Author(s)

J. G. Pelaez, G. R. Valiente & J. J. Reijmers

Abstract

Under certain circumstances it may be desired to place a submarine on the seabed. In this static situation it is possible to shut down vital systems required for manoeuvring, hence avoiding the radiation of sound. This bottoming should be considered as a controlled collision; however this operation is not without risk. First touch down may be anticipated, but hydrodynamic aspects will be influenced by the seabed. A change in trim and speed will result in an impact velocity of vulnerable structures, other than the reinforced area for initial touch down. The paper focuses on the impact of the aft rudder with the seabed following from a nose down first touch down. Depending on forward trim and downward velocity the rotation of the vessel and velocity of the aft rudder is analysed. Structural analyses are carried out, including soil mechanics to assess the property of the seabed. Nonlinear material behaviour, including strain rate effects is taken into account. Although the connotation collision suggests otherwise, bottoming shall be considered as a normal operation. This implies that the impact of the aft rudder on the seabed shall not result in a permanent set. With the explicit code LS Dyna the response on several downward velocities and trim angles is calculated. The criterion of no plastic deformation produces an operational window for trim and velocity to approach the seabed. Keywords: submarine, impact, seabed.

Keywords

submarine, impact, seabed