A conscientious investigation into the effect of Re and mass-ratio on two-degree-of-freedom vortex-induced vibrations

Abstract

Through a serious application of an overlapping mesh, vortex-induced vibration (VIV) of low-mass-rationale cylinders was computed in the range of 1.0×103<Re<2.0×104. An overlapping mesh is more controllable to deal with the dynamic mesh since there is no necessity to regenerate grids in this complete computational domain. Only boundary nodes are utilized to dispose of all steps each time. It is discovered that the cross-flow amplitudes can increase by approximately 30% in the resonance area when the in-line degree of freedom is taken into account. But the cross-flow amplitudes do not have any change outside the resonance area. In its mass ratio (m *= mass of cylinder/mass of displaced water) ranging from 1.0 to 40, the ratios of in-line amplitudes to cross-flow amplitudes decrease with the increasing m *, especially as m *<2.5, the ratios will be larger than 10%. Moreover, the phase differences between in-line displacements and cross-flow displacements also reduce as m * increases. However, the correlation coefficients between displacements at two directions are so random even a bit low. With regards to vortex mode, the ‘2S’ mode and the ‘2P’ mode are very applicable to the present work. Effect of Re is also investigated, this paper aims to prove that the ratios of amplitudes between two directions have few relations with Re, and then the relationship between relative amplitudes and mass ratios can be decoded hereof.