By utilizing a 3-D atmospheric circulation resolving method, the authors studied the air-sea interactive linkages between the tropical Indian Ocean and the Pacific Ocean in 1979-2008 E1 Nifio-Southern Oscillation （E...By utilizing a 3-D atmospheric circulation resolving method, the authors studied the air-sea interactive linkages between the tropical Indian Ocean and the Pacific Ocean in 1979-2008 E1 Nifio-Southern Oscillation （ENSO） events. Their findings showed that evident 3-D gear-coupling characteristics existed in the 1979-2008 ENSO events. Their resolving analyses also suggested that the general circulation showed stronger and wider sinking motions over the eastern Indian Ocean-western Pacific during the mature phase of 1979-2008 ENSO events, compared with the vertical velocities from the U.S. National Centers for Enviornmental Prediction （NCEP） reanalysis data. With their 3-D analysis method, the vertical velocity was resolved by two components, i.e. zonal and meridional components. It was found that the zonal component of the vertical velocities showed a strong sinking motion while the meridional components showed an upward motion during the prevailing phases of the ENSO events. In the tropics, the zonal component of the vertical velocities was found greater than the meridional component, reflecting the dominant characteristics of the vertical velocity, and the overall outcomes showed a strong sinking motion, although the two components also partially offset each other in the processes. Compared with the vertical velocities from NCEP reanalysis, the vertical motions calculated with the 3-D resolving analysis method demonstrate some advantages.展开更多
Individuals with hemiplegia suffer from impaired arm movements that appear as a marked change in arm stiffness. A quantitative measure of arm stiffness would characterize rehabilitation therapy effectively, while litt...Individuals with hemiplegia suffer from impaired arm movements that appear as a marked change in arm stiffness. A quantitative measure of arm stiffness would characterize rehabilitation therapy effectively, while little mechanism is designed to implement the function. A symmetrical five-bar linkage consisting of two revolute joints and three prismatic joints is presented. Inverse kinematics and forward kinematics are obtained first. Then inverse singularities and direct singularities of the mechanism are gained. The global stiffness index is defined based on the results of kinematics analysis. Finally, optimal dimensional synthesis of the mechanism in terms of maximum stiffness is conducted by genetic algorithms. The calculation results show that with the length of both the two linkage a=830 mm, the interacting angle of the two guides 2δ=4.48 radian, and the maximum range of displacement of the two carriers dmax=940 mm, the mechanism achieves highest rigidity and its workspace is singularity-free, which covers the human left and right arm range of motion. The proposed novel mechanism featuring high rigidity and a singularity-free workspace can provide rehabilitation training, also solve the problem of quantitative measure of arm stiffness.展开更多
This paper presents the idea of constructing reconfigurable limbs by integrating metamorphic linkages as subchains.The planar five-bar metamorphic linkages that have three phases resulting from locking of motors are c...This paper presents the idea of constructing reconfigurable limbs by integrating metamorphic linkages as subchains.The planar five-bar metamorphic linkages that have three phases resulting from locking of motors are considered.Under the assumption that the constraint exerted by the reconfigurable limb can switch between no constraint,a constraint force,and a constraint couple,the output motions of the metamorphic linkage in its two planar four-bar linkage phases are identified.By adding an appropriate joint to planar four-bar linkages with translational output,four planar five-bar linkages that can be employed in the construction of reconfigurable limbs are enumerated.Serial chains that can provide a constraint couple and a constraint force are synthesized based on screw theory.Reconfigurable limbs that have three configurations associated with the three distinct phases of the metamorphic linkages are assembled with planar five-bar metamorphic linkages and serial chains with four degrees of freedom.A class of reconfigurable parallel mechanisms are constructed by connecting a moving platform and a base with three identical reconfigurable limbs.The degrees of freedom of the reconfigurable parallel mechanism in different configurations with the metamorphic linkages in different phases are given.Finally,the actuation scheme for this kind of mechanisms is addressed.展开更多
针对分布式电动汽车中簧下质量增大,车辆平顺性和车轮接地性恶化的问题,设计了一种新型齿轮连杆式轮边动力吸振器。评估其在多连杆悬架中空间布置的可行性;考虑路面不平度与电机驱动时作用在其壳体上的反力矩,建立系统的动力学模型并推...针对分布式电动汽车中簧下质量增大,车辆平顺性和车轮接地性恶化的问题,设计了一种新型齿轮连杆式轮边动力吸振器。评估其在多连杆悬架中空间布置的可行性;考虑路面不平度与电机驱动时作用在其壳体上的反力矩,建立系统的动力学模型并推导其振动力学微分方程,利用MATLAB/Simulink建立三自由度振动模型,在新欧洲行驶循环(New European Driving Cycle,NEDC)工况下得到时域内的系统响应;结合计算结果分析动力吸振器弹簧刚度阻尼对车身加速度、车轮动载荷和电机振动的影响作用,并进行动力吸振器弹簧刚度和阻尼的优化设计;最后将该系统与传统汽车和一般轮毂电机驱动系统对比,分析其改善车辆平顺性和接地性的效果。结果表明,该新型齿轮连杆式轮边动力吸振器可以合理布置在多连杆悬架中,并可显著改善分布式驱动汽车车辆平顺性和车轮接地性。展开更多
基金Key knowledge innovation research project (KZCX2-YW-Q11-01)973 project (2006CB403600)National Natural Science Foundation of China project (40805034)
文摘By utilizing a 3-D atmospheric circulation resolving method, the authors studied the air-sea interactive linkages between the tropical Indian Ocean and the Pacific Ocean in 1979-2008 E1 Nifio-Southern Oscillation （ENSO） events. Their findings showed that evident 3-D gear-coupling characteristics existed in the 1979-2008 ENSO events. Their resolving analyses also suggested that the general circulation showed stronger and wider sinking motions over the eastern Indian Ocean-western Pacific during the mature phase of 1979-2008 ENSO events, compared with the vertical velocities from the U.S. National Centers for Enviornmental Prediction （NCEP） reanalysis data. With their 3-D analysis method, the vertical velocity was resolved by two components, i.e. zonal and meridional components. It was found that the zonal component of the vertical velocities showed a strong sinking motion while the meridional components showed an upward motion during the prevailing phases of the ENSO events. In the tropics, the zonal component of the vertical velocities was found greater than the meridional component, reflecting the dominant characteristics of the vertical velocity, and the overall outcomes showed a strong sinking motion, although the two components also partially offset each other in the processes. Compared with the vertical velocities from NCEP reanalysis, the vertical motions calculated with the 3-D resolving analysis method demonstrate some advantages.
基金Supported by National Natural Science Foundation of China(Grant No U1304510)Development Foundation for Outstanding Young Teachers of Zhengzhou University,China(Grant No.1421321076)
文摘Individuals with hemiplegia suffer from impaired arm movements that appear as a marked change in arm stiffness. A quantitative measure of arm stiffness would characterize rehabilitation therapy effectively, while little mechanism is designed to implement the function. A symmetrical five-bar linkage consisting of two revolute joints and three prismatic joints is presented. Inverse kinematics and forward kinematics are obtained first. Then inverse singularities and direct singularities of the mechanism are gained. The global stiffness index is defined based on the results of kinematics analysis. Finally, optimal dimensional synthesis of the mechanism in terms of maximum stiffness is conducted by genetic algorithms. The calculation results show that with the length of both the two linkage a=830 mm, the interacting angle of the two guides 2δ=4.48 radian, and the maximum range of displacement of the two carriers dmax=940 mm, the mechanism achieves highest rigidity and its workspace is singularity-free, which covers the human left and right arm range of motion. The proposed novel mechanism featuring high rigidity and a singularity-free workspace can provide rehabilitation training, also solve the problem of quantitative measure of arm stiffness.
基金supported by the National Natural Science Foundation of China(Grant Nos.51075025,51175029)Beijing Natural Science Foundation of China(Grant No.3132019)the Program for New Century Excellent Talents in University of China(Grant No.NCET-12-0769)
文摘This paper presents the idea of constructing reconfigurable limbs by integrating metamorphic linkages as subchains.The planar five-bar metamorphic linkages that have three phases resulting from locking of motors are considered.Under the assumption that the constraint exerted by the reconfigurable limb can switch between no constraint,a constraint force,and a constraint couple,the output motions of the metamorphic linkage in its two planar four-bar linkage phases are identified.By adding an appropriate joint to planar four-bar linkages with translational output,four planar five-bar linkages that can be employed in the construction of reconfigurable limbs are enumerated.Serial chains that can provide a constraint couple and a constraint force are synthesized based on screw theory.Reconfigurable limbs that have three configurations associated with the three distinct phases of the metamorphic linkages are assembled with planar five-bar metamorphic linkages and serial chains with four degrees of freedom.A class of reconfigurable parallel mechanisms are constructed by connecting a moving platform and a base with three identical reconfigurable limbs.The degrees of freedom of the reconfigurable parallel mechanism in different configurations with the metamorphic linkages in different phases are given.Finally,the actuation scheme for this kind of mechanisms is addressed.
文摘针对分布式电动汽车中簧下质量增大,车辆平顺性和车轮接地性恶化的问题,设计了一种新型齿轮连杆式轮边动力吸振器。评估其在多连杆悬架中空间布置的可行性;考虑路面不平度与电机驱动时作用在其壳体上的反力矩,建立系统的动力学模型并推导其振动力学微分方程,利用MATLAB/Simulink建立三自由度振动模型,在新欧洲行驶循环(New European Driving Cycle,NEDC)工况下得到时域内的系统响应;结合计算结果分析动力吸振器弹簧刚度阻尼对车身加速度、车轮动载荷和电机振动的影响作用,并进行动力吸振器弹簧刚度和阻尼的优化设计;最后将该系统与传统汽车和一般轮毂电机驱动系统对比,分析其改善车辆平顺性和接地性的效果。结果表明,该新型齿轮连杆式轮边动力吸振器可以合理布置在多连杆悬架中,并可显著改善分布式驱动汽车车辆平顺性和车轮接地性。
