Linear spin-up in a sliced cylinder

Abstract

spin-up and spin-down in a circular tank with a uniformly sloping bottom are studied experimentally and numerically for small values of the relative change in the angular velocity of the tank. Generally, the initial single-cell flow evolves into a number of smaller vortices. The evolution is compared with an analytical model based on an expansion of the flow field in linear Rossby waves (Pedlosky and Greenspan, 1967). Although it is possible to tune the experimental parameters in such a way that agreement with the theory is found, in most cases the experiments show shedding of vortices in the initial stage of the spin-up or spin-down, a phenomenon not described by the analytical model. Nonetheless, in such cases the analytical model still accounts for other observations: the alternating generation of cyclonic and anticyclonic vortices in the eastern part of the tank and their subsequent westward motion.     

平板对下游方柱流体动力性能影响分析

基于有限体积法求解二维粘性不可压缩Navier-Stokes方程,分别采用层流模型和Realizable k-ε模型研究Re=250和Re=104前置平板与下游方柱间的流动干扰现象,分析不同尺度的平板布置在不同位置时对下游方柱的绕流场及流体动力性能的影响。计算发现在方柱上游布置平板可以有效的控制方柱的绕流场,减小方柱的阻力系数和升力系数;随着平板尺度的增加,方柱的阻力系数、升力系数呈下降趋势;并且存在较好的平板布置区间,可以最大程度的降低方柱和平板的阻力系数及方柱的升力系数,从而达到良好的减振、降噪的效果。     

软土地基条件下大型圆筒海岸结构稳定性计算方法

针对一工程发生破坏的实例,对软土地基条件下大型圆筒海岸结构的设计与计算方法进行了比较分析,并对波浪水流作用下软土特性参数的选取、泥面冲刷对结构稳定性的影响等进行了讨论。提出了反复荷载作用下软土的动力特性、水流作用下结构周围泥面的冲刷演变规律以及波浪作用下大型圆筒结构与软土的动力相互作用等,这都是软土地基条件下大型圆筒海岸结构工程应用亟待解决的关键问题。     

Analytical Study on Wave Diffraction from a Vertical Circular Cylinder in Front of Orthogonal Vertical Walls

In this paper, the principle of mirror image is used to transform the problem of wave diffraction from a circular cylinder in front of orthogonal vertical walls into the problem of diffraction of four symmetric incident waves from four symmetrically arranged circular cylinders, and then the eigenfunction expansion of velocity potential and Grafs addition theorem are used to give the analytical solution to the wave diffraction problem. The relation of the total wave force on cylinder to the distance between the cylinder and orthogonal vertical walls and the incidence angle of wave is also studied by numerical computation.     

正交直墙前直立圆柱的波浪绕射的解析研究

应用镜像原理,将正交直墙前单个圆柱的波浪绕射问题,转化为4个对称布置圆柱的4向入射波浪的绕射问题。然后应用速度势的特征展开方法和Graf加法定理,建立了正交直墙前垂直圆柱的波浪绕射解析解。通过数值计算研究了圆柱与正交直墙间距离大小、波浪入射角等因素与圆柱上总波浪作用力的解析关系。     

空心圆柱仪模拟列车荷载下土中应力路径能力分析

土体作为各向异性散粒体材料,其动力特性依赖于所处的应力路径。列车荷载下地基土在最大剪应力空间呈心形线旋转应力状态,但目前还未见室内试验中模拟心形线应力路径的相关研究。首先提出了土体动力响应解的简化拟合形式,并通过典型列车荷载作用下地基土所受应力特征分析验证了该简化形式的合理性。针对目前国际上已有的3类空心圆柱仪（HCA）,推导出模拟列车荷载下地基土应力特征的加载方式：（1）双向振动HCA可通过确定轴力和扭矩的应力形式来实现心形线应力路径加载,此时球应力p的变化规律与轴力的加载波形一致,中主应力系数b在内、外压相等时呈余弦变化规律;（2）三向振动HCA在模拟列车荷载下的应力特征时,可以保持p不变或b恒为0.5;（3）四向振动HCA能够通过控制轴力、扭矩和内、外压的共同变化来较全面地模拟列车荷载下土单元体的应力特征,并可实现b为任意合理值且保持不变的前提下p、q之间保持恒定线性关系。并推导了3类HCA的加载参数在正应力均以压应力为主及中主应力方向维持在直径方向时的约束条件。     

制备TJ-1模拟月壤空心圆柱试样的新方法

针对TJ-1模拟月壤颗粒级配跨度大、粒径〉2mm．的颗粒含量多,采用常规方法制备空心圆柱试样容易出现粗细颗粒分离、试样整体不均匀的特点,提出改良型制备方法．首先采用分层欠压法与冰冻法相结合制备出孔隙比e=1．0的实心圆柱试样,并对实心样的均匀性进行评价,得到分层制备相同孔隙比的TJ-1模拟月壤均匀试样时每层试样的高度;...     

带横隔板圆柱绕流特性数值模拟

为揭示尾迹区添加横隔板对圆柱绕流流场特性影响,把多步格式引入到特征线算子分裂有限元法中,建立了基于多步格式的特征线算子分裂有限元法:在每个时间步内将Navier-Stokes方程分裂成对流项和扩散项,对流项时间离散采用多步格式,在每一子时间步内沿特征线展开并显式求解。方腔流数值模拟结果表明该算法既可降低对整体时间步长的要求又可提高计算精度。对比有无横隔板圆柱绕流流场和圆柱表面压力变化表明,横隔板可以有效地抑制绕流尾迹区涡旋脱落,提高圆柱背流面压力,减少圆柱上下表面的压力差。     

Variation of Flow Field Around Twin Cylinders with and Without the Outer Perforated Cylinder ? Numerical Study

Presence of the outer perforated cylinder reduces the direct wave impact on the inner cylinder, which has been testified by many researchers. However, the force reduction mechanism, which is complicated due to the wave-porous structure interaction, needs to be addressed in detail. The present study explains the mechanism with the aid of the computational fluid dynamics (CFD) tool STAR CCM+. This package is chosen for its capabilities to simulate viscous and turbulence effects caused by passage of waves. For the present study, flow fields around the twin cylinders with different orientations are examined with and without the outer perforated cover. Mechanism contributing to the reduction of force on the existing structure is explained in physical terms, and force reduction is quantified. The present study has direct application in the retrofitting application of offshore members.     

多圆环柱域上解析函数边值问题再论

讨论多圆环柱域上多个复变量的解析函数的一般形式的 Riemann- Hilbert边值问题。通过函数的解析变换 ,导出了解析函数一般形式的 Riemann- Hilbert边值问题的可解性 ,并给出了解的积分表达式。