Impact response of a circular membrane

The major objective of this study is to investigate the transverse deformation of a finite-circular membrane after normal impact by a blunt projectile. A separation-of-variables technique is used to solve the governing two-dimensional-membrane equation. From observations obtained from a high-speed film of the impact, it is shown that the predicted displacements are in close agreement with experimentation. The theoretical formulation is also supperted by comparison with the experimental results obtained by Beynet and Plunkett, who studied the analogous problem of a thin plate subjected to ballistic impact.     

On analysis of the steady flow in an irrectangular parallel-plate flow chamber

I.IntroductionForthestudyofrelationshipbetweencell'sgrowthandshearstress,thesubjectthatshouldbeworkedoutatfirstishowtosimulateshearstressenvironnlelltwhichsuitcell'sgrowthandofwhichtheshearstresscanbecalculatedconvelliently.NowthePPFCisoneofthemainapparatusesthatsimulatetheshearstressenvironmelltforcell'sgrowthinvitro.Forexample,tilerectangularPPFCisusedforthestudyoftherelationshipbetweentheendotheliumcells'injuryinartery,orplatelet'sadhesionordeformationalldatherosclerosisl3].Apartfromthe…     

A prediction model for the effective thermal conductivity of nanofluids considering agglomeration and the radial distribution function of nanoparticles

Conventional heat transfer fluids usually have low thermal conductivity, limiting their efficiency in many applications. Many experiments have shown that adding nanosize solid particles to conventional fluids can greatly enhance their thermal conductivity. To explain this anomalous phenomenon, many theoretical investigations have been conducted in recent years. Some of this research has indicated that the particle agglomeration effect that commonly occurs in nanofluids should play an important role in such enhancement of the thermal conductivity, while some have shown that the enhancement of the effective thermal conductivity might be accounted for by the structure of nanofluids, which can be described using the radial distribution function of particles. However, theoretical predictions from these studies are not in very good agreement with experimental results. This paper proposes a prediction model for the effective thermal conductivity of nanofluids, considering both the agglomeration effect and the radial distribution function of nanoparticles. The resulting theoretical predictions for several sets of nanofluids are highly consistent with experimental data.     

Prediction of the slug-to-churn flow transition in vertical two-phase flow

An assessment is made of the various viewpoints on the slug-to-churn flow transition in vertical upward flow in the light of recent experimental results obtained at Harwell Laboratory. It is found that the flooding model of McQuillan & Whalley and the bubble entrainment model of Barnea & Brauner give satisfactory results at low and high liquid flow rates, respectively. An improved model for flooding, which takes account of the effect of the falling film, has been proposed. It is shown that this new model is in good agreement with experimental results at both low and high liquid flow rates.     

安全壳中钢衬壳热屈曲问题理论与实验研究（Ⅱ）—实验部分

钢衬壳热屈曲问题是核工程安全壳设计中的主要问题,但实验研究方面的文章发表得不多。文中以２００兆瓦核电站安全壳中钢宙为研究对象,采用局部１：１模型,测得了钢衬壳热屈曲温度和应变载荷,给出了钢衬壳屈曲和初始后屈曲过程中挠度和温度关系。     

悬链线竖向集中力作用下的构形分析和张力计算

目前,悬链线在竖向集中力和均布荷载共同作用下的构形分析和受力计算的理论仍不完善。针对这一问题,通过引入悬链线的几何约束方程、力平衡方程和超越方程,建立了竖向集中力与均布荷载共同作用下的非线性方程组。采用牛顿迭代法求解方程组,得到了悬链线的构形和受力情况。为了验证理论计算的正确性,进行了算例和试验验证。结果表明,算例的计算结果与文献结论保持一致,试验测得的构形和水平张力大小与理论计算的构形和水平张力大小吻合较好。本文的理论计算可以更加简单精确地计算出悬链线在竖向集中力和均布荷载共同作用下的构形和受力情况,为实际工程提供重要的理论指导。     

Shock wave attenuation in partially confined channels

An approximate analytical solution is presented for the attenuation of planar shock waves in channels with perforated walls. The problem is considered as quasi-one-dimensional. Good agreement is found between the theoretical results and available experimental data regarding the rate of shock wave attenuation within the range of initial shock Mach numbers between 1.1 and 4 and perforation ratios between 4.5 × 10^–3 and 0.53. A correlation for the discharge coefficient of a single hole perforation is presented which gives quantitatively good agreement with particular experimental observations.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

The Random Nature of Column Failure

ABSTRACT

An approximate quasi-static theory is developed to predict large plastic deformation and perforation of spherical shells subjected to impact by blunt-ended projectiles at normal incidence. Based on experimental observations for quasi-static load-displacement characteristics, the problem of a spherical shell under normal impact by a flat-ended missile may be analyzed through the solutions to that of an equivalent circular plate struck transversely by the same missile. It is shown that the approximate theoretical predictions with a = 30 (here a is an empirical constant) are in good agreement with experimental data, in terms of maximum permanent transverse displacements and dimple radii. Furthermore, a theoretical formula for ballistic limits of spherical shells under missile impact is presented and the range of applicability of the theory is discussed.     

On the location of flame edge in Shadowgraph pictures of spherical flames: a theoretical and experimental study

In this paper, a theoretical model based on geometrical optics has been developed to analyze the light intensity pattern of Shadowgraph pictures of spherical flames. The theoretical results have been compared with experimental measurement of light intensity profiles across the flame front using commercially available image processing software. These results are in good agreement. The theory predicts that the sudden change of light intensity from dark to bright does not coincide with the flame edge unless the flame thickness is negligible. Experimental results agree very well with the theoretical predictions.     

Investigation of thermocapillary convective patterns and their role in the enhancement of evaporation from pores

The present work investigates the evaporation process from a liquid meniscus formed in capillary tubes of various sizes. A very strong convection within the liquid phase is observed; it is proposed that the non-uniform evaporation from the meniscus leads to a temperature gradient along the interface causing a surface tension gradient, which is the driving mechanism for the convection. The observed convection is shown to be clearly correlated to the evaporation rate and the volatility of the liquid. Unlike Marangoni convection observed by imposing a temperature gradient, this is a self-induced driving gradient caused by evaporative cooling effect.The Marangoni roll in the liquid phase has been visualized and characterized using seeding particles. It is shown in the present study that the observed convection contribute in enhancing the heat–mass transfer from the pore. The experimental results show that when the meniscus recedes inside the pore, the convection slows down and eventually stops. A theoretical model is developed to describe the temperature gradient, which establishes due to the evaporative cooling effect between the centre and the wedge of the meniscus. The results of the model show a good qualitative agreement with the experimental observations.     

Solve a contact problem by optimization method—to calculate the stresses for the softwheel in a harmonic gear

It is difficult to solve the contact problem by usual finite element program. In this paper, we express the contact problem as an optimization problem. In this form we do not need to know all boundary condition in advance. We only need to know the constraint conditions. This method is especially good for solving contact problem. Using this method, we calculate the stresses of the softwheel in the harmonic gear given by Shanghai Jiaotong University, and the results are in good agreement with the experimental results.     

ICE自由面台阶靶数据处理的直接计算方法

斜波压缩台阶靶实验中,不同厚度界面粒子速度历史与材料压缩特性参数存在联系。然而利用普遍采用的数据处理方法无法直接获得该联系。本文中借助特征线理论在建立上述关联的基础上,实现未知EOS下斜波压缩流场的直接计算过程。经数值计算表明,该方法不仅在无强度效应数据处理中能够准确计算理论值,而且在含有强度效应数据处理中也能够较好地逼近理论值,并可在真实实验数据处理中获得与文献符合较好的结果。该研究可为探索具有较完整理论的强度效应数据处理方法提供新途径。     

A constitutive equation of elastic-visco-plasticity for polymers

The rheological behavior and a constitutive relationship of elastic-visco-plasticity for polymers are investigated in this paper. Several sets of experiments have been carried out to determine the material constants and to test the validity of constitutive formulation. It is shown that the theoretical profiles are in good agreement with experimental results. The rheological characteristic and the strain-rate effect of model are analyzed by computer simulation.The project is supported by the National Natural Science Foundation of China     

含热传导的冲击动力学有限元程序的研究与应用

从有限变形的基本框架出发 ,建立了含热传导的冲击动力学基本控制方程和合适的初边条件。应用变分原理和伽辽金方法得出了控制方程相应的有限元列式 ,并探讨了数值计算中的几个关键算法 ,主要包括构型转换、旋转张量的算法、本构算法以及计算流程和程序框图等。利用自行研制的程序 ,对长脉冲激光辐照下靶目标的变形和破坏、冲击压缩变形及变形局部化等问题进行了数值模拟和研究 ,所得结果与实验和理论分析相吻合。     

方管在高速撞击下的能量吸收能力

本文报导了速度约为100m/sec的子弹高速撞击铝合金方管的实验,表明在这种撞击条件下仍与准静态实验中一样,方管仍呈现“开裂与卷曲”的变形破坏模式,并证实了在高速碰撞下方管仍是一种极好的能量吸收装置.理论分析表明,在这种撞击条件下惯性力仍是不重要的;计入了应变率效应之后,理论预计的方管承载能力与实验符合良好.     

A theoretical analysis for the dynamic axial crushing behaviour of aluminium foam-filled hat sections

A theoretical analysis was performed to predict the dynamic axial crushing behaviour of aluminium foam-filled top hat and double hat sections made from mild steel material. The deformation mode from the test results was used to create a deformation model for the theoretical analysis. According to the energy method and the superfolding element theory, the mean dynamic crushing loads of the aluminium foam-filled hat sections and the interactive effect between the aluminium foam and hat sections were theoretically predicted. The mean dynamic crushing loads and the interactive effect predicted by this theoretical analysis were in good agreement with the experimental results. The theoretical prediction results showed that the interactive effect was mainly from the aluminium foam.     

柱状装药爆炸条件下厚壁圆筒爆室内 流场及结构动力响应分析

借助非线性动力有限元程序ANSYS/LS-DYNA,采用基于罚函数的流固耦合算法,对厚壁圆筒爆 室在柱状装药爆炸作用下的动态响应过程进行了数值模拟研究。分析了厚壁圆筒爆室内柱状装药爆炸非定 常流场的演化过程以及筒体的动力响应特征。给出了爆炸流场的压力云图、筒壁受到的爆炸压力峰值及冲量 的分布规律、筒体的等效应力云图以及等效应力的分布规律等。流场压力及筒体应变的计算结果与实测结果 吻合较好,并将动力响应的有限元计算结果与理论解进行了比较,证明轴对称平面应变假设下的理论解可以 给出问题的保守估算。分析表明,该厚壁圆筒爆室在柱状装药爆炸作用下在弹性范围内工作,爆室的强度设 计是安全的。     

Adaptive computation of aeroacoustic sources for a rudimentary landing gear

We present our simulation results for the benchmark problem of the flow past a rudimentary landing gear using a General Galerkin FEM, also referred to as adaptive DNS/LES. In General Galerkin, no explicit subgrid model is used; instead, the computational mesh is adaptively refined with respect to an a posteriori error estimate of a quantity of interest in the computation, in this case, the drag force on the rudimentary landing gear. Turbulent boundary layers are modeled using a simple wall‐layer model with the shear stress at walls proportional to the skin friction, which here is assumed to be small and, therefore, can be approximated by zero skin friction. We compare our results with experimental data and other state of the art computations, where we find good agreement in sound pressure levels, surface velocities, and flow separation. We also compare with detailed surface pressure experimental data where we find largely good agreement, apart from some local differences for which we discuss possible explanations. Copyright © 2013 John Wiley & Sons, Ltd.     

Drag increment of internal waves generated by horizontally moving spheroid in supercritical regime

A theory on the drag increment of internal waves with a spheroid moving horizontally at a high velocity （or for large internal Froude number） in uniformly vertically stratified fluid （or ocean） is presented in the present paper. A surface source distribution is employed to model a hydrodynamic interaction between the spheroid and the stratified fluid. From theoretical results, it is shown that there exists an asymptote of zero-drag increment in supercritical regimes, where internal Froude numbers are larger than the critical internal Froude numbers. When the spheroid reduces to a sphere, the results in this paper is in good agreement with the previous theoretical and experimental results of the sphere.