Effect of the Three Gorges Reservoir on vertical distribution of suspended sediment concentration and estimation accuracy of depth-average concentration in downstream reaches

The sediment regime in the middle Yangtze River has been significantly changed from quasi-equilibrium to nonequilibrium since the impoundment of the Three Georges Reservoir (TGR). To understand the effects of the TGR on vertical distribution of suspended sediment concentration (SSC) and estimation accuracy of mean concentration, vertical sediment concentration and flow velocity data at the Shashi and Jianli hydrological stations in the reach before and after the impoundment were collected. Comparisons and analysis of vertical profiles of SSC before and after the TGR impoundment show that after the impoundment of the TGR, due to the coarsening of sediment particle size, the reduction in sediment load, and the significant decrease in sediment saturation, the vertical distribution of SSC in the downstream reaches became more uneven under medium and low water flows, which was reflected in the vertical gradient and the fluctuation degree of SSC significantly increased. In addition, the depth-average sediment concentrations were calculated by the selected-point method and the mean values calculated by the “multi-point method” were regarded as the “true mean” to evaluate the accuracy of the mean value calculated by the “few-point method.” It was found that the relative errors for the selected-point method were mainly positive before impoundment but mainly negative after impoundment. Additionally, the correction factors of one-point, two-point, and three-point methods and the position of the near-bed substituted point for the five-point method were given to reduce the error when the point measurements were used to calculate the depth-average sediment concentration in the downstream reaches.     

三峡水库汛期“蓄清排浑”动态运用方式计算研究

在入库沙量大幅减少的背景下,三峡水库持续开展汛期中小洪水调度,增大了汛期库区泥沙淤积和防洪风险,减少了水库下泄大流量的机会。在三峡水库汛期,开展“蓄清排浑”泥沙调度方式动态运用研究有助于进一步优化三峡水库汛期调度方式。利用三峡水库干支流河道一维非恒定流数学模型,探索开展了三峡水库汛期 “蓄清排浑”动态运用方式计算研究,并提出了汛期“蓄清排浑”动态运用方案。计算结果表明:三峡水库汛期“蓄清排浑”动态运用方式可以同时兼顾排沙、发电和防洪,“蓄清”水位150 m要优于155 m,“蓄清”运行期间库水位可选择在145~150 m之间浮动运行;建议将寸滩含沙量达到2.0 kg/m³且当日寸滩站入库流量≥25 000 m³/s的时间作为水库增泄“排浑”的起始时间,将出库含沙量降至约0.1 kg/m³作为“排浑”调度结束重新进入“蓄清”调度的泥沙参考因素。研究成果可为三峡水库汛期优化调度提供参考。     

深圳市降水变化特征及其未来变化情况预测

基于1998—2018年深圳市日降水资料,采用降水相对变率、集中度及集中期分析了月尺度、年尺度降水稳定性及其年内分配特征,运用Mann-Kendall非参数法和相关函数法对深圳市年降水量、降水稳定性和分配特征参数的变化趋势、突变特征及其未来降水变化特征进行分析与预估。结果表明:深圳市汛期降水稳定性比非汛期更好,年际降水分布稳定性较差,降水集中期为每年6—8月份,降水集中度处于0.23~0.72;降水量和降水分布特征参数均在2011—2013年发生突变,在发生突变后降水相对变率和集中度呈下降趋势,而年降水量和集中期呈上升趋势;深圳市未来降水序列变化趋势受过去变化特征的影响,其中未来年降水量有减少的趋势,降水集中程度逐渐增强,降水稳定性逐渐变差,年内降水分配均匀性变差,降水集中期持续向后推迟。研究成果为深圳市合理蓄水和用水提供科学依据,对水资源调度、利用以及防汛抗旱具有实际指导意义和重要的学术价值。     

氯和氯胺冲击消毒对二次供水管道生物膜的控制作用

针对建筑二次供水管壁生物膜对饮用水的生物安全性构成的潜在威胁,采用生物膜反应器(BAR)模拟二次供水管道,研究氯和氯胺冲击消毒过程对管壁生物膜的细菌总数、大肠杆菌和异养菌(HPC)灭活效果以及对生物膜结构的影响.结果表明,在第80天时生物膜中生物量达到最大,生物膜宏基因组分析表明,厚壁菌门(Firmicutes)、变形菌门(Proteobacteria)和拟杆菌(Bacteroidetes)为优势菌种.冲击消毒对生物膜的灭活效能与氯和氯胺的质量浓度以及CT值有关,在相同CT值条件下,高质量浓度氯和氯胺的灭活效果更佳.氯和氯胺的生物膜灭活效果对比可以看出,在低投量条件下,氯的细菌总数和大肠杆菌灭活效果好于氯胺,但氯的HPC灭活效果弱于氯胺;在高投量条件下,消毒剂质量浓度和CT值与生物膜的灭活效果无明显相关性,可以达到快速消毒的效果.在氯和氯胺的投加质量浓度为3.0 mg/L、CT值300~400 mg·min/L的最佳冲击消毒条件下,生物膜中细菌总数、大肠杆菌和HPC的灭活率均达到95%以上.从生物膜的表面特性分析可以看出,冲击消毒后生物膜结构破坏明显,生物膜变薄或脱落;氯冲击消毒对生物膜的破坏和削减程度优于氯胺,更有利于管道生物膜的控制.     

Characteristics of coal sludge slurry prepared by a wet-grinding process

Coal sludge slurry(CSS) is an alternative fuel and a potential competitive method for sludge reduction.Based on the researches of coal water slurry, we studied CSSs by using a wet-grinding process with different types of regional municipal sludge(sludge) in an orthogonal experiment. The sludge type,sludge mixing proportion, dosage of dispersant, and grinding time were tested in this study. The results show that water content and its occurrence characteristics in the sludge have primary hindering influences on slurry ability. The range of fixed-viscosity concentrations with raw wet sludge is from 50.78%to 44.40%(by weight), while the range is from 53.35% to 51.51%(by weight) with dry sludge. All of the CSSs exhibit shear-thinning behaviors with different variation trends, especially the CSSs with more than 15%(by weight) raw wet sludge in it. Adding the same proportion of raw wet sludge increases the thixotropic properties of CSSs and the highest area of thixotropy loop is 3065 Pa/s, while the highest value of dry sludge is 1798 Pa/s. Hydrophilic group plays an important role in adsorbing water and building three-dimension networks with other particles, which is the main reason for CSS properties.Therefore, the mechanism can be used to find the way for making high quality CSS.     

基于偏振光检测的溶液浓度测量方法研究

为了克服旋转检偏片法测量旋光性溶液浓度存在的误差大、精度低等不足,提出了一种基于旋转波片的偏振光检测溶液浓度的测量方法。采用PIN光电二极管对带有溶液浓度信息的偏振光信号进行探测,经过光电变换后利用信号调理电路实现信号处理、采集等,并将数据通过串口传送到上位机,利用LabVIEW程序进行数据处理与显示。实验结果表明,基于旋转波片的偏振光检测溶液浓度的测量方法测量精度为0.6%。该测量方法能够减小测量误差、提高测量精度,并且用户界面友好、结果显示直观。     

活性粉末混凝土冻融循环前后NaCl溶液的吸入特性

为更好地理解混凝土盐冻破坏机理,研究了NaCl溶液中NaCl质量分数对活性粉末混凝土溶液吸入量的影响规律,并比较了试件表面及芯部吸入面溶液吸入特性的差异;分析了冻融循环1 000次对溶液吸入特性的影响,给出了不同吸入面的毛细吸液系数.研究表明:活性粉末混凝土毛细吸液量随着NaCl质量分数的增大而减小;15~180 min和180~540 min两阶段溶液吸入量均与t1/2呈线性关系;试件表面毛细吸液系数远小于芯部;冻融循环1 000次后溶液吸入量显著降低,仅为冻融循环前的0.33倍;冻融循环1 000次后距离试件表面越远的吸入面毛细吸液系数越大.     

杯形件等温压扭复合成形模具失效分析及改进

为解决7A60铝合金杯形件等温压扭复合成形实验中凹模的早期失效问题,借助DEFORM有限元软件,从工艺特点、应力分布及模具结构等方面详细探讨和分析失效原因,应力集中、冷热循环热应力以及高温模具氧化是导致凹模转角处发生早期破裂的主要原因.基于"未裂先分"的方法对凹模结构进行改进,结果表明:模具改进效果较好,等效应力极值降低30%,有效避免了凹模的应力集中;杯形件成形效果较好,宏观上无明显缺陷,表层金属流线清晰可见.     

Analysis of stress-magnetic coupling effect in weak magnetic environment

Metal magnetic memory (MMM) signals are difficult to be analyzed due to noise interference, which limits its practical engineering application. A method of improving the magnetic signals is proposed in this paper by placing the excitation device which generates a weak external magnetic field about 100 A/m. The effect of the external magnetic field on the magnetic signals is studied using both finite element method (FEM) and uniaxial tensile tests. Comparison of the test data with the simulation ones of stress-magnetic coupling shows that the magnetic signals are strengthened and the measurement sensitivity of the detection system is greatly improved through the external magnetic excitation. Moreover, the FEM result has a good agreement with the testing results of No.20 steel plate. The proposed method has laid a foundation for further practical engineering application.     

多支化两亲聚合物合成及其原油乳化作用研究

通过自由基胶束共聚法制备了N-苄基-N-n-十六烷基丙烯酰胺/丙烯酰胺/丙烯酸钠三元共聚两亲聚合物-P(AM/BHAM/NaA),并优化了合成方案。该聚合物具有临界聚集浓度(CAC),当该两亲聚合物质量浓度高于700mg/L时,P(AM/BHAM/NaA)在水溶液中形成聚集体,并随着聚合物质量浓度的增加聚集体的流体力学半径增加,表观黏度也随之增加。P(AM/BHAM/NaA)具有良好的原油乳化能力,研究了不同质量浓度的两亲聚合物对原油乳化性能。结果表明,随着两亲聚合物质量浓度的升高,在水溶液中形成聚集体的体积增大,空间网络结构增大,乳化能力升高。