Application of wake oscillators to two-dimensional vortex-induced vibrations of circular cylinders in oscillatory flows

A nonlinear time-domain simulation model for predicting two-dimensional vortex-induced vibration (VIV) of a flexibly mounted circular cylinder in planar and oscillatory flow is presented. This model is based on the utilization of van der Pol wake oscillators, being unconventional since wake oscillators have typically been applied to steady flow VIV predictions. The time-varying relative flow–cylinder velocities and accelerations are accounted for in deriving the coupled hydrodynamic lift, drag and inertia forces leading to the cylinder cross-flow and in-line oscillations. The system fluid–structure interaction equations explicitly contain the time-dependent and hybrid trigonometric terms. Depending on the Keulegan–Carpenter number (KC) incorporating the flow maximum velocity and excitation frequency, the model calibration is performed, entailing a set of empirical coefficients and expressions as a function of KC and mass ratio. Parametric investigations in cases of varying KC, reduced flow velocity, cylinder-to-flow frequency ratio and mass ratio are carried out, capturing some qualitative features of oscillatory flow VIV and exploring the effects of system parameters on response prediction characteristics. The model dependence of hydrodynamic coefficients on the Reynolds number is studied. Discrepancies and limitations versus advantages of the present model with different feasible solution scenarios are illuminated to inform the implementation of wake oscillators as a computationally efficient prediction model for VIV in oscillatory flows.     

稀薄气体二维外部柱体绕流特性研究

本文采用直接模拟蒙特卡罗方法对稀薄气体二维外部柱体绕流问题进行了数值模拟。结果表明:外部绕流问题,在特定情况下会产生激波,激波的产生,不仅与气体的稀薄程度有关,还与来流马赫数有关。而气流与壁面之间的换热,随来流马赫数增加而增加,随气体稀薄程度增加而减小。     

Stagnation flow on a cylinder with partial slip--an exact solution of the Navier-Stokes equations

The stagnation slip flow on an axially moving cylinder is studied.The Navier–Stokes and energy equations reduce to nonlinearordinary differential equations under a similarity transform.For large slip, the flow field decays exponentially into potentialflow. The heat transfer can be expressed as an incomplete gammafunction. In general, the heat transfer increases with slip,Prandtl number and Reynolds number.     

有限长FGM圆筒的热/机应力的解析解

利用微分方程的级数求解方法,分析了两端简支的有限长功能梯度圆筒的轴对称稳态热弹性问题,推导出了稳态温度场与应力场的解析解。分析中采用指数函数模型来描述FGM圆筒中材料性能在厚度方向的连续变化,同时忽略温度对材料性能的影响。另外,论文以金属钼和多铝红柱石制成的功能梯度圆筒为例,给出了稳态温度场和应力场的数值结果。     

Thermoelastoplastic deformation of a thick-walled cylinder with a radial crack

The thermoelastoplastic fracture mechanics problem of a thick-walled cylinder subjected to internal pressure and a nonuniform temperature field is solved by the method of elastic solutions combined with the finite-element method. The correctness of the solution is provided by using the Barenblatt crack model, in which the stress and strain fields are regular. The elastoplastic problem of a cracked cylinder subjected to internal pressure and a nonuniform temperature field are solved. The calculation results are compared with available data. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 3, pp. 173–183, May–June, 2008.     

桥随路降法治理桥头跳车

分析软土地基上路堤与桥梁的沉降差异及跳车的原因,采用桥随路降的治理方法,应用柱式升降桥墩来调控桥面高程,使桥面降落高度与路面沉降量一致,保持道路竖曲线顺畅,消除桥头跳车.     

绕圆柱体自由表面磁流体流动和传热的研究

本文对在不同雷诺数下,绕圆柱体的磁流体自由表面流动及传热进行了模拟,分析了磁场对绕流圆柱尾迹和涡分离的影响,获得了两种雷诺数下的电磁力密度、流场和温度场分布。结果表明,磁场不仅影响了流动的形态,而且对湍流有抑制作用,降低了自由表面的更新机制,从而减少了传热能力;在相同的Hartmann数下,相比低雷诺数下的流动换热情况,高雷诺数下的湍流不能被完全抑制,自由表面与尾迹的相互作用也较强,因而自由表面换热也较强。     

Theory of oscillatory experiments with a coaxial cylinder viscometer

Equations are derived for the coaxial cylinder system in the combined oscillatory and steady-state shear mode. The limitations of the use of the various equations are presented. If the usual linear equations are used, the main limitation, in the case of oscillatory shear only, is that the frequency of measurement should be below 0.016 | ^*|/(r ₂ –r ₁ )². Here | ^*| is the modulus of the complex viscosity, is the density of the liquid andr ₁ andr ₂ are the radii of the cylinders. Furthermore it is shown that there is a small error in the numerical factor of the usually applied equations. The calculations are set up in such a way that extension to higher harmonics follows in a natural way. An experimental example illustrates the use of the derived equations.     

Improvement of the spinning electrophorometer for zeta potential measurements

In this study, bubbles are held by centripetal force at the center of a rotating cylinder filled with an aqueous solution. Their velocities along the axe of rotation, after application of an electrophoretic force, are used for the calculation of the so-called electrokinetic potential. But this process necessitates the elimination of the electro-osmosis which occurs on the interior sides of the glass cylinder by superposing a concurrent force on the bubble. Efficiency of DEAE-Dextran reticulated with 1,4 Butanediol Diglycidyl Ether can be tested by the observation of a cloud of latex microspheres injected in the interior of the tube and allowed to move in respect with the application of an electric field. The experimental control of these velocity profiles proves the adequacy of the polymer for many cases such as surfactant solutions, presence of electrolytes, utilization with moderate pH.The dynamic interpretation of the electrophoretic motion of bubbles is possible by considering that small ones behave like rigid spheres moving in a rotating fluid. In the second part of this paper and in a previous publication, we have experimentally proved that the use of the theoretical expressions of the forces involved for rigid spheres is justified for small bubbles. So, the electrokinetic potential can be expressed versus the velocity, leading to possible interpretations of the adsorption on gas-water interfaces.     

Crumpled laminations and manifolds of nonfinite type

Using a group-theoretic construction due to Bestvina and Brady, we build -manifolds which admit partitions into closed, connected -manifolds but which do not have finite homotopy type.