Research On Deformation Mechanisms Of Web Girders During Ship Collision And Grounding And Crashworthiness Of FPSO Side Structures

Ship collision and grounding is one of the major threats for the ships and offshore structures, and such accidents can lead to casualties, economical loss and environmental pollution. Ship web girders, including longitudinal girders, floors, web frames and so on, play an important role in ship structure performance and they can absorb a large portion of impact energy during ship collision and grounding accidents. Thus, it is of great importance to pay attention to the deformation mechanisms of web girders.In the thesis, the deformation mechanisms of web girders during ship collision and grounding are studied by the simplified analytical method and the non-linear finite element method. Furthermore, the crashworthiness of FPSO side structures subjected to collision by a rigid bulbous bow is investigated. The main work includes: 1. The existing methods for analyzing the internal mechanics of ship collision and grounding are introduced, and the basic theory of the simplified analytical method is expressed in detail. Moreover, a review of the previous researches on ship collision and grounding is presented. 2. The structural deformation characteristics of ship web girders are investigated and a new deformation model is proposed for web girders subjected to in-plane concentrated load. With the plastic mechanism analysis to the new model, the expressions for resistance and internal energy of web girders are obtained and verified by previous experiments and numerical simulations. 3. The behavior of ship bottom floor plating during grounding over seabed obstacle with large contact surface is explored through plastic mechanism analysis, and the formulae for resistances and internal energy of ship floor plating are derived and verified by numerical simulations. 4. A simplified analytical method is proposed for rapidly predicting responses of FPSO side structures in case of being struck by a ship with rigid bulbous bow. The numerical simulations are conducted to verify the proposed analytical method.The results and conclusions obtained in this thesis can contribute to the rapid and reliable assessment of the structural damage during ship collision and grounding accidents as well as structural design considering ship crashworthiness in the preliminary design stage.