Optimization design and experimental validation of a vortex-based suction cup for a climbing AUV

Abstract

This paper presents a climbing AUV, which is able to work in both swimming and climbing modes. The key issue in the design of a climbing robot is the choice of a reliable adhesion technique. Due to its great performance as regards payload, motion speed, simple system kinematics and gripping over a wide range of surfaces, a vortex-based suction cup is adopted to provide adhesion effect for the climbing motion of the AUV. Since the vortex-based suction cup is the core component of the vehicle, this paper mainly focuses on the structural and operational optimization of the suction cup by both Computational Fluid Dynamics (CFD) simulations and experimental validation. The proposed CFD simulation method is firstly verified by uncertainty study. The uncertainty analysis results indicate that the proposed simulation model and settings are reliable as reasonable agreements are found when comparing the computed results from varied grid size, iteration number, and time step cases. The total numerical uncertainties of the CFD simulation method for adhesion force and torque prediction are 1.50% and 1.46% of the average simulated values, respectively. In the CFD simulations, we investigate the effects of some key structural and operational parameters on the adhesion performance of the suction cup, including the vane number of impeller, the shape of cup shell, the adhesion gap (distance between cup bottom and wall surface), and the rotation rate of impeller. It can be concluded that more rotation rate of impeller can generate more adhesion force and more torque; smaller adhesion gap can produce more adhesion force but less torque; cup wall with inclined angle can increase the adhesion force and decrease the torque; the adhesion performance of the suction cup is less sensitive to the vane number of the impeller. CFD simulation results provide the basic design guidelines for the development of suction cup prototype. In the experiments, a specially designed testing platform is built up to validate and compare the performance of a set of suction cup prototypes, varied by different impeller and cup shell combinations. We compare the CFD simulation and experiment results of a 10-vane suction cup at a range of rotation rate conditions. The reasons of the discrepancy between CFD simulation and experiment results are mainly due to the open-loop control of the drive motor and the underestimate of the rotation rate in the experiments. The experimental results indicate that the effects of the structural and operational parameters on the generated adhesion performance are very complicated, and the effect of the structural parameters on the adhesion performance is influenced by the operational parameters, while the rotation rate and the adhesion gap play the key roles.