数字正交检波技术在主动探测中的应用研究

提出基于光学系统的“猫眼”效应,应用单频调制的连续激光,对扫描式红外热成像目标进行有效探测的新方法。分析了光学系统的后向反射特性,针对回波信号特征,提出利用回波信号的相位信息,采用直接采样的数字正交检波技术实现对低信噪比回波信号的可靠检测,并在外场试验中应用该方案对实际目标回波信号获得了满意的检测结果。     

变截面欧拉梁自由振动分析的重采样微分求积法

采用重采样微分求积法求解了变截面欧拉梁的自由振动问题。推导了变截面梁的控制方程离散格式,采用重采样矩阵方法对边界条件进行处理,给出了变截面梁自由振动算法。采用本文方法对不同类型截面形式和不同边界条件的变截面梁进行自由振动分析,并和其他解法进行比较。计算结果表明,本文方法可以适用于不同变截面类型和不同边界条件,计算精度与解析解吻合良好,具有良好的收敛性能。在同等精度条件下网格点数少于现有计算方法。重采样转换矩阵边界处理方法相比于传统边界处理方法具有更快的收敛性能。     

基于微分求积有限元法的双层微板系统振动特性研究

基于修正的偶应力理论和两变量精化的剪切变形理论,建立了由Winkler-Pasternak连续弹性夹层连接的双层微板系统的自由振动模型,着重推导了系统异步振动的运动微分方程和势能泛函。融合Gauss-Lobatto求积准则和微分求积准则构造了具有C¹连续性的微分求积有限元。通过与已有文献进行对比,验证了数值方法的有效性。详细讨论了各种因素对系统同步和异步振动特性的影响。结果表明,系统的自由振动特性对材料尺度参数、长宽比、长厚比以及边界条件呈现出依赖性;弹性夹层刚度仅对系统异步振动产生作用;随着模态阶次的增大,材料尺度参数和弹性夹层刚度对异步振动频率和模态的影响变得显著。     

Unified two-phase nonlocal formulation for vibration of functionally graded beams resting on nonlocal viscoelastic Winkler-Pasternak foundation

A nonlocal study of the vibration responses of functionally graded (FG) beams supported by a viscoelastic Winkler-Pasternak foundation is presented. The damping responses of both the Winkler and Pasternak layers of the foundation are considered in the formulation, which were not considered in most literature on this subject, and the bending deformation of the beams and the elastic and damping responses of the foundation as nonlocal by uniting the equivalently differential formulation of well-posed strain-driven (ε-D) and stress-driven (σ-D) two-phase local/nonlocal integral models with constitutive constraints are comprehensively considered, which can address both the stiffness softening and toughing effects due to scale reduction. The generalized differential quadrature method (GDQM) is used to solve the complex eigenvalue problem. After verifying the solution procedure, a series of benchmark results for the vibration frequency of different bounded FG beams supported by the foundation are obtained. Subsequently, the effects of the nonlocality of the foundation on the undamped/damping vibration frequency of the beams are examined.     

Differential quadrature method to stability analysis of pipes conveying fluid with spring support

It is a new attempt to extend the differential quadrature method (DQM) to stability analysis of the straight and curved centerline pipes conveying fluid. Emphasis is placed on the study of the influences of several parameters on the critical flow velocity. Compared to other methods, this method can more easily deal with the pipe with spring support at its boundaries and asks for much less computing effort while giving aceptable precision in the numerical results. Supported by National Key Project of China (No. PD9521907) and the National Science Foundation of China (No. 19872025).     

Adaptive Quadrature—Revisited

First, the basic principles of adaptive quadrature are reviewed. Adaptive quadrature programs being recursive by nature, the choice of a good termination criterion is given particular attention. Two Matlab quadrature programs are presented. The first is an implementation of the well-known adaptive recursive Simpson rule; the second is new and is based on a four-point Gauss-Lobatto formula and two successive Kronrod extensions. Comparative test results are described and attention is drawn to serious deficiencies in the adaptive routines quad and quad8 provided by Matlab.     

Multivariate orthogonal polynomials, homogeneous Padé approximants and Gaussian cubature

The connection between orthogonal polynomials, Padé approximants and Gaussian quadrature is well known and will be repeated in section 1. In the past, several generalizations to the multivariate case have been suggested for all three concepts [4,6,9,...], however without reestablishing a fundamental and clear link. In sections 2 and 3 we will elaborate definitions for multivariate Padé and Padé-type approximation, multivariate polynomial orthogonality and multivariate Gaussian integration in order to bridge the gap between these concepts. We will show that the new m-point Gaussian cubature rules allow the exact integration of homogeneous polynomials of degree 2m−1, in any number of variables. A numerical application of the new integration rules can be found in sections 4 and 5. This revised version was published online in June 2006 with corrections to the Cover Date.     

Computable error bounds and estimates for the conjugate gradient method

The conjugate gradient method is one of the most popular iterative methods for computing approximate solutions of linear systems of equations with a symmetric positive definite matrix A. It is generally desirable to terminate the iterations as soon as a sufficiently accurate approximate solution has been computed. This paper discusses known and new methods for computing bounds or estimates of the A-norm of the error in the approximate solutions generated by the conjugate gradient method.     

用DQM求解成层地基一维非线性固结问题

由于多层地基的一维非线性固结问题求解的复杂性,其解析解很难求得。本文基于Davis和Raymond一维非线性固结理论,利用DQM(Differential Quadrature Method)导了初始有效应力沿深度变化、任意边界条件、任意荷载作用下成层地基一维非线性固结的统一表达式,求得了孔压、有效应力和平均固结度的解答。通过解的收敛性分析讨论了DQM解的有效性。由于DQM解对于固结间题各种复杂条件具有统一的矩阵表达式,更便于编程计算和工程应用。最后,用本文解答对三层地基一维非线性固结问题进行了讨论。     

基于刚性约束的双移动机器人协同定位

准确、快速的状态估计是保证多机器人顺利完成协作搬运任务的关键.然而,大部分现有多机器人协同定位方法都存在一定的局限性,往往无法同时兼顾定位精度与计算复杂度.因此,本文从协作搬运任务的特点出发,将距离与方位的刚性约束条件引入协同定位中,同时根据机器人之间的紧密耦合关系建立起通用有效的运动模型和量测模型.最终在此刚性约束系统建模的基础上,提出一种基于高斯-厄米特求积分卡尔曼滤波（Quadrature Kalman Filter,QKF）的双移动机器人协同定位方法.仿真实验结果表明：与基于无约束模型的QKF协同定位方法相比,本文所提方法不但具有更高的定位精度,而且计算复杂度大大降低,有助于实现多机器人实时协同定位.