明渠沙纹床面湍流结构实验研究

沙纹的形成会显著地影响床面附近的湍流结构。论文通过水槽实验，模拟了天然河流中沙纹的形成，并针对最终形成的稳定沙纹形态，利用声学Doppler测速仪采集了沙纹床面不同位置处的高频流速过程数据，继而对脉动强度、雷诺应力、湍流动能及自相关函数等湍流特征量进行了计算，并分析了沙纹床面湍流结构和特点，为进一步的理论和数值研究提供了有价值的参考数据和依据。     

孤立子和湍流

本文在综述孤立子研究成果的基础上，结合湍流的特点深入分析了湍流的物理机制，对湍流的拟序结构等现象作了一些探讨，对负粘性现象提出了看法。认为孤立子有可能是流体质点间互相作用的基本形式之一，大量孤立子的统计特征量和湍流相关量之间应当有着密切的关系     

基于惯性耗散法的峡口岬角地形能耗分析

珠江河口峡口岬角地形(或者称"门")是珠江河口典型的高能耗区,研究其消能机制,对于解释珠江河口宏观动力现象,提高对河口动力过程的认识有重要意义。本文设计了峡口岬角局部突变地形的湍流能耗特性物理模型试验,采用Son Tek 16MHz ADV采集了高频流速数据,统计了时均流速及湍流特征量。利用"惯性耗散法"计算了峡口岬角突变地形与明渠水流的湍流动能耗率。峡口岬角地形的突变特征产生明显的形态阻力,本文试验工况引起的紊动强度量值是明渠的2倍到10多倍,湍流剪切应力较明渠水流大近2个数量级,湍流动能是明渠水流的40多倍,湍流动能耗散率比明渠水流湍流动能耗散率大2~3个数量级。从湍流局部平衡及能量传递理论看,峡口局部形态阻力导致时均流速的空间梯度、切应力增大及形成大量更小尺度的涡是湍流能耗率增加2~3个量级的重要原因。     

各向异性k—ε模型研究

本文放弃湍流粘性假设，直接从雷诺应力输动方程推导出雷诺应力显式表式。利用这个表达工重新构造动量方程，引入各向异性ｋ方程和ε方程，建立了新的湍流数学模型－各向异性ｋ－ε模型。利用实验结果和后台阶流场计算结果验证表明：这个雷诺应力表达式大大优于湍流粘性凤，由此建立的各向异性ｋ－ε模型不仅能够准确地模拟复杂流场的速度，而且能够成功地反映流场的湍动能，雷诺应力等湍流特征量，对回流区长度的模拟也非常成功。     

低雷诺数非线性k—ε湍流模型及其应用

本文发展了一人低雷诺数非线性ｋ－ε湍流模型，其特点是考虑了湍动能及湍动能耗散速度的非线性扩散过程，采用了一个非线性雷诺应力表达式，引入了壁面修正函数以考虑湍流的近壁低雷诺数效应。应用该模型计算了湍流槽流和湍流库埃特流。与实验结果的比较表明，所建模型对包括近壁区在内的整个计算域的各湍流量都能给出非常满意的预测结果。     

基于直接数值模拟数据和神经网络的湍流封闭模型构建

雷诺平均Navier-Stokes方程(Reynolds-averagedNavier-StokesRANS)是目前工程上高效数值模拟湍流的基本方法,但这一方法需要给出关于雷诺应力的湍流封闭模型。该文从环形方管流场的直接数值模拟(DirectNumerical Simulation,DNS)数据出发,构建了一种基于神经网络的湍流封闭模型。文中利用环形方管流场DNS结果中的平均速度场及其梯度场作为流动特征输入量,与雷诺应力张量中各分量分别建立神经网络映射,从而构造出平均速度场及其梯度场与湍流雷诺应力的非参数化映射关系。计算结果表明,通过对环形方管DNS数据的深度学习,神经网络模型可有效地表达湍流时平均流场与雷诺应力之间的映射关系,并且能够准确地重构DNS所给出的雷诺应力,进而采用RANS基本方程捕捉到传统湍流模型中难以模拟的湍流驱动二次流现象,为新型湍流封闭模型的构建及其工程计算的实现提供创新思路。     

基于混沌理论的明渠湍流速度特征

为了揭示湍流运动的混沌特征规律,选择明渠水槽试验,采用ADV测量沿程衰减的湍流速度场,结合混沌理论,对湍流速度时间序列进行相空间重构,计算对应的混沌特征参数(延迟时间、关联维度、Lyapunov指数、Kolmogrov熵),探究明渠湍流速度混沌特征。分析结果表明:明渠湍流具有混沌特征;安装湍流控制板后,沿水深向上方向和水流方向,湍流的混沌特性不断减弱;进一步通过与湍流统计平均参数比较表明,混沌特征参数的强弱能够反映出湍流涡结构在空间耗散和消亡的变化规律。     

幂律流体在圆管内湍流流动剪切率的近似计算

根据剪切率和能量耗散率的定义，建立了幂律流体湍流剪切率与能量耗散率的关系式。参照文献上对不可压缩牛顿流体湍流能量耗散率的近似算法，提出了一种幂律流体管内湍流能量耗散率的近似算法，从而得到了幂律流体管内湍流剪切率的实用近似算式，再利用湍流剪切率与脉动流剪切率的关系即可得到脉动流剪切率。计算得到的湍流剪切率分布及其随流动特性指数变化的特征与已知规律相符。     

珠江河口底边界层湍流事件研究

该文通过座底式支架的ADV,对珠江河口底边界层的湍流进行了一个全潮25 h的观测,并利用该资料对湍流事件进行了研究,探讨了湍流事件特征量在潮内的变化.研究结果表明:(1)河口湍流事件受潮汐过程的影响,各特征量变化带有明显的半日分潮特征,且急流和憩流时刻差异显著.(2)对于动量事件,憩流时刻事件发生的次数多,但持续时间短,贡献率低,而急流时刻次数少,持续时间长,贡献率高;对于泥沙事件,憩流时刻次数少,但持续时间长且强度高,急流时刻次数多,但持续时间短且强度低.(3)湍流事件发生的时间约占总时间的40％,事件的平均持续时间分别为0.07 s(动量事件)和0.05 s(泥沙事件).     

方腔热对流大规模数值模拟及其软硬湍流特性

该文对二维Rayleigh-Bénard(RB)热对流进行了大规模并行DNS模拟计算。计算中采用了上海超级计算机中心的1024个节点,获得了Pr?0.7,Ra?5×107―8×1011范围内一系列的计算数据和结果。研究结果发现:在二维RB热对流中存在不同的流态,当Ra小于6×108的流动状态为软湍流状态,Ra大于6×108为硬湍流状态;在软湍流状态大尺度环流(LSC)和角区旋涡保持相对稳定,LSC内涡量很小,在硬湍流状态,角区旋涡从边界层内脱落,进入到LSC中随之一起运动,且在LSC内存在大量的小涡旋;并且软湍流和硬湍流在传热效率上具有不同的标度率。     

An investigation of the instrumental variable-approximate maximum likelihood method of modeling and forecasting daily flows

The instrumental variable-approximate maximum likelihood (IV0AML) method provides a technique to develop better models for short-time increment hydrologic data. In this method, a recursive input-output model, which consists of a deterministic model and a stochastic noise model are used. These models handle the system and measurement noise separately. The instrumental variable method has been developed to eliminate the bias in parameter estimates.The IV-AML method is investigated in the present study. Parameters of daily rainfall-runoff models are estimated by the IV-AML and by least squares methods and compared. The effects of a rainfall filter on parameter estimates are also investigated. Forecast accuracies of models whose parameters are estimated by IV-AML and least squares methods are compared.The results indicate that the forecast accuracy of models whose parameters are estimated by least squares method is comparable to that of models whose parameters are estimated by IV-AML method. The rainfall filter, on the other hand, reduces the parameter variation and improves forecasts.     

OSCILLATION AMPLITUDE OF THE FREE END OF A FLEXIBLY MOUNTED RIGID CYLINDER IN TRIANGLE ARRANGEMENT

In this paper,the oscillation amplitude of the free end of a group of threecylinders are studied.The three cylinders are erected at the vertices of an equilateral trian-gle,and three arrangements are made in this study.One of the three cylinders is served asa working cylinder which is mounted by a flexible cantilever and two accelerometers areattached on the free end in two directions.The results of the three-cylinder arrangementare compared with those of two cylinders in tandem/side-by-side arrangement in the samecondition.The experimental results show that the rear cylinder of a group of three cylin-ders is affected more seriously than that of the corresponding two cylinders in the contrastarrangement.The main direction of oscillation is changed.The transversal oscillation isstronger than the longitudinal oscillation in the three-cylinder arrangement.On the con-trary,the transversal oscillation is much weaker than the longitudinal oscillation in two-cylinder arrangement.The largest transversal oscillat     

Comparative study of MPS method and level-set method for sloshing flows

This paper presents a comparative study of a meshless level-set method in the simulation of sloshing flows. The numerical moving particle semi-implicit （MPS） method and a grid based schemes of the MPS and level-set methods are outlined and two violent sloshing cases are considered. The computed results are compared with the corresponding experimental data for validation. The impact pressure and the deformations of free surface induced by sloshing are comparatively analyzed, and are in good agreement with experimental ones. Results show that both the MPS and level-set methods are good tools for simulation of violent sloshing flows. However, the second pressure peaks as well as breaking and splashing of free surface by the MPS method are captured better than by the level-set method.     

Numerical simulation of the internal wave propagation in continuously densitystratified ocean

A numerical model is proposed to simulate the internal wave propagation in a continuously density-stratified ocean, and in the model, the momentum equations are derived from the Euler equations on the basis of the Boussinesq approximation. The governing equations, including the continuity equation and the momentum equations, are discretized with the finite volume method. The advection terms are treated with the total variation diminishing （TVD） scheme, and the SIMPLE algorithm is employed to solve the discretized governing equations. After the modeling test, the suitable TVD scheme is selected. The SIMPLE algorithm is modified to simplify the calculation process, and it is easily made to adapt to the TVD scheme. The Sommerfeld＇s radiation condition combined with a sponge layer is adopted at the outflow boundary. In the water flume with a constant water depth, the numerical results are compared to the analytical solutions with a good agreement. The numerical simulations are carried out for a wave flume with a submerged dike, and the model results are analyzed in detail. The results show that the present numerical model can effectively simulate the propagation of the internal wave.     

求解流体与结构相互作用问题的ALE有限体积方法

本文发展了求解流体与结构相互作用问题的数值方法。采用任意拉格朗日－欧拉网格（ＡＬＥ）和有限体积方法对流体的控制方程进行空间离散，而时间项则采用三点向后差分格式；对于结构的运动方程采用Ｎｅｗｍａｒｋ积分法进行求解，为了求解耦合的流体和结构的运动方程，采用预测－多步校正法以避免反复迭代所导致的过大的计算量。作为本入方法的应用，计算了圆筒内一同轴圆柱的自由振动问题，在小振幅的情形下，将由计算获得的附加质     

弯曲河道床面形态规律的研究

本文对弯曲河道床面形态规律进行了较全面的理论分析与试验研究，给出了床面形态高度和波长的计算表达式，并用美国ＦａｌｌＲｉｖｅｒ原型观测资料进行了验证，结果令人满意     

基于自组织理论的黄土坡面细沟形成机理模型

作为面蚀向沟蚀转化的特殊阶段，细沟侵蚀在坡面侵蚀机理的研究中有着重要的意义。本文在对坡面侵蚀特点进行分析的基础上，应用自组织理论的基本思想建立了描述黄土坡面细沟形成和发育过程的模拟模型。分析表明，坡地侵蚀过程中降雨及微地貌对应于自组织系统中的无序输入，而纹沟、细沟和沟网等对应于自组织系统的有序输出。基于自组织理论的机理模型可以定量地预测坡面细沟发育的过程，而这些信息在过去只能依靠实验观测获得。模型预测与相同输入条件下的室内实验结果相近，从而说明了模型的合理性。本模型中未计入雨滴击溅的影响，这一影响也在计算结果中得到了反映。文中还对模型中参数选择的影响进行了讨论。     

Laboratory investigation of the hydroelastic effect on liquid sloshing in rectan- gular tanks

A sloshing experiment is conducted to study the hydroelastic effect in an elastic tank. For this purpose, a translational harmonic excitation is applied to a 2-D rectangular tank model. The lowest-order natural frequencies of the liquid in the tank are determined through the sweep test. The wave elevation and the sloshing pressure are obtained by changing the excitation frequency and the liquid depth. Then the characteristics and the variation of the elevation and the pressure are discussed. The results are compared with the experimental results and the theoretical calculations in a rigid tank. Our analysis indicates that, in the non- resonant cases, the elastic results, the rigid experimental results and the theoretical values are all close to each other. In contrast, under the resonant condition, the elastic experimental result is slightly smaller than the rigid one. Also, the theoretical values are smaller than the experimental results at the resonant frequency.     

Dynamic Optimal Monitoring Network Design for Transient Transport of Pollutants in Groundwater Aquifers

Optimal groundwater pollution monitoring network design models are developed to prescribe optimal and efficient sampling locations for detecting pollution in groundwater aquifers. The developed methodology incorporates a two dimensional flow and transport simulation model to simulate the pollutant concentrations in the study area. Different realizations of the pollutant plume are randomly generated by incorporating the uncertainty in both source and aquifer parameters. These concentration realizations are incorporated in the optimal monitoring network design models. Two different objectives are considered separately. The first objective function minimizes the summation of unmonitored concentrations at different potential monitoring locations. This objective function in effect minimizes the probability of not monitoring the pollutant concentrations at those locations where the probable concentration value is large. Although this probability is not explicitly incorporated in the model, a surrogate form of this objective is included as the objective function. The second objective function considered is the minimization of estimation variances of pollutant concentrations at various unmonitored locations. This objective results in a design that chooses optimal monitoring locations where the uncertainties in simulated concentrations are large. The developed optimization models are solved using Genetic Algorithm. The variances of estimated concentrations at potential monitoring locations are computed using the geostatistical tool, kriging. The designed monitoring network is dynamic in nature, as it provides time varying network designs for different management periods, to account for the transient pollutant plumes. Such a design can eliminate temporal redundancy and is therefore, economically more efficient. The optimal design incorporates budgetary constraints in the form of limits on the number of monitoring wells installed in any particular management period. The solution results are evaluated for an illustrative study area comprising of a hypothetical aquifer. The performance evaluation results establish the potential applicability of the proposed methodology for optimal design of the dynamic monitoring network for detection and monitoring of pollutant plumes in contaminated aquifers.     

弯曲河道纵向垂线平均流速平面分布的研究

本文以弯道水流运动方程作为分析的基础，根据弯道水流纵向流速沿垂线分布在凸岸区域眼从对数分布律，在四岸区域眼从抛物分布律，导出了分区域变自率动床弯道水流纵向垂线平均流速计算公式，并从理论上对河湾纵向垂线平均流速的横向分布和沿程变化规律进行了分析，同时给出了适用于定半经弯道的纵向垂线平均流速平面分布公式的简化形式。最后采用美国ＦａｌｌＲｉｖｅｒ野外水流观测资料对纵向垂线平均流速计算公式进行了验证计算，结果令人满意。