高温气流内顺/逆流喷雾的Eulerian-Lagrangian数值仿真(英文)

用Eulerian-Lagrangian方法对高温气流内顺/逆流喷雾过程进行了数值仿真。气相方程用Eulerian方法建立,用k-ε模型封闭;液滴相方程用Lagrangian方法建立,采用了随机轨道模型;考虑了气体和液滴间的双向耦合。结果表明,高温气流内喷雾后,气相流场内产生了速度亏损和温度亏损,气体出口压力变化不大,液滴运动决定于气流湍流强度和自身惯性力,液滴在气道内的停留时间决定于液滴运动特性和气流湍流强度;逆流喷雾对气流的影响比顺流喷雾时大。仿真结果与文献结果基本一致。

一种网-桁架式海上拦截装置仿真分析

针对海上设施的安全防护问题,提出了一种网-桁架式海上拦截装置,目的是在有效拦截来袭小艇撞击的同时尽量降低对拦截装置本身的损伤.为验证这一装置的有效性,基于显式动力学和欧拉-拉格朗日耦合方法对拦截装置拦截小艇过程进行数值模拟,设定小艇垂直撞击支撑柱、支撑柱间隙和45°撞击支撑柱、支撑柱间隙4种工况,每种工况包含10、20、30 m/s 3种速度.通过对这12组仿真的碰撞力、能量以及破损状态分析,全方位分析了该装置的防撞性能和对小艇的拦截效果.所有工况下该装置都能完成对小艇的拦截,说明这种装置具有优秀的拦截效果.

带椭球形气囊航行体落水-上浮过程仿真

针对水下发射模型试验中的模型低速落水问题,提出一种带椭球形气囊的航行体落水回收方案,两个气囊等距分布在航行体两侧,航行体与气囊之间用连接带相连。数值仿真基于Abaqus的耦合欧拉-拉格朗日方法,通过对比AUV头段入水的试验结果和仿真结果,验证数值方法的有效性。分析在不同姿态角和不同初始囊压的条件下,带气囊航行体低速落水后的运动过程、囊压变化以及连接带的受力情况。研究结果表明,航行体姿态角是影响落水-上浮过程的最重要因素,初始囊压次之;对于最大落水深度、囊压峰值、拉力峰值而言,趋于垂直落水的工况更加危险,最大落水深度为1.33倍航行体长度,最大囊压为3.7倍基准囊压,连接带最大拉力为2.2倍航行体重力。这些结论可为航行体落水回收的方案设计与结构参数设计提供参考依据。

风速对毛豆颗粒流态化行为影响的仿真分析

为了探究不同风速下毛豆颗粒流态化特性,提高速冻效率,基于欧拉-拉格朗日方法给出固体颗粒的运动方程,使用Fluent软件与Rocky颗粒仿真软件,进行毛豆颗粒在不同风速下的气固耦合仿真。结果表明,初始堆积高度100 mm的毛豆的初始流态化速度约为2.0 m/s,流态化过程中,床层边缘和中心区域气泡快速生成、膨胀,随后破裂,并且伴随少量颗粒喷射现象;压降和床层高度均呈现出周期性波动的特征,进入流化状态后,床层高度与进口风速呈正相关,2.6 m/s为最佳流态化风速。研究为食品流态化提供相关理论基础。

基于mixed Lagrangian/Eulerian方法的轮轨滚动接触特性分析

为了缩短有限元方法显式计算轮轨滚动接触的时间,采用mixed Lagrangian/Eulerian方法建立了轮轨滚动接触有限元模型.应用该模型对轮轨接触区的单元进行细化,计算了列车在启动、运行和制动工况下轮轨的接触特性.计算结果表明:不同工况下,轮轨滚动接触区最大Mises应力、最大接触应力和接触斑面积等法向特性变化幅度均在2%以内,但接触区纵向截面中Mises应力分布及纵向剪切应力分布有较大变化;启动和制动工况下,最大Mises应力和最大纵向剪切应力位置均比自由滚动时更接近于轮轨表面;不同工况下,摩擦力大小和方向发生变化,在列车牵引和制动工况中,摩擦力达到极限时轮轨间出现完全滑动,摩擦力方向与滑动方向相反,且不同速度等级下的纵向摩擦力变化幅度也在2%以内.

基于level set的Eulerian-Lagrangian耦合方法及其应用

提出了一种基于水平集的Eulerian-Lagrangian耦合方法,其中Lagrangian方法采用相容显式有限元拉氏方法,Eulerian方法采用基于近似Riemann解的有限体积Eulerian方法,多介质界面处理采用新的水平集和Ghost方法计算.给出了若干数值算例,包括激波管问题以及金属和气体的运动界面及其大变形问题,并分别与精确解和相容显式有限元拉氏方法的计算结果进行了对比.数值结果表明,该方法计算结果正确,精度较高,能够准确捕捉物质界面,适用于处理大变形问题.

基于Lagrangian-Eulerian耦合的放射性物质大气扩散模型研究

针对中尺度扩散下拉格朗日模型和欧拉模型在计算效率和准确度方面的矛盾,建立了适用于模拟核事故下放射性物质大气扩散的基于拉格朗日模型与欧拉模型耦合的预测模型,以国内某核电站为例进行了放射性物质扩散的虚拟算例模拟,对模型进行验证和分析。结果表明:拉格朗日-欧拉耦合模型可以较好地模拟放射性物质在大气中的扩散,不仅可以提升中尺度和大尺度下的计算效率,还可以有效减小欧拉模型初始条件所带来的系统误差。

A hybrid Lagrangian-Eulerian numerical model for sea-ice dynamics

A hybrid Lagrangian - Eulerian （HLE） method is developed for sea ice dynamics, which combines the high computational efficiency of finite difference method （FDM） with the high numerical accuracy of smoothed particle hydrodynamics （SPH）. In this HLE model, the sea ice cover is represented by a group of Lagrangian ice particles with their own thicknesses and concentrations. These ice variables are interpolated to the Eularian gird nodes using the Gaussian interpolation function. The FDM is used to determine the ice velocities at Eulerian grid nodes, and the velocities of Lagrangian ice particles are interpolated from these grid velocities with the Gaussian function also. The thicknesses and concentrations of ice particles are determined based on their new locations. With the HLE numerical model, the ice ridging process in a rectangular basin is simulated, and the simulated results are validated with the analytical solution. This method is also applied to the simulation of sea ice dynamics in a vortex wind field. At last, this HLE model is applied to the Bohai Sea, and the simulated concentration, thickness and velocity match the satellite images and the field observed data well.

Hybrid N-order Lagrangian Interpolation Eulerian-Lagrangian Method for Salinity Calculation

The Eulerian？Lagrangian method（ELM） has been used by many ocean models as the solution of the advection equation,but the numerical error caused by interpolation imposes restriction on its accuracy.In the present study,hybrid N-order Lagrangian interpolation ELM（Li ELM） is put forward in which the N-order Lagrangian interpolation is used at first,then the lower order Lagrangian interpolation is applied in the points where the interpolation results are abnormally higher or lower.The calculation results of a step-shaped salinity advection model are analyzed,which show that higher order（N=3？8） Li ELM can reduce the mean numerical error of salinity calculation,but the numerical oscillation error is still significant.Even number order Li ELM makes larger numerical oscillation error than its adjacent odd number order Li ELM.Hybrid N-order Li ELM can remove numerical oscillation,and it significantly reduces the mean numerical error when N is even and the current is in fixed direction,while it makes less effect on mean numerical error when N is odd or the current direction changes periodically.Hybrid odd number order Li ELM makes less mean numerical error than its adjacent even number order Li ELM when the current is in the fixed direction,while the mean numerical error decreases as N increases when the current direction changes periodically,so odd number of N may be better for application.Among various types of Hybrid N-order Li ELM,the scheme reducing N-order directly to 1st-order may be the optimal for synthetic selection of accuracy and computational efficiency.

Comparisons of some difference forms for compressible flow in cylindrical geometry on arbitrary Lagrangian and Eulerian framework

The study of cylindrically symmetric compressible fluid is interesting from both theoretical and numerical points of view. In this paper, the typical spherical sym- metry properties of the numerical schemes are discussed, and an area weighted scheme is extended from a Lagrangian method to an arbitrary Lagrangian and Eulerian （ALE） method. Numerical results are presented to compare three discrete configurations, i.e., the control volume scheme, the area weighted scheme, and the plane scheme with the addition of a geometrical source. The fact that the singularity arises from the geometri- cal source term in the plane scheme is illustrated. A suggestion for choosing the discrete formulation is given when the strong shock wave problems are simulated.

New Eulerian-Lagrangian Method for Salinity Calculation

A difference scheme in curvilinear coordinates is put forward for calculation of salinity in estuaries and coastal waters, which is based on Eulerian-Lagrangian method. It combines first-order and second-order Lagrangian interpolation to reduce numerical dispersion and oscillation. And the length of the curvilinear grid is also considered in the interpolation. Then the scheme is used in estuary, coast and ocean model, and several numerical experiments for the Yangtze Estuary and the Hangzhou Bay are conducted to test it. These experiments show that it is suitable for simulations of salinity in estuaries and coastal waters with the models using curvilinear coordinates.

FINITE ELEMENT ANALYSIS FOR CHIP FORMATION IN HIGH SPEED TURNING OPERATIONS BY ARBITRARY LAGRANGIAN EULERIAN METHOD

A two-dimensional finite element （FE） model for the high speed turning operations when orthogonally machining AISI H13 tool steel at 49HRC using poly crystalline cubic boron nitride （PCBN） is described. An arbitrary Lagrangian Eulerian （ALE） method has been adopted which does not need any chip separation criteria as opposed to the traditional Lagrangian approach. Through FE simulations temperature and stresses distributions are presented that could be helpful in predicting tool life and improving process parameters. The results show that high temperatures are generated along the tool rake face as compared to the shear zone temperatures due to high thermal conductivity of PCBN tools.

Efficient modeling of cable-pulley system with friction based on arbitrary-Lagrangian-Eulerian approach

In conventional modeling of a cable-pulley system, the cable must be finely meshed with Lagrangian elements for valid contact detections with pulleys, leading to extremely low efficiency. The sliding joint method based on the arbitrary-Lagrangian- Eulerian （ALE） formulation still lacks an efficient cable element, and in particular, modeling of friction between a sliding joint and the cable has not been studied. This paper presents efficient multi-body modeling of a cable-pulley system with friction. A variable- length cable element with a node movable along the cable, which is described with ALE, is developed to mesh the cable. A transitional cable element is then proposed to model the contact part of the cable by fixing its two nodes to the two corresponding locations of the pulley. Friction of the cable-pulley is derived as a simple law of tension decay and embedded in the multi-body system modeling. It is simplified as a generalized friction force acting only on the arc-length coordinate. This approach can use a rough mesh on the cable, and is free of contact detections, thus significantly saving computation time. Several examples are presented to validate the proposed method, and show its effectiveness in real engineering applications.

COMPARISON OF THE EULERIAN AND LAGRANGIAN TIDAL RESIDUALS IN THE BOHAI SEA

Tidal residual is very important to the transport of water particles, nutrients, plankton, etc. in the coastal sea. Eulerian scheme and Lagrangian scheme are two different ways to get the time averaged residual. Solution of the Bohai Sea’s hydrodynamic system using a semi implicit layer averaged numerical model yielded different direction Eulerian and Lagrangian tidal residuals. The latter were stronger than the former in most sea areas. Their different directions produced different circulation pattern in some areas. Compared with the Eulerian residual, the Lagrangian residual seemed to be more in accord with the observation.

A multifractal model for linking Lagrangian and Eulerian velocity structure functions

A multifractal model is developed to connect the Lagrangian multifractal dimensions with their Eulerian counterparts. We propose that the characteristic time scale of a Lagrangian quantity should be the Lagrangian time scale, and it should not be the Eulerian time scale which was widely used in previous studies on Lagrangian statistics. Using the present model, we can obtain the scaling exponents of Lagrangian velocity structure functions from the existing data or models of scaling exponents of Eulerian velocity structure functions. This model is validated by comparing its prediction with the results of experiments, direct numerical simulations, and the previous theoretical models. The comparison shows that the proposed model can better predict the scaling exponents of Lagrangian velocity structure functions, especially for orders larger than 6.

Simulation of sheet metal extrusion processes with Arbitrary Lagrangian-Eulerian method

An Arbitrary Lagrangian-Eulerian(ALE) method was employed to simulate the sheet metal extrusion process,aiming at avoiding mesh distortion and improving the computational accuracy.The method was implemented based on MSC/MARC by using a fractional step method,i.e.a Lagrangian step followed by an Euler step.The Lagrangian step was a pure updated Lagrangian calculation and the Euler step was performed using mesh smoothing and remapping scheme.Due to the extreme distortion of deformation domain,it was almost impossible to complete the whole simulation with only one mesh topology.Therefore,global remeshing combined with the ALE method was used in the simulation work.Based on the numerical model of the process,some deformation features of the sheet metal extrusion process,such as distribution of localized equivalent plastic strain,and shrinkage cavity,were revealed.Furthermore,the differences between conventional extrusion and sheet metal extrusion process were also analyzed.

爆裂轮胎精确建模及其动态特性仿真方法研究

汽车行驶中轮胎突然爆裂是极其危险的行驶工况,但轮胎爆裂过程的准确测试分析难度很大,而其现有仿真方法因需大幅简化使得难以描述轮胎爆裂过程的瞬态特性。针对此问题,本文中提出分别模拟胎内、外空气,且考虑轮胎各种材料失效特性、胎内空气与轮胎车轮总成流-固耦合的汽车轮胎爆裂过程仿真分析方法,实现轮胎滚动中爆胎过程的瞬态动力学特性仿真;并通过对比仿真和理论计算结果,验证仿真模型的正确性;同时,通过计算还获得爆裂轮胎内部空气泄漏规律和路面对轮胎径向力的变化特性,以及轮胎速度、胎压与裂口尺寸对爆胎过程持续时间和轮胎力学特性的影响机理。本文工作聚焦于仿真方法研究,对掌握爆裂轮胎瞬态特性、研究爆胎后整车动力学控制策略具有意义。

Lagrangian time scales and its relationship to Eulerian equivalents in turbulent channel flow

Lagrangian and Eulerian time scales were obtained from the direct numerical simulation of turbulent channel flow at two Reynolds numbers based on the friction velocity and channel half-height, Rer= 80, 100. The Lagrangian integral time scales and time microscales were compared to their Eulerian equivalents. It is found that the ratio of Lagrangian to TL Eulerian integral time scales is given by TE/TiE= 1 ＋ 0.1y＋ for y＋ ≤ 10, and that the ratios between the Lagrangian to theEulerian time microscales are almost the same irrespective of the components. Those increase with y＋ are approximated by ≈ 2.75 - 1.75 exp （-v＋/a） . These results also show that these expressions are independent of the Reynolds number.

A hybrid subcell-remapping algorithm for staggered multi-material arbitrary Lagrangian-Eulerian methods

A new flux-based hybrid subcell-remapping algorithm for staggered multimaterial arbitrary Lagrangian-Eulerian (MMALE) methods is presented. This new method is an effective generalization of the original subcell-remapping method to the multi-material regime (LOUBERE, R. and SHASHKOV,M. A subcell remapping method on staggered polygonal grids for arbitrary-Lagrangian-Eulerian methods. Journal of Computational Physics, 209, 105–138 (2005)). A complete remapping procedure of all fluid quantities is described detailedly in this paper. In the pure material regions, remapping of mass and internal energy is performed by using the original subcell-remapping method. In the regions near the material interfaces, remapping of mass and internal energy is performed with the intersection-based fluxes where intersections are performed between the swept regions and pure material polygons in the Lagrangian mesh, and an approximate approach is then introduced for constructing the subcell mass fluxes. In remapping of the subcell momentum, the mass fluxes are used to construct the momentum fluxes by multiplying a reconstructed velocity in the swept region. The nodal velocity is then conservatively recovered. Some numerical examples simulated in the full MMALE regime and several purely cyclic remapping examples are presented to prove the properties of the remapping method.