Research On Damage Characteristics And Similarity Law Of Pallet Structure Under Large Pulse Width Load Of Underwater Explosion

The deformation and failure mode of the hull structure through underwater impact load is not only related to the structural form and material parameters,but also closely related to the input load characteristics.In the case of maximum equivalent explosion source,the pulse width of the underwater large pulse width shock wave load can reach hundreds of times that of the traditional charge,and different damage modes will be produced during the coupling process with the underwater structure.Carrying out theoretical and experimental research on the damage mechanism and impact response of ship structures and scaled models under different underwater explosion loads plays an important role in improving the protection performance of ships.Therefore,it is particularly important to study the similar conversion relationship between the prototype and the model,and to realize the use of scaled model tests to predict the dynamic response process of the actual ship test.In this thesis,the method of combining numerical simulation and experiment is mainly used to study the characteristics of large pulse width load of underwater explosion and the damage characteristics of the typical plate structure of ships.Based on the characteristics of the shock wave,a distortion model and corresponding prediction coefficients are proposed and verified.Finally,a model similarity verification method based on nonlinear dynamic response analysis is proposed and verified.The main tasks of the thesis are:(1)In view of the study of the underwater propagation law of large pulse width loads,such as the distribution law of peak value and pulse width,a simulation model of the underwater explosion shock wave of the spherical charge was established,and the error of the shock wave peak value was compared with the empirical formula,and the model was verified Validity;Then select cylindrical and conical drug packets with different parameters,analyze the difference in shock wave propagation form of different drug packets,and compare and analyze the arrival time,peak pressure and duration at different measuring points,and the shock wave of the coneshaped charge on the side of the detonating end has obvious waveform characteristics of large pulse width.(2)In order to study the coupling law between the large pulse width load and the surface of the structure,the damage characteristics of the plate frame structure caused by the underwater large pulse width load are studied through the methods of numerical simulation and model experiment,and the conventional shock wave and the large pulse are analyzed and compared.The similarities and differences of the damage to the structure caused by the wide load are analyzed,and the influence of the waveform characteristics on the damage of the plate frame structure under different shock wave pulse width time is analyzed.The large pulse width load obtained by changing the shape of the drug packet can increase the damage to the structure to a certain extent,and the pulse width and peak value have a key effect on the damage of the structure.(3)Aiming at the damage and distortion model of large pulse width load structure,according to the π theorem and dimensional analysis,the underwater explosion similarity criterion that takes into account the peak pulse width of shock wave and the structure size is derived.The similarity criterion is transformed by the traditional spherical charge,and the distortion model with different reduction ratios for the structure and explosion source is obtained,and the validity of the prediction coefficient is verified.Next,considering the impact of the shock wave waveform characteristics on the structure,the impact of pulse width and peak distortion on the prototype result is proposed,and the prediction correction method is given.Either the distortion model based on the traditional spherical dynamite or the distortion model considering the shock wave characteristics can predict the shock response of the prototype well.(4)A nonlinear statistic Hurst exponent is proposed to characterize the nonlinear relationship in the impact response of the plate frame under water explosion,and the impact factors and different charges on the plate frame structure acceleration,velocity and displacement are discussed.The Hurst exponents of similar systems are demonstrated,and it is deduced that the Hurst exponents of the responses of similar systems remain equal,and verified based on the full geometric similarity and distortion model in the article.