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1.
采用流体体积分数的混合型多流体数值模型,将piecewise parabolic method (PPM)方法应用于可压缩多流体流动的数值模拟,拓展了以前提出的模型和数值方法,使它能够处理一般的Mie-Grneisen状态方程。采用双波近似和两层迭代算法求解一般状态方程的Riemann问题;并根据多流体接触界面无振荡原则设计高精度计算格式,对典型的纯界面平移问题可以从理论上证明本算法在接触间断附近压力和速度没有振荡,而且数值模拟结果表明界面数值耗散也被控制在2~3个网格之内。模拟了多种复杂的可压缩多流体流动,算例结果表明本文方法可以有效地处理接触间断、激波等物理问题,且具有耗散小精度高的特点。  相似文献   

2.
王涛  李平  柏劲松  汪兵  陶钢 《爆炸与冲击》2013,33(5):487-493
采用拉伸涡亚格子尺度应力模型对湍流输运中的亚格子作用项进行模式化处理,发展了适用于可压多介质黏性流动和湍流的大涡模拟方法和代码MVFT(multi-viscous flow and turbulence)。利用MVFT代码对低密度流体界面不稳定性及其诱发的湍流混合问题进行了数值模拟。详细分析了扰动界面的发展,流场中冲击波的传播、相互作用、湍流混合区边界的演化规律,以及流场瞬时密度和湍动能的分布和发展。数值模拟获得的界面演化图像和流场中波系结构与实验结果吻合较好。三维和二维模拟结果的比较显示,两者得到的扰动界面位置、波系及湍流混合区边界基本一致,只是后期的界面构型有所不同,这也正说明湍流具有强三维效应。  相似文献   

3.
本文所提算法适用于二维和三维多介质流体力学两步欧拉数值方法中输运计算的混合网格(包括自由面网格)界面处理。在一个混合网格中,界面被近似地看作直线(二维)或平面(三维)。整个方法分为三步:(1)第一步,用混合网格周围的八个网格的介质面积份额(二维)或二十六个网格的介质体积份额(三维)确定界面的法线方向;第二步,用混合网格的本身的介质面积份额(二维)或体积份额(三维)确定界面的方程(位置);第三步,用此直线方程求出通过网格边界的流以及下一时刻网格的面积份额(二维)或体积份额(三维)。最后给出了用此方法所做的一些数值计算及与SLIC算法的比较。  相似文献   

4.
利用Level Set方法隐式捕捉界面并能处理复杂的物质界面及其拓扑结构变化(如合并、交叉、破碎等)情况的优势,基于可压缩N-S方程的预处理技术,采用基于界面两侧介质黎曼关系的修正虚拟流体方法对介质边界进行处理;将只能应用于可压缩流动界面模拟的修正虚拟流体方法推广应用于不可压缩流动问题的模拟,数值模拟了气-水运动界面与近水面飞行器的相互影响规律。通过与将水面视为对称面的简化模型对比发现:利用自由运动界面模型计算的NACA6409翼型升力较小,能更准确地反映飞行器流场对水面形状的影响,其结果更为符合实际;文中还对比了翼型距水面不同高度时的结果,得到了翼型受水面影响的强弱与翼型距水面的高度成反比的结论。  相似文献   

5.
针对爆炸冲击波与建筑物结构相互作用过程,分析了冲击波与结构碎块作用机理,发展了一种能够模拟建筑物结构破坏及冲击波传播过程的计算模型和方法。采用建筑物结构工程毁伤载荷作为判据,处理结构在冲击波作用下的破坏问题;利用流固耦合界面算法处理结构运动引起的泄压效应,利用“虚拟网格通气技术”处理结构碎块对冲击波的阻碍作用,模拟了冲击波作用下典型建筑物的毁伤过程及冲击波传播过程。结果表明,该模型在模拟冲击波与结构的作用过程中,压力计算结果与非结构动网格模拟结果符合较好;在典型建筑物毁伤过程的数值模拟中,计算得到的建筑物毁伤效果和冲击波超压分布与建筑物物理毁伤特点符合。  相似文献   

6.
近些年来,深海矿产开发成为热点,其中涉及的固液混输问题逐渐引起学者的关注。如矿粒在海床上的输运,涉及水平管道的输运问题;矿粒从海床输运到海上浮式建筑物,涉及垂直管道的输运问题;矿粒在不同倾角管道内的输运,涉及倾斜管道的输运问题。对于该类问题,由于流体和固体之间的物理差异较大,对于固液两相往往采用不同的数值处理方法。本文使用MPS-DEM耦合方法模拟管道内的固液混输运动。用MPS方法模拟管道内流体的运动,用DEM方法追踪管道内颗粒的运动。在管道的进出口使用周期性边界条件,将多段管道之间进行拼接,从而实现了对超长管道内高雷诺数的颗粒输运现象的模拟。最后,分析管道颗粒和流场的速度及粒子分布等信息,分析流动特征。得到的结果会为超长管道内固液混输现象的研究提供一些借鉴意义及参考价值。  相似文献   

7.
有限弹簧法在钢筋混凝土细观断裂分析中的应用   总被引:6,自引:1,他引:5  
叙述了依据计算几何学的分割理论划分多边形单元的计算前处理系统,及其有限弹簧法在钢筋混凝土构件细观断裂数值模拟中的应用。该模拟系统的主要特色为:一是利用有限弹簧法的单元形状任意性来考虑混凝土断裂模拟时单元形状的影响;二是利用其变位不连续性模拟构件从微细裂缝到断裂的全过程;三是把钢筋和混凝土分别看成具有不同性质的微小构造单元来考虑其界面性质。数值模拟钢筋混凝土构件在拉伸作用下的断裂全过程,考察钢筋的螺纹抵抗作用及其保护层的约束机理。  相似文献   

8.
采用基于自适应Cartesian网格的level set方法对多介质流动问题进行数值模拟。采用基于四叉树的方法来生成自适应Cartesian网格。采用有限体积法求解Euler方程,控制面通量的计算采用HLLC(Hartern, Lax, van Leer, Contact)近似黎曼解方法。level set方程也采用有限体积法求解,采用Lax-Friedchs方法计算通量,通过窄带方法来减少计算量,界面的处理采用ghost fluid方法。Runge-Kutta显式时间推进,时间、空间都是二阶精度。对两种不同比热比介质激波管问题进行数值模拟,其结果和精确解吻合;对空气/氦气泡相互作用等问题进行模拟,取得令人满意的结果。  相似文献   

9.
作为空间自然对流热质输运的基本形式, 界面张力梯度驱动对流是流动和传热强耦合的复杂非线性过程, 也是一个多控制参数耦合作用的过程, 表现出丰富的流动时空特征. 界面张力梯度驱动对流是微重力流体物理的重要研究内容和学科前沿, 同时在空间燃料输运过程和空间能源或热管利用等空间流体管理问题中均有重要应用. 本文综述了界面张力梯度驱动对流向湍流转捩研究的背景意义、地面实验、空间实验及数值模拟的研究现状, 重点介绍了从非线性动力学角度来研究转捩规律的具体方法, 目前最常见的手段是对观测量的时间序列进行分析, 通过频谱分析及相空间重构等方法计算时间序列的特征量, 从而判断流动模式, 这类方法理论成熟, 计算简单, 但需要对大量数据进行繁琐的处理; 另一种方法是通过数值计算分岔来研究对流在时空中的转捩模式, 这类方法可以直接计算出分岔点, 但是复杂之处在于需要求解大规模的线性或非线性方程组, 本文详细阐述了两种方法的理论背景, 应用状况及局限性, 探讨了将两种方法相互结合, 在研究中互为补充的可能, 并对今后的研究方向提出了建议.   相似文献   

10.
界面不稳定性实验的数值研究   总被引:1,自引:0,他引:1  
柏劲松  李平  谭多望  姜洋 《力学学报》2007,39(6):741-748
采用多介质流体的三阶精度Piecewise Parabolic Method (PPM) 计算方法对界面不稳定性实验模型进行数值模拟,通过对Lawrence Livermore National Laboratary (LLNL)实验室的果冻环实验模型的数值计算,获得了与其计算和实验图像基本一致的结果, 从而验证和确认了计算方法和计算程序. 在此基础上,对于冲击波物理与爆轰物理实验 室设计的果冻内外界面10模峰对峰、峰对谷振幅为1\,mm扰动的界面不稳定性实验模型,给出 了果冻内外界面位置、速度和加速度历史曲线,详细分析了果冻内外界面不稳定性的发展、 演化过程,并给出了两种实验模型实验结果和对应的数值模拟结果.  相似文献   

11.
A numerical study was performed on flow and heat transfer involving moving free surfaces that occurs in mold filling processes such as casting and injection molding. In these problems, the calculation domain changes continuously and the numerical treatment of the moving interface tends to cause artificial diffusion. Among the solution algorithms based on the Eulerian method, the volume-of-fluid (VOF) method was used because the method is simple and efficient in handling the complex flow patterns inside the cavity. To solve the transport equation of free surface without artificial smearing of the interface the baby-cell method was employed in the geometric reconstruction of the free surface. Furthermore, a predictor–corrector method was adopted in the time integration of volume-of-fluid (VOF) transport equation to increase the accuracy. The proposed scheme was verified through several benchmark problems. In order to show the capability of the proposed method, several three-dimensional mold filling processes were solved. The current algorithm was applied to the floating body problem. Three-dimensional floating body problems were tested.  相似文献   

12.
13.
Large-scale high performance computation on 3D explosion and shock problems   总被引:1,自引:0,他引:1  
Explosion and shock often involve large deformation, interface treatment between multi-material, and strong discontinuity. The Eulerian method has advantages for solving these problems. In parallel computation of the Eulerian method, the physical quantities of the computaional cells do not change before the disturbance reaches to these cells. Computational efficiency is low when using fixed partition because of load imbalance. To solve this problem, a dynamic parallel method in which the computation domain expands with disturbance is used. The dynamic parallel program is designed based on the generally used message passing interface model. The numerical test of dynamic parallel program agrees well with that of the original parallel program, also agrees with the actual situation.  相似文献   

14.
We describe the formulation of a method for fluid-structure interaction involving the coupling of moving and/or flexible solid structures with multiphase flows in the framework of the Level Contour Reconstruction Method. We present an Eulerian-based numerical procedure for tracking the motion and interaction of a liquid-gas interface with a fluid-solid interface in the Lagrangian frame together with the evaluation of the fluid transport equations coupled to those for the solid transport, namely the left Cauchy-Green strain tensor field, in the Eulerian frame. To prevent excessive dissipation due to the convective nature of the solid transport equation, a simple incompressibility constraint for the strain field is enforced. A single grid structure is used for both the fluid and solid phases which allows for a simple and natural coupling of the fluid and solid dynamics. Several benchmark tests are performed to show the accuracy of the numerical method and which demonstrate accurate results compared to several of those in the existing literature. In particular we show that surface tension effects including contact line dynamics on the deforming solid phase can be properly simulated. The three-phase interaction of a droplet impacting on a flexible cantilever is investigated in detail. The simulations follow the detailed motion of the droplet impact (and subsequent deformation, breakup, and fall trajectory) along with the motion of the deformable solid cantilever due to its own weight as well as due to the force of the droplet impact.  相似文献   

15.
A coupled Lagrangian interface‐tracking and Eulerian level set (LS) method is developed and implemented for numerical simulations of two‐fluid flows. In this method, the interface is identified based on the locations of notional particles and the geometrical information concerning the interface and fluid properties, such as density and viscosity, are obtained from the LS function. The LS function maintains a signed distance function without an auxiliary equation via the particle‐based Lagrangian re‐initialization technique. To assess the new hybrid method, numerical simulations of several ‘standard interface‐moving’ problems and two‐fluid laminar and turbulent flows are conducted. The numerical results are evaluated by monitoring the mass conservation, the turbulence energy spectral density function and the consistency between Eulerian and Lagrangian components. The results of our analysis indicate that the hybrid particle‐level set method can handle interfaces with complex shape change, and can accurately predict the interface values without any significant (unphysical) mass loss or gain, even in a turbulent flow. The results obtained for isotropic turbulence by the new particle‐level set method are validated by comparison with those obtained by the ‘zero Mach number’, variable‐density method. For the cases with small thermal/mass diffusivity, both methods are found to generate similar results. Analysis of the vorticity and energy equations indicates that the destabilization effect of turbulence and the stability effect of surface tension on the interface motion are strongly dependent on the density and viscosity ratios of the fluids. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

16.
In this paper we present a numerical model for the coarse-grid simulation of turbulent liquid jet breakup using an Eulerian–Lagrangian coupling. To picture the unresolved droplet formation near the liquid jet interface in the case of coarse grids we considered a theoretical model to describe the unresolved flow instabilities leading to turbulent breakup. These entrained droplets are then represented by an Eulerian–Lagrangian hybrid concept. On the one hand, we used a volume of fluid method (VOF) to characterize the global spreading and the initiation of droplet formation; one the other hand, Lagrangian droplets are released at the liquid–gas interface according to the theoretical model balancing consolidating and disruptive energies. Here, a numerical coupling was required between Eulerian liquid core and Lagrangian droplets using mass and momentum source terms. The presented methodology was tested for different liquid jets in Rayleigh, wind-induced and atomization regimes and validated against literature data. This comparison reveals fairly good qualitative agreement in the cases of jet spreading, jet instability and jet breakup as well as relatively accurate size distribution and Sauter mean diameter (SMD) of the droplets. Furthermore, the model was able to capture the regime transitions from Rayleigh instability to atomization appropriately. Finally, the presented sub-grid model predicts the effect of the gas-phase pressure on the droplet sizes very well.  相似文献   

17.
柏劲松  李平  邹立勇  王涛 《力学学报》2008,40(4):464-472
在可压缩多介质流体动力学高精度欧拉计算方法多介质流体分段抛物方法 (multi-fluid piecewise parabolic method, MFPPM)基础上,运用算子分裂技术, 增加二阶空间中心差方法和两步Rung-Kutta时间推进 方法计算动力学黏性以及热流部分对流场的影响,发展适用于NS (Navier-Stokes)方程的可压缩多介质黏性流体计算方法多介质黏性流体分段抛物方法 (multi-viscousity-fluid piecewise parabolic method, MVPPM). 文中采 用MVPPM对英国AWE(atomic weapons establishment)激波管实验进行二维计算,给 出了与实验图像基本一致的计算结果;应用 MFPPM和MVPPM分别对二维柱对称内爆动力学界面不稳定性及其后期混合过程进行数值模拟, 给出内外界面演化、速度历史以及后期中心气穴不同半径内因RT(Rayleigh-Taylor)界面不 稳定性引起的混合量分布情况,从计算结果比较可见黏性对物质界面处混合量的分布影响明 显.  相似文献   

18.
A modified front‐tracking method was proposed for the simulation of fluid‐flexible body interactions with large deformations. A large deformable body was modeled by restructuring the body using a grid adaptation. Discontinuities in the viscosity at the fluid‐structure interface were incorporated by distributing the viscosity across the interface using an indicator function. A viscosity gradient field was created near the interface, and a smooth transition occurred between the structure and the fluid. The fluid motion was defined on the Eulerian domain and was solved using the fractional step method on a staggered Cartesian grid system. The solid motion was described by Lagrangian variables and was solved by the finite element method on an unstructured triangular mesh. The fluid motion and the structure motion were independently solved, and their interaction force was calculated using a feedback law. The interaction force was the restoring force of a stiff spring with damping, and spread from the Lagrangian coordinates to the Eulerian grid by a smoothed approximation of the Dirac delta function. In the numerical simulations, we validated the effect of the grid adaptation on the solid solver using a vibrating circular ring. The effects of the viscosity gradient field were verified by solving the deformation of a circular disk in a linear shear flow, including an elastic ring moving through a channel with constriction, deformation of a suspended catenary, and a swimming jellyfish. A comparison of the numerical results with the theoretical solutions was presented. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

19.
编写了适用于模拟具有高密度比、高压力比的强激波问题的二维柱对称多介质流体计算程序。利用有限体积方法求解流体的Euler方程组,采用level set方法捕捉爆炸产物与空气的运动界面,并通过求解物质界面两侧Riemann问题的精确解来计算爆炸产物与空气之间的数值通量。研制了三角形网格自适应技术来实现网格的自动加密和粗化,在保证捕捉激波峰值的前提下有效地提高了计算效率。利用计算程序对1 kt TNT当量的空气自由场强爆炸问题进行数值模拟,计算得到的峰值超压、冲击波到达时间等物理参数与点爆炸理论结果基本一致。  相似文献   

20.
We develop an Eulerian fixed grid numerical method for calculating multi‐material fluid flows. This approach relates to the class of interface capturing methods. The fluid is treated as a heterogeneous mixture of constituent materials, and the material interface is implicitly captured by a region of mixed cells that have arisen owing to numerical diffusion. To suppress this numerical diffusion, we propose a composite Riemann problem (CRP), which describes the decay of an initial discontinuity in the presence of a contact point between two different fluids, which is located off the initial discontinuity point. The solution to the CRP serves to calculate multi‐material no mixed numerical flux without introducing any material diffusion. We discuss the CRP solution and its implementation in the multi‐material fluid Godunov method. Numerical results show that a simple framework of the CRP greatly improves capturing material interfaces in the Godunov method and reproduces many of the advantages of more complicated interface tracking multi‐material treatments. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

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