出海水闸工程渗流特性计算分析研究

上海地区出海水闸的工程所处位置地质条件往往较差,一般具有地基承载力较差,地基土渗透性较强的特点。工程均需要设置防渗措施进行节渗。传统渗流计算方法一般为改进阻力系数法,该方法计算较为保守,对于复杂结构,无法将闸基各个部位的渗流计算结果进行具体量化,特别是无法对水闸侧向绕渗进行数值计算。三维有限元法的出现对水闸闸基渗流计算起到了很大帮助作用。本文以芦潮港水闸为例,将三维有限单元法和改进阻力系数法进行比较,并分别对水闸闸基渗流、侧向绕流进行计算,得出了准确可靠的计算结果。     

Investigating user perception on autonomous vehicle (AV) based mobility-on-demand (MOD) services in Singapore using the logit kernel approach

The rapid development of autonomous vehicles (AV) in recent years has drawn the attention of numerous countries in terms of its feasibility for use and deployment as individually-owned vehicles or for large-scale fleet planning and deployment as a mobility-on-demand (MOD) service. Singapore is no exception to this global trend and in her pursuit to be smart and car-lite, numerous efforts are made to have AV trials in place and test out their potential deployment in the city state. As one of the many prerequisites of AV planning, public perception on AV plays a vital role when designing any potential AV deployment scheme. As such, a stated preference survey comprising both online survey and field interviews/surveys, was performed island-wide to understand how commuters in Singapore perceive about different AV-based MOD modes. The logit kernel model is adopted to determine how different preference attributes and key demographic indicators can affect the use of AV-based MOD services over other existing first- and last-mile connection modes. The model results have identified how demographics such as gender, age, housing type, education level and income level can influence the travel mode choice. Also, the impacts brought by individuals’ stated preferences over convenience, privacy and familiarity of ride-hailing apps are also investigated. Such findings can provide useful insight in planning future car-lite towns and implementing AV-based MOD services in these towns.

     

地铁杂散电流腐蚀评估及建模分析的研究现状

随着我国地铁铺设里程的不断增加,钢筋混凝土、埋地管道等基础设施被广泛应用于地铁系统。地铁杂散电流泄漏会对基础设施造成严重破坏,混凝土钢筋和埋地金属的腐蚀问题值得城市运维部门的高度关注。分别从杂散电流作用下的金属腐蚀,杂散电流建模分析等方面,系统介绍了国内外对杂散电流金属腐蚀研究的现状和进展,并对杂散电流建模方案进行了比较与展望。     

Comparison of Biomechanical Properties and Hemodynamics of Three Different Vena Cava Filters

The interaction mechanism of three types of vena cava filters (VCFs) with blood vessels and their influence on the bloodstream during the process of implantation are investigated by finite element method and computational fluid dynamics. The VCF models are set up with Solidworks software. Using ABAQUS software, we simulate the working conditions of the VCFs in the vessel to analyze the stress distribution and radial support stiffness of the vessel wall and the filter surface. Using FLUENT software, we simulate and analyze the velocity, pressure and shear stress distributions of blood flow when the VCFs are at their working conditions. For the retrievable VCF (R-VCF), the peak stress at the working conditions of the VCF is the highest, the peak stress toward the vessel wall is the lowest, and the support stiffness is the lowest. For the permanent VCF (P-VCF), the peak stress at the working conditions of the VCF is the highest, the peak stress toward the vessel wall is the lowest, and the support stiffness is the highest. Because of the structure of scaffolding support units and the tendency to form intimal hyperplasia on their support units, both the convertible VCF (C-VCF) and the P-VCF can embed their support units in the hyperplasia skin. This effectively prevents them from harming blood veins through filter damage at the pulse load conditions. As the biomechanical property of the C-VCF is between those of the R-VCF and the P-VCF, it has smaller obstacle to blood flow after conversion and has some fragmentation effects on the thrombus. The results show that different types of VCFs differ in their biomechanical and hemodynamic properties after implantation. Therefore, the simulative analysis can provide a reference basis for filter design and clinical decision making.     

厦门海事局:开辟“海上绿色通道” 护航防疫物资海上运输

“厦门交管,华航3过东南报告线,计划经主航道进港靠泊海天码头,向您报告。”“华航3,这里是厦门交管,信息收到。我们从市口岸办了解到你船上有台胞捐赠的防疫物资,我们已经提前与港口管理部门协调好泊位,您可以进港靠泊,近期港内大雾天气频发,请您谨慎驾驶,注意瞭望,再会。”2月15日上午,载着台胞援鄂的40吨次氯酸消毒水的集装箱船“华航3”轮驶抵厦门港,厦门海事局船舶交通管理中心迅速启动“绿色通道”,设置专人专台保驾护航。     

基于交通供需条件的公交分担率计算方法

不同城市的社会经济状况和形态不尽相同，因此其公交分担率指标也不应是统一不变的，而应结合该城市自身特点，制定与之相适应的公交分担率指标。鉴于此，基于城市整体的交通供需条件，考虑地面公共交通与私家车的竞争关系，以系统出行效率最优为目标，建立公交分担率指标优化模型。通过对模型分析可得出，城市公交分担率发展目标与该城市的交通供需系数密切相关，当供需系数较低时（算例取G≤1），建议公交分担率为0；当供需系数较高时（算例取G≥3.5），建议公交分担率为100%；当1＜G＜3.5时，适宜的公交分担率在0~100%之间取得；适宜的公交分担率随着交通供需系数的增大呈上升趋势，且上升幅度逐渐减小；随着私家车-公交速度比增大，适宜的公交分担率呈下降趋势，两者关系曲线呈倒S形；公交平均载客率对适宜的公交分担率影响不明显。     

极地船蝶阀及管道内不同开度下海水—冰晶两相流流场特性及冲蚀数值模拟

文章以极地船海水冷却系统中的蝶阀及管道为研究对象,在Fluent平台上采用RNG k-ε湍流模型及DPM模型,计算得到了海水—冰晶两相流在蝶阀管道中的流场特性及冲蚀磨损,并选取3个有代表性的蝶阀开度即30°、60°和90°的计算结果进行对比。研究结果发现:蝶阀的开度越大,流场越稳定。各开度下阀板前、后缘与管壁间都存在2个高速区,且阀板前后压差随开度增大而减小,阀板后存在负压区域,涡流现象随开度增大逐渐消失。此外,蝶阀开度越大,蝶阀受到冰晶颗粒的冲蚀磨损越小,最大冲蚀速率也随之减小。研究还得到了蝶阀管道受冲蚀磨损较严重的位置,为船用蝶阀在不同工况下提供科学预测和参考。     

同步发电机励磁电流放大器研究

给出了励磁电流放大器所使用的Buck电路和电压双象限H桥功率主电路的工作原理,并针对后者分析了两路中心对称但占空比不同的PWM实现三电平工作方式(称为对称PWM法),同时提出了采用两路占空比相同但具有一定相位差的PWM控制方法以减小电流纹波(称为移相法)。给出了对称PWM法和移相法两种方式下的电流纹波计算公式,指出半周移相(180°移相)时电流纹波大为减小且几乎不受电源电压影响。利用Matlab对励磁电流放大器进行了仿真,构建了以DSP为控制核心的试验平台,并进行了发电机励磁调节试验。理论分析、数字仿真和试验结果表明,对不同工况下的纹波大小分析正确有效,试验所采用的励磁电流放大器调节性能优良。     

论以德治国与以德育人的现代价值

江泽民“以德治国”重要思想的提出,对强化思想道德教育,维护国家稳定,推进国家发展,具有重大而深远的意义。中国自古以来就有以德育人、以德治国的优良传统。在现代社会条件下实现以德治国与以德育人,必须提高对道德价值的认识,强化公民教育,从严治党、以德治党,发挥共产党员以德示范作用。     

长江菜园坝桥群河段通航条件试验

山区河流桥群河段的选址、桥梁间距及桥跨布置对桥区通航条件的影响较大。长江菜园坝桥群河段通航环境复杂,通过模型试验,按建桥的顺序研究桥梁建设对该河段通航水流条件、船舶操纵特性的影响。分析表明:石板坡重庆长江大桥对桥群河段通航条件的影响相对最大,航道变得狭窄、弯曲,通航净宽尺度不足,桥群河段的通航条件较差;菜园坝大桥主通航孔虽然一跨过通航水域,但与石板坡间距较近,下行船舶在通过菜园坝大桥后应及时调整航向和船位。为保障通航安全,应整体考虑桥群河段的通航安全措施。