The multi-terminal direct current(DC)grid has extinctive superiorities over the traditional alternating current system in integrating large-scale renewable energy.Both the DC circuit breaker(DCCB)and the current flow ...The multi-terminal direct current(DC)grid has extinctive superiorities over the traditional alternating current system in integrating large-scale renewable energy.Both the DC circuit breaker(DCCB)and the current flow controller(CFC)are demanded to ensure the multiterminal DC grid to operates reliably and flexibly.However,since the CFC and the DCCB are all based on fully controlled semiconductor switches(e.g.,insulated gate bipolar transistor,integrated gate commutated thyristor,etc.),their separation configuration in the multiterminal DC grid will lead to unaffordable implementation costs and conduction power losses.To solve these problems,integrated equipment with both current flow control and fault isolation abilities is proposed,which shares the expensive and duplicated components of CFCs and DCCBs among adjacent lines.In addition,the complicated coordination control of CFCs and DCCBs can be avoided by adopting the integrated equipment in themultiterminal DC grid.In order to examine the current flow control and fault isolation abilities of the integrated equipment,the simulation model of a specific meshed four-terminal DC grid is constructed in the PSCAD/EMTDC software.Finally,the comparison between the integrated equipment and the separate solution is presented a specific result or conclusion needs to be added to the abstract.展开更多
The flow control at low Reynolds numbers is one of the most promising technologies in the field of aerodynamics,and it is also an important source of the innovation for novel aircraft.In this study,a new way of nonlin...The flow control at low Reynolds numbers is one of the most promising technologies in the field of aerodynamics,and it is also an important source of the innovation for novel aircraft.In this study,a new way of nonlinear flow control by interaction between two flexible flaps is proposed,and their flow control mechanism is studied employing the self-constructed immersed boundary-lattice Boltzmann-finite element method(IB-LB-FEM).The effects of the difference in material properties and flap length between the two flexible flaps on the nonlinear flow control of the airfoil are discussed.It is suggested that the relationship between the deformation of the two flexible flaps and the evolution of the vortex under the fluid-structure interaction(FSI).It is shown that the upstream flexible flap plays a key role in the flow control of the two flexible flaps.The FSI effect of the upstream flexible flap will change the unsteady flow behind it and affect the deformation of the downstream flexible flap.Two flexible flaps with different material properties and different lengths will change their own FSI characteristics by the induced vortex,effectively suppressing the flow separation on the airfoil’s upper surface.The interaction of two flexible flaps plays an extremely important role in improving the autonomy and adjustability of flow control.The numerical results will provide a theoretical basis and technical guidance for the development and application of a new flap passive control technology.展开更多
With the continuous increase of aeroengine flight ceiling(>20 km),the thin atmosphere at high altitudes and the size effect all cause the compressor component inlet Reynolds number to decrease rapidly to a critical...With the continuous increase of aeroengine flight ceiling(>20 km),the thin atmosphere at high altitudes and the size effect all cause the compressor component inlet Reynolds number to decrease rapidly to a critical value(approximately 2.0×10^(5)),and the significant transition process on the blade/endwall surface leads to the sharp degradation of compressor performance,which seriously affects the engine fuel consumption and working stability at high altitudes.In this paper,the research progress on the internal flow mechanism and flow control methods of axial compressors at low Reynolds numbers is reviewed from the aspects of quantification and prediction of performance variation,flow loss mechanism related to separation and transition,efficient transition control and flow field organization.The development trend of the low-Reynolds-number effect of axial flow compressors is noted,and the difficulties and application prospects of aerodynamic design and efficient flow control methods for compressors under low Reynolds numbers at high altitudes are discussed.展开更多
Modern shipboard microgrids(SMGs)incorporating distributed energy resources(DERs)enhance energy resilience and reduce carbon emissions.However,the hierarchical control schemes of DERs bring challenges to the tradition...Modern shipboard microgrids(SMGs)incorporating distributed energy resources(DERs)enhance energy resilience and reduce carbon emissions.However,the hierarchical control schemes of DERs bring challenges to the traditional power flow methods.This paper devises a generalized three-phase power flow approach for SMGs that integrate hierarchically controlled DERs.The main contributions include:(1)a droop-controlled three-phase Newton power flow algorithm that automatically incorporates the droop characteristics of DERs;(2)a secondary-controlled three-phase power flow method for power sharing and voltage regulation;and(3)modified Jacobian matrices to incorporate various hierarchical control modes.Numerical results demonstrate the effectiveness of the devised approach in both balanced and unbalanced three-phase hierarchically controlled SMG systems with arbitrary config-urations.展开更多
The conventional Shear Stress Transport(SST)k–ωturbulence model often exhibits substantial inaccu-racies when applied to the prediction of flow behavior in complex regions within axial flow control valves.To enhance...The conventional Shear Stress Transport(SST)k–ωturbulence model often exhibits substantial inaccu-racies when applied to the prediction of flow behavior in complex regions within axial flow control valves.To enhance its predictive fidelity for internal flow fields,this study introduces a novel calibration framework that integrates an artificial neural network(ANN)surrogate model with a particle swarm optimization(PSO)algorithm.In particular,an optimal Latin hypercube sampling strategy was employed to generate representative sample points across the empirical parameter space.For each sample,numerical simulations using ANSYS Fluent were conducted to evaluate the flow characteristics,with empirical turbulence model parameters as inputs and flow rate as the target output.These data were used to construct the high-fidelity ANN surrogate model.The PSO algorithm was then applied to this surrogate to identify the optimal set of empirical parameters tailored specifically to axial flow control valve configurations.A revealed by the presented results,the calibrated SST k–ωmodel significantly improves prediction accuracy:deviations from large eddy simulation(LES)benchmarks at small valve openings were reduced from 7.6%to under 3%.Furthermore,the refined model maintains the computational efficiency characteristic of Reynolds-averaged Navier-Stokes(RANS)simulations while substantially enhancing the accuracy of both pressure and velocity field predictions.Overall,the proposed methodology effectively reconciles the trade-off between computational cost and predictive accuracy,offering a robust and scalable approach for turbulence model calibration in complex internal flow scenarios.展开更多
The nanofluid-based direct absorption solar collector(NDASC)ensures that solar radiation passing through the tube wall is directly absorbed by the nanofluid,reducing thermal resistance in the energy transfer process.H...The nanofluid-based direct absorption solar collector(NDASC)ensures that solar radiation passing through the tube wall is directly absorbed by the nanofluid,reducing thermal resistance in the energy transfer process.However,further exploration is required to suppress the outward thermal losses from the nanofluid at high temperatures.Herein,this paper proposes a novel NDASC in which the outer surface of the collector tube is covered with functional coatings and a three-dimensional computational fluid dynamics model is established to study the energy flow distributions on the collector within the temperature range of 400-600 K.When the nanofluid’s absorption coefficient reaches 80 m^(-1),the NDASC shows the optimal thermal performance,and the NDASC with local Sn-In_(2)O_(3) coating achieves a 7.8% improvement in thermal efficiency at 400 K compared to the original NDASC.Furthermore,hybrid coatings with Sn In_(2)O_(3)/WTi-Al_(2)O_(3) are explored,and the optimal coverage angles are determined.The NDASC with such coatings shows a 10.22%-17.9% increase in thermal efficiency compared to the original NDASC and a 7.6%-19.5% increase compared to the traditional surface-type solar collectors,demonstrating the effectiveness of the proposed energy flow control strategy for DASCs.展开更多
Control Flow Graphs(CFGs)are essential for understanding the execution and data flow within software,serving as foundational structures in program analysis.Traditional CFG construction methods,such as bytecode analysi...Control Flow Graphs(CFGs)are essential for understanding the execution and data flow within software,serving as foundational structures in program analysis.Traditional CFG construction methods,such as bytecode analysis and Abstract Syntax Trees(ASTs),often face challenges due to the complex syntax of programming languages like Java and Python.This paper introduces a novel approach that leverages Large Language Models(LLMs)to generate CFGs through a methodical Chain of Thought(CoT)process.By employing CoT,the proposed approach systematically interprets code semantics directly from natural language,enhancing the adaptability across various programming languages and simplifying the CFG construction process.By implementing a modular AI chain strategy that adheres to the single responsibility principle,our approach breaks down CFG generation into distinct,manageable steps handled by separate AI and non-AI units,which can significantly improve the precision and coverage of CFG nodes and edges.The experiments with 245 Java and 281 Python code snippets from Stack Overflow demonstrate that our method achieves efficient performance on different programming languages and exhibits strong robustness.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
Benefit evaluation of debris flow prevention and control projects was one of the essential contents of debris flow prevention and mitigation work.In order to scientifically and quantitatively evaluate the comprehensiv...Benefit evaluation of debris flow prevention and control projects was one of the essential contents of debris flow prevention and mitigation work.In order to scientifically and quantitatively evaluate the comprehensive benefit of debris flow prevention and control projects,this study identified nine factors as evaluation indicators from economic,social,and ecological aspects.The projection pursuit(PP) model based on the improved particle swarm optimization(IPSO) algorithm was used to construct a mathematical model to evaluate the benefit of debris flow prevention and control projects.The interpolation method was applied to divide the benefit grades.The debris flow prevention and control projects in Qipan,Taoguan,Chutou,Anjia,and Mozi gullies in Wenchuan County were chosen as typical cases for empirical analysis.The case study revealed that,among the criteria layer indicators,investment per unit of the protected area,investment per unit of the protected population,the amount of water and soil conservation,and reduction rate of accumulation fan had the most significant weights.The social and ecological benefits were found to be the more important in the target layer.The comprehensive benefit of Qipan,Taoguan,Chutou,Anjia,and Mozi gullies was found to be 4.44,4.83,1.95,3,and 2,respectively.The benefit ranking of the five gullies was consistent with their effectiveness in disaster prevention ranking in the flood season of 2019.Therefore,it could prove that the newly-built benefit evaluation model was practical and feasible,and the evaluation results of the sample could be reasonably interpreted,which verified the effectiveness of the methods.展开更多
The design of high-lift Low-Pressure Turbines(LPTs)causes the separation of the boundary layer on the suction side of the blade and leads to a strong secondary flow.This present study aims to minimize secondary losses...The design of high-lift Low-Pressure Turbines(LPTs)causes the separation of the boundary layer on the suction side of the blade and leads to a strong secondary flow.This present study aims to minimize secondary losses through endwall slot suction and incoming wakes in a front-loaded high-lift LPT cascade with Zweifel of 1.58 under low Reynolds number of 25000.Two slotted schemes for the boundary layer of the endwall were designed(Plan A and Plan B),and the effects of suction mass flow on secondary flow were studied.The underlying physics of the endwall boundary layer of the suction and secondary flow under unsteady wakes was discussed.The results show that slot suction at the endwall boundary layer can significantly suppress the secondary flow by removing low-momentum fluids.Plans A and B significantly reduced the secondary kinetic energy by 44.2%and 36.9%,respectively,compared with the baseline cascade at the suction mass flow ratios of 1%.With an increase in the mass flow ratio of suction,the secondary flow was gradually reduced in both Plans A and B.It is more beneficial to control the secondary flow to destroy the intersection of the pressure side and suction side of the horseshoe vortex before it develops into a passage vortex.Under unsteady wakes,the combined effects of incoming wakes and endwall boundary layer suction can further suppress the secondary flow at the suction mass flow ratios of 2%for Plan A,because the positive and negative vorticity inside upstream wakes accelerated the mixing of the main flow and secondary flow and thus increased the energy of secondary vortices.展开更多
Xinqiao Gully is located in the area of the 2008 Wenchuan M_(s)8.0 earthquake in Sichuan province,China.Based on the investigation of the 2023"6-26"Xinqiao Gully debris flow event,this study assessed the eff...Xinqiao Gully is located in the area of the 2008 Wenchuan M_(s)8.0 earthquake in Sichuan province,China.Based on the investigation of the 2023"6-26"Xinqiao Gully debris flow event,this study assessed the effectiveness of the debris flow control project and evaluated the debris flow hazards.Through field investigation and numerical simulation methods,the indicators of flow intensity reduction rate and storage capacity fullness were proposed to quantify the effectiveness of the engineering measures in the debris flow event.The simulation results show that the debris flow control project reduced the flow intensity by41.05%to 64.61%.The storage capacity of the dam decreases gradually from upstream to the mouth of the gully,thus effectively intercepting and controlling the debris flow.By evaluating the debris flow of different recurrence intervals,further measures are recommended for managing debris flow events.展开更多
The hypersonic shock-shock interaction flow field at double-wedge geometries controlled by plasma synthetic jet actuator is experimentally studied in a Ma = 8 high-enthalpy shock tunnel with the purpose of exploring a...The hypersonic shock-shock interaction flow field at double-wedge geometries controlled by plasma synthetic jet actuator is experimentally studied in a Ma = 8 high-enthalpy shock tunnel with the purpose of exploring a novel technique for reducing surface heat flux in a real flight environment. The results demonstrate that increasing the discharge energy is advantageous in eliminating the shock wave, shifting the shock wave interaction point, and shortening the control response time. The oblique shock wave can be completely removed when the actuator's discharge energy grows from 0.4 J to 11.5 J, and the displacement of the shock wave interaction point increases by 124.56%, while the controlled response time is shortened by 30 μs. Besides, the reduction in diameter of the jet exit is firstly proved to have a negative impact on energy deposition in a working environment with incoming flow, which reduces the discharge energy and hence decreases the control effect. The shock wave control response time lengthens when the jet exits away from the second wedge. Along with comparing the change in wall heat flux at the second wedge over time, the control effect of plasma synthetic jet actuator with and without inflation is also analyzed. When plasma synthetic jet works in inflatable mode, both the ability to eliminate shock waves and the shifting effect of the shock wave interaction point are increased significantly, and the wall heat flux is also reduced.展开更多
Bottom water coning is the main reason to reduce the recovery of horizontal bottom water reservoir. By water coning, we mean the oil-water interface changes from a horizontal state to a mound-shaped cone and breaks th...Bottom water coning is the main reason to reduce the recovery of horizontal bottom water reservoir. By water coning, we mean the oil-water interface changes from a horizontal state to a mound-shaped cone and breaks through to the wellbore. Autonomous inflow control device(AICD) is an important instrument maintain normal production after bottom water coning, however, the resistance increasing ability of the swirl type AICD is insufficient at present, which seriously affects the water control effect. Aiming this problem, this paper designs a multi-stage resistance-increasing and composite type AICD. The separation mechanism of oil-water two phases in this structure, the resistance form of oil-water single phase and the resistance-increasing principle of water phase are analyzed. Establishing the dual-phase multi-stage separation and resistance-increasing model, and verified by measuring the throttling pressure drop and oil-water volume fraction of the AICD, it is found that the composite type AICD has the effect of ICD and AICD at the same time, which can balance the production rate of each well section at the initial stage of production, delay the occurrence of bottom water coning. In the middle and later stages of production, water-blocking can be effectively increased to achieve water control and stable production.After structural sensitivity analysis, the influence law of various structural parameters on the water control performance of composite AICD was obtained. The simulation calculation results show that,compared with the existing swirl type AICD, composite AICD has higher sensitivity to moisture content,the water phase throttling pressure drop is increased by 4.5 times on average. The composite AICD is suitable for the entire stage of horizontal well production.展开更多
An intelligent wind tunnel using an active learning approach automates flow control experiments to discover the aerodynamic impact of sweeping jet on a swept wing. A Gaussian process regression model is established to...An intelligent wind tunnel using an active learning approach automates flow control experiments to discover the aerodynamic impact of sweeping jet on a swept wing. A Gaussian process regression model is established to study the jet actuator's performance at various attack and flap deflection angles. By selectively focusing on the most informative experiments, the proposed framework was able to predict 3721 wing conditions from just 55experiments, significantly reducing the number of experiments required and leading to faster and cost-effective predictions. The results show that the angle of attack and flap deflection angle are coupled to affect the effectiveness of the sweeping jet. Meanwhile, increasing the jet momentum coefficient can contribute to lift enhancement;a momentum coefficient of 3% can increase the lift coefficient by at most 0.28. Additionally, the improvement effects are more pronounced when actuators are placed closer to the wing root.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
As the demand for more efficient and adaptable power distribution systems intensifies, especially in rural areas, innovative solutions like the Capacitor-Coupled Substation with a Controllable Network Transformer (CCS...As the demand for more efficient and adaptable power distribution systems intensifies, especially in rural areas, innovative solutions like the Capacitor-Coupled Substation with a Controllable Network Transformer (CCS-CNT) are becoming increasingly critical. Traditional power distribution networks, often limited by unidirectional flow capabilities and inflexibility, struggle to meet the complex demands of modern energy systems. The CCS-CNT system offers a transformative approach by enabling bidirectional power flow between high-voltage transmission lines and local distribution networks, a feature that is essential for integrating renewable energy sources and ensuring reliable electrification in underserved regions. This paper presents a detailed mathematical representation of power flow within the CCS-CNT system, emphasizing the control of both active and reactive power through the adjustment of voltage levels and phase angles. A control algorithm is developed to dynamically manage power flow, ensuring optimal performance by minimizing losses and maintaining voltage stability across the network. The proposed CCS-CNT system demonstrates significant potential in enhancing the efficiency and reliability of power distribution, making it particularly suited for rural electrification and other applications where traditional methods fall short. The findings underscore the system's capability to adapt to varying operational conditions, offering a robust solution for modern power distribution challenges.展开更多
This study aims to optimize the inbound traffic flow on on-ramps by considering low time costs,good speed stability,and high driving safety for mixed traffic flow.The optimal inlet gap is identified in advance,and tra...This study aims to optimize the inbound traffic flow on on-ramps by considering low time costs,good speed stability,and high driving safety for mixed traffic flow.The optimal inlet gap is identified in advance,and trajectory guidance for vehicles entering the gap is determined under safety constraints.Based on the initial state and sequence of vehicles entering the merging area,individual vehicle trajectories are optimized sequentially.An optimization model and method for ramp entry trajectories in mixed traffic flow are developed,incorporating on-ramp vehicle entry sequencing and ordinary vehicle trajectory prediction.Key performance indicators,including driving safety,total travel time,parking wait probability,and trajectory smoothness,are compared and analyzed to evaluate the proposed approach.展开更多
The primary objective in aircraft transportation is to minimize turbulent drag, thereby conserving energy and reducing emissions. We propose a sector-shaped counter-flow dielectric barrier discharge plasma actuator, w...The primary objective in aircraft transportation is to minimize turbulent drag, thereby conserving energy and reducing emissions. We propose a sector-shaped counter-flow dielectric barrier discharge plasma actuator, which leverages jet synthesis for drag reduction. A drag control experiment was conducted in a low-speed wind tunnel with a controlled flow velocity of 9.6 m/s(Re = 1.445 × 10^(4)). This study investigated the effects of varying pulse frequencies and actuation voltages on the turbulent boundary layer. Using a hot-wire measurement system, we analyzed the pulsating and time-averaged velocity distributions within the boundary layer to evaluate the streamwise turbulent drag reduction. The results show that the local TDR decreases as the pulse frequency increases, reaching a maximum reduction of approximately 20.97% at a pulse frequency of 50 Hz. In addition, as the actuation voltage increases, the friction coefficient decreases, increasing the drag reduction rate. The maximum drag reduction of approximately 33.34% is achieved at an actuation voltage of 10 kV.展开更多
Cash flow is a core element for enterprises to maintain operations and development.Cash flow forecasting models,through systematic analysis of an enterprise’s historical cash flow data,trends in operating activities,...Cash flow is a core element for enterprises to maintain operations and development.Cash flow forecasting models,through systematic analysis of an enterprise’s historical cash flow data,trends in operating activities,and external environmental factors,scientifically predict the scale,direction,and fluctuation of cash flow within a certain period in the future.This article focuses on the application of cash flow forecasting models in enterprise investment and financing decisions,sorts out the types and core functions of the models,analyzes their specific roles in investment project screening,financing plan formulation,risk prevention and control,and fund allocation,points out the existing problems in current applications,and proposes optimization paths.Research shows that the scientific application of cash flow forecasting models can enhance the accuracy and rationality of enterprises’investment and financing decisions,and help enterprises achieve sustainable development.展开更多
The phenomenon of shock/shock interaction(SSI)is widely observed in high-speed flow,and the double wedge SSI represents one of the typical problems encountered.The control effect of single-pulse plasma synthetic jet(P...The phenomenon of shock/shock interaction(SSI)is widely observed in high-speed flow,and the double wedge SSI represents one of the typical problems encountered.The control effect of single-pulse plasma synthetic jet(PSJ)on double wedge type-Ⅵand type-ⅤSSI was investigated experimentally and numerically,and the influence of discharge energy was also explored.The findings indicate that the interaction between PSJ and the high-speed freestream results in the formation of a plasma layer and a jet shock,which collectively governs the control of SSI.The control mechanism of single-pulse PSJ on SSI lies in its capacity to attenuate both shock and SSI.For type-ⅥSSI,the original second-wedge oblique shock is eliminated under the control of PSJ,resulting in a new type-ⅥSSI formed by the jet shock and the first-wedge oblique shock.For type-ⅤSSI,the presence of PSJ effectively mitigates the intensity of Mach stem,supersonic jet,and reflected shocks,thereby facilitating its transition into type-ⅥSSI.The numerical results indicate that the peak pressure can be reduced by approximately 32.26%at maximum.Furthermore,the development of PSJ also extends in the Z direction.The pressure decreases in the area affected by both PSJ and jet shock due to the attenuation of the SSI zone.With increasing discharge energy,the control effect of PSJ on SSI is gradually enhanced.展开更多
基金supported in part by Natural Science Foundation of Jiangsu Province under Grant BK20230255Natural Science Foundation of Shandong Province under Grant ZR2023QE281.
文摘The multi-terminal direct current(DC)grid has extinctive superiorities over the traditional alternating current system in integrating large-scale renewable energy.Both the DC circuit breaker(DCCB)and the current flow controller(CFC)are demanded to ensure the multiterminal DC grid to operates reliably and flexibly.However,since the CFC and the DCCB are all based on fully controlled semiconductor switches(e.g.,insulated gate bipolar transistor,integrated gate commutated thyristor,etc.),their separation configuration in the multiterminal DC grid will lead to unaffordable implementation costs and conduction power losses.To solve these problems,integrated equipment with both current flow control and fault isolation abilities is proposed,which shares the expensive and duplicated components of CFCs and DCCBs among adjacent lines.In addition,the complicated coordination control of CFCs and DCCBs can be avoided by adopting the integrated equipment in themultiterminal DC grid.In order to examine the current flow control and fault isolation abilities of the integrated equipment,the simulation model of a specific meshed four-terminal DC grid is constructed in the PSCAD/EMTDC software.Finally,the comparison between the integrated equipment and the separate solution is presented a specific result or conclusion needs to be added to the abstract.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.92371201,52192633,11872293,and 92152301)the Natural Science Basic Research Program of Shaanxi(Grant Nos.2024JC-YBQN-0008,and 2022JC-03)+1 种基金Shaanxi Key Research and Development Program(Grant No.2022ZDLGY02-07)the Joint Natural Science Foundation of China with Guangdong Province for TianHe-II Supercomputer Resources,and the Research Start-up Foundation of Xi’an University of Science and Technology for the High-Level Talent.
文摘The flow control at low Reynolds numbers is one of the most promising technologies in the field of aerodynamics,and it is also an important source of the innovation for novel aircraft.In this study,a new way of nonlinear flow control by interaction between two flexible flaps is proposed,and their flow control mechanism is studied employing the self-constructed immersed boundary-lattice Boltzmann-finite element method(IB-LB-FEM).The effects of the difference in material properties and flap length between the two flexible flaps on the nonlinear flow control of the airfoil are discussed.It is suggested that the relationship between the deformation of the two flexible flaps and the evolution of the vortex under the fluid-structure interaction(FSI).It is shown that the upstream flexible flap plays a key role in the flow control of the two flexible flaps.The FSI effect of the upstream flexible flap will change the unsteady flow behind it and affect the deformation of the downstream flexible flap.Two flexible flaps with different material properties and different lengths will change their own FSI characteristics by the induced vortex,effectively suppressing the flow separation on the airfoil’s upper surface.The interaction of two flexible flaps plays an extremely important role in improving the autonomy and adjustability of flow control.The numerical results will provide a theoretical basis and technical guidance for the development and application of a new flap passive control technology.
基金co-supported by the National Natural Science Foundation of China(No.52306053)the Science Center for Gas Turbine Project,China(No.P2022-B-Ⅱ-005-001)the National Science and Technology Major Project of China(No.2017-Ⅱ-0010-0024)。
文摘With the continuous increase of aeroengine flight ceiling(>20 km),the thin atmosphere at high altitudes and the size effect all cause the compressor component inlet Reynolds number to decrease rapidly to a critical value(approximately 2.0×10^(5)),and the significant transition process on the blade/endwall surface leads to the sharp degradation of compressor performance,which seriously affects the engine fuel consumption and working stability at high altitudes.In this paper,the research progress on the internal flow mechanism and flow control methods of axial compressors at low Reynolds numbers is reviewed from the aspects of quantification and prediction of performance variation,flow loss mechanism related to separation and transition,efficient transition control and flow field organization.The development trend of the low-Reynolds-number effect of axial flow compressors is noted,and the difficulties and application prospects of aerodynamic design and efficient flow control methods for compressors under low Reynolds numbers at high altitudes are discussed.
基金supported in part by the Department of Navy award N00014-24-1-2287 and N00014-23-1-2124。
文摘Modern shipboard microgrids(SMGs)incorporating distributed energy resources(DERs)enhance energy resilience and reduce carbon emissions.However,the hierarchical control schemes of DERs bring challenges to the traditional power flow methods.This paper devises a generalized three-phase power flow approach for SMGs that integrate hierarchically controlled DERs.The main contributions include:(1)a droop-controlled three-phase Newton power flow algorithm that automatically incorporates the droop characteristics of DERs;(2)a secondary-controlled three-phase power flow method for power sharing and voltage regulation;and(3)modified Jacobian matrices to incorporate various hierarchical control modes.Numerical results demonstrate the effectiveness of the devised approach in both balanced and unbalanced three-phase hierarchically controlled SMG systems with arbitrary config-urations.
基金funded by Gansu Provincial Department of Education(Industrial Support Plan Project:2025CYZC-048).
文摘The conventional Shear Stress Transport(SST)k–ωturbulence model often exhibits substantial inaccu-racies when applied to the prediction of flow behavior in complex regions within axial flow control valves.To enhance its predictive fidelity for internal flow fields,this study introduces a novel calibration framework that integrates an artificial neural network(ANN)surrogate model with a particle swarm optimization(PSO)algorithm.In particular,an optimal Latin hypercube sampling strategy was employed to generate representative sample points across the empirical parameter space.For each sample,numerical simulations using ANSYS Fluent were conducted to evaluate the flow characteristics,with empirical turbulence model parameters as inputs and flow rate as the target output.These data were used to construct the high-fidelity ANN surrogate model.The PSO algorithm was then applied to this surrogate to identify the optimal set of empirical parameters tailored specifically to axial flow control valve configurations.A revealed by the presented results,the calibrated SST k–ωmodel significantly improves prediction accuracy:deviations from large eddy simulation(LES)benchmarks at small valve openings were reduced from 7.6%to under 3%.Furthermore,the refined model maintains the computational efficiency characteristic of Reynolds-averaged Navier-Stokes(RANS)simulations while substantially enhancing the accuracy of both pressure and velocity field predictions.Overall,the proposed methodology effectively reconciles the trade-off between computational cost and predictive accuracy,offering a robust and scalable approach for turbulence model calibration in complex internal flow scenarios.
基金Project(52476095)supported by the National Natural Science Foundation of ChinaProject(kq2506013)supported by Changsha Outstanding Innovative Youth Training Program,China。
文摘The nanofluid-based direct absorption solar collector(NDASC)ensures that solar radiation passing through the tube wall is directly absorbed by the nanofluid,reducing thermal resistance in the energy transfer process.However,further exploration is required to suppress the outward thermal losses from the nanofluid at high temperatures.Herein,this paper proposes a novel NDASC in which the outer surface of the collector tube is covered with functional coatings and a three-dimensional computational fluid dynamics model is established to study the energy flow distributions on the collector within the temperature range of 400-600 K.When the nanofluid’s absorption coefficient reaches 80 m^(-1),the NDASC shows the optimal thermal performance,and the NDASC with local Sn-In_(2)O_(3) coating achieves a 7.8% improvement in thermal efficiency at 400 K compared to the original NDASC.Furthermore,hybrid coatings with Sn In_(2)O_(3)/WTi-Al_(2)O_(3) are explored,and the optimal coverage angles are determined.The NDASC with such coatings shows a 10.22%-17.9% increase in thermal efficiency compared to the original NDASC and a 7.6%-19.5% increase compared to the traditional surface-type solar collectors,demonstrating the effectiveness of the proposed energy flow control strategy for DASCs.
基金Supported by the National Natural Science Foundation of China(62462036,62262031)Jiangxi Provincial Natural Science Foundation(20242BAB26017,20232BAB202010)+1 种基金Distinguished Youth Fund Project of the Natural Science Foundation of Jiangxi Province(20242BAB23011)the Jiangxi Province Graduate Innovation Found Project(YJS2023032)。
文摘Control Flow Graphs(CFGs)are essential for understanding the execution and data flow within software,serving as foundational structures in program analysis.Traditional CFG construction methods,such as bytecode analysis and Abstract Syntax Trees(ASTs),often face challenges due to the complex syntax of programming languages like Java and Python.This paper introduces a novel approach that leverages Large Language Models(LLMs)to generate CFGs through a methodical Chain of Thought(CoT)process.By employing CoT,the proposed approach systematically interprets code semantics directly from natural language,enhancing the adaptability across various programming languages and simplifying the CFG construction process.By implementing a modular AI chain strategy that adheres to the single responsibility principle,our approach breaks down CFG generation into distinct,manageable steps handled by separate AI and non-AI units,which can significantly improve the precision and coverage of CFG nodes and edges.The experiments with 245 Java and 281 Python code snippets from Stack Overflow demonstrate that our method achieves efficient performance on different programming languages and exhibits strong robustness.
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financially supported by the National Key Research and Development Program(No.2018YFC1505402)the National Natural Science Foundation of China(No.41871174)+1 种基金the Science and Technology Department of Sichuan Province(No.2020YFSY0013)the Fundamental Research Funds for the Central Universities Project(No.2682019CX19)。
文摘Benefit evaluation of debris flow prevention and control projects was one of the essential contents of debris flow prevention and mitigation work.In order to scientifically and quantitatively evaluate the comprehensive benefit of debris flow prevention and control projects,this study identified nine factors as evaluation indicators from economic,social,and ecological aspects.The projection pursuit(PP) model based on the improved particle swarm optimization(IPSO) algorithm was used to construct a mathematical model to evaluate the benefit of debris flow prevention and control projects.The interpolation method was applied to divide the benefit grades.The debris flow prevention and control projects in Qipan,Taoguan,Chutou,Anjia,and Mozi gullies in Wenchuan County were chosen as typical cases for empirical analysis.The case study revealed that,among the criteria layer indicators,investment per unit of the protected area,investment per unit of the protected population,the amount of water and soil conservation,and reduction rate of accumulation fan had the most significant weights.The social and ecological benefits were found to be the more important in the target layer.The comprehensive benefit of Qipan,Taoguan,Chutou,Anjia,and Mozi gullies was found to be 4.44,4.83,1.95,3,and 2,respectively.The benefit ranking of the five gullies was consistent with their effectiveness in disaster prevention ranking in the flood season of 2019.Therefore,it could prove that the newly-built benefit evaluation model was practical and feasible,and the evaluation results of the sample could be reasonably interpreted,which verified the effectiveness of the methods.
基金support for this work was provided by the National Natural Science Foundation of China(No.52206060)the National Science and Technology Major Project of China(Nos.J2019-Ⅱ-0021-0042 and J2019-Ⅱ-0002-0022).
文摘The design of high-lift Low-Pressure Turbines(LPTs)causes the separation of the boundary layer on the suction side of the blade and leads to a strong secondary flow.This present study aims to minimize secondary losses through endwall slot suction and incoming wakes in a front-loaded high-lift LPT cascade with Zweifel of 1.58 under low Reynolds number of 25000.Two slotted schemes for the boundary layer of the endwall were designed(Plan A and Plan B),and the effects of suction mass flow on secondary flow were studied.The underlying physics of the endwall boundary layer of the suction and secondary flow under unsteady wakes was discussed.The results show that slot suction at the endwall boundary layer can significantly suppress the secondary flow by removing low-momentum fluids.Plans A and B significantly reduced the secondary kinetic energy by 44.2%and 36.9%,respectively,compared with the baseline cascade at the suction mass flow ratios of 1%.With an increase in the mass flow ratio of suction,the secondary flow was gradually reduced in both Plans A and B.It is more beneficial to control the secondary flow to destroy the intersection of the pressure side and suction side of the horseshoe vortex before it develops into a passage vortex.Under unsteady wakes,the combined effects of incoming wakes and endwall boundary layer suction can further suppress the secondary flow at the suction mass flow ratios of 2%for Plan A,because the positive and negative vorticity inside upstream wakes accelerated the mixing of the main flow and secondary flow and thus increased the energy of secondary vortices.
基金supported by the project of the China Geological Survey(No.DD20221746)the National Natural Science Foundation of China(Grant Nos.41101086)。
文摘Xinqiao Gully is located in the area of the 2008 Wenchuan M_(s)8.0 earthquake in Sichuan province,China.Based on the investigation of the 2023"6-26"Xinqiao Gully debris flow event,this study assessed the effectiveness of the debris flow control project and evaluated the debris flow hazards.Through field investigation and numerical simulation methods,the indicators of flow intensity reduction rate and storage capacity fullness were proposed to quantify the effectiveness of the engineering measures in the debris flow event.The simulation results show that the debris flow control project reduced the flow intensity by41.05%to 64.61%.The storage capacity of the dam decreases gradually from upstream to the mouth of the gully,thus effectively intercepting and controlling the debris flow.By evaluating the debris flow of different recurrence intervals,further measures are recommended for managing debris flow events.
基金supported by the National Natural Science Foundation of China (Nos. 92271110, 12202488, 12072352 and T2221002)the National Major Science and Technology Project of China (Nos. J2019-II-0016-0037 and J2019-Ⅲ-0010-0054)the Natural Science Program of National University of Defense Technology, China (No. ZK22-30)。
文摘The hypersonic shock-shock interaction flow field at double-wedge geometries controlled by plasma synthetic jet actuator is experimentally studied in a Ma = 8 high-enthalpy shock tunnel with the purpose of exploring a novel technique for reducing surface heat flux in a real flight environment. The results demonstrate that increasing the discharge energy is advantageous in eliminating the shock wave, shifting the shock wave interaction point, and shortening the control response time. The oblique shock wave can be completely removed when the actuator's discharge energy grows from 0.4 J to 11.5 J, and the displacement of the shock wave interaction point increases by 124.56%, while the controlled response time is shortened by 30 μs. Besides, the reduction in diameter of the jet exit is firstly proved to have a negative impact on energy deposition in a working environment with incoming flow, which reduces the discharge energy and hence decreases the control effect. The shock wave control response time lengthens when the jet exits away from the second wedge. Along with comparing the change in wall heat flux at the second wedge over time, the control effect of plasma synthetic jet actuator with and without inflation is also analyzed. When plasma synthetic jet works in inflatable mode, both the ability to eliminate shock waves and the shifting effect of the shock wave interaction point are increased significantly, and the wall heat flux is also reduced.
基金supported by National Natural Science Foundation(52204050)Sichuan Science and Technology Program(2021ZHCG0013,22ZDYF3009)。
文摘Bottom water coning is the main reason to reduce the recovery of horizontal bottom water reservoir. By water coning, we mean the oil-water interface changes from a horizontal state to a mound-shaped cone and breaks through to the wellbore. Autonomous inflow control device(AICD) is an important instrument maintain normal production after bottom water coning, however, the resistance increasing ability of the swirl type AICD is insufficient at present, which seriously affects the water control effect. Aiming this problem, this paper designs a multi-stage resistance-increasing and composite type AICD. The separation mechanism of oil-water two phases in this structure, the resistance form of oil-water single phase and the resistance-increasing principle of water phase are analyzed. Establishing the dual-phase multi-stage separation and resistance-increasing model, and verified by measuring the throttling pressure drop and oil-water volume fraction of the AICD, it is found that the composite type AICD has the effect of ICD and AICD at the same time, which can balance the production rate of each well section at the initial stage of production, delay the occurrence of bottom water coning. In the middle and later stages of production, water-blocking can be effectively increased to achieve water control and stable production.After structural sensitivity analysis, the influence law of various structural parameters on the water control performance of composite AICD was obtained. The simulation calculation results show that,compared with the existing swirl type AICD, composite AICD has higher sensitivity to moisture content,the water phase throttling pressure drop is increased by 4.5 times on average. The composite AICD is suitable for the entire stage of horizontal well production.
基金supported by the National Natural Science Foundation of China (Grant No.92271107)。
文摘An intelligent wind tunnel using an active learning approach automates flow control experiments to discover the aerodynamic impact of sweeping jet on a swept wing. A Gaussian process regression model is established to study the jet actuator's performance at various attack and flap deflection angles. By selectively focusing on the most informative experiments, the proposed framework was able to predict 3721 wing conditions from just 55experiments, significantly reducing the number of experiments required and leading to faster and cost-effective predictions. The results show that the angle of attack and flap deflection angle are coupled to affect the effectiveness of the sweeping jet. Meanwhile, increasing the jet momentum coefficient can contribute to lift enhancement;a momentum coefficient of 3% can increase the lift coefficient by at most 0.28. Additionally, the improvement effects are more pronounced when actuators are placed closer to the wing root.
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.
文摘As the demand for more efficient and adaptable power distribution systems intensifies, especially in rural areas, innovative solutions like the Capacitor-Coupled Substation with a Controllable Network Transformer (CCS-CNT) are becoming increasingly critical. Traditional power distribution networks, often limited by unidirectional flow capabilities and inflexibility, struggle to meet the complex demands of modern energy systems. The CCS-CNT system offers a transformative approach by enabling bidirectional power flow between high-voltage transmission lines and local distribution networks, a feature that is essential for integrating renewable energy sources and ensuring reliable electrification in underserved regions. This paper presents a detailed mathematical representation of power flow within the CCS-CNT system, emphasizing the control of both active and reactive power through the adjustment of voltage levels and phase angles. A control algorithm is developed to dynamically manage power flow, ensuring optimal performance by minimizing losses and maintaining voltage stability across the network. The proposed CCS-CNT system demonstrates significant potential in enhancing the efficiency and reliability of power distribution, making it particularly suited for rural electrification and other applications where traditional methods fall short. The findings underscore the system's capability to adapt to varying operational conditions, offering a robust solution for modern power distribution challenges.
文摘This study aims to optimize the inbound traffic flow on on-ramps by considering low time costs,good speed stability,and high driving safety for mixed traffic flow.The optimal inlet gap is identified in advance,and trajectory guidance for vehicles entering the gap is determined under safety constraints.Based on the initial state and sequence of vehicles entering the merging area,individual vehicle trajectories are optimized sequentially.An optimization model and method for ramp entry trajectories in mixed traffic flow are developed,incorporating on-ramp vehicle entry sequencing and ordinary vehicle trajectory prediction.Key performance indicators,including driving safety,total travel time,parking wait probability,and trajectory smoothness,are compared and analyzed to evaluate the proposed approach.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61971345 and 52107174)。
文摘The primary objective in aircraft transportation is to minimize turbulent drag, thereby conserving energy and reducing emissions. We propose a sector-shaped counter-flow dielectric barrier discharge plasma actuator, which leverages jet synthesis for drag reduction. A drag control experiment was conducted in a low-speed wind tunnel with a controlled flow velocity of 9.6 m/s(Re = 1.445 × 10^(4)). This study investigated the effects of varying pulse frequencies and actuation voltages on the turbulent boundary layer. Using a hot-wire measurement system, we analyzed the pulsating and time-averaged velocity distributions within the boundary layer to evaluate the streamwise turbulent drag reduction. The results show that the local TDR decreases as the pulse frequency increases, reaching a maximum reduction of approximately 20.97% at a pulse frequency of 50 Hz. In addition, as the actuation voltage increases, the friction coefficient decreases, increasing the drag reduction rate. The maximum drag reduction of approximately 33.34% is achieved at an actuation voltage of 10 kV.
文摘Cash flow is a core element for enterprises to maintain operations and development.Cash flow forecasting models,through systematic analysis of an enterprise’s historical cash flow data,trends in operating activities,and external environmental factors,scientifically predict the scale,direction,and fluctuation of cash flow within a certain period in the future.This article focuses on the application of cash flow forecasting models in enterprise investment and financing decisions,sorts out the types and core functions of the models,analyzes their specific roles in investment project screening,financing plan formulation,risk prevention and control,and fund allocation,points out the existing problems in current applications,and proposes optimization paths.Research shows that the scientific application of cash flow forecasting models can enhance the accuracy and rationality of enterprises’investment and financing decisions,and help enterprises achieve sustainable development.
基金supported by the Independent Innovation Science Fund of National University of Defense Technology(No.24-ZZCX-BC-05)National Natural Science Foundation of China(Nos.92271110 and 12202488)+2 种基金the Major National Science and Technology Project(No.J2019-Ⅲ0010-0054)the National Postdoctoral Researcher Program of China(No.GZB20230985)the Natural Science Program of National University of Defense Technology(No.ZK22-30)。
文摘The phenomenon of shock/shock interaction(SSI)is widely observed in high-speed flow,and the double wedge SSI represents one of the typical problems encountered.The control effect of single-pulse plasma synthetic jet(PSJ)on double wedge type-Ⅵand type-ⅤSSI was investigated experimentally and numerically,and the influence of discharge energy was also explored.The findings indicate that the interaction between PSJ and the high-speed freestream results in the formation of a plasma layer and a jet shock,which collectively governs the control of SSI.The control mechanism of single-pulse PSJ on SSI lies in its capacity to attenuate both shock and SSI.For type-ⅥSSI,the original second-wedge oblique shock is eliminated under the control of PSJ,resulting in a new type-ⅥSSI formed by the jet shock and the first-wedge oblique shock.For type-ⅤSSI,the presence of PSJ effectively mitigates the intensity of Mach stem,supersonic jet,and reflected shocks,thereby facilitating its transition into type-ⅥSSI.The numerical results indicate that the peak pressure can be reduced by approximately 32.26%at maximum.Furthermore,the development of PSJ also extends in the Z direction.The pressure decreases in the area affected by both PSJ and jet shock due to the attenuation of the SSI zone.With increasing discharge energy,the control effect of PSJ on SSI is gradually enhanced.
