ESTIMATION OF THE TRANSVERSE CRUSH RESISTANCE OF A SECTION OF THE T23 FRIGATE

Ocean-going vessels are very complex structures, and can have displacements ranging from hundreds to tens of thousands of tons. In the case of bulk carriers and tankers, this can be as much as half-a-million tons. When in motion, they can possess very large amounts of kinetic energy even if their velocities are small. They therefore have the potential to cause serious damage in case they are involved in a collision. Ships moving in ports or harbours often move in limited space and there is always the possibility that an accidental collision may occur, albeit at a low velocity. If either the striking or struck ship carries sensitive or hazardous materials then the consequences of a collision may be far more serious than that consisting simply of structural damage to either ship. One way of reducing potential damage to ships carrying such cargo is to restrict the travel velocities of approaching ships to some limiting values. The reliable estimation of such velocities needs as a minimum a knowledge of the crush characteristics of at least the target vessel, and preferably that of the striking vessel too. The situation addressed in this paper is one where a moored vessel, a T23 frigate, is struck normally by a similar moving vessel. It is required to estimate the crush characteristics of the struck vessel around the chosen impact location. A knowledge of the crush characteristics can then be used to derive limiting approach velocities in order to minimise damage, intrusion, etc. in the struck vessel. A three-dimensional mesh of the struck section of the moored ship has been modelled using finite elements. The implicit algorithms in LS-DYNA3D(1) were used to simulate the crushing of this ship section. The paper presents the method of analysis and the derived crush characteristic, which is then used to estimate limiting velocities for an approaching vessel