Liquid Column Vibration Absorber Research Articles

Omnidirectional liquid column vibration absorbers for multi-story buildings

With non-identical cross sections, liquid column vibration absorbers (LCVAs) have expanded the versatility of tuned liquid column dampers (TLCDs) that are well-known vibration control devices in alleviation of resonant vibrations. In comparison, LCVAs present natural frequencies and control forces in wider ranges. However, LCVAs still suffer from unidirectionality so that their performance deteriorates when the resultant excitation deviates from their axis. This paper introduces an omnidirectional class of LCVAs, so called O-LCVAs, that have n (integer n ≥ 3 ) number of liquid columns with non-identical cross sections. Based on the Euler–Lagrange equation, the theory for application of multiple O-LCVAs in control of multi-story building structures with translational degree of freedoms (DoFs) in plane are developed. O-LCVAs can be set in any arbitrary orientations and attached to the same or different DoFs on the floors. A formal solution to involve excitations in disparate directions in the equation of motion is introduced. A designing process is proposed for multiple O-LCVAs tuned to multiple structural modes. The coupled control system is represented in state-space, employed in the simulation of a multi-story building exposed to a set of load cases including harmonic and seismic loadings. Additional study is conducted to investigate the role of distribution of multiple dampers when the liquid mass is the same. Moreover, experiments are carried out to verify the mathematical model. Investigations show the dynamic characteristics and the control performance of O-LCVAs are independent from the orientations of the dampers, which brings useful flexibility, for example, in limited architectural spaces. Consequently, O-LCVAs with random orientations can be tuned to resonant modes optimally and control them regardless of the excitation direction. Thanks to omnidirectionality, O-LCVAs can also detect the direction of resultant excitation like a physical sensor. • Omnidirectional liquid column vibration absorber (O-LCVA) is introduced. • The analytical model is derived for multi-story buildings. • The state-space formulation and a parameter optimization scheme are provided. • Experimental studies are conducted for the validation of the theory. • Control performance of multiple O-LCVAs is investigated numerically.

An experimental study on the damping characteristics and tuning of the liquid column vibration absorber

This paper deals with an experimental investigation of the damping characteristics of the liquid column dynamic vibration absorber. The laboratory test rig of a single degree of freedom system integrated with a liquid column dynamic vibration absorber was designed and manufactured to study the efficiency of this type of dynamic absorbers. The system response has been measured and recorded by using a (DXL-345) accelerometer and data acquisition system. The effects of mass ratio, length ratio, and the opening ratio of the central orifice on the vibration reduction of the main structure in free vibration mode were evaluated. The results showed that the tuned liquid column vibration absorber has a good ability to reduce or eliminate unwanted vibration by the suitable selection of the combination of its design parameters. The maximum damping of the main system was achieved at the mass, length and orifice opening ratios equal to 7.7 %, 87% and 74% respectively.

Reliability-based optimal control of semi-rigid steel frames under simulated earthquakes using liquid column vibration absorbers

Liquid column vibration absorbers (LCVAs) have been proved to be highly efficient in vibration suppression of buildings under earthquake and wind loads. This article proposes an efficient computational framework for reliability-based optimal design and placement of LCVAs in semi-rigidly connected buildings subjected to stochastic ground motions. The reduced function evaluations method is used as an efficient tool for structural reliability analysis, while a novel algorithm is proposed for efficient structural optimization. Excessive interstorey drifts of a building and absolute accelerations of its floors are considered as failure events in calculating the probability of failure of the building. The uncertainty regarding the characteristics of future earthquakes is accounted for by applying a probabilistic approach. The effects of pulse components of stochastic pulse-wise ground motions, fixity factor of semi-rigid beam-to-column connections and values of different parameters of LCVAs on the performance and safety of semi-rigidly connected steel-framed buildings are investigated.

Simulation of control characteristics of liquid column vibration absorber using a quasi-elliptic flow path estimation method

Tuned liquid column dampers (TLCDs) and liquid column vibration absorbers (LCVAs) are good substitutes for mechanical dampers to counter seismic activity exerted to tall buildings. The existing simplified effective length method could predict good results corresponding to test outcomes on TLCDs and LCVAs with small transition zones, but is found to yield larger discrepancy as larger transition zones are needed, often due to limited space constraints. The numerical panel method could be effectively employed to give more accurate results, but is not simple to formulate and needs to be re-modified for each new configuration. This paper proposes a new quasi-elliptic flow path estimation method to simulate control characteristics of TLCDs and LCVAs with relatively large transition boundary between the vertical columns and the horizontal cross-over duct, since liquid velocity’s variation inside the large transition boundary cannot be assumed to occur at a single point. The simulation results are compared with experimental investigations conducted on a shake table, yielding satisfactorily better outcomes for large transition zones, as well as for small transition zones. This new formulation has been verified with a few other studies and has been found to be an excellent viable option with a respectable better, or at least comparable, accuracy level.

INVESTIGATIONS ON DAMPING CHARACTERISTICS OF LIQUID COLUMN VIBRATION ABSORBER

ABSTRACTThis work deals with the damping characteristics and optimum performance of apassive liquid column vibration absorber (LCVA) which is effective to decrease thevibration of engineering systems. A numerical technique is applied to solve thenonlinear equations of motion to study the influence of the design parameters suchas frequency tuning ratio, length ratio, area ratio, blocking ratio and mass to mitigateexcessive vibrations. A constrained multi-objective optimization problem isconstructed and solved numerically to minimize the maximum master structuredisplacement in a broad range of excitation frequency with considering a limit of themaximum liquid displacement in the vertical tube as an extra objective. It is foundthat the best vibration attenuation can be achieved by using the LCVA with a uniformcross-section area while the non-uniform LCVA offer greater flexibility to modify thenon-appropriate total length. The TCVA mass and the structural damping have aninfluence on all optimum parameters. The optimal values of the blocking ratio areproportional and depend on the intensity of the excitation. The list of necessaryoptimal parameters and the corresponding performance indices are presented indesign tables as a guidance for industrial practices.

Dynamic response control of structures using liquid column vibration absorber: an experimental study

The performance and effectiveness of the liquid column vibration absorber (LCVA) in controlling the vibration of structures have been investigated in this paper. To evaluate the performance of LCVA system in mitigating the structural response under dynamic loading (i.e. harmonic excitation), a set of experiments are conducted on a scaled model of steel structure-LCVA system. LCVA have non-uniform cross-sectional dimensions of the horizontal and vertical columns whereas Tuned Liquid Column Damper (TLCD) carries same cross-sectional dimensions. For conducting a comparative study, same experiments were performed for TLCD also. Several excitation frequency ratios (0.5–2.0) and various mass ratios (5–7.5%) are considered in this study. The parameter, tuning ratio considered for all of the experiments is 1.0. The effectiveness of the LCVA and TLCD is measured based on the response reduction of the structure. From the experimental results, it is observed that LCVA has better performance in controlling the structural response.

Optimum LCVA for suppressing harmonic vibration of damped structures

Explicit design formulae of liquid column vibration absorber (LCVA) for suppressing harmonic vibration of structures with small inherent structural damping are developed in this study. The developed design formulae are also applicable to the design of a tuned mass damper (TMD) and a tuned liquid column damper (TLCD) for damped structures under harmonic force excitation. The optimum parameters of LCVA for suppressing harmonic vibration of undamped structures are first derived. Numerical searching of the optimum parameters of tuned vibration absorber system for suppressing harmonic vibration of damped structure is conducted. Explicit formulae for these optimum parameters are then obtained by a series of curve fitting techniques. The analytical result shows that the control performance of TLCD for reducing harmonic vibration of undamped structure is always better than that of non-uniform LCVA for same mass and length ratios. As for the effects of structural damping on the optimum parameters, it is found that the optimum tuning ratio decreases and the optimum damping ratio increases as the structural damping is increased. Furthermore, the optimum head loss coefficient is inversely proportional to the amplitude of excitation force and increases as the structural damping is increased. Numerical verification of the developed explicit design expressions is also conducted and the developed expressions are demonstrated to be reasonably accurate for design purposes.

Easy-to-tune reconfigurable liquid column vibration absorbers with multiple cells

This study proposes a retunable liquid column vibration absorber (LCVA) that can handle a wide range of natural frequencies while maintaining its original shape. The LCVA’s vertical tubes are divided into several smaller tubes (i.e., cells). Sealing a cell makes the liquid in it stand still so that only part of the liquid contained within the LCVA participates in the motion. By selecting appropriate configurations of sealed cells, the sectional area ratios of the vertical and horizontal tubes and the effective horizontal tube length are changed, which yields new natural frequencies to accommodate shifts in the natural frequency of a primary building. The proposed retunable LCVA is analytically evaluated and experimentally verified by using various patterns of sealed cells and a shake-table test to provide various natural frequencies while maintaining control performance.

Robust design of liquid column vibration absorber in seismic vibration mitigation considering random system parameter

The optimum design of liquid column dampers in seismic vibration control considering system parameter uncertainty is usually performed by minimizing the unconditional response of a structure without any consideration to the variation of damper performance due to uncertainty. However, the system so designed may be sensitive to the variations of input system parameters due to uncertainty. The present study is concerned with robust design optimization (RDO) of liquid column vibration absorber (LCVA) considering random system parameters characterizing the primary structure and ground motion model. The RDO is obtained by minimizing the weighted sum of the mean value of the root mean square displacement of the primary structure as well as its standard deviation. A numerical study elucidates the importance of the RDO procedure for design of LCVA system by comparing the RDO results with the results obtained by the conventional stochastic structural optimization procedure and the unconditional response based optimization.

Tuned vibration absorbers with nonlinear viscous damping for damped structures under random load

The classical problem for the application of a tuned vibration absorber is to minimize the response of a structural system, such as displacement, velocity, acceleration or to maximize the energy dissipated by tuned vibration absorber. The development of explicit optimal absorber parameters is challenging for a damped structural system since the fixed points no longer exist in the frequency response curve. This paper aims at deriving a set of simple design formula of tuned vibration absorber with nonlinear viscous damping based on the frequency tuning for harmonic load for a damped structural system under white noise excitation. The vibration absorbers being considered include tuned mass damper (TMD) and liquid column vibration absorber (LCVA). Simple approximate expression for the standard deviation velocity response of tuned vibration absorber for damped primary structure is also derived in this study to facilitate the estimation of the damping coefficient of TMD with nonlinear viscous damping and the head loss coefficient of LCVA. The derived results indicate that the higher the structural inherent damping the smaller the supplementary damping provided by a tuned vibration absorber. Furthermore, the optimal damping of tuned vibration absorber is shown to be independent of structural damping when it is tuned using the frequency tuning for harmonic load. Finally, the derived closed-form expressions are demonstrated to be capable of predicting the optimal parameters of tuned vibration absorbers with sufficient accuracy for preliminary design of tuned vibration absorbers with nonlinear viscous damping for a damped primary structure.

Bimodal vibration control of seismically excited structures by the liquid column vibration absorber

The possibility of controlling two modes of structural vibration due to earthquake excitation by considering the sloshing action in the vertical limbs of the liquid column vibration absorber (LCVA) has been explored in this paper. The structure has been modeled as a linear, viscously damped multi-degree-of-freedom (m.d.f.) system. The governing differential equations of motion for the damper liquid and for the coupled structure-LCVA system have been derived from dynamic equilibrium. The nonlinear orifice damping in the LCVA has been linearized by a stochastic equivalent linearization technique. A displacement transfer function formulation for the structure-LCVA system has been presented. The study has been carried out on a 2-d.f. example structure for which both the modes have significant contribution to the total response. The performance of the LCVA has been evaluated in the frequency domain with the base input characterized by a white noise power spectral density function and through a simulation study by subjecting the example structure-LCVA system to a recorded accelerogram. The results are compared with that of the liquid column damper and indicate superior performance of the LCVA. Furthermore, an LCVA has been designed for the example structure.

Closed-Form Optimum Liquid Column Vibration Absorber Parameters for Base-Excited Damped Structures

There have been significant development of techniques for determining optimum parameters of passive dampers and vibration absorbers, but most of the existing studies are limited to the case of an undamped primary structure. This paper aims to develop a first order approximation of the optimal liquid column vibration absorber (LCVA) parameters for suppressing the displacement response of a damped structure under white noise induced ground acceleration. The optimum parameters of a LCVA for the case of an undamped primary structure subjected to white noise induced ground acceleration are first derived and the results are then extended to the case where some damping exists in the primary structure by using a perturbation technique. The accuracy of the derived formulas is then verified through a comparison with the results obtained from numerical methods as well as the results of other studies found in the literature. Finally, a direct approach for determining the optimal head loss coefficient is presented in this study. It is demonstrated that the closed-form approach is capable of predicting the optimal liquid column vibration absorber parameters with reasonable accuracy for damped primary structure.

Stochastic earthquake response control of structures by liquid column vibration absorber with uncertain bounded system parameters

The present work deals with optimum design of liquid column vibration absorber (LCVA) for seismic vibration control of structures characterized by uncertain system parameters. This involves optimization of the frequency and damping properties of LCVA considering uncertain properties of the structure and ground motion parameters. The study on optimum design of tuned mass damper system considering random system parameters is noteworthy. But, the same is not the case for liquid dampers. Moreover, though the probabilistic methods are powerful, the approach cannot be applied in many real situations when the required detailed information about uncertain parameters is limited. In such cases, the interval method is a viable alternative. With the aid of matrix perturbation theory using first order Taylor series expansion of dynamic response function and its interval extension, the vibration control problem under bounded uncertainty is transformed to appropriate deterministic optimization problems. This requires optimizing two separate objective functions correspond to a lower bound and an upper bound optimum solutions. A numerical study is performed to study the effect of system parameter uncertainty on the optimization of LCVA parameters and its response reduction efficiency. Though the efficiency is not completely eliminated, the advantage of the LCVA tends to reduce as the level of uncertainty increases. It is also seen that neglecting the effect of system parameter uncertainty may overestimate the damper performance.

Passive control of seismically excited structures by the liquid column vibration absorber

The potential of the liquid column vibration absorber (LCVA) as a seismic vibration control device for structures has been explored in this paper. In this work, the structure has been modeled as a linear, viscously damped single-degree-of-freedom (SDOF) system. The governing differential equations of motion for the damper liquid and for the coupled structure-LCVA system have been derived from dynamic equilibrium. The nonlinear orifice damping in the LCVA has been linearized by a stochastic equivalent linearization technique. A transfer function formulation for the structure-LCVA system has been presented. The design parameters of the LCVA have been identified and by applying the transfer function formulation the optimum combination of these parameters has been determined to obtain the most efficient control performance of the LCVA in terms of the reduction in the root-mean-square (r.m.s.) displacement response of the structure. The study has been carried out for an example structure subjected to base input characterized by a white noise power spectral density function (PSDF). The sensitivity of the performance of the LCVA to the coefficient of head loss and to the tuning ratio have also been examined and compared with that of the liquid column damper (LCD). Finally, a simulation study has been carried out with a recorded accelerogram, to demonstrate the effectiveness of the LCVA.

전달함수를 이용한 LCVA의 설계변수 분석

본 연구의 목적은 첫째, 비선형성을 포함하는 액체기둥진동흡진기(LCVA)의 감쇠항에 대한 등가선형화된 운동방정식을 바탕으로하여 가진입력인 진동대 가속도와 출력인 제어력의 관계인 전달함수를 해석적인 식으로 규명하는 것이다. 둘째, LCVA의 주요설계변수인 수직기둥과 수평기둥의 단면적비의 변화에 따른 진동특성분석이다. 셋째, 동조의 수단으로 이용되는 수직기둥 액체의 높이를 변화시켜 진동특성을 분석하는 것이다. LCVA를 진동대 위에 설치하고 가진하여 제어력을 측정하여 실험 전달함수를 구하였다. 이것을 해석적인 전달함수와 비교 및 최적화작업을 수행하여 LCVA의 진동특성변수에 영향을 미치는 고유진동수, 감쇠비 및 질량비 등을 파악하였다. 실험결과, 액체 수위 및 단면적비의 변화에 따라 감쇠비 및 참여질량비의 특성이 변화하였다. 수직기둥과 수평기둥이 교차하는 엘보우에서 액체의 흐름 변화로 인하여, LCVA 실험체의 수직기둥 단면적이 작아질수록 감쇠비와 참여질량비가 증가하였다. The purpose of this study is to verify the transfer function of input acceleration and output control force by linearizing a velocity-dependent damping term of Liquid Column Vibration Absorber (LCVA). Analytical and experimental research is conducted to identify natural frequency, damping ratio and participated mass ratio of LCVA with various section ratios of vertical and horizontal areas. Findings obtained experimentally by the shaking table test are compared with analytical findings using optimization technique with constraints. The results indicate that the level of liquid and section ratio of LCVA affect the characteristics of damping ratio and mass ratio. Damping and mass ratio increase as the section of vertical column of LCVA decreases, due to turbulence in the elbow of LCVA.

Robust reliability-based design of liquid column mass dampers under earthquake excitation using an analytical reliability approximation

The robust reliability-based design of Tuned Liquid Column Dampers (TLCD) and Liquid Column Vibration Absorbers (LCVA) under earthquake excitation is studied. The design objective is the minimization of the probability of failure, where failure is defined as the first-passage of the dynamical system trajectory out of a hypercubic safe region in the space of the performance variables. These variables correspond to response characteristics of the system that are considered important. Versions of the approach are described for the case of a nominal model and the case considering model uncertainty. In the latter case the concept of robust probability of failure is employed which considers a set of possible models for the dynamic system. The nonlinear characteristics of the damper response are addressed by including the excitation intensity as an uncertain parameter in the system description. An analytical approximation is used for the reliability estimation that allows for computationally efficient, gradient-based design optimization. Numerical issues are discussed. The validity of the reliability approximation is checked by comparing the results to those derived through direct Monte Carlo simulation of the nonlinear model. Applications to dynamical systems with single and multiple degrees of freedom are presented. For the latter case, other standard control synthesis methods are also considered and significant differences are illustrated between them and robust reliability-based design. Although this study focuses on optimization of TLCDs and LCVAs, it shows the efficiency of the proposed methodology for other systems that also involve model uncertainty.

Simulation of characteristics of tuned liquid column damper using a potential-flow method

A tuned liquid column damper (TLCD) for the control of vibration of tall buildings comprises two vertical columns of liquid connected by a horizontal cross-over duct of the same width. A variation of this, with a cross-over duct different in width, is denoted as a liquid column vibration absorber (LCVA). Both TLCDs and LCVAs have been shown to be effective passive vibration control devices as long as their vibrational characteristics are properly designed in relation to those of the building in which they are installed. In previous research, prediction of the natural frequency of these dampers is based on the assumption that the liquid velocity within each leg of these dampers is constant and the transition between vertical and horizontal flows occurs at a single point. This assumption is valid for a TLCD and a LCVA when the widths of both the horizontal cross-over duct and the vertical columns are small compared to the overall dimensions of the damper. Different researchers have also suggested empirical modifications of this assumption for TLCDs, resulting in different estimates of the system’s natural frequencies. For buildings with limited space, it will be necessary to configure a TLCD with a width of vertical columns that is not small with respect to the overall dimensions of the damper, a configuration which has not yet been investigated in research. In this case, the variation in liquid velocity in the relatively large transition zone between the vertical columns and the cross-over duct cannot be ignored. A numerical potential-flow method, known as the numerical panel method, is utilized to simulate the velocity distribution of the fluid inside liquid dampers. The method allows an integral equation for the velocity potential to be formulated and solved numerically to determine the flow. These numerical solutions are verified with those obtained from existing experimental results. In addition, three full-scale models of LCVAs are investigated experimentally under free-vibration, spectral and prescribed base excitations. The results from the numerical panel method lead to improved prediction of the characteristics of TLCDs over a wide range of configurations, which is essential in controlling problems for the optimum performance of buildings.

Optimal design and performance of liquid column mass dampers for rotational vibration control of structures under white noise excitation

The effectiveness under optimal design of a Tuned Liquid Column Damper (TLCD) and a Liquid Column Vibration Absorber (LCVA), in suppressing structural rotational vibrations under white noise excitation are studied in this paper. The effects of deviating from the optimal design under white noise and the effect of the excitation intensity are also addressed. The analytical model is first developed for a structure with a damper. The nonlinear governing equation of the relative motion of the liquid column is linearized and the problem is analyzed in the frequency domain. A method to find optimal values for the tuning ratio, f , and the head loss coefficient, ζ , is developed and studied, considering the complications that are induced by the initial nonlinear form of the governing equations. The controlled performance of the LCVA and TLCD, with optimum values of f and ζ , are numerically investigated through an extensive parametric study. Finally the effect of f , ζ and the intensity of the excitation are addressed. The results show that the position of the damper relative to the rotational axis plays a significant role in determining the rotational vibration reduction, and that the LCVA is more adaptable with regards to its position relative to the structure, through the proper selection of the area of vertical to horizontal tube section ratio.

Vibration Control of the Wind-Excited 76-Story Benchmark Building by Liquid Column Vibration Absorbers

A study has been undertaken on the effectiveness of using liquid column vibration absorbers (LCVAs), in the suppression of wind-induced motion of the 76-story benchmark building. Much work has been undertaken on the behavior of the LCVA on an experimental level and its benefits have been demonstrated for wind-induced vibration control on a full-scale communications tower in Sydney, Australia, with a further installation being made on the “One Wall Center Building” Vancouver, Canada. The behavior of the LCVA has also been investigated numerically by use of computational fluid dynamics, and its potential has been illustrated in controlling a five-story building model. In this study, the LCVA adopted is composed of four identical columns of water. Initially, the performance of the LCVA is assessed without the inclusion of additional damping enhancing mechanisms. Subsequently, the same LCVA is considered with the inclusion of orifice plates, allowing a direct comparison of the two strategies. In order to address the issue of robustness, the sensitivity of the LCVA (with and without orifice) to mistuning is examined by perturbing the structural stiffness of the building by +15% and −15%, respectively. From this, an indication of the system performance under conditions of mistuning has been assessed. The performance of the adopted LCVA has also been compared to that of the sample tuned mass damper (TMD) control device. The overall response reductions of the LCVA are shown to be comparable to the TMD. Furthermore, it is shown that the LCVA has several inherent features that make it more attractive than the classical TMD.

Damping enhancements of a 5 storey benchmark building using liquid column vibration absorbers

This paper examines the response reduction capabilities of a passive fluid damper device known as the liquid column vibration absorber (LCVA), when installed on a 5 storey benchmark building structure requiring control. The 5 storey benchmark building, is a scaled model of 3.6 metres maximum height, that is excited at its base level on a shake table. The benchmark frame is one in a series of recognised benchmark buildings for research into control, as adopted by the hternational Association for Structural Control (IASC). The behaviour of the LCVA, unlike prior studies, has been examined utilising computational fluid dynamics (CFD) software, solving for the Navier Stokes equations. The dynamic behaviour of the structure is examined by utilisng capabilities of structural finite element software, adopting the Newmark time integration method of solution. In order to study the interaction of fluid and structure for vibration control conditions, two series of tests were conducted. The first examined the effective damping added to the structure by using the LCVA, under free vibration conditions. A comparison was made to uncontrolled free vibration of the structure, and the effective damping was evaluated based on the RMS response reduction achieved. The structure was then implemented with an appropriate single LCVA, and re-excited with a specified wind load. The wind load was simulated as an equivalent base acceleration. The resulting reduction in wind response was then examined. Using this approach, the potential of using the LCVA as a vibration control device is illustrated. Furthermore, the use of a coupled CFD structural analysis to understand the overall behaviour is demonstrated.