扭转塑性变形对6063铝合金拉伸力学性能的影响机理研究

扭转是一种常用的冷作硬化方法。本文通过实心圆轴扭转实验和预扭试件的单向拉伸实验,研究了扭转塑性变形程度对6063铝合金拉伸力学性能的影响。通过理论研究和硬度分析探究了造成这一影响的内在机理。结果表明,试件扭转后其内部形成的以屈服强度为特征参数的梯度结构,是造成预扭试件力学性能得到改善的根本原因。并且,扭转不同的角度,材料内部产生的梯度结构也是不同的。而不同的梯度结构对试件力学性能的影响则表现为后继拉伸屈服强度随预扭角度的增大而增大。为了预测预扭试件的后继拉伸力学行为,验证前述结论的正确性,建立了由内到外屈服强度逐渐变化的有限元模型。此模型代表了预扭转变形试件,对其施加位移载荷,模拟后继单向拉伸加载过程。模拟所得材料力学性能随扭转角的变化趋势与实验结果基本吻合,从而验证了扭转冷作硬化后,圆轴试件内部产生了以屈服强度为特征参数的梯度结构这一结论。同时,也提供了一种有效的预测材料扭转后拉伸力学性能的数值模拟方法。     

一种微型矢量水听器姿态测量系统

矢量水听器姿态校正的通常做法是将姿态测量系统捷联安装在声纳平台上,这种方案无法准确测量矢量水听器的姿态变化。针对这个问题,设计了一种微型姿态测量系统,并将其捷联封装在矢量水听器内部。系统采用MEMS陀螺测量角速度,用毕卡迭代算法解四元数姿态更新方程。用MEMS加速度计和磁力计分别测量重力方向和磁北方向,再使用扩展卡尔曼滤波对解算姿态角进行实时校正。经测试,该系统横滚角和俯仰角的静态误差小于0.2°,航向角的静态误差小于0.8°。摇摆实验中,横滚角和俯仰角的动态相对误差小于2.9%,航向角的动态相对误差小于3.6%。海上试验结果证明该姿态测量系统应用于矢量水听器可明显提高目标方位估计的精度。     

基于NURBS插值的三维渐进结构优化方法

提出一种基于等几何控制点密度变量的三维双向渐进结构拓扑优化方法。在当前列式下,高阶NURBS基函数被同时用于CAD模型中NURBS实体片的几何场、位移场和温度场以及密度场插值,实现了几何模型、分析模型和优化模型的有效统一,确保了位移场、温度场及密度场的高阶连续性;详细推导了基于等几何控制点密度变量的三维渐进结构法模型及其灵敏度分析列式;最后几个典型的数值算例,包括最小柔顺性、热传导优化问题及三维结构自由振动的基频最大化问题,验证了本文方法的有效性。     

Emission spectrum from an Al/Mg tracer in the blow-off region of a radiatively ablated capsule

A study of X-ray emissions from Al/Mg tracers buried at two different depths in a plastic shell is presented. The X-rays originating from the K-shell transitions of the Al/Mg ions begin to irradiate after the ablative heating wave has passed through the trace layer and are recorded with a streaked crystal spectrometer. Only emissions from the capsule with the trace layer buried at a smaller depth are observed. Hydrodynamic simulations and a collisional—radiative model including detailed atomic physics are used to investigate the measured spectrum. It is found that the effects of the radiative heating play important roles in the formation of the K-shell emission. The time correlation between the simulations and the measurements is obtained by comparing the measured time profile of the He α emission with the calculated one. The line ratio of Ly α to He α is also calculated and is found to be in fairly good agreement with the experimental data. Finally, the relation between the time profile of the He α emission and the ablation velocity is also discussed.     

Global exponential synchronization between Lü system and Chen system with unknown parameters and channel time-delay

This paper proposes a nonlinear feedback control method to realize global exponential synchronization with channel time-delay between the Lü system and Chen system,which are regarded as the drive system and the response system respectively.Some effective observers are produced to identify the unknown parameters of the Lü system.Based on the Lyapunov stability theory and linear matrix inequality technique,some sufficient conditions of global exponential synchronization of the two chaotic systems are derived.Simulation results show the effectiveness and feasibility of the proposed controller.     

Modified impulsive synchronization of fractional order hyperchaotic systems

In this paper, a modified impulsive control scheme is proposed to realize the complete synchronization of fractional order hyperchaotic systems. By constructing a suitable response system, an integral order synchronization error system is obtained. Based on the theory of Lyapunov stability and the impulsive differential equations, some effective sufficient conditions are derived to guarantee the asymptotical stability of the synchronization error system. In particular, some simpler and more convenient conditions are derived by taking the fixed impulsive distances and control gains. Compared with the existing results, the main results in this paper are practical and rigorous. Simulation results show the effectiveness and the feasibility of the proposed impulsive control method.     

基于梁平截面假设的复杂细长结构动力模型简化方法

针对纵向尺度显著大于横向的复杂细长结构,提出了一个基于梁平截面假设的模型简化方法,建立了具有物理意义的基向量。同时考虑这类结构截面变形的翘曲模式,增加了翘曲基向量,得到精度较高的简化动力模型。这样的简化模型可以用于原结构在不同边界条件的动力分析。结构频率计算的两个具体算例表明了简化方法的有效性。     

固-液复合润滑对轴承钢摩擦学性能的影响

为了提高GCr15钢的耐磨性和承载能力,采用低温离子渗硫技术在GCr15钢的表面制备了FeS固体润滑薄膜,在球-盘摩擦磨损试验机上对比研究了在基础油及2种含硫极压抗磨添加剂(ZDDP和SO)润滑条件下GCr15钢渗硫前后的摩擦学性能.利用SEM观察了磨损表面的形貌,利用XPS分析了磨损表面边界润滑膜化合物的价态及元素随深度的变化.研究表明:在摩擦过程中,表面的硫化层会阻碍润滑油中的添加剂与基体之间的作用,当添加剂与基体直接接触时其作用才能发挥.只有当硫化层破坏程度较小时,与添加剂的复合作用效果才较为明显.含硫添加剂与基体之间的反应可以补充硫化层因磨损失去的FeS,体现了显著的复合润滑效果.其中,高活性的硫烯比需要温度催化的ZDDP对硫化层的补充作用更明显.     

Global impulsive exponential synchronization of stochastic perturbed chaotic delayed neural networks

In this paper, the global impulsive exponential synchronization problem of a class of chaotic delayed neural networks (DNNs) with stochastic perturbation is studied. Based on the Lyapunov stability theory, stochastic analysis approach and an efficient impulsive delay differential inequality, some new exponential synchronization criteria expressed in the form of the linear matrix inequality (LMI) are derived. The designed impulsive controller not only can globally exponentially stabilize the error dynamics in mean square, but also can control the exponential synchronization rate. Furthermore, to estimate the stable region of the synchronization error dynamics, a novel optimization control algorithm is proposed, which can deal with the minimum problem with two nonlinear terms coexisting in LMIs effectively. Simulation results finally demonstrate the effectiveness of the proposed method.     

线性时变模型的求解及其在惯导误差旋转抑制中的应用

讨论了线性时变状态空间模型的求解方法,针对惯性导航旋转误差抑制问题,对建立的齐次时变模型进行转化,得到等价的非齐次定常模型。求解该模型,并推导了单向旋转和往复旋转条件下,由陀螺漂移激励的导航误差的解析表达式;利用线性系统的可加性,分析了转动对于其它误差源抑制的可行性;此外,还指出了转动条件下的误差谐振旋转频率。通过设计仿真模型,对比了静态和转动条件下的导航误差,表明针对该时变系统的求解方法有效,惯性导航动态误差分析导出的结论正确,为高精度航海导航系统的工程实现提供了有益的理论指导。