Implications for Underwater Shock Response of Adopting Simplified Structural Styles in Warships

Over the last two decades there has been increasing interest among naval ship designers to adopt design style elements, standards and practices from commercial shipbuilding. Notable among this is a transition from the highly complex structural styles prevalent during the Cold War to simpler, more readily produced structure. It is generally presumed that this will reduce ship procurement costs, but may also have an effect on operational characteristics, including vulnerability to hostile action. Many naval weapon systems employ shock from underwater explosions as their damaging mechanism. In severe cases shock can cause catastrophic loss of watertight integrity, but in even moderate cases of shock the resulting acceleration environment inside the ship can damage or destroy vital equipment. The research presented in this thesis attempted to quantify the effect of adopting simpler structural styles upon this damaging acceleration environment. A number of different frigate structural models were specifically designed, using different structural styles but to meet the same design strength criteria. These models were subjected to simulated underwater explosions using Fluid Structure Interaction Finite Element Analysis techniques and the resulting motions at likely equipment mounting points computed. Results are presented in the form of comparative shock response spectra and also compared against existing shock response prediction techniques. This thesis concludes that the adoption of certain simplified structural styles in warships can lead to significantly elevated shock response motions, compared to those expected from a ship with a more typical naval structural style. In particular, the adoption of reducing the number of stiffeners, or adopting lower cost stiffener profiles, may result in motions increased by a degree significant enough that they should be taken into account when specifying the shock tolerance or mounting arrangements for on-board equipment

Vulnerability of a low-cost combatant converted from a commercial ship

This paper describes a vulnerability study comparing two patrol combatants; one corvette designed in a conventional military style and one cost-expedient conversion of an off-the-shelf Platform Supply Vessel (PSV). Both ships were designed to carry the same payload and perform the same role. The Unit Procurement Cost (UPC) and annual fuel cost were estimated for each ship. A comparative study was then conducted which examined the vulnerability of each of five top-level functional systems in each design to attack by a series of generic threat weapons, ranging from shoulder-fired rockets to very large anti-ship missiles (ASM), considering damage by kinetic impact, blast and fragmentation. The results demonstrated that the converted PSV exhibited considerably better system vulnerability. The authors attribute the system vulnerability result as being primarily due to the much larger size and high void space fraction of the PSV, compared to the Corvette. It is likely that the Corvette may exhibit significantly better susceptibility and recoverability characteristics than the PSV, due to a combination of lower signatures, reduced size and better distributed damage control equipment