Study On Damage Mechanism In Ship Underwater Explosion And Structure Anti-Shock

In modern warfare, the warship facing increasingly serious threat, for the range, accuracy and combat power of anti-warship weapons have greatly improved. For the safety and vitality of a warship, the dynamic response under the action of underwater explosion (UNDEX) shock waves is an important research aspect in the field of ship structural dynamics. In order to enhance the anti-shock capability, we need to complete at least three complex tasks: The first is to study the explosive load, understanding the distribution and propagation characteristics of explosion shock loading. The second is to analyze and find out the structure dynamic response and damage mechanism of warship subjected to UNDEX loading. Finally, investigate effective and practical measures to enhance the capability of anti-explosion.According to the explosion source, it can be divided into aerial explosion and underwater explosions; According to the relative position between the Explosive to hull, it can be divided into contact explosion and non-contact explosion. The explosion was a chemical reaction of charge in a very short time, with a severe energy release. Highly nonlinear dynamic responses of Ship structure subjected to UNDEX loading involve the failure of material. While fluid-structure interaction problems in ship explosion in the calculation cannot be ignored. So it was no possible to get a precise mathematical model to solve this problem. At present the feasible methods have two, experiment and numerical simulation. Now the numerical simulation of ship UNDEX has become possible, with the rapid development of Numerical simulation technology. On the other hand, because the huge cost of explosion experiment, can’t take a series of experiments to investigate the rule of the structure dynamic responses. So numerical simulation has become one of the main instruments in this research field. Based on the solving technique of explicit non-linear finite element method, numerical simulation theory was summarized, the key technologies of the calculation was sum up, the nonlinear dynamic responses of ship structure subjected to UNDEX loading has been investigated by using finite element modeling code MSC.DYTRAN. According to the investigation in this dissertation, the major work and conclusions are listed as follows:The ship structure was meshed by the lagrangian CQUAD4 shell elements, the fluid was described by eulerian solid elements, the structure-fluid coupling algorithm was employ to transfer load between ship and explosion field. In many coupling algorithm, ALE coupling has a maximum calculation efficiency, profit from without rebuilding coupling interface, because the lagrangian and eulerian element have a same node at the interface. Considering the failure of material, the critical failure strain, which change according to element size, can be set by numerical simulation benchmarks tensile test.Based on the CJ detonation assumptions and JWL equation of state, the pressure of detonation products can be precise calculated. The“programmed burn”technique was used to model the detonation of explosive. A slab of explosive detonated at one end was calculated, the numerical simulation result show agreement with the Experiment.Transient dynamic response of clamped rectangular plates subjected to non-contact underwater explosion loading was analyzed based on the elaborate on the propagation, decadent, impulse of UNDEX shock wave, pulsation of bubble pressure. The local structure deformation and rupture was caused by Shock wave with the characteristics huge Peak pressure, short loading time. Warship local structure subjected to Bubble pulse pressure and fluid Static pressure has a similar Mechanics behavior. However, in some special circumstances, bubble pulse pressure will lead to ship whipping, due to the bubble pressure contains enormous energy and pulse frequency close to the natural frequency of ship.Based on the principle of fluid-structure interaction, should to take fluid and ship structure as a total dynamics system to study, in considering reflection and diffraction of fluid field, the conclusion can be reached that, in shock wave loading conditions, the pressure is a function of incident pressure and the structural deformation sparse wave, as described by Eq. (6.18). In bubble pulse pressure loading conditions, the pressure decided to incident pressure and additional water quality, as described by Eq. (6.19). On the basis of the numerical simulation method, the dynamic response of the component of a warship subjected to underwater explosion shock waves is analyzed, and the deformation damage mode of different components and the absorptive features of energy of the plastic deformation are investigated. Furthermore, the mutual relation between the explosive and relative position of the vessel is presented by the comparison of the structural damage mode. It can be drawn as follows: As for the ship subjected to underwater explosion shock waves, the outer plate, transversal frame and bulkhead mainly undertake the impact loads.Ship grid plate is the basic unit of structure, at the loading of UNDEX shock wave, the calculated results indicate that the tensile tearing at the support is the main failure mode of the plate under shock loading without considering the material defects of plate, the maximum central plastic deformation depended on the product of the peak pressure and the decay constant, the maximum central acceleration of plate and the peak pressure has a linear relationship.Tube widely used anti-shock due to the tube deformation with a long trip, structure acceleration stability, and the supply manufacturers. The loading carrying Capacity and energy absorption properties of tube has been investigated. The limit load of tube is proportional to the thickness of the wall, and inversely proportional to the radius.Based on the investigation of energy absorption properties of tube, the response of a novel sandwich structure design under blasting loading was numerically investigated. The sandwich structure uses thin walled tube as the core. the sandwich structure has excellent ability of anti-shock according to the numerical results.