Determining design parameters for recovery of aquaculture wastewater using sand beds

Design information for the use of sand beds to remove suspended solids from wastewater discharged from recirculating aquaculture systems (RAS) was developed. Wastewater from a commercial RAS tilapia farm with 2% total solids and 1.6% total suspended solids (TSS) was applied to sand columns to determine infiltration rates and phosphorus capture. Various hydraulic loading rates and drying periods between application events were evaluated. Infiltration rates stabilized after five application events to 3.5 cm/day (S.D.=1.7). Practically, all suspended solids were captured at the top of the columns, creating the primary resistance to infiltration. Concrete sand removed approximately 93% of the soluble phosphorous in the wastewater and wollastonite, an economical aggregate alternative to sand, removed at least 98%. A modified Darcy equation is presented to predict infiltration based upon TSS and the number of sequential applications.     

Darcy定律在测定油松木质部导特征中的应用

该介绍了一种测定油松幼树不同部位枝条导水性的方法－冲洗法。在立地条件相同或相近的情况下，选择年龄相近的4株油松幼树（8－10年生），用冲洗法进行测量。在此基础上，首次成功地将Darcy定律应用于树木木质部的导水特征分析。结果表明，油松幼树在相对分枝级、冠层、分枝方向等不同的情况下，比导率表现出不同的变化趋势。通过对平均比导率（Ks）差异的进一步分析， 能够较好地反映出油松木质部的导水特征和其在抗旱中的生态策略。     

基质渗透系数分析及其应用研究

[目的]比较不同基质的渗透系数及其在人工湿地中的适用范围。[方法]采用达西定律分析不同基质的渗透系数,结合中试分析人工湿地的净化能力。[结果]不同基质的渗透系数存在比较大的差异,砂子和炉渣的渗透系数比较高,且与其大颗粒粒径(>0.5 mm)呈显著正相关(P<0.05);而黄筋泥的渗透系数比较抵,不同比例的砂子和黄筋泥混合可以提高黄筋泥的渗透系数。以炉渣和砂子作为基质建立人工湿地工程时,人工湿地运行稳定,在水力负荷0.13 m/d的条件下,总氮、总磷、BOD5和高锰酸钾指数的去除率分别为43.52%3、0.26%、79.33%和63.96%。[结论]室内-中试试验结果说明达西定律可以作为一种简便的筛选人工湿地基质的方法。     

Effect of Initial Hydraulic Gradient on Consolidation of Sand drained Ground Improved by Vacuum Preloading

Because of the existence of initial hydraulic gradient in clay, non Darcy equation with initial hydraulic gradient was modified with classical consolidation theories of sand drained ground.And the approximate solution in the instance of vacuum preloading was presented.Based on this, the effect of initial hydraulic gradient on the seepage front, the pore water pressure and the average degree of consolidation were investigated.It was found that the spread of vacuum pressure was delayed because of initial hydraulic gradient, resulting in the dissipation of pore water pressure and the speed of soil layer consolidation.The hysteresis became more and more evident with the increase of initial hydraulic gradient.In addition, initial hydraulic gradient also caused some residual pore water pressure which could not reach vacuum pressure.Thus, the ultimate average degree of consolidation was less than 100%, which decreased with the increase of initial hydraulic gradient.     

基于能坡划分原理的大比降山区河流阻力特性

在山区河流水沙灾害河道修复中,河道阻力系数是一个非常重要的参数。普通天然河道的达西阻力系数是水深h与泥沙粒径d比值的函数,而在山区大比降粗糙河道中,其值随着坡降的改变而变化。为探究大比降河道达西阻力变化规律,该研究通过变坡水槽试验设置3种坡度（10°、25°、35°）更大的河道,试验时床面铺设中值粒径为0.5、1和1.85 mm的3种天然沙,流量设定为0.5～2.5 L/s,淹没度范围h/d为0.84～7.27,采取试验数据和经典文献数据共计48组,涵盖河道坡度范围0.97°～35°（对应比降S范围为17‰～573.6‰）,进而建立能够反映滚波影响的适用于山区大比降河流的达西阻力表达式。结果表明：1）大比降河道水流表面会产生滚波,使得达西阻力系数增大;2）大比降河流的能坡可划分为两部分：正常河道无滚波时的能坡以及河道水面滚波产生的额外能坡,前者及其对应的达西阻力系数可以利用传统的对数公式进行求取,后者可以利用总能坡与无滚波时的能坡相减得到;3）将建立的比降达西阻力公式计算结果与实测数据比较,可以发现绝大部分数据落在±20%误差线中,说明该研究提出的公式的计算精度较高。研究建立的大比降河流阻力计算模型可以揭示大比降河道水流能量消耗机理,为后续研究大比降河流问题提供理论基础。     

有限宽任意壁厚含油轴承润滑方程研究

通过对含油轴承润滑方程的分析研究,提出并建立了有限宽任意壁厚含油轴承润滑方程--改进的Darcy模型.利用改进的Darcy模型分析了渗透度、壁厚、偏心率对含油轴承压力、承载能力、摩擦因数性能的影响,并与Brinkman模型的计算结果进行了对比分析.该模型比Brinkman模型结构简单,计算量小,比Darcy模型更接近实际情况.     

The Numerical Simulation of Casting Process for Making Metal Matrix Composites

In this paper,a numerical simulation of the casting process for making the MMC.using the PEM, is studied.The convection of liquid metal and the release of latent heat of solidification are taken into account.The algorithm and program for axisymmetric casting model are developed to the problem of coupling between flow and heat transfer,as well as phase change.The variational curves of temperature,the position of flow front and the distrsbutions of volume fraction of solid metal in matrix and their variation with time are obtained.The influences of technological paarmeters to casting are discussed.     

Darcy定律在测定油松木质部导水特征中的应用

该文介绍了一种测定油松幼树不同部位枝条导水性的方法———冲洗法 .在立地条件相同或相近的情况下 ,选择年龄相近的 4株油松幼树 (8～ 10年生 ) ,用冲洗法进行测量 .在此基础上 ,首次成功地将Darcy定律应用于树木木质部的导水特征分析 .结果表明 ,油松幼树在相对分枝级、冠层、分枝方向等不同的情况下 ,比导率表现出不同的变化趋势 .通过对平均比导率 (Ks)差异的进一步分析 ,能够较好地反映出油松木质部的导水特征和其在抗旱中的生态策略 .