Research On Structure Reliability Of Ship Hull Subjected To Underwater Explosion

At being attacked by the underwater weapons, in the non-contact explosion cases, the warships structure will be destructed by the explosion shock-wave as well as the bubble pulsating load. The research of hull structure's ant detonation in the non-contact explosion situation has been of great importance to the countries that have power for navy. This paper first introduce the basic theory of structure reliability, developing a single variable decomposition method based on the design point to compute structural reliability, followed by study the shock-wave produced by underwater explosion, the bubble pulsation theory as well as the interaction of bubble and structure when the bubble pulsation and then analyzing the reliability of the warships structures under explosive loads based on the developed structure reliability method, and analyzing the reliability of the hull ultimate longitudinal strength under explosive loads also.In order to meet the demand for high accuracy reliability computational method in the actual project, a high accuracy reliability computational method is obtained by proposing higher order approximate through a single variable decomposition in the design point of the structure function. The results of examples calculations indicated that the results of the method developed in this paper and direct Monte Carlo simulation method are very close; the method developed in this paper has a higher precision compared to the FORM method in the situation of the approximately same number of computation times, explaining that the method developed in this paper relative to the FORM method can more precise approach the structure function with high efficiency, can be used to calculate the reliability of high precision engineering problems.The related elementary theory of shock-wave as well as the bubble pulsation caused by the underwater non-contact explosion is introduced. Expression of peak pressure of non-contact underwater explosion shock wave is derived using the energy density formula. The ships board protective structures are composed by the stiffened plates etc. The research of the response of stiffened plate structure under the explosion loads have been the important contents of the research of warships anti-detonation. This paper has established the simplification mathematical model of the underwater explosion shock wave. Considered the fluid-solid coupling between the water body and stiffened plates, the shock-wave load formula has been given. By the theoretical analysis of the dynamic response of the stiffened plate structure under the underwater non-contact explosion shock-wave load, the analytic expression of the dynamic response is obtained. Using the first time surmounting destruction model of the stochastic process level traversing theory, the dynamic reliability analysis of ships board stiffened plates under the explosion load is done.Taking the potential profile flow theory as the foundation, bubble pulsation model of underwater non-contact explosion has established, and the numerical simulation computation of underwater explosion bubble pulsating flow field had been carried on considered the energy loss between each pulsation. By the contrastive analysis of the computed result and the experimental data, we can see that the theoretical calculates for the calculation of the bubble pulsation's cycle and the bubble pulsation's speed are in good agreement with the actual situation, the error between the bubble pulsating pressure and the actual value is slightly big, but still in the project permission scope. The results had indicated that the model of bubble pulsation established in this paper is correct. From the view of conservation of momentum, the relative movement to the rectangular plate of the bubble at the same time of the pulsing has analyzed when existing clamped rectangular plate in water, deriving the law of relative movement equation, at the same time, the dynamic response of the stiffened plate structure under the underwater explosion bubble pulsating load is been researched, as well as its reliability.Regarding the overall longitudinal strength research, formerly literature did very little work on reliability analysis of ships overall longitudinal strength under extreme load status such as suffering explosion load. Considering the residual strength after partial injury of hull structure caused by the underwater explosion shock wave, applying the method developed in this paper, the reliability analysis of warships overall longitudinal strength under the underwater explosion bubble additional loads, the still water loads and wave loads has carried on. A variety of typical conditions according to different explosion distance is calculated, the corresponding conclusions were drawn:Compared with the normal loading states'computed results, we can see that the underwater explosion loads are the primary loads effected warships overall ultimate longitudinal strength reliability. The calculation results of three kinds working conditions considering the partial injury of hull structure caused by the underwater explosion shock wave show that, the reliable indicators of ship hull structures considering underwater explosion bubble additional loads are clear lower than the reliable indicators which not considering the bubble additional loads, indicating that the bubble additional loads must be in consideration for ship structural design in the extreme loading conditions. In the calculation of the reliability of overall ultimate longitudinal strength of warship subjected to the bubble additional loads, we must not ignore the impact of wave loads, considering the combined action of the bubble additional loads and the wave load.