Three-dimensional topography corrections of magnetotelluric data

Topographic effects due to irregular surface terrain may prevent accurate interpretation of magnetotelluric (MT) data. Three-dimensional (3-D) topographic effects have been investigated for a trapezoidal hill model using an edge finite-element method. The 3-D topography generates significant MT anomalies, and has both galvanic and inductive effects in any polarization. This paper presents two different correction algorithms, which are applied to the impedance tensor and to both electric and magnetic fields, respectively, to reduce topographic effects on MT data. The correction procedures using a homogeneous background resistivity derived from a simple averaging method effectively decrease distortions caused by surface topography, and improve the quality of subsurface interpretation. Nonlinear least-squares inversion of topography-corrected data successfully recovers most of structures including a conductive or resistive dyke.     

波流耦合下保守污染物迁移扩散的模拟研究

基于三维潮流和谱波浪模型,以及输移扩散模型和拉格朗日粒子追踪模型,构建了波流耦合下保守污染物的迁移扩散模型。模型基于非结构化网格,对近岸复杂岸线有很好的拟合,可用于大范围波流耦合计算。运用所建的耦合模型研究了旅顺港内外的潮流变化、波生流场、保守污染物输移、粒子运动、以及新水道对湾内污染物迁移的影响,模拟的潮流场与实测数据吻合较好。结果表明:潮流会在湾内近湾口处形成一逆时针涡,波浪对湾内影响较小,但波生流会改变湾口流场分布;在湾内处于涡中的水体潮流自净能力较强,而湾中及湾底则较弱,SE向波浪会降低湾内水体的自净能力;新潮流通道的开挖,会显著改善水体的自净能力,尤其对湾底浅水区域作用明显。     

Third-Order Stokes Wave Solutions of the Free Surface Capillary-Gravity Wave and the Interfacial Internal Wave

Based on the Stokes wave theory, the capillary-gravity wave and the interfacial internal wave in two-layer constant depth''s fluid system are investigated. The fluids are assumed to be incompressible, inviscid and irrotational. The third-order Stokes wave solutions are given by using a perturbation method. The results indicate that the third-order solutions depend on the surface tension, the density and the depth of each layer. As expected, the first-order solutions are the linear theoretical results (the small amplitude wave theoretical results). The second-order and the third-order solutions describe the nonlinear modification and the nonlinear interactions. The nonlinear impact appears not only in the n (n≥2) times'' high frequency components, but also in the low frequency components. It is also noted that the wave velocity depends on the wave number, depth, wave amplitude and surface tension.     

Evaluation of pullout load capacity of suction caissons in sand using a three-dimensional displacement approach

An investigation was conducted to obtain analytical solutions for the pullout behavior of a suction caisson undergoing inclined loads in sand. The inclined load is transformed into an equivalent load system in which the vertical, horizontal, and moment loads are applied on the center of the lid of the suction caisson. The vertical and lateral stiffness coefficients along the skirt of the suction caisson in sands are presented using the new three-dimensional elastic solutions taking into account the nonhomogeneous and nonlinear properties of the sand. The vertical, lateral, and rocking stiffness coefficients on the base of the suction caisson are presented considering the solutions of a hollow rigid cylindrical punch acting on the surface of a soil. The yield, pullout, and failure for sands with the nonhomogeneous and nonlinear characteristics are taken into consideration. The effects of the load inclination, the loading depth, and the aspect ratio on the pullout load capacity of the suction caisson are presented. Behaviour of the suction caisson in sand prior to failure is clarified from the relationship between tensile load, displacement, and rotation and that between depth, vertical pressure, and lateral pressure.     

分析土和结构相互作用的一种实用耦合方法

提出一种新的数值解与解析解耦合的理论和计算方法,研究土-结构相互作用(SSI)体系的地震动力响应。采用大型有限元软件OpenSees模拟复杂结构的非线性行为,用等效线弹性频域内解析解模拟地基土的行为,使用时域离散递归方法将频域内的解析解转化到时域内,再通过子结构边界上力和位移的协调条件来求解。二者之间的耦合和实时数据交流通过CS集成方法来实现。以一个单自由度算例和一个实际工程为例,验证此方法的精度、稳定性和工程实用性,对比在考虑和不考虑SSI体系情况下结构动力响应的区别。本文所提的耦合SSI计算方法和部分研究成果可为工程设计人员提供参考。     

Analytical model of well leakage pressure perturbations in a closed aquifer system

Deep saline aquifers are commonly used for disposal and storage of various surface fluids. The target injection zone must be hydraulically isolated from overlying zones in order to ensure containment of the injected fluids. Improperly plugged nonoperational abandoned wells that penetrate the injection zone are the main potential leakage pathways. Leakage through such wells may cause an observable pressure signal in a zone overlying the injection zone; such a signal can be used to detect the leakage. In this paper we develop an analytical model to evaluate the pressure change induced by leakage through a well in a multilayer system. Unlike previous analytical models on the topic, our model uses a closed system, which may significantly affect the strength and behavior of the pressure signal induced by leakage. The analytical model is first presented for a two-layer system centered at the leaky well location. We evaluate the leakage-induced pressure change using the Laplace transform of Duhamel’s superposition integral, yielding the solution in the Laplace domain. We then derive a late-time asymptotic solution using the final value theorem, which suggests that the leakage rate becomes constant after sufficient time. We then obtain the multilayer solution by extending the two-layer solution and presenting it in matrix form in the Laplace domain. We apply the solution to three examples. In the first example, we apply the analytical model to a two-layer system, investigating its behavior and comparing the results with a numerical solution. In order to demonstrate behavior and potential applications of the multilayer analytical model, we present two multilayer examples: one with identical layers and another, replicating a CO₂ storage site, with dissimilar layers. The leakage-induced pressure change does not necessarily decrease as the distance increases from the injection zone toward the surface.     

2010年6月广西凌云-凤山交界3级震群应力水平分析

2010年6月28日至8月15日,在广西凌云与凤山交界持续发生了高密集、高集中、高频率的震群活动,共记录地震3 071次,其中ML2~2.9级地震41次,3级以上地震3次,最大为7月1日10时27分3.2级地震。对此次震群的空间分布范围、2级以上地震震源机制解P轴优势方向、b值特征、应力降等进行了分析研究。结果表明,此次震群震中集中,深度较浅,震源机制解P轴没有形成优势分布,序列参数b值较高,约为1.21,应力降主要分布在0.19~2.0 Mpa之间,认为广西凌云-凤山交界3级震群是属于低应力背景下的地震活动,不具有前兆震群和前震序列的性质。分析结果对正确了解此次震群的特征、正确判断地震趋势具有一定的帮助作用。     

中国前新生代残留盆地油气勘探难点分析及对策

中国50年油气勘探的历程主要在新生代陆相生油的指导思想下,发现了大庆、胜利等大油田,取得了辉煌的成就,形成了一套针对新生代陆相断陷湖盆油气勘探的理论与方法.时至今日,能源的增长已远远跟不上经济的高速发展,提出“油气二次创业”,前新生代海相残留盆地就是主战场.残留盆地的勘探难点集中在三方面,一是勘探思路局限,二是勘探程度低,三是勘探技术的限制;根据这些难点提出5项对策来解决残留盆地的勘探问题.     

似水准椭球

提出了“似水准椭球”概念,给出了“似水准椭球”的“匀质分层”、“整体纬向”和“内匀外纬”3种模式的密度分布方式。针对“似水准椭球”密度分布的合理性和稳定性问题,初步提出了求解“似水准椭球”的拉格朗日函数和哈密顿积分的设想。     

气候模式模拟中海量数据的并行抽取与可视化分析诊断

在地球动力学和气候模拟等领域, 数值模拟产生的数据规模达到Tb至Pb量级。 实现这些海量数据的实时可视化和实时诊断分析面临很大的困难, 时空多尺度数据抽取可以解决这一瓶颈。 高精度数据的可视化结果展示需要高分辨率的显示设备, 并行的大屏幕显示技术是解决这一问题的有效手段。 地球科学数值模拟、 并行数据抽取和高分辨率显示都需要搭建高性能计算机集群。 本文在基于Lagrange插值的多维度、 多尺度、 多分辨率并行数据抽取算法的同时, 利用并行计算节点及LCD显示器, 基于Rocks cluster系统搭建起一个176核, 4×10×1024×1280分辨率的高性能计算模拟、 数据抽取和并行显示输出的集成平台, 并将该平台成功应用到气候模式模拟产生的海量数据的并行抽取和并行显示。