In the aircraft control system,sensor networks are used to sample the attitude and environmental data.As a result of the external and internal factors(e.g.,environmental and task complexity,inaccurate sensing and comp...In the aircraft control system,sensor networks are used to sample the attitude and environmental data.As a result of the external and internal factors(e.g.,environmental and task complexity,inaccurate sensing and complex structure),the aircraft control system contains several uncertainties,such as imprecision,incompleteness,redundancy and randomness.The information fusion technology is usually used to solve the uncertainty issue,thus improving the sampled data reliability,which can further effectively increase the performance of the fault diagnosis decision-making in the aircraft control system.In this work,we first analyze the uncertainties in the aircraft control system,and also compare different uncertainty quantitative methods.Since the information fusion can eliminate the effects of the uncertainties,it is widely used in the fault diagnosis.Thus,this paper summarizes the recent work in this aera.Furthermore,we analyze the application of information fusion methods in the fault diagnosis of the aircraft control system.Finally,this work identifies existing problems in the use of information fusion for diagnosis and outlines future trends.展开更多
Formation control of fixed-wing aerial vehicles is an important yet rarely addressed problem because of their complex dynamics and various motion constraints,such as nonholonomic and velocity constraints.The guidance-...Formation control of fixed-wing aerial vehicles is an important yet rarely addressed problem because of their complex dynamics and various motion constraints,such as nonholonomic and velocity constraints.The guidance-route-based strategy has been demonstrated to be applicable to fixed-wing aircraft.However,it requires a global coordinator and there exists control lag,due to its own natures.For this reason,this paper presents a fully distributed guidance-route-based formation approach to address the aforementioned issues.First,a hop-count scheme is introduced to achieve distributed implementation,in which each aircraft chooses a neighbor with the minimum hop-count as a reference to generate its guidance route using only local information.Next,the model predictive control algorithm is employed to eliminate the control lag and achieve precise formation shape control.In addition,the stall protection and collision avoidance are also considered.Finally,three numerical simulations demonstrate that our proposed approach can implement precise formation shape control of fixed-wing aircraft in a fully distributed manner.展开更多
We demonstrate two ultra-stable laser systems at 1064 nm by independently stabilizing two 10-cm-long Fabry–Pérot cavities.The reference cavities are on a cubic spacer,which is rigidly mounted for both low sensit...We demonstrate two ultra-stable laser systems at 1064 nm by independently stabilizing two 10-cm-long Fabry–Pérot cavities.The reference cavities are on a cubic spacer,which is rigidly mounted for both low sensitivity to environmental vibration and ability for transportation.By comparing against an independent ultra-stable laser at 578 nm via an optical frequency comb,the 1064 nm lasers are measured to have frequency instabilities of 6×10^-16 at 1 s averaging time.展开更多
The standard extended Kalman filter-based simultaneously localization and mapping(EKF-SLAM)algorithm has a drawback that it could not handle the sudden motion caused by the motion disturbance.This prevents the SLAM sy...The standard extended Kalman filter-based simultaneously localization and mapping(EKF-SLAM)algorithm has a drawback that it could not handle the sudden motion caused by the motion disturbance.This prevents the SLAM system from real applications.Many techniques have been developed to make the system more robust to the motion disturbance.In this paper,we propose a robust monocular SLAM algorithm.First,when the motion model-based system failed to track the features,a KLT tracker will be activated for each feature.Second,the KLT tracked features are used to update the camera states.Third,the difference between the camera states and the predictions is used to adjust the input motion noise.Finally,we do the standard EKF-SLAM with the new input motion noise.In order to make the system more reliable,a joint compatibility branch and bound algorithm are used to check the outliers,and an IEKF filter is used to make the motion estimation smoother when the camera encounters sudden movement.The experiments are done on an image sequence caught by a shaking hand-held camera,which show that the proposed method is very robust to large motion disturbance.展开更多
Mesoscale structures that form in gas-solid flows considerably affect interphase heat transfer.A filtered interphase heat transfer model accounts for the effects of unresolved mesoscale structures is required in coars...Mesoscale structures that form in gas-solid flows considerably affect interphase heat transfer.A filtered interphase heat transfer model accounts for the effects of unresolved mesoscale structures is required in coarse-grid simulations.In the literature,researchers obtain the filtered interphase heat transfer coefficient using a correction(Q)to the microscopic interphase heat transfer coefficient.Available models are based on filtered data in the range 0<Q<1.However,the percentage of filtered data in the range Q<0 and Q>1 is non-negligible.This percentage can reach approximately 20%when the dimensionless filter size is smaller than 1.028(66.7×the particle diameter).We proposed an improved filtered interphase heat transfer model by considering the data in the range Q<0 and Q>1.We evaluated the predictive power of our model in an a priori test.Our model has much better performance than other models when the dimensionless filter size△<8.222.展开更多
Working performances of the components made out of 49Fe-49Co-2V alloy are closely related to the surface integrity of the drilled holes,which are influenced remarkably by the cooling conditions.The present study focus...Working performances of the components made out of 49Fe-49Co-2V alloy are closely related to the surface integrity of the drilled holes,which are influenced remarkably by the cooling conditions.The present study focuses on the surface integrity differences between wet and dry drilled 49Fe-49Co-2V alloy holes.The drilled hole surface roughness and topographies,metallurgical and mechanical properties,and the exit characterizations were obtained using optical microscopy(OM),scanning electron microscopy(SEM),electron backscatter diffraction microscopy(EBSD),transmission electron microscopy(TEM),energy dispersive spectroscopy(EDS)and Vickers hardness techniques,etc.The effects of cooling conditions on the surface integrity were concluded and the influence mechanisms were analyzed based on the force and temperature differences in drilling process with different cooling conditions.It is found that the surface roughness and the thickness of refined-grain region of the dry drilled holes are larger than those of wet drilled holes;work hardening induced by wet drilling is more serious than dry drilling;chippings occurred in the exits of the wet drilled holes due to the material brittleness,which could be avoided by dry drilling.The surface integrity differences of wet and dry drilled holes are closely related to the force and temperature differences in drilling process with different cooling conditions.展开更多
基金supported by the National Natural Science Foundation of China(62273176)the Aeronautical Science Foundation of China(20200007018001)the China Scholarship Council(202306830096).
文摘In the aircraft control system,sensor networks are used to sample the attitude and environmental data.As a result of the external and internal factors(e.g.,environmental and task complexity,inaccurate sensing and complex structure),the aircraft control system contains several uncertainties,such as imprecision,incompleteness,redundancy and randomness.The information fusion technology is usually used to solve the uncertainty issue,thus improving the sampled data reliability,which can further effectively increase the performance of the fault diagnosis decision-making in the aircraft control system.In this work,we first analyze the uncertainties in the aircraft control system,and also compare different uncertainty quantitative methods.Since the information fusion can eliminate the effects of the uncertainties,it is widely used in the fault diagnosis.Thus,this paper summarizes the recent work in this aera.Furthermore,we analyze the application of information fusion methods in the fault diagnosis of the aircraft control system.Finally,this work identifies existing problems in the use of information fusion for diagnosis and outlines future trends.
基金partially supported by the STI 2030-Major Projects(No.2022ZD0208804)the Postdoctoral Fellows of Beihang“Zhuoyue”Program,China。
文摘Formation control of fixed-wing aerial vehicles is an important yet rarely addressed problem because of their complex dynamics and various motion constraints,such as nonholonomic and velocity constraints.The guidance-route-based strategy has been demonstrated to be applicable to fixed-wing aircraft.However,it requires a global coordinator and there exists control lag,due to its own natures.For this reason,this paper presents a fully distributed guidance-route-based formation approach to address the aforementioned issues.First,a hop-count scheme is introduced to achieve distributed implementation,in which each aircraft chooses a neighbor with the minimum hop-count as a reference to generate its guidance route using only local information.Next,the model predictive control algorithm is employed to eliminate the control lag and achieve precise formation shape control.In addition,the stall protection and collision avoidance are also considered.Finally,three numerical simulations demonstrate that our proposed approach can implement precise formation shape control of fixed-wing aircraft in a fully distributed manner.
基金supported by the National Natural Science Foundation of China(Nos.11654004,11822402,91636214,and 11804094)the National Key R&D Program of China(No.2017YFA0304403)。
文摘We demonstrate two ultra-stable laser systems at 1064 nm by independently stabilizing two 10-cm-long Fabry–Pérot cavities.The reference cavities are on a cubic spacer,which is rigidly mounted for both low sensitivity to environmental vibration and ability for transportation.By comparing against an independent ultra-stable laser at 578 nm via an optical frequency comb,the 1064 nm lasers are measured to have frequency instabilities of 6×10^-16 at 1 s averaging time.
基金supported by the National Natural Science Foundation of China(91120006,61273366 and 61231018)
文摘The standard extended Kalman filter-based simultaneously localization and mapping(EKF-SLAM)algorithm has a drawback that it could not handle the sudden motion caused by the motion disturbance.This prevents the SLAM system from real applications.Many techniques have been developed to make the system more robust to the motion disturbance.In this paper,we propose a robust monocular SLAM algorithm.First,when the motion model-based system failed to track the features,a KLT tracker will be activated for each feature.Second,the KLT tracked features are used to update the camera states.Third,the difference between the camera states and the predictions is used to adjust the input motion noise.Finally,we do the standard EKF-SLAM with the new input motion noise.In order to make the system more reliable,a joint compatibility branch and bound algorithm are used to check the outliers,and an IEKF filter is used to make the motion estimation smoother when the camera encounters sudden movement.The experiments are done on an image sequence caught by a shaking hand-held camera,which show that the proposed method is very robust to large motion disturbance.
基金This work was supported by the HPC Platform at Xi’an Jiao Tong UniversityNational Natural Science Foundation of China(grant numbers 52006172,21978228)+2 种基金Shaanxi Provincial Natural Science Basic Research Program-Youth Fund Project(grant number 2020JQ-050)Shaanxi Creative Talents Promotion Plan-Technological Innovation Team(grant number 2019TD-039)Fundamental Research Funds for the Central Universities(grant number cxtd2017004).
文摘Mesoscale structures that form in gas-solid flows considerably affect interphase heat transfer.A filtered interphase heat transfer model accounts for the effects of unresolved mesoscale structures is required in coarse-grid simulations.In the literature,researchers obtain the filtered interphase heat transfer coefficient using a correction(Q)to the microscopic interphase heat transfer coefficient.Available models are based on filtered data in the range 0<Q<1.However,the percentage of filtered data in the range Q<0 and Q>1 is non-negligible.This percentage can reach approximately 20%when the dimensionless filter size is smaller than 1.028(66.7×the particle diameter).We proposed an improved filtered interphase heat transfer model by considering the data in the range Q<0 and Q>1.We evaluated the predictive power of our model in an a priori test.Our model has much better performance than other models when the dimensionless filter size△<8.222.
基金co-supported by the National Science and Technology Major Project (No. 2017-Ⅶ-0002-0095)the Science Challenge Project (No. TZ2018006-0101-01)the Postdoctoral Science Foundation (No. 2019M661090)
文摘Working performances of the components made out of 49Fe-49Co-2V alloy are closely related to the surface integrity of the drilled holes,which are influenced remarkably by the cooling conditions.The present study focuses on the surface integrity differences between wet and dry drilled 49Fe-49Co-2V alloy holes.The drilled hole surface roughness and topographies,metallurgical and mechanical properties,and the exit characterizations were obtained using optical microscopy(OM),scanning electron microscopy(SEM),electron backscatter diffraction microscopy(EBSD),transmission electron microscopy(TEM),energy dispersive spectroscopy(EDS)and Vickers hardness techniques,etc.The effects of cooling conditions on the surface integrity were concluded and the influence mechanisms were analyzed based on the force and temperature differences in drilling process with different cooling conditions.It is found that the surface roughness and the thickness of refined-grain region of the dry drilled holes are larger than those of wet drilled holes;work hardening induced by wet drilling is more serious than dry drilling;chippings occurred in the exits of the wet drilled holes due to the material brittleness,which could be avoided by dry drilling.The surface integrity differences of wet and dry drilled holes are closely related to the force and temperature differences in drilling process with different cooling conditions.
