MODELING THE LONG TERM IMPACTS OF USING RIGID STRUCTURES IN STREAM CHANNEL RESTORATION1

Abstract: Natural channel designs often incorporate rigid instream structures to protect channel banks, provide grade control, promote flow deflection, or otherwise improve channel stability. The long term impact of rigid structures on natural stream processes is relatively unknown. The objective of this study was to use long term alluvial channel modeling to evaluate the effect of rigid structures on channel processes and assess current and future stream channel stability. The study was conducted on Oliver Run, a small stream in Pennsylvania relocated due to highway construction. Field data were collected for one year along the 107 m reach to characterize the stream and provide model input, calibration, and verification data. FLUVIAL-12 was used to evaluate the long term impacts of rigid structures on natural channel adjustment, overall channel stability, and changing form and processes. Based on a consideration of model limitations and results, it was concluded that the presence of rigid structures reduced channel width-to-depth ratios, minimized bed elevation changes due to long term aggradation and degradation, limited lateral channel migration, and increased the mean bed material particle size throughout the reach. Results also showed how alluvial channel modeling can be used to improve the stream restoration design effort.     

库存弹药事故人误危险性评估研究

提出了库存弹药事故人误的定义,从个体角度分析了人误事件发生的机理.构建了人误固有危险性的评价指标体系及评判标准,考虑了6类危险性抵消因子对人误的影响.最后,建立了评估库存弹药事故人误危险性的数学模型.     

跌落条件下箱装弹药安全性的数值评估

把箱装弹药简化为二自由度系统,将包装箱及弹体等效为线弹性材料,基于Matlab数学软件,运用四阶龙格-库塔法对系统进行数值分析,分别讨论了频率比、包装箱阻尼、质量、弹性系数、保险簧弹性系数以及跌落高度对保险元件冲击响应的影响。所得结论对弹药科学储运具有指导意义。     

加速寿命试验技术在弹药贮存可靠性工程中的应用

阐述了加速寿命试验的基本理论;以典型的恒定应力加速寿命试验和步进应力加速寿命试验应用案例,回顾了加速寿命试验技术在弹药贮存可靠性工程中的应用状况;指出失效机理研究、数据统计分析和实验结果验证是工程应用中待优化解决的3个突出问题,展望了加速寿命试验技术在工程应用中的发展趋势。     

仿真技术在弹药贮存中的应用

利用仿真技术测定弹药贮存的微环境,根据包装结构和弹药结构对弹药贮存的微环境进行了分析.采用较为简便的数学模型,找出了包装箱和弹药在变化的环境温度下的温度分布和变化规律,然后通过弹药贮存微环境的仿真设计,确定了计算软件的功能模块.使用该软件可计算任一时间弹药及其各包装部位微环境的温度.     

Experimental and modeling study of de novo formation of PCDD/PCDF on MSW fly ash

The effect of sulfur dioxide （SO2） on the formation of polychlorinated dibenzo-p-dioxins （PCDDs） and polychlorinated dibenzofurans （PCDFs） has been studied in an entrained-flow reactor （EFR） under simulated waste combustion conditions. A chlorination model based on conditional probability was employed to evaluate the homologue patterns of PCDDs and PCDFs. Results revealed that the presence of SO2 did not alter the formation pathway although SO2 suppressed PCDD/F formation. The prediction model of PCDF showed good agreement with the experimental data （R--0.95）, whereas the prediction for PCDDs did not correlate well with the experimental data. This may be explained because potential chlorination pathways play a significant role in PCDF formation, whereas PCDDs are mainly formed through condensation reactions. Furthermore, the result indicated that the steric hindrance during formation has more effects on PCDD than on PCDF due to the symmetric molecular structures of PCDDs.     

MPA法和Pushover法在掉层框架结构中的适用性对比分析

结合已有的规则结构分析结果,设置不同的掉层跨数、掉层数量的掉层结构,以逐步增量弹塑性时程分析(IDA)结果为依据,运用多模态Pushover法(MPA)和传统的Pushover法进行对比分析。结果表明:相对于规则框架结构,除MPA外,掉层结构的掉层部分在各类侧向力分布模式相对于IDA下的层间Pushover曲线有较大差异。SRSS分布下在掉一、二层位置,过高估计结构的响应。上接地层以上部位各侧向力下的层间Pushover曲线较IDA曲线误差较小。掉层的楼层的层剪力在上接地位置存在明显的突变。掉层跨数的改变对上部楼层弹塑性分析结果影响较小,但跨数的改变会改变同等烈度下结构的层间Pushover曲线和内力响应。与此同时,掉层跨数的增加会减轻"剪力突变"现象。伴随着掉层层数的增加,掉层部分均匀分布和倒三角分布与IDA下层间推覆曲线的差异会扩大。总之,相对于传统Pushover分析,MPA分析的结果更接近于相对准确值,需要进一步研究以提高精度。     

Effects of tourmaline on nitrogen removal performance and biofilm structures in the sequencing batch biofilm reactor

The effects of tourmaline on nitrogen removal performance and biofilm structures were comparatively investigated in two identical laboratory-scale sequencing batch biofilm reactors(SBBRs)(denoted SBBR1 and SBBR2) at different nitrogen loading rates(NLRs) varying from(0.24 ± 0.01) to(1.26 ± 0.02) g N/(L·day). SBBR1 was operated in parallel with SBBR2, but SBBR1 was filled with polyurethane foam loaded tourmaline(TPU) carriers and another(SBBR2) filled with polyurethane foam(PU) carriers. Results obtained from this study showed that the excellent and stable performance of SBBR1 was obtained. Ammonia nitrogen removal and total nitrogen removal were higher in SBBR1 than that in SBBR2 with increase of NLR. At an NLR of(0.24 ± 0.01) g N/(L·day), the majority of the spherical and elliptical bacteria were surrounded by the extracellular polymeric substance(EPS) and bacillus or filamentous bacteria in two SBBRs biofilms. When NLR increased to(1.26 ± 0.02) g N/(L·day), the clusters were more obvious in the SBBR1 biofilm than that in the SBBR2 biofilm. Bacteria in SBBR1 were inclined to synthesis more EPS, and the formed EPS could protect the bacteria from free ammonia(FA) under extreme condition NLR(1.26 ± 0.02) g N/(L·day). The results of polymerase chain reaction-denaturing gradient gel electrophoresis analysis showed that the microbial community similarity in SBBR2 decreased more obviously than that in SBBR1 with the increase of NLR, which the microbial community in SBBR1 was relatively stable.     

Pre- and post-beach response to engineering hard structures using Landsat time-series at the northwestern part of the Nile delta,Egypt

Analyses have been undertaken to examine shoreline positions established from remote sensing data along the northwestern part of the Nile delta from the Abu Qir Bay to Gamasa embayment (∼143 km length). The image data used (MSS, TM and ETM+ sensors) are acquired at unequal intervals between 1972 and 2006, i.e., covering a time span of 34 years. Automated waterline positions extracted from Landsat satellite images during this period of time were computer generated. A digital shoreline analysis software was used to calculate the annual rate of beach changes at 1,432 cross-shore transects prior to (1972–1990) and after protection (1993–2006). On comparison, rates estimated from three statistical approaches (the end point rate, the Jackknife and a weighted linear regression) at corresponding positions are successfully validated with those measured from ground survey. Before protection, results reveal longshore patterns wherein erosion along a coastal stretch gives way to accretion in an adjacent stretch, refining the sub-cells previously identified within the littoral system of the delta. Maximum shoreline retreat occurs along the Rosetta promontory (−138.52 m/year) and along the central bulge of the delta at Burullus headland (−6.07 m/year). In contrast areas of shoreline accretion exist within saddles or embayments between the promontories at west Abu Qir Bay (20.04 m/year), Abu Khashaba saddle (16.17 m/year) and Gamasa embayment (20.68 m/year). These rates of changes have been significantly altered by the construction of intensive shoreline protective structures built from 1990 to combat areas of rapid erosion at both the Rosetta promontory and Burullus–Baltim headland, ∼15-km length in total.     

酸雨对混凝土建筑物和文物损坏机理的研究

介绍了酸雨对混凝土建筑物和文物损坏机理的宏观分析,水泥中加入少量石膏,可延缓凝结时间,但当加入量大,将引起水泥膨胀,以致溃裂,探讨了酸雨对混凝土建筑物与文物损坏的微观分析,特别是酸雨等生成各种硫酸盐,通过从化学反应原理上分析了酸雨中二氧化硫与混凝土中钙离子反应生成石膏机理,从石膏特性上探讨了酸雨对混凝土建筑物和文物侵蚀机制,并由此提出了酸雨条件下保护混凝土建筑物和文物应对措施。