Numerical simulation of structure response outfitted with a tuned liquid damper

An integrated fluid–structure numerical model has been developed to simulate the response of a single degree of freedom (SDOF) structure outfitted with a Tuned Liquid Damper (TLD). The structure is exposed to random external excitations. A non-linear, two-dimensional, flow model has been developed using the finite-difference method. Unlike most existing flow models, the present model does not include any linearization assumptions; it rather solves the entire nonlinear, moving boundary, flow problem under conditions leading to large interfacial deformations. The free surface has been reconstructed using the volume of fluid method and the donor–acceptor algorithm. The Duhamel integral method has been used to determine the response of the structure. The effectiveness and accuracy of the flow model has been validated using a set of benchmark problems and experimental data. The numerical results of this model have been compared with results of an equivalent TMD model. The present fluid–structure model can be used as a valuable tool for performance evaluation and design of more effective tuned liquid dampers.     

Recent Advances on Vibration Control of Structures Under Dynamic Loading

In this paper, a review of recent journal articles on passive, active, semi-active, and hybrid vibration control of structures subjected to dynamic loading is presented. Passive systems reviewed include tuned mass damper (TMD), tuned liquid column damper (TLCD), tuned liquid column ball damper (TLCBD), circular TLCD (CTLCD), and pendulum TLCD (PTLCD). Active control systems include active tuned mass dampers (ATMD) and piezoelectric actuators. Semi-active systems include magnetorheological (MR) damper, negative stiffness devices (NSD), magneto-rheological damper TMD (MR-TMD), variable stiffness semi-active TMD (VS-STMD), variable damper STMD (VD-STMD), and recentering variable friction device (RVFD). Hybrid systems include active base isolation system and semi-active MR dampers with nonlinear base isolators. The current frontier of research is semi-active control of structures as well hybridization of various control systems. The problem is complex requiring integration of several different hardware and software technologies with structural design such as smart materials, adaptive dampers, actuators, sensors, and control and signal processing algorithms. This complexity also makes it an exciting area of research and development.     

A Simplified Optimization Strategy for Nonlinear Tuned Mass Damper in Structural Vibration Control

In this paper, a simplified optimization strategy for the nonlinear tuned mass damper (TMD) is presented, and the optimal parameter setting can be simply determined, by which the nonlinear TMD is effective over a wide frequency range. In the given numerical model, the nonlinear TMD is attached to the structure, which is represented by a single‐degree‐of‐freedom system, and the environmental load is assumed to be the Gaussian white noise process. Governing differential equations of motion of the coupled structure‐TMD system are derived, and the equivalent linearization method is introduced in the numerical calculation. The standard deviation of the structural displacement is adopted as the optimized objective function. Furthermore, it is pointed out that the response of the system can be controlled in a case of multiple probable steady‐state processes caused by the nonlinearity of the stiffness element. Different from the linear TMD, the performance of the nonlinear TMD may be influenced by the excitation. Thus, the performance sensitivity of optimal nonlinear TMD is investigated with different excitation intensities and structural damping ratios. The results show that the sensitivity may limit the engineering applications of nonlinear TMD.     

含饱和作动器的主动TMD振动控制研究

以含主动调谐质量阻尼器(TMD)的建筑结构为研究对象,研究作用于TMD上的作动器输出力小于设计控制力时的控制方法.为了确定系统控制率,在满足线性矩阵不等式约束的前提下,通过优化控制目标函数来达到.同时,为了保证控制效果,采用了峰-能量控制器.最后,以一座六层建筑物为例来说明本文方法的可行性.     

Tuned Mass Dampers

A review of representative research on tuned massed dampers (TMD) reported in journals in recent years is presented. TMDs are divided into four categories: conventional TMDs, pendulum TMDs (PTMDs), bi-directional TMDs (BTMDs), and tuned liquid column dampers (TLCDs).     

周期性冲击载荷作用下井字梁楼盖竖向振动的控制

针对周期性冲击载荷作用下井字梁楼盖异常振动问题,对某工业厂房井字梁楼盖进行现场动力特性测试,采用Abaqus软件建立局部楼盖有限元模型,研究周期性冲击载荷作用下井字梁楼盖的动力特性,并提出设置调谐质量阻尼器(tuned mass damper,TMD)、增设隔振支座等2种减振方案.结果 表明:4种不同TMD布置方式的减振效果不同,在设备4个支座处布置TMD的减振效果最佳;增设隔振支座后,采用有限元法得到各测点减振率为83.91％ ～88.80％.2种方案均能有效降低楼盖的竖向振动,可为结构振动控制提供参考.     

简谐载荷作用下井字梁楼盖竖向振动控制

为研究某工业厂房井字梁楼盖在简谐载荷作用下的异常振动问题,根据现场动力特性测试结果,采用有限元软件Abaqus建立井字梁楼盖局部板-柱模型,通过增设调谐质量阻尼器(tuned mass damper,TMD)和布置隔振器对井字梁楼盖的竖向振动研究进行控制.结果 表明:增设TMD和布置隔振器均可以使楼盖竖向振动峰值加速度减小;选择4个质量比为2％的TMD布置在设备支座附近梁下,通过布局优选可以得到最优的减振方案;布置隔振器比增设TMD的减振效果更好,布置隔振器后各响应拾取点减振率大于80％.     

车-桥系统的振动分析及控制

推导出了由变速行驶车辆与不同边界和路面不平桥梁组成的系统,在安装调质阻尼器(TMD)后的无量纲运动微分方程.作为其特例,研究了匀变速车辆与简谐路面简支桥梁系统,获得了桥梁跨中的无量纲最大挠度随加速度、减速度、初速度、质量比和路面不平度的变化规律,并对系统发生共振时进行TMD控制.数值计算表明:加速度、减速度、初速度和质量比对桥梁的影响均很大;路面不平度对桥梁的影响不可忽略,因为它甚至有可能使桥梁产生共振;TMD可明显减小桥梁的共振振幅.     

Efficient predictive vibration control of a building‐like structure

This paper presents the design of a model predictive controller (MPC) based on Laguerre functions for vibration control. The controller is tested in a building‐like structure consisting on a three‐story building with a passive vibration absorber. The structure is connected to an electromagnetic shaker, which excites the support of the superstructure, providing forces with a wide range of excitation frequencies, including some resonance frequencies of the structure. The overall controller is a hybrid vibration absorber conformed of (i) an active absorber, that is a predictive vibration control scheme, synthesised to actively attenuate the vibratory system response via (ii) a passive absorber, known as a tuned mass damper (TMD), located over the third story building to reduce the vibrations caused by harmonic forces acting on the base of the structure. The proposed predictive control strategy proves to be effective and efficient, improving system's performance with guaranteed stability and feasibility. Experimental and numerical results are included to illustrate the overall system performance.     

Nonlinear Dynamics of a Micromechanical Torsional Resonator: Analytical Model and Experiments

Mechanical microoscillators have been valuable tools for magnetic measurements of microscopic samples. This paper presents an analytical model for the dynamics of an electrostatically actuated torsional oscillator and validates it experimentally. While, at low excitations, the system is well described by a damped linear oscillator, at higher oscillation amplitudes, a nonlinear regime is observed. Nonlinearity is originated exclusively by the electrostatic driving and detection and can be tuned by modifying the excitation or detection bias voltages. The parameters of the analytical model are obtained from the device dimensions and material properties. No empirical or fitting parameters are needed except for the quality factor, which is extracted from the linear resonance curve. The proposed model can be a valuable and straightforward tool for the design and analysis of many other similar devices based on electrostatically actuated mechanical resonators.$hfill$ [2009-0164]      

改进后的TLD视频目标跟踪方法

TLD(tracking-learning-detection)是近期受到广泛关注的一种有效的视频目标跟踪算法.在原始TLD的基础上,对其进行改进,改进包括:在TLD的跟踪器中对其局部跟踪器的布置和局部跟踪器的跟踪成败预测方法进行改进,提高跟踪器的跟踪精度和鲁棒性;在TLD的检测器中引入基于Kalman滤波器的当前帧目标所在区域预估,缩小了检测器的检测范围,提高了检测器处理速度;在TLD的检测器中加入基于马尔可夫模型的方向预测器,增强了检测器对相似目标的辨识能力.通过实验对原始TLD和改进后的TLD进行了比较,实验结果显示改进后的TLD算法较原始TLD算法具备更高的跟踪精度和更快的处理速度,而且增强了对场景中相似目标的辨识能力.     

加速的TLD算法及其在多目标跟踪中的应用

TLD(Tracking-Learning-Detection)算法是近期受到广泛关注的一种长时间视觉跟踪算法.为提高该算法的运行速度,一种ATLD(Accelerated TLD)算法被提出,对原始TLD算法做了两方面改进:在检测模块引入基于灰色预测模型的目标位置估计和检测区域设置;运用基于NCC(Normalized Cross Correlation)距离的图像检索方法管理正负样本集.并在此基础上实现了多目标跟踪.通过实验比较了ATLD算法、原始TLD算法及两种近期改进的TLD算法.实验结果表明:ATLD算法在确保精度的前提下运行速度更快.     

Seismic energy dissipation-based optimum design of tuned mass dampers

Tuned mass dampers (TMDs) are a subclass of dynamic vibration absorbers that consist of a mass-spring-damper unit that is attached to a structure to adjust its response to seismic and wind loads. The efficacy, performance and optimum design of a TMD strongly depend not only on its mass, stiffness and damping as well as the input energy and the structure characteristics, but also on the structural response parameter(s) that the TMD is intended to mitigate. In that respect, this study evaluates the suitability of four objective functions for the optimum design of the TMD of an inelastic, steel moment-resisting frame (SMRF) under an artificial, white-noise excitation. The objective functions include 1) the maximum roof lateral displacement, 2) the maximum drift, 3) the root mean square of drifts and 4) the cumulative hysteretic energy of the SMRF. The results indicate that the SMRF equipped with a TMD optimized using the cumulative hysteretic energy of the SMRF as the objective function exhibits the best seismic response under the artificial earthquake. Further examining the response of the TMD-equipped SMRF under four historic earthquake records shows that equipping a structure with a TMD optimized using an artificial earthquake will not warrant that the structure will exhibit a better seismic performance in all measures compared with when no TMD is used. Put other way, while the minimization of cumulative hysteretic energy could be the best objective function for a case subjected to an artificial earthquake, under real earthquakes, none of the objective functions consistently results in a better seismic performance. This behavior is attributed to detuning effects arising from major structural damages and significant period shifts that occur during strong earthquakes.     

Structural topology optimization under harmonic base acceleration excitations

This work is focused on the structural topology optimization methods related to dynamic responses under harmonic base acceleration excitations. The uniform acceleration input model is chosen to be the input form of base excitations. In the dynamic response analysis, we propose using the large mass method (LMM) in which artificial large mass values are attributed to each driven nodal degree of freedom (DOF), which can thus transform the base acceleration excitations into force excitations. Mode displacement method (MDM) and mode acceleration method (MAM) are then used to calculate the harmonic responses and the design sensitivities due to their balances between computing efficiency and accuracy especially when frequency bands are taken into account. A density based topology optimization method of minimizing dynamic responses is then formulated based on the integration of LMM and MDM or MAM. Moreover, some particular appearances such as the precision of response analysis using MDM or MAM, and the duplicated frequencies are briefly discussed. Numerical examples are finally tested to verify the accuracy of the proposed schemes in dynamic response analysis and the quality of the optimized design in improving dynamic performances.     

基于性能需求的基础隔震结构附加调谐惯容阻尼器的优化设计研究

为了克服调谐质量阻尼器(Tuned Mass Damper,TMD)质量过大的缺陷,用惯容器(Inerter)代替TMD中的质量块,形成调谐惯容阻尼器(Tuned Inerter Damper,TID).将TID附加在基础隔震结构的隔震层,对TID进行优化设计研究.以两自由度基础隔震结构体系的简化模型为研究对象,以白噪声激励下的振动响应为指标对TID进行参数研究,确定了一种以隔震层水平位移控制为约束、以最小上部结构绝对加速度为优化目标的优化问题,在两种控制准则下对TID进行优化设计,与仅附加线性粘滞阻尼器(Linear Viscous Damper,LVD)的基础隔震结构进行比较,最终发现TID对基础隔震结构的性能控制有着良好的效果,能同时降低隔震层水平位移和上部结构绝对加速度,并且效果优于LVD.     

Analytical evaluation of modal covariance matrices

Dynamic excitations in the form of stationary random processes with normal distribution are completely defined by their power spectral and cross spectral density functions. The stationary response of a linear structure to such excitations will also consist of random processes with normal distribution. In a modal formulation the statistical quantities of all output processes are obtained from modal covariance matrices. The elements of these matrices represent integrals which are usually evaluated numerically. In lightly damped structures, however, the integrand shows pronounced peaks. Thus small integration steps may be necessary for accurate results. In the applications the spectral density functions are conveniently described by discrete values and piecewise polynomial interpolation. The elements of the modal covariance matrices can then be evaluated analytically. For lightly damped structures this method is much more effective than numerical integration and maintains full accuracy in the modal properties of the structural model. The accuracy and efficiency of the method is illustrated by a numerical example.     

Towards understanding the mechanism of action of the multidrug resistance-linked half-ABC transporter ABCG2: a molecular modeling study

The ATP-binding cassette protein ABCG2 is a member of a broad family of ABC transporters with potential clinical importance as a mediator of multidrug resistance. We carried out a homology and knowledge-based, and mutationally improved molecular modeling study to establish a much needed structural framework for the protein, which could serve as guidance for further genetic, biochemical, and structural analyses. Based on homology with known structures of both full-length and nucleotide-binding domains (NBD) of ABC transporters and structural knowledge of integral membrane proteins, an initial model of ABCG2 was established. Subsequent refinement to conform to the lipophilic index distributions in the transmembrane domain (TMD) and to the results of site-directed mutagenesis experiments led to an improved model. The complete ABCG2 model consists of two identical subunits facing each other in a closed conformation. The dimeric interface in the nucleotide-binding domain (NBD) involves a characteristic nucleotide sandwich and the interface in the TMD consists of the TM helices 1–3 of one subunit and the helices 5 and 6 of the other. The interface between the NBD and the TMD is bridged by the conserved structural motif between TM2 and TM3, the intracellular domain 1 (ICD1), and the terminal β-strand (S6) of the central β-sheet in the NBD. The apparent flexibility of the ICD1 may play a role in transmitting conformational changes from the NBD to the TMD or from the TMD to the NBD.     

Performance Enhancement for T–S Fuzzy Control Using Neural Networks

A new control scheme is proposed to improve the system performance for Takagi–Sugeno (T–S) fuzzy system using control grade functions tuned by neural networks. First, systematic modeling method is introduced to construct the exact T–S fuzzy model for a nonlinear control system. For the T–S fuzzy model, the system uncertainty affects only the membership functions. To cope with this problem, the grade functions, resulting from the membership functions of the control rules, are tuned by a back-propagation network. On the other hand, the feedback gains of the control rules are determined by solving a set of linear matrix inequalities (LMIs) which satisfy sufficient conditions of the closed-loop stability. As a result, both stability guarantee and better performance are concluded. The scheme is applied to a ball-and-beam system example verified by numerical simulations.     

考虑参数不确定性的主动悬架鲁棒H2/H∞混合控制

基于线性矩阵不等式方法,提出了一种新的考虑参数不确定性的鲁棒H2／H∞控制器设计方法,并用于车辆主动悬架设计．假定系统不确定参数是范数有界的,通过引入同一个Lyapunov矩阵来同时满足闭环系统的也和H∞性能条件,把鲁棒H2／H∞控制器设计转化为具有线性矩阵不等式约束的凸优化问题,进而应用内点法等凸优化技术进行求解．以四分之一车辆模型主动悬架设计为例,进行了数值仿真．结果表明,无论车辆簧上质量是否存在变异,鲁棒H2／H∞控制器均能给出很好的控制效果．