建筑结构被动控制发展动态

本文对建筑结构被动控制发展过程和动态者综述,主要介绍了建筑结构被动控制中常用的金属屈服阻尼器、摩擦阻尼器、可调质量阻尼器、粘弹性阻尼器、可调流体阻尼顺和粘性液体阻尼器。     

一种复合磁流变阻尼器的设计及性能试验

设计制作了一种新型的复合阻尼器,并在电液伺服动静万能试验机上对其进行了性能试验,重点研究了阻尼器在低频(1Hz)下的工作性能,并采用修正的非线性滞回双粘性模型,结合试验结果,确定了其中的模型参数.研究得到将永久磁场和电流磁场结合起来从而实现阻尼器的逆向控制的设计思路是可行的,铜质隔磁环的设置保证了磁力线沿理论设计的路径穿行,又使线圈避免与磁流变液的长期接触腐蚀从而提高其耐久性.所采用的修正的非线性滞回双粘性模型较好地模拟了阻尼器的低频性能,为此类阻尼器在低频下的应用提供了理论依据.阻尼器的阻尼力-位移滞回曲线比较饱满,阻尼力-速度曲线基本符合理论假定.在0.1~1Hz频段内,修正的非线性滞回双粘性模型中的各参数取值较为稳定.     

电流变阻尼器的动态特性实验研究

设计制造了一种多层滑动极板式电流变阻尼器，使用自制的电流变液，采用正弦激励，进行了这种电流变阻尼器的阻尼特性试验。研究了电流变阻尼器的载荷－位移迟滞特性和载荷－速率迟滞特性，同时研究分析了这种电流变阻尼器的周期能耗特性及等效粘性阻尼特性。结果表明，阻尼器的周期能耗量随外加电场强度的增加而增加，外加电场强度越大，阻尼器的等效阻尼系数越大。阻尼器的阻尼特性体现为库仑阻尼和粘性阻尼的组合，其中随外加电场强度可控的主要是库仑阻尼力，而且库仑阻尼力不仅与外加强度有关，也与阻尼器的运动速度有关。该阻尼器系统是一个强非线性系统，极板间电流变液在低剪切应变率时表现为Bingham塑性流体，在高剪切应变率时流变性态比较复杂，导致载荷－速率迟滞环出现多区域闭合现象。     

油阻尼器油膜压强与厚度关系的实验研究

阻尼器是机械结构中起到减振作用的重要部件.在各种阻尼器中,油阻尼器的应用非常广泛,这种阻尼器工作时,可能同时存在着粘性和挤压油膜两种阻尼作用.本文以离心机结构中的一种油阻尼器为研究对象,围绕油膜压强和油膜厚度之间的关系展开研究工作.实验采用激振器对阻尼芯进行单向简谐激振,并调节油膜厚度、激振频率、激振功率等参数,进行多组实验,得到油膜压强随油膜厚度的变化曲线,显示出粘性阻尼器随着油膜厚度的减小,逐渐向挤压油膜阻尼器过渡的过程.同时根据挤压油膜理论,采用雷诺方程和有限长轴承近似方法推导出实验用阻尼器模型的油膜压强表达式,将实验结果与理论公式加以对比,并进行一定的分析和讨论.     

磁流变阻尼器汽车悬架的非线性振动特性分析

通过对磁流变阻尼器sigmoid模型进行数值计算分析,揭示了各参数对该模型阻尼力的影响,证明了通过合理有效地选择参数可设计出符合工程实际应用的磁流变阻尼器.对确定性激励下磁流变阻尼器的Sigmoid模型进行了理论分析.指出了采用非线性的阻尼器模型能更精确地描述汽车悬架的振动特性.从而证明了磁流变阻尼器有良好的使用价值和Sigmoid模型磁流变阻尼器在汽车控制工程应用中的可行性.     

土-基础相互作用隔震体系地震随机响应分析

视地基土为各向同性的弹性半空间,用弹簧-粘性阻尼器模拟土对结构的影响,将地震激励模拟为平稳随机过程,对基础隔震体系的随机响应进行了分析。分析结果表明,地基土的性质对隔震结构有直接影响,但其影响比非隔震结构小得多。     

结构振动的滑模变结构半主动控制

研究应用磁流变阻尼器(MRD)对结构振动半主动控制的算法和原理。研制并对磁流变阻尼器进行了阻尼特性实验，采用非线性滞回双粘性模型描述磁流变阻尼器的阻尼特性，模型结果与实验结果非常一致。采用滑模控制算法和趋近律方法设计了半主动控制器。利用滑模控制方法所建立的控制器，本文给出了地震激励下结构振动半主动控制算例。计算分析表明，半主动滑模控制具有控制效果明显、鲁棒性好等优点，是一种非常有发展前途的控制方法。     

电流变阻尼器动力特性的研究

电流变液是一种可控流体，它在电场的作用下可从牛顿流体变为屈服剪应力较高的粘塑性体，且这种变化连续，可逆，迅速。本文在简要介绍了电流变阻尼器的原理和特点后，就电流变阻尼器的动力特性，如流量和阻尼力等，建立模型，将流体流动分为剪切流动和压差流动两种情况进行了讨论，并进行迭加，使流量和阻尼计算公式得到修正和完善，最后对阻尼力进行简化，提出压差流动占绝对优势，完全可以反映电流变阻尼器的阻尼特性，为进一步实现对阻尼器的控制提供了理论基础。     

聚苯胺体系电流变流体的阻尼机理及阻尼模型研究

对聚苯胺体系电流变流体在正弦信号作用下的阻尼力响应及其频谱特性进行了理论和实验研究。提出电流变流体的非线性阻尼力的频谱是由基频和频率为基频奇数倍的高次谐波分量组成。建立了由粘性阻尼和迟滞阻尼组成的电流变流体阻尼模型，通过对模型的傅立叶变换及数值仿真，验证了理论分析及阻尼模型的正确性。     

微振激励下黏弹性阻尼器微观链结构力学模型

减小微振动对高精密仪器至关重要,利用黏弹性阻尼器进行微振动抑制是一个新兴而又具有挑战性的课题.本文采用分子链网络模型方法分析了黏弹性材料的微观分子链结构,综合考虑材料分子链结构中的网络链和自由链对黏弹性材料力学性能的影响,提出一种基于材料微观分子链结构的微振激励下黏弹性阻尼器力学模型.模型分别采用标准线性固体模型和Maxwell模型来描述网络链和自由链中单个链的力学性能,并分别采用8链网络模型和3链网络模型考虑两种类型分子链的综合效应,引入温频等效原理描述温度对微振激励下黏弹性阻尼器力学性能的影响.该模型能够描述温度和频率对黏弹性阻尼器动态力学性能的影响,并能够反映黏弹性材料的微观结构与材料力学性能的关系.为验证所提模型的有效性及考察黏弹性阻尼器在微振激励下的耗能能力和动态力学性能,在微振条件下对黏弹性阻尼器进行了动态力学性能试验.研究结果表明黏弹性阻尼器具有较好的微振耗能能力,其动态力学性能受温度和频率影响较大,所提的力学模型能够精确地描述微振激励下黏弹性阻尼器动态力学性能随温度和频率的变化关系.      

任意荷载作用下液体粘滞阻尼器在桥梁工程中减震作用探讨

在桥梁工程中，当需要限制梁端的碰撞或过大的相对位移，经常会在梁端设置液体粘滞阻尼器。由于技术原因，液体粘滞阻尼器在桥梁设计中的参数选取基本上是通过全桥模型的地震非线性时程分析得到的。而在寿命期内，桥梁需要承受各种随机荷载，在具有不同力学特性荷载的激励作用下引起梁端纵向大的响应时，液体粘滞阻尼器是否始终起有利的减震作用，一直困扰着其在桥梁工程中的实践。在液体粘滞阻尼器力学特性研究的基础上，通过矩阵变换得到关于阻尼器的局部动力方程，从变形和受力两个方向对此问题进行探讨，得到液体粘滞阻尼器对于梁端的相对位移、相对速度、相对加速度均有减震作用。但不会得出始终对所有构件的受力有利的结论，并进行了验证。     

The developing heat transfer and fluid flow in micro-channel heat sink with viscous heating effect

The numerical modeling of the conjugate heat transfer and fluid flow through the micro-heat sink was presented in the paper, considering the viscous dissipation effect. Three different fluids with temperature dependent fluid viscosity are considered: water, dielectric fluid HFE-7600 and isopropanol. The square shape of the cross-section is considered with D _h  = 50 μm with a channel length L = 50 mm. As most of the reported researches dealt with fully developed fluid flow and constant fluid properties in this paper the thermal and hydro-dynamic developing laminar fluid flow is analyzed. Two different heat transfer conditions are considered: heating and cooling at various Br. The influence of the viscous heating on local Nu and Po is analyzed. It was shown that for a given geometry the local Po and Nu numbers are strongly affected by the viscous heating. Moreover the Po number attains the fully developed value as the external heating is equal with the internal viscous heating.     

高速铁路连续梁桥的共振响应与振动控制研究

以液体粘滞阻尼器为振动控制外部装置，主桥采用欧拉伯努利梁，通过中国和谐号动车组CRH380AL、日本新干线Shinkansen700和欧洲高速列车HSLMA8三种不同类型的高速列车对比，模拟分析了高速列车作用下桥梁结构共振响应的影响因素，以及粘滞阻尼器的阻尼系数与安装位置对桥梁结构振动响应的减振效果。研究结果表明，（1）合理有效地布置列车荷载轴距，可使桥梁结构发生基频共振的列车时速在运营时速之外，避免了桥梁结构发生较大振动峰值响应，即桥梁结构的基频共振；（2）随着粘滞阻尼器阻尼系数的增大，桥梁的加速度峰值在列车不同时速下均在减少，对桥梁振动有着不同程度的减振效果；（3）通过合理安置液体粘滞阻尼器，可有效降低高速列车作用下桥梁结构的共振响应；（4）随着粘滞阻尼器与主梁的连接点位置逐渐远离支座，粘滞阻尼器的减振效果逐渐明显；（5）随着粘滞阻尼器与桥台的连接点位置逐渐靠近支座，粘滞阻尼器的减振效果略有提升，但不明显。     

Effects of viscous dissipation on laminar forced convection with axially periodic wall heat flux

The laminar forced convection in a circular duct is investigated in the case of a sinusoidal axial variation of the wall heat flux. The axial heat conduction in the fluid is neglected, while the effect of viscous dissipation is taken into account. The heat transfer in the thermally developed region, where the temperature is the sum of a linear function and a periodic function of the axial coordinate, is analysed. Both the temperature field and the local Nusselt number are evaluated analytically. Comparisons with the solution in the absence of viscous heating are performed. It is shown that the effect of viscous dissipation on the temperature field may be relevant especially in the case of a sinusoidal wall heat flux distribution with a vanishing mean value. Received on 24 July 1998     

Design method for fluid viscous dampers

A basic design method of doubly acting fluid viscous dampers with double guide bars is presented. The flow of the viscoelastic fluid between two parallel plates, one of which is started suddenly and the other of which is still, is analyzed. According to this solution, the velocity and the shear stress of the fluid at the fringe of the piston are solved approximately. A mathematical model of viscous dampers is derived, and the shock test is carried out. From experimental results, the parameters of the mathematical model are determined. Consequently, a semi-empirical design equation is obtained. Applying this equation to a certain practical damper, the damping material is chosen and the physical dimensions of the damper are determined. Shock tests using this damper are performed. Theoretical results are in good agreement with experimental results, which validates the reliability of the calculated physical dimensions of the specimen damper and the validity of the basic design equation. An erratum to this article can be found at     

Conjugate heat exchange and hydrodynamics for a viscous incompressible fluid moving in a rectangular cavity

Numerical simulation was performed of the motion of a viscous incompressible nonisothermal fluid in an open rectangular cavity under conditions of forced convection and conjugate heat exchange. The effect of the jet dynamic parameter (Reynolds number) and fluid flow conditions on the character of motion and heat exchange of viscous incompressible nonisothermal fluids in rectangular cavities is studied. A hydrodynamic pattern of viscous flow in an open cavity under forced convection conditions (in the conjugate and nonconjugate formulations of the problem) is obtained. The effect of parameters of the model on the character of motion is studied. Temperature profiles for the solid and fluid phases are obtained. The effect of parameters of the model on the character of temperature distribution in both phases is studied.     

Carreau fluid flow due to nonlinearly stretching sheet with thermal radiation,heat flux,and variable conductivity

A sophisticated theoretical and mathematical model is proposed. It is verified that this model can estimate and monitor the detailed behavior for the steady Carreau fluid flow past a nonlinear stretching surface and the predicted phenomena due to the presence of heat flux, thermal radiation, and viscous dissipation. Despite the fact that some properties of the fluid do not depend on the temperature, the fluid thermal conductivity is assumed to depend on the temperature. Based on accelerating the fluid elements, some of the kinetic energy for the fluid can be turned to the internal heating energy in the form of viscous dissipation phenomena. The contribution in this study is that a similar solution is obtained, in spite of the high nonlinearity of the Carreau model,especially, with the heat flux, variable conductivity, and viscous dissipation phenomena.Some of the major significant findings of this study can be observed from the reduction in the fluid velocity with enhancing the Weissenberg number. Likewise, the increase in the sheet temperature is noted with increasing the Eckert number while the reverse behavior is observed for increasing both the radiation parameter and the conductivity parameter.Finally, the accuracy and trust in the proposed numerical method are validated after benchmarking for our data onto the earlier results.     

Numerical study of thermal convection in rotating channel flow

A numerical study is conducted on the effect of sidewall heating in the pressure-driven laminar flow of an incompressible viscous fluid through a rectangular channel that is subjected to a spanwise rotation. The time-dependent Navier-Stokes equations are solved along with the conservation equations for energy and mass by a finite-difference technique. The effect of weak to moderate sidewall heating on the overall flow structure at different rotation rates is studied. It is observed that for weak sidewall heating, the secondary flow structure is quite similar to the corresponding isothermal case. However, when the sidewall heating is moderate, various types of secondary flow fields are found to occur depending on the magnitude of the rotation. The influence of rotational speed on the net heat transport for different levels of sidewall heating is also studied. It is found that when the sidewall heating is weak, the basic secondary flow structure for the non-rotating case is of a unicellular form and an increase in the rotation speed leads to an increase in the net heat transfer due mainly to the rotationally driven transport of fluid from the high temperature to the low temperature region. On the other hand, when the sidewall heating is moderate so that the basic secondary flow structure for the non-rotating case has a multicellular configuration, an increase in the rotation speed leads to a decrease in the heat transport due to the weakening of the shear layer near the hot wall.     

Motion of a solidcontaininga spherical damper

For the purpose of modeling the motion of a solid with a cavity filled with a viscous fluid, M. A. Lavrent'ev [1] has proposed a model in the form of a solid with a spherical cavity in which another solid, spherical in shape, is enclosed. The sphere is separated from the cavity walls by a small, clearance in which viscous forces act (a lubricating film). This simple model with a finite number of degrees of freedom possesses certain mechanical properties of a solid with a cavity containing a viscous fluid. Study of this model is therefore of interest.The present paper examines certain properties of the model, which will be termed a solid with a damper. It is shown that for a highviscosity lubricant the motion of a solid with a damper can be described by the same equations which pertain to the motion of a solid with a spherical cavity filled with a high-viscosity fluid. Expressions relating the parameters of the systems are obtained. If these relations are fulfilled, the systems become mechanically equivalent.The steady motions of a free solid with a damper and their stability conditions are determined.These motions and stability conditions hold for a body with a cavity filled with a viscous fluid [2].