Optimized design and reliability of a hybrid ship hull

Sandwich panels are well known for providing high stiffness and strength with less weight than steel panels and are widely used to provide efficient structures. The past two decades have seen a tremendous increase of their use for marine applications.; The concept of hybrid hull is proposed which consists of steel boxes to resist the in-plane loads and sandwich panels to resist the lateral loads. In addition to the reduced weight, the sandwich core in the hybrid hull prevents the lateral buckling of steel. The sandwich skin separated by the core resists the bending stresses due to lateral loading.; The different theories which deal with the composite plates are described and the results for deflection and stresses are obtained. These theories are compared and appropriate formulations for deflection and stresses are chosen for the optimization analysis.; The sandwich panel materials are chosen for the skin and the core with consideration given to the joint with steel. Their advantages are highlighted over the other common alternatives.; The hybrid hull concept is applied to a medium sized ship which is chosen similar to a ship for which the safety indices are available for comparison. The major loads on any ship structure are considered for analysis. The ABS Rules and the second order strip theory are used for calculating the loads. The hybrid hull is analyzed to resist these loads.; The sandwich panel subjected to lateral loads and in-plane loads is optimized with respect to weight. Both stiffness and strength constraints are taken into account to obtain the optimized layers of skin along with the thicknesses of each skin layer and core.; Non-linear finite element analysis is performed of the half bulkhead + half bulkhead bottom hull to obtain the ultimate strength. The ultimate strength analysis reveals that the presence of core indirectly plays an important role in the compressive strength.; Reliability procedure is outlined determining the limit state equations for the overall failure and the local failure modes. The random variables of both strengths and loads are defined. The safety indices are determined using the first-order and the second-order reliability methods. Sensitivity analysis is performed for the various parameters and their relative importance is discussed. The safety indices and sensitivities are compared with those for the original ship and are found to be similar.