三层流体系统中初始扰动和密度比对孤立波生成的影响

本文讨论了初始扰动和密度比对三层流体系统中孤立波生成的影响出发点是所导得的ＫｄＶ方程和散射反演理论的结果。分析结果表明，增加初始扰动的高度和宽度会生成更多的孤立波，这与Ｍａｘｗｏｒｔｈ＾［３］的实验结果一致；此外，在较弱分层情形，密度比对孤波生成的影响极小，而在较强的分层情形，其影响较大。     

二维T-S波在壁面局部喷吸边界层流中的演化

采用壁面设置局部法向速度模拟喷吸条件,数值计算获得稳定的三维边界层基本流的数值解。在此基础上,研究不稳定的二维扰动T-S波在空间演化过程的非线性问题;探讨边界层壁面局部无量纲喷吸速度0.004,0.000 6对二维T-S波非线性演化的影响及其对增长率的贡献。数值计算结果表明,边界层平均流剖面的改变促进了扰动波的快速增长,增强了流体运动的不稳定性,扩大了中性曲线的不稳定区域范围,不稳定的二维T-S波获得了更大的增长率;不稳定的二维扰动T-S波在非线性演化过程中,由于非线性相互作用不断增强,逐渐诱导激发出三维扰动速度及高次谐波,其三维扰动基本波的流向波数和频率与二维扰动波的流向波数和频率相同;正、负相间流向涡及强剪切层已初步形成。     

水力机械运行中的拍振和共振问题探讨

拍振和共振是常见的自然现象,对水力机械稳定运行危害很大,但在对其研究中存在将二者混淆和对部分虚假拍振信号辨识不清等问题,需深入探讨。本文首先介绍了拍振波的基本原理,通过对几种特殊情况的分析说明了拍振波的拍振频率和幅值范围,并在分析拍振波本质特征、共振基本特征、扰动频率和固有频率差别的基础上进一步论述了拍振和共振的区别,提出了扰动频率和系统固有频率接近不会产生拍振、两个不同的扰动波即使频率相同也不可能产生共振等新见解;其次,本文还分析了采集信号不健全和高频载波两种虚假"类拍振波"的产生原因,提出了提高信号采集频率避免类拍振波和依据拍振波本质特征辨识拍振波的简单方法。     

径向温度梯度对β平面上斜压波热力结构影响的实验研究

本文用转环实验模拟方法研究了径向温度梯度对β平面上斜压波热力结构的影响。结果表明在转速相同的条件下，三波态流动对应的径向温度梯度比四波态流动的大；在三波态下，冷流闭势力强，急流向暖区推进，无量纲温度值跃变化深厚，流动表现为静力稳定；而在四波态下，冷流团势力减弱，急流向冷区收缩，无量纲温度值跃变化被抬升，低层表现为多小尺度运动。     

壁面粗糙度突变对湍流边界层的影响

本文探讨了湍流在流动不同粗糙度的壁面时粗糙度突变对为点下游流动的影响，假定粗糙度突为引起的扰动小扰动，流动物理量的扰动值满足自似分布，本文分析了得到了描述突点下游流动特性的长度尺度，速度剖面，时均流速及摩阻流速的表达式，并通过实验对理论分析的理论进行了验证。     

自由剪切流中沿流向变化的二次失稳研究

该文以考虑厚度变化的二维相干结构为背景流动作二次失稳研究,分析流向各位置处三维扰动展向空间尺度选择机制。结果表明:用能量法考虑流向变化影响及采用局部平行假设获得二维相干结构为基础流动,进行二次失稳分析的方法,可用于研究快速增长的二次失稳问题。还说明了三维相干结构的出现是二维相干结构对三维基本扰动的二次失稳的结果,这种失稳过程对展向波数有很强的选择性。     

孤立波作用下边界层的模拟与分析

孤立波作用下的边界层内的剪切力以及涡量变化对海啸传播和海底地形塑造十分重要。本文基于多区域谱方法,利用直接模拟(DNS)数值模型,对在具有矩形断面的U形水洞内的孤立波下的边界层流动进行了模拟。将数值模拟结果与解析解以及试验结果进行了对比,发现数值结果与后两者吻合得较好。模拟结果显示,在低雷诺数下,扰动不会改变流态,而随着雷诺数的增大,流态会变得十分复杂。中等雷诺数情况下,边界层内会产生正向的涡,并进行稳定的传播。在较高雷诺数情况下,流动进入层流向紊流发展的过渡期,此时边界层内会产生正涡以及负涡,并会在水深方向进行不规则运动。     

底部加热Poiseuille流的混合有限分析解

本文采用混合有限分析法求解了两无限平板间底部加热的Ｐｏｉｓｅｕｉｌｌｅ流动，并分析了初始扰动引入的必要和初始扰动的影响。     

水机电耦合系统建模及暂态分析

在水电系统研究中，水力系统与电力系统模型精度失配、缺乏全面的水机电数学模型是制约水电系统动态过程研究和提高仿真精度的主要原因。基于水机电各元件模型，采用积木式结构在MATLAB/Simulink环境下构建了水机电整体耦合系统模型，便于研究水力系统和电气系统之间的相互影响，分析水电站的暂态过程。基于该模型对单机无穷大系统进行了仿真研究，比较了电气系统扰动对水力系统的影响以及水力系统扰动对电气系统的影响，并对仿真结果进行了分析。     

固粒分区存在的旋转射流场稳定性研究

本文由理论分析得到了三种固粒存在形态下旋转射流失稳模型的扰动增长率及相关修正瑞利稳定性准则，根据该准则，对三种不同固粒存在形态下气一固流动模型在不同扰动性质和固粒属性下，由计算得到了对应的增长率曲线，给出了固闰属性及扰动央求充稳定性影响的重要结论，为工程中控制不同情况下的旋转射流场后续发展提供了理论依据。     

Numerical investigation of a swirling flow under the optimal perturbation

The nonlinear evolution of 3-D instability of a viscous swirling flow, namely, the Oseen vortex, is addressed by direct numerical simulation with a Reynolds number equal to 5000. The global optimal perturbation is considered as the initial perturbation. In axisymmetric cases, three flow regimes are found: (1) the linear growth; (2) the decay of perturbation energy; (3) secondary energy growth. The linear energy growth, which is characterized by the amplification of radial perturbations, is arrested by the interaction between the vortex ring and the Oseen vortex core. The development of the vortex structure is also investigated for non-symmetric flows.

     

二维平行壁面剪切流动的转捩与混沌模型

本文利用约化摄动方法，从理论上研究了二维平行壁面剪切流动的转捩与混沌现象，得到了描述二维平行壁面流动中的小振幅Ｔ－Ｓ波的演化方程为Ｋｏｒｔｅｗｅｇ－ＤｃＶｒｉｅｓ－Ｂｕｒｇｃｒｓ方程，反映Ｔ－Ｓ波衰减或增长率的参数为ＫｄＶ－Ｂｕｒｇｅｒｓ方程中的耗散系数Ｖ１与色散系数δ的比值ｖ１√δ，ｖ１和δ由流场结构决定的。当Ｔ－Ｓ波振幅被放大到一定程度后将受到的自由流中的高次或亚谐波的激励。经过分叉而进入混沌     

Experiments on the short-term development of sine-generated meandering rivers

This paper presents recent works on the simulation of short-term development of sine-generated meandering river in laboratory conditions. The influences of initial system parameters on the evolution process of rivers are investigated, including control over channel sinuousness, channel width and dominant discharge, eventually leading to different results of planforms. Measurements on the bank-line, flow field, bed topography and sediment transport rate were carried out. Braided rivers are easy to produce using non-cohesive sediments in floodplains, whereas environmental temperatures and humidities could influence the fluvial process by their effects on material cohesion. Channelized rivers were obtained in the “High Flow” conditions and the river corridor width was proven to be mainly connected with initial channel sinuousness and water discharge. Sickle-shaped and bamboo leaves-shaped sandbars were formed in the channels during the transformation process of meandering to braiding, the stability degree of sandbars reflects the adaption of channel morphology to hydrodynamic condition. Quantitative analysis confirms the formation of free steady bars, which manifests the free response as a downstream oscillation of the perturbation. Damping length is mainly affected by dominant discharge, channel width is the secondary factor, and channel sinuousness is the weakest factor. The wavelength of steady bars approximately equals to half of the initial streamwise wavelength. Sediment transport rate tends to increase with the increasing of channel sinuousness but stops growing due to the excessive increase of flow route and flow friction. The experiment results could be useful for verifying river pattern discriminant functions and offer a basis for further study on the morphological evolution of large-scale natural rivers, such as Yangtze River.     

THE VOF METHOD FOR STUDY OF WAVE RUN-UP AND BREAKING ON A SLOPING STRUCTURE

The volume of fluid method(VOF method)for numerical simulations describing wave run-up on a sloping structure including the overturning,breaking and.merging phenomena is presented.The flow motions are governed by the classical,two-dimen-sional Navier-Stokes equation for incompressible fluid.Computational results concerning the time evolution of the free surface and pressure distribution along water bed and slope boundary are given,showing how an initial solitary wave undergoes run-up,overturning,breaking and merging on the slope.It is found that most of the wave energy is lost after the wave breaking and merging.     

NUMERICAL STUDIES OF INTERNAL SOLITARY WAVE GENERATION AND EVOLUTION BY GRAVITY COLLAPSE

In this study, an analysis on the internal wave generation via the gravity collapse mechanism is carried out based on thetheoretical formulation and the numerical simulation. With the linear theoretical model, a rectangle shape wave is generated andpropagates back and forth in the domain, while a two-dimensional non-hydrostatic numerical model could reproduce all the observedphenomena in the laboratory experiments conducted by Chen et al. (2007), and the related process realistically. The model resultsfurther provide more quantitative information in the whole domain, thus allowing an in depth understanding of the correspondinginternal solitary wave generation and propagation. It is shown that the initial type of the internal wave is determined by the relativeheight between the perturbation and the environmental density interface, while the final wave type is related to the relative height ofthe upper and lower layers of the environmental fluid. The shape of the internal wave generated is consistent with that predicted bythe KdV and EKdV theories if its amplitude is small, as the amplitude becomes larger, the performance of the EKdV becomes betterafter the wave adjusts itself to the ambient stratification and reaches an equilibrium state between the nonlinear and dispersion effects.The evolution of the mechanical energy is also analyzed.     

岩溶地下水系统演化的数值模拟

为了研究岩溶地区泉域系统演化过程及对泉流量进行预测,耦合了渗流模型和岩溶动力模型,对均质和非均质2种条件下泉域系统进行了溶蚀演化模拟。从模拟结果上可以看出,均质含水系统初期水位变化较小,中后期下降明显,而非均质含水系统初期下降明显,中后期水位稳定;在张开度方面,非均质模型在相同时段内张开度的最在值却比均质系统要大4~5 cm。2个泉域系统的泉流量都经过了初期较小,中后期迅速增大的过程,只是增大的时间和每个时间点的泉流量不同,非均质系统增大时间更早,流量更大,分别用指数函数和多项式函数来拟合了均质和非均质系统泉流量过程曲线。研究结果为岩溶地下水系统演化模拟提供了一个新方法,同时也为岩溶地区地下水资源评价研究提供了科学依据。     

NUMERICAL SIMULATION OF A MATHEMATICAL MODEL FOR WAVE PROPAGATION ON NON-UNIFORM CURRENT AND DEPTH

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基于微震监测技术的深埋长大隧洞群岩爆时空分布规律分析

以锦屏二级水电站深埋引（排）水隧洞群为工程背景,介绍了微震监测系统的组成,并根据隧洞工程的特点,优选出紧跟掌子面移动整体协同传感器优化布置方案;利用现场微震数据,探讨了微震事件和岩爆的时空相关性。研究结果表明：微震活跃及平静时段与岩爆显现频繁及稀少时段相吻合,微震事件和岩爆的空间分布规律相一致,表明微震事件时空演化规律与岩爆时空分布规律具有良好的相关性。通过分析和研究微震事件时空分布规律,可以对岩爆灾害进行有效预测,为岩爆防治提供科学依据。