Topology optimization is an effective method to obtain a lightweight structure that meets the requirements of structural strength.Whether the optimization results meet the actual needs mainly depends on the accuracy o...Topology optimization is an effective method to obtain a lightweight structure that meets the requirements of structural strength.Whether the optimization results meet the actual needs mainly depends on the accuracy of the material properties and the boundary conditions,especially for a tiny Flapping-wing Micro Aerial Vehicle(FMAV)transmission system manufactured by 3D printing.In this paper,experimental and numerical computation efforts were undertaken to gain a reliable topology optimization method for the bottom of the transmission system.First,the constitutive behavior of the ultraviolet(UV)curable resin used in fabrication was evaluated.Second,a numerical computation model describing further verified via experiments.Topology optimization modeling considering nonlinear factors,e.g.contact,friction and collision,was presented,and the optimization results were verified by both dynamic simulation and experiments.Finally,detailed discussions on different load cases and constraints were presented to clarify their effect on the optimization.Our methods and results presented in this paper may shed light on the lightweight design of a FMAV.展开更多
Considering that the clutch cover assembly and driven disc assembly show common effect on the engagement/disengagement characteristics of the pull-type diaphragm spring clutches for heavy-duty commercial vehicles,the ...Considering that the clutch cover assembly and driven disc assembly show common effect on the engagement/disengagement characteristics of the pull-type diaphragm spring clutches for heavy-duty commercial vehicles,the diaphragm spring,cushion plate,and friction plate,are thoroughly analyzed in this paper.The A-L method and the micro-element method are used to analyze the mechanical properties of diaphragm spring and cushion plate,respectively.The mechanical characteristics are obtained via numerical simulation,and the deformation and load mechanical characteristics of the cushion plate are verified by experimental tests.According to the relationship between the pressure plate temperature and the friction coefficient of the friction plate,the influence of the change of the friction coefficient on the transmission torque characteristics of the clutch is analyzed.In view of the torque fluctuation in the process of engagement/disengagement,the mathematical model of torsional characteristics is established with consideration of the torsional characteristics of torsional damper.Modeling and simulation of the handling characteristics are carried out to evaluate the influence of the boosting characteristics of the hydraulic operated pneumatic booster on the clutch pedal operating force separation characteristics.Specific tests are also conducted,and the effectiveness of the established models is verified.展开更多
Blending the agility of aerial drones with the covert capabilities of underwater submersibles,the aerial-aquatic rotorcraft has garnered substantial interest due to their unparalleled capacity to traverse both air and...Blending the agility of aerial drones with the covert capabilities of underwater submersibles,the aerial-aquatic rotorcraft has garnered substantial interest due to their unparalleled capacity to traverse both air and water.Nevertheless,a critical hurdle for these vehicles lies in mitigating the adverse effects of repeatedly transitioning between these environments,particularly during water-surface takeoffs.Currently,research on the interference caused by rotors approaching water surfaces remains limited.This paper introduces a novel adaptive rotor aerodynamic model based on continuous finite vortex theory to predict rotor thrust within gas–liquid flow field.Initially,the model's sensitivity to system parameters was analyzed to optimize its predictive capabilities.Subsequently,a comprehensive ground/water experimental setup was designed to investigate the intricate aerodynamic interactions between the rotor flow field and water.By varying rotor sizes,the characteristics of the rotor flow field and water surface were examined at different rotor-water surface distances.The performance of different modeling methods was analyzed based on the rotor experimental data of a diameter of 0.38 m,and the prediction results were quantified using the percentage of the mean-square error.The results show that the average error of the finite vortex rotor model is the smallest.Finally,a novel transition boundary is proposed to divide the rotor flow field of the gas–liquid mixture into two stages.The thrust loss zone is defined to delineate the safe operating range of the aircraft,providing a basis for the design of aerial-aquatic rotorcraft.展开更多
This paper deeply discusses the causes of gear howling noise,the identification and analysis of multi-source excitation,the transmission path of dynamic noise,simulation and experimental research,case analysis,optimiz...This paper deeply discusses the causes of gear howling noise,the identification and analysis of multi-source excitation,the transmission path of dynamic noise,simulation and experimental research,case analysis,optimization effect,etc.,aiming to better provide a certain guideline and reference for relevant researchers.展开更多
This paper is concerned with the robust adaptive fault-tolerant control of a tandem coaxial ducted fan aircraft under system uncertainty, mismatched disturbance, and actuator saturation.For the proposed aircraft, comp...This paper is concerned with the robust adaptive fault-tolerant control of a tandem coaxial ducted fan aircraft under system uncertainty, mismatched disturbance, and actuator saturation.For the proposed aircraft, comprehensive controllability analysis is performed to evaluate the controllability of each state as well as the margin to reject mismatched disturbance without any knowledge of the controller. Mismatched disturbance attenuation is ensured through a structured Hinfinity controller tuned by a non-smooth optimization algorithm. Embedded with the H-infinity controller, an adaptive control law is proposed in order to mitigate matched system uncertainty and actuator fault. Input saturation is also considered by the modified reference model. Numerical simulation of the novel ducted fan aircraft is provided to illustrate the effectiveness of the proposed method. The simulation results reveal that the proposed adaptive controller achieves better transient response and more robust performance than classic Model Reference Adaptive Control（MRAC） method, even with serious actuator saturation.展开更多
Ducted fans are widely used in various applications of Unmanned Aerial Vehicles(UAVs)due to the high efficiency,low noise and high safety.The unsteady characteristics of ducted fans flying near the ground are signific...Ducted fans are widely used in various applications of Unmanned Aerial Vehicles(UAVs)due to the high efficiency,low noise and high safety.The unsteady characteristics of ducted fans flying near the ground are significant,which may bring stability problems.In this paper,the sliding mesh technology is applied and the Unsteady Reynolds Averaged Navier-Stokes(URANS)method is adopted to evaluate the influence of ground on the aerodynamic performance of ducted fans.The time-averaged results show that the ground leads to the decrease of duct thrust,the increase of rotor thrust and the decrease of total thrust.The transient results show that there exist small-scale stall cells with circumferential movements in ground effect.The stall cells start to appear at the blade root when the height is 0.8 rotor radius distance,and arise at both the blade root and tip when the height drops to 0.2.It is found that the unsteady cells rotate between blade passages with an approximate relative speed of 30%-80%of the fan speed,and lead to thrust fluctuations up to 37%of the total thrust.The results are essential to the flight control design of the ducted fan flying vehicle,to ensure its stability in ground effect.展开更多
A novel coaxial ducted fan structure aircraft is proposed to enable the aircraft near vertical walls at high altitudes.The state space equation of the system can be obtained by correlation deduction and identification...A novel coaxial ducted fan structure aircraft is proposed to enable the aircraft near vertical walls at high altitudes.The state space equation of the system can be obtained by correlation deduction and identification of the whole prototype model.Based on the duct test bench experiment and computational fluid dynamics(CFD)simulation analysis,the expressions between the different distances dWE from the rotor center of the prototype to the wall and the thrust,reaction torque,and tilting moment of the system under hovering conditions are obtained.The influence of the wall effect of the prototype is incorporated into the system model to analyze the relationship between distance dWE and the comprehensive controllability of the system.The results show that the system comprehensive controllability vector of other channels changes little with the decrease of the distance dWE,and only the controllability vector of the rolling channel increases significantly.At the same time,the tilting moment also increases significantly,which strengthens the tendency of the prototype to tilt towards the wall.展开更多
Ducted fans have been extensively used in Unmanned Aerial Vehicles(UAVs)for a variety of missions because of high efficiency,high safety and low noise.Wind,as a kind of typical meteorological condition,brings signific...Ducted fans have been extensively used in Unmanned Aerial Vehicles(UAVs)for a variety of missions because of high efficiency,high safety and low noise.Wind,as a kind of typical meteorological condition,brings significant aerodynamic interference to the ducted fan,which seriously threatens flight stability and safety.In this work,the numerical simulation with the Unsteady Reynolds Averaged Navier-Stokes(URANS)method and the sliding mesh technique is performed to evaluate the steady wind effect.The results show that the wind will lead to serious unsteady effects in the flow field,and the thrust fluctuates at the blade passing frequency of 200 Hz.As the wind speed increases,the rotor thrust increases,the duct thrust decreases,and the total thrust changes little.Flow instability may occur when the wind speed exceeds 8 m/s.As the angle of low-speed wind increases,the rotor thrust changes little,the duct thrust increases,and the total thrust increases.In addition,we figure out that cases with the same crosswind ratio are similar in results,and increasing the rotating speed or fan radius is beneficial to performance improvement in wind.The findings are essential to the ducted fan design and UAV flight control design for stable and safe operations in wind conditions.展开更多
In this work,the flow surrounding the train was obtained using a detached eddy simulation(DES)for slipstream analysis.Two different streamlined nose lengths were investigated:a short nose(4 m)and a long nose(9 m).The ...In this work,the flow surrounding the train was obtained using a detached eddy simulation(DES)for slipstream analysis.Two different streamlined nose lengths were investigated:a short nose(4 m)and a long nose(9 m).The time-average slipstream velocity and the time-average slipstream pressure along the car bodies were compared and explained in detail.In addition to the time-averaged values,the _(max)imum velocities and the pressure peak-to-peak values around the two trains were analyzed.The result showed that the nose length affected the slipstream velocity along the entire train length at the lower and upper regions of the side of the train.However,no significant effect was recognized at the middle height of the train along its length,except in the nose region.Moreover,within the train’s side regions(y=2.0-2.5 m and z=2-4 m)and(y=2.5-3.5 m and z=0.2-0.7 m),the ratio of slipstream velocity U_(max) between the short and long nose trains was notably higher.This occurrence also manifested at the train’s upper section,specifically where y=0-2.5 m and z=4.2-5.0 m.Similarly,regarding the ratio of _(max)imum pressure peak-to-peak values Cp-p_(max),significant regions were observed at the train’s side(y=1.8-2.6 m and z=1-4 m)and above the train(y=0-2 m and z=3.9-4.8 m).展开更多
This paper presents an Integrated physics-data-based(IPDB)modeling of lateral vehicle dynamics with moving-window data snapshots.The IPDB model encodes the fundamental physical principle of four-wheel vehicle motions ...This paper presents an Integrated physics-data-based(IPDB)modeling of lateral vehicle dynamics with moving-window data snapshots.The IPDB model encodes the fundamental physical principle of four-wheel vehicle motions and simultaneously carries out the adaptiveness of the data-driven approach.Specifically,the traditional physics-based lateral dynamics considering four-wheel interaction are first derived into an affine linear-parameter-varying model,in which the vehicle-related parameters and motion variables are separated.Then,by using the Kronecker product,the IPDB model,directly formulated by the data snapshots in the moving-window fashion,is obtained for system representation.As a result,the IPDB technique rendered model is physically interpretable.The impacts of moving window length on modeling performance are numerically studied.The IPDB model accuracy is validated with data from CarSim simulations and experiments with passenger vehicles under various scenarios.It is further demonstrated that the proposed IPDB model is more data-efficient than other data-driven methods since it only uses the data snapshot in the moving window to update the model recursively.This characteristic enables the IPDB method with online modeling capability to adapt to varying driving scenarios.展开更多
Railway lines in the Xinjiang wind area face severe wind disasters year-round,which seriously affects the safety and economy of the railway in China.Therefore,the wind characteristics and statistics of wind-induced ac...Railway lines in the Xinjiang wind area face severe wind disasters year-round,which seriously affects the safety and economy of the railway in China.Therefore,the wind characteristics and statistics of wind-induced accidents along the Xinjiang railway lines are presented and the basic research route for evaluating the train running safety under crosswinds and effective measures to improve the windproof performances of trains are proposed,which are meaningful to deal with wind-induced train accidents.Based on this research route,a series of numerical simulations are conducted to evaluate train safety and the corresponding measures are provided.The results show the following.The running safety of the train under crosswinds mainly depends on the aerodynamic loads acting on the train.The relationships between the safe speed limit and train type,the load weight,the embankment height,the road cutting depth,the railway line curve parameters,the yaw angle and other factors are obtained.The critical wind-vehicle speed relationship,as well as the engineering speed limit value under different running conditions,are determined.Large values of the aerodynamic and dynamic indices mainly appear in special locations,such as near earth-embankment-type windbreak walls,shallow cuttings and the transition sections between various types of windbreak walls.Measures such as increasing the height of the earth-embankment-type windbreak walls,adding wind barriers with reasonable heights in shallow cuttings and optimizing the design of different types of transition sections are proposed to significantly improve the safe speed limits of trains under crosswinds.展开更多
Automated driving systems are often used for lane keeping tasks.By these systems,a local path is planned ahead of the vehicle.However,these paths are often found unnatural by human drivers.In response to this,this pap...Automated driving systems are often used for lane keeping tasks.By these systems,a local path is planned ahead of the vehicle.However,these paths are often found unnatural by human drivers.In response to this,this paper proposes a linear driver model,which can calculate node points reflective of human driver preferences and based on these node points a human driver preferred motion path can be designed for autonomous driving.The model input is the road curvature,effectively harnessed through a self-developed Euler-curve-based curve fitting algorithm.A comprehensive case study is undertaken to empirically validate the efficacy of the proposed model,demonstrating its capacity to emulate the average behavioral pat-terns observed in human curve path selection.Statistical analyses further underscore the model's robustness,affirming the authenticity of the established relationships.This paradigm shift in trajectory planning holds promising implications for the seamless integration of autonomous driving systems with human driving preferences.展开更多
We present an iterative linear quadratic regulator(ILQR) method for trajectory tracking control of a wheeled mobile robot system.The proposed scheme involves a kinematic model linearization technique,a global trajecto...We present an iterative linear quadratic regulator(ILQR) method for trajectory tracking control of a wheeled mobile robot system.The proposed scheme involves a kinematic model linearization technique,a global trajectory generation algorithm,and trajectory tracking controller design.A lattice planner,which searches over a 3D(x,y,θ) configuration space,is adopted to generate the global trajectory.The ILQR method is used to design a local trajectory tracking controller.The effectiveness of the proposed method is demonstrated in simulation and experiment with a significantly asymmetric differential drive robot.The performance of the local controller is analyzed and compared with that of the existing linear quadratic regulator(LQR) method.According to the experiments,the new controller improves the control sequences(v,ω) iteratively and produces slightly better results.Specifically,two trajectories,'S' and '8' courses,are followed with sufficient accuracy using the proposed controller.展开更多
As a core part of an autonomous driving system,motion planning plays an important role in safe driving.However,traditional model-and rule-based methods lack the ability to learn interactively with the environment,and ...As a core part of an autonomous driving system,motion planning plays an important role in safe driving.However,traditional model-and rule-based methods lack the ability to learn interactively with the environment,and learning-based methods still have problems in terms of reliability.To overcome these problems,a hybrid motion planning framework(HMPF)is proposed to improve the performance of motion planning,which is composed of learning-based behavior planning and optimization-based trajectory planning.The behavior planning module adopts a deep reinforcement learning(DRL)algorithm,which can learn from the interaction between the ego vehicle(EV)and other human-driven vehicles(HDVs),and generate behavior decision commands based on environmental perception information.In particular,the intelligent driver model(IDM)calibrated based on real driving data is used to drive HDVs to imitate human driving behavior and interactive response,so as to simulate the bidirectional interaction between EV and HDVs.Meanwhile,trajectory planning module adopts the optimization method based on road Frenet coordinates,which can generate safe and comfortable desired trajectory while reducing the solution dimension of the problem.In addition,trajectory planning also exists as a safety hard constraint of behavior planning to ensure the feasibility of decision instruction.The experimental results demonstrate the effectiveness and feasibility of the proposed HMPF for autonomous driving motion planning in urban mixed traffic flow scenarios.展开更多
Ducted-fan drones are expected to become the main drone configuration in the future due to their high efficiency and minimal noise.When drones operate in confined spaces,significant proximity effects may interfere wit...Ducted-fan drones are expected to become the main drone configuration in the future due to their high efficiency and minimal noise.When drones operate in confined spaces,significant proximity effects may interfere with the aerodynamic performance and pose challenges to flight safety.This study utilizes computational fluid dynam-ics simulation with the Unsteady Reynolds-averaged Navier–Stokes(URANS)method to estimate the proximity effects.Through experimental validation,our computational results show that the influence range of proximity effects lies within four rotor radii.The ground effect and the ceiling effect mainly affect thrust properties,while the wall effect mainly affects the lateral force and the pitching moment.In ground effect,the rotor thrust increases exponentially by up to 26%with ground distance compared with that in open space.Minimum duct thrust and total thrust are observed at one rotor radius above the ground.In ceiling effect,all the thrusts rise as the drone approaches the ceiling,and total thrust increases by up to 19%.In wall effect,all the thrusts stay constant.The pitching moment and lateral force rise exponentially with the wall distance.Changes in blade angle of attack and duct pressure distributions can account for the performance change.The results are of great importance to the path planning and flight controller design of ducted-fan drones for safe and effi-cient operations in confined environments.展开更多
基金supported by the National Natural Science Foundation of China(No.11672022)。
文摘Topology optimization is an effective method to obtain a lightweight structure that meets the requirements of structural strength.Whether the optimization results meet the actual needs mainly depends on the accuracy of the material properties and the boundary conditions,especially for a tiny Flapping-wing Micro Aerial Vehicle(FMAV)transmission system manufactured by 3D printing.In this paper,experimental and numerical computation efforts were undertaken to gain a reliable topology optimization method for the bottom of the transmission system.First,the constitutive behavior of the ultraviolet(UV)curable resin used in fabrication was evaluated.Second,a numerical computation model describing further verified via experiments.Topology optimization modeling considering nonlinear factors,e.g.contact,friction and collision,was presented,and the optimization results were verified by both dynamic simulation and experiments.Finally,detailed discussions on different load cases and constraints were presented to clarify their effect on the optimization.Our methods and results presented in this paper may shed light on the lightweight design of a FMAV.
基金Supported by Technical Innovation Special Project(Major)of Hubei Province of China(Grant No.2020BED012)。
文摘Considering that the clutch cover assembly and driven disc assembly show common effect on the engagement/disengagement characteristics of the pull-type diaphragm spring clutches for heavy-duty commercial vehicles,the diaphragm spring,cushion plate,and friction plate,are thoroughly analyzed in this paper.The A-L method and the micro-element method are used to analyze the mechanical properties of diaphragm spring and cushion plate,respectively.The mechanical characteristics are obtained via numerical simulation,and the deformation and load mechanical characteristics of the cushion plate are verified by experimental tests.According to the relationship between the pressure plate temperature and the friction coefficient of the friction plate,the influence of the change of the friction coefficient on the transmission torque characteristics of the clutch is analyzed.In view of the torque fluctuation in the process of engagement/disengagement,the mathematical model of torsional characteristics is established with consideration of the torsional characteristics of torsional damper.Modeling and simulation of the handling characteristics are carried out to evaluate the influence of the boosting characteristics of the hydraulic operated pneumatic booster on the clutch pedal operating force separation characteristics.Specific tests are also conducted,and the effectiveness of the established models is verified.
基金the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(No.KYCX24_0532)the Key Laboratory of Cross-Domain Flight Interdisciplinary Technology,China(Nos.2024-KF03001,2024-KF03003)the National Natural Science Foundation of China(No.12272169)for the financial support。
文摘Blending the agility of aerial drones with the covert capabilities of underwater submersibles,the aerial-aquatic rotorcraft has garnered substantial interest due to their unparalleled capacity to traverse both air and water.Nevertheless,a critical hurdle for these vehicles lies in mitigating the adverse effects of repeatedly transitioning between these environments,particularly during water-surface takeoffs.Currently,research on the interference caused by rotors approaching water surfaces remains limited.This paper introduces a novel adaptive rotor aerodynamic model based on continuous finite vortex theory to predict rotor thrust within gas–liquid flow field.Initially,the model's sensitivity to system parameters was analyzed to optimize its predictive capabilities.Subsequently,a comprehensive ground/water experimental setup was designed to investigate the intricate aerodynamic interactions between the rotor flow field and water.By varying rotor sizes,the characteristics of the rotor flow field and water surface were examined at different rotor-water surface distances.The performance of different modeling methods was analyzed based on the rotor experimental data of a diameter of 0.38 m,and the prediction results were quantified using the percentage of the mean-square error.The results show that the average error of the finite vortex rotor model is the smallest.Finally,a novel transition boundary is proposed to divide the rotor flow field of the gas–liquid mixture into two stages.The thrust loss zone is defined to delineate the safe operating range of the aircraft,providing a basis for the design of aerial-aquatic rotorcraft.
文摘This paper deeply discusses the causes of gear howling noise,the identification and analysis of multi-source excitation,the transmission path of dynamic noise,simulation and experimental research,case analysis,optimization effect,etc.,aiming to better provide a certain guideline and reference for relevant researchers.
文摘This paper is concerned with the robust adaptive fault-tolerant control of a tandem coaxial ducted fan aircraft under system uncertainty, mismatched disturbance, and actuator saturation.For the proposed aircraft, comprehensive controllability analysis is performed to evaluate the controllability of each state as well as the margin to reject mismatched disturbance without any knowledge of the controller. Mismatched disturbance attenuation is ensured through a structured Hinfinity controller tuned by a non-smooth optimization algorithm. Embedded with the H-infinity controller, an adaptive control law is proposed in order to mitigate matched system uncertainty and actuator fault. Input saturation is also considered by the modified reference model. Numerical simulation of the novel ducted fan aircraft is provided to illustrate the effectiveness of the proposed method. The simulation results reveal that the proposed adaptive controller achieves better transient response and more robust performance than classic Model Reference Adaptive Control（MRAC） method, even with serious actuator saturation.
基金co-supported by the National Key Research and Development Program of China(No.2020YFC1512500)The Advanced Aviation Power Innovation institution,The Aero Engine Academy of ChinaTsinghua University Initiative Scientific Research Program.
文摘Ducted fans are widely used in various applications of Unmanned Aerial Vehicles(UAVs)due to the high efficiency,low noise and high safety.The unsteady characteristics of ducted fans flying near the ground are significant,which may bring stability problems.In this paper,the sliding mesh technology is applied and the Unsteady Reynolds Averaged Navier-Stokes(URANS)method is adopted to evaluate the influence of ground on the aerodynamic performance of ducted fans.The time-averaged results show that the ground leads to the decrease of duct thrust,the increase of rotor thrust and the decrease of total thrust.The transient results show that there exist small-scale stall cells with circumferential movements in ground effect.The stall cells start to appear at the blade root when the height is 0.8 rotor radius distance,and arise at both the blade root and tip when the height drops to 0.2.It is found that the unsteady cells rotate between blade passages with an approximate relative speed of 30%-80%of the fan speed,and lead to thrust fluctuations up to 37%of the total thrust.The results are essential to the flight control design of the ducted fan flying vehicle,to ensure its stability in ground effect.
基金Supported by the National Key Research and Development Project(2020YFC1512500)。
文摘A novel coaxial ducted fan structure aircraft is proposed to enable the aircraft near vertical walls at high altitudes.The state space equation of the system can be obtained by correlation deduction and identification of the whole prototype model.Based on the duct test bench experiment and computational fluid dynamics(CFD)simulation analysis,the expressions between the different distances dWE from the rotor center of the prototype to the wall and the thrust,reaction torque,and tilting moment of the system under hovering conditions are obtained.The influence of the wall effect of the prototype is incorporated into the system model to analyze the relationship between distance dWE and the comprehensive controllability of the system.The results show that the system comprehensive controllability vector of other channels changes little with the decrease of the distance dWE,and only the controllability vector of the rolling channel increases significantly.At the same time,the tilting moment also increases significantly,which strengthens the tendency of the prototype to tilt towards the wall.
基金This study was co-supported by the National Key Research and Development Program of China(No.2020YFC1512500),The Advanced Aviation Power Innovation institution,The Aero Engine Academy of China,and Tsinghua University Initiative Scientific Research Program,China.
文摘Ducted fans have been extensively used in Unmanned Aerial Vehicles(UAVs)for a variety of missions because of high efficiency,high safety and low noise.Wind,as a kind of typical meteorological condition,brings significant aerodynamic interference to the ducted fan,which seriously threatens flight stability and safety.In this work,the numerical simulation with the Unsteady Reynolds Averaged Navier-Stokes(URANS)method and the sliding mesh technique is performed to evaluate the steady wind effect.The results show that the wind will lead to serious unsteady effects in the flow field,and the thrust fluctuates at the blade passing frequency of 200 Hz.As the wind speed increases,the rotor thrust increases,the duct thrust decreases,and the total thrust changes little.Flow instability may occur when the wind speed exceeds 8 m/s.As the angle of low-speed wind increases,the rotor thrust changes little,the duct thrust increases,and the total thrust increases.In addition,we figure out that cases with the same crosswind ratio are similar in results,and increasing the rotating speed or fan radius is beneficial to performance improvement in wind.The findings are essential to the ducted fan design and UAV flight control design for stable and safe operations in wind conditions.
基金Project(52202426)supported by the National Natural Science Foundation of ChinaProjects(15205723,15226424)supported by the Research Grants Council of the Hong Kong Special Administrative Region(SAR),China+1 种基金Project(K2021J041)supported by the Technology Research and Development Program of China RailwayProject(1-BD23)supported by The Hong Kong Polytechnic University,China。
文摘In this work,the flow surrounding the train was obtained using a detached eddy simulation(DES)for slipstream analysis.Two different streamlined nose lengths were investigated:a short nose(4 m)and a long nose(9 m).The time-average slipstream velocity and the time-average slipstream pressure along the car bodies were compared and explained in detail.In addition to the time-averaged values,the _(max)imum velocities and the pressure peak-to-peak values around the two trains were analyzed.The result showed that the nose length affected the slipstream velocity along the entire train length at the lower and upper regions of the side of the train.However,no significant effect was recognized at the middle height of the train along its length,except in the nose region.Moreover,within the train’s side regions(y=2.0-2.5 m and z=2-4 m)and(y=2.5-3.5 m and z=0.2-0.7 m),the ratio of slipstream velocity U_(max) between the short and long nose trains was notably higher.This occurrence also manifested at the train’s upper section,specifically where y=0-2.5 m and z=4.2-5.0 m.Similarly,regarding the ratio of _(max)imum pressure peak-to-peak values Cp-p_(max),significant regions were observed at the train’s side(y=1.8-2.6 m and z=1-4 m)and above the train(y=0-2 m and z=3.9-4.8 m).
基金fulfilled by Southeast University are supported partially by the National Natural Science Foundation of China under Grant 52402467 and Grant 52394263partially by the Natural Science Foundation of Jiangsu Province under Grants NO.BK20241324 and BK20233002+1 种基金partially by the"Southeast University Interdisciplinary Research Program for Young Scholars"The work fulfilled by Tianyi He are supported by Natural Science Foundation under award 1941524.
文摘This paper presents an Integrated physics-data-based(IPDB)modeling of lateral vehicle dynamics with moving-window data snapshots.The IPDB model encodes the fundamental physical principle of four-wheel vehicle motions and simultaneously carries out the adaptiveness of the data-driven approach.Specifically,the traditional physics-based lateral dynamics considering four-wheel interaction are first derived into an affine linear-parameter-varying model,in which the vehicle-related parameters and motion variables are separated.Then,by using the Kronecker product,the IPDB model,directly formulated by the data snapshots in the moving-window fashion,is obtained for system representation.As a result,the IPDB technique rendered model is physically interpretable.The impacts of moving window length on modeling performance are numerically studied.The IPDB model accuracy is validated with data from CarSim simulations and experiments with passenger vehicles under various scenarios.It is further demonstrated that the proposed IPDB model is more data-efficient than other data-driven methods since it only uses the data snapshot in the moving window to update the model recursively.This characteristic enables the IPDB method with online modeling capability to adapt to varying driving scenarios.
基金the National Key R&D Program of China(Grant No.2020YFA0710903).
文摘Railway lines in the Xinjiang wind area face severe wind disasters year-round,which seriously affects the safety and economy of the railway in China.Therefore,the wind characteristics and statistics of wind-induced accidents along the Xinjiang railway lines are presented and the basic research route for evaluating the train running safety under crosswinds and effective measures to improve the windproof performances of trains are proposed,which are meaningful to deal with wind-induced train accidents.Based on this research route,a series of numerical simulations are conducted to evaluate train safety and the corresponding measures are provided.The results show the following.The running safety of the train under crosswinds mainly depends on the aerodynamic loads acting on the train.The relationships between the safe speed limit and train type,the load weight,the embankment height,the road cutting depth,the railway line curve parameters,the yaw angle and other factors are obtained.The critical wind-vehicle speed relationship,as well as the engineering speed limit value under different running conditions,are determined.Large values of the aerodynamic and dynamic indices mainly appear in special locations,such as near earth-embankment-type windbreak walls,shallow cuttings and the transition sections between various types of windbreak walls.Measures such as increasing the height of the earth-embankment-type windbreak walls,adding wind barriers with reasonable heights in shallow cuttings and optimizing the design of different types of transition sections are proposed to significantly improve the safe speed limits of trains under crosswinds.
基金supported by the European Union within the framework of the National Laboratory for Autonomous Systems.(RRF-2.3.1-21-2022-00002).
文摘Automated driving systems are often used for lane keeping tasks.By these systems,a local path is planned ahead of the vehicle.However,these paths are often found unnatural by human drivers.In response to this,this paper proposes a linear driver model,which can calculate node points reflective of human driver preferences and based on these node points a human driver preferred motion path can be designed for autonomous driving.The model input is the road curvature,effectively harnessed through a self-developed Euler-curve-based curve fitting algorithm.A comprehensive case study is undertaken to empirically validate the efficacy of the proposed model,demonstrating its capacity to emulate the average behavioral pat-terns observed in human curve path selection.Statistical analyses further underscore the model's robustness,affirming the authenticity of the established relationships.This paradigm shift in trajectory planning holds promising implications for the seamless integration of autonomous driving systems with human driving preferences.
基金Project (Nos. 90920304 and 91120015) supported by the National Natural Science Foundation of China
文摘We present an iterative linear quadratic regulator(ILQR) method for trajectory tracking control of a wheeled mobile robot system.The proposed scheme involves a kinematic model linearization technique,a global trajectory generation algorithm,and trajectory tracking controller design.A lattice planner,which searches over a 3D(x,y,θ) configuration space,is adopted to generate the global trajectory.The ILQR method is used to design a local trajectory tracking controller.The effectiveness of the proposed method is demonstrated in simulation and experiment with a significantly asymmetric differential drive robot.The performance of the local controller is analyzed and compared with that of the existing linear quadratic regulator(LQR) method.According to the experiments,the new controller improves the control sequences(v,ω) iteratively and produces slightly better results.Specifically,two trajectories,'S' and '8' courses,are followed with sufficient accuracy using the proposed controller.
基金National Natural Science Foundation of China under Grants U19A2083.
文摘As a core part of an autonomous driving system,motion planning plays an important role in safe driving.However,traditional model-and rule-based methods lack the ability to learn interactively with the environment,and learning-based methods still have problems in terms of reliability.To overcome these problems,a hybrid motion planning framework(HMPF)is proposed to improve the performance of motion planning,which is composed of learning-based behavior planning and optimization-based trajectory planning.The behavior planning module adopts a deep reinforcement learning(DRL)algorithm,which can learn from the interaction between the ego vehicle(EV)and other human-driven vehicles(HDVs),and generate behavior decision commands based on environmental perception information.In particular,the intelligent driver model(IDM)calibrated based on real driving data is used to drive HDVs to imitate human driving behavior and interactive response,so as to simulate the bidirectional interaction between EV and HDVs.Meanwhile,trajectory planning module adopts the optimization method based on road Frenet coordinates,which can generate safe and comfortable desired trajectory while reducing the solution dimension of the problem.In addition,trajectory planning also exists as a safety hard constraint of behavior planning to ensure the feasibility of decision instruction.The experimental results demonstrate the effectiveness and feasibility of the proposed HMPF for autonomous driving motion planning in urban mixed traffic flow scenarios.
文摘Ducted-fan drones are expected to become the main drone configuration in the future due to their high efficiency and minimal noise.When drones operate in confined spaces,significant proximity effects may interfere with the aerodynamic performance and pose challenges to flight safety.This study utilizes computational fluid dynam-ics simulation with the Unsteady Reynolds-averaged Navier–Stokes(URANS)method to estimate the proximity effects.Through experimental validation,our computational results show that the influence range of proximity effects lies within four rotor radii.The ground effect and the ceiling effect mainly affect thrust properties,while the wall effect mainly affects the lateral force and the pitching moment.In ground effect,the rotor thrust increases exponentially by up to 26%with ground distance compared with that in open space.Minimum duct thrust and total thrust are observed at one rotor radius above the ground.In ceiling effect,all the thrusts rise as the drone approaches the ceiling,and total thrust increases by up to 19%.In wall effect,all the thrusts stay constant.The pitching moment and lateral force rise exponentially with the wall distance.Changes in blade angle of attack and duct pressure distributions can account for the performance change.The results are of great importance to the path planning and flight controller design of ducted-fan drones for safe and effi-cient operations in confined environments.
