Research Of Failure Criterion Of Offshore Structural Collision

Public awareness and technical progress are setting new standards for safety at sea at the present time. The structural ability to withstand high accidental loads has been highly concerned. In order to avoid threatening life or the environment, ship structures have to be designed to survive under such kind of loads.The definition of failure criterion plays an important role in collision FEM simulation, the traditional failure criterion-Von Mises strain criterion is limitational on account of its theoretical defect. This paper aimed at exploring a new failure criterion, namely thickness strain & major strain criterion. By simulating a lateral loaded beam, it is evident that the application of V-M strain criterion could not simulate the failure process, while the new failure criterion was reasonable and realistic. According to the principle of energy equivalence, the micro element with void and micro crack was investigated for its mechanical response and characteristics of energy absorption. In order to avoid the influence on the simulation by different mesh sizes, a new meshing method was used for all simulations. In this method, the ratio of minimum length of an element to its thickness was chose as a constant. Using this method during simulation can not only improve the solution accuracy, but also standardize meshing process and conducive to popularizing the new failure criterion.Based on the mentioned theory and methods, three typical experimental results were used for defining the new failure criterion. Three different simulations were performed using nonlinear finite element software-LS-DYNA. Compared with the true force-displacement curve, the suitable thickness strain was found as the failure criterion. Then, by using the principle of energy equivalence, the suitable failure major strain could be calculated. At last, as a typical application example, a collision scenario between a semi-platform and supply ship was investigated based on the new failure criterion combination, and its dissipated energy was calculated. Combined with GL collision rules, the critical collision velocity of the semi-platform was calculated.