有限宽板孔边弹塑性变形测试

测量应变集中区域的弹塑性变形，对于研究材料损伤或微裂纹的产生，以预防宏观裂纹的产生及扩展具有重要的意义。为给航空发动机轮盘的损伤容限设计研究提供相关材料的力学实验参数，做了两个有限宽中心带孔试件的拉伸试验。试验中，采用单调逐级加、卸栽的循环加栽方式，并应用自动网格法和数字图像相关技术测量了孔用的全场位移分布。再应用最小二乘法将离散的位移分量拟合成二元多项式函数，求解出拉伸方向的应变分布，并给出孔边应力σ与孔边应变εy的关系曲线。     

浮筏的主动吸振控制实验研究

浮筏在低频减振方面存在较大不足,而这恰是主动减振的优势.将两者相结合,研究了浮筏的主动吸振控制问题.研制了一种主动吸振器,建立了以DSP F2812为核心的控制系统;提出了符号LMS算法,与广泛使用的滤波x-LMS等算法相比,该算法不需要精确的模型信息;在此基础上设计了自适应前馈主动吸振控制律,并在浮筏实验平台上进行主动吸振控制实验.实验结果表明,通过主动吸振控制,浮筏的低频减振能力得到了显著的改善.     

双重点最小二乘配点无网格法

配点类无网格法需要计算近似函数的二阶导数,因而在移动最小二乘(MLS)近似中至少要采用二次基函数。本文利用Voronoi图对双重点移动最小二乘近似法进行了改进,建立了基于Voronoi图的双重点移动最小二乘近似(VDG),并利用加权最小二乘法离散微分方程,导出了双重点最小二乘配点无网格法(MD GLS)。该方法将求解域用节点离散,并以节点为生成点建立Voronoi图,取Voronoi多边形的顶点为辅助点。近似函数及其二阶导数的计算过程可分解为两个步骤:首先用场函数节点值拟合辅助点处近似函数的一阶导数,再以辅助点处近似函数的一阶导数值拟合节点处近似函数的二阶导数。由于在每一步中只需计算MLS形函数及其一阶导数,这种近似方法需要较少的影响点和较小的影响域。同时借助于Voronoi结构的优良几何性质,可以快速地搜索影响点。研究表明,与基于MLS的加权最小二乘无网格法(MWLS)相比,这种方法可以显著提高计算效率,并且在精度和收敛性方面也有所改善。     

Recovery-Based Error Estimator for Natural Convection Equations Based on Defect-Correction Methods

In this paper, we propose an adaptive defect-correction method for natural convection (NC) equations. A defect-correction method (DCM) is proposed for solving NC equations to overcome the convection dominance problem caused by a high Rayleigh number. To solve the large amount of computation and the discontinuity of the gradient of the numerical solution, we combine a new recovery-type posteriori estimator in view of the gradient recovery and superconvergent theory. The presented reliability and efficiency analysis shows that the true error can be effectively bounded by the recovery-based error estimator. Finally, the stability, accuracy and efficiency of the proposed method are confirmed by several numerical investigations.     

An Enhanced Full-Form Model-Free Adaptive Controller for SISO Discrete-Time Nonlinear Systems

This study focuses on the full-form model-free adaptive controller (FFMFAC) for SISO discrete-time nonlinear systems, and proposes enhanced FFMFAC. The proposed technique design incorporates long short-term memory neural networks (LSTMs) and fuzzy neural networks (FNNs). To be more precise, LSTMs are utilized to adjust vital parameters of the FFMFAC online. Additionally, due to the high nonlinear approximation capabilities of FNNs, pseudo gradient (PG) values of the controller are estimated online. EFFMFAC is characterized by utilizing the measured I/O data for the online training of all introduced neural networks and does not involve offline training and specific models of the controlled system. Finally, the rationality and superiority are verified by two simulations and a supporting ablation analysis. Five individual performance indices are given, and the experimental findings show that EFFMFAC outperforms all other methods. Especially compared with the FFMFAC, EFFMFAC reduces the RMSE by 21.69% and 11.21%, respectively, proving it to be applicable for SISO discrete-time nonlinear systems.     

Modelling decision making and learning by low latitude hunter gatherers

Recent anthropological studies have demonstrated that low latitude ‘encounter’ foragers exploit their environments in energetically very efficient manners and closely track the environment as it changes. The paper begins to investigate how they manage to do this by proposing a simple decision making and learning rule developed from an evolutionary ecological basis. Having described the mathematical model the paper refers to simulation studies exploring this model which suggest that some of the seemingly complex aspects of hunter gatherer behaviour may result from the use of simple decision making and learning processes.     

Time behavior of stressed nonhierarchical networks

In this paper it is shown, by means of simulation, that interesting time behavior is observed for damaged and overloaded networks, and that adaptive, decentralized intelligence can have a dramatic influence on the overall network performance. The time behavior of nonhierarchical networks is modeled by a system of nonlinear difference equations among global variables, and bistability is shown to exist. Using a simple adaptive control mechanism, it is shown that, depending upon the value of a certain network variable, either limit cycle or steady state behavior results. A few ideas are discussed for applications of nonhierarchical communications to cellular automata and to decision-making systems.     

基于微光机电系统的微光学自适应微镜的研究

提出了一种利用热应力改变镜面曲率的可调焦微光学自适应微镜。与传统自适应微镜相比,采用该原理制作的微镜具有驱动电压低和驱动力较大的优点,而且制作简单。以硅为基底进行了表面热氧化、光刻显影、HF酸刻蚀、KOH湿法刻蚀,溅射铝膜等微加工工艺的研究,获得硅铝双金属可调焦微反射镜4×4阵列,单元尺寸3 mm×3 mm,单晶硅基底厚60μm,硅表面溅射的铝膜厚150 nm。该微镜的镜面填充率为100%,可变形镜面占总镜面面积的79%。利用激光波面干涉仪对可调焦微反射镜的动态性能进行了测试。实验表明,该微镜可产生单向连续变形,最大变形量15.8μm,非线性滞后27%,工作电压0~2.5V,可调焦范围∞~0.036 m。     

一种超混沌映射的单双参量自适应同步

利用参量自适应法实现了超混沌系统Kawakami映射的同步.通过严密的数学推导,给出了Kawakami映射在单参量自适应下实现同步的充分条件,并在双参量自适应控制下系统同样实现了同步.数值模拟结果显示,该映射输出具有类似于白噪声的宽谱特性,因此比较适合用于保密通信.     

分布式电极连续面型微变形反射镜力电耦合特性分析

针对基于MEMS技术制造的连续面型薄膜微变形反射镜,从薄膜理论出发对其力电耦合变形特性进行理论分析,导出了镜面变形表达式。利用该式及响应频率表达式,定量分析了镜面相关尺寸参数对变形量的关系,为变形镜的结构设计提供了可靠的理论依据。结果表明,当镜面厚度为1 μm且与驱动电极间距20 μm时,对控制电压不超过120 V,响应频率大于50 kHz的应用场合,变形镜镜面半径应在2.1～13.8 mm之间进行选择。仿真结果显示,驱动电压较小时,镜面变形与驱动电压平方近似成线性关系。