地形因素对雷电定位的影响与分析

针对目前我国电力系统的雷电探测定位系统采用基于VLF-LF雷电探测器接收雷电波地波及实际计算模型中采用真空雷电波波速的精度问题,研究和改正了雷电定位计算中由于地形因素引起的雷电波传播距离误差,并对雷电波传播速度进行了分析、比较和探讨.通过实例计算表明,提出的距离改正计算及雷电波波速的取值大大提高了雷电定位计算精度.     

竖直平板上层流降液膜表面波特性的实验研究

基于自主设计的平板降液膜流动实验台,分析了层流状态下竖直平壁上表面波在空间域和时间域上的演化过程,利用高速摄像机阴影成像法在Re为600~1 300下,对表面波形态、波速和频率等流动特性进行了实验研究,并在实验测量的基础上结合Matlab图像处理深入分析了表面波波速和频率等统计特征.结果表明:孤立波波速与Re具有线性正相关性,波速的变化范围也随Re的增大而增大,而孤立波频率与Re和沿程距离呈弱相关;通过Matlab编程得到实验中孤立波频率在7~13Hz内波动.     

天然气水合物沉积物颗粒影响实验CSCD

通过利用SHW-Ⅲ型水合物岩样声电力学测试装置,以石英砂和棕刚玉作为赋存介质,开展了60%、80%孔隙饱和度下不同颗粒对天然气水合物沉积物基础物性(声波波速、动态力学参数、胶结强度)影响的实验研究。得到纵波波速范围3542.6~4383.7 m/s,横波波速范围2163.9~2572.1 m/s,动态力学参数杨氏模量范围21.995~40.731 GPa,泊松比范围0.156~0.237等实验数据。当前实验条件下研究结果表明:不同颗粒类型、不同颗粒粒径作为天然气水合物沉积物骨架,最终形成的水合物沉积物电阻值相差不大;同一种颗粒粒径下的沉积物孔隙饱和度越高,声波传播速度越快,而相同类型的沉积物声波传播速度随其颗粒粒径的减小而增加;得到适用于60%、80%孔隙饱和度下一定颗粒粒径范围(0.42~1.8 mm)的以石英砂作为赋存介质时合成的天然气水合物沉积物声波波速拟合公式。通过压缩实验发现:天然气水合物沉积物的抗胶结程度随着沉积物颗粒粒径的减小而增强,随着孔隙饱和度的减小而下降。     

三峡建库后库区洪水波动力特性初步分析

本文采用水文、水力学相结合的方法,研究三峡建库后库区洪水波动力特性。首先,通过分析一般河道型水库洪水期水流规律,对三峡建库后库区水流特性进行了预测,其次提出一种水库洪水波模型识别方法,并对三峡工程175方案下百年一遇洪水的洪水波模型进行了研究,最后分析计算了各库段的洪水波波速。本文的结果可供三峡工程的规划设计及可行性论证参考。     

三角形壁面液膜孤立波特性的实验研究

液膜的孤立波特性是影响液膜表面形态的重要因素,也是影响液膜换热特性的主要原因之一。通过搭建降液膜流动实验台,对倾斜三角形壁面上液膜流动进行实验测量,分析不同倾斜角度、雷诺数和沿程距离下孤立波波速和频率的变化规律。结果表明:孤立波波速与雷诺数呈正相关;三角形壁面上的孤立波波速高于平板壁面上;孤立波波速随着沿程距离的增加而逐渐增大;孤立波频率与雷诺数、倾斜角度和沿程距离均无明显相关性,而与其自身的产生过程密切相关。     

不同厚度不同系列波状运动翼型的能量吸收特性

为改善做行波运动的翼型的能量吸收特性,基于计算流体力学方法,分析波长（0.6L~1.4L,L为中弧线长度）、振幅（0.02L~0.1L）与无量纲波速（0.1~0.9）对做行波运动的NACA4、NACA63与NACA65系列不同最大厚度的翼型以及行波运动板的能量吸收特性的影响。研究表明：当运动参数相同时,同一系列翼型的获能效率随最大厚度的增大而减小,且行波板的获能效率最高;当行波振幅与无量纲波速一定时,厚度相同的不同系列翼型的获能效率均随波长的增大而减小,且不同系列翼型的获能效率基本相当;当行波波长与无量纲波速一定时,厚度相同的不同系列翼型的获能效率均随振幅的增大而增大;当行波波长与振幅一定时,厚度相同的不同系列翼型的获能效率均随无量纲波速的增大而先增大后减小,且在无量纲波速c=0.45左右达到最大值。     

基于非接触式行波采集的分布式高压直流故障测距方法

为提高高压直流输电线路故障测距的精度和供电可靠性,提出一种基于非接触式行波采集的分布式高压直流高阻故障测距方法。该方法采用分布式安装方式,基于空间电压、电流行波电磁场的宽频带检测技术,采用宽频带电磁场传感器实现对暂态行波信号的无失真采集;研究了动态自适应波速算法,利用行波采集终端分布式安装的特点,通过在线测量不同线路区段的实时故障波速,对故障段的行波波速进行矫正计算,避免了波速误差对测距结果的影响,有效提高了测距精度。分布式行波采集终端不需要安装在输电线路上,避免了设备安装和维护导致的停电。仿真及现场试验验证了方法的有效性和实用价值。     

负温度梯度对预混气体反应波传播模态的影响

基于一维数值模拟研究了负温度梯度对氢气/空气混合气反应波传播模态的影响,重点论述燃烧模态的转变机理.研究表明:当反应波沿着负温度梯度传播时,可以观测到超声速爆燃向爆震、爆震向亚声速爆燃的转变;其中,超声速爆燃传播过程由顺序自燃控制;当其传播速度低于当地Chapman-Jouguet爆震速度时,会发生超声速爆燃向爆震的转变.此外,在低温区域也观测到了爆震向亚声速爆燃的转变.Zel’dovich(ZND)结构和RankineHugoniot曲线表明,诱导激波后混合气反应活性对维持爆震传播具有重要作用.     

负温度梯度对预混气体反应波传播模态的影响（英文）

基于一维数值模拟研究了负温度梯度对氢气/空气混合气反应波传播模态的影响,重点论述燃烧模态的转变机理.研究表明:当反应波沿着负温度梯度传播时,可以观测到超声速爆燃向爆震、爆震向亚声速爆燃的转变;其中,超声速爆燃传播过程由顺序自燃控制;当其传播速度低于当地Chapman-Jouguet爆震速度时,会发生超声速爆燃向爆震的转变.此外,在低温区域也观测到了爆震向亚声速爆燃的转变.Zel’dovich(ZND)结构和RankineHugoniot曲线表明,诱导激波后混合气反应活性对维持爆震传播具有重要作用.     

风电场输电线路单相接地故障定位研究

为改善风电场因输电线路短路故障造成的弃风窝电现象,提出一种基于风电场特性和行波原理的多分支输电线路故障定位方法。利用大型风电场普遍采用接地变压器的特点,得出其故障区间判据;通过推导出一种修正行波波速计算方法(理论上为实际波速),解决了现有行波波速计算的缺陷;采用灰色模型(gray model,GM)提高原始数据采样率降低量化误差,进一步提升行波定位精度。使用PSCAD/EMTDC仿真验证本方法的有效性,可用于风电场输电线路故障定位中。     

感潮河段洪潮补偿调度模型及应用

滨海流域进行实时预报调度时,通常建立将水库调度模型与下游感潮河段水位演算模型相结合的综合调度系统,以福建省山仔水库为例,利用主要控制断面的安全水位作为控制条件决定水库的放水过程。由于感潮河段受上游出库洪水与下游潮位的双重影响,河道水位出现复杂的周期性变化,采用以洪潮分离为出发点的双向波演算法构建感潮河段的水位演算模型,并结合感潮河段的水位变化趋势,考虑水库洪峰来临及下游河段相应时期高低潮位过程,动态调整水库下泄量,以提高下游河道的防洪标准。     

双点激光点火直接起爆的数值模拟

针对双点激光点火直接起爆过程中爆轰波的形成、发展和传播问题,采用高精度数值模拟方法求解带化学反应的二维欧拉方程组,研究了不同环境压力情况对流场结构与波系变化的影响.结果表明,环境压力会影响激波强度与爆轰波的传播速度,是决定双点激光点火形成的火核在碰撞过程中能否实现爆轰并维持爆轰波传播的重要因素,利用双激光点相互作用形成...     

基于栅格的二维分布式超渗产流水文模型

针对自然流域地形地貌对地表径流滞留的影响,将流域坡面汇流概化为二维模式,采用二维运动波汇流模型计算坡面汇流,应用二维运动波隐式差分方法进行求解,结合DEM技术,基于考虑土壤水分再分配的Green-Ampt超渗产流模型,河道汇流采用一维运动波汇流,构建了基于栅格的Grid-GA-2D模型,并将其与Grid-GA及陕北模型...     

Theoretical and experimental study on the heat transport in metallic nanofilms heated by ultra-short pulsed laser

In this paper the mechanism of heat transport in metallic nanofilms under ultra-short pulsed laser heating is examined theoretically and experimentally. In order to easily understand the non-equilibrium heat transport in metallic nanofilms the study of heat transport behavior is first carried out in dielectrics. The analyses indicate that there may be two kinds of wave phenomena in dielectrics subjected to a periodic surface temperature. One is the thermal wave governed by the C-V model based hyperbolic equation and the other is the diffusive wave governed by the Fourier model based parabolic equation. According to the hyperbolic two step model for non-equilibrium heat transport, such two kinds of wave phenomena can also occur simultaneously in the metallic nanofilms under pulsed laser heating, where the diffusive wave is induced by the electron temperature oscillation at the surface due to the non-equilibrium between electrons and lattices. Unlike the propagation speed of the thermal wave, the propagation speed of the diffusive wave depends not only on the medium properties but also the period of the temperature oscillation at the boundary. Hence, the propagation speed of the diffusive wave in the electron gas may be of as high as 10⁶ m s⁻¹, when the laser pulse duration is less than 1 ps. A transient thermoreflectance (TTR) system has been built to measure the transient electron temperature responses caused by the femtosecond laser heating and a pump-probe technique is used to ensure the femtosecond temporal resolution in the experiments. Different from the commonly used front heating-front detecting (FF) method for measuring the material properties, a rear heating-front detecting (RF) method is applied, so that measuring the propagation speed of heat becomes available. The non-equilibrium heat diffusion model is used to fit the measured normalized electron temperature profiles of 27.2 nm, 39.9 nm and 55.5 nm Au films. The best-fitted coupling factor G basically agrees with the theoretical value 2.3 × 10¹⁶ W m⁻³ K⁻¹. The propagation speed of the diffusive wave in the electron gas can be obtained by comparing the measured delay time of peak electron temperatures of Au films with different thicknesses. The average propagation speed of the temperature oscillation or diffusive wave in Au films for the range of thickness from 27.2 nm to 55.5 nm is equal to 8.1 × 10⁵ m s⁻¹, which is close to the value predicted by the non-equilibrium heat diffusion model.     

Wavelet analysis of the shaft order perturbation and stall inception in an axial compressor

An experiment was carried out in a low-speed large-scale axial-compressor. Dynamic pressure signals were measured and analyzed with a wavelet transform. At all stable operating condition, a shaft order perturbation was observed from the dynamic pressure signals and wavelet power spectrums. By measuring the tip clearance, blade pitches and blade thickness distributions, a rotor asymmetry was identified in this compressor, which is strongly linked to the shaft order perturbation. Modal wave appears at the near-stall operating point. The propagation speed of the modal wave is about 20% rotating speed. At the peak of the modal wave, the intensity of the shaft-order-perturbation increases obviously, while it decays very fast at the trough of modal wave. By throttling the compressor, modal stall occurs in several seconds and only one stall-cell was detected. The stall cell grows smoothly out of the modal wave and its propagation speed is increased to 30% rotor speed. In several revolutions before stall, the intensity of the modal wave is increasing and a shaft order perturbation produced by modal-wave grows into stall inception which indicate stall onset but not trigger stall.     

一维—二维耦合的水库下游地区洪水演进数学模型及应用

针对水库下游地区河道洪水与漫堤洪水模拟需求,建立了一维—二维耦合的洪水演进数学模型。一维模型采用Pressimann格式离散求解,二维模型采用能够适应复杂几何形状和多种流态的Osher格式求解,一维—二维连接处采用堰流公式实现水流交互。应用该模型模拟白溪流域2015年"苏迪罗"台风实际洪水,可得到洪水在计算区域的演进过程和淹没情况。对比模拟结果与实际情况可知,该模型计算合理、准确,计算结果可为防汛部门防洪预案制定、防汛调度决策提供技术支撑。     

黄河龙门河段揭河底洪水探析

通过统计、分析、计算相关水文资料,得出黄河中游龙门河段发生大面积揭河底的条件为:吴龙区间发生高含沙洪水,龙门洪峰径流量在6亿m3以上,输沙量在2.6亿t以上;龙门流量大于5 000 m3/s且持续时间大于5 h,含沙量大于400 kg/m3且持续时间大于3 h;龙门断面平均河床高程达到380.0 m以上。黄河龙门"揭河底"洪水对河床具有强烈的冲刷作用,冲刷深度较大,对河道形态调整同样具有很大影响。     

Continuity wave in the elongated bubble region of horizontal slug flow

Visualized observation on the wave feature in a horizontal slug flow was made with a high‐speed digital camera. It was found that the liquid film flow in the elongated bubble region of slug flow behaves as a continuity wave. Theoretical analysis was carried out and it reveals that the liquid film flow is a continuity wave with celerity the same as the translational velocity of the elongated bubble. The control equation for the liquid film height in the elongated bubble region was derived. The results predicted by the equation fit well with the observed data. A new conclusion was obtained that slug flow has continuity wave in it, explaining the stable slug flow wave characterization. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(8): 547–554, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20092     

线性扩散波洪水演算方法的应用研究

求解了线性扩散波方程在自由下边界条件下的解析解,着重探讨了如何将扩散波解析解用于天然河道的洪水演算之中。利用运动差分解的数值扩散在一定条件下可以模拟扩散波物理扩散的概念,导出了一类推求扩散方程数值解的方法,据此建立了具有预见期的洪水演算方法,并将这 两种方法应用于两条天然河道,均得到了较高的计算精度。     

基于有限差分法的扩散波沿程洪峰衰减值确定方法研究

为了使洪水波在河道中的传播规律有更明确的物理意义,将洪峰流量表示为河道位置和传播时间的复合函数,通过拉格朗日中值定理和有限差分法推导该变量对河道位置的二阶导数与对传播时间的二阶导数之间的关系,进而推导出洪峰流量沿程衰减值的有限差分表达式,并通过实例对该公式进行了验证。结果表明,该洪峰流量衰减值公式中的洪峰流量值具有明确的传播位置及传播时间信息,能够刻画出洪峰流量的时空衰减规律,且计算结果精度较高。