Theory And Its Applications Of Ship Dynamic Responses To Non-contact Underwater Explosions

A warship is not doubt in the situation during a war to encounter weapon attacks and to sustain the resulting damage. A contact explosion may usually cause structural damage of the ship, and thus induce parasitic shock damage of the equipments nearby on-board of the ship. A non-contact explosion near a ship although does not break the ship hull in most cases, usually produces shock damage of on-board equipments to relatively large extent. After the second world war, all the missions completed by a warship are fully relied on the operations of the shipboard mechanical and electronic marine device and systems, which are generally more frail than the ship hull in suffering from shock loadings. Evidently, extensive research on the damage effects of a ship arising from non-contact underwater explosions, as well as research on protect design of the shipboard equipments against the shock environment is of great importance in improving the survivability and battle capacity of the ship. The major research areas of a ship against non-contact underwater explosion include four sectors, namely, (1) the characteristics of fluid field disturbed by an underwater explosion (loadings of underwater explosion); (2) the analysis of transient fluid-structure interactions, and the corresponding dynamic responses of the ship; (3) safety assessment of the ship structure undertaking the elastic-plastic dynamic responses; and (4) determination of the shock environment imposed on the shipboard equipments, and evaluation of shock protection design. Obviously, theoretical research, experimental validation, and application experiences are all required to achieve the goal of each of these sectors. The present thesis is to describe the results of the effort made by the author towards a systematic research on the above-mentioned four sectors, mainly focusing on the theories and numerical prediction methods, rather than the damage protection techniques.The fluid loadings of underwater explosion excite the dynamic responses of the ship. No reasonable responses of the ship to underwater explosion may be predicted without correct description of the fluid loadings. By employing Cole's classical theory of bubble dynamics, the motion of bubble produced by the underwater explosion and the corresponding bubble pulsating pressure are calculated. A profile function of the shock wave and its parameters are determined according to the principle of wave profile similitude and the equality of impulses. Finally an analytic formula is derived to simulate the whole time history of the pressure fromthe front shock wave to the bubble pulsation, representing the fluid loadings of the underwater explosion. In this formula, included are the effects of the explosion weight, distance, depth and the measuring site on the fluid loadings. The comparisons of the results predicted by this formula, and those given by Cole's theory for the explosions with different explosion weight (l~1000kg) in different explosion depth (12~150m), show that this formula presents satisfactory precision, and can be employed for engineering predictions of the underwater explosion loadings.Design of a ship against explosion requires the theory of ship dynamic responses to the explosion. This is used to predict the structural damage, as well as the excitation of the foundation to the shipboard equipment concerned. The latter is referred to as the shock environment of the shipboard equipment. It is well known that the coupled interactions between the ship hull and the surrounding fluid field of explosion give rise great influence to both the fluid loadings over the structural wetted surface and the responses of the hull. Jt is the coupling effect that provides the major difficulties in the underwater explosion induced dynamic responses of the ship structure. The second order doubly asymptotic approximation method (DDA2) has been commonly employed in the world to deal with the coupling effect. However, the existing DAA methods although successful in tackling the interaction between the f...