地磁低点位移法的改进

中低纬度地磁场平静太阳日变化Z分量的极小值出现的时刻常被用于地震预报,即"低点位移"法,但现有算法的时间格式和人工绘制突变界线的模式会产生较大的误差,本文在第一部分针对这些误差改进了原有算法.第一项是改进了地磁低点时间的格式,第二项是引入了Voronoi剖分技术替代人工画线.前者过滤了假的突变界线,消除了系统误差;后者建立了突变界线与地磁台网低点数据之间的解析关系,使它们一一对应,消除了随机误差.本文第二部分内容是提出了新的时间格式与数字化突变界线的计算公式,并用程序实现计算任务.本文第三部分内容是在对地磁台网的低点时间跟踪的过程中,捕捉到了甘肃省周边几次地震前的地磁低点位移现象,并分析这些案例,在结论中证明该方法的可靠性.     

浅谈提高空中三角测量数据成果质量的3个关键环节

空中三角测量数据主要是为摄影测量提供定向框架数据,其质量决定最终产品的质量。笔者结合生产实践中遇到的实际问题,对提高空中三角测量数据成果质量的3个关键环节——航外控制测量,航内控制点量测,外业控制点的残差分析、空中三角测量成果检查及评定的重要性进行了阐述。     

基于独立分量分析的多次波自适应相减技术

针对多次波自适应相减这个关键问题,文中首次提出利用独立分量分析技术来实现多次波和一次波的分离（简称ICAAMS）. 现有的多次波自适应相减技术大都是采用输出信号（一次波）能量最小准则,基于二阶统计量的技术. 本文提出的ICAAMS采用了输出信号非高斯性最大准则,并利用高阶统计量来表征非高斯性. 简单的褶积模型和复杂的有限差分模型资料处理结果表明, 本文提出的方法可以有效地分离一次波和多次波.     

江阴互通桥梁的施工控制测量

结合无锡江阴互通桥梁施工实例,着重介绍了互通桥梁施工控制测量的测点布置和具体作业方法及拱度控制、标高控制和预压的方法;同时,文章还总结了控制测量过程中用到的一些新测量思路及方法。     

三维高阶深度偏移方程及其数值求解方法

从三维非均匀介质中的波动方程出发,利用拟微分算子理论,Ｐａｄｅ逼近方法及因式分解技巧,获得了非均匀介质的三维高阶深度偏移方程,相应地提出了逐次低阶方程方法、低阶方程组方法及分裂方法等３种求解方法．与二维情形不同,以上每一种方法在数值求解时均存在由测线坐标ｙ的出现而带来的困难．为了克服这一困难,我们提出了差分算子分解方法,避免了近年来人们竞相研究的ｘ－ｙ方向微分算子分裂带来的分裂误差,保持了应有的相容性,解决了这一令人烦恼的问题．     

Postbuckling of shear deformable stiffened anisotropic laminated cylindrical shell under axial compression

A postbuckling analysis is presented for a shear deformable anisotropic laminated cylindrical shell with stiffener of finite length subjected to axial compression. The material of each layer of the shell is assumed to be linearly elastic, anisotropic and fiber-reinforced. The governing equations are based on a higher order shear deformation shell theory with von Kármán-Donnell-type of kinematic nonlinearity and including the extension/twist, extension/flexural and flexural/twist couplings. The ‘smeared stiffener’ approach is adopted for the beam stiffeners. This arrangement allows the beam stiffeners to be assembled directly into the global stiffness matrix. The nonlinear prebuckling deformations and initial geometric imperfections of the shell are both taken into account. A singular perturbation technique is employed to determine the buckling loads and postbuckling equilibrium paths. The numerical illustrations concern the postbuckling response of perfect and imperfect, grid, axial, ring stiffened, and unstiffened shells. The results confirm that there exists a compressive stress along with an associate shear stress and twisting when the anisotropic shell is subjected to axial compression. The postbuckling equilibrium path is unstable for the moderately thick cylindrical shell under axial compression and the stiffened shell structure is imperfection-sensitive.     

Wave driven free surface motion in the gap between a tanker and an FLNG barge

When two vessels are moored side-by-side with a narrow gap between them, intense free surface motions may be excited in the gap as a result of complex hydrodynamic interactions. These influence the motions of the two vessels, and the forces in any moorings. The present paper uses first and second order wave diffraction analysis to investigate this phenomenon. Key theoretical aspects of the numerical analysis are first summarised, including the vital need to suppress “irregular frequency” effects; and results are given to validate the code used. The case of a tanker alongside a large floating FLNG barge is then considered in detail.     

On the adequacy of second-order models to predict abnormal waves

The paper is intended to extend the investigations about the nature of abnormal waves that have been reported in the work of Guedes Soares et al. (Characteristics of abnormal waves in North Sea states. Applied Ocean Research 25, [337–344]). The same dataset gathered at the oil platform North Alwyn in the North Sea during the November storm in 1997 is used along with the time series from the Draupner platform, in which an abnormal wave occurred. The data are reanalyzed from the viewpoint of the applicability of second-order models to fit large waves. The observed results confirm that the second-order approximation is not adequate to describe highly asymmetric and abnormal waves.     

Higher Harmonics Induced by Waves Propagating over A Submerged Obstacle in the Presence of Uniform Current

To investigate higher harmonics induced by a submerged obstacle in the presence of uniform current, a 2D fully nonlinear numerical wave flume（NWF） is developed by use of a time-domain higher-order boundary element method（HOBEM） based on potential flow theory. A four-point method is developed to decompose higher bound and free harmonic waves propagating upstream and downstream around the obstacle. The model predictions are in good agreement with the experimental data for free harmonics induced by a submerged horizontal cylinder in the absence of currents. This serves as a benchmark to reveal the current effects on higher harmonic waves. The peak value of non-dimensional second free harmonic amplitude is shifted upstream for the opposing current relative to that for zero current with the variation of current-free incident wave amplitude, and it is vice versa for the following current. The second-order analysis shows a resonant behavior which is related to the ratio of the cylinder diameter to the second bound mode wavelength over the cylinder. The second-order resonant position slightly downshifted for the opposing current and upshifted for the following current.     

伪近邻方法在ARMA系统阶数判别中的应用

从相空间重构的角度,提出利用伪近邻方法判别ＡＲＭＡ 系统的总阶数。该方法可在数据量较小和阈值固定的情况下判别ＡＲＭＡ 系统总阶数。数值计算表明,使用该方法判别线性ＡＲＭＡ系统总阶数,取得了比较满意的结果。