Trans RINA, Vol 157, Part A3, Intl J Maritime Eng, Jul-Sep 2015
no wave. Moreover also in the damaged case the mean pitch in wave presents slightly below the damaged trim with no wave. This behavior follows what has already been observed for the intact ship in Figure 11.
In Figure 12, the amplitude of the pitch response in wave is small, with no significant difference with the intact amplitude response; the heave, instead is characterized by reduced amplitude compared to the intact one. This behavior can be attributed to the non-linearity of the restoring and Froude-Krylov actions due to the increase in draft and forward trim.
The water loading details, for the implemented model, taking into account dynamic pressure on the damage hole and spilling, are given in Figure 13. The dynamic equilibrium after flooding in wave seems to be reached later than the no wave condition; the water loaded has its maximum and minimum respectively close to wave crest and trough, within a range of almost 9 ton.
Finally the simulation results, regarding the effect of the water trapped on the garage deck, for the intact ship in wave, are shown in Figure 14. The sample amount of water used for the calculation is 50 tons; the constant heeling moment due to the lateral wind is set at 1500 kNm. The ship behavior for this condition, with trapped water, is also compared to the results for the same condition but with no water (dashed line in Figure 14).
From the carried out simulations it is possible to notice how the water presence in the garage compartment leads to a mean roll value almost two times bigger than the case with no trapped water, to increased pitch motions; to slightly dampen heave responses. Figure 14 also reports by a dashed-dot line, the heel angle at the equilibrium, with water trapped and lateral wind moment and no wave. It is possible to notice how the mean rolling value is few degrees lower than the static value, due to the sloshing motions within the compartment.
Figure 14. Ship behavior with and without trapped water. 7. CONCLUSIONS
The paper presents the development and the applications of a time domain numerical simulation model, capable to predict the dynamic behaviour of a damaged fast ferry, in presence of head or following sea and heeling actions due to the wind. In particular the flooding of a damaged hull and the dynamic behavior of the vessel with water trapped in the garage was investigated.
The first part of the work dealt with some preliminary numerical applications, in order to assess the reliability of the results. The final equilibrium conditions for the intact and damaged ship were compared with the results of a hydrostatic code, showing a good match; the transient stages and ship response in wave were checked too.
From the applications carried out on the ship grounding in presence of longitudinal waves, taking into account dynamic pressure on the damage hole and spilling, it was possible to observe that the water loaded
has its
maximum and minimum respectively close to wave crest and trough, within a range of almost 9 ton.
Figure 13. Details of the ship flooding in wave simulation.
The simulation results, regarding the effect of the water trapped on the garage deck with constant wind heeling moment, show that the water presence in the garage compartment leads to higher ship roll and pitch motions.
©2015: The Royal Institution of Naval Architects
A-159
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