Simulation-Based Multiphysics Design and Adaptive Backstepping Control of a Dual-Propulsion Unmanned Aerial Underwater Vehicle

This study presents a simulation-based multiphysics design, modeling, and adaptive control framework for a dual-propulsion unmanned aerial underwater vehicle intended for aerial, near-surface, and fully submerged operation. The proposed platform uses four aerial rotors for flight and six underwater thrusters for submerged maneuvering, allowing medium-dependent actuation in air and water. Separate aerial and underwater six-degrees-of-freedom models are formulated and connected through a smooth altitude-dependent coordination strategy for the simplified near-surface region. Computational fluid dynamics is used to estimate submerged drag forces, while finite element analysis evaluates pressure-hull structural integrity at a depth of 20 m. At 0.2 m/s, the predicted horizontal and vertical drag forces are 1.62 N and 3.92 N, corresponding to quadratic damping coefficients of 40.5 and 98.0 N·s2/m2. The FEA results show that PMMA provides a safety factor of 7.8, with a maximum displacement of 0.53 mm under hydrostatic loading. An adaptive backstepping controller with projected gain tuning, disturbance compensation, and constrained actuator allocation is developed. MATLAB/Simulink simulations demonstrate bounded trajectory tracking under nominal conditions, 20% parametric uncertainty, modeled disturbances, and a 0.5 m/s ocean current.