Seismic response control with density-variable tuned liquid dampers

In this paper, the seismic effectiveness of a density-variable tuned liquid damper （DVTLD） with a sloping bottom is experimentally investigated through a series of shake table tests on a 1/4-scale, 3-story frame structure and numerically simulated by a new semi-analytical model. Special attention was given to reducing the first peak and maximum response under near- and far-field ground motions, and the robustness of a density-variable control system consisting of multiple DVTLDs with closely-spaced frequencies. Adaptable to earthquake excitations, the density-variable control system has been demonstrated to be more effective and more robust than its corresponding traditional tuned liquid damper in suppressing story drift and floor acceleration of the structure. Numerical simulations of the DVTLD-controlled structure agreed very well in phase with experimental results but somewhat overestimated the amplitude of the structural response.

Suppression of Wave-Excited Vibration of Offshore Platform by Use of Tuned Liquid Dampers

This paper describes experimental and theoretical investigations of Tuned Liquid Damper (TLD) characteristics for suppressing the wave-excited structural vibration. The structural model for the experiments is scaled according to a full size offshore platform by matching their dynamic properties. Rectangular TLDs of different sizes with partially filled liquid are examined. By observing the performance and behavior of TLDs through laboratory experiments, the Study investigates the influence of a number of parameters, including container size, container shape, frequency ratio, and incident wave characteristics. In an analytical study, a mathematical model that describes the nonlinear behavior of liquid in TLD and the interaction of TLD and structure is prerequisite. The validity of the model is evaluated and simulating results can reasonably match the corresponding experimental results.

Seismic Response Reduction for Fixed Offshore Platform by Tuned Liquid Damper

An approach to seismic response reduction for offshore platforms by the use of the tuned liquid damper is presented in this paper. First of all, the effects of the tuned frequency ratio and excited frequency ratio on the seismic response reduction of the platform structure are investigated. Based on the results, a mechanical model and equation of motion for the TLD-platform system are established. And then effectiveness of the appraoch is verified by numerical calculation.

Contribution of tuned liquid column gas dampers to the performance of offshore wind turbines under wind, wave, and seismic excitations

The main intention of the present study is to reduce wind, wave, and seismic induced vibrations of jacket- type offshore wind turbines （JOWTs） through a newly developed vibration absorber, called tuned liquid column gas damper （TLCGD）. Using a Simulink-based model, an analytical model is developed to simulate global behavior of JOWTs under different dynamic excitations. The study is followed by a parametric study to explore efficiency of the TLCGD in terms of nacelle acceleration reduction under wind, wave, and earthquake loads. Study results indicate that optimum frequency of the TLCGD is rather insensitive to excitation type. In addition, while the gain in vibration control from TLCGDs with higher mass ratios is generally more pronounced, heavy TLCGDs are more sensitive to their tuned frequency such that ill-regulated TLCGD with high mass ratio can lead to destructive results. It is revealed that a well regulated TLCGD has noticeable contribution to the dynamic response of the JOWT under any excitation.

Optimum geometry of tuned liquid column-gas damper for control of offshore jacket platform vibrations under seismic excitation

In this study, the effectiveness of a tuned liquid column-gas damper, TLCGD, on the.suppression of seismic-induced vibrations of steel jacket platforms is evaluated. TLCGD is an interesting choice in the case of jacket platforms because it is possible to use the structural elements as the horizontal column of the TLCGD. The objective here is to find the optimum geometric parameters, namely orientation and configuration of vertical columns, length ratio, and area ratio of the TLCGD, considering nonlinear damping of the TLCGD and water-structure interaction between the jacket platform and sea water. The effects of different characteristics of ground motion such as PGA and frequency content on the optimum geometry are also investigated and it is observed that these features have some influence on the optimum area ratio. Finally it is observed that pulse arrangement of ground acceleration is one of the most important parameters affecting the efficiency of a TLCGD. In other words, it is found that the TLCGD＇s capability to reduce the RMS responses depends only on the frequency content of the ground acceleration, but its capability to reduce the maximum responses depends on both the frequency content and the pulse arrangement of the ground acceleration.

Torsionally Coupled Response Control of Offshore Platform Structures Using Circular Tuned Liquid Column Dampers

In this paper, the control performance is investigated of Circular Tuned Liquid Column Dampers (CTLCD) over torsional response of offshore platform structures excited by ground motions. Based on the equation of motion for the CTLCD-structure system, the optimal control parameters of CTLCD are given through some derivations on the supposition that the ground motion is a stochastic process. The influence of systematic parameters on the equivalent damping ratio of the structures is analyzed with purely torsional vibration and translational-torsional coupled vibration, respectively. The results show that the Circular Tuned Liquid Column Damper (CTLCD) is an effective torsional response control device.

Impact of seismic excitation characteristics on the efficiency of tuned liquid column dampers

Various types of passive control systems have been used to suppress the seismic response of structures in recent years. Among these systems, Tuned Liquid Column Dampers （TLCDs） dissipate the input earthquake energy by combining the effects of the movement of the liquid mass in the container, the restoring force on the liquid due to the gravity loads and the damping due to the liquid movement through orifices. In this study, the effects of seismic excitation characteristics such as frequency content and soil condition on the seismic performance of TLCDs are investigated using nonlinear time-history analyses. In this regard, among the past earthquake ground motion records of Iran, 16 records with different parameters were selected. In the structural model developed, the attached TLCD is simulated as a Tuned Mass Damper （TMD） having the same vibration period and damping ratio as the original TLCD. The numerical results show that the seismic excitation characteristics have a substantial role on the displacement reduction capability of TLCDs and they should be considered accordingly in the design of TLCDs.

Wind-induced vibration control of bridges using liquid column damper

The potential application of tuned liquid column damper (TLCD) for suppressing wind-induced vibration of long span bridges is explored in this paper.By installing the TLCD in the bridge deck,a mathematical model for the bridge-TLCD system is established.The governing equations of the system are developed by considering all three displacement components of the deck in vertical,lateral,and torsional vibrations,in which the interactions between the bridge deck,the TLCD,the aeroelastic forces,and the aerodynamic forces are fully reflected.Both buffeting and flutter analyses are carried out.The buffeting analysis is performed through random vibration approach,and a critical flutter condition is identified from flutter analysis.A numerical example is presented to demonstrate the control effectiveness of the damper and it is shown that the TLCD can be an effective device for suppressing wind-induced vibration of long span bridges,either for reducing the buffeting response or increasing the critical flutter wind velocity of the bridge.

Stability and accuracy of central difference method for real-time dynamic substructure testing considering mass participation coefficient

For real-time dynamic substructure testing(RTDST),the influence of the inertia force of fluid specimens on the stability and accuracy of the integration algorithms has never been investigated.Therefore,this study proposes to investigate the stability and accuracy of the central difference method(CDM)for RTDST considering the specimen mass participation coefficient.First,the theory of the CDM for RTDST is presented.Next,the stability and accuracy of the CDM for RTDST considering the specimen mass participation coefficient are investigated.Finally,numerical simulations and experimental tests are conducted for verifying the effectiveness of the method.The study indicates that the stability of the algorithm is affected by the mass participation coefficient of the specimen,and the stability limit first increases and then decreases as the mass participation coefficient increases.In most cases,the mass participation coefficient will increase the stability limit of the algorithm,but in specific circumstances,the algorithm may lose its stability.The stability and accuracy of the CDM considering the mass participation coefficient are verified by numerical simulations and experimental tests on a three-story frame structure with a tuned liquid damper.

一种利用液体阻尼器减小单桩基础海洋平台在地震载荷下位移的新方法

The efficiency of a tuned liquid damper(TLD)in controlling the dynamic responses of offshore monopile platforms underseismic excitation has been investigated in this paper.Damping is performed by applying a type of reservoir inside a tower,which is designed optimally via seawater and a monopile body.Hydrodynamic forces due to water surface oscillation inthe reservoir act as resistant forces against structure vibration and displacement.Using ANSYS finite element(FE)software,a monopile structure with the same dimensions as the samples in the Persian Gulf climate was modeled and thenanalyzed in this research using the transient time history analysis related to the records of El-Centro,Kobe,and Tabasearthquakes for seismic investigation.The dynamic responses of the monopile platform with and without TLD werecompared after the completion of FE results.Findings show that using the mentioned TLDs reduced structure displacementby more than 50%based on the earthquake frequency content.

Distributed TLDs in RC floors and their vibration reduction efficiency

A novel distributed tuned liquid damper （DTLD） for reducing vibration in structures is proposed in this paper. The basic working principle of the DTLDs is to fill the empty space inside the pipes or boxes of cast-in-situ hollow reinforced concrete （RC） floor slabs with water or other liquid. The pipes or boxes then work as a series of small TLDs inside the structure, to increase the damping ratio of the entire structural system. Numerical simulation that accounts for the fluid- structure conpling effect is carried out to evaluate the vibration-reduction efficiency of the DTLDs. The results show that the DTLDs are able to considerably increase the damping of the structure and thus reduce its vibration. An additional benefit is that the DTLDs do not require architectural space to be added to the structure.

Periods and Energy Dissipations of a Novel TLD Rectangular Tank with Angle-adjustable Baffles

A novel tuned liquid damper (TLD) rectangular tank with two angle-adjustable baffles was pre- sented.The numerical analysis was performed using the commercial code FLUENT.The standard kinetic energy and dissipation rate turbulent model was employed,which was solved using volume of fluid (VOF) method able to treat both the free surface motion and the viscous stresses over the rigid walls accurately.The relationship between the natural periods of water and the angles of its baffles was studied by numerical sim- ulating of a case,and the changes of energy dissipations were investigated.The natural periods and dampers of the novel TLD can be changed in a wide range by adjusting the baffles' angle,thus it is more effective in controlling the vibration of structures in a wide frequency range.

Experimental Study on the Effectiveness of TLDs under Wave Loading

The objective of this study is to experimentally investigate the effectiveness of Tuned Liquid Dampers (TLDs) for suppressing the dynamic response of a platform structure subjected to wave loading and to explore the applicability of TLDs for suppressing the structural vibration of fixed offshore platforms. The experimental model is scaled according to a full size platform by matching its dynamic properties. Rectangular and circular TLDs of various sizes and water depths are examined. The experiments were performed in a 2-D wave flume. The effectiveness of TLDs is evaluated based on their response reduction. By observing the performance and the behavior of TLDs through laboratory experiments, the effects of a number of parameters including container shape, container size, number of dampers, frequency ratio, mass ratio, and incident wave characteristics are investigated.

Semi-Active TLCD Control of Fixed Offshore Platforms Using Artifical Neural Networks

In this paper, the control method for fixed offshore platforms using semi-active tuned liquid column damper (TLCD) is presented. The equation of motion for the platform-TLCD control system is given and the semi-active control strategy is established. A back propagation artificial neural network (ANN) is used to adjust the orifice opening of TLCD because of the nonlinear motion of liquid in TLCD. The effectiveness of the control method is verified by numerical examples.

A review on liquid sloshing hydrodynamics

Liquid sloshing in tanks is a very complex nonlinear free surface fluid flow problem,which must be considered in most of the marine engineering problems such as naval architecture,offshore engineering and so on.Violent liquid sloshing in large containers can damage the tank structure due to the direct liquid impacting action.Sloshing also affects the capsizing process of the liquid cargo ship.Some works on mitigating sloshing by using all kinds of the baffles were thus followed with interests.Oil layers with thinner thickness were shown to reduce the sloshing load of water in tanks.The sloshing characteristics in tanks with different sizes were different,therefore,scaling effect of sloshing should also be considered.Sloshing in a tank can also be used as tuned liquid dampers(TLDs)to dampen wind,wave and flow-induced motions of floating or fixed marine platforms.This paper present an overview on recent advances of liquid sloshing hydrodynamics including sloshing mitigation by using anti-sloshing baffle,layered fluids sloshing,scaling effect of sloshing and TLDs.

Fluid-Structure Interaction During Large Amplitude Sloshing and TLD Vibration Control

The arbitrary Lagrange-Eulerian (ALE) finite element method (FEM) was successfully used to analyze fluid-structure interaction with a free surface. The fluid was regarded as a convection dominated incompressible viscous with the viscous and the slip boundary conditions. Generalized variational principles were established for the problem with large amplitude sloshing due to the free fluid surface. The Newmark-β integration method with a predictor-corrector scheme was used to solve the nonlinear dynamic response of the coupled ALE-FEM equations. Numerical examples were given to analyze the effects of a tuned liquid damper (TLD) setting on the structure. The horizontal nonlinear displacement responses in time domain at the top of the structure and the fluid elevation histories along the wall were computed and compared with predictions of a simplified mass-spring system.

Parameter Optimization and Control Characteristics Analysis of TLMD System Based on Phase Deviation

Combined with the advantages and disadvantages of tuned liquid damper (TLD) and tuned mass damper (TMD),a double tuned liquid mass damper (TLMD) is proposed by replacing the rigid connection of TLD with the spring structure.The motion equation of a single-degree-of-freedom structure with a TLMD attached at its top is found under harmonic excitation.Comparing the energy consumption and amplitude of primary structure with equal mass ratio TMD,it is found that the energy dissipation performance of TLMD is better in the effective phase region.The interaction process between TLMD and structure is analyzed,and the formula of phase deviation between the relative velocity of tank and the displacement of primary structure is deduced.By analyzing the influence of mass ratio,frequency ratio,damping ratio and water depth ratio on the damping effect,the results show that the frequency ratio and liquid depth ratio have great influence on the size and location of deep resonance peak,and the mass ratio and damping ratio have great influence on the width of the effective frequency band.The formula of equivalent damping ratio is proposed based on the principle of energy and it is found that the equivalent damping ratio is related to the phase deviation and change with the frequency ratio of the external excitation.