Reliability Research And Nonlinear Response Of Ship Structure Subjected To Explosions

The ship was inevitable to be attecked by the arms in service. The way about reducing the damage and enhancing the life of ship were payed more attention to by the people concerned. So, it was very important to research the local destroy of ship under explosions, residual intensity and capsizing probability of damaged ship, the reliability assessment of damaged ship.The damage of thin steel plate subjected to contact explosions was a very complex nonlinear process. The initial crevasse had influence upon the whole damage process, so the critical damage study was significant on the anti-explosion of ship structure and design of projectile. In virtue of the wave solution of plastic dynamic response of plate and the dynamic fracture theory, the critical blasting charge was derived theoretically when onset of initial circumferential crack namely critical damage happened in thin plate subjected to explosions. And the theoretical expression of critical deformation of plate was also obtained. Also the method was carried out for calculation the crevasse radius by the energy theory. The theoretical calculated results through an example were compared with the experiment in the published literature and numerical simulation results, they were almost coincided. It could be seen that the method of this paper could perfectly solve the dynamic fracture of thin plate under contact explosions, which provides references for engineering.The destruction of ship defensive structure subjected to underwater contact explosions was studied with the methods of numerical simulation and experiment research. The multi-layer defensive structure under explosions was studied through experiments. Then, adopting the ALE method in LS-DYNA, the numerical method of multi-coupled surfaces was presented, which could be used to solve the problem of multi-cabin and multi-medium under explosions. The research was also done in the same condition using the numerical method, then the shape and size of crevasse and the peak value of pressure were obtained, which were consistent with the result of experiment on the whole. It was indicated the numerical simulation could do research perfectly.Considering the importance of liquid cabin in defensive structure, the antiexplosion capacity of the muliti-player grillage structure was studied using the numerical method, especially the influence of liquid cabin. Then, the simulation of the dynamical response process of the multilayer defensive structure subjected to underwater contact explosions was conducted. The deformation of the model of three layers vacant cabin and two layers vacant cabin, one layer liquid cabin and the changed water level in liquid cabin was analyzed and compared with each other. The crevasse radius of plate as well as effective stress, the pressure and deformation were described. It was revealed that liquid cabin could improve the antiexplosion capacity of multilayer plate-shell structure, and reduction of the water of liquid cabin properly could not affect the antiexplosion capacity of ship defensive structure.Because of the instantaneity and destructive of explosions, complexity of stiffened plate structure of ship, the reliability investigation of structure subjected to explosions was the difficult problem. Based on Monte Carlo method, the samples of random variables were obtained, then the simulations of multilayer plate-shell structure subjected to underwater contact explosions were done by LS-DYNA, and the maximum stress of each plate was obtained. The probability distributing was reached by fitting, then the destroy probability of each plate and system were gained based on the intensity rule and the basic theory of reliability.Residual ultimate strength of damaged ship was the important index of evaluating the life of ship. By studying each kind of element's behaviour in tension and compression, considering some influencing factors, the average stress-strain curve theoreticaliy was described. Then a program of ship hull girder ultimate strength was conducted with Fortran, according to the progressive collapse theory. The numerical results of Dowling 2 and Reckling 23 showed the validity of the proposed method. Adopting importance sampling method, a reliability analysis method was presented for ship hull structure based on the hull longitudinal ultimate strength failure. The effects of location of break and heel angle on residual bearing capacity in real ship were analyzed.Considering that the ship structure was under the short-time war environment, the wind and wave excitation were modelled as random processes and underwater explosive loading as irregular but determinate load. The stochastic differential equation of ship structure was founded, the nonlinear effect of structure rolling with large amplitude was also taken into account. Based on the standard stochastic averaging method, the transient probability density function of rolling angle of the ship under radom wind and wave excition was deduced, whose rolling motion was modeled as a single-degree-of-freedom. Then, applying the impulse response method, the response history of rolling angle of the ship subjected to occasionally explosions heeling moment was derived. Finally, the response of stochastic wind and wave moment and the response of explosion-induced moments were combined rationally, the transient probability density function of the combined roll angle was obtained by using the maximum entropy method, the capsizing probability of ship subjected to radom wind and wave was reached by outcrosing rate method, and the capsizing probability of ship under combined loads was also analyzed based on the rules about capsizing.