基于层面参数等效的碾压混凝土坝渗流场与应力场耦合分析

受施工、龄期、环境及服役期大坝承受的反复静动荷载等多因素影响,坝体和层面出现不同程度的劣化损伤,碾压层本体及层面物理参数呈渐变特性。针对碾压层内力学参数渐变的特性,提出了相应物理参数的等效算法,且给出了耦合性态参数间的数学转换关系,分析坝体应力场与渗流场相互影响机理,据此建立了考虑层内参数渐变的碾压混凝土坝渗流场与应力场耦合分析模型,并编制了相应的有限元分析程序。工程实例分析表明,耦合作用致使大坝的渗流场发生改变,坝体的应力较未耦合时普遍偏大,坝踵处的应力集中显著;渗流场与应力场耦合作用激励下的不利因素可为大坝的设计、施工及安全运行提供参考。     

Membrane bioreactor with nonwoven fabrics as solid–liquid separation media for wastewater treatment

A nonwoven fabric module was utilized as a solid–liquid separation medium in a membrane bioreactor (MBR) for treating wastewater. The experimental results indicated that nonwoven fabrics had lower filtration resistance than microporous membranes in MBR applications. The optimal aeration intensity was approximately 0.01m³/m² s. The effect of mixed liquor suspended solid concentration on filtration resistance was not significant at an operating flux of under 0.8m³/m² d in the study range. The performance of nonwoven fabrics in a MBR application was further demonstrated in a pilot test. Chemical oxygen demand (COD) and suspended solids (SS) in the effluent were maintained under 60 and 10 mg/L, respectively, whereas influent COD varied from 800 to 1800mg/L. The transmembrane pressure was maintained below 5 kPa at a permeation flux of 0.18m³/m² d. The experimental results demonstrated that nonwoven fabrics maintained stable operation in MBR applications under appropriate operating conditions.     

An overview of aqueous-phase catalytic processes for production of hydrogen and alkanes in a biorefinery

In this overview we discuss how aqueous-phase catalytic processes can be used to convert biomass into hydrogen and alkanes ranging from C₁ to C₁₅. Hydrogen can be produced by aqueous-phase reforming (APR) of biomass-derived oxygenated hydrocarbons at low temperatures (423–538 K) in a single reactor over supported metal catalysts. Alkanes, ranging from C₁ to C₆ can be produced by aqueous-phase dehydration/hydrogenation (APD/H). This APD/H process involves a bi-functional pathway in which sorbitol (hydrogenated glucose) is repeatedly dehydrated by a solid acid (SiO₂–Al₂O₃) or a mineral acid (HCl) catalyst and then hydrogenated on a metal catalyst (Pt or Pd). Liquid alkanes ranging from C₇ to C₁₅ can be produced from carbohydrates by combining the dehydration/hydrogenation process with an upstream aldol condensation step to form C–C bonds. In this case, the dehydration/hydrogenation step takes place over a bi-functional catalyst (4 wt.% Pt/SiO₂–Al₂O₃) containing acid and metal sites in a specially designed four-phase reactor employing an aqueous inlet stream containing the large water-soluble organic reactant, a hexadecane alkane sweep stream, and a H₂ inlet gas stream. The aqueous organic reactant become more hydrophobic during dehydration/hydrogenation, and the hexadecane sweep stream removes these species from the catalyst as valuable products before they go on further to form coke.     

三聚氰胺氰尿酸盐阻燃聚氨酯硬泡

将三聚氰胺氰尿酸盐(MCA)作为阻燃剂,采用一步全水发泡法,制备一系列硬质聚氨酯泡沫/三聚氰胺氰尿酸盐复合材料(RPUF/MCA),采用扫描电子显微镜(SEM)、热重分析(TG)、极限氧指数(LOI)、UL-94垂直燃烧、烟密度测试、傅立叶红外光谱(FT-IR)及拉曼光谱表征,研究了MCA对硬质聚氨酯泡沫(RPUF)泡孔结构、热稳定性、阻燃性及燃烧烟气密度的影响。研究表明,MCA能够显著提高RPUF/MCA的阻燃性能,30份的MCA使RPUF/MCA30达到UL-94 V-1级别,极限氧指数达到22.0%。热重测试结果表明,MCA的添加使成炭率降低;同时发现,MCA的添加降低了RPUF/MCA泡沫复合材料的初始热分解温度和复合材料的燃烧烟气密度,有效地提高了复合材料火灾安全性能。     

基于微观孔隙通道的饱和/非饱和土渗透系数模型及其应用

从微观角度揭示土体变形对饱和/非饱和渗透系数的影响机理,建立相应的预测方法,对于饱和/非饱和土的渗流分析及水力耦合研究具有重要的科学意义。利用流体力学理论,建立了微观孔隙通道渗透系数与等效孔径的关系,在此基础之上,结合毛细理论建立了饱和/非饱和渗透系数与土-水特征曲线的关系模型,并利用已有试验数据验证了模型的合理性。结合该模型与变形条件下土-水特征曲线预测方法,对变形条件下武汉黏性土饱和/非饱和渗透系数进行预测,结果表明黏性土在压缩变形条件下:饱和渗透系数呈数量级的减小,预测值与实测值均吻合较好;双对数坐标下,非饱和相对渗透系数在进气值之后随基质吸力增加而减小,不同初始孔隙比条件下其斜率近似不变,整体呈现"毛刷型"分布,相同基质吸力条件下,初始孔隙比越小,相对渗透系数越大;非饱和渗透系数,进气值之前近似为饱和渗透系数,进气值之后随基质吸力增大而减小,不同初始孔隙比的变化线近似重合。     

Location-Dependent Lane-Changing Behavior for Arterial Road Traffic

Lane-changing behavior plays an important role in characterizing urban arterial road traffic dynamics. This paper investigates efficiency-driven and objective-driven motives for drivers to change lanes on arterial roads. The former motive is determined by the circumstances of the surrounding traffic flow, whereas the latter depends on position. A location-dependent lane changing model is then established by weighing the two motives for lane changing. Both continuous and discrete versions of the arterial traffic model are obtained using the LWR (Lighthill–Whitham–Richards) model with the two types of lane changing. Simulations show that the proposed model can reproduce macroscopic traffic phenomena such as spillover and a decrease in the concomitant departure flow, which is the reason for capacity loss. It is concluded that 1) there exists a critical condition under which there is no capacity loss and that 2) a different flow composition could result in a different capacity loss, which varies according to the flow direction. Hence, traffic management and control should take this loss into account.     

The estimation of char reactivity from coal reflectogram

Measurements of the intrinsic reactivity of chars to oxygen are increasingly being sought as an indicator of the combustion potential of fuels. The coal reflectogram has been used to characterize the chemical properties of coal and its resultant char structure. In this study, six Australian coals varying in rank were separated using density separation technique to obtain vitrinite and inertinite rich fractions. Chars were obtained from these density fraction samples in a Drop Tube Furnace (DTF) at 1673 K. The reactivity of the chars was measured non-isothermally in a Thermal Gravimetric Analysis (TGA) in the temperature range of 573–1073 K. The results suggested that with the increase in the coal rank, the maximum reactivity of chars derived from vitrinite rich fractions decreases, while the reactivity of chars derived from inertinite rich fractions decreases with the increase in the inertinite content in samples and has no obvious relationship with rank. The kinetic parameters were derived using data from non-isothermal TGA after accounting for changing in surface area with conversion. The frequency factor is found to decrease with increasing coal FMR, defined as the summation of each reflectance value multiplied by its frequency, for a constant activation energy (E=146 kJ/mol). This suggests that the behavior of a maceral is characterized primarily by its reflectance distribution instead of the type of its parent coal.     

反拱法碳纤维加固RC梁的数值模拟分析

采用动力设备将钢筋混凝土梁向上反拱一定的弧度,然后在梁的下部外贴碳纤维布（CFRP）,待碳纤维布养护完全后,卸载,此时后加的碳纤维布与原钢筋混凝土梁同时进入工作状态。作者采用分析软件ANSYS模拟此过程,通过与直接用碳纤维布加固RC梁进行比较,得出反拱法加固RC梁能有效提高其承载能力,对类似工程具有一定的借鉴意义。     

基于Hoek-Brown准则的深部岩体力学参数及其应用

基于Hoek-Brown经验强度准则,采用最小二乘法拟合出岩体力学强度参数,并与H-B_02ed推荐的等面积拟合结果进行对比,结果发现两种拟合方法得出的岩体内摩擦角数值相差很小,但等面积拟合法得出的黏聚力强度远高于最小二乘拟合法。将两种强度参数拟合结果应用于深部矿体开采的数值模拟,发现采用最小二乘拟合法的岩体强度参数其模拟结果更接近工程实际。该方法对深部岩体力学参数的确定具有一定的借鉴意义。     

湿陷性黄土地基强夯有效加固深度预测

对强夯有效加固深度主要影响因素进行分析,考虑能量的转化,综合运用量纲守恒和最小二乘原理,结合一定量的湿陷性黄土地基强夯加固实例,推导了有效加固深度估算公式,并与其他公式进行比较;再结合另外两组湿陷性黄土地基实例,进一步探讨了本文公式的估算效果。新的公式反映了含水量与有效加固深度呈非线性相关,能使得计算效果更好,参数选用方便,对湿陷性黄土地基有一定参考价值。