Hazardous modal migration of spillway radial gates during operational FSI: Beyond static resonance criteria

Abstract

Although the dynamic instability of spillway radial gates (SRGs) during operational transitions poses a critical concern in hydraulic engineering, traditional static assessments often fail to capture such transient risk. This study addresses this gap by investigating the dynamic evolution of SRG vibration modes throughout operational phases. An operational fluid-structure interaction (FSI) framework is established and benchmarked against analytical solutions to effectively capture the coupled dynamic behaviors of the integrated gate-hoist-fluid system. Numerical outcomes reveal that incorporating hydraulic hoists drastically modifies the structural boundary conditions, wherein the continuous retraction of piston rods drives a dynamic stiffness reconfiguration that modulates higher-order coupled modes. Under submergence, the FSI, governed primarily by the hydrodynamic added mass effect, systematically suppresses structural natural frequencies, particularly for modes dominated by skin plate deformation along the flow direction. Notably, the fundamental vibration frequency manifests a highly non-stationary character during gate elevation, marked by a dramatic 65% rebound in its amplitude baseline as the coupled fluid volume diminishes. Furthermore, a critical hazardous modal migration is uncovered, characterized by a dominant vibration shift fluid-sensitive bending-rotation (B-R) coupling at small openings to structural bending-twisting (B-T) coupling at larger openings, which decisively alters the system’s dynamic stability thresholds. These findings provide a theoretical foundation for unravelling operational dynamic instability mechanisms and establishing dynamic safety envelopes to secure structural integrity under non-stationary conditions.