On the slamming of ships: Development of an approximate slamming prediction method

Slamming of ships is a phenomenon characterized by a high wave load of short duration. Usually the ships structure responds in a vibratory manner on this load; the response can be either a local or a global vibration mode or it can be in both modes together. These short duration loads are caused by large amplitude motions, even to the point that the fore body of the ship emerges from the water and slams upon re-entry, or they are caused by very steep waves that impact against the hull. The global elastic vibratory response of the structure is called whipping. It is characterized by a very low damping, so it takes many oscillations before it is extinguished. This dynamic response of the structure increases as well the maximum load as the number of load cycles relevant for fatigue damage due to seakeeping loads. Local and global responses can result in local high stresses such that it results in plastic deformation. Slamming loads can lead to catastrophic damage as illustrated by the accidents with the ferry Estonia and the container ship Napoli. Slamming loads are known to be a major reason for operators to change course and/or reducing speed, therefore there is a large effect on the economy of a ship. These aspects are the motivation for carrying out this study.