水力冲击内蕴初始裂纹混凝土致裂机理

为研究水力冲击内蕴初始裂纹混凝土破碎机理,采用光滑粒子流体动力学(SPH)方法建立了水力冲击含竖向裂纹混凝土数值模型,并基于图像处理技术,量化表征了混凝土致裂区破碎规律。研究表明:在初始裂纹弱作用区,水锤效应导致液固接触边界出现剪切断裂,贯通后形成近似"碗状"破碎坑;在初始裂纹强作用区,液固接触边界压剪应力和初始裂纹上部应力集中共同作用引发了初始裂纹上尖端裂纹;"水楔+砼楔"效应与初始裂纹下部应力集中导致了初始裂纹下尖端裂纹;水力冲击激发的应力波在自由边界和初始裂纹反射后相互叠加,引发了锥形裂纹;混凝土破碎度沿射流轴向呈非线性阶跃衰减,表明初始裂纹对混凝土破碎演化有明显阻断及强干扰作用。     

基于大型动三轴试验的粗粒土累积塑性应变概率模型研究

路基填土在长期交通动荷载作用下的累积塑性变形存在离散性。通过一系列粗粒土大型动三轴试验分析其累积塑性应变随围压、动应力及含水率的发展趋势和变化规律。结果表明:累积塑性应变及其稳定值随动应力的增加而增大,随围压的增加而减小,说明增大围压能有效抑制土体累积塑性变形的发展;土体的动力稳定性随含水率的减小而增加。基于半对数预测模型,运用灰色系统关联理论探究模型参数与含水率和动静应力比的相关性特征,并通过正态性检验论证得到控制粗粒土累积塑性应变发展速率的模型参数服从正态分布。基于概率失效理论,提出预测粗粒土填料累积塑性应变的概率模型,可较好地预测粗粒土填料在循环动荷载作用下的累积塑性应变发展区间。     

基于非线性瞬态响应的空间站柔性太阳翼在轨载荷分析

针对展开面积大、机构环节多、带有柔性索/膜结构的空间站太阳翼,建立精细的有限元模型、分析其在轨高强度激励条件下的瞬态变形和应力是强度设计所必须完成的环节。利用"间隙-接触"(Gap)单元的力学特性,将其倒置后作为钢丝绳与收藏箱的连接单元,一举解决了柔性阵面预紧力施加、钢丝绳不连续拉压刚度模拟以及收藏箱弹性变形补偿等多个问题,成功获得了太阳翼重要部件的瞬态剪力、弯矩等载荷结果,为产品设计提供了重要决策依据。结果表明基于线性模型的计算方法应用于此问题时存在显著不足。     

分数阶单自由度间隙振子的受迫振动

研究了含有分数阶微分项的单自由度间隙振子的受迫振动,利用KBM渐近法获得了系统的近似解析解。分析了分段线性系统的主共振,得到了分数阶阶次在0～2时分数阶项的统一表达式;发现分数阶微分项在分段系统中以等效线性阻尼和等效线性刚度的形式影响着系统的动力学特性,而间隙以等效非线性刚度的形式影响着系统的动力学特性。获得了主共振幅频响应的表达式,并得到了系统的稳定性条件;比较了系统主共振幅频响应的近似解析解和数值解,发现两者符合程度较高,验证了近似解析解的正确性;详细分析了分数阶项和间隙对系统主共振幅频响应的影响。研究表明KBM渐近法是分析分数阶分段光滑系统动力学的有效方法。     

航道整治对东流水道四大家鱼栖息地适宜度的影响

为探讨长江下游东流水道二期整治工程对河段内四大家鱼繁殖水流条件的影响,根据平面二维水流数学模型和四大家鱼适宜度曲线,建立了四大家鱼栖息地适宜度模型,并对东流水道不同时期的四大家鱼适宜度分布情况进行了数值模拟,初步评估了东流水道二期整治工程对四大家鱼适宜度的影响。结果表明:东流水道二期工程能增加四大家鱼产卵期理想的适宜性区域,有助于四大家鱼的产卵繁殖;对四大家鱼在生长期的影响因时期不同而有略有差异,在二期工程施工刚完成时不利于鱼群生长,但在施工完成较长一段时间后则有利于鱼群生长。建议在进行航道整治工程的整体布局和尺寸设计时考虑工程对目标鱼群栖息地适宜度的影响,使航道整治工程对目标鱼群栖息地适宜度的影响达到最小,甚至增加目标鱼群的理想适宜度和范围。     

Water Depth Information Extraction with Multi-spectralRemote Sensing in Coral Reefs Region

Water depth inversion is of great important to coral reefs’ protection and engineering construction of the coral reef region.As the correlation between the remote sensing radiance and the water depth is a very well,so the band ratio transform and the linear combination transform were adopted to the water depth inversion around coral reefs.Based on the complex topography of coral reefs,these two algorithms were optimized for the water depth inversion.Finally,our experimental results show that the improved ratio transform was suitable for retrieving water depths among 3~5 m and 5~10 m.While none of the models that mentioned in this paper performed well in water depth of 5~10 m,the preliminary conclusion was that coral reefs’ special topographic caused it.     

Effects of the Relocation of Chongqing Iron and Steel Group Industrial Area on Regional Ecological Quality

Urbanization is typically accompanied by the reconstruction or relocation of heavy industrial areas due to limited space and high standard environmental requirements.Taking "environment\|friendly relocation" of Chongqing Iron and Steel Group as an example,this study quantitatively compares and analyzes changes of the thermal and ecological conditions before and after the relocation.Main biophysical properties of the study area and land surface temperature(LST) were retrieved from the multi\|temporal Landsat serial satellite images.Urban Heat Island Index(URI) and Remote Sensing based Ecological Index(RSEI) were employed for the study.The results reveal that urban heat island effect of the industrial area was significantly mitigated and the ecological quality was significantly improved after the relocation,suggested by the decline of URI value from 0.387 in 2005 to 0.128 in 2014(a drop of 66.7%),and the rise of RSEI value from 0.398 to 0.553 during the same period(an increased of 38.9%).This is due largely to the halting of steel production,change of land cover types and properties caused by the “environment\|friendly relocation” of the industrial area.In general,the halting of steel production,the decrease of impervious surface and the increase of vegetation coverage can mitigate the heat island effect and improve the ecological quality.The result of this study can provide a useful case for reconstruction or relocation of urban heavy industrial area and promotion of city’s healthy sustainable development.     

Study on Mechanism of Methane Column Change Influencing Atmospheric Structure and Local Heavy Rain

In order to study the relationship between atmospheric methane content and local strong convective weather,relationships among the methane content and the atmospheric structure and the local heavy precipitation are studied by using the L3 methane daily inversion product retrieved by AIRS.The results show that the distribution of total methane column content in atmosphere is strongly affected by the topography and terrain,and the methane content fluctuates in the complex topography area,which has a good inverse correlation with the precipitation.Methane has radiation and chemical activity which can affect the ground gas radiation,change the vertical distribution of atmospheric temperature,and increase the atmospheric instability.The change of methane column could be used as a precursor to the occurrence of heavy rainfall.It can provide the new view and a reference for exploring the mechanism of local heavy rain combined with multi\|source meteorological data,analysis of atmospheric power,heat,water vapor conditions.      

Land Change Patterns and Driving Mechanism in Beijing since 1990 based on GEE Platform

Land-cover and land-use dynamics is a key component for global change,and it is a significant form of the impact of human activities on physical environment.Basing Google Earth Engine platform and Classification And Regression Tree method,selected seven types of cultivated land,forest,grassland,wetland,water body,artificial surface and bare land as classification system,the paper used Landsat 5 TM and Landsat 8 OLI images to interpret the land\|cover and land\|use since 1990 of Beijing.Simultaneously,the paper analyzed and summarized the character of land\|use changing and driving force.The results show that：(1) GEE has outstanding advantages in remote sensing data analysis and processing at regional scales.(2) The CART method has high accuracy of remote sensing classification,and the overall accuracy of validation of 6 land cover products is above 93%.The spatial consistency of 2010 products and GlobeLand30\|2010 data showed that the spatial consistency ratios of woodland,water body and cultivated land were 84.28%,74.75%and 73.56% respectively.The spatial consistency of the distribution is 74.0%.(3) The main land types in Beijing were cultivated land,woodland and artificial surface,and the area accounted for about 90%.During the period from 1990 to 2016,the artificial surface and woodland area increased,and the cultivated land and water were shrinking.The artificial surface area increase of 1 371 km²,and cultivated land shrinkage 40%;On Beijing plain area,artificial surface by the circle of “spread pie” expansion trend to “blossom everywhere” expansion trend;The expansion of the artificial surface is mainly achieved through the encroachment of cultivated land.We constructed a multidimensional stepwise linear equation model to analyze the driving force of land type change,indicated that rapid population growth,rapid economic development,government\|related policies and other socio\|economic development factors jointly drive the Beijing land-cover/land-use evolution process.     

基于交叉与变异组合的TSP问题研究

遗传算法是一种在自然选择与遗传机制基础上的随机化的搜索类算法,是求解TSP(Travelling Salesman Problem)问题的一种常用算法。但是该算法在解决TSP问题时,存在着收敛速度过慢,容易出现早熟的问题。本文针对该问题,创新性地提出使用5种交叉算法和3种变异算法进行组合的算法设计,得出15种不同的组合方法,然后使用Java语言进行编程实验,最后通过对中国144个城市相对坐标（CHN144）的实例进行测试,证明了在使用交叉算法与变异算法进行组合得出的15种组合方法中,使用三交换交叉算法与逆序变异算法进行结合,这种组合方式的遗传算法在解决TSP这一问题时能够取得最优的效果。