Water surface impact loads acts on bulbous bow of ships

As a part of the project study concerning on ship structural design for oil spill prevention by collision, optimal design of flexible bulbous bow structure is studied to absorb kinetic energy of the colliding ship. Such a flexible bulbous bow is named as buffer bow. To formulate design criteria of the buffer bow, the hydrodynamic impact forces acts on the bulbous bow was studied theoretically and experimentally. For theoretical study, shape of the bulbous bow was approximated by an ellipsoid and von Karman's momentum theory was applied to estimate the slamming impact loads with given impact velocity of the emerged bow to free surface. Wagner's impact theory was also applied to study the effect of free surface swell up. Based on the momentum theoy, an estimation method of the impact loads was proposed. To validate the estimation method, a experiment was conducted at the 80m square tank of NMRI. A self-propelling container ship model was used for the experiment. The vertical and lateral shearing forces and bending moments at the root of the bulbous bow were measured. In this paper, the results of the study are presented.