Under the consideration of harmonic fluctuations of initial tension and axially velocity, a nonlinear governing equation for transverse vibration of an axially accelerating string is set up by using the equation of mo...Under the consideration of harmonic fluctuations of initial tension and axially velocity, a nonlinear governing equation for transverse vibration of an axially accelerating string is set up by using the equation of motion for a 3-dimensional deformable body with initial stresses. The Kelvin model is used to describe viscoelastic behaviors of the material. The basis function of the complex-mode Galerkin method for axially accelerating nonlinear strings is constructed by using the modal function of linear moving strings with constant axially transport velocity. By the constructed basis functions, the application of the complex-mode Galerkin method in nonlinear vibration analysis of an axially accelerating viscoelastic string is investigated. Numerical results show that the convergence velocity of the complex-mode Galerkin method is higher than that of the real-mode Galerkin method for a variable coefficient gyroscopic system.展开更多
为全面评估航空器小于管制规定间隔事件中的管制员工作状态,提出1种管制员工作状态量化评估方法。首先,基于关键词的词频和共现频率挖掘小于管制规定间隔事件的致因,并在此基础上改进人因分析和分类系统(human factors analysis and cla...为全面评估航空器小于管制规定间隔事件中的管制员工作状态,提出1种管制员工作状态量化评估方法。首先,基于关键词的词频和共现频率挖掘小于管制规定间隔事件的致因,并在此基础上改进人因分析和分类系统(human factors analysis and classification system,HFACS)模型,构建小于管制规定间隔事件的管制员工作状态评估指标体系,合并相同致因因素以最终得到该事件的致因链条。其次,分析各层指标之间的关系,并构建事件致因复杂网络,通过网络的度中心性、介数中心性和PageRank值计算指标的综合权重,进而通过线性加权量化管制员工作状态的危险指数。最后,基于中国民用航空安全信息系统实际案例分析验证管制员工作状态量化评估方法。研究结果表明:繁忙空域/流量大、硬件设备故障、现场管理缺位是综合权重排名前3的关键致因因素;改进的HFACS模型能够全面揭示导致小于管制规定间隔事件发生的人为因素及其耦合关系,最终得到了341条事件致因链条;管制员工作状态评估结果与事件调查报告的结论基本一致,可验证本文所提方法的合理性。研究结果可为管制员工作状态评估提供参考。展开更多
为了提高永磁同步电机(permanent magnet synchronous motor,PMSM)驱动系统调速性能,解决传统滑模控制系统抖振与快速性之间的矛盾,提出一种PMSM改进滑模复合控制方案。首先,电流环设计了改进快速超螺旋滑模控制(improving fast super t...为了提高永磁同步电机(permanent magnet synchronous motor,PMSM)驱动系统调速性能,解决传统滑模控制系统抖振与快速性之间的矛盾,提出一种PMSM改进滑模复合控制方案。首先,电流环设计了改进快速超螺旋滑模控制(improving fast super twisting algorithm,IFSTA)来改善系统的抖振。其次,转速环使用改进指数趋近律设计滑模转速控制器(novel sliding mode speed controller,NSMSC)。最后,使用非线性扩展状态观测器(nonlinear extended state observer,NESO)来实时估计负载转矩扰动,通过估计的转矩信息对由NSMSC得到的q轴给定电流进行前馈补偿。仿真和试验表明,与传统滑模复合控制相比,采用改进复合控制策略的超调量减少了13.6%,系统抖振峰值降低了3.5 r/min,控制系统的整体性能得到提升。展开更多
基金Project supported by the National Natural Science Foundation of China (No. 10472060)Shanghai Leading Academic Discipline Project (No.Y0103)the Natural Science Foundation of Shanghai (No.04ZR14058)the Outstanding Youth Program of Shanghai Municipal Commission of Educatio(No.04YQHB088)
文摘Under the consideration of harmonic fluctuations of initial tension and axially velocity, a nonlinear governing equation for transverse vibration of an axially accelerating string is set up by using the equation of motion for a 3-dimensional deformable body with initial stresses. The Kelvin model is used to describe viscoelastic behaviors of the material. The basis function of the complex-mode Galerkin method for axially accelerating nonlinear strings is constructed by using the modal function of linear moving strings with constant axially transport velocity. By the constructed basis functions, the application of the complex-mode Galerkin method in nonlinear vibration analysis of an axially accelerating viscoelastic string is investigated. Numerical results show that the convergence velocity of the complex-mode Galerkin method is higher than that of the real-mode Galerkin method for a variable coefficient gyroscopic system.
