선체거더의 수중폭발 휘핑응답 해석을 위한 모델링 방법 연구

Abstract

An underwater explosion(UNDEX) interacts with the surrounding fluid in two different phases which are potentially damaging to a nearby surface ship. The first phase is a transient shock front which causes a rapid rise in the fluid velocity, and large inertial loading. It is named the shock wave which induces damage to shipboard equipments and local structure. The second phase in the explosion is a radial pulsations of the gas bubble with a duration much longer than the shock wave. The pulsations are a result of the imbalance of internal explosion product pressure and the fluid hydrostatic pressure. The bubble pulsations lead to quite significant pressure impulses on a nearby ship hull, they tend to excite the ship in heave and natural vertical vibration modes. Because the pulsation periods are often close to the two and three-noded bending vibration frequencies of a typical frigate-size warship, a near resonant condition can exist with the potential to cause large amplitude whipping displacements. These displacement in turn can overstress the hull and, in severe cases, lead to an overall hull failure. In this study, one and three dimensional whipping response analysis of a naval surface combatant of the Korean Navy subject to an UNDEX bubble pulse have been carried out. In 1-D analysis, the program 'UNDEXWHIP' developed by Korea Institute of Machinery and Materials has been used. This program is based on the thin-walled Timoshenko beam theory and the modal analysis method using 'wetted' vertical vibratory modes of the hull-girder. In 3-D analysis, a commercial program 'LS-DYNA/USA' has been used. Through comparison of result obtained by between 1-D and 3-D analysis, it has been confirmed that 1-D analysis results are in good agreement with 3-D analysis ones.