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.     

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.     

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.     

凌桥支线输水钢管(顶管)受力数值分析

凌桥支线工程是青草沙水源地原水工程陆域输水系统的主要组成部分,选择合理的输水管材对工程的安全及节能具有重要意义。在考虑土压、管道内压、地面堆载和交通载荷共同作用的同时,还考虑了土体的初始应力场及非线性变形特性,采用弹塑性力学模型与有限元方法,对凌桥支线输水管道的受力情况进行理论分析和数值模拟,得到输水管道应力应变变化规律,这将对凌桥支线输水工程管材的优化设计具有积极意义。     

Hydrodynamic effects on contaminants release due to rususpension and diffusion from sediments

Hydrodynamic effects play a very important role in the contaminants release from sediments. Experiments were perfor-med to study contaminants releasing characteristics due to resuspension. The time-dep...     

无纺织布喷熔射流拖网表面流场特性研究

本文的工作是对喷熔无纺织布的常用生产设备-喷熔机的风场特性及流动控制进行研究.通过理论分析、数值模拟和模型实验三个方面对问题展开了具体的研究,首先对喷熔机风场流动进行理论分析并建立数学模型,然后进行数值模拟,最后根据模型相似理论,制作比尺为3∶1的有机玻璃模型,使用90N10型热线风速测量系统(HFA),参考数值模拟工况对喷熔装置风场流动进行了实验测量,这三个部分工作彼此验证,补充和完善.数值模拟结果和实验测量结果基本一致,吸风装置工作状态对拖网板上方流场有重要影响.随着挡风板开度和主副吸风速度搭配的改变,拖网上方流场呈现规律性的变化.研究表明在恰当的挡风板开度和吸风速度下,拖网上方流场速度分布和压力分布的均匀性都有显著提高,进而使无纺布孔径更小更均匀,孔隙形状和孔隙结构更为规整,提高了无纺布的均匀性、强度以及过滤效率.     

车轮-地面耦合动力学行为的CDEM-DEM分析

越野车辆在软土路面上行驶时，其车轮-地面相互作用的动态力学行为极其复杂，车轮的下陷程度和通行能力均为车辆地面力学研究的重点。为探究车轮在软土路面通行时的动力学性能，本文提出了一种连续-非连续单元法（Continuous-discontinuous Element Method, CDEM）与颗粒离散元法（Discrete Element Method, DEM）相结合的耦合计算方法。该方法中，车轮采用CDEM单元进行描述，软土路面采用DEM颗粒进行描述，CDEM单元与DEM颗粒之间采用罚弹簧进行耦合，通过在车轮上施加动态扭矩，实现了车轮在软土路面上摩擦、滚动及前行过程的精确模拟。借助CDEM与DEM的耦合，探讨了车轮花纹、路障对车辆行驶过程中动力学行为的影响规律。研究结果表明：花纹车轮及光面车轮均在软土路面留下清晰可见的车辙；花纹轮胎较光面轮胎表现出更强的通行能力；花纹车轮转动速度较小，但其车轮平动速度远高于光面车轮，花纹车轮平动与其线速度之比约为12.78%，而光面车轮比值仅为2.80%；车轮在软土路面行驶过程中，相同质量下的光面车轮下陷深度远高于花纹车轮；车辆在含路障路面通行时，地...     

基于CDEM-MPM耦合的软地面车辆侵入规律研究

载荷装备通过软土地面会引起了软土地面的变形，车轮侵入软土的深度是软土地面装备通行性评估的重要参数。本文提出了连续-非连续单元法（Continuum-discontinuum Element Method, CDEM）与物质点法（Material Point Method, MPM）耦合的数值计算方法，建立了车轮-软土地面耦合模型，模拟了车轮和软土地面相互作用过程，定量分析车轮载重、软土弹性模量、软土强度参数（黏聚力、摩擦角）与软土表面压应力、侵入深度等参数之间的关系，获得车轮侵入软土深度的变化规律。研究表明：软土侵入深度与车轮载重接近线性正相关，相对改变量约为179%；与弹性模量非线性负相关，相对改变量约为23%；与强度参数非线性负相关，相对改变量约为164%。当车轮载重一定时，非线性变化的车轮侵入深度对软土强度参数更敏感。建立强度参数（黏聚力、摩擦角）和侵入深度变化的三维关系，可为软土地面装备通行性评估中现场待测的关键参数提供理论依据。     

装备野外通行路径优化算法研究进展

随着野外装备智能化的不断发展，野外环境下的装备路径优化成为近年来研究的重要领域之一，其在促进军事力量的发展和推动军事智能化的进程等方面起到重要作用。目前国内外对于既有道路下车辆优化方法的研究和总结较为成熟，但由于野外环境的复杂性和未知性，基于既有道路的优化算法无法在野外路径优化中直接应用。因此，本文基于国内外野外环境下的装备路径优化技术的研究现状，从环境建模和路径优化算法两个研究层面进行了归纳总结，并将野外路径优化算法分为单装备路径优化和多装备路径优化，阐述了各方法的适用范围与利弊，针对野外环境下的动力学问题，重点阐述了动力学约束下的装备路径优化算法，最后对未来野外路径优化算法的发展方向进行了展望。     

基于Bekker理论改进遗传算法的野外路径优化方法研究

随着装备智能化的发展，复杂野外环境下车辆的路径规划已成为关键技术之一，为军事力量发展、军事装备智能化提供重要保障。野外环境中有多种影响车辆行驶的因素，如障碍物、路面坑洼和泥泞等，传统城市道路的路径优化算法大多针对既有道路，难以满足在存在多种未知威胁的复杂野外环境下的路径优化要求。同时，目前路径优化算法对于野外复杂的土壤地质条件考虑较少，因此本文基于Bekker地面力学理论，结合改进的遗传算法，提出了一种考虑土壤对车辆行驶影响的改进遗传算法，该方法以路径行驶时间最短为优化目标，建立了适合野外环境的路径优化算法。含障碍物和含多种土壤的野外环境建模和路径优化结果表明：该优化算法建立了地面力学特性与车辆行驶的耦合作用，综合考虑了野外环境下的障碍物、土壤特征和车辆特性等因素，在复杂的野外环境下得到了车辆可以安全、高效和畅通通行的野外路径，为建立地形力学与路径优化算法的联系提供了参考。