Numerical research for contaminant release from un-suspended bottom sediment under different hydrodynamic conditions

Contaminant release from bottom sediments in rivers is one of the main problems to study the environmental hydrodynamics. Contaminant will release into the overlying water column under different hydrodynamic conditions through pore-water in sediment, the release mechanism can be roughly divided into convection diffusion, molecular diffusion and adsorption/desorption. In this article, phosphorus was as a typical contaminant with sorption. Through theoretical analysis of the contaminant release, according to different particle-sized and hydraulic conditions, the mathematics model of contaminant release can be established by the coupled Navier-Stokes equation, Darcy equation, solute transport equation and adsorption/desorption equation. Then that model was verified by flume experiment. Numerical studies show that, under different velocity, the instantaneous concentration of convection diffusion is about 6 times to 50 times larger than that of molecular diffusion during initial stages. The concentration of molecular diffusion is about 1 times to 4 times larger than to that of convection diffusion during late stages. Through analysis, the diffusive boundary layer near the interface can be obtained. In addition, the release will increase with particle size decreasing, and the release will be influenced much more by the size change when the particle size is relatively big under different velocity.     

底泥污染物释放水动力特性实验研究

在环境水动力学中,河口地区的河流底泥污染物释放扩散特性的研究越来越受到人们的重视.实际上,污染物在底泥和上覆水体之间的释放扩散,对上覆水体水质有很大影响.底泥污染物释放扩散受到底泥本身物理性质和上覆水体水动力特性的共同作用.本文对底泥污染物向上覆水体释放扩散规律进行了水槽实验,通过对水体中底泥释放污染物COD浓度的测量分析,初步得到了底泥污染物在动水条件下的释放机理.底泥污染物释放主要分为两种形式:一是底泥污染物泥水界面释放,二是底泥污染物起动悬浮释放.随后结合底泥污染物释放的水槽模拟实验,天然河道(苏州河)现场实测资料,对三者进行了分析比较.它们相互符合得较好,所反映的基本规律是一致的,表明了本文实验研究的合理性和可靠性.     

PIV直接测量泥沙沉速试验研究

本文应用激光测量仪器PIV对长江口水库泥沙水样在沉降筒中进行沉降速度场测量，得到了平均的泥沙沉速，并分析了含沙量、絮凝等因素对泥沙沉降的影响。同时通过试验发现PIV直接测量泥沙沉速是一种可行的、有效的试验方法。     

黏性浆液在小孔隙多孔介质中扩散的流固耦合分析

该文基于有效应力原理建立了描述黏性浆液在小孔隙多孔介质中扩散的流固耦合模型.通过对小孔隙多孔介质注浆过程中的浆液渗流场分布与固体骨架的应力应变特性的流固耦合分析,得到了各动态参数如孔隙率、应变率等的相互关系并在施工现场进行了试验.经过与施工现场试验数据对比,得到的数值分析结果与试验结果基本一致,验证了该流固耦合模型运用于注浆工程的可行性与实用性,可作为小孔隙多孔介质地层防渗注浆设计和注浆效果的初步评判.     

Experimental investigation on diffusive contaminant release from permeable sediment layer under unidirectional unsteady flow

The interfacial diffusive contaminant（phosphorus） release from permeable sediment layer into overlying water column under a unidirectional unsteady（periodic） flow condition was experimentally measured and analyzed. The experimental results indicate that the gross diffusive contaminant release rate is substantially enhanced as compared to that under a steady flow condition, and this enhancement trend is much more pronounced in an immediate release stage. The interfacial diffusive contaminant release rate tends to increase with the increasing flow velocity, decreasing period and augmenting amplitude for the case of the unsteady flow. The additional interfacial diffusive contaminant release under the unsteady flow condition may be related to the hydrodynamic response of the diffusive boundary layer to the flow unsteadiness of the overlying water, depending upon not only the periodic thickness variation of the diffusive boundary layer immediately above the sediment-water interface modulated by the temporal flow velocity of the overlying water column but also the intensified turbulent mixing between the overlying water and the pore-water within the superficial sediment layer induced by an alternate acceleration/deceleration fluctuation during each period.     

泥沙颗粒和孔隙水在底泥再悬浮污染物释放中的作用

在环境水动力学中,河流底泥污染物释放是人们研究的主要问题之一。污染物进入到水体中后会有一部分聚集在水体底泥中,并在底泥的上层形成一条污染底泥层。底泥再悬浮时,污染物会通过再悬浮颗粒以及孔隙水重新释放到上覆水体中。此文中分别以氯化钠和磷代表典型非吸附性污染物和吸附性污染物,研究底泥污染物释放中底泥颗粒相和水相在不同的水力条件下所起到的作用。研究表明,在底泥静止状态和瞬间悬浮条件下,底泥污染物的释放主要来自于水相孔隙水,非吸附性污染物的释放主要集中在这两个状态下;而在连续悬浮条件下,再悬浮颗粒的解吸释放起着主要的作用,吸附性污染物的释放大部分发生在此阶段。另外,此文还研究了两种类型的泥沙即粘性细颗粒泥沙和非粘性粗颗粒泥沙在底泥连续悬浮时的释放量和释放时间的异同。研究表明,再悬浮粗颗粒泥沙的污染释放量要比再悬浮细颗粒小,但前者释放持续的时间要比后者长。     

紊流边界层挟气能力的研究

本文通过试验和理论分析,对紊流边界层内紊动扩散系数的分布规律进行了研究,认为扩散系数在边界层内区和外区都可近似看成是直线变化。根据跟随性理论,计算了一般水流频率情况下,水流中可含的气泡直径,从而得出计算气泡上升速度的公式。文中还从输运基本方程出发,推导了掺气水流含气量的计算公式,提出了掺气减蚀保护长度主要是指边界层内紧靠边壁中含气浓度C≥7％的距离的概念,并考虑了掺气浓度沿程的变化,从而导出计算掺气保护长度的计算式.     

主蒸汽和给水管弯头内壁裂纹超声波检测法

采用手动直接接触的斜探头横波脉冲反射法，对重庆电厂东厂给水管弯头的两个侧面进行超声波探伤，发现七个弯头侧平面表面裂纹。该方法有很高的灵敏度和准确性，对探头的基本条件和修磨后的参数变化及修磨进行了较详细分析     

汽轮发电机主轴中心孔打磨机的研制和应用

一种新型的打磨机,具有整机重量轻,体积小,结构简单,易于操作等特点。它采用压缩空气为动力源,驱动扇形砂轮片在离心力的作用下,对汽轮机、发电机转轴中心孔表面进行打磨。     

Sediment rarefaction resuspension and contaminant release under tidal curren- ts

Based on experiment in tidal flume, this paper analyzes the sediment rarefactive phenomenon and hydraulic characteristics of sediment resuspension with different physical properties under the effect of tidal current. According to this experiment, sediment resuspension is related to the hydraulic characteristics of overlying water and its own dry density, namely the moisture content of sediment and deposition time. Generally, river sediment can be classified into the upper layer of floating sludge and lower layer of deposit sediment. Incipient velocity goes higher as the sediment layer goes thicker. Based on the experiment, incipient velocity formula of sediment can be obtained. There is a cohesive force among natural fine sediment whose resuspension is almost irrelevant to their diameters. Therefore, the critical incipient velocity is determined by the cohesive force instead of particle diameter. The lower layer of deposit sediment is generally not so easy to start up. And it will be rarified and release into the overlying water when contacting with overlying water. However, this rarefaction release velocity is gentle and slow. Under the same flow condition, annual loss amount of lower layer deposited sediment is about one fifth of upper layer of floating sediment. Flow velocity of tidal river and variation of the water level are asymmetrical, both of which vary under different tidal cycles. During long tidal cycle, flow velocity and water level change in the same phase and amplitude with tide. During the whole ebb and flow, flow direction does not change as the water level goes under the influence of acceleration and deceleration. As the tide cycle increases, the incipient velocity of sediment goes higher. This means that the long period tide cycle plays buffer effect on the resuspension of sediment, which makes the sediment not so easy both to start up and to suspend.