Study On Diffraction Characteristics And Pressure Distribution Of Cylindrical Shell Under Underwater Shock Wave

Predicting the hydrodynamic field around structure to underwater explosion is greatly complicated by the explosion of a high explosive,propagation of shock wave,complex fluid-structure interaction phenomena.Submarine is an important part of modern naval warfare and its cylindrical structure is special.Besides reflection wave and transmission wave,the diffracted shock wave on the back of cylindrical shell can't be ignored.In this paper,the ALE fluid-solid coupling method is used to simulate the pressure field during the interaction between shock wave and cylindrical shell structure.The formation process and characteristics of reflected shock wave,transmitted shock wave and diffracted shock wave are obtained.The numerical results are compared with the experimental and theoretical values to verify the reliability of the results.The evolution of the pressure field around the structure and the shock response characteristics of the structure under different structural forms,different interlayer media,different detonation distances and different water depths are analyzed.Firstly,this paper starts with the flat plate structure,the accuracy of the numerical simulation method used in this paper is checked by the theoretical values of reflected and transmitted waves calculated by Taylor plate theory.Comparing the numerical simulation nephogram of the diffraction field around the cylindrical shell with the numerical solution and the experimental photograph,a good consistency is found.Secondly,numerical simulations are carried out for single-layer and double-layer cylindrical shells under three experimental conditions.The numerical results are compared with the experimental results,which verifies the reliability of the conclusions in the above chapters.Then,the shock wave load characteristics of different structures(single-layer plate,double-layer plate,cylindrical shell),different inter-shell media and different detonation distances are studied.The shock wave pressure time-history curves which can reflect the reflection peak,transmission peak,diffraction peak and cavitation characteristics are obtained The influence factors of reflection,transmission and diffraction coefficient and the response characteristics of displacement and velocity of the structure are analyzed.Incident pressure and reflection pressure act on the front of cylindrical shell,cavitation zone appears near the shell.The back of a cylindrical shell is firstly subjected to radiation pressure and then to the superposition of diffracted shock waves.On this basis,the interaction process between double cylindrical shells and shock waves is further studied.The fluid pressure field generated by impact loads considering system response under different shell media,different detonation distances and different water depths is simulated.The displacement of two shells under impact load is shown by two-dimensional normal displacement diagram.Pressure state of flow field is reflected by pressure nephogram,'time-space' plots of the stress time history curve and 'time-space' plots of the stress.The diffraction coefficient of the flow field around the shell is less than 1,and that of the back is the smallest.The peak pressure of the diffracted shock wave is small and the pulse width is large.