The influences of die parameters on shear strain were investigated by using two-dimensional finite element simulation.New formulas of shear strain were proposed.According to the results of formulas,the shear strain sh...The influences of die parameters on shear strain were investigated by using two-dimensional finite element simulation.New formulas of shear strain were proposed.According to the results of formulas,the shear strain showed a linear dependence on the difference between internal and external fillet radius and the slope was determined by the intersection angle.The simulation results indicated that the velocities of the points from different zones were different in the specimen and the motion trajectories of different points did not follow geometrical laws.The influences of the average velocity and the motion trajectory on shear strain were incorporated in the formula to calculate the shear strain produced during equalchannel angular pressing process.The reliability of simulation results has been partially validated by experiments.展开更多
The past decades have witnessed the development of new X-ray beam sources with brightness growing at a rate surpassing Moore’s law.Current and upcoming diffraction limited and fully coherent X-ray beam sources,includ...The past decades have witnessed the development of new X-ray beam sources with brightness growing at a rate surpassing Moore’s law.Current and upcoming diffraction limited and fully coherent X-ray beam sources,including multi-bend achromat based synchrotron sources and high repetition rate X-ray free electron lasers,puts increasingly stringent requirements on stability and accuracy of X-ray optics systems.Parasitic motion errors at sub-micro radian scale in beam transport and beam conditioning optics can lead to significant loss of coherence and brightness delivered from source to experiment.To address this challenge,we incorporated optical metrology based on interferometric length and angle sensing and real-time correction as part of the X-ray optics motion control system.A prototype X-ray optics system was constructed following the optical layout of a tunable X-ray cavity.On-line interferometric metrology enabled dynamical feedback to a motion control system to track and compensate for motion errors.The system achieved sub-microradian scale performance,as multiple optical elements are synchronously and continuously adjusted.This first proof of principle measurement demonstrated both the potential and necessity of incorporating optical metrology as part of the motion control architecture for large scale X-ray optical systems such as monochromators,delay lines,and in particular,X-ray cavity systems to enable the next generation cavity-based X-ray free electron lasers.展开更多
The counter-rotating electrochemical machining(CRECM) shows unique potential in the machining of thin-walled rotating parts with complex convex structures. CREM realizes the shaping of complex convex structures throug...The counter-rotating electrochemical machining(CRECM) shows unique potential in the machining of thin-walled rotating parts with complex convex structures. CREM realizes the shaping of complex convex structures through the relative rotation of the cathode and anode.The complex motion pattern and electric field distribution make it difficult to apply the existing cathode design methods to CRECM. To solve this problem, the matrix equations of cathode motion based on the kinematics and the electric field simulation model are established. The motion trajectories and edge contours at different angles are analyzed. The rotational overlap theory of motion trajectories under the windows at different angles is proved. Besides, the relationship between electric field distribution and the convex structure forming under different angle windows is studied, and the fundamental reason for deviations occurs when the convex profile is rotated to coincide is revealed. Therefore, a prediction model of the sidewall dissolution is established to correct this deviation, thereby deriving a high-precision design formula for the cathode windows of the high convex structures. By designing a cathode with oval-like windows to curry out CRECM experiments, the array-arranged(30 × 5) circular high convex structure with a maximum roundness error of 0.065 mm is successfully fabricated.展开更多
Motion planning issues encountered in assembling airplanes by employing the 6PURU parallel mechanism are analyzed in this paper. A sine curve of the change rate of acceleration, which is called as jerk in the followin...Motion planning issues encountered in assembling airplanes by employing the 6PURU parallel mechanism are analyzed in this paper. A sine curve of the change rate of acceleration, which is called as jerk in the following text, is proposed for uniaxial flexible acceleration and deceleration planning based on the optimal time and velocity and acceleration constraints. Compared with other curves, the proposed curve can realize a continuous n-order derivative and the smooth change of the speed and acceleration. The method is computational^y simple and suitable for programming. In addition, a multiaxial coordinated movement scheme is proposed. The motion trajectory is no longer simply split into many single-direction trajectories nor are all single-direction planning trajectories combined directly. The multiaxial coordinated movement scheme aims to achieve synergic movement in multiple directions to ensure smoothness of the movement in the event of a kinematic error when maintaining a stable value. If the movement fails to achieve this goal, driving force mutations will deteriorate the effect of synergic movement. A physical model of the parallel mechanism is developed in simMechanics, and a holistic system model is completed in SIMULINK. The feasibility of the new planning algorithm is simulated and tested, and then, the multiaxial synergic movement planning method is proposed and verified.展开更多
Recognizing and reproducing spatiotemporal motions are necessary when analyzing behaviors andmovements during human-robot interaction. Rigid body motion trajectories are proven as compact and informativeclues in chara...Recognizing and reproducing spatiotemporal motions are necessary when analyzing behaviors andmovements during human-robot interaction. Rigid body motion trajectories are proven as compact and informativeclues in characterizing motions. A flexible dual square-root function (DSRF) descriptor for representing rigid bodymotion trajectories, which can offer robustness in the description over raw data, was proposed in our previousstudy. However, this study focuses on exploring the application of the DSRF descriptor for effective backwardmotion reproduction and motion recognition. Specifically, two DSRF-based reproduction methods are initiallyproposed, including the recursive reconstruction and online optimization. New trajectories with novel situationsand contextual information can be reproduced from a single demonstration while preserving the similarities withthe original demonstration. Furthermore, motion recognition based on DSRF descriptor can be achieved byemploying a template matching method. Finally, the experimental results demonstrate the effectiveness of theproposed method for rigid body motion reproduction and recognition.展开更多
In bottom-blown copper smelting processes,oxygen-enriched air is typically injected into the melt through a lance,generating bubbles that ascend and agitate the melt,enhancing mass,momentum,and heat transfer within th...In bottom-blown copper smelting processes,oxygen-enriched air is typically injected into the melt through a lance,generating bubbles that ascend and agitate the melt,enhancing mass,momentum,and heat transfer within the furnace.The melt’s viscosity,which varies across reaction stages,and the operating conditions influence bubble size and dynamics.This study investigates the interplay between melt viscosity and bubble diameter on bubble motion using numerical simulations and experiments.In particular,the volume of fluid(VOF)method andΩ-identification technique were employed to analyze bubble velocity,deformation,trajectories,and wake characteristics.The results showed that bubble ascent velocity increases with bubble size and decreases in viscosity,though viscosity variations minimally affect the maximum velocity.Larger bubbles or those in less viscous melts exhibit greater deformation.Bubbles ascend primarily in straight trajectories with minor lateral oscillations regardless of viscosity.In terms of wake dynamics,vortex sizes grow as viscosity decreases,with bottom-formed vortices expanding significantly with increasing bubble size,while lateral vortices are less influenced.展开更多
This paper presents a computationally efficient real-time trajectory planning framework for typical unmanned combat aerial vehicle （UCAV） performing autonomous air-to-surface （A/S） attack. It combines the benefits...This paper presents a computationally efficient real-time trajectory planning framework for typical unmanned combat aerial vehicle （UCAV） performing autonomous air-to-surface （A/S） attack. It combines the benefits of inverse dynamics optimization method and receding horizon optimal control technique. Firstly, the ground attack trajectory planning problem is mathematically formulated as a receding horizon optimal control problem （RHC-OCP）. In particular, an approximate elliptic launch acceptable region （LAR） model is proposed to model the critical weapon delivery constraints. Secondly, a planning algorithm based on inverse dynamics optimization, which has high computational efficiency and good convergence properties, is developed to solve the RHCOCP in real-time. Thirdly, in order to improve robustness and adaptivity in a dynamic and uncer- tain environment, a two-degree-of-freedom （2-DOF） receding horizon control architecture is introduced and a regular real-time update strategy is proposed as well, and the real-time feedback can be achieved and the not-converged situations can be handled. Finally, numerical simulations demon- strate the efficiency of this framework, and the results also show that the presented technique is well suited for real-time implementation in dynamic and uncertain environment.展开更多
Compared with traditional feedback control,predictive control can eliminate the lag of pose control and avoid the snakelike motion of shield machines.Therefore,a shield pose prediction model was proposed based on dyna...Compared with traditional feedback control,predictive control can eliminate the lag of pose control and avoid the snakelike motion of shield machines.Therefore,a shield pose prediction model was proposed based on dynamic modeling.Firstly,the dynamic equations of shield thrust system were established to clarify the relationship between force and movement of shield machine.Secondly,an analytical model was proposed to predict future multistep pose of the shield machine.Finally,a virtual prototype model was developed to simulate the dynamic behavior of the shield machine and validate the accuracy of the proposed pose prediction method.Results reveal that the model proposed can predict the shield pose with high accuracy,which can provide a decision basis whether for manual or automatic control of shield pose.展开更多
Multi-robot coordinated towing system is an under-constrained system.The dynamic response of the towing system can not be fully controlled since the rope can only provide a unidirectional constraint force to the suspe...Multi-robot coordinated towing system is an under-constrained system.The dynamic response of the towing system can not be fully controlled since the rope can only provide a unidirectional constraint force to the suspended object.Based on the kinematics of the multi-robot coordinated towing system with fixed-base,the Newton-Euler equations and Udwadia-Kalaba equations were used to establish the dynamics of the towing system.To obtain the motion trajectories with high stability and strong control,the motion trajectories of the towing system were optimized.During the towing,the transition from the relaxation state to the tension state of the rope was treated as a collision between the suspended object and the robot end.The trajectories of the towing system in terms of a single-variable and multiple-variable were solved,respectively.The simulation shows that the optimized trajectories are closer to reality and truly reflect the constraints of the ropes on the suspended object.The research results provide a basis for trajectory planning and control of the towing system.展开更多
Nonlinear behaviors of a free-floating body in waves were experimentally investigated in the present study. The experiments were carried out for 6 different wave heights and 6 different wave periods to cover a relativ...Nonlinear behaviors of a free-floating body in waves were experimentally investigated in the present study. The experiments were carried out for 6 different wave heights and 6 different wave periods to cover a relatively wide range of wave nonlinearities. A charge-coupled device （CCD） camera was used to capture the real-time motion of the floating body. The measurement data show that the sway, heave and roll motions of the floating body are all harmonic oscillations while the equilibrium position of the sway motion drifts in the wave direction. The drift speed is proportional to wave steepness when the size of the floating body is comparable to the wavelength, while it is proportional to the square of wave steepness when the floating body is relatively small. In addition, the drift motion leads to a slightly longer oscillation period of the floating body than the wave period of nonlinear wave and the discrepancy increases with the increment of wave steepness.展开更多
Frequent start-stops of automatic seedling transplanters would lengthen the seedling picking time due to alternating movement of the motor,and cause positioning errors and frequent motor vibrations when starting the m...Frequent start-stops of automatic seedling transplanters would lengthen the seedling picking time due to alternating movement of the motor,and cause positioning errors and frequent motor vibrations when starting the machine.To solve these problems and ensure the pick-up continuity of automatic transplanters,in this study the smooth circular arc interpolation algorithm and the least square method for multinomial curve fitting were used to conduct the trajectory planning of automatic transplanter based on the movement of the pick-up arm of the transplanter.Velocity and time curves were fitted in segments to acquire motion control parameters and further tracking control was conducted.The mathematical model of the control system was established using Simulink,and simulation analysis and system debugging test were performed.Experiments show that the trajectory curves obtained by MATLAB’s data processing can realize the continual and smooth motion trajectory of the pick-up arm;stepper motor velocity control can effectively track the planning curve and improve the seedling pick-up efficiency.The pick-up and pushing time of each motion of the planned plug seedling transplanter reduced by 1.0678 s and the start-stop times reduced from 6 to 1,which solved the frequent motor vibrations when starting the machine and improved the stability of the system.In addition,overstep and out-of-step of the motor at the start-stop moment were avoided and displacement error was reduced.展开更多
This paper described an improved underwater confrontation simulation method of naval amphibious operational training system. The initial position of submarine forces on the enemy is generated automatically, and the at...This paper described an improved underwater confrontation simulation method of naval amphibious operational training system. The initial position of submarine forces on the enemy is generated automatically, and the attacking distance model of torpedoes is established based on the kinematics theory, which is more flexible and reasonable to judge the launch condition compared to traditional method. The two kinds of confrontation behavior models on the enemy submarine are created to depict its tactical action from the defensive to the offensive as well as the contrary, ensuring that operational style is simulated more comprehensively and properly. The existing motion trajectory estimation and collision detection algorithms on operational platforms are also improved to reduce the iteration error and further enhance the detection accuracy of target hit.展开更多
To understand the influence of the initial release conditions on the separation characteristics of the store and improve it under high Mach number(Ma=4)flight conditions,the overset grid method and the Realizable k−ε...To understand the influence of the initial release conditions on the separation characteristics of the store and improve it under high Mach number(Ma=4)flight conditions,the overset grid method and the Realizable k−εturbulence model coupled with an equation with six degrees of freedom are used to simulate the store released from the internal bay.The motion trajectory and the attitude angle of the store separation under the conditions of different centroid,velocity,height and control measures are given by the calculated result.Through analysis,the position of the centroid will affect the separation of the store,which needs to be considered in the design.Increasing the launching height is conducive to the separation of the store.If the store has an initial velocity,it can leave the internal bay more quickly and reduce the probability of collision with the wall.Cylindrical rod and slanted aft wall control measures can improve the attitude of the store and make the store fall more smoothly.展开更多
In order to avoid the influence of noise variance on the filtering performances, a modified adaptive weighted averaging (MAWA) filtering algorithm is proposed for noisy image sequences. Based upon adaptive weighted av...In order to avoid the influence of noise variance on the filtering performances, a modified adaptive weighted averaging (MAWA) filtering algorithm is proposed for noisy image sequences. Based upon adaptive weighted averaging pixel values in consecutive frames, this algorithm achieves the filtering goal by assigning smaller weights to the pixels with inappropriate estimated motion trajectory for noise. It only utilizes the intensity of pixels to suppress noise and accordingly is independent of noise variance. To evaluate the performance of the proposed filtering algorithm, its mean square error and percentage of preserved edge points were compared with those of traditional adaptive weighted averaging and non-adaptive mean filtering algorithms under different noise variances. Relevant results show that the MAWA filtering algorithm can preserve image structures and edges under motion after attenuating noise, and thus may be used in image sequence filtering.展开更多
A mass-rod-disk system consisting of an oscillating mass attached to a rigid rotating disk by an elastic rod is designed to study rigid-flexible coupling mechanism.Suppose the rod is lightweight and has enough stiffne...A mass-rod-disk system consisting of an oscillating mass attached to a rigid rotating disk by an elastic rod is designed to study rigid-flexible coupling mechanism.Suppose the rod is lightweight and has enough stiffness,the theorems of linear momentum and angular momentum are applied to the mass-rod-disk system based on the kinematic description of the system.With respect to two deflections of the mass and one angular velocity of the system,a group of nonlinear differential equations are established where the tangential inertial force,centrifugal force,Coriolis force as well as the moments of additional inertial forces take important effects on the dynamic response.For the sake of description,these three types of inertial forces mentioned before are referred to as additional inertial forces in this paper.The horizontal deflections of the mass and the angular velocity of the disk rotating about a fixed-axis are numerically solved for the prescribed external torque.The oscillating trajectory of the mass is deeply influenced by the additional inertial forces,meanwhile the dynamic fluctuations of the angular velocity and rotary inertia of the system are strongly affected by the mass oscillation.展开更多
The use of the dipole force on atoms is a new technology that is used to build nanostructures. In this way, a high quality standard nano-grating can be obtained. Based on the semi-classical model, the motion equation ...The use of the dipole force on atoms is a new technology that is used to build nanostructures. In this way, a high quality standard nano-grating can be obtained. Based on the semi-classical model, the motion equation is investigated and the trajectories of atoms in double half Gaussian standing wave field are simulated. Compared with the Gaussian standing wave field, the double half Gaussian standing wave can well focus the Cr atoms. In order to obtain this kind of beam, a prism is designed and the experimental result shows that the beam is well generated.展开更多
Optimizing the power resources allocation method of low earth orbit(LEO)satellites to medium earth orbit(MEO)satellite'links is a significant way to construct efficient satellite constellations for satellite commu...Optimizing the power resources allocation method of low earth orbit(LEO)satellites to medium earth orbit(MEO)satellite'links is a significant way to construct efficient satellite constellations for satellite communication.A game theory power allocation method based on remaining visible time(RVT)of LEO-MEO satellites is proposed.Firstly,one LEO-MEO satellite network is classified as a cluster in which the RVT of LEO satellites is modeled.Secondly,the cost function of RVT concerning the character of orbit and throughput in each LEO satellite is mainly designed,which gives greater punishment of utility value to LEO satellites with less RVT and is an essential part of the reasonable utility function applied in diverse motion scenes.Meanwhile,the existence of Nash equilibrium for the proposed utility function in game theory area is proved.Thirdly,an off-cluster scheme for LEO satellites through the proposed threshold is raised to ensure the overall utility value of the whole LEO satellites in cluster.Finally,the performance improvement of the proposed algorithm to the baseline algorithm is verified through simulations in different scenarios.展开更多
基金Item Sponsored by Fundamental Research Funds for Central Universities of China(HEUCF20151002)
文摘The influences of die parameters on shear strain were investigated by using two-dimensional finite element simulation.New formulas of shear strain were proposed.According to the results of formulas,the shear strain showed a linear dependence on the difference between internal and external fillet radius and the slope was determined by the intersection angle.The simulation results indicated that the velocities of the points from different zones were different in the specimen and the motion trajectories of different points did not follow geometrical laws.The influences of the average velocity and the motion trajectory on shear strain were incorporated in the formula to calculate the shear strain produced during equalchannel angular pressing process.The reliability of simulation results has been partially validated by experiments.
基金support from the Laboratory Directed Research and Development program at the SLAC National Accelerator Laboratorythe National Science Foundation under Grant No.NSF-2011786Use of the Linac Coherent Light Source(LCLS),SLAC National Accelerator Laboratory,is supported by the U.S.Department of Energy,Office of Science,Office of Basic Energy Sciences under Contract No.DE-AC02-76SF00515.
文摘The past decades have witnessed the development of new X-ray beam sources with brightness growing at a rate surpassing Moore’s law.Current and upcoming diffraction limited and fully coherent X-ray beam sources,including multi-bend achromat based synchrotron sources and high repetition rate X-ray free electron lasers,puts increasingly stringent requirements on stability and accuracy of X-ray optics systems.Parasitic motion errors at sub-micro radian scale in beam transport and beam conditioning optics can lead to significant loss of coherence and brightness delivered from source to experiment.To address this challenge,we incorporated optical metrology based on interferometric length and angle sensing and real-time correction as part of the X-ray optics motion control system.A prototype X-ray optics system was constructed following the optical layout of a tunable X-ray cavity.On-line interferometric metrology enabled dynamical feedback to a motion control system to track and compensate for motion errors.The system achieved sub-microradian scale performance,as multiple optical elements are synchronously and continuously adjusted.This first proof of principle measurement demonstrated both the potential and necessity of incorporating optical metrology as part of the motion control architecture for large scale X-ray optical systems such as monochromators,delay lines,and in particular,X-ray cavity systems to enable the next generation cavity-based X-ray free electron lasers.
基金supported by the National Natural Science Foundation of China (no.52175414)National Natural Science Foundation of China for Creative Research Groups (51921003)+1 种基金Natural Science Foundation of Jiangsu Province of China (No. BK20220134)Postgraduate Research & Practice Innovation Program of Jiangsu Province (No. KYCX22_0344)。
文摘The counter-rotating electrochemical machining(CRECM) shows unique potential in the machining of thin-walled rotating parts with complex convex structures. CREM realizes the shaping of complex convex structures through the relative rotation of the cathode and anode.The complex motion pattern and electric field distribution make it difficult to apply the existing cathode design methods to CRECM. To solve this problem, the matrix equations of cathode motion based on the kinematics and the electric field simulation model are established. The motion trajectories and edge contours at different angles are analyzed. The rotational overlap theory of motion trajectories under the windows at different angles is proved. Besides, the relationship between electric field distribution and the convex structure forming under different angle windows is studied, and the fundamental reason for deviations occurs when the convex profile is rotated to coincide is revealed. Therefore, a prediction model of the sidewall dissolution is established to correct this deviation, thereby deriving a high-precision design formula for the cathode windows of the high convex structures. By designing a cathode with oval-like windows to curry out CRECM experiments, the array-arranged(30 × 5) circular high convex structure with a maximum roundness error of 0.065 mm is successfully fabricated.
基金supported by the National Science and Technology Supporting Plan of China (No. 2012BAF14G00)
文摘Motion planning issues encountered in assembling airplanes by employing the 6PURU parallel mechanism are analyzed in this paper. A sine curve of the change rate of acceleration, which is called as jerk in the following text, is proposed for uniaxial flexible acceleration and deceleration planning based on the optimal time and velocity and acceleration constraints. Compared with other curves, the proposed curve can realize a continuous n-order derivative and the smooth change of the speed and acceleration. The method is computational^y simple and suitable for programming. In addition, a multiaxial coordinated movement scheme is proposed. The motion trajectory is no longer simply split into many single-direction trajectories nor are all single-direction planning trajectories combined directly. The multiaxial coordinated movement scheme aims to achieve synergic movement in multiple directions to ensure smoothness of the movement in the event of a kinematic error when maintaining a stable value. If the movement fails to achieve this goal, driving force mutations will deteriorate the effect of synergic movement. A physical model of the parallel mechanism is developed in simMechanics, and a holistic system model is completed in SIMULINK. The feasibility of the new planning algorithm is simulated and tested, and then, the multiaxial synergic movement planning method is proposed and verified.
基金the Science and Technology Commission of Shanghai Municipality(No.20DZ2220400)the Interdisciplinary Program of Shanghai Jiao Tong University(No.YG2021QN117)。
文摘Recognizing and reproducing spatiotemporal motions are necessary when analyzing behaviors andmovements during human-robot interaction. Rigid body motion trajectories are proven as compact and informativeclues in characterizing motions. A flexible dual square-root function (DSRF) descriptor for representing rigid bodymotion trajectories, which can offer robustness in the description over raw data, was proposed in our previousstudy. However, this study focuses on exploring the application of the DSRF descriptor for effective backwardmotion reproduction and motion recognition. Specifically, two DSRF-based reproduction methods are initiallyproposed, including the recursive reconstruction and online optimization. New trajectories with novel situationsand contextual information can be reproduced from a single demonstration while preserving the similarities withthe original demonstration. Furthermore, motion recognition based on DSRF descriptor can be achieved byemploying a template matching method. Finally, the experimental results demonstrate the effectiveness of theproposed method for rigid body motion reproduction and recognition.
基金Supported by Yunnan Fundamental Research Projects(Nos.202301AT070469,202301AT070275)supported by Yunnan Major Scientific and Technological Projects(No.202202AG050002).
文摘In bottom-blown copper smelting processes,oxygen-enriched air is typically injected into the melt through a lance,generating bubbles that ascend and agitate the melt,enhancing mass,momentum,and heat transfer within the furnace.The melt’s viscosity,which varies across reaction stages,and the operating conditions influence bubble size and dynamics.This study investigates the interplay between melt viscosity and bubble diameter on bubble motion using numerical simulations and experiments.In particular,the volume of fluid(VOF)method andΩ-identification technique were employed to analyze bubble velocity,deformation,trajectories,and wake characteristics.The results showed that bubble ascent velocity increases with bubble size and decreases in viscosity,though viscosity variations minimally affect the maximum velocity.Larger bubbles or those in less viscous melts exhibit greater deformation.Bubbles ascend primarily in straight trajectories with minor lateral oscillations regardless of viscosity.In terms of wake dynamics,vortex sizes grow as viscosity decreases,with bottom-formed vortices expanding significantly with increasing bubble size,while lateral vortices are less influenced.
基金supported by the National Defense Foundation of China(No.403060103)
文摘This paper presents a computationally efficient real-time trajectory planning framework for typical unmanned combat aerial vehicle （UCAV） performing autonomous air-to-surface （A/S） attack. It combines the benefits of inverse dynamics optimization method and receding horizon optimal control technique. Firstly, the ground attack trajectory planning problem is mathematically formulated as a receding horizon optimal control problem （RHC-OCP）. In particular, an approximate elliptic launch acceptable region （LAR） model is proposed to model the critical weapon delivery constraints. Secondly, a planning algorithm based on inverse dynamics optimization, which has high computational efficiency and good convergence properties, is developed to solve the RHCOCP in real-time. Thirdly, in order to improve robustness and adaptivity in a dynamic and uncer- tain environment, a two-degree-of-freedom （2-DOF） receding horizon control architecture is introduced and a regular real-time update strategy is proposed as well, and the real-time feedback can be achieved and the not-converged situations can be handled. Finally, numerical simulations demon- strate the efficiency of this framework, and the results also show that the presented technique is well suited for real-time implementation in dynamic and uncertain environment.
基金Project(2023JBZY030)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(U1834208)supported by the National Natural Science Foundation of China。
文摘Compared with traditional feedback control,predictive control can eliminate the lag of pose control and avoid the snakelike motion of shield machines.Therefore,a shield pose prediction model was proposed based on dynamic modeling.Firstly,the dynamic equations of shield thrust system were established to clarify the relationship between force and movement of shield machine.Secondly,an analytical model was proposed to predict future multistep pose of the shield machine.Finally,a virtual prototype model was developed to simulate the dynamic behavior of the shield machine and validate the accuracy of the proposed pose prediction method.Results reveal that the model proposed can predict the shield pose with high accuracy,which can provide a decision basis whether for manual or automatic control of shield pose.
基金the National Natural Science Foundation of China(No.51965032)the Natural Science Foundation of Gansu Province of China(No.22JR5RA319)+1 种基金the Science and Technology Foundation of Gansu Province of China(No.21YF5WA060)the Excellent Doctoral Student Foundation of Gansu Province of China(No.23JRRA842)。
文摘Multi-robot coordinated towing system is an under-constrained system.The dynamic response of the towing system can not be fully controlled since the rope can only provide a unidirectional constraint force to the suspended object.Based on the kinematics of the multi-robot coordinated towing system with fixed-base,the Newton-Euler equations and Udwadia-Kalaba equations were used to establish the dynamics of the towing system.To obtain the motion trajectories with high stability and strong control,the motion trajectories of the towing system were optimized.During the towing,the transition from the relaxation state to the tension state of the rope was treated as a collision between the suspended object and the robot end.The trajectories of the towing system in terms of a single-variable and multiple-variable were solved,respectively.The simulation shows that the optimized trajectories are closer to reality and truly reflect the constraints of the ropes on the suspended object.The research results provide a basis for trajectory planning and control of the towing system.
基金financially supported by the National Natural Science Foundation of China(Grant No.11272079)the National Basic Research Program of China(973 Program,Grant No.2011CB013702)
文摘Nonlinear behaviors of a free-floating body in waves were experimentally investigated in the present study. The experiments were carried out for 6 different wave heights and 6 different wave periods to cover a relatively wide range of wave nonlinearities. A charge-coupled device （CCD） camera was used to capture the real-time motion of the floating body. The measurement data show that the sway, heave and roll motions of the floating body are all harmonic oscillations while the equilibrium position of the sway motion drifts in the wave direction. The drift speed is proportional to wave steepness when the size of the floating body is comparable to the wavelength, while it is proportional to the square of wave steepness when the floating body is relatively small. In addition, the drift motion leads to a slightly longer oscillation period of the floating body than the wave period of nonlinear wave and the discrepancy increases with the increment of wave steepness.
基金The research work was supported by the Project of National Natural Science Foundation of China(No.51565048)Excellent young teacher training program of Xinjiang Corps(CZ027213)Graduate Research and Innovation Project of Xinjiang Uygur Autonomous Region(XJGRI2017056)。
文摘Frequent start-stops of automatic seedling transplanters would lengthen the seedling picking time due to alternating movement of the motor,and cause positioning errors and frequent motor vibrations when starting the machine.To solve these problems and ensure the pick-up continuity of automatic transplanters,in this study the smooth circular arc interpolation algorithm and the least square method for multinomial curve fitting were used to conduct the trajectory planning of automatic transplanter based on the movement of the pick-up arm of the transplanter.Velocity and time curves were fitted in segments to acquire motion control parameters and further tracking control was conducted.The mathematical model of the control system was established using Simulink,and simulation analysis and system debugging test were performed.Experiments show that the trajectory curves obtained by MATLAB’s data processing can realize the continual and smooth motion trajectory of the pick-up arm;stepper motor velocity control can effectively track the planning curve and improve the seedling pick-up efficiency.The pick-up and pushing time of each motion of the planned plug seedling transplanter reduced by 1.0678 s and the start-stop times reduced from 6 to 1,which solved the frequent motor vibrations when starting the machine and improved the stability of the system.In addition,overstep and out-of-step of the motor at the start-stop moment were avoided and displacement error was reduced.
基金Supported by the National Natural Science Foundation of China(61401496)
文摘This paper described an improved underwater confrontation simulation method of naval amphibious operational training system. The initial position of submarine forces on the enemy is generated automatically, and the attacking distance model of torpedoes is established based on the kinematics theory, which is more flexible and reasonable to judge the launch condition compared to traditional method. The two kinds of confrontation behavior models on the enemy submarine are created to depict its tactical action from the defensive to the offensive as well as the contrary, ensuring that operational style is simulated more comprehensively and properly. The existing motion trajectory estimation and collision detection algorithms on operational platforms are also improved to reduce the iteration error and further enhance the detection accuracy of target hit.
文摘To understand the influence of the initial release conditions on the separation characteristics of the store and improve it under high Mach number(Ma=4)flight conditions,the overset grid method and the Realizable k−εturbulence model coupled with an equation with six degrees of freedom are used to simulate the store released from the internal bay.The motion trajectory and the attitude angle of the store separation under the conditions of different centroid,velocity,height and control measures are given by the calculated result.Through analysis,the position of the centroid will affect the separation of the store,which needs to be considered in the design.Increasing the launching height is conducive to the separation of the store.If the store has an initial velocity,it can leave the internal bay more quickly and reduce the probability of collision with the wall.Cylindrical rod and slanted aft wall control measures can improve the attitude of the store and make the store fall more smoothly.
基金Supported by National Natural Science Foundation of China (No.30500129)
文摘In order to avoid the influence of noise variance on the filtering performances, a modified adaptive weighted averaging (MAWA) filtering algorithm is proposed for noisy image sequences. Based upon adaptive weighted averaging pixel values in consecutive frames, this algorithm achieves the filtering goal by assigning smaller weights to the pixels with inappropriate estimated motion trajectory for noise. It only utilizes the intensity of pixels to suppress noise and accordingly is independent of noise variance. To evaluate the performance of the proposed filtering algorithm, its mean square error and percentage of preserved edge points were compared with those of traditional adaptive weighted averaging and non-adaptive mean filtering algorithms under different noise variances. Relevant results show that the MAWA filtering algorithm can preserve image structures and edges under motion after attenuating noise, and thus may be used in image sequence filtering.
基金This work is supported by the National Natural Science Foundations of China(No.11772071),NSAF(No.U1830115)the Fundamental Research Funds for the Central Universities(No.2020CDJQY-Z004).
文摘A mass-rod-disk system consisting of an oscillating mass attached to a rigid rotating disk by an elastic rod is designed to study rigid-flexible coupling mechanism.Suppose the rod is lightweight and has enough stiffness,the theorems of linear momentum and angular momentum are applied to the mass-rod-disk system based on the kinematic description of the system.With respect to two deflections of the mass and one angular velocity of the system,a group of nonlinear differential equations are established where the tangential inertial force,centrifugal force,Coriolis force as well as the moments of additional inertial forces take important effects on the dynamic response.For the sake of description,these three types of inertial forces mentioned before are referred to as additional inertial forces in this paper.The horizontal deflections of the mass and the angular velocity of the disk rotating about a fixed-axis are numerically solved for the prescribed external torque.The oscillating trajectory of the mass is deeply influenced by the additional inertial forces,meanwhile the dynamic fluctuations of the angular velocity and rotary inertia of the system are strongly affected by the mass oscillation.
基金Project supported by the Shanghai Nanoscience Foundation,China (Grant Nos.0852nm07000 and 0952nm07000)the National Natural Science Foundation of China (Grant Nos.10804084 and 91123022)+1 种基金the National Key Technology R&D Program,China (Grant No.2006BAF06B08)the Specialized Research Fund for the Doctoral Program of Ministry of High Education of China (Grant No.200802471008)
文摘The use of the dipole force on atoms is a new technology that is used to build nanostructures. In this way, a high quality standard nano-grating can be obtained. Based on the semi-classical model, the motion equation is investigated and the trajectories of atoms in double half Gaussian standing wave field are simulated. Compared with the Gaussian standing wave field, the double half Gaussian standing wave can well focus the Cr atoms. In order to obtain this kind of beam, a prism is designed and the experimental result shows that the beam is well generated.
基金Supported by the National Key Research and Development Program of China(No.2019YFB1803101)the Natural Science Foundation of Shanghai(No.19ZR1467200).
文摘Optimizing the power resources allocation method of low earth orbit(LEO)satellites to medium earth orbit(MEO)satellite'links is a significant way to construct efficient satellite constellations for satellite communication.A game theory power allocation method based on remaining visible time(RVT)of LEO-MEO satellites is proposed.Firstly,one LEO-MEO satellite network is classified as a cluster in which the RVT of LEO satellites is modeled.Secondly,the cost function of RVT concerning the character of orbit and throughput in each LEO satellite is mainly designed,which gives greater punishment of utility value to LEO satellites with less RVT and is an essential part of the reasonable utility function applied in diverse motion scenes.Meanwhile,the existence of Nash equilibrium for the proposed utility function in game theory area is proved.Thirdly,an off-cluster scheme for LEO satellites through the proposed threshold is raised to ensure the overall utility value of the whole LEO satellites in cluster.Finally,the performance improvement of the proposed algorithm to the baseline algorithm is verified through simulations in different scenarios.
