变速多移动质量耦合作用下柔性梁系统振动响应分析

针对多移动质量耦合作用下柔性梁的振动响应进行研究分析。根据柔性梁振动理论,考虑移动质量间相互运动与柔性梁弹性振动之间的耦合作用,建立了多移动质量-柔性梁系统的振动方程。采用时变力学系统数值求解方法,对多移动质量以不同运动形式作用下柔性梁系统的振动响应进行求解分析。计算结果表明：移动质量间相互运动的形式不同,梁的振动效果不同;与单个移动质量叠加作用相比,多移动质量间耦合作用下的梁的振动效果呈现显著的不同。     

空间弹簧阻尼并联振动模型的键图仿真

键图是振动系统建模的有效方法，它易于描述一维的单自由度和多自由度振动。将键图扩展应用到任意多个弹簧阻尼并联的空间多自由度振动系统，基于牛顿-欧拉法建立空间质量块的键图模型，将其和空间任意个并联的弹簧阻尼模型按照因果关系连接起来，再进一步补充添加角速度变换模块和运动学反解等模块就形成了描述空间多自由度振动系统的一般模型。以一个液压Stewart平台为实例进行仿真，仿真结果验证了模型的正确性，该模型对于研究空间复杂振动系统具有参考价值。     

人-板耦合系统动力特性研究

基于单自由度的人体模型,将分布人群简化成均匀连续分布的质量-弹簧-阻尼系统,并考虑楼板的阻尼,建立了有阻尼的分布人群-薄板耦合系统模型。分析了薄板与人体的频率比及人板质量比等参数对耦合系统动力特性的影响。以四边简支的均质矩形薄板为例,用有限元方法对该文结论进行了验证。研究成果可为人与结构相互作用及结构的人致振动分析提供参考。     

斜拉桥塔-索-桥耦合连续模型及其内共振分析

研究斜拉桥桥塔-斜拉索-桥面的连续耦合振动模型及其2∶2∶1和1∶1∶1内共振问题。计及拉索的重力垂度、倾角及空气阻尼等因素,将桥面简化为一端固支、一端受弹簧力作用的Bernoulli-Euler梁,桥塔视作受弹簧拉力和阻尼力的质量块,建立了桥塔-拉索-桥面连续耦合非线性振动模型。利用多尺度方法得到了系统发生内共振的条件,并求出系统的三个自由度稳态运动幅值所满足的关系式。对系统的内共振进行了数值模拟,验证了理论分析的正确性。结果表明,桥塔和拉索在初始扰动下会发生1∶1内共振,桥面在一次近似意义上仅仅提供了内共振产生的约束条件,但在内共振过程中没有参与系统各部分之间的能量交换。最后发现一定条件下,系统会出现混沌运动。     

均布人群对简支欧拉梁动力特性的影响

研究了作用在梁上的均匀分布人群对梁的动力特性的影响.将人群简化为均匀分布的弹性质量模型,考察了无阻尼的弹性质量和有阻尼的弹性质量两种模型对简支欧拉梁的动力特性的影响,得到了人群和梁耦合系统的频率和阻尼的解析表达式.并以此研究了分布质量与梁的质量之比对梁的频率和阻尼比的影响,得到了人群对结构动力特性影响的定性规律.结果表明:耦合系统在人体振动基频处分支出一系列的振动频率,并且当分布人群质量与结构质量之比达到一定程度时,均布的人群会对梁的振动特性产生显著的影响,明显改变梁的自振频率,显著提高梁振动的阻尼比.最后研究了梁的振动频率对人群-梁耦合系统阻尼比的影响.     

车桥耦合系统的非线性动力分析

研究了车桥耦合系统的非线性动力特性。基于哈密尔顿能量原理和欧拉-贝努利梁假设,考虑梁的几何非线性影响,建立了移动振动车辆模型下桥梁的耦合非线性振动方程,应用伽辽金法和Runge-Kutta法对方程进行求解,算例中探讨了车辆质量、车速、桥梁阻尼和桥跨径等参数对车-桥耦合系统非线性振动性能的影响。     

基于社会力模型的人群-桥梁竖向动力耦合效应研究

针对越来越多的轻质柔性人行桥在随机人群荷载作用下的结构振动问题,为了能够获得更为真实、精细的振动响应,建立考虑人群-结构相互作用的随机人群荷载模型尤为重要。首先利用移动弹簧-质量-阻尼模型模拟单人的动力学行为,并基于社会力模型,建立人群的随机运动模型,进而建立考虑人群-结构耦合振动的随机人群荷载模型。根据任意时刻人行桥和随机人群动力平衡,建立随机人群-人行桥耦合振动的控制方程。利用状态空间法求解人行桥动力参数随随机人群运动的变化情况,利用振型分解法求解耦合振动控制方程,探讨考虑人群-结构耦合振动的随机人群荷载对人行桥模态以及振动响应的影响。分析结果表明耦合系统模态变化量随着人数增加而增加。行人随机性与人群-结构相互作用对轻质结构的竖向动力响应影响很大,故在计算轻质结构振动响应时不可忽略。相比于加速度峰值,均方根加速度能够弱化随机波动的干扰作用,因此也采用了1-s均方根加速度更合理地衡量了结构的振动响应。     

含碰摩故障的新型转子-滚动轴承-机匣耦合动力学模型

针对航空发动机整机振动,建立了一种新型转子-滚动轴承-机匣耦合动力学模型.该模型具有如下特点:1)考虑转子、滚动轴承及机匣之间的耦合作用;2)考虑了实际航空发动机的弹性支承及挤压油膜阻尼效应;3)将转子考虑为等截面自由欧拉梁模型,运用模态截断法进行分析;4)考虑了滚动轴承间隙、非线性赫兹接触力以及变柔性VC(Varying Compliance)振动;5)考虑了转子与机匣之间的碰摩故障.运用数值积分方法获取了系统响应,研究了航空发动机的整机振动规律.     

覆盖增强主动约束层阻尼的旋转轴向FGM梁的热抑振研究EI北大核心CSCD

针对空间柔性机械臂容易发生热致振动的问题,以中心刚体-旋转梁模型为研究对象,在柔性梁表面部分覆盖增强主动约束层阻尼,研究了系统受热载荷冲击作用下的振动控制问题。假设基梁为适用于温度场的功能梯度材料(Functionally Graded Materials,FGM)梁,且材料特性沿轴向梯度分布。基于刚-柔耦合建模理论对温度场中的旋转FGM梁进行动力学建模,采用数值分析方法研究了增强主动约束层阻尼贴片位置/覆盖率、温度、结构宽度以及中心刚体半径等参数对结构末端变形的影响,经过对比找到了对结构振动影响较大的几个因素,包括贴片位置、贴片覆盖率以及结构宽度,可根据研究结果对结构进行优化,从而达到振动抑制的目的。     

非典型边界轴向移动绳的行波解及振动抑制

轴向移动绳系统广泛存在于工程设备中，因横向振动问题影响设备的正常运行而备受关注。针对具有非典型边界的轴向移动绳系统，应用行波反射叠加法，拓展了其在任意周期以及在给定初始条件均布简谐激励条件下的振动响应及能量解析解的求解。以边界控制进行振动抑制的方法具有简单、经济等优点。在轴向移动绳系统边界处设置质量-阻尼-弹簧的控制器以及控制力执行器，根据最优阻尼以及反射行波的振动抑制条件设计执行器的控制力，在第一个周期后快速抑制系统的横向振动，通过仿真体现自由和受迫振动时振动抑制的有效性。     

移动荷载列作用下简支梁振动响应参数研究

推导了移动荷载列作用下简支梁位移响应的精确解,在此基础上引入3个无量纲参数,研究了荷载移动速度、荷载频率及结构阻尼对桥梁响应的影响,分析了简支梁在一定荷载速度下的共振和消振现象发生机理。结果表明:桥梁跨中的最大位移响应并非随着荷载速度的增大而单调地增大,而是表现出一种类似正弦但波幅逐渐变大的方式;当移动荷载列以消振速度通过桥梁时,引起的桥梁余振响应趋近于零;简支梁的共振速度与移动荷载列的间距有直接关系,当共振速度同时又是消振速度时,共振现象被抑制;当简谐荷载移动速度较低时,梁体位移在荷载频率等于梁体第一阶自振频率时达到最大响应,随着荷载移动速度的增大,梁体位移达最大响应不再发生于荷载频率等于梁体第一阶自振频率的情况。     

Dynamics of Vortices and Solitons in a Bose-Einstein Condensate by an Oscillating Potential

We study numerically the dynamics of quantized vortices and solitons induced by an oscillating potential inside a trapped Bose-Einstein condensate. The dynamics of the topological defects is much different from the case for a linear uniform moving object; the metamorphosis between vortices and solitons is characteristic of the dynamics. We discuss how vortices are nucleated by an oscillating potential.     

Efficient numerical approach to unbounded systems subjected to a moving load

The present paper solves numerically the problem of vibrations of infinite structures under a moving load. A velocity formulation of the space–time finite element method was applied. In the case of simplex shaped space–time finite elements, the ‘steady state’ dynamic behaviour of the system was obtained. A properly performed discretization allowed of propagating information in a given direction at a limited velocity. The solutions were obtained under the assumption that the deformation is quasi-stationary, i.e., stationary in the coordinate system that moves with the load. The unbounded Timoshenko beam subjected to a distributed moving load was used as a test example. The dynamical system is placed on an elastic foundation. The matrices describing an infinite dynamical system subjected to a moving load are derived and the stability of the numerical scheme is analysed. The numerical results are compared with the analytical solutions in the literature and the classical numerical method.     

高速移动荷载下弹性半空间饱和地基动应力响应

对承受高速移动荷载的饱和多孔地基动应力响应开展了解析理论研究。引入势函数,进行Helmholtz代换,通过傅里叶变换得到了承受矩形分布的竖向与水平向移动荷载的三维饱和地基动应力的基本函解,数值积分求解逆变换,进而得到移动荷载下饱和地基动应力响应的理论解。基于饱和多孔介质的动应力理论解,分析了移动荷载速度及频率的动应力响应,进一步分析了水平及竖向移动荷载耦合作用下饱和地基的动应力。理论分析表明,荷载速度及其频率诱发地基动应力水平的放大效应,动应力水平随荷载移动速度增大呈现指数型放大效应,移动速度接近剪切波速时动应力水平达到峰值,而荷载速度与频率引发的动应力放大效应随地基深度增大而增强。考虑水平动载的耦合效应,地基的动剪应力和水平向正应力水平显著增大,而竖向动正应力变化不大。     

Computational study of unsteady viscous flow around a transversely and longitudinally oscillating circular cylinder in a uniform flow at high reynolls numbers

A finite difference simulation method for the time dependent viscous incompressible flow around a transversely and longitudinally oscillating circular cylinder at Reynolds numbers of Re=4×10³ and 4×10⁴ is presented. The Navier-Stokes equations in finite difference form are solved on a moving grid system, based on a time dependent coordinate transformation. Solution of the vortex street development behind the cylinder is obtained when the cylinder remains stationary and also when it is oscillating. Time eholution of the flow configuration is studied by means of stream lines, pressure contours and vorticity contours. The computer results predict the lock-in phenomenon which occurs when the oscillation frequency is close to the vortex shedding frequency in the transverse mode or around double the vortex shedding frequency in the longitudinal mode. The time dependent lift and drag coefficients are obtained by the integration of the pressure and shear forces around the body. The drag, lift and the displacement relations are also discussed.     

Dynamic response of a cracked beam subject to a moving load

Summary The dynamic response of a beam with a single-sided crack subject to a moving load on the opposite side is analyzed using Euler beam theory and the assumed mode method. The beam is modeled as two separate beams divided by the crack. Two different sets of admissible functions which satisfy the respective geometric boundary conditions are assumed for these two fictitious sub-beams. The rotational discontinuity at the crack is modeled by a torsional spring with an equivalent spring constant for the crack. The transverse deflection at the crack is matched by a linear spring of very large stiffness. Results of numerical simulations are presented for various combinations of constant axial velocity of the moving load and the crack size.     

Dynamic response of functionally graded beams in a thermal environment under a moving load

The dynamic response of functionally graded (FG) beams in thermal environment subjected to moving load is investigated based on the first-order shear deformation theory (FSDT). The initial thermal stresses are determined by solving the thermoelastic equilibrium equations. The finite element method (FEM) is adopted to develop a solution procedure for FG beams with general loading and boundary conditions. The convergence behavior and accuracy of the method are shown through the different numerical examples. Finally, the influences of temperature rise, material graded index, moving load velocity, and boundary conditions on the dynamic behavior of FG beams in thermal environment is presented.     

Drag on a sphere accelerating rectilinearly in a maxwell fluid

The exact solution for the drag on a sphere moving in an arbitrary manner along a rectilinear path in an otherwise still Maxwell fluid of infinite extent is presented. The method of solution is that used by Landau and Lifshitz. This technique is based on the fact that drag on an accelerating body can be obtained by integrating the drag on an oscillating body over all possible frequencies. The solutions for the drag for some particular type of accelerating motions are also presented. Discussion on the limits of applicability of the solution is also presented.     

The dynamic analysis of a suspended cable due to a moving load

The dynamic behaviour of a saggy suspension cable under a moving load was investigated. First of all, the updated Lagrangian formulation and the finite element method were used to derive the property matrices of a saggy suspension cable in order to define the discretized equations of motion. Then, the Jacobi method was applied to the determination of the natural frequencies and the mode shapes of the suspended cable. The moving-load-induced dynamic responses of the saggy suspended cable were obtained by using the Newmark direct integration method incorporated with the Newton–Raphson iteration technique. The influence of some pertinent factors, such as speed of moving load, ratio of axial rigidity to total cable weight (AE/⁰m?g⁰L) and ratio of moving load mass to total cable mass, is the key point of the dynamic analysis.