Methodic Errors in Laser Measurements of Euler Statistical Moments of a Nonuniform Turbulent Velocity Field

Probability distributions of the velocity obtained by means of laser Doppler spectroscopy with different ratios between the dimensions of the probe volume and the scales of the nonuniformity are studied using a model of a locally normal, spatially nonuniform turbulent field. Sample calculations of the measured probability distributions of the velocity and the statistical moments of these distributions up to the fourth order are presented for model examples that take into account the nonuniformity of the mean flow velocity and the intensity of turbulent fluctuations of the velocity. It is shown that the substantial deviations in the velocity distributions from the normal law which are observed in a number of experiments may be related to noncompliance with the locality condition.     

非均匀传输线的仿真模型建立方法研究

利用分段线性和等效电路模型,结合Hspice电路仿真软件,提出了一种建立非均匀传输线仿真模型的方法,给出了非均匀传输线的Hspice等效电路模型。通过一个有代表性的算例,利用文中提出的仿真模型建立方法,得出了时域范围内的Hspice仿真结果。最后通过与已有的方法结果比较表明：该方法有较高的计算精度,且计算速度快,占用计算机资源少。     

确定非均匀传输线网络时域灵敏度的伴随网络法

基于模量分析、特征值灵敏度和数值逆拉普拉斯变换技术,提出采用伴随网络法计算含有耦合均匀与非均匀传输线网络的时域灵敏度。通过求解原网络方程和伴随方程,可一次计算出任意输出对网络元件以及传输线电气参数的灵敏度,与扰动法相比效率更高。通过仿真实例与采用扰动法的计算结果进行比较,验证了所提方法和公式的正确性。     

Effect of nonlinear thermal radiation on silver and copper water nanofluid flow due to a rotating disk with variable thickness in the presence of nonuniform heat source/sink using the homotopy analysis method

An analysis of a steady axisymmetric heat transfer nanofluid flow due to a rotating disk having variable thickness in the presence of nonlinear radiation and nonuniform heat source/sink is presented. Water with Copper (Cu) and Silver (Ag) nanoparticles are utilized in the investigation. The governing equations along with boundary conditions are solved using the homotopy analysis method. A parametric study of the physical parameters is done and results are displayed in the form of graphs. The findings indicate that nonlinear radiation has a significant effect on temperature as well as on wall heat transfer when compared with linear case, which is more useful in few engineering processes.     

偏心度与间隙比对轴流泵流动激励力的影响

叶轮偏心将会引起轴流泵叶轮顶部间隙沿周向不均匀,从而导致附加的流动激励和噪声.利用计算流体力学商业软件Fluent模拟不同偏心度和间隙比的轴流泵非定常流场,研究周向非均匀间隙对泵内压强脉动及叶轮激励力的影响.结果表明:壁面压强脉动强度并不是在最小间隙处达到最大,而是出现在偏离最小间隙处约30°~60°的方向,并随着间隙比增大,脉动强度最大值发生位置逐渐向最小间隙处靠拢;同时,偏心造成的非均匀叶顶间隙引起了轴频处的压强脉动,在间隙比为2.5%下偏心度从0%增加到60%,轴频处的压强脉动相对增量为661.54%;叶轮受到的径向激励力时均值与偏心度呈线性关系,其斜率与间隙比的平方根成正比.     

非均匀沙不平衡输沙的理论研究

文中首先给出了由我们建立的床面泥沙交换理论导出的非均匀沙扩散方程的边界条件。建立了恢复饱和系数的表达式,包括了强平衡输沙和不平衡输沙两种情况。同时给出了泥沙在床面静止、滚动、跳跃与悬浮的概率方程和数值结果。引进了挟带分组泥沙的水量百分数,它是研究非均匀沙的重要概念和工具。进而论述不平衡输沙时总挟沙能力、挟沙能力级配及有效床沙级配的方程。证实了床沙质、冲泻质与全沙具有统一的挟沙能力。最后从理论上证明了在河道中粗细泥沙发生交换的现象。     

Effects of chain length on prebreakdown phenomena in straight-chain saturated hydrocarbon liquids

Prebreakdown light emission, currents, and streamers in straight-chain saturated hydrocarbon liquids, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, and n-decane, are investigated under nonuniform field conditions. The light inception voltage and the breakdown voltage increase with the chain length and the liquid's density. For a negative point, the breakdown voltage is much higher than the light inception voltage in all liquids but the difference decreases with the chain length. This voltage difference is not observed for a positive point except in n-pentane and n-hexane. The difference between the negative and positive breakdown voltages decreases with the chain length. Regarding the polarity effect, the negative breakdown voltage is much higher than the positive one in n-pentane, but there is no difference in n-decane. A negative density change streamer has a bushlike structure and propagates in stepped manner at an average speed between 70 and 160 m/s, while for a positive one, the structure is treelike having an average speed of a few kilometers per second. Only in n-pentane and in n-hexane, a slow positive bushlike streamer is observed whose average velocity is about 200 m/s, slightly faster than the negative bushlike one. © 1998 Scripta Technica. Electr Eng Jpn, 122(4): 8–16, 1998     

Turbo码MAP译码算法中量化问题的研究

针对Turbo码MAP(Max a Probability)译码算法的特点,对其量化方式进行了分析、讨论与仿真;着重讨论了量化范围、量化级数、均匀和非均匀量化等因素对译码器接收比特、前后向递推度量、附加信息和输出似然值的影响;分析了相应的译码性能;得出了较为合理的量化方法.     

天然河道水面曲线的迭代算法

由于天然河流复杂水力特性 ,传统水面曲线计算存在诸多不足。本文从非均匀流能量方程入手 ,推演出了以水深为变量 ,成果精确且操作简便的水面曲线计算的迭代形式 ,进而对迭代收敛性进行了简要分析 ,结合算例定量比较了各类河段流量模数公式造成水面曲线成果的偏离情况