双向嵌套法及其在水力计算中的应用

在水力计算数植模拟中，计算的网格步长约束着计算精度和工作量，计算的范围、计算的网格尺度和计算量总是一对矛盾，以平面二维水流运动方程为基础，兼顾到计算的网格步长、时间步长和计算的范围，应用了双向嵌套网格法，工程算例表明，双向嵌套网格法具有减少计算工作量、提高模式计算精度的特点。     

基于非结构网格的长江口二维三维嵌套潮流数值模拟

三维数学模型多应用于局部水域,无法模拟模型周边的大范围流场.为解决此问题,基于非结构网格有限体积法,建立了长江口二维三维潮流嵌套数学模型.模型嵌套边界采用近似处理方法,假设嵌套边界处网格单元分层水平流速服从多项式分布,该处理方法嵌套边界处的三维计算存在一定误差.将模型应用于长江口大范围水域潮流模拟计算.结果表明,潮位及二维三维潮流验证良好,计算精度满足规范要求,这说明该方法能够模拟大范围水域的二维及三维潮流运动.     

基于多重网格的地表水文与二维水动力动态双向耦合模型研究

针对流域洪涝模拟模型的计算精度、格式稳定性及计算效率等问题,本文提出基于多重网格技术的地表水文与二维水动力动态双向耦合模型(M-DBCM)。地表水文模型采用非线性水库法模拟降雨产流和径流;二维水动力模型采用浅水方程模拟洪水演进过程。采用不同分辨率的网格划分计算区域,在粗网格区域采用地表水文模型模拟降雨径流过程;在细网格区域采用二维水动力模型模拟洪涝积水区的水流运动。地表水文和二维水动力模型通过内部耦合移动界面(Coupling Moving Interface, CMI)实现无缝连接,保证通过CMI的水量和动量等通量守恒,提高模型的模拟精度。采用时间显式格式同时求解地表水文和水动力模型,在不同区域采用不同的计算时间步长,以提高模型的计算效率。通过典型案例验证本文构建的耦合模型的性能,结果表明本文提出的动态双向耦合模型能够在保证模拟精度的同时提高计算效率。     

渗流自由面数值模拟方法比较

结合最新提出的自由面适应网格法,与现行的2种固定网格法即变单元渗透系数法和初流量法进行数值模拟比较,以探讨各种方法在自由面渗流计算中的优缺点及其应用情况。试探性地选取3种固定网格方法进行系统的比较,即在精度、迭代步数、网格敏感度、初设自由面敏感性上进行多方位比较,分析各方法的灵活性、鲁棒性、数值稳定性、计算效率和可靠性...     

组合网格法在无压稳定渗流中的应用

针对无压稳定渗流分析过程中常遇到的线形结构问题,提出将组合网格法应用于无压稳定渗流计算。采用两套独立的网格,对整体区域采用尺寸较大的粗网格进行模拟,不考虑线形结构的影响,在线形结构附近则采用尺寸比较小的细网格进行模拟,考虑线形结构的影响。计算在粗细两套网格之间迭代调整,直到达到收敛精度。组合网格法大大简化离散工作量,且适应于非规则网格。数值计算结果表明,组合网格法合理可行,计算程序可靠,这为线形结构的无压稳定渗流分析提供了一种思路和方法。     

浮动网格法和ANSYS结合坝体不均匀剖分时的温控计算

由于非均匀剖分在坝体温控计算中是不可避免的,而通常采用的浮动网格法在处理该问题时实现计算编程很困难,文中提出了用大型有限元软件ANSYS和自己编制的有限元计算程序相结合的方法,来处理在坝体不均等网格剖分的情况下坝体的温控计算,实现了在大体积混凝土温控计算中网格浮动法的普遍应用.     

无网格法和有限元法的比较

无网格法是在有限元的基础上发展起来的新的数值方法,在处理大变形或网格"畸变"等问题时具有明显的优势.有限元法的形函数和离散系统方程是建立在网格上的,而无网格法在问题域中采用一系列分散节点来建立场变量插值,形函数定义于全域,随插值节点的移动而变化,故无网格法具有更高的计算精度,前处理工作量大大减少,无需后处理过程.由于无网格法中系统刚度矩阵较大,因此需要更多的CPU计算时间.     

贴体正交曲线网格自动生成技术研究

水流数值计算中计算网格好坏直接影响计算的收敛和精度,对二维曲线网格生成技术进行介绍,选择Poisson方程作为坐标转换方程,依据恒定摩阻流为有势流的特性,借助流线与势线正交的机理,导出以网格间距变化为调节因子的曲线坐标方程,并给出具体的算例.该方法简单、可靠、适应性强,可以解决水流数值计算前处理工作量大的困难.     

边界层网格尺度对泵站流场计算结果影响研究

壁面处的y+值是体现壁面边界层网格尺度的主要参数,对泵站流场数值计算结果有重要影响。为明确不同计算目标对y+的依赖性,以一泵站为研究对象,在网格数量无关性检查的基础上,从网格划分难易程度、数值计算精度和效率方面提出3种网格划分方案:全局非结构网格方案,指定边界层高度的全局非结构网格方案,以及指定边界层高度的分块结构网格方案,对应的y+值分别为10~2 000、10~1 000、10~500。方案二与方案三在模拟得到的流速分布均匀度方面几乎没有差别,涡量场的漩涡数量、涡量值和漩涡核心区分布位置也非常接近,而方案一则与之相差较大。研究发现,当只需了解泵站宏观水力性能时,可采用简单易行的方案一所对应的网格方案,y+范围可适当放宽到0~2 000;当要预测进水部分流场的流动特性,特别是漩涡分布特性时,需确保y+位于1 000以内,可采用方案二的网格方案;若对进水流场进行详细研究,或者进行除涡装置的研究时,则需使得整个计算域的y+满足30~500的要求,即采用方案三的网格方案。     

时间步长及网格尺度对物质输运数值模拟结果的影响

采用二维平面水动力一传质数学模型模拟了明渠有限时间排放源的情况下,保守物质在水流中的输运过程。计算了不同时间步长及网格尺度情况下保守物质的浓度分布变化情况,得到了多组次的平行计算结果。数值模拟结果表明,保守物质投放后,随水流逐渐向下游推移,在对流稀释和扩散作用下,峰值浓度逐渐下降;在保证计算稳定性的前提下,计算结果对时间步长不敏感;网格尺度对计算结果的影响局限在一定的区域内,但其影响程度与范围远较时间步长变化的作用明显。     

半自适应网格方法及其应用

本文发展了一种简单而有效的所谓半自适应网格方法，该方法的一个特点是所有的计算均在物理平面上完成。这种半自适应方法已被成功地应用于定常和非定常一维二维对流扩散方程初值问题的数值解，与存在精确解的结果比较表明，半自适应网格方法的结果具有很少的数值耗散，精度较好，与通常的差分方法比大约增加一倍多一点的计算时间，与变分或微分形式的自适应网格方法相比，大大减少了计算工作量。     

APPLICATION OF A MODIFIED QUICK SCHEME TO DEPTHAVERAGED k-( TURBULENCE MODEL BASED ON UNSTRUCTURED GRIDS

The modified QUICK scheme on unstructured grid was used to improve the advection flux approximation, and the depth-averaged turbulence model with the scheme based on FVM by SIMPLE series algorithm was established and applied to spur-dike flow computation. In this model, the over-relaxed approach was adopted to estimate the diffusion flux in view of its advantages in reducing errors and sustaining numerical stability usually encountered in non-orthogonal meshes. Two spur-dike cases with different defection angles (90oand 135o) were analyzed to validate the model. Computed results show that the predicted velocities and recirculation lengths are in good agreement with the observed data. Moreover, the computations on structured and unstructured grids were compared in terms of the approximately equivalent grid numbers. It can be concluded that the precision with unstructured grids is higher than that with structured grids in spite that the CPU time required is slightly more with unstructured grids. Thus, it is significant to apply the method to numerical simulation of practical hydraulic engineering.     

APPLICATION OF A MODIFIED QUICK SCHEME TO DEPTH- AVERAGED κ-ε TURBULENCE MODEL BASED ON UNSTRUCTURED GRIDS

The modified QUICK scheme on unstructured grid was used to improve the advection flux approximation, and the depth-averaged κ-ε turbulence model with the scheme based on FVM by SIMPLE series algorithm was established and applied to spur-dike flow computation. In this model, the over-relaxed approach was adopted to estimate the diffusion flux in view of its advantages in reducing errors and sustaining numerical stability usually encountered in non-orthogonal meshes. Two spur-dike cases with different defection angles （90°and 135°） were analyzed to validate the model. Computed results show that the predicted velocities and recirculation lengths are in good agreement with the observed data. Moreover, the computations on structured and unstructured grids were compared in terms of the approximately equivalent grid numbers. It can be concluded that the precision with unstructured grids is higher than that with structured grids in spite that the CPU time required is slightly more with unstructured grids Thus, it is significant to apply the method to numerical simulation of practical hydraulic engineering.     

雷达估算和雨量站插值降水精度的对比分析

以武汉多普勒天气雷达(CINRAD/SA)及其有效探测范围内的气象站和水文站的雨量观测资料为基础,运用集对分析方法确定雷达估算降雨场的Z-I关系,通过对雷达估算降雨和雨量站网格插值降雨进行对比分析,发现雷达估算降雨的精度要高于雨量站对网格降雨插值的精度,随着与被插值网格距离的增加,插值的误差随之增大。     

GRID GENERATION AND NUMERICAL SIMULATION OF 2-D RIVER FLOW

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＩｎｎａｔｕｒａｌｒｉｖｅｒ,ｔｈｅｓｈａｐｅｓｏｆｂｏｕｎｄａｒｉｅｓａｎｄｓｅｃ ｔｉｏｎｓａｒｅｏｆｔｅｎｉｒｒｅｇｕｌａｒ ,ｗｈｉｃｈｉｓａｄｉｆｆｉｃｕｌｔｐｒｏｂｌｅｍｆｏｒｎｕｍｅｒｉｃａｌｓｉｍｕｌａｔｉｏｎ .Ｔｏｓｏｌｖｅｔｈｉｓｐｒｏｂｌｅｍ ,ａｃｏｏｒｄｉ ｎａｔｅｔｒａｎｓｆｏｒｍａｔｉｏｎｍｅｔｈｏｄｉｓｏｆｔｅｎｕｓｅｄｔｏｔｒａｎｓｆｏｒｍｔｈｅｉｒｒｅｇｕｌａｒｒｅｇｉｏｎｉｎｔｈｅｐｈｙｓｉｃａｌｐｌａｎｅ(Ｘ ,Ｙ)ｔｏｔｈｅｒｅｇｕｌａ…     

SENSITIVE NUMERICAL SIMULATION AND ANALYSIS OF RAINSTORM USING NESTED WRF MODEL

1. INTRODUCTION In the field of meteorology, the numerical prediction of rainstorm is a recognized to be a difficult problem. Especially, the generation and development of rainstorm is closely related with the local terrain, physiognomy, and climatic para…     

HIGH ACCURATE SOLUTION OF INCOMPRESSIBLE VISCOUS FLOW WITH PRIMATIVE VARIABLE

This paper presents a higher order difference scheme for the computationof the incompressible viscous flows.The discretization of the two-dimensional incompress-ible viscous Navier-Stokes equations,in generalized curvilinear coordinates and tensor for-mulation,is based on a non-ataggered grid.The momentum equations are integrated intime using the four-stage explicit Runge-Kutta algorithm [1]and discretized in space us-ing the fourth-order accurate compact scheme[2]The pressure-Poisson equation is dis-cretized using the nine-point compact scheme.In order to satisfy the continuity constraintand ensure the smoothness of pressure field,an optimum procedure to derive a discretepressure equation is proposed [9][3]The method is applied to calculate the driven cavityflow on a stretched grid with the Reynolds numbers from 100 to 10000.The numerical re-sults are in very good agreement with the results obtained by Ghia et al [7]and includethe periodic solutions for high Reynolds numbers.     

Unstructured finite volume method for water impact on a rigid body

A new method is presented for the water impact simulation, in which the air-water two phase flow is solved using the pressure-based computational fluid dynamics method. Theoretically, the air effects can be taken into account in the water structure interaction. The key point of this method is the air-water interface capture, which is treated as a physical discontinuity and can be captured by a well-designed high order scheme. According to a normalized variable diagram, a high order discrete scheme on unstructured grids is realised, so a numerical method for the free surface flow on a fixed grid can be established. This method is implemented using an in-house code, the General Transport Equation Analyzer, which is an unstructured grid finite volume solver. The method is verified with the wedge water and structure interaction problem.     

RCCD三维温度场仿真分析的浮动网格法

针对碾压混凝土坝（RCD）三维有限元仿真分析,计算量过于庞大的问题,提出了基于“层合单元”及“生长单元”的“浮动网格法”。该方法可以大大减少单元数目,大幅度地提高计算效率,能精细地模拟施工过程且易编程,能快速得到高精度的坝体三维温度场的仿真解,具有广泛的工程应用前景。