Cell vertex finite volume discretizations in three dimensions

The cell vertex method is generalized to three dimensions. It is proved that there exists a one-parameter family of eight-point three-dimensional methods with second-order truncation error on parallelepipeds. Using different triangulations of control volume faces, various finite volume methods are derived. Some of these are identified as members of the aforementioned one-parameter family and may be regarded as second-order upwind schemes. A Fourier analysis is used to investigate the spectral properties of these discretizations. Numerical experiments illustrate that second-order global accuracy is achieved on parallelepiped grids, as suggested by the theory. Randomly perturbed, stretched, sheared meshes are used to test these methods to destruction. It is found that upwinding improves both the accuracy on distorted meshes and the spectrum of the discretization.     

Analytical evaluation of the elastic and plastic resistances of double symmetric rectangular hollow sections under axial force and biaxial bending

In the recent codes for the design of steel structures, the elastic–plastic methods of analysis are recognised to provide an efficient estimation of the ultimate resistance of some of these structures. These methods are usually based on some basic hypotheses, such as the creation of plastic hinges in the most stressed cross-sections, for instance.As the development of these plastic hinges depends on the interaction between the internal forces and on the cross-section shape, specific equations are required for the analysis of different types of cross-sections. However, most frequently, these equations are not available, or they are expressed by means of simplified expressions; this is usually the case when biaxial bending is involved.This paper presents new interaction criteria for the analysis of steel rectangular hollow sections subjected to an axial force and biaxial bending moments, at the elastic or the plastic limit states (as long as buckling phenomena are not involved). The plastic interaction criteria are presented, in a first step, for some particular combinations of the internal forces, such as axial loading with bending about a main axis, and biaxial bending without axial loading. Then, the global solution for the simultaneous combination of an axial force and bending moments about both the main axes of inertia are described in detail. All these plastic interaction criteria are compared with the corresponding plastic criteria adopted in the Eurocode 3 (EC3). Some suggestions are presented in order to improve the results given by these EC3 criteria.     

Solitary waves in a viscous liquid film flowing down a thin vertical cylinder

Several equations to describe the flow of a viscous liquid film on a thin cylinder are derived. The solitary-wave solutions to these equations are studied. The families of solutions are constructed for the first two eigenvalues that correspond to single-humped and double-humped waves. It is found that these families become similar as the similarity parameter increases. The dependencies of phase velocities and wave amplitudes on the free parameters of the problem are analyzed. The resulting solutions are compared with solitary waves in films on a flat surface.     

Asymmetrical three-DOFs rotational-translational parallel-kinematics mechanisms based on Lie group theory

The paper introduces four families of three-DOFs translational-rotational Parallel-Kinematics Mechanisms (PKMs) as well as the mobility analysis of such families using Lie group theory. Two of these families are mechanisms with one-rotational two-translational degrees of freedom (DOFs) and each of the other two has one-translational two-rotational DOFs. Four novel mechanisms are presented and discussed as representatives of these four families. Although these mechanisms are asymmetric, the components used to realise them are very similar and, hence, there is no great departure from the favourable modularity of parallel-kinematics mechanisms.     

AN UPPER BOUND ON RANDOM BUFFETING FORCES CAUSED BY TWO-PHASE FLOWS ACROSS TUBES

This paper investigates the random buffeting excitation forces that apply to tubes in two-phase cross-flows. The spectral magnitude of these forces is studied with the help of a database that includes most of the available experimental data on direct or indirect force measurements. Different fluid mixtures, namely steam–water, air–water and various types of Freon, as well as different thermohydraulic or geometrical situations are included in the database. Using a formalism similar in principle to that used successfully in the modelling of buffeting in single-phase flows, the scaling of the data is undertaken. While dynamic pressure, viscosity or surface tension are found not to be relevant parameters, gravity forces allow us to define appropriate dimensionless spectra for all cases. The meaning of these parameters as well as the effects of flow regimes or fluid mixtures are discussed. Finally, an upper bound on the magnitude of these forces, which is of practical applicability, is proposed.     

Energy-minimizing deformations of elastic sheets with bending stiffness

Necessary conditions for energy-minimizing deformations are derived for a theory of sheets in which the strain energy function depends on the second derivatives of the deformation as well as its first derivatives. All of these conditions are extensions of well-known necessary conditions in classical calculus of variations. The interpretation of some of these conditions as material stability conditions is explained.     

结构谐振动力响应的有限元、动凝聚、迁移子结构法

本文扩展了FETM法思想,结合子结构、动凝聚及Riccati变换理论,直接求解谐和激励下结构的受迫动力响应,从而节省了运行时间,严格控制了计算精度。本文编制了程序,并以振型叠加法运行结果为参照,对不同算例的运算效率作了比较。结果表明:本文方法在理论上、实践上是切实可行的。     

热冲击下物性与温度相关性对热弹性响应的渐进分析

计及材料物性与温度的相关性,基于Green-Naghdi能量无耗散广义热弹性理论(G-N II理论),对热冲击下具有变物性特征材料的热弹性响应进行了求解分析。借助Laplace正、反变换技术以及Krichhoff变换,在热物性参数随真实温度呈线性规律的前提下,推导了半无限大体受热冲击作用时热弹性响应的解析表达式,通过求解分析,得到了热冲击下热波、热弹性波的传播规律,位移场、温度场以及应力场的分布情况,以及物性随温度相关性对热弹性响应的影响效果。结果表明：当考虑材料物性随温度的变化时,热波、热弹性波的传播以及各物理场的分布均受到不同程度的影响,且物性随温度相关性对热弹性响应的作用效果将受到材料热-力耦合特性的影响。     

Mechanical requirements and structures of cyclic plasticity models

The condition of continuity in the large and in the small and Masing effect as the mechanical requirements for cyclic plasticity are first formulated. The basic characteristics of several well-known and frequently used cyclic plasticity models are examined with respect to fulfillment of these requirements, and their inevitable defects are indicated. It is concluded that among these models only the extended subloading surface model fulfills these requirements and is applicable to the prediction of elastoplastic deformation for cyclic loading, although unfortunately the other models, especially the multi, the two, and the initial subloading surface models, have been frequently adopted for metals, geomaterials, concretes, and so forth.     

Free and forced vibration of repetitive structures

In this paper, the vibration problems of some repetitive structures, including symmetric, cyclic periodic, linear periodic, chain, and axi-symmetric structures is investigated. Eigen-value problems derived from the vibration equations of these structures are established based on their continuous models. The special properties of the structural modes of these structures are deduced. Applying these properties can provide effective reduction approach to solving the natural and forced vibration problems of these structures by either numerical or experimental methods. Furthermore, these properties can be applied in other aspects such as evaluating the reasonableness of the discrete models of these repetitive structures.     

THE GENERALITY OF THE GENERAL EQUATIONS OF DYNAMICS 1)

理论力学中动力学普遍方程,在分析力学中称为d'Alembert--Lagrange原理。动力学普遍方程之普遍在于,由它不仅可导出动力学普遍定理,可导出完整约束系统和非完整约束系统的运动微分方程,还可导出积分变分原理。     

高Reynolds数下湍流边界层的尺度律

在过去的10多年内,对于高$Re$数零压力梯度湍流边界层,存在着关于平均速度的尺度律以及近壁区流动是否是普适的争论.介绍了这些争论的最近的态势. 看来, 对于这些争论还远不能得出结论.      

Influence of specimen gage length and loading method on the axial compressive strength of a unidirectional composite material

Various compression test methods for composite materials have been developed during the past few years incorporating specimens of different gage lengths and modes of load introduction. Most of these test methods are not recognized as standards at the present time. Thus the question arises as to whether these various test methods produce similar results.Two commonly used test fixtures are compared in detail here, viz., the ASTM Standard D 3410 IITRI compression test fixture, and another often referred to as the Boeing-Modified D 695 compression test fixture. The IITRI fixture loads a specimen of 12.7-mm gage length via shear through end tabs and wedge grips. The Boeing-Modified D 695 fixture also uses a tabbed specimen, but with only a 4.8-mm gage length and loaded directly on its ends.Hercules S2/3501-6 glass/epoxy and AS4/3501-6 carbon/epoxy unidirectional composites were used as the primary material configurations in the present comparison. Highstrength, highly orthotropic materials such as these are among the most difficult composites to test successfully in compression. However, a carbon/epoxy quasi-isotropic laminate was tested as well.The results obtained are compared with similar data available in the literature. It is concluded that there is relatively little influence of specimen gage length as long as it is sufficiently small so that gross buckling does not occur. Also, the differences between shear loading and end loading of the specimen are small, as long as the ends of the end-loaded specimen do not crush, and that in either case the tabs do not debond.     

保持香港优良海港的环境地质地貌条件

主要阐述了香港作为世界最大集装箱海港的各种优势,同时指出为保持这种优势应注意的一些事项。     

Heat generation at the tip of a moving crack

The high energy concentration at the tip of a moving crack causes irreversible deformations and produces heat as a consequence. The resulting temperatures were calculated by consideration of the crack tip as a moving heat-source of rectangular shape. In brittle materials with very small plastic zones and high crack velocities, these temperatures are predicted to be higher than 1000 K. For the experimental verification of these calculations, a very sensitive radiation thermometer was developed. It registers the intensity of the radiation at four wavelengths. By comparison of these intensities with that of black body radiation, the temperature was determined as 3200 K for glass and 4700 K for quartz.     

A Stability Result on the Orientation of Red Blood Cells in the Venule Network

We model blood as a non-Newtonian fluid. Red blood cells, white blood cells and platelets immersed in plasma, are modeled as a suspension where the particles, erythrocyte cell aggregates, are assumed to be in the shape of a rigid cylinder. The orientation of these particles is affected by various factors. In this article we look at the effect of magnetic fields on the orientation of these red blood cell particles. A proof of stability of solutions is given, under the assumption that the body is subjected to the effect of magnetic fields.     

Increased prevalence of Mediterranean and Muslim populations in mutation-related research literature

This paper assesses the prevalence of 569 population groups in mutation-related research literature by means of prevalence scores, calculated on the basis of a systematic search of the PubMed database. The main finding is that Mediterranean and Muslim populations are mentioned more often than other groups. The observed overrepresentation is attributed to the pervasiveness of hemoglobin disorders in these populations, the early decoding of hemoglobin and the relative commonness of consanguineous marriage in some of these populations. The paper points at potential benefits as well as predicaments that the intensive targeting of these populations for mutation research may entail.     

固体非均质炸药冲击点火与起爆模型研究进展

综述了固体非均质炸药冲击点火与起爆模型研究的进展,主要探讨基于经验数据模型、微观机制 模型和分子动力学理论模型这3类模型的理论基础、存在的问题和工程应用前景,认为基于微观机制点火与 起爆模型具有物理概念清晰以及能够预测实验结果的优点和较好的工程应用前景,提出了后续发展的建议。     

分子振动的局部模和键选择化学反应的可能性

1.前言激光这门新技术由于它的高单色性和可调谐等特点,人们一直关注它在化学领域内的应用。同位素分离和键选择性激发化学反应是最引人住目的两个问题。一般的化学反应由于不足在分子水平上进行控制的,其进程遵从统计规律,因此往往伴随着产生许多并不需要的中间产物和能量的浪费。如果人们能在分子水平上控制化学反应,即拆开需要拆开的键,组合需要组合的键,那就不但可以使反应在低温条件下进行,而且可能合成某些预      

Thermoelasto-viscous Materials

A thermoelasto-viscous material is defined by a set of constitutive laws in which the stress, entropy, heat flux and free energy are functions of the present configuration, temperature, temperature gradient and the rate of change of all three of these. Here these materials are presented within the framework of Walter Noll’s new theory of simple materials, so that the constitutive laws are specified without the use of a frame of reference. The Coleman-Noll procedure is carried out, and the symmetry group of the material is also discussed, both without using a frame of reference. It is then shown what form the constitutive laws of a fluid thermoelasto-viscous material take when a frame of reference is considered. Finally, the governing equations for these materials are explicitly obtained and discussed. The results in this paper may serve as a foundation for new and better mathematical models to deal with phenomena such as heat transfer, heat exchanges and thermophoresis.