A General Cavitation Model for the Highly Nonlinear Mie-Grüneisen Equation of State

A general one-fluid cavitation model is proposed for a family of Mie-Grüneisen equations of state (EOS), which can provide a wide application of cavitation flows, such as liquid-vapour transformation and underwater explosion. An approximate Riemann problem and its approximate solver for the general cavitation model are developed. The approximate solver, which provides the interface pressure and normal velocity by an iterative method, is applied in computing the numerical flux at the phase interface for our compressible multi-medium flow simulation on Eulerian grids. Several numerical examples, including Riemann problems and underwater explosion applications, are presented to validate the cavitation model and the corresponding approximate solver.     

Nonstationary wave turbulence

Summary Nonstationary regimes of the wave turbulence evolution are considered in the framework of isotropic kinetic equation. It is predicted analytically and confirmed by numerical experiment that there is a class of wave systems in which any initial distribution of the turbulence energy ink-space comes into a universal, Kolmogorovtype spectrum in a finite time. Before and after the formation of the Kolmogorov spectrum, two different self-similar regimes of evolution occur: the first one is responsible for explosively forming the universal spectrum and the second one determines energy dissipation.     

基于Visco-SCRAM模型的侵彻装药点火研究

针对弹体侵彻过程中装药的安全性,基于黏弹性统计裂纹力学(visco-statistical crack mechanics, Visco-SCRAM)模型计算装药整体温升、装药裂纹摩擦生热以及弹体装药与壳体摩擦生热,考察这3种机制对装药温升的贡献以及侵彻装药的点火机制,得到了装药点火对应的弹体侵彻临界初始速度。结果表明：(1)装药与弹体内壁摩擦生热对装药温升有一定贡献,随着弹体初始撞击速度的提高,摩擦生热对温升的贡献逐渐增大;(2)黏性、损伤和绝热体积变化导致的装药整体温升对装药点火的作用有限; (3)裂纹摩擦形成热点是侵彻装药点火的物理机制;(4)采用Visco-SCRAM模型可预测低强度、长脉冲载荷作用下的装药点火响应。

     

土中爆炸波与地下结构相互作用计算方法研究综述

土中爆炸波与结构相互作用是地下工程结构抗爆计算的理论基础,理论研究中通常在宏观试验基础上,引入合理的介质动力本构模型分析波动问题。针对工程防护中的计算模型和解析方法,综述了岩土介质中爆炸波与结构相互作用的现状和研究进展,内容包括土的动力本构模型,自由场中爆炸波的传播、爆炸波与箱型、圆柱形和直墙圆拱型等地下结构的相互作用等。重点阐述了常用的非饱和土和饱和土的动力本构模型、考虑松弛效应的土的综合弹塑性模型,一维平面波在不均匀介质和分层介质中的传播及地下结构爆炸荷载计算方面的研究成果,分析了各种模型和计算方法的适用范围和存在问题。

     

应用浮动冲击平台考核舰载设备响应分析

为研究安装甲板模拟器的浮动冲击平台系统考核舰载设备的机理,对整个系统建立有限元模型进行数值模拟并建立力学模型进行了理论分析。根据船体甲板结构产生的垂向低通滤波特性,提出甲板模拟器具有减缓高频冲击并满足设备安装频率要求的作用。将被试设备的浮动冲击平台考核系统简化为有阻尼的三自由度系统强迫振动模型,通过拉普拉斯变换方法求解了不同冲击环境下被试设备的响应。数值模拟与理论计算结果比较吻合,被试设备响应迅速达到峰值后逐渐衰减,振动频率由高频向低频过渡,在分析浮动冲击平台舰载设备考核系统长时间响应时需考虑阻尼的影响。

     

Comparison of implicit and explicit AUSM‐family schemes for compressible multiphase flows

This paper makes the first attempt of extending implicit AUSM‐family schemes to multiphase flow simulations. Water faucet, air–water shock tube and oscillating manometer problems are used as benchmark tests with the generic four‐equation two‐fluid model. For solving the equations implicitly, Newton's method along with a sparse matrix solver (UMFPACK solver) is employed, and the numerical Jacobian matrix is calculated. Comparison between implicit and explicit AUSM‐family schemes is presented, indicating that similarly accurate results are obtained with both schemes. Furthermore, the water faucet problem is solved using both staggered and collocated grids. This investigation helps integrate high‐resolution schemes into staggered‐grid‐based computational algorithms. The influence of the interface pressure correction on the simulation results is also examined. Results show that the interfacial pressure correction introduces numerical dissipation. However, this dissipation cannot eliminate the overshoots because of the incompatibility of numerical discretization of the conservative and non‐conservative terms in the governing equations. The comparison of CPU time between implicit and explicit schemes is also studied, indicating that the implicit scheme is capable of improving the computational efficiency over its explicit counterpart. Copyright © 2014 John Wiley & Sons, Ltd.     

An approach to control the spurious currents in a multiphase lattice Boltzmann method and to improve the implementation of initial condition

Multiphase lattice Boltzmann methods are known to generate spurious or parasitic currents at the fluid–fluid interfaces. This nonphysical phenomenon has to be avoided, or at least controlled, in order to achieve reliable solutions. In this article, a method to control these fictitious velocities via lattice refinement is proposed, which is based on interface thickness control for which both the spurious currents and the physical fluid–fluid interface thickness vanishes as the spatial resolution increases. It has been found that a proper interface thickness adjustment is required as the lattice refinement is applied, or an increase in spurious currents, instead of a reduction, can occur. By combining the new method with an appropriate multiphase flow initialization, the overall stability for high density O(1000) and viscosity O(100) ratios is greatly improved. Although this research has been conducted with a Rothman and Keller type lattice Boltzmann model, it is believed that other types of multiphase lattice Boltzmann models could benefit from the basic ideas underlying this research. Copyright © 2015 John Wiley & Sons, Ltd.     

刻槽式MEFP的成形及侵彻钢靶模式

多爆炸成形弹丸(MEFP)能有效提高炸药利用率和命中概率。基于LS-DYNA软件对刻槽式MEFP战斗部成形及侵彻双层无间隔钢靶模式进行了研究,得到了刻槽式MEFP战斗部成形及对靶板侵彻的数值计算结果。结果表明:刻槽式MEFP成形过程要经过翻转、头部挤压断裂、尾部拉伸断裂、交叉飞散、稳定飞行5个阶段, 聚能爆轰波对药型罩的径向力是其交叉飞散的主要原因;侵彻过程要经过开坑、联合侵彻、贯穿3个阶段。模拟结果与实验结果基本吻合。     

小尺寸管道内二氧化碳抑制甲烷爆炸效果的实验及数值模拟

为了有效防治矿井瓦斯爆炸事故, 以瓦斯的主要成分甲烷作为模拟气体, 运用自主设计改装的XKWB-S型小尺寸石英玻璃管道实验系统, 结合高速摄影仪, 并采用FLACS数值模拟软件, 研究惰性气体抑爆条件下甲烷燃烧爆炸特性, 进行体积分数为6%~27%的CO₂抑制体积分数为9%CH₄爆炸的实验及数值模拟, 结果表明:各组分混合气体在爆炸传播过程中, 爆炸压力、火焰锋面速度和气体运动速度均呈现一定程度的波动, 且压力和速度没有同时达到最大值; CO₂的加入有效抑制了甲烷/空气反应, 且添加CO₂体积分数越大, 抑爆效果越明显, 模拟结果与实验结果基本吻合。     

水/气多介质问题的界面处理方法

针对不可压缩可压缩水/气多介质问题, 提出一种新的界面处理方法。在可压缩水/气界面处构造Riemann问题, 在水中设音速趋于无穷大, 求解Riemann问题得到不可压缩可压缩水/气界面处流体的准确流动状态; 然后以此状态结合GFM(ghost fluid method)方法分别为2种流体定义界面边界条件, 将两相流问题转化为单相流问题计算, 通过求解level set方程来跟踪界面的位置。对各种不同的界面边界条件定义方法进行了比较, 数值模拟结果表明算法能准确地捕捉各类间断的位置, 证明了算法的有效性和稳健性。