陇东两类夏季雷暴的活动特征及影响因素分析

利用ECMWF-ERA5再分析资料、常规观测资料分析了甘肃陇东2009—2018年夏季雷暴活动特征及环境条件。结果表明:陇东年均雷暴日数为18.8~23.6 d,夏季雷暴占68.5%~74.7%。夏季雷暴主要分为偏北气流型和低槽影响型,其中偏北气流型以分散性干雷暴为主,较大的垂直温差、高空冷平流强度和近地面高温对雷暴发生具有显著影响;低槽影响型多伴有明显降水过程,显著影响因素为较高的低空温度、湿度和较强的不稳定能量。低槽影响型和偏北气流型雷暴分别占总数的30.5%和60%,这两种类型的雷暴更容易出现在陇东北部地区。低槽影响型雷暴呈逐月增加趋势,最大值出现在8月;偏北气流型雷暴呈单峰分布,最大值出现在7月。各站雷暴日数年际变化趋势在6、7月一致性较高;月雷暴日数均有3~5 a的变化周期,其中7、8月同步性较好。雷暴日数的月、年变化与相应类型主导因素相关明显。植被覆盖、气候带以及地形差异也对雷暴空间分布产生了重要影响。

面贴式异向旋转双转子永磁电机的磁场解析计算

采用解析法分析了面贴式异向旋转双转子永磁电机的空载磁场分布。模型在二维极坐标下建立,考虑了径向/平行充磁,内永磁/外永磁转子结构。为了准确计算磁场分布和齿槽转矩,不同于之前的引入相对磁导函数或复数保角变换方法,而是直接利用边界条件来考虑定子槽的影响。在气隙和槽区域内采用拉普拉斯方程,在永磁体区域采用泊松方程求解,并且认为永磁体的相对磁导率是不为1的常数。通过傅里叶变换和分离变量法得出各部分磁通密度的径向、切向分量。通过转子转动,得出槽口区域磁场变化,同时准确估计该种电机的齿槽转矩和反感电动势。与有限元法计算结果比较,两者吻合很好,肯定了该解析法的计算精度。

Effect of Configuration on Mass Transfer in a Filter-press Type Electrochemical Cell

Effect of configuration （structure of electrode, interelectrode gap, positions of inlet and outlet, volume of the cell and additional nets） on mass transfer characteristic of a filter-press type electrochemical cell has been studied. The mass transfer coefficients on the electrodes were obtained by using the well-known technique based on the determination of limiting diffusion current. It is found that mass transfer coefficients with mesh electrode are greater than that of with plate electrode. Mass transfer coefficient is decreased with interelectrode gap. While interelectrode gap achieved a certain value （7 ram）, mass transfer coefficient is steady, no more declining. Mass transfer characteristic for different positions of inlet and outlet are different and dimensionless number groups correlated equations are obtained by experiment. Mass transfer characteristic is the best when inlet located on the top and outlet on the bottom of the cell respectively. While magnified the volume of the cell to eight times, mass transfer characteristic changes little. Mass transfer characteristic without nets is lower than that of with additional nets in the exit region, but higher than that of with additional nets in the entry region.

An Experimental Study on the Wave-Induced Pore Water Pressure Change and Relative Influencing Factors in the Silty Seabed

In this study, a flume experiment was designed to investigate the characteristics of wave-induced pore water pressure in the soil of a silty seabed with different clay contents, soil layer buried depths and wave heights respectively. The study showed that water waves propagating over silty seabed can induce significant change of pore water pressure, and the amplitude of pore pressure depends on depth of buried soil layer, clay content and wave height, which are considered as the three influencing factors for pore water pressure change. The pressure will attenuate according to exponential law with increase of soil layer buried depth, and the attenuation being more rapid in those soil layers with higher clay content and greater wave height. The pore pressure in silty seabed increases rapidly in the initial stage of wave action, then decreases gradually to a stable value, depending on the depth of buried soil layer, clay content and wave height. The peak value of pore pressure will increase if clay content or depth of buried soil layer decreases, or wave height increases. The analysis indicated that these soils with 5% clay content and waves with higher wave height produce instability in bed easier, and that the wave energy is mostly dissipated near the surface of soils and 5% clay content in soils can prevent pore pressure from dissipating immediately.

Distribution, features, and influence factors of the submarine topographic boundaries of the Okinawa Trough

Based on multiple types of data, the topographical features of the Okinawa Trough(OT) have been characterized and a computation method has been proposed to determine the break point of continental shelf(BOS), foot point of the continental slope(FOS), the central axial point, and the maximum depth point. A total of 48 topographical profiles that crosscut the continental slope have been used to determine the trends of the BOS and FOS(the BOS and FOS lines) in the East China Sea(ECS). The trend of central axial points in the OT has been similarly determined by analyzing 39 topographical profiles across the axis of the trough. The BOS line forms the boundary between the continental shelf and slope. In the ECS, the BOS line roughly follows the 200 m isobath, continuously in the northern and middle parts of the OT, but jumping about somewhat in the south. The FOS line is the boundary between the continental slope and the bottom of the trough. The depth of the FOS increases gradually from north to south in the OT. Intense incisions by canyons into the slope in the southern part of the trough have led to the complex distribution of FOS. Topographical profiles crosscutting the northern, middle, and southern parts of the OT exhibit features that include: a single W-shape, a composite W-shape, and a U-shape, respectively, which suggests that in the middle and northern parts of the trough the central axial points are always located on seamount peaks or ridges associated with linear seamounts, whereas in the south they are found in the center of en echelon depressions. The line formed by the central axial points is the east-west dividing line of the OT, which indicates that the trough is a natural gap that prevents the extension of ECS continental shelf to the east. The distributions of the BOS and FOS lines are influenced by fluctuation of sea levels and submarine canyons, whereas the distribution of axis lines is controlled by tectonics and deposition.

Experimental study on fouling characteristics and influence factors of spiral-grooved tube

In this paper,we carried out a series of experiments on fouling characteristics of 6 kinds of spiral-grooved tubes to investigate the impact of hardness,temperature and structure parameters of cold water on fouling characteristics of spiral-grooved tube.Experimental results showed that when cold-water temperature decreased,fouling resistance of spiral-grooved tube also decreased.Asymptotic fouling resistance increased accompanied with increase of cold-water hardness.However,the asymptotic fouling resistance appeared to reduce when hardness increased to some extent.Geometric parameters of spiral-grooved tubes had remarkable effect on fouling resistance,which showed a tendency of decrease with increase of groove depth and decrease of pitch.In this study,the minimum asymptotic fouling resistance was observed in the spiral-grooved tube with small pitch and large groove depth.