Effects of soil–structure interaction on the design of tuned mass damper to control the seismic response of wind turbine towers with gravity base

This paper studies the effect of soil–structural interaction (SSI) on gravity‐based wind turbine towers equipped with tuned mass dampers (TMDs) subjected to earthquake loading. A small‐scale shaking table test of wind turbine towers with TMD was conducted, and the results showed that using TMD designed considering SSI resulted in larger vibration suppression. A simplified analytical numerical model was developed for SSI analysis considering TMD. The effect of soil site class and the earthquake intensity on the response reduction efficiency of the TMD was also discussed using the simplified model. It is concluded that the TMD efficiency depends not only on the soil stiffness but also on the characteristics of the applied ground motions, both of which are affected by the site classes and earthquake intensity levels. Moreover, the peak acceleration ratio (PAR), the root mean square acceleration ratio (RAR), the peak displacement ratio (PDR), and the root mean square displacement ratio (RDR) of the top of the wind turbine tower were obtained with and without TMD for different earthquake intensities and sites. These parameters can be used as references for the rational selection of TMD parameters considering SSI

Seismic performance on tuned liquid damper in novel wall interlocking block

Building structural vibrations are generally regarded to be a serviceability problem, mainly affecting the architectural façade, and occupant comfort. However, in extreme cases such as earthquakes, it may lead to structural collapse. The excessive building vibrations are sometimes seen due to the resonant effect. In this study, the following blocks were proposed and investigated: Tuned Liquid Damper block (i-Block), Friction Damper block (B-Block) and vertical supporting block (V-Block). The newly developed non-loadbearing cement interlocking-block masonry was incorporated with damping characteristics. The laboratory study has identified Young’s modulus of 3.3 N/m2 and Poisson’s ratio of 0.278 to be most optimum for dry-mix concrete. Meanwhile, based on various robustness tests, the i-Block was found to possess the most suitable mechanical properties for interlocking block damper. Geometrical aspects of the i-Block were fixed at internal dimensions of 190 mm (length) x 60 mm (width) x 90 mm (height) with varying water depth, dw in the range of 0 mm to 80 mm. In the dynamics tests, resonant Transmissibility’s ratio plot approaches were used to compare the control sample with different dw. The responses of sine-sweep resonant test have shown the increasing damping values which were compared by simulation and empirical calculation. It was found that natural frequencies, fn obtained from the test were considerably matching the numerical simulation and empirical calculation. Interestingly, a small portion of water at 5 mm dw was sufficient to increase the damping ratio of the overall performances. In the seismic simulation, the Northridge, El Centro and Loma Prieta ground motion were numerically simulated by Ansys software. The peak ground base shears to displacement hysteresis on structural responses have been reduced by 19%, 26% and 35% for Northridge, El Centro and Loma Prieta’s earthquakes respectively. Meanwhile, effective performances were observed at the top floor level in relation to the mass of lower water contents to overall structure mass ratio requirement. Therefore, i-Block can be used to provide damping and reduce responses to building from earthquake disasters

Analytical and Numerical Approaches on the Stiffness of Magnetorheological Fluid Filled Spring

A solid mechanical spring generally exhibits uniform stiffness. This thesis studies a mechanical spring filled with magnetorheological (MR) fluid to achieve controllable stiffness. The hollow spring filled with MR fluid is subjected to a controlled magnetic field in order to change the viscosity of the MR fluid and thereby to change the overall stiffness of the spring. MR fluid is considered as a Bingham viscoplastic linear material in the mathematical model. The goal of this research is to study the feasibility of such spring system by analytically and numerically computing the effects of MR fluid on the overall spring stiffness. For this purpose, spring mechanics and MR fluid behavior are studied to increase the accuracy of the analytical analysis. Numerical simulations are also performed to generate some assumptions, which simplify calculations in the analytical part of the analysis. The accuracy of the present analytical approach is validated by comparing the results to previously known experimental results. Overall stiffness variations of the spring, calculated through the developed equations, are also discussed for different spring designs. Simulation of a helical hollow spring with an annular cross section filled with MR fluid is performed using ANSYS by means of two-way Fluid-Structural Interaction (FSI). The simulation shows that MR fluid effect is capable of controlling the stiffness of the spring in some ranges

Numerical Analysis of the Dynamic Responses of Multistory Structures Equipped with Tuned Liquid Dampers Considering Fluid-Structure Interactions

Aims: The paper analyzes the effectiveness of tuned liquid damper in controlling the vibration of high rise building. The new contribution is considering the fluid-structure interaction of a water tank as a Tuned Liquid Dampers (TLD). Background: Currently, buildings are being built higher and higher, which requires TLDs to be larger as well. Therefore, the fluid pressure acting on the tank wall is more significant. In previous studies of liquid sloshing in TLDs, researchers simply ignored the effect of liquid pressure acting on the tank walls by making the assumption that the tanks are rigid. Currently, the failure of a tank because of FSI occurs regularly, so this phenomenon cannot be ignored when designing the tanks in general and TLDs in particular. Objective: To investigate the thickness of the tank wall affect to the TLD mechanism. Method: Numerical method was used for this research. Results: A TLD could be easy to design; however one could not bypass the fluid-structure interaction by assuming the tank wall is rigid. Conclusion: This kind of damper is very good to mitigate the dynamic response of structrure

Hybrid Active Vibration Control in Wind Turbine Towers

Due to the demand for renewable and clean energy sources, the generation of electricity from wind farms has become a reality in Brazil. The central unit of energy generation in these farms are the wind turbines composed of tower, nacelle, and blades. Reduction in mass and material is always desirable in these units due to the final cost impact on a wind farm consisting of several units. The main external excitation source in these systems is the wind, or the system itself, as in the case of possible imbalance. The design of the support tower and foundations must take into account quasi-static stresses as well as the varying and transient stresses the system may be exposed in the service life, which could lead to fracture or fatigue problems. Minimizing the mass of these structures and keeping their vibration levels at acceptable values is a difficult task that can be achieved by controlling vibration either passively (with Dynamic Vibration Absorbers, DVA) or actively with actuators. This paper proposes to investigate the active vibration control for wind turbine systems with hybrid active vibration control.

Magnetic Fields to Enhance Tuned Liquid Damper Performance for Vibration Control: A Review

Tuned Liquid Dampers (TLDs) are dissipative devices whose distinguished features like low cost in installation and maintenance or their multidirectional and multifrequency application to new and already existing structures make them an attractive damping option. Their working principle is similar to that of a Tuned Mass Damper but in this case the relative movement comes from a fluid that provides with mass, damping and stiffness. Moreover, TLDs can mitigate both horizontal and vertical vibrations. All these make TLDs worth deeply studying. TLD utilization in civil vibration control arose in the 1980s. From early years, different improvements have been implemented to achieve a better performance. Some of these modifications include passive variations in the geometry or the fluid. The use of smart materials applied on TLDs has also been of great interest since the 1990s and comprehends different configurations in which magnetic fields are used to passively or semi-actively improve the TLD performance. A lack of review is detected in this field. For this reason, a state-of-the-art review is presented in this paper. Its aim is to help researchers find a thorough, up-to-date classification of the different possibilities, configurations, numerical evaluation, materials used and also found limitations and future development in the application of magnetic fields on TLDs

Vibration suppression of offshore wind turbine foundations using tuned liquid column dampers and tuned mass dampers

Highly dynamic nature of the applied loads on flexible and lightly damped offshore wind turbine (OWT) foundations affects the lifetime and serviceability of the system. In this study, the excessive vibration responses of OWTs are minimized using tuned mass dampers (TMD) and tuned liquid column dampers (TLCD). Due to high efficiency of TLCDs and TMDs for certain loading conditions, a combined TLCD-TMD is also utilized to improve the overall performance in a wide range of loading conditions. First, a parametric study was performed that highlights the sensitivity of these structural control devices. The effect of two devices on fixed offshore wind turbine foundations for the benchmark 5MW NREL turbine in various loading patterns was investigated. Then, the model was subjected to stochastically generated wind loading in operational, parked, startup, and shutdown conditions. The results suggest that the standard deviation of the dynamic responses can be greatly reduced with all structural control devices. However, TMDs are more efficient in operational conditions, whereas TLCDs show better performances in parked conditions. This highlights the possibility and efficiency of a combined TLCD-TMD system in which the dynamic responses are minimized efficiently in a wider selection of loading conditions

Experimental and numerical studies on tuned liquid damper

Current trends in the construction industry demands taller and lighter structures, which are also more flexible and having quite a low damping value. This increases failure possibilities and also, problems from the serviceability point of view. Several techniques are available today to minimize the vibration of the structure, out of which concept of using of TLD is a newer one. The tuned liquid damper (TLD) is a liquid filled tank which uses liquid sloshing action to dampen the oscillations of a structure. They are cost effective and low maintenance dynamic vibration absorbers that are being used in flexible and lightly damped structures. A numerical algorithm was developed to investigate the response of the frame model, fitted with a TLD. A nonlinear TLD model was considered. A total of five loading conditions was applied at the base of the structure. First one was a sinusoidal loading corresponding to the resonance condition with the fundamental frequency of the structure, second one was corresponding to compatible time history as per spectra of IS-1893 (Part -1): 2002 for 5% damping at rocky soil and rest three were corresponding to time histories of past earthquake such as El Centro Earthquake record , Sanfranscisco Earthquake and Colianga Earthquake. A series of experimental tests are conducted on a SDOF structure-tuned liquid damper systems to evaluate their performance under harmonic excitation.The effect of the different parameters such as frequency ratio, depth ratio and mass ratio on the behavior has been studied. The effectiveness of the TLD was calculated in terms of percentage of reduction of amplitude of displacements of the structure

Application of Tuned Liquid Damper for Controlling Structural Vibration

Current trends in construction industry demands taller and lighter structures, which are also more flexible and having quite low damping value. This increases failure possibilities and also, problems from serviceability point of view. Several techniques are available today to minimize the vibration of the structure, out of which concept of using of TLD is a newer one. This study was made to study the effectiveness of using TLD for controlling vibration of structure. A numerical algorithm was developed to investigate the response of the frame model, fitted with a TLD. A linear TLD model was considered. A total of six loading conditions were applied at the base of the structure. First one was a sinusoidal loading corresponding to the resonance condition with the fundamental frequency of the structure, second one was corresponding to compatible time history as per spectra of IS-1894 (Part -1):2002 for 5% damping at rocky soil and rest four were corresponding to time histories of past earthquake such as 1940 El Centro Earthquake record (PGA = 0.313g), 1994 North Ridge Loading (PGA = 1.78g), 1971 Sanfernando Earthquake (PGA = 1.23g), 1989 Loma Prieta Earthquake (PGA = 0.59g). A ten storey and two bay structure was considered for the study. The effectiveness of the TLD was calculated in terms of amplitude of displacements at top storey of the structure. From the study it was found that, TLD can effectively used to control the vibration of the structure. TLD was more effective when it is placed at the top storey of the structure. Only TLD which were properly tuned to natural frequency of structure was more effective in controlling the vibration. The damping effect of TLD is sharply decreases with mistuning of TLD

Optimum tuning parameters of tuned mass dampers for vibration control of irregular highrise building structures

Tall buildings have become increasingly one-of-a-kind signature structures that are often irregular in plan and elevation with complicated dynamic behavior. Vibration control of irregular highrise building structures using a recently developed tuned mass dampers (TMD), the bidirectional TMD (BTMD), is investigated. A key issue for effective implementation of a TMD is the determination of their tuning parameters. Eight different sets of equations for tuning the parameters of TMDs are investigated using a 5-story building with plan and elevation irregularity, and a 15-story and a 20-story building with plan irregularity subjected to seismic loading. Appropriate equations are recommended for building structures with a fundamental period of vibrations of greater than one second