车路耦合非线性振动高阶Galerkin截断研究

将移动车辆模型化为运动的两自由度质量-弹簧-阻尼系统,道路模型化为立方非线性黏弹性地基上的弹性梁,并将路面不平度设定为简谐函数．通过受力分析,建立车路非线性耦合振动高阶偏微分方程．采用高阶Galerkin截断结合数值方法求解耦合系统的动态响应．首次研究不同截断阶数对车路耦合非线性振动动态响应的影响,确定Galerkin截断研究车路耦合振动的收敛性．研究结果表明,对于软土地基的沥青路面,耦合振动的动态响应,需要150阶以上的截断才能达到收敛效果．并通过高阶收敛的Galerkin截断研究了系统参数对车路耦合非线性振动动态响应的影响.     

连接阻尼对弹性杆纵向碰撞响应的影响

分析了刚度和阻尼并存的一般边界条件下线弹性杆与刚体的纵向碰撞过程,得到了碰撞后第一个波动周期杆振动的位移、速度和应力的解析表达式,讨论了碰撞持续时间为2倍杆长与波速比的条件.将导出的解析表达式通过具体的算例代入计算,讨论了不同质量比、不同连接刚度条件下连接阻尼对于碰撞过程中杆中质点速度及应力响应的影响.研究表明,连接阻尼改变了受碰撞弹性杆的振动模式,连接阻尼影响着碰撞反射波速度和应力的突变幅度;连接阻尼增大,杆中速度和应力响应分布变平缓:在连接刚度较大的情况下,连接阻尼变化对于杆中质点速度和应力影响较大;碰撞持续时间与质量比、连接刚度、连接阻尼及杆长有关,与碰撞的初速度无关;在质量比较大的情况下,连接阻尼使得反射波到达杆碰撞端时,杆端的应力有显著的变化.     

饱和粘弹性土层中端承桩纵向振动的轴对称解析解

基于弹性和饱和多孔介质理论,将桩和饱和土层分别视为单相弹性介质和饱和粘弹性介质,利用Helmholtz分解和变量分离法,在频率域研究了饱和粘弹性土层中端承桩纵向振动的动力特性,给出了饱和粘弹性土层中桩纵向振动时动力响应的轴对称解析解及桩头复刚度的解析表达式．通过数值计算,给出了桩头动刚度因子和等效阻尼随激励频率的响应,考察了饱和土物性参数、桩土模量比、桩长径比、桩Poisson比等参数对桩头刚度因子和阻尼的影响．研究表明:由于考虑了桩的径向变形效应以及饱和粘弹性土层对桩的径向力作用,轴对称精确解的桩头动刚度因子和阻尼分别与经典Euler-Bernoulli杆模型桩的桩头动刚度因子和阻尼有较大的区别,特别是在若干激励频率处．因此,经典Euler-Bernoulli杆模型桩的适用性具有一定的局限,更加精确的分析应采用三维精确模型．     

列车荷载引起路基振动研究分析

为了研究地基特性和轨道结构对列车振动荷载作用下地基振动问题,通过无限元边界与有限元边界相结合的有限元分析方法进行模型建立,把路堤高度、列车速度、阻尼系数、振动频率及轨道抗弯刚度因素考虑在内.结果表明,无限元边界与有限元边界相结合的有限元计算方法可以有效反映出地基振动效果,由列车荷载引起的地基振动响应随着路堤高度增加而减小;速度增加地基振动响应相应增加,并且低速与高速情况相应情况变化很大;列车低速时,轨道刚度对地基振动影响较小,相反高速时轨道刚度对振动响应影响较大;当列车速度低于剪切波速时阻尼系数改变对振动影响较小,高于剪切波速时,阻尼系数增大路堤周围地基振动水平明显减小;随着列车荷载振动频率增加,地基振动响应变化较小,但是具有减小趋势.     

水波中弹性浮板的减振问题研究

基于线性水波理论和Mindlin厚板动力学理论,采用Wiener-Hopf方法,分析研究了水面上弹性浮板对水波的动响应及其减振问题．首先,在不考虑弹性联接情况下,将分析计算结果与前人的计算结果及实验数据进行了对比,验证了该方法的有效性．其次,基于该方法分析了连接浮板与水底的弹簧刚度与浮板振动响应各参数之间的关系,从而为超大型浮台系统的设计提供理论依据．     

弹性板受撞击的动力响应分析

文献[1]分析了弹性板受撞击的动力响应,应用该方法的条件是撞击物可视为刚体且接触局部变形与撞击力的关系已知。木文提出了碰撞过程中碰撞反力的模拟表达式,对撞击物不作任何假设,避开接触局部变形问题,只考虑碰撞过程中板的动力响应,利用冲量、动量关系和动力微分方程及数值方法求解,因此适用范围更广。文中给出了算例,与已有正确解答符合得很好。     

约束阻尼悬臂梁瞬态响应近似解析解与实验分析

利用弹性悬臂梁模态叠加构造出约束阻尼悬臂梁的振动模态,基于Lagrange方程推导出了约束阻尼悬臂梁的控制方程,求解了在集中力突然卸载的情况下约束阻尼悬臂梁的动力响应．计算并测试了一系列铝合金约束阻尼悬臂梁模型的振动频率和瞬态响应,分析了阻尼层材料参数对铝合金约束悬臂梁瞬态响应时间的影响．采用了解析法以及实验法两种方法,结果表明,所采用的方法是可靠的．     

典型弹药系统基础振动激励的IPRK法分析

运用IPRK法对典型弹药系统基础振动激励问题进行了研究.在阐述IPRK法基本原理的基础上,根据典型弹药系统包装形式构建了基于易损部件的三自由度弹药公路运输振动力学模型.结合实例对IPRK法和高斯白噪声模拟的有效性进行了验证,同时通过与传统Runge-Kutta法进行比较,验证了方法具有很高的计算精度和计算效率.最后运用IPRK法分析了包装箱质量、缓冲包装刚度和阻尼对引信振动加速度响应的影响规律.     

基于时间有限元方法的旋转柔性叶片动力学响应分析

将时间有限元方法引入到柔性多体系统的数值计算中,研究了旋转柔性叶片系统的刚-柔耦合响应问题.首先,基于非线性梁理论,建立了旋转柔性叶片系统的中心刚体-柔性梁模型,构造柔性叶片系统考虑一次近似耦合的Lagrange函数;其次,采用假设模态方法对空间坐标进行离散,建立系统的时间有限元格式;最后,通过数值实验,分析了柔性叶片的动力学响应.该方法直接构造了系统的离散积分格式,并自动保证了该格式是保辛的,因而具有较高的数值精度和稳定性.数值结果表明:时间有限元可以有效地求解旋转柔性叶片系统内低频大范围运动与高频弹性振动之间的刚-柔耦合问题.     

有限流体域内不同位置处的柔性管涡致振动机理研究

针对有限流体域内柔性管的涡致振动问题,将柔性管离散为若干空间梁单元,流体域采用实体单元离散,建立了有限流体域内柔性管系统的流固耦合模型及数值计算方法,设计并加工圆柱流体域内柔性管振动专用实验装置,采用GWT-2B双轴加速度传感器对柔性管的振动进行监测,并与数值模拟结果进行对比,吻合程度较好.基于该文的模型和方法,对圆柱流体域内不同位置处柔性管的涡致振动机理进行研究.结果表明,柔性管偏离入口流速位置的角度越大,越容易发生流体弹性不稳定性,柔性管的振动愈剧烈;而正对入口流速的位置,不易发生流体弹性不稳定性,柔性管振动减弱.     

Analysis of an impact damper of vibrations

An analysis of the system with two degrees of freedom, which – provided that its parameters are properly selected – can operate as an impact damper of vibrations, is presented. The investigations have been carried out in two directions. In the first one, it has been assumed that the mass of the system playing the role of a damper is 10 times lower than the mass of the basic system and that this mass is suspended from a spring characterised by low stiffness. In the second case, the damper mass has been assumed to be four times smaller than the basic mass and it is suspended from a spring whose stiffness is four times lower than the stiffness of the basic system spring. Moreover, it has been shown that the impact damper of vibrations operates more efficiently than a classical dynamic vibration damper.     

On the oscillations of a thin-walled structure containing a fluid, in the presence of a hydrodynamic damper : PMM vol. 43, no. 6, 1979, pp. 1095–1101

A model of a hydrodynamic oscillation damper is proposed. The model is used to obtain the equations describing longitudinal oscillations of a structure which includes a shell partially filled with fluid, and contains a hydrodynamic damper. It is shown that the use of the damper leads to considerable increase in the damping of the oscillations of specified frequencies within the structure.

In modern technology one encounters various types of problems connected with restricting the amplitudes of the axisymmetric vibrations of shells and of the longitudinal oscillations of structures consisting of shells partially filled with fluid. Various devices have been proposed [1] for solving these problems. All these devices have a common feature, namely an elastic shell filled with gas and placed in the fluid. The natural frequency of oscillations of such a shell in a fluid can be tuned to required frequency. The effect of such a device is analogous to the effect of a dynamic vibration damper in mechanical systems [2]. A part of the fluid contained in the shell serves as the active mass of the dynamic damper, and for this reason we shall call such devices the hydrodynamic vibration dampers.     

Response and bifurcation of rotor with squeeze film damper on elastic support

This paper investigates the nonlinear response and bifurcation of rotor with Squeezed Film Damper (SFD) supported on elastic foundation. The motion equations are derived. To analyze the bifurcation of nonlinear response of SFD rotor, the Floquet Multipliers is obtained by solving the perturbation equations with numerical method. For computing Floquet Multipliers, a novel method is presented in this paper, which can begin integration at the stable solution. Simulation results are given in two figures. One figure, which consists of eight subfigures, gives the effect of rotating speed on the response of SFD damper supported on elastic foundation: with increasing rotating speed, the nonlinear response evolves from quasi-period to period, then jumps between different periods, and finally returns to quasi-period; the corresponding bifurcations are saddle-node bifurcation and secondary Hopf bifurcation. The second figure, which consists of six subfigures, shows that: the support stiffness has large influence on the response of bearings and film force in SFD; large support stiffness can lead to oil whirl in SFD.     

A tuning criterion for the inertial tuned damper. Design using phasors in the Argand–Gauss plane

A new approach to the design of a dynamic damper for a monomass oscillator is presented; the design procedure is then applied to control a multimodal oscillator. This new dynamics emerged from an analysis by means of phasors (rotating vectors in the Argand–Gauss plane) which revealed the phase relations between the damper and main oscillator. In particular this work introduces a geometric formalism, based on the use of phasors in the complex plane, for the sizing of inertial dampers applied to multimodal structural oscillators. Their damping effect depends on the fact that the response of the secondary oscillator (the damper) delays the response of the primary mass by 90°, so that the elastic force transmitted by the damper becomes a viscous force on the controlled oscillator. When such condition occurs we say that the damper is “tuned” to the main oscillator; the damping induced by the damper serves to limit the displacement of main oscillator. Our geometrical approach provides a method whose language is close to that of structural mechanics, thus paving the way to the professionals for: (i) sizing the damper parameters and (ii) evaluating the stability to the damped system and its performance limits. The aim of the development is that of exploring the use of dampers to control the response of buildings under horizontal seismic and aerodynamic loads.     

A control scheme based on ER-materials for vibration attenuation of dynamical systems

Based on a bang-bang control scheme acting on so called “electrorheological” fluids (ER-fluids), a vibration suppression method is proposed for a class of n-dimensional systems subjected to unknown perturbations. The proposed controller relates to robustness vis-a-vis unknown but bounded disturbances. Two approaches for designing the control scheme are presented and compared. On the one hand we employ Lyapunov stability theory; on the other hand there is an obvious reason for minimizing rate of energy change due to the spring/damper elements by varying the ER-fluid properties appropriately. The system under investigation is an n-degree of freedom one consisting of masses and spring/damper elements. The spring/damper elements contain an ER-fluid; their stiffness and damping properties are changed by varying an imposed electrical field. The changes in spring and damping properties can be effected in microseconds since the control does not involve the separate dynamics (inertia) of usual actuators. Detailed derivations are presented for a two-dimensional case and simulations are carried out for examples of smooth periodic and discontinuous periodic excitation forces.     

Investigation of Damping of Vibrations in a System With Two‐Disc Inseparable Clutch

This paper presents the results of tests on free and forced harmonic torsional vibrations in a system with a two‐disc inseparable clutch, with structural friction taken into account. Nonlinear histeresis loop describing the frictional‐elastic properties of the system was introduced into the model. The mathematical model of the vibrating system containing two disks inseparable clutch was built. During free vibrations of the system, its damping characteristics were tested by a digital simulation method. The vibration damping decrement as a function of amplitude torsional displacement was determined. When vibrations were harmonically forced, the amplitude ‐ frequency characteristics of the system were determined numerically. The system was used as a nonlinear torsional vibration damper in a linear system with a harmonic force. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Shaking table tests of a plate-column structure with semi-active tuned mass damper

This paper presents selected results of experimental tests carried out on the three-storey plate-column structure, which is a physical model of a building. On the top floor the semi-active tuned mass damper (STMD) is installed. That device is a kind of harmonic oscillator with a variable stiffness characteristic. The tuning of STMD is possible in the frequency range from 0 to 5 Hz, which allows to counteract the resonant vibration of plate-column structure for the three basic frequencies. The model's vibration are kinematically excited by using the earthquake simulator. It is assumed that during an experimental tests the plate-column structure's vibration are only excited by horizontal component of base motion (dominant influence on building's vibration). The aim of the experimental analysis presented in this paper is to verify the effectiveness of the semi-active tuned mass damper in vibration's amplitude reduction of the main structure. The tested device is prototype of STMD, which uses a competitive constructional solution of stiffness parameter control. By reason of above, special attention is focused on the testing of vibration eliminator in two aspects: change of stiffness characteristic (the rate of change), and the accuracy of tuning to the resonant frequencies. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

斜拉桥拉索-阻尼器系统非线性瞬态响应分析

考虑索的抗弯刚度、垂度及几何非线性的影响,得出了索-阻尼器系统的空间非线性振动偏微分方程,用中心差分法将偏微分方程在空间内离散,导出了系统的非线性振动常微分方程组．结合Newmark法及虚拟力法提出了一种用于求解非线性振动瞬态响应的杂交分析算法．并以典型的斜拉桥拉索为研究对象,给出了数值算例,并与Runge-Kutta直接积分法进行了比较,说明了杂交算法的准确性及有效性．为大跨斜拉桥拉索的振动控制研究提供了一种简便、有效、快速的时程分析方法．     

Mechanical model of a mistuned 2DOF-structure coupled by viscous damping

In this paper the vibration amplitude reduction of a mechanical system is investigated when applying a damper between different DOF of that structure. Thereby, an elementary mechanical model consisting of two mass-spring elements with slightly differing eigenfrequencies and which are connected via a viscous dashpot damper is regarded. To investigate the systems behavior, an analysis of the transfer function and its poles and zeros in the L APLACE domain is performed when varying the damping constant. This reveals that the achievable amplitude reduction depends on the mistuning of the system and that even ideal viscous damping leads to a coupling which results in a shift of eigenfrequencies. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Textile Drape as Mechanical Phenomenon

The paper copes with the based on the continuum mechanics simulation of the textile drape. A textile surface is treated as linear elastic two‐dimensional Cosserat continuum with independent in plane and out of plane material properties. Bending stiffness and in plane shearing stiffness measured with the Kawabata Evaluation System for Fabrics (KES‐F) are used in the calculations. Other necessary material constants in the model, which are not measurable in a direct way with the KES‐F and which are introduced in the model, are assumed. To solve the equilibrium equations of the system the Finite Element Method (FEM) is used. An implementation of the arc‐length algorithm makes the tracing of the full equilibrium path (pre‐buckling, critical and post‐buckling behaviour) possible. The paper proves that the simulation of the textile drape with the methods of continuum mechanics can be done regarding measured material mechanical properties and carrying out a stability analysis. By now, the stability analysis has not been examined by the FE textile researchers. Therefore neither critical and post‐buckling phenomena nor the ambiguity of the textile behaviour have been described or explained sufficiently.