Study on Prediction Method for Hydrodynamic Force Acting on a Ship Hull in Swaying Motion

When ship is moving in lateral direction at berthing in a harbour or when ship is moving with large drift angle at low speed, it is known that the component of cross flow drag dominates the hydrodynamic force acting on ship hull. It is important to develop prediction method for the cross flow drag from the view points of safe navigation of ships at low velocity in harbor or restricted water.One of the authors has already proposed the prediction method for the cross flow drag acting on a ship hull based on the vortex shedding model. However, the prediction method requires to determine the parameter comparing with the results of model test in order to define the positions of the free vortices that are shedded from the ship hull. Additionally, value of the parameter α that reduce the strength of the free vortices is defined uniformly along the ship length in spite of the change of sectional form.In this paper, we tried to improve the vortex shedding model by investigating the positions of separation points. We also investigated the longitudinal distribution of the parameter α. From these studies, it is shown that longitudinal distribution of the cross flow drag along the ship length can be predicted with comparatively high accuracy using the presented prediction method.