单次脉冲爆轰发动机工作过程的数值模拟

通过求解14组分和19个基元反应的CH4-O2-N2详细化学反应动力学机理的二维轴对称Navier-Stokes方程,对爆轰管内半球形高温火团引发的爆轰过程和爆轰波进入外流场后的全流场分布进行数值模拟。模拟结果显示了爆轰波在管内的成长、稳定传播、进入尾喷管后衰减为激波和进入外流场的全过程,以及爆轰管出口端附近区域的复杂涡与激波的相互作用。对轴线上的压力分布和封闭端的压力等进行了讨论,为脉冲爆轰发动机的开发研制提供参考信息。     

Approximate solution for the temperature field of 1-D soil freezing process in a semi-infinite region

Unfrozen liquid water always exists in the humid soil system below freezing point, and the amount of the unfrozen water decreases continuously with the temperature decreasing. This phenomenon is a special characteristic for the freezing of the humid soil system. The temperature field of 1-D soil freezing process in a semi-infinite region has been studied. The problem is a Stefan-like problem. After the continuous phase change process of soil water is divided into a finite number of substeps, the Stefan problem of a multi-phase material is obtained. A similarity solution is found and determined. In order to get the right solution of the nonlinear equations, a variable substitution technique is introduced. The approximate solution is verified by the numerical results of the continuous phase change model of soil freezing process. Finally, for practical purpose, the advancing factor of the freezing front and the mean squared error of the temperature caused by the measurement errors are defined. Computational examples concerning the effect of different parameters on the advancing factor of the freezing front and the effect of the measurement errors on the accuracy of the solution are presented and discussed.     

入水后爆炸问题的数值模拟技术

应用各种数值计算方法及计算处理技术,编制程序实现了对弹体入水后爆炸问题全过程的数值模拟.其中弹体与水,爆轰产物气体与弹壳之间的相互作用通过流固耦合技术来描述;水面与空气、爆轰产物与水、空气之间的相互作用采用VOF方法(Volume-of-Fluid)来描述;采用了刚体-柔体转换、单元失效删除等计算技术以更高效、更好地模...     

Numerical simulation of a fluid-saturated soil under a dynamically loaded pile

The behaviour of the soil under a dynamically loaded pile toe is studied. The soil is modelled as a fluid saturated porous continuum. The constitutive behaviour of the solid skeleton is described by the elasto-plastic model of Drücker-Prager. The wave propagation is simulated with a dynamical finite-element program.A two-phase model of soil gives useful information about effective stress and pore pressure in the soil. In saturated soil the main wave under the pile toe propagates more downards than in dry soil, due to the higher compressional stiffness in saturated soil. The plastic zone under the pile toe propagates with the velocity of the fast compressional wave. The pore fluid influences the plasticity strongly and can be expected to affect pile driving too.The distribution of effective stress and pore pressure under the pile toe depends on the permeability of the soil and cannot be calculated uniquely from a single-phase calculation. Therefore, a nonlinear soil cannot be modelled correctly as a conventional single-phase material.     

Numerical simulation of explosion processes in fronzen soil

At present, there are numerous experimental and theoretical papers concerned with the behavior of soft soils under explosive loading; e.g., see [1–5]. The case of frozen soils is quite different. There are known only a few papers presenting the results of experimental [6–8] and numerical [9, 10] studies. The numerical results were obtained by solving one-dimensional problems on the explosion of a spherical charge. In the present paper, we give the results of numerical studies of wave processes caused by the explosion of a spherical charge in a homogeneous or layered frozen soil with allowance for the free surface and the finite depth of the freezing boundary. Frozen and soft soils are modeled by Grigoryan’s medium with irreversible bulk and shear strains. We analyze how the free boundary and the interface affect the wave parameters. The results of numerical calculations are compared with known experimental data.     

饱和土中爆炸波传播问题的数值模拟

应用流体弹塑性力学的框架描述了爆炸荷载作用下饱和土介质的本构模型,包括体积压缩关系和强度关系。应用LS-dyna软件分析了三相饱和土介质中的爆炸波传播及其与结构的相互作用问题,并与先前完成的试验结果进行了对比,两者吻合较好。饱和土中爆炸波传播的一些特殊现象被重现,表明本构模型的描述是可行的。     

依兰陨石坑形成过程数值模拟研究

基于iSALE-2D仿真代码对依兰陨石坑的形成过程进行了研究,采用欧拉算法开展数值模拟,探讨了依兰陨石坑的撞击条件,统计分析了成坑过程中熔化层的形成与分布规律,结合点源成坑相似律模型,拟合得到强度机制下的成坑半径关系式。研究结果表明一颗直径120 m、撞击速度12 km/s的花岗岩质小行星垂直撞击地表形成一个与依兰陨石坑形态相似的陨石坑,再现了成坑形成的3个阶段：接触与压缩阶段、开坑阶段、后期调整阶段。大部分熔体在坑底呈分层堆叠分布,少量熔体随抛射物沉积在靶体表面,呈离散状分布,完全熔化材料质量约为撞击体质量的24倍。直径120 m、撞击速度12 km/s工况模拟结果与拟合的成坑半径关系式结果相对误差10.3%。     

脆性材料动态破坏过程的数值模拟

根据连续介质力学基本原理和离散元法基本思想，针对脆性材料动态破坏过程问题，推导出基于圆盘单元的正交各向异性离散元二维计算模型，并利用此模型计算了各向异性薄板在冲击载荷下的应力波传播问题。通过将计算结果与LS－DYNA程序相比较，表明了本文提出的离散元模型的精确性。另外，对钢弹侵彻下滑凝土圆板破坏过程这个典型的发生连续介质向非连续介质转化的动力学问题进行了数值模拟和动画显示，并同侵彻实验中出现的几种破坏形式进行了分析和对比，从而证明了本计算方法是计算和模拟脆性材料出现从连续介质向非连续介质转变的动态破坏问题的有力工具。     

Numerical simulation of coupled heat-fluid transport in freezing soils using finite volume method

A solution procedure using finite volume method has been established for the coupled heat-fluid transport model of freezing soils, and details about determination of the time step interval and discretization at special nodes have been introduced. Comparison between the simulation and the freezing experiments of silica flour and Zhangye loam has been conducted, and the calculated results are in general agreement with the experimental data. The research indicates that the moisture migration in the frozen zone is insignificant, and water mainly migrates from the frozen zone to the vicinity of the moving freezing front; the moving velocity of the freezing front has a great effect on the extent of moisture accumulation to the freezing front, and high extent of accumulation occurs when the freezing front advances slowly. Finally, an apparent heat capacity model has been suggested for the temperature calculation of the soil freezing process in low water content conditions; however, when the moisture migration is significant, water redistribution during the freezing process should be considered.     

Numerical simulation of pore-scale flow in chemical flooding process

Chemical flooding is one of the effective technologies to increase oil recovery of petroleum reservoirs after water flooding. Above the scale of representative elementary volume (REV), phenomenological modeling and numerical simulations of chemical flooding have been reported in literatures, but the studies alike are rarely conducted at the pore-scale, at which the effects of physicochemical hydrodynamics are hardly resolved either by experimental observations or by traditional continuum-based simulations. In this paper, dissipative particle dynamics (DPD), one of mesoscopic fluid particle methods, is introduced to simulate the pore-scale flow in chemical flooding processes. The theoretical background, mathematical formulation and numerical approach of DPD are presented. The plane Poiseuille flow is used to illustrate the accuracy of the DPD simulation, and then the processes of polymer flooding through an oil-wet throat and a water-wet throat are studies, respectively. The selected parameters of those simulations are given in details. These preliminary results show the potential of this novel method for modeling the physicochemical hydrodynamics at the pore scale in the area of chemical enhanced oil recovery.     

Numerical simulation of convective flows in a soil during the evaporation of water containing a dissolved admixture

The concentration profile is investigated for a solution that saturates a low-permeability soil. The simulation results showed the presence of three flow regimes. The salt accumulated near the phase transition boundary increases the solution density and may lead to the development of natural concentration-induced convection which interacts with the rising flow (forced convection). The stability threshold of the forced flow and the effect on it of natural convection that arises are determined. It is shown that at intense flow to the evaporation surface the admixture concentration increases at this boundary rapidly and reaches the saturation concentration. In this case, the admixture precipitates. In the slow evaporation regime the admixture diffuses from the high-concentration region, which prevents the development of convective flow.     

纤维复合材料损伤过程的数值模拟

利用界面断裂力学和有限元法数值模拟纤维增强复合材料的细观损伤过程，研究各种主要破坏模式之间的相互转变和影响，指出以断裂能和混合度表示的界面性能是控制复合材料损伤过程的主要细观参数。分析了界面韧度对破坏性能的影响，探讨了基于破坏模式控制的复合材料韧度设计的新途径。     

Numerical simulation of mushrooms during freezing using the FEM and an enthalpy: Kirchhoff formulation

The shelf life of mushrooms is very limited since they are susceptible to physical and microbial attack; therefore they are usually blanched and immediately frozen for commercial purposes. The aim of this work was to develop a numerical model using the finite element technique to predict freezing times of mushrooms considering the actual shape of the product. The original heat transfer equation was reformulated using a combined enthalpy-Kirchhoff formulation, therefore an own computational program using Matlab 6.5 (MathWorks, Natick, Massachusetts) was developed, considering the difficulties encountered when simulating this non-linear problem in commercial softwares. Digital images were used to generate the irregular contour and the domain discretization. The numerical predictions agreed with the experimental time–temperature curves during freezing of mushrooms (maximum absolute error <3.2°C) obtaining accurate results and minimum computer processing times. The codes were then applied to determine required processing times for different operating conditions (external fluid temperatures and surface heat transfer coefficients).     

Numerical simulation of transient thermal field in laser melting process

Numerical simulation of thermal field was studied in laser processing. The 3-D finite element model of transient thermal calculation is given by thermal conductive equation. The effects of phase transformation latent are considered. Numerical example is given to verify the model. Finally the real example of transient thermal field is given.     

冲击载荷下孔隙塌缩过程的数值模拟

爆炸压实过程中多孔体的孔隙闭合程度对压实效果起着决定性作用。利用LS-DYNA有限元程序,对无氧铜中的圆形孔隙塌缩过程进行了数值模拟。根据模拟结果分析得出,在6 GPa的冲击压力下,孔隙闭合时不同边界区域会发生爆炸焊接和射流侵彻,这2种结合机理可以使材料结合更牢固,提高材料的致密度和机械强度,实现高质量的爆炸压实。     

Numerical simulation of the process of autoregulation of the arterial blood flow

For describing the autoregulation of the blood flow in an artery under constant transmural pressure a mathematical model that takes into account the multilayer structure of the arterial wall, the diffusion and kinetic processes in the wall, and the nonlinear viscoelastic properties of the wall material is proposed. The limiting case of a thin-walled artery is studied analytically. The arterial-wall viscosity range on which the equilibrium state of the system is stable is estimated. Accurate stationary distributions of the nitric oxide, calcium and myosin concentrations in the arterial wall are found. Numerical simulation of the autoregulation process demonstrated the possibility of arterial adaptation to radius perturbations, the existence of slow oscillations, and system transition to a new equilibrium state with change in blood flow level. The results are in good agreement with the experimental data.     

Numerical simulation of the galvanizing process during GA to GI transition

This paper presents the application of a three‐dimensional finite element solution algorithm for the prediction of the velocity, temperature and species concentration fields in an industrial continuous galvanizing bath. Simulations were carried out using a parallel CFD software developed at IMI‐NRC. The turbulent flow, heat and mass transfer has been solved using a high Reynolds number k–ε model. Simulations were carried out for the case when the density of the molten metal depends only on the temperature and also for the case when both temperature and Al concentration affect the density. When considering the buoyancy effect of the Al concentration, differences are especially apparent during the melting of ingots with high Al content. Otherwise, thermal effects are dominant. The continuous monitoring of the temperature and the Al and Fe content in an industrial bath was used to validate the flow, temperature and compositional variations. A period of three hours, corresponding to three different ingot additions, was simulated successfully, resulting in a good agreement of the temperature and compositional variations. Copyright © 2006 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.     

Numerical simulation of cerebrospinal fluid hydrodynamics in the healing process of hydrocephalus patients

Three-dimensional computational models of the cerebrospinal fluid (CSF) flow and brain tissue are presented for evaluation of their hydrodynamic conditions before and after shunting for seven patients with non-communicating hydrocephalus. One healthy subject is also modeled to compare deviated patients data to normal conditions. The fluid-solid interaction simulation shows the CSF mean pressure and pressure amplitude (the superior index for evaluation of non-communicating hydrocephalus) in patients at a greater point than those in the healthy subject by 5.3 and 2 times, respectively.     

岩石试样弹塑性破裂过程的数值模拟分析

依据岩土类材料的非匀质性特性,并采用对材料参数进行随机赋值的方法研制了弹塑性破裂过程数值分析程序,并用实例证明了程序的可靠性。应用该程序对岩石试样弹塑性破裂过程进行数值模拟研究．分析表明：数值模拟结果与试验研究结果是吻合的。从而为工程岩体断裂分析提出了一种可能的方法与途径。