Experimental study on the auto-parametric internal resonance of a frame structure excited by water vortex-induced vibration in the flume

A small external excitation can trigger a strong auto -parametric internal resonance response in underwater structure. Currently, research on auto -parametric internal resonance primarily relies on theoretical methods and experimental approaches involving the simulation of water flow forces using vibrators. To more realistically reflect the auto -parametric internal resonance of structures in water, this study investigates the phenomenon of auto -parametric internal resonance of a Gamma -shaped frame structure induced by vortex -induced vibration in a laboratory flume. The results indicate that the auto -parametric internal resonance can be excited by water flow in the flume and the Gamma -shaped frame structure is more prone to experience normal resonance than auto -parametric internal resonance. However, the vibration intensity caused by auto -parametric internal resonance is significantly greater than that of normal resonance. The range of h / L (the ratio of water depth to the length of the vertical beam) for auto -parametric internal resonance in both the clamped -pined joint system (CPJS) and the pined -pined joint system (PPJS) is 0.307 - 0.364, but the flow velocity range for auto -parametric internal resonance in CPJS is broader than that in PPJS. When h/L is 0.307, the reduced velocity Ur ranges for the autoparametric internal resonance of CPJS and PPJS are 4.839 - 5.375 and 4.904 - 5.256, respectively. When h/L is 0.364, the Ur ranges for the auto -parametric internal resonance of CPJS and PPJS are 4.587 - 4.742 and 4.507 - 4.660, respectively.