A CFD study of the effects of the hull materials on the hydrodynamic characteristics of an autonomous underwater helicopter

Abstract

The hull material of an autonomous underwater helicopter (AUH) strongly influences its descent behavior and maneuverability. Numerical computations have been conducted to study the influences of hull materials during the diving of the AUH. This study employs a coupled computational fluid dynamics (CFD)—six-degrees-of-freedom (6DOF) framework to quantify how variations in hull material density modify AUH hydrodynamic characteristics during dive maneuvers. Time-resolved simulations were conducted to produce the pressure field, velocity, and resistance force histories, which were subsequently analyzed with the vehicle's trajectory and attitude responses. The results show that the diving motion of AUH is affected by the mass of the hull of AUH generated by the density of the hull material, which causes the pressure difference between the bow and aft of the AUH. As more time passes, the pressure gradient on the surfaces of AUH is changed by the motion of AUH. The velocity, pitch angle, and resistance force accelerate rapidly in the initial stage before reaching their maximum values. An increase in the input density of hull material leads to a higher migration velocity due to stronger negative buoyancy effects. Forces and pitch angle time histories reveal clear links between material-dependent hydrodynamics and maneuvering characteristics, suggesting tangible trade-offs between mass vehicle and resistance force. The use of carbon fiber reduces the resistance force by approximately 10 times compared to that of a titanium alloy. The pitch angle is only half that observed when using the aluminum alloy. This provides an approach that helps reduce energy consumption under operating conditions. The proposed CFD–6DOF approach provides a practical, physics-based pathway to inform material selection and hull design for next-generation AUHs.