Enhancing tunability of liquid storage tanks to function as deep tuned liquid dampers by use of a submerged stretched membrane

Abstract

This is a study on a deep, liquid-containing tank, such as an overhead water tank on a building, with a vertically submerged stretched membrane (SSM). Here, instead of the sloshing mode, which can become detuned and also affords a low damper mass ratio, the impulsive liquid–membrane interacting system is designed to serve as a dynamic vibration absorber. The requirement of tuning the frequency of the impulsive liquid–membrane interacting system to the structural frequency can be achieved without any imposition on the tank dimensions, which are generally fixed from the tank's functional requirements. The system frequency would remain unchanged so long the membrane would remain submerged below a minimum liquid depth, thereby allowing fluctuation of liquid level within a prescribed range of the tank depth. The formulation for obtaining the frequency of the impulsive liquid–membrane interacting system is derived, using the sub-domain partition approach. It is seen that through suitable adjustment of the design parameters of the membrane, the proposed tank damper can be tuned to both short-period and to long-period structures. Further, the impulsive liquid mass, which otherwise has no role to play in the damping mechanism of a tuned liquid damper (TLD), is here utilized to absorb and dissipate the vibrational energy. Through a time-domain study considering recorded seismic accelerograms, the significant control effectiveness of the proposed damper system is illustrated. Further, the results obtained from the equivalent mechanical model of the structure–damper system are compared with those from a finite element analysis of the fluid–structure system in the ANSYS Workbench environment.