Slamming response analysis of global load for large-bow flare naval ship in rough sea

Objectives When a large-bow naval ship encounters adverse sea conditions, bow flare slamming causes a hull girder whipping response which threatens the security of global longitudinal strength. The whipping bending moment resulting from slamming is related to the level of hull stiffness and bow flare shape. However, there are great differences in the structural arrangement and profile of different ship types, so it is necessary to carry out whipping response analysis.

Methods First, the COMPASS-WALCS-NE nonlinear time-domain hydro-elastic method is used to predict the hull girder response, and the results are compared and verified through a self-running subsection model test. Next, based on the obtained time histories of the resultant bow impact force, ship motion posture at typical moments and global load response of hull girders, the phase difference of high-and low-frequency components in the waveloads is analyzed, and the correlation between the midship's slamming moment and resultant bow flare slamming force is studied. Finally, the sensitivity analysis of the main design parameters affecting vertical bending moment is carried out.

Results In the designed sea conditions, the resultant slamming force has two peaks during bow water entry which correspond to the processes of bottom impact and bow flare impact respectively. The whipping bending moment is mainly caused by bow flare impact, but as the impact area is large and the resultant force far away from the midship, the slamming moment is at the same level as the wave bending moment. The slamming moment is very sensitive to changes in wave height.

Conclusions  The results of this study indicate that the effect of whipping impact resulting from slamming should be considered in the global longitudinal strength evaluation of large-bow naval ships; among them, the sagging vertical bending moment needs to be directly superimposed on the still water bending moment component and low-frequency wave load component, while the hogging vertical bending moment should be reduced to a certain extent and then superimposed considering dam-ping dissipation.