The reduced weight and improved efficiency of modern aeronautical structures result in a decreasing separation of frequency ranges of rigid and elastic modes.Particularly,a high-aspect-ratio flexible flying wing is pr...The reduced weight and improved efficiency of modern aeronautical structures result in a decreasing separation of frequency ranges of rigid and elastic modes.Particularly,a high-aspect-ratio flexible flying wing is prone to body freedomflutter(BFF),which is a result of coupling of the rigid body short-periodmodewith 1st wing bendingmode.Accurate prediction of the BFF characteristics is helpful to reflect the attitude changes of the vehicle intuitively and design the active flutter suppression control law.Instead of using the rigid body mode,this work simulates the rigid bodymotion of the model by using the six-degree-of-freedom(6DOF)equation.A dynamicmesh generation strategy particularly suitable for BFF simulation of free flying aircraft is developed.An accurate Computational Fluid Dynamics/Computational Structural Dynamics/six-degree-of-freedom equation(CFD/CSD/6DOF)-based BFF prediction method is proposed.Firstly,the time-domain CFD/CSD method is used to calculate the static equilibrium state of the model.Based on this state,the CFD/CSD/6DOF equation is solved in time domain to evaluate the structural response of themodel.Then combinedwith the variable stiffnessmethod,the critical flutter point of the model is obtained.This method is applied to the BFF calculation of a flyingwing model.The calculation results of the BFF characteristics of the model agree well with those fromthe modalmethod andNastran software.Finally,the method is used to analyze the influence factors of BFF.The analysis results show that the flutter speed can be improved by either releasing plunge constraint or moving the center ofmass forward or increasing the pitch inertia.展开更多
This study presents a high-speed geometrically nonlinear flutter analysis calculation method based on the highprecision computational fluid dynamics/computational structural dynamics methods.In the proposed method,the...This study presents a high-speed geometrically nonlinear flutter analysis calculation method based on the highprecision computational fluid dynamics/computational structural dynamics methods.In the proposed method,the aerodynamic simulation was conducted based on computational fluid dynamics,and the structural model was established using the nonlinear finite element model and tangential stiffness matrix.First,the equilibrium position was obtained using the nonlinear static aeroelastic iteration.Second,the structural modal under a steady aerodynamic load was extracted.Finally,the generalized displacement time curve was obtained by coupling the unsteady aerodynamics and linearized structure motion equations.Moreover,if the flutter is not at a critical state,the incoming flow dynamic pressure needs to be changed,and the above steps must be repeated until the vibration amplitude are equal.Furthermore,the high-speed geometrically nonlinear flutter of the wing-body assemblymodel with a high-aspect ratio was investigated,and the correctness of the method was verified using high-speed wind tunnel experiments.The results showed that the geometric nonlinearity of the large deformation of the wing caused in-plane bending to become a key factor in flutter characteristics and significantly decreased the dynamic pressure and frequency of the nonlinear flutter compared to those of the linear flutter.展开更多
The dynamic coupling between the fluttering motions and hydrodynamic characteristics of codend is essential in understanding the trawl selectivity through fish response and the drag force acting on the whole trawl.Thi...The dynamic coupling between the fluttering motions and hydrodynamic characteristics of codend is essential in understanding the trawl selectivity through fish response and the drag force acting on the whole trawl.This study investigated the effect of towing speed,warp length,warp tension,and catch size on the fluttering motions of Antarctic krill trawl codend during net shooting,towing,and hauling by using sea trial data.The time-periodicity of codend oscillation was analyzed by the Morlet wavelet transform method.Results indicated that the period of codend oscillation was between 50 s and 90 s and showed an increasing trend with the warp tension but a decreased value at the towing stage.The coefficient amplitude of codend oscillation was between 0 and 4 at the net shooting and hauling stages,and between 0.2 and 0.6 at the towing stage.The amplitude of codend oscillation increased with the warp tension,towing speed,and catch size,but decreased with the increase of the warp length.In addition,the period of codend oscillation increased with the towing speed at the net shooting and hauling stages,but decreased at the towing stage.These results from codend fluttering motions can improve the understanding of fish behavior and gear shape that modify the hydrodynamic force on the codend instantaneously.展开更多
BACKGROUND Left atrial flutter without prior cardiac interventions is uncommon,especially dual-loop macro-reentry atrial flutter.The critical step to ablate dual-loop macroreentry atrial flutter is to identify the dom...BACKGROUND Left atrial flutter without prior cardiac interventions is uncommon,especially dual-loop macro-reentry atrial flutter.The critical step to ablate dual-loop macroreentry atrial flutter is to identify the dominant loop and key isthmus.Although entrainment mapping could help identify the dominant loop and key isthmus,it may alter or terminate tachycardia.High-density mapping allows the generation of electroanatomic maps without altering or terminating tachycardia.CASE SUMMARY Here,we report a case of symptomatic left atrial flutter without prior intervention.In this case,high-density mapping revealed a dual-loop macro-reentry around the mitral annulus and central scar of the anterior wall.The propagation result showed that the dominant loop was around the mitral annulus,and the key isthmus was between the central scar and mitral annulus.The atrial flutter terminated successfully after ablation was performed.CONCLUSION In this case,we demonstrate that high-density mapping technology may help identify the dominant loop of dual-loop atrial flutter without entrainment,which makes ablation easier.展开更多
记账在资金快速流动的现代社会成为人们生活中不可缺少的一部分。随着各式各样移动设备的普及,如何在各种设备之间实现财政数据的共享也成为一大问题。基于该设计并开发了一款基于Flutter跨平台智能记账软件,该软件在实现跨平台数据同...记账在资金快速流动的现代社会成为人们生活中不可缺少的一部分。随着各式各样移动设备的普及,如何在各种设备之间实现财政数据的共享也成为一大问题。基于该设计并开发了一款基于Flutter跨平台智能记账软件,该软件在实现跨平台数据同步的同时,引入OCR(Opentical Character Rescognition,光学字符识别)技术实现批量记账,能够帮助用户进行高效的财务管理。展开更多
目的:评估无水乙醇注射Marshall静脉(vein of Marshall,VOM)在持续性心房扑动(简称房扑)、心房颤动(简称房颤)二尖瓣峡部线性消融中的有效性和安全性。方法:收集2019年9月—2020年5月上海市胸科医院采用射频消融+无水乙醇注射VOM治疗持...目的:评估无水乙醇注射Marshall静脉(vein of Marshall,VOM)在持续性心房扑动(简称房扑)、心房颤动(简称房颤)二尖瓣峡部线性消融中的有效性和安全性。方法:收集2019年9月—2020年5月上海市胸科医院采用射频消融+无水乙醇注射VOM治疗持续性房扑、房颤患者72例(VOM组)的临床资料,同时选择采用左房线性消融治疗持续性房扑、房颤患者72例作为对照(对照组)。入选患者均行二尖瓣峡部线性消融手术,术中验证二尖瓣峡部线阻断情况,术后随访房性心律失常和心包积液发生情况,均随访12个月以上。结果:VOM组术中验证二尖瓣峡部线阻断63例,其中需要联合心内和心外膜补点消融达到二尖瓣峡部线14例,未能阻断二尖瓣峡部线9例。对照组术中验证二尖瓣峡部线53例,未能阻断19例。随访12~20个月,VOM组房性心律失常复发20例,而对照组房性心律失常复发30例。结论:在持续性房扑、房颤消融治疗中,经VOM行无水乙醇注射能有效阻断二尖瓣峡部线性传导,有助于提高二尖瓣峡部线成功率,减少房颤消融术中二尖瓣峡部相关的房扑发生率,且不增加严重并发症的发生率。展开更多
基金This work was supported by the National Natural Science Foundation of China(No.11872212)and a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
文摘The reduced weight and improved efficiency of modern aeronautical structures result in a decreasing separation of frequency ranges of rigid and elastic modes.Particularly,a high-aspect-ratio flexible flying wing is prone to body freedomflutter(BFF),which is a result of coupling of the rigid body short-periodmodewith 1st wing bendingmode.Accurate prediction of the BFF characteristics is helpful to reflect the attitude changes of the vehicle intuitively and design the active flutter suppression control law.Instead of using the rigid body mode,this work simulates the rigid bodymotion of the model by using the six-degree-of-freedom(6DOF)equation.A dynamicmesh generation strategy particularly suitable for BFF simulation of free flying aircraft is developed.An accurate Computational Fluid Dynamics/Computational Structural Dynamics/six-degree-of-freedom equation(CFD/CSD/6DOF)-based BFF prediction method is proposed.Firstly,the time-domain CFD/CSD method is used to calculate the static equilibrium state of the model.Based on this state,the CFD/CSD/6DOF equation is solved in time domain to evaluate the structural response of themodel.Then combinedwith the variable stiffnessmethod,the critical flutter point of the model is obtained.This method is applied to the BFF calculation of a flyingwing model.The calculation results of the BFF characteristics of the model agree well with those fromthe modalmethod andNastran software.Finally,the method is used to analyze the influence factors of BFF.The analysis results show that the flutter speed can be improved by either releasing plunge constraint or moving the center ofmass forward or increasing the pitch inertia.
文摘This study presents a high-speed geometrically nonlinear flutter analysis calculation method based on the highprecision computational fluid dynamics/computational structural dynamics methods.In the proposed method,the aerodynamic simulation was conducted based on computational fluid dynamics,and the structural model was established using the nonlinear finite element model and tangential stiffness matrix.First,the equilibrium position was obtained using the nonlinear static aeroelastic iteration.Second,the structural modal under a steady aerodynamic load was extracted.Finally,the generalized displacement time curve was obtained by coupling the unsteady aerodynamics and linearized structure motion equations.Moreover,if the flutter is not at a critical state,the incoming flow dynamic pressure needs to be changed,and the above steps must be repeated until the vibration amplitude are equal.Furthermore,the high-speed geometrically nonlinear flutter of the wing-body assemblymodel with a high-aspect ratio was investigated,and the correctness of the method was verified using high-speed wind tunnel experiments.The results showed that the geometric nonlinearity of the large deformation of the wing caused in-plane bending to become a key factor in flutter characteristics and significantly decreased the dynamic pressure and frequency of the nonlinear flutter compared to those of the linear flutter.
基金This study was supported by the National Natural Science Foundation of China(No.31902426)the Shanghai Sailing Program(No.19YF1419800)the Special Project for Exploitation and Utilization of Antarctic Biological Resources of the Ministry of Agriculture and Rural Affairs(No.D-8002-18-0097).
文摘The dynamic coupling between the fluttering motions and hydrodynamic characteristics of codend is essential in understanding the trawl selectivity through fish response and the drag force acting on the whole trawl.This study investigated the effect of towing speed,warp length,warp tension,and catch size on the fluttering motions of Antarctic krill trawl codend during net shooting,towing,and hauling by using sea trial data.The time-periodicity of codend oscillation was analyzed by the Morlet wavelet transform method.Results indicated that the period of codend oscillation was between 50 s and 90 s and showed an increasing trend with the warp tension but a decreased value at the towing stage.The coefficient amplitude of codend oscillation was between 0 and 4 at the net shooting and hauling stages,and between 0.2 and 0.6 at the towing stage.The amplitude of codend oscillation increased with the warp tension,towing speed,and catch size,but decreased with the increase of the warp length.In addition,the period of codend oscillation increased with the towing speed at the net shooting and hauling stages,but decreased at the towing stage.These results from codend fluttering motions can improve the understanding of fish behavior and gear shape that modify the hydrodynamic force on the codend instantaneously.
基金the National Science Foundation of China,No.81800292.
文摘BACKGROUND Left atrial flutter without prior cardiac interventions is uncommon,especially dual-loop macro-reentry atrial flutter.The critical step to ablate dual-loop macroreentry atrial flutter is to identify the dominant loop and key isthmus.Although entrainment mapping could help identify the dominant loop and key isthmus,it may alter or terminate tachycardia.High-density mapping allows the generation of electroanatomic maps without altering or terminating tachycardia.CASE SUMMARY Here,we report a case of symptomatic left atrial flutter without prior intervention.In this case,high-density mapping revealed a dual-loop macro-reentry around the mitral annulus and central scar of the anterior wall.The propagation result showed that the dominant loop was around the mitral annulus,and the key isthmus was between the central scar and mitral annulus.The atrial flutter terminated successfully after ablation was performed.CONCLUSION In this case,we demonstrate that high-density mapping technology may help identify the dominant loop of dual-loop atrial flutter without entrainment,which makes ablation easier.
文摘记账在资金快速流动的现代社会成为人们生活中不可缺少的一部分。随着各式各样移动设备的普及,如何在各种设备之间实现财政数据的共享也成为一大问题。基于该设计并开发了一款基于Flutter跨平台智能记账软件,该软件在实现跨平台数据同步的同时,引入OCR(Opentical Character Rescognition,光学字符识别)技术实现批量记账,能够帮助用户进行高效的财务管理。
文摘目的:评估无水乙醇注射Marshall静脉(vein of Marshall,VOM)在持续性心房扑动(简称房扑)、心房颤动(简称房颤)二尖瓣峡部线性消融中的有效性和安全性。方法:收集2019年9月—2020年5月上海市胸科医院采用射频消融+无水乙醇注射VOM治疗持续性房扑、房颤患者72例(VOM组)的临床资料,同时选择采用左房线性消融治疗持续性房扑、房颤患者72例作为对照(对照组)。入选患者均行二尖瓣峡部线性消融手术,术中验证二尖瓣峡部线阻断情况,术后随访房性心律失常和心包积液发生情况,均随访12个月以上。结果:VOM组术中验证二尖瓣峡部线阻断63例,其中需要联合心内和心外膜补点消融达到二尖瓣峡部线14例,未能阻断二尖瓣峡部线9例。对照组术中验证二尖瓣峡部线53例,未能阻断19例。随访12~20个月,VOM组房性心律失常复发20例,而对照组房性心律失常复发30例。结论:在持续性房扑、房颤消融治疗中,经VOM行无水乙醇注射能有效阻断二尖瓣峡部线性传导,有助于提高二尖瓣峡部线成功率,减少房颤消融术中二尖瓣峡部相关的房扑发生率,且不增加严重并发症的发生率。