Clogging of saturated porous media by silt‐sized suspended solids under varying physical conditions during managed aquifer recharge

Managed aquifer recharge is an effective method for utilizing excess flood flows, but clogging of porous media is a limiting factor in the implementation of this water storage technique. In recent years, much research on the physical clogging of porous media during artificial recharge has been conducted. However, the understanding of clogging due to silt‐sized suspended solids (SS) is still inadequate, especially under varying physical conditions. Here, we subjected sand columns to controlled rates of flow and SS suspensions to investigate the influence of media size, SS size, SS concentration, and flow velocity on the clogging of porous media by silt‐sized SS. The results show that the diameter ratio of SS particles to sand grains is the dominant factor influencing the position of physical clogging. As pore velocity increased, the mobility of silt‐sized SS was enhanced and retention in the porous media decreased noticeably. The spatial retention profiles in the porous media were found to vary greatly at different flow velocities. The SS concentration of the infiltrating suspension also dramatically influenced the mobility and deposition of silt‐sized SS particles, such that high concentrations accelerated the clogging process. As the different physical factors changed, the breakthrough curves and retention profiles of silt‐sized SS particles changed obviously and the mechanisms of retention differed. On the whole, clogging position is mainly determined by particle size ratio, but clogging rate is dominated by a variety of factors including particle size ratio, SS concentration, and flow velocity.     

大庆地震台网近震震级偏差分析与校正

选取大庆地震台网2002-2009年近震报告资料,以《黑龙江省地震目录》给出的震级为标准,进行震级偏差统计.按地区分段校正后,震级精度明显提高.     

结构双层多重调谐质量阻尼器(DMTMD)控制策略的鲁棒性评价

基于定义的二类优化目标函数,评价双层多重调谐质量阻尼器(DMTMD)控制策略对漂移频率系数(DFR)摄动的鲁棒性。数值研究表明,使用第二类优化准则设计的DMTMD、双重调谐质量阻尼器(DTMD)和多重调谐质量阻尼器(MTMD)比使用第一类优化准则设计的DMTMD、DTMD和MTMD具有更高的对DFR摄动的鲁棒性。而且,使用第二类优化准则设计的总数为4的DMTMD、DTMD和总数为11的MTMD具有近似相同的对DFR摄动的鲁棒性。     

青海玛多MS7.4地震前b值时空变化特征

大量研究表明地震孕育过程中存在相对平静期,该阶段b值会相对下降,b值变化在地震活动性研究中起着十分重要的作用。2021年5月22日青海玛多发生MS7.4地震,为研究地震前b值时空变化特征,本文截取2009年至震前地震目录,将地震目录分为去除余震目录、完整地震目录,对比研究b值变化特征。研究发现,玛多MS7.4地震前1年b值开始低于均值且不断下降,至b值有上升趋势时地震发生,扩大到区域内其它5级以上地震,也符合此规律,地震发生后b值明显上升,短时间内又下降至较低位置,并一直处于较低位置直至下次地震发生;从b值空间扫描结果看,玛多MS7.4地震前,震中位于低b值区域,该位置为b值最低处;通过不同时间段的b值空间扫描结果,可发现玛多MS7.4地震发生前低b值区域向震中不断迁移,表明地震发生前震中附近应力不断集中;b值空间扫描时,完整地震目录掩盖了中强震震中区域低b值特性,去余震地震目录较好的凸显了中强震震中区域低b值特性。     

Simplified analysis of frame structures with viscoelastic dampers considering the effect of soil-structure interaction

In this study, simplified numerical models are developed to analyze the soil-structure interaction (SSI) effect on frame structures equipped with viscoelastic dampers (VEDs) based on pile group foundation. First, a single degree-of-freedom (SDOF) oscillator is successfully utilized to replace the SDOF energy dissipated structure considering the SSI effect. The equivalent period and damping ratio of the system are obtained through analogical analysis using the frequency transfer function with adoption of the modal strain energy (MSE) technique. A parametric analysis is carried out to study the SSI effect on the performance of VEDs. Then the equilibrium equations of the multi degree-of-freedom (MDOF) structure with VEDs considering SSI effect are established in the frequency domain. Based on the assumption that the superstructure of the coupled system possesses the classical normal mode, the MDOF superstructure is decoupled to a set of individual SDOF systems resting on a rigid foundation with adoption of the MSE technique through formula derivation. Numerical results demonstrate that the proposed methods have the advantage of reducing computational cost, however, retaining the satisfactory accuracy. The numerical method proposed herein can provide a fast evaluation of the efficiency of VEDs considering the SSI effect.     

A family-level macroinvertebrate biotic index for ecological assessment of lakes in Yunnan,China

Persistent economic growth in Chinese southwestern Yunnan Province is setting aquatic ecosystems in its plateau lakes under enormous pressure. While several different systems have previously been used to study these lakes, no existing methodology adequately measures both the chemical and biotic parameters of these water bodies. Here, we present a novel Biotic Monitoring Yunnan Lakes (BMYL) index that provides a general assessment tool for ecological deterioration that is caused by organic pollution. Principal Component Analysis is used to analyze the occurrence of families of macroinvertebrates and chemical properties of the lakes. In brief, families of macroinvertebrates were given a score from 10 to 1 based on sensitivity to organic enrichment and eutrophication. Sampling at each lake yielded an Average Score per Lake (ASPL) which is calculated by dividing the total BMYL by the total number of scoring families. High ASPL values characterize a biologically intact lake containing relatively large numbers of high scoring taxa, while lower ASPL values denote a polluted lake that does not support many high scoring taxa. The results of the BMYL show a notably more accurate characterization of the long-term health of concerned aquatic ecosystems than studies that use abundance levels of species or a simple analysis of chemical parameter.     

Distribution and source apportionments of polychlorinated biphenyls (PCBs) in mariculture sediments from the Pearl River Delta, South China

Surface and core sediments collected from six mariculture farms in the Pearl River Delta (PRD) were analyzed to evaluate contamination levels of polychlorinated biphenyls (PCBs). The ∑PCBs (37 congeners) concentrations ranged from 5.10 to 11.0 ng g(-1) (mean 7.96 ng g(-1)) in surface and 3.19 to 22.1 ng g(-1) (mean 7.75 ng g(-1)) in core sediments, respectively. The concentrations were significantly higher than that measured in the sediments of their corresponding reference sites, whereby the average enrichment percentages were 62.0% and 42.7% in surface and core sediments, respectively. Significant correlations (R2=0.77, p<0.05) of PCB homologue group proportions between fish feeds and surface mariculture sediments suggested that fish feed input was probably the main source for the enrichment of PCBs. Due to the fact that PCBs could be transferred along food chains, PCB contamination in fish feeds and mariculture sediments should not be overlooked.     

Development of a distributed hydrological model to facilitate watershed management

To facilitate precise and cost-effective watershed management, a simple yet spatially and temporally distributed hydrological model (DHM-WM) was developed. The DHM-WM is based on the Mishra-Singh version of the curve number method, with several modifications: The spatial distribution of soil moisture was considered in moisture updating; the travel time of surface runoff was calculated on a grid cell basis for routing; a simple tile flow module was included as an option. The DHM-WM was tested on a tile-drained agricultural watershed in Indiana, USA. The model with the tile flow module performed well in the study area, providing a balanced water budget and reasonable flow partitioning. The daily coefficient of determination and Nash-Sutcliffe coefficient were 0.58 and 0.56, for the calibration period, and 0.63 and 0.62 for the validation period. The DHM-WM also provides detailed information about the source areas of flow components, the travel time and pathways of surface runoff.

EDITOR A. Castellarin; ASSOCIATE EDITOR F.-J. Chang     

Nonlinear tidal waves in a kind of estuary with gradually varying cross-section

-Nonlinear tidal waves in a kind of estuary are studied in the paper using one-dimensional nonlinear hydrody-namic equations with friction. The estuary has exponentially varying width B=B0 e-bx and uniform depth h. The one-dimensional hydrodynamic equations are solved by perturbation method. It was found that our solution included two special cases, Pelisenpeki's solution and Airy's solution. The former can be got by letting b=0 in our solutions, and the latter by setting 6 = 0 and f= 0 (f is linear frictional coefficient). In terms of the second-order solution, the physical mechanism of nonlinear tidal waves in estuaries with gradually varying cross-section is explored. It is shown that, under the assumption of linear friction coefficient, shallow water constituent waves consist of two parts, one is produced by shallow water nonlinear effect outside the estuary, the other is generated by shallow water nonlinear effect inside estuary. In addition, the physical mechanism of the residual tidal current and