Experimental validation of CFD simulations of free-fall lifeboat launches in regular waves

Abstract

The loads on a free-fall lifeboat and the accelerations felt by the occupants during water-entry are influenced by a large number of parameters: drop height, presence of wind and waves, location of impact point relative to the wave crest. Therefore, testing the lifeboat design and performance by means of experiments becomes difficult and costly. Furthermore, the most critical conditions are not even possible to reproduce experimentally, due to the lifeboat's small size relative to the most severe waves. However, numerical simulations of lifeboat launching under different conditions are possible with the newly developed models in Computational Fluid Dynamics (CFD) solvers. In addition, CFD provides more data that can be used to improve the hull design. This paper presents results from new model tests and CFD simulations of lifeboat launches in oblique regular waves from 3 different directions. To the authors' knowledge, this is the first time CFD simulations of lifeboat launches in waves have been validated. The predicted accelerations of the lifeboat agreed well with the measured ones. The pitch velocity was slightly overestimated due to a slight difference in the geometric features at the bow between the CFD model and the physical model. The CFD simulations provided in general accurate or conservative estimates of the local pressure at various locations on the hull except on one location on top of the canopy where the pressure was slightly under-predicted. Furthermore, it has been shown that to improve the predictions of the pressure loads on the aft wall of the lifeboat, the compressibility of air has to be taken into account in the CFD simulations in order to capture the behavior of the air-pocket behind the lifeboat.