On an extension of the d’Alembert solution to initial–boundary value problems in multi-layered,multi-material domains

This work introduces a method for the exact solution of initial–boundary value problems for linear, one-dimensional conservation laws in multi-layered, multi-material domains. The method is based on the geometry of the solutions of such conservation laws and represents an extension of the d’Alembert solution to initial–boundary value problems in multi-layered, multi-material domains.     

多组份计算中封闭性模型研究

在使用单速度多组份方法计算多介质混合网格中的物理量时,需要给出一种封闭模型来使控制方程封闭。本文分析了压力增量相等封闭性模型存在基础遭到破坏的原因,之后在保证流场守恒性的前提下构造可以保证假设基础的可解方程组对压力增量相等封闭性模型进行修正,给出了一种改进方法。使用改进的模型进行了爆轰驱动飞片问题的计算,计算结果表明,改进的模型能很好的追踪物质界面和冲击波位置,同时较好的抑制界面处压力、内能震荡。     

Fluid–structure interaction approaches on fixed grids based on two different domain decomposition ideas

This paper presents two domain decomposition techniques for fixed grid fluid–structure interaction simulations that can be applied to the interaction of general structures with incompressible flows. One approach is based on an overlapping domain decomposition idea while the other uses non-overlapping domains. The first technique combines a fixed grid Chimera approach with arbitrary Lagrangean Eulerian based methods, the second one is based on an eXtended Finite Element Method (XFEM) strategy. Both techniques are used in a partitioned and strong coupling fluid–structure framework. The usage of such fixed-grid methods considerably increases the range of possible applications. Several test examples demonstrate key features of both methods.     

流固耦合分析的一种改进CBS有限元算法

针对流固耦合问题, 发展了一种基于任意拉格朗日-欧拉(ALE)描述有限元法的弱耦合分区算法. 运用半隐式特征线分裂算法求解Navier-Stokes方程, 在压力Poisson 方程中引入质量源项以满足几何守恒律; 运用子块移动技术更新动态网格, 并配以光滑处理防止网格质量下降; 采用Newmark-β 法求解结构运动方程. 为保持流体-结构界面处速度和动量守恒, 利用修正结合界面边界条件方法求解界面处速度通量和动量通量. 运用本方法分别模拟了不同雷诺数下单圆柱横向和两向流致振动、串列双圆柱两向流致振动. 计算表明, 本文方法计算效率高, 计算结果与已有实验和数值计算数据吻合.     

Numerical simulations for gas-structure interaction in inflated deployment of folded membrane boom

It is very important for gas-structure interaction between compressible ideal gas and elastic structure of space folded membrane booms during the inflatable deployment. In order to study this gas-structure interaction problem, Arbitrary Lagrangian-Eulerian (ALE) finite element method was employed. Gas-structure interaction equation was built based on equilibrium integration relationship, and solved by operator split method. In addition, numerical analysis of V-shape folded membrane booms inflated by gas was given, the variation of inner pressure as well as deployment velocities of inflatable boom at different stage were simulated. Moreover, these results are consistent with the experiment of the same boom, which shows that both ALE method and operator split method are feasible and reliable methods to study gas-structure interaction problem.     

Thermo-mechanically coupled investigation of steady state rolling tires by numerical simulation and experiment

In this contribution, a numerical framework for the efficient thermo-mechanical analysis of fully 3D tire structures (axisymmetric geometry) in steady state motion is presented. The modular simulation approach consists of a sequentially coupled mechanical and thermal simulation module. In the mechanical module, the Arbitrary Lagrangian Eulerian (ALE) framework is used together with a 3D finite element model of the tire structure to represent its temperature-dependent viscoelastic behavior at steady state rolling and finite deformations. Physically computed heat source terms (energy dissipation from the material and friction in the tire–road contact zone) are used as input quantities for the thermal module. In the thermal module, a representative cross-sectional part of the tire is employed to evaluate the temperature evolution due to internal and external heat sources in a transient thermal simulation. Special emphasis is given to an adequate material test program to identify the model parameters. The parameter identification is discussed in detail. Numerical results for three different types of special performance tires at free rolling conditions are compared to experimental measurements from the test rig, focusing especially on rolling resistance and surface temperature distribution.     

High order moment method for polydisperse evaporating sprays with mesh movement: Application to internal combustion engines

Relying on two recent contributions by Massot et al. [SIAM J. Appl. Math. 70 (2010), 3203–3234] and Kah et al. [J. Comput. Phys. 231(2012)], where a Eulerian Multi-Size Moment (EMSM) model for the simulation of polydisperse evaporating sprays has been introduced, we investigate the potential of such an approach for the robust and accurate simulation of the injection of a liquid disperse phase into a gas for automotive engine applications. The original model used a high order moment method in droplet size to resolve polydispersity, with built-in realizability preserving numerical algorithm of high order in space and time, but only dealt with one-way coupling and was restricted to fixed meshes. Extending the approach to internal combustion engine and fuel injection requires solving two major steps forward, while preserving the properties of robustness, accuracy and realizability: 1 – the extension of the method and numerical strategy to two-way coupling with stable integration of potential stiff source terms, 2 – the introduction of a moving geometry and meshes. We therefore present a detailed account on how we have solved these two issues, provide a series of verification of the proposed algorithm, showing its potential in simplified configurations. The method is then implemented in the IFP-C3D unstructured solver for reactive compressible flows in engines and validated through comparisons with a structured fixed mesh solver. It finally proves its potential on a free spray jet injection where it is compared to a Lagrangian approach and its reliability and robustness are assessed, thus making it a good candidate for realistic injection applications.     

New parallel method for adjacent disconnected unstructured 3D meshes

ABSTRACT

A new parallel method for simulations with non-overlapping disconnected mesh domains but adjacent boundaries is presented and studied. This technique allows simulations using 3D unstructured meshes that are independent.     

Numerical simulation of impact forces by a falling sphere in air using ALE finite element method

ABSTRACT

A numerical method is developed to simulate the process that a falling rigid sphere hits rigid ground and bounces back in air. The problem is treated as fluid-structure interaction problem based on the ALE finite element flow analysis. In order to introduce the numerical process of impact into the present staggered fluid-structure time marching algorithm, the impact force is applied to the equation of motion of the sphere. The magnitude of the impact force is determined by iteration so that the velocity of the sphere after impact converges to zero. Application of the impact force at a single time instant causes unphysical pressure oscillation. This has been suppressed by applying the impact force smoothly over multiple short time steps. In the present method impulse is evaluated instead of impact force. Computations with different density ratio of the sphere to air showed effect of the air on the sphere motion.     

一类格心型ALE有限体积格式方法

现在国内外流行的ALE有限体积格式基本上都基于交错网榕进行格式的离散.该类格武在进行重映时,速度、密度和能量需要分别进行重映计算,效率较低,而且由于速度在网格角点.而密度、能量在网格中心,重映时会出现动能和内能不协调现泉.本文在巳有格心型Lagrange有限体积格式研究的基础上,结合Abgrall R.等关于榕心型格式下的网格角点速度的计算方法,利用最小二乘法进行高阶插值多项式重构,构造了一类新的格心型的高精度Lagrangian有限体积格式,并结合有效的高精度ENO守恒重映方法,获得了一类格心型的高精度ALE有限体积格式.数值试验的结果说明本文的格式是有效的,高精度的,收敛的,并且避免了物理量的不协调现象.