Numerical Simulation of Two-Dimensional Flow over Three Cylinders by LatticeBoltzmann Method

The numerical simulation using the multiple relaxation time lattice Boltzmann method (MRT-LBM) is carried out for the purpose of investigating the two-dimensional flow around three circular cylinders. Among these three circular cylinders, one of the three cylinders on which a forced in-line vibrating is used to do this research and attempt to find out the effects of the movingcylinder and the other two rigid cylinders on the wake characteristics and vortex formation. As a benchmark problem to discuss the problem of lift coefficient r.m.s for these cylinders with spacing ratios T/D between other rigid side-by-side cylinders, and the calculation is carried out with two compared cases at Reynolds number of 100, two of the cylinders are rigid and the other one is an in-line vibrated cylinder lying downstream, in addition, forced vibrating amplitude and frequency are A/D= 0.5 and f_ν=0.4 (where A is the forced amplitude, D is the cylinder diameter, and f_ν stands for the vibrating frequency, respectively). The calculated results not onlyindicate that the spacing ratios T/D (T is the center-to-center spacing between the two upstream cylinders) have influence on the wake patterns and the formation of vortex shedding, but also analyze the lift coefficient r.m.s for the three cylinders with the spacing ratios S/D (where S is the center-to-center spacing between the center of upstream two side-by-side cylinders and downstream cylinder).     

VIBRATION ANALYSIS OF TWISTED CANTILEVERED CONICAL COMPOSITE SHELLS

The finite element method based on the Hellinger-Reissner principle with independent strain is applied to the vibration problem of cantilevered twisted plates and cylindrical, conical laminated shells. With a small number of elements, the present assumed strain finite element method is validated by convergence tests and numerical tests, comparing with the previous published vibration results for cantilevered conical shell. Computational effort and virtual storage reduce significantly due to good convergence. This study presents the twisting angle effect on vibration characteristics of conical laminated shells. Parameter studies with varying shallowness of cylindrical and conical shells are carried out. As the curvature increases, the fundamental mode shape changes from twisting mode to bending mode. For shells with a large curvature, the fundamental frequency, which is always characterized to bending mode, is almost constant independent of twisting angle. The twisting angle affects greatly twisting frequency and mode shape.     

基于浸入边界-多松弛时间格子玻尔兹曼通量求解法的流固耦合算法研究

针对流固耦合问题,发展了基于浸入边界-多松弛时间格子玻尔兹曼通量求解法(immersed boundary method multi-relaxation-time lattice Boltzmann flux solver,IB-MRT-LBFS)的弱耦合算法.依据多尺度Chapman-Enskog展开,建立不可压宏观方程状态变量和通量与格子玻尔兹曼方程中粒子密度分布函数之间的关系;采用强制浸入边界法处理流固界面使固壁表面满足无滑移边界条件,根据修正的速度求解动量方程力源项;结构运动方程采用四阶龙格-库塔法求解.格子模型与浸入边界法的引入使流固耦合计算可以在笛卡尔网格下进行,无需生成贴体网格及运用动网格技术,简化了计算过程.数值模拟了单圆柱横向涡激振动、单圆柱及串列双圆柱双自由度涡激振动问题.结果表明,IB-MRT-LBFS能够准确预测圆柱涡激振动的锁定区间、振动响应、受力情况以及捕捉尾流场结构形态,验证了该算法在求解流固耦合问题的有效性和可行性.     

气固两相圆柱绕流的直接数值模拟

本文运用谱元方法对气固两相圆柱绕流进行了直接数值模拟。在获得高精度计算流场信息基础上,进行颗粒扩散运动的研究。通过研究颗粒大小对颗粒扩散运动的影响来刻画气固两相圆柱绕流的物理特征。研究时发现,由于圆柱尾流独特的涡结构特征,颗粒在流场中心轴线附近区域的扩散机理主要是决定于吸力作用,该作用会驱使小颗粒卷吸进入圆柱尾部近壁区,甚至与圆柱后壁发生碰撞,这种扩散机理与混合层中颗粒扩散机理明显不同。     

Measurement of Sectional Profile of a Cylinder using a Sinusoidally Vibrating Light with Sinusoidal Intensity

A method for accurately measuring a sectional profile of a cylinder is proposed in which a sinusoidally vibrating sinusoidal grating is used to generate a sinusoidally vibrating sinusoidal intensity distribution. A light coming from the top point of the cylinder surface is extracted with an optical system to make an image of this point. A sectional profile of the cylinder is measured by detecting a phase of a time-varying signal contained in the image intensity at a position where the amplitude of the signal is maximum. Detection of the amplitude and the phase is carried out easily and exactly.     

基于有限差分法刚性圆柱体涡激振动响应特性数值研究

基于尾流振子模型对刚性圆柱体涡激振动响应特性进行数值研究.建立圆柱体结构振子及尾流振子之间的耦合方程,基于二阶精度中心差分格式对耦合模型先离散后迭代进行求解.对不同质量比及不同阻尼比圆柱体涡激振动响应的无量纲位移、无量纲升力、频率比及锁定区间等参数进行分析.结果表明数值方法可以很好地模拟刚性圆柱体的涡激振动响应特性.随着质量比的增加,锁定开始点逐渐延后,锁定结束点逐渐提前,锁定区间宽度逐渐变窄.     

Spectroscopic studies on Yb+ ions in liquid helium

An emission spectrum of the - (D1) transition and excitation spectra of the - (J=1/2 (D1) and 3/2 (D2)) transitions of Yb⁺ ions in liquid helium have been observed by means of a laser-induced fluorescence method. It has been found that all these spectra are blue-shifted from the ones in the free space, and also that the D2 excitation spectrum has double peaks. To understand these spectra, theoretical calculations have also been carried out based on a vibrating bubble model, in which the bubble surface is assumed to vibrate in the spherical (breathing), dipolar and quadrupolar modes. As a result, it has been found that the blue shifts are well understood with this bubble model, and also that the dynamic Jahn-Teller effect due to the quadrupole vibration of the bubble plays an important role for the double-peaked profile of the D2 excitation spectrum. Received 27 December 1999 and Received in final form 31 July 2000     

Flow patterns of cross-flow around a varicose cylinder

The near wake of a varicose cylinder has been experimentally investigated using Laser Induced Fluorescence (LIF) and Digital Particle Imaging Velocimetry (DPIV). The work aims to provide understanding to the mechanism of the cross flow around varicose cylinder as well as to comprehend why the introduction of relatively small degrees of spanwise waviness can have a significant effect on drag reduction and suppression of the cylinder vibration. The evolution of the flow patterns and the corresponding vortex interactions are obtained. The experimental results indicated that the wake width and the formation length vary along the span of the varicose cylinder. A wider wake and a longer formation length were observed in the saddle plane. In addition, an interpretation of the three-dimensional wake structures is postulated and conceptually shown. The numerical simulation by 3-D finite volume method is successful in predicting the flow features found by the experiments.     

Viscous near-wall flow in a wake of circular cylinder at moderate Reynolds numbers

Here we present the results of experimental investigation of a cross flow around a circular cylinder mounted near the wall of a channel with rectangular cross section. The experiments were carried out in the range of Reynolds numbers corresponding to the transition to turbulence in a wake of the cylinder. Flow visualization and SIV-measurements of instantaneous velocity fields were carried out. Evolution of the flow pattern behind the cylinder and formation of the regular vortex structures were analyzed. It is shown that in the case of flow around the cylinder, there is no spiral motion of fluid from the side walls of the channel towards its symmetry plane, typical of the flow around a spanwise rib located on the channel wall. The laminar-turbulent transition in the wake of the cylinder is caused by the shear layer instability.     

微尺度串列双圆柱绕流的分子动力学并行模拟

本文采用基于空间分解算法的分子动力学并行模拟方法,研究了微尺度、低雷诺数（Re=40）下串列等大的双圆柱绕流现象。结果表明：随着间距比L＊／D＊的增加,流动存在3种特征状态：当L＊／D＊〈1．1时,同单一物体的绕钝体流动相似;当1．1〈L＊／0＊〈3．5时,涡脱落现象只在下游圆柱出现,在两圆柱之间有交替附着于下游圆柱的...     

A wake oscillator with frequency dependent coupling for the modeling of vortex-induced vibration

The aim of this paper is to improve the phenomenological modeling of vortex-induced vibration of an elastically mounted cylinder in fluid flow. To this end an attempt is made to introduce a wake oscillator model that conforms to both the free and forced vibration experiments. This approach is new as in the past wake oscillator models have been tuned to the free vibration experiments only. First, an existing wake oscillator model is improved by properly including the effect of stall and that of the relatively large attack angles in the course of vortex-induced vibration. Then, to comply with the forced vibration experiments, the model is enhanced by introducing frequency dependent coupling. Such a coupling allows reproduction of the measured frequency dependence of the fluid force on the cylinder. The time domain representation of this coupling is a convolution integral. It is found in this paper that if the wake oscillator is modeled with a Van der Pol equation, it is impossible to find one set of frequency dependent coefficients that conforms to the forced vibration experiments at all amplitudes of cylinder motion. Moreover, the frequency dependencies identified for each frequency separately do not seem to satisfy the Kramers-Kronig relations. Based on the above findings, it is concluded that the nonlinearities in the wake oscillator model used in this paper cannot accurately model the results of vortex-induced vibration measurements. The idea proposed in this paper, that a consistent wake oscillator model must conform to the forced vibration experiments as well, is expected to be a powerful tool in the search for the correct nonlinearity.     

Dictums for problem solving and approximation in mathematical acoustics: examples involving low-frequency vibration and radiation

A sequence of dictums for mathematical acoustics is given representing opinions intended to be regarded as authoritative, but not necessarily universally agreed upon. The dictums are presented in the context of the detailed solution for a class of problems involving the forced vibration of a long cylinder protruding half-way into a half-space bounded by a compliant surface (impedance boundary) characterized by a spring constant. One limiting case corresponds to a cylinder vibrating within an infinite rigid baffle, and another limiting case corresponds to a vibrating cylinder on the compliant surface of an incompressible fluid. The second limiting case is identified as analogous to that of a floating half-submerged cylinder whose vibrations cause water waves to propagate over the surface. Attention is focused on vibrations at very low frequencies. Difficulties with insuring a causal solution are pointed out and dictums are given as to how one overcomes such difficulties. Various approximation techniques are described. The derivations involve application of the theory of complex variables and the method of matched asymptotic expansions, and the results include the apparent entrained mass in the near field of the cylinder and the radiation resistance per unit length experienced by the vibrating cylinder.     

流体低速绕流振动圆柱对流换热数值研究

运用Fluent的动态网格技术,对空气低速绕流振动圆柱的对流换热进行了研究,分析了流动和振动参数对换热的影响。数值计算表明,在本文计算范围内,壁面振动可使换热强化,最大可强化9倍,换热的强化随振幅和频率的增大而增大。场协同分析表明,圆柱振动强化换热的原因在于速度场和温度梯度场之间的协同程度得到了改善。     

叶轮机械叶片流体激振安全性的全功能分析

本文提出了对叶轮机械叶片流体激振安全性实行全功能数值分析的新概念和方法。实现气动力学和弹性力学的弱耦合计算,由弹性力学方法确定三维振型,用振荡流体力学方法确定三维条件下的三维振荡流场,确定在各种振幅条件下的非定常气动力作功与阻尼功,引入气动功等于阻尼功条件下的平衡振幅概念。根据平衡振幅确定叶片流体激振的动应力,并进行寿命评估。这种全功能分析将使叶轮机械流体激振的安全性分析更加符合工程实际的需要,也能够解释大量的流体激振破坏不属于瞬时突然破坏,而是一种疲劳破坏。     

On the flexural vibration of cylinders under axial loads: Numerical and experimental study

The flexural vibration of a homogeneous isotropic linearly elastic cylinder of any aspect ratio is analysed in this paper. Natural frequencies of a cylinder under uniformly distributed axial loads acting on its bases are calculated numerically by the Ritz method with terms of power series in the coordinate directions as approximating functions. The effect of axial loads on the flexural vibration cannot be described by applying infinitesimal strain theory, therefore, geometrically nonlinear strain–displacement relations with second-order terms are considered here. The natural frequencies of free–free, clamped–clamped, and sliding–sliding cylinders subjected to axial loads are calculated using the proposed three-dimensional Ritz approach and are compared with those obtained with the finite element method and the Bernoulli–Euler theory. Different experiments with cylinders axially compressed by a hydraulic press are carried out and the experimental results for the lowest flexural frequency are compared with the numerical results. An approach based on the Ritz formulation is proposed for the flexural vibration of a cylinder between the platens of the press with constraints varying with the intensity of the compression. The results show that for low compressions the cylinder behaves similarly to a sliding–sliding cylinder, whereas for high compressions the cylinder vibrates as a clamped–clamped one.     

A numerical study of transient flow around a cylinder and aerodynamic sound radiation

The fully 3D turbulent incompressible flow around a cylinder and in its wake at a Reynolds number Re = = 9×10⁴ based on the cylinder diameter and Mach number M = 0.1 is calculated using Large Eddy Simulations (LES). Encouraging results are found in comparison to experimental data for the fluctuating lift and drag forces. The acoustic pressure in far-field is commutated through the surface integral formulation of the Ffowcs Williams and Hawkings (FWH) equation in acoustic analogy. Five different sound sources, the cylinder wall and four permeable surfaces in the flow fields, are employed. The spectra of the sound pressure are generally in quantitative agreement with the measured one though the acoustic sources are pseudo-sound regarding the incompressible flow simulation. The acoustic component at the Strouhal number related to vortex shedding has been predicted accurately. For the broad band sound, the permeable surfaces in the near wake region give qualitative enough accuracy level of predictions, while the cylinder wall surface shows a noticeable under-prediction. The sound radiation of the volumetric sources based on Lighthill tensors at vortex shedding is also studied. Its far-field directivity is of lateral quadrupoles with the weak radiations in the flow and cross-flow directions.     

Semirigid vibrating rotor target calculation for reaction O(3p)+CH4 →CH3+OH

The time-dependent quantum dynamics calculation for reaction O(3p)+CH4→ CH3+OH is made, using of the semirigid vibrating rotor target (SVRT) model and the time-dependent wave packet (TDWP) method. The corresponding reaction probabilities of different initial states are provided. From the calculation of initial rovibrational state j= 0,v= 0, 1, we can see that the excitation of the H-CH3 stretching vibration gives significant enhancement of reaction probability and the reaction threshold decreases dramatically with the enhancement of the vibrating excitation, which indicates that the vibrating energy of reagent molecules contributes a lot to the molecular collision. As for the calculation of reaction probability of state v= 0, j= 0,1,2,3, the results show that the reaction probability rises significantly with the enhancement of rotational quantum number j while the reaction threshold has no changes. The spatial steric effect of the title reaction is studied and analyzed too after the calculation of reaction probability of states j= 5, k= 0-2, n= 0 and j=5, k=2, n=0-2 is made.     

Low-frequency harmonic vibration analysis with temporal speckle pattern interferometry

In this paper, the time sequence phase method (TSPM) has been applied to measure the displacement caused by low-frequency vibration in temporal speckle pattern interferometry (TSPI). The principle is that by capturing the temporal speckle patterns related to the object vibration, the whole-field displacement responses (amplitude and phase) of the vibrating object can be calculated through scanning these fluctuations. Thus, quantitative measurement can be carried out using a conventional ESPI system without a camera synchronized to the object vibration or a phase shifting system. The elaboration on the method is given and experimental results are presented.     

基于双色条纹投影的薄膜振动模式分析

结构光投影和条纹时间平均分析技术已被用于振动模式分析中,但由于投影单色正弦条纹时振动薄膜变形条纹傅里叶谱中零频涵盖范围较大,会限制滤波窗的选取范围,从而影响模式的最终重建结果。为提高振动模式重建的准确性,提出了一种利用π相移正弦条纹投影进行薄膜振动模式分析和振幅重建的方法,通过处理两个通道的条纹分量达到消除零频的目的。给出了该方法的理论分析,完成了相应的计算机模拟,分析了影响测量精度的因素。通过与投影单色正弦条纹的振动模式重建结果对比,表明该方法有较高的重建精度。不同激励频率下的实际薄膜振动实验结果也证明了该方法正确可行。     

A simple optical method for measuring the vibration amplitude of a speaker

A simple optical method has been proposed for measuring the vibration amplitude of a speaker vibrating with a frequency of approximately 10 kHz. The method is based on a multiple reflection between a vibrating speaker plane and a mirror parallel to that speaker plane. The multiple reflection can magnify a dispersion of the laser beam caused by the vibration, and easily make a measurement of the amplitude. The measuring sensitivity ranges between sub-microns and 1 mm. A preliminary experiment verified the reliability of this method.