Numerical Research On Near-field Underwater Explosion Loads And Its Damage On Surface Ship

In recent years,precision guidance technology has developed rapidly and is widely used in naval combat equipment.The probability of precision guidance weapons such as torpedoes and missiles hitting targets has greatly increased.As a result,the probability of surface ships and submarines encountering near-field underwater explosions in real sea battles varies with the increase.Related research has become the forefront and hotspot of domestic and foreign research.In this paper,we study two main near-field underwater explosion conditions encountered by surface ships during actual naval battles.Which includes shock damage characteristics of two typical side-type ship section structures in the near-side underwater explosion and near-field underwater explosion at the bottom of the ship.The near-field underwater explosion shock wave,bubble pulsation,bubble jet load and the effects of fluid-structure coupling damage on the marine structure near the explosion center are investigated.Firstly,LS-DYNA built-in ALE algorithm is used to calculate the propagation of underwater explosion shock wave in the flow field,and compared with the empirical formula.Then the shock response of air-backed plate and water-backed plate are studied for the underwater explosion shock wave of small equivalent explosive.Furthermore,we simulate the damage process of stiffened plates under near-field underwater explosion loads,and compare with experiments to verify the feasibility and accuracy of ALE algorithm in dealing with near-field underwater explosion problem.Next,the dynamic behavior of large-scale bubbles produced by the underwater explosion of large equivalent explosives under the combined influence of near-free surface,free surface and vertical rigid wall surface is studied to explore the effect of vertical rigid wall on the dynamic behavior of bubble,which provides reference for the characteristics of the bubble load of near-field underwater explosion.we develop the Runge-Kutta Discontinuous Galerkin(RKDG)two-phase flow numerical model,and then simulate the interaction between reflected shock wave and air bubble after the near-field underwater explosion shock wave propagates to the structure surface.Which lays solid foundation for the following research on the complex section models and the damage characteristics of the whole ship under the near-field underwater explosion loadsA measurement model of the anti-explosion performance of the ship section is proposed,and the damage characteristics of two typical side-style sections under near-field underwater explosion loads are compared.The damage and deformation comparison of single and double side sections are carried out from the breach and large plastic deformation respectively.It is concluded that the double side tank section structure has the better anti-explosion and anti-detonation performance due to the side inner panel and the sideboard stringer and rib reinforcement structures.Then the double-sided side tank section is taken as the research object to study the energy absorption of its main structures and shock environment of equipment under different near-field underwater explosion conditions.Finally,the whole process of shock damage under the combined action of shock wave,bubble pulsation and bubble jet load in the near-field underwater explosion of the ship is studied.According to the characteristics of the ship during different time intervals,it is divided into four phases:shock wave,bubble pulsation expansion,bubble pulsation contraction,and bubble jet The impact response,stress-strain distribution,and other aspects are used to investigate the impact damage characteristics of the ship.The coupling of local damage and total strength of the ship is analyzed,shock waves and bubble pulse loads in the early stage of near-field underwater explosion can cause initial damage to surface ship,and the bubble pulsation load causes the ship to do whipping motion and cracks in the bottom structure of the ship during the pulsation contraction phase,weakening the total strength of the ship.Then the bubble collapse jet load causes further damage to the damaged ship structure,causing the ship breaks at the bow,which completely lose vitality.