污染物及土壤水动力迁移的数值模拟

本文在分析水分及污染物在土壤中迁移物转化规律的基础上，建立了水分及污染物迁移的耦合数学模型。采用有限差分法离散水分方程和污染浓度方程，得到了数值计算模型。运用分散平均方法估算水力传导率，并用中心差分和隐式差分格式并存的系数矩阵求解方法，加快计算的收敛性。利用该数值计算模型，模拟计算了具有应用背景的水分及污染物在非饱和土壤中的迁移规律，数值计算成果得到了试验资料的验证，两者吻合良好，为研究和解决地下水污染问题提供了有效的手段     

Simultaneous one-dimensional water flow and mass transport of conservative solutes in porous media

Three variations of the Galerkin finite element method are used for the numerical solution of the one-dimensional, vertical water flow and mass transport equations in variably saturated porous media. The final result is a system of differential equations with derivatives depending only on time, which are approximated by a relationship leading to a second-order accuracy. Examples of two different soil types (clay loam and sandy) are presented to verify the accuracy of the numerical schemes. In these examples, saltwater is allowed to be infiltrated into the soil profile with different boundary conditions on the soil surface (Neuman or Dirichlet type). In some cases, the infiltration of saltwater is followed immediately by salt-free water.     

黄河有机污染物挥发特性研究

针对黄河多泥沙和有机物污染状况,研究清水和含沙量为1g/L、3g/L的混水中萘和2,6-二叔丁基对甲酚(BHT)两类有机污染物的挥发过程及规律,用气相色谱仪测定挥发过程溶液质量浓度的变化,实验数据用数学模型进行曲线拟合,得到挥发动力学方程、挥发速率常数和半衰期。分析有机物的物化性质、风速和泥沙含量等环境因素对挥发速率的影响,为确定黄河对有机污染物的承纳水平和总量控制提供依据。     

黄河大柳树河段河床演变的三维数值模拟

针对河岸冲刷、河床演变显著的河流,建立考虑河岸变形的三维水沙数值模型,对黄河大柳树河段的河势演变进行数值模拟分析研究。模型中利用三角形网格和局部网格移动及局部加密技术,采用有限体积法离散控制方程,以及基于非结构化同位网格中的SIMPLE算法进行数值求解。依据2011年11月至2012年10月黄河大柳树河段典型断面实测资料对数值模拟结果进行验证,模拟结果与实测结果吻合较好。结果表明该模型能够较好地模拟黄河大柳树河段的水流运动和河床演变,模型中提出的河岸修正技术和局部网格加密技术可有效提高模拟计算精度和效率。     

波涌畦灌水流运动的零惯量数值模拟

本文建立了波涌畦灌田面水流的零惯量数学模型，在水流推进和消退阶段分别采用四边形差分网格公式，对内部计算单元采用普赖斯曼追赶法计算，在畦首差分单元采用牛顿－拉普氏迭代法求解，对水流推进前峰单元用水量平衡方程计算，经田间试验资料验证，其计算值与实测值吻合较好。     

具有复杂计算域和地形的二维浅水流动数值模拟

本文采用非结构化网格的有限体积方法，对具有复杂计算域和地形的二维河道进行数值模拟。采用Roe格式的近似Riemann解计算界面通量，对地形变化源项采用特征分解平衡界面通量以保证格式的和谐性，对摩擦力源项采用隐式或半隐式求解以增加格式的稳定性。通过与混合流算例理论解比较，验证了格式是和谐性的并具有良好的间断捕捉能力与稳定性。应用此方法对地形复杂，存在多处险滩和深潭的某河段进行了实际模拟，数值计算结果和模型试验结果吻合较好。     

STUDY AND APPLICATION OF STEADY FLOW AND UNSTEADY FLOW MATHEMATICAL MODEL FOR CHANNEL NETWORKS

Based on the Preissmann implicit scheme for the one-dimensional Saint-Venant equation, the mathematical model for one-dimensional river networks and canal networks was developed and the key issues on the model were expatiated particularly in this article. This model applies the method of three-steps solution for channel-junction-channel to simulate the river networks, and the Gauss elimination method was used to calculate the sparse matrix. This model was applied to simulate the tree-type irrigation canal networks, complex looped channel networks and the Lower Columbia Slough networks. The results of water level and discharge agree with the data from the Adlul and field data. The model is proved to be robust for simulating unsteady flows in river networks with various degrees of complex structure. The calculated results show that this model is useful for engineering applications in complicated river networks. Future research was recommended to focus on setting up ecological numerical model of water quality in river networks and canal networks.     

条带覆盖下土壤水热动态的田间试验与模型建立

描述了夏玉米生长期间麦秸条带覆盖(行间覆盖)条件下土壤水热动态的田间试验.在此基础上，采用交替方向有限差分法建立了模拟苗期条带覆盖下土壤二维水热迁移的数值模型.其中覆盖部分土壤表面的边界条件由能量平衡方程确定.模型的输入只需常规气象资料、土壤水热迁移参数及覆盖参数.数值计算结果表明，该模型具有一定的实用价值。     

河床式电站大坝泄洪流场的三维数值模拟

 在1∶100水工模型试验的基础上,应用k-ε流数值模型,采用VOF方法,对低水头大流量河床式电站大坝泄洪流场进行了三维数值模拟。将计算得出的各工况下泄洪闸闸室及下游流场的流态,水面线,闸室内流速、压力分布等水力特性值与试验数据对比,发现计算值与试验值基本吻合。说明所选择的紊流数学模型,建立基本控制方程以及求解数学模型的离散方法是比较可靠的,可以为工程设计提供参考。     

曲线坐标系下波浪传播的数学模型及其比较与验证

引入自适应网格技术,建立了曲线坐标系下考虑能耗影响的缓变水深水域波浪传播的数值模拟模型,通过在模型中引入能量耗散项以更好地处理全透射边界。基于原型缓坡方程,完善了等水深的轴对称双导堤水域内波浪传播的精确解表达式及其计算结果;提供了等水深的环形河道水域内较为详细的精确解。在极坐标系下就等水深的轴对称双导堤水域内波浪的传播,推导了缓坡方程的小角度抛物近似模型的解析解表达式。就上述两水域内波浪传播的数值模拟模型的数值解、抛物近似模型的解、精确解进行了详细比较,说明数值解与精确解相吻合、数值模拟模型比小角度和大角度抛物近似模型具有更高的精度。数值模拟模型能较好地模拟水深复杂变化的地形上波浪的传播,能有效反映波浪传播过程中的多种物理现象。     

Application of 2-D sediment model to fluctuating backwater area of Yangtze River

Based on the characteristics of backflow,a two-dimensional mathematical model of sediment movement was established.The complexity of the watercourse boundary at the confluence of the main stream and the tributary was dealt with using a boundary-fitting orthogonal coordinate system.The basic equation of the two-dimensional total sediment load model,the numerical calculation format,and key problems associated with using the orthogonal curvilinear coordinate system were discussed.Water and sediment flow in the Chongqing reach of the Yangtze River were simulated.The calculated water level,flow velocity distribution,amount of silting and scouring,and alluvial distribution are found to be in agreement with the measured data,which indicates that the numerical model and calculation method are reasonable.The model can be used for calculation of flow in a relatively complicated river network.     

非线性抛物型缓坡方程的数值模拟

参考Lo对MNLS方程中非线性项的处理方法,但不转换到频域求解,同时采用Li修正的非线性弥散关系,对非线性抛物型缓坡方程在复数域进行数值模拟,并分别在Berkhoff椭圆地形及淹没圆形浅滩地形验证了该模型,得到了较好的结果。此模型可以有效地模拟非线性波浪问题。此非线性项的处理方法使得数值计算过程中不需迭代求解,同时减少了边界周期性的限制,易于操作编程,提高了计算效率。     

含内源污染平面二维水流-水质耦合模型

本文从紊动扩散理论出发根据浅水湖泊紊流扰动特性，推导出包含底泥污染的水质控制方程，并与浅水方程耦合，建立相应的平面二维水流-水质-底泥污染的数值模型。模型在有限体积法框架下应用黎曼近似解求得耦合方程的数值解。并以玄武湖为例进行模型验证。结果表明，数值解与实测值较吻合，证明预测结果可信。     

引黄济津河道水质数值模拟与预测

依据连续性方程、动量方程、自由表面方程、状态方程和水质输运方程,采用有限差分法,建立河道垂向二维水动力水质模型。根据2000-2001年第6次引黄数据资料对水质模型进行调试,建立引黄济津调水工程水质模型。利用已建立的模型,对2002-2003年第7次引黄河道水质进行了预测,并将预测结果与实测数据进行比较,预测结果与实测结果基本一致,表明该模型能较好地预测引黄济津河道水质状况。同时,根据污染物浓度峰值的变化情况,分析了污染物的输移扩散及降解转化规律。     

根系层储水量对随机腾发响应特性的初步分析

将潜在腾发量分成趋势分量与随机分量两部分，且假定该随机分量标准化后为正态白噪声过程，结合水量平衡方程推导出根系层储水量满足的随机微分方程.利用随机微分方程理论分析了土壤根系层系统中系统状态变量一根系层储水量对随机输入的响应特性，包括变量的转移概率密度、均值和标准差.利用田间墒情监测资料对理论模型进行了初步验证。     

数值求解 Boussinesq 方程的有限元法

本文基于有限元方法，采用线性单元，通过节点周围单元内的一阶导数的加权平均来确定单元节点上变量的一阶空间导数值，建立了求解Boussinesq方程的数值计算模型，模型中，时间的积分采用Adams-Bashforth-Moulton预报-校正法，对波浪传播情况的计算表明该模型可以给出令人满意的结果。     

Manoeuvring prediction based on CFD generated derivatives

This paper presents numerical predictions of ship manoeuvring motions with the help of computational fluid dynamics(CFD) techniques. A program applying the modular concept proposed by the Japanese ship manoeuvring mathematical modelling group(MMG) to simulate the standard manoeuvring motions of ships has been initially developed for 3 degrees of freedom manoeuvring motions in deep water with regression formulae to derive the hydrodynamic derivatives of the vessels. For higher accuracy, several CFD generated derivatives had been substituted to replace the empirical ones. This allows for the prediction of the maneuverability of a vessel in a variety of scenarios such as shallow water with expected good results in practice, which may be significantly more time-consuming if performed using a fully CFD approach. The MOERI KVLCC2 tanker vessel was selected as the sample ship for prediction. Model scale aligned and oblique resistance and Planar Motion Mechanism(PMM) simulations were carried out using the commercial CFD software Star CCM+. The PMM simulations included pure sway and pure yaw to obtain the linear manoeuvring derivatives required by the computational model of the program. Simulations of the standard free running manoeuvers were carried out on the vessel in deep water and compared with published results available for validation. Finally, simulations in shallow water were also presented based on the CFD results from existing publications and compared with model test results. The challenges of using a coupled CFD approach in this manner are outlined and discussed.     

计算域中存在直立岛式结构物时波浪传播的数值模拟

针对计算域中存在直立岛式结构物的复连通区域,提出了岛体边界条件,利用缓坡方程建立了在计算域中存在直立岛式结构物时波浪传播的数值模拟模型。模型适用于变水深水域问题,克服了解析解只能适用于等水深水域的不足。直立圆柱和无穷小厚度岛式防波堤周围波浪传播的数值算例表明,数值解与解析解吻合良好,说明所建立的数值模拟模型能有效地模拟复连通区域内的波浪传播。矩形固定式防波堤周围波浪场的数值模拟说明该模型对工程实际有较强的适应性。     

饱和-非饱和土中渗流Richards方程有限元算法

发展了一种求解理查森方程的一般有限元算法。该方法采用积分法处理孔隙水压力对时间的导数项,采用集中质量技术处理有限元方程中质量矩阵来保证数值稳定。所采用的质量守恒迭代方法不须改变迭代方式,采用一般的Picard迭代方法。该方法能求解入渗、地下水位瞬变和排水等范围广泛的饱和-非饱和渗流问题。对3个已公开发表具有详细试验数据的算例的模拟表明,该方法对入渗锋、稳定渗流地下水位和非稳定渗流溢出面都模拟很好。Picard迭代方法效率很高,且无数值振荡发生。     

NUMERICAL STUDY OF SQUARE-STERN SHIP WAVE IN SHALLOW WATER

This paper employed shallow water equations with moving pressure to calculate water waves generated by a square-stern ship in shallow water. The moving ship is considered as moving pressure on free surface. The finite element method with moving grids is used to solve the shallow water equations based on wave equation model [3]. A non-reflection boundary condition [5]is imposed on open boundaries surrounding the ship. 3-D surface elevations, depth-averaged horizontal velocities are presented. The numerical solutions are physically reasonable. It is found that wave resistance coefficients, draftchange and pitch angle vary rapidly in neighborhood of critical flow (Fh=u/ gh= 0. 9 -1. 1). The numerical results also indicate that the wave resistance coefficients, draft change and pitch angle of square-stern ship are larger than those of sharp-stern ship with the same hull structure at the same speed.