轮形阵列波束形成的优化设计

基于波束形成方法的噪声源识别中,阵列性能影响着声源识别的效果。针对轮形阵列,采用正交试验的方法,对阵列的几何参数进行优化设计。通过逐步缩小参数最优值的取值范围,使在传声器数目和阵列尺寸一定的情况下,阵列的声源识别效果得到改进。经优化,轮形阵列的最大旁瓣水平曲线在很宽的频率带上保持在16 dB以下,比普通轮形阵列的最大旁瓣水平降低了3 dB以上。验证了正交试验方法在阵列优化设计的可行性,为波束形成装置的开发提供了理论依据。     

总方差方法在光纤陀螺随机误差分析中的应用

总方差方法被引入到光纤陀螺随机误差特性分析当中,有效克服了传统 Allan方差法在长相关时间上计算易出现“崩溃”的问题。但用它直接分析光纤陀螺随机噪声存在算法偏差,不能真实反映角度随机游走噪声、量化噪声和指数相关噪声方差值,因此在算法上对总方差提出改进,使其适用于光纤陀螺噪声分析。对模拟的各项随机噪声进行仿真计算,验证改进后总方差方法可有效辨识噪声类型和水平。对光纤陀螺实测数据方差分析表明改进的总方差方法在平均因子较大的情况下可提高估计置信度,方差值稳定性好,比 Allan方差法能更精确地分析出噪声项系数。     

闪光CCD图像的中值-非线性扩散滤波

根据闪光CCD图像的特点,提出了一种中值-非线性扩散滤波(Median-NonlinearDiffusionFiltering,简称MNDF)方法。该方法采用中值预滤波来估计图像的真实边缘,通过求解偏微分方程(PartialDifferentialEquation,简称PDE)来进行非线性扩散滤波,充分发挥了中值滤波和非线性扩散滤波的优势,能更好地消除噪声、保护边缘。实验结果表明,在高斯噪声和脉冲噪声同时存在的情况下,MNDF方法取得的滤波效果较P-M方案和Catte方案要好,信噪比改善因子提高3~5倍,均方误差减小1.3~2.7倍。对闪光照相CCD图像取得了很好的消噪声结果,保护了边缘信息。     

结构物理参数识别的多尺度参数卡尔曼滤波方法

经过正交小波变换后,低尺度上测量信号的信噪比提高。应用小波变换将结构的激励信号和响应信号分解到不同尺度上,得到不同尺度上结构的状态方程和测量方程,结合动力学系统辨识的参数卡尔曼滤波方法,提出了结构物理参数的多尺度参数卡尔曼滤波辨识方法。理论分析和数值算例表明:在多尺度上对结构参数进行辨识比在单一尺度上辨识能获得更高的精度。     

超大型油轮降噪设计主传递路径族灵敏度方法

针对振动噪声传递路径降噪设计是提高船舶声学性能的有效措施之一。目标舱室振动噪声传递路径并不唯一，其中多条主要路径传递了大部分振动与噪声能量。利用作者提出的基于声振熵概念及图论中K则最短路径理论的声振熵赋权图法，能够快速识别船舶舱室噪声主要传递路径族。在此基础上，计算噪声主传递路径族上声学设计参数变化对目标舱室声压影响的灵敏度，调整有关声学设计措施，此即降噪设计主传递路径族灵敏度方法。提出适用于大型船舶噪声主传递路径分析及主传递路径族灵敏度的降噪设计通用流程，通过超大型油轮降噪声学设计实例，说明了该方法的有效性。     

Solving numerical difficulties for element-free Galerkin analyses

This study solves the numerical problems associated with the element-free Galerkin method (EFGM) to perform analyses efficiently in shared-memory computers. The truncation error is generally large for the moving least-squares approximation, and this can be overcome by using orthogonal basis functions, 16-byte floats, or the local origin. Then, the analysis accuracy is similar to that obtained with the reproducing kernel particle approximation. Determining the index array of the global stiffness matrix requires a large amount of computer memory. We thus propose a scheme to overcome this problem using slightly more computer time but much less computer memory. A binary search is also proposed to find the support domain nodes for Gaussian points, and this method is much more efficient than the linear search one. A Fortran module is developed to establish parallel solutions in the EFGM, and the programmer does not need to handle the global stiffness directly.     

最优有界控制下色噪声驱动多时滞拟线性系统瞬态响应

基于Fokker-Planck-Kolmogorov方程瞬态求解研究了受最优有界控制的色噪声驱动的多时滞拟线性系统的瞬态响应。利用等价变换将时滞系统转化为非时滞系统。在弱扰动假设下应用标准随机平均法得到振幅过程的部分平均It?随机微分方程。由动态规划原理和控制力界值条件得到最优有界控制率从而得到完全平均的Fokker-Planck-Kolmogorov方程。通过原系统的退化线性系统导出一组正交基并在该基空间内进行Galerkin变分得到近似瞬态响应。最后将该方法应用到受最优有界控制率和色噪声共同作用的时滞Duffing-Van Der Pol振子进行理论求解并综合讨论了色噪声、时滞、控制力和共振对系统瞬态响应的影响,采用Monte-Carlo模拟验证了所有理论和计算结果的正确性。     

Hierarchal triangular elements using orthogonal polynomials

Hierarchal elements are finite elements which have the useful property that elements with different polynomial orders can be used together in the same mesh without causing discontinuities. This paper introduces a new hierarchal triangular element in which the basis functions are constructed from orthogonal polynomials—Jacobi polynomials. The resulting element is shown to be better conditioned than the earlier hierarchal element of Rossow and Katz.¹ Recursive formulas allow the complete set of basis functions for an element to be efficiently evaluated at a given point. In addition, the formulas can be used to generate pre-computed (universal) matrices. Examples are given of universal matrices, up to order 4, for the generalized Helmholtz equation. An electromagnetic problem involving a length of transmission line is used to show the usefulness of the new elements.     

On Generalized Fibonacci Cubes and Unitary Transforms

 We present a new interconnection topology called generalized Fibonacci topology, which unifies a wide range of connection topologies such as the Boolean cube (or hypercube), classical Fibonacci cube, etc. Some basic topological properties of generalized Fibonacci cubes are established. Finally, we developed new classes of the discrete orthogonal transforms, based on the generalized Fibonacci recursions. They can be implemented efficiently by butterfly-type networks (like the Fourier, or the Haar transforms). A generalized Fibonacci cube based processor architecture (generalizing the known SIMD architecture — hypercube processor) can be efficiently used for hardware implementation of the proposed discrete orthogonal transforms. Received: October 31, 1996     

Modal analysis of astronomical bolometric interferometers

A procedure is described for modeling the behavior of astronomical bolometric interferometers. The scheme is based on the notion of eigenfields. The input and output eigenfields are those field distributions on the sky and at the detector to which the individual telescopes of an interferometer can couple. Eigenfields are more fundamental than eigenmodes and provide, regardless of optical configuration, an orthogonal basis for propagating the second-order statistical properties of a field from a source through the telescopes, through the beam combiners, and onto the detectors. With our scheme, it is possible to calculate the power coupled into coherent, partially coherent, and incoherent imaging arrays and to include the spatially distributed noise sources of the telescopes themselves.