BEHAVIOUR OF NITRATE IN A HETEROGENEOUS FIELD SOIL: MEASUREMENTS AND MODELLING ON DIFFERENT SPATIAL SCALES     

JÜRG HOSANG 《水文研究》1996,10(9):1193-1208

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Ethical aspects in the economic modeling of water policy options     

《Global Environmental Change》2015

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环礁沉积体系的过程-产物关系: 勘察式模拟初探     

高抒 《海洋与湖沼》2023,54(1):1-15

海洋沉积体系的定量模拟可分为仿真和勘察式模拟,后者的目标是建立沉积特征的连续谱、凝练新的科学问题。本文提出一个勘察式模拟的方法论框架,即根据控制方程确定自变量的定义域,进而由模拟计算给出应变量的值域,并结合物质收支平衡原理和“圆台状环礁”几何模型,以此方法预估环礁及其海底阶地物质输运和堆积格局。环礁是珊瑚礁的独特类型,其礁盘区提供了礁体生长和礁外坡、海底阶地堆积的几乎全部物源。结果表明,环礁自身生长受控于生物碎屑生产,而海底阶地的范围和沉积速率不仅决定于离礁悬沙通量,而且受到环礁外水深和海盆环流的制约。悬沙输运和重力流过程形成常态沉降和水下滑坡的交替沉积。此模型所预测的环礁沉积体系高程-面积曲线与南海环礁的实际曲线相对照,可获得环礁演化的机制信息。模拟结果还提示了需进一步研究的科学问题,如环礁生长规模及其控制机制、环礁沉积体系中周期性沉积的时间尺度、环礁外坡由于珊瑚生长自组织机制形成的重力流事件与地震等极端事件的对比和机制识别、环礁群的海底阶地沉积记录多样性、海面变化对环礁演化的影响和沉积记录、环礁人居环境安全等。  相似文献   

基于固定主应力轴假设的砂堆基底应力凹陷的研究   总被引：1，自引：0，他引：1  

毕港  韦健飞  周蕾 《岩土力学》2014,35(4):1141-1146

对砂堆三棱柱的基底应力分布及应力凹陷现象进行了研究,基于固定主应力轴假设（FPA假设）将砂堆分为应力状态已知的I区和应力状态未知的II区,并假设了II区内的多种剪应力分布来求解II区内的应力状态,最后,将不同剪应力分布假设下砂堆中线上的静止土压力系数值与Kulhawy公式计算值对比,可得出如下结论：基底法向应力存在应力凹陷现象,自然休止角越大（砂堆越紧密）,应力凹陷程度、应力凹陷范围越大;不同剪应力分布假设下,II区应力分布形态不同,法向应力极小值所在处也不同。剪应力二次方分布假设和三次方假设下砂堆基底应力分布最为合理、最为符合真实情形。  相似文献   

基于边坡渐进破坏特征对传统极限平衡法几点假设的合理分析     

曾锃  张泽辉  杨宏丽  尹小涛  党发宁 《岩土力学》2012,33(Z1):146-150

边坡的渐进破坏特征一直以来是边坡计算仿真中的一个难点。实际边坡的破坏很少是一个整体达到极限状态,突然滑动的过程,往往是逐步发展由局部破坏到最终整体失稳,即临界状态小扰动导致的链式多米洛骨牌式失稳。利用颗粒流软件,设计了0.1 m粒径高10 m土坡的数值模型,粒间黏聚力为36 kPa,摩擦系数为0.36。初始模型在重力作用下不会发生破坏,通过单独折减粒间黏聚力到18 kPa使得边坡破坏,监测竖向颗粒组group的变化获取每20 000个时间步的边坡破坏形态,实现200 000个时间步内边坡的渐进破坏过程。边坡总是从局部开始破坏,坡体物质的运移造成次一级破坏,形成最终的近似弧形的滑动面,说明滑体不是整体下滑,不是刚体,不是整体达到极限状态;坡体内应力的变化也不是单调的,有涨有落,均区别于当前极限平衡法中有限条块的刚体假设;滑动面上同时达到极限状态假设,问题本身是静不定的,通过给出条间力的传递方式使之静定可解;整体分析不能考虑破坏的局部化和渐进特征。这说明边坡计算方法的未来在于能反映动力问题和材料破坏特征的离散元方法。  相似文献   

基于平面应变简化假定的桩扭转振动理论精度研究   总被引：3，自引：1，他引：2  

胡昌斌  张涛 《地震工程与工程振动》2008,28(3):122-130

利用拉普拉斯变换对考虑桩土耦合扭转振动条件下,桩顶受到任意激振扭矩作用的端承桩桩顶频域及时域响应进行解析求解,推导求得了桩顶位移、速度频域响应,桩顶复阻抗的解析表达式和半正弦脉冲激励作用下的桩顶时域响应半解析解;将本文所得理论解与基于平面应变假定的桩基扭转耦合振动的频域解和时域解进行了全面对比研究,具体比较范围涉及土层对桩的局部复阻抗、桩顶复频响应、速度导纳、桩顶复刚度和桩顶时域响应等方面,并得到若干重要结论。研究成果校核了平面应变假定在桩基扭转振动理论研究中的合理运用,为进一步了解桩土耦合振动的内在机理提供理论支持。  相似文献   

A SIMPLE PROGNOSTIC CLOSURE ASSUMPTION TO DEEP CONVECTIVE PARAMETERIZATION:I          下载免费PDF全文

Chen Dehui  Philippe Bougeault 《Acta Meteorologica Sinica》1993,7(1):1-18

In this work,the problem of dependency of the predicted rainfall upon the grid-size in mesoscale numerical weatherprediction models is addressed.We argue that this problem is due to (i) the violation of the quasi-equilibrium assump-tion,which is underlying most existing convective parameterization schemes,and states that the convective activity maybe considered in instantaneous equilibrium with the larger-scale forcing;and (ii) the violation of the hydrostatic approx-imation,made in most mesoscale models,which would induce too large-scale circulation in occurrence of strong con-vection.On the contrary,meso-β and meso-α scale models,i.e.models with horizontal grid size ranging from 10 to 100km,have a capacity to resolve motions with characteristic scales close to the ones of the convective motions.Wehypothesize that a possible way to eliminate this problem is (i) to take a prognostic approach to the parameterization ofdeep convection,whereby the quantities that describe the activity of convection are no longer diagnosed from the instan-taneous value of the large-scale forcing,but predicted by time-dependent equations,that integrate the large-scale forc-ing over time;(ii)to introduce a mesoscale parameter which varies systematically with the grid size of the numericalmodel in order to damp large-scale circulation usually too induced when the grid size becomes smaller (from 100 km to10 kin).We propose an implementation of this idea in the frame of one existing scheme,already tested and used for along time at the French Weather Service.The results of the test through one-dimensional experiments with the Phase Ⅲof GATE data are reported in this paper;and the ones on its implementation in the three-dimensional model with theOSCAR data will be reported in a companion paper.  相似文献   

A SIMPLE PROGNOSTIC CLOSURE ASSUMPTION TO DEEP CONVECTIVE PARAMETERIZATION:Ⅱ          下载免费PDF全文

Chen Dehui  Philippe Bougeault 《Acta Meteorologica Sinica》1993,7(2):212-223

A series of 3D predictions,dealing with the development of a heavy storm observed during the OSCAR experiment,were carried out by utilizing the PERIDOT model,and introducing alternatively the cumulus parameterization scheme of Bougeault (1985) and the prognostic one (Chen,1989;Chen and Bougeault,1993),with three different grid sizes:160 km,80 km,40 km.The feasibility of the new prognostic scheme and its improvement on the problem of dependency of the predicted rainfall upon the grid size of the numerical model were verified by comparison of the rainfall observed and those predicted.The results demonstrate that,in general,the predicted rainfall increases when the grid size decreases for both diagnostic and prognostic schemes.However,with the new prognostic scheme,the numerical model is capable,on the one hand,for the larger grid sizes,to increase the rainfall,which is under-estimated with the scheme of Bougeault (1985);on the another hand,for the smaller grid sizes,to reduce the rainfall,which is usually over-estimated.In other word,there is an obvious improvement on the problem under study.  相似文献   

中国关于积云参数化方案的应用   总被引：9，自引：3，他引：6  

刘一鸣 《气象学报》1998,56(2):247-255

文中简要评述并比较了４类积云参数化方案,着重总结了各种积云参数化方案在中国的应用,最后结合中国特点讨论了积云参数化方案在应用中存在的一些问题和改进途径。  相似文献   

EXPERIMENTAL INVESTIGATIONS AND NUMERICAL SIMULATIONS OF REDUCING SECONDARY FLOWS AROUND A SPUR DIKE     

Xuelin TANG Xiang DING Zhicong CHEN Wenlong WANG 《国际泥沙研究》2006,21(2):145-157

1 INTRODUCTION The Yangtze River at the Three Gorges Project (TGP) site meanders with a complex morphology, including ridges like Jiuling Hill that projects into the approach navigation channel (Fig. 1). The approach navigation channel consists of a 530-m…  相似文献