Application of computational fluid dynamics in design of viscous dampers-CFD modeling and full-scale dynamic testing

Computational fluid dynamics(CFD)provides a powerful tool for investigating complicated fluid flows.This paper aims to study the applicability of CFD in the preliminary design of linear and nonlinear fluid viscous dampers.Two fluid viscous dampers were designed based on CFD models.The first device was a linear viscous damper with straight orifices.The second was a nonlinear viscous damper containing a one-way pressure-responsive valve inside its orifices.Both dampers were detailed based on CFD simulations,and their internal fluid flows were investigated.Full-scale specimens of both dampers were manufactured and tested under dynamic loads.According to the tests results,both dampers demonstrate stable cyclic behaviors,and as expected,the nonlinear damper generally tends to dissipate more energy compared to its linear counterpart.Good compatibility was achieved between the experimentally measured damper force-velocity curves and those estimated from CFD analyses.Using a thermography camera,a rise in temperature of the dampers was measured during the tests.It was found that output force of the manufactured devices was virtually independent of temperature even during long duration loadings.Accordingly,temperature dependence can be ignored in CFD models,because a reliable temperature compensator mechanism was used(or intended to be used)by the damper manufacturer.

THEORY AND EXPERIMENT ON THE VISCOUS HEATING OF FLUID DAMPER UNDER SHOCK ENVIRONMENT

A specially designed fluid damper used as negative shock pulse generator in the shock resistance test system to dissipate the shock input energy in transient time duration is presented. The theoretical modeling based on the three-dimensional equation of heat transfer through a fluid element is created to predict the viscous heating in the fluid damper under shock conditions. A comprehensive experimental program that investigates the problem of viscous heating in the fluid damper under different shock conditions is conducted on the shock test machine to validate the analytical expression. Temperature histories for the fluid within the damper at two locations, the annular-oriflce and the-end-of stroke of the damper, are recorded. The experimental results show that the theoretical model can offer a very dependable prediction for the temperature histories in the damper for increasing input velocity. The theoretical model and experimental data both clearly indicate that the viscous heating in the damper is directly related to the maximum shock velocity input and the pressure between the two sides of the piston head.

Performance of viscous fluid dampers coupling adjacent inelastic structures under near-fault earthquakes

The behavior of viscous fluid damper applied in coupling structures subjected to near-fault earthquake was studied.The structural nonlinearity was characterized by Bouc-Wen model and several near-fault ground motions were simulated by the combination of a recorded earthquake(background ground motion) with equivalent velocity pulses that possess near-fault features.Extensive parametric studies were carried out to find the appropriate damping coefficient.Performances of viscous fluid dampers were demonstrated by the relationship between the force and displacement,the maximal damper force and stroke.The control performances were demonstrated in terms of the response reductions of adjacent structures.The results show that the dynamic responses of adjacent structures are mitigated greatly.Proper damping coefficients of connecting fluid dampers have a small difference,while adjacent structures under different near-fault ground motions with the same peak acceleration.The maximum force of damper is about 0.8 MN,and the maximum damper stroke is about ±550 mm.Satisfied viscous fluid dampers can be produced according to the current manufacturing skills.

Improving the seismic torsional behavior of plan-asymmetric,single-storey,concrete moment resisting buildings with fluid viscous dampers

The optimal distribution of fluid viscous dampers（FVD）in controlling the seismic response of eccentric,single-storey,moment resisting concrete structures is investigated using the previously defined center of damping constant（CDC）.For this purpose,a number of structural models with different one-way stiffness and strength eccentricities are considered.Extensive nonlinear time history analyses are carried out for various arrangements of FVDs.It is shown that the arrangement of FVDs for controlling the torsional behavior due to asymmetry in the concrete structures is very dependent on the intensity of the peak ground acceleration（PGA）and the extent of the structural stiffness and strength eccentricities.The results indicate that,in the linear range of structural behavior the stiffness eccentricity es which is the main parameter in determining the location of optimal CDC,is found to be less or smaller than the optimal damping constant eccentricity e＊d,i.e.,｜e＊d｜ 〉 ｜es｜.But,in the nonlinear range of structural behavior where the strength eccentricity er is the dominant factor in determining the location of optimal CDC,｜e＊d｜ 〉 ｜er｜.It is also concluded that for the majority of the plan-asymmetric,concrete structures considered in this study with er ≠ 0,the optimal CDC approaches the center of mass as er decreases.

四主缆大跨悬索桥抗震性能分析及减震措施优化

以燕矶长江大桥为工程背景,首先,采用动力非线性时程法分析了燕矶长江大桥抗震性能,并研究了设置电涡流-摩擦组合型阻尼器和黏滞阻尼器对大跨悬索桥抗震性能的影响;然后,对附加电涡流-摩擦组合型阻尼器摩擦力、阻尼系数和阻尼指数开展了参数敏感性分析;最后,从耗能角度分析地震作用下电涡流-摩擦组合型阻尼器减震特点.结果表明:在E2地震作用下,桥塔关键截面抗弯能力均大于弯矩需求;在“纵向+竖向”地震作用下梁端纵向位移较大.设置塔梁处纵桥向阻尼器后,可有效降低主桥梁端纵向位移;增大摩擦力、阻尼系数与降低阻尼指数均可提升梁端纵向地震响应的控制效果,但参数变化对桥塔控制截面的地震响应影响较小.阻尼系数较大时,电涡流阻尼主导了电涡流-摩擦组合型阻尼器耗能,相较于黏滞阻尼器,电涡流-摩擦组合型阻尼器对梁端纵向位移控制效果更好.

铁路悬索桥车致纵向运动混合阻尼减振研究

针对铁路悬索桥在列车过桥时梁端纵向运动响应控制问题,提出了一种创新的混合阻尼减振方案,采用多种类型的阻尼器控制梁端位移,以满足不同的减振需求.以某在建大跨铁路悬索桥为工程背景,建立了空间桁架精细模型和等效单梁简化模型,系统研究了混合阻尼减振方案不同阻尼器参数对减振效果的影响.该方案将低指数黏滞阻尼器纵向安装于桥塔与加劲梁之间,同时在桥台与加劲梁之间纵向安装电涡流阻尼器.鉴于桥台结构的特殊性,电涡流阻尼器被设计为仅能承受压力的装置,并通过样机试验进行了验证.为了进一步提升减振性能,电涡流阻尼器还配备了摩擦耗能元件.该混合阻尼减振方案能够有效控制列车过桥时梁端的纵向运动响应,显著提高桥梁结构的安全性和耐久性,在类似工程中具有重要的参考价值和借鉴意义.

考虑泄漏和温度效应的黏滞阻尼器性能演变研究

黏滞阻尼器作为一种广泛使用的被动减振/震装置,其力学性能在全寿命周期内会发生演变。为探究其力学参数改变模式,揭示其性能演变机理,以油液泄漏和温度效应为主要影响因素开展了试验及仿真研究。首先,对不同漏油程度和环境温度下的黏滞阻尼器分别开展了滞回试验研究和黏温关系分析;其次,对黏滞阻尼器进行了流体动力学仿真,获得其性能演变规律;最后,建立了漏油与温度联合作用下黏滞阻尼器性能演变的力学模型,并对其进行了验证。研究结果表明,油液泄漏将导致滞回圈出现零力平台段,且平台长度与漏油比例成正比;温度升高会导致阻尼系数的减小,从而影响阻尼力峰值;所建立的性能演变模型能够较为精确地反映黏滞阻尼器力学性能的改变。

基于GA-BPNN代理模型的混合式黏滞阻尼器构造优化

采取CFD(computational fluid dynamics)数值模拟和基于代理模型的优化方法,研究混合式黏滞阻尼器在多参数设计空间内的构造参数优化问题。首先,分析黏滞阻尼器参数对力学性能的影响规律,基于正交试验理论选取间隙宽度、缸体内径、活塞厚度、阻尼孔直径为关键参数,利用优化拉丁超立方设计和CFD数值模拟获得初始样本点耗能性能指标;然后,使用遗传算法(genetic algorithm,GA)和反向传播神经网络(backpropagation neural network,BPNN)的方法构建代理模型,其能够准确反映构造参数耗能性能指标和构造参数之间的繁复关系。进一步地,循环更新GA-BPNN代理模型并结合非支配排序遗传算法(non-dominated sorting genetic algorithm-II,NSGA-II),以最佳耗能能力为目标,实现在全设计空间内的寻优,确定在典型阻尼介质黏度下双出杆混合式黏滞阻尼器的最优构造参数。最后,探讨了构造参数对黏滞阻尼器流动性能的影响机理。研究结果表明,优化双出杆混合式黏滞阻尼器构造参数在选用基于GA-BPNN代理模型的优化方法时,可有效提高计算效率且具有较高预测精度。从性能指标提升角度,全黏度下最优构造参数阻尼孔直径、活塞厚度、缸体内径和间隙宽度分别为1.31 mm、120.78 mm、199.87 mm、0.5 mm,相较于基准构造,最大阻尼力和能量耗材比分别提升33.8%和64.8%。该方法可为黏滞阻尼器构造参数优化及相关研究提供参考。

FVD与FPB在大跨长联减隔震体系梁桥中的联合作用机理研究

为验证液体黏滞阻尼器(FVD)与摩擦摆支座(FPB)组合在大跨长联减隔震体系梁桥中的应用效果,以一联(50+8×100+50)m预应力混凝土连续梁桥为工程背景,建立全桥有限元模型,通过输入场地地震安评报告提供的50年超越概率为2%的三条人工模拟地震波,开展单独及组合使用液体黏滞阻尼器和摩擦摆支座的大跨长联梁桥减隔震研究,从能量耗散的角度揭示液体黏滞阻尼器与摩擦摆支座组合在大跨长联减隔震体系梁桥中的联合作用机理。结果表明,大跨长联梁桥仅使用黏滞阻尼器,其长周期特性激发黏滞阻尼器充分发挥耗能,但无法避免对固定墩的地震损伤;仅使用摩擦摆支座隔震在纵(横)向强震下会引起支座位移超限;摩擦摆支座与黏滞阻尼器组合的减震机理为摩擦摆支座提供墩梁间的弱连接,激发墩梁间的相对速度,促进黏滞阻尼器(速度型)充分发挥阻尼耗能作用。另外,组合减震方案中摩擦摆支座为辅助耗能装置,黏滞阻尼器为主要耗能装置,且主控梁体位移;相比仅使用摩擦摆支座隔震,由于黏滞阻尼器激发的阻尼力增强了墩梁间约束,这种组合减隔震可能使结构输入能量增加,从而导致地震反应加剧。

大跨度连续梁桥SSAB与FVD组合应用减隔震技术研究

以某(88+152+88)m连续梁桥为工程背景,建立了采用液体黏滞阻尼器(FVD)的减震模型,采用非线性动力时程分析方法研究粘滞阻尼器对该桥抗震性能的影响。通过粘滞阻尼器在不同位置的布设,得出了最优的布置方案;通过基于阻尼力的参数分析,得出了最优的阻尼器型号。研究结果表明:当地震力较大时,单独采用阻尼器并不能完全达到理想的效果,此时,设置减震专用支座(SSAB)与阻尼器配合使用可进一步改善桥墩受力;减震专用支座可按滞后系统进行模拟,分析时可基于2种极端状况来模拟其恢复力模型,取屈服强度为设定的减震专用支座水平力限值时计算结果可控制设计。

黏滞阻尼器的试验方法及数据处理分析

随着减隔震技术的发展,黏滞阻尼器作为一种减震产品,其应用环境日趋复杂,为了保证产品的性能要求,把好产品应用前的质量关,就变得尤为重要。文中针对目前国内相关检测机构在黏滞阻尼器产品试验方法上的不透明、不统一等诸多问题,在多年来自身试验、经验积累的基础上,总结分析出了此类产品试验方法和数据处理分析的关键步骤与需要注意的细节,并在实际的试验工作中得到了很好的应用和改进。

基于RC框架地震易损性的阻尼器构造优化方案决策

基于GA-BPNN代理模型进行混合式黏滞阻尼器构造优化方案决策。首先,选取某款黏滞阻尼器及3个优化构造方案,利用CFD数值模拟获得阻尼器阻尼力-速度曲线及阻尼力-速度关系式,并布置于经抗震设计的RC框架结构中,获得4个设置不同构造黏滞阻尼器的RC框架。然后,选取22条地震波加速度时程曲线,采用增量动力分析(IDA)方法对设置不同构造黏滞阻尼器的RC框架及原框架结构进行结构计算,获得IDA曲线。最后,根据所选取的性能水准和地震概率需求模型,绘制地震易损性曲线,进行对比分析,从而对不同阻尼器构造优化方案进行决策。结果表明:设置黏滞阻尼器后,RC框架结构各层层间位移角会显著降低,有效提升结构抗震能力;8度多遇地震作用下,未设置黏滞阻尼器的RC框架结构轻微损坏的发生概率最大,8度设防地震作用下,设置优化构造1的黏滞阻尼器的RC框架结构发生严重破坏和倒塌概率最小;设置优化构造1的黏滞阻尼器的RC框架结构抗倒塌储备系数最大,相对于未进行优化构造的黏滞阻尼器,其抗倒塌储备系数提高14.32%。

组合减震加固技术在教学楼加固中的应用

分别采用传统加固方案、屈曲约束支撑(buckling restrained braces,BRB)加固方案、黏滞阻尼器(viscous fluid dampers,VFD)加固方案和BRB+VFD组合减震加固方案对某教学楼进行多遇地震作用下弹性时程分析和罕遇地震作用下弹塑性时程分析,对比分析层间位移角、层间剪力、附加阻尼比等。研究结果表明,多遇地震作用下,BRB+VFD组合减震加固方案中BRB可提供刚度,解决了底部薄弱层的问题,VFD可提供附加阻尼,减小了地震作用,进而减小了构件加固量。罕遇地震作用下,BRB+VFD组合减震加固方案下结构层间位移角更均匀,整体充分耗能且损伤较小,达到损伤控制和韧性结构要求。综合考虑,BRB+VFD组合减震加固方案为最优方案。

北京未来城学校教学楼钢结构设计与分析

北京未来城学校教学楼的地上部分采用钢框架结构,并设置2道结构缝将造型奇特的教学楼分为3个部分。教学楼地下部分不设缝连为整体,采用钢筋混凝土框架结构。钢连廊跨度为33 m,采用2层通高桁架结构。钢连廊与两侧主体结构采用弱连接,通过对比3种支座方案,选用布置金属摩擦摆隔震支座+黏滞阻尼器的方案。对钢连廊与两侧主体结构整体模型进行动力弹塑性时程分析,连廊整体作为刚体随3层主楼楼面发生地震响应,隔震支座的隔震效果显著。此外,介绍了本项目中钢筋混凝土梁与钢骨混凝土柱连接节点及梁配筋的注意事项,为后续相关工程设计提供参考。

科兴中维某框架结构减震加固设计

科兴中维某框架结构因工艺调整、抗震设防类别提高,采用增设黏滞阻尼器的消能减震加固方式。本文通过建立弹塑性模型进行大震弹塑性分析,结果表明本结构减震加固后,黏滞阻尼器起到了良好的减震耗能作用,结构顶点位移、层间位移角、基底剪力等关键指标均满足大震要求;地震能量主要由黏滞阻尼器及框架梁消耗,框架柱基本不参与耗能;减震加固后框架梁满足性能水准要求,框架柱包钢加固后满足性能水准要求。

新疆高烈度地区A中学教学楼建设消能减震设计研究

高烈度区域更易受到地震影响。研究高烈度区域教学楼消能减震设计有助于后期恢复、减少震后损失,提升生存保障。本文以A中学教学楼为研究对象,分析消能减震目标,采用规范消能减震技术及墙体黏滞流体阻尼器方案。研究结果表明,设防地震作用下教学楼主体弹性,粘滞流体阻尼器在中震下就开始屈服耗能,等效附加阻尼比平均值X向4.56%,Y向6.49%,能够满足3%附加阻尼比的要求,粘滞流体阻尼器效果明显。

结构-NFVD-TTMDI的控制性能

为了更好地发挥串并联调谐质量阻尼器惯容器(Tuned Tandem Mass Dampers-Inerters,TTMDI)的优势,进一步提高其有效性和鲁棒性,使其能够广泛地应用于实际工程中,提出了连接阻尼器为非线性液体黏滞阻尼器的串并联调谐质量阻尼器惯容器(Nonlinear Fluid Viscous Damper-Tuned Tandem Mass Dampers Inerters,NFVD-TTMDI)。在频域内推导出结构-NFVD-TTMDI系统的动力放大系数半解析解,进而定义了NFVD-TTMDI系统的最优化准则。采用迭代法进行等效线性化并使用FMINCON算法进行寻优,研究了不同阻尼指数υ对NFVD-TTMDI系统最优参数、减振有效性以及鲁棒性和质量块冲程的影响,并在时域内进行了验证。数值结果表明,相较于线性TTMDI,NFVD-TTMDI不仅具有相似的较高控制性能,而且当υ<1.0时其鲁棒性显著提高,同时对阻尼系数的需求显著降低,这些优势使得其在实际工程中更加经济有效。

Loss of energy dissipation capacity from the deadzone in linear and nonlinear viscous damping devices

In a viscous damping device under cyclic loading, after the piston reaches a peak stroke, the reserve movement that follows may sometimes experience a short period of delayed or significantly reduced device force output. A similar delay or reduced device force output may also occur at the damper＇s initial stroke as it moves away from its neutral position. This phenomenon is referred to as the effect of ＂deadzone＂. The deadzone can cause a loss of energy dissipation capacity and less efficient vibration control. It is prominent in small amplitude vibrations. Although there are many potential causes of deadzone such as environmental factors, construction, material aging, and manufacture quality, in this paper, its general effect in linear and nonlinear viscous damping devices is analyzed. Based on classical dynamics and damping theory, a simple model is developed to capture the effect ofdeadzone in terms of the loss of energy dissipation capacity. The model provides several methods to estimate the loss of energy dissipation within the deadzone in linear and sublinear viscous fluid dampers. An empirical equation of loss of energy dissipation capacity versus deadzone size is formulated, and the equivalent reduction of effective damping in SDOF systems has been obtained. A laboratory experimental evaluation is carried out to verify the effect of deadzone and its numerical approximation. Based on the analysis, a modification is suggested to the corresponding formulas in FEMA 3 5 6 for calculation of equivalent damping if a deadzone is to be considered.

FVD阻尼系数C和阻尼指数α对桥梁减震效果影响研究

论文以湖南省通平高速公路张家坡5×30 m等截面多跨连续梁桥为工程背景,建立了其右幅桥液体粘滞阻尼器(FVD)减震与左幅桥未减震模型,其中减震桥梁模型中的FVD采用Maxwell模型,以MIDAS有限元软件中的速度相关型非线性单元模拟。为了使FVD充分发挥减震作用并使减震设计有据可依,系统讨论了FVD阻尼系数C和阻尼指数α对桥梁减震效果的影响。分析计算结果表明,随着阻尼系数的增大,梁体位移越来越小,限位作用越来越明显,抑制了梁体纵桥向位移响应;随着阻尼指数的增大,阻尼力越来越小,耗能能力也越来越弱。合理选择阻尼器参数可以使结构的位移和内力得到有效控制。

FVD在等截面多跨连续梁桥减震中的应用及其效果分析

论文以湖南省通平高速公路张家坡5×30 m等截面多跨连续梁桥为工程背景,建立了其右幅桥液体粘滞阻尼器(FVD)减震与左幅桥未减震模型,利用非线性动力时程分析方法来研究FVD对该桥减震性能的影响。其中减震桥梁模型中的FVD采用Maxwell模型,以MIDAS有限元软件中的速度相关型非线性单元模拟。通过对左右两幅桥在地震作用下时程响应结果的对比,对等截面多跨连续梁桥FVD减震效果进行了分析,并探讨了液体阻尼器的合理安装位置。分析计算结果表明,合理设置液体阻尼器可以增大结构阻尼,提高减震能力,在保证桥梁其他部位弹性工作的前提下,使梁体顺桥向位移减少70%以上,桥墩底部顺桥向弯矩减少70%以上。为预防地震时梁端与桥台背墙碰撞、落梁、桥墩弯剪破坏等地震灾害提供了有效思路和办法,对高速公路多跨连续梁桥的减震设计和工程实践具有一定的参考作用。