利用极化角点指数进行数字曲线快速多边形近似

针对曲线结构特征,引入极化角点指数作为特征角点的候选依据,提出了一种与曲线起始点位置无关的基于角点检测的多边形近似算法。实验证明,此方法快速有效,结果稳定,噪声抑制效果较好。     

起伏地表条件下的声波散射数值模拟的积分方程法

从散射理论的角度来看,起伏地表可以看作是一种特殊的扰动介质,因此应用散射积分方程求解起伏地表条件下的散射场在理论上是可行的。从三维频率域声波方程出发,由格林函数定理,得出起伏地表条件下的散射积分方程。散射积分方程为关于起伏地表的面积分和与速度扰动体有关的体积分之和,同时给出了格林函数在奇异点的积分方法。由于数值离散求解积分方程存在着计算时间太长和存储内存不足的问题,采用电磁散射积分方程的拟解析近似的方法。在假设反射函数为缓变函数的基础上,最终得到其近似表达式,因此散射场的数值求解不必再借助于代数方程组,只要进行数值积分即可。这种方法避开了传统数值计算方法存在的问题,为地震散射波场快速正演模拟打下了基础。理论分析表明,这种方法适用于小扰动的问题。当扰动较大时,拟解析近似会产生较大的误差。     

顶点Pk覆盖问题的研究综述

顶点覆盖问题是经典的NP完全问题,在排序、计算机网络等现实生活中有许多的应用.近几年来,许多研究者开始探究它的推广形式——顶点P_k覆盖（VCP_k）问题,即寻找一个顶点子集,从拓扑结构图中删除后使得剩下的顶点导出的子图不包含P_k路,其中P_k是指包含k个顶点的路.本文简单介绍了VCP_k问题的应用背景,归纳了它在近似算法、精确算法、参数化算法3个方面的主要研究进展,并分析了一些主要的方法和技巧.在此基础上,对VCP_k问题及其相关问题的研究前景进行了展望.     

Time-domain identification of dynamic properties of layered soil by using extended Kalman filter and recorded seismic data

A novel time-domain identification technique is developed for the seismic response analysis of soil-structure interaction. A two-degree-of-freedom (2DOF) model with eight lumped parameters is adopted to model the frequency-dependent behavior of soils. For layered soil, the equivalent eight parameters of the 2DOF model arc identified by the extended Kalman filter (EKF) method using recorded seismic data. The polynomial approximations for derivation of state estimators are applied in the EKF procedure. A realistic identification example is given for the layered-soil of a building site in Anchorage, Alaska in the United States. Results of the example demonstrate the feasibility and practicality of the proposed identification technique. The 2DOF soil model and the identification technique can be used for nonlinear response analysis of soil-structure interaction in the time-domain for layered of complex soil conditions. The identified parameters can be stored in a database for use in other similar soil conditions. If a universal database that covers information related to most soil conditions is developed in the future, engineers could conveniently perform time history analyses of soil-structural interaction.     

GNSS海面散射信号的海面风场遥感

首先介绍了GNSS-R海洋遥感的发展过程,简要叙述了利用GNSS信号进行海洋动力学遥感测量的基本原理;然后分析了接收机天线的部分参数对GNSS信号可见数量的影响;最后详细阐述了GNSS海面散射信号的理论模型,该模型是利用几何光学限制的基尔霍夫近似建立起来的,并根据理论模型进行了数值仿真试验。结果证实了通过散射信号功率波形来反演海面风场理论上的可行性。     

GAAF在星载GPS实时定轨中的应用研究

为确保高精度星载GPS实时定轨算法能够应用于较低轨道卫星,提出了用地球引力近似函数法(GAAF)代替传统球谐函数递推法来计算地球引力加速度,在不降低实时定轨精度的同时,大幅减小高阶次重力场模型的轨道积分计算负荷,以满足计算能力有限的星载处理器的在轨处理要求。分析了影响GAAF计算精度的两个因素:伪中心位置拟合多项式的次数选取和经纬度格网大小的最优确定。用CHAMP卫星的实测GPS数据模拟实时定轨试验,结果表明,采用二次及以上伪中心拟合多项式,格网纬度小于0.75°、经度小于1.5°的GAAF时,实时定轨的轨道精度要优于70×７０阶次重力场模型直接参与实时定轨,且大幅降低实时定轨的计算负荷。     

Approximation approach to the SRM based on root decomposition in the simulation of spatially varying ground motions

The spectral representation method(SRM) is widely used to simulate spatially varying ground motions.This study focuses on the approximation approach to the SRM based on root decomposition,which can improve the efficiency of the simulation.The accuracy of the approximation approach may be affected by three factors: matrix for decomposition,distribution of frequency interpolation nodes and elements for interpolation.The influence of these factors on the accuracy of this approach is examined and the following conclusions are drawn.The SRM based on the root decomposition of the lagged coherency matrix exhibits greater accuracy than the SRM based on the root decomposition of the cross spectral matrix.The equal energy distribution of frequency interpolation nodes proposed in this study is more effective than the counter pith with an equal spacing.Elements for interpolation do not have much of an effect on the accuracy,so interpolation of the elements of the decomposed matrix is recommended because it is less complicated from a computational efficiency perspective.     

围岩参数Monte－Carlo有限元反分析

提出了应用隧道施工监测的随机值，采用蒙特一卡罗（Ｍｏｎｔｅ－Ｃａｒｌｏ）有限元随机反分析以反推地层参数和初始地应力分布的方法。反推参数不仅给出其均值，还给出参数的方差及分布类型，为地下结构稳定性和可靠性分析提供必要数据。为检验所提的反分析方法对工程的实用性，文中给出了一个实例。     

纬向切变基流中的非线性Rossby波

本文在半地转近似下讨论了纬向切变基流中的非线性正压Ｒｏｓｓｂｙ波，给出了存在波解的切变基流条件。     

我国月降水和气温网格点资料的处理和分析

用逐步搜索逼近法的客观分析技术计算出１９５１－１９９２年中国月降水量和月平均气温的格点资料，并利用图象识别原理对格点值和站点观测值进行了比较。