非对称尾部形状水翼水力阻尼识别方法研究

水力阻尼是影响流激振动幅值预测精度的关键参数,是水力机械流激振动领域研究的热点问题。非对称尾部形状水翼在涡激振动和升力的联合作用下,振动响应的平衡位置具有时变特性,采用传统自由振动衰减法获得的水力阻尼比误差大幅度增加,甚至失效。为了克服传统自由振动衰减法应用局限,本文借助双向流固耦合数值模拟方法获得流激振动响应位移,通过带通滤波结合平衡位置校准,研究了动水环境中对称和非对称尾部形状水翼水力阻尼的识别方法。结果表明,数值模拟可较准确获取低阶结构模态和尾部旋涡脱落频率,相比实验结果,低阶弯曲模态频率、低阶扭曲模态频率和15 m/s流速下脱落涡频率最大偏差分别为7.58%、2.90%和1.42%;带通滤波可消除周期性涡激振动对响应信号的影响,水力阻尼比识别偏差度从7.51%下降到1.92%;平衡位置校准方法可采用多项式拟合法、线性插值法和光滑样条曲线法,所对应的水力阻尼比识别偏差度分别为34.93%、3.53%和0.16%。工程上,可优先推荐滤波结合线性插值法,在需要高精度水力阻尼比的场合,则必须采用滤波结合光滑样条曲线法。     

复合材料水翼水动力响应数值模拟研究

该文针对NACA0009复合材料梯形水翼进行流固耦合数值计算,研究复合材料水翼水力阻尼及水弹性响应特性。研究建立了复合材料水翼流场模型、结构模型、流固耦合计算模型及湿模态模型,并利用实验结果对模型进行验证。模态分析结果表明：复合材料铺层角φ影响水翼模态振型,相比于φ=0°铺层,φ=+30°铺层和φ=-30°铺层水翼的一阶模态频率降低,二阶和三阶模态频率升高。研究进一步对水翼振动过程的阻尼特性进行分析,得到了水力阻尼比与流速的经验关系式,复合材料水翼水力阻尼比与流速成正比,且相比于φ=0°铺层,φ=+30°铺层和φ=-30°铺层水翼的水力阻尼比更大。分析了不同流速下复合材料水翼的水动力载荷特性：对于稳态水动力载荷,φ=+30°铺层水翼的载荷系数随流速增加而增大,φ=-30°铺层随流速增加而减小,φ=0°铺层随流速增加而略有增加;对于瞬态水动力载荷,初步分析表明,水翼受到的水动力作用形式与铺层角相关：相较于流速,铺层角φ对瞬态载荷分布的影响更大,且φ=+30°铺层水翼吸力面尾缘附近所受水动力比φ=0°铺层更大。     

空化对振动水翼附加质量和阻尼特性影响研究

抽水蓄能机组需频繁调节工况以适应电网需求。由此水力激振频率范围加宽,共振风险增加。附加质量和阻尼特性是评估共振工况点和共振幅值的关键参数。在空化发生时,叶片绕流流体从液相变成汽相,其复杂的流固耦合效应对叶片附加质量和阻尼特性产生影响。本文将叶片简化为NACA 0009水翼,探索了空化发生时基于双向流固耦合的附加质量和水力阻尼特性预测方法。结果表明,模拟得到的静水中固有频率和不同空化数下的空化脱落频率与实验结果吻合良好,相对误差分别在7.12%和8.76%以内。在空化数σ=1.04~2.02范围内,固有频率和水力阻尼随空化数的降低分别增大和减小,相对于实验的平均误差分别为9.69%和13.65%。内部流动分析表明反向射流导致前缘空化周期性脱落,吸力面的绕流速度下降则是空化发生后水力阻尼下降的主要原因。研究成果对抽水蓄能机组设计阶段预判空化时的叶片振动评估具有重要指导意义。     

基于流固耦合的农用风力机叶片应力及振动仿真研究

以农田水利工程使用的额定功率为1 000 W的小型水平轴风力提水机叶片作为研究对象,对叶片强度进行了单向流固耦合数值模拟,得到了叶片多种工况下的受力变形规律。基于流场计算结果,对叶片进行了预应力模态分析和无预应力模态分析,得到了叶片前6阶振型和不同工况下的固有频率。结果表明:叶根部位存在局部应力集中,风力机叶片静应力随风速增大有不同程度的增大,且最大静应力远小于许用应力,不足以使叶片产生裂纹。预应力作用使叶片固有频率有所增加,随风速增大影响越大,尤其对低阶频率影响更加明显,对叶片进行振动分析应进行考虑。     

离心泵叶轮水中固有频率经验下降系数分析及优化

在工程实际中,通常采用结构在空气中的自振频率乘以一个经验影响系数得出水中的自振频率,但是通过传统经验影响系数得出的结果与现实相比有很大的误差。本文选用能更加清楚表达水体对叶轮固有频率影响大小的下降系数进行研究。运用基于流固耦合的有限元方法对圆柱模型和两种离心泵叶轮进行模态计算,通过对结果的分析和比较发现：下降系数与结构的固有频率和振型有很大关系,采用分段取值更为合理,模态低阶取小值,高阶取大值,旋转振型取小值。最后对离心泵叶轮模型计算结果进行二次优化,得到更加符合实际的经验下降系数：模态前6阶除第3阶取0.05外,其余取0.15,第7—10阶取0.40。     

撑卧式平板钢闸门自振特性研究

采用有限元分析软件ANSYS获取闸门的自振频率和振型模态特性,对撑卧式平板钢闸门流固耦合效应下的模态进行了计算,结果表明:流固耦合对闸门振动特性具有很大影响,并且支撑桁架结构尺寸和形式对流固耦合作用明显.     

基于ANSYS的护镜门振动特性分析

护镜门作为大孔口跨度的新式闸门,特殊的力学结构导致其振动特性较为复杂。以南京三汊河双孔护镜门为实例,针对闸门在动水中启闭时,闸门振动频率与闸门开度和振型阶数的关系,基于ANSYS模态分析模块,采用广义Westergaard公式模拟流固耦合中的附加质量,对于护镜门的振动特性进行研究。结果表明:在低阶模态时,考虑附加质量法的流固耦合模型基本符合真实工况;闸门有发生共振和动力失稳的风险,需要优化闸门结构和改进启闭机构。文章可为之后护镜门设计和优化提供参考。     

混流式水轮机转轮振动特性

为掌握混流式水轮机转轮振动特性以及各部件对转轮固有频率的影响规律,采用有限元法并基于流-固耦合模态分析理论,以某转轮为例,建立分析模型。结果表明,受水体影响转轮各振型的固有频率会不同程度地降低,转轮整体振型如扭转、弯曲和抬升等振型对应的水中频率与空气中频率的比值依次减小,仅叶片振动时对应的水中频率与空气中频率比值随叶片振动形态的增强而增大;叶片振动对应的频率覆盖频域较宽,很难避免共振现象的发生;上冠减薄,转轮固有频率降低,下环减薄,转轮摆动、扭转、弯曲振型对应的固有频率提高,其他振型的固有频率均降低,出水边补强转轮固有频率提高。结合分析结果和影响因素,提出了补气、修整叶片出水边、改善泄水锥形式、加设稳流装置等改善转轮水中振动状态的措施。     

长岗坡渡槽流固耦合特性分析

以广东长岗坡渡槽为研究对象,考虑运行期水体与槽体间的耦合作用,运用ANSYS有限元软件建立渡槽流固耦合模型,采用Unsymmetric法提取有水和无水两种工况的模态结果,获得前5阶频率和主振型。结果表明:渡槽结构的基频为1.034 Hz;渡槽结构的主振型以横向振型和整体振型为主;运行水位工况的各阶频率均小于无水工况,水体的存在削减了结构自振,因此在结构抗震设计和安全评价时应考虑流固耦合作用。     

基于流固耦合的混流式水轮机转轮振动特性分析

为防止水轮机转轮发生共振,导致叶片产生共振裂纹,需要对水轮机的固有频率进行计算,使转轮的固有频率避开外界的激振频率。本文基于流固耦合方法,将CFD软件CFX与有限元软件ANSYS Workbench相结合,对某水电站混流式水轮机转轮进行了有限元模态分析计算,分别计算了转轮在有无预应力情况下对于模态计算结果的影响,并分别考虑了转轮在空气中和在水介质中的固有频率和振型。结果表明,转轮在有预应力情况下各阶固有频率会有所提高,提高幅度在0.5%以内,可以忽略预应力的影响;转轮在水中的各阶固有频率比在空气中均有明显的降低,且各阶频率降低程度不同,下降系数的总体趋势是随着阶次的提高而逐渐减小的。     

渡槽排架结构环境激励模态试验

为获得渡槽排架结构动力特性,开展渡槽排架单向单输入多输出(SIMO)法、双向多输入多输出(MIMO)法环境激励模态试验,选用增强频域分解法识别纵向、横向、双向模态参数。结果表明,SIMO法纵向模态绝大多数谱峰明显、识别效果较好,纵向模态比横向模态丰富;MIMO法纵向或以纵向为主的谱峰大多数明显,横向或以横向为主、双向模态除双向第2阶(即横向第1阶)谱峰明显外,其他较小,甚至未能识别;排架柱以弯曲振动为主,纵向低阶、高阶模态横梁分别以平动或转动刚体振动、弯曲振动为主,横向模态横梁为平动或不动刚体振动;两种方法识别出的模态频率误差较小,SIMO法结果更为可靠,尤其是低阶模态。从低阶识别精度、试验工作量及操作便捷性而言,排架结构环境激励模态试验选择单向SIMO法优于双向MIMO法。     

FREQUENCY RESPONSE ANALYSIS IN INTERNAL FLOWS

ＦＲＥＱＵＥＮＣＹＲＥＳＰＯＮＳＥＡＮＡＬＹＳＩＳＩＮＩＮＴＥＲＮＡＬＦＬＯＷＳ￥ＺｈａｎｇＬｉ－ｘｉａｎｇ（ＹｕｎｎａｎＰｏｌｙｔｅｃｈｎｉｃＵｎｉｖｅｒｓｉｔｙ，ＥｌｅｃｔｒｉｃＥｎｇｉｎｅｅｒｉｎｇ，Ｋｕｎｍｉｎｇ６５００５１，Ｐ．Ｒ．Ｃｈｉｎ...     

DIRECT NUMERICAL SIMULATIONS OF THE DYNAMICS OF PARTICLES WITH ARBITRARY SHAPES IN SHEAR FLOWS

A fluid-structure interaction method based on the arbitrary Lagrangian-Eulerian method and a dynamic mesh method was developed to simulate the dynamics of a rigid particle in shear flows. In the method, the governing equations for the fluid flow and particle motion were sequentially solved in a two-way coupling fashion. The mesh system was deformed or re-meshed by the dynamic mesh method. The method was employed to simulate the dynamics of a single particle suspended in a flow channel and the dynamics of the particle were studied. The simulation results show that the angular velocity is not only a function of the inclination angle, is but also influenced by the aspect ratio yielding a hysteresis, while the angular velocity obtained from the Keller-Scalak model is a function only of the inclination angle and does not show a hysteresis. The present simulations clearly demonstrate that the Fluid-Structure Interaction (FSI) module is very stable, accurate and robust.     

弱约束管道系统水锤研究与进展

充液管道中瞬变流的研究有着悠久的历史，积累了极为丰富的文献和资料。人们对系统不稳定流的认识也随着科学技术的进步不断发展开拓，内容及航空航天，石油化工，机械传动，水利电力等２０多个研究方向。     

THE RADIATION AND DIFFRACTION OF WATER WAVES BY A BOTTOM-MOUNTED CIRCULAR CYLINDER IN A TWO-LAYER FLUID

An analytical method was proposed to analyze the radiation and diffraction of water waves by a bottom-mounted circular cylinder in a two-layer fluid. Analytical expressions for added mass and damping coefficients, as well as the wave excitation forces of the circular cylinder were obtained by an eigenfunction expansion method. The hydrodynamic forces on the bottom-mounted circular cylinder in a two-layer fluid include not only the added mass and damping coefficients, but also the wave forces of the surface and internal-wave modes. This is different from the case of a homogenous fluid. Some examples were given, showing that density stratification can have a relative large effect on these hydrodynamic forces over a wide range of frequencies.     

ANALYSIS OF STABILITY CHARACTERISTICS OF NONLINEAR FLUID STRUCTURE INTERACTION SYSTEM IN INTERNAL FLOWS

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＩｎａｐｉｐｉｎｇｓｙｓｔｅｍｗｉｔｈｉｎｔｅｒｎａｌｆｌｏｗｓ,ａｎｕｎ ｓｔｅａｄｙｏｒｅｘｔｒｅｍｅｌｙｕｎｓｔｅａｄｙｆｌｏｗｉｎｄｕｃｅｄｂｙａｓｕｄｄｅｎｓｙｓｔｅｍｏｐｅｒａｔｉｏｎｏｒｖｉｂｒａｔｉｏｎｍａｙｃｒｅａｔｅａ ｐｒｅｓｓｕｒｅｓｕｒｇｅｃａｌｌｅｄｇｅｎｅｒａｌｌｙｗａｔｅｒｈａｍｍｅｒ.Ａ ｐｒｅｓｓｕｒｅｗａｖｅｐｒｏｐａｇａｔｉｎｇａｌｏｎｇｔｈｅｐｉｐｅｗｉｌｌｉｎｄｕｃｅｓａｎｉｎｔｅｎｓｉｖｅｉｎ ｔｅｒａｃｔｉｏｎｂｅｔｗｅｅｎ…     

基于FSI系统的(ui,p)格式大型渡槽动力分析

 槽体固体以位移为基本未知量,槽内水体以流场压力p为基本未知量,用能量变分原理推导了流固耦合(FSI)系流有限元分析的(ui,p)格式,给出流固耦合系统的动力特性方程,并基于FSI系统的(ui,p)格式建立渡槽槽体-水体-槽墩-基础-地基系统的力学模型,采用非对称模态提取法求解了渡槽的动力特性,并用隐式-显式积分算法计算了强震作用下大型渡槽的动力响应。计算结果表明,基于(ui,p)格式的流固耦合系统有限元分析的格式,考虑到槽体与水体的相互作用,简化了计算模型,提高了计算精度,同时也得出不同过水量下槽体结构动力特性和动力响应的变化规律等结论。     

Flow induced structural vibration and sound radiation of a hydrofoil with a cavity

The structural vibration and the sound radiation induced by the flow over a cavity on a hydrofoil are investigated experimentally and numerically. The large eddy simulation(LES) is adopted to calculate the flow field and the pressure fluctuation characteristics. A coupled finite element method/boundary element method approach is used to analyze the hydrofoil vibration and the structure-borne noise. The flow noise is calculated using an acoustic analogy by considering the surface pressure fluctuations as the dipole sources. A hollow hydrofoil with an orifice supported by four cylinder rods is constructed for the experiments. Modal tests are performed to obtain the natural frequencies of the hydrofoil in air and water. The vibro-acoustic experiments are carried out in the water tunnel at various free stream velocities with the orifice open and closed. A pressure transducer is used to measure the pressure fluctuations behind the downstream edge of the orifice. The triaxial accelerometers mounted on the side walls are used to measure the vibrational response of the hydrofoil. Furthermore, a hydrophone located in a box, filled with water is used to measure the sound radiation. The structure-borne noise and the flow noise are identified by their frequency properties. Reasonable agreements are observed between the numerical predictions and the experimental measurements.     

Hydrodynamic modeling of cochlea and numerical simulation for cochlear traveling wave with consideration of fluid-structure interaction

The cochlea is an important structure in the hearing system of humanity. Its unique structure enables the sensibility to the sound waves of varied frequencies. The widely accepted model of the cochlea is expressed as a long tube longitudinally divided by a membrane named the Basilar Membrane (BM), into two fluid-filled channels. Based on various assumptions for the cochlear fluid and structure, simplified mathematical and mechanical cochlear models were developed to help to understand the mechanism of the complex coupled system in the past decades. This paper proposes a hydrodynamic numerical cochlear model with consideration of the Fluid-Structure Interaction (FSI). In this model, the cochlear lymph is considered as in a Newtonian viscous fluid, and the basilar membrane is modeled as a composite structure. The traveling wave is simulated. Also focusing on the pressure in the fluid field, the results are compared with studies of Peterson and Bogert, where it was assumed that the slow compressive waves are traveling along the BM. Furthermore, the transmitting time of the cochlear traveling wave is also discussed.