Research On The Collapse Characteristics Of Ship Structures In Waves

The external force under extreme sea conditions and ultimate load-carrying capacity of ship structures are two important aspects for safety assessment.If the subjected loads exceed the structural capacity,ship structures will collapse progressively which may cause ship wrecks or accidents.In order to research the collapse characteristics of ship structures in waves,numerical calculation and model test are combined together to research the external loads and structural response.The numerical calculation system including the fluid force and structural response is established.Three-dimensional frequency-domain method is taken to calculate the external loads in extreme sea conditions.Then the external loads are transformed to structural model for nonlinear analysis so as to obtain the progressive collapse characteristics of ship structures in waves.Besides,aluminum alloy ship model is designed considering numerical calculation results,processing technology and the condition of wave-making tank.Then,collapse test of ship model in wave-making tank is carried out to research the progressive collapse characteristics of ship structures in waves.The main works are as follows.(1)Model design.Ship model with three cabins is designed considering the numerical calculation results,the characteristics of researched ship,dimension and wave-making ability of wave-making tank.The middle cabin is key part where collapse happens and its member dimension is determined by the external loads so that the ship structures will collapse progressively in wave-making tank.(2)Establish numerical calculation system including the fluid force and structural response.The external force of ship structures in designed loads and wave conditions is calculated and the external loads at every moment are transformed into nodal force.Then the nodal force is applied to ship structures for nonlinear analysis.After calculation,the stress distribution and deformation mode of ship structures at every moment are obtained so as to reveal the progressive collapse characteristics of ship structures in waves.(3)Model test.Measuring system for model test is established.The test data of wave condition,stress distribution of classic ship section,deformation characteristics,water pressure of designated position and ship motion state at every moment are collected.With the increment of wave height,the external loads of ship structures increase gradually,and finally the ship structures collapse progressively.Ship structures are subjected to compression stress caused by longitudinal bending and local bending compression stress caused by water pressure.When wave crest moves from bow to midship gradually,ship bottom structures yield and buckle.With the increment of compression stress,neutral axis moves up.Then deck and sheer strake structures yield.When ship structures reach its ultimate strength,its load-carrying capacity decreases rapidly and structural collapse happens.