Coupling BEM/FEM to linear frames analysis on elastic foundation

Orientador: Leandro Palermo JuniorDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e UrbanismoResumo: O presente trabalho está divido em quatro partes. Na primeira parte, utilizando o método dos elementos de contorno (MEC), se fez a análise de problemas bidimensionais com aproximação linear. Foi considerada a possibilidade de se aplicar a técnica de sub-regiões para se levar em conta a diversidade de materiais, bem como a suavização do contorno por mínimos quadrados para evitar a possíveis perturbações. Foi considerado a possibilidade de colocação de uma linha de carga no domínio. Na segunda parte, utilizando o método dos elementos finitos (MEF), se fez a análise linear de pórticos planos. Para este estudo foram utilizadas barras com dois nós e esses com três graus de liberdade. Na terceira parte, a análise elástica linear de meios contínuos (Estado Plano de Tensão Generalizado) enrijecidos com elementos lineares (barras) é estudada fazendo-se um acoplamento entre elementos modelados com o MEC e com o MEF. As fibras são modeladas pelo MEF com elementos lineares de três graus de liberdade por nó e quatro nós por barra. Os elementos planos são modelados pelo MEC com elementos isoparamétricos lineares no perímetro. É permitido o uso de sub-regiões com objetivo de generalizar o tratamento do meio elástico. Na quarta parte, utilizando o acoplamento MEF/MEF, se fez a análise linear de pórticos planos sobre base elástica. O acoplamento se dá entre as barras do pórtico e as barras introduzidas como enriquecedor no problema elástico bidimensional. Tendo em conta estes aspectos da formulação desenvolvida, alguns exemplos são apresentados para avaliação de seu desempenho nos problemas de engenhariaAbstract: This paper is divided into four parts . In the first part , using the boundary element method (BEM) , we did the analysis of two-dimensional problems with linear approximation . We considered the possibility of applying the technique of sub - regions to take into account different materials, as well as smoothing the contour by least squares to avoid possible disturbances . We considered the possibility of placing a load line in the field. In the second part, the linear analysis for plane frames was carried out with the finite element method (FEM). Bars with two nodes and three degrees of freedom were used in this study . In the third part, the linear elastic analysis of continuous media (Generalized Plane Stress problems) stiffened with one-dimensional elements (bars) is studied through between elements of the BEM and the FEM. The fibers are modeled by FEM with three degrees of freedom linear elements and using four-nodes. The plane domain is modeled with the BEM and using isoparametric elements. The use of sub - regions in order to generalize the treatment of the elastic medium is allowed. In the fourth part , using the FEM / FEM coupling , a linear analysis of plane frames on elastic foundation is carried out. Some examples are presented to evaluate the formulation behavior engineering problemsMestradoEstruturasMestre em Engenharia Civi

连通工程对富营养化湖泊沉积物中污染物的影响

为揭示东湖-沙湖连通工程对富营养化湖泊沉积物中污染物的影响,于2013年7月在东湖的水果湖及郭郑湖心采集了20 cm的柱状沉积物,按2 cm分层测定了总有机碳（TOC）、总氮（TN）、总磷（TP）、酸挥发性硫化物（Acid volatile sulfides,AVS）及同步提取金属（Simultaneously extracted metals,SEM）,并与2004、2006和2008年（TOC、TN和TP）及1999年（AVS、SEM）数据进行了比较;同时研究了郭郑湖沉积物氮磷的释放特性。结果表明,（1）水果湖沉积物中污染物含量普遍高于郭郑湖,在连通前均呈增加的趋势;连通后,TOC、TN的平均含量显著降低（P〈0.05）,与2008年比分别降低了25.1%和56.3%（水果湖）及31.9%、66.1%（郭郑湖）;TP平均含量虽略高于2008年,但水果湖沉积物低于2004及2006年,郭郑湖表层沉积物也低于历年,表明TP污染的趋势得到了遏制,湖水流动性的增强有利于沉积物中污染物含量的降低;（2）随着沉积物表层氧化还原状况的改善,表层沉积物AVS含量降低,且最高含量分别由26.4（水果湖）和26.2 mmol/kg（郭郑湖）降低到15.1和18.2 mmol/kg;SEM含量则升高,导致SEM/AVS上升,但SEM/AVS值均小于1,沉积物尚未呈现重金属毒性;（3）东湖沉积物中的氮磷存在潜在的释放风险,其释放与扰动强度有关,且污染物含量高的底层沉积物释放更明显。因此,连通工程有利沉积物中污染物含量的降低,但同时需要采取措施控制污染物释放的风险

疏浚对巢湖重污染入湖河流沉积物中污染物赋存及释放的影响

以巢湖重污染入湖河流双桥河为研究对象,研究了底泥疏浚对水质以及沉积物中总氮、总磷和有机质的短期影响及长期效应.结果表明,双桥河水质的季节变化显著,受上游城市污水及周边面源污染的影响,疏浚对水质改善作用不明显.表层沉积物中总氮、总磷及有机质含量在疏浚结束后1个月有所降低,但是2年后分别回复到疏浚前的189.77％、111.62％和152.87％.疏浚结束2年后,沉积物中磷主要以钙磷和有机磷的形式存在,铝磷和铁磷的含量较少,弱结合态磷的含量最低;但是表层沉积物中的弱结合态磷、铝磷和铁磷结合态磷含量较疏浚前分别升高了728.32％、13.52％和37.73％,并呈现出表层富集现象,存在较高的污染物释放风险.这可能是由沉积环境改变、外源污染未得到有效控制引起的.因此,为了维持疏浚的长期效果,应该对外源污染源进行有效控制

Spatial and Temporal Evolution and Driving Mechanism of Man-made Ditches in the Yellow River Delta from 1976 to 2015

人工沟渠作为湿地中高强度人类活动的缩影,强烈影响着湿地的水文过程与生态环境,成为湿地演变的主要驱动力之一.基于1976—2015年黄河三角洲27期遥感影像和1∶10万地形图,通过目视解译获得人工沟渠(农业沟渠和道路沟渠)数据,定量分析了人工沟渠的时空演变过程及驱动机制.结果表明:(1)黄河三角洲人工沟渠长度、密度呈明显的线性上升趋势,其长度、密度年均分别增长160km和53m/km2.农业沟渠长度、密度变化可分为两个发展阶段:2000年以前符合s型函数增长,2000年以后呈现出线性增长的趋势.道路沟渠的长度、密度变化一直表现为明显的线性上升趋势,其长度、密度年均分别增长141km和47m/km2.(2)黄河三角洲人工沟渠长度与农田面积呈显著的线性相关(P<0.05),与养殖池面积具有良好的对数关系(P<0.0001),与道路长度呈极显著的线性关系(P<0.0001).(3)多元回归分析结果表明,农田面积和道路长度对人工沟渠长度的协同影响达到99.9%(P<0.0001).&nbsp

Predicting the potential distribution of dominant species of the coastal wetland in the Yellow River Delta,China using MaxEnt model

Soil and vegetation community were investigated using the method of kilometer grid sampling. In addition,using the maximum entropy (MaxEnt) and the GIS spatial analysis technique, the potential distribution of dominant species in the Yellow River Delta and their major environmental variables and ecological parameters were quantitatively analyzed. The results showed that the dominant species of the coastal wetland were Tamarix chinensis,Phragmites australis and Suaeda salsa in the Yellow River Delta. Among the environmental variables,six variables were significant contributors to the potential distribution model of T. chinensis: NO_3~--N,salt,slope,Mg,altitude and NH_4~+-N. The environmental variables influencing the distribution of P. australis were NO_3~--N, salt,TP,pH,altitude and NH_4~+-N. NO_3~--N,salt and NH_4~+-N were the significant factors determining the potential distribution of S. salsa. The probability of presence of dominant species of the coastal wetland in the Yellow River Delta was positively correlated with salt,but it was negatively correlated with the other major environmental variables. The model predicted that the core potential distribution of dominant species in the Yellow River Delta was mainly in the coastal areas. In addition, P. australis had a wider range of distribution,compared with T. chinensis and S. salsa

Dynamic evolution of natural wetlands in Yellow River Delta and related driving factors

以1989、2000和2009年3期LandsatTM和ETM+影像为基本数据源,结合地理信息系统技术与实地考察校正,分析黄河三角洲自然湿地的演变动态及其驱动因子。结果表明,受水盐等因素的影响,自然湿地的分布在空间上呈现出规律性变化。1989—2000年,黄河三角洲的自然湿地面积的年变化率为-0.3,动态度为3.1,而在2000—2009年,其年变化率为-1.8,动态度为5.1,表明自然湿地面积变化情况有所加剧。对湿地变化原因的分析表明,黄河水情是自然因素中最重要的方面,部分自然湿地亚类之间存在相关性;养殖池、水田建设等人为因素与自然湿地的减少有着显著的相关性,灌草地减少则与居民和工矿建筑用地增加有密切关系。 &nbsp

Coastline change detection of the Yellow River Delta by satellite remote sensing

以黄河三角洲的Landsat TM/ETM+影像(1989~2009年)为数据源;采用遥感与地理信息系统技术;对黄河三角洲的岸线与面积变化进行监测。结果表明:1989年以来;黄河三角洲的岸线形状及长度均发生了较大变化;其中北部的刁口河流路区岸线向内陆蚀退明显;清水沟流路区的岸线整体向海域推进;部分区域有蚀退现象;神仙沟流路区主要为人工海堤;岸线变化不大。黄河三角洲的整体面积在1989~2009年处于增加中;但2006~2009年;面积变化为负值。从淤蚀情况来看;1989~2009年;黄河三角洲的淤蚀强度经历了"和缓-剧烈"的过程。这说明20年来黄河三角洲整体上处于增长发育中;但2006年后三角洲整体上呈现蚀退现象;同时黄河三角洲的淤蚀情况变得比以往更剧烈;意味着更强的海陆交汇作用和岸线变化。黄河的入海流路、水沙量、降水量等是影响三角洲岸线变化的重要因素;而人工堤坝能够在一定程度上维持海岸线的稳定。对黄河三角洲海岸线变化的研究有助于有效地管理和保护区域的社会和生态环境

纳米银在水-沉积物中的迁移机制研究

为研究纳米银（Ag NPs）在水体中的迁移、水-沉积物中的分配及转化机制,采用武汉东湖湖水及沉积物开展模拟实验,以硝酸银（Ag NO3）为参照,研究了Ag NPs和聚乙烯吡咯烷酮包裹纳米银Poly（vinylpyrrolidone）-coated silver nanoparticles（PVP-Ag NPs）在上覆水中的沉降、在沉积物中的迁移和形态分布、以及扰动释放过程。结果表明,上覆水银初始浓度均为75 mg/L的Ag NO3、Ag NPs及PVP-Ag NPs在120h后分别为0.086、0.957和2.770 mg/L,显示纳米银和硝酸银进入水体后120h内大部分沉入沉积物中,且经过包裹的纳米银比未包裹的纳米银在水中停留时间稍长;60d后三种银均主要分布在表层沉积物中,Ag NO3体系银含量随深度的增加而逐渐降低,Ag NPs和PVP-Ag NPs体系银在2 cm以上随深度的增加而增高,随后逐渐降低,表明纳米银比硝酸银具有更强的迁移能力。此外,PVP-Ag NPs在2—3 cm层中的银含量占总量的24.6%,而Ag NPs在同一层中含量仅为2.6%,说明前者的迁移能力更强。在沉积物中,硫化物和有机物是银的主要结合相。释放实验结果表明,沉积物中纳米银的释放量远小于硝酸银的释放量,表明纳米银一旦与沉积物结合就难以再次释放。以上实验结果为评价纳米银的生态安全提供了科学依据

1961～2010年黄河三角洲湿地区年平均气温和年降水量变化特征

利用中国地面气候资料日值数据集逐日气温和降水量插值数据,采用线性趋势分析、滑动距平和Mann-Kendall突变检测方法,研究黄河三角洲湿地区1961~2010年间的年平均气温和年降水量变化特征和趋势。结果表明,1961~2010年期间,黄河三角洲滨海湿地区年平均气温累计上升1.85℃,倾向率为0.037℃/a;年平均气温在1993年发生突变,研究区进入显著升温期;研究区年降水量累计下降121.42 mm,占同期年降水量的19.9%,降水主要集中于夏季;强降水日数和最大连续无降水日数显著减少,但极端降水频率与强度总体上保持稳定。1961~2010年期间,黄河三角洲湿地区气候以年平均气温升高、年..