Study of the Efficiency of Vertical Drains by an FEM Method in Soil Treatment for Road Projects: Case of the Development and Bitumination Works of the ROCADE Porto-Novo in Benin

This article aims to study the efficiency of coupled vertical drains for the treatment of long-lasting compressible clay soils for the road project platform of the ring road of Porto Novo, capital of Benin. The experimental data allowed us to estimate a consolidation of 29% in 9 months, justifying the drainage of the soil. In order to study the efficiency of drainage, a FEM model was proposed simulating different scenarios. These include a drainless road, pavements equipped with vertical drains with meshes of 0.5 m 0.5 m, 1 m 1 m and 1.5 m 1.5 m respectively and horizontal drains. The results expressed in terms of variations in vertical stresses, effective stresses and shear deformations revealed significant variations in pavement performance depending on the mesh size of the vertical drains. The configuration with a mesh of 0.5 m 0.5 m showed the least deformations, thus indicating a reduction in deformations and better stress distribution. However, the other mesh configurations showed variable results, underlining the importance of choosing the right mesh for the specific project conditions.

Developing a 2D vertical flow and sediment transport model for open channels using the Youngs-VOF method

A 2D vertical （2DV） numerical model, without o-coordinate transformation in the vertical direction, is developed for the simulation of flow and sediment transport in open channels. In the model, time-averaged Reynolds equations are closed by the k-e nonlinear turbulence model. The modified Youngs- VOF method is introduced to capture free surface dynamics, and the free surface slope is simulated using the ELVIRA method. Based on the power-law scheme, the k-e model and the suspended-load transport model are solved numerically with an implicit scheme applied in the vertical plane and an explicit scheme applied in the horizontal plane. Bedload transport is modeled using the Euler-WENO scheme, and the grid-closing skill is adopted to deal with the moving channel bed boundary. Verification of the model using laboratory data shows that the model is able to adequately simulate flow and sediment transport in open channels, and is a good starting point for the study of sediment transport dynamics in strong nonlinear flow scenarios.

A Numerical Simulation of Air Flow in the Human Respiratory System Based on Lung Model

The lung is an important organ that takes part in the gas exchange process. In the study of gas transport and exchange in the human respiratory system, the complicated process of advection and diffusion (AD) in airways of human lungs is considered. The basis of a lumped parameter model or a transport equation is modeled during the inspiration process, when oxygen enters into the human lung channel. The quantitative measurements of oxygen are detached and the model equation is solved numerically by explicit finite difference schemes. Numerical simulations were made for natural breathing conditions or normal breathing conditions. The respiratory flow results for the resting conditions are found strongly dependent on the AD effect with some contribution of the unsteadiness effect. The contour of the flow rate region is labeled and AD effects are compared with the variation of small intervals of time for a constant velocity when breathing is interrupted for a negligible moment.

Debris flow simulation 2D(DFS 2D):Numerical modelling of debris flows and calibration of friction parameters

Debris flows are rapid mass movements with a mixture of rock,soil and water.High-intensity rainfall events have triggered multiple debris flows around the globe,making it an important concern from the disaster management perspective.This study presents a numerical model called debris flow simulation 2D(DFS 2D)and applicability of the proposed model is investigated through the values of the model parameters used for the reproduction of an occurred debris flow at Yindongzi gully in China on 13 August 2010.The model can be used to simulate debris flows using three different rheologies and has a userfriendly interface for providing the inputs.Using DFS 2D,flow parameters can be estimated with respect to space and time.The values of the flow resistance parameters of model,dry-Coulomb and turbulent friction,were calibrated through the back analysis and the values obtained are 0.1 and 1000 m/s^(2),respectively.Two new methods of calibration are proposed in this study,considering the crosssectional area of flow and topographical changes induced by the debris flow.The proposed methods of calibration provide an effective solution to the cumulative errors induced by coarse-resolution digital elevation models(DEMs)in numerical modelling of debris flows.The statistical indices such as Willmott's index of agreement,mean-absolute-error,and normalized-root-mean-square-error of the calibrated model are 0.5,1.02 and 1.44,respectively.The comparison between simulated and observed values of topographic changes indicates that DFS 2D provides satisfactory results and can be used for dynamic modelling of debris flows.

Numerical Modeling of Sediment Transport and Its Effect on Algal Biomass Distribution in Lake Pontchartrain Due to Flood Release from Bonnet CarréSpillway

In order to protect the city of New Orleans from the Mississippi River flooding, the Bonnet Carré Spillway (BCS) was constructed from 1929 to 1936 to divert flood water from the river into Lake Pontchartrain and then into the Gulf of Mexico. During the BCS opening for flood release, large amounts of freshwater, nutrients, sediment, etc. were discharged into Lake Pontchartrain, and caused a lot of environmental problems. To evaluate the environmental impacts of the flood water on lake ecosystems, a two-dimensional numerical model was developed based on CCHE2D and applied to simulate the flow circulation, sediment transport and algal biomass distribution in Lake Pontchartrain. The effect of sediment concentration on the growth of algae was considered in the model. The numerical model was calibrated using field measured data provided by USGS, and then it was validated by the BCS Opening Event in 1997. The simulated results were generally in good agreement with filed data and satellite imagery. The field observation and numerical model show that during the spillway opening for flood release, the sediment concentration is very high, which greatly restricts the growth of algae, so there is no algal bloom observed in the lake. After the closure of BCS, the sediment concentration in the lake reduces gradually, and the nutrient concentration of the lake is still high. Under these conditions, numerical results and satellite imagery showed that the chlorophyll concentration was high and algal bloom might occur.

2-D智能纳米黑卡微观驱油机理可视化实验

由中国石油大学(北京)非常规油气科学技术研究院自主研发的2-D智能纳米黑卡是一种具有尺寸小、比表面积大等优势的片状纳米材料(尺寸为80×60×1.2 nm,比表面积约57 m^2/g)。本文使用不同孔隙度、渗透率的二维可视化模型,进行2-D智能纳米黑卡微观驱替可视化实验。通过分析岩心渗透率、颗粒浓度和注入速率等因素对驱油效果的影响,研究在微观条件下该纳米材料的微观渗流机理和运移规律。研究表明,该材料具有优异的亲水亲油平衡性,能够改变岩石表面润湿性,在两相界面产生楔形渗透压,形成微观回旋流,相对于以往如SiO2等球型纳米颗粒,具有更大的表面接触性。2-D智能纳米黑卡可有效驱替地层剩余油,剥离微小孔喉壁面上的油膜,扩大低渗层波及体积,提高原油采收率。

A VERTICAL 2D MATHEMATICAL MODEL FOR HYDRODYNAMIC FLOWS WITH FREE SURFACE IN σ COORDINATE

Numerical models with hydrostatic pressure have been widely utilized in studying flows in rivers, estuaries and coastal areas. The hydrostatic assumption is valid for the large-scale surface flows where the vertical acceleration can be ignored, but for some particular cases the hydrodynamic pressure is important. In this paper, a vertical 2t） mathematical model with non-hydrostatic pressure was implemented in the σ coordinate. A fractional step method was used to enable the pressure to be decomposed into hydrostatic and hydrodynamic components and the predictor-corrector approach was applied to integration in time domain. Finally, several computational cases were studied to validate the importance of contributions of the hydrodynamic pressure.

Two Dimensional Hydrodynamic Modelling of Northern Bay of Bengal Coastal Waters

Mathematical models have advancement to a point where they are considered to be an effective tool for simulating natural phenomena in coastal regions. This paper discusses the development of Bay of Bengal Model (BoBM), updating of the model with the recent bathymetry and shore line of islands and coastline and upgrading from rectangular grid to finer size of mesh grids by using latest version of MIKE21 FM modeling system. This model is very useful for the hydrodynamic study in the coastal region of Bangladesh. The article also presents the model set-up, boundary conditions and few calibration results of the model. The model applications clearly show the variation of the flow structure, their speed and direction separately for monsoon and dry season around the model area which covers the northern part of Bay of Bengal.

MIKE 21二维非恒定流模型在北京市延芳淀湿地洪水影响分析中的应用

为了研究拟建在北运河滩地上的延芳淀湿地对河道防洪安全的影响,控制湿地建设规模,不增加北运河50年一遇洪水出境洪峰流量,搭建了北运河MIKE 21二维非恒定流模型,模拟湿地建设前后北运河50年一遇洪水演进情况。采用2016年北运河"7.20"洪水监测数据,对模型进行了参数率定;分析了延芳淀湿地建设前后,50年一遇洪水下北运河河道及滩地槽蓄能力、河道水位、流速、流势等水力条件的时空变化。结果表明:滩地内建设延芳淀湿地降低了北运河槽蓄能力,减少了滩地消减洪峰量值,但通过调整湿地地形高程,仍能满足规划要求;湿地建设同时抬升了北运河洪水位,改变了洪水流势,对河道堤防建设有一定影响。研究成果不仅能够为延芳淀湿地的设计建设提供相关水力条件支持,也可以为北运河河道治理及防洪预案修订提供参考。

考虑不同水流交换模式的城市洪涝一维二维双向耦合模型

为准确模拟城市洪涝过程,以地表二维流动模型和SWMM一维管流模型为基础,同时考虑地表径流与地下管流交换的3种模式,构建了城市地表与地下管流双向耦合的水动力学模型。采用水槽试验算例和理论算例对耦合模型进行验证,并将耦合模型应用到英国Glasgow城市街区,分析排水管网和不同地表地下水流交换模式对城市洪涝过程的影响。结果表明:模型在试验算例和理论算例的模拟中均具有较好的精度和可靠性,模型能够准确地模拟具有排水管网的城市洪涝演进过程;与无排水系统相比,检查井简化法、雨水口法和雨水口-检查井法3种水流交换模式下Glasgow城市街区模拟的最大淹没面积分别减少9.3%、23.2%和24.5%,其中对重度积水的消减作用更显著,淹没面积分别减少43.6%、79.9%和80.9%;检查井简化法的消减作用要远小于雨水口法和雨水口-检查井法,后两者差异较小。雨水口法和雨水口-检查井法比较符合实际情况,且雨水口-检查井法的计算效率更高更简单,因此,在城市洪涝模拟中采用雨水口-检查井法考虑地表径流与地下管流交换过程更符合实际。

湖北碾盘山水利水电枢纽导流明渠和泄水闸联合过流模拟研究

湖北汉江碾盘山枢纽为Ⅱ等大(2)型工程,枢纽为河床式电站。目前导流明渠左侧副坝已施工完成,基坑内泄水闸已基本完工,电站厂房、船闸尚未完工。坝体临时度汛标准为100年一遇,当发生10年一遇以上洪水,由导流明渠和泄水闸联合下泄,由于种种原因,汛前围堰全部拆除难度较大,导致泄水闸不能完全按照泄流能力泄洪。因工期紧、施工度汛过流条件及工况复杂,物理模型试验往往不能及时模拟。通过平面二维水流数学模型,根据施工进度实时、动态模拟泄水闸与导流明渠联合过流工况,得出合理分流比,为施工安全度汛提供技术支撑。

ONE-AND TWO-DIMENSIONAL COUPLED HYDRODYNAMICS MODEL FOR DAM BREAK FLOW

1-D and 2-D mathematical models for dam break flow were established and verified with the measured data in laboratory. The 1-D and 2-D models were then coupled, and used to simulate the dam break flow from the reservoir tail to the dam site, the propagation of dam break waves in the downstream channel, and the submergence of dam break flow in the downstream town with the hydrodynamics method. As a numerical example, the presented model was employed to simulate dam break flow of a hydropower station under construction. In simulation, different dam-break durations, upstream flows and water levels in front of dam were considered, and these influencing factors of dam break flow were analyzed, which could be referenced in planning and designing hydropower stations.

小浪底水库垂向二维水温数值模拟研究

采用垂向二维水动力水温数学模型,研究模拟小浪底水库水温分布结构及年内变化规律。结果表明:小浪底水库库尾水深小,水温呈等温分布;坝前水深较大,会出现水温分层情况,具体表现为:4—6月坝前水温呈稳定分层结构,7—11月坝前水温呈等温分布,12月—次年3月坝前水温处于逆温结构。

Navigable flow condition simulation based on two-dimensional hydrodynamic parallel model

Navigable flow condition simulations can provide detailed information on water depth and velocity distribution, simulation speed is one of the key factors which influence real-time navigation. In this paper, a navigable flow condition simulation system is developed to provide useful information for waterway management and shipping safety. To improve the simulation speed of 2-D hydrodynamic model, an explicit finite volume method and Open MP are used to realize parallel computing. Two mesh schemes and two computing platforms are adopted to study the parallel model＇s performance in the Yangtze River, China. The results show that the parallel model achieves dramatic acceleration, with a maximum speedup ratio of 34.94？. The parallel model can determine the flow state of the navigable channel in about 4 min, efficiency is further improved by a flow simulation scheme database. The developed system can provide early warning information for shipping safety, allowing ships to choose better routes and navigation areas according to real-time navigable flow conditions.

河道立面二维非恒定水温及污染物分布预报模型

通过建立一种立面二维模型 ,考虑自由水面的变化 ,采用全显式的有限体积法模拟了河道流动的水温及悬浮污染物质分布 .该模型适用于大尺度水域中较长期的流动、水温及悬浮物质迁移问题 .通过优化取水口位置高程将水体中污染物质残存总量控制到最少 ,对水库实际流动、水温、悬浮物质分布的模拟结果与实际观测符合良好 .

自相似型各向异性自组织介质中地震波场动力学响应

地下岩石结构/构造和矿物组成在小尺度上存在的不均匀性和各向异性会导致地震波速度的分形分布,进而衍生出自组织介质模型.本文针对地球内部岩浆垂向侵入及横向溢流为特征的岩浆作用,开展自相似型各向异性自组织介质的地震波动力学响应研究.基于二维自组织介质模型和声波方程,本文利用有限差分法模拟了不同强度岩浆侵入和溢流作用形成的自组织介质中地震波场,并进行了波场特征分析.研究结果表明:(1)在横向溢流作用为主的自组织介质中,横向相关长度小于地震波波长的条件下,聚焦效应随着横向相关长度的增大而增强,地震波能量随之增强;反之,在横向相关长度大于地震波波长的条件下,散射效应随横向相关长度的增大而增强,地震波能量随之减弱.(2)在垂向侵入作用为主的自组织介质中,随着垂向相关长度增大,散射效应增强,地震波的能量也随之迅速减弱.(3)岩浆作用的自组织强度增强,地震波的能量增大,而中心频率无变化.(4)自组织介质具有相同的小尺度扰动,其速度梯度背景越小,地震波能量在炮点附近越集中.(5)当多层自组织介质共存,特征层位的波场特征仍以各自的自组织特性为主,因此利用实际资料中不同层位的地震反射特征可推测地下介质的自组织性质.

潮汐动力场准三维值模拟

本文建立了适用于海岸潮汐动力环境模拟的准三维数学模型，其特点是在成功实现二维全流模型计算的同时，求解流速差值（即流速与其垂线平均值之差）方程组，从而获得潮流速的垂直分布，并使两者结果相一致。在验证计算和应用于复杂海域的研究计算中，数值结果不仅与分析解取得一致，而且与实测值符合较好，证明该模型是实用有效的。

两种空化模型计算二维水翼空化流动研究

采用混合多相流模型和空化模型对攻角为6.5°的NACA66型二维水翼的空化流动进行数值研究.使用Singhal全空化模型(FCM)和Zwart-Gerber-Belamri(Z-G-B)空化模型,以实验数据为基准,对这两种空化模型得到的翼型表面压力分布系数和升、阻力系数以及流场结构进行了比较和分析,结果表明:FCM中,不凝结气体质量分数对计算结果影响较大,空化区长度随着不凝结气体质量分数的减小而变小;Z-G-B空化模型中,蒸发系数和凝结系数对结果有较大影响.总体说来,通过选取合理的经验系数,两种空化模型都给出了令人满意的空化流动结果.

抽水蓄能电站竖井式出水口三维数据模拟

盖板竖井式进 出水口是抽水蓄能电站采用的形式之一 ,出流工况的水力学问题是其难点问题。本文利用三维k ε紊流数学模型 ,针对西龙池抽水蓄能电站上水库盖板竖井式进 出水口 ,研究了抽水工况出流时竖井扩散段、孔口附近的流动特性 ,探讨孔口底板附近反向流速的成因。

天然分汊河道平面二维水流泥沙数值模拟研究

基于无结构化网格,采用有限元方法,建立起一种适合于分汊河道的平面二维水沙数学模型,模型采用质量集中的简化处理和预估校正的时间推进算法,较好地解决有限元计算存储量和计算速度。并以武汉天兴洲汊道段为例,进行水沙验证计算,验证结果与实际符合较好,证明模型能较好地模拟天然分汊河道的水流泥沙运动及河床变形情况,因此可为分汊型河道的整治提供技术支持。