Numerical model of fluid-structure interaction for water tower analysis of vibrations

Abstract

This paper deals with the aspects of vibration analysis of 3D numerical water tower models with the explicitly generated 3D finite element (FE) solid fluid model that simulates the fluid-structure interaction (FSI). The development and implementation of the 3D FE solid fluid model in modelling and analysing the system response is extremely important, both in terms of determining the impulsive and convective hydrodynamic pressure, and in terms of overall sizing of the water tower. Vibration of the water tower is calculated based on the analysis of its eigenvibrations, analysis of eigenvibrations occurring when charging and discharging the water tower reservoir (SFA - Staged Fluid Analysis), Steady-State Analysis (SSA) in the frequency domain and the analysis of the system response in the time domain (THA - Time History Analysis), followed by the transformation of the frequency domain response using the Fast Fourier Transform (FFT). The analysis of eigenvalues using the Ritz vectors (Ritz analysis) and the Power Spectral Density Analysis (PSDA) are carried out as the means of additional control and with the purpose of identifying vibration periods. The system's stiffness matrix and mass matrix are corrected using the 3D FE solid fluid model for analysing the water tower vibrations. Effects of the system's increasing vibration period are determined for the partially charged reinforced concrete (RC) water tower reservoir, given the strong action of the fluid mass that is excited for convective hydrodynamic action (sloshing) due to the water tower dimensions and the amount of fluid contained in the reservoir in this case.