Research developments in numerical methods of fluid-structure interactions in naval architecture and ocean engineering北大核心CSCD

流固耦合问题较为复杂,通常难以通过理论推导求得,而数值模拟则能提供一种有效的解决方案,并被广泛用于船舶与海洋工程领域。流固耦合数值方法根据其网格离散方式,可以分为贴体网格方法、非贴体网格方法、重叠网格方法和粒子类方法 4类,对这4类方法的特点及研究进展进行概述并总结得出:贴体网格方法和重叠网格方法均能精确捕捉界面的变形和演化,适合高雷诺数流动问题,在考虑结构变形时一般采用贴体网格方法,而考虑复杂几何形状的刚体运动时则常采用重叠网格方法;非贴体网格方法能够避免网格的更新操作,使计算较为简单,目前多用于模拟流动控制、水下柔性仿生航行器的研发以及多体运动干扰等问题;粒子类方法因其固有的拉格朗日属性,在模拟涉及自由液面剧烈变形、砰击、爆炸等强非线性流固耦合问题中发挥着重要作用。不同的流固耦合问题属性决定了不同方法的适用性,如何选取适合的数值方法,同时结合各类方法的优势开发新的计算方法以应对更为复杂的问题,是流固耦合算法开发的重要发展方向。     

三维方柱/平板组合体粘性绕流分块计算方法

本文提出了一个三维粘性不可压流动的分块耦合求解方法，发展了一套基于该方法的计算机程序，并针对三维方柱／平板组合体这一一般算例进行了计算，验证了流场分块耦合求解方法的可行性。     

对解泊松方程数值生成网格方法的一点改进

本文提出了一种生成网格的改进方法，此法的本质是交替地改善网格的正交性和汇聚性。此法的构思质朴，效果明显，尤其是对物面附近要求顾到网格的正交性和汇聚性两者时，此法提供了一种有效的控制手段。此法在计算船舶流体动力学中有较高的实用价值。     

舰船网格技术与设计研究

舰船网格化是未来信息化海战取得胜利的重要保证,在介绍网格系统特点和结构的基础上分析舰船网格的核心技术,并研究网格系统在舰船设计中的应用.     

动网格技术中局部重构方法的改进研究

Delaunay三角化方法是生成非结构网格常用的方法之一,其生成效率比阵面推进法高,但布点能力较弱.在解决大位移运动时常用方法是网格局部重构,但网格重构会增加计算工作量.文中针对局部重构方法中的窗口边界确定方法进行研究,提出了一种改进方法,不仅可以提高Delaunay三角化方法的布点能力,而且省去了繁琐的窗口边界提取步骤,提高了运动网格计算速度和网格质量;利用无量纲半径作为程序全局变量,在保证网格质量的前提下,提高了运动网格的智能性,减少了人工干预.     

基于重叠网格的某新型舟桥数值模拟

采用RANS方法和重叠网格计算了带自由液面的全航速范围内桥脚分置式门桥绕流问题.自由液面的模拟采用单相Level-Set方法,Reynolds应力采用k-ω模型,采用PISO算法求解RANS方程,获得门桥阻力、波型等参数.简要描述了重叠网格及单相Level Set自由液面模拟方法.通过对桥脚分置式门桥在全航速范围下数值求解与试验结果比较,结果表明本方法可有效模拟全航速下的门桥绕流问题.     

网格计算在电力系统的应用

网格（Grid）是近年来国际上兴起的一种重要信息技术，研究热点。从网格的发展现状、基本概念、结构和特点等出发，根据我国电力系统目前的实际情况，展望网格技术在电力系统中的可能应用。最后，根据满足互联需求的电力网格的基本特征和电力系统自身的特点，提出满足要求的网格模式。     

基于网格单元的通航水域搁浅风险评价方法研究

为保障船舶通航安全,专家和学者们进行了一系列关于通航水域风险因素识别、风险评价和风险预测的研究。本人将参考各国专家学者的研究成果,提出基于网格单元的通航水域搁浅风险评价方法。     

一种简单的结构网格边界正交化方法

给出了一种可实现网格边界正交化的代数方法,该方法简单明了易于实现.网格的正交化程度及范围可通过参数来控制.算例表明,网格在边界处的正交性是令人满意的.     

重叠网格在船舶CFD中的应用研究

文章采用RANS方法和重叠网格计算了带自由液面的船舶绕流问题。计算网格采用重叠网格的型式,自由液面的模拟采用单相Level-Set方法,Reynolds应力采用k-ω模型,采用体单元有限差分方法和PISO算法求解RANS方程。文中简要描述了重叠网格和单相Level Set自由液面模拟方法的数学模型及求解。通过对S60单体船型约束模和自由模型采用重叠网格的数值求解及与试验结果的比较表明该重叠可较好地模拟带自由液面船舶自由态绕流问题。另采用重叠网格对一简单的双体船和三体船进行了数值求解,计算结果也表明重叠网格和单相Level-Set方法可较好地模拟带自由液面的船舶绕流问题。     

A finite pointset method for the numerical simulation of free surface flow around a ship

In this paper, we present a Finite pointset method (FPM) for the numerical simulation of free surface flow around a ship in calm water. It is a Lagrangian and meshless particle scheme which is applied to the projection method for the incompressible governing equations. This requires the solution of Poisson problems in each time step, so a moving least squares (MLS) interpolants is used for the spatial derivatives in order to discretize the Poisson equation with pressure-Dirichlet condition of free surface flow in meshless structure. Meanwhile, an additional problem of the periodic particle locations redistribution in the present approach is still handled by MLS interpolants. With the proposed FPM technique, problems associated with the free surface flow around a ship are circumvented. A verification of numerical modeling is made using the Wigley hull and the validity of the proposed methodology is examined by comparing the detail of wave profile and wave-making resistance with Series 60 model. The results demonstrate that FPM is able to perform efficient and stable simulations of free surface flow around a ship.     

光滑质点流体动力学(SPH)及其算法特性

基于Lagrange观点的无网格方法计算是建立在一群可移动的自适应性的质点基础之上,对特大变形区域和自由表面的捕捉有着较高的精度.光滑质点流体动力学(SPH)是无网格方法的一种,本文阐述其理论基础和计算方法,主要包括:SPH的基本概念、核近似和粒子近似的基本原理,核函数的构造方法、SPH形式的流体运动方程、边界处理方法和数值算例等多方面内容.研究工作在了解SPH方法的理论特点和潜在优势的同时,也为相关问题的深入研究和改进奠定了理论和算法基础.     

溃坝模拟的光滑粒子流体动力学方法及其粘性特性(英文)

Smoothed particle hydrodynamics (SPH) is a Lagrangian meshless particle method. It is one of the best method for simulating violent free surface flows in fluids and solving large fluid deformations. Dam breaking is a typical example of these problems. The basis of SPH was reviewed, including some techniques for governing equation resolution, such as the stepping method and the boundary handling method. Then numerical results of a dam breaking simulation were discussed, and the benefits of concepts like artificial viscosity and position correction were analyzed in detail. When compared with dam breaking simulated by the volume of fluid (VOF) method, the wave profile generated by SPH had good agreement, but the pressure had only reasonable agreement. Improving pressure results is clearly an important next step for research.     

K2_SPH方法及其在二维水波模拟中的应用(英文)

Smoothed Particle Hydrodynamics (SPH) is a Lagrangian meshless particle method. However, its low accuracy of kernel approximation when particles are distributed disorderly or located near the boundary is an obstacle standing in the way of its wide application. Adopting the Taylor series expansion method and solving the integral equation matrix, the second order kernel approximation method can be obtained, namely K2_SPH, which is discussed in this paper. This method is similar to the Finite Particle Method. With the improvement of kernel approximation, some numerical techniques should be adopted for different types of boundaries, such as a free surface boundary and solid boundary, which are two key numerical techniques of K2_SPH for water wave simulation. This paper gives some numerical results of two dimensional water wave simulations involving standing wave and sloshing tank problems by using K2_SPH. From the comparison of simulation results, the K2_SPH method is more reliable than standard SPH.     

冰区航行船舶冰阻力数值研究进展

冰阻力是影响船舶在冰区航行性能的关键因素。当前主要的冰阻力研究方法有经验公式法、模型/实船试验法和数值模拟方法。数值模拟方式能够对船舶破冰的全过程进行快速模拟,且模拟成本低,参数易于控制 、结果较为准确,是一种比较适宜的冰阻力预报方法。随着计算技术的进步,各种数值模拟方法层出不穷,其中包括基于网格单元的有限元模型,基于无网格方法的离散元模型、SPH法、近场动力学模型等;近年来,网格模型与无网格模型的耦合方法也逐渐发展起来。文章简要梳理了冰区航行船舶冰阻力数值研究的进展,并基于研究现状提出尚需进一步解决的问题,意在为进一步提高冰阻力数值模拟精度提供参考。     

基于SPH法的径向滑动轴承动压润滑研究

为了研究润滑油膜的粒子性对流体动压润滑的影响,该文提出利用SPH方法（光滑粒子动力学方法）分析径向滑动轴承流体动压润滑,模拟结果通过计算流体动力学（CFD）软件FLUENT分析结果和润滑理论提供的解析解进行了比较验证。同CFD 法一样,SPH法的压力分布结果揭示了润滑理论忽略掉的流体惯性效应。三种方法速度场分析结果略有不同。因此,SPH模型由于反映了流体的粒子性,可成为求解滑动轴承中的复杂流体润滑问题的有效工具。     

基于无网格方法的复合材料层合板固有频率及特征值灵敏度分析

文章基于无网格法和弹性力学Hamilton正则方程,研究了复合材料层合板固有频率和特征值灵敏度分析问题。首先,结合径向基插值函数和修正后的H-R变分原理,推导了Hamilton正则方程的无网格列式。然后,以Multiquadric(MQ)、Gaussian(EXP)和薄板样条(TPS)为基函数,计算了复合材料层合板的固有频率及其特征值的灵敏度系数。文中的工作使得无网格法的优越性与弹性力学Hamilton正则方程的半解析法得到了有机的结合,为Hamilton正则方程提出了一种新的特征值灵敏度分析方法。     

水流对浮体作用的SPH方法模拟

水流与浮体相互作用时,运动情况十分复杂,目前很难准确有效地模拟。而SPH作为一种纯拉格朗日方法,无需构建网格,用核函数近似粒子进行离散,能较好地解决一些自由面大变形问题。文章利用SPH法对溃坝时引起的高速水流冲击浮体以及水体晃动时破损浮体的运动过程进行模拟。模拟结果表明,SPH法能有效地进行水流对浮体作用的研究。     

Using a random displacement model to simulate turbulent particle motion in a baroclinic frontal zone: A new implementation scheme and model performance tests

Numerical artifacts can limit accurate simulation of turbulent particle motion when Lagrangian particle-tracking models are implemented in hydrodynamic models with stratified conditions like fronts. Yet, modeling of individual particle motion in frontal regions is critical for understanding sediment dynamics as well as the transport and retention of planktonic organisms. The objective of this research was to develop a numerical technique to accurately simulate turbulent particle motions in a particle-tracking model embedded within a hydrodynamic model of a frontal zone. A new interpolation scheme, the ‘water column profile’ scheme, was developed and used to implement a random displacement model for turbulent particle motions. A new interpolation scheme was necessary because linear interpolation schemes caused artificial aggregation of particles where abrupt changes in vertical diffusivity occurred. The new ‘water column profile’ scheme was used to fit a continuous function (a tension spline) to a smoothed profile of vertical diffusivities at the x–y particle location. The new implementation scheme was checked for artifacts and compared with a standard random walk model using (1) Well Mixed Condition tests, and (2) dye-release experiments. The Well Mixed Condition tests confirmed that the use of the ‘water column profile’ interpolation scheme for implementing the random displacement model significantly reduced numerical artifacts. In dye-release experiments, high concentrations of Eulerian tracer and Lagrangian particles were released at the same location up-estuary of the salt front and tracked for 4 days. After small differences in initial dispersal rates, tracer and particle distributions remained highly correlated (r = 0.84 to 0.99) when a random displacement model was implemented in the particle-tracking model. In contrast, correlation coefficients were substantially lower (r = 0.07 to 0.58) when a random walk model was implemented. In general, model performance tests indicated that the ‘water column interpolation’ scheme was an effective technique for implementing a random displacement model within a hydrodynamic model, and both could be used to accurately simulate diffusion in a highly baroclinic frontal region. The new implementation scheme has the potential to be a useful tool for investigating the influence of hydrodynamic variability on the transport of sediment particles and planktonic organisms in frontal zones.     

时域有限水深格林函数及其导数的数值计算

精确快速地求取有限水深格林函数及它的导数是应用时域法求解有限水深水动力学问题的关键.通过对有限水深格林函数在不同区域渐近特性的分析,给出了使用多维Chebyshev多项式和渐近展开式快速近似计算有限水深格林函数及它的导数的方法.近似方法与直接积分方法的比较表明近似方法的计算工作量大幅减少,可以给出足够精度的计算结果.