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101.
This paper analyzes the effective parameters on lightning performance. The effects of tower height, breakdown electric field threshold, the ground slope of installation place, and the effect of the trees around the tower are investigated. A 3-D numerical analysis model is proposed to determine the number of direct lightning strokes to antennas. The communication tower, lightning rod, downward descending leader and upward leaders are modeled by different shapes of charges. Finally, a small-scale communication tower was built and tested in a high voltage laboratory. The experimental tests were consistent with the simulation results verifying the merits of the proposed method. 相似文献
102.
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104.
通过控制变量法对混流闭式冷却塔进行测试, 采用灰色关联分析法对影响出水温度的因素进行筛选, 将关联度较大的5个因子作为输入参数, 进而建立灰色_BP神经网络预测模型, 对混流闭式冷却塔的出水温度进行预测。操作参数包括进水温度、湿球温度、补水温度、循环水流量和风量, 输出值为出水温度。网络采用三层结构, 隐含层神经元数为4个, 迭代次数为30 000次, 使用不涉及训练阶段的实验数据来验证所建立的模型。结果表明, 灰色_BP神经网络模型比传统BP神经网络模型的预测结果更加准确, 其预测值与实际值的相关系数、平均相对误差、均方根误差, 分别为0.998 9、0.293 4%和0.152 9, 因而可认为灰色_BP神经网络是预测混流闭式冷却塔出水温度的有效工具。 相似文献
105.
Maurice Arrigoni 《Mathematische Nachrichten》1998,192(1):71-89
In this paper, we consider some conditions of finiteness related to the p-class field tower problem over an imaginary quadratic field, where p is an odd prime. 相似文献
106.
Daniel Smania 《Bulletin of the Brazilian Mathematical Society》2005,36(2):225-274
We study the dynamics of the renormalization operator for multimodal maps. In particular, we develop a combinatorial theory
for certain kind of multimodal maps. We also prove that renormalizations of infinitely renormalizable multimodal maps with
same bounded combinatorial type are exponentially close. Our results imply, for instance, the existence and uniqueness of
periodic points for the renormalization operator with arbitrary combinatorial type. 相似文献
107.
假设群A经自同构互素地作用在G上.设χ是G的一个A-不变不可约特征标,π(G,A)表示Glauberman-Isaacs特征标对映.对于B≤A,T.R.Wolf曾猜想χπ(G,A)是χπ(G,B)a的一个不可约成份,此处C=CG(A).设G=N(X)H且(|N|,|H|)=1,假定H是A-不变的且N是一个Sylow塔群,N的Sylow-子群是交换的.在本文中,我们证明了如果这个猜想对所有H的A-不变子群成立,则猜想对G也成立. 相似文献
108.
109.
拉线塔是一种含有柔索的非线性结构。在冲击波荷载作用下,拉线塔在三维空间内会产生大范围的非线性位移,用工程上常用的模型简化方法来分析大变形拉线塔的误差比较大。本文采用非线性有限元法编制的可在微机上运行的拉线塔非线性静、动力分析程序,计算了单根柔索的阶跃冲击响应与冲击波荷载作用下拉线塔的非线性几何大变形动力响应,计算结果与有关文献的计算结果以及试验结果非常吻合。 相似文献
110.
Aerodynamic interference between high cooling towers in the atmospheric boundary layer (ABL) and uniform flow has been discussed.
For the 1/1000 ABL model set up in the 2.25m low speed wind tunnel at Peking University, the similarity condition of the cooling
tower in the ABL, the simulation results of a single tower and some typical tower groups have been provided. Experiments showed
that the Circumferential pressure distributions were consistent between the smooth model tower and the prototype tower, and
between the rough model tower and the prototype tower with ribs; the two dimensional characteristics in the circumferential
pressure distribution were also noticeable around the middle 1/3 part of the tower after nondimensionalization by local dynamic
pressure. Results demonstrate that, in the flow with strong turbulence the lift coefficient of the downstream cylinder approaches
0.4. In the flow with weak turbulence, the pressure distribution reflects a strong nonsymmetry, and the lift coefficient or
stagnation pressure of the downstream cylinder switches alternately between 1 and 0, where a concentrated vortex rolls up
and then sheds toward the front of the downstream cylinder and exerts a decisive influence on the aerodynamic properties of
the downstream cylinder. 相似文献