The Analysis Of The Characters Of Structural Wall Pressure Subjected To Underwater Shock Wave

As carriers of the warship survivability,ship structures are impacted directly by the underwater explosion and determine the ship’s ability to survive fundamentally. So it has long been a focus of ship protection. Accurate prediction of loading is the prerequisite of strength evaluation. So the analysis of the wall pressure characteristics of structures subjected to underwater explosions has important practical significance for the warship protection.However, there are still some limitations about the mechanism of the loading generated by explosion. This article attempts to discuss the mechanism of the blast loading on structure surface in depth. The fluid-structure interaction (FSI) issue under weak and strong shock waves has been studied by both methods of theory and numerical in this paper. The beneficial impact of fluid-structure coupling for the blast mitigation to the structure was explored with a view to provide reference for protection system design and optimization and enhance structural impact resistance.First of all,a brief overview on the basic theory of shock waves spread was presented,and the influence of different forms of equations of state on the forms of the solution of reflected waves from the walls was shown.Secondly,Taylor flat theory (backed empty) and its extended form (backed water) were applied for the contrast analysis of wall pressure,dynamic response, impulse transmission and cavitation inception of the plate subjected to underwater shock waves. A method for FSI which considers the stress wave effect of structures was given and the effectiveness of the method was validated. It was applied to plate frames, rubber -covered plates and double-layer plate filled with water. The results show that the impulse transmission of the plate frame increases, because the vertical constructions of plate frame structure constituted waveguides for stress wave propagation. Rubber layer greatly weakens the wall pressure peak, but wall pressure width becomes longer. The outer plate of double-layer plate plays a role of cutting the shock waves making the pressure peaks of inter plate decease in contrast to the outer.Thirdly, impulse transmission and cavitation inception analysis of plates was implemented for different thickness and different backing conditions of plates in compressible flow under strong shock waves, which bore different type of shock loading profiles and intensities. A fluid-structure coupling parameter which is similar to the parameter of Taylor flat theory is defined. The theoretical solutions of extremely light plate and extremely heavy plate and different impulse estimating formulas for different shock loading profiles were given. Results show that impulse transmission and cavitation inception depend on the fluid-structure coupling parameter and backing conditions. Practical estimation formula of impulse transmission matches numerical solution very well,which would be fitted to arbitrary thickness and shock intensities, and they can save a lot of time used for numerical computation.Finally, the method for FSI which considers the stress wave effect was used for a full scale plate frame of a ship to compute wall pressure and impulse transmission,obtaining that impulse transmission of the plate frame was much more than the equal-area plate. Moreover, a numerical comparison was done to the test of an existing literature, found that single-layer plate speed and double-layer plate transmission pressure of numerical results were bigger than experimental values and the rise time of transmission pressure matched well with each other.