Research On Structural Response Of Multi-Module Flexible Connectors For Very Large Floating Structures

Due to the large dimensions and displacement of VLFS, the hull is devided into severalmodules connected by inter-module connectors, which allow for some relative motions betweenmodules, in order to reduce structural loads. The connectors are subject to huge forces and largeelastic deformations, which are very complex, so that the connection system is doomed to be theweakness of the whole system. The structural configuration, connecting method, dynamiccharacteristics, failure mode and strength estimation are key issues of the connection systemdesign. This thesis mainly carries out research on flexible connectors, dynamic characteristicsand fatigue strength estimation of inter-module connectors. The main contents are as follows:1. Firstly, the basic concept of VLFS, module connecting method and several flexibleconnectors are introduced. The design principle of flexible connectors is discussed, and a newball concept connector is analyzed, including its structural configuration and connecting process.2. Secondly, RMFC model theory are presented to give out the expression of the connectorforces and kinematic equation of floating structures in frequency domain, based on the kinematictheory of multiple floating structures， including dynamical theory and three-dimensionalpotential flow theory. Sesam/Wadam is adopted to calculate hydrodynamic forces of threedifferent models. The effects of connector stiffness, wave angle, sea state and number of moduleson body motion and connector loads are analyzed. The design parameters and the results of themodels are compared，also shallow water effect is analyzed to study dynamic characteristics ofconnectors of very large floating structures under shallow draft.3. At last, Patran/Nastran is adopted to calculate stress forces of connectors under differentwave angles and different frequencies, and the stresses RAO of dangerous spots of connectorsare extracted. After that, the S-N curve method and Fracture Mechanics method are adopted toassess the fatigue life of connectors, and the two different methods are compared. Seven differentS-N curves are adopted to calculate the fatigue life of connectors, and the contribution of waveangle and short term sea state to fatigue damage are analyzed. Single stage Paris law andtwo-stage Paris law are adopted to calculate the fatigue life of connectors with initial crack ofthirty different sets of sizes and shapes, and the effect of initial crack on fatigue life and crackgrowth is studied.