To reduce the pitch link loads of variable speed rotors, variable tuning frequency fluid- lastic isolators are proposed. This isolator utilizes the variation of centrifugal force due to the change of rotor speed to ch...To reduce the pitch link loads of variable speed rotors, variable tuning frequency fluid- lastic isolators are proposed. This isolator utilizes the variation of centrifugal force due to the change of rotor speed to change the tuning port area ratio, which can change the tuning frequency of the isolator. A rotor model including the model of fluidlastic isolator is coupled with a fuselage model to predict the steady responses of the rotor system in forward flight. The aeroelastic analyses indicate that distinct performance improvement in pitch link load control can be achieved by the utilization of variable frequency isolators compared with the constant tuning frequency isolators. The 4/rev （per revolution） pitch link load is observed to be reduced by 87.6% compared with the increase of 56.3% by the constant frequency isolator, when the rotor speed is reduced by 16.7%. The isolation ability at different rotor speeds in different flight states is investigated. To achieve overall load reduction within the whole range of rotor speed, the strategy of the variation of tuning frequency is adjusted. The results indicate that the 4/rev pitch link load within the whole rotor speed range is decreased.展开更多
目的研究不同类型高冲击运动对于骨密度（bone mineral density,BMD）和骨矿含量（bone mineral content,BMC）的影响。方法招募39名志愿者,其中伞兵、篮球运动员和作为对照组的普通大学生各13名,将其分成两组（第1组：20～22岁;第2组...目的研究不同类型高冲击运动对于骨密度（bone mineral density,BMD）和骨矿含量（bone mineral content,BMC）的影响。方法招募39名志愿者,其中伞兵、篮球运动员和作为对照组的普通大学生各13名,将其分成两组（第1组：20～22岁;第2组：23～25岁）,分别测量跟骨、第1～5跖骨、髋关节和腰椎（L1～4）BMD和BMC。结果篮球运动员跟骨、第1、2跖骨、总腰椎和髋部BMC显著大于伞兵和对照组;篮球运动员在腰椎、髋关节和股骨颈处BMD也显著大于其他组;伞兵和对照组在测量部位的BMD和BMC无显著性差异。结论 BMC与BMD并非总是正比于平时运动时的垂直地面反作用力。相比跳伞训练,篮球运动能更好提高BMC和BMD,这种变载荷运动作为训练方法,更有利于降低骨质疏松性骨折的风险。展开更多
When composite materials occur crack, their fibrous locations will produce bridging fibers. A symmetrical dynamic crack model of bridging fibers in unidirectional composite materials are not probed as deeply by virtue...When composite materials occur crack, their fibrous locations will produce bridging fibers. A symmetrical dynamic crack model of bridging fibers in unidirectional composite materials are not probed as deeply by virtue of the complexity, cockamamie and difficulty in mathematical operations. In the light of the theory of complex variable functions, the problems discussed can be facilely translated into Remann-Hilbert problems. Analytical solutions of the displacements, stresses and stress intensity factors under the action of variable loads Pt6/x6, Px6/t5 are attained, respectively. After those analytical solutions were used by superposition theorem, the solutions of arbitrary complex problems were acquired.展开更多
On the basis of the thin-shell theory and on the use of the transfer matrix approach, this paper presents the vibrational response and buckling analysis of three-lobed cross-section cylindrical shells, with circumfere...On the basis of the thin-shell theory and on the use of the transfer matrix approach, this paper presents the vibrational response and buckling analysis of three-lobed cross-section cylindrical shells, with circumferentially varying thickness, subjected to uniform axial membrane loads. A Fourier approach is used to separate the variables, and the governing equations of the shell are formulated in terms of eight first-order differential equations in the circumferential coordinate, and by using the transfer matrix of the shell, these equations are written in a matrix differential equation. The transfer matrix is derived from the non-linear differential equations of the cylindrical shells with variable thickness by introducing the trigonometric series in the longitudinal direction and applying a numerical integration in the circumferential direction. The natural frequencies and critical loads beside the mode shapes are calculated numerically in terms of the transfer matrix elements for the symmetrical and antisymmetrical vibration modes. The influences of the thickness variation of cross- section and radius展开更多
An elastic analysis of an internal central crack with bridging fibers parallel to the free surface in an infinite orthotropic anisotropic elastic plane was analyzed, and the crack extension should occur in the format ...An elastic analysis of an internal central crack with bridging fibers parallel to the free surface in an infinite orthotropic anisotropic elastic plane was analyzed, and the crack extension should occur in the format of self-similarity. When the fiber strength is over its maximum tensile stress, the fiber breaks. By means of complex variable functions, the problem considered can be easily translated into Reimann-Hilbert mixed boundary value problem. Utilizing the built dynamic model of bridging fiber pull-out in unidirectional composite materials, analytical solutions of the displacements, stresses and stress intensity factors under the action of increasing loads Pt5/x5, Px5/t4 are obtained, respectively. After those analytical solutions were used by superposition theorem, the solutions to arbitrary complex problems were acquired.展开更多
基金co-supported by the National Natural Science Foundation of China (Nos. 11202097 and 11472129)Aeronautical Science Foundation of China (No. 2013ZA52014)the Fundamental Research Funds for the Central Universities (No. NS2014007)
文摘To reduce the pitch link loads of variable speed rotors, variable tuning frequency fluid- lastic isolators are proposed. This isolator utilizes the variation of centrifugal force due to the change of rotor speed to change the tuning port area ratio, which can change the tuning frequency of the isolator. A rotor model including the model of fluidlastic isolator is coupled with a fuselage model to predict the steady responses of the rotor system in forward flight. The aeroelastic analyses indicate that distinct performance improvement in pitch link load control can be achieved by the utilization of variable frequency isolators compared with the constant tuning frequency isolators. The 4/rev （per revolution） pitch link load is observed to be reduced by 87.6% compared with the increase of 56.3% by the constant frequency isolator, when the rotor speed is reduced by 16.7%. The isolation ability at different rotor speeds in different flight states is investigated. To achieve overall load reduction within the whole range of rotor speed, the strategy of the variation of tuning frequency is adjusted. The results indicate that the 4/rev pitch link load within the whole rotor speed range is decreased.
文摘目的研究不同类型高冲击运动对于骨密度（bone mineral density,BMD）和骨矿含量（bone mineral content,BMC）的影响。方法招募39名志愿者,其中伞兵、篮球运动员和作为对照组的普通大学生各13名,将其分成两组（第1组：20～22岁;第2组：23～25岁）,分别测量跟骨、第1～5跖骨、髋关节和腰椎（L1～4）BMD和BMC。结果篮球运动员跟骨、第1、2跖骨、总腰椎和髋部BMC显著大于伞兵和对照组;篮球运动员在腰椎、髋关节和股骨颈处BMD也显著大于其他组;伞兵和对照组在测量部位的BMD和BMC无显著性差异。结论 BMC与BMD并非总是正比于平时运动时的垂直地面反作用力。相比跳伞训练,篮球运动能更好提高BMC和BMD,这种变载荷运动作为训练方法,更有利于降低骨质疏松性骨折的风险。
文摘When composite materials occur crack, their fibrous locations will produce bridging fibers. A symmetrical dynamic crack model of bridging fibers in unidirectional composite materials are not probed as deeply by virtue of the complexity, cockamamie and difficulty in mathematical operations. In the light of the theory of complex variable functions, the problems discussed can be facilely translated into Remann-Hilbert problems. Analytical solutions of the displacements, stresses and stress intensity factors under the action of variable loads Pt6/x6, Px6/t5 are attained, respectively. After those analytical solutions were used by superposition theorem, the solutions of arbitrary complex problems were acquired.
文摘On the basis of the thin-shell theory and on the use of the transfer matrix approach, this paper presents the vibrational response and buckling analysis of three-lobed cross-section cylindrical shells, with circumferentially varying thickness, subjected to uniform axial membrane loads. A Fourier approach is used to separate the variables, and the governing equations of the shell are formulated in terms of eight first-order differential equations in the circumferential coordinate, and by using the transfer matrix of the shell, these equations are written in a matrix differential equation. The transfer matrix is derived from the non-linear differential equations of the cylindrical shells with variable thickness by introducing the trigonometric series in the longitudinal direction and applying a numerical integration in the circumferential direction. The natural frequencies and critical loads beside the mode shapes are calculated numerically in terms of the transfer matrix elements for the symmetrical and antisymmetrical vibration modes. The influences of the thickness variation of cross- section and radius
文摘An elastic analysis of an internal central crack with bridging fibers parallel to the free surface in an infinite orthotropic anisotropic elastic plane was analyzed, and the crack extension should occur in the format of self-similarity. When the fiber strength is over its maximum tensile stress, the fiber breaks. By means of complex variable functions, the problem considered can be easily translated into Reimann-Hilbert mixed boundary value problem. Utilizing the built dynamic model of bridging fiber pull-out in unidirectional composite materials, analytical solutions of the displacements, stresses and stress intensity factors under the action of increasing loads Pt5/x5, Px5/t4 are obtained, respectively. After those analytical solutions were used by superposition theorem, the solutions to arbitrary complex problems were acquired.
