changes in power demand and generations. This paper presents analysis of the load flow problem in power system planning studies. The numerical methods: Gauss-Seidel, Newton-Raphson and Fast Decoupled methods were compared for a power flow analysis solution. Simulation is carried out using Matlab for test cases of IEEE 9-Bus, IEEE 30-Bus and IEEE 57-Bus system. The simulation results were compared for number of iteration, computational time, tolerance value and convergence. The compared results show that Newton-Raphson is the most reliable method because it has the least number of iteration and converges faster.
基金Knowledge Innovation Project of Institute of Geographic Sciences and Natural Resources Research, CAS, No.O9V90143ZZ
文摘For the low price of coal and ineffective environmental management in mining area, China is in the dilemma of the increasing coal demand and the serious environmental issues in mining area. The more coal that is exported from a region, the more heavily it suffers from the environmental impacts of coal export. In this paper, the temporal and spatial process of exporting coal from Shanxi to other provinces of China is traced between 1975 and 2005. The coal net export of Shanxi increased to 370.69 million tonnes in 2005, representing an average annual growth rate of 7.5% from 1975 to 2005. With the increase of the amount of coal export from Shanxi, the Environmental Loads Transfer （ELT） that import provinces input to mining areas of Shanxi are rising. Effective means of internalizing the environmental externality of ELT lie in： 1） setting up a coal sustainable development fund to restore environment of coal mining area; 2） enforcing environment tax, financial transfer payment and transferring advantage technology of pollution reduction to coal export area; and 3） reducing coal regional flow by reducing coal demand from power generation and heating and other industries.
基金This work was supported by the National Basic Research Program of China,National Nature Science Foundation of China(No.51675266)the Foundation Research Funds for the Center in NUAA(Nos.NJ20160038,NS2017011)Foundation of Graduate Innovation Center in NUAA(No.kfjj20170220)。
文摘A filtering method of aero-engine load spectrum based on the rain flow counting is proposed in this paper.Firstly,the original load spectrum is counted through the rain flow method to get the peak and valley values.Then,some data points in the original load spectrum are added between the peak and valley values.Finally,the filtering spectrum is obtained.The proposed method can reflect the path information of the original load spectrum.In addition,it can also eliminate the noise in the signal and improve the efficiency of signal processing,which is of practical significance for the research of aero-engine.
基金This work was supported by the CETC Joint Advanced Research Foundation(Grant Nos.6141B08010102,6141B08080101)the National Science and Technology Major Project for IND(investigational new drug)(Project No.2018ZX09201014).
文摘In today’s datacenter network,the quantity growth and complexity increment of traffic is unprecedented,which brings not only the booming of network development,but also the problem of network performance degradation,such as more chance of network congestion and serious load imbalance.Due to the dynamically changing traffic patterns,the state-of the-art approaches that do this all require forklift changes to data center networking gear.The root of problem is lack of distinct strategies for elephant and mice flows.Under this condition,it is essential to enforce accurate elephant flow detection and come up with a novel load balancing solution to alleviate the network congestion and achieve high bandwidth utilization.This paper proposed an OpenFlow-based load balancing strategy for datacenter networks that accurately detect elephant flows and enforce distinct routing schemes with different flow types so as to achieve high usage of network capacity.The prototype implemented in Mininet testbed with POX controller and verify the feasibility of our load-balancing strategy when dealing with flow confliction and network degradation.The results show the proposed strategy can adequately generate flow rules and significantly enhance the performance of the bandwidth usage compared against other solutions from the literature in terms of load balancing.
基金the supports of the National Natural Science Foundation of China (Nos.51636001 and 51706008)Aeronautics Power Foundation of China (No.6141B090315)China Postdoctoral Science Foundation (No.2017M610742)
文摘Previous studies showed that an axisymmetric hub-initiated disturbance defined as partial surge may initiate the stall of a transonic compressor; to reveal the instability evolution under full-span incompressible flow for different levels of hub loading and B parameter, an experimental investigation is conducted on a single-stage low-speed compressor. Experimental results show that under a uniform inflow condition without inlet flow distortion, a modal-type stall inception dominates in this low-speed compressor. When an inlet screen introducing hub distortion is used to increase the hub loading, a compressor stall is initiated by a modal wave, but large disturbances are present in the hub region before the compressor stall, which become stronger as the hub loading increases. Under high hub loading and large B parameter（implemented by adding hub distortion through an inlet screen and enlarging the outlet plenum volume, respectively）, a compressor stall is triggered by an axisymmetric hub-initiated disturbance, which is much different from the modal-like disturbances. The beginning of this axisymmetric disturbance may be captured over 800 rotor revolutions prior to the onset of stall, and the amplitude grows with time. The disturbance is hub-initiated because the disturbance signal at the hub is detected much earlier than that at the tip; meanwhile, the frequency of this axisymmetric disturbance changes with the length of the inlet duct. The characteristics of instability evolution in the low-speed compressor are also compared with those in a transonic compressor.
基金This work was financially supported by the National Natural Science Foundation of China(No.52074041)the Chongqing Talent Program(No.cstc2022ycjh-bgzxm0077)the Postgraduate Research and Innovation Foundation of Chongqing,China(No.CYS23060).
文摘In coal mining,rock strata are fractured under cyclic loading and unloading to form fracture channels.Fracture channels are the main flow narrows for gas.Therefore,expounding the flow conductivity of fracture channels in rocks on fluids is significant for gas flow in rock strata.In this regard,graded incremental cyclic loading and unloading experiments were conducted on sandstones with different initial stress levels.Then,the three-dimensional models for fracture channels in sandstones were established.Finally,the fracture channel percentages were used to reflect the flow conductivity of fracture channels.The study revealed how the particle size distribution of fractured sandstone affects the formation and expansion of fracture channels.It was found that a smaller proportion of large blocks and a higher proportion of small blocks after sandstone fails contribute more to the formation of fracture channels.The proportion of fracture channels in fractured rock can indicate the flow conductivity of those channels.When the proportion of fracture channels varies gently,fluids flow evenly through those channels.However,if the proportion of fracture channels varies significantly,it can greatly affect the flow rate of fluids.The research results contribute to revealing the morphological evolution and flow conductivity of fracture channels in sandstone and then provide a theoretical basis for clarifying the gas flow pattern in the rock strata of coal mines.
文摘Ecosystem conservation has become one of the purposes in river management as well as flood mitigation and water resources management, and understanding of river flow and morphology in a stream with vegetation becomes important. Recently 2D depth averaged analysis is familiar even in a stream with vegetation by taking account of form drag due to vegetation. However, the shear stress in vegetated area is not properly described because the resistance law due to bed roughness is not reasonably modified in vegetated area. In this study, we discussed the bed roughness boundary layer in flow with non-submerged vegetation to deduce a reasonable relation between U and u* in vegetated area toward improving the analysis of sediment transport. The results show that the modification of resistance law using by thickness, velocity distribution in that layer was found to bring significant improvement of accurate estimation of shear velocity and subsequently the sediment transport. The proposed modification is improved by 2D depth averaged analysis based on this concept, and its application is certificated through flume experiment.
文摘In this paper a procedure is established for solving the Probabilistic Load Flow in an electrical power network, considering correlation between power generated by power plants, loads demanded on each bus and power injected by wind farms. The method proposed is based on the generation of correlated series of power values, which can be used in a MonteCarlo simulation, to obtain the probability density function of the power through branches of an electrical network.
基金funded by the National Key R&D Program of China under Grant(No.2021YFB2011300)Science and Technology on Aircraft Control Laboratory,Innovation Foundation of CAST(No.CAST-2021-02-02)Open Foundation of the State Key Laboratory of Fluid Power and Mechatronic Systems(No.GZKF-202010).
文摘Load sensing pumps have been widely used in diverse hydraulic systems.Studies show that structural parameters have undeniable impacts on the characteristics and efficiency of the load sensing pump.The main purpose of this article is to study the influence of load sensing pump structure parameters on flow characteristics.In the present study,a nonlinear multi-parameter model is proposed for this type of pump.In this model,different parameters,including spool clearance,spool covering amount,internal leakage are considered to reflect the displacement adjustment process of the load sensing pump.Moreover,a frequency sweep method is proposed to analyze the frequency domain of the nonlinear mathematical model.An experiment rig was built to study the influence of key structural parameters on the dynamic follow-up characteristics of the pump flow.The obtained results show that the diameter of the orifice d can significantly affect the working characteristics of the pump.It is found that a large diameter of the orifice d can improve the phase following ability of the system,while a small diameter of the orifice d can reduce the bypass flow rate and increase the amplitude following ability.This paper provides a new consideration to study the dynamic follow-up characteristics of the load sensing pump.
基金Fundamental Research Funds for the Central Universities,China(No.2232020D⁃53)。
文摘Correlations among random variables make significant impacts on probabilistic load flow(PLF)calculation results.In the existing studies,correlation coefficients or Gaussian copula are usually used to model the correlations,while vine copula,which describes the complex dependence structure(DS)of random variables,is seldom discussed since it brings in much heavier computational burdens.To overcome this problem,this paper proposes an efficient PLF method considering input random variables with complex DS.Specifically,the Rosenblatt transformation(RT)is used to transform vine copula⁃based correlated variables into independent ones;and then the sparse polynomial chaos expansion(SPCE)evaluates output random variables of PLF calculation.The effectiveness of the proposed method is verified using the IEEE 123⁃bus system.
文摘Heat transfer between gas-solid multiphase flow and tubes occurs in many industry processes, such as circulating fluidized bed process, pneumatic conveying process, chemical process, drying process, etc. This paper focuses on the influence of the presence of particles on the heat transfer between a tube and gas-solid suspension. The presence of particles causes positive enhancement of heat transfer in the case of high solid loading ratio, but heat transfer reduction has been found for in the case of very low solid loading ratio (M s of less than 0.05 kg/kg). A useful correlation incorporating solid loading ratio, particle size and flow Reynolds number was derived from experimental data. In addition, the k-ε two-equation model and the Fluctuation-Spectrum- Random-Trajectory Model (FSRT Model) are used to simulate the flow field and heat transfer of the gas-phase and the solid-phase, respectively. Through coupling of the two phases the model can predict the local and total heat transfer characteristics of tube in gas-solid cross flow. For the total heat transfer enhancement due to particles loading the model predictions agreed well with experimental data.
文摘Because of the randomness and uncertainty,integration of large-scale wind farms in a power system will exert significant influences on the distribution of power flow.This paper uses polynomial normal transformation method to deal with non-normal random variable correlation,and solves probabilistic load flow based on Kriging method.This method is a kind of smallest unbiased variance estimation method which estimates unknown information via employing a point within the confidence scope of weighted linear combination.Compared with traditional approaches which need a greater number of calculation times,long simulation time,and large memory space,Kriging method can rapidly estimate node state variables and branch current power distribution situation.As one of the generator nodes in the western Yunnan power grid,a certain wind farm is chosen for empirical analysis.Results are used to compare with those by Monte Carlo-based accurate solution,which proves the validity and veracity of the model in wind farm power modeling as output of the actual turbine through PSD-BPA.
