One of the key issues for the design of membrane type Liquid Natural Gas (LNG) ships is to predict sloshing induced local loads for insulation systems, especially when a design concept or type of operation deviates significantly from present experience. Examples are a large increase in ship size or operation in unrestricted partially filled conditions, which have not been previously envisaged. Extensive experimental and theoretical studies have been carried out by MARINTEK and Lloyd's Register to investigate sloshing impact loads inside prismatic membrane tanks. Different tank geometries have been used. In the tests, high sloshing pressures were measured and the temporal and spatial distributions of high peak pressure were predicted. Principally, a practical procedure for assessment of 'design loads' for the membrane systems has been developed.
In addition to sloshing, increases in global loads due to bow and stern slamming can be another important factor to consider in large LNG ship design. Previous experimental studies indicate that the maximum midship bending moment can increase by 30–150% as a result of slamming induced whipping. Slamming also induces large vertical accelerations at the bow and stern. Good design of the bow and stern geometry can provide effective reduction of slamming loads and whipping responses.
