A new solution and data analysis for gas flow to a barometric pumping well

When an open well is installed in an unsaturated zone, gas will flow to/from the well depending on the pressure difference between the well and the surrounding media. This process is called barometric pumping and the well is called a barometric pumping well (BPW). Understanding subsurface gas pressure distribution and gas flow rate to/from a BPW is indispensable to optimize passive soil vapor extraction. This study presents a 2-D semi-analytical solution to calculate the subsurface gas pressure and gas flow rate to/from a BPW with and without a check valve. The problem is conceptualized as a mixed-type boundary value problem. The solution for pumping without a check valve is used to analyze the behavior of the radius of influence (ROI). Results show that ROI is time-dependent. It increases with radial gas permeability and decreases with vertical gas permeability. Field application of the solution without a check valve demonstrates the high accuracy of the developed solution.     

2010年2月24日沈阳地区冻雨成因分析

利用NCEP的全球数据同化系统（GDAS）1°×1°分析资料、NOAA的2.5°×2.5°全球格点资料和气象观测资料等,对2010年2月24日沈阳地区大范围冻雨灾害天气过程进行分析。结果表明：冻雨发生前期,沈阳地区的明显增温是导致大范围雨雪冰冻灾害的重要原因;925—750 hPa存在的t≥0℃温厚暖层是冻雨形成的必要条件;西南气流的建立有利于大量暖湿空气向东北地区输送,并决定了低温冰冻灾害发生的区域。中层温厚暖层的建立与破坏时间对冻雨的预报具有一定的指示意义。     

水位变化过程中边坡临界滑动场

库水位升降过程中,会引起边坡体内孔隙水压力分布的变化,对边坡的稳定性产生影响。对边坡临界滑动场进行改进,提出了可以考虑水位变化过程的边坡临界滑动场数值模拟方法,方便、快速地计算出边坡局部、整体安全系数在水位变化过程中的变化历程。通过对一个典型边坡在水位上升和下降过程中的稳定性分析,并和其他方法进行比较分析,结果表明,临界滑动场方法能搜索任意形状的最危险滑面,计算的安全系数是合理的。     

风向对半固定沙垄表面风速影响——以古尔班通古特沙漠为例

利用DETI可移动测风系统对古尔班通古特沙漠半固定沙垄表面风速进行实地观测,获取了主要风季不同风向条件下沙垄表面7个典型部位距离地表20 cm、40 cm、60 cm、100 cm和200 cm 5个高度的风速系列数据,系统研究风向对半固定沙垄表面坡面风速及风速廓线的影响。结果表明,迎风坡的气流加速和背风坡的风速降低现象在实际观测中得到证实,但受风向的影响甚大。垄顶风速放大率随入射角的增大呈指数关系递增,而背风坡风速占垄顶风速的比率则随入射角的增大呈线性关系递减。大角度入射气流速度变化主要受控于沙垄形态,小角度入射气流速度变化主要受控于地表植被状况。无论气流以何种角度入射,距沙垄表面20 cm高度气流的加速均较其他高度缓和。沙垄底部和坡中下部的风速廓线变化趋势基本一致,且呈较好的对数拟合关系;两坡中上部和垄顶部的对数拟合方程相关系数偏小;受回旋涡流的影响,风速廓线在背风坡上部有明显偏折,初步断定涡流中心在距地表40 cm左右的高度。     

横向沙丘背风侧气流重附风洞模拟

二次流在沙丘形成和形态维持过程中扮演着重要角色。沙丘迎风坡气流加速和背风侧气流分离是最常见的二次流形式。沙丘背风侧的二次流,尤其是气流分离形成的分离涡和气流重附对沙丘背风坡的塑造、沙丘间距和排列模式都具有重要的控制作用。因此,设计了一系列具有不同迎风坡坡度的横向沙丘模型,采用粒子图像测速技术,通过风洞实验模拟了沙丘背风侧的气流分离和重新附着。实验结果表明,当来流风速垂直于沙丘脊线时,沙丘背风侧的气流重附距离介于4\^8 H~10\^8 H之间(H为沙丘高度),最大重附距离出现在迎风坡坡度为15°的沙丘背风侧;沙丘迎风坡坡度是控制背风侧气流重附距离的主要因素,而自由风速对气流重附距离的控制作用较小。根据实验结果,还讨论了气流分离与重附对沙粒运移和沙丘形态维持的沉积学意义。     

Transition Regimes in Valley Airflows

A three-dimensional, non-hydrostatic model was used to examine the dynamical characteristics of morning and evening transition periods in the atmosphere over four idealised valleys. The simulations provided detailed structure over full diurnal cycles of the valley-wind system. An essentially two-dimensional simulation (Case 1) clearly showed valley-side slope flows, driven by pressure gradients and modulated by vertical diffusion and Coriolis effects. The rotation of the wind was clockwise on both valley sides, contrary to most observations in nature. Three-dimensional simulations (Cases 2–4) rectified this feature and that for Case 4 satisfactorily modelled the valley-plain wind system throughout the diurnal cycle. Three types of transition were identified with the aid of different tools: hodographs; space-time evolution of the wind fields; and the evolution of the forcing terms in the momentum and temperature equations. Whichever type or Case was considered, the evening transition was longer than the morning one and the along-valley transition followed the along-slope one. In Cases 1 and 4 the evening transition started up to 2 h before sunset and the morning transition started up to 2.5 h after sunrise. In the three-dimensional cases the evening transition began at about 1700 and ended at about 2400, starting at the bottom of the valley and propagating up both valley sides, but at different speeds. It also started at the ground and propagated vertically. The morning transition began at about 0900 and ended at about 1100, also starting at the bottom of the valley and propagating both vertically and up the valley sides, albeit with different regimes on the two sides. The along-valley transition lagged that on the slopes by about 1.5 h. In Case 1 the forcing terms were dominated by the pressure gradient and the vertical diffusion, with the Coriolis effects introducing an along-valley component to the slope flows. The three dimensional cases were more complex, with not only the addition of the effects of advection and horizontal diffusion but also more temporal variation of more of the forcings than in Case 1.     

有限水域近水面气流演化特征试验研究

气流作为湖泊、湿地等有限水域的主要驱动力之一,其演化特征是研究水-气间能量与物质传递的基础,决定了水域水环境与水生态格局,具有重要研究意义.采用室内风洞水槽,通过设置不同试验风速,研究近水面气流与风速和吹程的响应关系与演化特征,并将光滑壁面条件下的气流特征作为试验对照组,分析时间域内风速垂向分布形式、摩阻风速、特征粗糙...     

西湖叶绿素a周年动态变化及藻类增长潜力试验

通过1999年1－12月对杭州西湖主要湖区叶绿素a含量及水量理化指标的逐月测定,分析了西湖主要湖区叶绿素a含量周年动态变经特征及各种环境生态因子对叶绿素a的影响,并对湖水进行了藻类增长潜力试验,研究结果表明,西湖主要湖区叶绿素a含量总体保持在同一水平,年变化在41．16－191．26mg/m^3之间,年均值为为99．98mg/m^3。叶绿素a妗有明显的季节变化特征,夏季和初秋为高峰、冬季最低,水体总磷浓度与叶绿素a年周期动态变化一致,叶绿素a含量的季节变化与水温变化呈显著正相关,西湖为典型的蓝藻型湖,叫氮年均值为2．08mg/L总磷年均值为0．121mg/L,N:P大于17,水体中磷对藻类增长的促进作用比氮更加明显。     

三峡水库小江回水区水华暴发期浮游植物群落结构及其与环境因子的关系

三峡水库蓄水以来,支流水华频发,尤以小江情况最为严重,给三峡库区的生态安全带来较大隐患。为探究支流水华暴发特征和主控因素,于2014-2021年小江水华暴发期间在小江高阳江段进行浮游植物及环境因子调查,并使用单因素方差分析、聚类分析、百分比相似性分析以及基于距离的线性模型等方法,对小江水华暴发期间浮游植物和环境因子在不同年份不同水层间的差异以及二者的关系进行研究。结果表明:小江水华暴发期内,浮游植物的种类数在43~70种之间,其中2015年蓝藻种类数明显减少,2018年以后硅藻种类数明显减少;采样期间浮游植物平均细胞密度在0.66×10⁶~61.28×10⁶ cells/L之间,同期表层细胞密度明显高于中层和底层;各层水体间水华微囊藻、铜绿微囊藻、不定微囊藻等10种藻的密度存在明显差异,是主要差异种;显著影响表层、中层和底层浮游植物群落结构变动的环境因子是水位的日平均变幅;水位的日平均变幅与藻类优势种拟合关系显示,当日水位下降幅度在0.5 m以上时,浮游植物平均密度会呈指数级减少。研究结果可为三峡库区支流水华的防控提供数据支持。