Trans RINA, Vol 161, Part A4, Intl J Maritime Eng, Oct-Dec 2019
shared energy design as illustrated in Figure. 3, which is dependent on the relative stiffness of the striking ship and struck bridge. The stiffness of bridge pier is generally much larger than that of ship, which causes that the striking ship crush during collision instead of bridge pier. The analysis of bridge against ship impact can be classified as the strength design. Woisin (1976) formula was developed by regression analysis for database of ship-rigid wall impact experiments. Sha & Hao (2012) studied the influence of material characteristic on the deformation of the bridge pier, and the resultant impact force time histories were compared for considering the bridge material as rigid, elastic and nonlinear inelastic. It was found that the impact force is relatively independent of the pier material properties, and the interaction effect between bridge pier and ship is slightly, since the stiffness of bridge is significantly larger than that of ship bow. Moreover, the present aim to investigate the impact force of vessel. Hence, the bridge pier is assumed as rigid in the FE analysis, which ignore the deformation bridge pier and the interaction between the ship and bridge pier. The assessment formula that will be revised does not account for the influence of bridge pier shape. The influence of shape of bridge pier is not accounted for herein, which will be investigated in the future study.
impact velocities as expected. However, the histories of collision force and depth are very similar at the beginning for different impact velocity, especially for ballast load situation, which means that the stiffness of ship bow is more important for the impact force for the collision velocity under consideration. It is possible to adopt quasi static analysis to assess the impact force between the ship and bridge pier. The first peak force appears when the upper deck crushes in Figure. 6 (a). After the buckling of upper deck, the bulb bow start contact with bridge pier and the impact force drop down.
10 20 30 40 50 60
0 0 (a) Full load Figure. 3 Design principles base on relative strength
The head-on collision is generally considered as the critical scenario, which was adopted in the experiment by Woisin (1976) for regression analysis and the other assessment empirical formulae in the requirement, e.g. AASHTO (2007) and IABSE (1983). Hence, only head- on collision scenario is considered in the numerical simulations of impact between the ship and rigid bridge wall as shown in Figure. 2 (b). Four impact velocities with 2, 4, 6 and 8m/s are considered for full and ballast loads, which are 6,500t and 3,250t. The initial impact velocity is applied on the whole ship structure. The hydrodynamic mass coefficient is set as 0.07 to account for the influence of added water mass (Wang et al., 2002). There is not any restrain on the striking ship, which is assumed to movement freely. The simulation time for one single run is around between 6 hours and 10 hours that depends on the impact velocity.
2.3 RESULTS ANALYSIS OF FE SIMULATION
Figure. 4 shows the histories of the displacement and impact force of ship with various collision velocities. The indent depths of ship increase with the increment of
©2019: The Royal Institution of Naval Architects
10 20 30 40 50 60
0 0 1 2 3 4 Displacement (m) 5
2m/s 4m/s 6m/s 8m/s
6
2m/s 4m/s 6m/s 8m/s
1
2
3 Displacement (m)
(b) Ballast load Figure. 4 History of the displacement and impact force
With the increase of ship movement, the structure between transverse frames at bow folds and then crushes, see Figure. 4 and Figure. 5, which cause several wave shape histories of impact force appear between two transverse frames. These positions of wave of impact force are very close for different collision velocities. The histories of impact force at the beginning are similar for various collision velocities. The impact velocity influences significantly on the impact duration and maximum impact load, but slightly on the history of the impact depth and force at the beginning. It seems that relationship between impact depth and load mainly depends on the stiffness of ship bow. This illustrates that the quasi-static method used to assess the maximum force of ship is appropriately. The impact force also
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Impact force (MN)
Impact force(MN)
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