On the calculation of cumulative strain around full‐flow penetrometers in steady‐state conditions

An approximate solution for the effects of high strain rates, and gradual strength degradation, on the penetration resistance of penetrometers can be obtained by combining the strain‐path method with the classical upper bound theorem. The stream path calculations require the integration of the material constitutive equation along the streamlines. Unless the geometry is simple so that the integration can be evaluated analytically, numerical procedures are required to backtrack streamlines. The strain at any location is calculated by finding the streamline that passes through the given point and integrating the strain rate along that streamline from its inlet boundary. Thus, the calculations can be complicated, and errors can be accumulated during the calculation procedure. This paper presents an efficient approach for evaluating cumulative strains around penetrometers without the need to backtrack individual streamlines. In this approach, the strain components are treated as field variables. The global solution is obtained using the streamline upwind Petrov–Galerkin method. The new method together with an Eulerian‐based finite element formulation was used to study the cone penetration test and evaluate the effect of strain softening on the cone resistance. Copyright © 2014 John Wiley & Sons, Ltd.     

Pathline tracing on fully unstructured control-volume grids

The trend toward unstructured grids in subsurface flow modeling has prompted interest in the issue of streamline or pathline tracing on unstructured grids. Streamline tracing on unstructured grids is problematic because a continuous velocity field is required for the calculation, while numerical solutions to the groundwater flow equations provide velocity in discretized form only. A method for calculating flow streamlines or pathlines from a finite-volume flow solution is presented. The method uses an unconstrained least squares method on interior cells and a constrained least squares method on boundary cells to approximate cell-centered velocities, which can then be continuously interpolated to any point in the domain of interest. Two-dimensional tests demonstrate that the method correctly reproduces uniform and corner-to-corner flow on fully unstructured grids. In three dimensions using regular hexahedral grids, the method agrees well with established semianalytical methods. Tests also demonstrate that the method produces physically realistic results on fully unstructured three-dimensional grids.     

The impact of groundwater velocity fields on streamlines in an aquifer system with a discontinuous aquitard (Inner Mongolia,China)

Many numerical methods that simulate groundwater flow, particularly the continuous Galerkin finite element method, do not produce velocity information directly. Many algorithms have been proposed to improve the accuracy of velocity fields computed from hydraulic potentials. The differences in the streamlines generated from velocity fields obtained using different algorithms are presented in this report. The superconvergence method employed by FEFLOW, a popular commercial code, and some dual-mesh methods proposed in recent years are selected for comparison. The applications to depict hydrogeologic conditions using streamlines are used, and errors in streamlines are shown to lead to notable errors in boundary conditions, the locations of material interfaces, fluxes and conductivities. Furthermore, the effects of the procedures used in these two types of methods, including velocity integration and local conservation, are analyzed. The method of interpolating velocities across edges using fluxes is shown to be able to eliminate errors associated with refraction points that are not located along material interfaces and streamline ends at no-flow boundaries. Local conservation is shown to be a crucial property of velocity fields and can result in more accurate streamline densities. A case study involving both three-dimensional and two-dimensional cross-sectional models of a coal mine in Inner Mongolia, China, are used to support the conclusions presented.     

Hydrodynamic characterization and flocculation process in helically coiled tube flocculators: an evaluation through streamlines

This paper presents a hydrodynamic characterization of helically coiled tube flocculators (HCTFs) through streamline analysis and an efficiency evaluation of the flocculation process in these units. Physical experiment and CFD modeling allowed to relate flocculation process (estimated indirectly by analyzing turbidity removal efficiency for low turbidity values and low Reynolds numbers) and hydrodynamic characteristics observed along the unit (represented in this study by streamlines). This work analyzes streamline features and proposes the use of a new global hydrodynamic parameter \(\overline{{E_{\text{k}} }}\), concerning the average specific kinetic energy in a representative streamline of the unit, aiming to compare hydrodynamic characteristics in units with distinct hydraulic and geometric characteristics. Results show that this parameter has a strong adherence with the maximum turbidity removal efficiency observed in HCTFs. Moreover, it was possible to define an optimum range of velocity variation cycles in the representative streamline to achieve the maximum turbidity removal efficiency. This result indicates that knowledge of HCTFs streamlines’ characteristics can support the rational design of this type of unit.     

Effect of roughness on water flow through a synthetic single rough fracture

A single fracture is usually idealized theoretically as smooth parallel plates, but the real fractures are rough-walled with points of contact. Though relative roughness is considered in quantifying the flow through a single rough fracture (SRF) previously, additional factors such as the distribution of rough elements and bending degree of streamlines should be considered in order to obtain more accurate results. Semiempirical friction factor (f) and discharge per unit width (q) equations are first deduced taking relative roughness, roughness elements distribution and streamline reattachment length into consideration. A horizontal SRF model was then set up and a series of experiments and simulations were performed. Main conclusions are drawn: Recirculation of streamlines arises in the rough element and the intensity of the recirculation increases with the angle from which the streamlines enter into the rough elements and Reynolds number (Re); streamlines are discontinuously distributed when asperity height is large and nonlinear flow occurs; the nonlinearity of the flow increases with the increasing the asperity height and Re; the critical value of related roughness used to judge whether the influence of roughness on water flow through a SRF can be ignored or not should be much lower than 0.033; the revised f and q equations under laminar flow through a SRF are proved to be better when calculating the f and q values.     

全国地质资料目录服务中心异地负载均衡试验

目前全国地质资料目录服务中心系统处于单点运行,数据安全级别较低;利用现有的软硬件资源,通过部署智能DNS、反向代理服务器、Windows的DFS分布式文件系统、My SQL数据备份等,构建试验环境,实现数据的异地分布、负载均衡、备份和高可用。     

基于PC机群波动方程叠前深度偏移的并行计算策略

基于波动方程的叠前深度偏移技术是解决复杂地质地貌地区地震成像的一种非常有效的手段,但是在实际应用中面临着数据量巨大和计算量巨大的双重困难.以PC 机集群为硬件环境,以MPI消息传递并行编程环境为并行程序设计平台,研究设计出请求分配作业的主从模式来实现波动方程叠前深度偏移的并行计算,从而解决了动态负载均衡难题,采用的作业登记与分析技术解决了容错处理问题.理论模型数据和实际地震资料测试结果表明:程序运行稳定,并行效率高.对我国东部地区某三维地震数据进行了处理,用请求分配作业的主从模式比平均分配作业的主从模式节省了23.68%的时间.     

Influence of a low-viscosity layer between rigid inclusion and viscous matrix on inclusion rotation and matrix flow: A numerical study

We have used 2-D finite element modelling to investigate the influence of a permanent low-viscosity layer between matrix and inclusion on matrix flow and inclusion rotation under viscous simple shear flow. Rigid inclusions of different shape (circle, square, ellipse, lozenge, rectangle and skewed rectangles) and aspect ratio (R) were used. The calculated matrix flow pattern is neither bow tie nor eye-shaped. It is a new flow pattern that we call cat eyes-shaped, which is characterized by: (i) straight streamlines that slightly bend inwards at the inclusion's crests; (ii) elongate eye-shaped streamlines on each side of the inclusion; (iii) stagnation points in the centre of the eyes; (iv) absence of closed streamlines surrounding the inclusion; (v) changes in flow configuration with inclusion orientation; the lines of flow reversal bend and tilt, closed streamline circuits may disappear, and streamlines may bend outwards at the inclusion's crests.Concerning inclusion rotation, the numerical results show that: (i) a low-viscosity layer (LVL) makes inclusions with R = 1 rotate synthetically, but the rotation rate depends upon shape (circle or square) and orientation. Therefore, shape matters in the slipping mode. (ii) All studied shapes with R > 1 rotate antithetically when starting with the greatest principal axis (e₁) parallel to the shear direction ( = 0°); (iii) rotation is limited because there is a stable equilibrium orientation (_se) for all studied shapes with R > 1. (iii) There is also an unstable equilibrium orientation (_ue), and both _se and _ue depend upon inclusion's R and shape.The present numerical results closely agree with previous results of analogue experiments with a permanent low viscosity interface. Only minor deviations related with small shape differences were detected.     

Global Ocean Data Assimilation System Design and Algorithm Acceleration Based on Local Ensemble Transform Kalman Filter

An integrated analysis about computational time complexity of the Local Ensemble Transform Kalman Filter (LETKF) was performed. It is found that the calculation step of inverse matrix of the error covariance in ensemble space is the most computationally intensive and time consuming. In a parallel computing environment, the uneven distribution of CPU calculations in this step directly leads to low computational efficiency. To solve this problem, a new load balancing strategy was designed based on the "greedy algorithm". A high-performance parallel ocean data assimilation system based on the LETKF was developed and tested using this strategy. This system was based on the Parallel Ocean Program 2 (POP2) of the Community Earth System Model (CESM). The optimal interpolated sea surface temperature data (OISST) and Argo temperature profile data from January to February, 2004 were assimilated into the POP2. The results show that data assimilation effectively reduces the root mean square error of temperature and salinity. Using the new strategy, the exact same results are obtained but the computation time is reduced by half. At higher resolution (0.1°×0.1°),the computing performance is still doubled, indicating that this load balancing scheme is stable and reliable. In addition, the new method has high scalability and portability with great potential to be applied in operational forecasting.     

基于局地集合变换卡尔曼滤波的全球海洋资料同化系统设计及算法加速

通过对局地集合变换卡尔曼滤波(LETKF)算法的计算时间复杂度的完整分析,发现计算集合空间分析场误差协方差的逆矩阵这一过程计算量最大,耗时最长。且在并行计算环境下,该步骤CPU计算量分配不均是影响计算效率的直接原因。为解决这一问题,采用“贪心算法”设计了一套新的负载均衡策略,并使用该策略开发了一个基于LETKF和并行海洋模块2(POP2)的高性能并行海洋资料同化系统。将2004年1~2月日平均的最优插值海表温度资料(OISST)和同时期的Argo温盐剖面资料同化进入POP2。结果表明,同化有效降低了温度和盐度的均方根误差。同时,在不改变计算结果的前提下,相比原始同化系统,新系统计算性能提升1倍。在更高分辨率(0.1°×0.1°)下,该系统的计算性能仍然可以提升1倍,说明新设计的负载均衡方案稳定可靠。该方案具有很强的可扩展性和移植性,在业务预报中有广泛的应用前景。     

Fast 3D Reservoir Simulation and Scale Up Using Streamtubes

This paper presents an implementation of a semianalytical method for oil recovery calculation in heterogeneous reservoirs that is both fast and accurate. The method defines streamline paths based on a conventional single-phase incompressible flow calculation. By calculating the time-of-flight for a particle along a streamline and assigning a volumetric flux to each streamline, the cumulative pore volume of a streamtube containing the streamline can be calculated. Subsequently, the streamtube geometries are kept constant and the effects of the time varying mobility distribution in two-phase flow are accounted for by varying the flow rate in each streamtube, based on fluid resistance changes along the streamtube. Oil recovery calculations are then done based on the 1D analytical Buckley–Leverett solution. This concept makes the method extremely fast and easy to implement, making it ideal to simulate large reservoirs generated by geostatiscal methods. The simulation results of a 3D heterogeneous reservoir are presented and compared with those of other simulators. The results shows that the new simulator is much faster than a traditional finite difference simulator, while having the same accuracy. The method also naturally handles the upscaling of absolute and relative permeability. We make use of these upscaling abilities to generate a coarse curvilinear grid that can be used in conventional simulators with a great advantage over conventional upscaled Cartesian grids. This paper also shows an upscaling example using this technique.     

Velocity interpolation and streamline tracing on irregular geometries

Streamline tracing on irregular grids requires reliable interpolation of velocity fields. We propose a new method for direct streamline tracing on polygon and polytope cells. While some numerical methods provide a basis function that can be used for interpolation, other methods provide only the fluxes at the faces of the elements. We introduce the concept of full- and raw-field methods. Full-field methods have built-in interpolation but are often not defined on general grids such as polygonal and polyhedral grids which we examine here. Also, reliability issues may arise on non-simplicial meshes in terms of not being able to reproduce constant velocity fields. We propose an interpolation in H(div) and H(curl) valid on general grids that is based on barycentric coordinates and that reproduces uniform flow. The interpolation can be used to compute the streamline directly on the complex cell geometry. The method generalizes to convex polytopes in 3D, with a restriction on the polytope topology near corners that is shown to be satisfied by several popular grid types. Numerical results confirm that the method is applicable to general grids and preserves uniform flow.     

Assessing flow paths in a karst aquifer based on multiple dye tracing tests using stochastic simulation and the MODFLOW-CFP code

Karst systems show high spatial variability of hydraulic parameters over small distances and this makes their modeling a difficult task with several uncertainties. Interconnections of fractures have a major role on the transport of groundwater, but many of the stochastic methods in use do not have the capability to reproduce these complex structures. A methodology is presented for the quantification of tortuosity using the single normal equation simulation (SNESIM) algorithm and a groundwater flow model. A training image was produced based on the statistical parameters of fractures and then used in the simulation process. The SNESIM algorithm was used to generate 75 realizations of the four classes of fractures in a karst aquifer in Iran. The results from six dye tracing tests were used to assign hydraulic conductivity values to each class of fractures. In the next step, the MODFLOW-CFP and MODPATH codes were consecutively implemented to compute the groundwater flow paths. The 9,000 flow paths obtained from the MODPATH code were further analyzed to calculate the tortuosity factor. Finally, the hydraulic conductivity values calculated from the dye tracing experiments were refined using the actual flow paths of groundwater. The key outcomes of this research are: (1) a methodology for the quantification of tortuosity; (2) hydraulic conductivities, that are incorrectly estimated (biased low) with empirical equations that assume Darcian (laminar) flow with parallel rather than tortuous streamlines; and (3) an understanding of the scale-dependence and non-normal distributions of tortuosity.     

Cache-efficient parallel eikonal solver for multicore CPUs

Numerical solution of the eikonal equation is frequently used to compute first-arrival travel times for a given velocity model in seismic applications. Computations for large three-dimensional models become expensive requiring the use of efficient parallel solvers. We present new parallel implementations of the fast sweeping and locking sweeping methods optimized for shared memory systems such as multicore CPUs; we call them block fast sweeping method (BFSM) and block locking sweeping method (BLSM). Proposed methods are based on the domain decomposition approach with a special attention paid to high efficiency of the cache utilization and task execution synchronization. Performance tests on realistic models show high parallel efficiency of 85–95% on modern multicore CPUs and require the same number of iterations to converge as do the serial sweeping methods. We also highlight the importance of properly selecting the stopping criterion in the iterative sweeping methods aiming for a balance between computational time and accuracy of the result required by an application. In particular, we show that in seismic applications one can reach reasonable accuracy of computed travel times while dramatically reducing the number of iterations compared to the case of using the full convergence stopping criterion.     

不同渗流条件下无限斜坡稳定性分析方法探讨

顺层滑坡和冻土地区的浅层滑坡如融冻泥流和热融滑塌等，其斜坡深长比很小，一般属于无限斜坡类型，这类滑坡的形成往往与地下水的存在有关。本文应用有效应力原理推导了不同渗流条件下无限斜坡稳定性分析的计算模式，对各种不同表达形式的安全系数进行了讨论和对比，得出在流线平行于斜坡条件下。两类特殊条件(干土坡、饱水土坡)下的分析结果与相同情况下安全系数统一式结果相一致的结论；流线为相互平行的水平线、流线与坡向一致两种情况分别为孔晾压力和安全系数的两种特例。     

Parallel finite element analysis of seismic soil structure interaction using a PC cluster

This paper describes an implementation of a highly scalable parallel computational facility with high speedup efficiency using relatively low-cost hardware, which consists of a cluster of desktop personal computers (PCs) connected via a 10-Gigabit Ethernet. Two-levels of parallelization were implemented. Communication between different PCs was achieved using message passing interface (MPI) protocol. Domain decomposition was automated and based on element numbering. Domain continuity was assured largely by re-numbering the elements using a “front squasher” code prior to decomposition. Within each PC, the shared memory parallelization was implemented using either the open-multiprocessing (OpenMP) or the MPI protocol. Analysis of three different problems with number of degrees-of-freedom ranging from about 129,000 to about 2,260,000 shows a speedup efficiency generally above 70%. Super-linear speedup was achieved in several of the cases examined in this study, with the hybrid MPI-OpenMP approach generally performing better compared to the pure MPI method for parallelization. The results demonstrate the feasibility of acquiring a parallel computing facility with relatively modest outlay that is within the reach of consulting or engineering offices.     

张八岭地区变质地层序列与构造型式

运用构造与地层相结合的理论和方法，通过对张八岭地区已完成和正在进行的１０幅１：５万地质填图资料分析和典型地区的构造追踪，初步认为：北将军（岩）组自下而上分为三段，时代置于中元古代，获铅同位素年龄样值为１８２１±４１６Ｍａ；西冷（岩）组自下而上分为三段，时代置于青白口纪。区内主要存在三期构造交形：早期为一系列呈ＮＷＷ－近ＥＷ向的紧闭同斜褶皱，中期以韧性剪切带发育为特征，晚期以ＮＮＥ向为主的宽缓褶皱。三期变形共同叠加，形成区内基本构造格架。并对变形机制作初步探讨。     

空间信息网格中动态复制策略的研究

空间信息网格项目数据量大，用户遍及各地，对数据文件的请求延时大、占大量带宽。复制可以节省带宽、减少时延、均衡负载、改善系统可靠性。采用动态复制技术可以使用户有效地获得所需的数据。详细地论述了动态复制策略以及空间信息网格中的复制管理机制、复制服务流程和具体实施。     

Seismic-reflection profiles of the central part of the Clarendon–Linden fault system of western New York in relation to regional seismicity

Geological and geophysical research in upstate New York, with few exceptions, has not definitively associated seismicity with specific Proterozoic basement or Paleozoic bedrock structures. The central part of the Clarendon–Linden fault system (CLFS) between Batavia and Dale, NY is one of those exceptions where seismicity has been studied and has been spatially associated with structure. The CLFS is either a complex system of long faults with associated shorter branches and parallel segments, or a region of many short faults aligned north–south from the Lake Ontario shore southward to Allegany County, NY. Interpretation of 38 km of Vibroseis and approximately 56 km of conventional seismic-reflection data along 13 lines suggests that the CLFS is a broad zone of small faults with small displacements in the lower Paleozoic bedrock section that is at least 77 km long and 7–17 km wide and spatially coincident with a north-trending geophysical (combined aeromagnetic and gravity) lineament within the basement. The relative offset across the faults of the system is more than 91 m near Attica, NY. The CLFS is the expression of tectonic crustal adjustments within the Paleozoic rock above the boundary of two basement megablocks of differing petrologic provinces and differing earthquake characteristics that forms the eastern side of the Elzevir–Frontenac boundary zone. Deep seismic-reflection profiles display concave-eastward listric faults that probably merge at depth near the mid-crustal boundary layer. An interpretive vertical section provides the setting for refined definitions of the CLFS, its extensions at depth and its relation to seismicity. Most modern seismicity in western New York and the Niagara Peninsula of Ontario occurs in apparent patterns of randomly dispersed activity. The sole exception is a line of seven epicenters of small earthquakes that trend east from Attica, NY into the Rochester basement megablock. Earthquakes may be triggered at the intersections of north- and east-trending brittle faults within the Niagara basement megablock. Current interpretations of the mechanisms for earthquake generation in western New York and the Niagara Peninsula of Ontario require conservative estimates of seismic hazards that assume that an earthquake the size of the 1929 Attica, NY, event (M_b=5.2) or larger could occur anywhere in the Eastern Great Lakes Basin (EGLB). The broad zone of small-displacement faults that marks the CLFS in the lower Paleozoic sedimentary section and the uppermost basement may not provide the structural environment for generation of earthquakes in western New York. If this interpretation is correct, most seismicity is generated within the Niagara basement megablock beneath or west of the CLFS. Consequently, we may have to look to the deeper tectonic regime of basement megablocks to understand the distribution of modern seismicity in the EGLB.     

基于傅氏变换有限差分的三维波动方程正演模拟并行算法

傅氏变换有限差分(即FFD)混合波场延拓法波动方程正演模拟精度高,但三维FFD因其计算复杂、数据存储巨大而难以推广。这里提出三维FFD一步法正演模拟并行算法,把一个串行的大规模频率循环分割成并行的多个小规模频率循环,并发执行多个波场延拓来提高运算速度,并通过由给定的资源设定并行数,以及适时重排三维数据,大大增强了算法的适应性和时效性。通过对比并行和非并行正演实验,验证了算法的有效性。