Hydrodynamic load simplification

Abstract

Stiffened panels at the water line of a ship experience in-plane loads due to ship bending and torsion, as well as out-of-plane loads due to wave impacts. Wave impacts weaken the panel with respect to in-plane loads, but are hard to predict because of complex physics. The in-plane strength of the panel supports the surrounding ship structure. Hence, it is important to know in what detail the wave impacts should be determined, while making minimum error in the in-plane ultimate strength. The importance of load details is evaluated as follows. First, the complex loading is applied to the structure and the ultimate strenght of the structure is evaluated. Then, details of the load are omitted, in this case by changing the resolution of the load. Finally the effect of omission of details becomes clear, by comparing the ultimate strength of different wave impact load resolutions. Non-linear finite element calculations are performed to assess the unloaded ultimate strength, as well as the ultimate strength for different load resolutions. The load is a breaking wave on a rigid wall. Applied resolutions range from 0.1 m to uniform pressure over the stiffened panel. It is found that the ultimate strength under static loading either over- or underpredicts the ultimate strength of the panel independent of resolution. Further, the ultimate strength under a dynamic uniform loading is also not representative. Different resolutions are, again, of minor influence. Tests with a different panel confirm the findings. It is therefore concluded that, for the load and structure under investigation: there is little effect of load resolution, as long as it grossly resembles the pressure map. Dynamic calculations should be performed at all times.