Optimal design of anti sway inner cavity structure of agricultural UAV pesticide tank

Abstract: Aiming at the problem of agricultural UAV (unmanned aerial vehicle) instability caused by the shaking of liquid in the pesticide tank, the tank was optimally designed by arranging horizontal and vertical grille in the empty tank. The grilles were mainly to increase damping, thereby weakening the vibration of the liquid. The horizontal grille contained a number of gaps ranging from 0 to 7, and the vertical grille contained a number of gaps ranging from 0 to 10. The displacement amplitude of the liquid center relative to the tank in the excitation direction and the impact force of liquid on the side walls of the tank were taken as the evaluation conditions. At 0-0.55 s, the acceleration of the uniformly accelerated rectilinear motion was 2 m/s2, the speed remained constant at 0.55-1.1 s, and at 1.10 s, the speed was reduced to 0. The simulation condition was to simulate the acceleration and rapid stop of the UAV. The VOF (volume of fluid) model and k-epsilon model in Fluent software were used to simulate the anti sway effect of horizontal and vertical damping grille with 10%, 30%, 50%, 70% and 90% liquid filling rate, 30%, 50%, 70% arranged height and different shapes. The simulation results showed that the peak value of the liquid velocity at the vertical direction in the rectangular empty box appeared in the area near the wall of the box, and the peak value of the liquid velocity in the excitation direction appeared in the central area of the box; and 2 kinds of damping grilles both reduced the variation of the gravity center of the sloshing liquid in the excitation direction. In the case of liquid impact on the tank, the horizontal damping grille would increase the liquid impact on the tank when the depth of liquid filling and the arrangement of horizontal grille overlapped, in other cases, the horizontal grille could reduce the impact force of the liquid to the tank, and the impact force tended to be stable when the slot number was 6. The vertical damping grille could effectively reduce the impact force of the liquid to the tank under every condition of the liquid filling rate, and the impact force would be stable when the number of the grooves was 9. In order to verify the reliability of the simulation analysis, the liquid sloshing test platform was designed. The rail length of the testing platform is 1.2 m, and a three-phase AC (alternating current) motor is used to drive the liquid box. A color high-speed camera with 1 000 fps was used to collect sequential images of the liquid in the box. According to the simulation result, a tank with double horizontal grille and vertical grille was made and a bench test was carried out. An empty box and an optimized box were contrasted in the test, and both boxes were tested at 10%, 30%, 50%, 70% and 90% liquid filling depth. The tests were conducted with 10 repetitions. The test result was in agreement with the simulation result, which confirmed that the optimized tank had a better inhibitory effect on liquid sloshing. Compared with the empty tank, after optimization of the grilles, the sway time of the waving liquid was reduced significantly. The optimized box can play a better effect of calming down the waving liquid. The result will be helpful for enhancing the stability of the UAV in case of emergency braking of hitting by the wind.