机敏柔性梁的振动主动控制

提出了用于机敏结构中振动主动控制的仿人控制算法,对压电阻尼技术进行了理论和实验研究,给出了传感器,执行器和受控结构之间的关系,用ＰＺＴ作执行元件实现了柔性梁振动主动控制系统,给出了实验结果。     

关于地质工程设计中突破口预测方法的研究

理论研究及工程实践都已表明, 地质工程的破坏往往是从某些特定的部位开始逐渐发展起来的。据此而提出的优先监测突破口和重点加固突破口这两个设计原则, 已被成功地应用于一些地质工程并被证明具有重要实用价值。所以, 对于一个具体地质工程来说, 如何确定该工程可能出现的突破口的部位, 便成为工程设计的重要步骤之一。本文拟从突破观点出发, 讨论确定突破口的几种主要方法。最后作者还将结合五强溪水电站左岸船闸边坡工程的实际应用进一步加以说明。     

A parallel two-level finite element method for the Navier-Stokes equations

Based on domain decomposition, a parallel two-level finite element method for the stationary Navier-Stokes equations is proposed and analyzed. The basic idea of the method is first to solve the Navier-Stokes equations on a coarse grid, then to solve the resulted residual equations in parallel on a fine grid. This method has low communication complexity. It can be implemented easily. By local a priori error estimate for finite element discretizations, error bounds of the approximate solution are derived. Numerical results are also given to illustrate the high efficiency of the method.     

Pull-in instability of a typical electrostatic MEMS resonator and its control by delayed feedback

Pull-in instability of the electrostatic microstructures is a common undesirable phenomenon which implies the loss of reliability of micro-electromechanical systems. Therefore, it is necessary to understand its mechanism and then reduce the phenomenon. In this work, pull-in instability of a typical electrostatic MEMS resonator is discussed in detail. Delayed position feedback and delayed velocity feedback are introduced to suppress pull-in instability, respectively. The thresholds of AC voltage for pull-in instability in the initial system and the controlled systems are obtained analytically by the Melnikov method. The theoretical predictions are in good agreement with the numerical results. It follows that pull-in instability of the MEMS resonator can be ascribed to the homoclinic bifurcation inducing by the AC and DC load. Furthermore, it is found that the controllers are both good strategies to reduce pull-in instability when their gains are positive. The delayed position feedback controller can work well only when the delay is very short and AC voltage is low, while the delayed velocity feedback will be effective under a much higher AC voltage and a wider delay range.     

电子封装元件的高阶层离散均匀化分析

将均匀化理论应用于具有非完全(单层内)周期性微结构的倒装焊底充胶电子封装元件,建立了高阶逐层离散层板模型,用解析法分析热载荷下结构的温度应力. 计算结果与有限元解的比较表明,该分析模型和方法是有效的,而且比较简便. 算例分析结果显示,胶层厚度、焊点密度、胶与焊点材料的模量比和体积比,对于焊点温度应力有明显影响.     

酚醛玻璃钢动态本构关系的实验研究

本文叙述了在轻气炮上作高速撞击实验,使用碳膜压阻传感器,一次记录多个应力历史波形,用Lagrange分析和路径线方法,求材料动态本构关系的方法。给出了应力在2 GPa、应变率4105S-1以下酚醛玻璃钢的数值形式本构关系。探讨了强应力脉冲在酚醛玻璃钢中传播衰减的物理原因。     

界面裂纹萌生与扩展的分子动力学模拟

运用分子动力学模拟方法研究了裂纹在界面端处萌生与沿界面扩展的临界条件. 模拟考虑了一双相材料的3种模型,即构成90°/90°和 90°/180°夹角的两个界面端和一个界面裂纹. 模拟采用了包含原子区域与连续区域的并发型多尺度模型,即在界面端尖端和裂纹尖端附近 采用分子动力学(MD)方法,MD区域之外则按照线弹性有限元方法分析. 结果表明,在断裂启动时刻,3个模型沿界面的最大应力均达到界面理想强度;而且,其界 面能恰好足以克服界面材料的本征内聚能. 因此,界面端裂纹萌生与沿界面扩展的断裂条件可以通过界面理想强度和内聚能联系起来. 并基于模拟计算结果提出了界面断裂启动的统一准则.     

国产MOCVD-YBCO带材高温超导线圈研制与磁场温度特性研究

超导磁体的场强与超导材料的载流能力、磁体口径和低温环境有密切关系.为了在中高温区域实现高磁场强度的超导磁体,采用国产第二代高温超导带材,成功绕制出内直径为100 mm的高温超导线圈.该超导线圈在77,65,55和46 K不同温区下进行了性能测试,其最大运行电流分别为65,147,257和338 A,对应的中心磁场强度分别为0.78,1.77,3.1和4.08 T.所研制的超导线圈的中平面上磁场基本一致.     

Study of Carbon Nanotube Supported Co-Mo Selective Hydrodesulphurization Catalysts for Fluid Catalytic Cracking Gasoline

In this paper, carbon nanotube supported Co-Mo catalysts for selective hydrodesulphurization （HDS） of fluid catalytic cracking （FCC） gasoline were studied, using di-isobutylene, cyclohexene, 1-octene and thiophene as model compounds to simulate FCC gasoline. The results show that the Co-Mo/CNT has very high HDS activity and HDS/hydrogenation selectivity comparing with the Co-Mo/γ-Al2O3 and Co-Mo/AC catalyst systems. The saturation ratio of cyclohexene was lower than 50%, and the saturation ratio of 1,3-di-isobutylene lower than 60% for the Co-Mo/CNT catalysts. Co/Mo atomic ratio was found to be one of the most important key factors in influencing the hydrogenation selectivity and HDS activity, and the most suitable Co/Mo atomic ratio was 0.4. Co/CNT and Mo/CNT mono-metallic catalysts showed lower HDS activity and selectivity than the Co-Mo/CNT bi-metallic catalysts.     

基于随机共振的2PSK信号相干接收误码率的研究*

针对在信道环境恶劣的情况下,数字信号接收端的误码率较高的问题,提出一种基于自适应参数调节双稳随机共振系统降低误码率的新方法,得到了输入信噪比小于0db、相干解调接收二进制相移键控信号(binary phase shift keying,简记为2PSK)条件下,系统误码率与输入信噪比的仿真曲线。研究表明：通过非线性双稳系统的2PSK在输入信噪比达到-7.4db时较传统线性解调系统误码率可降低20.1%,这正是对2PSK信号在信道环境恶劣情况下传输的一个补充,对数字带通信号传输具有一定的参考价值。