Liquid Damper Research Articles

Optimum Parameters of a Tuned Liquid Column Damper in a Wind Turbine Subject to Stochastic Load

Parameter optimization for tuned liquid column dampers (TLCD), a class of passive structural control, have been previously proposed in the literature for reducing vibration in wind turbines, and several other applications. However, most of the available work consider the wind excitation as either a deterministic harmonic load or random load with white noise spectra. In this paper, a global direct search optimization algorithm to reduce vibration of a tuned liquid column damper (TLCD), a class of passive structural control device, is presented. The objective is to find optimized parameters for the TLCD under stochastic load from different wind power spectral density. A verification is made considering the analytical solution of undamped primary system under white noise excitation by comparing with result from the literature. Finally, it is shown that different wind profiles can significantly affect the optimum TLCD parameters.

A combined system of tuned immersion mass and sloshing liquid for vibration suppression: Optimization and characterization

Tuned liquid dampers (TLDs) and tuned mass dampers (TMDs) have been widely used in suppression of structural vibrations. However, the combination of TLDs and TMDs has been rarely investigated. This paper proposes a new vibration suppression system that combines sloshing liquid with tuned mass immerged in it. The vibration attenuation process of the combined system without structure damping is numerically simulated and characterized by using an implicit coupling approach of segregated solvers. The simulation results indicate that the proposed system, tuned immersion mass with liquid damper (TIMLD), can dissipate energy with liquid sloshing while maintaining the energy absorbing capacity of the mass by resonance. Thus, it exhibits a better vibration suppressing performance than conventional vibration suppression systems such as TLD and TMD. The energy absorbing capacity of the combined system with sloshing liquid is much better than that with liquid filled fully. Distinguishing liquid free sloshing frequency significantly from vibration frequency helps the mass to maintain its energy absorbing capacity by resonance. Affected by the resonant structure and excited by the mass, liquid sloshing can dissipate energy significantly, which constitutes the mechanism of vibration suppression of this proposed system. In light of this mechanism and in an attempt to guarantee the mass resonance and to increase the energy dissipation of the liquid, the combined system has been optimized and characterized.

Optimal design of tuned liquid column dampers for seismic response control of base-isolated structures

In this paper, the use of a tuned liquid column damper (TLCD) as a cost-effective means to control the seismic response of a base-isolated structure is studied. A straightforward direct approach for the optimal design of such a device is proposed, considering a white noise model of the base excitation. On this base, a direct optimization procedure of the TLCD design parameters is performed and optimal design charts are presented as a ready-to-use practical design tool. Comparison with the optimal parameters obtained considering a classical iterative statistical linearization technique proves the reliability of the proposed approach. The performance of the base-isolated TLCD-controlled structure is examined and compared with that of the simple base-isolated one (without TLCD), using a set of 44 recorded ground motions as base excitation. Theoretical and numerical results show that the TLCD is rather effective in reducing the response of base-isolated structures under strong earthquakes. Therefore, considering its advantageous characteristics and its overall beneficial effects, TLCDs can be considered as practical and appealing means to control the seismic response of base-isolated structures.

Investigation on damping performance of new type oscillator-liquid combined damper

An oscillator-liquid combined damper (OLCD) is a union of tuned mass damper (TMD) and sloshing liquid damper (SLD), on the aspects of the structure and the function. The combined damper absorbs energy with its tuned oscillator and dissipates energy using the interactions between the sloshing liquid and the oscillator. The processes of vibration suppressing with oscillator-liquid combined dampers were numerically simulated, and some key parameters that obviously affect the damper performance were studied in this paper. The results show that the mass ratio of the oscillator, the density and viscosity of the liquid and the shape of the oscillator all affects the suppressing ability of the combined damper through its variable energy absorbing ability and energy dissipating ability. Proper parameters that strengthen the energy dissipating were suggested. Then, a flexible plate type oscillator was presented for further improvement of combined damper performance, because elastic bending of the plate type oscillator can enhance energy dissipation via more intense waves and turbulent shear flows.

Experimental study on control performance of tuned liquid column dampers considering different excitation directions

Abstract This paper gives experimental tests’ results for the control performance of Tuned Liquid Column Dampers (TLCDs) installed on a prototype structure exposed to ground motions with different directions. The prototype structure designed in the laboratory consists of top and bottom plates with four columns. Finite element analyses and ambient vibration tests are first performed to extract the natural frequencies and mode shapes of the structure. Then, the damping ratio of the structure as well as the resonant frequency, head-loss coefficient, damping ratio, and water height-frequency diagram of the designed TLCD are obtained experimentally by the shaking table tests. To investigate the effect of TLCDs on the structural response, the prototype structure-TLCD coupled system is considered later, and its natural frequencies and related mode shapes are obtained numerically. The acceleration and displacement time-histories are obtained by the shaking table tests to evaluate its damping ratio. To consider different excitation directions, the measurements are repeated for the directions between 0° and 90° with 15° increment. It can be concluded from the study that TLCD causes to decrease the resonant frequency of the structure with increasing of the total mass. Damping ratio considerably increases with installing TLCD on the structure. This is more pronounced for the angles of 0°, 15°, 30° and 45°.

Optimal design of semiactive MR-TLCD for along-wind vibration control of horizontal axis wind turbine tower

Present study aims to address the design of smart vibration control scheme for horizontal axis wind turbine tower using magneto-rheological tuned liquid column damper. With this in view, a reduced order model of the blade-tower system is used, considering centrifugal stiffening and gravitational effects that lead to time-dependent dynamic stiffness matrix. Aerodynamic load on the blades is modeled using blade element momentum theory. Semiactive control law in linear quadratic regulator framework is developed to mitigate the along-wind vibration of the tower. To implement the control law, multiblade coordinate transformation is adopted that converts the system matrices in the nonrotating framework to tackle its time dependency. The performance of the proposed control algorithm is demonstrated using numerical simulations with and without controller. Clipped optimality of the control force is imposed to keep the parameters of magneto-rheological tuned liquid column damper in the feasible range. Finally, sensitivity analysis is carried out to demonstrate the performance envelope of the proposed control algorithm for different operational scenario. Results presented in this paper clearly demonstrate that the proposed algorithm can be employed for effective along-wind vibration control of large HWAT tower.

Nonlinear modeling and validation of air spring effects in a sealed tuned liquid column damper for structural control

The present study focuses on an experimental investigation of nonlinear air spring effects in a passive sealed Tuned Liquid Column Damper (TLCD). The aim is to quantify the polytropic process representing the pressure-volume variation in a sealed air column and examine the extent of stiffness nonlinearity present in the system. This is accomplished by measuring pressure data using pressure transducers and liquid elevations using wave gauges. The mathematical model of the sealed TLCD considering the pressure-volume relation in the sealed air column as an isentropic process is presented and validated with the experimental results. The expressions for nonlinear and linearized air spring stiffness and linearized natural frequency of the damper are presented. The effect of linearization of the air spring stiffness on damper performance is examined and found to be acceptable under certain conditions. It is seen that though the passive sealed TLCD is intrinsically nonlinear, both in damping and in stiffness, the effect of the stiffness nonlinearity is small and the system possesses a natural frequency which may be effectively used for the purpose of tuning. Finally, the variation of the damper frequency due to change in different design parameters is presented to demonstrate the options to utilize this damper in the high frequency range where the conventional open TLCD is not applicable.

Invited Review: Recent developments in vibration control of building and bridge structures

This paper presents a state-of-the-art review of recent articles published on active, passive, semi-active and hybrid vibration control systems for structures under dynamic loadings primarily since 2013. Active control systems include active mass dampers, active tuned mass dampers, distributed mass dampers, and active tendon control. Passive systems include tuned mass dampers (TMD), particle TMD, tuned liquid particle damper, tuned liquid column damper (TLCD), eddy-current TMD, tuned mass generator, tuned-inerter dampers, magnetic negative stiffness device, resetting passive stiffness damper, re-entering shape memory alloy damper, viscous wall dampers, viscoelastic dampers, and friction dampers. Semi-active systems include tuned liquid damper with floating roof, resettable variable stiffness TMD, variable friction dampers, semi-active TMD, magnetorheological dampers, leverage-type stiffness controllable mass damper, semi-active friction tendon. Hybrid systems include shape memory alloys-liquid column damper, shape memory alloy-based damper, and TMD-high damping rubber.

Hybrid passive control system of TLD and TMD for seismic response mitigation of Tall Buildings

Using Tuned liquid damper is one of the passive control methods in structures. The system consists of some water tanks that are installed at the highest level of structure. The water turbulence created inside them is used to reduce the seismic oscillation of structure. Therefore, the damper characteristics (tank size and depth of water in it) should be selected in such a way that the frequency of water in the reservoir is tuned with the frequency of structural vibrations. The controlling force to reduce the structural vibrations is created by the pressure difference caused by the difference in surface levels of the liquid in the end chambers which acts as a shear force at the bottom of tanks. It is required to obtain the water surface level at different times to calculate the controlling force caused by tuned liquid dampers. In the present study, the parameters of damper have been simultaneously minimized by Genetic Algorithm (GA) method and based on single-purpose function (displacement of the top story) and multi-purpose functions (displacement and acceleration of the top story). Optimal Pareto Front objective functions are utilized to achieve optimal responses. A 20-story building has been investigated as a numerical example to carry out this study. In this study the comparisons between TLD system and TMD system, i.e. integrated TLD-TMD system is made with the application of Genetic Algorithms. The author codes all the numerical solutions and Genetic Algorithm program.

Investigating the Effect of Viscous Damper on Seismic Behavior of Steel Dual Frames with Divergent Bracing Affected by Near and Far Fields Earthquake to Fault

Current study is sought to study the effect of linear and nonlinear liquid viscous dampers on steel frames having dual systems of bending frame and divergent bracing. These frames were first designed according to regulations of Iran’s 2800 standard and tenth chapter of national regulations of construction (planning and performing steel construction) through equivalent static method then frames were modelled again in non-linear analysis software and time history non-linear analyses were done on them with installing viscous dampers on these frames using recorded near and far faults. In this study the effect of viscous dampers will be investigated on seismic behaviour of mentioned frames and results will be proposed in form of maximum graphs of relative displacements, stories lateral displacements, base shear maximum, waste energy graphs and dampers’ force-displacements. All non-linear analyses have been done in PERFORM-3D software.

Evaluate pressure drop of slat screen in an oscillating fluid in a tuned liquid damper

Tuned liquid dampers (TLDs) are considered economical and effective dynamic vibration absorbers. Using of slat screens in TLDs can increase the inherent damping factor of TLDs. In many former numerical efforts, screens were modeled as a hydraulic resistance point as a function of the screen solidity ratio without the ability to consider the effect of the screen pattern. Clear understanding of the pressure drop across the slat screens, as the major factor for controlling the inherent damping of TLDs, enrolls a great effect on improving the performance of TLDs. Two slat screens with the same solidity ratio and different patterns could cause the different levels of the pressure drop and so inherent damping in TLDs. In the developed algorithm, the fluid flow through the screen is fully resolved and the effect of the screen pattern on the TLD's performance is taken into account. The numerical results of the developed algorithm have been validated against experimental work. Using this algorithm, a new pressure drop model for the slat screens has been developed considering the effects of the screen pattern through introducing two new concepts called the effective solidity ratio (Seff) and the slat ratio (SR) which they can imply the physical significance of screen pattern.

Study of Responses of 64-Story Rincon Building to Napa, Fremont, Piedmont, San Ramon Earthquakes and Ambient Motions

We analyze the recorded responses of a 64-story, instrumented, concrete core shear wall building in San Francisco, California, equipped with tuned sloshing liquid dampers (TSDs) and buckling restraining braces (BRBs). Previously, only ambient data from the 72-channel array in the building were studied ( Çelebi et al. 2013 ). Recently, the 24 August 2014 Mw 6.0 Napa and three other earthquakes were recorded. The peak accelerations of ambient and the larger Napa earthquake responses at the basement are 0.12 cm/s/s and 5.2 cm/s/s respectively—a factor of ∼42. At the 61st level, they are 0.30 cm/s/s (ambient) and 16.8 cm/s/s (Napa), respectively—a factor of ∼56. Fundamental frequencies (NS ∼ 0.3, EW ∼ 0.27 Hz) from earthquake responses vary within an insignificant frequency band of ∼0.02–0.03 Hz when compared to those from ambient data. In the absence of soil-structure interaction (SSI), these small and insignificant differences may be attributed to (1) identification errors, (2) any nonlinear behavior, and (3) shaking levels that are not large enough to activate the BRBs and TSDs to make significant shifts in frequencies and increase damping.

Characterisation of instantaneous dynamic parameters in vibration analysis of tuned liquid column dampers

Liquid dampers are attractive for engineering applications to suppress undesired vibration resulting from wind, wave and earthquake excitation. This is particularly relevant to tuned liquid column dampers due to their high volumetric efficiency, consistent behaviour and nonlinear but quantifiable damping mechanism. The paper investigates instantaneous dynamic parameters of such dampers. A simplified analytical model, numerical simulations and experimental work are undertaken to reveal time-variant behaviour of natural frequency and damping. The major focus is on experimental analysis and wavelet identification. The latter is based on the concept of wavelet ridges and the Crazy Climbers optimisation algorithm.

Overhead water tank shapes with depth-independent sloshing frequencies for use as TLDs in buildings

Sloshing water in the overhead water tank of a multi-storeyed building may be utilized to act as a tuned liquid damper for vibration control under wind and earthquake excitation. In conventional rectangular or circular water tanks, tuning presents difficulties as the sloshing frequency varies significantly with change in the depth of water in the tank. To address this issue, in this paper, we find shapes of tanks wherein the sloshing frequency is essentially independent of water depth over a large and useful range of water levels. Both two-dimensional as well as axisymmetric (three-dimensional) tank shapes are found. We use a direct boundary element method to find the sloshing frequencies in each case. In each case, a tentative simple analytical form for the tank shape is chosen with three free parameters, and these parameters are adjusted to obtain shapes where the first lateral sloshing frequency has negligible variation with water depth. For axisymmetric tanks, the circumferential (azimuthal) variation in field variables is restricted to the first harmonic, in the interest of lower computational effort. For both planar and axisymmetric cases, the working range of water depths is taken to be from 0.2 to 2 times the tank width. In both cases, the variation in first lateral sloshing mode frequency is found to be under 0.2% over the working range. In comparison, for constant width tanks such as the rectangular or circular ones, over the same range of water depths, the corresponding variation is more than 60 times greater.

Vibration Control of Horizontally Excited Structures Utilizing Internal Resonance of Liquid Sloshing in Nearly Square Tanks

Passive control of vibrations in an elastic structure subjected to horizontal, harmonic excitation by utilizing a nearly square liquid tank is investigated. When the natural frequency ratio 1:1:1 is satisfied among the natural frequencies of the structure and the two predominant sloshing modes (1,0) and (0,1), the performance of a nearly square tank as a tuned liquid damper (TLD) is expected to be superior to rectangular TLDs due to internal resonance. In the theoretical analysis, Galerkin's method is used to determine the modal equations of motion for liquid sloshing considering the nonlinearity of sloshing. Then, van der Pol's method is used to obtain the expressions for the frequency response curves for the structure and sloshing modes. Frequency response curves and bifurcation set diagrams are shown to investigate the influences of the aspect ratio of the tank cross section and the tank installation angle on the system response. From the theoretical results, the optimal values of the system parameters can be determined in order to achieve maximum efficiency of vibration suppression for the structure. Hopf bifurcations occur and amplitude modulated motions (AMMs) may appear depending on the values of the system parameters. Experiments were also conducted, and the theoretical results agreed well with the experimental data.

Vibration Control of Two-Degree-of-Freedom Structures Utilizing Sloshing in Nearly Square Tanks

This paper investigates the vibration control of a towerlike structure with degrees of freedom utilizing a square or nearly square tuned liquid damper (TLD) when the structure is subjected to horizontal, harmonic excitation. In the theoretical analysis, when the two natural frequencies of the two-degree-of-freedom (2DOF) structure nearly equal those of the two predominant sloshing modes, the tuning condition, 1:1:1:1, is nearly satisfied. Galerkin's method is used to derive the modal equations of motion for sloshing. The nonlinearity of the hydrodynamic force due to sloshing is considered in the equations of motion for the 2DOF structure. Linear viscous damping terms are incorporated into the modal equations to consider the damping effect of sloshing. Van der Pol's method is employed to determine the expressions for the frequency response curves. The influences of the excitation frequency, the tank installation angle, and the aspect ratio of the tank cross section on the response curves are examined. The theoretical results show that whirling motions and amplitude-modulated motions (AMMs), including chaotic motions, may occur in the structure because swirl motions and Hopf bifurcations, followed by AMMs, appear in the tank. It is also found that a square TLD works more effectively than a conventional rectangular TLD, and its performance is further improved when the tank width is slightly increased and the installation angle is equal to zero. Experiments were conducted in order to confirm the validity of the theoretical results.

Experimental Investigations into CLCD with Identification of Tuning and Damping Effects

AbstractIn this paper, the results of an experimental investigation on the characterization of a compliant liquid column damper (CLCD) are presented to validate its tuning criterion and to establis...

Dynamic simulation of unrestrained interlocking Tuned Liquid Damper blocks

The objective of the study is to develop a new construction material as an alternative for expensive dampers. A Tuned Liquid Damper (TLD) system that is cast in a concrete masonry unit has been proposed. The block has been examined in its individual characteristics to consider the resonant effect of the building subjected to a wide range of water depth, dw, from 5mm to 80mm. The TLD block was designed to internal dimensions of 190mm (length)×60mm (width)×90mm (height) in accordance to the Uniform Building Code (UBC) and Eurocode 8. Sine-sweep responses results were plotted in transmissibility ratio, ut/ug to frequency ratio, ω/ωn. The block at a depth of dw was simulated and empirically calculated. Tests for dw of 50mm, 60mm, and 70mm have verified the fundamental frequency, fn, to be similar with the simulated and calculated eigenvalues. Further study of the combined structural model and TLD blocks test as a system has been compared with the numerical simulations. The results varied by approximately 2%. The system has recorded reduction of responses immediately at the test of dw, 5–80mm. Optimum performance has been recorded at 60mm. The test results employed half-power bandwidth to obtain the damping ratio. The damping has been contributed by both viscous damping component and inertia of the moving water body. The Rayleigh stiffness damping component has not been identified to participate in the forced excitation performance reduction. It was found that the new innovative block with tuned liquid can significantly increase the damping characteristics. Hence, the research is necessary to propose an alternative new construction material to withstand earthquake and wind disasters on buildings.

Seismic response control by tuned liquid dampers for low-rise RC frame buildings

The Tuned Liquid Damper (TLD) is a passive supplemental damping device which can be used for effective mitigation of wind and earthquake induced responses. The use of TLDs in low to medium rise reinforced concrete (RC) buildings is a less explored area and needs to be investigated. The objective of the present study is to evaluate the applicability of flat bottom rectangular TLD to low-rise buildings using normal water and a sugar–water solution (higher density then normal water). Also, in flat bottom rectangular TLD the circulation of the liquid continues even after the excitation stops, which is detrimental to the structure and this issue has been addressed here. For this purpose a series of tests has been carried out for parametric study on such TLDs, varying the ratio of water depth to length of tank, excitation frequencies and amplitudes. The applicability of TLD in RC building has been investigated using a three-storey 1/4 scale RC building model. The model has been tested in a shake table. TLDs have been mounted on the roof of the building model and the dynamical response of the model without TLD and with TLD using normal water and water-sugar solution have been carried out. It has been found that flat bottom rectangular TLD can control the vibration response of low rise building model satisfactorily. Also, the sugar–water solution gives better performance in reducing the structural response.

Tuned liquid column damper for suppressing pitching motion of a floating rectangular box structure

This paper aims to investigate the possibility and effectiveness of applying a tuned liquid column damper (TLCD) to suppress pitching motion of a floating box structure. A mathematical model of the TLCD-floating structure interaction system is developed, and the associated equations of motion are derived using a Lagrangian approach. Then, the procedures for numerically obtaining the optimum parameters of the TLCD for the undamped system under harmonic excitation are proposed using Den Hartog's method. The presented examples demonstrate that the TLCD can efficiently suppress the pitching motion of the floating box structure and has potential for applying to the development of floating housing.