The variation of the nonlinear contact stiffness induced by the elastic wheel-holding effect between the aircraft and tractor has an important effect on the vibration characteristics of an airfield towbarless traction...The variation of the nonlinear contact stiffness induced by the elastic wheel-holding effect between the aircraft and tractor has an important effect on the vibration characteristics of an airfield towbarless traction system,making it essential for ensuring the safety of this emerging towing-out mode.In this paper,the frequency evolutionary tendency of the traction system is studied and obtained considering the variation of nonlinear contact stiffness for the first time.A novel modal analysis method,based on a derived nonlinear contact relationship,is proposed to investigate the vibration characteristics for mechanical system.Frequency veering and mode exchange phenomena in the low-order modes are observed due to the variation of nonlinear contact stiffness.These findings are further validated by the experimental results of a scaled-down model.In addition,it is also found that the veering critical point will be shifted with the external loads.The study provides valuable insights into the vibration characteristics and frequency veering behavior of similar mechanism-based systems,such as towbarless traction system,and has important implications for improving their design and operational performance.展开更多
本文述评了Peter van der Veer比较印度和中国的现代性经验的研究,即关于自殖民时期到后殖民时期,两国民族主义、现代性努力、宗教和世俗势力之间的纠缠和演化的研究。本文认为van der Veer的中印比较研究对曾占支配地位的"现代化...本文述评了Peter van der Veer比较印度和中国的现代性经验的研究,即关于自殖民时期到后殖民时期,两国民族主义、现代性努力、宗教和世俗势力之间的纠缠和演化的研究。本文认为van der Veer的中印比较研究对曾占支配地位的"现代化理论范式"进行了反思,他主要挑战了将欧美的现代性作为理想型、而非西方社会的现代性只是对西方现代性的模仿的观念,以及世俗化的观念。本文介绍了他相关思想的几个重要方面,尤其"帝国的现代性"情境下中印民族主义与宗教的关系、世俗化作为国家工程在两国的发展和两国表征在身体上的民族精神即瑜伽和气功。本文最后指出了van der Veer中印比较研究中的一些不足,但仍然认为他的思想是开拓性的,他对世俗化理论和其背后的现代化理论的挑战和反思代表着这个领域最先进的理念。展开更多
The frequency veering of a metal porous rotating cantilever twisted plate with twist angle and stagger angle is investigated.Metal porous materials may have the characteristics of gradient or uniform distribution alon...The frequency veering of a metal porous rotating cantilever twisted plate with twist angle and stagger angle is investigated.Metal porous materials may have the characteristics of gradient or uniform distribution along the thickness direction.Based on the classical shell theory,considering the influence of centrifugal force produced by high-speed rotation,the free vibration equations of a rotating cantilever twisted plate are derived.Through the polynomial function and Rayleigh-Ritz method,the natural frequencies and mode shapes of the metal porous cantilever twisted plate in both static and rotating states are derived.The accuracy of the present theory and calculation results is confirmed by a comparison between them and the results available from the literature and those obtained from Abaqus.The influences of the thickness ratio,porosity,twist angle,stagger angle and rotational velocity on the frequency veering and mode shape shift of the rotating cantilever twisted plate with porous material under three different distributions are analyzed.It should be mentioned that the frequency veering accompanied by mode shape shift occurs in both static and dynamic states.展开更多
According to the mapping theory in complex plane, the geometric features of eigen frequency loci of systems undergoing free vibrations are investigated. It is concluded that the phenomena of curve coalescence and veer...According to the mapping theory in complex plane, the geometric features of eigen frequency loci of systems undergoing free vibrations are investigated. It is concluded that the phenomena of curve coalescence and veering can be described in a unified manner from the singularities of mapping from the complex parameter plane onto the complex frequency plane. The formation of a branch point in the parameter Space is the foundation of explaining localization and veering phenomena. By the use of condensation to reduce the dimension of a system, the scope of application of the geometric theory is widely expanded. The theory is applied to examples to verify the validity of the proposed approach. The present work is an improvement and extension of recent work by M. S. Traintafyllou et al..展开更多
Under the premise of fully respecting Technical Leaflet T3developed by the International Table Tennis Federation(I T T F),this paper proposes an effective method for testing the veer degree of the table tennis ball ba...Under the premise of fully respecting Technical Leaflet T3developed by the International Table Tennis Federation(I T T F),this paper proposes an effective method for testing the veer degree of the table tennis ball based on airflow suspension and machine vision.By sequentially capturing the images of the ball in the stable state of spinning and suspension,a set of fitting circle centres from different circular sections can be obtained by circle fitting through the least square method.The minimum circumscribed circle(MCC)diameter of these centres is served as a basic parameter to evaluate the veer degree of the ball.Experimental results show that this diameter can effectively reflect the veer degree of the ball.The method proposed in this papercan provide a technical basis for the veer online testing of the table tennis ball.展开更多
In this study, the influence of geometrical parameters on the curve veering phenomenon in a tor-sional system with stepped shaft is investigated. Three approximate solutions including finite el-ement, Rayleigh-Ritz an...In this study, the influence of geometrical parameters on the curve veering phenomenon in a tor-sional system with stepped shaft is investigated. Three approximate solutions including finite el-ement, Rayleigh-Ritz and discretization methods, along with an exact solution are employed to obtain the natural frequencies of the structure. The study reveals that, under specific circumstances, the results obtained by approximate methods are very close to the exact solution. The curve veering behavior is manifested irrespective of the method employed. It is concluded that for the structure studied the curve veering behavior is not because of the approximate techniques used to compute the natural frequencies, and is an inherent behavior of the structure.展开更多
This article presents a methodology to determine the risk of aircrafts lateral runway excursion during landing via mathematical risk modeling. In addition, the methodology is demonstrated by means of detailed calculat...This article presents a methodology to determine the risk of aircrafts lateral runway excursion during landing via mathematical risk modeling. In addition, the methodology is demonstrated by means of detailed calculation of the lateral runway excursion risk value during the landing of the aircraft Airbus A310-200, in view of the maximum landing weight and the appropriate range of landing velocities according to the International Civil Aviation Organization specification. Obviously, the calculation demonstrates that the developed math solutions and equations presented herein are powerful tools to evaluate the risk of lateral runway excursion of the majority of aircrafts and for any airport. The method is also applicable to assess the residual level of risk at any specific airport and its deviation compared to the recommended safety level. Consequently, the presented mathematical solutions to determine the risk rate of lateral runway excursion during landing offers airports’ operational and safety management departments a viable tool so that appropriate measurements could be adopted. Finally, it is a methodology not only to assess the risk but also to determine the appropriate runway width.展开更多
基金co-supported by the Key Projects of the Civil Aviation Joint Fund of the National Natural Science Foundation of China(No.U2033208)。
文摘The variation of the nonlinear contact stiffness induced by the elastic wheel-holding effect between the aircraft and tractor has an important effect on the vibration characteristics of an airfield towbarless traction system,making it essential for ensuring the safety of this emerging towing-out mode.In this paper,the frequency evolutionary tendency of the traction system is studied and obtained considering the variation of nonlinear contact stiffness for the first time.A novel modal analysis method,based on a derived nonlinear contact relationship,is proposed to investigate the vibration characteristics for mechanical system.Frequency veering and mode exchange phenomena in the low-order modes are observed due to the variation of nonlinear contact stiffness.These findings are further validated by the experimental results of a scaled-down model.In addition,it is also found that the veering critical point will be shifted with the external loads.The study provides valuable insights into the vibration characteristics and frequency veering behavior of similar mechanism-based systems,such as towbarless traction system,and has important implications for improving their design and operational performance.
文摘本文述评了Peter van der Veer比较印度和中国的现代性经验的研究,即关于自殖民时期到后殖民时期,两国民族主义、现代性努力、宗教和世俗势力之间的纠缠和演化的研究。本文认为van der Veer的中印比较研究对曾占支配地位的"现代化理论范式"进行了反思,他主要挑战了将欧美的现代性作为理想型、而非西方社会的现代性只是对西方现代性的模仿的观念,以及世俗化的观念。本文介绍了他相关思想的几个重要方面,尤其"帝国的现代性"情境下中印民族主义与宗教的关系、世俗化作为国家工程在两国的发展和两国表征在身体上的民族精神即瑜伽和气功。本文最后指出了van der Veer中印比较研究中的一些不足,但仍然认为他的思想是开拓性的,他对世俗化理论和其背后的现代化理论的挑战和反思代表着这个领域最先进的理念。
基金The authors acknowledge the financial support of National Natural Science Foundation of China(grant nos.11872127,11832002,and 11732005)the Qin Xin Talents Cultivation Program,Beijing Information Science&Technology University(QXTCP A201901)the Project of High-level Innovative Team Building Plan for Beijing Municipal Colleges and Universities(No.IDHT20180513).
文摘The frequency veering of a metal porous rotating cantilever twisted plate with twist angle and stagger angle is investigated.Metal porous materials may have the characteristics of gradient or uniform distribution along the thickness direction.Based on the classical shell theory,considering the influence of centrifugal force produced by high-speed rotation,the free vibration equations of a rotating cantilever twisted plate are derived.Through the polynomial function and Rayleigh-Ritz method,the natural frequencies and mode shapes of the metal porous cantilever twisted plate in both static and rotating states are derived.The accuracy of the present theory and calculation results is confirmed by a comparison between them and the results available from the literature and those obtained from Abaqus.The influences of the thickness ratio,porosity,twist angle,stagger angle and rotational velocity on the frequency veering and mode shape shift of the rotating cantilever twisted plate with porous material under three different distributions are analyzed.It should be mentioned that the frequency veering accompanied by mode shape shift occurs in both static and dynamic states.
基金This work was partially supported by the NNSFC and the ASFC.
文摘According to the mapping theory in complex plane, the geometric features of eigen frequency loci of systems undergoing free vibrations are investigated. It is concluded that the phenomena of curve coalescence and veering can be described in a unified manner from the singularities of mapping from the complex parameter plane onto the complex frequency plane. The formation of a branch point in the parameter Space is the foundation of explaining localization and veering phenomena. By the use of condensation to reduce the dimension of a system, the scope of application of the geometric theory is widely expanded. The theory is applied to examples to verify the validity of the proposed approach. The present work is an improvement and extension of recent work by M. S. Traintafyllou et al..
文摘Under the premise of fully respecting Technical Leaflet T3developed by the International Table Tennis Federation(I T T F),this paper proposes an effective method for testing the veer degree of the table tennis ball based on airflow suspension and machine vision.By sequentially capturing the images of the ball in the stable state of spinning and suspension,a set of fitting circle centres from different circular sections can be obtained by circle fitting through the least square method.The minimum circumscribed circle(MCC)diameter of these centres is served as a basic parameter to evaluate the veer degree of the ball.Experimental results show that this diameter can effectively reflect the veer degree of the ball.The method proposed in this papercan provide a technical basis for the veer online testing of the table tennis ball.
文摘In this study, the influence of geometrical parameters on the curve veering phenomenon in a tor-sional system with stepped shaft is investigated. Three approximate solutions including finite el-ement, Rayleigh-Ritz and discretization methods, along with an exact solution are employed to obtain the natural frequencies of the structure. The study reveals that, under specific circumstances, the results obtained by approximate methods are very close to the exact solution. The curve veering behavior is manifested irrespective of the method employed. It is concluded that for the structure studied the curve veering behavior is not because of the approximate techniques used to compute the natural frequencies, and is an inherent behavior of the structure.
文摘This article presents a methodology to determine the risk of aircrafts lateral runway excursion during landing via mathematical risk modeling. In addition, the methodology is demonstrated by means of detailed calculation of the lateral runway excursion risk value during the landing of the aircraft Airbus A310-200, in view of the maximum landing weight and the appropriate range of landing velocities according to the International Civil Aviation Organization specification. Obviously, the calculation demonstrates that the developed math solutions and equations presented herein are powerful tools to evaluate the risk of lateral runway excursion of the majority of aircrafts and for any airport. The method is also applicable to assess the residual level of risk at any specific airport and its deviation compared to the recommended safety level. Consequently, the presented mathematical solutions to determine the risk rate of lateral runway excursion during landing offers airports’ operational and safety management departments a viable tool so that appropriate measurements could be adopted. Finally, it is a methodology not only to assess the risk but also to determine the appropriate runway width.
