为研究梅雨期极端对流系统的微物理特征,利用2013-2014年江淮梅雨期间南京溧水S波段双偏振雷达探测资料和地面自动站小时降水资料,统计分析了两类极端对流降水系统的微物理特征及差异.这两类极端对流系统的定义基于地面降水强度和雷达回波顶高,分别为所有对流中降水强度最强的1％(R类:小时降水强度＞46.2mm/h)和对流发展高度最高的1％(H类:20 dBz回波顶高＞14.5 km).结果 显示这两类极端对流系统仅有30％的样本重合,显示了二者之间的弱相关性.对于相同的反射率因子ZH,R类极端对流系统的近地面差分反射率因子ZDR通常较H类极端对流小约0.2dB,表明R类极端对流具有较小的平均粒径.结合双偏振雷达反演的粒子大小和相态分布显示,虽然两类极端对流都表现出海洋性对流降水特征,但R类极端对流较H类极端对流的总体雨滴粒径更小而数浓度更高,导致R类极端对流系统的地面降水更强.与R类极端对流系统相比,H类极端对流系统的上升运动更强,将更多的水汽和过冷水输送到0℃层以上,有利于形成更大的冰相粒子(如霰粒子等),并通过融化形成大雨滴.以上研究表明,梅雨期降水强度和对流发展深度并没有必然的联系,极端降水主要是中等高度的对流引起.

对一比转数为148.8的设计混流泵进行试验和数值模拟研究,比较不同流量工况下混流泵性能的试验与数值计算结果,两者吻合较好.在流场内部设置监测点,捕捉压力脉动由动静干涉无叶区向导叶出口的发展过程.分析不同工况下的混流泵各测点的压力脉动,发现导叶内部各测点压力脉动主要受叶轮转动影响,主频为叶频;由动静干涉的无叶区到导叶出口,平均压力逐渐增大,而压力脉动的幅值强度越来越弱;非设计工况下的压力脉动变化更复杂.上述结果可为混流泵进一步的优化设计提供参考.

Three kinds of Al-Zn-Ga-Si sacrificial anodes with differ-ent compositions were designed and prepared for developing low voltage sacrificial anodes used for cathodic protection of high strength steels in ocean environment. The electrochemical per-formance of the three sacrificial anodes was evaluated by using galvanostatic method. Their micro-morphologies upon dissolution were observed by using a scanning electron microscope. Moreo-ver,their metallographic structures were observed by using a met-allographic microscope. Results show that the Al-alloy anode containing 0.3%Zn,0.1%Ga and 0.9%Si has good comprehen-sive electrochemical performance,which had an operating poten-tial of-820～-780 mV,current efficiency of 83% and goodmorphology after dissolution. Moreover,the grain size of the alu-minum alloy decreased with increasing content of alloying element Si,and the amount of segregation phases increased therewith.