## 1 Introduction  
Gate vibration is a common phenomenon in water resource and hydropower projects. The vibration is motivated by the hydrodynamic loads, and the flow field around the gate also produces changes in turn, which forms the fluid-structure interaction between the fluid and gate structure [1]. Strong fluid-structure interactions can cause gate structure deformation or even destruction, posing a serious threat to the safety and stability of the water conservancy project. [PERSON] [2] divided the flow-induced vibration into three categories based on its induced mechanism, and gate vibrations jointly induced by flow instability and structure feedback mechanisms are the most common. [PERSON] [3] and [PERSON] [4], through a physical model test, pointed out that the main cause of gate vibration was the vortex formed by the destruction of the free shear layer at the gate bottom. [PERSON] [5, 6] posited that gate vibration was caused by downstream vortex resonance and pointed out that the slope of lift coefficient curve was taken as a criterion by which to judge the gate dynamic stability. [PERSON] and [PERSON] [7] reckoned that the fluid feedback force induced by gate vibration mainly included two aspects: pressure pulsation caused by flow and alternating excitation derived from the vortex at the gate bottom. [PERSON] et al. [8] expounded that the curved gate vibration belonged to the self-excited vibration in the small gate opening. [PERSON] et al. [9] simplified the curved gate into the plane gate, established load relations through the potential flow theory, and explored the influence of additional mass and wave-transmitted energy on the gate vibration. Based on physical model tests, [PERSON] et al. [10] monitored the gate vibration and obtained the characteristics of the flow field by particle imaging technology. The results showed that the smaller was the gate opening height and the larger was the flow discharge, the more obvious was the gate vibration, which indicated that the discharge had a direct influence on the gate vibration. The physical experiment of [PERSON]'s [6] was inversely simulated by the numerical method [11]. It was found that when the ratio between the opening height and the gate width was 0.8, the gate vibration intensity reached its maximum. The simulation result showed that the horizontal vibration was stronger than the vertical vibration at the fixed gate opening, and a similar result was obtained from their physical model test [12]. Although considerable research has been devoted to gate vibration in fixed gate openings, less attention has been paid to it in operation processes. Compared with the fixed gate opening, the gate constraint condition has changed. For some water conservancy projects in the southwest of China, the water depth in front of the emergency gate is relatively high and flow velocity has exceeded 18-20 m/s. The fluid-structure interaction between the gate and fluid makes the hydrodynamic loads change, which alters the holding force and finally affects the selection of the hoist capacity. Failure of gate-lifting and gate-closing has occurred in the past [13]. The current studies are to examine whether gates can be closed safely and quickly to ensure safe operation. There are still some problems for the calculation of hoist capacity in the design stage, such as the hydrodynamic loads and the effect of gate vibration in operation processes. Few studies have been conducted to investigate the relationship between gate vibration and holding force in operation processes. [PERSON] et al. [12] examined the relationship between the holding force and gate vibration through the physical model test. Nevertheless, it is impossible to accurately obtain the relationship between the hydrodynamic loads and flow discharge with gate vibration. Thus, the purpose of this study is to establish a fluid-structure interaction simulation and to explore the characteristics related to gate operation processes. The study is divided into six parts.