Simulating a conical tuned liquid damper

SummaryThis study focuses on the optimization of tuned liquid dampers (TLDs) by using metaheuristic methods using a natural phenomenon as inspiration. Unlike tuned mass dampers (TMDs), TLDs consist of two parts of bodies that contain the passive liquid that is stationary and the active part of the liquid that involves in sloshing. To optimize the amount of optimum active and passive liquids by finding the best dimensional properties of the liquid tank, a two‐degree‐of‐freedom (DOF) model was used as TLD in the dynamic analysis used in the optimization that aims to reduce the maximum displacement of the structure under earthquake excitations. For this purpose, water, oil, and glycerin liquids were selected for TLD. TLD parameters were optimized with the help of Jaya algorithm, flower pollination algorithm (FPA), harmony search (HS) algorithm, and teaching–learning‐based optimization (TLBO). Total acceleration and maximum displacement were evaluated after optimization. The performance of TLD under earthquake excitations has been also compared with TMDs. According to the results, the optimized TLD has a better performance than TMD, and Jaya algorithm has a slightly better performance than the other algorithms.

Floating Production Storage and Off-loading (FPSO) systems are being utilized world widely by offshore industries. The surge response of FPSO subjected to severe sea states needs to be suppressed in order to keep a particular station for operational purposes. The oil cargo tanks of FPSO can be used as passive dampers for minimizing the surge displacement response of FPSO. These cargo tanks can act as Tuned Liquid Dampers (TLDs) if the natural frequency of the liquid oscillation in containers is tuned to the surge natural frequency of FPSO or tuned to the excitation frequency. The containers can be partitioned into several tanks (as Multiple Tuned Liquid Dampers, MTLDs) with different lengths and liquid depths. The natural frequencies of MTLDs can also be distributed over a range around the natural frequency of FPSO. The present study attempts to comprehend the response control of FPSO under surge motion and so the FPSO is modeled as a single degree of freedom under random sea state. The containers can be modeled as either linear TLDs or nonlinear TLDs. Each linear TLD can be modeled by an equivalent Tuned Mass Damper (TMD) analogy based on linear wave theory. In order to account the nonlinear liquid motion in TLD, an impact damper analogy is used along with the TMD analogy. The study includes the efficiency and robustness of MTLD and it compares the response control obtained by using linear MTLDs and nonlinear MTLDs.

Numerical flow models to simulate tuned liquid dampers (TLD) with slat screens

Researchers have developed and applied tuned liquid dampers (TLDs) to reduce the vibration of civil structures. Previous studies have focused on using a large number of identical TLDs (single-frequency TLDs) or many multi-frequency TLDs to reduce the structural dynamic response. In those works, the optimal parameters of TLDs were determined through the optimal parameter of equivalent tuned mass dampers. In this study, a new approach is proposed to directly determine the optimal parameters of multiple identical TLDs (MITLD). Furthermore, different aspects including the best configuration control effectiveness, robustness, and sensitivity to changes in the water level of MITLD are explored. Parametric studies are also conducted to find the fundamental characteristics of MITLD and the effective domains of the MITLD’s main parameters. The results obtained from this work agree well with those of earlier research works. Based on this fundamental research, recommendations given include: (1) MITLD is effective in controlling the dynamic response of structures with low natural frequencies, (2) MITLD is very sensitive to the variation of the water level height in TLDs, and (3) a difference in the natural frequency of the main structure leads to a significant performance decrease of the MITLD.

Experimental study on the efficiency of tuned liquid dampers for vibration mitigation of a vertically irregular structure

Damping devices are used to reduce the dynamic response of a structure by energy dissipation. Common types of damping devices are fluid viscous dampers, tuned mass dampers, and tuned liquid dampers. This project aims to study the effectiveness of TMD and TLD in controlling the response of the structure when it is subjected to acceleration records of different earthquakes. A 20-storey reinforced concrete bare frame structure has been subjected to two earthquake acceleration records with and without dampers in SAP 2000. The dampers are modelled using link elements. The structure is attached with TMD and TLD having a mass of 0.5%, 2%, 4%, 6%, 8% and 10% of the modal mass. The analysis procedure used is nonlinear modal time history analysis (FNA). The variation in base shear and top storey displacement has been obtained and plotted.

A conventional tuned liquid damper (TLD) generates a relatively small control force associated with low density of sloshing water. To overcome this main drawback, proposed in this study is a new TLD system composed of water and fine particles in a rectangular tank of sloping bottom. The effectiveness of the proposed mass-variable TLD system was demonstrated with shake table tests. In comparison with a conventional TLD, the mass-variable TLD can more effectively reduce structural responses particularly under large external excitations. The mass-variable TLD can also be effective in the earlier stage of an earthquake event due to the increasing mass nature as the excitation increases. This attribute makes the new TLD particularly attractive under impulsive loads such as near-field ground motions.

Substructure shake table testing (SSTT) is an advanced experimental technique that is suitable for investigating the vibration control of secondary structure-type dampers such as tuned mass dampers (TMDs). The primary structure and damper are considered as analytical and experimental substructures, respectively. The analytical substructures of existing SSTTs have mostly been simplified as SDOF structures or shear-type structures, which is not realistic. A common trend is to simulate the analytical substructure via the finite element (FE) method. In this study, the control effects of four dampers, i.e., TMD, tuned liquid damper (TLD), particle damper (PD) and particle-tuned mass damper (PTMD), on a frame were examined by conducting virtual SSTTs. The frame was modeled through stiffness-based beam-column elements with fiber sections and was solved by a family of model-based integration algorithms. The influences of the auxiliary mass ratio, integration parameters, time step, and time delay on SSTT were investigated. The results indicate that the TLD had the best performance. In addition, SSTT using model-based integration algorithms can provide satisfactory results, even when the time step is relatively large. The effects of integration parameters and time delay are not significant.

Tuned liquid dampers with a Keulegan–Carpenter number-dependent screen drag coefficient

Real-time hybrid shaking table testing method for the performance evaluation of a tuned liquid damper controlling seismic response of building structures

SummaryTuned liquid dampers provide structure control with the help of the liquid mass in tanks that are attached to the structure. The mass ratio affects the optimum tuned liquid damper (TLD) parameters. This study examines the effect of mass ratio on the control performance of TLD devices in providing seismic control of structures with different damping ratios. For this purpose, TLD devices with different mass ratios were placed on two different single‐story steel and reinforced concrete structure models, and their performance under earthquake excitation was investigated. TLD parameters for obtaining the optimum displacement level in the 0.5‐ and 1.0‐s structure natural period for both structure types were optimized with the Jaya algorithm (JA), which is a metaheuristic algorithm. By using the optimum TLD parameters, the structural displacement and total acceleration values were obtained by the critical earthquake analysis. When the results are examined, it is understood that TLD mass increase from a 20% mass ratio for both structure types and selected structure periods does not have a significant effect on TLD control performance.

The excessive lateral vibrations of Londons Millenium Bridge and the Toda Park Bridge in Japan due to a large number of crossing pedestrians have raised an unexpected problem in footbridge constructions. Secondary tuned structures, like the conventional tuned mass damper (TMD) or the tuned liquid damper (TLD) were installed to the bridge in order to suppress these vibrations. In the present investigation it is proposed to apply the more efficient and more economic tuned liquid column damper (TLCD), which relies on the motion of a liquid mass in a sealed tube to counteract the external motion, while a built‐in orifice plate induces turbulent damping forces that dissipate kinetic energy. For optimal tuning of TLCDs the natural frequency and equivalent linear damping coefficient have to be chosen suitable, likewise to the conventional TMDs, as given in Den Hartog [1]. The advantages of TLCDs are: simple tuning of natural frequency and damping, low cost of design and maintenance and a simple construction. A mathematical model of a three degree‐of‐freedom (DOF) bridge coupled with an optimal tuned TLCD is derived and analyzed numerically. Furthermore, a small scale experimental model set‐up has been constructed in the laboratory of the TU‐Insitute. The experimental results are in good agreement with the theoretical predictions and indicate that TLCDs are effective damping devices for the undesired pedestrian induced footbridge vibrations. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Wind-induced responses of an airport tower — efficiency of tuned liquid damper

An analytical model for describing the effectiveness of tuned liquid damper (TLD) with submerged nets for suppressing horizontal vibration of structures is proposed. Dissipation energy due to the liquid motion under sinusoidal excitation is calculated based on nonlinear shallow water wave theory. In particular, the effects of hydraulic resistance produced by nets installed in a tank on the performance of TLDs are examined. The results of dissipation energy theoretically obtained are confirmed by experiments. To show the effectiveness of the proposed analytical model for TLD-structure interaction problems, the case in which TLD with nets is installed on top of a pylon of a cable-stayed bridge is described and the calculated results are compared with the actual experimental data. In the calculation, it is shown that the optimal damping factor, as is the case for tuned mass dampers (TMD), can be produced by the nets, and the effectiveness of TLD with nets are demonstrated.

This paper introduces a new type of tuned liquid damper (TLD) having a relatively simple, easy-to-model behavior and high effectiveness in controlling structural vibrations. It consists of a traditional TLD with addition of a floating roof. Since the roof is much stiffer than water, it prevents wave breaking, hence making the response linear even at large amplitudes. The roof also facilitates the incorporation of supplemental devices with which the level of damping of the liquid vibration can be substantially augmented. This newly proposed TLD, denoted as tuned liquid damper with floating roof (TLD-FR), maintains the traditional advantages of TLDs (low cost, easy installation and tuning), but its numerical characterization is much simpler because the floating roof suppresses higher sloshing vibration modes, resulting in a system that can be represented by a single-degree-of-freedom model. An efficient numerical scheme, where the dynamic behavior of the TLD-FR is expressed as a second-order lineal system of equations, is discussed and validated by scaled experimental tests. The equations of motion of a structure equipped with a TLD-FR are then derived and manipulated to offer a unifying representation dependent upon only four model characteristics of the TLD-FR: The first three (mass, frequency and damping ratios) are common for all type of mass dampers, whereas the final one, termed efficiency index, is related to a similar parameter used to characterize liquid column dampers. Through this approach, the behavior of the proposed TLD-FR can be easily correlated with the behavior of other well-known linear mass damper devices. The relationship between these parameters and the geometrical characteristics of the TLD-FR is also examined. Finally, the identification of the optimal characteristic of the TLD-FR (natural frequency and damping) under stationary stochastic excitation is discussed.