Numerical and Experimental Study of Effects of Installing Rotatable Baffles on Characteristics of Tuned Liquid Damper (TLD) Seyed Mehdi Zahrai Associate professor, School of Civil engineering University of Tehran Tehran, Iran mzahrai@ut.ac.ir Saeed Abbasi Ph.D. candidate, School of Civil Engineering University of Tehran Tehran, Iran Sabbasi_mr@yahoo.com Abstract—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. 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. Numerical simulations, validated by experimental works, show that using these baffles result an increase in damping ratio of TLD up to 20% while without baffles the damping ratio is 3%. Frequency of sloshing of inside water increases to about 3 Hz while without baffles it is almost 1 Hz. Results show that the rate of change in damping and frequency takes place in baffles orientation between 30 to 50 degrees and 40 to 50 degrees respectively. Keywords-Tuned liquid damper (TLD), VOF method, Rotatable baffles, Passive dampers, Structural control I. INTRODUCTION The next generations of tall structures are being designed to be lighter and more flexible, making them susceptible to wind and earthquake type of excitations. Efforts to mitigate response of these structures created a new research approach named structural control [1]. Vibration control devices are categorized in passive devices, active devices, semi-active devices and hybrid devices [2]. A wide variety of active/passive control systems have been proposed and used in practice. A special case of control devices is tuned liquid damper (TLD) using a liquid (water) as the energy dissipater. TLD is a rectangular or circular tank partially filled with water. Energy dissipation in this device occurs through viscous performance, wave breaking, tank geometry and its roughness, surface contamination and so on. TLDs are categorized in two main groups: shallow and deep [3]. This is measured counting the ratio of liquid depth to tank length along with the wave propagation, if this ratio is less than 0.15, the TLD is shallow. Utilizing TLDs for structural control has been the subject of a wide variety of studies [4], [5] and [6]. Also a detailed theoretical and experimental investigation of the dynamic effects of TLDs mostly for suppressing wind effects has been presented in references [7], [8] and [9]. A conventional TLD is generally tuned to a single frequency. To overcome this limitation, the TLD usually is used to control the structural response of SDOF or semi-SDOF structures such as airport towers. Utilizing multiple TLDs with various depths of inside water and consequently distributed natural frequencies over a certain bandwidth is not practically feasible because regularly the number of tanks is large and maintenance of them is not easy, now keeping the different depths of water inside would be more difficult. II. VARIABLY TUNED LIQUID DAMPER Angular frequency of nth mode of sloshing in a container is calculated as Eq. (1) using linear theory of waves: ω n 2 = nπg L tanh ൬ nπh L ൰ (1) In which ω is angular frequency, n: mode number, g: gravity acceleration, L: length of the tank and h is depth of inside water of the tank. Linear damping is calculated via Abramson’s equation (1966) as Eq. (2): ζ f = ඨ ν f a 32 ⁄ ඥg (2) In this equation ν is fluid (water) viscosity. As it can be seen, the sloshing frequency of water inside the tank is a function of length of the tank and ω increases as L decreases and the concept of variably tuned liquid damper is based on it. In Fig. (1) the model of TLD with some standing baffles is shown. In this study the dimensions of modeled tank without baffles are as follows: L x =112 mm, L y =632 mm, h=70 mm (h is the depth of water). Baffles are installed in one third and two third of the length of the tank in y direction. When the baffles ore open (θ=0 degrees), the tank acts as a simple TLD with some obstacles. When the baffled ore closed (θ=90 degrees), the tank is divided into three equal parts each one with new length of L’ x =200 mm. The thickness of baffles in simulation is 16mm because the thickness of used acrylic panel in experimental part is 16mm. 169 2011 International Conference on Technological Advancements in Civil Engineering (ICTACE 2011) 978-1-4244-9541-2/11/$26.00 © 2011 IEEE