激光与材料相互作用研究中的气体物理学

强激光辐照材料时,烧蚀蒸气吸收部分或全部激光辐射,成为部分离化等离子体.它的传播称为激光支持的吸收波(LSAW).LSAW屏蔽入射激光,同时发射易被材料表面吸收的短波长辐射.研究这些过程,可用辐射流体力学描述蒸气的运动。为了求解辐射流体力学方程,必须利用气体物理力学方法,算出蒸气的状态方程和不透明度.本文对涉及的一些气体物理力学问题,进行了概略介绍.      

核武器研制中的力学问题

 简要介绍了核武器研制中遇到的力学问题,涉及固体力学、流体力学、化学反应流体力学、辐射流体力学等学科.介绍了核武器研制中力学问题的特点, 即与各种物理问题的强耦合, 学科的交叉.     

《力学名词》已定稿付印

<正> 经过7年的工作,《力学名词》(第一批)已审定、定稿付印,将在1993年公布.这次公布的名词,共2500多条,分成5个部分:通用词(普通物理中力学部分、理论力学和材料力学),一般力学,固体力学,流体力学,以及其他(交叉,应用学科和新分支).除了委员会成员的工作外,学会一些专业会议(如“三流”专业会议)和个人(如梅凤翔)提供了不少有用的材料.定     

《力学名词》已定稿付印

经过7年的工作,《力学名词》(第一批)已审定、定稿付印,将在1993年公布.这次公布的名词,共2500多条,分成5个部分:通用词(普通物理中力学部分、理论力学和材料力学),一般力学,固体力学,流体力学,以及其他(交叉,应用学科和新分支).除了委员会成员的工作外,学会一些专业会议(如“三流”专业会议)和个人(如梅凤翔)提供了不少有用的材料.定     

国际计算力学协会(IACM)将举行第二届计算力学会议(WCCM)

由国际计算力学协会举办的第二届计算力学世界大会(World Cougress on Computational Mechanics)将于1990年8月27—31日在西德斯图加特举行.征稿内容包括固体力学、流体力学、应用物理与化学、计算机及数值方法四大部分.该大会的联系人姓名、地址为:     

国际计算力学协会(IACM)将举行第二届计算力学会议(WCCM)

<正> 由国际计算力学协会举办的第二届计算力学世界大会(World Cougress on Computational Mechanics)将于1990年8月27—31日在西德斯图加特举行.征稿内容包括固体力学、流体力学、应用物理与化学、计算机及数值方法四大部分.该大会的联系人姓名、地址为:     

爆室内强爆炸中的流固耦合计算

为评估强爆炸的毁伤效应,在已有的辐射流体力学及结构动力学响应部分工作的基础上,本文采用流固耦合方法对耦合界面进行了处理,并考虑辐射输运引起的能量沉积过程,使得强爆炸产生的辐射波、冲击波和结构动力学响应两部分可以较好地耦合计算,从而能够较完整地模拟爆室内强爆炸的辐射流体动力学过程.计算结果与定性物理分析相符,证明了算法的...     

与实验固体力学有关的几个光学问题

.前言力学与光学都是较成熟的学科,过去两个学科虽自独立地发展,但从历史角度来看光学经常是由于力学技术的发展而被促进.近年来,激光技术结合空气动力学创造出强有力的高能激光器,它为瞬间摧毁敌机或导弹提供可能手段.激光核聚变应用了流体力学、磁流体力学理论,再结合其他学科理论提出了向心压缩聚爆理论,所需加热激光能量大大减少,从而提供了一条获得聚变能的可能途径.同样,激光技     

关于流体力学方法论问题

 力学是以实验为基础的科学. 流体力学中绝大多数重要的概念和原理都源于实验. 对 于流体力学问题，数值模拟与物理实验的本质区别并未消失；数值模拟不能代替物理实验， 大规模数值模拟的结果仍需由巧妙设计的物理实验来检验其正确性.     

工程力学要为我国经济建设服务

今天和大家座谈,我想讲下面四个问题:1.什么是工程力学?物理学家认为,力学是物理的一部分.这是指古典力学而言的.但工程力学不同于古典力学.十九世纪古典力学基本上处于停滞阶段.Love 教授关于弹性力学的书及 Lamb 教授关于流体力学的书是前一时期固体力学与流体力学的发展最高水平的总结.本世纪二十、三十年代,用已有的理论和方法已不能解决工 ...     

High‐order discontinuous Galerkin nonlocal transport and energy equations scheme for radiation hydrodynamics

The nonlocal theory of the radiative energy transport in laser‐heated plasmas of arbitrary ratio of the characteristic inhomogeneity scale length to the photon mean free paths is applied to define the closure relations of a hydrodynamic system. The corresponding transport phenomena cannot be described accurately using the Chapman–Enskog approach, that is, with the usual fluid approach dealing only with local values and derivatives. Thus, we directly solve the photon transport equation allowing one to take into account the effect of long‐range photon transport. The proposed approach is based on the Bhatnagar–Gross–Krook collision operator using the photon mean free path as a unique parameter. Such an approach delivers a calculation efficiency and an inherent coupling of radiation to the fluid plasma parameters in an implicit way and directly incorporates nonequilibrium physics present under the condition of intense laser energy deposition due to inverse bremsstrahlung. In combination with a higher order discontinuous Galerkin scheme of the transport equation, the solution obeys both limiting cases, that is, the local diffusion asymptotic usually present in radiation hydrodynamics models and the collisionless transport asymptotic of free‐streaming photons. In other words, we can analyze the radiation transport closure for radiation hydrodynamics and how it behaves when deviating from the conditions of validity of Chapman–Enskog method, which is demonstrated in the case of exact steady transport and approximate multigroup diffusion numerical tests. As an application, we present simulation results of intense laser‐target interaction, where the radiative energy transport is controlled by the mean free path of photons. Copyright © 2016 John Wiley & Sons, Ltd.     

岩土类颗粒物质宏-细观力学研究进展

岩土类颗粒物质在自然界、工程建设以及日常生活中普遍存在,其运动特性的研究在力学界已经开展了几十年.在近20年开展的一系列小尺寸物理实验中,颗粒物质表现出许多新奇现象,人们从物理角度开展了系统研究,在统计力学中,颗粒固体的流体动力学等理论研究以及实验检测技术等方面都取得突破性进展,深刻地揭示了颗粒材料的物理机制,促使力学...     

DISSIPATION MECHANICS AND EXACT SOLUTIONS FOR NONLINEAR EQUATIONS OF DISSIPATIVE TYPE—PRINCIPLE AND APPLICATION OF DISSIPATION MECHANICS(Ⅰ)

This work is the continuation and the distillation of the discussion of Refs. [1-4].(A)From complementarity principle we build up dissipation mechanics in this paper.It is a dissipative theory of correspondence with the quantum mechanics.From this theorywe can unitedly handle problems of macroscopic non-equilibrium thermodynamics andviscous hydrodynamics. and handle each dissipative and irreversible problems in quantummechanics.We prove the basic equations of dissipation mechanics to eigenvalues equationsof correspondence with the Schr(?)dinger equation or Dirac equation in this paper.(B)We unitedly merge the basic nonlinear equations of dissipative type, especially theNavier-Stokes equation as a basic equation for macroscopic non-equilibrium ther-modynamics and viscous hydrodynamics into integrability condition of basic equation ofdissipation mechanics. And we can obtain their exact solutions by the inverse scatteringmethod in this paper.     

二维拉氏辐射流体力学人为解构造方法

人为构造解方法是复杂多物理过程耦合程序正确性验证的重要方法之一,适用于二维拉氏大变形网格的流体、辐射耦合人为解模型较为少见。针对拉氏辐射流体力学程序正确性验证的需要,从二维拉氏辐射流体力学方程组出发,基于坐标变换技术,给出了拉氏空间到欧氏空间的物理变量导数关系式,开展了辐射流体耦合的人为解构造方法研究,构造了一类质量方程无源项的二维人为解模型,并应用于非结构拉氏程序LAD2D辐射流体力学计算的正确性考核,为流体运动网格上的辐射扩散计算提供了一种有效手段。数值结果显示观测到的数值模拟收敛阶与理论分析一致。     

2D radiation-hydrodynamics modeling of laser-plasma targets for ion stopping measurements

Two-dimensional radiation hydrodynamics calculations were performed to analyze how a homogeneous plasma layer for ion-stopping measurements can be created by direct laser irradiation of thin carbon foils. At the initial stage, the assumed (so as to imitate the discussed experimental conditions) strongly non-uniform intensity distribution in the laser spot leads to the formation of relatively dense and cold clumps in the plasma. However, it is shown that after several nanoseconds the clumpy structure dissipates predominantly due to the energy transport by thermal radiation. Laser irradiation schemes with the fundamental and doubled frequency light, as well as one- and two-sided heating of the target foil are analyzed and compared. We find that the two-sided irradiation with the doubled laser frequency creates a fully ionized plasma layer and allows to reduce the plasma column-density variations to a level of ?1%.     

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一定长度的薄壁构件在纵向或横向荷载作用下，未达到材料极限破坏前就有 可能发生弹性弯扭屈曲失稳的问题. 分析了工字型截面悬臂钢梁的此类问题，应用平衡 法和能量法导出构件在轴向和横向荷载作用下的弹性弯扭屈曲微分方程，利用里兹法求其临 界载荷，并确定截面固定时的极限特征长度.     

A numerical method to simulate turbulent cavitating flows

The objective of this paper is to develop a numerical method for simulating multiphase cavitating flows on unstructured grids. The multiphase medium is represented using a homogeneous mixture model that assumes thermal equilibrium between the liquid and vapor phases. We develop a predictor–corrector approach to solve the governing Navier–Stokes equations for the liquid/vapor mixture, together with the transport equation for the vapor mass fraction. While a non-dissipative and symmetric scheme is used in the predictor step, a novel characteristic-based filtering scheme with a second order TVD filter is developed for the corrector step to handle shocks and material discontinuities in non-ideal gases and mixtures. Additionally, a sensor based on vapor volume fraction is proposed to localize dissipation to the vicinity of discontinuities. The scheme is first validated for simple one dimensional canonical problems to verify its accuracy in predicting jump conditions across material discontinuities and shocks. It is then applied to two turbulent cavitating flow problems – over a hydrofoil using RANS and over a wedge using LES. Our results show that the simulations are in good agreement with experimental data for the above tested cases, and that the scheme can be successfully applied to both RANS and LES methodologies.     

AN APPROXIMATE ANALYSIS OF FREQUENCY RESPONSE OF A CRACKED HINGEDHINGED BEAM

A new method based on a modified line-spring model is developed forevaluating the natural frequencies of vibration of a cracked beam.This model inconjunction with the Euler-Bernoulli beam theory,modal analysis and linear elasticfracture mechanics is applied to obtain an approximate characteristic equation of acracked hinged-hinged beam.By solving this equation the natural frequencies aredetermined for different crack lengths in different positions.The results show goodagreement with the solutions through finite element analysis.The present method maybe extended to analyze other cracked complicated structures with various boundaryconditions.     

功能梯度板的非线性动力分析

非线性材料功能梯度板件的动力分析是属于在数学方程上同时具有变系数、非线性、非定常特征的固体力学问题.文中首先将问题的变系数非线性偏微分方程组转化为各向异性常系数非线性常微分方程,然后用小参数法求得解析解,适用于各种形状、边界及功能梯度分布的板件非线性弹性振动分析.