Water exit model and takeoff control for a morphing cross-media vehicle

The water exit of a morphing cross-media vehicle is a nonlinear, multi-coupled, physical process with strong disturbance. It severely affects the subsequent flight of the vehicle after leaving the water. Because of the short duration, it requires very fast response time from the controller. To overcome the shortcomings of existing research on the water exit process of morphing cross-media vehicles, a possible solution of uncontrolled water exit and controlled takeoff is proposed. A water exit dynamic model is established after properly simplifying the complexity and unpredictability of the underwater environment, in consideration of changing variables, such as buoyancy, wetted area, and added mass. A numerical simulation is conducted to prove the validity of the model. Furthermore, an improved sliding-mode controller is designed to ensure that the cross-media vehicle reaches the target conditions after leaving the water and to prevent the vehicle falling back into the water. Simulation results demonstrate the reasonability and feasibility of the proposed solution. These conclusions can provide valuable reference information for solving control problems in morphing cross-media vehicles.