Numerical study on multiphase evolution and molten pool dynamics of underwater wet laser welding in shallow water environment

Abstract

Underwater wet laser welding (UWLW) is a promising and labor-saving in-situ repair technique in aquatic environments, which simplifies the arduous dismantling and transportation processes of repairing underwater equipment on land. However, the thermo-physical mechanism during UWLW is still unclear. This study presents, for the first time, a thermal multi-phase flow model to study the heat transfer, fluid dynamics, and phase transitions involved in the UWLW process at shallow water column depths (water depth ≤ 4 mm). A dual-cone volumetric heat source model considering the laser energy distribution in both the water and metal is proposed. The driving forces, including gravity, surface tension, and the water/metal vapor recoil pressure are taken into account. The simulated weld profiles are in good agreement with the experimental results. The results indicate that in the UWLW process, laser heating creates a water keyhole, forming a localized dry region (LDR) above the molten pool. The LDR isolates the water from the molten pool and protects the laser-metal interactions, thereby making the welding environment similar to that of in air laser welding (IALW). Due to the water evaporation, the upper rear and sides of the molten pool during the UWLW pocessess a higher cooling rate compared to the IALW case, resulting in a higher temperature gradient and smaller molten pool dimensions. The results contribute to a better understanding of the complex interactions in UWLW process.