Systematic Investigation of Loads and Motions of a Bulk Carrier in Extreme Seas

Abstract

During their lifetime ships often operate in severe weather and rough sea states. To ensure survival, a precise knowledge of global and local loads is an inevitable integral part for a safe design. One of the key parameters for ship design is the vertical bending moment. Not only vertical forces but also longitudinal forces can contribute to this bending moment. As the overall effect of longitudinal forces is still not fully understood, all structural loads are investigated in detail, especially in extreme seas. Within the project “Handling Waves”, funded by the European Union, three segmented ships, equipped with force transducers, are investigated systematically at several cruising speeds and in various deterministic wave sequences to identify structural loads, i.e. the vertical bending moment as well as the superimposing longitudinal forces. Within this paper a detailed overview of the results for the bulk carrier is given and both, frequency- and time-domain results are presented. With Response Amplitude Operators (RAOs), delivered by frequency-domain analysis, the profound data for the standard assessment of structures, concerning seakeeping behaviour, operational limitations and fatigue are obtained. In addition, time domain analyses in rogue waves such as the so called “New Year Wave” provide essential data for extreme motions and structural loads. Former investigations on a FPSO revealed that, due to the location of the neutral axis, the longitudinal forces are significant and generate a counteracting moment compared to the vertical bending moment [1]. The new results show to what extent the above mentioned conclusions are applicable for various hull designs.