The naval ship has to ensure the safety from the enemy attack and damages so that it must be able to accomplish a given task. Like this ability of the naval ship is expressed in ability of the security for the survivability, and the survivability especially can be expressed the relationship of susceptibility, vulnerability and recoverability. Surface naval ship is easily noticeable by the enemy and moreover there are many attack weapons to surface naval ship. Therefore, it is important for modern naval ships, especially combat naval ships, to establish countermeasure of vulnerability for survivability. In this study, The author reviewed the developing procedure for the technique of the naval ships structures considering survivability and described the basic design concept, analysis method and so on.
It is known that the countermeasure of vulnerability is to establish the double hull structure, box girder, blast hardened bulkhead, protection wall against fragments and so on, and it must be decided within possible design conditions. Among these methods, it is known that the installation of box girder and blast hardened bulkhead is the one of the most economical and efficient method. In order to design naval ship considering survivability, it is demanded that designers should establish the reasonable attack scenarios, which generally are divided into external and internal explosions to the ship. Explosion may induce local damage as well as global collapse to the ship. Therefore possible damaged should be realistically estimated in the design stage.
The general underwater explosion problem begins with an explosive charge of a certain size and material located at a depth below the free surface of the water surrounding it. The water is assumed to behave as a compressible fluid that is incapable of supporting significant tension. The ship is on the free surface of the water, and depending on the location of the explosive relative to the ship, The important result of the explosion are the ship's early and late time response, however it is important to first understand the phenomena of a generic underwater explosion. In this thesis, the author studied the method of the naval ship design and analysis against underwater explosion.
The numerical simulation of collision and explosion etc. have achieved collision analysis and complex analysis of structure-fluid interaction problem was begun to achieve in code of LS-DYNA, MSC/DYTRAN etc.. that is explicit hydrocode. There is ALE (Arbitrary Lagrangian-Eulerian) technique by representative analysis technique of structure-fluid interaction problem, and it can be applied that explosive and air can be modeled with fluid element and hull structures can be modeled with structure element. In this thesis, the author used ALE technique to simulate explosion analysis and investigated survival capability of damaged naval ships.
Fragment protection concepts are discussed covering materials, concepts and objectives. The purpose of fragment protection material is to stop or slow down a threat projectile such that any resulting system deactivation is acceptable. Typical ship hull and deckhouse external plating is insufficient to stop most threat projectiles, thus requiring additional armor. In this thesis, the author recommend that once threat weapon characteristics are defined, an iterative analysis approach as outlined be conducted until a satisfactory design is achieved.