Rectangular Tuned Liquid Damper Research Articles

Experimental Investigation to Evaluate the Dynamic Properties of a Scaled Rectangular Tuned Liquid Damper Using High-Speed Videos

The use of tuned liquid dampers (TLDs) as an alternative to reduce the response of flexible structures with a low amount of structural damping is a viable option. The correct characterization of the dynamic properties of the TLD plays an important role in the performance of the TLD-main structure system. This work presents the results of an experimental study to evaluate the dynamic properties of a scaled rectangular TLD using high-speed videos. For the experimental investigation, a scaled rectangular TLD is subjected to lateral displacement of the sinusoidal type with amplitudes that range from 5 to 40 mm and frequency equal to 0.625 Hz. The dynamic properties of the TLD system are identified with the use of high-speed videos with a duration of 28.96 s and recorded at 500 frames per second (fps). The recorded videos are analyzed with the software Tracker to extract time histories of wave elevation at predefined locations. The frequency and damping of the TLD system are identified from the time histories of wave elevation through Fourier analysis and free-vibration decay. The findings of this study revealed that the identified dynamic properties of the TLD by using high-speed videos presented small differences with respect to the target values, with errors that range from 0.93 to 2.9% for frequency and from 1.6 to 8.8% for damping, indicating that the use of high-speed videos can be an alternative to evaluate the dynamic properties of TLD systems.

Numerical investigation of structural models equipped with tuned liquid damper

Tuned liquid dampers (TLDs) are introduced in structural systems to suppress vibration of the structure due to dynamic actions. Using a grid-based Finite Volume Method-Finite Element Method (FVM/FEM), efficiency of TLDs of cylindrical and rectangular geometries was evaluated by performing a two-way Fluid-Structure Interaction (FSI) analysis. The nonlinear sloshing response of fluid was simulated by employing a three-dimensional Navier–Stokes equation as the governing equation and occurrence of wave breaking was accounted by using Volume of Fluid (VOF) method for free surface tracking. Utilizing the developed numerical model, a series of three-dimensional transient analysis were conducted on a structure with and without TLDs aiming to investigate effect of base excitation amplitude. The result show that maximum performance of TLDs at resonance is obtained when the forcing ratio is limited to 0.1, and for this case, both cylindrical and rectangular TLDs displayed comparable efficiency. Effect of excitation frequency fe was also investigated under a wide range of the forcing ratio showing that as fe increases, the natural frequency of coupled TLD-structural system approaches the natural frequency of un-damped structural system.

Mitigating Structural Vibrations due to Earthquake with Application of Slope Bottom Tuned Liquid Dampers

Earthquakes are one of man’s most feared natural phenomena, producing almost instantaneous destruction of buildings and other constructed facilities. In order to mitigate damage of structures and save the life, various measures are adopted and use of structural control devices is one of them . Structural control devices can enhance the integrity of structures without increasing the dimensions of structural members. In this study, an attempt has been made to systematically investigate the performance of structural control device namely, tuned liquid damper (TLD) for controlling the dynamic response of reinforced concrete (RC) framed structure. Dynamic analysis of a 10 story RC framed structure with both flat and slope (W or central slope) bottom rectangular TLDs, subjected to five earthquake time histories have been performed. Key results have been presented in the form of tuning ratio, liquid mass reduction and displacement response reduction due to slope at bottom TLD. For the case of TLDs with central slope, the analyses have been performed for slope angle ranging from 5-14º. Based on the study, it has been observed that, tuning ratio of TLD decreases with increase of central slope at the bottom of TLD, the variation of liquid mass reduction with slope angle has been observed to be linear and reduction in displacement of structure increases with increase in central slope angle.

Shaking table substructure test of tuned liquid damper for controlling earthquake response of structure

For precisely disclosing the seismic performance of tuned liquid damper (TLD) vibration control structures, the shaking table substructure test (STST) method is presented and experimentally validated, and the parametric effects on the reduction efficiency of TLD are further investigated by using the STST method in this paper. Firstly, one optimal design method of TLD for high-rise structures is presented. Secondly, the STST based on three variable control method (TVCM) for the TLD vibration control structures is presented. Thirdly, the effectiveness and robustness of the STST for TLD vibration control structures are validated by a series of tests on one three-story-frame structure with a rectangular TLD. Finally, the parametric effects on the reduction efficiency of TLD, in terms of mass ratio and liquid depth, are investigated using the STST method. Experimental results show that the displacement and acceleration responses of the STST match well with that of the traditional shaking table tests under El Centro (NS, 1940) and Taft earthquake wave record excitations, which indicates the effectiveness and the robustness of the STST based on TVCM for TLD vibration control structures. It is also shown from the experimental results that the best mass ratio and liquid depth are 4% and 40 mm, respectively, which are consistent with the optimal designs of TLD. Moreover, the control performance of TLD is not only related to its parameters but also related to the spectral characteristics of ground motion excitations.

Incompressible smoothed particle hydrodynamics model of a rectangular tuned liquid damper containing screens

Damping screens are often installed within a tuned liquid damper (TLD) to increase the energy dissipation beyond what the sloshing liquid alone can provide. Many numerical models exist to study the response of a TLD; however, there are often associated limitations on fluid depth or excitation amplitude. The smoothed particle hydrodynamics (SPH) method can capture the fully nonlinear TLD response without limitation by solving the Navier–Stokes equations throughout the fluid domain. A two-dimensional explicit incompressible SPH model is presented and validated against a hydrostatic and dam break flow scenario. The damping screens are modelled in SPH on a macroscopic level using Morison’s equation for force on an object submerged in fluid flow. This implementation is computationally efficient compared to explicitly modelling the damping screens using solid particles as it allows for a much larger initial particle spacing. The SPH model results for screen forces, wave heights, and TLD sloshing water forces are validated against experimental time and frequency response data. The SPH model is found to be in excellent agreement with the experimental data for a range of TLD tank dimensions (L=0.966 and 1.524 m), fluid depths (h/L= 0.05 to 0.25), excitation amplitudes (X0/L= 0.0025 to 0.031), and excitation frequencies (β=0.7 to 1.3). The presented SPH model for a TLD with damping screens can be used to study the nonlinear response of a rectangular TLD.

Shaking table tests on a SDOF structure with cylindrical and rectangular TLDs having rotatable baffles

Control of vibrations against extraordinary excitations such as wind and earthquake is very important to the protection of life and financial concerns. One of the methods of structural control is to use Tuned Liquid Damper (TLD), however due to the nature of TLD only one sloshing frequency can be created when the water is sloshing. Among various ideas proposed to compensate this problem, by changing the angle of some rotatable baffles embedded inside a TLD, a frequency range is created such that these baffles are tuned manually at different frequencies. In this study, the effect of cross sectional shape of container with rotating baffles on seismic behavior of TLD is experimentally studied. For this purpose, rectangular and cylindrical containers are designed and used to suppress the vibrations of a Single Degree-Of-Freedom (SDOF) structure under harmonic and earthquake excitations considering three baffle angles. The results show that the rectangular-shaped damper reduces the structural response in all load cases more than the damper with a cylindrical shape, such that maximum differences of two dampers to reduce the structural displacement and structural acceleration are 5.5% and 3% respectively, when compared to the cases where no baffles are employed.

Seismic Control of Structures Using Sloped Bottom Tuned Liquid Damper

Tuned liquid damper (TLD) as an economical passive damper has gained importance because of its efficiency in suppressing the undesirable motion of a structure due to devastating earthquakes when it is rigidly attached to the structure. This phenomenon has been studied previously, but mostly limited to rectangular- or cylindrical-shaped TLD. The present study is aimed at determining the potential of the sloped bottom tuned liquid damper to suppress the unwanted vibration of the structure subjected to earthquake ground motion. Three different earthquake ground motions characterized by low-, intermediate- and high-frequency contents are selected for the dynamic analysis of the TLD–structure coupled system. A parametric study on the sloped bottom TLD and its interaction with the sustaining structural system is conducted. The structural equations, which are coupled with fluid equations, are solved by the Newmark-[Formula: see text] method with average acceleration, while the fluid equations are solved using velocity potential-based finite element method. The liquid domain in the TLD is comprised of a combination of three-node triangular and four-node quadrilateral elements. The result shows the reduction in structure response is significant with less amount of water in sloped bottom TLD rather than rectangular TLD.

Rectangular and Cylindrical TLDs with Rotatable Baffles to Improve Seismic Behavior of Structures, a Numerical Study

One of structural passive control methods is to use Tuned Liquid Damper (TLD). However, because of the nature of the TLD, only one tuning frequency can be created when the water is sloshing. To fix this problem, some installed rotatable baffles can be embedded inside TLD called Variably Baffled TLD (VBTLD) where by changing the angle of the baffles a tuning frequency range is created. This gives the passive control system the capability to be pre-tuned according to the desired frequency. In this paper, the effects of rectangular and cylindrical shapes of container on behavior of VBTLD are studied and numerically validated with experimental results. There are four baffles inside each damper tuned manually in different cases. In numerical investigation, the rectangular TLD created greater returning force than cylindrical TLD in all depth and angle selections. By increasing the baffle angle, from 0 ° to 80 ° at the water depths of 4, 5.2 and 6.4 cm, the control forces are increased 59.8%, 38.4% and 30.2% respectively for rectangular TLD and 58.4%, 50.4% and 46.1% for cylindrical TLD.

Tuned liquid dampers with porous media

A tuned liquid damper (TLD) filled with porous media is developed to promote an additional damping force for the conventional system. According to Darcy's law, the permeability of porous media and liquid viscosity form a damping force linearly proportional to fluid velocity. In this paper, an equivalent mechanical system considering the damping due to porous media in rectangular TLD is established. In contrast to the other operating TLDs with damping devices, the natural frequency and damping ratio of TLD in the present paper can be obtained without using empirical formulas. The dynamic characteristics and performances are also discussed.

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.

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.

Analysis of Performance Test Result of a Rectangular Tuned Liquid Damper by Direction of Wind

This study conducted a vibration table excitation test in order to evaluate performance of a tuned liquid damper (TLD), which was installed for vibration attenuation in a high-rise building, according to its installation direction. The TLD's base shear force and wave height characteristics changed according to excitation direction. When the excitation direction of the TLD was lower than 45 degrees, base shear force and wave height were the same as excitation direction at zero degree. However, when the excitation direction was 45 degrees or higher, base shear force and wave height were affected by excitation amplitude at 5mm or larger.

An experimental study on tuned liquid damper for mitigation of structural response

Abstract This paper investigates the performance of unidirectional tuned liquid damper (TLD) that relies upon the motion of shallow liquid in a rigid tank for changing the dynamic characteristics of a structure and dissipating its vibration energy under harmonic excitation. A series of experimental tests are conducted on a scaled model of structure-tuned liquid damper systems to evaluate their performance under harmonic excitation. One rectangular and one square TLD with various water depth ratios are examined over different frequency ratios, and time histories of accelerations are measured by precisely controlled shaking table tests. The behaviour of TLD is also studied by changing the orientation of the rectangular TLD subjected to the given range of harmonic excitation frequencies. The effectiveness of TLD is evaluated based on the response reduction of the structure. From the study, it is found that for each TLD, there exists an optimum water depth that corresponds to the minimum response amplitude, and the maximum control of vibration is obtained under resonance condition with the attachment of TLD.

The Influence of Tank Orientation Angle on a 2D Structure-Tuned Liquid Damper System

Tuned liquid dampers (TLDs) utilize sloshing fluid to absorb and dissipate structural vibrational energy, thereby reducing wind induced dynamic motion. By selecting the appropriate tank length, width, and fluid depth, a rectangular TLD can control two structural sway modes simultaneously if the TLD tank is aligned with the principal axes of the structure. This study considers the influence of the TLD tank orientation on the behavior of a 2D structure-TLD system. The sloshing fluid is represented using a linearized equivalent mechanical model. The mechanical model is coupled to a 2D structure at an angle with respect to the principal axes of the structure. Equations of motion for the system are developed using Lagrange’s equation. If the TLD and structure are not aligned, the system responds as a coupled four degree of freedom system. The proposed model is validated by conducting structure-TLD system tests. The predicted and experimental structural displacements and fluid response are in agreement. An approximate method is developed to provide an initial estimate of the structural response based on an effective mass ratio. The results of this study show that for small TLD orientation angles, the performance of the TLD is insensitive to TLD orientation.

Autoparametric Resonances of Elastic Structures Coupled With Two Sloshing Modes in a Square Liquid Tank

Nonlinear vibrations of an elastic structure coupled with liquid sloshing in a square tank subjected to vertical sinusoidal excitation are investigated. In the theoretical analysis, the ratios of the natural frequencies of the structure and two sloshing modes satisfy 2:1:1. The equations of motion for the structure and seven sloshing modes are derived using Galerkin’s method while considering the nonlinearity of sloshing. The linear damping terms are then incorporated into the modal equations to consider the damping effect of sloshing. The frequency response curves are determined using van der Pol’s method. The influences of the liquid level, the aspect ratio of the tank cross-section, the deviation of the tuning condition, and the excitation amplitude are investigated. When the liquid level is high, and depending on the excitation frequency, there are three patterns of sloshing: (i) both (1,0) and (0,1) sloshing modes appear at identical amplitudes; (ii) these two modes appear at different amplitudes; and (iii) either (1,0) or (0,1) mode appears. Small deviations of the tuning condition may cause Hopf bifurcations to occur followed by amplitude modulated motion including chaotic vibrations. Bifurcation sets are also calculated to illustrate the influence of the system parameters on the response of the system. It is found that for low liquid levels, square tuned liquid dampers (TLDs) work more effectively than rectangular TLDs. Experiments were also conducted in order to confirm the validity of the theoretical results and were in good agreement with the experimental data.

Equivalent mechanical models of tuned liquid dampers with different tank geometries

This paper focuses on the development of equivalent mechanical models for tuned liquid dampers (TLDs) with rectangular, vertical-cylindrical, horizontal-cylindrical, and hyperboloid (conical) tank shapes under external excitation in the transverse direction. Potential flow theory is utilized to obtain the free-surface response amplitude and the corresponding velocity of the sloshing liquid and Lagrange’s equations are used to determine the generalized properties. Morison’s equation and the virtual work method are used to estimate an equivalent viscous damping ratio based on the screen loss coefficient. The equivalent mechanical properties derived in this paper model the fundamental sloshing mode only and are restricted to small response amplitudes. Subsequently, the equivalent mechanical properties including effective mass, natural frequency, and damping ratio of the TLDs, having different tank geometries, are compared. It is found that the effective mass values for horizontal-cylindrical and hyperboloid TLDs are larger than the effective mass values for vertical-cylindrical and rectangular TLDs. The increased effective mass values for horizontal-cylindrical and hyperboloid TLDs can result in improved tuned liquid damper performance given the same total liquid mass as that of rectangular or vertical-cylindrical TLDs.

Shallow rectangular TLD for structural control implementation

A simple and practical model for the application of shallow rectangular tuned liquid damper (TLD) in structural vibration control is presented in this paper. The dynamic properties of shallow liquid in rectangular containers subjected to forced horizontal oscillation are analysed directly from the continuity and momentum equations of fluids. Following some practical assumptions, the nonlinear partial differential equations describing the wave movement of shallow liquid in rectangular containers are established and a numerical procedure for the solutions of these equations is proposed based on the finite element method. The formula for determining the control force provided by a shallow rectangular TLD is presented. The advantage of the proposed approach for the modeling of shallow rectangular TLD is that it simplifies a three-dimensional problem into a one-dimensional problem and therefore reduces the computation efforts significantly. The whole process forms a solid foundation and provides a simplified procedure for the design and analysis of shallow rectangular TLD.

WAVE-EXCITED STRUCTRURAL VIBRATION MITIGATION WITH TUNED LIQUID DAMPER

The major objective of this study is to experimentally and theoretically investigate the characteristics of rectangular Tuned Liquid Damper (TLD) under wave excitation. An obvious engineering motivation for this study is to explore the applicability of TLDs for suppressing the structural vibration of offshore platforms. The structural model used to perform experiments is scaled according to a full size platform by matching their dynamic properties. Rectangular TLDs of different sizes and water depths are examined. By observing the performance and the behavior of TLDs through laboratory experiments, the influence of a number of parameters is investigated. In an analytical or numerical study, a mathematical model that describes the nonlinear behavior of liquid in TLD and the interaction between TLD and structure is prerequisite. Validity of the mathematical model to simulate the behavior of liquid in TLD and TLD-structure interaction has been evaluated based on the experimental results.

Modeling of Deepwater-Type Rectangular Tuned Liquid Damper With Submerged Nets

An analytical model for describing the effectiveness of deepwater-type tuned liquid damper (TLD) with submerged nets for suppressing horizontal vibration of structures is proposed. TLD is a damping device for suppressing the vibration of long-period structures such as high-rise buildings, tall towers, the pylons of cable-stayed bridges, and so on. The damping force is created by the hydrodynamic force caused by the sloshing of water contained in rectangular tanks located on top of such structures. In this study, we proposed the dynamical model for analyzing deepwater-type TLD (DTLD) where the liquid depth is deep compared with the length of the rectangular tank. In particular, the effect of hydraulic resistance produced by submerged nets installed in the tank is examined intensively. In the analysis of DTLD, employing finite amplitude wave theory, we obtained the hydrodynamic force and the dissipation energy by using Galerkin method, taking the effect of submerged nets into account. The calculated results thus obtained are compared with experimental results, by which the validity of the modeling methodology is confirmed. Finally, the case in which DTLD with nets is installed on an actual structure is investigated both theoretically and experimentally and the performance of DTLD is illustrated.