大气低频振荡的水平波状结构的理论解释

本文把慢变介质中波动的传播理论应用于正压大气中传播的Rossby波。慢变介质与域的球面性和基流的纬向结构有关。得到了波射线路径方程,导出了波作用密度守恒关系和波动能量密度变化方程,这与观测结果是一致的,并给出了低频振荡水平波状结构的简单解释。     

Rossby waves on the Sun as revealed by solar 'hills'

It is a long-standing puzzle that the Sun's photosphere--its visible surface--rotates differentially, with the equatorial regions rotating faster than the poles. It has been suggested that waves analogous to terrestrial Rossby waves, and known as r-mode oscillations, could explain the Sun's differential rotation: Rossby waves are seen in the oceans as large-scale (hundreds of kilometres) variations of sea-surface height (5-cm-high waves), which propagate slowly either east or west (they could take tens of years to cross the Pacific Ocean). Calculations show that the solar r-mode oscillations have properties that should be strongly constrained by differential rotation. Here we report the detection of 100-m-high 'hills' in the photosphere, spaced uniformly over the Sun's surface with a spacing of (8.7 +/- 0.6) x 10(4) km. If convection under the photosphere is organized by the r-modes, the observed corrugated photosphere is a probable surface manifestation of these solar oscillations.     

CISK—Kelvin波.CISK—Rossby波和低频振荡

本文应用描写低纬大气运动的一个斜压半地转的wave-CISK模式,讨论了由CISK机制激发的Kelvin波和Rossby波,即所谓的CISK-Kelvin波和CISK-Rossby波。分析表明:wave-CISK机制对于大气低频振荡起重要的作用。     

带β项的非线性涡旋Rossby波的演变过程

利用多重尺度摄动法,推导出当考虑Rossby参数β作用时,非线性涡旋Rossby波的波包振幅的演化方程是非线性的Schrodinger方程．对受Rossby参数β影响的涡旋Rossby波的本征值问题进行分析,指出Rossby参数β对涡旋Rossby波传播的影响．     

半地转近似下正压大气中的非线性波动

本文在半地转近似下讨论了正压模式大气中的非线性 Rossby 波.结果表明:这些非线性 Rossby 波可以是椭圆函数形式的波、孤立波或冲击波;产生这些波动的条件是由一个称之为“总能量”的物理量给出的,同时还敏感地依赖于相应量的初相值;文中还求出了一支没有线性近似对应的新频率的非线性波解,它纯粹是非线性效应的产物.     

大气中的非线性Rossby波和Pseudo-Rossby波——(Ⅰ)正压大气情形

本文利用相角函数和常微分方程相轨线分析方法,讨论了半地转近似下正压Rossby波的存在和求解问题;结果表明:在描述Rossby波的方程中,除了具有通常意义的Rossby波解外,还存在一支Pseudo-Rossby波解;而且正压Rossby波的频率对一定的波动有一确定上界,这个上界由大气平均厚度与地理纬度确定;同时也分析了波动特征参量与拟能及地理参数间的关系.     

变分原理在波浪理论研究中的应用

研究波浪在传播过程中由于缓变地形所引起的折射和绕射现象以及在水流影响下波浪的变形,是海岸动力学中一个十分有意义的课题.本文利用变分原理推导了一、二阶Stokes波的方程,并给出在波浪和水流共同作用下结合波浪折射和绕射的波动方程.其结果与已有的理论结果完全一致.     

潮汐锁相行星的大气环流与气候

红矮星是宇宙中数量最多的恒星,其表面辐射温度比太阳的辐射温度低得多,因此,红矮星的宜居带与恒星的距离非常近．因为距离其恒星较近,在强大引力的作用下,位于红矮星宜居带内的宜居行星很可能是潮汐锁相行星．锁相行星的特征是其一侧永远面对恒星,另一侧则永远背对恒星,从而形成极端不均匀的加热．我们在本文中使用一个真实的大气环流模式与平板海洋相耦合来研究锁相行星表面的气候要素和大气环流特征．我们特别针对两种自转速度进行了模拟试验．结果发现,在慢速自转条件下（自转和公转周期均为243天）,大气环流基本是热力驱动的下层辐合和上层辐散的运动,行星的表面仅有恒星直射点附近比较湿润,其他区域均比较干燥,背阳面尤其寒冷．在快速自转条件下（自转和公转周期均为l天）,科里奥利力的作用比较显著,大气环流以纬向西风为主,并呈现波动特征,赤道上空出现超级旋转的西风急流,湿润区域显著扩大．EP通量诊断分析表明,赤道超级旋转急流是由于热带Rossby波随高度向极地方向传播所产生的EP通量在赤道附近的辐散造成的．     

大气中非线性Rossby波和Pseudo—Rossby——(Ⅱ)斜压大气情形

本文利用文(1)中的方法,讨论了半地转近似下斜压Rossby波的存在和求解问题,分析表明,在描述Rossby波的方程中,除了具有通常意义的Rossby波解外,还存在一支Pseudo—Rossby波解.     

倾斜粘弹性覆盖层中P-SV波的广义射线法及物理模型实验

本文用数值计算和超声物理模型实验两种方法研究倾斜粘弹性覆盖层中P-SV波的传播。理论方法是Pao,Ziegler和王贻荪的广义射线法的推广。文中导出了由第j次广义反射波产生的第(j+1)次广义反射波的一般形式。数值结果和物理模型实验结果是一致的。     

A modified density based cavitation model for time dependent turbulent cavitating flow computations

The predictive capability of transport equation-based cavitation models including the Kubota cavitation model (Model-1) and interfacial dynamics cavitation model (Model-2), is evaluated for the attached turbulent cavitating flows. In this study, the test problem is the unsteady cloud cavitating flows around a Clark-Y hydrofoil. Based on the evaluations of existing models, we identified the differences between these two vaporization and condensation processes in the affected region, and provided a modified density based cavitation model (Model-3). The numerical results of the cavity shapes, velocity distributions and dynamics of the cavity oscillations were compared to existing experimental data. Compared with the other cavitation models, a significant improvement for the numerical results of unsteady cavitating flows has been obtained with the new model. Our study provides the information for further modeling development.     

Numerical Study of Void Fraction Distribution Propagation in Gas-Liquid Two-Phase Flow

A dynamic propagation model was developed for waves in two-phase flows by assuming that continuity waves and dynamic waves interact nonlinearly for certain flow conditions. The drift-flux model is solved with the one-dimensional continuity equation for gas-liquid two-phase flows as an initial-boundary value problem solved using the characteristic-curve method. The numerical results give the void fraction distribution propagation in a gas-liquid two-phase flow which shows how the flow pattern transition occurs. The numerical simulations of different flow patterns show that the void fraction distribution propagation is determined by the characteristics of the drift-flux between the liquid and gas flows and the void fraction range. Flow pattern transitions begin around a void fraction of 0.27 and end around 0.58. Flow pattern transitions do not occur for very high void concentrations.     

云状空化流动数值模拟的空化模型评价

为深入了解空化模型对云状空化流动计算的影响,分别采用Kubota,Singhal,Merkle,Kunz四种不同的空化模型对绕水翼的云状空化流动进行了数值模拟,获得了空穴形态和升、阻力等流场动力随时间的变化特性. 通过与实验结果的对比表明,这四种空化模型均可以准确地捕捉云状空化区域的空穴形态和空泡脱落的非定常细节;不同空化模型对计算所得的空穴形态和长度、绕翼型速度矢量场、升阻力均有影响, 但对流场动力特性的主要频谱分布影响不大.     

一个含地形的二阶矩湍流闭合的大气中尺度数值模式

建立了一个包含地形作用的二阶矩湍流闭合的二维大气中尺度数值模式，该模式不仅具有描述大气边界层及其内湍流结构的能力，而且还能很好地模拟非线性地形波、波破碎观象以及波破碎区内的湍流结构．     

Shear instabilities in granular flows.

Unstable waves have been long studied in fluid shear layers. These waves affect transport in the atmosphere and oceans, in addition to slipstream stability behind ships, aeroplanes and heat-transfer devices. Corresponding instabilities in granular flows have not been previously documented, despite the importance of these flows in geophysical and industrial systems. Here we report that breaking waves can form at the interface between two streams of identical grains flowing on an inclined plane downstream of a splitter plate. Changes in either the shear rate or the angle of incline cause such waves to appear abruptly. We analyse a granular flow model that agrees qualitatively with our experimental data; the model suggests that the waves result from competition between shear and extensional strains in the flowing granular bed. We propose a dimensionless shear number that governs the transition between steady and wavy flows.     

水口电站日调节不稳定流数值模拟

用一维不稳定流数学模型模拟枯水期水口电站下游日调节不稳定流。选择Preissmann差分格式,把模型转化为有限差分方程组,并用“双扫描”法求解。依据水文气象资料,确定旁侧入流,用满宁方程反推糙率,并拟合了糙率随水深、流量变化的曲线。电站出流过程线、解放大桥水位过程线分别作为上、下边界条件,局部水头损失考虑了桥墩阻水和淮安分流的影响,在IBM-286机上实现了坝下长约72km河段内,日调节不稳定流的衰减过程的模拟运算。     

Winter cold of eastern continental boundaries induced by warm ocean waters

In winter, northeastern North America and northeastern Asia are both colder than other regions at similar latitudes. This has been attributed to the effects of stationary weather systems set by elevated terrain (orography), and to a lack of maritime influences from the prevailing westerly winds. However, the differences in extent and orography between the two continents suggest that further mechanisms are involved. Here we show that this anomalous winter cold can result in part from westward radiation of large-scale atmospheric waves--nearly stationary Rossby waves--generated by heating of the atmosphere over warm ocean waters. We demonstrate this mechanism using simulations with an idealized general circulation model, with which we show that the extent of the cold region is controlled by properties of Rossby waves, such as their group velocity and its dependence on the planetary rotation rate. Our results show that warm ocean waters contribute to the contrast in mid-latitude winter temperatures between eastern and western continental boundaries not only by warming western boundaries, but also by cooling eastern boundaries.     

采空区顶板大面积冒落诱发冲击气浪模拟

基于采空区冒落过程中冒落岩体与空气相互作用中能量的守恒与转化,建立了冲击气浪风速模型,设计制作了模拟实验测试装置。实验表明,随着下落高度增加,冲击气浪风速增加幅度略有减缓,采用大断面空间小尺寸的"打气筒"模型计算能够更好地反映冒落过程中的气体流动过程,但应该以"打气筒"和"绕流"的复合模型表征冲击起浪。在实验基础上建立的实验模型与理论模型有很好的相似性。     

斜压大气中的Rossby和赝Rossby波

本文在半地转近似下,运用波动方程行波解的常微分方程分析,讨论了斜压大气中的Rossby波和赝疆Rossby波问题。     

三水源新安江模型参数不确定性分析PAM算法

针对水文模型参数不确定性分析常用方法 收敛速度缓慢,容易陷入参数空间局部最优区域等 问题,提出了PAM (parallel adaptive metropolis) 算法;对三水源新安江模型参数不确定性进行分析 研究。实例研究表明显著提高了计算速度和求解质 量,参数后验分布结果为区间预报提供了条件。