基于VOF-Simulink的跨介质无人机仿真分析

Simulation Analysis of a Cross-Medium UAV Based on VOF-Simulink

摘要: 针对跨介质无人机水面起飞过程中浮力补偿衰减、水面效应变化以及旋翼升力需求动态调整等问题，本文建立了结合Fluent VOF多相流仿真与MATLAB/Simulink动力学建模的联合分析方法。首先，基于VOF模型对无人机在纯空气、近水面和远水面三种工况下的流场分布与升力响应进行数值模拟，分析自由液面对旋翼气动特性的影响；随后，将CFD仿真得到的升力数据引入Simulink，构建考虑吃水深度变化、浮力衰减和高度相关升力修正的水面连续起飞动力学模型。结果表明，近水面工况下旋翼稳态升力约为10.0 N，相较纯空气工况下的8.8 N提高约13.6%；当桨盘距水面高度与桨叶半径之比H/R大于0.8时，水面效应对升力的影响明显减弱。Simulink仿真进一步表明，起飞初期静浮力能够抵消部分重力并提高有效升力裕度，随着机体逐渐离水，浮力补偿减小，旋翼需承担的净升力需求增加，系统加速度呈下降趋势。研究结果揭示了跨介质无人机水面起飞阶段升力、浮力与水面效应之间的耦合机理，可为后续自主起降控制、抗扰动控制律设计和起飞过程参数优化提供参考。

Abstract: To address buoyancy compensation decay, water-surface effect variation, and the dynamic rotor lift demand during water-surface takeoff of a cross-medium UAV, this study establishes a coupled analysis method that integrates Fluent VOF multiphase-flow simulation with MATLAB/Simulink dynamic modeling. A VOF model is first used to simulate the flow-field distribution and lift response under pure-air, near-water-surface, and far-water-surface conditions, so as to evaluate the influence of the free surface on rotor aerodynamic performance. The lift data obtained from the CFD simulations are then introduced into Simulink to build a continuous water-surface takeoff model that accounts for draft variation, buoyancy decay, and height-dependent lift correction. The results show that the steady rotor lift near the water surface is approximately 10.0 N, which is about 13.6% higher than the pure-air value of 8.8 N. When the ratio between the rotor disk height above the water surface and the blade radius, H/R, exceeds 0.8, the influence of the water-surface effect is significantly weakened. The Simulink results further indicate that static buoyancy offsets part of the vehicle weight during the initial takeoff stage and increases the effective lift margin. As the vehicle leaves the water, buoyancy compensation decreases, the net lift demand borne by the rotors increases, and the acceleration gradually declines. The proposed approach reveals the coupled mechanism among lift, buoyancy, and water-surface effect during cross-medium takeoff, and provides a reference for autonomous takeoff control, disturbance-rejection control design, and parameter optimization.