半圆柱壳挠曲问题解析解精确性的研究

壳体力学已于上世纪由多位专家发展成熟,其中简支柱壳挠曲问题采用改进莱维解法的三角级数法解出,但是其解法复杂,手算难以完成．为讨论其结果的精确性,通过编写运行基于MATLAB的运算程序导出实例化解析解,与基于力学基本理论的推想假设对比,再引入有限元计算结果进行比较研究．最终发现,理论解析解应力和位移具有分布形式大致准确性,但仍存在不容忽视的细节与局部性问题．研究表明,理论解法工程意义有限,结果尚需改进．     

闽江福州河段环境工程地质问题的评价研究

江河环境工程地质问题是环境工程地质学研究的重要课题。江河沿岸环境地质条件是影响和决定沿江城市环境质量的重要背景 ;是控制和影响沿江河岸城市的环境容量和质量的重要因素。本文以闽江下游福州河段为例 ,概要评述了闽江福州河段的水动力条件和流水地质作用类型、强度等状况 ;分析研究了该河段的流水地质作用和地貌环境变化动态及其与沿江河岸人类各种工程建设活动的互相作用的特征和规律。对促进和提高沿江河岸“人—地系统”和谐协调平衡发展水平 ,正确规划、预测和评价沿江河岸各类工程建设发展的经济和社会效益及其前景 ,都具有重要意义.     

受压油管屈曲变形与内外层杆管接触分析

针对机械采油工程中杆管偏磨问题, 考虑直井内受压油管屈曲变形与套管、 抽油杆的双层接触, 以及油管和抽油杆的变截面结构和环空间隙, 采用有限元结构稳定性分 析方法对受压油管进行失稳计算, 将求得的多阶失稳波形叠加值作为油管柱的初始位移, 再 采用大位移和接触非线性分析方法模拟受压油管屈曲变形, 以及与套管和抽油杆间的接触摩 擦, 为套管内受压油管屈曲变形分析提供了一种计算方法.     

Reflection and Transmission of Elastic Waves at the Interface Between Water and a Double Porosity Solid

The reflection and transmission of an incident plane wave at an interface between water and a fluid-saturated double porosity solid are investigated. The properties of the three compressional waves and one shear wave in double porosity media are discussed in detail. The effect of the viscosity, permeability, and porosity on the phase velocity and attenuation of four bulk waves is presented. Comparison between the double porosity theory and the Biot theory reveals that there exists obvious difference in the phase velocity, attenuation and the reflection and transmission coefficients. Two cases of boundary conditions, i.e., the sealed-pore and the open-pore boundaries, are introduced in the numerical calculation. At last, the effect of the fracture permeability and porosity on the reflection and transmission coefficients considered. It is revealed that the amplitudes of the reflected and transmitted waves strongly depend the boundary condition, fracture permeability, and porosity.     

THE ANALYSIS OF THE ENTIRE ELASTO-PLASTIC PROCESS OF A BEAM WITH ONE DEGREE OF INDETERMINACY UNDER A CONCENTRATED LOAD

对跨中集中载荷作用下一次超静定梁的弹塑性加载和变形全过程进行了分析。根据受力变形特点,集中载荷作用下一次超静定梁的加载过程可分为4 个阶段,分别是弹性阶段、固支端附近塑性变形区扩展阶段、固支端和集中载荷作用点附近塑性变形区双扩展阶段、固支端保持为塑性铰同时附近卸载而集中载荷作用点附近塑性变形区继续扩展直至形成第2 个塑性铰阶段。在弹性阶段,弯矩内力和挠度与外载荷是线性比例关系,在第2,3 两个阶段,弯矩和挠度与外载荷是复杂的非线性关系,在第4 阶段,弯矩与外载荷是线性关系但不是比例关系而挠度与外载荷是更为复杂的非线性关系。给出了全过程任意点的弯矩和挠度计算公式,可供结构设计参考应用。     

Stability and local bifurcation of parameter-excited vibration of pipes conveying pulsating fluid under thermal loading

The parametric excited vibration of a pipe under thermal loading may occur because the fluid is often transported heatedly. The effects of thermal loading on the pipe stability and local bifurcations have rarely been studied. The stability and the local bifurcations of the lateral parametric resonance of the pipe induced by the pulsating fluid velocity and the thermal loading are studied. A mathematical model for a simply supported pipe is developed according to the Hamilton principle. Two partial differential equations describing the lateral and longitudinal vibration are obtained. The singularity theory is utilized to analyze the stability and the bifurcation of the system solutions. The transition sets and the bifurcation diagrams are obtained both in the unfolding parameter space and the physical parameter space, which can reveal the relationship between the thermal field parameter and the dynamic behaviors of the pipe. The frequency response and the relationship between the critical thermal rate and the pulsating fluid velocity are obtained. The numerical results demonstrate the accuracy of the single-mode expansion of the solution and the stability and local bifurcation analyses. It also confirms the existence of the chaos. The presented work can provide valuable information for the design of the pipeline and the controllers to prevent the structural instability.     

Numerical simulation and visualization of fiber suspension in a turbulent round jet

The turbulent properties of the fiber suspension in a turbulent round jet are numerically simulated and visualized, and some of the results are compared with the experimental data. The effects of the Reynolds number, fiber volume fraction, and aspect ratio are analyzed. The results show that the fiber injection in the flow has a delay effect on the streamwise velocity decay along the jet axis, and such an effect becomes more obvious with the increases in the fiber volume fraction and aspect ratio and the decrease in the Reynolds number. The flow with fibers shows an increase in the streamwise velocity along the radial direction, and the increase magnitude is directly proportional to the fiber volume fraction and aspect ratio and inversely proportional to the Reynolds number. The presence of fibers makes the turbulent kinetic energy and Reynolds stress increase, and the extent increases with the fiber volume fraction, Reynolds number, and fiber aspect ratio.     

A unified nonlinear formulation for plate and shell theories

A general geometrically exact nonlinear theory for the dynamics of laminated plates and shells under-going large-rotation and small-strain vibrations in three-dimensional space is presented. The theory fully accounts for geometric nonlinearities by using the new concepts of local displacements and local engineering stress and strain measures, a new interpretation and manipulation of the virtual local rotations, an exact coordinate transformation, and the extended Hamilton principle. Moreover, the model accounts for shear coupling effects, continuity of interlaminar shear stresses, free shear-stress conditions on the bonding surfaces, and extensionality. Because the only differences among different plates and shells are the initial curvatures of the coordinates used in the modeling and all possible initial curvatures are included in the formulation, the theory is valid for any plate or shell geometry and contains most of the existing nonlinear and shear-deformable plate and shell theories as special cases. Five fully nonlinear partial-differential equations and corresponding boundary and corner conditions are obtained, which describe the extension-extension-bending-shear-shear vibrations of general laminated two-dimensional structures and display linear elastic and nonlinear geometric coupling among all motions. Moreover, the energy and Newtonian formulations are completely correlated in the theory.     

叠片式气体箔片推力轴承热特性分析

叠片式气体箔片推力轴承具有制造工艺简单、散热能力强等优点，针对该新型轴承提出了相应的热特性分析模型，通过数值仿真分析得到轴承气膜及各元件的温度，并对关键影响参数进行了重点分析. 研究结果表明:由于气膜在半径较大位置处的线速度大，其剪切产热效果明显，温度越高，气膜的高温区分布在靠近周向末端和顶箔侧；气膜、顶箔和推力盘温度均会随推力盘转速和轴承载荷的增大而升高；向箔片结构中通入冷却气流可以获得良好的降温效果，轴承温度随着箔片内通入冷却气流量的增大，先迅速下降后趋于平缓.      

利用有限元法计算径向磁轴承性能

利用非线性有限元方法(FEM)计算了一种径向磁轴承(定子具有8磁极常规结构)的转子在无偏心以及偏置电流分别为0.5 A、1.0 A和1.5 A下的电磁力及其电流刚度与位置刚度,预测了径向磁轴承的承载力,给出了其磁场分布图,并与磁轴承的线性化模型参数进行了比较.结果表明,基于有限元方法得到的计算值同试验结果一致,可以为径向磁轴承的设计和分析提供依据.     

A theory of flexoelectricity with surface effect for elastic dielectrics

The flexoelectric effect is very strong for nanosized dielectrics. Moreover, on the nanoscale, surface effects and the electrostatic force cannot be ignored. In this paper, an electric enthalpy variational principle for nanosized dielectrics is proposed concerning with the flexoelectric effect, the surface effects and the electrostatic force. Here, the surface effects contain the effects of both surface stress and surface polarization. From this variational principle, the governing equations and the generalized electromechanical Young-Laplace equations are derived and can account for the effects of flexoelectricity, surface and the electrostatic force. Moreover, based on this variational principle, both the generalized bulk and surface electrostatic stresses can be obtained and are composed of two parts: the Maxwell stress corresponding to the polarization and strain and the remainder relating to the polarization gradient and the strain gradient. The theory developed in this paper provides the underlying framework for the analyses and computational solutions of electromechanical problems in nanodielectrics.     

Transport of dissolved oxygen at the sediment-water interface in the spanwise oscillating flow

The distribution and concentration of dissolved oxygen(DO)play important roles in aerobic heterotroph activities and some slow chemical reactions,and can affect the water quality,biological communities,and ecosystem functions of rivers and lakes.In this work,the transport of high Schmidt number DO at the sediment-water interface of spanwise oscillating flow is investigated.The volume-averaged Navier-Stokes(VANS)equations and Monod equation are used to describe the flow in the sediment layer and the sediment oxygen demand of microorganisms.The phase-averaged velocities and concentrations of different amplitudes and periods are studied.The dependence of DO transfer on the amplitude and period is analyzed by means of phase-average statistical quantities.It is shown that the concentration in the sediment layer is positively correlated with the turbulence intensity,and the DO concentration and penetration depth in the sediment layer increases when the period and amplitude of the oscillating flow increase.Moreover,in the presence of oscillating flow,a specific scaling relationship exists between the Sherwood number/oxygen consumption of aerobic heterotrophs and the Reynolds number.     

Covariant formulation of the tensor algebra of non-linear elasticity

This work aims at obtaining a covariant representation of the elasticity tensor of a hyperelastic material when the elastic strain energy potential is written employing the volumetric–distortional decomposition of the deformation. This requires the careful definition of some fundamental fourth-order tensors: the identity, the spherical operator, and the deviatoric operator, which appear in the material and spatial expressions of the elasticity tensor. These operators can be defined in the spatial or the material setting and admit pulled-back and pushed-forward forms, respectively. These forms are intimately related to the pulled-back and pushed-forward metric tensors, and are somewhat awkward to derive in Cartesian coordinates, because of the loss of the distinction between a vector space and its dual, and therefore between objects having contravariant and covariant components, which obey to different transformation laws. The relationship between the deformation and the various forms of the identity, spherical, and deviatoric operators can be entirely clarified only within a covariant theory, where the central role played by the spatial and material metric tensors, and their pulled-back and pushed-forward counterparts, which are deformation tensors, can be emphasised.     

低频弹性波超材料的若干进展

超材料是一类新兴的具有超常物理性质的人造周期/拟周期材料, 能够改变电磁波、声波以及弹性波等在介质中的传播特性. 因在航天、国防以及民用科学等方面的巨大应用潜力, 超材料自被提出后便受到极大的关注并引发研究热潮. 弹性波超材料是超材料的一种, 能够基于弹性波与超材料结构的相互耦合作用实现对弹性波的操控. 带隙是评估弹性波超材料实现弹性波操控的重要工具, 其性质与超材料的材料参数、晶格常数以及局域振子的固有频率相关. 受制于超材料的承载能力、外观尺寸以及局域振子结构等因素, 利用传统超材料开启低频(约100 Hz)弹性波带隙依然存在较大困难. 文章首先简要介绍超材料开启弹性波带隙的基本原理, 然后从低频弹性波超材料基本结构与低频带隙实现方法、低频带隙优化与调控策略、低频带隙潜在应用等三个方面详细总结低频弹性波超材料的研究工作. 其中, 低频带隙超材料的基本结构主要包括布拉格散射型超材料、传统局域共振型超材料以及准零刚度局域共振超材料. 文章通过总结低频弹性波超材料的研究进展, 分析了目前研究中的不足并对未来低频弹性波的研究方向进行了展望.      

纳米孪晶和梯度纳米结构金属强韧特性研究进展

金属材料在航空、航天工业以及民用工业等领域具有广泛的应用，如何获取同时具备高强度和良好塑性的金属材料一直是材料、物理、力学等不同学科长期以来亟待解决的难题.传统的强化方法包括应变强化、固溶强化、相变强化、晶粒细化强化和第二相弥散强化等，均会使材料的韧性或塑性降低.近年来，实验研究发现通过界面设计和微结构调控来可以制备出高强高韧的金属材料，认为位错与各类界面的相互作用、以及微结构优化对应力集中的削弱是材料强化和韧化的主要原因.根据已有实验观察，人们通过原子尺度方法定量分析高强高韧金属材料的变形机理，揭示其强化和韧化机制；同时，发展出基于变形机理的理论模型和有限元方法定量描述高强高韧金属的力学行为.论文将重点介绍纳米孪晶金属和梯度纳米结构金属的强韧特性研究进展，并对新型纳米结构金属材料的强韧特性优化进行展望.     

Temperature stress analysis for bi-modulus beam placed on Winkler foundation

The materials with different moduli in tension and compression are called bi-modulus materials. Graphene is such a kind of materials with the highest strength and the thinnest thickness. In this paper, the mechanical response of the bi-modulus beam subjected to the temperature effect and placed on the Winkler foundation is studied. The differential equations about the neutral axis position and undetermined parameters of the normal strain of the bi-modulus foundation beam are established. Then, the analytical expressions of the normal stress, bending moment, and displacement of the foundation beam are derived. Simultaneously, a calculation procedure based on the finite element method(FEM) is developed to obtain the temperature stress of the bi-modulus structures. It is shown that the obtained bi-modulus solutions can recover the classical modulus solution, and the results obtained by the analytical expressions, the present FEM procedure, and the traditional FEM software are consistent, which verifies the accuracy and reliability of the present analytical model and procedure. Finally, the difference between the bi-modulus results and the classical same modulus results is discussed, and several reasonable suggestions for calculating and optimizing the certain bi-modulus member in practical engineering are presented.     

Effects of dynamic load on flow and heat transfer of two-phase boiling water in a horizontal pipe

An experimental investigation was performed to obtain the flow and heat transfer characteristics of single-phase water flow and two-phase pipe boiling water flow under high gravity (Hi-G) in present work. The experiments were conducted on a rotating platform, and boiling two-phase flow state was obtained by means of electric heating. The data were collected specifically in the test section, which was a lucite pipe with inner diameter of 20 mm and length of 400 mm. By changing the parameters, such as rotation speed, inlet temperature, flow rate, and etc., and analyzing the fluid resistance, effective heat and heat transfer coefficient of the experimental data, the effects of dynamic load on the flow and heat transfer characteristics of single phase water and two-phase boiling water flow were investigated and obtained. The two-phase flow patterns under Hi-G condition were obtained with a video camera. The results show that the dynamic load significantly influences the flow characteristic and boiling heat transfer of the two-phase pipe flow. As the direction of the dynamic load and the flow direction are opposite, the greater the dynamic load, the higher the outlet pressure and the flow resistance, and the lower the flow rate, the void fraction, the wall inner surface temperature and the heat transfer capability. Therefore, the dynamic load will block the fluid flow, enhance heat dissipation toward the ambient environment and reduce the heat transfer to the two-phase boiling flow.     

EFFECT OF TWO-DIMENSIONAL MICROPILLAR ARRAYED TOPOGRAPHY ON SPREADING OF INSOLUBLE SURFACTANT-LADEN DROPLET

针对二维微柱阵列壁面上含不溶性活性剂液滴的铺展过程,采用润滑理论建立了液膜厚度和浓度演化模型,采用数值计算方法得到了液滴的铺展特征及相关参数的影响. 研究表明：活性剂液滴在微柱阵列壁面上铺展时,在壁面凸起处衍生出隆起结构,壁面凹槽处衍生出凹陷结构,随时间持续,隆起和凹陷均向两侧移动,且数量不断增加. 活性剂液膜流经凸起时,隆起高度呈驼峰形变化. 增大预置液膜厚度或活性剂初始浓度,铺展区域隆起和凹陷数量增多,液滴铺展速度加快. 增加凹槽深度或减小斜度会使毛细力作用增强,液膜破断可能性加大;增大凹槽宽度可加速活性剂液滴的铺展,加剧液膜表面波动幅度.     

Behavior of probability density functions in a binary gas jet

A helium/air mixture free round jet into still air was investigated using a laser Doppler anemometer and a hot-wire type concentration probe. The jet Reynolds number was 4,300 and the jet-to-ambient fluid density ratio was set at 0.64. Simultaneous measurements of the mixture density and the axial and radial velocities were carried out in both the near and far fields of the jet. A detailed analysis of the turbulent mass transfer and jet characteristics has been presented by So et al. (1990). This paper reports on the higher order statistics and the characteristics of the single and joint probability density distributions of the mixture density and the axial and radial velocities. The behavior of these distributions across and along the jet is analyzed and compared with other single and joint probability density distributions.