多自由度系统及结构非线性自由振动的摄动谐波平衡法

本文在谐波平衡法的基础上,引入摄动的思想,得出了解多自由度系统及结构的非线性自由振动的新方法。其解的形式为小参数和谐波的级数形式,因此,其解不会遗漏任何项,方程为线性的代数方程;利用线性变换,将系数矩阵变换为对角阵,一旦求出线性模态,就可得其解,比线性化迭代法优越得多。算例表明,本文方法对于小振幅有较高的精度,对于较大振幅其结果也是令人满意的。     

非线性支撑下悬臂输流管道的Hopf分叉特性

研究了外激励作用下非线性支撑悬臂输流管道系统的Hopf分叉特性,建立了外激励作用下非线性支撑悬臂输流管道系统的动力学方程,并采用Galerkin方法离散动力学方程,由增量谐波平衡(IHB)法推导了方程的近似解析解,由Floquet理论判定了解的稳定性,同时给出了系统的Hopf分叉点。利用数值算法和IHB法研究了支撑位置、支撑结构刚度和阻尼对系统Hopf分叉特性的影响规律。研究表明:系统的幅频特性在Hopf分叉前后发生了改变,响应频率由外激励频率变为系统的自激振动频率,且系统Hopf分叉后,幅值显著增大。该研究结果可为悬臂管道的振动控制提供理论基础。     

全电坦克炮控系统升压电源偏磁抑制方法

基于推挽拓扑结构设计,研究了一种全电坦克炮控系统用升压电源,但推挽电路存在着难以消除的偏磁现象,使得升压电源的可靠性降低。详细阐述了推挽电路中偏磁现象产生的原因,针对性地提出了串入箝位电容、采用电流内环控制、优化电路布局等偏磁抑制方法。实验结果表明：所采用的推挽电路偏磁抑制方法具有结构简单、抑制效果好的优点,提高了全电坦克炮控系统升压电源的可靠性。     

磁悬挂天平五自由度位置传感器的数学分析

磁悬挂平天的位置传感器具有一定的特殊性,它需要同时获取被悬挂的飞行器模型的多自由度位置分量。本文对这一问题进行了研究,并讨论了其工程实现问题。     

设备管理系统的排队论分析

该文应用排队论的理论分析了设备损修系统中最优设备的解法。     

EXTENDED DETERRENCE IN THE MIDDLE EAST

The article presents and analyzes the US extended deterrence commitments in the Middle East as well as those provided by regional states, and assesses the effectiveness and credibility of these commitments. The article then proceeds to analyze a situation wherein Iran successfully develops nuclear weapons. It considers first the security requirements and alternatives of Gulf Cooperation Council (GCC) states, and then proceeds to assess the stability—or instability—of an Israeli-Iranian nuclear balance. The enhancement of US extended deterrence in the region is required in order to deter Iran, reassure allies, and contribute to the stability of an Israeli-Iranian nuclear balance. The article also discusses several contextual issues, such as: the future form of US extended deterrence; distinguishing between the latter and other US extended deterrence commitments; and the different approaches of specific GCC states and Israel.     

磁悬挂天平的变结构控制

鉴于磁悬挂天平系统强烈的非线性特性及存在的多种不确定性 ,针对非匹配不确定性情况设计了变结构控制器。根据对悬浮时模型受力图的分析及其模型两端电磁力、电流和电压的平衡关系 ,并以Y轴方向受力为例 ,讨论了磁悬挂天平的非线性变结构设计过程。该设计的目的是使镇定误差趋近于 0 ,其设计步骤包括期望性能到期望力的传递、满足滑动模态可达条件的控制力到控制电压的传递、控制电压的求解。同时对设计的结果进行了仿真分析 ,仿真结果表明磁悬挂天平的变结构控制系统具有良好的动态性能     

一种优化神经网络映射算法——吸收算法

本文揭示了神经计算的本质──并行分布处理,并以此为基础提出了时间步的概念。分析了映射算法的两个重要概念──负载均衡和通讯开销,并提出了映射分配准则。在神经网络的映射分配中引入图论的有关思想,提出了一种优化的神经网络映射算法──吸收算法。最后给出了重要的试验结果,这些数据表明吸收算法是一种有效的映射算法。     

机体/推进一体化飞行器动导数频域计算方法

运用Etkin非定常气动力模型,将谐波平衡法应用于复杂外形动导数辨识。计算结果表明:谐波平衡法和时域方法的动导数辨识结果一致,与实验值吻合,验证了程序的正确性和谐波平衡法的可靠性。采用谐波平衡法对类X-51高超声速机体/推进一体化飞行器WR-A进行动导数辨识,并与时域方法的计算结果比较,考察了该方法在复杂外形下数值模拟非定常流动和动导数辨识的能力。实验结果表明:对于WR-A这种复杂外形飞行器,谐波平衡法也能在保证精度的同时具有较高的计算效率。     

Classical geopolitics,realism and the balance of power theory

Since the end of World War II, classical geopolitics as a particular form of realism has been disengaged from the development of mainstream realist theories. This disengagement has not only concealed the value of classical geopolitics as a framework of analysis for policy and strategy, but also created an increasing rift between theory and policy in contemporary realist theories. This paper seeks to reengage classical geopolitics with mainstream realist theories by clarifying its realist traits and analytical characteristics, (re)stating its core propositions and probing into its potential contribution to the development of mainstream realist theories. This paper contends that classical geopolitics, while having a distinctive pedigree, can arguably be considered an integral part of the family of realist theories in view of its basic theoretical assumptions concerning international anarchy, the unit of analysis and power politics. As a framework of analysis, classical geopolitics incorporates three interrelated strategic propositions. Those three propositions not only constitute the theoretical core of classical geopolitics, but also manifest a peculiar balance-of-power conception that is essentially distinct from those proposed by mainstream realist theories. This paper argues that those three propositions combined promise to fill in prominent lacuna in the balance-of-power research programme, and also have significant implications for contemporary world politics.