Self-propelled robots have attracted significant attention due to their remarkable ability to navigate confined terrains.These robots usually have deformable structures while having discontinuous contact forces with t...Self-propelled robots have attracted significant attention due to their remarkable ability to navigate confined terrains.These robots usually have deformable structures while having discontinuous contact forces with the ground,resulting in a complex nonlinear system.To provide a solid foundation for the locomotion prediction and optimization for the self-propelled robots,it is necessary to conduct dynamic modelling and locomotion analysis of the robot.Motivated by these issues,this paper proposes a vibration-driven surrogate dynamic model for a deformable self-propelled robot and presents a detailed dynamic analysis.The surrogate dynamic model is employed to classify various types of stick-slip locomotion.Subsequently,the corresponding experiment demonstrates that the surrogate dynamic model effectively predicts the locomotion of the robot,particularly three types of stick-slip locomotion induced by discontinuous friction.Finally,a multi-objective coordinated optimization regarding the locomotion velocity,the cost of transport,and the energy conversion rate of the self-propelled robot is conducted,aiming to comprehensively enhance the robot’s locomotion performance.Additionally,suggestions for the selection of actuation parameters are presented.展开更多
The oscillation of large space structure(LSS)can be easily induced because of its low vibration frequency.The coupling effect between LSS vibration control and attitude control can significantly reduce the overall per...The oscillation of large space structure(LSS)can be easily induced because of its low vibration frequency.The coupling effect between LSS vibration control and attitude control can significantly reduce the overall performance of the control system,especially when the scale of flexible structure increases.This paper proposes an optimal placement method of piezoelectric stack actuators(PSAs)network which reduces the coupling effect between attitude and vibration control system.First,a spacecraft with a honeycomb-shaped telescope is designed for a resolution-critical imaging scenario.The coupling dynamics of the spacecraft is established using finite element method(FEM)and floating frame of reference formulation(FFRF).Second,a coupling-effect-reducing optimal placement criterion for PSAs based on coupling-matrix enhanced Gramian is designed to reduce the coupling effect excitation while balancing controllability.Additionally,a laddered multi-layered optimizing scheme is established to increase the speed and accuracy when solving the gigantic discrete optimization problem.Finally,the effectiveness of the proposed method is illustrated through numerical simulation.展开更多
Large space truss structure is widely used in spacecrafts.The vibration of this kind of structure will cause some serious problems.For instance,it will disturb the work of the payloads which are supported on the truss...Large space truss structure is widely used in spacecrafts.The vibration of this kind of structure will cause some serious problems.For instance,it will disturb the work of the payloads which are supported on the truss,even worse,it will deactivate the spacecrafts.Therefore,it is highly in need of executing vibration control for large space truss structure.Large space intelligent truss system(LSITS) is not a normal truss structure but a complex truss system consisting of common rods and active rods,and there are at least one actuator and one sensor in each active rod.One of the key points in the vibration control for LSITS is the location assignment of actuators and sensors.The positions of actuators and sensors will directly determine the properties of the control system,such as stability,controllability,observability,etc.In this paper,placement optimization of actuators and sensors(POAS) and decentralized adaptive fuzzy control methods are presented to solve the vibration control problem.The electro-mechanical coupled equations of the active rod are established,and the optimization criterion which does not depend upon control methods is proposed.The optimal positions of actuators and sensors in LSITS are obtained by using genetic algorithm(GA).Furthermore,the decentralized adaptive fuzzy vibration controller is designed to control LSITS.The LSITS dynamic equations with considering those remaining modes are derived.The adaptive fuzzy control scheme is improved via sliding control method.One T-typed truss structure is taken as an example and a demonstration experiment is carried out.The experimental results show that the GA is reliable and valid for placement optimization of actuators and sensors,and the adaptive fuzzy controller can effectively suppress the vibration of LSITS without control spillovers and observation spillovers.展开更多
In this study the effects of the actuation waveforms on the droplet generation in a drop-on-demand inkjet printing are studied systematically by numerical simulations.Two different types of waveforms,namely the unipol...In this study the effects of the actuation waveforms on the droplet generation in a drop-on-demand inkjet printing are studied systematically by numerical simulations.Two different types of waveforms,namely the unipolar and bipolar actuations,are investigated for three fluids with different physical properties.We focus on two key parameters,which are the dwell time and the velocity amplitude.For the unipolar driving,the ejection velocity and the ejected liquid volume are both increased as the velocity amplitude becomes larger.The dwell time only has minor effects on both the ejection velocity and the ejected liquid volume.The ejection velocity decreases significantly for large liquid viscosity,while the influences of viscosity on the ejected liquid volume are much weaker.Four different droplet morphologies and the corresponding parameter ranges are identified.The droplet radius can be successfully reduced to about 40%e of the nozzle exit radius.For the bipolar waveforms,same droplet morphologies are observed but with shifted boundaries in the phase space.The minimal radius of stable droplet produced by the bipolar waveforms is even smaller compared to the unipolar ones.展开更多
The performance of space antennas is significantly affected by thermal deformation owing to the harsh thermal environment in space.This results in potential degradation in pointing accuracy and overall functionality.T...The performance of space antennas is significantly affected by thermal deformation owing to the harsh thermal environment in space.This results in potential degradation in pointing accuracy and overall functionality.This study focused on the analysis and control of thermal deformation in large-scale two-dimensional planar phased array antennas.Employing the finite element method,we developed a comprehensive thermal and structural model of the antenna.This enabled us to simulate the steady-state temperature field and the associated thermal deformation at various orbital positions.To address this deformation issue,we propose an innovative shape-control approach that utilizes distributed cable actuators.The shape control challenge was reformulated into a layered optimization problem concerning actuator placement and force application.In the outer optimization layer,a discrete particle swarm optimization algorithm was used to determine the optimal locations for the actuators.In the inner optimization layer,quadratic programming was subsequently applied to calculate the optimal control forces for each actuator.We validated the proposed method by numerically simulating a novel large-scale two-dimensional planar phased array antenna.The results demonstrated the effectiveness of our method in mitigating thermal deformation and maintaining the structural integrity and shape accuracy of the antennas.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.11932015,12072237,and 12372022)the Shanghai Gaofeng Project for University Academic Program Development,and the Fundamental Research Funds for the Central Universities(Grant No.22120220590).
文摘Self-propelled robots have attracted significant attention due to their remarkable ability to navigate confined terrains.These robots usually have deformable structures while having discontinuous contact forces with the ground,resulting in a complex nonlinear system.To provide a solid foundation for the locomotion prediction and optimization for the self-propelled robots,it is necessary to conduct dynamic modelling and locomotion analysis of the robot.Motivated by these issues,this paper proposes a vibration-driven surrogate dynamic model for a deformable self-propelled robot and presents a detailed dynamic analysis.The surrogate dynamic model is employed to classify various types of stick-slip locomotion.Subsequently,the corresponding experiment demonstrates that the surrogate dynamic model effectively predicts the locomotion of the robot,particularly three types of stick-slip locomotion induced by discontinuous friction.Finally,a multi-objective coordinated optimization regarding the locomotion velocity,the cost of transport,and the energy conversion rate of the self-propelled robot is conducted,aiming to comprehensively enhance the robot’s locomotion performance.Additionally,suggestions for the selection of actuation parameters are presented.
基金supported by National Natural Science Foundation of China(No.U23B6001).
文摘The oscillation of large space structure(LSS)can be easily induced because of its low vibration frequency.The coupling effect between LSS vibration control and attitude control can significantly reduce the overall performance of the control system,especially when the scale of flexible structure increases.This paper proposes an optimal placement method of piezoelectric stack actuators(PSAs)network which reduces the coupling effect between attitude and vibration control system.First,a spacecraft with a honeycomb-shaped telescope is designed for a resolution-critical imaging scenario.The coupling dynamics of the spacecraft is established using finite element method(FEM)and floating frame of reference formulation(FFRF).Second,a coupling-effect-reducing optimal placement criterion for PSAs based on coupling-matrix enhanced Gramian is designed to reduce the coupling effect excitation while balancing controllability.Additionally,a laddered multi-layered optimizing scheme is established to increase the speed and accuracy when solving the gigantic discrete optimization problem.Finally,the effectiveness of the proposed method is illustrated through numerical simulation.
基金supported by the National Natural Science Foundation of China (Grant No. 10472006)
文摘Large space truss structure is widely used in spacecrafts.The vibration of this kind of structure will cause some serious problems.For instance,it will disturb the work of the payloads which are supported on the truss,even worse,it will deactivate the spacecrafts.Therefore,it is highly in need of executing vibration control for large space truss structure.Large space intelligent truss system(LSITS) is not a normal truss structure but a complex truss system consisting of common rods and active rods,and there are at least one actuator and one sensor in each active rod.One of the key points in the vibration control for LSITS is the location assignment of actuators and sensors.The positions of actuators and sensors will directly determine the properties of the control system,such as stability,controllability,observability,etc.In this paper,placement optimization of actuators and sensors(POAS) and decentralized adaptive fuzzy control methods are presented to solve the vibration control problem.The electro-mechanical coupled equations of the active rod are established,and the optimization criterion which does not depend upon control methods is proposed.The optimal positions of actuators and sensors in LSITS are obtained by using genetic algorithm(GA).Furthermore,the decentralized adaptive fuzzy vibration controller is designed to control LSITS.The LSITS dynamic equations with considering those remaining modes are derived.The adaptive fuzzy control scheme is improved via sliding control method.One T-typed truss structure is taken as an example and a demonstration experiment is carried out.The experimental results show that the GA is reliable and valid for placement optimization of actuators and sensors,and the adaptive fuzzy controller can effectively suppress the vibration of LSITS without control spillovers and observation spillovers.
基金National Natural Science Foundation of China(Grants 91848201,11988102,11521202,11872004.11802004)The authors also acknowledge the partial support from the Beijing Natural Science Foundation(Grants L172002)+1 种基金A.B.Aqecl would like to thank the Chinese Scholarship Council(CSC)for providing Chinese Government Scholarship(CGs)The numericalsimulations were performed on the National Super Computing Centerin Tianjin.China.
文摘In this study the effects of the actuation waveforms on the droplet generation in a drop-on-demand inkjet printing are studied systematically by numerical simulations.Two different types of waveforms,namely the unipolar and bipolar actuations,are investigated for three fluids with different physical properties.We focus on two key parameters,which are the dwell time and the velocity amplitude.For the unipolar driving,the ejection velocity and the ejected liquid volume are both increased as the velocity amplitude becomes larger.The dwell time only has minor effects on both the ejection velocity and the ejected liquid volume.The ejection velocity decreases significantly for large liquid viscosity,while the influences of viscosity on the ejected liquid volume are much weaker.Four different droplet morphologies and the corresponding parameter ranges are identified.The droplet radius can be successfully reduced to about 40%e of the nozzle exit radius.For the bipolar waveforms,same droplet morphologies are observed but with shifted boundaries in the phase space.The minimal radius of stable droplet produced by the bipolar waveforms is even smaller compared to the unipolar ones.
基金the National Natural Science Foundation of China(grant numbers 12172214 and 12102252)Fundamental Research Funds for the Central Universities(grant number USCAST2023-25).
文摘The performance of space antennas is significantly affected by thermal deformation owing to the harsh thermal environment in space.This results in potential degradation in pointing accuracy and overall functionality.This study focused on the analysis and control of thermal deformation in large-scale two-dimensional planar phased array antennas.Employing the finite element method,we developed a comprehensive thermal and structural model of the antenna.This enabled us to simulate the steady-state temperature field and the associated thermal deformation at various orbital positions.To address this deformation issue,we propose an innovative shape-control approach that utilizes distributed cable actuators.The shape control challenge was reformulated into a layered optimization problem concerning actuator placement and force application.In the outer optimization layer,a discrete particle swarm optimization algorithm was used to determine the optimal locations for the actuators.In the inner optimization layer,quadratic programming was subsequently applied to calculate the optimal control forces for each actuator.We validated the proposed method by numerically simulating a novel large-scale two-dimensional planar phased array antenna.The results demonstrated the effectiveness of our method in mitigating thermal deformation and maintaining the structural integrity and shape accuracy of the antennas.
