非结构化改进差分法在波动方程中的应用

在计算声学领域中,有限差分法是一种比较传统的数值模拟方法.差分法简单易行而且效果突出,然而此方法只能在结构网格中使用,很难计算几何边界较为复杂的区域.基于高斯定理构造单元梯度的方式,在二维空间上,提出了一种改进的有限差分法(Improved Finite Difference Method,IFDM).IFDM可以使用...     

Probabilistic evaluation for the implicit limit-state function of stability of a highway tunnel in China

This paper presents a practical algorithm for the first-order reliability method (FORM) to deal with the implicit nature of a limit-state function (LSF) in reliability assessment of stability of a working highway tunnel, which is constructed in a mountainous area in China. First, a mechanical model to determine the LSF that is not explicitly known with complex non-linear behaviour is formulated for the primary support provided by the combination of shotcrete and rockbolts. After reviewing concisely the basic concepts relevant to the FORM, the central difference approximation is subsequently introduced to estimate the partial derivatives of the LSF. By consideration of Taylor’s formula, this LSF can be transformed into an equation involving a single unknown described as the reliability index, and then the resulting solution procedure for determination of the reliability index can be rendered based on the derivation rule of compound function. A flow for tunnel reliability problem posed by the implicit LSF in applying the FORM is further developed. Eventually, the proposed methodology for the LSF in the non-explicit circumstance is used to perform the probabilistic evaluation for such a working tunnel where the choices of values of step length coefficient affecting the calculation results are suggested. Comparisons are made with the Monte-Carlo simulation method (MCSM) to assess the computational accuracy and efficiency of the algorithm proposed in this paper. It is shown that the MCSM used to obtain the “exact” solutions entails the formidable computational effort, whereas the current algorithm that alleviates the computational labour dramatically can provide an efficient way of implementing reliability calculations for the implicit LSF and offer results which are found to be in satisfactory agreement with the “exact” ones when the step length coefficient is properly taken.     

围岩温度场及调热圈半径的半显式差分法解算

 建立了解算巷道围岩温度场分布、调热圈半径的数学模型及优于一般差分格式的解算围岩温度场的异步长半显式差分格式,编制了解算围岩温度场分布及调热圈半径的计算机程序,解算出了围岩温度分布规律;并通过实测数据与解算结果的对比,证明了异步长半显式差分格式的正确性及高精度。     

移动网智能管道发展的挑战和应对

探讨了移动智能管道的定义和内涵,分析目前移动网智能管道发展的架构、能力完善和协同、管道价值挖掘、运营机制优化这4个方面的挑战,并给出了应对策略。     

引起阻焊膜色差的关键因素分析

在PCB阻焊外观品质控制中,阻焊的颜色是比较重要的一项控制点,对于使用同一型号阻焊油墨的一款生产板,板面阻焊出现明显的色差,客户一般不接受,目前业内对于引起阻焊色差的深层原因罕见报道。本文主要针对阻焊色差问题,研究了阻焊厚度、预烘时间、曝光能量、热固化温度时间等对阻焊颜色的影响,尝试从光学角度和阻焊的微观结构来解释引起阻焊色差的根本原因,同时研究了阻焊膜的色差所带来的可靠性问题,从结合力和其耐化学性方面做深入探讨。     

对相似递推程差的一种修正方法

利用相似递推法,即可将基于短基线的相差测量结果拓展到长基线多站无源定位系统,由于双站相差测距法实际上是建立在三站定位技术之上的,且测量精度与量值巨大的光速无关,所以就能实现比现有双站测向和三站时差法更高的定位精度。但为实现准确定位,必须对递推程差进行修正。本文在已有分析的基础上,利用双站间的交会角,给出了一种更适用于工程设计的递推程差修正方法。     

短距双站在远距基准点上观测目标的定位精度

在基于时差一方位测量的短距双基站的数百公里之外,选定一个地图基准位置,并以此地图基准位置作为计算分析远距目标位置的几何坐标起始点。先由双站间的时差方程和几何关系解得目标相对于双站的测距式,然后,利用双站测距式以及双站与远距地图基准点之间的几何关系解得目标相对于地图基准点的径向距离和方位。虽然测向误差很大,但误差分析表明只要双站与地图基准点之间的距离足够远,就能在双站距离小于10km的情况下,使目标与地图基准点之间的测距误差满足小于5％R的精度要求。     

Automatic rotational symmetry determination for shape analysis

The determination of the rotational symmetry of a shape is useful for object recognition and shape analysis in computer vision applications. In this paper, a simple, but effective, algorithm to analyse the rotational symmetry of a given closed-curve shape S is proposed. A circle C with the centroid of S as the circle center and the average radius of S as the circle radius is superimposed on S, resulting in the intersection of C and S at a set of points. By theoretical analysis, the relationship between the order N_s of the rotational symmetry of S and the number of intersection points between C and S is established. All the possible values for N_s are determined. And finally N_s is determined by evaluating the similarity between S and its rotated versions. In the proposed algorithm, only simple pixel operations and second-order moment function computation are involved. Several problems caused by the use of discrete image coordinates are analysed and solved for correct decision-making in the algorithm. Good experimental results are also included.     

对不同洁净室测试规范中条文差异的探讨

本文根据有关国家标准和行业标准，结合工程测试实践，对洁净室洁净度测定中必要测点数及每个测点的必要采样次数等问题进行探讨。