复合材料曲壁板颤振特性分析

基于Marguerre曲板理论、von Karman大变形理论和气动力活塞理论建立超音速气流中三维复合材料曲壁板的有限元模型。分析了不同边界条件下复合材料曲壁板的曲率对曲壁板颤振边界特性的影响规律。结果显示:1)当曲率较小时,颤振是由曲壁板前两阶模态耦合产生,颤振临界动压随着曲率的增大而减小;2)当曲率较大时,颤振危险模态会随曲率增大而发生变化,颤振临界动压也会表现出复杂的变化规律;3)曲率较小时,四边固支曲壁板的颤振临界动压高于四边简支曲壁板;4)当曲率较大时,四边简支曲壁板的颤振临界动压可能大于四边固支曲壁板。     

轴向运动粘弹性Rayleigh梁的参激振动稳定性

研究了轴向运动粘弹性Rayleigh梁参激振动的稳定性。根据广义哈密顿原理建立轴向运动Rayleigh梁横向振动的控制方程,同时考虑轴力的变化。采用多尺度方法直接求解控制方程,推导出主共振和组合共振的可解性条件;利用Routh-Hurwitz稳定性判据导出了稳定性边界方程;进而确定梁两端简支和固支边界条件下,因共振而产生的失稳区域。数值算例给出了两端简支和固支边界条件下弯曲刚度,支撑刚度,粘弹性系数以及平均速度对前两阶主共振及组合共振稳定性区域的影响。     

ANSYS特征值法在计算外压圆筒弹性失稳中的应用讨论

针对弹性范围内外压圆筒,采用ANSYS软件特征值法对其进行稳定性分析,并与目前常见的理论计算公式、设计标准算图进行对比分析。结果表明:采用壳单元Shell 181,当Mx>2.83时,ANSYS软件中特征值法(LBA)所得结果与Mises公式吻合较好,且与设计标准中外压算图中的数据基本一致;弹性分析中,边界条件的设置对临界失稳压力的计算值有较大的影响,固支边界条件下的临界失稳压力计算值大于简支边界条件。     

水下压缩气体储能管道振动特性分析

水下压缩气体储能作为一种柔性规模的储能技术，是向可再生、可持续能源结构过渡的新兴推动力。水下管道输气过程中经常发生液体积聚，从而促使管道内单相流转变为复杂的气液两相流。由于不稳定的两相流动与管道之间产生了耦合作用，引起管道振动，进而影响水下压缩气体储能系统的运行。基于ANSYS对储能管道和管道支撑结构进行了有限元分析。建立了有限元模型并对管道进行模态分析，通过对比有无流固耦合下管道的固有频率，得出流固耦合的存在会降低管道的固有频率。并进一步分析管道固定结构对管道振动特性的影响，对比3种不同固定方式，发现固支-固支支撑结构相对比固支-简支与简支-简支抗振效果好。     

含横向导支端Euler-Bernoulli梁弯曲振动的固有特性分析

分析了起重机抗倾覆稳定性动态设计过程中,将起重机结构抽象成具有横向导支端的Euler-Bernoulli梁结构的必要性,计算并研究了此类梁在简单边界条件——两端导支(S-S)、导支-自由(S-F)、导支-简支(S-SS)和导支-固支(SC)下的弯曲振动固有频率和振型函数。用数值算法计算发现:一端导支另一端自由或导支横梁存在横向刚体模态;一端导支一端自由或导支及一端导支一端简支或固定的两种横梁的振动特性十分相似;导支端将引起振型函数凹凸性的变化。最后,对近工况复杂导支-弹性支撑与约束下的横梁模态参数进行了求解。     

边界条件对薄壁加筋板压缩稳定性能的影响

应用非线性有限元方法对加筋板的压缩稳定性进行建模数值计算,通过定义加筋板有限元模型中四边节点的约束条件模拟压缩稳定性试验中承载端简支、固支边界条件以及常用的刀口支持、螺栓顶压、夹板夹持等侧边支持夹具,根据有限元计算结果分析承载端和侧边边界条件对加筋板压缩稳定性能的影响。计算结果表明,当承载端边界约束条件为固支时,结构的屈曲载荷与承载能力均比承载端简支时有一定的增加;当承载端简支时,结构的屈曲形式与破坏失效形式随侧边边界约束条件的不同而不同,相比于侧边自由的情况,侧边施加约束可以增加结构的屈曲载荷与承载能力;当承载端固支时,不同侧边边界约束条件下结构的屈曲形式与屈曲载荷基本相同,相比于侧边自由的情况,侧边施加约束可以增加结构的承载能力。     

起重机简支斜板的局部稳定性研究

为了分析起重机斜板结构的局部屈曲失稳问题。针对斜坐标系下纵向载荷作用斜板的屈曲控制微分方程、简支边界条件,进行无量纲化。同时,给出微分求积法(DQM)求解简支斜板局部屈曲失稳临界载荷的具体方法。以单向轴压作用下简支斜板为例,首先通过对比验证DQM数值解的精确性;最后对起重机简支斜板结构参数与屈曲临界载荷之间的关系进行了研究。     

200单元硅基单压电变形镜的设计与测试

针对天文望远镜对变形镜的需求,设计了200单元级硅基单压电变形镜并对其进行了性能测试。首先,通过有限元方法对单压电变形镜进行结构建模,分析比较了电极排列形式和边界支撑方式对变形镜性能的影响。然后,制备了3款200单元变形镜样机(环形简支,环形固支,六边形简支)。最后,利用干涉仪测量了变形镜的影响函数,并通过激光多普勒测振仪测量其频响特性。仿真与实验结果表明:致动器在50V电压下变形量可达1μm,固支条件下谐振频率在1kHz左右,对前100项Zernike像差具有良好的校正能力。该变形镜在低成本天文自适应光学系统中具有应用潜力。     

边界条件和激励位置对高速列车车窗声振特性影响研究

为研究高速列车车窗的振动声辐射和隔声,基于Hamilton原理和声学Rayleigh积分建立了车窗的有限元-边界元耦合模型.利用矩形薄板在自由、简支和固支等经典边界条件下的模态分析结果、无限大板的隔声验证了模型的正确性.基于验证后的模型,对比了车窗在经典边界条件下的声辐射和隔声,分析了点激励位置对车窗声辐射的影响,研究...     

旋转锯片空气动力学噪声特性计算与分析

为分析旋转刀具在气流作用下的声学特性,基于多场耦合计算方程建立了流场-结构-声场联合仿真模型,通过弹性体与流场的动力学计算得到了结构强迫振动响应,利用边界元法将振动响应信息作为声学边界,获取了锯片的声场辐射信息,噪声预估值与实测结果吻合良好。研究了锯片旋转过程中周围流场媒介的层流、湍流特性对锯片振动的影响规律;揭示了流-固耦合作用对声场时域、频域影响作用机制;确定了锯片空载噪声辐射的方向特性;分析了锯片尺寸结构对噪声的影响规律,为低噪声锯片的设计提供了参考依据。     

篦齿封严气弹稳定性影响因素研究

为探究篦齿封严气弹失稳机制,理论分析了篦齿封严结构动力学与气弹稳定性判定公式,建立了篦齿封严结构动力特性数值求解模型与气弹稳定性求解模型,并验证该了方法的准确性;研究了篦齿环齿间距、壁厚以及转速对篦齿封严固有频率与气弹稳定性的影响规律,揭示了篦齿封严气弹失稳影响机制。研究表明：齿间距、壁厚对固有频率的影响程度随着节径数的增加而增大,对前三阶固有频率影响不大;转速对于第一阶固有频率影响最大;篦齿封严齿间距的增加会导致固有频率和气弹稳定性的下降;篦齿封严壁厚的增加可引起固有频率的升高,并且可以有效改善气弹稳定性;升高转速会引起篦齿环固有频率较明显的增加,对气弹稳定性影响较小。     

Direct numerical simulation of channel flow with wall injection

The present study investigates turbulent flows subject to strong wall injection in a channel through a Direct Numerical Simulation technique. These flows are pertinent to internal flows inside the hybrid rocket motors. A simplified model problem where a regression process at the wall is idealized by the wall blowing has been studied to gain a better understanding of how the near-wall turbulent structures are modified. As the strength of wall blowing increases, the turbulence intensities and Reynolds shear stress increase rapidly and this is thought to result from the shear instability induced by the injected flows at the wall. Also, turbulent viscosity grows rapidly as the flow moves downstream. Thus, the effect of wall-blowing modifies the state of turbulence significantly and more sophisticated turbulence modeling would be required to predict this type of flows accurately.     

Effect of boundary condition history on the symmetry breaking bifurcation of wall-driven cavity flows

A symmetry breaking nonlinear fluid flow in a two-dimensional wall-driven square cavity taking symmetric boundary condition after some transients has been investigated numerically. It has been shown that the symmetry breaking critical Reynolds number is dependent on the time history of the boundary condition. The cavity has at least three stable steady state solutions for Re=300-375, and two stable solutions if Re>400. Also, it has also been showed that a particular solution among several possible solutions can be obtained by a controlled boundary condition.     

固体颗粒对低黏度介质润滑特性的影响

基于水-固两相单流体模型,研究润滑过程中的固体颗粒对低黏度润滑介质的影响。以无限宽楔形滑块为计算模型,推导出特定假设条件下考虑惯性力和界面滑移的低黏度介质润滑的雷诺方程,并通过不同条件下雷诺方程的求解,探讨固体颗粒含量对低黏度介质润滑特性的影响。结果表明:在对低黏度介质润滑特性进行研究时,需考虑其惯性力和界面滑移影响;固体颗粒的存在一定程度上增大润滑膜的压力和承载能力,颗粒含量越大,承载能力越大,但颗粒含量对润滑膜整体的压力分布状态几乎不会产生影响;惯性力增大固体颗粒对润滑介质的影响程度,而界面滑移减小固体颗粒对润滑介质承载能力的影响,发生滑移时,颗粒基本不影响润滑膜的承载能力。     

An analytical approach on the tribological behaviour of pocketed slider bearings with boundary slip including cavitation

Slider bearing performance depends on the boundary conditions at the interface between the solid surfaces and the fluid. This paper presents the combined effect of pockets and boundary slip on the load support and friction of parallel sliding systems using analytical solutions for a simple pocketed bearing. The effect of cavitation was of particular interest with respect to the inlet suction mechanism. It was demonstrated that applying boundary slip in a pocketed slider bearing gives a reduction in load support compared with the textured bearing without wall slip. Adding slip over the whole surface could retard the presence of cavitation. The influence of boundary slip is explored, and was found to significantly affect the frictional behaviour. Copyright © 2016 John Wiley & Sons, Ltd.     

Nonlinear viscose flow induced nonlocal vibration and instability of embedded DWCNC via DQM

Nonlinear thermo free vibration and instability of viscose fluid-conveying double-walled carbon nanocones (DWCNCs) are studied using Hamilton’s principle and differential quadrature method (DQM). The small-size effects on bulk viscosity and slip boundary conditions of nanoflow through Knudsen number (Kn) is considered. The nanocone is simulated as a clamped-clamped Euler-Bernoulli’s beam embedded in an elastic foundation of the Winkler and Pasternak type. The van der Waals (vdW) forces between the inner and outer nanocones are taken into account. The detailed parametric study is conducted, focusing on the combined effects of the nonlocal parameter, apex angles, aspect ratio, temperature change, fluid viscosity, boundary conditions and the elastic medium coefficient on the dimensionless frequency and critical fluid velocity of DWCNCs. The results show that the small-size effect on flow field is remarkable on frequency and critical fluid velocity of DWCNC. Also, the nonlinear frequency and critical flow velocity decrease with increasing the nonlocal parameter and cone semi-vertex angle. The results are in good agreement with the previous researches.     

Molecular dynamics simulation of poiseuille flow in ultra thin film

The effect of a solid wall on Poiseuille flow of ultra thin film has been simulated by molecular dynamics for a simple Lennard-Jones fluid. Results showed that the velocity profile and flow are consistent with the prediction of the Stokes equations when the film thickness is considerably greater than the molecular ‘diameter’; that Poiseuille or hydrodynamic flow will be blocked by the solid walls, and the effective viscosity will increase as the film thickness corresponds more closely to only a few molecular diameters; and that when the film thickness is reduced to just the molecular diameter, the fluid molecules between the walls will be solidified or crystallised, and the Poiseuille flow will vanish. This may be one of the mechanisms of transition from hydrodynamic to boundary lubrication.     

Wave propagation in an elastic/viscoplastic hollow sphere

An analysis of the dynamic problem of a hollow sphere is presented. The medium is assumed elastic/viscoplastic, satisfying Mises condition, isotropic hardening and viscoplastic incompressibility. The cavity is subjected to a radially applied and continuously maintained impact load. The analysis for viscoplastic waves is based on the method of characteristics and a generalized form of Malvern's theory for strain-rate dependent materials. A bilinear shear stress-shear strain curve is considered and calculations are carried out on the IBM 7094 computer. The paper examines the influence of the important parameters governing spherical wave propagation on the response of the sphere; these parameters include the level of strain hardening, the viscosity coefficient, Poisson's ratio and the geometry of the sphere. It is shown that the degree of strain hardening has a significant effect on the amplitude of the oscillations with the period unaffected. The viscosity coefficient becomes more influential as the wall thickness of the sphere increases.     

Effect of Reynolds number and boundary layer thickness on the performance of V-cone flowmeter using CFD

The effect of Reynolds number and boundary layer thickness on the performance of V-cone flowmeter has been evaluated using computational fluid dynamics (CFD). The shear stress transport k-ω (SST k-ω) turbulence model has been adopted for closure. The performance of two V-cone flowmeters with different beta ratios (β) viz., 0.6 and 0.7 for a fixed vertex angle (ϕ) of 60° has been analysed as a function of Reynolds number (Re). The results show that the coefficient of discharge (C_d) increases with Reynolds number in the laminar and transition flow regimes whereas it is nearly constant in turbulent flow regime. From the results, it can be concluded that C_d is independent of Re for values equal to 4000 and beyond. Further, it is also seen that the performance of the V-cone flowmeter is not affected by the upstream boundary layer thickness if the velocity profiles having different boundary layer thickness are extracted from an axial distance of 10D and more are fed at 5D upstream of the meter. However, the meter is sensitive to the extracted velocity profile from an axial distance of 5D and uniform velocity profile being fed at 5D upstream. The value of C_d may be sensitive as a result of the pressure variation due to the obstruction.     

基于有限元的盾构机主轴承腔内润滑特性研究

盾构机主轴承具有尺寸大、承受载荷高且转速慢的特点,研究其主轴承腔内润滑状况,对于保证盾构机主轴承的可靠性至关重要。运用三维建模软件及流体仿真软件对盾构机主轴承进行建模及腔内流体域仿真,研究主要润滑参数包括进油口位置分布、进油口的选择、润滑油黏度对腔内润滑状态的影响,以及腔内润滑状态与温度的关系。结果表明：进油口位置分布对润滑状态有着较大影响,非对称进油口分布对这种极低速旋转及重载的盾构机主轴承更有利;为改善润滑状态,进油口应分主进油口和副进油口,保持主进油口常开,副进油口的打开视工况而定;润滑油黏度对润滑状态及温度都有较大影响,存在最佳黏度区间使得温度保持较低水平且润滑状态良好;对应位置润滑油体积分数与温度成反比关系。