International Shipbuilding Progress

The character of the ship structure and the loadings encountered in the design of ships poses a special problem of plate instability. A semianalytical method has been proposed in the paper to analyse the stability of ship plating and allied plated structures. The method is general and can be used to study the buckling of plates having any boundary and loading conditions, as well as for isotropic, orthotropic and variable thickness plates. It is simple and economic. Rectangular plates having different end conditions and loadings have been analysed. Excellent accuracy has been obtained.

Recent evidence has shown that there can be significant changes in transverse static stability with forward speed for fast round bilge displacement hull forms leading to lateral instability in extreme cases. Preliminary measurements have been made of the pressure distribution at two stations on a typical round bilge hull form in both the stable and unstable regimes. The results correlated with the observed instability phenomenon and showed that in general the change in righting moment was largely related to changes in the buoyancy forces due to wave formation. The results also showed that on the two sections investigated the dynamic pressures exhibited a net downward force on the hull.

The work described is part of a programme exploring the utility of digital signal-processing techniques for studying certain aspects of the behaviour of water-waves. When such studies are undertaken in a closed wave-tank reflections from the boundaries can be troublesome. To this end a cepstral analysis has been attempted on wave-height measurements to locate and assess these reflections. The auto-regressive power-spectral estimate has been used to obtain the cepstrum with some success and the results are compared with those obtained by more conventional data processing methods.