Ground effect modeling and dynamic response analysis of a subsea autonomous underwater vehicle near seabed with terrain

Overcoming the disturbance caused by hydrodynamic ground effect (GE) has become a significant challenge for subsea autonomous underwater vehicles (AUVs) operating in proximity to the seabed. However, previous research has paid less attention to the influence of terrain-induced GE and its impact on the dynamic response of AUVs. This paper aims to develop a mathematical model of the GE acting on AUVs. First, data on the hydrodynamic forces induced by the GE are collected through computational fluid dynamics simulations. Then, the GE-induced lift force and pitch moment coefficients are fitted as functions of the altitude and horizontal position using radial basis functions. Furthermore, the proposed model is integrated into dynamic simulations of an AUV with a nested proportional-integral-derivative controller to analyze the performance of the AUV during depth tracking in the presence of GE. The result indicates that the nonlinear effect of the terrain is negligible when the nondimensional horizontal position |x/L|>1, while sharp changes in forces and moments occur when the AUV enters and leaves the nonlinear GE region (−0.5<x/L < 0.75). When x/L = 0.375, the depth error peaks, and the pitch angle reaches its maximum positive value, corresponding to the highest collision risk. Sudden changes in hydrodynamic disturbances and control hysteresis are the primary threats to the security of subsea AUVs near complex terrains. In addition, the proposed method reduces computation time by 75% compared to the conventional interpolation method during the dynamic simulation. This study provides foundational support for the control of subsea AUVs, enhancing their stability and safety.