Study On Fatigue Strength Of Flexible Connectors Of Very Large Floating Structures

The large scale of the super large floating body(VLFS)is huge and thus VLFS need to be divided connected in a certain way according to functional requirements.The connector is the weakest part in the whole system.Due to long time operation of VLFS at sea,environmental cyclic loads induced by wind,wave and flow may exceed the fatigue limit of connector structures which will cause structural collapse of connectors,release and collision of modules.It will also lead to disastrous consequences.In order to ensure the operational safety of VLFS,it is necessary to accurately evaluate the fatigue strength of connectors.In this paper,fatigue strength study is conducted on a flexible articulated connector using theory method,numerical simulation and model test.The main research contents are shown as below:(1)The basic concept and connection mode of modules of VLFS are outlined.Several structural types of flexible connectors are introduced.A hinge connector consisting of nylon sandwich and a pipe shaft strengthened by circular frames is analyzed and the main parameters,structural type and meber material are given.(2)Connector load and module motion are calculated using rigid module flexible connector(RMFC)model on a VLFS with transverse pontoons and shallow draft.The influence of connector stiffness and wave angle on the motion of floating body and connector load are studied.The reason for the peak value of longitudinal load of connectors with different stiffness is analyzed.(3)Model test of fatigue strength of the flexible connector is conducted and hot spot stress,crack propagation and fatigue life are measured.Structural stress of the flexible connector is also calculated by nonlinear finite element method considering the effect of contact,flexible sandwich and hole.Evaluation method of fatigue strength of the flexible connector is also given based on theory of S-N curve and crack propagation separately.Comparative analysis is also conducted with test results.(4)The stress of the flexible connector under different wave angles and frequencies is calculated by nonlinear finite element method and the stress transfer function of dangerous nodes is extracted.The fatigue spectrum of the flexible connector in actual sea state is analyzed by theory of S-N curve and crack propagation respectively.The influence of nylon sandwich on the fatigue life of steel part of the connector is also analyzed.