Numerical modeling of hyperpycnal flows in an idealized river mouth

Numerical experiments in an idealized river mouth are conducted using a three-dimensional hydrodynamics model (EFDC model) to examine the impacts of suspended sediment concentration (SSC), settling velocity of sediment and tidal mixing on the formation and maintenance of estuarine hyperpycnal flows. The standard experiment presents an illustrative view of hyperpycnal flows that carry high-concentrated sediment and low-salinity water in the bottom layer (>1.0 m in thickness) along the subaqueous slope. The structure and intra-tidal variation of the simulated hyperpycnal flows are quite similar to those previously observed off the Huanghe (Yellow River) mouth. Results from the three control experiments show that SSC of river effluents is the most important parameter to the formation of hyperpycnal flows. High SSC will increase the bulk density of river effluents and thus offset the density difference between freshwater and seawater. Low SSC of river effluents will produce a surface river plume, as commonly observed in most large estuaries. Both the settling velocity of sediment particles and the tidal mixing play an important role in maintaining the hyperpycnal flows. Increasing settling velocity enhances the deposition of sediment from the hyperpycnal layer and thus accelerates the attenuation of hyperpycnal flows, whereas increasing tidal mixing destroys the stratification of water column and therefore makes the hyperpycnal flows less evident. Our results from numerical experiments are of importance to understand the initiation and maintenance of hyperpycnal flows in estuaries and provide a reference to the rapidly decaying hyperpycnal flows off the Huanghe river mouth due to climatic and anthropogenic forcing over the past several decades.     

淤泥质潮流深槽最大冲刷深度的一个概念模型

以概念模式方法计算了淤泥质潮流深槽的最大深度,探讨了涨落潮流速、涨落潮历时、深槽淤泥质物质粒径、深槽顶底部原始深度、水道长度等因素对潮流深槽最大深度的影响。概念模式的假设条件是:(1)深槽形态为长方体,底部纵向坡度为0;(2)沉积物粒径无垂向变化;(3)只考虑潮流作用的影响,涨、落潮流速在时间序列上呈正弦分布;(4)不考虑细颗粒物质的粘性和絮凝作用。模拟结果显示:(1)涨、落潮历时对深槽最大深度的影响很小。(2)优势潮流流速与最大深槽深度之间存在着幂函数关系。(3)深槽的底质粒径、深槽的长度均与最大冲刷深度呈正相关关系。(4)深槽顶部水深与最大深度呈负相关关系。(5)由于潮汐水道深度与潮流流速和沉积物侵蚀强度之间具有负反馈关系,因此水道冲刷存在着一个极限,即最终可以达到均衡状态。潮流深槽的均衡态特征和达到均衡态所需的时间可运用沉积动力学方法来确定;同时,若应用深槽的真实参数,进一步减少模型的假设条件,可望使该模型具有实际的应用价值。     

Implementing quality control on a random number stream to improve a stochastic weather generator

For decades, stochastic modellers have used computerized random number generators to produce random numeric sequences fitting a specified statistical distribution. Unfortunately, none of the random number generators we tested satisfactorily produced the target distribution. The result is generated distributions whose mean even diverges from the mean used to generate them, regardless of the length of run. Non‐uniform distributions from short sequences of random numbers are a major problem in stochastic climate generation, because truly uniform distributions are required to produce the intended climate parameter distributions. In order to ensure generation of a representative climate with the stochastic weather generator CLIGEN within a 30‐year run, we tested the climate output resulting from various random number generators. The resulting distributions of climate parameters showed significant departures from the target distributions in all cases. We traced this failure back to the uniform random number generators themselves. This paper proposes a quality control approach to select only those numbers that conform to the expected distribution being retained for subsequent use. The approach is based on goodness‐of‐fit analysis applied to the random numbers generated. Normally distributed deviates are further tested with confidence interval tests on their means and standard deviations. The positive effect of the new approach on the climate characteristics generated and the subsequent deterministic process‐based hydrology and soil erosion modelling are illustrated for four climatologically diverse sites. Copyright © 2007 John Wiley & Sons, Ltd.     

Identifying rock blocks based on hierarchical rock-mass structure model

Rock-masses are divided into many closed blocks by deterministic and stochastic discontinuities and engineering interfaces in complex rock-mass engineering. Determining the sizes, shapes, and adjacent relations of blocks is important for stability analysis of fractured rock masses. Here we propose an algorithm for identifying spatial blocks based on a hierarchical 3D Rock-mass Structure Model (RSM). First, a model is built composed of deterministic discontinuities, engineering interfaces, and the earth’s su...     

A discrete global grid system for earth system modeling

To support Earth system modeling, we propose a discrete global grid system that expresses multi-resolution spatial data. Specifically, a unified coding model that expresses a grid of nodes, edges, and cells is constructed for a triangular discrete global grid system. To fulfill the requirements of practical applications, we design a code-based topological query method for this grid system and an algorithm to transform between grid codes and geographic coordinates. We evaluate the Global Finite Volume Community Ocean Model (Global-FVCOM) on the triangular discrete global grid system in the proposed uniform coding model. The ocean tidal waves simulated by the Global-FVCOM running on the coded grid are then compared with results obtained using a traditional irregular spherical grid system, and the results display comparable accuracy. The uniform coding model proposed in this paper provides a triangular discrete global grid system that can represent multi-resolution spatial data and can be used in Earth system models. This unified coding model can also be applied to the geographic coordinate system made up of latitudes and longitudes, as well as diamond and hexagonal grids.     

盆地地史模拟述评

论述了盆地地史模拟的一般研究方法，认为回剥法是现今重建盆地沉积史与构造史最精确的方法详细讨论了地坟实校正、不整合处理和构造沉隆分析等主要数学模型及其适用范围；并在介绍地史模拟研究历史和研究现状的基础上，指出了地史模拟的发展方向。     

青海共和盆地下白垩统烃源岩地球化学特征及其生油意义

我国西北大部分地区在早白垩世处于挤压为主的构造环境,但共和地区处于伸展的构造环境,发育了巨厚的下白垩统湖相沉积。我们首次在共和盆地下白垩统发现了一套２５８．１５ｍ 厚的烃源岩。这一发现改变了以往西北白垩系烃源岩仅分布在祁连－秦岭以北的观点, 这对于研究我国西北地区白垩系烃源岩的分布和油气田的形成具有重大意义。共和盆地下白垩统从下到上分为万一段、万二段、万三段、万四段。万一段和万四段是炎热干旱气候条件下形成的红色沉积, 基本没有生烃能力。万二段烃源岩是一套炎热潮湿气候条件下形成的浅湖－半深湖相沉积, 烃源岩有机质丰度达到了中到好烃源岩的丰度标准, 干酪根类型以Ⅰ２ 型为主。该烃源岩在Ｋ２ 早期（９０．０１Ｍａ） 进入生油门限, 开始生油, 从Ｋ２ 晚期（７４．１１Ｍａ） 以来,一直处于大量生油的成熟阶段。下白垩统万三段沉积时期, 水体时深时浅, 暗色泥岩和红色泥岩交替出现。暗色泥岩属于中等烃源岩, 其有机质类型主要为Ⅱ型。它在晚白垩世 （７８．０２Ｍａ） 进入生油门限, 但一直到第四纪 （１．５Ｍａ） 才进入大量生油的成熟阶段。共和盆地下白垩统烃源岩发育, 具有形成中小型油气田的可能性。     

隧道水平冻结施工引起地表冻胀的历时预测模型

隧道水平冻结施工过程中,土体冻结引起体积膨胀,进而会在地表产生冻胀现象。实际工程一般采用多根冻结管形成冻结壁。冻结壁交圈前,地表冻胀由多个冻土柱的叠加膨胀变形引起;冻结壁交圈后,地表冻胀则由整个冻结壁的膨胀变形引起。鉴于此,考虑冻结壁的形成过程,基于随机介质理论,建立了隧道水平冻结施工引起地表冻胀位移的历时预测模型。同时对冻结外锋面半径和冻胀区域外半径这2个关键参数的取值方法进行了相关探讨。最后针对两个工程案例,采用该计算模型对地表冻胀位移进行分析,得到地表冻胀位移随时间的变化规律,并与现场实测结果相比较,验证了模型的可靠性。该模型应用于隧道水平冻结施工前、冻结期内任意时刻的地表冻胀位移预测,可为工程冻结实施方案的合理确定提供有效依据。     

基于ArcEngine的数字高程模型更新方法研究

采用COM技术,以ARCENGINE所提供的类库和凸包算法,实现了数字高程模型(DEM)数据更新的边界检测和利用矢量地形数据采集更新数字高程模型数据的方法。保证了数字高程模型数据的精度,可以满足数字高程模型的现势性需求。     

基于OLHS随机模拟的地下水源地保护区划分

为解决确定性模型可能为地下水源地划分带来的保护不足或过保护问题,探索采用基于正交拉丁超立方抽样法的地下水模型研究,并结合粒子反向追踪技术,进行地下水流随机模拟和对应保护区的概率统计分析,最终得到具有分布概率的保护区范围。为验证该方法的实用性与可靠性,选取北京市平谷区王都庄应急水源地进行实例应用研究。在考虑渗透系数和降雨补给量随机抽样组合基础上进行地下水流动随机模拟,并完成对应保护区划分和加权统计。与确定性模拟划分结果相对比:一级保护区中,确定性模拟划分结果仅相当于随机模拟结果中统计概率70%以上的范围;对于二级保护区,确定法对应保护面积相当于随机模拟结果中50%概率以上的范围。实例研究表明,基于正交拉丁超立方抽样的随机模拟法可完成多个不确定性输入变量条件下的随机模拟,且在小样本数的基础上获得理想结果,适用于复杂水文地质条件下的地下水源地保护区划分研究。