Nonlinear phenomena in vibrations of embedded carbon nanotubes conveying viscous fluid

Various nonlinear phenomena such as bifurcations and chaos in the responses of carbon nanotubes(CNTs)are recognized as being major contributors to the inaccuracy and instability of nanoscale mechanical systems.Therefore,the main purpose of this paper is to predict the nonlinear dynamic behavior of a CNT conveying viscousfluid and supported on a nonlinear elastic foundation.The proposed model is based on nonlocal Euler–Bernoulli beam theory.The Galerkin method and perturbation analysis are used to discretize the partial differential equation of motion and obtain the frequency-response equation,respectively.A detailed parametric study is reported into how the nonlocal parameter,foundation coefficients,fluid viscosity,and amplitude and frequency of the external force influence the nonlinear dynamics of the system.Subharmonic,quasi-periodic,and chaotic behaviors and hardening nonlinearity are revealed by means of the vibration time histories,frequency-response curves,bifurcation diagrams,phase portraits,power spectra,and Poincarémaps.Also,the results show that it is possible to eliminate irregular motion in the whole range of external force amplitude by selecting appropriate parameters.

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.

Improving the seismic performance of base-isolated liquid storage tanks with supplemental linear viscous dampers

Large tanks are extensively used for storing water,petrochemicals and fuels.Since they are often cited in earthquake-prone areas,the safe and continuous operation of these important structures must be ensured even when severe earthquakes occur,since their failure could have devastating financial and socio-environmental consequences.Base-isolation has been widely adopted for the efficient seismic protection of such critical facilities.However,base-isolated tanks can be located relatively close to active faults that generate strong excitations with special characteristics.Consequently,viscous dampers can be incorporated into the isolation system to reduce excessive displacement demands and to avoid overconservative isolator design.Nonetheless,only a few studies have focused on the investigation of seismic response of base-isolated liquid storage tanks in conjunction with supplemental viscous dampers.Therefore,the impact of the addition of supplemental linear viscous dampers on the seismic performance of tanks isolated by single friction pendulum devices is investigated herein.Four levels of supplemental damping are assessed and compared with respect to isolators′displacement capacity and accelerations that are transferred to the tanks.

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.

Efficiency of the motion amplification device with viscous dampers and its application in high-rise buildings

After nearly a decade of application and investigation, a motion amplification device with viscous dampers for energy dissipation has been recognized as an effective solution to mitigate wind or seismic excitation, especially for stiff structural systems. As a result of compensation of amplified motion, it has been proved that the efficiency of viscous damper largely depends on the motion amplification device configuration, particularly for device stiflhess. In this paper, a ＂scissor-jack＂ type of motion amplification device, called a ＂toggle brace damper＂ system, is studied. It is demonstrated that the efficiency of such a device reflected by its amplification factor is not merely a function of its geometric configuration, but is highly dependent on the support elements＇ stiffness as well, similar to the mechanism of a leverage arm. Accordingly, a mathematical model in terms of complex modulus of the viscous damper with consideration of the support brace＇s stiffness is established. The results indicate that the efficiency of the motion amplification device with viscous dampers significantly depends on the stiffness of the support elements. Other parameters, such as toggle brace configuration and damping values of the viscous damper, are studied and compared. As an application example, numerical analyses are conducted to study the dynamic performance of a 39-story office tower installed with toggle brace dampers constructed on soft soil in a reclaimed area, under a combined effect of the vortex shedding of an adjacent existing 52-story building and earthquakes. The results show that viscous dampers with a motion amplification system using a properly designed toggle brace device proved to be an effective solution to alleviate the external excitations.

Research on suppress vibration of rotor misalignment with shear viscous damper

A new type of shear viscous damper for rotating machinery is designed. The new damper with good stability and reliability can inhibit all kinds of frequency multiplication vibration caused by misalignment in the condition of nonstop machine. It analyzes and discusses the use of the shear viscous damper for misalignment vibration response inhibition with a finite element method, and experi ments are extensively carried out with a laboratory test rig. Both the simulation and experimental re suits basically agree well in that, the damper can effectively control the misalignment vibration of the rotor system and improves the stability of the plitude of one time running speed component bration has been basically eliminated. entire rotor system. Experimental results show the am decreases by 30% , and the two time running speed vibration has been basically eliminated.

Wind-Induced Vibration Control for Substation Frame on Viscous Damper

In order to study the wind-induced vibration control effect of the viscous damper on the large-scale substation frame,this paper takes the large-scale 1000 kV substation frame of western Inner Mongolia as an example.The time-history sample of pulsating wind load is simulated by harmonic superposition method based on Matlab software.6 kinds of viscous damper arrangement schemes have been designed,and SAP2000 finite element software is used for fine modeling and input wind speed time history load for nonlinear time history analysis.The displacement and acceleration of a typical node are the indicators of wind vibration control.The wind-induced vibration control effects of different schemes under different damping parameters have compared,and the damping parameters are analyzed for the optimal layout scheme.The results show that a viscous damper has installed in the lower layers of the substation;a viscous damper is placed between the ground column and the lattice beam.It is an integrated optimal solution.The wind-induced vibration control effect of the optimal scheme is sensitive to the viscous damper parameters,and the control effect does not increase linearly with the increase of the damping index and the damping coefficient.Corresponding to different damping indexes,the damping coefficient has a better range of values.

Mitigation of micro vibration by viscous dampers

This study proposes a micro vibration mitigation system using viscous dampers to solve the problem of vibration in a high-tech building. Due to the operating frequency of the air conditioners and fundamental mode of the floors, a resonant phenomenon is occasionally experienced at the upper levels of the structure. Several strategies were considered, and viscous dampers combined with a suspension system were chosen to mitigate this annoying situation. A theoretical analysis was first executed to determine the optimal design value of the damper and the suspension spring. An efficient reduction in floor velocity of approximately 50 % was achieved by the proposed system. Practical verifications including a performance test of the micro-vibration-oriented dampers, the pragmatic application result, and a comparison in one-third octave spectrum was then carried out. The performance of the system was demonstrated by the data measured. It alleviated more trembling than was numerically expected. The energy absorbed by the viscous dampers is illustrated by the hysteresis loops and the one-third octave spectrum. It is found that with the proposed system, the vibration can be effectively captured by the viscous damper and converted to lower frequency-content tremors. The success of this project greatly supports the proposed standard two-stage analysis procedure for mitigating micro-vibration problems in practice. This research extends the use of viscous dampers to a new field.

Vibration control in reticulated shells using viscous dampers system

A finite-element analysis program was developed for the reducing vibration system of viscous damper incorporated into reticulated shells, and a lot of numerical calculations were done on vibration control in reticulated shells. With viscous dampers suitable for reticulated shells designed are developed, and performance tests run for them one K6 reticulated shell model is designed and developed, and a reducing vibration shaking table experiment was conducted with a viscous damper on this shell model. All these come to a conclusion that the reducing vibration system of viscous damper can be applied to reticulated shells.

A quasi-zero-stiffness isolator with a shear-thinning viscous damper

Quasi-zero-stiffness(QZS)vibration isolators have been widely studied,because they show excellent high static and low dynamic stiffnesses and can effectively solve low-frequency and ultralow-frequency vibration.However,traditional QZS(T-QZS)vibration isolators usually adopt linear damping,owing to which achieving good isolation performance at both low and high frequencies is difficult.T-QZS isolators exhibit hardening stiffness characteristics,and their vibration isolation performance is even worse than that of linear vibration isolators under a large excitation amplitude.Therefore,this study proposes a QZS isolator with a shear-thinning viscous damper(SVD)to improve the vibration isolation performance of the T-QZS isolators.The force-velocity relation of the SVD is obtained,and a dynamic model is established for the isolator.The dynamic responses of the system are solved using the harmonic balance method(HBM)and the Runge-Kutta method.The vibration isolation performance of the system is evaluated using force transmissibility,and the isolator parameters are analyzed.The results show that compared with the T-QZS isolators,the proposed QZS-SVD isolator achieves the lower initial vibration isolation frequency and peak value,and exhibits better vibration isolation performance at medium and high frequencies.Moreover,the proposed isolator can withstand a large excitation amplitude in the effective vibration isolation range.

Experimental study on barrel viscous dampers and pipe hoops in pipeline vibration reduction

The centrifugal air compressor outlet pipeline vibration was not decreased after barrel viscous dampers were installed in a petrochemical plant in Tianjin.A pipeline-damper experiment apparatus was built for studying the influence factors of the barrel viscous damper and pipe hoop in pipeline vibration reduction.The performance of the damper under different frequency and amplitude was researched respectively,the results showed that damping effect dependsed mainly on frequency and was not related to amplitude.Damper will fail when its vibration frequency exceeds its limit working frequency which was 40 Hz in test.The mechanical properties and energy dissipation were analyzed by using the Maxwell model,which explains experimental results well.According to damping effect and calculation of stiffness with ANSYS in different hoop width,hoop stiffness should match pipe stiffness and keep uniform along transfer path.Damping effect will get worse when local stiffness is too small or too large.Finally,the outlet pipeline vibration was decreased by 70%after using appropriate pipe hoop width and replacing the original damping liquid.

Study on Vibration Characteristics of Stay Cable-Nonlinear Viscous Damper System

Tension cables are easily prone to generating varied vibrations under the action of external loads, which adversely affects the safety of bridges. Therefore, it is necessary to take effective measures to suppress the vibrations of tension cables. Cable end dampers are widely used in vibration reduction for cable-stayed bridges due to their convenient installation and low costs. However, the previous studies on the tension cable-viscous damper systems mostly adopt the linear method, and the weakening effect of the flexibility of mounting brackets on the damper vibration reduction is not sufficiently taken into account. Therefore, this paper adopts the improved Kelvin model to conduct the derivation, solution, and parametric analysis of vibration equations for the stay cable-nonlinear viscous damper systems. The results of parametric analysis show that the maximum modal damping ratio that can be obtained by cables and the corresponding optimal damping coefficient of dampers are correlated with the damping nonlinear coefficient α, stiffness nonlinear coefficient β, vibration order n, installation position a/L, and stiffness coefficient μ, etc.;among them, n damping nonlinear coefficient α and stiffness nonlinear coefficient β are the key parameters that affect the parameter design of dampers, where damping nonlinear coefficient α mainly controls the optimal damping coefficient and stiffness nonlinear coefficient β mainly controls the maximum damping ratio. Based on the parametric analysis, the design principles of dampers and value requirements of key parameters under different vibration suppression objectives are presented.

Simplified design of nonlinear damper parameters and seismic responses for long-span cable-stayed bridges with nonlinear viscous dampers

Viscous dampers are widely used as passive energy dissipation devices for long-span cable-stayed bridges for mitigation of seismic load-induced vibrations.However,complicated finite element(FE)modeling,together with repetitive and computationally intensive nonlinear time-history analyses(NTHAs)are generally required in conventional design methods.To streamline the preliminary design process,this paper developed a simplified longitudinal double degree of freedom model(DDFM)for single and symmetric twin-tower cable-stayed bridges.Based on the proposed simplified longitudinal DDFM,the analytical equations for the relevant mass-and stiffness-related parameters and longitudinal natural frequencies of the structure were derived by using analytical and energy methods.Modeling of the relationship between the nonlinear viscous damper parameters and the equivalent damping ratio was achieved through the equivalent linearization method.Additionally,the analytical equations of longitudinal seismic responses for long-span cable-stayed bridges with nonlinear viscous dampers were derived.Based on the developed simplified DDFM and suggested analytical equations,this paper proposed a simplified calculation framework to achieve a simplified design method of nonlinear viscous damper parameters.Moreover,the effectiveness and applicability of the developed simplified longitudinal DDFM and the proposed calculation framework were further validated through numerical analysis of a practical cable-stayed bridge.Finally,the results indicated the following.1)For the obtained fundamental period and longitudinal stiffness,the differences between results of the simplified longitudinal DDFM and numerical analysis were only 2.05%and 1.5%,respectively.2)Relative calculation errors of the longitudinal girder-end displacement and bending moment of the bottom tower section of the bridge obtained from the simplified longitudinal DDFM were limited to less than 25%.3)The equivalent damping ratio of nonlinear viscous dampers and the applied loading frequency had significant effects on the longitudinal seismic responses of the bridge.Findings of this study may provide beneficial information for a design office to make a simplified preliminary design scheme to determine the appropriate nonlinear damper parameters and longitudinal seismic responses for long-span cable-stayed bridges.

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.

基于特斯拉阀的黏滞阻尼器减震性能研究

针对一种基于特斯拉阀单向流通性的新型黏滞阻尼器,利用MTS landmark电液伺服试验系统对单双阀两种工况的阻尼器进行多振幅多频率循环加载;基于流体在特斯拉阀内的沿程损失建立理论模型,用MATLAB软件对新型阻尼器及传统孔隙式黏滞阻尼器进行仿真分析,分组讨论新型阻尼器的耗能减震性能。试验及仿真结果表明:新型阻尼器是一种无刚度的速度相关型阻尼器,试验值与仿真值基本吻合,较传统阻尼器减震性能突出;单阀阻尼器其性能受流体速度影响存在适用局限性,可通过调整阀门组数以调节阻尼器耗能性能。

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.

泸定地震中典型隔震建筑震害分析

为落实国务院744号令关于在“两区八类建筑”中推广使用隔震技术的要求,推动隔震技术的健康发展,对位于泸定地震震中的两栋隔震建筑的震害情况进行了调查。分析了某教学行政楼中隔震层的阻尼器及连接件、支墩震害原因,介绍了某宿舍楼的隔震支座震损情况,对两栋建筑隔离缝等构造处理的不合理导致震损的不足之处进行了全面、系统总结。提出了隔震建筑设计应全专业协调,避免过多设置隔离缝将建筑分割过于零碎;与阻尼器连接支墩需进行剪扭验算;穿越隔震层的设备管道的柔性连接应设置U形段预留变形长度,宽度较大的隔离缝应注意防掉落及通行需求的设计及构造等改进意见。并对隔震结构的施工,产品的检验、验收及建设单位责任提出了相关要求。