Tuned liquid dampers under large amplitude excitation

This paper investigates the performance of a new type of cost-efficient damper for mitigating wind and earthquake induced vibrations in tall buildings. Tuned Liquid Damper (TLD) is a type of Tuned Mass Damper (TMD) where the mass is replaced by a liquid (usually water). A TLD 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. The effectiveness of TLD is evaluated based on the response reduction of the structure which is a two-storied steel building frame. Various parameters that influence the performance of TLD are also studied.

Doboku Gakkai Ronbunshu, 1989

The interaction between rectangular Tuned Liquid Damper (TLD) and structure is investigated both experimentally and theoretically. A TLD-structure interaction model is developed where the dynamic interaction force is theoretically evaluated by applying the nonlinear shallow water wave theory. Good agreements are found between the experimental results and the theoretical simulation within the range where no breaking of wave occurs inside the TLD. Effectiveness of TLD is demonstrated for sinusoidal forced excitation. An example of TLD design procedure is also given using the TLD-structure interaction model.

International Journal of Engineering, 2022

To endure strong ground motions in large earthquakes, structures need to be equipped with tools to damp the huge amounts of energy induced by these excitations. In conventional buildings, seismic energy is often handled by a combination of rigidity-ductility measures and energy dissipation solutions. Since these buildings often have very low damping capability, the amount of energy dissipated within their elastic behavior phase tends to be negligible. Passive dampers are vibration control systems that can serve as valuable tools for controlling strong forces and reducing the probability of structural failure under seismic loads. In Tuned Liquid Dampers (TLDs), energy is dissipated by exploiting the behavior and characteristics of the liquid contained in the damper's tank. When the structure is subjected to external stimuli, the force transferred to the damper starts moving the liquid that lies stationary in the damper's tank, getting dissipated in the process. There are various classes of TLDs with different tank shapes, aspect ratios, and mechanisms of action, each with its properties and features. Another cause of energy dissipation in TLDs, in addition to the viscosity of the liquid, is the base shear force that is applied to the damper's intersection with the main structure with a phase difference relative to the external excitation, because of the difference between hydrostatic forces exerted on the walls at the two ends of the tank. Therefore, the level of liquid interaction with the damper's walls is also a determinant of the damping of external forces and thus the seismic response of the structure. The study investigated a new type of TLD with a double-walled cylindrical tank. To examine the effect of this TLD on the seismic response, a series of models were built with different liquid heights in the tank's inner and outer walls and subjected to several seismic excitations on a shaking table. The results showed that using this type of damper reduced the seismic response of the structures. Also, the reduction in seismic response was found to change significantly with the amount of liquid in the damper.

In traditional tuned liquid damper (TLD) installations, TLD tank(s) are tuned to a single optimal frequency as determined by well-known dynamic vibration absorber theory. A multiple tuned liquid damper (MTLD) is created when the sloshing frequencies are distributed over a range near the structural frequency. In this paper, an equivalent mechanical model for a structure–MTLD system is developed. A third-order nonlinear multimodal model is employed to assess nonlinear fluid affects and serve as independent model verification. To the authors' knowledge, this is the first time the nonlinear energy dissipation associated with damping screens and the nonlinear coupling amongst slosh-ing modes has been considered for MTLD systems. MTLD systems consisting of one (traditional TLD), two, and three tanks are used to reduce the resonant response of a single degree of freedom structure. The MTLD provides structural control that is superior to a traditional TLD. The MTLD is less sensitive to the structural excitation amplitude, which enables the device performance to be maintained at low amplitude excitations associated with common wind events. The MTLD is also shown to be more robust to changes to the structure's natural frequency than the traditional TLD. Since many TLD installations require multiple tanks to satisfy space restrictions, the findings of this paper are highly relevant to structural engineering. This paper shows that by slightly altering the fluid depth of each tank, improved structural control performance can be achieved at little additional cost.

ASCE Proceedings of Civil Engrg. in the Oceans VI

Sloshing motions are monitored during and outside resonance above and below the critical water depth in a square tank with base dimensions of 1 × 1 m 2 . We investigate the free surface motion as a function of the wave steepness in shallow to deep water for different excitation cases. The test cases include sway and heave base excitation. These investigations are carried out in the depth-to-width, h/b = 0.2, 0.3, 0.6. The system is extremely sensitive to initial conditions and the system has a dynamic form of bistability for certain forcing frequencies and amplitudes. This makes it possible for the system to exhibit very interesting hysteresis effects. It is shown that the free surface behave as a soft oscillator in deep water and as a hardening spring near the shallow water limit when the tank is excited horizontally. We also identified that the Faraday peaks exhibit hardening (h/b=0.2) and softening (h/b=0.6) spring behavior when the tank is excited in a pure vertical motion with a frequency twice the first sloshing frequency. The associated wave form is "mushroom" shaped at certain time instances which resembles the Richtmyer-Meshkov instability.

Simulation Modelling Practice and …, 2003

In recent years, tuned liquid dampers (TLD) have proved a successful control strategy for reducing structural vibrations. The present study focuses on the frustum-conical TLD as an alternative to the traditional cylindrical tank. If compared to the cylindrical reservoir, the cone-shaped TLD allows calibrating its natural frequency through varying liquid depth, which makes it suitable for a semi-active implementation, and attains the same level of performance with a fewer mass, at least for small fluid oscillations. A linear model is presented which can interpret TLDÕs behaviour for small excitations. For larger amplitudes, strong nonlinearities occur and the linear model is no longer predictive. Consequently, for a frustum-cone TLD subjected to harmonic excitations, a tuned mass damper (TMD) analogy is established where TMD parameters vary with the excitation amplitude.

International Journal of Numerical Methods for Heat & Fluid Flow, 2005

Purpose-This paper presents a new numerical model that, unlike most existing ones, can solve the whole liquid sloshing, nonlinear, moving boundary problem with free surface undergoing small to very large deformations without imposing any linearization assumptions. Design/methodology/approach-The time-dependent, unknown, irregular physical domain is mapped onto a rectangular computational domain. The explicit form of the mapping function is unknown and is determined as part of the solution. Temporal discretization is based on one-step implicit method. Second-order, finite-difference approximations are used for spatial discretizations. Findings-The performance of the algorithm has been verified through convergence tests. Comparison between numerical and experimental results has indicated that the algorithm can accurately predict the sloshing motion of the liquid undergoing large interfacial deformations. Originality/value-The ability to model liquid sloshing motion under conditions leading to large interfacial deformations utilizing the model presented in this paper improves our ability to understand the problem of sloshing motion in tuned liquid dampers (TLDs), which would eventually help in constructing more effective TLDs.

Proceedings of the 5th Intl. World Congress on Computational Mechanics

A fully nonlinear finite difference model has been developed based on inviscid flow equations. Numerical experiments of sloshing wave motion are undertaken in a 2-D tank which is moved both horizontally and vertically. Results of liquid sloshing induced by harmonic and earthquake base excitations are presented for small to steep non-breaking waves for steepness up to 0.3. Good agreement for small horizontal forcing amplitude is achieved between the numerical model and first order small perturbation theory. For large horizontal forcing, nonlinear effects are captured by the numerical model. The effect of the simultaneous vertical and horizontal excitation in comparison with the pure horizontal motion is examined. It is shown that vertical excitation causes the instability of the combined motion for a certain set of frequencies and amplitudes of the vertical motion. It is also found that in addition to the resonant frequency of the pure horizontal excitation, two additional resonance frequencies exist due to the combined motion of the tank. The dependence of the nonlinear behaviour of the solution on the wave steepness is discussed. It is found that for the present problem nonlinear effects become important when the steepness reaches about 0.1.

Doboku Gakkai Ronbunshu, 1988

A new kind of damper, Tuned Liquid Damper (TLD) relying on motion of shallow liquid in a rigid cylinder, is experimentally studied. Prototype-sized circular containers with diameters 40 cm and 60 cm and partially filled with water, are attached to a single-degreeof-freedom structural model with natural period of 2 sec. The damper effect is measured in terms of the increase in the logarithmic rate of decrement of free oscillation of the main structure. The structural displacements range from 8 cm down to 0.25 cm. It is seen that, for large damping effect at small amplitude of structural vibration, it is necessary to tune the fundamental sloshing period of the liquid to the natural period of structure; hence the name Tuned Liquid Damper. Breaking of surface waves, which is dependent on structural vibration amplitude, appears to be a major mechanism of energy dissipation in the range of displacements considered. Also investigated are the effects of: ratio of liquid frequency to structure frequency; liquid viscosity; container bottom roughness; container roof height; ratio of liquid mass to structure mass; and container diameter.

Earthquake Engineering & Structural Dynamics, 1995

Damper (TMD) analogy, equivalent mass, stiffness and damping of the TLD are calibrated from the experimental results. These parameters are functions of the TLD base amplitude. Some important properties of the TLD are discussed on the basis of these results.

International Journal of Research in Engineering and Innovation

Earthquake Engineering & Structural Dynamics, 1995

A tuned liquid damper (TLD), which consists of rigid tanks partially filled by liquid, is a type of passive control device relying upon liquid sloshing forces or moments to change the dynamical properties and to dissipate vibrational energy of a structure. An analytical non-linear model is proposed for a TLD using rectangular tanks filled with shallow liquid under pitching vibration, utilizing a shallow water wave theory. The model includes the linear damping of the sloshing liquid, which is an important parameter in the study of a TLD as it affects the efficiency of the TLD. Shaking table experiments were conducted for verification; good agreement between the analytical simulations and the experimental results was observed in a small excitation amplitude range. The simulations of TLD-structure interaction by using the proposed model show that the TLD can efficiently suppress resonant pitching vibration of a structure. It is also found that the effectiveness of a TLD for suppressing the pitching vibration depends not only on the mass of liquid in the TLD but also on the configuration of the liquid as well as upon the position where the TLD is located. If the configuration of the liquid, i.e. the liquid depth and the TLD tank size, is designed suitably, the TLD can have a large suppressing moment and can be very effective even with a small mass of liquid.

Journal of Computational Physics, 2004

A fully non-linear finite difference model has been developed based on inviscid flow equations. Numerical experiments of sloshing wave motion are undertaken in a 2-D tank which is moved both horizontally and vertically. Results of liquid sloshing induced by harmonic base excitations are presented for small to steep non-breaking waves. The simulations are limited to a single water depth above the critical depth corresponding to a tank aspect ratio of h s =b ¼ 0:5. The numerical model is valid for any water depth except for small depth when viscous effects would become important. Solutions are limited to steep non-overturning waves. Good agreement for small horizontal forcing amplitude is achieved between the numerical model and second order small perturbation theory. For large horizontal forcing, nonlinear effects are captured by the third-order single modal solution and the fully non-linear numerical model. The agreement is in general good, both amplitude and phase. As expected, the third-order compared to the second-order solution is more accurate. This is especially true for resonance, high forcing frequency and mode interaction cases. However, it was found that multimodal approximate forms should be used for the cases in which detuning effects occur due to mode interaction. We present some test cases where detuning effects are evident both for single dominant modes and mode interaction cases. Furthermore, for very steep waves, just before the waves overturn, and for large forcing frequency, a discrepancy in amplitude and phase occurs between the approximate forms and the numerical model. The effects of the simultaneous vertical and horizontal excitations in comparison with the pure horizontal motion and pure vertical motion is examined. It is shown that vertical excitation causes the instability associated with parametric resonance of the combined motion for a certain set of frequencies and amplitudes of the vertical motion while the horizontal motion is related to classical resonance. It is also found that, in addition to the resonant frequency of the pure horizontal excitation, an infinite number of additional resonance frequencies exist due to the combined motion of the tank. The dependence of the non-linear behaviour of the solution on the wave steepness is discussed. It is found that for the present problem, non-linear effects become important when the steepness reaches about 0.1, in agreement with the physical experiments of Abramson [Rep. SP 106, NASA, 1966].

Simulations conducted on single degree of freedom structures (SDOFs) connected rigidly to a tuned liquid damper (TLD) under various excitations show that TLD can reduce structural response to these excitations considerably if properly designed. TLD is a rectangular (or circular) rigid tank partly filled with water where its sloshing frequency is tuned to natural frequency of structure. As increasing the base excitation level, TLD is more efficient, which is because of more energy dissipation via sloshing and wave breaking. A conventional TLD is generally tuned to a single frequency. Because of this limitation, the TLD usually is used to control the structural response of semi-SDOF structures. Overcoming this drawback, some standing baffles are suggested to be installed inside the TLD which can rotate around their vertical axis. The numerical simulations show that these baffles can change the damping ratios, frequency of sloshing and sloshing forces especially in baffles orientation between 30 to 50 degrees. This can be utilized to make the TLD, variably tuned liquid damper.

Soil Dynamics and Earthquake Engineering, 2012

Nonlinear behavior of liquid sloshing inside a partially filled rectangular tank is investigated. The nonlinearity in the numerical modeling of the liquid sloshing originates from the nonlinear terms of the governing equations of the fluid flow and the liquid free surface motion as a not known boundary condition. The numerical simulations are performed for both linear and nonlinear conditions. The computed results using linear conditions are compared with readily available exact solution. In order to verify the results of the nonlinear numerical solution, a series of the shaking table tests on rectangular tank were conducted. Having verified linear and nonlinear numerical models, they are used for computation of near wall sloshing height at a series of real scale tanks (with various dimensions) under the both harmonic and earthquake base excitation. Finally, the nonlinear effects on liquid sloshing modeling are discussed and the practical limitations of the linear solution in evaluating the response of seismically excited liquids are also addressed.