A generalized form of material gradation applicable to a more broad range of functionally graded materials(FGMs) was presented.With the material model,analytical expressions of crack tip higher order stress fields in ...A generalized form of material gradation applicable to a more broad range of functionally graded materials(FGMs) was presented.With the material model,analytical expressions of crack tip higher order stress fields in a series form for opening mode and shear mode cracks under quasi-static loading were developed through the approach of asymptotic analysis.Then,a numerical experiment was conducted to verify the accuracy of the developed expressions for representing crack tip stress fields and their validity in full field data analysis by using them to extract the stress intensity factors from the results of a finite element analysis by local collocation and then comparing the estimations with the existing solution.The expressions show that nonhomogeneity parameters are embedded in the angular functions associated with higher terms in a recursive manner and at least the first three terms in the expansions must be considered to explicitly account for material nonhomogeneity effects on crack tip stress fields in the case of FGMs.The numerical experiment further confirms that the addition of the nonhomogeneity specific terms in the expressions not only improves estimates of stress intensity factor,but also gives consistent estimates as the distance away from the crack tip increases.Hence,the analytical expressions are suitable for the representation of crack tip stress fields and the analysis of full field data.展开更多
A simple method for disturbance decoupling for matrix second-order linear systems is proposed directly in matrix second-order framework via Luenberger function observers based on complete parametric eigenstructure ass...A simple method for disturbance decoupling for matrix second-order linear systems is proposed directly in matrix second-order framework via Luenberger function observers based on complete parametric eigenstructure assignment. By introducing the H2 norm of the transfer function from disturbance to estimation error, sufficient and necessary conditions for disturbance decoupling in matrix second-order linear systems are established and are arranged into constraints on the design parameters via Luenberger function observers in terms of the closed-loop eigenvalues and the group of design parameters provided by the eigenstructure assignment approach. Therefore, the disturbance decoupling problem is converted into an eigenstructure assignment problem with extra parameter constraints. A simple example is investigated to show the effect and simplicity of the approach.展开更多
针对观测器估计精度偏低及高速列车系统的强耦合、受外界扰动、参数时变等问题,提出一种基于补偿函数观测器的分数阶非奇异快速终端滑模控制算法(Compensating Function Observer-Fractional Order Non-singular Fast Terminal Sliding ...针对观测器估计精度偏低及高速列车系统的强耦合、受外界扰动、参数时变等问题,提出一种基于补偿函数观测器的分数阶非奇异快速终端滑模控制算法(Compensating Function Observer-Fractional Order Non-singular Fast Terminal Sliding Mode Control,CFO-FONFTSMC),以提高高速列车速度控制的鲁棒性和控制精度.首先,建立高速列车纵向多质点动力学模型,设计高精度的补偿函数观测器对系统的总扰动进行实时估计并补偿;然后,设计一种带状态负指数控制律的分数阶非奇异快速终端滑模控制算法,用于对列车的运行曲线进行跟踪控制,并通过李雅普诺夫稳定性理论证明系统在有限时间内的收敛性;最后,以CRH3型高速列车参数和合肥站-蚌埠南站的实际线路为实例,分别跟踪理想运行曲线和节能优化运行曲线进行实验验证.仿真结果表明:所提算法跟踪理想运行速度曲线的平均误差为0.01377 km/h,跟踪带干扰的节能优化运行速度曲线的平均误差为0.0364 km/h,相较于基于扩张状态观测器的滑模和非奇异快速终端滑模控制方法,所提方法具有最小的跟踪误差和更高的跟踪精度,验证了其有效性和可行性,可为列车速度跟踪控制领域的研究提供参考.展开更多
针对视觉算法在检测航拍图像中密集小目标时容易受到目标重叠、遮挡等情况干扰的现象,提出了一种基于高阶空间特征(目标形状、位置等信息的高级表示)提取的Transformer检测头HSF-TPH(Transformer prediction head with high-order spati...针对视觉算法在检测航拍图像中密集小目标时容易受到目标重叠、遮挡等情况干扰的现象,提出了一种基于高阶空间特征(目标形状、位置等信息的高级表示)提取的Transformer检测头HSF-TPH(Transformer prediction head with high-order spatial feature extraction)。所提检测头中将自注意力机制中的二阶交互扩展到三阶以生成高阶空间特征,提取更有区分度的空间关系,突出每一个小目标在空间上的语义信息。同时,为了缓解骨干网络过度下采样对小目标信息的压缩,设计了一种高分辨率特征图生成机制,增加头部网络的输入特征分辨率,以提升HSFTPH检测密集小目标的效果。设计了新的损失函数USIoU,降低算法位置偏差敏感性。在VisDrone2019数据集上开展实验证明,所提算法在面积最小、密度最高的人类目标的检测任务中实现了mAP50指标10个百分点以上的性能提升。展开更多
基金Project(20080431344) supported by Postdoctoral Science Foundation of ChinaProject(51021001) supported by the National Natural Science Foundation of China
文摘A generalized form of material gradation applicable to a more broad range of functionally graded materials(FGMs) was presented.With the material model,analytical expressions of crack tip higher order stress fields in a series form for opening mode and shear mode cracks under quasi-static loading were developed through the approach of asymptotic analysis.Then,a numerical experiment was conducted to verify the accuracy of the developed expressions for representing crack tip stress fields and their validity in full field data analysis by using them to extract the stress intensity factors from the results of a finite element analysis by local collocation and then comparing the estimations with the existing solution.The expressions show that nonhomogeneity parameters are embedded in the angular functions associated with higher terms in a recursive manner and at least the first three terms in the expansions must be considered to explicitly account for material nonhomogeneity effects on crack tip stress fields in the case of FGMs.The numerical experiment further confirms that the addition of the nonhomogeneity specific terms in the expressions not only improves estimates of stress intensity factor,but also gives consistent estimates as the distance away from the crack tip increases.Hence,the analytical expressions are suitable for the representation of crack tip stress fields and the analysis of full field data.
文摘A simple method for disturbance decoupling for matrix second-order linear systems is proposed directly in matrix second-order framework via Luenberger function observers based on complete parametric eigenstructure assignment. By introducing the H2 norm of the transfer function from disturbance to estimation error, sufficient and necessary conditions for disturbance decoupling in matrix second-order linear systems are established and are arranged into constraints on the design parameters via Luenberger function observers in terms of the closed-loop eigenvalues and the group of design parameters provided by the eigenstructure assignment approach. Therefore, the disturbance decoupling problem is converted into an eigenstructure assignment problem with extra parameter constraints. A simple example is investigated to show the effect and simplicity of the approach.
文摘针对观测器估计精度偏低及高速列车系统的强耦合、受外界扰动、参数时变等问题,提出一种基于补偿函数观测器的分数阶非奇异快速终端滑模控制算法(Compensating Function Observer-Fractional Order Non-singular Fast Terminal Sliding Mode Control,CFO-FONFTSMC),以提高高速列车速度控制的鲁棒性和控制精度.首先,建立高速列车纵向多质点动力学模型,设计高精度的补偿函数观测器对系统的总扰动进行实时估计并补偿;然后,设计一种带状态负指数控制律的分数阶非奇异快速终端滑模控制算法,用于对列车的运行曲线进行跟踪控制,并通过李雅普诺夫稳定性理论证明系统在有限时间内的收敛性;最后,以CRH3型高速列车参数和合肥站-蚌埠南站的实际线路为实例,分别跟踪理想运行曲线和节能优化运行曲线进行实验验证.仿真结果表明:所提算法跟踪理想运行速度曲线的平均误差为0.01377 km/h,跟踪带干扰的节能优化运行速度曲线的平均误差为0.0364 km/h,相较于基于扩张状态观测器的滑模和非奇异快速终端滑模控制方法,所提方法具有最小的跟踪误差和更高的跟踪精度,验证了其有效性和可行性,可为列车速度跟踪控制领域的研究提供参考.
文摘针对视觉算法在检测航拍图像中密集小目标时容易受到目标重叠、遮挡等情况干扰的现象,提出了一种基于高阶空间特征(目标形状、位置等信息的高级表示)提取的Transformer检测头HSF-TPH(Transformer prediction head with high-order spatial feature extraction)。所提检测头中将自注意力机制中的二阶交互扩展到三阶以生成高阶空间特征,提取更有区分度的空间关系,突出每一个小目标在空间上的语义信息。同时,为了缓解骨干网络过度下采样对小目标信息的压缩,设计了一种高分辨率特征图生成机制,增加头部网络的输入特征分辨率,以提升HSFTPH检测密集小目标的效果。设计了新的损失函数USIoU,降低算法位置偏差敏感性。在VisDrone2019数据集上开展实验证明,所提算法在面积最小、密度最高的人类目标的检测任务中实现了mAP50指标10个百分点以上的性能提升。
