Parameterization of the roughness length over the sea in forced and free convection

In the condition of free convection, the Charnock relation is inadequate. In this paper we extend the Charnock relation to include the effect of free convection on the roughness length. As a result, the singularity in the Monin–Obukhov similarity theory can be avoided. This paper shows two approaches to derive the roughness length formula in the forced and free convections. The first approach is based on the mixing length theory and the use of the observational data of the vertical velocity variance. We introduce a new vertical velocity scale based on the vertical velocity variance; this velocity variance is well behaved in the atmospheric boundary layer and easy to obtain from field experiments. The second approach is based on the theoretical framework of Sykes et al. (Q R Met Soc, 119: 409–421). From that framework, we develop a theory to obtain the roughness length formula. The results of these two approaches are in agreement with each other. In the past, a multiplication factor associated with free convection was considered to be a constant. This paper shows that this multiplication factor is, in fact, also dependent on the depth of the mixing height. In previous studies, experimental works were often conducted without taking into account the depth of the mixing height. Not taking into account the mixing height in the estimation of the roughness length in free convection would result in an inaccurate estimate of the roughness length and hence the drag coefficient. An erratum to this article can be found at     

Fuzzy logic approach to calculation of thermal hazard distances in process industries

In this paper, a general procedure to deal with uncertainties in each stage of consequence modeling is presented. In the first part of the procedure, the sources of uncertainty are identified and confirmed by sensitivity analysis for the source term, dispersion, physical effects and consequence analysis. While the second part comprises an application of the fuzzy logic system to each step of the consequence modeling. The proposed procedure is verified by the case study for a pool fire liquefied natural gas (LNG) on water. The results in terms of thermal radiation distances are compared with calculations obtained using the Monte Carlo method and with experimental data. The consequence model based on fuzzy logic approach provides less uncertain and more precise results in comparison to the deterministic consequence model.     

小兴安岭天然林不同林分汞含量分布特征与生物质汞库估算

植被主要通过叶片气孔吸收大气气态单质汞,森林植被是大气汞重要的汇.量化森林生物质汞库对了解全球汞循环至关重要.为揭示森林乔木层（乔木层分为树干、树叶、树枝、树根和树皮）、灌木层、草本层和凋落物层（凋落物层分为未分解层（Oi）、半分解层（Oe）和已分解层（Oa））汞含量和汞库分配,本研究选取黑龙江省凉水自然保护区小兴安岭原始林阔叶红松林、次生原始林云冷杉林和次生原始林白桦林3种原始林开展植物和凋落物汞含量和汞库调查.结果表明,乔木层各组织中汞含量遵循树皮 > 树叶 > 树枝 > 树根 > 树干的规律,云冷杉林乔木层汞含量总体上高于阔叶红松林及白桦林乔木层汞含量.凋落物中汞含量排序为Oa > Oe > Oi,原始林阔叶红松林凋落物汞含量高于次生原始林白桦林凋落物汞含量,但低于次生原始林云冷杉林凋落物汞含量.进一步估算生物质总汞库发现云冷杉林、阔叶红松林和白桦林分别为212、192和163 μg·m^-2.乔木层地上部分是森林生物质汞库的主体,其树皮汞库占总汞库的37.4%~43.5%,灌木层和草本层仅占总汞库的1%左右.本研究可为进一步评估森林生态系统在大气汞循环中的作用及预测森林火灾发生时生物质燃烧汞释放潜势提供基础数据.     

Influence of welding speed and power on residual stress during gas tungsten arc welding (GTAW) of thin sections with constant heat input: A study using numerical simulation and experimental validation

The temperature distribution and residual stresses for a GTAW circumferential butt joint of AISI 304 stainless steel using numerical simulation have been evaluated. For evaluation of weld induced residual stresses, the analysis of heat source fitting was carried out with heat inputs ranging from 200 to 500 J/mm to arrive at optimal heat input for obtaining proper weld penetration and heat affected zone (HAZ). For this chosen heat input, the influence of different weld speeds and powers on the temperature distribution and the residual stresses is studied. The heat source analysis revealed the best choice of heat input as 300 J/mm. The residual stresses on the inner and outer surfaces, and along the radial direction were computed. Increase in temperature distribution as well as longitudinal and circumferential residual stresses was observed with the increase in weld speed and power. The validity of the results obtained from numerical simulation is demonstrated with full scale shop floor welding experiments.     

生化法处理造纸废水的试验研究

采用UASB反应器和A/O池组合的生化法进行了造纸废水处理的试验研究.结果表明,UASB反应器处理造纸废水,废水可生化性得到明显改善.COD去除率与水力停留时间呈正相关性,UASB反应器水力停留时间取24 h合适.该生化法COD去除率达93.33％,氨氮去除率达87.72％,系统出水COD浓度能满足造纸行业低档纸回用水要求.造纸废水中污染物成分比较复杂,经过UASB反应器和A/O池处理后有机成分变化比较明显,污染物种类梯级减少.通过A/O池处理,污染物减少一半,主要是小分子和低碳烷烃类,还含有少量难降解有机物.     

淮南矿区不同塌陷年龄积水区环境效应分析

采煤塌陷水域是淮南矿区一种特殊的地表水体。文章选择矿区不同塌陷年龄的塌陷水域,监测分析其水质理化指标和重金属元素。结果表明:塌陷水域环境状况因塌陷年龄和周边环境差异而不同,具有季节性变化。水域受到了不同程度的污染,部分理化指标随时间增长有累计效应。与国家地表水质量标准比较,水域重金属元素除了Hg严重超标外,其它As、Se、Cd、Cr、Cu、Pb、Zn等均不超标,未对塌陷水域构成重金属污染。通过对不同塌陷水域环境效应进行分析与评价,可为其综合利用提供一定的理论依据。     

DO对水解酸化池与好氧MBR组合工艺运行效果的影响研究

针对溶解氧（DO）、气水比对水解酸化池与好氧MBR组合工艺处理污水效果的影响和能耗问题．从气水比对DO的影响,DO对COD与色度去除效果的影响等方面来讨论气水比,溶解氧以及污水处理效果之间的最佳运行点。试验结果表明。在P（MLSS）分别为5．81、4．25、2．19g／L的运行条件下,MBR的最佳气水比为39：1、28．1.18：1;DO变化速率随污泥浓度的下降而升高;DO的变化对COD、色度的去除效果影响并不显著。     

Cancer risk assessment from exposure to trihalomethanes in tap water and swimming pool water

We investigated the concentration of trihalomethanes （THMs） in tap water and swimming pool water in the area of the Nakhon Path- om Municipality during the period April 2005-March 2006. The concentrations of total THMs, chloroform, bromodichloromethane, dibromochloromethane and bromoform in tap water were 12.70-41.74, 6.72-29.19, 1.12-11.75, 0.63-3.55 and 0.08-3.40 μg/L, respectively, whereas those in swimming pool water were 26.15-65.09, 9.50-36.97, 8.90-18.01, 5.19-22.78 and ND-6.56 μg/L, respectively. It implied that the concentration of THMs in swimming pool water was higher than those in tap water, particularly, brominated-THMs. Both tap water and swimming pool water contained concentrations of total THMs below the standards of the World Health Organization （WHO）, European Union （EU） and the United States Environmental Protection Agency （USEPA） phase Ⅰ, but 1 out of 60 tap water samples and 60 out of 72 swimming pool water samples contained those over the Standard of the USEPA phase Ⅱ. From the two cases of cancer risk assessment including Case Ⅰ Non-Swimmer and Case Ⅱ Swimmer, assessment of cancer risk of nonswimmers from exposure to THMs at the highest and the average concentrations was 4.43×10^-5 and 2.19×10^-5, respectively, which can be classified as acceptable risk according to the Standard of USEPA. Assessment of cancer risk of swimmers from exposure to THMs at the highest and the average concentrations was 1.47×10^-3 and 7.99×10^-4, respectively, which can be classified as unacceptable risk and needs to be improved. Risk of THMs exposure from swimming was 93.9%-94.2% of the total risk. Cancer risk of THMs concluded from various routes in descending order was： skin exposure while swimming, gastro-intestinal exposure from tap water intake, and skin exposure to tap water and gastro-intestinal exposure while swimming. Cancer risk from skin exposure while swimming was 94.18% of the total cancer risk.     

干化-干湿转化对鄱阳湖湿地土壤氮矿化的影响

本研究采集鄱阳湖湿地3种典型植被(虉草、苔草、芦苇)土壤,在室内分别设置30%WHC(最大持水量)、50%WHC和80%WHC 3种水分条件培养1个月,分别模拟重度干旱、轻度干旱和适宜水分环境,然后添加水分到200%WHC模拟干湿转化过程;基于~(15)N同位素稀释法计算干化-干湿转化过程中湿地土壤的总氨化速率和总硝化速率.土壤干化过程中,芦苇带土壤总氨化速率最高,虉草带土壤总硝化速率最高;土壤总氨化速率和总硝化速率都随干旱程度增强而降低,轻度干旱条件下总硝化速率的降低比总氨化速率更明显;除水分条件外,总氨化速率主要受土壤碳含量影响,总硝化速率主要受pH值影响.土壤湿化过程中,苔草带和芦苇带土壤氮总氨化速率在1 d内变化较小,1～5 d不断下降;虉草带重度干旱土壤氮总氨化速率在湿化后呈上升趋势,轻度干旱土壤只在湿化后1 d内明显增大;3种植被土壤总硝化速率都在1 d内明显下降,此后维持较低水平.干化过程中,氨氧化古菌(AOA)和氨氧化细菌(AOB)丰度对土壤总硝化速率的影响相近,湿化过程中AOB丰度的影响相对增大.     

储罐池火特性研究进展

总结了常见池火特性参数如燃烧速率、火焰形态、火焰脉动、热辐射通量的半经验公式,计算得出燃烧速率、火焰拖曳直径、火焰脉动随储罐直径变化规律,火焰倾角随风速变化规律,热辐射通量随距离的变化规律,确定了多个公式的适用范围,指出了多个特性参数存在的问题,并提出了未来的研究方向。