三体船在斜浪规则波中运动响应预报方法研究

对于三体船在波浪中的水动力预报,航速效应和主体与片体间水动力干扰效应是水动力载荷合理预报的关键之处,需合理考虑.二维半势流理论可较为准确反映上述效应,已在三体船顶浪中垂向运动响应理论预报上获得了较为满意的结果.在此基础上,该文探讨了该方法在三体船斜浪中运动特别是横摇预报上的应用.为较准确获得三体船横摇运动时粘性阻尼贡献,采用三体船模静水中自由横摇衰减试验获得了自由横摇运动衰减曲线,并经能量法处理获得了船舶横摇阻尼系数.然后,结合二维半理论,获得了三体船运动数值解.数值解与斜浪规则波中运动响应模型试验结果符合较好,反映本文所采用的数值方法可较好地预测三体船斜浪中水动力载荷和运动,可用于三体船在波浪中耐波性评估.     

3-D NONLINEAR SUPERCAVITATING FLOW IN A GRAVITY FIELD

In this paper,perturbation method and Fourier-cosine-expansion method are used to solve a 3-D nonlinear problem of a supercavitating flow in an inclined field of gravity at large Froude numbers.By expanding the velocity potential into a power series of a small parameter,the original 3-D nonlinear problem is reduced to a number of 2-D ones. The solutions of the first three orders are derived in detail and expressed in terms of the complete elliptic integrals of the first and second kinds.Then the boundary integral equation method is applied to get the numerical solutions for each order.Computational results are provided for supercavitating flows past cones under various flow conditions.     

THE SLOP FLUX METHOD FOR NUMERICAL BALANCE IN USING ROE＇S APPROXIMATE RIEMANN SOLVER

Imbalance arises when the Roe’s method is directly applied in the shallow water simulation.The reasons are different for the continuity equation and the momentum equations.Based on the Roe’s method,a partial surface method is proposed for a perfect balance for the continuity equation.In order to generate a mathematically hyperbolic formulation,the momentum equations are split,which causes incompatibility in the calculation of the momentum equations.In this article a numerical approach named the Slop Flux Method(SFM)is proposed to balance the source terms and the flux gradient based on the finite volume method.The method is first applied to shallow water equations.The model is verified by analytical results of classical test cases with good agreement.Finally the method is applied to a steady flow simulation over a practical complicated topography and the result shows good balance and conservation.     

含裂隙含水层污染物生物降解数值方法

本文讨论了含裂隙介质地下水污染物输运与生物降解非线性方程组数值求解方法.方程含有对流项、扩散项、生长、死亡、吸附、解吸、趋化和孔隙与裂隙介质界面间的交换项的非线性偶合，使算法十分困难.本文讨论了无生化过程时的几种求解方法，数值结果表明：用三次迎风插值法对常见的对流项占优势，且场变量有较大梯度的问题较适用.在讨论有生化反应过程时，利用对流项与生化反应项的特征时间量级估算，给出了求生化过程作用子步的时间步长估算办法.用上述方法所得到的模拟结果与解析解、无化学反应和有化学反应的实测值对比，吻合很好     

基于建筑密度系数的二维城市洪水数值模拟

城市密集建筑群的存在对城市洪水演进有很大影响,而根据建筑物的尺寸和高程采用高分辨率网格进行逐渐构建的方法在大范围洪水数值模拟中有一定的局限性。因此,如何高效模拟出建筑群在洪水中的影响对城市洪灾风险评估至关重要。在浅水方程中引入了建筑密度系数以反映建筑群对城市洪水运动的影响,并建立二维城市洪水数值模型。模型采用中心迎风格式计算界面通量,并对界面两侧变量进行线性重构,使其在空间上有二阶精度。为保证模型的和谐性和稳定性,底床坡度项采用中心差分法离散,底床摩擦项和局部水头损失项用半隐式法离散。当库朗特数满足条件时,模型能保证计算水深在任何时刻是非负的。算例分析表明,模型在计算中可以将建筑群区域视为一个整体,受网格疏密制约较小。在计算精度相近的情况下,计算需时约为高分辨率网格法的1/50,能够简便、高效地模拟洪水在城市建筑群中演进的过程。     

Simulation of water entry of an elastic wedge using the FDS scheme and HCIB method

The hydroelasticity of water entry of an elastic wedge is simulated using a code developed using the flux-difference splitting scheme for immiscible and incompressible fluids and the hybrid Cartesian/immersed boundary method. The free surface is regarded as a moving contact discontinuity and is captured without any additional treatment along the interface. Immersed boundary nodes are distributed inside a fluid domain based on the edges that cross an instantaneous body boundary. Dependent variables are reconstructed at each immersed boundary node with the help of an interpolation along a local normal line for providing a boundary condition for a discretized flow problem. A dynamic beam equation is used for modeling the elastic deformation of a wedge. The developed code is validated through comparisons with other experimental and computational results for a free-falling wedge. The effects of the elastic deformation of the wedge on the pressure fields and time histories of the impact force are investigated in relation to the stiffness and density of the structure. Grid independence test is carried out for the computed time history of the force acting on an elastic wedge.     

A NEW FINITE VOLUME METHOD FOR SOLVING SHALLOW WATER EQUATIONS

This paper presents a new numerical model using the finite volume method witharbitrary polygonal elements,It is suitable for simulating the shallow water problem with com-plex topography and boundary conditions.The calculated results show that this kind of methodhas the advantages of good stability,convenience of solving,easy programming,less,computingtime and storage,high accuracy,ect.     

GA-ILP Method for Optimization of Water Distribution Networks

Optimization of water distribution networks has been of central importance for recent decades. Genetic Algorithms (GA) are the most famous metaheuristics widely used for this purpose with great success. However, the fact that GA basically requires a large number of computations, has led to investigate for faster solvers. In this research, a new approach is proposed in which a simple GA is linked with the Integer-Linear Programming (ILP) method resulting in a hybrid optimization scheme. Using the mathematical method of ILP, the search space is significantly reduced thereby a limited number of evaluations are required to achieve a good solution. The approach is applied to two benchmark pipe-networks in order to show its ability in terms of accuracy and speed. The results are then compared with the previous works. The obtained results indicate that the proposed model is computationally efficient, like classic methods, while is still very promising in finding the global optimum like the nature-inspired metaheuristics.     

A TVD-WAF-based hybrid finite volume and finite difference scheme for nonlinearly dispersive wave equations

A total variation diminishing-weighted average flux(TVD-WAF)-based hybrid numerical scheme for the enhanced version of nonlinearly dispersive Boussinesq-type equations was developed. The one-dimensional governing equations were rewritten in the conservative form and then discretized on a uniform grid. The finite volume method was used to discretize the flux term while the remaining terms were approximated with the finite difference method. The second-order TVD-WAF method was employed in conjunction with the Harten-Lax-van Leer(HLL) Riemann solver to calculate the numerical flux, and the variables at the cell interface for the local Riemann problem were reconstructed via the fourthorder monotone upstream-centered scheme for conservation laws(MUSCL). The time marching scheme based on the third-order TVD RungeKutta method was used to obtain numerical solutions. The model was validated through a series of numerical tests, in which wave breaking and a moving shoreline were treated. The good agreement between the computed results, documented analytical solutions, and experimental data demonstrates the correct discretization of the governing equations and high accuracy of the proposed scheme, and also conforms the advantages of the proposed shock-capturing scheme for the enhanced version of the Boussinesq model, including the convenience in the treatment of wave breaking and moving shorelines and without the need for a numerical filter.     

A Standardized Index for Assessing Seawater Intrusion in Coastal Aquifers: The SITE Index

A large number of coastal aquifers worldwide are impacted by seawater intrusion. A major aim of European Directives 2000/60/EC and 2006/118/EC is to achieve good ecological status in groundwater bodies, including coastal aquifers. To this goal, information is needed about the current state of, and changes over time in, individual aquifers. This information can be obtained by applying methods that determine the status of aquifers in an uncomplicated manner. Methods for this type of assessment must comply with three essential criteria. First, calculation of the index must be straightforward and should be based on easy-to-obtain or commonly available data. Next, the index should be able to highlight important characteristics in understandable terms. Finally, the results should be objective and should be expressed in such a way that different time periods and different aquifers can be compared. In this paper we describe the development of a method to characterize seawater intrusion that meets these criteria and is based on four basic parameters: surface area, intensity, temporality, and evolution. Each parameter is determined by specific calculations derived from the groundwater chloride concentrations. Results are specified as a numerical index and an alphanumeric code. This index, known as SITE, has been applied to four Mediterranean coastal aquifers. The standardized results allowed us to discriminate between, and objectively compare the status of these groundwater bodies. Further, this index will make it possible to prioritize management actions and evaluate the effectiveness of these actions over time.     

中风化凝灰岩嵌岩桩抗拔承载特性研究

针对某建筑工程地下室抗浮设计问题,为了确定中风化凝灰岩地层嵌岩抗拔桩设计承载力,开展了5根0．7ｍ和0．8ｍ两种直径抗拔桩现场试验。试验结果表明各试桩加载至设计值时均为缓变形,最大位移为6．92ｍｍ～10．67ｍｍ,试验中岩层侧摩阻力未充分发挥,安全富裕较大。通过国内外不同规范方法对5根试桩极限抗拔承载力进行计算发现,理论计算得到的嵌岩桩极限抗拔承载力普遍大于设计值,且国外ＡＡＳＨＴＯ方法和加拿大岩土工程手册方法均明显大于建筑桩基规范,且嵌岩段长度越大,计算结果差异越显著。通过试验和理论计算均表明中风化凝灰岩嵌岩段的极限侧阻力发挥潜力较大,可作为抗拔桩的良好持力层。     

A coupled 1-D and 2-D channel network mathematical model used for flow calculations in the middle reaches of the yangtze river

A coupled one-dimensional (1-D) and two-dimensional (2-D) channel network mathematical model is proposed for flow calculations at nodes in a channel network system in this article.For the 1-D model, the finite difference method is used to discretize the Saint-Venant equations in all channels of a looped network.The Alternating Direction Implicit (ADI) method is adopted for the 2-D model at the nodes.In the coupled model, the 1-D model provides a good approximation with small computational effort, while the 2-D model is applied for complex topography to achieve a high accuracy.An Artificial Neural Network (ANN) method is used for the data exchange and the connectivity between the 1-D and 2-D models.The coupled model is applied to the Jingjiang-Dongting Lake region, to simulate the tremendous looped channel network system, and the results are compared with field data.The good agreement shows that the coupled hydraulic model is more effective than the conventional 1-D model.     

A spacetime discontinuous Galerkin method for the two-dimensional unsteady convection-dispersion problems

The unsteady two-dimensional convection-diffusion (CD) equation, which is the governing equation of the unsteady two-dimensional convection-dispersion problem, as the water contamination problems, has a mixed hyperbolic-parabolic character. When the equation has a strong mixed hyperbolic character, the exact solution is nonsmooth. In this case, the conventional numerical methods give approximate solutions which either oscillate or smear out the sharp front of the exact solution. The spacetime discontinuous Galerkin method (STDGM) is an extention of the space discontinuous Galerkin method (SDGM), applying the discontinuity in the time direction, as well as in space. Both these methods are respective modifications of the standard Galerkin finite element method (SGM). In this paper, the STDGM is applied to solve the CD equation, when the Péclet number has extremely high values, which means a strong mixed hyperbolic character. With this method, three artificial diffusion terms are introduced by modifying the test functions of the finite element method. These functions include the discontinuity int, x andy axis. The results obtained from the analytical solution of the problem are used for testing the numerical solution, applying both the space-discontinuous Galerkin method (SDGM) and the STDGM and are presented in diagrams, from which useful observations, comparisons and conclusions can be drawn.     

System identification modelling of ship manoeuvring motion based onε- support vector regression

Based on the ?- support vector regression, three modelling methods for the ship manoeuvring motion, i.e., the white-box modelling, the grey-box modelling and the black-box modelling, are investigated. The o o10 /10, o o20 / 20 zigzag tests and the o35 turning circle manoeuvre are simulated. Part of the simulation data for the o o20 / 20 zigzag test are used to train the support vectors, and the trained support vector machine is used to predict the whole o o20 / 20 zigzag test. Comparison between the simulated and predicted o o20 / 20 zigzag test shows a good predictive ability of the three modelling methods. Then all mathematical models obtained by the modelling methods are used to predict the o o10 /10 zigzag test and o35 turning circle manoeuvre, and the predicted results are compared with those of simulation tests to demonstrate the good generalization performance of the mathematical models. Finally, the modelling methods are analyzed and compared with each other in terms of the application conditions, the prediction accuracy and the computation speed. An appropriate modelling method can be chosen according to the intended use of the mathematical models and the available data for the system identification.     

MODELING DAM-BREAK FLOOD OVER NATURAL RIVERS USING DISCONTINUOUS GALERKIN METHOD

A well-balanced numerical model is presented for two-dimensional, depth-averaged, shallow water flows based on the Discontinuous Galerkin (DG) method. The model is applied to simulate dam-break flood in natural rivers with wet/dry bed and complex topography. To eliminate numerical imbalance, the pressure force and bed slope terms are combined in the shallow water flow equations. For partially wet/dry elements, a treatment of the source term that preserves the well-balanced property is presented. A treatment for modeling flow over initially dry bed is presented. Numerical results show that the time step used is related to the dry bed criterion. The intercell numerical flux in the DG method is computed by the Harten-Lax-van Contact (HLLC) approximate Riemann solver. A two-dimensional slope limiting procedure is employed to prevent spurious oscillation. The robustness and accuracy of the model are demonstrated through several test cases, including dam-break flow in a channel with three bumps, laboratory dam-break tests over a triangular bump and an L-shape bend, dam-break flood in the Paute River, and the Malpasset dam-break case. Numerical results show that the model is robust and accurate to simulate dam-break flood over natural rivers with complex geometry and wet/dry beds.     

水管冷却混凝土温度场分析

在文献【3】的基础上，基于冷却水管与混凝土之间热量交换的平衡原理，提出水管冷却混凝土温度场问题有限元求解的改进迭代算法。通过试验验证及在工程中的应用，说明该算法不但在理论上精确、严密，而且具有很高的迭代计算效率和计算精度。     

分析供水边界含水层抽水试验数据的新方法

提出了一种分析直线供水边界含水层抽水试验数据的新方法。本文将井函数中的2个级数表达式分别采取不同的简化方式，建立了一个二元线性回归方程。将试验数据分别转换为对应回归方程中因变量和自变量的数据后，利用线性最小二乘法计算回归方程中的常数，然后利用这些常数计算含水层参数和映射井至观测井间的距离。与传统方法相比较，本文方法不需预先绘制专门图解曲线；不存在人为的随意性对计算结果精度的影响，计算过程易于程序化。     

Evolving Effective Hydraulic Model for Municipal Water Systems

Constructing a robust hydraulic network model is vitally important, but a time-consuming task. Over last two decades, several approaches using optimization techniques have been developed for identifying model parameters. Although most of the methods can make the model agree with field observations, few are able to achieve a good level of accuracy in terms of determining the correct model parameters for a water distribution system. The previously developed methods appear to be lacking versatility for users to specify calibration tasks given real data for a real system. This paper proposes a comprehensive framework for evolving a hydraulic network model. Calibration tasks can be specified according to data availability and model application requirements. It allows an engineer to (1) flexibly choose any combination of the model parameters such as pipe roughness, junction demand and link (pipes, valves and pumps) operational status; (2) easily aggregate model parameters to reduce the problem dimension for expeditious calculation and (3) consistently specify boundary conditions and junction demand loadings that are corresponding to field data collection. A model calibration is then defined as an implicit nonlinear optimization problem, which is solved by employing a competent evolutionary algorithm. With this methodology, a modeler can be fully assisted to carry out not only a single parameter optimization run, but also a variety of calibration tasks in a progressive manner according to practical system conditions, thus it is possible to achieve a good model calibration with high level of confidence. The method has been applied to the model of a municipal water system to demonstrate the efficacy and robustness of the evolutionary modeling practices.     

感潮河段盐水入侵的河口水质模型

盐潮入侵将严重影响内河水质。本文考虑强混合型河口潮汐的特点,采用同步不同格式对河口盐潮入侵问题的流场及浓度场进行数值计算。采用欧拉-拉格朗日混合解法将对流-扩散方程中的扩散项和对流项分裂求解,应用高精度时间序列插值的特征差分隐格式求解对流项,扩散项采用传统的有限差分法。在汊口处,将描述河网汊口水质变化的三维对流扩散方程在汊口控制体体积积分,变量间的插值分布采用Panankar提出的幂函数,得到新的汊口离散方程。计算与实测结果比较表明,本文提出的方法有效可行。     

岩石类材料应变梯度损伤模型研究及应用

本文提出基于应变梯度的损伤模型，并用于材料局部化损伤模拟预测中。在有限元数值计算中对平面问题，使用平面高阶连续高精度单元和有限差分方法耦合，在保证精度情况下可提高计算效率，还避免对传统有限元程序作较大的改动；对三维情况，本文构造了四面体高阶连续单元。算例表明该模型对于避免有限元数值方法局部化预测模拟的单元网格依赖性有非常好的效果，其预测出的局部化损伤与实际破坏情况非常相近。