结构动力学模型中阻尼特性参数的修正

将结构分析计算的稳态位移响应和相应实测数据的差异映射为具有能量意义的误差范数，通过最小化该误差范数来修正与结构系统有关的阻尼特性参数．通过计算的或实测的频响函数获得稳态响应数据，使用的幅值在理论上完全包含了所有的复模态信息，参数值正过程采用迭代的方式．给出仿真算例，并对实验数据有噪声和无噪声两种情况进行了研究，结果表明方法合理且可行．     

高精度惯导系统重力扰动的阻尼抑制方法

重力扰动已经成为高精度长航时惯导系统的主要误差源之一。针对船用高精度惯导系统的重力扰动抑制问题,从舰船INS误差模型出发,推导了重力扰动在惯导系统中的传播特性。仿真结果表明垂线偏差将引起系统较大的舒拉振荡误差。为抑制重力扰动对系统的影响,引入常速度误差反馈阻尼网络和相位超前串联阻尼网络。分析了重力扰动在水平阻尼网络中的传递特性,实现了相应滤波器的设计。在此基础上完成了实验验证,海上试验结果表明,所引入的两种阻尼网络都能够阻尼掉重力扰动引起的舒拉振荡型导航误差,其中,相位超前串联阻尼网络效果更优,抑制率达到70%以上。     

高效耗能摩擦阻尼钢筋混凝土框架结构减震性能分析

研究了高效耗能摩擦阻尼器的减震机理。利用力学原理,分析了地震作用下高效耗能摩擦阻尼器的摩擦阻尼力放大系数变化规律,推导了设置高效耗能摩擦阻尼器结构的等效阻尼比计算公式。在此基础上,对分别设置传统摩擦阻尼器和高效耗能摩擦阻尼器的框架结构进行了地震反应分析,结果表明,高效耗能摩擦阻尼器通过将较小的摩擦阻尼力放大可以显著降低结构地震反应,减震效果良好;利用本文给出的等效阻尼比分析得出结构顶层位移反应幅值,与阻尼等效前相应值误差不超过10%。     

Damping of tubes due to internal two-phase flow

Two-phase internal flow is present in many piping system components. Although two-phase damping is known to be a significant constituent of the total damping, the energy dissipation mechanisms that govern two-phase damping are not well understood. In this paper, damping of three different clamped–clamped tubes subjected to two-phase air–water internal axial flow is investigated. Experimental data are reported, showing a strong dependence of two-phase damping on void fraction, flow velocity and flow regime. Data-points plotted on two-phase flow pattern maps indicate that damping is greater in a bubbly flow regime. The two-phase damping ratio reaches a maximum value at the highest void fraction before the transition to a churn flow regime. An analytical model that relates the two-phase damping ratio to the interface surface area is proposed. The model is based on rigid spherical bubbles in cubic elementary flow volumes. The analytical results are well correlated with the experiments.     

DYNAMIC CHARACTERISTICS OF VIBRATION ISOLATION SYSTEM WITH CUBIC STIFFNESS AND HYSTERESIS 1)

包含立方刚度和Bouc-Wen 型滞回的隔振系统具有复杂的非线性动力学特性。系统无阻尼响应模型可基于无滞回恢复力建立,利用谐波平衡法和泰勒展开求得近似解析解。系统有阻尼响应模型可利用解析/数值联合方法求解,该方法基于谐波平衡法和Levenberg-Marquardt 迭代算法,对于滞回产生的多值非光滑函数项,先计算时域响应再通过快速傅里叶变换求解谐波项系数。上述方法在含水平绞制梁的非线性隔振系统分析中得到有效应用。分析表明,在Bouc-Wen 型滞回和立方刚度的综合影响下,隔振系统呈现渐软–渐硬特性,滞回阻尼和线性阻尼都可以有效抑制共振,但前者高频隔振效果优于后者。     

求解Rayleigh阻尼系数的加权最小二乘法

在地震反应分析过程中,提出了一种优化方法以解决Rayleigh阻尼系数计算时选择两阶合理参考频率的难题。该方法是以反应谱理论为基础,以结构位移峰值误差最小为目标函数。将位移反应谱用一阶Taylor级数近似计算,从而将目标函数简化为加权最小二乘法的方程。随后以框架结构为例,讨论了模态个数和阻尼比模型对Rayleigh阻尼系数计算的影响,并与传统方法、最小二乘法及基于多参考振型的加权最小二乘法进行比较。计算结果表明,最小二乘法由于忽略了模态贡献的影响,不是计算Rayleigh阻尼系数的合理方法。当模态个数所包含的累积振型参与质量达90%以上,本文方法所得Rayleigh阻尼系数计算结果稳定,结构动力反应的计算精度高。     

地震反应分析中Caughey阻尼系数的优化解

传统方法建立Caughey阻尼矩阵时,存在选择多个合理参考频率及避免负模态阻尼比的问题。为此,基于地震反应谱分析,以结构的峰值位移误差最小为优化目标,将模态阻尼比大于零为约束条件,提出了优化Caughey阻尼系数的约束二次规划方法。然后,以一个直径90米,高15米的穹顶结构为例,讨论说明当结构的显著贡献模态多且不同动力反应相关显著贡献模态的频率有巨大差异时,采用Caughey阻尼矩阵的必要性。同时,分析比较了传统方法和优化方法对结构地震反应误差的影响。计算结果表明：传统方法选择的参考频率忽略了不同模态对动力反应贡献的差别,动力反应的计算误差无法有效控制;优化方法可使显著贡献模态的阻尼比合理,因此,对于4阶以上Caughey级数,优化方法的计算误差都小于传统方法。     

Research on linear/nonlinear viscous damping and hysteretic damping in nonlinear vibration isolation systems

A nonlinear vibration isolation system is promising to provide a high-efficient broadband isolation performance. In this paper, a generalized vibration isolation system is established with nonlinear stiffness, nonlinear viscous damping, and Bouc-Wen(BW)hysteretic damping. An approximate analytical analysis is performed based on a harmonic balance method(HBM) and an alternating frequency/time(AFT) domain technique.To evaluate the damping effect, a generalized equivalent damping ratio is defined w...     

Active Control of Shallow,Slack Cable Using the Parametric Control of End Tension

This study presents a practical, fieldable active controller applicable to shallow, slack cables. The controller is based upon an underlying theory that does not assume that the inertial forces are negligible in the direction of the cable chord. The theoretical framework is developed, and an experimental verification is presented. The experiments utilized a TV camera to track a small number of LED targets on the controlled cable, a commercial X-Y tracker and a PC to compute the cable's present position and velocity, and a linear actuator to vary the cable's tension. A Kalman filter was employed to smooth the position estimates and provide least-squares estimates of the cable velocity. The stability limits for the phase and amplitude of the control signal were established. An analytical estimate of the induced damping expected from the control algorithm is derived. Experimental measurements of the cable frequency and induced damping compared well with theoretical predictions. It is shown that he proposed active control approach is a simple, reliable, as well as an effective, method for vibration attenuation in lightly damped, shallow, slack cables.     

基于瞬变流和遗传算法的管道泄漏辨识

输水系统管道的泄漏影响瞬变水击波波形的畸变和衰减特性,对泄漏的定位和定量是泄漏辨识研究的重要环节.考虑水力瞬变中非恒定摩阻的影响,将泄漏参数反映在建立的管道瞬变流时域数学模型中,给出离散网格和求解方法,分析不同泄漏参数对瞬变水击波的影响,用遗传算法结合瞬变流时域模型的特征线法最小化管道测点压力实测和计算响应值的均方误差来辨识泄漏参数,其中实测信号首先经过预滤波和小波去噪处理.通过模型试验对瞬变流数学模型和泄漏反问题分析模型作了率定和验证,结果表明此法能有效的辨识出小泄漏参数,并且检测信号主动,阀门扰动可操作性强.     

作大范围回转运动柔性梁斜碰撞动力学研究

为正确估计由于碰撞引起的多柔体系统动力学特性的变化,针对作大范围回转运动的柔性梁与一固定斜面发生斜碰撞的情况,在考虑刚柔耦合效应的多柔体系统动力学建模理论的基础上,利用假设模态法建立起重力场作用下的柔性梁一致线性化动力法向碰撞过程中系统的动力行为。基于Ｈｅｒｔｚ接触理论和非线性阻尼项建立法向碰撞接触模型,基于线性切向接触刚度建立柔性梁切向碰撞接触模型,提出的数值算法保证了计算结果的合理性,给出的仿     

Steady-state motion of a plate with a discontinuous mass

An “exact” solution employing the normal mode approach is presented for the steady-state motion of a plate of arbitrary shape and with arbitrary boundary conditions that is provided with a discontinuous mass. The plate is viscously damped and the excitation is furnished in the form of distributed and/or concentrated loads that vary sinusoidally. The rigid mass, which may act as a vibration damper, can be applied to any point in the structure. Experimental studies with a mechanical model corroborate the theoretical results. Results of the analysis are applied to cantilever and simply-supported square plates subjected to base excitation and discrete loads. The effects of all system parameters, including damper location and mass ratio, mode shapes, viscous damping, and excitation frequency are determined. It is found that the system under consideration is an efficient device for reducing the vibration of plates, particularly cantilevered ones.     

On the averaging principle for one-frequency systems. Seminorm estimates for the error

We extend some previous results of our work (Morosi and Pizzocchero in J. Phys. A: Math. Gen. 39:3673–3702, 2006) on the error of the averaging method, in the one-frequency case. The new error estimates apply to any separating family of seminorms on the space of the actions; they generalize our previous estimates in terms of the Euclidean norm. For example, one can use the new approach to get separate error estimates for each action coordinate. An application to rigid body under damping is presented. In a companion paper (Morosi and Pizzocchero, 2006), the same method will be applied to the motion of a satellite around an oblate planet.     

基于水平阻尼的星光/惯性组合校准技术

根据星光/惯性组合导航系统舰载使用特点,考虑以SINS、CNS、LOG三者组合,设计组合校准方案。在SINS/CNS/LOG组合过程中,利用惯导系统的短期高精度特性,设计基于水平阻尼的卡尔曼滤波器对惯导舒勒周期进行补偿。星光/惯性组合校准技术建立在水平阻尼基础上,借助星光导航的航向和位置信息完成惯导位置误差、失准角和陀螺漂移的修正,从而实现组合系统长航时、远航程高精度导航。最后通过仿真对比试验验证星光/惯性组合导航系统校准方案的有效性。仿真结果表明:SINS/LOG组合后,惯导24 h位置误差CEP≤1.48 n mile,且位置误差会随时间积累;而SINS/CNS/LOG组合系统采用星光信息24 h一点校方案,第一次和第二次点校后,48 h和72 h惯导位置误差CEP≤0.5 n mile。由此可见,采用星光信息后,该组合方案能够显著提高惯导导航精度,达到延长惯导系统重调周期目的。     

The application of controlled variable magnetic eddy current damping to the study of vortex-induced vibrations

A powerful variable magnetic eddy current damping system has been constructed and utilized in an experimental study of vortex-induced vibrations (VIV). This damping system allows us to impose precise values of nearly ideal viscous damping over a wide range of damping values of interest. This new damping system offers improvements over previously utilized damping methods. Unlike most studies of VIV, where the damping cannot be independently controlled, we are able to impose our system damping independent of the other system parameters. Also, because the system only requires that a thin conductive plate be attached to the oscillating system, the overall mass of the system does not increase dramatically and still allows the investigation of very low mass systems. Finally, the system can operate in a steady-state fashion, supplying a constant damping value for an extended period of time, or in a transient fashion, where the damping value is intentionally varied over time. With this damping system, we have systematically explored both steady and transient damping effects on VIV behavior and provide a brief overview of some sample results.     

伴随变阻尼作用的干摩擦下的车辆系统非线性动力学分析

对分段线性阻尼和干摩擦共同作用下的车辆悬挂系统进行了非线性动力学分析研究，阐述了判定系统周期运动稳定性的理论方法；利用数值模拟方法分析了具有不同阻尼参数组合的系统对简谐激励的振动响应，并分析了由干摩擦引起的粘-滑振动行为．结果表明：提高摩擦力对抑制响应有利，但车辆系统在低速下运行时会出现复杂的粘-滑振动，轮轨之间产生较大的瞬时刚性冲击；而通过增加轮对与侧架的弹性悬挂可以有效减弱这种瞬时刚性冲击．     

Coupled vibrations of a partially fluid-filled cylindrical container with an internal body including the effect of free surface waves

Internal bodies (baffles) are used as damping devices to suppress the fluid sloshing motion in fluid-structure interaction systems. An analytical method is developed in the present article to investigate the effects of a rigid internal body on bulging and sloshing frequencies and modes of a cylindrical container partially filled with a fluid. The internal body is a thin-walled and open-ended cylindrical shell that is coaxially and partially submerged inside the container. The interaction between the fluid and the structure is taken into account to calculate the sloshing and bulging frequencies and modes of the coupled system using the Rayleigh quotient, Ritz expansion and Galerkin method. It is shown that the present formulation is an appropriate and new approach to tackle the problem with good accuracy. The effects of fluid level, number of nodal diameters, internal body radius and submergence ratio on the dynamic characteristics of the coupled system are also investigated.     

Rotor whirl damping by dry friction suspension systems

An efficient and automatic attenuation technique for the whirling motion of rotating machinery can be achieved by supporting the journal boxes elastically and providing them with suitable rubbing surfaces subject to dry friction normal to the shaft axis. The critical flexural speeds are easily cut off and the whirl amplitude is minimized throughout the frequency range. Confining the usual operative angular speed of the rotor in the range of adhesive contact between the dry friction surfaces, there is no significant increase of power dissipation or heat production as a whole due to this type of suspension system, whose task is just to suppress the resonant peaks when passing the critical speeds. Moreover, the wear of the rubbing surfaces can be easily compensated by use of suitable spring loading systems for the friction contact. The dry friction damping is also compared with an equivalent viscous damping, where the equivalence has to be understood in terms of work dissipated per single revolution of the rotor. As for other conventional cases, the shaft hysteresis is found to exert a destabilizing effect above the first critical speed, which however can be compensated by the other dissipation sources. The system stability is here studied perturbing the periodic motion and applying the Floquet theory.     

弹簧-金属丝网橡胶组合减振器迟滞力学模型及实验研究

金属丝网橡胶材料是一种完全由金属丝编织成的多孔复合材料,与传统螺旋卷制金属橡胶材料相比,其改进了成型工艺,剔除了制备过程中大量的手工工艺干扰,提高机械化程度,重合度更高,拥有更稳定的力学性能.由于金属丝网橡胶材料具有承载能力高、阻尼大、耐高温、耐低温、耐老化、抗油抗腐蚀等优良特性,在很多方面强于传统橡胶,多用于航空航天、船舶、军事武器等军工工业.弹簧$\!$-$\!$-$\!$金属丝网橡胶组合减振器具有可设计刚度和较高承载能力,但因其具有复杂的非线性迟滞特性,目前相关材料的本构模型还难以准确描述其力学特性.本文在弹簧$\!$-$\!$-$\!$金属丝网橡胶组合减振器静态迟滞力学性能实验的基础上,结合其干摩擦阻尼迟滞特性,提出了一种迟滞力学性能理论模型.根据减振器迟滞实验恢复力$\!$-$\!$-$\!$位移曲线特点,利用参数分离的方法将迟滞曲线分解为弹性恢复力和干摩擦阻尼力,分别建模求解等效刚度和干摩擦阻尼系数,以此建立了组合减振器理论模型,并与实验结果进行对比及进行误差分析,验证了理论模型的准确性.      

Effects of Damping and Circulatory Forces on Dynamic Instability of Gyroscopic Conservative Continuous Systems

ABSTRACT The title problem is studied, with emphasis on the small damping and circulatory force case. It is shown that small internal and/or external damping forces and/or smalt (as well as large) circulatory forces in general destabilize an otherwise stable gyroscopic conservative system. A condition for no destabilizing effects of these small forces is obtained, A concept of "perfect" system in elastic stability of nonconservative problems is also presented. An example problem is given for demonstration purposes.