大地电磁场三维地形影响的数值模拟

用边界单元法解决了大地电磁(MT)三维地形影响的数值模拟问题.采用特殊的网格剖分,数值模拟方法,可以在微机上运行.在二维地形上,其结果与二维模拟结果基本吻合,对三维地形的模拟结果表明,三维模拟与二维模拟有较大差别.     

基于ArcEngine的应急三维可视化系统设计与实现

提出余震序列动态模拟及三维地形可视化功能的实现方法和关键技术,以ArcEngine为开发组件,实现数据管理、专题查询、余震地震序列动态模拟、地形分析、三维浏览显示等功能,建立基于ArcEngine的应急三维可视化系统.在2011年云南缅甸7.2级地震、盈江5.8级地震应急响应中,系统在余震序列动态模拟生成、三维地形模拟显示、影响场破裂方向初判及宏观震中判定上取得良好效果.     

三维地形频率域人工源电磁场的边界元模拟方法

提出了一种用边界元法计算频率域人工源三维地形电磁场的数值模拟方法.首先用矢量积分理论和电磁场边界条件，将上半空间（空气）和下半空间（地下介质）两个区域电磁场边值问题变为仅对地形界面的两个矢量面积分方程.然后将对地形界面的积分剖分为一系列的三角单元积分.在三角单元积分中，假设单元中电磁场为无限大气空间电磁场与地形影响的叠加,并假设地形影响为常项,这样既保证了计算精度又使得计算方法简便.通过分解和计算，每一个矢量面积分方程分解为对应三个坐标方向的三个常量线性方程，这些线性方程组成了对角占优的线性方程组，可用SSOR方法求解.文中给出了垂直磁偶源的垂直磁场地形影响的例子.     

基于有限差分正演的带地形三维大地电磁反演方法

本研究实现了一套基于有限差分（FD）方法的大地电磁测深数据带地形三维反演算法及代码.其中,在大地电磁场正演数值模拟方面,开发了起伏地形条件下基于交错网格剖分、有限差分方法的大地电磁测深三维正演代码;在满足平面波场假设的前提下,使用长方体网格剖分模拟三维起伏地形,实现了带地形三维正演计算;并设计理论模型进行试算,经试算结果与前人的有限元法计算结果对比,验证了所研发的带地形三维正演计算的正确性与可靠性.在反演方面,本研究基于非线性共轭梯度方法编写了大地电磁测深带地形三维反演代码,试验了不同的共轭梯度搜索因子β,避免了目标函数对海森矩阵（参数二次导数矩阵）的显式计算和存储,初步实现了大地电磁资料的带地形三维反演.最后,对一系列理论模型进行正演计算,利用其生成的合成数据模拟实测数据进行反演,并与现有的不带地形大地电磁测深三维反演结果比较,检验了所研发的带地形三维反演计算的可靠性与稳定性.     

考虑海底地形的三维频率域可控源电磁响应有限体积法模拟

为了提高海洋可控源电磁的地形响应模拟精度,探讨了三维交错网格剖分有限体积法求解频率域电磁场解的数值方法.在似稳场近似条件下,推导了有限差分法和有限体积法低频电磁场控制方程的离散表达式.通过对离散表达式的分析比较表明,有限体积法较之有限差分具有更高的计算精度,同时也具有与有限差分相当的计算效率.对含地形界面网格单元电导率采用加权平均处理,通过与二维有限元程序的计算结果对比,验证了该方法可以有效提高有限体积法对地形变化的模拟精度.应用有限体积法计算了一个三维带地形储层模型的可控源电磁响应,分析表明地形变化对电场分量影响明显,磁场分量对地形变化不敏感.     

基于非结构网格的电阻率三维带地形反演

地表起伏地形在野外矿产资源勘察中不可避免,其对直流电阻率法勘探影响巨大.近年来,电阻率三维正演取得诸多进展,特别是应用非结构网格我们能够进行任意复杂地形和几何模型的电阻率三维数值模拟,但面向实际应用的起伏地形下电阻率三维反演依然困难.本文基于非结构化四面体网格,并考虑到应用GPS/GNSS时,区域地球物理调查中可非规则布设测网的实际特点,实现了任意地形(平坦或起伏)条件下、任意布设的偶极-偶极视电阻率数据的不完全Gauss-Newton三维反演.合成数据的反演结果表明了方法的有效性,可应用于复杂野外环境下的三维电法勘探.     

三维复杂山谷地形SV波垂直输入地震反应分析

本文基于显式有限元法研究了地震波垂直入射时三维复杂山谷地形对地震地面运动的影响,在数值分析中应用了三维化二维的解法和黏弹性人工边界的处理方法,实现了地震波垂直输入下三维复杂场地地震动数值模拟,并验证了该方法的合理性.以四川桃坪地区一山谷地形作为研究对象,基于地表高程数据分别建立了二维和三维场地模型,对比研究表明:在复杂地形情况下考虑二、三维模型时具有明显差异,三维模型能更真实地反映地形变化对地震动的影响,复杂地形条件下有必要考虑三维实际场地模型.本文对边界自由场的处理方法也可用于处理三维复杂场地地震动斜入射问题,为三维复杂地形场地地震效应研究提供参考.     

基于潮波运动三维数值模拟的海洋连续深度基准面建立方法研究

海洋深度基准作为海洋深度起算的垂直基准,对海洋大地测量、海洋物理调查等科研活动具有重要意义.鉴于传统的海洋深度基准面存在离散、非连续等缺陷,本文开展了基于潮波运动三维数值模拟的海洋连续深度基准面构建方法研究.研究结果显示,本文采用的有限体积的海岸海洋三维潮波运动模式FVCOM,具有构建三角格网灵活,可精确适用于不规则海岸边界的特点,并在地形特征较典型区域——长江口南支水域为实验区,开展了三维潮波运动的数值模拟.模拟所得各个格网节点处的平均潮差较好地符合了当地潮汐动力作用变化的规律,并以平均潮差为基础进一步建立了连续深度基准面,同南支区域6个已知深度基准的长期验潮站相比,深度基准面最大差值为5.5 cm,差值绝对值均值为2.6 cm,模拟结果内符合精度较高;且整个模拟所得的南支深度基准面的变化规律更符合长江口南支的潮汐变化特征.本文思想为海洋连续垂直基准的建立提供了一种新的思路,相比较于传统的几何插值拟合法,本文方法更具合理性和可靠性.     

海洋可控源电磁三维非结构矢量有限元数值模拟

本文实现了海洋可控源电磁三维矢量有限元数值模拟.由于采用非结构四面体单元进行三维网格剖分,该方法可以模拟复杂电性异常体和海底地形.一维模型的数值模拟结果表明,电场实、虚部均与解析解吻合得相当好,计算误差基本小于1%.二维模型的计算结果与已有的二维自适应非结构有限元模拟结果吻合很好.带地形模型的数值模拟结果显示,海底地形对电场影响很大,有可能掩盖海底油气藏产生的异常.     

强地面运动数值模拟中三维物理模型的建立方法——以昆明盆地为例

基于活动断层的地震危害性综合评价可为城市规划和工程建设提供科学依据, 强地面运动数值模拟则是进行地震危害性预测和评价的重要方法, 而建立以第四系为主体的符合真实地层结构的三维物理模型是保证数值模拟结果可靠性的必要条件之一. 本文以昆明盆地为例, 综合利用地震地质、钻孔、地形地貌、DEM、地震勘探、波速测试等资料,以剪切波速为主要分层指标,参考地层层序, 结合ArcGIS等多种软件和相关的编程技术,采用将相邻介质分界面（层网）在深度方向上逐层叠加的方法建立三维物理模型;详细阐述了建立三维物理模型的主要技术思路和实现过程, 同时建立三维物理模型的数据库,为强地面运动数值模拟提供模型数据和参数. 文中还针对不同类型的探测、实验数据,总结了相应的技术处理方法和需要注意的问题.      

Application of 3D hydrodynamic and particle tracking models for better environmental management of finfish culture

Hydrographic conditions, and particularly current speeds, have a strong influence on the management of fish cage culture. These hydrodynamic conditions can be used to predict particle movement within the water column and the results used to optimise environmental conditions for effective site selection, setting of environmental quality standards, waste dispersion, and potential disease transfer. To this end, a 3D hydrodynamic model, MOHID, has been coupled to a particle tracking model to study the effects of mean current speed, quiescent water periods and bulk water circulation in Mulroy Bay, Co. Donegal Ireland, an Irish fjard (shallow fjordic system) important to the aquaculture industry. A Lagangrian method simulated the instantaneous release of “particles” emulating discharge from finfish cages to show the behaviour of waste in terms of water circulation and water exchange. The 3D spatial models were used to identify areas of mixed and stratified water using a version of the Simpson-Hunter criteria, and to use this in conjunction with models of current flow for appropriate site selection for salmon aquaculture.The modelled outcomes for stratification were in good agreement with the direct measurements of water column stratification based on observed density profiles. Calculations of the Simpson-Hunter tidal parameter indicated that most of Mulroy Bay was potentially stratified with a well mixed region over the shallow channels where the water is faster flowing. The fjard was characterised by areas of both very low and high mean current speeds, with some areas having long periods of quiescent water. The residual current and the particle tracking animations created through the models revealed an anticlockwise eddy that may influence waste dispersion and potential for disease transfer, among salmon cages and which ensures that the retention time of waste substances from cages is extended.The hydrodynamic model results were incorporated into the ArcView^TM GIS system for visualisation and interrogation of results and to allow effective holistic environmental management and site selection for fish cage aquaculture.     

预应力锚杆(索)框架梁加固边坡的仿真试验分析

采用数值仿真试验方法研究了预应力锚杆框架梁支护体系中框架梁和锚杆的受力特点,为地震引发滑坡灾害的防治提供依据.研究结果表明:框架梁的弯矩在锚头处取得最大值, 且随锚固预应力的增加而增大,但并不呈线性关系;即使在相同土质条件和同一锚固预应力作用下,坡脚处框架梁的弯矩要高于坡顶;此外,锚杆的预应力均存在一定的损失,施加的预应力值越高,预应力损失越大,且坡脚锚杆的预应力损失比坡顶小.     

Experimental study on three dimensional movements of particles Ⅱ Effects of particle diameter on turbulence characteristics

Based on the 3D PTV （Particle Tracking Velocimetry） measuring system, the 3D movement characteristics of particles with four different diameters were investigated. Under specific flow conditions, the impact of particle diameters on 3D motion of particles was studied, and the turbulence characteristics were analyzed by different statistical methods. The results showed that the turbulence intensity of coarse particle decreased as the diameter increased. In near wall region, the probability density distributions of longitudinal and vertical fluctuation velocities both deviated from the normal distribution; while in the outer region, the probability density distribution of vertical fluctuation velocity approximately agreed with the normal distribution.     

How soil texture,channel shape and cross-sectional area affect moisture dynamics and water loss in irrigation channels

To enhance the utilization efficiency of farmland irrigation water and reduce the leakage of water conveyance channels, the leakage process of channels was simulated dynamically. The simulated results were compared with data measured in laboratory experiments, and the performance of the model was evaluated. The results indicated that the simulated values of the model were consistent with the observation values, and the R² values varied between 0.91 and 0.99. In addition, based on the laboratory experiments, a water supply system (Mariotte bottles) and soil box were built using plexiglass. Three influencing factors, namely, the channel form, soil texture and channel cross-sectional area, were varied to observe and calculate the resulting cumulative infiltration amount, infiltration rate and wetting front migration distance. HYDRUS-3D software was used to solve the three-dimensional soil water movement equation under different initial conditions. The results demonstrated that the U-shaped channel was more effective than the trapezoidal channel in increasing the utilization efficiency of the water resources. A U-shaped channel with a small channel cross-sectional area should be adopted and the soil particle size should be prioritized in the construction of water conveyance channels for farmlands. The simulation results were in agreement with the observed results, which indicates that HYDRUS-3D is a reliable tool that can accurately simulate the soil moisture movement in water conveyance channels. The research results can provide a reference for the design and operation of farmland irrigation systems.     

Particle tracking experiments in match-index-refraction porous media

A low-cost, noninvasive, three-dimensional (3D), particle tracking velocimetry system was designed and built to investigate particle movement in match-index-refraction porous media. Both a uniform load of the glass beads of the same diameter and a binary load of the glass beads of two diameters were used. The purpose of the experiments is to study the effect of the two loads on the trajectories, velocity distribution, and spreading of small physical particles. A total of 35 particles were released and tracked in the uniform load and 46 in the binary load. The 3D trajectory of each particle was recorded with two video camcorders and analyzed. It is found that the particle's velocity, trajectory, and spreading are very sensitive to its initial location and that the smaller pore size or heterogeneity in the binary load increases the particles' velocity and enhances their spreading as compared with the uniform load. The experiments also verified the previous finding that the distribution of the particle velocities are lognormal in the longitudinal direction and Gaussian in two transverse directions and that the particle spreading is much larger along the longitudinal direction than along the traverse directions.     

NUMERICAL STUDY ON THE MIXING OF UNSORTED SEDIMENT PARTICLES DISCHARGED INTO A CROSS-FLOW BY MULTIPHASE PARTICLE-IN-CELL （MP-PIC） METHOD

The mixing characteristics of dredged sediments of variable size discharged into cross-flow are studied by an Eulerian-Lagrangian method. A three-dimensional (3D) numerical model has been developed by using the modified k-ε parameterization for the turbulence in fluid phase/water and a Lagrangian method for the solid phase/sediments. In the model the wake turbulence induced by sediments has been included as additional source and sink terms in the k-ε model; and the trajectories of the sediments are tracked by the Lagrangian method in which the sediment drift velocities in cross-flow are computed by a multiphase particle-in-cell (MP-PIC) method and the diffusion process is approximated by a random walk model. The hydrodynamic behavior of dumped sediment cloud is governed by the total buoyancy on the cloud, the drag force on each particle and velocity of cross-flow. The cross-flow destroys more or less the double vortices occurred in stagnant ambience and dominates the longitudinal movement of sediment cloud. The computed results suggest satisfactory agreement by comparison with the experimental results of laboratory.     

基于非降阶汉密尔顿算子的三维立体层析反演

不同于前人在射线中心坐标系下基于降阶汉密尔顿算子建立立体层析矩阵,本文详细讨论了在三维直角坐标系下,基于非降阶汉密尔顿算子通过射线扰动理论导出三维立体层析所需的数据空间对模型空间的一阶线性关系,进而建立三维立体层析矩阵.在建立这个庞大且稀疏的系数矩阵后,实施规则化使得该矩阵方程的求解能够收敛到一个合理的结果.理论数据的严格测试证实了三维立体层析矩阵建立的正确性,为实际应用奠定了理论基础.     

一种辐射成像三维可视化系统的实现

辐射成像技术在医疗诊断、无损检测和工业探伤领域有着重要的应用,三维可视化技术与辐射成像技术的结合有助于帮助人们以更直观和形象的方式对病灶和被检物进行检查,从而提供更为有效的信息和检查结果。本文介绍了一种基于辐射数据而构建的三维可视化系统的实现,通过系统分析和整体设计,模块级的实现、交互控制和界面设计等四个方面阐述了基本思路,对于辐射成像可视化系统的研究有一定的借鉴意义。     

基于空间连续性的4DCT图像排序算法研究

4DCT图像应用于肿瘤的放线治疗中,能够在全呼吸周期中定位肿瘤的运动,同时有效地减少运动伪影的产生。目前,4DCT在临床应用中需要依靠外部呼吸信号检测装置提供呼吸信号运动信息。本文提出了一种4DCT自动图像排序算法,不需要外部呼吸监测装置,在Cine扫描模式下采集图像数据,从第一个床位开始,利用空间连续性特征,寻找相邻床位之间呼吸相位相同的图像,将其归入相应的图像集合中,以此类推,直到全部床位的图像都归入到相应相位的图像集合中,构成4DCT重建所需要的图像数据集合。本文的算法应用于呼吸体模数据和临床图像数据,观察三维重建图像和冠状面重组图像。对比单独使用的三维重建算法,本算法较好地消除了呼吸运动伪影,能够清楚观察到模拟肿瘤的运动和器官在呼吸运动过程中的变化情况。     

Modeling surface and ground water mixing in the hyporheic zone using MODFLOW and MT3D

We used a three-dimensional MODFLOW model, paired with MT3D, to simulate hyporheic zones around debris dams and meanders along a semi-arid stream. MT3D simulates both advective transport and sink/source mixing of solutes, in contrast to particle tracking (e.g. MODPATH), which only considers advection. We delineated the hydrochemically active hyporheic zone based on a new definition, specifically as near-stream subsurface zones receiving a minimum of 10% surface water within a 10-day travel time. Modeling results indicate that movement of surface water into the hyporheic zone is predominantly an advective process. We show that debris dams are a key driver of surface water into the subsurface along the experimental reach, causing the largest flux rates of water across the streambed and creating hyporheic zones with up to twice the cross-sectional area of other hyporheic zones. Hyporheic exchange was also found in highly sinuous segments of the experimental reach, but flux rates are lower and the cross-sectional areas of these zones are generally smaller. Our modeling approach simulated surface and ground water mixing in the hyporheic zone, and thus provides numerical approximations that are more comparable to field-based observations of surface–groundwater exchange than standard particle-tracking simulations.