几种人造湿地植物和土壤含氮量分析

采用凯氏定氮仪测定了藜、艾蒿、酸模、芦苇、狗尾草、水稻和野生大豆7种人造湿地植物的根、茎叶和植物生长土壤的含氮量.结果表明,艾蒿茎叶的含氮量为6.50 g/kg,比野生大豆、狗尾草、酸模、水稻、芦苇和藜茎叶平均含氮量高3.85 g/kg,艾蒿根的含氮量为8.66 g/kg,比藜、野生大豆、酸模、狗尾草、水稻、芦苇根的含氮量平均高3.42 g/kg,野生大豆生长的土壤含氮量为0.090 g/kg,比自然状态、芦苇、水稻和对照土壤的含氮量平均高0.03 g/kg,利用人造湿地处理污水需要植物的含氮量高和土壤的含氮量低,以便能够更有效的吸收污水中的氮.     

超大直径泥水盾构带压进舱换刀技术研究与应用

对于复杂地质条件下的盾构掘进,刀具更换往往不可避免。由于地质的复杂性、多变性和周边条件的局限性,常常无法实施盾构周边土体加固常压进舱换刀。带压进舱换刀技术以无需地层加固、地质适应性强、对周边环境要求低和影响小等特点,解决了苛刻条件下的换刀难题。为了能实现强渗透地层气压状态下开挖面稳定,采用室内试验对进舱泥膜的气密性进行了研究,研究结果表明： 进舱泥膜不仅要在开挖面形成一层致密的不透气泥皮型泥膜,还需在地层中形成均匀的透渗带泥膜,方能达到最佳的闭气效果。基于研究成果,南京纬三路过江通道N线工程实现了泥水盾构开挖面大面积气压支护进舱作业,并采用压缩空气作业与饱合潜水作业完成了盾构刀盘的维修和刀具的检查与更换。     

钢管混凝土外加强环节点抗震性能有限元分析

钢管混凝土结构节点的抗震性能的研究一直受到人们的重视,低周反复加载试验结果指出,加强环式节点滞回曲线饱满且稳定,但同时也发现,在节点域会出现鼓胀现象.为了解释这一现象,对加强环式节点进行了低周反复加载非线性模拟分析.分析内容包括节点的滞回耗能指标、节点域变形及节点域塑性扩展三部分.研究指出:(1)节点的滞回曲线饱满稳定,耗散系数都在2.0以上,表明节点整体延性很好;(2)腹板焊缝孔开孔过大,节点滞回曲线有不重合现象,可见腹板焊缝孔尺寸需要控制;(3)节点域柱壁有明显的变形,规律与滞回曲线相似,表明节点滞回曲线主要是由柱壁变形而非梁端塑性变形贡献的;(4)在反复荷载作用初期,环板就出现了贯穿的塑性带,而在相隔相当长的荷载循环之后,梁面上才有塑性出现.由于在反复荷载作用下,节点域发生了明显的变形,且在环板上形成贯穿的塑性带.     

基于粒子群算法的多配送中心选址研究

配送系统设计时,除了使系统的总费用最小外,还要满足各个需求点对时间的要求.综合考虑选址的物流成本和服务水平,在说明了建模的假设条件后,以经济性为决策目标,以时效性为约束条件,建立了带时效性约束的单个产品混合整数非线性规划模型.根据模型的特殊结构和粒子群算法解决复杂问题的优势,运用粒子群算法进行了求解.将多配送中心选址模型及算法应用于某一快递企业的选址问题,用实际调研的数据得出了一个最优选址方案.     

地铁车站下穿既有线安全施工技术

北京地铁九号线军事博物馆站下穿一号线区间隧道,在下穿施工过程中,必须保证既有线路的正常运营。为此,先进行超前支护,再采用多分部的CRD法施工,大刚度和强度初支进行支护,并采用三维数值方法分析了车站隧道下穿施工对既有线的影响,施工过程中的多项现场监测结果表明,既有结构的沉降和新建隧道结构受力都控制在安全范围之内,保证了既有隧道的正常和新建隧道安全。     

Investigation on blanking of thick sheet metal using the ductile fracture initiation and propagation criterion

In metal forming processes such as sheet blanking, severe plastic deformation localizes in a narrow shear band near blanking clearance, and ductile fracture occurs at the final stage. Because the combinations of large nonlinear strain localization, displacement discontinuity and ductile fracture brought obstacles to numerical simulation, a ductile fracture initiation criterion model and an elasto-plastic finite element method (FEM) were presented to simulate localized severe plastic deformation. Initiation and propagation of cracks were treated by deletion-and-replacement approach. The distributions and developing trends of effective strain and damage were predicted, the influence of blanking clearance on fracture was discussed, and an experiment was performed to explore the forming mechanism.     

Study on toughening on crack prevention of jointed rock masses with different pre-stress anchor cables

The major reason of the failure of jointed rock-mass is the formation of the plastic zone near the crack tip of I-II mixed crack which leads to the growth, propagation of the branched crack under load condition. In the paper, the failure judgment of mini-plastic zone??s displacement is derived by the Mises yielding rule. The anchor cable is simulated by the different link elements and inflicting pre-strains according to the difference of mechanism of the consolidated segment and free segment. The stress and strain fields near crack tip of twain collinear cracks of different angles and consolidated conditions are simulated by iso-parametric element with eight nodes. The iso-parametric element with eight nodes is degenerated to singular element at crick tip to simulate crack. It is shown that the mini plastic zone??s displacement near the crack tip begins to increase, then decreases with the increase of the angle of the crack. The better consolidated condition is, the smaller the angle of crack tip is when the mini plastic zone??s displacement near the crack tip arrives at the biggest value. The mini plastic zone??s displacement near the crack Tip 2 is bigger than that near the crack Tip 3. The crack is easier to failure with the increase of load.     

Ignition-proof properties of a high-strength Mg-Gd-Ag-Zr alloy

<正>A high-strength Mg-15.3Gd-l.8Ag-0.3Zr(GQ152K,mass fraction) alloy was prepared by conventional ingot metallurgy process.The solution and aging(denoted as T6) treated alloy exhibits remarkable mechanical properties with ultimate tensile strength of 421 MPa and tensile yield strength of 309MPa.It has higher igniting temperature of 1208 K.Moreover,it can stand against flame at 1203 K for over 6 min in vertical burning tests, and its flammabiUty behavior is very similar to that of 6101A1 alloy.Vertical burning tests appear to be able to directly study the flammability behavior of Mg alloys and it appears to be a good approach to study the flammability behavior of Mg alloys in an aircraft fire accident.     

Formation of nanometer coherent structures during spinodal decomposition and ordering coexistence phase transformation in Fe-24Al alloys

The nanometer coherent structure evolution of spinodal decomposition and ordering coexistence phase transformation in Fe-24Al alloys is investigated by the microscopic phase field kinetic model. The results show that the concentration and long-range order parameters all continuously change towards to their equilibrium values during phase transformation. With the increase of elastic interaction energy, the anisotropy along [01] or [10] elastic soft direction is more obvious and the time reaching equilibrium state is also shortened. According to the results, the formation of nanometer coherent structures during phase transformation is composed of the initial decreasing stage of order degree stage, the incubation stage, the continuous increasing stage of concentration order parameter and long-range order parameter, and the later stable stage. The spinodal decomposition and ordering is interaction; the initial ordering stage is a necessary condition of the coexistence phase transformation. The nanometer coherent structures are not found to grow during the whole phase transformation. The simulation results are in accordance with the results in experiment obtained by the aging treatment in Fe-24Al alloys.     

基于GPRS的架桥机远程状态监测系统设计

以TLJ900型架桥机为监测对象,设计了一套基于GPRS的远程监测系统。该系统由机载可编程控制器(PLC)、无线传输模块GPRS DTU以及远程监控中心的服务器等组成;其中,PLC在完成架桥机整个工作过程主控功能的基础上,同时将采集的钢结构应变、支腿倾角等信息通过GPRS DTU模块上传给远程监控中心服务器,在服务器端实现数据实时显示、数据分类存储、历史数据查询等功能。实验结果表明,该系统达到了架桥机的远程安全监测设计目标,此系统可为架桥机远程故障诊断和维修提供技术保障。