模拟波浪运动的三维自由表面流动数值模型

基于Navier-Stokes方程建立了三维自由表面流动数值模型来模拟波浪运动.模型中Navier-Stokes方程的求解采用两步投影法,计算域的空间离散采用交错网格.采用满足自由表面运动学边界条件的水位控制方程来计算自由表面.通过数值结果与解析解的比较,验证了本文建立的三维自由表面流动数学模型可以精确的模拟线性色散波以及孤立波沿平底坡和非平底坡的传播.     

Large eddy simulation of free-surface flows

This paper introduces and discusses numerical methods for free-surface flow simulations and applies a large eddy simulation(LES) based free-surface-resolved CFD method to a couple of flows of hydraulic engineering interest. The advantages, disadvantages and limitations of the various methods are discussed. The review prioritises interface capturing methods over interface tracking methods, as these have shown themselves to be more generally applicable to viscous flows of practical engineering interest, particularly when complex and rapidly changing surface topologies are encountered. Then, a LES solver that employs the level set method to capture free-surface deformation in 3-D flows is presented, as are results from two example calculations that concern complex low submergence turbulent flows over idealised roughness elements and bluff bodies. The results show that the method is capable of predicting very complex flows that are characterised by strong interactions between the bulk flow and the free-surface, and permits the identification of turbulent events and structures that would be very difficult to measure experimentally.     

自由表面流动数值模拟方法的探讨

本文建立和开发了一个用于求解具有自由表面的二维不可压缩粘性流体流动的Navier-Stokes方程的数值模型,这个模型采用ALE方法描述流体的运动,基本方程组中的流速和压力利用Projection 2方法来解耦,空间离散采用有限单元法,而时间离散则采用semi-implicit方法,自由表面位置则通过求解相应的偏微分方程来确定,而计算过程中网格的调整则采用了新的方法,算例结果令人满意,表明方法可行。     

Wavy properties and analytical modeling of free-surface flows in the development of the multi-domain method

The wavy(oscillatory both in space and in time) properties of free-surface flows due to presence of floating bodies are analyzed within the framework of the potential-flow theory by assuming that the fluid is perfect and flow irrotational. A so-called new multi-domain method has been developed based on the fluid domain division by an analytical control surface surrounding bodies and the application of different methods adapted in the external and internal domains. In the analytical domain external to the control surface, the fundamental solution satisfying the linear boundary condition on the free surface associated with a point singularity(often called Green function and referred here as point solution) is applied to capture all wavy features of free-surface flows extending horizontally to infinity. Unlike classical studies in which the control surface is discretized, the unknown velocity potential and its normal derivatives are expressed by expansions of orthogonal elementary functions. The velocity potential associated with each elementary distribution(elementary solutions) on the control surface can be obtained by performing multi-fold integrals in an analytical way. In the domain internal to the control surface containing the bodies, we could apply different methods like the Rankine source method based on the boundary integral equations for which the elementary solutions obtained in the external domain playing the role of Dirichlet-to-Neumann operator close the problem.     

高浓度水流流速仪的研制与应用

作为一种复杂的固液两相流动，高浓度水流由于固体颗粒浓度高、颗粒级配宽及流动的可视性差等特点，致使其测流一直成为制约高浓度水流运动机理研究的瓶颈性问题。本文依据毕托管工作原理，通过液压传感方式感应测量高浓度水流动水压力和计算机数据采集处理等方法，成功地研制了新型感压式高浓度水流流速仪，并在室内天然沙与粉煤灰高含度水流试验中得到了应用。该流速仪研制成功为进一步研究高浓度水流流速分布规律、揭示其水流结构与输沙机理创造了有利条件。     

虚拟水库大坝的三维建模方法研究

结合潘家口和大黑汀水库大坝三维模型建设工作流程和关键技术的介绍,得出虚拟水库大坝三维建模的一般方法。     

河道堤防模拟决口水利计算简化法

本文分析了堤防决口泛区水流机理,提出了决口水利计算简化算法的公式及列表试算求解的方法,说明了决口泛区图绘制应注意的问题。     

复杂黏弹性流体运动的数值计算方法

本文提出了一个能够描述具有复杂黏弹性的流体在各种条件下发生变形和流动的数学模型,并建立了相应的数值求解方法.数值方法是在计算流体动力学中常用的SMAC方法的基础上改进时间步进格式,依据问题的性质合理选用显式或隐式,从而达到提高计算效率的目的.数值模型被应用于Oldroyd-B黏弹性流体平板剪切流起动问题的计算,得到的数值解与理论解吻合良好.论文还对针对平板间平行流动进行数值实验,对算法的稳定性和收敛性进行了分析.     

明渠水流边壁影响修正的计算方法

针对窄深明渠及岸壁附近的明渠水流泥沙运动进行研究时,常常需要除掉岸壁的作用以便了解床面剪切应力的影响.以往对边壁影响修正的方法是基于一些没有完全被验证的假设,床面剪切力的计算数值可能受所采取的边壁修正的方法影响.本研究在分析可靠资料的基础上,发现爱因斯坦对数阻力公式不但可以用于计算不同断面形式的平均的水流情况,而且可以分别用于边壁和床面的阻力计算.将分别对应于边壁和床面的爱因斯坦阻力公式应用阻力计算中,可以解决方程组不闭合的问题.试验资料分析表明,本文提出的方法有较高的精度.     

Assessment of the predictive capability of RANS models in simulating meandering open channel flows

The predictive capability of Reynolds-averaged numerical simulation(RANS) models is investigated by simulating the flow in meandering open channel flumes and comparing the obtained results with the measured data. The flow structures of the two experiments are much different in order to get better insights. Two eddy viscosity turbulence models and different wall treatment methods are tested. Comparisons show that no essential difference exists among the predictions. The difference of turbulence models has a limited effect, and the near wall refinement improves the predictions slightly. Results show that, while the longitudinal velocities are generally well predicted, the predictive capability of the secondary flow is largely determined by the complexity of the flow structure. In Case 1 of a simple flow structure, the secondary flow velocity is reasonably predicted. In Case 2, consisting of sharp curved consecutive reverse bends, the flow structure becomes complex after the first bend, and the complex flow structure leads to the poor prediction of the secondary flow. The analysis shows that the high level of turbulence anisotropy is related with the boundary layer separation, but not with the flow structure complexity in the central area which definitely causes the poor prediction of RANS models. The turbulence model modifications and the wall treatment methods barely improve the predictive capability of RANS models in simulating complex flow structures.     

Membrane finite element method for simulating fluid flow in porous medium

A new membrane finite element method for modeling fluid flow in a porous medium is presented in order to quickly and accurately simulate the geo-membrane fabric used in civil engineering. It is based on discontinuous finite element theory, and can be easily coupled with the normal Galerkin finite element method. Based on the saturated seepage equation, the element coefficient matrix of the membrane element method is derived, and a geometric transform relation for the membrane element between a global coordinate system and a local coordinate system is obtained. A method for the determination of the fluid flux conductivity of the membrane element is presented. This method provides a basis for determining discontinuous parameters in discontinuous finite element theory. An anti-seepage problem regarding the foundation of a building is analyzed by coupling the membrane finite element method with the normal Galerkin finite element method. The analysis results demonstrate the utility and superiority of the membrane finite element method in fluid flow analysis of a porous medium.     

自由面区域变换法解三体船兴波问题

为求解三体船兴波问题,基于线性自由面条件的势流兴波理论Rankine源方法,利用物理平面与计算平面的转换关系计算自由面上物理量的导数,开发了三体船兴波阻力预报程序.采用该方法和程序,对不同侧体布局的Wigley三体船兴波阻力及波形进行计算,并将计算结果与模型试验结果、其他作者数值计算结果进行比较,验证了该方法对三体船的适用性,表明采用贴水线网格及自由面区域变换法解三体船兴波问题可提高三体船兴波问题求解效率.     

用蒙特卡罗法解有压隧洞出口段水流问题

利用不规则游动网格的蒙特卡罗法对有压隧洞出口段水流进行了数值模拟。根据数值计算与模型试验结果的比较,得出具有凸形曲面边界（包括折面底坡）负压区的存在不仅是边界层分离所致,边壁弯曲使过流产生的离心力也是产生负压的重要原因的结论。计算结果表明：蒙特卡罗法灵活简单、结果稳定,计算结果与实测结果吻合较好。     

求解浅水流动的分步有限元方法

本文将分步有限元的计算方法引入到浅水方程组的求解中。该方法起源于Taylor-Ga!erkin(T-G)方法，但数值稳定性优于T-G法并具有三阶精度。由于计算中没有引入高阶的空间导数项，实现起来比Taylor-Galerkin方法简单，适用于非线性和多维问题的求解。计算模型中包含了零方程和双方程的紊流模型，可以根据需要选择。文中详细介绍了初始和边界条件的取法，并通过五个算例验证了计算模型的可靠性。     

An unstructured mesh method for numerical simulation of violent sloshing flows

An unstructured mesh Reynolds-averaged Navier-Stokes(RANS)solver has been developed for numerical simulation of violent sloshing flows inside a tank with complicated inner structures.The numerical solver employs the unstructured multi-dimensional tangent hyperbolic interface capturing method(UMTHINC)for free-surface capturing combined with various turbulence models.The sloshing motion is numerically modeled using the body-force method which introduces a source term into the momentum equation corresponding to the tank motion profile.Numerical simulations of the tank sloshing problems are performed for different test cases with various oscillation frequencies.The performance of the interface capturing method has been discussed and the effect of turbulence model choice on loading predictions is highlighted by studying several RANS models and analyzing its effect on fluid motion and impact pressure.Numerical simulations of the sloshing inside the tank with a vertical baffle has also been conducted and a discussion is provided on different numerical treatment of the baffle.     

Development of a method for assessing flood vulnerability.

Over the past few decades, a growing number of studies have been conducted on the mechanisms responsible for climate change and the elaboration of future climate scenarios. More recently, studies have emerged examining the potential effects of climate change on human societies, including how variations in hydrological regimes impact water resources management. According to the Intergovernmental Panel on Climate Change's third assessment report, climate change will lead to an intensification of the hydrological cycle, resulting in greater variability in precipitation patterns and an increase in the intensity and frequency of severe storms and other extreme events. In other words, climate change will likely increase the risks of flooding in many areas. Structural and non-structural countermeasures are available to reduce flood vulnerability, but implementing new measures can be a lengthy process requiring political and financial support. In order to help guide such policy decisions, a method for assessing flood vulnerability due to climate change is proposed. In this preliminary study, multivariate analysis has been used to develop a Flood Vulnerability Index (FVI), which allows for a comparative analysis of flood vulnerability between different basins. Once fully developed, the FVI will also allow users to identify the main factors responsible for a basin's vulnerability, making it a valuable tool to assist in priority setting within decision-making processes.     

A study of hybrid prediction method for ship parametric rolling

The parametric rolling(PR) in the head or following waves has been considered as one of the main stability failure modes in the development of the 2nd generation Intact Stability criterion by the International Maritime Organization(IMO).According to previous studies,the estimation methods of the roll damping affect the prediction of the PR significantly,and most of them are based on experiment data or Ikeda’s empirical formula.The accuracy of the estimation method for the roll damping could be a key aspect for the validity of its prediction for the full scale ship.In this research,a hybrid prediction method is developed for the numerical prediction of the parametric rolling when experiment data are not available for the roll damping.Comparison study is also carried out between the hybrid method and a nonlinear dynamics method,where the roll damping is estimated by the simplified Ikeda’s method and the direct CFD prediction method in a direct non-linear simulation based on the 3-D CFD approach in the model scale.It is shown that the results of the hybrid method are in satisfactory agreements with the model experiment results,and the method can be used for analysis especially at the early design stage where experiment data are often not available.     

处理二维浅水流动中动边界问题的淹没节点法

针对浅水流动中的动边界问题,本文设计一种淹没节点方法,根据网格单元各节点的被淹没情况,即单元水面高程和各节点高程的差值,对单元平均水深和单元界面处平均水深进行修正,运用高精度无振荡的FDS格式和有限体积法求解含有动边界的二维浅水方程。除对单元水深和界面水深进行修正外,离散方程形式与传统方法相同,实现过程简单。应用该方法对两个典型算例进行了数值模拟,模拟结果分别与其他学者的模拟结果和精确解高度吻合。表明本文方法精度较高、实现过程简单、可以有效解决浅水方程的间断、动边界和河床起伏问题。     

An Eulerian SPH method with WENO reconstruction for compressible and incompressible flows

While Eulerian smoothed particle hydrodynamics(SPH)method has received increasing attention in scientific and industrial communities owing to its high spatial accuracy,it exhibits excessive numerical dissipation due to the fact that the flux is derived in particle pair pattern.In this paper,we adopt a one-dimensional weighted essentially non-oscillatory(WENO)reconstruction to reduce the numerical dissipation and improve the overall accuracy particularly in capturing the contact discontinuity.The underlying principle is to construct a 4-point stencil along the interacting line of each particle pair and then the WENO scheme is applied to reconstruct the initial states of the Riemann problem which determines the flow flux.A set of benchmark tests for both compressible and incompressible flows are studied to investigate the accuracy,robustness and versatility of the proposed Eulerian SPH method with the WENO reconstruction(ESPH-WENO).     

Development of a hybrid ozonation biofilm-membrane filatration process for the production of drinking water.

Drinking water sources in Norway are characterized by high concentrations of natural organic matter (NOM), low alkalinity and low turbidity. The removal of NOM is therefore a general requirement in producing potable water. Drinking water treatment plants are commonly designed with coagulation direct filtration or NF spiral wound membrane processes. This study has investigated the feasibility and potential of a hybrid process combining ozonation and biofiltration with a rotating disk membrane for treating drinking water with high NOM concentrations. Ozonation will oxidize the NOM content removing colour and form biodegradable organic compounds, which can be removed in biological filters. A constructed water was used in this study which is representative of ozonated NOM-containing water. A rotating membrane disk bioreactor downstream the ozonation process was used to carry out both the biodegradation as well as biomass separation in the same reactor. Maintenance of biodegradation of the organic matter while controlling biofouling of the membrane and acceptable water production rates was the focus in the study. Three operating modes were investigated. Removal of the biodegradable organics was consistent throughout the study indicating that sufficient biomass was maintained in the reactor for all operating conditions tested. Biofouling control was not achieved through shear-induced cleaning by periodically rotating the membrane disks at high speed. By adding a small amount of sponges in the membrane chamber the biofouling could be controlled by mechanical cleaning of the membrane surface during disk rotation. The overall results indicate that the system can favorably be used in an ozonation/biofiltration process by carrying out both biodegradation as well as biomass separation in the same reactor.