圆柱结构顺流向第一不稳定区内涡激振动的研究

在实际工程中圆柱结构顺流向的涡激振动比较常见,其对结构的疲劳破坏影响也十分显著。该文分析了弹性支承圆柱在顺流向第一不稳定区内的涡激振动,运用Van der Pol方程描述对称旋涡脱落的尾迹特性,采用尾流振子模型计算结构响应,并研究了质量-阻尼参数和质量率对顺流向涡激振动的影响机理。数值计算结果表明,在第一不稳定区内,弹性支承圆柱顺流向涡激振动存在临界质量率。     

圆柱及其组合体水动力与涡激振动计算

本文对圆柱及其组合体在海洋中运动所受定常阻力、振动附加阻力、波激力和涡激力等给出了经验公式,特别对于组合体涡激共振情况,给出了振幅估算方法。根据文中公式和计算方法,对一水下装置进行了自由振动、涡激振动和各种流体作用力与结构应力的计算,发现该装置可能在1．5m／s的低速发生强烈的涡激振动,导致装置疲劳损坏或不能正常使用,而高速下流体阻力和波浪力则是结构破坏的主要原因。     

附加附属管的隔水管涡激振动离散涡模拟

该文采用离散涡数值方法,对附加附属管的隔水管涡激振动问题进行了模拟。计算了配置4–10根附属管情况下隔水管涡激振动问题,将附加附属管后隔水管的受力系数、振幅与裸管的结果进行比较,同时也研究了不同来流攻角对附属管涡激振动的影响。结果表明,附加附属管后隔水管振幅与裸管相比,受力系数与振幅均有不同程度地减小,对隔水管涡激振动的抑制效果明显。不同数量的附属管对来流攻角的敏感性也各不相同,附加6、8和10根附属管都有很好的抑制效果,其中附加10根附属管对隔水管的抑制效果最好,减幅约达到50%,且对来流攻角的敏感性也最低。     

基于LES的水工钢闸门流激振动数值模拟研究

针对钢闸门流激振动机制的复杂性以及钢闸门流激振动在工程实际中的多发性,以二维平板钢闸门为例,基于ADINA有限元分析软件,建立了不同开度的流场有限元模型和固体有限元模型,探究了不同开度时水工钢闸门动力响应规律,阐明了单、双向流固耦合作用下钢闸门动力响应差异,揭示了水工钢闸门流激振动机制。结果表明：1)随着开度的增大,流场不同位置处脉动压力逐渐减小,钢闸门附近旋涡脱落的频率逐渐降低;2)对于水工钢闸门而言,可以采用单向流固耦合代替双向流固耦合进行计算;3)水工钢闸门流激振动产生的机制主要是钢闸门周围旋涡脱落频率与钢闸门结构第一阶自振频率一致或相近,导致钢闸门发生了共振。     

海洋隔水管涡激振动的三维数值模拟研究

流体场采用k-ω湍流模型进行三维CFD数值模拟,固体场采用基于三维实体单元的有限元方法进行模拟,通过一种新的方法实现流-固耦合交界面的无缝数据交换,参考Lehn(2003)长径比为482的模型实验完成隔水管流向与横向涡激振动的三维数值模拟。模拟结果与实验结果吻合良好,都反映了多阶振动模态特性。引入激发速度解释了多阶振动模态的现象。进一步分析表明,大长径比柔性隔水管发生涡激振动时流场尾流区涡的脱落呈现多种涡结构模式,尾涡动力特性在不同截面的变化体现出明显的三维特征。同时隔水管振动时出现非对称弯曲大变形现象,运动轨迹呈现变形的8字形。研究同时表明,顺流向的振动响应不可忽略。     

均匀来流中振动圆柱层迹涡结构的数值研究

本文从涡量流函数形式的Ｎ－Ｓ方程出发，对于不同的振动频率，振幅首次数值研究了均匀来流中沿任意方向振动的圆柱粘性绕流的涡脱泻现象。文中着重探讨了近迹复杂的涡结构及其非定常演经过程，不仅能够再现实验研究中所发现的一些重要的流动现象，同时还进一步预示了某些新的流场结构，使数值计算起到与实验研究相辅相成的作用。     

均匀来流中振动圆柱尾迹涡结构的数值研究

本文从涡量流函数形式的N-S方程出发,对于不同的振动频率、振幅,首次数值研究了均匀来流中沿任意方向(参见图1,0°相似文献   

水轮机迷宫环间隙不均诱发的结构振动特性研究

以某原型水轮机组受迷宫环间隙不均诱发的结构振动为研究对象,采用加权余量的伽辽金法建立其流固耦合的有限元方程,利用声学理论求解流固耦合方程。计算得到了水轮机座环在迷宫环不平衡水流作用下动力响应的双振幅值,讨论了水轮机座环的振动特性。计算结果表明:受结构自身刚度在各个方向的差异,座环横向振动幅值大大高于竖向;间隙不均在环向的分布特性对结构振动影响较大。更多还原     

振荡流下细长柔性圆柱涡激振动数值分析

涡激振动是造成立管疲劳破坏的最主要原因之一。目前,多数柔性圆柱涡激振动的数值模拟与模型试验,都是基于均匀流、剪切流和阶梯流等稳定流作用下,而振荡流作用下的柔性圆柱涡激振动研究相对较少。实际远洋深海情况下,细长柔性立管所处的海洋环境更为复杂,因而有必要深入研究复杂流场作用下的柔性圆柱涡激振动现象。该文采用切片法并基于开源Open FOAM平台开发的细长柔性立管流固耦合求解器viv-FOAM-SJTU,进行振荡流作用下细长柔性圆柱的涡激振动数值模拟。该文主要研究不同振荡流周期对细长柔性圆柱涡激振动的影响。数值模拟结果表明振荡周期与柔性圆柱涡激振动半振荡周期内的"锁定"区域大小密切相关,同时也观察到了间歇性涡激振动,模态跃迁等现象以及涡激振动的产生、锁定和消亡过程。     

阻尼比对水电站厂房结构脉动压力数值计算的影响

基于ANSYS计算软件,建立了水电站厂房结构三维有限元模型;采用Rayleigh阻尼,研究了阻尼比对水电站厂房结构在脉动压力荷载作用下的结构振幅、振动速度、振动加速度的影响规律。结果表明:阻尼比对水电站厂房结构脉动压力数值计算结果有较大影响,阻尼比越大,结构的振动响应越小,阻尼的存在有助于减弱结构的振动;实际数值计算分析中须考虑结构阻尼的影响并采用合理的阻尼模型。     

A NEW WAKE OSCILLATOR MODEL FOR PREDICTING VORTEX INDUCED VIBRATION OF A CIRCULAR CYLINDER

This article proposes a new wake oscillator model for vortex induced vibrations of an elastically supported rigid circular cylinder in a uniform current. The near wake dynamics related with the fluctuating nature of vortex shedding is modeled based on the classical van der Pol equation, combined with the equation for the oscillatory motion of the body. An appropriate approach is developed to estimate the empirical parameters in the wake oscillator model. The present predicted results are compared to the experimental data and previous wake oscillator model results. Good agreement with experimental results is found.     

PREDICTION OF VORTEX-INDUCED VIBRATION OF LONG FLEXIBLE CYLINDERS MODELED BY A COUPLED NONLINEAR OSCILLATOR:INTEGRAL TRANSFORM SOLUTION

The Generalized Integral Transform Technique(GITT) was applied to predict dynamic response of Vortex-Induced Vibration(VIV) of a long flexible cylinder.A nonlinear wake oscillator model was used to represent the cross-flow force acting on the cylinder,leading to a coupled system of second-order Partial Differential Equations(PDEs) in temporal variable.The GITT approach was used to transform the system of PDEs to a system of Ordinary Differential Equations(ODEs),which was numerically solved by using the Adams-Moulton and Gear method(DIVPAG) developed by the International Mathematics and Statistics Library(IMSL).Numerical results were presented for comparison to those given by the finite difference method and experimental results,allowing a critical evaluation of the technique performance.The influence of variation of mean axial tension induced by elongation of flexible cylinder was evaluated,which was shown to be not negligible in numerical simulation of VIV of a long flexible cylinder.     

NONLINEAR FLUID DAMPING IN STRUCTURE-WAKE OSCILLATORS IN MODELING VORTEX-INDUCED VIBRATIONS

A Nonlinear Fluid Damping(NFD)in the form of the square-velocity is applied in the response analysis of Vortex-Induced Vibrations(VIV).Its nonlinear hydrodynamic effects on the coupled wake and structure oscillators are investigated.A comparison between the coupled systems with the linear and nonlinear fluid dampings and experiments shows that the NFD model can well describe response characteristics,such as the amplification of body displacement at lock-in and frequency lock-in,both at high and low mass ratios.Particularly,the predicted peak amplitude of the body in the Griffin plot is in good agreement with experimental data and empirical equation,indicating the significant effect of the NFD on the structure motion.     

离心泵输送粘油时叶轮内部流动模型

利用二维激光测速测量了离心泵输送粘油时最优和小流量工况下大出口角小包角叶轮内部流动。试验表明，在叶片吸力面存在已经分离的尾流，压力面不存在射流，叶轮内部流动与射流／尾流模型不符，尾流宽度与工况有关。     

NUMERICAL EXPERIMENTS OF THREE DIMENSIONAL MIXING OF NATURAL GAS AND AIR

This study presents the numerical results for the three-dimensional natural gas-air mixing in a rectangular subsonic channel under the standard datum state. The lower and upper decomposition method was employed to obtain the solutions of the full Navier-Stokes equations capable of describing compressible fluid mixing. Grid was generated by the area orthogonal technique. The results indicate that three-dimensional mixing between Natural Gas (NG) and air has more complicated compressible waves around the injection nozzle,The presence of injection with large speed can suppress the boundary separation happened occurring at the top wall due to the channel expansion, but makes the near-wake flow more complicated. The mixing region can be widened by increasing the injection speed. The recurrence of the vortex structure and the coherent structure can be found from the full Navier-Stokes simulation. It can be concluded that the increase in the injection velocity can improve the effectiveness of mixing of NG and air in the near wake of the injectors.     

均匀来流中大长径比深海立管涡激振动特性

提出了一种对大长径比深海立管涡激振动特性进行三维耦合数值模拟的方法。其中,流场采用大涡模拟方法进行三维数值模拟,结构振动采用基于薄壳模型的有限元方法进行数值计算,并采用一种将流场和结构响应数据进行实时传输的新方法,实现了流体与固体之间的三维耦合数值模拟。在雷诺数Re=3400和11000下,对某长径比为1200的深海立管模型在均匀来流中的横向涡激振动特性进行了数值模拟与分析。结果表明,大长径比柔性立管的横向振动响应对其尾涡动力特性会产生显著影响,包括会出现涡泄频率显著增大和多频涡泄等复杂现象。尽管来流是均匀的,但立管的横向振动响应会出现明显的多模态特征,除了包含有与涡泄频率一致的振动响应外,还包含有其它频率成分的振动响应。特别地,还会出现多种高阶模态振动共存的非对称复杂弯曲变形等现象。研究表明,该方法为研究深海立管涡激振动特性及其工程预报的相关问题提供了一种有效的途径。     

不同长细比圆柱绕流的大涡模拟

自从人们对层流圆柱绕流现象有了系列研究及清楚的认识后,逐渐把目光投向湍流的圆柱绕流问题,但高雷诺数下的圆柱绕流具有很强的三维特性,因此在数值计算时模型轴向长度的选取是大家关心的问题。该文基于开源软件OpenFOAM运用LES计算了4种不同长细比圆柱的静止圆柱绕流(包括一个二维算例),重点分析和对比了结果中的一些基础参数如St数、平均阻力系数等,与实验结果吻合良好。文中还进一步分析了时均顺流向速度U在流场中沿流向和横向的分布,发现长细比为π的圆柱算例中,计算域的轴向尺度已经能满足圆柱下游靠近圆柱处的流场中的三维结构的发展。     

NEAR WAKE OF A MODEL HORIZONTAL-AXIS WIND TURBINE

An experimental investigation on the properties of the near wake behind the rotor of a Horizontal-Axis Wind Turbine (HAWT) was carried out at model scale. Measurements were made with a stationary slanted hot-wire anemometer using the technique of phase-locked averaging. The primary aim is to study the formation and development of the three-dimensional wake. Five axial locations were chosen within four chord lengths of the blades over a range of tip speed ratios. The results show that during the downstream development of the wake, the wake centre traces a helical curve with its rotation direction opposite to that of the rotor. The distribution of mean velocity behind the HAWT rotor reveals an expansion and a decay of the three-dimensional wake. The shapes of the mean velocity distribution are similar along the blades span at the same downstream axial location. It is shown that the turbulence levels in the wake are higher than those in the non-wake region. The circumferential component and the radial component of the turbulence intensity are higher than the axial component. Our study offers some food of thought for better understanding of the physical features of the flow field as well as the performance of HAWT.     

近断层地震动作用下高耸补压塔地震反应分析

由于近场脉冲地震中含有幅值较大的速度脉冲,其表现出的基本特征通常不同于远场地震。为研究近断层地震和地基刚度对补压塔结构动力响应的影响,以某拟建补压塔为研究对象,考虑流固耦合和地基辐射阻尼,建立水体-结构-基础三维有限元模型,采用时程分析方法研究不同地基刚度、不同地震动类型对结构动力的响应规律。利用1999年集集地震的3组不同类型的地震动记录,即远场、近场无脉冲和近场脉冲型,采用精度较高的波动输入方法和黏弹性人工边界对构筑物进行动力分析。研究表明：不同的地震动特性和土-结构相互作用效应对补压塔的结构响应有显著影响,在地基刚度不大时,近场脉冲型地震位移响应是远场地震的2.5倍以上,鞭稍效应更为明显。近场脉冲型地震动对结构响应影响程度与结构第一周期有显著的相关性。研究结果可为近场区域高耸水工结构设计提供理论依据。