Enhancing the Survivability of Flexibly Connected Modular Floating Structures Using a Novel Submerged Floating Mooring System

The survivability of modular floating structures operating in harsh marine environments is critical to their safe and reliable deployment. To enhance the survivability of a flexibly connected modular floating platform under extreme sea conditions, a novel submerged floating mooring system (SFMS) is proposed. The SFMS integrates a mooring system with buoyancy adjustment devices, enabling the structure to switch between surface and submerged modes in response to environmental conditions. This submergence capability facilitates rapid spatial relocation and significantly improves the floating structure’s resistance to extreme conditions while reducing operation and maintenance requirements. Numerical simulations were performed using the SESAM software to evaluate the effectiveness of the proposed SFMS under extreme sea states. Compared with the mild sea condition, the extreme sea condition increases the motion responses of modules by 89.8–197.4%, leading to excessive connector loads and potential failure risks in some steel wires of the connectors. After submergence, the motion response was reduced by 45.8–80.0%, accompanied by substantial reductions in mooring line tensions, connector loads, and vertical accelerations. These improvements effectively enhance both the structural safety and habitability of the floating platform. Furthermore, wave direction exhibits a certain influence on the performance of the submerged structure, remaining within the acceptable fluctuations. In addition, the system performance is improved generally as the submergence depth increases. Considering safety and comfort, a submergence depth of 20 m under extreme sea conditions is an appropriate selection. The findings demonstrate that adaptive submergence enabled by the proposed SFMS is a promising strategy for improving the survivability of modular floating structures in severe marine environments.