共查询到20条相似文献，搜索用时 15 毫秒
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A numerical model is presented to determine hydraulic and solids residence times and effluent concentrations from activated sludge reactors systems. Mass balance equations for biomass and substrate are numerically solved to determine the effects of different variables. Dimensionless quantities and computer techniques are used to express the results generally. Monod kinetics and reactors-in-series principles are applied to explain variations in axial dispersion andwastewater quality experienced in real systems. By means of the numerical approach, the variation of the ratio between the hydraulic residence time of a given reactor and that of an equivalent plug-flow tank with the same inlet and outlet conditions is investigated. Using the numerical results obtained, graphs are plotted for designing plug-flow activated sludge systems. Experimental data reported in literature is also evaluated to demonstrate the cases where the existing classical solution to the problem differs from the exact results. 相似文献
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扬程-水位逐次逼近策略优化梯级泵站群级间河道水位 总被引：2，自引：2，他引：0
级间输水河道水位优化对降低梯级调水系统运行能耗,提高系统整体优化运行效益意义重大。该文针对各级并联泵站群初始扬程及提水负荷已定条件下的梯级调水系统优化运行数学模型,考虑级间输水河道特点,采用大系统二级分解-动态规划聚合与河网非恒定流模拟相结合的逐次逼近选优策略,开展梯级泵站群整体优化运行下的级间输水河道水位优化研究,获得满足河道防洪除涝、通航、生态等水位要求的各泵站优化运行方案。该方法既可较快确定各级泵站群给定提水扬程及提水负荷下的优化运行费用,又能较好地降低系统输水过程中输水河道水位变化对泵站既定提水扬程的影响,对进一步开展复杂边界条件下梯级输水系统优化运行研究具有一定理论价值。以南水北调东线江苏境内淮安一、二、四站~淮阴一、三站梯级输水系统为典型实例,在淮安站群初始扬程4.13 m、100%负荷,淮阴站群初始扬程2.7 m、100%负荷条件下,4次数模和2次数模相比站上(下)最大水位差最小,平均为6.51 cm,即3次并联站群优化运行下扬程匹配度最高;确定了对应的各级泵站群机组各时段优化运行叶片安放角或机组转速,获得较泵机组定角恒速运行下7.56%的运行效益;且4次数模下各河道水位变幅最小,平均水位变幅14.9 cm;对应的各河道高低水位值及其出现间隔可满足通航及生态水位要求。 相似文献
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Maria A. Theodoropoulou 《Water, air, and soil pollution》2007,181(1-4):235-245
In order to estimate the longitudinal and transverse dispersivities of pore networks, an explicit method, based on the calculation of the transient variation of the spatial moments of the solute concentration over a disordered medium, is used to analyze visualization miscible displacement experiments and calculate the components of velocity vector and dispersion tensor. The longitudinal dispersion coefficient commonly estimated by using the 1-D advection dispersion coefficient is smaller than that calculated by the present method which accounts for the transverse dispersivity. The numerical predictions of the contaminant spreading in a macroscopically homogeneous porous medium are reliable presuming that correct values of longitudinal and transverse dispersivity are used. 相似文献
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A study was made of hydrodynamic dispersion in columns of pumice particles of different equivalent diameters and over a range of flow velocities. Dispersion is described by the first and second order moments of the elution curves. Two models are used to give a numerical analysis of the dispersion: a model using an apparent hydrodynamic dispersion coefficient and one using mixing cells with exchange (MCE). The part played by the stationary phase is described, and the molecular diffusion coefficient within the porous particles is calculated. 相似文献
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It is common practice to fit mathematical models to radionuclide activity–depth profiles in soils in order to quantify rates of vertical migration through the soil profile. We have fitted six such models to 21 different activity–depth profiles of radiocaesium (137Cs) derived from Chernobyl and determined relations between the models and the values of their parameters. The advection and dispersion parameters obtained using four solutions to the advection–dispersion equation (each based on different initial and boundary conditions or different simplifications) are in good agreement. We further develop a relation between parameter values obtained using the advection–dispersion models and those determined by a simpler exponential function of the form Aexp(–Bt) where t is the time and A and B are parameters to be estimated. One of the advection–dispersion models proved to be significantly better than the others in terms of goodness-of-fit, versatility and ease of use. A simple model, using calculations based on measured characteristics of the activity–depth profile, was shown to accord well with parameters derived from more complex models based on statistical curve fitting. We have also evaluated the ‘residence time’ or ‘compartmental’ model approach to characterizing radionuclide activity–depth profiles. We relate such models to a numerical solution of a simple advection equation, and we show that apparent dispersion in compartmental models is an artefact of numerical dispersion, which can be quantified by the Courant condition. For activity profiles that have a significant advection component, using solutions to the advection–dispersion equation, we have observed a strong positive correlation between advection and dispersion in the profile. 相似文献
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用红壤、赤红壤和砖红壤3种土壤胶体,测定胶体悬液在不同频率时的电导和直流电导,用以观察频散现象。结果表明,各种胶体的电导频散能力因土壤类型而异,红壤最强,赤红壤次之,砖红壤最弱。呈现明显频散所需要的频率,红壤和赤红壤为10千赫左右,砖红壤约为100千赫。可变电荷土壤的类型对电导频散的影响与土壤胶体所带的电荷总量密切相关。对于同一种胶体,悬液相对电导率(某一频率时的电导率与300赫时的电导率之比)随胶体浓度的增加而变大。红壤悬液在各种电解质存在时的电导频散曲线的形状不同,其中KCl者为一斜上直线,Ca(NO3)2,和CaCl2,者则为上翘的曲线。在1到100千赫之间,频散的顺序为:KCl>Ca(NO3)2>CaCl2。呈现明显频散所需要的频率,对KCl者为1千赫左右,Ca(NO3)2者约为10千赫,CaCl2者高达100千赫左右。在同一频率下,红壤胶体悬液的相对电导率随KCl溶液浓度的增加(10-5—10-3mol/L)而减小。 相似文献
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滴头流道结构对悬浮颗粒分布影响的数值分析 总被引：1，自引：8，他引：1
迷宫滴头内部结构复杂尺寸微小,研究流道结构对悬浮颗粒浓度分布的影响对于流道优化有重要意义。该文采用正交试验方法设计齿形流道,根据两相流理论,利用计算流体动力学软件对设计滴头进行了液固两相流数值分析。模拟得到入流浓度及颗粒大小不同时滴头内的速度及颗粒浓度分布,分析了结构参数、颗粒大小及入流浓度对悬浮颗粒浓度分布的影响。研究结果表明：流道结构参数对颗粒分布均有影响,程度从大到小顺序为：齿角度－齿间距－流道深度－齿高;入流颗粒大小为流道最小尺寸的1/10～1/6时滴头不易堵塞;齿高与齿间距的比值小于0.5时有利于提高滴头的抗堵塞性。研究为滴头结构优化提供参考。 相似文献
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内镶式滴灌带绕流流道水力性能研究 总被引：4，自引：6，他引：4
该文运用水力学公式、数值模拟和快速原型试验研究了绕流流道滴灌带的水力性能，并建立了设计流量与流道结构参数之间的计算模型。数值模拟得到的流场水力结构显示水流的水头损失主要集中在流道的拐角，分支和交汇处。在数值模拟的基础上，利用快速成形技术制造出16种结构形式的绕流流道，并进行压力与流量特性试验。试验结果表明：绕流流道的流态指数为0.5左右，且受流道的截面积和单元数的影响较小；而流量系数则随截面积的增加而增加，随单元数的增加而减小。144组试验数据的回归结果显示：流量随流道的截面积和工作压力的增加而增大，随单元数的增加而减小；其中，截面积影响最大，单元数次之，最后是工作压力。 相似文献
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Alexander P. Economopoulos 《Water, air, and soil pollution》1992,61(3-4):339-363
A new point source pollutant dispersion model is developed, allowing fast evaluation of the critical one-hour-average ground concentrations, along with the corresponding receptor distance and meteorological conditions (wind speed and stability class) for urban or rural areas, under gradual or final plume rise and with or without buoyancy induced dispersion assumptions. Relatively unstable pollutants can be dealt-with, while site-specific meteorological data are not required, as the computed concentrations are maximized against all credible combinations of wind speed, stability class and mixing height, as well as against all receptor distances. The model combines, under a constrained numerical extremization algorithm, the minimum mixing height model of Benkley and Schulman, with the dispersion relations of Pasquill-Gifford and Briggs for rural and urban settings respectively, the buoyancy induced dispersion correlation of Pasquill, the power-law wind profile exponent values of Irwin and the buoyant plume rise relations of Briggs. The model is well suited for air pollution management studies, as it allows fast and accurate screening of selected point sources in study areas and evaluation of the ways to have thier impact reduced, as well as, for regulatory purposes, as it allows the setting of minimum stack size requirements as function of the exit gas volume and temperature, the pollutant emission rates, and the hourly pollutant concentration standards. 相似文献
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Simulation of Biodegradation in Infiltration Seepage— Model Development and Hydrodynamic Calibration
Wastewater sanitation using infiltration seepage belongs to the attached growth treatment line for pollutant waste. In a specific geographical context, and for a population of approximately 500 to 1000 population equivalent, it seems to be a good choice. Despite its rustic reputation, it is a considerably complex treatment line. The aim of this study is to contribute—using numerical simulation—to the understanding of the physical and biochemical phenomena which develop inside an infiltration seepage bed. The aspects which are essential to bacterial activity—the hydrodynamics of the porous medium, the development of the active biomass, transport of substrate, oxygen transfer and consumption—are dealt with. The splitting operator technique is used; its advantage is the separate solution of the convection, dispersion and kinetics equations; each with appropriate numerical techniques. By testing a methodical verification of the model, based on the analytical solutions, we learn that the hydrodynamic dispersion and the rate of degradation have opposite effects on the efficiency in decreasing the pollution loads. Moreover, a significant result which is obtained is the evaluation of the oxygenation capacities in relation to some of the treatment line's key parameters. Finally, we carried out by experiments a successful calibration of the flow model. 相似文献
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A numerical model of biofilm reactors was tested using Monod typebiological kinetics in terms of the properties of feed solutionand dispersion. The model is based on computer techniques andthe numerical evaluation of the normalized biofilm mathematicalmodel. The effect of inlet parameters including concentration,flow rate, mass transfer coefficient and biofilm thickness wereinvestigated using the computer program developed. The numericalmodel was also applied to experimental data to demonstrate itsvalidity. In thin biofilms kinetic coefficients and otherparameters such as molecular diffusivity can be determinedbased upon experimental results. In thick biofilms, however, anadditional kinetic parameter or any other quantity related tomass transfer is a prerequisite in the evaluation ofexperimental data. 相似文献
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冻胀破坏是寒区渠道衬砌破坏的主要方式,建立合理的冻胀力学模型是渠道衬砌抗冻胀设计的基础。该文基于Winkler假定,将渠道基土的冻胀效应等效为一组相互独立且垂直或平行于衬砌板的弹簧。冻胀量通过弹簧的伸长量体现,冻胀力通过弹簧被压缩产生的反力体现。结合梯形渠道冻胀时衬砌板的受力特点,应用SL23-2006《渠系工程抗冻胀设计规范》冻胀量的计算成果,建立基于弹性地基梁理论的梯形渠道混凝土衬砌冻胀力学模型,其合理性通过与甘肃省靖会总干渠梯形渠道的前人试验和数值模拟结果进行比较验证。结果表明,该文模型计算的冻胀量和冻胀反力的分布规律与前人的试验和数值模拟基本吻合;计算的冻胀量和试验结果整体相对平均误差为4.72%,计算结果合理。该文模型与现行规范推荐的冻胀量计算成果有机衔接,可为寒区渠道抗冻胀设计提供参考。 相似文献
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电站尾水渠内鱼道进口位置布局 总被引：1，自引：1，他引：0
电站尾水渠是上溯鱼类较为理想的聚集场所,利用电站尾水渠合理布置鱼道进口,是目前大中型河流鱼道建设中的研究热点之一。该文通过数值模拟,结合鱼类游泳能力,对利用电站尾水诱鱼的鱼道进口布置进行研究。结果表明:机组运行方式、鱼道进口位置与出流方向均对鱼道进口诱鱼水流产生较大影响。机组运行方式决定了尾水渠内主流的位置,并在主流两侧形成多个回流区。回流区水流的旋转方向和位置对鱼道进口诱鱼水流的影响较大,鱼道进口的诱鱼水流动量较小,其出流方向应与回流区水流方向一致,并可根据电站运行方式,设置多个鱼道进口。主流与回流区之间的过渡区域是布置鱼道进口的重点区域。该研究结果可为优化改进大中型河流鱼道进口设计提供重要参考。 相似文献