Bionic design of configuration of rigid wheel moving on sand and numerical analysis on its traction performance

Abstract: It is very important to enhance the wheel traction performance for improving the traveling ability of the vehicle in the loose sand circumstance. The toenail, which is the key part of ostrich foot possessing the excellent running ability on sand, was regarded as the bionic prototype. Through bionic optimization of the wheel lug structure, the rigid wheel with bionic wheel lugs moving on sand with higher traction performance was designed. A kind of lunar soil simulants was selected as the experimental loose sand material. Using the built-in language FISH and the relevant command of Discrete Element Method (DEM) software PFC2D(r), the dynamic simulation system, which was suitable for simulating the interactions between the rigid wheel with irregular structure and the loose sand material, was established. The simulation system was validated by the combination between laboratory test and DEM simulation. The interactions between the rigid wheel with bionic wheel lugs and the lunar soil simulants were simulated. The thrusts of lunar soil simulants were composed of four parts. The first part is the horizontal component forces of the tangential contact forces of the lunar soil simulant particles on the wheel outer boundary rim. The second part is the horizontal component forces of the normal contact forces of the lunar soil simulant particles on the wheel outer boundary rim after the bottom dead center. The third part is the normal contact forces of the lunar soil simulant particles on the lateral wall of the wheel active edge. The fourth part is the microscopic acting forces just like the horizontal positive component forces of the tangential contact forces. The moving wheel is subjected to the strong normal contact forces, caused by the compaction of the loads on the wheel and the cutting between the active side of the wheel rim and the lunar soil simulants. Because of the influences of the contact constitutive model characteristic of the lunar soil simulant particles, the small tangential contact forces of the lunar soil simulant particles are small. At the same time, the simulated results of the rigid wheel with bionic wheel lugs were compared with those of the rigid wheel with rectangular wheel lugs under the same simulation conditions. The simulated results showed that the bionic wheel lug presents three advantages. Firstly, the bionic wheel lug could solidify the loose lunar simulants under the moving wheel through driving the lunar simulant particles toward the bottom left part, which provided the larger adhesive forces for locomotion. In contrast, the rigid wheel with rectangle wheel lugs tended to increase the local voids by driving the lunar soil simulants toward different directions. Secondly, while entering into the lunar soil simulants, the bionic lug reduced the disturbance on the surface layer particles of the lunar soil simulants by the three typical smooth curves of the bionic lug, which caused the small angles between the bionic lug and the lunar soil simulant surface. Due to the sharp angle of the rectangular lug, the rectangle lug obviously disturbed the lunar soil simulant surface and made the lunar soil particles tend to move upward. Thirdly, comparing the rigid wheel with bionic wheel lugs to the rigid wheel with rectangle wheel lugs, the drawbar pull of the former was larger than the latter by 5.2% when the wheel slip coefficient was 50%. More lugs contacted with the lunar soil simulants in the rigid wheel with bionic wheel lugs and more contact force lines under this rigid wheel could account for the above quantitative results. This research provided a new design way to improving the tractive performance of the rigid wheels traveling in the loose sand condition.