基于模糊动态模型的多变量系统模糊控制

采用模糊动态模型对多变量复杂非线性系统进行模糊控制.首先针对局部线性动态模 型设计状态反馈控制器,然后利用模糊推理确定整个系统的控制;在一系列局部模型通过模糊 隶属函数连接得到的连续的全局模型中,全面考虑其它关联子系统对标称线性系统的摄动,并 利用大系统分散控制关联稳定性的概念和方法,得到了闭环模糊系统稳定的充分条件.仿真例 子验证了该设计方法的正确性.     

地下水扰动作用下地基土体渗透破坏试验研究

为分析近年来中国西南地区频繁发生的"天坑"形成原因,从渗流破坏理论出发,通过自主设计循环变水压渗透试验装置模拟地下水扰动过程,研究了地下水扰动作用下地基土体的变形破坏机制。首先通过现场和室内试验获得土样的基本物理化学性质,排除由碳酸盐溶洞导致地表塌陷的可能性。在此基础上,为模拟地下水循环扰动对土体的渗透破坏作用,采用饱和土渗流理论,设计了1种变压型常水头渗透试验装置,通过自动循环地改变水头大小模拟地下水扰动对土体的破坏机制,分析实验前后土样级配组成、水头变化和土样变形破坏特性,试验表明土样在地下水扰动作用下细颗粒明显减少,土体级配结构发生改变,土体承载力降低并最终导致土体塌陷。变压型常水头渗透破坏试验研究表明,该方法较好地阐明了该地区"天坑"形成机制。     

基于太阳能电源的图像采集系统

利用光伏转换与控制技术,将太阳能光伏运用于图像采集上,开发出一套基于太阳能光伏电源的图像采集系统。前级在硬件上采用BUCK型DC-DC电路,软件上提出了固定电压法结合双向扰动观察法的最大功率点跟踪算法,后级图像采集由AVR控制数字摄像头OV7620完成图像采集并传输至上位机。测试结果表明,该系统能够快速、精确、稳定地追踪到太阳能电池板的最大功率点,并且只需稍作修改便可应用于各种需要图像采集的场合。     

He's homotopy perturbation method for fourth-order parabolic equations

In this paper, He's homotopy perturbation method is applied to fourth-order parabolic partial differential equations with variable coefficients to obtain the analytic solution. The method is tested on six examples, which reveal its effectiveness and simplicity.     

A parameter uniform B-spline collocation method for solving singularly perturbed turning point problem having twin boundary layers

A numerical scheme is proposed to solve singularly perturbed two-point boundary value problems with a turning point exhibiting twin boundary layers. The scheme comprises B-spline collocation method on a non-uniform mesh of Shishkin type. Asymptotic bounds are established for the derivative of the analytical solution of a turning point problem. The present method is boundary layer resolving as well as second-order accurate in the maximum norm. A brief analysis has been carried out to prove the uniform convergence with respect to the singular perturbation parameter ? by decomposing the solution into smooth and singular components. Some relevant numerical examples are also illustrated to verify computationally the theoretical aspects.     

Coefficients perturbation methods for higher-order differential equations

In this paper, we develop a general approach for estimating and bounding the error committed when higher-order ordinary differential equations (ODEs) are approximated by means of the coefficients perturbation methods. This class of methods was specially devised for the solution of Schrödinger equation by Ixaru in 1984. The basic principle of perturbation methods is to find the exact solution of an approximation problem obtained from the original one by perturbing the coefficients of the ODE, as well as any supplementary condition associated to it. Recently, the first author obtained practical formulae for calculating tight error bounds for the perturbation methods when this technique is applied to second-order ODEs. This paper extends those results to the case of differential equations of arbitrary order, subjected to some specified initial or boundary conditions. The results of this paper apply to any perturbation-based numerical technique such as the segmented Tau method, piecewise collocation, Constant and Linear perturbation. We will focus on the Tau method and present numerical examples that illustrate the accuracy of our results.     

A perturbation approach for a type of inverse linear programming problems

We consider an inverse linear programming (LP) problem in which the parameters in both the objective function and the constraint set of a given LP problem need to be adjusted as little as possible so that a known feasible solution becomes the optimal one. We formulate this problem as a linear complementarity constrained minimization problem. With the help of the smoothed Fischer–Burmeister function, we propose a perturbation approach to solve the inverse problem and demonstrate its global convergence. An inexact Newton method is constructed to solve the perturbed problem and numerical results are reported to show the effectiveness of the approach.     

A new homotopy perturbation method for system of nonlinear integro-differential equations

In this paper, a new homotopy perturbation method (NHPM) is introduced to obtain exact solutions of system of nonlinear integro-differential equations. Theoretical considerations are discussed. Two examples are given to demonstrate the efficiency of NHPM to the classical HPM and variational iteration methods.     

Scattering loss in optical waveguide with trapezoidal cross section

To get the scattering loss of the trapezoidal core waveguide, a new analysis model is presented based on the perturbation equivalent method and modified effective-index method. Firstly, the trapezoidal core waveguide is successfully equivalent to the rectangular one with both restricting the same optical field energy by adopting the perturbation method. Then, the equivalent rectangular core waveguide is decomposed into two slab waveguides by employing the modified effective-index method. The trapezoidal core waveguide scattering theory model is established based on the slab waveguide scattering theory. With the sidewalls surface roughness in the range from 0 to 100 nm in the single model trapezodial core waveguide, optical simulation shows excellent agreement with the results from the scattering loss model presented. The relationship between the dimension and side-wall roughness with the scattering loss can be determined in the trapezoidal core waveguide by the scattering loss model.     

气象集合预报的研究进展

集合预报是数值预报发展的一个重要方向,相对于单一的确定性预报,它考虑了初值及模式的不确定性,其结果反映了未来天气的多种状况,能为用户提供确定性预报所不能提供的信息(如预报结果的可信度等)。降水信息是水文预报系统的核心输入,单一的降水预报存在着不确定性,从而使得水文预报也存在不确定性。这种不确定性制约了水利工程调度的科学性。集合预报在一定程度上能解决这种不确定性。从而在水文领域,气象集合预报具有较高的应用价值。为了水文工作者能够更好地应用集合预报,本文首先基于系统的角度,对集合预报系统中的初值扰动、模式扰动和集合预报产品等研究现状及成果进行了评述,然后分析了降水集合预报产品在水文预报领域中的应用情况,最后对集合预报在水文领域中的应用进行了展望。