3-D Flight Performance Simulation of a Liquid-Filled Quadrotor

The modeling of a quadrotor with complex internal or external loads is rather important and difficult in terms of ensuring accurate trajectory tracking and strong robustness. This paper mainly studies the dynamics performance of a liquid-filled quadrotor in a 3-D maneuvering flight environment. The non-inertial smoothed particle hydrodynamics (NI-SPH) method is adopted for the precise modeling of the liquid. Derivations for the rigid dynamics model of the quadrotor based on Newton-Euler formulation are also conducted. A multi-scale time stepping iteration method is introduced here for the fluid-structure interaction (FSI) iteration framework. This work enforces the quadrotor's 3-D commanded trajectory and simulates the dynamics performance of the coupled system. Three different types of loads, empty load, constant load, and sloshing load, are systematically compared. Results show that the quadrotor with a sloshing load usually has a higher overshoot compared with the other two cases. The trajectory tracking error in the vertical direction is much smaller than those in horizontal directions. Moreover, the quadrotor with an onboard load damped much faster when it stops to hover, which is because of the gravity angular stiffness. Sloshing effect deteriorates the position and attitude tracking accuracy, which leads to the fluctuation in the speeds of the UAV rotors. The sloshing forces in horizontal and vertical directions are around 20% and 5% of the weight of the whole liquid. These results help to gain a better understanding of the sloshing behaviors and could enlighten researches on slosh suppression methods in future.