Investigated effects of cylinder proximity on the hydrodynamic performance of axisymmetric AUV by using CFD

Abstract

1Autonomous underwater vehicles (AUVs) are widely used in confined and structure-rich underwater environments such as offshore platforms, subsea mining, and infrastructure inspection. In such conditions, hydrodynamic performance is strongly influenced by wall proximity effects, which modify resistance and flow separation, thereby affecting energy efficiency and operational safety. This study presents a numerical investigation of the hydrodynamic performance of an axisymmetric AUV operating near a cylindrical offshore structure. Commercial CFD simulations are conducted for Reynolds numbers ranging from 0.87 × 10⁶ to 3.48 × 10⁶ and clearance distances defined by the ratio h/L_A from 0.32 to 1.61. The near-wall results are systematically compared with open-water conditions. The results indicate that the resistance coefficient of the AUV remains approximately constant at 0.005 in open water. However, in near-wall operation, it increases significantly up to 64.3%, reaching values between 0.0091 and 0.0136. When h/L_A < 0.9, resistance increases sharply as the clearance decreases, whereas beyond this value, the wall effect diminishes and the resistance coefficient stabilizes. Flow field analysis reveals pronounced pressure asymmetry and enhanced flow separation in close-proximity conditions, explaining the observed resistance increase. These findings contribute to improving energy efficiency, maneuverability, and operational safety of AUVs operating near offshore structures and in confined underwater environments.