Fluid-structure Interaction And Dynamic Response Of Sandwich Structure Subjected To Underwater Impulsive Loadings

The high-intensity shock wave loading generated by underwater explosions is the main threat in the ship’s service life,which can cause damage to the ship and even cause fatal damage.Due to the strong fluid-structure interaction effect,the structure subjected to underwater explosion undergoes more complicated structural response than that of the air explosion.When a naval structure is subjected to an underwater explosion load,not only the initial shock wave load must be considered,but the secondary load caused by the localized cavitation collapse is an important cause of local damage to the structure,which needs to be focused on.It is of great scientific significance and reference value to study the fluid-structure interaction effect and structural response under the underwater explosion to the design of protective structure of the naval vessels.Based on this,the dissertation studies the fluid-structure interaction and the dynamic response of the corresponding structure caused by underwater explosion impulsive loading.The main research includes:Firstly,a diffuser-type pressure shock tube was used to test the dynamic response of typical metal sandwich structure subjected to different underwater impulsive loadings.By comparing different failure modes,the effects of core,impulsive intensity and the loading area on fluid-structure interaction,the dynamic deformation and failure of the metallic sandwich structures are analyzed.The results of the study indicate that metallic sandwich structures undergo counterintuitive behavior with reverse and asymmetric deformation with large loading area,which is different from the case with a smaller loading area.The reverse and asymmetric deformation modes are related to the core and impulsive intensity,indicating the distribution of the underwater impulse during the fluid-structure interaction phase is axisymmetric.Then,the modified pressure shock tube was used to test the dynamic response of foam core structures with different core subjected to different underwater impulsive loadings and a finite element model is established.The effects of core and the impulsive intensity on the dynamic response of the sandwich structure and cavitation effect are studied.The results indicate that changing the core structure and underwater impulsive intensity has little effect on the propagation of the breaking front,while the propagation velocity of the closing front decreases with increasing underwater impulsive intensity.For a single-layer homogeneous foam core sandwich structure,the propagation velocity of the closed front increases as the strength of the core decreases.For the density graded foam core sandwich structure,changing the gradient of the core has little effect on the propagation of the closing front.Finally,a theoretical study was carried out on the dynamic response of the sandwich beam with the clamped back plate boundary subjected to underwater impulsive loading.Based on the one-dimensional impact theory,fluid-structure interaction theory and cavitation effect theory,an analytical models considering the large deformation of the structure,fluid-structure interaction effect and cavitation effect is established.Based on the theoretical analysis model,the finite element method was used to simulate and verify the accuracy of the theoretical model.