2D numerical flow modeling in a macro‐rough channel

A 2D numerical flow model, developed at the Research unit of Hydrology, Applied Hydrodynamics and Hydraulic Constructions at ULg, has been applied to flows in a macro‐rough channel. The model solves the shallow water equations (SWE) with a two length scale, depth‐integrated k‐type approach for turbulence modeling. Data for the comparison have been provided by experiments conducted at the Laboratory of Hydraulic Constructions at EPFL. In the experiments with different non‐prismatic channel configurations, namely large‐scale cavities at the side walls, three different 2D flow characteristics could be observed in cavities. With the used numerical model features, especially regarding turbulence and friction modeling, a single set of bottom and side wall roughness could be found for a large range of discharges investigated in a prismatic channel. For the macro rough configurations, the numerical model gives an excellent agreement between experimental and numerical results regarding backwater curves and flow patterns if the side wall cavities have low aspect ratios. For configurations with high aspect ratios, the head loss generated by the preservation of important recirculation gyres in the cavities is slightly underestimated. The results of the computations reveal clearly that the separation of turbulence sources in the mathematical model is of great importance. Indeed, the turbulence related to 2D transverse shear effects and the 3D turbulence, generated by bed friction, can have very different amplitude. When separating these two effects in the numerical models, most of the flow features observed experimentally can be reproduced accurately. Copyright © 2009 John Wiley & Sons, Ltd.     

斜放四角锥扁网壳的非线性弯曲理论

双层网壳是大型空间结构的主要结构形式,斜放四角锥扁网壳就是其中一种.它主要依靠上、下表层承受载荷,网壳腹部则比较空而且柔.根据斜放四角锥扁网壳的几何和力学特点,在三个基本假定的基础上,把它连续化并等效成一夹层扁壳.先从能量和内力等效的角度来分析它的本构关系,然后运用虚功原理,推导出斜放四角锥扁网壳几何非线性弯曲理论的基本方程.     

浅水回流的混合有限分析解

混合有限分析法是一种在局部矩形单元上进行离散的数值格式,为了适应非规则边界,建立了Sigma坐标系的浅水回流数学模型。采用1)风引起的回流,2)密度驱动的回流,3)假潮,来检验数学模型和数值方法。计算结果和相应的分析解的比较表明模型和方法是可行的有效的。该技术可用于近海水域的水流和水质的数值模拟。     

包含泥沙冲淤的浅水方程的混合有限元法(Ⅰ)——时间连续的情形

研究由水动力方程、 泥沙输运方程和河床变化方程组成的浅水方程的初边值问题, 讨论其广义解和混合有限元解的存在性, 并导出半离散混合有限元解的误差估计, 这些估计是最优阶的．     

卤化银乳剂制备中的新型掺杂剂

本文综述了近年来乳剂制备中常用的新型掺杂剂,较详细地介绍了两种能提高光电子利用效率的掺杂剂,即过渡金属络合物浅电子陷阱掺杂剂和羧酸盐(酯)有机空穴陷阱掺杂剂,总结了掺杂剂的选择原则,并举例说明了掺杂剂对乳剂感光度的影响.     

基于神经网络对扁壳结构载荷位置识别问题的研究

在建立扁壳结构识别问题的力学模型基础上,运用神经网络方法构造了三层结构的神经网络,并以此对扁壳在集中力作用下的载荷位置的识别问题进行了研究,结果表明,采用有限元方法获取基本样本,运用神经网络方法对扁壳结构载荷位置的识别具有较好的效果。     

Delineating sources of groundwater recharge and carbon in Holocene aquifers of the central Gangetic basin using stable isotopic signatures

Stable isotopes of water (δ²H, δ¹⁸O) and δ¹³C_TIC were used as a tool to trace the recharge processes, natural carbon (organic and inorganic) source and dynamics in the aquifers of the central Gangetic basin, India. Stable isotope (δ²H, δ¹⁸O) record of groundwater (n?=?105) revealed that the groundwater of Piedmont was recharged by meteoric origin before evaporation, while aquifers of the older and younger alluvium were recharged by water that had undergone evaporation loss. River Ganges and its tributaries passing through this area have very little contribution in recharging while ponds play no role in the recharging of adjacent aquifers. The connectivity of shallow aquifers of aquitard formation (comprised of clay/sandy clay with thin patches of fine grey sand), i.e. 25–60?m below ground level (bgl) with the main upper aquifer (at a depth of >120?m?bgl) was found to be higher in older and younger alluvium. Negative values of δ¹³C_TIC (median ?9.6 ‰; range ?13.2 to ?5.4 ‰) and high TIC (median 35?mM; range 31–46?mM) coupled with low TOC (median 1.35?mg/L; range 0.99–1.77?mg/L) indicated acceleration in microbial activity in the younger alluvium, especially in the active floodplain of river Ganges and its proximity.     

Constrained Hamilton variational principle for shallow water problems and Zu-class symplectic algorithm

In this paper, the shallow water problem is discussed. By treating the incompressible condition as the constraint, a constrained Hamilton variational principle is presented for the shallow water problem. Based on the constrained Hamilton variational principle, a shallow water equation based on displacement and pressure (SWE-DP) is developed. A hybrid numerical method combining the finite element method for spatial discretization and the Zu-class method for time integration is created for the SWEDP. The correctness of the proposed SWE-DP is verified by numerical comparisons with two existing shallow water equations (SWEs). The effectiveness of the hybrid numerical method proposed for the SWE-DP is also verified by numerical experiments. Moreover, the numerical experiments demonstrate that the Zu-class method shows excellent performance with respect to simulating the long time evolution of the shallow water.     

明渠条件下单丁坝绕流特征的数值模拟Numerical simulations of flows around a single spur dike in an open channel

丁坝结构广泛应用于水利工程中,用以调整水流和护滩固堤,维护优良的水道通航条件。针对单丁坝局部水流,基于非结构网格,采用有限体积法（FVM ）,建立了三维自由表面水流模型,湍流模型采用S‐A一方程模型。针对非淹没、正挑单丁坝,开展了系列 Fr数条件下的水流模拟。重点分析丁坝局部流动结构,探讨丁坝坝根处局部涡系演化等特征,研究了丁坝下游回流区长度和宽度的变化,总结了丁坝引起的剪切流的沿程变化特征。     

Modified (2+1)-dimensional displacement shallow water wave system and its approximate similarity solutions

Recently, a new (2+1)-dimensional shallow water wave system, the (2+1)-dimensional displacement shallow water wave system (2DDSWWS), was constructed by applying the variational principle of the analytic mechanics in the Lagrange coordinates. The disadvantage is that fluid viscidity is not considered in the 2DDSWWS, which is the same as the famous Kadomtsev—Petviashvili equation and Korteweg—de Vries equation. Applying dimensional analysis, we modify the 2DDSWWS and add the term related to the fluid viscidity to the 2DDSWWS. The approximate similarity solutions of the modified 2DDSWWS (M2DDSWWS) is studied and four similarity solutions are obtained. For the perfect fluids, the coefficient of kinematic viscosity is zero, then the M2DDSWWS will degenerate to the 2DDSWWS.