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.     

套索式黏滞阻尼器位移放大系数的 理论和实验研究

考虑了支撑杆弹性变形的影响,提出了精确计算套索式黏滞阻尼器位移放大系数的方法;借助SAP2000分析软件,研究了套索式黏滞阻尼器在不同工况下放大系数的变化情况,并通过试验对理论分析和模拟结果进行了验证.研究结果表明:套索式黏滞阻尼器的实际位移放大系数小于刚性理论计算值,支撑杆的弹性变形应予以考虑;在其他条件一定的情况下,位移放大系数随加载频率的增大而减小.本文提出的方法考虑了支撑杆件的刚度,能够更加合理地计算套索式黏滞阻尼器的位移放大系数.     

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。     

阻尼器布置偏心距对阻尼器耗能的影响研究

在结构的消能减震中,粘滞阻尼器常采用悬臂墙式布置.研究发现,在实际使用过程中,悬臂墙式阻尼器不同的偏心距会进一步影响阻尼器在结构中的耗能效果.为了分析阻尼器布置偏心距对其耗能的影响,从而修正结构附加阻尼比,引入阻尼器布置偏心距位移参数.结果表明:当阻尼器居中布置时,其布置偏心距位移参数大于1,修正后的附加阻尼比计算结果略大于\"抗规\"计算,这说明\"抗规\"计算相对保守;当阻尼器布置存在偏心时,其布置偏心距位移参数小于1,修正后的附加阻尼比计算结果小于\"抗规\"计算,这说明采用修正后的附加阻尼比计算更为合理.这验证了本文提出的基于阻尼器布置偏心距位移参数修正附加阻尼比的计算方法具有更好的计算精度,从而为分析阻尼器在结构中的耗能提供理论指导.     

附设黏滞阻尼器的装配式悬臂挡土墙动力响应研究

为提高装配式悬臂挡土墙抗震性能,将黏滞阻尼器附设在装配式悬臂挡土墙上,形成一种新型装配式悬臂阻尼挡土墙,通过黏滞阻尼器耗散地震能量达到减震目的.为研究该新型挡土墙的动力响应,采用ABAQUS软件,建立了两组三维有限元对比模型,一组为无滑体的阻尼悬臂挡土墙及对比模型,另一组为包含滑坡体的新型阻尼挡土墙及对比模型.对模型施以Vrancea地震波,研究了附设黏滞阻尼器的装配悬臂挡土墙抗震性能,并进行参数分析,讨论了混凝土强度、装配尺寸、阻尼器关键参数对其力学性能的影响.结果表明:附设黏滞阻尼器的装配悬臂挡土墙相较于对比模型,立板最大荷载减小约50％,最大应力减小约60％,立板最大水平位移由6.69mm减小至1.24mm,抗震性能显著提高;随着立板厚度、阻尼系数的增大,附设黏滞阻尼器的装配悬臂式挡土墙抗震性能有所提高,而混凝土强度、阻尼指数需要合理选择.     

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,其工程应用时所获得的结构地震动响应表达式复杂,但其可用滤波方程表示为基于白噪声激励的随机过程.利用非黏滞阻尼结构的微分型本构关系和Kanai-Tajimi谱的滤波方程,将基于复杂地震动激励卷积-微分型动力方程转化为基于白噪声激励的全微分型动力方程组;然后基于复模态法及Dirac函数的性质,获得了耗能结构系列响应(位移及速度)0～2阶谱矩的简明解;最后,分析了基于首超破坏准则及Markov假定的非黏滞阻尼结构的动力可靠度.对一算例运用所提方法与虚拟激励法进行对比分析,证明所提封闭解的正确性和高效性,并可作为虚拟激励法精度的验证方法.     

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     

Two-dimensional models of magma flows in a volcanic conduit taking the magma compressibility and thermal effects into account

Two steady-state models of magma flow in a conduit are considered, with and without allowance for magma compressibility. As distinct from studies [{xc1}–{xc6}], in which either simplified equations were solved or unrealistic values of the parameters were used, in the present study the complete systems of equations are solved and the values of the parameters correspond to magma flow in a volcanic conduit. The secondary flows obtained in [{xc5}] for model conditions are not formed when the magma is simulated by an incompressible fluid and all the terms of the equations are taken into account. When the magma compressibility is taken into account, in the isothermal case and for constant magma viscosity the entire flow is adequately described by the one-dimensional isothermalmodel, although this approach is not formally applicable.     

Asymptotic partition of energy in micropolar mixture theory of porous media

The aim of this paper is to study the asymptotic partition of the energy associated with the solution of the initial-boundary value problem who describes the behavior of binary homogeneous micropolar mixtures of an isotropic micropolar elastic solid with an incompressible micropolar viscous fluid. Some Lagrange-Brun identities are established. Using the Cesáro means of various parts of total energy, the relations that describe the asymptotic behavior of mean energies are established. The author acknowledges support from the Romanian Ministry of Education and Research through CEEX program, contract CERES-2-CEx06-11-12/25.07.2006.     

The Development of the Asymptotic Viscous Dissipation Profile in a Vertical Free Convective Boundary Layer Flow in a Porous Medium

The effect of viscous dissipation on the development of the boundary layer flow from a cold vertical surface embedded in a Darcian porous medium is investigated. It is found that the flow evolves gradually from the classical Cheng–Minkowycz form to the recently discovered asymptotic dissipation profile which is a parallel flow.     

A New Model for Viscous Dissipation in Porous Media Across a Range of Permeability Values

In this paper a unified mathematical theory for the viscous dissipation term in the governing Brinkman equation is derived. This term has, unlike other models, the correct asymptotic behaviour in both the fully Darcy and Newtonian fluid flow limits.     

A METHOD OF ASSESSING THE EFFECTS OF ARTIFICIAL DISSIPATION IN NAVIER–STOKES CODES

A new method of estimating the extent of the artificial dissipation effects in any solution obtained with a Navier–Stokes flow solver is described. Rather than recalculating the flow on a more refined grid, the solver may be used on the same grid to calculate the flow of an ‘artificially dissipative fluid’, which is a fluid having dissipate properties which arise entirely from the solution method itself. This is done by setting the viscosity and heat conduction coefficients in the Navier–Stokes solver to zero everywhere in the flow, while at the same time applying the usual boundary conditions at solid boundaries. An ‘artificially dissipative flow’ solution will be found where the dissipation effects depend entirely on the solver itself. By comparing this solution with that obtained on the same grid with the solver working in its normal mode, one can estimate whether further grid refinement is required, without necessarily producing an extensive series of solutions on different grids.     

Analytical Solution for the Effect of Viscous Dissipation on Mixed Convection in Saturated Porous Media

A new analytical solution is introduced for the effect of viscous dissipation on mixed convection flow and heat transfer about an isothermal vertical wall embedded in Darcy and non-Darcy porous media with uniform free stream velocity. The effect of viscous dissipation on mixed convection in both regimes has been analyzed for both the aiding and opposing flows using Gebhart number, Ge _x =gx/c _p. The governing parameters are Re, Ra, Pe and Ge _x . The case of Re=0 corresponds to Darcy mixed convection region and Re/Pe is identified as the mixed convection governing parameter, Ra=0 leading to pure forced convection. A good agreement was found between the numerical and analytical solutions. It was found from the Nusselt number results that viscous dissipation lowers the heat transfer rate in both Darcy and Forchheimer flow regimes for aiding as well as opposing flows.     

带有摩擦耗能元件的框架结构动力分析

本文提出粘性屈服模型来模拟摩擦耗能元件的力-速度关系,该模型是连续变化的,克服了库仑摩擦模型不连续导致数值计算复杂的缺点,在进行摩擦耗能体系的动力分析中,采用缩减自由度技术,并作适当的变换,则带有摩擦耗能元件体系的动力分析归结为求解微分代数方程,本文采用增量型Rosenbrock二级三阶半隐式Runge-Kutta法求解该方程,以考虑框架和支撑的材料和几何非线性.对带有摩擦耗能元件的钢框架进行了弹塑性动力分析,研究了支撑刚度与结构层刚度的比值、摩擦力的大小以及地震波类型等参数对体系的影响.