Vortex-induced vibration of two elastically coupled cylinders in side-by-side arrangement

Vortex-induced vibration (VIV) of two elastically coupled circular cylinders in side-by-side arrangement is investigated numerically. The Reynolds-averaged Navier–Stokes equations are solved by the finite element method for simulating the flow and the equation of motion is solved for calculating the vibration. The mass ratio (the ratio of the mass of the cylinder to the displaced fluid mass) is 2 and the Reynolds number is 5000 in the simulations. Simulations are carried out for one symmetric configuration (referred to be Case A) and one asymmetric configuration (referred to be Case B). In both Case A and Case B, the primary response frequencies of the two cylinders are found to be the same both inside and outside the lock-in regimes. Five response regimes are found in both cases and they are the first-mode lock-in regime, the second-mode lock-in regime, the sum-frequency lock-in regime and two transition regimes. When the vibration is transiting from the first- to the second-mode lock-in regimes, the vibration of each cylinder contains both first- and the second-mode natural frequencies, and the vibrations are usually irregular. In the transition regime between the second-mode lock-in and the sum-frequency lock-in regimes, the response frequencies of both cylinders increases with an increase in the reduced velocity until they are close to the sum of the two natural frequencies. In both cases, the lower boundary reduced velocity of the total lock-in regime (the sum of the five lock-in regimes) is about 3 and the upper boundary reduced velocity is about 11 times the first-to-second-mode natural frequency ratio.     

Research on coupled thermo-hydro-mechanical dynamic response characteristics of saturated porous deep-sea sediments under vibration of mining vehicle

The excessive deformation of deep-sea sediments caused by the vibration of the mining machine will adversely affect the efficiency and safety of mining. Combined with the deep-sea environment, the coupled thermo-hydro-mechanical problem for saturated porous deep-sea sediments subject to the vibration of the mining vehicle is investigated. Based on the Green-Lindsay(G-L) generalized thermoelastic theory and Darcy's law, the model of thermo-hydro-mechanical dynamic responses for saturated porous deep-sea sediments under the vibration of the mining vehicle is established. We obtain the analytical solutions of non-dimensional vertical displacement, excess pore water pressure, vertical stress, temperature, and change in the volume fraction field with the normal mode analysis method, and depict them graphically. The normal mode analysis method uses the canonical coordinate transformation to solve the equation, which can quickly decouple the equation by ignoring the modal coupling effect on the basis of the canonical mode. The results indicate that the vibration frequency has obvious influence on the vertical displacement, excess pore water pressure, vertical stress, and change in volume fraction field. The loading amplitude has a great effect on the physical quantities in the foundation, and the changes of the physical quantities increase with the increase in loading amplitude.     

Dynamic coupled thermo-hydro-mechanical problem for heterogeneous deep-sea sediments under vibration of mining vehicle

Due to the influence of deep-sea environment, deep-sea sediments are usually heterogeneous, and their moduli of elasticity and density change as depth changes.Combined with the characteristics of deep-sea sediments, the thermo-hydro-mechanical coupling dynamic response model of heterogeneous saturated porous sediments can be established to study the influence of elastic modulus, density, frequency, and load amplitude changes on the model. Based on the Green-Lindsay generalized thermoelasticity t...     

二维系统传递矩阵法

以薄板横向振动的振动特性问题为例提出了二维系统传递矩阵法. 从质点和无质量梁的传递 矩阵出发,建立了按列排列的薄板子结构的传递矩阵. 用二维系统传递矩阵法获得了整个板 的总体传递方程,从而可得到板在任意一种边界条件下的特征方程. 数值求解了两种情况下 薄板横向振动的固有振动特性. 计算结果表明,用该方法可用于研究类似薄板的二维系统的 动力学问题,且无需建立系统的总体动力学方程.     

火箭上面级星敏感器/陀螺组合定姿实时仿真系统

针对运载火箭上面级惯性导航设备提供的姿态信息随时间累积而误差逐渐增大的问题,提出了基于扩展卡尔曼滤波的星敏感器/陀螺组合姿态确定算法,并为加快工程样机研制设计了基于Matlab/dSPACE平台的实时仿真系统。基于地心第二轨道坐标系和上面级体坐标系,给出了姿态角定义,推导了姿态转换矩阵。通过分析组合定姿方案和姿态状态估计方法,设计了基于误差四元数的滤波器;为减少算法的计算量,采用了离线计算次优增益矩阵的方法。进行了星敏感器在回路中的半实物仿真。仿真结果表明组合定姿精度优于50″,且能够准确估计陀螺常值漂移。该算法精度高,速度快,实时仿真系统具有很好的参考和应用价值。     

Transfer matrix approach of vibration isolation analysis of periodic composite structure

The transmission properties of elastic waves propagating in a three-dimensional composite structure embedded periodically with spherical inclusions are analyzed by the transfer matrix method in this paper. Firstly, the periodic composite structures are divided into many layers, the transfer matrix of monolayer structure is deduced by the wave equations, and the transfer matrix of the entire structure is obtained in the case of boundary conditions of displacement and stress continuity between layers. Then, the effective impedance of the structure is analyzed to calculate its reflectivity and transmissivity of vibration isolation. Finally, numerical simulation is carried out; the experiment results validate the accuracy and feasibility of the method adopted in the paper and some useful conclusions are obtained. Project (No. 50075029) supported by the National Natural Science Foundation of China.     

变截面钢板弹簧刚度计算的传递矩阵法

钢板弹簧悬架是商用汽车的关键部件,对整车的平顺性以及操纵稳定性有着重要影响,采用变截面少片簧代替多片簧是整车轻量化的重要趋势。由于变截面钢板弹簧成型的复杂性,传统的设计计算方法存在较大误差。在精确分析梯形梁单元变形特性的基础上,提出了一种新的变截面板簧刚度计算的传递矩阵法。对于广泛应用的各种变截面板簧,一般只需十来个单元即可得到非常逼近于有限元精确分析的结果。最后,通过不同类型板簧和不同方法的对比计算验证了该方法的有效性。     

拱暨索拱面内稳定性研究的传递矩阵法

为探究拱桥面内稳定问题求解的新途径,应用传递矩阵法对径向均布荷载作用下的圆拱面内屈曲微分方程进行解答,利用边界条件导出其特征方程,从而求得其屈曲荷载。同时,结合力法以及拱上荷载集度与轴力的关系,将该理论方法推广到承受集中荷载的变截面拱以及索拱组合结构的稳定分析中,并和有限元ANSYS计算结果进行对比,验证了本文理论和方法的正确性。最后,研究了不同荷载工况下的边界条件、圆心角和截面惯性矩对拱结构面内稳定性的影响。结果表明,索拱结构的面内稳定性优于纯拱结构。     

一种可用于运载火箭的SINS/GNSS自主导航方案

研究了一种可用于运载火箭的SINS/GNSS自主导航方案。起飞前捷联惯组采用基于惯性系重力加速度积分的解析粗对准和卡尔曼滤波精对准,起飞后采用SINS/GNSS卡尔曼滤波组合导航反馈实时修正姿态、速度和位置。仿真结果表明捷联惯组水平自主对准误差0.01°,方位自主对准误差1.5°,起飞后经组合导航修正后的姿态误差小于0.2°,速度误差小于0.4m/s,位置误差小于40m,考虑所有误差的蒙特卡罗仿真结果满足火箭入轨精度要求,此方案具有较高的工程应用价值。     

箭载捷联惯导系统水平自对准的两种实用方法

箭载惯导系统的方位对准一般通过外界直接瞄准装订,而水平对准利用惯导系统的惯性器件测量和计算来实现.在运载火箭初始对准过程中,箭体受发射场阵风等干扰因素的影响而使得惯导系统产生角晃动与线晃动,水平对准方法必须具备抗晃动干扰的能力.根据运载火箭初始对准中的水平姿态角及其变化比较小的特点,建立了俯仰角与偏航角之间相互解耦的对准误差方程.提出了应用控制原理和数字滤波进行水平对准的两种方法,计算机仿真表明了这两种方法有效可行.与传统的卡尔曼滤波对准相比,本文的方法具有运算简单、计算量小和便于工程应用等优点.     

耦合路面损伤的车辆随机动荷载特性研究

为准确分析车辆对不平整路面作用的实际动荷载,在传统计算方法的基础上,进一步考虑了永久变形和平整度劣化等路面损伤累积的影响,提出了耦合损伤的车辆随机动荷载分析方法.通过计算轴载作用下路面各点的永久变形,推导路面不平整度的更新方程,将其引入车-路系统动力方程,采用Matlab编制求解程序,即可得到任意时间路面各点受到的车辆随机动荷载序列.基于该方法分析了车辆随机动荷载沿轮迹的分布变化,研究了随机动荷载系数随轴次的演化规律.结果 表明,车辆随机动荷载是随时间逐渐增大的动态演化过程,其沿轮迹的分布具有空间可重复性,随着轴载作用,动荷载的离散程度增大,将引起路面各点的损伤累积差异增大;而车辆行驶速度越低,新建路面越不平整,动荷载随时间演化速率越快,对路面造成的损伤越大.     

Novel method for research on exposure to nonlinear vibration transferred by suspension of vehicle

The paper presents novel method for research on exposure to nonlinear vibration of passenger car suspension as nonlinear dynamical system. Also paper provides a discussion on the results of studies addressing the impact exerted by damping properties of shock absorber on the vibrations being generated. The research was conducted on the car forced to vibration by the exciter machine with changeable frequency. The paper addresses results of analysis of application of one of the time-frequency representation techniques to the identification of structure of vibration. The obtained representation of the vibration allows determining time function of separate frequency bands, which represents the isolated vibration dynamics phenomena. Considering the variability of the time and frequency distribution of the vibration even in selected analysed bands, the time function was developed as exposure to vibration estimator. The recommended method makes use of function of exposure to vibration. The advantage of these method is possibilities of precise analysis of chosen frequency bands. The investigations conducted confirm considerable susceptibility to changes in the technical condition of shock absorber with regard to the assessment of human exposure to vibrations.     

不同轮轨接触模型在车桥耦合振动中的比较

以工程实例为研究对象,建立了整车-整桥系统耦合振动数值分析模型。考虑车轮的跳轨和挤密情况,建立了单边弹簧-阻尼系统弹性轮轨接触模型。采用基于多体系统动力学和有限元法结合的联合仿真技术,计算了两种轮轨接触时动车组列车以不同车速通过大跨度连续桥梁的耦合振动响应。数值计算结果表明:两种轮轨接触模型的桥梁动力响应比较接近;列车的横向轮轨力、轮重减载率和脱轨系数相差较大,当速度为350km/h时,横向轮轨力增大了46.5%,轮重减载率增大了130.8%,脱轨系数增大了24.66%;用单边-弹簧阻尼系统弹性轮轨接触模型更符合实际。     

结构地震反应分析的频域传递矩阵法

本文将传递矩阵法的应用范围由结构的固有振动分析推广到频域内的地震反应分析。文中具体给出了弯剪粱结构的单元传递矩阵的频域形式。用这种频域内的传递矩阵，结合离散傅里叶变换，即可求得多自由度弯剪梁体系的地震反应。同样地，可用这种方法计算各种串联多自由度体系在其它动力荷载下的反应。该方法精度良好且比相应的有限元法节省计算机ＣＰＵ时间。     

液体火箭爆炸地面有害气体生成与扩散分析

建立了自燃液体推进剂运载火箭爆炸时地面残余推进剂蒸发模型和产生的有害气体在大气中的扩散模型,给出了N2O4/UDMH液体推进剂爆炸产生的地面推进剂残留量、推进剂污染区直径、大气环境中地面残余N2O4和UDMH推进剂蒸发速率等参数的实验结果。利用该理论模型对大型运载火箭发生意外爆炸事故产生的地面残余推进剂蒸发时间和形成的有害气体危害范围进行了估算。该理论模型可为航天发射场制定安全防护措施提供有用的评估方法。     

Design for a specified natural frequency of elastically constrained axially graded bars

This study derives some closed-form analytic as well as numeric solutions for the axially graded elasticallyconstrained bar with polynomial varying modulus of elasticity, along the axial coordinate. The solutions allow for vibration tailoring in such a manner that the bar possesses the pre-selected natural frequency.     

双材料单伸臂叠合梁的界面滑移与自振特性分析

将叠合梁划分为接触区和分离区,接触区界面间的摩擦作用会对叠合梁的滑移、刚度和自振频率产生影响.本文给出了单伸臂叠合梁在均布荷载和集中力作用下,考虑叠合界面摩擦作用的滑移应变和滑移分布的表达式;推导了考虑叠合界面间摩擦力及摩擦力产生的抵抗弯矩共同作用下的截面刚度.假设梁按等波长和等刚度两种形式自由振动,运用传递矩阵法推导...     

弹性约束边界圆环板面内自由振动的二维弹性解

基于二维线弹性理论,应用哈密顿原理导出弹性约束边界圆环板面内自由振动的控制微分方程。采用微分求积法(DQM)数值研究了弹性约束边界圆环板面内自由振动的频率特性。通过设置弹性刚度系数为0或∞,问题退化为四种典型边界圆环板的面内自由振动,与已有文献的计算数值结果进行比较,证实本文的分析求解方法行之有效。最后全面考虑了圆环板边界条件、几何系数及刚度系数对自振频率的影响。     

Numerical investigation on vortex-induced vibration of an elastically mounted circular cylinder at low Reynolds number using the fictitious domain method

A direct numerical simulation of two-dimensional (2D) flow past an elastically mounted circular cylinder at low Reynolds number using the fictitious domain method had been undertaken. The cylinder motion was modelled by a two degree-of-freedom mass–spring–damper system. The computing code was verified against a benchmark problem in which flow past a stationary circular cylinder is simulated. Then, analyses of vortex-induced vibration (VIV) responses, drag and lift forces and the phase and vortex structures were carried out. Results show that the cylinder's non-dimensional cross-flow response amplitude reaches its summit of 0.572 in the ‘lock-in’ regime. The ‘2S’, instead of the ‘2P’, vortex shedding mode is dominated in the ‘lower’ branch for this 2D low-Re VIV. A secondary oscillation is observed in the lift force when ‘lock-in’ occurs. It is shown that this secondary component changes the phase, offset the energy input by the primary component and thus reduces the cylinder responses. Effects of the Skop–Griffin parameter on cylinder responses were also investigated.