Simulating Entrainment and Particle Fluxes in Stratified Estuaries

Settling and entrainment are the dominant processes governing noncohesive particle concentration throughout the water column of salt-wedge estuaries. Determination of the relative contribution of these transport processes is complicated by vertical gradients in turbulence and fluid density. A differential-turbulence column (DTC) was designed to simulate a vertical section of a natural water column. With satisfactory characterization of turbulence dissipation and saltwater entrainment, the DTC facilitates controlled studies of suspended particles under estuarine conditions. The vertical decay of turbulence in the DTC was found to obey standard scaling law relations when the characteristic length scale for turbulence in the apparatus was incorporated. The entrainment rate of a density interface also followed established grid-stirred turbulence scaling laws. These relations were used to model the change in concentration of noncohesive particles above a density interface. Model simulations and experimental data from the DTC were consistent over the range of conditions encountered in natural salt-wedge estuaries. Results suggest that when the ratio of entrainment rate to particle settling velocity is small, sedimentation is the dominant transport process, while entrainment becomes significant as the ratio increases.     

3D Numerical Modeling of Flow and Sediment Transport in Open Channels

A 3D numerical model for calculating flow and sediment transport in open channels is presented. The flow is calculated by solving the full Reynolds-averaged Navier-Stokes equations with the k ? ε turbulence model. Special free-surface and roughness treatments are introduced for open-channel flow; in particular the water level is determined from a 2D Poisson equation derived from 2D depth-averaged momentum equations. Suspended-load transport is simulated through the general convection-diffusion equation with an empirical settling-velocity term. This equation and the flow equations are solved numerically with a finite-volume method on an adaptive, nonstaggered grid. Bed-load transport is simulated with a nonequilibrium method and the bed deformation is obtained from an overall mass-balance equation. The suspended-load model is tested for channel flow situations with net entrainment from a loose bed and with net deposition, and the full 3D total-load model is validated by calculating the flow and sediment transport in a 180° channel bend with movable bed. In all cases, the agreement with measurements is generally good.     

3D Numerical Modeling of Flow and Sediment Transport in Laboratory Channel Bends

The development of a fully three-dimensional finite volume morphodynamic model, for simulating fluid and sediment transport in curved open channels with rigid walls, is described. For flow field simulation, the Reynolds-averaged Navier–Stokes equations are solved numerically, without reliance on the assumption of hydrostatic pressure distribution, in a curvilinear nonorthogonal coordinate system. Turbulence closure is provided by either a low-Reynolds number k?ω turbulence model or the standard k?ε turbulence model, both of which apply a Boussinesq eddy viscosity. The sediment concentration distribution is obtained using the convection-diffusion equation and the sediment continuity equation is applied to calculate channel bed evolution, based on consideration of both bed load and suspended sediment load. The governing equations are solved in a collocated grid system. Experimental data obtained from a laboratory study of flow in an S-shaped channel are utilized to check the accuracy of the model’s hydrodynamic computations. Also, data from a different laboratory study, of equilibrium bed morphology associated with flow through 90° and 135° channel bends, are used to validate the model’s simulated bed evolution. The numerically-modeled fluid and sediment transportation show generally good agreement with the measured data. The calculated results with both turbulence models show that the low-Reynolds k?ω model better predicts flow and sediment transport through channel bends than the standard k?ε model.     

Mass Balance in Eulerian-Lagrangian Transport Simulations in Estuaries

This paper investigates the generation of flow mass errors in finite-element shallow water models and the effect of these errors in the mass conservation of Eulerian-Lagrangian transport simulations. Flow mass errors are shown to be similar for several primitive and wave equation formulations. These errors occur primarily in areas of steep bathymetric gradients and near complex boundaries. Forcing Eulerian-Lagrangian transport simulations with nonconservative flow fields generates important mass imbalances, which can be mitigated by refining the flow grid. Comparatively, refining the transport grid only reduces marginally the mass errors.     

Circulation in Stratified Lakes due to Flood-Induced Turbidity Currents

The river inflow in a natural lake with important suspended sediment load during floods, can impact water quality by mobilizing dissolved matters like phosphorous from deep to surface waters. Generally due to thermal stratification in prealpine lakes, the water column is stable. It does not mix vertically unless acted on by outside forces, for example, currents or winds. Since Lake Lugano has a strong thermal stratification, river inflow exhibits different modes of density currents, from surface flows and thermocline intrusion to bottom currents. Turbidity currents are the direct cause of the downward water flow, and at the same time at the origin of upward directed flow. In this study, the impact of river born turbidity currents in Lake Lugano under varying ambient conditions was investigated using field measurements at the inflow river and inside the lake, together with a full three-dimensional numerical model of the entire lake. The paper characterizes the induced circulation of the turbidity plume and gives some indications on the relevance of turbidity currents on the lake.     

基于PHT3D软件的酸法地浸采铀过程模拟探讨

运用反应运移模拟软件PHT3D建立酸法地浸采铀一维模型,阐明强酸低含氧情况下地浸采铀过程中铀水解与迁移的时空演化规律。模拟结果表明,铀矿溶解后,四价铀最多,六价铀次之;矿层水溶液的pe(电位)和pH在时间上的变化与各个液相主要组分的浓度变化相关,pe和pH变化曲线的交点为液相主要组分浓度显著变化的起点;铀矿不仅会溶解也伴随着铀矿微量生成的现象,且溶解沉淀的量与位置有关。     

Formula for Sediment Transport in Rivers, Estuaries, and Coastal Waters

The aim of the present study is to develop a formula for the relationship between flow strength and sediment discharge. The appropriate definition of energy dissipation rate E in the theorem of Bagnold in 1966 is discussed and it is found that the sediment transport rate gt in unidirectional flows can be well predicted when E is defined as the product of bed shear stress τ0 and near bed velocity u*′. Then the linear relationship between u*′E and the sediment transport rate is examined using measured data. The good agreement between measured and predicted values indicates that the phenomena of sediment transport can be reasonably described by the near bed flow characteristics. As the hydrodynamic modelers are able to calculate the bed shear stress and near bed velocity in various cases now, thus the new relationship may provide numerical modelers a tool to calculate the sediment transport in rivers, estuaries and coastal waters. To prove this, the simplified analytical expressions of E and u*′ in wave-current flows and coastal waters are derived, the results are checked with the available data over a wide range of flow conditions; and good agreements are achieved, indicating that the presumption is valid in the cases investigated.     

3D Modeling of Ripping Process

Due to environmental constraints and limitations on blasting, ripping as a ground loosening and breaking method has become more popular than drilling and blasting method in both mining and civil engineering applications. The best way of estimating the rippability of rocks is to conduct direct ripping runs in the field. However, it is not possible to conduct direct ripping runs in all sites using different dozer types. Therefore, the utilization of numerical modeling of ripping systems becomes unavoidable. A complex ripping system can better be understood with three-dimensional (3D) models rather than two-dimensional models. In this study, 3D distinct element program called 3DEC was used to investigate the ripping process. First, the ripping mechanisms were investigated and then the individual factors that affect the rippability performance of dozers were reviewed. The rippabilities of rocks depend not only on the rock properties, but also machine or dozer properties. Thus, ripper production and rock rippability with D8 type of dozers were also determined by direct ripping runs on different open pit lignite mines within the scope of this research. Production values obtained from numerical modeling were compared with field production values obtained from the case studies. This comparison shows that the model gives consistent and adequate results. Hence, a link has been established between the field results and the 3D models.     

三维空间实体建模研究

为了在计算机中真实再现人类赖以生存的客观世界,首先对现有的各种地形模型(如等高线模型、TIN和RSG)进行分析,选取TIN和RSG两种数据模型相结合的方法进行研究,并对接边处进行光滑处理,以达到真实表达地形特征的目的;其次分析建筑物模型的建模方法以及数据获取途径;然后用三角形构造算法,对地形与地物模型进行有机集成,最后用三维空间实体建模方法对鄱阳湖区进行了大比例尺三维再现。     

Quantifying Uncertainty in Estuarine and Coastal Ocean Circulation Modeling

A methodology is developed to describe the effect of errors (or uncertainty) in the specification of certain drivers (bathymetry, river inflow, and wind speeds) on the circulation computed by a three-dimensional estuarine and coastal hydrodynamic circulation model. The methodology is based on first order variance analysis. Two analytical examples are used to illustrate the method and to provide a context for interpreting real world settings. An application of the method to a model of the N.Y./N.J. Harbor Estuary shows that current predictions are considerably sensitive to the accurate specification of bathymetry, and are usually more sensitive than water level predictions to errors in bathymetry. Estuarine properties with a strong seasonal (or spatial) component such as temperature or salinity did exhibit a sensitivity to driver accuracy that shifted from one season (or regime) to another. Bathymetry appears to control the circulation of the N.Y./N.J. Estuary more than the dynamic forcing of the winds and the Hudson River inflow, perhaps due to the fact that the estuary is primarily tidally driven.     

矿床的三维可视化仿真技术与系统

研究了矿床三维可视化的相关技术,提出了一种实现矿床三维可视化仿真系统的框架.在Windows系统下,以VC⁺⁺为开发平台,利用OpenGL三维图形库,成功地开发了矿床三维可视化仿真系统的原型,实现了三维钻孔图显示、任意地质剖面显示与矿体的真三维显示,并且支持3D旋转、平移、无级缩放等交互操作.应用某地下铁矿的数据,得出了符合实际的结果,初步验证了有关技术与系统原型的可行性.     

Modeling Fate and Transport of Roadside-Applied Herbicides

A physically based, one-dimensional, mathematical model is developed to simulate transport of herbicides applied to roadsides into adjacent surface water. Herbicide transport by overland flow, infiltrating water, and subsurface flow is considered. The model accounts for advection, dispersion, equilibrium linear sorption in the soil, and first-order decay of the herbicides. Chemical transport between soil and overland flow is described using a rate-limited mass exchange between the two compartments that is proportional to the difference between the chemical concentration in overland flow and the pore water with a proportionality constant that is a function of overland flow characteristics and rain intensity. For simulating overland and subsurface flow, the kinematic wave equation is solved using a Crank–Nicolson finite difference scheme. Richards’ equation is solved using a Galerkin finite element method to model infiltration, and the transport equation is solved using a finite difference method. The model is calibrated and verified using extensive field data on the runoff of five herbicides with a range of physical–chemical properties at two field sites. Good agreement is obtained between predicted and measured event-mean concentrations in runoff and the herbicide concentration remaining in the application-zone soil.     

巴彦乌拉铀矿床精细三维地质建模

地浸采铀是一种通过溶浸液与砂岩矿层中含铀矿物发生溶解反应的矿石原位开采方法,厘清矿层及矿层上覆下伏含水层三维结构,对提高地浸采铀效率具有重要意义。在资料收集的基础上,结合测井数据,采用地质统计学方法,对地浸采区地层及矿层进行精细刻画,建立了相应三维地质模型,根据模型模拟结果分析了含矿含水层的空间结构特征。结果表明,含矿含水层主要岩性为粗砂岩;含矿含水层各种岩性孔隙连通性较好,透水岩性分布较均匀;采区地层倾向大致为325°,倾角为6.76°。顶部隔水层厚度呈南部和中部较厚、北部和西部较薄的特点,发育7个隔水顶板天窗;矿层贴近隔水底板,厚度由北部向各个方向逐渐减薄,矿层厚度与含矿含水层厚度呈正相关。三维地质结构模型的构建完整、直观地展示了巴彦乌拉铀矿C12采区地层、岩体的三维空间分布特征,可以为进一步开展地浸采铀数值模拟研究提供科学依据。     

3D Surface Modeling and Measuring System for Pneumatic Caisson

In order to build a 3D model environment of a pneumatic caisson for excavator operators and managers, a modeling and measuring 3D surface system of unmanned pneumatic caisson was presented in this paper. The whole system is based on two 3D laser scanners for the pneumatic caisson by acquiring the surface data of pneumatic caisson and successive data processing for surface reconstruction and measurement. Registration and reconstruction are also discussed in this paper. In order to convert two point sets into one common coordinate, Hough transforms were used to extract planes and then by using their parameters to register the two point sets. As for surface reconstruction using triangular meshing, a new method based on curves was presented. When combined with the real-time pose and location of the excavators, the 3D environment can be used as a “virtual reality” operating environment for excavation operators. The whole system has been applied in a pneumatic caisson of an underground project in a Shanghai subway, which proved to be working well, with less than 16-s work cycle (period of a single 180° 3D laser scan), at an estimated resolution of less than 20 mm.     

3D Numerical Modeling of MICROCYSTIS Distribution in a Water Reservoir

A 3D computational fluid dynamics program was used to calculate the wind-induced accumulation of phytoplankton in Eglwys Nynydd, a water supply reservoir in Wales. The computational fluid dynamics model solved the Navier-Stokes equations for the water velocities using the SIMPLE method to calculate the pressure. Two turbulence models were tested: a zero-equation model and the k-ε model. An unstructured nonorthogonal 3D grid with hexahedral cells was used. The distribution of the blue-green algae Microcystis was calculated by solving the transient convection-diffusion equation for phytoplankton concentration, based on the modeled flow field. The numerical model included algorithms for calculating the growth rate of phytoplankton and simulating the response of the algae to changes in underwater light intensity. The model was validated by comparing the horizontal distribution patterns produced by simulation with those recorded during a field survey of surface concentrations. The results demonstrated reasonable agreement, particularly when using the k-ε turbulence model. The main parameter affecting the results was the effective diameter of the Microcystis colonies.     

Field Test and 3D FE Modeling of Decked Bulb-Tee Bridges

This paper summarizes field-testing of eight decked bulb-tee girder bridges as well as development of three-dimensional finite-element (FE) models. Using the calibrated 3D FE models, parametric studies have been performed to study the effect of shear connectors and intermediate diaphragms on live-load distribution and connector forces. It was found that: (1) in all cases studied, the live- load distribution factor (DF) for a single-lane loaded bridge was smaller than one for a double-lane loaded bridge; (2) connector forces caused by wheel loads were not uniform along the longitudinal joint—adding intermediate diaphragms tended to reduce the difference among horizontal shear forces in connectors; (3) the maximum horizontal shear force increased with the increase of the connector spacing—intermediate diaphragms reduced the maximum horizontal shear force in connectors; (4) the maximum vertical shear force and in-plane normal tensile force in connectors do not necessarily increase with the increase of the connector spacing; and (5) the summation of connector forces in each direction along the longitudinal joint remained constant irrespective of the number of connectors in the joint.     

边坡复杂地质结构三维可视化及数值模型构建

地质模型的精确性是露天矿边坡稳定性数值分析可靠性的决定因素。针对地质体间相互交叉、穿切的复杂性和无规律性,研究了基于非均匀有理B样条NURBS（Non-Uniform Rational B-Spline）的自由曲面生成技术。以矿山普遍采用的二维地质勘探剖面图为基础数据,通过对其进行矢量化处理提取出岩土体边界离散点信息,建立起NURBS三维地质体分界曲面,据此以MIDAS软件为平台制定了边坡工程复杂地质结构三维可视化及数值模型构建方案,并选取江西城门山露天矿边坡工程进行了应用实践。结果表明,运用该技术构建复杂边坡地质体模型,方法简单可靠,可极大提高模型的精度和建模效率,不仅使复杂地质体得以形象再现,同时可为边坡稳定性分析提供可靠的有限元数值计算模型。     

2D and 3D Numerical Modeling of Combined Surcharge and Vacuum Preloading with Vertical Drains

This paper presents a three-dimensional (3D) and two-dimensional (2D) numerical analysis of a case study of a combined vacuum and surcharge preloading project for a storage yard at Tianjin Port, China. At this site, a vacuum pressure of 80?kPa and a fill surcharge of 50?kPa were applied on top of the 20-m-thick soft soil layer through prefabricated vertical drains (PVD) to achieve the desired settlements and to avoid embankment instability. In 3D analysis, the actual shape of PVDs and their installation pattern with the in situ soil parameters were simulated. In contrast, the validity of 2D plane strain analysis using equivalent permeability and transformed unit cell geometry was examined. In both cases, the vacuum pressure along the drain length was assumed to be constant as substantiated by the field observations. The finite-element code, ABAQUS, using the modified Cam-clay model was used in the numerical analysis. The predictions of settlement, pore-water pressure, and lateral displacement were compared with the available field data, and an acceptable agreement was achieved for both 2D and 3D numerical analyses. It is found that both 3D and equivalent 2D analyses give similar consolidation responses at the vertical cross section where the lateral strain along the longitudinal axis is zero. The influence of vacuum may extend more than 10?m from the embankment toe, where the lateral movement should be monitored carefully during the consolidation period to avoid any damage to adjacent structures.     

Modeling Transport of Gaseous Ozone in Unsaturated Soils

The use of in-situ ozone venting is an effective and economic technology to remediate soils contaminated with organic chemicals. A model was developed in this study to describe the transport of gaseous ozone in unsaturated soils. Mass balance equations for soil organic matter, phenanthrene, and ozone were incorporated into the model. The model was found to fit the experimental data obtained from one-dimensional columns, using the previously published rate expressions for the reactions of ozone with soil organic matter and phenanthrene. However, it was observed that the initial unsteady-state conditions for the gas pressure resulted in minor deviations between the simulated and experimental results. Based on the simulated results, the reactions of ozone with phenanthrene and organic matter can be modeled as either parallel or serial reactions. As the initial distribution of contaminant would be nonuniform and some contaminant would be sorbed or trapped in immobile regions, it is recommended that in situ ozonation be ceased no sooner than when the effluent ozone concentrations begins to stabilize.