Head Sea Slamming Pressures Prediction on a Frigate Ship Hull (A Numerical Study)

As a relatively high-speed warship a frigate has to maintain the capability to operate in rough seas. At this sea condition the ship certainly often experiences slamming since it normally has a low draft. This paper presents a numerical prediction of the slamming pressure on a frigate ship. The frigate has a typical V-shape hull form and operated at a head-sea condition which assumed to have maximum slamming load/pressure. The locations of prediction are determined for places which are prone to dynamic loads that affected the performance of warships. The locations are the tip of the bow which is usually a sonar dome, and a quarter of the area of the bow of the ship length which is the location of weapons systems, and the area aft (stern) in where a helipad , helicopter hangars, and the weapons systems are mainly placed . The main dimension of the vessel for this study is LPP = 120m, B = 15.89m, D = 9.365 m and T = 4. 83 m, with a service speed of V = 25 knots. The environmental condition of the open sea is selected as JONSWAP spectrum with a significant height Hs of 5 m, and a peak period Tp of 13,782 secs. Steps of slamming loads prediction from the procedure of Slamming Strength Assessment of the American Bureau of Shipping (ABS) Rules of 2011 is applied for this study. It starts with a Response Amplitude Operator (RAO) motion calculation of the frigate to obtain the range of peak frequencies in which the response of relative vertical motion and velocity is a maximum. Then, these frequencies are set to be the working frequencies for calculating the pressure distribution of the ship hull. These calculation results are used to obtain the design slamming pressure by applying the formula from ABS Guide for Slamming Loads and Strength Assessment for Vessels, 2011 (see references). The comparison of the result of this study to a well- known Stavovy & and Chuang method and modified data from Mariner full- scale measurement has been made and found that they agree well each other. Accordingly this information of the pressure can be used for preliminary life assessment and size determination of the structural component of the frigate.