Stepwise superposition approximation approach for analytical solutions with non-zero initial concentration using existing solutions of zero initial concentration in contaminate transport

Analytical solutions for contaminant transport are widely used for both theoretical and practical purposes.However,many existing solutions are obtained subject to an initial condition of zero concentration,which is often unrealistic in many practical cases.This article proposed a stepwise superposition approximation approach to solve the non-zero initial concentration problem for first-type and third-type boundary conditions by using the existing zero initial concentration solution.Theoretical examples showed that the approach was highly efficient if a proper superposition scheme with relative concentration increments was constructed.The key parameter that controlled the convergence speed was the time increment（△t） multiplied by the rate constant（λ）.The approach served also as an alternative way to make a convenient concentration calculation even if the non-zero initial concentration solution of a problem was known.

Stress concentration coefficients of optimized cope-hole welded detail

The fatigue performance of optimized welded detail has been investigated by fatigue experiments of three welded specimens under different loadings.In addition,local finite element models of this welded detail were established using finite element software ANSYS.The influences of different factors such as plate thickness,plate gap and initial geometric imperfections on the stress concentration coefficient(SCC) were discussed.The experimental results indicate that the fatigue life of three specimens for this welded detail is 736,000,1,044,200 and 1,920,300 times,respectively.The web thickness,the filler plate thickness and the initial geometric imperfection have relatively less effect on the SCCs of this welded detail.However,cope-hole radius is influential on the SCCs of the web and the weld.The SCC of weld is significantly affected by the weld size and plate gap,but the SCCs of other parts of the welded detail are hardly affected by the plate gap.

Combustion characteristics of low concentration coal mine methane in divergent porous media burner

Low-concentration methane(LCM) has been one of the biggest difficulties in using coal mine methane.And previous studies found that premixed combustion in porous media is an effective method of low calorific gas utilization. This paper studied the combustion of LCM in a divergent porous medium burner(DPMB) by using computational fluid dynamics(CFD), and investigated the effect of gas initial temperature on combustion characteristic, the distribution of temperature and pollutant at different equivalence ratios in detail. Besides, the comparison of divergent and cylindrical burners was also performed in this paper. The results show that: the peak temperature in DPMB increases as the increasing of equivalence ratio, which is also suitable for the outlet NO discharge; the linear correlation is also discovered between peak temperature and equivalence ratios; NO emission at the initial temperature of 525 K is 5.64 times,larger than NO emission at the initial temperature of 300 K. Thus, it is preferable to balance the effect of thermal efficiency and environment simultaneously when determining the optimal initial temperature range. The working parameter limits of divergent burner are wider than that of cylindrical one which contributes to reducing the influence of LCM concentration and volume fluctuation on combustion.

高岭土对含有Cu^(2+)和Pb^(2+)污水吸附性实验

这是一篇环境工程领域的论文。为了研究高岭土对含有Cu^(2+)和Pb^(2+)污水吸附性能的影响,开展了不同初始浓度、温度、吸附时间、高岭土掺量和pH值作用下高岭土吸附重金属离子实验,并分析了高岭土对Cu^(2+)和Pb^(2+)共同吸附实验结果。结果表明:高岭土吸附金属Pb^(2+)离子的效果要好于高岭土吸附金属Cu^(2+)离子的效果。结合实验结果和经济效益而言,在初始浓度为200 mg/L,pH值为6、温度为30℃,高岭土掺量为1.5 g,吸附时间为2.0 h时,高岭土对金属Pb^(2+)和Cu^(2+)离子的吸附效果较优,其中金属Pb^(2+)离子的吸附量分别达到了56.38、56.22、58.76、35.75、和42.42 mg/g,金属Cu^(2+)离子的吸附量45.99、47.45、47.27、25.26、22.52 mg/g。整体上,高岭土对共同吸附金属离子(Cu^(2+)、Pb^(2+))的吸附量要小于单一离子的吸附量,这是由于两个金属离子在吸附过程中会相互影响对方的吸附过程。Langmuir模型对实验曲线的拟合度要远远高于Freundlich模型对实验曲线的拟合度,这就说明了Langmuir等温吸附模型更加适用于高岭土吸附金属离子吸附量的变化规律,进而证明了高岭土吸附重金属离子属于表面吸附,被吸附的重金属离子都是相互独立存在的。

瓦斯气体水合固化作用影响因素分析

瓦斯与水的水合作用可以促使煤层中的瓦斯气体以水合物的形态固化于煤层之中,为研究外在条件对瓦斯水合物生成的影响,自主搭建了静态水合物合成实验装置,开展了瓦斯水合作用实验,分别考察了促进剂添加量、初始压力对瓦斯水合作用的影响规律,分析了促进剂、初始压力对瓦斯水合物生成促进作用机理。结果表明:促进剂的添加有效增加了水合作用效果但却存在极限浓度,当促进剂浓度介于3 wt%-8.7 wt%时会促进水合作用的进行,浓度达到8.7 wt%时作用效果最佳,而当促进剂浓度在14.4 wt%时,则会减缓水合作用进程;初始压力与水合作用效果呈正相关关系,初始压力越高水合作用的速率越快,水合作用时间越长;通过对反应余气中甲烷组分的监测表明,促进剂和初始压力能够改变水合作用的进程,对于瓦斯水合固化效果起着决定性的作用。

非饱和半空间受埋置集中力作用初值解

基坑开挖和盾构掘进引起的环境效应是城市岩土工程中的重点,现有研究较少考虑土体的非饱和性。基于连续介质力学建立三维非饱和固结方程,假定初始时段体变为0,孔压和气压不随时间变化,引入McNamee和Schiffman位移函数,将固结方程的初解问题解耦为一组调和方程,通过Hankel变换将偏微分方程组转换为常微分方程组,利用边界条件和连续条件给出变换域内的位移和应力初值解答,最后通过Hankel逆变换给出原非饱和半空间域的解析解答,通过退化算例验证文中方法的正确性。算例分析表明,埋置集中力作用下,随着饱和度减小,位移逐渐减小,超静孔压则呈现先增加后减小的趋势。文中解答可以作为基本解,用于基坑开挖和盾构掘进等工程施工引起的非饱和地层位移场和应力场分析以及对邻近构筑物影响研究。

湘潭市城区夏季VOCs光化学损耗特征及来源解析

挥发性有机物(VOCs)化学活性差异较大,如仅通过观测浓度开展VOCs来源解析将降低活性较强物种的贡献,不利于以缓解臭氧(O_(3))污染为目的的VOCs减排。为有效降低光化学损耗对于VOCs来源解析的影响,文章通过光化学老化方法估算湘潭市城区夏季VOCs的初始浓度,矫正光化学损耗的影响,进而利用正交矩阵因子分解模型(PMF)开展VOCs来源解析研究。研究结果表明,观测期间湘潭市城区夏季VOCs平均观测浓度为(23.90±5.79)×10^(-9)(体积浓度,下同),初始浓度为(31.28±15.17)×10^(-9)。其中烯烃变化最大,是观测浓度的4.33倍,其次是芳香烃(1.87倍)。白天光化学平均总消耗量为14.66×10^(-9),以烯烃光化学消耗量为主,占总消耗量的70.7%。初始浓度、O_(3)和气温的日变化趋势基本一致,15时达到最大值,光化学损耗量也处于最大小时值(22.69×10^(-9))。O_(3)污染日烯烃和芳香烃光化学损失大于非污染日,烯烃和芳香烃的光化学损失是臭氧生成的重要来源。湘潭市城区夏季VOCs初始浓度PMF源解析结果显示工业源的贡献占比最高,观测浓度结果显示二次转化是最高的贡献源类。

城市不同下垫面降雨径流水质监测及特征研究

城市面源污染是仅次于农业面源污染的第二大非点源污染,也是影响城市水生态系统健康的重要原因。随着城市化的快速发展,下垫面改变导致城市河流洪峰增大,河流污染加剧。基于沥青屋面、砖砌路面、油毡屋面和绿地四种典型城市下垫面的5场降雨径流监测试验资料,分析了不同下垫面条件下的降雨径流污染水平、径流水质变化特征和初始冲刷效应。结果表明:(1)4种下垫面的降雨径流总氮质量浓度均属于劣Ⅴ类水;四种下垫面的总磷污染程度相对较轻,沥青屋面、砖砌路面、油毡屋面和绿地的降雨径流总磷质量浓度优于Ⅳ类水的频率分别为80%、16%、88.46%和5.56%;沥青屋面、砖砌路面、油毡屋面和绿地的降雨径流总悬浮物质量浓度分布范围分别是7~798、15~569、10~871和44~378 mg/L。(2)总氮和总磷的径流污染水平排序为:砖砌路面>绿地>沥青屋面>油毡屋面;总悬浮物的径流污染水平排序为:绿地>砖砌路面>油毡屋面>沥青屋面。(3)中雨情景下各下垫面不同污染指标变化趋势差异较大,而小雨情景下受人为活动影响较大的下垫面的各污染指标浓度较高。(4)各下垫面污染物的初始冲刷强度排序均为:总悬浮物>总磷>总氮;各下垫面的初始冲刷强度排序为:沥青屋面>油毡屋面>砖砌路面>绿地。(5)沥青屋面和油毡屋面降雨径流中的总悬浮物和总磷具有较好的同源性,而砖砌路面降雨径流中的总磷与总氮和总悬浮物都具有较好的同源性。综合而言,各下垫面总氮和总悬浮物的场次降雨径流平均浓度远超于地表水Ⅴ类水质标准,会对城市水体造成污染,可根据不同下垫面的特点采取相应措施来降低污染物浓度。

集中阻尼弦初值问题的解析复模态叠加法

实际工程中常用黏滞阻尼器对斜拉索进行减振,然而基于阻尼拉索系统模态叠加法求解系统动力时程问题的研究还很少。研究设置集中黏性阻尼器的拉索在任意给定初始条件下的自由振动问题,提出采用解析复模态叠加法进行求解的思路。给出系统复模态正交性条件,并提出利用正交性条件确定复模态叠加系数的思路。通过三个数值算例,验证了方法的正确性和高效性。该文计算结果表明,对于集中阻尼弦初值问题,一般只需利用系统的前数阶模态进行叠加即可得到理想的结果。

Why Are Arctic Sea Ice Concentration in September and Its Interannual Variability Well Predicted over the Barents–East Siberian Seas by CFSv2?

To further understand the prediction skill for the interannual variability of the sea ice concentration(SIC)in specific regions of the Arctic,this paper evaluates the NCEP Climate Forecast System version 2(CFSv2),in predicting the autumn SIC and its interannual variability over the Barents–East Siberian Seas(BES).It is found that CFSv2 presents much better prediction skill for the September SIC over BES than the Arctic as a whole at 1–6-month leads,and high prediction skill for the interannual variability of the SIC over BES is displayed at 1–2-month leads after removing the linear trend.CFSv2 can reasonably reproduce the relationship between the SIC over BES in September and such factors as the surface air temperature(SAT),200-hPa geopotential height,sea surface temperature(SST),and North Atlantic Oscillation.In addition,it is found that the prescribed SIC initial condition in August as an input to CFSv2 is also essential.Therefore,the above atmospheric and oceanic factors,as well as an accurate initial condition of SIC,all contribute to a high prediction skill for SIC over BES in September.Based on a statistical prediction method,the contributions from individual predictability sources are further identified.The high prediction skill of CFSv2 for the interannual variability of SIC over BES is largely attributable to its accurate predictions of the SAT and SST,as well as a better initial condition of SIC.

基于“源头”本义理解把握“精神之源”的三个向度——关于伟大建党精神与中国共产党精神谱系关系的再认识

如何理解伟大建党精神是中国共产党的“精神之源”,把握伟大建党精神与中国共产党精神谱系的内在关系,是需要深入思考的重要理论问题。基于“源头”的本义进行分析,更能有效阐释清楚“精神之源”的政治意涵,更能贴近“精神之源”所要表达的政治论断和政治意境。从起始性来看,伟大建党精神是中国共产党精神谱系的精神肇始;从贯通性来看,伟大建党精神是中国共产党精神谱系的精神凝练;从存在性来看,伟大建党精神是中国共产党精神谱系的精神原点。

Effects of sludge retention time,carbon and initial biomass concentrations on selection process:From activated sludge to polyhydroxyalkanoate accumulating cultures

Four sequence batch reactors（SBRs） fed by fermented sugar cane wastewater were continuously operated under the aerobic dynamic feeding（ADF） mode with different configurations of sludge retention time（SRT）, carbon and initial biomass concentrations to enrich polyhydroxyalkanoate（PHA） accumulating mixed microbial cultures（MMCs） from municipal activated sludge.The stability of SBRs was investigated besides the enrichment performance. The microbial community structures of the enriched MMCs were analyzed using terminal restriction fragment length polymorphism（T-RFLP）. The optimum operating conditions for the enrichment process were： SRT of 5 days, carbon concentration of 2.52 g COD/L and initial biomass concentration of3.65 g/L. The best enrichment performance in terms of both operating stability and PHA storage ability of enriched cultures（with the maximum PHA content and PHA storage yield（YPHA/S） of61.26% and 0.68 mg COD/mg COD, respectively） was achieved under this condition. Effects of the SRT, carbon concentration and initial biomass concentration on the PHA accumulating MMCs selection process were discussed respectively. A new model including the segmentation of the enrichment process and the effects of SRT on each phase was proposed.

Biodegradation of bezafibrate by the activated sludge under aerobic condition:Effect of initial concentration,temperature and pH

Lab-scale experiments were conducted to investigate the effect of initial concentration,temperature and pH on the removal of bezafibrate(BF)by activated sludge under aerobic condition.The results showed that adsorption of BF onto activated sludge was negligible,and biodegradation was the main removal mechanism of BF.The removal of BF in the aqueous phase by the activated sludge can be described by a pseudo-first-order reaction.The reaction rate constants had a negative relationship with the initial concentration of BF,and dramatically reduced from 0.050 to 0.007 h^-1,when the temperature dropped from 20℃to 10℃.Variation of pH between 5.0 and 9.0 did not have significant influence on the removal of BF,indicating a high adaptation of microorganism in the activated sludge responsible for BF degradation to a wide pH range.The findings of this study are helpful to improve the removal of pharmaceuticals during the wastewater treatment plants by selecting the appropriate process variables,and eventually eliminate their release to the environment.

Effect of Initial Concentrations on Solidification of Ammonium Chloride Water Solution

The effect of initial concentrations on solidification of ammonium chloride water solution is numerically investigated in detail.The solidifying process.with the cold wall temperature lower than the eutectic temperature,is assumed to be one-dimensional,and controlled by heat conduction only.The simulation reveals that:(1) The solid-mush interface grows in a linear manner,while the growth rate of the mush-liquid interface decreases in a parabolic manner,with increasing initial concentrations.(2) The temperature field in the whole region has parabolic characteristics,but is shows a linear feature in the solid zone and mushy zone.(3) The concentration always has linear characteristics in the much.(4)The solid fraction distribution is strongly affected by the initial concertration.The solidification process shows quite different features,especially at small and high initial concentrations.

液氮冻融-微波注热急速冷热冲击下饱水煤力学及渗流特征研究

为研究饱水、冻融与温度因素耦合作用下煤岩力学及渗流特征,以王庄煤矿9105工作面原煤为研究对象,采用非接触式数字图像处理技术开展液氮冻融与微波注热条件下煤岩三轴加载实验。研究结果表明:原始煤岩经液氮冻融、液氮饱水冻融、液氮饱水冻融不同温度处理后,煤岩抗压强度、弹性模量降低,泊松比升高,剪切应变值增大;原始煤岩在压密、弹性、屈服和破坏4阶段应力集中现象无明显变化,但经3种条件处理后,煤岩局部应力集中在破坏阶段出现明显扩增现象;相比于原始煤岩初始渗透率,经冻融处理后煤岩初始渗透率为1.44×10^(-3)μm^(2),增幅较小;经饱水冻融、饱水冻融后50℃、100℃温度处理,煤岩初始渗透率增幅较为明显;经饱水冻融后150℃温度处理后煤岩初始渗透率为7.40×10^(-3)μm^(2),增幅显著提高。研究结果可为深部低渗透煤层瓦斯增透提供指导,对提高井下瓦斯抽采效率具有参考意义。

初始应力下巷道围岩瞬态P波扰动响应研究

为了解决工程现场中动态扰动对巷道围岩稳定性造成影响的问题,揭示动力扰动对地下结构破坏的理论机理,基于波函数展开法,求解了无初始应力状态下圆形巷道周边的动态应力分布。并通过LS-DYNA有限元软件研究了弹性巷道围岩中初始应力对动态应力集中的影响。在垂直方向应力为30 MPa和孔洞轴向方向应力为10 MPa条件下,分别取不同侧压系数,得到在无初始应力状态下和有初始应力状态下的圆形巷道周边的动态应力集中因子(DSCF)以及动态应力放大系数(DSAF)的分布。研究表明初始应力对圆形巷道动态响应的影响并不是简单的线性叠加,而是一个动态的应力平衡过程;初始应力状态下,DSCF的分布与无初始应力分布大致相同,在侧压系数为1时,孔边的最大DSCF较无初始应力状态下的增大了0.3左右;在初始应力状态下,孔边的应力变化会出现不规律的波动,在动载应力下降段,孔边将出现主应力的偏转和应力释放,导致急剧的应力变化;孔洞周边围岩的DSAF随侧压系数的增大而减小。

基于激光空化技术的酸性黑溶液降解特性研究

为了研究激光技术在废水降解领域中的应用,采用激光诱导空化技术对酸性黑溶液进行降解,通过紫外分光光度计对降解后的溶液进行分析表征,获得激光能量和溶液初始质量浓度对降解能力的影响;结合空泡动力学理论和空化化学效应,揭示了激光空化降解酸性黑溶液的机理。结果表明,随着激光能量的增加,初始质量浓度为20 mg/L的酸性黑溶液的降解率从0.78%逐步增加到27.28%;在100 mJ激光能量下,当溶液中酸性黑溶液的初始质量浓度从5 mg/L提升至20 mg/L时,降解率从98.55%降低至7.63%;激光能量越高,降解率越大;初始质量浓度过大,则激光空化难以对酸性黑溶液进行降解。该研究推进了激光空化降解染料等有机废水技术的发展。

承德市降水对细颗粒物和可吸入颗粒物的清除作用分析

利用承德市2018—2020年逐小时细颗粒物(PM_(2.5))和可吸入颗粒物(PM_(10))监测数据和气象观测资料,分析PM_(2.5)和PM_(10)基础浓度时间变化特征及不同风速影响下浓度变化规律,探讨基础浓度和风速订正后降水对污染物的湿清除作用。结果表明:(1)PM_(2.5)和PM_(10)基础浓度均值均为11月至次年3月较大,4、10月次之,5—9月较小。(2)秋、冬季风对PM_(2.5)清除效果较明显;风对PM_(10)全年总体有清除作用,但风速大于8 m/s,会导致春季PM_(10)浓度暴增。(3)降水过程对PM_(2.5)和PM_(10)均有很好的清除作用,清除率大多随着降水等级的增大而增大,降水对PM_(10)的清除率高于PM_(2.5)。(4)中雨及以上等级降水过程结束后,PM_(2.5)和PM_(10)空气质量指数均为良好及以上等级。(5)当PM_(2.5)和PM_(10)初始质量浓度高于60、110μg/m^(3)时,不同等级的降水过程均可明显降低PM_(2.5)和PM_(10)浓度。当PM_(2.5)和PM_(10)初始质量浓度低于60、110μg/m^(3)且雨强小于5 mm/h时,PM_(2.5)和PM_(10)浓度有反弹升高现象,其中当雨强小于2 mm/h时,初始浓度越低反弹的可能性越高。

湍流扩散环境中基于前馈神经网络的信源定位算法

为实现湍流扩散环境中的信源定位,提出了一种基于前馈神经网络(FNN)的定位方法.在FNN中联合交叉熵函数和均方误差函数作为损失函数,并在数据输入前增加了批量归一化层防止测试集过拟合.利用仿真得到的分子浓度数据对FNN模型进行训练,并使用测试集验证了所提方法的性能.仿真结果表明:在20 m仿真长度的湍流管道中,对于定位和初速度识别均在20次迭代内达到收敛;得到的平均定位误差为0.2 m,且误差在0.69 m范围内的概率达到90%,初速度识别的准确率达到95.4%.所提方法可以实现不同分子释放速度条件下的信源定位并识别发射分子的初速度,极大地减少了接收机的布置.

影响低温等离子体降解VOCs因素的研究进展

随着生态环境越来越重要,由于挥发性有机物(VOCs)对人类健康和生存环境有着重大的影响,因此大气污染防治也变得十分重要。归纳了目前几种降解VOCs的技术及优缺点,包括冷凝技术、吸附技术、催化燃烧技术、光催化技术等。主要针对低温等离子体技术介绍其降解VOCs的技术原理,并对其影响因素进行了综述,突出了反应物初始浓度和电源参数对其影响的重要性。对低温等离子体技术未来发展方向进行了展望。