附加黏滞阻尼器结构附加等效阻尼比算法研究

本文基于应变能概念,从附加等效阻尼比计算的基本理论出发,结合国内外相关规范、导则及论文,讨论了几种计算附加非线性黏滞阻尼器建筑结构的附加等效阻尼比实用估计方法.以一个实际工程为算例,比较附加黏滞阻尼器结构和两种不同估计方法得到的附加等效阻尼比的阻尼结构在地震时程下的响应,验证了各方法计算结果满足工程精度情况.     

考虑弯剪变形的黏滞阻尼器布置机构位移放大系数计算

现有的黏滞阻尼器布置机构的位移放大系数计算公式是基于结构剪切型侧移模式推导的,而多高层建筑结构的侧移模式一般为弯剪型,这有可能导致采用现有方法计算多高层建筑结构中的黏滞阻尼器的位移放大系数和附加阻尼比不准确。采用解析几何方法,推导了单层弯剪型结构和一般多高层结构中阻尼器布置机构位移放大系数的计算公式,包括对角布置机构、剪刀撑布置机构、下套索布置机构、上套索布置机构。按照阻尼器布置机构位移放大系数现有计算方法和本文提出的方法,采用应变能法计算了多层钢框架结构中布置黏滞阻尼器的附加阻尼比,并与自由振动衰减法的计算结果进行了对比,本文方法的计算误差不到1%。这验证了本文提出的考虑弯剪变形的黏滞阻尼器布置机构位移放大系数的计算方法对一般多高层结构具有更好的计算精度。     

附加黏滞阻尼器减震结构基于性能的抗震设计方法

本文以位移设计方法的概念为主,结合能力谱法提出附加黏滞流体阻尼器结构基于位移的初步设计方法.首先讨论了减震结构基于性能设计方法的实现途径并加以比较;其次定量研究了使用加速度反应谱转换为位移反应谱的条件,分析指出真实位移反应谱(均值)与转换得到的位移反应谱随着场地特征周期的增大,两者之间的差值逐渐增大;在场地条件相同的情况下,阻尼比越大两者的差异也越大.最后结合我国抗震设计规范,给出了主体结构保持弹性状态时,非迭代法确定附加黏滞流体阻尼器的减震结构设计流程.非线性时程分析结果表明该设计方法实用、有效.     

材料黏滞系数与损耗因子的频率相关性研究

针对黏弹性材料KV阻尼模型的黏滞系数与复阻尼模型的损耗因子间的关系,由单自由度体系的结构动力学分析,并基于结构振动响应的一致性,推导建立了黏滞系数与损耗因子在结构线性稳态简谐振动和自由振动时的一般关系式;并利用该关系式,试验研究了纤维混凝土材料黏滞系数和损耗因子的频率相关性.结果表明,黏滞系数与损耗因子间的关系在稳态简谐振动和自由振动时的表达形式相同,只是频率取值不同;纤维混凝土的损耗因子和黏滞系数都随频率增加而降低,且在0.5～1.0Hz频段降幅显著,而后渐趋平缓;相比于素混凝土,纤维混凝土的黏滞系数和损耗因子与激振频率的相关性更强.试验所得纤维混凝土频率相关的黏滞系数、损耗因子及推导所建立的两参数关系式为构建物理意义明确且又便于结构振动反应分析的阻尼系数或阻尼矩阵奠定了基础.      

SMA叠层变刚度水平万向阻尼器滞回性能研究

利用NiTi形状记忆合金(Shape Memory Alloy,简称SMA)的超弹性特性,开发了一种新型SMA叠层变刚度水平万向阻尼器,介绍了其基本构造和工作原理,建立了阻尼器恢复力计算模型并开展了滞回性能参数分析,研究了SMA张拉应变、SMA直径、阻尼器层数以及每层SMA丝根数对阻尼器行程、刚度、耗能、等效阻尼比的影响.研究结果表明：SMA叠层变刚度水平万向阻尼器的恢复力-位移滞回曲线呈饱满的纺锤形,阻尼器具有良好的能量耗散能力、自复位功能、大行程以及变刚度特性;随着SMA张拉应变由0.03不断增大至0.06,阻尼器最大行程不断减小而单位循环耗能呈先增大后减小趋势;随着SMA直径不断增大,阻尼器刚度和耗能能力不断增大而最大行程和等效阻尼比不变;随着叠层层数不断增大,阻尼器最大行程和单位循环耗能不断增加而刚度不断降低;随着每层SMA布置数量由8根增大至16和32根,阻尼器刚度和单位循环耗能不断增大而最大行程和等效阻尼比变化不明显.     

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.      

基于Kanai-Tajimi谱的非黏滞阻尼结构地震动响应的简明闭式解

针对非黏滞阻尼结构基于Kanai-Tajimi谱的卷积-微分混合动力方程解法较繁琐的问题,提出了 一种新的简明封闭解法.非黏滞阻尼模型能较好地模拟实际工程材料的阻尼特征,常以指数型核函数的卷积形式表示,给出其对应的微分型本构关系.Kanai-Tajimi谱随机地震动模型能较好地描述场地的随机地震动特性,其工程应用时所获...     

粘滞和粘弹性阻尼器减震结构的随机响应特性

利用积分型本构关系,针对带支撑任意线性粘滞和粘弹性阻尼器单自由度耗能结构,建立了微分和积分混合地震响应方程;基于随机平均分析法,推导出耗能结构振幅与相位瞬态联合概率密度函数、位移与速度瞬态联合概率密度函数、位移与速度瞬态响应方差、振幅动力可靠性、振幅首超时间任意阶统计矩的一般解析解;给出了带支撑广义Maxwell阻尼器和广义微分模型阻尼器耗能结构上述各种随机响应特性,从而建立了带支撑任意线性粘滞和粘弹性阻尼器单自由度减震结构的各种随机响应特性分析的统一解析解法。     

氟橡胶O型圈低压气体密封黏滞摩擦特性实验

开展了低气体密封压力条件下的氟橡胶O型圈低压黏滞摩擦特性实验研究.对氟橡胶O型圈与不锈钢2Cr13摩擦副的摩擦力的时变曲线进行测量,重点分析了密封压力、O型圈压缩率和滑动速度对O型圈黏滞摩擦力的影响规律.结果表明:随压缩率的增加,氟橡胶O型圈摩擦力增加,并呈现出明显的回弹特征,即滞后摩擦力增加且释放时间增加;随着密封压力的增加,其所受最大静摩擦力、滑动摩擦力与滞后摩擦力均呈现非线性变化,且存在一极大值;减小往复运动速度,摩擦力数值增大,但摩擦力极值对应的密封压力值变小.     

多自由度Maxwell阻尼器减震结构(Ⅰ)——随机响应特性

对多自由度带支撑Maxwell粘滞阻尼器减震结构的随机响应特性进行了系统研究。建立了结构一般运动方程;将运动方程按原结构振型展开,将运动方程化为振型广义坐标的微分和积分混合地震响应方程组;基于多自由度随机平均法理论,获得了结构随机平均It方程组的解析式,推导出耗能结构各振型振子的振幅与相位瞬态联合概率密度函数、位移与速度瞬态联合概率密度函数、位移与速度瞬态响应方差的一般解析解;根据SRSS组合方法,给出了耗能结构随机地震响应方差的一般解析式,从而建立了此类耗能结构随机响应特性分析的完备解析解法。     

流体阻尼器中粘性发热的反馈作用与热平衡研究

主要针对长阻尼孔形式下的流体阻尼器进行分析,在三参数模型的基础上研究了流体粘性发热对流体阻尼力的反馈作用,从而建立了含热能转换与热交换的阻尼器的动力学模型,同时对系统的热平衡状态进行了分析。最后通过数值分析对该时变系统从时域和频域上讨论了粘性发热对隔振效果的影响,发现温度变化对共振频率的漂移及幅值大小的影响较大。     

Spatial Motion of a Rod in a Viscous Fluid Flow

Equations of spatial motion of a curved finitelength rod in a viscous fluid flow are derived. Analytical solutions of problems on the motion of a straight rod under conditions of pure shear, simple shear, and uniaxial extension of the fluid are obtained. Longitudinal stability of the straight rod during its spatial motion is considered. Effective viscosity of a suspension filled by rigid straight rods is evaluated.     

Control Problems for the Steady-State Equations of Magnetohydrodynamics of a Viscous Incompressible Fluid

Control problems for a steady-state model of the magnetohydrodynamics of a viscous incompressible fluid in a bounded domain with an impermeable, perfectly conducting boundary are formulated. The resolvability of the problems is studied, the use of the Lagrange principle is justified, and optimality systems are analyzed.     

Flow Asymptotics of a Viscous Compressible Fluid with Discontinuous Initial Data

Asymptotics of a continuous solution to a plane problem on the motion of a viscous incompressible fluid with discontinuous initial velocity and pressure fields is studied by the boundarylayer method with simultaneous stretching of space and time coordinates.     

Steady Film Flow of a Highly Viscous Heavy Fluid with Mass Supply

Asymptotic models of a thin layer of highly viscous heavy incompressible Newtonian fluid are constructed for steady axisymmetric (plane) flow on a curved rigid surface with distributed or point mass supply on a surface section near the axis (plane) of symmetry. Examples of analytical and numerical investigations of the free-surface shape and hydrodynamic-parameter fields are given. The models constructed are generalized for the case of a viscoplastic fluid and solutions which can be used for describing extrusive volcanic eruptions are obtained.     

Effects of Viscous Dissipation on Unsteady Free Convection in a Fluid Past a Vertical Plate Immersed in a Porous Medium

The effects of viscous dissipation on unsteady free convection from an isothermal vertical flat plate in a fluid saturated porous medium are examined numerically. The Darcy–Brinkman–Forchheimer model is employed to describe the flow field. A new model of viscous dissipation is used for the Darcy–Brinkman–Forchheimer model of porous media. The simultaneous development of the momentum and thermal boundary layers are obtained by using a finite difference method. Boundary layer and Boussinesq approximation have been incorporated. Numerical calculations are carried out for various parameters entering into the problem. Velocity and temperature profiles as well as local friction factor and local Nusselt number are shown graphically. It is found that as time approaches infinity, the values of friction factor and heat transfer coefficient approach steady state.     

Flow of a Nonlinearly Viscous Fluid over the Surface of a Rotating Flat Disk

The flow of a nonlinearly viscous (power-law) fluid over the surface of a rotating flat disk is investigated. A solution form which makes it possible to reduce the complete system of partial differential equations to a system of ordinary differential equations is found. This system is integrated using the Runge-Kutta method and reduction to a Cauchy problem on the basis of Newton's method. The velocity and pressure fields in a power-law fluid film flowing over the surface of a rotating flat disk are found numerically.     

Bifurcation of a Main Steady-State Viscous Fluid Flow in a Plane Divergent Channel

The evolution of steady-state viscous incompressible fluid flows in a plane divergent channel is investigated. For the classical formulation of the Jeffery-Hamel problem a complete solution is given as a function of the determining parameters. For a fixed angle of divergence the behavior of the main unimodal flow is determined as a function of the Reynolds number. Critical values at which the flow pattern bifurcates and the steady-state unimodal flow ceases to exist are found. The mechanism of bifurcation is established and its diagram is constructed. This mechanism and the diagram were not previously known in the scientific literature in connection with the investigation of the Jeffery-Hamel problem. The critical Reynolds number at which bifurcation occurs is given as a function of the channel divergence angle. The results may be of interest for hydromechanical, technological, and geophysical applications.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, 2005, pp. 25–36.Original Russian Text Copyright © 2005 by Akulenko and Kumakshev.     

Effect of the Hydrodynamic Interaction of a Large Number of Particles on Their Sedimentation Rate in a Viscous Fluid

The gravity-induced sedimentation of a large number of identical spherical particles in a viscous fluid is considered. The hydrodynamic interaction of all the particles is taken into account. The problem is modeled numerically for random locations of 1–100 particles forming different configurations. A dependence of the mean sedimentation rate on the particle number and concentration in the cloud is obtained and compared with previous results.     

Transformation of Long Nonlinear Waves in a Two-Layer Viscous Fluid Between a Gently Sloping Lid and Bottom

Dynamics of three-dimensional disturbances of the interface between two fluid layers of different densities is considered analytically and numerically. An evolutionary integrodifferential equation is derived, which takes into account long-wave contributions of inertia of the layers and surface tension, small but finite amplitude of disturbances of the interface between two incompressible immiscible fluids, gentle slopes of the lid and bottom, and nonstationary shear stresses at all boundaries. Numerical solutions of this model equation for several (most typical) nonlinear problems of transformation of two- and three-dimensional waves are obtained. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 6, pp. 45–57, November–December, 2005.