Two kinds of contact problems in three-dimensional icosahedral quasicrystals

Two kinds of contact problems, i.e., the frictional contact problem and the adhesive contact problem, in three-dimensional(3D) icosahedral quasicrystals are discussed by a complex variable function method. For the frictional contact problem, the contact stress exhibits power singularities at the edge of the contact zone. For the adhesive contact problem, the contact stress exhibits oscillatory singularities at the edge of the contact zone. The numerical examples show that for the two kinds of contact problems, the contact stress exhibits singularities, and reaches the maximum value at the edge of the contact zone. The phonon-phason coupling constant has a significant effect on the contact stress intensity, while has little impact on the contact stress distribution regulation. The results are consistent with those of the classical elastic materials when the phonon-phason coupling constant is 0. For the adhesive contact problem, the indentation force has positive correlation with the contact displacement, but the phonon-phason coupling constant impact is barely perceptible. The validity of the conclusions is verified.     

Experimental study on the flow regimes past a confined prism undergoing self-sustained oscillations

An experimental study based on Particle Image Velocimetry (PIV) is presented with the objective of studying the flow regimes that appear in the flow past a confined prism undergoing self-sustained oscillations at low Reynolds numbers (Re). The square-section prism, placed inside a 3D square cross-section vertical channel with a confinement ratio of 1/2.5, was tethered to the channel walls and, therefore, it was allowed to move freely transverse to the incoming flow. Re (based on the prism cross-section height) was varied in the range from 100 to 700. Three different prism to fluid density ratios (m¹) were considered: 0.56, 0.70, and 0.91. These two parameters, Re and m¹, were used to map the results obtained. In particular, it was found that five different regimes appear: (1) steady prism with steady recirculation bubble, (2) steady prism with unsteady vortex shedding wake, (3) large amplitude low frequency oscillating prism with unsteady vortex shedding wake, (4) small amplitude high frequency oscillating prism with unsteady vortex shedding wake, and (5) irregular/chaotic motion of both the prism and the wake. The PIV results and associated numerical simulations were used to analyze the different prism and wake states.     

饲喂频率对鲈鱼生长及体生化成分的影响

选取同一种饵料设置1次·d-1、2次·d-1、3次·d-1、4次·d-14个饲喂频率,采用静水连续充气养殖系统,在盐度为26.0%～27.0%、温度为26～30℃条件下对鲈鱼(85.95±2.04)g进行为期40d的生长实验.结果表明:(1)饲喂频率影响鲈鱼的生长是由食物转化率和摄食率的提高共同引起的.(2)水分含量随饲喂频率的增高而保持不变;蛋白质含量随饲喂频率的增加,基本保持不变;脂肪含量随饲喂频率的增高而明显减少;灰分含量随饲喂频率的增多而明显增加.(3)鲈鱼的适宜饲喂频率为2次·d-1.     

锥形模圆柱体超塑性挤压非局部摩擦分析

为了考虑金属材料表面微凸结构对模具与工件接触区域上的非局部摩擦效应,在锥形模圆柱体超塑性挤压加工分析中,采用Oden等提出的非局部摩擦定律代替经典的库仑摩擦定律,利用主应力法或工程法建立了相应问题的积微分形式的力平衡方程.在简化的情况下,采用摄动法求得所论问题的近似解,并分析了影响应力的非局部效应的相关因素.     

卫星运动预测及规避的建模与求解

近年来,随着各国侦查卫星系统的不断完善,有效根据观测数据预测卫星的轨迹,同时建立适当的规避防范措施变得尤为重要·通过研究地面监测站监测的卫星数据及地理信息,提出了一种基于三维坐标系变换的卫星轨迹求解模型,具体建立模型的方法为:建立4种不同的坐标系,通过卫星坐标在4种坐标系中的变换,将地面检测站检测到的卫星数据进行处理,拟合出卫星的六个运动参数,得出卫星运动轨迹方程,并较为精准的预测卫星被观测站观测到的情况,以及任意时刻星下点的经纬度坐标.针对卫星的运动情况,为满足我方军事目标的运动需求,根据新疆地图建立军队行军路线的有向图,然后,在考虑卫星规避的情况下对每条路线进行模拟分析,最终,通过每条路线模拟分析的结果进行比对,得出最优的行军路线.     

Reconstruction of n-dimensional convex bodies from surface tensors

In this paper, we derive uniqueness and stability results for surface tensors. Further, we develop two algorithms that reconstruct shape of n-dimensional convex bodies. One algorithm requires knowledge of a finite number of surface tensors, whereas the other algorithm is based on noisy measurements of a finite number of harmonic intrinsic volumes. The derived stability results ensure consistency of the two algorithms. Examples that illustrate the feasibility of the algorithms are presented.     

A hypersingular integral equation for the floating body problem

A new boundary integral equation formulation for the floating body problem, which is defined on a bounded domain and includes a hypersingular and a nonlocal part, is proved to satisfy a Gärding inequality. Under the assunlption of uniqueness it is shown, that an approximating sequence of related semidiscrete integral operators is uniformly bounded invertible.     

Nonaxisymmetric Free Convection Flow over a Rotating Disk in a Viscoelastic fluid with Magnetic Field

The non axisymmetric motion produced by a buoyancy-induced secondary flow of a viscoelastic fluid over an infinite rotating disk in a verticalplane with a magnetic field applied normal to the disk has been studied.The governing Navier Stokes equations and the energy equation admit a self similar solution. The system of ordinary differential equations has been solved numerically using Runge-Kutta Gill subroutine.The turning moment for the viscoelastic fluid is found to be less than that of the Newtonian fluid but the turning moment is increased due to the magnetic parameter. The resultant force due to the buoyancy-induced secondary flow increases with the magnetic parameter but reduces as the viscoelastic parameter increases. The quantity of fluid, which is pumped outwards due to the centrifuging action of the disk, for the viscoelastic fluid is more than that of the Newtonian fluid. The buoyancy-induced secondary flow boundary layer is much thicker than the primary boundary layer thickness. The thermal boundary layer due to the primary flow increases with the magnetic parameter decreases as the viscoelastic parameter increases. The heat transfer increases with the viscoelastic parameter but decreases as the magnetic parameter increases. The effect of the viscoelastic parameter is more pronounced on the secondary flow than on the primary flow.     

水下爆炸气泡融合动态特性研究

在自然界中,气泡融合是一种重要的物理现象．基于势流理论,采用边界积分法,对水下爆炸气泡融合进行数值模拟研究．依据已有的数值研究成果和实验数据,建立气泡融合三维动力学数值模型,数值模拟结果与实验值吻合良好．应用该文开发的三维计算程序,分析距离、水深等特征参数对气泡融合动态特性的影响,得到了一些规律性的曲线和结论,旨在为水下爆炸气泡融合机理和动态特性研究提供理论参考．     

三维可压Euler方程简单波及双重波结构

本文研究了三维可压欧拉方程简单波解和双重波解的结构.给出了简单波的流动区域是被一族相互独立的平面所覆盖,沿着每个平面u,v,w从而p,ρ,c均为常数.双重波的流动区域是被一族相互独立的直线所覆盖,沿着每个特征平面u,v,w从而p,ρ,c均为常数.