顶管施工引起的土体扰动理论分析及试验研究

近年来，顶管施工技术在中国得到迅速发展，并广泛应用于给排水管道工程，但顶管施工中土体的扰动机理及土体性状的变化有待深入研究与探讨。在前人的基础上，研究了顶管施工引起土体扰动的机理，提出了更加准确的土体扰动分区图。对某顶管工程进行了现场监测，内容包括地面变形、深层土体移动、孔隙水压力、土压力、地下水位以及顶管施工现场记录。测试结果表明土体扰动受土质条件、施工技术和现场控制程度的影响，其中现场控制程度(包括顶力、土压力、管线纠偏和注浆压力)的影响最大。土压力、孔隙水压力、地下水位、地面变形及深层土体移动的变化都跟掘进机与测试断面之间的距离有直接关系。当掘进机离测点还有一段距离(6～7m)时，土压力、孔隙水压力和地下水位上升达到峰值。地面隆起及深层土体移动则是在掘进机尾部离开测点时达到最大，随后总体上呈下降趋势。现场测试结果很好地验证了土体扰动理论。     

Examining spatially varying relationships between land use and water quality using geographically weighted regression I: model design and evaluation

Traditional regression techniques such as ordinary least squares (OLS) can hide important local variations in the model parameters, and are not able to deal with spatial autocorrelations existing in the variables. A recently developed technique, geographically weighted regression (GWR), is used to examine the relationships between land use and water quality in eastern Massachusetts, USA. GWR models make great improvements of model performance over OLS models, which is proved by F-test and comparisons of model R² and corrected Akaike Information Criterion (AIC_c) from both GWR and OLS. GWR models also improve the reliabilities of the relationships by reducing spatial autocorrelations. The application of GWR models finds that the relationships between land use and water quality are not constant over space but show great spatial non-stationarity. GWR models are able to reveal the information previously ignored by OLS models on the local causes of water pollution, and so improve the model ability to explain local situation of water quality. The results of this study suggest that GWR technique has the potential to serve as a useful tool for environmental research and management at watershed, regional, national and even global scales.     

百年生态 和谐茶冲——安徽泾县茶冲村整治规划

结合皖南泾县茶冲村的生态环境,就该村的"山、水、林、田、路、屋"编制整治规划,按照政府统一部署实施;为彰显茶冲生态特色,建设和谐乡村,探索可行和借鉴的新思路。     

无粘结预应力沉淀池内力测试与有限元分析

介绍某污水处理厂无粘结预应力沉淀池内力测试技术 ,理论计算无粘结预应力筋的有效应力及其在池壁上产生的等效荷载。采用ANSYS有限元程序对池内注水前后的分析与现场测试结果的对比结果表明 ,通过在沉淀池池壁中建立有效预加应力 ,满足了沉淀池的正常使用要求     

等离子体激励对飞行器流场影响的数值研究

针对传统飞行器控制方式的缺点,采用小尺度等离子体流动控制技术对飞行器流场影响进行研究。在前人的实验模型及飞行参数进行研究的基础上建立三维模型,采用数值仿真方法,研究了等离子体激励器位置和注入能量大小对飞行器流场及表面压力分布的影响。仿真结果表明：等离子体与边界层的相互作用可改变飞行器外部激波的初始结构,并在激励位置附近形成局部高压区;随着注入能量的增加,高压区峰值及作用范围分别扩大;等离子体激励产生的扰动具有三维传播特性,对飞行器侧壁面甚至对整个壁面周向压力分布产生影响。     

火药燃烧生成等离子体规律数值仿真研究

为了研究火药燃烧生成等离子体规律,分析了火药燃烧时的物理化学过程,建立了火药燃烧时生成等离子密度规律数学模型,并对火药燃烧时等离子体生成规律进行数值模拟仿真。将数值模拟的结果与试验结果进行对比,确定模型的正确性与可行性。利用所建立的数学模型,分析不同的装药结构参数对等离子体的影响,得到了等离子体密度变化的规律,为下一步提高等离子体生成浓度奠定基础。     

自由弛豫信号截取时长对NMOR铷原子磁力仪性能的影响

基于非线性磁光旋转(nonlinear magneto-optical rotation, NMOR)效应的铷原子磁力仪通过特定时长的自由弛豫正弦振荡信号可获得拉莫尔进动频率和外磁场值,因此自由弛豫信号的截取时长能够影响原子磁力仪的性能指标。重点研究了在500 nT背景磁场条件下自由弛豫信号截取时长对原子磁力仪灵敏度和磁场测量值的影响。测量结果表明,用噪声功率谱方法标定的灵敏度指标随着自由信号截取时长的增加逐渐减小并趋于稳定,约0.2 pT/Hz~(1/2);交变磁场实验表明该磁力仪所得的磁场值是特定截取时长内磁场波动的平均。因此本文NMOR原子磁力仪所得的高灵敏度指标一定程度上是通过数学方法平均了自由弛豫信号截取时长内的磁场值波动。该方法对其他原子磁力仪或实验装置灵敏度的标定和磁场测量值的分析具有一定的借鉴意义。     

混凝土CT中数据采集系统设计

混凝土超声层析成像仪作为现今混凝土质量检测的主流仪器,其数据采集系统的性能好坏决定了该仪器检测结果的可信度。选用ANALOG DEVICES公司的16 bit、最大采样频率25 MHz的模数转换芯片LTC2203作为该系统的核心元件。放大调理电路由可调增益放大器AD603和差分芯片THS4521组成。将超声波探头采集到的信号进行放大并差分输出给LTC2203。考虑到数据传输的可靠性和传输速度,在FPGA内,用FIFO对数据进行缓冲并通过DMA搬运至SDRAM中。通过串口将数据传输给PC端的MFC程序,对采集到的数据进行处理。实现了对频率范围至少在1 kHz^500 kHz内的超声波探头的匹配,且等效输入噪声在57.4μV左右。经测试,该数据采集系统能较好的还原被测数据,提高了混凝土超声层析成像仪的可靠性。     

Evaluation of prestress losses in prestressed concrete specimens subjected to freeze–thaw cycles

Prestressed concrete structures are considered to be reliable and durable. However, their long-term performance when subjected to frost attack is still unclear. In this work, experiments were carried out to evaluate the prestress losses in post-tensioned prestressed concrete specimens subjected to freeze–thaw cycles (FTCs). Two cases were considered: in one case, a series of specimens were prepared and tested in a freeze–thaw chamber; in the second case, the same series of specimens were tested in an indoor environment (outside the chamber). The difference between the prestress losses of the specimens inside the freeze–thaw chamber and those outside the chamber equalled the prestress losses due to FTCs. When using mathematical models to predict the prestress losses due to the FTCs, it was found that they were relatively small when the concrete was slightly damaged. However, they increased rapidly when the FTCs were repeated. The eccentricity of the prestress wires led to larger prestress losses when subjected to FTCs. Moreover, the same cross section and eccentricity resulted in similar prestress losses due to the FTCs, and the relatively high-strength concrete could withstand more FTCs.     

连续刚构桥的内力包络图

利用计算机仿真的方法给出了连续刚构桥的内力包络图.令汽车标准荷载以足够小的步长在桥梁上通过,每一步用有限单元法画出桥梁结构的内力图.当移动荷载的加重车移出桥梁时,这些内力图将充填成一个区域.这个区域的边界线就是相应内力的包络图.此内力包络图的算法可以取代影响线方法.