Simulation Research On Damage Of Semi-submersible Platform Under Underwater Explosion Wave And Fragment

The semi-submersible platform plays an extremely important role in the oil and gas exploration process,but it does not rule out the destruction of the platform by torpedoes in terrorism and naval warfare.The underwater explosion of the torpedo not only generates high-temperature and high-pressure shock wave acting on the structure,but also has the high-speed fragment to penetrate and destroy the target structure.Therefore,the semi-submersible platform is studied under the action of underwater explosion shock wave,fragment and the combination of the shock wave and fragment to provide a basis for designing impact resistant structures.The paper mainly studies the damage of structure under the action of underwater explosion shock wave,fragment and the combination of the shock wave and fragment by the numerical simulation.The correctness of the numerical model is verified by theoretical formula and literature experimental data.(1)The pressure decay process of underwater non-contact explosion shock wave is analyzed.Secondly,the deformation law of the platform under different explosive positions is studied.The deformation of the explosive surface is the largest,and the deformation energy is also the largest.The shock wave is mainly transmitted to the internal structure through the outer plate in the platform.Thirdly,the dynamic response of the floating plate under different impulsive factors is discussed.The relationship between the deformation of the plate and impulsive factor,the specific impulse,the peak value of the shock wave are analyzed.The formula is obtained by fitting the acceleration and the peak value of the shock wave.Then the longitudinal and vertical impact responses of the platform are discussed,and the relative safety areas of the platform are evaluated at both ends of the platform and above the waterline.(2)The damage mechanism of the broken edge of platform under the underwater contact explosion is analyzed,and the size of the damaged area is calculated.(3)As for the problem that the fragment penetrates the ballast tank,the process of the fragment penetrating the ballast tank goes through four stages: penetration into the front plate,water attenuation,cavity evolution and penetration.Secondly,the influence of the initial velocity,size,thickness and the presence or absence of liquid factors on the attenuation of the fragment speed and the deformation law of the plate are discussed.The variation law of the shock wave pressure,impulse and the size of the fracture is analyzed,providing the basis for designing impact resistant structures.(4)The method of using the full restart in the ANSYS/LS-DYNA program is introduced.The deformation,the energy characteristics and impact response are compared under the action of underwater explosion shock wave,fragment and the combination of the shock wave and fragment,showing that the material element stress is greater than the simple linear superposition value.The fracture is obviously increased and the rib is torn.The absorbed energy under the action of underwater explosion shock wave and fragment is greater than the energy under the action of underwater explosion shock wave alone.The acceleration and the speed peak increase for the existence of broken mouth.(5)Based on the above,the optimization of the impact-resistant structure is carried out.Based on the traditional single-layer and double-layer structure,three types of sandwich structures are proposed.The anti-explosion performance and anti-penetration performance of the structure are summarized.The cylindrical shell sandwich structure has good performance of impact resistant.