Numerical Simulation of Wave Field at the Kemena River Mouth in Kalimantan Island

-By use of the parabolic equation of numerical simulation of wave which is suitable forlarge-angle propagation and Crank-Nicolson differential method,the wave field at the Kemema Rivermouth has been studied for analysis of sediment movement in the area.In order to reflect wave energy lossaccurately,the Bretchneider-Reid formula is quoted and the friction coefficient in the formula is discussedin this paper.The calculation results indicate that the wave becomes a little damped at the mouth ofKemena River influenced by the topography and bottom friction,and the wave at the east beach is higherthan that at the west beach,because the east beach extends out.     

Sensitivity Analysis on GIS Procedures for the Estimate of Soil Erosion Risk

Land degradation by water erosion is one of the majorissues in the field of environmental planning. Soilerosion and sediment transport are spatiallydistributed processes, and their evaluation can beeasily realised by means of the use of GeographicInformation Systems. The greater availability ofdigital and geo-lithological data managed and storedinside GIS has implied the development of techniquesand procedures aimed at the definition of the spatialprediction of erosion and deposition rates across acatchment. In this paper using terrain data measuredon an experimental basin in southern Italy, asensitivity analysis on different GIS-basedmethodologies for the estimate of a Length-Slope factorhas been developed with the aim of determining whichof these is more reliable for spatial erosion riskassessment. Specifically, by using the unit stream powertheory, different estimates are shown, depending on thescheme adopted to represent the hydrological andtopographic three-dimensional effects inside theLength-Slope factor. The performances of theprocedures analysed have been evaluated through theinformation content of the corresponding spatialdistributions, estimated as an entropy measure. Theresults obtained have shown that among the approachesutilised to describe the routing of the surface runoffalong the hillslope profiles, the two-dimensionalscheme appeared to be more realistic both on divergingand converging surfaces. Such a scheme, during thecomputational phases also aimed at distinguishing the areasof the basin experiencing net erosion from those areasexperiencing net deposition, resulted, being inaccordance with on-site investigations.     

人影高炮作业落区的一种判定方法

提出了人影高炮弹丸轨迹的运动方程,根据方程计算理论弹丸落点并得出安全区外扩的误差范围。针对人影高炮作业射界设定安全区的情况,提出落点位于安全区内外的判定方法,从而在理论上给出判断人影高炮作业安全性的问题。     

Gully morphological characteristics in the loess hilly‐gully region based on 3D laser scanning technique

Gully morphology characteristics can be used effectively to describe the status of gully development. The Chabagou watershed, located in the hilly‐gully region of the Loess Plateau in China, was selected to investigate gully morphological characteristics using a 3D laser scanning technique (LIDAR). Thirty‐one representative gullies located at different watershed locations and gully orders were chosen to quantitatively describe gully morphology and establish empirical equations for estimating gully volume based on gully length and gully surface area. Images and point cloud data for the 31 gullies were collected, and digital elevation models (DEMs) with 10‐cm resolution were generated. ArcGIS 10.1 was then used to extract fundamental gully morphological parameters covering gully length (L), gully width (W_T) and gully depth (D), and some derivative morphological parameters, including gully head curvature (C), gully width–depth ratio (w/d), gully bottom‐to‐top width ratio (W_B/W_T), gully surface area (A_g) and gully volume (V_g). The results indicated that gullies in the upper watershed and the second order were more developed based on their high values of gully head curvature. The potential for gully development increased from the second order to the fourth order. Within the same gully orders, gullies in the lower watershed were more active with more development potential. A method for differentiating between gully head and gully sidewalls based on the gully head curvature value was proposed with a mean relative error of 8.77%. U‐shaped cross‐sections were widely distributed in the upper watershed and upper positions of a gully, while V‐shaped cross‐sections were widely distributed in the lower watershed and lower positions of a gully. V–L and V–A_g empirical equations with acceptable accuracy were established and can be used to estimate gully erosion in the Loess hilly‐gully region. Copyright © 2017 John Wiley & Sons, Ltd.     

利用EMD和子波振幅谱与相位谱关系的时变子波提取方法

本文首先分析了地震波在黏弹介质的传播规律,基于黏弹介质地震波动方程总结了时变子波振幅谱和相位谱的关系,从而得出结论,准确估计子波相位谱初值和不同时刻的子波振幅谱是实现时变子波准确提取的必要条件.在此基础上,针对传统方法限制子波振幅谱形态且受限于分段平稳假设的问题,提出了一种利用EMD(Empirical Mode Decomposition)和子波振幅谱与相位谱关系的时变子波提取方法,根据子波对数振幅谱光滑连续而反射系数对数振幅谱振荡剧烈的特点,采用EMD方法将不同时刻地震记录的对数振幅谱分解为一组具有不同振荡尺度的模态分量,通过滤除振荡剧烈分量、重构光滑连续分量提取时变子波振幅谱;再应用子波振幅谱和相位谱的关系提取时变子波相位谱,将分别提取的振幅谱和相位谱逐点进行合成,最终实现时变子波的准确提取.本文方法不需要求取Q值,适用于变Q值的情况,具有良好的抗噪性能.数值仿真和叠后实际资料处理结果表明,相比传统的分段提取方法,利用本文方法提取的时变子波准确度更高,研究成果对提高地震资料分辨率具有重要意义.     

射线类偏移成像中的模型平滑处理研究

本文从能量泛函的角度着手,基于速度梯度,采用最速下降法推导了基于偏微分方程的速度模型平滑公式,用于解决射线类偏移成像过程当中速度模型的平滑处理问题.同时针对偏微分方程速度模型平滑系数中阈值k的选取对速度模型空间结构的影响,在简单的高速体速度模型上分析了不同k值的选取对原始速度模型空间结构的改变,并通过射线路径和时间场的对比分析证明偏微分方程速度模型平滑处理相对于卷积算子平滑的优越性.最后通过在Marmousi、Sigsbee2A原始速度模型以及平滑处理后的速度模型上的成像结果分析验证偏微分方程模型平滑的有效性.     

低信噪比地震资料FDOC-seislet变换阈值消噪方法研究

地震数据本质上是时变的,不仅有效同相轴表现出确定性信号的时变特征,而且复杂地表和构造条件以及深部探测环境总是引入时变的非平稳随机噪声.标准的频率-空间域预测滤波只适合压制平面波信号假设下的平稳随机噪声,而处理非平稳地震随机噪声时,需要将数据体分割为小窗口进行分析,但效果不够理想,而传统非预测类随机噪声压制方法往往适应性不高,因此开发能够保护地震信号时变特征的随机噪声压制方法具有重要的工业价值.压缩感知是近年出现的一个新的采样理论,通过开发信号的稀疏特性,已经在地震数据处理中的数据插值以及噪声压制中得到了应用.本文系统地分析了压缩感知理论框架下的地震随机噪声压制问题,建立了阈值消噪的数学反演目标函数;针对时变有效信息具有的可压缩性,利用有限差分算法求解炮检距连续方程,构建有限差分炮检距连续预测算子(FDOC),在seislet变换框架下,提出一种新的快速稀疏变换域———FDOC-seislet变换,实现地震数据的高度稀疏表征;结合非平稳随机噪声不可压缩的特征,提出了一种整形迭代消噪方法,该方法是一种广义的迭代收缩阈值(IST)算法,在无法计算稀疏变换伴随算子的条件下,仍然能够对强噪声环境中的时变有效信息进行有效恢复.通过对模型数据和实际数据的处理,验证了FDOC-seislet稀疏变换域随机噪声迭代压制方法能够在保护复杂构造地震波信息的前提下,有效地衰减原始数据中的强振幅随机噪声干扰.     

基于非结构化网格的边界积分方程方法的断层自发破裂模拟

地震自发破裂模拟是震源动力学研究的重要内容,了解复杂的断层动力学破裂过程对深入认识震源特征和解释运动学反演结果具有重要意义.基于边界积分方程方法的破裂模拟已经被广泛使用,大多采用的是平面断层模型的结构化网格划分.由于实际的断层往往具有较为复杂的几何特征,为了更为灵活地刻画断层几何复杂性,我们建立断层模型的三角形网格离散方案,通过精确的解析解形式来计算断层各个单元之间的应力格林函数,联立滑动弱化摩擦准则和非奇异边界积分方程,对断层的自发破裂过程进行了模拟.在简单的平面断层模型下,将计算结果与前人的结果进行了对比,验证了方法的正确性与有效性.对于几种常见的复杂断层模型,例如弯折、阶跃、含障碍体断层等,我们模拟了其破裂过程并对计算结果进行了比较与分析.模拟结果表明,非结构化网格划分的边界积分方程方法能够很好地模拟平面矩形断层或由其组成的规则断层,同时也能成功地模拟具有复杂几何形状的不规则断层上的动力学破裂过程.本研究的结果显示了边界积分方程方法在模拟复杂断层系统的动力学破裂问题上具有较广阔的应用前景.     

基于多重网格预条件求解平均导数法离散的Helmholtz方程

有限差分法求解Helmholtz方程,依赖于两点:1差分格式的构造;2高效的求解算法.本文采用平均导数法离散Helmholtz方程.该差分格式有三点好处:1能适用于横纵不等间距采样;2在完全匹配层区域(PML),差分方程与微分方程逐点相容;3能将一个波长内的采样点数减少至少于4.求解离散的Helmholtz方程的算法一般分为直接法和迭代算法.直接法由于内存需求太大而无法适用于大规模问题;基于Krylov子空间的迭代方法结合多重网格预条件算法是一种快速高效求解方法,然而对于横纵不等间距采样(在多重网格中称为各向异性问题),经典的多重网格方法失效.本文分析了经典多重网格的三个重要组成部分:完全加权限制算子,点松弛技术以及双线性延拓算子,进而采用了半粗化技术代替全粗化技术,线松弛技术代替点松弛技术以及依赖差分算子的延拓算子代替双线性延拓算子,使得各向异性问题变得收敛;而且对于非均匀介质中-低频率的迭代问题,我们获得了较为满意的收敛速度.     

虚拟波动域三维海洋可控源电磁场正演模拟

本文基于对应原理将似稳态条件下频率域电磁场扩散方程转换成虚拟波动域电磁场波动方程,采用高阶时域有限差分进行求解,引入复频移完全匹配层吸收边界条件,降低了内存需求,提高了计算效率,并在虚拟波动域用伪δ函数离散电偶极源,实现了虚拟波动域任意取向电偶极源三维海洋可控源电磁场高阶时域有限差分正演算法.通过与拟解析解和频率域三维可控源电磁场数值模拟结果的对比,验证了本文算法的正确性和高效性,且探讨了网格参数和边界条件对不同频率电磁场模拟结果的影响.