Influence of structural damping and fluid compressibility on harmonic vibrations in concrete gravity dam

Abstract

In this research, the coupled fluid-structure forced vibrations (harmonic load) of the Koyna gravity dam are studied. Using the finite element method (FEM), the influence of structural damping and fluid compressibility are studied for different reservoir dimensions of the dam. The numerical approach is done through the U-P formulation (structure displacement and pressure for fluid). Thus, the spectral response of structural displacements and of hydrodynamic pressures were investigated with different structural damping rates, both considering incompressible and compressible fluids. With analyses, the greater the effect of the structure's damping, the lower the displacement and the hydrodynamic pressure amplitudes. The structural damping has the same effect tendency in both incompressible and compressible fluids. Furthermore, for the incompressible fluid, the coupled modes are not infuenced by the length of the reservoir, there are no acoustic modes identifed and the mass modes are predominantly identifed. With the compressible fluid, the analysis of the dominant modes showed that the fundamental mode is not altered by the length of the reservoir, but from the second mode onwards, each cavity geometry predominates in the vibration, and it is necessary to evaluate the frequency range of the structure and the fluid separately. Therefore, the harmonic numerical analysis of the present study contributes with innovative results of the Koyna dam and in the analysis of the effects involved in Fluid-Structure Interaction (FSI) simulations of other problems related to Dam-Reservoir Interaction (DRI).

Keywords:
Finite Element Method; dam-reservoir interaction; fluid-structure interaction