DYNAMICS OF ROTORS IMMERSED IN ECCENTRIC ANNULAR FLOW. PART 1: THEORY

A theoretical model is developed for predicting the dynamic behaviour and stability of a rotating shaft immersed in both a concentric or eccentric fluid annulus. Of specific concern here are geometries presenting a moderate flow-confinement, for which scarce results exist. Theoretical results show that moderate gap configurations lead to quite distinct flow forces, when compared to typical bearing configurations. Also, the annulus eccentricity is shown to be a very important parameter, controlling rotor dynamics and stability. In a companion paper (Part 2), experimental results are reported and favourably compared with the present theory.     

LINEAR AND NONLINEAR DYNAMICS OF CANTILEVERED CYLINDERS IN AXIAL FLOW. PART 1: PHYSICAL DYNAMICS

This paper is the first in a three-part study of the dynamics of cantilevered cylinders in axial flow. After an extensive literature review, the physical dynamics of the system is examined; specifically (a) the experimental behaviour of elastomer cylinders in water flow, and (b) the energy transfer mechanisms, discussed from a work–energy perspective without solving the equations of motion. In general, the system loses stability by divergence and, as the flow velocity is increased, it is subject to second- and third-mode flutter, provided that the free end is well-streamlined; if, however, the free end is blunt, these instabilities do not occur. Oscillations are generally three-dimensional (orbital). The experimental observations are in good qualitative agreement with those expected from the energy transfer analysis, and in reasonably good quantitative agreement with solutions of the linearized equation of motion (obtained from Part 3 of this study). For some shapes of the free-end, resonances are observed with a fairly constant Strouhal number.     

LINEAR AND NONLINEAR DYNAMICS OF CANTILEVERED CYLINDERS IN AXIAL FLOW. PART 2: THE EQUATIONS OF MOTION

In this paper a nonlinear equation of motion is derived for the dynamics of a slender cantilevered cylinder in axial flow, generally terminated by an ogival free end. Inviscid forces are modelled by an extension of Lighthill's slender-body work to third-order accuracy. The viscous, hydrostatic and gravity-related terms are derived separately, to the same accuracy. The equation of motion is obtained via Hamilton's principle. The boundary conditions related to the ogival free end are also derived separately. The paper is concluded by a discussion of the methods used to obtain the solutions presented in Part 3 of this study.     

VIBRATIONS OF CIRCULAR CYLINDRICAL SHELLS WITH NONUNIFORM CONSTRAINTS,ELASTIC BED AND ADDED MASS. PART II: SHELLS CONTAINING OR IMMERSED IN AXIAL FLOW

The model introduced in Part I of the present study is extended to take into account a flowing fluid, a mean radial pressure and initial pre-stress in circular cylindrical shells. The axial flow can be external, internal or annular and is described by the potential theory for inviscid and incompressible fluid. The computer program DIVA has been developed. It takes into account all the following complicating effects on the vibrations of circular cylindrical shells: (i) nonuniform boundary conditions around the shell edges including elastic boundary conditions; (ii) fluid–structure interaction including both flowing and quiescent fluids; (iii) internal, external and annular fluids; (iv) effect of a mean radial pressure and initial pre-stress; (v) elastic bed of partial extension in circumferential and longitudinal directions; (vi) intermediate constraints; (vii) added masses. It can be considered the most complete computer program specifically dedicated to dynamics of circular cylindrical shells. The Flügge theory of shells is used to describe the shell deformations. The system has been proved to be conservative for any combination of boundary conditions with restrained displacement at the shell ends. Numerical results show that shells clamped at the upstream end and simply supported at the downstream end have a larger critical velocity than simply supported shells, solving the paradox of Horáček and Zolotarev.     

HPAM溶液在石英微圆管中的流动实验

针对HPAM溶液在油藏孔隙中的复杂渗流特性问题,在内径为10$\sim$350$\mu$m微圆管中进行了部分水解聚丙烯酰胺(HPAM)溶液的流动实验. 实验结果表明：在本文实验条件下,HAPM溶液在管径尺度较小的微圆管内的流动规律明显偏离常规尺度下的非牛顿流体力学流动规律,其截面平均流速高于按照常规尺度流动推算出的结果,且管径越小,偏离程度越大,微尺度效应越强.     

摆动液压缸圆环螺旋流的流动及内泄漏研究

考虑液压油的黏度随温度与压强的变化, 以连续性方程、N-S方程、能量方程为基础,推导出螺旋摆动液压缸内部圆环螺旋流的速度方程及泄漏量方程. 运用大型通用CFD仿真软件fluent对螺旋摆动液压缸内部的圆环螺旋流流场及泄漏规律进行数值仿真. 对螺旋摆动液压缸内螺旋流动的理论计算与仿真结果进行对比分析, 结果表明理论推导正确, 从而为螺旋摆动缸内泄漏及容积耗损提供理论依据.     

破碎岩体非等温渗流的非线性动力学研究

分别从固体及流体导热的能量方程出发,导出破碎岩体非等温渗流的能量本构方程, 结合渗流的连续性方程、运动方程、状态方程等建立了破碎岩体非等温渗流的一维非线性动力学方程组;结合Mathcad软件计算得到了系统的无量纲化平衡态, 利用逐次亚松弛迭代法分析了对应于不同参数时平衡态的稳定性;指出非等温渗流系统存在鞍结分岔及折叠突变, 与等温渗流相比, 考虑温度场的破碎岩体渗流动力系统更容易发生渗流突变.      

地球物理流体动力学的发展和室内实验研究的影响

系统介绍了大气、海洋与新兴的地质系统中的流体力学,尤其是通过室内实验的研究进展．详细描述了诸如羽流、湍流、卷挟、异重流、海洋环流、混合层、双扩散、盐指、锋面、岩浆库、地幔对流、板块运动、热斑等有趣的地球物理现象,它们对于了解因浮力引起的对流的机理是十分重要的．同时在气候、环境、灾害、成矿等领域有广泛的应用．论文反映了在 Ｇ．Ｉ． Ｔａｙｌｏｒ, Ｇ．Ｋ． Ｂａｔｃｈｅｌｏｒ领导下剑桥研究组的风格──通过小型室内实验了解机理,再用应用数学方法求解问题,他们对流体力学的发展作出了重大贡献．     

沉管隧道横向动力响应分析的多体动力学方法

沉管隧道横向地震响应分析是沉管隧道结构抗震设计的重点.根据沉管隧道的结构特点和接头剪力键的节点构造,建立了沉管隧道的多刚体-剪切铰-黏性阻尼铰多体动力学模型,并应用多体动力学中的离散时间传递矩阵法(multibody system discrete time transfer matrix method,MS-DT-TMM)建立了数学模型及表达式,同时编写Matlab程序进行求解实现.设定算例分别采用MS-DT-TMM和传统有限元法(finite element method,FEM)对沉管隧道横向地震响应进行对比分析,两者吻合较好,表明MS-DT-TMM应用于沉管隧道横向动力响应分析的可行性和有效性.     

柔性多体系统动力学实验研究综述

介绍了国内外柔性多体系统动力学实验研究现状,分为三个方面,即理论模型验证实验、动力学特性的实验研究和其它实验.柔性多体系统动力学建模理论的发展经历了3个阶段:运动-弹性动力学(KED)方法、传统混合坐标方法和计及了动力刚化效应的各种非线性理论.关于这些理论的模型验证实验均在本文中作了重点介绍.文中还对柔性多体系统动力学性态的研究实验也作了介绍,包括系统模态特性和共振等非线性力学行为.关于机械臂控制和碰撞研究实验虽有提及,但不作为重点.随后,着重介绍了柔性体弹性振动位移的测量和阻尼因素的处理这两个在实验不可避免但又难以解决的问题,尤其是结构阻尼和大范围运动引起的空气阻力.最后指出了今后的研究方向.文中对一些较为重要的实验装置也着重予以介绍,并给出了部分实验图片及数据曲线,以给读者一个更好的理解和参考.      

环形截面螺旋管道内的粘性流动

根据张量分析,建立了非正交的曲线柱坐标系巾的N-S方程,采用摄动法求解环形截面螺旋管道内的粘性流动。结果表明:环形截面上存在二次流     

配置环形线电极的单极机中的磁流体力学流动

给出配置了环形线电极的单极机中的磁流体力学解析解. 由于问题是线性的, 求解可简化为基本解的叠加, 可利用单极机在两个区域中的基本解的衔接来求得解析解. 讨论了基本解的性质. 利用非完全电极可改善Hartmann 边界层、增加装置中的质量流量. 应用基本解讨论了连续电极的单极机.     

环形截面螺旋管道内二次流动特性的研究

从曲线柱坐标系下的N-S方程出发,以曲率和挠率为小参数,采用摄动法求解了环形截面螺旋管道内的黏性流动,给出了完全二阶摄动解,结果表明：当挠率为零时,二次流表现为上下对称的四个涡;当挠率不为零,涡的对称性遭到破坏,二次涡的强度和个数受De数和环形截面内外径之比δ的影响,轴向速度最大值在De数较小时靠近管道的内侧,随着De数的增加,其最大值向外侧移动。     

心瓣流体动力学研究进展

心瓣流体动力学是近年来才形成的一门新兴边缘学科分支。本文比较全面地介绍了该学科的主要研究内容、研究特点、发生发展的历史和现状,以及笔者及其同事在这方面的工作,提出并论述了对学科发展有重大影响的几个富有挑战性的问题,从而预示了学科的发展方向      

AERODYNAMICALLY GENERATED ACOUSTIC RESONANCE IN A PIPE WITH ANNULAR FLOW RESTRICTORS

An experimental study of the coupling between fluid dynamic instabilities and an acoustic field is performed for the case of a pipe with annular flow restrictors, representing a segmented solid propellant booster. As long as the distance between the restrictors remains smaller than the length of the flow recovery region behind the upstream restrictor, the fluid flow can amplify the acoustic pereturbations at the frequencies of the acoustic modes, leading to strong resonance for specific flow velocity ranges. A physical explanation is proposed, linking the amplification of the acoustic perturbation to the phase and frequency of vortex shedding from the restrictors. An approximate semi-empirical correlation is developed for the critical Strouhal number of the phenomenon as a function of the restrictor size and other problem parameters.     

ANALYSIS OF VELOCITY ANNULAR EFFECT OF OSCILLATORY FLOW INSIDE PARALLEL PLATE CHANNEL

为了分析管内交变流动速度环状效应的特性,通过数值模拟对平板流道内可压缩交变流动的速度环状效应进行研究．根据速度环状效应的产生机理,分析得出在黏性流体管内交变流动中必然存在速度环状效应,并且在流道截面中心速度为零相位下最容易观察到速度环状效应．为了定量描述速度环状效应,根据流道中心速度为零相位下的速度分布曲线的斜率情况,提出定量评价指标速度环状效应系数,并针对平行平板流道内层流交变流动,利用该评价指标定量分析了无量纲参数（包括瓦伦西数Va和最大雷诺数Remax）对速度环状效应的影响．     

平板流道交变流动速度环状效应分析

为了分析管内交变流动速度环状效应的特性, 通过数值模拟对平板流道内可压缩交变流动的速度环状效应进行研究. 根据速度环状效应的产生机理, 分析得出在黏性流体管内交变流动中必然存在速度环状效应, 并且在流道截面中心速度为零相位下最容易观察到速度环状效应. 为了定量描述速度环状效应, 根据流道中心速度为零相位下的速度分布曲线的斜率情况, 提出定量评价指标速度环状效应系数, 并针对平行平板流道内层流交变流动,利用该评价指标定量分析了无量纲参数(包括瓦伦西数Va和最大雷诺数Re_max)速度环状效应的影响.      

PERTURBATION SOLUTION OF NON-NEWTONIAN FLUID AXIAL LAMINAR FLOW THROUGH ECCENTRIC ANNULI

Using the perturbation method, the axial laminar flow of Non-Newtonian fluid through an eccentric annulus is studied in the present paper. The relative eccentricity ε is taken as a perturbation parameter, and the first order perturbation solutions of the problem, such as velocity field, limit velocity and pressure gradient, are all obtained.