During high-speed rotation,the surface of aeronautic spiral bevel gears will generate significant pressure and viscous forces,which will cause a certain amount of windage power loss and reduce the efficiency of the tr...During high-speed rotation,the surface of aeronautic spiral bevel gears will generate significant pressure and viscous forces,which will cause a certain amount of windage power loss and reduce the efficiency of the transmission system.Based on the computational fluid dynamics,this paper analyzes the windage power loss of a single spiral bevel gear and a spiral bevel gear pair under oil injection lubrication.In addition,the shroud is used to suppress gear windage loss,and the clearance size and opening angle of the designed shroud are optimized.Finally,by comparing and analyzing the experimental results,the following conclusions were obtained:(1)For a single gear,the speed is the most important factor affecting windage loss,followed by the hand of spiral,and rotation direction;(2)For gear pairs,under oil injection lubrication,the input speed has the greatest impact on windage power loss,followed by the influence of oil injection port speed,temperature and oil injection port pressure;(3)Installing a shroud is an effective method to reduce windage power loss;(4)In the pure air phase,the smaller the clearance between the shroud and the gear surface,and the smaller the radial direction between the shroud and the shaft,the better the effect of reducing windage;(5)In the two-phase flow of oil and gas,it is necessary to design oil drainage holes on the shroud to ensure the smooth discharge of lubricating oil and improve the drag reduction effect.展开更多
This paper comprehensively investigates the buckling load and the stability of a planar linear array deployable structure composed of scissor-like element(SLE)under compression.At present,the researches on deployable ...This paper comprehensively investigates the buckling load and the stability of a planar linear array deployable structure composed of scissor-like element(SLE)under compression.At present,the researches on deployable structure are mainly focused on configuration design and dynamics characteristics of the mechanisms,but less on structural instability.In fact,when the external load exceeds the structural critical load value,the deployable structure will be permanently deformed or even collapse directly and no longer have any bearing capacity.To address this issue,a new stability model is derived using linear elastic analysis method and substructure method to evaluate the buckling characteristics of the deployable structure with n SLEs when it is carried out in space,which can accurately obtain the structural instability load and can be used quantitatively to optimize the structure for making it have the most stable configuration.In addition,the effects of the number of elements,the length,material properties and flexibility of the bar,and the deployment degree on the buckling of the scissor deployable structure are investigated,and the results of the theoretical analysis are compared with simulation and analytical results,respectively,confirming that the proposed stability model not only is able to effectively predict the structural instability load but also determine which part of the deployable structure is unstable.It can be concluded that the stability of the deployable structure gradually decreases with the increase of the number of elements or the bar flexibility.In the calculation process,the critical load of each sub-element should be considered,and the minimum value of the critical loads of all subunits can be regarded as the instability load of the whole structure.展开更多
Purpose–The purpose of this paper is to develop a proof-of-concept(POC)Forward Collision Warning(FWC)system for the motorcyclist,which determines a potential clash based on time-to-collision and trajectory of both th...Purpose–The purpose of this paper is to develop a proof-of-concept(POC)Forward Collision Warning(FWC)system for the motorcyclist,which determines a potential clash based on time-to-collision and trajectory of both the detected and ego vehicle(motorcycle).Design/methodology/approach–This comes in three approaches.First,time-to-collision value is to be calculated based on low-cost camera video input.Second,the trajectory of the detected vehicle is predicted based on video data in the 2 D pixel coordinate.Third,the trajectory of the ego vehicle is predicted via the lean direction of the motorcycle from a low-cost inertial measurement unit sensor.Findings–This encompasses a comprehensive Advanced FWC system which is an amalgamation of the three approaches mentioned above.First,to predict time-to-collision,nested Kalmanfilter and vehicle detection is used to convert image pixel matrix to relative distance,velocity and time-to-collision data.Next,for trajectory prediction of detected vehicles,a few algorithms were compared,and it was found that long short-term memory performs the best on the data set.The lastfinding is that to determine the leaning direction of the ego vehicle,it is better to use lean angle measurement compared to riding pattern classification.Originality/value–The value of this paper is that it provides a POC FWC system that considers time-to-collision and trajectory of both detected and ego vehicle(motorcycle).展开更多
基金Supported by National Natural Science Foundation of China(Grant Nos.51175422,61973011)Shaanxi Provincial Natural Science Basic Research Plan of China(Grant No.2022JM-195)+1 种基金Fundamental Research Funds for the Central Universities of Chinathe Research Start-up Funds of Hangzhou International Innovation Institute of Beihang University(Grant No.2024KQ036)。
文摘During high-speed rotation,the surface of aeronautic spiral bevel gears will generate significant pressure and viscous forces,which will cause a certain amount of windage power loss and reduce the efficiency of the transmission system.Based on the computational fluid dynamics,this paper analyzes the windage power loss of a single spiral bevel gear and a spiral bevel gear pair under oil injection lubrication.In addition,the shroud is used to suppress gear windage loss,and the clearance size and opening angle of the designed shroud are optimized.Finally,by comparing and analyzing the experimental results,the following conclusions were obtained:(1)For a single gear,the speed is the most important factor affecting windage loss,followed by the hand of spiral,and rotation direction;(2)For gear pairs,under oil injection lubrication,the input speed has the greatest impact on windage power loss,followed by the influence of oil injection port speed,temperature and oil injection port pressure;(3)Installing a shroud is an effective method to reduce windage power loss;(4)In the pure air phase,the smaller the clearance between the shroud and the gear surface,and the smaller the radial direction between the shroud and the shaft,the better the effect of reducing windage;(5)In the two-phase flow of oil and gas,it is necessary to design oil drainage holes on the shroud to ensure the smooth discharge of lubricating oil and improve the drag reduction effect.
基金the National Natural Science Foundation of China(Grant No.51175422)the Natural Science Basic Research Plan in Shaanxi Province of China(Grant No.2019JQ-753)the Ph D Research Startup Foundation of Xi’an University of Technology(Grant No.102-451119003)。
文摘This paper comprehensively investigates the buckling load and the stability of a planar linear array deployable structure composed of scissor-like element(SLE)under compression.At present,the researches on deployable structure are mainly focused on configuration design and dynamics characteristics of the mechanisms,but less on structural instability.In fact,when the external load exceeds the structural critical load value,the deployable structure will be permanently deformed or even collapse directly and no longer have any bearing capacity.To address this issue,a new stability model is derived using linear elastic analysis method and substructure method to evaluate the buckling characteristics of the deployable structure with n SLEs when it is carried out in space,which can accurately obtain the structural instability load and can be used quantitatively to optimize the structure for making it have the most stable configuration.In addition,the effects of the number of elements,the length,material properties and flexibility of the bar,and the deployment degree on the buckling of the scissor deployable structure are investigated,and the results of the theoretical analysis are compared with simulation and analytical results,respectively,confirming that the proposed stability model not only is able to effectively predict the structural instability load but also determine which part of the deployable structure is unstable.It can be concluded that the stability of the deployable structure gradually decreases with the increase of the number of elements or the bar flexibility.In the calculation process,the critical load of each sub-element should be considered,and the minimum value of the critical loads of all subunits can be regarded as the instability load of the whole structure.
文摘Purpose–The purpose of this paper is to develop a proof-of-concept(POC)Forward Collision Warning(FWC)system for the motorcyclist,which determines a potential clash based on time-to-collision and trajectory of both the detected and ego vehicle(motorcycle).Design/methodology/approach–This comes in three approaches.First,time-to-collision value is to be calculated based on low-cost camera video input.Second,the trajectory of the detected vehicle is predicted based on video data in the 2 D pixel coordinate.Third,the trajectory of the ego vehicle is predicted via the lean direction of the motorcycle from a low-cost inertial measurement unit sensor.Findings–This encompasses a comprehensive Advanced FWC system which is an amalgamation of the three approaches mentioned above.First,to predict time-to-collision,nested Kalmanfilter and vehicle detection is used to convert image pixel matrix to relative distance,velocity and time-to-collision data.Next,for trajectory prediction of detected vehicles,a few algorithms were compared,and it was found that long short-term memory performs the best on the data set.The lastfinding is that to determine the leaning direction of the ego vehicle,it is better to use lean angle measurement compared to riding pattern classification.Originality/value–The value of this paper is that it provides a POC FWC system that considers time-to-collision and trajectory of both detected and ego vehicle(motorcycle).
