Vortex-induced vibrations of piggyback pipelines near the horizontal plane wall in the upper transition regime

Slender subsea structures like pipelines, jumpers and umbilicals when exposed to currents may experience vortex-induced vibrations (VIV), which can shorten their fatigue life and increase the risk of structural failure. In the present study, flow around different configurations of a piggyback pipeline close to a flat seabed has been investigated using the two-dimensional (2D) Unsteady Reynolds-Averaged Navier Stokes (URANS) equations with the k − ω Shear Stress Transport (SST) turbulence model. The Reynolds number (based on the free stream velocity and large cylinder diameter) is equal 3.6 × 10⁶ corresponding to upper-transition regime. The drag forces acting on the cylinders and base pressure coefficient value are well predicted by the present simulations, while the other hydrodynamic quantities (root-mean-square lift coefficient, Strouhal number) are predicted reasonably well as compared to published experimental data. The piggyback pipeline in the present study is modeled as two circular cylinders with a diameter ratio d/D = 0.2 (D denoting diameter of the large cylinder, d is diameter of the small cylinder). These two cylinders are clamped together at a distance G/D = 0.2. The two rigidly coupled cylinders are elastically supported and free to vibrate in two degrees of freedom. The effects on the vibration amplitudes and hydrodynamic forces are analyzed. The flow structures around the cylinders are investigated to explain the variations in observed structural responses. Depending on the angular position (α) of the small cylinder, the lock-in regime is narrower (α = 0°) or significantly wider (α = 180°) when compared to that of a single cylinder.     

对复合标底招标报价的探讨

总结和积累了招投标活动的实践经验，针对各类工程找出自身预算与招标人标底的差异，介绍了使未知因素变为可预测因素的方法和寻求投标报价的内在规律，以尽可能的减少盲目性，提高投标报价的准确率。     

Cavitation erosion research in France: the state of the art

An important part of the French research program on cavitation erosion, conducted from 1980 to 1995, was devoted to pitting. Histograms of pit size have been extensively used to characterise the hydrodynamic aggressiveness of a cavitating flow. Numerous erosion tests, limited to the incubation period, were carried out on similar test sections, for different velocities, liquids, length scales, and materials. Scaling laws were discussed and two kinds of methods for prediction of the erosion rate were proposed. The first one is based upon the estimation of the aggressiveness of the prototype cavitating flow, from pitting tests on a model and the simulation of the prototype histogram of pits on an appropriate device. The second one is based upon a correlation between the advanced stage of erosion and the incubation period, consisting of a proper adimensionalization of the mass-loss curve. After several years of research and the development of special facilities, devices and techniques, more deterministic procedures for predicting cavitation erosion could now be developed, based not upon erosion tests, but upon the characterization of the aggressiveness of the cavitating flow in terms of impact loads and the analysis of the mechanical and metallurgical response of the material to successive impacts.     

基于统计特征的轨道交通站点乘降量预测算法研究

针对现有预测方法因未考虑城市轨道交通站点乘客的随机性,致使乘降量预测精度不高的问题,提出一种基于统计特征的客流量预测方法。依据日期、时段、天气、突发事件等因素将历史数据进行分类。建立基于乘降量统计特征的分布模型,根据其预测客流的统计特征,结合随机数产生算法,产生的随机数即为客流乘降量预测值,最后结合算例予以说明,证明该模型的可行性。     

ATS车次号自动识别系统解决方案

针对重庆轨道交通2号线ATS车次号系统需要人工输入和校核的问题,引入了ATS车次号自动识别系统,并对车次号追踪识别程序进行了优化,减轻了调度员的工作量,同时也提高了整个系统的准确性和稳定性。     

线性算子P—条件数的一些性质

众所周知,常用的线性算子的条件数有 k—条件数和 P—条件数。笔者讨论了 P—条件数的一些性质,得到如下主要结果:(1)给出了 P(T)=k(r)的充分必要条件;(2)给出了 P(T)=1时,线性算子 T 的谱的构成和 P(T)=1的一些条件;(3)把线性算子 P—条件数的一些性质推广到了伪 P—条件数的情形。     

切诺基I—4汽油机燃烧系统的改进

针对美国切诺基I－4汽油机在我国使用较低辛烷值汽油的特定情况下出现爆震、排气温度高等问题，用天津大学发明的射流燃烧系统取代原机斜楔型燃烧系统。结果，改用新燃烧系统的I－4S汽油机，在使用较低辛烷值汽油时，动力、经济性能优于用同样汽油机的I－4，排气温度也显著降低，大大改善了发动机的使用条件。     

柴油机非对称喷油嘴内部空化流动特性的数值研究

柴油机喷油嘴内部喷嘴流量和空化现象直接影响到燃油的喷射和雾化,进而影响柴油机的性能和排放。以两种非对称柴油机喷油嘴——小压力室喷油嘴(mini-sac)和无压力室喷油嘴(VCO)为例,通过Fluent软件对其进行空化和流量数值仿真,研究入口压力和背压参数对质量流量变化的影响。研究结果表明:在相同进出口压力下,mini-sac型喷油嘴各孔的流量均比VCO型的大;在较低和中等进口压力下VCO型喷油嘴各孔比mini-sac型更容易产生空化,而在较高的进口压力下这两种类型喷油嘴各孔产生空化难易程度基本一致;当进口压力不变时,随着出口压力的降低,在无空化产生时其质量流量与压力差呈线性关系;当空化出现时其质量流量继续增加,当出现超空化现象时该孔的质量流量不再变化;随着各孔的轴向夹角的增大,流量越小,空化越容易;对于这两种喷油嘴来说,只有mini-sac型孔3和孔4的空化出现在喷孔的上端和下端,其余孔的空化都只产生在上端。     

车用直喷汽油机喷雾特性研究

利用高速摄影在定容弹内对缸内直喷汽油机多孔喷油器进行喷雾特性试验研究,揭示了直喷高速液体射流的喷雾特性(贯穿距、喷雾锥角)与无量纲数(韦伯数、雷诺数及气液密度比)之间的关系。结果表明,韦伯数和气液密度比对喷雾宏观特性有显著的影响,雷诺数对喷雾特性的影响不明显。