Abstract
Thruster configuration dictates the hydrodynamic stability of underwater welding vehicles, yet standard design protocols rarely penalize undesired forces and moments that compromise precision. This study proposes a multi-index performance evaluation framework that integrates propulsion capability and disturbance minimization into a unified metric. Key indices include the Propulsion Index (PI), Balance Improvement Index (BI), and a final Comprehensive Performance Index (CPI) for multi-scenario ranking. Through CFD-based simulations, a three-stage optimization is conducted, comparing layout schemes, installation angles (30°/45°/60°), and arm lengths (0.75×/1.0×/1.5×). Results show that Layout I achieves a CPI of 0.8592, which is 1.28% higher than that of Layout II. The 45° installation-angle scheme obtains the highest CPI of 0.8592, corresponding to improvements of 14.15% and 16.31% over the 30° and 60° schemes, respectively. For the arm-length optimization, the original arm length also achieves the highest CPI of 0.8592, outperforming the 0.75× and 1.5× arm-length schemes by 6.96% and 2.52%, respectively. These results confirm that the symmetric Layout I with 45° inclined thrusters and the original arm length provides the best overall compromise between task-direction propulsion and hydrodynamic disturbance suppression.